The Elements of Physiology and Hygiene  

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"How it is that anything so remarkable as a state of consciousness comes about as the result of irritating nervous tissue, is just as unaccountable as the appearance of the Djinn when Aladdin rubbed his lamp." --The Elements of Physiology and Hygiene (1868) Thomas Henry Huxley

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The Elements of Physiology and Hygiene (1868) is a book by Thomas Henry Huxley.

Full text of 1868 edition[1]

The elements of physiology and hygiene "homas Henry Huxley, William Jay Youmans ^w:^ • ^ [ARVARD UNIVERSITY.

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) pages. \ Large 12mo. Oman Antl- A8 K. Ar^'OLU. Beautiful, K ly, 2 vols. LIBRARY MUSEUM ( 3F COMPARATIVE ZOOLOGY Bequest of WALTER FAXON Ars* ay tuo kno. , BTanners, IS. By Tbomas Qd Mary. 8vo. | }Uoay is: 195//. Complete in 7 [ d to the Set. i tntad,4to. mpsi«. 102,page8. tany. Illos- 1 Digiti2 Id by JUN 16 1921 StaxLciard. S!cl\2catiOfial ^Worlcs. dllesple'w Land Snrveylnc t Tbeoretiesl and PractieaL By W. M. GiLLESPiJB, LL.D., Civil Engineer, Profoasor of Civil Engineering in Union College ; aathor ot ** Manual of Boads and Eallways," etc Witk Four hundred engravings, and a Map Bhowing the Variation of the Needle in the United States. 1 vol 6vo. 424 pages. Grabam's finglfsb SKynonymes, Classified and Explained. With practical Exercises, designed for Schools and Private Tuition ; with an Introduction and illustrative authorities. By HsofttT Rkxd, LL.D. 12mo. 844 pages. Gnizot's History of Civilization In Eurcpe«  I Greene's History of tike Middle A^es. 12rao. Jacobs.— Learning to Spell, to Read, to UTrlte, and to Compose. By J. A. Jacobs, A.M., principal of the Ken- tucky Institute for the education of Deaf Mutes. 16aio. 882 pages. 514 illustrations. Keislitlcy^s Mytboloscy* ISmo. Abridgment of the Author's larger work, KcEppen's Historical Geog^rapby* 2 vols. 12mo. Hlstorlcc-Geoffraplilcal Atlas of the MiddieAges. Folio. ■ Tbe Geograpliy and Atlas,— Complete in 1 voL, folio. lAthantH Hand-Boofe of tbe Engllsb I«lteratare«  12mo. 808 pages, LyelPs Principles of Geology* 8vo. 848 pages. REannal of Klementary Geoloyy* MarsbHi Book-Keeping by Single Entry« New Edition. Printed in eolors. 8yo. 142 pages. • BootcKeepIng by Double Entry. Printed in oolors. 8vo. 320 pages. BLANKS TO EACH OP ABOVE. Per set JKandeTllle's Neir Series of RraCIng Books. Pbimabt BxADiR. A profusely illustrated 16mo. SxooKD Bkadcr. With numerous illustrations. 16mo. Thi«o Beadeb. For Common Schools and Academies. 12mo. FouBTn Readkb. For Common Schools and Academies. 12mo. Firrn Beadbb. Designed for Academies and Advanced Sohools. With Biographical Notes. l2mo. 892 pagvis. Cloth sides. KuMBTTS or Rbadimo and Obaiobt. 8yOb Pr SES END OF THIS t^tVIOB.





THE ELEMENTS PHYSIOLOGY AND HYGIEUE; A TEXT-BOOK FOR EDUCATIONAL INSTITUTIONS, THOS. n. HUXLEY, LL.D., F. R. S., AND WM. JAY YOUMANS, M. D. WITH NUMEROUS ILLUSTRATIONS. NEW TOEK: D. APPLETON AND COMPANY, 90, 92 & 94 GRAND STREET. 1869.


Entered, accordin* to Act of Congress, In the year 1868, by D. APPLETON & CO., In the Clerk's Office of the District Court of the United States for the Southern District of New York.


PEEPACE. A FEW words are necessary to explain the joint authorship of the present volume. My friend and teacher, Professor Huxley, having been for a considerable tinie engaged in the preparation of an element- ary work on Physiology, at such brief intervals as he could snatch from his laborious scientific researches, and it having been suggested to him that its republication in this country might be desirable, he confided the early sheets of the work to me, to make such additions of matter and modifications of form as might be thought proper to adapt it to the cu'cum- stances and requirements of American education. This I have done to the best of my judgment by contributing eight chap- ters to the present edition : the first, on the relation of Physiol- ogy to the other sciences ; and the last seven, forming Part II., which treats briefly of general Hygiene, or the application of the principles of Physiology to the art of preserving health. I have also numbered the paragraphs of the work continuously, prefixed headings to them, and appended a set of questions to the whole. His aim in the preparation of the Physiology, and its lead-


IV PREFACE. ing and most important characteristics, are thus described by Pro£ Huxley : " My object in writing it has been to set down, in plain and concise language, that- which any person who desires to become acquainted with the* principles of Human Physiology may learn, with a fair prospect of having but little to unlearn as our knowledge widens. " It is only by inadvertence, or from an error in judgment, therefore, that the work contains any statement, or" doctrine, which cannot be regarded as the common property of all physiologists. I have endeavored simply to play the part of a sieve, and to separate the well-established and the essen- tial from the dotibtful and the unimportant portions of the vast mass of knowledge and opinion we call Human Phys- iology." That there was imminent need of the performance of this task by some able hand, a critical examination of our popular text-books of Physiology will abundantly attest But it is not to be inferred that this has been done by merely collating old views which have long passed current, and neglecting the results of the most recent inquiry. In true science, the essen- tial progress of which consists in the rigorous sifting and veri- fication of opinions, the latest knowledge is ever the clearest and the ripest. It will therefore be found that, while Prof. Huxley's work inexorably winnows away the chaff of discred- ited doctrine and doubtful speculation, it nevertheless em- bodies the valid and established results of the latest investiga- tions, and may therefore be accepted as a brief exposition of the actual present state of knowledge upon the subject. Probably, the most important advance which has been lately made in the field of science consists in the establish-


PREFACE. V ment of the great principle of the correlation and conserva- tion of forces. Accordingly, regarding Physiology as strictly the science of vital actions or living forces, Prof. Huxley tacitly conforms the whole plan of his work to this funda- mental principle. Committing himself to no unsettled theo- ries respecting the transformations of energy, he neverthe- less views the living organism dj/namicalli/, as a problem of the disturbance and restoration of equilibrium between the receipt and expenditure of matter and force. The functions of alimentation, circulation, respiration, and secretion, and the exercise of physical and mental power, are considered in the light of losses and gains to the system, and with constant reference to the physiological balanee of forces. Another marked and important feature of Prof. Huxley's work is the style in which it is written. With plainness and concision of language he has attained an admirable compres- sion of statement by which a large body of facts and principles is brought within the narrowest compass of lucid presentation. While excessive simplification and expansion of style may be suited to scientific works designed for merely popular reading, the case is different with a class-room manual intended for syste- matic study. Here the object is not only to inform the under- standing, but to call out and discipline the powers of the mind through continuous efforts of thought Prof. Huxley's elemen- tary treatise, while it embodies an amount of physiological science such as every educated person ought to possess, will also be found in its concentration of thought and compactness of ex- pression well adapted for the higher purposes of mental culture. My own additions to the volume have been made in response to a growing demand that the subject of Hygiene, in both its bodily and mental aspects, shall receive increasing


VI PEEFACE. attention in general education. I trust that the acknowledged importance of this subject, as well as the advantage of dealing with it separately, after the Physiology has been mastered, will in some degree promote the favorable reception of the work by the teachers of the country. I take this occasion to express thanks to my brother, Dr. E. L. Youmans, for superintending the passage of the work through the press, and for various important suggestions ; and also to Dr. Wm. A. Hammond, of New York, for having kindly read the proofs of the closing chapter on Mental Hygiene. . W, J. Y. State Normal School, Winona, Minn., October, 1867.


CONTENTS. PAET I. ELEMENTARY PHY8I0L00T. CHAPTER I. FAOB Relations of PnTSiOLoaY to other Branches op Sctence, . 11 SectI 1, — ^Nature of Scientific Knowledge, . . . .11 2.-^The Preparatory Sciences, 13 3.-:— The Biological Sciences, 14 CHAPTER II. A General View op the Structure and Functions op the Hu- man Body, 19 Sect. 1. — ^Work and Waste, 20 2. — Outlines of the Bodily Structures, ... 23 3.— The Bodily Tissues, 26 4. — ^The Combination of Actions, .... 29 6. — ^Nutrition, Circulation, Excretion, .... 32 CHAPTER m. The Vascular System and the Circulation, .... 35 Sect. 1. — The Vascular System, 85 2. — Connections and Structure of the Heart, . . 44 3. — ^Working of the Heart and Vessels, ... 52 4. — The General Circulation, . ... . . 59 CHAPTER IV. Of the Blood and Lymph, 65 Sect. 1. — Its Microscopical Elements, .... 65 2. — ^Its Physical and Chemical Pi-operties, ... '72


Vlll CONTENTS. CHAPTER V. Of Respiration, Sect, 1. — Arterial and Venous Blood, . 2. — :The Lungs and their Office, 3. — ^The Respiratory Mechanism, 4. — Inspiration and Expiration, 6. — ^Effects of Respiration, CHAPTER VI. The Sources op Loss and of Gain to the Blood, Sect. 1. — Sourcesof Loss to -the Blood, 2. — Losses and Gains by the Liver, 8. — Sources of Gain to the Blood, CHAPTER Vn. The Function of Alimentation, . . Sect. 1. — ^Properties of Food-Stuffs, . 2. — Preliminaries of Digestion, 3. — Stomach-Digestion, 4. — Intestinal-Digestion, CHAPTER VIII. Motion and Locomotion, Sect. 1. — Instruments of Motion, 2. — Mechanism of Bodily Movements, 3. — ^Movements of Locomotion, 4. — ^Vocal Movements, . . . CHAPTER IX. Of Sensations and Sensory Organ?, . Sect. 1. — Reflex Action — Groups of Sensations. 2. — ^Touch, Taste, and Smell, . 3. — ^The Mechanism of Hearing, . 4. — ^Working of the Auditory Mechanism, CHAPTER X. The Organ of Sight, .* Sect. 1. — Structure and Action of the Retina, . 2. — ^The Luminous Agent, . 3. — ^The Intermediate Apparatus, . 4 — ^Focal Adjustment, 6. — Appendages of the Eyeball, PAGE 81 81 84 90 95 100 106 106 120 124 133 133 140 145 148 153 153 156 168 110 111 111 180 188 196 201 201 207 209 211 216


CONTENTS. • IX CHAPTER XL PAGE Sensations and Judgment, 219 Sect. 1. — Compound Sensations, 219 2. — Delusions of Judgment, 222 3. — ^Visual Sensations and Mental States, . . .229 CHAPTER XII. The Nervous System and Innervation?, 236 Sect. 1.— The Spinal Cord— Reflex Action, .... 236 2.— The Brain, ....... 246 3.— The Cerebral Nerves, 249 4. — Unconscious Cerebration, 262 CHAPTER Xm. Histology ; or, the Minute Structure of the Tissues, . . 255 Sect. 1. — Dermal Tissues, 255 2.--Interior Tissues, 260 3. — Osseous Tissues, 263 4. — Muscular and Nervous Tissues, .... STO PAET 11. ELEMENTARY HYGIENE, CHAPTER Xiy. Scope and Aims of Hygiene, .... . . 275 CHAPTER XV^. Air and Health, 282 Sect. 1. — ^Impurities of the Air, 282 2.— Morbid Effects of Impure Air, . . . .287 3.— Purification of the Air, 291 CHAPTER XYI. Water and Health, 296 Sect. 1.— Physiological Office. of Water, .... 296 2.— Different Kinds of Water, 297 3.— Morbid Effects of Impure Water, ... 302 4.— Purification of Water, 306


CONTENTS. CHAPTER XVn. Food and Health, . , Sect. 1. — The Alimentary Principles of Food, , 2. — Animal Foods, .... 3.— Vegetable Food, . . . . 4. — ^Auxiliwry Foods, .... 6. — Culinary Preparation of Foods, 6. — ^Injurious Effecta»of Bad Diet, CHAPTER XVIII. Clothing and Health, Sect. 1. — Properties of Clothing Material, 2. — ^Manner of Dressing the Body, CHAPTER XIX. Exercise and Health, . Sect. 1. — Labor and Exercise, 2,— Effects of Regulated Exercise, . 3. — ^Excessive and Insufficient Exercise, CHAPTER XX. Mental Hygiene, Sect. 1. — Relations of Mind and Body, 2. — ^Forms of Mental Impairment, . 3. — Causes of Mental Impairment, . PAGE 308 308 312. 315 318 d24 326 334 334 33Y 344 344 345 349 353 353 357 375


PAET I. ELEMENTARY PHYSIOLOGY. CHAPTER I RELATIONS OF PHYSIOLOGT TO OTHER BRANCHES OF 8CIENCK INTRODUCTOEY. Section I. — Nature of Scientific Knowledge, 1. How it Originates. — ^Physiology is one of the branches of Science, and we cannot better commence its study than by forming clear ideas of the general nature of science itself, and of the relations which this branch of it bears to its other parts. By mapping out the family of Sciences to which Physiology belongs, and upon which it depends, we may get a definite conception of its position and relations in the group : to this the present chapter will be devoted. Man has been called the Interpreter of Nature, and Science defined as its right interpretation. But the true interpretation of Nature is a slow and difficult work. There is a curiosity in the human mind to seek explanations and understand the rea- sons and causes of things ; but at first its questions are put at random and answered vaguely, and knowledge is then rude and imperfect With increasing experience questions are put more sharply and go deeper, and then come clearer explanations and a better understanding of things. In this way knowledge upon


12 ELEMENTABY PHYSIOLOGY. many subjects grows to be more and more perfect ; and when it becomes so accurate and sure that it is capable of being proved to persons of suitable intelligence, it is called science. The science of any subject is the highest and most exact knowledge upon that subject. 2. The Order of Nature. — That which makes science pos- sible is the regularity of Nature's order, and it is only possible so far as that order can be traced. All the appearances and effects of Nature with which we can becopae acquainted are known as Phenomena; those which exist together constitute the order of Coexistences ; those which follow each other in a regular succession form the order of Sequences. Thus all the • various parts of the human body, as bones, blood-vessels, nerves, and fluids, and its simultaneous operations, as of breath- ing, digestion, circulation, constitute its coexistences ; while the succession of its numerous actions and effects, as for example the agreeable feeling and' renewed strength which follow the taking of food, constitutes its sequences. A scientific inquiry into the order of Nature, therefore, resolves itself into an investioration of the relations of coexistence and sequence among all objects, while each science is a statement of the coexistences and sequences of some particular part of Nature. If there are any subjects which have no coexistences and no sequences ascertainable by the human mind, those subjects are incapable of becoming sciences. 3. Connection of the Sciences.--Science is thus the most perfect knowledge of Nature in all her aspects. But the parts Qf Nature are intimately connected in one great whole; there- fore the sciences which give an account of Nature must also be intimately connected together. They overlap and interlace in the closest manner, so as to be in a very great degree mutually dependent on each other. To understand any one of them, it is therefore important to have some knowledge of the others most nearly related to it, and upon which it essentially de- pends.


THE PREPAEATOEY SCIENCES. 13 Section II. — The Preparatory Sciences. 4. Mathematics. — ^The least dependent of all the sciences, and at the same time the simplest and the easiest, is that which considers the number and the forms, or shapes of objects, and this is Mathematics^ or the science of quantity. We cannot thmk of things except as having form or outline, and the science which deals with forms and their relations is termed Geometry; nor can we think of them except as one or many — that is, as being numbered, and a knowledge of the combina- tions and relations of numbers constitutes the science of Arith- metic. So simple, clear, and definite are these ideas that they may actually be considered apart from the things to which.they apply, so that arithmetic can deal, as it were, with pure num- bers rather than with things numbered, and geometry with space rather than the objects contained in space. The ideas may be thus abstracted from the realities, hence mathematics is known as the most abstract of the sciences ; and as the ideas with which it deals are few,, it has been carried to the highest perfection of any science. As in all other sciences we have constantly to use mathe- matical ideas, a certain amount of elementary arithmetic and geometry is useful and important as a preparation for this kind of study. 5. Physics. — ^The science which comes next is that which passes to the actual study of things ; which goes from ideas of number to those of the objects numbered ; from the notion of space to that which occupies space, or which adds to mathe- matical conceptions those of matter and force. It considers the universal and essential properties of matter, the forces which act on it to produce motion, and the resulting laws of motion. This branch of science is called Physics or Natural Philosophy, and treats of the resistance, weights, pressures, mutual attractions, and general properties of material bodies. It is not so simple as mathematics, yet the conceptions with


14 ELEMENTARY PHYSIOLOGY. wLich it deals are so few that it has been worked out to a con- siderable degree of perfection. 6. Chemistry. — If there were only one kind of matter in the universe, as iron or sulphur, there could still be a science of physics. But there is a large' number of elementary bodies in Nature which combine intimately together in various propor- tions and give rise to that infinite diversity of material sub- stances which we see around us. These all have the general physical properties, but they have also certain special and pecu- liar properties which are different in different kinds of matter. The knowledge of these gives rise to the science of chemistry, which treats of substances as simple or compound, how they are constituted, and how they act upon and change each other. But a knowledge of the universal and constant properties of bodies should precede the study of the more special and vari- able properties ; hence physics prepares for chemistry. The ideas which pertain to chemistry are far more numerous and complex than those of physics, and accordingly chemistry is much more backward than physics in its development. Section III. — The Biological Sciences, 7. Biology. — ^All the objects of Nature may be divided into two great classes — ^the living or the organic, and the not-living or the inorganic. Biology is the name of that comprehensive science which treats of living matter and living things in all their grades, forms, and varieties. But iu entering the field of biology we do not begin anew ; we carry with us a stock of mathematical, physical, and chemical conceptions. We have still to deal with numbers and forms, with the motion and rest of masses, and with the composition and internal changes of substances. These are indispensable keys to biological phe- nomena, and not an intelligent step can be taken without them ; but there is also a new order of ideas which is peculiar to this great field of thought, as those of organic structure, vital func- tion, grdwth, development, waste and repair, alimentation,


THE BIOLOGICAL SCIENCES. 15 reproduction, &c. Biological subjects are therefore far more difficult to investigate, and are incapable of the exactness which belongs to the inoi^anic sciences ; still they comprise a great body of certain and most valuable knowledge. 8. Divisions of Biology. — The first division of Biology is that which everybody recognizes — the division into plants and animals, which gives rise to the two sciences of Botany and Zoology, But while this division is most obvious and natural, it does not answer the full purpose of scientific classifi- cation, which aims to group together all phenomena of the same kind, thus avoiding repetition in their treatment. Every living being, whether plant or animal, presents the same series of questions for consideration ; vegetable-biology would there- fore be simply going over again the inquiries of animal-biology. These inquiries may be arranged into four groups, giving rise to four fundamental divisions of biological science. 9. Morphology. — ^This word, in its derivation, signifies the doctrine of forms. Applied to the organic world it is that division of Biology which treats of the forms or structures of living beings. It has several branches. For example, no living being is throughout of homogeneous substance ; the most of them are highly complex, from the union of many dissimilar parts. The statement of this structure constitutes Anatomy^ and if it is carried down to the minutest microscopical elements of the organism, it is known as Histology, Again, no living being retains the same form and size throughout the course of its existence, but all grow, or pass through a series of changes, sometimes simple, sometimes very complicated, and the statement of these changes of form consti- tutes the branch of Morphology termed Development, Furthermore, when the structure and development of any number of plants or animals have been ascertained, the question then arises of their resemblances and differences. Thus the panther and the cat are more like each other than either is like the dog ; but they and the dog are more like each other than either is like the sheep ; while sheep, dog, and cat resemble


16 ELEMENTARY PHYSIOLOGY. each otlier more tban either does a fowl. In this way plants and animals which resemble each other in internal and external characters are arranged into groups to which a common name is applied, and this is Classification. The rude divisions of the vegetable world into trees, shrubs, and plants, and of the ani- mal world into beasts, birds, and creeping-things, science car- ries out in a precise and accurate manner for all the races of living beings. Classification depends upon anatomy and de- velopment, and is grounded upon the facts which they have established, and the fulness with which this is done indicates the completeness of the science of Morphology. 10. Distribution. — ^This is the second great division of Biology. Very few plants or animals are found all over the world ; most of them are restricted to limited areas of the earth's surface. Of terrestrial animals and plants, some are found only at particular elevations ; while of aquatic creatures, some are found only at certain depths. Again, great numbers of animals and plants have existed in former periods of the earth's history which do not now exist, and we get a knowl- edge of them through their fossil relics. The definition of the range of any plant or animal under any of these conditions — its location in space or in time — which leads to the knowledge of its environing circumstances, is its Distribution. 11. Physiology. — If we suppose an animal dead and petri- fied, its study might still give rise to all the branches of science hitherto enumerated. Not only would it exemplify the laws of quantity, physical properties, and a chemical constitution, but also all the branches of Morphology. Its structure or anatomy could be determined, its relations to other living be- ings, or its place in classification, and its position in space and in time, that is, its relations to surrounding nature, or its distri- bution. But when we conceive of it as alive, in motion, and undergoing changes, a new order of phenomena and a new set of inquiries are presented, which give rise to the science of' Physiology, the third great branch of Biology. Every living being does certain things, performs certain


THE BIOLOGICAL SCIENCES; 17 actiofis which are called functions, and is so far to be regarded as a machine working toward a given end. Physiology, there- fore, considers the living being as a machine in action^ and in- quires into the uses, operations, and mutual influence of its parts and the conditions under which its activity is maintained. Dealing with force or power, it considers living organisms under their dynamical aspects as Morphology regards them in their statical Qs^Qcis. Physiology is divided into animal and vegetable physiology, and animal physiology is again divided into Comparative Phy- siology, which treats of the inferior races, and Human Physiol- ogy, which considers the physiological phenomena of man. Because many of the inferior creatures have a simpler consti- tution, and are more accessible for purposes of investigation, the study/ of compaiative physiology has been a great help to the advance of human physiology, and some knowledge of the former is of much, value in prosecuting the latte^^ 12. Etiology.— Physiology treats of power, of which we know nothing except in its results. It involves the idea of causes producing eflfects, and is therefore a causal science. Morphology says that in such-a,nd-such circumstances the living being is structured so-and-so. These are eflects, and how pro- duced it is the business of physiological research, as far as possible, to explain. The physiology of individual life thus expands into a broad inquiry concerning the causes of vital phenomena in general, and the limits within which living beings can be affected by external conditions. This more compre- hensive physiology is termed Etiology, which literally signifies the doctrine of causes, and forms a fourth branch of biological science. The laws of the variations of living beings, of the modifications of individual organisms and successions of organ- isms, and of the influence of physical agencies on their posi- tion in space or their persistence in time, or the " dynamics of distribution,." as it has been called, belong to this division of the general subject. It is the most complicated and least per- fect of all the branches of Biolog}^


18 ELEMENTARY PHYSIOLOGY. 13. Claims of Physiological Study. — ^There are two classes of reasons why Physiology should be well studied by all who aspire to be in any tolerable degree educated. The first is, that it is a part, and a most important part, of the great order of Nature which the human mind is adapted to understand. The first duty of a rational being is to cultivate in the best manner possible the higher powers of his nature, an.d in no way can this be done so well as by studying the plan of Nature, which is full of harmony, beauty, and the highest instruction. Thou- sands of the greatest minds that have appeared in the world have been occupied for ages in discovering the truths of Nature, and a large amount of the most valuable and interesting knowl- edge has thus been reached, of which past generations knew little, and the acquisition of which is the noble privilege of the present time. Is it right that all this vast research which has employed the genius of ages should go for nothing in education — that all ihis wealth of knowledge should be passed by as if it had no existence, and the young people of this country grow up as ignorant of it as if they had Hved a dozen centuries ago ? 14. Applied Physiology— Hygiene. — Another and an im- perative reason for studying Physiology is, that it opens to us a true understanding of our own natures. It teaches us how to take care of ourselves, to preserve health, to economize steength, . and to improve and invigorate all our faculties. A large amount of the suffering of life comes from self-exposure and self-abuse, which take numberless forms. These may be avoid- ed through proper knowledge conscientiously applied. The truths of Physiology should therefore be inculcated and en- forced early and earnestly, and with the emphasis of high reli- gious duty. Physiology treats of the laws of the human constitution in a state of health ; but so important is the application of physio- logical principles to the art of preserving health and preventing disease, that a second part has been added to the present work, treating definitely and separately of this application, the princi- ples and rules of which constitute the art of Hygiene,


THE BIOLOGICAL SCIENCES. 19 CHAPTER II. A GENERAL VIEW OF THE STEUCTHEE AND FUNCTIONS OP THE HUMAN BODY. 15. How bodily Actions are Studied.— The body of a liv- ing man performs a great diversity of actions, some of wbich are quite obvious; others require more or less careful obser- vation ; and yet others can only be detected by the employ- ment of the most delicate appliances of science. Thus, some part of the body of a living man is- plainly always in motion. Even in sleep, when the limbs, head, and eyelids may be stiU, the incessant rise and fall of the chest con- tinue to remind us that we are viewing slumber and not death. But a little more careful observation is needed to detect the motion of the heart ; or the pulsation of the arteries ; or the changes in the size of the pupil of the eye with varying light ; or to ascertain that the air which is breathed out of the body is hotter and damper than the air whicb is taken in by breathing. And lastly, when we try to ascertain what happens in the eye when that organ is adjusted to diflferent distances ; or what in a nerve when it is excited ; or of what materials flesh and blood are made ; or in virtue of what mechanism it is t^at a sudden pain makes one start — we have to call into operation all the methods of inductive and deductive logic ; all the resources of physics and chemistry ; and all the delicacies of the art of experiment. 16. Scope of Human Physiology. — The sum of the facts and generalizations at which we arrive by these various modes of inquiry, be they simple or be they refined, concerning the actions of the body and the manner in which those actions are brought about, constitutes the science of Human Physiology. An elementary outline of this science, and of so much anatomy as is incidentally necessary, is the subject of the following


20 ELEMENTAKY PHYSIOLOGY. chapters, of which I shall devote the present to aa account of so much of the stracture and such of the actions (or, as they are technically called, "functions") of the body, as can be ascertained by easy observation, or might be so ascertained if the bodies of men were as easily procured, examined, and subjected to experiment as those of animals. Section I. — Work and Waste. 17. Bodily Loss or Expenditiire. — Suppose a chamber with walls of ice, through which a current of pure ice-cold air passes, the walls of the chamber will of course remain un- melted. Now, having weighed a healthy living man with great care, let him walk up and down the chamber for an hour. In doing this he will obviously exercise a great amount of mechanical force, as much, in fact, as would be required to lift and push his weight through the distance which he has raised himself at every step, and transported himself by all his steps. But, in addition, a certain quantity of the ice will be melted or con- verted into water, showing that the man has given oflF heat in abundance. Furthermore, if the air which enters the chamber be made to pass through lime-water, it will cause no cloudy white precipitate of carbonate of lime, because the quantity of carbonic acid in ordinary air is so small as to be inappreciable in this way. But if the air which passes out is made to take the same course, the lime-water will soon become milky, from the precipitation of carbonate of lime, showing the presence of carbonic acid, which, like the heat, is given off by the man. Furthermore, even if the air be quite dry as it enters the chamber, that which is breathed out of the man, and that which is given off from his skin, will exhibit clouds of vapor, which vapor, therefore, is derived from the body. After this experiment has continued for a longer or a short- er time, let the man be released and weighed once more. He will be found to have lost weight.


WORK AJSTD WASTE. 21 Thus a living, active man constantly exerts mechanical forcCy gives off heaty evolves carbonic acid and water^ and undergoes a loss of substance. 18. A Physiological Xncome indispensable. — Plainly, this state of things could not continue for an unlimited period, or the man would dwindle to nothing. But long before the effects of this gradual diminution of substance become apparent, they are felt by the subject of the experiment in the form of the two imperious sensations called hunger and thirst. To still these cravings, to restore the weight of the body to its former amount, to enable it to continue giving out heat and water and carbonic acid at the same rate for an indefinite period, it is absolutely necessary that the body should be supplied with each of three things and with three only. These are, firstly, fresh air; secondly, drink, consisting of water in some shape or other, however much it may be adulterated ; thirdly, food, in which that compound known to chemists as protein^ and containing carbon, hydrogen, oxygen, and nitrogen, must be contained if it is to sustain life indefinitely ; and in which fatty and starchy or sac- charine matters ought to be contained, if it is to sustain life conveniently. 19. Forms of Excretions. — Of this food a certain small proportion of useless and indigestible material leaves the body in the condition in which it entered it, and without ever being incorporated with its substance, as excrementitious matter. But, under healthy conditions, and with otily so much food as iff necessary, no important proportion of either protein matter, or fat, or amylaceous, or saccharine food leaves the body by this or any other channel. Almost every thing that leaves the body, in fact, does so either in the form of water^ or of carbonic acid, or of a third substance called urea; and of certain com- paratively unimportant saline compounds. 20. Absorption of Oxygen. — Chemists have determined that these products which leave the body and are called excre- tionsy contain, if taken altogether, far more oxygen than the food and water taken into the body. Now, the only possible


22 ELEMENTAKY PHYSIOLOGY. source wliencc the body can obtain oxygen, except from food and water, is the air which surrounds it. And careful investi- gation of the air which leaves the chamber in the imaginary experiment described above, would show, not only that it has gained carbonic acid from the man, but that it has lost oxygen in equal or rather greater amount to him. 21. Variation of the Physiological Balance. — Thus, if a man is neither gaining nor losing weight, the sum of the weights of all the substances above enumerated which leave the body, ought to be exactly equal to the weight of the food and water which enter it, together with that of the oxygen which it absorbs from the air. And this is proved to be the case. Hence it follows that a man, in health, and " neither gain- ing nor losing flesh," is incessantly oxidating and wasting away and periodically making good the loss. So that if he could be confined in the scale-pan of a delicate spring balance, like that used for weighing letters, in his average condition, the scale- pan would descend at every meal and ascend in the intervals, oscillating to equal distances on each side of the average posi- tion, which would never be retained for longer than a few minutes. There is, therefore, no such thing as a stationary condition, and what wo call such is simply a condition of varia- tion within narrow limits — a condition in which the gains and losses of the numerous daily, transactions of the economy bal- ance one another. 22. Conditions of this Balance. — Suppose this condition of daily physiological balance to be reached, it can be main- tained only under the condition that the quantity of the me- chanical work done, or of heat or other force evolved, remains absolutely stationary. Let such a physiologically balanced man lift a heavy body from the ground, and his previous loss of weight will be imme- diately increased by a definite amount, which cannot be made good unless a proportionate amount of extra food be supplied to him. Let the temperature of the air fall, and the same re- sult will occur, if his body remains as warm as before.


WORK AKD WASTE. 23 On tlie otiier hand, diminish bis exertion and lower his pro- duction of heat, and either he will gain weight or some of his food will remain unused. 23. Equation of Food and Force. — Thus, in a properly nourished man, a stream of food is constantly entering the body in the shape of complex compounds containing comparatively little oxygen ; as constantly, the elements of the food are leav- ing the body, combined with more oxygen. And the incessant breaking down and oxidation of the complex compounds which enter the body is definitely proportioned to the amount of force tjie body exerts, whether in the shape of heat or otherwise : just in the same way as the amount of work to be got out of a steam-engine, and the amount of heat it and its furnace give ofi*, bear a strict proportion to its consumption of fuel Section II. — Outlines of the Bodily Structure, 24. Structure of the Vital Mechanism. — From these gen- eral considerations regarding the nature of life, considered as physiological work, we may turn for the purpose of taking a like broad survey of the apparatus which does the work. We have seen the general performance of the engine, we may now look at its build. The human body is obviously separable into head, trunk, and Umbs. In the head, the brain-case, or skull, is distinguish- able from the face. The trunk is naturally divided into the chest or thorax, and the abdomen or belly. Of the limbs there are two pairs — the upper, or arms, and the lower, or legs; and legs and arms again are subdivided by their joints into parts which obviously exhibit a rough correspondence — thigh and arm, leg and forearm, ankle and wrist, fingers and toes, plainly answering to one another. And the last two, in fact, are so similar that they receive the same name of " digits ; " while the several joints of the fingers and toes have the com- mon denomination of " phalanges." The whole body thus composed is seen to be bilfrterally symmetrical ; that is to say, if it were split lengthways by a


24 ELEMENTAEY PHYSIOLOGY. groat knife, which should be made to pass along the middle line of both the dorsal and ventral (or back and front) aspects, the two halves would almost exactly resemble one another. 25. Tlie Vertebral Column. — The bisected aspect of one- half of the body, divided in the manner described (Fig. 1), would exhibit, in the trunk, the cut faces of thirty-three bones, joined together by a very strong and tough substance into a long column, which lies much nearer the dorsal than the ven- tral aspect of the body. The bones thus cut through are called the bodies of the vertebrae. They separate a long, narrow canal, called the spinal canal, which is placed upon their dorsal side, from the spacious cavity of the chest and abdomen, which is lodged upon their ventral side. There is no direct commu- nication between these two cavities. 26. Internal Organs. — The spinal canal contains a long white oord — ^the spinal cord — which is an important part of the nervous system. The ventral chamber is divided into the two subordinate cavities of the thorax and abdomen by a re- markable partition, the diaphragm (Fig. 1, i^), which is con- cave toward the abdomen, and convex toward the thorax. The alimentary canal (Fig. 1, Al.) traverses these cavities from one end to the other, piercing the diaphragm. So does a long double series of distinct masses of nervous substances, which are called ganglia, are connected together by cords, and constitute the so- called *' sympathetic " (Fig. 1, Sy,), The abdomen contains, in addition to these two sets of organs, the two kidneys, one placed against each side of the vertebral column, the liver, the pan- creas, or " sweet-bread," and the spleen. The thorax encloses, besides its segment of the alimentary and sympathetic canal, the heart in the middle, and the two lungs, one on each side. 27. The Head and Brain. — ^Where the body is succeeded by the head, the uppermost, of the thirty-three vertebral bod- ies is followed by a continuous mass of bone, which extends thrpugh the whole length of the head, and, like the spinal column, separates a dorsal chamber frona a ventral one. The dorsal chamber, or cavity of the skull, opens into the spinal


OUTLINES OF THE BODILY STEUCTUEE. 25 canal, and cont^uns a mass of nervous matter called the brain, which is continuous with the spinal cord, the brain and the spinal chord together constituting what is termed the cerebro- spinal ms {as,, as.). The ventral chamber, or cavity of the face, is almost en- tirely occupied by the pharynx and mouth, which are the upper expanded terminations of the alimentary canaL 28. The Human Body a Double Tube.— Thus the study of F\g. 1, a diagrammatic section of the human body, taken vertically throngh the median plane. 0.8. the cerebro-splnal nervous system ; N the cavity of the nose ; M that of the mouth; At,, Al. the alimentary canal represented as a simple straight tube; ZTthe heart; D the diaphiagm ; 8y. the sympathetic ganglia. Fig. 2, a transverse vertical section of the head taken parallel with the line ao; letters as before. Fig. 8, a transverse section taken along the line c d ; letters as before. 2


26 ELEMENTARY PHYSIOLOGY. a longitudinal section shows us that the human body is a double tube, the two tubes being completely separated by the spinal column and the bony axis of the skull — the dorsal tube containing the cerebro-spinal axis ; the ventral, the alimientary canal, the sympathetic nervous system, and the heart, besides other organs. Transverse sections,- taken perpendicularly to the axis of the vertebral column, or that of the skull, show still more clearly that this is the real fundamental structure of the human body, and that the great difference between the head and the trunk lies in the different size of the dorsal cavity relatively to the ventral. In the head the former cavity is very large in proportion to the size of the latter (Fig. 2) ; in the thorax or abdomen, it is very small (Fig. 3). The limbs contain no such chambers as the body and head ; but, with the exception of certain branching tubes filled with fluid, which are called vessels and lymphatics, are solid, or semi-solid, throughout Such being the general character and arrangement of the parts of the human body, it wiD next be well to consider into what constituents it may be separated by the aid of no better means of discrimination than the eye and the anatomist's knife. Section III. — The Bodily Tissues. 29. The Skin. — ^With no more elaborate aids than these, it becomes easy to separate that tough membrane which invests the whole body, and is called the skin, or integument^ from the parts which lie beneath it Furthermore, it is readily enough ascertained that this integument consists of two portions : a superficial layer, which is constantly being shed in the form of powder or scales, composed of mmute particles of homy mat- ter, and is called the epidermis ; and of a deeper part, the der- mis^ which is dense and fibrous. The epidermis, if wounded, neither gives rise to pain nor bleeds. The dermis, under like circumstances, is very tender, and bleeds freely. A practical


THE BODILY TISSUES. 27 distinction is drawn between the two in sliaving, in the €ourse of which operation the razor ought to cut only epidermic struc- tures ; for if it go a shade deeper, it gives rise to pain and hseroorrhage. 30. Mucous Membranes. — ^The skin can be readily enough removed from all parts of the exterior, but at the margins of the apertures of the body it seems to stop, and to be replaced by a layer which is much redder, more sensitive, bleeds more reacKly, and is rendered moist by giving out a more or less tenacious fluid, called muciLS, Hence, at these apertures, the integument is said to stop, and to be replaced by mucous mem' hrane, which lines all those interior cavities, such as the ali- mentary canal, into which the apertures open. But, in truth, the integument does not come to an end at these points, but is directly continued into the mucous membrane, which last is simply an integument of greater delicacy, but consisting funda- mentally of the same two layers, a deep, fibrous, sanguine, and sensitive layer, and a superficial, liomy, insensible, and blood- less one, now called the- epithelium. Thus every part of the body might be said to be contained between the walls of a double bag, formed by the epidermis, which invests the outside of the body, and the epithelium, its continuation, which lines the internal cavities. 31. Connective Tissue. — The dermis, and what answers to it in the mucous membranes, are chiefly made up by a fila- mentous substance, which yields abundant gelatine on being boiled, and is the matter which tans when hide is made into leather, and which is called areolar^ fibrous, or, better, connec- tive tissue.* The last name is the best, because this tissue is the great connecting medium by which the different parts of the body are held together. Thus it passes from the dermis be- tween all the other organs, ensheathing the muscles, coating the bones and cartilages, and eventually reaching and entering into the mucous membranes. And so completely and thoroughly ♦ Ereiy sQcli conatituent of the body, aa epidermis or epithelium, is called a «*ti88ue.'»


28 ELEMENTARY PHYSIOLOGY. does the connective tissue permeate almost all parts of the body, that if every other tissue could be dissected away, a com- plete model of all the organs would be left composed of this tissue. Connective tissue varies very much in character; sometimes being very soft and tender, at others — as in the ten- dons and ligaments, which are almost wholly composed of it — attaining great strength and density. 32. The MuBdea. — Among the most important of the tis- sues imbedded in and ensheathed by the connective tissue, are some whose presence and action can be readily determined during life. If the upper arm of a man whose arm is stretched out, be tightly grasped by another person, the latter, as the man bends up his fore-arm, will feel a great mass which lies at the fore part of the arm, swell and become prominent As the arm is extended again, the swelling vanishes. On removing the skin, the body which thus changes its configuration, is found to be a mass of red flesh, sheathed in connective tissue; and attached by the tendons, into which that tissue passes at each end, on the one hand, to the shoulder- bone, and on the other to one of the bones of the fore-arm. This mass of flesh is the muscle called biceps, and it has the peculiar property of changing its dimensions — shortening and becoming thick in proportion to its decrease in length — ^by the influence of the will as well as by other stimuli. It is by reason of this property of muscular tissue that it becomes the great motor agent of the body ; the muscles being so disposed be- tween the systems of levers which support the body, that their shortening necessitates the motion of one lever upon another. 33. The Cartilages and Bones. — ^These levers form part of the system of hard tissues which constitute the skeleton. The softer of these are the cartilages^ composed of a dense, firm sub- stance, ordinarily known as " gristle." The harder are the hones, which are masses either of cartilage or of connective tissue hardened by being impregnated with phosphate and carbonate ,

THE BODILY TISSUES. 29 of lime. They are animal tissues ^hich have become, in a manner, naturally petrified; and when the salts of lime are ex- tracted, as they may be, by the action of acids, a model of the bone in soft and flexible animal matter remains. No fewer than 206 separate bones are ordinarily reckoned in the human body. Of these, thirty-eight enter into the com- position of the long axis, and five into that of the side walls of the cerebro-spinal cavity. Twenty-four ribs bound the chest laterally, twelve on each side, and most of them are connected by cartilages with the breast-bone. In the girdle which sup- ports the shoulder, two bones are reckoned; in that to which the legs are attached, three. There are thirty bones in each of the arms, and in each of the legs. All these bones are fastened together by ligaments or by cartilages, and where they play freely over one another a coat of cartilage furnishes the surfeces which come into contact The free surfaces of those articular cartilages which enter into a joint, again, are lined by a delicate synovial membrane, which secretes a lubricating fluid — ^the synovia. Section IV. — The Combination of Actions, 34. How we stand upright. — ^Though the bones of the skeleton are all 'strongly enough connected together by liga- ments and cartilages, the joints play so freely, and the centre of gravity of the body, when erect, is so high up, that it is im- possible to make a skeleton, or a dead body, support itself in the upright position. That position, easy as it seems, is the result of the contraction of a multitude of muscles which op- pose and balance one another. Thus, the foot affording the surface of support, the muscles of the calf (Fig. 4, 1.) must con- tract, or the legs and body would fall forward. But this ac- tion tends to bend the leg ; and to neutralize this and keep the leg straight, the great muscles in front of the thigh (Fig. 4, 2) must come into play. But these, by the same action, tend to bend the body forward on the legs ; and if the body is to be


30 ELEMENTAKY PHYSIOLOGY. kept straigbt, tbey must be neutralized by tbe action of tbe muscles of tbe buttocks and of the back (Fig. 4, UL). Fio. 4. A DiAGBAM TVLvtmtkma thh AirAomcBNTB of sous of titb most iMPOBTAirr MUBCLES WHICH KRBP THV BODT IN THB ERBOT POBTITRB. I. The mnscles of the calf. II. Those of the back of the thigh. III. Those of the Bpine which tend to keep tbe body from falling forward. 1. The muscles of the front of the leg. 2. Those of the fW>nt of the thigh. 8. Those of the A*ont of the abdomen. 4, 5. Those of the firont of the neck, which tend to keep the body irom falling backward. The arrows indicate the direction of action of the muscles, the foot being fixed. The erect position, then, which we assume so easily and without thinking about it, is the result of the combined and accurately proportioned action of a vast number of muscles. What is it that makes them work together in this way ?


THE COMBINATION OF ACTIONS. 31 35. Belation of the Mind to the Mnsples. — Let any per- son in the erect position receive a violent blow on the head, and you know what happens to him. On the instant he drops prostrate in a heap, with his limbs relaxed and powerless. What has happened to him ? The blow may have beenso in- flicted as not to touch a single muscle of the body ; it may not cause the loss of a drop of blood : and, indeed, if the " concus- sion," as it is called, has not been too severe, the sufferer, after a few moments of unconsciousness, will come to himself, and be as well as ever again. Clearly, therefore, no permanent in- jury has in this case been done to any part of the body, least of all to the muscles, but an influence has been exerted upon a something which governs the muscles. And this influence may be the effect of very subtle causes. A strong mental emo- tion, and even a very bad smell, will, in some people, produce the same effect as a blow. These observations might lead to the conclusion that it is the mind which directly governs the muscles, but a little fur- ther inquiry will show that such is not the case. For people have been so stabbed or shot in the back as to cut the spinal cord, without any considerable injury to other parts ; and in this case they lose the power of standing upright as much as before, though their minds may remain perfectly clear. And not only have they lost Ahe power of standing upright under these ckcumstances, but they no longer retain any power of either feeling what is going on in the legs, or, by an act of their volition, causifig motion in them. 36. The Spinal Cord converts Impressions into Move- menta — And yet, though the mind is thus cut off from the lower limbs, a controlling and governing power over them still remains in the body. For, if the soles of the disabled feet be tickled, though no sensation will reach the body, the legs will be jerked up just as would be the case in an uninjured person. And if a series of galvanic shocks be sent along the spinal cord, the legs will perform movements even more powerful than those which the will could produce in an uninjured person.


32 ELEMENTABY PHYSIOLOGY. And, finally, if the. injury is of such a nature that the cord is crushed or profoundly disorganized, all these phenomena cease ; tickling the soles, or sending galvanic shocks along the spine, will produce no effect upon the legs. By examinations of this kind carried still further, we aiTive at the remarkahle result that the brain is the seat of all sensa- tion and mental action, and the primary source of all voluntary muscular contraction ; while the spinal cord is capable of re- ceiving an impression from the exterior, and converting it not only into a simple muscular contraction, but into a combina- tion of such actions. Thus, in general terms, we may say of the cerebro-spinal axis that it has the power of converting impressions from with* out into simple, or combined, muscular contractions. 37. Special Sensations. — ^But you will further note that these impressions from without are of very different characters. Any part of the surface of the body may be so affected as to give rise to the sensations of contact, or of heat or cold ; and any and every substance is able, under certain circumstances, to produce these sensations. But only a very small part of the body is competent to be affected in such a manner as to pro- duce in us the sensations of taste or smell, of sight or of hear- ing; and only a few substances, or particular kind of vibrations, are able so to affect those localities. These limited parts of the body, which put us in relation with particular kinds of sub- stances, or forms of force, are what are termed sensory organs^ of which we have two for sight, two for hearing, two for smeU, and one, or more strictly two, for taste. Section V. — Nutrition^ Circulation^ Excretion. 38. Constant Renewal of Tissuea^-And now that we have taken this brief view of the structure of the body, of the organs which support it, of the organs which move it, and of the organs which put it in relation with the surrounding world.


83 or, in other words, enable it to move in hannony with in- fluences from without, we must consider the means by which all this wonderful apparatus is kept in working order. All work, as we have seen, implies waste. The work of the nervous system, and that of the musclas, therefore implies con- sumption either of their own substance or of something else. And as the organism can make nothing, it must possess the means of obtaining from without that which it wants, and of throwing from itself that which it wastes ; and we have seen that, in the gross, it does these things. The body feeds, and it excretes. But we must now pass from the broad fact to the mechanism by which the fact is brought about. The organs which convert food into nutriment are the organs of alimenta- tion ; those which distribute nutriment all over the body are , organs of circulation ; those which get rid of the waste prod- ucts are organs of excretion. 39. Alimentary Apparatus. — ^The organs of alimentation are the mouth, gullet, stomach, and intestines, with their ap- pendages. What they do is to receive and grind the food ; to act upon it with chemical agents, of which they have a store ; and in this way to separate it into a nutritious solution, and nnnutritious dregs or faeces, 40. Mechanism of Distribution. — ^A system qf minute tubes, with very thin walls, termed capillaries, is distributed through the whole organism except the epidermis and its products, the epithelium, the cartilages, and the substance of the teeth, and, on all sides, these tubes open into others, which are called arte- ries and veinsy and becoming larger and larger, at length open into the heart, an organ which, as we have seen, is placed in the thorax. During life, these tubes, and the chambers of the heart, with which they are connected, are all full of liquid, which is, for the most part, that red fluid with which we are all familiar as blood. The walls of the heart are muscular, and contract rhythmi- cally, or at regular intervals. By means of these contractions the blood which its cavities contain is driven in jets out of 2*


34 ELEMENTABY PHYSIOLOGY. these cavities into the arteries, and thence into the capillaries, whence it returns by the veins into the heart again. This is the circulation of the blood. 41. Exchanges of the Blood. — Now, the nutritive solu- tion which is formed by the process of digestion, traverses the thin membrane which separates the cavity of the aliraentaiy canal from the innumerable cavities of the vessels in the walls of that canal, and so enters the blood, with which they are filled. Whirled thence by the torrent of the circulation, the blood, thus charged with nutritive matter, enters the heart, and is thence propelled into the organs of the body. To these or- gans it supplies the nutriment with which it is charged ; from them it takes their waste products, and so returns by the veins, loaded with useless and injurious excretions, which take the form, sooner or later, of water, carbonic acid, and urea. • 42. Drainage of Waste Matters from the Body. — These excretionary matters are separated from the blood by the excre- tory organSy of which there are three — the skin, the lungs, and the kidneys. Different as these organs may be in appearance, they are constructed upon one and the same principle. Each, in ultimate analysis, consists of a very thin membrane, with one face free, or in communication with the exterior of the body, and the other in contact with the blood which has to be purified. The excreted matters are, as it were, strained from the blood, through this membrane, on to its free surface, and thence make their &cape. Every one of these organs eliminates the same products, viz., water, carbonic acid, and urea, or some nitrogenous com- pound of like import. But they eliminate them in various pro- portions, the skin giving off much water, little carbonic acid, and still less urea ; the lungs giving off much water, much car- bonic acid, and a minimum of urea, or ammonia (which is one of the products of the decomposition of urea) ; the kidneys sep- arating much water, much urea, and a minimum of carbonic acid. 43. Double Function of the Lunga — Finally, the lungs


35 play a double part^ being not merely eliminators of waste, or excretionary products, but importers into the economy of a substance whicb is not exactly either food or drink, but some- thing as important as either, to wit, oxygen. It is oxygen which is the great sweeper of the economy ; which, introduced by the blood, into which it is absorbed, into all the corners of the organism, seizes upon those organic molecules which are broken down by their work, lays hold of their elements, and combines with them into the new and simpler forms, carbonic acid, water, and urea. And in doing all this, the oxidation, or, in other words, the burning of these eflfete matters, gives rise to an amount of heat which is as efficient as a fire to raise the blood to a temperature of about 100°; and this hot fluid, incessantly renewed in all parts of the economy by the torrent of the circulation, warms the body as a house is warmed by a hot-water apparatus. CHAPTER III. THE VASCULAR SYSTEM AlH) THE CIRCULATION. Section I. — Hie Vascular System. 44. Capillary Yessela — Almost all parts of the body are vascular ; that is to say, they are traversed by minute and very close-set canals, which open into one another so as to consti- tute a small-mcshed network, and confer upon these parts a spongy texture. The canals, or rather tubes, arc provided with distinct but very delicate walls, composed of a structureless membrane, in which at intervals small oval bodies termed nuclei are imbedded. These tubes are the so-called capillaries. They vary in diameter from -yuVxr*^ ^ ttJVit*'^ ^^ ^^ ^°^^ ' they are sometimes disposed in loops, sometimes in long, some- times in wide, sometimes in narrow meshes ; and the diameters


36 ELEMENTARY PHYSIOLOGY. of these mcsbes, or, in other words, the interspaces between the capillaries are sometimes hardly wider than the diameter of a capillary, sometimes many times as wide (Figs. 5, 6, 7, 8). These interspaces are occupied by the tissue which the capilla- ries permeate, so that the ultimate anatomical components of the body are, strictly speaking, outside the vessels, or extra- vascular. But there are certain parts which, in another and broader sense, are also said to be extra-vascular or non-vascular. These are the epidermis and epithelium, the nails and hairs, the sub- stance of the teeth, and the cartilages ; which may end do at- tain a very considerable thickness or length, and yet contain no Fig. 6. yo o ■ Fig. 7. Fig. S. Fig. 5, Capillaries of muscle: Fig. 6, Looped capillaries of the finger; Fig. 7, Capil- laries of the lungs ; Fig. 8, Of fet However, as we have seen that all the tissues are out- side the vessels, these diflfer only in degree from the rest. The


THE VASCULAR SYSTEM. 37 circumstaDce that all the tissues are outside tbe vessels, by no means interferes with their being bathed by the fluid which is inside the vessels, for the walls of the capiUaries arc so exceed- ingly thin that their fluid contents readily exude through them, and permeate the tissues in which they lie. 45. The Smaller Arteries and Veins. — Of the capillary tubes thus described, one kind contains, during life, the red fluid, blood, while the others are filled with a pale, watery, or milky fluid, termed lymph or chyle. The blood-capillaries are contin- ued on diflerent sides into somewhat larger tubes with thicker walls, which are the smallest arteries and veins. The mere fact that the walls of these vessels are thicker than those of the capillaries, constitutes an important difference between the capillaries and the small arteries and veins ; for the walls of the latter are thus rendered far less permeable to fluids, and the irrigation of the tissues, which is effected by the capil- laries, cannot be performed by them. Fio. 9. A minute artery (a\ endin? In (b) larger and (c) smaller capillarlea. d. Nuclei imbedded in the walls of the capillaries. The most important difference between these vessels and the capillaries, however, lies in the circumstance that their walls are not only thicker, but that they are more complex, being composed of several coats, one of which consists of mus-


38 ELEMETH'ABY PHYSIOLOGY. cular fibres (Fig. 11), which are directed transversely, so as to encircle the artery or vein (at a, Fig. 9). This coat lies in the middle ; inside it, and lining the cavity of the vessel, is a layer of very delicate epithelial cells (Fig. 10; Fig. 12, c). Outside the muscular layers is a sheath of fibrous tissue (a, Fig. 13). The muscular fibres themselves are flattened, spindle-shaped bands, each with an elongated rod-like nucleus in the middle (Fig. 11). Fio. 10. Fio. 11. Fig. 10.— Epithelial cells of the arteries. Fig. 11.— Muscular fibres of the arteries : the middle one treated with acetic acid shows more distinctly the nucleus a. 46. Contractility of the Vascular Fibres. — ^When these fibres exercise that power of contraction, or shortening in the long and broadening in the narrow direction, which, Jis was stated in the preceding chapter, is the special property of mus- cular tissue, they, of course, narrow the calibre of the vessel, just as squeezing it in any other way would do, and this contraction may go so far as, in some cases, to reduce the cavity of the vessel almost to nothing, and to render it practically impervious. 47. Circulating Vessels controlled by Nerves.— The state of contraction of these muscles of the small arteries and veins is regulated by the nerves supplied to the vessels, or, in other


THE VASCULAR SYSTEM. 39 words, the nerves determine whether the passage through these tubes shall be free and wide, or narrow and obstructed. Thus, while the small arteries and veins lose the function of directly irrigating the tissues, which the capillaries possess, they gain that of regulating the supply of fluid to the irrigators, or capil- laries themselves. The contraction or dilatation of the artenes, supplying a set of capillaries, comes to the same result as low- ering or raising the sluice-gates of a system of irrigation-canals. Fig. 12. Fio. 13. ^ Fig. 12.— A small artery. Fig. 18.— A small vein, both treated with ncetlc add; o fibrous coat; 6 muscular coat; o epithelial coat 48. Differences between Arteries and Veins. — The smaller arteries and veins severally unite into or are branches of larger arterial or venous trunks, which again spring from still larger ones, and these at length communicate by a few principal sepa- rate arterial and venous trunks with the heart. The smallest arteries and veins, as we have seen, are similar in structure, but the larger arteries and veins differ widely, for the larger arteries have walls so thick and stout that they do not sink together when empty ; and this thickness and stout- ness arises from the circumstance that, not only is the muscular coat very thick, but that in addition a strong coat of very elastic fibrous substance is developed outside the muscular


40 ELEMENTAEY PHYSIOLOGY. layer. Thus, when a large artery is pulled out and let go, it stretches and returns to its primitive dimensions almost like a piece of india-rubber. The larger veins, on the other hand, contain but little either elastic or muscular tissue. Hence, their walls are thin, and they collapse when empty. This is one great difference between the larger arteries and the veins ; the other is the presence of what are termed valves in a great many of the veins, especially in those which lie in muscular parts of the body. 49. Action of the Valves of the Veina— These valves are pouch-like folds of the inner wall of the vein. The bottom of the pouch is turned toward those capillaries into which the vein opens. The free edge of the pouch is directed the other way, or toward the heart The action of these pouches is to impede the passage of any fluid from the heart toward the cap- illaries, while they do not interfere with fluid passing in the opposite direction (Fig. 14). The working of some of these valves may be very easily demonstrated in the living body. "When the arm is bared, blue veins may he seen running from the hand, under the skin, to the upper arm. The diameter of Fig. 14. ^ DlAGRAHMATIO SeCTTONS OF VeINS WITH VaLVES. In the upper, the blood Is supposed to bo flowing in the direction of the arrow, toward the heart ; in the lower, the reyerse way. C capillary side ; H heart-side. these veins is pretty even, and diminishes regularly toward the hand, so long as the current of the blood which is running in them from the hand to the upper arm is uninterrupted. But if a finger be pressed upon the upper part of one of


THE VASCULAB SYSTEM. 41 these vciDs, and then passed downward along it, so as to drive the blood which it contains backward, sundry swellings, like little knots, will suddenly make then* appearance at several points in the length of the vein, where nothing of the kind was visible before. These swellings are nothing more than the dilatations of the wall of the vein, caused by the pressure of the blood on that wall, above a vidve which opposes its back- ward progress. The moment the backward impulse ceases the blood flows on again ; the valve, swinging back toward the wall of the vein, affords no obstacle to its progress, and the dis- tension caused by its pressure disappears (Fig. 14). The only arteries which possess valves are the primary trunks — ^the aorta and pulmonary artery — which spring from the heart, and they will be best considered with the latter organ. Fio. 15u Tins Lymphatics of thtb Front of thb Rionr Asm. flrTiytnphaticjGrlands, or ganglia, as they am somoiimes called. These ganglia arc not to be confounded with nervous ganglia.


4:2 ELEMENTARY PHYSIOLOGY. 60. The Lymphatica — Besides the capillary network and the trunks connected with it, which constitute the blood-vascular system, all parts of the body which possess this system, except the brain and spinal cord, the eye-balls, the gristles, tendons, and perhaps the bones, also contain another set of what are termed lymphatic capiUaries, mixed up with those of the blood- vascular system, but not directly communicating with them ; and, fiirther, differing from the foregoing in opening into larger vessels on only one side. That is to say, they are connected only with trunks which carry fluid away from them, there being none which bring any thing to them. These trunks re- semble the small veins not only in this respect, but, further, in being abtmdantly provided with valves, which fully allow of the passage of liquid from the lymphatic capillaries, but ob- struct the flow of any thing the other way. The lymphatic trunks differ from the veins, in that they do not rapidly unite into larger and larger trunks, which present a continually increasing calibre, and allow of a flow without in- terruption to the heart ; but that, remaining nearly of the same size, they, at intervals, enter and ramify in oval bodies called lymphatic glands, whence new lymphatic trunks arise (Fig. 15). In these glands the lymphatic capillaries and passages are closely interlaced with blood capillaries. Sooner or later, however, the great majority of the smaller lymphatic tninks pour their contents into a considerable tube, which lies in front of the back-bone, and is called the thoracic duct ; this opens at the root of the neck into the conjoined trunks of the great veins which bring back the blood from the left side of the head and the left arm (Fig. 16). The remaining lymphatics are connected by a common canal with the corresponding vein on the right side. Where the principal trunks of the lymphatic system open into the veins, valves are placed, which allow of the passage of fluid only from the lymphatic to the vein. Thus the lymphatic ves- sels are, as it were, a part of the venous system, though, by reason of these valves, the fluid which is contained in the veins


THE VASCULAR SYSTEM. 43 cannot get into the lymphatics. On the other hand, every facility is afforded for the passage of the fluid contained in the lymphatics into the veins. Indeed, in consequence of the nu- merous valves in the lymphatics, every pressure on, and con- traction of, their walls, not being able to send the fluid back- ward, must drive it more or less forward, toward the veins. Fio. la The THOBAao Duct. a The receptacle of the chyle: &the trnnk of the thoracic dnct, opening Into the Junction of the left Jafmlar (/) andsnbclavian (g) veins; </Iynaphatic glands placed in the lambar and intercostal regions ; h h the cut cesophngns. Two veins are st'cn running along beside the lower part of the thoracic duct, and Jnst above its middle, one (the left) crosses under the duct and joins the othiur. These are the azygos veins. 61. The Lacteala — The lower part of the thoracic duct is dilated, and is termed the receptacle or cistern of the chyle (a. Fig. 16). In fact, it receives the lymphatics of the intestines, which, though they differ in no essential respect from other


44 ELEMENTARY PHYSIOLOGY. lymphatics, are called lacteah^ because, after a meal containing much fatty matter, they are filled with a milky fluid, which is termed the chyle. The lacteals, or lymphatics of the small in- testine not only form networks in its walls, but send blind pro- longations into the little velvety processes termed villi^ with which the mucous membrane of that intestine is beset The trunks which open into the network lie in the mesentery (or membrane which suspends the small intestine to the back wall of the abdomen), and the glands through which these trunks lead are hence termed the mesenteric glands. Section II. — Connections and Structure of the Heart, 62. The Heart and the Great Vessels, — ^It will now be desirable to take a general view of the arrangement of all these different vessels, and of their relations to the great central or- gan of the vascular system — ^the heart (Fig. 17). All the veins of every part of the body, except the lungs, the heart, itself, and certain viscera of the abdomen, join to- gether into larger veins, which, sooner or later, open into one of two great trunks (Fig. 17, V.CS. V,CJ,) termed the supe- rior and the inferior vena cava^ which debouch into the upper or broad end of the right half of the heart. All the arteries of every part of the body, except the lungs, are more or less remote branches of one great trunk — the aorta (Fig. 17, Ao,)y which springs from the lower division of the left • half of the heart The arteries of the lungs are branches of a great trunk (Fig. 17, P,A,) springing from the lower division of the right side of the heart. The veins of the lungs, on the contrary, open by four trunks into the upper part of the left side of the heart (Fig. 17, P.V.), Thus the venous trunks open into the upper division of each half of the heart — ^those of the body in general into that of the nght half; those of the lungs into the upper division of the left half; while the arterial trunks spring from the lower


CONNECTIONS AND 8TBUCTUEE OP THE HEART. 45 moieties of each lialf of the heart — ^that for the body in gen- eral from the left side, and that for the lungs from the right TLU JXL Fig. 17. DiAOBAX OF Tire Hbabt and Vessels, wirn the Coitrsb op the Cibcttlatiok. Z.A. left anricle ; L. V. left ventricle ; Ao. aorta: AK arteries to the upper part of the body; AK arteries to the lower part of the body ; JI.A. hepatic artery, which eun- plles the liver with part of its blood ; F'. veins of the lower pjrt of the body ; V.P. vena portae; ^F. hepatic vein; V.C.L inferior vena cava ;k. ^. A superior vena cava; F*. veins of the upper part of the body; /?. J. right auricle; J?. F right ventricle: P.A. pulmonary artery ; Lff. lung; P. V. pulmonary vein ; Let. lacteals ; Zy. lymphatic; Th,D. thoracic duct. The arrows indicate the course of the blood, lymph, and chyle. The vessels which contain arterial blood have dark contours, while those which carry venous blood have light contours.


46 ELEMENTARY PHYSIOLOGY. side. Hence it follows that the great artery of the body, and the great veins of the body, are connected with opposite sides of the heart ; and the great artery of the lungs and its veins also with opposite sides ; while the veins of the body open into the same side as the arter}' of the lungs, and the veins of the lungs open into the same side as the artery of the body. 53. Coronary Arteries and Vein. — The arteries which open into the capillaries of the substance of the heart are called coromxry arteries^ and arise, like the other arteries, from the aorta, only close to its origin. But the coronary vein, which is formed by the union of the small veins which arise from the capillaries of the heart, does not open into either of the vensD cava?, but directly into the division of the heart into which these cava open — that is to say, into the right upper division. 64. Hepatic Vessels. — The abdominal viscera referred to above, the veins of which do not take the usual course, are the stomach, the intestines, the spleen, and the pancreas. These veins all combine into a single trunk, which is termed the vena ported (Fig. 17, V,P,), but this trunk does not open into the vena cava inferior. On the contrary, having reached the liver, it enters the substance of that organ, and breaks up into an immense multitude of capillaries, which ramify through the liver, and become connected with those into which the artery of the liver, called the hepatic artery (Fig. 17, H.A,\ tranches. From this common capillary mesh-work veins arise, and unite, at length, into a single trunk, the hepatic vein (Fig. 17, H. Fl), which emerges from the liver, and passes into the inferior vena cava. The portal vein is the only great vein in the body which branches out and becomes continuous with the capillaries of an organ like an artery. 65. The Heart — ^The heart, to which all the vessels in the body have now been directly, or indirectly, traced, is an organ, the size of which is usually roughly estimated as equal to that of the closed fist of the person to whom it belongs, and which has a broad end turned upward and backward, and rather to the right side, called its base ; and a pointed end turned down-


CONNECTIONS AND STBUCTDRE OF THE HEART. 47 ward and outward, and to the left side, so as to lie opposite the interval between the fifth and sixth ribs, which is called its apex (Fig. 19). It is lodged in the chest, between the lungs, nearer the front than the back wall of the chest, and it is enclosed in a sort of double bag — the perkardiurjv— one h&lf of the double bag being closely adherent to the heart itself, while the other, which is continuous with this upon the great vessels, at a little distance from the base of the heart, loosely envelops the fore- Traksvebsb Sbction of the Cdest, with the Heabt and Lungrin Place. J>. v. dorsal vertebra, or joint of the backbone; Ao. Ao'. aortti, the top of its arch being cut away in this section; S.C. superior vena cava; P. A. pulmonary artery, dividing into a branch for each lunz; L.P. B.P. left and risrht pulmonary veins; Br. bronchi; BM L.L. right and left lungs; <E. the gullet or oesophagus. going. Between the two layers of the pericardium is a small, completely closed cavity, hned by an epithelium, and secreting into its interior a small quantity of clear fluid. The outer layer of the pericardium is firmly connected with the upper surface of the diaphragm. But the heart cannot he said to depend altogether upon the diaphragm for support, inasmuch as the great vessels which issue from or enter it, and for the most part pass upward from its base, help to suspend it and keep it in place. 56. The Auricles and Ventricles. — Thus the heart is coated outside by one layer of the pericardium. Inside, it con-


48 ELEMENTARY PHYSIOLOGY. tains two great cavities or " divisions," as they have been termed above, completely separated by a fixed partition which extends from the base to the apex of the heart, and consequently having no direct communication with one another. Each of these two great cavities is further subdivided, not longitudinally, but trans- versely, by a movable partition. The cavity above the parti- j?. j:vi Tnx Heabt, great Vessels, and Lungs. Front Yaw, R, V. right ventricle ; Z. V. left ventricle; R.A. right auricle; L.A. left auricle: Ao, aorta; P. A. pulmonary artenr; P. V. pulmonarv veins; B.L. right lun^; L.L. left lung; F.^. vena cava superior; 8.C. subclavian vessels; C. carotids; B. and L.J.V. right and left Jugular veins; V.L vena cava inferior; T, trachea; R, bronchi tion on each side is called the auricle — right or left, as the case may be ; the cavity below the partition is called the ventricle of its side. Each of the four cavities has the same capacity, and is ca- pable of containing from four to six cubic inches of water ; but the walls of the auricles are much thinner than those of the ventri- cles, and are of equal thickness, while, of the ventricles, the left has a much thicker wall than the right. 67. Their unequal Wort — In fact, as we shall sec, the ventricles have more work to do than the auricles, and the left ventricle more to do than the right Hence the ventricles have


CONNECTIONS AND STKUCTUKE OF THE HEABT. 49 more muscular substance than the auricles, and the left ventri- cle than the right ; and it is this excess of muscular substance which gives rise to the excess of thickness observed. TCX

R^/:

Fig. 20. Fis. 21. Fig. 20, thb Left SroE, and Fig. 21, the Eight Side of the Heabt dissected. Fig. 20.— Z.^. theleft anricle; P.V. the four pulmonary veins ; c ef , a style passed through the auriculo- ventricular aperture; M.V. the mitral valves; <y 6, a stvle passed through the left ventricle into the aorta; £,A. R. V. parts of the right side of the heart; P. A. pulmonary artery. Fig. 21. — P.A. the right auricle ; V.( '.& superior vena cava ; V.C.I, inferior vena cava, the gtyk'S/e, c d being passed through them Into the auricle; a ft, style passed through the auriculo- ventricular aperture ; T. V. tricuspid valve; H. V. right ven- tricle; 8.L. semilunar valves at the base of P.A. the pulmonary artery, through which the style g h\s passed ; L.A. L. V. parts of the leit side of the heart 58. Muscular Fibres and Fibrous Eings. — The muscular fibres of the heart are not smooth, nucleated bands, like those of the vessels, but are bundles of transversely-striped fibres, and resemble those of the chief muscles of the body, except that they have no sheath or sarcolemma, such as we shall find to exist in the latter. Almost the whole mass of the heart is made up of these muscular fibres, which have a very remarkable and complex arrangement ; but it has an internal lining called the endocar- dium ; and at the junction between the auricles and ventricles the apertures of communication between their cavities, called


50 ELEMEin'ARY PHYSIOLOGY. the auriculo-ventricular apertures, are strengthened by fibrous rings. To these rings the movable partitions or valves be- tween auricles and ventricles, the arrangement of which must next be considered, are attached. 59! Valves of the Heart ; their Structure and Action. — There are three of these partitions to the right auriculo-ventric- ular aperture, and two to the left. Each is a broad, thin, but very tough and strong production of the endocardium, of a tri- angular shape, attached by its base, which joins on to its fellow, to the auriculo-ventricular ring, and at its apex depending into the ventricular cavity. On the right side there are, therefore, three of these broad, pointed membranes, whence the whole apparatus is called the tricuspid valve. On the left side there are but two, which when detached from all their connections but the auriculo-ventricular ring, look something like a bishop's mitre, and hence this is called the mitral valve. The edges and apices of the valves are not completely free and loose. On the contrary, a number of fine but strong ten- dinous cords, called ckordce tendinece, connect them with some column-like elevations of the fieshy substance of the walls of the ventricle, which arc termed columnce carnece. From this arrangement it follows that the valves oppose no obstacle to the passage of fluid from the auricles to the ventri- cles ; but if any should be forced the other way, it will at once get between the valve and the wall of the heart and drive the valve backward and upward. Partly because they soon meet in the middle and oppose one another's action, and partly be- cause the chordce tendinece hold their edges and prevent them from going back too far, the valves thus forced back give rise to the formation of a complete transverse partition, through which no fluid can pass between the ventricle and the auricle. Where the aorta opens into the left ventricle and where the pulmonary artery opens into the right ventricle, another valvu- lar apparatus is placed, consisting in each case of three pouch- like valves similar to those of the veins, and called the semilu-


CONNECTIONS AND 6TEUCTUEE OF THE HEAET. 51 nar valves, but placed on the same level and raeeting on the middle line, so as completely to stop the passage when any fluid is forced along the artery toward the heart On the other hand, these valves flap back and allow any fluid to pass from the heart into the artery with the utmost readiness. The action of the auriculo-ventricular valves may be demour strated with great ease on a sheep's heart, in which the aorta and pulmonary artery are tied and the greater part of the auri- cles cut away, by pouring water into the ventricles through the auriculo-ventricular aperture. The valves then usually close themselves, and they may be made to do so at once by gently squeezing the ventricles. So, in like manner, if the base of the aorta or pulmonary artery be cut out of the heart so as not to injure the valves, water poured into the upper ends of these vessels will cause the valves to close tightly, and allow nothing to flow out after the first moment. Fio. 22. The valves of the heart displayed by cutting away both auricles and all but the bas«  of the pulmonary artery (A) and aorta iB)\ <7, the tricuspid; i>, the mitral Talve ; a, a style i)a8sed into the coronary vein. Thus the arrangement of the auriculo-ventricular valves is such that any fluid contained in the chambers of the heart can be made to pass through the auriculo-verftricular apertures in


52 ELEMENTARY PHYSIOLOGY. only one direction, that is to say, from the auricles to the ven- tricles; and on the other hand, the arrangement of the semilu- nar valves is such that fluid in the ventricle passes easily into the aorta and pulmonary artery, but that none can be made to travel the other way from the artery to the ventricle. 60. Bliythm of its Movement— Systole and Diastole.— Like all other muscular substances, that of the heart is contrac- tile ; but unlike most muscles, the heart contains within itself a something which causes its diflPerent parts to contract in a definite succession and at regular intervals. If the heart of a living animal be removed from the body, it will go on pulsating for a longer or shorter time, much as it did while in the body. And careful attention to these pulsations will show that they consist of — (1) A simultaneous contraction of theValls of both auricles. (2) Immediately following this, a simultaneous con- traction of the walls of both ventricles. (3) Then comes a pause or state of rest, after which the auricles and ventricles contract again in the same order as before, and their contrac- tions are followed by the same pause as before. If the auricular contraction be represented by A", the ven- tricular by V*', and the pauses by — , the series of actions will be as follows: A^ T' — ; A" V^ — ; A^ V^ — ; etc. Thus, the contraction of the heart is rhythmical^ two short contrac- tions of its upper and lower halves respectively being followed by a pause of the whole, which occupies about as long as the two contractions. The state of contraction of the ventricle or auricle is called its systole — the state of relaxation, during which it undergoes dilatation, its diastole, • Section III. — Working of the Heart and Vessels, 61. Working of the Heart. — Having now acquired a notion of the arrangement of the different pipes and reservoirs of the circulatory system, of the distribution of the valves, and of the rhythmical contractions of the heart, it will be easy to


, WORKmO OF THE HEART AND VESSELS. 53 comprehend what must happen if (the whole apparatus con- taining blood) the first step in the pulsation of the heart occurs and the auricles contract. By this action each auricle tends to squeeze the fluid which it contains out of itself in two direc- tions — the one toward the great veins, the other toward the ventricles ; and the direction which the blood as a whole will take will depend upon the relative resistance offered to it in these two directions. Toward the great veins it is resisted by the whole mass of the blood contained in the veins. Toward the ventricles, on the contrary, there is no resistance worth mentioning, inasmuch as the valves are open. The walls of the ventricles, in their uncontracted state, are flaccid and easily dis- tended, and the whole pressure of the arterial blood is taken off" by the semilunar valves, which are necessarily closed. There- fore, when the auricle contracts only a ver}^ little of the fluid will flow back into the veins, and the great mass of it will pass at once into the ventricles. As the ventricles become distended, the blood getting behind the auriculo-ventricular valves will bring them toward one another, and almost shut them. The auricles now cease to contract, and immediately that their walls relax, fresh blood from the great veins flows into and slowly distends them again. But the moment the auricular systole is over, the ventricu- lar systole begins. The walls of each ventricle contract vigor- ously, and the first effect of that contraction is to shut the au- riculo-ventricular valves completely, and to stop all egress tow- ard the auricle. The pressure upon the valves becomes very considerable, and they might even be driven upward if it were not for the chordce tendinece which hold down their edges. Furthermore, as the contraction continues, and the cavity of the ventricle becomes diminished, the points of the wall of the heart to which the chordce tendinece are attached approach the edges of the valves, and thus there is a tendency to allow of a slackening of these cords, which, if it really took place, might permit the edges of the valves to flap back and so de- stroy their utility. This tendency, however, is counteracted by


54 ELEMENTARY PHYSIOLOGY, the connection of the chordcB tendinem not directly to the walls of the heart, but to those muscular pillars, the columnce cornece^ ■which stand out from its substance. These muscular pillars contract at the same time the substance of the heart does ; and thus, just so far as the contraction of the latter brings them nearer the valves, do they, by their own contraction, pull the chordoi tendinece as tight as before. By the means which have now been described the fluid in the ventricle is debarred from passing back into the auricle ; the whole force of the contraction of the ventricular walls is therefore expended in overcoming the resistance presented by the pressure of the blood in the arteries on the semilunar valves, which is the result partly of the weight of that fluid, partly of the elastic resistance of the arterial walls to further distension, and partly of the friction and inertia of the blood contained in the arterial ramifications and capillaries. It now becomes obvious why the ventricles have so much more to do than the auricles, and why valves are needed between the auri- cles and ventricles, while none arc wanted between the auricles au3d the veins. All that the auricles have to do is to fill the ventricles, which offer no active resistance to that process. Hence the thinness of the walls of the auricles, and hence the needlessness of any auriculo- venous valve, the resistance on the side of the ventricle being so insignificant that it gives way at once befoie that afforded by the pressure of the blood in the veins. On the other hand, the ventricles have to overcome a great resistance in order to force fluid into elastic tubes which are already full ; and if there were no auriculo- ventricular valves, the fluid in the ventricles would meet with less obstacle in pushing its way backward into the auricles and thence into the veins than in lifting the semilunar valves. Hence the necessity, firstly, of the auriculo-ventricular valves ; and secondly, of the thickness and strength of the walls of the ventricles, and since the aorta, body, capillaries, and veins form a much larger system of tubes, con- taining more fluid and offering more resistance than the pulmo-


WORKING OF THE HEART AND VESSELS. 55 nary arteries, capillaries, and veins, it follows that the left ven- tjicle needs a thicker muscular wall than the right 62. The Working of the Arteries,— Thus, at every systole of the auricles, the ventricles are filled and the auricles emptied, to be slowly refilled by the pressure of the fluid in the great veins, which is amply suflScient to overcome the passive resist- ance of their relaxed walls. And at every systole of the ven- tricles the arterial systems of the body and lungs receive the contents of these ventricles, and the nearly emptied ventricles remain ready to be refilled by the auricles. We must now consider what happens in the arteries. When the contents of the ventricles are suddenly forced into these tubes (which are already fiill), a shock is given to the whole mass of fluid which they contain. This shock is propa- gated almost instantaneously throughout the fluid, becoming fainter and fainter in proportion to the increase of its mass in the capillaries, and finally cease to be discernible. If the vessels were tubes of a rigid material, like gas-pipes, the fluid which the arteries contain would be transported forward as far as this impulse was competent to carry it, at the same instant as the shock throughout their whole extent ; and as the arteries open into the capillaries, the capillaries into the veins, and these into the heart, there would be returned to the auricles almost at the same moment that the ventricles contract a quantity of fluid exactly equal to that driven out of the ventricles. However, the vessels are not rigid, but, on the contrary, very yielding tubes; .and the great arteries, as we have seen, have especially elastic walls. What happens then when the ventricular systole takes place is — 1st, The sudden slight shock already mentioned. 2d, The dilatation of the great arteries by the pressure of the Increased quantity of blood forced into them. Finally, when the systole is over, the force stored up in the dilated arterial walls in the shape of elastic tension, comes into play and exerts a pressure on the fluid — ^thc first eff'ect of which is to shut the semilunar valves ; the second, to drive the fluid


56 ELEMENTARY PHYSIOLOGY. from the larger arteries along the smaller ones. These it di- lates in the same fashion. The fluid then passing into the cap- illaries, the ejection of a corresponding quantity of fluid from them into the veins, and finally from the veins into the heart, is the ultimate result of the ventricular systole. 63. The Beat of the Heart. — Several of the practical re- sults of the working of the heart and arteries just described now become intelligible. For example, between the fifth and sixth ribs, on the left side, a certain movement is perceptible by the finger and by the eye, which is known as the beating of the heart. It is the result of the striking of the apex of the heart against the pericardium and through it, on the inner wall of the chest, at this point at the moment of the systole of the ventricles. When the systole occurs, in fact, two things happen : in the first place, in consequence of the manner in which the muscular fibres of the heart are disposed, its apex bends upward sharply, and in the second place, jts face is thrown a little downward and forward in consequence of the stretching and elongation of the aorta by the blood which is thrown into it. The result of one or other, or both of these actions com- bined, is the upward and forward blow of the apex of the heart which we feel. 64. The Sounds of the Heart.— Secondly, if the ear isapr plied over the heart certain sounds are to be heard, which re- cur with great regularity at intervals corresponding with those of every two beats. First comes a longish dull sound ; then a short sharp sound ; then a pause ; then the long, then the sharp sound, then another pause, and so on. There are many differ- ent opinions as to the cause of the first sound, and perhaps physiologists are not yet at the bottom of the matter ; but the second sound is without doubt caused by the sudden closure of the semilunar valves when the ventricular systole ends. That such is the case is proved by the experiment which has been performed of hooking back the semilunar valves in a living animal, when the second sound ceases at once. 65. The Pulse in the Arteries. — Thirdly, if the finger be


WOBKINa OF THE HEART AITD VESSELS. 57 placed upon an artery, such as that at the wrist, what is termed the pulse will be felt ; that is to say, the elastic artery dilates somewhat at regular intervals, which answer to the beatings of the heart. The pulse which is felt by the finger, however, does not correspond precisely with the beat of the heart, but takes place a little after it, and the interval is longer the further the artery is from the heart The beat in the artery on the inner side of the ankle, for example, is a little later than the beat of the artery in the temple. The reason of this is that the finger is only delicate enough to distinguish the dilatation of the ar- tery by the wave of blood which is driven along it by the elastic reaction of the aorta, and is not competent to perceive the first shock caused by the systole. But if instead of the fingers very delicate levers be made to rest upon any two arte- ries, it will be found that the pulse really begins at the same time in both, the shock of the systole making itself felt all over the muscular system at once ; and that it is only the actual fluid which is propelled into the two arteries by the elastic reaction of the greater vessels, which takes longer to reach and distend the more distant branch. 66. Jetting of Blood from cut Arteries. — Fourthly, when an artery is cut the outflow of the fluid which it contains is increased by jerks, the intervals of which correspond with the Intervals of the beats of the heart. The cause of this is plainly the same as that of the pulse ; the force which would be em- ployed in distending the walls of the artery, were the latter en- tire, is spent in jerking the fluid out when the artery is cut. 67. Why the Capillaries are Pnlseless.— -Fifthly, The pulse, under ordinary circumstances, is no longer to be de- tected in the capillaries nor in the veins. This arises from several circumstances. One of them is that the capacity of the branches of an artery is greater than the capacity of the trunk, and the capacity of the capillaries is greater than that of the small arteries. Ilencc, supposing the capacity of the trunk to be 10, that of its branches 60, and that of the cap- illaries into which these open 100, it is clear that a quantity 6*


58 ELEMENTAEY PHYSIOLOGY. of fluid thrown into the trank, sufficient to dilate it by one- tenth, and to produce a very considerable and obvious eflfect, could not distend each branch by more than -g^th, and each capillary by yj^th of its volume in amount, an effect which might be quite imperceptible. 68. Subdivision of the Heart-Stroke. — Furthennore, the flow of the fluid is retarded by the subdivision of the tubes which contain it ; and the multitude of minute impulses into which the primary blow of the systole is subdivided in the small vessels, become lost among these obstacles and fused into one general and steady pressure. This loss of the distinct effect of the heart's action may be likened to the result of pumping into a horse-trough. Where the water flows into the trough, the splashes and waves, caused by the intermitting fall of water from the pump, are very obvious ; but from a tap open at the other end of the trough, the water will flow steadily and evenly. 69. Cause of a steady Capillary Flow. — Finally, in con- sequence of the resistance to the passage of the fluid, resulting from the extremely minute size and subdivision of the capilla- ries, the fluid to a certain extent accumulates in the arteries, and keeps their walls in a constant state of distension, which is only increased at each successive beat of the heart. In other words, one beat follows another before the effect of the first has ceased. As the effect of each systole becomes diminished by the causes above mentioned, that of this constant pressure be- comes more obvious and gives rise to a steady passage of the fluid from the arteries toward the veins. In this way in fact the arteries perforip the same functions as the air-reservoir of a fire-engine, which converts the jerking impulse given by the pumps into the steady flow of the delivery-hose. Such is the general result of the mechanical conditions of the organs of the circulation combined with the rhythmical activity of the heart. Tliis activity drives the fluid contained in these organs out of the heart into the arteries, thence to the Capillaries, and from them through the veins to the hcaii


THE GRNEEAL CIRCULATION. 69 again ; and in tbe course of these operations it gives rise inci- dentally to the beating of the heart, the sounds of the heart, and the pulse. Section IV. — The General Circulation. 70. The Course of the Circulation. — It is now neces- sary to trace the exact course of the circulation as a whole. And we may conveniently commence with the portion of the blood contained at any moment in the right auricle. The contraction of the right auricle drives that fluid, for the reason above mentioned, into the right ventricle ; the ventricle then contracts and forces it into the pulmonary artery ; from hence it passes into the capillaries of the lungs. Leaving these, it returns by the four pulmonary veins to the left auri- cle ; the contraction of the left auricle drives' it into the left ventricle; that of the left ventricle forces it into the aorta. The branches of the aorta convey it into all parts of the body except the lungs, and from the capillaries of all these parts, ex- cept the intestines and certain other viscera in the abdomen, it is conveyed by vessels which gradually unite into larger and larger trunks into either the superior or the inferior vena cava, which carry it to the right auricle once more. But the blood brought to the capillaries of the stomach and intestines, spleen and pancreas, by these arteries is gathered into veins which unite into a single trunk — the vena portce. The vena portae distributes its blood to the liver, mingling with that supplied to the capilla- ries of the same organ by .the hepatic artery. From these capil- laries it is conveyed by small veins which unite into a large trunk — the hepatic vein, which opens into the inferior vena cava. This course of the blood from the abdominal viscera to the hepatic vein is called the portal circulation. The heart itself is supplied with blood by the two coronary arteries which spring from the root of the aorta just above two of the semilunar valves. The blood from the capillaries of the heart is carried back by the coronary vein, not to cither vena


60 ELEMENTARY PHYSIOLOaY. cava, but to the right auricle, its opening into which is pro- tected by a valve, so as to prevent the right auricle from driv- ing the venous blood which it contains back into the vessels of the heart. 71. Eoutes of the Travelling Blood-Paxticles. — ^Thus, the shortest possible course which any particle of the blood can take, in order to pass from one side of the heart to the other, is to leave the aorta by one of the coronary arteries, and return to the right auricle by the coronary vein. And in order to pass through the greatest possible number of capillaries, and return to the point from which it started, a particle of blood must leave the heart by the aorta and traverse the arteries which supply the alimentary canal, spleen, and pancreas. It then enters, Istly, the capillaries of these organs; 2dly, the capillaries of the liver ; 3dly, after passing through the right side of the heart, the capillaries of the lungs, ftom which it re- turns to the left side and eventually to the aorta. Furthermore, from what has been said respecting the lym- phatic system, it follows that any particle of matter which enters a lacteal of the intestine will reach the right auricle by the superior cava, after passing through the lymph capillaries and channels of sundry lymphatic glands ; while any thing which enters the adjacent blood capillary will reach the right auricle by the inferior cava, after passing through the blood capillaries of the hver. 72. Nervous Control and the Circulation — We have seen that the small arteries and veins may be directly affected by the nervous system, which controls the state of contraction of their muscular walls, and so regulates their calibre. The effect of this power of the nervous system is to give it a certain con- trol over the circulation in particular spots, and to produce such a state of affairs, that, although the power of the heart and the general condition of the vessels remain the same, the state of the circulation may be very different in different localities. 73. Explanation of Blushing. — Blushing is such a purely local modification of the circulation, so that it will be instructive


THE GENERAL CIECULATION. 61 to consider what happens in blushing. An emotion — some- times pleasurable, sometimes painful — takes possession of the mind, thereupon a hot flush is felt, the skin grows red, and ac- cording to the intensity of the emotion these changes are con- fined to the cheeks only, or extend to the " roots of the hair," or " all over." What is the cause of these changes ? The blood is a red and hot fluid ; the skin reddens and grows hot because its ves- sels suddenly contain an increased quantity of this red and Lot fluid ; and its vessels contain more, because the small arteries suddenly dilate, the natural moderate contraction of their mus- cles being superseded by a state of relaxation. In other words, the action of the nerves which cause this muscular contraction is suspended. On the other hand, in many people, extreme terror causes the skin to grow cold and the face to appear pale and pinched. Under these circumstances, in fact, the supply of blood to the skin is greatly diminished, in consequence of an excessive stimulation of the nerves of the small arteries, which causes them to contract and so cut oflf the supply of blood. 74. Experimental Proof of this. — ^That this is the real state of the case may be proved experimentally upon rabbits. These animals, it is true, do not blush naturally, but they may be made to blush artificially. If, in a rabbit, the sympathetic nerve which sends branches to the vessels of the head is cut, the ear of the rabbit, which is covered by so delicate an integ- ument that the changes in its vessels can be readily perceived, at once blushes. That is to say, the vessels dilate, fill with blood, and the ear becomes red and hot The reason of this is, that when the sympathetic is cut, the nervous stimulus which is ordinarily sent along its branches is interrupted, and the muscles of the small vessels, which were slightly contracted, become altogether relaxed. And now it is quite possible to produce pallor and cold in the rabbit's ear. To do this it is only necessary to irritate the cut end of the sympathetic which remains connected with the vessels. The nerve then becomes excited, so that the rauscu-


G2 ELEMENTARY PHYSIOLOGY. lar fibres of the vessels are tbrown into a violent state of con- traction, which diminishes their calibre so much that the blood can hardly make its way through them. Consequently, the car becomes pale and cold. 75. Eelation of tUs Nervous Control to Disease. — The practical importance of this local control exerted by the ner- vous system is immense. When exposure to cold gives a man catarrh, or inflammation of the lungs, or diarrhoea, or some still more serious afiection of the abdominal viscera, it is brought about in this way. The impression made by the cold on the skin is conveyed to the nervous centres, and so influen- ces the vaso-motor nerves^ as the nerves which govern the walls of the vessels are called (see par. 47), of the organ affected, as to cause their partial paralysis, and produce that state of conr/estion (or undue distension of the vessels) which so com- monly ends in inflammation. 76. Nervous Control over the Heart.— Is the heart, in like manner, under the control of the central nervous system ? As we all know, it is not under the direct influence of the will, but every one is no less familiar with the fact that the actions of the heart are wonderfully affected by all forms of emotion. Men and women often faint, and have sometimes, been killed, by sudden and \aolent joy or sorrow ; and when they faint or die in this way, they do so because the perturba- tion of the brain gives rise "to a something which arrests the heart as dead as you stop a stop-watch with a spring. On the other hand, other emotions cause that extreme rapidity and violence of action which we call palpitation. Now there are three sets of nerves in the heart : one set are supplied by ganglia, or masses of nerve-cells, in its sub- stance ; another set come from the sympathetic nerve ; a third set are branches of a remarkable nerve, which comes straight from the brain, and is called the pneumogastric nerve. There is every reason to believe that the regular rhythmical succes- sion of the ordinary contractions of the heart depends upon the ganglia lodged in its substance. At any rate, it is certain


THE GENERAJi CIECULATION. 63 that tliese movements depend neither on tHe sympathetic nor on the pneumogastric, since they go on as well when the heart is removed from the body.

  • . In the next place, there is much reason to believe that the

influence which increases the rapidity of the heart's action is exerted through the sympathetic. And, lastly, it is quite certain that the influence which arrests the heart's action is supplied by the pneumogastric. This may be demonstrated in animals, such as frogs, with great ease. 77. The Circulation directly observed .—If a frog be pithed, or its brain destroyed, so as to obhtcrate all sensibility, the animal will continue to live, and its circulation will go on per- fectly well for an indefinite period. The body may be laid open without causing pain or other disturbance, and then the heart will be observed beating with great regularity. It is pos- sible to make the heait move a long index backward and for- ward, like the inverted pendulum which musicians term a met- ronome ; and if frog and index are covered with a glass shade, the air under which is kept moist, the index will vibrate with great steadiness for a couple of days. It is easy to adjust to the frog thus prepared, a contrivance by which electrical shocks may be sent through the pneumo- gastric nerves, so as to irritate thefti. The moment this is done the index stops dead, and the heart will be found quies- cent, with relaxed and distended walls. After a little time the influence of the pneumogastric passes ofi*, the heart recommen- ces its work as vigorously as before, and the index vibrates through the same arc as formerly. With careful management, this experiment may be repeated very many times ; and after every arrest by the irritation of the pneumogastric, the heart resumes its work. 78. Proof of the Cironlation in Man. — ^The evidence that the blood circulates in man, although perfectly conchisive, is almost all indirect. But certain of the lower animals, the whole, or parts, of the body of which are transparent, readily


64 ELEMENTABY PHYSIOLOGY. afford direct proofof the circulation, the blood visibly rushing from the arteries into the capillaries, and from the capillaries Fig. 24. Fig. 23.— Two toes of a frog's foot, with the intervening web, slightly enlarged; a, veins; 6, arteries connected.by a networlc of capillaries. Fig. 24.— A small portion of tiienet-work magnitled ; a b are snoall veins, and d capil- laries, all tlillof large oval blood corpuscles, moving in the direction indicated bv the arrows; c, star-shaped, colored patches or pigment cells in the fh)g'8 skin. into the veins, so long as the animal is alive and its heart is at work. The animal in which the circulation can be most con- veniently observed is the frog, as the web between its toes is very transparent, and the particles suspended in its blood are so large that they can be readily seen as they slip swiftly along


ITS MICROSCOPICAL ELEMENTS. 65 with the stream of blood, when the toes are fastened ont, and the intervening web examined under even a low magnifying power (Fig. 24). CHAPTER IV. OF THE BLOOD AND LTMPa Section I. — Its Microscopical Elements, 79. How to examine it. — In order to become properly ac- quainted with the characters of the blood it is necessary to ex- amine it with a microscope, magnifying at least three or four hundred diameters. Provided with this instnunent, a hand lens, and some slips of thick and thin glass, the student will be enabled to follow the present chapter. The most convenient mode of obtaining small quantities of blood for examination, is to twist a piece of string, pretty tightly, round the middle of the last joint of the middle or ring finger of the left hand. The end of the finger will im- mediately swell a little, and become darker colored, in con- sequence of the obstruction to the return of the blood in the veins, caused by the ligature. When in this condition, if it be lightly pricked with a sharp clean needle (an operation which causes hardly any pain), a good-sized drop of blood will at once exude. Let it be deposited on a glass slide, and covered lightly and gently with a thin glass, so as to spread it out evenly into a thin layer. Let a second slide receive another drop, and let it be put under an inverted tumbler so as to keep it fi-om drying. Let a third drop be dealt with in the same way a few granules of common salt being first added to the drop. 80. Its Appearance when magnified. — To the naked eye the layer of blood upon the first slide will appear of a pale red- dish color, and quite clear and homogeneous. But on viewing


66 ELEMENTARY PHYSIOLOGY. itjjfith even a pocket lens, its apparent homogeneity will dis^ appear, and it will look like a mixture of excessively fine yel- lowish-red particles, like sand, or dust, with a watery, almost colorless, fluid. Immediately after the blood is drawn the par- ticles will appear to be scattered very evenly through the fluid, but by degrees they aggregate into minute patches, and the layer of blood becomes more or less spotty. Tlic "particles" are what are termed the corpuscles of the blood ; the nearly colorless fluid in which they arc suspended is Xha ploLSTna. 81. Coagulation. — The second slide may now be exam- ined. The drop of blood will be unaltered in form, and may perhaps seem to have undergone no change. But if the slide be inclined it will be found that the drop no longer flows ; and, indeed, the slide may be inverted without the disturbance of the drop, which has become solidified, and may be removed with the point of a penknife, as a hemispherical gelatinous mass. The mass is quite soft and moist, so that this setting, or coagulation, of a drop of blood is something very diff^erent from its drying. On the third slide, this process of coagulation will be found not to have taken place, the blood remaining as fluid as it was when it left the body. The salt, therefore, has prevented the coagulation of the blood. Thus this very simple investigation teaches that blood is composed of a nearly colorless plasma, in which many colored corpuscles are suspended ; that it has a remarkable power of coagulating; and that this coagulation may be prevented by artificial means, such as the addition of a neutral salt. 82. The Blood Corpuscles. — ^If, instead of using the hand lens, the drop of blood on the first slide be placed under the microscope, the particles, or corpuscles of the blood will be found to be bodies with very definite characters, and of two kinds, called respectively the red corpuscles and the colorless corpuscles. Tlie former are much more numerous than the lat- ter, and have a yellowish-red tinge ; while the latter, somewhat


ITS MICROSCOPICAL ELEMENTS. 67 larger than tlie red corpuscles, are, as their name implies, pale and devoid of coloration. 83. Their Size, Form, ajid Appearance. — ^The corpuscles differ also in other and more important respects. The red corpus- cles are flattened circular disks, on an average ^^i^^h of an inch in diameter, and having about one-fourth of that thickness. It follows that rather more than 10,000,000 of them will lie on a space one inch square, and that the volume of each corpuscle does. not exceed TTO.TUuiTnro.innF*^ ^^ ^ cubic inch. 4^ @ Fio. 25. Fia. 26. Corpuscles op Hitman Blood. Fig. 25.— Red Corpnscles: a, a corpuscle seen edpreways; &, a corpuscle in an altered fitatr\ arising fk-om pressure. A small rounded red corpuscle, such as may be frequently met with in the blood, is represented beside the larger discoidal ones. Fig 26.— Colorless Corpuscles: a, a colorless corpuscle acted upon by diluted ace> tic acid, showing its nucleus. The broad faces of the disks are not flat, but somewhat con- cave, as if they were pushed in toward one another. Hence the corpuscle is thinner in the middle than at the edges, and when viewed under the microscope, by transmitted light, looks clear in the middle and darker at the edges, or dark in the mid- dle and clear at the edges, according to circumstances. When the disks roll over and present their edges to the eye, on the other hand, they look like rods. All these varieties of appear- ance may be made intelligible by turning a round biscuit or a muffin, bodies similar in shape to the red corpuscles, in various ways before the eye. 84. Structure and Changes of Form. — The red corpuscles are very soft, flexible, and elastic bodies, denser externally than in their interior, where they consist of a semifluid, or quite fluid matter, containing an albuminous substance termed globulin, in


68 ELEMENTARY PHYSIOLOGY. fiolutioD, and are reddened by their peculiar coloring matter, which is called hcematin. The interior substance contains no structure of any kind From the density of the outer as com- pared with the inner substance of each corpuscle, they are, practically, small flattened bags, or sacs, the form of which may be changed by altering the density of the plasma. Thus, if it be made denser by dissolving saline substances or sugar in it, water is drawn from the contents of the corpuscle to the Sense plasma, and the corpuscle becomes still more flattened. On the other hand, if the plasma be diluted with water, the lat- ter forces itself into and dilutes the contents of the corpuscle, causing the latter to swell out, and even become spherical ; and, by adding dense and weak solutions alternately, the corpuscles may be made to become successively spheroidal and discoidal. Exposure to carbonic acid gas causes the corpuscles to swell out ; oxygen gas, on the contrary, makes them flatten. c Fio. 27. SUCCESSITB FOBMB ASSITMBD BT COLOBLE88 CORPU8CLE8 OP HVMAN BlOOD. The interval between the forms ah cd was a minute ; between d and e two minutes; BO that the whole series of changes from a to e took Ave minutes. 85. The Colorless Corpuscles are larger than the red corpus- cles, their average diameter being ^^W*^ ^^ an inch. They arc further seen, at a glance, to differ from the red corpuscles by the extreme irregularity of their form, and by their tendency to attach themselves to the glass slide, while the red corpuscles float about and tumble freely over one another. A still more remarkable feature of the colorless corpuscles, than the irregularity of their form, is their irritability. The form of a red corpuscle is changed only by influences from without, such as pressure, or tha like ; that of the colorless cor- puscle is undergoing constant alteration, as the result and ex-


ITS MICROSCOPICAL ELEMENTS. C9 pression of changes taking place in its own substance. To see these changes well, a microscope with a magnifying power of five or six hundred diameters is requisite ; and even then, they are so gradual, that the best way to make sure of their exist- ence is to make a drawing of a given colorless oorpuscle at in- tervals of a minute or two. This is what has been done with the corpuscle represented in Fig. 27, in which a represents the form of the corpuscle when first observed ; 6, its form a minute afterward ; r, that at the end of the second ; c?, that at the encf of the third ; and c, that at the end of the fifth minute. Careful watching of a colorless corpuscle, in fact, shows that every part of its surface is constantly changing — undergoing active contraction, or being passively dilated by the contraction of other parts. It exhibits contractility in its lowest and most primitive form. 86. Structure and -Contractility. — While they are thus living and active, no correct notion can be formed of the struc- ture of the colorless corpuscles. By diluting the blood with water, or still better, with water acidulated with acetic acid, the corpuscles are killed, and become distended, so that their real nature is shown. They are then seen to be spheroidal bags, or sacs, with very thin walls ; and to contain in their interior a fluid which is either clear or granular, with a spheroidal vesicu- lar body, which is called the nucleus (Fig. 26). It sometimes, though very rarely, happens that the nucleus has a red tint. The sac-like colorless corpuscle, with its nucleus, is what is called a nucleated cell. It will be observed that it is living, in a free state, in the plasma of the blood, and that the cell wall, or sac, exhibits an independent contractility. In fact, except that it is dependent for the conditions of its existence upon the plasma, it might be compared to one of those simple organisms which are met with in stagnant water, and are called AmoehoB, 87. Their Development and Derivation. — That the red corpuscles are, in some way or other, derived from the color- less corpuscles may be regarded as certain ; but the steps of the process have not been made out with perfect certainty.


TO ELEMENTARY PHYSIOLOGY. There is very great reason, however, for believing that the red corpuscle is simply the nucleus of the colorless corpuscle some- what enlarged ; flattened from side to side; changed, by de- velopment within its interior of a red coloring matter; and set free by the but^ting of the sac or wall of the colorless corpus- cle. In other words, the red corpuscle is a free nucleus. The origin of the colorless corpuscles themselves is not certainly determined ; but it is highly probable that they are constituent cells of the sohd substance of the body which have been de- tached and carried into the blood, and that this process is largely effected in what are called the ductless glands, from whence the detached cells pass, as lymph<orpuscles, directly or indirectly, into the blood. The following facts are of importance in their bearing on the relation between the different kinds of corpuscles : (a) The invertebrate animals which have tme blood corpus- cles, possess only such as resemble the colorless corpuscles of man. {h) The lowest vertebrate animal, the Lancelot (Amphioxus), possesses only colorless corpuscles; and the very young em- bryos of all vertebrate animals have only colorless and nucle- ated corpuscles. (c) All the vertebrated animals which lay eggs have two kinds of corpuscles — colorless corpuscles, like those of man, and large red-colored corpuscles, which are generally oval, and further differ from those of man in presenting a nucleus. In fact, they are simply the colorless corpuscles enlarged and colored. {d) All animals which suckle their young (or what are called mammals) have, like man, two kinds of corpuscles : color- less ones, and small colored corpuscles — the latter being always flattened, and devoid of any nucleus. They are usually circu- lar, but in the camel tribe they are elliptical. And it is worthy of remark that, in these animals, the nuclei of the colorless corpuscles become elliptical. (e) The colorless corpuscles differ much less from one an- other m size and form, in the vertebrate series, than the colored.


ITS MICEOSCOPICAL ELEMENTS. 7l The latter are smallest in the little Musk Deer, in which animal they are about a quarter as large as those of man. On the other hand, the red corpuscles are largest in the Amphibia (or Frogs and Salamanders), in some of which animals they are ten times as long as in man. Fio. 28. Bed CoBPirscLSS of Hum^n Blood abbanoed im Coiiebent Bo^ls. One free red corpnscle and one colorless corpuscle are seen, and the plasma in tbe field of view is traversed by very delicate filaments of fibrin. 88. Red Corpuscles tend to cohere in EoUs.— As the blood dies, its several constituents, which have now been de- scribed, undergo marked changes. The colorless corpuscles lose their contractility, but other- wise undergo little alteration. They tend to cohere neither with one another, nor with the red corpuscles, but adhere to the slide on which they are placed. It is quite otherwise with the red corpuscles, whicb at first, as we have seen, float about and roll, or slide, over each other qifite freely. After a short time (the length of which varies in different persons, but usually amounts to two or three minutes) they seem, as it were, to become sticky, and tend to cohere ; and this tendency increases until, at length, the great majority, of them become applied face to face, so as to form long series, like rolls of coin. The end of one roll cohering with the sides of another, a network of various degrees of closeness is pro- duced ; the corpuscles remain thus coherent for a certain length of time, but eventually separate and float freely again. The


72 ELEMENTARY PHYSIOLOGY. addition of a little water, or dilute acids, or saline solutions, will at once cause the rolls to break up. It is from this running of the corpuscles together into patches of network that the change noted above in the appear- ances of .the layer of blood, viewed with a lens, arises. So long as the corpuscles are separate, the sandy appearance lasts ; but when they run together, the layer appears patchy or spotted. The red corpuscles rarely, if ever, all run together into rolls, some always remaining free in the meshes of the net. In con- tact with air, or if subjected to pressure, many of the red cor- puscles become covered with little knobs, so as to look like minute mulberries — an appearance which has been mistaken for a breaking up, or spontaneous division, of the corpuscles (Fig. 25, b). 89. Blood Crystals. — There is a still more remarkable* change which the red blood corpuscles occasionally undergo. Under certain circumstances, their contents, consisting of the colorless substance called Ghhuliny which fills the red blood corpuscles, and of their coloring matter, termed Hcematin^ separate from the outer shell of the corpuscles as crystals, which in man have the shape of prisms ; in other animals take other forms. Treat- ment of the blood with oxygen and with carbonic acid, in sun- light, greatly facilitates this process, so that the easiest way to see these blood crystals is to expose a drop of blood to the air, then moisten it with water, and then, by breathing several times on it, supply it with carbonic acid. The color of the drop brightens as the ciystals form in it. Section IL — Its Physical and Chemical Properties. 90. Coagulation. — ^Wlien the layer of blood has been drawn ten or fifteen minutes, the plasma will be seen to be no longer clear. It then exhibits multitudes of extremely delicate filaments of a substance called Fibrin^ which have been de- posited from it, and which traverse it in all directions, uniting


rrs PHYSICAL AND CHEMICAL PEOPEETIES. T3 with one another and with the corpuscles, and binding the whole into a semi-solid mass. It is this deposition of fibrin which is the cause of the apparent solidification^ or coagulation, of the drop upon the second slide ; but the phenomena of coagulation, which are of very great importance, cannot be properly understood until the behavior of the blood, when drawn in larger quantity than a drop, has been studied. 91. Separation of the Constituents.— When, by the ordi- . nary process of opening a vein with a lancet, a quantity of blood is collected into a basin, it is at first perfectly fluid ; but in a quarter of an hour, and sometimes in less than half that time, it separates into two very different constituents — ^the one a clear yellowish liquid, the other a red semi-solid mass, which lies in the liquid, and is paler in color and firmer at the surface than in its deeper part. The liquid is called the serum; the semi-solid mass the clot, or crassamentum. Now the clot obviously contains the corpuscles of the blood, bound together by some other sub- stance ; and this last, if a small part of the clot be examined microscopically, will be found to be that fibrous-looking matter, fibrin^ which has been seen forming in the thin layer of blood. Thus the clot is equivalent to the corpuscles plus the fibrin of the plasma, while the serum is the plasma ininu^ the fibrinous elements which it contained. 92. The Bnfiy Coat. — The corpuscles of the blood arc slightly heavier than the plasma, and therefore, when the blood is drawn, they sink very slowly toward the bottom. Hence the upper part of the clot contains fewer corpuscles and is lighter in color, than the lower part — there being fewer cor- puscles left in the upper layer of plasma for the fibrin to catch when it sets. And there are some conditions of the blood in which the corpuscles run together much more rapidly and in denser masses than usual ; so that they more readily overcome the resistance of the plasma to their falling, just as feathers stuck together in masses fall much more rapidly through the 4


74 ELEMENTABY PHYSIOLOGY. air than the same feathers when loose. When this is the case, the upper stratum of plasma is quite free from red corp\iscles before the fibrin forms in it, and consequently the uppermost layer of the clot is nearly white : it receives the name of the huffy coat. After the clot is formed, the fibrin shrinks and squeezes out much of the serum contained within its meshes ; and, other things being equal, it contracts the more, the fewer corpuscles there are in the way of its shrinking. Hence, when the buffy coat is formed, it usually contracts so much as to give the clot a cup-like upper surface. Thus the buflfy coat is fibrin naturally separated from the red corpuscles ; the same separation may be effected, artificially, by whipping the blood with twigs as soon as it is drawn, until its coagulation is complete. Under these circumstances the fibrin will collect upon the twigs and a red fluid will be left behind, consisting of the serum plus the red corpuscles, and many of the coloriess ones. 93. Influencing Conditions. — ^The coagulation of the blood is hastened, retarded, or temporarily prevented by many cir- cumstances. (a) Temperature, — A high temperature accelerates the coagulation of the blood ; a low one retards it ; and blood kept at the freezing-point of water will not coagulate at all. Blood thus kept fluid will, however, coagulate when its tem- perature is raised, and blood has been thus cooled and warmed till near coagulation for three successive times without losing its coagulability. (b) The addition of soluble matter to the blood. — Many saline substances, and more especially sulphate of soda and common salt, added to the blood in sufficient quantity, prevent its coagulation ; but cos^lation sets in when water is added, so as to dilute the saline solution. (c) Contact unth living or not-living matter, — Contact with not-living matter promotes the coagulation of the blood. Thus, blood drawn into a basin begins to coagulate first where it is


ITS PHYSICAL AND CHEMICAL PB0PEETIE8. 75 in contact with the sides of the basin ; and a wire introduced into a living vein will become coated with fibrin, although per- fectly fluid blood surrounds it. On the other hand, direct contact with living matter retards, or altogether prevents, the coagulation of the blood. Thus blood remains fluid for a very long time in a portion of a vein which is tied at each end. The heart of a turtle remains alive for a lengthened period (many hours or even days) after it is extracted from the body ; and, so long as it remains alive, the blood contained in it will not coagulate, though a portion of the same blood taken out of the heart will coagulate in a few minutes. Blood taken from the body of the turtle, and kept from coagulating by cold for some time, may be poured into the ► separated heart, and then will not coagulate. Freshly deposited fibrin acts like living matter, coagulable blood remaining fluid for a long time in tubes coated with such fibrin. 94. Nature of the Process of Coagulation.— The coagu- lation of the blood is an altogether physico-chemical process, dependent upon the properties of certain of the constituents of the plasma, apart from the vitality of that fluid. This is proved by the fact that if the coagulation of blood-plasma be prevented by cold, and it be greatly diluted, a cun*ent of carbonic acid gas passed through it will throw down a white substance, which white substance, dissolved in a weak solution of potash or soda, coagulates and yields a clot of true pure fibrin. It would be absurd to suppose that a substance which has been precipitated from its solution, and redissolved, stiU remains ahve. There are reasons for believing that this white substance consists of two constituents of yery similar composition which exist separately in living blood, and the union of which is the cause of the act of coagulation. These reasons may be briefly stated thus : — The pericardium and other serous cavities in the body contain a clear fluid, which has exuded from the blood- vessels, and contains the elements of the blood without the


76 ELEMENTARY PHYSIOLOGY. blood corpuscles. This fluid sometimes coagulates spon- taneously, as the blood-plasma would do, but very often shows no disposition to spontaneous coagulation. When this is the case, it may nevertheless be made to coagulate, and yield a true fibrinous clot, by adding to it globulin in any of^its shapes. This globulin is, as we have seen, the chief constituent of the blood-corpuscles: it exists in the serum of blood which has coagulated, and may be precipitated therefrom, as a white powder, by the action of carbonic acid : it is found also in con- nective tissue, the cornea, lens, and humors of the eye, and in other fluids of the body. 95. Globulin and Fibrinogen. — Globulin may be dried or kept in alcohol, without diminishing its power of generating fibrin when it is added to serous effusions. It is most active in a very weakly alkaline solution. Too much alkali and any* acidity completely suspend its action. Thus globulin, added under proper conditions to serous effusion, is a coagulator of that effusion, giving rise to the development of fibrin in it. It does so by its interaction with a substance contained in the serous effusion, which can be extracted by itself, and then plays just the same part toward a solution of globulin, as glob- ulin does toward its solution. This substance has been called fibrinogen. It is exceedingly like globulin, and may be thrown down irom serous exudation by carbonic acid, just as globulin may be precipitated from the serum of the blood. When re- dissolved in an alkaline solution, and added to any fluid con- taining globulin, it acts as a coagulator of that fluid, and gives rise* to the development of a clot of fibrin in it. In accord- ance with what has just been stated, serum of blood which has completely coagulated, may be kept in one vessel, and pericar- dial fluid in another, for an indefinite period, without the coag- ulation of either. But let them be mixed, and coagulation sets in. Thus it seems to be clear, that the coagulation of the blood, and the formation of fibrin, are caused primarily by the inter-


ITS PHYSICAL AISTD CHEMICAL PEOPEETIES. 77 action of two substances (or two modifications of the same sub- stance), globulin and fibrinogen^ the former of which exists in great abundance in the corpuscles of the blood, and in some tissues of the body ; while the latter is known at present only in the plasma of the blood, and the lymph, and the chyle, and fluids derived from them. 96. The Physical Qualities of the Blood. — ^The proverb that " blood is thicker than water," is literally true, as the blood ia not only " thickened " by the corpuscles, of which it has been calculated that no fewer than 70,000,000,000 (eighty times the number of the human population of the globe) are contained in a cubic inch, but is rendered slightly viscid by the solid matters dissolved in the plasma. The blood is thus ren- dered heavier than water, its specific gravity being about 1055. In other words, twenty cubic inches of blood have about tho same weight as twenty-one cubic inches of water. The cor- puscles are heavier than the plasma, and their volume is usually somewhat less than that of the plasma. Of colorless corpus- cles there are usually not more than three or four for every thousand of red corpuscles; but the number varies very much, increasing ihortly after food is taken, and diminishing in the intervals between meals. The blood is, furthermore, hot, its temperature being about 100° Fahrenheit. 97. The Chemical Composition of the Blood. — Considered chemically, the blood is an alkaline fluid, consisting of water, solid and gaseous matters. The proportions of these several con- stituents vary according to age, sex, and condition, but the following statement holds good on the average : In every 100 parts of blood there are ^79 parts of water and 21 parts of dry solids; in other words, the water and the solids of the blood stand to one another in about the same proportion as the nitrogen and the oxygen of the air. Eoughly speaking, one-quarter of the blood is dry, solid matter; three-quarters water. Of the 21 parts of dry solids, 12 (= ^ths) belong to the corpuscles. The remaining 9 are about two-thirds (6*7 parts = ^Jths) albumen (a substance like white of Qgg^ coagu-


^8 ELEMENTABY PHYSIOLOGY. lating by heat), and one-third (= ^th of the whole solid mat- ter), a mixture of saline, fatty, and saccharine matters, sundry products of the waste of the body, and fibrin. The quantity of the latter constituent is remarkably small in relation to the conspicuous part it plays in the act of coagulation. Healthy blood, in fact, yields, in coagulating, not more than from two to four parts in a thousand of its weight of fibrin. The total quantity of gaseous matter contained in the blood is equal to rather less than half the volume of the blood ; that is to say, 100 cubic inches of blood will contain rather less than 50 cubic inches of gases. These gaseous matters arc carbonic acid, oxygen, and nitrogen ; or, in other words, the same gases as those wliich exist in the atmosphere, but in totally different proportions; for whereas air contains nearly three-fourths nitrogen, one-fourth oxygen, and a mere trace of carbonic acid, the average computation of the blood gases is nearly two-thirds carbonic acid, rather less than one-third ox- ygen, and not one-tenth nitrogen. It is important to observe* (a) that blood contains much more oxygen gas than could be held in solution by mere water »t the same temperature and pressure ; (6) that this power of holding oxygen appears in some way to depend upon the cor- puscles, firstly, because mere serum has no greater power of absorbing oxygen than water has, and, secondly, because a solution of hsematin al>sorbs oxygen very readily ; and (c) that some substances which arc capable of being oxidated with great readiness — such as pyrogallic acid — ^are not affected by their passage through the blood. Thus it would appear that the oxygen is not quite free, but is held in some sort of loose chemical combination with a constituent of the blood contained in the corpuscles. The corpuscles differ chemically from the plasma, in con- taining a large proportion of the fats and phosphates, all the iron, and almost all the potash, of the blood ; while the plas- ma, on the other hand, contains by far the greater part of the chlorine and the soda.


rrS PHYSICAL AND CHEMICAL PKOPEETIES. 79 98. Influence of Age, Sex, and Food upon the Blood. — ^The blood of adults contains a larger proportion of solid constitu- ents than that of children, and that of men more than that of women ; but the diflference of sex is hardly at all exhibited by persons of flabby, or what is called lymphatic, constitution. Animal diet tends to increase the quantity of the red cor- puscles ; a vegetable diet and abstinence to diminish them. Bleeding exercises the same influence in a still more marked degree, the quantity of red corptiscles being diminished there- by in a much greater proportion than that of the other solid constituents of the blood. 99. Total dnantity of Blood in the Body.— The total quantity of blood contained in the body varies at different times, and the precise ascertainment of its amount is very diffi- cult. It may probably be estimated, on the average, at not less than one-tenth of the weight of the body. 100. Vivifying Influence of Blood over the Tisanes. — The function of the blood is to supply nourishment to, and take away waste matters from, all parts of the body. It is ab- solutely essential to the life of every part of the body that it should be in such relation with a current of blood, that matters can pass freely from the blood to it, and from it to the blood, by transudation through the walls of the vessels in which the blood is contained. Furthermore, this vivifying influence de- pends upon the corpuscles of the blood. The proof of these statements lies in the following experiments : If the vessels of a limb of a living animal be tied in such a manner as to cut off" the supply of blood from the limb without affecting it in any other way, all the symptoms of death will set in. The hmb will grow pale and cold, it will lose its sensibility, and volition will no longer have power over it ; it will stiffen, and eventually mortify and decompose. But if, even when the death stiffening has set in, the lig- atures are removed, and the blood is allowed to flow into the limb, the stiffening speedily ceases, the temperature of the part rises, the sensibility of the skin returns, the will regains power


80 ELEMENTARY PHYSIOLOGY. over the muscles, and, in short, the part rcturas to its nonnal condition. If, instead of simply allowing the blood of the animal operated upon to flow again, such blood, deprived of its fibrin by whipping, but containing its corpuscles, be artificially passed through the vessels, it will be found as efiectual a restorative as entire blood ; while, on the other hand, the serum (which is equivalent to whipped blood without its corpuscles) has no such efiect. 101. Transfosion of Blood. — Furthermore, it is not neces- sary that the blood employed should be that of the very same animal. Men, or dogs, bled to apparent death may be at once and eflectually revived by filling their veins with blood taken from another man or dog, an operation which is known by the name of transfusion. Nor is it absolutely necessary for the success of this opera- tion that the blood used in transfusion should belong to an animal of the same species. The blood of a horse will per- manently revive an ass, and, speaking generally, the blood of one animal may be replaced without injurious effects by that of another closely-allied species ; while that of a very different animal will be more or less injurious, and may even cause im- mediate death. . 102. The Lymph, — ^which fills the lymphatic vessels, is, like the blood, an alkaline fluid, consisting of a plasma and corpuscles, and coagulates by the separation of fibrin from the plasma. The lymph difters from the blood in its corpuscles being all of the colorless kind, and in the very small proportion of its solid constituents, which amount to only about five per cent. Lymph may, in fact, be regarded as blood minus its red corpuscles, and diluted with water, so as to be somewhat less dense than the serum of blood, which contains about eight per cent, of solid matters. A quantity of fluid equal to that of the blood is probably poured into the blood, daily, from the lymphatic system, ■f his fluid is in great measure the mere overflow of the blood


AETERIAL AND VENOUS BLOOD. 81 itself — plasma whicli has exuded from the capillaries into the tissues, and which has not been taken up again into the venous current ; the rest is due to the absorption of chyle from the alimentary canaL CHAPTER V. OF EESPIEATION. Section l,^^Arterial and Venous Blood, 103. High Complexity of the Blood.— The blood, the general nature and properties of which have been doscribed in the preceding chapter, is the highly complex product, not of any one organ or constituent of the body, but of all. Many of its features are doubtless given to it by its intrinsic and proper structural elements, the corpuscles; but the general character of the blood is also profoundly aftected by the cir- cumstance that every other part of the body takes something from the blood and pours something into it The blood may be compared to a river, the nature of the contents of which is largely determined by that of the head- waters, and that of the animals which swim in it ; but which is also very much aflfectcd by the soil over which it flows, the water-weeds which cover its banks, and by affluents from distant regions — ^by irrigation works which are supplied from it, and by drain-pipes which flow into it. 104. Blood rendered venous in the Capillaries. — One of the most remarkable and important of the changes efiected in the blood is that which results, in most parts of the body, from its simply passing through capillaries, or, in other words, through vessels, the walls of which are thin enough to permit a free exchange between the blood and the fluids which permeate the adjacent tissues. Thus, If blood be taken from an artery supplying a limb, il 4*


82 ELEMENTARY PHYSIOLOGY. will be found to have a bright scarlet color; while blood drawn at the same time from the vein of the limb, will be of a pur- plish hue, so dark that it is commonly called " black blood." And as this contrast is met with in the contents of the arteries and veins in general (except the pulmonary artery and veins), the scarlet blood is commonly known as arterial^ and the black blood as venous. This power of converting arterial into venous blood re- mains in most parts of the body so long as life persists. Thus, if a limb be cut off and scarlet blood be forced into its arteries by a syringe, it will issue from the veins as black blood so long as the limb exhibits signs of persistent vitality; and when these disappear the blood will no longer be changed. 106. DifEerence between Arterial and Yenons Blood.— When specimens of venous and of arterial blood are subjected to chemical examination, most of the differences between them are found to be very small and inconstant As a rule, there is lather more water in arterial blood, and rather more fatty mat- ter. But the gaseous contents of the two kinds of blood differ widely in the proportion which the carbonic acid gas bears to the oxygen, there being a smaller quantity of oxygen and a greater quantity of carbonic acid, in venous than in arterial blood. And it may be experimentally demonstrated that this dif- ference in the gaseous contents is the only essential difference between venous and arterial blood. For if arterial blood be shaken up with carbonic acid so as to be thoroughly saturated with that gas, it loses oxyojen, gains carbonic acid, and acquires the hue and proportion of venous blood ; while, if venous blood be similarly treated with oxygen, it gains oxygen, loses carbonic acid, and takes on the color and properties of arterial blood. Furthermore, the same result is attained, though more slowly, if the blood, in either case, be received into a bladder, and then placed in the carbonic acid or oxygen gas ; the thin moist ani- mal membrane allowing the change to be effected with perfect ease, and offering no serious impediment to the passage of either gas.


ARTERIAL AND VENOUS BLOOD. 83 108. Diffasion of Oases. — The physico-chemical processes involved in the exchange of carbonic acid for oxygen when venous is converted into arterial blood, or the reverse, in the cases mentioned above, arc not thoroughly understood, and are probably somewhat complex. It is known (or) that gases, mechanically held by a fluid in a given proportion, tend to diffuse into any atmosphere to which they arc exposed, until they occupy that atmosphere in corresponding proportions ; and (6) that gases, separated by a dry porous partition, or simply in contact, diffuse into one an- other with a rapidity which is inversely proportioned to the square roots of their densities. Now, a knowledge of these physical principles does, in a rough way, lead us to see how the gases, contained in the blood, may effect an exchange with those in the air, whether the blood be freely exposed, or enclosed in a membrane. But the appli- cation of these principles gives no more than this sort of gen- eral insight, seeing that, in the first place, the gases of the blood are not held merely mechanically in it; and, secondly, that when arterialization takes place through the walls of a bladder, or any other thin animal membrane, the matter is still further complicated by the circumstance that moisture dissolves car- bonic acid far more freely than it will oxygen, and hence that the wet bladder has a very different action upon carbonic acid from that which it has upon oxygen. Thus a moist bladder, partially filled with oxygen and suspended in carbonic acid gas, becomes rapidly distended in consequence of the carbonic acid gas passing into it with much greater rapidity than the oxygen passes out. 107. Cause of the Change of Color in Blood.— The cause of the change of color in the blood — of its darkening when ex- posed to carbonic acid, and its brightening when under the influence of oxygen, is not thoroughly understood. There is reason to think, however, that the red corpuscles are rendered somewhat flatter by oxygen gas, while they are distended by the action of carbonic acid. Under the former circumstances


84: ELEMENTARY PHYSIOLOGY. ihey may, not improbably, reflect the light more strongly, so as to give a more distinct coloration to the blood ; while, un- der the latter, they may transmit more light and so allow the blood to appear darker and duller. 108. Conditions of its Chemical Changes. — Whatever may be their explanation, however, the facts are certain, (1) that arterial blood, separated by only a thin membrane from car- bonic acid, or from a fluid containing a greater amount of carbonic acid than itself, becomes venous ; and (5) that venous blood, separated by only a thin membrane from oxygen, or a fluid containing a greater proportion of free oxygen than itself, becomes arterial. In these facts lies the explanation of the conversion of scarlet blood into dark blood as it passes through the capil- laries of the body,* for the latter are bathed by the juices of the tissues which contain carbonic acid, the product of their waste and combustion, in excess. On the other hand, if we seek for the explanation of the conversion of the dark blood in the veins into the scarlet blood of the arteries, we find, 1st, that the blood remains dark in the right auricle, the right ven- tricle, and the pulmonary artery ; 2d, that it is scarlet not only in the aorta, but in the left ventricle, the left auricle, and the pul- monary veins. Obviously, then, the change from venous to arterial takes place in the pulmonary capillaries, for these are the sole chan- nels of communication between the pulmonary arteries and the pulmonary veins. Section II. — The Lungs and their Office. 109. The Essence-natnre of Eespiration.— But what aro the physical conditions to which the blood. is exposed in the pulmonary ^capillaries ? These vessels are very wide, thin walled, and closely set, so as to form a network with very small meshes, which is con* tained in the substance of an extremely thin membrane^ Thii


TOE LUNGS AND THEIR OFFICE. 85 membrane is in contact with the air, so that the blood in each capillary of the lung is separated from the air by only a deli- cate pellicle formed by its own wall and the lung membrane. Hence an exchange very readily takes place between the blood and the air ; the latter gaining moisture and carbonic acid, and losing oxygen. This is the essential step in respiration ; that it really takes place may be demonstrated very readily, by the experi- ment described in the second chapter, in which air expired was proved to differ from air inspired, by containing more heat, more water, more carbonic acid, and less oxygen ; or, on the other hand, by putting a ligature on the windpipe of a living animal so as to prevent air from passing into or out of the lungs, and then examining the contents of the heart and great vessels. Venous blood will be found on both sides of the Fig. 29. Back View of the Neck and Thorax of a Human Subject from which THB Vertebral Column and whole Posterior Wall of the Chest is sup- POSRD to be removed. i/. moutb; <7AglottlH; Tr. traobea; iLX. left lansr; i?.Z. rljrht lunjr; 5r. bronchus! P. A. pulmonary arttry: P.V. palmonary veins; Ao. aorta, D. diaphragm; Hi heart; V.C.l. vena cava inferior.


86 ELEMENTARY PHYSIOLOGY. heart, and in the pulmonary veins and aorta, as much as in the vena cava and pulmonary, artery. But though the passage of carbonic acid gas and hot watery vapor out of the blood, and of oxygen into it, is the essence of the respiratory process — and thus a membrane with blood on one side, and air on the other, is all that is absolutely neces- sary to effect the purification of the blood — yet the accumula- tion of carbonic acid is so rapid, and the need for oxygen so incessant in all parts of the human body, that the former could not be cleared away, nor the latter supplied, with adequate rapidity, without the aid of extensive and complicated acces- sary machinery — ^the arrangement and working of which must next be carefully studied. 110. Mechanism of Eespiration. — The back of the mouth or pharynx communicates by two channels with the external air. One of these is formed by the nasal passages, which can- not be closed by any muscular apparatus of their own ; the other is presented by the mouth, which can be shut or opened at will. Immediately behind the tongue, at the lower and front part of the pharynx, is an aperture-^the glottis — capable of being closed by a sort of lid — the epiglottis — which covers it, or by the shutting together of its side boundaries, formed by the so-called vocal chords. The glottis opens into a cham- ber with cartilaginous walls — the larynx ; and leading from the larynx downward along the front part of the throat, where it may be very readily felt, is the trachea^ or windpipe. If this last be handled through the skin, it will be found to be firm and resisting. Its walls are, in fact, strengthened by a series of cartilaginous hoops, which hoops are incomplete behind, their ends being united only by muscle and membrane, where the trachea comes into contact with the gullet or oesophagus. * The trachea passes into the thorax, and then divides into two branches, a right and a left, which are termed the bronchi. Each bronchus enters the lung of its own side and then divides into a great number of smaller branches, which are called the bronchial tubes. As these diminish in size, the cartilages


THE LUNGS AND THEIR OFFICE. 87 which are continued all through the bronchi, and their large ramifications, become smaller and eventually disappear, so that the smallest bronchial tubes have wholly muscular and mem- branous walls. Thus, while the trachea and bronchi are kept permanently open and pervious to air, the smaller bronchial tubes may be almost closed by the contraction of their mus- cular walls. Fick 80. Fig. 81. mum^ Fia. 32. Fio. 80.— Two air-cells (l>) with the ultimate bronchial tube (o) which opens into them. Fio. 31.— a section through the walls (a) of several air-cells with their epithelium (&). Fig. 32.— The capillaries of the air-cells. The finer bronchial tubes end at length in elongated dila- tations, about -^th of an inch in diameter on the average, which are called the air-cells^ and which have sacculated walls. Tlie very thin walls which separate these air-cells are supported by much delicate and highly elastic tissue, and carry the wide and close-set capillaries into which the pulmonary artery pours its blood. Thus, the blood contained in these capillaries is


88 ELEMENTARY PHYSIOLOGY, exposed on both sides to the air — ^being separated from the air- cell on either hand only by the very delicate pellicle which forms the wall of the capillary, and the lining of the air-sac. 111. The Provision for the Eenewal of Air. — Hence no conditions can be more favorable to a ready exchange between the gaseous contents of the blood and those of the air in the air-cells, than the arrangements which obtain in the pulmonary- capillaries ; and, thus far, the structure of the lung fully enables us to understand how it is that the large quantity of blood poured through the pulmonary circulation is enabled to be ex- posed in very thin streams, over a large surface, to the air. But this very circumstance would only render the extraction of the oxygen from the pulmonary air, and its saturation with carbonic acid, a very speedy and complete process, if it were not for the special arrangements by which a certain quantity of this air is incessantly removed and replaced by fresh air. 112. Inspiration and Expiration. — If an adult man, breathing calmly in the sitting position, be watched, the respi- ratory act will be observed to be repeated thirteen or fourteen times every minute. Each act consists of certain components which succeed one another in a regular rhythmical order. First, the breath is drawn in, or insjnred ; immediately after- ward it is driven out, or expired ; and these successive acts of inspiration and expiration are followed by a brief pause. Thus, just as in the rhythm of the heart we have auricular systole, ventricular systole, pause ; so in similar order in the chest, in- spiration, expiration, and pause succeed one another. At each inspiration in an adult well-grown man about thirty cubic inches of air are inspired, and at each expiration the same, or a slightly smaller, volume (allowing for the increase of tem- perature of the air so expired). 113. Differences between Inspired and Expired Air. — The expired air differs from the air inspired in the following particulai-s : {a) Whatever the temperature of the external air, that cx- f)lred is nearly as hot as the blood, or between 90° and 100°.


THE LUNGS AND THEIR OFFICE. 89 (6) However dry the external air may be, that expired is quite, or nearly, saturated with watery vapor. (c) Though ordinary air contains nearly 2,100 parts of oxy- gen, and 7,900 of nitrogen, with not more than three parts of carbonic acid, in 10,000 parts, expired air contains about 470 parts of carbonic acid, and only between 1,500 and 1,600 parts of oxygen, while the quantity of nitrogen suffers little or no change. Speaking roughly, air which has been breathed once has gained five per cent of carbonic acid, and lost five per cent, of oxygen. The expired air contains, in addition, a greater or less quantity of animal matter of a highly decomposable character. (d) Very close analysis of the expired air shows, firstly, that the quantity of oxygen which disappears is always slightly in excess of the quantity of carbonic acid supplied; and secondly, that the nitrogen is variable — that in the expired air being sometimes slightly in excess of, sometimes slightly less than, that in the inspired air, and sometimes remaining sta- tionary. 114. The Amount of Work done by the Lungs. — ^Tliree hundred and fifty to four hundred cubic feet of air are thus passed through the lungs of an adult man taking little or no exercise, in the course of twenty-four hours, and are charged with car- bonic acid, and deprived of oxygen to the extent of nearly five per cent., which amounts to about eighteen cubic feet of the one gas taken in, and of the other given out. Thus, if a man be shut up in a close room, having the form of a cube seven feet in the side, every particle of air in that room will have passed through his lungs in twenty-four hours, and a fourth of the oxygen it contains will be replaced by carbonic acid. The quantity of carbon eliminated in the twenty -four hours is pretty clearly represented by a piece of pure charcoal weigh- ing eight ounces. The quantity of water given off from the lungs in the twenty-four hours varies very much, but may be taken on the average as rather more than half a pint, or about nine ounces.


90 ELEMENTARY PHYSIOLOGY. It may fall below this amount, or increase to double or treble the quantity. Section III. — The Respiratory Mechanism. 115. Mechanism of the Eespiratory Movements. — The mechanical arrangements by which the respiratory movements essential to the removal of the great mass of effete matters, and the importation of the large quantity of oxygen indicated, are effected, are to be found in — (a) the elasticity of the lungs. (6) The mobility of the sides and bottom of the thoracic cavity in which the lungs are contained. (a) The thorax may be regarded as a completely shut con- ical box, with the small end turned upward, the back of the box being formed by the spinal column, the sides by the ribs, the front by the breast-bone, the bottom by the diaphragm, and the top by the root of the neck (Fig. 29). The two lungs occupy almost all the cavity of this box which is not taken up by the heart. Each is enclosed in its serous membrane, the pleura. So long as the walls of the thorax are entire, the cavity of each pleura is practically oblit- erated, that layer of the pleura which covers the lung being in close contact with that which lines the wall of the chest ; but if a small opening be made into the pleura, the lung at once shrinks to a comparatively small size, and thus develops a great cavity between the two layers of the pleura. If a pipe be now fitted into the bronchus, and air^blown through it, the lung is very readily distended to its full size ; but, on being left to itself, collapses, the air being driven out again with some force. The abundant clastic tissue of the walls of the air-cells is, in fact, so disposed as to be greatly stretched when the lungs are full ; and, when the distending cause is removed, this elasticity comes into play and drives the greater part of the air out again. The lungs are kept distended in the dead subject, so long as the walls of the chest are entire, by the pressure of the


THE RESPIEATOEr MECHANISM. 91 atmosphere. For though the elastic tissue is all the while pulling, as it were, at the layer of pleura which covers the lung, and attempting to separate it from that which lines the chest, it cannot do so without developing a vacuum between these two layers. To effect this, the elastic tissue must pull with a force of more than that of the external air, or fifteen pounds to the square inch, an effort far beyond its powers, which do not equal more than one-fourth of a pound on the square inch. But the moment a hole is made in the pleura, the atmospheric pressure inside the lung is equalized by that outside it, and the elastic tissue, freed from its opponent, ex- erts its full power on the lung. 116. Walls of the Bronchial Tubes— Cilia.— The lungs are elastic, whether alive or dead. During life the air which they contain may be further affected by the contractility of the muscular walls of the bronchial tubes. If water is poured into the lungs of a recently-killed animal, and a series of elec- tric shocks is then sent through the bronchial tubes, the latter contract, and the water is forced out. Lastly, during life a further source of motion in the bronchial tubes is provided by llie cilia — minute filaments attached to the epithelium of the tubes, which incessantly vibrate backward and forward, and JET Fio. 88. Fig. 84. Ffg. 88.— (£1 7.) External Intercostal muscles. Fig.. 84.— (7. 7.) Internal Intercostal muscles. The chest Is supposed to be di* Tided vertically through the middle ot the breast-bone {St.) and back-bone ( V. C.)


92 ELEMENTARY PHYSIOLOGY, work in such a manner as to sweep liquid and solid matters outward, or toward the trachea. 117. Movements cf the Chest-Walls.— (6) The ribs arc attached to the spine, so as to be freely movable upon it ; but, when left to themselves, they take a position which is inclined obliquely downward aud forward.* Two sets of muscles, called inter coslals^ pass between the successive pairs of ribs on each side. The outer set, called external intercostals^ run from the rib above obliquely downward and forward to the rib below. The other set, internal intercostals, cross these in direction passing from the rib above, downward and backward to the rib below. The action of these muscles is somewhat puzzling at first, but is readily understood if the principle that, when a mtiacle contracts^ it tends to ^make the distance between its two ends as short as possible ^ be borne in mind. Let a and 6, Fig. 35, be Pio. 85. Fig. 86. Fig. 87. Fig. 35, Models illastratlng the action of the exiernal and internal intercostal muscles. Fig. 86, inspiratory elevation. Fig. 87, expiratory depression. two parallel bars, movable by their ends upon the upright c, which may be regarded as at the back of the apparatus, then a line directed from a? to y will be inclined downward and for- ward, and one from w to z will be directed downward and backward. Now, it is obvious that there is one position of the

  • I purposely neglect the consideration of the cartilages of the ribs in order not to

complicate the question unnecessarily.


THE RESPIRATORY MECHANISM. 93 rods, and one only, in which the points x and y are at the shortest possible distance, and one position only in which the points w and z are at the aliortest possible distance ; and these are, for x and y the position Fig. 36, and for w and z the position Fig. 37. These positions are respectively such that the points Xy y, and w, z, are at the ends of a straight line perpendicular to both rods. Thus, to bring x and y into this position, the parallel rods in Fig. 35 must move upward ; and to bring w and z into it, they must move in the opposite way.* If the simple apparatus just described be made of wood, hooks being placed at the points ar, y, and w, z ; and an clastic band, as long when left to itself as the shortest distance be- tween these points, be provided with eyes which can be readily put on to or taken oflf these hooks : it will be found that when the bars are in the horizontal position Fig. 35, the elasticity of the band hooked on to x and y will bring them up into the position in Fig. 36 ; while, if hooked on to w and z, it will force them down into the position shovm in Fig. 37. Substitute the contractility of the external and internal intercostal muscles for the elasticity of the band, and it will precisely exemplify their action ; and it is thus proved that the external intercostals raise, and the internal intercostals depress, the bony ribs. 118. The Diaphragm — is a great partition situated be- tween the thorax and the abdomen, and always concave to*thc latter and convex to the former. From its middle, which is tendinous, muscular fibres extend downward and outward to the ribs, and two, especially strong, masses, which are called tfce pillars of the diaphragm^ to the spinal column. When these muscular fibres contract, therefore, they tend to make the diaphragm flatter, and to increase the capacity of the thorax at the expense of that of the abdomen, by thrusting down the bottom of the thoracic box. Fig. 38. 119. Action of Different Farts compared. — Let us now consider what would be the result of the action of the parts


94 ELEMENTARY PHYSIOLOGY, of the respiratory apparatus, which have been described, if the diaphragm alone should begin to contract at regular intervals. When it contracts it increases tte vertical dimensions of the thoracic cavity, and tends to pull away the lining of the bottom of the thoracic box from that which covers the base of Fig. 38. The Diaphbaom viewed from tde -lower or abdominal side. V. C. /., th« vena cava inferior ; (E., the cesophagns ; Ao., the aorta ; Th. Z)., the thoracic duct, cat where they pass through the niaphrajrm, the broad white tendinous middle of which is easily distinguished from the radiating muscular fibres which pass down to the ribs and into th<^ pillars in front of the vertebrae. the lungs ; but the air immediately rushing in at the trachea, proportionately increases the distension of the lungs, and pre- vents the formation of any vacuum between the two pleurae at this point. When the diaphragm ceases to contract, so much of the elasticity of the lungs as was neutralized by the contrac- tion of the diaphragm, comes into play, and the extra air taken in is driven out again. We have, in short, an Inspiration and an Expiration, Suppose on the other hand that, the diaphragm being qui- escent, the external intercostal muscles contract. The ribs will be raised from their oblique position, the antero-posterior dimensions of the thoracic cavity will be increased, and the lungs will be distended as before to balance the enlargement.


INSPIRATION AND EXPIRATION. 95 If now the external intercostals relax, the action of gravitj upon the ribs, and the elasticity of the lungs, will alone suflSce to bring back the ribs to their previous positions and to drive out the extra air ; but this expiratory action may be greatly aided by the contraction of the internal intercostals. Section IV. — Inspiration and Expiration. 120. Accessory Mnsdes. — Thus it appears that we may have either diaphragmatic respiration or costal respiration. As a gen- eral rule, however, not only do the two forms of respiration coin- cide and aid one another — ^the contraction of the diaphragm tak- ing place at the same time with that of the external intercostals, and its relaxation with the contraction of the internal inter- costals — but sundry other accessory agencies come into play. Thus, the muscles which connect the ribs with parts of the spine above them, and with the shoulder, may, more or less extensively, assist inspiratioji ; while those which connect the ribs and breastbone with the pelvis and form the front and side walls of the abdomen, are powerful aids to expiration. In fact, they assist expiration in two ways : first, directly, by pull- ing down the ribs ; and next, indirectly, by pressing the vis- cera of the abdomen upward against the under surface of the diaphragm, and so driving the floor of the thorax upward. It is for this reason that, whenever a violent expiratory effort is made, the walls of the abdomen are obviously flattened and driven toward the spine, the body being at the same time bent forward. » In taking a deep inspiration, on the other hand, the walls of the abdomen are relaxed and become convex, the viscera being driven against them by the descent of the abdomen — the spine is straightened, the head thrown back, and the shoulders outward, so as to afford the greatest mechanical advantage to all the muscles which can elevate the nbs. 121. How Eespiration differs in the two Sexes. — It is a remiarkable circumstance that the mechanism of respiration


96 ELEMENTABY PHYSIOLOGY. is somewhat different in the two sexes. In men, the diaphragm takes the larger share m the process, the upper ribs moving comparatively little; in women, the reverse is the case, the respiratory act being largely costal. Sighing is a deep and prolonged inspiration. " Snifting " is a more rapid inspiratory act in which the mouth is kept shut, and the air made to pass through the nose. Coughing is a violent expiratory act in which, a deep in- spiration being lirst taken, the glottis is closed and then buret open by the violent compression of the lungs by the expiratory muscles, the diaphragm being relaxed and the air driven through the mouth. In sneezing, on the contrary, the cavity of the mouth is shut off and the air forced through the nasal passages. Fio. 89. Fio. 4a Diagrammatic Sections op tiih Body m Fig. 89, Inspiration ; Fij;^. 40, expiration: Tf. trachea: SL sternum; D. diaphragm: Ah, abdominal walls. The shading indicates the stationary air.


INSPIRATION AND EXPIRATION. 97 122. Eesidual, Supplemental, and Tidal Air. — It thus appears that the thorax, the lungs, and the trachea constitute a sort of bellows without a valve, in which the thorax and the lungs represent the body of the bellows, while the trachea is the pipe ; and the effect of the respiratory movements is just the same as that of the approximation, and separation of the handles of the bellows, viz., to drive out and draw in the air through the pipe. There is, however, one difierence between the bellows and the respiratory apparatus, of great importance in the theory of respiration, though frequently overlooked, and that is, that the sides of the bellows can be brought close to- gether so as to force out ail, or nearly all, the air which they contain ; while the walls of the chest, when approximated as much as possible, still enclose a very considerable cavity (Fig. 40) ; so that, even after the most violent expiratory effort, a very large quantity of air is left in the lungs. The amount of this air which cannot be got rid of, and is called Residual air, is, on the average, from 75 to 100 cubic inches. About as much more in addition to this remains in the chest after an ordinary expiration, and is called Supplemental air. In ordinary breathing, 20 to 30 cubic inches of what is con- veniently called Tidal air pass in and out. It follows that, after an ordinary inspiration, 100 + 100 + 30 = 230 cubic inches, may be contained in the lungs. By taking the deepest possi- ble inspiration, another 100 cubic inches, called Complemental air, may be added. 123. The Stationary Air plays the part of a Middle- man. — It follows from these data that the lungs, after an ordi- nary inspiration, contain about 230 cubic inches of air, and that only about one-seventh to one-eighth of this amount is breathed out and taken in again at the next inspiration. Apart from the circumstance, then, that the fresh air inspired has to fill the cavities of the hinder part of the mouth, and the trachea, and the bronchi, if the lungs were mere bags fixed to the ends


98 ELEMENTARY PHYSIOLOGY. of the bronchi, the inspired air could only occupy that one- fourteenth to one-sixteenth of the capacity of each nearest the bronchi, to be driven out again at the next expiration. But as the bronchi branch out into a prodigious number of bron- chial tubes, the inspired air can only penetrate for a certain dis- tance along these, and can never reach the air-cells at all. Thus the Residual and Supplemental air taken together are, under ordinary circumstances, stationary — ^that is to say, the air comprehended under these names merely shifts its outer limit in the bronchial tubes, as the chest dilates and contracts, without leaving the lungs; the tidal air, alone, being that which leaves the lungs and is renewed in ordinary respiration. It is obvious, therefore, that the business of respiration is essentially transacted by the stationary air, which plays the part of a miiddle-man between the two parties — the blood and the fresh tidal air — who desire to exchange their commodities, carbonic acid for oxygen, and oxygen for carbonic acid. Now there is nothing interposed between the fresh tidal air and the stationary air; they are aeriform fluids, in complete contact and continuity, and hence the exchange between them must take place according to the ordinary laws of gaseous dif- fusion. 124. Compositipn of the Stationary Air.— Thus, the stationary air in the air-cells gives up oxygen to the blood, and takes carbonic acid from it, though the exact mode in which the change is effected is not thoroughly understood. By this process it becomes loaded with carbonic acid, and deficient in oxygen, though to what precise extent is not known. But there must be a very much greater excess of the one, aftd defi- ciency of the other, than is exhibited by inspired air, seeing that the latter acquires its composition by diffusion in the short space of time (four to five seconds) during which it is in con- tact with the stationary air. In accordance with these facts, it is found that the air ex- pired during the first half of an expiration contains less car- bonic acid than that expired during the second half. Further,


INSPIRATION AND EXPIEATION. 99 when the frequency of respiration is increased without altering the volume of each inspiration, though the percentage of car- bonic acid in each inspiration is diminished, it is not duninished in the same ratio as that in which the number of inspirations increases ; and hence more carbonic acid is got rid of in a given time. Thus, if the number of inspirations per minute is increased from fifteen to thirty, the percentage of carbonic acid evolved in the second case remains more than half what it was in the first case, and hence the total evolution is greater. 125. Nervous System controls Eespiration. — Of the various mechanical aids to the respiratory process, the nature and working of which have now been described, one, the elas- ticity of the lungs, is of the nature of a dead, constant force. The action of the rest of the apparatus is under the control of the ner\'Ous system, and varies from time to time. As the nasal passages cannot be closed by their own action, aif has always free access to the pharynx, but the glottis, or entrance to the windpipe, is completely under the control of the nervous system — ^the smallest irritation about the mucous membrane in its neighborhood being conveyed, by its nerves, to that part of the cerebro-spinal axis which is called the me- dulla oblongata. The medulla oblongata, thus stimulated, gives rise, by a process which will be explained hereafter, termed reflex action^ to the contraction of the muscles which close the glottis, and commonly, at the same time, to a violent contrac- tion of the expiratory muscles, producing a " cough." The muscular fibres of the smaller bronchial tubes, no less than the respiratory pump itself, formed by the walls and floor of the thorax, are under the complete control of the nerves which supply the muscles, and which are brought into action in consequence of impressions conveyed by the pneumogastric and other nerves. 126. Eespiration and Circnlation compared. — From what has been- said, it is obvious that there are many analogies be- tween the circulatory and the respiratory apparatus. Each


100 ELEMENTARY PHYSIOLOGY. consists essentially of a kind of pump which distributes a flftid (aeriform in the one case, liquid in the other) through a series of ramified distributing tubes to a system of cavities (capilla- ries or air-cells), the volume of the contents of which is greater than that of the tubes. In eaqh, the pump is the cause of motion of the fluid, but that motion may be regulated, locally, by the contraction or relaxation of the muscular fibres contained in the walls of the distributing tubes. But, while the rhythmic movement of the heart depends upon a nervous apparatus placed within itself, that of the respiratory apparatus results mainly from the opera- tion of a nervous centre lodged in the medulla oblongata. Section V. — Effects of Respiration, 127. Their Secondary Phenomena. — As there are certain secondary phenomena which accompany, and are explained by, the action of the heart, so there are secondary phenomena which are similarly related to the working of the respiratory apparatus. These are — (1) the respiratory sounds, and (2) the efiect of the inspiratory and expiratory movements upon the circulation. 128. The Respiratory Mnrmnrs. — The respiratory sounds, or murmurs, are audible when the ear is applied to any part of the chest which covers one or other of the lungs. They ac- company inspiration and expiration, and very much resemble the sounds produced by breathing through the mouthy when the lips are so applied together as to leave a small interval. Over the bronchi the sounds are louder than over the general surface. It would appear that these sounds are produced by the motion of the air along the air-passages. 129. Inspiration assists the Circulation.— In conse- quence of the elasticity of the lungs, a certain force must be expended in distending them, and this force is found exper- imentally to become greater and greater the more the lung is extended ; just as in stretching a piece of india-rubber more


EFFECTS OF BESPIEATION. 101 force is required to stretcli it a good deal, than is needed to stretch it only a little. Hence, when inspiration takes place, and the lungs are distended with air, the heart and the great vessels in the chest are subjected to a less pressure than are the blood-Tessels of the rest of the body. For the pressure of the air contained in the lungs is ex- actly the same as that exerted by the atmosphere upon the surface of the body; that is to say, fifteen pounds on the square inch. But a certain amount of this pressure exerted by the air in the lungs is counterbalanced by the elasticity of the distended lungs. Say that in a given condition of inspiration a pound pressure on the square inch is needed to overcome this elasticity, then there will be only fourteen pounds' pres- sure on every square inch of the heart and great vessels. And hence the pressure on the blood in these vessels will be one pound per square inch less than that on the veins and arteries of the rest of the body. If there were no aortic, or pulmo- nary, valves, and if the composition of the vessels, and the pressure upon the blood in them, were everywhere the same, the result of this excess of pressure on the surface would be, to drive all the blood from the arteries and veins of the rest of the body into the heart and great vessels contained in the thorax. And thus the diminution of the pressure upon the thoracic blood cavities produced by inspiration, would prac- tically suck the blood from all parts of the body toward the thorax. But the suction thus exerted, while it hastened the flow of blood to the heart in the veins, would equally oppose the flow from the heart to the arteries, and the two effects would balance one another. 130. Unequal Pressures fiEicilitate the Circulatioii.~As a matter of fact, however, we know — (1.) That the blood in the arteries is constantly under a very considerable pressure, while that of the veins is under little or no pressure. (2.) That the walls of the arteries are strong and elastic, while those of the veins are weak and flabby.


102 ELEMENTARY PHYSIOLOGY. (3.) That the veins have valves opening toward the heart : and that, during the diastole, there is no resistance of any moment to the free passage of blood into the heart; while on the other hand, the cavity of the arteries is shut off from that of the ventricle during the diastole, by the closure of the semi- lunar valves. Hence it follows that equal pressures applied to the surface of the veins and to that of the arteries must produce very dif- ferent effects. In the veins the pressure is something which did not exist before ; and, partly from the presence of valves, partly from the absence of resistance in the heart, partly from the presence of resistance in the capillaries, it all tends to ac- celerate the flow of blood toward the heart In the arteries, on the other hand, the pressure is only a fractional addition to that which existed before ; so that during the systole it only makes a comparatively small addition to the resistance which has to be overcome by the ventricle ; and during the diastole^ it superadds itself to the elasticity of the arterial walls in driv* ing the blood onward toward the capillaries, inasmuch as all progress in the opposite direction is stopped by the semilunar valves. It is, therefore, clear that the inspiratory movement, on the whole, helps the heart, inasmuch as its general result is to drive the blood the way that the heart propels it. 131. Effect of Expiration on the Circulation. — In expira- tion, the difference between the pressure of the atmosphere on the surface, and that which it exerts on the contents of the thorax through the lungs, becomes less and less in propor- tion to the completeness of the expiration. Whenever, by the ascent of the diaphragm and the descent of the ribs, the cavity of the thorax is so far diminished that pressure is exerted on the great vessels, the veins, owing to the thinness of their walls, are especially affected, and a check is given to the flow of blood in them, which may become visible as a venous pulse in the great vessels of the neck. In its effect on the arterial trunks, expiration, like inspiration, is, on the


EFFECTS OF BESPmATION. 103 whole, favorable to the circulation ; the increased resistance to the opening of the valves during the ventricular systole being more than balanced by the advantage gained in the addition of the expiratory pressure to the elastic reaction of the arterial walls during the diastole. When the skull of a living animal is laid open and the brain exposed, the cerebral substance is seen to rise and fall synchronously with the respiratory movements ; the rise cor- responding with expiration. 132. Stoppage of the Heart by Distensioii of the Lungs.— Hitherto, I have supposed the air-passages to be freely open during the inspiratory and expiratory movements. But if, the lungs being distended, the mouth and nose are closed, and a strong expiratory effort is then made, the heart's action may be stopped altogether.* And the same result occurs if, the the lungs being partially emptied, and the nose and mouth closed, a strong inspiratory effort is made. In the latter case the excessive distension of the right side of the heart, in con- sequence of the flow of blood into it, may be the cause of the arrest of the heart's action, but, in the' former, the reason of the stoppage is not very clear. 133. Circtimstances modifying Bespiration. — The activ- ity of the respiratory process is greatly modified by the cir- cumstances in which the body is placed. Thus, cold greatly increases the quantity of air which is breathed, the quantity of oxygen absorbed, and of carbonic acid expelled : exercise and the taking of food have a corresponding effect. In proportion to the weight of the body, the activity of the respiratory process is far greatest in children, and diminishes gradually with age. The excretion of carbonic acid is greatest during the day and gradually sinks at night, attaining its minimum about mid- night, or a little after. The quantity of oxygen which disappears in proportion to the carbonic acid given out, is greatest in carnivorous, least in ♦ There is danjjfcr in attempting this experiment


104 ELEMENTARY PHYSIOLOGY. herbivorous animals — greater in a man living on a flesh diet, than when the same man is feeding on vegetable matters, • 134. Asphyxia.. — When a man is strangled, drowned, or choked, or is, in any other way, prevented from inspiring or expiring suflBciently pure atmospheric air, what is called as- phyxia comes on. He grows " black in the face ; " the veins become turgid; insensibility, not unfrequently accompanied by convulsive movement, sets in, and he is dead in a few minutes. But in this asphyxiating process two deadly influences of a distinct nature are cooperating ; one is the deprivation of oxy- gen, the other is the excessive accumulation of carbonic acid in the blood. Oxygen starvation and carbonic acid poisoning, each of which may be fatal in itself, are at work together. The effects of oxygen starvation may be studied separately by placing a small animal under the receiver of an air-pump and exhausting the air. In this case no accumulation of car- bonic acid is permitted, but, on the other hand, the supply of oxygen soon becomes insufficient, and the animal quickly dies. And if the experiment be made in another way, by placing a small mammal, or bird, in air from which the carbonic acid is removed as soon as it is formed, the animal will nevertheless die as soon as the amount of oxygen is reduced to ten per cent, or thereabouts. The directly poisonous effect of carbonic acid, on the other hand, has been very much exaggerated. A very large quantity of carbonic acid, ten to fifteen or twenty per cent., may be con- tained in air, without producing any very serious, immediate effect, if the quantity of oxygen be simultaneously increased. 135. How it destroys Life. — Whichever may be the more potent agency, the effect of the two, as combined in asphyxia, is to produce an obstruction, firstly, in the pulmonary circulj\- tion, and, secondly, in the veins of the body generally. The lungs and the right side of the heart, consequently, become gorged with blood, while the arteries and left side of the heart gradually empty themselves of the small supply of dark and


EFFECTS OF BESPIEATION. 105 unaerated blood which they receive. The heart becomes par- alji^ed, partly by reason of the distension of its right side, partly from being supplied with venous blood; and all the organs of the body cease to act. 136. Respiratory Poisons. — Whatever may be the case for carbonic acid (which seems to be a poison rather neg- atively, in virtue of its interference with oxygen, than from any positive ill qualities of its own), carbonic oxide, arseniuretted hydrogen, and sulphuretted hydrogen, are undoubtedly in themselves poisons of a deadly kind, and, when taken into the blood by the lungs, produce the worst effects. 137, Slow Asphyxiation. — It is not necessary, however, absolutely to strangle or drown a man in order to asphyxiate him. As, other things being alike, the rapidity of diffusion between two gaseous mixtures depends on the difference of the proportions in which their constituents are mixed, it fol- lows that the more nearly the composition of the tidal air ap- proaches that of the stationary air, the slower will be the dif- fusion of carbonic acid outward and of oxygen inward, and the more charged with carbonic acid and defective in oxygen will the air in the air-cells become. And, on increasing the pro- portion of carbonic acid in the tidal air, a point will at length be reached when the change effected in the stationary air is too slight to enable it to relieve the pulmonary blood of its carbonic acid, and to supply it with oxygen to the extent required for its arterialization. In this case the blood, which passes into the left side of the heart, and is thence distributed to the body, being venous, all the sjmiptoms of insensibility, loss of muscular power, etc., which have been enumerated above as the result of supplying the brain and muscles with venous blood, will follow, and a state of suffocation, or asphyxia, will supervene. Asphyxia takes place whenever the proportion of carbonic acid in tidal air reaches ten per cent, (the oxygen being dimin- ished in like proportion) ; and it of course makes no difference Avhether the quantity of carbonic acid in the air breathed is 6*


106 ELEMENTARY PHYSIOLOGY. increased by shutting out fresli air; or by increasing tbe num- ber of persons who are consuming the same air ; or by suf er- ing combustion, in any shape, to carry off oxygen from the air. 188. VitalNecessity of Ventilation.— The deprivation of oxygen, and the accumulation of carbonic acid, cause injury, however, long before the asphyxiating point is reached. Un- easiness and headache arise when less than one per cent, of the oxygen of the air is replaced by other matters ; while the persistent breathing of such air tends to lower the tone of the system, and predisposes it to disease. Hence the necessity of suflBcient air and of ventilation for every human being. To be supplied with respiratory air in a fair state of purity, every man ought to have at least 800 cubic feet of space to himself, and that space ought to be freely ac- cessible by direct, or indirect, channels to the atmosphere. CHAPTER VI. THE SOURCES OF LOSS AND OP GAIN TO THE BLOOD. Section I. — Sources of Loss to the Blood, 139. Distribntion of Arterial Blood.— The blood, which has been afirated, or arterialized, in the lungs by the process described in the preceding chapter, and then, having been car- ried from the lungs by the pulmonary vein to the left auricle, has been forced by the auricle into the ventricle and by the ventricle into the aorta, is distributed by the great arteries which spring from that vessel, as it traverses the thorax, to the head, the arms, and the walls of the body. Passing through the diaphragm (Fig. 38), the aortic trunk enters the cavity of the abdomen, and becomes what is called the abdominal aorta^ from which vessels are given off to the viscera of the abdomen. Finally, the main stream of blood flows into the iliac arteries, "whence the viscera of tbe pelvis and the legs are supplied.


SOURCES OF LOSS TO THE BLOOD. 107 From the arteries the blood, as we have seen, enters the capiU layes and, as it traverses them, the products of the waste of the tissues constantly pour into it. Furthermore, as the blood contains living corpuscles, which, like all other living things, decay and die, it follows that if the blood is to be kept pure, the waste matters thus incessantly poured into, or generated in it, must be as constantly got rid of, or excreted. 140. The Various Drains upon the Blood. — ^Tbn^ dis- tinct sets of organs are especially charged with this office of continually excreting carbonic acid, water, and urea. They are the LungSy the Kidneys^ and the Skin ; and hence, these three great organs may be regarded as keeping up so many drains upon the blood — as so many channels by which it is constantly losing substance. Further, the blood, as it traverses the capillaries, is con- stantly losing matter by exudation into the surrounding tis- sues. •-? Another kind of loss takes place from the surface of the body generally, and from the interior of the air-passages and lungs. From the former, heat is constantly being given off by radiation, evaporation, and conduction ; from the latter, chiefly by evaporation. 141. Loss by the Liver and Lungs. — ^The blood which enters the liver is constantly losing material to that organ ; but the loss is only temporary, as almost all the matter lost, con- verted into sugar and into bile, reenters the current of the cir- culation in the liver itself, or elsewhere. Again, the loss of matter and of heat by the lungs, in respiration, is partially made up by the no less constant gain which results from the quantity of oxygen absorbed at each inspiration, and from the heat generated by this oxygen in the tissues. And the loss by exudation from the capillaries is, in some degree, compensated by the gain from the lymphatics and ductless glands. 142. Other Losses and Gains. — In the instances just men- tioned the loss and gain are constant, and go on while life and


108 ELEMENTARY PHYSIOLOGY. healtli last But there are certain other operations which cause either loss or gain to the blood, and which are not con- tinuous, but take place at intervals. These are, on the side of loss, the actions of the many secretory glands which separate certain substances from the blood at recurrent periods, in the intervals of which they are quiescent. On the side of gain, they are, the contractions of the muscles, which, during their activity, cause a great quantity of waste materials to appear in the blood ; and the operations of the alimentary canal^ which, for a certain period after it is sup- plied with food, pours new materials into the blood. Under some circumstances, the skin may become a source of gain by absorbing fluids. The sources of loss and gain to the blood may be conve- niently arranged in the following tabular form : A. Incessantly active Sources of Loss or Gain to the Blood. a. Sources of Loss. L Loss of matter, 1. The lungs. 2. The kidneys. 3. The skin. 4. The liver. 6, The tissues generally, IL Loss of heat, 1. The free surfaces of the body. h. Sources of Gain. L Gain of matter, 1. The lungs. 2. The liver. 3. The spleen, ductless glands, and lymphatic system. 4. The tissues generally. IL Gain of heat, 1. The blood itself and the tissues generally.


SOUBCES OF LOSS TO THE BLOOD. 109 B. Intermittei^ly active Sources of Loss or Gain to THE Blood. a. Source of Loss. 1. Many secreting glands. 5. Sources of Gain. 1. Tlie muscles. 2. The alimentary canaL 3. The skin. 143. Constant Loss by the Kidneys. — ^In the preceding chapter I have described the operation by which the lungs withdraw from the blood much carbonic acid and water, with a fractional quantity of urea, and take oxygen into the blood ; I now proceed to the second source of continual loss, the Kid- neys. Of these organs there are two, placed at the back of the abdominal cavity, one on each side of the lumbar region of the spine. Each is shaped like the kidney of a sheep, but somewhat larger, — its depressed or concave side turned inward, and its convex side outward (Fig. 41). From the middle of the concave side (called the hilus) of each kidney, a long tube with a small bore, the Ureter^ proceeds to the bladder {BL), The latter is an oval bag placed in the pelvis, the walls of which contain abundant unstriped muscular fibre, while it is lined, internally, by mucous membrane, and coated externally by the peritoneum. The ureters open side by side, but at some little distance from one another, on the posterior and in- ferior wall of the bladder ; in front of them is a single aperture which leads into the canal called the Urethra^ by which the cavity of the bladder is placed in communication with the ex- terior of the body. The openings of the ureters enter the wall of the bladder obliquely, so that it is much more easy for fluid to pass from the ureters into the bladder than for it to get the other way, from the bladder into the ureters. . Mechanically speaking, there is little obstacle to the free


110 ELEMENTABY PHYSIOLOGY. flow of fluid from the ureters into the bladder, and from the bladder into the urethra, and so outward ; but certain mus- cular fibres arranged circularly around the part called the

  • ' neck" of the bladder, which passes into the urethra, consti-

tute what is termed a sphincter^ and are usually, during life, iu a state of contraction, while the other muscular fibres of the bladder are relaxed. It is only at intervals that this state of ■mi Fio. 41. The kidneys {K) ; ureters ( Ur) ; with the aorta (Ao\ and vena cava inferior ( V. O.I.) ; and the renal arteries and veins. Bl. is the bladder, the top of which is cut oflf so as to show the openings of the ureters (1 1), and that of the urethra (2). matters is reversed ; and the walls of the bladder contracting, while the sphincter relaxes, its contents, the urine^ arc dis- charged. But, though the expulsion of the secretion of the kidneys from the body is thus intermittent, the excretion itself is constant, and the urinary fluid incessantly flows, drop by drop, from the opening of the ureters into the bladder, where it accumulates, until its quantity is sufficient to give rise to the uneasy sensations which compel its expulsion. 144. Kidneys and Lungs compared. — Tlie excretion of nitrogenous waste and water with a little carbonic acid, by the


SOURCES OF LOSS TO THE BLOOD. Ill kidneys, is thus strictly comparable to that of carbonic acid water, with a little urea, by the lungs, in the air-cells of which carbonic acid and watery vapors are incessantly accumulating, to be periodically expelled by the act of expiration. But the operation of the renal apparatus differs from that of the respi- ratory organs, in the far longer intervals between the excretory acts, and still more in the circumstance that, while what the lungs take into the body is as important as what they give out, the kidneys take in nothing. 145. Composition of Benal Excretions. — ^The renal ex- cretion has naturally an acid reaction, and consists of urea and uric acid ; sundry other animal products of less impor- tance ; with saline and gaseous matters, held in solution by a large quantity of water. The quantity and composition of the urine vary greatly ac- cording to the time of day, the temperature and moisture of the air, the fasting or replete condition of the alimentary canal, and the nature of the food. Urea and uric acid are both composed of the elements car- bon, hydrogen, oxygen, and nitrogen, but urea is by far the more soluble compound, and greatly exceeds the uric acid in quantity. An average healthy man excretes by the kidneys about fifty ounces, or 24,000 grains, of water a day. In this are dissolved 600 grains of urea, but not more than 10 to 12 grains of uric acid. The amount of other animal matters and of saline sub- stances, varies from one-third as much to nearly the same amount as the urea. Tlie saline matters consist chiefly of common salt, phosphates and sulphates of potash, soda, lime, and magnesia. The gases are the same as those in the blood, namely, carbonic acid, oxygen, and nitrogen. But the quan- tity is, proportionably, less than one-third as great ; and the carbonic acid is in very large, while the oxygen is in very small, amount. The avcrapre specific gravity does not differ very widely from that of blood serum, being 1*020.


112 ELEMENTABY PHYSIOLOGY. 146. The Stmcture of the Kidney. — It will be observed that all the chief constituents of the urine are already contained in the blood, and indeed, it might almost be said to be the blood devoid of its corpuscles, fibrin, albumen, and iron. Speak- ing broadly, it is such a fluid as might be separated from the blood by the help of any kind of filter which had the property of retaining these constituents, and letting the rest flow off. The filter required is found in the kidney, to the structure of which we must now turn. When a longitudinal section of a kidney is made (Fig. 42), the upper end of the ureter (d) seems to widen out into a basin-, like cavity (c), which is called the pelvis of the kidney. Into this, sundry conical elevations project, the summits of which present multitudes of minute openings — the final terminations of the tubuli, of which the thickness of the kidney is chiefly made up. If the tubules are traced from their openings toward the outer surface, they are found, at first, to lie parallel with one Fi<J. 42. Londtudinal section of the hnman kidney, a, the cortical substance ; b, the medul- lary substance; c, the pelvis of the kidney , d, the ureter. another in bundles, which radiate toward that surface, and sub- divide as they go ; but at length they spread about irregularly, and become interlaced. From this circumstance alone, the middle, or medullary^ part (marrow, medulla) of the kidney looks different from the superficial, or cortical^ part (bark, t(yrtex) ; but, in addition, the cortical part is more abundantly


80UECES OF LOSS TO THE BLOOD. 113 supplied with vessels than the medullary, and hence has a darker aspect. Each tubule (or, at any rate, most of them) ends at last in a dilatation (Fig. 43), which is called a McUpi- ghian capsule. Into the summit of this a small vessel (/), one of the ultimate branches of the renal artery ^ enters, and imme- diately breaks up into a bunch of looped capillaries, called a glomerulus (h), which nearly fills the cavity of the capsule. The blood is carried away from this glomerulus by a small vein (g)y which does not, at once, join with other veins into a larger venous trunk, but opens into the network of capillaries which surrounds the tubule, thus repeating the portal circulation on a small scale. Fig. 44. Fig. 4a-MalpigliIflm capaule (o) with its contained glomenilus (h) and the begin- ning of the tubule (6) into which it opens, c, d, epithelium in place ; e, epithe- ^- ^iTri^l the tubule detached; /, the artery; jjr, the vein; k, the glomerulus. Fig. 44.— The epithehum magnified. ^ Tlie tubule has an epithelial lining (d) continuous with that of the pelvis of the kidney, and the urinary passages generally. The epithelium is thick and plain enough in the tubule, but it becomes very delicato, or even disappears, in the capsule and on the glomerulus.


114 ELEMENTARY PHYSIOLOGY. 147. The Filtering Mechanism. — It is obvious from this description that the surface of the glomerulus is, practically, free, or in direct communication with the exterior ; and further, that, in each vessel of the glomerulus, a thin stream of blood constantly flows, only separated by the very delicate membrane of which the wall of the vessel is composed from the cavity of the tubule. The Malpighian capsule may, in fact, be regarded as a funnel, and the membranous walls of the glomerulus as a piece of very delicate filtering paper, into which the blood is poured. 148. Changes of the Blood while passing through the Kidneys. — ^The blood which supplies the kidneys is brought directly from the aorta by the renal arteries, so that it has but shortly left the heart. The venous blood which enters the heart and is propelled to the lungs, charged with the nitro- genous, as well as with the other, products of waste, loses only an inappreciable quantity of them in its course through the lungs ; so that the arterial blood which fills the aorta is pure only as regards carbonaceous waste, impure as regards urea and uric acid. In the healthy condition, the walls of the minute renal arteries and veins are relaxed, so that the passage of the blood is very free, and but little waste, arising from muscular con- traction, is thrown into the renal blood. Furthermore, as the urine contains very little oxygen and much carbonic acid, such carbonaceous waste as arises from this source is probably counterbalanced. Hence, so long as the kidney is performing its functions properly, the blood which leaves the organ by the renal vein is as bright scarlet as that which enters it by the renal artery. Strictly speaking, it is the purest blood in the body, careful analysis having shown that it contains a sensibly smaller quantity of urea and of water than that of the left side of the heart This diflerence is, of course, a necessary result of the excre- tion of the urinary fluid from the blood as it travels through the kidney ; what is less intelligible, at present, is the circum-


SOURCES OF LOSS TO THE BLOOD. 115 stance that the plasma of the hlood of the renal vein yields little or no fibrin, and hence differs but little from serum. 149. The Nervous System controls the Eenal Excretion. — Irritation of tbe nerves which supply the walls of the vessels of the kidney has the immediate effect of stopping the excre- tion of urine, and rendering the renal blood dark and venous. The first effect would appear to be explicable by the diminu- tion of the pressure exerted upon the blood in the Malpighian tufts, in consequence of the diminution in size of the channels — the small arteries — by which the blood reaches them. And the second effect is probably, in part, a consequence of the first — the excretion of carbonic acid by the urine ceasing; while, to a greater extent, it is the result of the pouring in of carbonic acid into the renal blood, in consequence of the work of the muscles of the small vessels, and the waste which results therefrom. 160. The Loss by the Skin. — That the skin is a source of continual loss to the blood may be proved in various ways. If the whole body of a man, or one of his limbs, be enclosed in a caoutchouc bag, full of air, it will be found that this air under- goes changes which are similar in kind to those which take place in the air which is inspired into the lungs. That is to say, the air loses oxygen and gains carbonic acid ; it receives a great quantity of watery vapor, which condenses upon the sides of the bag, and may be drawn off by a properiy disposed pipe ; and, fiirthermore, a minute quantity of urea accumulates upon the surface of the limb or body. Under ordinary cir- cumstances no liquid water appears upon the surface of the integument, and the whole process receives the name of the in- sensible perspiration. But, when violent exercise is taken, or under some kinds of mental emotion, or when the body is exposed to a hot and moist atmosphere, the perspiration be- comes sensible, — is visible in the form of scattered drops upon the surface. 151. ftnantity of the Cntaneous Excretions. — The quan- tity of sweat, or perspiration, varies immensely, according to


116 ELEMENTABY PHYSIOLOGY. the temperature and other conditions of the air, and according to the state of the blood and of the nervous system. It is estimated that, as a general rule, the quantity of water ex- creted by the skin is about double that given out by the lungs in the same time. The quantity of carbonic acid is not above ■^th or ^th that excreted by the lungs. The precise quantity of urea excreted is not known. In its normal state the sweat is acid, and contains fatty matters, even when obtained free from the fatty products of the sebaceous glands. Ordinarily, perspiration, as it collects upon the skin, is mixed with the fatty secretion of these glands ; and, in addition, contains scales of the external layers of the epidermis, which are constantly being shed. 152. respiration by Simple Transudation. — In analyzing the process by which the perspiration is eliminated from the body, it must be recollected, in the first place, that the skin, even if there were no glandular structures connected with it, would be in the position of a moderately thick, permeable membrane, interposed between a hot fluid, the blood, and an atmosphere which is, usually, far from saturated with watery vapor, and which, at any rate in temperate climates, ceases to be so saturated the moment it comes into contact with the skin, the temperature of which is, ordinarily, twenty or thirty decrees above its own. A bladder filled with water at 100°, though it possess no sensible pores, will assuredly allow evaporation to take place freely through its substance ; and, from its relation to the blood, the skin is such a bladder full of hot fluid. Thus, perspiration to a certain amount must always be going on through the substance of the integument ; but what the amount of this perspiration may be, cannot be ascertained, because a second and very important source of the perspira- tion is to be found in what are called the sweat-glands, 153. Sweat-glands. — All over the body the integument presents minute apertures, the ends of channels excavated in the epidermis or scarf-skin, and each continuing the direction


SOURCES OF LOSS TO THE BLOOD. 117 of a minute tube, usually about ^^^tb of an ineb in diameter, and a quarter of an incb long, wbicb is imbedded in tbe dermis. Eacb tube is lined witb an epitbelium continuous with the epi- dermis. The tube sometimes divides, but, whether single or branched, its inner end or ends are blind, and coiled up into a sort of knot, interlaced with a mesh work of capillaries (Fig. 45). The blood in these capillaries is therefore separated from the cavity of the sweat-gland only by the thin walls of the capil- laries, that of the glandular tube, and its epithelium, which, taken together, constitute but a very thin pellicle ; and the ar- rangement, though different in detail, is similar in principle, to that which obtains in the kidney. In the latter, the vessel Tig. 45.— Section o^tbe 8kin showing the sweat-frlands. a, the epidermis ; 6, its deep- er layer, the rete Malpiqhii ; e d, the dermis, or true skin ; /, fat cells ; ff, tho coiled end of a sweat-gland ; A, Its duct ; i, its opening on the surface of the epidermis. Fig. 46.— A section of the skin showing the roots of the hairs and the sebaceous glands ; &, muscle of ; c, the hair-sheath on the left hand. makes a coil within the Malpighian capsule, which ends a tubule. Here the perspiratory tubule coils about, and among, the vessels. In both cases the same result is arrived at — namely, the exposure of the blood to a large, relatively free, surface, on to which certain of its contents transude. The number of these glands varies in different parts of the


118 ELEMENTARY PHYSIOLOGY. body. They are fewest in the back and neck, where their number is not much more than 400 to a square inch. They are more numerous on the skin of the palm and sole, where their apertures follow the ridges visible on the skin, and amount to between two and three thousand on the square inch. At a rough estimate, the whole integument probably possesses not fewer than from two millions and a quarter to two millions and a half of these tubules, which therefore must possess a very great aggregate secreting power. 154. These Glands are controlled by the Nervous System. — ^The sweat-glands arc greatly under the influence of the nervous system. This is proved, not merely by the well- known effects of mental emotion in sometimes suppressing the perspiration and sometimes causing it to be poured forth in immense abundance, but has been made a matter of direct ex- periment. There are some animals, such as the horse, which perspire very freely. If the sympathetic nerve of one side, in the neck of a horse, be cut, the temperature of that side of the head rises, and it becomes injected with blood (par. 74) ; and, at the same time, sweat is poured out abundantly over the whole surface thus affected. On irritating the end of the cut nerve, which is in connection with the vessels, the muscular walls of the latter, to which the nen'^e is distributed, contract, the congestion ceases, and with it the perspiration. 165. Variations in the Perspiratory Loss3S.— The quan- tity of matter which may be lost by perspiration, under certain circumstances, is very remarkable. Heat and. severe labor combined, may reduce the weight of a man two or three pounds in an hour, by means of the cutaneous perspiration alone ; and, as there is some reason to believe, that the quantity of solid matter carried off from the blood does not diminish with the increase of the amount of the perspiration, the quan- tity of urea eliminated by profuse sweating may be consider- able. The difference between blood which is coming from, and that which is going to, the skin, can only be concluded from


S0UECE8 OF LOSS TO THE BLOOD. 119 the nature of the substances given out in the perspiration ; but arterial blood is not rendered venous in the skin. 156. The LungSy Skin, and Kidneys compared. — It will now be instractive to compare together, in raore detail than has been done in the third chapter, the three great organs — lungs, kidneys, and skin — which have been described. In ultimate anatomical analysis, each of these organs con- sists of a moist animal membrane separating the blood from the atmosphere. Water, carbonic acid, and urea pass out from the blood through the animal membrane in each organ, and constitute its secretion or excretion ; but the three organs differ in the absolute and relative amounts of the constituentsof which they permit the escape. Taken by weight, water is the predominant excretion in all three : most solid matter is given off by the kidneys ; most gaseous matter by the lungs. The skin partakes of the nature of both lungs and kidneys, seeing that it absorbs oxygen and exhales carbonic acid and water, like the former, while it excretes urea and saline matter in solution like the latter; but the skin is more closely related to the kidneys than to the lungs. Hence, when the free action of either of the two former organs is interrupted, its work is usually thrown upon the other. In hot weather, when the ex- cretion by the skin increases, that of the kidneys diminishes, and the reverse is observed in cold weather. This power of mutual substitution, however, only goes a little way ; for if the kidneys be extirpated, or their functions much interfered with, death ensues, however active the skin may be. And, on the other hand, if the skin be covered with an impenetrable varnish, the temperature of the body rapidly falls, and death takes place, though the lungs and kidneys re- main active.

iGcmglq 120 ELEMENTARY PHYSIOLOGY. Section II. — Losses and Gains hy the lAver. 157. Structure and Connections of the Liver. — ^The liver is a constant source both of loss, and, in a sense, of gain to the blood : of loss, because it forms from the blood a peculiar fluid, the hile ; of gain, if not in quantity, at any rate in kind of mat- ter, because it elaborates from the blood which enters it, a sub- stance, glycogen^ which is capable of passing very readily into a kind of sugar, called glucose. Furthermore, it is very prob- able that the liver is one source of the colorless corpuscles of the blood. The liver is the largest glandular organ in the body, ordi- narily weighing about fifty or sixty ounces. It is a broad, dark, red- colored organ, which lies on the right side of the body, immediately below the diaphragm, with which its upper surface is in contact, while its lower surface touches the intes* tines and the right kidney. The liver is invested by a coat of peritoneum, which keeps it in place. It is flattened from above downward, convex and PIQ.4T. The liver viewed from below, a, vena cava ; ft, vena porta ; c, bile duct ; <?, hepatic artery ; I, gall-bladder. smooth above, where it fits into the concavity of the lower sur- face of the diaphragm. Flat and irregular below (Fig. 47), it is thick behind, but ends in a thin edge in front.


LOSSES AND GAINS BY THE LIVEE. 121 Viewed from below, as in Fig. 47, the inferior vena cava, a, is seen to traverse a notch in the hinder edge of the liver as it passes from the abdomen to the thorax. At b the trunk of the vena portce is observed dividing into the chief branches which enter into, and ramify through, the substance of the organ. At d, the hepatic artery^ coming almost directly from the aorta, similarly divides, enters the liver, and ramifies through it; while at c is the single trunk of the duct, called the hepatic duct, which conveys away the bile brought to it by its Fig. 48. <7,nltimate branches of the hepatic duct; 5, liver-cells. right and left branches from the liver. Opening into the he- patic duct is seen the duct of a large oval sac, l, the gall-blad- der. The duct is smaller than the artery, and the artery than the portal vein. If the branches of the artery, the portal vein, and the bile duct, bo traced into the substance of the liver, they will be found to accompany one another, and to branch out and sub- divide, becoming smaller and smaller. At length the portal vein and hepatic artery will be found to end in the capillaries, which traverse, like a net-work, the substance of the smallest obvious subdivisions of the liver substance — polygonal masses of one-tenth of an inch in diameter, or less, which are termed the lobules. Every lobule is seated by its base upon one of the ramifications of a great vein — ^the hepatic vein — and the blood 6


122 ELEMENTAEY PHYSIOLOGY. of its capillaries is poured into that vein by a minute veinlet which traverses the centre of the acinus, and pierces its base. Thus the venous blood of the portal vein and the arterial blood J2np:\ Fig. 49. A section of part of the liver, to show H. V. the hepatic vein, with L. the lobules or acini of the liver, seated upon its walls, and sending their Intralobular veins into it of the hepatic artery reach the surface of the lobules by the ultimate ramifications of that vein and artery, become mixed in the capillaries of the acinus, and are carried off by its intra- lobular veinlet, which pours its contents into one of the rami- fications of the hepatic vein. These ramifications, joining together, form larger and larger trunks, which at length reach the hinder margin of the liver, and finally open into the vena cava inferior^ where it passes upward in contact with that part of the organ. Thus the blood with which the liver is supplied is a mixture of arterial and venous blood.


LOSSES AND GAINS BY THE LIVER. 123 What ultimately becomes of the ramifications of the hepatic duct is not certainly known. Lined by an epithelium, which is continuous with that of the main duct, and thence with that of the intestines, into which the main duct opens, they may be traced to the very surface of the lobules, but no farther. Whether they end blindly, as some think, or whether, as others conceive, they expand and close the liver-cells, is not clearly proved. In either case, any fluid separated from the blood by the lobules, must readily find its way into them. In the lobules themselves all the meshes of the blood-ves- sels are occupied by the liver-cells, many-sided minute bodies, each about ^^jViT*^ ^^ ^^ ^"^^ ^^ diameter, possessing a nucleus in its interior, and frequently having larger and smaller granules of fatty matter distributed through its substance (Fig. 48, b). It is in these that the active powers of the liver are supposed to reside. 158. The Active Powers of the Liver-Cells. — The nature of these active powers is determined by ascertaining — a. The character of that fluid, the bile, which incessantly flows down the biliary duct, and which, if digestion is not going 'on, and the passage into the intestine is closed, flows back into and fills the gall-bladder. And 6. The difference between the blood which enters the liver and that which leaves it in respect of the constituents of the bile. 159. The Bile— its ftuantity and Compositioii. — a. The total quantity of bile secreted in the twenty-four hours varies, but probably amounts to not less than from two to three pounds. It is a greenish-yellow, slightly alkaline, fluid, of ex- tremely bitter taste, consisting of water, with from 17 per cent, of solid matter, to half that quantity, in solution. The solids consist chiefly of a resinous substance, composed of carbon, hydrogen, oxygen, nitrogen, and sulphur, which exists iu com- bination with soda. This bihary matter, or bilin, may be sepa- rated by chemical processes into two acids, called 'the Tauro- cholic (which contains all the sulphur) and the Glycocholic ;


124 ELEMENTAEY PHYSIOLOGY. and it isdconsequently said to be a combination of taurocholatfi and glycocholate of soda. Besides this bilin, its chief con- stituent, the bile contains a crystallized fatty substance, choles- terine, together with a peculiar coloring matter which contains iron, and is probably related to the haematin of the bJood. h. Of these constituents of the bile the water, the clioles- teiine, and the saline matters, alone, are discoverable in the blood ; and though doubtless some diflerence obtains between the blood which enters the liver and that which leaves it, in respect of the proportional quantity of these constituents, great practical diflSculties lie in the way of the precise ascer- tainment of those ditferences. The blood of the hepatic vein, however, is certainly poorer in water than that of the portal vein. 160. Bile is formed in the Liver-Cells.— As the essential constituent of bile, bilin, is not discoverable in the blood which enters the liver, it must be formed at the expense of the tissue of that organ itself, or of some constituent of the blood passing through it. However this may be, it is a very curious circumstance that, as almost all the bile which is formed in the intestines is reabsorbed by the vessels in their walls, it must, in some shape or other, enter the liver a second time with the current of the portal blood. Section HI. — Sources of Gain to the Blood, 161. The Skin as an Organ of Bespiration. — ^We must next consider the chief sources of constant gain to the blood ; and, in the first place, the sources of gain of matter. The Jungs and sMn are, as has been seen, two of the prin- cipal channels by which the body loses liquid and gaseous matter, but they are also the sole means by which one of the most important of all substances for the maintenance of life, oxygen, is introduced into the blood. It has already been pointed out that the volume of the oxygen taken into the blood by the lungs* is rather greater than that of the carbonic acid given out.


SOTJECEB OF GAIN TO THE BLOOD. 125 How much is taken in by the skin of man is not certainly known, but in some of the lower animals, such as the frog, the skin plays a very important part in the performance of the respiratory function. 162. Beaction of the Liver upon the Blood. — ^The blood leaving the liver by the hepatic vein not only contains pro- portionally less water and fibrin, but proportionally more cor- puscles, especially colorless corpuscles, and, what is still more important, a larger quantity of liver-sugar, or glucose, than that brought to it by the portal veins and hepatic artery; and these differences are irrespective of the nature of the food. That the blood leaving the liver should contain propor- tionally less water and more corpuscles than that entering it is no more than might be expected, from the fact that the for- mation of the bile, which is separated from this blood, neces- sarily involves a loss of water and of some solid matters, while it does not abstract any of the corpuscles. We do not know why less fibrin separates from the blood of the hepatic vein than from the blood brought to the liver. But the reason why there is always more sugar in the blood leaving the liver than in that entering it ; and why, in fact, there is plenty of sugar in the blood of the hepatic vein even when none whatever is brought to it by the hepatic artery, or portal vein, has only been made out by careful and ingenious experimental research within the last few years. 163. Proof of the Sugar-forming Function of the Liver. — If an animal be fed upon purely animal food, the blood of the portal vein will contain no sugar, none having been absorbed by the walls of the alimentary canal, nor will that of the he- patic artery contain any, or, at any rate, but the merest trace. Nevertheless, plenty will be found, at the same time, in the blood of the hepatic vein and in that of the vena cava, from the point at which that vein opens, as far as the heart. Secondly, if, from an animal so fed, the liver be extracted, and a current of cold water forced into the vena portce, it will flow out by the hepatic vein, carrying with it all the blood of


126 ELEMENTARY PHYSIOLOGY. the organ, and will, after a time, pour out colorless, and de- void of sugar. Nevertheless, if the organ be left to itself at a moderate temperature, sugar will soon again become abundant in it. Thirdly, from the liver, washed as above described, a sub- stance may be extracted, by appropriate methods, which re- sembles starcb, dextrine, and gum in chemical composition, consisting as it does of carbon united with hydrogen and oxy- gen, the latter being in the same proportions as in water. This " amyloid " substance is glycogen. It may be dried and kept without change for long periods. But, like the vegetable starch and dextrine, this animal amyloid, which is necessarily formed in the liver, since it is certainly not contained either in the blood of the portal vein, or in that of the hepatic aitery, is very readily changed by contact with many nitrogenous matters, which act as ferments, into sugar. Fourthly, it may be demonstrated that a nitrogenous fer- ment, competent to change the " amyloid " glycogen into saccharine "^^wcose," exists under ordinary circumstances in the liver. Putting all these circumstances together, the riddle of the appearance of sugar in the blood of the hepatic vein and vena cava, when neither it nor any compound out of which it is easily formed exists in the blood brought to the hver, is readily explained. The liver forms glycogen out of the blood with which it is supplied. The same blood supplies the ferment which, at the temperature of the body, very speedily converts that com- paratively little soluble glycogen into very soluble sugar; and this sugar is dissolved and carried away by each intralobular vein to the hepatic vein, and thence to the vena cava. 164. Gain by the Lymphatics. — The lympfiatic system has been aheady mentioned as a feeder of the blood with a fluid which, in general, appears to be merely the superfluous drain- age, as it were, of the blood-vessels ; though at intervals, as \ \ VjOOQ IC SOUECES OF GAIN TO THE BLOOD. 127 we shall see, the lacteals make substantial additions of new matter. It is very probable that the multitudinous lymphatic glands may effect some change in the fluid which traverses them, or may add to the number of corpuscles in the lymph. The glandular bodies, which like the Ijmaphatic glands are devoid of ducts and are abundantly supplied with lymphatics, are the thyroid gland, which lies in the part of the throat below the larynx, and is that organ which when enlarged by disease gives rise to " Derbyshire neck " or " goitre ; " the thymus gland, situated at the base of the heart, largest in infants, and gradually disappearing in adult and old persons ; and the supra renal capsules, which lie above the kidneys. Nothing is cer- tainly known of the functions of any of these bodies. 165. The Spleen— its Functions unknown. — We are as much in the dark respecting the oflSce of the large viscus X>?/t Fig. 50. The spleen {Spl.) with the splenic artery {Sp. AX Below this is seen the splenic vein running to help to form the vena portcB ( V.P.). Ao. the aorta; D. a pillar of the diaphraf^m ; P. D. the pancreatic duct exposed by dissection in the sub- stance ol the pancreas ; D. M. the duodenum ; B. D. the biliary duct opening with the pancreatic duct at aj; y, the intestinal vessels. called the spleen, which lies upon the left side of the stomach in the abdominal cavity. It is an elongated flattened red body, abundantly supplied with blood by an artery called the


128 ELEMENTAEY PHYSIOLOGY. splenic artery^ which proceeds almost directly from the aorta. The blood which has traversed the spleen is collected by the splenic vein^ and is carried by it to the vena portcB^ and so to the liver. A section of the spleen shows a dark red spongy mass dotted over with minute whitish spots. Each of these last is the section of one of the spheroidal bodies called corpuscles of the spleen, which are scattered through its substance, and con- sist of a solid aggregation of bodies, like the white corpuscles of the blood, traversed by a capillary net- work, which is fed by a small twig of the splenic artery. The dark-red part of the spleen in which these corpuscles are imbedded is composed of fibrous and elastic tissue supporting a very spongy vascular net-work. The elasticity of the splenic tissue allows the organ to be readily distended, and enables it to return to its former size after distension. It appears to change its dimensions with the state of the abdominal viscera, attaining its largest size about six hours after food is taken, and falling to its minimum bulk six or seven hours later, if no food be taken. The blood of the splenic vein is found to contain propor- tionally fewer red corpuscles, but more colorless corpuscles and more fibrin, than that in the splenic artery ; and it has been sup- posed that the spleen is one of those parts of the economy in which the colorless corpuscles of the blood are especially pro- duced. 166. The Gain of Heat— its Source. — ^It has been seen that heat is being constantly given off from the integument and from the air-passages: and everything that passes from the body carries away with it, in like manner, a certain quantity of heat. Furthermore, the surface of the body is much more exposed to cold than its interior. Nevertheless, the tempera- ture of the body is maintained very evenly at all times and in all parts, within the range of two degrees on either side of 99° Fahrenheit. This is the result of three conditions: — The first, that heat


60UE0ES OF GAIN TO THE BLOOD. 129 is constantly being generated in the body. The second, that it is as constantly being distributed through the body. The third, that it is subject to incessant regulation. Heat is generated whenever oxidation takes place ; and hence, whenever protein substances, or fats or aniyloidal mat- ters, are being converted into the more highly oxidated waste products, urea, — ^uric acid, carbonic acid, and water, — ^heat is necessarily evolved. But these processes are taking place in all parts of the body by which vital activity is manifested, and . hence, every capillary vessel and every extravascular islet of tissue is really a small fireplace in which heat is being evolved, in proportion to the activity of the chemical changes which are going on. *" 167. Distribution of Heat by the Blood-Current.— But as the vital activities of different parts of the body, and of the whole body, at different times, are very different ; and as some parts of the body are so situated as to lose their heat by radia- tion and conduction much more easily than others, the tem- perature of the body would be very unequal in its different parts and at different times, were it not for the arrangements by which the heat is distributed and regulated. Whatever oxidation occurs in any part, raises to an equiv- alent temperature the blood which is in that part at the time. But this blood is swiftly hurried away into other parts of the body, and rapidly parts with its increased temperature to them. On the other hand, the blood of the surface of the body, the temperature of which is lowered by evaporation and radiation, suffers only a very slight loss of heat before it is transported into the deeper parts and there becomes warmed by contact, as well as by the oxidating processes in which it takes a part. Thus the organs of circulation are comparable to a vast system of hot-water pipes — ^the constant flow of fluid through which should be effected by a pump, while the water should be warmed, not by a great central boiler as usual, but by a mul- titude of minute gas-jets, disposed beneath the pipes, not evenly, but more here and fewer there. It is obvious that, 6*


130 ELEMENTARY PHYSIOLOGY. however much greater the heat applied to one part of the sys- tem of pipes than to another, the general temperature of the ^^ water would be even throughout, if it were kept moving with sufficient quickness by the pump. 168. Evaporation regiilates Temperature. — If such a system were entirely composed of closed pipes, the temperature of the water might be raised to any extent by the gas-jets. On the other hand, it might be kept down to any required degree by causing a larger, or smaller, portion of the pipes to be wet- ted with water, which should be able to evaporate freely — as, for example, by wrapping them in wet cloths. And the greater the quantity of water thus evaporated, the lower would be the temperature of the Vhole. Now the regulation of the temperature of the human body is effected on this principle. The vessels are closed pipes, but a great number of them are enclosed in the skin and in the mucous membrane of the air-passages, which are, in a physical sense, wet cloths freely exposed to the air. It is the evaporar tion from these which exercises a more important influence than any other condition upon the regulation of the tempera- ture of the blood, and consequently of the body. 169. Begolative Agency of the Nervous System. — But as a further nicety of adjustment, the wetness of the regulator is itself determined by the state of the small vessels, inasmuch as exudation from these takes place more readily when the walls of the veins and arteries are relaxed, and the blood distends them and the capillaries. But the condition of the walls, of the vessels depends upon the nerves by which they are sup- plied, and it so happens that cold produces irritation of these nerves with contraction of the small vessels — moderate warmth, the reverse. Thus the supply of blood to the surface is lessened and loss of heat thereby checked, when the external temperature is low ; while, when the external temperature is high, the supply of blood to the surface is increased, the fluid exuded from the vessels pours out by the sweat-glands, and the evaporation of


SOURCES OF GAIN TO THE BLOOD. 131 this fluid checks the rise in the temperature of the superficial blood. Hence it is that, so long as the surface of the body per- spires freely, and the air-passages are abundantly moist, a man may remain with impunity, for a considerable time, in an oven in which meat is being cooked. The heat of the air is ex- pended in converting his superabundant perspiration into va- por, and the temperature of the blood is hardly raised. 170. Intermittent Action of the Glands. — The chief inter- mittently active sources of loss to the blood are found among the glands proper, all of which are, in principle, narrow pouches of the mucous membranes, or of the integument of the body, lined by a continuation of the epithelium or of the epidermis. In the glands of Lieberkukn, which exist in immense numbers in the walls of the intestines, each gland is nothing more than a simple blind sac of the mucous membrane, shaped like a small test-tube, with its closed end outward, and its open end on the inner surface of the intestine. The sweat-glands of the Fig. 52. Fig. 61.— A salivary duct, with &, its lateral ramifications, and (f, tbo ultimate blind ends of these. Fig. 52.— Two of the blind ends magnified. skin, as we have already seen, are equally simple, blind, tube- like involutions of the integument, the ends of which become coiled up. The sebaceous glands^ usually connected with the


132 ELEMENTARY PHYSIOLOGY. hair-sacs, are shorter, and their blind ends somewhat sub- divided, so that the gland is divided into a narrow neck and a more dilated and sacculated end. The neck by which the gland communicates with the free surface is now called its duct. More compUcated glands are produced by the elongation of the duct into a long tube, and the division and subdivision of the blind end into multitudes of similar tubes, each of which ends in a dilatation. These dilatations, attached to their branched ducts, somewhat resemble a bunch of grapes. Glands of this kind are called racemose. The salivary glands and the pancreas are such glands. Now, many of these glands, such as the salivary, the pan- creas (and the perspiratory, or sudoriparous glands, which it has been convenient to consider already), are only active when certain impressions on the nervous system give rise to a par- ticular condition of the gland, or of its vessels, or of both. 171. Action of the Salivary Glands.— Thus the sight or smell, or even the thought of food, will cause a flow of saliva into the mouth ; the previously quiescent gland suddenly pour- ing out its fluid secretion, as a result of a change in the con- dition of the nervous system. And, in animals, the salivary glands can be made to secrete abundantly, by irritating a nerve which supplies the gland and its vessels. How far this effect is the result of the mechanical influence of the nerve on the. state of the circulation, and how far it is the result of a more direct influence of the nerve upon the state of the tissue of the gland itself, is not at present determined. The liquids poured out by the intermittent glands are al- ways very poor in solid constituents, and consist chiefly of water. Those poured on to the surface of the body are lost, but those which are received by the alimentary canal are doubt- less in great measure reabsorbed. 172. Gain of Waste Products from the Muscles.— The great intermittent sources of gain of waste products to the blood are the muscles, every contraction of which is accompanied by a waste of matter, and a pouring of their waste products into


PB0PHBTIE8 OF FOOD-STUFFS. 133 the blood. That much of this waste product is carbonic acid is certain from the facts, (a) that the blood which leaves a con- tracting muscle is always highly venous, far more so than that which leaves a quiescent muscle ; and (6) that muscular exer- tion at once immensely increases the quantity of carbonic acid expired : but whether the amount of nitrogenous waste is in- creased under these circumstances, or not, is a point yet under discussion. CHAPTER VII. THE FUNCTION OF ALIMENTATION. Section I. — Properties of Food-Stuffs. 173. The Alimentary Canal the Chief Source of Gain.— The great source of gain to the blood, and, except the lungs, the only channel by which altogether new material is intro- duced into that fluid, is the alimentary canal, the totality of the operations of which constitute the function of alimentation. It will be useM to consider the general nature and results of the performance of the function of alimentation before study- ing its details. 174. Quantity of Dry, Solid, and Gaseous Aliment daily taken.— A man daily takes into his mouth, and thereby intro- duces into his alimentary cana], a certain quantity of solid and liquid food, in the shape of meat, bread, butter, water, and the like. The quantity of chemically dry, solid matter, which must thus be taken into the body, if a man of average size and activity is neither to lose, nor to gain, in weight, has been found to be about 8,000 grains. In addition to this his blood absorbs by the lungs about 10,000 grains of oxygen gas, mak- ing a grand total of 18,000 giains (or nearly two pounds and three-quarters avoirdupois) of daily gain of dry, solid, and gas- eous matter.

Goosle^ 134: ELEMENTAEY PHYSKJLOGY. 176. Daily Loss of Dry Solids. — The weight of dry solid matter passed out from the alimentary canal does not, on the average, amount to more than one-tenth of that which is taken into it, or 800 grains. By no other channel does any appre- ciable quantity of solid matter leave the body, and it therefore follows that 7,200 grains of solid must pass out of it, in either the gaseous or the liquid form, as well as the 10,000 grains of oxygen. Further, as the general composition of the body re- mains constant, it follows, either that the elementary constitu- ents of the solids taken into the body must be identical with those of the body itself: or that, in the course of the vital pro- cesses, the food alone is destroyed, the substance of the body remaining unchanged : or, finally, that both these alternatives hold good, and that food is, partly, identical with the wasting substance of the body and replaces it; and, partly, differs from the wasting substance, and is consumed without repla- cing it. 176. Classification of Aliments. — As a matter of fact, all the substances which are used as food come under one of four heads. They are either what may be termed Proteids, or they are Fats^ or they are Amyloids^ or they are Minerals, Proteids are substances analogous in composition to Protein, and contain the four elements — carbon, hydrogen, oxygen, and niti'ogen, sometimes united with sulphur and phosphorus. Under this head come the Gluten of flour ; the Albumen of white of egg, and of blood serum ; the Fibrin of the blood ; the Syntonin, which is the chief constituent of muscle and flesh, and Casein, the chief constituent of cheese ; while Gelatin, which is obtained by boiling from connective tissue, and Chon- drin, which may be produced in the same way from cartilage, may be considered to be outlying members of the same group. Fats are composed of carbon, hydrogen, and oxygen only, and contain more hydrogen than is enough to form water if united with the oxygen which they possess. All oils and vegetable and animal fatty matters come under this division.


PE0PERTIE8 OF FOOD-STUFFS. 135 Amyloids are substances which also consist of carbon, hy- drogen, and oxygen only. 33ut they contain no more hydro- gen than is just sufficient to produce water with their oxygen. These are the matters known as Starch, Dextrine, Sugar, and Gum, It is the peculiarity of the three groups of food-stuffs just mentioned that they can only be obtained (at any rate, at present) by the activity of Uving beings, whether animals or plants, so that they may be conveniently termed vital food-stuffs. Food-stuffs of the fourth class, on the other hand, or Mimr erals, are to be procured as well from the not-living, as the living, world. They are water, and salts of sundry alkalies, earths, and metals. To these, in strictness, oxygen ought to be added, though, as it is not taken in by thp alimentary canal, it hardly comes within the ordinary acceptation of the word food. 177. intimate Coinpositioii of Aliments. — In ultimate analysis, then, it appears that vital food-stuffs contain either three or four of the elements : carbon, hydrogen, oxygen, and nitrogen ; that mineral food-stuffs are water, and salts. But the human body, in ultimate analysis, also proves to be com- posed of the same four elements, plus water, and the same saline matters as are found in food. More than this, no substance can serve permanently for food — ^that is to say, can prevent loss of weight and change in the general composition of the body — ^unless it contains a cer- tain amount of protein in the shape of albumen, fibrin, syutonin, or casein. While, on the other hand, any substance which contains protein in a readily assimilable shape, is competent to act as a permanent food. But the human body, as we have seen, contains a large quantity of protein in one or the other of the four forms which have been enumerated ; and, therefore, it turns out to be an indispensable condition, that every substance which is to serve permanently as food, must contain a sufficient quantity of the most important and complex component of the body ready made. It must also contain a sufficient quantity of the mineral


136 ELEMENTABY PHrSIOLOGY. ingredients which are required. Whether it contains either fats x>T amyloids, or both, or is devoid of both, its essential power of supporting the life and maintaining the weight and composition of the body remains unchanged. 178. No absolute Necessity for other Food-Stuffs.— The necessity of constantly renewing the supply of protein arises from the circumstance that the*6ecretion of urea from the body (and consequently the loss of nitrogen) goes on continually, whether the body is fed or not : while there is only one form in which nitrogen (at any rate, in any considerable quantity) can be taken into the blood, and that is in the form of a solution of protein. If protein be not supplied, therefore, the body must needs waste, because there is nothing in the food compe- tent to make good the loss of nitrogen. On the other hand, if protein be supplied there can be no absolute necessity for any other but the mineral food-stuffs, be- cause protein contains carbon and hydrogen in abundance, and hence is competent to give origin to the other great products of waste, carbonic acid and water. In fact, the final results of the oxidation of protein are car- bonic acid, water, and ammonia; and these, as we have seen, ai'e the final shapes of the waste products of the human economy. 179. Nitrogen Starvation. — From what has been said, it becomes readily intelligible that whether an animal be herbiv- orous or carnivorous, it begins to starve from the moment its vital food-stuffs consist of pure amyloids or fats, or any mixture of them. It suffers from what may be called nitrogen starva- tion, and, sooner or later, will die. In this case, and still more in that of an animal deprived of vital food altogether, the organism, so long as it continues to live, feeds upon itself, and its excretions are all necessarily formed at the expense of its own body ; whence it has been rightly enough observed that a starving sheep is as much a carnivore as a lion. 180. Disadvantages of a purely Nitrogenons Diet. — But though protein is the essential element of food, and under


PROPERTIES OF FOOD-STUFFS, 137 certain circumstances may suffice, by itself, to maintain the body, it is a very disadvantageous and uneconomical food. Albumen, which may be taken as the type of the proteids, contains about 63 parts of carbon and 16 of nitrogen hi 100 parts. If a man were to be fed upon white of egg^ therefore, he would take in, speaking roughly, 3 J parts of carbon for every part of nitrogen. But it is proved experimentally, that a healthy full-grown man, keeping up his weight and heat, and taking a fair amount of exercise, eliminates 4,000 grains of carbon to only 300 grains of nitrogen, or, roughly, only needs one-thirteenth as much nitrogen as carbon. However, if he is to get his 4,000 grains of carbon out of albumen, he must eat 7,547 grains of that sub- stance. But 7,647 grains of albumen contain 1,132 grains of nitrogen, or nearly four times as much as he wants. To put the case in another way, it takes about four pounds of fatless meat to yield 4,000 grains of carbon, whereas one pound will furnish 300 grains of nitrogen. Thus a man confined to a purely proteid diet, must eat a prodigious quantity of it. This not only involves a great amount of physiological labor in comminuting the food, and a great expenditure of power and time in dissolving and absorb- ing it ; but throws a great quantity of wholly profitless labor upon those excretory organs, which have to get rid of the nitro- genous matter, three-fourths of which, as we have seen, is super- fluous. 181. Economy of Physiological Power. — Unproductive labor is as much to be avoided in physiological, as in political, economy ; and it is quite possible that an animal fed with per- fectly nutritious protein matter should die of starvation, the loss of power in the various operations required for its assimilation overbalancing the gain ; or the time occupied in their perform- ance being too great to check waste with sufficient rapidity. Tlie body, under these circumstances, falls into the condition of a merchant who has abundant assets, but who cannot get in his debts in time to meet his creditors.


138 ELEMENTARY PHYSIOLOGY. 182. Economy of a Mixed Diet. — These considerations lead us to the physiological justification of the universal prac- tice of mankind in adopting a mixed diet, in which proteids are mixed either with fats, or with amyloids, or with both. Fats may be taken to contain about 80 per cent of carbon, and amyloids about 40 per cent. Now it has been seen that there is enough nitrogen to supply the waste of that substance per diem, in a healthy man, in a pound of fatless meat ; which also contains 1,000 grains of carbon, leaving a deficit of 3,000 grains of carbon. Eather more than half a pound of fat, or a pound of sugar, will supply this quantity of carbon. The former, if properly subdivided, the latter, from its solubility, passes with gi'eat ease into the economy, the digestive labor of which is consequently reduced to a minimum. 183 Advantages of a Mixed Diet. — Several apparently simple articles of food constitute by themselves a mixed diet Thus butcher's meat commonly contains fi-om 30 to 50 per cent, of fat. Bread, on the other hand, contains the proteid, gluten, and the amyloids, starch and sugar, with minute quan- tities of fat. But, from the proportion in which these proteid and other constituents exist in these substances, they are neither, taken alone, such physiologically economical foods, as when they are combined in the proportion of about 200 to 75 ; or two pounds of bread to three-quarters of a pound of meat per diem, 184. Intennediate Changes of the Food. — It is quite certain that nine-tenths of the dry solid food which is taken into the body, sooner or later leaves it in the shape of carbonic acid, water, and urea (or uric acid) ; and it is also certain that, as the compounds which leave the body are more highly oxi- dated than those which enter it, and as free oxygen is nowhere eliminated, all the oxygen taken in by the lungs passes away in these compounds. The intermediate stages of this conversion are, however, by no means so clear. It is highly probable that the amyloids and fats are very frequently oxidated in the blood, without.


PROPERTIES OF FOOD-STUFFS. 139 properly speaking, ever forming an integral part of the sub- stance of the body ; but whether the proteids may undergo the same changes in the blood, or whether it is necessary for them first to be incorporated with the living tissue, is not positively known. So, again, it is certain that, in becoming oxidated, the ele- ments of the food must give off heat, and it is probable that this heat is suflScient to account for all that passes off by the body ; but it is possible, and indeed probable, that there may be other, minor, sources of heat. 185. Objections to the Common Classifloation. — Food- stuffs have been divided into heat-producers and tissue-formers — the amyloids and fats constituting the former division, the pro- teids the latter. But this is a very misleading classification, inasmuch as it implies, on the one hand, that the oxidation of the proteids does not develop heat ; and, on the other, that the amyloids and fats, as they oxidize, subserve only the produc- tion of heat. Proteids are tissue-formers, inasmuch as no tissue can be produced without them ; but they are also heat-producers ^ not only directly, but because, as we have seen, they are compe- tent to give rise to amyloids by chemical metamorphosis within the body. If it is worth while to make a special classification of the vital food-stuffs at all, it appears desirable to distinguish the essential food-stuffs, or proteids, from the accessory food-stufl's, or fats and amyloids — the former alone being, in the nature of things, necessary to life, while the latter, however important, are not absolutely necessary. 186. Purpose of the Alimentary Mechanism. — All food- stuffs being thus proteids, fats, amyloids, or mineral matters, pure or mixed up with other substances, the \^holc purpose of the alimentary apparatus is to separate these proteids, etc., from the innutritions residue, if there be any ; and to reduce them into a condition either of solution or of excessively fine subdivision, in order that they may make their way through


140 ELEMENTAEY PHYSIOLOGY. the delicate structures which form the walls of the vessels of the alimentary canal. To these ends food is taken into the mouth and masticated, is insalivated, is swallowed, undergoes gastric digestion, passes into the intestine, and is subjected to the action of the secretions of the glands attached to that viscus ; and, finally, after the more or less complete extraction of the nutritive constituents, the residue, mixed up with cer- tain secretions of the intestine, leaves the body as the fceces. Section II. — Preliminaries of Digestion. 187. The Mouth and PhaJTrnx, — The cavity of the mouth is a chamber with a fixed roof, formed by the hard palate (Fig. 63, l\ and with a movable floor, constituted by the lower jaw, and the tongue (A:), which fills up the space between the two branches of the jaw. Arching round the margins of the upper and the lower jaws are the thirty-two teeth, sixteen above and sixteen below, and, external to these, the closure of the cavity of the mouth is completed by the cheeks, at the sides, and by the lips, in front When the mouth is shut, the back of the tongue comes into close contact with the palate ; and, where the hard palate ends, the communication between the mouth and the back of the throat is still further impeded by a sort of fleshy curtain — the soft palate, or velum — the middle of which is produced into a prolongation, the uvula (/), while its sides, skirting the sides of the passage, ox fauces, are double muscular pillars, which are termed the pillars of the fauces. Between these the tonsils are situated, one on each side. The velum with its uvula comes into contact below with the upper part of the back of the tongue, and with a sort of gristly lid-like process connected with its base, the epiglottis {e). Behind the partition thus formed is the cavity of the pharynx^ which may be desciibcd as a funnel-shaped bag with muscular walls, the upper margins of the wide end of which are attached to the base of the skull, while its lateral margins


PBELTMTNABIES OF DIGESTION. 141 are continuous with the walls of the cheeks, and the lower walls with the floor of the mouth. The narrow end of the pharyn- geal bag passes into the gullet or oesophagus (6), a muscular- walled tube, which affords a passage into the stomach. Fio. 63. A section of the month and nose, taken vertically, a little to the left of the middle line— a, the vertebral column; 6, the gullet; c, the windpipe; <f, the thyroid cartilaf^e of the larnyx; «, the epiglottis: /, the uvula; (7, the opening of the left Eustachian tube; 7i, the opening of the left lachrvmal duct; {, the hyold bone; X;, the tongue ; 2, the. hard palate; m n, the base of the skull; op q, the superior, middle, and inferior turbinal bones. The letters g/e^ ore placed in the pharynx. There are no fewer than six distinct openings into the pharynx — ^four in pairs, and two single ones in the middle line. The two pairs are, in front, the hinder openings of the nasal cavities. At the sides, close to these, are the apertures of the Eustachian tubes (g). The two single apertures are, the hinder opening of the mouth between the soft palate and the epiglottis ;


142 ELEMENTABY PHYSIOLOGY. and, behind the epiglottis, the upper aperture of the respiratory passage, or the glottis. 188. The Salivary Olands. — The mucous membrane which lines the mouth and the pharynx is beset with minute glands, the buccal glands ; but the great glands from which the cavity of the mouth receives its chief secretion, are the three pairs which, as has been already mentioned, are called parotid j sub- maxillary^ sublingual^ and which secrete the saliva. (Fig. 64.) Each parotid gland is placed just in front of the ear, and its duct passes forward along the cheek, until it opens in its in- terior, opposite the second upper grinding tooth. The submaxillary and sublingual glands lie between the lower jaw and the floor of the mouth, the submaxillary farther Fig. 64. A dissection of the rfeht side of the face, showing, at, the snhllngaal ; &, the snbmaz- illary glands, with their ducts opening beside the tongue in the floor of the month at (2; c, the parotid gland and its dact, which opens on the side of the cheek at e. back than the sublingual. Their ducts open in the floor of the mouth below the tip of the tongue. The secretion of these, mixed with that of the small glands of the mouth, constitutes the saliva — a fluid which, though thin and watery, contains a small quantity of animal matter, which has certain very peculiar properties. It does not act upon proteid food-stuffs, nor upon fats, but if mixed with starch and kept at a moderately warm


PBELTMTNABIES OF DIGESTION. 143 temperature, it turns that starch into grape-sugar. The im- portance of this operation becomes apparent when one reflects that starch is insoluble and useless as nutriment, while sugar is highly soluble and readily oxidable. 189. The Teeth.— Each of the thirty-two teeth which have been mentioned consists of a crown which projects above the gum, and of one or more fangs, which are imbedded in sockets, or what are called alveoli, in the jaws. The eight teeth on opposite sides of the same jaw are con- structed upon exactly similar patterns, while the eight teeth which are opposite to one another, and bite against one another above and below, though similar in kind, differ somewhat in the details of their patterns. The two teeth in each eight which are nearest the middle line in the front of the jaw, have wide but sharp and chisel-like edges. Hence they are called incisors, or cutting teeth. The tooth which comes next is a tooth with a more conical and pointed crown. It answers to the great tearing and holding tooth of the dog, and is called the canine or eye tooth. The next two teeth have broader crowns, with two cusps or points on each crown, one on the inside and one on the outside, whence they are termed bicuspid teeth, and sometimes false grinders. All these teeth have usually one fang each, except the bicuspid, the fang of which may be more or less completely divided into two. The remaining teeth have two or three fangs each, and their crowns are much broader. As they crush and grind the matters which pass between them, they are called molars, or true grinders. In the upper jaw theb crowns present four points at the four comers and a diagonal ridge connecting two of them. In the lower jaw the complete pattern is five-pointed, there being two cusps on the inner side and three on the outer. 190. Working of the Jaw. — The muscles of the parts which have been described are so arranged that the lower jaw can be depressed to open the mouth and separate the teeth, or


144 ELEMENTARY PHYSIOLOGY. raised in such a manner as to bring the teeth together, or moved obliquely from side to side, so as to cause the face of the grinding teeth and the edges of the cutting teeth to slide over one another. And the muscles which perform the ele- vating and sliding movements are of great strength, and con- fer a corresponding force upon their grinding and cutting movements. In correspondence with the pressure they have to resist, the superficial substance of the crown of the teeth is of great hardness, being formed of enamel, the hardest sub- stance in the body, so dense and hard, indeed, that it will strike fire with steel. But notwithstanding its extreme hard- ness, it becomes worn down in old persons, and at an earlier afje in savaffcs who live on coarse food. 191. Masticating and Swallowing. — ^When solid food is taken into the mouth it is cut and ground by the teeth, the fragments which ooze out upon the outer side of their crowns being pushed beneath them again by the muscular contrac- tions of the cheeks and lips, while those which escape on the inner side are thrust back by the tongue, until the whole is thoroughly rubbed down. While mastication is proceeding, the salivary glands pour out their secretion in great abundance, and the saliva mixes with the food, which then becomes interpenetrated not only with the salivary fluid, but with the air which is entangled in the bubbles of the saliva. When the food is suflSciently ground it is collected, en- veloped in saliva, into a mass or bolus, which rests upon the back of the tongue, and is carried backward to the aperture which leads into the pharynx. Through this it is thrust, the soft palate being lifted and its pillars being brought together, while the backward movement of the tongue at once propels the bolus and causes the epiglottis to incline backward and downward over the glottis, and so to form a bridge by which the bolus can travel over the opening of the air-passage with- out any risk of tumbling into it. While the epiglottis directs the course of the bolus below and prevents it from passing


PEELEMINAEIES OF DIGESTION. 145 into the trachea, the soft palate guides it ahove, keeps it out of the nasal chamber, and directs it downward and backward toward the lower part of the muscular pharyngeal funnel By this it is immediately seized and tightly held, and the muscular fibres contracting above it, while they are compara- tively lax below, it is rapidly thrust into the cesophagus, grasped by it, and propelled along it, in the same way, until it reaches the stomach. 192. Drinking. — Drink is taken in exactly the same way. It does not fall down the pharynx and gullet, but each gulp is grasped by it and passed down. Hence it is that jugglera are able to drink standing upon their heads, and that a horse, or ox, drinks with its throat lower than its stomach, feats which would be impossible if fluid simply fell down the gullet into the gastric cavit}^ During these processes of mastication, insalivation, and deg- lutition, what happens to the food is, first, that it is reduced to a coarser or finer pulp; secondly, that any matters it carries in solution arc still more diluted by the water of the saliva; thirdly, that any starch it may contain begins to be changed into sugar by the peculiar constituent (ptyalin) of the saliva. Section III. — Stomach-Digestion. 193. The Stomach and the Gastric Jnice. — The stomach, like the gullet, consists of a tube with muscular walls com- posed of smooth muscular fibres, and lined by an epithelium ; but it differs from the gullet in several circumstances. In the first place, its cavity is greatly larger, and its left end is pro- duced into an enlargement which, because it is on the heart side of the body, is called the cardiac dilatation (Fig. 55, b). The opening of the gullet into the stomach, termed the cardiac aperture, is consequently nearly in the middle of the whole length of the organ, which presents a long, convex, greater curvature, along its front or under edge, and a short concave, 7


146 ELEMENTARY PHYSIOLOGY. lesser curvature, on its back or upper contour. Toward its right extremity the stomach narrows, and, where it passes into the intestine, the muscular fibres are so disposed as to form a sort of sphincter around the aperture of communication— the pylorus (Fig. 56^ d). Fio. 55. The stomach laid open behind— flr, the cesophairns ; ft, the cardiac dilatation ; r, the lesser curvatiuo; rf, the pylorus; 6, the biliary duct;/, the pall-bladder; c^, the pancreatic duct, opening in common with the cystic duct opposite A ; A, i, the duodenum. The mucous membrane lining the wall of the stomach is very delicate, and multitudes of small simple glands open upon its surface. Among these are others (Fig. 56) which possess a somewhat more complicated structure, their blind ends being subdivided. It is these peptic (/lands which, when food passes into the stomach, throw out a thin acid fluid, the gastric juice. The acidity arises from the presence of lactic or hydrochloric acids, but in addition to these constituents the gastric juice possesses another called pepsin, which appears to be a protein compound not altogether dissimilar to ptyalin. Tims, when the food passes into the stomach, the contrac- tions of that organ roll it about and mix it thoroughly with the gastric juice.


STOMACH-DIGESTION^ 147 194. Artificial Digestion. — ^It is easy to ascertain ex- perimentally the properties of the gastric juice by putting a small portion of that part of the mucous membrane which Fio. 56. One of the glands which secrete the gastric juice, highly magnified. contains the peptic glands into water containing small pieces of meat, hard-boiled egg, or other proteids, and keeping the mixture at a temperature of about 100®. After a few hours it will be found that the white of egg has become dis- solved, if not in too great quantity, while all that remains of the meat is a pulp consisting chiefly of the connective tissue and fatty matters which it contained. This is artificial diges- tion, and it has been proved by experiment that precisely the same operation takes place when food undergoes natural di- gestion within the stomach of the living animal.

The proteid solution thus effected is called a peptone, and has pretty much the same characters, whatever the nature of the proteid which has been digested. The dilute acid alone is competent slowly to dissolve the proteid, but the pepsin in the gastric juice is the chief source of its solvent power. 196. Absorption from the Stomach.— By continual roll- ing about, with constant additions of gastric juice, the food becomes reduced to the consistence of pea-soup, and is called chyme. In this state it is, in part, allowed to escape through the pylorus and to enter the duodenum, but a great deal of the fluid (consisting of peptone mixed with saliva and any saccha- rine fluids resulting from the partial conversion of starch or otherwise) is at once absorbed, making its way, by imbibition, through the walls of tbe delicate and numerous vessels of the stomach into the current of fhe blood, which is rushing by the gastric veins to the vena portce. Section IV. — Intestinal Digestion. 196. The Large and Small Intestines.— The intestines form one long tube, with mucous and muscular coats, like the stomach ; and like it they are envelpped in peritoneum. They are divided into two portions — ^the small intestines and* the large intestineSy the latter having a much greater diameter than the former. The small intestines again are subdivided into the duodenum^ the jejunum, and the ileuMy but there is no natural line of demarcation between these. The duodenum, however, is distinguishable as that part of the small intestine which im- mediately succeeds the stomach, and is beat upo» itself and fastened by the peritoneum against the back wall of the abdo- men in the loop shown in Fig. 65. It is in this loop that the head of the pancreas lies (Fig. 60). The ileum (a, Fig. 67) is no wider than the jejunum or duodenum, so that the transition from the small intestine to the large (e) is quite sudden. The opening of the small in- testine into the large is provided with prominent lips which


INTESTINAL DIGESTION. 149 project into the cavity of the foiiner and oppose the passage of matters from it into the small intestine, while they readily allow of a passage the other way. This is the ileo-ccecal valve. The large intestine forms a blind dilatation beyond the ileo-csecal valve, which is called the ccecum ; and from this an elongated blind process is given off, which, from its shape, is called the vermiform appendix of the caecum (Fig. 67, b). The caecum lies in the lower part of the right side of the abdominal cavity. The colon, or first part of the large intes- tine, passes upward from it as the ascending colon ; then making a sudden turn at a right angle, it bends across to the left side of the body, being here called transverse colon, an4 next, sud- Fio. 57. The termination of the ilonm, a, in the cjecum, nnd the continnatlon of the latter into the colon, o; dy the ileo-colic valve; c, the aperture of the appendix vermi- formU (b) into the ccecum. denly bending backward along the left side of the abdomen, becomes the descending colon. This reaches the middle line and becomes the rectum, which is that part of the large intes- tine which opens externally. 197. Their Parts and Actions.— The mucous membrane of the whole intestine is provided with numerous small, and for the most part simple, glands (named after Lieberkiihn and Brunner), which pour into it a secretion, the intestinal juice, the precise functions of which are unknown.


150 ELEMENTARY PHYSIOLOGY. Structures peculiar to the small intestine are the valvules conniventeSy transverse folds of the mucous membrane, which increase the surface; and the villij which are minute thread- like processes of the mucous membrane on the valvulce conni- ventes and elsewhere, set side by side, like the pile of velvet. Fio. sa Two villi of the small intestines— «, substance of the vlllns; ft, its epithelium, of which some cells are seen detached at b^ ; o d^ the artery and vein, with their connecting capillary net-work, whit:h envelops and hides, «, the lacteal radicle which occupies the centre of the villus and opens into a net-work of lacteal ves- sels at its base. Each villus is coated by epithelium and contains in its interior the radicle, or commencement, of a lacteal vessel, between which and the surface of the villus lies a capillary net-work with its afferent artery and efferent vein. Peculiarities of the large intestine are the arrangement of the longitudinal muscular fibres of the colon into three bands, which are shorter than the walls of the intestine itself, so that the latter is thrown into puckers and pouches ; and the disposi- tion of muscular fibres around the termination of the rectum into a ring-like sphincter muscle, which keeps the aperture firmly closed, except when defecation takes place. The intestines receive their blood almost directly from the aorta. Their veins carry the blood which has traversed them to the vena portce.


INTESTINAL DIGESTION. 151 198. Peristaltic Contraction. — The fibres of tlie muscular coat of the intestine, which lies between its mucous membrane and its serous, or peritoneal, investment, are disposed longitu- dinally and circularly, and the circular fibres of any part con- tract, successively, in such a manner that the lower fibres, or those on the side of the anus, contract after the upper ones, or those on the side of the pylorus. It follows from this so-called peristaltic contraction^ that the contents of the intestines are constantly being propelled, by successive waves of contraction, from their upper toward their lower parts. 199. Entrance of Bile and Pancreatic Juice.— The only secretions besides those of the proper intestinal glands which enter the intestine, are those of the liver and the pancreas — the bile and the pancreatic juice. The ducts of these organs have a common opening in the middle of the bend of the duo- denum ; and, since they pass obliquely through the coats of the intestine, their aperture serves as a kind of valve, obstructing the flow of fluid from the duodenum, but permitting its passage to the duodenum (Figs. 50 and 55). As the chyme fills the duodenum, the pancreas comes into activity, and its secretion, with the bile fi-om the gall-bladder, flows through the common aperture, and, mixing with the chyme, converts it into what is called ckyle. 200. Chyle— Absorption from the Intestines. — Chyle difiers from chyme in two respects. In the first place, the alkali of the bile neutralizes the acid of the ch3rme; in the- second place, both the bile and the pancreatic juice appear to exercise an influence over the fatty matters contained in the chyme, which facilitates the subdivision of these fats into very minute separate particles. The chyme, in fact, which results from the digestion of fatty food, is mere mixture of watery fluid with oily matters which are ready to separate from it and unite with one another. In the chyle, on the other hand, the fatty matters are suspended in the fluid, just as oil may be evenly difiused through water by gradually rubbing it up with white of egg into what is termed an emulsion, or as the fat ( = butter)


152 ELEMENTARY PHYSIOLOGY. of milk is naturally held suspended in the watery basis of milk. The chyle, with these suspended particles, looks white and milky, for the same reason that milk has the same aspect — the multitude of minute suspended fatty particles reflecting a great amount of light The conversion of starch into sugar, which seems to be sus- pended wholly, or partially, so long as the food remains in the stomach, on account of the acidity of the chyme, is resumed as soon as the latter is neutralized, the pancreatic and intestinal juices operating powerfully in this direction. As the chyle is thrust along the small intestines by the grasping action of the peristaltic contractions, the dissolved matter which it contains is absorbed, in the ordinary way, by the vessels of the villi. The minute particles of fatty matter, on the other hand, are squeezed through the soft substance of the epithelium into that of the villi ; and so, in the long run, into the vessels; just as mercury may be squeezed by pressure through the pores of a wash-leather bag. As the net-work of capillaries lies outside the lacteal radicle in each villus, it would appear that the blood-vessols must carry off the greater part of the chyle ; but much of i\ enters the lac- teals, fills them, and only enters the blood after a roundabout passage through the mesenteric lymphatics and the thoracic duct 201. Digestion in the Lai^e Intestines. — The digested matters, as they are driven along the small intestines, gradually become deprived of their peptones, fats, and soluble amyloids, and are forced through the ileo-csecal valve into the caecum and large intestine. Here they acquire an acid reaction and the ' characteristic fecal odor and color, which become more and more marked as they approach the rectum. It has been sup- posed that a sort of second digestion occurs in the upper part of the large intestine.


INSTEUME]!n:8 OF MOTION. 153 CHAPTER Vm. MOTION AND LOCOMOTION. Section I, — Instruments of Motion. 202. The Vital Eddy. — In the preceding pages we have studied the manner in which the incomings of the human body are converted into its outgoings. We have seen that matter, in the form of vital and mineral foods, is constaptly appro- priated by the body, to make up for the loss of matter, in the shape, chiefly, of carbonic acid, urea, and water, which is as constantly going on. The vital foods are derived directly, or indirectly, from the vegetable world ; and the products of waste either are such compounds as abound in the mineral world, or immediately decompose into them. Consequently, the human body is the centre of a stream of matter which sets incessantly from the vegetable and mineral worlds into the mineral world again. It may be compared to an eddy in a river, which may retain its shape for an indefinite length of time, though no one particle of the water of the stream re- mains in it for more than a brief period. But there is this peculiarity about the human eddy, that a large portion of the particles of matter which flow into it have a much more complex composition than the particles which flow out of it. To speak in what is not altogether a metaphor, a large part of the atoms which enter the body are piled up in large heaps, and tumble down into small heaps before they leave it. The force which they set free in thus tumbUng down, is the source of the active powers of the organism. 203. Organs of Motioii. — These active powers are chiefly manifested in the form of motion — movement, that is, either of part of the body, or of the body as a whole, which last is termed locomotion:

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154 ELEMENTARY PHYSIOLOGY. The organs which produce motion in the human body arc of two kinds : Cilia and Muscles, 204. Action of the Cilia. — Cilia are filajnents of extremely small size, attached by their bases to, and indeed growing out from, the free surfaces of epithelial cells. They are in inces- sant waving motion, so long as life persists in them ; and the motion of a cilium continues even for some time after the epithelial cell, with which it is connected, is detached from the body. Not only does the movement of the cilia thus go on independently of the rest of the body, but it cannot be con- trolled by the action of the nervous system. The cause of the movement of each cilium would appear to be the alternate con- traction and relaxation of opposite sides of its base ; but why these alternations take place is unknown. Although no other part of the body has any control over the cilia, and though, so far as we know, they have no direct communication with one another, yet their action is directed toward a common end — the cilia, which cover extensive sur- faces, all working in such a manner as to sweep whatever lies upon that surface in one and the same direction. Thus, the cilia which are developed upon the epithelial cells which line the greater part of the nasal cavities and the trachea with its ramifications, tend to drive the mucus in which they work, outward. In addition to the air-passages, cilia are found, in the hu- man body, in the ventricles of the brain, and in one or two other localities ; but the part which they play in man is insig- nificant in comparison with their function in the lower animals, among many of which they become the chief organs of loco- motion. 205. Muscular Contraction. — ^Muscles are accumulations of fibres, each of which has the power, under certain condi- tions, of shortening in length, while it increases its other di- mensions, so that the absolute volume of the fibre remains unchanged. This power is called muscular contractility ; and whenever a muscular fibre contracts, in virtue of this power, it


INSTRUMENTS OF MOTION. 155

tends to bring its two ends, with whatever may be fastened to them, together. Muscles may be conveniently divided into two groups, ac- cording to the manner in which the ends of their fibres are fastened ; into muscles not attached to sohd levers, and muscles atJiached to solid levers. 206. Hollow Muscles not attached to Solid Levers. — The muscles which come under this head are what are, sometimes, appropriately called hollow muscles, inasmuch as they enclose a cavity, or surround a space ; and their contraction produces a diminution in the capacity of that cavity, or the extent of that space. The muscular fibres of the heart, of the blood-vessels, of the lymphatic vessels, of the alimentary canal, of the ducts of the glands, of the iris of the eye, are so arranged as to form hollow muscles. In the heart the muscular fibres are of the striated kind (see Chapter XIIL), and their disposition is exceedingly com- plex. The cavities which they enclose are those of the auri- cles and ventricles ; and, as we have seen, the fibres, when they contract, do so suddenly and together. The iris of the eye is like a curtain, in the middle of which is a circular hole. The muscular fibres are not striated (see Chapter XITT.), and they are disposed in two ways : some radi- ating from the edges of the hole to the circumference of the curtain ; some arranged in circles, concentrically with the aperture. The muscular fibres contract suddenly and together, the radiating fibres necessarily enlarging the hole, the circular fibres diminishing it. In the alimentary canal the muscular fibres are also of the un striated kind, and they are disposed in two layers ; one set of fibres arranged parallel with the length of the intestines, the others being disposed circularly, or at right angles to the fonner. The contraction of these muscular fibres is successive; that is to say, all the muscular fibres, in a given length of the in-

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156 ELEMENTARY PHYSIOLOGY. testines, do not contract at once, but those at one end contract first, and the others follow them until the whole series have contracted. As the order of contraction is, naturally, always the same, from the upper toward the lower end, the effect of this peristaltic contraction is, as we have seen, to force any matter contained in the alimentary canal, from its upper tow- ard its lower extremity. The muscles of the walls of the ducts of Ihe glands^ have a substantially similar arrangement. Section II. — Mechanism of Bodily Movement, 207. Muscles attached to Definite Levers. — The great majority of the muscles of the body are attached to distinct levers, formed by the bones ; and to understand their action, we must have a knowledge of the different kinds of levers, and be able to refer the various combinations of the bones to their appropriate lever-classes. A lever is a rigid bar, one part of which is absolutely or relatively fixed, while the rest is free to move. Some one point Fia. 69. Pi&. 60. Fig. 61 The upper three flffures represent the three kinds of levers ; the lower, the foot, when It takes the character of each kind— W. Weight or resistance ; F. ftilcmm ; P. power. of the movable part of the lever is set in motion by a source of power, in order to communicate more or less of that motion to another point of the movable part, which presents a resist- ance to motion in the shape of a weight or other obstacle. 208. Three Orders of Leyers. — Three kinds of levers are enumerated by mechanicians^ the definition of each kind de-


MECHANISM OF BODILY MOVEMENT. 157 pending npon the relative positions of the point of support, or fulcrum; of the point which bears the resistance, weight, or other obstacle to be overcome by the power ; and of the point to which the source of power employed to overcome the ob- stacle is applied. If the fulcrum be placed between the power and the weight, so that when the power sets the lever in motion, the weight and the power describe arcs, the concavities of which are turned toward one another, the lever is said to be of the first order (Fig. 69). If the fulcrum be at one end, and the weight be between it and the power, so that weight and power describe concentric arcs, the weight moving through the less space when the lever moves, the lever is said to be of the second order (Fig. 60). And if, the fulcrum being still at one end, the power be between the weight and it, so that, as in the former case, the power and weight describe concentric arcs, but the power moves through the less space, the lever is of the third order (Fig. 61). 209. Levers of the First Order. — ^In the human body, the following parts present examples of levers of the first order. (a) The skull in its movements upon the atlas, aa fulcrum. (b) The pelvis in its monements upon the heads of the thigh-bones, as fulcrum. (c) The fooj, when it is raised, and the toe tapped on the ground, the ankle joint heing fulcrum (Fig. 69). I have not given the position of the weight and power in either of these cases, because they are reversed according to circumstances. Thus, when the face is being depressed, the power is applied in front, and the weight to the back part, of the skull ; but when the face is being raised, the power is be- hind and the weight in front. The like is true of the pelvis, according as the body is bent forward, or backward, upon the legs. Finally, when the toes, in the action of tapping, strike the ground, the power is at the heel, and the resistance in the front of the foot Butj when the toes are raised to repeat the


158 ELEMENTABY PHYSIOLOGY. act, the power is in front, and the weight, or resistance, is at the heel, being, in fact, the inertia and elasticity of the muscles and other parts of the back of the leg. But, in all these cases, the lever remains one of the first class, because the fulcrum, or fixed point on which the lever turns, remains between the power and the weight, or resistance. 210. Levers of the Second Order. — The following are three examples of levers of the second order : (a) The thigh-bone of the leg which is bent up toward the body and not used, in the action of hopping. For, in this case, the fulcrum is at the hip-joint. The power (which I assume to be furnished by the rectus muscle of the front of the thigh) acts upon the knee-cap; and the posi- tion of the weight is represented by that of the centre of grav- ity of the thigh and leg, which will lie somewhere between the end of the knee and the hip. (jb) A rib when depressed by the rectus muscle of the ab- domen, in expiration. Here the fulcrum lies where the rib is articulated with the spine ; the power is at the sternum — virtually the opposite end of the rib ; and the resistance to be overcome lies between the two. (c) The raising of the body upon the toes, in standing on tiptoe, and in the first stage of making a step forward (Fig. 60). Here the fulcrum is the ground on which the toes rest ; the power is applied by the muscles of the calf to the heel ; the resistance is so much of the weight of the body as is borne by the ankle-joint of the foot, which of course lies between the heel and the toes. 211. Levers of the Third Order.— Three examples of levers of the third order are — (a) The spine, head, and pelvis, considered as a rigid bar, which has to be kept erect upon the hip-joints (Fig. 4). Here the fulcrum lies in the hip-joints ; the weight is at the centre of gravity of the head and trunk, high above the


MECHANISM OF BODILY MOVEMENT. 159 fulcrum ; the power is supplied by the extensor, or flexor, muscles of the thigh, and acts upon points comparatively close to the fulcrum. (b) Flexion of the forearm upon the arm by the biceps muscle, when a weight is held in the hand. In this case, the weight being in the hand and the fulcrum at the elbow-joint, the power is applied at the point of attach- ment of the tendon of the biceps, close to the latter. (c) Extension of the leg on the thigh at the knee-joint. Here the fulcrum is the knee-joint ; the weight is at the centre of gravity of the leg and foot; the power is applied by the ligament of the knee-cap, or patella, to the tibia, close to the knee-joint. 212. One Fart may represent the Three Kinds. — In studying the mechanism of the body, it is very important to recollect that one and the same part of the body may represent each of the three kinds of levers, according to circumstances. Tlius it has been seen that the foot may, under some circum- stances, represent a lever of the first, in others of the second order. But it may become a lever of the third order, as when one dances a weight resting upon the toes, up and down, by moving only the foot. In this case, the fulcrum is at the ankle-joint, the weight is at the toes, and the power is fur- nished by the extensor muscles at the front of the leg, which are inserted between the fulcrum and the weight (Fig. 61). 213. Different Kinds of Joints. — It is very important that the levers of the body should not slip, or work unevenly, when their movements are extensive, and to this end they are con- nected together in such a manner as to form strong and defi- nitely arranged joints or articulations. (a) Imperfect joints are those in which the conjoined levers (bones or cartilages) present no smooth surfaces, capable of rotatory motion, to one another, but are connected by contin- uous cartilages, or ligaments, and have only so much mobility as is permitted by the flexibility of the joining substance. Examples of such joints as these are to be met with in the


160 ELEMENTARY PHYSIOLOGY. vertebral column — the flat surfaces of the several joints, or ver- tebra3, being connected together by thick plates of very elastic fibro-cartilage, which confer upon the whole column consid- erable play and springiness, and yet prevent any great amount of motion between the several vertebrae. The pubic bones are united together, and the haunch-bones with the sacrum, by fibrous or cartilaginous tissue, which allows of only a slight play, or may merely confer a little more elasticity than if the joint were formed by the direct apposition of bones. 214. Structure and Working of Joints. — In all perfect joints, the opposed surfaces of the bones which move upon one another are covered with cartilage, and are contained in a Fio. 62. A section of the Wp-jo!nt taken through the acetabulum and the middle of the head and neck of the thigh-bone.— X. T, Ligamentum teres, or round ligament, sort of sac, which lines these cartilages and the side walls of the joint ; and which, secreting a viscid lubricating fluid — ^the synovia — is called a synovial membrane.


MECHiLNISM OF BODILY MOVEMENT. 161 The opposed surfaces of the articular cartilages are sphe- roidal, cylindrical, or pulley-shaped ; and the convexities of the one answer, more or less completely, to the concavities of the other. Sometimes, the two articular cartilages do not come di- rectly into contact, but are separated by independent plates of cartilage, which are termed inter-articular. The opposite faces of these inter-articular cartilages are fitted to receive the faces of the proper articular cartilages. While these coadapted surfaces and synovial membranes provide for the free mobility of the bones entering into a joint, the nature and extent of their motion is defined, partly, by the forms of the articular surfaces, and, partly, by the disposition of the ligaments or firm fibrous cords which pass from one bone to the other. 215. Ball-and-Socket Joints. — ^As respects the nature of the articular surfaces, joints may be what are called ball-and- socket joints, when the spheroidal surface furnished by one bon^ plays in a cup fiimished by another. In this case the motion of the former bone may take place in any direction, but the extent of the motion depends upon the shape of the cup — being very great when the cup is shallow, and small in propor- tion as it is deep. The shoulder is an example of a ball and socket joint with a shallow cup ; the hip of such a joint with a deep cup (Fig. 62). 216. Hinge-Joints are single or double. In the former case, the nearly cylindrical head of one bone fits into a corre- sponding socket of the other. In this form of hinge-joint the only motion possible is in the direction of a plane perpendicu- lar to the long axis of the cylinder, just as a door can only be made to move round an axis passing through its hinges. The elbow is the best example of this joint in the human body (Fig. 63). The knee and ankle present less perfect specimens of it. A double hinge-joint is one in which the articular surfaces of each bone are concave in one direction, and convex in another, at right angles to the former. A man seated in a


162 ELEMENTAET PHYSIOLOGY. saddle is " articulated " with the saddle by such a joint. For the saddle is concave from before backward and convex from side to side, while the man presents to it the concavity of his Fig. ea Lonritndlnal and vertical section throngrb the elbow-joint—/?: Ilumenis; Ul nlna; Tr. the triceps muscle which extends the arm : £L the hiceps iou3cle which flexes it. * ^ legs astride, from side to side, and the convexity of his seat, from before backward. The metacarpal bone of the thumb is articulated with the bone of the wrist, called trapezium^ by a double hinge-joint. 217. A Pivot- Joint is one in which a given bone furnishes an axis, or pivot, on which another turns ; or itself turns on its own axis, resting on another bone. A remarkable example of the former arrangement is afforded by the atlas and axis, or two uppermost vertebrae of the neck (Figs. 64, 65). The axis possesses a vertical peg, the so-called odontoid process (6), and at the base of the peg are two, obliquely-placed, articular


MECHANISM OF BODILY MOVEMENT. 1(53 surfaces (a). The atlas is a ring-like bone, with a massive thickening on each side. The inner side of the front of the ring plays round the neck of the odontoid peg, and the under surfaces of the lateral masses glide over the articular faces on each side of its base. A strong ligament passes between the inner sides of the two lateral masses of the atlas, and keeps the hinder side of the neck of the odontoid peg in its place (Fig. 64). By this arrangement, the atlas is enabled to rotate through a considerable angle cither way upon the axis, without any danger of falling forward or backward — accidents which would immediately destroy life by crushing the spinal marrow. The lateral masses of the atlas have, on their upper faces, concavities (Fig. 64, a) into which the two, convex, occipital Fig. 64. Fio. 65. Fig. C4. — The ntlas viewed from above ; a at, npnor articular surface of its lateral mass for the con(h los of the Pk"ll: ?>, the i)ec: of the axis vertebra. Fig. 65. —Side view of the axis vertebra; o, articular surface for the lateral mass of the atlas ; &, peg or odontoid process. condyles of the skull fit, and in which they play upward and downward. Thus the nodding of the head is effected by the movement of the skull upon the atlas, while, in turning the head from side to side, the skull does not move upon the atlas, but the atlas slides round the odontoid peg of the axis ver- tebra. The second kind of pivot-joint is seen in the forearm. If the elbow and forearm, as far as the wrist, are rested upon a table, and the elbow is kept firmly fixed, the hand can never- theless be freely rotated so that either the palm, or the back, is turned directly upward. AVTien the palm is turned upward,

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164: ELEMENTARY PHYSIOLOGY. the attitude is called supination (Fig. 66) ; when the back, pronation (Fig. 67). 218. The Eadius and Ulna. — The forearm is composed of two bones ; one, the ulna, which articulates with the humerus at the elbow by the hinge-joint already described, in such a manner that it can move only in flexion and extension, and has no power of rotation. Hence, when the elbow and wrist are rested on a table, this bone remains unmoved. But the other bone of the forearm, the radius, has its small upper end, shaped like a very shallow cup with thick edges. Fio. 67. Fi6. 66. Fig. 66.— The bones of the rigrht forearm In supination, Fig. 67— in pronation.— ZT. humerus; Ji. radius; U. ulna. The hollow of the cup articulates with a spheroidal surface fur- nished by the humerus ; the lip of the cup, with a concave de- pression on the side of the ulna. The large lower end of the radius bears the hand, and has,


MECHANISM OF BODILY MOVEMENT. 165 toward the ulna, a concave surface which articulates with the convex side of the small lower end of that bone. Thus the upper end of the radius turns as a pivot on the double surface, furnished to it by the ball of the humerus, and the partial cup of the ulna ; while the lower end of the radius can rotate round the pivot furnished to it by the lower end of the ulna. In supination^ the radius lies parallel with the ulna, with its lower end to the outer side of the ulna (Fig. 66). In pronation, it is made to turn on its own axis above, and round the ulna below, until its lower moiety crosses the ulna, and its lower end lies on the inner side of the ulna (Fig. 67). 219. The Ligaments which keep the mobile surfaces of bones together are, in the case of ball-and-socket joints, strong fibrous capsules which surround the joint on all sides. In hinge joints, on the other hand, the ligamentous tissue is chiefly ac- cumulated on those aspects of the joint on which motion does not take place, as lateral ligaments. In some cases ligaments are placed within the joints, as in the knee, where the bundles of fibres which cross obliquely between the femur and the tibia are called crucial ligaments ; or, as in the hip, where the round ligament passes from the bottom of the acetabulum to the ball furnished by the head of the femur (Fig. 62). Again, two ligaments pass from the apex of the odontoid peg to either side of the -margins of the occipital foramen ; these, from their function in helping to stop excessive rotation of the skull, are called check ligaments (Fig. 68, a). In one joint of the body, the hip, the socket or acetabulum (Fig. 62) fits so closely to the head of the femur, and the cap- sular ligament so completely closes its cavity on all sides, that the pressure of air must be reckoned among the causes which prevent dislocation. This has been proved experimentally by boring a hole through the floor of the acetabulum, so as to ad- mit air into its cavity, when the thigh-bone at once falls as far as the round and capsular ligaments will permit it to do, show- ing that it was previously pushed close up by the pressure of the external air. H

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166 ELEMENTARY PHYSIOLOGY. 220. Various Kinds of Movements of Joints. — The differ- ent kinds of movement of which the levers thus connected are capable are called flexion and extension ; abduction and adduc- tion ; rotation and circumduction. The vertebral colnmn in the upper part of the neck laid open, to show— a, the check _ lisament of the axis; &, the broad li^ment which extends from the front margin of the occipital foramen along the hinder faces of the bodies of the vert-ebni;; it Is cut through, and the cut ends turned bacic to show, c, the special ligament which connects the point of the ** odontoid" peg with the front margin ctf the occipital foramen; /. the Atlas; //. the axis. A limb is flexed^ when it is bent; extended, when it is straightened out. It is abducted, when it is drawn away from the middle line; adducted, when it is brought to it It is rotated, when it is made to turn on its own axis ; circumducted, when it is made to describe a conical surface by rotation round an imaginary axis. No part of the body is capable of perfect rotation like a wheel, for the simple reason that such motion would neces- sarily tear all the vessels, nerves, muscles, etc., which unite it with other parts. 221. Means of affecting them. — Given two bones united by a joint, and they may be moved one upon another in, at fewest two, different directions.- In the case of a pure hinge- joint their directions must be opposite and in the same plane ;


MECHANISM OF BODILY MOVEMENT. 167 but, in all other joints, they may be in several directions and various planes. In the case of a pure hinge-joint the two practicable move- ments will be effected by attaching muscles to the bones on opposite sides of the joint (e. e., on the side toward which one of the bones moves when the joint is bent, and on the side from which it moves). When either of these muscles con- tracts, it will pull its attached ends together and bend the joint toward the side on which it is placed. In the other extreme form of articulation — the ball-and- socket joint — movement in any number of planes may be ef- fected, by attaching muscles in corresponding number and direction, on the one hand, to the bone which affords the socket, and on the other to that which furnishes the head. Circumduction will be effected by the combined and successive contraction of such muscles. 222. Tendons and their Eimctions. — ^It usually happens that the part to which one end of a muscle is attached is ab- solutely or relatively fixed, while that to which the other is fixed is movable. In this ciase the attachment to the fixed bone is termed the origin^ that to the movable bone the inser- tion of the muscle. The fibres of muscles are sometimes fixed directly into the parts which serve as their origins and insertions ; but, more commonly, strong cords or bands of fibrous tissue, called ten- dons, are interposed between the muscle proper and its place of origin or insertion. When the tendons play over hard sur- faces it is usual for them to be separated from these surfaces by sacs containing fluid, which are called hursce; or even to be invested by synovial sheaths. Usually, the direction of the axis of a muscle is that of a straight line joining its origin and its insertion. But in some muscles, as the superior oblique muscle of the eye, the tendon passes over a pulley formed by a ligament, and completely alters its direction before reaching its insertion (Figs. 86 and 87).


168 ELEMENTARY PHYSIOLOGY. Again, there are muscles which are fleshy at each end, and have a tendon in the middle. Such muscles are called digastric^ or two-bellied. In the curious muscle which de- presses the lower jaw, and specially receives this name of rfe- gastric^X\iQ middle tendon runs through a pulley connected with the hyoid bone ; and the muscle, which passes downward and forward from the skull to this pulley, after traversing it, runs upward and forward, to the lower jaw (Fig. 69). Fio. 69. The course of the digastric muscle.— A its posterior belly ; D\ Its anterior bellvr ; between the two is the tendon passing through its pulley connected with Uy. the hyoid bone. Section III. — Movements of Locomotion, 223. Walking. — We may now pass from the consideration of the mechanism of mere motion to that of locomotion. When a man who is standing erect on both feet proceeds to walky beginning with the right leg, the body is inclined so as to throw the centre of gravity forward ; and, the right foot being raised, the right leg is advanced for the length of a step, and the foot is put down again. In the mean while, the left heel is raised, but the toes of the left foot have not left the ground when the right foot has reached it, so that there is no moment when both feet are off the ground. For an instant, the legs form two sides of an equilateral triangle, and the cen- tre of the body is consequently lower than it was when the legs were parallel and close together.


MOVEMENTS OF LOCOMOTION. 169 The left foot, however, has not been merely dragged away from its first position, but the muscles of the calf, having come into play, act upon the foot as a lever of the second order, and thrust the body, the weight of which rests largely on the left astragalus, upward, forward, and to the right side. The mo- mentum thus communicated to the body causes it, with the wliole right leg, to describe an arc over the right astragalus, on which that leg rests below. The centre of the body conse- quently rises to its former height as the right leg becomes ver- tical, and descends again as the right leg, in its turn, inclines forward. When the left foot has left the ground the body is supported on the right logy and is well in advance of the left foot ; so that, without any further muscular exertion, the left foot swings for- ward like a pendulum,, and is carried, by its own momentum, beyond the right foot, to the position in which it completes the second step. 224. Economy of Force in Walking. — When the inter- vals of the steps arc so timed that each svv'inging leg comes for- ward into position for a new step, without any exertion on the part of the walker, walking is effected with the greatest possible economy of force. And as the swinging leg is a true pendu- lum, the time of vibration of which depends, other things being alike, upon its length (short pendulums vibrating more quickly than long ones), it follows that, on the average, the natural step of shoil-legged people is quicker than that of long-legged ones. 225. Running and Jumping. — In running there is a pe- riod when both legs are off the ground. The legs are ad- vanced by muscular contraction, and the lever action of each foot is swift and violent. Indeed, the action of each leg resem- bles, in violent running, that which, when both legs act to- gether, constitutes a jump^ the sudden extension of the legs adding to the impetus, which, in slow walking, is given only by the feet, 8

^J 170 ELEMENTAEY PHYSIOLOGY. Section IV. — Vocal Movements. 226. Conditions of the Production of Voice.— Perhaps the most singular motor apparatus in the body is the larynx^ by the agency of which voice is produced. fmA Fio. 70. Diagram of the larynx, the thyroid cartilage beinsr supposed to be transparent, and allowing the right arytenoid cartilage {Ar.\ vocal ligament ( F.),and thyro-aryte- noid muscle {Th.A.\ the upper part of the cricoid cartilage ((>.), and the atuich- ment of the epiglottis (Ep.\ to be seen ; CM. the right crieo-thyroid muscle ; TV. the trachea \ Ily, the hyoid bone. The essential conditions of the production of the human voice are : a. The existence of the so-called vocal chords. h. The parallelism of the edges of these chords, without which they will not vibrate in such a manner as to' give out sound. c, A certain degree of tightness of the vocal chords, without which they will not vibrate quickly enough to produce sound. d. The passage of a current of air between the parallel edges of the vocal chords sufficiently powerful to set the chords vibrating. 227. The Vocal Chords. — ^The vocal chords are, properly speaking, not " chords " at all, but elastic cushions with broad


VOCAL MOVEMENTS. 171 bases, fixed to the larynx, and sharp free edges, which consti- tute the lateral boundaries of the glottis. In front, the ends of the edges of these vocal cushions are attached, close to- Fio. 71. A vertical and transverse section throuffli the larynx, the hinder half of which is re- m(»ved.— ^. Eplaclottis ; TK thyroid cartilage ; a, cavities called the Tenlricles of the lari/nx'above the vocal lijfaments (F); x the right thyro -arytenoid mus- clo cut across ; Cr, the cricoid cartilage. gether, to the reentering angle of the thyroid cartilage ; be- hind, to the arytenoid cartilages. These, when left to them- selves, diverge, so that, in the quiescent state, the aperture of the glottis is V-shaped, the point of the V. being forward and the base behind (Fig. 72). Under these circumstances a cur- rent of air passing through the glottis produces no sound; whence it is that ordinary expiration and inspiration take place quietly. 228. The Cartilages of the Larynx.— The thyroid car- tilage is a broad plate of gristle bent upon itself so as to have a V shape, and so disposed that the point of the V is turned for- ward, and constitutes what is commonly called " Adam's apple." Above, the thyroid cartilage is attached to the hyoid bone.


172 ELEMENTARY PHYSIOLOGY, Below and beLind, its broad sides are produced into little elongations or horns, which are connected by ligaments with the outside of a great ring of cartilage, the cricoid, which forms, as it were, the top of the windpipe. The cricoid ring is much higher behind than in front, and a gap, filled up only by mem- brane, is left between its upper edge and the lower edge of the. front part of the thyroid, when the latter is horizontal. Con- sequently, the thyroid cartilage can be moved up and down through the space left by this membrane, turning upon the articulation of its horns with the hinder part of the cricoid, as upon hinges. When it moves downward, the distance between the front part of the thyroid cartilage and the back of the cri- coid is necessarily increased ; and when it moves back again to the horizontal position, diminished. There is, on each side, a large muscle, the crico- thyroid, which passes froni the outer side of the cricoid cartilage obliquely upward and backward to the thyroid, and pulls the latter down (Fig. 'ZO). ^n/u Pig. 72. The parts surronnding the glottis partially dissected and viewed fyrom above.— 7%. The thyroid cartilage; Cr. the cricoid cartilage; F, the edges of the vocal liga- ments bounding the glottis ; Ary. the arytenoid cartilage ; Th.A. thyro-aryte- noid ; C.a.l. lateral crico-arytenoid ; Ca.p. posterior crico-arytenoid ; Ar. p. pos- terior arytenoid muscles. 229. The Muscles of the Larynx. — ^The two arytenoid cartilages are perched side by side upon the upper edge of the


VOCAL MOVEMENTS. 173 back part of the cricoid, and are freely articulated therewith. Muscles are so disposed as to pull them toward, or away from, one another ; and a pair of strong muscles which proceed from their bases to the reentering angle of the thyroid alongside the vocal chords, and are called thyro-arytenoid^ tend to pull the thyroid cartilage up when it has been depressed by the crico- thyroid muscles. When the muscles called posterior arytenoid, which, pass- ing between the two arytenoid cartilages, cause them to ap- proach one atiother, contract, they bring the hinder ends of the vocal chords together, and make their edges parallel. The expiratory muscles now force air from the chest through the larynx, and a musical note, the voice, is produced. Fig. 78. Diagrramofamodel illnstrating the action of the Icvors and muscles of the larynx. The stand and vertical pillar represent the cricoid and arytenoid cartilages, while the rod (6 c), moving on a pivot at c, takes the place ot the thyroid cartilage ; a b is an elastic band representing the vocal ligament Parallel with this runs a cord fastened at one end to b c, and at the other, passing over a pulley to the weight B. This represents the thyro-arytenoid muscle. A cord attached to the middle of & C and passing over a second pulley to the weight -4, represents the crico- thyroid muscle. It is obvious that when the bar (& c) is pulled down to the posi- tion c d^ the elastic band (a b) is put on the stretch. 230. Notes— Eange and Quality of Voice—Other things being alike, the musical note will be low or high, according as the vocal chords are relaxed or tightened ; and this again de- pends upon the relative predominance of the contraction of the crico-thyroid and thyro-arytenoid muscles : for when the thyro- arytenoid muscles are fully contracted, the thyroid cartilage


174 ELEMENTAEY PHYSIOLOGY. will be pulled up as far as it can go, and the vocal chords will be as lax as they can be ; while, when the cri co-thyroid mus- cles are fully contracted, the thyroid cartilage will be pulled down as far as it can go, and the vocal chords will be stretched as far as possible. The range of any voice depends upon the difference of ten- sion which can be given to the vocal chords, in these two posi- tions of the thyroid cartilage. Accuracy of singing depends upon the precision with which the singer can voluntarily adjust the contractions of the thyro-arylienoid and cricothyroid mus- cles — so as to give his vocal chords the exact tension at which their vibration will yield the notes required. The quality of a voice — treble, base, tenor, etc., on the other hand, depends upon the make of the particular larynx, the primitive length of its vocal chords, their elasticity, the amount of resonance of the surrounding parts, and so on. Thus, men have deeper notes than boys and women, be- cause their larynges are larger and their vocal chords longer — whence, though equally elastic, they vibrate less swiftly. 231. Speech— Vowel and Consonant Sounds.— 5/>eecA is toice modulated by the throat, tongue, and lips. Thus voic«  may exist without speech ; and it is commonly said that speech may exist without voice, as in whispering. This is only true, however, if the title of voice be restricted to the sound pro- duced by the vibration of the vocal chords ; for, in whispering, there is a sort of voice produced by the vibration of the mus- cular walls of the Hps, which thus replace the vocal chords. A whisper is, in fact, a very low whistle. The modulation of the voice into speech is effected by changing the form of the cavity of the mouth and nose, by the action of the muscles which move the walls of those parts. Thus, if the pure vowel sounds E (as in he\ A (as in hay\ ^' (as in ah\ (as in or\ 0' (as in oA), 00 (as in cool), are pronounced successively, it will be found that they may be all formed out of one note, produced by a continuous expira-


VOCAL MOVEMENTS. 175 tiori, tbe mouth being kept open, but the form of its aperture being changed for each vowel. It will be narrowest, with the lips most drawn back, in E, widest in A\ and roundest, with the lips most protruded, in 00. Certain consonants also may be pronounced without inter- rupting the current of the expired air, by modification of the form of the throat and mouth. Thus the aspirate, H, is the result of a little extra expira- tory force — a sort of incipient cough. S and Z, Sh and J (as in jugular =^G soft, as in gentry), Th, Z, iJ, F, F, may like- wise all be produced by continuous currents of air forced through the mouth, the shape of the cavity of which is pecu- liarly modified by the tongue and lips, 232. Elocking the Air-Current. — All the vocal sounds hitherto noted so far resemble one another, that their produc- tion does not involve the stoppage of the current of air which traverses either of the modulating passages. But the sounds of Jf amd iVcan only be formed by blocking the current of air which passes through the mouth, while free passage is left through the nose. For Jf, the mouth is shut by the lips ; for N, by the application of the tongue to the palate, 233. Explosive Consonants. — The other consonantal sounds of the English language are produced by shutting the passage through both nose and mouth ; and, as it were, for- cing the expiratory vocal current through the obstacle furnished by the latter, the character of which obstacle gives each con- sonant its peculiarity. Thus, in producing the consonants B and P the mouth is shut by the lips, which are then forced open in this explosive manner. In T and D the mouth pas- sage is suddenly barred by tbe applicatiou of the point of the tongue to the teeth, or to the front part of the palate ; while in ^ and G (hard, as in go) the middle and back of the tongue are similarly forced ao^ainst the back "part of the palate. 234. Speaking - Machines. — An artificial larynx may be made by the proper adjustment of elastic bands, which take the place of the vocal chords ; and when a current of air is forced

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176 ELEMENTARY PHYSIOLOGY. through these, due regulation of the tension of the bands will give rise to all the notes of the human voice. As each vowel and consonantal sound is produced by the modification of the form of the cavities, which lie over the natural larynx ; so, by placing over the artificial larynx chambers to which any requi- site shape can be given, the various letters may be sounded. It is by attending to these facts and principles that various speaking-machines have been constructed. 235. Tongneless Speech. — Although the tongue is credited with the responsibility of speech, as the "unruly member," and undoubtedly takes a very important share in its produc- tion, it is not absolutely indispensable. Hence, the apparently fabulous stories of people who have been enabled to speak after their tongues had been cut out by the cruelty of a tyrant or persecutor, may be quite true. Some years ago I had the opportunity of examining a per- son, whom I will call Mr. E., whose tongue had been removed as completely as a skilful surgeon could perform the operation. When the mouth was widely opened, the tnincated face of the stump of the tongue, apparently covered with new mucous membrane, was to be seen, occupying a position as far back as the level of the anterior pillars of the fauces. The dorsum of the tongue was visible with difficulty ; but I believe I could dis- cern some of the circumvallate papillae upon it. None of these were visible upon the amputated part of the tongue, which .had been preserved in spirit ; and which, so far as I could judge, was about 2^ inches long. When his mouth was open, Mr. E. could advance his tongue no farther than the position in which I saw it ; but he informed me that when his mouth was shut, the stump of the tongue could be brought much more forward. Mr. E.'s conversation was peifectly intelligible; and such words as thinJc, the, cow, kill, were well and clearly pro- nounced. But tin became fin ; tack, facJc or pack ; \o\\,pool ; dog, thog ; -dine, vine ; dew, thew ; cat, catf ; mad, madf ; goose, gooth : big, pig, hich, pick, with a guttural ch.


VOCAL MOVEMENTS. 177 In fact, only tlio pronunciation of those letters the foi-ma- tion of which requires the use of the tongue was affected ; and, of these, only the two which involve the employment of its tip, were absolutely beyond Mr. R.'s power. He converted all fs and (Ts into /'s, p^s, v'», or.th's, Th was fairly given in all cases ; s and sh, I and r, with more or less of a lisp. Initial g*s and Jo's were good ; but final g^s were all more or less gut- tural. In the former case, the imperfect stoppage of a current of air by the root of the tongue was of no moment, as the sound ran on into that of the following vowel; while, when the letter was terminal, the defect at once became obvious. CHAPTER IX. OF SENSATIONS AND SENSORY 0KGAN3. Section I, — Rejlex Action — Groups of Sensations, 236. EffereEt and Afferent Nerves. — The agent by which all the motor organs (except the cilia) described in the pre- ceding chapter are set at work is muscular fibre. But, in the living body, muscular fibre is made to contract only by a change which takes place in the motor or efferent nerve j which is distributed to it. This change again is effected only by the activity of the central nervous organ^ with which the motor nerve is connected. The central organ is thrown into activity immediately or ultimately, only by the influence of changes which take place in the molecular condition of nervts, called sensory or afferent^ which are connect ed», on the one hand, with the central organ, and, on the other hand, with some other part of the body. Finally, the alteration of the afferent nerve is itself produced only by changes in the condition of the part of the body with which it is connected, and which usually re- sult from external impressions. 8*


178 ELEMENTARY PHYSIOLOGY. 237. Conveyance of Molecular Impressions. — Thus the great majority (if not the whole) of the movements of the body and of its parts are the eft'ect of an influence (technically termed a stimulus or irritation) applied directly, or indirectly, to the ends of afferent nerves^ and giving rise to a molecular change, which is propagated along their substance to the central nervous organ with which they are connected. The molecular activity of the afierent nerve communicates itself to the central organ, and is then transmitted along the motor nerves, which pass from the central organ to the muscles affected. And when the disturbance in the molecular condi- tion of the efferent nerves reaches their extremities, it is com- municated to the muscular fibres, and causes their particles to take up a new position, so that each fibre shortens and be- comes thicker. 238. Beflex Action. Sensations and Consciousness. — Such a series of molecular changes as that just described is called a reflex action — ^the disturbance caused by the irritation being as it were reflected back, along the motor nerves, to the muscles. A reflex action, strictly so called, takes place without our knowing any thing about it, and hundreds of such actions are going on continually in our bodies without our being aware of them. But it very frequently happens that we learn that something is going on, when a stimulus affects our afferent nerves, by having what we call a feeling or sensation. We class sensations along with emotioois, and volitianSj and thoughts^ under the common head of states of consciousness. But what consciousness is, we know not; and how it is that any thing so remark^le as a state of consciousness comes about as the re- sult of irritating nervous tissue, is just as unaccountable as the appearance of the Djin when Aladdin rubbed his lamp in the story, or as any other ultimate fact of nature. 239. Subjective Sensations. — Sensations are of very vari- ous degrees of definiteness. Some arise within ourselves, we know not how or where, and remain vague and undefinablei


KEFLEX ACTION — GROUPS OF SENSA'HONS. 179 Such are the sensations of uncomfortdblenesSy of faintnessy of fatiguCy or of restlessness. We cannot assign any particular place to these sensations, which are very probably the result of aft'ec- tions of the afferent nerves in general, by the state of the blood, or that of the tissues in which they are distributed. And how- ever real these sensations may be, and however largelv they enter into the sum of our pleasures and pains, they tell us ab- solutely nothing of the external world. They are not only diffuse, but they are subjective sensations. 240. The Muscular Sense. — What is termed the muscular sense is less vaguely localized than the preceding, though its place is still incapable of being very accurately defined. This muscular sensation is the feeling of resistance which arises when any kind of obstacle is opposed to the movement of the body, or of any part of it; and it is something quite different fiom the feeling of contact, or even of pressure. Lay one hand flat on its back upon a table, and rest a disk of cardboard a couple of inches in diameter upon the ends of the outstretched fingers ; the only result will be a sensation of contact — the pressure of so light a body being inappreciable. But put a two-pound weight upon the cardboard and the sen- sation of contact will be accompanied, or even obscured, by the very different feeling of pressure. Up to this moment the fingers and arm have rested upon the table ; but now let the hand be raised from the table, and another new feeling will make its appearance — ^that of resistance to effort. This feeling comes into existence with the exertion of the muscles which raise the arm, and is the consciousness of that exertion given to us by the muscular sense. Any one who raises or carries a weight knows well enough that he has this sensation ; but he may be greatly puzzled to say where he has it Nevertheless, the sense itself is very deli- cate, and enables us to form tolerably accurate judgments of the relative intensity of resistances. Persons who deal in arti- cles sold by weight are constantly enabled to form very precise estimates of the weight of such articles by balancing them in

Googl^ 180 ELEMENTARY PHYSIOLOGY. their bands ; and, in this case, they depend in great measure upon the muscular sense. 241. The Higher Senses. — In a third group of sensations, each feeling, as it arises, is assigned to a definite part of the body, and is produced by a stimulus applied to that part of the body ; but the bodies, or forces, which are competent to act as stimuli, are very various in character. Such are the sensations of touchy taste^ and smelly which arc restricted to the membranes which cover the surface of the body and line the mouth and nasal cavities. And lastly, in a fourth group of sensations, each feeling requires for its production the application of a single kind of stimulus to a very specially modified part of the integument. The latter serves as an intermediator between the physical agent of the sensation and the sensory nerve, which is to con- vey to the brain the impulse necessary to awake that state of consciousness, which we call the sensation, in it. Such are the sensations of sight and hearing. The physical agents which can alone awaken these sensations (under natural circumstances) are light and sound. The modified parts of the integument, which alone are competent to intermediate between these agents and the nerves of sight and hearing, are the eye and the ear, 242. General Plan of a Sensory Organ. — In every sensory organ it is necessary to distinguish the terminal expansion of the aflerent or sensory nerve, and the structures which inter- mediate between this expansion and the physical agent which gives rise to the sensation. And in each group of special sensations there are certain phenomena which arise out of the structure of the organ, and others which result from the operation of the central apparatus of the ner\'ous system upon the materials supplied to it by the sensory organ. Section II. — Touchy Taste, and Smell, 243. The Sense of Touch.— -The sense of Touch (including that of heat and cold) is possessed, more or less acutely, by all


181 parts of the free surface of tke body, and by the walls of the mouth and nasal passages. Whatever part possesses this sense consists of a membrane (integumentary or mucous) composed of a deep layer made up of fibrous tissue, containing a capillary net-work and the ulti- mate terminations of the sensory nerves ; ayd of a supei'ficial layer consisting of epithelial or epidermic cells, among which are neither nerves nor vessels. Wherever the sense of touch is delicate, the deep layer is not a mere flat expansion, but is raised up into multitudes of small, close-set, conical elevations, which are called papillce. In the sldn, the coat of epithelial or epidermic cells does not follow the contour of these papillae, but dips down between them and forms a tolerably even coat over them. Thus, the points of the papillae are much nearer the surface than the general plane of the deep layer whence these papilla) proceed. Loops of vessels enter the papillaj, and the fine ultimate terminations of the sensory nerve fibres distributed to the skin terminate in them, but in what way has not been thoroughly made out. In certain cases, the delicate fibrous sheath, or neurilemma^ of the nc^^^e which enters the papilla, enlarges in the papilla into an oval swelling, which is called a tactile corpuscle. These corpuscles are only found in the papillae of those localities which are endowed with a very delicate sense of touch, as in the tips of the fingers, the point of the tongue, etc. 244. Functions of Epithelium. — It is obvious from what has been said that no direct contact takes place between a body which is touched and the sensory nerve, a thicker or thinner layer of epithelium, or epidermis, being situated be- tween the two. In fact, if this layer is removed, as when a surface of the skin has been blistered, contact with the raw surface gives rise to a sense of pain, not to one of touch prop- erly so called. Thus, in touch, it is the epidermis, or epithe- lium, which is the intermediator between the nerve and the physical agent, the external pressure being transmitted through

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182 ELEMENTARY PHYSIOLOGY. the horny cells to tbe subjacent ends of the nerves, and the kind of impulse thus transmitted must be modified by tlie thickness and character of the cellular layer, no less than by the forms and number of the papillae. 245. Varjrii^ Tactile Sensibility. — Certain very curious phenomena appertaining to the sense of touch are probably due to these varying anatomical arrangements. Not only is tactile sensibility to a single impression much duller in some parts than in others — a circumstance which might be readily accounted for by the different thickness of the cellular layer — but the power of distinguishing double simultaneous impres- sions is very different. Thus if the ends of a pair of com- passes (better if blunted with pointed pieces of cork) are sep- arated by only one-tenth or one-twelfth of an inch, they will be distmctly felt as two, if applied to the tips of the fingers ; whereas if applied to the back of the hand in the same way, only one impression will be felt ; and, on the arm they may be separated for a quarter of an inch, and still only one impres- sion will be perceived. Accurate experiments have been made in different parts of the body, and it has been found that two points can be dis- tinguished by the tongue, if only one-twenty-fourth of an inch apart ; by the tips of the fingers if one-twelfth of an inch dis- tant; while they may be one inch distant on the cheek, and even three inches on the back, and still give rise to only one sensation. 246. The Sense of Warmth or Cold.— The feeling of warmth, or cold, is the result of an excitation of sensory nerves distributed to the skin, which are probably distinct from those which give rise to the sense of touch. And it would appear that the heat must be transmitted through the cellular layer to give rise to this sensation ; for just as touch- ing a naked nerve, or the trunk of a nerve, gives rise only to pain, so heating or cooling an exposed nerve, or the trunk of a nerve, gives rise not to a sensation of heat or cold, but simply to pain.


183 Again, the sensation of heat, or cold, is relative rather than absolute. Suppose three basins be prepared, one filled with ice-cold water, one with water as hot as can be borne, and the third with a mixture of the two. If the hand be put into the hot-water basin, and then transferred to the mixture, the latter will feel cold ; but if the hand be kept awhile in the ice-cold water, and then transferred to the very same mixture, it will feci warm. Like the sense of touch, the sense of warmth varies in deli- cacy in different parts of the body. The cheeks are very sensitive, more so than the lips ; the palms of the hands are more sensitive to heat than their backs. Hence a washerwoman holds her flat-iron to her cheek to test the temperature, and one who is cold spreads the palms of his hands to the fire. 247. The Sense of Taste— the Tongue.— The organ of the sense of Taste is the mucous membrane which covers the tongue, especially its back pait and the hinder part of the palate. Like that of the skin, the deep, or vascular, layer of the mucous membrane of the tongue is raised up into papilla;, but these arc large, separate, and have separate coats of epi- thelium. Toward the tip of the tongue they are for the most part elongated and pointed, and are called filiform ; over the rest of the surface of the tongue, these are mixed with other, larger, papillse with broad ends and narrow bases, dixWad fungi- form ; but toward its root there are a number of large papil- la;, set in the shape of a V w^ith its point backward, each of which is like a fungiform papilla surrounded by a wall. These are the circumvallate papillse (Fig. 74, C.p,), The larger of these papillaB have subordinate small ones upon their surfaces. They are very vascular, and they receive nervous filaments from two sources, the one the nerve called glossojiharyngeal, the other the fifth nerve. Tlie latter chiefly supplies the front of the tongue, the former its back and the adjacent part of the palate; and there is reason to believe that it is the latter re- gion which is more especially the seat of the sense of taste.

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184 ELEMENTAEY PHYSIOLOGY. The great majority of the sensations we call taste, how- ever, are in reality complex sensations, into which smell and even touch largely enter. Fig. 74. The moutb widely opened, to show the tonsrue and palate.— ?7». tbo uvula; Tr. the tonsil between the anterior and posterior pillars of the fauces; C.p. circumval- late papilbo ; F. p. fungiform papillre. The minute filiform papilhe cover the interspaces between these. On the right side the tongue is partially dissected to show the course of the filaments of the glossopharyngeal nerve, V/lI. 248. Smell— Mechanism of the Nostrils. — ^The organ of the sense of Smell is the delicate mucous membrane which lines a part of the nasal cavities, and is distinguished from the rest of the mucous membrane of these cavities — firstly, by pos- sessing no cilia ; secondly, by receiving its nervous supply from the olfactory, or first, pair of cerebral nerves, and not, like the rest of the mucous membrane, from the fifth pair. Each nostril leads into a spacious nasal chamber, separated, in the middle line, from its fellow of the other side, by a parti-


TOUCH, TASTE, AND SMELL. 185 tion or septum, fonned partly by cartilage and partly by bone, and continuous with that partition which separates the two nostrils one from the other. Below, each nasal chamber is separated from the cavity of the mouth by a floor, *the bony palate (Figs. V5, 76, 77), and when this bony palate comDs to an end, the partition is continued down to the root of the tongue by a fleshy curtain, the soft palate, which has already been described. The soft palate and the root of the tongue jpa Fig. 75. Fio. 76. Vertical longitudinal sections of the nn?al cavity. — The left-hand figure represents the outer wall of the right nasal cavity; the fight-hand figure the left side of the middle partition or septum of the nose, which forms the right wall cf the left nasal cavity. /, the olfactory nerve and its branches; F, branches of the fifth nerve; Pa. the palate which sepai-ates the nastd cavity from that of the mouth; S. T. the superior tnrbinal bone; M. T. the middle turbinal; /. T. the inferior turbinal. The letter /is placed in the cerebral cavity, and the partition on which the olfactory lobe rests, and through which the filaments of the olfactory nerves pass, is the cribriform plate. together, constitute, under ordinary circumstances, a transverse movable partition between the mouth and the pharynx, and it will be observed that the opening of the larynx, the glottis, lies behind the partition ; so that while the latter is complete, no passage of air can take place between the mouth and the pharynx. But above and behind the partition are the two hinder openings of the nasal cavities (which are called the pos- terior nares) separated by the termination of the septum, and by means of these wide openings the air passes, with great readiness, from the nostrils along tlie lower part of each nasal chamber to the glottis, or in the opposite direction. It is by means of the passages thus freely open to the air that we breathe, as we ordinarily do, with the mouth shut (Fig. 63).


186 ELEMENTARY PHYSIOLOGY, Each nasal chamber rises, as a high vault, far above the level of the arch of the posterior nares — in fact, about as high as the depression of the root of the nose. The uppermost and front part of its roof, between the eyes, is formed by a delicate horizontal plate of bone, perforated like a sieve by a great many small holes, and thence called the cribriform plate (Fig. 11), It is this plate alone which, in this region, separates the cavity of the nose from that which contains the brain. The olfactory lobes, which are directly connected with, and, indeed, a part X2T- A transverse and vertical section of the nasal cavity taken nearly through the letter /in the loresroing figure.— C>. the cribriform plate; S. T.^ M. T. the chambered superior and middle turblnal bones on which and on the septum, Sp, the fila- ments of the olfactory nerve are distributed; /. T. the inferior turbinal bone; PI. the ^)alate ; An. the Antrum or chajiiber which occupies the greater part of the maxillary bone and opens into the nasal cavity. of the brain, enlarge at their ends, and their broad extremities rest upon the upper side of the cribriform plate, sending im- mense numbers of delicate filaments, the olfactory nerves, through it to the olfactory mucous membrane (Figs. 75, V6). On each wall of the septum this mucous membrane forms a flat expansion, but, on the side walls of each nasal cavity, it follows the elevations and depressions of the inner surfaces of what are called the upper and middle turbinal^ or spongy bones. These bones are called spongy^ because the interior of each is


I i TOUCH, TASTE, AND SMELL. 187 occupied by air cavities separated only by very delicate parti- tions, and communicating with the nasal cavities. Hence the bones, though massive-looking, are really exceedingly light and delicate, and fiilly deserve the appellation of spongy (Fig. 77). There is a third light scroll-like bone distinct from these two, and attached to the maxillary bone, which is called the inferior turbinal, as it lies lower than the other two, and im- perfectly separates the air-passages from the proper olfactory chamber (Fig. 77). It is covered by the ordinary ciliatecl mucous membrane of the nasal passages, and receives no fila- ments from the olfactory nerve (Figs. 75, 76), 249. The Eeason of "Sniffing."— From the arrangements which have been described it is clear that, under ordinary cir- cumstances, the gentle inspiratory and expiratory currents will flow along the comparatively wide, direct passages afforded by so mueh of the nasal chamber as lies below the middle turbinal, and that they will hardly move the air enclosed in the narrow interspace between the septum and the upper and middle •spongy bones, which is the proper olfactory chamber. If the air currents are laden with particles of odorous mat- ter, these particles can only reach the olfactory membrane by diffusing themselves into this narrow interspace ; and if there be but few of these particles, they will run the risk of not reach- ing the olfactory mucous membrane at all, imless the air in contact with it be exchanged for some of the odoriferous air. Hence it is that, when we wish to perceive a faint odor more distinctly, we sniff*, or snuff" up, the air. Each sniff* is a sudden inspiration, the effect of which must reach the air in the olfac- tory chamber at the same time as, or even before, it aflfects that at the nostrils, and thus must tend to draw a little air out of that chamber from behind. At the same time, or immediately afterward, the air sucked in at the nostrils, entering with a sud- den vertical rush, part of it must tend to flow directly into the olfactory chamber, and roplacc that thus drawn out. The loss of smell which takes place in the course of a severe cold may, in part, be due to the swollen state of the mucous


188 ELEMENTARY PHYSIOLOGY. membrane which covers the inferior turbinal bones, which thus impedes the passage of odoriferous air to the olfactory chamber. Section III. — The- Mechanism of Hearing, 250. Structure of the Organ. — The essential organ of the sense of Hearing consists, on each side, of two parts, the mem- branous labyrinth, and the scala media of the cochlea, both of which small organs are lodged in the midst of a dense and solid mass of bone (thence called petrosal), forming a part of the temporal bone, and entering into the base of the skull. Each of these essential constituents of the organ of hearing is, substantially, a membranous bag filled with a fluid, and sup- ported in fluid. In the interior of each, certain small, mobile, hard bodies are contained ; and the ultimate filaments of the auditory nerves are so distributed upon the walls of the bags that their terminations must be knocked by the vibrations of these small hard bodies, should any thing set them in motion. It is also quite possible that the vibrations of the fluid contents- of the sacs may themselves suflSce to affect the filaments of the auditory nerve ; but, however this may be, any such effect must be greatly intensified by the cooperation of the solid particles. - In bathing in a tolerably smooth sea, on a rocky shore, the movement of the little waves, as they run backward and for- ward, is hardly felt by any one who lies down upon the beach ; but, if the beach be sandy and gravelly, the pelting of the showers of little stones and sand, which are raised and let fall by each wavelet, makes a very definite impression on the nerves of the skin. Now the membrane on which the ends of the auditory nerves are spread out is virtually a sensitive beach, and waves which, by themselves, would not be felt may be readily per- ceived if they suffice to raise and let fall hard particles. In the membranous labyrinth these hard bodies are hair- like filaments, or minute particles of calcareous sand. The latter are called otoconia, or otolithes.


THE MECHANISM OF HKARIKG. 189 The epithelium (a, Fig, 78) which covers the termination of the nerves in the ampullse (see p. 190) which is produced into long stiff slender hair-like processes {b, Fig. 78), which are, of course, readily affected by any vibration of the endolymph, and communicate » the impulse to the end of the nerves. In Fro. 73. The delicate stiff filaments which are set upon the inner walls of the ampullae. the vestibular sac (p. 100), on the contrary, these hairs arc scanty or absent, but the minute angular octoconia serve the same purpose. In the scala media of the cochlea organized structures, minute, rod-like bodies, having a definite form, length, and more or less cellular structure, the fibres of Corii, appear to serve the same object. 251. The Vestibule, — For simplicity's sake, the membra- nous labyrinth and the scala media have liithcrto been spoken of as if they were simple bags ; but this is not the case, each bag having a very curious and somewhat complicated form. Tlius the membranous lahyrinth has the figure of an oval


190 ELEMENTAEY PHYSIOLOGY. vestibular sac, with which the hooplikc semicircular canals are connected. These are three in number, and two being vertical are called the anterior aud posterior vertical semicircular canals; while the third, lying outside, and horizontally, is termed the external, or horizontal semicircular canal. One end of each of these canals is dilated into what is called the ampulla (Figs. 80, 82). It is upon the walls of these ampullae and those of the vestibular sac that the nerves are distributed (p. 189). The fluid which fills the cavities of the semicircular canals and sac is termed endolymph. That which separates these delicate structures fi'om the bony chambers in which they are contained is the perilymph. Each of these fluids is little more than water. 252. The Cochlea. — In the scala media of the cochlea the primitive bag is drawn out into a long, band-like tube, which is~coiled two and a half times on itself into a conical spiral, and lies in a much wider chamber of corresponding form, ex- cavated in the petrous bone {Coc, Fig. 80). Each edge of the scala media is fastened to the walls of the containing chamber, which thus becomes divided into two passages, which com- municate at the summit of the spire, but are elsewhere sepa- rate. These two passages are called respectively the scala tympani and scala vestihuli, and are filled with perilymph. The fibres of the auditory nerve (vii. Fig. 79) are distrib- uted to the whole length of |he scala media. They enter it by the edge which is attached to the inner wall of the bony cochlea, formed by the central pillar or mx>diolus, round which the cavity winds. That wall of the scala media (e) which separates it from the scala vestibuli is called the upper membrane of Corti, The opposite wall, which separates it from the scala tvmpani, is the basilar membrane. It is very elastic, and on it rests the fibres of Corti (C C), each of which is composed of two filaments joined at an angle. An immense number of these filaments are set side by side, with great regularity, throughout the


THE MECHANISM OF HEARING. 191 whole length of the scala media, so that this presents almost the appearance of a keyboard, if viewed from either the scala ji5^a.5T Sca,V ~^ScaM SccuJ^I. Pig. 79. A spcHon tliron^h the %c.ala media of the cochlea.— a, The inner wall pillar, or modi- olus of the bony cochlea; e, its outer wall ; Sea. T. the cavity of the scala tym- pani; Sea. V. thp cavity of the Pcala vestibuli ; iSca. 3f. the cavity of the scola me'lia itself; ef, the elastic haaiJar membrane which separates the scala media itself from the scala tvmpani ; V, a vessel which lies in this cut through ; f, the so-called upper membrane of Corti which tieparntes the scala media from the scala vestibuli; C C\ the fibres of Corti ; VII. the filaments of the auditory nerve. vestibuli or the scala tympani. The ends of the nerves come into close relation with these fibres, which are capable of being agitated by the slightest impulse.


192 ELEMENTAKY PHYSIOLOGY 253. The Bony Labyrintli. — These essential parts of the organ of bearing are lodged in chambers of the petrous part of the temporal bone. Thus the membranous labyrinth is contained in a cavity of corresponding form, of which that part which lodges the sac is termed the vestibule, and that which contains the semicircular canals, the bon7/ semicircular canals. Furthermore, it has already been seen that the scala media is contained in a spirally-coiled chamber, the cochlea, which it divides into two passages. Of these, one, the scala vestlbuli, is so called because it opens directly into the vestibule ; and hence it is that the perilymph fills these scalae as well as the vestibule and semicircular canals, the whole being placed in communication by the wide aperture which leads from the vestibule into the scala vestibuli. In the fresh state, the bony labyrinth, as this collection of cavities in the petrous bone is termed, is perfectly closed ; but in the dry skull there are two wide openings, termed fenestroe. lEJfcC Fig. 80. Transverse section tbrough the skle walls of the skull to show the parts of the ear.— Co. Concha or external ear; E.M. external auditory meatus; Ty.3I. tympanic membrane : Inc. Mall, incus and malleus ; A,S.C. ,KS.C..P.S. C. anterior, posterior, and external semicircular canals; Coc. coch]ea;' Eu. Eustachian tube; I.M. in- ternal auditory meatus, through which the auditory nerve passes to the organ of bearing.


THE MECHANISM OF HEARING. 193 or windows, on its outer wall. Of these fcnestroD, one, termed ovalis (the oval window), is situated in the wall of the ves- tibular cavity ; the other, rotunda (the round window), behind and below this, is the open end of the scala cochleoe. In the fresh state, each of these windows, or fenestrse, is closed by a fibrous membrane continuous with the periosteum of the bone. The fenestra rotunda is closed only by membrane; but fastened to the centre oi Wi^ fenestra ovalis, so as to leave only a narrow margin, is an oval plate of bone, the base of the stapes or stirrup-bone. 254. Tympanuin and EustacMan Tube. — ^Thc outer wall of the bony labyrinth is still far away from the exterior of the skull. Between it and the visible opening of the ear, in fact, are placed in a straight line, first, the drum of the car, or tympanum; secondly, the long cxteraal passage, or meatus (Fig. 80). The dnim of the car and the external meatus would form one cavity, were it not that a delicate membrane, the tympanic membrane {Ty. M,), is tightly stretched in an oblique direc- tion, across the passage, so as to divide the comparatively small cavity of the dram from the meatus. The membrane of the drum thus prevents any communica- tion between the drum and the exterior, by means of the me- atus, but such a communication is provided, though in a round- about way, by the Eustachian tube {Uu, Fig. 80), which leads directly from the fore part of the drum inward to the roof of the pharynx, where it opens. 255. The Auditory Ossicles. — Three small bones, the au- ditory ossicles, lie in the cavity of the tympanum. One of these is the stapes^ a small bone shaped like a stirrup. The foot- plate of this bone is, as already mentioned, firmly fastened to the membrane of the fenestra ovalis, while its hoop projects inward into the tympanic cavity (Fig. 82). Another of these bones is the malleus {Mall. Figs. 80, 82), .or hammer-bone, a long process of which is similarly fastened

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194 ELEMENTARY PHYSIOLOGY. to the inner side of the tympanic membrane (Fig. 81). The rounded surface of the head of the malleus fits into a corre- sponding pit in the other end of the third bone, the incus or anvil-bone, which has two processes — one, horizontal, which rests upon a support afforded to it by the walls of the tympa- num ; while the other, vertical, descends almost parallel with the long process of the malleus, and articulates with the stapes, or rather with a little bone, the os orhiculare which is united with the stapes (Figs. 81, 82). FiQ. 81. The membrane of the drum of the ear seen from the Inner side, with the small bones of the ear; and the walls of the tympanum, with the air-cells in the mastoid part of the temporal bone. — M.C. Mastoid cells; 3IalL malleus; Inc. incus; Si. stapes; a 6, lines drawn thiough the horizontal axis on which the malleus and incus turn. The three bones thus form a chain between the fenestra ovalis and the tympanic membrane; and the whole series turns upon a horizontal axis, the two ends of which, formed by the horizontal process of the incus and the slender pro- cess of the malleus, rest in the walls of the tympanum. The general direction of this axis is represented by the line a h in Fig. 81, or by a line perpendicular to the plane of the paper, passing through the head of the malleus in Fig. 82. It follows, therefore, that whatever causes the membrane of the drum to vibrate backward and forward, must force the handle of the malleus to travel in the same way. This must cause a corresponding motion of the long process of the incus,


THE MECHANISM OF HEAEING. 195 the end of wliicli must drag the stapes backward and forward. And, as this is fastened to the membrane of the fenestra ovalis, which is in contact with the perilymph, it must set this fluid vibrating throughout its whole extent, the thrastings in of the Fig. 62. A diagram illnstratlvc of the relative positions of the yarious parts of the ear.— ^ M. external auditory meatas ; TV. JV. tympanic membrane ; 7^. tympanum ; 3/rt//. malleus; /ne. incus; Stp. stapes; F.o. fenestra ovalis; F.r. fenestra rotunda; Ell. Eustachian tube; m. L. membranous labyrinth, only one semicircnlar canal with its ampulla being represented; Sea. Fi, Sea. T.^ Sea. M. the scalsQ of the cochlea, which is supposed to be unrolled. membrane of the fenestra ovalis being compensated by cor- responding thrustings out of the membrane of the fenestra rotunda, and vice versa. The vibrations of the perilymph thus produced will affect the endolymph, and this the otolithes ; by which, finally, the auditory nerves will be excited. 256. The Muscles of the Tympantun. — ^The membrane of the fenestra ovalis and the tympanic membrane will necessarily vibrate the more freely the looser they are, and the reverse. But there are two muscles — one, called the stapedius, which passes from the floor of the tympanum to the orbicular bone, and the other, the tensor tympanic from the front wall of the


196 ELEMENTARY PHYSIOLOGY. drum to tlie malleus. Each of the muscles when it contracts tightens the membranes in question, and restricts their vibra- tions ; or, in other words, tends to check the effect of any cause which sets these membranes vibrating. 257. The Concha. — The outer extremity of the external meatus is surrounded by the concJia or external ear (Fig. 80, Co,), a broad, peculiarly-shaped, and, for the most part, carti- laginous plate, the general plane of which is at right angles with that of the axis of the auditory opening. The concha can be moved in various directions by muscles which pass to it from the side of the head. Section IV. — Working of the Auditory Mechanism. 258. Nature of Sound. — ^The manner m which the com- plex apparatus now described intermediates between the physi- cal agent, which is the condition of the sensation of sound, and the nervous expansion, the affection of which alone can excite that sensation, must now be considered. All bodies which produce sound are in a state of vibration, and they communicate the vibrations of their own substance to the air with which they are in contact, and thus throw that air into waves, just as a stick waved backward and forward in water throws the water into waves. The aerial waves, produced by the vibrations of sonorous bodies, in part enter the external auditory passage, and in part strike upon the concha of the external ear and the outer sur- face of the head. It may be that some of the latter impulses are transmitted through the solid structure of the skull to the organ of hearing ; but before they reach it they must, under ordinary circumstances, have becom© io scanty and weak, that they may be left out of consideratioa The aerial waves which enter the meatus all impinge upon the membrane of the drum and set it vibrating, stretched membranes taking up vibrations from the air with great readi- ness.


• WORKING OF THE AUDITORY MECHANISM. 197 259. Vibrations of the Tympanum. — ^The vibrations thus set up in the membrane of the drum are communicated, in part, to the air containjM in the drum of the ear, and, in part, to the malleus, and thence to the other auditory ossicles. The vibrations communicated to the air of the drum im- pinge upon the inner wall of the tympanum, on the greater part of which, from its density, they can produce very little effect. Where this wall is formed by the membrane of the fenestra rotunda^ however, the communication of motion must necessarily be greater. The vibrations which are communicated to the malleus and the chain of ossicles may bo of two kinds : vibrations of the particles of the bones, and vibrations of the bones as a whole. If a beam of wood, freely suspended, be very gently scratched with a pin, its particles will be thrown into a state of vibra- tion, as will be evidenced by the sound given out, but the beam itself will not be moved. But, if a strong wind blow against the beam, it will swing visibly, without any vibrations of its particles among themselves. On the other hand, if the beam be sharply struck with a hammer, it will not only give out a sound, showing that its particles are vibrating, but it will also swing, from the impulse given to its whole mass. Under the last-mentioned circumstances a blind man stand- ing near the beam would be conscious of nothing but the sound, the product of molecular vibration, or invisible oscilla- tion of the particles of the beam ; while a deaf man, in the same position, would be aware of nothing but the visible oscil- lation of the beam as a whole. 260. Their Tranfanission. — ^Thus, to return to the chain of auditory ossicles, while it seems hardly to be doubted that, when the membrane of the drum vibrates, they are set vibrat- ing both as a whole and in their particles, it depends upon subsidiary arrangements whether the large vibrations, or the minute ones, shall make themselves obvious to the auditory nerve, which is in the position of our deaf, or blind, man. The evidence at present is in favor of the conclusion, that

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198 ELEMENTARY PHYSIOLOGY. it is the vibrations of the bones, as a whole, which are the chief agents in transmitting the impulses of the aerial waves. For, in the first place, the dispositfJn of the bones and the mode of their articulation are very mhch against the trans- mission of molecular vibrations through their substance, while, on the other hand, they are extremely favprable to their vi- bration en masse. The long processes of the malleus and incus swing, like a pendulum, upon the axis furnished by the short processes of these bones ; while the mode of connection of the incus with the stapes, and of the latter with the edges of the fenestra ovalis, allows of free play, inward and outward, to that bone. And, in the second place, it is affirmed, as the result of experiments, that the bone called columella, which, in birds, takes the place of the chain of ossicles in man, does actually vibrate as a whole, and at the same rate as the mem- brane of the drum, when aerial vibrations strike upon the latter. 261. The Action of the Auditory Uuscles. — ^Thus, there is reason to believe that when the tympanic membrane is set vibrating, it causes the process of the malleus, which is fixed to it, to swing at the same rate ; the head of the malleus con- sequently turns through a small arc on its pivot, the slender process. But the turning of the head of the malleus involves that of the head of the incus upon its pivot, the short process. In consequence, the long process of the incus swings through an arc as nearly as possible equal to that described by the handle of the malleus. But the long process is so fixed to the stapes that it cannot vibrate without, to a corresponding ex- tent and at the same rate, pulling this out of, and pushing it in to, the fenestra ovalis. But every pull and push imparts a corresponding set of shakes to the perilymph, which fills the bony labyrinth and cochlea, external to the membranous laby- rinth and scala media. These shakes are communicated to the endolymph and fluid of the scala media, and, by the help of the otolithes and the fibres of Corti, are finally converted into impulses, which act as irritants to the ends of the vestibular and cochlear divisions of the auditory nerve.


WORKING OF THE AUDITOEY MECHANISM. 199 262. Intensity and duality of Sounds— how discrim- inated. — The difference between the functions of the mem- branous labyrinth (to which the vestibular nerve is distributed) and those of the cochlea are, perhaps, not quite so certainly made out, but the following conclusions are highly probable : The membranous labyrinth is an apparatus whereby sounds are appreciated and distinguished according to their intensity or quantity ; but it does not afford any means of discriminating their qualities. The vestibular nerve tells us that sounds are low or loud, but gives us no impression of tone, or melody, or harmony. The cochlea, on the other hand, discriminates the quality rather than the quantity or intensity of sound. There is great reason to believe that the excitement of any single filament of the cochlear nerve gives rise, in the mind, to a* distinct musical impression ; and that every fraction of a tone which a well- trained ear is capable of distinguishing, is represented by its separate nerve-fibre. Thus, the scala media resembles a key- board, in function, as well as in appearance, the fibres of Corti being the keys, and the ends of the nerves representing the strings which the keys strike. If it were possible to irritate each of these nerve-fibres experimentally, we should be able to produce any musical tone, at will, in the sensorium of the per- son experimented upon, just as any note on a piano is pro- duced by striking the appropriate key. 263. Probable Function of the Fibres of Corti. — A tuning- tbrk may be set vibrating, if its own particular note, or one harmonic with it, be sounded in its neighborhood. In other words, it will vibrate under the influence of a particular set of vibrations, and no others. If the vibrating ends of the tuning- fork were so arranged as to impinge upon a nerve, their re- peated minute blows would at once excite this nerve. Suppose that of a set of tuning-forks, tuned to every note and distinguishable fraction of a note in the scale, one were thus connected with the end of every fibre of the cochlear nerve ; then any vibration communicated to the perilymph would

^ 

200 ELEMEKTAEY PHYSIOLOGY. affect the tuning-fork wMcli could vibrate with it, while the rest would be absolutely, or relatively, indifferent to that vibra- tion. In other words, the vibration would give rise to the sensation of one particular tone, and no other, and every mu- sical interval would be represented by a distinct impression on the sensorium. It is believed that the fibres of Corti are competent to per- form the function of such tuning-forks ; that each of them is set vibrating to its full strength by a particular kind of wave sent through the perilymph, and by no other ; and that each affects a particular fibre of the cochlear nerve only. The fibres of the cochlear nerve may be excited by internal causes, such as the varying pressure of the blood and the like. And in some persons such internal influences do give rise to veritable musical spectra, sometimes of a very intense character. But for the appreciation of music produced external to us, we depend upon the intermediation of the scala media and its Cortian fibres. '264. Function of the Tympanic Muscles and Eustachian Tube. — It has already been explained that the stapedius and tensor tympani muscles are competent to tighten the membrane of the fenestra ovalis and that of the tympanum, and it is probable that they come into action when the sonorous im- pulses are too violent, and would produce too extensive vibrations of these membranes. They therefore tend to mod- erate the effect of intense sound, in much the same way that, as we shall find, the contraction of the circular fibres of the iris tends to moderate the effect of intense light in the eye* The function of the Eustachian tube is, probably, to keep the air in the tympanum, or on the inner side of the tympanic membrane, of about the same tension as that on the outer side, which could not always be the case if the tympanum were a closed cavity.


BTBUCTC3JE AND ACTION OF THE KETINA. 201 CHAPTER X. THE ORGAN OF SIGHT. Section I. — Structure and Action of the Retina. 285. Oeneral Structure of the Eye. — ^In studying the organ of the sense of sight, the eye, it is needful to become acquainted, firstly, with the sensory expansion in which the optic nerve terminates, and its properties ; secondly, with the physical agent of the sensation ; thirdly, with the intermediate apparatus by which the physical agent is enabled to act upon the nervous expansion. The ball of the eye is a globular body, moving freely in a chamber, the orhit^ which is furnished to it by the skull. The optive nerve, the root of which is in the brain, leaves the skull by a hole at the back of the orbit, and enters the back of the globe of the eye, not in the middle, but on the inner, or nasal, side of the centre. It then spreads out on the inner surface of the wall of the globe of the eye into a very delicate layer, varying in thickness from -^\h of an inch to less than half that amount, which is termed the retina. This retina is the only termination of sensory nervous fibres which can be afibcted, by any agent, in such a manner as to give rise to the sensa- tion of light. 266. The Surface of the Eetina.— If the globe of the eye bo cut in two, transversely, so as to divide it into an anterior and a posterior half, the retina will be seen lining the concave wall of the posterior half as a membrane of great delicacy, and, for the most part, of even texture and smooth surface. But, exactly opposite the middle of the posterior wall it presents a slight circular depression of a yellowish hue, the macula lutea, or yellow spot ; and at some distance from this, toward the inner, or nasal, side of the ball, is a radiating appearance, pro- 9*

j 202 ELEMENTARY PHYSIOLOGY. duced by tlie entrance of the optic nerve and the spreading out of its fibres into the retina. 267. Microscopic Structure of the Eetina. — A vertical section of the retina, in any region except the yellow spot and the entrance of the optic nerve, presents the appearance repre- sented in Fig. 83. On its inner side, a, it is bounded by a Fig. 83. A vertical section of the retina —a. The limiting membrane next to the vitreons humor ; 6, the layer of gan^'lionic corpascles; between these the fibres of the optic nerve, which are cut across in this section, run ; c. the inner layer qf granules ; d, the outer layer qf granules separated bv the tntergranular layer. The in- terval between b and c is the Jinety-granular layer; e is the layer of rode and cones in immediate contact with the choroid by their outer ends. The vessels ramify between a and c The fine vertical lines running through all the layers from the cones and rods are the radial Jtbres. which spread out fan-wise as they near the limiting membrane. The total thickness of the section here figured does not exceed ^\h of an inch. structureless membrane, the limiting membrane^ which separates it from the vitreous humor, with which we shall hereafter be- come acquainted. Externally it consists of a vast multitude of minute, rod-like, and conical bodies, ranged side by side, per- pendicularly to the plane of the retina. This is the lat/er of rods and cones, and occupies about a quarter of the whole thick- ness. From the inner ends of the rods and cones very deli-


BTEUCTUEE AND ACTION OF THE BETINA. 203 cate radial fibres pass and spread out into branches, which are continued into the limiting membrane. Between the layer of rods and cones and the hmiting membrane, and interposed between the*radial fibres, are layers of granules d, c; while at h there is a layer of ganglionic corpuscles with ramified pro- cesses. It is of less importance to remember these circum- stances, however, than the facts, that the fibres of the optic nerve spread out between the limiting membrane (a) and the ganglionic corpuscles (6); and that the vessels which enter along with the optic nerve ramify between the limiting mem- brane and the layer c. Thus, not only the nervous fibres, but the vessels, are placed altogether in front of the rods and cones. At the entrance of the optic nerve itself the nervous fibres predominate, and the rods and cones are absent. In the yel- low spot, on Ihe contrary, the cones are abundant and close set, without the interposition of rods, and the nervous fibres disappear. 268. The Sensation of Light. — The most notable property' of the retina is its power of converting the vibrations of ether, which constitute the physical basis of light, into a stimulus to the fibres of the optic nerve — which fibres, when excited, have the power of awakening the sensation of light in, or by means of, the brain. The sensation of light, it must be understood, is the work of the brain, not of the retina; for if an eye be de- stroyed, pinching, galvanizing, or otherwise irritating the optic nerve, will still excite the sensation of light, because it throws the fibres of the optic nerve into activity ; and their activity, however produced, brings about in the brain certain changes which give rise to the sensation of light Light, falling on the optic nerve, does not excite it ; the fibres of the optic nerve, in themselves, are as blind as any other part of the body. But just as the delicate filaments of the ampullae, or the otoconia of the vestibular sac, or the Cor- tian fibres of the cochlea, are contrivances for converting the deUcate vibrations of the perilymph and endolymph into impulses which can excite the auditory nerves, so the struc-


204 ELEMENTARY PHYSIOLOGY. turcs in the retina appear to be adapted to convert the infinitely more delicate pulses of the luminiferous ether into stimuli of the fibres of the optic nerve. 269. The "Blind Spot"— The sensibility of the difl'erent parts of the retina to light varies very greatly. The point of entrance of the optic nerve is absolutely blind, as may be proved by a very simple experiment. Close the left eye, and look steadily with the right at the cross on the page, held at ten or twelve inches' distance. The black dot will be seen quite plainly, as well as the cross. Now, move the book slowly toward the eye, which must be kept steadily fixed upon the cross ; at a certain point the dot will disappear, but as the book is brought still closer it will come into view again. It results from optical principles that, in the first position of the book, the figure of the dot falls be- tween that of the cross (which throughout lies upon the yellow spot) and the entrance of the optic nerve ; while, in the second position, it falls on the entrance of the optic nerve itself; and, in the third, inside that point So long- as the image of the spot rests upon the entrance of the optic nerve it is not per- ceived, and hence this region of the retina is flailed the blind spot 270. Duration of Lmninous Impressions. — ^The impres- sion made by light upon the retina is not merely coexistent with the time the light affects it, but has a certain duration of its own, however short the time during which the light itself lasts. A flash of lightning is, practically, instantaneous, but the sensation of light produced by that flash endures for an appreciable period. It is found, in fact, that a luminous im- pression lasts for about one-eighth of a second ; whence it fol- lows, that if any two hmiinous impressions are separated by a less interval, they are not distinguished from one another. For this reason a " Catherine-wheel," or a lighted stick turned round very rapidly by the hand, appeal's as a circle of


STRUCTDEE AND ACTION OF THE KETINA. 205 fire ; and the spokes of a coach-wheel at speed are not sepa- rately visible, but only appear as a sort of opacity, or film, within the tire of the wheel. 271. Exhaustion of the Betina. — ^The excitability of the retina is readily exhausted. Thus, looking at a bright light rapidly renders the part of the retina on which the light falls, insensible ; and on looking fix)m the bright light toward a moderately-lighted surface, a dark spot, arising fix)m a tempo- rary blin(hies8 of the retina in this part, appears in the field of view. If the bright light be of one color, the part of the retina on which it Mis becomes insensible to rays of that color, but not to the other rays of the spectrum. This is the explanation of the appearance of what are called complementary colors. For example, if a bright-red wafer be stuck upon a sheet of white paper, and steadily looked at for some time with one eye, when the eye is turned aside to the white paper, a greenish spot will appear of the size and shape of the wafer. The red image has, in fact, fatigued the part of the retina on which it fell for red fight, but has left it sensitive to the remaining colored rays of which white light is composed. So that, when white light falls upon this part, the red rays in the white light have no effect, and the result of the operation of the others is a greenish hue. If the wafer be green^ the complementary i7naye, as it is called, is red. 272. Color Blindness. — ^In some persons the retina appears to be affected in one and the same way by rays of light of various colors, or even of all colors. Such color-blind persons are unable to distinguish between the leaves of a cherry-tree and its finiit by the color of the two, and see no difference be- tween blue and yellow clotb. This peculiarity, which is simply unfortunate for most per- sons, but may be dangerous if unknowingly possessed by rail- way guards or sailors, may arise either from a defect in the retina, which renders it unable to respond to different kinds of luminous vibrations, or it may proceed from some unusual absorptive power of the humors of the eye.


206 ELEMENTARY PHYSIOLOGY. 273. LuminoiLs Effects of Pressure on the Eye. — The sensation of light may be excited by other causes than the im- pact of the vibrations of tlie luminiferous ether upon the retina. Thus, an electric shock sent through the eye gives rise to an apparent flash of light ; and pressure on any part of the retina prpduces a luminous image, which lasts as long as the pressure, and is called a phosphene. If the point of the finger be pressed upon the outer side of the ball of the eye, a luminous image is seen — which, in my own case, is dark in the centre, with a bright ring at the circumference (or as Newton described it, like the " eye " in a peacock's tail) — and this image lasts as long as the pressure is continued. Most persons, again, have experienced the remarkable display of subjective fireworks which follows a heavy blow upon the eyes, produced by a fall from a horse, or by other methods well known to English youth. It is doubtful, however, whether these effects of pressure, or shock, really arise from the excitation of the retina proper, or whether they are not rather the result of the violence done to the fibres of the optic nerve apart irom the retina. 274. Function of the Bods and Cones. — ^The last para- graph raises a distinction between the "fibres of the optic nerve," and the " retina " which may not have been anticipated, but which is of much importance. We have seen that the fibres of the optic nerve ramify in the inner fourth of the thickness of the retina, while the layer of rods and cones forms its outer fourth. The light, therefore, must fall first upon the fibres of the optic nerve, and, only after traversing them, can it reach the rods and cones. Conse- quently, if the fibrill^B of the optic nerve themselves are capa- ble of being affected by light, the rods and cones can only be some sort of supplementary optical apparatus. But, in fact, it is the rods and cones which are aflected by light, while the fibres of the optic nerve are themselves insensible to it The evidence on which this statement rests is — a. The blind spot is full of nervous fibres, but has no cones or rods.


THE. LUMINOUS AGENT. 207 b. The yellow spot, where the most acute vision is situated, is full of close-set cones, but has no nerve fibres. c. If you go into a dark room with a single small bright candle, and looking toward a dark wall, move the light up and down, close to the outer side of one eye, so as to allow the light to fall very obliquely into the eye, one of what are called Purkinje's figures is seen. This is a vision of a series of diverging, branched, red lines on a dark field, and in the inter- space of two of these lines is a sort of cup-shaped disk. The red lines are the retinal blood-vessels, and the disk is the yellow spot. As the candle is moved up and down the red lines shift their position, as shadows do when the light which throws them changes its place. Now, as the light falls on the inner face of the retina, and the images of the vessels to which it gives rise shift their posi- tion as it moves, whatever perceives these images must needs lie on the other, or outer, side of the vessels. But the fibres of the optic nerve lie among the vessels, and the only retinal structures which lie outside them are the granular layers and the rods and cones. Just as, in the skin, there is a limit of distance within which two points give only one impression ; so there is a minimum distance by which two points of light falling on the retina must be separated in order to appear as two. And this distance corresponds pretty well with the diameter of the cones. Thus it would appear that these remarkable structures, set upon the outer surface of the retina, with their ends turned toward the light, are like so many finger-points, endowed with a touch delicate enough to feel the luminous vibrations. Sbction it. — The LumirKms Agent. 275. The Convex Lens. — ^The physical agent which gives rise to vision is light ^ which is now conceived to be a very attenuated fluid, the ether, vibrating in a particular way. The properties of this physical agent and the principles of optics


208 ELEMENTARY PHYSIOLOGY. must be studied elsewhere. At present it is only 'necessary to advert to some facts, of whicli every one can assure himself by simple experiments. An ordinary spectacle glass is a trans- parent body denser than the air, and convex on both sides. If this lens be held at a certain distance from a screen or wall in a dark room, and a lighted candle be placed on the oppo- site side of it, it will be easy to adjust the distances of candle, lens, and wall, so that an image of the flame of the candle, up- side down, shall be thrown upon the wall. 276. Formation of the Luminous Picture. — The spot on which the image is formed is called the focus. If the candle be now brought nearer to the lens, the image on the wall will enlarge, and grow blurred and dim, but may be restored to brightness and definition by moving the lens farther from the wall. But if, when the new adjustment has taken place, the candle be moved away from the lens, the image will again be- come confused, and the lens will have to be brought nearer the wall to restore its clearness. Thus a convex lens forms a distinct picture of luminous objects, but only at its focus ; and that focus is nearer when the object is distant, and farther off when it is near. 277. Effect of varying the Convexity.—Suppose, how- ever, that, leaving the candle unmoved, a lens with more con- vex surfaces is substituted for the first, the image will be blurred, and the lens will have to be moved nearer the wall to give it definition. And if, on the other hand, a lens with less convex surfaces is substituted for the first, it must be moved farther from the wall to attain the same end. In other words, other things being alike, the more convex the lens the nearer its focus ; the less convex, the farther off its focus. If the lens were elastic, pulling it at the circumference would render it flatter, and thereby lengthen its focus ; while, when let go again, it would become more convex, and of shorter focus. Anv material more refractive than the medium in which it


TUE LUMTNOUB AGENT. 209 is placed, if it have a convex surface, causes the rays of light which pass through the less refractive medium to that surface to converge toward a focus. If a watch-glass be fitted into one side of a box, and the box be then filled with water, a candle maybe placed at such a distance outside the watch- glass, that an image of its flame shall fall on the opposite wall of the box. If, under these circumstances, a doubly convex lens of glass were introduced into the water in the path of the rays, it would act (though less powerfully than if it were in air) in bringing the rays more quickly to a focus, because glass refracts light more strongly than water does. A camera ohscura is a box, into one side of which a lens is fitted, so as to be able to slide in and out, and thus throw dis- tinct images of bodies, at various distances, on the screen at the back of the box. Hence the arrangement just described might be termed a water camera. Section III. — The Intermediate Apparatus, 278. The Visual Mechanism. — ^The intermediate organs, by means of which the physical agent of vision, light, is en- abled to act upon the expansion of the optic nerve, comprise three kinds of apparatus : {a) A " water camera," the eyeball ; (6) muscles for moving the eyeball ; (c) organs for protecting the eyeball, viz., the eyelids, with their lashes, glands, and muscles; the conjunctiva; and the lachrymal gland and its ducts. The eyeball is composed, in the first place, of a tough, firm, spheroidal case consisting of connective tissue, the greater part of which is white and opaque, and is called the sclerotic {Scl, Fig. 84). In front, however, this fibrous capsule of the eye, though it does not change its essential character, becomes transparent, and receives the name of the cornea ( Cn. Fig. 84). The corneal portion of the case of the eyeball is more convex than the sclerotic portion, so that the whole form of the ball is such as would be produced by cutting off a segment from


210 ELEMENTARY PHYSIOLOGY. the front of a splieroid of the diameter of the sclerotic, and replacing this by a segment cut from a smaller, and conse- quently more convex, sphere. 279. The Humors and Grystalline Lens. — The comeo- sclerotic case of the eye is kept in shape by what are termed the humors — watery or semi-fluid substances, one of which, the aqueous humor, distends the corneal chamber of the eye, while the other, the vitreous j keeps the sclerotic chamber full. The two humors are separated by the very beautiful, trans- parent, doubly convex crystalline lens {Cry, Y\g, 84), denser and capable of refracting light more strongly, than either of the humors. The crystalline lens is composed of fibres having a somewhat complex arrangement, and is highly elastic. It is more convex behind than in front, and it is kept in place by a delicate, but at the same time strong and elastic, membranous frame or suspensory ligament^ which extends from the edges of the lens to what are termed the ciliary processes of the cho- roid coat. 280. Ths Choroid and Ciliary Processes.— Tliis choroid coat ( Ch. Fig. 84) is a highly vascular membrane, in close con- tact with the sclerotic externally, and lined, internally, by a layer of small polygonal bodies containing much pigmentary matter, C2X\QdL pigment-cells. These pigment-cells are separated from the vitreous humor by the retina only. The rods and cones of the latter are in immediate contact with them. The choroid lines every part of the sclerotic, except where the op- tic nerve enters it, at a point -below, and to the inner side of the centre of the back of the eye ; but when it reaches the front part of the sclerotic its inner surface becomes raised up into a number of longitudinal ridges, with intervening depres- sions, terminating within and in front by rounded ends, but passing, externally, into the iris. These ridges are the ciliary l^rocesses ( C,p, Fig. 84). 281. The Iris and Ciliary Muscle. — The iris itself (/r. Fig. 84) is, as has already been said, a curtain with a round hole in the middle, provided with circular and radiating


THE INTERMEDIATE APPARATUS. 211 unstriped muscular fibres ; and capable of having its central aperture enlarged or diminished by the action of these fibres, the contraction of which is extremely rapid. The edges of the iris are firmly connected with the capsule of the eye, at the junction of the cornea and sclerotic, by the connective tissue which enters into the composition of the so-called ciliary lig- ament. Unstriped muscular fibres, having the same attach- ment in front, spread backward on to the outer surface of the choroid, constituting the ciliary muscle {Cm. Fig. 84). If these fibres contract, it is obvious that they will pull the choroid forward ; and, as the frame, or suspensory ligament, of the lens is connected with the ciliary processes (which simply form the anterior termination of the choroid), this pull- ing forward of the choroid comes to the same thing as a relax- ation of the tension of that suspensory ligament, which, as I have just said, like the lens itself, is highly elastic. The iris does not hang down perpendicularly into the space between the front face of the crystalline lens and the posterior surface of the cornea, which is filled by the aqueous humor, but applies itself very closely to the anterior face of the lens, so that hardly any space is left between the two (Figs. 84, 85). Section IV. — Focal Adjustment. 282. The Iris a Self-reg^ting Diaphragm. — ^The eye- ball, the most important constituents of which have now been described, is, in principle, a camera of the kind described above — a water camera. That is to say, the sclerotic answers to the box, the cornea to the watch-glass, the aqueous and vitre- ous humors to the water filling the box, the crystalline to the glass lens, the introduction of which was imagined. The back of the box corresponds with the retina. But further, in an ordinary camera obscura, it is found de- sirable to have what is termed a diaphragm (that is, an opaque plate with a hole in its centre) in the path of the rays, for the

j| 

212 ELEMENTARY PIiySIOLOGY. purpose of moderating the light and cutthig off the marginal rays which, owing to certain optical properties of spheroidal surfaces, give rise to defects in the image formed at the focus. In the eye, the place of this diaphragm is taken by the iris, which has the peculiar advantage of being self-regulating ; Horizontal Bection of the eyeball— iSb?. The sclerotic coat; Cn. the cornea; R. the at- tachments of the tendons of the recti muscles ; Ch. the choroid ; C.p. the ciliary processes; Cm. the ciliary muscle; Ir. the iris; Aq. the aqueous humor; Cry. the crystalline lens ; Vt. the vitreous humor ; Et. the retina ; Op. the optic nerve ; Ml. the yellow spot The section has passed through a ciliary process on the left side, and between two ciliary processes on the right. dilating its aperture and admitting more light when the light is weak ; but contracting its aperture and admitting less light when the illumination is strong. 283. Necessity of Adjustment. — In the water camera^ con- structed according to the description given above, there is the defect that no provision exists for adjusting the focus to the varying distances of objects. If the box were so made that its back, on which the image is supposed to be thrown, received distinct images of very distant objects, all near ones would be


FOCAL ADJUSTMENT. 213 indistinct. And if, on the other hand, it were fitted to receive the image of near objects, at a given distance, those of either nearer, or more distant, bodies would be blurred and indis- tinct. In the ordinary camera this diflSculty is overcome by sliding the lenses in and out, a process which is not compati- ble with the construction of our water camera. But there is clearly one way, among many, in which this adjustment might be effected — namely, by changing the glass lens; putting in a less convex one when more distant objects had to be pictured, and a more convex one when the images of nearer objects were to be thrown upon the back of the box. But it would come to the same thing, and be much more convenient, if, without changing the lens, one and the same lens could be made to alter its convexity. This is actually what is done in the adjustment of the eye to distances. 284. Experiment — Adjustment requires Effort.— The simplest way of experimenting on the adjustment of the eye is to stick two stout needles upright into a straight piece of wood, not exactly, but nearly in the same straight line, so that, on applying the eye to one end of the piece of wood, one needle {a) shall be seen about six inches off, and the other {h) just on one side of it at twelve inches' distance. If the observer look at the needle h he will find that he sees it very distinctly, and without the least sense of effort ; but the image of a is blurred and more or less double. Now, let him try to make this blurred image of the needle a distinct He will find he can do so readily enough, but that the act is ac- companied by a sense of fatigue. And furthermore, in pro- portion as a becomes distinct, h will become blurred. Nor will any effort enable him to see a and h distinctly at the same time.- 286. The Mechanism of A^ustment explained. — Mul- titudes of explanations have been given of this remarkable power of adjustment, but it is only within the last few years that the problem has been solved, by the accurate determination of the nature of the changes in the eye which accompany the act.


214 ELEMENTARY PHYSIOLOGY. When the flame of a taper is held near, and a little on one side of, a person's eye, any one looking into the eye from a proper point of view will see three images of the flame, two upright and one inverted. One upright image is reflected from the front of the cornea, which acts as a convex mirror. The second proceeds from the front of the crystalline lens, which has the same effect ; while the inverted image proceeds from the pos- terior face of the lens, which, being convex backward, is, of course, concave forward, and acts as a concave mirror. Suppose the eye to be steadily fixed on a distant object, and then adjusted to a near one iil the same line of vision, the position of the ball, of course, remains unchanged. Further- more, the upright image reflected from the surface of the cor- nea, and the inverted image from the back of the lens, remain unchanged, though it is demonstrable that their size or appar- ent position must change if either the cornea, or the back of the lens, alter either their form or their position. But the second upright image, that reflected by the front face of the lens, changes both its size and its position ; and that in such a manner as to prove that the front face of the lens has become more convex. The change of form of the lens is, in fact, that represented in Fig. 85. Fio. 85. ninstrates the change in the form of the lens when adjastcd— ^ to distant, S to near objects. These may be regarded as the facts of adjustment with which all explanations of that process must accord. They at once exclude the hypotheses (1) that adjustment is the result of the compression of the ball of the eye by its muscles, which would cause a change in the form of the cornea; (2) that ad-


FOCAL ADJUSTMENT. 215 justment results from a shifting of the lens bodily, for its hinder face does not move ; (3) that it results from the pres- sure of the iris upon the front face of the lens, for under these circumstances the hinder face of the lens would not remain stationary. This last hypothesis is further negatived by the fact that adjustment takes place equally well when the iris is absent One other explanation remains, which is, in all probability, the true one, though not altogether devoid of diflSculties. The lens, which is very elastic, is kept habitually in a state of ten- sion by the elasticity of its suspensory ligament, and conse- quently has a flatter form than it would take if lefTto itself. If the ciliary muscle contracts, it must, as has been seen, relax that ligament, and thereby diminish its elastic tension upon the lens. The lens, consequently, will become more convex, returning to its former shape when the ciliary muscle ceases to contract, and allows the choroid to return to its ordinary place. If this be the true explanation of adjustment, the sense of effort we feel must arise from the contraction of the ciliary muscle. 286. Limits of the Power of Adjustment. — Adjustment can take place only within a certain range, which admits of great individual variations. As a rule, no object which is brought within less than about ten inches of the eye can be seen distinctly without effort. But many persons are bom with the surface of the cornea more convex than usual, or with the refractive power of the eye increased in some other way ; while, very generally, as age draws on, the cornea flattens. In the former case, objects at ordinary distances are seen indistinctly, because these images fall not on the retina, but in front of it ; while, in the latter, the same indistinctness is the result of the rays of light etriking upon the retina before they have been brought to a focus. The defect of the former, or short-sighted people, is amended by wearing concave glasses, which cause the rays to diverge ; of


216 ELEMENTARY PHYSIOLOGY. the latter, or long-sighted people, by wearmg convex glasses, which make the rays converge. Section V. — Appendages of the EyehalL 287. Action of the Muscles of the EyebalL — ^The muscles which move the eyeball are altogether six in number — four straight muscles, or recti^ and two oblique muscles, the ohliquL The straight muscles are attached to the back of the orbit, round the edges of the hole through which the optic nerve passes, and run straight forward to their insertions in the sclerotic — one, the superior rectus, in the middle line above ; one, the inferior^ opposite it below ; and one half way on each side, the external and internal recti. The eyeball is completely imbedded in fat behind and laterally; and these muscles turn Fio. 86. The muscles of the eyeball viewed from above and from the outer side.— . Fig. 8a A front view of the eye, with the eyelids.— Lachrymal gland, Z. (?., and Lachrymal duct, L. D, is irritated by pungent vapors, or when painful emotions arise in the mind, the secretion of the lachrymal gland exceeds the drainage power of the lachrymal duct, and the fluid, accumu- lating between the lids, at length overflows in the form of tears.


COMPOUND SENSATIONS. 219 CHAPTER XL SENSATIONS AND JUDGMENT. Section I. — Compound Sensations, 290. Our Sensations mostly Composite.— In explaining tlie functions of the sensory organs, I have hitherto confined myself to describing the means by which the physical agent of a sensation is enabled to irritate a given sensory nerve ; and to giving some account of the simple sensations which arc thus evolved. Simple sensations of this kind are such as might be produced by the irritation of a single nerve fibre, or of several nerve fibres by the same agent Such are the sensations of contact, of warmth, of sweetness, of an odor, of a musical note, of white- ness, or redness. But very few of our sensations are thus simple. Most of even those which we are in the habit of regarding as simple, are really compounds of different sensations, or of sensations with ideas, or judgments. For example, in the preceding cases, it is very difficult to separate the sensation of contact from the judgment that something is touching us ; of sweetness, from the idea of something in the mouth ; of sound or light, from the judgment that something outside us is shining, or sounding. 291. The Sensation of Smell the Simplest. — The sensa- tions of smell are those which are least complicated by acces- sories of this sort. Thus, particles of musk diffuse themselves with great rapidity through the nasal passages, and give rise to the sensation of a powerfiil odor. But beyond a broad notion that the odor is in the nose, this sensation is unaccompanied by any ideas of locality and direction. Still less does it give rise to any conception of form, or size, or force, or of succes- sion, or contemporaneity. If a man had no other sense than that of smell, and musk were the only odorous body, he could


220 ELEMKNTAEY PHYSIOLOGY. have no sense of outness — no power of distinguishing between the external world and himself. 292. Analysis of a Tactile Sensation. — Contrast this with what may seem to be the equally simple sensation obtained by drawing the finger along the table, the eyes being shut. This act gives one the sensation of a flat hard surface outside one- self, which appears to be just as simple as the odor of musk, but is really a complex state of feeling compounded of (a) Pure sensations of contact. (b) Pure muscular sensations of two kinds — the one arising from the resistance of the table, the other from the actions of those muscles which draw the finger along. (c) Ideas of the order in which these pure sensations succeed one another. (d) Comparisons of these sensations and their order, with the recollection of like sensations similarly arranged, which have been obtained on previous occasions. (c) Recollections of the impressions of extension, flatness, &c., made in the organ of vision when these previous tactile and muscular sensations were obtained. Thus, in this case, the only pure sensations are those of contact and muscular action. The greater part of what we call ttie sensation is a complex mass of present and recollected ideas and judgments. 293. Complexity of the Notion of Bonndness. — Should any doubt remain that -we do thus mix up our sensations with our judgments into one indistinguishable whole, shut the eyes as before, and instead of touching the table with the finger, take a round lead pencil between the fingers, and draw that along the table. The " sensation " of a flat hard substance will be just as clear as before ; and yet all that we touch is the round surface of the pencil, and the only pure sensations we owe to the table are those afforded by the muscular sense. In fact, in this case, our *' sensation " of a flat hard surface is en- tirely a judgment based upon what the muscular sense tells us is going on in certain muscles.


COMPOUND SENSATIONS. 221 A still more striking case of the tenacity with which we adhere to complex judgments, which we conceive to be pure sensations, and are unable to analyze otherwise than by a pro- cess of abstract reasoning, is afforded by our sense of roundness. Any one taking a marble between two fingers will say that he feels it to be a single round body ; and he will probably be as much at a loss to answer the question how he knows that it is round, as he would be if he were asked how he knows that a scent is a scent. Nevertheless, this notion of the roundness of the marble is really a very complex judgment, and that it is so may be shown by a very simple experiment If the index and middle fingers bo crossed, and the marble placed between them, so as to be in contact with both, it is utterly impossible to avoid the belief that there are two marbles instead of one. Even looking at the marble, and seeing that there is only one, does not weaken the apparent proof derived from touch that there* are two.* The fact is, that our notions- of singleness and roundness are, really, highly complex judgments based upon a few simple sen- sations; and when the ordinary conditions of those judgments are reversed, the judgment is also reversed. With the index and middle fingers in their ordinary posi- tion, it is of course impossible that the outer sides of each should touch opposite surfaces of one spheroidal body. If, in the natural and usual position of the fingers, their outer surfaces simultaneously give us the impression of a spheroid (which it- self is a complex judgment), it is in the nature of things that .there must be two spheroids. But when the fingers are crossed over the marble, the outer side of each finger is really in con- tact with a spheroid ; and the mind, taking no cognizance oT the crossing, judges in accordance with its universal expe- rience that two spheroids, and not one, give rise to the sensa- tions which are perceived.

  • A Indlcroas form of this experiment is to apply the crossed fingers to the end

of the nose, when It at once appears double ; and, in spite of the absurdity of the con- viction, the mind cannot expel it, so long as the sensations last.


222 ELEMENTAEY PHYSIOLOGY. Section IL — Delusions of Judgment. 294. There are no '^Delufdons of the Senses." — Phenom- ena of this kind are not uncommonly called delusions of the senses ; but there is no such thing as a fictitious, or delusive, sensation. A sensation must exist to be a sensation, and if it exists it is real and not delusive. But the judgments we form respecting the causes and conditions of the sensations of which we are aware, are very often erroneous and delusive enough ; and such judgments may be brought about in the domain of every sense, either by artificially contrived combinations of sensations, or by the influence of unusual conditions of the body itself. The latter give rise to what are called subjective sensations. Mankind would be subject to fewer delusions than they are, if they "Xjonstantly bore in mind their liability to false judgments, due to unusual combinations, either artificial or natural, of true sensations. Men say, " I felt," " I heard," " I saw " such and such a thing, when, in ninety-nine cases out of a hundred, what they really mean is, that they judge that cer- tain sensations of touch, hearing, or sight, of which they were conscious, were caused by such and such things. 295. Subjective Sensations. — Among subjective sensations within the doniaia of touch are the feelings of creeping and prickling of the skin which are not uncommon in certain states of the circulation. The subjective evil smells and bad tastes which accompany some diseases are very probably due to similar disturbances in the circulation of the sensory organs of smell and taste. Many persons are liable to what may bo called auditor g spectra — ^music of various degrees of complexity sounding in their ears, without any external cause, while they arc wide awake. I know not if other persons arc similarly troubled, but in reading books written by persons with whom I am ac- quainted, I am sometimes tormented by hearing the words


DELUSIONS OF JUDGMENT. 223 pronounced in the exact way in which these persons would utter them, any trick or peculiarity of voice, or gesture, being, also, very accurately reproduced. And I suppose that every one must have been startled, at times, by the extreme distinct- ness with which his thoughts have embodied themselves in ap- parent voices. The most wonderful exemplifications of subjective sensa- tion, however, are afforded by the organ of sight Any one who has witnessed the sufferings of a man labor- ing under delinum tremens (a disease produced by excessive drinking), from the marvellous distinctness of his visions, which sometimes take the form of devils, sometimes of creeping ani- mals, but almost always of something fearful or loathsome, will not doubt the intensity of subjective sensations in the domain of vision. 296. Bemarkable Case of Delusive Appearances. --But that illusive visions of great distinctness should appear, it is not necessary for the nervous system to be thus obviously de- ranged. People in the full possession of their faculties, and of high intelligence, may be subject to such appearances, for which no distinct cause can be assigned. The best iUustration of this is the famous case of Mrs. A. given by Sir David Brewster, in his " Natural Magic," the chief points of which I proceed to quote : " (1) The first illusion to which Mrs. A. was subject, was one which affected only the ear. On the 21st of December, 1830, about half-past four in the afternoon, she was standing near the fire in the hall, and on the point of going up to dress, when she heard, as she supposed, her husband's voice calling her by name. * y , come here ! come to me ! ' She imagined that he was calling at the door to have it opened ; but upon going there and opening the door, she was surprised to find no person there. Upon returning to the fire she again heard the same voice calling out very distinctly and loudly,

  • , come, come here I ' She then opened two other doors

of the same room, and upon seeing no person, she returned to


224 ELEMENTARY PHYSIOLOGY. the fireplace. After a few moments she heard the same voice still calling, * Come to me, come ! come away ! ' in a loud, plaintive, and somewhat impatient tone; she answered as loudly, * Where are you ? I don't know wheixi you are,' still imagining that he was somewhere in search of her; but re- ceiving no answer, she shortly went up-stairs. On Mr. A.'s return to the house, about half an hour afterward, she inquired why he called to her so often, and where he was, and she was of course greatly surprised to learn that he had not been near the house at the time. A similar illusion, which excited no par- ticular notice at the time, occurred to Mrs. A. when residing at Florence, about ten years before, and when she was in perfect health. When she was undressing after a ball, she heard a voice call her repeatedly by name, and she was at that time unable to account for it. " (2) The next illusion which occurred to Mrs. A. was of a more alarming character. On the 30th of December, about four o'clock in the afternoon, Mrs. A. came down-stairs into the drawing-room, which she had quitted only a few minutes before, and on entering the room she saw her husband, as she supposed, standing with his back to the fire. As he had gone out to take a walk about half an hour before, she was surprised to see him there, and asked him why he had returned so soon. The figure looked fixedly at her with a serious and thoughtftil expression of countenance, but did not speak. Supposing that his mind was absorbed in thought, she sat down in an arm- chair near the fire, and within two feet, at most, of the figure, which she still saw standing before her. As its eyes, however, still continued to be fixed upon her, she said, after the lapse of a few minutes, * Why don't you speak ? ' The figure imme- diately moved off toward the window at the farther end of the room, with its eyes still gazing on her, and it passed so very close to her in doing so, that she was struck by the cir- cumstance of hearing no step or sound, nor feeling her clothes brushed against, nor even any agitation in the air. " Although she was now convinced that the figure was not


DELUSIONS OF JUDGMENT. 225 her husband, yet she never for a moment supposed that it was any thing supernatural, and was soon convinced that it was a spectral illusion. As soon as this conviction had established itself in her mind, she recollected the experiment which I had suggested of trying to doubie the object ; but before she was able distinctly to do this, the figure had retreated to the win- dow, where it disappeared. Mrs. A. immediately followed it, shook the curtains, and examined the window, the impression having been so -distinct and forcible, that she was unwilling to believe that it was not a reality. Finding, however, that the figure had no natural means of escape, she was convinced that she had seen a spectral apparition like that recorded in Dr. Hibbert's work, and she consequently felt no alarm or agita- tion. The appearance was seen in bright daylight, and lasted four or five minutes. When the figure stood close to her, it concealed the real objects behind it, and the apparition was fully as vivid as the reality. " (3) On these two occasions Mrs. A. was alone, but when the next phantom appeared, her husband was present. This took place on the 4th of January, 1830. About ten o'clock at night, when Mr. and Mrs. A. were sitting in the drawing- room, Mr. A. took up the poker to stir the fire, and when he was in the act of doing this, Mrs. A. exclaimed, ' Why, there's the cat in the room ! ' * Where ? ' exclaimed Mr. A. * There, close to you,' she replied. * Where ? ' he repeated. * Why, on the rug to be sure, between yourself and the coal-scuttle.' Mr. A., who had still the poker in his hand, pushed it in the direction mentioned. * Take care,' cried Mrs. A., * take care ! you are hitting her with the poker.' Mr. A. again asked her to point out exactly where she saw the cat. She replied,

  • Why, sitting up there close to your feet on the rug ; she is

looking at me. It is Kitty — come here, Kitty 1 ' There were two cats in the house, one of which went by this name, and they were rarely, if ever, in the drawing-room. " At this time Mrs. A. had no idea that the sight of the cat was an illusion. When she was asked to touch it, she got up 10*

VjOOQ IC 

226 ELEMENTARY PHYSIOLOGT. for the purpose, and seemed as if she were pursuing something which moved away. She followed a few steps, and then said,

  • It has gone under the chair.' Mr. A. assured her that it was

an illusion, but she would not believe it. He then lifted up the chair, and Mrs. A. s^w nothing more of it. The room was searched all over, and nothing found in it There was a dog lying on the hearth, who would have betrayed great uneasiness if a cat had been in the room, but he lay perfectly quiet In order to be quite certain, Mr. A. rang the bell, and sent for the cats, both of which were found in the housekeeper's room. " (4) About a month after this occurrence, Mrs. A., who had taken a somewhat fatiguing drive during the day, was preparing to go to bed about eleven o'clock at night, and, sit- ting before the dressing-glass, was occupied in arranging her hair. She was in a listless and drowsy state of mind, but fully awake. When her fingers were in active motion among the papillotes, she was suddenly startled by seeing in the mirror the figure of a near relative, who was then in Scotland, and in perfect health. The apparition appeared over her left shoulder, and its eyes met hers in the glass. It was enveloped in grave- clothes, closely pinned, as is usual with corpses, round the head and under the chin ; and though the eyes were open, the features were solemn and rigid. The dress was evidently a shroud, as Mrs. A. remarked even the punctured pattern usu- ally worked in a peculiar manner round the edges of that gar- ment Mrs. A. described herself as, at the time, sensible of a feeling, like what we conceive of fascination, compelling her, for a time, to gaze upon this melancholy apparition, which was as distinct and vivid as any reflected reality could be, the light of the candle upon the dressing-table appearing to shine fully upon its face. After a few minutes she turned round to look for the reality of the form over her shoulder, but it was not visible, and it had also disappeared from the glass when she looked again in that direction.

  • 'k * * *

" (7) On the l7th March, Mrs. A. was preparing for bed.

VjOOQ IC 

DELUSIONS OF JUDGMENT. 227 She had dismissed her maid, and was sitting with her feet in hot water. Having an excellent memory, she had been think- ing upon and repeating to herself a striking passage in the Edinburgh Review^ when, on raising her eyes, she saw seated in a large easy- chair before her the figure of a deceased friend, the sister of Mr. A. The figure was dressed, as had been usual with her, with great neatness, but in a gown of a peculiar kind, such as Mrs. A. had never seen her wear, but exactly such as had been described to her by a common friend as having been worn by Mr. A.'s sister during her last visit to England. Mrs. A. paid particular attention to the dress, air, and appear- ance of the figure, which sat in an easy attitude in the chair, holding a handkerchief in one hand. Mrs. A. tried to speak to it, but experienced a diflSculty in doing so, and in about three minutes the figm*e disappeared. "About a minute afterward, Mr. A. came into the room, and found Mrs. A. slightly nervous, but fully aware of the de- lusive nature of the apparition. She described it as having all the vivid coloring and apparent reality of life ; and for some hours preceding this and other visions she experienced a pecu- liar sensation in her eyes, which seemed to be relieved when the vision had ceased.

"(9) On the 11th October, when sitting in the drawing- room, on one side of the fireplace, she saw the figure of an- other deceased friend moving toward her from the window at the farther end of the room. It approached the fireplace, and sat down in the chair opposite. As there were several persons in the room at the time, she describes the idea uppermost in her mind to have been a fear lest they should be alarmed at her staring, in the way she was conscious of doing, at vacancy, and should fancy her intellect disordered. Under the influence of this fear, and recollecting a story of a similar efiect in your * work on demonology, which she had lately read, she summoned

  • Sir Walter Scott; to whom Sir David Brewster's letters on natural magic were

addressed.


238 ELEMENTARY PUYSIOLOGY. up the requisite resolution to enable her to cross the space be- fore the firephice, and seat herself in the same chair with the figure. The apparition remained perfectly distinct till she sat down, as it were, in its lap, when it vanished." 297. Personal Characteristics. — It should be mentioned that Mrs. A. was naturally a person of very vivid imagination, and that, at the time the most notable of these illusions ap- peared, her health was weak from bronchitis and enfeebled di- gestion. It is obvious that nothing but the singular courage and clear intellect of Mrs. A. prevented her from becoming a mine of ghost-stories of the most excellently authenticated kind. And the particular value of her history lies in its showing, that the clearest testimony of the most unimpeachable witness may be quite inconclusive as to the objective reality of something which the witness has seen. 298. The Senses not at Fault,— Mrs. A. undoubtedly saw what she said she saw. The evidence of her eyes as to the ex- istence of the apparitions, and of her cars to those of the voices, was, in itself, as perfectly trustworthy as their evidence would have been had the objects really existed. For there can be no doubt that exactly those parts of her retina, which would have been aflTected by the image of a cat, and those parts of her auditory organ, which would have been set vibrating . by her husband's voice, were thrown into the same condition by some internal cause. What the senses testify is neither more nor less than the fact of their own affection. As to the cause of that affec- tion they really say nothing, but leave the mind to form its own judgment on the matter. A hasty or superstitious per- son in Mrs. A.'s place would have formed a wrong judgment, and would have stood by it on the plea that " she must believe hei* senses." 299. Ventriloquism. — ^The delusions of the judgment, pro- duced not by abnormal conditions of the body, but by \inusual or artificial combinations of sensations, or by sugojestions of


DELUSIONS OF JUDGMENT. 229 ideas, are exceedingly numerous, and, occasionally, are not a little remarkable. Some of those which arise out of the sensation of touch have already been noted. I do not know of any produced through smell or taste, but hearing is a fertile source of such errors. What is called Ventriloquism (speaking from the belly), and is not uncommonly ascribed to a mysterious power of producing voice somewhere else than in the larynx, depends entirely upon the accuracy with which the performer can simulate sounds of a particular character, and upon the skill with which he can suggest a belief in the existence of the causes of these sounds. Thus, if the ventriloquist desire to create the belief that a voice issues from the bowels of the earth, he imitates with great accuracy the tones of such a half- stifled voice, and suggests the existence of some one uttering it by directing his answers and gestures toward the ground. These gestures and tones are such as would be produced by a given cause ; and no other cause being apparent, the mind of the bystander insensibly judges the suggested cause to exist. Section III. — Visual Sensations and Mental States, 300. Optical Delnsions. — ^The delusions of the judgment through the sense of sight, optical delusions, as they are called, are more numerous than any others, because such a great number of what we think to be simple visual sensations, are really very complex aggregates of visual sensations, tactile sen- sations, judgments, and recollections of former sensations and judgments. It will be instructive to analyze some of these judgments into their principles, and to explain the delusions by the appli- cation of these principles. 301. Externality of Visible Objects. — When an external bodi/ is felt by the touch to he in a given place, the image of that body falls on a point of the retina, which lies at one end of a straight line joining the body and the retina, and traversing a

, 230 ELKMILNTARY J'lIYSIOLOOY, particular region of the centre of the eye. This straight line is called the optic axis. Converself/, when any part of the surface of tJie retina is ex- cited^ the luminous sensation is referred by the mind to some point outside the body^ in the direction of the optic axis. It is for tbis reason that when a phosphene is created by pressure, say on the outer and lower side of the eyeball, the luminous imago appears to lie above, and to the inner side of the eye. Any external object which could produce the sense of light in the part of the retina pressed upon, must, in fact, occupy this position ; and hence the mind refers the light seen to an object in that position. 302. The laveraion of the Visual Imagca— The same kind of explanation is applicable to the apparent paradox that, while all the pictures of external objects are certainly inverted on the retina by the refracting media of the eye, we neverthe- less see them upright. It is diflScult to understand this, until one reflects that the retina has, in itself, no means of indicating to the mind which of its parts lies at the top, and which at the bottom ; and that the inind learns to call an impression on the retina high or low, right or left, simply on account of the asso- ciation of such an impression with certain coincident tactile impressions. In other words, when one part of the retina is affected, the object causing the affection is found to be near the right hand; when another, the left; when another, the hand has to be raised to reach the object ; when yet another, it has to be depressed to reach it And thus the several im- pressions on the retina are called right, left, upper, lower, quite irrespectively of their real positions, of which the mmd has, and can have, no cognizance. 303. Correspondence of Objects and Images. — WJien an external body is ascertained by touch to be single, it forms but one image on the retina of a single eye ; and when two or more images fall an the retina of a single eye, they ordinarily proceed from a corresponding number of bodies which are distinct to the touch.


VISUAL SENSATIONS AND MENTAL STATES. 231 Conversely, the sensation of two or more images is judged by the mind to proceed from two or more objects. If tvfo pin-holes be made in a piece of cardboard at a dis- tance less than the diameter of the pupil, and a small object like the head of a pin be held pretty close to the eye, and viewed through these holes, two images of the head of the pin will be seen. The reason of this is, that the rays of light from the head of the pin are split by the card into two minute pen- cils, which pass into the eye on either side of its centre, and cannot be brought to one focus on account of the nearness of the pin to the eye. Hence they fall on different parts of the retina, and each pencil being very small, makes a tolerably distinct image of its own on the retina. Each of these images is now referred outward (p. 229) in the direction of the appro- priate optic axis, and two pins are apparently seen instead of one. A like explanation applies to multiplying glasses and doubly refrojcting crystals, both of which, in their own ways, split the pencils of light proceeding from 2^ single object into two or more separate bundles. These give rise to as many images, each of which is referred by the mind to a distinct ex- ternal object 304. Judgment of Distance— Perspective. — Certain visual phenomena ordinarily accompany those products of tactile sen- ' sation to which we give the name of size, distance, and form. Thus, other things being alike, the space of the retina, covered by the image of a large object, is larger than that covered by a small object ; while that covered by a near object is larger than that covered by a distant object ; and, other conditions being alikCy a near object is more brilliant than a distant one. Fur- thermore, the shadows of objects differ with the forms of their surfaces, as determined by touch. Conversely, if these visual phenomena can be produced, they inevitably suggest a belief in tlie existence of objects competent to produce the corresponding tactile sensations. What is caWed perspective, whether solid, or aerial, in draw- ing or painting, depends, on the application of these principles.


232 ELEMENTARY PHYSIOLOGY. It is a kind of visual ventriloquism — ^tlie painter putting upon his canvas all the conditions requisite for the production of images on the retina, having the fonn, relative size, and inten- sity of color, of those which would actually be produced by the objects themselves in nature. And the success of his pic- ture, as an imitation, depends upon the closeness of the resem- blance between the images it produces on the retina, and those which would be produced by the objects represented. 305. Magnifying Olasses. — ^To most persons the image of a pin, at five or six inches fi'om the eye, appears blurred and indistinct — the eye not being capable of adjustment to so short a focus. If a small hole be made in a piece of card, the cir- cumferential rays which cause the blur are cut off and the image becomes distinct. But at the same time it is magnified, or looks bigger, because the image of the pin occupies a much larger extent of the retina when close than when distant. All convex glasses produce the same effect — while concave lenses diminish the apparent size of an object, because they diminish the size of its image on the retina. 308. Why the Sun and Moon look larger near the Horizon. — ^The moon, or the sun, when near the horizon ap- pear very much larger than they are when high in the sky. When in the latter position, in fact, we have nothing to com- pare them with, and the small extent of the retina which their images occupy suggests small absolute size. But, as they sot, we see them passing behind great trees and buildings which we know to be very large and very distant, and yet occupying a larger space on the retina than the latter do. Hence the vague suggestion of their larger size. 307. Judgment of Form by Shadows.— If a convex sur- face be lighted from one side, the side toward the light is bright — that turned from the light, dark, or in shadow — while a concavity is shaded on the side toward the light, bright on the opposite side. If a new half-crown, or a medal with a well-raised head upon its face, be lighted sideways by a candle, we at once know


VISUAL SENSATIONS AND MENl'AL STATES. 233 the head to be raised (or a cameo) by the disposition of the light and shade ; and if an intaglio, or medal on which the head is hollowed out be lighted in the same way, its nature is as readily judged by the eye. But now, if either of the objects thus lighted be viewed with a convex lens, which inverts its position, the light and dark sides will be reversed. With the reversal the judgment of the mind will change, so that the cameo will be regarded as an intaglio, and the intaglio as a cameo ; for the light still comes from where it did, but the cameo appears to have the shadows of an intaglio, and vice versa. So completely, how- ever, is this interpretation of the facts a matter of judgment, that if a pin be stuck beside the medal so as to throw a shadow, the pin and its shadow, being reversed by the lens, will suggest that the direction of the light is also reversed, and the medals will seem to be what they really are. 308. Judgment of Changes of Form. — WJienever an ex- ternal object is watched rapidly changing itsform^ a continuous series of different piciiires of the object is impressed upon the same spot of tlie retina. Conversely, if a continuous series of different pictures of one object is impressed upon one part of the retina, the mind judges that they are due to a single external object, undergoing changes of form. This is the principle of the curious toy called the thauma- trope, by the help of which, on looking through a hole, one sees images of jugglers throwing up and catching balls, or boys playing at leap-frog over one another's backs. ' This is man- aged by painting at intervals, on a disk of card, figures and jugglers in the attitudes of throwing, waiting to catch, and catching ; or boys " giving a back," leaping, and coming into position after leaping. The disk is then made to rotate before an opening, so that each image shall be presented for an in- stant, and follow its predecessor before the impression of the latter has died away. The result is, that the succession of dif- ferent pictures irresistibly suggests one or more objects under-


234 ELEMENTARY PHYSIOLOGY. going successive changes — the juggler seems to throw the balls, and the boys appear to jump over one another's backs. 309. Single Vision with Two Eyes. — When an external object is ascertained by touch to be single^ the centres of its reti- nal images in the two eyes fall upon the centres of the yellow spots of the two eyeSy when both eyes are directed toward it ; but if there be two external objects, the centres of both their images cannot fall, at the sams time, upon the centres of the yel- low spots. Conversely, when the centres of two images, formed simul- taneously in the two eyes, fall upon the centres of the yellow spots, the mind judges the images to be caused by a single exter- nal object : but if not, by two. This seems to be the only admissible explanation of the facts, that an object which appears single to the touch and when viewed with one eye, also appeal's single when it is viewed with both eyes, though two images of it are necessarily formed; and on the other hand, that when the centres of the two im- ages of one object do not fall on the centres of the yellow spots, both images are seen separately, and we have double vision. In squinting, the axes of the two eyes do not converge equally toward the object viewed. In consequence of this, when the centre of the image formed by one eye falls on the yellow spot, the corresponding part of that formed by the other eye does not, and double vision is the result. 310. The Fseudoscope. — In single vision with two eyes, the axes of the two eyes, of the movements of which the muscular sense gives an indication, cut one another at a greater angle when the object approaches, at a less angle when it goes farther of. Conversely, if without changing the position of an object, the axes of the two eyess, which view it can be made to cmiverge or diverge, the object will seem to approach or go farther off. In the instrument called the pseudoscope, mirrors or prisms are disposed in such a manner that the rays of light from a stationary object can be caused to alter the angle at which


VISUAL SENSATIONS AND MENTAL STATES. 235 they enter the two eyes, and so require the axes of these eyes to become more or less convergent.. In the former case the object seems to approach ; in the latter, to increase its dis- tance. 311. Judgment of Solidity— the Stereoscope.— TTAe/i a body of moderate size, ascertained hy touch to he solid, is viewed with both eyes, the images of it, formed hy the two eyes, are necessarily different {one showing more of its right side, the otJier of its left side), Nevertheless, they coalesce into a common image, which gives the impression of solidity. Conversely, if the two images of the right and left aspects of a solid body be made to fall upon the retince of the two eyes in such a way as to coalesce into a common image, they are judged by the mind to proceed from the single solid body which alone, under ordinary circumstances, is competent to. produce them. The stereoscope is constructed upon this principle. What- ever its form, it is so contrived as to throw the images of two pictures of a solid body, such as would be obtained by the right and left eye of a spectator, on to such parts of the retina) of the person who uses the stereoscope as would receive these images, if they really proceeded from one solid body. The mind immediately judges them to arise from a single external solid body, and sees such a solid body in place of the two pictures. The operation of the mind upon the sensations presented to it by the two eyes is exactly comparable to that which takes place when, on holding a marble between the finger and thumb, ■we at once declare it to be a single sphere (p. 221). That which is absolutely presented to the mind by the sense of touch in this case is by no means the sensation of one spheroidal body, but two distinct sensations of two convex surfaces. That these two distinct convexities belong to one sphere, is an act of judgment, or process of unconscious reasoning, based upon many particulars of past and present experience, of which we have at the moment no distinct consciousness.


236 ELEMENTARY PHYeiOLCOY. CHAPTER XII. THE NERVOUS SYSTEM AND INNEEVATION. Section I. — The Spinal Cord^— Reflex Actions. 812. Tho General ITeryoTzs System. — The sensory organs arc, as we bave seen, the channels through which particular physical agents are enabled to excite tbe sensory nerves with which these organs are connected ; and the activity of tbese nerves is evidenced by tbat of the central organ of the nervous system, which becomes manifest as a state of consciousness — the sensation. We have also seen that tbe muscles' are instruments by which a motor nerve, excited by the central organ with which it is connected, is able to produce motion. The sensory nerves, the motor nerves, and the ccntrrJ organ, constitute the greater part of the nervous system^ which, with its function of innervation^ we miist now study somewhat more closely, and as a whole. 313. The Cerebro-Spinal and Sympathetic Systems.^ The ner\ous apparatus consists of two sets of nerves and nerve centres, which are intimately connected together, and yet may be conveniently studied apart These are the cerebrospinal system and the sympathetic system. The former consists of the cerebrospinal axis (composed of the brain and spinal cord) and the cerebral and spinal nerves, which are connected with this axis. The latter comprises the chain of sympathetic ganglia, the nerves which they give off, and the nervous cords by which they are connected with one another and with the cerebro- spinal nerves. 314. Membrane of the Cerebro-Spinal Axis. — The cere- brospinal axis lies in the cavity of the stull and spinal column, the bony walls of which cavity are lined by a very tough fibrous


THE SPINAL COED — REFLEX ACTIONS. 237 membmne, serving as the periosteum of the component bones of this region, and called the dura mater. The brain and spinal corithemselves are closely invested by a very vascular fibrous tissue, called pia mater, which is continued, more or less exten- sively, into the substance of these organs along with the ves- sels. The outer surface of the pia mater ^ and the inner sur- face of the dura mxiter, pass into a delicate fibrous tissue, lined by an epithelium, which is called the arachnoid membrane. Thus one layer of arachnoid coats the brain and spinal cord, and another lines the dura mater. As these layers become continuous with one another at various points, the arachnoid forms a sort of shut sac, like the pericardium ; and, in com- mon with other serous membranes, it secretes a fluid, the arachnoid fluid, into its interior. The interspace between the internal and external layei-s of the arachnoid of the brain is, for the most part, very small ; that between the corresponding layers of the arachnoid of the spinal cord is larger. 315. The Sj^inal Cord. — ^The spinal cord (Fig. 89) is a column of grayish-white soft substance, extending from the top of the spinal canal, where it is continuous with the brain, to about the second lumbar vertebra, where it tapers oflf to a point A deep fissure, the anterior fissure, divides it in the middle line in front, nearly down to its centre ; and a similar fissure, the posterior fissure, also extends nearly to its centre in the middle line behind. The pia mater extends into each of these fissureij, and supports the vessels which supply the cord with its blood. In consequence of the presence of these tissues, only a narrow bridge of the substance of the cord connects its two halves, and this bridge is traversed throughout its entire length by a minute canal, the central canal of the cord. Each half of the cord is divided longitudinally into three equal parts, by the lines of attachment of two parallel series of delicate bundles of nervous filaments, the roots of tlie spinal nerves. The roots of the nerves which arise along that line which is nearer the posterior surface of the cord are called ^s- terior roots ; those which arise along the other line are the an-


238 ELEMENTARY PHYSIOLOGY. terior roots. A certain number of anterior and posterior roots, on the same level on each side of the cord, converge and form anterior and posterior bundles, and then the two bundlcs,#nte- rior and posterior, coalesce into the trunk of a spinal nerve ; but, before doing so, the posterior bundle presents an enlarge- ment — the ganglion of the posterior root. The trunks of the spinal nerves pass out of the spinal canal by the intervertebral foramina, or apertures between the verte- bra), and then divide and subdivide, their ultimate ramifica- tions going to the muscles and to the skin. There are thirty-one pairs of these spinal nerves, and, con- sequently, twice as many sets of roots of spinal nerves given off, in two lateral series, from each half of the cord. Fig. 89. Fio. 90. The spinal cord. — Fig. 89, a front view of a portion of the cord. On the left side, the anterior roots, ^.^., are entire ; on the right side they iM*e cat, to show the pos- terior roots, P.R. Fig. 90, a transverse section of the cord. A. the anterior fissure ; P. the posterior Assure; G. the central canal; C. the gray matter; W. the white matter. A.R, the anterior root, P.R. the posterior root, '&n. the ganglion, and 71 the trunk, of a spinal nerve. 316. Transverse Section of the Cord. — A transverse sec- tion of the cord (Fig. 90) shows that each half contains two substances — a white substance on the outside, and a grayish-red substance in the interior. And this gray substance is so dis- posed that, in transverse section, it looks something like a crescent, with one end bigger than the other, and with the concave side turned outwjird. The two ends of the crescent are called its horns or conma, the one in front being the ante- rior comu ; the one turned backward the posterior comu, Tlie convex sides of the cornua of the two halves approach one an-


THE SPINAL COED REFLEX ACTIONS. 239 other, and are joined by the bridge which contains the central canal. Many of the nerve fibres of which the anterior roots are composed may be traced into the anterior cornu, while those of the posterior roots enter the posterior comu. 317. Physiological Properties of Wervea — ^The physio- logical properties of the organs now described are very remark- able. If the trunk of a spmal nerve be irritated in any way, as by pinching, cutting, galvanizing, or applying a hot body, two things happen : in the first place, all the muscles to which fila- ments of this nerve are distributed, contract ; in the second, acute pain is felt, and the pain is referred to that part of the skin to which fibres of the nerve arc distributed. In other words, the effect of irritating the trunk of a nerve is the same as that of irritating its component fibres at their terminations. The effects just described will follow upon irritation of any part of the branches of the nerve ; except that when a branch is irritated, the only muscles directly affected, and the only part of the skin to which pain is referred, will be those to which that branch sends nerve fibres. And these effects will follow upon irritation of any part of the trunk of a nerve up to the point at which the anterior and posterior bundles unite. 318. Functions of Anterior and Posterior Boots. — If the anterior bundle of root fibres be irritated in the same way, only half the previous effects are brought about That is to say, all the muscles to which the nerve is distributed contract, but no pain is felt So again, if the posterior, ganglionated, bundle be irritated, only half the effect of irritating the whole trunk is produced. But it is the other half; that is to say, none of the muscles to which the nerve is distributed contract, but intense pain is re- ferred to the whole area of skin to which the fibres of the nerve are distributed. It is clear enough, from these experiments, that all the power of causing muscular contraction which a spinal nerve


240 ELEMENTARY PHYSIOLOGY. possesses, is lodged in the fibres which compose its anterior roots ; and all the power of giving rise to sensation, in those of its posterior roots. Hence the anterior roots are commonly called motor^ and the posterior sensory, 319. Experiment— Paralysis.— The same truth may be illustrated in other ways. Thus, if, in a living animal, the an- terior roots of a spinal nerve be cut, the animal loses all con- trol over the muscles to which that nerve is distributed, though the sensibility of the region of the skin supplied by the nerve is perfect. If the posterior roots be cut, sensation is lost, and voluntary movement remains. But, if both roots be cut, neither voluntary movement nor sensibility are any longer possessed by the part supplied by the nerve. The muscles are said to be paralyzed, and the skin may be cut, or burnt, without any sen- sation being excited. If, when both roots are cut, that end of the motor root which remains connected with the trunk of the nerve be irri- tated, the muscles contract; while, if the other end be so treated, no apparent effect results. On the other hand, if the end of the sensory root connected with the trunk be irritated, no apparent effect is produced, while, if the end connected with the cord be thus served, violent pain immediately follows. When no apparent effect follows upon the irritation of any nerve, it is not probable that the molecules of the nerve re- main unchanged. On the contrary, it would appear that the same change occurs in all cases; but a motor nerve is con- nected with nothing that can make that change apparent save a muscle ; and a sensory nerve with nothing that can show an effect but the central nervous system. 320. Molecular Changes in Irritated Nerves. —It will bo observed that in all the experiments mentioned there is evidence that, when a nerve is irritated, a something, probably a change in the arrangement of its molecules, is propagated along the nerve fibres. If a motor or a sensory nerve be irritated, at any point, contraction in the muscle, or sensation in the central organ, immediately follows. But if the nerve be cut, or even


THE SPINAL CORD REFLEX ACTIONS. 241 tightly tied at any point between the part irritated and the nguscle or central organ, the effect at once ceases, just as cut- ting a telegraph-wire stops the transmission of the electric cur- rent or impulse. When a limb, as we say, " goes to sleep," it is because the nerves supplying it have been subjected to pres- sure sufficient to destroy the nervous * continuity of the fibres. We lose voluntary control over, and sensation in, the limb, and these powers are only gradually restored as that nervous con- tinuity returns. Having arrived at this notion of an impulse travelling along a nerve, we readily pass to the conception of a sensory nerve as a nerve which, when active, brings an impulse to the central organ, or is afferent; and of a motor nerve, as a nerve which carries away an impulse from the organ, or is efferent. It is very convenient to use these terms to denote the two great classes of nerves ; for, as we shall find, there are aflferent nerves which are not sensory, while there may be in man, and cer- tainly are in animals, efferent nerves which are not motor, in the sense of inducing muscular contraction. 321. The Negative Deflection. — ^There is no difference in stnicture, in chemical or in physical character, between affer- ent and efferent nerves. The impulse which travels along them requires a certain time for its propagation, and is vastly slower than many other forces — even slower than sound. It is found that, during life, the trunk of a nerve is in a state of electrical activity, the ends of any segment being in a different polar condition to its surface. Hence, if one pole of a galvanometer be connected with the cut end of a nerve, and the other with its surface, a current passes, and the needle is deflected to a certain extent — say 20 degrees. If, under ♦Their "nervous continuity "—because thefr physical continuity is not inter- rupted as a whole, but only that of the substance which acts as a conductor of the nervous influence ; or, it may be that only the conducting power of a part of that substance is interfered with. Imagine a telegraph cable, made of delicate caoutchouc tubes, filled with mercury— a squeeze would interrupt the " electrical continuity " of the cable, without destroying its physical continuity. This analogy may not be ex- act, but It helps to make the nervous phenomena intelligible. 11


242 ELEMENTAEY PHYSIOLOGY. these circumstances, the nerve be irritated (the result of which, of course, is the propagation of an impulse along its molecules), the deviation of the needle at once diminishes, falling, say, to 15 degrees. This is called negative deflection^ and the importance of the experiment consists in the demonstration which it aflfords of the existence of a close relation between the force proper to nervous matter and one of the ordinary forces of natnre, elec- tricity — ^though this close relation must by no means be mis- taken for identity. 322. Properties of the Spinal Cord. — ^Up to this point our experiments have been confined to the nerves. We may now test the properties of the spinal cord in a similar way. If the cord be cut across (say in the middle of the back), the legs and all the parts supplied by nerves which come off below the sec- tion, will be insensible and incapable of movement by any ef- fort of the will ; while all the parts above the section will retain their ordinary powers. When a man hurts his back by an accident, the cord is not unfrequently so damaged as to be virtually cut in two, and then paralysis and insensibility of the lower part of the body ensue. If, when the cord is cut across in an animal, the face of the end below the cnt, or away froril the brain, be irritated, violent movements of all the muscles supplied by nerves given off from the lower part of the cord take place, but there is no sensa- tion. On the other hand, if the posterior root of any nerve attached to the part of the cord, which is still connected with the brain, be irritated, great pain ensues, but there is no move- ment of the muscles of the part below the cut. 323. Keflex Action through the Spinal Cord. — Thus it may be said that, in relation to the brain, the cord is a great mixed motor and sensory nerve. But it is also much more. For if the trunk of a spinal nerve be cut through, so as to sever its connection with the cord, an irritation of the skin to which the sensory fibres of that nerve are distributed, produces neither motor nor sensory effect.


THE SPINAL CORD — ^REFLEX ACTIONS. 24:3 But if the cord be cut through, so as to sever its connec- tion with the brain, irritation applied to the skin of the parts below the section, though it gives rise to no sensation, may produce violent motion of the parts supplied with motor nerves from the segment of the cord below the section. Thus, in the case supposed above, of a man whose legs are paralyzed and insensible from spinal injury, tickling the soles of the feet will cause the legs to kick out convulsively. And, as a broad fact, it may be said that, so long as both roots of the spinal nerves remain connected with the cord, irritation of any afferent nerve is competent to give rise to excitement of some, or the whole, of the efferent nerves so cortnected. If the cord be cut acroSs a second time at any distance from the first section, the efferent nerves below the second cut will no longer be affected by irritation of the afferent nerves below the cut — ^but only of those above the cut. Or, in other words, in order that an afferent impulse may be converted into an efferent one by the spinal cord, the afferent nerve must be in uninterrupted material communication with the efferent nerve, by means of the substance of the spinal cord. This peculiar power of the cord, by which it is competent to convert afferent impulses into efferent ones, is that which distinguishes it physiologically, as a central organ, from a nerve, and is called reflex action. It is a power possessed by the gray matter, and not by the white substance of the cord. 324. Distribution of Eeflex Eflfects.— The number of the efferent nerves which may be excited by the reflex action of the cord, is not regulated by the number of the afferent nerves which are stimulated by the irritation which gives rise to the reflex action. Nor does a simple excitation of the afferent nerve by any means imply a corresponding simplicity in the arrangement and succession of the reflected motor impulses. Tickling the sole of the foot is a very simple excitation of the afferent fibres of its nerves ; but, in order to produce the mus- cular actions by which the legs are drawn up, a great multitude of efferent fibres must act in regulated combination. In fact,


244 ELEMENTAEY PHYSIOLOGY. in a multitude of cases, a reflex action is to be regarded rather as an order given by an afferent nerve to the cord, and executed by it, than as a raere re"bound of the afferent impulse into the first efferent channels open to it. 326. The Spinal Cord as a Conductor.— Thus the spinal cord is, in part, merely a transmitter of impressions to and from the brain ; but, in part, it is an independent nervous centre, capable of originating combined movements upon the reception of the impulse of an afferent nerve. Regarding it as a conductor, the question arises, do all parts of it conduct all kinds of impressions indifferentiy ? Or are certain kinds of impressions communicated only through particular parts of the cord? Thp following experiments farnisli a partial reply to these questions : If the anterior half of the white matter of the dorsal part of the cord be cut through, the will is no longer capable of exerting any influence on the muscles which are supplied with nerves from the lower segment of the cord. A similar section, carried through the posterior half of the white matter in this region, has no effect on the transmission of voluntary impulses. It is obvious, therefore, that in the dorsal part of the cord, nervous impulses from the brain are sent through the anterior part of the white matter. 326. Conduction of the Gray Matter. — ^The posterior half of the white matter may be cut through at one point, and the anterior half at a point a little higher up, so that all the white fibres shall be divided transversely by the one cut or the other without any destruction of the material continuity of the cord, or damage to the gray matter. When this has been done, irritation of those sensory nerves which are connected with parts below the section excites the sensation of pain as strongly as ever. Hence it follows, that the afferent impulses, which excite pain when they reach the brain, pass through, and are conveyed by, the gray matter. And it has been found, by experiment, that, so long as even a


THE SPINAL COED — KEFLEX ACJTIONS. 245 small portion of the gray matter remains entire, these afferent impulses are efficiently transmitted. Singularly enough, how- ever, irritation of the gray matter itself does not cause pain. If one half of the cord, say the right, be cut through, trans- versely, down to its very middle, so as to interrupt all con- tinuity of both white and gray matter between its upper and lower parts, irritation of the skin of the right side of the body, below the line of section, will give rise to as much pain as be- fore, but all voluntary power will be lost in the muscles of that side. Hence it foUows, that the channels by which the afferent impulses are conveyed must cross over, from the side of the cord which they enter to the opposite side ; while the efferent impulses, sent down from the brain, must travel along that side of the cord by which they pass out If this be true, it is clear that a longitudinal section, taken through the exact middle of the cord, will greatly impair, if not destroy, the sensibility of both sides of the body below the section, but will leave the muscles perfectly under the control of the will. And it is found experimentally that such is the case. Section II. — The Brain. 327. The Yaso-motor Centres. — Such are the functions of the spinal cord, taken as a whole. But particular regions of this organ appear to be charged with the special function of acting as centres for those vasomotor nerves which supply the muscles of the vessels and of many of the viscera. For example, the muscles of the walls of the vessels of the ear and of the skin of the head generally, are made to contract, as has been already mentioned, by nervous fibres derived, im- mediately, from the sympathetic. These fibres, however, do not arise from the sympathetic ganglia, but simply pass through them on their way from the spinal cord, to the upper dorsal region of which they can all be traced. At least, this is the only conclusion to be drawn from the facts, that irritation <Jf


210 ELEMENTAEY PHYSIOLOGY. this region of the cord produces the same effect as irritation of the vaso-motor nerves themselves, and ' that destruction of this part of the cord paralyzes them. Fig. 91. The base of the brain. --^. frontal lobe: B. teniporal lobe of the cerebral hemispheres; G.G. corpus callosum; Cb. cerobcllnm ; M. mednlla oblongata; P. the pitnltary body; /. the olfactory nervo ; II. the optic nerve ; III. IK VI, the nerves of the mascles of the eye; V. the trigeminal nerve; VII. the portlo dnra; VIII. the auditory nerve ; IX. the glossopharyngeal; X the pneumogastrlc ; XI. the spinal accessory ; XII. the hypoglossal, or motor nerve of the tongne. The number VL Is placed upon the Pmis Varolii. The crura cerebri are the broad bundles of fibres which lie between the thiid and the fourth nerves on each side. The gray matter of the upper part of the cord is therefore a vaso-motor centre for the head and face. 328. Outlines of Anatomy of the Brain. — The brain (Fig. 91) is a complex organ, consisting of several parts, the hindermost of which, termed medulla oblongata^ passes insen-


THE BRAIN. 247 sibly into the spinal cord, and, in its lower part, has the same structure as the spinal cord. Above, however, it widens out, and the central canal, spreading with it, becomes a broad cavity, which (leaving cer- tain anatomical minutiae aside) may be said to be widely open above. This cavity is termed the fourth ventricle. Over- hanging the fourth ventricle is a great laminated mass, the cerebellum {Cb. Figs. 91, 93). On each side, this organ sends down several layers of transverse fibres, which sweep across Pig. 92. A vertical and transyerse section of the brain, taken lust behind the pituitary body, P.^Sv. the Sylvian flssare; CO. the corpus callosom; F. the fornix : V. the latetal ventricle ; Th. the optic thalamns ; Op. the optio nerve; ///. the third ventricle; V. the lateral ventricle; F', its descending horn. the brain and meet in the middle line of its base, forming a kind of bridge (called Pons Varolii, Fig. 91) in front of the medulla oblongata. The longitudinal nerve fibres of the me- dulla oblongata pass forward among, and between, these layers of transverse fibres ; and become visible, in front of the pons, as two broad diverging bundles, called crura cerebri (Fig. 91). Above the crura cerebri lies a mass of nervous matter raised up into four hemispherical elevations, called corpora quadriffemina (Fig. 93). Between these and the crura cerebri is a narrow


248 ELEMENTAEY PHYSIOLOGY. passage, which leads from the fourth ventricle into what is termed the third ventricle of the brain (Fig. 92, ///.). The third ventricle is a narrow cavity lodged between two great masses of nervous matter, called optic thalamic into which the crura cerebri pass. The roof of the third ventricle is merely membranous; and the peculiar body of unknown function, the pineal gland, is connected with it The floor of the third ventricle is produced into a sort of funnel, which ends in another anomalous organ, the pituitary/ hody (Figs. 92, 93). The third ventricle is closed, in front, by a thin layer of nervous matter ; but, .behind this, on each side, there is an aperture in the boundary wall of the third ventricle which leads into a large cavity : this occupies the centre of the cere- bral hemispTiere, and is called the lateral ventricle (Fig. 92). Each hemisphere is enlarged backward, downward, and for- ward, into as many lobes ; and the lateral ventricle presents corresponding prolongations, or comua. The floor of the lateral ventricle is formed by a mass of nervous matter, called the corpus striatum, into which the fibres that have traversed the optic thalamus enter (Figs. 92, 93). The hemispheres are so large that they overlap all the other parts of the brain, and, in the upper view, hide them. Their applied faces are separated by a median fissure for the greater part of their extent ; but, inferiorly, are joined by a thick mass of transverse fibres, the corpus callosum (Figs. 91, 92, (7.C). The outer surfaces of the hemispheres are marked out into convolutions, or gyri, by numerous deep fissures (or sulci), into which the pia mater enters. One large and deep fissure which separates the anterior from the middle division of the hemi- sphere is called the fissure of Sylvius (Fig. 92, Sy.). 329. Arrangement of the White and Oray Matter. — In the medulla oblongata the arrangement of the white and gray matter is substantially similar to what it is in the spinal cord ; that is to say, the white matter is external, and the gray inter- nal. But, in the cerebellum and cerebral hemispheres, the gray matter is external and the white internal ; while, in the optic


THE CEEEBRAL NEEVES. 24:9 thcUami and corpora striata, gray matter and white matter are variously intermixed Section III. — The Cerebral J^erves, 380. Their DistributioiL — Nerves are given off from the brain in pairs, which succeed one another from before back- ward, to the number of twelve (Fig. 93). The Jirst pair, counting from before'backward, are the ^tfao- tory nerves, and the second are the optic nerves. The functions of these have already been described. The third pair are called wiofwe* oculi (movers of the eye), because they are distributed to all the muscles of the eye ex- cept two. The nerves of the fourth pair and of the sixth pair supply, each, one of the muscles of the eye, on each side ; the fourth going to the superior oblique muscle, and the sixth to the ex- ternal rectus. Thus the muscles of the eye, small and close together as they are, receive their nervous stimulus by three distinct nerves. Each nerve of the fifth pair is very large. It has two roots, a motor and a sensory, and frirther resembles a spinal nerve in having a ganglion on its sensory root It is the nerve which supplies the skin of the face and the muscles of the jaws, and, having three chief divisions, is often called trigeminal. The seventh pair furnish with motor nerves the muscles of the face, and some other muscles, and are called /aaaZ. The eighth pair are the auditory nerves. As the seventh and eighth pairs of nerves leave the cavity of the skull together, they are often, and especially by English writers on anatomy, reckoned as one, divided into portio dura, or hard part (the facial) ; and portio mollis^ or soft part (the auditory) of the " seventh " pair. The ninth pair in order, the glossopharyngeal, are mixed nerves ; each being, partly, a nerve of taste, and, partly, a motor nerve for the pharyngeal muscles. 11*


250 ELEMENTARY PHYSIOLOGY. The tenth pair is formed by the two pneumogastric nerves. These very important nerves, and the next pair, are the only cerebral nerves which are distributed to regions of the body remote from the head. The pneumogastric supplies the larynx, the lungs, the liver, and the stomach. Fig. 98. A diagram Illustrating the arrangement of the parts of the brain and the origin of the nerves.— JK the cerebral hemispheres; C.& con>as striatum; Th. optic thala- mus; P. pineal gland; PL pituitary body; CQ. corpora quadrigemina; (7ft. cerebellum; Jf. medulla oblongata ; I.-Xll. the pairs or cerebral nerves; Sp, 1, 8fp, % the first and second pairs of spinal nerves. The eleventh pair again, called spinal accessory, differ widely from all the rest, in arising from the sides of the spinal marrow, between the anterior and posterior roots of the dorsal nerves. They run up, gathering fibres as they go, to the medulla ob- longata, and then leave the skull by the same aperture as the pneumogastric and glossopharyngeal. They are purely motor nerves, while the pneumogastric is mainly sensory, or at least afferent. As, on each side, the glossopharyngeal, pneumogas- tric, and spinal accessory nerves leave the skull together, they are frequently reckoned as one pair, which is then counted as the eighth. The last two nerves, by this method of counting, become


THE CEEEBEAL NEEVES. 251 the ninth pair, but they are, really, the twelfth. They are the motor nerves which supply the muscles of the tongue. 331. Olfitctory and Optic Nerves. — Of these nerves, the two foremost pair do not properly deserve that name, but are really processes of the brain. The olfactory pair are prolonga- tions of the cerebral hemispheres ; the optic pair, of the walls of the third ventricle ; and it is worthy of remark, that it is only these two pair of what may be called false nerves which arise from any part of the brain but the medulla oblongata — all the other, true nerves, being indirectly, or directly, traceable to that part of the brain, while the olfactory and optic nerves are not so traceable. 332. Effects of Injuries to the Hednlla Oblongata. — As might be expected from this circumstance alone, the me- dulla oblongata is an extremely important^ part of the cerebro- spinal axis, injury to it giving rise to immediate evil conse- quences of the most serious kind. Simple puncture of one side of the floor of the fourth ven- tricle at onceyjroduces an increase of the quantity of sugar in the bloo^^b^ond that which can be destroyed in the organ- ism. The sugar passes off by the kidneys, and thus this slight injury to the medulla gives rise to the disease called diabetes. More extensive injuiy arrests the respiratory processes, the medulla oblongata being the nervous centre which gives rise to the contractions of the respiratory muscles, and keeps the respi- ratory pump at work. If the injuries to the medulla oblongata be of such a kind as to irritate the roots of the pneumogastric nerve violently, death supervenes by the stoppage of the heart's action in the manner already described (p. 62). 333. Crossing of Lnpnlses in the Medulla. — ^The chan- nels of the afferent impulses, which are transmitted by the cord • to the brain and awake sensation there, as we have seen, cross from one half of the cord to the other, immediately after they enter it by the posterior roots of the spinal nerves ; while the channels for the efferent, or volitional, impulses from the brain

Googl| 252 ELEMENTABY PHYSIOLOGY. remain, throughout the cord, in that half of it from which they will eventually pass by the anterior roots. But, at the lower and front part of the medulla oblongata, these also cross cover ; and the white fibres which convey them are seen passing ob- liquely from left to right and from right to left in what is called the decussation of the anterior pyramids (Fig. 91). Hence, any injury, at a point higher up than the decussation, to the nerve fibres which convey motor impulses from the brain, paralyzes the muscles of the body and limbs of the opposite side. Division of one of the crura cerebri^ say the right, there- fore, gives rise to paralysis of the left side of the body and limbs, and the animal operated upon falls over to the left side, because the limbs of that side are no longer able to support its weight. But as the motor nerves given off from the brain itself do not cross over in this way, it follows that disease or injury at a given point on one side of the medulla oblongata, involving at once the course of the volitional motor chann^to the spinal marrow and the origins of the cerebral mot™mfves, will affect the same side of the head as that of the injury, but the opposite side of the body. If the origin of the left facial nerve, for example, be injured, and the volitional motor fibres going to the cord destroyed, in the upper part of the medulla oblongata, the muscles of the • face of the left side will be paralyzed, and the features will be drawn over to the opposite side, the muscles of the right side having nothing to counteract their action. But it is the right arm, and the right leg and side of the body, which will be powerless. Section IV. — Uncomcious Cerebration, 334. Seat of Tntelligence and WilL — The functions of most of the parts of the brain which lie in front of the medulla oblongata are, at present, very ill understood ; but it is certain


UN00NS0I0U8 CEREBBATION. 253 that extensive injury, or removal, of the cerebral hemispheres puts an end to intelligence and voluntary movement, and leaves the animal in the condition of a machine, working by the reflex action of the remainder of the cerebro-spinal axis. Thus there can be no doubt that the cerebral hemispheres are the seat of powers, essential to the production of those phenomena which we term intelligence and will ; but there is no satirfactory proof, at present, that the manifestation of any particular kind of mental faculty is especially allotted to, or connected with, the activity of any particular region of the cerebral hemispheres. 335. Keflex Action of the Brain. — ^Even while the cerebral hemispheres are entire, and in faW possession of their powers, the brain gives rise to actions which are as completely reflex as those of the spinal cord. When the eyelids wmk at a flash of light, or a threatened blow, a reflex action takes place, in which the aflerent nerves are the optic, the eflerent, the facial. When a bad smell causes a grimace, there is a reflex action through the same motor , nerve, while the olfactory nerves constitute the afferent chan- nels. In these cases, therefore, reflex action must be effected throqgh the brain, all the nerves involved being cerebral. When the whole body starts at a loud noise, the afferent auditory nerve gives rise to an impulse which passes to the medulla oblongata, and thence affects the great majority of the motor nerves of the body. 336. Beflez Actions in Beading Akud. — ^It may be said that these are mere mechanical actions, and have nothing to do with the acts which we associate with intelligence. But let us consider what takes place in such an act as reading aloud. In this case, the whole attention of the mind is, or ought to be, bent upon the subject-matter of the book ; while a multitude of most delicate muscular actions are going on, of which the reader is not in the slightest degree aware. Thus the book is held in the hand, at the right distance from the eyes ; the eyes are moved, from side to side, over the lines, and up and down


254 ELEMENTARY PHYSIOLOaY. the pages. Further, the most delicately adjusted and rapid movements of the muscles of the hps, tongue, and throat, of the laryngeal and respiratory muscles, are involved in the production of speech* Perhaps the reader is standing up and accompanying the lecture with appropriate gestures. And yet every one of these muscular acts may be performed with utter unconsciousness, on his part, of any thing but the sense of the words in the book. In other words, they are reflex acts. 337. Artificial Beflez Actions— Education.— The reflex actions proper to the spinal cord itself are natural, and are involved in the structure of the cord and the properties of its constituents. By the help of the brain we may acquire an infinity of artificial reflex actions. That is to say, an action may require all our attention and all our volition for its first, or second, or third performance, but by frequent repetition it becomes, in a manner, part of our organization, and is per- formed without volition, or even consciousness. As every one knows, it takes a soldier a long time to learn his drill — to put himself, for instance, into the attitude of " at- tention " at the instant the word of command is heard. But, after a time, the sound of the word gives rise to the act, whether the soldier be thinking of it or not There is a story, which is credible enough, though it may not be true, of a prac- tical joker, who, seeing a discharged veteran carrying home his dinner, suddenly called out " Attention*! " whereupon the man instantly brought his hands down, and lost his mutton and potatoes in the gutter. The drill had been thorough, and its effects had become embodied in the man's nervous structure. The possibility of all education (of which military drill is only one particular form) is based upon the existence of this power which the nervous system possesses, of organizing con- scious actions into more or less unconscious, or reflex, opera- tions. It may be laid down as a rule, that, if any two mental states be called up together, or in succession, with due fre- quency and vividness, the subsequent production of the one of


UNCONSCIOUS CEREBRATION. 256 them will suflSce to call up the other, and that whether we de- sire it or not. The object of intellectual education is to create such indis- soluble, associations of our ideas of things, in the order and relation in which they occur in nature ; that of moral educa- tion is to unite, as fixedly, the ideas of evil deeds with those of pain and degradation, and of good actions with those of pleasure and nobleness. 338. The Sympathetic System. — ThQ sympathetic system consists, chiefly, of a double chain of ganglia, lying at the sides and in front of the spinal column, and connected with one another, and with the spinal nerves, by commissural cords. From these ganglia nerves are given off, which for the most part follow the distribution of the vessels, but which, in the thorax and abdomen, form great net-works, or plexuses^ upon the heart and about the stomach. It is probable that a great proportion of the fibres of the sympa- thetic system is derived from the spinal cord ; but others also, in all probability, originate in the gangha of the sympathetic itself. The sympathetic nerves influence the muscles of the vessels generally, and those of the heart, of the intestines, and of some other viscera; and it is probable that their ganglia are centres of reflex action to afferent nerves from these organs. But many of the motor nerves of the vessels are, as we have seen, under the influence of particular parts of the spinal cord, though they pass through sympathetic ganglia. CHAPTER XIII. HISTOLOGY; OB, THE MINUTE STRUCTUEE OP THE TISSUES. Section I. — Dermal Tissues. 339. The Microscopical Analysis of J;he Body. — The va- rious organs and parts of the body, the working of which has now been described, are not merely separable by the eye and


256 ELEMENTARY PHYSIOLOGY. the knife of the anatomist into membranes, nerves, muscles, bones, cartilages, and so forth ; but each of them is susceptible of a finer analysis, by the help of the microscope, into certain minute constituents which, for the present, are the ultimate structural elements of the body. 340. Nudei and Cells.— There is a time when the human body, or rather its rudiment, is of one structure throughout, consisting of a more or less transparent matrix, through which are scattered minute rounded particles of a dififerent optical aspect. These particles are called nuclei; and, as the matrix, or matter in which these nuclei are imbedded, readily breaks up into spheroidal masses, one for each nucleus, and these in- vesting masses easily take on the form of vesicles or cells, this primitive structure is called cellular, and each cell is said to be nucleated. As development goes on, the nuclei of this indifferent tissue simply increase in number, by division and subdivision ; but the substance in which they are imbedded, commonly called Fig. 9fi. Fig. 94.— Vertical eecUon of a layer of epidermis, or epithelium, firom its free to its deep surface. . ,.^ Fig. 9&---Lateral Tiews of the cells df which this hijer is composed at the different heights, ahed. Fig. 96L~8caIes such as d viewed from their flat sides.


DERMAL TISSUES. 257 the cell wall, and intercellidar substance, becomes very variously modified, both chemically and stracturally, and gives rise to the peculiarities of the different, completely formed tissues. 341. Epidermis and Epithelium. — ^Among these, the epidermis and some forms of epithelium present the simplest stracture, next to the blood and lymph corpuscles described above (Chapter IV). These tissues are constantly growing in their deepest parts, and are, as constantly, being shed at their surfaces. The deep part consists of a layer of such globular nucleated cells, as have been mentioned, the number of which is con- stantly increasing by the spontaneous division of the nuclei and cells. The increase in number thus effected causes a thrusting of the excess of cell population toward the surface ; on their way to which they become flattened, and their walls acquire a horny texture. Arrived at the surface, they arc mere dead homy scales, and are thrown off. Epithelium of the kind just described is called squamous. It is found in the mouth, and its scales may always be obtained in abundance by scraping the inside of the lip. ^ Fig. 97. Ciliated epitholinm.— a, the submucous vascular tissue ; &, the deep layer of young epithelium cells; c, the cylindrical fUU-grown cells, with (d) the cilia. In other parts of the alimentary tract, as in the intestines, the full-grown epithelial cells are placed side by side with one another, and perpendicular to the surface of the membrane. Such epithelium is called cylindrical (Fig. 58).


258 ELEMENTAEY PHYSIOLOGY. In many glands (Fig. 66) the epithelial cells remain glohu- lavy and enlarging, eventually burst and disappear, to be re- placed by others. Ciliated epithelium is usually of the cylindrical kind, and differs from other epithelium only in the circumstance that one, or more, incessantly vibrating filaments are developed from the free surface of each cell. PiQ. 100. Fig. 98.— A longitadinal and verticftl section of a nail: a, the fold at the base of the nail ; &, the nail ; c, the bed of the nalL Fig. 99 is a transverse section of the same — a, small lateral folds of tho intefimment ; ft, nail; c. bed of the nail, with its ridges. Fig. 100 is a highly-magnified view of a part of the foregoing— c, the ridges ; cf, the deep layers of epidermis ; e, the homy scales, coalesced Into nail substance. 342. Naik. — In certain regions of the integument, the epi- dei-mis becomes metamorphosed into nails and hairs. Underneath each nail the deep layer of the integument is


DERMAL TISSUES. 259 peculiarly modified to form the bed of the nail. It is very vas- cular, and raised up into numerous parallel ridges, like elongated papilla) (Figs. 99, 100). The surfaces of all these are covered with growing epidermic cells, which, as they flatten and be- come converted into horn, coalesce into a solid continuous plate, the nail. At the hinder part of the bed of the nail, the integument forms a deep fold, from the bottom of which, in like manner, new epidermic cells are added to the base of the nail, which is thus constrained to move forward. The nail, thus constantly receiving additions from below and from behind, slides forward over its bed, and projects be- yond the end of the finger, where it becomes worn or cut off, 343. Hair& — ^A hair, like a nail, is composed of coalesced homy cells, but instead of being only partially sunk in a fold of the integument, it is at first wholly enclosed in a kind of bag, the hair-sac, from the bottom of which a papilla, which answers to a single ridge of the nail, arises. The hair is developed by the conversion into horn, and coalescence into a shafty of the superficial epidermic cells coating the papilla. These coalesced and comified cells being continually replaced by new growths from below, which undergo the same metamorphosis, the shaft of the hair is thrust out until it attains the fiill length natural to it. Its base then ceases to grow, and the old papilla and sac die away, but not before a new sac and papilla have been formed by budding from the sides of the old one. These give rise to a new hair. The shaft of a hair of the head consists of a central pith, or medullar^/ matter, of a loose and open tex- ture, and sometimes containing air; of a cortical substance surroimding this, made up of coalesced elongated horny cells ; and of an outer cuticle, composed of flat homy plates, arranged transversely round the shaft;, so as to overlap one another by their outer edges, like closely-packed tiles. The superficial epidermic cells of the hair-sac also coalesce by their edges, and become converted into sheaths, which embrace the root of the hair, and usually come away with it, when it is plucked out. Two sebaceous glands commonly open into the hair-sac


260 ELEMENTABY PHYSIOLOGY. near its opening, and supply the hair with a kind of natural pomatum ; and delicate unstriped muscular fibres are so con- nected with the hair-sac, as to cause it to pass from its ordi- nary oblique position into one perpendicular to the skin, when they contract (Fig. 46). Fig. lot Part of the shaft of a hair enclosed within its sac and treated with canstlc soda, which has caused the shaft to become distorted. — a, medulla ; b. cortical port; e, cuUcle of the shaft ; d and e, inner and outer root-shcaths ; / wall of the hair-sac They are caused to contract by the influence of cold and terror, which thus give rise to " horripilation " or "goose-skin," and the " standing of the hair on end." Sbction II. — Interior Tissues. 344. The CryBtalline Iens.--The crystalline lens is com- posed of fibres (p. 210), which are the modified cells of the epidermis of that inverted portion of the integument, from which the whole anterior chamber of the eye and the lens are primitively formed. 345. Cartilage. — ^While epithelium and epidermis are found only on the free surfaces of the organs, gristle, or cartilage, is a deep-seated structure (see Chapter VIII). It is composed of a semi-transparent, resisting, elastic matter, which yields the substance called chondrine by boiling, and contains a great number of minute cavities, in which lie single nucleated cells, or groups of such cells (Fig. 102). These cells increase in number by division. Cartilage contains no vessels, or only such as extend into it from adjacent parts.


INTERIOB TISSUES. 261 846. Connective Tissue. — Connective Tissue (also called fibrous, or areolar^ or sometimes cellular tissue). Fig. 102. A section of cartilage, showing tLo matrix (a\ with the groups of cells (5) contain- ing nnclel (c) and mt globules {d). This tissue, the most extensively diffused of all in the body, consists of bands or cords, or sheets of whitish substance, having a wavy, fibrous appearance, and capable of bebg split Fig. 108. Fro. 104. Connective tissue.— Fig. 108, unchanged— <r, connective tissue ; 6, tat cells ; Fig. 104, acted upon by acetic acid, and showing (a) the swollen and transparent gelatine- yielding matter, and (b) the clastic fibres.


262 ELEMENTAJBY PHYSIOLOGY. • up mechanically into innumerable fine filaments. This tissue swells up and yields gelatine when it is boiled in water. The addition of strong acetic acid also causes it to swell up and be- come transparent, entirely losing its fibrous aspect ; and, further, reveals the presence of two elements which acetic acid does not affect, viz., nuclei and elastic fibres of different degrees of fine- ness If the acid be now neutralized by a weak alkali, the connective tissue assumes its former partial opacity and fibril- lated aspect The nuclei are the descendants of those which existed in the indifferent tissue from which the connective tissue has proceeded — while the elastic fibres, like the gelatine-yield- ing fibres, proceed from the metamorphosis of the matrix. The proportion of elastic fibre to the gelatine-yielding con- stituents of connective tissues varies, in different parts of the body. Sometimes it is so great that elasticity is the most marked character of the resulting tissue. Ligaments and tendons are simply cords, or bands, of very dense connective tissue. In some parts of the body the con- nective tissue is more or less mixed with, or passes into, carti- lage, and such tissues are called fihro-cartilages (see Chapter VIII.). Fat cells.— Fig. 105, having their nataral aspect; Fig. 106, collapsed, the fat being Fig. 105. Fia. lOGu Fig. 107. _ ^. 105, having their nataral as] exhausted ; Fig. 107, with fatty crystals. 347. Fat Cells are scattered through the connective tissue, in which they sometimes accumulate in great quantities. They are spheroidal sacs, composed of a delicate membrane, on one


INTERIOR TISSUES. 263 side of wliich is a nucleus, and distended by fatty matter, from which the more solid fats sometimes crystallize out. Ether will dissolve out the fat, and leave the sacs empty and col- lapsed (Fig. 106). Considerable aggregations of fat cells are constantly pres- ent in some parts of the body, as in the orbit, and about the kidneys and heart, but elsewhere their presence, in any quan- tity, depends very much on the state of nutrition. Indeed, they may be regarded simply as a reserve, formed from the nutriment which has been taken into the body in excess of its average consumption. 348. Pigment-Cells are either epidermic or epithelial cells, in which colored granules are deposited, or they are particular cellular elements of the deeper parts of the body, in which a like deposit occurs. Thus the color of the choroid and of the iris arises from the presence of a layer of such cells. Section III. — Osseous Tissues. 349. Structure of Bone. — ^Bone is essentially composed of an animal basis impregnated with salts of carbonate and phos- phate of lime, through the substance of which are scattered minute cavities — the lacunce, which send out multitudinous ramifications, called canaliculi. The canaliculi of diflferent lacunse unite together, and thus establish a communication be- tween the different lacunae. If the earthy matter be extracted by dilute acids, a nucleus is constantly found in each lacunae ; and, not unfrequently, the intermediate substance appears mi- nutely fibrillated. In a dry bone the lacunae are usually filled with air. When a thin section of such a bone is, as usual, covered with water and a thin, glass, and placed under the microscope, the air in the lacunae refracts the light which passes through them, in sucji a manner, as to prevent its reaching the eye, and they appear black. Hence the lacunae were, at one time, supposed to be solid bodies, containing the lime salts of the bone, and were called bone corpuscles (Fig. 110).


284 ELEMENTARY PHYSIOLOGY. All bones, except the smallest, are traversed by small canals, converted by side branches into a net-work, and con- taining vessels supported by more or less connective tissue and fatty matter. Those are called Haversian canals (Figs. 108, 109). They always open, in the long run, upon the surface of the bone, and there the vessels which they contain become connected with those of a sheet of tough connective tissue, which invests the bone, and is called periosteum. In many long bones, such as the thigh-bone, the centre of the bone is hollowed out into a considerable cavity, containing great quantities of fat, supported by a delicate connective tis- sue, rich in blood-vessels, and called the marrow, or medulla. The inner ends of the Haversian canals communicate with this cavity, and their vessels are continuous with those of the mar- row. When a section of a bone containing Haversian canals is made, it is found that the lacunae are dispersed in concentric zones around each Haversian canal, so that the substance of the bone appears laminated ; and, where a medullary cavity exists, more or fewer of these concentric lamellae of osseous substance surround it. 850. How Bones g^ow. — This structure arises from the mode of growth of bones. In the place of every bone there exists, at first, either cartilage, or connective tissue hardly altered from its primitive condition of indiflferent tissue. When ossification commences, the vessels from the adjacent parts extend into the ossifying tissue, and the calcareous salts are thrown down around them. These calcareous salts invade all the ossifying tissue, except the immediate neighborhood of its nuclei, around each of which a space, the lacuna, is left. The lacunae and canaliculi are thus, substantially, gaps left in the ossific matter around each nucleus, whence it is that nuclei are found in the lacunae of fully-formed bone. Bone, once formed, does not remain during life, but is con- stantly disappearing and being replaced in all its parts. Never- theless, the growth of a bone, as a general rule, takes place


OSSEOUS TISSUES. 265 only by addition to its free ends and surfaces. Thns the bones of the skull grow in thickness, on their surfaces, and in breadth Fig. 10& FiQ. 109. FiQ, 110. Fig. lOS. — A transTerse section of bone in the neighborhood of two Haversian canals, a a; 2>. lacunse. Fig. 109.— A longitudinal section of bone with Haversian canals, a a, and lacnnsD, & (less magnifled than the preceding). Fig. 110.— Lacunse, c, and canalicull, a, very highly magnified. 12


266 ELEMENTAUY PHYSIOLOGY. at their edges, where they unite by sutures; and when the sutures are once closed, they grow no more. The bones of the extremities, which are preceded by com- plete cartilaginous models, grow in two ways. The cartilage of which they consist grows and enlarges at its extremities un- til the bones have attained their full size, and remains to the end of life as articular cartilage. But in the middle, or shaft, of the bone, the cartilage does not grow with the increase in the dimensions of the bone, but becomes coated by successive layers of bone, produced by the ossification of that part of the periosteum which lies nearest to the cartilage. The shaft of the bone thus formed is gradually hollowed out in its interior to form the medullary cavity, so that, at last, the primitive cartilage totally disappears. When ossification sets in, the salts of lime are not diflfused uniformly through the whole mass of the preexisting cartilage, or connective tissue, but begin to be deposited at particular points called centres of ossification, and spread from them through the bone. Thus, a long bone has usually, at fewest, three centres of ossification— one for the middle or shaft, and one for each end ; and it is only in adult life that the three bony masses thus formed unite into one bone. 361. Structure of the Teeth. — Teeth partake more of the nature of bones than of any other organ, and are, in feet, partially composed of true bony matter, here called cement; but their chief constituents are two other tissues, called dentine and enamel. Each tooth presents a crown, which is exposed to wear, and one or more fangs, which are buried in a socket furnished by the dense mucous membrane of the mouth, which consti- tutes the gum. The line of junction between the crown and the fang is the neck of the tooth. In the interior of the tooth is a cavity, which communicates with the exterior by canals, which traverse the fengs and open at their points. This cavity is tbb pulp cavity. It is occupied by a highly-vascular and nervous tissue, the dental pulp, which is continuous below.


OSSEOUS TISSUES. 267 through the opening at the point of the fang, with the mucous membrane of the gum. The chief constituent of a tooth is dentine— a. dense calci- fied substance containing less animal matter than bone, and further differing from it in possessing no lacunae, or proper canaliculi. Instead of these it presents innumerable, minute, parallel, wavy tubuli, which give off lateral branches. The Fig. Ill, Tertical— rig. 112, horizontal section of a tooth.— a, enamel of the crown ; &, pnlp cavity ; e, cement of the tangs ; (f, dentine. wider ends of these tubules open into the pulp cavity, while the narrower ultimate terminations ramify on fhe surface of the dentine, and may even extend into the enamel or cement (Kg. 115). The enamel consists of very small six-sided fibres, set closely, side by side, at right angles to the surface of the den- tine, and covering the crown of the tooth as far as the neck, toward which the enamel thins off and joins the cement (Figs. 113, 114). Enamel is the hardest tissue of the body, and contains not more than two per cent, of animal matter. The cement coats the fangs, and has the structure of true


268 ELEMENTABY PHYSIOLOGY. bone ; but as it exists only in a thin layer, it is devoid of Haversian canals (Fig. 116). 362. How Teeth are Developed.— The development of the teeth commences long before birth. A groove appears in Fig. 118. Fio. 114. Fig. 116. Fig. 118.— Enamel fibres viewed in transverse section. Fig. 114. — Enamel fibres separated and viewed laterally. Fig. 115.— A section of a tooth at the junction of the dentine (a) with the cement («); h c, irregular cavities in which the tubules of the dentine end; cL, fine tubules con tinned A'om them;/ (7, lacuusB and canaliculi of the cement (All these figures are very highly magnified.) the gum of each side of each jaw ; and, at the bottom of thife groove of the gum, five vascular and nervous papillce arise,


OSSEOUS TISSUES. 269 making twenty in all. The walls of the groove grow together, between and over each of the papillae, and thus these become enclosed in what are called the dental sacs. Each papilla gradually assumes the form of the future tooth. Next a deposit of calcific matter takes place at the summit of the papilla, and extends thence, downward, toward its base. In the crown the deposit takes on the form of enamel and den- tine ; in the root, of dentine and cement As it increases it encroaches upon the substance of the papilla, which remains as the tooth pulp. The fully-formed teeth press upon the up- per walls of the sacs in which they are enclosed, and causing a more or less complete absorption of these walls, force their way through. The teeth are then, as it is called, cut The cutting of this first set of teeth, called deciduous^ or milk teeth, commences at about six months, and ends with the second year. They are altogether twenty in number — eight being cutting teeth, or incisors; four, eye teeth, or canines ; and eight, grinders, or molars. Each dental sac of the milk teeth, as it is formed, gives off a little prolongation of itself, which becomes lodged in the jaw, enlarges, and develops a papilla from which a new tooth is formed. As the latter increases in size it presses upon the root of the milk tooth which preceded it, and thereby causes the absorption of the root and the final falling out, or shedding, of the milk tooth, whose place it takes. Thus every milk tooth is replaced by a tooth of what is termed the permanent dentition. The permanent incisors and canines are larger than the milk teeth of the same name, but otherwise differ little from them. The permanent molars, which replace the milk molars, are small, and have only two points in their crowns, whence they are called bicuspid. They never have more than two fangs. 353. The Permanent Holaxa — We have thus accounted for twenty of the teeth of the adult. But there are thirty-two teeth in the complete adult dentition — ^twelve grinders being added to the twenty teeth which correspond with, and replace,


270 ELEMENTAEY PHrSIOLOaY. those of the milk set When the fifth, or hindermost^ dental sac of the milk teeth is formed, the part of the groove which lies behind it also becomes covered over, extends into the back part of the jaw, and becomes divided into three dental sacs. In these, papillee are formed and give rise to the great perma- nent back grinders, or molars^ which have four, or five, points upon their square crowns, and, in the upper jaw, commonly possess three fangs. The first of these teeth, the anterior molar of each side, is the earHest cut of all the permanent set, and appears at six years of age. The last, or hindermost, molar is the last of all to be cut> usually not appearing till twenty-one or twenty-{wo years of age. Hence it goes by the name of the wbdom tooth." Section IV. — Muscular and Nervous Tissues. 354. Husole, Striated and Smooth.— Muscle is of two kinds, striated and smooth. Striated muscle j of which all the ordinary muscles of the trunk and limbs consist, is com- posed of bundles of fibres, usually united at their ends to cords or sheets of connective tissue — ^the tendons (see Chapter VIIL). The bundles are enveloped in, and bound together by, coilnec- tive tissue, which supports the vessels and nerves of the mus- cle, and sometimes forms a dense sheath on its exterior, called SL/ascia. Into the ultimate striated mtiscular fibre neither vessels, nor connective tissue, enter. Each fibre is, in fact, enveloped in a sheath formed by a tough, elastic, transparent, structure- less membrane, the sarcolemma (Pig, 119). The sarcolemma is not contractile, but its elasticity allows it to adjust itself, pretty accurately, to the changes of form of the contractile substance which it contains. This contractile substance, when uninjured, presents a very strongly-marked transverse striation, its substance appearing to be composed of disks of a partially opaque substance, in regu-


MUSCULAR AND NEEVOUS TISSUES. 271 lar alternation with others of a more transparent matter. A more faint longitudinal striation is also observable. When the sarcolemma is torn, the contractile substance either divides into disks (Fig. 118), or more frequently and readily breaks up into minui^ fihrillcB (Figs. 116, 117), each of which, viewed Fig. 116. Fig. 11& Fia. U9. Fig. 116.— A muscular fibre, devoid of sarcolemma, and breaking up atone end into its JlbriUaf. Fig. 117.— Separate fibrlllfls. Fig. lia— A muscular fibre breaking up Into disks. . , . , , ^ , , ^„ ., Fig. 119.— A muscular fibre, the contractile substance of which (a) is torn, while the sarcolemma (b) has not giyen way. by transmitted light, presents dark and light parts, which al- ternate at intervals exactly corresponding with the distance of the transverse striae in the entire fibre. Nuclei are observed here and there in the contractile substance within the sarco- lemma. In the heart, the muscular fibres arc striated, and have the


272 ELEMENTAEY PHYSIOLOGY. same essential stractnre as that just described, but they possess no sarcolemma. Smooth muscle consists of elongated band-like fibres, de- void of striation, each of which bears a rod-like nucleus. These fibres do not break up into fibrillse, and have no sarcolemma (Fig. 11). Fig. 120. ^ Fig. 121 Fig. 128. Fig. 120.— A nerve fibre in its fresh and unaltered condition. Fig. 121.— A nerve fibre In which the jrreater part of the sheath and coagulated con- tents {a b) have been stripped off from the axis cylinder (c c). Fig. 122.— A nerve fibre, the npper part of which retains its sheath and coagulated contents, while the axis cylinder {a a) projects. Fig. 123. — A ganglionic corpuscle — a^ its nucleus. 355. Nervous Tissue. — Nervous tissue contains two ele- ments nerve fibres imd ganglionic corpuscles. Ordinary nerve fibres, such as constitute the essential constituents of all but the olfactory nerves, are, during life, or when perfectly fresh, sub- cylindrical filaments of a clear, somewhat oily, look. But, shortly after death, a sort of coagulation sets up within the


MUSCULAR AND KEBVOUS TISSUES. 273 fibre, and it is then found to be composed of a very delicate stractareless outer membrane (wLich is not to be confounded with the neurilemma), forming a tube, through the centre of which runs a solid filament, the axis cylinder. Between the axis cylinder and the tube is a fluid, from which a solid, strongly refracting matter has been thrown down and lines the tube. Such is the structure of the larger nerve fibres, which lie, side by side, in the trunks of the nerves, bound together by delicate connective tissue, and enclosed in a sheath of the same substance, called the neurilemma. In the trunks of the nerve the fibres remain perfectly distinct from one another, and rarely, if ever, divide. But when the nerves enter the central organs, and when they are distributed, the nerve fibres frequently divide into branches. In any case, they tecome gradually finer and finer ; until, at length, axis cylinder, sheath, Fig. 124. Papillfie of the skin of the finger.— a-, a large papilla containing a tactile corpuscle («) with its nerye {d)\ &, other papiUsB, without corpuscles, but containing loops of Tcssels, c. and contents are not separable, and the nerve becomes a ho- mogeneous filament, the ultimate termination of which, in the sensory organs and in the muscles, is not yet satisfactorily made out. 12*


274 BLEMENTAEY PHYSIOLOGY. 356. Tactile Corpnsdes. — ^At page 181 mention is made of peculiar bodies called tactile corpuscleSy oval masses of spe- cially modified connective tissue in relation with the ends of the nerves in the papilla of the skin. In Fig. 124 four such papillse, which have been rendered transparent and stripped of their epidermis, are seen, and the largest contains a tactile corpuscle (c). In the central organs, on the other hand, it is certain that, in many cases, the fine ends of the nerve fibres are continued into the processes of the ganglionic corpuscles. The olfactory nerves are pale flat fibres, without any dis- tinction into axis, cylinder, and contents, but with nuclei set at intervals along their length. 357. Oanglionic Corpusclea — Ganglionic corpvscles are chiefly found in the cerebro-spinal axis ; in the ganglia of the posterior nerve roots, and in those of the sympathetic; but they occur also elsewhere, notably in some of the sensory organs (see Chapter X.). They are spheroidal bodies, containing a central cavity, in which a nucleus lies (Fig. 123, a), and sending off* one, two, or more prolongations, which may divide and subdivide ; and which, in some cases, unite with the prolongations of other ganglionic corpuscles, while, \n others, they are continued into nerve fibres.


PART 11. ELEMENTARY HYGIENE. CHAPTER XIV.- "scope and aims of hygiene. 358. Twofold Value of Knowledge.— Knowledge may be considered as having a twofold value, intellectual and practi- cal. In an intellectual point of view, all real knowledge, no matter how great or how small the subject, how near or how remote, how useful or how useless, has a value which is due to intrinsic truth, to the pleasure of its pursuit, and the mental benefits which result from its acquisition. The pure love of truth, for its own sake, is a very powerful incentive to the well- cultivated intellect, and is the main impulse which has prompt- ed to scientific research and the extension of the boundaries of knowledge. But it sometimes becomes so absorbing a passion as to obscure that value of knowledge which lies in its uses. Science elucidates the laws of nature, and the human mind has a high satisfaction in this work, but the principles of science have an exalted value in their applications to art, or as fumisliing enlightened rules of action. 359. Practical Knowledge. — ^Knowledge has thus a prac- tical value ; but by this I do not mean merely its application to productive occupations, as the mechanic arts or agriculture, although it has a high value here. By practical knowledge is


276 ELEMENTABY HYGIENE. to be properly understood that which is capable of serving for guidance in the various circumstances of life, or which has a definite bearing on human welfare. Man is a being constituted for action ; all knowledge which will enable him to act most efficiently, which will help him to economize his energies and gain the largest results with the smallest expen- diture of force, is practical knowledge. He is an organized being of high complexity ; his system is liable to derangement from many causes, which produce bodily and mental suffering and disease ; the knowledge which is necessary to avoid these results is practical knowledge. He is a social being, and capa- ble of varied enjoyment : whatever understanding of his own nature, or the laws and constitution of society, will help him to the discharge of his social duties, or enable him to increase his happiness, is also of the nature of practical knowledge. 360. Applied Physioli^. — In the previous part of' the present work the student has been occupied in getting an un- derstanding of the truths of physiological science, or the ac- tions of the living system in normal conditions. This knowl- edge has two great practical applications : the first to Hygiene^ or the art of preserving health ; and the second to Medicine, or the art of restoring it. When the vital machine has once be- come seriously deranged in any of its movements, profound knowledge and great skill and experience, may be required to set it right again, and this is the work of the physician, who has to devote his life to professional study. But happily it requires less knowledge to keep what we already have than to recover it when lost How to take care of the health, or to avoid many causes of disease, may be learned by all. That general acquaintance with the mechanism and working of the living system, which all persons, even moderately educated, should possess, is not only valuable to guard it agaiiftt in- jury, but also to improve its various powers and capabilities. If life and its opportunities be valuable, what knowledge can compare in importance with that which teaches how it is to be prolonged and its various capacities augmented ?


- SCOPE AND AIMS OF HYGIENE. 277 361. False Conceptions of Disease. — In early ages it was the custom to explain all effects in nature by supposing per- sonalities like our own which produced them. The air, the earth, the forest, the streams, the sea, were peopled with ima- ginary beings, who were believed to be the agents by which all the operations of nature were carried on. The regular ac- tions of the living system were thought to be due to spirits which inhabited it, and its disorders to the agency of evil spirits. Though these superstitious long since passed away, the ideas which replaced them involved errors of a kindred nature. Diseases were no longer considered as personal agencies to be driven out by exorcism, but there still lingered the idea that they were things, independent existences or en- tities, which were in some mysterious way thrust into the sys- tem, and "expelled" from it by the action of medicines. Vague notions of this kind still widely prevail, and great num- bers regard diseases as things that come arbitrarily, or are " sent " by Divine Providence as judgments or punishments for sins. Views of this kind are unfavorable to hygienic efforts. We can easily understand that minds folly possessed by them will tend to a passive acquiescence in what is felt to be un- avoidable, and the propitiation of Divine favor by fasting, humiliations, and prayers, will take the place of intelligent, ngilant, and systematic measures for the prevention of disease. In past times, indeed, such notions have operated as powerfol hinderances to hygienic precautions. When quarantine regu- . lations were first instituted to prevent the spread of contagion by ships from port to port ; and when vaccination was proposed as a preventive of small-pox, religious ideas were aroused into antagonism, and these beneficent measures were denounced as impiously contravening the Divine designs which employed plagues as scourges to punish the transgressions of mankind. In this way false theories of the nature and causes of disease acted as an obstruction to hygienic improvement.


278 ELEMENTARY HYGIENE. 362. The true Idea of Health and Disease. — Modem physiology has brought us to a better understanding of the subject. As stated in the first chapter, and as. illustrated throughout the work, physiology is the science of vital power. Power is the accompaniment of material change, and the man- ifestation of all animal functions we have seen to be dependent upon vital transformations. Not only is the living body in constant visible movement, but in all its minutest parts and tis- sues there is an incessant metamorphosis — ^a rapid escape and renewal of the constituent atoms, and it is in this that life essen- tially consists. That active and unimpeded metamorphosis and prompt elimination of waste products which gives rise to the highest and most vigorous life, constitutes Health ; while the obstruction, depression, or perversion of these vital changes constitutes Disease. We thus escape from the mischievous error that maladies are foreign intrusions— substantive exist- ences which get mysterious lodgment in the living organism, and find that they are simply disturbed physiological actions. A disease may consist in the loss of power to remove or ex- crete normal but injurious products ; or perverted transforma- tions may give rise to wrong products, and these may create still further disturbance, but in all cases the essence of disease is to be regarded as morbid activity. Gout^ for example, is a malady in which bad habits pervert the nutritive changes and ori^nate morbid products ; — ^its chief peculiarity being the deposition of urate of soda in and about the joints. In health there is scarcely a trace of this salt to be found in the blood, and even this small proportion is being con- stantly thrown off. Certain conditions of living, however, such as the habitual use of wines or malt liquors, and high feeding upon animal substances, attended with but little exercise, are known greatly to increase its quantity and seriously to interfere with its excretion. It is then deposited as a foreign or morbid in- gredient in the joints. Careful avoidance of the causes which give rise to this condition of the blood secures complete free-


SCOPE AND AIMS OF HYGIENE. 279 dom from attack, even in those who may have inherited a strong predisposition to the disease. 363. Control over the Causes of Disease.— We have seen how directly and vitally the great fonctions of the system are dependent upon various conditions, such as diet, air, water, clothing, exercise, by which the healthy changes of life are carried forward. Those agencies, in their right action, are causes of health ; but when altered in their influence, they be- come causes of disease. The vital supply of gases, liquids, and solids, which maintain the transformations of life, if deficient in quantity or deteriorated in quality, speedily produces bodily derangement ; while just in proportion to the importance of these normal actions is the evil of their effects when perverted. By the power which intelligence confers over these conditions, man has a lai^e control over the causes of distm*bed health. Diseases may baffle the physician's penetration and defy his remedial sldll ; but, what is of far more importance, hygienic knowledge enables us to avoid them. The efficiency of pre- vention is proverbial, and we have examples of the value of sanitary knowledge and precautions on the most impressive scale. 364. Examples of the Application of Hygienic Frinciplea — Cholera msiy be taken as an illustration. In former times, when sanitary questions were but little understood, the ap- proach of this terrible disease struck terror into the hearts of the people, who were powerless, as the pestilence swept away multitudes of the population of the principal towns. Its coming was awaited with a horrible dread; and when it ap- peared, all efforts were addressed to the relief of those attacked, and medicines, though almost uniformly powerless, were, never- theless, almost the sole resource of the physician. But the connection between the disease and certain conditions, as filth, bad air, overcrowding, and irregularities of living, so common in cities, began at length to be perceived, and steps taken to remove the causes. The adequacy of these measures has been fully vindicated, and, with the knowledge that its conditions


280 ELEMENTARY HYGIENE. are controllable, the predisposing alarms have ceased, the rav- ages of the epidemic have been greatly circumscribed, and there is the amplest experience to show that thorough, yet simple, measures of purification are suflBcient for its complete prevention. Another example is furnished by Scurvy. This disease, which, until recently, has been the scourge of the sailor and soldier, and for centuries was regarded as wholly beyond the power of remedies, also turns out to be fully preventable. " There is no more interesting fact in the history of medicine than that this condition, which has been looked upon at various times as plague, as a mysterious infliction of Divine justice, against which man could only strive in vain, or as a disease inseparable from long voyages, should have been proved by evidence of a most satisfactory character to arise from causes in the power of man to prevent, and to be curable by means which every habitable country affords." Instead of inquiring into the conditions of its origin, and seeking means of preven- tion, the medical profession was for hundreds of years en- gaged in ransacking nature, with the hope of finding some- thing that might prove an effectual remedy. TJiis was sought in vain until attention was turned to its cause, which was found to consist in a lack of vegetable food, and the sim- ple precaution of famishing it has been the signal for the almost total disappearance of the disease. Many other illus- trations might be given of the efficiency of hygienic resources to arrest and prevent the spread of dangerous maladies, but they are needless. 365. Bemedial Influence of Hygienic Agencie8.^Another important consideration deserves to be stated in this place : it is that hygienic measures have a most important remedial value. If the causes of health, when modified or perverted, become causes of disease, to whatever extent restorative medi- cines may be desirable, it is certain that the first dictate of wisdom is to rectify these wrongly-acting causes. Medical treatment, thus, has its hygienic resources, and, with the en-


SCOPE AND AIMS OF HYGIENE. 281 largement of rational experience, these resources are coming into greater and greater prominence. All who have watched the progress of the healing art in recent times, will note that among the most enlightened practitioners there has been a steadily diminishing confidence in medication, and an increas- ing reliance upon the sanitary influence of nature. It is noto- rious that in proportion to people's ignorance of their own con- stitutions and the true causes of disease, is their credulous confidence in pills, potions, and quackish absurdities, and while this ignorance continues, there will of course be plenty of doctors who will pander to it. And not the least of the benefits which will follow the better diffusion of physiological and sanitary information will be the protection of the com- munity from the numberless impostures of charlatanism and a better discrimination of the qualifications of competent phy- sicians. 366. Hygienic Knowledge inevitably beneficial. — ^It is often said to be unnecessary to increase and diffuse knowledge on the subject of preserving health, as people will not use that which they already have. It is true that often they do not ; and this is part of a still larger truth, that only rarely does human action completely conform to the state of intelli- gence. That derangement of the organism which constitutes a form of insanity, in which the intellect sees what is right, while the diseased impulses drive irresistibly toward the wrong, is but a morbid exaggeration of the common experience of mankind, who "see the right, but still the wrong pursue." But when due allowance is made for the force of habit which urges people on in the old courses, after they are reprobated by the judgment, there will be found still a constant tendency to adjustment between thought and action. Character, which is that organic stamp or moulding of human nature by which its actions are determined, adapts itself but slowly to ideal states ; still, such adaptation is constantly going forward, and it is in this that human progress essentially consists. In the matter of hygiene, much, as we have seen, has already been done to


282 ELEMENTAEY HYGIENE. make action harmonize with thought, while the more vividly truths are mentally realized, the more powerful will be the ten- dency to bring practice into conformity with them. While, therefore, it is not to be expected that, by the introduction of the study of physiology and hygiene into schools, disease will at once disappear, and everybody live to be a hundred years old, it is nevertheless certain that the diffusion of this kind of knowledge is the only road to amelioration. As it has already led to great improvement, it cannot fail, in future, to lead to still more extensive improvement In the following chapters I propose to call attention to the various agents and activities which have a bearing, more or less direct, upon bodily and mental health. CHAPTER XV, AIE AND HEALTH. Section I. — Impurities of the Air, 367. Constitution of the Atmosphere. — The chief constit- uents of the atmosphere are a pair of elements, oxygen and nit- rogen, and a pair of compounds, carbpnic acid and watery vapor. The student will remember that, in treating of respira- tion (Chap, v.), it was stated that oxygen forms 21 per cent, and nitrogen 79 per cent, very nearly, of the bulk of the air. Oxy- gen is the life-sustaining element, and requires to be kept up to this standard for healthy respiration. Nitrogen is the negative or diluting element of the air. The proportion of carbonic acid varies from three to six parts in 10,000, while the watery vapor varies also from -^ to ^hs ^^ t^® atmos- pheric volume. Minute traces of other substances may also be obtained, but the foregoing constituents, in the propor-


IMPUBinES OF THE AIR. 283 tions named, form tbe external atmosphere, or what is com- monly known as pure air. But air is rendered impure or unfit for respiratory pur- poses both by disturbance in the proportion of its normal con- stituents, and by many substances in the shape of gases, vapors, and solid particles which are thrown into it from numberless sources. Those arising from the habitations and works of men are of the most importance, in a hygienic point of view, both because we are constantly exposed to their influence, and because they are most completely subject to control 368. Thiir Eelation to the Senses. — ^Many of these impuri- ties can be detected neither by taste nor smell, and are inhaled without any knowledge of their presence. Others are recog- nized at first; but as the nerves soon lose their delicate sensi- bility of discrimination, the senses are unreliable monitors. Hence, injurious influences, that do not result in immediate and painful disease, are generally apt to be neglected. There is, besides, a false logic in the case, it being inferred that, because the senses lose their susceptibility to morbific influences, the system therefore becomes accustomed and adapted to them, when they cease to be detrimental But no error could be more pernicious, as it leads to carelessness and indifference with respect to those insidious agencies which slowly and silently sap the foundations of health. Common instinct is sufficient to guard agdnst palpable causes of injury ; intelligence alone can protect us from the latent and deeper agencies of physio- logical mischief. 369. Carbonic Acid as an Impnrity. — ^This substance is constantly generated in the body, and is therefore, to a cer- tain extent, one of its natural constituents. But when not promptly thrown from the system, its action becomes quickly injurious. The proportion of carbonic acid naturally existing in the atmosphere we may assume to be inoffensive, but all increase is deleterious. Air containing 1 per cent, of it is soporific, depressing, and produces dulness and headache. From 5 to 8 per cent, renders it dangerous to breathe, while


284 ELKMENTAEY HYGIENE. 10 to 12 per cent, makes it speedily destructive to life. When breathed pure it causes suffocation. Air contaminated with it acts as a narcotic poison. The symptoms of poisoning by it are throbbing headache, with a feeling of fulness and tight- ness across the temples, giddiness, and palpitation of the heart The pulse falls, respiration is slow and labored, the skin cold and livid, and convulsions and delirium ensue, which are fol- lowed by death. A cubic foot of air of average purity contains a little less than a cubic inch of carbonic acid. A cubic foot of air, as it comes from the lungs in ordinary respiration, contains up- ward of 70 cubic inches of carbonic acid. The quantity poured into the air by combustion is enormous. In Manches- ter, England, Angus Smith has calculated that 15,000 tons arc daily thrown out The products of firing pass into the exter- nal air, and, if gaseous, are rapidly diffused, but those of light- ing are for the most part allowed to disseminate in the apart- ment. The combustion of 1 cubic foot of coal gas consumes the oxygen of 10 cubic feet of air, and produces 2 cubic feet of carbonic acid. The combustion of a pound of oil consumes the oxygen of 130 cubic feet of air, and produces about 21 cubic feet of carbonic acid. A pei-son, by breathing, adds 1 per cent of carbonic acid to 55^ cubic feet of air in an hour, which would vitiate to this extent 1 foot per minute, while this effect is much increased by the surface exhalations. These facts show the rapidity with which the breathing medium of inhabited apartments tends to become deteriorated. 870. Watery Vapor as an Impurity. — ^Air saturated with moisture acts injuriously upon the system by refusing to re- ceive the gerspiration which is offered to it by the skin and lungs. This produces the feeling of oppression and languor which even the most robust often feel in close and sultry days. By this obstruction of insensible perspiration, not only are the waste matters generated in the system unduly retained, but miasmas introduced through the lungs by respiration are pre- vented from escaping. This would lead us to expect a greater


IMPURITIES OF THE AIR. 285 prevalence of epidemic diseases in moist than iti dry districts, a fact observed in the case of cholera, which follows the banks of rivers, and revels in damp, low situations. Moisture joined with warmth has a relaxing and weakening influence upon the body. The debilitating effect of the sirocco upon the system, and its lowering and dispiriting influence upon the mind, are due to a heated atmosphere surcharged with moisture. Air, cold and damp, has a peculiarly chilling and penetrating effect, as illustrated by the east winds of spring in New England. Dry air, by promoting the insensible perspiration, has a strengthening, exhilarating influence. Cold, dry air is invig- orating. Too dry an atmosphere, however, desiccates the exposed surfaces, and tends to inflame them. Dry climates, which quicken evaporation, are recommended for relaxed and languid constitutions, with profuse secretion, as in cases of humid asthma or chronic catarrh. 371. Oi^nic Matter, — This is a common impurity of the atmosphere, and is often present in dangerous proportions. It exists in the form of vapors, or suspended matters, and is found most abundantly difiused in the air of dwellings, hos- pitals, etc., and in the vicinity of decaying organic substances. In health it is thrown off from the lungs by the process of respiration, and also by exhalation from the skin. The quan- tity has been estimated all the way from 10 to 240 grains per diem for each adult. It varies, however, with the circum- stances, the body excreting a much greater amount during a state of activity than when it is inactive. That coming from the lungs consists of an organic vapor, holding in suspension epithelium ^ells that have become detached from the mucous surfaces of the air-passages, pharynx, mouth, etc. By the skin more is given out. Twice as milch moisture leaves the body by this route as by the lungs, and it carries with it into the atmosphere fatty matters, epidermic debris, and also small quantities of urea. This organic matter, when drawn through sulphuric acid, darkens it ; through permanganate of potash, decolorizes it ;


286 ELEMENTABY HYGIENE. and through pure water, renders it offensive. It is probably in a state of combination with water, as the most hygroscopic substances, such as wool, feathers, and damp walls, absorb it in largest quantities. It has a peculiar, foetid smell, and on decom- position yields ammonia, being therefore nitrogenous. It is oxidized slowly, and is supposed to float through the air in clouds instead of undeigoing rapid diffusion. The foetid odor of a bedroom in the morning, after it has been occupied during the night, well attests the presence of these organic vapors in the air. In the air of sick-rooms and hospitals organic matters ac- cumulate in large quantities unless there is the most thoroc^ ventilation. In addition to the amount contributed hf respi- ration, which is often much laiger in sickness than in health, the exhalations from the skin are greatly increased, and large quantities of effluvia also escape from the discharged evacu- ations. Moscatti, who condensed the watery vapor of a hos- pital ward at Milan, describes it as being ^^ slimy, aifd having a marshy smell." The dust of a ward in St Louis, in Paris, was discovered by Chalvert to contain, in one experiment, 36 per cent, and in another, 46 per cent of organic matter, which consisted chiefly of epithelium, and when burnt gave an odor of horn. Pus-cells have been discovered in the air of an oph- thalmic ward, and epithelium-cells are found in that of all iU- ventilated rooms. It is very likely that the specific poison of small-pox, scarlet fever, measles, diphtheria, etc., consisfcs of molecular organic matter thrown off from the skin and mucous surfaces. If not n^idly oxidized, it no doubt retains its poi- sonous properties, and through the medium of the atmosphere conveys the disease. It is also equally probable that the ema- nations from cholera evacuations may, through the medium oi an impure atmosphere, propagate cholera. In the air of dwellings, starch-cells, particles of cotton, wool, etc., are very common. Injurious exhalations from the imperfect combustion of oil, tallow, gas, and other illuminating substances, are scarcely less so.


- mPUBITIES OF THE AIR. 287 The action of these various forms of organic matter upon the system is regarded as directly poisonous. Hammond found in an atmosphere charged with this impurity, and from which the carbonic acid and moisture had been withdrawn, that a mouse died in 45 minutes. Dr. Parkes says that he has known cases " in which the inhalation of such an atmosphere for three or four hours produced in men decided febrile symptoms, in- creased temperature, quickened pulse, furred tongue, loss of appetite, and thirst, for even 24 or 48 hours subsequently." 372. The Cellar a Beservoir of Bad Air.— Confined air, without access of sunlight, soon becomes dank and uuwhole- some. In the cellars of dwellings this is a common condition <^ng a large part of the year ; the confined air is loaded with decomposing organic matter, given off from the masses of de- caying vegetables with which they are stored. This foul air reaches the inhabitants of upper apartments in such small quan- tities as not usually to produce any marked manifestation of disease, yet dangerous fevers have ofken arisen from n(^lect of cleanliness in this particular. Section II. — Morbid Effects of Impure Air. 373. In the Case of Vaxious Trades. — ^The most palpable examples of the injurious effects of breathing contaminated air are furnished by the circumstances of certain industrial occupations. As a class, the miners of England break down prematurely from bronchitis and pneumonia, caused by the at- mosphere in which they live. The coDiers of Durham and Northumberland,*however, where the mines are well ventilated, do not appear to suffer from an excess of pulmonary disease. In the various trades, involving the inhalation of much dust by the workmen, bronchitis and its attendant disease, em- physema, are very common. . In the pottery trade, this malady occurs so frequently as to be known as the ** potter's asthma." Stone-cutters, grinders in steel, button-makers, workers in flax factories, etc., are all specially liable to bronchitis. Dr.


288 ELEMENTAEY HYGIENE. Grenliow states that, of 107 flax-factory operatives, whose cases were taken indiscriminately, 79 were suffering from bron- chial irritation, and in 19 of these there had beeij haemoptysis. Among 27 hacklers, 23 were diseased. The suspended parti- cles are drawn into the air-passages at each inhalation, and there find lodgment upon the delicate mucous surfaces with which they come in contact. The irritation thus set up dis- turbs the working of the lungs, and, if maintained, eventually ends in organic disease. Brass-founders, coppersmiths, plumbers, white-lead manu- facturers, house-painters, workers in mercury, match-makers, are all subject to peculiar forms of disease produced by inhaling the fumes with which their business contaminates tljp air. These fumes gain access to the blood, and through this to the whole system, producing severe local disturbance in many cases, and always affecting the general health. 874. Scrofula. — The accumulation of carbonic acid and organic matter in ill-ventilated dwellings, workshops, hospitals, and other places, by its depressing and disturbing influence upon the vital powers, is promotive of various disorders, but of none more generaUy than that imperfect and perverted state of the nutritive ftmctions known as scrofula. Baudo- loque, an eminent French physician, affirms " that the repeated respiration of the same atmosphere is a primary and efficient cause of scrofula," and that " if there be entirely pure air, there may be bad food, bad clothing, and want of personal cleanliness, but that scrofulous diseases cannot exist." Agam he says : " Invariably it will be found on examination that a truly scrofulous disease is caused by a vitiated air, and it is not always necessary that there should have been a prolonged stay in such an atmosphere. Often a few hours each day is sufficient, and it is thus that persons may live in the most healthy country, pass the greater part of the day in the open air, and yet become scrofiilous, because of sleeping in a con- fined place where the air has not been renewed." AVhen scrofula localizes itself in the lungs, there is pulmo-


MORBID EFFECTS OF IMPUEE AIR. 289 nary or tubercular consumption. The tubercles which in this disease make their appearance in the pulmonary organs, con- sist of crude, coagulated, half-organized masses of albumen, the abortive products of incomplete nutrition. In this manner, bad air, by producing the strumous condition, becomes a cause of consumption. It seems but natural to expect that the or- gans with which the foreign ingredients of the atmosphere come more immediately into contact, and the blood-vessels of which they must enter on their passage into the system, should feel in a distinctive manner their noxious influence. This ex- pectation is strengthened by observation and experiment upon both men and animals. It is a matter of common knowledge amongst physicians that where individuals habitually breathe impure air, and are , exposed to the other debilitating causes which generally influence more or less the inhabitants of dark, ill-ventilated dweUings, scrofula, and consumption as one of its forms, are very apt to be engendered. In 1832, at Nor- wood School, in England, where there were 600 pupils, scro- fula broke out extensively among the children and carried off" great numbers. This was ascribed to bad and insuflScient food. Dr. Amott was employed to investigate the matter, and immediately decided that the food " was most abundant and good," assigning "defective ventilation and consequent atmospheric impurity " as the true cause. 375. Effects of the Air of Sick-Booms. — ^The impurities of a sick-room atmosphere consist largely of organic matter, which not unfrequently bears the specific poison of the disease. This is the case with the exanthemata as well as with other contagious febrile affections. On uncovering a scarlet-fever patient in the direct rays of the sun, a cloud of fine dust may be seen to rise firom the body^-contagious dust, that in unven- tilated locaUties is but slowly dispersed or destroyed, and that may for days retdn its poisonous qualities. Diseases of this character are undoubtedly propagated in other ways, but a confined atmosphere probably does more than all other causes put together toward aiding their diflfusion. 13


290 ELEMENTARY HYGIENE. Besides bearing the specific poison, an atmosphere of this character is exceedingly depressing to those brought within the range of its influence. Interfering with the aeration and the nutritive capacity of the blood, it lowers the powers of the system, and thus paves the way for epidemic visitations of a malignant and fatal type. 376. Effects of Impure Air upon the Course of Disease. — Foul air increases the severity of disease, rendering a fatal result much more probable, and, even if this is avoided, greatly prolongs the period of convalescence. It also predisposes to complications, and renders recovery more likely to be followed by subsequent trouble. This appears to hold true of all dis- eases, but especially of the febrile. It is known that in the treatment of typhus and typhoid fevers, the freest ventilation, even to the extent of placing the patient in the open air, re- duces their mortality more than half, and greatly shortens the time of recovery. A like provision in the treatment of scarlet fever, measles, small-pox, diphtheria, etc., not only renders them much less severe, but does away in a great degree with the necessity for medication, and also markedly diminishes the liability to those distressing sequelae which in less favorable conditions so often supervene. 877. Consumption. — ^Probably those afflicted with con- sumption and other pulmonary complaints sutler more from the eflfects of foul air than any other invalids. The reason is obvious. The capacity of the lungs is more or less reduced, hence less air can be conveyed to the blood, and if this is de- ficient in oxygen and contains impurities, the blood is directly affected and the malady much aggravated. 378. Its Effects upon Inherited Taints. — Inherited ten- dencies to disease, particularly of a scrofulous character, are rapidly developed by impure air. The incompleteness of nu- trition gives strength to the lurking predisposition. Instances are constantly recurring in which consumptive tendencies are developed to a fatal issue through various bad conditions, impure air being the most potent agency. And physicians


MORBID EFFECTS OF IMPUBE Am. 291 are aware that the constant presence of a pure atmosphere, • with other means for healthy nutrition, will hold the predis- position in check, and maintain the system above the plane of its influence. 379. Morbid Mental Effects of Bad Air.— Breathing an impure atmosphere injures the mind as well as the body. K the blood which is sent from the lungs to the rest of the sys- tem is imperfectly aerated, no organ feels it more than (he brain. Its immediate effect is to cloud the mind and depress its energy ; sharpness of attention, clearness of apprehension, and readiness of memory are all impaired. " The health of the mental and bodily functions, the spirit, temper, disposi- tion, the correctness of the judgment and brilliancy of the imagination depend directly upon pure air." Dr. Bay remarks : " In a school, or hospital, or other con- siderable assemblage of people, the purity of the air may be pretty accurately measured by the amount of cheerfulness, activity, and lively interest which pervades it; and yet so little do people think or care about this subject, that under existing arrangements there are very few who do not every day of their lives inspire more or less highly vitiated air. The listlessness and stupidity of students, and especially of children confined in the school-room, are often due to the bad state of the air they breathe. Using the brain in a vitiated atmos- phere is like working with a blunted instrument, and the effect of course must be aggravated where the inexperienced are first learning the use of the iHstrument. Section III. — Purification of the Air. 380. Nature's Besources. — The purification of the general atmosphere is maintained by various agencies. By the law of diffusion all gases intermingle, so that where impurities are set free at any point they tend to exhale, or difiuse away, and thus become weakened and lost in the great body of the at- mosphere. Diftusion may take place through the chinks and


292 ELEMENTARY HYGIENE. •openings, of rooms, but it proceeds so slowly that it is not to be relied upon for ventilation. The mixture of large masses of air and the dispersion and dilution of local impurities are also effected by the winds. Gaseous exhalations are washed out and absorbed from the atmosphere by the fall of rains. The earth's vegetation destroys carbonic acid, while the oxygen slowly bums up the numberless combustible vapors and con- taminations which are thrown into the air. By these means the earth's atmosphere is constantly maintained respirable and pure. 381. Ventilation. — The object of ventilation is to extend these natural means of purification to the air of dwellings, hos- pitals, workshops, and, indeed, to all places where impurities are liable to accumulate and prove injurious. Taking the ex- ternal air as the standard of purity, it aims to conduct it through those places in a manner that, without inconvenience to their inmates, shall accomplish the rapid and thorough dilu- tion and transfer of whatever impurities their atmosphere may contain. To do this effectually and without risk to the health and comfort of the inmates, tho ventilation must conform to certain indispensable conditions. The air which enters must itself be pure. This may generally be secured by taking it from almost any exposed situation, unless there be some special source of impurity in close proximity. It is desirable, if pos- sible, particularly in cities, to introduce the air from a level a few feet above the surface, as there are more or less exhalations constantly floating in air next the ground. 382. Amoirnt of Air required. — ^It must be in sufficient quantity. We find Nature's standard of purity in the exter- nal atmosphere, and, other things equal, the nearer we ap- proach this in our dwellings, the healthier will be their in- mates. The earlier authorities on ventilation varied greatly in their estimates of the quantity necessary, some placing it as low as 60 cubic feet per head per hour, while others consid- ered 600 cubic feet as not too much. More thorough investi-


I PURIFICATION OF THE AIR. 293 gations have since been made, and it is found that even the highest of these estimates is quite insufficient The object to be attained is so to dilute the products of respiration and transpiration, and of combustion and lighting, as to keep the air always pure and fresh. The successive ex- periments made by "Grassi and others have shown that allow- ances successively given of 10 cubic metres (= 363 cubic feet), of 20 cubic metres (= 706 cubic feet), of 30 cubic metres (= 1,059 cubic feet), were not enough for one man, and the quan- tity was gradually increased till 60 cubic metres (2,118 cubic feet) were allowed. The air in the cell of a prisoner who re- ceived this ration seemed pure to the senses. Dr. Parkes says : " From a number of experiments in which the outflow of air was measured, and the carbonic acid simultaneously de- termined, I have found at least 2,000 cubic feet per hour must be given to keep the carbonic acid at 6 or 6 per 1,000 vol- umes, and to entirely remove the foetid smell of organic mat- ter." Dr. Sankey, from careftil experiments with a ventilating fan, found that, when in a ward in the London Fever Hospital 800 cubic feet per head per hour were supplied, the ventilation was insufficient. It has been stated, from extensive observations, that in mines, if it be wished to keep up the greatest energy of the men, no less than 100 cubic feet per man per minute (= 6,000 cubic feet per hour) must be given. If the quantity is reduced to one-third, or even one-half, there is a decided diminution in the amount of work performed. If possible, the supply for the sick should be unlimited. In some diseases, so much organic matter is thrown off, that scarcely any ventilation is sufficient to remove the odor. Such diseases as pyaemia, typhus and typhoid fevers, small-pox, and the like, are best treated in the open air. This is found of the utmost value, more important even than diet and medicines. Grassi mentions that the air in a ward in the Hospital Necker, in Paris, was perceptibly tainted by emanations from ti can-


294: ELEMENTARY HYGIENE. cerous ulcer, although the ventilation at the time was 3,600 cubic feet per head per hour. 383. Heating the Air. — ^The temperature of the air must be carefully regulated. In this climate, cooling the air is rarely necessary, but in the colder months of the year the incoming air requires to be warmed sufficiently for comfort, and in such manner as not to disturb the normal proportions of its con- stituents. The great danger is that of overheating it, whereby its capacity for moisture is greatly increased and ventilation becomes converted into a kiln-drying process scarcely less in- jurious than impure air. The policy should be to introduce large quantities of air raised only to a proper breathing tem- perature (60® to 70° Fah.), the temperature to be maintained by a steady and rapid change, so directed as to remove the cooler air of the apartment, and replace it with that freshly warmed. It may be said that this involves a much greater loss of heat than the opposite course, viz., the raising to a high temperature of small quantities of air. Even if this were true, which is not the case, waste of heat would be far prefer- able to the loss of health, which the latter process involves, both by the increased drying power it gives the air, and by insufficient ventilation. The heat imparted to the air in this process becomes a means of promoting its movement. With this as a motive power, by the aid of flues and ventilating shafts, very thorough purification may be obtained. 384. Bate of Movement. — The motion of the air must be imperceptible. Air may move at the rate of 100 feet per minute without violating this requirement ; but it is a much greater velocity than is needed for ventilating purposes ; that is to say, after the air has once entered the apartment In the flues, of course, a much greater velocity is necessary. If there is little or no interference from outside currents, the air within the building may readily be made to move in a body from above downward, and the rapidity of its movement can be easily regulated. It may be objected to this downward move-


PUEIFICATION OF THE AIB. 295 ment that the natural tendency of impurities is upward, with the course of the warmer air, and that by being made to take a downward direction they are brought back again to be re- inhaled. If it were true that the impurities, as such, imme- diately rose to the ceiling and escaiped from the apartment, the objection would hold; but this is not the case. On the contrary, it is known that the carbonic acid and other gaseous impurities are equally diflfused, and the weight of the organic substances and other suspended matters leads to the inference that they would gravitate toward the floor, particu- larly when rising currents of w^rm air are excluded, as they should be, by introducing it at the top of the room. In no other way can so steady and equable a movement be obtained as by introducing the warm air at the top and removing it below; and, apart from any theoretical considerations, it is found to yield excellent practical results. 385. Other Means of Purification. — ^In certain special cases where the air is being rapidly contaminated by foul or poisonous exhalations, and where, either from confinement or other cause, the purifying agencies of nature are unable to work with sufficient rapidity and vigor, recourse is had to various chemical substances, with a view to the immediate de- struction of such emanations. The more common substances used as deodorizers and destroyers of foul emanations are char- coal, compounds of chlorine (or mixtures which evolve this gas), nitrous acid, and sulphurous acid. Charcoal presents an immense absorbent surface to the air, a cubic inch of beechwood coal equalling in surface 100 square feet (Liebig). It is therefore a powerful oxidizer of organic matter, catching and holding the particles in contact with oxygen, already within it, until their destruction is accom- plished. Its effects are especially marked with sewage gases and with the organic emanations in disease. Of the different kinds, animal charcoal is regarded as best for disinfecting pur- ' poses. Permanganate of Potash^ or Soda (Condy's Fluid), gives


296 ELEMENTARY HYGIENE. off oxygen, and rapidly destroys organic matter. Ammoni- acal compounds are at once decomposed. Permanganate of soda, taken into the mouth, quickly destroys the odor of to- bacco (Hoffman). Compounds of chlorine act through the liberation of chlo- rine gas, which rapidly decomposes sulphuretted hydrogen and sulphide of ammonium, and also destroys organic odors. It may be obtained by moistening chloride of lime, or soda, when it slowly escapes into the atmosphere. It is also easily evolved by mixing 1 part of powdered binoxide of manganese with 4 parts of common salt and 4 of dilute sulphuric acid. A gentle heat will aid the evolution. The gas, however, will corrode all exposed metallic surfaces. Nitrous acid may be evolved by placing nitre in sulphuric acid, or by dropping a bit of copper into dilute nitric acid. It is a very efficient disinfecting agent, but irritating to the air- passages and lungs. The ease with which it yields up a por- tion of its oxygen makes it a powerful oxidizer, which acts rapidly upon organic emanations. Sulphurous acid is given off when sulphur is burned. It decomposes sulphuretted hy- drogen, and acts with energy upon organic substances. CHAPTER XVI. WATEE AND HEALTH. Section L — Physiological Offices of Water. 386. AmoTint in the Body.— The student is aware that water is a very large constituent of all parts of the body. The bones contain 130 parts of it in 1,000; muscle, 750; brain, 789 ; blood, 795 ; and it forms nearly three-fourths the entire weight of the body.


PHYSIOLOGICAL OFFICES OF WATER. 297 387. It is the Instrument of Change. — ^Water gives ful- ness and flexibility to the softer tissues, and is the great agent of movement within the system. It performs the same oflSce of transportation and exchange in the vital economy that it does by oceans, rivers, and canals in the commerce of the world. Nutritive substances cannot enter the system, nor the debris of the tissues leave it, except in a state of solution ; it is the office of water to bring them into this condition, and con- vey them to their various places of destination. 388. Its Solvent Power. — ^Water performs these duties by virtue of its remarkable powers as a solvent Perfectly neutral itself, it becomes sweet, sour, salt, astringent, bitter, or poison- ous, accordingly as the bodies it dissolves possess* these proper- ties. It readily takes up either gaseous, liquid, or solid sub- stances, and thus* becomes a means for their rapid and wide- spread diffusion. 889. ftnantity daily taken.— Water is taken not only in the form of drink, but it is a large constituent of the various food-stuffs ; hence any estimate of the quantity passing into the system, to be reliable, must include both these sources of sup- ply. It has been found that a healthy adult man ordinarily takes from 70 to 90 ounces in 24 hours. The amount, how- ever, varies greatly in different circumstances, sometimes, from individual peculiarities, falling much below, and at other times considerably Exceeding this figure. 390. Its Excretion. — Water is constantly escaping from the system, either in a fluid or vaporized form, and carries with it the various substances * resulting from the wear and tear of the tissues. Of all that is expelled, about 48 per cent, is dis- charged with the urine and faces, and about 52 per cent by the lungs and skin. Of the latter, the skin discharges nearly twice as much as the lungs. Section II. — Different kinds of Water. 891. Its Foreign Ingredients.— Owing to its extraordi- narily solvent power, water, in a natural condition, is never 13*

J 

298 ELEMENTARY UYGIENE. found free from foreign ingredients, which modify its char- acter according to the quantity present, and their own pecu- liar properties. This gives rise to the several varieties that we know as hard-water, soft-water, mineral-water, and sea-water. 392. Soft-Water. — ^This is water that gives a feeling of softness in washii^, from the absence of certain mineral sub- stances, which render it rougb or hard. Rain-water may be taken as a fair example, for when caught in the open country, it is the purest water that Nature provides. It is not entirely free from foreign matters, however, for, as it falls through the air, it absorbs oxygen, nitrogen, carbonic acid, ammonia, and organic substances, and also washes out any impurities which the atmosphere may happen to contain. Thus, in the vicinity of the ocean the air contains traces of common salt ; in the neighborhood of cities, various saline, organic, and gaseous impurities, while dust is raised from the ground and scattered through it by winds. These are all rinsed out of the air by rain. In passing through it, water becomes highly aerated ; that is, acquires an atmo^here of its own, which contains from ten to fifteen per cent, more oxygen than ordinary air. This gives to water its agreeable taste. Soft water, which is free from dissolved mineral matters, makes its way into organized tissues with much more readiness than hard water. It also exerts a more powerful solvent, or extractive action, and is thus a better vehicle for conveying alimentary substances into the living system. In culinary operations, where the object is to soften the texture of animal and vegetable compounds, or to extract from them and present in a liquid form some of their valuable parts, as in making soups, broths, stews, or infusions, as tea and coffee, soft water is much to be preferred. In consequence of its aeration, rain-water is both healthy and pleasant as a beverage. The greatest benefits have re- sulted in. many cases from its use, where the spring and well waters were largely impregnated with earthy salts.


DIFFERENT KINDS OF WATER. 299 893. Hard Water. — Rain-water, as it penetrates the- ground, absorbs a large proportion of carboniC acid from the air in the interstices of the soil, which is 250 times richer in this gas than the air above. The presence of this absorbed carbonic acid greatly increases the solvent power of water upon mineral substances. Passing more or less deeply into the earth, it dissolves various substances which it meets ; hence the difference between spring and well waters, which are gen- erally hard, and rain-water, which has not come in contact- with the ground. The life and sparkle of spring and well water are due to the presence of carbonic acid thus taken up, and when this is found in a considerable degree, it is safe to infer the additional presence of large quantities of saline impu- rities. The usual ingredients of well and spring water are lime, magnesia, soda, and oxide of iron, combined with carbonic and sulphuric acids, which form carburets and sulphates. Common salt is also often present. The most usual ingredients, how- ever, are carbonate and sulphate of lime. Carbonate of lime, or limestone, is not soluble in pure water, but dissolves in water containing free carbonic acid. The amount of mineral matter found i% water varies greatly. The water of the river Loka, in Sweden, which flows over in- soluble granite, contains only -^^ of a grain of mineral matter in an imperial gallon. Common well and spring waters con- tain from 5 to 70 grains per gallon. Sea-water contains 2,600 grains to the gallon ; and that from some parts of the Dead Sea, or the Great Salt Lake of Utah, as much as 20,000 grains to the gallon. 394. Mineral Waters are usually those of springs which are highly charged with one or more mineral ingredients. Those abounding in salts of iron are called chalybeate waters. If the waters are brisk and sparkling, carbonic acid is present, and they are termed carbonated j or acidulous, 395. Limestone Waters. — ^Tbcse are also clear, sparkling waters, of agreeable taste. They differ from the water of chalk districts, in containing more sulphate of lime and less carbon-


300 ELEMENTABY HYGIENE. ate, and in dolomitic districts mach sulphate and carbonate of magnesia. TBey contain little organic matter, but are very hard, soften little on boiling, and are generally unwholesome. 396. Sand and Oravel Waters. — ^These vary in character in different regions. Some are very pure, containing less than 5 grains of mineral matter in a gallon, and less than 1 grain of organic matter. Others again, particularly such as flow over soft sand-rock, are liable to be very impure, containing much • chloride of sodium, carbonate of soda, iron, and a little lime and magnesia, amounting altogether to from 30 to 80 grains per gallon. The organic matter may also be in large amount, from 4 to 10 grains per gallon, or even more. 897. Alluvial Waters. — ^These are generally highly charged with carbonate of Hme, sulphate of lime, sulphate of magnesia, chloride of sodium, carbonate of soda, iron, silica, and often with organic matter. The amount of solids per gallon ranges from 20 to 120 grams. 398. Surface and SubHSOil Water.— This is often very impure. Cultivated lands, with rich, manured soils, ftimish a water often containing both organic matter and salts in large quantity. In towi\i, and among the habitations of men, the sur&ce and shallow well-water frequently contains large quanti- ties of nitrites and nitrates, sulphates and phosphates of lime, and soda and chloride of sodium. Organic matter, also, exists often in large amount 399. Marsh-Water. — ^This is always impure from the presence of much organic matter, which is chiefly of vegetable origin, and varies in quantity from 10 to 60 grains in the gal- lon. The proportion of mineral ingredients is usually small, unless the marsh be salt, when the mineral constituents of sea- water are present. 400. River-Water. — ^This varies much in the number and quantity of its constituents. Coming from various sources, it is even more complex in constitution than spring or well water. Oftentimes it is greatly contaminated by the sewage of towns and the refuse of manufacturing operations which are carried


DIFFERENT KINDS OF WATER. 301 on along its banks, and it is also likely to contain a large amount of organic matter. 401. Sea-Water. — The solid constituents of sea- water amount to about 3^ per cent, of its weight, or nearly half an ounce to the pound. It is unfit for use unless distilled. It then answers well for cooking purposes, and, if thoroughly aerated, is palatable. Any organic matter remaining after dis- tillation may be removed, by passing the water through a charcoal filter, or by letting it stand for a few days. Care should be taken that no lead finds its way into distilled water, as it is rapidly taken up. Many cases of lead-poisoning have occurred on board ships, partly from the use of minium in the apparatus, and partly from the use of zinc pipes, with lead in their composition. 402. Pnrity of Water. — ^Perfectly pure water can only be obtained by the most careful processes of distillation, and is never found as such in a natural state. Hence the diflficulty of defining what are properly impurities, particularly when we bear in mind the fact that water containing considerable quan- tities of foreign matter may be used for long periods together, without producing any recognizably injurious results. Expe- rience has shown, however, that certain conditions are neces- sary to health, and cannot be neglected with impunity. The water should be transparent and colorless, free from odor, and without taste. It should also be well aerated, and aflford no deposit on standing; above all, it should be free from organic matter. Probably the less it contains of saline ingredients the better. The Sanitary Congress held at Brussels, in 1863, de- cided that the total amount ought not to exceed 86 grains per gallon. But this furnishes no reliable criterion, as a far less quantity of sulphate of lime, or magnesia, is known to be in- jurious, while the proportion of carbonate of lime, or soda, may considerably exceed this, and produce no manifestly bad effects. 403. Organic Impurities in Water. — ^These vary exceed- ingly in character and amount, and may be either mechanically


302 ELEMENTARY HYGIENE. suspended or dissolved in the water. If suspended, and of vegetable origin, their presence will often be indicated by a peculiar yellowish or brownish tinge, such as most are famUiar with in the water of marshes or peat-bogs. If of animal origin, they may impart no tinge, and are more likely to be dissolved. They are derived from numberless sources, but those of most importance, hygienicaUy, are furnished by the habitations and trades of men. Rain-water carries down from the air floating organic impurities, and it may also become contaminated by decaying leaves that have accumulated on the roofs of houses. Cisterns are also liable to receive impurities from the leaking of sinks or waste-pipes, or by the washing in of leaves from the roof. Shallow wells are extremely apt to become contami- nated by floods carrying in organic surface impurities. Deep wells frequently drain large areas about them, and are very often, particularly in towns, rendered impure and even offensive by collecting the drainage from cess-pools, vaults, etc. In epi- demics of typhus and typhoid fever and cholera, cases have occurred where it was known that the specific poison of the disease found its way into the system by this means. Springs and streams oftentimes receive the discharges from large man- ufectories; and although the water appears pure, an exami- nation reveals the presence of organic matter. The effects of this contamination may be shown by taking a little of the sediment that has accumulated at the bottom of a cistern, and placing it in a bottle of perfectly pure distilled water, when in a short time, if the weather be warm, it will smell offensively. Thus, at ordinary summer temperatures, this organic matter is liable to undergo putrefactive change, and it is then that it ex- erts its most baneful effects upon the system. This is, no doubt, one.of the causes of the greater prevalence of diarrhoeas and dysenteries during the warmer portions of the year. Section III. — Morbid Effects of Impure Water. 404. Dyspepsia. — ^Water containing sulphate of lime, chlo- ride of calcium, and the magnesia salts, has a decided tendency


MORBID EFFECJTS OF IMPUEE WATEB. 303 to produce stomacliic and intestinal derangements. Dr. Suth- erland found that the hard water of the sandstone rocks, which was formerly much used in Liverpool, exerted a marked effect in producing constipation, lessening the secretions, and causing visceral obstractions ; and in Glasgow, the substitution of soft for hard water, according to Dr. Leech, lessened the prevalence of dyspeptic complaints. The exact amount capable of pro- ducing these symptoms has not been determined. In a well- water which was found so injurious that men would not drink it, there were present 19 grains of carbonate of lime, 11 grains of 'sulphate of lime, and 13 grains of chloride of sodium per gallon. The total solids were 60 grains per gallon. Iron, in quantities sufficient to give the water a slightly ferruginous taste, often produces dyspepsia, headache, and general uneasiness. 405. Diarrlioea. — ^That this disease often originates in the use of bad water, there is no doubt. Great numbers of in- stances are on record where it was traced directly to this cause, and where its removal was followed by a disappearance of the disease. Mineral matters, either dissolved or suspended, will give rise to it if present in considerable quantity. The water of many rivers holds in suspension fine particles of clay or marl in great abundance, particularly at certain seasons, and, if drank for any length of time, will produce diarrhoea. Hammond instances the Mississippi, Missouri, Rio Grande, and Kansas Rivers as examples. The use of waters containing dis- solved mineral substances, particularly sulphates, will also cause diarrhoea. *' Parent Duchatelet noticed the constant excess of patients furnished by the prison of St. Lazare, in conse- quence of diarrhoea, and he traced this to the water, which ' contained a very large proportion of sulphate of lime and other purgative salts ' " (Parkes). Waters impregnated with nitrate of lime will produce diarrhoea. Brackish water acts in the same way, probably from the large quantity of chloride of sodium it contains. Dissolved or suspended organic matter, whether of vegetable


304: ELEMENTARY HYGIENE. or animal origin, will cause diarrhoja. In the recent war, great numbers of cases occurred from the use of marsh or ditch water, which ceased when wells were sunk. Water con- taining foecal matter, sulphuretted hydrogen, or other sewage products, often occasions the worst forms of diarrhoea, attended sometimes with marked choleraic symptoms — such as purging, vomiting, and cramps — even when the senses give no indica- tion of these impurities. The effects of sulphuretted hydrogen are well shown by a case that occurred in the recent war in Mexico. The French troops suffered greatly at Orizaba, from the use of water taken from sulphurous and alkaline springs. This produced dyspep- sia and diarrhoea, attended with enormous cructntions after meals, the eructed gas having a strong smell of sulphuretted hydrogen. Sewage gases, setting back through untrapped overflow pipes into tanks and cisterns, often contaminate the water very rapidly. 406. Dysentery — ^This also frequently results from the use of impure water. The impurities which produce it appear to be of the same kind as those which cause the allied condition of diarrhoea. The drainage from grave-yards contains large quantities of organic matter and nitrates, and its use is very liable to produce this disease. Water contaminated by the discharges of dysenteric patients is known to produce dysen- tery in others, and thus the disease oftentimes becomes epidemic. 407. Cholera. — Symptoms of this malady often follow the use of water containing sewage or decomposing organic matter. Many believe that it is capable of producing the dis- ease, but this point is still unsettled. The use of water ren- dered impure by the presence of choleraic evacuations, how- ever, is known -to give rise to the disease in others, and in towns this is found a ready means of propagation. In addition to the production of cholera from drinking water containing cholera-stools, it is quite certain that the use of impure water of any kind predisposes to cholera, though it


MOEBID EFFECTS OF IMPURE WATER. 305 cannot absolutely produce it. It probably acts by keeping up a constant irritation in the alimentary canal, thus causing diarrhoea, which in cholera epidemics usually precedes the outbreak of the graver disease. 408. Malarious Fevers. — There is strong evidence in sup- port of the belief that these are often produced by drinking marsh or ditch water. They are supposed to be caused by some specific poison generated in mirshy regions ; and that this may find its way into the blood through the agency of water, as well as of air, there is no reason to doubt. Mr. Blower, of Bedford, England, mentions a case in which, in the parish of Houghton, almost the only family which escaped ague at one time was that of a farmer who used well-water, while all the other inhabitants drank ditch-water. Numerous instances point to impure water as a frequent source of typhoid fever. Doubtless, water contaminated by decomposing sewage, or evacuations from typhoid patients, not only predisposes to the disease, but conveys its specific poison. In yellow fever, like dysentery, typhoid fever, and cholera, the alimentary mucous membrane is primarily affected. Hence, there is strong probability that the cause is also swallowed in this case, and enters with the drinking-water. 409. Goitre, or enlargement of the thyroid gland, is most common in limestone regions, and is held by some to be caused by drinking water highly impregnated with lime and magnesia salts. Johnston states that in the jail at Durham, England, when the water contained 77 grains per gallon of lime and magnesia salts, all the prisoners had swellings of the neck. These disappeared when a purer water, containing 18 grains per gallon, was obtained. 410. Entozoa, or those parasitical creatures which infest other animals, may find their way into the body by means of the drinking-water. While some enter with the food, others (in the embryo state) are known to exist in great numbers in river-water, and doubtless are often swallowed when such yrater is used for drinking purposes.


306 ELFMENTAEY UYOIENE. Section IV. — Purification of Water, 411. Examination by the Senses. — If water is examined by the unaided senses, the information obtained is very limited and should not be relied upon. They will only indicate ex- treme conditions, and are very liable to overlook the most characteristic impurities. Taste, for instance, even though it be extremely delicate, is wholly untrustworthy. Organic mat- ter, when dissolved, is often quite tasteless ; 65 grains of car- bonate of soda and 70 of chloride of sodium per gallon are imperceptible; 16 grains of carbonate of lime give no taste, and 25 grains of sulphate of lime very little. If^ from its eflfects, a given water is suspected of impurity, and its use can- not be avoided, examination of it should be intrusted to some competent person. 412. Distillation. — ^Water njay be most thoroughly puri- fied by distillation, but this is impracticable when considerable quantities are required, and besides, the water is not fit to drink Until aerated. To render it perfectly pure, it must be redis- tilled at low temperatures, in silver vessels. 413. Boiling and Freezing. — ^Boiling Mils most animal and vegetable organisms that water may contain, expels gases, and precipitates carbonate of lime. It is the latter that consti- tutes the fur or crust often seen lining tea-kettles and boilers. Freezing renders water much purer, by expelling a large proportion of its saline contents. Carbonate and sulphate of lime may be thus got rid of. But, like boiling and distillation, freezing expels the air and thus renders the water insipid. In all these cases the water regains its palatability on standing. 414. Purification by Chemical Mean8.-^The addition of two or three grains of alum to the quart cleanses muddy or turbid water, but often renders it harder than before. When alum is added, the water should not be used under 24 hours. Permanganate of potash destroys organic matter and ammo- niacal compounds by rapid oxidation, and may be used with advantage for this purpose.


PURIFICATION OF WATER. 307 415. Filtration. — ^Tbis is the most effective and practicable method of purification, and is within the reach of every one. Many substances will answer as filters, such as crushed char- coal, sand, or porous sandstone, flannel, wool, sponges, or any other porous media. Of all these, charcoal is the best. It will remove 88 per cent, of organic matter, and 28 per cent, of min- eral matters. If the water is moderately good, 1 pound bf charcoal will purify 600 pounds or 60 gallons, ^imal char- coal is better than vegetable, though both lose their purifying power sooner or later. It is quickly restored, however, by ex- posure to air and slight heat. Filters of charcoal should be made of considerable thickness, and the coal finely crushed and well pressed together. The effect of the charcoal is supposed to be chiefly chemical, as it brings the large quantity of oxygen which it holds into the closest contact with any oxidizable mat- ters in tbe water. Sand is much used, and answers well for a time, but re- quires to be often renewed. 416. Action of Water on Lead.— Water is known to pos- sess the power of corroding lead, and forming compounds with it which, if dissolved, render the water highly poisonofts. All waters act upon it more or less, but it is only when the lead is dissolved that the water containing it becomes dangerous. When ordinary water is placed in contact with lead, the free oxygen it contains combines with the metal, forming oxide of lead, with which the water immediately unites, produdng hy- drated oxide of lead, which is nearly insoluble. There is also more or less carbonic acid existing in all natural waters ; this combines with the oxide of lead, forming carbonate of lead, which is also highly insoluble. But if there be in the water much carbonic acid, a bicarbonate of lead is formed, which is very soluble, and therefore remains dissolved in the water. Hence, waters which abound in free carbonic acid, as also those which contain bicarbonates of lime, magnesia, and pot- ash, are most liable to become poisoned by lead. Water con- taining common salt acts upon the metal, forming a soluble


308 ELEMENTABY HYGIENE. poisonous chloride of lead. The presence of organic matter, nitrites and nitrates, imparts to the water a powerfully corrosive action. If the water contains vegetable or fetty acids of any Mud, or sour milk, or cider, its action on lead is greatly in- creased, and it is more likely to dissolve the compounds formed. On the other hand, waters containing sulphates and phosphates ate little injured, these salts exerting a protective influence on the lead. The lead itself is more easily acted, upon if other metals, such as iron, zinc, or tin, are in contact with it. Galvanic ac- tion is set up, which greatly facilitates corrosion. Dr. Hassal says that "while very soft water cannot be stored for a lengthened period, with impunity, in leaden ves- sels, the danger of the storage of hard water, under the same circumstances, is in most cases much greater. This danger, however, is to be estimated neither by the qualities of hard- ness or softness, but altogether depends upon the chemical constitution of each different kind of water. Thus, if this be ever so soft, and contain free carbonic acid, its action on lead will be great ; whereas, if it be hard from the presence of sul- phates 'and phosphates principally, and contain but few bicar- bonates, little or no solution of the lead will result" CHAPTER XYII. FOOD AND HEALTH. Section 1. — The Alimentary Principles of Food. 417. The Four Oronps. — ^It was stated in Chapter YIL, Section L, that all substances used as foods may be classed under four heads, either as Proteids, Fats, Amyloids, or Min- erals. It is desirable to recapitulate and somewhat extend the observations there made.


THE ALIMENTARY PEINOIPLES OP FOOD. 30d 418. The Froteids. — This group of alimentary principles consists of Gluten, Fibrin, Albumen, Syntonin, Casein, and Gelatin, which are characterized by the presence in their com- position of a large amount of nitrogen. Gluten is the adhesive principle of grain, and is a grayish, tough, elastic substance, left when the starch is thoroughly washed away from flour. From its resemblance to the fibrous part of meat, it is known as vegetable fibrin. Animal fibrin exists dissolved in the blood, and solidifies into a fine net-work as the blood coagulates. It constitutes the bulk of lean meat. Casein is the curdy principle of milk, which is separated by coagulation, and forms the chief ingredient of cheese. It ex- ists in large quantity (20 to 28 per cent.) in beans and peas, and is known as vegetable casein. Albumen is a transparent, glairy, coagulable fluid, familiar to all as white of egg. It is a large constituent of animal fluids and tissues, and occurs in the seeds and juices of plants. Syntonin is the chief constitu- ent of muscle or flesh. It closely resembles albumen in com- position, but, unlike it, is not a product of the vegetable king- dom. Gelatin is an animal product, chiefly obtained from bones and tendons. It is not found in the vegetable kingdom, and is used for food, principally in the form of jellies and soups. All the foregoing substances, except gelatin, have a re- markable similarity of composition. They present varieties of aspect and physical properties, and differ in consistency, solu- bility, and behavior with heat ; but they serve a common pur- pose in the animal economy — that of furnishing material for the formation of the tissues — and on this account have a high nutritive value, and are to a great extent mutually replaceable. 419. The Fats. — ^These occur in both plants and animals, and, whatever their source, they have a great similarity of com- position. Like the proteids, they differ in physical properties, but are capable of replacing each other as articles of diet. They are essential to the formation of both muscular and ner- vous tissue, and, from their large amount of hydrogen and car-


310 ELEMENTABT HYGIENE. bon, are the most energetic supporters of the calorifying function. 420. The Amyloids. — ^This group comprises the starches, sngars, and gums — principally vegetable products, and, in one form or another, is a large constituent of our ordinary food. Starch is abundant in grain, peas, beans, and potatoes. The dif- ferent preparations known as sago, tapioca, arrow-root, and the like, are almost entirely starch extracted from different species of plants. Starch is capable of conversion into sugar, and is thus changed by the juices of the alimentary canal Sugar is pro- duced by both plants and animals, but our supply comes chiefly from the vegetable kingdom, where it is contained in great abundance in sap, fruit, and seeds. By the agency of heat, starch may be converted into gum, known as dextrine. Gums are vegetable products widely distributed, but not in great abundance. Their composition is similar to that of starch and sugar, and their dictetical function is supposed to be the same. 421. Their Offices. — ^It has until lately been supposed that as the nitrogenous and non-nitrogenous substances are clearly separated by chemical compositions, they are sharply divided in their physiological effects. The first were supposed to nour^ ish the tissues, the decomposition of which .was believed to be the sole source of animal power, while the fatty and amyloid group served only to maintain animal heat by their oxidation. Bat while it is maintained that the bodily tissues can only be reproduced from the nitrogenous elements, it is admitted that the decomposition of these tissues must be a source of heat ; and recent researches have established that the combustion of the hydro-carbons is a source of power, the heat produced being converted into mechanical force. 422. Kineral Aliments. — ^The inorganic or mineral con- stituents of food consist of water and various saline substances. Common saltr occurs in all forms of food, but in larger propor- tion in animal than in vegetable tissues. An instinctive crav- ing impels animals to seek for a larger supply of it than is fur- nished in their food. Chloride of potassium, phosphate of lime,


THE ALIMENTARY PRINCIPLES OF FOOD. 311 and alkaline carbonates are indispensable to digestion, and are furnished in combination with the various aliments. 423. Necessity for a Mixed Diet — The usaal forms of food are combinations of these alimentary principles. * Milk, for example, is a highly complex animal product, containing water, casein, butter, sugar, and various mineral salts — repre- sentatives of each of the fom* classes of alimentary principles. By its excess of salts and nitrogenous matter, it is suited to the wants of the infant, or rapidly grow^pg state of the constitution, but it is not a complete or properly balanced diet for the adult. In the majority of cases, no single article of food is thus com- plete in its composition, there being usually one or more of the essential elements of a perfect diet wanting. This is the case with the various meats, all of which abound in nitrogenous and fatty substances, but are deficient in the amyloid elements. On the other hand, most vegetables are rich in starch and sugar, but deficient in nitrogenous matters. Bread is nitroge- nous, amylaceous, and inorganic, but lacks fat ; while Indian com contains less of the nitrogenous element, but a large amount of starch and 8 or 10 per cent, of fat. As no one arti- cle of food, therefore, contains these four classes of materials in the proportions requisite to a perfect diet, we are obliged to mix our various food-stuffs. Confinement to a single aliment- ary principle, or to any one class of them alone, is sure to be followed by disease. It has been shown, by repeated experi- ments, that dogs confined to the exclusive use of either starch, iat, or albumen, soon die of starvation. Like experiments be- gun upon men were productive of a corresponding disturbance, and doubtless, if carried out, would have resulted in the same way. The proteids are first in importance, as much the larger part of the mass of the body is derived from them, and, when given alone, will sustain its powers longer than any other class of aliments. Hence, it is easy to see why exhaustion follows so much more quickly when they are withheld, than when other kinds of food are unsupplied. But the amyloids and fats are


312 ELEMENTAEY HYGIENE. also reqaisitc, and the body feels the want of them sooner or later, even though the proteids are furnished in abundance. Section II. — Animal Foods. Foods may be conveniently divided into three classes : animal food, vegetable food, and auxiliary food; substances derived from animals, such as milk, eggs, and meats, are ex- amples of the first class. • 424. Hilk. — ^As this liquid contains all the elements ne- cessary for complete nutrition, it has been regarded as the type of composite foods, but, as just remarked, it is only completely adapted to a certain stage of animal life. A hundred parts of cow's miJk contain of casein, 4.48; of butter, 3.13 ; of milk- sugar, 4.47 ; salts, .60 ; and of water, 87.32. This, however, is only an average statement, as no two cows give milk exactly alike in composition, while the milk of the same cow varies with the food. The milk of goats and ewes is richer in solids than that of the cow. Human milk is poorer in casein, and contains a larger proportion of sugar than cow's milk ; hence, when the latter is substituted for it in the case of infanta, a lit- tle sugar should be added. In cities, milk is often largely adulterated with water. If much water has been added, it may be detected by applying the specific gravity test. The specific gravity of unadulterated milk ranges from 1.026 to 1.033 ; the average is about 1.030. Two-parts water to eight-parts milk will reduce its specific gravity to 1.024; four-parts water to six-parts milk, to 1.018. Good milk should be of a full white color, perfectly opaque, without deposit, and free from any peculiar taste or smell. It should give a neutral reaction, and have a specific gravity of at least 1.028. 425. Butter and Cheese. — These furnish the nutritive con- stituents of milk in a concentrated form. Butter is habitually associated with substances which are deficient in fat, and is held to promote their digestibility. All butter contains casein,


ANIMAL FOODS. 313 which is derived from the milk skimmed off with the cream, but the less it contains the less liable it is to become rancid. E^^lcidity is chiefly owing to changes in the oil produced by decomposition of the casein. Butter in this condition is unfit for food, as it is indigestible, and has been known to produce dyspepsia and diarrhoea. Cheese is rich in nitrogenous mate- rial, and when fresh is regarded as excellent food. It is very liable, however, to undergo chemical change,* and when this is once set up it becomes irritating and indigestible. The pecu- liar flavor of old cheese arises from this commencing decompo- sition, and it often disturbs weak stomachs. In this condition it is said to aid digestion, and is sometimes taken in small quantities as a condiment. 426. Eggs. — ^These are both nitrogenous and fatty, and, when properly cooked, are easily digested and highly nutri- tious. They contain no starch or sugar, and should therefore be eaten in connection with such articles as supply these ali- ments. Eggs are most wholesome when boiled sufficiently to coagulate the white without hardening the yolk. Hard-boiled or fried eggs digest with difficulty. 427. Ueats. — ^Whatever their source, these are essentially the same in constitution, that is, they all contain a large amount of nitrogenous matter, in union with much fat and various im- portant salts. Their advantage as a diet is, that they contain a large amount of nutriment in a highly concentrated form, are easily digested when properly cooked, and admit of ready , assimilation. Fresh meat varies in quality with different animals, and with the age, sex, and condition of the individual from which it was obtained, as well as with the character of the food upon which it was fattened. Stall-fed cattle make the finest beef, and corn-fed swine the best pork. The nicest mutton is ob- tained from sheep fattened on fresh, succulent pasturage. In all cases the animal should be free from disease, and of medium fatness, to make its flesh a healthy and economical food. The muscle should be of a firm, yet not sodden, consistence, of a 14


314 ELKMENTABY .HYGIENE. • pale-reddish color, somewhat lighter toward the centre than at the surface, and show no disposition to tear across its fibres. The fat should be white, or but slightly tinged with yellow, and also firm to the touch. The pale, moist muscle marks the young animal; the dark colored, the old one. The meat should be free from any disagreeable odor, and the muscles, when cut across, should present a uniform solidity. Any mar- bling, or points .where the knife passes more easily than at others, indicates commencing decomposition. As a rule, the flesh of young animals is tenderer, and more easily digested than that of old ones ; veal, however, is an exception, so far as digestibility is concerned. The flesh of young animals contains more water than that of old ones, consequently it is more juicy, but bulk for bulk less nutritious. 428. Salt Ueat. — ^Beef and pork are commonly preserved for future use by salting, and in this condition are largely em- ployed as food. Salting, however, reduces the nutritious value of meat, detracts from its flavor, and renders its digestion more diflBcult It does this by extracting a portion of its juices, which remain dissolved in the brine, thus leaving the fibres of the meat harder and consequently less easily acted upon by the fluids of the stomach. 429. Poultry and Oame. — ^Meat of this kind is more easily digested than that just considered, but is regarded as less nu- tritious. It is not so juicy as butcher's meat, and, as a rule, contains less fat Broths made from it have a delicate flavor, and contain considerable nutriment, hence they make an excel- lent food for convalescents. 430. Pish. — ^The flesh of fish is very similar in composition to that of other animals. It is somewhat poorer in nitrogenous matter, but richer in important salts, and contains a higher pro- portion'of water than butcher's meat It is generally of easy digestion, but it should not be used exclusively, nor for a long period together, as it is liable to produce a scorbutic state of the system. The fle^h of fish nn- dergoes rapid decomposition, and is then highly iiyurious. It


VEGETABLE FOOD. 315 should be eaten only when it is perfectly fresh. Salt fish, like salt beef or pork, is much inferior to fresh, and extremely in- digestible. 431. Crabs and Lobsters. — ^The flesh of these animals re- sembles that of fish, but it is less easily digested. It is pe- culiarly prone to decomposition, and, when eaten in this state, often produces sickness and sometimes proves fatal. 43^. Clams and Oysters. — Clams, either raw or cooked, are extremely indigestible. Oysters are much less so. They are most easily digested when raw, and, if cooked, should be either stewed or roasted. Section III. — Vegetable Food. 433. Wheat. — Of vegetable food-stuffs, the most important and widely-used are the cereal grains. Among these wheat ranks first, both in point of nutritive value and in the ease with which it is digested. With the exception of mijk, it approaches more nearly the standard of a perfect food, and will sustain the powers of the body for a longer period than any other article of diet It contains from 10 to 16 per cent of gluten ; from 60 to 70 per cent of starchy matter, and a small proportion of fat, besides certain important alkaline and earthy phosphates. Its* proportion of water is very low, averaging about 12 per cent, bulk for bulk ; therefore it is richer in solids than any other food. The starchy elements of the seed exist most abundantly in and about its centre, while its glutinous, fetty, and mineral constituents are found in greatest quantity toward the surface. The coat immediately beneath the husk is espe- cially rich in gluten, and therefore highly valuable as food. In the process of grinding, this is often lost by passing into the bran, the result being a whiter, but much less nutritious flour. The soft wheats yield the whitest flours, as they contain more starch and less gluten than the hard or flinty varieties. Good wheat should yield at least 80 per cent of flour. The quality of wheaten flour may be best determined by the


316 * ELEMENTAEY HYGIENE. practical test of baking. Still something may be told by its appearance. It should contain very little bran, and its starch should be white, or with the . very slightest tinge of yellow. The flour ought not to be lumpy, or if so, the lumps should readily give way under the slightest pressure. Grittiness in- dicates that the starch-grains arc changing, and such flour will give an acid bread. When compressed in the hapd, good flour will adhere in a lump, and retain the imprints of the fingers longer than that of inferior grade. If cast against the wall, a portion^ should firmly adhere. The dough made with good flour is ductile and elastic, and may be drawn out into long strips, or rolled into thin sheets without breaking. Flour becomes whiter with age, but it is at the expense of flavor, sweetness, and nutritive value. The greater the propor- tion of gluten, the sooner will this deterioration take place. Flour is sometimes contaminated by the presence of fungi or insects, and they always indicate inferior quality. It is also occasionally adulterated with the flour of other grains, which can only be detected by the microscope. 434, Eye. — ^This comes next to .wheat in nutritive value, though it furnishes less flour to the bushel, and that of a de- cidedly darker color. Its gluten appears to contain more casein and less vegetable fibrin than that of wheat, conse- quently it is less tenacious. Owing to this quality, bread made from rye flour does not rise well, and is liable to become heavy on cooling. Eye bread soon becomes acid, and with many is not easily digested. ' 435. Buckwheat. — ^This is poor in nitrogenous and fatty constituents, but rich in starch. Bread made from buckwheat flour does not rise well, owing to its deficiency in gluten. It is, therefore, chiefly consumed in making griddle-cakes, which, while warm, are light and palatable, but not well received by- weak stomachs. 438. Indian Com contains a much larger proportion of fat than any other grain in common use. It is also rich in starch, but has far less nitrogenous matter than either wheat


VEGETABLE FOOD. 817 or rye. This, which is known aa zein^ is not of a glutinous, adhesive nature, and hence maize flour, or meal, will not make a dough, or fermented bread. In the preparation of articles of food from Indian meal, long cooking is necessary, when it makes both a palatable and highly nutritious food, which is easily digested. 437. Eice. — As an article of diet, rice possesses the advan- tage of an extremely digestible starch-grain. It has, however, but small proportions of nitrogenous matter, fat, and salts ; hence, in rice-eating nations, it is habitually taken with such other food as will best supply these wants. 438. Peas and Beans are much alike in composition, and both rich in nitrogenous constituents, often containing as high as 26 per cent, of vegetable casein, or Ugumen, They also contain much sulphur and phosphorus, together with an aver- age proportion of salts, and but a small quantity of water. They are, therefore, very nutritious, and rank first among con- centrated strength-imparting foods. They are somewhat indi- gestible, however, and liable to produce flatus. When eaten, it should be in small quantity, and only by thos^of an active habit of body. 439. Succulent Vegetables. — Of these, potatoes are the most valuable and most extensively used. They contain in 100 parts — Water, H Proteids, 1.5 Fats, ...... .1 Amyloids, 28.4 1 They are thus seen to abound in amylaceous materials and salts, but contain a low proportion of nitrogenous matters, and very little fat. Owing to this deficiency, wo habitually associate them with meat, when they form an easily-digested and valu- able food. Turnips, beets, carrots, parsnips, etc., contain more water than potatoes, and are less easily digested. Their solid por-


318 ELBMKNTAEY HYGIENE. tions consist mainly of starch and sugar, with a small percent- age of fat and salts. They each possess a peculiar, volatile principle, which adds much to their flavor, and causes thera to be eaten more as a relish than as a strength-giving food. Onions and cabbage are more watery than the preceding, but their solid parts contain a very large proportion of nitro- genous matter. They are relished chiefly for their pungency, but should be eaten only at intervals, as they are likely to cause flatus and indigestion. 440. The Fruits. — These consist mostly of water and cel- lulose, with varying amounts of fruit sugar, and small quantities of potash, soda, and lime, in combination with certain organic acids. Their juices contain a gelatinous substance termed pectine, which forms the basis of the various jellies. Fruits are prized more for those qualities which relate to their taste than for nourishing and strengthening power. Nevertheless, they are valuable as sources of the alkaline and earthy carbo- nates, and useful when eaten in moderate quantity, as safe- guards against constipation. They are most -wholesome when cooked, but Jn all cases the skins, seeds, and cores should be rejected, as indigestible and prolific sources of irritation. Section lY.^-Aimliari/ Foods. 441. Auxiliary foods comprise a class of substances very extensively employed to give relish to other dietary compounds, to provoke the digestive organs, and for nervous stimulation, rather than for any nutritive properties of their own. Useful when taken with care, they are liable to prove most injurious when too freely indulged in. Under this head come the various condiments and beverages. 442. The Condiments. — Vinegar is essentially a solution of acetic acid in water. Good vinegar ought to contain at least 5 per cent, of the acid. Commercial vinegar is often largely adulterated, and some samples which pass under the name are made of sulphuric acid and water, colored with burnt sugar,


AUXILIARY FOODS. 319 and without a trace of acetic acid in their composition. Vine- gar in small quantities, by augmenting the acidity of the stomach, may reenforce the gastric juice, and promote the di- gestion of the proteids. Black pepper consists of an active principle (peperin), a pungent essential oil, and an acrid resin. It is a powerful stimulant of the digestive organs, increasing the flow of saliva and gastric juice in a marked degree. In the powdered state it is frequently adulterated with linseed meal, starch, mustard, buckwheat bran, etc. These may be detected by the micro- scope ; but it is safest to purchase the berries and grind them as wanted. Cayenne pepper resembles black pepper in properties, but is a much more powerful stimulant. Its habitual use, there- fore, cannot be recommended, and if taken at all, it should be only in the smallest quantity. The sharp, acrid smell and taste of nmstard are due to the volatile oil it contains. Used in small quantities, it is a gentle stimulant ; in large doses, it acts as an emetic. Like all arti- cles of its class, it is subject to sophistication. Among the substances added, the most common are turmeric and some form of starch. Sulphate of lime and chalk are also sometimes used as adulterants. , 443. Beverages.— Tea.— This consists of the leaves of the tea-shrub, grown and prepared chiefly in China. Many vari- eties are known in commerce, the differences between which are due probably to different modes of culture and prepara- tion. The substances for which tea is most prized as a beverage are— ^r«/, a peculiar volatile oil, which gives the tea its agree- able flavor; second, a vegetable alkali, rich in nitrogen, and known as thein, — ^the active principle of tea ; and third, tannic acid, which gives the tea its astringent quality. Of the first, tea contains less than 1 per cent. ; of the second, from 1^ to 6 per cent. ; and of the tannic acid, which is in combination with the thein, from 14 to 16 per cent. It contains, besides, about


320 ELEMENTARY HYGIENE. 20 per cent, of gluten, and is also rich in salts, but these last ingredients are not usually obtained in the beverage. In making tea, it is desirable to obtain from the leaves the largest possible amount of matter, without destroying its flavor. If the tea is boiled, the volatile oU is driven off with the steam — and yet a boiling temperature is required to dissolve the compound of thein and tannic acid, the most important con- stituent of the leaf.' To preserve the one and obtain the other is the principal object, and this is best attained by pouring boiling water upon the leaves in close vessels, and allowing them to steep for a time, with the temperature slightly below the boiling point Tea acts as a gentle stimulant upon the nervous system, without producing subsequent perceptible depression. It also quickens the pulse somewhat, and increases the amount of pul- monary carbonic acid exhaled. It produces an astringent effect upon the bowels, but not to any harmful extent. It hastens digestion and is invigorating, but it should not be taken in excess, as it is apt to induce wakefulness and an irritable state of the system. Chreen tea is more injurious in this respect than black, often giving rise to nervous tremors. Tea of all sorts is liable to the grossest adulteration, green teas being worse in this respect than the black varieties. The Chinese heighten their color, or fcxe them, as it is termed, by the addition of Prussian blue, indigo, turmeric, gypsum, and China clay. A bright-green color is to be looked upon with suspicion, as the pure article always presents a dull, faded green appearance. The leaves of other plants are often mixed with tea. Sometimes, also, exhausted tea leaves or grounds are bought up, their astringent property restored by the addi- tion of catechu, and colored with black lead, or logwood, they are sold again as genuine tea. Another fraud of great preva- lence consists in mixing inferior qualities of tea with better sorts, and cheating the purchaser by selling the compound at the price of the best article. In selecting tea, it should appear not to be too much


AUXILIAEY FOODS. 321 broken up, or mixed with dirt, and the leaves should vary somewhat in size and color. The best teas contain portions of the stalk and flower. Old teas do not possess so rich a flavor as fresh, owing to the loss of a portion of their vola- tile oil. 444. Coffee. — Coffee, Hke tea, contains a volatile oil, a ve- getable alkali {caffein), and tannic acid. It also contains from 12 to 15 per cent, of amylaceous material, in the shape of sugar and gum, and nearly the same quantity of nitrogenous matter, in various forms, besides being rich in salts. But very small quantities of these latter substances find their way into the beverage. The agreeable flavor of coffee is due to its volatile oil, which is present in very minute proportions, and requires the action of heat to develop it. This is done by the process of torrefying. The cafibin is almost identical in composition with the thein of tea, and, like it, is the active principle of the beverage. It is present in small quantity, rarely reaching 1 per cent. The quantity of tannic acid is usually less than 6 per cent., conse- quently coffee is much less astringent than tea. The action of coffee upon the system is similar to that of tea. It is a stimulant, and promotes the digestion and assimi- lation of food. It both enlivens the mind and invigorates the body, relieving the depression of fatigue, and in this way un- doubtedly tends to diminish the liability to disease. There is a peculiar physiological effect exerted by coffee and tea, and probably also by alcohoUc beverages when taken in small amount — a retardation of destructive metamorphosis. The renal products of muscular waste are found to be dimin- ished after their use ; while experience has shown that they may replace, in diet, a certain amount of ordinary food. De Gasparin, in his observations upon the regimen of the Belgian miners, found that " the addition of a quantity of coffee to the daily rations enabled them to perfonn their arduous labors on a diet which was even below that found necessary in prisons and elsewhere, where the article was not employed." The 14*


822 ELEMENTARY HYGIENID. comparative effects of coffee, tea, and alcohol, in enabling men to endure cold and hardship, are thus stated by Dr. Hayes, in describing the experiences of Arctic exploration : " Dr. Kane's parties, after repeated trial, took most kindly to coffee in the morning, and tea in the evening. The coffee seemed to last throughout the day, and the men seemed to grow hungry less rapidly after taking it than after drinking tea, while tea soothed them after a day's hard labor, and the better enabled them to sleep. They both operated upon fiatigued and over-taxed men like a charm, and their superiority over alcoholic stimulants was very marked." In the process of roasting, the coffee should be first care- fully dried in an open pan, over a gentle fire, until it becomes yellow. It should then be scorched in a covered vessel, to pre- vent the escape of aroma, taking care, by proper agitation, to prevent any portion from being burnt, as a few charred grains communicate a bad odor to the rest. The operation should be continued until the coffee acquires a deep cinnamon or chest- nut color, and an oily appearance, or until the peculiar fi^- grance of roasted coffee is sufficiently strong. Unroasted coffee may be kept for any length of time, and grows better with age. After roasting, it is constantly losing flavor ; hence, it is well to roast but a small quantity at once, and this ought to be kept in close vessels, and ground as it is wanted for use. This course necessitates the purchase of the berry and home pre- paration, but the additional trouble is more than compen- sated by the superior beverage thus obtained. The finer it is ground, the more readily, of course, will it yield its soluble constituents. Ground coffee is very extensively adulterated ; — Whence an- other inducement for purchasing the whole berries. Various substances are employed as adulterants, such as roasted peas, beans, com, turnips, carrots, potatoes, etc. But the substance most commonly used is chiccory, which has a large white pars- nip-like root, abounding in a bitter juice. A little of this, when roasted, gives as dark a color and as bitter a taste to


AUXILIAEjT FOODS. 323 water as four times the quantity of coffee, and, as it only costs about one-third as much, the temptation is very strong to mix it with ground coffee. So great is the demand for chiccory for this purpose, that it is itself adulterated with roasted barley and wheat grains, acorns, mangel wurzel, sawdust, peas, and beans. Venetian red is sometimes added to give it a coffee color, and even this is cheapened by the addition of brick-dust. The microscope detects many of these foreign substances, while some can be identified only by chemical means. In the preparation of the beverage, we are met by the same difficulty that was encountered in the case of tea ; that is, a high heat will drive off the aroma, while yet it is requisite to the extraction of the active principle — caffein. To obviate this difficulty, take two portions of coffee, boil the first for five minutes in the required amount of water ; then, after set- tling a moment, decant the water upon the second portion, and allow it to steep for a few moments without additional heat. Allow it to settle, pour off the liquor for use, and retain the grounds for the next day's boiling. A fresh portion furnishes the aroma, and can be in its turn subjected to the boiling process. 445. Cocoa and Cliocolate. — ^These are prepared from the cacao heanSy which are derived from a fruit resembling a short, thick cucumber, grown upon the small cacao-tree of the West Indies, Mexico, and South America. The bean is brittle, of a dark-brown color internally, and has a slightly astringent but decidedly bitter taste. In preparing it for use, it is roasted in the same way as coffee, until the aroma is fiiUy developed. The bean is now more brittle, lighter in color, and less astrin- gent and bitter than before. The beans contain about 60 per cent, of fatty matter, called butter of cacao, and from 20 to 25 per cent, of albuminous and starchy material. They also con- tain a peculiar nitrogenous substance called theobromine similar in nature and properties to thein and caffein. The beans, crushed to a paste between hot rollers, and mixed with starch, sugar, etc., form common cocoa. Chocolate is made by grind-


324: ELEMENTARY HYGIENE. ing the recently-shelled beans to paste, mixing this with sugar, and flavoring it with vanilla, cinnamon, and the like. When used as a beverage, the chocolate or cocoa is scraped into pow- der, mixed with water and milk, and brought to a boiling heat. As thus prepared, chocolate is refreshing to the spirits, and highly nutritious. Section V. — Culinary Preparation of Foods, 446. Cooking has a twofold object— ^r*^, to soften the food, and thus facilitate its solution in the digestive juices ; and second^ to develop its flavor, and thus render ^it more agreeable to the palate. When the operation is properly per- formed^ both these purposes may be attained, and yet by im- proper management both may be defBated. For example, in cooking meats, it is desirable to retain their flavor, preserve their juices, and soften their texture, and with the requisite care, all this may be accomplished ; yet how often does care- less or improper management give us a hard, dry, tasteless mass, as indigestible as it is unpalatable I Over-cooking should be specially avoided, as it results in waste and loss of sapidity, without in any respect improving the character of the food. 447. Cooking of Ueats. — Boiling. — Meats lose from 25 to 35 per cent, of their weight by this process. If it is desired to retain their juices and flavor, the pieces should be cut large, and when first put in, the water should be boiling. This co- agulates the albumen near the surface of the piece, and thus prevents further escape. After boiling three or five minutes, the heat should be lowered to about 160°, and maintained at that point until the completion of the process. If the temper- ature is kept above 170°, the muscular tissue shrinks, and be- comes hard and indigestible. In making broth, the object is to extract the juices ; hence the meat should be cut into small •pieces and placed in cold water. After standing a little time, it may be slowly heated to about 160° ; never much above this. Coagulation of the albumen is thus prevented, and the con- tained juices extracted. A nutritious beef broth, or beef tea,


CUI/INAEY PEEPABiiTION OF FOODS. 325 may be made without heat, by adding to a pint of cold water half a pound of finely-cut, fresh, lean beef and four or five drops of hydrochloric acid. Slight heat and a few drops more acid considerably increase the amount of extract. Boasting is one of'the best methods of cooking meat It not only develops the flavor, but preserves the juices, and leaves the meat in a condition to be easily digested. The loss is about 25 per cent, and is chiefly water. The process should bo commenced with an intense heat, so as to coagulate the al- bumen of the surfece and form a slight superficial crust. Af- terward it should be done very slowly, so as to avoid harden- ing the inner portions. Stemng is analogous to roasting, only the meat is cut up, and continually moistened with its own juices. Like boiling and roasting, it should be done at a low heat Tough meat is best cooked in this manner. Baking requires to be conducted with great care, or there is danger of drying up the meat Constant basting prevents this to some extent, but the method is inferior to roasting. Frying is the worst possible way in which meat can be cooked. The oil or fiat requiring a high temperature to bring it to the boiling point, the meat is thus rendered extremely hard and the fet not unfrequently burnt. Broiling is to be preferred to frying. It has much the same effect as roasting, and, like that process, should not be carried too far — 2l high heat at first, sufficient to encrust the outside, and then a low temperature to complete the work. 448. Cooking of Vegetables— These are usually boiled, and are best cooked by this means. Care should be taken not to overdo them. Thorough softening is sufficient, as, when the process is carried beyond this, their structure is rapidly broken down, and a large proportion of their salts and juices lost in the water. The quality of the water employed exercises an important influence. Soft water exerts a much more powerful ' extractive action than hard, hence food boiled in it is often- times rendered insipid by the loss of its salts and juices! When it is desirable to obtain these in a liquid form, as in making


326 ELKMENTABY HYGIENE. soups, brotbs, or infusions, soft water is to be preferred. In those cases where it is not the object to dissolve out the con- tents of a structure, but rather to preserve it firm and entire, hard water is the best. To prevent the over-dissolving action of soft water, salt is often added, and proves quite efiectuaL Section VI. — Injurious Effects of Bad Diet 449. Effects of Excess in Diet.— The influence of food upon health is immediate and powerful, and is manifested in various ways. Imperfect diet is chiefly injurious by its excess, by its deficiency, by the wrong proportions of its elements, and by the unwholesome condition of the articles consumed. The quantity of food that it is proper to take, varies, of course, with different circumstances: those thinly clad and exposed to cold require more than the well-protected ; those in active exercise more than the sedentary or persons of inactive habits ; while the growing need, proportionally to their size, more than adults. But whatever the circumstances, if the quantity of food taken exceed the demands of the system, evil consequences are certain to follow. The immediate results of over-eating are lethargy, heaviness, and tendency to sleep. Overtaxing of the digestive oi^ans soon deranges their func- tions, and is a conmion and efficient cause of dyspepsia. If the food is not absorbed from the digestive apparatus into the system, it rapidly undergoes chemical decomposition in the idimentary canal, and often putrefies. Large quantities of gas are thus generated, which give rise to flatulence and colicky pain. Dyspepsia, constipation, and intestinal irritation, caus- ing diarrhoea which does not empty the bowels, are produced. If digestion be strong, and its products are absorbed, an excess of nutriment is thrown into the blood, and the circulation overloaded. If food is not expended in force, the natural alternative is its accumulation in the system, producing pleth- oric or abnormal increase of muscle, tissue, and fat This is accompanied by congestion of important organs, mal-assimi-


INJUEIOUS EFFECTS OF BAD DIET. 327 lation of nutritive material, and increased proneness to derange- ment and diseased action. The excretory processes are like- wise certain to be disturbed, whicb often leads to the retention of waste products, with per\'ersion and poisoning of the blood, and a train of evil consequences. 450. Effects of Deficient Diet. — ^As food is the source alike of the material organism and of the power it exerts, if a due supply of it is withheld, there is defective nutrition, which reduces the structures and impairs the strength. Habitual in- sufficiency of food lowers the vital powers and depresses the functions. There is loss of mental vigor and muscular energy, digestive disturbance, anaemia, and a tendency to those maladies which result from debility and undervitalized conditions. The resistance of the system to the numerous causes of disease is diminished : typhus and typhoid fevers are peculiarly diseases of the poorly-fed. In childhood, lack of sufficient food is often the cause of stunted growth and chronic disease, and in later life the parent of depraved appetites and moral perversities. Of the effects of stinted food upon mind and character. Dr. Moleshott observes : " There is another instinct by which the vigor of mind is vanquished in a more melancholy way. Hun- ger desolates head and heart. Though the craving for nutri- ment may be lessened to a surprising degree during mental exertion, there exists nothing more hostile to the cheerfulness of an active, thoughtful mind, than the deprivation of liquid and solid food. To the starving man, every pressure becomes an intolerable burden ; for this reason, hunger has effected more revolutions than the ambition of disaffected subjects. It is not, then, the dictate of cupidity or the claim of idleness which prompts the belief in a natural human right to work and food." 461. Amoxmt of Food daily required. — Although this is variable in different circumstances, yet definite standards have been reached when dealing with large bodies of men in given cases. It has been shown that generally, in the case of the adult male, from ten to twelve ounces of carbon and from four to five


328 ELEMENTARY HYGIENE. ounces of nitrogenizod matter (estimated dry) are daily dis- charged from the organism, and that to replace this, there is required a daily consumption of from two to three pounds of solid food. Dr. Dalton says : " From experiments performed while living on ^n exclusive diet of bread, fish, meat, and butter, with coffee and water for drink, we have found that the entire quantity of food required during twenty-four hours, by a man in full health, and taking free exercise in the open air, is as follows : Meat, . . . .16 ounces, or 1*00 lbs. avoirdupois. Bread, . . . 19 •» " 1-19 " " Butter, or fat, . . 3^ " " 22 " " Water, ... 62 fluid oz. " 8-38 " " That is to say, rather less than two and a half pounds of solid food, and rather over three pints of liquid food." " It is undoubtedly true that the daily ration has frequently been diminished considerably below the physiological standard in charitable institutions, prisons, etc. ; but when there is com- plete inactivity of body and mind, this produces no other effect than that of slightly diminishing the weight and strength. The system then becomes reduced without any actual disease, and there is simply a diminished capacity for labor. But in the alimentation of large bodies of men subjected to exposure, and frequently called upon to perform great labor, the question of food is of vital importance, and the men collectively are like a powerful machine, in which a certain quantity of material must be furnished in order to produce the required amount of force. This important physiological fact is most strikingly exemplified in armies ; and the history of the world presents few examples of warlike operations in which the efficiency of the men has not been impaired by insufficient food. " The United States army-ration is the most generous in the world ; and the result has been that, in the recent civil war, scurvy and other diseases which are usually so rife in armies subject to the exposure and fatigue incident to grand military operations, have been comparatively rare. In some


INJUEIOUS EFFECTS OF BAD DIET. 329 of the long and arduous campaigns of tbe war, the marches made by large bodies of troops, and the labor performed, showed an amount of endurance heretofore unknown in mili- tary history. The excellent physical condition of the men was further evidenced by the remai'kable percentage of recoveries after serious wounds and surgical operations, and the slight prevalence of the ordinary diseases, except those of malarial origin."— (Dr. Flint.) The following is the army ration of the United States soldier : Bread or flour, 22 ounces. Fresh or salt beef (or pork or bacon, 12 oz.), . 20 " Potatoes (three times per week), . . . .16 " Rice, 1-6 «  Coffee (or tea, 0-24 oz.), 1*6 " Sugar, 2-4 " Beans, 0-64 gilL Vinegar, ...•.,. 0-32 «  Salt, • . . . 016 " 452. Effects of a badly-constituted Diet. — There may be sufficient bulkiness in the food taken, but such a misproportion among its elements as to pervert the functions and give rise to various maladies. The several elements of food-stuffs are not replaceable. Deficiency of the proteids results in muscular debility and prostration; while, if too great a quantity be taken, they charge the system with imperfectly-assimilated compounds and wrongly-changed products of decomposition, which produce a gouty state of the constitution. Deficiency of the fats induces defective nutrition and leanness ; while ex- cess of them not only tends to produce obesity, but if more be taken than can be stored or consumed, the burden of dis- posing of the excess falls upon the liver, which may itself be- come diseased from over-action, or its secretions be thrown into the blood, giving rise to a bilious condition of the system. If the saline elements are withheld, softening, or deformity of the bones, or rickets, is the legitimate consequence. If the supply of fresh vegetable food is cut off for a lengthened period,

i 

830 ELEMENTABT HYGIENE. a scorbutic condition of body is produced. Hence, for the preservation of health, mixed food and a various, well-balanced diet are indispensable. In the case of infants and children, where food subserves the double purpose of maintaining activity and growth, there must be extra provision in the diet for the development of muscular and bony tissues. Milk, though a liquid, by its abundance of salts and casein, is adapted to this end But too frequently, after weaning, the food of children is given with no reference to this important condition. Sago, tapioca, arrow- root, and jellies, which rank lowest in nutritive value, with per- haps other substances less objectionable, but still inadequately nourishing, are frequently made use of, to the serious injury of the growing constitution. 463. Effects of a Deficiency of Pat— It is believed that a lack of oleaginous elements in diet predisposes to consump- tion. The immediate cause of this disease, as has been al- ready observed, is an abortive or perverted nutrition, tubercle being produced instead of healthy tissue. The seeds of con- sumption are most generally sown in the system in youth, when there is a double demand upon nutrition, for current waste and steady growth. There is, however, sufficient proteid matter present to nourish the structures ; some other condition must, therefore, be wanting. Eminent physiologists have lately maintained that the faulty nutrition which results in tubercle is caused by a deficiency of oily substances, and therefore such of these bodies as are easiest digested and absorbed have been indicated as remedies. Cod-liver oil has come into use for this purpose. Dr. Hughes Bennett, who first introduced this oil to the notice of the public, states that butchers, cooks, oilmen, tanners, and others who are constantly coming in contact with fatty matter, are less liable than others to tubercular disease ; and Dr. Simpson has observed that children and young persons employed in wool factories, where large quantities of oil are daily used, are generally exempt from scrofula and pulmonary consumption. These £su;ts would indicate that even the ab-


INJUBIOUB 35FFECTS OF BAD DIET. 331 sorption of fatty matter through the skin may powerfully influ- ence nutrition. Dr. Bennett says that, to prevent consumption during youth, indulgence in indigestible articles of food should be avoided, especially pastry, unripe fruit, salted provisions, and acid drinks ; while the habit of eating a certain quantity of fet should be encouraged, and, if necessary, made imperative. Dr. Carpenter observes : " There is a strong tendency and increasing reason to believe that a deficiency of oleaginous matter, in a state fit for appropriating by the nutritive pro- cesses, is a fertile source of diseased action, especially that of a tuberculous character ; and that the habitual use of it in large proportions would operate favorably in the prevention of such maladies, as cod-liver oil unquestionably does in their cure." Dr. Hooker, in a report on the diet of the sick, says : "1st. Of all persons between the ages of 15 and 22 years, more than one-fifth eat no fat meat. 2d. That of persons at the age of 45, all except less than one in fifty habitually use fat meat 3d. Of those who have abstained, a few acquire an appetite for it, and live to a good old age, while the great proportion die of consumption before 45. 4th. Of persons dying of con- sumption between the ages of 15 and 45, nine-tenths, at least, have never used fet meat" 464. Unwliolesoine Foods. — Articles of food differ in di- gestibility, some being readily dissolved and assimilated, while others are chained in the stomach with such difficulty as to irritate and injure the organ. Animal food is more easily digested than vegetable, as it represents vegetable food that has been already once digested, and its insoluble portions separated. But the chief cause of unwholesomeness in foods is their bad condition. The qualities which render them easily digestible within the system, make them readily changeable without it ; hence their tendency to " spoil," and the facility of injurious culinary changes. Bread, sour and heavy from un- skilftil working or damaged flour, butter rancid and offensive, potatoes sodden, and meat tainted or diseased, are examples of unwholesome diet, which produce disturbance in the system


332 ELEMENTARY HYGIENE. and often serious disease. Meat that has entered upon decora- position, or the flesh of diseased, immature, or over-driven animals, is unfit for use. They are liable to produce gastric disturbance and diarrhoea, or they may be actively and dan- gerously poisonous. 455. Flesh Parasites. — The disease known as "measles" in the pig is due to little parasitic animals which infest the flesh. When pork is thus affected, there are found scattered through the areolar or connective tissues numerous opaque or whitish points, which consist of little membranous bags, or cysts^ each containing a small embryonic animal, known as the Cysticercua celluloms. These microscopic creatures are devel- oped from the eggs of the common tape-worm (^anta 5o?et«m). Dr. Kiichenmeister fed a number of cysticerci to a criminal at different periods before his execution, varjang from 12 to 72 hours, and, upon post-mortem examination of the body, no less than ten young taenia were found in the intestine, four of which could be distinctly recognized as specimens of Taenia solium (Dalton). The cysticerci are sometimes found in the organs of the human body as well as in those of the lower animals. They are most likely to be met with in the voluntary muscles, but have been observed in the tissue of the heart, and, what is more remarkable, in such organs as the eye and brain. Their presence in the muscles is not known to be harmful, inasmuch as they have been found in considerable numbers in those of individuals who were accidentally killed while in a state of apparently perfect health. The Trichina spiralis is another parasite which infests the muscles of the pig, and is also found in those of the human subject A muscle containing trichina appears as if thickly beset with small whitish specks. Each speck is in reality a cyst, which contains a single trichinae, a minute, worm-like animal, coiled up in a spiral form. "When straightened out, it measures about ^ of an inch in length, and about -j^ of an inch in diameter. Like the cysticerci, these animals find their way into the human


INJURIOUS EFFECTS OF BAD DIET. 333 stomacb, and thence, by means of the circulation, to the mus- cles, where they are occasionally found in immense numbers. They have been discovered in the muscles of persons who died by accident, and were otherwise apparently healthy ; and also, and much more frequently, in subjects who bave died from slow and debilitating disease. Within a few years past, it has been determined that the presence of these parasites not un- frequently gives rise to a peculiar disease, which has received the name of Trichiniasis. This aflfection is said to be highly febrile, often resembling typhoid or even typhus fever, and at- tended with excessive pain in the limbs and oedema. In selecting meat, if the lean flesh looks speckled or blotched, it should bo suspected. When the cysticerci are in great numbers, the flesh crackles as its fibres are cut across. The trichinae, if enclosed within a cyst, are easily seen with the naked eye ; but, if not, the microscope alone detects them. These creatures are said to be very tenacious of life, often sur- viving intense cold and a boiling heat. It is alleged, however, that thorough smoking cfiectually destroys them.

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334 ELEMENTABY HYOIENB. CHAPTER XVIII. CLOTHING AND HEALTH. Section I. — Properties of Clothing Material 456. Purposes to be subserved. — ^The principal object of clothing being to defend the body against the eflfects of heat and cold, it is obvious that the qualities best suited to these purposes are what we are to seek in the selection of fabrics for wearing apparel in diflTerent seasons and climates, and at dif- ferent times. These qualities are chiefly connected with the relations of fabrics to heat and moisture. The body is con- stantly losing heat both by conduction and evaporation. In cold weather, the object is to prevent this loss as far as possi- ble ; in warm weather it is desirable to promote it ; hence, we select our clothing with a view to these different purposes, wearing the free conductors and ready, absorbers in summer, and the non-conductors and slow absorbers in winter. - As^far as is consistent with these primary objects clothing should be light, durable, and readily cleansed. It should also be of such a character as will allow of the free passage of the exhalations from the skin, and yet not be readily absorbent of moisture from without, Imperviousness is a very objectionable quality, and may, by retaining the cutaneous excretions in contact ^itb the body, lead to serious disease. 457. Linen as an Article of CHotliing.— -This is a good conductor, and allows the free escape of heat. It is also a rapid absorber of moisture, which it readily gives off by evapo- ration from the external surface of the body. For this reason, it produces a rapidly-cooling effect, even in hot weather, and is thus well adapted for summer use. It should not, however, under any circumstances, be worn next the skin, as it not only quickly cools the surface itself but is incapable of preventing sudden chills from other causes.


PEOPEETIES OF CLOTHING MATEEIAL. 835 458. Cotton as an Article of Qothing. — ^This is ar worse conductor of heat than linen, and consequently warmer. It is likewise less absorbent of moisture, and is therefore prefer- able for under-garments, or when it is desirable to avoid the cooling action produced by the evaporation of moisture from Sk material in contact with the body. It ranks neict to linen as a fabric for summer wear, being a much better conductor of heat and absorber of moisture than either silk or wool 459. Woollen as an Article of Clothing.— Woollen fab- rics, owing to their coarseness and porosity, are capable of detaining within their meshes considerable amounts of atmos- pheric air, and this makes them bad conductors of heat. It is upon this property of imprisoning air within its interstices that the warmth of clothing in a great measure depends. The air itself is an excellent non-conductor of heat, and when mate- rials are worn which have the power of entrapping its particles, the body is virtually encased in a garment of air, and its heat thereby prevented from escaping. The denser the fibre and the closer the texture, the less air there will be retained, and, hence, the cooler the clothing. The converse is equally true, though to a more limited extent. In any clothing, if warmth is the object, the texture must be suflSciently close to prevent the passage of currents, but up to this point the more open it is, the better. Woollens also possess a great capacity for moisture, though they take it up and give it out very slowly. This is another valuable quality, giving them great advantages as articles of clothing. Every one may have noticed how readily linen and cotton become wet, while woollen in the same length of time is scarcely more than dampened. The former will also dry rapidly, while woollen parts with its moisture at a much slower rate. It is, therefore, a better protection against wet than cither linen or cotton, and much warmer while wet, as the evaporation from its external surface is not nearly so rapid as from the surfaces of other materials. The water absorbed by different fabrics penetrates their fibres, and is also held between


336 ELEMENTARY HYGIENE. them in the interstices of the cloth. The latter can be wrung out, and is called water of interposition. The former is only got rid of by evaporation, and is termed hydroscopic water. Woollen greatly exceeds either linen or cotton in this power of hygroscopic absorption, taking up at least double the amount of water in proportion to its weight, and quadruple in proportion to its surface. " This property is a most important one. During perspi- ration, the evaporation from the surface of the body is neces- sary to reduce the heat which is generated by exercise. When the exertion is finished, evaporation still goes on, often to such an extent as to chill the frame. When dry woollen clothing is put on after exertion, the vapor from the surface of the body is condensed in the wool, and gives out again the large amount of heat which had become latent when the water was vaporized. Therefore, a woollen covering, from this cause alone, at once feels warm whe» used during sweating. In the case of cotton and linen, the perspiration passes through and evaporates from the external surface without condensation ; the loss of heat then continues. These facts make it plain why dry woollen clothes are so. useful after exertion." — (Parkes.) As an equalizer of the temperature and protector of the surface against sudden chills, wool stands at the head of all our usual wearing fabrics, and, when it can be tolerated, jjhould be constantly worn next the skin. 460. Color influences the relations of clothing to solar heat, though it does not affect it in regard to non-luminous heat, such as that emitted from stoves. Black clothes absorb heat in a sunny day ; while white clothes reflect more of it The power of absorption decreases as the shade grows lighter. Thus, black absorbs the most, blue next, then green, yellow, and lastly white. Color also affects the relations of cloth to moisture, the darker colored materials absorbing more moisture than the light colored. Black will absorb nearly as much again as white.


MANNER OP BEESSING THE BODY. 337 Section II. — Manner of Dressing the Body, 461. Its Importance. — Much more depends upon this than upon the materials used. The best fabrics improperly put on may be the source of all sorts of diseases, while the poorest, if used with judgment, are capable of conferring a goodly degree of comfort. 462. The Clotliing should be Light.— All garments should be as light as is consistent with the main objects for which they are worn. "Weight does not necessarily imply warmth, and it often becomes a source of excessive fatigue and discom- fort. Warmth is better attained by putting on several layers of light, loose-fitting garments, than fewer layers of heavy clothing. As before stated, it is not the clothing itself, but the air imprisoned by it, which secures warmth ; and the air is not only held within the meslies of the cloth, but a stratum is retained underneath each additional layer»of clothing. It is, therefore, desirable to multiply the number of layers, which . is only possible when light materials are used. 463. It should be Loose. — Every one knows that loose clothing is warmer than that which fits the body closely, and this alone should be sufficient reason for adopting it. But tight-fitting garments are in other respects very injurious. They obstruct the flow of blood, restrict the natural motions and healthy exercise of the parts, and not unfi-equently pro- duce deformities of the worst character. Many have observed the eflects of a tight-fitting head-dress in obstructing the circu- lation. Constricting the neck is even worse. The great veins which carry the blood from the head back to the heart lie very superficially in the neck, and, when any thing tight is worn closely about it, the flow of blood is obstructed, and venous congestion of the brain results. 464. Compression of the Chest and Abdomen. — It is, likewise, of the greatest importance that the motions of the chest and abdomen should not be interfered with. There is probably no part of the body where fi*eedom of action and of 15


I 338 ELEMENTARY HYGIENE. circulation is more absolutely required tlian here. At the junction of the chest with the abdomen are located the lower portions of the lungs, the spleen, stomach, liver, etc. There are also given off from the aorta at this point several large ves- eels, which carry blood to the adjacent viscera. The diaphragm, the most important muscle engaged in the process of respiration, is likewise found in this immediate vicinity. Every function of the body calls for the utmost freedom of movement in this important region. And yet it is the almost universal practice among females to bind down these parts often to half their natural dimensions. Reference to Fig. 125 shows this to be one of the roomiest portions of the body when left in its natural condition. Fig. 125. A dlftgiam Bhowisg the natural fonn of the healthy chest, and the proper positiaQ of the oisans which it contains. Fig. 126 shows the distortion which oft^n results from com- pression. This deformity is not the worst of the evils which follow the practice of compressing these parts. The diaphragm ]m hampered in its actions, and the process of respiration thus


MAimEB OF DEESSING THE BODY. 339 directly interfered with. The lungs and heart are compressed, and the stomach and liver either forced out of place, or, what Fig. 126. A diagram Bhowing the deformity produced by compression. IS woi'se, squeezed into much less space than they would natu* rally occupy. The portal circulation is thus obstructed, and the viscera, like the brain in the former case, become the seat of venous engorgement. It is hardly necessary to add that the troubles induced by this state of things are of the most serious character. Disease! of the liver, dyspepsia, and consumption are among its legiti- mate and certain results, while other disorders of a less definite character are, no doubt, traceable to the same ejQBcient cause. The compression, when early applied, as it usually is, finds the bones of the chest soft and yielding, so that they readily give way. If the constriction is continued, as it is likely to be, for fear of losing the " beauty of the form," the bones, as age ad- vances, harden and conform to the unyielding limitations with-

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340 ELEMENTARY HYGUaJE. out, and thus arise permanent and life-long deformity of the chest and continued restraint of its important organs. The persistence with which this practice is followed by females, betrays either outrageous ignorance or an almost criminal dis- regard of consequences. 465. Compression of the Feet. — ^This is a common prac- tice, that often results in distortion and great discomfort Fig. 127 shows the deformity produced by compression, while Fig. Fig. m. Fio. 128. 128 gives the natural shape of the foot. When we are walking with the feet unrestrained, each foot, as it receives the weight of the body, broadens slightly, and lengthens to the extent of half an inch or more. Freedom of motion in the foot itself is thus seen to be a natural requisite, and without it ease, grace, and comfort in walking are out of the question. Compression by the boot or shoe not only prevents this freedom of action, but also gives rise to deformity of the feet. The sole of the boot should be as wide as and somewhat longer than the foot when the weight of the body is resting upon it. The upper- leather requires to be soft and yielding, and not so tight as to pinch the foot down upon the sole. The toe of the boot ought to be wide, leaving the toes perfect freedom of movement. If too narrow, they are made to override each other, thus producing ingrowing toe-nails, corns, bunions, etc. The heels should be low and broad, so as to furnish a firm support. High heels throw the feet forward toward the


MANNER OF DEESSmG THE BODY. 341 points of the boots, and tend to produce flattening of the arch of the foot. 466. ClotMng should favor Uniformity of Temperature. — In health, all parts of the body have an average temperature of about 98° Fahr., and this is regulated and maintained by the ckculation of the blood. This uniformity of temperature throughout the body is of the utmost importance, and as it is controlled through the circulation, any thing which disturbs this should be carefiilly avoided. Clothing may do it in various ways, producing local results often of a very injurious nature. Compression obstructs the flow of blood, and at the same time forces out what the part already contains. Over-clothing par- ticular points leads to the accumulation of heat and consequent relaxation of the vessels, when more than the normal supply of blood flows in, and congestion results. A lack of clothing, by affording insuflicient protection, permits the rapid escape of heat, and thus the temperature may fall below the healthy standard, while the surface blood is driven inward, producing congestion of the internal organs. Compression, wherever ap- plied, causes paleness, diminishes the calibre of the vessels, and is attended with an immediate lowering of the temperature. Hence the cold feet and hands caused by tight boots and tight gloves. Of the other causes of disturbance, both are generally operating: while one part is overheated by a superabundance of clothing, another part may at the same time be suffering from cold. This is often the case with children, who may be seen in cold weather loaded with clothing about the chest and neck, while the legs and lower portions of the trunk are hardly more than covered. 467. Disturbance of Vascular Parts.--Certain organs of the body are more vascular than others ; that is, their blood- vessels are larger and more numerous, and they receive a pro- portionately larger supply of blood. The throat, the lungs, the liver, and kidneys, are examples. Owing to their extreme vascularity, these organs are peculiarly liable to become the seat of engorgement if overheated by clothing or otherwise.


342 ELEMETqTABY HYGIENE. especially when other regions are at the same time imperfectly protected. An instance forcibly illustrating the bad effects of habitually overheating a part recently came within the writer's notice. A boy, 16 years old, had been daily employed for a period of about three months in the winter season, in a work- shop where he was obliged to stand with his back very near a hot stove. This maintained an almost constant congestion of the kidneys, which had led, when I saw him, to well-marked Bright's disease. The region of the kidneys is commonly overdressed by the lapping at this point of the garments which clothe the trunk and lower extremities. In this way, two or three extra thicknesses are commonly obtained, and a tendency is thus created toward the accumulation of blood in these im- portant organs. 468. Overdressing the Throat. — Muffling the throat is very common, particularly among children, and it is often re- marked that those who wrap it the most are the ones who suf- fer most from its disorders. This practice is perhaps respon- sible for more sore throats, coughs, and croups, than all other causes put together ; and A^hen this overdressing of the neck is supplemented, as it commonly is in children, by short dresses And thinly-clad extremities, the conditions are most complete for the production of all sorts of throat and lung affections. 469. Flannel next the Skin. — ^Uniformity of temperature is greatly promoted by constantly wearing next the skin some non-conducting material, such as flannel or silk. This prevents sudden chilling of the surface, which, in our variable climate, is liable to take place at any time, unless specially guarded against. Flannel is found by experience to be best for this purpose ; but, in those cases where it irritates the skm, cotton- flannel or silk may be conveniently substituted. Linen should never be used. The good effects of wearing flannel next the skin the year round are unquestionable. In both cold and hot climates it is found to be an efficient safeguard against dis- ease ; and there are few who cannot soon become accustomed to its use.


MANNER OF DRESSING. THE BODY. 343 470. Clothing of Children. — Erroneous notions upon this subject lead to wrong practice, which is followed by the most pernicious consequences. Many entertain the idea that their constitutions may be hardened by exposure ; but, instead of any such vague benefit, specific and positive injuries are produced. Clothing, diet, and healthy growth are intimately correlated. Food is the source of all bodily function and power, and the supply of force from this source is necessarily limited. Each day's bodily exercise, each day's mental exercise, each day's waste, repair, and growth of all the organs, and the definite amount of heat required to maintain the system at 98° during the 24 hours — each and all are at the expense of the food daily digested, and any overtaxing in one direction involves corre- sponding deficiencies in others. If the body is insufficiently clothed, there is extra loss of power through waste of heat, and a necessary reaction upon the constitution. The waste of heat entails a lowering of vital processes, and body and brain fail to reach a vigorous development Thus, the naked legs and arms of children, which so please the vanity of silly mothers, are at the cost of their perfected constitutions. The exuberant energy ©f childhood is not to be carelessly squandered, but carefully economized and directed to its highest uses. 471. Clothing in Advanced Age. — As the bodily func- tions decline in vigor with advancing life, the protecting influ- ence of clothing becomes more necessary. The incapability of the aged to resist cold is well known, and fatal consequences frequently follow from persisting in old habits, and neglecting the indications of Nature for increased warmth and abundance of apparel.


344 ELEMENTABY HYGIENE. CHAPTER XIX. EXERCISE AND HEALTH. Section L — Labor and Exercise, 472. Man intended for Action. — ^Anatomy and Physi- ology alike proclaim that the purpose of the human constitution is activity. The provision for varied and complex movement is seen in the jointed skeleton, the contractile muscles, the controlUng nerves, and the power-supplying apparatus of di- gestion and circulation. Thus the whole economy of the organism testifies that its end is action. Moreover, the cir- cumstances of life involve the necessity of action. Effort must be put forth for the maintenance of existence, and for the gratification of the various faculties of our nature. 473. Labor. — This great end of our being flihds its legiti- mate and natural expression in labor, which is human action applied to various materials and objects, for the attainment of some productive or useful result. The necessity of labor is thus doubly provided for in the construction of the human tabric and the order of external nature, and, when performed with due regard to the laws and rights of our being, it is in every respect a benefit and a blessing. But when pursued to excess, as has unhappily been too common in the past history of man- kind, it is perverted- into degrading drudgery, and then be- comes a curse. As skilful and effective labor involves intelligence, time and thought are needed to secure aptness in its performance, and the narrower the range of effort, the greater is the facility attained. This restricts the individual to specific pursuits, and gives rise to that diversified system of division of labor which has grown to such vast complexity in modern society. The tendency of this system is to call into intense cxercige a portion — ^perhaps but a small portion — of the activity of the individual,


LABOR AND EXEECISE. 345 and to leave the remainder of his powers unused. In many vo- cations the hands only are brought into requisition, while the body is unexercised ; in others, the muscular system alone is involved, while the brain remains unoccupied ; in other cases the brain is active and the body at rest, or perhaps a portion only of the brain is exerted, as in numerical computation and managing accounts. 474. Exercise. — Thus the tendency of modem life is to overwork a narrow portion of the human constitution and un- derwork the remainder, so that a large part of it is not called into the activity for which it was designed, and which is neces- sary to health. There are few persons whose habitual activi- ties are so complete that they do not require to be supple- mented by various artificial exertions, while this need is still more imperative with those of sedentary habits and the classes of leisure. To meet these various emergencies, and give to the unused portions of the human system their requisite action, is the object of exercise. Section II. — Effects of Regulated Exercise, 475. Transformation of Physiological Forces. — All thoso vital processes which are essential to life, as digestion, circula- tion, respiration, secretion, are carried on independently of the will, and give rise to a large and constant amount of activity in the system. But labor and exercise are performed by calling into action an additional system of agencies — ^those of the vol- untary muscles — and to maintain these in a state of activity, involves an extra requisition upon the various involuntary organs. As the materials of the body are derived from the substance of the food, so all vital power is derived from the force stored up in the food. Organic matter is in a state of molecular tensioii, and, when decomposed, these tensions arc given out in the form of physical forces. Food is organic mat- ter, suited to undergo assimilation, and then to give out its molecular tensions in various forms, as animal heat, muscular 15* ^-

VjOOQ IC J 

346 ELEMENTAET HTGIENB. power. It follows tliat in work, or exercise, the voluntary muscular system draws upon the involuntary functions for its supply of energy ; and hence, in proportion to the force ex- pended, is the general exaltation of the vital processes. 476. Exercise, Waste, and Bepair. — ^Bodily exertion thus increases atomic changes, and quickens that metamorphosis of tissues in which health essentially consists. Exercise is at the expense of waste ; waste involves repair, and these augmented processes call into higher action the whole apparatus of supply and excretion. Habitual exercise is thus the cause and condi- tion of that vital renovation of parts which is the source and measure of constitutional vigor. 477. Effect upon the Circulation. — As the circulation ministers immediately to all the functions, its energy rises and falls with their activity. Exercise increases the movements of the heart in both force and frequency, and accelerates the flow of blood through all parts of the body. The circulation is also aided by the contractions of the voluntary muscles, which, by pressing upon the walls of the veins, tend to force along the current of blood. Moreover, this increased activity of the cir- culation meets the increased demand of the muscles for new material, to renew the disintegrated structures ; and it also etfects the speedy removal of all waste products, by rapidly transferring them to the proper eliminating organs. Thus, the complex stream from which nutritive materials are constantly drawn, and into which waste matters are constantly poured, is directly affected, both in its composition and rate of movement, by the state of action of the voluntary muscles. Exercise also, it is well known, heightens the calorifying functions. It is through the increased activity of the circula- tion that the body is warmed by exercise. This is the reason why walking is so effectual in warming the feet, and why exertion of any kind raises the temperature of the parts em- ployed. 478. Effect upon Bespiration — Circulation and resplra* tion are accelerated together by exercise, as whatever quickenii


EFFECTS OF EEGULATED EXEECISE. 347 the pulse hastens the breathing. It being the office of respira- tion to furnish the prime mover of vital changes^ — oxygen — and to rid the system of the chief product of such change — carbonic acid — this process is doubly subservient to the great dynamic objects of the organism. It follows that a fundamen- tal condition of exercise is unimpeded respiration. If the pul- monary circulation and the elimination of carbon are in any way interfered with, the power of continued exertion rapidly declines. As thus muscular movement depends immediately upon the excretion of carbonic acid from the system, and as this, in turn, depends upon the state of the air itself, we see that an impure atmosphere is unfavorable to vigorous and healthfbl exercise. This explains the lassitude and indisposi- tion to effort in unventilated houses, workshops, and factories. Exercise should, therefore, as much as possible, be carried on in the open air, or in places which admit of the freest ven- • tilation. 479. Effects upon Digestion. — As power comes from food in the case of the living machine, increased expenditure of power, of course, implies increased consumption of food; hence, exercise. sharpens the appetite. In those who indulge in active and regular exercise, digestion is effected with greater ease, and the process is more rapidly and more thoroughly completed than in those of inactive habits. In many cases, where the digestive function has become impaired, either from habitual inactivity or a too close application of the mind, relief can easily come through systematic and judicious exercise. Im- mediate exertion after a full meal is injurious, for several rea- sons. ^ The distended condition of the stomach interferes with the free movement of the diaphragm and heart, and thus both respiration and circulation are mechanically impeded, while the diversion of blood and nervous force to the muscles with- draws them from the digestive organs and hinders their functions. 480. Effect upon the Skin. — ^With exercise, the skin be; comes redder and hotter, from the increased amount of blood


348 ELEMENTAEY HYGIENE. it receives. During exertion, heat is rapidly developed within the body, but its accumulation is prevented by the escape of water through the skin. No amount of external cold is able to prevent this outward passage of fluid, though it may slightly hinder evaporation. There is, therefore, little danger of chill during active exercise ; but when exertion is over, there is great danger of it, for the heat of the body rapidly declines, while evaporation continues, which still more reduces the tempe- rature. During exertion, the skin may be exposed without danger ; but during the intervals of rest, it should be covered sufficiently to prevent the least feeling of coolness of the surface. 481. Exercise should be Segular. — Like eating and sleeping, exercise should become a regular and persistent daily habit. It is an imperative necessity of the system, and, as an element of personal hygiene, is indispensable. If it be resorted to in any form of bodily training, as in military drill, rowing, or other athletic effort, it is found that the periods of exertion must not be less than half an hour, in order to take hold of the system, and produce the positive effect of bodily discipline. 482. The Mind in I^ercise. — Exercise, or simple muscu- lar movement, whatever may be its value for health, has in itself very few attractions, and will be avoided rather than prac- tised, unless there is connected with it something capable of calling the mind into pleasurable activity. When taken merely from a sense of duty, or " because the health requires it," ex- ercise becomes a drag and a bore, without vigor and of httle benefit When, however, it can be made the means of enjoy- ment, by associating with it something agreeable and exhila- rating, it becomes at once spontaneous, vigorous, and hearty, and its value to the health, both of mind and body, is increased in a great degree.


EXCESSIVE AND INSUFFICIENT EXERCISE. 349 Section III. — Excessive and Insufficient Exercise, 483. Effects of Over-exertion. — ^With the proper amount of exercise, the muscles increase in size, hardness, and elastic vigor, until the equilibrium of waste and repair is carried to its highest point. Exercise is at the expense of the part in action ; in vigorous exertion, decomposition prevails over renewal. The muscles can bear this for a certain length of time, and then de- mand rest, in which repair prevails over waste, and restores the balance. If exertion be pushed still further, the equilibrium is lost ; destructive changes prevail over reparative, and the mus- cle begins to degenerate and lose power. Prolonged exertion, without sufficient rest, impairs nutrition, and renders the mus- cular fibres soft and flabby. Nature thus provides for the rhythm of activity and repose. The involuntary muscles, as we have seen, — ^those of the heart and chest, — act in this inter- mitting way, and are thus kept up to a constant state of vigor. The law is equally imperative for the voluntary muscles, and the proper rest is to be secured either by ceasing from activity, or by calling different sets of muscles into alternate exercise. When the muscles are weak, repair goes on more slowly than when they are "in condition." Hence, in any effort at ac- quiring strength by exercise, either after sickness or prolonged sedentary occupation, the exercise should at first be very light, and of short duration, with long intervals of rest. As the strength slowly increases, the exercise may be increased, but exhaustion in all such cases is to be carefully avoided. Excessive exercise often produces palpitation, and some- times hypertrophy and valvular disease of the heart. During exertion, if the heart is not oppressed, its movements, though rapid and forcible, are regular and equal ; but when it becomes embarrassed, the pulse-beats are quick, unequal, and at last be- come irregular, indicating injury to the organ. All great or sudden efforts ought to be carefully avoided, as they not only affect injuriously the muscular system, by direct overstrain, but


350 ELEMENTARY HYGIENE. it is at such times that blood-vessels are ruptured, and that the walls of important cavities give way. Kest after exertion is one of the most important conditions of health. Work or exercise carried habitually to the length of exhaustion, by lowering the bodily vigor and depressing the powers of the constitution, not only diminishes resistance to the encroachments of disease, but greatly reduces the capability of recovery in cases of siclmess. Particularly in childhood, when the bones are yet incompletely ossified, and the muscles undeveloped, excessive labor or exertion is liable to entail. per- manent injury. If persisted in, arrested development of either body or mind can hardly fail to result. From the age of 15 to 25, although full growth may have been reached, the powers of endurance have not attained their maximum, and all ex- hausting tasts require to be avoided. Young soldiers break down under the toils and privations of the camp sooner than mature men. This is also true in civil life, where the young and immature are called upon to match their powers with those in the maturity of manhood; and the remark is equally applicable to the female, under the spur of competition with the male sex. The consequences are seen in broken-down constitutions and premature decay. 484. Effects of Insufficient Exercise. — Inaction contra- venes the supreme design of the human constitution, and is therefore adverse to its health. As bodily vigor results only from active and well-regulated exercise, the absence of such exercise must entail bodily debility. As exertion favors nutri- tion and the healthy development of active parts, inaction im- pairs nutrition, reduces the size of the muscles, and gives rise to feebleness. The amount of injury in the case may, however, depend much upon accompanying circumstances. If abstinence from exercise be attended by abstinence in diet, there will still be loss of power, low vitality, and diminished resistance to morbific influences ; the evils will be rather of a negative char- acter. But if deficient exercise be accompanied by a free in- dulgence of the appetite, perverted nutrition and positive dia-


EXC5ESSIVE AND INSUFFICIENT EXEECISE. 351 ease will be the necessary consequence. Nutritive materials tliat would be reduced and excreted through bodily exertion, accumulate in the system, clogging its movements, deranging its functions, and deteriorating its structures. Not only is there an abnormal accumulation of fat, amounting to actual disease, but an aberration of the nutritive forces, that under- mines the healthy structure of the tissues. Nor is this muscu- lar deterioration hmited merely to the parts that are unused ; the involuntary mechanism becomes implicated. Deficiency of exercise often leads to fatty degeneration of the heart, with loss of power and derangement of the circulation. In short, as vigorous and systematic exercise is a prime condition of the general health, so the want of it favors the approach of disease, which may take many forme, according to the circumstances of the constitution. 485. Amoimt and Conditions of Exercise. — As to the amount of exercise necessary to meet the requirements of the healthy individual, no precise rules can be given ; that amount will vary with many circumstances. Persons of sedentary habits would be seriously injured by attempting to perform an amount of work which, to others of a more active turn, would hardly exceed the bounds of recreation. The inmate of the workshop or factory would be speedily exhausted by the ordinary tasks of the out-door laborer. In any given case, the amount of exercise should be determined and regulated by the state of the constitution. That exercise is deficient which does not engage the vigorous action of the chief muscles of the system for a considerable period each day ; and that too great which, passing beyond the point of simple fatigue, is prolonged to the period of exhaustion. The sedentary, if they would acquire strength, must begin with light exertion, limited to short periods, and take ample time for rest. Nothing is more erroneous, and, if carried into practice, more injurious, than the notion that great exertion will augment the strength of those unaccustomed to active ex- ercise. The growth of muscle, in both substance and power,


352 ELEMENTAEY HYGIENE. is a gradual process, and one that is retarded rather than has- tened by overwork. If exhaustion or restlessness follows ex- ercise, we may be certain that it has been overdone, and will be productive of weakness rather than strength. As has been stated in a previous chapter, an abundant sup- ply of pure air is at all times a vital necessity of health ; but tlie demands of the system in this respect aijp greatly increased during active muscular exertion. As the diminution of waste products is a result of oxidation, it is hindered by breathing an impure atmosphere. For this further reason, open-air exer- cise is much superior, as a health-promoting agent, to that carried on within the walls of a gymnasium or other confined area. 486. Bemedial Influence of Exercise. — If thus exercise be an essential condition of health, and the want of it a fruitful cause of disease, it is obvious that only by the reestablishment of the needed exercise can health be regained. But in many cases the diseases induced make the required eflfort either im- possible or very diflScult. What is known as the movement- cure is a kind of dynamic treatment, in which the patient is subjected by the physician to various kinds of artificial exer- cise. In many cases of local weakness and partial paralysis, by the help of skilfully-constructed mechanical contrivances, these parts are gradually brought into action, and healthy- power slowly recovered. The principle in this case is valu- able, and, important as a remedial agency, its employment has accomplished much good, and more is to be expected from its fiirther development


EELATIONS OF MIND AND BODY. 353 CHAPTER XX. MEI^TTAL HYGIENH Section I. — Relations of Mind and Body. 487, Mental Health a Physiological ftuestion.— Thus far we Lave confined attention mainly to the influences which act on the general bodily health, but the principles of hygiene have a still higher ^plication. The mind has its states of health and vigor, of debility and disease, like the body, and these states are influenced by definite causes in the former case as well as in the latter. Mental philosophy, as commonly un- derstood, explains to us the operations of 'thought and feeling as we discover them in the working of our own minds, and takes Httle account of the part played by the corporeal system in the control of these processes. But if we would understand the conditions of mental health, and the nature and causes of mental impairment, the body must at once be taken into ac- count. The study of mental phenomena in their corporeal relations thus becomes the business of the physiologist. He sees that mind is not only intimately dependent upon the body, but that they have close and powerful reactions; states of body determining conditions of mind, and states of mind influencing conditions of body. Nature presents the problem, not of mind separate, but of mind and body bound up in a living unity, and the physiologist must take the question as he finds it. 488, The Brain and the Mind. — It is now universally admitted that the brain is the grand nervous centre of thought and feeling — the material instrument of the mind, and that all mental actions are accompanied and conditioned by physiolo- gical actions. From the high complexity of composition of nervous matter, it is extremely unstable and prone to change. The brain is therefore not only, like all other parts of the body.


354 ELEMENTAEY HYGIENE. subject to the double metamorphosis of waste and repair, but the transformations take place in this organ with more rapidity than in any other part of the system. Upon these changes the mental operations are vitally dependent, and if in any way they are interfered with, there is disturbance of the intellectual processes. If the cerebral circulation is lowered, mental activity is diminished ; if accelerated, the mind's action is exalted. Various foreign substances introduced into the blood-stream alter the course of thought^ some affecting it one way and some another, but each, through its specific physiological effects, producing characteristic psychological effects. Inflam- mation of the brain induces delirium, while different diseases of the organ, or perversions of the blood circulating through it, give rise to various forms of insanity. It is important to note, not only that mind and body are both governed by laws, but that they are to a great extent governed by the same laws. Whatever improves the physical qualities of the brain, improves also the mind; whatever deteriorates the brain, impairs the mind. They have a com- mon development, are equally increased in vigor, capacity, and power by systematic and judicious exercise, and are alike in- jured by deficient or excessive effort The brain is exhausted by thinking as much as the muscles by acting, and, Uke the exhausted muscles, it requires time for the restoration of vigor through nutritive repair. As thus the mind is dependent upon the conditions of the brain, while the brain is controlled by the bodily system, we see how impossible it is to deal with the mental powers in a practical way without taking the ma- terial organization into account. The objection often made, that this method of considering mind involves or leads to materialism, is altogether groundless. Materialism is a doctrine of causation which afiSrms that mind is a prodiLct of organization. But the degree to which mind is organically conditioned and limited is a pure question of fiEict and observation, and is totally independent of all speculation upon the former subject. If, to assert that " the brain is the


EELATI0N8 OF MIND AND BODY. 355 organ of the mind," involves materialism, it can only be said that all intelligent persons are to be ranked as materialists; but if not, then certainly the physiological inquiry which aims merely to trace out the details of the connection between mental mani- festations and corporeal states, is not obnoxious to the charge. There is nothing in the subsequent working out of the particu- lars that is not involved in the first broad assumption. 489. Mental Health and Disease. — ^The observations made in regard to the true nature of diseases (361-2) — that they are nothing more than per\'erted physiological actions — ^need to be here repeated with emphasis. Those who habitually think of the mind as a separate entity merely coexisting in some vague way with the body, will naturally look upon mental derange- ments as disorders of this entity — diseases of an abstraction. But this view has proved misleading and injurious in the extreme. So long as maladies of the mind were regarded as demoniac possessions, or as " fermentations taking place in a spiritual essence," all rational causality was excluded, and the arts of relief and prevention were irapossible. When, how- ever, it became established that mind depends upon definite physiological conditions, there was no escape from the conclu- •ion that physiological perversions are causes of mental derangement. " Fair weather and foul equally depend upon the laws of meteorology ; health and disease equally depend upon the laws of animal life." As mental health is dependent upon the due nutrition, stimulation, and repose of the brain, mental disease is to be regarded as resulting from the interruption or disturbance of those conditions. In showing that mental weakness is a concomitant of bodily debility, and mental abeiTation a consequence of bodily dis- order, the physiologist lays the sure foundations of a practical Mental Hygiene^ the province of which is to consider the various causes which disturb the harmony and impair the vigor of mental actions. Taking note of the multiplied forms and de- grees of disturbance and degeneracy to which the mental na- ture of man is subject, it traces them to their numerous causes.


356 ELEMENTAEY HYGIENE. and discloses the extent to which they are avoidable. As bodily and mental health depend to a great degree upon the same conditions, all that has been said in the foregoing chapters concerning the sanitary influences which affect the corporeal system has likewise its bearing upon health of mind. But the Tnental aspects of the subject are so generally overlooked as to demand special consideration. Diseases of the brain are, above all others, complex and obscure. Those of subordinate parts affect only the organic functions ; but when the higher nervous centres become dis- ordered, thought, feeling, will, conduct, and character are im- plicated, and the whole circle of individual relations and actions becomes a study of symptoms — a field of diagnosis. So great is the difficulty and responsibility of the task, that only the educated and capable physician who devotes his life to this specialty is competent to deal with these cases. And yet all members of the community have a vital interest in the subject : because, firsts health and vigor of mind are of the highest im- portance, while each person has these interests in his own im- mediate care ; second^ the causes which undermine them are numerous and insidious ; third, every one is liable to be called upon to act responsibly with reference to others who may be the subjects of mental impairment ; fourth, society has a duty to perform toward the defective-minded, which should be per- formed, not ignorantly, but intelligently ; and, finally, because a real knowledge of the characteristics and causes of mental deterioration is the key to a true understanding of the consti- tution of human nature. While, therefore, that detailed and deeper understanding of these questions which is necessary to discriminate their minor distinctions is only to be expected of the professional expert, such a general acquaintance with the leading types of mental disease as will facilitate an understanding of causes is needed for all. A section of the present chapter may there- fore be properly devoted to their description and illustra- tion.


FOEMS OP MENTAL IMPAIEMENT. 357 Section II. — Forms of Mental Impairment 490. Modes of Mental Action. — ^Mental effects are mani- fested by the brain in a threefold form, as Intellect, Feeling, and Will, The intellect is the perceiving or knowing part of the mind, including perception, niemory, reason, imagination, and judgment. The mental nature has also an affective side, consisting of feelings, sentiments, emotions, passions. The intellect is discriminative, and has relation to the reality or truth of things ; the feSlings are impulsive, and have regard to pleasure or pain. The will is the determinative or volitional part of the mental constitution, and has relation to effect or action. The intellect is an eye that sees an end to be attained and the means of reaching it ; the feelings, or desires, furnish the impulse to its attainment, and when these rise to suflScient intensity, they issue in a volition, which puts the body in movement to secure the thing desired. These are not separate elements of our psychical being, but inter work so closely and harmoniously as to give rise to per- fect mental unity. Still the distinction is so ftmdamental as to be recognized, both in the study of the healthy human fac- ulties and also in their morbid manifestations. There is an insanity which is predominantly intellectual, disclosing itself in disordered sensation, perception, memory, judgment, and reason, without deeply involving the feelings ; and there is an emotional insanity, which consists in the unregulated action of the impulses, while the intellect may be but slightly disturbed. But usually all these faculties are more or less involved in the mental disturbance. 491. Aberrations of the Intellect. — ^In Chapter XL, Sec- tion n., it was stated that, owing to certain conditions of body, false appearances and various disturbances of the senses are liable to arise. These errors are of several Muds. Hallucinations, — The case of Mrs. A., the details of which were given (296), belongs to a class of deceptions in which


358 ELEMENTAEY HYGIENE. objects appear to be present, when in reality they are not ; sensations are perceived, although there are no material objects to produce them. All the senses are subject to these decep- tions; sights, sounds, tastes, smells, and contacts are experi- enced when there are no realities to cause them. Mental mis- takes of this kind are known as hallucinations. They are very connnon, and the greatest minds are often subject to them. Byron fancied he was visited by a spectre, which, he confesses, was but the eftect of an overworked brain. Dr. Johnson said that he distinctly heard the voice of his mother calling " Sam," although she was, at the time, residing a long way oflf. Goethe positively asserts that he one day saw the exact counterpart of himself coming toward him. Descar- tes, after long confinement, was followed by an invisible per- son, calling upon him to pursue the search of truth. Luther imagined he saw the devil, and threw his inkstand at him. Bullucinations may thus coexist with a sound state of the rea- son, which recognizes their true character. In tbc insane they assume a thousand singular and fant^tic forms. Illusions, — ^Again, an object may be perceived, but misun- derstood, or mistaken for something else. In this case there is an illusion. These, also, are very common. The apparent flight of the trees and fences as we glide swiftly along in the railway-train is an example of illusion, which is immediately corrected by the judgment The mirage at sea, or on the des- ert, is another illustration. When the imagination becomes morbidly excited through the influence of fear, superstition, or otherwise, there is great liability to illusion. The folds of drapery, or pieces of furniture, seen by a pale, uncertain light, are taken for apparitions; the clouds are transformed into fighting armies, or the heavens appear filled with blood. When the mind becomes more deeply perverted, one person is mis- taken for another; animals arc mistaken for men, and con- versely, an old hat for a royal crown, and a handful of pebbles for heaps of gold. jOeZimorw.— In the foregoing cases the seat of error is, not


FOEMS OF MENTAL IMPAIRMENT. 359 the senses themselves, but the judgment in relation to objects of sense. But the mind is liable to deceptions, and various false notions, which have no immediate reference to sense-per- ceptions, as where a person believes he is a prophet, or a king, or is the victim of a conspiracy to take his life, or has lost his soul. False impressions of this kind are characterized as delu- sions. From the illustrations given, it will be seen that hallucina- tion and illusion may coexist with a sound state of the reason, which comprehends their real nature, and it is maintained that, in some cases, the mind can rectify its own delusions. But if, in any of these circumstances, the individual is incapable of recognizing or correcting them when an appeal is made to his reason, the case is one of delusional insanity, or insanity of the intellect. These delusions are, of course, liable to involve the feelings, and the character of the insanity may depend upon the emo- tions excited. A person under the delusion of pride, who fancies himself an emperor or an angel, may be harmless ; but if, under the delusion of fear, he imagines those around him to be enemies, seeking to take his life, or if he hears voices com- manding him to kill them, his insanity is dangerous, and ne- cessitates restraint. 492. Emotional Insanity. — By this is understood a de- rangement of the affections, an abnormal deficiency of moral sense, or morbid activity of the propensities, which gives rise to extravagance of conduct. These diseases of feeling do not necessarily involve insanity of the intellect A person may have a good degree of intelligence with a very low and defec tive moral nature, or he may be driven by insane impulses to the commission of acts which his judgment condemns. In the healthy balance of the faculties, reason guides the passions ; but these may be so morbidly exalted, that reason loses its empire ; it can counsel, but no longer control. Moral perver- sities of character may be congenital, or from birth, when the whole life of the individual is morally unhealthy, or it may be


360 ELEMENTAEY HYGIENE. due to various causes, the effects of which are seen in a pro- found change in the conduct. Examples of the former kind are numerous where inertness or obtuseness of the moral nature, and a controlling activity of the lower propensities, have been witnessed from childhood, and over which threats, rewards, and punishments were with- ' out influence. Cases of this kind are well represented by the individual described by Dr. Crawford : " He exhibited a total want of moral feeling and principle, yet possessed considerable intelligence, ingenuity, and plausi- bility. He has never been different from what he now is ; he has never evinced the slightest mental incoherence on any point, nor any kind of hallucination. He appears, however, so totally callous with regard to every moral principle and feeling, so totally unconscious of ever having done any thing wrong, so completely destitute of all shame or remorse when reproached for his vices or his crimes, and has proved himself so utterly incorrigible through life, that it is almost certain that any jury before which he might be brought, would satisfy their doubts by returning him insane." In the other class of cases, persons in whom mental de- rangement had never appeared, become the subjects of a gradual change of feeling and conduct. They are noticed to be unusually absorbed, reserved, and irritable upon the slightest provocation. As the cloud gathers, there is increas- ing suspicion and moroseness, and, without perhaps knowing the reason, the patient's friends regard him as an altered man. At last the storm bursts, and some outrageous act is committed. If it is not a breach of law, he is pronounced insane, and sent to the asylum ; if in violation of law, he is probably declared a criminal, and sent to prison or to execution. Or the case may terminate in suicide, under a blind impulse to self-destruction. A good illustration of emotional insanity is given by Dr. Maudsley. A married lady, aged thirty-one, who had only one child a few months old, was for months afflicted with a strong and persistent suicidal impulse, without any delusion.


FORMS OF MENTAL IMPAIRMENT. 361 or any disorder of tlie intellect. After some weeks of anxious care from her relatives she was sent to an asylum, so frequent were her suicidal attempts. She was quite rational, even in her great horror and reprobation of the morbid propensity, and bitterly deplored the grief and trouble she caused her friends. Nevertheless, her attempts at suicide were unceasing — at one time trying to strangle herself, and again refusing all food. After she had been in the asylum for four months she appeared to be undergoing a slow and steady improvement, and watch- fulness was somewhat relaxed ; but one night she suddenly slipped 'out of a door, cUmbed a high garden-wall with sur- prising agility, and threw herself headlong into a reservoir of water. She was got out before life was quite extinct ; and after this attempt, gradually regained her cheerfulness and love of life. Her family was saturated with insanity. Dr. Maudsley exclaims : " In face of such an example of uncontrollable im- pulse what a cruel mockery it is to measure the lunatic's respon- sibility by his knowledge of right and wrong ! — implying that there are those who would limit insanity to derangement of the intellect — a derangement so profound as to obliterate the capa- bility of even discriminating between right and wrong. There has been a reluctance to admit the existence of what is termed moral insanity on the part of many, who confine their attention to the practical difficulties it involves as regards society ; but with those who make it their business to study the facts in a true scientific spirit there is no shadow of doubt in the matter. Examples, like those above mentioned, innumerable and end- lessly varied, but all presenting the same marked and essen- tial features, are to be rationally accounted for. It being ad- mitted that derangement of the intellect is due to disease of its organ, and furthermore that the brain is the instrument of feeling as well as of thought, there can be no escape from the conclusion that cerebral disorder may also give rise to insanity of the feelings and propensities. The conviction of all emi- nent physiologists and pathologists upon the subject is thus expressed by Dr. Carpenter : 16


362 ELEMENTAET HYGIENE. "* There may be no primary disorder of the intellectual faculties, and the insanity may essentially consist in a tendency to disordered emotional excitement, which affects the course of thought, and consequently of action, without disordering the reasoning powers in any other way than by supplying wrong materials to them. Moral insanity may, and frequently does, exist without any disorder of the intellectual powers, or any delusion whatever.' " Dr. Ray makes the following judicious and forcible obser- vations upon the practical aspects of this subject: "While people clearly recognize the infinite diversity of intellectual gifts, and would no more expect the fruits of genius and talent from those who had been denied by Nature the slightest por- tion of either, than we should grapes from thorns or figs from thistles, they are in the habit of believing that for all practical purposes the moral endowments of men iare equal Not exactly that they are equally benevolent, equally honest, equally true to the i-ight and the good ; but that they might be if they chose. They never would think of saying to men, * Here is poetry, here is philosophy, here is art ; you have the capacity to excel in either; take your choice, and be rewarded or punished accordingly.' " In the moral sense or faculty it is easy to recognize two different elements, viz., the power to discern the distinction between right and wrong, virtue and vice, the honest and the base, and the disposition to pursue the one and avoid the other. These elements, like these of the intellect, are une- qually developed in different men, which inequality may be either congenital or produced in after-life by moral or physical causes. And thus, though a person may act with perfect free- dom of will, unconscious of any irresistible bias, yet it is obvi- ous that his conduct is actually governed more by these varia- ble conditions of his moral nature than by any abstract notions formed by the intellect. " From the unquestioned fact that the brain is the material instrument of the mind, we are led to the inevitable conclusion


F0EM8 OF MENTAL IMPAIEMENT. 363 that its physical condition must modify more or less its mental manifestations, moral as well as intellectual. It is said, in the common form of speech, that a person is good or had hecause he cj^ooses to he the one or the other; and it is all very true, and suflScient perhaps, for our rough estimates of responsibility, but it does not answer the essential question. What determines the choice ? In the considerations here pre- sented, and in these only, is to be found a satisfactory answer to this question." 493. Mania. — This is the term applied to a large class of cerebral disorders, in which the balance of the mental forces is lost, and the mind is in a state of preternatural excitement It generally involves both the intellect and the feeling, but is more markedly a perversion of the impulses and propensities. Mania is either acute or chronic. Acute Mania is that form of mental disease commonly known as raving madness. It presents the aspect of high emo- tional excitement, the facial expression showing wildness, dis- traction, anger, or fear. In the paroxysms of acute mania, there is violence of speech and action. The patient raves, laughs, weeps, sings, laments, shouts, prays, and threatens ; bis utterance is loud, rapid, and impetuous ; his voice harsh ; he manifests a total disregard of cleanliness and decency, and a dangerous destructiveness in relation to those around him, or even to senseless objects. " The condition of the mental faculties in acute mania pre- sents the widest differences. In many instances no trace of delusion can be discovered in a patient who is vociferating, swearing, laughing, reproaching, in constant movement, and without sleep. The observations and the remarks are some- times found to have a certain kind of cleverness, and shrewd appreciation of all that is taking place. The attention skips from object to object with choreic rapidity and abruptness, causing exaggerated and absurd emotional states, but in many instances not falsifying the judgment. In most cases, how- ever, delusions and hallucinations exist, and the task of detect-


Z64: EJ.EMENTABY HYGIENE. ing tbem is not diflScnlt ; for in tbis form of disease the patient is so demonstrable, that he usually dins his delusion into your ears (Bucknill and Tuke). ACUTE MANIA. EeprcsentB the physiogTJomy of a case of acute mania. The patient is a woman thirty years of age, whose insanity was brought on by loss or character, want, and dis- tress. There Is mnch emotional and intellectual disturbance, with compara- tively little deranfferaent of the physical health. She believes that she is tormented by witches, and that she is compelled by them to make noises resembling dogs, cats, etc. She sometimes destroys crockery and glass, and attempts to get up the chimney ; says she is cat to pieces, and that all the people around her are murderers. She strikes without warning straightforward blows at the faces of those who converse with her.* Chronic Mania is in most instances the result of the acute form of the disease. " It represents the rudderless and shat- tered state of the vessel after the tornado of raving madness has swept by." There is mental debility, persistent delusion, and less violent emotional disturbance. Chronic mania which has not passed through the acute stage frequently presents a remarkable vigor of the intellectual functions, in so far as they are ijot affected by delusion. Patients with this form of disease not only retain the per-

  • This likeness and those that follow (excepting the case of idiocy), which repre-

sent the leading types of mental disease, are engraved from photographs taken ftom the life, and given in the authoritative work of Drs. Bucknill and Take on Insanity.


FORMS OF MENTAL IMPAIRMENT. 365 ceptive faculties in all their activity, but' the memory also is found to be tenacious, and even the judgment, on matters un- connected with the delusive opinions and perverted emotions peculiar to the case, may be found to be suflSciently trust- worthy. 494. Monomania. — By this is understood a malady of the mind similar in character to mania, but limited to a single sub- ject, or involving only a single faculty. The patient may be the subject of a single delusion, which, being the result of dis- ease, he cannot overcome, although upon all other subjects the mind is healthy ; or some one emotion may acquire a morbid Fig. 180. MONOMANIA. Eepresents a case of the monomania of pride. It is the portrait of a woman of thirty- eight, who labors ander the delaslon that she is her ms^csty's person ; she is not her mt^esty, but hor person, a distinction on which she lays great stress. She is proud and dii^ifled in her demeanor. Out of the commonest materials of dress she contrives to make a distinguished appearance. She fastens the skirt of her dress low, so as to form a sort of train, and with arms folded, the head, with its coronal ornaments, thrown proudly back, she would, If permitted, main- tain an erect and regal position from morning till nitiht. The intense pride ex- pressed in the turn of head and eye, and in the tirm, compressed lips, canntit be mlstAken. It is the physiognomy of an exaggerated emotion transmuted into one delusive idea. ascendency and domination over the whole character. Mono- manias are of various Mnds. In homicidal mania there is an insane propensity to kill ; in suicidal mania an irresistible im-


366 ELEMENTAET HTQIENB. pulse to self-destruction — a marked case of this kind has been already described (492); kleptomania is a diseased propen- sity to theft ; and in pyromania there is an impulse to bum buildings. There are also monomanias of pride, vanity, etc. Dr. Bucknill describes the following representative case : " An industrious, honest, well-informed artisan had a fever, which resulted in an attack of maniacal excitement. From this he speared to recover, but his temper was altered ; ho became irritable, suspicious, and quarrelsome. After the lapse of more than a year he declared himself to be the Son of God. His temper now improved, and at the present time the delusive opinion is, perhaps, as nearly the sole mental affection as is ever seen in cases of so-called monomania. Occasionally there are outbursts of violence toward those whom he thinks ought to obey him ; but on the whole he is docile, and on other matters reasonable, and works industriously at his trade." 495. Melancholia. — ^The forms of mental impairment thus far noticed are marked by undue intensity or exaltation of the cerebral function : we now pass to the consideration of those of an opposite character, which exemplify teficient or depressed conditions of the mental constitution. While, for example, the monomaniac is excited, lively, and gay, " living without himself and diffusing among others the excess of his emotions," the melancholiac is sad and sorrowful, and fastens all his gloomy thoughts upon himself. In simple melancholia the patient loses his interest in life, feels depressed and unequal to his duties, is cheerless, moody, and taciturn. His thoughts are centred upon his own desper- ate condition, which he believes to be more wretched than that of any other person. He magnifies every circumstance which can be regarded as of unfavorable omen, and is unable to realize those which are favorable ; he misconstrues every observation that is addressed to him, and when he reads, every sentence appears intended especially for him, if of a gloomy nature. One pours forth his grief in sad and wailing accents ; Another is depressed and silent. He is a prey to gloom^ apprehensions,


FORMS OF MENTAL IMPAIRMENT. 367 forbodes constant evil, and often sits from morning till night bemoaning his unhappy situation. Melancholia takes a variety of forms. It may be an exag- geration of the patient's natural character, and have a long period of development ; it is often a consequence of other forms of insanity,* and may spring from the grief that follows sudden calamity. Dr. Connolly records the case of a lady whose only son dropped dead in the midst of apparent health. The shock Fig. 181. MELANCHOLIA Represents a case of snicidal melancholia. It Is that of a carpenter of steady habits, aged fifty-six, and insane fonr months before admission to the asylum. He had been dull and depressed, and could not attend to his trade ; refused to take food be- cause it was too good for him ; was restless bv day and sleepless by night; said that he must be burnt or scalded to death, and made frequent attempts to get at the hot-water taps that he might scald himself, and to a duck'pond that he might druwn himself. He said that his wife had given him poison in a cake, and after that he had to be fed with a spoon till the time of his death, which occurred In a few months, from exhaustion, after several attacks of epilepsy. overwhelmed her with grief. In a few weeks her state became that of deep melancholia, in which she never alluded to her be- reavement, but was ever reproaching herself as sinful, unworthy to live, and deserving of eternal condemnation. She became insensible to all ordinary occurrences and aflfections, indiflferent to her family, inactive and silent, and attempted suicide.


368 ELEMENTARY HYGIENE. The diseased depression of the feelings characteristic of melancholia may exist without impairing the intellectual opera- tions, but it is generally accompanied by delusions and hallu- cinations, although these usually derive their tone from the character of the disorder. They are insane explanations of the patient's wretchedness, or gloomy forebodings of what is to happen to him in the future. 498. General Paralysis is defined to be a form of msanity characterized by a progressive diminution of mental power and by an incapacity which gradually increases and invades the Fig. 182. GENEEAL PAEALYSIS. Eeprcsents the pliyslognomy of a case of general paralysis— a man, aged forty-eighL who had been insane three months before his admission to the asylum. He had been destructive of clothing and violent to his wife, attempting to pull her ears ott. He said it was his duty to Itill her, and yet that he was always at prayer with her and for her. Althougn he would kick or scratch any ])atieat who inadvertently- touched him, his general condition in the asylum was tranquil, verging gradually to mindlessness. ' He had only in a modified degree the delusions of grandeur ; he used to say he had a gold watch ajQd chain, and very fine clothes, but they were in jwwu. The portrait shows the curtain -like face, devoid of all expression, a perfect blank of thought and feeling The head is well shaped, and the features are handsome; but the amount of intellectual expression is less even than that displayed in the lace of the Idiot whole muscular system. Its victims are generally men in strong health, from the better classes of society. " General paralysis


FOEMS OF MENTAL IMPAIEMENT. 369 is emphatically the disease of manhood, for it is hardly ever met with before thirty, or after sixty ; the fact agi'ees well with the supposition that the sole cause of the disease may some- times lie in the agitation and anxieties incident to the most active period of life. Women seldom suffer from general paralysis." The earliest symptoms of motor derangement affect the tongue, and are evinced in thickness of speech and imperfect articulation of words, especially in those abounding with con- sonants ; as the disease advances, the muscles of the trunk and lower limbs are affected, and the walk becomes shuffling and tottering, articulation becomes more indistinct, the brows droop, the power of using the arms is impaired, the sphincters relaxed, and the patient may be choked to death by a lump of food sticking in the throat which he cannot swallow. It is a curious fact that the mental derangement accompany- ing this striking and fatal decay of bodily energy takes the form of an exaggerated feeUng of personal power and importance. At first there may be manifested a lack of the usual energy ; but as the disorder increases, there come extravagant delusions of grandeur and capability of accomplishment. " The patient fancies himself possessed of wealth and power illimitable, and is often fantastically imaginative. One man imagines himself the possessor of ship-loads of gold and silver and precious stones; another fancies himself greater than God; another says he can lift the world, and that all the children that are born in all parts thereof issue from his loins. This man, also, says that he is heavier than the world, and that all the men in the world cannot lift him. We invite him to lie down, and lift him with ease ; he immediately explains the fact that our success is owing to the buoyancy of the angels that are in hhn " (Dr. Bucknill). 497. Dementia. — This form of mental impairment consists in extreme debility which results from loss, obliteration, or decay of the faculties. The first indication of its approach is loss of memory, especially as to recent events, the reason and 16*


I J 370 ELEMENTAEY HYGIENE. judgment being still good within the sphere of distinct recol- lection. The second stage has been defined to be loss of judg- ment or an incapacity of ordinary reasoning. From this point Fio. 188. PEIMAEY DEMENTIA. Eepresents the aspect of a woman, aged forty, the victim of primary dementia. She had a severe attack of typhus fever when nineteen years of age, after which, her hus- band says, " her jaw dropped and she has never been perfectly right since." She was admitted in a condition of extreme filth and personal neglect^ and mentally was void of sensation^ emotion, and thought On her blank physiognomy there are no traces of passion, telling of former storms of mania ; there is not even the slightest effort of attention which corrugates the brow of the idiot. She never laughs,' weeps, or indicates any annoyance ; knows none of the attendants by name, and if she were not fed like an infant, would die of starvation. She is £at, has a good color, and the physical ftinctions are performed well, affording a good example of the extent to wnich physical health may be retained when the activity of the cerebral ftmctions is reduced to its lowest ebb. the malady may advance to the stage of incomprehensiorif the individual affected being incapable of understanding the mean- ing of any thing said to him. The thoughts are incoherent and the detenninations vague, uncertain, and aimless. The last stage is marked by the loss of all sense, volition, and even instinct, the victim of disease having sunk to a mere organic existence. Dementia is said to be primary when it is the first stage of the mental disorder, and develops itself directly by loss of memory, the power of attention, and executive ability. It is


FORMS OF MENTAL IMPAIRMENT. 371 secondary, or consecutive, wlien it appears as a consequence of other diseases. Insanity in its various forms often degener- ates into dementia. Fig. 184. SECONDARY DEMENTIA. This likeness is of a woman, aged forty-nine, the subject of secondary dementia. Her Insanity of two and a half years' standing began with acute maniacal excitement, with delusions of a religious type and suicidal desire. She thougbt that her eoul was separated from her body, and that it was forever lost. She tried to strangle herselt After admission to the asylum the violence sul sided, and she passed into a state of chronic excitement, which has continued with ^aadually decreasing mental powers. She holds imaginary conversations with perboiis she has known in early life, and this hallucination has caused that earnest, inquiring look so faithfully given in the portrait. The general expression of the face is that ot'mindlcssness, combined with deep lines ofemotional excitement which presents a marked con- trast to the foregoing case of primary dementia. 498. Idiocy. — ^This term is applied to that profound infirm- ity of the cerebro-spinal system vi^hich is due to arrested devel- opment before birth, or in early infancy, and which perverts or destroys the reflex, instinctive, and intellectual * functions. Idiots are incapacitated in their movements, senses, feelings, understanding, and will. The characteristics of this condition are manifested in different degrees. In the lowest form of idiocy there is total mental vacuity. Its victim is deaf, dumb, and blind, without taste or smell, and is hardly alive to external ' impressions. The functions of or- ganic life are but ill-performed, the helpless creature being


372 ELEMENTABT HYGIKNE. ! below even the vegetable and he would perish but for the con- stant care of others. Fio. 185. IDIOCY. This cut is tram a photograph of J. K., at the Eanttall's Island House of Eefuge. Ho is twenty -four years of age, four feet seven and a half inches high, and weighs . Boventy-two pounds. His head Is but fourteen and a half inches in circum- ference, its growth having been arrested at birth. Mentally he is a child, with only the fointest rudiments of intelligence. He knows his attendants and his name, and attempts to speak a few words, but is incapable of definite articu- lation. He feeds himself with a spoon, the food having been prepared for him. He shows his red cap with vanity, and is not without affection. He is usnaity pagsive and quiet, ana gives but little trouble except when provoked ; his feeble and torpid mind being only roused by external stimulation. His is a remarkable case of congenital idiocy, in which persistent efforts at improvement have accom- plished but little. A grade higher than this manifests imperfect sensation, feeble power of motion, and the dawn of intellectual and moral capacity. The idiot may be capable of moving about, shuns the cold, and gives notice of his desire for food, but recognizes


FOEMS OF MENTAL IMPAIRMENT. 373 nobody and cannot help himself, while all his actions are with- out reflection or object. Then there are those, still more elevated in the scale, who begin to be conscious of their sensations, who recognize per- sons and objects to which they are capable of becoming attached. They have a feeble self-direction and employ signs, gestures, or cries, to make known their wants, or they may use badly- artftulated words. The degradation of idiots is displayed in the vacant stare, everted lips, slavering mouth, irregular teeth, frequent strabis- mus, imperfect senses, defective speech, and uncertain, swaying walk Their heads are generally, but not always, small, the smallest, however, appertaining to the most degraded. Idiotic heads are more commonly malformed, the skull assuming end- lessly-diversified shapes of contortion. 499. Imbecility. — This term denotes a degree of mental deficiency not so low as that of idiocy — a development rather retarded than arrested. It is sometimes congenital, while idiocy is always so. The memory and understanding of the imbecile are in a state of feebleness, but they are capable of some educa- tion, and of acquiring various simple arts. Like idiocy, .imbe- cility has its grades, some being so mentally torpid as only to be aroused by influences from without " They cannot follow a conversation, still less a discussion. They regard as serious things the most gay, and laugh at those that are the most sad. They reply correctly, but you must not ask them too many questions, nor require from them responses which demand re- flection." They are equal to the performance of many of the ordinary duties of life, and are often able to take care of them- selves. Others display considerable shrewdness, and are con- stantly indulging in jokes ; they pass for half-witted people whose droll behavior and ready repartees create amuse- ment. With more mind and stronger impulses than idiots, but with imperfect self-control, imbeciles are more apt to be vicious. They are passionate and suspicious, and are liable to delusions


374: ELEMENTARY HYGIENE. of the evil intentions of others, which often make them dan- gerous. Fio. 188. IMBECILITY. BepresenU a c&b« of congrenltal imbecility in a yonth aged twenty-seyen. He is the son of a weak-minded father, and has always been of a weak mind. When first admitted he was dirty in his habits, restless and mischievons, bat has become cleanly, quiet, and docile. His intellectual power is very low, and the likeness welj represents the yacant, expressionless stare of imbecility. 500. Degrees of Mental Impairment. — ^We have here briefly described the leading forms of mental disease, which, in their ultimate stages, dissolve the responsible relation of their victim to society. What, to do with these cases is a question for the physician and the judge ; but from the point of view of Mental HygienCj which aims at their prevention, our attention is drawn to the definite causes of mental impairment which are seen in many other effects besides those of overt insanity. There is much ' perverted mental action that never passes into Inania ; much mental weakness that never reaches dementia ; much morbidity of feeling that never ripens into moral insan- ity. The classes in which mental defects are so prominent that the State must assume their charge, are deplorably numer- ohs; yet they form but a fraction of the total amount of


CAUSES OF MENTAL IMPAmMENT. 375 mental weakness and incapacity whicli exists in the commu- nity. Massaclmsetts reports three thousand insane, twelve hundred idiots, about five hundred blind, and four hundred deaf-mutes. But, besides these, she has ten thousand paupers, — ^persons incapable of taMug care of themselves — ^and a large criminal class who, from moral perversity, in which low and deficient organization plays a leading part, become the scourge of society. And, besides these conspicuous cases of unhealthy mental constitution, there are scattered through society thou- sands more who are more or less disqualified for the duties of life by intellectual inability and moral weakness. No one can observe the inmates of a school-room without being struck by the very considerable proportion of those who are mentally deficient, backward, and stupid, or wayward, wilful, and vicious of temper. In the circle of our neighbors how many can be recollected who, by reason of mental deficiency, are practically incompetent and unfit for self-guidance and self-maintenance in the sharp conflicts and competitions of society. But whether the phenomena of mental impairment are total or partial, they are to be looked upon as due to the same general causes, and to these we will now give attention. Section HI. — Causes of Mental Impairment 601. Insanity the Besnlt of Concurring Influences. — ^As the organ of the mind is the most delicate and complex of all parts of the living system, while its manifestations are so varied as to comprehend the whole circle of human thought and feel- ings, it is natural to suppose that the causes of cerebral impair- ment will be varied and complex in an equal degree. These causes are usually regarded as twofold, moral and physical. The former are those which take effect through the mind, as anxiety, over-study, or reverses of fortune ; the latter are those which act directly upon the physical system without the inter- vention of the mind, as blood-poisoning by fever or narcotics, or an injury to the head. Another division is into predispos- ing and exciting causes. Predisposing causes are such as act


376 ELEMENTAEY HTGIENK remotely, or by slow degrees, to undermine the mental health ; while exciting causes are those untoward events which imme- diately precede the breaking down of the mind. It is a com- mon error to assign some shock or calamity as the efficient and adequate cause of an insane outbreak, whereas the real caus- ality lies farther back, and the occurrence in question is only the occasion of its development The germ of the insanity may have been deeply latent in the constitution, and a long train of influences may have been at work to impair the cerebral vigor, while some event, perhaps of slight importance in itself, serves to bring on the final catastrophe. When it is said that a person has become insane through disappointment or religious excitement, we are not to suppose that this is the whole statement : the question arises, how is it that others in quite similar circum- stances are unaffected f The human mind is not so constituted as to snap by a sudden strain, like cast-iron ; insanity suddenly produced by the action of a single cause is of the riarest occur- rence. Only by a "conspiracy of conditions," internal and external, proximate and remote, is the fabric of reason usually overthrown. We will first notice the inamediate physiological actions by which health of mind is destroyed, and this will prepare us to understand how the remoter causes of mental impairment take effect. 602. Nntrition of the Cerebral Strnctures.— If the mind is dependent upon the brain, it follows that each act of mind has its physical conditions, and this conditioning must of course be in accordance with the structure of the organ. The men- tal mechanism consists essentially of millions of cells and fibres, the former of which are the generators and the latter the trans- mitters of force. In thinking and feeling, these are called into exercise, and according to its intensity exhausted ; while their functional power is restored by nutritive assimilation. The stiTicture of the parts being perfect, mental coherency, energy and health depend upon their perfect nutrition. On the other hand, disordered mental manifestations are due to incapacitated


CAUSES OF MENTAL IMPAIRMENT. 377 structures which are immediately caused by imperfect nutri- tion. It is here, in their disturbance of the nutritive operations of the brain, that most of the causes of mental impairment take effect. " We attribute a large share of mental disease to pa- thological conditions of the brain -whose most prominent char- acteristic is defective nutrition of the organ. In a very large proportion of cases this deficient nutrition is manifested after death in an actual shrinking of th^ brain — a shrinking which is coextensive with the duration and the degree of the loss of men- tal power. This loss of power marks all instances of cerebral decay, and is consequently a condition of most chronic cases of excitement " (Bucknill and Tuke). The effect of impaired nutrition is to produce derangements of structure, and these take many forms in the various cases of cerebral disease. The microscope has done much to elucidate the pathological changes of the brain, but such is the marvel- ous delicacy of the organ that microscopists are still intensely occupied in making out the subtle details of its normal struc- ture. Many physical indications of nervous disorder no doubt remain to be discovered ; but from the peculiar complexity and difficulty of the case, a large amount of infirmity of nerve-ele- ment will probably never be detected by physical means. Nu- trition results from a relation between nerve-tissue and the blood ; the causes of its perversion are therefore to be sought in various disturbances of the circulation as well as in the nerve- element itself. 503. Disturbance in the Cerebral Circulation. — Nutrition is dependent upon the supply of blood ; in the brain, perhaps, more closely than in any other organ. The gray substance of the cerebral convolutions which are devoted to the higher mental operations, is richly supplied with minute blood-vessels which impart to the cells the material of their renewal, and remove the waste products of their activity. The quantity and quality of the blood they transmit must therefore exert a determining influence over the functions and health of the organ.


378 ELEMENTAEY HYGIENE. 604. Congestion and its Effects. — As mental action de- pends upon the interchange taking place between the blood- capillaries and the nerve-cells, it follows that increased excitar tion and interaction of ideas is accompanied by increasing interchange and demand for more blood. Or if, from any cause, there is excessive brainward determination of blood, the plethora of the capillaries gives rise to increased mental excitement If this heightened activity is prolonged beyond due limits, and especially if the brain is weakly organized, a state of mor- bid congestion is induced, and over-stimulation is followed by stagnation of ideas, head-swimming, and emotional depression and irritability. " There are few students who are not practi- cally conversant with the slighter symptoms of cerebral conges- tion. Absorbed in some intellectual pursuit, the student's head becomes hot and painful, and his brain even feels too large for his' skull. With exhausted powers of thought and attention, be retires at a late hour, as he hopes, to rest, but be finds that he cannot sleep ; or, if he does, his repose is unrefreshing and dis- turbed by dreams. An hour's freedom from thought before retiring to bed would have enabled the partly-congested brain to recover itself." The stagnation of the cerebral currents and imperfect re- moval of noxious products, with the irregularities of excitement and depression which are the results of frequent brain-conges- tion, produce defective nutrition, which tends to impair the soundness of the organ. 606, Anmmia, or bloodlessness, the opposite state of con- gestion, produces similar mental effects. Insufficiency of healthy blood, whether caused by its actual loss from the system, or by poverty and dilution of the fluid through want of food, imper- fect digestion, or any of the numerous anti-hygienic influences, by impairing the nutritive powers, enfeebles the organ and powerfully predisposes to insanity. The impediment to cell- nutrition, though arising from an opposite cause to the state of congestion, produces similar mental effects. In hypersemia,


CAUSES OF MENTAL IMPAIRMENT. 379 witli liot head and fulness of the cerebral vessels, the mental functions are discharged with slowness and diflSculty. In anaemia, with pale fec6, cool head, and weak pulse, the cerebral organs are in a state of irritable weakness, easily excited to ac- tion ; the action, however, being powerless and irregular. " The blood itself may not reach its proper growth and development by reason of some defect in the function of the glands that minister to its formation, or, carrying the cause still further back, by reason of wretched conditions of life ; there is, in consequence, a defective nutrition generally, as in scrofu- lous persons, and the nervous system shares in the general deli- cacy of constitution, so that, though quickly impressible and lively in reaction, it is irritable, feeble, and easily exhausted. In the condition of anaemia we have an observable defect in the blood, and palpable nervous suffering in consequence ; head- aches, giddiness, low spirits, and susceptibility to emotional excitement, reveal the morbid effects. Poverty of blood, it can admit of no doubt, plays the same weighty part in the * production of insanity as it does in the production of other nervous diseases, such as hysteria, chorea, neuralgia, and even epilepsy. The exhaustion produced by lactation is a well-rec- ognized cause of mental derangement ; and a great loss of blood during child-birth has sometimes been the cause of an out- break of insanity " ( Dr. Maudsley). 606. Perversions of the Blood. — ^Although the blood is a compound of wondrous complexity, and undergoing incessant change by active influx and drainage, yet in health its consti- tution is preserved in such exquisite balance, that the cerebral engine of thought and emotion is kept in harmonious and per- fect action. This harmony is disturbed not only by excess or deficiency of the vital stream, but in a marked degree by the presence in it of various impurities. Every grade of mental disease, from the mildest' depression to the fury of delirium, may be produced by the accumulation in the blood of the waste matters of the tissues. The presence in the blood, for example, of unexcretcd bile, so affects the nervous substance as


J 380 ELEMENTABY HYGIENE. to engender the gloomiest feelings, from which the individual cannot free himself, although he knows that the cause of his depression is not in the actual condition of external circum- stances, but is internal, and of a transient nature. But it only requires the prolonged action of this cause to carry this morbid state of nerve-element to that further stage of degeneration which shall result in the genuine melancholia of insanity. So also the non-evacuation of urinary products in the blood of a gouty patient acts upon the brain to produce an irritability which the mind cannot prevent ; and this, too, if not arrested by medical resources, is liable to pass on to maniacal excite- ment. In like manner suppressed discharges, the morbid products of typhus and typhoid fevers, and organic poisons generated in the system by small-pox or syphilis, and not promptly elimi- nated, are often efficient causes of nutritive perversion in the brain which result in various forms of mental disorder. Various substances introduced into the blood, as opium, hashish, belladonna, take eflfect upon the brain, each perverting the mental functions in a manner peculiar to itself. Ingested alcohol produces an artificial insanity, in which the various types of mental disease are distinctly manifested. Its first effect is a gentle stimulation and a mental excitement, such as often precedes an outbreak of mania. This is followed by a rapid flow of ideas, an incoherence of thought and speech, and an excitement of the passions, which disclose automatic dis- turbance and diminished vohmtary control, as in delirium from other causes. A condition of depression and maudlin melan- choly succeeds, as convulsion passes into paralysis — ^the last scene of all being one of dementia and stupor. 507. Nutritive Repair of the Brain. — But independent of the quantity or quality of the blood supplied to the brain, it is liable to certain conditions of exhaustion and nutritive de- generacy to an extent far greater than the other organs of the body. These other organs have various means of escape from overtasking ; if they cannot increase their power so as to en-


CAUSES OF MENTAL IMPAIRMENT. 381 dure the burden imposed, they can refuse to act, or throw the excess of labor upon some other part. Overtaskiug the stomach destroys appetite, and the task is no longer imposed. K the muscular system is worked beyond its power, it does not itself break down, but the excessive strain is thrown upon the nervous system, which receives the injury. The overtasked lungs throw part of their burden upon the skin and liver, and the overworked liver is relieved, by the kidneys. But the economy of the organism affords the brain no vicarious relief; if overburdened, it must suffer alone. Excessive exer- tion of the brain produces an excitement, which, instead of ceasing, is augmented by the very debility which it causes. The exhaustion continues the overwork, which again increases the exhaustion. The degeneration of nerve-element thus pro- ceeds at a rapid rate of increase, which results in permanent perversion and degradation of the mental functions. The conditions of rest and nutritive renovation of the mind's organ are provided for in the mechanism of the solar system, by which the quietude of night, darkness, and silence alternates with the stimulation of light and day. The recovery of its tone through nutritive repair undoubtedly takes place in the brain during the suspension of its functional activity in sleep. That sleep should be sound in quality and sufficient in quantity is one of the first conditions of mental health and vigor, and the want of it, as all have observed, reacts powerfiilly upon the state of the feelings. " The ill effects of insufficient sleep may be witnessed on some of the principal organic functions ; but it is the brain and nervous system that suffer chiefly and in the first instance. The consequences of a very protracted vigil are too well kribiVn to be mistaken ; but- many a person is suf- fering, unconscious of the cause, from the habit of irregular and insufficient sleep. One of the most common effects is a degree of nervous irritability and peevishness which even the happiest self-discipline can scarcely control. That buoyancy of the feelings, that cheerful, hopeful, trusting temper, which springs far more from organic conditions than from mature and definite


382 ELEMEKTARY HYGIENE. convictions, give way to a spirit of dissatisfaction and dejection • while the even demeanor, the measurei activity, are replaced * either by a lassitude that renders any exertion painful, or an impatience and restlessness not very conducive to happiness." Such are the eflfects upon the healthy constitution of that slight disturbance of brain nutrition which accompanies insuf- ficient repose ; but when this state of things is much protracted or takes eflfect upon a weakly-organized nervous system, the mental integrity becomes endangered. Sleeplessness is both a symptom and an immediate cause of cerebral disorder. Buck- nill and Tuke observe : " Want of refreshing sleep we believe to be the true origin of insanity dependent upon moral causes. Very frequently when strong emotion leads to insanity, it causes in the first instance complete loss of sleep." The quality of the sleep, moreover, that is, whether it be total or partial, is of the first importance. In painful and harassing dreams the emotional perturbation continues, and the individual awakens exhausted rather than invigorated. It is probable that in such cases, when the mind is abandoned to fantasy, and the control of the judgment is lost, the wasteful activity of certain parts of the brain may exceed that of the waking state. Various cases are mentioned in which patients have ascribed their attacks of mania to the influence of frightftd dreams. We thus see in what mental impairment, in its various degrees, really consists. To the physiologist the question of healthy mental activity resolves' itself into, that of the sound- ness of nerve-element, and of the vigor and completeness of nutrition; while mental impairment is seen to result from instability of the nerve-structures consequent upon defective nutrition. In this view, therefore, all causes, physical or moral, immediate or remote, which influence the nutritive operations of the system, have a bearing, more or less direct, upon mental conditions and character. We will now pass to some of the remoter influences by which mental health is impaired. 508. Hereditary Transmissioii. — ^The living constitution


CAUSES OF MENTAL IMPAIRMENT. 383 is powerfully influenced by many slow-working agencies. The causes of mental deterioration produce efi'ects in time, and through successive generations. Hereditary transmission thus becomes a leading factor in the problem of mental impairment, and accounts for many of the agencies by which it is produced. It is well known that like produces like in the organic world : the oak descends from a parent oak ; horses from an- cestral horses ; characters are inherited ; and thus the identity of each species is preserved. But while the distinctive ele- ments of the type are always transmitted, there is a tendency to variation in minor peculiarities. The child has a double origin, drawing its family traits from two different sources. It cannot inherit both sets of characters. The parental quali- ties may mingle equally in the offspring, or the marks of one parent may predominate over those of the other, or even ex- clude them. Again, the parents themselves have inherited the traits of their progenitors, and these may be more fully brought out in their offspring than in themselves, so that the child is made to represent many individuals. Thus, in the course of generations, by the blending of diverse stocks, special or family traits tend to fade away and disappear. Mental characters follow the same law as external features, although they are more obscurely indicated. Bodily defects and diseases are also transmissible. Con- sumption, gout, asthma, cancer, leprosy, scrofula, apoplexy, unsoundness of teeth, and even long-sight, short-sight, and squinting, are liable to be inherited. Of course these diseases are not transmitted in all cases of their occurrence, nor do they always pass directly from parent to offspring; one or two gen- erations may be skipped, and the malady appear in the distant descendants. Hence, strictly speaking, it is not the disease that is hereditary, but a predisposition to it, which may either be neutralized and disappear, remain dormant, or break out, according to cirQumstances. There is, perhaps, no form of constitutional defect more markedly hereditary than morbidities of the nervous system.


384 ELEMENTABT HTQIENE. Esquirol observes tliat of all diseases insanity is the most hereditary. The proportion of cases in which this malady is ascribed to predisposition, has been variously estimated at from one-fourth to nine-tenths ; probably at least one-half of all these cases of disease have this origin. Extensive and care- ful inquiry has led to the conclusion that predisposition to in- sanity on the part of the mother is more liable to be trans- mitted to children than a like tendency on the part of the father, but it is the daughters that are most exposed ; the ma- ternal defect, while it is equally dangerous to the sons as the paternal, is twice as dangerous to the daughters. The common notion, that insanity is inherited only when madness in a parent reappears as madness in the child, is a most serious error. That which is transmitted is nervous infirmity, which may assume an endless variety of forms. Parental nervous defect may issue in one member of the family in unbalanced character, which is manifested in violent outbreaks of passion and unaccountable impulses, while another may go smoothly through life without exhibiting a trace of it, and a third will break down into mania upon some trying emei^ency. As features are modified by descent, so are dbeases, and none assume so wide a diversity of aspect as those of the nervous system. " If, instead of limiting attention to the individual, we scan the organic evolution and decay of a family — ^processes which, as in the organism, are sometimes going on simultaneously — then it is made sufficiently evident* how close are the fimda- mental relations of nervous diseases, how artificial the divisions between them may sometimes appear. Epilepsy in the parent may become insanity in the offspring, or insanity in the parent epilepsy in the child ; and chorea or convulsions in the child may be the consequence of great nervous excitability, natural or accidental, in the mother. In families in which there is a strong predisposition to insanity, it is not uncommon to find one member afflicted with one form of nervous disease and another with another; one suffers, perhaps, from epilepsy.


CAUSES OF MENTAL IMPAIRMENT. 385 another from neuralgia or hysteria, a third may commit sui- cide, and a fourth become maniacal. General paralysis is a disease which is usually the result of continual excesses of one sort or another ; but it may unquestionably occur without any marked excesses, and when it does so there will mostly be dis- coverable an hereditary taint in the individual " (Dr. Maudsley). 509. Debilitated Stock a Source of Criminality. — ^How the running down of stock through loss of vital power by hereditary influences should swell the ranks of the dependent classes, or those incapable of self-support, is obvious ; but this cause is equally powerful in reenforcing the dangerous classes who fill our jails and prisons. Immoral training and vicious associations are undoubtedly among the potent agencies by which these are educated for the career of vice and crime, but a cooperating^ cause of far greater power is low organization or defective cerebral endowment. They begin life with a ner- vous system incapable of the higher controlling functions. The children of paupers generally inherit a lack of bodily and mental vigor, while the offspring of criminals have transmitted to them a disturbed balance of constitution — an activity of certain propensities, with a congenital weakness of the restrain- ing sentiments. Upon this point a writer of large observation and experience of these classes. Dr. S. G. Howe, observes : " There is a common opinion that in classes and individu- als of low organization the purely animal appetites are apt to be fierce and ungovernable, but it is not so; on the contrary, as a general rule, the whole nature is let down and enfeebled; and persons in this condition are docile and easily governed. Sometimes, indeed, there is fearful activity of the animal na- ture in persons of very low organization, which impels them to commit shocking outrages; but these are exceptional cases, and the passions are usually the consequences of drink, or of insanity, rather than of intensity of nature. As a rule, in the classes marked by low and degenerate organization, the animal instincts and impulses are not stronger than in the others. On the contrary, the classes of higher bodily organization and 17


386 ELEMENTARY HYGIENE. vigor have more fire and potency even of animal appetites ; and their superiority comes, not from lack of impulses and temptations, but from greater activity and power of the restraining faculties of reflection and of conscience." In the light of these facts, the causes of mental impair- ment acquire a new and startling significance. The various agencies which are adverse to health not only shorten the duration of life, but they degrade its quality ; while dete- riorated life involves debilitated intellect and perverted moral powers. The general causes of impaired health which have been noticed, impure air, overcrowding in apartments, bad water, and insuflScient food, exposure to weather from inadequate clothing, want of exercise, or exhausting labor, and the whole array of bad physical conditions, by undermin- ing the bodily vigor and lowering the nutritive operations, be- come powerful and extensive causes of mental impairment, and stand in close relation to the evils and vices of society. Their baneful influence, however, is not measured by their immediate effects upon the individual ; their power is multiplied by trans- mission, for they inflict upon his posterity the curse of a bad descent. Evil habits and bad conditions of life may not in the first case reach the extent of mental derangement, but they so impair the vital stamina that their victim bequeathes to his chil- dren enfeebled and degenerated nervous organizations, whicli are incapable of withstanding the strains and shocks of social experience. The lowered vitality and perverted nutrition of the •parent become feeble-mindedness or insanity in the offspring. Hence, " for the moral and intellectual elevation of the race, we are to look not exclusively to education, but to whatever tends to improve the bodily constitution, and especially the qualities of the brain. In our schemes of philanthropy we are apt to deal with men as if they could be moulded to any desirable purpose, provided only the right instrumentalities are used ; ignoring altogether the fact that there is a physical organ in the case, whoso original endowments must limit very strictly the range of our moral appliances. But, while we are


CAUSES OF MENTAL IMPAIRMENT. 387 bringing to bear upon them all the kindly influences of learn- ing and religion, let us not overlook those physical agencies which determine the eflScacy of the brain as the material instru- ment of the mind " (Dr. Ray). 510. Overtasking the Emotions. — ^Increase of insanity is undoubtedly a concomitant of advancing civilization. The savage state is marked by simple and unchangeable social insti- tutions, uniformity of manners and habits, limited wants, the discipline of privation, imperturbable resignation, feeble affec- tion, and few emotions. The savage rarely laughs and rarely sheds tears. The mental disorders, therefore, to which he is liable, correspond to his imperfect development; they are idiocy and imbecility — ^the mental diseases of children. On the contrary, in the civilized state there is a high and varied development of the emotions : all the circumstances of refined society conspire to intensify the feelings. Pride, ambition, fear, grief, domestic trouble, speculation, reverses of fortune, great successes, and great failures, exemplify the excitement and intoxication of the emotions to which a highly-civilized people are continually subjected. In this country the intense and universal passion for wealth, the periodical convulsions of politics, and the stimulation of free competition for place and profit, carry to a high point the strain upon the feelings. Worse than all, our education, instead of being a training to self-control, and a systematic discipline of the emotions through a calm cultivation of the sciences of Nature, is too generally conducted in the same spirit of excitement : studies are pur- sued under the spur of sharp competition for the prizes and applause of public examinations, and, in place of sober and solid attainment, our culture degenerates into a mere prepara- tion for trade and politics. This state of things is far from favorable to mental stability. The victims of overtasked and perverted emotion fill our asylums, and it is impossible to view the increasing tendencies to social and public excitement with- out grave solicitude for its future effects. 511. Overtasking the Intellect. — This is an extensive


388 ELEMENTARY HYGIENB. cause of mental derangement, though perhaps less so than those just considered. The baneful eftects of cerebral exhaustion have already been noticed (507), and that study is often carried to this injurious length is notorious. Moderate use undoubt- edly develops and strengthens the brain, and it is equally cer- tain that if the amount of work is carried much beyond this point, the organ is endangered. Among the causes of insan- ity tabulated in insane asylum reports, excess of study figures as an inconsiderable item; but this belongs to the class of causes which mainly act by paving the way to a mental break- down. Cases like that of Hugh Miller, where, after an intense and protracted strain, the brain at last gives way, are by no means infrequent ; but in many an over-stimulated child or over- worked student there may be only sown the seeds of future mental disease, while other circumstances, such as loss of rest, grief, or disappointment, may cause the seed to germinate, and itself be taken as the cause, whereas it is in reality only the occasion. It has been objected to this view that the lunatic asylums are chiefly peopled with inferior rather than highly-cultivated minds ; but inferior minds are just those most likely to be in- jured by excessive study. The more highly developed the brain, the greater is its capacity of endurance. In his testi- mony before the Parliamentary School Commission, Dr. Car- penter announced his conviction, as a physiologist who had specially studied the question, that the children of the educated classes are capable, without injury, of twice as many hours of school-study as the children of the uneducated classes. What amount of labor the brain will endure without over- straining, depends upon various conditions, such as the age, original vigor of constitution, habits as to physical exercise, and intensity of application. The brain of the adult will bear, unharmed, an amount of labor which would be most injurious to a young person, and men of active habits can endure, with- out fatigue, mental application, which would be dangerous to the sedentary. Probably six hours a day of close brain-work


CAUSES OF MENTAL IMPAIRMENT. 389 is the maximum that the organ will endure without detriment. Mental labor may be prolonged, it is true, to double this length of time without apparent injury to the brain ; but in most cases the quality of the work perfoimed will be found to indicate a lack of strength, vigor, and spontaneity. In order, to disprove the unhealthfiilness of this kind of exertion, attention has been called to the full ages reached by successful brain-workers who have achieved eminence in the various departments of mental activity. The collated results, however, have little value, for in the first place no one doubts that the cultivated brain is capable of a vast amount of labor, extending through a long lifetime, if judiciously exercised. In the second place, the biographies of eminent brain-workers actually show a vast amount of ill-health and suffering due to excessive study, while the number of those who achieve dis- tinction as thinkers, and then pass to premature graves as a consequence of it, is by no means small ; and in the third place, such a report is necessarily one-sided, as it deals only with the successes, and takes no account of the multitudes of failures of which the world never hears. It is not to be forgotten, however, that there are evils of mental under-action as well as of over-action. While there is no evidence that in the case of uncultured savages the brain is liable to become diseased from lack of exercise, the same thing cannot be affirmed of the cultivated races. The progress of civilization in these races is accompanied by a higher develop- ment and increasing complexity of cerebral organization, and this higher condition can only be maintained by a correspond- ingly higher degree of functional exercise. Without that activ- ity which its greater perfection implies and requires, the brain of the civilized man degenerates. A well-constituted organ demands exercise, and there can be no doubt that pleasurable, productive brain-work can be pursued to a great extent, in the form of close and severe mental labor, without injury. It is the evil accompaniments that generally work the mischief; the poisoning of the blood in the stagnant air of close, un ventilated


390 ELEMENTARY HYGIENE. apartments ; the resuming of work directly after dinner, and prolonging it into the late hours of the night ; the provocation of stimulants and irregular habits ; the hard, repulsive task- work continued without recreation, and the unrelieved tension of anxiety that frets and strains and soft;ens the delicate gray mat- ter of the brain, and ends at last in paralysis or imbecility. 512. Early Symptoms of Mental Impairment — Of all the calamities to which man is liable, none is so appalling as the loss of reason, and when the diseases which cause it are far advanced, they are mostly beyond the reach of restorative measures. But a calamity so terrible does not come unheralded. Mental disease has its gradual beginning — its period of incu- bation, as the alienist physicians term it — ^which is accom- panied by various signals of impending diflSculty ; and it is important that these early indications should be understood by all. One of the gravest warnings of approaching cerebral disease is debilitated attention and loss of memory. When an indi- vidual begins to fail in his customary power of keeping his mind to a subject, or forgets the names of familiar persons and objects, or is unable to make simple numerical calcula- tions with his usual facility and -accuracy, or oddly transposes his words in conversation, there is serious ground for appre- hending softening of the brain or apoplectic seizure. Slight deviations of the facial features, the trifling elevation of an eye- brow, the drawing aside of the mouth a hair's breadth, or a faint faltering of the speech, are dangerous intimations of the advance of paralysis. The more active forms of mental disease have also their early symptoms. Preternatural acuteness of the senses, caus- ing exaggerations of sight, hearing, and smell, is the frequent precursor of a maniacal outbreak. The sensibility is not only exalted, so that the individual sees, hears, feels, and smells more keenly than in health, but it is often vitiated ; he sees double, agreeable odors become disgusting, and pleasant tastes offensive. A prickling sensation, or a sense of coldness, or


CAUSES OF MENTAL IMPAIEMENT. 391 grittiness in things touched, is sometimes experienced. In the case of a man who died of apoplexy, there was for some time previous to his illness a feeling in both hands as if the skin were covered with minute and irritating particles of dust and sand. The approach of mental disease is also foreshadowed in the conduct Singularity or eccentricity of deportment is not, in itself^ to be taken as evidence of mental alienation. A large margin must be allowed for individual peculiarities ; there are naturally crooked sticks as well as straight ones. Whatever be the bent of the character, it is in the deviations from it that we are to watch for evidence of morbid action. But, when a person, who is well known to a circle of friends, begins to manifest unaccountable singularities of behavior; when a quiet and modest man becomes noisy and boastful ; when a habitually cautious man begins to embark in wild and reckless schemes ; when a person of a serious turn suddenly becomes hilarious, or one of a Hvely and buoyant disposition sinks into despondency ; when an affectionate person turns jealous and suspicious with* no apparent reason, or one of usually steady industrious habits becomes idle, neglectful of business, and takes to running about — ^in such cases there is reason to believe that trouble is brewing. These deviations from cus- tomary habits " are the switch-points which indicate that the mind is leaving the main line, and that, if left to itself, it will speedily career to destruction." Sometimes the earliest symptoms of cerebral derangement are manifested in the consciousness itself, and while no indica- tions of disorder are disclosed in the outward behavior, the in- dividual finds himself becoming the victim of morbid thoughts, which he cannot banish. A patient, writing to Dr. Cheyne, observed : " I am not conscious of the decay or suspension of any of the powers of my mind. I am as well able as ever I was to attend to my business. My family suppose me in health ; yet the horrors of a mad-house are staring me in the face. I am a martyr to a species of persecution from within.


392 ELEMENTARY OTGIENE. wHcli is becoming intolerable. I am urged to say the most shocking things ; blasphemous and obscene words are ever on my tongue/' 513. Hints and Freoautions. — It is a serious error to sup- pose that, because there may be a predisposition to insanity in a family, therefore the members of it are to regard their danger in the light of a fetality from which there is no escape ; on the contrary, these are preeminently the cases in which, to a wise discretion, forewarning is forearming. The instances are prob- ably very few in which latent tendencies are developed into actual disease in spite of all precaution. It wDl generally bo found that the outbreak is due to some immediate disturb- ing agency which might have been avoided. Where such a tendency exists, the education, occupation, and habits should be ordered with the strictest reference to it : the establishment of strong bodily health should be a para- mount conaderation. The phyacal education should be specially directed to strengthen the nervous system- and diminish its excitability. Much study, bodily inaction, con- finement to warm rooms, sleeping on feathers, are all favor- able to undue nervous susceptibility. In the education of children thus circumstanced, that is, in their brain-exercises, it is of the first importance to remember that whatever tends in any degree to impair the mental health, acts with redoubled power when cooperating with morbid tendencies. While the brain is yet plastic and pliable, a little mismanagement — ihe humoring of precocity, the repression of physical and nervous activity, or over-stimulation of thought, may awaken the germs of mental disorder, and lead to the most injurious consequences. To persons thus predisposed, steady and agreeable occupa- tion, which does not try the patience or the temper, or involve much responsibility, excitement, or exhaustion, is in the high- est degree desirable. Religious, political, and reformatory gatherings, where the passions are aroused and the sympathies excited, should be carefully avoided, together with all excite-


CAUSES OF MENTAL IMPAIEMENT. 393 ments which tend to disturb the sleep. In respect to the mental habits, in such cases, Dr. Ray has the following excellent prac- tical suggestions : "Persons predisposed to mental disease should carefully avoid a partial, one-sided cultivation of their mental powers — a fault to which their mental constitution renders them pecu- liai'ly liable. Let them bear in mind that every prominent trait of character, intellectual or moral, every favorite form of mental exercise, is liable to be fostered at the expense of other exercises and attributes, until it becomes an indication of actual disease. Hero lies tlieir peculiar danger, that the very thing most agreeable to their taste and feelings is that which they have most to fear. "There is another disposition of miud to be carefully shunned by the class of persons in question — that of allow- ing the attention to be engrossed by some particular interest to the neglect of every other, even of those most nearly con- nected with the welfare of the individual. The caution is espe- cially necessary in an age whose intellectual character is marked by strife and conflict, rather than calm contemplation or philo- sophical inquiry ; and in which even the good and the true are pursued with an ardor more indicative of .neiTOus excitement than of pure, unadulterated emotion. The prevalent feeling is, that whatever is worth striving for at all, is worthy of all possi- ble zeal and devotion ; and, supported by the sympathy and cooperation of others similarly disposed, the coldest natures become, at last, willing to go as far and as fast as any. " Where the mind of a person revolves in a very narrow circle of thought, it lacks entirely that recuperative and invigo- rating power which springs from a wider comprehension of things, and more numerous objects of interest. The habit of brooding over a single idea is calculated to dwarf the soundest mind ; but to those unfortunately constituted, it is positively dangerous, because they are easily led to this kind of partial mental activity, and arc kept from running into fatal extremes by none of those conservative agencies which a broader disci- 17*


394 EJiEMEKTABY HYGIENE. pline and a more generous culture naturally furnish. The re- sult of this continual dwelling on a favorite idea is, that it comes up unbidden, and cannot be dismissed at pleasure. Rea- son, fancy, passion, emotion — every power of the mind, in short — are pressed into its service, until it is magnified into gigantic proportions and endowed with wonderful attributes. The conceptions become unnaturally vivid, the general views narrow and distorted, the proprieties of time and place are dis- regarded, the guiding, controlling power of the mind is dis- turbed, and, as the last stage of this melancholy process, reason is completely dethroned." 514. Medical Management — Although diseases of the higher nervous centres, when they become seated, are, to a great extent, incurable ; yet, in their incipient stages, they are in most cases quite amenable to treatment. But, unhappily, those instances where delay is fraught with the greatest danger are, of all others, most liable to be neglected in their earlier stages. K the liver or the lungs get out of order, there is usually incontinent haste to consult the physician; but if the very organ of reason is in danger of giving way, a mys- tery is made of it, and the dictates of common-sense are unheeded. Nor is mere neglect the worst aspect of the case ; false notions of delicacy frequently became hinderances to early and decisive action. The ancient superstition, which connected insanity with special Providential disfevor, descends to U3 in the shape of prejudices which speak of it still as a " taint," and lead to a culpable obliquity in dealing with it. Physi- cians of the largest experience attest that, even when they are consulted in these cases, there is often the greatest difficulty in getting at the real conditions ; both the patient and his friends studiously concealing or flatly denying the facts. The progress of medical science and the impulses of public philanthropy have called into existence those noble institu- tions, where alone physical and moral medication can be best united, and which are generally administered by physicians of


CAUSES OF MENTAL IMPAEBMENT. 395 the largest experience in tliis department of practice. When, therefore, an individual begins to manifest symptoms which excite the apprehensions of his family or friends, no time should be lost in procuring the best professional advice and securing the advantages which those establishments offer ; and if the patient is placed in an &sylum, the friends, remem- bering that time is generally an all-important element of re- covery, should largely trust the discretion of the medical super- intendent in regard to the proper duration of his confinement.


QUE STIO]srS. CHACTER I. 1. How does science arise ? 2. What makes science possible ? What are phenomena ? How are they divided ? What is the essence of scientific inquiry ? 3. What is said of the connection of the sciences ? 4. With what class of ideas does mathematics deal ? 6. Of what does physics treat ? 6. What makes chemistry possible ?. Where should it come in the order of study ? 7. What is biology ? How is it related to mathematics, physics, and chemistry ? What great questions are peculiar to it ? 8. What are the divisions of biology ? 9. With what order of facts does morphology deal ? What are its principal subdivisions ? How is it related to classification ? 10. What is meant by distribution ? 11. Of what does physiology treat ? What are its subdivisions ? 12. What is etiology ? 13 and 14. Why should physiology be studied ? CHAPTER II. 15. How are the bodily actions studied.? 16. What facts may we thus obtain ? lY. Describe the ice-chamber experiment. What docs it show ? 18. How is the strength restored and the loss made good ? 19. In what form is matter excreted from the body ? 20. What is said of the absorption of oxygen ? 21. What is meant by the physiolojiical balance? 22. How may it be maintained ? What conditions disturb it? 23. What determines the amount of force set free ? .24. Give an outline of the bodily structure. 25. Describe the vertebral column. What cavities do the bodies of the vertebraB separate ? 26. 'What does the spinal canal contain? How is the ventral cavity divided ? What canal traverses the two ventral chambers ? What else does the abdomen contain ? What the thorax ?


QUESTIONS. 397 27. Describe the head. What are contained within its cavities ? 28. What does a longitudinal section prove? What is showa by transverse sections ? What is said of the limbs ? 29. Describe the layers of the skin. 80. How does the skin differ from mucous membrane ? 31. What is connective tissue ? 82. What is said of the muscles ? 83. What constitutes the skeleton ? How many bones does it con- tain ? How are they fastened together ? 34. What enables us to stand upright ? 86. What of the relation of the mind to the muscles ? 36. What organs control the actions of the muscles ? What special power does the cerebro-spinal axis possess ? 37. What is meant by " special sensations " ? Name the organs which receive only certain kinds of impressions ? What are they called ? 88. What is said of the renewal of tissues ? 39. What are the organs of alimentation ? 40. Name the organs of distribution. 41. What is meant by the exchanges of the blood ? 42. Name the principal excretory organs. In what respects do they resemble each other ? 43. What important additional purpose do the lungs fulfil ? CHAPTER in. 44. Describe the capillaries. What is their function ? How arc they distributed ? 45. Of what are the capillaries continuations ? How do they differ from the small arteries and veins ? How are the muscles of the small arteries disposed ? 46. What does their contraction effect ? 47. How is their contraction regulated ? 48. Wherein do the arteries and veins differ ? 49. Describe the valves of the veins. How may then: action be demonstrated ? What arteries possess valves ? 50. Describe the lymphatics. Where are they distributed ? Where do they discharge their contents ? 51. What are the lacteals ? What is their function ? 62. What large trunks pour venous blood into the heart ? From what great trunk do most of the ai*teries spring ? What vessels carry blood to and from the lungs ? Into what parts of the heart do these various trunks open? 63. What vessels supply the substance of the heart ? 64. What great vessel carries venous blood from the abdominal viscera to the heart ? Through what great organ does it ramify ? 66. What is the average size of the heart ? What its shape and posi- tion ? By what membrane is it enclosed ? 66. Describe the cavities of the heart. What are they called ? 67. What is their relative amount of work ? 68. What tissue makes up the walls of the heart ? What membrane lines the cavities of the heart ? How arc the communicating apertures strengthened ? What are attached to these rings ? 69. Describe the structure and attachments of the heart-valves. What

^ 

398 QUESTIONS. TaWes close the right auriculo-ventricular aperture? What the left? How are the free edges of the valves supported ? What is the action of these valves ? What valves are situated at the commencement of the aorta and pulmonary artery? What is their action? How may the action of the valves be demonstrated ? 60. What is said of the rhythm of the heart ? What b meant by

    • systole l^ and " diastole " ?

61. Describe the worldng of the heart. 62. What is the action of the arteries ? 63. What constitutes the beat of the heart ? 64. What is said of the sounds of the heart ? 65. What constitutes the pulse ? 66. Why does the blood jet from cut arteries ? 67. Why are the capillaries pulseless ? 68. How do the subdividing arteries affect the flow of -blood? 69. What causes the steady capillary flow ? 10. Trace the course of the blood from the right auricle. How is the heart itself supplied ? VI. What is the shortest complete circuit the blood can make ? The longest ? 72. How does the nervous system affect the circulation ? 73. What happens in blushing ? 74. How may this be proved ? 75. What relation has this nervous control to disease ? 76. What relation does the heart bear to the nervous system ? 77. How may the movements of the heart be directly observed ? 78. What is the proof that the blood circulates ? CHAPTER IV. 79. How may we obtain blood for examination ? 80. How does it appear to the naked eye ? How under the pocket lens? 81. What takes place when a drop is left to itself? What is the effect of salt upon it ? 82. How many kinds of corpuscles docs the blood contain ? 83. Describe them. 84. What is the structure of the red corpuscles ? 85. What are the peculiarities of the white corpuscles ? 86. How may the real nature of the corpuscles be determined ? 87. What is supposed to be their origin ? What is said of the cor- puscles of the lower animals ? 88. What occurs to the corpuscles when the blood dies ? 89. How are blood-crystals formed ? 90. What is meant by coagulation ? 91. Into what constituents does the blood separate ? 92. What is the buffy coat ? 93. What conditions influence coagulation ? 94. What is the nature of the process ? 95. What causes the blood to coagulate ? 96. Name some of the |)hysical properties of the blood. 97. What is its chemical composition ? 98. How does age influence the blood ? Sex ? Food ?


QUESTIONS. 399 99. What is the total amount in the body ? 100. What is the function of the blood ? To what does it owe its vivifying influence ? 101. What is said of the transfusion of blood ? 102. What of the lynaph ? CHAPTER V. 103. What gives the blood its complex composition ? 104. How is the blood changed in the capillaries y 106. In what respects do arterial and venous blood differ? 106. What is said of the difiusion of gases ? 107. Why does the blood change color ? 108. How is this change explained ? 109. Describe the capillaries of the lungs. 110. Tnice^he air-passages from the mouth to the air-cells. 111. What is said of this mechanism? 112. What are inspiration and expiration ? 113. State the difference between inspired and expired air. 114. What quantity of dr passes through the lungs in 24 hours? To what extent is it vitiated ? How much carbon and water is eliminated in 24 hours ? 115. What mechanism carries on the respiratory movements ? What is said of the elasticity of the lungs ? 116. How do the bronchial tubes facilitate the movement of air? IIY. Describe the action of the chest-walls. Explain the action of the interca«ital muscles. 118. What is the diaphragm ? Explam its action. 119. What occurs when the diaphragm acts alone? What, if only the chest-walls are brought into play ? 120. What other muscles aid the process ? 121. How does the respiration differ in the sexes ? 122. What is meant by residual air? Supplemental air ? Tidal air? 123. What constitutes the stationary air ? What part does it play in respiration ? 124. What is the composition of the stationary air ? 125. How is the nervous system related to respiration? 126. In what are respiration and circulation analogous ? 127. What are the secondary phenomena of respiration ? 128. What is said of the respiratory murmurs ? 129. How does respiration assist the circulation ? 130. What are the facts relating to this point ? 131. How does expiration affect the circulation ? 132. How may the action of the heart be arrested ? 133. What circumstances modify the respiratory function ? 134. What occurs when a man is strangled ? 135. How is life destroyed by this means ? 136. What is said of respiratory poisons ? 13Y. What is slow asphyxiation ? 138. Why is ventilation so important ? CHAPTER VI. * 139. Describe the distribution of arterial blood throughout the body. 140. What great organs are constantly draining the blood ?

J 

400 QUESTIONS, ^141. What ia said of its losses in the liver and lungs ? 142. What »re the intermittent sources of loss and gain to the blood f 143. Give the position and anatomy of the kidneys. 144. In what respects are the lungs and kidneys alike ? 145. What is the composition of the renal excretion ? What is its average daily amount ? Its average of specific gravity ? 146. Describe the structure of the kidney. 147. What is said of its filtering mechanism ? 148. From what source are the kidneys supplied with blood ? How do they change the blood ? 149. How is the excretory action of the kidneys controlled ? 160. What does the blood lose through the skin ? 161. What quantity of matter is thus lost? What is the composition of the sweat ? , 152. Give the conditions of its escape. 163. What is said of the sweat-glands? What of "their distribu- tion? 164. How is the action of the sweat-glands controlled ? 165. What conditions increase the amount of perspiration ? 166. In what respects are the lungs, kidneys, and skin alike? 157. What does the blood lose in the liver ? What does it gain ? Describe the liver. With what great vessels is it connected ? Give its . internal anatomy. What route does the blood take in its passage through the liver ? What is said of the liver-cells ? 168. What is then- function ? 169. What is the daily quantity of bile excreted ? Its composition? 160. What becomes of the bile ? 161. What organs furnish the blood with oxygen? 162. What does the blood gain in the liver? What docs it Jose? 163. How may the sugar-forming power of the liver be proved ? 164. What does the blood gain from the lymphatics ? What of the " ductless glands " ? 165. What is said of the spleen ? What is its supposed function? 166. Through what channels does the body lose heat ? What is the source of bodily heat ? 167. How is the heut of the body equalized ? 168. How does evaporation afifect the temperature ? 169. What relation has the nervous system to temperature ? 170. What is said of the action of the glands ? What is the duct of a gland ? What are racemose glands ? What determines the activity of certain glands ? 171. In what way are the salivary glands called into action ? What is the character of their secretion ? 172. What does the blood gain from the muscles ? CHAPTER VII. 173. What is another great source of gain to the blood ? 174. How much solid material does a man daily receive ? How much oxygen ? 175. What is the daily loss of dry solids? In what shape does the balance leave the body ? 176. How are foods classified ? What are Proteids ? Give examples.


QUESTIONS. 401 What is the composition of fat ? What are Amyloids ? Give some ex- amples. What is meant bv " vital food-stuffs " ? What are mineral food- stuffs? Ill, What is the composition of the vital food-stuffs? The mineral food-stuffs ? What constitutes a permanent food? 178. What occurs if protein is not supplied ? What is said of the ne- cessity of other food-stuffs ? 179. What is meant by nitrogen starvation ? 180. 181. What are the disadvantages of a purely nitrogenous diet? 182. Why is a mixed diet desirable ? 183. What constitutes a mixed diet ? 184. What is said of the mtermediate changes of the food ? 185. What are the objections to the ordinary classifications of food ? 186. What is the purpose of the alimentary apparatus ? 187. Describe the cavity of the mouth and pharynx. What organs do they contain ? Name the openings into the pharynx ? 188. Give the names and positions of the different salivary glands. How does the saliva affect the food ? 189. Describe the teeth. 190. Describe the working of the jaws. 191. What occurs to the food during mastication? Describe the operation of swallowing. 192. How ar^ fluids swallowed ? 193. Describe the stomach. What is the character of its lining mem- brane? What glands does it contain ? What fluids do these glands pour out ? What are the properties of the gastric juice ? 194. What is meant by artificial digestion? 195. By what routes does the food leave the stomach? 196. What is said of the intestines ? How are they divided ? Where is the ileo-caecal valve situated ? What is the caecum ? The vermiform appendix ? 197. What glands are found in the intestinal mucous membrane? What other structures ? 198. What is peristaltic contraction? 199. What glands pour their secretions into the duodenum ? What is said of the chyme ? 200. What is chyle ? How does it differ from chyme ? What changes does the chyme undergo in the intestine ? What juices effect this change ? In what way does the chyle reach the blood ? 201. What is going on in the large intestine ? CHAPTER Tin. 202. What is meant by the "vital eddy"? What maintains the active powers of the body ? 203. In what way are the activities of the body manifested ? What is locomotion ? Name the organs of motion. 204. Describe the cilia. How do they act? Where are they situ- ated? 205. How do the muscles give rise to motion ? Into what two groups may the muscles be divided ? 206. What muscles are not attached to solid levers ? What is the character of their fibres ? What is said of their contractions ?

Googlc' 402 QUESllONS. 207. What muscles are attached to solid levers ? What is a lever? 208. How many orders of levers are described ? What is a lever of the first order ? Of the second order ? Of the third order ? 209. What levers of the first j)rder are found in the human body? 210. What of the second order? 211. What of the third order? 212. How may a single part of the body represent the three kinds of levers ? 213. How many kinds of joints are found in the human body? 214. Describe the structure and movements of a perfect joint 215. What are ball-and-socket joints ? 216. What are hmge-jomts? 217. What is a pivot-joint? Give an example from the human body. 218. Describe the bones of the fore-arm. How are they articu- lated together ? What is meant by pronation and supination ? 219. What are ligaments ? How do the ligaments differ in the differ- ent jomts ? What is said of the hip-joints ? 220. What different movements are the joints capable of executing ? 221. How are these movements effected? In what way are they limited? 222. What is meant by the origin and insertion of a muscle? How are the muscles attached to the bones ? What direction does the axis of a muscle usually take ? The exceptions ? 223. Describe the operation of walking. 224. When does a man walk with least effort ? 225. What is said of running and jumping ? 226. What conditions are essential to the production of voice ? 227. Describe the vocal chords. To what are they attached ? 228. What cartilages enter into the structure of the lamyx ? 229. Describe the muscles of the larynx. What does their action effect ? How are musical notes produced ? 230. When will the musical note be low ? When high ? Upon what does ran^e of voice depend ? Upon what the quality of voice ? 231. What is speech ? How is the voice modulated ? What is said of the vowel sounds ? What of consonant sounds ? 232. What sounds require blocking of the air-current ? 233. What are explosive consonants ? 234. How are speaking-machines constructed ? 236. What is said of tongueless speech ? What example is given ? CHAPTER IX. 236. How are the muscles made to contract? 237. What calls the nerves into action ? 238. What is reflex action ? What is a sensation ? With what are sensations classed ? 239. What are subjective sensations ? 240. What is said of the muscular sense ? How may its existence be demonstrated ? 241. What is said of the higher senses ? 242. Give the general plan of a sensory organ. 243. Where is the organ of the sense of touch located ? What are papillae ? What is a lactUe corpuscle ?


QUESTIONS. 403 244. What is interposed between it and external objects ? 245. What is said of varymg lactile sensibility ? 246. What gives rise to the feelings of warmth and cold ? 247. Where is the organ of the sense of taste found ? Describe the papillaB of the tongue. 248. Where is the organ of the sense of smell located ? Describe the nasal passages. The nasal chambers. What do these nasal chambers contain ? 249. How are odors brought in contact with the olfactory apparatus ? 250. Where is the organ of hearing situated ? Of what does it essen- tially consist ? What bodies are found in the membranous labyrinth ? In the scala-^media i 251. What part of the ear is called the vestibule ? What are the semicircular canals ? What the ampullae ? What fluids form a part of the mechanism ? 252. Where is the scala-media situated ? What part is known as the scala iympani ? The scala veslibuli ? What peculiar mechanism is found within the scala-media ? 258. What is the bony labyrinth ? What fenestras does it contain ? 254. What part of the ear is known as the drum ? How is this sep- arated from the external meaims f In what way does the drum conmiuni- cate externally ? 255. What are the auditory ossicles ? What two points do they con- nect ? What is their purpose ? How are the perilymph and endolymph set vibrating ? 256. What muscles are connected with the tympanic membrane ? 257. What is the concliaf 258. What conditions are necessary to the production of sound? How is sound transmitted to the ear ? 259. How do the aerial vibrations affect the tympanic membrane ? Into what two kinds of vibrations may bodies be thrown ? 260. Which are supposed to transmit the impulses of the aerial waves? 261. Describe the actions of the auditory muscles. 262. What part of the ear is supposed to take cognizance of the in- tensity of sounds ? What part is concerned with the quality of sounds ? 263. What is the probable function of the fibres of corti ? 264. What is the purpose of the eustachian tubes ? CHAPTER X. 266. What part of the eye is called the retina? 266. What is seen on the centre of the retina ? 267. Describe the microscopic^ structure of the retina. 268. What is the function of the retina ? What is said of the sensa- tion of light ? 269. in what respects do different parts of the retina differ ? What is the blind spot ? * 270. What is said of the duration of luminous impressions ? 271. Can the retina become exhausted? What are complimentary colors ? 272. What is color blindness ? 273. What appearances are produced by pressure upon the eyeball.


404 QUESTIONS. 274. What is the function of the rods and cones ? What are Pur- kinje* 9 figures f 275. What physical agent gives rise to vision ? What is a convex lens ? Describe the experiment with the candle and lens. 276. What is meant by the " focus " ? What is adjustment of the eye ? When does the lens give a distant picture ? What is the effect of moving the object ? 277. What follows from varying the convexity of the lens ? What relation does convexity bear to the focus ? How does a convex surface affect the rays of light? Describe the experiment with the watch-glass and water-box. What is a camera obscura ? 278. What organs must the light pass through to reach the retina ? Give the structure of the eyebalL 279. What are the humors of the eye? By what organ are tlie humors separated ? Describe the crystalline lens. 280. Describe the choroid eaaXt What is its position? Where are the cUiary processes situated ? 281. Describe the iris. Where is it situated? What of the ciliary muscle ? What relation has the iris to the lens ? 282. How does the eyeball resemble a water-camera ? 283. How is the focus adjusted in a camera obscura ? How in the eye ? 284. Describe the experiment What does it show ? 285. What is sdd of the mechanism of adjustment ? What are the facts of adjustment ? What explanations of the process have beeu offered ? Which is the most probable ? 286. What limits the power of adjustment ? 287. Name the muscles of the eyeball. What are their respective positions ? What does their action effect ? 288. Describe the structure of the eyelids. What muscles move them? 289. Where is the conjunctiva situated? Describe the lachrymal ap- paratus ? What is the source of the tears ? 290. What is meant by a simple sensation ? What is the character of most of our sensations ? 291. What sensations are the simplest? 292. Of what does a tactile sensation consist ? 293. What is said of complex sensations and judgments ? 294. Why are delusions of the senses impossible ? What is said of delusive judgments ? 295. What are subjective sensations ? What examples are given ? 296. Relate the case of Mrs. A. What senses were implicated ? To what class did her peculiar sensations belong ? 297. What conditions eeemed to favor their development? What prevented her forming false judgments ? 298. Were her senses really at fault ? 299. How many outside causes give rise to dehisive judgments ? Give an example. 800. What is said of optical delusions ? 301. What is meant by the optic axisf How is the position of a phosphene accounted for ? 802. What is said of the inversion of visual images ? 303. How do objects and their visual images correspond in number ? What is the action of multiplying glasses ?


QUESTIONS. 405 304. Upon what does perspective depend ? 305. How does the distance of an object affect its visual image ? How do convex and concave glasses afifect it ? 306. Why do the sun and moon look larger near the horizon ? 307. What is said of the judgment of form by shadows ? 308. What is the principle of the (haumatrope ? 309. What is the explanation of squinting ? 310. Give the principle of the pseudoscope, 811. What of the «fe»'tfOsc?o/)€ / CHAPTER XII. 312. Of what is the bulk of the nervous system made up ? 313. "What two systems constitute the nervous apparatus ? 314. Where is the cerebrospinal axis located t What membrane sep- arates it from the bone ? What other membranes surround the brain and cord ? 815. Describe the spinal cord. How is it divided? Describe the roots of the spinal nerves. 316. What does a transverse section of the cord show ? 817. What follows the irritation of a spinal nerve ? 818. What are the functions of the anterior and posterior roots ? 319. What results from cutting the anterior root of a spmal nerve? The posterior root ? Both roots ? 320. How are impressions propagated along the nerves ? What is an afferent nerve ? 321. What is negative deflection? 322. What occurs when the spinal cord ia cut across ? What when the end remote from the brain is irritated ? 323. What power does the cord possess independently of the brain ? 324. What is said of the distribution of reflex effects ? 325. Do all parts of the cord possess a like conducting power ? 326. What is said of the conducting power of the gray matter ? 327. What special functions have certain regions of the cord ? 328. Describe the medulla oblongata. What cavity does it contain ? What overhangs this cavity? What is the pons varolii? Into what parts do the fibres of the medulla pass ? What elevations are found be- tween the crura-cerebri ? Where is the third ventricle situated ? Into what masses of nervous matter do the crura-cerebri pass ? Where is the pineal gland located ? The pitiiitary body ? Where are the lateral ven- tricles situated ? What forms the floor of the lateral ventricles ? What is said of the hemispheres of the brain ? How are they connected ? What is said of the outer surfaces of the hemispheres ? 329. How are the white and gray matter arranged in tlie medulla ob- longata ? In the cerebellum and cerebral hemispheres ? 330. How many pairs of nerves are given off from the brain ? Name the first pair. The second. The third. In what muscles is the third pair distributed ? Where are the fourth and sixth pairs distributed ? Describe the origin and distribution of the fiflh pair. In what muscles does the seventh pair terminate? The eighth pair terminate? What is the function of the ninth pair ? What organs does the tenth pair sup- ply ? Describe the course of the eleventh pair. Give the origin and dis- tribution of the twelfth pair.


406 QUESTIONS. 831. What is said of the olfactory and optic nerves ? 832. What effects follow injuries of the medulla oblongata ? 833. What direction do the afferent impulses take in the medulla ob- longata*? Giye the course of the fibres in the anterior pyramids. What would be the effect of dividing one of the crura-cerebri ? 834. What is the function of the cerebral hemispheres? 335. What is said of the reflex action of the brain? 836. What takes place in reading aloud ? 837. What is meant by " artificial reflex actions " ? 838. What is sud of the sympathetic system t CHAPTER Xm. 839. What is said of the microscopical analysis of the tissues ? 840. What is the early primitive structure of the body ? 841. What is the character of the epidermis and epithdium? How do these tissues grow ? What is sqvuxmous epithelium ? What kind of epithelium lines the alimentary canal ? What is ciliated epithelium ? 842. From what kind of tissue are the noils developed ? 343. Of what are hairs composed ? Describe their growth. How are the haurs kept supplied with oil? What is meant by horripilathn, or " goose skin " ? 844. What is the structure of the crystaUine lens? 345. Of what is cartilage composed ? 346. What is the structure of connective tissue ? How is it affected by being boiled in water ? How does acetic acid affect it? Of what are ligaments and tendons composed ? What isfbro^ariilagei 34'7. Describe fat-cells. 848. What are pigment-cells ? 849. Describe the minute structure of bone. What are lacunce? ConalicitU? What were the lacunae once supposed to be? Describe the Haversian canals. What is periosteum? What is found in the cavities of the bones ? 850. How do bones grow? What are sutures? In what kind of material are bony matters first deposited ? What is meant hy ^centres of ossification f 851. Of what are the teeth composed ? Name the different parts of a tooth. What is the character of dentine? What is the structure of enamd? 352. How are the teeth developed ? Which are the deciduous, or milk teeth ? When do they appear ? 353. How are the permanent teeth formed ? How divided ? When do they begin to appear ? How long before the set is completed ? 354. What two kinds of muscles are found in the body ? Of what arc the striated composed? What is a fascia? The' sarcolemma? What docs it enclose? Of what is the contractile substance made up ? What is the structure of smooth muscle ? 355. What are the elements of nerve tissue ? Describe the structure of a nerve fibre. How do the nerve fibres terminate ? 856. What is a tactile corpuscle F What is the structure of the olfactory nerves ? 357. Where are ganglionic corpuscles found ? What is their structure ?


QUESTIONS. 407 F-A.RT SECOND, CHAPTER XIV. 858. What is said of the twofold value of knowledge ? 859. What is meant by " practical knowledge " ? 860. Of what practical value is a knowledge of physiology ? What is said ot its importance ? 861. What were some of the old notions regarding disease V How did such views affect the community ? 862. What is the true idea of health and disease ? How is this illus- trated in the case of gout ? 863. When do the agencies of health become sources of disease? What is the chief value of hygienic knowledge ? 364. Name some of the results that have followed its application. 865. What is said of its value as a remedial means ? 866. How must it necessarily affect the actions? CHAPTER XV. 367. Give the constitution of the atmosphere. How is it rendered impure ? 868. How do atmosphenc impurities affect the senses ? 869. What is said of carbonic acid as an impurity ? In what propor- tion is it thrown out from the lungs ? From what other sources does the air of apartments receive it ? 870. What is the effect of air saturated with moisture ? Of dry air ? 871. In what form is organic matter found in the air? What are some of its sources ? By what means may we determine its presence ? What is said of its presence in the air of sick-rooms and hospitals ? How does it affect the system ? 872. What is said of the air of cellars ? 878. How does air contaminated by certain trades affect the health ? 874. What effect has impure au: upon the scrofulous? Relate the case of the Norwood school. 875. What relation has an impure atmosphere to the spread of dis- ease? 876. How does impure air affect the course of disease ? What is of first acQOunt in the treatment of febrile complaints ? 377. How are consumptives influenced by impure air ? 378. How does bad air affect inherited taints ? 879. What is its effect upon the mind ? 880. How does nature purify the air ? 881. What is the object of ventilation ? How may pure air be ob- tained ? 882. What should be the standard of purity in air ? Give the estimates. 888. How should the air be heated, and why ? 884. What must be attended to in regulating the movement of the air? 885. When are other means of purification required ? What sub- stances are most efficient as disinfectants ?


408 QUESTIONS. CHAPTER XVI. 886. What proportion of water do the various tissues contain ? 887. What duties docs it perform in the economy ? 888. What leading property fits it for this oflSce ? 389. The average daily consumption of an adult ? 890. What is said of its excretion ? 891. What gives rise to the several varieties of water. 892. What is said of soft water ? 893. How is hard water formed ? 894. What are mineral waters ? 895. Oive the characters of limestone water. 896. What is said of sand and gravel waters ? 897. What are the foreign ingredients of alluvial waters ? 898. The impurities of surface and sub-soil waters f 899. What is said of marsh-water ? 400. What is the general character of river- water ? 401. What is said of sea-water? 402. How may perfectly pure water be obtmned ? What water may be re«;arded as most healthy ? 408. What is said of the organic impurities of water ? 404. What kinds of impurities are likely to produce dyspepsia ? 406. What kinds of water are said to produce diarrhoea ? 406, 407. Are dysentery and cholera ever caused by impure water ? 408. How are malarious fevers often produced ? 409. What is the supposed cause of goitre ? 410. What animals may pass into the body with the drinking-water ? 411. Are the senses alone trustworthy in the examination of water? 412. What is said of distillation as a means of purification ? 413. What is the effect of boiling and freezmg ? 414. What chemical substances are sometimes used as purifiers ? 415. What is said of filtration ? 416. How is water aflfected by contact with lead ? CHAPTER XVII. 417. Into what four groups may food be classed ? 418. What is said of the proteids ? 419. What of the fats as articles of diet ? 420. What substances belong to the amyloid group ? 421. To what uses are these various food-stufis applied ? 422. What are the mineral aliments? 423. Why is a mix^<d diet necessary ? 424. What is said of milk as food *? 425. Of butter and cheese ? 426. What is the composition of eggs, and how should they .be cooked ? 427. What is said of the various meats ? 428. Why is salt inferior to fresh meat ? 429. What peculiarity does poultry and game present ? 430. How is the flesh of fish regarded as food ? 431. 432. What is said of ci^bs and lobsters ? Clams and oysters ? 433. Why is wheat such a valuable food ?


. QUESTIONS. 409 434. IIow does rye compare with wheat? 435. What of buckwheat ? 436. How does Indian corn differ from wheat and rye ? 437. What advantage does rice possess over other foods ? 438. What is said of peas and beans ? 439. Give the composition of potatoes. Why should the succulent vegetables be eaten with meat ? 440. What is said of the fruits ? 441. What are auxiliary foods ? 442. What substances come under the head of condiments ? 443. Why is tea valuable as a beverage ? How should it be made ? What is its action ? How is it adulterated ? 444.* What is the composition of coffee ? How should the beverage be prepared ? 445. What is said of cocoa and chocolate ? 446. What should cooking aim to accomplish ? Why should over- cooking be avoided ? 447. How does boiling affect meat ? How should the process be con- ducted ? What is said of roasting ? Stewing ? Frying ? 448. How should vegetables be cooked ? 449. What are some of the effects of over-eating ? 450. What are the effects of deficient diet ? 451. Amount of food daily required. 452. What results from a badly-constituted diet ? 453. What i^ said cf a diet deficient in fat ? 454. What constitutes unwholesome food ? 455. Give . an account of the cysticercus celulosus. Of the trichina spiralis. CHAPTER XVIII. 456. What is said of the purposes for which clothing is worn ? 457. What of linen as an article of clothing ? 458. How does cottou differ from linen ? 459. What are the properties of woollen clothing? Its relations to moisture ? 460. How does color influence the character of clothing? 461. What is of more importance than the character of the fabric? 462. Why should clothing be light ? 463. Why should it be worn loose ? 464. What is said of compressing the chest and abdomen ? 465. What results from compressing the feet ? 466. How is uniformity of temperature to be maintained ? 467. How is a part affected when habitually over-heated ? 468. Why is over-dressing the throat pernicious ? 469. What is said of wearing flannel next the skin ? 470. How should children be clothed ? 471. Why should the aged be well protected ? CHAPTER XIX. 472. What renders it evident that man is intended for action ? 473. What is said of labor ? What causes division of labor ? How does it affect the individual ? 18


410 QUESTIONS. 474. How does exercise remedy the evil ? 475. Describe the transformation of physiological forces. 476. Why is habitual exercise invigorating ? 477. How does exercise affect the circulation ? How the tempera- ture? 478. What is its influence upon respiration ? Why should we exercise in pure air ? 479. How does exercise affect digestion ? Why is immediate exercise after a full meal injurious ? 480 What is the effect of exercise upon the skin ? 481. How should exercise be regulated ? 482. What are the most favorable conditions for exercise ? 483. Why is over-exercise injurious? How is proper rest to be secured ? How should exercise be managed after sickness ? How does over-exerdse injure the system? Why does it particularly injure the young ? 484. What are the consequences of insufficient exercise ? Describe its operation in different circumstances. 486. What is said of the amount and conditions of exercise ? What course should the sedentary pursue ? Why is pure air specially necessary during exercise ? 486. What is the value of the " movement-cure " ? CHAPTER XX. 487. Wliy is mental health a physiological question ? 488. What is said of the office and changes of the brain ? What is the effect of disturbing its normal movement ? Describe the mutual rela- tions of the mind and brain. What is remarked as to materiahsm ? 489. What constitutes diseased What error is to be guarded against ? How is mental disease to be regarded? On what is Mental Hygiene founded ? What is its province ? What is said of diseases of the brain ? Why have all a vital interest in the subject ? 490. Describe the modes of mental action. How are these psychical elements to be regarded ? In what forms may insanity manifest itself? 491. What are hallucinations ? Examples. What are illusions ? Examples. • Delusions ? What is delusional insanity ? 492. Describe the different phases of emotional insanity. Give the example of congenital perversity. How is the other class of cases affect- ed ? Describe the case given by Dr. Maudsley. What is said of moral insanity ? Repeat the remarks of Dr. Carpenter. Of Dr. Ray concern- ing moral endowments. What of the different elements in the moral faculty ? To what conclusion are we led ? 493. What is mania? Its kinds? What is acute mania? Give the mental differences in cases of acute mania mentioned by Bucknill and Tuke. Describe chronic mania. 494. In what does monomania consist? Mention different kinds. Give the case described by Dr. Bucknill. 495. How is melancholia manifested ? Describe the victim of simple melancholia. What are its forms ? Relate the case mentioned by Dr. Conolly. How does melancholia affect the intellect ? 496. Define general paralysis. Who are generally its victims ? De-


QUESTIONS. 411 scribe the progress of the disease. How is the accompanying mental im- pairment manifested? Examples. 497. In what does dementia consist ? What are its stages ? When is it primary ? When secondary ? * 498. What is idiocy ? Describe its degrees. How is idiocy dis- played ? 499. What does the term idiocy denote? How is it manifested? How do imbeciles compare with idiots ? 500. What is said of perverted mental action that never passes into mania ? 501. Why are the causes of cerebral impairment varied and complex ? How are they usually di^dded ? What are predisposing causes ? Excit- ing causes ? ' What error is mentioned ? In what way is insanity usu- ally caused ? 602. What is said of each mental act ? What is the composition and action of the mental mechanism ? What are the results of its perfect or imperfect nutrition ? Repeat the remarks of BUcknill and Tuke. What further effect is due to impaired nutrition ? 503. What is said of the blood transmitted to the brain ? 504. What are the relations between mental excitement and the brainward flow of blood ? How is congestion induced, and what are its eflfects ? 505. What is anaemia, and how caused ? What are its eflfects as com- pared with those of hyperaemia ? Give Dr. Maudsley's remarks upon the subject. 506. What keeps the brain in harmonious action ? How may its har- mony be further disturbed ? Mention examples of perversion of blood. How does alcohol affect the brain ? 507. How does the brain differ in action from other organs of the body ? How does nature renovate the brain ? What is a prime condi- tion of mental health ? What are the effects of insufficient sleep ? What of disturbed sleep ? In what does mental health consist ? From what arises mental impairment ? Hence, what causes influence mental char- acter ? 508. Give the estimates relative to the transmission of insanity. What is transmitted, and how ? Repeat the remarks of Dr. Maudsley. 509. How is debilitated stock a source of criminality? What is Dr. Howe's opinion upon this subject ? Name some of the causes of mental impairment and their operation. Give the observations of Dr. Ray. 510. What comparison is made between the savage and the civilized man ? What are our peculiar perils as a nation ? 511. What is said of overtasking the intellect? Repeat the testi- mony of Dr. Carpenter. What conditions control the amount of healthful brain-work ? How is the argument against the unwholesome effect of excessive brain-work met ? In what respect does the brain of the savage and the civilized man differ ? What usually works the mischief in cerebral application ? 512. How is cerebral disease heralded ? How the more active forms ? In what manner is the conduct affected ? "The consciousness ? • 513. What hints and precautions are given? How should children thus predisposed be managed ? How adults ? What is Dr. Ray's advice when there is a predisposition to mental disease? 614. What is said of medical management ?


II^TDEX. Abilomen, 28. Abdominal aorta, 106. Abduction and adduction, IGd Absorption, 148, 152. Accessory tood-stuffii, 189. Ascending colon, 149. Acetabalum, 165. Acidulous waters, 299. Action, man intended for, 844.

    • of the valves, 60.

Active powers, 158. AdamVapple, 171. Adjustment of the eye, 212, 215. Adulteration of milk, 812. Adulteration of vinegar, 81S. Aerial waves, 196. Afferent nerves, 177. Agencies of purification, S91. Air, 21.

    • contamination of, by various trades,

287. " danger of ovcr-heatins, 294, " heating of the, 294. '* inspired and expired. 88w " in respiration. 97. •* in the lungs, 97. " as affected by exercise, 852. Air-cells, 87. Albumen, 134, 809. Alcohol, effect of; 880. Alinientary*api)aratu8 83. canal, 24, 108, 133. Alimentation, 83.

    • daily gains of, 183.

" object of, 139. Alluvial waters, 800. Alveoli, 143. Ammonia, 84, 826. Amoeba, 69. Amount tf air required for ventilation, 292. Amphibia, blood-corputck-s oi; 71. Amphioxus, 70. AmpulliB, 189. Amyloids, 129, 184, 808. " prove injurious as diet, ^35. Anatomy, 15. . ** outlines of, 28. Animal charcoal, 807.

    • foods, 812.

Ankle-joint,i61. . Ajius, 151. Aorta, 44. Applied physiology, 276. Aqueous bimior, 210. Arachnoid membrane and fluid, 287. Areolar tissue, 27. Arms, bones of the, 29. Arteries, 88, 87. Arteries and veins, difference between the, 89. Ai-tcrial blood, 82. Artery, hepatic, 121. " venal, 114:

  • » splenic, 128.

Articulation, 159. Artificial reflex actions, 254. Arytenoid cartilages, 171. Asphyxia, 101 " causes of, 105. " slow, 105. Atlas, 162. Atmosphere, constitution of tie, 282. " impurities of the, 283, 29S. Atmospheric impurities, their reLitions to the senses, 283. Atoms, 153. Auditory muscles, 198.

  • t nerves, 188, 195.

" ossicles, 193. Auditory spectra, 222. Auricles, 47. Auriculo-ventricular ring, 50. " ** valves, 50. Auxiliary food, 818. Axis, 162. Axis, cerebro-splnal, 236. Axis-cylinder, 278. Axis, the optic, 230. Ball and socket-joints, iGt.


. INDEX. 413 Basilar membrane, 190. Beans and peas, 817 Beef, 818. Beef-tea, 824. ^ Beets, 817. ^ Biceps muscle, 28. Bicuspid teeth, 143. Bile, 107, 120, 124, 15t Bile-duct, 12a ^ Bilin, 123, 124. ^ Bilioasncss, 327. Biology, 14.

    • divisions of, 15.

Black clothes, 884.

    • pepper, 819.

Bladder, 110. Blind spot. 204. Blood, appearance of, when magniHed, 05. " arterial and venous, 81.

  • '• arterial distribution of, 106.

"" changes of the, 88.

    • circulation of the, 84.

^ coagulation of the, 66.

  • ' composition of the, 77, 81.
    • corpuscles ot 66.
    • crystals ol^ 72.
    • flow of, through the heart, 53.

" perversions of. 879.

    • poverty of, 879.

" purification o^ 86. " quantity in the body, 79. " sources of loss and gain to the, 106, 109. " " thicker than water," 77. '* transftision of, 80. " and lymph, 65. Blow on the head, effect of a, 81. Blushing, 60. Body, functions of the, 19. Boiling, 806, 824. Bone, 28.

  • • structure of, 268.

Bony labyrinth, 192. Brain, 25.

    • and mind, 358.

" anatomy ot, 246.

    • congestion of, 878.
    • convolutions of^ 248.
    • diseases of, 856.

" hemispheres of. 248. " influence of, 862. " lobes ot; 248. " nutritive repair of, 880. " reflex actions of, 268. • " seat of sensation, 32.

    • sulci of the, 248.

" use of, 3Sa Bread 138, 311. Brcast-bono, 29. Brewster, Sir D., 223. Bright'a,disease, 840. Brr/iling, 325. Bronchitis, 287. Bronchi, 91, 97, 100. Bronchial tub^ 86, 91. Bmnner*s glands, 149. Buccal glands, 142. Buckwheat, 316. Bafly coat, 7a Bunions, 389. Butcher^s meat, 138. Bursal, 167. Butter, 812. Butter of cacao, 823. Cacao-beana, 823. Caicum, 149. Oaffein, 821. Camera obscura, 209. Canaliculi, 268. Canals of the ear, 190. Canine teeth, 143. Capillaries, 83, 37. " causes of steady flow in, 58. " of the limgs, 84. " why pulseless, 57. Capsular ligament, 165. Carbon, 134, 13a • Carbonate of lime, 20, 28, 299. " of soda, 300. Carbonic acid, 20, 34^ 82, 188.

    • ** as an atmospheric impu-

rity, 283. Carbonic acid, excretion of, 107.

    • ** proportion of, in surface

soil, 299. Carbonic acid, quantity thrown off by the lungs, 284. Carbonic acid, poisonous nature of, 1C4. Carbonated waters, 299. Cardiac dilatation, 145. Cartilage, 28, 26a " articular, 29. Caruncula lachrymalis, 217. Casein, 134. 809. Catherine wheel, 204. Causes of disease, 279. Cavities of the heart, 48. Cayenne pepper, 319. Cellars, foul air oi; 287. Cerebellum, 247. Cerebral hemispheres, functions of the, 252. Cerebral circulation, disturbance of, 877. " nerveir, 249. " structures, nutrition of, 876. Ccrebro-spinal axis, 25, 286. " " functions of the, 31. « system, 286. Cerebration, unconscious, 252. Chalybeate waters, 299. Changes of the food, 133. Charcoal as a deodorizer, 295. Charcoal-filters, 307. Check-ligaments, 165. Cheese, 812. Chemistry, 14. Chest, 24. " bones of the, 20. Chest-walls, 92. Chewing, 144. Chloride of potassium, 310.

  •  »* of sodium, 300. •

Chlorine as a disinfectant, 296. Chocohite, 823. Cholera, 304. " as influenced by hygienic meas- ures, 279.


414 INDEX. Cholesterlne, 121 Chondrln, 184. 260. Chorda tendlua, 50. 54 Choroid coat, 210. Cbyle, 43. 151. Chyme, 149. Cilia, 01. 154. ^ ^ ^^^ " movements of Ine, lt>4. CI Mary processe:*, 210. " iljfamont, 211. '* mascle, 211. Ciliated epithelium, 25S. CircumductioD, 166; Circulatory apimratus, 38. Circulation affected by exercise, 846L

  • » compared to a river, 81.

" course of the. 59.

    • evidence of; 63.

Clrcumvallate paplllfle, 133. Cistern-water, 802. Cistern of the chyle, 43. Clams, 315. Classification, 10. Clothing, 832. '^ absorption of moisture by, 838. " children's. 841. for the aged, 341. Clot, 7a Cochlea, 188, 190.

    • Ainctlon of, 199.

Cochlear nerve, 199. Cocoa, 828. Cod-liver oil, 82a Coffee, 821. " adulteration of 822. Cold, 182. Colic, 82a Colon, 149. ^ Color-blindness, 205. Columnae comese, 50, M Combination of actions, 29. Complementary colors, 205. Complex sensations, 219. Compression of the chest, 835. » of the feet, 883. Concha, 19a Condiments, 8ia Conditions influenciuj tbo coagulation of the blood, 74 Condy's fluid, 295. CoD^stion, 62, 340, 37a Conjunctiva, 209, 217. Connective tissue, 27, 261. " Consonants, 175. Constipation, 32a Constricting the neck, 385. Consumption, 233, 323.

    • of oxygen, 18a

Controlling action of the nerves, 8a Control over the circulation, 60. " the heart, 62. »* " respiration, 99. Convex lens, 208. Convolutions of the brain, 24a Cooking, 82a Cornea, 209. Corns, 889. Coronary arteries and vein, 4a Corpora quadrigemina, 247. Corpora striata, 24A. Corpus callosum, 248. Corpuscles of bone, 203. ^ '* of human blood, 26a ^ ** of spleen, 12a Costal respiration, 94. Cotton, 88a Coughing, 9a Crabs and lobsters, 8Uk Crassamentnm, 78. Cribriform plate, 186. Cricothyroid muscles, 162. Cricoid cartilage, 171. Crucial ligaments, 166. Crura cerebri, 247. Crystalline lens, 210, 260. Cutting teeth, 144. Cylindrical epithelium, 257. Cysticercus celluiosus, 880. Debilitated stock, 885. Deciduous teeth, 269. Deep wells, 802. Deficiency of lat, 32a Deficient diet, 82a Deglutition, 144. Delirium tremens, 22a Delusions, 859. Instances of, 223-22a « of the judgment, 222. »♦ optical, 229. Dementia, 369, 370. Dentine, 267. DetKlorizers, 295. Dermis, 2a Descending colon, 149. Development 15.

    • of blood corpnscles, 69.

Dextrine, 126, 135. Diaphragm, 24, 47, 93 Diaphragmatic respiration, 94. Diaphragm of the eye, 211. Diatrhoea, 32a

    • caused by river- water, 80a

Diastole, 52. Digastric muscle, 168. Digestion, artificial 147. " how affected "by exercise, 847,

  • second, 151.

Disease, old notions of, unfavorable to hygienic efforts, 277.

    • open-air treatment o^ 29a
    • propasration of, 290.

" true idea of, 27a

  • ' causes of; 279.

DiHtillation, 806. Dorsal chamber, 24. Double hinge-joint, 161. Dressing the body, 835. Drinking, 145. Drum of the ear, 198. «  Dry air, 285. Duct, hepatic, 121. Ducts of the glands, 165. Ductless glands, 70. Duodenum, 148. Dura mater, 287. Duration of Hght-imprcssions, 204 Durham jail, 805. "i


INDEX. 415 Durham and Northumborland, colliers o£ 287. Dysentery, 804. Dyspepsia, 802, 82a Earthy carbonates, 818. Ear, 180. Ease in walkln;::, 838. EatinR, 144. Economy of mixed diets, 188. Efferent nerves, 177. Eggs, 818. EfN)W-joint, 161. Elementary Hygiene, 273. Elimination of heat, 189. Emotion, 60, 178. Emphysema, 287. Enamel of the teeth, 267. Endocordinm, 49. Endolymph, 189, 190. Engorgements, 840. Entozoa, 805. Epidermis, 26, 267. Epiglottis, 86, 140. Epithelial cells of the arteries, 88. < Epithelium, 27, 181, 189. 257, 286. Erect position of man, 29. Essential food-stuffs, 189. Etiology, 17. Eustachian tube, 141, 198.

    • ** function of the, 200.

Evaporation, 180. Excess of food, 826. Excretion, 88. Excretions, forms of, 21. Excretion of carbonic acid, 99, 108. Excrementitious matter, 21. Excretory organs, 84. Exercise, 845.

  • ' amount and time of, 851.
    • . effect upon circulation. 846.
    • " •* digestion, 847.
  • ' « respiration, 846.

»' « « skin, 847. " excessive, 849. mind in, 84a " Insufficient, 849. ^ remedial influence of, 852.

    • regularity of, 84&

Exhaustion of the retina, 206. Expiration, 88. Explosive consonants, 176. Extension, 166. Extra vascular parts, 86. Eye, 180, 201. " adjustment of the, 212, 215. " humors of the, 210. Eyeball, 209. Eyelashes, 217. Eyelids, 209, 217. Facial nerve, 249. Faeces, 21, 88. Fascia, 270. Fats. 184, 188, 80a Fat-cells, 262. Fat, pure, livjurious as diet, 185. Fauces, 140s. Feeling, 178. Feeling, loss of, 81. Fenestras ovalis, 198. '• rotunda, 198. Fibrenogih, 76. Fibres of Corti, 189. " " " ftmction of, 199. Fibrillffi, 271. Fibrin, 72, 184, 809. Fibro-cartilage, 160, 262. Fibrous tissue, 27. Filiform papillae, 188. initers, 807. Filtration, 807. Fish, 814. Fissures of the cord, 287. Fissure of Sylvius, 24S. Flatulence, 826. • Flesh parasites, 829. Flexion, 166. Flour, 816. Focus, 20a Food, 21. Food and force, 28. Food of children, 321. Food-stuffs, 184. Foot, 29. Fore-arm, 168. Form of the boot, 889. Foul air, efffects of, upon the course of disease, 290. Foul air, effects of, upon inherited taints, 290. Foul air, effect of, upon the mind, 291. French troops in Mexico, 804. Frog, experuncnt with the, 68. Fruit, 8ia Frying, 806, 824. Functions of the spinal nerves, 289. Fungiform papillae, 183. Galtanlc shocks, effects of, 81. Gall-bladder, 121, 151. Game, 814. Ganglia, 62. Ganglia, sympathetic, 24. Ganglionic corpuscles, 272. Gaseous diffusion, 73. • Gastric juice, 146. Gelatine, 27, 184, 262, 309. Glands, buccal, 142. " lachrymal, 217. « Meibomian, 217. " parotid, 217. " of Lieberkahn. 181, 149. •* submaxillary, 142. " sublineual, 142. Globulin, 62, 7a Glommerulus, 118. Glosso-pharyngeal nerve, 183, 249. t Glottis, 89, 96, 142, 185. Glucose. 120. Gluten, 184, 815. Glycogen. 120, 12a Glychocolic acid, 123. Glychocolate of soda, 124. Goats* milk, 812. Goose-skin, 260. Goitre, or Derbyshire neck, 127, 805. Gout, 278.


416 INDEX. Oras8l'8 experlmcntfl, 203. Gray matter, 238. Grinding-teetb, 144. GuUet, 141. Gura, 120, 810. Hnpmatln, 68, 72. Hairs, 30, 269. llallQoinations, 857. Hard water, 299, 803. Haversian canals, 264. Head, 23.

  • ^ movements of the, 163.

Hearing, 180.

    • sense oil 1S8.

Heart, 21, 8:J.

  • ' beating o4 the, CO.
    • position, 47.

" Bounds of the. C6. •* stmoture of tne, 46.

    • rhythm of the, 62.
  • " walls of the, 68.
    • working of the, 62.

Heat, generation of, 123.

  • ' producers, 189.

" regulation of, 180. Hepatic circulation, 121. »* artery, 46, 121. " duct, 121.

    • vein, 46, 120.

Hereditary transmission, 882. " " cfbodily defects, 888. " *♦ of insanity, 884. High-heeled boots, 839. Hilus, 109. Hinge-Joints, 161. Hip-Joint, 161 Histology, 16, 266. Hollow muscles. 159. Horripilation, 26. Human millc, 812. Human body, structure of the, 23, 26. " ** waste and renewal of tbe, 22. Humerus, 164. Humors of the eye, 210. Hunger. 21, 826. Hydrochloric acid, 146L Hydrogen, 21, 184. Hygiene, 18. Hygienic agencies, remedial influence of; 280. Hygienic knowledge, effect of, upon the actions, 281. Hygroscopic water, 834. Hyold bone, 171. TcG-chamber experiment, 20. Idiocy, 871. Ileum, 148. Ileo-cffical valve, 149. Iliac arteries, 106. Illusions, 858. Imbecility, 878. Imperfect Joints, 159. Impure water, efl"ect of, upon the senses, 806. Incisor teeth, 143. Incus, 194 Indian com, 811, 816. Ingrowing toe-nails, 839. Inherited taints, 290. Insalivation, 144. Insanity, emotional, 869. " causes ot, 875, 876.

  • ' precautions as to, 892. 893.

Insensible perspiration, 115, 284. Integument, 26. Intellect, aberrations ot^ 867. Interarticular cartilage, 161. Intercostal muscles, 92. Intermittently active sources of loss, 181. Intermittent action of the glands, 181. Intervertebral foramina, 288L Intestines, 14a Intestinal circulation, 150. " Juice, 149. Intralobular veinlet, 122. Invertebrate animals, blood corpuscles o^ 70. Iris, 155. 210. Iron, 800. Jaws, the, 143; Jejunum, 148. Joints, 29, 169. Judgments and sensations, 220. Jugglers, how they drink standing on their heads, 145. Jumping, 168. Kidneys, 24, 84, 112. Kidneys and lungs compared, 110. " medullary and cortical ports, 112. " shape and position of the, 109, 113. Knowledge, twofold value of, 275, Labor, 844. Lachrymal gland, 217. " sac, 217. Lacteals, 48, 152. Lactic acid, 141. Lncuns, 268. Lancelot, 70. Largo intestine, 148, 152. Larynx, 86, 170. Lateral ligaments, 166. Lead poisoning, 801. Legs, Doces of the, .29. Levator muscle of the eyelid. 217. Levers of the body, 156. Ligaments, 29, 161, 262. Light, 207. ^ sensation of. 208. Light and heavy clothing, 835. Lighting, products of; 286. Limbs, 28. Lime-water, 20. Limestone-wators. 299. . Limiting-membrane, 202. Linen, 882. Lips, 183. Liver, 24, 120. " cells, 123. " sugar, 126. Lobules of the liver, 120. Locomotion, 158. Long-sight, 215.


INDEX. 417 Loose clothinnf, 833. Lower jaw, 143. Lungs, 24, 44. " amount of work done by Iho, 89. " double function of the, 84. « elasticity of the, 90. " ydneys, and skin, compared, 119. Lymph, 878. " corpuscles, 70. Lymphatic capillaries, 42.

    • glands,- 42.

" system, 126. Macula lutea, 201. Magnifying glasses, 282. Malarious fevers, 8i)5. Malleus, 198. Malpighian capsule, 113. Mammals, blood-corpuscles of the, 70. Man, erect position of, 29. Mania, 863, 864. Marrow, 264. Marsh-water, 800. Mastication, 144. Materialism, 854. Mathematics. 18. Matter, whence gained, 124. Meats, 813. Meatus, 193. Mechanical force, 21. Medical management, 894. Medulla oblongata, 99, 246. " " decussation of fibres In 251. Meibomian glands, 217. Melancholia, 866. Membrane of Corti, 190. Membranous labyrinth, functions of the, 199. Mental action, modes of, 857. " disease, 855, 879.

    • evolutions, 81, 61.

" health, 853. " hygiene, foundations of, 855 " impairment, degrees of, 874. " " in what consists, 355. " over-action, evils of, 8S8. " under-action, 889. Mesenteric glands, 44. Mesentery, 41 Milk, 812, 827. Milk-teeth, 269. Mind, controlling power of the, 81.

  • ' in exercise, m

Mineral aliments, 810. " ingredients of water, 209. Mitral valve, 50. Mixed diets, 138, 311, 827. Modiolus, 190. Modulation of the voice, 174. Molars, 269. Molar-teeth, 143. Monomania, 365. «  Moral insanity, 858. " perversities, 859.

  • ^ sense, elements of, 8G2.

Morphology, 15. Motion, 163. Motor nerves, 177. 18* Motores oculi, 249. Mouth, 25, 140, 185. Movements of the joints, 166. Mucous, 27. " membrane, 27. Muflaing the throat, 840. Multiplying glasses, 231. Muscles, 28, 154. " insertion of, 167. " of the alimentary capal, 154. " of the eye, 216. " of the heart. 154. " of the lymphatiQ vessels, 151. " origin oi; 167. " structure of, 210. Muscular contractility, 154. " fibres of the arteries, 88. " fibres of the heart, 49.

    • sense, 179.

" waste, 182. Musical notes, 173. Musk-deer, blood-corpuscles of the, 71. Mustard, 819. Mutton, 818. Nails, 86, 253. Nasal cavities, 141. " chambers, 185. " passages, 86. Nature's standard of purity, 292. Negative deflection, 241. Nerve fibres, 272. Nerves, motor and sensory, 240. ". of the heart, 62. Nervo-tissue, structure o^ 272. Neurilemma, 181, 278. Nitrogen, 21, 89, 134, 282. • *' starvation, 136. Nitrous acid, 296. Norwood school, 289. Nucleated cell, 69, 256. Nuclei, 85, 256. Nutrition, 82. " of cerebral structures, 876. Objects and their visual images, 230. Odontoid process, 162. (Esophagus, 141. Olfactory nerves, 134, 186, 249. Onions, 818. Openings of the pharynx, 141. Optic axis, 230. " nerves, 201, 203, 249. " thalami, 248. Optical delusions, 229. Orbit, 201. Organic matter, presence of, in various waters, 299, 300. Osorbiculare, 194. Ossification, 264. " centres of; 266. Otoconia, 188. Otolithes, 188, 195. Outlines of anatomy, 23. Overcooking, 827. Over-exercise, 849. Overtasking the brain, 882.

    • " emotions, 887.

" " intellect, 887, SSa


1 .418 INDEX. Osidation. 85, 129. Oxygen, 85, 89, 184, 2S2. "* ab5ori>tioD of; 121. Oysters, 81Sl Pducreofl, 24, 182, 14a Pancreatic juice, 151. Palate, 140, 188. Papillie, 181. Paralysis, 240. ♦* gencjral, 868. Parkers experiments, 293. Parotid glands, 142. Parsnips, 817. Peas and beans, 817. Pectine, 81& Pelvis of the kiOaey, 112. Pepsin, 148. Peptic glands, 148. Peptone, 147. Pericardium, 47, 75, 237. Perilymph, 190, 195. Periosteum, 264. Peristaltic contraction, 150. Peritoneum. 120, 148. Permanent food, 185. Permanganate of potash, 295. Perspiration, 117, 281. Pharynx, 85, 140, 185. Phenomena, coexistences and seqaences oi;i2. Phosphorus, 184, 20a Phosphate of lime, 2a Physics, 18. Physiology, divisions ot^ 11. " study of, la " human, 19. Physiological balance, 22. Pia-mater, 287. Pigment-cells, 210, 268. Pineal gland, 24a Pituitary body, 24a Pivot-joint, 162. Plasma, 66, 72. Pleura, 90. Plexuses, 256. Pnoumogastric nerve, 68, 250. Pons Varolii, 247. Portio dura, 249. Portio mollis, 249. Posterior arytenoid muscles, 17a " nares, 185. Potatoes, 817. Potter's asthma, 287. Poultry, 814. Practical knowledge, 276. Production of voice, 17a Pronation, 164. «  Proteids, 184, 80a Protein, 21.

    • necessity for its supply, 186.

Pscudoscope. 284. Ptyalism, 146. Pulmonaiy artery, 44. »* consumption,. 288, 290. " veins, 44. Pulse, 6a Punctum lachrymalc, 217. Purification of air, 291. Purification of water, 8061 Purklnie's figures, 207. Pus-cellii, 28& Pylorus, 146. Quality of voice, 174. Radial fibres, 202. Bacemose glands, 182. Bain-water, 29a Bange of voice. 174. Beceptacle of toe chyle, 4a Beotum, 150. Beflex action, 99, 178, 242. " ** arUflcial, 254 Begnlation of the tenoperatore, 180. Benal apparatus, 109, lia

    • circuktlon, 114.

Besidual air, 97. Bespiration, 84.

    • affected bv exercise, 846L

"" and chx^ulation compared, 99.

    • • different in the two sexes, 95.
    • effect of, upon the circulation,

100. »* in children, lOa ^ mechanism of; 86. Respiratory sounds, 100. Reparation, 88. Retina, 201. Bhythm of the heart, 52. Bibs, 29, 90. Bice, 867. Bickets, 827. Biver- water, 800. Boasting, 824. Bods and cones, 202.

    • " functions of the, 206.

Rotation, 166. Round ligaments, 165. Routes of tb« circulation, 66. Running, 168. Uye, 816. Salamanders, blood-corpuscles of, 71. Saline substances, effect of, on the blood, 65. Saliva, 142. Salivary glands, 132. Salts, 136. Salt meat, 814. Sand-and-gravel waters, 800. Sankey's experiments, 298. Sanitary congress, 801. Sarcolemma, 49, 270. Scala media, 188. 190.

  • • tympani, 190.

" vestibuli, 190. Scarf-skin (see Epidermis). Science, 11. Sciences, connection of, 12. Sclerotic, 209. Scrofula, 28a Scurvy, 280. Sea-water, 801. Sebaceous glands, 131, 116, 259. Secretory glands, 107. " " action of, 182. Semicircular canals, 190.


INDEX. 419 Semilunar valves, 51. Sensation, 82, 178.

    • tactile, analysis ot 220.

Sensations and Judgments, 220. Senses, delusions or the, 222. Sensitive beach, 188. Sensory organs, 85. " nerves, 177. Semm, 78. Sewage gases, 804. Shallow wells, 800. Sheath, 27. Short-sight, 215. Shoulder-Joint, 161. Sick-room atmosphere, 289. Sighing, 96. Sight, 180. Simple sensations, 219. Skeleton, 2&

    • number of bones in, 29.

Skin, 20, 26, 115, 116, 119, 847.

    • respiratory Itmction ot 124.

Skull, 24. Sleep, insufljcient, 881. »' • quality of, 882. Small intestine, 14& Smell, 180.

    • eflfects of a bad, 81.

" loss oA 187. " sense of, 184. "• sensation of, 219. Smooth muscles, 270. Sneezing, 96i SnifBing, 96. Soft palate, 140. »* water, 298.

    • " penetrating power, 298,

Solvent power of water, 296. Sound, 196. Spcakms-machines, 174. Speech, 174. Sphincter, 110, 150. Spinal accessory nerres, 250. " canal, 24.

  • ' column, bones of the. 29.

" cord, 24, 287. " ** conducting power of, 244.

    • " properties o^ 242, 244.

" »* injuries to the, 81. " nerves, 287. »» " anterior roots of, 289 " « functions ot, 289. " " posterior roots of, 239. Spleen, 24, 127, 180. Splenic artery, 128. "• vein, 128. Spongy bones, 187. Squinting, 284. Stapedius, 195. Stapes, 198. Starch, 126, 185, 810. " cells. 286. Starvation, 826. States of consciousness, 178. Stationary air, 97. " ** composition ol^ 98. Stereoscope, 288. Stewing, 824. Stiraalas, 17a Stomach, 145. '* cardiac aperture of; 145. Stretched membranes, 196. Structure of the kidneys, 112. Striated muscles, 270. Subiected sensations, 222, 178. Sublingual glands, 142. Submaxillary glands, 142. Subsoil water, 800. Substance, loss of, 21. Sogar, 185, 810. Sulci, 248. Sulphate of lime, 299. Sulphur, 184. " waters, 299. Sulphurous acid, 296. Sulphuretted hydrogen, 804. Supination, 164. Supplemental air, 97. Supra-renal capsules, 127. Smiiftco-water, 800. Suspensory ligament, 210. Sutures, 26& Swallowing, 144. Sweat-glands, 116, 181. " quantity of, 115. Sweet-bread, 24. Sympathetic nervous system, 24. " system, 286, 255. Synovia, 29, 160. Synovial membranes, 29. Syntonin, 184, 809. Systole, 82. Tactile corpuscles, 181, 274. " sensibility, 182. Tannic acid, 819. Taurocholic acid, 128. Tape-worm, 880. Taste, sense of, 188. Tea, 819. »* making of, 820. " adulteration of, 820. Tears, 2ia Teeth, 86, 140, 14a " cement of, 267.

    • crowns of the, 148.

" dentine of; 267. " development of, 26a " enamel of, 267. « fangs of the, 148. " structure of, 266.

    • pulp cavity of; 266.

Temperature, effect of, on the blood, 74. Temporal bone, 188. Tendons, 167, 262. Tensor tympani, 195, Thanmotrope, 288. Tbein, 819. Theobromin, 82a Thirst, 21. Thoracic duct, 42. Thorax, 28, 88, 94, 9a Thoughts, 17a Tbymous glands, 127. Thyroid cartilage, 171.

    • *• action of, 17a

Thyroid ghind, 127. Thyro-arytenoid muscles, 173.


420 INDEX. Tidal air, 97. Tight booU and shoes, 838w Tight clothing, 886. TisBues. 27. Tissae furmcrs, 139. Tongue, 140. ^ mucous membrane of, 1S3.

    • papilla) <)fi 188.

Toii^eless 8i»eech, 176. Tonsils, 140. Touch, sense of, 150. Trachea, Sa Transformations of physiological forces, 845. * Transmission of vibrations, 197. Transmissions of impressions, 241. Transudation, 116. Transverse colon, 149. I'rapezinm, 162. Trichina spiralis, 881. Tricuspid valve, 50. Trigeminal nerves, 249. Trunk, 28. % Tubercular consumption, 288. Tuning-fork, 199. Turbinal bones, 187. Turnips, 817. Tymfiannm, 193. Tympanic membrane, 193.

  • ^ muscles, function of the, 200.

Ulna, 164. Uneconomical food, 186. Uniformity of body, 239. Unproductive labor, 187. Unwholesome food, 324. Urea, 21, &i Ureters, 109. .Urethra. 109. Uric acid. 111. Urinary excretion, 1 10. " products, 880. Urine, constituents of, 111.

    • daily quantity of. 111.

" • specific gravity ofl 111. UvuLo, 140. Valve, ileo-ciccal, 149. Valves of the arteries, 41. « " »* lymphatics, 42. " " " veins, 40. ValvnliB conniventes, 150. Vapor of the body, 20. Vascular system, 85. Vasomotor nerves, 62. Vegetable foods, 816. Veins, 28, 87, 89. Vena cava, 44, 46, 121.

  • • portio, 46, 121, 125.

Venous blood, 81. " pulse, 102L VcutilaUon, 106, 292. Ventilation, conditions of, 292, 295. ^ effects ot, in mines, 298. »• u u Qp,,n tijo gj^.^^ 298.

    • movement of air in, 294.

Ventral chamber, 24. Ventricle, 48. Ventricles of the brain, 248. Ventriloquism, 228. Vermiform appendix, 149. Vertebral colmnn, 24, 160. Vertebr©, 24. Vertebrate animals, blood-corpuscles ot 70. Vestibule, 189, 192. Vestibular sac, 190. Vibrations of the tympanum, 197. VUll, 44, 161. Vinegar, 818. Visual images. Inversion of^ 280. Visual size and form, 282. Vital eddv, 15a Vital food-stuffs, 185. Vitreous humor, 202, 210. Vocal chords, 86, 170.

    • cushions, 171.

Voice, 170. Volition, 178. Vowel sounds, 174. Walking, 168. Walls of the heart, 49. Warmth, 182. Waste of the muscles, 182. " pipes, 802. WaUr, 21, 1Z5. " action of. in the organism, 297.

    • amount daily taken, 297.

" and health, 296. " camera, 209. " excretion o^ 119. " of interposition, 884. " poisoning, by lead, 807. '* proportion In the several tissues,

    • purity of, 298, 801.

Watery vapor, 20. 282, 2S4. Wearing flannel, 840. Weight, gain of, 22.

  • ^ loss of, 22.

Wheat, 815. White clothes, 884. Will, the, 857. Windpipe, 86, 172. Wisdom-teeth, 270. Woollen, 88a Work and waste, 20, 88. Working of the arteries, 65. Wrist, 168. Tellow-spot, 201. Zein, 817.


D. APPLETON A CO:S PUBLICATIONS. THE PHYSIOLOGY PATHOLOGY OF THE MOD. By henry MAUDSLEY, M. D., London. 1 volnnie, Svo. Cloth. Price, $4.00. CONTENTS : Part I.— Tlie Pliyslolosry of tlte Idlad. CnAPTER 1. On the Method of the Stadv of the Mind.

  • ' 2. The Mind and the Nervonsflystem.

" 8. The Spinal Cord, or Tertiary Nervous Centres ; or, Nervous Cen- tres of Keflex Action. " 4. Secondary Nervous Centres; or Sensory Ganglia; Sensorium Commune. " 6. Hemisphericdl Ganglia; Cortical Cells of the Cerebral Hemi- spheres: Ideational Nervous Centres; Primary Nervous Centres; Intellectoriura Commune. •• 6. The Emotions. 7. Volition.

    • 8. Motor Nervous Centres, or Motorium Commune and Actuation or

EflTection.

    • 9. Memory and Imagination« 

Part II.— Tlie Patliolog j of tlie Mind. Chap. 1. On the Causes of Insanity, j Chap. 4. On the Pathology of Insanity. " 2. On the Insanity of Early Life. " 6. On the Diagnosis of Insanity. " 8. On the Varieties of Insanity. | " 6. On the Prognosis of Insanity. Chapter 7. On the Treatment of Insanity. " The first part of this work may be considered as embodying the raost advanced expression of the new school in physiological psy- chology, which has arisen in Europe, and of which Bain, Spencer, Leycoch, and Carpenter, are the more eminent English representa- tives." — Home Journal, " The author has professionally studied all the varieties of insan- ity, and the seven chapters he devotes to the subject are invaluable to the physician, and full of important suggestions to the metaphy- sician." — Boston Transcript, " [n. the recital of the causes of insanity, as found in peculiarities of civilization, of religion, of age, sex, condition, and particularly in the engrossing pursuit of wealth, this calm, scientific work has the solemnity of a hundred sermons ; and after going down into this ex- ploration of the mysteries of our being, we shall come up into active life again chastened, thoyghtful, and feeling, perhap?, as we never felt before, how fearfully and wonderfully we arc made." — Evening Gazette


J>. APPLETON d: 00:8 PUBLICATIONS. THE PHYSIOLOGY OF MAN; DX8I0NKD TO EEPEESENT THE EXISTING STATE OF PHYSIOLOGICAL SCIENCE, A3 APPLIED TO THE EUNOTIONS OF THE HUMAN BODY. By AJJSTTN Tni:,I]STr, Jr., Mi. D. Alimentation; Digestion; Absorption; Lymph and Oliyle. 1 Yoliune, 8yo. Cloth. Price, $4.60. BJSCXJITTLT PUBZISMJED. THE FIRST VOLUME OF THE SERIES BY -A.TJSTIN" TrJLjlN'X\ Jr., ]VE. D., CONTAININQ Introdnotion ; The Blood; The Oiionlation ; Bespiiation. 1 volume, 8yo. Cloth. Price, $4.50. " Professor Flint is engaged in the preparation of an extended work on human physiologj, in which he professes to consider all the subjects usually regarded as belonging to that department of phys- ical science. The work will be divided into separate and distinct parts, but the several volumes in which it is to be published will form a connected series." — Providence Journal, It is free from technicalities and purely professionil terms, and instead of only being adapted to the use of the medical faculty, will be found of interest to the general reader who desires clear and concise information on the subject of man physical" — Evening Post. " Digestion is too little understood, indigestion too extensively suffered, to render this a work of supererogation. Stomachs will have their revenge, sooner or later, if Nature's laws are infringed upon through ignorance or stubbornness, and it is well that all should un- derstand how the penalty for * high ^living ' is assessed." — Chicago Evening Journal, "A year has elapsed since Dr. Flint published the first part of his great work upon human physiology. It was an admirable treatise — distinct in itself— exhausting the special subjects upon which it treated." — Philadelphia Inquirer.


D. APPLETON & a0:8 PUBLICATIONS. Manual of Ancient and Modern History. By W. Taylor, LL. D., M. R. A. S. Revised by C. S. Henry. D. D 1 voL, 8vo, 870 pages. ANCIENT HISTOET, Sbpaeatblt, 868 pages. Containing the Political History, Geographical Position, and SocUl State of the principal Nations of Antiquity, carefully digested from the ancient Wiiters, and illustrated by the discoveries of modem scholars and travellers. MODE&N HISTOET, Bepaeatblt, 812 pages. Containing the Rise and Progress of the principal European Nations, their Political History, and the changes in their Social Condition ; with a History of the Colonies founded by Europeans. Inquiry is often made by those who have not the time or opportunity for an extended course of historical reading, for a work that embraces within reasonable compass the leading events of Ancient and Modem History, and will ^ve them a correct idea of its leading features stripped of unimport- ant details. Such a work will be found in this compilation of Dr. Taylor. With the view of bringing a general knowledge of the past within the reach of all classes of readers, he has selected the great facts connected with the rise and progress of nations, their customs, religion, and political institutions, and carefully digested them in a clear and comprehensive summary. For the purposes for which it is designed, it is believed that this work has no equal. It is this conviction on the part of those who have examined it, that has led to its extensive introduction as a text-book into the academies and collegies of our land. Some of its distinguishing features are mentioned below. In preisenting facts, the author has not overlooked the philosophy of history, but has traced events to their causes, and directed attention to the progress of civilization and its effects on society. Thus exhibited in their connection, as parts of the great plan of Providence in the government of the world, events are understood as well as remembered, and the reader receives a no less valuable lesson in philosophy than In history. A knowledge of its climate, natural features, towns and cities, is otten essential to the proper understanding of a country's history. To meet this want, a brief geographical outline is in every case prefixed. The accentu- ation of proper names, as they occur, is another feature of great practical value. Dryness is generally characteristic of condensed historical outlines ; in the present case it is avoided by the vigorous style of the author, and the introduction of interesting anecdotes and episodes that serve to relieve the mind, and bring out in clear light the peculiarities of individual or national character. The American edition has been revised throughout by Dr. Henry, and enlarged by the introduction of an admirable chapter on American Historv.


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2>. APPLETON <fc CO:S PUBLICATIONS, History of English Literature. By WILLIAM SPALDING, A.M., Professor of Logic, Rhetoric, and Metaphysics, in the University of St. Andrews. 12mo, 418 pages. The above work is offered as a Text-book for the use of advanced Schools and Academies. It traces the literary progress of the nation from Anglo* Saxon times to the present day, and furnishes a comprehensive outline of the origin and growth of our language. Those literary monuments of early date which are thought most worthy of attention, are described with con- siderable fuhiess and in an attractive manner. Constant effort is mado to arouse reflection, both by occasional remarks on the relations between in- tellectual culture and the world of reality and action, and by hints as to the laws on which criticism is founded. The characteristics of the most cele- brated modem works are analyzed at length. The style of the author is remarkably dear and interesting, compelling: the reader to linger over his pages with unwearied attention. Manual of Grecian and Roman Antiquities. By Dr. E. F. BOJESEN, with Notes and Questions by Rev. THOMAS K. ARNOLD. l2mo, 209 pages. The present Manuals of Greek and Roman Antiquities are far superior to any thing on the same topics as yet offered to the American public A leading Review of Germany says of the Roman Manual : — " Small as the compass of it is, we may confidently affirm that it is a great improvement on all preceding works of the kind. We no longer meet with the wretched old method, in which subjects essentially distinct are herded together, and connected subjects disconnected, but have a simple, systematic arrangemeni| by which the reader readily receives a clear representation of Roman life. We no longer stumble against countless errors in detail, which, though long ago assailed and extirpated by Niebuhr and others, have found their last place of refuge in our manuals. The recent investigations of philologists and jurists have been extensively, but carefully and circumspectiy used."


J D, APPLETON <fc C0:8 PUBLICATIONS. Elements of Logic. With an Introductory view of Philosophy in general, and a Preliminai^ View of the Iteason. By Henrt W. Tappan. 12mo, 467 pages. Not considering Logic as an abstraction, Prof. Tappan assigns it its proper place among kindred sdences, and takes the student over the whole field of Philosophy, that the connection of its Tarious parts may be distinctly perceived. He presents the subject, not merely as a method of obtainiug Inferences from truths, but also as a method of establishing those first truths and general principles that must precede all deduction. The great starting- points of theory, the sources to which we must look for premises in every department of science, are viewed in connection with Logic ; the rela^ns between . the two are examined ; and the proper understanding of both is thus greatly facilitated. This is new ground ; yet it is what the profound thinker and all who would master the subject have long needed. In carrying out this plan, the author begins with Philosophy in general ; shows the distinction between the Phenomenal and the Metaphenomenal, the ObjecUve and the Subjective, the Sensual and the Transcendental ; defines Ideas and the laws of their developuient ; and then proceeds to treat of the divisions of General Philosophy, Metaphysics, and Nomology — ^in the latter of which, with Ethics, Esthetics, and Somatology, Logic is included. The interesting questions inddentally opened up, such as the Criteria of a True Philosophy, receive attention, and then, after a brief preliminary view of the Reason and its functions, we are introduced to Lo^c Proper. The evolution of Ideas, in all their variety, is first set set forth at length ; and numerous important points, now for the first time found in a system of Logic, such as the relation between matter and spirit, right and wrong, free- dom and responsibility, are discussed in a manner which proves the author a practical adept in the science he would teach. Inductive and Deductive Lo^c follow ; the latter of which embraces all the rules, principles, and formulae to be found in the text-books of former dialecticians, and to which, for the most part, they confine themselves. The work closes with t^ masterly dissertation on the nature of proofj its different kinds, degrees of evidence, drcumstantial evidence, reasoning from experience and analogy, and the calculation of chances. Important as these Bubjecta are, and intimately as they are connected with the work of the dialectician, they have heretofore had no place in treatises on Logic ; Mr. Tappen is the first to unfold ihdr comiection with this science, and the clearness and comprehensiveness with which he has treated them leave nothing to be desired.


/>. AP.PLETON ik CO:a PUBLICATIONS. Elements of Moral Philosophy : Analytical) Synthetical, and Practical. By Hubbard Winslow. 12uiOk 480 pages. This work is an original and thorough examination of the fundamental laws of Moral Science, and of their relations to Christianity and to practical life. It has already taken a firm stand among our highest works of literature and science. From the numerous commendations of it by our most learned and competent men, we have room for only the following brief extracts : From Rev. Thoiias H. Sxinneb, D.D., qfihe Union TTuol. Soe^ 2/1 T, . "It is a work of uncommon merit, on a Bubject very difficult to bo treated well. His analysis is complete. He bos shanned no onostlon which his purpose required him to answer, and he has met no adversary which ne has not overcome.^* lYom Ebv. L. p. Hiokok, Viee-PrMident of Union College, " I deem the book well adapted to the ends proposed in the pre&ce. The style is clear, the thoughts perepicuous. I think it calculated to do good, to promote the tmtb, to diffuse light, and impart Instruction to the community, in a department of study of the deepest interest to mankind.** From Rkv. James "Walkee, D.D., President qf Harvard University, " naving careftilly examined the more critical parts, to which my attention has been especially directed, I am free to express my conviction of the great clearness, discrimi- nation, and accuracy of the work, and of its admirable adaptation to its object.** From Rev. Rat Pauieb, D.D., of Albany. ^ I have examined this work with great pleasure, and do not hesitato to say that in my Judgment it is greatly* superior to any treatise I have seen, in all the essential rciiulsites of a good text-book.'^ From Peop. Rosseait D. HrrcnoocK, D.D., of the Union Theol. JSoc^ 2f. T. "The task of mediating between science and the popular mind, is one that requires A peculiar gift of perspicuity, both in thought and style ; and this, I think, the author possesses in an eminent degree. I am pleased with its comprehensiveness, its plainness, auA its fidelity to the Christian stand-point.** , From Peof. Henet B. SMirn, D.D., of the Union Theol, 8oe,^ N, T. " It commends itself by its clear arrangement of the topics, its perspicuity of lan- guage, and its constant practical bearings. I am particularly pleasea with its views of conscience. Its frequent and pertinent illustrations, and the Scriptural character of its explanations of the particular duties, will make the work both attractive and v<Uuab}«  as a teict-book, in imparting instruction upon this vital part of philosophy.** From "W. D. "Wilson, D.D., Professor cf Intellectual and Moral Philosophy in Hobart Free College, "I have examined the work with care, and have adopted it as a text-book in lie study of Moral Science. I consider it not only sound in doctrine, but clear and system- atic in method, and withal pervaded with a prevailing healthy tone of scnthoent, which cannot fail to leave behind, in addition to the truths it inculcates, an imprc/^iou in favor of those truths. I esteem this one of the greatest merits of the book. In this respect it has no equal, so fUr as I know ; and I do not hesitate to speak of it as being fureferable to any other work yet published, for use in all institutions where ^?t^ Philosophy forms a department in the course of instruction.**


D. APPLETON & CO:S PUBLICATIONS. A. History of Philosophy An Epitome. By Dr. Albert ScnwEaLEn. Translated from the t rigi nal German, by Julius H. Seelye. 12mo, 365 pages. This translation is designed to supply a want long felt by both teachers and students in our American colleges. We have valuable histories cf Philosophy in English, but no manual on this subject so clear, concise, and comprehensive as the one now presented. Schwegler's work bears the marks of great learning, and is evidently written by one who has not only studied the original sources for such a history, but has thought out for him- self the systems of which he treats. He has thus seized upon the real germ of each system, and traced its process of development with great deamesa and accuracy. The whole history of speculation, from Thales to the present time, is presented in its consecutive order. This rich and important field of study, hitherto so greatly neglected, will, it is hoped, receive a new im- pulse among American students through Hr. Seelye^s translation. It ia a Dook, moreover, invaluable for reference, and should be in the possession of every public and private library. From L. P. Hiokok, VZce-Preaident of Union ColUge, " I havo liod opportunity to hear a largo part of Mr. Seolyo's translation ol Schweg- ler* s History of Philosophy read firom mannscript, and I do not hesitate to say that it Is a fkithfol, clear, and remarkably precise English rendering of this inyaloable Epitome of the History of Philosophy. It is exceedingly desirable that It should be given to American students of philosophy in the English language, and I have no ezpectatiou of its more favorable and successful accomplishment than in this present attempt I should immediately introduce it as a text-book In the graduato^s dejmrtment under my own instruction, if it be favorably published, and cannot doubt that other teachers \i\\\ rejoice to avail themselves of the like assistance ftom it^ Ff-om Heotiy B. SMrrn, Prqfeasor qf Christian Theology^ Union Theological Seminary^ N. Y, "It will well reward diligent study, and is one of the best works for a text book in oar colleges upon this neglected branch of scientific Investigation." From N. Pobteb, PrqfsMor of Intsllectual Philosophy in Yale College. " It is the only book translated ftom the German which professes to give an account of the recent German systems which seems adapted to give any intelllglblo informa- tion on the subject to a novice. From Geo. P. Fisiier, Prqfessor ofDivirUty in Tale College. " It Is really the best Epitome of the History of Philosophy now accessible to the English studenf From JosEPn Haven, Prqfessor of Mental Philosophy in Amherst College. "As a manual and brief sununary of the whole range of speculative inquiry, I KJiod nf no worfe which stipes me more favorably."


D, APPLETON <fc C0:8 PUBLICATIONS, Lectures on the True, the Beautifiil, and the Good. By M. VICTOR COUSIN. Translated by 0. W. WIGHT. 1 voL, 8vo, 391 pages. Cousin is confessedly the soundest of modem philosophers. The foundei and head of the Eclectic School, his teachings by the intrinsic force of trotli have, with all earnest thinkers, superseded the insuffident systems that pre- ceded it The theory on which they are based may justly be called a high- toned spiritualism, whose tendency is to subordinate the sensual and to ennoble mankind. It teaches the spirituality of the soul, the freedom and responsibility of human action, the dignity of justice, and the beauty of (Parity. It sustains religious sentiment, seconds art, supports the right, and purifies society. Such is the general character of Cousin^s philosophy. In these Lectures, the latest production of his great mind, it is presented in a condensed, striking, and attractive form. After taking a brief view of the philosophy of the nineteenth century, and the relation which his theory sustains to other systems, the author enters at once upon his subject. Under the head of " the True," he considers the existence, origin, and value of Universal and Necessary Principles ; God, the principle of principles ; and mysticism of sentiment and philosophy. Under " the Beautiful," he treats of Beauty in nature and art, and adds a valuable chapter on French art in the seventeenth oentui^. Under the head of **the Good," he surveys the whole field of Ethics, reviews the theory of Expediency and other defective systems, and finally brings us to Deity as the grand embodiment of all that is good in the universe. No one can master the system of Ethics here set forth by Cousin, without feeling that it has made him wiser, nobler, and better. History of Modern Philosophy. By M. VICTOR COUSIN. Translated by 0. W. WIGHT. 2 7olfl^- 8vo, 801 pages. Philosophy of Sir William Hamilton. Edited by a W. WIGHT. Svo, 580 pages.


D. APPLETON & C0:8 PUBLICATIONS, Course of Ancient Geography : Arranged with Special Reference to Convenience of Recitation. B^ Prof: H. L SCHMIDT, D.D., of Columbia CoUege. 12mo, 828 pages. The object of this work is to faeilitate study. With nothing new to teach in the department of Ancient Geography, there is much necessity of breaking up the great masses of knowledge accumulated on the subject by classical scholars, and rendering the subject itself, its general features, and principal parts, more easily accessible to the student. Nothing is introduced into the book but what the student in reading is coAStantly required to know. The best authorities have been consulted, carefully compared, and freely used throughout No pains have been spared to render the work as correct as our knowledge of the ancient world wiU permit. The volume opens with a short account of the Geography known to Ihe ancients ,at different periods, and of the gradual extension of their knowledge. Then the author begins with the Ancient Geography of Europe — Greece is de- scribed in ample detail, and Italy in the same manner. Then follows all that is known of Asia Minor. This constitutes what may be termed Classi- cal Geography — ^that portion of Ancient Geography which the student most constantly needs in the study of classical authors. To present this properly is the main design of the work. After this the author returns to Europe — again to Asia — and lastly, treats the Ancient Geography of Africa. This order seemed the most natural in a work of the kind, as it is based upon the relative importance, in classical authors, of those countries ; the author also took upon this point the advice if a number of distmguished instructors. All the matter presented is broken up into short paragraphs, and these arc numbered ; and questions which refer to the facts given in these para' graphs, and marked respectively with the corresponding numbers, are gives in the lower margin. This at once assists the pupil and the teacher. In this work every material division of the ancient world is noted, and the name of every pea, lake, river, or town is ^ven; in many instances, the derivation and etymology of the names are added. The book is sufficiently full for every practical purpose, not only of the school-room, but for refer- ence in general reading of ancient authors. It has a copious Index that much enhances its value in this respect. From th€ Recorder. "This very satisfactory work makes a valnable addition to the library of (he eiasslcal student, and also to the series of text-books to be nsod during the courso of Maderoioal and collegiate study."


D, APPLETON & CO:S PUBLICATIONS, Historical and Miscellaneous Questions. From tho Eighty-Fourth London Edition. With large additions : Em bracing the Elements of Mythology, Astronomy, Architecture Heraldry, etc., adapted for Schools in the United States, by Mr Julia Lawrehce. Embellished with Nunerous Engra\ings oi Wood. Fourth American Edition, Revised and Corrected, with x Chapter on the American Constitution by RICHMAL MANGNALL 12mo, S96 pages. Mangnairs Questions has attained an enviable repntation on both sides of the Atian (10 as a condensed abstract of history, art, science, and general information. It is ii the tofrm of question and answer, and is adapted to tho higher classes in common schoolr and academies. The variety of subjects embraced, tho difficulty of obtahilng suitable text-t>ooks relating to many of them, much more of finding any single work that con- tains them all, and the Judgment displayed by the author in selecting what is important and presenting great fiicts and leading principles in a striking manner that impressei them on tho mind, have gained for this work an extensive and well-deserved circula Uon. A careful revision and the intro<lnction of much that is important to thr American student, enhance the value of the pre8e;it edition. An idea may be formed of the extensive and important ground it covers ftom the following table of CONTENTS. A short View of Scripture History, from the Creation to the Return of the Jews. Questions from the Early Ages to tho time of Julius Ceesar. Miscellaneous Questions in Grecian History. Miscellaneous Questions in General History— chiefly Ancient. Questions containing a Sketch of tho most remarkable Events fh)m the Chris- tian Era to the close of the Eighteenth Century. Miscellaneous Questions in Boman His- tory. Questions in English History, trova. the Invasion of Caesar to the Reformation. Continuation of Questions in English Hist'vy, from the Reformation to the Present Time. Abstract of Early British History. Abstract of English Reigns from tho Conquest Abstract of the Scottish Reigns. Abstract of the French Reigns, from Pharamond to Philip I. Continuation of the French Reigns, fh>m Louis VL to Louis Philippe. Questions relating to the History of America, from its Discovery to the Pres- ent Time. Abstract of Roman Kings and most dis- tinguished Heroes. Abstract of the most celebrated Grecians. Of Heathen Mythology in General Abstract of the Heathen Mythology. The Elements of Astronomy. Explanation of a few Astronomlctl Terms. List of Constellationik Questions on Common Subjects. Questions on Architecture. Questions on Heraldry. Explanation of such Latin Words and Phrases as are seldom Englished. Questions on the H 'story of the MiddU Affcs.





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[jlJillK Standard. X^dixcatioxxal "Worlds ^ Rpemer's Polyjsrlot Reader* 6 \oU. l2mo. Consisting of a Series of English Extracts, translated into Freucli, German, Spanish, and Italian respectively. The several volumes designed as mutual Keys to each. Sbakesperlan Reader, By Johk W. S. Hows. 12mo. Sdunidt,— Course of Ancient Geography* Arranged with special reference to convenience of recitation. By Proil H. I. Schmidt; D.D., of Columbia College. 12mo. 8^ pages. Spaldins's History . of Enffiisli liiteratur^. Scliiresier9s History of Pliilosopliy* An Epitome. By Dr. Albisi^ ScHWBOLEtt. Translated fi'om the original Ger- man, by Jitlius H. Sbbltb. 12mo. 805 pages. SeirelVs First History of Greece. 18mo. 858 pagea Cliiid's First History of Rome» 18mo. Tenney's Analysis of Derivations and Definitions of English Words. (Just publUhed.) Tappan's Elements of Logic. By Henkt W. Tappan. Chancellor <tf Mich. University. 12mo. 467 pages. Taylor's Manual of Ancient and Modern History. Svo. 870 pages. fTebster^s Elementary Spellins-Book* **The National Standard.^ More than one million copies are sold annually. irorthen's Fir^t Lessons in Meclianics. With prao- ticftl appUeationa designed for the use of Schools. 12mo. TTilson. Am ISlementary Treatise on Locic By W. D. Wiuo^r, D.D.„Hobart f^roe CoU«g«. 12mo. 425 paget. ITinsloir^ Elemeiits df Moral Pkllosopky ; Aaa^ thetical, Synthetical, an^.PracticaL 12mo. 480 pafree. Tonmans' GKomical ITorks. Consisting gf: Nbw Class-Book OF CHBMI8TBT. (Ju^t published.^ ' Oksvioal Chart, on rollers. CiniaoAL Atlab. Large 4to. 105 pagM The Havd-Book or Hou-skhold Scibnoe. A popular ac- count of Heat, Light, Air, Alliment, and Cleansing, In their Scientific principles and Domestic applications. 12mo. Illustrated. 4T0 pages. D. APPLETON & CO., N. Y., WllsL BBKO .A. I>esoriptive Catalofi^^ie of English, Latin, Greek, French, Spsnish, ItalUn, Hebrev, and Syrlai text-books, to those applying ft)rlt



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