THE LIBRARY 
 
 OF 
 
 THE UNIVERSITY 
 OF CALIFORNIA 
 
 PRESENTED BY 
 
 PROF. CHARLES A. KOFOID AND 
 MRS. PRUDENCE W. KOFOID 
 
OQ a 
 
 I ' 
 
 s "S 
 
 
IN 
 
 ADVANCED PHYSIOLOGY, 
 
 BY LOUIS J. RETTGER, A. M., 
 
 Professor of Biology in The Indiana State Normal School. 
 
 TERRE HAUTE, IND. 
 THE INLAND PUBLISHING COMPANY 
 
 1898 
 
Copyrighted, 1898, 
 BY Louis J. RETTGER. 
 
 -BECKTOLD 
 
 PRINTING AND BOOK MFG.CO. 
 ST. LOUIS, MO. 
 
PREFACE. 
 
 There are two extremes open in writing a brief treatise 
 on any natural science. One is to state briefly and explic- 
 itly those facts which are seriously questioned by no one. 
 It is to enumerate and tabulate what is definitely known 
 about the subject. In the field of animal physiology there 
 is much which is "settled" information, and which it is be- 
 lieved, will not be materially changed by the developments 
 of the future. Most of the gross anatomy is finished, by no 
 means all, but many points in histology are determined, 
 while in pure physiology there are fewer things that are con- 
 sidered explained. Thus the phenomena of respiration and 
 the dynamics of the blood flow are to a very large extent 
 known in terms of chemical and physical laws. To limit a 
 book to this would be to make it stereotyped, dead, and leave 
 the reader with the impression that physiology like Sanskrit 
 was finished, and like every finished problem had no longer 
 a living interest of its own. Most of the ordinary text- 
 books err on this side. They state ex cathedra, fact after 
 fact, they seldom give the reasons which have led physi- 
 ologists to adopt the views in question, and they seldom 
 leave the idea that many things are still being studied with 
 the hope that more study will give new light. Most text- 
 books leave the mind of the student with the belief that all 
 has been told, that there is nothing more to add, and that 
 therefore there is no need for him to try to improve on the 
 text-book, by making his own observation. The feeling of 
 the authority of the text-book in physiology has robbed 
 many a student of the desire to investigate the subject 
 further. L,ike the Scholastics of the Middle Ages they turn 
 to the book as to Aristotle, fully convinced that all know- 
 ledge is contained in it, and that what is not contained is 
 impossible of access. 
 
 The other extreme is to give in detail all the scientific 
 controversies of the past and present. It is to state indis- 
 criminately pros and cons until the conviction settles over 
 one that nothing is definite and all is confusion. Especially 
 true is this when these conflicting views are at once pre- 
 sented to the beginner in the subject. 
 
 (iii) 
 
IV STUDIES IN ADVANCED PHYSIOLOGY. 
 
 There are in physiology, as, possibly, in all other 
 sciences, many problems at present which admit of different 
 interpretations, and which must be referred to the investi- 
 gations of the future for their correctness or their faultiness. 
 It would not be treating the reader right to shower him 
 with all sides of these questions, but the author has endeav- 
 ored to present that view in each case which seems most 
 generally accepted by scientific men, and awaiting future 
 verifications to show the value of the claim. By taking 
 this median course it is believed that the book will give to 
 its readers all of the main known facts, and in addition 
 acquaint them with many of those questions which are now 
 demanding the attention of physiologists. This will put 
 the science of physiology in its true light, it will show that 
 it is a living science, still at work trying to interpret living 
 problems. While it will show the present limitations of 
 our knowledge it will suggest future possibilities. 
 
 It is hoped that the study of this book may result in a 
 more lively appreciation of physiological phenomena, and 
 an added interest in teaching the subject in our common 
 schools. 
 
 It has been the aim to choose the illustrations for this 
 book with the greatest possible care. They have been 
 selected from quite a number of sources, and the proper 
 credit has in each case been given with every figure. Quite 
 a number of the histological illustrations are from Schafer's 
 Essentials of Histology. The author desires hereby to 
 thank Messrs. L,ongmans, Green & Company, the publish- 
 ers of that prince of text-books, Quain's Anatomy, for their 
 permission to reproduce several of the illustrations found 
 therein. The colored plates on the circulation of the blood 
 have been made possible by their courtesy. The author is 
 also under many obligations to D. Appleton & Company, 
 publishers of Osier's Practice of Medicine, for permission 
 to reproduce the colored plates illustrative of the nervous 
 
 Louis J. RETTGER. 
 Terre Haute, Indiana, 
 Aug. 12, 1898. 
 
SABLE OF (CONTENTS. 
 
 PAGE. 
 
 Introduction 1 
 
 CHAPTER I. 
 An Epitome of the History of Physiology. 
 
 Hippocrates. Aristotle. Praxagoras. Herophilus and the Alex- 
 andrian School. " Galen. Vesalius. Servetus. Fabricius. 
 Harvey. Later investigators 5 
 
 CHAPTER II. 
 The Cell and its Life. 
 
 Historical view. A typical cell. The division of the cell. Physi- 
 cal basis of heredity 22 
 
 CHAPTER III. 
 The Teaching of Physiology and the Public Health. 
 
 History of Sanitation. Bacteriology. Bacteria. How germs 
 produce disease. Theories of immunity. Unsolved prob- 
 lems. Practical guidance. Rules of Indiana Board of> 
 Health 29 
 
 CHAPTER IV. 
 General Definitions. 
 
 Anatomy. Comparative Anatomy. Histology. Embryology. 
 
 Classification 46 
 
 CHAPTER V. 
 The Blood. 
 
 General points. Amount. Composition. Red corpuscles, (size, 
 form, color, surface, composition, consistency, origin, de- 
 struction). Haemoglobin. Spectrum of haemoglobin. Blood 
 crystals. White corpuscles. Blood plates. Blood plasma. 
 
 Coagulation. Serum. Phenomena of osmosis 49 
 
 (v) 
 
VI STUDIES IN ADVANCED PHYSIOLOGY. 
 
 CHAPTER VI. 
 The Supporting Tissues. PAGE. 
 
 The Skeleton. Minute structure of bone. Origin and growth of 
 bone. Process of ossification. Chemical composition of 
 bone. Cartilages. Connective tissues proper. Humors. 
 Formation of cartilage and connective tissues. Hygiene of 
 supporting tissues. Joints. Ligaments 75 
 
 CHAPTER VII. 
 Muscles and the Phenomena of Contraction. 
 
 Kinds of Muscles. Voluntary muscles. Minute structure. Growth 
 of muscle. Finer structure of the muscle fibre. Plain mus- 
 cular tissue. Cardiac muscle. Chemistry of muscle. Elas- 
 ticity. Muscle stimuli. A single contraction. Tetanus. 
 Wave of contraction. Lifting power of muscles. Changes 
 in volume. Muscle fatigue-. Blood supply of muscles. 
 Electrical phenomena in muscles. Wave of negative varia- 
 tion. Rigor mortis. Source of muscular energy. Mechan- 
 ics of muscles. Levers. Mathematics of levers. Hygiene 
 of muscles 112 
 
 CHAPTER VIII. 
 The Circulation. 
 
 General arrangement. Route of one complete circulation. The 
 heart (position, coverings, cavities, vessels arising from, 
 valves of heart). The arterial system. The venous system. 
 The pulmonary circulation. The portal circulation. His- 
 tology of arteries, veins and capillaries. Phenomena of the 
 heart's beat (rate, systole, diastole, filling of heart, sounds 
 of heart). Cardiograms. Pathological sounds of the heart. 
 Amount of blood forced out per beat. Energy and work 
 of the heart. Innervation of the heart. The dynamics of 
 the blood stream. Arterial pressure. Venous pressure. 
 Pressure in capillaries. Rate of blood flow. Time of one 
 complete circulation. Pulse (cause, kinds of, rate, meas- 
 urements of). Innervation of blood-vessels. Changes in 
 the circulation at birth 146 
 
 CHAPTER IX. 
 The Lungs and the Processes of Respiration. 
 
 Anatomy of respiratory system. Pathological conditions of sys- 
 tem. Mechanics of respiration. Ventilation. Chemistry of 
 respiration. Phenomena of external respiration. Dalton's 
 law of gases. The role of the red corpuscles. Phenomena 
 of internal respiration. Elimination of carbon dioxide. The 
 innervation of the respiratory system 202 
 
TABLE OF CONTENTS, Vll 
 
 CHAPTER X. PAGE. 
 
 The Larynx and the Production of Articulate Speech. 
 
 Anatomy of larynx. Manipulation of larynx in the production of 
 
 sounds. Range of human voice. Vowels. Consonants 239 
 
 CHAPTER XL 
 Glands and the General Physiology of Secretion. 
 
 Historical. Secretion. Anatomy of glands. Process of secre- 
 tion. Histological changes in secreting cells. Innervation 
 of glands .. 249 
 
 CHAPTER XTI. 
 The Digestive Organs and their Anatomy. 
 
 Mouth. Teeth. Structure of a typical tooth. Hygiene of the 
 teeth. Development and origin of the teeth. Tongue. 
 Papillae. Taste-bulbs. Gullet. Stomach. Gastric glands. 
 Small intestine. Villi. Large intestine. Mucous glands. 
 Pancreas. Liver. Thyroid gland. Spleen. Adrenal bodies. 
 Thymus gland. Carotid gland. Coccygeal gland. Pituitary 
 body 264 
 
 CHAPTER XIII. 
 Foods and their Physiological Value. 
 
 Losses of the body. Classes of foods. A mixed diet. Relative 
 amounts in an average daily diet. Flavors, condiments, 
 stimulants. Alcohol. Physiological effects of alcohol 308 
 
 CHAPTER XIV. 
 Digestion and the Digestive Agents. 
 
 Historical. Saliva and salivary digestion. Theory of hydrolysis. 
 Stomach and gastric digestion. Pepsin. Pancreatic juice. 
 Trypsin. Amylopsin. Steapsin. Bile. Bile salts. Bile 
 pigments. General function of bile. Intestinal juice. ... 327 
 
 CHAPTER XV. 
 Absorption and the Routes of Food. 
 
 Absorption of peptones. Absorption of the sugars. Absorption 
 of the fats. General physiology of the liver. Glycogen. 
 Hepatic action on albumens. Formation of urea 352 
 
Vlll STUDIES IN ADVANCED PHYSIOLOGY. 
 
 CHAPTER XVI. PAGE. 
 
 Nutrition and the Metabolic Changes in the Tissues. 
 
 General questions. Uses of the classes of foods. Use of proteids. 
 Disintegration of living 1 tissue. Formation of urea. For- 
 mation of C0 2 . Reconstruction of living tissue. Use of fats 
 and sugars. Nutritive equilibrium. Kreatin. Kreatinin. 
 Inter-relation of fats and carbohydrates 365 
 
 CHAPTER XVII. 
 The Maintenance of the Animal Heat. 
 
 Normal temperature of body. Warm-blooded, cold-blooded ani- 
 mals. Variations in temperature. Conditions affecting the 
 temperature. The regulation of the temperature. Thermo- 
 genic nerves. Quantitative determinations of the source 
 and expenditure of heat. The amount of heat lost by the 
 body 376 
 
 CHAPTER XVIII. 
 
 The Kidneys, the Skin and the General Physiology of 
 Excretion. 
 
 Kidneys. Anatomy of urinary organs. Circulation through kid- 
 neys. Uriniferous tubules. Urine. Composition of urine. 
 Source of the urea. Skin. Epidermis. Dermis. Nails. 
 Hairs. Sebaceous glands. Sweat glands. Nerves of sweat 
 glands. Composition of sweat 385 
 
 CHAPTER XIX. 
 The Anatomy and Physiology of the Nervous System. 
 
 Nerve systems. Nervous elements. Nerves. Nerve Trunks. 
 Plexuses. Nerve centers. Ganglia. Dura mater. Pia mater. 
 Arachnoid membrane. Spinal cord. Spinal nerves. Brain. 
 Weight of brain. Convolutions. Interior of brain. Ven- 
 tricles. Cranial nerves. Sympathetic system. Histology 
 of nervous system. Neurons. Minute structure of nerves 
 and nerve trunks. Gray fibres. Development of nerves. 
 Regeneration of nerves. Neuroglia. Nerve stimuli. Nature 
 of a nervous impulse. Kinds of nerve fibres. Finer archi- 
 tecture of central nervous system. Arrangement of motor 
 neurons. Arrangement of sensory neurons. Medulla. 
 Function of cerebellum. Function of midbrain. Function 
 of cerebrum. Localization of centers in the brain. Physi- 
 ological topography of the brain. Consciousness. Sleep. 
 Hypnotic phenomena. Time relations in psychic phe- 
 nomena. Personal equation 409 
 
TABLE OF CONTENTS. ix 
 
 CHAPTER XX. 
 The Organs of Special Sense. PAGE. 
 
 Common sensations. Special sensations. Structure of an organ 
 of special sense. Neurosis. Psychosis. Development of 
 the special senses. The objectification of our sensations. 
 The relation between neurosis and psychosis. The psycho- 
 physical law. Confusion of sensations and inferences from 
 sensations 469 
 
 CHAPTER XXL. 
 Touch, Temperature, Muscular Sense, Taste, Smell. 
 
 The anatomy of the end organs of touch. Pacinian corpuscles. 
 Tactile cells. End bulbs. Touch corpuscles. The absolute 
 touch sensitiveness. The power of localization and the touch 
 areas. The sense of temperature. The muscular sense. 
 The sense of taste. Taste bulbs. The nature of a taste 
 sensation 477 
 
 CHAPTER XXII. 
 The Ear. 
 
 The nature of sound. The production of sound. The range of 
 the number of vibrations in the production of sound. The 
 transmission of sound in the air and its velocity in the same. 
 Reflection and refraction of sound. The physical proper- 
 ties of sound. Harmony. Sympathetic vibrations. The 
 external ear. The middle ear. The membranous ear. 
 Histology of the membranous labyrinth. The minute struc- 
 ture of the membranous cochlea. The functions of the in- 
 dividual parts of the membranous ear. The localization of 
 sound 494 
 
 CHAPTER XXIII. 
 The Eye and the Physiology of Vision. 
 
 Historical. The nature of light. The rate of transmission. The 
 number of vibrations in waves of light. The spectrum. 
 Complementary colors. The colors of objects by transmitted 
 or reflected light. The refraction of light and the property 
 of lenses. The formation of images by lenses. The anat- 
 omy of the eye (eyebrows, eyelids, lachrymal apparatus, 
 muscles of the eyeball, the globe of the eye, sclerotic coat, 
 choroid coat, ciliary muscles and the muscles of accomoda- 
 
X STUDIES IN ADVANCED PHYSIOLOGY. 
 
 tion, optic nerves, microscopic structure of the retina). The 
 eye as a purely physical instrument. The normal or emme- 
 tropic eye (myopia, hypermetropia, astigmatism, cataract, 
 spherical aberration, chromatic aberration, muscae-voUtan- 
 tes, presbyopia) . The manipulation of the eye as an opti- 
 cal instrument. How do we focus the eye? The dioptrics 
 of the eye. The luminosity of eyes. The physiology of 
 color sensation. Color blindness. The Young-Helmholtz 
 theory. Normal or trichromatic eyes. The Hering theory. 
 After-images. Explanation of negative after-images. 
 Double vision. The advantages of two eyes. Optical illu- 
 sions . . 529 
 
INTRODUCTION. 
 
 What are the reasons that entitle the subject of physiol- 
 ogy to a place in the common school curriculum? There 
 are now so many subjects, on the educational value of 
 which most educators are agreed, that unless physiology 
 can do for the student what these do, it ought to give way 
 to better fields of study. 
 
 In many cases no doubt it is taught simply because it is 
 prescribed by law, and its injunctions are not questioned. 
 In other cases its study is considered desirable, or even 
 necessary, because physiology concerns itself so largely 
 with hygienic considerations, and so is believed to exert a 
 helpful influence on the general health. Possibly this is 
 the main purpose our legislators had in mind when, by 
 statute, physiology was made one of the common school 
 branches. No one will deny the value, in fact the neces- 
 sity, of having clear conceptions of hygienic rules and 
 thoroughly understanding the laws of sanitation. It is the 
 author's firm belief that if the knowledge of the nature of 
 contagious and infectious diseases and of the means of 
 their spreading, was more generally possessed, perfected 
 sanitation would be declared a necessity, and the public 
 health would be greatly improved. Such a result would 
 repay a thousand times the cost of teaching such practical 
 information. It is however a question whether it usually 
 pays to have the study of physiology degenerate into formal 
 rules of health, and recipes for disease. Such formal, 
 theoretical knowledge seldom becomes of practical benefit. 
 Most of us eat what our pocketbooks can afford and what 
 experience shows agrees with us. We regulate our exer- 
 cise by the amount of time available, and our inclination to 
 take it. The desirability of bathing arises from something 
 deeper than a mere intellectual perception of its value. 
 
 (i) 
 
2 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 The tramp probably possesses, in some instances, a theoret- 
 ical knowledge of the efficacy of soap and water, but it 
 does not therefore become a practical belief. 
 
 In teaching small children it is of course desirable to 
 make almost all the work of this hygienic character. 
 Physiology is a science that pre-supposes some knowledge 
 of physics and chemistry, and that cannot be assumed in 
 really elementary classes. In addition small children have 
 a morbid curiosity aroused when dealing with anatomical 
 structures that is frequently productive of more evil than 
 good. But with advanced classes physiology can be studied 
 to the greatest advantage, provided that we do so in a 
 scientific way. While in a strict sense physiology does not 
 at all include anatomy, either gross or minute, yet as gen- 
 erally conceived it is made to include this, and in such a 
 sense it is used by the author. While pure physiology is 
 a science of experiments, like physics and chemistry, and 
 not a science of observation like botany and zoology, and 
 as from the difficulty of the experiments, not many of them 
 can be repeated by the student himself, yet there are 
 numerous simpler experiments of deepest physiological 
 import which the student can perform for himself. Some 
 experiments in artificial digestion with prepared extracts, 
 the nature of the flow of liquids in iron and rubber tubes to 
 illustrate circulation, the phenomena of blood coagulation, 
 and finally the many experiments to be made in the study 
 of the special senses, all these will afford abundant oppor- 
 tunities to perform experiments of the highest educational 
 value. But it is when we include anatomy that the oppor- 
 tunities are greatest. It is never necessary in elementary 
 instruction to call to aid vivisections, or even ordinary 
 dissections of a nature often calculated to be repulsive. 
 Let all these be proscribed. But the meat market itself 
 will afford a multiplicity of material which will serve 
 to illustrate all the more important fields of anatomy. 
 Now it is believed that while a large part of the matter of 
 physiology must be informational, and although this is often 
 
INTRODUCTION. 3 
 
 of the greatest value, the best thing this subject can do for 
 the student is to allow him to make his own observations as 
 far as possible, and to make his own interpretations of 
 experiments from related facts out of his own experience. 
 There is not so much educational value in knowing that the 
 heart possesses auricles, ventricles and valves, as there is 
 in finding and understanding them when a real heart is being 
 examined. There is an endless difference in mental value 
 between learning a few curious things about the brain from 
 the book or a cheap model, or even the description of a 
 teacher, and in studying for ourselves, in detail, the varied 
 anatomy of a real sheep's brain. One leaves us with hazy 
 and dim ideas, the only real, tangible thing of which are the 
 words to symbolize them, but the other results in real, 
 definite, and lasting information. To have dissected out the 
 salivary glands on the sheep's head, furnished by the meat 
 market ; to have seen the Eustachian tube ; to have cut out 
 the tonsils ; observed the large circumvallate papillae on the 
 tongue ; to have seen the lens and separated the coats of the 
 eye ; to have hunted for and found the middle ear with its 
 chain of bones, possibly to have laid open the cochlea; to 
 have seen all these things on a single sheep's head, will be 
 of more lasting benefit and real educational worth than the 
 ability to repeat from memory a chapter at a time of the 
 latest edition of Quain's Anatomy. If, to carry the sug- 
 gestion a little further, the student could observe and study 
 with his own eyes the sympathetic system as it hangs dis- 
 played in every meat market, if he could but see one 
 ganglion, one nerve trunk, and really learn to know it, if 
 he could grasp with the fingers of his hand as well as those 
 of his mind a single typical gland, crush with his thumb but 
 one lymphatic nodule to know it, if in short he could get 
 a living knowledge of the more important structures alone, 
 he would not only have acquired facts which are indelible 
 and can be turned to practical advantage, but he will have 
 acquired a discipline in their acquisition which will give 
 added power to the entire mind. Furthermore, and possibly 
 
4 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 best of all, he is acquiring new facts in the way lie will be 
 obliged to acquire them when he leaves the school, and 
 when there will no longer be a teacher to diagram every 
 difficulty on the board in colored crayons, and when the 
 student will no longer be carried each day ' ' three pages in 
 advance." 
 
 By making his own actual observations on actual tan- 
 gible material he is not only training his powers of observa- 
 tion which are directly concerned, but by the care required 
 to verify his observations, and by strict reasoning of the 
 mind to properly interpret his observations, he is developing 
 all those faculties of mind which are required in the acqui- 
 sition of any new truth. He will learn what it often costs 
 to make but one point, he will see what painstaking efforts 
 it frequently requires to establish but one new fact, and he 
 will not be discouraged when later on he finds it hard to 
 make progress. He will know that to learn but one point 
 as it ought to be learned is making more real progress than 
 to have many poured into him. He will have somewhat of 
 a criterion by means of which to gauge his own pace. It 
 is certainly an attitude of mind brought about by scientific 
 study not to accept too quickly what seems still unproved, 
 be it from the assurances of the patent-medicine quack to 
 the politician with his latest schemes on finance. Huxley 
 compared knowledge with the virus of vaccination. When 
 the virus is fresh, when it comes directly from its original 
 source, it is wonderfully potent, but passed through the 
 tissues of other animals it is gradually weakened and may 
 finally have no effect at all. So knowledge gained first- 
 hand, from the objects themselves, from the experiments 
 themselves, is wonderfully potent, but passed through the 
 tissues of several text-books or handed down through several 
 teachers, it is gradually weakened until finally when it is 
 administered it is too weak to save us from the intellectual 
 epidemics of the day. 
 
CHAPTER I. 
 
 AN EPITOME OF THE HISTORY OF PHYSIOLOGY. 
 
 The word physiology now used to designate this and 
 kindred subjects, has a very remote origin. Etymologi- 
 cally it means a discourse on nature, from the Greek words 
 physis (0"'<H?), meaning nature, whence the word physical, 
 and logos (?-<w), meaning a discourse. In this original 
 sense it was employed by the earliest writers to include all 
 the natural sciences. Soon astronomy was set off as a spe- 
 cial science, and the term restricted to all subjects that 
 deal with natural phenomena and natural objects close at 
 hand. Little by little as human knowledge widened, 
 and the accumulated observations and experiments in 
 any one field became considerable, this field was sepa- 
 rated from the general study of nature, physiology, and 
 designated by its own peculiar name. In this way the 
 accumulating facts in the domain of chemistry gave rise to 
 the alchemy of the Middle Ages, and when later alchemy 
 was stripped of its superstitions and fancies, it rose to the 
 dignity of the science of chemistry. Soon purely physical 
 facts were separated off as the science of natural philosophy 
 and have become the science of physics. This eliminating 
 process has continued with the progress of science until the 
 original term physiology, which means the study of entire 
 nature, has been contracted so as to apply only to that 
 science which seeks to explain vital phenomena, be it in 
 plant or in animal. 
 
 Etymologically physiology is the parent science and all 
 others outgrowths of it. But not only in an etymological 
 sense is physiology of early origin. While logically phys- 
 iology follows physics, chemistry, botany and zoology, and 
 
 (5) 
 
6 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 presupposes them at many steps, yet historically almost the 
 exact opposite is true. It is a trait of the human mind ap- 
 parently to attack a problem by attempting at once the 
 explanation of its deepest questions. Thales, Anaximan- 
 der, Anaximenes, Heraclitus and other early Grecian phil- 
 osophers busied themselves with trying to explain the ulti- 
 mate essence of things before the world had made even 
 the first real attempt to learn something of the things them- 
 selves. 
 
 HIPPOCRATES. 
 
 Ancient writers cite Hippocrates of Macedon as the 
 person in whom physiological observations began. He is 
 often called the " Father of Medicine." Hippocrates was 
 a contemporary of Socrates and Plato, and he is especially 
 deserving of credit because he insisted that the proper way 
 to study disease and health was by observation and experi- 
 ment, and not by the application of general deductions. 
 He antedated Bacon many centuries in trying to establish 
 the inductive method of scientific investigation. While 
 Hippocrates added but little to the physiological con- 
 ceptions of his times, he described numerous phenomena 
 with great care, and made observations and experiments 
 which made him the foremost physician of his time. We 
 still speak of the Hippocratic face after death, of the 
 Hippocratic sleeve for straining syrups and decoctions, and 
 in our drug stores may still be bought the wine of Hippo- 
 crates, supposed to be made after the formula of that early 
 physician. 
 
 AEISTOTLE. 
 
 But while Hippocrates has possibly the honor of being 
 the first scientific physician, the honor of being the first to 
 study physiology scientifically belongs to' Aristotle, often 
 called the "Father of the Sciences." True it is that 
 Aristotle laid down many of the fundamental conceptions 
 of our sciences of to-day. One is astonished at his general 
 knowledge, and in many cases the careful investigations of 
 
HISTORY OF PHYSIOLOGY. 7 
 
 later times have shown the accuracy of his observations on 
 points which at first seemed mere fancies of his mind. He 
 wrote several works on physiological matters. His works 
 entitled, " Natural History of Animals," " On the Parts of 
 Animals," on "Animal Locomotion," "On Respiration," 
 are in part preserved, while a treatise on anatomy seems to 
 have been lost. From these writings the views of his 
 time are accessible. The main purpose with Aristotle 
 was to explain the function of every part and organ 
 described. Some of the main conceptions of Aristotle are 
 here briefly given: The heart is the central organ, and 
 the motive power of the whole body. It is the seat of 
 vitality, because it is the source of the animal heat of the 
 body, all the warmth of the body being produced by the 
 heart. The heart makes the blood, gives to it its vital stimu- 
 lus, and then sends it all over the body through the blood 
 vessels. The blood does not circulate, it never returns to 
 the heart, but as fast as it is used up at the periphery of 
 the body it is replaced in the heart. The blood is stored 
 in the blood vessels as in a jar. Whence the name blood 
 vessel used to this day. (The name "aorta" dates from 
 Aristotle.) Aristotle describes the stomach and intestines, 
 and hints at the proper conception of absorption. He 
 describes the trachea by the name artery, and says that it 
 carries air into the lungs. In the lungs the spiritus or 
 pneuma is extracted from the air and by channels (pul- 
 monary artery and veins, no doubt referred to) this 
 "spirit" substance is carried to the heart, where it is 
 mixed by the heart with the blood, and serves to give it 
 its vital stimulus. The ancient notion that the air or 
 ' ' spiritus ' ' is the vital principle still lingers in our every- 
 day language when we refer to vital things as spiritual, or 
 call the active element of wine spirits, although now hav- 
 ing an entirely different meaning. Aristotle explains all 
 vital processes as caused by lieat. Heat was the "causa 
 operandi " for everything. "Heat changes the metals, 
 disintegrates ores, liquids, and then vaporizes ice, causes 
 
8 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 the embryo to grow in the egg; in short, heat causes all 
 the processes of life." "But this heat must not go too 
 high, and so we have respiration, which enables us to 
 breathe in cold air and so cool the blood. For this reason 
 we breathe the faster the hotter we are ! ' ' 
 
 While much of Aristotle's information is remarkably 
 exact when we remember his times, and shows him to have 
 been a scientist such as the world has rarely seen since, yet 
 here and there we find ideas that seem somewhat puerile. 
 Thus he says with great earnestness "that in all his dissec- 
 tions, and he has made many, he has always found the 
 windpipe leading to the lungs and the oesophagus to the 
 stomach, nor has he ever found them interchanged." 
 
 PRAXAGORAS. 
 
 The views of Aristotle were extended by Praxagoras, 
 whose important addition to physiological knowledge was 
 the distinction he found between arteries and veins. He 
 also noticed the pulsations of the arteries and the absence 
 of a pulse from the veins. This was a material gain. But 
 with this discovery there crept in a misconception which 
 remained for centuries and formed the fundamental con- 
 ception of all the earlier physiologists. This was that the 
 veins are filled by, and carry the blood, but that the arteries 
 have no liquid of any kind in them, but carry the mysterious 
 "spiritus" or "pneuma," something akin but not exactly 
 the same as ordinary air. This misconception arose no 
 doubt from the observation that after death the arteries are 
 empty and all the blood practically is found in the veins. 
 The word artery, arteria, was used by Aristotle for the 
 trachea, as it was clearly an air- tube, but was by Praxagoras 
 applied to the pulsating blood-vessels under the idea that 
 they too contained air. We still use the name artery, 
 although since the time of Galen we know that they carry 
 blood and not air. None of the works of Praxagoras are 
 preserved, but his views are quoted by later writers. 
 
HISTORY OF PHYSIOLOGY. 9 
 
 HEEOPHILU8 AND THE ALEXANDRIANS. 
 
 Praxagoras had for his pupil the anatomist Herophilus, 
 whose influence contributed to the renown of the school at 
 Alexandria, whose greatest achievements were in the realm 
 of anatomy, physiology and medicine. The great Alexan- 
 drian museum became the center of learning of the ancient 
 world. Scholars from all parts of the world gathered there 
 to prosecute their studies. The attendance is given by 
 some writers as having reached 10,000 students at one 
 time. A glance at some of the names will convince one of 
 the pre-eminence of this first great university of the world. 
 Here Euclid wrote his geometry, here Ptolemy worked out 
 the "Ptolemaic" astronomy, Archimedes his physics. 
 Here originated the theological disputes between Arius and 
 Athanasius which culminated in the Nicene creed. Here 
 the dissection of the human body was allowed by law, and 
 the bodies of condemned criminals were turned over to the 
 students of anatomy. Here the anatomists, Herophilus and 
 Hrasistratus, were the first "professors of anatomy" in a 
 public institution. Many anatomical structures were here 
 first described and still bear their ancient names, the tri- 
 cuspid valves of the heart, the duodenum, the calamus 
 scriptorius, etc. Erasistratus distinguished between con- 
 nective tissue cords and true nerves, and even distin- 
 guished between sensory and motor nerves. 
 
 A marvelous advance was made by Herophilus in the 
 conceptions of brain and spinal cord. By earlier writers 
 they were regarded as unimportant collections of fat-like 
 tissues something like the marrow of the bones. The fact 
 that the earlier observers could see nothing in these struc- 
 tures except a soft structureless mass led to this error. The 
 term "spinal marrow" still used is probably a relic of the 
 times when this organ was not understood. Herophilus 
 made the brain the seat of conscious activities; the center 
 to which sensations are carried and the sourcs of voluntary 
 movements. What a step forward in the field of physio- 
 logical research ! But with all these advances they never 
 
10 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 doubted the truth of the conceptions of Praxagoras regard- 
 ing the arteries. They were in all calculations supposed to 
 to carry air or spuitus. This spirit us or pncuma they 
 made the subject of many fanciful theories. It was still 
 believed to be taken in by the breath and then carried to 
 the heart, to be distributed by the arteries. It was the 
 principle of life, and we have the ancient belief still illus- 
 trated in the familiar expression "the breath of life." 
 
 This spiritus by its vital energy caused the arteries to 
 pulsate. Brasistratus carried this notion so far as to rec- 
 ognize two kinds of spiritus. One which was taken from 
 the air is carried in the arteries and left side of heart, and 
 the other a higher spiritus made from the first by the brain 
 and stored in the ventricles of the brain (whence their 
 use) , from there to be distributed over the body by the 
 nerves giving feeling and volition, while the part that 
 remained in the brain became the bearer of consciousness 
 and individuality. This was called the "psyche," a name 
 retained to this day in such terms as psychical, psychology, 
 etc., while we still speak of animal spirits, and sometimes 
 hear of the nerves containing nervous flttid. Fever was 
 believed to be due to the filling of the large arteries with 
 blood and so interfering with the movements of the pneuma, 
 while inflammation resulted when the blood was driven by 
 the pneuma to the ends of the arteries, whence their dis- 
 tension. In a wound the artery contained blood, because 
 as the air, or pneuma, leaked out and so caused a vacuum, 
 blood soaked in to take its place. Normally blood was 
 contained in veins only. 
 
 GALEN. 
 
 The physiology of the ancients reached its culminating 
 point in the learned Galen, who practiced medicine in the 
 city of Rome when the Eternal City had reached the zenith 
 of its importance. He was a Grecian by birth and no doubt 
 belonged to that class of Greeks which had been called to 
 Rome to superintend the instruction of the imperial city. 
 
HISTORY OF PHYSIOLOGY. 11 
 
 Galen was the medical adviser of the imperial family itself 
 and so probably the most learned physician of Rome. It 
 is due to the genius of Galen to have put an end to some 
 of the misconceptions clustering around the idea of the 
 pneuma and the arteries. He established the fact that the 
 arteries normally contain blood. He describes that having 
 laid bare the axillary artery of an animal while it was pul- 
 sating regularly, and so according to the established notion 
 containing pneuma, he pricked it with a fine needle, and 
 found that in the very first instance blood came out, and 
 TLO\. pneuma, followed later by blood, which had soaked in. 
 When such a pulsating artery was cut the blood spurted 
 out forcibly at once, showing that it must have contained 
 blood before opening. What a simple and conclusive exper- 
 iment ! and yet it had taken the world centuries to think of 
 it. He also described the heart very carefully, and even 
 investigated successfully the changes in the circulation at 
 birth, having found the foramen ovale and the duct of 
 Botallus (duct us arteriosus] , and noted tke closing of the 
 former and the atrophy of the latter. (See chapter on 
 "Changes of the Circulation at Birth.") The discovery 
 of the true blood-carrying function of the arteries was 
 another tremendous step in the right direction, but in trying 
 to work out his idea of the system of blood vessels Galen was 
 led into several new misconceptions. From an historical 
 standpoint, however, they are of peculiar interest. Galen 
 made the liver the seat of the elaboration of the blood. 
 The portal circulation carries the foods from the stomach 
 and intestines to the liver (and in this he was correct) and 
 by the liver this food material was transformed into blood. 
 From the liver two vessels arose, one running downward to 
 the lower part of the trunk, and lower extremities ; the other 
 running upward to the heart. (In this way he had inter- 
 preted the large vena cava running through the liver to the 
 heart.) Through the right side of the heart the ascending 
 vessel was extended to the head and upper part of the body 
 (our descending vena cava and innominate veins) and 
 
12 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 through the ventricle of the heart to the lungs (our pulmo- 
 nary artery) . This system he called the venous system and 
 the blood venous blood. This venous blood was dark, being 
 rich in nutritive matter and intended to give to all the 
 organs to which it was distributed the proper substantial 
 nourishing matters. On the left side of the heart and in 
 the arteries there was an entirely different kind of blood, 
 and having no connection in any way w r ith the other or 
 venous blood. This blood he termed the arterial blood. 
 It was lighter in color and weight and carried the vitalizing 
 pneuma dissolved in it which it received in the lungs. It 
 also carried warmth to all parts of the body, which warmth 
 was produced in the left side of the heart. Both kinds of 
 blood ran to all organs, so that each organ could choose 
 whether it wanted the nutritive, rich, thick, venous blood, 
 or the quick, pulsating, active pneuma~conta.inmg arterial 
 blood. It was still believed that the vitalizing influence now 
 dissolved in the liquid blood, the pneuma, caused the prop- 
 erties of sensation and motion. 
 
 Galen, however, adds a new idea to explain the source 
 of the arterial blood. The venous blood is elaborated from 
 the food carried to the liver by the portal vein, but there 
 seemed at first sight no way to account for the production of 
 the lighter arterial blood. The vital spirits were extracted 
 from the air and added to it in the lungs, from which place 
 the blood carried the vital spirits to the left side of the heart, 
 where the finishing touches were given to it, and from which 
 it was sent out over the body. Galen solves this point by 
 admitting that there are pores, very tiny ones though, 
 through the thick ventricular septum, so that the finer parts 
 of the blood from the right side could soak through these 
 invisible openings to the left side. Further he contended, 
 and this seems remarkable now, that the arteries and veins 
 anastomose with each other at their outer ends by means of 
 excessively fine sieve-like canals and pores, so that again 
 some of the lighter parts of the venous blood could gradually 
 soak into the arterial svstem, and so replenish the arterial 
 
HISTORY OF PHYSIOLOGY. 13 
 
 blood as it was used up. This view Galen supported by the 
 observed fact that when an artery of an animal was cut, not 
 only the arteries, but the veins, also, became emptied in a 
 very short time. 
 
 Middle Ages. 
 
 With Galen the progress of the ancients in physiology 
 conies to a close. A thousand years have elapsed before 
 physiological phenomena receive the least attention, and 
 nonsensical metaphysical debates on theological abstrac- 
 tions crowd out of the mind of the Middle Ages even the 
 known conceptions of the past. Miracle cures replaced 
 the medicines of Galen and Hippocrates, and superstition 
 gave way to the anatomy of the ancients. More than ten 
 centuries separate Galen from the first students of anatomy 
 in the universities of Italy. But the Middle Ages had car- 
 ried the seeds of physiology through these years of read- 
 justment, and when the Italian Renaissance came, anatom- 
 ical and physiological studies felt the mental awakening. 
 For the first time in modern history, lectures on, and dis- 
 sections of the human body formed a part of the regular 
 program of studies of the universities. Mondini of Bologna, 
 1315, wrote a treatise on anatomy and dissection which 
 remained the authorized text-book in most schools of med- 
 icine almost into the sixteenth century. Only twelve years 
 after the invention of printing this treatise was printed 
 in full, and by the year 1550 it had no less than thirteen 
 editions. 
 
 The anatomy of the body is in many instances carefully 
 described, and the chief value of the book is from an 
 anatomical standpoint. In his physiological views the 
 established notions are not questioned. During the Renais- 
 sance the works of the ancients were seen to be so much 
 better than their present productions that practically implicit 
 confidence was given to all things that had the authority 
 of the past. Aristotle and Galen were not to be ques- 
 tioned, and it seemed senseless and unpardonable to try to 
 
14 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 improve on what they said, and useless to try to add 
 materially to their knowledge. Galen's views of the vital 
 spirits and the circulation are accepted. Mondini adds his 
 interpretation of the meaning of the auricles. They are 
 to act as overflow reservoirs for the ventricles, to store the 
 excess of blood or vital spirits when the ventricle is manu- 
 facturing these too rapidly. 
 
 Two hundred years later, in 1514, the chair of anatomy 
 and physiology at Bologna was occupied by the surgeon, 
 Carpi, who published a treatise on anatomy even more 
 extensive than that of Mondini, but not differing from his 
 predecessor in any of his fundamental physiological con- 
 ceptions. 
 
 VESALIUS. 
 
 A new era in physiology was ushered in by the Dutch 
 anatomist, Vesalius, 1537, whose immense credit lies not 
 so much in what he himself contributed to the science of 
 physiology as in the position he took with reference to the 
 ideas of the past. He boldly antagonized many of Galen's 
 views, showed that many of his observations had been con- 
 ducted on animals and not on the human body itself, and so 
 recognized the necessity for more definite descriptions. 
 With Vesalius the absolute charm of the all-sufficiency of 
 the past was broken, and he strongly suggested the neces- 
 sity of beginning anew the investigations of anatomy and 
 physiology, and the subjection of the ideas of the ancients to 
 a careful and impartial test. He boldly denied that there are 
 pores through the ventricular septum as Galen describes, 
 and insisted that the traditional view of the blood circula- 
 tion was wholly inadequate to explain all the facts, and he 
 might have discovered the circulation of the blood had he 
 remained the professor of anatomy at Padua and not been 
 made court physician at Madrid. 
 
 */:/? FETUS. 
 
 The next great step forward in physiology came from an 
 unexpected source and in a remarkable manner. The far- 
 
HISTORY OF PHYSIOLOGY. 15 
 
 reaching statement that the blood passes from the right side 
 of the heart through the lungs, and by means of anastomos- 
 ing connections is transferred to the pulmonary vein and so 
 returned to the left side of the heart, was made by the 
 Spanish theologian, Servetus. Serve tus wrote a number of 
 speculative treatises on theological disputes, which were 
 condemned as heterodox by both the Catholic church and 
 by Protestants. After the publication of his book, the 
 Errors of the Trinity, he was obliged to leave his home, 
 and under an assumed name entered the university of Paris, 
 and studied medicine. But even in the field of medicine 
 he was considered as little orthodox as he was in his theo- 
 logical views, and he was compelled to withdraw one of his 
 medical publications by order of the Medical Council. 
 
 After drifting around for some time as a practicing phy- 
 sician he decided to publish a book which should set forth 
 his theological views in detail. Soon afterwards appeared 
 his book entitled, the Restoration of Christianity. In 
 explaining in this book the workings of the Holy Spirit, he 
 adds an exposition of the vital spirit of the human body. 
 In this exposition he says that the blood goes to the lungs 
 from the right side of the heart, assumes a bright color in 
 tlie lungs, and is then transferred to the pulmonary vein. 
 Here it is mingled with the inspired air, is relieved of some 
 waste products, and then returns to the heart, where the 
 u vital spirit " is made out of the arterial blood. Hence 
 the soul resides in the blood and not in the solid organs. 
 This soul is nourished from the inspired air and the finest 
 constituents of the blood. "It, the soul, is a thin spirit 
 elaborated by the power of heat, of a bright golden hue 
 and fiery potency, containing in itself the substance of 
 water, air and fire. The very mind itself, the highest 
 form of the soul, resides in the choroid plexus of the 
 ventricles of the brain. (The choroid plexus is a network 
 of blood vessels lining the ventricles of the brain.) The 
 hollow ventricles of the brain are to permit air to be drawn 
 through the nose and ethmoid bone, and stored up in them, 
 
16 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 so as to renew the spirit in the adjacent blood vessels and 
 to ventilate the mind. However, in the abysses of these 
 ventricles evil spirits often hide which make war upon our 
 own spirit, and which are not put to flight until the assist- 
 ance of the Holy Spirit is invoked. While consciousness 
 resides in the choroid plexus, faith resides in the heart, 
 because as faith is a fundamental virtue it resides where the 
 vital spirit is originally made." Strange that with such a 
 medley of beliefs, some of which seem to border on the 
 blasphemous in their material conceptions of the Holy 
 Spirit, there should be included in the plainest terms such a 
 wonderful discovery as the circulation of the blood through 
 the lungs. Servetus's book was at once seized as heretical, 
 and poor Servetus, surrounded by all the copies of his book 
 that could be found, was burned at the stake in 1553. Two 
 of these original books still exist, one at Paris and the 
 other at Vienna. 
 
 FABEIC1US. 
 
 The anatomists, Falloppius (whence the name Fal- 
 loppian tubes) , Botallus (duct of Botallus) , Varolius 
 (pons varolii) , Eustachius (Eustachian tube), and others, 
 whose names are familiar to us from anatomical struc- 
 tures that still bear their name, added to the science 
 of anatomy rather than physiology. However, in 1574 
 another important step forward was made by Fabricius, in 
 the remarkable discovery that the veins normally possess 
 valves. As it was found that these valves all opened 
 towards the heart, it seems almost impossible that Fabri- 
 cius should not have stumbled upon the fact of the circu- 
 lation of the blood as we know it to-day. But Fabricius 
 made the blood flow from the heart outwards, against the 
 valves, and he explained the valves, by saying that they 
 prevented the too rapid flow from the heart to the organs. 
 When there was danger of congesting the organs, the 
 valves tended to close and so shut off more or less com- 
 pletely the supply of blood to that organ. The idea of the 
 ( ( vital spirits ' ' taken in at the lungs was still unques- 
 
HISTORY OF PHYSIOLOGY. 17 
 
 tioned, but there was laid additional emphasis on the 
 further idea that respiration was intended to cool or 
 refrigerate the blood, and the increased breathing, follow- 
 ing heavy exercise and the consequent rise in bodily tem- 
 perature, seemed in this view amply explained. 
 
 Modern Physiology. 
 
 HARVEY. 
 
 The real Renaissance of physiology dates from the cel- 
 ebrated name of William Harvey, a lecturer in anatomy in 
 the College of Physicians in L,ondon. To him we are 
 indebted for the discovery of the circulation of the blood, 
 as we now understand it. With this discovery a myriad of 
 older conceptions were forever swept away, and the founda- 
 tion laid for a real scientific study of physiological phe- 
 nomena. Harvey was convinced that the older views con- 
 cerning the heart were wrong. He was an indefatigable 
 experimenter, and was sure from his observations on the 
 living heart that it was nothing more than a pump. He 
 showed that the veins carried blood to the heart, for when 
 he tied the veins the portion next the heart became empty 
 and soon the heart itself was empty, while the vein beyond 
 the ligature was distended with accumulating blood. As 
 soon as he removed the ligature from the veins the dis- 
 tended portions emptied themselves, the veins became filled 
 near the heart, and the heart itself was distended. If, on 
 the other hand, he ligatured an artery the portion next to 
 the heart became largely swollen, the blood was gorged in 
 the distended heart, while the artery away from the ligature 
 gradually emptied itself. Now, when the ligature was re- 
 moved the heart emptied the blood into the relieved artery 
 at once. Nothing could be clearer. Harvey explained the 
 function of auricles and fairly accurately described the phe- 
 nomena of the heart's beat. 
 
 This remarkable discovery was published in the year 
 1628, which date may be considered the beginning of Mod- 
 ern physiology, and the close of its "Middle Ages." The 
 
18 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 book was written in Latin, as was usual in those times, and 
 is called Exercitatio Anatomica de Motui Cordis et San- 
 guinis in Animalibus. A copy of this original edition is 
 now in the Astor Library in New York. It seems curious, 
 however, that Harvey should not have believed in a direct 
 anastomosing of the arteries and veins. Such a notion had 
 been advanced by former anatomists, and it seems but nat- 
 ural that Harvey should at once have accepted this view to 
 explain the translation of the blood from the arteries to the 
 veins, the only missing point to establish his discovery. 
 Just how the translation is effected Harvey was unable to 
 answer. 
 
 Harvey's discovery made a profound impression upon 
 the thinkers of his day. It was a revolution in the accepted 
 doctrines of more than 2,000 years. It did away with the 
 somewhat fascinating "vital spirits," with the "moving 
 force" inherent in "arterial blood," and with the mystic 
 functions ascribed to the heart and lungs. It made the 
 heart a mere muscular pump, it explained all the valves of 
 the heart and veins simply as those of an ordinary water 
 pump, it explained the mysterious pulse as a mere wave 
 caused by the contraction of the heart forcing the inert 
 blood into the arteries, just as would have occurred if water 
 instead of blood had been used. It did away with the idea 
 of two kinds of blood, venous and arterial, and showed that 
 one was changed into the other in the lung by being put in 
 contact with the air. Men are always slow to part with 
 ideas that have the prestige of the past, and so we find 
 Harvey's views at once stubbornly opposed. The learned 
 physician, James Primerose, wrote a lengthy treatise oppos- 
 ing Harvey's views in which he criticises Harvey very 
 severely for taking "too great license in impugning the 
 doctrine of the ancients." 
 
 LATER INVESTIGATORS. 
 
 Harvey's experiments were, however, so convincing that 
 it was useless to question them, but the authority of Galen 
 
HISTORY OF PHYSIOLOGY. 19 
 
 was still too strong and several attempts were made to 
 adapt the views of Harvey to the conceptions of Galen. 
 Riolan, the anatomist of the celebrated Paris School, pub- 
 lished his Circulation of the Blood, 1648, in which he 
 tried to show that Galen was correct in the main, but that 
 a little, just a little blood circulated from the arteries 
 through to the veins. It did not, however, circulate 
 through the lungs, but the venous blood reached the arter- 
 ies by passing through the ventricular septum. The lung 
 was to furnish the " vital spirits" as before understood. 
 
 Gradually Harvey's views were adopted, and a new 
 epoch in physiology ushered in. In 1651 Bartholini and 
 Rudbeck announced the discovery of the system of lym- 
 phatics, thus adding another chapter to the circulation, and 
 in 1655 the circulation of blood was finally demonstrated as 
 a fact by Marchetti of the University of Padua, who injected 
 a human cadaver and was thus enabled to follow the trans- 
 lation of the injected fluid through the entire circulation. 
 
 The capstone of the fact of the circulation was finally 
 added by the celebrated physiologist Malpighi, of the Uni- 
 versity of Bologna, 1661. It was he who saw for the first 
 time the circulation through the capillaries. He examined 
 with a " magnifier" the lung tissues of a frog, and to his 
 surprise found the long disputed connections between the 
 arteries and the veins. The discovery and description of 
 the "plexus of capillaries" belong to Malpighi. Soon 
 afterwards with the just-invented microscope, L,eeuwenhoek 
 of Holland, the pioneer in microscopy, discovered the " red 
 globules" circulating in the blood. By this chain of dis- 
 coveries was established one of the most important chapters 
 in physiology the circulation of the blood. 
 
 A long line of illustrious physiologists has contributed its 
 discoveries from that time to the present. The phenomena of 
 respiration were cleared up when Priestly and L,avoisier dis- 
 covered oxygen gas and explained the nature of oxidation. 
 Priestly and L,avoisier were misled, however, in believing 
 that the lung was the seat of the oxidation in the body, 
 
20 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 and that the heat made here was carried over the body by 
 the blood. The important fact that the oxidation is in the 
 tissues themselves was finally established by Liebig and 
 Pfliiger in their study of muscular tissue in 1867. The 
 nervous control and regulation of breathing studied first by 
 L,e Gallois in 1812 was extended by Flourens in 1842, 
 Traube 1847, and Rosenthal 1862. The processes of secre- 
 tion were also soon investigated. The notions of the an- 
 cients on this point were very primitive. They regarded the 
 discharge of the mucous phlegm from the nose as an elim- 
 ination from the brain which soaked through the ethmoid 
 bone into the nose. The study of glands by Peyer, Brun- 
 ner and Malpighi soon established the anatomy of secretory 
 tissues. The action of nerves on glands was brought to 
 light by the successful experiments of L,udwig and Bernard 
 of our own day, who succeeded in producing the salivary 
 secretion by the artificial stimulation of the nerves going 
 to the gland. The celebrated physiologist of Berlin, Du 
 Bois Reymond, brought to light a multitude of observations 
 on the electrical properties of living tissues. To that most 
 remarkable scientist, Helmholtz, of Berlin, we are indebted 
 largely for the accurate knowledge we now possess of the 
 physiology of the eye and the ear. The Young-Helmholtz 
 theory of color is still the best interpretation of color sen- 
 sations, and the studies in the physics of harmony have 
 solved for us to a very large extent the problem of the ear. 
 When to this is added the measuring of the rate of transmis- 
 sion of nervous impulses and the exposition of the law of 
 the conservation of energy, it will be seen how much has 
 been added by this scholar. 
 
 The history of special problems in physiology will be 
 found noted in their respective places in the book. It is 
 hoped that the foregoing epitome may show the interested 
 reader the long road by which our familiar ideas have 
 reached us. It is believed that a clearer perception of the 
 efforts and the struggles which it has cost great men to 
 interpret for us these phenomena may result in a quickened 
 
HISTORY OF PHYSIOLOGY. 21 
 
 appreciation of their labors. It finally justifies us in the 
 belief that the future will contribute to the science of physi- 
 ology as much as the past has done, and that many prob- 
 lems which are still almost wholly unsolved may be rapidly 
 Hearing their solution. 
 
CHAPTER II. 
 
 THE CBIvIy AND ITS LIFE. 
 
 Probably the most fundamental conception in biology is 
 that of the cellular structure of all animals and plants. The 
 discovery that all living things are made up of separate and 
 individual cells laid the scientific foundation for the sciences 
 of histology and embryology, and very materially modified 
 physiological investigation. It is the bridge that connects 
 plants and animals, and is the key to the proper understand- 
 ing of the phenomena of their growth and development. 
 But such a far-reaching and clarifying conception did not 
 appear suddenly. Our present notions are the result of 
 much investigation and reach back through the observations 
 of many years. The ease and familiarity with which we 
 now speak of cells, of protoplasm, of nucleus, etc., might 
 argue at first sight that we are dealing with a long estab- 
 lished, always-evident bit of knowledge, while as a matter 
 of fact these ideas are even now in the process of formation. 
 
 HISTORICAL VIEW. 
 
 When L,eeuwenhoek, the pioneer in the use of the micro- 
 scope, began to extend human observations with the aid of 
 this added sight a new world was opened, and with avidity, 
 sometimes with mere curiosity, observers subjected all sorts 
 of things to the scrutiny of the microscope. In this way 
 Robert Hooke, of England, 1667, while examining some- 
 what indiscriminately all sorts of things with his rude micro- 
 scope, placed a thin section of ordinary cork under the 
 instrument and noticed that the section contained innumer- 
 able little chambers which, because of this, he called cells. 
 He had, of course, no idea as to the meaning of these cham- 
 bers, but used the term " cell " as we still employ the word 
 (22) 
 
THE CEU, AND ITS LIFE. 
 
 23 
 
 nowadays when speaking of the chamber of a prison as a 
 cell. Although Hooke's notion regarding these chambers 
 or cells has long since been changed, the term he applied 
 to them has remained, and there is little probability that it 
 will ever be displaced, so firmly is it established in biolog- 
 ical science. 
 
 Fig. 1. A SECTION OF WOOD SHOWING 
 THE CHAMBERED APPEARANCE. 
 
 Fig. 2. CELLS IN GROWING WOOD. 
 
 Several years later (in 1671) Malpighi and Grew each 
 published a treatise on structural botany in which this 
 chambered or cellular appearance was noted as occurring 
 in many other vegetable tissues besides cork. For more 
 than a century nothing further was done, and it was not till 
 the beginning of our own century that the observations in 
 this direction were renewed. In 1812 Moldenhauer, a Dutch 
 scientist, by macerating plant tissues succeeded in isolating 
 individual cells. (Experiment easily repeated with a ripe, 
 mealy apple.) This changed the idea of Hooke that cells 
 were but empty chambers in a homogeneous mass, to the 
 correct view that cells are individual structures having a 
 solid wall enclosing the chamber. In this way the cell 
 wall and not the empty space seemed to be the essential 
 thing. Soon after this, however, Corti and Amici found 
 that many cells are filled with a liquid sap, and in several 
 instances they had observed this sap circulating in the cell 
 without being affected by an external power. Such further 
 observations emboldened Meyen, in 1838, to venture the 
 assertion that a part of the cell sap must surely be alive. 
 
24 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 In the meantime Robert Brown, 1831, had discovered the 
 nucleus inside the cell. Thus little by little the contents 
 were considered as the essential thing of the cell, rather 
 than the cell wall. To help this view the botanist, Unger, 
 in 1843 made a series of discoveries of a then astounding 
 character. In examining the green scum everywhere plen- 
 tiful on moist flower pots (vaucheria) , he saw the cell sap 
 l< crawl " out of the old cell wall and creep away. This is 
 the common phenomenon of rejuvenescence easily observed, 
 in which the protoplasm leaving the old cell wall becomes 
 active for a while, and then produces a new vaucheria 
 thread. But to Unger it was a plain case of the sap of a 
 plant cell turning into an animal. The misinterpretation 
 was strengthened when soon afterwards Kritzing observed 
 green amoeboid cells changing into filaments of algae. Here 
 was a case of an animal changing to a plant. But it estab- 
 lished one thing as correct that the cell contents are the 
 essential thing and the cell wall quite secondary. To the 
 mysterious contents endowed seemingly with vital proper- 
 ties, Hugo von Mohl in 1846 gave the name protoplasm . 
 
 All these views were then moulded into a definite theory 
 by Schleiden in 1849. It will be observed that up to this 
 time all the observations had been confined to plants, but 
 in 1849 the histologist, Schwann, showed that animals, too, 
 are made up of cells, and applied the cell theory equally to 
 them. The theory was therefore called the "Schleiden and 
 
 ( __ i 
 
 Fig. 3. CELLS FROM THE ANIMAL BODY (CORNEA). (After Schafer.) 
 c, columnar cells; p, polygonal cells; fl, flattened cells. 
 
 Schwann cell theory." The manner in which these cells 
 
THE CEU, AND ITS LIFE. 25 
 
 originated was not known, although the current notion was 
 that new cells arose " in between " old cells. That a tiny 
 granule, the nucleus, was in some manner deposited 
 between already formed cells, and that around this nucleus 
 the rest of the cell gradually arose by a process of precipi- 
 tation like the growth of a crystal in a supersaturated solu- 
 tion of that substance. How inconsistent that view was 
 with all the facts of heredity seemed not to be considered. 
 The remarkable advance in knowledge, that a new cell 
 arises only by a division of a pre-existing cell is due to the 
 botanist Nageli, who had observed this manner of cell pro- 
 duction. And when finally Max Schultze in our own day 
 proved the identity of protoplasm, whether taken from plant 
 or animal, the cell theory as we now understand it, was in 
 its general outlines established. Added proof was further 
 given to this theory (now really a fact) when Dujardin and 
 Haeckel showed that many of the lowest animal and plant 
 forms were in reality nothing more than single cells. 
 
 A TYPICAL CELL. 
 
 As the cell figures so prominently in the proper under- 
 standing of nearly all histological structures and throws so 
 much light on physiological properties and the problems 
 of heredity, a more general account of it is here given 
 as an introduction to the histological matter further on. A 
 typical cell consists of a mass of protoplasm surrounded by 
 a cell wall, and containing within it a nucleus. Food 
 material also frequently occurs diffused through the pro- 
 toplasm. Recently there was discovered a further structure, 
 lying usually close to the nucleus, the centrosome. The 
 exact nature of this body is not yet fully established, but 
 it seems to play a very important part in the division of the 
 cell. The nucleus is made up of a substance which stains 
 deeply when treated with the usual staining agents and has 
 been called chromatin. The nucleus is that part of the 
 cell which seems to influence and determine the func- 
 tion of the cell, and from the important role it plays in 
 
26 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 Fig. 4 . AMCEBA. (After Leidy.) 
 n, nucleus; cv, contractile vacuole 
 (excretory organ); N, food vacuoles; 
 ek, exoplasm ; en, endoplasm. 
 
 Fig. 5. A TYPICAL CELL FROM THE INTES- 
 TINAL EPITHELIUM OF A WORM. (Carnoy.) 
 me, membrane of cell ; pc, protoplasm of the 
 cell ; mn, membrane of nucleus ; pn, achroma- 
 tin of the nucleus; bn, the chromatin filament 
 about to change into the separate chromo- 
 somes. 
 
 the formation of a new cell, is believed to be the carrier of 
 those qualities and properties which we are wont to desig- 
 nate as those of heredity. In cells which have lost the 
 power of division the nucleus practically disappears, but it 
 is conspicuous in eggs which are about to usher in a period 
 of active cell division. By a chemical modification of the 
 protoplasm of the cell, the cell is differentiated into the re- 
 quired tissue in question. By changes of some kind in the 
 protoplasm of the cells are brought about all those phenom- 
 ena of physiology such as secretion, absorption, assimilation, 
 contraction, and some physiologists go on to add conscioiis- 
 ness and thozight, a step by no means yet fully warranted. 
 
 These various activities of the cells will be discussed 
 in their appropriate chapters, and attention is called here 
 briefly only to the somewhat complicated, but interesting 
 process of the indirect division of the cell. 
 
 THE DIVISION OF THE CELL. 
 
 When the process of cell division, called karyokinesis, is 
 about to be ushered in, the centrosome lying close to the 
 
THE CEIJ, AND ITS IJFE. 27 
 
 nucleus is seen to divide, and the two parts move toward 
 the opposite ends or poles of the cell. Just what these 
 centrosomes are is still an unsettled question. Radiating 
 from these centrosomes there soon appear little delicate 
 threads, believed by some observers to have been derived 
 from the achromatin of the nucleus; by others, from the 
 protoplasm of the cell body. The threads between the 
 centrosomes seem to be continuous, that is, extending 
 from one centrosome to the other, and thus forming a so- 
 called "spindle." The continuity of these threads is 
 questioned by others, who believe that they extend no 
 further than the " equatorial plate." In the meantime the 
 nucleus undergoes changes by which the chromatin of the 
 nucleus appears as a more or less coiled thread, which soon 
 breaks up into a number of V-shaped loops called chromo- 
 somes. The number of these chromosomes varies for the 
 different species of animals or plants, but in the same 
 species it is practically constant. These chromosomes 
 arrange themselves in the region of the "equatorial plate." 
 A longitudinal splitting of each chromosome doubles the 
 original number of Vs. Half of the V's now move toward 
 the one pole, the other half to the opposite pole. 
 Whether the spindle threads serve in any way to draw or 
 guide the individual V's is an interesting but unsolved 
 question. When the chromosomes have arrived at their 
 destination the individual V's again fuse together, and soon 
 two nuclei have replaced the original one. The cell proto- 
 plasm now seems to arrange itself with reference to the two 
 new nuclei, and a constriction of the old cell wall, or the 
 formation of a new wall along the line of the equatorial 
 plate finally produces two separate and distinct cells, which 
 in turn, by repeating this same process, may produce two 
 more, etc. The extreme care in dividing the nucleus 
 (which is the bearer of heredity) shows that nature takes 
 every precaution to give to each daughter-cell an exact 
 proportion of all those attributes which heredity passes 
 from one generation of cells or individuals to the next. 
 
28 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 Fig. 6. SHOWING SOME OF THE STAGES IN THE DIVISION OF THE CELL. 
 
 It is interesting to observe that simple animals, who 
 in comparison with the mammals, say, have but little that 
 is passed on to the succeeding form, show a much simpler 
 type of cell division. When we remember that in the 
 chromosomes of the egg there are housed in their finer 
 structure those determining influences which later on will 
 reappear in the shape, size, structure, coloration, intona- 
 tion of voice, and even instincts of a wonderfully com- 
 plicated adult individual, we are not surprised to see the 
 care with which the chromosomes are elaborated, for the 
 important purpose of producing a new cell. While it 
 explains in no sense the real cause of heredity, it is appar- 
 ent that in this process there is a valuable suggestion as to 
 the actuality of a physical basis for heredity. 
 
CHAPTER III. 
 
 THE TEACHING OF PHYSIOLOGY AND THE 
 PUBLIC HEALTH. 
 
 No one will question the validity and appropriateness of 
 hygienic considerations in a treatise on physiology. To 
 promote the individual and the general health are the pur- 
 poses assigned to physiology by the law which made it a 
 common school subject. While, of course, there is danger 
 of materially destroying the educational value of physiology 
 by having it degenerate into a dried and cut code of empir- 
 ical formulae, mostly without any real practical value; while 
 the ordinary school often sins by spending valuable time in 
 giving platitudinous advice which it was never the intention 
 to have followed to the letter, there is, on the other hand, 
 the possibility of repaying a thousand-fold the money and 
 time expended in teaching physiology if there could be put 
 into the practical belief of all its students a clear percep- 
 tion of the fundamental laws that govern proper sanitation 
 and of the scientific methods of preventing disease. To 
 be obliged to acknowledge, as true it is, that most of the 
 diseases of the human body are due to agencies which it is 
 entirely possible to control, and even eradicate, by properly 
 directed sanitary and hygienic methods, shows how urgent 
 is the necessity of impressing this information upon the 
 attention of the public at large. 
 
 In a perfectly healthy community, possessed of a per- 
 fect system of sanitation and barring the direct introduction 
 of disease by admitting affected persons from the outside, 
 the infectious and contagious diseases would and could 
 never appear. Diphtheria and scarlet fever would leave 
 children untouched, and consumption and typhoid would 
 disappear from the lists of mortality. It is, however, use- 
 
 (29) 
 
30 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 less to effect sanitary reforms by the ipse dixit of the 
 law. The efficiency of a law is directly proportional to the 
 number of people who thoroughly believe in its provisions, 
 and 'a widely disseminated knowledge of the conditions of 
 health and disease must precede the statutory enactment of 
 sanitary laws. Our national health must depend upon the 
 education of the masses in this direction, for repeated sys- 
 tematic attempts by some of our cities to force people into 
 cleanliness and virtue by police regulations have proved 
 how fruitless such procedures are in the end. The public 
 at large is too conservative in its modes of thinking, to fully 
 acknowledge the value of these proposed hygienic reforms, 
 for the notion that nearly all disease is due to a violation by 
 us of some sanitary law is too recent to be fairly established 
 in the public mind. The wonderful insight into the nature 
 of contagious diseases and their prevention is almost wholly 
 a product of the present decade. 
 
 HISTORY OF SANITATION. 
 
 But it must not be assumed that the value of sanitary 
 precautions was not appreciated at all in former times, for 
 the injunctions and directions of the Mosaic code were but 
 the attempts of the Jews to tabulate what experience had 
 proved to them to be valuable in preserving their national 
 life. Their regulations with reference to their food, and 
 their treatment of lepers clearly instance this point. The 
 observance of this code is no doubt one of the causes of the 
 persistence of the Jewish nation through historic time, and 
 explained the comparative immunity of the Jews from the 
 epidemics of the Middle Ages. The cruel and hard, but 
 terribly effective code of Lycurgus for the Greeks had not 
 a little to do with the production of the manhood of early 
 Greece, and the abandonment of this code by the later 
 Greeks was one of the elements that contributed to their 
 national decay. 
 
 The Romans also appreciated the value of proper drain- 
 age, and the Cloaca Maxima of Rome stands as a monument 
 
TEACHING OF PHYSIOLOGY AND PUBLIC HEALTH. 31 
 
 to this day to that effect. The remains of the aqueducts 
 around Rome show on what a stupendous scale the city was 
 furnished -with pure drinking water. On the other hand, 
 history plainly tells us that the wanton violation of physio- 
 logical laws by the pleasure-loving Romans of later days, 
 together with the epidemics that repeatedly devastated the 
 Imperial city, had much to do with the decline and fall of 
 the empire. 
 
 It is, however, in the Middle Ages that we see the most 
 flagrant violations of the laws of health. The clothing of 
 the people was made almost entirely of wool, and little 
 suited to the varying temperatures. The dwelling houses 
 were of the rudest construction; and clean floors were 
 unknown. New straw was placed from time to time upon 
 the floors of dwellings to cover up the filth that had accu- 
 mulated there. A writer of this period states that when- 
 ever he went into a house of this kind he was immediately 
 seized with a fever. Strong ale and sour wine, usually 
 drunk to excess, were prolific sources of disease, and 
 highly seasoned and salted meats formed the substance of 
 the daily diet. Streets were unpaved, and almost to the 
 close of the Middle Ages the man who would have started 
 to walk down the streets of Paris itself on a rainy day 
 would have stepped into mud up to his ankles. Sewers 
 were unknown, and the filth and garbage were turned over 
 to the slow process of decomposition in their very midst. 
 
 When one remembers that there was constant fighting, 
 that people were crowded in walled fortresses and towns 
 without pure air, and finally adds that the country was 
 filled with murderers, marauders and thieves, with frequent 
 famines to augment this class, one can appreciate what was 
 meant by Darwin's notion of the " survival of the fittest." 
 Only the strongest and heartiest survived ; the weak went 
 to the wall. It was an illustration of Darwin's law with 
 barbarous reality. But it gave to the modern age a picked 
 race of stronger and heartier people. One is not surprised 
 that under such conditions epidemics were plentiful and 
 
32 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 famines frequent. Thus, in the twelfth century there are 
 recorded fifteen general epidemics; in the thirteenth cen- 
 tury, twenty general epidemics; in the fourteenth century, 
 eight. It was in 1348 that Europe was devastated with the 
 epidemic called " The Black Death," or "The Great Mor- 
 tality." In London, alone, 100,000 people were carried 
 away, and it is estimated that on the continent of Europe 
 not less than one-fourth of the population, that is, more 
 than 25,000,000 of people, fell prey to its ravages. The 
 imagination of to-day fails to picture the horror and black 
 despair of the time. Throughout all this period epidemics 
 were believed to be visitations from an angry God, and 
 there were not missing observations of armies fighting in 
 the air, and other supernatural phenomena which served as 
 warnings and forerunners of these dread times. 
 
 With the middle of the seventeenth century there 
 dawned a better day. Improved methods of agriculture 
 and commerce materially bettered the daily food of the 
 people. The introduction of tea and coffee replaced the 
 baneful effects of strong ale and spirits; and the intro- 
 duction of the potato displaced the highly seasoned meats. 
 Cotton and linen goods were revolutionizing clothing. But 
 possibly the greatest advance of all was the discovery of 
 soap. With the introduction of this now indispensable 
 article the reign of filth and uncleanliness began to weaken. 
 More and more general attempts at municipal cleanliness 
 resulted, and it began to dawn in the minds of men that 
 disease and filth had a causal connection. Men learned for 
 the first time that the prevention of disease might be inves- 
 tigated as a scientific problem. Several remarkable dis- 
 coveries about this time helped materially in the sanitary 
 evolution of civilization at large. One of these was the 
 discovery of Captain Cook that that dread disease, scurvy, 
 might be entirely prevented. This disease had for cen- 
 turies decimated the ranks of soldiers and sailors, and was 
 the especial dread of every ship's crew. The simple 
 
TEACHING OF PHYSIOLOGY AND PUBLIC HEALTH. 33 
 
 addition of lime juice to the food of every sea-going vessel 
 precluded the possibility of this sickness. 
 
 Another cause of great mortality was repeated out- 
 breaks of jail fever in the prisons of the country. This 
 disease was frequently carried from the prisons to the outer 
 world. It was later recognized as the typhus fever of 
 to-day. It was due to the careful observation of John 
 Howard that this disease was traced to filth and over- 
 crowding. Reforms based upon this have made jails 
 healthier than many homes, and this disease one of the 
 rarest occurrence. 
 
 Then, in 1796, came the discovery of Edward Jenner 
 that smallpox might be prevented by the process of vacci- 
 nation. While the absolute validity of vaccination is still 
 questioned by some people to-day, there is no doubt about 
 the fact that the mortality due to this disease has been 
 many times reduced by this process. 
 
 THE SCIENCE OF BACTEEIOLOGY. 
 
 It was reserved to our own day to give us a scientific 
 insight into the cause of disease. The science of bacteri- 
 ology is a product of the last few years. At first a small 
 branch of the science of botany, bacteriology has com- 
 manded more and more attention; has ramified in wider 
 and wider directions until now it has the dignity of a dis- 
 tinct science ; and there are perhaps few subjects of study 
 which are to-day being pursued with such an avidity, and 
 in which the results obtained have proved of such unspeak- 
 able worth. An elementary understanding of the more 
 important conceptions of bacteriology is necessary to a 
 proper appreciation of hygienic laws. No one any longer 
 questions the cause of all our contagious and infectious 
 diseases. It is a matter of every-day comment to speak of 
 the various germs producing respectively the various con- 
 tagious diseases. A short summary of the growth of this 
 science may be a matter of interest. 
 
34 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 BACTERIA. 
 
 Very tiny living objects, visible only with the higher 
 power of the microscope, had frequently been observed by 
 botanists and zoologists. Their almost universal distribu- 
 tion had been commented upon. Attempts were made to 
 properly classify them in the system of nature. At first 
 regarded as animals, they have finally been relegated to the 
 domain of botanists, and are now viewed as belonging to 
 the plant kingdom. But little attention was paid to them 
 until the remarkable observation was made that there 
 seemed to be a causal connection between such micro- 
 organisms and certain known diseases. It is due to the 
 genius of the Frenchmen Davaine, Pasteur and Chauveau 
 to have given us the germ theory of disease, our notions of 
 fermentation, and the first successful attempts at pro- 
 tective inoculation, The first disease that was clearly 
 proved to be due to such organisms was the splenic fever, 
 which about the middle of this century was playing such 
 havoc with the sheep and cattle of the continent. Beyond 
 the peradventure of a doubt it was shown by these French- 
 men that these little germs not only caused the disease in 
 the animals studied, but that such germs might actually be 
 taken into the system of other animals, and so produce the 
 disease anew. 
 
 A wonderful addition to our knowledge was made in 
 1872, when Klebs explained the phenomena of the inflam- 
 mation of wounds and blood poisoning. He had occasion 
 to examine numerous wounded soldiers of the Franco - 
 Prussian war, and observed that in the wounds and 
 abscesses of such individuals there were always found such 
 organisms, and he proved that even deeper portions of the 
 body to which the inflammation had extended had been so 
 diseased by the migration of these micro-organisms along 
 channels that he was able to trace. Few discoveries have 
 done so much to alleviate human suffering and to lessen 
 the dangers of surgical operations as this knowledge that 
 
TEACHING OF PHYSIOLOGY AND PUBLIC HEAI/TH. 35 
 
 inflammation is due to the introduction of a foreign organ- 
 ism. And when finally the celebrated Lister, of Eng- 
 land, perfected his methods of antiseptics in surgery, the 
 scientific basis was laid for present surgical skill. Only 
 three years later, in 1875, Klebs succeeded in rinding the 
 bacillus of diphtheria. 
 
 Then what a contribution it was to medical knowledge 
 when the German bacteriologist, Koch, in 1882, pub- 
 lished his preliminary article in which he proved that that 
 dread disease, consumption, was caused by such a micro- 
 organism! Discovery followed discovery, and in the space 
 of but a few years the germs which cause cholera, hydro- 
 phobia, lockjaw, leprosy, malaria, typhoid, and other fevers 
 were discovered. With this' discovery it was possible to 
 make experiments with a view of preventing these diseases. 
 It was possible to work out the life-history of the germ 
 under what conditions it would grow best ; under what con- 
 ditions it would be retarded in its growth; what agency 
 would suffice to destroy it ; in what manner it could be car- 
 ried from place to place ; through what avenues it reached 
 the body. This explained at once how garbage and filth 
 of any kind were a prolific source of disease. This explained 
 general epidemics, but it also suggested efficient ways of 
 protection. The sterilizing action of heat was clear, and 
 the use of antiseptics was susceptible of everybody's 
 understanding. To show what a clear insight it gave into 
 diseases previously not at all understood, common malarial 
 fever may be taken as an illustration. 
 
 No one could explain why a patient should every third 
 or fourth day be seized with a fever paroxysm and be com- 
 paratively free from the disease during the intervening pe- 
 riod. No hint was obtainable anywhere. What was its 
 immediate cause? Bacteriology has revealed that this com- 
 mon ailment is due to a tiny organism (sporozoa) which 
 lives as a parasite in the red corpuscle of human blood. 
 Introduced into the blood from various poorly drained areas 
 containing much decayed organic matter, it finally finds 
 
36 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 lodgment in the corpuscles. The corpuscle containing this 
 parasite loses its vital properties, is robbed of its coloring 
 matter, the haemoglobin, and so materially reduces the 
 efficiency of the blood to nourish the body. Two kinds 
 of parasites have been found which differ from one another 
 in the time required for producing new spores. In one 
 species each parasite produces a brood of new spores every 
 third day. In the second parasite the new brood arises 
 every fourth day. It is the formation of this new brood of 
 spores every third or fourth day which causes the malarial 
 paroxysm, probably because in the formation of the spores 
 some poisonous substance is eliminated. If, as it often 
 happens, the .patient houses in his blood two sets of these 
 parasites whose times of spore formation varies, the par- 
 oxysms vary accordingly, and so explain why the chill may 
 recur on successive days, then miss a day only to recur 
 again on the fourth day. We understand how the destruc- 
 tion of the red corpuscles of the blood by these infesting 
 parasites will produce the anaemia, so characteristic of 
 malarial fever. 
 
 The germ of the only too prevalent typhoid fever we can 
 now produce in pure .cultures in the laboratory test tube. 
 We can see how it thrives and multiplies in decaying 
 organic matter. It can easily be observed what a healthy 
 medium sewage water is, and we can follow through all its 
 vicissitudes this agent of mortality. Bacteriology answers 
 satisfactorily the prevalence of consumption, the agent that 
 carries off more victims than probably any half dozen other 
 diseases combined. Nuttall, of Johns Hopkins Hospital, 
 in making quite a number of careful calculations found that 
 a patient only moderately advanced in the disease elimi- 
 nated from his body in the sputum during a short period of 
 twenty-four hours, from one and one-half, to four and one- 
 third billions of bacteria. These billions form part of the 
 dust which by the winds is spread broadcast and carries 
 infection to the first susceptible lung, or washed away by 
 the rains finally finds its way back through drinking water 
 
TEACHING OF PHYSIOLOGY AND PUBLIC HEALTH. 37 
 
 to some person, there to set going the various forms of 
 gastric or intestinal tuberculosis. 
 
 In such a brief account we are not specially concerned 
 with the question what bacteria are. Suffice it to say that 
 they are minute organisms, among the smallest known. 
 Several typical forms are usually described. Thus the little 
 round globular form, such as the germ that causes erysip- 
 elas, is called micro-cocczis. The short rod-like form, such 
 as the one that induces the decomposition of flesh, is called 
 bacterium. (Used in this instance in a special way and not 
 referring to the whole group.) Longer rod-like forms are 
 represented by the germs of consumption, typhoid fever, 
 leprosy, lockjaw, etc., and are called bacilli. The comma 
 bacillus of Asiatic cholera has a slightly bent shape not 
 unlike the comma, whence its name, and belongs to the 
 order of the vibrios. In typhus recurrent fever occurs 
 the cork -screw -like form called spiro-chaeta, while the 
 undulating snake-like form frequently found in the mouth 
 and the teeth, is called spirillum. In addition to the 
 active forms most bacteria are able to produce, when the 
 necessity arises, spores which are able to resist drought or 
 any other unfavorable circumstance for a long time, only to 
 germinate again as soon as proper conditions arise. The 
 resistance of some of these spores is almost incredible. 
 The spores of the hay bacillus, found in ordinary hay, may 
 be boiled several minutes without injuring their vitality. 
 Spores may be formed either by the protoplasm of a bac- 
 terium forming a thick wall around itself for extra protec- 
 tion, or by the protoplasmic contents of a bacillus splitting 
 up into several small globular bodies which are soon pro- 
 vided with a thick coat, and in this form mingle with the 
 dust of the atmosphere to be wafted and scattered by every 
 breeze that stirs. 
 
 But it must not be supposed that all germs are disease- 
 producing. Many of them are of the utmost benefit to us. 
 The germs that cause the ordinary decomposition of organic 
 matter by returning it to the elements, keep things clean 
 
38 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 and pure, while the bacteria which are found in such great 
 numbers in the soil act as a biological filter, destroying all 
 the impurities so that the water at a reasonable depth is 
 entirely free from organic particles. The very plants are 
 dependent upon the bacteria of the soil for their nitrog- 
 enous food. Botanists assure us that were it not for the 
 nitrification caused by the bacteria in the ground the entire 
 plant world would be reduced to a stunted growth. The 
 very processes of digestion in the human body are helped 
 along by bacteria which live normally in the human intes- 
 tine, and some of the most extensive commercial enterprises 
 are dependent upon fermentations brought about by the aid 
 of these small organisms. 
 
 HOW GERMS PRODUCE DISEASE. 
 
 The question naturally arises, just in what manner these 
 bacteria produce their respective diseases in the body. Is 
 it due to the depredations of the bacteria themselves, or 
 some product which they produce while in the body? No 
 one will question the fact that much harm results from the 
 actual destruction of tissues literally eaten up by these 
 germs. The gradual disintegration of the consumptive 
 lung is more than sufficient evidence, but it is now gener- 
 ally conceded that the injurious effects of these bacteria are 
 due to poisons which they elaborate in the body rather 
 than to their own immediate presence. These poisons 
 directly attack the tissues, and to their effect are due the 
 symptoms of the disease. It has been possible to extract 
 these poisons from animals afflicted with certain diseases 
 and then to inject this poison, free from the bacteria which 
 produced it, into healthy animals, there to reproduce all the 
 symptoms of the disease in question. It is probable that 
 these poisons are similar to the alkaloids of the organic 
 chemist. 
 
 THEORIES OF IMMUNITY. 
 
 The explanation of the fact that the first attack of many 
 infectious diseases renders the person immune from a 
 
TEACHING OF PHYSIOLOGY AND PUBLIC HEALTH. 39 
 
 succeeding one is not yet at hand. A number of inter- 
 esting theories have been advanced to account for this 
 immunity. Pasteur held that there was a special food in 
 the body which these bacteria needed and which was com- 
 pletely used up in the first attack, thus making the second 
 one impossible; but as the blood changes in composition 
 so rapidly it seems impossible that such elements would not 
 again soon be introduced if they were normally in the 
 blood. Then Chauveau ventured the opinion that these 
 germs produce excretions which finally render the blood 
 unfit for them to live in and thus prevent the recurrence of 
 the disease. When we remember how quickly the system 
 normally throws off foreign poisons it seems hardly possible 
 that the body should retain these excretions for such a long 
 time as the immunity seems to last. L,ater, Grawitz pro- 
 posed the idea that the outcome of a disease was the out- 
 come of the battle waged between the bacteria in our bodies 
 and the living tissues, that if the tissues managed to 
 obtain the upper hand and destroy the bacteria the training 
 so acquired would increase their vital energy and resisting 
 power and so cut short a second attack, something as a 
 regiment of veterans would be less easily overcome in battle 
 than a corps of raw recruits. Succeeding this Buchner 
 gave as his explanation that in a first attack the places at 
 which the bacteria were introduced became more resistant 
 and so prevented the introduction of succeeding ones. This 
 went on the supposition that all kinds of bacteria had their 
 specific places through which alone they could enter the 
 body. It is not necessary to state that this explanation 
 found little support. 
 
 Then came the now celebrated theory of Metchnikoff , 
 which holds that the white corpuscles of the blood and 
 lymph are scavengers going up and down between the tis- 
 sues, and picking up foreign particles wherever found. 
 This picking up is nothing more than the process of amoe- 
 boid digestion. This theory is now very generally accepted, 
 and observations clearly show that these corpuscles do take 
 
40 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 into themselves under some circumstances foreign particles. 
 Thus if a pus cell from a wound be examined it is usually 
 found to contain many foreign particles, usually bacteria. 
 The corpuscles with their load of included bacteria are then 
 probably sent to the spleen or liver, there disintegrated, and 
 the injurious products eliminated from the body in accord- 
 ance with the regular physiological process. This theory 
 explains in a very interesting way the phenomena of the 
 inflammation of wounds and the gathering of sores. In a 
 wound such as an open cut the bacteria of the air fall at 
 the first exposure and there in the rich nutritious blood 
 begin a course of active development. Soon, however, 
 white corpuscles congregate around the wound, the blood 
 usually following through the openings in the capillaries 
 caused by their migrations, hence the redness. These cor- 
 puscles move regularly towards the infected center, remov- 
 ing the germs as they progress, until finally all of the cor- 
 puscles with their incepted germs meet in the center of the 
 wound there to be, possibly mechanically, pressed out as 
 pus. It is known that wounds entirely protected from germ 
 contamination will not inflame at all, and surgical opera- 
 tions of the most violent character with modern antiseptic 
 improvements may be carried out without any appreciable 
 amount of inflammation. Possibly the added vitality that 
 is supposed to come to these amoeboid cells in their first 
 successful battle enables them to cut a second venture 
 short. That these corpuscles are concerned in the elimina- 
 tion of foreign particles from the blood is probably above 
 question, but that this explains all the phenomena of 
 immunity is another matter. 
 
 The most recent view and possibly the best substan- 
 tiated one of all is the acclimatization theory, which tries 
 to explain that we are immune from a second attack by 
 having become accustomed or acclimated to the poisons in 
 the first attack. To use a not very elegant analogy, it is 
 like the boy who can smoke his second cigar without getting 
 sick, because he has been somewhat hardened by the first 
 
TEACHING OF PHYSIOIjOGY AXD PCBUC HEALTH, 41 
 
 '.' -;.:.i::.:: :: .- :-r:>.:; -;;; > 
 to be treated to a terrific dose of nicotine would be to grad- 
 ually more and more accustom himself to the injurious 
 : : 
 
 Just what may be accomplished by gradually inuring the 
 body to poisons is remarkable. By slowly increasing doses, 
 sir -;;.:.::-. e r_:iy zilly be ^ n; ::; .in: ;:::;:.$ >; I.i: s e :;::.: 
 they would have produced instant death if administered for 
 the first time. Arsenic eaters are able to take amounts of 
 that drug which would be out of the question by one who 
 had never taken it before. Passably this view explains the 
 philosophy of vaccination and anti-toxine methods. As 
 gwfty one knows vaccination for smallpox consists in intro- 
 duong a weakened form of that virus into the body which 
 there produces a mild attack of smallpox. In this attack 
 the poison is developed so slowly and gradually that the 
 body can adjust itself to these increasing amounts and a 
 succeeding attack of the violent form, would thus not be 
 able to strike down the energies of the body at the very 
 onset before possibly the body had had time to overcome the 
 dangerous intruder. In the anti-toxine method now used in 
 diphtheria the seium of a horse which has had diphtheria,, 
 and in which blood, therefore, is found some of this diphthe- 
 retic poison, is injected in small doses into the body of the 
 patient suspected of developing diphtheria. The poison so 
 injected in small, or slightly increasing doses gradually 
 allows the body to adjust itself to it so that later on wtien the 
 disease has produced greater quantities of this same poison 
 the tissues have been acclimated to it to such an extent that 
 the poison does not prove fatal. As the bacteria them- 
 selves can not live when the amount of the poison which 
 they have formed becomes too great it may be too, that the 
 introduction of some of this poison into a patient's blood 
 will serve to check the growth of the microbes. 
 
 PROBLEMS, 
 
 Hie specific germs of measles, yellow fever, and even 
 
 :: . : ye: : .ef.::::e~.y k:;. -,-.-_-.. ": ..: :: ::: :;:c 
 
42 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 success bacteriologists have had in studying other infectious 
 diseases we may reasonably expect light on these points in 
 the not very remote future. 
 
 PRACTICAL GUIDANCE. 
 
 It was not the province of this chapter to discuss at any 
 length bacteriological problems. Its purpose was to call 
 attention to a few scientific facts which should form the 
 basis for a sensible appreciation of sanitary and hygienic 
 laws; and when we remember that most people die with 
 some form of infectious or contagious disease, surely no 
 excuse is needed to press such information upon the atten- 
 tion of the common -school teacher who has the greatest 
 opportunities for distributing it. It is intended that the few 
 points here given shall lead to such a general and interested 
 observance of all rules and regulations to advance the gen- 
 eral health, that disease may become more infrequent, and 
 the length of human life and happiness thereby materially 
 increased. Possibly nothing better can be done in this case 
 than to quote here the rules and regulations recently issued 
 by the Indiana State Board of Health, which are so clear and 
 to the point that they are given without further comment: 
 
 Explanation. 
 
 " Simultaneously with the annual opening of the public schools, diph- 
 theria, measles, mumps, scarlet fever and many other diseases usually 
 increase. This is caused by the congregating of the pupils. They mass 
 together and contact spreads infection. Some few pupils may have just 
 recovered from a communicable disease, or they may be from families 
 that have been smitten, and, being infected, they transmit disease to those 
 who are susceptible. It is reasonable to assume that the suddenly imposed 
 confinement in the schools after a period of freedom frets the children for a 
 few days, causing more or less nervousness and so resistance is temporarily 
 lowered. In this way susceptibility may be increased, and sickness may 
 more readily follow. To do all that is possible to prevent the usual school- 
 opening increase in illness is the object of these rules. 
 
 " It is ordered in the rules that desk tops and banisters be washed with 
 soap and water and afterward be treated with a disinfectant. This is 
 required because disease germs may be planted upon exposed desk tops and 
 banisters by infected persons, and, being transferred by the children's hands 
 
TEACHING OF PHYSIOLOGY AND PUBLIC HBAI/TH. 43 
 
 to their mouths, disease results. The washing and disinfecting will do much 
 to prevent infection from this source. 
 
 " Open water buckets and large tin cups are condemned because the 
 dipping of water with cups which are used by many introduce spittle into the 
 supply ; and, besides, open buckets catch dust and dirt. Diphtheria, 
 diarrhoea, sore mouth and other complaints have been transmitted in this 
 way. This source of disease may be avoided to a considerable degree by 
 supplying a covered tank with a large free-flowing faucet and a small cup. 
 The opening of a large faucet will furnish a strong stream, which will sud- 
 denly fill the cup and wash the saliva from the edge. Ample drainage must 
 be provided for carrying away the waste water. 
 
 " Slates are condemned because of their uncleanliness. Writing and 
 figures being obliterated as they frequently are with spittle, and as the damp 
 slates readily collect dust, the danger of the transmission of disease in this 
 way is very great. Small children generally place pencils and pens in their 
 mouths, and if these articles are promiscuously distributed without being 
 sterilized, as the rules direct, infection may result. The collecting of pencils 
 seems necessary to always insure one to each pupil. 
 
 "Spitting is prohibited because it is a possible source of disease, is 
 filthy and is unnecessary. 
 
 *' It may seem shocking and unnecessary to many to exclude con- 
 sumptives from the schools, but when we stop to think that tuberculosis 
 causes one in every seven deaths, killing more people annually than cholera, 
 smallpox, diphtheria, scarlet fever and yellow fever combined, then it is time 
 to lay aside that sentiment and pity which would perpetuate disease and 
 death, and take on those qualities in that higher form which makes them 
 forces for more abundant and better life. 
 
 " These rules may seem trifling and unnecessary to those who have not 
 given consideration to modern sanitation, but the teacher more than any other 
 public officer may secure the physical well-being of the pupils as well as their 
 intellectual advancement. 
 
 " It is hoped that all the school authorities of the State will promptly 
 enforce these rules." 
 
 Special lliiles. 
 
 RULE i. All teachers of public, private and parochial schools, all 
 county, city and town health officers and all school authorities shall refuse 
 admittance to the schools under their jurisdiction of any person from any 
 household where contagious disease exists, or any person affected with any 
 evident or apparent communicable disease, or any person who may recently 
 have been affected with diphtheria, membranous croup, scarlet fever, whoop- 
 ing cough, contagious skin disease, measles or other communicable disease, 
 until first presenting a certificate signed by a reputable physician stating that 
 danger of communicating such disease is past, and said certificate is approved 
 and indorsed by the Health Officer in whose jurisdiction the person may 
 reside. 
 
 RULE 2. School Commissioners, School Trustees in cities "and towns, 
 nd Township Trustees, and all authorities governing private or parochial 
 
44 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 schools, shall have the school houses under their control put in sanitary con- 
 dition before school is opened and kept so throughout the year. Floors shall 
 be scrubbed, windows cleaned, desks and all woodwork washed with soap 
 and water and treated with a disinfectant. Windows shall be in repair, so 
 that ventilation may be made perfect. Heating apparatus shall be efficient 
 and in good order, and dirty walls and banisters made clean. Banisters and 
 tops of desks shall be washed with soap and water and treated with a disin- 
 fectant once each week.* 
 
 RULE 3. School Commissioners, School Trustees in cities and towns, 
 and Township Trustees, shall provide small drinking cups not to hold over a 
 gill. Buckets or pails to dip from are condemned, and reservoirs or tanks of 
 ample size having large, easy acting, free flowing faucets shall be provided. 
 When water is drawn direct from public water pipes or pumps, reservoirs or 
 tanks are, of course, not required. Ample drainage facilities for waste water 
 shall be provided and the pupils directed to allow the cups to flow over when 
 the water is drawn. Drinking cups shall be cleaned and sterilized daily. 
 
 RULE 4. Slates are condemned. Paper tablets or pads shall be used 
 instead. Riveted metal boxes of tin or galvanized iron with hinged covers 
 and of proper size, or other approved apparatus to subserve the same purpose, 
 shall be provided for each school room. These are to receive pens or pencils, 
 which must be collected from the children each day, and shall not be again 
 distributed until box or apparatus with the pencils and pens have been steril- 
 ized by heating in an oven at or above boiling heat for one-half hour. 
 School Commissioners and School Trustees in cities and towns, and Town- 
 ship Trustees, are directed to enforce this rule. 
 
 RULE 5. Heating and ventilating shall be looked after with great care. 
 Every school room shall be provided with a thermometer and a temperature 
 not exceeding 75 Fahrenheit, nor less than 65 be maintained during school 
 hours. School Commissioners and School Trustees in cities and towns, and 
 Township Trustees, are directed to enforce this rule. 
 
 RULE 6. Janitors when sweeping shall use damp sawdust or slightly 
 sprinkle, in order to prevent dust. Dusting shall be done with damp cloths. 
 School Commissioners and School Trustees in cities and towns, and Town- 
 ship Trustees, are directed to enforce this rule. 
 
 RULE 7. The water supply shall be pure and wholesome, and closet or 
 privy facilities shall be unobjectionable. School Commissioners and School 
 Trustees in cities and towns, and Township Trustees, are directed to enforce 
 this rule. 
 
 *The disinfectant for treating desk tops, banisters, etc., and for use in urinals and 
 closets may be cheaply made by the following formula and kept on hand in any quantity 
 desired. To make ten gallons: Chlorinated lime. 40 ounces; soft water, ten gallons. 
 Thoroughly stir together and let stand until clear. The undissolved lime will fall to the 
 bottom and the clear supernatant liquid may be used on the desks, banisters, base 
 boards, etc. The fresh milky mixture, as well as the creamy sediment, may be used in 
 urinals, closets and sinks. This disinfectant is not poisonous or dangerous. Chloride of 
 lime of the best quality may be purchased in quantity for 5 cents per pound. The cost of 
 the disinfectant is, therefore, less than 2 cents per gallon. The use of all patent or secret 
 disinfectants is discouraged by the State Board of Health. 
 
TEACHING OF PHYSIOLOGY AND PUBLIC HEALTH. 45 
 
 RULES. Spitting on the floor of any school building is absolutely for- 
 bidden. Teachers and all school authorities are directed to enforce this rule. 
 
 RULE 9. School Commissioners and School Trustees in cities and 
 towns, and Township Trustees, shall not employ teachers who are afflicted 
 with pulmonary tuberculosis or any constitutional contagious disease ; neither 
 shall they permit pupils so affected to attend school ; nor shall they permit 
 filthy or unclean pupils to attend the schools under their control. 
 
CHAPTER IV. 
 GENERAL DEFINITIONS. 
 
 PHYSIOLOGY. 
 
 Physiology is that science which seeks to discover and 
 interpret those phenomena of plants and animals which we 
 are wont to designate as vital. Man himself belongs to the 
 animal world, and his physiology is to be the subject of 
 this book. But as most of our knowledge of human phy- 
 siology is derived from experiments on the lower animals, 
 it would be nearer the exact state of things to call this 
 treatise "Studies in Advanced Animal Physiology. ' ' But the 
 processes and phenomena of life are universal, and the 
 division into even plant and animal physiology is arbitrary 
 rather than natural. There is but one physiology, because 
 there is but one life, although it may be illustrated in vary- 
 ing aspects in different groups of beings. The plant phys- 
 iologist as well as the animal physiologist is addressing 
 himself to the solution of the same problem: What is life, 
 and what are its phenomena ? 
 
 Physiology did not become a science in the real sense 
 of the word until it was discovered that physiological pro- 
 cesses were based upon the general laws of nature, and that 
 vital phenomena were never in conflict with inorganic 
 laws. It was not until even recent years, almost in our 
 own decade, that the old notion of a vital energy was 
 finally abandoned. Formerly a phenomenon of life was con- 
 sidered sufficiently explained when it was said that it was 
 the product of a mysterious vital energy, whose workings 
 need not at all be in conformity with the established laws of 
 nature, and which, consequently, could not form a proper 
 subject for scientific inquiry. But the idea of this vital 
 energy is gone forever, and the fundamental maxim of to- 
 ' (46) 
 
GENERA^ DEFINITIONS. 47 
 
 day is that all physiological phenomena (excepting those of 
 consciousness, possibly) may be explained in terms of 
 chemistry and physics. Thus, what uses organs and tissues 
 have, becomes a physical and chemical question in essence 
 rather than a biological one. 
 
 ANATOMY. 
 
 Before, however, vital phenomena can be studied, it is 
 necessary that we should know the structure of the body 
 exhibiting these phenomena; and so physiology must 
 always be logically preceded by the study of anatomy. As 
 these phenomena usually exhibit themselves in the ultimate 
 biological structure of tissues and organs, anatomy must be 
 extended with the aid of a microscope to the minute struc- 
 ture of every part. The study of this minute structure is 
 designated as histology. 
 
 COMPARATIVE ANATOMY. 
 
 After the structure of the body in question is known, 
 and the function of the various parts established, and pos- 
 sibly even some notion gained as to the care that ought to 
 be exercised in properly preserving it, that is, its hygiene 
 understood, our knowledge is still very inadequate. We 
 must compare the form in question with other animal forms, 
 for the most helpful knowledge of anything is frequently 
 that which deals with the relations of that thing to others. 
 Thus, the study of comparative anatomy helps to materi- 
 ally clarify the individual anatomy in question. 
 
 EMBRYOLOGY. 
 
 
 
 But even this information is inadequate. Even when 
 we have made extended comparisons with the related forms 
 much is still left unsolved until we know how this individual 
 structure came to be. The science which seeks the 
 sequence of changes which finally leads to the adult form 
 from its primitive beginning in the egg, is the science of 
 embryology. 
 
48 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 CLASSIFICATION. 
 
 When all of these data concerning any living thing are 
 known we have the information at hand to properly classify 
 it in the grand system of nature, and to determine in what 
 group or family it finds its natural place. 
 
 A mere glance at the human body reveals a multiplicity 
 of structures, all, however, co-ordinated to one general pur- 
 pose. Thus, we have the system of the supporting tissues, 
 which preserve the form and sustain the weight of the 
 body ; a complicated system of muscles used in performing 
 our movements ; a generally distributed nervous system to 
 exercise a controlling influence, and so on through the many 
 instances which might be here adduced. For arbitrary 
 rather than natural reasons the discussion of human physi- 
 ology is here divided into the following chapters, each of 
 which seeks to treat in detail of some particular system of 
 the body. 
 
CHAPTER V. 
 
 THE BLOOD. 
 
 GENERAL POINTS. 
 
 When an incision is made into a living body there at 
 once streams out a reddish-looking liquid familiar to every 
 one as blood. If this substance, which seems at first sight 
 nothing but a liquid, is examined under a lens, it is found 
 that the liquid itself is not red, but that its color is due to 
 little particles which are colored red, suspended in it." These 
 little particles are the red corpuscles of the blood, whose 
 coloring is due to an iron compound called haemoglobin. 
 So accustomed have we become to the association of red- 
 ness with blood that one feels tempted at first view to deny 
 the existence of blood to those forms whose circulating 
 liquid is not colored red. But the blood of most of the 
 invertebrates is colorless and devoid of this pigment. 
 
 The necessity for blood is too evident to need comment. 
 Tissues in various parts of the body must have nourish- 
 ment brought to them and must have their wastes removed, 
 and these results can be obtained only by having a circu- 
 lating medium which shall answer to this purpose. Some 
 of the few-celled animals so small that the juices may 
 reach all parts of their bodies by the mere process of 
 osmosis, possess no real blood at all. Most of the lower 
 forms are, however, provided with a circulating fluid quite 
 similar to the blood of the vertebrates, except that it con- 
 tains no red corpuscles. The colorless blood of the clam 
 and oyster are matters of common observation. In some 
 of these invertebrates the liquid itself is colored red with 
 haemoglobin, as for instance, in the earth worm, whose 
 reddish blood vessels are easily seen through the transpar- 
 ent skin, while in certain exceptional forms actual colored 
 4 (49) 
 
50 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 elements containing haemoglobin, no doubt identical with 
 blood corpuscles, do really occur. It is a matter of interest 
 that coloring matters other than haemoglobin occur. Thus 
 in the cuttlefish, some snails, and the lobster, a bluish com- 
 pound containing traces of copper, called hsemocyanin, 
 colors the blood. 
 
 The white corpuscles are distributed throughout the blood 
 of the invertebrate world. When we come to the verte- 
 brated or back-boned animals, there are in addition to these 
 white corpuscles, the red ones. The lowest vertebrate 
 animal (amphioxus), however, possesses no red corpuscles. 
 
 AMOUNT. * 
 
 The amount of blood in the human body has been esti- 
 mated by a number of observers to be about one-thirteenth 
 of the weight of the body, thus making for the average 
 person from twelve to fifteen pounds of blood, and calcu- 
 lating a pound of blood to measure about a pint, would 
 give us in the neighborhood of one and one-half gallons of 
 this fluid. This amount of blood is at any one time dis- 
 tributed as follows: One-fourth of it is in the heart and 
 the neighboring large blood vessels, one-fourth of it is 
 found in the liver, one-fourth in the capillaries of the vol- 
 untary muscles, the remaining one-fourth being distributed 
 over the rest of the. body. If fresh blood drawn from the 
 veins or arteries of an animal be allowed to run into a 
 vessel and there prevented from clotting, in a way to be 
 noted later, the suspended particles or corpuscles being a 
 little heavier than the liquid, sink to the bottom and occupy 
 about fifty per cent, of the volume in their wet condition. 
 Examination of these solid particles of the blood reveals 
 two kinds of corpuscles one the red corpuscle already 
 mentioned, the other the colorless corpuscle, sometimes 
 called lymph corpuscle or leucocyte. The existence of a 
 third corpuscle, that of the placques or blood tablets, as 
 a distinct structure, is questioned by some physiologists, 
 and a further discussion of this element of the blood is 
 
THK BLOOD. 
 
 51 
 
 Fig. 7. HUMAN BLOOD. MAGNIFIED ABOUT 1000 DIAMETERS. (After Schafer.) 
 r, r, single red corpuscles seen lying flat; r', r' , red corpuscles on their edge and 
 viewed in profile; r", red corpuscles arranged in rouleaux; c, c, crenate red corpuscles; 
 p, a finely granular pale corpuscle; g, a coarsely granular pale corpuscle. Both have two 
 or three distinct vacuoles, and were undergoing changes of shape at the moment of ob- 
 servation; in g, a nucleus also is visible. 
 
 included in the explanation of the phenomena of coag- 
 ulation. 
 
 THE RED COEPUSCLES OF THE BLOOD. 
 
 1. Their Size and Form. The red corpuscles of human 
 blood are biconcave, circular disks having a diameter of 
 g-Toif inch. They have no definite membrane and are with- 
 out a nucleus. In fresh blood these corpuscles show a 
 tendency to run together in rows called rouleaux, the 
 reason for which is not definitely known. The peculiar 
 reflection of the light through the concave center gives to 
 them when viewed with a microscope the appearance of 
 having a nucleus. It is, however, a mere optical illusion. 
 The size of these corpuscles as a rule increases as we go 
 down the animal scale. The largest corpuscles are found 
 in the salamander-like proteus, in which they can be actu- 
 ally individually seen by the unaided eye. In Figure 8 
 there are indicated drawn to the same scale, the relative 
 sizes and forms of red corpuscles of several different ani- 
 
52 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 Fig. 8. RED BLOOD CORPUSCLES. (After Frey.) 
 
 1, human; 2, camel; 3, pigeon; 4, proteus; 5, salamander; 6, frog; 7, snake; 8, lani- 
 prey. (a, surface view; l>, side view.) (Drawn on same scale.) 
 
 mals. With the exception of the camel, whose corpuscles 
 are slightly oval, all the corpuscles of the mammals are 
 round. They are further easily distinguished from those of 
 the lower animals, as in the latter the red corpuscles 
 possess a distinct nucleus. It is interesting that in the em- 
 bryonic state of the human being nucleated corpuscles 
 occur. 
 
 2. Color. When seen singly the corpuscles do not 
 appear red but have a yellowish tint, sometimes shading 
 over into a greenish. This is due, of course, to the dilution 
 of the coloring matter when a single corpuscle is looked at. 
 But the color of ordinary blood is not alone due to the 
 actual color of the haemoglobin, but also to the reflection of 
 the light from the innumerable little concave mirror-like 
 surfaces of these corpuscles. This explains why blood 
 becomes "laky" in color when the coloring matter is 
 extracted from the corpuscles and dissolved in the liquid. 
 Such laky blood becomes transparent and dark in color. If, 
 on the other hand, certain mineral salts be added to the 
 blood which cause the corpuscle to shrink, the blood 
 
THE BLOOD. 53 
 
 becomes much brighter in color, because owing to .the 
 shrinkage of these corpuscles, the light which is reflected 
 from them is correspondingly concentrated. 
 
 3. Number. Careful and repeated counts of the num- 
 ber of red corpuscles contained in human blood have been 
 made showing that in a cubic millimeter of blood (small 
 drop) there are in males about five millions, and in females 
 about four and one-half millions. This number varies a 
 little; it is decreased after a hearty meal, after severe hem- 
 orrhages, after prolonged fasting, or in such sickness as 
 leukaemia, in which the decrease in number explains the 
 general paleness of complexion. The number to the cubic 
 millimeter varies, however, greatly in different animals. In 
 the form proteus with its huge corpuscles, there are thirty- 
 six thousand ; in the frog four hundred thousand ; in birds 
 three million six hundred thousand, while in the llama, of 
 South America, it reaches the enormous number of fourteen 
 millions. Compared with the white corpuscles, in human 
 blood there are from four to five hundred red to one white. 
 
 4. Surface. In spite of their small size such large 
 numbers give a combined surface which is surprisingly 
 large. Taking the amount of blood in the average body as 
 about six pints, the total surface of all the contained cor- 
 puscles would not be far from four thousand square yards. 
 This would be a surface that would require more than 
 eighty steps to walk across it at its shortest distance. It is 
 a surface over twenty-five hundred times greater than the 
 entire surface of the body. As about one hundred and sev- 
 enty-six cubic centimetres of blood pass into the lungs in 
 each second of time, it means that a corpuscle surface of 
 not much less than one hundred square yards is exposed to 
 the action of the oxygen in this short space of time. Does 
 this not help one to understand the rapidity with which the 
 oxygen is taken up and distributed as well as the amount 
 carried? 
 
 5. Composition. The essential element of the red blood 
 corpuscle is the red haemoglobin imbedded, so to speak, in 
 
54 ADVANCED STUDIES IN PHYSIOLOGY. 
 
 the. frame work or body of the corpuscle, which latter is 
 called the stroma. As haemoglobin is soluble in many 
 liquids it can easily be dissolved out of the corpuscle and 
 the colorless body, or stroma left. Haemoglobin possesses 
 in a remarkable way the ability to unite with oxygen when 
 that gas is plentiful, and to give it up again when the gas 
 is not plentiful. It is this property which gives to it its 
 important function in the body. A large amount of oxygen 
 is required in the body to keep up the relatively high and 
 constant temperature, and to make possible the large 
 expenditures of energy which are necessary to maintain 
 life. The mere liquid plasma of the blood would be per- 
 fectly unable to carry this oxygen in sufficient amounts. 
 While this plasma, like water, which is its main constit- 
 uent, can dissolve a little oxygen we know that fishes 
 derive their oxygen out of the water in which it is dissolved 
 our own experience shows us how limited this supply is, 
 and how constantly water must be renewed in aquaria to 
 make possible the existence of life in it. It is estimated 
 that the haemoglobin carries about nine-tenths of all the 
 oxygen. It is not necessary to call attention to the result 
 that would follow doing away with this haemoglobin and so 
 reducing the oxygen supply ninety per cent. 
 
 The Oxygen -carry ing Property of HcemogloUn. 
 
 The at first puzzling question, why the haemoglobin 
 should unite with the oxygen in the lungs and then give it 
 up in the tissues and not attempt at times to carry the oxy 
 gen from the tissues to the lungs, is easily explained on 
 physical and chemical grounds. Haemoglobin will combine 
 with the oxygen when it is exposed to an atmosphere that 
 has a pressure of at least one-sixth of the normal atmos- 
 pheric pressure. Exposed to an atmosphere less than one- 
 sixth of the normal pressure it not only refuses to unite 
 with oxygen, but actually disunites with the oxygen which 
 it already has and sets it free. Now we know that the 
 atmosphere is composed of about four-fifths of nitrogen and 
 
THE BLOOD. 55 
 
 one-fifth of oxygen, and as the combined pressure of these 
 two gases is, generally speaking, fifteen pounds to the 
 square inch, it is evident that the oxygen part of that pres- 
 sure is one-fifth of that, or three pounds, while in an atmos- 
 phere diminished to one-sixth of fifteen pounds, or two and 
 one-half pounds, the oxygen part of this would be one-sixth 
 of three pounds, or one-half pound. 
 
 To state it again, haemoglobin will unite with oxygen 
 when it is exposed to an oxygen pressure of one-half pound 
 or more, and will not only refuse to unite, but actually dis- 
 unite when it is exposed to an oxygen pressure less than 
 one-half pound. As the oxygen pressure in the lung is 
 three pounds, it explains the union with that gas there, 
 while the fact that it gives up its oxygen in the tissues is 
 accounted for by the simple physical reason that the oxygen 
 pressure in the tissues is less than one-half pound, as the 
 oxygen there is being continually used up by the hungry 
 tissues. Why this haemoglobin should be " boxed up " in 
 corpuscles and not simply dissolved in the plasma of the 
 blood, is evident. It could carry as much oxygen in one 
 case as in the other; but as much of the plasma soaks 
 through the capillaries, becomes lymph, bathes the tissues, 
 and only after a considerable time is finally poured back 
 into the blood stream, it means that any haemoglobin dis- 
 solved in this would have been able to carry but one load, 
 instead of a hundred, possibly, by being whirled along with 
 the blood stream. 
 
 When combined with oxygen (then called oxyhaemo- 
 globin) it is of a bright red color, the color of arterial blood. 
 Haemoglobin is an albuminous compound characterized by 
 a relatively large amount of iron, although in actual quan- 
 tity the iron contained is less than one-half of one per cent. 
 This iron, however, plays a very important role in the 
 oxygen-carrying process. The rapidity with which ordi 
 nary iron unites with oxygen, or as we say, " rusts," may 
 account for its presence here. 
 
56 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 Blood Crystals. 
 
 As before stated, haemoglobin can be dissolved out of 
 a corpuscle by adding to the blood an excess of water, 
 chloroform, or other solvent. If to such a solution, made 
 icy cold, some alcohol be added, the haemoglobin will 
 separate, and fall to the bottom as well-defined red crystals 
 called blood or haemoglobin crystals. It is exceedingly 
 
 * . . - 
 
 *' - 
 
 Fig. 9. HEMOGLOBIN CRYSTALS. 
 1, a typical crystal. Fig. 10. HEMIN CRYSTALS. 
 
 difficult to preserve these crystals, as they disintegrate 
 easily. 
 
 Under ordinary circumstances haemoglobin disintegrates ' 
 into an albumen called globulin, and into a dirty brown 
 substance called haematin. Hence the dirty brown red 
 appearance of old stains and the discoloration of the skin 
 which follows a severe bruise and is familiar to every boy 
 as a " black eye." The discoloration of the skin is due to 
 the blood which has stagnated in the bruised tissues, the 
 haemoglobin of which has disintegrated into a substance 
 almost identical with haematin called haematoidin. 
 
 Sometimes it becomes desirable to establish the identity 
 of stains believed to be blood stains. It is not at all un- 
 usual in legal proceedings incident to murder trials, to 
 attempt to prove that certain spots or stains are really 
 blood stains. Such a proof is easily made. If from the 
 old blood stain some of this dark haematin be removed to a 
 
THE BLOOD. 
 
 57 
 
 glass slip, a crystal of common salt added, and a drop of 
 glacial acetic acid poured over it, the hsematin will unite 
 with some hydro-chloric acid liberated, and form character- 
 istic crystals called haemin crystals. 
 
 The Spectrum of Hemoglobin. 
 
 Another characteristic property of haemoglobin is its 
 absorption lines when viewed with a spectroscope. When 
 ordinary white light is viewed with a spectroscope it is 
 broken up into those characteristic colors with which we 
 are familiar as the spectrum. If, now, such a beam of 
 ordinary light be passed through a solution of oxyhsemo- 
 globin before reaching the spectroscope, the spectrum is not 
 complete; but there appear two very dark black lines in 
 that part of the spectrum where the red shades over into 
 the yellow and that into the green. If now the oxygen be 
 taken out of the oxyhsemoglobin and a ray of light passed 
 through this venous haemoglobin be examined, there 
 appears in the spectrum one dark band, in position almost 
 exactly between the two stripes of the oxyhsemoglobin. 
 This single absorption band for the haemoglobin, and the 
 two bands for the oxyhaemoglobin are so characteristic that 
 
 Oxyhaemogflobin. 
 
 CO- haemoglobin. 
 
 Fig. 11. SPECTRUM OF HEMOGLOBIN AND ITS COMPOUNDS. (C, D, E, etc., Fraunhofer 
 lines.) 
 
58 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 the presence of very small amounts of blood in any solution 
 can be established beyond a donbt. 
 
 Haemoglobin shows a strong affinity for carbon monox- 
 ide, the poisonous substance which forms a large part of 
 ordinary illuminating gas. This affinity is in fact so strong 
 that when the haemoglobin has once united with the car- 
 bon monoxide it is almost impossible to displace it. This 
 fact renders gas poisoning extremely dangerous, for even 
 when such a patient is brought into the fresh air, he is 
 unable to get oxygen, because the haemoglobin will not let 
 go of its carbon monoxide, and so he is liable to suffocate 
 even in an oxygen atmosphere. Haemoglobin so united 
 with carbon monoxide has a bright arterial appearance, 
 and persons who have died of gas suffocation maintain the 
 bright arterial color even long after death. Such a corpse 
 retains a redness of skin which makes it at first sight seem 
 almost impossible that the individual should be dead. As 
 accidents of gas poisoning are not at all infrequent in 
 cities, it is worth while to know how to establish such a 
 cause of death. 
 
 In addition to the haemoglobin, which amounts in a 
 dried corpuscle to over, ninety per cent., there is an albu- 
 men called globulin, further traces of fat, and of two organic 
 substances, cholesterin and lecithin (to be studied further in 
 later chapters), and finally salts of potassium, phosphates, 
 and traces of ordinary common salt. In the live condition 
 of the corpuscle a large quantity of water enters into its 
 constitution. 
 
 6. Consistency. In consistency the red corpuscle seems 
 to be made up of a homogeneous, jelly-like substance 
 which possesses remarkable powers of elasticity. In exam- 
 ining the blood streaming through the blood vessels one 
 may find here and there a corpuscle caught where an artery 
 divides, very much stretched out of its natural shape, yet 
 springing back to its original form as soon as the stress is 
 over. This is no doubt a valuable property in enabling the 
 
THE BLOOD. 
 
 59 
 
 corpuscles to elbow their way through the delicate capil- 
 lary channels. 
 
 7. The Origin of the Red Corpuscles. One of the 
 most difficult chapters in physiology is that dealing with 
 the origin of the red corpuscles, and a number of conflict- 
 ing theories are even now seeking support. To trace the 
 origin of the red corpuscles it is necessary to study the 
 blood of an animal before its birth. Such examination of 
 human embryos shows that in early uterine life the red cor- 
 puscles are nucleated and possess the power of amoeboid 
 movement. They are, in fact, very similar to the white 
 corpuscles of the blood except that they are colored with 
 haemoglobin. These corpuscles arise in this way: 
 
 Some of the connective tissue cells become somewhat 
 elongated and have their nuclei divide up into many 
 
 Fig. 12. EMBRYONIC DEVELOPMENT OP BLOOD CORPUSCLES IN CONNECTIVE TISSUE 
 
 CELLS, AND THE TRANSFORMATION OF THE LATTER INTO BLOOD CAPILLARIES. (After 
 
 Schafer.) 
 
 , an elongated cell with fluid protoplasm and containing corpuscles which are still 
 round; 6, a more hollowed cell in which the corpuscles have become disc-shaped; c, the 
 manner of union of such a tissue cell (c ft) containing here only one corpuscle with an 
 already formed capillary, (a and c from a new-born rat, 6 from a fostal sheep.) 
 
 smaller nuclei. These nuclei soon seem to round them- 
 selves, become tinted red with haemoglobin, and are in fact 
 the nucleated red corpuscles of the embryo. The connective 
 
60 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 tissue cells in which by a nuclear division they were formed, 
 elongate very rapidly and soon touch similar elongations of 
 neighboring tissue cells. Where they touch, the partition 
 dividing them melts away and the cavities of the cells are 
 converted into a system of capillaries. This system of 
 capillaries is soon connected with larger blood vessels and 
 so these nuclei find themselves in the general circulation 
 at once. The protoplasm of the tissue cell becomes liqui- 
 fied and helps to form the plasma of the blood. This 
 intra-cellular mode of development of red blood corpuscles 
 does not continue after birth, unless it be in animals such 
 as the rat, which are born in a very immature condition. 
 For this reason we must in the adult body seek for their 
 origin elsewhere. 
 
 It is now fairly well established that in adult life they 
 arise in the red marrow of the bones. In this red marrow 
 there may be observed corpuscles which seem identical with 
 the nucleated red corpuscles of the embryo. In fact, it 
 seems probable that the nucleated embryonic corpuscles 
 migrating into the red marrow of the bones have been the 
 lineal ancestors of the nucleated red corpuscles in the adult 
 marrow. These corpuscles seem to divide like ordinary 
 
 < Q fe 
 
 Fig. 13. H^EMATOBLASTS IN PROCESS OF DIVISION. From the red marrow of the Guinea- 
 pig. (After Schafer.) 
 
 corpuscles, possess the power of amoeboid movement, and 
 differ from the ordinary white corpuscles apparently in little 
 more than the possession of the haemoglobin. These 
 nucleated red corpuscles form the ordinary non-nucleated 
 corpuscles of the blood by having the nucleus gradually 
 atrophy and disappear. In fact, according to some observ- 
 ers the nucleus is said to be extruded from the corpuscle 
 and then dissolved, while the non-nucleated body is carried 
 away by the blood stream as a newly created blood cor- 
 puscle. These marrow corpuscles have been called ery- 
 
THE BLOOD. 61 
 
 throblasts or more frequently haematoblasts. The view is 
 held by many observers that these hsematoblasts are not the 
 lineal descendants of the nucleated red corpuscles of the 
 embryo, but are being regularly derived from the ordinary 
 white corpuscles of the blood found in the marrow. 
 
 8. Length of Life of Red Corpuscles. That red cor- 
 puscles are being produced daily in great numbers is 
 evident from the fact that so many are destroyed in the 
 spleen and liver. The coloring matter of the bile is 
 derived from disintegrated red corpuscles, and the number 
 of corpuscles required to colof to such an extent the large 
 amount of bile daily eliminated exceeds calculation. It is, 
 of course, not possible to tell how long a red corpuscle will 
 retain its vitality and properly perform the functions ascribed 
 to it, but there are reasons to believe that the ordinary 
 length of life of such a corpuscle varies from three, to pos- 
 sibly not more than eight or ten weeks. To replace the 
 entire number of corpuscles in the body every two months 
 means a daily manufacture of them by the billions. In 
 fact, it seems a little like a fairy story to be told that for 
 every beat of the pulse nearly twenty millions of these 
 organisms die. Such a wholesale manufacture of them is 
 to be explained by the rapidity with which these haemato- 
 blasts are supposed to divide. The older view that red cor- 
 puscles were directly derived from the white ones, or from 
 the blood tablets, has been abandoned as not at all in 
 accordance with observed facts. The red or blood-forming 
 marrow is found in the extremities of most of the bones of 
 the trunk, and in the bones of the skull. It is interesting 
 that when the blood -formation process is very active the 
 yellow marrow itself may be changed into red through all 
 the bones. 
 
 9. The Destruction of the Red Corpuscles. The fact 
 that corpuscles are short lived brings up naturally the ques- 
 tion as to the manner of their destruction and elimination. 
 As the pigments of the bile are derived from broken 
 down corpuscles there is no doubt that many of them are 
 
62 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 disintegrated in the liver. Just in what manner we do not 
 know. In the spleen, too, there occur so-called blood-cor- 
 puscle-containing cells, that is, large white corpuscles which 
 seem to have eaten up decrepid corpuscles and to be in the 
 process of digesting them. Just how these cannibal cells 
 are able to single out worn-out corpuscles and leave normal 
 ones untouched is probably accounted for by the fact that 
 old corpuscles are sticky, and so remain attached, while 
 normal ones are carried on with the blood stream. 
 
 THE WHITE OE COLORLESS CORPUSCLES. 
 
 Much less numerous than the red are the white cor- 
 puscles of the blood. These corpuscles may be taken as 
 types of a living cell, possessing in some degree all the 
 properties that characterize ordinary one-celled animals. 
 As given before, the number of the white as compared with 
 that of the red is about one to three or four hundred. They 
 vary much in size, many of them are even smaller than 
 the red corpuscles, others differ but little from them, while 
 the larger ones measure from one and one-third times 
 to twice the size of the red. They possess no cell wall, but 
 seem composed throughout of a granular kind of prote- 
 
 Fig. 14. FORMS OF A WHITK BLOOD CORPUSCLE SKETCHED AT INTERVALS DURING ITS 
 
 AMCEBOID MOVEMENTS. 
 
 a. Beginning of movement; b, formation of pseudopodia; c, the nucleus itself changes 
 its form; d, the corpuscle at last dead. 
 
THE BLOOD. 63 
 
 plasm in which is imbedded the large, clearly discernible 
 nucleus. Their most remarkable property is that of being 
 able to throw out processes called pseudopodia and to wan- 
 der from place to place like the ordinary fresh water 
 amoeba, hence these motions are called amoeboid. By vir- 
 tue of this amoeboid movement the white corpuscles are 
 able to wander through the spaces between the tissues, and 
 even to bore their way through the delicate walls of the 
 capillaries. When such a phenomenon is viewed under a 
 microscope it is seen how a corpuscle will attach itself to 
 the side of the capillary, probably by virtue of its natural 
 stickiness. Soon there is seen projecting on the outside 
 of the capillary a tiny little process which gradually becomes 
 larger at the expense of the corpuscle until finally the full 
 corpuscle has thus wedged its way through. This phenom- 
 enon of wandering out of capillaries is especially marked 
 in the early stages of inflammation when the holes so made 
 through the capillaries frequently become so large and so 
 numerous as to permit the red corpuscles to be mechan- 
 ically forced through, and thus for the blood itself to seep 
 into the tissues, hence no doubt the redness and the swell- 
 ing of the inflammation. By virtue of this movement they 
 are further able to pick up foreign particles by flowing 
 around the particle until it is included in the cell, a method 
 exactly similar to that of the amoeba when it secures its 
 food. Foreign particles are thus literally eaten up by these 
 cells. 
 
 As mentioned in a previous chapter, it is highly prob- 
 able that bacteria which find their way into the blood are 
 thus mechanically picked up and so rendered harmless. 
 Particles injected into the blood of transparent animals, 
 such as the water flea, being picked up by the colorless 
 corpuscles of the blood, may be watched under the micro- 
 scope. They probably serve in the disintegration of old 
 tissues, for it is possible to find in the blood of some 
 amphibians when they are losing their tails, such as the 
 change from the tadpole to the frog, some of these cells 
 
64 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 actually containing bits of muscle and nerve of the disin- 
 tegrated organ. Being thus able to wander up and down 
 the avenues of the body, in, between, and through the tis* 
 sues, they have been called wandering cells. For this 
 reason these corpuscles are not at all confined to the 
 blood, but occur with a similar frequency in lymph, in the 
 marrow of bones, and probably the so-called connective 
 tissue corpuscles are but slightly differentiated white cor- 
 puscles. Their migration in the formation of pus has been 
 mentioned in a preceding chapter. 
 
 It seems probable that these corpuscles are instrumental 
 in absorbing the fat from the intestines by mechanically 
 carrying it from the villi into the lacteals, while the fat cir- 
 culating in the body which is not needed by the tissues is 
 carried by such corpuscles and stored away in different 
 parts forming adipose tissue. Such fat-eating cells, some- 
 times called plasma cells, may become so distended with 
 fat that the cell body is reduced to a slight envelope sur- 
 rounding the huge fat globule. White corpuscles possess the 
 power to multiply by the process of ordinary cell division. 
 This may occur any place in the body, e. g. in the blood, 
 but more regularly occurs in what are known as lymphatic 
 glands . 
 
 Lymphatic glands are not glands in any true sense of 
 that term, but are large aggregations of white corpuscles 
 housed in a capsule of connective tissue. The fact that 
 through such capsules lymphatic vessels flow, has given 
 them the name of lymphatic glands. In these glands the 
 cells grow and divide, and by the lymph stream circulating 
 through it the additions are carried out into the body. Such 
 lymphatic glands are familiar to us as -the tonsils, the thy- 
 mus gland, the patches of Peyer, and numerous little lym- 
 phatic nodules distributed all over the body. In the spleen, 
 too, these corpuscles seem to be formed in an analagous 
 way. 
 
 The fate of these corpuscles is difficult to determine in 
 all cases. There is reason to believe that in addition to the 
 
THE BLOOD. 
 
 65 
 
 cells which are lost in the formation of pus, worn-out cor- 
 puscles are sent to the spleen and the liver to be disinte- 
 grated. That these white corpuscles may take part in the 
 
 a.L. 
 
 \ 
 
 tr. 
 
 Fig. 15. LYMPHATIC GLAND, DIAGRAMMATIC SECTION. (After Sharpey.) 
 , I, lymphatic running- into gland; e, I, same issuing; C, connective tissue capsule; 
 M, tr, connective tissue ground work; I, s, lymph space; corpuscles indicated in part of 
 gland only. 
 
 formation of new tissues and so, becoming differentiated, 
 become muscle or connective tissues, or whatever tissue 
 needed, is stated by many observers but denied by others, 
 and future investigation must settle the dispute. The rela- 
 tion of these corpuscles to the coagulation of blood is men- 
 tioned in the discussion of that process. 
 
 THE BLOOD PLATES. 
 
 Recently attention has been called to a third corpuscle of 
 the blood, the blood plates, blood tablets, or blood plaques. 
 These are corpuscles much smaller than the red corpuscles, 
 are pale or colorless, and in shape vary from the round to 
 the decidedly oval form. Their number has been given by 
 5 
 
66 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 observers as varying from eighteen thousand to twenty-five 
 thousand in a cubic millimeter of blood. They break down 
 with remarkable rapidity as soon as blood is shed, and this 
 
 Fig. 16. BLOOD CORPUSCLES AND PLATELETS IN A SMALL VEIN OF THE RAT'S MESEN- 
 TERY. (After Osier.) 
 
 probably may account for the fact that they were only re- 
 cently discovered. Just where these come from is still a 
 matter of question. By some they are believed to be merely 
 parts of disintegrated white corpuscles, but as they have 
 been observed in the circulating, unharmed blood, this view 
 is probably not correct. Possibly they are nothing more 
 than very small white blood corpuscles. A very important 
 role has been assigned to these little plates, because it is 
 believed by a number of physiologists of rank that in the 
 disintegration of these plates the fibrin ferment is formed, 
 which starts the coagulation of the blood. The fact that 
 they disintegrate so rapidly when the blood is put under an 
 abnormal condition may be for the purpose of setting going 
 at once this process of coagulation. 
 
 Historical. The colorless corpuscles were discovered by Hewson, and 
 their amoeboid motions, in the case of human corpuscles, by Davaine in 1850. 
 The blood tablets were first described by Bizzozero. 
 
 THE BLOOD PLASMA. 
 
 The liquid part of the blood is called the blood plasma. 
 When the corpuscles are removed from it it has a clear, 
 slightly yellowish color, a rather insipid sweetish taste, is a 
 little alkaline in its reaction, and of a specific gravity a little 
 greater than water. Its most striking property is its power 
 to form in a rather short time a so-called clot, and a thor- 
 ough understanding of the composition of this liquid must 
 be preceded by a discussion of the process of coagulation. 
 
THE BLOOD. 67 
 
 THE COAGULATION OF THE BLOOD. 
 
 It is a matter of common observation that when the blood 
 is allowed to stream from a severed vessel into a jar it forms 
 in a very short time a solid, trembling jelly. This happens 
 in the blood of a pigeon almost instantaneously; in the 
 blood of a horse, coagulation is slower, while in man it is 
 medium. Soon the top of the jelly or clot becomes cupped, 
 and a transparent or slightly colored liquid appears over it. 
 This cupping is due to the contraction of the clot, which, 
 continuing, soon pulls the clot loose from the walls of the 
 vessel, and by its continued contraction forces out larger 
 and larger quantities of the liquid just referred to, which is 
 called serum. If the blood had been prevented from clot- 
 ting so rapidly, which might have been done by subjecting 
 it to a cold temperature, the corpuscles would have settled 
 to the bottom, leaving a clear liquid on top. As the white 
 corpuscles are not quite as heavy as the red, they are the 
 last to settle, and there is formed a whitish layer over the 
 top called the "buffy coat." 
 
 As soon as the temperature is raised the blood begins to 
 clot. If blood, however, as it is streaming into the jar be 
 stirred with a stick, or as we say, "whipped," it does not 
 clot regularly at all ; but there may be seen collected on the 
 stick a bundle of threads whose removal from the clot has 
 prevented the "blood from solidifying. If these threads be 
 removed from the stick and carefully washed to free them 
 from entangled corpuscles, they are seen to consist of a 
 mass of stringy matter which has been called fibrin. Evi- 
 dently the clotting of the blood is due to the fonnati6n of 
 these threads all through the clot, in the meshes of which 
 threads the corpuscles are mechanically included. The 
 later contraction of these threads squeezes out the con- 
 tained serum. The difference, therefore, between blood 
 plasma and blood serum is the absence of the fibrin from 
 the latter. Just from what this fibrin comes, and what are 
 the causes that have led to its sudden formation are ques- 
 tions for further study. 
 
68 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 Without going into the many controversies of this prob- 
 lem, the most generally accepted theory is here given in 
 explanation of coagulation ; but it must be remembered that 
 many points are not yet clear, and that the observations of 
 the future may materially change our present notion. Ac- 
 cording to the observations of Alexander Schmidt, later 
 modified by Hammarsten, there are in the blood three main 
 albumens. These are fibrinogen, fibrinoplastin, sometimes 
 called paraglobulin, and serum albumen. The serum 
 albumen takes no part in the coagulation, and its purpose 
 in the blood is to afford a nutritive substance for the tissues. 
 If the blood plasma had no other function, this one albumen 
 would no doubt suffice as a food for all cells of the body ; 
 but as serum albumen clots only when subjected to the 
 action of heat or strong chemical reagents the coagulation of 
 the blood would be impossible, and the danger from hem- 
 orrhages would be always imminent. To prevent this loss 
 of blood other albumens are added. Of these, fibrinogen 
 possesses the property of being easily changed into fibrin 
 under certain definite conditions. To follow these suc- 
 cessive stages in detail let us imagine the finger suddenly 
 cut. As soon as the incision is made into the flesh and the 
 vessels traversing it, the blood finds itself in an abnormal 
 condition and the blood tablets at once begin to disinte- 
 grate, no doubt because they are not able to live under the 
 changed environment. In their disintegration they form a 
 substance which is called fibrin ferment. This fibrin fer- 
 
 Fig. 17. NETWORK OF FIBRIN THREADS RADIATING FROM SMALL CLUMPS OF BLOOD- 
 PLATELETS. (After Schafer.) 
 
 ment at once reacts upon the fibrinogen, causing that to 
 change into fibrin, and thus a clot arises. A somewhat 
 analagous case might be cited in the curdling of milk by 
 
THE BLOOD. 69 
 
 means of the ferment known to every cheese-maker as 
 " rennet." If a little of this rennet be added to even large 
 quantities of milk, in a very short time, by the action of 
 this ferment, the milk curds. It has not been possible to 
 get fibrin ferment pure, but neither have we been able as 
 yet to get rennet in a similar form. This fibrin ferment is 
 probably not produced in a purposive way by the tablets, 
 but results as a mere element of disintegration when they 
 die. Thus the strings of fibrin in the clotted blood existed 
 in the normal blood in the form of the liquid, fibrinogen. 
 This liquid did not change into fibrin, because no fibrin fer- 
 ment is present in normal blood, for the reason that the 
 blood plates do not disintegrate under such normal con- 
 ditions. It has been noted, though, that if a solution con- 
 taining such a ferment be injected in considerable quantities 
 into the veins of an animal, internal coagulation at once re- 
 sults. The presence of fibrinoplastin seems to facilitate this 
 process, although it takes no direct part in it, for the blood 
 serum has as much fibrinoplastin as it had before the clot- 
 ting took place. Just how the substance may facilitate a 
 chemical process without directly taking part in it does not 
 seem clear, but chemistry offers a number of analogies. 
 Fibrinogen will not, however, change into fibrin, even in 
 the presence of the fibrin ferment, unless there be found in 
 solution in it certain salts, especially common salt and the 
 salts of lime. If by adding a little oxalic acid the lime salts 
 are removed from fresh blood it does not coagulate at all. 
 This fact has led some observers to believe that the fibrin 
 was really a compound of the fibrinogen and the calcium, a 
 calcium-fibrinogenate. 
 
 Possibly this matter of coagulation may more easily be 
 understood by following the method of making an artificial 
 clot. If a solution of pure fibrin, such as may be secured 
 from a hydrocele fluid, be put in a vessel, it will not coagu- 
 late instantaneously at all. If now to this fibrinogen traces 
 of common salt and lime salts be added, and then some 
 fibrin ferment introduced, it will begin to coagulate at once, 
 
70 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 and the clot seems in every way a typical normal blood clot. 
 If, however, some fibrinoplastiu had also been added, the 
 clot would have formed a little more quickly, but the final 
 product would not have differed from the first in any notice- 
 able way. 
 
 The question naturally arises why blood does not coagu- 
 ' late in the body? If a blood vessel be removed from the 
 body and the ends tied, the blood will not clot for hours. 
 In fact, it is possible to cut out a turtle's heart and have 
 the blood remain liquid in it for seven or eight days, and 
 yet such blood when exposed in many other ways begins to 
 clot at once. Some have tried to ascribe to the lining of 
 healthy blood vessels a sort of inhibitory function, but this 
 is a mere explanation of words and not of ideas. The point 
 remains that for some yet unexplained reason the fibrin 
 ferment does not seem to have been produced, possibly 
 because the blood plates and corpuscles have not been dis- 
 integrated in a way calculated to produce this ferment. 
 Such abnormal conditions as a bruised blood vessel, expos- 
 ure to the air, contact with foreign bodies, serve to disinte- 
 grate them and so start the process of coagulation. 
 
 While in the discussion so far the formation of the fibrin 
 ferment has been attributed to the blood plates, there is 
 little doubt but that the white corpuscles as well, in their 
 disintegration, form this fibrin ferment. This may explain 
 why in certain diseases of the body in which corpuscles 
 disintegrate in large numbers internal clots have been 
 formed, interrupting the circulatory course and so causing 
 death. It is not an infrequent observation too that in per- 
 sons suffering from blood poisoning, a disease in which 
 large quantities of corpiiscles are lost, there is a tendency 
 towards the formation of internal clots, which frequently 
 prove fatal before the full effects of the blood poisoning have 
 had time to arrive. In fact, in fevers generally the amount 
 of fibrin ferment in the blood seems a little more abundant. 
 While in the daily life of a healthy individual many such cor- 
 puscles disintegrate, they do not do so in sufficient numbers 
 
THE BLOOD. 71 
 
 to form material amounts of fibrin ferment, and so the 
 blood is prevented from clotting. Though this explanation 
 at first sight seems sufficient, a closer study shows that it 
 does not yet answer all the observed facts in coagulation of 
 blood, and there are many observers who offer modified 
 theories to account for this phenomenon. Thus, we do not 
 know from what source the fibrinogen is derived. Al. 
 Schmidt, the originator of the theory here given, believes 
 that the fibrinogen and the fibrinoplastin both, as well as 
 fibrin ferment, are derived from the disintegration of white 
 corpuscles. This might explain why at the point where 
 clotting begins and where, therefore, large numbers of 
 these corpuscles are dissolved, added amounts of fibrinogen 
 should form and thus facilitate clotting. 
 
 But to recapitulate : The best explanation now available 
 is that there is present in normal human blood dissolved in 
 the plasma about two-tenths per cent, of an albumen known 
 as fibrinogen. This fibrinogen in the presence of common 
 salt and lime salts will change into insoluble fibrin threads 
 under the influence of this fibrin ferment, at present believed 
 by all to be derived from the colorless corpuscles of the 
 blood. The property of coagulation is by no means pecu- 
 liar to fibrinogen. Most albumens possess it more or less 
 fully shown. The liquid casein of milk easily coagulates 
 into cheese under the action of the rennet ferment. The 
 liquid albumen of living muscles soon clots after death, 
 producing the so-called death stiffening, or rigor-mortis. 
 Even ordinary egg albumen can easily be made to coagu- 
 late by the action of heat or chemical agents. 
 
 The liquid that is left after the blood has clotted is 
 called serum. 
 
 THE COMPOSITION OF SERUM. 
 
 The serum of ordinary blood contains about ninety per 
 cent, of water. It contains two albumens which have indi- 
 rectly taken part in the formation of the clot called fibrino- 
 plastin and serum albumen. This serum albumen must not 
 
72 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 be confused with the serum itself. Serum is the name 
 applied to the entire liquid after the fibrinogen has been 
 removed in the form of fibrin, while serum albumen is but 
 one of the albumens found in this liquid. Fibrinoplastin, so 
 called by Al. Schmidt, and called paraglobulin by Kiihne, 
 is present to the amount of about one per cent. The serum 
 albumen forms four or five per cent. These two albumens 
 are insoluble in pure water, but are soluble in water con- 
 taining a little common salt, which latter accounts for their 
 being in solution in normal blood. The two differ but very 
 little from each other, but they may be separated if to a 
 solution of serum at a temperature of about ninety-five 
 degrees Fahrenheit, crystals of magnesium sulphate be 
 added to saturation. The fibrinoplastin is by this process 
 precipitated out of the solution. 
 
 As stated before, the serum albumen is the main nutri- 
 tive factor of the blood. It is almost identical with liquid 
 egg albumen, and differs from it only in its reaction with 
 certain chemical agents. It is this albumen which in 
 pathological conditions of the kidneys, such as Bright 's 
 disease, is eliminated in the excretion. Both serum albu- 
 men and fibrinoplastin may be made to coagulate if blood 
 serum be heated to a temperature of about one hundred 
 and seventy-six degrees Fahrenheit. 
 
 The serum further contains traces of fat in the form of 
 fine granules, to the amount of about one-half per cent. 
 After a diet rich in fats the amount may reach one per 
 cent. Traces of grape sugar in amounts varying from one- 
 tenth to three-tenths of a per cent, occur. This amount 
 may also greatly vary with a diet rich in sugars. It further 
 contains in very small amounts a number of organic nitrog- 
 enous compounds, such as kreatin, urea, and uric acid, 
 substances with which we shall be further concerned in the 
 discussion of assimilation and nutrition. The mineral salts 
 are represented in an amount reaching not quite one per 
 cent. Of these common salt, or sodium chloride, forms 
 more than half, and sodium carbonate a good portion of the 
 
THE BLOOD. 73 
 
 remainder. It is an interesting fact to note that while the 
 potassium salts are contained so largely in the corpuscles, 
 the sodium salts figure in a similar role in the liquid. A 
 yellow pigment of a nature not understood, and traces of a 
 substance to which the characteristic odor of blood is due, 
 finally complete the list of things which enter into the com- 
 position of blood. There are, of course, dissolved in the 
 blood certain gases, but the discussion of these is post- 
 poned to the chapter on respiration. 
 
 In the discussion of blood, that of lymph is naturally 
 included, lymph being in fact nothing but the plasma of 
 the blood which has by osmotic processes soaked through 
 the walls of the capillaries and so bathed the tissues. To 
 use an arithmetical expression, lymph is blood minus the 
 red corpuscles. White corpuscles are present in lymph 
 owing to the fact that they are able to pass through the 
 capillary walls, and in general are able to wander among 
 the tissues. Occurring so plentifully in lymph, has given 
 to them the name by which they are frequently called, that 
 of lymph corpuscles. It is well to keep in mind that the 
 migration of these corpuscles through the walls of the capil- 
 laries, as it is normally done, does not necessarily injure 
 them. Probably they press their way through tiny open- 
 ings made between the cells which form the capillary wall. 
 In any case the opening made is so small that it is at once 
 closed up. 
 
 THE PHENOMENON OF OSMOSIS. 
 
 The phenomenon of osmosis referred to so frequently in 
 physiological discussion is the phenomenon of the diffusion 
 of liquids through a membrane in such a way that the com- 
 positions of the two liquids tend to become similar. Thus, 
 if a moist animal membrane, such as a stretched bladder, 
 be taken and placed so as to divide a vessel in two compart- 
 ments, and then water containing sugar be placed in one 
 compartment, and salty water in another, osmotic currents 
 are soon set up through the membrane, by means of which 
 
74 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 / 
 
 part of the sugar is carried to the salty side and part of the 
 salt to the sugary side. These currents continue so, sec- 
 ondary causes not preventing, until the proportion of sugar 
 and salt are the same throughout. In an exactly sim- 
 ilar way the plasma of the blood containing in solution a 
 number of nutritive substances passes through the wall of 
 the capillary into and between the tissues, where these 
 nutritive substances are being continually taken up by the 
 tissues, and so an equilibrium never established. On the 
 other hand, a number of waste products which are formed 
 in the tissues pass into the blood. 
 
CHAPTER VI. 
 
 THE SUPPORTING TISSUES. 
 
 The supporting tissues are comprised of those tissues 
 which give support to the delicate organs of the body and 
 their component cells. They are distributed throughout the 
 entire body and give form and shape to the same. Includ- 
 ing all the connective tissues and not merely the bony 
 skeleton, these supporting tissues would preserve the actual 
 size, appearance, and contour of the body, even if every 
 vestige of their tissues could be removed. The body with 
 nothing but its system of supporting tissues would remain 
 apparently so unaltered that the absence of all the vital 
 parts might not even be suspected by the observer. 
 
 The supporting tissues naturally fall into four divisions : 
 First, the osseous; second, the cartilaginous; third, the 
 connective; and fourth, the humors. All of these tissues 
 are alike, in the fact that they are formed not out of cells, 
 but from the product of cells, somewhat in the way in 
 which a cobweb is formed not out of spiders, but as the 
 product of their secretion. Not being made up of living 
 cells, therefore, these tissues are in a sense dead matter, 
 although the cells that produce them frequently remain in 
 the tissue, forming a very integral part of its structure. 
 The cells that produce bone are called bone corpuscles, or 
 osteoblasts; the cells that form cartilage are the cartilage 
 cells, or chondrioblasts ; those that form the connective 
 tissues and the humors are called connective tissue cor- 
 puscles. All of these cells resemble very closely the white 
 corpuscles of the blood, and are probably nothing but 
 slightly differentiated cells set apart for the purpose of 
 secreting and maintaining the supporting frame-work of 
 the body. 
 
 (75) 
 
76 
 
 STUDIES IN ADVANCED PHYSIOLOGY, 
 
 Fig. 18. THE ENTIRE SKELETON. 
 
 a, 6, skull; c, cervical vertebrae; d, sternum; e, lumbar vertebrae; /, ulna; g, radius; 
 h, carpal bones; i, metacarpal bones; A-, phalanges ; I, tibia; w, fibula; n, tarsal bones; 
 o, metatarsal bones; P, phalanges; ry, patella; r, femur; S, os innominatnm; t, humerus; 
 u, clavicle. 
 
THE SUPPORTING TISSUES. 
 
 77 
 
 Bony Tissue. 
 
 Osseous tissue is familiar to every one as the tissue of 
 which bone is composed. The bones of the body in their 
 proper articulations form the skeleton. The skeleton con- 
 sists of a trunk, two pairs of extremities, their supporting 
 girdles, and the skull. 
 
 The trunk is composed of seven cervical vertebrae, twelve 
 dorsal, five lumbar, the sacrum, and the coccyx. 
 
 VERTEBRA. 
 
 The first vertebra called the 
 atlas differs from the rest in that 
 the body of the atlas has grown to 
 the next vertebra, the axis, forming 
 a pivot, the odontoid process on 
 which the head turns. The cervi- 
 cal vertebra has a few characteris- 
 tics by means of which it may be 
 
 Cot) 
 
 4V 
 
 Fig. 19. SPINAL COLUMN. 
 
 (vSide view.) 
 
 (', cervical; D, dorsal; L, 
 lumbar; S, sacrum; Co, 
 coccyx. 
 
 Fig. 20. ATLAS. (Seen from above.) 
 Dotted lines, position of transverse ligament to 
 hold in place the odontoid process ; oblique line, in- 
 sertion of ligament into a bony tubercle; other lines, 
 articulating surfaces. 
 
 Fig. 21. ATLAS AND AXIS, FRONT VIEW. 
 Upper line, odontoid process; remaining lines, 
 articulating processes. 
 
78 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 Fig. 22. A TYPICAL CERVICAL VERTEBRA. 
 
 Showing intra-vertebral foramen and bifid spinous process. 
 
 recognized. Its spinous process is bifid, and the transverse 
 process appears with an opening called the intra-vertebral 
 foramen. Through this the intra-vertebral artery ascends 
 to the brain. This is not really a hole through the trans- 
 verse process of the cervical vertebra, but is a space left 
 between the transverse process and the stump of a rib which 
 is fused with it, there being in early life indications of the 
 presence of ribs throughout the cervical region. The dorsal 
 vertebrae are at once recognized in having the articulating 
 facets for the ribs, and in having their spinous processes 
 
 Fig. 23. A DORSAL VERTEBRA FROM THE 
 RIGHT SIDE. 
 
 Two upper lines, facets for the articula- 
 tion of ribs; left line below, inferior articular 
 process; middle line below, vertebral notch 
 (exit of nerves, etc.) ; right line below, facet 
 for lower rib. 
 
 Fig. 24. I,T T MBAR VERTEBRA FROM 
 ABOVE. 
 
 t'pper line, inferior articulating pro- 
 cess; lower line, superior articulating 
 process. 
 
THE SUPPORTING TISSUES. 
 
 79 
 
 drawn downward. This latter arrangement is better adapted 
 for the attachment of the heavy muscles of the body. The 
 lumbar vertebrae have proportionately a much larger body, 
 and the processes relatively much shorter and thicker. The 
 sacrum consists in reality of five fused vertebrae, the indi- 
 vidual ones being still clearly traceable on it. This fusion 
 
 SUP. ARTIE. PHOC. 
 
 Fig. 25. THE SACRUM, FRONT VIEW. 
 
 aids materially in giving strength to that portion of the col- 
 umn where it is connected with the hip bone. The coccyx 
 consists of from two to four or five very much reduced verte- 
 brae and serves as far as we know no special function. The 
 individual vertebrae are separated by pads of elastic carti- 
 lage which give them a certain amount of lateral motion, 
 and which also serve as cushions to break the jars. The 
 double curvature of the entire column still further serves to 
 reduce this to a minimum. 
 
 BIBS. 
 
 Attached to the dorsal vertebrae are twelve pairs of ribs, 
 which extend slightly downward, then upward, and enclose 
 the organs of the chest. With the exception of two on each 
 side, called the floating ribs, they are attached to the ster- 
 num, or breast bone, by means of elastic cartilages, which 
 permit a slight movement at these points. 
 
80 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 PECTOEAL AND PELVIC GIEDLES AND THE EXTREMITIES. 
 
 More or less firmly attached to this trunk are the two 
 girdles of the body, the pectoral girdle, supporting the arms, 
 and the pelvic girdle, for the attachment of the limbs. The 
 pectoral girdle consists on each side of two bones, the 
 
 Fig. 26. RIGHT CLAVICLE, FROM ABOVE. 
 
 Fig. 27. ANTERIOR VIEW OF RIGHT 
 SCAPULA. 
 
 clavicle and the scapula. The clavicle articulates with the 
 manubrium of the breast bone and with the large acromion 
 process of the scapula. This serves to hold the shoulder 
 back in place. Animals that walk on their four limbs have 
 the clavicle reduced to a mere splint or thread of cartilage, 
 as it would be in their case undesirable to have the shoul- 
 ders pitched back. This reduction of the clavicle allows 
 the shoulders of these animals to drop under the body, a 
 position much better suited for supporting their weight. 
 
THE SUPPORTING TISSUES. 
 
 81 
 
 The scapula, or shoulder blade, is not connected with 
 the back bone, but lies imbedded in the muscles of the 
 shoulder. This loose attachment aids materially in giving 
 freedom of motion to the arm. The scapula really consists 
 of two bones, the scapula proper and the coracoid bone, 
 which latter, however, has been reduced to a mere process, 
 which has grown on to the scapula, and which is called the 
 coracoid process. In birds this coracoid process is a very 
 large and distinct bone, and serves to support the wings, 
 
 CONDYLE 
 
 Fig. 28. THE RIGHT HUMERUS FROM BE- 
 FORE. 
 
 Fig. 29. THE BONES OF THE RIGHT HAND 
 
 SEEN FROM BEFORE. 
 
 *, scaphoid; I, lunar; c, pyramidal; P, 
 pisiform; t, trapezium; next, the trapezoid; 
 then, the osmagnum; u, unciform; /, V, 
 metacarpals; 1,2,3, phalanges; *, sesamoid 
 bones. 
 
 while the- clavicle loses its attachment with the breast bone, 
 and meeting the clavicle on the other side forms the so-called 
 ' ' wish bone. ' ' Articulating in the glenoid fossa of the scap- 
 6 
 
82 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 ula is the bone of the forearm called the humerus. This 
 articulates at the elbow with two bones, the radius and the 
 ulna. The ulna forms the main articulation, forming really 
 the hinge joint of the elbow. The backward process on the 
 ulna, which prevents the backward flection of the elbow 
 joint, is called the olecranon process. This is really an 
 elbow cap, similar to the knee cap, which, however, in this 
 case has become firmly attached to the ulna. 
 
 At the wrist the radius and ulna articulate with a series 
 of eight bones called the carpal bohes. Here the radius 
 forms the main articulation, and by rotating around the ulna 
 the hand is pronated and supinated. These carpal bones 
 are followed by five metacarpal bones, to which in turn are 
 connected three phalanges for each finger, the thumb hav- 
 ing but two. The radius is on the thumb side of the wrist. 
 
 ISCHIUM 
 
 Fig. 30. RIGHT os INNOMINATUM. 
 
 Attached to the sacrum on each side is the os innom- 
 inatum, so called because the early anatomists were not 
 able to name it after any object they knew. This bone 
 
THE SUPPORTING TISSUES. 
 
 83 
 
 really consists of three bones, which have grown together, 
 the large flat upper ilium, which connects with the sacrum, 
 the lower ischium, which supports the weight of the body 
 in a sitting posture, and the forward pubic bone, which by 
 
 Fig. 31. ADULT MALE PELVIS, SEEN FROM BEFORE. (Upper.) 
 
 ADULT FEMALE PELVIS, SEEN FROM BEFORE. (Lower.) 
 
 (After Allen Thompson.) 
 
 articulating with the pubic bone on the other side forms the 
 front wall of the pelvis. The large articulating facet for the 
 head of the femur is called the acetabulum. A large hole 
 formed through the bone, the thyroid foramen, serves for 
 the exit of nerves and blood vessels from the pelvic cavity. 
 Attached to the innominate bone is the femur, the long bone 
 of the thigh. This articulates at the knee with the tibia. 
 
84 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 Along the outside of the tibia and serving to brace this ar- 
 ticulating surface with the femur lies the smaller fibula. 
 
 MAUEOLUS 
 
 Fig. 32. RIGHT TIBIA AND FIBULA, FROM 
 
 STYLOID PROCESS 
 
 Fig. 33. RIGHT RADIUS AND ULNA IN SUPI- 
 
 NATION OF THE HAND. 
 
 At the ankle the tibia articulates with the astragalus, 
 which, however, represents two of the tarsal bones grown 
 together. This fusion to form the astragalus explains the 
 presence of but seven tarsal bones. The large tarsal 
 bone forming the heel, into which the tendon Achilles is 
 attached, is the heel bone, or os,calcaneum. These tarsal 
 bones, then, connect with the metatarsal, which are in turn 
 followed by a series of three phalanges for each toe, and 
 two for the big toe. In the hands and feet, especially of 
 persons who are in the habit of doing hard manual labor, 
 
THE SUPPORTING TISSUES. 
 
 85 
 
 there are developed frequently at the joints small, extra 
 bones, called sesamoid bones. The rather large knee cap 
 is probably nothing more than such a sesamoid bone, which 
 
 nncwmup ' 
 Fig. 34. THE RIGHT FEMUR FROM BEHIND. 
 
 Fig. 35. THE BONES OF RIGHT FOOT, SEEN 
 
 FROM ABOVE. 
 
 A, navicular bone; 6, astragalus; c, d, 
 os calcaneum; e, internal cuneiform; /, 
 middle cuneiform; g, external cuneiform; 
 h, cuboid bone; 1, V, metatarsals; 1,2,3, 
 phalanges. 
 
 has finally become persistent. Such sesamoid bones prob- 
 ably serve to lessen the friction of the tendons pulling from 
 the joint. 
 
 THE SKULL. 
 
 The bones of the skull serve to enclose the brain and to 
 give support to the face and its organs. The bones which 
 enclose the brain, or cranium, are eight: the frontal, two 
 parietals, two temporals, one occipital, one sphenoid, and one 
 ethmoid. The bones which serve to form the face are the 
 
86 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 two nasal bones, the two lachrymal bones, two malar bones, 
 the upper maxilla, the two palatine bones, the lower maxilla, 
 
 Fig. 36. FRONT VIEW OF MALE SKULL AT ABOUT TWENTY YEARS. (Allen Thomson.) 
 
 1, frontal eminence; 2, glabella, between the superciliary ridges, and above the trans- 
 verse suture of union with the nasal and superior maxillary bones ; 3, orbital arch near 
 the supraorbital notch; 4, orbital surface of great wing of sphenoid, between the sphe- 
 noidal and the spheno-maxillary fissures; 5, anterior nasal aperture, within which are 
 seen in shadow the vomer and the turbinate bones; 6, superior maxillary bone at the 
 canine fossa above the figure is the infraorbital foramen; 7, incisor fossa; 8, malar bone; 
 9, symphysis of lower jaw; 10, mental foramen; 11, vertex, near the coronal suture; 12, 
 temporal fossa; 13, zygoma; 14, mastoid process; 15, angle of the jaw; 16, mental pro- 
 tuberance. In this skull there are fourteen teeth in each jaw, the wisdom teeth not hav- 
 ing yet appeared. 
 
 the vomer, and the two turbinates. Suspended by cartila- 
 ginous threads from the temporal bone is the hyoid bone, 
 which serves to give support to the muscles of the tongue. 
 It is entirely impossible to give any satisfactory descrip- 
 tions, and even in good pictures, any adequate notion of the 
 
THE SUPPORTING TISSUES. 
 
 87 
 
 arrangement of bones. The enumeration of the bones and 
 the cuts here given are intended 
 to serve only as a manual in the 
 hands of the student who is for- 
 tunate enough to have an actual 
 skeleton before him for study. 
 Detailed descriptions of the in- 
 dividual bones is deemed un- 
 necessary, but the detail given 
 in the pictures, together with 
 
 Fig. 37. THE HYOID BONE. 
 
 Z 
 
 Fig. 38. A SIDE VIEW OF THE SKULL. 
 
 O, occipital bone; T, temporal; Pr, 
 parietal; F, frontal; S, sphenoid; Tsp, 
 wing of sphenoid; Z, malar; MX, maxilla ; 
 N, nasal; E, ethmoid; L, lachrymal; Md, 
 inferior maxilla. 
 
 JMi 
 
 the accompanying names, ought to be the points which the 
 student should verify for himself on every bone in question. 
 
88 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 THE MINUTE STRUCTURE OF BONES. 
 
 Little need be said concerning the gross structure of 
 bones. A mere glance will show one the difference between 
 the long bones, such as the femur or hu~ 
 merus, the short bones, such as those of 
 the tarsus and carpus, the tabular bones, 
 like the parietal bones of the skull, and the 
 irregular bones, which do not seem to fit 
 in any of the preceding classes. If, fur- 
 ther, a long bone, such as the humerus, 
 say, be examined, it is easily seen to con- 
 sist of a long shaft made up of hard, dense, 
 apparently homogeneous bone, with some- 
 what expanded ends, intended for articu- 
 lating surfaces. Numerous little holes are 
 visible, through which blood-vessels and 
 nerves enter the bone. If such a bone be 
 sawed in two a large, empty space appears 
 through the shaft, known as the medullary 
 cavity. It is filled in life with a yellowish 
 substance consisting mostly of fat, called 
 the yellow marrow. At the end the bone 
 is seen to be cancellated or spongy. In 
 this cancellated bone is found the red mar- 
 row, the seat of the formation of the red 
 corpuscles of the blood. Further than this 
 nothing can be made out as to the struc- 
 
 If a tabular 
 bone such as the parietal be examined, 
 
 Fig. 39. THE GROSS AN- A .-1,1 -. i 
 
 ATOMY OP A LONG ture with the unaided eye. 
 
 BONE. (Humerus.) 
 
 numerous little openings into it for the 
 entrance and exit of blood-vessels 
 
 a, medullary 
 containing the marrow; 
 I, shaft of hard bone; c, 
 spongy or cancellated 
 
 are 
 
 bone; d, terminal card- a g a | n v i s ibl e , while if it be broken it shows 
 
 that it is made up of two plates, the denser 
 
 bone on the outside and an intervening layer of spongy 
 
 bone called diploe. The structure of the parietal bone is 
 
THE SUPPORTING TISSUES. 
 
 89 
 
 repeated in a number of the irregular bones of the body, 
 which have on the outside some denser bone, while the 
 interior is more or less spongy. It will be recalled that 
 
 Fig. 40. LONGITUDINAL SECTION OF THE HEAD OF THE FEMUR SHOWING THE CANCEL- 
 LATED STRUCTURE AT END, AND SOLID BONE OF SHAFT. (From a photograph by 
 
 Zaaijer.) 
 
 in the spongy part of all these bones, no less than in those 
 of the long bones, red marrow occurs. 
 
 To discover the real structure of bone it is necessary to 
 grind a bone into an exceedingly thin section, so that it 
 may be viewed with a microscope. If such a cross section, 
 
90 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 say from the shaft of the humcrus, be taken, it is found to 
 be not homogeneous at all, but pierced by a set of canals 
 running mainly in a longitudinal direction, known as Haver- 
 sian canals. Through these canals run blood-vessels, nerves 
 
 Fig. 41. TRANSVERSE SECTION FROM THE SHAFT OF THE HUMERUS, SHOWING THRKE 
 
 HAVERSIAN SYSTEMS COMPLETE. 
 
 The Haversian canals, lacunae and canaliculi appear black, being filled with air and 
 debris from the grinding. 
 
 and lymphatics. Around each Haversian canal lie from 
 several to many series of cylindrical plates, or lamellae, 
 between which occur in characteristic rows little openings 
 called lacunae. Running out from each lacuna are many 
 divergent and branching canals called canaliculi, which 
 connect with similar canals from the immediately surround- 
 ing lacunae. The canaliculi of the lacunae next to the 
 Haversian canal open into the Haversian canal. By this 
 system of lacunae and canaliculi nourishment may soak 
 from the Haversian canal through every portion of the bone. 
 These lacunae are in life each filled by a little corpuscle 
 not unlike an ordinary white blood-corpuscle, called an 
 osteoblast. Arms from these osteoblasts extend through the 
 
THE SUPPORTING TISSUES. 91 
 
 canaliculi and come in contact with similar arms of neigh- 
 boring osteoblasts. In this way there is really a system of 
 direct communication between the living parts of the entire 
 
 Fig. 42. AN OSTEOBLAST IN DETAIL. 
 
 o, the wall of the lacuna where the bone corpuscle has shrunk away from it. 
 
 v bone. These osteoblasts are the agents which secrete the 
 bone substance surrounding them, somewhat like the clam 
 secretes its surrounding calcareous shell. The bone sub- 
 stance, or the matrix, as it is called, appears perfectly 
 homogeneous, but with proper reagents there may be 
 brought to view many little fibres permeating it in all 
 directions. These fibres, no doubt, add materially to the 
 strength and consistency of the bone, somewhat as the 
 hairs frequently mixed with mortar materially serve to keep 
 that from crumbling. These fibres were named after the 
 person who first carefully described them, and called the 
 fibres of Sharpey. The firmness of the matrix is due to the 
 large amount of mineral matter which it contains, there 
 being about sixty-five per cent, of inorganic matter in bone. 
 Of these inorganic constituents the most abundant is cal- 
 cium phosphate. In small quantities there occur combina- 
 tions of fluorine, chlorine and magnesia. Small quantities 
 of calcium carbonate are present. In this matrix the osteo- 
 blasts are not merely included by chance, but remain there 
 in order to look after the constant wear and repair of the 
 osseus tissue. By extracting the proper ingredients from 
 the lymph which seeps to them, they are enabled wherever 
 either the cell itself or its arms touch, to secrete new bone, 
 
92 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 and in this way to preclude any material disintegration of 
 bone in any part of the body. As the bone substance is 
 everywhere riddled, even to the smallest bits, with these 
 osteoblasts and their ramifications to such an extent that 
 
 Fig. 43. LAMELLAE TORN FROM A PARIETAL BONE TO SHOW THE FIBRES OF SHARPEY, 
 c, c. (After Sharpey.) 
 b, thick opaque portion of bone, a, holes where fibres had been. 
 
 the point of an ordinary pin would really cover many of 
 them, one can understand under what thorough supervision 
 the repair of normal bone is, and how even in the smallest 
 and most out-of-the-way portions a disintegration or soften- 
 ing in any way is at once remedied. The osteoblasts when 
 once included in these lacunae are never able to leave them, 
 but remain there until death or until the processes of age in 
 later life cause many of them to apparently disintegrate and 
 disappear. This disappearance of the corpuscles from old 
 bones, as well as the continued calcajeous depositions in it, 
 accounts for the brittleness of the bones of old people and 
 the difficulty with which broken portions are healed. 
 
 The Haversian canal with its series of lamellae, lacunae 
 and canaliculi, is called the Haversian system. Where 
 these systems meet, irregular bits of bone frequently fill in 
 the space between. Around the outside of the entire bone 
 
THE SUPPORTING TISSUES. 93 
 
 there is a rather strong fibrous membrane completely invest- 
 ing it except at the ends, called the periosteum. This is a 
 membrane mostly of white fibres and some yellow elastic 
 tissue, which serves to carry the blood-vessels which are to 
 enter and nourish the bone. In the meshes of this perios- 
 teum the entering blood-vessels divide and branch, and so 
 plunge into the bone at many different points. * Immedi- 
 ately under the periosteum is a layer of ordinary osteoblasts. 
 The connection of these osteoblasts with the formation of 
 bone is mentioned further on. 
 
 The current notion that the periosteum is the thing that 
 nourishes the bone and even produces it is correct only in 
 so far as it carries and distributes the blood-vessels which 
 enter the bone, and has under it the bone corpuscles which 
 form new layers of bone. For this reason, if in any surgical 
 operation or otherwise the periosteum is removed from the 
 bone, the bone soon dies for lack of nourishment. The 
 'ability of the periosteum with the osteoblasts underneath it 
 to form bone is strikingly illustrated in instances where 
 such periosteum removed from a bone was tunneled in 
 among muscles and in that position gradually developed a 
 new bone. But it must be remembered that this formation 
 of new bone was in no part a function of the periosteum 
 itself, which is a mere connective tissue membrane, nor 
 even of the blood-vessels which it carries in numbers, but 
 of the osteoblasts included under it. 
 
 If some of the cancellated bone from the ends be exam- 
 ined in a similar way under a microscope as the section 
 taken from a shaft, the view is quite similar, except that 
 the Haversian systems are a little larger and their arrange- 
 ment not so compact. 
 
 ORIGIN AND GROWTH OF BONE. 
 
 In the way in which bones originate in the body they 
 are divided into two classes, called the membrane bones 
 and the cartilage bones. Membrane bones are those bones 
 which have never been preceded by cartilage, but have 
 
94 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 developed directly from a membrane. A typical example 
 of such a membrane bone is the parietal bone of the 
 skull. 
 
 Growth of Cartilage Bones. Cartilage bones are those 
 bones which are preceded by cartilage which has been 
 removed and, later, bone deposited in its place, or as com- 
 monly stated in our text-books, bones which ossify from 
 cartilage. If the limb of a young animal be examined in 
 embryonic life even before the cartilages have made their 
 appearance, the following series of changes may easily be 
 noticed: 
 
 In earliest life such a limb budding out from the body 
 would consist throughout of perfectly similar cells, the 
 original descendants of the primitive egg cell. Soon after, 
 among many other changes, there might be noticed, in the 
 place where the cartilage is to appear, to form, say the 
 humerus, a number of cells similar to the others in appear- 
 ance, which, however, begin to secrete between themselves 
 a substance familiar to us as cartilage. In this cartilaginous 
 matrix these cells, which we may now call cartilage cells or 
 chondrioblasts, multiply and by a continued secretion from 
 these the matrix of the cartilage family results. As this 
 cartilage is plastic, and may extend by interstitial growth, 
 it soon comes to possess the form intended for the future 
 bone. A membrane soon invests this cartilage except at the 
 ends, which membrane will become the future periosteum, 
 which now, as it surrounds cartilage, is called the peri- 
 chondrium. 
 
 This membrane becomes filled with blood-vessels, and 
 underneath it, that is between it and the cartilage, there 
 come to lie numerous little corpuscles, the osteoblasts of 
 the future bone. At this stage of the process no bone is yet 
 present, there being but a solid cartilage rod of the form of 
 the intended humerus, surrounded by the membrane. Soon 
 after this the process commonly called the process of ossi- 
 fication begins. 
 
THE SUPPORTING TISSUES. 95 
 
 This is generally understood to mean the turning of the 
 cartilage into bone, but such a change in no sense takes 
 place. Ossification really consists in the gradual removal 
 of the cartilage and in the formation of entirely new bone. 
 The changes which convert this cartilage into the bony 
 humerus, as we know it, are as follows: * 
 
 A little before the process of bone formation begins, it 
 may be noticed that the cartilage at the point of ossification 
 becomes somewhat gritty, probably due to the deposit of 
 extra mineral matter in the cartilage. In the case of the 
 humerus this point is near the middle of the shaft. Soon 
 after this, peculiar large cells burrow and absorb a pas- 
 sageway for themselves from under the periosteum through 
 the cartilage until they reach the middle of the shaft. Here 
 these large cells continue their process of dissolving and 
 absorbing the cartilage, and so tunneling it in every direc- 
 tion. These large cells are called osteoclasts, or possibly 
 more generally myelo-plaques. By the eating away of the 
 cartilage in this way the central portion of the cartilagin- 
 ous humerus is soon converted into an intricate system of 
 tunnels, which gradually extend further and further towards 
 the ends of the bone. The absorption of the cartilage is 
 probably explained as due to the digestive action of the 
 liquid which these myelo-plaques secrete. What happens to 
 the cartilage cells themselves when their matrix is removed 
 is not yet definitely known. According to some observers the 
 cartilage cells, too, are absorbed; while according to other 
 observers these cells when liberated change into bone cells, 
 and figure in a way to be described later. In the tunnels 
 so made, blood-vessels from the periosteum grow, and from 
 the same place large numbers of osteoblasts follow up these 
 channels. These osteoblasts secrete bits of bone against 
 the walls of these tunnels, possibly not unlike the stone 
 masonry that lines many railroad tunnels. When finally all 
 
 * As the changes in the case of this bone are, except for local differences the same 
 for every other, this one instance may suffice to explain the phenomena of ossification 
 wherever occurring. 
 
96 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 the cartilage is removed and nothing but this mesh-work of 
 masonry left, there is produced in the center of the humerus 
 what is familiar to us as spongy bone. Be it observed, 
 however, that this spongy bone is in no sense derived from 
 the cartilage, but is an entirely new product, and that all 
 the cartilage, together with its cartilage cells, has been 
 removed. While these changes are going on in the shaft 
 of the bone the osteoblasts under the periosteum have begun 
 to secrete bone there, and so have surrounded the cartilag- 
 inous shaft with a fine casing of osseous tissue. Layer 
 after layer of bony lamellae is added until there has been 
 formed a cylinder of bone of quite appreciable thickness, 
 moulded right over the original cartilage. In this way the 
 new bone receives at once the shape intended for it. While 
 the strength of the shaft is thus added to under the peii- 
 osteum, new osteoclasts, or myelo-plaques begin to remove 
 the spongy bone just deposited where the cartilage was 
 removed. In this way by the continued absorbing action 
 of these cells there is soon formed an empty space, the 
 beginning of the medullary cavity. The tunneling of the 
 cartilage extends further and further towards the ends of 
 the bone. These tunnels are then immediately lined with 
 layers of bone by succeeding osteoblasts, and so the forma- 
 tion of spongy bone proceeds gradually towards the extrem- 
 ities. This spongy bone is, however, at the rear end being 
 continually absorbed by other osteoclasts, and so the medul- 
 lary cavity reaches further and further towards the opposite 
 ends. If this continued uninterrupted and with the rapidity 
 with which it goes on for a while, it would soon remove all 
 of the cartilage, even to the very ends. But this stage is 
 never reached, for while the cartilage is being continually 
 encroached upon and removed at one end it keeps elongat- 
 ing above, continuing "to do so until the full length of the 
 adult bone has been reached. As the cartilages at the ends 
 grow the periosteum creeps further and further along it and 
 begins the deposition of bone. In this way the bony shaft 
 follows pari passu the enlargement of the cartilage. Thus 
 
THE SUPPORTING TISSUES. 97 
 
 it will be seen that bones grow in length really by the car- 
 tilaginous ends growing, and then the cartilage being 
 removed from the inner side in the manner just described. 
 
 In this way not only has the entire cartilage of the shaft 
 been removed, but as the periosteum forms more and more 
 bone beneath itself osteoclasts begin to remove bone from 
 the medullary cavity side, and so this cavity becomes larger 
 and larger. The explanation of this probably consists in 
 the fact that the first bone deposited by the periosteum is 
 not as strong as that which is later on deposited, and so it is 
 removed in order to avoid surplus weight. This eating 
 away of the bone from the inner side continues for a long 
 time, and so it happens that the medullary cavity of an 
 adult bone may be very much larger than the piece of car- 
 tilage which originally filled it. From these statements it 
 is clear that the bone grows in thickness only by the addi- 
 tion of layers around the outside by the osteoblasts under 
 the periosteum. The older notion that a bone deposit also 
 takes place by osteoblasts which line the medullary cavity 
 no longer seems valid. 
 
 The encroachment of the bone into the cartilage at the 
 end does not reach the ends of the bone as we see it in the 
 adult specimen, but after the cartilage has grown to the size 
 intended for the future bone, independent centers of ossifi- 
 cation start up in these ends with processes identical with 
 those just described. In this way the bony epiphyses, as 
 they are called, at the ends of most long bones arise. L,ater 
 on the cartilage between the epiphyses is gradually ab- 
 sorbed from both sides and the bone becomes continuous, 
 or, as we say, the bone becomes "knitted." This does not 
 take place until quite late. For instance, in the humerus 
 the lower epiphysis unites with the shaft about the seven- 
 teenth year; the upper epiphysis about the twentieth year. 
 In the femur the upper end is joined to the body of that 
 bone about the nineteenth year, and the lower end becomes 
 knitted about the twentieth year. In the fibula this knit- 
 ting is still later, occurring at the lower end about the 
 
98 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 twenty-first year, and at the upper end about the twenty- 
 fourth year. The individual vertebrae which fuse together 
 
 Fig. 44. PART OF A LONGITUDINAL SECTION OF THE DEVELOPING FEMUR OF THE RAB- 
 BIT. DRAWN UNDER A MAGNIFYING POWER OF 350 DIAMETERS. (From Klein and 
 Noble Smith.) 
 
 a, rows of flattened cartilage-cells; b, greatly enlarged cartilage-cells close to the ad- 
 vancing bone, the matrix between is partly calcined; c, d, already formed bone, the os- 
 seous trabeculae being covered with osteoblasts (<?), except here and there, where a giant- 
 cell or osteoclast (/), is seen, eroding parts of the trabeculae; g, h, cartilage-cells which 
 have become shrunken and irregular in shape. From the middle of the figure downwards 
 the dark trabeculae, which are formed of calcined cartilage matrix, are becoming covered 
 with secondary osseovis substance deposited by the osteoblasts. The vascular loops at 
 the extreme limit of the bone are well shown, as well as the abrupt disappcarmu-c of the 
 cartilage-cells. 
 
 to form the sacrum, and which are ossified from five differ- 
 ent centers, unite as late as the twenty-fifth year, while the 
 
THE SUPPORTING TISSUES. 99 
 
 three bones that form the- os innominatum, unite about the 
 same time. Thus we may see that the human body does 
 not reach its skeletal maturity until about twenty-five years 
 of age. From a hygienic standpoint this ought not to be 
 forgotten, for loads that a man of thirty may carry without 
 the least danger, may prove disastrous for a lad of eighteen 
 or nineteen, in spite of the strength of his muscles. 
 
 Some interesting experiments have been made in order 
 to determine the manner of growth of bones, by feeding 
 young pigs madder. In this madder there seems to be a 
 compound which colors bone in which it is deposited red. 
 When, now, such a pig in question has for a month or two 
 been fed with madder, and is then killed and the bone 
 examined, it is found that there is a layer of reddish bone 
 immediately under the periosteum and zones at the ends 
 where the cartilage has been encroached upon. All the 
 bone, however, next to the medullary cavity remains un- 
 stained. By taking such a pig and feeding it this madder, 
 in alternate months, it is possible to produce characteristic 
 rings of red and white, encircling the shaft of the bone 
 under the periosteum and zones of red and white alternat- 
 ing at the extremities. That the shaft itself does not grow 
 is easily demonstrated by driving some pointed pegs into 
 the shaft of a living bone, and then measuring their relative 
 distances after a certain period has elapsed. In the shaft 
 of the bone these pegs do not separate, showing that no 
 elongation has taken place. If, however, one of the pegs 
 be inserted in the cartilaginous end the regular elongation 
 appears. 
 
 The bone which is deposited under the periosteum is 
 deposited in successive layers, much like the layers of an 
 onion. These layers of lamellae do not show the character- 
 istic arrangement of the Haversian systems, as described 
 on a former page. To explain how these circumferential 
 lamellae become later changed into the characteristic Haver- 
 sian systems is at present no easy matter, but it is believed 
 on good grounds that the circumferential lamellae are actu- 
 
100 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 ally removed piecemeal, and replaced by a new growth of 
 bone extending into it from beneath. To state it again, it 
 is probably the migration of the Haversian systems of the 
 deeper portions of the bone into the outer layers, accomr 
 plished no doubt by a piecemeal absorption of these outer 
 layers and the re-deposition of new bone, showing the 
 Haversian system. It is possible that this change from the 
 stratified appearance of the layers under the periosteum to 
 the normal Haversian systems is to be accounted for on the 
 grounds that the latter system is better adapted for the 
 nourishment of the bone, and that possibly for physical 
 reasons the columnar arrangement of the Haversian systems 
 is stronger than that of the stratified lamellae. Future 
 investigation, however, must solve for us a number of ques- 
 tions still unanswered in this matter. 
 
 While the bones do not grow, as we ordinarily use that 
 term, after the twenty-fifth year, they may change their 
 shapes to some extent ; for throughout the greater part of 
 life there is an absorption of bone in some places where it is 
 no longer needed, and a continued deposition in other places 
 where added strength is desired. When bones are mechan- 
 ically broken they are united by having osteoclasts first 
 remove the dead bone from the broken ends, and then hav- 
 ing the osteoblasts cement the pieces together with new 
 bone, which may in some cases even be preceded by a 
 formation of cartilage. This removal of the dead bone is 
 probably identical in process with the removal of the car- 
 tilage and bone regularly occurring in their growth. 
 
 Such bone absorption occurs in the milk dentation and 
 also explains the occasional loosening of the permanent set 
 of teeth, owing to the removal of the cement, which is really 
 bone. 
 
 While in the long bones there is usually a single center 
 of ossification, near the middle of the shaft, with later ones 
 to form the epiphyses, they may be much more numerous 
 in irregular bones. Thus in the irregular sphenoid bone 
 
THE SUPPORTING TISSUES. 
 
 101 
 
 there are as many as eight different points at which the 
 process of ossification begins. 
 
 Growth of Membrane Bones. The second class of bones 
 comprises the membrane bones. As previously stated, these 
 are bones which are never preceded by cartilage. A typi- 
 cal illustration of such a membrane bone is the parietal. 
 Preceding this bone in early life there is just an ordinary 
 connective tissue membrane, containing no mineral deposit 
 
 Fig. 45. PART OF THE DEVELOPING PARIETAL BONE OF A FOETAL CAT. (After Schafer.) 
 sp, bony spicules, with some of the osteoblasts imbedded in them, producing the 
 lacunae; ost, osteoblasts partly imbedded in the newly formed bone; of, osteogenic fibres 
 prolonging the spicules, with osteoblasts between them and applied to them; a, granules 
 of calcareous deposit between the osteogenic fibres; at b the granules have become 
 blended, and the matrix is clearer; at c a continuity is established between the two adja- 
 cent spicules. 
 
 of any kind. Portions of this membrane are still evident 
 on the skull of a new-born child, and are familiar as the 
 fontannelles. In the meshes of this membrane osteoblasts 
 find their way, which begin at once to secrete over it the 
 mineral matter of the bone. By this continued secretion of 
 
102 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 bone in and around this membrane the fully formed parietal 
 comes to be. While not strictly analagous, the primitive 
 membrane might be compared with the periosteum, next to 
 which, as in the long bone, occurs the mineral deposit. 
 
 CHEMICAL COMPOSITION OF BONE. 
 
 The chemical composition of bone has been referred to. 
 Human bone consists of sixty-five per cent, inorganic mat- 
 ter and thirty- five per cent, organic matter. This organic 
 matter consists of a matrix called osseine, with which the 
 inorganic constituents so combine that even under a micro- 
 scope it looks homogeneous. This osseine is easily changed 
 by boiling it, into the familiar gelatine. In fact, much of 
 the gelatine of commerce is derived from the bones of 
 slaughtered animals, and an integral ingredient of the soup 
 made by boiling a soup bone is gelatine. It figures further 
 in a variety of roles in the preparation of foods and desserts 
 familiar to every household cook. The mineral salts are 
 mainly calcium phosphate and calcium carbonate, and from 
 this mineral part of bone-earth much of the phosphorus of 
 commerce is derived. By placing a bone in weak hydro- 
 chloric acid it is possible to dissolve out the mineral salts 
 and leave nothing but the organic portions. Such a bone 
 is soft and flexible. On the other hand, it is possible to re- 
 move the organic portion by what is known as calcining the 
 bone in a hot fire, which burns up all the organic matter. 
 In this way the bone-dust of commerce is made. When 
 the organic matter of a bone is not completely burned up, 
 but charred, it forms the familiar bone-black used in many 
 ways in the arts and in commerce, especially in the purifi- 
 cation of sugar. 
 
 HISTORICAL. 
 
 As early as 1736 Nesbitt showed that some flat bones 
 were formed perfectly independently of cartilage, and even 
 insisted that the cartilage was often destroyed in cases 
 where it did precede the real bone structure. The primi- 
 
THE SUPPORTING TISSUES. 
 
 103 
 
 live cartilage he explained as a mere temporary substitute 
 used to mould the shape of the succeeding bone, but as he 
 was unable to actually demonstrate his views as they are 
 now demonstrated with the microscope, they were but little 
 credited until Sharpey, in 1846, made clear beyond all ques- 
 tion the manner of the formation of bone and the replace- 
 ment of the cartilage. 
 
 Cartilages. 
 
 The second kind of the supporting tissues comprises 
 the cartilages, familiar under the more common name of 
 gristle. Cartilage differs from bone in the fact that the 
 cells which fill it are not branched, but smooth, and the 
 matrix does not possess a system of canals and canaliculi. 
 As a rule the mineral ingredients are much less in propor- 
 tion than in bone, although in older cartilages a calcifica- 
 tion takes place which results in giving to the cartilage as 
 
 Fig. 46. HYALINE CARTILAGE FROM THE LOWER END OF TIBIA. (After Schafer.) 
 , 6, c, different arrangement of cell groups ; d, layer of calcified cartilage ; e, bone. 
 
 great a proportion of earthy matter as bone possesses. 
 But such calcified cartilage is structurally entirely different 
 from bone. 
 
104 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 Three fairly distinct types of cartilage occur, the hya- 
 line, the yellow elastic and the white fibrous. In the hya- 
 line cartilage, as the name suggests, the matrix seems en- 
 tirely homogeneous ; that is, devoid of any fibrillation. In 
 this structureless material the cartilage cells are imbedded. 
 A view held by some histologists that this apparently struc- 
 tureless matrix is permeated by a system of very fine canals , 
 lacks verification. Such hyaline cartilage is found regularly 
 at the ends of bones, where a smooth, articulating surface 
 is necessary. The yellow elastic cartilage differs from hya- 
 line in having the matrix made up of densely packed yellow 
 elastic fibres, in the close meshes of which the cartilage 
 cells are lodged. Such cartilage occurs in the ear and the 
 
 Fig. 47. YELLOW ELASTIC CONNECTIVE 
 TISSUE FIBRES. (After Sharpey.) 
 
 Fig. 48. YELLOW ELASTIC CARTILAGE 
 
 FROM THE EAR. 
 
 tip of the nose, and is peculiarly well adapted to admit 
 slight alterations in position or form. The white fibrous 
 cartilage, as the name suggests, is composed of a matrix of 
 closely pressed white fibres, with the contained cartilage 
 cells packed between them. Such cartilage is found in 
 many places as disks between articulating bones ; it binds 
 together contiguous bones forming connecting fibres between 
 
THE SUPPORTING TISSUES. 
 
 105 
 
 them, and in still other cases it lines bony grooves in which 
 tendons of muscles glide. Such cartilage is pre-eminently 
 
 '*HJ 
 
 Fig. 49. WHITE FIBROUS CARTILAGE FROM AN INTERVERTEBRAL DISK. (After Schafer.) 
 
 fitted for positions where strength and rigidity are required. 
 The cartilages shade off insensibly and without any sharp 
 line of demarkation into the connective tissues proper, that 
 
 Fig. 50. TRANSITION FROM CARTILAGE. 
 a, through the intermediate form b, to connective tissue, 6, on the right. 
 
 tissue which pervades all the organs of the body and is the 
 framework of every structure. 
 
 Connective Tissues Proper. 
 
 Of these connective tissues proper, two varieties occur. 
 The elastic is composed of thick, wavy, yellow elastic threads, 
 which frequently branch. This tissue is found in those parts 
 of the body where elasticity is desirable, as for instance, in 
 the walls of the arteries and veins, and is to a large extent 
 the prevailing tissue in the lung. The white fibrous tissue, 
 on the other hand, is composed of bundles of smaller, 
 straighter white threads possessing little or no elasticity. 
 This tissue is especially well exhibited in the tendons and 
 
106 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 gives to these their strength. As far as the fibres are con- 
 cerned, there is but little difference between the yellow 
 elastic and the ^ white fibres -of cartilage, and the corre- 
 
 Fig. 51. CONNECTIVE TISSUE CORPUSCLES. (After Schafer.) 
 
 sponding ones of connective tissue, their classification into 
 cartilage or connective tissue being determined rather by 
 the closeness of these threads and the shape of the cor- 
 puscles which are included. In the cartilages, on account 
 
 Fig. 52. FIBRES OF AREOLAR TISSUE. 
 
 of the firm texture, the cells are round and have little lati- 
 tude to move about. In the connective tissues, on the 
 
THE SUPPORTING TISSUES. 107 
 
 other hand, the meshes being much more open, the enclosed 
 cells become much branched and have the power to move 
 about. Such wandering connective tissue corpuscles are 
 not always easily distinguished from wandering blood cor- 
 puscles. While in the case of cartilage the yellow elastic 
 varieties and the white fibrous varieties are found tolerably 
 separate, in the connective tissues we frequently find both 
 making up the framework of the structure in question. 
 Such a mixture of yellow elastic and white fibrous tissue is 
 called areolar tissue, and is particularly well exemplified in 
 the connective tissue under the skin. 
 
 Humors. 
 
 A final kind of supporting tissues frequently classed with 
 the connective tissues proper are the humors of the eye. In 
 these the matrix has never become hard with mineral de- 
 positions, has never developed fibres in it of any kind, but 
 remains almost perfectly liquid. The connective tissue 
 cells which have formed these humors, later on atrophy and 
 practically disappear, leaving this structureless matrix 
 behind. 
 
 FORMATION OF CARTILAGE AND CONNECTIVE TISSUE. 
 
 In their manner of formation all the supporting tissues 
 are alike. They are not made by a direct differentia- 
 tion of cells into these tissues, but, as stated once before, 
 are formed as a secondary product by the cells. In the 
 case of bone, this deposition has been treated at length. In 
 the remaining supporting tissues the origin is quite similar, 
 save that the cartilages and connective tissues are not added 
 continually from the outside, but grow throughout the en- 
 tire substance; that is, it is a growth by intussusception. 
 The cartilage cells in the matrix retain the power to divide, 
 and new cells formed by such division separate by the 
 secretion of more matrix between them. In the case of the 
 yellow elastic cartilage this has been specially worked out. 
 Here the matrix is first deposited in the form of little 
 
108 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 granules, probably secreted or excreted by the cartilage 
 cells, which granules later on in some way not yet under- 
 stood, fuse, forming the characteristic fibres. While most 
 cartilages have a membrane around them called the peri- 
 chondrium, such a membrane does not figure in any way as 
 it does in the formation of bone, but is here merely an en- 
 veloping membrane supplied, of course, with blood-vessels. 
 
 Fig. 53. DEVELOPMENT OF ELASTIC TISSUE BY THE DEPOSITION OF ROWS OF ELASTIC 
 
 GRANULES, 0, FINALLY FUSING INTO A PLATE-LIKE EXPANSION OF ELASTIC SUBSTANCE 
 
 INDICATED AT P. (After Ranvier.) 
 
 The method of origin of yellow elastic tissue just cited, 
 probably does not differ from the manner in which the con 
 nective tissues proper and the humors arise, save that in 
 these the corpuscles which have produced them may actu- 
 ally wander out and leave nothing but their product behind. 
 The supporting tissues being thus not directly composed of 
 cells, possess no physiological activity, and when once 
 formed probably remain entirely unaltered during life. The 
 various forms do not differ much in chemical composition, 
 except the yellow elastic, all yielding when boiled, a variety 
 of gelatine. Their similar nature is further indicated in the 
 fact that they replace each other easily. Thus, cartilages 
 are replaced by bone, and broken bones are sometimes 
 cemented together by the formation of cartilage. 
 
 HYGIENE OF SUPPORTING TISSUES. 
 
 In reference to the supporting tissues, little need be 
 said from the standpoint of their hygiene. It is, of course, 
 
THE SUPPORTING TISSUES. 109 
 
 apparent that in young persons the food should contain suf- 
 ficient amounts of mineral salts, otherwise the bones will 
 not acquire their intended hardness. Milk is peculiarly 
 adapted for this, containing quite a large amount of earthy 
 matter. It not infrequently happens that children, in 
 spite of an apparently rich diet, are really starving for 
 want of the mineral matters which are needed to give con- 
 sistency to these supporting tissues. The final hygienic 
 recommendation that no unusual strains of any kind shall 
 be placed upon any of them while they are in their forma- 
 tive period, is too plain to need further comment. 
 
 JOINTS. 
 
 The supporting tissues not only serve to give form and 
 outline to the body, but in the case of bones they serve to 
 make a system of levers to accomplish the various move- 
 ments of which the body is capable. To permit such move- 
 ments, bones are articulated together to form more or less 
 movable joints. In the body there are found four kinds of 
 movable joints. They are, first, the gliding joints; second, 
 the pivot joints; third, the hinge joints, and fourth, the 
 ball-and-socket joints. In addition to these movable joints, 
 bones articulate in such a way as to preclude motion. In- 
 stances of such articulation are plain in the bones of the 
 skull, where the bones remain separate until the skull has 
 reached its mature size. Such articulations are called 
 sutures. 
 
 In the gliding joints a number of bones glide over each 
 other to such an extent as to permit quite a little motion. 
 Instances of such joints are in the wrists. and ankles. Here 
 the carpal and tarsal bones gliding over each other permit 
 all the different motions of which the wrist and ankle are 
 possible. There are but two instances of pivot joints in the 
 body. The plainest instance is the joint between the atlas 
 and the axis, where the odontoid process of the axis forms 
 the pivot, around which the atlas rotates. A second illus- 
 tration is in the case of the forearm, where, by the peculiar 
 
110 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 gliding motion of the radius at the elbow, the hand may be 
 pronated and supinated by having the radius turn on the 
 ulna as a pivot. The hinge joints occur in greater num- 
 ber, being found in the elbow, the knee, and in the phal- 
 
 Fig. 54. ARTICULATIONS OF THE PELVIS AND HIP-JOINT, SEEN FROM BEFORE. THE 
 
 ANTERIOR HALF OF THE CAPSULAR LIGAMENT OF THE LEFT HIP-JOINT HAS BEEN 
 REMOVED, AND THE FEMUR ROTATED OUTWARDS. (Allen Thomson.) 
 
 1, anterior common ligament of the vertebrae passing down to the front of the 
 sacrum; 2, ilio-lurnbar ligament; 3, anterior sacro-iliac ligament; 4, placed in the great 
 sacro-sciatic foramen, points to the small sacro-sciatic ligament; 5, a portion of the great 
 sacro-sciatic ligament; 6, anterior ligament of the symphysis pubis; 7, obturator mem- 
 brane; 8, capsular ligament of hip-joint; the figure is placed on its ilio- femoral band; 9, 
 upper part of the divided capsular ligament of the left hip-joint near the place of its at- 
 tachment to the border of the acetabulum ; 10, placed on the os pubis of the left side above 
 the transverse ligament of the acetabular notch. The head of the femur is withdrawn 
 partially from the socket, so as to show the iuterarticular ligament stretched from the 
 transverse ligament. 
 
 anges of hand and foot. The joint which seems capable of 
 giving the greatest latitude of motion, is the ball-and- 
 socket joint, examples of which are the joints at the shoul- 
 der and at the hip. 
 
 In order to make these articulating surfaces as smooth 
 as possible, bits of cartilage cover the ends of the bones. 
 These are covered next to the joint by a delicate membrane 
 
THE SUPPORTING TISSUES. 
 
 Ill 
 
 called the synovial membrane, which secretes a fluid known 
 as the synovial fluid, intended probably as a kind of lubri- 
 cant to reduce the friction to a minimum. To make these 
 
 Fig. 55. Fig. 56. 
 
 Fig. 55. RIGHT KNEE-JOINT, FROM THE INNER SIDE AND ANTERIORLY. (Allen Thomson.) 
 1, tendon of the rectus muscle near its insertion into the patella; 2, insertion of 
 the vastus internus into the rectus tendon and side of the patella; 3, ligamentum patel- 
 lae descending to the tubercle of the tibia; 4, capsular fibres forming a lateral ligament 
 of the patella prolonged in part from the insertion of the vastus internus downwards 
 towards the inner tuberosity of the tibia; 5, internal lateral ligament; 6, tendon of the 
 semimembranosus muscle. 
 
 Fig. 56. THE LIGAMENTS OF THE WRIST JOINT, DORSAL VIEW. 
 
 joints firm and preclude the possibility of displacement, 
 they are wrapped with a series of ligaments extending 
 from one bone to the other, so as to make impossible the 
 relative displacement of the articulating surfaces. 
 
CHAPTER VII. 
 
 MUSCLES AND PHENOMENA OF CONTRACTION. 
 
 Probably the most striking characteristic of any living 
 body is its ability to move. But this power of motion is by 
 no means a property of all living things. The entire realm 
 of plants, with exceptions of course which need not concern 
 us here, is devoid of the power of actual movement, and 
 there are some animals whose ability to move from place to 
 place is entirely wanting. The movements of our bodies 
 are caused by the contraction of organs familiar to every 
 one as the muscles. There are, however, in the body struc- 
 tures other than the muscles which possess this power to a 
 certain extent. Thus, many of the varieties of white cor- 
 puscles, such as the white blood corpuscles, cartilage cells, 
 connective tissue cells, are able to move from place to 
 place. Such locomotion is described as amoeboid. The 
 power of active movement also occurs in ciliated cells 
 which are found lining the entire respiratory system, with 
 the exception of the pharynx and the internal lung cells, 
 and which occur also in the internal genital ducts. Such 
 cells consist of a main body which shows no power of 
 motion, but is continued at one end into a number of 
 thread-like prolongations, which have the power of moving 
 rapidly backwards and forwards. The expulsion of the 
 phlegm from the respiratory passages up into the mouth is 
 accomplished by such ciliated action. It is interesting to 
 observe that all the cilia of a membrane seem to move in 
 harmony, the movements of the cilia sweeping across the 
 surface like waves of moving grain through a wind-swept 
 wheat field. In the internal genital ducts they serve to 
 (112) 
 
MUSCLES AND PHENOMENA OF CONTRACTION. 113 
 
 propel the re-productive elements. The real organs of 
 movement are, however, the muscles. A careful examina- 
 tion of the entire muscular system of the body shows at 
 once three tolerably distinct kinds of muscles. First, the 
 voluntary or skeletal muscles ; or, on account of their mi- 
 croscopic appearance to be described later, cross-striated 
 muscles. Second, the involuntary, visceral or plain muscles. 
 Third, the muscles which form the heart, and which differ 
 materially from both of the preceding, and occupy from 
 an anatomical point of view an intermediate position. 
 
 Voluntary Muscles. 
 
 As the name indicates, these muscles are under the con- 
 trol of the will. This is, however, not absolutely true, as 
 there are a number of muscles over which the control of the 
 will has been lost. Thus, there are some muscles of the ear 
 which, if they could be used, would serve to move that 
 organ, but the power to move them has been entirely lost. 
 That nearly all of these muscles are attached to bones has 
 given them the name of skeletal muscles. But there are 
 exceptions to this as well. Thus the circular mucles enclos- 
 ing the mouth or the eyes, are not attached at all to any 
 bone, and yet are voluntary in the highest degree. The 
 real classification is based upon their minute structure, and 
 in this all agree in showing under the high power of the 
 microscope peculiar cross striations to be discussed later. 
 
 TYPES OF VOLUNTARY MUSCLES. 
 
 A typical muscle is composed of a thick, central portion 
 called the belly, which tapers at each end into a thick 
 string of white fibrous tissue familiar as the tendon. From 
 this type, however, there are many deviations. Thus the 
 muscle which serves to bend the arm forward, ends at the 
 shoulder in two tendons instead of one. This has given 
 the name of biceps to this muscle. Immediately under the 
 
114 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 arm lies the muscle 
 
 Fig. 57. SHOWING THE 
 
 SUPERFICIAL MUSCLES 
 OF THE RIGHT ARM, 
 FROM BEFORE. 
 
 1, l', pectoralis major; 
 2, 2', deltoid; 3, 3', 3", 
 biceps; 4, 4', brachialis 
 auticus; 5, 5', triceps. 
 Numbers from 6-17 refer 
 to muscles and tendons of 
 fore-arm and hand. 
 
 which serves to extend the arm, which 
 ends in three tendons at the shoulder, 
 and is called the triceps. Then again 
 there are muscles which have a tendon 
 in the middle, thus dividing the muscle 
 into two portions. Such a muscle is 
 called a digastric muscle, that is, has 
 two bellies. Sometimes even more than 
 two occur, when the muscle is called a 
 polygastric muscle. Instances of such 
 polygastric muscles are found in the 
 anterior abdominal wall. Closer exam- 
 ination of a typical muscle will show 
 it divided up into bundles separated 
 from each other by intervening con- 
 nective tissue. On a cross section of 
 a muscle these bundles would appear 
 as irregular areas, and are familiar to 
 every one in the characteristic appear- 
 ance of a piece of lean beefsteak. This 
 connective tissue not only extends 
 through the muscle, dividing it up into 
 bundles which are called fasciculi, but 
 envelopes the entire muscle. It serves 
 to carry the nerves and blood-vessels 
 through the muscle, and is called the 
 perimysium. 
 
 HISTOLOGY OF VOLUNTARY FIBRES. 
 
 Fibrillation. For a more detailed study the microscope 
 must be called to aid, and it is then seen that the fasciculi 
 are divided into still smaller bundles, and that the smaller 
 bundles are finally composed of the ultimate fibres. These 
 muscle fibres all run in the same direction, which accounts 
 for the splitting observed on any piece of boiled beef. If 
 
MUSCLES AND PHENOMENA OF CONTRACTION. 115 
 
 such a small bundle be teased under the microscope into its 
 
 Fig. 58. SEVERAL VOLUNTARY MUSCLE FIBRES. (After Sharpey.) 
 a, end view of fasciculus ; 6, 6, individual fibres ; c, a fibre splitting: into longitudinal 
 fibrils. 
 
 ultimate fibres, the following points may be noticed con- 
 cerning their finer structure: 
 
 Striation. The fibres appear cross-striped. This is not 
 due, however, to markings running on the outside of a 
 
 Fig. 59. PORTION OF A HUMAN MUSCULAR 
 
 FIBRE SHOWING THE ALTERNATE LIGHT 
 AND DARK BANDS, AND IN THE LIGHT 
 r.A.XI) THE MK.M15RANE OF KRAUSE. 
 
 (After Sharpey.) 
 
 Fig. 60. Two VOLUNTARY FIBRES. (After 
 
 Gegenbaur.) 
 
 n, nuclei under sarcolemma ; s, sar. 
 colemma visible where the fibre is torn. 
 
 muscle, but it is due to the fact that a muscle fibre is com- 
 
116 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 posed of alternating light and dark disks, somewhat like a 
 stack of coin might be composed of alternate copper cents 
 and silver dimes. If a crushed portion of a fibre be exam- 
 ined it is possible to make out a delicate covering extend- 
 ing entirely around the fibre, known as the sarcolemma. In 
 this sarcolemma lie the more or less semi-liquid contents, 
 which exhibit the striation referred to. 
 
 Nuclei. Scattered along the fibre here and there, and 
 lying immediately underneath the sarcolemma, are nuclei. 
 
 Measurements of an Individital Fibre. Measurements 
 of these fibres in an adult muscle give a length of from one- 
 half inch to an inch and a half, and a width of about one 
 five-hundredth of an inch. L,ittle floating gossamer threads 
 cut in lengths of an inch or more may serve to give us an 
 idea of their actual size. It will be seen from their length 
 that an individual muscle fibre does not run the entire 
 length of a muscle, as many muscles are five, six, or more 
 inches in length. 
 
 Attachment to Tendons. A delicate fibril from the ten- 
 don may be traced to the end of a muscle fibre where it is 
 directly cemented to the sarcolemma. An older view that 
 the tendons are but the connective tissue of a muscle 
 extended, is no longer tenable. Whether such tendon 
 fibrils run to both ends of all fibres, is still a matter of 
 question. Some histologists claim two or more muscle fibres 
 may be cemented end to end; others again that the muscle 
 fibres are twisted and intertwined with each other some- 
 what like threads in a rope, and that tendons attach them- 
 selves merely to the outermost fibres. The probability of 
 the matter, however, is that in the majority if not in all 
 cases each individual fibre receives at both of its ends a 
 delicate little fibril from the tendon, which fibril is directly 
 and firmly cemented to its sarcolemma. This would make 
 each individual muscle fibre in reality a separate muscle. 
 
 Blood Supply. A voluntary muscle is quite vascular, 
 each fibre being invested with a capillary net-work almost 
 
MUSCLES AND PHENOMENA OF CONTRACTION. 117 
 
 along its entire length. These capillaries, together with the 
 
 Fig. 61. SHOWING THE MANNER IN WHICH THE CAPILLARIKS ARK SUPPLIED TO THE 
 
 VOLUNTARY FIBRES. (E- A. S.) 
 
 nerves, are carried by the connective tissue perimysium , 
 which wraps more or less completely each individual fibre. 
 
 Nerves. Each muscle fibre is connected with a nerve. 
 The nerve penetrates the sarcolemma and then has its axis 
 
 Fig. 62. MUSCLE FIBRES FROM A LIZARD TO SHOW THE MANNER OF TERMINATION OF 
 
 THE MOTOR NERVE IN THE SO-CALLED "END ORGANS." (After KuhllC.) 
 
 a, side view; b, surface view of cud organ. 
 
118 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 cylinder expand into a broad plate-like structure known as 
 the muscle plate, or the nerve plate. In this nerve plate 
 occur numerous nuclei. This nerve plate is probably noth- 
 ing more than the expansion of nervous protoplasm by 
 which the contact between nerve and muscle is made the 
 more intimate. 
 
 Color. Ordinarily voluntary muscles appear red. Ex- 
 ceptions to this are, however, familiar to us all in the case 
 of the breast meat of domestic birds, which is white. 
 The redness of ordinary muscle is due to its containing 
 traces of haemoglobin, which it has probably derived from 
 the continued coursing of the blood in such large quantities 
 through its substance. Muscles which are not much used 
 and which, therefore, have their blood supply much re- 
 duced, are white. Thus in wild birds which use their 
 wings in continued flight, the breast muscles also are dark. 
 Whether this haemoglobin is contained in the muscle for a 
 specific purpose, or as a mere accidental coloring, caused 
 by the circulating blood, is not clear. Possibly it may 
 enable the muscles to store up in themselves for ready use, 
 a small reserve supply of oxygen. 
 
 Growth of Muscle. The dimensions of a muscle just 
 given are by no means invariable. In fact, the individual 
 muscle fibres actually grow in size for a long time, being 
 many times larger in an adult than in a very young child. 
 The growth of muscle, resulting from continued properly di- 
 rected muscular exercise, such for instance as with the 
 blacksmith in the use of his arms, increases the size, and so 
 of course, strength of the individual muscle fibres already 
 formed. Reasoning in an opposite direction, the apparent 
 atrophy of. an unused muscle may be due to a peculiar 
 shrinking of the individual muscle fibres rather than a 
 direct absorption of them. But it seems probable that new 
 muscle fibres may also arise after birth. There are found 
 scattered throughout the muscular substance small spindle- 
 shaped cells, designated as muscle cells, or more frequently 
 
MUSCLES AND PHENOMENA OF CONTRACTION. 119 
 
 on account of their shape, spindle cells. These cells when 
 occasions seem to demand elongate, their nuclei multiply, 
 the external layer develops the sarcolemma and the interior 
 protoplasm, at first structureless, receives gradually the 
 characteristic cross markings. These cross marks seem to 
 appear first toward the outside, and later on extend through 
 the middle. The nuclei at first distributed through the pro- 
 toplasm take their position under the sarcolemma, and in 
 this way a new muscle fibre has been produced. A sec- 
 ond method of muscle formation is claimed, in which the 
 new fibres arise by a longitudinal splitting of old ones. 
 There is no doubt but what under the microscope such 
 splitting fibres may be occasionally seen, but whether these 
 are fibres in process of formation, or whether they may not 
 be fibres that are undergoing degeneration, is a question 
 still unsolved. 
 
 THE FINER STRUCTURE OF THE MUSCLE FIBRE. 
 
 The histological points mentioned so far may be made 
 out without any question by any good observer possessed 
 of a good compound microscope. But when we have seen 
 the muscle composed of alternating light and dark bands, 
 it has not yet been made out to what kind of a structure 
 this appearance is due. On account of the extreme mi- 
 nuteness it is difficult to establish the ultimate structure very 
 plainly, so that what is given in explanation of its finer 
 anatomy is to a large extent theory. 
 
 A single fibre is easily seen to consist of still finer fib- 
 rils, as is evidenced by the fact that the ends of a fibre will 
 fibrillate out into delicate fibrils, much like an ordinary 
 twisted rope when its end is unwound. These finer threads 
 are called fibrils, and bundles of them are believed to make 
 each individual muscle fibre. But when subjected to cer- 
 tain chemical agents a muscle fibre may also be made to 
 split horizontally into small disks somewhat like the stack 
 of coin referred to, might be thrown over and fall into the 
 individual pieces. This would seem to show that the fibrils 
 
120 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 themselves are made up of component pieces, in some way 
 attached end to end to make up the entire length. These 
 component parts of each fibril are called the muscular units 
 or the sarcomeres. When the muscle fibres break up into 
 these disks the line of cleavage runs through the middle of 
 the light band. With very high powers there may be dis- 
 cerned at this point a little darker line, which is probably a 
 membrane, and has been called Krause's membrane. In 
 the longitudinal splitting of the fibre into the fibrillse, such 
 as a specimen of muscle hardened in alcohol readily does, 
 the lines of splitting seem to be in a peculiar inter-columnar 
 substance which binds the individual fibrils together. 
 
 From these two manners of breaking up it can easily be 
 seen that the individual sarcomere is that portion of a fibril 
 which extends from the middle of one light band, or from 
 Krause's membrane, to the middle of the next white band. 
 It is, therefore, light at both ends and contains its dark 
 band in its middle. These sarcomeres, lying in even rows, 
 give to the entire muscle fibre the banded appearance. The 
 light material next to Krause's membrane seems to be 
 a thin, active kind of protoplasm called hyaloplasm. The 
 dark band in the middle really consists of two dark bands 
 separated through the middle by a light band called the 
 band of Hensen. These dark bands, as may easily be seen 
 by referring to the diagram, have little comb-like projec- 
 tions extending up and down, which next to the band of 
 Hensen are united together on each side to a common base. 
 Whether these prongs or teeth are solid, or whether they 
 are hollow tubes, cannot be determined. They probably 
 consist of a firmer kind of protoplasm, and are in each sar- 
 comere called the sarcosome. The transparent columnar 
 substance, which seems to cement the individual fibrillae 
 together, is of a similar kind of protoplasm called sarco- 
 plasm. Thus the individual sarcomere would have hyalo- 
 plasm at its ends, have the sarcosome or dark portion in 
 the center, and be connected with neighboring sarcomeres 
 by the intermediate sarcoplasm. 
 
MUSCLES AND PHENOMENA OF CONTRACTION. 121 
 
 When a muscle contracts it may be seen that the white 
 band becomes narrower, but that the teeth-like projections 
 of the sarcosome become pushed further apart and dis- 
 
 S.E. 
 
 Fig. 63. DIAGRAM OF A SINGLK SARCOMERK. 
 
 A, in relaxed condition; B, in contraction; K, K, membrane of Krause; H, membrane 
 of Hensen ; S, E, the darker sarcous element. 
 
 tended. The phenomena of contraction according to this 
 view are therefore explained in this manner. When a nerv- 
 ous impulse reaches the muscle directing it to contract, in 
 some way yet entirely unknown, the hyaloplasm by its 
 activity flows in between the prongs of the sarcosome and 
 distends these. In this way each sarcomere is slightly 
 shortened. The multiplication of this shortening through 
 all of the sarcomeres that make up a muscle fibre produces 
 a movement of the entire muscle. Whether this hyalo- 
 plasm forces itself in between these prongs, or whether it 
 distends the sarcosome by flowing into these prongs, which 
 in the latter view would be hollow, is not known. While 
 this serves in a physical way to make clear to us the real 
 manner in which a muscle fibre shortens, it leaves as un- 
 answered as before what causes the hyaloplasm in this 
 active way to flow into the sarcosome and bulge it out 
 laterally, thus shortening the long diameter of the fibre. 
 
 Plain Muscular Tissue. 
 
 Plain muscular tissue also is composed of fibres; but 
 these fibres are very much smaller than those of voluntary 
 muscular tissue, and possess no cross markings whatever. 
 They are so much smaller than the voluntary that on an 
 average the length of an involuntary is less than the width 
 of a voluntary. These plain muscle fibres are about one 
 
122 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 six-hundredth of an inch in length and very narrow, re- 
 sembling elongated spindles. They seem to show a very 
 faint longitudinal striation, and possess near their center a 
 very evident nucleus. It is impossible to establish a cell 
 wall, like a sarcolemma, though probably enveloped with a 
 dark, denser layer. They are never joined to tendons, but 
 are cemented together to form sheets of muscle. Bach 
 muscle fibre is probably supplied with its own nerve; but 
 in this case the nerve has no end plate, but after encircling 
 the fibre once or twice ends abruptly in the nucleus. They 
 are not very vascular, and in cross-sections of involuntary 
 muscular tissue, the capillaries of which have been injected 
 so as to make them readily visible, there may be as many 
 as twenty-five or thirty rows of plain cells between neigh- 
 boring capillaries. 
 
 II 
 
 Fig. 64. INVOLUNTARY MUSCLE FIBRE CELLS, FROM A HUMAN ARTERY. (After Kb'lliker.) 
 a, nucleus; ft, a fibre treated with acetic acid to render it more transparent. 
 
 These cells have the power of shortening their long 
 axis, but do not possess to any such extent as the volun- 
 tary muscles the ability to contract quickly or energetically. 
 They are peculiarly well adapted to the visceral organs, 
 where it is evident that the movement ought to be very 
 slow, gradual and measured. Examples of this tissue may 
 be found in the walls of the stomach and intestines, in the 
 
MUSCLES AND PHENOMENA OK CONTRACTION. 123 
 
 walls of the arteries, around the finer divisions of the bron- 
 chial tubes, and in numerous other places. 
 
 Cardiac Muscle. 
 
 The third kind of muscular tissue occurs only in the 
 heart. The fibres in this case are cross-striped, very simi- 
 lar to the voluntary. They are not quite as wide as the 
 voluntary, but are very much shorter, a typical heart fibre 
 being usually only about twice as long as it is wide. It 
 possesses near its center an evident nucleus, in which no 
 doubt, the nerve ends. There are no tendons, but the 
 cells are cemented together in bands of fibres. Very fre- 
 quently these cells are branched, a property possessed by 
 neither of the other kinds of fibres. Because of this cross- 
 striation and its size it is evident that it is an intermediate 
 
 Fig. 65. Six CARDIAC MUSCLE FIBRES. (After Schafer.) 
 b, c, showing branching of cells. 
 
 kind of muscle possessing some of the properties of both, 
 and therefore peculiarly well adapted for use in the heart, 
 where much greater energy of contraction is desired than 
 in the ordinary involuntary muscles. 
 
 The Chemistry of Muscle. 
 
 The muscles possess about seventy-five per cent, of 
 water, traces of various mineral salts, bits of grape sugar, 
 
124 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 and a peculiar kind of muscle sugar called inosit: further, 
 traces of haemoglobin, whence their color, bits of organic 
 compounds such as kreatin, which will be discussed further 
 in the chapter on excretion, and finally the important sub- 
 stance, muscle albumen. Just in what form this muscle 
 albumen is in a living muscle it is impossible to determine, 
 for in order to investigate the albumen it is, of course, 
 always necessary to destroy the vitality of the muscle. If, 
 however, perfectly fresh muscle be taken and then cooled 
 almost to the freezing point, then cut into small pieces and 
 the liquid pressed out through a cloth, there may be filtered 
 out in this way a slightly yellowish-colored fluid called 
 muscle plasma. This muscle plasma at ordinary tempera- 
 tures coagulates much like the blood, and soon presses out 
 of itself a serum much like a blood clot would, which serum 
 is called muscle serum. The substance, which forms the 
 solid portion of the clot, is familiar to all students of physi- 
 ology under the name of myosin. This myosin is insoluble 
 in water, but soluble in common salt solutions, and also 
 soluble in dilute acids. When dissolved in dilute acids it 
 is changed into syntonin, which is, therefore, in reality 
 merely an acid solution of myosin. The blood plasma 
 which has been pressed out of the clot contains several 
 albumens, the principal one being ordinary serum albumen. 
 The nutritive value of muscles is derived, to a large 
 extent, from these albumens. As most of them are, how- 
 ever, insoluble in water and easily coagulated by heat, but 
 little of the albumens is removed by boiling. The mineral 
 salts and the flavors are of course easily extracted by boil- 
 ing water, and so may give to the liquid quite a strong 
 taste, which may mislead the person into the belief that the 
 strong taste is an evidence of its nutritive value. It is well 
 to bear this in mind, as attempts are frequently made to 
 nourish people on variously prepared soups and broths, in 
 the belief that the boiling of the meat has extracted from 
 it its nutritive ingredients. A little of the albumen may pos- 
 sibly thus be extracted, but the nutritive property of it is 
 
MUSCLES AND PHENOMENA OF CONTRACTION. 125 
 
 obtained only in the digestion of the muscle substance 
 itself. Special preparations of broth in which the muscle 
 substance has been at first digested artificially, and thus 
 made an ingredient of the broth have, of course, their full 
 nutritive value. 
 
 Elasticity. 
 
 The ordinary muscles possess to some extent an elas- 
 ticity which enables them when they are stretched by any 
 weight to return to their former position as soon as the 
 stress is removed. Naturally in the body all muscles are 
 slightly stretched, even when entirely relaxed, for a muscle 
 cut from one of its connections at once draws up and 
 becomes materially shorter. This is one of the dangers 
 accompanying the fracture of a bone, for as soon as the 
 controlling action of the bone is destroyed the muscles pull 
 themselves together, and so the ends of the bone may be 
 materially displaced. The advantage of having the muscles 
 on a stretch all the time is, that as soon as they begin to 
 contract they begin to pull upon the bones at once and no 
 time or energy is lost in first pulling up any slack of the 
 muscle itself. 
 
 Physiology of Muscular Contraction. 
 
 Thus far the muscle has been considered as an inert 
 structure, and all that has been said would apply to a dead 
 muscle as well as one still living. But living muscles 
 possess the property to contract when they are properly 
 stimulated. 
 
 MUSCLE STIMULI. 
 
 The usual stimulus to usher in a muscular contraction 
 is a nerve stimulus, but it may be stimulated in other ways. 
 First, by mechanical stimuli: Sudden pressure, tearing, 
 pricking, etc., produce each time a contraction of the 
 affected muscle. Second, thermal stimuli: A sudden change 
 of temperature causes the muscles to contract. The limits 
 of such changes are from almost freezing up to about one 
 hundred and ten degrees. Above and below these tern- 
 
126 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 peratures the muscles cease to react. Third, chemical 
 stimuli: A number of chemical agents will stimulate the 
 muscles. Such agents are fumes of nitric oxide, sulphur 
 dioxide, hydrochloric acid, but especially ammonia gas. 
 Fourth, electrical stimuli: A current of electricity may 
 in different forms induce the muscles to very vigorous 
 activity, and one of the best worked-out chapters on muscle 
 physiology is its reaction to electrical stimuli. 
 
 The question whether these stimuli affect the muscles 
 themselves, and not the nerves in the muscles, can be defi- 
 nitely answered by saying that the stimuli affect the muscles 
 themselves directly. For instance, ammonia stimulates the 
 muscles, but does not affect the nerve. Still again some 
 muscles, for instance the sartorius of the thigh, have no 
 nerves in their ends, yet the muscle there may be stimu- 
 lated to contraction. The best proof is, however, that 
 furnished by the South American poison called curare. 
 This curare lames the motor nerves, but a muscle with such 
 a lamed nerve will still react to all of the preceding stimuli. 
 This curare is used by many of the South American Indians 
 in their chase and warfare. The end of the arrow is im- 
 pregnated with the curare, and when the arrow is intro- 
 duced into the flesh of an animal it drops down motionless 
 to the ground. Its circulation and all of its sensory nerves 
 are left intact, but there is a complete paralysis of all vol- 
 untary action. The animal of course dies by suffocation, 
 being unable to move the muscles of respiration. 
 
 A SINGLE CONTRACTION. 
 
 Having now called attention to the stimuli which produce 
 muscular contraction, a closer study of such a contraction 
 itself naturally follows. If in order to study it more advan- 
 tageously, a frog's muscle be entirely cut out from the body 
 and then suspended from a hook, it may still be made to 
 contract, and on account of its isolation, the phenomena of 
 such a contraction much better studied. Usually a piece of 
 nerve running to the muscle is left connected with it and 
 
MUSCLES AND PHENOMENA OF CONTRACTION. 127 
 
 the stimuli are applied to the nerve, and through this the 
 muscle induced to contract. If now such a muscle makes a 
 contraction, the same occurs with such rapidity that to the 
 unaided eye it seems but a rapid shrinking and a return to 
 its former position. If, however, the lower end of the 
 muscle be fastened to a lever, and this lever be made to 
 write on a drum revolving at a known speed, the contrac- 
 tion will pull the muscle and consequently the lever up, and 
 a curve will be described on the revolving surface. On this 
 curve the various phenomena are then at leisure determin- 
 able. The arrangement for such a demonstration may be 
 seen in the accompanying diagram. 
 
 Fig. 66. ARRANGEMENT FOR SECURING MYOGRAMS. 
 
 P, the moving recording surface, which by the projection at d opens the circuit in K 
 at c, and so induces a break current iap which passing through the muscle stimulates it. 
 In this way the moment of stimulation is determined exactly, it being the moment of 
 contact of d with c. The curve is then recorded as in figure. 
 
 If now the exact moment be noted at which the impulse 
 reaches the muscle it is found that the muscle does not con- 
 tract at once, but that there is a short period after the im- 
 pulse reaches the muscle before it begins to shorten. This 
 period is about one-hundredth of a second, and is called the 
 latent period. During this period the nervous impulse has 
 probably originated molecular changes in the muscle pre- 
 paratory to the contraction. The latent period is succeeded 
 by a steady contraction of the muscle to a maximum, fol- 
 lowed by the relaxation of the muscle to its original position. 
 
128 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 This movement up and down occupies about nine-hun- 
 dredths of a second, making the entire time about one-tenth 
 of a second. Just what these molecular changes in the 
 
 Fig. 67. CURVE OF A SINGLE CONTRACTION. 
 
 R, a, the latent period; a, 6, the gradual contraction to a maximum; b, c, the some- 
 what more sudden relaxation ; c, d, a slight rise owing to the inertia of the recording 
 lever, and having nothing to do with the muscle contraction itself. 
 
 muscle are, which occur during the latent period, it is im- 
 possible to tell, but it is interesting to note that by means 
 of a galvanometer (an instrument for detecting currents of 
 electricity) electrical currents are indicated in the muscle 
 running from the parts furthest removed from the nerve to 
 the part directly stimulated by the nerve. These currents 
 are called the currents or waves of negative variation. What 
 meaning these currents have which flow in a muscle during 
 the latent period is not known, but they are external evi- 
 dences of complicated molecular changes in the muscle sub- 
 stances itself, which make possible the succeeding contrac- 
 tion. Such a contraction which follows a single stimulus 
 is called a simple contraction. Such a simple contraction 
 occurs, as long as the vitality of the muscle is left intact, 
 as often as a stimulus is applied. If, however, the stimuli 
 are applied so rapidly that the second stimulus enters the 
 muscle, before the relaxation from the first stimulus has 
 occurred, the muscle contracts still more. It is, so to speak, 
 a superposition of the second contraction upon the first. 
 Such a superposition does not, however, go on indefinitely; 
 that is, there cannot be super-imposed a third onto a second, 
 or a fourth onto a third indefinitely, for soon a maximum is 
 reached beyond which, no matter how many stimuli are sent 
 in, the muscle will not contract. 
 
MUSCLES AND PHENOMENA OF CONTRACTION. 129 
 TETANIC CONTRACTIONS. 
 
 But with very rapidly entering stimuli the muscle re- 
 mains in one spasmodic contraction. Such a continued and 
 uninterrupted contraction is spoken of as a tetanus. All 
 the contractions of muscles caused by the will are such 
 tetanic contractions, for the impulses sent along voluntary 
 paths to our muscles are sent at the rate of about ten per 
 second. The fact that a voluntary muscle receiving im- 
 pulses at such a constant rate does not remain in one con- 
 tinuous and constant contraction, is due to the fact that 
 although the rate of the stimuli remains the same, the force 
 of these stimuli may vary, and so the force of the con- 
 traction varies accordingly. 
 
 THE WAVE OF CONTRACTION. 
 
 When a stimulus reaches a muscle the entire muscle 
 does not begin to contract at once, but the contraction pro- 
 ceeds in the form of a wave, beginning at the point where 
 the impulse enters and extending to the opposite ends. 
 Somewhat like a wave in a trough of water caused by the 
 introduction of a pebble, starts at the point where the peb- 
 ble strikes it and proceeds from this point in opposite direc- 
 tion to the ends of the trough. That is to say, the part of 
 the muscle next to the nerve begins to shorten, and then in 
 consecutive order portions further away from it follow. This 
 wave of contraction can be easily noticed on a muscle as a 
 little swelling which runs from the insertion of the nerve to 
 the opposite ends. This rate has been measured, and is 
 in the living muscle (not cut out of the body) about thirty 
 or forty feet per second, while in muscles which have been 
 cut out of the body, on account of their reduced vitality, it 
 is only about fifteen feet per second. In plain muscle tissue 
 the rate of such a wave reaches the low minimum of three 
 to four inches per second. Such a wave of contraction in 
 plain muscular tissue may be easily seen in the creeping 
 peristaltic motion of the intestine. The phenomena here 
 
 described and the times in which they occur apply only to 
 9 
 
130 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 living muscles. Muscles which have begun to die, or have 
 been fatigued by excessive work, or have been cooled too 
 much, or have been heated to above one hundred and ten 
 degrees, react much more slowly, and finally refuse to act 
 at all. 
 
 The Actual Lifting Power of Muscles. 
 
 It is the function of muscles to pull and lift, and their 
 maximum capacity to lift is of course a matter of general in- 
 terest. The amount which a muscle can lift varies with its 
 cross-section in the same way that the capacity of a rope to 
 sustain a weight depends upon the thickness of the rope. 
 With frog's muscle, experiments indicate that a muscle a 
 square centimeter in cross-section can lift about six and one- 
 half pounds. A square centimeter of muscle in man may 
 lift as much as twenty-five pounds under the stimulus of the 
 will. When we remember that some muscles are many 
 square centimeters in cross-section the force with which they 
 may be made to lift and pull is easily explained. 
 
 Amount of Shortening of Muscles. 
 
 Another question of interest is the proportionate length 
 to which a muscle may contract itself. This, of course, 
 varies somewhat with different muscles. A short, thick 
 muscle would not shorten itself as much as a longer slender 
 muscle. Varied experiments indicate that the actual reduc- 
 tion in length may be from sixty-five to eighty-five per cent, 
 of the entire muscle. 
 
 Changes in Volume. 
 
 A muscle when it contracts occupies a little less volume 
 than it did in an expanded state. This is no doubt due to 
 the fact that in the contraction, some of the muscle sub- 
 stance is more compressed. This may be easily demon- 
 strated by hanging a muscle in a vessel of water and then 
 making it contract. On the contraction, the height of the 
 water in the vessel sinks a trifle. 
 
MUSCLES AND PHENOMENA OF CONTRACTION. 131 
 
 Muscle Fatigue. 
 
 One of the most familiar phenomena of our muscles is 
 their fatigue resulting from hard work. This fatigue is 
 caused by an accumulation of waste matter in the muscle 
 substance, owing to its active work. This may be easily 
 demonstrated by taking a frog's muscle, and causing it to 
 contract until it is thoroughly fatigued and refuses to react 
 to further stimuli. If now such a muscle be washed with 
 water which contains a little salt, so as to make the water 
 as nearly like blood serum as possible in that respect, it 
 begins to contract again with apparently renewed energy. 
 The only explanation available is that the salt water in 
 question washed out some of the waste products. Of course 
 this could not be continued indefinitely, for soon the muscle 
 fibre not being nourished would be robbed of all its mate- 
 rial, and so a final exhaustion ensue. This explains why a 
 muscle fatigued revives so quickly when it is moved about 
 freely, and for a few minutes the blood is allowed to stream 
 into it uninterruptedly. This feeling of fatigue, however, 
 does not come directly from the muscles. The muscle fibres 
 are supplied with motor nerves only, and it is probably im- 
 possible to receive a sensory impression from them. There 
 are, however, distributed between the muscle fibres sensory 
 nerves, and from these we derive our muscular sensations. 
 Some of these nerve fibres seem to end in little special end 
 organs which suggest the Pacinian bodies of the mesentery. 
 In fact, some histologists believe that the spindle cells men- 
 tioned on a preceding page* as cells which develop later in- 
 to new muscle fibres, are not muscle cells at all, but are 
 sensory cells connected with nerves, and that from these 
 to a large extent we get our muscular sensations. 
 
 The Blood Supply. 
 
 The vitality of a muscle is very dependent upon its blood 
 supply. If the artery going to a muscle be cut, or if only 
 venous blood be able to reach it, the muscle at once begins 
 
 *See page 119, 
 
132 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 to atrophy. There is in the body a nervous arrangement 
 by which the blood-vessels leading to the muscle are at 
 once enlarged as soon as that muscle is called into action. 
 These are the dilator nerves, which will be treated in detail 
 in the chapter on circulation. By this arrangement a work- 
 ing muscle receives an extra amount of nourishment, and 
 of oxygen, to carry on its added work. The vitality of a 
 muscle seems also to be dependent upon its connection with 
 the nervous system. A muscle with its nerve cut begins to 
 atrophy at once. The fibres become shrunken and turbid, 
 and soon lose their power of contractility. This explains 
 why in persons suffering with paralysis the muscles begin 
 so rapidly to shrink and weaken. 
 
 Electrical Phenomena in Muscles. 
 
 When a muscle is cut out of the body and tested with a 
 galvanometer there may be demonstrated running through 
 its substance small currents of electricity. The central or 
 uncut portion of the muscle seems to be positive with refer- 
 ence to the cut ends. Thus, if the wires be placed one on 
 the center of the muscle and the other at the end, a current 
 runs through the wires from the central portion toward the 
 ends, and of course in the muscle, to complete the circuit, 
 from the ends toward the center. These currents have been 
 
 Fig. 68. DIAGRAM TO SHOW THE DIRECTION OF THE MUSCLE CURRENTS IN AN- EXCISED 
 
 MUSCLE. 
 
 e,f, central positive portion; o, c, b, d, cut negative ends. The lines with arrows in- 
 dicate the direction a current would take between the points touched. In lines 6, 7, 8, no 
 current appears for obvious reasons. 
 
MUSCLES AND PHENOMENA OF CONTRACTION. 133 
 
 called the muscle currents. They have, however, probably 
 no real physiological significance, because it has been found 
 in many different fields that a tissue which is injured and 
 dying becomes electrically negative to tissues left unhurt. 
 As the muscle where it was cut at the ends has begun to 
 die, these ends have become negative with reference to the 
 central unhurt portion. For this reason when connections 
 are made currents circulate. These currents are, conse- 
 quently, not found in living muscle, because in this latter 
 case there are no dying portions to be negative. 
 
 WAVE OF NEGATIVE VARIATION. 
 
 If now, such a cut-out muscle be connected with the 
 galvanometer, and the presence of the current circulating 
 through it indicated by the rotation of the magnetic needle, 
 and if while this is going on, the muscle be stimulated to 
 contraction, it is found that during the latent period the 
 needle tends to swing back to its original position. This 
 indicates that during this latent period there must have 
 been set up in the muscle substance currents of electricity 
 which run counter to the first currents, and so neutralize 
 them to some extent, causing the needle to swing back 
 toward its resting point. This current is called the wave of 
 negative variation. This wave is explained on grounds sim- 
 ilar to that of the ordinary muscle currents. The muscle 
 substance not only when dying, but also when stimulated, 
 becomes negative at such points. As the nerve enters the 
 muscle near the middle, and as, therefore, the point of 
 stimulation arises here, this becomes negative toward the 
 ends of the fibres which the stimulus has not yet reached. 
 Thus there will be set up counter currents tending to run 
 from the more positive ends to the negative middle. But 
 as these run in exactly the opposite direction to the cur- 
 rents caused by the dying negative ends, they tend to neu- 
 tralize each other more or less, and so the needle swings 
 back toward the resting point. 
 
134 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 This wave of negative variation referred to occurs in liv- 
 ing muscle, and its presence there may be indicated by a 
 sensitive galvanometer. The rate of this wave has been 
 measured, and is in the muscles of mammals about three 
 meters per second. The time required for this wave to 
 traverse the entire muscle is only about one three-hun- 
 dredths of a second. As the latent period is about one one- 
 hundredth of a second, this wave of negative variation is 
 entirely over before the wave of contraction follows. 
 
 This wave then has physiological meaning. The deflec- 
 tion of the magnetic needle connected with the muscle in- 
 dicates that there are going on in this latent period peculiar 
 molecular changes, the nature of which we do not yet at all 
 understand, but which get the muscle ready for the con- 
 traction which follows just an instant later. This wave run- 
 ning along a muscle may be actually used to stimulate the 
 nerve of another muscle. If, for instance, two muscles 
 with their nerves intact be removed from a frog, which 
 muscles we will call here A and B, and the nerve of A be 
 laid on the muscle of B, and then the nerve of B stimulated 
 so that B will contract, it is found that not only does B con- 
 tract, but A contracts also. This is explained in this way: 
 "Every time B is stimulated by its nerve a wave of negative 
 variation runs along it, which wave acts as an electrical 
 stimulus to the nerve of A which rests on it, and so the 
 nerve of A, being stimulated, produces a contraction of the 
 muscle of A. If, then, B is tetanized, a corresponding te- 
 tanus is produced in A, showing that each single impulse 
 has its own wave of negative variation preceding it. 
 
 Rigor Mortis, or Death-Stiffening. 
 
 Soon after death, varying from a few minutes to not 
 more than several hours, the muscles of the body become 
 intensely rigid, preventing the bending at the joints, a con- 
 dition familiar as ' ' death-stiffening, ' ' or rigor mortis. This 
 rigor begins as a rule in the muscles of the lower jaw and 
 neck, then seizes the upper extremities and gradually ex- 
 
MUSCLES AND PHENOMENA OF CONTRACTION. 135 
 
 tends to the lower extremities. After some time this rigor 
 begins to disappear and the dead body again becomes mov- 
 able at its joints. This loosening is usually attributed to 
 the beginning stage of decomposition, but this is probably 
 not right. According to the more general explanation rigor 
 mortis is due to the clotting of the muscle plasma. Such a 
 formation of a solid muscle clot would of course at once ex- 
 plain the immobility of the body. A more recent view, 
 however, and one which seems to have most in its favor, 
 explains rigor mortis as a final severe contraction of the 
 muscles brought about by the chemical changes which in- 
 duce death. It would be, in other words, a severe tetanus 
 produced by a series of disintegrating chemical changes 
 which accompany the dissolution of life. According to 
 this view the relaxation which follows after the rigor would 
 be merely a return of these muscles to their relaxed condi- 
 tion. That this rigor is probably a contraction and not a mere 
 coagulation of internal albumens is further supported by the 
 fact that a good deal of heat is liberated, and that the 
 muscles show all those phenomena which accompany ordi- 
 nary severe contraction. 
 
 The Source of Muscular Energy. 
 
 The view that muscles possessed a kind of vital energy, 
 which of course Could not therefore be measured like or- 
 dinary physical energies, has long been abandoned, and we 
 know now that muscles must derive their energy to contract 
 in accordance with the same laws that determine what the 
 energy - yielding power of an ordinary steam engine or 
 dynamo shall be. Muscle energy is identical per se with 
 physical and chemical energies. The question now arises, 
 in what manner, from the material that is carried to it by the 
 blood, does it get its energy to produce heat and motion? 
 Without going into a discussion of older views, the follow- 
 ing seems the explanation most in accord with all the ob- 
 served facts. 
 
136 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 When a muscle contracts some of its living muscle sub- 
 stance disintegrates into simpler compounds, and by this 
 disintegration energy is set free which the muscle utilizes, 
 much as in the case of a bit of nitroglycerine. The nitro- 
 glycerine disintegrates into simpler chemical compounds, 
 and by the disintegration a large amount of energy is liber- 
 ated to lift the rock, remove the stump, or what not. A 
 muscle contraction is, therefore, in reality a muscular sub- 
 stance explosion differing from the nitroglycerine analogy, 
 in the fact that there are but particles, here and there, 
 throughout its substance which disintegrate, and not the 
 entire muscle itself. The old view that a muscle contracts 
 because at the time of its contraction something is oxidized 
 is not correct. This may be proved by removing from a 
 muscle all traces of oxygen and then stimulating it. It 
 will contract as usual. Muscles must, however, have 
 nourishment and air carried to them to be built up, to have 
 these wastes repaired, but not to produce the direct con- 
 traction. As for the same reason there would have to be 
 carried to the nitroglycerine factory all the ingredients to 
 make nitroglycerine without any intention whatever of 
 having the explosion occur by doing so. 
 
 Now, muscle substance is mainly albuminous. The 
 question at once arises whether any foods other than albu- 
 mens may serve to nourish the muscles.' That other foods 
 may figure so is argued by the fact that most of our muscu- 
 lar domestic animals are herbivorous; that is, their food 
 consists largely of other than albuminous material. There 
 seems, therefore, a difficulty at first in explaining how 
 foods not albumens, that is, containing no nitrogen, can be 
 built into living muscle substance which is albuminous, that 
 is, which does contain nitrogen. This apparent difficulty 
 is removed, however, at once, by observing that a working 
 muscle seems to retain all the nitrogenous products which 
 have resulted in the muscle disintegration. Or, to be more 
 explicit and to the point, the living muscle albumen disin- 
 tegrates into products which contain the nitrogen and into 
 
MUSCLES AND PHENOMENA OF CONTRACTION. 137 
 
 other products free from the nitrogen. The main nitrogen- 
 free product resulting from this muscular explosion is car- 
 bon dioxide (CO 2 ) , which is then eliminated through the 
 lungs. The nitrogenous products are, however, retained by 
 the muscle and with nitrogen-free foods, such as fats and 
 sugars, may be re-combined to form new living albumen. 
 This albumen may then disintegrate a second time, the 
 nitrogen-free products such as carbon dioxide may be sent 
 out, while the nitrogenous products are again retained, again 
 to be united with fats and sugars and built into new muscle 
 substance. 
 
 Observations made on working muscles are in marked 
 harmony with this view. Thus, every one knows that the 
 harder one works the more carbon dioxide does one breathe 
 out of the lungs ; but very careful experiments have shown 
 that the amount of nitrogen eliminated through the kidneys 
 does not all vary with the work done, a man working hard 
 not eliminating any more nitrogen than one idle. If, of 
 course, all these nitrogenous products formed in the disin- 
 tegration of muscle could be retained and thus used over 
 and over again, somewhat like a brass shell might be re- 
 loaded and so used over and over again in firing, if nothing 
 were lost, there would be no necessity in a full grown man 
 of introducing new albumens into his system. But in these 
 repeated disintegrations, although most of the nitrogenous 
 products are saved and used over and over again, a little 
 incidental loss, a kind of wear and tear incident to all 
 changes results, and it is this little bit which is then sent 
 to the kidneys finally be to eliminated. To replace this 
 wear and tear it is absolutely necessary to put into the blood 
 new nitrogen-containing foods such as albumens. This ex- 
 plains in an unusually clear way how such substances as 
 fats, sugars, and the starches may be gradually utilized in 
 building up muscle substance. It explains further, the im- 
 possibility of doing without albumens, that is, nitrogenous 
 foods, altogether. It explains why the carbon dioxide is in 
 a general way doubled in amount when the work is doubled. 
 
138 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 It explains, finally, why the working body will eliminate 
 practically no more nitrogen from the kidneys than an idle 
 one. Much in the same way as a machine standing still 
 may have as much rust and wear and tear in its machinery 
 as an engine in proper use. 
 
 The reason at last why in a working muscle the arteries 
 are thrown open and the arterial blood carrying the oxygen 
 and the nutritive substance of the plasma streams pell 
 mell through the muscle is, therefore, not to have it con- 
 tract the more, but to give it the opportunity of repair- 
 ing its substance as rapidly as it is being disintegrated. 
 The blood stream would be like the soldier carrying the 
 ammunition to the gunners, in order that they might make 
 good with new powder the losses resulting in their rapid 
 firing. 
 
 The Mechanics of the Muscles. 
 
 THREE CLASSES OF LEVERS. 
 
 With the exception of a few muscles which surround 
 cavities, like the muscle around the mouth, all voluntary 
 muscles are inserted into bones, and produce with these 
 various kinds of levers used in supporting or moving the 
 frame. In every lever there are three points : the point about 
 which the lever turns, called the " fulcrum," the point at 
 which the weight is placed, and the point at which the 
 power is applied. According to the way in which these 
 three points are grouped, levers are divided into those of 
 the first class, the second class, and the third class. In a 
 lever of the first class the fulcrum lies between the "power" 
 and the "weight." A familiar illustration of such a lever 
 is found in the ordinary weighing balance, which is a beam 
 suspended in the middle from a fixed point, the fulcrum, 
 while the ' ' weight ' ' and the ' ' power ' ' are applied at the 
 opposite ends. Numerous other illustrations might be ad- 
 duced. The further illustration of the teetering-board will 
 suffice. There are few levers of this kind in the body. 
 The nodding of the head is one. In this instance the ful- 
 crum is at the point where the occipital bone rests on the 
 
MUSCLES AND PHENOMENA OF CONTRACTION. 139 
 
 atlas, the power is applied where the muscles of the neck 
 are inserted into the skull, while the final weight of the 
 head might represent the "weight." A second illustra- 
 tion of this lever is found in the act of bowing. In this 
 case the fulcrum is at the hip joint, the "power " is applied 
 where the muscles of the hip are inserted to pull the body 
 backwards, while the forward weight of the body represents 
 the "weight." In such a lever little is gained except a 
 change of direction; a power pulling down may, with such 
 a lever, pull a weight up. 
 
 In a lever of the second class the ' ' weight ' ' is between 
 the fulcrum and the u power." The ordinary wheelbarrow 
 is a lever of this class, having its fulcrum at the forward 
 wheel, the " weight " in the bed, and the " power " applied 
 where the hands grasp the handles. A crowbar in prying 
 upwards, as in rolling a barrel, is a further illustration. 
 There are not very many levers of this order in the body. 
 The best illustration of this lever is found in the ankle. 
 When the body is lifted the toes become the fulcrum, the 
 weight of the body rests on the astragalus, while the 
 4 ' power ' ' is applied at the end of the heel where the ten- 
 don Achilles of the calf of the leg is applied. It is evident 
 that by means of such a lever a greater weight may be lifted 
 than the power could lift directly, for the experience of 
 everyone will convince him that by means of a wheel- 
 barrow a man may lift a greater load than he could by 
 directly hoisting it with his arms. 
 
 A lever of the third class has the ' ' power ' ' between the 
 fulcrum and the weight. Most of the levers of the body are 
 of this kind. The flexing of the forearm at the elbow is an 
 illustration of this class. Here the fulcrum is at the elbow, 
 the weight is in the hand where the object to be lifted is 
 held, and the power where the tendon of the biceps muscle 
 is imbedded in the radius. It is evident that in such a 
 muscle much power is lost, for the muscle, in order to raise 
 a certain weight at the end of the radius, would have to 
 pull much more than that weight by pulling on the radius 
 
140 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 near the elbow. Just as it is more difficult to lift a heavy 
 weight on the end of a long fork than it would be to pick it 
 up directly. But while such power is lost, rapidity of mo- 
 tion is gained, but a slight contraction of the biceps muscle 
 causing the hand to move through quite a distance. Such 
 arrangements in our bodies indicate that the levers were 
 intended rather for dexterity and rapidity of motion than 
 for the ability to lift mere weights. However, in the case 
 of the ankle, at which point we have to lift at each step 
 the weight of the entire body, a lever of the second class is 
 put, an arrangement by which a person is never obliged to 
 pull as much on his muscles as the weight of his body 
 actually is. 
 
 THE MATHEMATICS OF LEVEES. 
 
 In every lever, no matter whether of the first, second or 
 third class, the distance from the power to the fulcrum is 
 called the "power-arm" (pa) , while the distance from the 
 "weight" to the fulcrum is called the "weight-arm" (wa) . 
 In all three classes of levers the following simple arithmeti- 
 cal proportion holds true: That the P: W: \wa:pa. Hence, 
 if three of these factors are given, by the simplest mathemat- 
 ical process the fourth may be determined. To illustrate in a 
 specific case : If we assume in the case of the foot the dis- 
 tance from the toes to the astragalus to be seven inches, 
 and the distance from this point in the astragalus to the 
 point where the tendon is attached to the heel bone two 
 inches, we have the power-arm of seven inches plus two 
 inches, or nine inches, and the weight-arm seven inches. 
 If, now, a man's body weighs, say, 160 pounds, which is 
 therefore the weight, how many pounds must his tendon 
 Achilles pull in order to raise him on his toes? By the 
 equation P X pa = W X iva. Calling the power x gives 9;r 
 = 7X160. x = 124% pounds. Thus, by means of this 
 arrangement, to lift a body of 160 pounds requires a pull of 
 only 124 pounds at the heel. 
 
 Or, to take a second example in the case of the fore- 
 arm. Suppose the distance from the elbow to the point in 
 
MUSCLES AND PHENOMENA OF CONTRACTION. 141 
 
 the hand where the weight rests to be fourteen inches, and 
 the distance of the point where the biceps muscle is attached 
 to the radius, to be three inches from the elbow. With 
 what power would the biceps muscle have to contract to 
 raise fifty pounds in the hands? In this case the power-arm 
 is three inches and the weight-arm fourteen inches. By 
 the terms of the equation 3 x = 14 X 50 and x = 233 l7 3 
 pounds. In this case much power is lost, for to lift but 
 the rather small weight of fifty pounds requires a pull of 
 233Va pounds of the biceps, and this on the supposition 
 that the biceps is pulling in the most advantageous direc- 
 tion, while as a matter of fact pulling at an angle adds a 
 further disadvantage. But while much power is lost in this 
 way, but a slight contraction of the biceps moves the hand 
 through a much greater distance. By means of these var- 
 ious levers all through the body we are enabled to accom- 
 plish the familiar movements of walking, running, jumping, 
 swimming, and so on. The exact manner in which these 
 various movements are brought about may be so easily de- 
 termined by direct observation that a full discussion of them 
 is here omitted. 
 
 The Hygiene of Muscles. 
 
 There are but two things in the body which are under 
 our immediate control. One of these is the system of vol- 
 untary muscles, and the second is the central nervous sys- 
 tem. These two systems are placed in our own hands, and 
 for the growth and development of them, we ourselves are 
 directly responsible, and as on the development of these 
 two systems nearly all the other systems depend, we are 
 enabled in an indirect way to be masters of our whole 
 frame. There are, therefore, but two kinds of exercise 
 under our immediate control muscular exercise and nerv- 
 ous exercise. Two kinds of education or, rather, two 
 phases of the same education are, therefore, possible, a 
 physical education and the education of the mind. No one 
 questions for a moment that the mind, if left to itself to 
 
142 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 shift as it may, if never carefully directed, will ever become 
 properly developed. But we do not yet seem to be so clear 
 in reference to the muscular system. In these days, when 
 intellectuality is frequently made to count so much more 
 than health, the exercise of the body is put in the back- 
 ground, in fact, lost sight of too often. "A sound mind in 
 a sound body" is an old maxim, and its validity is not 
 questioned by thoughtful people. But not only do we want 
 a sound body in order to have a sound mind, we want a 
 sound body for its own sake. It is absolutely indispensable 
 in those trades which demand manual labor and physical 
 exercise, and is a necessity in intellectual pursuits and 
 sedentary occupations. This is evidenced by the number 
 of men engaged in brain work who fall by the wayside 
 while they are yet young. It is illustrated every day in men 
 of especial mental acumen who have their sun set while it 
 is yet day. Exercise is the education of the body, in which 
 sense the term education is identical with that when ap- 
 plied to the mind. Properly directed exercise is the fitting 
 of each part to fill its place fully, and to have it completely 
 adapted to the other parts. Exercise is not the excessive 
 or peculiar development of one side or another, it is the 
 all-round development, the result of which is so tersely ex- 
 pressed in that familiar word u health." In olden times 
 exercise was made the larger part of the training of the 
 young soldier and sailor. Common experience has proved 
 that this was an indispensable preparation for the taxing and 
 arduous endurance of warfare, but they selected the strong, 
 the brave, the courageous, while the weak, the undeveloped, 
 were neglected and pushed to the wall. In too many ways 
 does this ancient notion still crop out with us. How many 
 times in our schools and colleges are not the strong picked 
 out for such training and exercise to appear in competitive 
 games, while the weaker ones who need it most are permitted 
 to sit in silence in the grandstand and watch the sport. 
 
 In the physiological use of the term exercise, reference is 
 not had to the production of special strength nor the 
 
MUSCLES AND PHENOMENA OF CONTRACTION. 143 
 
 peculiar training for an especial exertion, but to that 
 rounded training that makes for health. We all know that 
 properly directed exercise strengthens the muscles, vitalizes 
 the body and increases its powers of resistance and of work. 
 To the athlete such a system of rigorous training is recog- 
 nized by everybody to be indispensable. But not only the 
 soldier on his marches or the athlete in his contests, but the 
 minister, the teacher, the lawyer and the merchant as well 
 will later be called upon to undergo as much fatigue and will 
 have demands made upon their bodily strength no less than 
 the former. The many failures to meet these demands in 
 the sedentary vocations ought to be a warning. The intel- 
 lectual professions are rilled with many men who in spite of 
 their sincerest efforts, in spite of a real enthusiasm in 
 their work, drag themselves through their tasks with 
 languor and pain, weariness and discouragement, and with 
 the imminent possibility of a nervous break-down always 
 hanging over their heads, when by a properly exercised 
 and educated body they might have been enabled to prose- 
 cute their work with pleasure and comfort. 
 
 What accounts for this seeming neglect of our bodily 
 health? The principal reason is no doubt the fierce com- 
 petition in the field of nerve and brain. From the nursery 
 to the college or university the nervous strain goes on. 
 Entrance tests, promotions, appointments to scholarships 
 or fellowships, competitive examinations, grades of merit, 
 late hours, weary reading, a slavishness to books, a strain- 
 ing after facts, a crowding and cramming, until finally the 
 man is brought to a halt in his mad career by finding his 
 body weakening under the protracted pressure, and his 
 energies both of mind and frame irreparably injured. In 
 America especially a premium is put upon intellectual pre- 
 cocity. Pale, bookish children are put on the grandstand 
 for exhibition, to be admired by parents and patrons, while 
 the ruddy-faced, broad-shouldered boy whose mind too fre- 
 quently runs to games and to whom the attractions which 
 field and meadow, and wood and stream afford are prefer- 
 
144 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 able to the prosy text-book, is ridiculed and classed as a 
 dullard. But in spite of the praise showered upon the 
 former, it ought to be an object of our pity, while the ruddy 
 health and the out-door instincts of the latter ought to be 
 things to emulate. This does not mean at all that the 
 training of the mind ought to be put into the background, 
 for no less than the muscles the mind needs its proper 
 amount of exercise to grow, but when such mental exercise, 
 especially in children, has reached the point of fatigue, 
 considerations of health call for a halt and invite attention 
 to the bodily wants of the child in question. 
 
 Modern life has become such a severe struggle for exist- 
 ence that in the battle all else is lost sight of except the 
 ultimate goal desired, and so persons subject themselves 
 to greater and greater mental pressure in the firm belief 
 that they cannot afford as a matter of time and money to 
 stop in their foolish expenditure and look after the wants 
 of their mere bodily frames. A second reason is possibly 
 found in that element of American civilization character- 
 ized by foreigners as our " hurry." We object to walking 
 when it is possible to ride; we object to doing anything 
 with our hands when it may be done more quickly in other 
 ways. To take sufficient time for our meals seems fre- 
 quently impossible on account of the demands on our time 
 made by our business, while to break into the hurry and 
 routine of the daily work by taking a quiet, restful walk in 
 the open, fresh air an hour in the morning and an hour in 
 the evening seems entirely out of the question. We act on 
 the apparent belief that all of our business is so pressing 
 that we must jump on the quickest car home, eat our dinner 
 in the most hurried way, make the closest connection for a 
 car returning, and return at the end of such a day's work 
 not earlier than supper. The third reason is possibly found 
 in the fact that when one becomes accustomed to doing 
 without exercise there grows upon one more and more a dis- 
 inclination to take it. In this way exercise becomes more 
 and more a task, is more and more dreaded, avoided, and 
 
MUSCLES AND PHENOMENA OF CONTRACTION. 145 
 
 the muscles on account of their continued idleness become 
 more and more weakened, until finally healthy bodily exer- 
 cise becomes not only a hardship, but an impossibility. 
 
 No directions can be given with reference to the amount 
 of exercise to be taken. In the case of young children, 
 their love of outdoor games is a natural solution to this 
 question. In the case of adults, especially those who are 
 engaged in sedentary professions, at least two or three hours 
 a day ought to be taken in good, invigorating out-door ex- 
 ercise. If an equipped gymnasium, such as are becoming 
 more and more prevalent, be not available, the best substitute 
 is a brisk walk in the open air. To get the proper amount 
 of exercise for an average individual, the walk of a day 
 ought to amount at least to three or four miles. If, how- 
 ever, the out-door exercise may be changed into some kind 
 of a game which shall bring about a mental relaxation, as 
 well as mere physical exercise, much additional is gained, 
 for the individual who walks along engrossed in his usual 
 train of thoughts loses the most helpful effects of. his ramble. 
 There can be no questioning of the fact that the many 
 national out-door games in England have had very much to 
 do in making the English character, and possibly no greater 
 good could befall this nation than to have encouraged in it 
 a more and more general appreciation of out-door sports 
 in which it would be possible for everyone to participate. 
 
CHAPTER VIII. 
 
 THE 'CIRCULATION. 
 
 In order that the blood may be of service in the body it 
 is necessary that it be kept in circulation. This for two 
 reasons: It must bring new nourishment and new oxygen 
 to the part in question, otherwise the tissue would soon be 
 exhausted, and it must carry away those products of de- 
 composition resulting from the activity of the tissues, other- 
 wise these products would accumulate to such an extent 
 as to become poisonous and prevent further work. To ac- 
 complish these purposes the entire amount of blood is kept 
 in one constant whirl, not stopping even for an instant 
 throughout the entire life of the individual. The stoppage 
 of blood an instant or two would at once entail death. 
 And when it is told that a single particle of blood is whirled 
 along at such a speed that it makes one complete circulation 
 in little more than half a minute, passing in that short in- 
 terval twice through the heart, through the capillaries of 
 the lung and over the system, one may realize with what 
 energy and rapidity the circulation is going on. The main 
 reason for this speed is found in the necessity for carrying 
 the oxygen to the tissues rather than the nutritive portions 
 of the blood. These nutritive substances soak rather slowly 
 through the tissues in the lymph, while the blood itself, con- 
 fined in definite vessels, is hurried along at pell-mell speed 
 back to the lungs to carry to the tissues new quantities of 
 oxygen. 
 
 In many of the lower animals the necessity for a circu- 
 lation is not so great. Thus some of the very tiny forms are 
 able to have their nutritive substances soak through all parts 
 of their bodies by the simple process of osmosis, while the 
 air, too, may be taken in sufficient quantities through the 
 (146) 
 
(Facing Page 146. See Page 155 et seq.) 
 
 Fig. 74. THE ARTERIAL AND VENOUS SYSTEMS IN JUXTAPOSITION. (From Quain, after 
 Allen Thomson.) 
 
 The explanation of the letters and numbers will be evident from references to the 
 text and to the other figures. 
 
TH?; CIRCULATION. 147 
 
 exterior without having special avenues set apart for carry- 
 ing it. Then on account of the sluggishness of many of 
 the invertebrates, and the further fact that their bodies 
 need not be kept at the relatively high temperature of warm- 
 blooded animals, their need of a rapid circulation does not 
 exist. In such cases, as for instance the clam, the blood 
 circulates in a much slower and less perfect system than in 
 higher forms. 
 
 In the insects an entirely different arrangement is found. 
 The activity which many of this class exhibit would make 
 it imperative to have at the disposal of their tissues abund- 
 ant quantities of oxygen, and if such were to be carried by 
 the blood from some central lung, it would have to run at a 
 speed possibly none slower relatively than that found in us. 
 But oxygen in these little active creatures is not carried by 
 the blood directly, but is carried through special vessels which 
 branch and re-branch, carrying the air from the exterior to 
 every part of the body. In other words, the insects have a 
 system of air arteries and air capillaries permeating the en- 
 tire body to the minutest parts, and by this system sufficient 
 quantities of oxygen are carried. The blood in this case, 
 being relieved of its main function, circulates in a very im- 
 perfect way, and the blood system is not at all well de- 
 veloped. 
 
 Simplified conditions are also met in the lower forms of 
 vertebrates. Thus in fishes the heart consists of but one 
 auricle and one vertricle. In the frogs and allied forms 
 there are two auricles, but one ventricle only, while, finally, 
 m the higher forms we have four distinct cavities of the 
 heart. By this means the blood reaches the heart twice in 
 one complete circulation instead of only once, as in the 
 fishes, and is thus with almost double energy forced on in 
 its course. 
 
 THE GENERAL ARRANGEMENT OF THE CIRCULATORY SYSTEM. 
 
 To have any liquid circulate it is necessary that at one 
 point at least in its course it may be subjected to a proper 
 
148 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 power to propel it. In every water- works system there 
 must be at least one central pumping 1 station. The central 
 station in the circulation of the blood is, of course, the 
 heart. From this arise vessels which lead the blood away 
 from it, called arteries. These arteries are of two sets, one 
 carrying the impure blood to the lung, the pulmonary arter- 
 ies, the other carrying the pure blood over the entire body, 
 the systemic arteries. The arteries divide and sub-divide 
 as they proceed, and finally entering their respective tissues 
 lead into the plexuses, or net-works of tiny capillaries. In 
 these capillaries the walls are thin enough to permit the 
 nourishment held in solution in the plasma to dialize through 
 and soak in among the tissues. The oxygen, too, in the 
 capillaries becomes disassociated from the corpuscles which 
 have carried it to this point, and along with some of the 
 plasma which soaks through it enters the lymph of the tis- 
 sues. It will be seen, therefore, that in the capillaries the 
 arterial stream, so to speak, divides, the larger portion of 
 it, together with all of the corpuscles, remaining in the 
 capillaries, and, being returned to the heart through the 
 veins, while the other part soaks through the capillary 
 walls and slowly and leisurely circulates between, and per- 
 meates, the tissues. This latter part is designated as lymph. 
 Lymph, therefore, is but that portion of the blood which has 
 dialized out through the thin capillary walls. 
 
 The returning streams, then, are two. First, the veins 
 which carry the returning blood that has not left the capil- 
 laries, and which, because they contain all the red corpuscles, 
 look red, and are therefore spoken of as blood veins; and 
 second, a system of so-called veins, the lymphatics, quite 
 similar to the ordinary blood veins which gather up the 
 lymph of the tissues, and finally through the thoracic duct 
 return this stream to the original blood circulation, where 
 the thoracic duct empties itself into the left subclavian vein. 
 
 THE ROUTE OF ONE COMPLETE CIRCULATION. 
 
 Starting with a drop of blood say in the right ventricle, 
 it is sent by the contraction of this chamber through the 
 
THE CIRCULATION. 149 
 
 pulmonary artery issuing from it, to the lungs. Here it 
 suffers changes which will be discussed further on, the re- 
 sults of which are, that the dark venous blood is changed 
 into the light arterial blood, which is then, by means of the 
 pulmonary veins, returned to the left side of the heart. 
 Here it flows into the left auricle, at once proceeds to the 
 left ventricle, and by means of this powerful ventricle it is 
 
 Fig. 69. DIAGRAMMATIC REPRESENTATION OF THE CIRCULATION OF WARM-BLOODED 
 
 ANIMALS. 
 
 o, auricles; v, ventricles; P, pulmonary capillaries; (7, systemic capillaries; a, a, aorta; 
 v, c, vena, cava; a, p, v, p, pulmonary artery and vein. 
 
 forced out through the issuing aorta and sent over the body. 
 Carried by arteries it finally reaches the capillaries of the 
 
150 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 tissue ill question, and after losing some of its substance 
 into the lymph, it is returned by means of the veins to the 
 right auricle as impure blood, and from the right auricle 
 proceeds to the right ventricle, which was its starting 
 point. It will thus be seen that in one complete circula- 
 tion the blood passes through the heart twice, and passes 
 through at least two sets of capillaries, those of the lung 
 and the systemic capillaries. It has already been stated 
 that this proceeds with such rapidity that the time required 
 for such a complete circulation is but little more than half 
 a minute. 
 
 THE HEART. 
 
 1. Position. The energy to keep this entire current 
 moving is furnished by the heart, which is a large, muscular 
 organ situated in the chest extending from about the second 
 to the fifth ribs. While it varies in size under varying cir- 
 cumstances its average size may be roughly indicated by 
 comparing it with the double fists of the person. It is 
 placed diagonally in the chest, with the apex extended 
 
 Fig. 70. DIAGRAM TO SHOW RELATIVE POSITION OF HEART IN THE CHEST. 
 
 towards the left side striking the chest wall in front, about 
 between the fifth and sixth ribs, while the base extends 
 
THE CIRCULATION. 151 
 
 upwards and towards the right. As the beat of the heart 
 may readily be felt where the apex touches the chest, this 
 has given rise to the popular statement that the heart is on 
 the left side. As far as actual material is concerned, prob- 
 ably as much of it lies on the right side as on the left. 
 
 2. Coverings. It does not, however, hang loose in the 
 chest, but is supported by a double membrane covering it, 
 called the pericardium. The heart does not really lie inside 
 the pericardium, although at first appearance it seems to 
 do so. It is entirely on the outside of it, and the interior 
 of the pericardium is really the space filled by the peri- 
 cardial fluid between the two membranes. If an ordinary 
 foot-ball only loosely distended be pressed down over a fist 
 so as to surround the fist, we should have an analogous ex- 
 ample. It is evident in this case that the fist is not in the 
 collapsed foot-ball at all. This pericardium is attached to 
 the walls of the chest, and in this manner the rather heavy 
 heart is supported. The pericardium is really but a con- 
 tinuation of the pleura. 
 
 3. Cavities. As pointed out in a previous chapter, the 
 muscular tissue of which the heart is composed is of a 
 peculiar kind, called the cardiac muscle. This muscle is 
 thrown into such folds and sheets as to form the four cav- 
 ities of the heart. Of these, the upper cavities are small, 
 and their walls quite thin. In a cut-out heart they are usu- 
 ally collapsed, and look more like little muscular append- 
 ages than large chambers. On account of their flap-like 
 appearance they are called " auricles;" that is, little ears. 
 
 The two lower cavities comprise nearly all the substance 
 of the heart, are entirely separate from the upper cavities 
 as seen from the outside, have comparatively very thick 
 walls, the left being much the thicker, and are called "ven- 
 tricles." It is the contraction of the ventricles that forces 
 the blood through the arteries. 
 
 4. Vessels Arising from the Heart. A number of ves- 
 sels are connected with the heart, carrying blood to it (the 
 
152 
 
 STUDIKS IN ADVANCED PHYSIOLOGY. 
 
 veins) and from it (the arteries). Into the right auricle 
 open several large veins the descending vena cava, the as- 
 cending vena cava, the azygos vein, and several small 
 
 Fig. 71. VlRW OF HEART AND GREAT VESSELS FROM BEFORE. (Quain.) 
 
 3, pulmonary artery cut off; 1, arch'of aorta; 2, left ventricle; 4, aorta; 5, right auricle; 
 6, left auricle; 7, innominate veins joining to form the descending vena cava; 8, ascending 
 vena cava; 9, hepatic veins; + + left coronary artery. 
 
 coronary veins. The right ventricle is connected with the 
 large pulmonary artery leading to the lungs. The left 
 auricle has opening into it, usually three or four pulmonary 
 veins, while the left ventricle communicates with the large 
 aorta, which through its many branches carries the blood 
 over the entire system. From the aorta close to the heart, 
 two arteries arise which lead through the substance of the 
 heart itself and nourish it. These are the coronary arter- 
 ies. A conspicuous branch of these coronary arteries and 
 the corresponding returning coronary veins, may be easily 
 
THE CIRCULATION. 
 
 153 
 
 seen on the exterior along the partition which divides the 
 right and left ventricles. 
 
 5. The Valves of the Heart. In order that by means 
 of the contractions the blood may flow in the proper direc- 
 tion, the heart is provided with a series of valves, four in 
 number, two between the auricles and the ventricles, one at 
 the beginning of the pulmonary artery, the fourth at the 
 beginning of the aorta. The valves below the auricles 
 are called auriculo- ventricular valves. The valve between 
 the right and left auricle consists of three flaps so arranged 
 
 Fig. 72. THE HEART WITH SIGHT AURICLE AND RIGHT VENTRICLE EXPOSED. 
 1, descending vena cava; 2. ascending vena cava; 2', hepatic arteries; 3, 3', 3", walls 
 of auricle; 4, wall of ventricle; 4', papillary muscle; 5,5', 5", tricuspid valves; 6, semi- 
 lunar valves; 7, pulmonary artery; 8, aorta; 9, branches of aorta; 10, left auricle; 11, left 
 ventricle. 
 
 that when they are brought together they close the opening 
 leading to the auricle. This is the tricuspid valve. The 
 
154 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 valve between the left auricle and left ventricle consists of 
 but two flaps, and is therefore called the bicuspid, or, from 
 its resemblance to a mitre, the mitral valve. A rather rough 
 illustration of these valves may be made by cutting say the 
 top of an ordinary tomato can in such a way that it will be 
 divided into three triangular flaps, meeting at a point in the 
 middle of the surface, somewhat like a pie cut into equal 
 thirds. If these parts of the can were then bent downward 
 into the can one might easily see how a liquid could be 
 poured into the can. But if these flaps should by the liquid 
 poured in them be gradually lifted up, until finally they 
 should all meet again, and joining with their edges fit per- 
 fectly, one may see how the return of such water out through 
 this opening would be prevented. Such is in a general way 
 the condition of things in the heart. To prevent these 
 valves in the heart from turning upwards into the auricles, 
 they are fastened to the walls of the ventricles by means of 
 strong cords called the chordae tendinae. Such cords do 
 not end, however, abruptly in the wall of the ventricle. If 
 such were the case, these cords on the contraction of the 
 ventricles would become slack, and so allow the valves to 
 turn back into the auricles. To prevent the production of 
 such slack, the cords run into special muscles attached to 
 the ventricular walls, which by their contraction pull in the 
 slack on the cords as rapidly as it is produced by the ap- 
 proximation of the ventricular walls in the heart beat. These 
 muscles are called the papillary muscles. 
 
 At the orifice of the pulmonary artery and of the aorta 
 are the semilunar valves. These consist in each case of 
 three sack-like flaps attached to the wall of the issuing ves- 
 sel in such a way that when they are distended with blood 
 they meet in the center and prevent the flow of blood past 
 them. These semilunar valves do not differ materially from 
 the valves which occur regularly in veins. These valves 
 permit the blood to push the flaps apart in entering the 
 vessel, but do not permit the flow in the opposite direction. 
 On the middle of the margin of each of these flaps there is 
 
a, occipital bone; 6, fifth 
 cervical vertebra ; c, d, c, first, 
 sixth and twelfth rib respect- 
 ively; /, fifth lumbar vertebra. 
 
 I, superior vena cava; 2, 2', 
 right and left subclavian 
 veins; 3, right internal jugu- 
 lar vein; 4, 4', right and left 
 external jugular veins; 5, 5', 
 right and left vertebral veins ; 
 6, left subclavian vein at its 
 junction with the thoracic 
 duct; 7, 7', 8, mammary and 
 intercostal veins ; 9, 9, 9, large 
 azygos vein ; 10, thoracic duct ; 
 
 II, inferior vena cava; 12, 
 junction of azygos vein with 
 left renal vein; 13, 13', lumbar 
 veins connected both with 
 azygos vein and vena cava; 
 14, exteral iliacs. (A portion 
 of the ascending vena cava, 
 together with the hepatic 
 veins emptying into it, are 
 here shown cut away.) 
 
 14 V 
 
 (Facing Page 155.) 
 
 Fig. 75. THE VENA CAVA AND THE PRINCIPAL VENOUS TRUNKS. (From Quain, after 
 Allen Thomson.) 
 
THE CIRCULATION. 155 
 
 a little cartilaginous nodule called the nodule of Arantius, 
 or corpus Arantii. These may possibly serve to make the 
 edges fit more perfectly. The manner in which these valves 
 
 Fig. 73. THE SEMILUNAR VALVES OF THE AORTA. (Allen Thomson.) 
 , l>, c, the individual pouches. 
 
 act may be easily demonstrated on a beef's heart by open- 
 ing the ventricles until the semilunar valves in question are 
 exposed, and then pouring water down the pulmonary artery 
 or the aorta toward the heart. In so doing the semilunar 
 pouches as distended, meet in the center, and prevent the 
 progress of the liquid. 
 
 THE DISTRIBUTION OF THE VESSELS OVER 'THE BODY. 
 
 1. The Arterial Stream. It is the aorta which springs 
 from the left ventricle of the heart from which all the sys- 
 temic arteries take their origin. The first arteries branch- 
 ing off, are the two coronary arteries of the heart, which 
 leave the aorta just above the semilunar valves. The aorta 
 then makes a turn to the left, and descends through the 
 chest and abdomen. From the arch of the aorta several im- 
 portant arteries arise. The first is the innominate artery 
 which at once divides into the subclavian, which goes to 
 the arm, and into the right common carotid, which goes to 
 the head. From the right subclavian springs the intra- 
 vertebral artery which goes to the head, passing through the 
 intra- vertebral foramina of the cervical vertebrae. The com- 
 mon carotid divides into an external carotid and an internal 
 carotid, the former going to the face and scalp, the inner 
 to the brain. A little to the right of the origin of the in- 
 nominate artery the left common carotid leaves the arch of 
 the aorta. In its branching and destination it is the same 
 
156 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 as the right common carotid. Further to the left on the 
 arch of the aorta the left subclavian artery arises, going to 
 the arm. From it, too, arises a left intra- vertebral artery 
 taking a similar course on the left side as the corresponding 
 one on the right.. The subclavian arteries are in each arm 
 continued as the brachial arteries, and at the elbow divide 
 into two arteries called the radial and the ulnar arteries. It 
 is the right radial artery at the wrist on which the nature of 
 the pulse is usually determined by the physician. These two 
 arteries then divide and in the hand form the anastomosing 
 branches which finally lead into the ultimate capillaries. 
 
 Just below the arch of the aorta, but still in the chest, 
 numerous small arteries take their origin, which supply the 
 intercostal muscles. These are called the intercostal arter- 
 ies. Lying a little anterior to these in each case are small 
 arteries going to the lungs, called the bronchial arteries. 
 These must not be confounded with the pulmonary arteries 
 which carry the blood to the lungs. The bronchial arteries 
 carry arterial blood, intended for the nourishment of the 
 lung, and not sent to that place to be purified. 
 
 At the point where the aorta pierces the diaphragm it 
 gives off the artery for that organ called the phrenic artery. 
 Immediately below the diaphragm a number of important 
 arteries leave the aorta frequently so close together as to 
 take a common origin. This common origin or common 
 trunk is, when present, called the cceliac axis. Frequently, 
 however, these arteries arise, although close together, still 
 separately. These arteries are the hepatic artery, going to 
 the liver, the splenic artery to the spleen, the gastric artery 
 to the stomach, and the pancreatic artery to the pancreas. 
 A little further down on the aorta the superior mesentery 
 artery carries arterial blood to the small intestines. Then 
 follow the two large renal arteries, then the spermatic arter- 
 ies going to organs in the pelvis, then the somewhat larger 
 inferior mesenteric artery supplying the large intestine, and 
 finally a few lumbar arteries supplying the body wall. At 
 this point the abdominal aorta divides into a right and left 
 
(Facing Page 157.) 
 
 Fig. 76. THE CIRCULATION AT THE BASE OF THE BRAIN, THE CIRCLE OF WILLIS. (From 
 
 Quain, after Allen Thomson.) 
 
 1, left internal carotid artery; 2, left anterior cerebral artery; X, the anterior com- 
 municating artery; 3, left middle cerebral artery, passing into fissure of Sylvius, and 
 seen here running over the island of Reil, by the cutting away of the left temporal lobe; 
 4, left posterior communicating artery; 5, basilar artery; 6, left posterior cerebral artery; 
 7, 8, 9, cerebellar and vertebral arteries. 
 
THE CIRCULATION. 157 
 
 common iliac. This in each case divides into an external 
 iliac and an internal iliac. The internal iliac supplies 
 blood to the organs of the pelvis, while the external iliac 
 leaves the trunk and descends through the thigh as the 
 femoral artery. At the knee it is called the popliteal artery, 
 which then divides into the anterior and posterior tibial 
 artery. 
 
 The arterial supply of the brain deserves special atten- 
 tion. At the base of the brain surrounding the optic tracks 
 and the pituitary body there is a circular blood vessel into 
 which all the arteries that supply the brain empty. These 
 supplying arteries are the two internal carotids and the two 
 intra- vertebral arteries. The two intra- vertebral arteries, 
 however, unite when they reach the medulla and form the 
 basilar artery which runs from the middle of the medulla to 
 reach the circular blood vessel. This circular blood vessel 
 is called the Circle of Willis. From it in turn arise the 
 numerous arteries which finally supply the brain. By this 
 rather remarkable arrangement several things are accom- 
 plished. Every part of the brain may receive blood brought 
 to it in as many as four different channels. Further, the 
 amount of the blood supply of the brain will be constant 
 throughout its entire substance; and lastly, the pulse of the 
 carotid and intra-vertebral arteries is materially rediiced in 
 the Circle of Willis, and so the blood reaches the brain 
 largely relieved of these rhythmic pulsations. 
 
 THE VENOUS SYSTEM. 
 
 The blood returns from the head and neck on each side 
 in three vessels called the external and internal jugular 
 veins, and the vertebral vein. From the arm the blood is 
 returned through the subclavian vein. The subclavian veins 
 on each side have emptying into them the external jugular, 
 then the vertebral, and then join with the large internal 
 jugulars to form the innominate veins. There are thus two 
 innominate veins, although only one innominate artery. 
 The two innominate veins, after receiving several small 
 
158 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 veins, unite to form the descending vena cava. Into the 
 descending vena cava there opens usually right close to the 
 heart the large azygos vein, which brings the blood from 
 the back body wall to the heart. Into the right auricle 
 itself open several coronary veins. The blood is returned 
 from the limbs through the external saphenous vein and the 
 internal crural vein. These unite on entering the pelvic 
 region into the external iliac vein, which then joins with 
 the internal iliac vein, returning the blood from the pelvic 
 region to form the right or left common iliac vein as the 
 case may be, which then unite and form the ascending 
 vena cava. Into the ascending vena cava the large renal 
 veins pour the blood which has just been through the kid- 
 neys, while close to the heart several hepatic veins enter 
 it, bringing the blood which has just passed through the 
 liver. In the lumbar region branches connect the ascend- 
 ing vena cava with the azygos vein, thus enabling blood 
 from that region to reach the heart by either of two chan- 
 nels. 
 
 THE PULMONARY CIRCULATION. 
 
 The circulation of the blood through the lungs for pur- 
 poses of purification is designated by a special name, and 
 is called the pulmonary circulation. This consists of a 
 pulmonary artery springing from the right ventricle and 
 leading to the two lungs, and the pulmonary veins, from 
 three to five in number, which bring the blood back to the 
 left auricle after its oxygenation in the capillaries of the 
 lung. 
 
 THE PORTAL CIRCULATION. 
 
 In enumerating the veins which empty into the ascend- 
 ing vena cava, one is at first surprised that there are no 
 veins from the stomach, spleen, pancreas, or intestines. 
 The blood, however, which has been carried to these 
 organs is gathered up in a special vein called the portal 
 vein, which is, therefore, of course, made by the conjunc- 
 tion of the gastric vein, the splenic vein, the pancreatic 
 vein and the intestinal veins. This portal vein carries all 
 
(Facing Page 158.) 
 Fig-. 77. THE ABDOMINAL AORTA AND ITS PRINCIPAL BRANCHES. (From Quain, after 
 
 Allen Thomson.) 
 
 a, hyoid bone; b, pneumogastric nerves; c, c, c, trachea and bronchial tubes; d, 
 oesophagus; c, <?, lacteals and thoracic duct; /, /, azygos vein; g, kidneys; g' ', suprarenal 
 body; h, lumbar vertebra. I, I', I", thoracic aorta; II, abdominal aorta; 1, coronary arte- 
 ries; 2, innominate; 3, left common carotid; 4, left subclavian; 5, (on bronchial tubes) 
 bronchial arteries; 6, (on thoracic aorta) oesophageal arteries; 7, (in thorax) intercostal 
 arteries; 8, (on abdominal aorta) phrenic artery; 9, coeliac axis with gastric, splenic and 
 hepatic arteries cut short; 10, superior mesenteric artery; at same level the large renal 
 arteries; below 10 the spermatic arteries; 11, lumbar arteries; below II the inferior mes- 
 enteric artery. For explanation of figures in region of neck see the text. 
 
THK CIRCULATION. 159 
 
 this blood to the liver, where it passes through the 
 capillaries of that organ before reaching the hepatic veins 
 and so returns to the heart. 
 
 It will be observed that the blood passing this way 
 passes in one complete circulation through three sets of 
 capillaries instead of two. This circulation of blood through 
 the stomach, spleen, pancreas, intestine and liver is called 
 the portal circulation. The physiological reasons why the 
 blood from the spleen, stomach, and intestines should first 
 be sent to the liver before being returned to the heart, will 
 be discussed in detail in the chapter on nutrition. In an- 
 ticipation it may be said here that some of the deepest phy- 
 siological reasons exist for such a course. 
 
 THE HISTOLOGY OF ARTERIES, VEINS AND CAPILLARIES. 
 
 Examining with the microscope, an artery is seen to 
 consist of three coats, called the inner, the middle and the 
 outer coat. The inner coat consists of a delicate membrane 
 of closely packed elastic tissue, on the outside of which 
 there is a still more delicate serous membrane of flattened 
 cells bound to the elastic membrane by a finely fibrillated 
 connective tissue. The middle coat consists of alternating 
 layers of plain muscular tissue, which is usually arranged 
 circularly, and layers of yellow elastic fibers running mainly 
 longitudinally. The outer coat is the toughest, and is 
 made up mainly of closely felted bundles of white fibrous 
 
 Fig. 78. CROSS-SECTION OF PORTION OF THE WALL OF HUMAN TIBIAL ARTERY. (E. A. S.) 
 a, inner epithelial coat; 6, the elastic fenestra ted membrane ; c, muscular layer; d, 
 outer coat of connective tissue fibres mainly. 
 
 tissue. This coat then gradually shades off into the looser 
 connective tissue in which the artery is packed. These 
 
160 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 coats give to the arteries much strength and elasticity, 
 while the development of the muscular coat makes contrac- 
 tion and dilatation possible. 
 
 In veins the inner and middle coat are much reduced, 
 but the outer coat of strong, white fibrous tissue is present. 
 For this reason veins have much thinner walls and easily col- 
 lapse when empty, and, of course, have practically no 
 power of muscular contraction and dilatation. However, 
 owing to the strength of the outer coat, they are, neverthe- 
 less, not easily torn. With the exception of the larger veins 
 near the heart, veins have valves in their course. These 
 valves are semilunar folds fastened in such a way as to allow 
 the flow of blood towards the heart, but preventing it in the 
 
 Fig. 79. VALVES IN VEINS. 
 a, laid open to show pockets; b, inner view with valves closed; c, as seen from outside. 
 
 opposite direction. These valves may occur singly, but are 
 more often in pairs, while in some instances three occur at 
 the same point. By compressing the veins near the wrist 
 the positions of the valves in the congested portions may 
 be recognized by the swollen points along the veins. 
 
 Capillaries have all these coats absent, except only the 
 innermost membrane of flattened epithelial cells. This ex- 
 treme thinness of wall, it being only one cell thick, permits 
 readily the phenomena of osmosis and the migration of the 
 white blood corpuscles. 
 
 The boundary lines between arteries and capillaries on 
 the one hand, and capillaries and veins on the other, are 
 
THE CIRCULATION. 161 
 
 not sharp by any means. The arteries as they grow smal- 
 ler and branch more and more, gradually lose the thickness 
 of their walls, until finally without a single sudden break in 
 
 Fig. 80. CAPILLARIES AS SEEN IN THE WEB OF A FROG'S FOOT. 
 
 the transition, but the inner coat remains, when it is 
 somewhat arbitrarily called a capillary. On the other side, 
 the capillaries have added to them little by little extra ele- 
 ments in their walls, and shade off without a sudden transi- 
 tion here into the veins. By the term capillary, therefore, 
 is included that small portion where all the coats save the 
 innermost are absent, and is more a physiological unit than 
 an anatomical one. 
 
 THE PHENOMENA OF THE HEARTS BEAT. 
 
 Everybody is familiar with the fact that throughout life 
 the activity of the heart is shown in what is familiarly called 
 the "heart's beat." This beat may be easily recognized 
 in any of three ways: First, where the apex of the heart 
 touches the chest wall on the front and left side there may 
 be felt at each beat a little push or jar, caused by the pres- 
 sing of the heart against this portion of the chest. The 
 point at which this is most pronounced is between the fifth 
 and sixth ribs. Second, it may be felt in the pulse where 
 the beat of the heart appears as a wave running along the 
 larger arteries of the body. As this is usually more con- 
 venient for observation the phenomena of the heart's beat 
 are usually studied in these pulsations. Third, the beat of 
 the heart may be easily detected by the sounds which occur 
 11 
 
162 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 whenever the heart beats. From the fact that the activity 
 of the heart was so evident, and the further fact that the 
 final evidence of death was usually considered to be the 
 stopping of the heart, the heart received an undue import- 
 ance, traces of which till remain with us to this day in 
 many words derived from the word " heart,'' which we use 
 to express courage, emotions, vitality, inner-life, and so on. 
 The finest qualities of persons we sometimes still designate 
 as the " heart" of the man, when, of course, from a scien- 
 tific standpoint the heart has long been shown to be nothing 
 more than a big muscular pump. 
 
 1. The rate of beat. The most easily determined 
 thing about the heart beat is its rate. This is in middle 
 adult life about seventy-two per minute. It is much higher 
 in the foetus, which just before birth reaches 140. From 
 this it gradually sinks through childhood until about the 
 twenty-first year, when the average rate of seventy-two is 
 reached. The rate is a few beats slower in men than in 
 women. L,arge persons usually have a slightly lower rate 
 than small persons. The actual rate, however, in anybody 
 is subject to great variation. These variations may be owing 
 to temperature, muscular exercise, strong emotions, or be 
 consequences of fevers or administered drugs. 
 
 2. The events occurring in a single heart beat. Although 
 the time occurring between two successive heart beats is 
 normally less than a second, by means of proper apparatus 
 the individual events which occur in a heart beat may be 
 easily demonstrated. L,et us imagine the condition of the 
 heart at the very instant after a beat is over. L,et us suppose 
 that auricles and ventricles are empty, and the muscular sub- 
 stance of the heart is thoroughly relaxed. In this condition 
 the blood is entering the auricles, and as. the auriculo-ventric- 
 ular valves are open the blood at once falls through them into 
 the ventricles. The continued influx of the blood through 
 the auricles, gradually fills the ventricles and floats up the 
 auriculo-ventricular valves. Soon the point is reached 
 
THE CIRCULATION. 163 
 
 when the ventricles are passively full, and the blood now 
 begins to back up in the auricles. Dividing the time of a 
 complete heart beat into ten periods, the time occupied in 
 this passive filling of the heart occupies six-tenths of the 
 complete time. 
 
 At this juncture the auricles begin to contract and force 
 their added amount of blood into the ventricles, which, 
 being already practically filled with blood, now become 
 gorged and distended. By this means the auriculo- ventric- 
 ular valves become tightly closed. The time required for 
 the contraction of the auricles is about one-tenth of the 
 time. It is not necessary to state here that the two auricles 
 contract together, and the two ventricles together, as if 
 they were in each case but a single structure. 
 
 The reason why the auriculo-ventricular valves are closed 
 by the forcing of this extra blood into the ventricles, may 
 be explained by comparing the ventricles to a crowded 
 room. It is easily possible to imagine a room so crowded 
 as to make it impossible to open the door, especially if the 
 crowding should be behind the door. As soon as the au- 
 ricles have finished their contraction the ventricles begin to 
 contract with much greater force. Just at the beginning of 
 this contraction, when the muscles of the ventricles are 
 becoming taut and tense, the first sound of the heart is 
 heard. Just how it is produced will be explained further 
 on. By the continued contraction of the ventricles the 
 blood is pressed harder and harder, until finally the pressure 
 is sufficient to open the semilunar valves, and the blood 
 flows into the outgoing vessel. The time required by the 
 ventricles in their contraction is about three-tenths of the 
 total period. As soon as the blood has been pressed into 
 the vessels the muscular fibres of the heart relax. The blood 
 in the pulmonary artery and aorta, being under consider- 
 able pressure, tends to flow back into the relaxed heart, but 
 in so doing it distends the semilunar valves and closes 
 them. This is the moment when the second sound of the 
 heart occurs. This sound is therefore easily explained. It 
 
164 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 is but the sound caused by the "slamming shut" of the 
 doors which lead from the pulmonary artery and aorta back 
 into the heart. 
 
 It will be noticed that the heart in its beat is at rest dur- 
 ing a greater period than it is at work. The auricles work 
 but one part in ten, the ventricles but three parts in ten, 
 while the entire heart counted as a unit would work but 
 four parts, and be at complete rest, that is, passively re- 
 laxed, during six parts of the time. If the chest wall had 
 been removed and the heart exposed, changes in its form 
 might easily have been observed. During the contraction 
 the base of the heart would have changed somewhat from 
 an oval form to a rounded form, while the apex would 
 have been drawn toward the base and become blunter. A 
 material change in the position of the heart does not occur. 
 
 Such is, in a general way, the series of events in one 
 beat. L/et us now turn to the individual events in detail. 
 
 The Filling of the Heart. 
 
 Each heart beat consists of two periods: A period of 
 contraction, which is called the systole, and a period of re- 
 laxation called the diastole. Thus we have an auricular 
 systole of one-tenth and a diastole of nine-tenths of a beat 
 period, and a ventricular systole of three-tenths and a ven- 
 tricular diastole of seven-tenths. The filling of the heart 
 falls, of course, in the diastole. 
 
 The question naturally arises, as the heart is in a per- 
 fectly relaxed and passive condition, what are the agencies 
 that propel the blood forward and cause it to fill the emp- 
 tied chambers? It was formerly supposed that the pressure 
 of the arterial blood behind the venous blood propelled this 
 backward to the heart. But such a view can easily be shown 
 to be erroneous, for when a vein near to the heart is opened 
 there is no pressure of blood inside it, but there may be 
 actually a tendency to a vacuum, and air be very easily 
 sucked in. This proves beyond question that venous blood 
 is sucked toward the heart and not pushed. No doubt the 
 
THE CIRCULATION. 165 
 
 mere elasticity of the muscular walls gives a slight suction, 
 much as a sponge unnaturally compressed would as soon 
 as the pressure was relieved, spring to its more natural 
 dimensions. The suction due to this elastic expansion of 
 the walls is, however, a very small factor, and the main 
 power of suction is derived from the aspiration of the thorax 
 itself. As everyone knows the pressure in the thorax is 
 less than on the outside, and a wound through the chest wall 
 would at once suck air into the chest. 
 
 In the inspiration the suction action becomes perfectly 
 evident, and a big stream of air rushes through nostrils and 
 mouth into the thorax. If the individual so breathing were 
 in a medium of water, the water would be sucked into the 
 chest with the same relative ease as air. But not only 
 does the windpipe lead into the chest, but the veins do also. 
 Consequently, when the chest enlarges there is a sucking 
 action not only upon the outside air but also upon the out- 
 side blood, and the air through the trachea and blood 
 through the veins are sucked heartwards. In very forced 
 expiration the condition of things may be reversed and the 
 veins instead of being sucked may be compressed. But even 
 in this compression the blood is pushed on towards the heart 
 as the valves in the veims interfere with its backward flow. 
 Thus, whether the veins are sucked or compressed, the re- 
 sult is much the same. 
 
 That the sucking action of the chest has much to do 
 with drawing the blood into the heart is made evident in the 
 filling of the big veins and the stagnation of the venous 
 stream which occurs when we hold our breath for some 
 time. A person unable to get his breath becomes, as we 
 say, black and blue in the face. He does so because he is 
 no longer able to suck the venous blood issuing from the 
 veins of his skin into the empty heart. As, however, 
 the heart even when the chest wall is cut open, still has 
 venous blood flowing into it in slight quantities, it shows 
 that a small amount of the sucking action must be due to 
 the elastic expansion of the heart itself. It is interesting 
 
166 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 to note in this connection that the heart in many of the 
 lower animals is forcibly expanded as well as contracted. 
 In the case of the cray-fish and lobster, for instance, large 
 muscular cords run from the edges of the heart to the body 
 wall, and by their contraction the heart is forcibly dis- 
 tended. 
 
 During this filling of the heart, as has been stated be- 
 fore, the blood does not accumulate in the auricle, but runs 
 unhindered into the ventricle until both ventricle and auricle 
 are passively filled. At this point the systole of the auricle 
 begins. The auricle does not completely empty itself, the 
 contraction probably going no farther than the reduction of 
 the dimensions of the auricle to about that of the vena 
 
 cava. 
 
 The Auricular Contraction. 
 
 The auricular contraction begins at the mouth of the veins 
 and runs like a wave toward the ventricles. This explains 
 why the blood is not forced back into the veins rather than 
 into the already filled ventricle. As has been stated, this time 
 occupies about one-tenth of a heart-beat period. While the 
 auricular contraction lasts, the on-rushing blood of the veins 
 is of course checked for an instant. This slight checking of 
 the venous stream caused by the inability of the stream to 
 drop into the auricle during the systole of that structure, 
 causes a slight pulsation along the veins known as the venous 
 pulse. This venous pulse is not at all so well marked as the ar- 
 terial pulse , and is due to an entirely different thing. It starts , 
 however, from the mouth of the large veins at the auricle 
 and runs along the veins much like an arterial pulse along 
 arteries. By the contraction of the auricles the already 
 filled ventricle is forcibly distended and so enabled to throw 
 more blood out on its systole. Further, by the pressing of 
 the blood into the ventricles the auriculo-ventricular valves 
 have, in a way already described, been closed. At this 
 point, of course, the systole of the ventricles begins. Dur- 
 ing this period the auricles act as reservoirs for the entering 
 venous blood and in *Hs role they probably perform their 
 
THE CIRCULATION. 167 
 
 most important function. Except for this reservoir in 
 which the venous blood may temporarily accumulate there 
 would have been quite a marked stagnation interfering 
 materially with the progress of the venous stream, but by 
 this means the blood flows on into the heart uninterruptedly 
 while the ventricles are beating, and by the time the auricles 
 are filled the ventricles have finished their beat, they relax 
 and the accumulated blood of the auricles drops at once 
 into the emptied ventricles. 
 
 The Contraction of the Ventricles. Sounds of the Heart. 
 
 At the beginning and again at the close of the ventricu- 
 lar systole the familiar sounds of the heart occur. The 
 first sound is somewhat dull and represented by the syllable 
 ( ' lubb." It was at first supposed to be due to the closing 
 of the auriculo- ventricular valves, but this is not true. 
 These valves are closed before the systole begins, and in 
 experiments these valves have actually been pinned back, 
 and yet the sound occurred. Still better evidence that the 
 first sound is not due to the closing of these valves lies in 
 the fact that when an emptied heart is made to contract the 
 sound still occurs. While not fully understood, there seems 
 no doubt but that this sound is partially due to the sudden 
 tension of the muscular walls of the ventricles. The ven- 
 tricular walls becoming suddenly very much stretched and 
 taut, produce a series of vibrations which we recognize as 
 sound. A not very close analogy may be cited in the case 
 of an ordinary guitar string. If such a string at first hang- 
 ing loosely be suddenly as with a jerk tightened, it will be 
 set into vibration and sound just as if it had been pulled by 
 the fingers. That this sound is due to the tension of the 
 muscles seems corroborated by the fact that the sound lasts 
 during the entire systole. That is, it continues as long as 
 the ventricular walls are taut. 
 
 Towards the close of the systole is heard the second 
 sound. This is shorter and louder, and is plainest in the 
 regions of the aorta and pulmonary artery. It has been 
 
168 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 represented by the syllable " dupp." This sound is due to 
 the sudden closing of the two semilunar valves. Ordinarily 
 the semilunar valves of the aorta and pulmonary artery close 
 so nearly at the same time that the sound is heard as one. 
 After violent exercise, however, when the pressure in the 
 aorta is materially increased, the semilunar valves at its 
 origin close perceptibly sooner than those of the pulmonary 
 artery, and there are two distinct second sounds. The 
 earlier closing of the valves in the aorta is due to the greater 
 pressure or blood forcing them together, just as two doors 
 entirely alike would close at different moments if winds of 
 different strengths should strike them. 
 
 Cardiograms. 
 
 All these observations on the events of a heart beat may 
 be best studied by means of cardiograms. These cardio- 
 
 Fig. 81. CARDIOGRAMS OF THE RIGHT AURICLK (R V) AND THE RIGHT VENTRICLE 
 (E K) OF A HORSE. THE DOTTED LINES CONNECT SAME INSTANTS OF TIME. 
 
 grams are tracings made by placing systems of levers on the 
 ventricle and auricle, so arranged that the systole of these 
 will raise the levers and the diastole lower them. If, now, 
 the ends of such moving levers be made to trace a 
 line on a plate moving past them at a known speed, there 
 will result curves such as those pictured in figures 81 and 82. 
 The cardiogram in figure 82 is one made on a pathologic- 
 ally exposed human heart, and so is peculiarly valuable as 
 giving the actual course of events in man himself. In this 
 
THE) CIRCULATION. 
 
 169 
 
 and in the other figure the upper curve of the cardiogram 
 represents the events in the auricle, the lower those in the 
 
 \ . - 
 
 Fig. 82. CARDIOGRAMS OF THE RIGHT AURICLE (o d) AND RIGHT VENTRICLE (v d) TAKEN 
 
 ON AN EXPOSED HUMAN HEART. (After Franck.) 
 
 Vertical lines indicate same instants of time. 
 
 ventricle. The two are so arranged that vertical lines con- 
 nect the same instants of time. 
 
 The cardiogram of the horse in figure 81 was obtained 
 by pushing a tube provided with a rubber bulb at its end 
 through the jugular vein in the neck into the right auricle, 
 and a second such tube through the auricle into the ven- 
 tricle. The relative compressions of the bulbs in the diastole 
 and systole were then recorded with a tambour and the 
 curves obtained. Such a tambour consists essentially of a 
 light metallic box, covered on one side with a thin piece of 
 
 Fig. 83. A TAMBOUR. 
 T, the metal box ; H, the recording lever resting on the rubber membrane. 
 
 stretched rubber. On this rubber rests the recording lever. 
 The metallic box is connected with a tube from the heart, 
 
170 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 and the slightest variations in pressure cause the rubber, 
 and consequently the recording lever resting on it, to move 
 up or down as the pressure is positive or negative. The 
 recording lever is then made to write on a suitable surface 
 which is moved along it. Rough cardiograms may be made 
 by connecting two tambour boxes with a rather inelastic 
 tubing, then firmly pressing one over the point in the chest 
 where the cardiac impulse is most perceptible, and arrang- 
 ing the other tambour for the usual way of recording. The 
 pulsations of the chest wall caused by the heart beat will 
 be transmitted through the system of tambours and be re- 
 corded on the moving surface. It may not be out of place 
 in this connection to call attention to the fact that this car- 
 diac impulse is not caused by the chest wall being tapped 
 or struck by the heart. The heart never leaves the chest 
 wall, but the impulse is caused by the sudden tension pro- 
 duced at this point when the systole occurs. Much as a 
 person might produce an impulse on a sensitive surface by 
 first laying his hand gently on the surface and then sud- 
 denly pulling it up into a fist without removing it from the 
 surface. 
 
 On account of the thick wall which separates the tam- 
 bour from the heart these cardiograms do not give the finer 
 
 Fig. 84. THE POINTS IN THE CARDIOGRAM OF THE VENTRICLE AT WHICH DIFFERENT 
 
 PHYSIOLOGISTS PLACE THE OCCURRENCE OF THE SECOND SOUND. 
 
 detail and are not altogether trustworthy. In their finer 
 determination there are still a number of points not yet per- 
 fectly established. Thus, observers have not been able to 
 
THE CIRCULATION. 171 
 
 agree at what point in the ventricular systole the second 
 sound occurs. In figure 84 are given the views of several 
 of the leading physiologists. It is also an unsettled ques- 
 tion whether the ventricles completely empty themselves, 
 or force out only a certain proportion of the contained blood. 
 Evidence seems to point, however, to the fact that the ven- 
 tricles are practically emptied at each systole. 
 
 Pathological Sounds of the Heart. 
 
 In a normal heart the auriculo-ventricular valves are 
 hermetically closed and permit no blood to flow back. 
 Sometimes, however, these valves become deranged in some 
 way and cease to close perfectly, thus allowing at each con- 
 traction of the ventricle a slight regurgitation of blood into 
 the auricle. The escape of this blood through the imper- 
 fect valves gives a murmuring sound easily detected by the 
 physician by means of a stethoscope, and always an evi- 
 dence that there is a valvular insufficiency. 
 
 THE AMOUNT OF BLOOD FORCED OUT FROM THE HEART. 
 
 It has been difficult to determine exactly the amount of 
 blood forced out from each ventricle at each beat. (It is, 
 of course, unnecessary to point out that the average amount 
 must be the same for both ventricles.) The amount of 
 blood which is found in the ventricles of a corpse is not 
 perfectly reliable, as post mortem changes may have af- 
 fected the size of the heart. The first experiments to de- 
 termine this point gave 175 to 180 grams as the amount 
 sent out by each ventricle at each systole. L,ater experi- 
 ments gave 100 grams, while more recently the amount has 
 been put down as low as fifty grams. Taking 100 grams 
 as probably not far from the truth, it would mean that in 
 one minute (seventy-two beats) 7,200 grams pass through 
 each ventricle, or in one hour 432, 000 grams. This is ap- 
 proximately 900 pounds, or, expressed in fluid measure, about 
 112 gallons. In other words, nor far from three barrels. 
 And as the other ventricle handles a similar amount, it 
 
172 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 means that in the short period of one hour, an amount of 
 blood not far from six barrels traverses the heart. 
 
 THE ENERGY WITH WHICH THE HEART WORKS. 
 
 In determining the actual work done by anything it is 
 not sufficient to know the amount of matter handled, but we 
 must also know the distance through which it is lifted. 
 Thus, in pumping liquids, it requires just twice as much 
 work to pump the same amount of liquid twice as high. 
 The energy with which the ventricles force out their con- 
 tained blood is not difficult to calculate. Repeatedly veri- 
 fied experiments show that the left ventricle sends its blood 
 out with such force, that if there were no friction it would 
 be thrown vertically upwards about a distance N of nine feet. 
 The force with which the right ventricle throws out the 
 same amount of blood is one-third as much, being in this 
 case a distance of only three feet. Or, to explain this still 
 further, it means that the left ventricle forces the blood out 
 with an energy that would cause the blood to rise nine feet 
 high in a tube, barring friction. Or, to re-state it again, it 
 means that if there were no friction in the arteries the heart 
 would force blood, say, up to the finger tips if the arms 
 should be held vertically upwards, even though the distance 
 from the finger tips to the heart were nine feet. 
 
 , Now, work is the product of the amount of matter 
 lifted, and the distance through which it is lifted. A unit 
 of work is a foot-pound. A foot-pound is the amount of 
 work required to lift one pound one foot high. Knowing 
 the amount of blood which each ventricle throws out and 
 the height to which it would be thrown if unhindered, it is 
 easy to determine the amount of work the heart is enabled 
 to do in definite periods of time. Thus, at every beat the 
 left ventricle throws out 100 grams, or about 3-nr ounces, 
 or about .22 pound, taking approximate figures only. The 
 amount of work is expressed by the product of the numbers 
 giving the amount and height. Thus the work of the left 
 ventricle for one beat would be 9X.22; that is, 1.98 foot- 
 
THE CIRCULATION. 173 
 
 pounds. For convenience sake let us say two foot-pounds. 
 In seventy-two beats (one minute) the amount of work 
 would be 144 foot-pounds. In an hour, 8,640 foot-pounds. 
 
 As the right ventricle lifts the blood only one-third as 
 far, the amount of work it does is just one-third that of the 
 left ventricle. Adding this one- third to the amount of work 
 the left ventricle does in an hour makes 11,520 foot-pounds. 
 Re-stating that again, it means that in one hour the heart 
 has expended an amount of energy that would have lifted 
 11,520 pounds one foot high. 
 
 In the case of a man weighing 160 pounds, it would lift 
 him in one hour to a distance of 72 feet, or in one day 1,728 
 feet. Even if the strong muscles of the skeleton should be 
 asked daily to carry the body up a mountain side to a dis- 
 tance of 1,728 feet, it would by no means prove an easy 
 task. Yet such is the amount of work the heart does day 
 in, day out, without showing signs of fatigue. To state 
 this in still another way if the heart weighing 300 grams 
 should expend all its energy in lifting itself only, it would 
 raise itself in one hour to a distance of 13,000 feet. In 
 ability to do work, the heart is equal to -g-J-^- of a horse- 
 power. 
 
 THE INNERVATION OF THE HEART. 
 
 1. The Source of the Stimuli. So far the question 
 has been ignored, what causes the heart to contract? Does 
 it beat in obedience to stimuli which reach it from the out- 
 side, like the right arm in obedience to impulses from the 
 brain, or does it beat by stimuli that originate within itself ? 
 This general question can be easily answered definitely by 
 observing that a frog's heart cut out of the body will con- 
 tinue under proper circumstances to beat for days, and the 
 heart of a warm-blooded animal will beat as long as it is 
 properly supplied with nourishment and oxygen. This 
 settles conclusively that the impulses to beat do not reach 
 the heart from the outside, but are intrinsic. The question 
 then arises whether these intrinsic stimuli are produced by 
 nerve centers within the heart or by the heart muscle itself. 
 
174 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 There is, of course, considerable difficulty in making ex- 
 tended observations on the heart of mammals, but it is quite 
 easy to make such observations on cold-blooded forms, 
 especially on the frog and terrapin. If, now, a frog's heart 
 be carefully examined for nerves, two clumps of ganglia 
 may be found, one clump lying near the opening of the 
 large veins, in the so-called sinus. These ganglia are 
 called after their discoverer, the ganglia of Remak. The 
 second clump of ganglia lies in the septum of the auricles 
 close to the auriculo- ventricular valves. These ganglia are 
 called the ganglia of Bidders. The apex of the ventricle is 
 entirely free from nerve cells. As has been stated, such a 
 heart properly treated will continue beating for days with 
 its regular rhythm. If, now, the portion containing the 
 ganglia of Remak be cut away from the rest of the heart, 
 the heart stops beating at once, while the sinus which still 
 contains the ganglia of Remak continues its beat without 
 interruption. This observation was first made by Stannius, 
 and is still spoken of as the experiment of Stannius. 
 
 It would seem that the only way to explain this would 
 be to assume that the ganglia of Remak are automatic 
 ganglia which produce the beating, and that the other 
 ganglia are stimulated reflexly by these. For if a heart so 
 severed from the ganglia of Remak be stimulated in some 
 mechanical way it will beat for a while more or less irregu- 
 larly, but soon comes again to a standstill. This experi- 
 ment then would seem to be a clear assurance that the beat 
 of the heart is inaugurated by the ganglia of Remak, and 
 is therefore of a purely nervous origin. The function of 
 the ganglia of Bidders could be explained by supposing that 
 they were stimulated by the ganglia of Remak, and so the 
 contraction carried into the ventricles. But there are many 
 facts which will not admit of such a simple solution to the 
 problem. If, for instance, the apex of the heart, which of 
 course contains no nerve cells, be cut off from the rest of 
 the heart it may be made to beat regularly. Here, of course, 
 is a clear case that the beat is not due to nervous influence. 
 
THE CIRCULATION. 175 
 
 Physiologists have, therefore, been driven to the belief that 
 the heart muscle itself has a kind of automaticity which 
 helps to produce the rhythmic beat. 
 
 That these muscle cells themselves must be to some ex- 
 tent automatic may be further conclusively shown by cut- 
 ting out a strip of muscle from a terrapin's heart, which has 
 no ganglia in it, and observing that such a strip will continue 
 to beat rhythmically if it is once started to do so. Nervous 
 influence is here again entirely out of the question. There 
 are still other reasons to think that heart muscle is auto- 
 matic and determines its own rhythm. Thus, the heart mus- 
 cle cannot be thrown into a tetanic contraction, no matter 
 how rapid the stimuli. If the heart contracts at all it will 
 beat with its own rhythm. Then again, the contraction of 
 the heart does not vary with the strength of the stimulus. 
 A slight stimulus will not produce a slight contraction, and 
 a stronger stimulus a stronger contraction, as in the case of 
 all other muscles; but if the stimulus acts at all, be it strong 
 or weak, it will produce the natural rhythmic beat. 
 
 What has been said so far with reference to the innerva- 
 tion of the heart has been observed on the lower animals, 
 but there is every reason to believe that practically the 
 same conditions exist in the higher animals. By way of 
 summary be it stated what the condition of things prob 
 ably is in the human heart. Near the mouths of the veins 
 entering the auricles are groups of ganglia called here, also, 
 the ganglia of Remak. A second group of ganglia occurs 
 in the septum between the auricles at the place where this 
 touches the ventricles; that is, in the walls between the 
 two auriculo- ventricular valves. But unlike the frog, scat- 
 tered ganglia are found through the apex of the heart. As 
 in the case of all animals where observations have been 
 made, the impulse to beat in the human heart is intrinsic 
 and is due probably to two things. First, the ganglia 
 themselves in the heart are probably automatic. Second, 
 the heart muscles as well possess an automaticity, and the 
 beat is the result of these two similarly directed influences. 
 
176 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 The word 1 1 automatic ' ' has been used a number of 
 times, and a definition of the meaning of this term is im- 
 perative in order to understand what is meant by saying 
 that both the ganglia of the heart as well as the muscle 
 itself are automatic. Such a definition of this term is un- 
 fortunately not yet forthcoming. Physiologists are so far 
 entirely unable to explain what it is that causes the ganglia 
 to originate their nervous impulses, or the muscle to con- 
 tract at definite periods. There is probably something 
 either in the structure of the heart or the manner in which 
 it works that excites the ganglia or the muscle substance, 
 but so far it has been impossible to locate that. Thus the 
 term automatic is used to designate a physiological con- 
 dition of things, the meaning of which we do not yet have. 
 
 2. Nerves reaching the heart from the outside. In 
 addition to the intrinsic nerves of the heart three kinds of 
 nerves reach it from the outside. Two of these nerves 
 reach the heart from the vagus or pneumogastric nerve 
 coming from the brain. The third kind reaches it from 
 the sympathetic system. 
 
 The fibres of the pneumogastric which run to the heart 
 are really not fibres of the pneumogastric at all ; they are 
 fibres of the eleventh pair of cranial nerves called the spinal 
 accessory. A branch of the spinal accessory nerve unites 
 itself with the pneumogastric and follows the course of the 
 pneumogastric through the skull and the neck. If this 
 cardiac branch of the pneumogastric be examined histo- 
 logically it is found to consist of two sets of fibres, a set of 
 small fibres and a set of larger ones. Both, however, are 
 medullated. On reaching the heart the large fibres can be 
 traced into the heart, leading probably to the intrinsic 
 ganglia, while the set of small fibres seems to run along the 
 surface of the heart and loses itself in the walls of the 
 ventricles mainly. These smaller nerves are sensory and 
 carry to the brain the sensations of the heart. 
 
THE CIRCULATION. 177 
 
 Tlic Pneumogastric or Cardio -inhibitory Nerves. 
 
 The larger nerves, ending probably in the intrinsic 
 ganglia themselves, exercise a peculiar and interesting con- 
 trol over the beat of the hear,t. When they are stimulated 
 they cause the beat to be slowed, and if sufficiently stimu- 
 lated may cause the heart to stop beating altogether. For 
 this reason they are called inhibitory nerves. When these 
 inhibitory nerves by sufficient stimulation cause the heart 
 to stand still the heart stands still in diastole, perfectly re- 
 laxed, and not contracted in a systole. These cardio-inhib- 
 itory nerves not only slow the rate of the beat, but they 
 make the individual beats weaker. The result of this ac- 
 tion is, of course, to reduce the blood pressure in the arter- 
 ies, because the heart no longer forces the blood into these 
 arteries at the accustomed rate. These nerves seem to be 
 acting all the time in our bodies and thus continually keep- 
 ing the rate of the heart beat in check. For when both 
 nerves are cut the heart at once begins to beat faster, be- 
 cause the inhibitory action of the vagi has been removed. 
 
 Inhibitory Center. 
 
 It is, of course, not these nerves themselves that are in- 
 hibitory, for nerves are but the avenues of impulses trans- 
 mitted to them. These inhibitory impulses originate in a 
 center which lies in the medulla, called the cardio-inhibitory 
 center. From this center the inhibitory fibres of the vagi 
 run to the heart, and it is of course this center which is in 
 a continual state of excitation and so continually exercising 
 a checking control of the heart. 
 
 This cardio-inhibitory center may be stimulated to in- 
 creased action in several ways. First, increased blood 
 pressure in the cranium causes an increased inhibitory 
 action. This may be shown by boring a little hole in the 
 cranium of an animal and then forcing into the cranium 
 some non-irritating liquid. A slowing of the heart beat at 
 once follows. This also explains why in apoplexy the pulse 
 sinks so rapidly. (Apoplexy is due to the bursting of blood 
 12 
 
178 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 vessels in the brain and the accumulation of blood in 
 organ.) This may further explain why a person in lying 
 down usually has the rate of his pulse lowered, for in the 
 lying posture the pressure of blood in the brain is, of course, 
 suddenly increased. The fact that such an increase of blood 
 pressure should at once by stimulating the cardio-inhibitory 
 center cause the heart to beat slower, is a very fortunate 
 circumstance, for it reduces the possibility of the rupture of 
 blood vessels and consequent hemorrhages. Second, the 
 center is further stimulated by psychic influences. Strong 
 emotions may affect it. Thus, fainting, which is usually 
 due to a flurry of the emotions, results from a stoppage of 
 the heart caused by the inhibitory action of the vagi. 
 When this stoppage lasts but an instant no serious damage 
 results, but when the inhibition has been so violent as to 
 prevent the heart from resuming its beat for even a little 
 while, death may result for lack of circulation. The third 
 exciting cause is the lack of oxygen. If venous blood only 
 is allowed to run through the center the rate of pulse is 
 soon reduced and finally stops altogether. This is, of 
 course, the explanation of the observed fact that in cases 
 of suffocation the pulse sinks so rapidly and the heart ceases 
 to beat so soon. Fourth, this center may be stimulated by 
 afferent impulses coming from other sensory nerves. A 
 severe blow on the pit of the stomach may cause the heart 
 to stand still for an instant. Here the afferent impulse 
 goes from the sensory nerves of the abdomen to the brain, 
 and there acts in an exciting way on the cardio-inhibitory 
 center. Fifth, in addition to these impulses which affect the 
 center directly there are a number of drugs and poisons 
 which act upon the vagus nerve and so affect the beat of 
 the heart. Thus the poison muscarin stimulates the ends 
 of the vagus nerve in the heart and so may bring the heart 
 to a standstill. The drug atropin lames the vagi and so 
 produces an acceleration in the heart beat, while nicotine 
 seems first to stimulate the nerves and so reduce the pulse, 
 then later to lame the nerves and so by weakening the in- 
 hibitory influence to increase the rate of beat. 
 
THE CIRCULATION. 179 
 
 The Depressor Nerves. 
 
 It was pointed out previously that along with these in- 
 hibitory nerves in the pneumogastric there reach the heart 
 along the same avenue some sensory or afferent nerves. 
 These instead of going to the ganglia are probably distrib- 
 uted between the muscle fibres themselves, and carry to the 
 medulla sensations from the heart. Of course these sensa- 
 tions very seldom reach consciousness and so we are not aware 
 of them, but in the medulla these afferent impulses from 
 the heart affect the centers and bring about important phy- 
 siological results. In a normal heart about the only sensa- 
 tion that might be expected to come from the heart would 
 be the sensation due to too great a pressure of blood in that 
 organ. Such afferent impulses brought by this nerve to the 
 medulla cause immediate dilatation of arteries all over the 
 body, a condition of things which at once serves to reduce 
 the blood pressure. Artificial experiments confirm this as- 
 sertion, for if this nerve be cut and its central end, that is 
 the end connected with the medulla, stimulated, a dilata- 
 tion of the blood vessels over the body occurs and the 
 blood pressure sinks at once. On account of this action 
 this afferent nerve was called the depressor nerve, because 
 the result of its impulses is to depress; that is, to lower the 
 pressure in the arteries. In the rabbit this depressor nerve 
 runs as a separate and distinct nerve to the heart, while in 
 most animals and in man, as already pointed out, it runs 
 along the common pneumogastric trunk. 
 
 Cardio- accelerator or Sympathetic Nerve. 
 
 In addition to these two extrinsic nerves a third one 
 reaches the heart. This is a nerve which increases the rate 
 of heart beat and is called the cardio-accelerator. This 
 cardio-accelerator has its origin in the medulla and spinal 
 cord, also, but runs from this through the communicating 
 branches to the sympathetic ganglia lying in the lower 
 cervical and upper dorsal region, and from these ganglia 
 reaches the heart. Passing as it does from these sympa- 
 
180 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 thetic ganglia this nerve has usually been called the sym- 
 pathetic nerve. When stimulated it not only increases the 
 rate of the heart beat but for a little while also the strength 
 of the individual beat. In its influence on the heart it is 
 not so pronounced as the vagi, for if at the same instant 
 the vagi and the sympathetic nerves be stimulated the rate 
 of the heart beat is slowed, showing that the vagi are more 
 effective. Just under what circumstances in life these ac- 
 celerator nerves are brought into play is still not wholly 
 solved. It is probable, however, that the increase in the 
 rate of pulse which follows muscular exercise is due to such 
 sympathetic stimulation. 
 
 The Accelerator Center. 
 
 These accelerator nerves come from an accelerator cen- 
 ter which lies in the medulla, also. This center is called 
 the cardio-accelerator center. It is not in a state of con- 
 tinuous excitation, as in the case of the inhibitory center, 
 but like the latter, it may be excited by stimuli reaching it 
 from other sources. Thus psychic influences such as 
 strong emotions usually increase the rate of heart beat, 
 familiar to everybody in the common experience of having 
 " the heart rise into one's throat." Powerful stimulation 
 of sensory nerves in general may result in a marked quick- 
 ening of the heart beat. This quickening of the beat, of 
 course, at once raises the arterial pressure and so enables 
 the animal to make sudden and especially vigorous efforts. 
 This arrangement may be but the attempt of nature to put 
 at our disposal for sudden emergencies an increased circu 
 lation to make possible increased exertions, and so materi- 
 ally helD in the preservation of our safety. 
 
 Summary. 
 
 By way of summary the innervation of the heart is 
 briefly re-stated. 
 
 The beat of the heart itself is due to the automaticity of 
 the muscular substance itself, and also to the automatic 
 
THE CIRCULATION. 181 
 
 action to the intrinsic ganglia of the heart. These gan- 
 glia with their nerves leading to the muscle cells inaug- 
 urate the heart beat. To control this heart beat two kinds of 
 nerves reach it from the exterior: first, the vagi or pneumo- 
 gastric nerves, which because they slow, and if sufficiently 
 stimulated, stop the heart beat, are called cardio-inhibitory 
 nerves. These are normally in constant excitation; and so 
 the heart beat is always a little slower than it would of its 
 own account be. Second, the sympathetic or accelerator 
 nerves reaching it by way of the sympathetic ganglia, the 
 physiological action of which is to increase the rate of the 
 beat. 
 
 All these nerves, the intrinsic, cardio-inhibitory and the 
 sympathetic, are concerned in the movement of the heart. 
 They are not sensory. But in addition to these three motor 
 nerves an afferent nerve reaches the heart carrying sensa- 
 tions to the medulla. This afferent nerve, because when it 
 is stimulated by conditions in the heart, it causes a dilatation 
 of the blood vessels in all parts of the body, is called the 
 depressor nerve. The dilatation of the arteries everywhere 
 is, of course, not due to the depressor nerve itself; it 
 simply carries the afferent impulse to the medulla, and from 
 centers in the .medulla the impulses to dilate the arteries 
 arise. 
 
 Finally, it need not here be noted that these nerves are 
 in pairs, a pneumogastric on each side and a sympathetic 
 right and left. 
 
 THE DYNAMICS OF THE BLOOD STREAM IN THE VESSELS. 
 
 1. The Blood Pressure. The anatomy and the general 
 distribution of arteries, veins and capillaries have already 
 been given; but there still remains the discussion of the 
 phenomena of the blood in motion. By the beat of the heart 
 the blood is thrown into the arteries, where it accumulates 
 until it reaches a certain pressure sufficient to force it out 
 through the small capillaries at the peripheral ends. The 
 most apparent observation probably in examining an artery 
 
182 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 would be the fact that the artery seems to be distended, 
 and the blood in it under considerable pressure. This 
 pressure is, of course, produced by the resistance offered to 
 the flow of blood through the small arteries and capillaries 
 on the one end and the continued pouring in of blood by 
 the heart at the other end. The condition of things differs 
 in no way from that of a city water- works system. In that 
 case the central pump usually forces the water into the 
 mains at such a rate that often a heavy pressure results. 
 Especially so in cases of fire when the central pumps are 
 made to run faster than usual. If there were no resistance 
 at the farther ends of these water mains, no pressure would 
 arise, but the water would flow out at one end as rapidly as 
 it entered at the other. But the pressure in the mains re- 
 sults from the internal resistance due to friction given to 
 the stream as it tries to traverse the smaller pipes at the 
 distal extremity. In such a system with the pump going at 
 a regular rate the pressure in the mains would rise and rise 
 until finally a pressure would result which would be able to 
 force out at its peripheral end as much water in a given 
 time as the pump poured into it at the other end. Thus, 
 in such a system, if in a case of fire the central pump should 
 increase its speed the pressure throughout all the mains 
 would at once rise, and continue to do so until it would be 
 able to force through all the finer ramifications as much 
 water as entered. It is easy to determine what the amount 
 of this pressure is in the case of the blood-vessels. From 
 general considerations which govern the supply of all streams 
 flowing in closed tubes, the pressure must be greatest near- 
 est the heart and become gradually less towards the peri- 
 phery. Just as in water mains the pressure is greater near 
 the station and gradually decreases toward more distant 
 places. 
 
 Arterial Pressure. 
 
 The blood pressure in the human arteries has been 
 measured in cases of amputation. Experiments of this kind 
 
THE CIRCULATION. 183 
 
 in the case of the femoral artery showed a pressure of about 
 120 millimetres, or about 5 inches of mercury. Experi- 
 ments on tibial arteries made the pressure higher, results 
 indicating here 160 millimetres, or about 6| inches of 
 mercury, while the average pressure indicated by a sphyg- 
 mometer (an instrument which may be used on an artery 
 without injuring it), reaches about 180 millimetres, or 7 
 inches of mercury, in the case of the radial artery. As the 
 pressure in the aorta must be somewhat greater than in any 
 of these arteries, it is probably not far from 200 millimetres, 
 or 8 inches of mercury. 
 
 To more fully understand what is meant by a pressure 
 of eight inches of mercury, comparison may be made with 
 the barometer. Here the pressure of the air is also meas- 
 ured by a column of mercury. As every one knows, the 
 air pressure supports about thirty inches of mercury. As 
 the atmospheric pressure to the square inch is about fifteen 
 pounds it means that every two inches of mercury indicate 
 one pound of pressure to the square inch. Thus, therefore, 
 an arterial pressure of eight inches of mercury means a 
 pressure against every square inch of arterial wall of four 
 pounds. As mercury is a little over thirteen times heavier 
 than water or blood, it means that the arterial pressure 
 would lift a column of blood or water thirteen times eight 
 inches, or not far from nine feet. To state the same thing 
 in still another way, it means that, disregarding friction, 
 blood would spurt from such an artery at such a pressure 
 vertically upward, nine feet. 
 
 In the pulmonary artery the pressure is only about one- 
 third of that in the aorta. This relatively low pressure in 
 the pulmonary system is, of course, equally easily explained 
 when we recall that the blood traverses a much shorter 
 distance, and that the lung capillaries are more easily 
 traversed. 
 
 Pressure in Capillaries. 
 
 The arterial pressure sinks rapidly in the smaller arteries 
 and in the capillaries is very slight indeed. There are 
 
184 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 especial reasons why this ought to be so. The capillary 
 walls are exceedingly thin and would not be able to with- 
 stand any material pressure, but would be easily ruptured 
 and so disastrous hemorrhages ensue. 
 
 Pressure in Veins. 
 
 The pressure in the large veins is usually negative, that 
 is to say, there is an actual sucking action. The blood in 
 the veins is not pushed towards the heart from behind, but 
 is sucked up towards the heart by the aspiratory action of 
 the chest, especially in inspiration. If by holding the 
 breath the blood be allowed to accumulate in the veins, 
 there may be produced a temporary venous pressure, espe- 
 cially if by active muscular exertion the smaller veins be 
 compressed and so the blood forced towards the heart. But 
 under normal conditions it seldom reaches a pressure of 
 more than three to five millimetres of mercury, a very slight 
 one compared with the high arterial pressure. 
 
 Variation in Arterial Pressure. 
 
 The arterial pressure is, of course, immediately influ- 
 enced by the rate of the heart beat. If the heart beats 
 faster, the pressure rises; if slower, it sinks. Thus, in 
 cases of excitement, when the heart beats fast, the in- 
 creased pressure resulting therefrom not infrequently leads 
 to the bursting of blood-vessels and apoplexy. Normally 
 when as a result of increased muscular effort the heart is 
 made to beat faster, general experience testifies to an in- 
 creased arterial pressure. 
 
 In the second place the arterial pressure may be varied 
 by the contraction or dilatation of the peripheral arteries. 
 It will be remembered that the arteries especially were pro- 
 vided with a coat of plain muscular tissue. This coat is 
 under nervous control, and by it the arteries are enabled to 
 contract their lumen or to dilate it. It is, of course, at 
 once apparent that a contraction of the small blood-vessels 
 increases the arterial pressure in the same way that closing 
 
THE CIRCULATION. 185 
 
 the nozzle of a hose at once increases the pressure of the 
 water in it. In fact, the explanation of such a common 
 thing as a cold is found in the fact that, due to a compres- 
 sion of the vessels of the skin, caused as a rule by an 
 exposure to suddenly lowered temperatures, an increased 
 arterial pressure results and the blood is driven in undue 
 amounts through the vessels of the interior organs which 
 are thereby congested and an inflammation results which we 
 designate as a cold. 
 
 In the third place, there is a slight variation produced 
 by the rhythmic beat of the heart. It is easily understood 
 how the sudden injection of a ventricle full of blood into 
 the arteries will cause the pressure in them to rise a little, 
 while during the diastole of the heart as the blood is con- 
 tinually flowing out into the capillaries the pressure tends 
 to sink a little. This variation is, however, very slight, 
 amounting to little more than a few millimetres of mercury. 
 As the average pressure of the aorta is as much as 200 mil- 
 limetres of mercury, the periodic rise and fall of but a few 
 millimetres causes practically no effect. 
 
 THE CHANGING OF THE INTERMITTENT FLOW FROM THE HEART 
 INTO THE CONSTANT FLOW OF THE CAPILLARIES. 
 
 If capillaries like those in a frog's foot be examined and 
 the blood be seen circulating through them, it may be 
 noticed that the blood flows smoothly and regularly, show- 
 ing no pulsations. Even through the smaller arteries the 
 blood stream seems to all external appearances to be per- 
 fectly constant and regular. As the blood is, however, 
 poured into the arteries by the heart in periodic pulsations 
 the question arises, how such an intermittent flow is changed 
 into a regular and continuous one. This is readily ex- 
 plained if it be remembered that the real force which drives 
 the blood from the arteries into the capillaries is the force 
 exerted by the elastic walls of the arteries which are much 
 distended and which in trying to regain their original di- 
 mensions press upon the contained blood. Much as water 
 
186 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 may be compressed by forcing it into a hose of very elastic 
 rubber and then closing both ends. If slight openings into 
 such a distended rubber hose would be made, the water 
 would at once be forced out by the elasticity of the walls. 
 The pressure of the blood, which, of course, is but the 
 amount of compression due to the elastic walls, is, as has 
 been stated, 200 millimetres of mercury, or four pounds to 
 the square inch (in the aorta) . It is this pressure which 
 forces the blood onward. Even when the heart is not 
 beating at all, the pressure still continues in the vessels 
 keeping the stream in motion. When the heart throws in 
 its amount of blood at each beat this arterial pressure is 
 raised but very little, only three to four millimetres. Such 
 a slight change in the pressure would not affect the flow 
 through the capillaries at all, any more than the fluctuation 
 of a few pounds of pressure in the central pump of a water- 
 works station could be detected by the individual who is 
 watching the stream issue from the nozzle of his hose in a 
 distant section of the city. 
 
 THE RATE AND TIME OF THE BLOOD FLOW. 
 
 1. Rate. The rate at which the blood moves forward in 
 these vessels varies at different points along its course. It 
 is fastest near the heart and becomes gradually slower towards 
 the peripheral ramifications. This different rate of flow, is, 
 of course, compensated by the fact that the combined lumen 
 of the arteries and veins becomes gradually larger as we ap- 
 proach the periphery. This is easily understood by watch- 
 ing the flow of water in a river. Where the river is wide the 
 flow is sluggish, but where the banks of the river approxi- 
 mate each other the river may have quite a swift current. 
 Thus, the forward motion of the water on Lake Erie is prob- 
 ably not perceptible, but when the forward flow of the lake 
 becomes narrowed between the banks of the Niagara River it 
 may be changed into a torrent. The fact that the blood does 
 not flow as rapidly in the veins as it does in the arteries is due 
 to the same thing, the veins being correspondingly larger. 
 
THE CIRCULATION. 187 
 
 While it lias been impossible to measure the exact rate 
 of flow in the vessels in man, repeated experiments have 
 been made on the lower animals, and certain inferences 
 have been drawn from them with reference to the condition 
 of things in the human body, which are probably not very 
 far from the truth. Such calculations show that the blood 
 in the human carotid flows about 400 millimetres, or six- 
 teen inches in a second. In the smaller arteries it is, of 
 course, less, while finally in the narrow capillaries the blood 
 moves through a distance of about -gV of an inch only in a 
 second. As capillaries in a very general way are about -V 
 of an inch long, it means that it takes the blood about one 
 second to traverse them. In the larger veins the rate 
 is from 100 to 125 millimetres, that is, from four to five 
 inches per second. This rate may be much modified by 
 variations in the energy of the respiratory movements. As 
 in the case of the smaller arteries, so with the smaller 
 veins, the rate is much slower than four inches. 
 
 2. Time. These measurements of the rapidity of the flow 
 have been made on the lower animals by interpolating be- 
 tween the cut ends of the vessel some form of bent glass 
 tube through which the gradual streaming of the blood could 
 be visible throughout. As the rate of flow is different for 
 nearly all portions in the course, it is impossible by this 
 means to calculate how much time would be required for 
 the blood to make its round through lung or tissues. It is, 
 however, possible to make such determination and to dis- 
 cover very accurately the exact amount of time it takes a 
 drop of blood to pass through the routes of circulation. 
 Thus, if some substance which could easily be detected be 
 injected into the carotid artery of a horse and the re-appear- 
 ance of such injected substance watched for in the blood 
 returning from the jugular veins, the time to traverse the 
 circulation between these two points would be at once 
 given. Experiments of this kind on lower animals and cal- 
 culations from these to the human body show that on an 
 average the time required for the blood to make one com- 
 
188 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 plete circulation is about thirty-two seconds. Of this time 
 about nine seconds are lost in passing through the pul- 
 monary circulation, the other twenty-three through the 
 systemic . 
 
 The real rapidity with which the blood moves may, 
 therefore, be readily appreciated from this when we remem- 
 ber that a corpuscle of blood might in the course of such a 
 short time as one hour carry 120 loads of oxygen to the 
 head. It means that the entire amount of blood in the body 
 is moved in a period of time no greater than one minute 
 twice over the entire course of circulation. If one should 
 fancifully try to calculate how many loads of oxygen on an 
 average a red corpuscle would carry in the course of a 
 month, the figures would no longer be comprehensible; 
 while if the calculation should be extended in computing 
 the actual distance which such a corpuscle had covered in 
 this vast number of trips the result might possibly be com- 
 prehended only when reduced to miles. 
 
 In this connection it may be well to repeat that this 
 whirl of blood is mainly for the purpose of carrying in an 
 uninterrupted flow the supply of oxygen to all parts of the 
 body, and only incidentally to carry the nourishment and to 
 remove the waste, even though these two latter are, of 
 course, indispensable. 
 
 THE PULSE. 
 
 1. Cause of Pulse. The sudden injection of several 
 ounces of blood at each beat into the aorta causes the walls 
 of the aorta to be additionally distended right at the heart 
 in order to make room for this new amount. This expan- 
 sion at the origin of the aorta is made possible by the elas- 
 ticity of its wall. But by this elasticity the walls, distended 
 so suddenly, try to regain their original position, and in so 
 doing start a wave along the artery familiar to us all as the 
 pulse, much like a pebble thrown into the water will start 
 at that point a series of waves running in every direction. 
 Of course in the case of the aorta, the only direction possi- 
 ble is toward the periphery. 
 
THE CIRCULATION . 189 
 
 2. Rate of Speed of Pulse. This wave runs at a defin- 
 ite speed along the arteries, which is in man about twenty- 
 five or thirty feet per second. This rate shows that a pulse 
 wave runs out at its peripheral end and is over before the 
 succeeding one is inaugurated. This wave must not be 
 understood as an actual forward movement of the blood, 
 but is a mere pressure wave, just as in the motion of waves 
 on a surface of water, the water itself does not move for- 
 ward with the waves, but moves up and down in almost the 
 same place, as is indicated by observing any floating object 
 which does not travel along with the wave at all. 
 
 3. Kinds of Pulses. An examination of the pulse wave 
 enables the practiced physician to learn much about the 
 state of things in the general circulation. Thus, a phy- 
 sician can distinguish four different kinds of pulses: First, 
 \kzpulsusfrequens, or the pulsus rarus, depending on the 
 number of heart beats per minute. Second, the pulsus 
 celer, or the pulsus tardus, depending on the quickness 
 with which a single beat is t accomplished. It indicates 
 whether in the individual beat of the heart the ventricles 
 contract energetically or slowly. This must not be con- 
 founded with the rate of the pulse or \hz pulsus frequens , for 
 the heart might beat but fifty times a minute, say, a very 
 slow rate, and yet perform each beat with a quick, jerky 
 systole. Third, t\\e pulsus magnus, or the pulsus parvus, 
 depending on the amount of blood which is thrown into the 
 arteries at each beat. A pulsus magmis, or big pulse, 
 would be indicated by the increased size of the artery in 
 question, while a pulsus parvus, or small pulse, would be 
 indicated by a more or less collapsed artery. Fourth, the 
 pulsus durus, or the pulsus mollis, that is, a hard pulse or 
 a soft pulse, depending on the amount of pressure necessary 
 to completely compress an artery, and so prevent the blood 
 from flowing past the point of compression. In other words, 
 the pulse is hard when the pressure of blood is high and 
 vice versa. Here, also, a hard pulse must not be con- 
 founded with a big pulse. Thus it is possible to conceive 
 
190 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 a condition of things in which a greatly increased peri- 
 pheral resistance in the arteries should arise and produce a 
 hard pulse, and yet the heart itself might force but a small 
 amount of blood into the artery at each beat and so indicate 
 a small pulse at the same time. 
 
 4. Physiological Measurements of the Pulse and Ar- 
 terial Pressure in General. Every one knows that the pres- 
 sure in the arteries may be easily determined by feeling it 
 with the finger. The rhythmic variation in arterial pres- 
 sure which we call the pulse, is commonly examined in this 
 way. But in order to show with much finer detail all the 
 phenomena of arterial pressure, various forms of sensitive 
 instruments have been devised. Possibly the most satis- 
 factory one is the sphygmograph. This consists essentially 
 of a sensitive recording lever placed on the artery in such a 
 way that any increase in the pressure of the artery will raise 
 the lever. The lever itself is then arranged to write on 
 some suitable moving surface and so a curve of pressure is 
 obtained. The philosophy of such an instrument is almost 
 too simple to need further explanation. Every one knows 
 that by putting the finger on the pulse we feel the wall of 
 the artery rise. In fact, this rising we called the pulse. If, 
 now, instead of the finger a sensitive lever be placed on the 
 artery, it is, of course, easy to see that at the moment the 
 pulse wave is under the lever it will lift the lever, and if 
 the distal end of the lever is provided with a recording point 
 
 Fig. 85. SPHYGMOGRAPHIC CITRVKS, i KOM HTM AN KADIAI. AUTKRY. 
 
 a curve will be the result. The sphygmograph possesses 
 the great advantage that it can be used easily and without 
 any injury to the blood vessels, and so is adapted for the 
 
THE CIRCULATION. 191 
 
 study of the pulse of man himself. In Figure 85 there are 
 indicated such sphygmograph curves. 
 
 On animals there is more generally used an instrument 
 called the kymograph. This is in principle a revolving 
 drum run by clockwork on which the recording lever traces 
 the desired curves. This lever rests on the mercury in one 
 limb of a U-shaped tube, while the other limb of this U- 
 shaped tube (D in Figure 86) is directly connected with the 
 cut end of the artery to be examined. To prevent the 
 blood from touching the mercury there is put over it in that 
 part of the tube some liquid which will prevent the blood 
 from clotting. Upon connection with the artery the pres- 
 sure of the blood of course at once forces the mercury down 
 one limb of the tube and necessarily up in the other, but as 
 the recording lever moves up and down with the mercury 
 on which it rests it records all these variations in pressure. 
 An examination of the figure of the kymograph will easily 
 show how a slight increase of arterial pressure will at once 
 cause the recording lever to be raised, while a decrease at 
 once lowers it. On the revolving drum this recording lever 
 will of course then describe curves such as those pictured 
 in Figure 86, which reproduce in excellent detail for per- 
 manent study all the variations of pressure in the artery ex- 
 amined. On such kymograph tracings as those traced on 
 the drum in the figure here given, the small curves indi- 
 cate the individual pulse waves, or what is the same thing 
 finally, the heart beats, while the larger waves indicate the 
 movements of breathing. In the case of a dog the arterial 
 pressure rises through inspiration and sinks during expira- 
 tion. The explanation of this periodic respiratory rise and 
 fall of arterial pressure is not yet possible, nor has it been 
 definitely proved that it exists in man. If we, therefore, 
 since we do not understand fully these respiratory curves, 
 turn our attention to the pulse waves themselves, each is 
 seen to consist of a straight and rapid rise of pressure to a 
 maximum height, while the fall of pressure, or the down- 
 ward wave, is not at all straight and gradual. There is 
 
192 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 placed on the descent a second smaller wave, and in some 
 instances a third. The second wave, however, like a notch 
 
 Fig. 86. LUDWIG'S KYMOGRAPH. 
 
 A, revolving drum to receive tracings; JF?, pendulum of the clockwork to rotate drum ; 
 C, the U-shaped mercury tube ; Z>, where connection is made with the blood vessel to be 
 examined; E, F, the piston raised or lowered by the mercury on which it rests; 6, the 
 recording lever. 
 
THE CIRCULATION. 193 
 
 on the descending part of the curve, is always present. 
 This presence of two crests on the pulse wave has given to 
 it the name of dichrotic. The explanation of this second 
 or smaller wave superposed on the first, is still not wholly 
 satisfactory. Various suggestions are offered by different 
 physiologists, but the probability is that the second wave is 
 due to the reflection of the pulse wave against the semi- 
 lunar valves. 
 
 To explain this more fully let us picture the condition 
 of things just at the moment the ventricle forces its con- 
 tents into the aorta. Here, in order to make room for the 
 sudden addition, the aorta expands close to the heart, 
 which expansion then in the form of a wave proceeds from 
 that point to the periphery; but, like the waves caused by 
 a pebble in the water, they would naturally run in all di- 
 rections, and so the pulse wave would start to run back 
 towards the heart. But scarcely started in that direction, 
 it would meet the closed semilunar valves and be there re- 
 flected backwards on the heels of the original pulse wave 
 and run with it to the tips of the arteries. Just as a loud 
 sound proceeding in a certain direction might have upon 
 its heels a slight echo caused by some precipice just behind. 
 
 THE INNEBVATION OF THE BLOOD VESSELS. 
 
 Many experiences and observations show that blood ves- 
 sels have a nervous control separate from the control of the 
 heart. Thus, blushing with embarrassment, or turning 
 pale with fright, or becoming flushed with exercise clearly in- 
 dicate that nerves must affect the contraction and dilatation 
 of arteries. The fact that arteries have muscular tissue in 
 their walls makes such a contraction or dilatation intelligible, 
 and no doubt the nerves in question reach these muscles. 
 Experiments have not failed to disclose such nerves which, 
 when stimulated, cause the arteries either to contract or 
 expand. Being thus concerned in controlling the motion 
 of the muscles of the arteries, they are called vaso-motor 
 nerves. In their physiological effect these vaso-motor 
 
194 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 nerves are of two kinds; first, vaso-motor nerves which 
 when stimulated cause the arteries to contract the vaso- 
 constrictor nerves; second, vaso-motor nerves which when 
 stimulated cause the arteries to dilate vaso-dilator nerves. 
 
 1. Vaso-consttictor nerves. The vaso-constrictor nerve 
 fibres are found in almost every part of the body. They 
 seem in a continued state of excitation, keeping the arteries 
 to which they go constantly contracted, for when such a 
 nerve is cut the arteries affected at once dilate. The ex- 
 planation of this is found in the fact that the cutting of the 
 vaso-constrictor nerves puts an end to the tonic influence 
 which they possess and the arteries freed from their con- 
 trol expand to their natural dimensions. Why the arteries 
 should be kept continually contracted is not hard to under- 
 stand. There are times when certain organs of the body 
 in order to do special work need an extra supply of blood. 
 The stomach needs more blood during digestion than when 
 idle between meals. Now, by keeping the gastric arteries 
 in a tonic or continued contraction they may be dilated by 
 relaxing the muscles when the process of digestion begins. 
 As arteries cannot forcibly expand (muscle fibres can never 
 be made to expand forcibly) , they must be contracted reg- 
 ularly in order to make an expansion when desired pos- 
 sible. While cutting a constrictor nerve causes a dila- 
 tation in the vessels affected because, as already stated, 
 the tonic control is cut off, a stimulation of the nerve 
 causes an increased contraction in the artery supplied. If 
 in a rabbit the constrictor nerve going to the transparent 
 ear be stimulated, the ear flap at once becomes pale. 
 
 Distribution of Faso- Constrictor Nerves. 
 
 The course of these constrictor nerves throughout the 
 body is about as follows: First. In the head they arise in 
 the medulla, pass from this into the sympathetic ganglia of 
 the neck, from which they proceed to all parts of the head, 
 usually running along with the cranial nerves. The tri- 
 geminal nerve, especially, is rich in such constrictor fibres. 
 
THE CIRCULATION. 195 
 
 Second. The constrictor nerves of the chest and abdomen 
 take their origin in the medulla, also, then through the 
 spinal cord they reach the sympathetic ganglia of the chest 
 and abdomen by means of the communicating branches, 
 and from these ganglia they proceed to the visceral organs. 
 The constrictors going to the organs in the abdominal 
 region go mainly through the large splanchnic nerves and 
 the solar plexus from which they spread in all directions. 
 As there are so many and such large arteries in the ab- 
 domen this splanchnic nerve is probably the most important 
 constrictor nerve in the body. Third. Constrictor nerves 
 going to the trunk and the extremities arise in the medulla, 
 also, pass down the cord and through the communicating 
 branches reach the sympathetic ganglia. From these they re- 
 join the spinal nerves and with them are distributed at the 
 periphery. It will thus be seen that all the constrictor nerves 
 arise in the medulla, but that before reaching their destina- 
 tion they pass through sympathetic ganglia. For this 
 reason they are often called sympathetic nerves. 
 
 The Vaso- Constrictor Center. 
 
 These nerves are governed by a center which lies in the 
 medulla where they originate. This center is automatic, 
 and is in constant excitation, and so, as stated before, there 
 is a continued contraction in all the arteries supplied. But 
 this vaso-constrictor center may be inhibited in part, that 
 is, it may be prevented from keeping the arteries con- 
 tracted. Such an inhibition would, of course, result in a 
 dilatation of the arteries affected. In this way the blood sup- 
 ply of the visceral organs, especially, is largely controlled. 
 What, now, are the influences that inhibit this center and 
 so cause a dilatation? 
 
 First: Psychic influences inhibit it. The explanation 
 of blushing lies in the fact that psychic influences (embar- 
 rassment, shame, etc.), reach that part of the center con- 
 trolling the arteries of the face and inhibit it, and the 
 
196 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 muscles freed from their regular control relax and expand 
 to their natural dimensions. 
 
 Second: Different afferent nerves may inhibit it. When 
 food enters the stomach the sensory impulses reaching the 
 brain from the stomach inhibit that part of the vaso-con- 
 strictor center which governs the gastric arteries, and these 
 removed from the tonic stimulus to remain contracted di- 
 late, and so the mucous gastric membrane becomes red and 
 flushed with blood. 
 
 Third: This vaso-constrictor center is very energetic- 
 ally inhibited by impulses reaching it from the depressor 
 nerves of the heart. As stated in a former paragraph, this 
 tierve is probably normally stimulated when the pressure of 
 the blood in the heart (and so, of course, elsewhere), be- 
 comes too great. Such impulses on reaching the vaso- 
 constrictor center in the medulla forcibly inhibit it, and an 
 immediate dilatation of arteries results, the consequence 
 of which is that the blood pressure at once sinks. Such a 
 general sinking of blood pressure is usually accomplished 
 by having that part of the constrictor center inhibited which 
 governs the abdominal viscera, and which at once arrests 
 the 'tonic action of the splanchnic nerve. As a result of 
 this the many large and small arteries through stomach 
 and intestines, etc., enlarge, the blood streams through, 
 and the arterial pressure is relieved. On the other hand, 
 to stimulate the splanchnic nerve, that is, to make this tonic 
 action stronger and so produce an increased contraction, 
 may diminish the size of the abdominal blood-vessels to 
 such an extent as to press out of them as much as twenty- 
 seven per cent, of their contained blood supply. The ef- 
 ficiency of and the necessity for such a nicely regulated 
 control of the blood supply for the various organs is, 
 of course, quite apparent. 
 
 Under some circumstances this constrictor center may 
 be actually stimulated. Thus, turning pale with fright is 
 due to the flurried stimulation of its activity. 
 
THE CIRCULATION. 197 
 
 2. Vaso-dilator nerves. In addition to the vaso-con- 
 strictor nerves there are vaso-dilator nerves. These nerves 
 are not, however, in a state o-f tonic excitation, but are 
 brought into play at special times only. Thus, when a 
 voluntary muscle is made to exercise, the arteries supplying 
 that muscle at once dilate. This might at first seem due 
 to an inhibition of that part of the constrictor center gov- 
 erning the arteries of these muscles, but there can actually 
 be found nerves which when stimulated cause a direct di- 
 latation. These dilator nerves come from the cerebro- 
 spinal system and are most apparent in the voluntary mus- 
 cles and numerous glands (submaxillary w and parotid) . 
 They run to the intrinsic ganglia distributed through the 
 muscular coat of the arteries (to which also the vaso-con- 
 strictor nerves run) and here inhibit the action of these 
 vaso-constrictor nerves, the result of which is, of course, a 
 dilatation. They run along with the trunks of the cranial 
 and spinal nerves, and anatomically are not distinguishable 
 from them. When the spinal nerve going to the muscle is 
 cut and the peripheral end stimulated not only does the 
 muscle contract, but the artery in the muscle dilates. Such 
 dilator nerves serve as additional means to regulate the 
 local supply of blood, and in the case of muscles, probably 
 accompany the motor nerves so that the best activity of the 
 muscle would be made possible by simultaneous increase in 
 the supply of blood to it. The vaso-dilator center lies in 
 the medulla, also, but seems not to play such an important 
 role as the constrictor center. 
 
 3. Comparison of the innervations of the heart and 
 blood vessels. There is a striking homofogy between the 
 nerves of the heart and the blood vessels. 
 
 1. Both have distributed in their muscles intrinsic 
 ganglia. 
 
 2. To both there run nerves, the stimulation of which 
 causes an increase in the contraction. In the case of the 
 heart this nerve is called the cardio-accelerator, and causes 
 
198 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 the heart to contract more rapidly. In the case of the ves- 
 sels it is the vaso-constrictors. These nerves, as already 
 stated, when stimulated cause an increased contraction here. 
 In the case of the heart, as well as the vessels, these nerves 
 come directly from the sympathetic system, although they 
 take their real origin in the cerebro-spinal system. 
 
 3. Both heart and vessels are supplied with nerves 
 which inhibit; that is, nerves, a stimulation of which 
 causes a reduction in the amount of contraction. In the 
 case of the heart this inhibitory nerve is the vagus, pneu- 
 mogastric, or tenth cranial nerve. In the case of the ves- 
 sels it is the vaso-dilators. As the vagus causes the heart 
 muscle to relax, so the dilators cause the arterial muscles 
 to relax. In both cases they are cerebro-spinal nerves and 
 reach their destination without the intervention of the sym- 
 pathetic system . 
 
 4. The heart is supplied with an accessory nerve called 
 the depressor, which carries to the medulla sensations from 
 the cardiac muscle. While, in the case of the vessels no 
 such a typical sensory nerve exists, there are, of course, 
 distributed to them nerves of general sensation, by means 
 of which sensory impulses from them reach the brain. 
 
 CHANGES IN THE CIRCULATION WHICH OCCUR AT BIRTH. 
 
 It is evident that the lungs are not functional before 
 birth. The blood must, therefore, seek its fresh supply of 
 oxygen elsewhere. This has necessitated the blood taking 
 a somewhat different course up to the moment of birth from 
 the one it retains ever after. 
 
 The foetus not only gets its nourishment, but its oxygen 
 supply also from a structure known as the placenta, or 
 "after-birth." This is a structure which grows out from 
 the foetus and intertwines itself closely with the uterine 
 wall; so closely, indeed, that the nourishment in the blood 
 flowing through the uterus may seep across into the foetal 
 capillaries of the placenta, and along with it the oxygen 
 carried by the arterial blood of the mother passes through 
 
THE CIRCULATION. 199 
 
 the capillary walls and is taken up by the foetal red cor- 
 puscles. There is, of course, no mixing whatever of the 
 maternal and foetal bloods. The two remain perfectly dis- 
 tinct, and the transfer of nourishment and oxygen is made 
 through the delicate capillary walls. This placenta is, 
 therefore, the foetal lung. Running to this placenta through 
 the umbilical cord or naval stalk from the foetus is a large 
 artery arising from the abdominal aorta. This carries the 
 blood from the foetus to the placenta. Here it passes 
 through the placental capillaries and is gathered up in the 
 veins and brought back to the foetus through the umbilical 
 cord by the umbilical vein. This, although called a vein, 
 contains arterial blood, having just received in the placenta 
 both its new supply of nourishment and oxygen. Upon 
 reaching the foetus this umbilical vein flows through the 
 liver, and from the liver the blood reaches the ascending 
 vena cava, by means of which it is carried to the right 
 auricle. This pure blood, going through the vena cava 
 in the way just described, does not drop from the right 
 auricle into the right ventricle, but goes from the right 
 auricle at once into the left auricle through an opening in 
 the auricular septum called the foramen ovale. The course 
 of blood in this direction is facilitated by a peculiar flap or 
 valve on the right auricle so placed that it guides the cur- 
 rent of blood across into the left auricle. This little flap is 
 called the Eustachian valve. This transfer is materially 
 aided by the fact that the ascending vena cava flows around 
 to the back of the right auricle before emptying into it, and 
 so has its opening close to the auricular septum. The pure 
 blood so transferred to the left auricle now drops into the 
 left ventricle, and by its systoles is forced out through the 
 aorta. For reasons to be pointed out in a moment, most of 
 this pure blood goes to the head and neck through the 
 innominate and carotid arteries. Thus, these rather more 
 important portions of the body are supplied with the best 
 available blood. 
 
200 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 From these regions, that is from head and neck, the 
 blood is again gathered up by veins, and finally by the vena 
 cava descending, carried to the right auricle. But here 
 this current of venous blood is so poured into the right 
 auricle that it does not meet the current of pure blood flow- 
 ing through it to the left auricle. The descending vena 
 cava opens into the auricle at the opposite side and from 
 above, and in this way the stream of venous blood which it 
 bears at once drops through into the right ventricle. This 
 crossing of two streams, one arterial and one venous in the 
 right auricle, may be easily understood by showing how 
 readily one might construct pipes leading into a room in 
 such a way as to have two currents flow through it and yet 
 have them separate and distinct; having one, for instance, 
 in one corner drop into the room from above, into a collect- 
 ing funnel below, while the other stream might at an oppo- 
 site corner be carried across from one wall to another inde- 
 pendently of the former, especially if a flap or plank like 
 the Eustachian valve should be added. 
 
 The stream of venous blood having reached the right 
 ventricle in the manner described, is now by the systole of 
 the right ventricle forced out into the pulmonary artery, 
 and would naturally go to the lungs ; but the lungs do not 
 at this time contain air. They are collapsed, and it would 
 be almost impossible and entirely useless to force this 
 stream of blood through them. This difficulty is remedied, 
 however, by a communicating branch which connects the 
 pulmonary artery with the arch of the aorta, and so enables 
 the venous blood to pass from the pulmonary artery through 
 this connecting duct into the descending aorta. This con- 
 necting duct is called the duct of Botallus. As this duct 
 of Botallus reaches the aorta after it has given off its vessels 
 to the head it prevents the flow of this venous stream in 
 that direction. But this venous stream, together with a 
 little pure blood which finds its way through the arch of the 
 aorta from the left ventricle, descends ^ through the aorta, 
 and while a little of it is carried by arteries which supply 
 
THE CIRCULATION. 201 
 
 the posterior part of the body, most of it is again by the 
 umbilical artery carried to the placenta, there to have its 
 oxygen supply renewed. 
 
 At the moment of birth a number of changes occur. 
 The circulation of blood through the placenta is stopped, 
 and now with the first breath drawn into the lungs these 
 organs expand and allow the stream from the pulmonary 
 arteries to pass through them. Within a few hours the 
 opening from one auricle into the other begins to be closed 
 up, and the duct of Botallus becomes filled by depositions 
 of fat and connective tissue in its lumen. The stumps of 
 the umbilical artery and vein practically disappear, and the 
 circulation which is to be maintained throughout life is 
 established. It, however, not infrequently happens that 
 the opening in the auricular septum remains through life, 
 and in some cases even the duct of Botallus remains open. 
 Such individuals, must, of course, have their circulation 
 materially interfered with. The Eustachian valve in the 
 heart becomes almost obliterated, although even on an 
 adult heart traces of it, as well as the thin partition closing 
 the auricular septum, and the solid string, the remains of 
 the duct of Botallus, may still be readily seen. In this 
 rather remarkable way, without a break, the foetal circula- 
 tion becomes changed in a moment into the regular circu- 
 lation of the fully developed body. 
 
CHAPTER IX. 
 
 THE LUNGS AND THE PROCESSES OF 
 RESPIRATION. 
 
 The circulation of the blood treated in the preceding 
 chapter leads naturally and without a break to the consider- 
 ation of the phenomena of respiration. It was pointed out 
 that the main reason for the mad rush of the blood is to 
 carry out the functions of respiration. Respiration consists 
 essentially in two gaseous interchanges. One of these takes 
 place in the lungs. Here oxygen is taken up by the red 
 corpuscles and carbon dioxide thrown off from the plasma. 
 The second gaseous interchange occurs in the tissues of the 
 body and is the exact reverse of the first, for here the 
 oxygen is liberated and the carbon dioxide picked up. 
 
 These two respiratory interchanges are complementary. 
 The one in the lung is called external respiration, the one 
 in the tissues internal respiration. We are first concerned 
 with the processes as they take place in the lungs. 
 
 THE ANATOMY OF THE RESPIRATORY SYSTEM. 
 
 The principal structure concerned in external respir- 
 ation is the lung. Into this air is drawn through the mouth 
 and nostrils by way of the trachea. At the upper portion 
 of the trachea where it leads into the pharynx is a dilata- 
 tion called the " voice-box." Here by suitable arrange- 
 ments the outgoing air sets into vibration stretched mem- 
 branes which produce the sounds of speech. For a detailed 
 description of this organ, the voice-box, or larynx, the 
 student is referred to a subsequent chapter on "The Voice. ' ' 
 
 The windpipe, or trachea as it is called, may be easily 
 felt by placing the finger on the throat. The large dilated 
 portion is the voice-box just noted, while the tube extend- 
 (202) 
 
THE LUNGS AND RESPIRATION. 
 
 203 
 
 ing downward from that is the trachea proper. This con- 
 sists essentially of a dense fibrous tissue in which are im- 
 bedded horseshoe-shaped pieces of cartilage which serve to 
 
 Fig. 87. THK AIR PASSAGES AND LUNGS FROM BEFORE. L,UNG TISSUE REMOVES ON 
 
 RIGHT LUNG TO SHOW RAMIFICATIONS OF BRONCHIAL TUBES. 
 
 a, larynx; b, trachea; d, bronchial tube. 
 
 keep the trachea open. The open ends of these horseshoes 
 are backward, that is, next to the gullet, and the absence 
 of bands of cartilage here no doubt materially facilitates 
 swallowing. 
 
 The trachea is lined on the inside with several layers of 
 epithelial cells, of which the innermost layer is ciliated. 
 These cilia move in regular rhythm and in such a way that 
 any material resting on them is driven forward toward the 
 mouth. In this way the mucus, or phlegm, is removed. 
 The trachea at its lower end divides into two branches, 
 called the bronchial tubes, and these in turn divide and sub- 
 divide repeatedly until finally a perfect system of ramifica- 
 tions of tubes is the result. At the end of each of these 
 finer ramifications there is a sack-like dilation called the 
 alveolus. The wall of this alveolus is thrown into little 
 pouches, each pouch being called an air cell. It is neces- 
 sary to remember here that the term "cell" is not used in 
 
204 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 its scientific sense, but in the original sense it had, meaning 
 a little chamber. In this way one single alveolus may, by 
 
 Fig. 88. CILIATED EPITHELIUM FROM THE TRACHEA OF A RABBIT. (After Schafer.) 
 w 1 , m 2 , m 3 , mucus-secreting cells lying between the ciliated cells. 
 
 the folding of its walls, give rise to a great many air cells. 
 In the walls of these air cells run the pulmonary capillaries, 
 and at this point the gaseous interchange of the blood takes 
 
 Fig. 89. DIAGRAMMATIC REPRESENTATION OF THE TERMINATION OF A F.ROXCHIAL TUBE 
 . IN A GROUP OF ALVEOLI. (After Schafer.) 
 
 B, bronchial tube; L. , bronchiole; A, atrium; 1, Alveolus; c, c, individual air 
 cells. 
 
 place. The anatomy of the bronchial tubes and their finer 
 divisions does not differ materially from that of the trachea. 
 The cartilaginous rings, however, become less regular and 
 
THE LUNGS AND RESPIRATION. 
 
 205 
 
 there is a gradual thinning out of the inner epithelium, 
 which in the final branches is reduced to a single layer 
 of ciliated cells. In the alveolus, finally, the wall is made 
 up of elastic tissue lined on the inside by a single layer of 
 flat epithelial cells. The very small bronchial tubes pos- 
 sess a little plain muscular tissue, so that they are actually 
 able to contract and expand, and thus reduce or increase 
 the amount of air which reaches the alveolus. The space 
 between the alveoli and the branches of the bronchial tubes 
 is filled with connective tissue, through which nerves, 
 arteries, and veins pass. 
 
 Fig. 90. SECTION OF LUNG, SHOWING SEVERAL, CONTIGUOUS ALVEOLI, WITH THE BLOOD- 
 VESSELS IN THE SAME INJECTED. (After F. E. Schultze.) 
 a, a, c, c, partitions and edges of alveoli; 6, artery giving off capillaries. 
 
 The lung is covered on the outside by a delicate serous 
 membrane, called the pleura. This surrounds the lung 
 closely at all points except at the root of the lung, the point 
 where the arteries and veins, and bronchial tubes enter it, 
 at which point the pleura is reflected and lines the inside of 
 the chest wall. 
 
206 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 PATHOLOGICAL CONDITIONS OF THE RESPIRATORY SYSTEM. 
 
 While there is not a single system in the body which is 
 immune from the attacks of disease, and though in many 
 individuals the respiratory system is among the most invul- 
 nerable, yet the general fact remains that this system more 
 than any other becomes the seat of pathological conditions. 
 This system is especially apt to become congested and in- 
 flamed as a consequence of exposure to cold. When this 
 inflammation is limited to the trachea, the bronchial tubes 
 and its larger divisions, we speak of it as a mere cold on 
 the chest, or bronchitis. As a consequence of a congested 
 condition of the respiratory mucous membrane it frequently 
 becomes sore, and is marked by an excessive secretion of 
 mucus, often to such an extent as to more or less clog 
 the passages. This excessive mucus is, of course, the 
 familiar phlegm, which forms such an annoyance of an 
 ordinary cold. Possibly the meaning of this extra mucous 
 secretion may be found in the fact that it acts as a kind of 
 protection to the inflamed membrane beneath, and serves 
 to prevent the introduction into that membrane of foreign 
 particles, be they ordinary grains of dust or more injurious 
 germs. This phlegm is, therefore, figuratively speaking, 
 a kind of natural salve which nature puts over these con- 
 gested portions to prevent the danger of exposure to foreign 
 elements. 
 
 This congestion may also extend into the air passages of 
 the nose and so produce the familiar " cold in the head," 
 and as the mucous membrane of the pharynx is continued 
 into the middle ear through the Eustachian tube, that organ 
 is frequently drawn into the inflammation. When such a 
 congestion of the nasal passages continues and becomes the 
 seat of ulcerations, it leads to the too-common catarrh. 
 But the term " catarrh " is not, strictly speaking, confined 
 in its application to a chronic inflammation of the nasal pas- 
 sages. The term "catarrh" means inflammation, and in 
 such a sense is applied to an inflammation wherever it may 
 occur. Thus, bronchitis is but a catarrh of the bronchial 
 
^HE LUNGS AND RESPIRATION. 207 
 
 tube-s. An inflammation of the mucous membrane of the 
 stomach is called a "catarrh" of the stomach, while even an 
 inflammation of the eye due to exposure is spoken of as an 
 ophthalmic catarrh. 
 
 As long as the inflammation is confined to the larger air 
 passages no especial danger ensues. But this inflammation 
 may become extended into the alveoli of the lung. This 
 condition is a much more serious one, and is called pneu- 
 monia. Colds, catarrh and pneumonia are not, however, 
 mere congestions. If they were, the effects of the conges- 
 tion ought to disappear when the proper vascular supply is 
 re-established. These diseases owe their dire results to the 
 infection of germs. The bacterium of pneumonia has been 
 recently, actually, quite satisfactorily isolated. Arctic ex- 
 plorers report their perfect immunity from colds in regions 
 which are free from bacteria. We must look upon the con- 
 gestion of the air passages or lungs more as a favorable cir- 
 cumstance for bacterial infection, which infection once hav- 
 ing secured a foothold, produces the real disease. That the 
 resistance of the respiratory organs to germs is materially 
 weakened in congestions is attested by the relative ease 
 with which consumption is induced in weak persons, as a 
 consequence of a " cold." 
 
 The pleura, also, may. become the seat of inflammation, 
 giving rise to a disease called pleurisy. 
 
 The smaller bronchial tubes near to where they open 
 into the alveoli, possess in their walls some plain muscular 
 fibres. Ordinarily these are relaxed and so free access of 
 air is permitted to the alveoli. But under certain conditions 
 these muscles go into a tonic contracted state, thus materi- 
 ally reducing the quantity of air which is able to get into 
 the alveolus and so making it difficult for the person in 
 question to get a sufficient amount of air. This condition 
 is called asthma. 
 
 Finally, the most serious pathological condition of the 
 lung is consumption. This, as has been pointed out, is a 
 disease which is due to the ravages of bacteria living in that 
 
208 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 organ. When we remember that on an average about every 
 one person in seven is afflicted with this disease, that it car- 
 ries off as its prey more people than pretty nearly all of the 
 more violent contagious diseases combined, and when we 
 remember that by improper ventilation, the crowding of 
 persons into close rooms, this disease is highly communica- 
 ble, we are more than justified in every reasonable effort to 
 prevent its spread, and especially its spread to children, 
 who, on account of their age, may yet happily be free from 
 its fatal touch. 
 
 * 
 
 THE MECHANICS OF RESPIRATION. 
 
 1. Movements of Respiration. In order for the blood 
 to be continually supplied with fresh oxygen it is necessary 
 that this gas should be constantly renewed in the lungs. 
 This renewal is brought about by the movements of respira- 
 tion. The essential feature of all the movements of in- 
 spiration is an enlargement of the chest. By enlarging the 
 chest additional room is made, and the air rushes in from 
 the outside to occupy this extra space. Just as in an ac- 
 cordion when it is drawn apart, air streams into it through 
 the various valves made for that purpose. Or, as in the 
 case of a pump, when the piston is lifted, and so additional 
 room made in the pump cylinder, the water under the pres- 
 sure of the atmosphere rushes in to fill this extra space. 
 This enlargement of the chest may occur in three different 
 ways. 
 
 First, it may be enlarged in an up-and-down direction. 
 This is accomplished by the contraction of the muscles of 
 the diaphragm. The diaphragm is a dome-shaped structure 
 with the dome or convexity extending chestward. By the 
 contraction of the muscles in this dome it is pulled down- 
 ward, the dome becomes flattened and the chest cavity en- 
 larged a corresponding amount. 
 
 Second, f he chest may be enlarged by increasing its 
 dimensions in a forward-back direction. This is done by 
 raising the breast bone. By noting the skeleton it may be 
 
THK LUNGS AND RESPIRATION. 209 
 
 seen that the breast bone is connected with numerous pairs 
 of ribs which extend from the breast bone backwards and up- 
 wards. If, now, by proper muscles these ribs are raised, 
 the result will be that not only the breast bone will move 
 upward, but also forward. This may readily be exemplified 
 by joining both hands and letting them rest in front on the 
 pelvic region. If, now, the arms be raised up, not only are the 
 hands raised, but they are also pushed away from the body, 
 and when the arms are extended directly forward may be 
 almost two feet or more from the trunk, whereas in their 
 original position they rested immediately against it. 
 
 A third enlargement of the chest is the lateral enlarge- 
 ment. This is brought about by the fact that not only are 
 the ribs lifted up, but they rotate outward. This enlarge- 
 ment may be illustrated in the example of the raising of the 
 folded hands also. If, in addition to the lifting of the 
 hands, as in the preceding illustration, the arms be some- 
 what bent and rotated outwards, it is at once apparent that 
 the lateral diameter is increased. 
 
 While an inspiration results from an enlargement of the 
 chest, an expiration is due to a contraction of the chest. 
 Under ordinary circumstances an expiration is a passive 
 process. We expand the chest and take air in by an active 
 contraction of muscles, but we expire by simply relaxing 
 the muscles and letting the chest drop back to its natural 
 dimensions. Sometimes, however, the expiration may be- 
 come forced. This may be accomplished in three different 
 ways, which are the exact opposites of those given for en- 
 larging the chest. That is, the diaphragm may be pushed 
 up further into the chest and become more dome-shaped 
 than before. This is done by contracting the abdominal 
 muscles and so pressing the stomach, liver and intestines 
 up against the diaphragm, and in this way lifting it up. 
 Or, a forced expiration may result from pulling the breast 
 bone downwards and rotating the ribs inward. 
 
 It is unnecessary to say that generally all three ways are 
 used at the same time, although the breathing of men is 
 14 
 
210 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 more largely with the diaphragm, while that in women is 
 more largely with the ribs. 
 
 The muscles that move the ribs up and down are called 
 the intercostal muscles. Of these muscles there are two 
 sets, the external intercostals and the internal intercostals. 
 The external intercostals are so arranged that the insertion 
 point on the lower rib is always forward from the insertion 
 on the upper rib, while in the internal intercostals the re- 
 verse is true. To show how the contraction of the ex- 
 ternal intercostals raise the ribs and breast bone, while the 
 
 Fig. 91. DIAGRAM TO ILLUSTRATE THE MANNER OF ENLARGEMENT OF CHEST. 
 
 internal intercostals pull it down, a little piece of apparatus 
 may be constructed such as the one indicated in the accom- 
 panying diagram. If, now, a piece of rubber be stretched 
 in such a way as to correspond with the pull of the ex- 
 ternal intercostals it will raise the bars. When arranged 
 like the internal intercostals it will pull it forcibly down- 
 wards. That such would result is of course easily seen by 
 studying Figure 92. The line a b' , corresponding to the ex- 
 ternal intercostals is shortened, which, of -course, is analo- 
 gous to the contraction of the muscle itself. Shortening can 
 take place only when both beams are pulled upward, while 
 the exactly opposite is the result with the internal inter- 
 costals. 
 
 2. The Rate of These Movements. The rate at which 
 inspirations follow each other varies considerably under 
 different circumstances, but on an average in an individual 
 
THE LUNGS AND RESPIRATION. 
 
 211 
 
 who is not conscious that his breathing movements are 
 being observed, the rate is from fifteen to twenty per 
 minute. It is greater in children, and in infants is on an 
 
 Fig. 92. DIAGRAM TO SHOW THE OPERATION OF THE EXTERNAL AND INTERNAL INTER- 
 COSTAL MUSCLES. 
 R, R", r, r", ribs in elevated position; R, R', r, r', ribs in depressed condition; a, 6. 
 
 external intercostals; a', &', same contracted elevating the ribs; d', c', internal intercos- 
 
 tals; d, c, same contracted depressing ribs. 
 
 average as high as forty-four. From this it gradually sinks 
 during childhood until the adult rate of fifteen to twenty 
 just given is reached. This rate, however, may be much 
 influenced by emotions, by muscular exercise and by tem- 
 perature. 
 
 3. The Capacity of the Lungs. The capacity of the 
 lungs no less than the rate varies with different classes of 
 people, and even with individuals of the same class. On 
 an average, however, in a properly exercised person the 
 following figures do not come very far from the actual con- 
 dition of things : 
 
 If a person breathe out as much air as he can possibly 
 do, or, in other words, if he reduce the capacity of his 
 lungs as far as he is able to do, he still has in his lungs a 
 considerable amount of air. During life it is impossible, of 
 course, to get the lung- perfectly air free, and so the amount 
 of air which is left in the lung after the most forced ex- 
 piration possible, can be measured only after death. Ex- 
 periments of this kind give about 1,640 centimeters, or 
 
12 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 about 100 cubic inches as the amount of air which it is im- 
 possible, even by the most violent expiration, to remove. 
 These 100 cubic inches are called the " residual' 7 air. But 
 in ordinary respirations we do not breathe out as much as 
 we can, and under these circumstances there is left in the 
 lung 1,640 centimeters, or 100 cubic inches additional. 
 That is to say, in ordinary breathing there are in the lung 
 at the end of an expiration 200 cubic inches of air. These 
 extra 100 cubic inches are called the "supplemental" air, 
 which, together with the residual air, forms the * 'stationary" 
 air of 200 cubic inches. Now, at an ordinary breath we 
 take in about 500 centimeters, or 30 cubic inches, and of 
 course breathe out the same amount at an ordinary breath. 
 This air is called the "tidal" air. But we are able by a 
 forced inspiration to take in more than we do ordinarily. 
 We seldom breathe as deeply as we can. By a forced in- 
 spiration the lung is able to take in 100 cubic inches more. 
 These extra 100 cubic inches are called the "complemental" 
 air. The amount of air which one is able to breathe from 
 the deepest expiration possible to the deepest inspiration 
 possible is called the "vital capacity." This would then 
 consist of the supplemental air, 100 cubic inches, the tidal 
 air, 30 cubic inches, and the complemental air, 100 cubic 
 inches. In all 230 cubic inches; that is, approximately an 
 even gallon. 
 
 Such determinations of the capacity of the lung, of 
 course with the exception of the residual air, may be easily 
 made by means of the spirometer, an instrument found in 
 almost every well-equipped gymnasium. 
 
 4. The Amount of Air Used. In the mechanics of res- 
 piration there have been considered so far the following 
 topics: 1. The movements of respiration, or those changes 
 by means of which the capacity of the chest is enlarged and 
 contracted, and so the air drawn into it or forced out. 2. 
 The rate of these movements. 3. The capacity of the 
 average lung. A very important topic in the mechanics of 
 breathing still remains to be answered. It is the question 
 
THE IvUNGS AND RESPIRATION. 213 
 
 of the amount of air necessary to properly supply the lungs, 
 which includes the rather important subject of ventilation. 
 
 Ventilation. 
 
 As stated before, we take in at each breath about thirty 
 cubic inches of air; that is, about half a liter. As about 
 fifteen breaths are taken on an average per minute, this 
 makes the amount of air taken into the lungs in that time 
 450 cubic inches. But the problem of the amount of air is 
 not so simple as that. If each mouthful of air as it is 
 breathed out could at once be snatched away from the mouth 
 and so enable a fresh mouthful to be- taken in, 450 cubic 
 inches would suffice. By making careful experiments it has 
 been shown that every mouthful of air that we breathe 
 out is mixed with the outside air and vitiates three times as 
 much additional air, to such an extent as to make it no 
 longer fit for respiration. Or, in other words, every mouth- 
 ful we breathe becomes mixed with three additional mouth- 
 fuls outside, in a way to make the four mouthfuls so result- 
 ing perfectly unfit for further respiration. Therefore, the 
 amount of air actually required per minute is not 450 cubic 
 inches, but four times 450 cubic inches, or 1,800 cubic 
 inches per minute. This is just a little over one cubic foot. 
 These figures express rather important results and ought to 
 be kept in mind by persons who have the ventilation of 
 crowded rooms in charge. Fresh air ought to be admitted 
 at the rate of one cubic foot per minute for each person in 
 the house. This does not, of course, mean the production 
 of a draft, it being entirely possible to renew the air at this 
 rate even in a fairly crowded room without subjecting any 
 body in it to exposure to a draft. 
 
 For proper ventilation an amount of space between 
 500 and 1,000 cubic feet for each person ought to be avail- 
 able. In some of the better hospitals where the crowding 
 of patients is not permitted, "and where the subject of proper 
 ventilation is treated as of the primest importance, the 
 amount of space allowed to each patient is often even more 
 
214 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 than this. These figures ought not to be passed over 
 thoughtlessly, but ought to serve as a criterion in judging 
 whether any room in question is really capable of housing 
 one, or two, or three individuals, as the case may be. 
 Students, especially, are sometimes not overly careful in. 
 crowding two or three into a small room, the capacity of 
 'I which would be but little more than that required for a 
 single occupant. 
 
 Wliat Vitiates Air? 
 
 It was pointed out that in breathing, oxygen is taken 
 from the air and carbon dioxide given to it. But air be- 
 comes vitiated and is no longer fit to be breathed, not be- 
 cause too much of the oxygen has been removed, or because 
 too much carbon dioxide is present in it. In an atmosphere 
 in which the amount of oxygen should be materially reduced 
 the blood could still get all of that gas it would need. An 
 atmosphere containing quantities of carbon dioxide very 
 much greater in proportion than that in the air of badly 
 ventilated rooms, would still be perfectly harmless to 
 breathe. Of course if the oxygen supply should be reduced 
 so much as to make it impossible to get enough of that gas, 
 or if there should be so much carbon dioxide in the atmos- 
 phere that it would almost entirely replace the oxygen, as 
 it is sometimes in deep wells or in mines, then the carbon 
 dioxide would prove injurious and fatal, but not because it 
 itself is injurious or poisonous, but simply because it has 
 displaced the necessary oxygen. 
 
 The thing that makes air which has been breathed once 
 no longer fit for respiration is the fact that such expired air 
 contains organic impurities which have been breathed out 
 from the lungs. It is impossible to determine just what these 
 impurities are, but they are probably volatile substances of a 
 poisonous nature, or may actually be particles of decayed 
 lung or other organic tissue. It is this organic admixture 
 that plays havoc in instances of insufficient ventilation. An 
 idea of the large amount of such organic material breathed 
 out may be gained when we remember how frequently the 
 
THE LUNGS AND RESPIRATION. 215 
 
 breath of persons is tainted more or* less strongly with ob- 
 jectionable odors, which in many cases are not necessarily 
 due to a careless condition of the teeth, but due to sub- 
 stances either volatile, or to small particles of disintegrated 
 tissue which have emanated from the lungs. Our bodies 
 seem peculiarly susceptible to such eliminated particles, and 
 an atmosphere that has been vitiated even to a small extent 
 with them becomes at once unpleasant to our nostrils, and 
 if in spite of this warning we persist in breathing it, there 
 results finally a dullness, a headache, or a general indisposi- 
 tion which, if continued from day to day, surely and inevit- 
 ably leads to an undermining of the general health and 
 energies, and may succeed in cutting the life unnaturally 
 short. 
 
 There are persons who seem to think that the import- 
 ance of ventilation as it is urged* by persons who have 
 studied that subject is somewhat of a scientific fad, and the 
 day is not yet here when persons who have the ventilation 
 of crowded rooms in charge always appreciate the impor- 
 tance of the duty so assigned to them. In determining the 
 amount of air which ought to be admitted into a room, 
 stoves which consume large quantities of oxygen, or gas jets 
 which use up a certain supply of the same gas, must be 
 taken into consideration, for the consumption of oxygen in 
 a stove may, under certain circumstances, be many times 
 that of a single person. Then, further, as there are always 
 emanating from a heated stove certain poisonous gases, the 
 necessity for a more perfect ventilation than ordinary is at 
 once apparent > 
 
 THE CHEMISTRY OF RESPIRATION. 
 
 1. Composition of Inspired and Expired Air. The 
 composition of the air which we inspire is about as follows : 
 
 Nitrogen 79 per cent. 
 
 Oxygen 20 " 
 
 Carbon Dioxide 004 " 
 
 Water in amounts depending on the humidity of the atmosphere. 
 
216 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 In addition to these gases there was recently discovered 
 another gas resembling nitrogen in some of its properties, 
 and called "Argon" by its discoverer, but as this gas does 
 not figure in the processes of respiration a consideration of 
 it may be for our purposes omitted. 
 
 If now with such inspired air we compare expired air, 
 we find that a number of changes have occurred in the 
 lungs. First, the expired air is warmer, due to its having 
 remained for some time in the warm lung. Second, as a 
 consequence of this increase in temperature it has expanded 
 slightly in volume, so that the expired air seems at first a 
 little larger than inspired air, and for this reason it tends 
 to rise. However, when expired air is reduced to the same 
 temperature and pressure as the inspired air, it is found to 
 be a little less in volume, showing that a part of the air has 
 actually been taken into the body and kept there. Third, ex- 
 pired air contains a much larger amount of moisture. This 
 is especially evident on a cold day when the breath, as we 
 say, becomes visible, due to the condensation of the large 
 amount of moisture in it. So far the changes are merely 
 physical changes. There is, however, fourth, quite a dif- 
 ference in the chemical composition of the two. The ex- 
 pired air has lost five per cent, of oxygen and gained about 
 four per cent, of carbon dioxide, and finally, fifth, the 
 expired air contains traces of volatile organic substances, 
 and possibly particles of disintegrated tissue to which the 
 vitiation of respired air is due. 
 
 It requires special chemical experiments to show that 
 five parts of the twenty parts of oxygen have been removed. 
 On the other hand, the addition of the four parts of carbon 
 dioxide to expired air may be easily shown in a very simple 
 experiment. If a person breathe, by means of a glass tube, 
 "through a flask or bottle containing lime-water, the carbon 
 dioxide will unite with the lime-water, and a white precipi- 
 tate will form insoluble in the water which soon settles to 
 the bottom. 
 
THE LUNGS AND RESPIRATION. 217 
 
 The composition of expired air may then be tabulated 
 as follows: 
 
 Nitrogen 79 per cent. 
 
 Oxygen 15 " 
 
 Carbon Dioxide 4 "' 
 
 Water in increased amounts. 
 Organic substances. 
 
 2. The Amount of Oxygen Consumed in One Day and 
 the Amount of Carbon Dioxide Eliminated in the same 
 Period. As the amount of oxygen which is taken up by 
 the blood while in the lung is five per cent, of the entire 
 air, we are easily able to calculate, knowing the amount we 
 breathe in at each breath and the number of breaths in a 
 given time, just how much oxygen under ordinary pressure 
 we can consume in, say a day. Such calculations give as 
 the daily oxygen consumption twenty to twenty-five cubic 
 feet. The carbon dioxide is a little over four per cent, and 
 in a day amounts to from sixteen to eighteen cubic feet. 
 
 To all students who have taken even elementary courses 
 in chemistry, oxygen and carbon dioxide are things of 
 knowledge. For the sake of persons who have had no 
 training in chemistry it may be in place here to refer briefly 
 to the nature of these two substances. 
 
 Oxygen is a gas which forms about a fifth of the ordi- 
 nary atmosphere, and is that element of the atmosphere 
 which makes burning possible. It is ordorless, tasteless, 
 colorless, and so not easily perceived by the senses, yet 
 forming an integral part of the very atmosphere in which we 
 move, and chemically familiar to everybody as the element 
 in the atmosphere which as the draft we lead into stoves and 
 lamps to make combustion possible, it needs no further ex- 
 planation. Pure oxygen very materially increases the energy 
 of combustion, and in an atmosphere of pure oxygen even 
 such an apparently incombustible thing as a steel wire may 
 be made to burn easily. In the air, however, the oxygen is 
 very much diluted with the inert gas called nitrogen which 
 serves, therefore, in this process of respiration as a mere 
 diluting agent and plays no active role itself. 
 
218 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 Carbon dioxide (CO L .) is the gas which results when 
 carbon, or things which contain carbon, such as \vood or 
 coal, are burned. It is colorless, and in diluted amounts 
 tasteless and odorless, and so not readily perceived when 
 mixed with the gases of the atmosphere. In a pure form 
 carbon dioxide is familiar as the gas which rises from a 
 freshly-drawn glass of soda-water, the soda fountains being 
 charged and the pressure in them produced by this gas. 
 It is the gas which causes the effervescence when vessels 
 containing any of the so-called (( sparkling liquids, " such 
 as pop or champagne, are opened. 
 
 THE PHENOMENA OF EXTERNAL RESPIRATION. 
 
 1. The Supply of Oxygen. Possibly the best way to 
 arrive at a proper understanding of the exact way in which 
 the gaseous interchange in the lungs is accomplished is to 
 get a clear picture of the actual condition of things in that 
 organ. In the first place, in the alveoli is fresh air, brought 
 there by the movements of respiration. In the walls of 
 these alveoli lie the pulmonary capillaries, into which the 
 venous blood coming from the right side of the heart enters. 
 This venous blood in the capillaries is separated from the 
 air in the alveoli by the membranes which form the walls 
 of the capillaries and the linings of the alveoli. Thus there 
 seems to be at first a difficulty in having the air and the 
 blood put in direct contact. Experiments, however, show 
 that a moist membrane which may separate a liquid from a 
 gas may be for all practical purposes disregarded. Thus, 
 if a glass vessel be taken, filled with a certain liquid and a 
 moist membrane stretched carefully over it, and then the 
 vessel be put into an atmosphere of a certain gas, the result 
 will be much the same as if that membrane had been left 
 entirely off, the only difference being that the presence of 
 the membrane slightly retards the rapidity of the gaseous 
 interchange. Thus this apparent difficulty at once disap- 
 pears and we may therefore imagine the venous blood of the 
 capillaries and the air in the alveoli in immediate contact. 
 
THE LUNGS AND RESPIRATION. 219 
 
 The next question that suggests itself is the exact man- 
 ner in which the gases of the air enter the blood, and how 
 those of the blood enter the air. In order to understand 
 this it is desirable to turn aside a little and explain some- 
 what in detail one of the most familiar laws of the physical 
 laboratory, the law which governs the absorption of gases 
 by liquids. 
 
 D ALTON'S LAW OF THE ABSORPTION OF GASES BY LIQUIDS. 
 
 When in any experiment a liquid and a gas are brought 
 together the liquid will at once absorb or dissolve in itself 
 some of this gas, the amount so dissolved depending on the 
 pressure which that gas exerts on the liquid, and varying di- 
 rectly with that pressure. This is not a physiological phe- 
 nomenon but a general physical law, and applies to all liquids 
 and gases. It was named after the physicist who first care- 
 fully proved and formulated the law, and called " Dalton's 
 L,aw of the Absorption of Gases." This law of the absorp- 
 tion of gases announces the observed fact that the amount 
 of gas which any liquid absorbs depends on the pressure 
 which that gas exerts on the liquid and varies directly with 
 it; that is, if the pressure is doubled the amount of gas so 
 dissolved is doubled ; if the pressure is reduced to one-half 
 the amount of gas dissolved is reduced one-half. 
 
 There are many familiar illustrations of this law. For 
 instance, in the manufacture of the familiar soda-water it is 
 deemed desirable to have ordinary water absorb very large 
 quantities of carbon dioxide. Under ordinary pressure 
 water absorbs but little carbon dioxide, but to remedy this, 
 the water to be made into soda-water is subjected in a 
 proper system of tanks to a very great pressure of the car- 
 bon dioxide gas, and in conformity to Dalton's law the water 
 absorbs increased quantities of that gas. The heavier the 
 pressure in such a charged soda-fountain, the more gas will 
 the water absorb. The same thing is illustrated in the bot- 
 tling of mineral waters. Here the ordinary water is sub- 
 jected to a high pressure of carbon dioxide gas, too, and 
 under this high pressure the mineral water dissolves into it- 
 
220 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 
 
 self increased quantities, and in that condition is forced into 
 bottles which are then tightly sealed, in order to retain the 
 gas at the original pressure. A bottle of mineral water that 
 had been filled from a tank subjected to a carbon dioxide 
 pressure twice as great as that of a second tank would have 
 twice as much carbon dioxide gas in it as a similar bottle 
 filled from the second tank. 
 
 The water of our wells and streams is, of course, in 
 contact with the air, and the air presses on it with a pres- 
 sure equal to fifteen pounds to the square inch. In conform- 
 ity to the law just given certain and definite amounts of air 
 are dissolved or absorbed by the water. Thus the oxygen 
 which is absorbed in ordinary river water and which serves 
 for the respiration of fishes is accounted for in this way. 
 Dalton's law might be stated in another way which may 
 help to make this matter clearer. Liquids absorb gases un- 
 til the pressure of the gas dissolved in the liquid is just the 
 same as the pressure of that gas above the liquid. A few 
 illustrations may prove helpful. If, in the case of an ordi- 
 nary engine boiler a valve be opened in the lower part of 
 the boiler where the water is, the water is forced out with 
 the same pressure as the steam would be forced out from the 
 upper part of the boiler. That is to say, the pressure in the 
 water of the boiler is the same as the pressure of the steam 
 above that water. Or, to illustrate further, in a bottle not 
 quite filled with some heavily charged mineral water there is 
 a certain amount of gas above the liquid. If the stopper 
 from such a bottle should be removed not only would the gas 
 above the liquid be forced out, but the gas dissolved in the 
 liquid would try to relieve itself of the pressure to which it 
 has been subjected, and so flow out of the bottle, frequently 
 carrying bits of the liquid along with it as a froth or foam. 
 As soon as a glass of heavily charged soda-water is drawn 
 and placed on the table to be served, the (CO 2 ) gas which 
 was dissolved in the water, now being relieved of the pres- 
 sure of the gas above it, leaves the water and causes the 
 familiar froth, or, as it is called, the effervescence of that 
 
THE UJNGS AND RESPIRATION. 221 
 
 liquid. This loss of gas in all these cases would continue 
 until finally the pressure of the gas in the liquid itself would 
 sink as low as the pressure of that gas in the atmosphere 
 above the liquid, when things would come to a standstill. 
 
 The phenomenon of boiling is a still further illustration 
 of this same fact. As the water becomes gradually more 
 and more heated the pressure of steam in the liquid rises 
 correspondingly, until finally a point is reached at which the 
 pressure of the steam in the liquid is a little greater than 
 the pressure of the atmosphere above the liquid. As a re- 
 sult of this the water is thrown upward to allow the steam to 
 escape. This throwing up of the water is, of course, the 
 familiar boiling of the liquids. For this reason we ought to 
 expect that water would boil more quickly the lower the at- 
 mospheric pressure. Such is, of course, the case, and water 
 will boil on high mountainous altitudes at very much re- 
 duced temperatures. Finally, it may not be altogether out 
 of place to call renewed attention to the fact that such a gas 
 absorbed in or dissolved by a liquid is not held in that liquid 
 in the form of bubbles, but is thoroughly dissolved in it and 
 to the eye invisible. Thus, a bottle of heavily charged 
 mineral water will appear without a bubble in it as long as 
 it remains corked, and yet at the moment of opening, in- 
 numerable bubbles will at once form throughout the liquid, 
 sometimes with such rapidity as to cause the whole liquid 
 to froth. 
 
 With this little side excursion into the realm of physics, 
 let us turn again to the condition of things in the lungs 
 and see the application there of Dalton's law. 
 
 A difficulty at once confronts us. The air is not a 
 single gas. It is made up of at least three gases. It con- 
 tains about four-fifths nitrogen, one-fifth oxygen, and then 
 traces of CO 2 . The experiments of the physicist again 
 help us out here, for in all cases where a liquid is subjected 
 to a mixture of gases each gas acts independently of all the 
 others; that is, the amount of one gas which will be ab- 
 sorbed by a liquid is not in any way influenced by the 
 
222 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 presence of any other gases. We have in every case to do 
 only with the pressure of the one gas in question. Now, 
 one-fifth of the atmosphere is oxygen, four-fifths nitrogen, 
 disregarding for the moment the other ingredients. As the 
 pressure of the atmosphere is fifteen pounds to the square 
 inch, a fifth of that is due to oxygen; that is, the pressure 
 of oxygen to the square inch is three pounds, while the 
 pressure of the nitrogen, the remaining four-fifths of the 
 atmosphere, is of course four-fifths of fifteen pounds, or 
 twelve pounds. In studying the action of the oxygen in 
 the lung, we need only to take into account the fact that 
 the oxygen presses on the blood in the capillaries with a 
 pressure equal to three pounds to the square inch, and we 
 may, without fear of any complications, entirely disregard 
 the presence of the other gases. For if the blood should be 
 put into a closed vessel and all the nitrogen of the air in 
 that vessel be removed chemically, no difference would re- 
 sult. In conformity with the law of Dal ton, oxygen will 
 be absorbed by the plasma until the pressure of the oxygen 
 in the plasma becomes the same as the pressure of oxygen 
 above it; that is, three pounds; and the nitrogen will be 
 absorbed by the plasma until the pressure of nitrogen in it 
 will be equal to the pressure of nitrogen immediately 
 above it. 
 
 So far there would be not one iota of difference between 
 what happens to the venous blood in the lung and what 
 happens to the water in a river. Both subjected to the 
 same atmosphere would dissolve the same proportion of 
 oxygen and nitrogen. Animals which have colorless blood 
 only, for instance, the oyster or the crayfish, get their 
 supply of oxygen from the amount of this gas which the 
 water of their blood will dissolve. As every one knows, 
 however, ordinary water does not dissolve very much 
 oxygen, and fishes which are put in an aquarium must have 
 the water renewed at very frequent intervals, as the oxygen 
 supply of the water is rapidly exhausted. For this reason 
 animals that can get no other oxygen except that carried 
 
THE LUNGS AND RESPIRATION. 223 
 
 by the liquid of the blood are necessarily cold-blooded, and 
 frequently very sluggish, much like a fire which, devoid of 
 a good draft, would have to burn slowly and smoulder. But 
 in the case of the blood of all higher animals a new factor 
 is added. This new factor is the haemoglobin contained in 
 the red corpuscles. This haemoglobin has the chemical 
 property of combining with oxygen whenever the pressure 
 of the oxygen is a half pound or more, and of giving up the 
 oxygen just as soon as the pressure of oxygen surrounding 
 it sinks below a half pound. This property of haemoglobin 
 is by no means a unique one. There are many chemicals 
 which, under high pressure, will form combinations with 
 other substances, and at lower pressure will again disunite. 
 We have here to do not with a mysterious physiological 
 problem, but with a simple every-day chemical fact. 
 
 THE EOLE OF THE BED CORPUSCLES. 
 
 I/et us now see just what role the red corpuscle with its 
 haemoglobin plays in the pulmonary capillaries. In a way 
 described above the oxygen is absorbed by the plasma and 
 the oxygen pressure in the same will at once begin to 
 rise. When, however, this pressure in the plasma rises 
 above a half pound the haemoglobin will at once seize the 
 oxygen absorbed in the plasma and unite chemically with 
 it. This oxygen so taken out of the plasma is, of course, 
 replaced at once by fresh oxygen which streams in from the 
 outside. As the pressure of the oxygen in the air is three 
 pounds to the square inch, it will continue to stream into 
 the plasma until the pressure there will be three pounds. 
 But before the pressure reaches three pounds, in fact, just 
 as soon as it passes the half-pound limit, the haemoglobin in 
 the red corpuscles will pick out the oxygen from the 
 plasma, unite chemically with it, and so prevent the pres- 
 sure in the plasma from reaching three pounds. This will 
 go on until finally all of the haemoglobin has united with 
 oxygen; that is, until all of the haemoglobin has been 
 changed into oxyhaemoglobin. After this point is reached 
 
224 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 the oxygen will continue to stream into the plasma until the 
 pressure in the plasma reaches three pounds, and then 
 everything will come to a standstill. Of course at this 
 juncture the blood is pushed onward into the pulmonary 
 veins and is as arterial blood sent back to the left side of 
 the heart, to be, of course, in the lung replaced by fresh 
 venous blood from the pulmonary arteries. 
 
 By way of summary the condition of things in this 
 arterial blood as it leaves the lungs is re-stated. The 
 plasma of the arterial blood has oxygen dissolved in it to 
 a pressure of three pounds to the square inch, or at least 
 not very far from that. All the haemoglobin has been 
 changed into oxyhaemoglobin, and as this oxyhsemoglobin 
 is in the plasma surrounded by an oxygen pressure of moi;e 
 than half a pound it does not disunite with its oxygen. In 
 this condition of things the blood is sent out through the 
 arteries over the entire body and finally reaches the capil- 
 laries in the tissues. This is the seat of the internal 
 respiration. 
 
 THE PHENOMENA OF INTERNAL EESPIEATION. 
 
 1. The Oxygen Supply. In order here, also, to more 
 thoroughly understand just what takes place in this gaseous 
 interchange, let us picture the exact condition of things in 
 the tissues. The arterial blood, as described, is in the tis- 
 sue capillaries. Just outside of the capillaries lies the 
 lymph which bathes the tissues, and in which lie the live 
 cells of the body, the units for which the nourishment of 
 the blood and the oxygen which it carries are intended. 
 These cells immersed in the lymph have a great avidity for 
 oxygen, and use it up as fast as it is carried to them. Stat- 
 ing this in a more scientific way, there is in the lymph, 
 bathing healthy tissues, never much free oxygen, and of 
 course there can then be no oxygen pressure. We have the 
 lymph with no oxygen pressure in it, separated from the 
 plasma of the blood which has a three-pound pressure, by 
 a thin capillary wall. It was pointed out in discussing 
 
THE LUNGS AND RESPIRATION. 225 
 
 external respiration that the presence of such a membrane 
 does not in any way hinder gaseous interchange, and so we 
 may again imagine the plasma in the capillaries in immedi- 
 ate contact with the lymph bathing the tissues. As there 
 is a three-pound pressure in the plasma, and no pressure in 
 the lymph, the oxygen will stream from the plasma into the 
 lymph, just as in opening a bottle of mineral- water where 
 the pressure of the gas in the bottle is much greater than 
 the pressure of that gas on the outside of the bottle, the 
 gas will stream out into the air surrounding the bottle. 
 This streaming of oxygen out of the plasma will continue , 
 until finally the oxygen pressure of the plasma sinks to a 
 half pound. 
 
 It will be noticed that up to this point the red corpuscles 
 have taken no part at all in the process of the gaseous 
 interchange, but as soon as the oxygen pressure in the 
 plasma sinks to or below a half pound the haemoglobin is 
 no longer able to remain united with the oxygen, but dis- 
 associates. The oxygen so liberated from the oxy haemo- 
 globin flows into the plasma with which it is surrounded, 
 and from the plasma in turn the oxygen streams into the 
 lymph. This will continue until finally all of oxyhaemo- 
 globin has been disunited, and until almost all the oxygen 
 from the plasma has streamed into the lymph. The oxygen 
 does not accumulate in the lymph, for in the tissues this 
 gas is used up almost as fast as it is brought, and so the 
 oxygen pressure in the lymph, in spite of the amount of 
 gas carried to it, remains practically nothing. The fact that 
 the oxygen does not accumulate but is used up as fast as it 
 is brought explains why it is impossible, even for a very 
 short interval of time, to be deprived of air. It takes but 
 a minute or more of a loss of air to induce the fatal effects 
 of suffocation. About the instant when all the oxygen has 
 been taken out of the blood, this /is pushed into the veins 
 and sent back to the heart for a fresh supply. 
 
 Here, also, by way of summary, the condition of things 
 in the venous blood as it leaves the tissues is re-stated. 
 
226 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 The oxygen pressure in the plasma is very low, less than a 
 half pound. For this reason all of the oxyhsemoglobin has 
 been disassociated and the haemoglobin only is left. Thus 
 it will be seen that the reason why the blood does not give 
 off any of its oxygen until it reaches the tissues is, that all 
 through the arteries the pressure of the oxygen in the 
 plasma remains constant, but sinks below the critical half 
 pound limit in the capillaries only. In the chapter on Blood 
 it was stated that by far the larger amount of oxygen was 
 carried by the corpuscles and a relatively small amount 
 only by the plasma. The proportion is given by some physi- 
 ologists as ten to one, but while this is true, it will be 
 noticed from the preceding that the plasma and the oxygen 
 dissolved in it, play a most important role in the process of 
 respiration. 
 
 2. The Elimination of the Carbon Dioxide. But the 
 preceding is only half of the story. In the process of res- 
 piration not only is oxygen taken up in the lungs and 
 carried to the tissues, but carbon dioxide is picked up in the 
 tissues and eliminated from the lung. There now remains 
 a more detailed description of the actual manner in which 
 this carbon dioxide is picked up in the capillaries and finally 
 thrown out in the lungs. 
 
 Carbon dioxide is produced when any tissue in the body 
 is in action. It is the result of activity of the brain no less, 
 probably, than that of the muscle, but on account of the 
 difficulty of observation, the finer details as to the sources 
 of the carbon dioxide have been worked out for the muscles. 
 In the chapter on the nutrition of the muscle it was 
 pointed out that the food brought by the plasma and the 
 oxygen brought by the blood were built up into living 
 muscle. It is important, therefore, to bear in mind that as 
 far as we now know the oxygen carried to the muscles is 
 not used in burning them, as is so frequently stated, but is 
 used in building them up. Consequently the carbon dioxide 
 does not arise as the immediate product of combustion due 
 to the arrival of the oxygen in the muscles. In the case 
 
THE LUNGS AND RESPIRATION. 227 
 
 of the tissues there is no analogy with the stove. In the 
 stove the fuel and the entering oxygen at once combine, 
 combustion occurs, and carbon dioxide is the result. But 
 in the muscle the food and the oxygen are not at once 
 burned, but are in a way, entirely unknown to us, built 
 into living tissue, much as in the manufacture of gunpow- 
 der all the various elements are built up without any com- 
 bustion taking place, until later, when it is purposely 
 ignited. Upon the ignition of the gunpowder it at once 
 breaks up into a number of burned products, not the least 
 one of which is, by the way here, carbon dioxide. The 
 carbon dioxide in the muscles is due to a disintegration of 
 parts of the muscle substance itself. Thus, the amount of 
 carbon dioxide formed in the muscles will vary directly 
 with the amount of muscular work done in the same way 
 as the amount of smoke in battle will vary directly with the 
 number of shots fired. 
 
 To show that carbon dioxide may be formed in a muscle 
 when there is no oxygen present, the following experiment 
 will suffice: If a living muscle, say from a frog, be put in 
 a closed case and all the oxygen withdrawn it will, when 
 properly stimulated, contract as usual, and the production 
 of CO 2 follows. In fact, the absence of even traces of oxy- 
 gen does not seriously affect the muscle for a while, but it 
 keeps on contracting for some time and finally becomes 
 exhausted because its reserve material, not being replen- 
 ished, is gradually used up. If the CO 2 in the muscle were 
 the result of the direct burning of the oxygen as soon as it 
 enters the muscle, such an experiment with such results 
 would be impossible. 
 
 As all living cells are continually at work, if not in 
 giving rise to motion at least in producing heat and in 
 keeping up the bodily temperature, so there is going on 
 continually in our tissues a production of CO 2 . This gas 
 will at once be absorbed by the surrounding lymph in con- 
 formity with the law of Daltoii. Thus there will come to 
 be in the lymph quite a little CO 2 pressure. In the blood 
 
228 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 of the capillaries there is no CO 2 , as the arterial blood just 
 coming from the lungs has practically no CO 2 in it (the air 
 itself having practically none) , so in further conformity with 
 Dalton's law the CO 2 will stream into the plasma of the 
 blood, the walls of the capillaries being entirely disre- 
 garded. But, as everyone knows, ordinary water (and 
 plasma is mainly water) cannot absorb very much CO 2 at 
 ordinary pressures. When we do want the water to absorb 
 larger quantities, as in the manufacture of soda-water, such 
 water must be subjected to very high gas pressures. The 
 difficult problem therefore presents itself of explaining how 
 the large amounts of CO 2 which are breathed out at each 
 breath are really carried by the blood. In the first place, 
 the corpuscles of the blood do not carry CO 2 . Blood with 
 the corpuscles left in it carries a little more CO 2 than when 
 the corpuscles are taken out, but this is due to the fact 
 that the corpuscles themselves are soaked with plasma, and 
 the plasma, like any liquid, will absorb certain amounts of 
 CO 2 . We must, therefore, look to the plasma itself as the 
 carrying agent of this gas. And yet by experiment it can 
 be conclusively shown that we breathe out much more CO 2 
 at each breath than could be absorbed by the plasma in that 
 time. In short, while some of the CO 2 is absorbed by the 
 plasma, some of it must be held in chemical combination. 
 Now just what this chemical combination is, physiologists 
 can not yet determine. It seems, however, highly probable 
 that as the blood is normally alkaline, much of the CO 2 in 
 the capillaries of the tissue unites with the alkaline sub- 
 stances of the blood and forms carbonates. To .even the 
 most elementary student in chemistry the following expla- 
 nation, though given unfortunately in technical, chemical 
 terms, will seem very clear: There are contained in ven- 
 ous blood certain quantities of (Na 2 CO 3 ) sodium carbon- 
 ate. When a liquid containing Na 2 CO 3 has added to it 
 CO 2 gas, it forms a new combination with this gas, and 
 there results Na H CO 3 , sodium bicarbonate. This Na H 
 CO 3 is possibly more familiar to us as ordinary baking- 
 
THE LUNGS AND RESPIRATION. 229 
 
 soda. As this substance is very soluble in water, and con- 
 sequently soluble in blood plasma, large quantities of it 
 could be easily carried in solution. 
 
 By way of summary what has occurred in the capillaries 
 of the tissue may be re-stated thus: First, the CO 2 has 
 resulted from an actual breaking down of the living tissue. 
 Second, from the tissue it has been absorbed by the lymph 
 which bathes the tissues. Third, from the lymph it streams 
 into the blood plasma. Here a certain quantity of it is car- 
 ried, merely absorbed or dissolved in it. Fourth, in the 
 plasma a larger quantity of the CO 2 enters into chemical 
 combination with some of the alkaline substances, possibly 
 Na 2 CO 3 , (sodium carbonate,) and forms Na H CO 3 (so- 
 dium bicarbonate) . This sodium bicarbonate is easily sol- 
 uble in the plasma, and so in solution is carried lungward 
 in the venous stream. 
 
 3. The Elimination of Co 2 in the Lungs. The final 
 scene in this drama of the respiration is, of course, the elimi- 
 nation of this CO 2 from the blood into the lungs. When 
 the venous blood reaches the pulmonary capillaries the CO 2 
 dissolved in the plasma of the blood at once begins to pass 
 out of the blood into the air, since the pressure of the CO 2 
 in the air is practically nothing. This streaming out of 
 the CO 2 is, therefore, in regular obedience to the law of 
 Dalton. In this way all the CO 2 merely dissolved in the 
 plasma is finally eliminated. If venous blood were put 
 under the receiver of an air pump and the air above it 
 then exhausted, it would be possible to pump out of the 
 blood practically all of the CO 2 absorbed in it. This por- 
 tion of the gas then presents no difficulty. It streams out 
 into the lung for the same reason that the bubbles of gas 
 stream out of a bottle of mineral-water when that mineral- 
 water conies in contact with the air. But the difficulty 
 presents itself when we try to explain in what manner the 
 CO 2 , which is chemically combined in the sodium salt, is 
 liberated. 
 
230 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 It was stated that ordinary Na H CO 3 is the familiar 
 baking-soda. Baking-soda is used to get the CO 2 gas 
 which is liberated from it when sour milk, or for that 
 matter any acid is poured over it. Everybody is familiar 
 with the fact that if baking-soda be taken and anything 
 sour be added to it, it begins to froth and bubble, and large 
 quantities of CO 2 gas stream out. This is exhibited 
 especially well in the common Seidlitz powder. Here 
 Na H CO 3 and some acid (tartaric, etc.) are mixed to- 
 gether, as a result of which the liquid begins to effervesce 
 very strongly. The addition of some acid to the soda has 
 liberated large quantities of CO 2 gas. Common soda-water 
 (which is but water charged heavily with CO 2 ) derives 
 its name from the fact that formerly this CO 2 gas was de- 
 rived from ordinary soda by pouring acids over it. Now it 
 is highly probable that the chemical substance in venous 
 blood carrying the CO 2 in combination, is soda, and to 
 liberate the CO 2 so contained some acid must be present. 
 The acid in the case of the lung is oxy haemoglobin. While 
 haemoglobin itself is very faintly acid, oxyhaemoglobin is 
 much more markedly acid. Although this oxyhaemoglobin 
 is not acid enough to appear sour to the taste, it is acid 
 enough to act upon the soda dissolved in the plasma and 
 liberate the CO 2 . It is at once apparent that this oxyhaemo- 
 globin, being formed in the lungs, was not present in 
 venous blood. Consequently there was no liberation of the 
 CO 2 in the veins, but arrived at the capillaries of the lungs 
 the haemoglobin becomes converted into oxhyaemoglobin, 
 which, acid in its nature, at once reacts upon the soda in 
 the plasma and liberates from this the CO 2 , which then 
 streams out into the lungs. 
 
 Thus it will be seen that the CO 2 is carried in two 
 ways ; one part of it dissolved in the plasma, which when it 
 arrives at the lungs passes from the plasma into the air of 
 the alveoli in obedience to the general law of gases; the 
 other part united chemically with substances, sodium car- 
 onate (Na 2 CO 3 ) in venous blood to form sodium bicar- 
 
THE LUNGS AND RESPIRATION. 231 
 
 bonate (Na H CO 3 ), and so dissolved and carried to the 
 lung, where it is liberated by the acid action of the 
 oxy haemoglobin. It will thus be seen that even the ap- 
 parently simple phenomena of the gaseous interchanges in 
 the blood, in lungs and capillaries are carried on in strict 
 obedience to known physical and chemical laws and 
 arranged with a nicety which is certainly striking. 
 
 So far nothing has been said of the nitrogen of the 
 atmosphere. This gas seems to play no part whatever in 
 the respiration of the body. It is, of course, carried by the 
 blood, just as any other gas, but is not used up by the 
 tissues, and so serves only to help maintain the pressure of 
 internal liquids against the air. 
 
 THE INNERVATION OF THE RESPIRATORY SYSTEM. 
 
 The nerves which are immediately concerned in the 
 movements of respiration are the motor nerves, going to the 
 intercostal muscles and to the diaphragm, and for forced 
 expirations to the muscles of the abdominal wall. All these 
 motor nerves come from the spinal cord, but take their 
 origin further up in the medulla. Hence, cutting the 
 upper end of the spinal cord at once destroys the power to 
 breathe, because it cuts through the path of these motor 
 nerves. 
 
 1. The Respiratory Center. These nerves, however, 
 are but the mere avenues along which the impulses to 
 breathe are carried. The impulses themselves originate in 
 the respiratory center, which lies in the medulla just at the 
 end of the calamus scriptorius in the fourth ventricle. 
 (See Brain.) It seems to be a paired center, for when the 
 medulla is cut through the middle line the breathing on 
 each side continues, but an injury to the center itself at 
 once stops breathing. As we usually think an animal is dead 
 as soon as it stops breathing, this point has been called the 
 "vital point." A rather horrible example of an injury to 
 this center is the execution by hanging. In this form of 
 taking life the odontoid process of the axis is pulled out of 
 
232 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 its accustomed place by the drop of the body and goes 
 crushing through the medulla. As the respiratory center 
 lies just at this point it is destroyed, and an immediate par- 
 alysis of all the muscles of respiration ensues. In conse- 
 quence of this the criminal dies by suffocation, not being 
 able to get more air. Such a displacement of the neck is 
 called ' 'breaking of the neck. ' ' It is tolerably easy to locate 
 this point by introducing sharp-pointed needles into the 
 medulla. A point is soon found which, upon being pierced 
 results at once in a respiratory paralysis, and the position 
 of this point in the floor of the fourth ventricle has just been 
 noted. We must look to this center, therefore, as the source 
 of our respiratory impulses. 
 
 The question at once arises, what causes this center to 
 send out impulses along the motor nerves just mentioned? 
 A few simple experiments serve to materially clarify this. 
 If an individual breathes very rapidly and deeply, and so 
 gets into his lungs, and consequently into his blood, in- 
 creased amounts of oxygen, the center becomes quiescent, 
 and for a little while there is no tendency or temptation to 
 breathe. This might seem to show that it is the absence 
 of sufficient oxygen which normally stimulates the center, 
 for as soon as the blood is richly supplied with oxygen by 
 taking repeated deep breaths, the center becomes inactive. 
 On the other hand, if the supply of air be cut off and the 
 blood in the body becomes strongly venous, the center be- 
 comes more and more irritable, sends out stronger and 
 stronger impulses to breathe, until finally the impulses be- 
 come so strong and scattered as to produce convulsions. In 
 such venous blood there is still a little oxygen, but much 
 carbon dioxide, and the opinion has been advanced that it 
 is not so much the lack of oxygen as it is the presence of 
 carbon dioxide that stimulates the center. Other physiol- 
 ogists, to reconcile both views, combine the two notions 
 and state that the absence of oxygen, as well as the pres- 
 ence of carbon dioxide, serve to irritate and stimulate the 
 center to action. It seems, however, difficult to conceive 
 
THE LUNGS AND RESPIRATION. 233 
 
 how a thing which is absent may serve as a positive stimu- 
 lus. This savors just a little of a mental absurdity. It is 
 perfectly conceivable how the presence of the carbon diox- 
 ide in blood might stimulate the center, but experiments 
 have been made by passing different kinds of blood heavily 
 charged with carbon dioxide through the center, and yet 
 the center has failed to be materially stimulated by these 
 large quantities of that gas. Of late, therefore, physiolo- 
 gists have, looked elsewhere for the substance in question. 
 Quite a suggestive experiment was made when blood 
 which had just passed through a severely-exercised muscle 
 was then injected into the arteries which traverse the respir- 
 atory center. A very violent stimulation was at once the 
 result. This would seem to indicate that when tissues such 
 as the muscle are hard at work there is a production of waste 
 products of some kind which act as a powerful irritant to 
 this center. This irritating waste product may possibly be 
 eliminated in the lungs, or possibly destroyed when the 
 blood becomes arterial, either case explaining why increased 
 breathing will serve to lessen the stimulating effect of this 
 substance. If, for instance, the blood does not succeed in 
 passing to the lungs rapidly enough, this irritating waste 
 product accumulates in the blood, and so stimulates the 
 center to more and more activity. If, on the other hand, 
 by the process of breathing this substance is eliminated, 
 either through the lung or destroyed in the blood as soon 
 as it becomes arterial, we can understand why when such 
 blood passes through the center the center remains quiet 
 and inactive. This will explain why there are no respira- 
 tory movements before birth, for at this time the blood 
 stream is richly supplied with oxygen from the maternal 
 wall. This waste product is given no chance to accumu- 
 late in the blood, but by the oxygen from the placenta it is 
 continually removed. On account of this the center is not 
 at all stimulated and so remains perfectly dormant, sending 
 out not a single impulse to breathe. However, at the mo- 
 ment of birth, when the circulation with the placenta is cut 
 
234 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 off, and the supply of oxygen becomes short and this waste 
 product, therefore, accumulates, the center becomes at once 
 irritated by it to a greater and greater extent, until finally 
 the movements of respiration are ushered in. 
 
 That condition in which the blood is so richly supplied 
 with oxygen that there is no tendency to breathe, is called 
 apnce. The condition in which the center is normally stim- 
 ulated is called eupnce, while finally that condition in which 
 there is not an adequate supply of oxygen, and which leads 
 to the phenomena of suffocation and to the convulsions 
 accompanying the same is called dyspnce. From these defi- 
 nitions it will be seen that the condition of respiration be- 
 fore birth is that of apnce. But it not infrequently happens 
 that even before birth the circulation with the placenta is 
 interrupted, the oxygen supply of the foetus is cut off, and 
 so dyspnce results, which may lead to real active respiratory 
 movements. 
 
 As the tissues are always in action and as this irritating 
 substance, therefore, must continually be forming, we are 
 forced to believe that this center must be continually irri- 
 tated by this substance. The question then at once arises, 
 why this center which is being constantly and without in- 
 terruption irritated will give rise to impulses which are 
 periodic. Why would not a continued stimulation of this 
 center produce a tetanus just in the same way as a continued 
 stimulation of the nerve of the muscle would produce a con- 
 tinued tetanic contraction? This is explained by supposing 
 that there is a kind of resistance in this center, and that an 
 impulse does not result until this intrinsic resistance to act 
 is overcome. 
 
 This center is, using a rather far-fetched metaphor, a 
 kind of intermittent spring. Such an intermittent spring 
 will discharge its waters periodically in spite of the fact 
 that its supply flows into it at a constant and uniform rate. 
 So in this center. The stimuli from this irritating substance 
 normally found in venous blood, and possibly, as was stated, 
 a waste product of the active tissues, keep flowing in, ac- 
 
THE LUNGS AND RESPIRATION. 235 
 
 cumulating their force, so to speak, until finally such stim- 
 uli give rise to a respiratory impulse. Or, to take another 
 illustration. We may imagine a box, the bottom of which is 
 held in place by a spring. If, now, water be poured into this 
 box and the spring have an appreciable amount of strength , 
 it will not at once drop, but the water will accumulate in 
 the box, rise to a higher and higher level, until finally the 
 weight of the water in the box will become greater than the 
 strength of the spring supporting the bottom, when the 
 bottom will drop out, and the water flow out with one 
 gush. As soon as the vessel has thus emptied itself the 
 spring again pushes the bottom in place, and the process 
 repeats itself. Here, too, we see how a source that is con- 
 stant is changed into an effect which is periodical. 
 
 2. Nervous Control of the Respiratory Center. But this 
 center reflexly stimulated by the blood which traverses it, 
 may be controlled within certain limits by nerves going 
 to it. 
 
 (1) Those nerves from the brain which are under the 
 control of the will reach it, and every one is familiar with 
 the fact than within a wide range he is able to control his 
 movements of respiration, but that as soon as this range is 
 passed the movements go on independently of the will. 
 
 (2) Sensory nerves of the body which, when violently 
 stimulated, affect this center. Thus, excessive pain in 
 almost any region of the body at once influences the rate of 
 breathing. 
 
 (3) The most important influences reaching this center 
 come from the sensory nerves of the lung itself. These 
 sensory nerves run in the large vagus trunk. 
 
 That these sensory nerves play a most important role in 
 controlling the center, may be understood from the follow- 
 ing experiment: If the vagus on one side be cut, no marked 
 effect follows; but cutting both vagi, there at once results 
 a very much slowed breathing. The number of breaths may 
 sink to one-fourth, or even one-sixth of the normal. The 
 
236 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 individual breaths are, however, deeper. If, now, the cen- 
 tral ends of the vagi, that is those connected with the brain, 
 be stimulated with electrical stimuli, the number of breaths 
 begins to rise to the normal; Here is, of course, an evident 
 control of the respiratory movements. If these vagi are then 
 excessively stimulated there ensues sometimes a relaxation 
 of the respiratory muscles, that is a passive expiration; 
 at other times a standstill of the chest and lungs in the 
 position of an inspiration, in which the respiratory muscles 
 are in a state of tetanic contraction. Here we have then 
 apparently a double effect; sometimes relaxation, sometimes 
 greater contraction. This double effect shows that the vagi 
 have two kinds of nerve fibres in them going from the lungs 
 to the center. First, those that stimulate the center to 
 greater respiratory exertion; and, secondly, those that tend 
 to inhibit the center. 
 
 The rather interesting question now presents itself: Un- 
 der what circumstances does each of the nerves act ? The 
 solution of this question is probably found in the following 
 experiment: If the lung of an animal whose chest has just 
 been opened, be forcibly distended by pressing air into it, 
 there is at once developed a strong desire on the part of 
 the animal to breathe out. An expiration is induced. If, 
 on the other hand, the air be sucked out of the lung and 
 the lung so tend to collapse, there at once follows a strong 
 inclination for an inspiration. In other words, when the 
 lung expands the center is inhibited, breathing movements 
 stop, and the muscles relax. But the lung expands in an 
 inspiration, consequently an inspiration induces an ex- 
 piration. But in an expiration the lung is compressed, and 
 this compression of the lung stimulates the center to act 
 more energetically; that is, the center tends to breathe, 
 but actively breathing means to inspire. Thus the ex- 
 piration serves to induce an inspiration. We find, then, in 
 these nerves a kind of self-regulating arrangement which 
 stated again is as follows: When the center sends an im- 
 pulse to the muscles of respiration and the chest is thus 
 
THE LUNGS AND RESPIRATION. 237 
 
 enlarged, the lung is correspondingly expanded. But such 
 an expansion of the lung at once affects those sensory 
 nerves in it which, when stimulated, inhibit the center; 
 that is, cause it to stop. So, as the inspiration proceeds 
 and the lungs expand more and more these nerves are more 
 and more stimulated, the center is more and more in- 
 hibited, and is finally brought to a standstill. As soon as 
 this happens the muscles of respiration relax and the chest 
 collapses of its own accord; that is, a passive expiration 
 follows. But in this passive expiration the lung is com- 
 pressed, and this compression of the lung affects the second 
 pair of sensory fibres which serve to stimulate the center to 
 greater activity. Thus, as the lungs collapse more and 
 more, these stimuli become stronger and stronger, and so 
 finally arouse the center to a renewed contraction. 
 
 (4) In addition to these two sensory nerves, which 
 in the manner just indicated so materially influence the 
 activity of this center, there is one additional nerve which 
 exercises a marked effect. This is the nerve which goes to 
 the larynx. This nerve when stimulated, strongly inhibits 
 the center, and so tends to make an inspiration impossible. 
 As this nerve is no doubt stimulated in the varying acts of 
 swallowing, singing, talking, and so on, there seems some 
 reason for this arrangement. Thus, in the act of swallow- 
 ing the center is inhibited, and so the possibility of choking 
 is materially reduced, while in the act of talking or singing 
 stimulation of this nerve tends to check the rate of breath- 
 ing, a circumstance which materially helps to sustain the 
 voice. 
 
 When all these rather remarkable niceties in the nervous 
 control of the movements of respiration are stated, there yet 
 remains much that requires further investigation, and it is 
 possible that the researches of the immediate future may 
 materially modify and clarify our present knowledge of this 
 subject. 
 
238 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 Those modified forms of breathing familiar to us all as 
 sneezing or coughing, may be so easily investigated by 
 each student for himself that a further description of them 
 is here deemed unnecessary. 
 
CHAPTER X. 
 
 THE LARYNX AND THE PRODUCTION OF 
 ARTICULATE SPEECH. 
 
 The only property which man possesses par excellence 
 to the exclusion of all other animals is that of ' articulate 
 speech. The voice is something which belongs to the 
 human larynx alone. Many of the lower animals are able 
 to produce characteristic sounds, and these sounds some- 
 times, as in the case of birds, may extend through quite a 
 wide scale and be of a complicated character; but it goes 
 without question to say that they possess none of the real 
 peculiarities of articulate speech. The human voice con- 
 sists of sounds which are produced by the vibrations of two 
 elastic bands called the vocal cords placed in the voice- 
 box. This voice-box, or larynx, is really no more than a 
 dilatation of the upper portion of the trachea so arranged 
 with a series of cartilage as to enable the air driven through 
 it to set the vocal cords in vibration. The consideration 
 of the voice immediately after the subject of respiration, is 
 based upon its somewhat secondary connection with the 
 trachea and lungs. Fundamentally the physiology of res- 
 piration and that of articulate speech have nothing in 
 common. 
 
 The vocal cords vibrating alone would produce but 
 feeble sounds quite different from the ordinary sounds of 
 the voice. The vibrations of the vocal cords are, there- 
 fore, strengthened by resonance cavities, like the vibrations 
 of a violin string are very integrally strengthened by the 
 resonance of the violin frame underneath, or as the note of 
 an organ pipe is very dependent indeed upon the resonance 
 cavity in the long tube of the pipe in question. The reso- 
 nance cavities for the vocal cords are the larynx itself, the 
 
 (239) 
 
240 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 throat, the mouth, and in the production of some sounds 
 even the nose. By changing the relative dimensions of 
 these resonance cavities the quality of the individual sounds 
 of the voice may be much varied, just as the player on the 
 sliding trombone varies his notes by varying the relative 
 lengths of the resonance cavities in his instrument. The 
 pitch of the voice will be dependent upon the length and 
 tension of these vocal cords, just as the pitch of a piano 
 string is dependent upon its length and tension, while the 
 loudness 'will depend upon the strength with which the 
 vocal cords are made to vibrate. 
 
 We have now to consider the anatomical arrangement 
 af the larynx by which the vibration of the cords and the 
 production of the voice is effected. 
 
 THE ANATOMY OF THE LAETNX. 
 
 The larynx is the expanded upper portion of the trachea. 
 It consists of three main cartilages, the general arrange- 
 ment of which is about as follows: At the base of the 
 larynx is the cricoid cartilage. This cartilage entirely sur- 
 rounds the base of the larynx like a ring surrounds a finger. 
 This cricoid cartilage actually resembles in its shape a sig- 
 net ring, the signet of which is, however, towards the back, 
 and the band of the ring forwards. This band may be felt 
 by pressing the finger hard against the base of the larynx 
 in front. Placed upon the band of this ring, that is, 
 towards the front of the trachea, is the thyroid cartilage. 
 This cartilage really consists of two cartilages which meet 
 in front., leaving a V-shaped slit. The two halves after 
 partially encircling the larynx do not meet behind, as the 
 signet of the cricoid cartilage separates them. This is the 
 largest of the cartilages and is the one we have in mind 
 when we speak of the "Adam's apple." The V-shaped slit 
 in this Adam's apple is readily felt with the finger. The 
 sides of the thyroid cartilage where they join the signet of 
 the cricoid behind are prolonged upwards into two horns, 
 indicated by C s, in Fig. 93. Similar horns, although not 
 
THE LARYNX AND ARTICULATE SPEECH. 241 
 
 quite so large, extend downward a short distance, shown at 
 C z, in the same figure. On the signet of the cricoid behind 
 
 Fig. 93. THE CARTILAGES OF THE LARYNX FROM BEHIND. 
 
 t, thyroid; Cs, Ci, superior and inferior horns of thyroid; **, cricoid cartilage; t, 
 arytenoid cartilage; Pv, corner to which the posterior end of vocal cord is attached; Pm, 
 point of insertion of the muscles which approximate or separate the vocal cords; co, 
 cartilage of Santorini. 
 
 are placed the two arytenoid cartilages. These arytenoid 
 cartilages are so placed on the cricoid as to permit a good 
 deal of motion. They can be pulled apart, approximated, 
 and even rotated by muscles which reach them. Bach ary- 
 tenoid cartilage is a triangular structure with its base rest- 
 ing on the cricoid. On the top of each arytenoid cartilage 
 is situated a small cartilage known as the cartilage of San- 
 torini. A little forward of this on each side is finally a still 
 smaller cartilage known as the cartilage of Wrisberg. In 
 order to understand the manipulation of the voice-box, how- 
 ever, no special attention need be paid to either the car- 
 tilages of Santorini or Wrisberg. 
 
 From the inner corner of the base of each arytenoid car- 
 tilage, marked P v in the diagram, there extends forward 
 across the larynx to be inserted in front in the thyroid car- 
 tilage, an elastic membrane, the true vocal cord. These 
 cords are, however, not separate and distinct strings but 
 
242 STUDIES IN ADVANCED PHYSIOLOGY . 
 
 the mucous membrane lining the larynx is reflected over 
 these and so makes the vocal cords really membranes, free 
 only along their inner edge. The analogy of these mem- 
 branes might be found in a drum, the membrane of which 
 had been slit from one end to the other through its middle. 
 As the forward ends of the vocal cords are inserted in the 
 immovable thyroid cartilage, their length and tension must 
 be varied by the movements of the arytenoid cartilages be- 
 
 Fig. 94. THE INSIDE OF THE VOICE-BOX, 
 
 a, of arytenoid cartilage; cv, vocal cord; t, thyroid cartilage; s, cartilage of Santorini; 
 cap, articulation of arytenoid with the cricoid cartilage ; c, c, cricoid cartilage ; cth, space 
 between thyroid and cricoid cartilages. 
 
 hind. It was pointed out that these cartilages connect with 
 the signet of the cricoid in a very movable joint, and there 
 now remains the description of the muscles by which the 
 desired movements are to be brought about. 
 
 THE MANIPULATION OF THE LARYNX. 
 
 1. The movements which bring the vocal cords into the 
 position found in quiet breathing. In quiet breathing, 
 when the passage of air through the larynx produces no vi- 
 brations, the vocal cords are relaxed and separated, and so 
 
THE LARYNX AND ARTICULATE SPEECH. 243 
 
 the slit between them, called the glottis, is wide open. 
 This widening of the glottis is produced by two sets of mus- 
 cles called the crico-arytenoids (posterior and anterior) . 
 (The student will find much help in remembering the names 
 of these muscles if he keeps in mind that the name in every 
 case is derived from the two cartilages between which the 
 muscle exerts its pull.) The crico-arytenoid muscles are 
 muscles which are fastened at the outer basal corner of the 
 arytenoid, at the point marked P m in the diagram. From 
 this point one runs forward to be inserted on the inner side 
 of the cricoid, the anterior cricoid-arytenoid ; one backward 
 to be inserted on the back side of the cricoid, the posterior 
 crico-arytenoid. A moment's reflection will show that the 
 simultaneous contraction of these two muscles will tend to 
 pull the arytenoid cartilage to which they are attached out- 
 wards, and as this is true for both arytenoids, they will be 
 pulled apart, and as the vocal cords are attached to these 
 they will also be separated and the glottis opened. To make 
 this perfectly clear imagine a muscle attached at the point 
 P m , and inserted immediately below that at the base of the 
 cricoid. When that muscle contracts it is evident that the 
 arytenoid will be pulled out; that is, away from its fellow, 
 and so the glottis opened. 
 
 2. The movements which bring the vocal cords into a 
 position to vibrate. In the production of vocal sounds the 
 glottis is very much narrowed. The vocal cords, and con- 
 sequently the arytenoids to which they are attached, are 
 moved towards each other. This approximation of the ary- 
 tenoids is brought about by two sets of muscles called 
 transverse and oblique arytenoids. The transverse aryten- 
 oids are bands of muscles which run from one arytenoid di- 
 rectly across to the other. The oblique arytenoids run from 
 the lower portion of one arytenoid to the upper portion of 
 the second arytenoid. It is quite obvious that by the con- 
 traction of these two sets of muscles, transverse and oblique, 
 the arytenoids will be pulled together, the vocal cords at- 
 tached to them brought closer together and the glottis nar- 
 
244 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 rowed. When, now, the air is driven past these stretched 
 membranous flaps they are set in vibration and the tone 
 arises. 
 
 3. Movements which bring aboitt the change of the 
 pitch. Any one familiar with musical instruments is aware 
 that there are two ways in which to heighten the pitch of a 
 string, or in this case a membrane. One method is to in- 
 crease its tension, as we do by tightening a violin string, 
 the other by shortening the string, a procedure also used on 
 the violin, where, by the placing of the finger, the length of 
 the string is varied to suit the pitch. Both of these methods 
 are used in the larynx. 
 
 First, the vocal cords are stretched. This is accom- 
 plished by the contraction of muscles which lie towards the 
 front of the larynx, extending from the cricoid band to the 
 thyroid cartilage above it. This is the crico-thyroid mus- 
 cle, one of which lies on each side of the larynx. When 
 these muscles contract they pull the thyroid cartilage down 
 toward the cricoid. The cricoid band being fastened se- 
 curely to the upper portion of the trachea, is immovable, and 
 so the only motion possible is the downward one of the thy- 
 roid above it. But as the vocal cords are attached in front 
 to the thyroid cartilage they will be pulled down with it and 
 
 .A w 
 
 t 
 
 1 
 
 1 
 
 txEI 
 
 1.0--^ / 2 
 
 '>-->OW, j 
 
 1 ^ 
 
 d \ 
 
 Fig. 95. TO SHOW THE MANNER OF PRODUCING CHANGES IN THE PITCH OF HUMAN 
 
 VOICE. (Martin). 
 
 For the explanation of figures see text. 
 
 will therefore be stretched. Reference to Figure 95 will 
 make this clear. Here c is the signet of the cricoid carti- 
 
THE LARYNX AND ARTICULATE SPEECH. 245 
 
 lage, d the band encircling the upper end of the trachea, / 
 and t parts of the thyroid cartilage, a the arytenoid carti- 
 lage, v c the vocal cords. Now, the crico-thyroid muscles 
 are attached atdfand inserted near /, and when they contract 
 they pull I down into the position of /'. But this stretches 
 the vocal cords, as the distance from a to t is shorter than 
 the distance from a to '. An apparent paradox appears 
 here. In the position f the vocal cords are actually 
 longer than in the position /, and yet in the longer position 
 are used to produce higher pitches. Other things being 
 equal, the longer string will produce a lower note, but the 
 slight increase in length here is much more than compen- 
 sated by an increase in the tension of it, and so the pitch 
 is raised. It is this crico-thyroid muscle which is most 
 commonly brought into play in the change of the pitch of 
 the voice. To bring the vocal cords, or rather to bring 
 the thyroid cartilage back into its natural position, there is 
 a muscle lying within each vocal cord and extending from 
 its insertion in the arytenoid to its insertion in the thyroid. 
 This muscle, the thyro-arytenoid is, therefore, the direct 
 antagonist of the crico-thyroid. 
 
 Second, the pitch of the voice is also changed by short- 
 ening the vocal cords. This is accomplished by the crico- 
 arytenoid muscles already referred to in explaining the 
 widening of the glottis. When the anterior crico-arytenoids 
 contract it is evident that the arytenoids will be made to 
 rotate on their vertical axes in such a way that the point P m 
 is drawn inward and forward, but the point Pv to which the 
 vocal cords are attached drawn outwards and backwards. A 
 simultaneous contraction of the two anterior crico-arytenoids 
 would result in moving the inner points (Pv) together, and 
 if the contraction were strong enough, might put them in 
 contact. As the vocal cords are attached at the inner 
 points they will be brought into contact with each other and 
 so those portions of the vocal cords be prevented from vi- 
 brating. In other words, the vibrating portion of each 
 vocal cord is made shorter, and consequently the pitch is 
 
246 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 increased. If, for instance, the posterior halves of the vocal 
 cords were touching and so not sounding, the sounding 
 portion would be only half as long as before, and our knowl- 
 edge of music would make it evident that the pitch would 
 be just an octave higher. For when a violin string is 
 pressed down at this middle point its pitch is raised by one 
 octave. By varying the length along which the vocal 
 cords are thus pressed against each other, that is, by vary- 
 ing the length of the sounding vocal cord, a corresponding 
 range in pitch is effected. 
 
 4. The range of the humaji voice. The range of the 
 human voice is not far from three octaves, although great 
 singers have frequently exceeded this. On account of the 
 much shorter voice-box in children, the pitch of their 
 voices is much higher. In the case of boys there occurs about 
 the time of puberty a somewhat rapid elongation of the 
 vocal cords, referred to in the common expression, the 
 "breaking of the voice. ' ' This elongation causes a material 
 deepening of the voice, but as the elongation is not the 
 same for all individuals, so there are differences in pitch 
 which we recognize in designating some as bass singers, 
 others as tenor singers. In the case of girls no such elong- 
 ation of the vocal cords seems to take place, and so the 
 pitch of a woman's voice remains about an octave higher 
 
 -Sopran 
 
 -Alt- 
 
 FGABcdefga'bcd e f g a bed e f g a 1} c 
 Bass 
 
 -Tenor- 
 
 Fig. 96. THE ORDINARY RANGE OF VOICE. 
 
 through life. The average range of the human voice for 
 the four usual divisions, bass, tenor, alto and soprano, is 
 indicated in the accompanying diagram. 
 
THE LARYNX AND ARTICULATE SPEECH. 247 
 
 SPEECH. 
 
 Speech is a combination of vocal sounds (vowels) , with 
 noises (consonants) . Vowels have musical and harmonic 
 properties ; consonants are not tones in this sense at all . 
 
 The vowels, A, K, I, O, U, and their derivatives are 
 produced by changing the relative dimensions of the reson- 
 ance cavities connected with the voice-box. As far as the 
 vocal cords are concerned the same vibrations might pro- 
 duce all of the different vowels. Which vowel it shall be is 
 determined by the resonance cavities . Thus , no matter which 
 vowel we sound, the vocal cords act alike if the pitch be 
 the same, and whether it shall be A, E, I, O, U, or any of 
 their derivatives will depend upon the quality or timbre 
 which is given to these vibrations by the sounding cavities. 
 Any one can assure himself of this by sounding A, as in 
 father, and then without any change in the vocal cords 
 change his mouth to the position of O, and then OO. I is, 
 of course, a combination consisting of A, as in father, and 
 E as in feet. The same is true of U, consisting of E, as in 
 feet, and OO as in loose. That the production of the 
 vowels is dependent upon the form of the resonance cavities 
 is a subject which each person interested can so easily 
 verify for himself that further discussion seems unnecessary. 
 
 Consonants are sounds which are produced in most in- 
 stances with little help of the vocal cords, but are brought 
 about by modifications of the manner in which the blast of 
 air is expelled through the mouth. For instance, the cur- 
 rent of air may be interrupted near the teeth, as in the con- 
 sonant T, or by the tip of the tongue, as in the letter D, or 
 by the lips, as in the letter P, or even by the soft palate at 
 the root of the tongue, as in the letter G (in the word go) . 
 Some of the consonants are produced by a sudden explosive 
 blast of airj as for instance. D, G, B, K, T, P. Others are 
 continuous, being produced by the rush of air through nar- 
 row passages either between the lips, as in F, or the teeth, 
 as in S, or when the approximation is still closer, as in TH. 
 In the case of L, the tongue is pressed against the hard 
 
248 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 palate and the air allowed to escape on its sides. With 
 some consonants there is an admixture of vocal sounds, as 
 in B, D, G (hard), V and Z. In the production of other 
 consonants the nose is called into play as a resonance cav- 
 ity, and so arise M, N and NG. In the consonant R there 
 is a vibratory motion, either dental, as is more common in 
 the English language, or gutteral, more usual in the Ger- 
 man. H, finally, is hardly more than a laryngeal sound, 
 little more than hard breathing. 
 
 Whispering differs from true speech in the absence of 
 all vowels. It is, therefore, in a physical sense, a noise 
 only. In whispering, although the glottis is considerably 
 narrowed, the cords are not stretched enough to vibrate, 
 and the air made to rush past them is therefore thrown, not 
 into regular, but into irregular vibrations . Such irregular vi- 
 brations as happen to coincide in period with the air in the 
 throat or mouth serve to characterize the vowels, while con- 
 sonants are produced in the ordinary way. 
 
 In the discussion of the voice reference has always been 
 to what is commonly known as the chest voice. It is pos- 
 sible in addition to produce what are called falsetto tones, 
 but the manner in which this is accomplished is not yet 
 satisfactorily known. 
 
CHAPTER XL 
 
 GLANDS AND THE GENERAL PHYSIOLOGY OF 
 SECRETION. 
 
 HISTORICAL. 
 
 The ancients had practically no knowledge of secretion. 
 They thought that the phlegm from the nose was a dis- 
 charge from the brain. Their other views were not less 
 mistaken. This misconception lasted until 1660, when 
 Schneider's researches on the olfactory membrane proved 
 its falsity. About this time, too, a number of eminent an- 
 atomists appeared, whose researches on the structure of 
 glands materially cleared up the meaning of these organs. 
 The names of many of these noted anatomists are still re- 
 tained in connection with the terminology of glands. Thus, 
 Glisson (Capsule of Glisson in the liver), Stenson (Duct of 
 Stenson in the salivary glands), Peyer (Patches of Peyer in 
 the intestines), Brunner (Glands of Brunner in the duode- 
 num), and Malpighi (Malpighian corpuscles of kidneyj. 
 Our anatomical knowledge became finally fairly complete 
 when in 1830 Johann Mueller's large treatise on glands was 
 published. 
 
 Thus far, all the work had been of an anatomical nature 
 and the physiological process of secretion remained for 
 some time longer entirely unknown. The view held was 
 that the blood capillaries actually communicated with the 
 ultimate tubules of the ducts of the gland, and that the 
 secretion was a kind of direct separation from the blood, in 
 which the corpuscles did not take part, because the smaller 
 tubules of the duct were too tiny to allow them to pass from 
 the blood. The correct view of the process of secretion, 
 however, soon followed the discovery of the cellular struc- 
 ture of animal tissues by Schwann, and the discovery of 
 
 (249) 
 
250 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 the physical process of osmosis. The influence of the 
 nerves on secretion was then demonstrated in vivisections 
 made by Ludwig in 1851, who by electrically stimulating 
 the cerebral nerve going to the submaxillary of the dog 
 caused a secretion of saliva, which rose to the height in the 
 tube of 200 millimeters of mercury, while the height of the 
 blood in the carotid artery rose to 112 millimeters of mer- 
 cury only. The action of the sympathetic nerve on secretion 
 and the changes of the vascular supply of glands were in 
 1858 discovered by Claude Bernard. Finally the micro- 
 scopist, Heidenhain, made a series of researches on the 
 histological changes in secreting cells, which have demon- 
 strated that the secreting cells themselves are the seat of 
 active chemical changes which form the secretions. 
 
 SECEETION. 
 
 The term "secretion" is frequently made to apply to a 
 varying number of things. Sometimes all the substances 
 which are given off by the blood are called secretions. This 
 would make the lymph which oozes out of blood capillaries 
 a secretion, and would also make the gases which figure in 
 respiration secretory products. This use of the term secre- 
 tion is, however, much too wide, for physiologically speak- 
 ing, lymph and the blood gases do not figure in any way as 
 the product of glands proper. In the second place, the 
 term "secretion" is made to apply to all the discharges of 
 all the various glands. There is no special objection to this 
 application of the term. Other physiologists, however, speak 
 of secretions and excretions, calling "secretions" those 
 products of the glands which are intended for a further use 
 in the body, and apply the term "excretions" to. those 
 glandular discharges which are intended for no further use, 
 but are simply to be thrown off. But even these uses of 
 the term are not satisfactory, because it is not always easy 
 to tell whether a certain secretion is directly intended for 
 further use, or is a mere waste product to be eliminated. 
 To do away with such an ambiguity, therefore, the term 
 
GLANDS, GENERAL PHYSIOLOGY OF SECRETION. 251 
 
 secretion is here applied to all the products of all the 
 glands. Before following out in detail, now, what the ex- 
 act process of secretion is, it is necessary to turn to the 
 anatomy of glands. 
 
 1. Glands and Their Anatomy. Here additional am- 
 biguities are at once misleading. There are a number of 
 structures in the body designated as glands which are not 
 true glands in any sense of that term. They were called 
 glands by anatomists who were ignorant of their real 
 nature, and these names given to them in this way still 
 cling to them in spite of our knowledge that they are not 
 glands at all. Just as we call the primitive inhabitants of 
 America Indians without intending to express in any way 
 the misconception that they are residents of the East 
 Indies. Such entirely different structures are the pineal 
 gland of the brain, which instead of being a gland is 
 really but the stump of an optic nerve. Such structures, 
 too, are the lymphatic glands, which are aggregations of 
 white blood corpuscles, and have absolutely nothing to do 
 with secretion in any way. 
 
 In addition to the structures just mentioned, which are 
 at the very first glance seen to belong to entirely different 
 tissues, we have several structures which, while they may 
 be the seat of chemical changes in the blood passing through 
 them, yet have no ducts, and do not pour out distinct secre- 
 tions. They are, therefore, not infrequently called "duct- 
 less" glands. Examples of such are the spleen, the thyroid 
 gland and the adrenal glands. Disregarding all these, then, 
 it may be said that a typical gland consists of a basement 
 membrane of connective tissue bearing a surface of secret- 
 ing cells on one side, and supplied with numerous blood 
 vessels on the other. In addition to these three main ele- 
 ments there are, of course, nerves which in some instances 
 have actually been traced by anatomists into the secreting 
 cells themselves. Finally in the interstices, as in all other 
 tissues, are the lymphatics. It will be seen from this that 
 
252 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 a gland is but a surface of secreting cells supported by a base- 
 ment membrane, richly supplied with blood-vessels under- 
 neath the membrane, and subject to the control of nerves. 
 
 Fig. 97. FORMS OF GLANDS. SIMPLE SACCULAR GLAND FROM AMPHIBIAN SKIN. (Flem- 
 ming.) SIMPLE TUBULAR GLAND FROM HUMAN INTESTINE. (Flemming.) GLAND 
 
 FORMED OF A SIMPLE DUCT-SYSTEM. (Flemming.) CONSTRUCTION OF A LOBULE OF 
 
 A COMPOUND RACEMOSE GLAND (a, duct; &, 6, branches of duct; c, secreting alveoli). 
 PART OF A SMALL RACEMOSE GLAND, SHOWING THE TUBULAR CHARACTER OF THE 
 ALVEOLI. (Flemming.) 
 
 A gland, however, spread out as such a flat surface, 
 would take up a very great deal of room in order to secrete 
 the amounts necessary to the body. To save space, there- 
 fore, these glandular surfaces become pitted in and folded, 
 and in this manner result the various forms of glands. Ex- 
 amples of the typical surface glands are not wanting. Thus, 
 the peritoneum, the pleura and the pericardium have such 
 
GLANDS, GENERAL PHYSIOLOGY OF SECRETION. 253 
 
 flat surfaces which secrete the serous fluids. Nearly all the 
 other glands, however, are modified. Usually space is saved 
 by pitting in the secreting surface and thus tubular glands 
 arise. Sometimes these, instead of being straight and 
 tubular, become rounded and sac-like, in which case such 
 a gland is called a racemose gland. When several such 
 tubular or racemose glands have a common duct leading 
 from them, the entire structure is spoken of as a compound 
 gland. . 
 
 Illustrations of the simple tubular glands may be found 
 in the gastric glands of the stomach, and in the crypts of 
 Ljeberkiihn. Illustrations of the simple racemose glands 
 occur in the sebaceous or oily glands of the skin. How- 
 ever, most of the larger glands, such as the pancreas and 
 the salivary glands, are of the compound racemose kind. 
 Such a compound racemose gland might be compared to a 
 
 Fig. 98. SECTION OF A RACEMOSE GLAND, SHOWING THE COMMENCEMENT OF A DUCT 
 
 IN THE SECRETING ALVEOLI. (After Shafet.) 
 
 a, an alveolus; 6, basement membrane lining the duct d'; c, connective tissue be- 
 tween the alveoli; d, duct; s, semilunar reserve cells. 
 
 very full bunch of grapes in which the central stalk figures 
 as the single duct, while the individual grapes represent the 
 ultimate sac-like expansions, in which the process of secre- 
 
254 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 tion occurs. If, now, between such bunches of grapes we 
 should imagine a very full network of blood-vessels and a 
 supply of nerves, we should have a coarse but possibly a 
 helpful analogy. 
 
 2. The Process of Secretion. Such an arrangement of 
 a gland with a basement membrane and blood-vessels natur- 
 ally suggests the possibility of secretion being a mere case 
 of physical filtration. We know, for instance, that if a 
 liquid containing things in solution be put into a membran- 
 ous bag, such a liquid by the process of osmosis reaches 
 the outside. There are, however, certain facts which make 
 it at once perfectly plain that the process of secretion is not 
 a process of physical filtration. Quite a number of glands 
 secrete substances which are not found in the blood at all. 
 They secrete substances which they themselves have pro- 
 duced. Thus, for instance, the pepsin of the stomach, or 
 trypsin of the pancreas, and the ptyalin of the salivary 
 glands are not contained in blood at all. Such special pro- 
 ducts which the glands have themselves produced are called 
 specific elements. In this sense we speak of the hydro- 
 chloric acid, rennet, and pepsin of the stomach as the spe- 
 cific elements of that organ. If secretion were a physical 
 filtration, specific elements would be impossible. 
 
 But the question then recurs, may not the remaining 
 elements of a secretion be merely filtered through. This 
 question must be answered in the negative for several rea- 
 sons. First, glands secrete at certain times only, while if it 
 were a physical filtration the process ought to go on all the 
 time, for even when a gland is at rest the blood circulates 
 through it freely. Second, a certain poison called atropine 
 (of frequent use in the physiological laboratory) destroys 
 the secreting power of a gland at once, but it does not 
 change the blood pressure in the gland at all. Such a 
 poisoning action would be impossible in the case of simple 
 filtering. Third, glands may be stimulated to such increased 
 action that the pressure of the secretion may actually ex- 
 ceed the pressure of the blood in the gland; a condition of 
 
GLANDS, GENERAL PHYSIOLOGY OF SECRETION. 255 
 
 things never possible in simple osmosis. Fourth, glands 
 may be made to secrete even when they contain no circu- 
 lating blood. Thus, if the sciatic nerve in an amputated 
 limb of an animal be stimulated the sweat glands may be 
 made to secrete, when it is evident that there is no circu- 
 lating blood in the severed limb. We are driven, therefore, 
 to the conclusion that secretion is a phenomenon of the liv- 
 ing gland cells themselves, and its ultimate nature we un- 
 derstand as little as we do the ultimate nature of muscle 
 activity or nervous impulses. It is a chemical process whose 
 explanation is not yet at hand. 
 
 3. Histological Changes in Secreting Cells. On the 
 other hand, while we do not understand the exact nature of 
 the process of secretion, we are able to observe on a gland 
 certain histological changes in rest and in action. Thus, 
 when a gland starts to secrete it at once becomes flushed 
 with blood, due to the enlargement of the arteries traversing 
 it. Such a dilatation has, however, nothing to do with the 
 gland itself, but has been brought about by nerves which run 
 to the arteries direct, and which were stimulated at the 
 same time the gland cells were stimulated. The purpose of 
 such an increase in the supply of blood to a working gland 
 is, of course, very apparent. It is to carry abundant ma- 
 terial to the gland, and supply it with sufficient amounts of 
 oxygen to sustain its activities. It differs in no essential 
 way from the condition of things in a working muscle. 
 
 But histological changes may be observed in the secret- 
 ing cells themselves, for a gland that has been actively 
 secreting looks quite different under the microscope from 
 one which has been at rest for some time. If, for instance, 
 two animals as nearly alike as possible be taken, and one 
 of them be starved for a day, and thus the pancreas of that 
 animal be given no occasion to pour out its secretion, and 
 the animal be then killed and the pancreas observed histo- 
 logically, it may be seen that the gland cells are distended 
 and that their outer portions, that is, the portions next to 
 the lumen of the gland, are filled with granules, while those 
 
256 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 portions of the cells next to the basement membrane seem 
 clearer and more protoplasmic. If, now, for comparison 
 with this gland there be examined the pancreas of the sec- 
 ond animal, which was plentifully fed eight or ten hours 
 before being killed, quite a different appearance of the 
 secreting cells is at once evident. The cells seem smaller, 
 and the granular layer is almost wholly absent, the whole 
 cell now from basement membrane to, lumen appearing 
 clear. 
 
 It is not difficult to account for the relative appearances 
 of these two glands. In the working gland which has just 
 been called upon for a copious secretion the granules have 
 been used up; have, in other words, been changed into a 
 part of the secretion of the gland. If, however, a gland 
 which has been copiously secreting, be given opportunity 
 to recuperate, the granules again begin to appear, become 
 
 Fig. 99. PARTS OF GLANDS. (After I^angley.) 
 
 A, at rest, almost filled with zymogen granules; B, after a short period of activity; 
 C, after a prolonged secretion. In A and B, the nuclei are obscured by the granules. 
 
 more and more plentiful, and soon occupy almost half of 
 the space of the cell. The condition of things is then this: 
 In the process of secretion the pancreatic cells (which 
 gland is here used as an illustration of glands in general) 
 change these stored-up granules into the secretion, while 
 during the period of apparent rest the gland seems engaged 
 in manufacturing and storing up these granules ready for 
 the next secretion. It will thus be seen that the process of 
 secretion in cells is essentially a process of growth. The 
 secreting cells take proper nourishment from the blood 
 bathing them, and in that way construct within themselves, 
 
GLANDS, GENERAL PHYSIOLOGY OF SECRETION. 257 
 
 possibly out of their own substance, the specific elements 
 in question. Somewhat like a sheep by taking the proper 
 nourishment into its body, and by chemical changes in its 
 tissues, may produce the woolly covering of the skin. 
 
 That the specific elements of glands are thus built out 
 of the cells themselves is especially well shown in the case 
 of the oil glands of the skin. In those glands some of the 
 cells may be seen to grow large, then by internal chemical 
 changes their own substance apparently disintegrates into 
 oil, a change which continues until finally the whole cell 
 falls into pieces, and its debris forms the secretion. In 
 other cells the destruction is not complete, but only por- 
 tions of the cell break up into the secretion in question. In 
 such cases, of course, an individual cell by continuing to 
 grow and continuing to form out of its substance the spe- 
 cific element may remain active for an indefinite time, while 
 in the case of cells where the disintegration is complete, 
 new cells must continually be forming to replace those that 
 break down. 
 
 In the case of the pancreas a complete destruction of 
 the cells does not occur, as it does in the case of the oil 
 gland. To take a not very close analogy, the secretion of a 
 gland is not a product made by the cell in the same sense 
 that a table is a product made by a carpenter, but the secre- 
 tion is a product derived from the cell substance itself, as 
 the table is a product of the oak tree. 
 
 In the case of the pancreas these granules are not, how- 
 ever, identical with its specific element. The main specific 
 element of the pancreas is called trypsin, whose marked 
 influence in digestion will be discussed later. But the 
 granules in the pancreas cells are not trypsin. They are 
 some antecedent substance out of which, however, by slight 
 changes trypsin is produced. The granules are called tryp- 
 sinogen granules; that is, by the etymology of that word, 
 the producers of trypsin. 
 
 Several- fortunate circumstances arise by this arrange- 
 ment. Trypsin is soluble and could not easily be stored up in 
 17 
 
258 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 the gland. It has a digestive action which might lead it to 
 attack the gland itself in which it is stored. Both of these 
 difficulties are avoided by forming the trypsinogen granules. 
 These are, in the first place, solid and can easily be stored. 
 In the second place they do not have the active digestive 
 properties of the trypsin and so exert no digestive action at 
 all. When, then, finally the trypsin is needed all this stored 
 trypsinogen may by slight changes be at once transformed 
 into trypsin and so poured out in large quantities into the 
 intestines. Trypsin is a digestive fluid of rather complex 
 composition and it would be practically impossible for the 
 pancreas to secrete large quantities of this at sudden notice, 
 but by devoting all of its resting period to the production 
 of these trypsinogen granules, storing these up in the outer 
 part of each cell, and then just at the moment when the 
 trypsin is needed changing these trypsinogen granules into 
 the soluble trypsin, sudden and large quantities of trypsin 
 are at once available. 
 
 What has been said with reference to the pancreas applies 
 to the mucous glands. Here during rest are produced gran- 
 ules which at the proper occasion are changed into mucus 
 and poured out. These stored granules are called mucino- 
 gen granules. While it has been impossible to actually 
 demonstrate a similar condition of things in the gastric 
 gland, there is every reason to believe that here, also, dur- 
 ing the resting period of the stomach the peptic cells are 
 storing up granules of pepsinogen. Such granules not being 
 easily dialyzable could be stored in the cell, and not having 
 the active digestive property of regular pepsin, would exert 
 no chemical effect on the glands themselves. Then, at the 
 moment food enters the stomach, these pepsinogen granules 
 are, by slight additional changes, transformed into the pep- 
 sin and so poured on the food. Possibly a similar antece- 
 dent substance is present in the salivary glands from which 
 the specific element ptyalin is derived, a kind of ptyalino- 
 gen. It is well, however, to keep in mind that the actual 
 presence of granules of the nature just described can be 
 
GLANDS, GENERAL PHYSIOLOGY OF SECRETION. 259 
 
 easily demonstrated in the case of the pancreas and the mu- 
 cous glands only, and that its application to other glands is 
 upon probable grounds only. 
 
 THE INNERVATION OF GLANDS. 
 
 That glands are under direct nervous control is a matter 
 of every-day experience. The tear glands respond at once 
 to intense emotions, and the common expression to have 
 one's "mouth water" shows that the salivary glands are di- 
 rectly influenced by states of mind. Such nervous influ- 
 ences are not so apparent in the case of the sweat glands, 
 but even there intense emotion or anxiety may produce a 
 copious sweating even when the surrounding temperature 
 would tend the other way. In the case of the stomach 
 and pancreas there are such evidences of innervation. Se- 
 cretion in the stomach at once induces secretion in the pan- 
 creas, explained only by the fact that these two organs are 
 connected by nerves. There is no more reason why glands 
 should be automatic, that is, independent of nervous con- 
 trol, than why muscles should be. Glandular activity is no 
 less an activity than muscular exertion. The regulation of 
 the periods of secretion so that the product may be availa- 
 ble just at the moment that it is needed could be effected 
 only by nervous control. The saliva flows when food is 
 masticated in the mouth, the gastric or pancreatic juices 
 are poured into the alimentary canal as soon as the mucous 
 membrane in stomach and intestine is stimulated by enter- 
 ing foods, while the gall-bladder contracts and pours its 
 contents of bile into the duodenum for the same reason. 
 
 The manner of the innervation of glands has, however, 
 been worked out carefully and explicitly in the case of the 
 salivary glands only, and the account here given is that of 
 the submaxillary gland itself, but there is every reason to 
 believe that in the main the nervous arrangement of the 
 other glands is the same. In order to understand how this 
 has been worked out, a few experiments in the stimulation 
 
260 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 of the nerves going to the submaxillary gland will materi- 
 ally aid: 
 
 1. The cerebro-spinal nerves. If the nerve coming 
 from the brain and going to the submaxillary gland be cut, 
 and the end of the nerve connected with the gland be stim- 
 ulated, a copious secretion of saliva immediately results. At 
 first the saliva is perfectly normal, but as the gland is being 
 stimulated longer and longer, the secretion becomes more 
 and more watery, and finally contains little else than water 
 and dissolved salts. The ptyalin, the specific element of 
 saliva and the mucin are no longer present. If the nerve 
 or gland be not too much affected by excessive work such a 
 secretion of watery saliva may be continued for a long 
 time. 
 
 From this experiment it is evident that the nerve from 
 the brain, the corda tympani, as it is usually called, causes 
 an abundant flow of a watery secretion from the gland, but 
 does not seem to be directly concerned in the production of 
 any of the specific elements of the secretion. What the 
 gland pours out is simply material which it has taken from 
 the blood. It is not anything which the gland has made 
 itself. Such parts of a secretion which are derived directly 
 from the blood are called transudations, and it seems that 
 the cerebro-spinal nerve is therefore directly concerned 
 with the transudations. These transudations, however, 
 serve to wash the specific elements out of the gland. For 
 this reason the saliva which first begins to flow contains 
 ptyalin and mucin, because these elements were stored up 
 in the gland and were then washed out. But as soon as 
 this stored supply is exhausted nothing but the transuda- 
 tions continue. These transudations may, then, flow from 
 the gland for an indefinite period, because as the blood 
 supply in the gland is kept constant the source from which 
 the transudations are derived does not diminish. When, 
 finally, such a gland stops secreting it is probably more a 
 nervous exhaustion than a glandular one. This will ex- 
 
GLANDS, GENERAL PHYSIOLOGY OF SECRETION. 261 
 
 plain why the flow of tears may continue indefinitely, the 
 lachrymal secretion being entirely a transudation and con- 
 taining no specific element of the lachrymal glands them- 
 selves'. It will also explain why by thinking of palatable 
 foods, etc., the mouth begins to water. It is a stimulation 
 of the cerebro-spinal nerve, the result of which is an im- 
 mediate flow of the transudatory part of the saliva. It must 
 not be imagined, however, that the flow of tears or the flow 
 of this watery saliva is a mere filtration from the blood. It 
 is an actual picking up of these materials from the blood by 
 the gland cells themselves. If it were a mere filtration 
 there is no reason why the tears should not flow at an un- 
 varying rate all the time. 
 
 2. The sympathetic nerves. In addition to the cerebro- 
 spinal nerve to the submaxillary gland this gland is supplied 
 with branches from the sympathetic system. When these 
 nerves are stimulated the gland begins to secrete saliva, 
 also, but the saliva is now of an entirely different kind. 
 Instead of being watery it now becomes exceedingly viscid 
 and ropy, and contains a much greater proportion of the 
 specific elements of the secretion. Continued stimulation 
 of the sympathetic nerve may cause the saliva to cease 
 flowing altogether ; but this is because the secretion has be- 
 come so thick and concentrated that it is not able to force 
 its way through the delicate tubes. Evidently the sympa- 
 thetic nerve has to do with the production of the specific 
 elements themselves, and in no integral way whatever is it 
 concerned with the transudation elements. It seems to 
 govern the production of those things which the gland must 
 make for itself and store up. If, now, after the sympa- 
 thetic nerve has been stimulated for some time and the 
 saliva has thus been made thick and ropy, the cerebro- 
 spinal nerve be also stimulated, there is at once a copious 
 flow of saliva. Under the influence of the latter nerve large 
 quantities of water and mineral salts are actively picked up 
 by the gland from the blood and passed through into the 
 tubules, washing out the specific elements formed. 
 
262 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 There is, therefore, no difficulty in interpreting these 
 phenomena. To restate it, it is this. The gland cells re- 
 ceive two kinds of nerves. First, those from the cerebro- 
 spinal system, which when stimulated cause the transuda- 
 tions to wash the specific elements out of the glands. 
 Secondly, the sympathetic nerves which control the pro- 
 duction of the specific elements themselves. The sympa- 
 thetic nerve is no doubt more or less in action all the time, 
 and in this way the gland is busy in the production of the 
 specific elements in the periods of apparent rest when there 
 is no secretion flowing from the gland, while the cerebro- 
 spinal nerve is called into play at the moment the secretion 
 is wanted, and brings" about a copious flow of water and 
 mineral salts through the gland, by means of which these 
 specific elements are carried out. Of course just at this 
 time the stored antecedent granules in the various glands 
 are finally changed into the regular specific elements; 
 otherwise the transudations would not be able to carry them 
 out. For instance, in the pancreas the trypsinogen granules 
 would not be affected by the water and salt secreted, but it 
 would at that point change into the soluble trypsin which is 
 readily washed out. 
 
 It was pointed out before that along with the stimula- 
 tion of the cerebro-spinal nerve there is a stimulation of the 
 vaso-dilator nerves going to the arteries of the glands, so 
 that while the transudations are being poured Out of the 
 gland the gland itself seems flushed with the distended 
 arteries. From the foregoing it is evident that the gland is 
 not exerting itself most at the time the secretion is actively 
 pouring out, but that the real constructive period of activity 
 is the one between such times of flow, the period during 
 which the specific element is gradually built and stored up. 
 It was pointed out that the cerebro-spinal nerve seems 
 wholly concerned with the water and the salt transudations, 
 and the sympathetic nerve wholly with the production of 
 the specific elements. While this is in the main true, there 
 are physiologists who believe that the cerebro-spinal nerve 
 
GLANDS, GENERAL PHYSIOLOGY OF SECRETION. 263 
 
 also exerts a slight influence in the production of the 
 specific element, and, on the other hand, that the sympa- 
 thetic nerve to some extent exerts an influence on the 
 secretion of the water. While such a condition of things is 
 not at all improbable, experiments on glands such as the 
 one just described clearly demonstrate that in the main 
 cerebro-spinal nerves govern transudation, the function of 
 which is to wash out the specific elements when such are 
 produced, while the sympathetic nerve is concerned in the 
 production of these specific elements themselves. 
 
 So far there has been considered only the general phy- 
 siology of secretion; that is, those phenomena which are 
 common to all glands. The special physiology of the in- 
 dividual glands is reserved for a detailed discussion, when 
 these glands are treated in connection with their special 
 functions. 
 
CHAPTER XII. 
 
 THE DIGESTIVE ORGANS AND THEIR 
 ANATOMY. 
 
 In the discussions in the preceding chapters the blood 
 was made the source of all of the elements needed for the 
 tissues or secreted by the glands. In the chapter on respi- 
 ration alone was it pointed out that in turn the blood derived 
 its source of oxygen from the air, and that it derived its 
 supply of carbon dioxide from the tissues. In several chap- 
 ters there is now to be pointed out in what manner the 
 blood, which is the medium between the external world and 
 the tissues of the body, derives its supply to enable it in 
 turn to supply the tissues. 
 
 The necessity for such a food supply is entirely too evi- 
 dent to need further comment. An organ stops work soon 
 after its supply of blood is cut off. But the blood is in no 
 sense a living tissue; has no vitality of its own; is, as far 
 as the tissues are concerned, a foreign body; is nothing 
 more, in short, than the circulating store-house out of 
 which, as it passes along, the hungry tissues may pick up 
 what they need for their own life. To cut the nutritive 
 value.of the blood down below a certain average composition, 
 or to put into the blood injurious substances will at once re- 
 act upon the tissues which derive their supplies from it. 
 But there are very few bodies which can at once be carried 
 by the blood and serve as nourishment for the live tissues. 
 Nearly all foods are in a solid state, and in this condition 
 they are unable to pass into the circulation. Even many 
 foods in a liquid condition to begin with, are nevertheless 
 not available as foods when directly placed in the blood. 
 Thus, the albumen of an egg, certainly one of the most 
 nutritious of foods, is to some extent poisonous when in- 
 (264) 
 
DIGESTIVE ORGANS AND THEIR ANATOMY. 265 
 
 jected directly into the blood-vessels, and is not utilized at 
 all as nourishment. 
 
 Then again, the vitality of the tissues depends largely 
 upon the constancy and permanency of the blood supply, 
 and to place at once into the blood stream varying quanti- 
 ties and diverse kinds of foods would react at once, and ma- 
 terially interfere with the normal and continued activity of 
 the cells. To transform foods and change them into sub- 
 stances which may be carried by the blood and utilized by 
 the tissues, there is provided by the body one of the most 
 extensive and complicated systems, familiarly termed the 
 alimentary system or digestive apparatus. Before noticing 
 how the foods are affected and in what manner they are pre- 
 pared for the blood, it is necessary to become acquainted 
 with the anatomy of this system itself. 
 
 THE MOUTH. 
 
 ' The mouth serves as the entrance place for not only the 
 solid and liquid foods, but also for the gaseous food, the 
 oxygen of the air, a food in no less sense than bread and 
 butter. However, in the mouth the solid and liquid foods 
 are carried to the pharynx and gullet and into the stomach, 
 while the gaseous food in the manner already described, is 
 carried to the lungs. The lung is in no far-fetched sense, 
 then, an adjunct of the alimentary canal, intended to digest 
 that food which, on account of its gaseous condition, does 
 not need the action of further juices to prepare it for ab- 
 sorption. Leading out of the mouth are six openings: The 
 two posterior nares, connected with the nose and serving as 
 passage-ways for the air ; two Eustachian tubes leading from 
 the back of the mouth to the ear, and to be described 
 further in the chapter on hearing; the pharynx, leading into 
 the gullet, and in front of the pharynx, the larynx, or voice- 
 box leading to the trachea. While the mouth, tongue and 
 teeth figure in an integral way in the formation of speech, 
 we are concerned here only with their digestive function. 
 
 This is mainly the process of mastication, made possible by 
 
266 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 the presence of the teeth for crushing the food and the 
 tongue for manipulating it during this act. 
 
 1. THE TEETH. 
 
 Arranged in a single row in both upper and lower jaw 
 are the teeth. These appear first as a temporary set about 
 the sixth or seventh month and disappear at about the sixth 
 or seventh year. This temporary set is usually called the 
 milk dentition for evident reasons. It is at once followed 
 by a permanent set, which consists of thirty-two individual 
 teeth, sixteen above and sixteen below. Taking half of 
 either row, the two in front are called the incisors, or cut- 
 ting teeth. They have a peculiar chisel-like edge, making 
 them specially adapted for cutting. These are followed 
 by a single canine tooth, sometimes called the eye-tooth (in 
 upper jaw) . The name canine is derived from the fact that 
 this tooth is especially developed in the carnivorous ani- 
 mals, and is there used for tearing the food. To make rl 
 more efficient as a tearing tooth in the carnivora, it is fre- 
 quently much longer than the others; in fact, sometimes so 
 long as project from the mouth. The canine is followed by 
 two premolars, called bicuspids also, from the fact that they 
 have but two fangs. The premolars are the teeth of the 
 permanent set which have replaced the molars of the milk 
 dentition. Following the two premolars we have three 
 molar teeth not represented at all in the temporary set. 
 These molars are called tricuspids also, from the fact that 
 they have three fangs. Both the premolars and the molars 
 are especially adapted for the crushing and grinding of 
 foods. The last premolar does not usually appear until from 
 the eighteenth to the twenty-fifth year, and has for this 
 reason been called the "wisdom" tooth. 
 
 There is a marked analogy between the teeth of man and 
 those of many of the lower mammals, but modifications of 
 this typical arrangement are met with in certain classes of 
 animals. Thus, in animals like the sheep and cow, which are 
 obliged to pick the grass very closely, the upper front teeth 
 
DIGESTIVE ORGANS AND THEIR ANATOMY. 
 
 267 
 
 are missing and the lower teeth strike against an upper pad. 
 In the class of rodents or gnawers, which includes such 
 forms as the rat and the squirrel, the incisors are remark- 
 ably developed. They keep growing throughout life, and 
 have to be kept short by being worn off against each 
 other. In this way these teeth are kept continually very 
 sharp. It not infrequently happens that such a rodent 
 
 breaks off one of the 
 incisors, in which case 
 the opposite incisor no 
 longer worn away, 
 grows indefinitely, and 
 may finally grow 
 around back into the 
 head of the animal and 
 cause its 'death. ;, : 
 
 The Structure of a Tooth. 
 
 The typical tooth, 
 such as a canine, for 
 instance, consists of 
 three parts the fang 
 imbedded in the jaw, 
 the neck, and the 
 crown projecting from 
 the gums. If such a 
 tooth be cut in two 
 longitudinally there is 
 disclosed in the center 
 a large cavity known 
 as the "pulp" cavity 
 and opening to the ex- 
 terior through the 
 fangs. At these points 
 
 ^ig. 100. VERTICAL SECTION OFAPREMOLAR OF THE nerves and blood-VCS- 
 
 CAT. (After waideyer.) sels enter the pulp cav- 
 
 c, pulp cavity; J, enamel; 2, dentine; 3, cement; . ^, . -, -, 
 
 4, dental periosteum; 5, bone of lower jaw. ity. The main body of 
 
268 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 the tooth is made of a substance known as dentine, or ivory. 
 In composition it is not very different from bone, but his- 
 tologically it is not the same. Dentine possesses neither 
 Haversian canals nor lacunae, and so, of course, has no 
 osteoblasts imbedded in its substance. Running, however, 
 from the pulp cavity outward and permeating the dentine 
 everywhere are fine tubules, each about Toinr of an inch 
 in diameter. Near the outside of the dentine these tubules 
 frequently open into large irregular spaces known as inter- 
 globular spaces. The function of these spaces is not known. 
 
 Fig. 101. SECTION OF FANG OF HUMAN CANINE. (After Waldeyer.) 
 1, cement, with lacunae and lamellae; 2, layer of interglobular spaces; 3, dentinal 
 
 tubules. 
 
 Through these dentinal tubules, for a little distance at least, 
 arms of dentinoblasts extend, which are immediately con- 
 cerned with the growth and repair of the dentine. These 
 
DIGESTIVE ORGANS AND THEIR ANATOMY. 
 
 269 
 
 dentinoblasts lie next to the dentine in the pulp cavity and 
 are probably not essentially different, except in position, 
 from the osteoblasts in bone. The reason for the absence 
 of lacunae and Haversian canals in the ivory is of course 
 apparent. Such a system of holes and spaces would materi- 
 ally interfere with the hardness and solidity of dentine and 
 so make it much less serviceable in the crushing of foods. 
 
 In the fang this dentine is covered over by a thin 
 layer of cement by means of which it is bound to the 
 jaw-bone. This cement is nothing but ordinary bone, 
 and as such contains lacunae and not infrequently Haversian 
 canals. 
 
 On the crown the dentine is covered over with a coat- 
 ing of an exceedingly hard substance known as enamel. 
 This is totally different from the dentine both in structure 
 and in origin. The dentine is essentially bone, but the 
 enamel is derived from the skin, like the nails of the fin- 
 gers. There has, however, been such a mineral deposition 
 
 Fig. 102. ENAMEL PRISMS. (After Kb'lliker.) 
 
 A, fragments and single columns of enamel; B, surface view, showing the hexagonal 
 ends of the prisms. 
 
 in these epidermal cells as to transform them into the hard- 
 est substance in the body. In structure the enamel con- 
 sists of more or less hexagonal prisms arranged vertically 
 
270 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 with reference to the stress to which they are subjected. 
 In a perfectly new tooth which has not suffered any abra- 
 sion the enamel is covered over with a slight cuticle, also 
 of skin origin, which, however, at once disappears when 
 the tooth is put to hard use. 
 
 Hygiene. 
 
 While in the dentine of a tooth a slight growth and re- 
 pair may be possible, it is not possible to remedy a defect 
 in the tooth when it assumes at all large dimensions, while 
 of course a cracking or loss of the enamel is at once irre- 
 parable. As the teeth are almost wholly of a mineral na- 
 ture they are subject to the action of acids, and as in the 
 decomposition of foods various organic acids are produced 
 there is a constant corroding action going on which may 
 finally destroy the teeth. While the enamel is over them, 
 this corroding action is largely prevented, but as soon as 
 the hard enamel gives way and the acids have direct access 
 to the softer dentine beneath, the corroding influence pro- 
 ceeds more rapidly. This explains in the clearest way the 
 necessity for absolute cleanliness of teeth in order to pre- 
 serve them. 
 
 Around the teeth, sometimes even in spite of good care, 
 there is formed a deposit familiar as tartar. This is not wholly 
 derived from bits of food which have not been removed, but 
 the tartar is mainly a deposit of lime salts derived from the 
 saliva. In ordinary saliva lime salts are present, and as the 
 teeth are continually bathed in such a lime solution a de- 
 position of these salts around the teeth goes on and so gives 
 rise to the crusty tartar. This act of deposition is illus- 
 trated in the lime crusts which form on the inside of kettles 
 or boilers in which hard water has been continually kept. 
 When such tartar is merely a pure lime deposit it is pos- 
 sible that it may interfere in no way with the teeth, except, 
 possibly, to irritate the gums, when these are pressed down 
 on the tartar underneath them and so produce bleeding, but 
 most frequently there is deposited along with this tartar and 
 
DIGESTIVE ORGANS AND THEIR ANATOMY. 
 
 271 
 
 in it, much decayed food material, in which case the tartar 
 itself with these decaying impurities in it becomes a source 
 of infection and needs immediate removal. 
 
 The hygiene of the teeth forms such an integral part of 
 a person's general sense of order and cleanliness that it 
 would be entirely out of place to comment further on it in 
 this connection. 
 
 The Development of the Teeth. 
 
 As pointed out previously, the* teeth when once fully 
 formed are not able to grow or repair themselves in any ma- 
 terial way. This is absolutely true of the 
 enamel. After that has been formed in 
 the first appearance of the tooth, it is 
 never possible to be replaced later. How- 
 ever, with the dentine a slight repairing 
 action may be noticed. If, for instance, 
 on the crown or neck of the tooth where 
 the enamel has been removed, the dentine 
 has been worn away and a cavity so re- 
 sulted, there is not infrequently deposited 
 in the pulp cavity on the dentine in a 
 position corresponding exactly with the 
 corroded place on the outside a new bit 
 of bone-like dentine which serves to coun- 
 teract, to some extent at least, the corro- 
 sive action on the outside. Even the 
 dentinal tubules which extend into the 
 dentine so softened or corroded become 
 
 Fig. 103. LONGITUDINAL o 11J . 1 
 
 SECTION OF AN INCISOR filled with calcareous depositions and the 
 
 rT G D T T ' R ; tooth so becomes firmer and consequently 
 AND /, POINTS CORRE- more resistant to decay. Reference to 
 
 , . ... .-, , . 
 
 the accompanying diagram will explain 
 t hi s> The cement of the teeth is within 
 certain limits easily replaced. It is prac- 
 tically nothing but bone and is secreted by a kind of peri- 
 osteum which covers the jaw-bone and which dips into the 
 
 SPONDING TO PLACES OF 
 
 DENUDED DENTINE ON 
 THE EXTERIOR. (After 
 
 Salter.) 
 
272 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 sockets in which the teeth are held. It not infrequently 
 happens that teeth quite loose are in a short time again 
 firmly set in their places. 
 
 Origin of the Enamel. The manner in which the teeth 
 arise originally may be tolerably easily understood by ex- 
 amining a section from the jaw-bone of a foetus, in which 
 the rudiment of the teeth are just making their appearance. 
 In such an examination it will be found that the first indi- 
 cation of teeth is a pitting in of the epithelium of the 
 mouth (the skin) in the form of a groove, which occupies 
 about that position on the jaw where later the row of teeth 
 is to appear. This groove of epithelial cells grows down 
 into the substance of the jaw, and from this groove there 
 grow out little side projections which soon begin to shape 
 themselves into the forms of the crowns of the intended 
 teeth. This epithelial outgrowth produces the enamel of 
 the teeth, so that this part of it appears in a developing 
 
 ^ 
 
 Xg. 
 
 (After 
 
 Fig. 104. SECTION THROUGH A DEVELOPING MILK MOLAR OF A HUMAN EMBRYO. 
 
 Rose.) 
 
 L. E. L., labiodental lamina; M.E., the epithelium of the mouth; Z.L., dental 
 lamina, spreading: out at P.p. to form the enamel cap of the future bicuspidate tooth ; 
 Z. S., the condensed tissue forming the dental sac. 
 
 tooth some time before the body of the tooth, the dentine, 
 arises. The cells of the lowest row of these lateral out- 
 growths become columnar and elongated and form the enamel 
 prisms. According to some anatomists these hexagonal 
 
DIGESTIVE ORGANS AND THEIR ANATOMY. 273 
 
 prisms result from a direct calcification of these columnar 
 cells themselves, and in this way they account for the hex- 
 agonal shape of the prisms. Other anatomists hold that the 
 enamel prisms are formed from secretions which these cells 
 produce at one end. It is impossible to determine just 
 which of these two views is correct, the probability being 
 that the cells themselves become hardened into the prisms, 
 just as in the case of the finger nail similar epithelium cells 
 become hardened into these horny structures. The upper 
 layers of cells of this lateral outgrowth become changed into 
 the enamel cuticle which was referred to as covering a per- 
 fectly new tooth. 
 
 Formation of Dentine. As soon as the enamel crown 
 begins to arise in the way just indicated, cells appear im- 
 mediately underneath it, which begin to deposit dentine 
 next to the enamel. These cells, called dentinoblasts, or 
 by others odontoblasts, secrete a matrix which hardens at 
 once into the ivory. In this matrix these cells extend pro- 
 toplasmic processes which become imbedded in the dentine, 
 and which in the fully formed tooth are the protoplasmic 
 
 Fig. 105. SECTION OF DEVELOPING DENTINE FROM AN INCISOR OF A YOUNG RAT. (After 
 
 Schafer.) 
 
 a, outer layer of fully formed dentine ; &, soft matrix, with a few nodules of calcareous 
 matter already in it ; c, odontoblasts with arms extending into the dentine ; d, pulp cavity 
 with contained pulp. 
 
 processes lying in the dentinal tubules. These dentino- 
 blasts, however, do not wall themselves in as in the case of 
 bone, but always remain outside of the dentine in the pulp 
 cavity. Thus the dentine surrounding one or more den- 
 tinal tubules from the enamel entirely down to the pulp 
 18 
 
274 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 cavity is the product of a' single odontoblast. In an adult 
 tooth these odontoblasts in reduced number may still be 
 found next to the pulp cavity. 
 
 The growth of a tooth begins with the crown and ex- 
 tends to the fang. As this growth proceeds downwards the 
 crown is gradually pushed upwards and so soon appears 
 above the gums. While the tooth is thus developing the 
 jaw-bone around it is also developing, and so when the 
 tooth appears it finds itself firmly placed in its bony socket. 
 In the case of the milk dentition the cement which forms 
 seems to be removed by the action of osteoclasts, and so 
 these teeth soon drop out and are replaced by the perma- 
 nent set. These permanent teeth develop in a way perfectly 
 analogous to that of the milk dentition. From the epi- 
 thelium groove from which the lateral enamel outgrowths, 
 or milk teeth arise, secondary outgrowths arise which are 
 later on to form the enamel coverings of the permanent 
 teeth. These epithelial cells concerned in the formation 
 of the enamel are called adamantoblasts . The epithelium 
 groove of course soon disappears after the lateral out- 
 growths from it have resulted, and no vestige of it remains 
 in the adult jaw. 
 
 2. THE TONGUE. 
 
 The tongue is a muscular organ with its base attached to 
 the floor of the mouth and to the hyoid bone, and covered 
 over with a sensitive mucous membrane. On this mucous 
 membrane there are developed three kinds of papillae. 
 Scattered all over the tongue are small pointed projections 
 known as the filliform papilla. They are not very well 
 developed in man, but are in many of the lower animals. 
 The intense roughness of a cow's tongue is due to these 
 filliform papillae, while with many of the carnivora these 
 papillae enable them to scrape the bones and remove from 
 them by their rasping action all shreds of flesh. They 
 function mainly in man to give the tongue a certain rough- 
 ness so that it may more readily manipulate the food in the 
 act of mastication and in swallowing. 
 
DIGESTIVE ORGANS AND THEIR ANATOMY. 
 
 275 
 
 Not so numerous as the filliform, but scattered over 
 almost the entire tongue are somewhat larger, blunter 
 papillae known as the fungiform. The position of these 
 
 Fig. 106. SURFACE VIEW OF THE HUMAN TONGUE. (After Sappey.) 
 1, 2, circumvallate papillae; 3, fungiform papillae; 4, filliform papillee; 5, oblique folds; 
 6, mucous and lymphoid follicles ; 7, tonsils; 8, tip of epiglottis , 9, median glosso-epiglot- 
 tic fold. 
 
 papillae may easily be recognized on the tongue in the red- 
 dish spots which mark the tip of the tongue at times. 
 Nerves of taste are distributed to these, and their function 
 is no doubt in connection with this sense. 
 
276 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 But the sense of taste is most acute on the third form of 
 papillae known as the circumvallate papilla. These are 
 the largest of all, and may readily be seen on the back of 
 the tongue, where they are arranged in a V-shaped way, 
 with the open end of the V forwards. There are about a 
 dozen individual circumvallate papillae in this V. These 
 papillae do not project materially above the surface of the 
 tongue, but seem to be set down in the mucous membrane 
 of the tongue, being surrounded with a kind of moat not 
 unlike the moat of mediaeval castles. In the walls of this 
 moat, both outer and inner, are found special taste bulbs, 
 which will be described later, and which seem especially 
 concerned in the sensation of taste. The presence of these 
 acute taste bulbs at the base of the tongue explains the 
 familiar fact that foods are most sapid at the instant they 
 are being swallowed. Possibly the explanation of this is 
 that with animals at least, and possibly with man, it serves 
 as an inducement to the swallowing of food. 
 
 On the back of the tongue just at the pillars of the throat 
 are the tonsils. These are lymphatic glands about the size 
 of a small bean, and apart from their general function as 
 lymphatic glands they seem to serve in no special way in 
 their position on the tongue. The mucous membrane cov- 
 ering the tonsils is deeply pitted at these points, and the 
 position of the tonsils may be readily recognized by these 
 mucous pits. 
 
 When by the action of the tongue and pharynx the food 
 is swallowed it is carried over the opening leading into the 
 larynx by the epiglottis, a cartilaginous flap which at the 
 moment of deglutition bends down and covers the passage- 
 way to the lungs. The food is thus carried over the epi- 
 glottis and is seized by the involuntary muscles of the gullet 
 or oesophagus and so sent to the stomach. 
 
 3. THE GULLET OR (ESOPHAGUS. 
 
 The alimentary canal, although more or less arbitrarily 
 divided into the gullet, stomach, and small and large intes- 
 
DIGESTIVE ORGANS AND THEIR ANATOMY. 
 
 277 
 
 tines, is in reality but a single continuous tube with but 
 slight local variations. For this reason a description of the 
 coats of the alimentary canal will apply almost equally well to 
 
 all parts of its course. The alimen- 
 tary canal is made up of four dis- 
 tinct coats. On the outside there 
 is a serous coat, which is in the 
 oesophagus . a' reduplication of the 
 pleura, and in the abdomen a redu- 
 plication of the peritoneum. Next 
 to this thin serous coat is a thick 
 muscular coat consisting of two por- 
 tions ; an outer portion in which the 
 fibres run longitudinally, and an 
 inner portion in which the fibres 
 run circularly. It is not necessary 
 to repeat that these muscle fibres 
 are of the plain involuntary variety. 
 Between the longitudinal and 
 circular muscles there run numer- 
 ous blood-vessels to supply this 
 coat, and there occurs, also, a com- 
 plex network of ganglia, and nerve 
 fibres known as the plexus of A tier- 
 bach. From this plexus the mus- 
 cles are directly innervated. Next 
 to the muscular coat is a sub-mu- 
 cous coat consisting largely of are- 
 
 P ig. 107. DIAGRAMMATIC SECTION 
 
 THROUGH THE COATS OF THE olar tissue, with contained blood- 
 
 STOMACH. (After Mall.) i j -i 1 , j 
 
 vessels and lymphatics and serving 
 
 m, mucous membrane; d, duct . 
 
 of gastric giand; m. m., muscular mainly to bind down to the muscu- 
 
 lar coat the large mucous coat. In 
 this sub-mucous coat there is a 
 second well-developed network of 
 
 ganglia and nerve fibres known as the plexus of Meissner. 
 
 From this plexus the mucous membrane and its glands are 
 
 innervated. The last, and in some ways the most essential 
 
 coat of mucous membrane; s. m., 
 submucous coat; c. m., circular 
 muscles; Lm,, longitudinal mus- 
 cles; s., serous coat. 
 
278 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 coat, is the mucous coat, which consists of two portions: A 
 portion next to the sub-mucous, largely fibrous, containing 
 
 Fig. 108. THE PLEXUS OF MEISSNER. (After Cadiat.) 
 
 a, a, ganglia; 6, 6, network of nerves; c, a small blood-vessel; d, a nerve passing to 
 muscular layer of mucous membrane, or to the villi. 
 
 numerous blood-vessels, lymphatics, and nerves, and an 
 outer covering of epithelium cells. 
 
 In the gullet there is practically no modification of this 
 typical arrangement. The epithelium of the mucous mem- 
 brane differs, however, from that of the stomach and intes- 
 tines in being many-layered. However, close to the junction 
 of the oesophagus with the stomach these layers are reduced, 
 and in the stomach and intestines but a single layer remains. 
 
 4. THE STOMACH. 
 
 The stomach is but a local dilatation of the alimentary 
 tract, and serves as a temporary halting place for the diges- 
 
DIGESTIYK ORGANS AND THEIR ANATOMY. 
 
 279 
 
 tion of food. The shape of the stomach is at once evident 
 from the accompanying diagram. It lies mainly to the left 
 side of the body, being displaced from a median position 
 by the large liver which occupies the corresponding right 
 position. The portion next to the oesophagus is the cardiac 
 portion, that portion connected with the intestine, the py- 
 loric portion. The upper curvature is spoken of as the small 
 
 Fig. 109. THE HUMAN STOMACH. 
 
 A, cardiac end; c, fundus; P, sphincter muscle, pyloric end; lines indicate longitudi- 
 nal muscle fibres. 
 
 curvature, the lower as the large curvature. The big sac- 
 like dilatation formed by the large curvature, called the fun- 
 dus of the stomach, varies greatly in size with the varying 
 amount of food taken. In a not-too-distended stomach the 
 dimensions are about nine or ten inches in its long diam- 
 eter, and from five to seven inches in its short diameter. 
 The outer or serous coat is a part of the peritoneum which 
 lines the abdominal cavity, and which is folded around the 
 stomach as the mesentery. At the front of the stomach, 
 however, this fold is extended downwards over the intes- 
 tines as a large covering or apron, and is called the great 
 amentum. This omentum frequently becomes the seat of 
 fatty deposition, and no doubt materially serves to protect 
 the underlying viscera from changes of temperature. 
 
 The muscular coat is a little modified from the typical 
 arrangement, there being three instead of two parts. The 
 
280 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 outer muscle fibres run longitudinally. The middle coat is 
 circular, but inside of the middle coat there is a third coat 
 not quite complete, in which the direction of the fibres is 
 oblique. This especial development of the muscles is no 
 doubt intended to make possible the movements of the 
 stomach which accompany gastric digestion. 
 
 The sub-mucous coat binds down to the muscular coat 
 the large glandular mucous coat of the stomach. This 
 mucous coat is covered on the inside with a single-lavered 
 
 Fig. 110. A CARDIAC GLAND FROM THE Fig. 111. A GASTRIC GLAND STAINED BY 
 
 DOG'S STOMACH. (After Klein and No- 
 ble Smith.) 
 
 d, duct of gland; b, base or fundus; c, 
 ordinary peptic cell; p t oxyntic cell. 
 
 CHROMATE OF SILVER, SHOWING THE 
 EXTENSION OF THE LUMEN INTO THE 
 NETWORKS SURROUNDING THE OXYN- 
 TIC CELLS, FOR THE EXIT OF THK ACID 
 SECRETION OF THESE CELLS. (After 
 
 Miiller.) 
 
 epithelium, which everywhere dips down into the mucous 
 coat and forms pits, or more properly speaking, tubular 
 glands. These glands are the gastric glands. The epi- 
 thelial lining of the inside of the stomach is continued into 
 
DIGESTIVE ORGANS AND THEIR ANATOMY. 281 
 
 these glands, and forms the secreting cells of the same. 
 These cells lining the glands are spoken of as the chief cells, 
 or on account of the fact that they secrete pepsin they are 
 called peptic cells. During the resting periods of the stomach 
 these cells become filled with pepsinogen granules, which 
 when digestion commences, are changed into pepsin and 
 poured into the stomach in a manner indicated in detail in 
 the preceding chapter. 
 
 But in the gastric glands everywhere except near the 
 pyloric end, there are found underneath these peptic cells, 
 scattered here and there, other more oval cells which are 
 called oxyntic cells. This name is derived from the fact 
 that these oxyntic cells produce the hydrochloric acid of the 
 gastric juice. Although these oxyntic cells seem to lie un- 
 derneath the peptic cells and not to connect at all with the 
 lumen of the gland, special histological methods show that 
 there are delicate canals leading from these oxyntic cells in- 
 to the duct, so making possible the easy transfer of the 
 hydrochloric acid into the stomach. While most of these 
 gastric glands are simply tubular glands extending the depth 
 of the mucous coat, it not infrequently happens that two or 
 more gastric glands may have a common duct. 
 
 Both the mucous and the sub-mucous coat of the stom- 
 ach are richly supplied with blood-vessels which reach the 
 stomach through the gastric artery, a branch of the cceliac 
 axis. The stomach is supplied with both cerebro-spinal and 
 sympathetic nerves. Branches of the pneumogastric go 
 to the stomach direct, and nerves from the solar plexus 
 just back of the stomach also reach it, while sympathetic 
 nerves run mainly to the gastric arteries. 
 
 5. THE SMALL INTESTINE. 
 
 The alimentary canal is continued beyond the stomach as 
 the small intestine. There is a tolerably sharp demarca- 
 tion between the pyloric end of the stomach and the begin- 
 ning of the intestine, due to the presence of an especially 
 developed sphincter muscle at the pyloric orifice, which is 
 
282 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 usually closed, -and opens only from time to time to allow 
 properly digested food to pass. The small intestine is 
 much coiled, and has a length of about twenty feet. The 
 coils, however, do not lie superimposed one on the other in 
 the abdominal cavity, but are all suspended in mesenteric 
 slings from the back bone. This suspension not only keeps 
 the folds from resting upon each other, but also prevents 
 them from being relatively displaced. The first twelve 
 inches of the intestine are called the duodenum (which 
 means twelve) , because in this portion of the intestine but 
 little active digestion is going on, the mixture of the foods 
 with the pancreatic juice and the bile taking place here. 
 
 By far the larger portion of the remainder is called the 
 jejunum ) while the final third is spoken of as the ileiim. 
 This division is quite arbitrary, and the commencement of 
 the ileum is roughly stated to be that point where the disin- 
 tegration of food has begun to reach the putrefactive stage. 
 
 The structure of the intestinal walls does not vary very 
 much from the typical four coats. On the outside is the 
 serous coat, a reduplication of the peritoneum, and called 
 the mesentery. In these folds of the mesentery the loops 
 of the intestines are of course supported, and through these 
 folds blood-vessels, nerves and lymphatics reach them. 
 The muscular coat consists of an outer longitudinal and an 
 inner circular, between which are the nerve plexus of Auer- 
 bach and numerous blood-vessels. The muscular coat is 
 followed by the submucous, in which there are numerous 
 blood - vessels and lymphatics and the nerve plexus of 
 Meissner. The submucous is followed in turn by the mu- 
 cous coat, the principal coat of the intestine. This mucous 
 coat shows a number of peculiarities. In the first place, it 
 is even in a fairly distended intestine thrown into numer- 
 ous transverse folds called valvulcz conniventes, the pur- 
 pose of which is to afford a greater secreting surface, and 
 at the same time to form lateral pouches in which the food 
 will be detained and so better acted upon by the digestive 
 juices. Close examination of the mucous membrane shows 
 
DIGESTIVE ORGANS AND THEIR ANATOMY. 
 
 283 
 
 it to be covered with fine projections not entirely unlike the 
 "pile" on velvet. Examination with the microscope shows 
 
 Fig. 112. PORTION OF THE SMALL INTESTINE TO SHOW THE VALVUL.E CONNIVENTES. 
 (Brinton.) 
 
 that these little projections are finger-like protrusions of the 
 mucous membrane. These are called the ( 'villi, ' ' and are in 
 
 Fig. 113. SECTION OF A HUMAN INTESTINAL MUCOUS MEMBRANE, SHOWING THREE COM- 
 PLETE VILLI AND six CRYPTS OF LJEBERKUHN. (After Bohm and v. Davidoff.) 
 
 an integral way concerned in the absorption of the foods. 
 Between these villi and dipping down into the mucous mem- 
 
284 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 brane are small glands called the crypts of Lieberkuhn. 
 The epithelial lining that covers the mucous membrane is 
 one-layered. This epithelium extends down into the crypts 
 of L,ieberkiihn and forms in them the secreting cells. It is 
 also continued over the villi. A single villus, therefore, 
 consists of a layer of epithelium covering the fibrous cen- 
 tral portion, through which run numerous blood-vessels, 
 while in the center of the villus there is a single large lym- 
 phatic called here a lacteal. The rich supply of blood- 
 vessels to such a villus accounts for the efficiency of these 
 structures in the process of absorption, while the central 
 lacteal is the avenue through which the fats reach the body 
 in a manner to be described in the succeeding chapter. 
 
 Fig. 114. INJECTED VILLI OF THE HUMAN INTESTINE. (After Teichmann.) 
 a. b, lacteals (white); c, horizontal lacteals; d, networks of blood-vessels (dark). 
 
 Nerves and bits of plain muscular tissue distributed through 
 the body of the villus also occur. These bits of plain 
 muscular tissue make possible the slight powers of con- 
 traction which are said to materially aid in their absorptive 
 capacity. 
 
 The villi extend from the beginning of the duodenum 
 through the length of the small intestine. The crypts of 
 Ivieberktilm between them have a similar distribution. In 
 
DIGESTIVE ORGANS AND THEIR ANATOMY. 
 
 285 
 
 the duodenum there are found additional glandular struc- 
 tures called the glands of Brunner. They are somewhat 
 longer tubular glands which extend down to the submucous 
 coat. The ducts of these open into the intestine between 
 the crypts of Lieberkuhn. The glands of Brunner have no 
 especial function, and are in all probability but glands 
 similar to the peptic glands of the stomach, which have 
 reached down into the commencement of the intestine. 
 They secrete small amounts of pepsin which, however, in 
 the intestine are of no value at all. We may therefore speak 
 of these glands of Brunner as ordinary gastric glands 
 which have been continued beyond the pyloric orifice. The 
 crypts of L,ieberkiihn are similar to the gastric glands, but 
 are much shallower and never possess added oxyntic cells. 
 Of course the secretion which they produce, the intestinal 
 juice, differs materially from the gastric juice. 
 
 As the small intestine is to a much greater extent than 
 the stomach the seat of absorption, we find that the walls 
 
 Fig. 115. SECTION OF AN INJECTED ILEUM, SHOWING THE INJECTED LACTEALS, VILLI, 
 
 TWO PATCHES OF PEYER, ETC. (After Frey.) 
 
 a, a, a, villi; 6, crypts of I,ieberkuhn; c, muscular layer of mucous membrane; d, d, 
 e, e, patches of Peyer; f, g, g, g' , networks of lacteals. 
 
 are richly supplied with networks of blood-vessels and 
 lymphatics. Scattered very generally along the intestine in 
 
286 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 the submucous coat are nodules of lymphatic tissue which 
 are called the patches of Peyer. These patches may be but 
 tiny nodules invisible to the unaided eye, or may attain the 
 size of lumps distinctly visible and easily felt. Such larger 
 patches may materially distend the submucous coat and 
 may even reach up into the mucous coat displacing the villi 
 in the manner indicated in Figure 115. That such lymphatic 
 glands are scattered so generally through the wall of the 
 small intestine, and even occur in numbers in the mesent- 
 ery, suggests that the leucocytes which arise in these glands 
 may in some direct way be concerned with the phenomena 
 of absorption. 
 
 6. THE LARGE INTESTINE. 
 
 The small intestine leads into the large intestine. At 
 the point of the junction there is a valve called the ilio- 
 colic valve, so arranged that food may easily pass into the 
 large intestine but cannot pass in the reverse direction. 
 The opening of the small intestine into the large is, how- 
 ever, not a terminal one, the ilio-colic valve being situated 
 on the side of the large intestine. That portion which is 
 back of this valve is spoken of as the blind sac or the 
 cczcum. Attached to the caecum there is a small hollow 
 continuation known as the vermiform appendix. While 
 both the caecum and vermiform appendix in man are quite 
 small and probably have no function at all as far as we 
 know, these structures are very large in the herbivorous 
 animals, and in them serve to hold the food in order to sub- 
 ject it more thoroughly to the digestive action of the juices 
 and the absorptive action of the intestine. 
 
 The large intestine differs materially from the small not 
 only in its larger size, but also in its structure. The mus- 
 cular coats are not so well developed, the circular coat in 
 places being entirely absent. This arrangement of the cir- 
 cular coat gives the wall of the large intestine its pouched 
 appearance. On the mucous coat there are no villi at all. 
 The crypts of L,ieberkuhn of the small intestine are here 
 replaced by quite similar tubular glands which, however, 
 
DIGESTIVE ORGANS AND THEIR ANATOMY. 
 
 287 
 
 do not produce a special intestinal juice, but secrete mucus 
 only. They are-, therefore, spoken of as the mucous glands 
 
 Fig. 116. GLANDS OF THE LARGE INTESTINE. (After Heidenhain and Klose.j 
 6, longitudinal section ; c, transverse section ; both showing mucous secreting goblet 
 
 cells. 
 
 of the large intestine. Except that they are a little larger 
 and that they contain numerous mucus-secreting goblet 
 cells, they are analogous to the crypts of the small intes- 
 tine. The mucous secretion of these glands serves to lubri- 
 cate the walls of the large intestine and so renders more 
 easy the translation of the foods. The large intestine is 
 much shorter than the small, consisting of three turns only: 
 an upward turn on the right side of the body, known as the 
 ascending colon, a turn running horizontally across the 
 abdominal cavity just beneath the stomach, known as the 
 
288 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 transverse colon, and a descending section on the left side 
 known as the descending colon, which then finally through 
 the rectum communicates with the exterior. 
 
 7. THE PANCREAS. 
 
 The pancreas is a long, slender gland of reddish yellow 
 color and lies immediately below and back of the stomach 
 in the first fold of the duodenum. It is about five or six 
 inches long and from three-quarters to an inch in thickness. 
 In structure this gland resembles very closely the salivary 
 glands, being of the compound racemose type. The secret- 
 ing cells have the characteristic glandular appearance and 
 are so large as to practically fill the lumen of the tubes. 
 Examined under the microscope the cells at rest may be 
 seen to be more or less filled with trypsinogen granules, 
 while when examined after a period of activity the cells 
 seem clear. In both cases, however, the lumen of the tube 
 is exceedingly small. A large duct runs from one end of 
 the gland to the other and collects all of the pancreatic 
 juice, carrying it to the duodenum. This central duct 
 may be easily seen with the unaided eye as a whitish tube, 
 receiving along its course innumerable smaller branches 
 from the tubules which it passes, and finally, in conjunc- 
 tion with the bile-duct from the liver flows at an oblique 
 angle through the muscular wall of the intestine and pours 
 its secretion into that organ. This duct is called the pan- 
 creatic duct, or the duct of Wirsung. Sometimes an acces- 
 sory duct is given off which opens into the duodenum about 
 an inch or more above the main pancreatic duct. Indeed, 
 in some instances this accessory duct may become larger 
 than the main duct. This accessory duct is called the duct 
 of Santorini. The pancreas is richly supplied with blood- 
 vessels from the coeliac axis, and lymphatics and nerves 
 may be easily traced to it. On account of its action on 
 starches the pancreas is called by the Germans the "ab- 
 dominal salivary gland." Not infrequently it is referred to 
 by our butchers as the abdominal sweetbread, in this case 
 
DIGESTIVE ORGANS AND THEIR ANATOMY. 289 
 
 not to be confounded with the regular sweetbread of the 
 neck, th,e thymus gland. 
 
 8. THE LIVEE. 
 
 By far the largest gland in the body is the liver. It has 
 the irregular shape familiar to all, as it is displayed at 
 the meat market. The human liver is divided into two 
 main lobes, a larger right lobe and a smaller left lobe, 
 separated more or less by the round ligament of the liver 
 which is the remnant of a blood-vessel of embryonic life. It 
 measures on an average from five to seven inches in its 
 greatest vertical extent, and its greatest transverse diameter 
 is about the same. In bulk the liver occupies about 100 
 cubic inches and weighs from three and one-half to four 
 and one -half pounds. It is thus about -gV to iV of the 
 weight of the whole body. In foetal life it is proportion- 
 ately, however, much heavier, being at birth sometimes as 
 much as iV of the entire bodily weight. It has a character- 
 istic dull reddish brown color. The ease with which it 
 may be cut or torn is readily exemplified on the butcher's 
 
 Fig. 117. CROSS-SECTION OF A PORTAL CANAL. (Capsule of Glisson.) 
 v, portal vein; d, bile-duct; o, hepatic artery; I, lymphatic; 6, blood-vessel in the 
 tissue of the canal itself. 
 
 counter. It is covered over with peritoneum, but has in ad- 
 dition a covering of its own called the capsiile of Glisson. 
 19 
 
290 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 This is a capsule of connective tissue which extends entirely 
 over the liver, but which underneath extends in the form of 
 solid branched trabeculse up into the gland and forms the 
 framework of its inner structure . The point underneath where 
 this capsule of Glisson enters the liver is called the portal 
 fissure. These trabeculae of connective tissue are here rami- 
 fied through the interior, carrying in their ramifications 
 branches of the portal vein, the hepatic artery and the bile- 
 duct. If one should imagine a much-branched elm tree 
 covered with heavy canvas, and this canvas folded around 
 the main stem near the ground, and made, so to speak, 
 continuous with it, he would have an analogy to the struc- 
 ture of the liver, the canvas representing the capsule of 
 Glisson covering the entire gland, but at the portal fissure 
 connected with a system of ramifications extending through- 
 out the entire gland. If, now, we should imagine passing 
 through the stem, and through every branch of this tree, 
 even down to the finest twigs, three tubes running side by 
 
 Fig. 118. LONGITUDINAL SECTION OF A PORTAL CANAL CONTAINING A PORTAL VEIN 
 
 P. P.; TO THE RIGHT AND NEXT TO THE VEIN THE SMALLER BILE-DUCT; AND NEXT 
 TO THIS THE STILL SMALLER HEPATIC ARTERY. THE INDIVIDUAL LOBULES OF THE 
 
 LIVER ARE PLAINLY SHOWN. (After Kieruau.) 
 
 side, the analogy would be still more helpful. These tra- 
 beculse which run upward from the capsule of Glisson carry 
 
DIGESTIVE ORGANS AND THEIR ANATOMY. 291 
 
 the same name, so that we speak of the capsule of Glisson 
 in the liver containing the three ducts just mentioned. 
 These ramifications finally surround the real units of the 
 liver structure, which are the hepatic lobules. These lob- 
 ules are spherical, or on account of being pressed by jux- 
 taposition, polyhedral masses. They are visible to the 
 naked eye, giving to the liver that marked-off appearance 
 readily discernible on a fresh specimen, and accounting for 
 the granular feeling when fried liver is masticated or rolled 
 between the teeth. The lobules are made up of innumerable 
 hepatic cells, arranged mote or less in rows, radiating from 
 the center of each lobule outward. Around and between 
 these lobules the final ramifications, of portal vein, hepatic 
 artery and bile duct run. These end branches are called 
 respectively the interlobular portal vein, the interlobular 
 hepatic artery and the interlobular bile-duct. 
 
 From the plexus of the interlobular portal vein capil- 
 laries arise which run into the lobule from all directions in 
 such a way as to meet in the center. This capillary net- 
 work pervading each lobule is called the lobtilar plexiis. 
 While this lobular plexus is formed mainly from capillaries 
 arising from the portal vein, there seems little doubt but 
 that into this same lobular plexus, blood from the interlob- 
 ular hepatic arteries is poured. We have here then a con- 
 dition of things in which a single capillary plexus is fed by 
 two streams a portal vein and a hepatic artery. The 
 question naturally arises, why this mixing of the blood from 
 the portal vein and hepatic artery might not have occurred 
 before entering the liver at all, doing away with a double 
 system of vessels ramifying throughout the substance of the 
 liver. The explanation is found in the fact that the hepatic 
 artery is used mainly to carry nutritious blood to the various 
 ducts in connection with the liver, and to the connective 
 tissue everywhere pervading it, and that its primary func- 
 tion is not to carry blood to the liver cells themselves. It 
 seems, however, very improbable indeed from the size of 
 the hepatic artery, that all the blood passing through it 
 
292 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 should be used in merely nourishing inactive ducts and 
 passive connective tissue, and it is therefore quite probable 
 
 Fig. 119. DIAGRAMMATIC REPRESENTATION OF TWO HEPATIC LOBULES. (After Schafer.) 
 P, interlobular branches of portal vein ; h, intralobular vein ; S, sublobular vein ; the 
 lobular plexus of capillaries is plainly shown. 
 
 that much of the blood of the hepatic artery is mixed with 
 the blood from the portal vein in the lobular capillaries of 
 each lobule. 
 
 After the mixed blood passes through the lobular plexus 
 it is collected in the center of each plexus in a small vein 
 called the intralobular vein, a word signifying, of course, 
 the vein within, and not between the lobules. The intra- 
 lobular veins carry the blood out of the lobules, and uniting 
 with the intralobular veins of neighboring lobules form the 
 siib-lobular veins, which, by uniting with other similar 
 veins finally form the hepatic veins which carry the blood 
 just passed through the liver in the manner described into 
 the vena cava. The hepatic veins are usually several in 
 number, and as the vena cava runs apparently right through 
 the liver they are very short indeed, and are nothing more 
 than veins in the liver substance itself. The interlobular 
 bile-ducts also send capillary projections into each lobule, 
 which, however, do not meet in the center, each capillary 
 duct ending, or more properly speaking, beginning, blind 
 
DIGESTIVE: ORGANS AND THEIR ANATOMY. 293 
 
 near the middle of the lobule. These capillary ducts run 
 in-between the liver cells, and into them is poured the se- 
 cretion of the bile, which then through the complicated 
 system of bile-ducts is finally carried to the intestine. 
 
 In order to store the secretion of the liver, so that 
 larger quantities may be available when they are needed, 
 the bile-duct is connected by means of a cystic duct with 
 the gall-bladder, a small muscular pouch several inches in 
 diameter, lying under the liver. The bile reaches this gall- 
 bladder by being prevented from reaching the intestine, the 
 duct leading to the intestine being closed by sphincter mus- 
 cles, and thus forcing the bile up into the gall-bladder. 
 From time to time these sphincter muscles relax, and with 
 a simultaneous contraction of the gall-bladder the bile is ex- 
 pelled in spurts into the duodenum. That portion of the 
 duct which leads from the liver to where the duct from the 
 bladder meets it is called the hepatic duct. The duct lead- 
 ing to the bladder is called the cystic duct, while that part 
 of the duct formed by the union of the two and which con- 
 nects with the duodenum is called the common bile-duct 
 (ductus choledochus) . As stated before, this duct opens 
 with the pancreatic duct. 
 
 The liver is supplied with lymphatics, running mainly 
 in the capsule of Glisson. Nerves reach it from the left 
 pneumogastric and from the sympathetic through the solar 
 plexus of the mesentery. Like the blood-vessels, these 
 lymphatics and nerves enter the liver at the portal fissure. 
 
 THE DUCTLESS GLANDS. 
 
 The various structures so far described in this chaptei 
 are structures intimately and integrally connected with the 
 process of digestion. There are, however, found along the 
 alimentary canal, though not immediately connected with 
 it, other organs commonly designated as the ductless glands. 
 While it is probable, in fact known, that the function of 
 some of these glands is not related immediately to the pro- 
 cess of digestion, yet it is customary, on account of their 
 
294 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 position, possibly, to treat them in connection with the di- 
 gestive tract. This is at least allowable, since the func- 
 tion of several of these structures is practically not at all 
 understood, and so could not be scientifically treated any 
 better in connection with other topics. These ductless 
 glands include the thyroid glands, the thymus gland, the 
 spleen, the adrenal bodies, scattered lymphatic glands, the 
 carotid glands, and the coccygeal gland. 
 
 1. The thyroid glands. The thyroid glands are two 
 large dark reddish, vascular structures situated in the neck 
 just below and to the side of the voice-box. The two lobes 
 are usually connected with a transverse portion called the 
 isthmus. It varies in length, each lobe measuring an inch 
 to an inch and a half, while the thickest portion is about 
 an inch. The isthmus connecting these two lobes is about 
 one-half an inch wide and about three-quarters of an inch 
 long. Examined roughly the structure of the organ seems 
 to be granular. This is borne out by a microscopic examin- 
 
 Fig. 120. SHOWING THE RELATIVE POSITIONS AND SIZES OF THE THYMUS AND THYROID 
 
 GLANDS IN A CHILD. (After Sappey.) 
 
 1,2,3,4, thymus gland; 6, thyroid gland, covered with a number of blood-vessels. 
 All the other numbers refer to blood-vessels. 
 
 ation of the gland, which shows that it is composed of in- 
 numerable vesicles which are bound together more or less 
 firmly by intervening areolar tissue. Each vesicle is usu- 
 ally quite small, at best just visible to the unaided eye. 
 
DIGESTIVE ORGANS AND THEIR ANATOMY. 295 
 
 However, in certain diseases of the thyroid glands, such as 
 goitre, these vesicles may become greatly distended and 
 plainly discernible to the naked eye. 
 
 The wall of these vesicles is made up of a single-layered 
 epithelium, in which the individual cells are somewhat cub- 
 ical or columnar. In the interior there is found a yellowish 
 fluid, which is no doubt the material secreted by these epi- 
 thelial cells. This same fluid also occurs in the areolar tissue 
 between the vesicles. This fluid on account of its appearance 
 is spoken of as a colloid substance. In certain forms of goitre 
 this colloid substance accumulates to such an enormous ex- 
 tent as to increase the size of the gland to many times its orig- 
 inal dimensions. The connective tissue between the vesicles 
 is richly supplied with blood-vessels and lymphatics, which 
 seems to indicate the important part which this gland plays 
 
 Fig. 121. SECTION OF A HUMAN THYROID GLAND. (After Schafer.) 
 Two complete vesicles and portions of three others are shown. The colloid material 
 filling both the vesicles and the spaces between is indicated. In the center of figure is a 
 blood-vessel cut across, next to this a plasma cell. 
 
 in the economy of the body. The composition of this col- 
 loid material has not been satisfactorily determined. By some 
 observers it is stated that it contains proportionately large 
 amounts of phosphorus. More recent experiments have 
 shown that besides containing substances of an albuminous 
 or proteid nature it contains a compound of iodine called 
 thyro-iodine. 
 
296 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 Function. The function of this gland has not been made 
 satisfactorily clear. When the gland is removed from the 
 body peculiar pathological symptoms result, associated with 
 mental disturbances which finally result in insanity and death. 
 It has therefore been supposed by some physiologists that 
 this gland normally removes from the body a kind of poison 
 which, when it accumulates, causes all these pathological 
 symptoms. Such physiologists would look upon the thyroid 
 body as an anti-toxine agent. In fact, certain observers 
 have tried to establish that in animals deprived of the thy- 
 roid body there was actually an accumulation of poisons in 
 the blood to such an extent that when this blood was in- 
 jected into other animals it poisoned them. The difficulty 
 of taking into consideration all possible errors in such an 
 experiment makes it impossible to rely with assurance up- 
 on its results, and more recently physiologists have gone to 
 the view that the thyroid glands do not remove a substance 
 from the body which is injurious, but produce a substance 
 for the body which is not only beneficial but indispensable. 
 Experiments have been made by injecting extracts of the 
 thyroid gland into animals, the result being a beneficial 
 quickening of the general body metabolism. Physiologists 
 holding this view would explain the pathological symptoms 
 which follow the loss of these glands, such as the diminu- 
 tion of muscular strength, failure of the mental powers, 
 swelling of the connective tissues, and excessive dry ness of 
 the skin, as a result of the absence of this necessary tonic 
 secreted in the thyroids, and it ought therefore to follow, if 
 this view is correct, that the administration of an extract of 
 the thyroid gland ought to" produce the normal condition. It 
 is a remarkable fact that in human beings suffering from 
 such symptoms as the result of the loss of the function of 
 the thyroid, injections of thyroid extract, or even feeding 
 them some fresh gland soon restores the individual to a 
 practically normal condition. 
 
 It is unfortunate, from a physiological point of view, 
 that a gland which seems to play such an important role in 
 
DIGESTIVE ORGANS AND THEIR ANATOMY. 297 
 
 the life of the body and which is so indispensable to its ex- 
 istence, should be so poorly understood. Investigators have 
 not, however, abandoned the research, and it is possible 
 that the development of the next few years may throw hope- 
 ful light on this subject.* 
 
 1 Sometimes there are found in the immediate neighbor- 
 hood of the thyroids small nodules of similar tissue which 
 are called para-thyroids. These are no doubt identical with 
 the regular thyroid glands in structure and function. When 
 in certain animals the removal of the main thyroid does not 
 produce immediate death, these para- thyroids may be, no 
 doubt, under such circumstances fulfilling the same function. 
 
 2. The Spleen. Lying on the left side of the body 
 in a position corresponding somewhat to the liver on the 
 
 * With the permission of Dr. Robert Hessler, the Pathologist of the Central Indiana 
 Hospital for Insane, at Indianapolis, extracts from a recent clinical report of his are 
 here added. These extracts are reports of cases of Thyroid Medication. 
 
 CASE) I. This is the case mentioned in my former paper; a young man who had 
 lain immovable in bed for over three years, and who could not be aroused by any means; 
 was fed twice a day by means of a stomach-tube. Under constantly increasing doses of 
 thyroid gland he gradually returned to life, but showed a tendency to relapse on with- 
 holding the remedy. Under very large doses symptoms of exopthalmic goitre appeared. 
 He has received thyroids since November 1, 1895, and still requires moderate daily doses 
 to enable him to move about. He is in the best ward in the hospital, goes out to his 
 meals, and takes walks about the grounds. Mentally he is sluggish, and is not inclined 
 to exert himself; there is some mental impairment. Whether he will ever fully recover 
 is still a question. 
 
 CASE) II. A middle-aged German, cataleptic for three years, retained for a long 
 time any position in which he was placed, even the most awkward. He promptly re- 
 sponded to the thyroid treatment, and in a few weeks was able to be about, and the rem- 
 edy was discontinued. After gaining strength and regaining the use of his extremities 
 he had been practically bedfast for three years he for several months assisted the florist 
 in all sorts of work about the grounds, and ultimately returned home well in body and in 
 mind. He remembered the condition he had been in, and fully appreciated what had 
 been done for him. A long account which he wrote about himself, on recovering, is 
 worthy a psychologist's study. He had realized more or less fully at all times what went 
 on about him, but his actions were dominated by delusions. 
 
 CASE) IV. This was a man approaching middle age who had been in the hospital 
 several years before, in a cataleptic condition, but since nothing could be done for him at 
 that time, his relatives had taken him home. He was re-admitted to the hospital early in 
 May, 18%, in a stuporous condition, as if asleep ; no mental reactions could be obtained with 
 stimuli of any kind. Sensitiveness to painful stimuli greatly diminished. In poor bodily 
 condition; weight 88 pounds; his normal weight had been about 150. Extremities 
 wasted; little motion of them; in fact, they were almost anchylosed from non-use. 
 Hands and fingers contracted; attempts to straighten them brought on symptoms of pain. 
 After a few days of observation in the hospital he was placed on desiccated thyroids in in- 
 creasing doses. After a month's treatment, signs of awakening appeared, and in three 
 months there was some activity, both bodily and mental. Massage was actively applied. 
 At the end of September, under a daily dose of thirty-five grains, vomiting and diarrhoea 
 
298 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 right, is a soft dark purplish organ called the spleen. Its 
 dark purplish color at once enables the observer to distin- 
 guish it from the pancreas, which is light colored. Popu- 
 ularly the spleen is referred to as the "melt." ' It has no 
 ducts leading from it all. It is supplied from the aorta 
 with a rather large splenic artery and connected with the 
 vena cava with a large splenic vein. It is covered over with 
 peritoneum, but in addition to this has a connective tissue 
 capsule of its own. This capsule is largely fibrous, but con- 
 tains also bands of plain muscular fibres, to the presence of 
 which the contractions and dilatations which this organ un- 
 dergoes may be referred. From this fibrous capsule trabec- 
 ulse extend in through the gland and form a fine network 
 throughout its interior. This network is, of course, almost 
 
 appeared thyroidism and the remedy was stopped for a few days and then resumed 
 under a decreased dosage of ten grains a day, slowly increased in the course of time. By 
 November he was able to sit up in bed and made attempts to use his extremities ; the 
 mental condition was fair. He continued to improve rapidly, and by the middle of Janu- 
 ary, 1897, he was able to rise and put on his coat; he even attempted to write a letter. 
 During March thyroids were discontinued; the daily dose at that time was twenty-five 
 grains. The patient at this time was able to use his legs to some extent, and by the mid- 
 dle of the summer he was able to walk about unassisted. This recovery was truly re- 
 markable. He has not had any further thyroid medication since March. Unfortunately, 
 mental improvement did not keep pace with the bodily. The patient had been a mild 
 maniac years ago, and symptoms of this would crop out now and then; he is, therefore, 
 still detained in the hospital. 
 
 CASE) XVI. Age thirty-three ; recently passed the acute mania stage and became 
 chronic. At the beginning of the thyroid treatment he was quiet and well-behaved, al- 
 though delusional and wholly irrational. Under the influence of the gland he became more 
 active; marked symptoms of acute mania reappeared; the heart acted powerfully, and the 
 eyes bulged slightly. Such a reaction was, of course, not desired, and the remedy was 
 stopped, after having been given for several weeks. He soon relapsed to his former quiet 
 condition. 
 
 Conclusions. My conclusions, based on my experience, may be briefly stated about 
 as follows: 
 
 Under moderate continued doses of thyroid gland there is a marked bodily reaction 
 in many cases, but not in all. Some cases require comparatively large amounts before 
 any reaction occurs. There is a distinct stimulation of the nervous system, manifested 
 in various ways, and all bodily activities are increased. Tissue metabolism, especially of 
 the muscular and nervous systems, is markedly increased; a considerable loss in body 
 weight occurs in a short time; on suspending the remedy a rapid gain in weight usually 
 follows. In some cases there is a temporary lighting up of sensory or motor activities, 
 one or both, which soon disappear on discontinuing the remedy. Some cases of a certain 
 type (cataleptics) are benefited permanently; apparently all that is required for a restor- 
 ation to a life of normal activity is the stimulus derived from the substance of the gland. 
 
 In moderate doses no ill results are produced. Under very large continued doses 
 a reaction occurs which is essentially an artificial attack of exopthalmic goitre, Any un- 
 favorable symptoms appearing under large dosage promptly disappear on withholding 
 the remedy. 
 
DIGESTIVE ORGANS AND THEIR ANATOMY. 299 
 
 wholly connective tissue, and so far as structure is con- 
 cerned reminds one of the connective tissue of lymphatic 
 glands. In the meshes of this connective tissue is the 
 spleen pulp. This is loosely contained and may, when the 
 gland is cut, be more or less completely washed out, leav- 
 ing the framework exposed. When the spleen is cut and 
 this pulp forced out it looks very much like clotted blood, 
 which in fact it mainly is. Such pulp examined with a 
 microscope is seen to consist of ordinary red and white 
 blood corpuscles, the latter in relatively greater number 
 than in normal blood. Among these are many connective 
 tissue cells, found here, no doubt, for the same reason that 
 they occur in all the connective tissues. Among the white 
 blood corpuscles, however, there may be seen now and then 
 in fresh spleen pulp somewhat larger cells exhibiting to a 
 much greater extent amoeboid movements. These cells not 
 infrequently have in them" red corpuscles in all stages of 
 disintegration, and from this observation physiologists have 
 naturally come to the belief that these cells in the spleen 
 must be concerned in the destruction of red corpuscles. 
 These cells are called the splenic cells. 
 
 The blood-vessels of the spleen are peculiarly interest- 
 ing. The artery on entering the spleen divides and sub- 
 divides, but the smaller arteries are not connected with 
 veins by means of capillaries as in other portions of the 
 body, but the arteries open abruptly, right into the spleen 
 pulp, thus allowing the blood to soak at large through the 
 interstices of the gland. On the other hand the veins orig- 
 inate as open ducts collecting the blood which has soaked 
 through the pulp. At the ends of these small arteries, that 
 is, just where they open abruptly into the spleen pulp and 
 to a somewhat smaller extent at the beginning of the veins, 
 there are situated little nodules of lymphatic tissue not un- 
 like the patches of Peyer in the intestines. These may be 
 exceedingly small, or may reach dimensions so as to be 
 plainly visible as whitish specks to the unaided eye. These 
 aggregations of white corpuscles are called the Malpighian 
 
300 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 corpuscles of the spleen. It must be remembered, however, 
 that the word ' * corpuscles ' ' is here not used in its usual 
 
 Fig. 122. VERTICAL SECTION OF A PORTION OF THE HUMAN SPLEEN. (After Kolliker.) 
 a, A, fibrous capsule; 6, 6, fibrous trabeculse running through gland; c, c, Malpighian 
 corpuscles; d, d, injected arteries; e, the spleen pulp. 
 
 sense, that it does not refer to a single structure, but to 
 an aggregation of white corpuscles in the form of a lym- 
 phatic nodule. In this sense a patch of Peyer in the intes- 
 tine might be called a Malpighian corpuscle of the intestine. 
 Further, these Malpighian corpuscles must not be confounded 
 with the splenic corpuscles just referred to, which are really 
 true corpuscles, but which are found mainly in the inter- 
 stices between the Malpighian corpuscles. From the struc- 
 ture of the spleen it will be noticed that it is essentially a 
 lymphatic gland, but that unlike true lymphatic glands 
 blood and not lymph traverses it. By the arrangement of 
 the blood-vessels the blood is brought into close contact 
 with the cells that go to make up the splenic pulp, and it 
 is there no doubt subjected to important physiological mod- 
 ifications, which unfortunately are not sufficiently under- 
 stood. 
 
 The function of the spleen is still a chapter- reserved for 
 future investigation. That it is not essential to life is proved 
 
DIGESTIVE ORGANS AND THEIR ANATOMY. 301 
 
 by the fact that the spleen may be taken out of an animal 
 without in any serious way inconveniencing it. It shows a 
 slight connection with the process of digestion in the fact 
 that soon after a meal the spleen becomes materially larger, 
 then contracts again during the fasting period. In addition 
 to these meal pulsations, observers have noticed that it un- 
 dergoes at all times slight contractions and expansions. 
 They have been stated by some to be at the rate of about 
 one expansion per minute. These secondary expansions are, 
 however, quite slight, and may be due to slight changes in 
 blood pressure. Various functions have been ascribed to 
 it. It has been supposed that red corpuscles were formed 
 here. This is true during foetal life and for a short time 
 after birth, but there is really no evidence at all for the view 
 that in adult life red corpuscles are formed here. Then, on 
 the other hand, it has been believed by many to be a place 
 where red corpuscles are destroyed. In evidence of this 
 fact is cited the observation just mentioned, that certain 
 cells of the spleen frequently have in their interior red cor- 
 puscles in all stages of disintegration. A further fact which 
 helps to support this view is the large proportionate amount 
 of iron which is found in the spleen, and it has been be- 
 lieved that this iron comes from the destruction of the iron- 
 containing-hsemoglobin of red corpuscles. While there 
 seems, therefore, at present much probability that this view 
 is the correct one, it is not yet an undisputed fact. The 
 ability to produce new white corpuscles has been ascribed 
 to the spleen. This is no doubt true. The presence of 
 much lymphatic tissue in the spleen would make readily 
 possible the formation of new white corpuscles just as in all 
 other lymphatic tissue. Recently the view has been ad- 
 vanced that in the spleen there is formed a kind of ferment 
 which when it reaches the pancreas (through the blood) 
 changes the trypsinogen contained in this gland into the 
 trypsin. There is so little evidence to support this view 
 that it has been accepted by practically no physiologists of 
 any note. In short, w*e may say of the function of the spleen, 
 
302 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 first, that containing much lymphatic tissue, it gives rise to 
 white corpuscles; second, that the splenic pulp is no doubt 
 largely instrumental in removing from the blood passing 
 through it degenerate red corpuscles. 
 
 The fact that the spleen may be removed without seri- 
 ous injury to an animal may be explained on the ground 
 that there are many lymphatic glands in the body able to 
 produce white corpuscles, and that the destruction of the 
 red corpuscles naturally done by the spleen might be as- 
 sumed by the liver, in which, regularly, a wholesale destruc- 
 tion takes place. 
 
 3. TJie adrenal bodies. Situated immediately above 
 each kidney there is a small glandular mass called the ad- 
 renal body, or not infrequently, the supra-renal body. The 
 right and left adrenals do not have the same form, but are 
 about the same in bulk. They measure from one to two 
 inches from above downward, and from about one inch 
 to an inch and a half from side to side. Their thickness is 
 only about one-fifth of an inch. From these dimensions it 
 will be seen that they are by no means tiny structures, and 
 from their size and the richness of their vascular supply 
 one might suspect that they play an important role in the 
 
 Fig. 123. SECTION THROUGH THE SUPRA-RENAL BODY. (After Allen Thomson.) 
 _ r, kidney; w, supra-renal vein; the distinction between cortex and medulla is also 
 shown. 
 
 body. Each adrenal body is covered with a capsule of con- 
 nective tissue through which is visible the somewhat yellow- . 
 ish or brownish yellow gland. The gland itself is composed 
 
DIGESTIVE ORGANS AND THEIR ANATOMY. 303 
 
 of an outer cortical region, of a deep yellow color, consisting 
 of rods of cells and an inner medullary portion of a more 
 blackish color and quite soft and pulpy. 
 
 A closer examination of this gland reveals that the cor- 
 tex consists of a framework of connective tissue, in which 
 are imbedded column-like groups of cells. In these col- 
 umns of cells there is, however, no lumen visible, so that 
 they are evidently not like the tubular glands found else- 
 where. The medullary portion consists of a much looser 
 framework of connective tissue, richly supplied with capil- 
 laries, while distributed through the interstices of this 
 framework there are groups of cells which resemble some- 
 what those found in the cortex. The function of these 
 structures, like that of the thyroid and spleen, is still in 
 doubt. The removal of these bodies is rapidly followed by 
 death. The symptoms which follow such removal are great 
 muscular weakness and relaxation of most of the blood-ves- 
 sels, and a general prostration. Similar symptoms occur 
 in a disease in man known as Addison's disease, which 
 clinical evidence has referred to pathological conditions of 
 the adrenal bodies. This disease is especially marked by 
 the appearance of bronzed patches on the skin, and so the 
 view has arisen that possibly these supra-renal bodies are 
 concerned in the elimination of an injurious pigment from 
 the blood, which, when it accumulates, produces the gen- 
 eral poisonous effects, and finally, if sufficiently concentrated, 
 discolors the skin to a deep bronze. On the other hand, 
 some observations seem to indicate that this gland does not 
 remove an injurious pigment from the blood, but that it 
 adds some beneficial substance which, when removed, leads 
 to the described results. Aqueous extracts of the adrenal 
 bodies have been made and injected into the blood-vessels 
 of living animals with the result that it affected in a remark- 
 able way the action of the heart, the blood-vessels, and even 
 the voluntary muscles. It made the contractions of the 
 heart more prolonged, strongly contracted the blood-vessels, 
 and so produced a great increase in blood pressure and pro- 
 
304 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 longed the contractions of the voluntary muscles. The ef- 
 fects of such an injection are soon worn off, showing that 
 the active principle of the extract is soon destroyed or 
 eliminated from the body. It will be seen, however, that 
 at best our knowledge is in a most unsatisfactory state, and 
 while it is possible that these adrenals may be concerned in 
 forming some kind of tonic substance which proves bene- 
 ficial and indispensable to the proper working of other tis- 
 sues, it seems more probable that it is concerned with the 
 removal of injurious substances already present in the 
 blood. This latter view is materially strengthened by the 
 observation that Addison's disease, marked especially by 
 accumulation of such pigment, follows abnormal conditions 
 of these adrenal bodies. 
 
 4. The Thymus Gland. The thymus gland is a tem- 
 porary structure which is quite large in early life, reaching 
 its maximum size about the second or third year of life, and 
 then gradually dwindling away until adult life, when it is 
 practically gone. It is situated in the lower region of the 
 neck and the upper part of the chest, and when at its max- 
 imum development is quite large. Its dimensions about 
 the time of birth are two inches in length and about one 
 and a half inches in width, with a thickness of about one- 
 
 Fig. 124. PART OF THE MEDULLA OF A THYMUS GLAND, SHOWING SEVERAL OF THE 
 
 RETICULAR FIBRES, A NUMBER OF LYMPHOID CELLS CALLED THYMUS CORPUSCLES, a; 
 
 AND TWO CONCENTRIC CORPUSCLES, 6. (After Cadiat.) 
 
 third of an inch. In some of the lower animals this gland 
 may reach rather remarkable dimensions. In a calf it may 
 be as much as six or eight inches in length and two or 
 
DIGESTIVE ORGANS AND THEIR ANATOMY. 305 
 
 three inches in width. The gland figures in the business 
 of the meat dealer, and is sold under the name of sweet- 
 breads. 
 
 The thymus is made up of two lobes of almost the same 
 size, which lobes, however, usually lie close together, meet- 
 ing each other at their inner surfaces. In structure the 
 thymus gland is a typical lymphatic gland. It is invested 
 with a capsule of fibrous connective tissue, from which 
 trabeculse extend into the gland, subdividing it and form- 
 ing a framework throughout its interior. In the meshes of 
 this framework are imbedded innumerable white corpuscles. 
 The trabeculae extending in from the capsule divide the in- 
 terior off into little chambers or lobules in which the cor- 
 puscles show an arrangement in two layers, an outer layer 
 of ordinary white corpuscles closely packed, and similar in 
 every way to lymphoid structure wherever found. The 
 fact that these cells are spoken of as the thymus corpuscles 
 must not lead to the idea that they are in any way different 
 from ordinary lymphoid corpuscles. In the center of each 
 lobule the corpuscles are not arranged so closely, and there 
 are found here and there imbedded among the ordinary cor- 
 puscles nests of cells which show a concentric structure. 
 These are called the concentric corpuscles of Hassall. 
 Each nest seems to be composed of a covering of hardened 
 epithelium cells enclosing one or more granular cells. 
 While the meaning of these concentric corpuscles is not 
 wholly clear, there is much reason to believe that they are 
 but remains of a primitive epithelial tube which occurs in a 
 developing thymus and so have no physiological signifi- 
 cance. 
 
 From its structure it would seem, then, that the thymus 
 gland is but a gigantic lymphatic nodule and as such is con- 
 cerned in the production of new white corpuscles. That it 
 disappears in advancing life may be easily accounted for by 
 the fact that new lymphatic nodules appear in many other 
 parts of the body which may relieve the thymus from the 
 necessity of further use. That the thymus reaches such a 
 20 
 
306 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 relatively large size in early life would indicate that either 
 lymphatic tissue has not appeared abundantly in other parts 
 of the body, or that in the growing organism there is an 
 especially great demand for new cells. Unlike, however, 
 ordinary lymphatic glands, the thymus seems richly sup- 
 plied with blood-vessels. Fine vessels penetrate to the in- 
 dividual follicles, forming a plexus around them and send- 
 ing converging capillaries into the medullary portion. The 
 lymphatics which transverse the interstices of the gland are 
 very large. It is poorly supplied with nerves, although a 
 few filaments derived from the pneumogastric and the sym- 
 pathetic system reach the gland by way of its arteries. 
 
 5. The Carotid Glands. Situated just above the point 
 at which the common carotid artery on each side divides 
 into an internal and external branch there is a small gland- 
 ular nodule called the carotid gland. It has a connective 
 tissue capsule, trabeculse from which extend into the in- 
 terior, dividing it into small lobules. These lobules are 
 composed of masses of epithelium-like cells, around and be- 
 tween which there are distributed numerous blood capillaries. 
 Their physiological importance may be dismissed by saying 
 that we have absolutely no knowledge as to what their func- 
 tion is. 
 
 6. The Coccygeal Gland. The coccygeal gland is a 
 small glandular nodule only two or three millimeters in 
 diameter, situated at the apex of the coccyx. It does not 
 differ materially in structure from the carotid glands, being 
 composed of masses of epithelium-like cells surrounded with 
 blood capillaries. Concerning this gland we are also com- 
 pletely in the dark, both as to the manner in which it de- 
 velops and as to its function. 
 
 7. The Pituitary Body. Situated at the end of the in- 
 fundibulum of the brain (which see) there is a small glandu- 
 lar nodule about the size of a small pea known as the 
 pituitary body. It is enclosed in a special prolongation of 
 the dura mater and is composed of two lobes. In color it 
 
DIGESTIVE ORGANS AND THEIR ANATOMY. 307 
 
 is of a reddish gray appearance. It owes its name to the 
 belief of the ancients that it discharged the Cl pituita" 
 (phlegm) into the nostrils. In structure it consists of con- 
 nective tissue, in which there are imbedded numerous 
 branched cells. 
 
 There is possibly no reason for treating of this structure 
 in connection with the organs concerned in digestion, or 
 even in connection with the ductless glands, except for the 
 fact that experiments seem to indicate that its function is 
 closely allied to that of the thyroid glands. Complete re- 
 moval of the pituitary body causes immediate death. Death 
 is preceded by symptoms such as general prostration and 
 spasms, and mental weakness, which are quite similar to 
 those following the removal of the thyroids. This has led 
 many observers to believe that physiologically the pituitary 
 body is a thyroid, and is able to assume to some extent at 
 least, the functions of these glands. However, the con- 
 dition of our knowledge is best stated by saying that with 
 the exception of a few hints we have at present no clue to 
 its real physiological value. 
 
CHAPTER XIII. 
 
 FOODS AND THEIR PHYSIOLOGIC AL VALUE. 
 
 Having thus described the structure of the organs con- 
 cerned in digestion, the next question naturally arising is 
 the necessity for such a system. The body is a machine, 
 and apart from the mysterious property which it possesses, 
 which we call l 'life," it is subject to all the physical laws 
 which govern other machines. We may even go further, 
 and say that although we do not understand what consti- 
 tutes life, all experiments force us to the belief that this prop- 
 erty itself is never in violation of physical and chemical 
 laws. Machines must be supplied with energy to enable 
 them to do their work. There must be the pressure of 
 steam, the electro-motive force of a dynamo, the momentum 
 of running water, or what not, to set things in motion. As 
 soon as the source of energy is cut off the machine stops. 
 The idea of creating a perpetual-motion machine, one which 
 when set going will create the force with which to run, is a 
 scientific absurdity. Not only have thousands of failures to 
 construct one proved that, but one of the most firmly estab- 
 lished laws of science, possibly one of the most fundamental 
 discoveries of this century, has been the law that energy 
 can neither be created nor destroyed. This law is called 
 the " law of the conservation of energy." A great advance 
 was made when it was proved that the energy of the living 
 body is subject to this same law. Formerly it was believed 
 that the working energy of the body was a mysterious kind 
 of vital force which seemed to be in continued spontaneous 
 creation in the body. It may be said that the real science 
 of physiology was born when this notion was abandoned. 
 
 While, however, energy is indestructible it may easily 
 be changed from one form to another. Steam pressure may 
 (308) 
 
FOODS AND THEIR PHYSIOLOGIC AL VALUE. 309 
 
 be changed to motion, this in a motor to electricity, the 
 electricity in a lamp to light, in a coil of wire to magnetism, 
 and in the motor of the street-car back again to motion. 
 While such a change from one form to another is possible 
 and readily accomplished, the change so made is always in 
 definite and fixed proportions. An always invariable and 
 fixed amount of heat is changed into a corresponding cer- 
 tain amount of motion, or vice versa. If in an engine run- 
 ning a factory, lighting and heating it as well, every bit of 
 energy could finally again be collected it would be found to 
 be identical in amount with the original energy producing 
 all, even though in the meantime it might have passed 
 through a half dozen other forms. The forms of energy 
 just mentioned have been forms which might be readily rec- 
 ognized "as energy. There is something moving or dyna- 
 mic about the current of electricity, about the light of the 
 lamp, or the heat in the furnace. Such evident energies 
 are spoken of as dynamic or kinetic energies. But energy 
 may appear in a latent form. A barrel of gunpowder or a 
 cartridge of dynamite, although neither electrified, nor 
 heated nor in motion, possesses a large amount of inherent 
 energy. But a small spark is necessary to transform what 
 is latent into energy of the most dynamic kind. Such latent 
 or resting energy is spoken of as potential energy. The 
 energy which comes from the burning of wood or coal is of 
 this potential kind. 
 
 The form of energy most suited to the body is this kind 
 of latent energy. It can be easily demonstrated that the 
 food constituting an ordinary meal, if dried, can easily be 
 made to burn and yield considerable quantities of dynamic 
 energy. Sugar, fats, meats, breads, all these may be made 
 to burn and give up the latent energy stored in them. It is 
 this energy which is the source of supply to the body. As 
 far as our knowledge goes now it has been impossible to get 
 energy apart from matter. In fact, it is impossible to think 
 of energy except in terms of matter, and energy has some- 
 times been defined as matter in motion, in which the motion 
 
310 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 may be either a motion of the whole mass, a molecular 
 motion, or even an atomic one. For this reason the body 
 which desires primarily the energy to make possible its 
 activity, must take into itself large quantities of material in 
 which the energy is bound. 
 
 So far we have considered the human body as a machine 
 completely constructed and needing no repair, needing only 
 energy to run it. But it is evident that there are other ne- 
 cessities for introducing outside material into it. For many 
 years of its life it must increase in size, and this it can do only 
 by appropriating from the food those substances which it can 
 build into its own tissues. Even when fully matured there 
 is a continued waste which needs new material to replace 
 it. The necessity for foods, therefore, is two-fold: First, 
 to furnish the material out of which the tissues of the body 
 may be constructed; and, secondly, to furnish material out 
 of which the body may derive the energy required for its 
 activity. In order to understand how much this shall be, 
 it is desirable to examine what the losses of the body are 
 under normal conditions. 
 
 THE LOSSES OF THE BODY. 
 
 1. In Matter. Careful investigations upon persons of 
 average size and conditions show that in the course of a day 
 there is lost from the body in the form of matter about nine 
 pounds. In this is not included that undigested portion of 
 the food which never really becomes part of the body. 
 About five pounds of this loss is through the lungs. It 
 seems at first surprising to think that even in so short a 
 time as one day there should have been breathed out of the 
 lungs a quantity of gas reaching the amount of about five 
 pounds. It seems not quite so surprising that about three 
 pounds or more of this is eliminated from the kidneys. 
 The remainder is thrown off from the skin or poured as ex- 
 cretions into the alimentary canal. Evidently, therefore, 
 from the mere standpoint of matter it is necessary to put 
 into the body each day nine pounds of suitable substances 
 
FOODS AND THEIR PHYSIOLOGIC AI, VALUE. 311 
 
 capable of replacing these nine pounds of loss. The sub- 
 stances lost from the body are, in the lungs, carbon dioxide 
 and watery vapors; in the kidneys, water and a number of 
 nitrogenous substances and salts; and from the skin, water 
 and salts mainly. The losses of the body in excretions poured 
 into the intestinal canal are certain ingredients of the bile, 
 to be discussed later. Possiby one ought to add in this con- 
 nection occasional losses of the cuticle of the skin or epi- 
 thelium cells from the mouth, which, however, do not 
 figure in a material sense in this calculation. 
 
 2. In Energy. In energy the losses of the body are 
 mainly of two kinds. By far the greater part of the energy 
 is expended in the form of heat. A relatively small pro- 
 portion of it gives rise to muscular motion. It is a matter 
 of interest that in our bodies about one-fifth only of all the 
 energy is utilized in muscular activity ; but four-fifths in the 
 maintenance of the bodily temperature. While this seems 
 but a small per cent., it is much greater than in even the 
 best of engines, the amount of energy in these to be util- 
 ized in actual motion being from one-eighth to one-tenth, 
 while in the ordinary engines possibly not more than one- 
 fifteenth or one-twentieth is utilized. When one remembers 
 that in a locomotive only one bushel of coal out of ten is 
 really expended in pulling the train, and the other nine lost 
 in heating the engine and in friction, one is tempted to 
 believe that the most helpful discoveries of the future may 
 be in enabling us to realize a greater per cent, of the energy 
 in active work. 
 
 The amount of heat lost by an average person in one 
 day is tolerably difficult to determine. Experiments have, 
 however, been made, the result of which show that if all the 
 heat radiated from a working body in one day were collected 
 it would be sufficient to raise the temperature of about 100 
 pounds of water from zero to the boiling point. This, too, 
 seems at first too much when we remember that the tem- 
 perature of the body remains fairly constant, rarely exceed- 
 ing that of 98 degrees Fahrenheit. It must, however, be borne 
 
312 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 in mind that this temperature is maintained by a continued 
 radiation of heat from the body, or by a loss of heat in the 
 evaporation of the sweat of the skin. Such a continued 
 loss during twenty-four hours would not be inconsiderable. 
 Evidently, therefore, to replace this loss of energy there 
 must be introduced into the body as food, substances which 
 when they are burned will give the amount of heat required, 
 and of course in addition, the energy required for the move- 
 ment of the muscles, which, as stated, is about one-fifth 
 more in amount. 
 
 In giving as the losses in energy muscular activity and 
 heat, no attention is paid to other possible forms of energy 
 in connection with secretion, or with the nervous system. 
 In the former there are probably no other forms of energy 
 concerned, while what the nature of the energy is in nerves 
 and psychic states we are at present perfectly unable to 
 state. That such states are accompanied by the production 
 of heat is a known fact, but that all the energy is trans- 
 formed into heat is another question. 
 
 The exact manner, now, in which the body is able to 
 appropriate these foods and build them up into its own tis- 
 sues, or the manner in which it derives from these foods 
 the energies it expends, will be more fully discussed in the 
 chapter on nutrition. 
 
 THE CLASSES OF FOODS. 
 
 It would be entirely out of place here to enumerate the 
 large list of substances which figure as foods. These are 
 sufficiently familiar. A study of the varied menu of our 
 tables shows that all foods may be divided into a few 
 typical classes in which the foods of a class not only close- 
 ly resemble each other, but in which those of one class 
 are clearly distinguishable from those of any other. These 
 classes are, first, albumens, or proteids; second, albumin- 
 oids; third, carbohydrates; fourth, hydrocarbons; fifth, in- 
 organic salts; sixth, zvater. 
 
FOODS AND THEIR PHYSIOLOGICAL, VALUE. 313 
 
 1. The Proteids. The proteids, or albumens, are foods 
 characterized by containing nitrogen in composition. For 
 this reason they are frequently spoken of as the nitrogenous 
 foods. In addition to the nitrogen they contain carbon, 
 oxygen, hydrogen, and traces of other elements. The pro- 
 teids are familiar in the form of egg albumen, myosin or 
 the lean of meat, casein, the substance of cheese, gluten, 
 the main ingredient of the grains or cereals, and legumen, a 
 vegetable albumen found in relatively great proportion in 
 peas and beans. All the albumens of our diet probably fall 
 into one or the other of these classes. Meats of different 
 sources are physiologically alike and differ only in the mat- 
 ter of flavor and digestibility ; hence all forms of meat would 
 be included under the term "myosin." 
 
 These foods are the main and substantial foods, and 
 have always been recognized as the essential foods, with- 
 out one or more of which it would be impossible to live. 
 Evidently one purpose of foods is to make new tissues; but 
 the tissues, in fact protoplasm wherever found, contains 
 nitrogenous substances closely allied to proteids and albu- 
 mens, and so it is absolutely necessary that to produce 
 these in the body, nitrogenous foods must be taken. In 
 the carbohydrates and hydrocarbons there is no nitrogen, 
 and consequently if our diet should consist wholly of these 
 the tissues of the body would gradually waste away and a 
 death by starvation would ensue. But these proteids or al- 
 bumens do not figure as tissue builders only in the body. 
 They are an integral source of energy. Without trying to 
 press an analogy, it may be helpful to recall that many sub- 
 stances having nitrogen in combination are peculiarly well 
 fitted as sources of energy. One needs only to think of 
 gun-powder with its contained nitre, or of nitro-glycerine 
 with its contained nitrogen, or of a number of other energy- 
 yielding substances which depend for this property largely 
 upon the fact that they have in their composition nitrogen. 
 Disregarding here numerous objections which the chem- 
 ist might urge, it may be said that like these formidable 
 
314 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 explosives the nitrogenous proteids of the body are a mild 
 form of explosive out of which, under proper circumstances, 
 large amounts of energy may be utilized. The discussion 
 of the manner, however, in which it is believed to be done 
 is postponed to the chapter on nutrition. 
 
 2. The Albuminoids. The albuminoids resemble the 
 albumens or proteids in containing nitrogen. The nitrogen, 
 however, seems in such a combination as not to be avail- 
 able to the body as food, as it is in the case of the proteids. 
 For this reason the albuminoids are not able to replace the 
 proteids. The most familiar example of the albuminoids is 
 gelatine found in soups or used in numerous desserts. This 
 gelatine is derived from the connective tissues.. It contains 
 carbon, oxygen, hydrogen, nitrogen, and traces of other 
 substances, resembling, therefore, as just stated, the pro- 
 teids ; but the contained nitrogen seems not to be assimila- 
 ble by the tissues, and so this food must figure in the 
 body rather like a non-nitrogenous than a nitrogenous food. 
 Regularly, however, the amount of albuminoids taken as 
 food is so small that it does not figure materially in the 
 economy of the body at all. 
 
 3. Carbohydrates. In the carbohydrates are included 
 the starches and sugars. The name "carbohydrates" 
 naturally suggests carbon and water as entering into their 
 composition, and such is, in a certain sense, true. All 
 carbohydrates are composed of carbon, hydrogen and oxy- 
 gen, but the hydrogen and oxygen are present in the pro- 
 portion of water; that is, two atoms of hydrogen to every 
 one atom of oxygen. An important point is that they con- 
 tain no nitrogen. The composition of the commoner car- 
 bohydrates will easily explain this. Thus the composition 
 of cane sugar is, Ci 2 H 2 2 On; of glucose, C c Hi 2 O G ; 
 of starch, C 6 H 10 O 3 . 
 
 The physiological value of these foods lies in the fact 
 that they figure as sources of energy. It will be pointed 
 out in the following chapter that probably the main source 
 
FOODS AND THEIR PHYSIOLOGICAL VALUE. 315 
 
 of muscular and heat energy is derived from the carbohy- 
 drates. They, too, form the bulk of our foods, there being 
 few dishes indeed of which either the starches or the sugars 
 do not form an integral part. In addition they are perhaps 
 the most digestible of all foods, and finally a reason not to 
 be neglected, they are possibly the cheapest of foods. It 
 seems a rather queer coincidence that the carbohydrates are 
 the foods best suited to the process of digestion, best suited 
 as sources of energy, best suited to the palate, and finally, 
 best suited to our expenses. These coincidences are, no 
 doubt, the result of dietary evolution. The close relation- 
 ship of the starches and sugars is evident from the ease with 
 which the starches are changed into sugars or sugars into 
 starches. 
 
 4. Hydrocarbons. In the hydrocarbons are included 
 the fats and oils. As indicated by their name they contain 
 mainly hydrogen and carbon. A little oxygen is also in 
 combination, but the hydrocarbons differ essentially from 
 the carbohydrates in the fact that the hydrogen and the 
 oxygen are not present in the proportion of water. Com- 
 pared with the carbohydrates the hydrocarbons contain rela- 
 tively more carbon and hydrogen and less oxygen. For this 
 reason when they are burned they give rise to much more 
 energy. There would be quite a material difference in the 
 amount of heat liberated between the combustion of a bar- 
 rel of sugar and a barrel of oil. It is for such reasons that 
 the fats are peculiarly well suited as a diet in winter or in 
 colder climates, and the Esquimau who drinks his blubber 
 supplies himself with one of the best foods for the liberation 
 of heat. The distinction between fats and oils is a rather 
 arbitrary one. Hydrocarbons which at ordinary tempera- 
 tures are more or less solid, are spoken of as fats, those which 
 at these temperatures are in a liquid condition are called oils. 
 
 It is well to bear in mind that fats contain no nitrogen, 
 and that therefore their physiological value in the body is 
 similar to that of the starches and sugars. It would be im- 
 possible for an animal to live long if its diet were limited 
 
316 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 entirely to fats, or even to fats, starches and sugars. While 
 the fats are sources of greater energy than the carbohy- 
 drates, and so better suited for colder climates, they seem 
 not so well suited for temperate climates, and not at all for 
 tropical regions. Even in the latitude of Indiana, the fats 
 and oils have not nearly the general food value of the car- 
 bohydrates. Used to supplement the proteids, starches and 
 sugars, they are of course very desirable. The commoner 
 examples of the hydrocarbons are butter, lard, tallow, and 
 the vegetable oils. 
 
 5. The Inorganic Salts. In the common use of the 
 term " food," such articles as common and other inorganic 
 salts are not included, but there is as much of a necessity 
 for the presence of some of these salts to make possible the 
 normal functions of the body as there is that proteids, sugars 
 and fats shall replace the waste. With the exception of 
 common salt, which is added as a special ingredient, usu- 
 ally however more for the palate than for its physiological 
 value, the other inorganic salts reach us as regular ingredi- 
 ents of the foods. In nearly all of our solid foods there is 
 a small proportion of mineral matter. This may easily be 
 demonstrated by burning bits of these foods. There are 
 practically no foods which do not leave, when burned, bits 
 of ash. This ash of course constitutes the mineral salts 
 contained in the original substance. While all of these salts 
 do not find their way into the body, the body is able to dis- 
 solve and assimilate such of them as are especially needed 
 in the work of the tissues for the building up of mineral 
 constituents of such tissues as bone or enamel. A few of 
 the commoner mineral salts which are required in the body 
 are here given. 
 
 For the growth of bone there are required salts of mag- 
 nesium and calcium (lime) ; for the haemoglobin of the 
 blood, traces of iron ; for the blood and lymph of the body, 
 considerable quantities of common salt\ as an integral por- 
 tion of the red corpuscles and other tissues, potash salts. 
 
1-OODS AND THEIR PHYSIOLOGICAL VALUE. 317 
 
 While these are the main mineral ingredients a chemical 
 examination of the body would reveal small traces of quite 
 a number of additional inorganic salts, which may be omit- 
 ted here. Not only are these salts needed to build up the 
 mineral constituents of tissues, such as bone or enamel, but 
 they are also needed to make possible the proper working 
 of the tissues. Thus it is known that animals from which 
 common salt ha^s been kept will become materially deranged, 
 suffering what is called a " salt craze," and the continued 
 withholding of the salt may finally induce fatal results. The 
 exact manner in which this salt figures will be treated fur- 
 ther on. 
 
 6. Water. On account of its abundance and free access 
 everywhere, water is not classed as a food, but is such in 
 an essential way, although of course no energy can be di- 
 rectly derived from the same ; but as an agent for dissolving 
 other foods, as an ingredient forming by far the largest 
 amount of all the tissues, it plays a first role in digestion 
 and nutrition. 
 
 A MIXED DIET. 
 
 Very few of the foods as they are served to us on the 
 dinner table belong wholly to one or another of these 
 classes. In nearly every case they are mixtures of some or 
 all of them, and their dietetic value will depend upon the 
 relative proportions in which they contain these classes as 
 ingredients. The multitude of dishes ranging from the 
 highly flavored and seasoned ones of tables of plenty, down 
 to the simpler foods of the peasant's meal, are but mixtures 
 in varying proportions. The different character which the 
 varying dishes possess is usually much more a matter of 
 flavor or condiment than it is a matter of nutritive value. 
 
 In order to fully understand the nutritive value of the 
 food then, and leaving out entirely the matter of flavor, the 
 influence of which ceases with the palate, it is necessary to 
 
318 STUDIKS IN ADVANCED PHYSIOLOGY. 
 
 make an analysis of these mixtures and to determine the 
 amounts of each one of the classes just mentioned. The 
 accompanying table, modified slightly from Herman, shows 
 in a very striking way the composition of most of the com- 
 moner articles of food. By reference to it it will be seen 
 that the animal foods, such as the meats, contain very little 
 of carbohydrates, but relatively much of proteids and fat. 
 Of course the percentage of fat will vary within wide lim- 
 its, and will depend largely upon the condition of the ani- 
 mal examined. The leaner the animal, evidently the less 
 proportion of fat and the relatively larger proportion of pro- 
 teid. On the other hand, meat in which there is a good 
 deal of fat might finally have the fat in excess of the pro- 
 teid, a condition for instance found in ordinary breakfast 
 bacon. For this reason the animal foods, that is the meats, 
 have always been looked i:pon as the chief sources of the 
 nitrogenous foods, and as nitrogenous foods can not be dis- 
 pensed with in the diet, these foods have become popularly 
 viewed as almost if not wholly indispensable. 
 
 On the other hand, the vegetable foods are quite sharply 
 distinguished by their relatively large amount of carbohy- 
 drates and rather small amounts of proteids and fats. Thus 
 the food value of the potato consists almost wholly of the 
 starch which it contains. Rice is nearly all starch. Even 
 in corn the starch is the largest ingredient, although in it 
 there are not inconsiderable quantities of proteid. In 
 wheat, in which the proteid gluten forms quite an integral 
 part of its composition, the carbohydrates occur in large 
 proportion. A rather remarkable exception of what has just 
 been stated occurs in the composition of peas, beans, and 
 other leguminous foods. In these the percentage of proteid 
 actually exceeds that found in meats. This explains why 
 these vegetables have commonly accredited to them such a 
 high nutritive value, and why sometimes in cases of mili- 
 tary operations when it is difficult to transport meats, beans 
 have been found a satisfactory substitute. 
 
FOODS AND THEIR PHYSIOLOGICAL VALUE. 
 
 319 
 
 By reference to the table, an interesting comparison 
 may be made between the composition of cow's milk and 
 human milk. It will be seen that cow's milk contains rela- 
 tively more proteid, but on the other hand, less sugar and 
 less fat. For this reason, when cow's milk is to be rend- 
 
 Beef 
 
 T i I i 1 I I ! I 
 
 Mutton 
 Pork 
 Chicken 
 Game 
 Fish 
 
 1 j ( . ( 
 
 I i|| ..| 1 
 
 -_ g 1 1 1 1 , 
 
 i : r 1 1 1 1 1 1 
 - : n 1 i 1 i 1 1 
 
 Eggs 
 Human Milk 
 Cow's Milk 
 Butter 
 Cheese 
 
 Beans 
 
 ".. ... ,! 1 1 
 
 I 1 1 1 ! ! 
 
 -^^ , , , 1 1 1 
 ' i 1 i i i i i ' 
 
 9 10 2\0 30 l|0 5J0 60 ?|0 8\0 S\0 /6 
 
 i i i i _ 
 
 Peas 
 Rice 
 
 
 Wheat Flour 
 
 ii ill 1 
 
 f 1 -" '.- . ' 1 
 
 Maccaroni 
 
 - -J ' ! ' . . -, ' 1 
 
 Rye Bread 
 
 ; * ... ' ' ^ ^T- ' ' ' i 
 
 Potatoes 
 
 i E! ,- , 1 
 
 Turnips 
 Spinach 
 
 i ;ii ,. . 1 
 1 1 ! 1 1 I ... 1 u 
 
 Fruit, fresh 
 Fruit, dried 
 
 ] 
 
 <fU - ' . 1 L-L^ 1 ! 1 
 M 20 30 ?0 SO 60 70 SO 30 JO 
 
 txv^.?] i..'..w. i i i SSUBR 
 'roteids. Fats. Carbo- Woody Water Ash. 
 hydrates. tissue. 
 
 Fig. 125. TABLE GIVING RELATIVE COMPOSITION OF THE COMMONER FOODS. 
 
 ered as nearly of the composition of human milk as possi- 
 ble, it is diluted with water in order to dilute the extra 
 amount of proteids in the cow's milk, and then there is ad- 
 ded cream and sugar to bring these up to the increased per- 
 centage in the human milk. The interested reader will be 
 able to answer so many questions bearing directly on these 
 points here under consideration by referring directly to the 
 table given, that an extended comment on the composition 
 of the commoner foods is deemed unnecessary. 
 
320 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 THE EELATIVE AMOUNTS OF THESE CLASSES OF FOODS RE- 
 QUIRED BY AN AVERAGE INDIVIDUAL AND THE 
 VALUE OF A MIXED DIET. 
 
 The experience of every one has shown that it is not 
 desirable to limit one's diet exclusively to one kind of food. 
 If one had nothing but meat he would get much more nitro- 
 gen than would be necessary in trying to get the amount of 
 carbon which the body requires, the relative amount of car- 
 bon being so small in the proteids. If one limited his diet 
 to a substance which was rich in fats and sugars, but con- 
 tained only traces of nitrogen, he would have to eat un- 
 necessarily large quantities of fats and sugars to get the 
 proteid necessary for his body. The most sensible way, 
 therefore, of determining the composition of one's diet is to 
 take enough proteid food to give to the body all the nitro- 
 genous food it needs, and then to supply it further with the 
 necessary amounts of carbon and hydrogen, to take foods 
 especially rich in these, such as fats and sugars. 
 
 A very natural question is: What are the relative 
 amounts of these classes of foods which an average working 
 body needs, say in a day? A great many and careful ex- 
 periments have been made and the results of these do not 
 vary materially. We may, therefore, give the average fig- 
 ures with much probability that they state the correct con- 
 dition of things. In an experiment by Pettenkofer and Voit 
 on a workingman twenty-eight years old, weighing about 
 150 pounds, it was found that when not at work he needed 
 
 137 grams of proteid. 
 72 grams of fat. 
 352 grams of carbohydrates. 
 
 On a day when this same workman was at regular work he 
 
 consumed 
 
 137 grams of proteid (same as when at rest). 
 
 173 grams of fat. 
 
 352 grams of carbohydrates. 
 
 It will be noticed that the extra work entailed an extra con- 
 sumption of fat. Other observers have changed this experi- 
 ment just 'a little. They, too, found that the amount of 
 
FOODS AND THEIR PHYSIOLOGICAL VALUE. 321 
 
 proteids needed either at work or at rest was about the 
 same. They did not, however, increase the amount of fat 
 given when working, but made the increase in the carbo- 
 hydrates, and then found that under such circumstances 
 the man to be satisfied consumed much larger quantities of 
 these. 
 
 Similar experiments were tried on a young physician, 
 whose diet in one day consisted of: 
 
 127 grams of proteid. 
 89 grams of fat. 
 362 grams of carbohydrates. 
 
 As average figures, therefore, the following little table may 
 
 suffice : 
 
 Water 3,000 grams. 
 
 Proteids 131 " 
 
 Fats 88 
 
 Carbohydrates 400 " 
 
 In such an average diet there are 20 grams of nitrogen and 
 312 grams of carbon. This proportion is about the propor- 
 tion normally desired by the body. These 20 grams of ni- 
 trogen could be secured from the following amounts of 
 
 foods : 
 
 Cheese- 272 grams. 
 
 Peas 520 " 
 
 Lean meat 538 
 
 Wheat flour 800 
 
 Eggs 900 (about 18 eggs.) 
 
 Milk 3,000 
 
 Potatoes 4,600 
 
 Turnips ~ 8,700 
 
 A glance at the figures just shown will give at once the 
 relative nutritive value of the main foods. Cheese, consist- 
 ing almost wholly of casein and being in tolerably compact 
 form, is probably by weight the most nutritious. Eggs, on 
 the other hand, in spite of our notion that they are so nu- 
 tritious, would not yield to the body the required amount 
 of nitrogen unless the diet should average eighteen or more 
 eggs per day. In order to get sufficient proteids out of a 
 diet of potatoes it would require the consumption of a per- 
 fectly unwieldy lot, while if the attempt should be made to 
 21 
 
322 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 get the necessary amount of proteids from turnips, for in- 
 stance, an amount not less than 8,700 grams would have to 
 be consumed each day. Evidently, therefore, it is desira- 
 ble that the body should derive its nitrogen supply from 
 those foods which appear first in the table just given. 
 
 The 312 grams of carbon which on an average the body 
 needs per day might be derived from the following amounts 
 of foods: 
 
 Fat meat 450 grams. 
 
 Corn meal 800 " 
 
 Wheaten flour 824 
 
 Rice 900 
 
 Peas 1,000 
 
 Cheese 1,200 
 
 Eggs 2,200 (about 43 eggs.) 
 
 Lean meat 2,600 
 
 Potatoes 3,100 
 
 Milk 4>6oo 
 
 Turnips 10,000 
 
 These figures at once give us a clue as to the most 
 desirable kind of a diet. It will evidently consist first, of 
 one or more of those substances which are very rich in pro- 
 teid, such as cheese, peas or beans, meat, cereal flour or 
 eggs, in order to get the proper nitrogen supply, and then 
 for the carbon needed to turn to the second table and get 
 either the fat meats which are especially rich in carbon, or 
 else some of the more starchy foods like corn, wheat, rice 
 or potatoes. 
 
 FLAVOES, CONDIMENTS, AND STIMULANTS. 
 
 In describing the classes of foods so far, it has been 
 done without very much attention to the distinctions which 
 the palate would make. In the actual eating of foods these 
 secondary flavors and condiments not infrequently play 
 a very determining role. However, all these flavors, no 
 matter how pleasant they may be to the palate, have prac- 
 tically no digestive value at all, and so for pure physio- 
 logical reasons need not be considered. The dainty dis- 
 tinctions of taste which the various kinds of meats afford 
 
FOODS AND THEIR PHYSIOLOGICAL VALUE. 323 
 
 cease as soon as the food has passed the tongue. Even 
 the hundred and one varieties of flavors of our fruits, and the 
 artificial flavors of our desserts share the same fate. Salt, 
 of course, which is sometimes viewed as a seasoning sub- 
 stance figures as a food, but the peppers, or spices, and the 
 mustards are foods in no sense. We derive no nourishment 
 from them, and they serve merely to give gist to the taste, 
 and sometimes by their stimulating action to arouse the 
 often too dormant digestive organs. To this same class 
 belong the teas and coffees. These now almost universal 
 drinks owe their popularity to peculiar organic compounds 
 called theine and caffeine, respectively, which, while of no 
 nutritive value, have a slight stimulating effect. In addition 
 to this a cup of hot tea or coffee during meal time is fre- 
 quently quite potent to arouse the stomach to secretion, a 
 result which might, however, be equally well brought about 
 by drinking a glass of hot water. The rather baneful 
 effects which follow from an excessive use of these are too 
 well known to need mention here. 
 
 ALCOHOL. 
 
 Almost .as far back as history carries us, man has more 
 or less generally added alcohol in some of its forms to the 
 articles of his daily consumption,. and even at this present 
 day the wines and beers are in many places regular dishes 
 at the table, and the question naturally arises, what the nu- 
 tritive value of this substance is. Alcohol is, of course, 
 never taken in its pure form, but in varying grades of dilu- 
 tion as given in the table below: 
 
 Rums and whiskies from 60 to 80 per cent. 
 Brandies " 40 to 60 " 
 
 Wines ranging from 40 down to 5 per cent. 
 Beers " " 4 " i 
 
 Ordinary commercial alcohol is a colorless liquid of a 
 peculiar penetrating odor and of a very inflammable nature. 
 It is used in the arts very extensively as a solvent for in- 
 iminerable substances, and in the sciences it is used in 
 
324 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 large quantities as a preserving fluid for anatomical and 
 zoological specimens. 
 
 It is produced by a process called fermentation. This is 
 a process brought about by a little plant called the "yeast 
 plant," which by its action upon sugar converts it into 
 alcohol and carbon-dioxide gas and several minor products. 
 In the distillery or the brewery this process of fermenta- 
 tion is allowed to go on until the desired per cent, of alco- 
 hol has been reached. The carbon dioxide gas is allowed 
 to escape, and gives to the fermenting vats their frothy or 
 "brewing" appearance. The condition of things in the 
 making of yeast bread is the same. Here, too, some yeast 
 which has either been specially put in, or else allowed to 
 fall in from the air, acts upon some of the sugar in the 
 dough, resulting in the formation of alcohol and carbon 
 dioxide gas. The carbon dioxide gas in its attempt to 
 escape from the dough forms innumerable little bubbles 
 throughout it, and so causes the bread to "rise" or become 
 light. The alcohol, of course, evaporates in the process of 
 baking. The same thing is again illustrated in the famil- 
 iar canning of fruits. Here the fruit to be preserved is 
 boiled, the primary intention of which is to destroy all 
 germs and all yeast plants in it, and then the fruit before 
 it has a chance to cool is put into jars and these then her- 
 metically sealed. If, however, the sealing is defective and 
 air, as we say, gets in, fermentation is soon set up and the 
 sugar in the fruit is ushered along in the process towards 
 the formation of alcohol and remoter substances. It is not, 
 however, the air which sets this process going. It is the 
 introduction of some yeast plants along with the air which 
 is the source of the trouble. 
 
 The chemical and physical properties of alcohol in its 
 various forms need not be dwelt upon here, the primary 
 question in this instance being its physiological effects. 
 This, in a general way, is its apparent stimulating power. 
 Administered to animals it quickens, for a while at least, 
 the general tone of nearly all the organs. It produces a tem- 
 
FOODS AND THEIR PHYSIOLOGICAL VALUE. 325 
 
 porary exhilaration which is pleasant, and which no doubt 
 explains the desire which has so generally prompted man- 
 kind to use it. There are so many good books now avail- 
 able giving the detailed and specific action of this substance 
 on the various organs, and on the body in general, that such 
 a detailed account is deemed unnecessary here. That alco- 
 hol taken in excess produces derangements of the most 
 serious nature in almost all the organs, is a point which no 
 man can doubt who has seen the brutish drunkard lying in 
 the gutter. Whether alcohol in moderate quantities is a 
 food or not, whether in small amounts it may not be helpful, 
 is a question which does not concern us here. Suffice it to 
 say that all physiology and possibly all medicine has shown 
 conclusively that there is absolutely no necessity for a sound 
 man to add alcohol in any of its forms to his daily diet. The 
 person who persists in doing so must seek his reason else- 
 where, while the fact that in innumerable instances it has 
 done unspeakable harm, is equally well established. With- 
 out denying for a moment, or disregarding the effect of 
 alcoholic excesses upon the various tissues of the body, the 
 point remains that the truest reason against the use of this 
 substance is a moral one. The fact that the heart of the 
 toper is unnaturally stimulated by his whiskey, is a very 
 insignificant fact compared with the more serious one that 
 this whiskey in its effects has broken possibly a wife's and 
 a mother's heart; the fact that the drinking of alcohol 
 lowers the temperature of the body of the toper is a very 
 trifling fact compared with the more awful one that it has 
 given babies cold feet for want of shoes, and wives cold 
 backs for want of warm clothing; that it has made homes 
 cold, and has reduced the warmth of a thousand friends. 
 The fact that it may curdle the liver is of small conse- 
 quence when compared with the more serious fact that it 
 too frequently curdles the sentiments, the hopes, and the 
 aspirations. That alcoholic excesses may produce the ugly 
 ulcerations of the drunkard's stomach is possibly not so 
 
326 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 lamentable as the many blotches on virtue which it has pro- 
 duced in our industrial civilization. A certain firm on one 
 Saturday evening paid out to its workingmen four hundred 
 marked ten-dollar bills. The following Monday one hun- 
 dred of these marked ten-dollar bills were deposited in the 
 city banks by different saloon keepers of the place. When 
 one remembers how many shoes, how many dresses, how 
 many pieces of nutritious meat, how many little toys for 
 playful children, how much happiness, in short, for innu- 
 merable homes might have been purchased with these one 
 hundred marked ten-dollar bills which found their way into 
 the saloons, one need not be told further about the lament- 
 able physiological and moral effects. A mighty step in the 
 right direction will have been made when every young per- 
 son fully realizes that by avoiding the demon of drink the 
 chances are greater that he will always have an abundance 
 of good friends, that he will be able to enjoy what is best 
 in life, that he will be a helpful member of his community 
 and that he will always have a dollar in his pocket with 
 which to buy bread for himself and his own. 
 
CHAPTER XIV. 
 
 DIGESTION AND THE DIGESTIVE AGENTS. 
 
 HISTORICAL. 
 
 Our knowledge concerning the process of digestion does 
 not reach back very far. The notion of the ancients was 
 very primitive indeed. They likened the digestion in the 
 body to a kind of cooking, and in the middle ages this 
 notion was carried so far that they actually thought one 
 purpose of the animal heat of the body, especially the 
 warmth of the internal organs, was to cook the foods. It 
 was as late as the seventeenth century before definite notions 
 of digestive ferments in the stomach arose ; but these fer- 
 ments were looked upon as causing only a very fine me- 
 chanical separation of the food. However, Reaumur, in 
 1752 proved that the agent of digestion was the gastric 
 juice, and that this digestion could be accomplished with- 
 out any mechanical helps. The sour re-action which Reau- 
 mur had noticed was established by Prout in 1834, to be 
 due to free hydrochloric acid. Two years later, in 1836, 
 Schwann discovered the pepsin. In 1834 a Canadian by 
 the name of Beaumont was enabled to make a series of ob- 
 servations on a man whose stomach had been exposed by a 
 wound, and upon which the digestive processes could be 
 fairly accurately followed. In the same year Eberle suc- 
 ceeded in making artificial gastric juice, and conducted 
 experiments in digestion with the same. The sugar-forming 
 action of the saliva was discovered by Leuchs in 1831. Our 
 knowledge of the digestive processes in the intestine did 
 not begin until 1848, when Claude Bernard established the 
 fact that pancreatic juice digested fats. Nine years later, 
 in 1857, Corvisart discovered that pancreatic juice digested 
 
 (327) 
 
328 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 proteids. Although first discovered by Corvisart the pro- 
 teid-digesting nature of pancreatic juice was finally worked 
 over and established with its present exactness by Ku'hne 
 in 1867. The intestinal juice was first secured in a pure 
 form by Thiry in 1865. 
 
 THE DIGESTIVE AGENTS. 
 
 We have now to consider the various changes, chemical 
 and physical, by means of which the solid and usually in- 
 soluble food is converted into a liquid form, suitable to be 
 absorbed from the walls of stomach and intestine and passed 
 into the blood. The process of digestion begins, of course, 
 in the mouth. No attention is here paid to peculiar changes 
 helpful in the process of digestion which have been brought 
 about by the cooking or baking of the intended food. Thus 
 it is a familiar fact that the crust of bread is more digest- 
 ible than the inner part, the process of baking having 
 changed the starch in question into a form which is more 
 easily soluble. The first step in the digestion, as far as the 
 body is concerned, is that of mastication. This is merely 
 a mechanical process by means of which the food is broken 
 up and so enabled to be swallowed. During the process of 
 mastication, however, the food is mixed with the first of 
 the digestive fluids, called the "saliva." The salivary 
 ducts of the parotid and submaxillary glands open at the 
 base of the molar teeth and are so arranged that bits of 
 saliva are introduced whenever the molars are inserted into 
 a morsel of food. In addition to this, of course, a good 
 deal of saliva flows into the front part of the mouth from 
 the sublingual gland, and is there more or less thoroughly 
 mixed by the rotating action of the tongue. 
 
 1. Saliva and Salivary Digestion. Saliva is a clear, 
 transparent liquid when filtered. When taken from the 
 mouth it is somewhat cloudy, owing to the fact that it has 
 solid substances in it: bits of food and epithelial cells which 
 have been detached from the mucous membrane of the 
 
DIGESTION AND THE DIGESTIVE AGENTS. 329 
 
 mouth. Very frequently, too, \vhite cells, probably identi- 
 cal with white blood corpuscles are present. These are 
 corpuscles which have probably wandered out from deeper 
 tissues along with the secretion. They have been called 
 salivary corpuscles, although now recognized as nothing 
 more than escaped leucocytes. Saliva is a little heavier 
 than water and is alkaline. The quantity secreted in a day 
 is, of course, subject to the widest variations, varying from 
 200 to 2,000 grains. Saliva contains the following constitu- 
 ents in 1,000 parts: 
 
 Water 994-2 
 
 Mucin 2.2 
 
 Ptyalin 1.3 
 
 Inorganic Salts 2.2 
 
 The inorganic salts are largely chloride of potassium and 
 sodium, and phosphates of calcium and magnesium. These 
 inorganic salts in the saliva are interesting from the fact 
 that small amounts of them are deposited around the teeth 
 and give rise to the formation of tartar. The mucin pres- 
 ent in the saliva is ordinary mucus or phlegm, and is really 
 an addition to the saliva from the mucous glands in the 
 mouth. This mucus has no distinct value further than that 
 by its ropy and sticky nature it serves to hold bits of the 
 food together and so makes swallowing easier. Incidentally 
 along with the saliva it serves to keep the mouth moist. 
 The main and distinct constituent of saliva is the ptyalin. 
 This belongs to the class of substance called enzymes, or 
 ferments, and has the property of being able to convert 
 starch into sugar. 
 
 THE THEORY OF HYDROLYSIS. 
 
 As the term "enzyme" or ferment occurs repeatedly in 
 physiology (the pepsin in the stomach, the trypsin in the 
 pancreas, and others being ferments), a word in explana- 
 tion of these substances and the manner in which they are 
 supposed to act is given. 
 
 There are two kinds of ferments; one, that of living fer- 
 ments, of which the many forms of bacteria and the yeast 
 
330 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 plant are good illustrations. These ferments are really liv- 
 ing beings which are able in some way to set up chemical 
 processes which we have chosen to call fermentation pro- 
 cesses. The other class consists of unorganized, dead sub- 
 stances. They are chemical ferments. To this second 
 class belong almost all the digestive ferments of the body. 
 Ferments have the power of breaking up certain substances 
 and changing them into new compounds. Thus ptyalin, 
 as just stated, changes starch into sugar. It is probable 
 that these ferments produce these results in the following 
 way : They cause the substance to be changed to take up 
 one or more molecules of water, and then split this combi- 
 nation into two or more smaller bodies. This action is well 
 shown in the change which takes place in cane sugar. Not 
 infrequently cane sugar is changed into two sugars called 
 dextrose and levulose. This change from cane sugar to 
 dextrose and levulose is represented chemically in the fol- 
 lowing equation: 
 
 Cin H 22 On+H 2 = C 6 H 12 6 + C 6 H 12 O 6 
 Cane Sugar -f Water = Dextrose + L,evulose. 
 
 A similar change occurs in the mouth. Under the in- 
 fluence of the ptyalin the starch is made to combine chem- 
 ically with more water and the resulting molecule is then 
 split up, sugar being the result. Ptyalin is present in many 
 of the lower animals, especially the herbivorous animals, 
 but seems to be absent in the carnivora. It was, until 
 recently, believed that the sugar which resulted from 
 the action of the ptyalin on starch was ordinary grape 
 sugar, but later investigation has shown that this is in- 
 correct, and that the resulting sugar is maltose, a sugar 
 very closely related chemically to ordinary cane sugar. 
 However, the starch is not at once changed into maltose, but 
 there seems to be between the beginning starch and the 
 final maltose a number of intermediate stages with which, 
 however, in this elementary treatise we are not concerned. 
 
 The physiological value of ptyalin is evident. Starch is 
 insoluble, and could not pass through the walls of the ali- 
 
DIGESTION AND THE DIGESTIVE AGENTS. 331 
 
 mentary canal, but by its conversion into maltose this diffi- 
 culty is at once remedied, maltose being quite dialyzable. 
 On account of the short time during which the food remains 
 in the mouth but a very small part of the starch is con- 
 verted into maltose. But we shall see in the discussion of 
 the pancreas that this process is again picked up in the in- 
 testine and there completed. The ptyalin is unable to act 
 in an acid medium, and so as soon as the food reaches the 
 stomach its digestive action ceases, but when later the food 
 is passed into the small intestine and the acid of the stom- 
 ach gives way to the alkalinity of the intestine, the saliva 
 renews its digestive action, so that possibly the greatest ef- 
 fect of the saliva is produced, not in the mouth, but in the 
 intestine. The digestive action of the ptyalin may be easily 
 demonstrated by taking a dish of boiled starch and adding 
 a little saliva containing ptyalin to it. By keeping this dish 
 then at a temperature of about 98 Fahrenheit the starch is 
 rapidly converted into sugar and may be detected quite 
 easily by the taste and by chemical re-actions. 
 
 2. The Stomach and Gastric Digestion. The process 
 of digestion in the stomach is almost wholly a chemical one 
 and is only incidentally mechanical. The food remains 
 here one or more hours, varying with its digestibility, dur- 
 ing which time it is subjected to a slight churning process. 
 Slight peristaltic movements creep across the stomach, the 
 effect of which is to more or less mix and re-mix the gas- 
 tric contents and so materially aid the juice in reaching all 
 the particles of the food. The stomach owes its power to 
 digest to the gastric juice. This juice is by no means a 
 simple substance, but is a mixture of several things. Its 
 composition is in 1,000 parts about as follows: 
 
 993 parts water. 
 
 2 " hydrochloric acid. 
 
 3 " pepsin. 
 2 " salts. 
 
 In addition to these substances, which can be more or less 
 quantitatively determined, there are present in the gastric 
 
332 STUDIES IN ADVANCED PHYSIOLO'GY 
 
 juice several other substances which it is not yet possible to 
 secure in a pure form, but the presence of which can be 
 easily demonstrated by the actions which they exert. One 
 of these is the ferment called "rennet," a ferment which 
 coagulates milk. Traces of mucin also are present. 
 
 a. Pepsin. The principal ingredient of gastric juice 
 is the ferment called "pepsin." This is an organic com- 
 pound of an albuminous nature, possessing almost all the 
 characteristics of ordinary peptones. It has the property 
 of digesting albumens and albuminoids, transforming the 
 albumens into soluble peptones and the albuminoids into 
 dialyzable gelatin. It is able to effect these changes, how- 
 ever, only in an acid solution, which explains the presence 
 of the free hydrochloric acid in the stomach. In fact, it is 
 possible that the pepsin and the acid may in conjunction, 
 as a pepsin-acid, effect these changes. 
 
 The change from the non-dialyzable and sometimes solid 
 proteids to the liquid and dialyzable peptones is, however, 
 not a direct one. As in the case of the conversion of sugar 
 into maltose by the ptyalin so here there are between the 
 beginning proteids and the final peptones a number of 
 intermediate stages designated as acid albumens and pro- 
 teoses. By the experiments of Kiihne and Chittenden quite 
 a number of these intermediate products have been deter- 
 mined and studied, and these experimenters have worked 
 out a table showing the stages through which the proteids 
 pass toward the final peptones. However, in an elementary 
 text-book these changes are too intricate to be dwelt upon, 
 the significant fact being that a large part of the proteids 
 of the stomach are converted by the continued action of the 
 gastric juice into peptones, while the intermediate stages 
 and any proteids not affected by the gastric digestion are 
 passed into the intestine and there their change into pep- 
 tones is completed by the action of the pancreatic juice. 
 
 . It must not be understood that a proteid is merely a 
 solid albumen and a peptone a liquid albumen. The vital 
 
DIGESTION AND THE DIGESTIVE AGENTS. 333 
 
 difference between a proteid and a peptone is in the power 
 of dialysis. A proteid dialyzes little if at all, while a pep- 
 tone does so readily. Egg albumens even when in a liquid 
 form, as we find it in an egg which has been subjected to 
 the process of incubation for several days, is by no means a 
 peptone. In spite of its liquid form it is but little dia- 
 lyzable, and if taken into the alimentary canal would have 
 to be transformed into dialyzable peptones in no less a way 
 than a bit of solid meat. Peptones further possess the 
 property of not being coagulated when subjected to heat. 
 This is, of course, also true of certain proteids; as, for in- 
 stance, the proteid in milk which may be boiled without 
 coagulating the milk. But the peptones, in addition to not 
 being coagulated by boiling, are not precipitated when 
 treated with alkalies, mineral acids or various salts. In 
 short, a peptone is an albumen in such a liquid form that it 
 is easily dialyzable and is not taken out of its liquid form 
 by any of the common reactions which coagulate and pre- 
 cipitate ordinary albumens. Every one is familiar with the 
 fact that most common albumens will coagulate when 
 heated, and that the albumen in milk will coagulate when 
 treated with an acid. This latter is the common process of 
 curdling. While the introduction of alkalies or strong 
 mineral salts will at once precipitate these albumens in the 
 form of white insoluble flakes it does not precipitate pep- 
 tones. 
 
 It is not possible to get pepsin in an absolutely pure 
 form. For commercial purposes, however, it may be 
 secured with satisfactory purity. For these purposes it is 
 extracted from the gastric mucous membrane of various 
 animals, and then mixed with starch or sugar of milk and 
 placed on the market. For laboratory experiments to show 
 artificial gastric digestion the pepsin may be secured by 
 taking the gastric mucous membrane of an animal, cutting 
 it up very finely, and then extracting the pepsin from it 
 with glycerine. These glycerine extracts if properly diluted 
 and acidulated, readily digest proteids subjected to their 
 action. 
 
334 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 In the medical field pepsin in some form or other is fre- 
 quently given to supplement the lack of this material in the 
 stomach. In fact, the disease called by the too-general 
 term dyspepsia, is, as the name indicates, frequently inter- 
 preted as a lack of the pepsin. Dyspepsia is, however, a 
 pathological condition of the alimentary canal which is 
 much more frequently not connected directly with the ab- 
 sence or presence of the pepsin, but is due to bacterial fer- 
 mentation set up in the carbohydrates. 
 
 b. Hydrochloric Acid. Gastric juice contains about 
 two parts of free hydrochloric acid in a thousand. This 
 fact is somewhat remarkable, as it is the only mineral acid 
 in the body which occurs in a free condition. It is inter- 
 esting to note in this connection that a certain mollusk of the 
 genus Dolium secretes a salivary juice which contains beside 
 the free hydrochloric acid free sulphuric acid. Of the ex- 
 act manner in which this acid is formed in the stomach we 
 know as yet nothing. There is a good deal of evidence 
 pointing to the oxyntic cells of the stomach as the seat 
 of the production, but the chemistry of it is still missing. 
 The only reasonable explanation is that some of the neu- 
 tral salts, like common salt, which is a combination of 
 sodium and hydrochloric acid, are split into the free acid 
 which then passes into the stomach, and the alkaline base 
 which passes into the blood and which may account for the 
 fact that the blood is normally alkaline even when no alka- 
 line salts are found in the food. 
 
 c. Rennet. In the making of cheese it was long an 
 observed fact that sweet milk could be made to curdle 
 quickly and effectively by adding to the milk a piece of the 
 mucous membrane of a calf's stomach, or of some animal 
 living upon a milky diet. There seems to be in the mucous 
 membrane in question a ferment which has the power to 
 coagulate milk. This ferment is called "rennet" or 
 remain. It has not been possible to get this rennet in a 
 pure form, and so its composition is not known. It is 
 
DIGESTION AND THE DIGESTIVE AGENTS. 335 
 
 found in a much more concentrated form in the stomachs 
 of sucking animals, for which reason these stomachs are 
 used in the preparation of cheese, but in diluted and weaker 
 forms it maybe extracted from the stomachs of all mammals. 
 No doubt the curdling of milk in the adult stomach is 
 largely due to the presence of the acid in the stomach ; but 
 it can be shown that gastric juice may be perfectly neutral 
 and still retain its power of curdling milk. The chemical 
 nature of this process is not known. Possibly it is not very 
 unlike the coagulation of blood, a fact which seems to gain 
 credence in the observation that the milk will not clot or 
 curdle unless lime salts are present. The action of the 
 rennet, however, goes no further than the curdling of the 
 milk. As soon as this is effected its action ceases, and by 
 the pepsin the milk is converted into soluble peptones. 
 
 The mineral salts are the chlorides and phosphates of 
 potassium, calcium, magnesium and iron, but as they figure 
 in no integral way in gastric digestion we are not specially 
 concerned with them here. 
 
 GASTRIC DIGESTION OF CARBOHYDRATES AND 
 HYDROCARBONS. 
 
 Gastric juice exerts no digestive action upon the 
 starches. The starches in a perfectly unaltered condition 
 are passed into the intestine, and their digestion there 
 turned over to the pancreas. Nor are the sugars affected, 
 although there would be no special reason for a change in 
 sugars, as all the sugars are soluble and dialyzable to begin 
 with. Neither are the fats affected. Bits of tallow, lard 
 or butter suffer no digestive changes in the stomach, save 
 that by the general mixing of the stomach they are broken 
 up into small bits. However, very frequently the fats are 
 eaten not as pure fat, but in the form of droplets of fat en- 
 closed in albuminous coverings. Thus in ordinary milk and 
 cream, the butter is held in the form of minute droplets, 
 each surrounded by a thin albuminous envelope. To get 
 the butter in a pure form it is of course necessary to break 
 
336 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 these envelopes and allow the contents to run together, a 
 result which is easily brought about by the mechanical 
 crushing- of these envelopes in the familiar process of 
 churning. It might, however, be brought about just as 
 easily by adding bits of pepsin and acid to the cream and 
 allowing this pepsin to digest away the albuminous cover- 
 ings, and so permit the buttery droplets to run together. 
 
 Such a condition of things we meet with in the stomach. 
 Fats taken in the form of such droplets, as in milk or cream, 
 have their albuminous covering digested away by the gas- 
 tric juice, and the fatty contents liberated. Or when fatty 
 meat is taken, the connective tissue covering as well as the 
 coverings of the fatty cells are digested away and the con- 
 tained fat set free. But this action is clearly an action on 
 the albumens and albuminoids, and has really nothing to do 
 with the digestion of the fats themselves. 
 
 Gastric juice will digest the albuminoids. Bits of white 
 fibrous tissue, or ordinary connective tissue or cartilage are 
 disintegrated and the gelatine extracted. 
 
 SUMMARY. 
 
 When the process of gastric digestion, after a period of 
 four or five hours comes to an end, we find the following 
 state of things: 
 
 First. The change from the starch to the sugars begun 
 by the ptyalin in the mouth is temporarily arrested in the 
 acid juice of the stomach. 
 
 Second. A large part of the proteids have been taken 
 through several intermediate stages and been finally changed 
 into dialyzable peptones. 
 
 Third. Starches have in no wise been affected. 
 
 Fourth. Pure fats have not been affected at all, but fats 
 when surrounded with albuminous envelopes, as in the case 
 of milk or cream, or of fat meat, have had these albumin- 
 ous coverings digested away, and been thus liberated. 
 
 Fifth. Sugars have not been acted upon. 
 
DIGESTION AND THE DIGESTIVE AGENTS. 337 
 
 Sixth. The milk has been curdled by the acid of the 
 stomach and by the rennin, and more or less fully converted 
 into peptones by the pepsin. 
 
 Seventh. A number of mineral salts which we take into 
 the body daily, as ashy ingredients of our foods, have been 
 dissolved by the acid of the stomach and so enabled to 
 pass into the blood. In this way much of the mineral mat- 
 ter for the body, which would be perfectly insoluble in water 
 is dissolved, and so rendered suitable for the body's pur- 
 poses. With the gastric contents in this condition the py- 
 loric sphincter from time to time relaxes, and the now 
 fairly semi-liquid food is passed into the duodenum to be 
 further subjected to the action of the succeeding digestive 
 agents. 
 
 The explanation why the stomach does not digest itself 
 is given by some as due to the resistance of its epithelial 
 lining, by means of which it is protected from the digestive 
 action of the juice, the keratin of the epithelium cells being 
 indigestible. Others find the explanation in the circulating 
 alkaline blood through the walls, by means of which the 
 walls themselves can never become acid, and so never sus- 
 ceptible to the action of the gastric juice. It is interesting 
 to note that ulcerations of the mucous membrane become 
 susceptible to self-digestion, which may finally lead to the 
 formation of holes through the gastric wall. 
 
 3. The Pancreatic Juice. Fresh pancreatic juice is a 
 clear, viscid, alkaline, rapidly putrefying liquid, slightly 
 heavier than water, coagulating completely when subjected 
 to boiling. Its composition is as follows: 
 
 First, albumens. Just what the exact nature of these 
 albumens is has not yet been determined. They coagulate 
 easily upon being boiled. Whether, in fact, they have any 
 digestive action at all is still questionable. 
 
 Second, several ferments or enzymes. These enzymes 
 are trypsin, amylopsin, and steapsin. 
 
 Third, a number of mineral salts, mostly sodium salts. 
 
 Fourth, water. 
 22 
 
338 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 About ninety per cent, of the pancreatic juice is water. 
 Dissolved in it are the mineral salts, to which the alkalinity 
 of this juice is due, for unlike the gastric juice, the ferments 
 of the pancreatic juice can act in an alkaline medium only, 
 and not in an acid one. The pre-eminence of pancreatic 
 juice as a digestive agent, exceeding very much that of the 
 pepsin or ptyalin, is due to the presence of the three fer- 
 ments named, trypsin amylopsin and steapsin. 
 
 Trypsin. Trypsin is a very powerful ferment changing 
 with great energy proteids into peptones. It is this ferment 
 which acts iipon all those proteids left unacted upon by the 
 stomach, and upon all of the intermediate stages left incom- 
 plete by the pepsin. Here, too, the change from the pro- 
 teids to the peptones is not a simple and direct one, there 
 being a number of intervening stages called here, also, pro- 
 teoses, the final resulting stage, however, being peptone in 
 no essential way distinguishable from the peptone made by 
 the stomach. The powerful digestive action of trypsin is 
 shown in the fact that some of "the peptone is disintegrated 
 still further into two substances called leudn and tyrosin, 
 substances which the chemist may readily detect where pan- 
 creatic digestion is going on, but the physiological signifi- 
 cance of which we are at present not at all able to under- 
 stand. The peptones are, of course, the source of the ni- 
 trogenous foods of the body, but why some of the peptones 
 should be broken up, that is, digested still further into 
 bodies like leucin and tyrosin, bodies which seem to play 
 no part as foods, is not at all clear. The trypsin is also able 
 to digest any albuminoids which may have escaped diges- 
 tion in the stomach. 
 
 Amylopsin. Amylopsin is a ferment of the pancreatic 
 juice identical with the ptyalin of the saliva, and like this 
 ptyalin possesses the property of changing starch into mal- 
 tose. The pancreas is called by the Germans the "Ab- 
 dominal Salivary Gland," no doubt because of the identity 
 of its action on the starches, with the salivary glands. The 
 
DIGESTION AND THE DIGESTIVE AGENTS. 339 
 
 starches which are left entirely unacted upon in the stomach, 
 are now subjected anew to ferments. The ptyalin of the 
 saliva continues its action, while the amylopsin added from 
 the pancreatic juice soon completes the digestion of the 
 starches and effects their entire change into soluble mal- 
 tose. There is no good reason for calling the ptyalin of the 
 pancreatic juice by a new name unless it be that the term 
 "amylopsin" indicate the source from which the ptyalin is 
 derived. 
 
 Steapsin. Steapsin is a ferment of the pancreatic juice 
 which has the property of splitting fats into a fatty acid and 
 glycerine. The chemical nature of this change is the same 
 as that of ptyalin. Under the action of the steapsin the fat 
 is made to combine with more water and the resulting 
 molecule is then split up into glycerine and a free fatty acid. 
 It has not been possible to isolate this steapsin, and so we 
 know at present nothing about its chemical nature. The 
 splitting up of fats into a fatty acid and glycerine is, how- 
 ever, a very common occurrence and familiar to every one. 
 When butter becomes old, it acquires an offensive, rank 
 odor. This is due to the fact that the butter, which is a 
 pure fat, has been split, in this case by an organic ferment, 
 into an acid called butyric acid, and glycerine. It is the 
 butyric acid which has the disagreeable odor. The same 
 thing is true of other fats. Exposed for a long time they 
 become, as we say, strong and rank, the explanation of 
 which is found in the fact that these pure fats have been 
 split into a fatty acid, hence their odor, and glycerine. 
 These fatty acids may be made to combine easily with some 
 form of alkali and so soap produced. Soap is, in fact, 
 nothing but the combination of a fatty acid with some suit- 
 able alkali. In the once very common manufacture of 
 household soap, the rank fats were boiled in a kettle with 
 some form of lye, the resulting combination being soap. 
 
 The physiological value of the ferment, steapsin, is 
 found not immediately in the fact that it splits these fats up 
 into glycerine and fatty acid, but in the succeeding fact, that 
 
340 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 the fatty acids so produced in the intestine, unite with some 
 of the alkaline ingredients present and form soap. It can 
 be easily shown in a chemical laboratory that the formation 
 of soap is practically impossible when a perfectly pure fat 
 is used. Traces of a fatty acid must be present to help the 
 process along. In the intestine this fatty acid is produced 
 by the steapsin and so the formation of soap rendered pos- 
 sible and simple. 
 
 The question then at once arises, what the physiological 
 value of soap is in the intestine. In the first place, soap is 
 soluble and dialyzable, while ordinary fat is not very dialyz- 
 able, and so if the fats are changed into soap it will make 
 quite easy the transfer of these substances into the blood. 
 The same is true of glycerine also, which is always formed 
 when the fats split up into a fatty acid. 
 
 The main purpose, however, of the soap is probably to 
 aid in the emulsification of the remaining fats. It was 
 pointed out in discussing the action of the gastric juice on 
 fats that all the fats were liberated. In the intestine they 
 are prepared for absorption. A small per cent, of them, as 
 just indicated, is changed into fatty acid, and then into 
 soap. The rest is emulsified. An emulsification of an oil 
 or fat is effected when the oil in question is shaken up very 
 thoroughly with some liquid, so that the two seem to have 
 been intimately mixed and the fat is prevented from run- 
 ning together by being suspended in tiny droplets sur- 
 rounded by a thin envelope to prevent them reuniting. 
 Thus, cream is an emulsion of butter, the tiny particles of 
 butter being surrounded by an albuminous covering and so 
 prevented from running together. Lather is an emulsion 
 of air and soap-suds. The significance of the emulsifica- 
 tion of the fats lies in the fact that the bits of fat in the in- 
 testine are separated into very tiny particles small enough 
 to pass through the walls of the alimentary canal in a 
 manner to be described in the following chapter. In large 
 chunks or bits this would be impossible, but reduced to 
 
DIGESTION AND THE DIGESTIVE AGENTS. 341 
 
 tiniest globules the absorbing cells of the intestine are able 
 to manage them properly. 
 
 In the emulsion of these fats the soap formed in the in- 
 testine seems to figure directly. Probably the tiny little 
 droplets of fat are surrounded by thin envelopes of soap and 
 so prevented from reuniting. That soap is pre-eminently 
 fitted in making an emulsion is evident as soon as we think 
 of soap-suds and lather. We have, therefore, to picture to 
 ourselves the way in which the fat is acted upon about as 
 follows: The liberated fats of the stomach reach the in- 
 testine, meet some of the steapsin ferment, and are then 
 partly split into a fatty acid and glycerine. The fatty acid 
 at once unites with some alkaline ingredient of the pan- 
 creatic juice or bile and soap is formed. This soap by 
 means of the peristaltic motions of the intestine is shaken 
 up with the remaining fats and emulsifies them, so getting 
 them ready for absorption. That some of the fats in the 
 form of soap, finally reach the blood, is probable, but the 
 physiological value of this soap is in its emulsifying action 
 upon the remaining and larger portion of the fats. 
 
 Summary. What, then, is the final state of things 
 after the process of pancreatic digestion has continued for 
 several hours? 
 
 Of course while the pancreatic digestion has been going 
 on the bile has been poured into the intestine and has pro- 
 duced some effects, and the intestinal juice has also been 
 acting. But leaving this out of consideration for the pres- 
 ent the final state of things is about as follows : 
 
 First: All the proteids which the stomach has left un- 
 touched and all those proteids which the stomach has 
 only partially changed into peptones, have been completely 
 changed into peptones by the trypsin. 
 
 Second: Any albuminoids that may have escaped di- 
 gestion in the stomach are dissolved and the gelatine ex- 
 tracted. 
 
342 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 Third: All the starches are finally changed into maltose 
 by the renewed action of the ptyalin of the saliva, but 
 mainly by that of the amylopsin ferment of the pancreas. 
 
 Fourth: The fats have been doubly affected. A small 
 part has been saponified, that is, made into soap by the 
 steapsin, and the remainder has been emulsified. Sugars 
 have been left untouched. It will be seen, therefore, that 
 at this stage of digestion all the proteids, all the fats, all 
 the starches are ready for absorption. The sugars alone 
 have escaped any action. 
 
 4. The Bile. The liver plays but a very small part in 
 the process of digestion, and the bile which it pours into 
 the duodenum must not be classed in importance along with 
 the digestive agents so far considered. The liver is an ex- 
 ceedingly important organ when the phenomena of nutri- 
 tion and metabolism in the body are considered, but plays 
 a minor role in digestion. In fact, bile is largely an excre- 
 tory product. It digests nothing itself, although incidentally 
 it does serve several digestive purposes. Human bile is of 
 a golden color, exceedingly bitter, neutral in its re-action, 
 and emitting a peculiar characteristic odor. It is a little 
 heavier than water. When the bile is taken from the gall- 
 bladder it contains a mucin-like substance which was added 
 to it in its passage through the bile-ducts and in its stay in 
 the gall-bladder. This was formerly designated as ordinary 
 mucin, but its re-actions are not those of ordinary mucin, 
 and it is probably a slightly different product. However, 
 in a general way we may still speak of it as mucin. While 
 the color is usually a golden yellow it changes its color so 
 readily as to appear sometimes a greenish yellow, some- 
 times a greenish brown, still other times pure green or 
 brown. These changes in color are brought about by dif- 
 ferent degrees of oxidation of the bile pigments. 
 
 The quantity of bile secreted during a day for average 
 persons is from 600 to 900 cubic centimeters. In animals 
 which have no gall-bladder the bile is poured into the in- 
 testine in a continuous stream, but in those possessing a 
 
DIGESTION AND THE DIGESTIVE AGENTS. 343 
 
 gall-bladder the secretion is allowed to accumulate in that, 
 from which in turn it is ejected in spurts at stated periods 
 into the duodenum. The average composition of bile in- 
 cludes the following substances in 1,000 parts: 
 
 Water about 900 parts, 
 Mucin about 25 parts, 
 Bile salts about 30 parts, 
 Cholesterin about 2 parts, 
 Mineral salts about 10 parts, 
 
 Also traces of soap, fats, and lecithin. In addition to these 
 there are traces of bile pigments, to which the color of the 
 bile is due. The large amount of water serves, of course, 
 as the fluid medium in which all the other substances are 
 dissolved and by which they are carried. 
 
 The Bile Salts. The most important constituents of the 
 bile are the bile salts. These are the sodium salts of two 
 peculiar acids called glychocholic acid and taurocholic acid. 
 It would be out of place here to go into the chemistry of 
 these organic acids. It may, however, be of interest to call 
 attention to the point that the taurocholic acid contains 
 sulphur. These two acids are not found in the blood, but 
 are made by the cells of the liver and by these poured into 
 the bile-ducts. They are probably substances which have 
 resulted from the breaking down of some proteid or albu- 
 minoid substance in the process of metabolism, and are 
 primarily intended for removal from the body. It is inter- 
 esting, however, to note that these bile salts are re-digested 
 in the intestine, and are almost wholly re -absorbed into 
 the system. These bile salts have some important func- 
 tions; in fact, they are considered indispensable, and are 
 treated by some physiologists as by no means mere excre- 
 tions, but special secretions intended for specific purposes. 
 In the first place these bile salts hold in solution the cho- 
 lesterin of the bile. Cholesterin is insoluble in the bile as 
 soon as the bile salts are removed. It is a non-nitrogenous 
 substance very widely distributed in the body, being found 
 especially abundant in the white matter of nerve tissues. In 
 
344 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 small amounts, however, it is found in all animal and plant 
 cells. This cholesterin is, therefore, probably not formed 
 in the liver, but is merely eliminated by the liver cells from 
 the blood, and poured into the bile secretion to be removed 
 from the body. As far as we know now it is a pure excre- 
 tion, the accumulation of which in the blood would prove 
 dangerous. It is sometimes precipitated in the bile-ducts 
 or gall-bladder and so gives rise to the formation of gall 
 stones, which may in many cases consist of pure cholesterin, 
 the removal of which from the gall-bladder or bile-ducts 
 is frequently a matter of the severest pain, and oftentimes 
 results fatally. In the second place these bile acids seem 
 to facilitate the absorption of fats from the intestine, and to 
 help materially in the emulsion of the fats, a point to be 
 discussed later. The exceedingly bitter taste of bile is due 
 to these organic bile salts. 
 
 The Bile Pigments. The bile owes its color to the pres- 
 ence of small amounts of substances called bile pigments. 
 These pigments, according to the animals from which they 
 are taken, are of two kinds, the golden bilirubin or the 
 greenish biliverdin. The bilirubin is present in fresh human 
 bile and occurs normally in the bile of most carnivora. On 
 the other hand the bile pigments in the case of most herbi- 
 vorous animals is the greenish biliverdin. Biliverdin and 
 bilirubin are practically the same, one being only a slight 
 oxidation product of the other, and it is very easy by this 
 means to change one into the other. This fact is made use 
 of in detecting the presence of bile pigments. If to some 
 human bile in a test-tube a little fuming nitric acid be 
 added, the acid being heavier will sink to the bottom, the 
 bile being in contact with it above. At this point of con- 
 tact the bilirubin undergoes a succession of color changes, 
 through green, blue and violet, to yellow. This play of 
 colors is due to the successive stages of oxidation of the 
 bile pigments. The bilirubin is in the first stage changed 
 to green, a change due to the formation of biliverdin. In 
 
DIGESTION AND THE DIGESTIVE AGENTS. 345 
 
 such a test tube the colors will arrange themselves one 
 above the other in the order indicated, the most advanced 
 stage of oxidation being of course next to the nitric acid, 
 the least advanced stage of oxidation on top of the liquid. 
 This characteristic re-action for the detection of bile pig- 
 ments, familiar to all physiological laboratories, is called 
 "Gmelin's re-action. " It is a very sensitive one, and by 
 means of it the presence of bile pigments has been detected 
 in other liquids of the body, as for instance, the secretion 
 from the kidneys. The bile pigments are of especial inter- 
 est, because it is fairly well established that they are derived 
 from haemoglobin. When the red corpuscles break down 
 in the circulation or disintegrate in the spleen or liver, the 
 colored haemoglobin is sent to the liver, and by the liver 
 cells is converted into bilirubin or biliverdin. Haemoglobin 
 contains iron, but bilirubin and biliverdin are iron -free. 
 This shows that the iron in the haemoglobin must be re- 
 tained in the liver, and possibly dropped back into the blood 
 and sent to the marrow of the bones, to be used anew in 
 the formation of fresh haemoglobin. The amount, there- 
 fore, of bilirubin or biliverdin eliminated in the bile would 
 give us a clue to the rapidity of corpuscular disintegra- 
 tion. 
 
 Bile is practically a watery solution of certain mineral 
 salts which holds in solution goodly quantities of the or- 
 ganic bile salts. These organic bile salts hold in solution 
 the cholesterin of the bile, and finally the bile pigments to 
 which the color is due. In addition to these main constitu- 
 ents there are found in bile traces of fats and soaps, and a 
 peculiar substance called lecithin, which is interesting be- 
 cause it is always found in nervous tissues and characterized 
 by containing phosphorus. It is no doubt a mere disinte- 
 gration product resulting from the activity of these tissues 
 and sent to the bile merely to be removed as a waste 
 product. 
 
 The reason for the presence of the fats and soaps in the 
 bile is still missing. 
 
346 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 The General Physiology of Bile. Our knowledge of 
 the physiological value of bile still leaves much to be de- 
 sired. Here more than with any other of the digestive 
 agents our knowledge is fragmentary, and there is at present 
 still no unanimity among leading physiologists as to the role 
 which it plays. It seems probable, however, that the intro- 
 duction of bile into the duodenum accomplishes the follow- 
 ing results : 
 
 First. Bile is a slightly alkaline liquid, and as such 
 poured in large quantities into the intestine it overcomes 
 and destroys the acidity of the food as it comes from the 
 stomach, and so prepares the material for the pancreatic 
 digestion, which can only occur in an alkaline medium. 
 
 Second. Bile possesses to a considerable extent the 
 property of emulsifying fats, and so materially assists 
 the pancreatic juice in this function. This property of 
 the bile is derived from the organic bile salts. It has 
 been stated by some physiologists that bile has the prop- 
 erty of splitting up pure fats into fatty acids, and so to as- 
 sist the steapsin of the pancreatic juice in the formation of 
 soaps. The emulsifying power of bile can be readily dem- 
 onstrated by simply shaking up bile and oil, the result of 
 which is a fairly stable emulsion. 
 
 Third. Bile is a mild stimulant and so starts the peris- 
 taltic actions of the intestine. It has been observed that a 
 sudden gush of bile into the intestines will cause a peristal- 
 tic contraction to begin at that point and to creep slowly 
 downward. It would, so to speak, be nature's laxative and 
 the sluggishness of the intestines which follows the with- 
 holding of bile from them, as in various cases of bilious- 
 ness, may be partly explained in this way. This stimulat- 
 ing effect of the bile is again due to the glychocholic and 
 taurocholic acid salts. 
 
 Fourth. It is asserted by some physiologists, but stren- 
 uously denied by others, that bile helps in the absorption 
 of fats. It was first stated that an animal membrane moist- 
 ened with bile would allow fats to traverse it more easily, 
 
DIGESTION AND THE DIGESTIVE AGENTS. 347 
 
 but its validity is questioned. Just how it aids in the ab- 
 sorption of fats can not be told. The fact, however, remains 
 that in an animal in which none of the bile is allowed to 
 reach the intestine, which may be done easily by making 
 a biliary fistula, the fat is not so readily absorbed from the 
 intestine but accumulates there, and it may in large quan- 
 tities be actually lost from the body. By turning the stream 
 of bile back into the intestine and renewing the feeding of 
 fats, at once larger quantities of the fats are absorbed and 
 practically none are passed out. 
 
 We know that the absorption of fat is not a physical 
 process, like the dialysis of sugar through the membrane, 
 but is a physiological process in which the epithelial cells 
 of the intestines actively pick up the fat, and it is probable 
 that the helpful action of the bile in the absorption of fats 
 is due to the direct stimulus which it exerts upon the epi- 
 thelial cells. A stimulus possibly not unlike the one which 
 it exerts upon the muscles of the intestine in arousing them 
 to greater peristaltic activity. 
 
 Fifth. Bile is to a slight extent antiseptic, that is, it 
 destroys, or more properly, retards putrefying changes. 
 Such an antiseptic function has been assigned to it in the 
 intestine. But before calling attention to this antiseptic in- 
 fluence it will be desirable to explain more in detail the 
 reasons for the putrefying changes which occur here. Putre- 
 faction is a process of disintegration, a kind of fermenta- 
 tion caused by bacteria. Such bacteria, however, are not 
 dangerous ones; many are not only harmless, but actually 
 helpful. Such helpful bacteria live in untold numbers 
 normally and regularly in the human intestine. Here in 
 the nutritious contents of the intestine they induce putre- 
 factive changes, the important result of which is a soften- 
 ing and partial disintegration of the food. This softening 
 and partial disintegration no doubt aids materially in their 
 digestion, and without this disintegrating bacterial influence 
 the efficiency of the digestive changes would be very ma- 
 terially impaired. Digestion itself is a sort of disintegra- 
 
348 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 tion, a putrefying process, resulting not only in softening 
 but actually in liquifying foods. It is customary in some 
 portions of the globe to submit meats to a partial decompo- 
 sition with a view of increasing its digestibility, and it is a 
 common procedure in the manufacture of certain forms of 
 cheese to allow them to proceed very far along in the pro- 
 cess of decay in order to render them more digestible (some 
 say palatable) . Similar processes are constantly at work in 
 the intestine, and so in a very short time, acted upon by 
 untold numbers of these bacteria, putrefactive changes en- 
 sue and the food is hurried down the process of disintegra- 
 tion, and by the digestion finally turned into the proper 
 dialyzable form. But however desirable such a softening may 
 be it is absolutely necessary that this decay do not go be- 
 yond a certain stage. If it does, the food entirely disinte- 
 grates and ceases to have any nutritive value whatever. 
 The point, therefore, is to so regulate and control these 
 putrefactive changes that they shall not endanger the nu- 
 tritive value of the foods, but shall stop at the point where 
 the needs of digestion are accomplished. It is believed 
 that the bile exerts such an influence. Thrown into the in- 
 testine in large amounts it acts as a slight antiseptic, check- 
 ing, and so preventing an undue putrefaction. It is an ob- 
 served fact that in animals whose bile is not allowed to flow 
 into the intestine the decaying influences are much greater 
 and putrefaction is excessive. 
 
 5. The Intestinal Juice. As described in the chapter 
 on the anatomy of the digestive system, the mucous mem- 
 brane of the small intestine contains innumerable little 
 glands called the crypts of L,ieberktihn, the secretion from 
 which is called the intestinal secretion or succus entericus. 
 The glands of Brunner play no part in this secretion. They 
 are, as was pointed out, merely escaped peptic glands, and 
 so have no physiological value in the place where they are 
 found. On account of the scantiness of the intestinal se- 
 cretion, it is exceedingly difficult to get this fluid in even 
 
DIGESTION AND THE DIGESTIVE AGENTS. 349 
 
 practical purity. The best success in obtaining it, is made 
 by an operation called a Thiry fistula, which consists in 
 cutting out from the course of the intestine a loop, and then 
 sewing the cut ends together again. In that way the food 
 is again enabled to pass uninterruptedly along the intestine, 
 save that the intestine has been shortened by the loop re- 
 moved. The two cut ends of this loop are then sewed into 
 the abdominal wall so as to connect with the exterior. The 
 nerves and blood vessels of this cut loop are left untouched, 
 and so when food passes along the intestine, secretion is 
 also induced in this separated piece. This secretion is then 
 collected and studied. 
 
 Such a fluid is light yellow and strongly alkaline. It 
 possesses traces of albumin and is a little heavier than 
 water. The alkalinity of this solution is due to the pres- 
 ence of a relatively large amount of sodium carbonate, but 
 the general chemical constitution further than that is not 
 known. In spite of statements by some physiologists to 
 the contrary, there is no satisfactory evidence that the in- 
 testinal juice exerts any action whatever upon proteids or 
 fats. Upon starches it has a slight effect. It contains a 
 ferment much like the amylopsin of the pancreas which 
 changes starch into sugar. However, on account of the 
 scantiness of the intestinal juice this figures very little in 
 ordinary digestion. The important use of the intestinal 
 juice seems, however, to be its action upon the sugars. It 
 contains a ferment capable of converting cane sugar, mal- 
 tose and lactose into ordinary glucose or grape sugar. The 
 sugars which occur regularly in our diet are ordinary cane 
 sugar (the sugar of commerce) , lactose (the sugar in sweet 
 milk), and maltose, the sugar into which the starches 
 eaten have been changed by the ptyalin and the amylopsin. 
 None of these sugars are, however, found in the blood. 
 The sugar in the blood is glucose or grape sugar, and it 
 was long a question just how the sugars of the diet were 
 changed into the sugar of the blood. This change occurs 
 in the wall of the intestine under the action of the intestinal 
 
350 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 juice. It is desirable to point out again that this change of 
 the sugars does not occur in the contents of the intestine. 
 The intestinal juice is too scanty to have much effect there, 
 but occurs while the sugars, which are quite dialyzable, are 
 in the act of passing through the intestinal wall. Here in 
 the mucous membrane moistened with the intestinal juice, 
 cane sugar, maltose and lactose are changed into glucose, 
 and in that form all the carbohydrates eaten reach the 
 blood. 
 
 GENERAL SUMMARY. 
 
 First. The proteids are not affected by the saliva. By 
 the gastric juice they are more or less completely changed 
 into peptones, and by the pancreatic juice the change from 
 proteids into peptones is made complete, save that in the 
 pancreatic digestion some of the peptones are digested still 
 further into compounds called leucin and tyrosin. 
 
 Second. The albuminoids are not affected by the saliva 
 but digested by the gastric juice, and the digestion when 
 incomplete completed by the pancreatic juice. 
 
 Third. The starches are acted upon by the ptyalin of 
 the saliva and partially changed into maltose. In the 
 stomach all action upon the carbohydrates is suspended. 
 In the intestine the ptyalin renews its action, but is aided 
 by the amylopsin of the pancreatic juice and so all the 
 starches are changed into maltose. This maltose, then, 
 together with the cane sugar taken in the food and the lac- 
 tose from the milk, is changed by the intestinal juice into 
 glucose or grape sugar, in its passage through the walls. 
 
 Fourth. The fats are not acted upon by the saliva and 
 are not directly affected by the gastric juice either except 
 to be liberated when surrounded with albuminous envel- 
 opes, but in the intestines they are saponified by the steap- 
 sin and emulsified by the soap so produced, and by the 
 bile. 
 
 Fifth. A number of mineral substances insoluble in 
 water are dissolved in the free hydrochloric acid of the 
 stomach, and in solution reach the blood. At the end of 
 
DIGESTION AND THE DIGESTIVE AGENTS. 351 
 
 the process of digestion, then, we have these resulting com- 
 pounds: First, peptones; second, gelatine; third, glucose; 
 fourth, soaps and emulsified fats. We have now to con- 
 sider in what manner and by what routes these final pro- 
 ducts of digestion reach the tissues of the body. 
 
CHAPTER XV. 
 
 ABSORPTION AND THE ROUTES OF FOOD. 
 
 In the preceding chapter the various changes were fol- 
 lowed by which the undigested foods were transformed into 
 substances which were able to dialyze through the alimen- 
 tary wall into the blood. It was until recently believed 
 that the absorption of all of the foods, with the possible ex- 
 ception of fat, was a mere physical process, and therefore 
 animal membranes were taken to establish experimentally 
 the details of the process. More recent work in this field 
 proves conclusively that we have to do here with something 
 more than mere physical osmosis; something more than 
 mere filtration. We have to do here with living epithelium 
 cells, which in a very active way, and according to physio- 
 logical laws of their own, materially modify the simple 
 physical process. 
 
 No doubt much of the food employed does pass into the 
 blood by simple physical osmosis, but there is reason to be- 
 lieve that by far the largest proportion of the food absorbed 
 is transferred into the system in consequence of the active 
 participation of the living epithelium cells. This will ex- 
 plain why a dead piece of intestine has lost to so great an 
 extent its power to absorb. 
 
 The exact way in which these living cells participate in 
 this absorption we do not at present understand. Simple 
 physical osmosis, however, may be easily studied on dead 
 animal membranes. If, for instance, such a membrane be 
 placed between two liquids of different composition, currents 
 are at once set up through it tending to equalize the com- 
 position of the two fluids, the strength of the currents de- 
 pending upon the dialyzing power of the substances dis- 
 solved. Thus, if on one side of such a membrame a solu- 
 tion of salt be placed,- and on the other side a solution of 
 
ABSORPTION AND THE ROUTES OF FOOD. 353 
 
 sugar, the salt will tend to flow toward the sugar side and 
 the sugar toward the salt side. These currents will con- 
 tinue until finally the composition of both sides is the same. 
 The ease, however, with which substances pass through 
 membranes varies materially and is probably not the same 
 with any two substances. Some, like the soluble mineral 
 salts and sugars, dialyze easily, while others, such as albu- 
 mins, dialyze with great difficulty. But not only do sub- 
 stances in solution pass through the membrane, but the 
 water itself seeps through. Thus, if a solution of salt be 
 placed on one side of an animal membrane and pure water 
 on the other, not only will the salt seep across, but the 
 water from the pure side will flow toward the salt side, and 
 in this way by the dilution of the salt solution an equilibrium 
 is finally established. 
 
 An example of osmosis can be readily illustrated on an 
 ordinary hen's egg. Every one is familiar with the fact 
 that a hen's egg which has been kept a day or two has at 
 its blunt end an air space. This space is enclosed between 
 the two walls of the shell membrane. If, now, the shell 
 and that part of the membrane adhering to it be removed 
 from above the air space, and the egg then partially immersed 
 in water, osmotic currents will set in. Water will tend to 
 flow into the egg and bits of salt and albumin out into the 
 water. But as albumin is practically non-dialyzable, much 
 more water will flow in than albumin out, and so the contents 
 of the egg will increase in size and the partially collapsed 
 shell membrane again be distended as it was in the fresh egg. 
 If these osmotic currents are allowed to continue, the result 
 will soon be that the shell membrane will be burst by the 
 increased pressure caused by the water which the osmotic 
 currents have carried into it. 
 
 When it was just stated that absorption in the alimentary 
 canal has the vitality of the epithelium cells as an import- 
 ant factor, it was not intended to deny the prominent role 
 played by osmotic currents. Thus, a draught of water 
 readily passes into the blood, 110 doubt for the reason that 
 23 
 
354 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 the blood is saltier than the pure water, and so the water 
 in osmotic currents flows into the blood. On the other 
 hand, if sufficient salty water should have been drunk and 
 the contents of the alimentary canal become saltier than the 
 blood, water would run from the blood into the alimentary 
 canal and the thirst be exaggerated. These osmotic cur- 
 rents explain the physiological action of certain salts which 
 are sometimes prescribed by the physician. Such mineral 
 salts, usually Epsom salts, increase the saltiness in the in- 
 testine so greatly that currents of water from the blood pass 
 into the intestine and thus produce the medicinal effects of 
 that drug. On the other hand, if these salts were injected 
 into the blood and the saltiness of the blood thereby materi- 
 ally increased, larger quantities of water than usual would 
 be absorbed from the intestine and so constipation produced 
 or exaggerated. 
 
 To trace out in detail these processes of absorption, it 
 may be desirable to treat of each class of foods separately. 
 It is not necessary to call attention to the absorptive pro- 
 cess in the various portions of the alimentary canal, because 
 experiments conclusively show that practically all the ab- 
 sorption occurs in the small intestine. It seems a little re- 
 markable at first to find that practically no absorption at all 
 occurs in the stomach. Experiments have been made over 
 and over again to show that dialyzable substances, even 
 water itself, are absorbed in very small quantities indeed 
 from the stomach. As a digestive agent it has an import- 
 ant role, but as an absorbing organ it figures little indeed. 
 Experiments have been tried on animals by injecting water 
 into the stomach and keeping it there an hour or more, and 
 then determining how much of it had been absorbed in the 
 meantime. Such experiments show that but a trifling 
 amount is thus absorbed. We have to imagine, therefore, 
 that nearly all of the liquids and dialyzable substances 
 which we take into the stomach and which seem to reach 
 the blood so quickly are at once passed by the stomach into 
 the duodenum and absorbed from that place. Even alcohol 
 
ABSORPTION AND THK ROUTES OF FOOD. 355 
 
 is not readily absorbed. Traces of peptones and sugars, 
 and possibly salts may be absorbed when one speaks mathe- 
 matically, but for practical physiological purposes we have 
 to turn to the small intestine for this function. 
 
 THE ABSORPTION OF THE PEPTONES. 
 
 It will be remembered that the various proteids taken in 
 the body are by the digestive changes of the pepsin and 
 trypsin finally converted into peptones, leaving out of con- 
 sideration for the present small bits of peptones which have 
 been disintegrated still further into leucin and tyrosin. 
 These peptones are dialyzable, and so there seems at first 
 no difficulty in understanding how they might enter the 
 blood. But the difficulty presents itself quite seriously when 
 it is recalled that peptones are not found in the blood any- 
 where, not even in the blood coming directly from the in- 
 testines. Evidently these peptones are changed after leaving 
 the intestine and before reaching the blood. In fact pep- 
 tones injected into the blood are poisonous. The blood 
 coming from the intestines and carrying the absorbed food 
 contains not a trace of peptone, but contains those albumens 
 of the blood treated at length in the chapter on coagu- 
 lation. It is, therefore, evident that the peptones were 
 changed back into albumens in the act of passing through 
 the intestinal walls. Experiments have been made to dem- 
 onstrate this fact. Portions of fresh intestine have been 
 removed from the body, filled with a solution of peptones, 
 and the ends tied. This intestine was then immersed in a 
 liquid containing not a trace of peptones and allowed to 
 remain there until most of the peptones had disappeared in 
 the intestine, but not a trace of peptone was found in the 
 outside solution. Here it was present in the form of albu- 
 mens. It would be interesting to know in what manner this 
 change was effected. Is it due to the action of the epi- 
 thelium cells? Is it a change brought about by the lym- 
 phatic tissue which is so plentiful in the walls of the 
 intestine? These questions are, however, much more easily 
 
356 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 asked than answered. The physiological significance of 
 this change from peptones into the albumens of the blood 
 is apparent. In the first place the peptones act as poisons 
 in the blood. In the second place, being changed back into 
 albumens they are robbed of their dialyzing power, and so 
 there is prevented, possibly, the loss of the albumens in 
 kidneys or glands, or even back again into the intestine, for 
 peptones would dialyze into the intestine as easily as out 
 of it. 
 
 THE ABSORPTION OF THE SUGARS. 
 
 No serious difficulty presents itself in understanding the 
 absorption of the sugars. By the digestive actions of the 
 ptyalin and the amylopsin, all the starches are changed 
 to maltose, and finally by the action of the ferment in the 
 intestinal juice all the various sugars taken in our diet, and 
 the maltose derived from the starch are changed into dex- 
 trose or grape sugar in their passage through the abdominal 
 wall. In the form of dextrose it reaches the blood, and by 
 the portal circulation is carried to the liver, where it is 
 affected in a manner soon to be described. 
 
 THE ABSORPTION OF THE FATS. 
 
 A greater difficulty presents itself in understanding the 
 absorption of fats. That portion of the fats which is 
 saponified and so rendered soluble (for soaps are soluble), 
 will readily dialyze into the blood, but most of the fat is ab- 
 sorbed in its solid form; that is, in the form of finely 
 emulsified droplets. A histological examination of the 
 small intestine during fat-absorption shows droplets of fat 
 in the epithelium cells, between them, and even under them, 
 reaching into the lacteals. It is, of course, out of the ques- 
 tion here to speak of physical osmosis. Droplets cannot 
 filtrate. We are driven to the conclusion that it is the 
 epithelium cells that line the intestine which actively pick 
 them up; that is, ingest these droplets of fat into their 
 bodies, pass them along through their protoplasm, and 
 finally eject them again from the under side into the spaces 
 
ABSORPTION AND THK ROUTES OF FOOD. 
 
 357 
 
 leading to the central lacteal. The droplets of fat are 
 pushed in some inexplicable way through the epithelium 
 cells towards the central lacteal. Possibly the epithelium 
 cells pick up these droplets of fat much as the amoeba picks 
 up its food. 
 
 Additional factors in fat absorption are the white cor- 
 puscles, so plentifully distributed in the wall of the intes- 
 tine. It is believed (and there is fairly good histological 
 evidence for this belief) that the corpuscles wander in be- 
 tween the epithelium cells, ingest particles of fat like an 
 amoeba, and then wander back through the interstices of 
 the tissue and drop their load of fat into the central lacteal, 
 accomplishing this by disintegrating themselves and so lib- 
 
 Fig. 126. SECTION- OF A FROG'S INTESTINE TREATED WITH OSMIC ACID TO SHOW AB- 
 SORPTION OF FAT. (After Schafer.) 
 I, lacteal; c, white corpuscles with contained fat granules; ep, intestinal epithelium; 
 
 Kt>\ its striated border. The fat granules become smaller and smaller as they approach 
 
 the lacteal. 
 
 crating their contained fat. On sections of the villi one 
 may frequently see these white corpuscles with contained 
 fat droplets in all positions ranging from between the epi- 
 thelium cells to the central lacteal. 
 
 But all the fat suffers a peculiar change in its passage 
 into the lacteal. In the intestine it was in the form of drop- 
 lets. In the lacteal it is in the form of small particles as 
 fine as the finest dust. But not only this mechanical change 
 has occurred; there has been a chemical one. In the lac- 
 teal the fat is not present as butter, or lard, or tallow, 
 forms in which it was taken in the food, but has been 
 
358 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 changed into that peculiar form of fat characteristic of the 
 animal which has eaten it. In the human body these dust 
 particles of fat in the lacteal are now no longer butter and 
 lard, but are human fat. As with so many other things we 
 still have no knowledge of the manner in which this chemi- 
 cal change is effected. It may be in place to call attention 
 to the fact that but little fat reaches the blood vessels. 
 Practically all of it is carried by the lacteal. These vessels 
 owe their name to the circumstance that after a meal they 
 are usually filled with a white milky substance, the particles 
 of fat in question. It was formerly believed that they ab- 
 sorbed all the food, and so were erroneously called absorb- 
 ents. We know that the proteids, and the sugars, and the 
 albumens are carried by the portal circulation to the liver. 
 
 It has been pointed out by some physiologists that pos- 
 sibly the involuntary muscular tissue found in the villi of 
 the intestine produces a kind of contraction and expansion 
 of each villus, and so the central lacteal is enabled to suck 
 or force the fat into itself. These contractions of the villi, 
 they hold, may be due to the stimulation caused by the bile, 
 and in this way they explain the observed fact that bile 
 seems to aid in the absorption of fats. Through these lac- 
 teals the fat is carried towards ,the thoracic duct, and by 
 this poured into the left subclavian vein and so distributed 
 by the circulation. The further changes which this fat 
 undergoes will be discussed later. 
 
 The various salts, the water and the albuminoids in the 
 form of gelatin, present no difficulties in their absorption 
 and need not be further treated. 
 
 When finally all foods have been absorbed the following 
 is the state of things : 
 
 First. The peptones changed back into the albumens 
 are carried by the portal circulation to the liver. 
 
 Second. All the sugars changed into dextrose, are also 
 carried by the portal circulation to the liver. 
 
 Third. The various salts and the water drop into the 
 portal circulation largely; possibly, also, the soluble soaps, 
 the glycerine and the albuminoids. 
 
ABSORPTION AND THE ROUTES OF FOOD. 359 
 
 Fourth. The emulsified fats changed physically and 
 chemically are carried by the lacteal and thoracic duct and 
 dropped into the general circulation. 
 
 We have now to consider the physiological consequence 
 of the transfer of these sugars and proteids to the liver be- 
 fore reaching the circulation at large. 
 
 THE GENERAL PHYSIOLOGY OF THE LIVEE. 
 
 Some of the most important functions of the liver are in 
 connection with the phenomena of general assimilation, and 
 a discussion of the liver from this standpoint is reserved for 
 the next chapter. We have to do in this connection only 
 with the function of the liver as it affects the proteids and 
 the carbohydrates in their passage through it into the body. 
 
 1. Glycogenic Function. The most apparent function 
 of the liver, and one of the most important as well, is its 
 formation of glycogen. Glycogen resembles very much 
 ordinary starch in many particulars, and is, in fact, fre- 
 quently called animal starch. The liver forms this gly- 
 cogen by changing the dextrose carried to it by the portal 
 vein, into this compound. The point to the formation of 
 this glycogen is the ability of the liver to store this sub- 
 stance in its cells and then to dole it out to the blood from 
 time to time as it is needed. It would, of course, be prac- 
 tically impossible to store in an organ flushed with circula- 
 ting blood dialyzable dextrose, but by changing the dextrose 
 into an insoluble starch like glycogen it is easily retained. 
 
 The question might naturally arise concerning the ne- 
 cessity of storing any of the dextrose at all, and the objec- 
 tions to having all of it pass into the general circulation at 
 once. These questions are readily answered. In the first 
 place, quite a large amount of each meal is carbohydrate 
 food, and if all this in the form of dextrose should be in- 
 jected into the blood at once it would materially alter the 
 composition of the blood and so lead to nutritive disturb- 
 ances. The prime necessity of the blood is a practically 
 uniform composition. In the second place, such largely 
 
360 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 increased amounts of sugar in the blood would lead to dia- 
 betic results in the kidneys, for it is a commonly observed 
 fact among physicians that an excess of sugars soon reveals 
 itself by a sugary elimination from the kidneys. To avoid 
 both of these dangers all the excess of sugar immediately 
 after a meal is stored in the liver, and observations have 
 been made on the human liver showing that the amount of 
 glycogen so stored may reach 10 per cent, of the weight of 
 that organ. Then during the interval between this meal and 
 the following the liver doles out from time to time this glyco- 
 gen, and so serves to maintain the uniform composition of 
 the blood, adding the glycogen to it as fast as the sugar is 
 used by its tissues. This addition to the blood is, however, 
 not made in the glycogen itself, but this is converted back 
 into dextrose in the liver, and in that form sent into the 
 blood. 
 
 This glycogen may be readily detected. It may be seen 
 microscopically in the liver cells in the form of clear lumps, 
 which when treated with iodine give the chemical test for 
 glycogen. Every chemical student is familiar with the 
 fact that the usual reaction to detect the presence of starch 
 is to treat the same with a solution of iodine. The starch 
 will at once turn a very deep blue. Glycogen, however, 
 does not turn a deep blue, but turns a wine red color, and 
 in this way is easily detected. Unlike starch, too, it is 
 somewhat soluble in water; more readily soluble in hot 
 water, and by this means the glycogen may be readily ex- 
 tracted from minced liver. 
 
 It will be seen, therefore, that the liver is a kind of 
 store-house, keeping a temporary reserve supply of glycogen 
 to be used up in the intervals between meals. It is, to use 
 a common figure, the pocket change to supply the daily 
 needs of the tissue. It is quite interesting to note that the 
 liver is not the only organ in the body which is thus able to 
 take sugar out of the blood and store it up within itself as 
 a reserve supply in the form of glycogen. Glycogen is 
 found in other parts of the body. In white corpuscles, in 
 
ABSORPTION AND THE ROUTES OF FOOD. 361 
 
 the placenta, but especially in the voluntary muscles. 
 These voluntary muscles seem to be able to take some of 
 the sugar out of the blood and store it up as glycogen 
 within themselves as a reserve supply to fall back upon in 
 times of activity. A muscle which has been working for 
 some time loses all its glycogen. This reserve supply has 
 been used by the muscle to build up its tissues. It is an 
 attempt of these organs to have at their immediate disposal 
 a certain reserve supply without being directly dependent 
 upon the blood-stream at critial moments. The difference 
 between the voluntary muscles and the liver, however, is 
 that the reserve supply of glycogen in the muscles is in- 
 tended merely for the use of the muscles, while the liver 
 acts as a temporary storehouse for the entire system. 
 
 We have now followed the sugar into the liver, watched 
 its change into the animal starch called glycogen, saw it 
 stored in the liver cells and between meals doled out again 
 to the blood as sugar. What further change this sugar suf- 
 fers in the circulation and in the tissues to which it has been 
 carried will be discussed in the chapter on nutrition. 
 
 2. The Albumens. The albumens, too, are carried to 
 the liver. One might be tempted at first to suppose that 
 the sudden excess of albumens also is stored here, and then 
 like the sugar is dropped back into the blood as necessity 
 requires. But there is no place in the body where albu- 
 mens can be stored. All the albumens available are in the 
 circulating blood and lymph. Fats may be stored in fatty 
 tissue and remain stored there for a long time. Sugars 
 may be temporarily stored in the liver, but there is no 
 storehouse for the albumens. These must drop into the 
 general circulation at once. Here, however, the danger 
 would present itself of increasing excessively the amount of 
 albumens in the blood after a meal, and so producing 
 nutritive disturbances here as well as with the sugars. 
 Even a greater danger might ensue. The accumulating 
 albumens of the blood might begin to be eliminated from 
 
362 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 the kidneys and so induce B right's Disease in some of its 
 forms. The point, therefore, is to regulate in some way 
 the amount of albumens in the blood to avoid this excess. 
 
 As the albumens cannot be stored but one alternative is 
 left. They must be destroyed as albumens. This de- 
 struction takes place in the liver. Here the excess of the 
 albumens is broken up; that is, disintegrated chemically 
 into two main products. One product contains the nitro- 
 gen of the albumen and is the urea, which is then sent to 
 the kidneys to be eliminated. The other part is a non- 
 nitrogenous part, and is by the liver changed into fat or 
 sugar, or both, and so made possible to be retained in the 
 body. Whether this non-nitrogenous portion of the excess 
 albumen is changed to sugar or to fat seems to depend to 
 some extent upon the disposition of the animal in this 
 matter. In breeding animals for fattening purposes special 
 attention is paid to this fact, and those animals are selected 
 which, as we say "fatten easily, " and so a race finally 
 comes to be, every member of which shows a tendency to 
 convert all extra albumens into fat. In many instances, 
 however, there is a tendency towards the formation of 
 sugar, and so in spite of the richest diet but little headway 
 is made in laying up fat. If this excess is turned into 
 sugar in the liver it may, of course, at once be changed 
 into glycogen and so stored for future purposes. If it is 
 changed into fat it is dropped into the general circulation 
 and distributed over the body. 
 
 We have thus far, then, found two sources of the gly- 
 cogen in the liver. The first and main source, the sugars 
 of the body; second, a derivative from the excess proteids. 
 It does not seem possible that the fats are able in any way 
 to be changed into the glycogen. This change of the pro- 
 teids by their disintegration ^or burning in the liver into 
 urea and into glycogen, has a medical value in the fact 
 that persons suffering with diabetes must not only avoid the 
 carbohydrates, but must be equally careful not to take an 
 excess of ordinary proteids lest the formation and loss of 
 
ABSORPTION AND THE ROUTES OF FOOD. 363 
 
 the sugar continue. That portion of the proteids taken 
 which is needed to maintain the proper composition of the 
 blood is then without change of any kind allowed to pass 
 through the liver and added to the general blood stream. 
 
 The thing in the albumens which makes them impos- 
 sible to be stored is the nitrogen they contain. This nitro- 
 gen, as pointed out, is burned into the substance called 
 "urea," is then allowed to drop back into the blood stream, 
 and from this blood stream it is eliminated by the kidneys. 
 The liver is therefore the seat of the urea formation. But 
 it may be well at this place to point out that there is a 
 second source from which the liver makes its urea. This 
 second source is from the burned up tissues. Various pro- 
 ducts of tissue disintegration (and tissues are largely al- 
 buminous) reach the liver, and by the liver are burned into 
 urea and then sent to the kidneys, as in the first case. The 
 source of the urea is therefore a double one ; one directly 
 from the burning of the excessive albumens in the liver, 
 the second from the burning of tissue wastes sent to the 
 liver from all the organs of the body. The liver is, there- 
 fore, not only a storehouse, it is to some extent also a cre- 
 matory for the nitrogenous wastes. 
 
 The final state of things is then as follows : 
 First. Definite amounts of the albumens have been 
 allowed to pass through the liver and circulate in the 
 blood. 
 
 Second. Quantities of dextrose or grape sugar are from 
 time to time doled out from the reserve supply of glycogen 
 in the liver and dropped into the blood stream. 
 
 Third. Into this blood stream are carried all the fats 
 absorbed by the lacteals. 
 
 Fourth. In this blood, too, are the various mineral 
 salts and the water taken in the foods. 
 
 The question which now presents itself is, in what 
 manner are these nutritive factors of the blood used by the 
 
364 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 tissues ? How are the tissues able to grow by taking these 
 substances ? How are they able to derive energy and 
 warmth from these sources? We are therefore ready to 
 follow somewhat in detail the phenomena of assimilation in 
 the tissues themselves. 
 
CHAPTER XVI. 
 
 NUTRITION AND THE METABOLIC CHANGES 
 IN THE TISSUES. 
 
 The scene of activity is now shifted from the alimentary 
 system, from the liver, and even from the circulating blood 
 and directed to the individual living cells wherever in the 
 body they may occur. Here the most vital part in the his- 
 tory of the foods is played; it is here where the food is 
 built into new tissues ; it is here where the energies of the 
 body are liberated. 
 
 A number of perplexing questions at once present them- 
 selves, the solution of which in every case is not yet forth- 
 coming. Are all of the foods taken into the body built up 
 into living tissue, or are some of them merely oxidized 
 without ever becoming an integral part of the body ? Is 
 the energy derived by a direct oxidation of these foods, or 
 is the energy a result of the disintegration of living ma- 
 terial ? When oxygen and its properties were first dis- 
 covered by Priestly and Lavoisier, the conclusion seemed 
 irresistible that the oxidations of the body occurred in the 
 lungs. According to this view it was explained that the 
 animal heat originated here, and was by the circulating 
 blood carried over the body, and in this manner the neces- 
 sary energy for bodily work distributed. It was, however, 
 soon found that the blood coming from the lungs was not 
 warmer than that going to the lungs, and so this view had 
 to be abandoned. The seat of oxidation was later placed 
 in the blood, then in the liver, then in other organs; but 
 there is no question at all now but that the seat of oxidation 
 is in the individual living cells in the various tissues all 
 over the body. It is in the living tissues where the union 
 of the foods and the oxygen occurs. 
 
 (365) 
 
366 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 One of the most vital questions is whether these living 
 cells can take some of the food out of the blood or lymph, 
 and with the oxygen from the lungs produce an oxidation 
 and so derive heat and energy for their own use. In other 
 words, do these cells manipulate the foods like the fireman 
 manipulates his coal? If so, how is the heat of such an 
 oxidation transformed into the kind of energy needed, be 
 it motion or be it chemical changes in secretion ? Or may 
 not the foods from the blood and the oxygen from the lungs 
 be built up in the living cells into living tissues, and then 
 by the burning up or chemical disintegration of this living 
 matter the energy, liberated ? To use a not very close 
 analogy, are the foods in the body burned like the coal in 
 the furnace to heat the rest of the house, or are the foods 
 like weather-boards, shingles, rafters and floors built into 
 the structure of the house, and then by partial oxidation 
 heat the house ? Does the body maintain its equilibrium 
 of temperature and derive its supply of energy out of its liv- 
 ing supply, or from the external foods? 
 
 Of course there is no question at all as to what happens 
 to some of the foods when the body is growing. Evidently 
 they are built up into new tissues. The increase in weight 
 and size from infancy to maturity is such a magical trans- 
 lation of dead food matter into living tissue. The question 
 is here merely, are all the foods treated in this way, or may 
 a part be used merely for fuel purposes. Unfortunately 
 physiologists seem unable to agree on this point. There 
 are not lacking some who maintain, and apparently with 
 good evidence, that a large part of the food is directly oxi- 
 dized in the tissues under the influence of the living cell 
 without that food ever becoming an integral part of those 
 cells. They maintain that a proportion of the food circula- 
 ting in the blood circulates as fuel, while another part, not 
 different in kind, however, is destined to be built up into 
 tissue. They look upon the problem of nutrition as an in- 
 stance of the carpenter who uses part of his lumber to con- 
 struct his building and a second part of the lumber to burn 
 
NUTRITION AND THE CHANGES IN THE TISSUES. 367 
 
 in his furnace to heat the building. According to this view 
 the proteids or albumens of the blood are looked upon as 
 the source of the new tissues, while the remaining albu- 
 mens not so needed, and the fats and carbohydrates are 
 used for direct oxidation purposes only. 
 
 Acknowledging that we are not yet able to answer 
 definitely these intricate questions, there seems a good 
 deal of probability that this view is not entirely correct. 
 Repeated and careful experiments seem to lead to the con- 
 clusion that under normal circumstances all of the foods are 
 first built into living tissue and then oxidized. The marked 
 exception to this is in the case of excessive proteids taken 
 into the body, which since they cannot be stored and must 
 be eliminated, must be burned in the liver in the manner 
 indicated in the preceding chapter. Here, of course, is a 
 clear instance of a food directly oxidized by the living cells 
 of the liver without ever becoming an integral part of that 
 tissue. But it would hardly be right to look upon this ex- 
 cess of proteid as a food. Its very disintegration argues 
 that it was not intended as a food but was eliminated as an 
 injurious ingredient. The normal amount of proteids, how- 
 ever, of the blood, as well as the sugars and the fats, and 
 of course the oxygen, must all be looked upon as tissue 
 formers. But with the exception of certain special tissues in 
 the body, such as the supporting tissues, all are essentially 
 albuminous in their nature, and it seems at first difficult to 
 understand how the fats and the sugars, which are not at 
 all albuminous, containing no nitrogen whatever, could 
 possibly be built into living tissues which are albuminous, 
 that is, contain nitrogen. 
 
 In the case of the proteids this difficulty is absent. We 
 must imagine a peculiar constructive chemical process 
 going on in the living cell by means of which the proteid 
 from the lymph, possibly with some salts, is combined with 
 the oxygen and built up into some highly complex sub- 
 stance which we call protoplasm. Just as in the manu- 
 facture of gunpowder the charcoal and the oxygen contained 
 
368 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 in the nitre, together with the other substances, are mixed 
 together in such a way as to hold a large amount of latent 
 energy. Gunpowder possesses enough oxygen within itself 
 to burn itself up completely. In fact, it is this intra-molar 
 oxidation which is the explosion. Gunpowder explodes be- 
 cause in every part of its substance there is enough oxygen 
 present to burn up the other ingredients. 
 
 So we must imagine that the living cell is able in some 
 at present entirely inexplicable way to take dead proteid 
 and salts and to combine these with the oxygen from the 
 lung in such a way that a kind of living gunpowder pos- 
 sessing much latent energy is produced. This view of the 
 use of the oxygen from the lung changes completely the 
 current notion. Usually we speak of the necessity of get- 
 ting more oxygen in exercise in order that there may be a 
 larger supply of this gas to burn up the tissues and so pro- 
 duce the energy. According to this view (and there is 
 every probability that it is the correct one) the extra de- 
 mand of the oxygen in exercise results from the necessity 
 of building up new living tissue, of making new living gun- 
 powder to replace that which has been used up in the exer- 
 cise in question. The oxygen, then, is not the cause of the 
 liberation of the energy; it is the result. Just as in a bat- 
 tle there would be greater demands for fresh supplies of 
 gunpowder to replace the increased amounts being used up. 
 
 This constructive building up of proteids and oxygen 
 into living matter does not present the difficulties which at 
 once appear when we think of the sugars and the fats. The 
 question arises, in what manner do these foods figure? In 
 the first place it is well to remember that according to this 
 view proteids alone can build up new tissue. Sugars and 
 fats by themselves cannot do so. Of course such a thing is 
 a chemical absurdity. We must therefore credit to the pro- 
 teid every bit of new tissue that appears, and imagine its 
 appearance in the manner just indicated. 
 
 The main characteristic of living tissue is its ability 
 to do some kind of work. Life in this sense is energy, 
 
NUTRITION AND THK CHANGES IN THE TISSUES. 369 
 
 either stored up or in action. When, now, these tissues 
 are called upon for work of any kind the energy to accom- 
 plish this is derived from the chemical disintegration of a 
 part of its living tissue, just as energy might be derived 
 by the chemical disintegration of a bit of nitro-glycerine. 
 We have therefore to look upon all manifestations of the 
 energy in the body, be it muscle, or nerve, or gland, as 
 a disintegration and burning up and dying of a part of 
 this tissue. In such a chemical disintegration a good deal 
 of energy is liberated, partly in heat to maintain the tem- 
 perature of the tissues, or in the case of the muscles, in 
 additional energy to contract them. The products of such 
 a chemical disintegration are mainly as follows: 
 
 The carbon of the living tissue appears as carbon dioxide COz 
 
 The hydrogen as water HaO, 
 
 And the nitrogen in the form of a compound closely related 
 to urea. 
 
 The carbon dioxide is of course at once removed through 
 the lungs in the manner explained at great length in the 
 chapter on respiration. The water drops into the blood and 
 is so lost track of, but the urea-like product, this remnant 
 which contains the nitrogen of the living molecule, is not 
 lost from the tissue, but is retained. The living cell which 
 retains this nitrogenous remnant of the disintegration is 
 able to use this remnant again to build up 'new living tis- 
 sue. It is able to use the same nitrogen over again and 
 needs only a new supply of carbon, hydrogen and oxygen 
 to replace the amounts of these substances lost in the car- 
 bon dioxide and the water. This supply of carbon, hydro- 
 gen and oxygen it is able to take from either the fats or 
 sugars of the blood and the oxygen constantly brought from the 
 lungs. The living cell is able to re-combine the nitrogenous 
 remnant with the carbon, oxygen and hydrogen derived 
 from the sugars or fats, and an added amount of oxygen 
 from the lungs into a new living tissue molecule having the 
 same composition as the original. This molecule may 
 again under nervous or other influences be dissociated and 
 24 
 
370 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 so give rise to the liberation of new energy, carbon dioxide 
 and water being the result, as in the first case, but the ni- 
 trogenous remnant being again saved and by combination 
 with new fats or sugars and the oxygen from the lungs, be 
 built for a second, a third, or fourth time into living tissue. 
 If this view is correct it would explain why the loss in nitro- 
 gen does not vary with the work, a man resting eliminating 
 from his body about as much as a man working. 
 
 When it is said that the nitrogenous remnant is saved, 
 there is to be added that a small portion of this nitrogenous 
 remnant, however, is lost; some possibly accidentally car- 
 ried away by the circulating fluid, some possibly chemically 
 unfit to be used again. It is this little loss, this wear and 
 tear, which is sent to the liver and in the liver is burned 
 into urea and then eliminated from the kidney. But this 
 wear and tear may almost be as much in a resting person 
 as in an active person, just as the wear and tear of an en- 
 gine that is in proper use may not exceed the wear and tear 
 of an engine standing idle on the sidetrack. 
 
 Some interesting experiments have been made showing 
 that the loss of the nitrogen from the body is not at all 
 proportional to the work done. Persons have ascended 
 mountains and during the period of such exertions, as well 
 as before and after, careful quantitive determinations were* 
 made of the amount of urea eliminated from the kidneys. 
 It was found that even in such laborious work as mountain 
 climbing the nitrogenous loss from the body was not pro- 
 portionately larger, in fact hardly materially larger than the 
 loss while resting. On the view just given of the manner 
 in which the nitrogen is used over and over again this is 
 readily understood. 
 
 The amount of carbon dioxide produced, and of course 
 the water, is however, directly proportional to the amount 
 of work done. At each chemical disintegration a certain 
 amount of carbon, oxygen and hydrogen is lost, which must 
 be replaced in the next constructive process by an equal 
 amount of new material. Evidently, therefore, the amount 
 
NUTRITION AND THE CHANGES IN THE TISSUES. 371 
 
 of this carbon, hydrogen and oxygen will be proportional to 
 the amount of work done. This at once explains, too, 
 the increased breathing of oxygen with increased exertion, 
 and also explains the necessity for increased amounts of food 
 with increased exertion. 
 
 But such an increase of foods need not at all be proteid, 
 but may be fatty or carbohydrate. Of course a certain 
 amount of proteid is absolutely indispensable, since proteid 
 alone can replace the slight wear and tear just referred to. 
 To eat more proteid food than necessary to replace this loss 
 simply necessitates the body to eliminate it. In physiolog- 
 ical terms we speak of a person or animal as being in a pro- 
 teid equilibrium when the nitrogen taken in his foods equals 
 in amount the nitrogen eliminated from the kidneys. In 
 the same way we speak of a person as being in a carbon 
 equilibrium when the carbon taken in his foods is equal to 
 the carbon eliminated from his lungs. If more is eliminated 
 than is taken in in any of these cases starvation and emacia- 
 tion are the result. If more of these foods is taken than is 
 needed one or both of two results may follow: Some of 
 the surplus food, as for instance the fat, may be stored in 
 the tissues for future use and so the person become fat, in 
 the ordinary use of that term; or secondly, the nutritive 
 equilibrium of that individual raised to a higher level. This 
 needs a word of explanation. It is possible in a long con- 
 tinued diet to establish a nutritive equilibrium at an almost 
 starvation diet. The tissues of the body will adjust them- 
 selves to the income, and finally establish an equilibrium at 
 that level. This means that the losses will exactly balance 
 the gains and the body will seem to hold its own. If, now, 
 the amount and quality of the foods be suddenly increased, 
 there is at first a tendency of the body to eliminate these 
 extra foods, especially the proteids, but finally the tissues 
 will adjust themselves to the new order of things, will use 
 up increased quantities of food in their daily work, until 
 finally a new nutritive equilibrium is established. As a sim- 
 ple analogy an illustration may be taken from the social 
 
372 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 world : Persons are able to maintain a financial equilibrium 
 with a small income, but there is no difficulty at all in soon 
 adjusting one's self to an added income and so establishing 
 an equilibrium on a higher level. 
 
 But this does not always mean that when a body is not 
 losing in weight it is holding its own in the fullest sense. 
 It is doing so at a low nutritive level, but it is still starva- 
 tion, and the general beneficial effects that are recognizable 
 in a community of well-fed people clearly argues the physi- 
 ological necessity of establishing in a healthy body at least a 
 medium, still better, a high nutritive equilibrium. 
 
 These metabolic changes and the final products have 
 been fairly well determined only in the case of muscular 
 tissue. What the final chemical changes are in glands 
 ganglia and in nerve fibers, is still a wholly closed book. 
 However, from a merely physical and chemical standpoint 
 the energies liberated by the muscles are by far the bulk of 
 the body's whole expenditure. 
 
 By way of summary, then, we have to ascribe to the 
 main classes of foods these nutritive values: 
 
 First. Proteids. (a) All new tissue, that is, all living tis- 
 sue which has not replaced the old, but is an actual addition, 
 can only be built up from the proteids of the blood and lymph. 
 Hence the somewhat larger proportion of proteids needed 
 in the diet of animals which are in the growing period. 
 (b) Excesses of proteids are broken up in the liver into a 
 non-nitrogenous portion which may appear there as sugar 
 or as fat, and a nitrogenous portion appearing as urea. The 
 sugar or fat so produced from these proteids will then figure 
 just as the other fats and sugars. 
 
 Second. The Albuminoids. These do not figure in an 
 important way, and it is highly improbable that the nitro- 
 gen which they contain can in any material way be utilized 
 like the nitrogen of proteids. Probably the albuminoids 
 figure in the same role as the sugars and the fats. 
 
 Third. TJic Sugars and the Fats. These are the non- 
 
 <D 
 
 nitrogenous foods, but in the tissues these non-nitrogenous 
 
NUTRITION AND THE CHANGES IN THE TISSUES. 373 
 
 foods are combined under the influences of the living cell 
 with the nitrogenous remnant there of a previous disintegra- 
 tion, and so built up into living tissue. These sugars and 
 fats supply that part of the food which in the disintegration 
 of the living tissue is lost ; they supply the carbon and the 
 hydrogen. As these, therefore, cannot be used a second 
 time, new amounts of sugars or fats must be taken to replace 
 them. In this way the consumption of sugars and fats of 
 the blood must be proportional to the amount of work done. 
 Of course, if sugars and fats are not given in sufficient 
 amounts, or are excluded altogether, the body is able to 
 derive this oxygen, carbon and hydrogen from proteids 
 alone. But then this great excess of proteid must be first 
 dissociated in the liver, and so sugar or fat produced, and 
 these be the immediate foods of the tissues. Carnivorous 
 animals can live upon a diet of meat alone, and in such cases 
 the quantity of meat will, to a large extent, be proportional 
 to the work done. But the proportion is not in the nitrogen 
 which it contains, but in the carbon and hydrogen which 
 are needed. 
 
 An ideal physiological diet, therefore, is one that con- 
 tains enough proteid to replace the wear and tear of the 
 body on a high nutritive equilibrium, and then has the car- 
 bohydrates and fats as the sources from which the carbon 
 and hydrogen are derived. Increased work, therefore, would 
 demand not primarily an increase in the proteids, but would 
 at once demand a proportional increase in the fats and 
 sugars. 
 
 It was pointed out that a little of the nitrogenous rem- 
 nant which results from the disintegration of a part of the 
 living cell is lost, possibly accidentally, more probably be- 
 cause it is no longer fit to be used. This nitrogenous rem- 
 nant no longer retained by the cell is dropped into the blood 
 and is by the blood carried to the liver. This substance 
 appears in several different stages of oxidation and is known 
 to the chemist as kreatin or kreatinin. This kreatin aris- 
 ing in the tissues of the body and carried to the liver by the 
 
374 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 blood is ill the liver burned still further into urea, and then 
 sent to the kidneys to be eliminated. 
 
 We have thus seen two sources of urea in the body, one 
 derived from the immediate burning up of the excess pro- 
 teids in the liver, the other derived from the kreatin and 
 similar compounds of the tissue destruction. But the for- 
 mation of this urea occurs in both cases in the liver. The 
 kidneys take no part whatever in the production of this sub- 
 stance, but are concerned wholly and only with its elimina- 
 tion. When the diet is naturally rich in the proteids, and 
 when, therefore, increased amounts of these urea-like sub- 
 stances appear in the blood, the kidneys are frequently un- 
 able to eliminate this from the body as rapidly as it is being 
 formed, and so there is a tendency towards the accumula- 
 tion of uric compounds in various parts of the body, especi- 
 ally at the joints, producing the somewhat aristocratic 
 disease called the " gout." These uric poisons in the blood 
 serve to irritate the tissues and so produce quite abnormal 
 conditions. The remedy is, of course, the removal of these 
 poisonous salts from the blood. One of the best agents in 
 the physician's hand is some form of salicylic acid, in which 
 these salts are soluble, and which when taken into the blood 
 tends to dissolve them out of the tissues. Along with such 
 tendencies to gout the increased demands made on the kid- 
 neys may finally result in the impairment of their energies, 
 and so Bright 's Disease be induced, a disease alarmingly 
 frequent among persons addicted to a luxurious table. 
 
 Whether the familiar rheumatism is due to an accumula- 
 tion of metabolic products in the blood is still unsettled. 
 Some look upon it as a disease due to germs, others as a 
 cold affecting nerve centers, and by still others, and possi- 
 bly most, as a result of the accumulation of lactic acid in 
 the blood. It has even been claimed by one observer that 
 it was possible to produce rheumatism artificially by an in- 
 jection of lactic acid into the system. 
 
NUTRITION AND THE CHANGES IN THE TISSUES. 375 
 THE INTER- RELATION OF THE FATS AND CARBOHYDRATES. 
 
 It was of course long known that a proteid diet might 
 result in the fattening of an animal; also that proteids 
 might give rise to sugar. It has been an important but 
 difficult question whether the carbohydrates ever give rise 
 to fats; whether a sugary diet leads directly to the produc- 
 tion of fatty tissues. Until very recently it was almost uni- 
 versally held that the carbohydrates could not form fats in 
 the body, and that the fattening resulting from adding a 
 carbohydrate food was due merely to the saving of fats, 
 these being substituted for them. Just as on the dinner 
 table it might be possible to produce an accumulation of 
 bread by having plenty of pie. Of late, however, investi- 
 gations have been made which seem to show that carbohy- 
 drates in the body may be changed into fats and so stored. 
 Attention is here called to this claim since it is possible 
 that future observations may establish its correctness; but 
 the point remains that in spite of these claims there is much 
 evidence that fats are never the direct result of the sugars 
 or the sugars of the fats, and that there is in, no way a 
 direct causal relation between them. 
 
 No attention has been given to the nutritive importance 
 of the water and the salts. It has not been deemed neces- 
 sary to go into detail here. Water is the general solvent of 
 the body and the medium in which the cells live, and as 
 such is absolutely indispensable. The salts, -too, are neces- 
 sary parts, frequently being directly used in the formation 
 of tissues, as in the case of bones and red corpuscles, or 
 directly serving an intermediate function in the process of 
 osmosis or solution. 
 
 The attempt has been made in the chapter to try to pic- 
 ture the phenomena which take place in the individual liv- 
 ing cells while these cells are in growth or action. We 
 have now to determine somewhat more quantitatively the re- 
 sults of the energy so derived, the purposes of this energy, 
 especially that of the temperature of the body, and finally 
 the manner in which this temperature is maintained at a 
 steady and fixed level under normal conditions. 
 
CHAPTER XVII. 
 
 THE MAINTENANCE OF THE ANIMAL HEAT. 
 
 As long as the body is alive heat is being produced in 
 it. Even a muscle that may be showing not a bit of con- 
 traction is nevertheless developing a certain amount of heat. 
 Heat is a constant product of the transformation of energy 
 in the body. The most noteworthy fact in examining this 
 heat-production is its steady maintenance under normal 
 conditions. Thus the temperature of an average adult is 
 about 37 l lioC.) and this temperature is maintained through 
 summer, through winter, and through all of the vicissitudes 
 of every-day life with almost mathematical exactness. 
 
 Animals which have such a constant temperature are 
 spoken of as homothermous ; that is, as the etymology of 
 the word shows, of constant temperature. Animals pos- 
 sessing a constant temperature have one which is usually 
 above the temperature of their surroundings. They are 
 warm-blooded. This is true of nearly all the higher ani- 
 mals. As we descend the scale, however, this condition 
 changes, and we find the temperature of the lower animals 
 determined almost wholly by their immediate environment. 
 Their temperature rises or sinks with the temperature of 
 their surroundings. Such animals are called poikilother- 
 mous\ that is, of several temperatures. More frequently 
 such animals are spoken of as cold-blooded animals, but it 
 not infrequently happens that the temperature of such a 
 cold-blooded animal may even be higher than that of a 
 warm-blooded animal, provided the medium in which it 
 lives rises above that temperature. Examples of cold- 
 blooded animals are the fishes, amphibians and reptiles. 
 (376) 
 
THE MAINTENANCE OF THE ANIMAL HEAT. 377 
 
 VARIATIONS IN TEMPERATURE. 
 
 The temperature of warm-blooded animals is not abso- 
 lutely constant by any means. Thus, mammals which go 
 into a winter sleep, hibernate, as we say, have their tem- 
 perature sink several degrees, in this way approaching some- 
 what the cold-blooded animals. The advantage of being 
 able to lie in this protracted sleep at a somewhat reduced 
 bodily temperature is, of course, very evident when we re- 
 member the saving of tissue on this account. Some of the 
 mammals show a transition to the lower classes in their 
 temperature. Thus, the temperature of the monotremes, a 
 group of animals to which the Duck-bill belongs, is nor- 
 mally no higher than 30 C. 
 
 There are also differences in the temperatures of differ- 
 ent classes of warm-blooded animals. Thus, as a rule, the 
 temperature of larger animals is less than that of smaller 
 ones. In the case of birds the highest temperature is 
 reached, running up as high as from 40 to 45 C. This 
 in the human body would be a fever-heat and would in all 
 probability prove fatal. This relatively much higher tem- 
 perature in birds no doubt facilitates muscular contraction, 
 and may be easily explained by relating it to the flight of 
 birds. 
 
 But differences in temperature may occur in the same 
 individual. Thus, there are differences on account of age. 
 The temperature of an infant is usually the highest, being 
 about 37 9 /io C. From this it sinks to about 37Vio, which 
 is the temperature of active adult life. As age advances 
 the temperature sinks still further, and at seventy is about 
 36 8 /io. However, in real old age it begins to rise again 
 and frequently reaches 37 4 /io, almost the temperature of an 
 infant. Numerous observations seem to show, too, that 
 the temperature in females is slightly lower than in males. 
 
 There are even differences in temperature in the differ- 
 ent regions of the same body, the highest temperature be- 
 ing reached in the liver and the internal glands, where it 
 is not infrequently and normally from 38 to 39 C. The 
 
378 STUDIES IX ADVAXCKD PHYSIOLOGY. 
 
 lowest temperature is in the most exposed portions of the 
 skin, such as the ear flaps, where on account of the ex- 
 cessive radiation of heat it may sink materially. 
 
 So far the variations in temperature have been normal 
 variations. In addition, however, to these there occur the 
 variations caused by external agents, either by the immedi- 
 ate surroundings or by pathological conditions within the 
 system. The limits of temperature which may be so pro- 
 duced are considerable. One of the lowest temperatures 
 recorded is 24 6 /ioC., the temperature of a drunken man. 
 The upper limits have been reached in fevers, when the 
 temperature may rise from 37 5 /io to 41 5 /io C. Expressed 
 in Fahrenheit degrees, the variations in temperature are 
 from 76, in the case of the drunkard, to 106, in the case 
 of fevers. Sometimes just before death temperatures from 
 110 to 113 have been recorded. 
 
 CONDITIONS AFFECTING THE TEMPERATURE. 
 
 The temperature is affected in a number of ways. The 
 first and most apparent agency is, of course, the external 
 environment. The temperature is higher on an average in 
 summer than in winter. It is increased by taking hot 
 things into the stomach, or by subjecting the whole body 
 to a hot bath. 
 
 Secondly, the most usual agency affecting the tempera- 
 ture is the oxidation in the body. When this oxidation in- 
 creases, as in the case of muscular work or exertions of any 
 kind, the temperature increases along with it. It is the 
 commonest experience of course that hard work makes one 
 warm . 
 
 A third agency affecting the temperature is the blood- 
 flow, especially through the skin. When the blood-vessels 
 in the skin are dilated and much blood traverses it, it is 
 there exposed to the radiating influences and is materially 
 cooled. On the other hand, when the blood-vessels of the 
 skin are contracted and little blood passes through there, 
 much less opportunity is given for the heat to radiate from 
 
THE MAINTENANCE OF THE ANIMAL HEAT. 379 
 
 the skin. This is one of the most efficient means the body 
 has to maintain its temperature equilibrium. 
 
 One of the deceptive results of alcoholic drinks is the 
 feeling of warmth experienced. This is due to the fact that 
 under the action of the alcohol the blood-vessels of the skin 
 have been dilated and the warm blood from the visceral 
 organs traverses it, giving to the skin its sense of warmth. 
 As a matter of fact, however, this exposes the warm blood 
 to the exterior, and the result is a material loss of bodily 
 temperature in spite of the deceptive feeling. 
 
 Fourth, the temperature may be materially affected by 
 the administration of drugs. It may be increased by such 
 drugs as atropine, strychnine, caffeine, and others; on the 
 other hand, materially decreased by quinine, morphine, 
 large doses of alcohol and others. These medicinal prop- 
 erties of drugs frequently enable the physician to increase, 
 or more usually in cases of fevers, to decrease the tempera- 
 ture from a dangerously high point to the normal. 
 
 There is no question any more but that the temperature 
 of the body may be directly affected by nerves carrying 
 their impulses from nerve centers especially concerned in 
 the regulation of the bodily heat. These thermogenic 
 nerves, as they are called, are vital agents in the regulation 
 of the temperature, a topic which naturally arises at this 
 point. 
 
 THE REGULATION OF THE TEMPERATURE. 
 
 Any one who has ever had any practical experience in 
 trying to maintain a uniform temperature in a room or 
 house, even with the best modern heating appliances, re- 
 alizes the great difficulty he has undertaken. In spite of 
 the most improved modern contrivances and in spite of 
 constant watching, the temperature of a large building will 
 vacillate through many degrees in the course of a day. 
 One is therefore naturally surprised to find the temperature 
 of the body subjected in so many different ways to every 
 change in external conditions remain so constant, and the 
 
380 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 question naturally arises, in what manner the production of 
 this heat is maintained and regulated so perfectly ? 
 
 The agencies which figure in this regulation are of two 
 kinds : 
 
 1. Artificial Agencies. Such artificial agencies are, 
 first, clothing and fuel; second, increased exercise. It is 
 the commonest experience to maintain the temperature of 
 the body on a cold day by increasing vigorously the amount 
 of exercise. Third, with the approach of cold weather we 
 change more or less consciously the kind and quantity of 
 foods, eating in winter as a rule not only more food, but 
 food of greater. heat-producing quality. Fourth, as pointed 
 out just above, we may regulate the temperature to some 
 extent by the administration of drugs, a regulation fre- 
 quently called in in the reduction of temperatures in feverish 
 conditions. 
 
 2. Natural Agencies. The second group of agencies 
 are those which might be designated as the natural ones ; 
 that is, agencies which come into play without our con- 
 scious intervention. These are, first, an increased activity of 
 the heart and lungs in cold weather; second, contraction 
 or relaxation of the capillaries of the skin; third, the per- 
 spiration of the skin, in the evaporation of which much heat 
 may be eliminated from the body; fourth, a natural in- 
 creased hunger; fifth, involuntary movements, such as the 
 familiar shivering and chattering of teeth which follow un- 
 clue exposure to cold; sixth, the thermogenic nerves. 
 
 THERMOGENIC NERVES. 
 
 It has now been settled beyond a matter of question that 
 there are nerves in the body which are concerned directly 
 with the production of heat. The centers from which 
 these thermogenic nerves arise, lie probably in the spinal 
 cord. These centers in the spinal cord may, however, be 
 stimulated or inhibited by higher centers lying in the brain 
 and medulla. Repeated experiments in this direction seem 
 
THE MAINTENANCE OF THE ANIMAL HEAT. 381 
 
 to indicate that there are heat-accelerator-centers as well as 
 heat-inhibitory -centers. These have been localized especi- 
 ally in the region of the floor of the brain occupied by the 
 corpora striata. These centers in a reflex way stimulate 
 the centers of the spinal cord to greater heat production, or 
 inhibit them and so lessen the heat production. In this 
 way it is believed the heat equilibrium is so successfully 
 maintained. 
 
 Under normal conditions these heat centers are adjusted 
 or set for a temperature of 37 l /io C., but in abnormal con- 
 ditions, such as fevers, they may become set or adjusted 
 for a higher temperature. Experiments on the lower 
 animals show that they may also be set for temperatures be- 
 neath the normal. It would be interesting to know just what 
 it is in the case of fevers which changes the readjustment 
 of these centers from the normal point to the fever point. 
 But this information is not at hand. Possibly some of the 
 poisons of the disease may act as an irritant upon these 
 centers and thus disturb the equilibrium. Unfortunately, 
 too, we have no knowledge yet in what specific manner 
 such drugs as quinine act in the reduction of these fever 
 temperatures. 
 
 It is, of course, not necessary to say that these thermo- 
 genic nerves running to the various tissues in the body are 
 not anatomically distinguishable, but that the existence of 
 such centers and such nerves is based wholly upon physio- 
 logical grounds. 
 
 QUANTITATIVE DETERMINATIONS OF THE SOURCE AND EXPEND- 
 ITURE OF HEAT. 
 
 Heat may be measured just as corn or wheat. The unit 
 of heat measure is called the calorie. A calorie of heat is 
 the amount of heat necessary to raise the temperature of one 
 gram of water from zero degrees to one degree C. Or, de- 
 fining it more generally, a calorie is the amount of heat re- 
 quired to raise one gram of water one degree C. As the 
 amount of water in any given case can be accurately meas- 
 
382 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 ured, and as the temperature may be equally accurately 
 measured by thermometers, it is no specially difficult task to 
 determine quantitatively the amount of heat under investiga- 
 tion. It is only necessary to take every precaution possible 
 that none of the heat shall be lost by radiation or convection, 
 but that all of it shall be transferred to a known quantity of 
 water and so measured. 
 
 Such calori-metric measurements have been made for a 
 number of substances and the quantity of heat which they 
 produce in burning accurately determined. Thus, one gram 
 of carbon produces 8,080 calories; one gram of hydrogen, 
 34,460; one gram of proteids, 5,778; one gram of fat, 
 9,372, and one gram of sugar, 4,116 calories. One is at 
 first astonished at this stupendous amount of heat. On the 
 other hand, it explains easily how it is possible for a body 
 to derive all its energy and heat from comparatively small 
 amounts of proteids, fats and sugars. 
 
 To the older investigators it seemed impossible that the 
 muscular energy and the large amount of heat lost from a 
 living body should all be derived from the quantitatively 
 small amount of food taken. This error was, however, due 
 to their ignorance of the exact amount of heat which even 
 such small portions of food produce when burned. That 
 this amount of heat seems large is due to the fact that in 
 the every day oxidations of the physical world such a very 
 large proportion of the heat is entirely lost. 
 
 THE AMOUNT OF HEAT LOST BY THE BODY. 
 
 Experiments have been made to determine the amount 
 of heat lost by the human body in a day. These were made 
 by placing the person to be examined in a close-jacketed 
 calorimeter so that all the heat which his body produced 
 could be measured by measuring the temperature of the 
 calorimeter and its water jacket. The experiment was, 
 practically speaking, to confine an individual in a relatively 
 small chamber, or still better, chest, out of which little if 
 any heat could be lost by convection or radiation. The re- 
 
THK MAINTENANCE OF THE ANIMAL HEAT. 383 
 
 suits of such experiments would, of course, vary largely ac- 
 cording to the nature of the person experimented upon. In 
 a person resting, about 2,500,000 calories are liberated in 
 one day ; or, measuring that in terms of the water which it 
 would heat, it would be an amount of heat sufficient to raise 
 56 pounds of ice water to the boiling point. These figures 
 are materially increased for a day of regular work. In a 
 working day no less than 3,700,000 calories are produced. 
 This amount of heat would be sufficient to raise 83 pounds 
 of water from the freezing to the boiling point. 
 
 These figures appear at first startling and it seems almost 
 incredible that in one day, losses so large should occur. 
 However, the fact that this heat is being continually radi- 
 ated little by little explains this popular error. It is further 
 interesting to know that the amount of heat lost by the en- 
 tire body, plus the amount of energy lost in muscular motion, 
 is about the same as the food taken during the day would 
 give if directly oxidized outside of the body. This agree- 
 ment between the theoretical amount of heat in the foods 
 taken and the actual amount of heat lost in the body when 
 that body is in a state of nutritive equilibrium proves with- 
 out further question the source of all the energy of the body 
 and the absurdity of calling in any so-called vital force to 
 explain an apparent discrepancy. 
 
 The interesting question at once follows, in what man- 
 ner this large amount of heat is daily lost from the body. 
 Here, too, fairly accurate experiments help us out and show 
 about the following distribution of the loss: 
 
 73 per cent, direct radiation from the skin; 
 
 i4*/2 " evaporation of the perspiration from the skin; 
 
 7 2 Ao from the lungs; 
 
 3 5 /io " in the warmth of the expired air; 
 
 i 8 /io " lost in warming the excretions of the body. 
 
 It was pointed out in a previous chapter that of the 
 available energy of the body about five-sixths is lost in heat, 
 and only one-sixth utilized in actual muscular movements. 
 This seems a very heavy proportion of loss of heat, and yet 
 
384 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 when compared with the best engines it reveals that the 
 body is very much superior indeed to them all. It is a very 
 fine engine which can utilize one-eighth of its total energy, 
 while most ordinary engines utilize no more than from one- 
 tenth to one-twentieth. As the workings of the human 
 body are subject to the same physical laws to which arti- 
 ficial engines are subject, it reveals the marked superiority 
 of the body with reference to the energy at its disposal. 
 
CHAPTER XVIII. 
 
 THE KIDNEYS, THE SKIN, AND THE GENERAL 
 PHYSIOLOGY OF EXCRETION. 
 
 We have in the preceding chapters traced the foods 
 through the various changes which they surfer in digestion ; 
 they have been followed through the intestinal walls into 
 the blood or lymph streams. The changes which some of 
 them undergo in the liver has been explained. We have 
 seen them distributed in the blood and carried to the indi- 
 vidual tissues. It was pointed out how at this place these 
 foods were built up into living tissue, and how by the dis- 
 integration of this tissue the energy was produced. There 
 now remains the final question concerning the nature of the 
 waste products which result from this destruction and their 
 final elimination from the body. This closing chapter in 
 the history of the foods and tissues has therefore to do with 
 the skin and the kidneys, the organs whose duty it is to 
 take the final products of metabolism and remove them 
 from the body. 
 
 THE KIDNEYS. 
 
 The kidneys are large, bean shaped organs lying on the 
 back wall of the abdomen. They have a reddish character- 
 istic color, but are usually more or less imbedded in con- 
 nective or adipose tissue. The right and left kidneys do 
 not lie at the same level, the difference in position between 
 the two being often several inches. On account of their 
 proximity to the back wall of the abdomen pains in the 
 kidneys are usually referred to the small of the back. A 
 large branch from the aorta, the renal artery, carries blood 
 to each kidney, and a corresponding vein carries the return- 
 ing blood to the ascending vena cava. 
 
 25 (385) 
 
386 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 In its gross structure a kidney shows a connective tissue 
 covering called the capsule. The kidney itself shows two 
 
 Ua, 
 
 Fig. 127. THE URINARY ORGANS FROM BEHIND. (Henle.) 
 
 A, aorta; Vc, venacava; Ar, renal artery; Vr, renal vein ; R, right kidney; U, ureter; 
 Vu, bladder; Ua, urethra. 
 
 well marked areas, an outer one, reddish in appearance in 
 a fresh specimen, and somewhat granular, called the cor- 
 
KIDNEYS, SKIN, AND GENERAL EXCRETION. 
 
 387 
 
 .r, and an inner layer, whitish, revealing numerous glis- 
 tening threads running towards the pelvis of the kidney. 
 This second area is called the medulla. Between the cor- 
 tex and the medulla the main blood-vessels of the kidney, 
 both arteries and veins take their course. The interior of 
 the kidney is hollow, and is called the pelvis. This pelvis 
 connects with the ureter, by means of which duct the se- 
 cretion is carried to the bladder. The medulla breaks in 
 the pelvis into several (five to ten) pyramidal projections, 
 called the pyramids of Malpighi. At the ends of these 
 
 Fijf. 128. DIAGRAMMATIC SECTION THROUGH PART OF KIDNEY PARALLEL TO TUBULES. 
 
 (After Testut.) 
 
 ff, papilla; b, medulla; c, cortex; 2, capsule; 3, tubules in medulla; 4, blood-vessels; 
 9, Malpighian corpuscles. 
 
 pyramids numerous uriniferotis tubules open into the pelvis. 
 The depressions between the pyramids are called the 
 calyces. 
 
388 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 All the points so far could easily be made out on a kid- 
 ney without the use of any -lens. For the final structure, 
 the courses of the blood-vessels and the uriniferous tubules, 
 recourse must be had to histological sections. For the sake 
 of clearness it may be advisable to follow at first the course 
 of the blood-vessels for some distance without paying atten- 
 tion to other structures, and then to turn to the uriniferous 
 tubules. 
 
 1. The Circulation of Blood Through the Kidneys. 
 The renal artery enters the kidney at the hilum, and at once 
 divides into numerous branches which run in every direc- 
 tion between the cortex and the medulla. From these main 
 branches there arise smaller ones, which run directly out- 
 wards through the cortex to the capsule. These branches 
 in turn divide into shorter branches, and these short 
 branches soon terminate each in a small knot of blood- 
 vessels, giving to the whole the appearance of a bunch of 
 grapes. This network of blood-vessels is not really a 
 capillary network. It is rather a nodule of small twisted 
 arteries, with walls, however, sufficiently thin to allow the 
 water and the salt of the circulating blood to pass out at 
 this point somewhat readily. It is, therefore, well to bear 
 in mind that the blood as it re-issues from this knot is still 
 
 Fig. 129. A, SHOWING THE RELATIONS OF THE BLOOD-VESSELS AND URINIFEROUS TU- 
 BULE; B, A SINGLE GLOMERULUS FROM A PIG'S KIDNEY. (After Bowman and Lud- 
 wig.) 
 
 arterial. Upon leaving this knot, called a Malpighian cor- 
 puscle or glomerulus, the artery soon divides into capillar- 
 
KIDNEYS, SKIN, AND GENERAL EXCRETION. 389 
 
 ies which surround in a very intricate way the uriniferous 
 tubules lying in the cortex. It is at this point that the real 
 secretion of the kidney takes place. After having passed 
 from the capillaries it is gathered up in veinlets, which 
 carry the blood back to the larger veins lying between the 
 cortex and the medulla, which in turn unite at the hilum 
 and leaving the kidney form the renal vein. 
 
 The circulation through the medulla is much simpler. 
 Small arteries run inward from the main branches between 
 the cortex and medulla, and divide up into capillaries 
 which there surround the uriniferous tubules, while corre- 
 sponding veins collect this blood and carry it back to the 
 larger veins lying between the cortex and medulla, where it 
 joins the regular venous stream. The circulation of the 
 blood from the medulla is for nutritive purposes only, and 
 no active secretion takes place here. The real physiology 
 of the kidney belongs to the cortex. 
 
 2. The Course of the Uriniferous Tubule. It was 
 just pointed out that from the main arteries lying between 
 the cortex and medulla smaller arteries ran directly out- 
 wards through the cortex towards the capsule; that these 
 arteries gave off a number of lateral branches, and that these 
 lateral branches soon ended in arterial knots called the 
 Malpighian corpuscles, but that the blood reissued from 
 these knots still arterial and then divided up into capillar- 
 ies surrounding the uriniferous tubules. It now remains to 
 trace with reference to this course for the blood, the course 
 of the secreting tubules. 
 
 The secreting or uriniferous tubules are very long tubes 
 intricately folded and bent and form almost all of the re- 
 maining portion of the cortex. Each uriniferous tubule be- 
 gins as a sac-like dilatation surrounding a Malpighian cor- 
 puscle and forms, so to speak, the capsule around these 
 corpuscles. The blood-vessels, however, do not really lie 
 inside of this dilatation, but as in the case of the heart and 
 pericardium, folded in by a reduplication of the wall. It is 
 
390 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 at this point that almost all of the water of the secretion 
 finds its way unto the uriniferous tubnles. 
 
 This dilatation connects with the regular tubular portion 
 of the duct. The portion immediately following the dilata- 
 tion is called the neck. Beyond the neck the tubule be- 
 comes somewhat convoluted, and is spoken of as the first 
 convoluted tubule. It then descends abruptly through the 
 cortex down into the medulla, this portion being called the 
 descending limb of Henle. In the medulla it makes a sharp 
 turn, called the loop of Henle and then ascends again 
 through medulla and cortex to almost the point of begin- 
 ning, this ascending portion being called the ascending 
 limb of Henle. It then usually bends and runs back almost 
 to its Malpighian corpuscle, this portion being called, be- 
 cause of its convoluted nature, the second convoluted 
 tubule. Near its Malpighian body it makes a sharp turn 
 again, flowing in an opposite direction, and on account of 
 
 Fig. 130. DIAGRAM SHOWING THE COURSE OF TWO URINIFEROUS TUBULES. (After 
 Klein.) 
 
 A, cortex; B, medulla; C, papilla; a, a', regions free from glomeruli. 
 For meaning of numbers see text. 
 
 the somewhat angular turns is called the zig-zag tubule. 
 This zig-zag tubule soon leads into one of the large collect- 
 
KIDNEYS, SKIN, AND GENERAL EXCRETION. 391 
 
 ing tubules, into which other zig-zag tubules enter, and by 
 means of this large collecting tubule which runs from cor- 
 tex and medulla, the secretion is finally poured into the 
 pelvis of the kidney. These large collecting ducts are 
 called the ducts of Bellini. The whitish glistening threads 
 so characteristic of the medulla are such ducts of Bellini. 
 The course of the uriniferous tubule as just given permits, 
 of course, of certain variations, but is with a surprising 
 regularity the usual one. 
 
 Most of the cortex and even some of the upper portions 
 of the medulla consists of these closely packed tubules with 
 their accompanying blood-vessels. On cross sections each 
 tubule shows a single layer of columnar epithelial cells rest- 
 ing on a small basement membrane, and it is these epithelial 
 cells which play the physiological role of the kidney. It is 
 these cells which pick out of the blood the nitrogenous 
 waste products and pass them into their lumen. At the 
 
 Fig. 131. TUBULES FROM A SECTION OF THE DOG'S KIDNEY. (After Klein and Noble 
 
 Smith.) 
 
 a, capsule, enclosing glomerulus; n, neck; c, c, convoluted tubules; /, from the limb 
 of Henle (in the medulla) ; d, a. collecting tubule. 
 
 Malpighian corpuscle, that is, at the very head of the urin- 
 iferous tubule, water, and some salts of course, are -being 
 continually poured into the tubule, and this stream serves 
 to wash out other substances passed into it. The fact that 
 urea and many other nitrogenous compounds are with diffi- 
 culty soluble in water at ordinary temperatures accounts for 
 the large volume of water required by the kidney to wash out 
 this product. We have therefore to look upon the function 
 
392 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 of the Malpighian corpuscles of the cortex as mechanical 
 rather than physiological, serving merely as flush basins at 
 the top of the tubule to keep this lumen perfectly clear of 
 obstructions, while the cells that line the tubule are the 
 physiological agents directly concerned in picking out of the 
 blood the waste products in question. 
 
 It may be well to repeat at this point the fact that these 
 nitrogenous products are not formed by the kidney at all. 
 Derived in the form of kreatin or kreatinin, or similar sub- 
 stances from the breaking down of the tissues, they are car- 
 ried to the liver and there changed to urea and its kindred 
 compounds, from which place by means of the regular blood 
 stream they reach the kidney, and in this organ are merely 
 picked up by the tubular epithelium and eliminated. It 
 must not, however, be supposed that this elimination of the 
 nitrogenous products is a mere physical filtration. It is an 
 active physiological process, depending upon the vital 
 energy of the epithelial cells that line the tubules. It is due 
 to the special activity of these cells that these waste pro- 
 ducts are removed, and that many other almost equally di- 
 alyzable substances are not permitted to pass through. In 
 cases of inflammation, or in cases of the more or less gen- 
 eral disintegration of these epithelial cells, other substances 
 do pass into the secretion and such diseases as diabetes or 
 Bright 's disease are the result. 
 
 The elimination of the water and salt in the glomeruli 
 or the Malpighian corpuscles, is to a very large extent a 
 physical process. This is proved by the fact that the amount 
 of such water and salt eliminated from the kidney is to some 
 extent directly proportional to the amount of blood which 
 passes through the kidney and to the arterial pressure in the 
 kidney, hence any rise in arterial pressure or any increase 
 in the swiftness of the blood stream will usually reveal itself 
 in an increased secretion from that organ. That it is 
 nothing but a physical filtration is not claimed. In fact, it 
 is probable that even the lining cells of the corpuscle exert 
 a physiological action. 
 
KIDNEYS, SKIN, AND GENERAL EXCRETION. 393 
 
 That the phenomena of secretion are controlled by nerves 
 is evident for several reasons. States of the emotions, ex- 
 cessive pain, may affect the amount of such secretion 
 through this, innervation. It has, however, not been possi- 
 ble so far to trace these nerves to their final terminations. 
 There is no objection, though, against believing that these 
 nerves end in or near the epithelium cells of the tubules and 
 capsule, and that the increased or decreased secretion is not 
 wholly due to vascular changes. A number of drugs known 
 as diuretics affect the kidneys, causing an increase in its se- 
 cretion, but whether due to vascular changes or to a direct 
 stimulus of the secreting cells is not clear. 
 
 THE KIDNEY SECRETION. 
 
 The amount of urine eliminated in one day is about 
 1,600 grams. Its specific gravity is 1,020, that is, slightly 
 heavier than water. Its composition consists of 96 per cent. 
 water and 4 per cent solids. These 4 per cent, solids are: 
 
 (1) Urea and its derivatives; uric acid, kreatin and xan- 
 thin. 
 
 (2) Aromatic bodies such as hippuric acid, kresol, indol, 
 
 (3) Oxalic acid in the form of calcium oxalate. 
 
 (4) Pigments. 
 
 (5) Mineral salts; sodium chloride, phosphates and 
 sulphates of potassium, calcium, magnesium, ammonia in 
 the form of urate. In addition to these solids slight quan- 
 tities of CO 2 are dissolved in the liquid. 
 
 The most important of these solid bodies is the urea. Its 
 chemical composition is given in the formula CO (NH 2 ) 2 - 
 It is the final product of nearly all the albumens and albu- 
 minoids which have been used up in the tissues. It is, 
 therefore, the substance in which the nitrogen of the foods 
 is eliminated. Reference to the chemical formula will show 
 that it contains a relatively large amount of nitrogen. 
 This substance is interesting as having *been the first or- 
 ganic substance which was produced artificially in the la- 
 
394 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 boratory. In 1828 the chemist Wohler discovered that by 
 allowing a solution of ammonium cyanate (NH 4 CON) to 
 stand exposed to the air it changed into urea CO (NH 2 ) 2 . 
 
 It will be noticed in comparing the chemical composi- 
 tions of these two substances that they have the same rela- 
 tive number of atoms. Urea is, therefore, but a re-arrange- 
 ment of the molecular structure of ammonium cyanate. It 
 was, of course, easy to make ammonium cyanate out of its 
 elements in the laboratory, and so it became possible to 
 make urea artificially in the chemist's retorts. Before this 
 time it had been believed without question that all organic 
 compounds, that is, compounds made by plants or animals, 
 differed essentially from compounds made artificially. It 
 was believed that in the construction of organic compounds 
 vital forces were at work in addition to chemical affinities. 
 This wonderful discovery at once showed the error of this 
 view and opened the way for the increased study of organic 
 compounds and for the artificial manufacture of innumera- 
 ble ones now on the markets. It was the first blow to break 
 down the distinction between organic and inorganic chem- 
 istry. 
 
 This urea may be extracted from tne secretion in a pure 
 solid form. It crystallizes in white four-cornered prisms, or 
 when crystallized very rapidly, in fine needles. The solid 
 crystals are soluble in water, alcohol, and many other solu- 
 tions, but are perfectly insoluble in ether. 
 
 If a solution containing urea be allowed to stand for some 
 time exposed to the air, it ferments under the action of 
 germs falling into it from the air, and the urea uniting 
 chemically with some of the water changes into ammonium 
 carbonate. This change is called the fermentation of the urea. 
 Ammonium carbonate, more familiar as the salts of harts- 
 horn, has its peculiar characteristic odor, and it is to this 
 substance that the odor of fermented urine is due. 
 
 The derivatives of urea, such as uric acid, kreatin, xan- 
 thin and others, are found in relatively small amounts. Under 
 certain conditions, however, the uric acid may accumulate 
 
KIDNEYS, SKIN, AND GENERAL EXCRETION. 395 
 
 in the body, and acting as a poison deposited usually in the 
 joints, give rise to the familiar symptoms of gout and kin- 
 dred diseases. 
 
 The aromatic bodies, such as hippuric acid, kresol, in- 
 dol and skatol are found in very small quantities. Hippuric 
 acid, however, occurs in relatively very large amounts in 
 the renal secretion of herbivorous animals. The kresol, in- 
 dol and skatol are substances which have resulted from the 
 disintegration of albumens in the intestine, but having 
 been absorbed by the blood are eliminated again through 
 the kidneys. 
 
 The characteristic color of the renal secretion is due to 
 a number of pigments. The best known of these is the 
 pigment known as uro-bilin. This uro-bilin is probably de- 
 rived from the same source as the bilirubin of the bile, that 
 is, from the disintegration of red corpuscles, or more ex- 
 actly, from the haemoglobin of red corpuscles. 
 
 The mineral salts include a number of mineral sub- 
 stances which are the products of tissue disintegration, but 
 in addition excesses of salts which have been directly elim- 
 inated from the blood. Experiments show that when cer- 
 tain mineral salts in increased quantities reach the blood 
 they are at once eliminated in this manner. On this account 
 the eating of even excessive amounts of salt has no directly 
 injurious effect whatever upon the body. 
 
 It is sometimes of the utmost importance to the physi- 
 cian to be able to determine the composition of urine, espe- 
 cially when the presence of sugar or albumen is suspected. 
 
 Quite a large additional number of chemical substances 
 occur in more or less minute quantities in the secretion, but 
 the nature of these substances from a chemical standpoint 
 is so complicated, and in the real physiology of the body 
 they play such an unimportant role that in this discussion 
 they are omitted altogether. 
 
 By way of summary it may be stated then that the real 
 significance of the physiology of the kidney lies in its 
 power to eliminate superfluous or injurious substances, 
 
396 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 and to rid the body of the nitrogenous products resulting 
 from the metabolism of the tissues. The kidneys are able, 
 when necessary, to eliminate hurriedly accidentally received 
 substances, such, for instance, as poisons of one kind or 
 another, and so prevent the liability of injury from them. 
 This no doubt explains the power of the body to recover 
 from such poisonings. 
 
 While most of the work of secretion thus devolves upon 
 the kidneys, they are able to be relieved in part by the skin, 
 which, in addition to its functions as a protection to the 
 body, serves quite materially in a manner similar to that of 
 the kidney, and in cases where the kidneys have been over- 
 worked and have lost some of their vitality, assumes this 
 extra duty. On the other hand, when the skin for some 
 reason is prevented from exercising this excretory function 
 an unnaturally increased amount of work is thrown upon 
 the kidneys. 
 
 THE SKIN. 
 
 The covering of the body, or the skin, consists of two 
 essentially different layers ; an outer layer made up of cells 
 entirely, called the cuticle of epidermis, and an inner layer 
 consisting almost wholly of connective tissue fibers, with 
 contained blood-vessels, glands, nerves and so on, called 
 the corium or cutis-vera, that is, true skin. 
 
 1. Epidermis. The epidermis is a stratified epithelium 
 composed wholly of epithelial cells. These cells are, 
 however, not all alike, the cells of the deeper layers, next 
 to the cutis-vera, being more cuboidal in shape than the 
 flattened and dead cells forming the horny covering at the 
 surface. The gradation from these dead flattened cells on 
 the outside to the living cuboidal cells next to the corium is 
 tolerably gradual. The lowest layer of cells, that immedi- 
 ately in contact with the corium, is called the Malpighian 
 layer of the epidermis. It consists of well-marked nucle- 
 ated cells of pronounced cuboidal form. It is these cells 
 which by their division give rise to all of the remaining 
 cells of the epidermis. The cells of this Malpighian layer 
 
KIDNEYS, SKIN, AND GENERAL EXCRETION. 
 
 397 
 
 divide, and thus the top layers of the epidermis are being 
 continually pushed further and further out by the addition 
 
 Fig. 132. SECTION OF SKIN AJO> SUBCUTANEOUS TISSUE. (After Kolliker.) 
 a, horny layer; b, Malpighian layer of epidermis; c, corium; rf, subcutaneous fatty 
 tissue; e, papillae; f, fat; g, sweat gland; h, duct; i, mouth of sweat gland. 
 
 of new cells from beneath. The layers of these derived 
 cells, lying close to the Malpighian layer, also resemble 
 the Malpighian layer in having well-defined nuclei and 
 in their cuboidal shape. But further outward a chem- 
 ical change sets in, by means of which the substance 
 of these cells seems changed into a horny material akin 
 to the keratin of ordinary horns, while in addition to 
 this chemical change they become more and more flattened, 
 losing more and more the appearance of cells until at the 
 top of the epidermis they occur as mere horny scales, which 
 from time to time, by contact with other bodies or by the 
 friction of towel, etc., are broken off from the skin. 
 
 The layer of the epidermis in which this chemical change 
 takes place is readily visible in sections as much clearer 
 looking, due to the fact that the cells have undergone a 
 transformation into the somewhat transparent horny ma- 
 
398 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 terial. For this reason it has been termed the stratum 
 lucidum. 
 
 It will therefore be observed that the epidermis is not at 
 all in any way derived from the dermis beneath. The der- 
 mis is fibrous, the epidermis cellular. The epidermis is 
 a result of the continued division of the Malpighian layer 
 of the epidermis, and when this layer is not present, as in 
 serious wounds, scalds or bruises, it is absolutely impossi- 
 ble for the epidermis to appear. Under such conditions at- 
 tempts are frequently made to graft portions of the Mal- 
 pighian layer from another body on to this spot, and if the 
 graft is successful the epidermis begins to grow from 
 these places by the proliferation of the Malpighian cells en- 
 grafted. These Malpighian cells are further of interest in 
 the fact that in them lie the pigments which characterize 
 the various races of mankind. A certain amount of pig- 
 ment also occurs in the cells above the Malpighian layer, 
 but it is much less pronounced, and the intense black of the 
 colored races, or the red of the -Indian is the color which 
 shines through the somewhat transparent epidermis from the 
 Malpighian layer at its base. 
 
 2. Corium. The corium or true skin is the fibrous 
 part of the skin lying immediately beneath the epidermis. 
 It consists almost wholly of closely packed white fibrous 
 tissue, containing, however, a small amount of yellow elas- 
 tic fibers. In the meshes of these fibers are found con- 
 nective tissue corpuscles, imbedded nodules of fat, blood- 
 vessels and nerves, and finally the glands of the skin. 
 
 The true surface of the corium is thrown up into pecu- 
 liar papillae sometimes simple, sometimes branched, which 
 project up into the epidermis. In these papillae thert lie 
 in some instances loops of blood-vessels, more generally 
 tactile corpuscles concerned in the sense of touch. These 
 papillae are arranged in defined rows, and as the epidermis 
 follows these papillae they show on the outside of the skin 
 as those peculiar lines and furrows so evident on the 
 
KIDNEYS, SKIN, AND GENERAL EXCRETION. 399 
 
 fingers and the palm of the hand. These furrows are prob- 
 ably not alike in any two individuals . When once formed 
 
 Fig. 133. SECTION OF THE HUMAN EPIDERMIS, SHOWING TWO VASCULAR PAPILLA BE- 
 NEATH. (After Heitzmann.) 
 BP, loop of capillaries; Dp, duct of sweat gland; EB horny layer of epidermis; PL, 
 
 stratum lucidum; V, Malpighian layers of epidermis. 
 
 they never change, the impressions of the furrows on an 
 infant's thumb being identical with the impression of the 
 same thumb in old age. In some countries impressions are 
 made of the furrows of the fingers or thumbs of criminals 
 in order that they may keep a perfectly trustworthy de- 
 scription of them, it being impossible for the criminal to 
 change this part of his personal appearance. The absolute 
 correspondence of an impression so taken at any time and 
 the thumb offered in evidence would be incontrovertible 
 proof of the identity of the man. These papillae while 
 present over nearly all portions of the skin are especially 
 plentiful in those portions of the body where the sense of 
 touch is peculiarly acute. 
 
 Through the corium run the blood-vessels, veins and 
 capillaries. The epidermis has no direct vascular supply, 
 although the tips of capillary loops do sometimes reach 
 slightly beyond the Malpighian layer. The epidermis is 
 therefore obliged to draw its nourishment from the lymph 
 
400 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 distributed beneath it. This is, of course, in accordance 
 with the common observation that blood is not drawn as 
 long as the cut is confined to the cuticle. 
 
 Nerves also traverse the corium and are distributed to 
 the contained blood-vessels and glands, while the special 
 nerves of touch end in the touch corpuscles. Small rami- 
 fications of nerves penetrate the epidermis and run in 
 among the epithelial cells, ending usually between these in 
 little knob-like swellings, or terminating in certain espe- 
 cially modified cells which have been interpreted as sensory 
 cells in the epidermis. A detailed description of these cells 
 and the touch corpuscles is reserved for the chapter on the 
 4 ' Special Senses." 
 
 Fig. 134. SBCTION OF THE SKIN SHOWING TWO PAPILLA. (After Biesiadecki.) 
 a, vascular papilla, containing a capillary loop from the artery c; fc, sense papilla, 
 
 containing a tactile corpuscle t; d,f,f, three nerve fibers, running to and around the 
 
 papilla. 
 
 The corium is held to the underlying tissues by a loose 
 coat made up almost wholly of connective tissue fibers. 
 
 In some places this binding coat is rather poorly de- 
 veloped, leaving the skin loose and giving it much latitude 
 of movement. * In others the skin is bound firmly down to 
 
KIDNEYS, SKIN, AND GENERAL EXCRETION. 401 
 
 the flesh and the transition from the skin is so gradual as to 
 be indeed difficult to follow. The fibrous nature of the 
 corium may be a matter of easy observation on any piece of 
 leather, a torn edge here displaying frequently very satis- 
 factorily the tanned shreds of fibers which go to make up 
 the material. The process of tanning consists in nothing 
 more than taking plexuses of connective fibers, forming the 
 corium or true skin, and treating these with a substance 
 called tannin, by means of which they are hardened and 
 transformed into a substance which increases their strength 
 as well as their resistance to decay. It need not be added 
 that the epidermis does not figure at all in this process. 
 
 SPECIAL MODIFICATIONS OF THE EPIDERMIS. 
 
 1. Nails. The epidermis is in certain portions of the 
 body specially modified to form hairs or nails. A nail is a 
 portion of very much-thickened epidermis, the component 
 cells of which are much more closely packed, and the chem- 
 ical change of which into keratin or horn is more complete. 
 The posterior part of a nail is concealed in a groove of the 
 skin, and it is at this point that the nail increases in length 
 by the formation of new epithelial cells. The nail grows in 
 thickness by the proliferation of cells from the bed of the 
 nail, the thickest portion of the nail being the exposed end. 
 The nail usually presents near its root a lens-shaped white 
 area known as the lunula. This whitish appearance is due 
 to an opacity at this point, resulting from the thickness of 
 the nail bed immediately under it, the cells of which are in 
 very active division to increase the thickness of the nail. 
 The cells of the root and bed of the nail, in active process 
 of division are soft, while those longest formed and next the 
 surface or end of the nail are in increasing degrees horny, 
 differing, however, from the horny cells of the ordinary 
 epidermis in the fact that they seem to possess spiny pro- 
 cesses, by means of which they are firmly interlocked and 
 united. 
 26 
 
402 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 That the nail is an epidermal structure is not only 
 proved from its composition of epidermal cells, but also 
 proved by the source from which the root of the nail is de- 
 rived. In very early life, as early as the third month of 
 uterine life, the epidermis at the point where the root of 
 the nail is to form bends inward forming a groove, which 
 groove finally imbedded in the deeper layers of the skin be- 
 comes the matrix for the growing nail. It is said that the 
 continued rate of growth of a nail is about one-thirtieth of 
 an inch per week. As in case of epidermis in any part of 
 the skin a new nail is able to appear only when in the pull- 
 ing away of the old one the deeper layers, the Malpighian 
 layers, of the nail root are left intact. 
 
 2. The Hair. A second modification of the epidermis 
 is the hairs. They appear about the third or fourth month 
 of embryonic life as growths from the Malpighian layer down 
 into the deeper parts of the corium. This ingrowth soon 
 divides into an outer wall of epidermal tissue which becomes 
 the wall of the hair follicle, and an inner portion which 
 appears as the hair. The growing portion of the hair is at 
 the bottom of the hair follicle where the Malpighian cells 
 are in constant process of division. This point of growth is 
 spoken of as the root of the hair, and on account of the 
 continued proliferation of new cells is highly vascular. 
 These blood-vessels really lie in the corium, but the corium 
 at this point usually extends some distance into the hair 
 root, like a papilla, on which and around which the dividing 
 cells of the hair root are placed. At the root the cells which 
 go to make up the shaft of the hair are more or less alike, 
 but a differentiation at once begins, and along the shaft 
 proper the following structure of the hair may be easily 
 made out with the microscope. 
 
 Surrounding the hair is a single layer of flattened cells 
 forming a kind of scaly covering. This is called the hair 
 cuticle. Beneath this thin cuticle is the real fibrous por- 
 tion of the hair. In most hairs this fibrous portion consti- 
 
KIDNEYS, SKIN, AND GENERAI, EXCRETION. 
 
 403 
 
 tutes the entire remainder of the shaft. It consists of deli- 
 cate fibers closely packed together, running of course in the 
 longitudinal direction of the shaft. Finer investigation re- 
 veals that these fibers are in turn com- 
 posed of flattened and elongated cells. 
 On these dried and elongated cells rem- 
 nants of nuclei may sometimes be still 
 visible. In the cells that make this 
 fibrous portion there is a deposit of pig- 
 ment to which the hair in question owes 
 its color. In older hairs air spaces may 
 arise by a kind of drying process, which 
 by their reflection of the light give to 
 the hair a grayish appearance. Such 
 hairs, when soaked in certain liquids 
 become entirely transparent, these air 
 spaces being filled up with the liquid in 
 question, but when the hair is again 
 dried the liquid evaporates, the air again 
 enters these spaces and the old color re- 
 appears. It is said by some observers 
 that the pigment of the hair, be it 
 black, brownish or reddish, is carried to 
 the cells at the root of the hair by pe- 
 culiar wandering pigment cells reach- Fig 
 ing it. 
 
 In some cases the interior of the hair a> mouth of follicle . 6f 
 is occupied with a kind of medulla or neck; c ' root; ^^ coats of 
 
 /. . . the dermis; /, g, outer and 
 
 pith. ThlS pith IS COmpOSed Of rOWS Of inner root sheathes of epi- 
 
 cells of a generally angular form. It is hal^i.^kh-ThaT^; 
 especially apt to appear in advancing m > fat ; n, an-ector muscle; 
 
 . f , . .,.. o, papilla of cuds; s, Mal- 
 
 years, and the whiteness of hair is usu- P i g hian layer; , sebaceous 
 ally due to the contained air which lies glands - 
 in the spaces among these cells, and in some instances ac- 
 tually in the cells. These air spaces are of course pro- 
 duced by the drying of the hair in its exposure to the 
 atmosphere. 
 
 ,IN 
 LONGITUDINAL SECTION. 
 
 (After Biesiadecki.) 
 
404 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 On cross sections the shaft of the hair is usually round. 
 In some individuals, however, and in certain races it is 
 more regularly flattened. Such hairs show a natural tend- 
 ency to curl on account of the unequal growths at the different 
 angles. The size of these hair shafts is also a racial char- 
 acteristic. It is rather small in the Caucasian race, much 
 larger in the Mongolian, and reaches possibly its maximum 
 diameter in the American Indian and the Japanese. 
 
 It need not be pointed out that like the nails and epider- 
 mis, hairs are able to be replaced only when the reproduc- 
 ing Malpighian layer at the root of the hair is left intact. 
 
 Sebaceous Glands. Along the tube of the hair follicle 
 in which the shaft is immersed in the skin there opens reg- 
 ularly a sebaceous duct carrying a fatty secretion from the 
 sebaceous gland into the follicle, there to be poured upon 
 the shaft of the hair. This sebaceous gland is a flask-like 
 outgrowth from the epidermal cells of the follicle, and is 
 therefore epidermal in its origin. The function of this se- 
 cretion is not only to preserve somewhat the vitality of the 
 hair, but by being poured upon the skin to keep that in 
 pliable condition and to protect the same from excessive 
 evaporation. The secretion from these sebaceous glands is 
 of a fatty nature. In places where the hairs are minute 
 these sebaceous glands seem to open directly on the surface 
 of the skin, an arrangement especially noticeable on the 
 skin of the face. The secretion of such glands may fre- 
 quently become thickened and so choke up the glands in 
 question, a condition which usually results in the formation 
 of a pimple, which is nothing more than an attempt of na- 
 ture to empty the gland by a process of suppuration. Some- 
 times the mouth of the gland becomes filled with particles 
 of dust or dirt pressed down into them, and so gives rise 
 to the familiar blackhead. These glands seem to be emp- 
 tied as a rule by the contraction of muscles which are found 
 attached to each hair follicle. These muscles are bands of 
 plain muscular tissue attached at one end to the under sur- 
 face of the corium, at the other to the lower portions of the 
 
KIDNEYS, SKIN, AND GENERAI, EXCRETION. 405 
 
 hair follicle. By their contraction it is probable that a lit- 
 tle of this sebaceous secretion is squeezed out of the gland 
 into the follicle. These muscles are specially apt to con- 
 tract under certain conditions such as exposure to the cold, 
 and by this contraction the follicle is pulled upward and 
 projects slightly beyond the rest of the epidermis, producing 
 the little elevations described under the somewhat senseless 
 term of goose-skin. 
 
 These glands as well as hairs are absent from certain 
 portions of the skin such as the palms of the hands and the 
 soles of the feet. A very specialized form of such a sebaceous 
 gland is found among the tail feathers of certain birds and is 
 called the uro-pygeal gland. The secretion here is so 
 abundant that the bird in question may by means of its bill 
 take the secretion for the oiling of its entire coat of feath- 
 ers. A special form of these glands in the human body is 
 found along the upper and lower eyelids. These glands are 
 known as the Meibomian glands. The function of the se- 
 cretion at this point is to keep the edge of the lids some- 
 what oily and so prevent the tears from running out of the 
 eye over these eyelids. This is accomplished by taking 
 advantage of the familiar fact that water does not very 
 readily run across an oiled surface. In the ear there are 
 found certain sebaceous glands secreting a thick, fatty sub- 
 stance familiar as the ear-wax. These glands, however, 
 are anatomically not true sebaceous glands at all, in spite 
 of the nature of their secretion, but belong to the tubular 
 sweat glands. It is in fact just possible that these are not 
 modified sebaceous glands at all, but are really sweat glands 
 which have taken on a different function. 
 
 THE SWEAT GLANDS. 
 
 Distributed all over the body, except on the palms of 
 the hands and on the soles of the feet, are long tubular 
 glands known as the sweat or sudoriferous glands. These 
 are simple tubular glands, the lower portion of the tube, 
 however, being rolled up into a coil. This coil lies in the 
 
406 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 deeper portions of the corium, or more generally in the sub- 
 cutaneous tissue. From this coil a tubular duct runs 
 through the corium and epidermis, carrying its secretions 
 to the surface of the skin. Instead of running directly up- 
 wards the duct winds through the corium and epidermis in 
 a spiral cork-screw fashion. A cross-section of the tube of 
 this gland shows it to be composed of an investment of con- 
 nective tissue and an inner layer of columnar cells enclosing 
 the lumen. The coiled portion of the tube in the sub- 
 cutaneous tissue is richly supplied with blood-vessels and 
 nerves. The reason for this coiling of the tube is no doubt 
 explained in the saving of space. The explanation of the 
 spiral winding of the duct through the skin is not apparent. 
 These glands are especially plentiful on the forehead 
 and under the arms. Rough calculations have placed the 
 number of sweat glands on the entire body at about 2,000,- 
 000. 
 
 1. Nerves. That these glands are under the control of 
 the nervous system is beyond question. It is an every-day 
 observation that states of emotion, fright or pain directly 
 affect the perspiration of the body and thus clearly point 
 to the existence of sweat centers in the spinal cord and 
 brain. But evidence still more direct is at hand. It is 
 possible to amputate a limb of a cat, for instance, and by 
 stimulating the sciatic nerve, along which the sweat fibers 
 run, to produce droplets of sweat on the balls of the feet, 
 and this even when there is no increase in the blood supply ; 
 in fact, when the circulation has entirely stopped. This is 
 conclusive proof that the process of sweating is not a sim- 
 ple filtration of water and salt from the lymph or blood in 
 and through these glands, but that it is a physiological 
 phenomenon under direct nervous control, and to a large 
 extent independent of vascular conditions. 
 
 Experiments seem to point to the existence of lower 
 sweat centers in the spinal cord which may, however, under 
 special conditions be controlled by higher centers in the 
 
KIDNEYS, SKIN, AND GENERAL EXCRETION. 407 
 
 brain itself. The existence of such higher sweat centers of 
 the brain was just pointed out in the familiar experience of 
 everybody that strong emotions, especially great anxiety, at 
 once shows itself in an increased activity of these glands. 
 There are certain drugs which have a very specific effect 
 on these glands. Thus, pilocarpine will stimulate the 
 glands to active secretion, while, on the other hand, the 
 administration of atropine more or less completely checks it. 
 
 2. Composition of the Sweat. The secretion of these 
 glands, or the sweat as it is called, has a composition not 
 yet well determined. It is difficult to get the fluid free 
 from a sebaceous admixture. It seems to consist, however, 
 of water, common salt and traces of a number of alkaline 
 salts. The most important organic constituent of sweat is 
 the urea. This becomes especially plentiful when for some 
 reason the function of the kidneys has been impaired. But 
 even when these are normally discharging their duty there 
 is a larger proportion of urea in the sweat than could be 
 accounted for by simple filtration, pointing to the fact that 
 the cells which make up the tube of the sweat glands in an 
 active physiological way pick up the urea from the blood 
 and eliminate it from the body in the perspiration. In ad- 
 dition to this urea fine chemical analyses have shown the 
 presence in minute quantities of some of the other sub- 
 stances found in the secretion of the kidneys. For such 
 reason the skin has been called an excretory tissue in ad- 
 dition to a protective one and classed physiologically with 
 the kidneys and lungs. It was formerly believed that the 
 death which soon followed the varnishing of the skin of an 
 animal, a procedure which stopped up all the 'pores of 
 the skin, was due to the fact that this excretory function of 
 the skin had been stopped. Such an explanation is, how- 
 ever, wrong, later experiments proving that the death of 
 such a varnished animal results from the increased loss of 
 heat which the varnished surface of the body radiates 
 away. 
 
408 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 It was in the chapter on heat pointed out in what an 
 important and integral way the perspiration figured in main- 
 taining a constant and unvarying temperature of the body. 
 
 3. Origin of Sweat Glands. In their origin sweat 
 glands, too, are epidermal. They arise in early embryonic 
 life as outgrowths of the epidermis, these down-growths soon 
 becoming hollow and with secondary changes transforming 
 themselves into the adult structure of the gland. 
 
CHAPTER XIX. 
 
 THE GENERAL ANATOMY AND PHYSIOLOGY OF 
 THE NERVOUS SYSTEM. 
 
 In the discussion of the various systems of the body so 
 far, they have been treated as acting more or less inde- 
 pendently of each other. We have now left to consider 
 that large system whose function it is to co-ordinate these 
 various systems into a harmoniously working whole. This 
 statement of the function of the nervous system covers at 
 one sweep its entire physiology, notwithstanding the mul- 
 titude of ways in which this is accomplished. Possibly the 
 most fundamental point in discussing this system is its one- 
 ness or unity. Sometimes for arbitrary reasons or for mere 
 convenience sake we speak of several nervous systems. 
 This is physiologically wrong. The entire system of nerves, 
 ganglia and higher centers are all bound together and phy- 
 siologically are a unit. This is true even in spite of the 
 fact that certain parts of this system have more or less 
 specialized functions, for even in this case the co-ordina- 
 tion and the successive subordination is finally so perfect 
 that unifying results only are reached. It seems desirable, 
 however, in order to facilitate the discussion of these 
 nervous tissues to adopt the usual classification into 
 
 First, the cerebro-spinal system, including the brain 
 and the cranial nerves, and the spinal cord and the spinal 
 nerves. 
 
 Second, the sympathetic system, including two chains 
 of ganglia lying along the back-bone and extending from 
 the upper cervical through the lumbar region, and the 
 nerves which emanate from these ganglia. 
 
 Third, the sporadic system, not a connected system at 
 all, but consisting of various ganglia scattered throughout 
 
 (409) 
 
410 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 the body not included in the two other systems. Such 
 ganglia are those of the heart, the plexuses of Auerbach 
 and Meissner in the intestine, the intrinsic ganglia of 
 blood-vessels, the solar plexus of the mesentery, etc. A 
 sharp distinction between these three systems cannot at all 
 be drawn. The spinal nerves are connected with the sym- 
 pathetic nerves, and both these nerves may run into spora- 
 dic ganglia. 
 
 NERVOUS ELEMENTS. 
 
 In studying in detail any of these systems two kinds of 
 nervous structures are at once discernible: 
 
 1. Nerves, Nerve Trunks and Plexuses. By dissect- 
 ing a body one meets almost everywhere whitish looking 
 threads which are nerves. These might easily be mistaken 
 for tendon threads or other connective tissue fibers. If by 
 means of the scalpel the course of such a thread or cord is 
 followed it is soon seen to divide and sub-divide until the 
 finer ramifications are lost among the muscles or glands or 
 in the skin. If the microscope should be called to aid it 
 would be possible to actually see these nerve terminations 
 in many instances, such as their endings in the nerve- 
 plates of the voluntary muscles or in the tactile corpuscles 
 of the skin. If, on the other hand, one should follow the 
 course of such a nerve inward, it would be seen to unite 
 with other nerves, until finally the nerve would be found 
 entering the spinal cord or brain, or at least some central 
 ganglion. Such whitish cords are called nerve trunks. A 
 cross-section of such a nerve trunk would show that it is 
 composed of very many smaller cords, the nerve fibers, and 
 that the trunk is really nothing more than a collection of 
 fibers running in the same direction wrapped in a common 
 envelope of white connective tissue. It is this white con- 
 nective tissue envelope and not the nerve substance itself 
 which gives to the nerve trunk the color in question. Not 
 infrequently by following a nerve trunk it might be seen to 
 send off communicating branches to other nerve trunks, and 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 411 
 
 these in turn to still others, and so there would be produced 
 networks of fibers. These networks are called plexuses. 
 It is by means of these plexuses that an individual nerve 
 fibril of one trunk may find its way into other trunks and so 
 reach removed parts of the body. This makes it possible 
 for a nerve trunk to contain near its end fibers which it did 
 not have at its beginning, but which reached it along its 
 course. While such plexuses are very generally distributed 
 all over the body there are peculiarly large ones in the 
 shoulder and lumbar regions, forming respectively the spinal 
 nerve plexuses that go to the arms and limbs. 
 
 2. Nerve Centers or Ganglia. When the course of a 
 nerve is followed inward it is soon found to end either in the 
 brain, spinal cord, sympathetic system, or in isolated gan- 
 glia over the body. All these structures named are nerve 
 centers; that is, they are nervous centers from which nerve 
 fibers arise. These nerve centers may be large, as many of 
 those in the brain, or they may be small aggregations of 
 nervous tissue like the individual centers of the sympa- 
 thetic system. Centers lying more or less separate and 
 having a distinct outline are called ganglia. 
 
 A ganglion is in essence nothing more than a group of 
 nerve cells with which the nerve fibers entering the gan- 
 glion are physiologically connected. These groups of nerve 
 cells are of course usually surrounded with a more or less 
 complete coat of connective tissue intended for protection. 
 While anatomically this description suits all ganglia, phy- 
 siologically there are distinct kinds. 
 
 From this it will be seen that the entire nervous system 
 is composed of nerve cells more or less grouped into dis- 
 tinct ganglia and of nerve fibers which run out from these 
 ganglia connecting them with each other, or connecting the 
 ganglia with distant glands, muscles, skin, etc. A detailed 
 histological description of these nerve fibers and their 
 coats, and of the nerve ganglia and their aggregation in 
 turn into larger centers is reserved for the chapter on the 
 
412 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 finer architecture of the nervous system, it being the inten- 
 tion in these preliminary paragraphs to deal simply with 
 those points of the nervous system included under its gross 
 anatomy. 
 
 THE BRAIN AND SPINAL CORD. 
 
 By far the most important system, both with reference 
 to its special psychical functions and its general control 
 over the other systems, is the cerebro-spinal system. This 
 consists of the brain and spinal cord, and the nerves issu- 
 ing from them. The brain and spinal cord are continuous 
 through the foramen magnum, a large opening in the occip- 
 ital bone. 
 
 The Membranes of the Cerebro- Spinal System. 
 
 In the examination of these systems one is peculiarly 
 impressed with the efficient way in which they are enclosed 
 within bony and membranous coverings. The brain is en- 
 cased in the bony cranium, while the spinal cord is almost 
 equally protected in the neural arches formed by the verte- 
 brae. In addition to this bony envelope both brain and 
 spinal cord are covered with three membranes. Lying 
 next to the nervous tissue is a delicate thin membrane 
 called the pia-mater. This dips down into all the convo- 
 lutions and configurations of brain and spinal cord, and 
 serves especially to carry the blood-vessels nourishing them. 
 Ikying next to the bone is an exceedingly tough dense mem- 
 brane formed almost wholly of white closely woven con- 
 nective fibers called the dura-mater. Between the dura- 
 mater and the pia-mater there is a spongy membrane called, 
 on account of its web-like nature, the arachnoid membrane. 
 The dura-mater figures not only as an enveloping membrane 
 of the brain and spinal cord, but serves as a periosteum for 
 the cranial bones as well. While these membranes sur- 
 round the brain very closely the dura-mater does not invest 
 the spinal cord in the same way, but here frequently leaves 
 quite a space between the pia-mater and itself, in this way 
 covering even the spinal root ganglia lying along the spinal 
 
ANATOMY. PHYSIOLOGY, OF NERVOUS SYSTEM. 413 
 
 cord. In fact, the dura-mater is loosely attached around 
 the spinal cord and does not serve as a periosteum for the 
 
 Fig. 136. SECTION OF THE SPINAL CORD SHOWING TKE ARRANGEMENT OF ITS INVEST- 
 ING MEMBRANES. (After Key and Retzius.) 
 
 a, dura mater; b, arachnoid; c, posterior septum; d, e,f, subarachnoid tissue; A, an- 
 terior root fibers cut; A, I, subarachnoid space. ^ ^ ' 
 
 vertebrae, these bones having a periosteum of their own. 
 In the meshes of the arachnoid membrane there is usually 
 contained a small quantity of lymph-like liquid called the 
 cerebro-spinal liquid. It is not probable that this has any 
 specific function. 
 
 The Spinal Cord. 
 
 The spinal cord is a cylinder of nervous matter enclosed 
 in the neural arches. Its average length is about seven- 
 teen inches. It does not, therefore, reach from the cer- 
 vical region entirely through the lumbar. In fact, the 
 neural space in the lower lumbar region is occupied by a 
 number of nerve fibers from the spinal cord, while the cord 
 itself is here reduced to a slender filament called the filum 
 terminate which runs to the end of the neural canal in the 
 sacrum. 
 
 The cord is not quite round in cross-section, it being a 
 little wider from side to side than from before backwards. 
 Its average diameter is about three-fourths of an inch. It 
 
414 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 shows, however, two enlargements along its course, one in 
 the cervical region called the cervical enlargement, and a 
 second at the beginning of the lumbar region called the 
 lumbar enlargement. It weighs from one and one-half to 
 two ounces. 
 
 The spinal cord gradually shades off into the brain, and 
 the point at which one is said to cease and the other to be- 
 gin is quite arbitrary. There is no 
 sudden transition from one to the other. 
 If a cross-section be made, the cord is 
 seen to consist of two halves, this bi- 
 lateral arrangement being caused by 
 two deep grooves or fissures running 
 longitudinally along the cord and al- 
 most separating it into a right and left 
 lobe. The division, however, is not 
 complete, the anterior and the posterior 
 fissures not meeting, but the two hemi- 
 spheres being connected near the mid- 
 dle by a commissure consisting partly 
 of gray matter, and anterior to this of 
 white matter. The posterior fissure 
 reaches down to the gray matter, and 
 the anterior fissure to the white com- 
 missure just referred to. In the center 
 of the gray commissure is the cross- 
 section of a canal running lengthwise 
 through the spinal cord and connected 
 in the brain with the ventricles. This 
 is called the central canal, or canal is 
 centralis. It probably has no specific 
 physiological function, but its presence is easily explained 
 by reference to the embryonic development of the spinal 
 cord and brain. 
 
 A cross-section of the cord does not show a uniform ap- 
 pearance, but shows a grouping into two tissues, so dis- 
 posed that the central gray substance is arranged somewhat 
 
 Fig. 137. CROSS-SECTION OF 
 
 HUMAN SPINAL CORD, 
 TWICB NATURAL SIZE. 
 
 A, cervical region; B, dor- 
 sal region ; C, lumbar region ; 
 a, anterior root; p, posterior 
 root. 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 415 
 
 in the form of a capital "H." The commissure of this H 
 is the gray commissure just mentioned, which contains the 
 central canal. Each limb of the H shows, however, a 
 shorter and thicker anterior branch and a somewhat more 
 slender posterior branch. These are called respectively the 
 anterior and posterior horns or cornua. The remaining 
 portion of the cord outside of this central H is composed of 
 white matter which examination with the microscope re- 
 veals to be cross-sections of nerve fibers which are here 
 passing along the cord. The central gray-shaped H owes 
 its grayish color to the fact that it contains aggregations of 
 nerve cells, which are always gray, and of nerve fibers 
 which do not possess the white medullary coat, and so are 
 also gray. On the other hand, the white appearance of the 
 surrounding portions is due to the presence of the white 
 medullary coats of the nerve fibers. Just anterior to the 
 gray commissure is the white commissure already men- 
 tioned, formed by fibers connecting the white matter of one 
 side with the white of the other. By means of the horns 
 of the gray matter the area of the cord is divided into 
 several easily distinguishable regions. The white matter 
 included between the anterior horns is spoken of as the 
 anterior white column, that included between the posterior 
 horns is called the posterior white column, while that por- 
 tion on each side lying in the hollow of each of the cres- 
 cent-shaped limbs is called the lateral column. These 
 columns are of the deepest interest in the discussion of the 
 course of fibers through the brain and cord, a point to be 
 treated further on 
 
 The Spinal Nerves. 
 
 If a cross-section of the cord had been made between the 
 origins of the spinal nerves, the section as just described 
 would have included all the points visible. If, however, the 
 section should have passed through that region of the cord 
 from which a pair of spinal roots takes its issue several ad- 
 ditional points would appear. Running out from the an- 
 terior and posterior horns, fibers might be traced leaving 
 
416 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 the cord, running for some distance laterally from the cord 
 as separate trunks, but before leaving the dura-mater, unit- 
 ing on each side to form a single spinal nerve. On the 
 posterior root of the spinal nerve just previous to its union 
 with the anterior root, occurs a ganglion called for evident 
 reasons the posterior spinal root ganglion. The physiolog- 
 ical significance of these roots need not concern us here, 
 save the preliminary statement that the fibers which leave 
 the cord from the anterior horn are motor in their nature ; 
 that is, carry impulses outward towards the muscles, while 
 the fibers entering at the posterior horn are sensory fibers 
 carrying sensations inward to the cord and brain. 
 
 Immediately after the formation of the spinal nerve by 
 the union of sensory and motor trunks it divides into three 
 branches, a posterior primary, distributed mainly to the 
 skin and muscles of the back, an anterior primary, giving 
 off nerves for the sides and ventral portion of the trunk 
 and for the limbs, and a third communicating branch which 
 runs to the neighboring sympathetic ganglion. It is through 
 this connecting branch that the co-ordination and subordi- 
 nation of the sympathetic system is effected. 
 
 Thirty-one pairs of such spinal nerve trunks arise from 
 the spinal cord, leaving the neural canal through the inter- 
 vertebral foramina. Each of these spinal nerves has a 
 specific name, the name being derived from the vertebra 
 situated immediately in front of it. Thus, the nerve that 
 arises between the second and third thoracic vertebrae is the 
 second thoracic spinal nerve ; that which arises between the 
 fourth and fifth lumbar vertebrae is the fourth lumbar nerve. 
 The spinal nerves which arise in the lower lumbar, sacral 
 and coccygeal region run down through the neural canal, 
 occupying the space in this portion which the cord has 
 further up, the cord being here reduced to the filum ter- 
 minale. This big bunch of nerves is called the horse's 
 tail, or cauda eq^l^na. 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 417 
 GENERAL DISTRIBUTION OF THE SPINAL NERVES. 
 
 It would be quite undesirable from the standpoint of an 
 elementary text-book to give with surgical exactness the 
 distribution of these thirty-one pairs of spinal nerves. 
 Suffice the general statement that these spinal nerves sup- 
 ply the voluntary muscles of the neck and the trunk ; that 
 as the phrenic nerve they control the diaphragm; as sen- 
 sory nerves they are distributed to the entire skin of neck, 
 trunk and limbs, while as motor nerves they innervate the 
 muscles of the limbs and figure in all their voluntary move- 
 ments. In a word, it may be said that the spinal nerves 
 innervate all that portion of the body below the head from 
 which we derive special sensations or in which we are able 
 to produce voluntary movements. In addition to this, com- 
 municating branches reach the sympathetic system and 
 bring it into physiological connection with the brain and 
 spinal cord. 
 
 THE BRAIN. 
 
 Under the term "brain" is included all that portion of 
 the cerebro-spinal system lying above and including the 
 medulla oblongata. It consists of three main divisions ap- 
 parent at once to the unaided eye: the large fore-brain or 
 cerebrum, the hind-brain consisting of the cerebellum and 
 the medulla oblongata lying immediately below it, and the 
 mid-brain lying between the cerebrum and hind-brain and 
 consisting of the corpora quadrigemina and crura cerebri. 
 
 Weight. The weight of the brain varies considerably, 
 an average weight being in the neighborhood of fifty 
 ounces in the adult male and about forty-five in the female. 
 Of this weight of fifty ounces the fore-brain or cerebrum 
 weighs about forty-four, being therefore very much larger 
 than the hind-brain and mid-brain together. In fact, it 
 laps entirely over the other portions, so that a view from 
 above would not disclose either the cerebellum or mid- 
 brain. This especial development of the fore-brain is, how- 
 ever, a characteristic of the human species alone. As we 
 
418 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 go down the animal scale the relative difference decreases 
 until in some of the lower vertebrates the fore-brain is the 
 smallest of the divisions. This is especially true in the 
 fishes, in which the mid-brain or optic lobes form the bulk 
 of this organ. The cerebellum and medulla, on the other 
 hand, do not decrease in the same proportion, but are rela- 
 tively large in all animals. The disproportionate size of the 
 human cerebrum makes possible those higher psychical 
 functions which belong to man alone. 
 
 Convolutions. The cerebrum is divided by a deep 
 median fissure into two almost separate halves called the 
 cerebral hemispheres. Viewed from the top and sides the 
 surface of the cerebrum is thrown into deep convolutions or 
 gyri. While these convolutions occur in the brains of many 
 of the lower animals they are much deeper in the human 
 species, and there is even an increase in the depth as we 
 proceed from the lower to the higher races of mankind. 
 These convolutions find their explanation in the fact that 
 the surface of the brain is thereby materially increased. 
 Rough calculations on the actual surface of the average 
 brain show that it may reach an extent almost equal to 
 that of the larger portion of the trunk itself, but by means 
 of these foldings this surface is enclosed in the relatively 
 small cranium. The desirability for a large cortical surface 
 is apparent when it is remembered that the principal cells 
 concerned in sensation and volition are found here. While 
 these convolutions seem to run without any appearance at 
 regularity, and while in detail they do differ somewhat in 
 different individuals, their general plan is constant, and by 
 means of them spots on the cortex of the brain are local- 
 ized. A few of the principal convolutions only, need be 
 mentioned here. One of these is the large fissure of Syl- 
 vius, on each side of the brain which lies between the lateral 
 lobes of the brain and the main portion, running from the 
 base of the brain upwards and backwards towards the oc- 
 cipital region. Connecting with the fissure and running 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 419 
 
 upwards towards the top of the brain separating from the 
 main portion of the cerebrum, the frontal lobes, is the 
 fissure of Rolando. The fissure of Sylvius is important as 
 being the most apparent and deepest furrow. The fissure 
 of Rolando is interesting as being the region along which 
 many of the centers of conscious volition have been by ex- 
 periments localized. If the fissure of Sylvius be opened 
 with the fingers it discloses to view a lobe of the brain 
 hidden in this fissure known as the Island of Rcil. If from 
 the top the two cerebral hemispheres be pushed apart it will 
 be seen that the median fissure reaches down to a white 
 band of connecting fibers which runs from one hemisphere 
 to the other. This band of connecting fibers is called the 
 corpus callosum. 
 
 Base of Drain. If now the base of the cerebrum be 
 studied it reveals a number of structures easily recognizable 
 with the unaided eye. Lying immediately under the frontal 
 lobes are the olfactory lobes. These are bits of grayish, 
 nervous tissue and are the nerves concerned in the sense of 
 smell. They are quite inconspicuous in man, but in some 
 of the lower animals reach very large proportions, some- 
 times being larger than the cerebral hemispheres themselves. 
 This may probably be interpreted as meaning that the sense 
 of smell is relatively dull in man as compared with many of 
 the lower forms, which have to rely upon this sense in 
 searching for their food or avoiding their enemies. 
 
 Immediately back of the olfactory lobes the large optic 
 nerves arise. These optic nerves seem to cross at the base 
 of the brain in the optic commissure and are continued back 
 into the brain beyond this commissure as the optic tracts. 
 These tracts may be followed some distance around the 
 crura cerebri into the tissue of the brain. There is not a 
 complete crossing, however, of the optic nerves at the com- 
 missure, but the decussation is limited to half of the fibers 
 so that the optic nerve on each side consists of half of the 
 fibers from its own optic tract, the other half from the op- 
 posite optic tract which reached it in the commissure. 
 
420 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 Immediately behind the optic commissure there is a fun- 
 nel-like projection called the infundibulum. At the end of 
 this infundibulum lies a peculiar gland-shaped body familiar 
 as the pituitary body, a structure described in the chapter 
 on the ductless glands. The infundibulum is hollow, the 
 cavity in the same being an extension of the third ventricle. 
 On account of the thinness of its walls and the difficulty 
 with which the pituitary body is removed from the skull, 
 these structures are usually torn off in prepared brains and 
 the place of the infundibulum is indicated only by an open- 
 ing leading into the third ventricle. 
 
 Posterior to the infundibulum and just in the angle of 
 the crura cerebri lie two small whitish elevations each about 
 the size of a small bullet, the corpora albicantia. It will be 
 pointed out further on that these corpora albicantia are pro- 
 jections caused by the sudden bending back at this point of 
 the fornices, which are bands of nerve fibers running 
 through the brain. These fibers run to the bottom of the 
 brain as if to leave it at this point, and then make a sharp 
 turn and run almost directly backwards. It is this lobe of 
 the fornix which projects from the brain below, and which, 
 consisting of white nerve fibers, gives to these structures 
 their peculiar appearance. 
 
 Following this it may be noticed that the continuation 
 of the cord here divides into two forks, one running to the 
 right hemisphere and the other to the left. These two forks 
 are called the legs of the brain, or the crura cerebri. They 
 are, of course, the big tracts by means of which the hemis- 
 pheres of the brain are put in direct communication with the 
 nervous system below. 
 
 Near the middle of the crura cerebri arises the third pair 
 of cranial nerves, the stumps of which usually appear as rel- 
 atively large nerves. 
 
 A little distance farther back lies the pons Varolii, 
 readily distinguishable as a thickened band around the me- 
 dulla. This pons or bridge consists largely of fibers which 
 run across the cord at this point and connect the two sides 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 421 
 
 of the cerebellum. In a general way, disregarding certain 
 sets of fibers the cerebellum and the pons may be compared 
 to a signet ring, the band of which is the pons, the signet 
 being the large cerebellum itself, the finger the cord pass- 
 ing between. It is well to repeat again that this analogy is 
 not quite true either anatomically or physiologically, but the 
 detailed course of the fibers at this point will be followed in 
 a succeeding chapter. 
 
 Immediately back of the pons is the medulla, with its 
 widest portion near the pons and gradually tapering back- 
 ward until it reaches the size of the cord into which it 
 gradually blends. Along the pons and the medulla arise the 
 remaining cranial nerves. 
 
 While all of these structures at the base of the brain 
 have been described in connection with the cerebrum, some 
 belong to the mid or hind-brain in reality. The fore-brain 
 extends to the beginning of the crura cerebri and the 
 mid-brain as seen from below includes the crura cerebri, 
 while the hind-brain consists of the pons, medulla oblon- 
 gata and cerebellum. If by means of the fingers the cere- 
 brum and cerebellum be pushed apart by tearing away the 
 brain coverings which hold them in place, here, the dorsal 
 view of the mid-brain appears. This is marked by four 
 hemispherical eminences called the corpora quadrigemina. 
 Of these the anterior pair is much larger and is called the 
 nates, the posterior pair the testcs. These corpora quadri- 
 gemina occupy on the dorsal side of the mid-brain the posi- 
 tion held by the crura cerebri on the base. If the cerebrum 
 and the mid-brain be torn apart somewhat, there will be 
 seen lying, just anterior to the corpora quadrigemina and 
 on the median line of the body, a small gland-like structure 
 about the size of a pea or smaller, known as the pineal 
 gland. This pineal gland is not connected with the mid- 
 brain at all, but arises from the two optic thalami lying 
 immediately anterior. This structure was the object of some 
 speculation formerly when the view was advanced that being 
 the only unpaired structure in the brain it must be the seat 
 
422 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 of the soul, the soul being considered an individual and not 
 divisible into halves. Such speculation soon came to grief, 
 however, when it was discovered that this pineal gland was 
 relatively larger in the lower animals, and as greater dimen- 
 sions of soul were not to be attributed by these thinkers to 
 the brute creation, this view had to be abandoned. Its sci- 
 entific explanation is now, however, evident, it being noth- 
 ing more than the stump of an optic nerve which in the 
 early history of evolution connected with a third eye. All 
 traces of the eye are gone in all the higher animals, but the 
 proximal stump of the nerve is still present. In some of the 
 lower animals, certain forms of lizards, the pineal gland 
 still connects with a retinal structure, although even here it 
 has ceased to be functional. 
 
 The surface of the cerebellum differs essentially from that 
 of the cerebrum. It has no true convolutions, although 
 marked by a series of transverse ridges. It is divided into 
 three lobes, a central or middle lobe and the two lateral 
 lobes. At the outer lower edge of each lateral lobe there is 
 a small added lobe called the flocculus. 
 
 The Interior of the Brain. 
 
 The Ventricles of the Brain. Before describing the 
 structures lying within the brain it seems desirable to show 
 the topography of the ventricles of the brain in order that 
 the other structures may be located with reference to these. 
 
 The central canal of the spinal cord runs upward into the 
 medulla and here widens out into a large ventricle called 
 the fourth ventricle of the brain. This ventricle lies im- 
 mediately below the cerebellum. Instead of lying in the 
 center of the medulla it lies very close to the dorsal surface, 
 that is, next to the cerebellum, and separated from it by a 
 very thin wall only. This wall is easily torn and the inte- 
 rior of the ventricle laid bare. The width of the ventricle 
 here is considerable, a half inch or more. Proceeding up- 
 wards the ventricle again narrows into a small canal in the 
 mid-brain and as such a small canal passes entirely through 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 423 
 
 this part. This small caiial is known as the aqueduct of 
 Sylvius, or more usually the iter. This iter lies between 
 the copora quadrigemina and the crura cerebri. Immediately 
 upon reaching the cerebrum the iter enlarges into the third 
 ventricle. This ventricle lies between the optic thalami and 
 extends down into the infundibulum already described. Both 
 the fourth ventricle, the iter, and the third ventricle lie in a 
 median position. At the forward end, the third ventricle 
 narrows into two openings, known as the foramina of 
 Monro, and each of these opens at once into a large lateral 
 ventricle which lies within each cerebral hemisphere. These 
 lateral ventricles are relatively very large, and extend from 
 near the front of the brain to the occipital region, while a 
 horn of this ventricle dips down almost to the bottom of 
 the lateral lobes. 
 
 The two lateral ventricles are separated from each other 
 by a thin partition, which partition in front of the third 
 ventricle is called the septum hicidum. This septum luci- 
 dum is really double, enclosing a small space within itself. 
 This space is called the fifth ventricle of the brain. It is 
 necessary, however, to bear in mind that this fifth ventricle 
 is not a true ventricle at all. It has no connection what- 
 ever with the other ventricles, and is really only an acci- 
 dental opening formed in the septum lucidum as the brain 
 developed. . 
 
 Interior Structures. If with a scalpel sections of the cer- 
 ebrum parallel to the base of the brain should be cut off 
 there would soon be reached the bottom of the fissure divid- 
 ing the brain into two hemispheres. Examination of this 
 bottom shows it to be made up of a sheet of white nerve 
 fibers extending from one hemisphere to the other. This 
 sheet of connecting fibers is the corpus callosttm. If after 
 having been laid open, the corpus callosum is gently cut 
 loose and lifted off the structures below it, the two lateral 
 ventricles come to view, the corpus callosum forming the 
 roof of these lateral ventricles. The two lateral ventricles 
 
424 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 can then be easily seen to be separated from each other by 
 a band of tissue running perpendicularly along the median 
 line of the brain from the corpus callosum to the floor of 
 the ventricles, while towards the front of the brain this 
 septum would be continuous with the septum lucidum. 
 
 If the corpus callosum should be entirely removed the 
 entire floor of each ventricle is exposed. In the anterior 
 portion of this floor lie the corpora striata, eminences of gray 
 nerve matter each about the size of an almond. In position 
 these corpora striata lie just to the right and left of the sep- 
 tum lucidum. The floor in the posterior portion of the 
 ventricles is made by a triangular mass of white tissue with 
 its broad side towards the mid-brain and tapering towards 
 the septum lucidum. This white tissue bends abruptly 
 downward posteriorly at each side and runs to the base of 
 the lateral lobes of the brain following the ventricle in this 
 region. This broadened portion is called the hippocampiis . 
 Towards the septum lucidum this becomes gradually nar- 
 rower and where it bends downwards it is on each side called 
 \htfornix (pillar). Immediately under the fornix on each 
 side, and between it and the optic thalamus beneath is the 
 foramen of Monro already referred to. The fornices are not 
 continuous with the septum lucidum, as they seem at first 
 sight to be, but bend abruptly downwards in front of the 
 third ventricle reaching the base of the brain. Here they 
 make a sharp turn recognizable as the corpora albicantia, 
 and end in the optic thalami. 
 
 The hippocampi are like the corpus callosum composed 
 of nerve fibers and are one of the most important bands of 
 association fibers in the brain. If by means of the scalpel 
 the fornices be cut and this entire bit of nerve fiber matter 
 lifted off or folded back there are disclosed two large bodies 
 immediately below them called the oplic thalami. The optic 
 thalami lie immediately anterior to the nates. Between the 
 optic thalami lies the third ventricle, the roof which is there- 
 fore practically formed by this band of nerve fibers just 
 removed. 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 425 
 
 The continuation of the third ventricle down into the 
 infundibulum is now apparent. Running across the third 
 ventricle from one side to the other may be seen several 
 commissures serving to connect the sides. The attachment 
 of the pineal gland to the optic thalami is now also evident. 
 From the blood-vessels which supply the brain several 
 arterial branches reach the third ventricle and are from the 
 third ventricle carried through the foramina of Monro into 
 the lateral ventricles, where as the choroid plexus of the 
 brain they line the walls of these ventricles more or less 
 completely and serve to nourish them. It not infrequently 
 happens that these delicate blood-vessels are injured and a 
 hemorrhage of the brain occurs, inducing apoplexy. 
 
 If an incision should be made through the corpus stria- 
 turn it would be seen to be divided in its posterior region 
 into an inner and outer portion by a band of white nerve 
 fibers. This band is called the internal capsule and consists 
 of a large number of nerve fibers which are on their way 
 from the surface of the cerebral hemisphere to the cord. 
 
 The Cranial Nerves. 
 
 Twelve pairs of nerves arise from the base of the brain, 
 the names of which in their successive order and the distri- 
 bution of which are as follows: 
 
 First. The olfactory nerve passing through the cribri- 
 form plate of the ethmoid and innervating the membrane of 
 the nose. It is the nerve of smell. It differs materially 
 from other nerves in that the fibers are not wrapped up into 
 definite nerve trunks by a connective tissue epineurium. 
 
 Second. The optic nerves leading to the eye and spread- 
 ing out there in the retina. They are wholly sensory, carry- 
 ing the visual sensations to the brain. 
 
 Third. The motores occult. These arise from the crura 
 cerebri and are distributed to the muscles of the eye, ex- 
 cluding, however, the external rectus and superior oblique. 
 They are motor nerves and control the movements of the 
 eye which these muscles produce. In addition to that, fibers 
 
426 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 from the motores occuli reach the muscles of accommoda- 
 tion and the muscles of the iris. It is this latter nerve 
 which in a reflex way causes the contraction of the pupil 
 when the eye is subjected to an increased amount of light. 
 It is interesting to note that a contraction or relaxation 
 of the muscles of the iris is never confined to one eye alone, 
 but that both eyes move in unison. It is evident, there- 
 fore, that the motores occuli of the right and left eye are in 
 direct anatomical communication with each other at or near 
 their place of origin. Fibers from this same nerve control 
 the muscles of the upper eye-lid. That this nerve is the 
 most important motor nerve of the eye may be readily seen 
 from its innervation, and a section of the nerve induces at 
 once the relaxation and closing of the upper eye-lid ; the 
 impossibility to move the ball of the eye, a dilatation of the 
 pupil, and the impossibility of a contraction of the same 
 even when subjected to a strong light, and finally a paral- 
 ysis of the accommodation of the eye so that the focus of 
 the eye is immovably set for distant objects. 
 
 Fourth. The pathetici. The pathetici leave the brain 
 immediately anterior to the pons Varolii, innervate the su- 
 perior oblique muscles and so help to control the move- 
 ments of the eye in so far as they are affected by these 
 muscles. The cutting of the patheticus nerve seems to 
 show no immediate results in the eye, but an animal so 
 treated is unable to fix its gaze upon a certain point when 
 its head is turned. By the paralysis of the superior oblique 
 muscle the eyeball affected is rotated along with the head. 
 In this way the two eyes are not directed to the same point 
 and a double vision occurs. 
 
 Fifth. The trigeminales . The fifth pair of nerves, the 
 trigeminales, contain both motor and sensory fibers. They 
 arise from the medulla each in two roots, the smaller of 
 which contains the motor fibers which arise from centers in 
 the floor of the fourth ventricle, while the larger is sensory. 
 This larger root before joining the motor one passes 
 through the large Gasscrian ganglion. The sensory fibers 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 427 
 
 arise in a number of scattered places in the medulla, and in 
 this way are brought into direct communication with quite 
 a number of different centers and fibers. After the passage' 
 of the sensory branch through the Gasserian ganglion it 
 unites with the motor branch to form the main trunk. This 
 trunk, however, soon divides into three main branches, 
 hence the name of the nerve, which in a general way are 
 distributed as follows: a. The ophthalmic branch going to 
 the muscles and skin of the forehead and upper eyelid, and 
 the mucous membrane of the nose. b. The superior max- 
 illary branch innervating the skin of the temples, the cheeks 
 and the angle of the mouth and upper teeth, and within the 
 mouth the mucous membrane or pharynx and soft palate. 
 c. The inferior maxillary, distributed to the side of the 
 head, the external ear, the skin of the lower part of the 
 face, the lower teeth, the salivary glands, the top of the 
 tongue and the muscles which move the lower jaw in the 
 process of mastication. 
 
 While anatomically it is thus divided into three branches 
 physiologically it contains quite a number of different kinds 
 of nerves as follows: (1) Sensory nerves. It is the sen- 
 sory nerve for the dura mater, for the skin of the entire 
 face, for the orbit of the eye as well as the ball of the eye, 
 for the nose, the mouth, the top of the tongue, the gums, 
 the teeth, the surface of the ear and the auditory meati. In 
 a word, by means of this nerve the sensation of touch is 
 made possible in all the regions mentioned. (2) Motor 
 fibers. It innervates the muscles of mastication, a muscle 
 of the soft palate and the tensor muscle of the midde ear. 
 (3) Secretory fibers to the lachrymal glands, arousing 
 these to the secretion of the tears. (4) Gustatory nerves 
 which are distributed to the tongue. This function is de- 
 nied by some observers, but it is probable that the sensations 
 of sweet and sour at the tip of the tongue are carried by this 
 nerve. (5) Vaso-motor fibers for the blood-vessels of the 
 eye, the gums and the tongue, by means of which the vas- 
 cular supply of these structures is to a certain extent con- 
 
428 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 trolled. (6) Reflex nerves; that is, nerve fibers which by 
 a reflex action bring about the involuntary closing of the 
 eyelid, such as winking, or which cause coughing and 
 sneezing, or the involuntary movements of swallowing when 
 the soft palate is stimulated. (7) Fibers which in a reflex 
 way bring about not muscular contractions, as in number 6, 
 but secretions of saliva or tears, occasioned by the stimula- 
 tion respectively of the mucous membrane of the mouth or 
 an irritation of the conjunctiva of the eye. 
 
 Sixth. The abducentes. The abducentes nerves arise 
 from the medulla and are distributed to the external recti of 
 the eyes controlling their movements. The sectioning of 
 this nerve causes a turning of the affected eyeball inwards. 
 
 Seventh. The faciales. The faciales or facial nerves 
 arise on the floor of the fourth ventricle and are distributed 
 mainly to the muscles of the face. It is, therefore, almost 
 wholly a motor nerve and is of special importance from the 
 fact that it is the nerve which controls the muscles of ex- 
 pression and mimicry. 
 
 Eighth. The acoustid. The nerves acoustici or audi- 
 tory nerves have their origin in centers in the floor of the 
 fourth ventricle of the medulla and innervate the inner ear. 
 They are sensory and carry to the brain the sensations of 
 sound. 
 
 Ninth. The glossopharyngcah. The glossopharyngeal 
 nerves are the nerves of taste and are distributed mainly to 
 the posterior portions of the tongue. Fibers, however, 
 reach the tip of the tongue as well, which fibers are be- 
 lieved by some physiologists to cause the sensation of bitter 
 at this point. The sensations of sweet and sour are by 
 these same investigators referred to the trigeminal nerve. 
 On the back of the tongue, however, the glossopharyn- 
 geal nerves are able to carry sensations of sweet and sour 
 as well. They also innervate the mucous membrane of the 
 back of the nose and the pharynx. They contain a few mo- 
 tor fibers for certain muscles of the pharynx, and send to the 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 429 
 
 parotid gland the nerves which control the secretion of the 
 same. 
 
 Tenth. The vagi. The vagi or pneumogastrics are the 
 longest of the cranial nerves and their distribution widest. 
 They send branches to the pharynx, gullet, larynx, wind- 
 pipe, lungs, heart, stomach, and even read; the solar plexus 
 in the mesentery. They contain: First. Motor fibers for 
 the muscles of the pharynx, oesophagus and larynx, for the 
 muscular coat of the stomach and the muscles of the princi- 
 pal portion of the small intestine. Second. Inhibitory fibers 
 for the heart. Third. Sensory fibers for the throat, the 
 oesophagus and lungs. Fourth. Reflex fibers which affect 
 the process of inspiration and expiration. FiftJi. In man, 
 finally, it contains the depressor nerve (separate in the 
 rabbit) which runs from the heart to the brain and carries 
 sensory impulses to the brain. This depressor figures inte- 
 grally in the vascular supply of the body. 
 
 Eleventh. The accessorii. The spinal accessory nerves 
 in reality arise from the cervical portion of the spinal cord, 
 but run into the skull alongside of the spinal cord, receiv- 
 ing a few fibers from the medulla and then pass out with 
 the pneumogastric nerves. Bach gives off a branch to the 
 pneumogastric nerve, while the main portion of the trunk 
 is distributed to the muscles of the shoulder. 
 
 T^velfth. The hypoglossi. The hypoglossal nerves are 
 the motor nerves of the tongue and innervate all of the 
 muscles of the same. They carry, however, a few sensory 
 and vaso-motor fibers to the tongue. This nerve is of espe- 
 cial interest in the consideration of the process of mastica- 
 tion, and better still in the production of articulate speech. 
 
 The Sympathetic System. 
 
 The sympathetic system consists of two chains of ganglia 
 lying alongside the backbone and easily visible when the 
 chest and abdominal viscera are removed. Each chain con- 
 sists of twenty-four ganglia. In the coccygeal region the 
 two chains meet in a median - placed ganglion, making, 
 
430 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 therefore, the total number of sympathetic ganglia twenty- 
 four pairs and one; that is, forty-nine ganglia. The gan- 
 glia on each side are connected with each other by means 
 of nerves, while the first ganglion in the cervical region is 
 connected in turn with the brain. 
 
 In addition to the connections which each ganglion has 
 with the one preceding and the one following, two other 
 nerves arise from it. One of these is the communicating 
 branch already referred to in the description of the spinal 
 cord, a branch by means of which the sympathetic ganglion 
 is anatomically connected with the spinal cord. The other 
 is the visceral nerve proper, the nerve trunk distributed to 
 the viscera, carrying to the same the impulses of this cen- 
 tral ganglion, or conveying to these ganglia impulses from 
 the viscera. A very important nerve of this kind is the 
 sympathetic nerve which reaches the heart and is already 
 familiar as the cardio-accelerator. The visceral branches 
 of a number of abdominal ganglia unite to form a common 
 nerve trunk on each side called the splanchnic nerve. This 
 nerve is distributed to the abdominal viscera through the 
 solar plexus in the mesentery. 
 
 The term sympathetic is a rather unfortunate one, as it 
 frequently leads to the impression that it is mainly concerned 
 with phenomena to which the somewhat vague term of sym- 
 pathy is applied. That, to use a stereotyped expression, it 
 keeps one part of the body in sympathy with another. 
 Such an expression is, of course, from a scientific standpoint 
 perfectly meaningless. If the term " visceral" system could 
 be generally applied to it this misinterpretation might be 
 avoided, while at the same time the term "visceral" would 
 give a clue to the function of this system which is in a 
 general way concerned with the physiological activities of 
 the visceral organs. 
 
 General Histology. 
 
 Having in the previous paragraphs called attention to 
 the systems as a whole and their relation to each other, the 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 431 
 
 next step is to study in detail the individual units of which 
 these systems are composed. 
 
 The unit by the multiplied arrangements of which the en- 
 tire structure of the nervous system is built up is called the 
 neuron. A neuron is a nervous cell together with the nerves 
 running out from it. By this name, therefore, is included 
 not the nerve cell merely, but the nerve fiber as well. It 
 has the advantage of doing away with that arbitrary dis- 
 tinction between nerve cells and nerve fibers, and gives em- 
 phasis to the fact that a nerve cell with the fibers springing 
 from it is a unit physiologically as well as anatomically. 
 
 But the value of this name is further increased by the 
 fact that all the neurons in the entire nervous system are 
 supposed to be distinct and independent anatomically and 
 possibly to some extent physiologically. A neuron is to the 
 nervous system what a single citizen is to the state. In 
 fact, recent researches show that the different neurons of 
 the body are not in direct anatomical continuity, but that 
 each is an anatomical entity, and that impulses from one 
 neuron to the other can be sent only by having one neuron 
 act as a stimulus in arousing a new impulse in the second. 
 It is not the simple original impulse that can reach the sec- 
 ond neuron, any more than in two persons joining hands is it 
 the pain experienced by one that is transmitted to the other. 
 The first as a stimulus must reproduce the same pain in the 
 second anew. The relative arrangements and the super- 
 position of the various neurons of the central nervous system 
 will be discussed further on in this chapter, it being the 
 point here to treat of their general histology merely. 
 
 Neurons. 
 
 One of the most remarkable things about a neuron is 
 usually its size. While there are neurons lying within the 
 central nervous system only a few centimeters or less in 
 length, there are, on the other hand, neurons having a 
 length of several feet. Such neurons, for instance, as reach 
 from the cortex of the brain to the lumbar cord, or still 
 
432 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 others reaching from the spinal cord to the ends of the 
 extremities. Anatomically neurons are classed on the basis 
 of the number of nerves issuing from the cell body. A 
 nervous cell with a single nerve fiber issuing from it is 
 spoken of as mono-neuric. These mono-neuric cells are, 
 however, physiologically really di-neuric, the single nerve 
 containing passages leading towards the cell and away from 
 
 it, and so being practically 
 the same as two separate 
 nerves. The usual type is 
 the di-neuric neuron. 
 
 More than two nerves, 
 however, may arise, in 
 which case the neuron is 
 spoken of as poly-neuric. 
 Illustrations of di - neuric 
 neurons may be found in 
 such ganglia as the spinal 
 root ganglia, in which a 
 nerve runs to each cell body 
 and a second nerve away 
 from it. Usually one of the 
 fibers or extensions of the 
 cell body becomes a typi- 
 cal nerve, while the other 
 branches sub-divide repeat- 
 edly and form a perfect 
 network of smaller fibrils 
 reaching out in various di- 
 rections. Such branched terminations are spoken of from 
 their resemblance to trees as dendrons. These dendrons do 
 not reach to distant points like the nerve does to skin, mus- 
 cles or sense-organs, but seem to terminate among the neigh- 
 boring cells and it is believed that impulses from one cell to 
 another are carried by dendrons of these contiguous nerves. 
 A neuron, therefore, consists essentially of two parts; 
 the cell body and its extensions into nerves and dendrons. 
 
 Figf. 138. A POLY-NEURIC GANGLION CELL. 
 
 (After Gegenbaur.) 
 
 Dotted line indicates the main axis-cylin- 
 der. 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 433 
 
 The cell body is usually much larger than that of other cells 
 in the body and is composed of granular protoplasm contain- 
 
 Fig. 139. TWO CORPUSCLES OF PURKINJE FROM THE CEREBELLUM SHOWING THEIR IN- 
 VESTMENT WITH DENDRONS FROM CELLS OF THE OUTER GRAY MATTER. (After 
 
 Ramon y Cajal.) 
 
 a, axis-cylinder of corpuscle of Purkinje; &, network of dendrons. 
 
 ing a relatively large nucleus. The cell body is really the 
 center of energy. We must imagine that here, in some 
 chemical way no doubt, energy is liberated which takes the 
 form of nervous activity. That such a breaking down of 
 the substance of nerve cells occurs when they are being 
 stimulated has been satisfactorily proved by experiments in 
 which nerve cells were subjected to long continued stimuli, 
 then examined with a microscope and compared with similar 
 cells not so stimulated. Such stimulated cells shrink in 
 volume, and in the plainest way indicate a severe loss of 
 their substance. The nucleus becomes much smaller. 
 Similar observations have been made on old nerve cells. 
 Here, too, the cell body becomes shrunken and the nucleus 
 practically disappears. Sometimes the cell body may dis- 
 appear altogether. 
 
 The Nerves. 
 
 While in a direct sense the term "nerve" might include 
 the dendrons it is more usually referred to the main fiber 
 leading from the cell to muscle, skin, sense-organ, or other 
 neurons. If such a nerve be examined a little distance 
 
 28 
 
434 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 away from the center from which it originated, it seems in 
 a fresh condition almost homogeneous, but when allowed to 
 stand or treated with proper re-agents it soon resolves itself 
 into three structures. 
 
 Axis- Cylinder. Running through the 
 center of the nerve fiber as a continuation 
 of the nerve cell itself is the axis-cylin- 
 der. This is the real nerve matter of the 
 fiber, and is the only one that is really 
 physiologically concerned in the carrying 
 of nervous impulses. In fact, the two 
 other coats may sometimes be absent alto- 
 gether, but an axis-cylinder can never be 
 absent. 
 
 Medullary Sheath. Surrounding the 
 axis-cylinder is a thick whitish-looking 
 coat called the medullary sheath. This 
 medullary sheath seems interrupted at in- 
 tervals of about one-twenty-fifth of an 
 inch, which interruptions are called the 
 nodes of Ranvier. The medullary coat 
 between two consecutive nodes contains a 
 large nucleus and gives evidence that this 
 inter-node is of cellular origin. Chem- 
 ically the medullary coat consists of a 
 substance called myelin, a substance 
 somewhat akin to that derived from cer- 
 tain connective tissues. 
 
 Fig. 140. MEDULLATED 
 
 NERVE-FIBER TREATED 
 
 WITH OSMIC ACID. (After 
 Key and Retzius.) 
 
 Primitive Sheath. Around the med- 
 ullary coat in turn is a thin epithelial coat 
 
 E, node of Ranvier; K, 11 i ,1 1 , t 
 
 nucleus of medullary called the primitive sheath or neurolem- 
 
 and ax 
 
 show. 
 
 primitive sheath ma or by ot hers the sheath of Schwann. 
 
 is - cylinder also 
 
 The medullary coat ceases near the cell 
 from which the axis-cylinder arises, but the primitive sheath 
 is usually continued over the cell body itself. This sheath 
 further dips down into the nodes of Ranvier. 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 435 
 
 Two opposing views are prevalent as to the nature of 
 the axis-cylinder. According to one view this cylinder 
 consists of a bundle of still finer fibrillae, too small to be 
 resolved by the microscope, and along these fine fibrillae the 
 nervous impulses are supposed to pass. The presence of 
 many such fibrillae in a single axis-cylinder would explain 
 how a single nerve fiber might branch near its termination, 
 as many do. By others the axis-cylinder is looked upon as 
 a tube of nervous plasm, through which the nervous impulse 
 finds its way, and the branching of the nerve fibers is ex- 
 plained in the same way as the terminal branchings of a 
 water-main. 
 
 The medullary sheath forms soon after the appearance 
 of the axis-cylinder and arises from certain cells which sur- 
 round the axis-cylinder much like a string of spools would 
 surround a wire passing through them. The substance of 
 these enclosing cells after they have elongated is changed 
 into myelin, retaining, however, its nucleus. The divisions 
 between contiguous cells is still indicated by the nodes of 
 Ranvier. 
 
 While the matter of origin of the medullary sheath is, 
 therefore, fairly clear we are almost entirely at sea for its 
 physiological explanation. That it serves as a kind of insu- 
 lation for the nervous impulse somewhat like the silk around 
 a copper wire seems hardly true. There is nothing to 
 warrant such a belief. That it may serve as a protection 
 against changes of temperature, and possibly even in a 
 mechanical way, may be true in some cases but would hardly 
 explain the existence of a medullary sheath in the brain or 
 spinal cord itself where fluctuations of temperature certainly 
 do not occur. The statement that nerves do not become 
 functional until the medullary coat is developed does not 
 necessarily mean that the function depends upon this coat. 
 It may simply mean that the axis-cylinder becomes func- 
 tional about the same period that the medullary sheath 
 
436 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 appears. Until further light, therefore, is thrown upon the 
 subject we must look upon this coat as practically unex- 
 plained. 
 
 Gray Fibers. 
 
 Not all nerve fibers possess the medullary coat. The 
 majority of the fibers of the sympathetic system are devoid 
 of it as well as a number of cerebro-spinal nerves. 
 
 As the medullary coat is white it gives when present the 
 white appearance to the fiber, and for this reason medul- 
 lated fibers are frequently referred to as white fibers. The 
 absence of the coat, however, allows the gray color of the 
 axis-cylinder to appear, and for this reason non-medullated 
 fibers are usually referred to as gray fibers. It is well to 
 bear in mind, however, that this is a purely arbitrary dis- 
 tinction depending wholly upon an accidental covering and 
 refers in no way to differences in the nervous matter itself. 
 
 Nerve Trunks. 
 
 Nerve fibers do not as a rule run singly, but are col- 
 lected into large bundles familiar as nerve trunks. Ex- 
 amples of such nerve trunks may be the sciatic nerve or 
 optic nerve ; in fact any of those whitish threads which in 
 ordinary dissection appear as nerves. Such trunks are 
 easily recognized as nerve trunks by their whitish appear- 
 ance ; but this whitish appearance is really due to the con- 
 nective tissue which is wrapped around the enclosed fibers. 
 A cross-section of a nerve trunk would reveal about the 
 following general arrangement: 
 
 The individual nerve fibers are grouped in from one to 
 many definite bundles called funiculi. Bach funiculus is 
 closely invested in a coat of connective tissue called the 
 perineurium, while branches from this perineurium extend 
 into the funiculus supporting more or less completely the 
 individual fibers and forming the endoneurium. These 
 funiculi are then together wrapped in a common coat of 
 connective tissue passing all around them and between 
 them called the epineurium. Through these connective 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 437 
 
 tissue coverings blood-vessels and lymphatics find their way 
 as through other tissues. Along the course of the nerve 
 
 Fig. 141. SECTION OF A NERVE TRUNK (HUMAN). (After Schafer.) 
 ep, epiueurium; per, perineurium; end, endoneurium ; v, blood-vessels; f, fat cells 
 stained with osniic acid. 
 
 trunk funiculus after funiculus is given off as a separate 
 branch, and finally the individual funiculus is separated 
 until at the end of the nerve trunk this separation is ex- 
 tended to the nerve fibers themselves. 
 
 The Development of Nerves. 
 
 One of the most interesting chapters in embryology is 
 the development of the nervous tissues and the organs de- 
 rived from them. Such study shows that the nervous cells 
 are derived from peculiar cells called neuroblasts, which 
 cells by their amoeboid movements are able to place them- 
 selves in definite positions through the body and then later, 
 by a kind of polarization, are able to determine the direc- 
 tion of the nerves issuing from them. When one is re- 
 
438 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 minded of the innumerable number of nerve cells compos- 
 ing the nervous system, of their intimate inter-relation, and 
 yet at the same time of the definite way in. which they are 
 connected by their fibers, one can appreciate the precision 
 with which these primitive neuroblasts must have distrib- 
 uted themselves while determining their direction of growth. 
 In fact, there are not lacking physiologists who believe that 
 forms of nervous derangement, from insanity downwards, 
 are due to possible accidental misplacements and malforma- 
 tions of these primitive neuroblasts. 
 
 A second interesting point concerning these neuroblasts is 
 that they do not increase in number after about the third or 
 fourth month of fcetal life, and that the entire development 
 of the nervous system following that is due to an expan- 
 sion of already formed neurons and the establishment of 
 more and more complicated channels of connection. 
 
 Possibly the most important fact from a teacher's stand- 
 point to remember, is that the development of these channels 
 of association, these anatomical connections between differ- 
 ent neurons, is not completed until up to and even past 
 maturity, and explains the physiological impossibility for 
 the existence of nervous or mental faculties in the young 
 which later on will naturally appear. 
 
 The Regeneration. 
 
 When a nerve is cut, the end of the nerve fiber severed 
 from the cell body to which it belonged disintegrates, and 
 a new nerve fiber to innervate the place of the old arises as 
 an outgrowth from the stump of the end in connection with 
 the cell. If, however, the severed ends of such a nerve be 
 connected they seem soon to have grown together. This 
 growing together does not, however, affect the axis-cylin- 
 der, for the axis-cylinder grows down through the coats of 
 the old nerve not unlike the growing of a rootlet through 
 the soil. In this growth it is no doubt guided by the path 
 of the old fiber itself, with the medullary coat and primitive 
 sheath of which, contact seems to have been made. 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 439 
 
 Such a regeneration of fibers does not differ in any way 
 from the manner in which nerve fibers arise in the embryo. 
 The spinal nerves grow out from the spinal cord and pene- 
 trate further and further until they finally reach their in- 
 tended terminations. The optic nerve (together with the 
 retina) is a direct outgrowth of the brain. The auditory 
 nerve is a growth from the brain, which finally reaches and 
 connects with the developing ear. 
 
 Neuroglia. 
 
 Ill the brain and spinal cord where the neurons are 
 closely packed they seem to be supported and held in place 
 by a peculiar kind of connective tissue differing entirely 
 from that which supports other tissues. The supporting 
 tissue here consists of large, many-branched cells, looking 
 very much indeed like nerve cells. The many branches of 
 these cells seem to connect and form a supporting mesh- 
 work for the more delicate nervous tissue. These support- 
 ing cells and the network which arises from them are spoken 
 of as the neuroglia. These cells are not connective tissue 
 cells, but are in origin related to the nervous cells, having 
 been derived from the same primitive source. In sections 
 of the spinal cord these cells may be easily mistaken for 
 nerve cells, differing, however, from them in the absence of 
 all nervous functions and so, of course, anatomically in the 
 absence of nerves. 
 
 GENERAL PHYSIOLOGY OF THE NERVOUS SYSTEM. 
 
 Before going into the physiology of special portions of 
 the system it is desirable to treat of those physiological 
 properties which all nervous tissues have in common. In 
 fact, the specific physiologies of the special portions are due 
 more to the origin and distribution of the nerves than to 
 any physiological difference in their activities. 
 
 The general physiology of a nerve may be summed up in 
 the statement that it is to convey a nervous impulse. This 
 impulse may arise either in the cell of which the nerve is a 
 
440 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 continuation, and from this be carried to muscle or gland, 
 or else in some sense-organ to be carried inwards to the 
 appropriate center. This brings up the question, in what 
 manner a nerve may be stimulated to transmit such im-. 
 pulses. 
 
 Nerve Stimuli. 
 
 In the laboratory it is possible to stimulate a nerve arti- 
 ficially in the following ways : 
 
 1. By Mechanical Stimuli. A tap, a pinch or blow on 
 a living exposed nerve excites it and is the occasion of an 
 impulse through the nerve. A familiar illustration of this 
 is found in striking the crazybone at the elbow, which is 
 in reality striking the nerve at this point. The blow occa- 
 sions an impulse which runs to the brain, and by the brain 
 is referred, although erroneously, to the fingers. 
 
 2. Thermal Stimuli. Sudden change in the tempera- 
 ture excites the nerve, be the change upward or downward. 
 If this change, however, is very gradual, the nerve seems 
 to be able to accustom itself to the change and no direct 
 impulse arises. 
 
 3. Chemical Stimuli. Quite a number of substances 
 chemically alter a nerve fiber and so stimulate it. Thus 
 immersing the end of a nerve in a strong solution of com- 
 mon salt excites it. Here, too, if such a nerve be placed in 
 a very dilute solution and this solution then gradually made 
 more concentrated no excitation follows. 
 
 4. Electrical Stimuli. One of the most satisfactory 
 ways to stimulate a nerve in experimental physiology is by 
 means of the electrical current. An electric shock passing 
 through a nerve fiber at any part along its course power- 
 fully excites it. Even a sudden change in the strength of 
 the current through a nerve excites it. A steady current, 
 however, has no effect, but when such a current is suddenly 
 broken, the sudden disappearance of the ciirrent acts as a 
 stimulus. 
 
 The explanation of all these stimuli lies in the siidden- 
 ness with which any change is brought about in the nerve 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 441 
 
 fiber, be this sudden "change electrical, thermal, mechanical 
 or chemical. Of course the stimuli so far enumerated are 
 all artificial stimuli which in the normal physiology of the 
 body are never called into play. The natural nerve stimuli 
 are of two kinds: 
 
 First, stimuli which arise in the nerve centers in a way 
 so far entirely unexplained. These are stimuli which are 
 produced in the nerve cells themselves and by these sent 
 out along the fibers. Such stimuli are those produced by 
 the cells of the cortex of the brain, which produce the con- 
 traction of the fingers or toes. They may be spoken of 
 as central stimuli. These are always called into play in the 
 production of motor impulses. 
 
 The second kind is peripheral stimuli which are best ex- 
 hibited in the organs of special sensation. Thus in the eye, 
 light in some way excites the optic terminations in the ret- 
 ina. In the ear vibrations in the cochlea excite the audit- 
 ory hairs on the basilar membrane, while on the skin gen- 
 erally, foreign bodies in their effect upon the tactile cor- 
 puscles usually occasion a stimulus interpreted in the mind 
 as sensations of touch. 
 
 These peripheral stimuli are, however, not limited to the 
 special sense-organs. Such stimuli may originate in any 
 part of the body. In the stomach the presence of food may 
 produce a stimulus which is carried to the brain, and there 
 in a reflex way translated into a motor impulse to move the 
 muscles of the stomach. In fact, it will be pointed out that 
 the special sense-organs are nothing more than contrivances 
 by means of which stimuli which are too feeble to excite 
 nerves in general are so manipulated in a specially con- 
 structed sense-organ as to make possible such an excita- 
 tion. 
 
 Do Nervous Impulses Differ Among Themselves? 
 
 Some nerves carry motor impulses, others tactile im- 
 pulses, still others visual impulses, and the question natur- 
 ally arises do these impulses differ inter se? 
 
 The older physiologists entertained the view that the 
 different results produced by different impulses were due to 
 
442 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 these impulses themselves. That the sensation of sight 
 was produced by the optic nerve as such, and that a muscle 
 contracted in obedience to a peculiar motor nervous im- 
 pulse. Soon after, this very sweeping distinction was nar- 
 rowed down to a disvision into two kinds of nervous im- 
 pulses those which produced motion and those which re- 
 sulted in sensation. That such impulses were inherently 
 different was occasioned by the observation that when a 
 motor nerve was cut and the end connected with the muscle 
 pinched a contraction followed, but that when the central 
 end was pinched no sensation followed. While on the other 
 hand, when the sensory nerve was cut, no motion resulted 
 upon the distal end being pinched, but a decided sensation 
 followed the stimulation of the central end. There is, how- 
 ever, every reason to believe that these impulses do not dif- 
 fer among themselves, but that the difference in results is 
 due to the different endings which these nerves have. A 
 sensory nerve cannot produce motion for the simple reason 
 that it is not in contact with muscles, while a motor nerve 
 cannot produce sensation for the simple reason that it does 
 not run to centers where such sensations are received. 
 
 That all nerve fibers are physiologically alike seems 
 further evident from the following reasons: (1.) A micro- 
 scopic and chemical analysis shows no differences whatever 
 between the nerve fibers. (2.) All nerve fibers carry im- 
 pulses in both directions. For instance, when a nerve is 
 stimulated in the middle of its course the impulse runs from 
 this point towards both ends with equal facility and rapidity, 
 and this is true whether the nerve be a sensory or a motor 
 one. (3.) The nature of the nervous impulse seems to be 
 the same no matter what may have been the occasion for 
 its excitation. Thus a nervous impulse resulting from the 
 pinching of a nerve is, as far as we are able to detect, per- 
 fectly identical with the impulses produced by an electric 
 current, or even by the natural end organ itself. Thus, the 
 impulse which runs along the optic nerve, regularly occa- 
 sioned by light falling on the retina, is identical with the 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 443 
 
 impulse carried by the optic nerve when this nerve is elec- 
 trically stimulated. 
 
 Having now seen the oneness of all nervous impulses 
 the question arises, what is its nature? 
 
 The Nature of a Nervous Impulse. 
 
 Soon after the electrical current became known many 
 attempts were made by the older physiologists to explain 
 nervous impulses in terms of electricity. The analogy 
 between the nerves of the body and a system of telephone 
 or telegraph wires was too striking to be overlooked. But 
 all attempts to explain one in terms of the other have so 
 far been a failure. That a nervous impulse is not of an 
 electrical nature is evident for several reasons: A nervous 
 impulse will not travel along a dead nerve, or even a nerve 
 which has been numbed by cold. A nervous impulse will 
 not pass across a cut in a nerve, even though the two cut 
 ends be fastened together. Surely if nervous impulses were 
 of an electrical nature they would still pass in spite of these 
 difficulties. It has been possible to measure the rate at 
 which nervous impulses move. This measurement was first 
 accomplished by the physiologist Helmholtz. The experi- 
 ment is simple enough. A muscle was cut out from the 
 body of an animal and a long portion of the nerve leading 
 to it left intact. The muscle and nerve preparation were so 
 arranged that the time could be very accurately measured 
 between the moment when the nerve was stimulated and the 
 moment when the muscle contracted. The nerve was now 
 stimulated close to its insertion in the muscle, and the time 
 that elapsed between the stimulation of the nerve and the 
 contraction of the muscle carefully observed. Next, the 
 nerve was stimulated at its further end, that is, the nervous 
 impulse had now to go further through the nerve than it did 
 in the first instance. Again the time elapsing between the 
 moment of stimulation and the moment of contraction was 
 noted. The difference in time was of course the extra time 
 needed in the second case for the impulse to traverse the 
 added length of nerve. 
 
444 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 In such a simple way the experiment proved the rapidity 
 of a nervous impulse to be 28 meters; that is, a little over 
 92 feet per second. These, however, are the figures for the 
 motor nerves of the frog. The rate of transmission is some- 
 what faster in the motor nerves of warm-blooded animals, 
 and is here probably not far from 100 feet per second. 
 
 Experiments on sensory nerves are, of course, not so 
 easy, but there is reason to believe that the speed of the 
 impulse is about the same as that of the motor nerves. 
 Such a speed of about 100 feet per second is, of course, 
 exceedingly slow compared with the rate of transmission of 
 an electric impulse, and would seem to settle conclusively 
 the difference between the two. 
 
 That a nervous impulse is of a chemical nature seems 
 disproved by the fact that no exhaustion occurs in a nerve in 
 the transmission of this impulse. It has been possible in 
 experiments to send long continued repeated impulses along 
 a nerve without noticing at the close of the experiment that 
 the nerve had been thereby exhausted. Such stimulation of 
 course commonly exhausts the muscle with which the nerve 
 is connected, or if a sensory nerve the centers to which it 
 goes, but in a very slight degree, if any, the fiber itself. If 
 it were a chemical change it would be difficult to see how 
 an exhaustion caused by the chemical disintegration could 
 be avoided. The only explanation left, therefore, seems to 
 be that it is some kind of a molecular change which travels 
 along the fiber, a molecular change, however, of the nature 
 of which we are still wholly at sea. 
 
 Several things about the impulse are known. Its rate 
 of speed is about 100 feet per second. We also know that 
 the nervous impulse is in the nature of a wave, which is 
 about 18 millimeters in length. This is a little over seven- 
 tenths of an inch. 
 
 The wave-like nature of the impulse is evident from, 
 and can be measured by, a peculiar electrical wave which 
 runs along the nerve fiber with the nervous impulse, which 
 electrical wave is easily detected by means of the galvano- 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM 445 
 
 meter. If the electrodes of a sensitive galvanometer be 
 placed on a nerve and an impulse then be transmitted along 
 the nerve the needle of the galvanometer will be deflected 
 in such a way as to reveal the presence of a current at the 
 moment the nervous impulse is passing. This current has 
 been called the current of negative variation. This wave 
 of variation travels, of course, with the same speed as the 
 impulse, and the time it takes to pass a certain point can be 
 easily determined. One has simply to note at what instant 
 the deflection of the needle begins and the instant it ceases. 
 Measurments of this kind have shown that the wave takes 
 only about .0007 of. a second to pass. Thus, knowing its 
 rate of speed and the time consumed in passing a given 
 point, it is a simple mathematical calculation to show that 
 it is a little over seven-tenths of an inch in length. The 
 needle further indicates that at first this current is very- 
 feeble, then rises to a maximum, then gradually falls and 
 disappears. 
 
 This wave" of negative variation is but a result of the 
 nervous impulse and is caused by the molecular changes in 
 the nerve fiber as the impulse proceeds, much as in the 
 running of a train there might be along the rails accom- 
 panying the train currents of electricity caused by the fric- 
 tion of the running wheels, which current might be easily 
 detected by a galvanometer even though the train itself 
 should be invisible. 
 
 KINDS OF NERVE FIBERS. 
 
 Any real division of nerve fibers is obviously possible 
 only on the basis of the organs or centers with which they 
 are connected. On this basis nerve fibers are divided into 
 two classes, the first called the afferent or sensory fibers, the 
 second the efferent or motor fibers. The terms sensory and 
 motor are, however, not very fortunate ones, as there are 
 some afferent fibers that never carry sensations which reach 
 consciousness, while many of the motor fibers carry impulses 
 which do not reach muscles. A more detailed classification 
 is usually made as follows: 
 
446 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 First. Sensory fibers which, when stimulated, produce 
 sensations of which we are conscious. The best illustra- 
 tions of these sensory fibers are the nerves of the special 
 senses. 
 
 Second. Reflex sensory fibers which when excited carry 
 sensations to the brain, which, however, do not usually 
 reach consciousness, but in the lower brain centers give rise 
 to motor impulses without the intervention of the will. The 
 best illustration of these possibly is the narrowing of the 
 pupil when subjected to a strong light. Some of these reflex 
 sensory fibers may occasionally come within the reach of 
 consciousness. Many of them, however, are entirely outside 
 of it. Such are the reflex sensory fibers, for instance, whicli 
 carry the sensations from the stomach, when food reaches 
 it, to the brain, to be there translated into impulses leading 
 to the active secretion of the glands of the stomach or to 
 the contraction of its walls. 
 
 Third. Inhibitory sensory fibers; fibers whicli when 
 stimulated carry sensations to nervous centers which seem 
 to inhibit their action. So, for instance, the biting of the 
 lips may succeed in preventing a spasm of sneezing. 
 
 The three classes so far mentioned are included iinder 
 the usual term of sensory fibers. Of the efferent nerve 
 fibers physiologists usually make the following classes: 
 
 Fourth.. Motor fibers proper, those which innervate the 
 muscles and produce their contractions. Under this head 
 are included not only the nerves which run to the skeletal 
 muscles, but also the nerves which run to some of the in- 
 voluntary muscles, especially the vaso-motor fibers which 
 run to the muscular coats of the blood-vessels. 
 
 Fifth. Secretory fibers. These are fibers distributed to 
 the cells which constitute the various glands of the body and 
 which govern their secretion. 
 
 Sixth. Inhibitory nerves whicli inhibit muscular action, 
 the clearest example of which is the inhibitory nerve of the 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 447 
 
 heart, the excitation of which slows the rate of beat in this 
 organ. 
 
 All the nerves so far mentioned are nerves which run to 
 the periphery. There are, of course, in addition to these, 
 many nerves which never get beyond the central nervous 
 system, but which run in this for their entire course and 
 serve to connect the various centers within the same, car- 
 rying between these centers impulses similar to those car- 
 ried by peripheral nerves. 
 
 THE GENERAL PHYSIOLOGY OF NERVE CENTERS. 
 
 We are in this discussion not yet concerned with the 
 special functions of the various nerve centers, but merely 
 with those phenomena which apply more or less fully to all 
 nerve cells. In this general way nerve cells or collections 
 of the same into ganglia, are classed as follows: 
 
 1. Automatic Centers. These are centers which do not 
 seem to depend on some specific external impulse to arouse 
 them, but which seem to act more or less independently of 
 all such stimuli. The best illustration is possibly that of 
 the higher centers in the brain which we are wont to desig- 
 nate as the centers concerned in free volition. In addition 
 to these higher psychic centers there are lower automatic 
 ones, such, for instance, as the automatic centers in the 
 heart causing the beat of the same entirely independently, so 
 far as we know, of external stimuli. Such automatic cen- 
 ters may, of course, be aroused, and within certain limits, 
 controlled by outside stimulation, but such outside stimula- 
 tion need not be the invariable occasion for their acting. 
 
 2. Reflex Centers. These are centers found mainly in 
 the spinal cord, but present also in the brain, to which sen- 
 sory impulses are carried, and which as a result of such im- 
 pulses originate motor impulses in harmony with these sen- 
 sations. When working normally these reflex centers are 
 groups of cells which co-ordinate the incoming impulses 
 and the outgoing impulses to produce purposive results. 
 When a person unknowingly touches a hot stove with his 
 
448 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 fingers the sensation produced by the burning is carried to 
 the reflex centers in the spinal cord and by these reflex 
 centers motor impulses are sent out to remove the hand. 
 These motor impulses are in harmony with the incoming 
 impulses and are intended for specific purposes. 
 
 The medulla oblongata contains many of the higher re- 
 flex centers. Such, for instance, as the reflex centers oc- 
 casioning respiration; the reflex center controlling the 
 general vascular supply ; the reflex center regulating the 
 general temperature of the body, and others. In the brain 
 are reflex centers co-ordinating sensations and motions 
 without the intervention of consciousness, while in the 
 spinal cord are quite a number of centers concerned in the 
 manipulation of the trunk and limbs. 
 
 3. Junction Centers. In addition to the automatic cen- 
 ters which seem to have the power to originate nervous 
 impulses and the reflex centers which are able to co-ordi- 
 nate sensations and movements without appealing to con- 
 sciousness there are a number of ganglia, the function of 
 which seems to be entirely that of a relay station or junction 
 center. For instance, the spinal root ganglion is in all prob- 
 ability nothing more than a relay station serving merely to 
 act as a center of nourishment and strength to the nerve 
 fiber itself, and having nothing to do with the impulses 
 traversing it save to make more possible their transmission. 
 Much as in a system of telegraph wires there are relays of 
 batteries, from time to time, concerned only in making the 
 transmission of the impulses originated in other ways pos- 
 sible. In still other cases nerve centers seem to be mere 
 junction centers; that is, centers of distribution. A single 
 impulse running into such a center will be distributed 
 through the many cells in that center and flow out of it in- 
 creased many fold. The ganglia in the mesentery and ali- 
 mentary canal probably serve in this manner and make 
 possible that the few impulses reaching these organs will be 
 finally multiplied and distributed as to reach each individual 
 muscle fiber composing them. 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 449 
 
 Having now treated of these general points which apply 
 more or less fully to nerve cells wherever found, the ques- 
 tion naturally follows, what are the special functions of the 
 various nerve centers found in the body, and what are 
 the specific paths of the fibers connecting these centers 
 with each other and with the periphery ? We are therefore 
 concerned next with the finer architecture of the central 
 nervous system. 
 
 THE FINER ARCHITECTURE AND THE SPECIAL PHYSIOLOGY 
 OF THE CENTRAL NERVOUS SYSTEM. 
 
 Perhaps in no department of the field of physiology 
 have the views been so materially modified of late as in the 
 conceptions of the structure of the central nervous system. 
 Recent studies of such men as Golgi, Van Gehuchten, 
 Ramon y Cajal, and others have completely changed our 
 notions of the fundamental structure of nervous tissue. It 
 is now believed, and with the best of evidence, that the 
 entire nervous system is made up of separate and distinct 
 units called neurons, a general description of which occurred 
 in the preceding pages. 
 
 These neurons are practically all alike, at least ana- 
 tomically, unless we except those of the cerebrum to which 
 we are at present obliged to assign psychic functions. No 
 neuron is connected with any other neuron directly, but the 
 impulse from one to another is effected at the point where 
 they lie either close together or in possible direct contact. 
 The old notion of a continuous network of nerve fibers per- 
 vading the entire system is done away with. 
 
 In such separate and distinct neurons the cell body is 
 the physiological and nutritive center. To this center im- 
 pulses are carried by some of its branches, and from it in 
 turn impulses are carried out by other branches. A section 
 of any of the branches or nerves of such a neuron at once 
 results in the death of that end of the nerve severed from 
 the cell body. It is the purpose in this paragraph to show 
 in an elementary way but with some special detail the man- 
 ner in which these neurons are arranged and superposed. 
 29 
 
450 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 1. Arrangement of the Motor Neurons. The arrange- 
 ment of the motor neurons is about as follows: In the 
 cortex of the brain near the fissure of Rolando are certain 
 large cells which give off small branches in various direc- 
 tions and usually one long branch, the nerve fiber proper. 
 This extends from the cortical region through the crus 
 cerebri of its side, and in the medulla crosses to the opposite 
 side of the cord. It then descends through the spinal cord 
 in the so-called lateral column of that side, commonly des- 
 ignated the crossed pyramidal tract, and finally enters the 
 anterior horn of the spinal cord and ends there in the fine 
 network of dendrons, which closely invest similar short 
 dendrons of the motor cells of the anterior horn. These 
 motor cells are the cell bodies of the second neurons, and 
 their nerve fibers extend from the anterior horn through the 
 anterior roots of the spinal nerve to the muscles in ques- 
 tion. In other words, from the point in the brain where the 
 volition arises to the point in the muscle where the con- 
 traction is produced there are two neurons, one reaching 
 from the brain, where the cell body is, through the cord to 
 the anterior horn, the second neuron reaching from this 
 point to the muscle. This is the usual course of the motor 
 neurons. 
 
 A second course is, however, possible. Many motor 
 fibers arising in the cortex do not cross to the opposite side 
 in the medulla, but descend the spinal cord on the same 
 side along the anterior tracts, and then along in the course 
 of the spinal cord cross to the other side, through the an- 
 terior commissure of the cord. It will be seen, however, 
 that all these motor fibers finally reach the opposite side of 
 the cord, and the difference between the fibers in the 
 lateral column and those in the direct pyramidal tract is a 
 secondary one. The fact that some cross in the medulla 
 and others in the cord further down is no real difference. 
 In either case these neurons from the brain end in the an- 
 terior gray horns, and there connect with the second motor 
 neurons which reach to the muscles. The general arrange- 
 
(Facing Page 450.) 
 
 Fig. 144. DIAGRAMMATIC CROSS-SECTION OF THK SPINAL CORD SHOWING THE MOTOR, 
 
 RED, AND SENSORY, BLUE, PATHS. (After Van Gehuchten.) 
 
 1, crossed or lateral pyramidal tract; 2, direct, or anterior pyramidal tract; 3, posterior 
 sensory columns ; 4, direct cerebellar tract ; 5, antero-lateral ground bundles ; 6, crossed 
 sensory, or antero-lateral ascending tract. 
 
 (Facing Page 450.) 
 
 Fig. 142. DIAGRAM OF THE MOTOR PATHS SHOWING THEIR MANNER OF CROSSING EITHER 
 IN THE PYRAMIDS OR LOWER IN THE CORD. (After Van Gehuchten.) 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 451 
 
 ment of this is schematically indicated in the accompanying 
 diagram, in which the reader will find it possible to follow 
 the description of the text. 
 
 2 . The A rrangement of the 
 Sensory Neurons. The sensory 
 neurons are more complicated, 
 but in a general way here, too, 
 there are two neurons reaching 
 from the sense-organ to the 
 brain. The first neuron has its 
 cell body in the spinal root 
 ganglion. From this body one 
 nerve goes to the touch corpus- 
 cles, say of the finger, while 
 from the same body a second 
 nerve fiber runs into the poste- 
 rior horn of the spinal cord. 
 To repeat : One neuron bridges 
 the distance from the point of 
 touch in the finger to the spinal 
 
 COrd with the Cell body of this Fig- 143 DIAGRAM TO SHOW PATHS OF 
 
 NERVE-FIBERS IN THE SPINAL CORD. 
 
 (After v. Lenhossek.) 
 
 neuron located in the spinal 
 root ganglion. The endings of 
 
 M, voluntary muscle; If, skin of 
 
 ., . -., ,, 1 1 hand; T, touch corpuscle; HW, posterior 
 
 this sensory fiber m the cord root spinal nerve . VWt anterior root 
 are in a general way as follows: spinal nerve; pp > sensor y nerve '- # 
 
 spinal root ganglion; s, cell body of sen- 
 As SOOn aS the fiber reaches sory neuron; m, motor cells in anterior 
 
 the posterior horn it divides in- 
 
 to an ascending and a descend- & lion ; . 6 a continuation of sensory 
 
 . neuron c, upwards and downwards 
 
 ing branch Which paSS Up and through gray matter of posterior horn; 
 
 down respectively through the * * ne " r K on lying entirely within the 
 
 cord, and by means of the collaterals a a, 
 gray matter of the posterior connecting opposite sides of the cord. 
 
 horn. From these branches ^%SXS 
 
 smaller branches called collat- P aths there described. 
 erals are given off at right angles. Some of these main 
 branches or collaterals may run into the anterior horns, and 
 there end in capillary dendrons which invest the motor cells 
 
452 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 found here. It is this arrangement af the neurons of sensa- 
 tion and motion which makes the simple reflex actions of 
 the cord possible. 
 
 Other branches or collaterals with their dendrons invest 
 cells found in Clark's column. These cells in Clark's 
 column are the beginnings of new neurons which reach 
 from Clark's column in the spinal cord to the cerebellum, 
 the fibers ascending in the direct cerebellar tract. In this 
 way sensations are carried to the motor cells of the cerebel- 
 lum and make the reflex actions of the cerebellum possible. 
 
 None of the two paths just mentioned, however, result 
 in conscious sensation. There is a third path which leads 
 to the cerebrum itself. This path is about as follows: The 
 sensory nerves or branches from them, leave the posterior 
 horn of the spinal cord and ascend towards the brain through 
 the posterior columns. Many of these fibers run as far as 
 the medulla. In the gray matter of the medulla, however, 
 their dendrons invest new cells, nerves from which, after 
 crossing in the medulla, extend to the cortex of the brain. 
 
 While most of the sensory fibers running up the pos- 
 terior column connect with their second neuron in the me- 
 dulla, many of them run into the gray matter of the spinal 
 cord before reaching the medulla, and there invest cells the 
 nerves from which then cross to the opposite side of the 
 spinal cord and reach the cortex of the brain. The path for 
 these crossed sensory fibers of the cord is the antero-lateral- 
 ascending tract. 
 
 An additional sensory path needs mentioning. Some of 
 the branches or collaterals of the sensory fibers may con- 
 nect with neurons in the gray matter of the cord, which run 
 to the opposite side of the cord and connect with other 
 neurons there. That such paths exist is proved by the fact 
 that when the sensory fibers of one side of the spinal cord 
 are cut sensation is not lost, but seems actually for a little 
 while to be increased. This can, of course, only be ex- 
 plained by assuming that fibers must connect with the oppo- 
 site or uninjured side of the cord. 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 453 
 
 With the motor impulses the case is different. When 
 the motor fibers of one side are cut that side is completely 
 paralyzed, even when the other side is left intact, showing 
 that the motor paths are direct. 
 
 3. Summary of Nerve Paths. To summarize, then, 
 there are the following sensory paths : 
 
 First. The neuron extending from the finger to the 
 spinal root ganglion and from there in turn to the posterior 
 horn of the spinal cord, may run directly to the anterior 
 horn and invest with its dendrons a motor cell there, and 
 so produce the path for the simple spinal cord reflexes. 
 
 Second. The first sensory neuron may run not to the 
 motor cells, but to the cells forming Clark's column and in- 
 vest one of these with its dendron, which cell in turn as a 
 new neuron extends to the cerebellum and makes possible 
 the cerebellar reflexes. 
 
 Third. The first neuron or branches of it may connect 
 with a neuron of the spinal cord which runs to the opposite 
 side of the spinal cord and there connects with other 
 neurons. This path makes possible the radiation of sensa- 
 tions to both sides of the spinal cord. 
 
 Foitrth. The first neuron may connect with neurons 
 running to the cerebrum (a) by running up through the 
 posterior columns and connecting with the second neuron 
 in the medulla, which neuron there crosses and goes to the 
 opposite cerebral hemisphere; or (b) the first neuron after 
 ascending a short distance through the posterior column 
 enters the gray matter of the cord and there connects with a 
 neuron which crosses to the opposite side of the cord, and 
 in the antero-lateral tract reaches the cerebral hemispheres 
 the same as the neurons which cross in the medulla. 
 
 4. Where Do the Sensory Neurons End in the Brain? 
 A very interesting question now arises, with what do these 
 sensory neurons connect in the cortex of the brain? While 
 this is possibly still debatable ground, it seems very proba- 
 
454 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 ble that these sensory neurons with their capillary dendrons 
 at their ends invest the motor cells which form the first 
 neurons of the motor path. If this be true, it gives to these 
 cells the wonderful faculty of not only serving as voluntary 
 motor cells, but as conscious sensory cells. In other words, 
 in these cortical cells the consciousness of sensation as well 
 '* as the consciousness of volition is located. 
 
 5. Comparison of Sensory and Motor Paths. It will 
 be noticed that in the sensory, as in the motor path, there 
 are essentially two neurons between the periphery and the 
 brain. Further, both sensory and motor neurons cross, either 
 in the medulla, or further down in the cord. An interesting 
 difference between the sensory and motor neurons lies in the 
 fact that in one case the cell body of the lower neuron lies 
 
 Fig. 145. DIAGRAM SHOWING THE PATHS OF FIBERS IN THE CEREBRO-SPINAL SYSTEM. 
 
 Outgoing arrows indicate motor, incoming arrows sensory fibers. 
 
 JK, R, right and left cerebral hemispheres; G, G, gray matter of mid-brain, optic thai- 
 ami and upper medulla; H, H, lower portion of medulla where the cranial nerves take 
 their origin; H,H (at bottom of figure), the gray matter of spinal cord; la, motor nerves; 
 Ib, sensory nerves; 6, G, fibers connecting the hemispheres; Ic, half-crossed optic fibers; 
 5,5, fibers connecting different portions of same hemisphere; 2,2, crossed pyramidal 
 tract; 2', 2', direct pyramidal tract crossing in the cord; #, 3, sensory fibers, some cross- 
 ing in the pyramids (others have crossed in the cord, not shown), but all passing through 
 the gray matter G. By reference to the text the diagram will be more intelligible. 
 
 outside of the spinal cord, in the spinal root ganglion, while 
 in the case of the motor neurons it lies inside of the spinal 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 455 
 
 cord, in the gray matter of the anterior horns. This differ- 
 ence of position is, of course, physiologically a secondary 
 one. 
 
 The sensory cranial nerves find their counterparts of the 
 spinal root ganglia in the sensory ganglia which they pos- 
 sess. Such, for instance, as the Gasserian ganglion of the 
 fifth cranial nerve. 
 
 It simplifies the conception of the sympathetic system, 
 to look upon the sympathetic ganglia lying along the spinal 
 cord as a second set of spinal root ganglia containing sen- 
 sory and possibly motor neurons, which in this case reach 
 from the spinal cord to the viscera, instead of to the body 
 wall and skin as in the case of the spinal root ganglia proper. 
 This conception of the sympathetic ganglia as spinal root 
 ganglia lends a unity to the entire nervous system, doing 
 away at once with the too general notion that the sympa- 
 thetic system is a special system only incidentally connected 
 with the spinal cord. 
 
 THE MEDULLA. 
 
 In the medulla the general arrangement of gray and 
 white matter found in the cord is materially varied from for 
 several reasons. In the first place, the decussation of the 
 motor and sensory fibers displaces the gray matter. In 
 addition to that we find here many new centers. In the 
 medulla are located, for instance, the center governing 
 respiration, that governing the temperature of the body, 
 that governing the vascular supply, and others. In addi- 
 tion to that we find here much gray matter, the cells of 
 which are probably the second neurons of sensation just 
 described. Here, also, are a number of centers connected 
 with the nerves of the special senses. The exact location 
 of these centers is omitted from this elementary discussion 
 as being too complicated. There remains, therefore, for 
 further description the arrangement of fibers and centers in 
 the cerebellum and cerebrum. 
 
456 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 SPECIAL FUNCTIONS OF THE BRAIN AND COED. 
 
 It was pointed out that the function of the spinal cord is 
 two-fold. First, it serves as a tract along which sensory and 
 motor fibers run that connect the brain with the distant por- 
 tions of the body. Second, it consists of centers which are 
 concerned in the simple reflex actions. Thus, if a frog be 
 taken and its brain removed, and the toe of such a frog 
 pinched, the leg will be drawn up with almost as much 
 precision as in the case of an uninjured frog. A piece of 
 blotting paper soaked with an irritating solution, such as an 
 acid, placed on his skin will produce a series of the most 
 perfectly co-ordinated movements. If the foot be held firmly 
 and then pinched the frog at first tries to pull away the 
 injured foot and upon repeated failures to accomplish this it 
 will bring into play the foot on the other side to effect his 
 purpose. Here is a case in which the reflexes have become 
 complicated, have called in the opposite side of the spinal 
 cord, and yet are all so co-ordinated as to be directly pur- 
 posive. 
 
 The question whether there are any automatic centers 
 in the spinal cord is still an open one, but the evidence 
 seems to show that it possesses reflex centers only. Instances 
 of impulses which seem to have originated in the spinal 
 cord have generally been traceable to outside influences for 
 their occasion. These outside influences are of course two. 
 First, sensations, carried by the sensory neurons directly to 
 it. In this case a reflex action arises without the interven- 
 tion of the brain. Second, motor impulses from the higher 
 centers of the brain. These higher impulses from the brain 
 calling into action these motor centers produce the ordinary 
 voluntary movements as we know them. 
 
 While most of the reflexes of the spinal cord are natural, 
 that is, inherited, it is possible by training to establish 
 reflexes of a highly acquired character. Much of the quick 
 perception and delicate touch of an artist on most any kind 
 of an instrument is due to the establishment of fine reflexes 
 in his spinal cord. Such an artist is frequently able to re- 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 457 
 
 act to his sensations without the direct intervention of his 
 brain. 
 
 SPECIAL PHYSIOLOGY OF THE MEDULLA. 
 
 In the medulla, too, we find reflex centers, but the reflex 
 centers are here of a higher kind. They are still involuntary 
 and largely outside of the control of the will, but are not the 
 simple muscular reflexes of the cord. They are the higher 
 reflexes governing complicated systems in the body. In 
 fact, it may be proper to speak of the reflexes here as the 
 systemic reflexes. Instances of the reflex centers of breath- 
 ing, circulation and temperature have already been noted. 
 In addition to these we find in the medulla some of the 
 simpler reflexes, the sensation occasioning which are derived 
 from the special senses. 
 
 THE PHYSIOLOGY OF THE CEREBELLUM. 
 
 It is exceedingly difficult to determine definitely the func- 
 tions of such complicated structures as the cerebrum and 
 the cerebellum. The structures are so delicate and the 
 methods of operation upon them to determine their func- 
 tions so coarse that it is frequently difficult to argue from 
 cause to effect. One can easily imagine how much progress 
 would be made by an individual trying to understand the 
 workings of a watch by standing off at a distance and firing 
 pistol shots at it and then noting the result ; firing first at the 
 hand, then the face of the watch, then spring or case. One 
 can easily see the almost utter hopelessness of ever getting 
 at a complete knowledge of a watch by such rude means, 
 and yet incisions or stimulations, in fact all of the experi- 
 ments made on the brains of animals have been relatively 
 as rough and inexact as the firing of a pistol into the deli- 
 cate watch. A few general points are, however, available. 
 
 It seems probable that the function of the cerebellum is 
 that of a large motor center to whose jurisdiction are con- 
 signed the ordinary habitual motions of the body ; walking, 
 running, in case of animals, flying or swimming. These 
 motor habits are doubtless acquired painfully and slowly 
 
458 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 by the cerebrum, as for instance, in the case of an infant 
 learning to walk or crawl. As they are repeated over and 
 over again they become more and more habitual. They 
 seem to be delegated more and more by the conscious cere- 
 brum to the lower cerebel- 
 lum, and in this way the 
 activity of the cerebrum 
 left to higher functions in- 
 stead of continually wast- 
 ing its strength in looking 
 after the contraction of 
 the muscles in moving the 
 body. 
 
 If, for instance, the cere- 
 bellum be removed from 
 the brain of a pigeon the 
 animal sits quietly, seems 
 to be conscious of dan- 
 ger; seems, in short, to 
 retain most of its psychic 
 functions, but is awkward 
 in its walk, stumbles and 
 falls easily, and flies with 
 the greatest difficulty. It 
 has lost control, apparent- 
 ly, of the motions which 
 originally it performed 
 with rapidity and precis- 
 ion. Removals of the cere- 
 bellum from other animals 
 have in a general way 
 shown similar results. 
 
 Without going into fur- 
 ther detail the whole point 
 may be summed up in the statement that it is the governing 
 center for the general habitual motions of the body. The 
 physiological value of this is at once clear when we remem- 
 
 Fig. 146. SECTION OF THE CORTEX OF CERE- 
 BELLUM. (After Sankey.) 
 a, pia-mater with contained blood-vessels; 
 &, external layer of gray matter; c, layer of cor- 
 puscles (nerve cells) of Purkinje; d, inner gran- 
 ule layer; e, medulla. 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 459 
 
 her that by delegating the control over these complicated 
 motions to the cerebellum the cerebrum is enabled to turn 
 its attention to higher functions. 
 
 THE PHYSIOLOGY OF THE MID -BRAIN. 
 
 In giving the functions of the mid-brain it is desirable 
 to include the optic thalami, for although these bodies are 
 anatomically classed with the cerebrum they belong physi- 
 ologically to the mid-brain. The crura cerebri of the mid- 
 brain are, of course, mere bands of fibers connecting spinal 
 cord and brain, so that we have to do here only with the 
 corpora quadrigemina of the dorsal side. 
 
 The difficulty of experimenting on these structures, 
 since they are hard to reach without injuring other parts of 
 the brain, makes our knowledge somewhat fragmentary. 
 Enough evidence is, however, at hand to show that the 
 corpora quadrigemina, especially, are great reflex centers 
 between visual impressions and the motor impulses which 
 govern the movements of the eyeballs. Here, without the 
 intervention of consciousness, the visual sensations produce 
 reflexes, by means of which the eyeballs are turned as oc- 
 casion or necessity requires. Every one is aware that he 
 keeps his eyeballs in constant motion turning hither and 
 thither as one object after another arrests his attention, and 
 yet does all of this without any real conscious intervention. 
 It is only when special points come up demanding special 
 scrutiny that we become consciously aware and in a volun- 
 tary way direct the muscular movements of the eye. That 
 visual sensations figure so prominently in all our actions, 
 shows the necessity, or at least the great desirability, of 
 having a reflex center where these many visual sensations 
 may be properly interpreted and reflected in purposeful 
 motor impulses. 
 
 But not only do the motor impulses of the eye originate 
 here but the optic thalami and mid-brain seem also to be 
 materially concerned in receiving the visual sensations and 
 reflecting them in purposeful locomotary impulses. It is 
 
460 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 an every-day experience that one will go along a path step- 
 ping over all obstacles, walking around obstructions, getting 
 out of the way of passers-by or vehicles, stepping carefully 
 sometimes over pools of water, even ascending steps, and 
 yet do all of this without the slightest apparent intervention 
 of consciousness. During all of this time a person may be 
 deeply absorbed in some train of thought, and if he were 
 questioned at the end of his journey about any of the de- 
 tails of the way would be utterly unable to recall even a 
 few. It is of course also evident that nearly all of the 
 motions of the body are guided by the sensations of sight. 
 True an individual may walk or run with his eyes shut and 
 depend upon other sensations, but that is only possible 
 where the individual knows the road to begin with, or is 
 supremely indifferent to accidents. Ordinarily speaking, 
 the visual impressions which never reach consciousness are 
 the guides which determine the motions of the body. These 
 complicated reflexes have their seat in the optic thalami or 
 mid-brain, and for the final execution of some of the habitual 
 movements of the body the cerebellum also comes into play. 
 It needs no special comment to point out what a saving of 
 energy it is to the higher centers of the brain to be relieved 
 from the interpretation of the crowd of sensations pouring 
 in through eye (or ear) and their proper reflection into cor- 
 respondingly purposeful motor impulses. 
 
 It will be pointed out later that the place where visual 
 sensations come into the field of consciousness lies in the 
 occipital lobes of the brain. Here seems to be the curtain 
 of the mind against which the images are projected for 
 direct and conscious scrutiny. But a small proportion, 
 however, of the visual sensations reach this high conscious 
 center. Most of them never get beyond the sub-conscious 
 and reflex centers of optic thalami and mid-brain. An 
 animal whose occipital lobes are removed, and which is 
 therefore consciously blind, is still able to avoid obstacles 
 in its way and prevent itself from stumbling over obstruc- 
 tions by going around them, on account of the fact that the 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 461 
 
 sub-conscious reflexes referred to are still intact. Such a 
 dog, however, makes no difference between an obstacle, as 
 a dish of food, or a dangerous or threatening obstruction. 
 He is able to make no conscious interpretation, and by his 
 sub-conscious centers both the inviting food before him or 
 the threatening rod are mere obstacles to be avoided lest he 
 should run against them. 
 
 Leaving now all of these lower centers of the nervous 
 system we reach finally the cerebrum itself, where, as far 
 as we know, the nerve centers have associated with them 
 for the first time that peculiar property which we are wont 
 to designate as consciousness. 
 
 THE PHYSIOLOGY OF THE BRAIN AND THE LOCALIZATION 
 OF CENTERS. 
 
 The careful work of such men as Jackson, Hitzig, 
 Fritsch, Beevor, Horseley and Ferrier has enabled us to 
 mark off the physiological topography of the cortex of the 
 brain and to establish for definite portions of the cortex 
 certain specific and definite functions. Their researches 
 have completely disproved the older notion that the entire 
 brain acted as a unit in every brain act; that a sensation, or 
 a volition, or a memory were actions participated in by the 
 entire brain as one structure. We now know that memory 
 is no such a simple thing, but that in certain portions of 
 the brain are stored auditory sensations, in other visual 
 sensations, and so on. We know that in certain portions of 
 the brain the voluntary impulses arise that move the foot ; 
 in other definite regions those that govern the movements of 
 the hand. It has even been possible by pathological ob- 
 servations to establish the position of the center of speech. 
 The topography of the brain as given in the accompanying 
 diagram is that now generally accepted. 
 
 The position of these centers has been determined ex- 
 perimentally in one or more of the following ways : 
 
 First. It not infrequently happens that persons are born 
 possessing certain brain malformations. By the post mortem 
 30 
 
462 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 determination of these anatomical malformations and their 
 comparison with the observed mental acts, deductions have 
 been arrived at as to the function of the parts affected. 
 
 Second. Occasionally a normal brain is pathologically 
 injured either by compression, as in accidents, by inflam- 
 mation in disease, or by the formation of tumors in certain 
 portions of its structure. It was by noticing the fact that 
 the presence of a tumor in the left frontal lobe of the brain 
 was always associated with the loss of speech that that cen- 
 ter was finally localized in that region. 
 
 Third. Upon animals it has been possible to cut off 
 certain regions of the brain to note the physiological effects of 
 such excisions. It was, for instance, by the extirpation of 
 the occipital lobes of the brain that the center of conscious 
 vision was definitely located. 
 
 Fourth. By stimulation experiments made directly on 
 the cortex of the brain. A new era in brain physiology was 
 ushered in when Fritsch, Hitzig, and later Ferrier, suc- 
 ceeded in producing movements by electrically stimulating 
 certain regions of the cortex of the brain. By subjecting 
 various portions of the cortex to such stimuli and noting 
 what muscles of the body were affected by the motor im- 
 pulses so originated, it was soon relatively easy to map out 
 the motor topography of the cortex, and it is upon these ex- 
 periments that the results in the diagram are based. 
 
 Fifth. For the determination not only of the centers of 
 the brain, but of the nerve fibers which extend from them, 
 two methods of study suggested themselves, (a) In the 
 embryonic development of animals it was found that certain 
 cells and certain nerve fibers developed sooner than others, 
 so that in this way it was possible to give the region and 
 follow the course of certain nerve fibers before neighboring 
 ones with which they might later be confused had de- 
 veloped, (b) A method productive of even more results 
 than this was what was called the Wallerian method, or the 
 method of degeneration. It has already been pointed out. 
 
-8 
 
 A3 
 
 VTSU' 
 
 (Facing Page 463.) 
 
 Fig. 147. DIAGRAM OF THE VISUAL PATHS. (Modified from Vialet.) 
 OP. N, optic nerve; OP. C, optic commissure; OP. T, optic tract; OP. R, optic radia- 
 tions; V. S, visual speech center; A. S, auditory speech center; M. S, motor speech cen- 
 ter. A lesion or section at 1 causes blindness of that eye; at 2, blindness of the outer half 
 of each eye ; at 3, blindness of the nasal half of that eye ; similar lesions at 3 and 3', blind- 
 ness of nasal halves of both retinas; at 4, blindness of nasal half of one eye and temporal 
 half of opposite eye; at 8, on left side, word blindness 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 
 
 463 
 
 that when the cell bodies to which nerves are attached are 
 destroyed in any way, these nerves at once die to their per- 
 iphery. By this method it was possible to destroy certain 
 brain centers and thus destroy the entire bundle of nerves 
 leading out from it. This, o"f course, enabled the observer 
 to determine over what part of the body the nerve centers 
 in question had jurisdiction. It was this method of degen- 
 eration that helped materially in giving us our knowledge 
 as we now have it of the courses of the fibers in the spinal 
 cord. 
 
 THE PHYSIOLOGICAL TOPOGRAPHY OF THE BRAIN. 
 
 1. The Motor Areas. The motor areas of the brain lie 
 along the fissure of Rolando. At the top of this fissure are 
 the motor areas governing the toes. These are followed by 
 motor nerves which govern regions gradually higher up, 
 until at the bottom of the fissure of Rolando we come to 
 those motor areas concerned in the control of lips, larynx 
 and mouth. The proximity of these motor centers to the 
 speech center on the left side is worth noting. 
 
 2. The Seat of Conscious Tactile Sensations. But not 
 only are these motor centers concerned in the production of 
 the voluntary impulses. They are also the seat of the sen- 
 sations which arise in the portions, the motions of which 
 they control. Thus the motor area along the fissure of Ro- 
 lando governing the muscles of the finger is probably also 
 the center in which the sensory impulses coming from the 
 finger are finally interpreted as conscious sensations. This 
 area ought, therefore, more properly to be called the motor- 
 sensory area. 
 
 3. The Visual Center. In the occipital lobes the visual 
 center is located. It is of interest to point out here that 
 while for the motor areas the right side of the brain gov- 
 erns the left side of the body, and vice versa, there is not 
 such a complete crossing for the optic nerves. There is, in 
 fact, in the optic nerve only a half crossing. In the right 
 
464 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 occipital lobe arise the fibers for the left half of each retina, 
 while from the left occipital lobe the right half of each re- 
 tina is innervated. This half decussation, of course, occurs 
 in the optic commissure. The destruction of one of the 
 occipital lobes, therefore, produces blindness in the oppo- 
 site half of each eye. 
 
 4. The Auditory Center. Immediately below the fis- 
 sure of Sylvius, in the upper convolution of each temporal 
 lobe is located the center of hearing. Here are stored 
 away the memories of the meanings of all heard words and 
 sounds. Some investigators give the center for perception 
 of musical sounds as somewhat forward from the place where 
 ordinary sounded words are stored. 
 
 5. The Centers for Taste, Smell and Speech. Below 
 the auditory centers in the temporal lobes seem to be located 
 the centers for taste and smell. One of the most interest- 
 ing of all of the centers, and strange, too, one of the first 
 to be localized, is the center of speech. This lies in the 
 left frontal lobe immediately anterior to the motor areas 
 governing lips, pharynx and mouth. The fact that this 
 center is usually located on the left side is explained by the 
 circumstance probably that most persons write with their 
 right-hand, which is a 'form of speaking as far as the intel- 
 lectual part of it is concerned. Persons who have habitu- 
 ally written with their left-hands would be more liable to 
 have the center of speech located on the right side. The 
 interesting question arises, why such a center should be on 
 the one side only? There is no satisfactory reason for this, 
 unless it be that as speech is such a unit, and as its coher- 
 ency would require such a careful co-ordination of two sides, 
 it would hardly be probable that such could be accomplished 
 from the action of two separate centers. .There is the possi- 
 bility of directing the two eyes to two different objects, as 
 in the case of cross-eyed persons, and the ability thus to 
 see, to some extent at least, double. Similar double sen- 
 sations are possible with the ear. Double motions from the 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 465 
 
 right and left side are perfectly natural, but it can be easily 
 seen that coherent speech is a unity which could not easily 
 result from the actions of two separate sources or agencies. 
 
 CONSCIOUSNESS. 
 
 The question is repeatedly asked in what sense conscious- 
 ness is a physiological property. This whole point may 
 be dismissed as far as its physiology is concerned by the 
 statement that of its real nature we know scientifically ab- 
 solutely nothing. Held by some to be merely a high form 
 of mechanical or chemical changes in certain cells, the 
 phenomena of consciousness have been reduced to merely 
 physical phenomena and so robbed of what we know as their 
 free will . Such investigators to be consistent deny that there 
 is such a thing as free will, but that all the multiplied inter- 
 changes of sensation and volition are just so many neces- 
 sary causes and effects. On the other hand, other observers, 
 usually without much scientific training, at one blow divorce 
 consciousness from all forms of brain activity and hold it to 
 be perfectly aloof and independent from changes which 
 occur in nervous cells. To such individuals the brain is a 
 secondary organ and its function somewhat questionable. 
 Possibly the true ground lies somewhere between the two. 
 It is the simplest every-day observation that states of con- 
 sciousness are, so far as we know, indissolubly locked with 
 states of brain. On the other hand, it seems in violation of 
 all knowledge that consciousness is but a necessary physical 
 result from the clash of nervous molecules. From the 
 standpoint of physiology it is, however, well to remember 
 that with this question, interesting as it may seem, we have 
 in this field at present nothing to do. 
 
 SLEEP. 
 
 The lower centers of the brain, the mid-brain and spinal 
 cord, and of course the sympathetic system, are in con- 
 tinued physiological activity. At no time during the normal 
 existence of the individual are the physiological functions 
 
466 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 of these centers suspended for a moment. In the higher 
 conscious centers of the brain there is, however, a marked 
 exception. At certain periods there supervenes what we 
 familiarly designate as "sleep." This common phenomenon 
 so easily experienced is nevertheless one of the most difficult 
 of explanation, and we are at present entirely at a loss to 
 understand what the exact nature of sleep is. We know 
 that it concerns only the higher conscious centers. The 
 reflex centers below are in their regular activity, unless we 
 should modify this by the statement that during sleep the 
 activities here are sometimes reduced, but never suspended. 
 
 Going to sleep is a sudden thing, although it is preceded 
 by a short period in which the sensations become gradually 
 dimmed. Waking up, too, is a somewhat sudden event. 
 What an interesting question it would be to determine, if 
 possible, just what occurred when sleep suddenly super- 
 venes or when later on with similar suddenness conscious- 
 ness returns. It is held by some physiologists that sleep 
 results when no impressions reach the brain. This, of 
 course, is at once faulty in its general application, because 
 it is possible to go to sleep even amidst a confusion of noises 
 and sensations. On the other hand, however, experiments 
 have been made with animals with paralyzed sensory nerves 
 and which were in addition to this blind and deaf on one 
 side. When under such circumstances the only remaining 
 sources of sensation to the brain, that is, the opposite eye 
 and ear were closed, the animal at once dropped to sleep 
 and awakened as soon as these avenues of impression were 
 opened. 
 
 It has been suggested, but only as a suggestion and not 
 a scientific fact, or even theory, that sleep may result from 
 the slight withdrawal of the dendrons surrounding the cere- 
 bral cells. It is, of course, conceivable that these dendrons 
 might separate to a slight extent, possibly separate so far as 
 to make the transmission of an impulse more difficult, and 
 that this separation, like the opening of the switch on 
 a switch board would produce a cessation of the flow of 
 
ANATOMY, PHYSIOLOGY, OF NERVOUS SYSTEM. 467 
 
 impulses, and so produce sleep, and that waking would 
 consist in the moving together of these dendrons and so 
 re-establishing the natural flow of impulses. 
 
 During sleep the entire range of conscious centers may 
 not be affected. Sometimes certain centers or portions of 
 certain centers seem to remain awake, and then these cen- 
 ters, relieved from the controlling influences of neighboring 
 centers run riot and give rise to the production of dreams. 
 When the centers so awake happen to be motor centers 
 there may be produced forms of sleep in which more or less 
 extended movements occur familiar to us under the name of 
 somnambulism . 
 
 That sleep is not due to the lack of blood in the brain, 
 and so be a phenomenon like fainting, is easily disproved 
 by experiments which show that the blood supply in the 
 brain while asleep sinks very little below the normal. 
 
 HYPNOTIC PHENOMENA. 
 
 Hypnotism is by many looked upon as an abnormal 
 variety of somnambulism. There is, however, connected 
 with this subject of hypnotism so much that is questionable 
 and suspicious along with the little that is real and scientific, 
 that it is exceedingly difficult to come to definite scientific 
 conclusions. It is explained by some as a peculiar sleep, 
 and looked upon by others as a mere form of embarrassment 
 and frightened imagination. 
 
 TIME RELATIONS IN PSYCHIC PHENOMENA. 
 
 That mental processes take a certain amount of time is 
 an e very-day observation. The exact measurement of simple 
 and definite psychical acts was first made as a result of the 
 observation that astronomers of equal care and precision 
 did not record the passage of a star across the hairs of 
 their observing telescopes at the same instant. This differ- 
 ence in time was at first attributed to a greater or less care- 
 lessness in the observer. Repeated experiments soon showed 
 that there was a difference in time even when both observers 
 
468 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 had with the greatest precision noted the transit just at the 
 moment they saw it in the telescope. These little differ- 
 ences of time were, therefore, due to the differences of time 
 in the nervous systems of the observers, and so it became 
 necessary to find out for each observer the time that he 
 required to record the observation. This was called his 
 personal equation. 
 
 In the field of physiological psychology a great deal of 
 work has been done in determining the reaction time of the 
 various centers. This is the interval between the percep- 
 tion of anything and its interpretation. A multitude of 
 books are available everywhere, and it seems undesirable 
 in this treatise to enter in detail into this field. Interesting, 
 however, .are the points that this reaction time may be 
 shortened by practice, and that the reaction time may in a 
 general way be taken as a physiological index of the 
 individual's education of the sense in question. It is of 
 course understood that the reaction time for complicated 
 psychical processes will be correspondingly longer than for 
 simpler ones, and that they need not necessarily be the 
 same for the different sense organs. The shortest re- 
 action time is possibly that of the eye. The further large 
 field of interesting observations which has to do with the 
 interpretation of sensations and their association in memory 
 must here be referred to the field of physiological psychology 
 in which the advances have in recent years been so great as 
 to rank that science as one of the co-ordinate biological 
 sciences of the day, whose field has, therefore, by the 
 necessities of such an extension been more or less excluded 
 from^purely physiological considerations. 
 
CHAPTER XX. 
 
 THE ORGANS OF SPECIAL SENSE. 
 
 Whenever the sensory nerves in any part of the body are 
 properly affected, a nervous impulse arises which is then 
 conveyed to the inner centers and may there give rise, and 
 usually does give rise, to what we ordinarily call a sensa- 
 tion. Very few tissues, indeed, in the body do not have 
 this property of sensation. These are the hairs, the nails, 
 portions of cartilage and bone, and other forms of con- 
 nective tissue, but with these obvious exceptions every 
 tissue in the body is able to produce by its proper nerves, 
 changes and sensations in the brain. 
 
 Sensations, however, differ at once fundamentally and 
 fall into two groups. In one group we have the sensations 
 which give states of feeling of our own body usually with- 
 out any relation at all to the outer world. The other sen- 
 sations seem to be projected beyond the body into the 
 external world and produce in us ideas concerning the 
 phenomena of our own environment. Thus, we have the 
 common sensations of the body and the special sensations. 
 
 The common sensations are the general feelings of pain, 
 of hunger and thirst, fatigue and buoyancy and possibly all 
 the varied feelings accompanying disease. In no instance 
 probably are these feelings ever projected into the world of 
 things. From these we gain absolutely no notion of our 
 environment. 
 
 In the second class belong the sensations which are 
 produced by the organs of special sense and those general 
 sensations of touch in so far as they give to us knowledge 
 of external things. It is with these latter sensations that 
 this chapter concerns itself. 
 
 There is possibly not a hard and fast line dividing 
 special sensations from the common sensations. Thus, for 
 
 (469) 
 
470 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 instance, a slight pressure on the finger gives an idea of 
 the nature of the object touched. A material increase of 
 such a pressure produces pain and no longer helps \\s in 
 understanding the environment. If in the case of the eye 
 a normal amount of light gives perceptions of sight, an ex- 
 cessively strong light blinds and hurts. It is probable that 
 many forms of pain, if not all of them, are excessive stim- 
 ulations of the nerves. On the other hand it is possible, 
 especially with the sense of touch to make the stimulation 
 of the nerves so slight as to render a distinct perception 
 difficult. The resulting sensations in such a case we com- 
 monly designate as those of a tickling or irritating nature. 
 
 THE STRUCTURE OF AN ORGAN OF SPECIAL SENSE. 
 
 The ordinary phenomena of the external world do not 
 as a rule affect nerves directly. In order to have such 
 phenomena produce a nervous impulse it is necessary to 
 provide the nerve with some form of specially adapted ap- 
 paratus which shall receive the external impressions and 
 translate or manipulate them in such a way as to give rise 
 to a nervous impulse. In fact the difference between nerves 
 of special sense and the ordinary nerves of the body lies in 
 this fact. Thus we have for an optic nerve the special ap- 
 paratus of the eye, the retina, for the auditory nerve the 
 labyrinth of the ear, and for the special sense of touch 
 peculiarly adapted corpuscles and end bulbs. The first 
 requisite, therefore, is a specially adapted end organ. 
 These end organs are in turn differentiated among them- 
 selves, one being adapted to one particular kind of external 
 impressions, such as light, say, another constructed on an 
 entirely different plan so as to catch the vibrations of sound. 
 A third so arranged as to be easily affected by changes in 
 pressure. 
 
 But these end organs serve merely to start the nervous 
 impulses. They do not produce sensations of sight, hear- 
 ing or touch. In fact, the nervous impulses running along 
 the optic nerve, the auditory nerve or touch nerve are in all 
 
THE ORGANS OF SPECIAL SENSE. 471 
 
 probability perfectly identical, and the reason that one gives 
 rise to sensations of light, the other to those of sound, and 
 a third to perceptions of touch is not due to any difference 
 in these impulses, but is due to the centers in the brain in 
 which they end. Although such a thing is entirely impos- 
 sible in reality it is possible to imagine, and justly so, that 
 if the auditory nerve could be made to run to the visual 
 center in the brain, sound would be interpreted as light, 
 while if the optic nerve should end in the upper temporal 
 lobe, colors would be interpreted as sounds. 
 
 A complete organ of special sense, then, is a special 
 nerve center in the brain and a special apparatus at the 
 distal end of a nerve connected with it. The phenomena 
 of the special sensations therefore naturally fall into two 
 kinds: the phenomena that take place in the end organs, 
 and those that take place in the brain. Our knowledge of 
 the processes which occur in the brain center is from a phy- 
 siological standpoint so meager that for evident reasons it is 
 here omitted altogether. Pure physiology concerns itself 
 now mainly with those nervous changes which occur at the 
 distal end of the nerve. We may speak of a complete sen- 
 sation consisting of two events; the first, a neurosis a 
 nervous impulse of some kind produced in a special way in 
 a special end organ and conveyed along a nerve to a special 
 center in the brain. The second event, the psychosis, a 
 conscious perception and interpretation of this nervous state 
 as a sensation. It is difficult here to avoid confusion in 
 the employment of the word tc sensation. " Frequently it 
 is used to include both the nervous changes and the psycho- 
 logical results which it calls forth. At other times the word 
 "sensation" is used to designate merely the psychological 
 result. The reader must himself judge carefully from the 
 context in which the word occurs what application is given 
 to the term. 
 
 The neurosis is always the cause of the psychosis, unless 
 one should except certain forms of mental hallucination 
 which appear so real to the person as to be objectified. 
 
472 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 While this relation of cause and effect is absolutely clear, it 
 is equally clear that there is not a bit of similarity between 
 the neurosis and the psychosis. In other words, vibrations 
 in the internal ear, or even the nervous impulses which 
 such vibrations produce are absolutely different in kind from 
 those psychological sensations which we designate as sound, 
 and there is clearly no similarity between an ethereal vibra- 
 tion or the stimulation of a rod or cone in the eye and what 
 we psychologically call light. Between the two there is a 
 chasm that cannot at present be bridged, and so all at- 
 tempts at explanation are useless and out of place. To 
 prove the assertion that there is no similarity in essence be- 
 tween physical light and psychological sensation of light one 
 needs only to be reminded that the psychological sensation 
 of light can easily be produced when no physical light is 
 present. One needs only to be struck on the head or to 
 have the optic nerve stimulated, electrically or otherwise, to 
 perceive in the most emphatic and clearest way sensations 
 interpreted as those of light. The stimulation of the audi- 
 tory nerve will produce a ringing noise in a perfectly 
 quiet medium. 
 
 To summarize, then, sensations differ in their modes or 
 modality, a difference caused by the centers in the brain to 
 which they go. Of the sensations of a separate and distinct 
 mode, such as those of sight, there may be distinctions in 
 quality, such as those of red, green or blue lights, or in in- 
 tensity, such as a strong or faint light. There may be dif- 
 ferent qualities which we recognize as differences in touch, 
 or different intensities which we recognize in loudness or 
 softness. The modality of a sensation is determined by the 
 brain center to which the nerve goes, while the quality and 
 the intensity of the sensations of the single modality are 
 normally determined by the end organ itself. 
 
 THE DEVELOPMENT OF THE SPECIAL SENSES. 
 
 From an anatomical, especially an embryological point 
 of view, it is at once apparent that the special sensations 
 
THE ORGANS OF SPECIAL SENSE. 473 
 
 are but special modifications of the general sensations of 
 the body. In fact, comparative anatomy could even in 
 such a complicated structure as an eye find between the 
 highly developed human eye and the mere pigment spot in 
 the skin of some of the lowest animals many intervening 
 gradations. The little pigment spot at the tip of the ray of 
 the starfish which enables that animal to detect possibly 
 the direction of the light merely, is but a slight advance in- 
 deed from the property of general sensations possessed by 
 its entire nervous system. The localization of the pigment 
 at other points than those of the tip of the ray might suffice 
 to arouse light sensations. Such exceedingly simple forms of 
 eye, were, however, in the development of the animal forms 
 more and more expanded, specialized and complicated, un- 
 til finally, from a somewhat common sensation, there re- 
 sults the highly modified retina of the eye with its acces- 
 sories. 
 
 THE OBJECTIFICATION OF OUR SENSATIONS. 
 
 If it is true that special sensations are but specialized 
 general sensations, the question naturally arises why such 
 special sensations should be referred to the external world, 
 whereas the general sensations are not so referred. The 
 answer to this is at hand. It is among the simplest obser- 
 vations on children or adult defective people to show that 
 these special sensations are at first not objectified. The 
 reference of our sensations to the external world is gradual 
 and the result of our early education and experience. In 
 the case of touch, for instance, an object is brought in con- 
 tact with the skin and a sensation results. By repeated ob- 
 servation it has been found that such a sensation comes from 
 the foot, say. This the individual has found by observing 
 possibly an object lying on his foot. Removing the same, 
 he noted the cessation of the sensation. In this way he 
 finally infers when he feels this same sensation that it must 
 come from the foot. These inferences become so trust- 
 worthy finally to the individual that he does not realize at 
 
474 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 all that they are mere mental inferences, but he seems ac- 
 tually to feel the sensation in his foot. 
 
 What is true of the sensation of touch might be equally 
 applicable to all the other senses. That the reference of 
 our sensations is a mere matter of inference may be proved 
 by the fact that the "seeing of stars" (which results from 
 a blow on the head) is projected through the eyes into the 
 external world. A blow on the ulnar nerve at the elbow 
 (the crazy-bone) results in a sensation which is referred not 
 to the elbow where it arose, but to the fingers and hand. 
 This mistake occurs from the fact that the brain has been 
 accustomed to believing that all sensations carried by the 
 ulnar nerve come from the hand. The truth of this belief 
 has been established to the brain over and over again, and 
 so when this impulse reaches the brain along the ulnar 
 nerve it is without question referred to the same place, and 
 this reference by the brain is so distinct and real that it is 
 really hard to believe that the pain is not actually in the 
 fingers. 
 
 That the reference of our sensations to the external 
 world is a matter of acquirement is proved further by the 
 possibility of educating the brain in this matter. Blind 
 people who rely much more upon their sense of touch be- 
 come remarkably proficient in localizing touches, even to 
 the extent of being able to read raised print rapidly and ac- 
 curately with their finger tips. It is also stated that per- 
 sons who had been blind and whose eyesight was suddenly 
 restored, by some kind of operation probably, did not at 
 first see objects at a distance, but referred all of their 
 visual sensations to the eye itself. Such persons felt a 
 distant tree, not as an object of the external world, but as 
 a peculiar and new sensation in the eyeball. 
 
 THE RELATION BETWEEN NEUROSIS AND PSYCHOSIS. 
 
 It was just pointed out that there is the relation of cause 
 and effect between the nervous excitation in the end organ 
 and the mental change in the brain. There is a relation of 
 
THE ORGANS OF SPECIAL SENSE. 475 
 
 cause and effect between the excitation of the retina under 
 the influence of light and the conscious perception of light 
 in the brain. Attempts have been made to establish a 
 mathematical relation between the two. That there is some 
 kind of a quantitative relation between the two is probable, for 
 we know that a stronger stimulation of the retina by stronger 
 light causes a stronger sensation. A harder stroke on the 
 piano causes an increased loudness in our mental percep- 
 tion. Two weights resting on the hand are perceived more 
 strongly than one. The question, however, is, what is, in 
 mathematical terms, this definite relation. Several attempts 
 have been made by means of extended experiments on the 
 various sense organs to determine such a mathematical 
 relation, the most noteworthy being that of the celebrated 
 psychologist Fechner and known as Fechner's " Psycho- 
 physical L,aw. ' ' This Psycho-physical law is, however, only 
 a modification of the psycho-physical law of the physiologist 
 Weber, whose work on the special senses is one of the 
 classics on that subject. This psycho-physical law says that 
 when the stimuli affecting the end organs vary in a geometric 
 ratio the intensity of the subjective sensation varies in an 
 arithmetical ratio. That is, if five units of light would pro- 
 duce a sensation one, then to produce a sensation twice as 
 strong requires twenty-five lights. To increase the subjec- 
 tive perception of the intensity of the light to three times 
 its original, would require one hundred and twenty-five 
 lights. Or, to state the law in another way, the subjec- 
 tive sensation increases directly as the logarithm of the 
 strength of the stimulus. 
 
 While this law is applicable in many instances it is seri- 
 ously at fault in others. For instance, if one looks at a 
 line five inches in length and then wants a sensation of a 
 line twice as long it is of course nonsense to say that that 
 must be twenty-five inches in order to appear twice as long. 
 It approaches, however, the truth of things in connection 
 with the eye and ear. Every one knows that two candles 
 in a room do not make it twice as light as one. candle. 
 
476 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 Two voices do not sound twice as loud as one. The 
 experiment may be easily tried in a room where there are 
 several gas jets. After one jet has been lighted and the 
 intensity of the illumination of the room noted, it will take 
 a number of additional gas jets to make the room seem 
 doubly as light. 
 
 CONFUSION OF SENSATIONS AND INFERENCES FROM 
 SENSATIONS. 
 
 Many of our so-called special sensations are really not 
 sensations at all, but are inferences. To see the height of 
 a tree is an inference; to see the solidity of an object is an 
 inference; distance is wholly a matter of judgment, and the 
 perception of size a mere comparison. It, therefore, not 
 infrequently happens that our sensations mislead us. In 
 justice to the sensations, however, which in a normal body 
 probably never mislead but invariably tell the truth, it ought 
 to be said that it is not the sensations themselves which mis- 
 lead, but the inferences which we choose to draw from them. 
 In calling attention to these inferences it is not the purpose 
 here to carry the argument so far as to say with certain 
 philosophers that everything is an inference and nothing a 
 matter of knowledge ; that to see a certain color plainly 
 with the eye is not a trustworthy bit of knowledge, but a 
 mere inference drawn from a certain state of the body. 
 With this Cartesian philosophy physiology does not concern 
 itself, and the sensations which arise in the body normally 
 in every way are treated at once as trustworthy bits of 
 knowledge from which as premises true inferences may 
 logically be drawn. 
 
 The special sense organs are discussed in the following 
 chapters in the order of their complexity, the simplest being 
 taken first. 
 
CHAPTER XXI. 
 
 TOUCH, TEMPERATURE, MUSCULAR SENSE, 
 TASTE, SMELL. 
 
 It was long known that sensations of touch were brought 
 about by the stimulation of sensory nerves and that the 
 section of such nerves destroyed the sensation, but it was 
 rather late before the special end organs of touch were dis- 
 covered. The first known end organs of touch were the 
 Pacinian corpuscles, discovered by Vater in 1741. The 
 touch corpuscles were not discovered until 1852, when they 
 were described by Wagner and Meissner. It was in 1846, 
 however, when E. H. Weber published his work that physi- 
 ologists arrived at the present conception of the sensation 
 of touch and temperature. 
 
 THE ANATOMY OF THE END ORGANS OF TOUCH. 
 
 Every part of the skin is sensitive, being supplied with 
 sensory nerves. Usually these nerve fibers end in plexuses, 
 the final terminations of which, in the form of little fibrils, 
 which have lost their medullary coat, end in the dermis, or 
 may reach even in among the cells of the Malpighian layer 
 of the epidermis and there terminate without any special 
 end organ. In those portions of the skin, however, where 
 the sensation of touch is specialized special end organs are 
 found. These are of several kinds: 
 
 1. The Pacinian Corpuscles. These, as just stated, 
 were the first discovered, a fact due, no doubt, to their 
 relatively large size, ranging from a fifteenth to a tenth of 
 an inch in length. In the transparent omentum of the cat 
 they are readily recognized with the unaided eye as little 
 whitish translucent bodies. They are found in large num- 
 bers in the areolar tissue under the skin of the hand and 
 
 (477) 
 
478 
 
 STUDIES IN ADVANCED PHYSIOLOGY 
 
 foot and occasionally elsewhere, as in tendons and liga- 
 ments, or (especially true of the cat) in the mesentery. A 
 
 Fig. 149. A PACINIAN CORPUSCLE FROM THE CAT'S MESENTERY. (After Ranvier.) 
 n, nerve; n', its continuation through the core m; a, termination of nerve in distal 
 end; d, c t coats or capsules; /, a channel for the nerve. 
 
 Pacinian corpuscle is made up of a body of connective tissue 
 which shows quite a number of concentric rings. These 
 rings are really capsules. If one were to imagine a great 
 number of egg shells placed one within another and the 
 space between the contiguous egg shells filled with a little 
 liquid the analogy to the Pacinian corpuscle would be appar- 
 ent. In the center of these concentric capsules there is a 
 soft core in which a nerve fiber ends. 
 
 2. The tactile cells. The tactile cells seem nothing more 
 than specialized cells of the lower layers of the epidermis. 
 In regions of the skin where sensation is very acute there 
 are found near the Malpighian layer certain cells which 
 seem to stain more deeply, are larger, more oval and more 
 granular than the ordinary epidermal cells. Delicate nerve 
 fibers can be traced to them which, according to some ob- 
 servers, end in networks which invest these tactile cells like 
 
TOUCH, TEMPERATURE, MUSCULAR SENSE. 
 
 479 
 
 the dendrons in the spinal cord but which, according to 
 other observers, are said to pierce the cells and end directly 
 in them. 
 
 3. End bulbs. The end bulbs are found especially in 
 
 Fig. 150. END-BULBS FROM THE HUMAN CONJUNCTIVA. (After Longworth.) 
 n, nerve running to end-bulbs. 
 
 the sensitive conjunctiva. The sensory fibers which reach 
 the cornea branch and rebranch into finer fibers which form 
 
 Fig. 151.- A SINGLE END-BULB, MUCH ENLARGED. (After L.ongWOrth.) 
 a, entering nerve; b, capsule containing' nuclei; c, c, portions of the nerve within cut 
 across; d, e t cells making up the core. 
 
 a kind of network in the cornea. From this network 
 branches go into the epithelium of the conjunctiva, pierce 
 
480 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 it and end on the outer surface of the conjunctiva in 
 little bulb-like terminations which float in the tears. The 
 statement of Conheim that these end bulbs actually project 
 from the cornea and float in the lachrymal fluid which con- 
 tinually bathes the cornea explains very satisfactorily the 
 extreme sensitiveness of the conjunctiva. Other observers, 
 however, deny that these end bulbs actually project above 
 the cornea, but hold that they are imbedded in the surface 
 epithelium of the cornea. Similar end bulbs occur in the 
 lips and the mouth. 
 
 4. The touch corpuscles. The touch corpuscles are 
 probably the. most important of all the tactile end organs, 
 as they are found in large numbers in the skin of the hands 
 
 Fig. 152. SECTION OF THE SKIN SHOWING TWO PAPILLAE, ONE CONTAINING A CAPILLARY 
 
 LOOP O, THE OTHER CONTAINING A TACTILE CORPUSCLE. (After Biesiadecki.) 
 
 d, entering nerve of three fibers ; /, /, three fibers cut within the corpuscle. The 
 fibrous connective tissue capsule is plainly shown. 
 
 and toes, regions which are most frequently used as organs 
 of touch. They do, however, occur in other places such, 
 for instance, as the forearm, lips and tongue. The ex- 
 treme sensitiveness of the nipple is due to these same cor- 
 puscles. They lie in the dermis where the papillae extend 
 
TOUCH, TEMPERATURE, MUSCULAR SENSE. 481 
 
 up into the epidermis, which papillae cause the character- 
 istic arrangement of the fine lines so readily discernible in 
 the palm of the hands and fingers. Some of the papillae 
 contain blood-vessels, but the majority of them contain 
 touch corpuscles so that by examining these little ridges on 
 the hand one is able to trace real rows of these tactile cor- 
 puscles imbedded just beneath. They are quite small, be- 
 ing only 3^0" of an inch in length. In outline they are oval 
 and consist of a capsule of connective tissue fibers wound 
 round and round. One or more nerve fibers reach each 
 corpuscle, and after making several turns around it enter 
 the capsule losing at that point their medullary coats. The 
 axis cylinder, however, penetrates the connective tissue 
 capsule, branches several times and ends in little bulb- 
 shaped enlargements among the meshes of the same. 
 
 Possibly the explanation of the action of all these end 
 organs lies in the fact that any pressure on such a corpuscle 
 would be much more likely to be transmitted by it to the 
 contained nerve, just as fingers placed between two boards 
 would be much more likely to notice an increase of pres- 
 sure near them than if not so situated. 
 
 A very interesting form of touch corpuscles, although 
 not found in the human body, occurs in the beak of certain 
 birds, such as the duck. A corpuscle here consists of a 
 capsule of connective tissue in which lie several cuboidal 
 cells one above the other somewhat like several bricks 
 
 n 
 
 Fig. 153. CORPUSCLE OF GRANDRY FROM THE DUCK'S TONGUE. (After Izquierdo.) 
 n, nerve. 
 
 might be stacked in a row. A nerve penetrates the cap- 
 sule and sends off branches which finally end between these 
 cells. No doubt a pressure transmitted to this corpuscle is 
 
482 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 transmitted by the cells more effectively to the delicate 
 nerve filaments between them. Just like a finger, to use 
 the same illustration again, would be more susceptible if 
 placed between bricks in such a row. This variety of 
 touch corpuscle is designated as Grandry's corpuscle. 
 
 THE ABSOLUTE TOUCH SENSITIVENESS. 
 
 By the term of absolute sensitiveness is generally under- 
 stood the minimum stimulus which is yet able to produce a 
 sensation at the particular point in question. All parts 
 of the skin have not the same absolute sensibility. Things 
 which at certain portions produce no sensation at all are 
 at other places perceived with the greatest clearness.' The 
 highest absolute sensibility seems to be on the forehead, 
 where a minimum pressure of no more than .002 of a gram 
 is sufficient to produce a sensation. On the temples about 
 .05 of a gram; on the lower lip and fingers .5 of a gram, 
 on the forearm it requires 9 grams and on the skin of the 
 thigh as much as 17 to 20 grams. 
 
 If instead of allowing a weight to rest, as was the case 
 in the determination of the figures just given, one should 
 take a hair or bristle of known stiffness and that should be 
 moved across the skin in question, the minimum pressure 
 perceivable is much reduced. In such experiments the 
 forehead perceives a pressure as little as .0007 of a grain; on 
 the arm or leg about .06. These figures of course corre- 
 spond with the experience of every one that the forehead, 
 skin of the face generally, the lips and fingers are able to 
 perceive differences in pressure which are entirely out of 
 the question on most other portions of the body. 
 
 THE POWER OF LOCALIZATION AND THE TOUCH AREAS. 
 
 The power to localize a touch sensation is a result of 
 experience. It may be materially improved by practice 
 but, other things being equal, the varioiis portions of the 
 skin show naturally a very different localizing ability. Thus, 
 at the tip of the tongue two points as close together as 
 
TOUCH, TEMPERATURE, MUSCULAR SENSE. 483 
 
 one millimeter may still be perceived as distinct points; 
 at the tip of the finger we perceive as two objects, points 
 as close as two millimeters ; on the wrist and arm the power 
 to localize becomes much less and a distance of four or five 
 millimeters apart hardly produces a double sensation. The 
 lips require 4 mm. ; the tip of the nose 6 mm. ; the eyeball 
 10 mm. ; the forehead 20 mm. ; the back of the hand 28 
 mm., and the middle of the back and neck require as much 
 as 60 mm. between the two points to be perceived as double. 
 That the absolute sensibility and the power to localize 
 are different is evident in the case of the forehead, where 
 absolute sensibility is possibly greater than in any other 
 portion of the skin, but where the power of localization is 
 only possible when the points applied are as much as 20 
 mm. apart. This relative power of localization has been 
 generally described in terms of touch circles. The diam- 
 eters of such circles being the least distance between two 
 points to be perceived as double. The touch areas, there- 
 fore, on the point of the tongue are exceedingly small, only 
 1 mm. in diameter, while on the other extreme, the touch 
 circles on the middle of the back are as much as 60 mm. in 
 diameter. Two points, then, placed within such a circle 
 are perceived as one, or in other words, to perceive two 
 points placed on the skin as two, requires that the two 
 points shall fall in different touch circles. It is very neces- 
 sary, however, to remember that these touch areas are not 
 definite anatomical structures, and that, for instance, it is 
 quite impossible with a pencil to divide the skin of the back 
 into such circles so that in every case two points coming 
 within a circle would produce a single sensation, or placed 
 in adjacent ones, a double sensation. For, if one point 
 should be placed close to the edge of one such area and the 
 other point right on the boundary line of the adjacent area 
 so that the actual distance between the two points should 
 be less than 60 mm., they are perceived as one. It is, 
 therefore, not at all possible that the existence of these cir- 
 cles are brought about by the fact that each circle has 
 
484 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 a single nerve going to it, and so carries but a single im- 
 pulse, no matter in what part of the circle it is stimulated. 
 That this notion is wrong is clearly proved by the fact that 
 by practice this circle may be made much smaller, a thing 
 which would be utterly impossible if they were anatomical 
 units. The possible explanation is that the nerves coming 
 from certain portions of the skin run in such a way through 
 the centers in the cord or brain as to produce more of a 
 radiation into the neighboring fibers or cells, and so prevent 
 a very accurate localization. Practice in such a case would 
 be merely the experience to eliminate these radiations and 
 to be able to define the sensation at last to the exact nerve 
 fibers in question. 
 
 It is given by some observers that on an average each 
 touch area contains about twelve touch corpuscles. If this 
 be really true, the explanation of these touch areas may 
 consist in the possible fact that the stimulation at any point 
 stimulates not only the touch corpuscle immediately under- 
 neath or next to it, but about a dozen of the adjoining ones, 
 and so a rather compound sensation is carried. Where 
 these twelve are closely huddled, as in the case of the 
 tongue or lip, the power to localize the affected spot would 
 be quite definite, while in the case of the scattered corpus- 
 cles at other portions of the skin, the area would be too 
 large for exact definition. 
 
 THE SENSE OF TEMPERATURE. 
 
 Not only is the skin able to perceive tactile impressions 
 but it is also able to take note within certain limits of the 
 temperature of the objects affecting it. This ability to per- 
 ceive the warmth of anything is, however, not an absolute 
 one like that of a good thermometer, but is only relative. We 
 are only able to tell whether a thing is hotter or colder than 
 the part of the skin affected, or when the comparison is en- 
 tirely between outside objects we are enabled simply to de- 
 termine of these which is the warmer. This may be easily 
 proved by immersing one hand in warm water and the other 
 
TOUCH, TEMPERATURE, MUSCULAR SENSE. 485 
 
 in cold water for some time. If, now, both hands be 
 plunged into hike-warm water it will appear warm to one 
 hand and cold to the other. 
 
 The ability to determine differences in temperature lies 
 within comparatively narrow limits. A reduction of a tem- 
 perature much below that of the body soon produces pain. 
 An elevation of a temperature much higher a corresponding 
 pain or burn. The finest distinctions in temperature are 
 made when these temperatures are about those of the body. 
 Different regions of the body show different abilities to per- 
 ceive changes in temperature. A few given in the order of 
 their ability, beginning with the best, are, the point of the 
 tongue, eyelids, cheeks, lips, neck. It is interesting to 
 note that the hands and feet seem to follow no regular rule 
 at all, but are warm or cold or insensitive under the most 
 varying conditions. Possibly this is the result of the ex- 
 posure which these parts surfer almost continually to the 
 ever-changing temperature of their environment and so be- 
 come somewhat dulled. 
 
 The sense of temperature is very exactly localized. In 
 fact, changes in the temperature of two points may some- 
 times aid in their perception as two when otherwise they 
 would have been perceived as single. The general feel- 
 ing of cold and heat are not really sensations of the en- 
 tire body, but are simply extended skin sensations. The 
 body feels cold when the skin is cold, even though the 
 interior of the body may be warm. This, for instance, 
 is proved by the chills of many fevers, which chills are 
 usually accompanied with an actual increase of inner tem- 
 perature. On the other hand, the general feeling of warmth 
 which the toper experiences after his draught is really not 
 an increase of bodily heat at all, but is simply explained 
 by the fact that under the action of alcohol the blood 
 from the warmer visceral organs is driven through the skin. 
 As an actual fact from the radiation of the heat going on 
 in the skin his bodily heat is actually being more rapidly 
 reduced. 
 
486 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 The experiments made by Blix and Goldscheider proved 
 the existence of distinct temperature nerves, and showed 
 that there are on the body warm points and cold points, 
 and that whenever a warm point is stimulated, no matter 
 what the stimulus, a sensation of warmth results, while 
 when a cold point is stimulated, even though it be with a 
 warm object, a cold sensation results. These points are of 
 course normally so arranged that the cold points are more 
 easily affected by cold and the warm points by increase of 
 heat. It is possible, however, to use electrical stimuli to 
 affect both and so produce in one class cold sensations and 
 in the other warm sensations even though the temperature 
 in the meantime may have varied not a bit. 
 
 These temperature nerves, however, do not end in special 
 nerve end-organs but in networks of fibers not wholly un- 
 like the dendrons described in connection with the central 
 nervous system. These warm and cold points are, therefore, 
 definite anatomical structures and it is possible by carefully 
 exploring the skin with a sharp-pointed instrument to desig- 
 nate these points and to make an exact map of the temper- 
 ature topography. 
 
 Finally it seems probable that there is a distinct center 
 for cold sensations and another for warm sensations. The 
 probability of this is suggested by the fact that an arm or 
 limb, when subjected to pressure, and so has as we say 
 4 'gone to sleep," is still able to perceive warmth but is in- 
 sensible to cold. 
 
 THE MUSCULAR SENSE. 
 
 When the muscles are called into action one is clearly 
 conscious of a sensation coming apparently from these 
 muscles and informing one of their extent and degree of 
 contraction. It is perfectly easy for an individual with 
 closed eyes to determine exactly the position and move- 
 ments of his muscles. This can only be accomplished by 
 the mind's taking note of the sensory impulses that come 
 from the skin of the part moved and from the sensory 
 
TOUCH, TEMPERATURE, MUSCULAR SENSE. 487 
 
 nerves distributed among the ligaments and muscles of the 
 same part. In fact, for the proper manipulation of the 
 muscles we are largely dependent upon the impressions 
 which accompany the use of them. An individual with 
 sensation lost in the arm is unable to control the move- 
 ments of that arm. It not infrequently happens that when 
 an arm goes to sleep, the power to move it returns before 
 sensation returns, but the motions so accomplished are 
 of the most clumsy and inaccurate kind. Experiments 
 have shown that horses whose trigeminal nerve (the sensory 
 nerve to the head) had been cut, found it perfectly impos- 
 sible to perform even such simple muscular actions as the 
 chewing of their food. A frog whose spinal sensory nerves 
 are cut finds the greatest difficulty in the performance of 
 his otherwise simplest motions. That these guiding sensa- 
 tions do not come entirely from the skin is shown by the 
 fact that the skin may be entirely removed from a portion 
 of a frog's body without interfering with the accuracy of 
 the movement of his muscles, provided the sensory nerves 
 going to these muscles are left intact. 
 
 In the chapter on the histology of the muscles it was 
 pointed out that muscles themselves are not sensitive in any 
 way, but that the sensations which seem to come from the 
 muscles really come from sensory nerves which are distrib- 
 uted in among such muscles. Even the sense of fatigue 
 of muscles has such an origin. 
 
 But not only are we able to determine the amount of 
 motion, but it is possible actually to measure the intensity 
 of the muscle contraction. In this way we are enabled to 
 form judgments as to the weight of things. A weight must 
 change from at least one-fortieth to one-tenth of its entire 
 amount in order to perceive a difference. No doubt, how- 
 ever, the ability to make these distinctions varies within wide 
 limits and is largely perfected by practice. Individuals who 
 are in the habit of weighing things become finally so pro- 
 ficient as to be almost trustworthy in that matter. There 
 are many illusions in connection with the matter of the 
 
488 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 judgment of weights. Of objects that have the same weight 
 those that are larger seem lighter. Again, an object seems 
 lighter when it is elevated with both hands, instead of one. 
 No doubt we judge of the weight of objects by noticing the 
 amount of effort necessary to bring about the required 
 motion. Such a sensation is really not one of the muscles, 
 it is a measurement of the brain's own activity in the inten- 
 sity of its motor impulses. This does not preclude the pos- 
 sibility that sensory nerves distributed in among the muscles 
 may take part in giving us our sensations of passive move- 
 ments. Not only are we able to perceive motions which we 
 voluntarily make, but we are also able to perceive passive 
 movements. To be suddenly moved forward, to have this 
 motion checked or to be turned right and left, or to have the 
 rapidity of the motion varied is at once a matter of knowl- 
 edge. It seems very probable, however, that this knowl- 
 edge of passive movements is in no sense connected with 
 the muscles, or even due to the inertia of the body or its 
 centrifugal actions, but that it is due entirely, or at least 
 largely, to changes which are occasioned by lymph move- 
 ments in the semi-circular canals of the ear, in connection 
 with which a detailed explanation of this matter is given. 
 
 THE SENSE OF TASTE. 
 
 The sense of taste is located in certain parts of the mucous 
 membrane of the mouth, especially on the mucous membrane 
 covering the tongue. The under side of the tongu,e is not 
 sensitive to taste. The same is true of the lips and gums 
 and the cheek. It is asserted, however, that in small chil- 
 dren these parts are able to give sensations of taste. The 
 exact location of these taste areas may be easily established 
 by taking a sapid powder and applying it point for point 
 over these areas. A liquid would not be satisfactory for 
 this purpose, as it would naturally spread to the neighboring 
 areas. The sense of taste may also be anatomically located 
 by the presence of taste bulbs. These taste bulbs, dis- 
 covered by Loven and Schwalbe in 1867, are small barrel- 
 
TOUCH, TEMPERATURE, MUSCULAR SENSE. 
 
 489 
 
 shaped bodies filled with a number of spindle-like cells 
 hich at their lower extremities are connected with the 
 
 Fig. 154. SECTION OF PAPILLAE FROM TONGUE OF RABBIT, SHOWING POSITION OF TASTE- 
 BUDS. (After Ranvier.) 
 71, nerve cut across; v, vein; a, gland; g, a single taste-bud. 
 
 nerves of taste and at their upper end are pointed and pro- 
 ject to the exterior. A rather rough analogy might be made 
 
 \. iit 
 
 Fig. 155. A SINGLE TASTE-BUD MUCH ENLARGED. (After Ranvier.) 
 p, the open pore; *, taste cells; m, white corpuscle filled with granules- r, supporting: 
 cell; e, ordinary tongue epithelium. 
 
 by imagining an ordinary flour-barrel filled with a number 
 of sticks, their lower ends connected with wires but the 
 
490 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 upper ends of the sticks somewhat pointed and projecting 
 above the body of the barrel free into the exterior. These 
 taste bulbs are most plentiful in the circular depressions 
 around the circumvallate papillae and the free ends of the 
 sensory cells project into this groove . They are also found, 
 although not so plentifully, on the fungiform papillae and 
 even on the soft palate and epiglottis. Their preponderance 
 towards the back of the tongue and mouth explains the 
 common experience that the sense of taste is most acute in 
 those regions. In fact, the sense of taste is rather imperfect 
 at the tip of the tongue. Yet the tip seems best adapted for 
 sour sensations but not so well for bitter sensations. The 
 acuteness of the sensation in the back of the mouth possibly 
 finds its explanation in the tendency which this gives to the 
 animal to swallow its food. 
 
 The anatomical arrangements for the perception of taste 
 at the tip of the tongue are quite different from the taste 
 bulbs, the sensory nerves here ending merely in fine net- 
 works of fibrils. In the description of the cranial nerves 
 in the preceding chapter the glossopharyngeal was pointed 
 out as the main nerve of taste, while the taste sensations 
 from the tip of the tongue were ascribed to the trigeminal. 
 Some physiologists have tried to make the difference in the 
 nerves going to these areas explain the difference in the 
 acuteness of the sensation, but more recent work seems to 
 show that even the fibers that go to the tip of the tongue 
 are derived from the glossopharyngeal nerve which reach 
 the tip of the tongue along the trunk of the trigeminal 
 nerve. 
 
 THE NATURE OF A TASTE SENSATION. 
 
 Gustatory sensations are produced by substances, either 
 in solution when introduced into the mouth, or dissolved by 
 the liquids in the mouth. Gases dissolved in the liquids of 
 the mouth may thus give rise to actual tastes. In what 
 manner these substances act upon the nerve endings to 
 produce the sensations of sweet, or sour, or salty, etc., is 
 entirely unknown. We are at present entirely unable to 
 
TOUCH, TEMPERATURE, MUSCULAR SENSE. 491 
 
 form the remotest conception of it. It seems probable 
 though, that there are separate nerves for the separate 
 tastes, inasmuch as experiments show that certain papillae 
 give certain tastes only, no matter how stimulated, while 
 other papillae give other tastes. Possibly the tips of the 
 taste cells are chemically affected by sapid substances, cer- 
 tain cells readily by acids, sour substances, others by sub- 
 stances of the family of the sugars, producing the sweets, 
 and so on. These impressions are then conveyed to the 
 brain, and in the brain in a perfectly subjective way what 
 we call the " taste" arises. 
 
 That there is a large subjective element in taste is prob- 
 able from such experiments as these: Pure distilled water 
 when tasted immediately after tasting salty water tastes 
 distinctly sweet. Still more remarkable is the fact that a 
 dilute solution of sugar becomes distinctly sweeter to the 
 taste when a little bit of salt has been added to it. The 
 intensity of the sensation depends not only on the strength 
 of the solution to be tasted, but also on the amount of taste 
 area in the mouth in contact with that solution. For this 
 reason a person tasting a thing tries to spread it out as much 
 as possible over his sensory area. Rubbing the substance, 
 pressing it against tongue or palate sharpens the taste, no 
 doubt because it facilitates the introduction of the sapid 
 substance into the depressions around the circumvallate 
 papillae in which the taste buds lie. 
 
 Taste sensations are frequently confused with odors. 
 Possibly in the majority of instances when a person imagines 
 he is tasting something, the sensation is really due to his 
 olfactory sense. With the destruction of the sensibility of 
 the nose goes the possibility to taste such apparently sapid 
 substances as coffee, tea, or the ordinary flavors of fruits. In 
 fact, the number of tastes are limited and are usually classed 
 in four kinds, namely, bitter, sour, sweet and salty. In 
 each class there are, of course, large numbers of slightly 
 varying qualities. 
 
492 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 THE SENSE OF SMELL. 
 
 The sense of smell is located in the olfactory region, 
 which includes the mucous membrane covering the folds of 
 the ethmoid bone, and the turbinated bones. The mucous 
 membrane in these parts is not provided with cilia, as it is 
 in the regular respiratory tract behind. The difficulty of 
 establishing definite end organs con- 
 cerned in the sense of smell is even 
 greater than in those of taste, and the 
 histology of the mucous membrane 
 reveals but slightly differentiated struc- 
 tures for this purpose. There are, how- 
 ever, in the epithelium covering this 
 mucous membrane certain more slender 
 cells placed in between the ordinary 
 epithelial cells. These more slender or 
 sensory cells are connected with fibers 
 from the olfactory nerve beneath, are 
 pointed at the upper end, which point 
 projects very slightly above the mucous 
 membrane into the nasal cavity. The 
 statement of some observers that in the 
 human nose these sensory cells have 
 
 Fig. 156. OLFACTORY CELLS, little hairs or cilia at their end is prob- 
 (After M. schuitze.) ao ly not true. It is true, however, in 
 
 1, from the frog; 2, human; ,-t r i j j 1 't 
 
 a. ordinary epUhelial cells! the CaSG f birds aild amphibians. 
 
 6, olfactory cells; c, peri- TllCSC pOSSCSS OU the ends of tllCSC 
 
 pheral process prolonged ,11 11 i ATA-I 
 
 in i into fine hairs ; a, their cells rather long immovable hairs . The 
 central ends connected a b se nce of such hairs in man may 
 
 with the nerve. * 
 
 account for his bluntness of this sense 
 
 when compared with the intense acuteness of that of some 
 of the lower animals. The tips of these cells projecting into 
 the nasal cavity are the points where the stimuli that pro- 
 duce sensations of odor affect the nerves. It is at once ap- 
 parent how much more efficient such a stimulus would be 
 when acting upon a number of sensitive protoplastic hairs 
 projecting freely above the surface than when obliged to act 
 
TOUCH, TEMPERATURE, MUSCULAR SENSE. 493 
 
 on a relatively blunt end only slightly raised above the gen- 
 eral epithelial level. 
 
 As in the case of taste, so here there is absolutely no 
 knowledge at present as to the exact manner in which the 
 sensations of smell are produced. Possibly here, too, the 
 subjective element plays a very important part, for it not 
 infrequently happens that a person who has experienced an 
 exceedingly unpleasant odor (such, for instance, as those 
 associated with a corpse) will have this odor recur after 
 that from time to time with the clearest exactness, although 
 every possibility of the offending gases actually having af- 
 fected the nose was precluded. Smell sensations are oc- 
 casioned by the introduction of gaseous substances only, 
 but the intensity of the sensation depends not only upon 
 the strength of the gas, but also upon the circumstance that 
 this gas must stream through the nose. A gas allowed to 
 rest in the nose soon ceases to affect the membrane. For 
 this reason the air is always sniffed when the odor of any- 
 thing is to be detected. 
 
 One of the most remarkable things about the sense of 
 smell is that it may be aroused by almost inconceivably 
 small quantities of odorous matter. Musk, for instance, 
 may fill large spaces with its odor and do so for relatively 
 long times, and yet not lose measurably in weight. 
 
 A further interesting fact is the inability we have of 
 forming anything like a scale of odors, or even our inability 
 to divide them into related groups. In fact, we are unable 
 to designate them with definite names, but apply to them 
 the names of the objects in which they occur. We are also 
 further entirely unable to analyze odors into their compo- 
 nents, a thing which can be easily done in the matter of 
 colors with the eye, or still more easily with sounds in the 
 ear. Even when one nostril is filled with an odor of one 
 kind and the other nostril with a different odor, the two 
 sensations do not blend at all, but we perceive now the one, 
 now the other, depending upon the relative strength or sen- 
 sitiveness of the two nostrils. 
 
CHAPTER XXII. 
 
 THE EAR. 
 
 The ear is an apparatus constructed according to such 
 physical and physiological laws as will enable it to take 
 cognizance of sound vibrations. The adaptation of this organ 
 to physical sound vibrations is one of remarkable perfec- 
 tion, exceeding, possibly, any other instrument which has 
 to do with the manipulation of sound waves. Evidently, 
 therefore, it is necessary in order to understand the anatomy 
 and physiology of this sense organ to become somewhat ac- 
 quainted with the physical properties of sound waves. 
 
 THE NATURE OF SOUND. 
 
 Sound, that is, sound viewed from its physical stand- 
 point, is a vibratory motion. The body moving may be 
 either gaseous, liquid or solid. The vibration is, however, 
 a molar vibration ; the mass of the medium in question must 
 vibrate. In this sound differs fundamentally from heat and 
 light, which are also forms of motion, but these latter are 
 produced by the molecular motion of the body giving out 
 the heat or light. This distinction may be easily made 
 clear by imagining a bell struck first with a hammer. The 
 blow sets in vibration the entire mass of the bell. This vi- 
 bration may be felt with the finger, and a small object sus- 
 pended near the bell is violently thrown away from it as 
 soon as it touches it. One is able almost to see the oscil- 
 lation of the whole metal backwards and forwards. If the 
 bell be grasped and held firmly it soon ceases to vibrate and 
 the sound is gone. If, on the other hand, such a bell 
 should be placed over a fire it would gradually become 
 warmer and warmer, and if the heating process should con- 
 tinue, might even be raised to a red heat, and so produce 
 light. In this instance it is not the whole mass of the bell 
 (494) 
 
THK EAR. 495 
 
 moving together, but it is a molecular motion throughout 
 its substance. Touched with an object, the heat vibrations 
 do not cease, and a small piece of metal placed in contact 
 with it is not violently thrown off. In other words, sound 
 is a vibratory motion of the mass of an object, heat and 
 light of its component molecules. 
 
 THE PRODUCTION OF SOUND. 
 
 From the vibratory nature of sound it follows that 
 sounds may be produced in an endless variety of ways, the 
 requirement in each case being simply that some kind of a 
 body be set in rapid motion and that this motion be trans- 
 mitted to a suitable medium. A familiar object for the pro- 
 duction of sound is the tuning-fork, the vibrations of which 
 are very apparent when sounding; in the case of the organ 
 the metal tongue is set in vibration by the air thrown against 
 it; in the piano it is the strings made to vibrate by the 
 stroke of the key against them, while in wind-instruments 
 the air itself within is set into definite oscillations. 
 
 THE RANGE OF THE NUMBER OF VIBRATIONS IN THE PRODUC- 
 TION OF SOUND. 
 
 It is not every vibration that produces a sound. It is not 
 until the vibrations reach a certain frequency that they be- 
 come perceptible to the ear. The minimum number of vi- 
 brations to be so perceptible varies a little for different ears, 
 but is in the neighborhood of sixteen per second. A string 
 vibrating fewer times than sixteen per second produces no 
 perceptible sound, although its vibrations may be distinctly 
 visible to the eye. Vibrations above this lower limit are 
 audible. There is, however, an upper limit beyond which 
 the ear is not able to go. This upper limit also varies for 
 different ears, but seems to be in the neighborhood of 60,- 
 000 vibrations to the second. These limits between which 
 the human ear is able to appreciate sounds comprise a range 
 of about thirteen octaves. A high-grade piano has usually 
 no more than seven octaves, or seven and one- third. The 
 
496 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 superiority of the ear as an organ for catching sound several 
 octaves higher and lower than the piano is at once apparent. 
 The compass of the human voice is about three octaves 
 only. Deep F of the bass singer has about 87 vibrations, 
 and the upper G of the soprano about 775 vibrations per 
 second. Voices exceed these limits only in very excep- 
 tional cases. It will be pointed out later that the limits of 
 the ear are not limits imposed by the vibrations themselves, 
 but that these limits are produced in consequence of the 
 anatomy of the ear, the basilar membrane having an extent 
 of about thirteen octaves only. It is, of course, entirely 
 possible, in fact probable, that an anatomical extension of 
 this structure in the ear would have materially increased the 
 range of the musical scale which might be perceived. 
 
 THE TRANSMISSION OF SOUND IN THE AIR AND ITS VELOCITY 
 
 IN THE SAME. 
 
 The usual medium for the transmission of sound is, of 
 course, the air. Sound is unable to pass through a vacuum. 
 A sounding body placed under a bell jar of an air-pump and 
 the air then exhausted, cannot be heard, no matter how 
 violently it may be in motion. The admission of air into 
 the receiver, and so the formation of a medium around it 
 for the transmission of sound at once makes the sound loud 
 and clear. Sound waves in air differ, however, in form from 
 those produced by the tuning-fork or a string. The sound 
 waves in air go in all directions from the sounding point 
 in the form of concentric spheres, somewhat like the circles 
 that radiate from the surface of a body of water from the 
 point where a pebble has been thrown into it. In the case 
 of the air, these waves do not extend in the form of circles 
 but in the form of spheres. In a sound wave the particles 
 of air are set in motion in such a way that they produce 
 spheres of condensed air and rarefied air, and it is these 
 waves of condensation and rarefaction that are transmitted, 
 and, of course, not the particles of air themselves. 
 
THE EAR. 497 
 
 These waves go with a velocity which can be readily 
 determined. That sound waves are much slower than rays 
 of light is proved by the experience of every one who has 
 seen the steam of the whistle of an approaching train 
 several moments before he hears the sound. Or he may 
 have noticed the discharge of a gun or the flash of the 
 lightning before he hears the sounds which these have pro- 
 duced. The velocity of sound vibrations through the air 
 depends upon the density of the air, and as the density of 
 the air depends upon the temperature it is usually said that 
 the velocity of a sound depends upon the temperature of 
 the medium. At the temperature of freezing, the velocity of 
 sound is about 1,092 feet per second. For each additional 
 degree of centigrade the velocity is increased about two 
 feet per second, so that at ordinary mild temperatures the 
 velocity of sound in air is not far from 1,120 feet per 
 second. 
 
 REFLECTION AND REFRACTION Ol SOUND. 
 
 Sound being a vibratory motion it is subject to the same 
 laws of reflection and refraction as light. A sound wave, 
 for instance, striking a high wall or precipice is reflected 
 back and gives rise to what is familiarly known as the echo. 
 An echo in sound is, therefore, like the reflected image in 
 a mirror in the case of light. 
 
 But not only may sound be reflected like an echo, it may 
 be refracted like light through lenses. To do this it is simply 
 necessary to pass the sound wave through a denser medium 
 to converge it, or a rarer medium to diverge it. A large 
 rubber bag shaped like a double convex lens and filled 
 with carbon dioxide, which is denser than air, serves as a 
 condensing lens, somewhat like glass does for light. Very 
 seldom, however, are sound lenses brought into use. 
 
 A familiar result, depending upon the refraction of sound, 
 
 is produced in the carrying of sound by the winds. It is 
 
 apparent that a sound is much plainer when the wind blows 
 
 from that direction. The familiar explanation is, of course, 
 
 32 
 
498 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 that the sound, like autumn leaves, has been blown along 
 by the wind. This is, however, a mere figure of speech. 
 The real explanation consists in the fact that the air being 
 blown over the ground and meeting with resistance there is 
 somewhat condensed, and being therefore denser on the 
 ground than it is further up where there is no resistance to 
 be overcome, the sound waves are deflected towards the 
 ground, by this denser air near it acting like an ordinary 
 lens. In this way much of the sound which would other- 
 wise have radiated upwards into the sky is refracted to the 
 ground and so the perception of the sound made more 
 distinct. The analogy in the case of light occurs, for 
 instance, at the rising or setting of the sun when by means 
 of the refraction of the atmosphere the sun becomes visible 
 in the morning really before it comes above the horizon, 
 and remains visible in the evening some time after it has 
 really set, due to the fact that the rays of light which would 
 have gone off into space are by the atmosphere, like a lens, 
 bent down to the ground. 
 
 THE PHYSICAL PEOPEETIES OF SOUND. 
 
 1. The Intensity or Loudness. Sounds are easily dis- 
 tinguished as louder or softer, and this distinction in loud- 
 ness is described as the intensity of the sound. This in- 
 tensity is produced by the intensity of the vibration, not by 
 the frequency or number of vibrations. This must remain 
 the same. The intensity is in the added distance through 
 which a single vibration moves. Thus, in the case of a 
 piano string if it be struck very lightly, it vibrates up and 
 down through a very small distance, if it be struck harder 
 the number of its vibrations is not increased, but the string 
 at every vibration passes through a greater amplitude. The 
 explanation of intensity may be easily shown to the eye by 
 the pendulum. One can easily satisfy himself that a pendu- 
 lum of a definite length makes no more vibrations in a given 
 time when it swings out far to the right and left at each 
 beat, than when it moves but little out of its vertical posi- 
 
THE EAR. 499 
 
 tion. No matter if the pendulum of a large clock should 
 move through an arc of only a degree, or if it should move 
 through an arc of ninety degrees would the number be 
 changed, but it is of course evident that when moving 
 through ninety degrees the stroke is more intense than 
 when moving through one. 
 
 If a tuning-fork by means of a point at its vibrating ends 
 could be allowed to trace its vibrations on a revolving drum 
 the intensity of the sound would be pictured to the eye by 
 the height of its waves. Intensity, therefore, is usually 
 explained by saying that it is that property of a sound which 
 depends upon the amplitude of the vibration. Loudness in 
 sound is brightness in the case of light. 
 
 2. Pitch. We readily distinguish sounds as higher or 
 lower, and we speak of bass, alto, tenor and soprano parts 
 when we haVe these distinctions in mind in the case of 
 singing. This highness or lowness, or, in other words, the 
 pitch of a sound, depends upon the number of vibrations 
 per given time, of which the sound is composed. For in- 
 stance, sixteen, or more generally thirty-two vibrations per 
 second is the lowest note audible. Middle C on a piano 
 (French pitch) is 256 vibrations per second, while the 
 upper C on the piano has over 2,000 vibrations to the 
 second. Pitch is expressed in another way, by stating that 
 it is that property which depends upon the length (not 
 height or amplitude) of the vibrations. This is but saying 
 the same thing in another form. In a note which has 2,000 
 vibrations per second the individual waves must be much 
 shorter than in a note that has but 32. Just as in a chain 
 having 100 links to the foot, the individual links must be 
 much shorter than a chain having but three links to the 
 foot. Evidently the number of links and the length of the 
 individual links express the same thing. 
 
 Other things being equal, the pitch which a sounding 
 body will produce will in the case of tuning-forks or vibrat- 
 ing tongues depend upon the length of the fork or tongue, 
 
500 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 the pitch being higher the shorter the tongue. In the case 
 of stringed instruments the pitch depends upon the tight- 
 ness with which the string is stretched, as well as upon the 
 length of the string. In the tuning of a violin, for instance, 
 the pitch of the string is first determined by the tightness, 
 and after that, the pitch is varied by shortening the length 
 of the string in definite proportions by placing the finger 
 upon the same. 
 
 3. The Quality of Sounds. If in the same room a 
 note should be sounded by each of a half dozen instruments 
 and the intensity and pitch of this note be made as nearly 
 the same as possible, the ear could nevertheless distinguish 
 without the least difficulty between the sounds produced by 
 the violin, the piano, the horn, the organ, or the human 
 voice. This property of a sound by means of which, even 
 when pitch and intensity are the same, we are able to make 
 these very definite distinctions is called the quality of a 
 sound. There are, therefore, as many different qualities 
 as there are kinds of sounds. Even in the case of human 
 beings nearly every voice has its own quality and we are 
 able to recognize an individual very readily by his voice. 
 The question now arises what the physical basis for the dis- 
 tinctions is. 
 
 This is not so easily made clear without having at one's 
 disposal a more detailed knowledge of harmonics than can 
 be assumed in this discussion. A few hints or suggestions, 
 however, as to its explanation may be helpful. If we pic- 
 ture to ourselves sound waves in the form of water waves, 
 it is evident that the height of a wave represents the loud- 
 ness of the sound, and the length of the wave; that is, the 
 distance from the crest of one wave to the crest of the next 
 one, represents the pitch. Now, in this analogy the form 
 of the wave determines the quality of it. Every one who 
 has been at the lakeside or at the seashore, or, still better, 
 far out on the ocean, must have been struck with the variety 
 of the forms of waves from the gentle, undulating swell with 
 
THE EAR. 501 
 
 its unbroken glassy surface like a bulged mirror, to the 
 ploughed, choppy waves of the English Channel or Irish 
 Sea. He has noticed how the surface of a big wave is 
 sometimes covered with smaller waves, and these individual 
 smaller waves, in turn, roughened with ridges upon them. 
 It is not difficult to see how the form of a wave on L,ake 
 Michigan might differ materially from the form of a wave 
 on another body of water, even though the height of the 
 waves and the lengths of them be the same. This differ- 
 ence in form produces the quality of the wave, and if we 
 had special senses to take cognizance of such water waves, 
 probably one would have no difficulty in distinguishing be- 
 tween a Lake Michigan wave and a wave from the Gulf of 
 Mexico, or another from the middle of the Atlantic. 
 
 Leaving this analogy and defining quality in the terms 
 of sound waves it is this: The quality of the sound de- 
 pends upon the number of secondary waves or secondary 
 sounds which are super-imposed upon the first fundamental 
 wave or sound. This was conclusively shown by the ex- 
 periments of Helmholtz, who, by means of properly com- 
 bined tuning-forks was actually able to produce the qual- 
 ities of different instruments. To use the analogy of light, 
 quality would be produced by taking a fundamental color 
 and then tinting or shading that color within narrow limits 
 by the addition of secondary colors. If, therefore, the 
 quality of a sound is due to its compounding, the question 
 naturally arises, what would be the quality of a sound per- 
 fectly pure without the admixture of secondary waves. 
 Such sounds are produced with relative purity by tuning- 
 forks, and any one who has heard a high-grade tuning-fork 
 must have been struck by its mellow, pure, unmixed qual- 
 ity. If, now, to such a fundamental pure sound other 
 tuning-forks in varying strength and of proper pitch be 
 added it would be possible to reproduce the piano note, or 
 tone of the violin, and we may add even the quality of the 
 human voice. 
 
502 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 HARMONY. 
 
 A succession of notes varying in pitch and possibly 
 other properties is spoken of as a melody. Melodies need 
 conform to no especial physical rule, but are almost wholly 
 determined by the likes or dislikes of the composer. A 
 pleasing melody to one is not necessarily so to the next. 
 A much more definite arrangement of notes occurs in har- 
 mony. By harmony is understood the consonance of two 
 or more sounds. Any two sounds when sounded together 
 are by no means necessarily harmonious. In fact, if the 
 sounds were selected at random the chances would be very 
 much in favor of their proving discordant to the ear. Har- 
 mony is dependent upon the consonance of definite specific 
 sounds, and is, at least with the majority of civilized people, 
 the same for all persons. Every normal ear hears as a pleas- 
 ant sound the consonance of a note and its octave. Every 
 player on the piano knows that C and G produce a pleasant 
 effect when sounded together; that the same is true of C 
 and E, or C and F, confining ourselves in this illustration 
 to the key of C. C and B produce a discord, C and G^ are 
 displeasing. We have now to determine what physical 
 property it is that determines the consonance or dissonance 
 of notes. In doing so it is necessary to bear in mind that a 
 consonance or dissonance is first determined by the ear, 
 apart from any physical considerations of the sounds in 
 question. A person who knows not the first elements of 
 the nature of sound may be perfectly able and is perfectly 
 able to feel the pleasurable effects of certain combinations 
 of sounds, and the displeasing effects of others. The proper 
 chords on a piano or in an orchestra please the ears of the 
 attuned or untuned alike, within large limits. The determi- 
 nation of the physical nature of harmony, therefore, consists 
 merely in determining the relations of notes which have been 
 previously selected by the ear as harmonious. 
 
 When, now, notes which are harmonious are examined 
 experimentally, it is soon established that the physical basis 
 of harmony is the simple matnematical ratio of tJie number 
 
THE EAR. 503 
 
 of vibrations of the component sounds, and the notes are 
 more harmonious as the mathematical ratio of their numbers 
 of vibrations becomes simpler and simpler. Kvidently the 
 simplest mathematical ratio is 1 to 1, but this, of course, is 
 unison. The next simplest mathematical ratio is 1 to 2. 
 This is the ratio of a note and its octave \ that is to say, the 
 octave above a note has always just twice as many vibra- 
 tions as the note itself. If middle C, therefore, has 256, the 
 C just above in order to be a harmonious octave must have 
 512. The next simplest ratio is 2 to 3. This ratio is found 
 to exist between a note and the perfect fifth of that note. 
 Using the key of C in all of this, it is the combination of C 
 and G. In other words, for every two vibrations in C, G 
 has three, or, if C has 256 G has 384 per second. The next 
 simplest ratio possible is 3 to 4, and this proportion in their 
 vibrations exists between C and F. The ratio of 3 to 4 is 
 thus found in \\\o. perfect fourth. The ratio of 4 to 5 is the 
 ratio of the interval between C and E, or the major third. 
 The ratio of 5 to 6, 6 to 7, 7 to 8, 8 to 9, and so on, are 
 becoming too complicated to appear harmonious to the ear, 
 and we feel these ratios as dissonances. But there are other 
 simple ratios; 3 to 5 is a simple ratio, and this is a ratio 
 which exists between C and A, the major sixth. The ratio 
 of 1 to 3 exists between C and G in the next octave, while 
 the ratio of 1 to 4 exists between C and the upper C of the 
 next octave. 
 
 All these ratios are simple ratios, and it is this simplic- 
 ity of ratio, which is simply the rhythm of their vibrations 
 expressed mathematically, that produces the effect of har- 
 mony upon the ear, or rather, upon the mind. 
 
 Complex ratios become more and more dissonant, while * 
 very complex ratios finally lose all harmonious qualities and 
 tend to become mere noise. If the question be asked why 
 notes having a simple ratio to each other appear pleasant, 
 or harmonious, the answer would have to be referred out- 
 side of the domain of physiology. It would probably be 
 that the mind naturally and for inexplicable reasons likes 
 
504 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 definite rhythms, and when these rhythms are easily per- 
 ceived; that is, are mathematically simple, we become con- 
 scious of this pleasure. 
 
 Something of this rhythm appeals to the eye. Soldiers 
 that march in unison present a pleasing appearance. A 
 company of soldiers composed of a column of adults and a 
 column of boys marching in such a way that the boys would 
 take two steps while the adult soldiers took one step would 
 be very pleasing to the eye. The interval between the two 
 columns of soldiers would really be an octave. We can 
 imagine the pleasing effect of two columns marching with 
 such regularity that for every two steps of one column the 
 other should take three, so that at every third step of the 
 second column all of the soldiers would step together. 
 This would be the interval of 2 to 3, or the perfect fifth. 
 If, finally, all mathematical ratio should be lost, or at least 
 become very complex, we would no longer be able to per- 
 ceive any rhythm in the march, and the column now would 
 present nothing but an ordinary crowd rushing in confusion 
 down the street. This, in terms of sound, is mere noise. 
 
 In the building of a musical instrument, therefore, such, 
 for instance, as the piano, which has only a certain number 
 of keys, the point is to pick out those notes which bear 
 these simple ratios and omit those of complex ratios. In 
 this way there is produced what is commonly called the 
 scale, consisting of eight sounds. The vibrations determin- 
 ing these notes are in the proportion of the numbers as here 
 given : 
 
 CDEFGABC 
 1, 9 /s, 5 A> 4 /3, 3 / 2 , 5 /3, 15 /s, 2. 
 
 Cleared of fractions these proportions may be expressed 
 by the numbers, 
 
 CDEFGABC 
 
 24, 27, 30, 32, 36, 40, 45, 48. 
 
 Thus for every 24 vibrations of C, D will have 27, A 40, 
 and the upper C 48, etc. 
 
THE EAR. 505 
 
 Evidently in harmonics we are not concerned with the 
 absolute number of vibrations but only with the relative. 
 We may select as the number of vibrations of our funda- 
 mental note any desired number, but once having selected 
 this number arbitrarily, the others must bear these definite 
 ratios to it. Thus, the French standard for middle C is 
 about 256; the C of the Italian opera has about 273, while 
 a Musical Congress in 1834 at Stuttgart recommended 264 
 as a standard for middle C. 
 
 Expressed then in physical terms, a harmonious chord on 
 the piano is a combination of those notes which bear simple 
 mathematical ratios. Taking the key of C, such a chord 
 would be composed of C-E-G and C, or C-F-A and C. 
 These are the ordinary combinations. Music begins to be 
 less and less harmonious as the ratios become more com- 
 plex, and when the ratios can no longer be perceived at all 
 we speak of sounds as mere noise. 
 
 SYMPATHETIC VIBRATIONS. 
 
 In order to understand the manner in which sounds in 
 the air finally succeed in stimulating the internal ear, it is 
 necessary to understand those phenomena of vibrating 
 bodies designated as sympathetic vibrations. It is a very 
 general experience, when singing a clear note near some 
 musical instrument, that the musical instrument will catch 
 up that tone and give it out itself. Sometimes it is neces- 
 sary to remove instruments from the room to prevent this 
 interference. Two tuning-forks tuned alike and placed 
 near each other mutually affect each other. If one tuning- 
 fork be sounded the vibrations from that tuning-fork will 
 put the second tuning-fork in vibration, even though it was 
 perfectly silent to begin with, and the second tuning-fork 
 may go on sounding after the first one has been mechanic- 
 ally stopped. In a music store where numbers of instru- 
 ments are found close together the strong sounding of a 
 chord on one piano will usually set similar chords vibrating 
 in the other pianos. These phenomena are produced by 
 
506 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 having the strings of the other instruments set in sympa- 
 thetic vibration by the sound waves emanating from the 
 first. 
 
 It must be noted, however, that one note will produce a 
 sympathetic vibration of another only when the two notes 
 so produced are of the same pitch, or bear at least harmonic 
 ratios to each other. To sing middle C into a piano will 
 set in vibration the string of middle C, not that of D or B. 
 To understand the nature of sympathetic vibrations thor- 
 oughly means to understand the manner in which the vibra- 
 tions of the air are finally transmitted to certain chords in 
 the ear. 
 
 The ear has a piano-board in it and sounds entering it 
 will set in sympathetic vibration those chords which are 
 attuned to them. 
 
 The physical explanation of these sympathetic vibrations 
 is simple. One can easily see how a very slight wind which 
 would come in regular puffs might set a very heavy object 
 swinging after a while if these puffs should occur at such 
 regularities that they would always strike the swinging 
 object just at the proper time. When the waves of air are 
 synchronous with the vibrations of the body a slight wave 
 may soon put in motion a relatively large body. If we 
 imagine an individual sitting in a swing and pushed with 
 but one finger, but the push administered just at the moment 
 when the person is swinging away from the finger, so as to 
 get the full benefit of the push, the swing may be soon set 
 in motion by these slight finger tips. 
 
 So with the vibrations entering the ear and striking a 
 certain string whose vibrations are exactly attuned to it, 
 they finally set it going and so give rise to the production of 
 a second sound which is the counterpart of the first. 
 
 Having in this preliminary way called attention to some 
 of the elementary but fundamental properties of sound, it 
 is possible to more intelligently understand the somewhat 
 complicated anatomy of the auditory apparatus itself. 
 
THE EAR. 507 
 
 THE ANATOMY OF THE EAR. 
 
 The sense of hearing has, of course, from time imme- 
 morial been attributed to the ear, and some explanations as 
 to the manner in which 'hearing occurred were advanced 
 with fair accuracy by very early writers. It was, however, 
 reserved for the last decade to very materially advance our 
 knowledge. It was impossible to understand the percep- 
 tion of musical sounds until Corti, in 1846, worked out 
 carefully the anatomy of the cochlea, and especially the 
 membranous cochlea. The rods of Corti bear this observer's 
 name. The finer anatomy of the vestibule and the ampullae 
 was understood when the work of Max Schultze on these 
 structures was published in 1850. In 1842 the physiologist 
 Florens, and in 1869 Goltz advanced the idea that the semi- 
 circular canals were not directly concerned with hearing, 
 but were organs of equilibrium. It was, however, reserved 
 for Helmholtz to study with the greatest care the individual 
 parts of the ear, and to him we are indebted largely for the 
 present conception we have of the function of that organ, 
 as well as for the theory of harmony in terms of which the 
 various phenomena of musical sounds are ext>lained. 
 
 THE EXTERNAL EAR. 
 
 The external ear is composed of the outer shell of the 
 ear called the concha, and the opening leading to the tym- 
 panic membrane designated as the auditory meatus. 
 
 1. Concha. The concha consists mainly of elastic 
 cartilage and serves to collect the sound like a funnel and 
 direct it into the auditory meatus. As such a collector of 
 sound it is, however, very deficient in human beings. The 
 external ear may be entirely removed without apparently 
 interfering with the acuteness of hearing. In the lower ani- 
 mals its efficiency as a collector is unquestioned. In these 
 animals it is relatively much greater, is more definitely 
 funnel-shaped, and is movable in such a way that it may be 
 placed in the most advantageous position in gathering the 
 sound. In the human ear it has lost most of these proper- 
 
508 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 ties and so may be looked upon, physiologically at least, as 
 an inherited remnant of a once more serviceable structure. 
 
 Fig. 156. A SEMI-DIAGRAMMATIC SECTION THROUGH THE RIGHT EAR. 
 
 A, auditory nerve; S, semicircular canal; <?, meatus; M, concha; T, tympanic mem- 
 brane; P, middle ear; R, Eustachian tube; S, cochlea; Vt, scala vestibuli; Pt, scala tym- 
 pani; r, round foramen; o, oval foramen. (The membranous cochlea is not shown.) 
 
 2. Meatus. Through the auditory meatus the sound 
 waves are led to the tympanic membrane. The meatus is 
 lined with skin, in which are imbedded numerous wax 
 glands, the secretion of which serves to keep the wall of the 
 passage, as well as the tympanic membrane at its end, in a 
 pliable condition. The presence of relatively large hairs in 
 it serves mechanical purposes only, in preventing access to 
 foreign bodies. It was held by some physiologists that the 
 external' auditory meatus serves as a resonance cavity for the 
 sounds, but owing to its small size this physical effect is very 
 trifling, and what resonance there is in connection with the 
 ear belongs probably entirely to the middle ear. 
 
 As the efficiency of the eye may be materially increased 
 by the addition of optical instruments, so it is possible to 
 magnify the perceptive capacity of the auditory meatus by 
 special instruments, such as ear- trumpets and the profes- 
 sional stethoscope. 
 
THE EAR. 509 
 
 THE MIDDLE EAR. 
 
 The middle ear or tympanum consists of a small cavity 
 lying between the external auditory meatus and the inner 
 ear. Its size in man is from three-quarters of an inch in its 
 widest dimension to about a half inch in the direction at 
 right angles to this. It is, therefore, although a small 
 opening almost as large as the entire internal ear, or in 
 space equal to the external auditory meatus. 
 
 1. Eustachian Tube. This cavity is filled with air 
 which is able to reach it through the Eustachian tube. 
 This tube runs from the middle ear and opens into the back 
 part of the mouth. By means of this tube the pressure of 
 air in the tympanum is kept the same as that of the sur- 
 rounding atmosphere, and so barometric changes in it do 
 not exert their effect upon the tympanic membrane as 
 would otherwise happen. Through this Eustachian tube 
 the mucous membrane of the middle ear is a continuation 
 of the mucous membrane of the mouth, a condition which 
 unfortunately makes possible the extension of an inflam : 
 mation into the middle ear from the mouth, such as occurs 
 in some forms of catarrh. An inflammation of the middle 
 ear and Eustachian tube soon causes the closing of the 
 Eustachian tube by its swelling, and thus the only exit 
 for the matter which may be produced is by rupturing the 
 tympanic membrane and escaping through the auditory 
 meatus. Such a result is usually designated as a gathering 
 in the head. The Eustachian tube is usually closed, the 
 two walls of it are pressed together and separate regularly 
 only during the process of swallowing. The explanation 
 of the regularly closed condition is found in the fact that 
 such a closing prevents the sound from entering the middle 
 ear by that avenue, and so to some extent interfering with 
 the sound reaching it regularly, and, secondly, that it pre- 
 vents the sounds produced in the mouth (the voice) , from 
 reaching the ear with the force that they would do if this 
 canal were open. 
 
510 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 2. Tympanic Membrane. The tympanum or middle 
 ear is separated from the auditory meatus by a delicate 
 membrane called the tympanic membrane. This mem- 
 brane consists of three coats : a connective tissue membrane 
 covered on the outside with the skin of the auditory meatus 
 and on the inside with the mucous membrane of the middle 
 ear. This tympanic membrane is set somewhat diagonally 
 across the end of the meatus and its surface toward the 
 meatus is concave. This concavity is produced by the 
 circumstance that the malleus is by its handle firmly at- 
 tached at the middle of this membrane and tends to pull it 
 inward. Its concavity towards the exterior possibly serves 
 to gather up the sound waves and center them on the spot 
 where the malleus is attached. 
 
 The tympanic membrane is affected by sound waves in 
 such a way that it is set into vibrations corresponding pre- 
 cisely with the vibrations of the entering sounds. This 
 function of the membrane is well shown in the telephone. 
 The box into which one speaks has stretched across it at its 
 base, just in front of the electric magnet a delicate metal 
 diaphragm. Against this diaphragm or tympanic membrane, 
 so to speak, the voice is thrown and sets it into vibrations 
 which correspond exactly to the vibrations of the air affect- 
 ing it. Such a telephone membrane is able to catch the 
 vibrations of a high note as well as a low note. It is, in 
 fact, able to transmit to the magnet back of it all the vibra- 
 tions which strike it. 
 
 Such is almost exactly the case with the tympanic mem- 
 brane. This membrane has, however, one or two arrange- 
 ments by means of which it can adjust itself to sounds. 
 Attached to the malleus there is a muscle called the tensor 
 tympani, by the contraction of which the tympanic mem- 
 brane is pulled further inward, thereby made more concave 
 and of course becoming more stretched. This probably 
 helps in the perception of high sounds. It is further pos- 
 sible that this tensor tympani is brought into play when we 
 listen attentively for some time to a definite sound. One 
 
THE EAR. 511 
 
 can readily understand that a tightly stretched membrane 
 is more serviceable for collecting sounds, especially high 
 sounds, than a less taut one. 
 
 There seems little reason, though, for attributing very 
 much to this muscle. The membrane in the telephone is 
 able to catch the widest range of tones without its stretch 
 being varied, and so there seems no difficulty in attributing 
 the same physical possibilities to its analogue in the ear. 
 
 3. The Bones of the Ear. The vibrations of this tym- 
 panic membrane must now be carried across the middle ear 
 to the internal ear where the real sensory apparatus of the 
 ear lies. This is done by a series of three small bores, 
 known as the hammer, anvil and stirrup; or, using their 
 Ivatin equivalents, the malleus, the incus and the stapes. 
 These three bones really represent four bones ; as the incus 
 consists really of two separate bones, the incus proper and 
 the small, round orbiczdar bone which finally grows to it 
 and which serves to attach the incus to the stapes. These 
 three bones are arranged in such a way as to form a system 
 of levers, by means of which the vibrations of the tympanic 
 membrane are carried across the middle ear and with 
 mathematical precision transmitted to the inner ear through 
 the oval foramen. 
 
 A somewhat ingenious arrangement is found in the ar- 
 ticulation of the malleus and the incus. These at their 
 point of contact fit into each other in a kind of dovetail 
 fashion, owing to the presence of peculiar interlocking 
 teeth, so arranged, however, that the least motion of the 
 malleus inwards is at once by means of these cog-like teeth 
 transmitted to the incus and so to the internal ear. A 
 violent motion, however, of the malleus outward does not 
 draw the incus with it. In this way there is prevented the 
 possibility of having the stirrup pulled out of the oval fora- 
 men in case the tympanic membrane should be suddenly 
 and forcibly pressed outward. The value of this arrange- 
 ment is evident when we remember how easily one might 
 
512 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 in certain forms of blowing, force the air through the Eu- 
 stachian tube into the middle ear, and thereby push out the 
 
 Fig. 157. THE BONES OF THE MIDDLE EAR, WITH ARROWS INDICATING THE DIRECTION 
 
 OF MOVEMENT OF EACH BONE IN THIS SERIES OF LEVERS. a, am, FULCRUM POINTS. 
 
 tympanic membrane, the result of which would be to pull 
 its chain of bones with it, even at the risk of pulling the 
 stapes entirely out of its moorings. But this is prevented 
 by the arrangement of the teeth between the incus and 
 malleus in the manner just stated, so that while a motion 
 inward is at once communicated to the incus, a motion out- 
 ward affects the malleus alone. 
 
 The exact manner in which these bones work may be 
 easily understood from the accompanying diagram, in which 
 the direction of motion of the various parts is indicated by 
 arrows. It will be noticed that the malleus moves like a 
 lever of the first class, its fulcrum being near its middle 
 at the point where it is fastened by means of the ligaments 
 to the wall of the middle ear. 
 
 4. The Cavity of the Middle Ear. The function of 
 the middle ear is its ability to act as a resonance cavity. 
 But for this fact the tympanic membrane might have been 
 stretched across the oval foramen at once. Sounds are ma- 
 terially strengthened when brought near resonators. The 
 note of a violin is to a very large extent made possible by 
 the resonance of the violin frame beneath the string. It is 
 the piano-board almost as much as the string that gives the 
 tone, while in the case of a horn, tones would be impossible 
 without the resonance cavities in the horn. A tuning-fork 
 
THE EAR. 513 
 
 sounded by itself sounds but feebly, but placed on a reso- 
 nance box of the proper kind it is increased many-fold 
 in strength. So, too, in the middle ear the air serves such 
 resonance purposes. Even the bone surrounding the mid- 
 dle ear is very porous, indeed, and it is not impossible that 
 this porosity may help to increase still further this reso- 
 nance function. 
 
 It will be noticed that both external and middle ears 
 were purely physical arrangements to transmit the sound 
 in a definite way to the internal ear where the real act of 
 perception occurs. 
 
 THE INTERNAL EAR. 
 
 The real sensory internal ear, that part to which the 
 auditory nerve is distributed, is a series of membranous 
 canals and sacs which lie in corresponding openings in 
 the petrous portion of the temporal bone. We have there- 
 fore to do first with the bony internal ear, by which is 
 meant nothing more than that system of spaces in the 
 bone in which the membranous or sensory ear is located. 
 The membranous ear does not, however, occupy all of the 
 space of the bony ear, but floats in the perilymph, a liquid 
 which fills this space. 
 
 The bony ear shows three well-marked divisions which 
 appear also in the membranous ear. First, the vestibule; 
 second, the semi-circular canals; third, the cochlea. These 
 three portions are continuous so that the perilymph in the 
 vestibule might, if it could be set in motion, pass through 
 any one of the semicircular canals or flow up the windings 
 of the cochlea. 
 
 1. Vestibule. The vestibule has a large opening com- 
 municating with the middle ear. This is the foramen 
 ovale into which the end of the stapes fits. It is evident, 
 therefore, that the vibrations communicated to the internal 
 ear by the stapes reach the perilymph of the vestibule. 
 
 Connected with the vestibule towards the back and 
 slightly above are three semicircular canals arranged like 
 33 
 
514 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 the three diameters of a cube. One is vertical, the other 
 vertical at right angles to this, and the third horizontal. 
 
 Fig. 158. RIGHT BONY LABYRINTH SEEN FROM THE OUTER SIDE. (After Sbmmerring.) 
 The smaller figure below gives the actual size. 1, vestibule; 2, foramen ovale; 3, 4, 5, 
 semicircular canals; 6, 7, 8, cochlea; 9, foramen rotundum. (The immediate walls of the 
 bony labyrinth are denser than the outer portions, and the view above results when the 
 softer bone has been, piece by piece, picked away.) 
 
 2. Cochlea. At the forward end of the vestibule this 
 space communicates with the cochlea. This structure, 
 named from its resemblance to a snail shell, has two and 
 one-half windings. It is a tube coiled up like a snail shell, 
 possibly merely to save space. Drawn out it would be a 
 straight tube not unlike a small dinner-horn. 
 
 The cavity of this coiled tube is, however, divided into 
 an upper and a lower chamber, the upper one being called 
 the scala vestibuli, the lower the scala tympani. The divi- 
 sion is formed partly by a partition of bone called the lamina 
 spiralis and partly by a thin membrane called the basilar 
 membrane. These two chambers are so arranged that the 
 scala vcstibtili is a direct continuation of the cavity of the 
 vestibule. 
 
 The scala vestibuli runs to the top of the cochlea, and 
 at the top, on account of the absence of the partition at 
 this point, it communicates with the scala tympani, while 
 the scala tympani at its lower end communicates with the 
 middle ear through the round foramen. Both these scalac 
 are filled with perilymph. 
 
THE EAR. 515 
 
 Let us imagine the possibility of an object moving around 
 in the perilymph. Such an object starting in the vestibule 
 might move backwards and pass through any one of the 
 three semicircular canals, going up one and down the other. 
 Afterwards it might move back through the perilymph of 
 the vestibule and go into the scala vestibuli. This it might 
 ascend, by taking the two and one-half turns of the cochlea, 
 to the very summit. The continuity of the partition all 
 along the cochlea formed by the lamina spiralis and the 
 basilar membrane would make it impossible to pass into the 
 scala tympani. But at the very top this partition is absent, 
 and the scala vestibuli connects with the scala tympani. 
 The imaginary object might, therefore, pass into the scala 
 tympani, descend through two and one-half turns the scala 
 tympani, and finally reach the round foramen which leads 
 into the middle ear. There is, of course, stretched across 
 this foramen a delicate membrane which prevents the peri- 
 lymph from flowing into the middle ear. If the imaginary 
 object at the round foramen were to return to the vestibule 
 it could do so only by re-ascending the scala tympani to 
 the top of the cochlea, passing into the scala vestibuli and 
 descending the scala vestibuli to the vestibule. 
 
 3. The Path of a Sound Wave Through the Inner Ear. 
 Perhaps it will be helpful in understanding the reason for 
 this arrangement to follow a sound wave after it has reached 
 the oval foramen by way of the stapes. 
 
 The wave is (1) transmitted by the movements of the 
 stapes to the perilymph of the vestibule. In the perilymph 
 the vibrations run in every direction, but, as we shall find 
 that the perception of sound occurs in the cochlea, we are 
 interested only with those vibrations which reach it. The 
 vibrations which reach the semicircular canals do not, as 
 far as we know, figure in any way in hearing and so may 
 be disregarded. From the vestibule the sound goes, (2) 
 up the continuation of the perilymph through the scala 
 vestibuli of the cochlea to the top of same. (3) At the top 
 
516 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 where the partition is missing the sound wave reaches the 
 scala tympani and, (4) then descends the scala tympani to 
 the round foramen by the movements of the membrane of 
 which it is (5) finally led back into the middle ear and 
 so lost. A sound wave does not, therefore, go into the 
 internal ear to be there lost, but is passed through the same 
 in such a way, that the reflection of a sound wave back- 
 wards in the form of an echo is prevented. It is evident 
 that if one vibration after another should run into the peri- 
 lymph, that unless these vibrations could pass out again 
 they would be reflected back, and meeting new vibrations 
 entering produce a confusion that would preclude the pos- 
 sibility of distinctly hearing. We shall see that the ear 
 perceives these waves as they pass unhindered by. 
 
 Having examined the bony labyrinth it is possible to 
 place in it more intelligently the real sensory or membran- 
 ous part. 
 
 THE MEMBRANOUS EAR. 
 
 In the vestibule the membranous ear consists of two 
 sac-like expansions connected by means of a narrow bridge. 
 The sac nearest the cochlea is called the sacculus, the one 
 nearest the semicircular canals the utriculus. The sacculus 
 and utriculus float in the perilymph. They are hollow struc- 
 tures and are filled with a liquid called the endolymph. As 
 the membranous ear is an entirely closed structure the peri- 
 lymph around it and the endolymph within it are in no place 
 in direct communication. 
 
 Arising from the utriculus are three membranous semi- 
 circular canals which pass through the bony semicircular 
 canals, occupying, however, only a relatively small part of 
 the space of these. On one limb of each semicircular canal 
 near to where it arises from the utriculus there is a marked 
 expansion called an ampulla. This dilatation is shared by 
 the bony canal as well. 
 
 Connected with the sacculus there is a small tube which 
 leads into the cochlea and extends to the very top. This is 
 the membranous cochlea. It is really nothing but a tube- 
 
THE EAR. 
 
 517 
 
 like extension of the sacculus coiled two and one-half times, 
 and in the bony cochlea lies just above the basilar mem- 
 brane. It is in the cochlea triangular in form, the basilar 
 
 s.e. 
 
 Fig. 159. THE MEMBRANOUS INNER EAR. 
 
 u, utriculus with contained macula acustica; s, sacculus with contained macula acus- 
 tica; *. s. c, superior, p. s. c, posterior, e. 8. c, external semicircular canal, the crista acus- 
 tica being indicated in each ampulla; c, r, canalis reunieus, connecting the membranous 
 cochlea with the sacculus ; c, c, the membranous cochlea ; s, e, the ductus endolymphaticus. 
 This duct serves to connect the utriculus and the sacculus, and ends blind below in the 
 sac-like enlargement called the saccus endolymphaticus. 
 
 membrane being the floor of it, and the membrane of Reiss- 
 ner being one of the sides. It lies, therefore, between the 
 scala tympani and the scala vestibuli, and for that reason is 
 frequently called the scala media. The scala media is filled 
 
 Fig. 160. SECTION OF THE LEFT COCHLEA OF A CHILD, six TIMES NATURAL SIZE, SHOW- 
 ING THE MODIOLUS, THE SCALA TYMPANI, SCALA VESTIBULI, AND SCALA MEDIA. 
 
 (After Reichert.) 
 
 with endolymph, which is in direct continuity with the endo- 
 lymph in the sacculus, but is entirely shut off from the peri- 
 lymph around it. In this membranous cochlea we find the 
 
518 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 organs of Corti and the endings of the nerves and so the 
 points in the ear where physical vibrations give rise to 
 nervous sensations. 
 
 THE HISTOLOGY OF THE MEMBRANOUS LABYRINTH. 
 
 1. Sacculus and Utriciilus. Both sacculus and utricu- 
 his are hollow, sac-like structures rilled with endolymph. 
 There is found, however, at those points on the sacculus 
 and utriculus where the auditory nerve enters them a small 
 projection called the maciila acustica. This macula acustica 
 is a kind of a projection inward, on the top of which there 
 are the auditory hairs projecting into the endolymph. These 
 auditory hairs are really continuations of the auditory cells 
 which are found in the macula acustica and which are con- 
 nected at their bases directly with the auditory nerve. 
 
 In the mucilaginous matrix between these auditory cells 
 there are imbedded very small stones called the otoliths. 
 These otoliths are composed of calcium carbonate and their 
 function is probably to help stimulate the nerve cells by 
 their inertia when set in motion by the endolymph. The 
 otoliths in man are only microscopic crystals, but in the 
 fishes and some of the invertebrates they become quite large, 
 a half inch or more in diameter. 
 
 2. Semicircular Canals. Connected with the utriculus 
 are three semicircular canals each of which possesses on 
 one of its limbs an enlargement known as the ampulla. A 
 cross-section of such an ampulla shows, projecting into the 
 interior of it the crista acustica. This projects inward 
 relatively much further than the macula acustica just re- 
 ferred to. 
 
 An epithelium of auditory cells connected with the audi- 
 tory nerve covers the crista. Delicate hairs from these pro- 
 ject into the surrounding endolymph. At other portions of 
 the semicircular canal it is a smooth tube lined with ordi- 
 nary epithelium, and has at these portions probably no definite 
 sensory functions. 
 
THE EAR. 519 
 
 THE MINUTE STRUCTURE OF THE MEMBRANOUS COCHLEA. 
 
 The position of the membranous cochlea between the 
 scala vestibuli and scala tympani has been referred to. Its 
 shape as a triangular tube running from the sacculus to 
 the top of the cochlea has been stated. Speaking approxi- 
 mately its boundaries are as follows: The upper side formed 
 by the membrane of Reissner separates it from the scala 
 vestibuli ; the lower side is formed by the basilar membrane 
 and a part of the lamina spiralis, these two separating it 
 from the scala tympani. Its outer wall is formed by the 
 wall of the bony cochlea itself. 
 
 1. Basilar Membrane. The essential structure in this 
 membranous cochlea is the basilar membrane. This, al- 
 though called a membrane, really consists of a number of 
 strings of varying length stretched from the edge of the 
 lamina spiralis to the outer wall. These strings are shortest 
 at the base of the cochlea and become gradually longer 
 towards the top. If this basilar membrane were removed 
 from the cochlea and straightened out it would have the 
 appearance given in Figure 161. Such a structure suggests 
 at once various kinds of musical instruments built on this 
 plan. The soundingrboard of a piano is fashioned after 
 
 Fig. 161. DIAGRAM SHOWING THE GRADUAL LENGTHENING OF THE CORDS IN THE BASI- 
 LAR MEMBRANE, , d, d, d' , AND THE CORRESPONDING INCREASE IN THE WIDTH OF 
 THE ORGANS OF CORTI, a, ft, a, 6'. 
 
 such a plan, the shorter strings of the board representing 
 the treble notes, the longer ones the bass notes. This 
 
520 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 basilar membrane consists of about 3,000 such strings laid 
 side by side. Other things being equal the lengths of these 
 individual strings will determine the pitch of their vibra- 
 tions, so that the basilar membrane has its high strings 
 near the base of the cochlea, its low ones near the top. 
 This basilar membrane is, in fact, the sounding-board of 
 the ear, and the various strings of this sounding-board are 
 set up in sympathetic vibrations by the sound waves which 
 pass through the cochlea. 
 
 It will be remembered that the sound waves from the 
 vestibule ascend the cochlea through the scala vestibuli, 
 and while ascending this they do not affect the basilar mem- 
 
 Fig. 162. SECTION ACROSS THE BASAL TURN OF THE HUMAN COCHLEA. (After Retzius.) 
 D. C, scala media; s. v, scala vestibuli; s. t, scala tytnpani; R, membrane of Reissner; 
 Mt, tectorial membrane ; 6. m, basilar membrane ; t C, tunnel formed by the rods of Corti ; 
 n, nerve; sp. I, spiral lamina; sp, sulcus spiralis; 1. sp, spiral ligament; I, limbus; h, i, 
 inner hair cells; h, e, outer hair cells, with hairs from same projecting through the reticu- 
 lar membrane. 
 
 brane, as the membrane of Reissner intercepts. At the top 
 of the cochlea the sound passes into the scala tympani, and 
 
THE EAR. 521 
 
 while descending the scala tympani the vibrating perilymph 
 in the same is in direct contact with the basilar membrane 
 and at this point sets into vibrations, in a sympathetic way 
 already explained, the strings which are attuned to that 
 particular vibration. In other words, the human ear is but 
 the second tuning-fork set into motion by the first one. It 
 is the piano that responds again with the notes sung into it. 
 The student will have gone far in understanding the 
 exact manner of hearing when he has made clear to himself 
 the complete analogy of the basilar membrane to a musical 
 sounding-board on which are stretched as many as 3,000 
 differently attuned strings. It must be noticed further that 
 the proper vibrations of these strings is a purely physical 
 result, and would happen in a dead ear or an ear constructed 
 out of metal almost as readily as in a living ear. 
 
 2. Rods of Corti. Standing on this basilar membrane 
 are two rows of rods which lean towards each other in such 
 a way as to form a tunnel underneath. These two series of 
 rods are called the rods of Corti. One series rests on the 
 basilar membrane just at the point where it is attached to 
 the lamina spiralis; the other, or outer rods, rest upon the 
 basilar membrane itself. The rods next to the lamina 
 spiralis, the inner rods, seem to be more slender and are 
 also more numerous than the outer rods, the numbers be- 
 ing about 6,000 and 4,500 respectively. 
 
 At the base of the cochlea the rods of Corti are higher 
 but stand closer together than they do towards the top, 
 where they are lower and wider. (See Figure 161.) 
 
 3. Reticular Membrane. Where the two sets of rods 
 meet there is attached a membrane which extends out 
 horizontally some distance over the basilar membrane. 
 This membrane is called the reticular membrane, the name 
 being derived from the fact that it is pierced with very many 
 small openings through which the hair endings of the audi- 
 tory cells beneath extend. 
 
522 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 4. Tectorium. From the lamina spiralis there extends 
 a membrane over the rods of Corti and reticular membrane 
 called the tectorium or tectorial membrane. It serves for 
 purposes of protection to these delicate structures under- 
 neath. The groove formed between the lower portions of 
 the lamina spiralis and the tectorial membrane is called the 
 sulcus spiralis. 
 
 D 
 
 Fig. 163. STRUCTURE OF A SINGLE ORGAN OF CORTI, AND TO THE RIGHT THEIR ARRANGE- 
 MENT INTO A SERIES, SUPPORTING THE FENESTRATED RETICULAR MEMBRANE. 
 
 i, internal rod; e, external rod; t, articulation of the two rods; ft, beginning of reticu- 
 lar membrane; n, nerve; 6, basilar membrane. 
 
 5. Auditory Hairs. This sulcus spiralis is lined with 
 cuboidal cells, which are continued over the margin of the 
 basilar membrane as columnar cells, some of which bear 
 on their upper end short, stiff hairs. These cells between 
 the rods of Corti and the sulcus spiralis are termed the 
 inner hair-cells. Similar cuboidal cells are found on the 
 basilar membrane beyond the rods of Corti, which cells end 
 in delicate stiff hairs that project through the openings in 
 the reticular membrane. These are called the outer hair- 
 cells. 
 
 Where the basilar membrane joins the outer wall of the 
 cochlea these cells lose their cuboidal appearance and 
 gradually shade off into the ordinary epithelium which lines 
 the outer wall and the inner wall of the membrane of Reiss- 
 ner. These outer and inner hair-cells or auditory cells are 
 connected at their bases with nerve fibers from the auditory 
 nerve reaching them through the lamina spiralis. The 
 reader to orient himself properly must study the descrip- 
 tion just given in terms of the accompanying diagrams. 
 
THE EAR. 523 
 
 THE FUNCTION OF THE INDIVIDUAL PARTS OF THE 
 MEMBRANOUS EAR. 
 
 1. Utriculus, Saculus, and Semicircular Canals. 
 Regular auditory functions were formerly attributed to 
 these. The suggestion was even made that these struc- 
 tures aided in the perception of noises, while to the cochlea 
 was referred the perception of musical sounds. Such a 
 distinction is, of course, absurd at once, the difference 
 between noise and music being a physical and not a physi- 
 ological one. Later Florens and Goltz pointed out that 
 these structures were really not concerned at all with the 
 direct sense of hearing, but that they figured as organs of 
 equilibrium. Animals from which the semicircular canals 
 have been removed show the greatest difficulty in standing 
 still or moving readily and with precision. They seem to 
 be unable to tell the position of their bodies and show all 
 the symptoms ordinarily associated with intense dizziness. 
 An animal so robbed of these structures performs the most 
 senseless and awkward movements. It seems perfectly help- 
 less and is scarcely able to eat unaided. The question then 
 arises, in what manner these structures figure as equilibrium 
 organs. 
 
 First. The three semicircular canals are arranged like 
 the three diameters of a cube, and so there is no motion 
 possible which does not fall in the plane of one or more of 
 these canals. 
 
 Second. These canals are filled with endolymph which 
 is in communication at both ends with the utriculus and so 
 is able to circulate somewhat through these canals. 
 
 Third. A movement of the head in any direction will 
 cause a backward flow of the endolymph in the semicircular 
 canal affected, due to the inertia of that liquid, just as in 
 the starting of a train the passengers by their inertia are 
 thrown backwards. This backward motion of the endo- 
 lymph affects the hairs projecting into it in the ampulla 
 somewhat like a stream of air over a field of grain, and in 
 
524 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 this way a sensation is produced which in the mind is in- 
 terpreted in terms of position or movement. If, however, 
 the motion in a certain direction should continue, the endo- 
 lymph inside would soon adjust itself to that motion, just 
 as after a train has started the passengers no longer feel a 
 tendency to be thrown backwards. A sudden stopping now 
 of the train throws the passengers violently forward. So a 
 sudden stopping of the motion of the body, say for instance 
 from a circular motion, will cause the endolymph on ac- 
 count of its inertia to be thrown forwards and in this way 
 affect the projecting hair cells and give rise to a sensation 
 of motion. Possibly this is the explanation of the dizziness 
 which results when a rotary motion of the body suddenly 
 ceases. To the individual it seems that he is still moving. 
 One point in favor of the view that these organs are 
 wholly organs of equilibrium is the fact that the perception 
 of all sounds can be satisfactorily explained in the cochlea, 
 and so there is no necessity to begin with for attributing 
 auditory sensations to these structures. On the other hand, 
 however, none of the invertebrates have a cochlea, and yet 
 it would be entirely wrong to think that these animals are 
 without the sense of hearing. Evidently, therefore, in the 
 invertebrates at least, structures very analagous indeed to 
 utriculus, sacculus and ampulla are directly concerned in 
 the perception of sound, and it may be possible that even 
 in the human being this property has not been entirely lost, 
 but has simply been overshadowed by the addition of a new 
 structure to the ear, the cochlea. 
 
 2. The Function of the Cochlea. The anatomy of the 
 cochlea readily shows how a vibration descending the scala 
 tympani is brought in direct contact with the basilar mem- 
 brane, and how there by sympathetic vibrations it sets into 
 motion some one of the many strings which is attuned to it. 
 Arrangement is thus made in purely physical ways to set in 
 vibration the proper string in any case, but it is an equal 
 physical necessity that such vibration should cease as soon 
 as the sound producing it ceases. It would, of course, be 
 
THE EAR. 525 
 
 very undesirable to have the basilar string in the ear vibrate 
 after the sound producing it has ceased. Short, sharp stac- 
 cato notes would be an impossibility and there would result 
 in the ear a blending and running together of sounds which 
 would preclude the possibility of fine music. For this rea- 
 son there are placed dampers on these strings, much after 
 the fashion of dampers on pianos. The rods of Corti seem 
 to have this function. Resting continually on the basilar 
 membrane they so weigh down these strings as to make 
 them cease their vibrations as soon as the force beneath 
 them producing the vibration has ceased. Just as in the 
 case of a piano the string is brought to quiet when the pedal 
 is on, as soon as the finger is taken from the key. 
 
 Up to this point everything in connection with the ear 
 has been purely physical. It would happen in a dead ear 
 as readily as in a living one provided the tissues were left 
 intact, but there now remains the necessity for some kind of 
 an arrangement by means of which the vibrations of these 
 strings in the ear may be communicated to the brain. This 
 is accomplished by means of the auditory cells which stand 
 on the basilar membrane and which are directly connected 
 with the auditory nerve. 
 
 When a certain string of the basilar membrane is set in 
 motion it is evident that the hair cells resting on it will be 
 moved up and down with it, and possibly this vibratory mo- 
 tion of the hair cells serves to originate a nervous impulse 
 which is then along the ordinary channels sent to the brain 
 and there interpreted as sound. 
 
 A second possibility exists. The long stiff hairs which 
 are found projecting from the tops of these auditory cells 
 pass through little perforations in the recticular membrane, 
 and it may be that when these nervous cells move up and 
 down with the vibrations of the cord these delicate hairs are 
 rubbed against the recticular membrane and so produce a 
 friction which serves to originate a nervous impulse, which 
 then, as in the other case, finally gives rise to the percep- 
 tion of sound. That it must be either the movement of the 
 
526 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 cells up and down or this friction of their delicate hairs in 
 the reticular membrane, or possibly both of these which 
 serve as a stimulus for the nervous impulse, is beyond 
 question. 
 
 Here is the point at which the physical vibrations give 
 rise to physiological, that is, nervous impulses, but it must 
 be borne in mind after all that the real conscious apprecia- 
 tion of sound occurs only in the auditory centers in the 
 brain. Sound is a purely psychological experience, and the 
 ear and the nerves leading from it to the brain serve merely 
 as accessory pieces of apparatus to call into being these 
 psychical acts. 
 
 Very few sounds, however, are so simple as to affect but 
 a single string of the basilar membrane. Most sounds are 
 composite sounds (hence their quality) and frequently 
 composite sounds in turn are blended into harmonies. The 
 ear, however, has the ability to perceive all the individual 
 sounds that enter into such a composition and so we must 
 imagine that in the perception of the concert note there are 
 as many strings of the basilar membrane thrown into vibra- 
 tion as there are individual component notes in the concert.- 
 The ear is even able to analyze such a concert note so care- 
 fully that it may follow some of the individual notes in it. 
 No one finds it difficult when hearing the rendition of an 
 orchestral piece of music to follow a certain instrument, or 
 in a chorus to listen with special attention to a certain 
 voice. This analysis is possible because in the basilar 
 membrane as many individual strings are affected as there 
 are such component notes. 
 
 A somewhat interesting question arises when we remem- 
 ber that although the ear has only about 3,000 strings it is 
 able to perceive many more than 3,000 pitches. This may 
 seem at first inexplicable. Possibly the explanation may 
 consist in assuming that when a pitch is sounded which 
 has not its direct counterpart in the ear but lies between 
 the pitches of two adjoining strings, it will affect both of 
 them, and this possible blending may give rise to a new 
 
THE EAR. 527 
 
 perception of pitch. It is even possible to imagine that the 
 relative strength with which the two adjoining strings are 
 affected will give rise to a corresponding series of inter- 
 mediate pitches. 
 
 THE LOCALIZATION OF SOUND. 
 
 The ability which we possess to determine the direction 
 from which a sound comes is an acquired ability. In local- 
 izing a sound w r e instinctively move the head through a 
 series of positions and try to determine in which position 
 the sound is clearest. Having once found this position we 
 have learned by experience in which direction we must 
 then look. When the head is held perfectly immovable the 
 localization of sound is very difficult indeed; in fact, it is 
 almost impossible unless, of course, the sounds be so near 
 that the difference in the acuteness of hearing between the 
 two ears gives us a clue as to its direction. When a sound 
 is familiar we determine its distance by its strength. It is, 
 however, a purely subjective inference which it is possible 
 to vary artificially, as for instance on the stage, when by 
 soft playing, distance is suggested, while the gradual 
 strengthening of the tones is interpreted as a movement of 
 the sources of music towards the hearer. 
 
 In the ear there are sometimes perceived sounds which 
 are not produced by regular sound vibrations. Such sounds 
 are, for instance, the buzzing of the ears produced by the 
 vibrations of air in the external meatus, when this air has 
 been separated from the external atmosphere by bits of wax 
 in the meatus, or by vibrations in the air of the middle ear, 
 caused by an unnatural closing of the Eustachian tube. 
 Beating sensations are usually caused by the pulsations of 
 the arteries in the external meatus. Sensations of friction 
 no doubt find their explanation in the circulation of the 
 blood, while the peculiar ringing of the ears which some 
 people are able to produce at will, especially when they 
 contract the muscles of mastication, is explained by some 
 as a contraction of the tensor tyinpani, and so a stretching 
 
528 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 r 
 
 of the tympanic membrane, by others as a voluntary open- 
 ing of the Eustachian tube. 
 
 Finally, it is of interest to reflect that the two ears are 
 as a rule attuned alike, at least so nearly alike that ordi- 
 narily we perceive a note in unison. It not infrequently 
 happens, however, that there is such a difference in the two 
 ears as to lead to the perception of the same sound at 
 different pitches, a pathological condition which when ag- 
 gravated leads to the most serious results in the apprecia- 
 tion of tones. No less remarkable than the complete 
 harmony of the two ears is the continuance of such har- 
 mony through all the vicissitudes of a person's life. Few 
 are the instruments, indeed, which do not need repeated at- 
 tention in order to hold them at their proper pitches. In 
 the basilar membrane of the ear, however, this attunement 
 seems not only one of remarkable operation to begin with, 
 but practically never requires a secondary interference. Its 
 superiority to all forms of artificial musical instruments in 
 the number of notes which it is able to perceive, in the ex- 
 actness with which it catches and reproduces all the varied 
 forms of the sounds which reach it, and in the accuracy 
 with which it remains in perfect attunement, may well 
 awaken our wonder and admiration. 
 
CHAPTER XXIII. 
 
 THE EYE AND THE PHYSIOLOGY OF VISION. 
 
 That the eye is the seat of vision is a bit of knowledge 
 as old possibly as humanity, but it was not until 1602, when 
 Kepler compared the human eye with the camera obscura, 
 that any considerable attempt was made in the explanation 
 of its function. Some time previous Porta had invented the 
 camera obscura, and so it was but a natural step for Kepler 
 to make this the basis for his explanation of the eye. Kep- 
 ler's explanation was practically nothing more than merely 
 the statement of such an analogy and did not deal with 
 specific details. A few years later, 1609, the Jesuit 
 priest Scheiner noted the inversion of the image on the ret- 
 ina, and made the further important discovery that the 
 pupil contracted or expanded with the varying accommoda- 
 tion of the eye. In 1695 the optician Huyghens constructed 
 an artificial eye and demonstrated on the same the action 
 of spectacles. During the next century nothing seemed to 
 be added to the knowledge of the eye. In 1801 Young 
 (the founder of the present Young-Helmholtz Theory of 
 Vision) noted and explained astigmatism. L,ong-sight and 
 short-sight had been previously observed, and Huyghens 
 had actually explained the action of spectacles in remedy- 
 ing these defects. 
 
 Up to the beginning of this century, and even later, 
 nothing was known of the manner in which the eye was 
 accommodated for far and near. The necessity for such a 
 power of accommodation had been noted by Kepler, and 
 Descartes had actually suggested the thought that the 
 power of accommodation resulted from the ability of the 
 lens to change its form, but it was not until 1801 that 
 Young demonstrated this change in experiments on his own 
 34 (529) 
 
530 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 eyes. Objectively this change in the form of the lens was 
 demonstrated by the reflection of images from the surfaces 
 of the lens, by L,angenbeck in 1849, and verified by Helm- 
 holtz in 1853. The ciliary muscles had been noted by 
 Briicke in 1846, and in 1856 Helmholtz attributed the 
 motor agency in accommodation to this muscle, and for- 
 warded the theory of accommodation as it still stands. The 
 innervation of this muscle was discovered by Hensen and 
 Volckers in 1868. The finer structure of the retina was 
 worked out by H. Muller's researches on the eye, 1855, 
 although as early as 1851 Helmholtz had designated the 
 rods and cones as the points sensitive to light. The blind 
 spot had been discovered by Mariotte as early as 1668. In 
 1876 the vision purple found in the rods was discovered by 
 Boll. 
 
 Our knowledge of the physiology of color sensations has 
 been of slow growth. In 1657 the celebrated Newton in his 
 studies on the spectrum discovered the different refractive 
 indices of the different colors and their composition into 
 white light. In 1690 Huyghens proposed the wave theory of 
 light, while in 1746 Euler demonstrated that the difference 
 in colors depends on the rate of light vibrations, or what is 
 the same thing, the length of the waves. A theory of color 
 sensations was advanced by Young in 1807 which modified 
 by Helmholtz is to-day possibly still the best explanation at 
 hand. The Young-Helmholtz theory does not, however, 
 offer a satisfactory explanation for several observed facts, 
 and to include these a second entirely different theory was 
 advanced by Ewald Hering in 1872. Quite a number of 
 other observers have added to our knowledge on this sub- 
 ject. Such has been in briefest outline the path of the dis- 
 coveries which have led to our present understanding of the 
 eye. It may be in place at this point to add that there re- 
 mains very much still unexplained about the eye, and that 
 there are few subjects in physiology concerning which ad- 
 ditional information is more sorely wanted. 
 
THK EYE AND THE PHYSIOLOGY OK VISION. 531 
 
 SOME OF THE ELEMENTARY PHYSICAL CONCEPTIONS OF LIGHT 
 
 NECESSARY TO A PROPER UNDERSTANDING OF THE 
 
 PHYSIOLOGY OF THE EYE. 
 
 The eye is a complicated piece of apparatus especially 
 designed to translate light impressions into nervous impres- 
 sions. Its construction is for a specific purpose and its 
 anatomy dependent upon the physical properties of the 
 light it is to translate. It is, therefore, entirely impossible 
 to understand the raison d^etre of the eye's structure with- 
 out having an elementary conception at least of some of the 
 physical properties of light. 
 
 1. The Nature of Light. For a long time light was 
 looked upon as small particles of matter projected in straight 
 lines from a luminous body. These little particles passed 
 into the eye, and there in some way produced the sensation 
 of light. A lamp, therefore, would be something like a 
 spherical Gatling-gun throwing its missiles in every con- 
 ceivable direction at a very great velocity. These particles 
 were looked upon as exceedingly small and light, and able 
 to penetrate even such hard substances as glass. 
 
 This material projection of light had soon to be aban- 
 doned as thoroughly unable to explain all of the phenomena 
 at hand. As a result of more exacting study there was ad- 
 vanced soon what is now familiarly known as the undulatory 
 theory of light, the theory which conceives of light as oscil- 
 lations or waves of some suitable medium. This medium 
 is the ether, possibly a hypothetical substance, and yet one 
 to the actual existence of which we are driven by the ne- 
 cessity of the mind. 
 
 This ether is a very light imponderable medium offering 
 little if any resistance to objects moving through it. It not 
 only pervades all space, but seems also to pervade many 
 solid objects, such as glass and others which we are wont 
 to call transparent. Rays of light are conceived as vibra- 
 tions passing through this medium, in which the actual 
 particles of the medium move but little out of their place, 
 
532 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 while the wave, however, transmitted from particle to par- 
 ticle travels with inconceivable rapidity. Speaking gen- 
 erally, light is like sound a wave motion, but these waves 
 differ in several respects from each other. In the case of 
 light the medium is ether and in sound air, or water, or 
 solids. The rapidity of transmission is very different, and 
 the form of the wave is quite unlike that of the sound wave. 
 In the transmission of a sound wave through the air the 
 particles of air carrying the wave move backwards and for- 
 wards in the direction in which the sound is moving. In 
 light, however, the individual particles of ether move at 
 right angles to the direction of the ray of light. If it were 
 possible to picture a ray of light approaching one it would, 
 using a very rough analogy indeed, look somewhat like a 
 wheel, the hub being the line of direction, while the indi- 
 vidual spokes would represent the directions in which the 
 particles of ether are thrown by the wave at that point. If 
 one could now think of such a wheel squarely approaching 
 one and imagine the spokes radiating from it in every di- 
 rection to be rapidly drawn into the hub and projected 
 again, one would have a very rough idea of the picture of 
 an approaching wave of light. 
 
 2. The Rate of Transmission. It was impossible for a 
 long time to make actual calculations of the rate with which 
 a ray of light travels, as its rapidity was so great that for all 
 practical purposes it was instantaneous. The opportunity 
 of measuring light passing through immense distances pre- 
 sented itself when the phases of the satellites of Jupiter were 
 carefully noted. When the earth is between the sun and 
 Jupiter, that is as close to Jupiter as its orbit permits, the 
 time for the phases of one of Jupiter's satellites was carefully 
 determined. Six months later the earth is, of course, further 
 removed from Jupiter by the distance of the earth's orbit. 
 Calculations now showed that the phases of the satellite in 
 question were a little over sixteen minutes slow. The ex- 
 planation of the sixteen minutes' tardiness consisted in at- 
 tributing this loss of time to the time required by the light 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 533 
 
 to pass the added distance of the earth's orbit. In other 
 words, it took a ray of light a little over sixteen minutes to 
 cross the earth's orbit, a distance of some one hundred and 
 eighty million miles. This makes the distance traveled per 
 second about 186,000 miles. 
 
 Thus, a ray of light would have a sufficient speed to travel 
 around the earth's surface about seven or eight times be- 
 tween two successive ticks of a second hand. 
 
 3. The Number of Vibrations in Waves of Light. If 
 light is a wave motion the problem presents itself of having 
 the number of vibrations per second measured. Without 
 going into the physical explanation of the manner in which 
 this is accomplished, save the statement that such measure- 
 ments have been made and the number of vibrations per 
 second determined with relative accuracy, the interesting 
 fact at once comes to light that the number of vibrations 
 determines the color of the light just as in the case of 
 sound the number of vibrations determines the pitch. The 
 pitch of a light is its color. The lowest pitch in light 
 visible to the eye is red; the highest pitch is violet. When 
 the vibrations become less frequent than those in red or 
 more numerous than those in violet they do not affect the 
 eye and seem like perfect darkness. This darkness below 
 the red and above the violet is, however, not a physical 
 darkness; it is a physiological darkness. Even though the 
 etherial vibrations are there the physiological capacity of 
 the eye is not large enough to include them. 
 
 Using approximate figures only, there are in red light 
 400,000,000,000,000 per second; in violet, 800,000,000,- 
 000,000. The lowest base note in light consists of four 
 hundred trillions ; the highest note of eight hundred trillions 
 per second. Between these two extreme pitches of color 
 are the other colors of the spectrum. Thus green, which 
 is about half way between the red and violet, has in the 
 neighborhood of six hundred trillions. 
 
 4. The Spectrum. Ordinary sunlight, the ordinary 
 light of the day, is what we usually designate " white" 
 
534 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 light. This white light is not a simple light but consists 
 of all the vibrations from the red to the violet. In other 
 words, white light is a concert of all the pitches of light. 
 In music we are able to analyze the individual sounds that 
 go into a complicated harmony, but in light the eye is un- 
 able to make such an analysis, and this combination of all 
 of the colors of the spectrum is perceived as one color and 
 called white. 
 
 By means of a prism it is possible to separate this white 
 light, to analyze it, and get each color by itself. The re- 
 sult of such a procedure is the spectrum familiar to every 
 one, if not in the laboratory, at least in the rainbow. By 
 means of such a prism the colors are strung out, from the 
 red at one end to the violet at the other, and the position of 
 each color is determined by the number of vibrations per 
 second which it has. Commonly we say that in this scale 
 we are able to perceive seven distinct colors. These are: 
 red, orange, yellow, green, blue, indigo, violet. 
 
 Reference to the number of vibrations in red light and 
 violet light shows that violet light is just an octave above 
 red light. It possesses just about twice the number of 
 vibrations, and it is extremely interesting to note that at 
 the violet end the red reappears. In fact, violet is nothing 
 but the blue, with which is mixed a little red, possibly the 
 red of the next octave. It is apparent, therefore, that our 
 range of vision extends over but one octave of colors, from 
 the red at the lower end to the red at the upper end, where 
 it reappears to blend with the blue forming the violet. 
 What the color sensations would be if the range of vision 
 should extend over more than one octave it is entirely im- 
 possible to say. If, however, they should be reproductions 
 of the first octave one can see that nothing would be gained 
 by their presence as far as new colors are concerned, and 
 as the eye is perfectly unable to analyze a compound color, 
 is unable to perceive its inherent harmony, there is but 
 an added reason for the limitation of the range of vision to 
 a single octave. 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 535 
 
 The seven colors of the spectrum are usually spoken of 
 as the fundamental colors, because by the mixture of two 
 or more of these it is possible to produce all the other 
 colors. Thus the proper combination of all seven forms 
 white; the absence of all of them gives the perception 
 black. Black is in light what a rest is in music, but while 
 in the ear a rest is perceived as the absence of any positive 
 sensation, in the eye an absence of all light is interpreted 
 as a positive sensation, and so black seems to be a definite 
 color. By mixing any of the fundamental colors with white 
 we get the varying tints of these colors ; by mixing them 
 with black the corresponding shades. Thus red and white 
 make pink, red and black brown; green and white produce 
 light green, green and black olive, blue and white the light 
 blues, blue and black the blue blacks. Red and blue form 
 purple, purple and green produce white. Mixing colors 
 near each other in the spectrum produces an intervening 
 color. Thus red and yellow form orange. 
 
 It must be especially borne in mind that in all instances 
 of the combinations just given the sensations are mixed and 
 not pigments. Thus on a color disk partly red and partly 
 blue the color purple will arise upon a rapid rotation of 
 that disk. If one should mix pigments quite a different re- 
 sult would occur. To mix red and blue combined in cer- 
 tain proportions produces not purple at all, as when 
 sensations are mixed, but produces green, the explanation 
 of which will be given further on. 
 
 5. Complementary Colors. Two colors (sensations) 
 which when mixed together produce white, are spoken 
 of as complementary colors. For each color of the spec- 
 trum it is possible, if the color purple be added, to find a 
 second color complementary to it. The relations of these 
 colors are given in Figure 164, where the colors of the 
 spectrum are so arranged that those directly opposite each 
 other from the point called white are complementary. The 
 use of indigo or blueing in the process of laundering con- 
 
536 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 sists in neutralizing the yellow of the linen, yellow and 
 indigo forming white. 
 
 Blue 
 
 Fig. 164. GRAPHIC REPRESENTATION OF THE FORMATION OF WHITE OUT OF THE SERIES 
 
 OF COMPLEMENTARY COLORS. 
 
 The line frohi the green should be continued to the purple, as green and purple are 
 complementary colors. 
 
 6. The Colors of Objects by Transmitted or Reflected 
 Light. So far the colors have been described as vibrations 
 of ether proceeding from a luminous body, and by the 
 number of such vibrations per second the light will have 
 its color determined. But most bodies are not luminous; a 
 window pane is not luminous but transmits light through 
 it ; the wall of a house is not luminous but is seen only by 
 the light which it reflects from some luminous source. 
 Ordinarily this transmitted or reflected light is sunlight. 
 Even though the rays of the sun do not shine directly into 
 the room, some of the rays have been reflected by the grass 
 or sky, or objects on the ground in such a way as to reach 
 the wall in question, and being reflected from this in turn 
 into the eye, the wall becomes visible. 
 
 The question then presents itself, what determines the 
 color of such a transparent piece of glass or of the opaque 
 wall? 
 
 First, objects colored by transmitted light. A red win- 
 dow pane seems red because it has absorbed all the other 
 colors in the light which passes through it, but transmits 
 unhindered the red light reaching it. Like the gold digger 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 537 
 
 who picks out of the sands the yellow gold, but allows 
 the white sands to be washed through his fingers, so this 
 window pane picks out all the colors of the spectrum, while 
 the red color, like the sand in the analogy, it allows to pass 
 through. We can easily understand how a boy looking 
 over an assortment of marbles would pick out for his own 
 use and put into his pocket all those of certain desirable 
 colors and reject possibly all those of some, to him, unsatis- 
 factory color. So this window pane picks out and absorbs 
 from the composition of colors which reach it in the white 
 light certain colors, while it rejects, that is, allows to pass 
 without hindrance, the red light which falling into the eye 
 finally arouses there the corresponding sensation. It is evi. 
 dent that such a window pane could look red only when red 
 light reached it, since that is the only light it allows to pass 
 through. If blue light alone should reach it the blue would 
 be entirely absorbed and the result would be no light at all 
 traversing it, the window pane would look black. One may 
 easily try the experiment of looking through a piece of red 
 glass at an intensely blue object. The red glass is opaque 
 to the blue. A similar experiment would be to take a red 
 glass and a blue glass and let a beam of light pass through 
 both. As this beam of wfcite light passes through the blue 
 glass plate all the red and yellow would be absorbed and 
 nothing but the blue be permitted to pass. But blue light 
 is absorbed by the red pane, which allows only red light to 
 pass through, but as all the red light was absorbed by the 
 blue plate, no light at all passes through. The two trans- 
 parent glasses act like an opaque object. 
 
 Second, what is the explanation of the color of the objects 
 around us, such as the cover of a book, the tint of a ribbon, 
 or the shade of a paint ? The explanation is similar to that 
 given in the case of transmitted light. White light falls on 
 the ribbon, and if this ribbon should reflect all the light 
 that it received, it too, would appear white. But the rib- 
 bon absorbs some of the colors and reflects only those colors 
 which it cannot absorb. In the case of the red ribbon, 
 
538 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 green, blue, violet, and even some yellow are absorbed, and 
 so only the red light remains to be reflected. A rather far- 
 fetched analogy might be found in throwing against a wall 
 a handful of different objects, nearly all of them very sticky 
 indeed, but mixed with these several elastic rubber balls. 
 If such a handful of objects were hurled against a wall, not 
 all of them would be reflected. Most of the sticky objects 
 would remain attached to the wall, and possibly the rubber 
 balls alone be reflected. So in the sunlight, which is a 
 mixture of the fundamental colors, practically all of the 
 colors are absorbed by the ribbon, while the red, like the 
 rubber ball in the analogy, is reflected, and as we judge of 
 the color of an object by the light which comes from it, we 
 designate it as red. As a matter of fact, however, the color 
 of an object by reflected light is always the color which it 
 has rejected. 
 
 7. The Refraction of Light and the Property of Lenses. 
 Light passes in straight lines through a medium of uniform 
 density. If, however, it passes from a less dense to a more 
 dense medium it is bent from its course. Such a bending 
 of rays of light is called refraction, and upon this property 
 of light depends the use of lenses. A lens is nothing more 
 than a transparent medium of greater density than the air, 
 and so will bend the rays of light from their original direc- 
 tion. It would be entirely out of place in this discussion to 
 go into detail in the matter of refraction, and it will suffice 
 to call attention to the ordinary kinds of lenses and the 
 manner in which they refract the light. 
 
 Convex lenses, either convex on both sides (double con- 
 vex lens) or plain on one side (single convex lens) bend 
 the rays of light together, and if the lens be a fairly good 
 one, all the rays in a beam of light may be finally bent so 
 as to meet at a certain point back of the lens known as the 
 focus. The amount of the bending of the rays will depend, 
 other things being equal, upon the convexity of the lens, 
 being greater, the greater the convexity. Illustrations of 
 such results are familiar to ever one in the ordinary burning 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 
 
 539 
 
 glasses, by means of which the parallel rays of the sun are 
 concentrated at one point sufficiently to start ignition. 
 
 If the lens be concave, either on both sides (double con- 
 cave) or on one side (single concave) the rays of light will 
 be bent apart; that is, scattered. This action of lenses will 
 be more evident by comparison of Figures 165 and 166, 
 where the course of rays of light through such lenses is 
 shown by a series of lines. Some lenses may be concave on 
 one side and convex on the other, called concavo-convex 
 lenses, and such lenses will either converge the light or 
 scatter the light, according as the convexity is greater or less 
 than the concavity. 
 
 Fig. 165. To SHOW THE CONVERGING ACTION OF A CONVEX LENS. 
 
 Fig. 166. TO SHOW THE DISPERSIVE ACTION OF A CONCAVE LENS. 
 
 F, the focus at which the dispersed rays would meet if continued. 
 
 For the purpose of understanding the eye it is especially 
 desirable to bear in mind the fact that the convexity of a 
 lens will determine the extent of the refraction of the light 
 through it and also the position of a focus back of it. The 
 more convex the lens is the closer will be the focus behind 
 the lens, the less convex it is the further removed from the 
 lens will be this focus. Upon these simple considerations 
 
540 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 of the refraction of light is based the use of spectacles, and 
 even the use of the eye itself, this containing within itself 
 several refracting media which obey in every way the physi- 
 cal laws that govern light refraction. 
 
 8. The Formation of Images by Lenses. By means of 
 a good lens or a system of lenses there may be produced 
 an image of an object placed in front of the lens. The 
 microscope, the telescope and the photograph camera at- 
 test this fact. In the camera a sensitive plate is put back 
 of the lens in such a position that the image produced by 
 the lens falls directly on it, and there in chemical ways 
 leaves its impress on the sensitive plate. There is in the 
 eye an exactly analogous result, the eye being in practically 
 every particular a high grade camera in which the sensitive 
 plate is replaced by the still more sensitive retina, and in 
 order to perceive objects clearly the image produced by the 
 lens and humors of the eye must fall directly upon the re- 
 tina. The point under explanation here is to show under 
 what circumstances an image arises. An image results 
 when a number of rays of light emanating from the same 
 point are so bent by a lens as to meet again at a certain 
 point back of the lens. As the rays of light from any point 
 on a luminous body radiate in every direction; that is, 
 diverge more and more, it is evident that they would never 
 meet unless these divergent rays should be bent together 
 by some refracting medium; hence no image is possible 
 when the lens is removed. The function of the lens is to 
 collect this divergent pencil of rays from the point in qiies- 
 tion, and bend it together to meet in a corresponding point 
 back of the lens. 
 
 If at this second point a screen be held there appears an 
 image the exact counterpart of the object. But any object 
 consists of but an infinite number of individual points, and 
 so it is the function of the lens to take the divergent rays 
 from each of these infinite points and converge them to a 
 corresponding number of infinite points behind the lens. 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 541 
 
 In this manner there arises the complete image of the entire 
 object. Figure 167 shows this action of the lens for two 
 given points. Reference to it will also show that the image 
 will be inverted. This is also true of the image on the retina. 
 With these physical conceptions of the nature of light 
 and its properties we are ready to understand with more 
 meaning the detailed anatomy of the eye. 
 
 Fig. 167. DIAGRAM TO ILLUSTRATE THE REFLECTION AND THE REFRACTION OF LIGHT. 
 At A the beam of light is reflected, illuminating the arrow a c, at B. From all points 
 of the arrow a c, the light is reflected in all directions. Two such divergent beams are 
 shown as refracted by the convex lens L L, and brought to points a' and c', producing at 
 these points images of the points a, c. As this is true for all points on a c, there will be a 
 complete image at a' c'. The lines at S' S', and S" S", show positions of screen where 
 the image is blurred. 
 
 THE ANATOMY OF THE EYE. 
 
 While the eyeball itself contains the sensitive retina and 
 the refracting media, and so the essential parts of the eye, 
 it is provided with a number of appendages which make its 
 use in vision much more efficient. On account of its sen- 
 sitiveness it needs special organs for protection. A system 
 of muscles enable it to make rapid movements, while a 
 lachrymal apparatus protects it from an accumulation of 
 dust and other foreign particles. 
 
 1. The Eyebrows. The function of these is so ap- 
 parent from every-day experience, preventing the perspira- 
 tion of the forehead from running over the eyeball but 
 turning it aside down the cheeks, that further statement is 
 unnecessary. That they act in shading the eye is probably 
 only exceptionally true. 
 
542 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 2. The Eyelids. Each eye is provided with two main 
 eyelids and the remnant of a third. Of these the upper 
 eyelid is the one which has the greatest range of motion, 
 and by the movements of which the lachrymal secretion is 
 being continually washed across the globe. In addition to 
 distributing the tears it serves purposes of protection against 
 foreign particles and for the exclusion of light when that 
 is too intense, or when, as in sleep, it is to be excluded 
 altogether. The functions of the upper eyelid apply to a 
 certain extent equally to the lower eyelid. 
 
 At the edge of these eyelids are found the eyelashes, 
 rows of hairs serving to prevent foreign particles from get- 
 ting into the eye, and possibly shading the cornea. Be- 
 tween these hairs open the ducts of specially developed 
 sebaceous glands, known as the Meibomian glands, which 
 secrete a fatty substance specially evident in certain cases 
 of inflammation, where this secretion becomes so excessive 
 as to stick the eyelids together. This secretion serves not 
 only to keep the edge of the eyelids pliable, but prevents the 
 tears from running over the eyelids, it being a general phy- 
 sical fact that water does not readily flow over an oily 
 surface. Of course in the act of crying the amount of the 
 secretion increases so much that this oily edge no longer 
 serves as a sufficient barrier, and so the tears stream down 
 the cheeks. 
 
 Lining the under sides of the eyelids both upper and 
 lower and reflected back over the front of the cornea is the 
 conjunctiva. Few membranes in the body, especially those 
 exposed to the exterior, are so richly supplied with nerves 
 and so sensitive to all foreign objects. The explanation of 
 placing such a very sensitive membrane under the eyelids 
 and over the cornea lies in the fact that it prevents us from 
 becoming careless about injurious particles reaching the 
 eye, and so gives iis no rest until the irritating object is 
 removed. 
 
 The lifting of the upper eyelid is effected by muscles 
 running down into the eyelid. The closing of the eye is 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 543 
 
 due to the contraction of a circular muscle which runs 
 through the upper and lower eyelids and so encircles the 
 open space which separates the upper from the lower lid. 
 
 In addition to the two regular eyelids there is present in 
 man the rudiment of a third eyelid. This may be readily 
 observed as a red vertical fold at the inner corner of the 
 eye, and in some individuals reaching almost to the iris. 
 This eyelid is especially developed in many animals, such 
 as birds, and can by these animals be drawn entirely over 
 the front of the eyeball. When so fully developed it is 
 called the nictitating membrane. 
 
 In this remnant of the nictitating membrane is a small 
 reddish elevation readily recognizable called the caruncula 
 lachrymalis, consisting of a number of sebaceous glands 
 imbedded in this fold. 
 
 3. The Lachrymal Apparatus. To keep the surface 
 of the eyeball perfectly clear and to remove particles of 
 dust, there is provided for each eye a lachrymal apparatus 
 consisting of a tear gland and a system of ducts. 
 
 Fig. 168. THE LACHRYMAL APPARATUS. 
 
 1, lachrymal gland; 2, lachrymal ducts; 3, 3, the puncta lachrymalia ; 4, the nasal sac; 
 5, the nasal duct. 
 
 The lachrymal or tear gland lies not in the inner, but in 
 the upper and outer part of the orbit under the edge of the 
 frontal bone. It is about the size of an almond. From 
 this gland (which histologically is an ordinary racemose 
 
544 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 gland) , run quite a number of ducts which open in a row 
 under the upper eyelid. From this point the secretion is 
 washed over the front of the eye by the ordinary movements 
 of the eyelids, such as those of winking, and so the cornea 
 is kept moist and clear and free from dust. The secretion 
 is finally led off by two lachrymal canals, which arise each as 
 a small pore called the punctum lachrymalis found on each 
 lachrymal papilla. These lachrymal papillae are readily 
 recognized as small reddish elevations at the inner angle of 
 the upper and lower eyelids. The lachrymal canals soon 
 unite, opening into the nasal duct, the upper portion of 
 which is somewhat enlarged and called the lachrymal sac. 
 The lower portion of the nasal duct opens into the back 
 part of the nose chamber, and from this place the tears find 
 their way into the throat and are swallowed. Ordinarily the 
 amount of the secretion so poured into the throat is so slight 
 that we take no notice of it. In violent weeping, however, 
 the secretion may become so plentiful as to necessitate re- 
 peated acts of swallowing. 
 
 4. The Muscles of the Eyeball. The rapidity and ex- 
 actness with which the eyeball may be moved attest the 
 presence of a system of eye muscles. Each globe is pro- 
 vided with six muscles ; four of these are straight muscles 
 and two are oblique. The straight muscles lie, one on top 
 of the eye the superior rectus, one below the eyeball, 
 the inferior rectus, one on the outer side external rec- 
 tus, and the fourth on the inner side internal rectus. 
 It is readily seen that by means of these four muscles the 
 globe of the eye may be turned in any direction save a 
 rotary one. To make this motion possible there are two 
 oblique muscles. One of these is fastened to the top of the 
 eyeball, runs inward towards the nose, and there passes 
 through a tendonous loop like a pulley, to be inserted near 
 where the recti are. This is the superior oblique muscle. 
 The inferior oblique muscle arises at the back of the orbit, 
 near the lachrymal sac. From this point it passes slightly 
 outwards and backwards beneath the eyeball, and is inserted 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 
 
 545 
 
 into it posteriorily. The exact movements which each of 
 these muscles is able to produce may be readily seen from 
 their manner of attachment. 
 
 One of the most striking things about these muscles is 
 the harmony with which they work. In normal eyes the co- 
 ordination is almost perfect. When, however, one or more 
 of these muscles cease to be so carefully adjusted, either as 
 a cause of paralysis or of other causes, there results what is 
 familiarly called the "squint,' 7 which is a right or a left, an 
 external or internal squint, according to the muscle affected. 
 An exaggerated condition of a squint is finally termed 
 "cross-eyed." 
 
 Fig. 169. SEMIDIAGRAMMATIC SECTION OF THE EYEBALL. 
 (The reader will find the explanation of the section in the text.) 
 
 5. The Globe of the Eye. The globe of the eye is a 
 spherical body an inch or more in diameter, with a large 
 35 
 
546 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 portion of it visible from the outside. It is not evenly 
 spherical, but consists of segments of two spheres, the 
 larger sphere composing most of the eyeball, the smaller 
 sphere forming the cornea. 
 
 The globe is a completely closed ball pierced only at one 
 end, where the optic nerve and the blood-vessels for the 
 retina enter it. The walls are, of course, provided with 
 blood-vessels and nerves which enter it, but consist almost 
 wholly of very tough connective tissue so strong that in the 
 case of a beef's eye one may be able to stand on an eye 
 without breaking these coats. 
 
 In a general way these coats are described as consisting 
 of three, called the outer or sclerotic coat, the middle or 
 choroid coat, and the inner coat or the retina. 
 
 Enclosed within these coats are three refracting media; 
 the aqueous humor, the crystalline lens, and the vitreous 
 humor. 
 
 6. Sclerotic Coat. The sclerotic coat is the outer coat 
 and is by far the strongest and toughest. It consists almost 
 entirely of closely packed white connective tissue. This 
 coat is visible from the outside as the white of the eye. 
 Immediately in front of the eyeball this coat is transparent 
 and is called the cornea. The sphericity of the cornea is 
 greater than that of the eyeball itself. 
 
 The sclerotic coat covers the entire eye save at the back 
 where the optic nerve and the retinal blood-vessels pass 
 through it. The cornea is covered over in front with the 
 conjunctiva, and on its inner side is lined with a layer of epi- 
 thelial cells called the membrane of Descemet. 
 
 7. The Choroid Coat. Immediately beneath the scle- 
 rotic coat is the choroid coat. This is not nearly so tough 
 as the sclerotic, but is much more vascular and readily 
 recognizable in the dissection of the eye by the black pig- 
 ment which it contains. It is, in fact, the choroid coat to 
 which the black inner walls of the eyeball are due, and the 
 presence of this pigment in the choroid explains largely its 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 547 
 
 function. All good optical instruments are painted black 
 inside, so as to do away with the possibility of reflection 
 from the walls, which would materially interfere with the 
 clearness of the image. The cornea is not in contact with 
 the choroid, but at this point the sclerotic coat and the 
 choroid are separated and so a space produced which is 
 filled with a watery liquid called the aqueous humor. The 
 pigment of the choroid is also different at this place, and in- 
 stead of being black is brown or blue, or whatever other 
 color we find the eyes to have. This colored portion of the 
 choroid coat seen through the cornea is called the iris. 
 
 Just in the middle line of the eyeball the iris has an 
 opening known as the pupil, and visible on the eye as a 
 dark disk within the iris. This dark disk is really a hole, 
 but seems dark because no light conies out of it, just as an 
 opening into a mine would seem dark if there were no light 
 beneath. 
 
 Within the choroid coat lies the retina. The retina is 
 but an expansion of the optic nerve and does not run en- 
 tirely around the eye. The impossibility of throwing an im- 
 age on the forward portions of the inner wall of the eye 
 would render useless the extension of the retina so far. 
 
 Filling the large posterior chamber is the vitreous 
 humor, a transparent glassy-looking liquid having about 
 the consistency of the white of an egg. This vitreous 
 humor is enclosed in a delicate membrane extending all 
 around it, known as the hyaloid membrane. This mem- 
 brane seems a single layer in most portions, but towards 
 the front it divides into two layers, and in the space so 
 formed there is imbedded the rather large crystalline lens. 
 
 As the eyeball is distended even to a slight pressure 
 with the vitreous humor, all the coats are held in place and 
 a collapse of the eyeball is prevented. In fact, the pressure 
 of the vitreous humor in the hyaloid membrane is normally 
 such as to stretch this somewhat, and as the lens is im- 
 bedded between the layers of this membrane it is by the 
 stretching of this hyaloid membrane always in a state of 
 
548 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 compression, and so continually flattened. The relation of 
 this fact to the power of accommodation will be evident a 
 little further on. 
 
 That part of the hyaloid membrane which immediately 
 surrounds the lens is called the capsule of the lens, while 
 that next to the capsule of the lens is spoken of as the sus- 
 pensory ligament. 
 
 8. Ciliary Muscles and the Muscles of Accommodation. 
 There occur in the iris two sets of muscles ; a circular set 
 by the contraction of which the pupil is made smaller, and 
 a radial set, the contraction of which causes an increase in 
 the opening of the pupil. In addition to these muscles of 
 the iris there are found imbedded in the choroid coat just at 
 the point where the choroid coat and the cornea meet, a 
 system of muscles known as the muscles of accommoda- 
 tion. These muscles are attached firmly at one end where 
 the cornea and the choroid unite, from which point they ex- 
 tend backwards through the choroid in such a way that when 
 they contract they pull the choroid coat forward towards the 
 cornea. It will be pointed out that by means of these mus- 
 cles the eye is focussed for far and near. At the point 
 where the cornea and the iris meet there is a small canal 
 running around the eye, called the canal of Schlemm. Be- 
 tween the two layers of the hyaloid membrane where they 
 separate to enclose the lens there is a second canal en- 
 circling the lens called the canal of Petit. Between the 
 suspensory ligament and the iris there is usually a small 
 space which is but a continuation of the space containing 
 the aqueous humor. This space is called the posterior 
 chamber of the aqueous humor. 
 
 Reference to the diagram of the eyeball will show its 
 close analogy to a camera, in which the refracting media 
 are the cornea, the lens and the humors. The image will 
 fall on the retina, and as the light usually enters the eye in 
 a certain straight direction the image will regularly fall 
 straight behind the lens. This point on the retina where 
 the most acute vision occurs is called the yclloiv spot. It 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 549 
 
 is visible on the retina as a yellowish depression. When 
 we wish to see objects in detail, such, for instance, as the 
 print on a page, we allow the image to fall on this yellow 
 spot. Images which fall on other portions of the retina are 
 still visible but not distinctly so. At the spot where the 
 optic nerve enters the eye the retina has no sensitiveness to 
 light. This spot is called the blind spot. It may be easily 
 found by trying the experiment suggested in Figure 170, in 
 which the cross and circle are so arranged that when one 
 falls on the yellow spot the other falls on the blind spot 
 and so becomes invisible. The blind spot is sometimes 
 called the optic mound, the yellow spot the macula lutea, 
 while the pit in its center is called the fovea centralis. 
 The retina at this point is so thin that the black choroid 
 may be seen shining through it. 
 
 Fig. 170. DIAGRAM TO DEMONSTRATE THE POSITION OF THE BLIND SPOT. (Close the left 
 eye, and holding the figure about a distance of a foot from the face, look directly at 
 the cross.) 
 
 At the optic mound a number of blood-vessels which 
 reach the eye along with the optic nerve spread out through 
 the retina and supply this coat with its proper nourishment. 
 
 9. The Optic Nerves. In the chapter on nerves atten- 
 tion was called to the optic nerves; how these nerves met 
 in the optic commissure and how the optic tracts passed 
 from this point to the midbrain and occipital lobes. It was 
 also pointed out that the crossing of the optic nerves at the 
 commissure is only a partial one, and is of such a nature 
 
550 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 that each side of the brain controls corresponding halves 
 of the retina, so that the loss of the right optic tracts, for 
 instance, would result in blindness of the left halves of 
 both retinas. Of course if the optic nerve itself were cut 
 then the entire retina to which it went would become blind. 
 
 10. The Microscopic Striicture of the Retina. In order 
 to understand the physiology of the eye it is not absolutely 
 necessary to go into the histological structure of very many 
 of its parts. An exception to this, however, is the retina, 
 which, as the seat of vision, has an exceedingly delicate 
 structure, by means of which the light may be perceived. 
 The microscope readily reveals ten distinct layers. These 
 are, beginning with the one next to the hyaloid membrane, 
 as follows: 
 
 First, a thin transparent membrane called the internal 
 limiting membrane. 
 
 Second, a nerve fiber layer continuous with the optic 
 nerve at one end and extending further into the retina at 
 the other. 
 
 Third, the nerve cell layer, an ordinary ganglionic layer 
 with which the nerves of the second layer probably connect. 
 
 Fourth, an inner molecular layer seen to consist of thin 
 sections of very small granules, which granules, however, 
 are probably systems of dendrons cut across. It seems prob- 
 able that this molecular layer is a layer in which the dend- 
 rons of consecutive neurons meet. This is succeeded by, 
 
 Fifth, the inner nuclear layer, consisting of larger 
 granules, which are undoubtedly small nerve cells, so that 
 this layer may be looked upon as a second ganglionic layer. 
 Next to this is found, 
 
 Sixth, the outer molecular layer, differing from the 
 inner molecular layer only in being much narrower. This 
 is succeeded by, 
 
 Seventh, the outer nuclear layer similar in construction 
 to the inner nuclear layer and ganglionic in its function. 
 The outer nuclear layer is bordered by a very thin mem- 
 brane called, 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 
 
 551 
 
 Eighth, the external limiting membrane, followed by, 
 Ninth, the rod and cone layer, the layer in which the 
 actual nervous stimuli arise. As the name indicates, two 
 kinds of structures are found here, somewhat longer and 
 narrower rods, and scattered between these shorter and 
 thicker cones. These rods and cones project into, 
 
 Tenth, the pigment-cell layer, which lies in contact with 
 the choroid just beneath. 
 
 Fig. 171. DIAGRAMMATIC REPRESENTATION OF THE STRUCTURE OF THE RETINA. (After 
 
 Y. Cajal.) 
 
 a, layer of rods S and cones Z Z\ F, F, fibers of Miiller; A, h, external limiting mem- 
 brane; b, outer nuclear layer; c, outer molecular layer; d, inner nuclear layer; e, inner 
 molecular layer; /, nerve cell layer; g, nerve fiber layer; k, k, internal limiting mem- 
 brane. The rods are composed of a highly refractive end portion and a somewhat more 
 protoplasmic basal portion which then, continued through the cells K in the layer &, end 
 in the layer c in little round buttons. Several such buttons seem in turn invested by the 
 dendrons of a single cell H from the layer d. The cones also have a refractive terminal 
 portion, but a more rounded ellipsoid basal portion of protoplasmic structure, from which 
 a relatively large fiber at once passes through the layer b, and ending in dendrous in the 
 layer c, invests the dendrons of a single cell of the layer d. The layer d contains also 
 cells L, which run outward only, and cells M, which send dendrons inward only. The 
 superposition of neurons is quite evident, there being in the retina itself at least three 
 such superposed units. 
 
 Here and there through the retina may be seen some- 
 what stronger fibers reaching from the internal limiting 
 membrane as far as the rod and cone layer. They serve 
 probably for purposes of support and are called the fibers 
 of Miiller. The meaning of the layers of the retina will be 
 more evident by reference to Figure 171, which is a diagram- 
 
552 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 matic representation of the relative arrangement of these 
 layers. It will be seen that the retina consists of a number 
 of neurons, the cell body of the first neuron being in the 
 third layer. From these large cells nerve fibers extend in 
 one direction along the optic nerve to the brain, but toward 
 the fourth layer are given off short dendrons which meet 
 with similar dendrons from the second neurons, the cells of 
 which lie in the inner nuclear layer. These cells send their 
 dendrons into the sixth layer to meet similar dendrons be- 
 longing to neurons whose cells lie in the outer nuclear 
 layer. 
 
 These cells extend a nerve fiber into the rod and cone 
 layer. In fact, the rods are merely special terminations of 
 these nerves. The cones seem to be partly of a cellular na- 
 ture themselves, which connect with the lower neurons in 
 the outer molecular layer and end in the rod and cone layer 
 in the characteristic points found on these cones. 
 
 To resume, then, the retina consists of three systems of 
 neurons super-imposed one above the other, the individual 
 neurons being exceedingly small, but, on the other hand, 
 exceedingly numerous. This decrease in size and cor- 
 responding increase in numbers is necessitated by the deli- 
 cacy which the retina must possess to be affected by light 
 and so make possible the perception of two points of light 
 very close to each other. The touch areas for light in the 
 retina must be very much smaller indeed than the touch 
 areas for the portions of the skin since we are able to see 
 two points of light which are separated by a distance meas- 
 urable only with difficulty. 
 
 A somewhat surprising arrangement of the retina at first 
 sight consists in the relative position of the first and ninth 
 layer. Naturally one would expect to see the rods and 
 cones turned towards the light. In reality they are in the 
 human eye, as in the eye of all vertebrates, turned away 
 from the light and the light has to permeate the eight 
 super-imposed layers before affecting the sensitive rods and 
 cones. This inversion of the retina is easily understood 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 553 
 
 when the embryonic development of the eye is studied. 
 Very early in such development the retina can be seen folded 
 in such a way that what would naturally have been towards 
 the light is turned away from the light. In the invertebrates 
 the rods and cones turn towards the light, and eyes having 
 such an arrangement are, therefore, usually referred to as 
 invertebrate eyes. 
 
 THE EYE AS A PURELY PHYSICAL INSTRUMENT. 
 
 The ability of the eye to bend rays of light passing 
 through its refracting media and to produce an image on or 
 near the retina is a purely physical property. Such results 
 would occur in an eye that had been removed from the 
 body. A stimulation of the rods and cones, however, and 
 the consequent production of nervous impulses, which, when 
 reaching the brain are interpreted as color, are physiologi- 
 cal processes and can be duplicated in no artificially con- 
 structed instrument. Before proceeding to the physiology 
 of the eye it seems desirable to call attention to those ar- 
 rangements and properties which it shares with all optical 
 instruments, and to the defects which may arise in the eye 
 in common with other optical instruments. 
 
 THE NORMAL OR EMMETROPIC EYE. 
 
 When the eyeball and its refracting media are so con- 
 structed that parallel rays of light shall meet in a focus on 
 the retina when the eye is in a resting condition, it is called 
 a normal or emmetropic eye. Rays of light are for prac- 
 tical purposes considered as parallel when they come from 
 a point removed from the eye about twenty-five feet or more. 
 An emmetropic eye, therefore, may be defined as one which 
 in its natural resting position is in focus for distant objects. 
 Many eyes do not conform to this requirement, but show in 
 a greater or less degree one or more of the following optical 
 defects: 
 
 1. Myopia, or Short Sight. In a myopic or short- 
 sighted eye the image falls in front of the retina, produced 
 
554 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 by either one or both of the following causes: (a) The 
 ball may be too long from before backwards, and in this way 
 the retina too far behind the lens to receive the image. 
 Or, (b) the lens may be too convex. It may converge 
 the rays of light too much and so bring them to a focus 
 sooner than ought to have been done. When myopia is the 
 result of a long eyeball it is frequently a natural defect. 
 When, however, it is due to too great a convexity of the 
 lens it may be an acquired defect. An individual who has 
 been in the habit of looking closely at things held very near 
 the eye, has been obliged in doing so, to keep his lens 
 strongly curved, and the continuation of such a state of 
 things is liable to finally fix itself and so there arises short- 
 sightedness, which necessitates that all objects be held close 
 to the eye to be distinctly visible. 
 
 In such acquired myopia there has occurred really no in- 
 herent change in the lens, the change has been in the mus- 
 cle itself, which, owing to its constant tension in looking 
 closely, has finally become somewhat fixed in this position, 
 and by this fixation of the muscle the lens remains, on ac- 
 count of its elasticity, in constant excessive convexity. 
 
 The remedy for short-sightedness is obvious. As the 
 rays of light are bent too much a lens must be placed before 
 the eye which shall disperse them to such an extent that the 
 image shall be thrown on the retina. Concave spectacles 
 are therefore demanded, the extent of the concavity depend- 
 ing upon the degree of myopia. 
 
 a --- 
 
 Fig. 172. THE MYOPIC EYE AND ITS CORRECTION. 
 
 The tendency to acquire myopia when the eye is re- 
 peatedly subjected to a close strain shows the necessity de- 
 volving upon teacher and parent to prevent the habit of 
 reading continuously with the book unnaturally close. It 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 555 
 
 is an element of optical hygiene to insist that persons with 
 normal eyes to begin with shall hold objects, such as a 
 printed page, at a reasonable distance from the eye. 
 
 2. Long Sight or Hypermetropia. Hypermetropia 
 occurs when the image in the eye would naturally fall be- 
 hind the retina, or since this is actually impossible, the 
 real state of things is the absence of a focus altogether, the 
 rays of light falling on the retina in a circle before they 
 have met in a point. The causes of this defect are two. 
 (a) It may consist of a shortening of the eyeball from be- 
 fore backwards, so that the retina now is in front of its 
 natural position. Or, () since the rays of light are not 
 converged enough the lens may be too nearly flat. The 
 remedy in this instance is equally obvious. The converg- 
 ing power of the eye must be increased, and so convex 
 glasses are needed. 
 
 As the image of an object is pushed further and further 
 back in the eye the closer the object itself is placed to the 
 eye, and as in the far-sighted individual this shifting of the 
 image, backwards exaggerates the difficulty, such persons 
 have a clearer vision when the object is removed some dis- 
 tance, whence, of course, the name "far-sightedness." 
 
 Fig. 173. THE HYPERMETROPIC EYE, AND ITS CORRECTION. 
 
 It is well to point out, though, that in many cases far- 
 sighted children will develop a habit of holding the book 
 too close to the eye and so leave the impression on the ob- 
 server that they are near-sighted. Such a far-sighted child 
 in looking at the page before him does not see it distinctly, 
 and prompted by the desire to look more closely and mis- 
 led by his usually correct experience that approach to an 
 object increases the distinctness of its vision, he moves the 
 
556 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 page closer to his eye. The increase in the intensity oi the 
 light" temporarily increases the clearness, but the difficulty 
 is soon exaggerated and so frequently a second attempt to 
 see more clearly is made by moving the object still closer. 
 Teachers especially should be on the lookout for such cases 
 since the confounding of far-sight with near-sight might 
 lead to undesirable results. Far-sightedness also very gen- 
 erally induces inflamed conditions of eyes and eyelids, and 
 seems a predisposing cause in the production of styes. 
 
 3. Astigmatism. The distinctness of an object, as any 
 one will readily understand who has handled lenses of any 
 kind, depends upon an even curvature and density of the 
 lens in question. If the surface of a lens be made un- 
 even, a greater or less distortion of the image occurs. If, 
 for instance, a drop of water is allowed to run across the 
 front of a pair of spectacles, objects seen through them are 
 at once distorted. The water in this case having about the 
 same density as glass, acts really like a bit of extra glass 
 put on the spectacles, and so the surface of it is made un- 
 even. The spectacles under these circumstances are astig- 
 matic. 
 
 Exaggerated cases of astigmatism are also observable on 
 nearly all window panes, for seldom (except in the case of 
 plate glass) is a window pane so even as not to distort the 
 objects seen through it, while sometimes the distortion is 
 so great as to transform a straight object seen through it 
 into a series of zig-zags. 
 
 It is not necessary that a lens should have such exagger- 
 ated cases of unevenness to be astigmatic. It may, in fact, 
 be quite smooth, but if the curvature in one direction differs 
 from the curvature in another direction, a distortion or rela- 
 tive change of focus for the various parts of the lens will 
 arise. Rays of light passing through the lens where it has 
 a greater curvature will come to a focus sooner than rays 
 of light passing through portions of a lens having a lesser 
 curvature. 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 557 
 
 Applying this to the eye we find that it not infrequently 
 occurs that a cornea possesses such irregularities of curva- 
 ture, and astigmatism is the result. The presence of as- 
 tigmatism can be readily detected by looking at a disk on 
 which are placed the numerals arranged like those on the 
 face of a clock. Astigmatic persons will see some of these 
 numerals in focus, while others are indistinct and blurred. 
 When the focus is changed to the blurred ones and these 
 become distinct, the first become blurred. Or if one look at 
 a system of concentric rings, such as given in Figure 174, 
 astigmatic persons will perceive certain sectors in which the 
 lines are blacker and more distinct, bordered by portions 
 where they are blurred and indistinct. 
 
 Fig. 174. FIGURES TO DEMONSTRATE THE EXISTENCE OF ASTIGMATISM. 
 
 To remedy astigmatism it is necessary to grind a special 
 lens of such a form that it shall exactly counteract the in- 
 distinctness of the cornea, the lens being more rounded 
 where the cornea is not rounded enough, and hollowed out 
 where the cornea possesses too much curvature. The fit- 
 ting of a lens for astigmatism must in each case be a bit of 
 special work, there being possibly no two cases of astig- 
 matism exactly alike. 
 
 4. Cataract. Cataract is an optical defect arising 
 from the opacity of the lens. When light is no longer 
 able to penetrate this readily, a more or less complete 
 blindness results, the only remedy for which is the removal 
 of the lens from the eye and the substitution for it of an 
 artificial lens in front of the eye. 
 
 In addition to the usual cataracts of the lens, there 
 occur sometimes slight opacities in the cornea. 
 
558 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 5. Spherical Aberration. Spherical aberration is not 
 so much .a real defect of the eye as it is a somewhat uni- 
 versal defect of all lenses, and it is therefore in common 
 with all lenses shared by the crystalline lens. All the rays 
 of light passing through a lens do not meet at the same 
 point, but the rays of light passing near the edge of the 
 lens are brought to a focus sooner than those passing nearer 
 the middle, and consequently when the edge of the lens is 
 in focus the center is blurred, and vice versa. Instances of 
 such spherical aberration are frequently noticeable on or- 
 dinary opera-glasses, where when objects seen through the 
 middle of the lens are in focus the field around the edge of 
 the lens seems blurred. There would be two ways to remedy 
 this defect. One to cut the light out of the edge of the lens 
 by placing a circular shutter over it. Such is, in fact, very 
 usual in optical instruments, and photographers frequently 
 interpolate a shutter having a small hole in it through 
 which the light is able to reach the center of the lens only. 
 A similar arrangement exists in the eye where the iris cuts 
 off the entire outer portion of the crystalline lens and per- 
 mits the light passing through the pupil to reach the cen- 
 ter of the lens only. V 
 
 A second way to remedy spherical aberration would be 
 to increase somewhat the density of the middle of the lens, 
 for as the rays of light passing through the edge of the lens 
 are bent more an increase of the density of the middle of the 
 lens would bend the rays passing through it more, and so 
 the foci would coincide. Both of these plans are followed 
 in the eye, the function of the iris having just been pointed 
 out, and in addition to this the lens has a slightly greater 
 density in the middle, the result of these two agencies being 
 to reduce this defect in most eyes to an imperceptible mini- 
 mum. 
 
 6. Chromatic Aberration. A second almost universal 
 defect of lenses is chromatic aberration. This defect arises 
 from the unequal refraction which the different colors suffer 
 while passing through a lens. It will be remembered that the 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 559 
 
 formation of a spectrum is the result of such an unequal 
 bending, the red rays being bent least, the violet rays most. 
 Evidently, therefore, since white light is composed of the 
 seven fundamental colors, the violet rays being bent more 
 than the red rays will come to a focus sooner, and in this 
 way there will be produced a number of foci corresponding 
 to the number of different colors, and objects will appear 
 violet, greenish, or red, according as the violet, green, or 
 red focus falls on the retina. 
 
 Fig. 175. DIAGRAM TO ILLUSTRATE THE CHROMATIC ABERRATION OF THE EYE. 
 r, r', red rays; t?, ', violet rays; V, violet focus; B, red focus; m, n, position of image 
 with a red border; p, s, position of image with a violet border. 
 
 This chromatic aberration is most marked near the edge 
 of a lens, and a peep through most opera-glasses shows this 
 defect very plainly. While the center of the field is plain 
 white, the edge of the field is tinted with some color due to 
 chromatic aberration. This defect is reduced to an almost 
 imperceptible minimum in the human eye by the exclusion 
 of the light through the edge of the lens. 
 
 7. Muscae-Volitantes. While the humors of the eye 
 are practically quite transparent there occur not infrequently 
 small opaque particles floating in them, the shadow of which 
 is by the light entering the pupil thrown against the retina 
 and there perceived as a more or less black object, which by 
 the mind is projected out into space. These are the flying 
 motes. These opaque particles are remnants of embryonic 
 blood-vessels in the humor. 
 
 8. Presbyopia. As the name indicates, this is a disease 
 which arises usually in advancing age. The ability to focus 
 
560 STUDIES IN ADVANCED PHYSIOLOGY, 
 
 the eye depends upon the elasticity of the lens. But this 
 elasticity becomes gradually reduced and in old age fre- 
 quently disappears altogether. Such persons are unable to 
 accommodate their eyes for far and near, a defect familiarly 
 called old-sight. 
 
 To remedy this it is obvious that several pairs of lenses 
 are required to adjust the eye to several distances. Such 
 persons will not infrequently have one system of lenses for 
 far objects, a second system for relatively near objects, the 
 objects in a room, for instance, and a third system to be 
 pressed into service in such acts of vision as the reading of 
 a printed page. 
 
 THE MANIPULATION OF THE ETE AS AN OPTICAL INSTRUMENT. 
 
 Every optical instrument must have some arrangement 
 by means of which it can be focussed. In the photograph 
 camera this focussing consists in moving the lens forward 
 or backward, or in changing the relative position of the 
 sensitive plate behind the lens. The microscope is focussed 
 by lifting the tube of the microscope or dropping it closer 
 to the object on the stage. In the telescope the focus is 
 produced by shifting the relative positions of the lenses. 
 Evidently there must be in the eye some arrangement by 
 means of which it, also, may be focussed. 
 
 That such is the case is the commonest experience of 
 every-day life. We are conscious of a change in the eye 
 when we turn our view from a distant object to one close 
 by, and this change in the eye is independent of any move- 
 ment of the eyeball. We may close one eye and then look 
 at two points lying in the same direction so that there is no 
 turning of the eyeball, and yet a change from the focus of 
 one to the focus of the other is a clearly perceivable one. 
 This change in the eye is called the accommodation of the 
 eye, and the question arises, how this is brought about. 
 
 HOW DO WE FOCUS THE EYE f 
 
 It is at once out of the question to think this is brought 
 about by a lengthening of the eyeball, like a camera, or the 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 561 
 
 shifting of the position of the retina, as in the telescope, 
 and surely the lens cannot move from the position in which 
 it is so firmly held by the suspensory ligament. The 
 change of focus is produced by a change in the curvature 
 of the lens. That this is true may be easily demonstrated 
 by the following experiment: If with suitable apparatus 
 one observe the images reflected out of the eye it is not at all 
 difficult to notice three such. A very clear reflection from 
 the front of the cornea, a second image reflected from the 
 front of the lens, and a third image from the posterior sur- 
 face of the lens. If these three surfaces remain in the same 
 position the relative positions of the images will remain, but 
 if one or more of these surfaces should change in any way, 
 the relative position and sizes of these images would vary. 
 If, now, a person from whose eyes such images are reflected 
 be asked to focus his eye for a distant object, and the posi- 
 tion of the images noted, and the person be then asked to 
 change the focus to a near object, two of the images change. 
 The image from the front of the cornea is unaffected, show- 
 ing that the cornea lias remained stationary. The image 
 from the back margin of the lens changes just a little, in 
 such a way as to show that this surface has become more 
 convex. The greatest change occurs to the image reflected 
 from the front of the lens. This moves much more rela- 
 
 a, 6 # 
 
 Fig. 176. THE REFLECTIONS OF TWO BRIGHT SQUARES FROM THE CORNEA, FRONT AND 
 
 BACK OF LENS, A IN REST; B WHEN THE EYE IS ACCOMMODATED FOR A NEAR OB- 
 JECT. THE IMAGES a, a, FROM CORNEA DO NOT CHANGE, NOR DO THOSE c, c, FROM 
 
 BACK OF LENS, BUT 6 IN FIGURE 23 IS MUCH SMALLER, SHOWING AN INCREASE IN 
 THE CONVEXITY OK THE FRONT OF LENS. 
 
 lively and shows that the front of the lens has been pushed 
 forward and become much more rounded. A clearer proof 
 36 
 
562 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 of the change of form of lens in the accommodation of the 
 eye cannot be desired. 
 
 This change also accords with what we know of the 
 property of lenses. We know, for instance, that when an 
 object is moved closer to a lens the image which the lens 
 forms is pushed further back, and if this pushing back is 
 not desired the rays of light must be bent more; that is, 
 brought to a focus sooner, a result easily produced by in- 
 creasing the convexity of the lens. The problem, there- 
 fore, narrows itself down to the explanation of the manner 
 in which this change of lens is brought about. The first 
 element of this explanation is found in the elasticity of the 
 lens. It is a quite elastic structure made up of almost trans- 
 parent cells, and is in its usual position continually unnatu- 
 rally flattened. This is proved by seeing that when the lens 
 is removed from the eye it at once becomes more nearly 
 round than before. It is flattened in spite of its elasticity 
 by the pull which the capsule of the hyaloid membrane 
 exerts upon it, and this pull is brought about by the pres- 
 sure of the vitreous humor which it exerts upon the hyaloid 
 membrane around it. The lens is flattened out much like 
 a foot-ball would be flattened out if it should be put under 
 a person's coat and the individual should then distend his 
 lungs with air. To make the analogy more complete we 
 might imagine the foot-ball placed between the outer cloth 
 of the coat and the lining, and the coat then buttoned up. 
 If now the chest were expanded, as the vitreous humor ex- 
 pands the hyaloid membrane, the foot-ball would be mate- 
 rially flattened. Thus, to repeat, in the natural resting 
 condition of the eye the lens is flattened, and if the eye be 
 a normal one, therefore adjusted to far objects. An in- 
 crease in the convexity of the lens is brought about by 
 producing a slack in the capsule and suspensory ligament 
 surrounding the lens. This slack is produced by the action 
 of the ciliary muscles already described. These, it will be 
 remembered, are muscles imbedded in the choroid coat, one 
 end fixed to the point where the choroid coat is firmly 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 
 
 563 
 
 attached to the sclerotic coat, the other ending loosely in 
 the choroid coat where this runs backward around the eye- 
 ball. It is evident that when these ciliary muscles contract 
 they will tend to pull the choroid coat forward; that is, 
 towards the lens. As the hyaloid membrane lies immedi- 
 ately underneath the choroid coat it will be pulled forward 
 along with the choroid coat and so thereby produce a slack- 
 ening of the tension of the hyaloid membrane, where it 
 encloses the lens. As soon as the slack is produced, the lens 
 by its inherent elasticity becomes more rounded, and by its 
 increased convexity the focus of the eye is changed for a new 
 distance. To maintain this focus it is evident that the cil- 
 iary muscles must remain contracted and keep this slack, 
 for as soon as the ciliary muscles relax the choroid coat and 
 the hyaloid membrane with it move back to their original 
 position under the pressure of the vitreous humor inside. 
 
 Fig. 177. TO SHOW THE RELATIVE SHAPES OF LENS WHEN AT REST (LEFT HALF) AND 
 WHEN ACCOMMODATED FOR NEAR OBJECTS (RIGHT HALF). 
 
 For explanation of other structures see the text. 
 
 To recur to the analogy above, let us imagine the foot- 
 ball between the cloth and the lining of the coat. The coat 
 represents, therefore, the hyaloid membrane. To represent 
 the choroid coat around this hyaloid membrane imagine an 
 overcoat put over the coat. It will be readily seen that if 
 the overcoat could by means of the hands or any agency be 
 pulled forwards towards the chest, it would tend to pull the 
 
564 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 coat underneath it with it, and there would be produced in 
 the coat a slack over the chest. The elastic foot-ball im- 
 bedded in the coat would at once take advantage of this 
 slack and try to return to its natural round position. As 
 soon as the forward pull on the sides of the overcoat 
 ceased, the overcoat and the coat underneath it would fall 
 back to their natural position under the regular pressure of 
 the enclosed body. Accommodation is thus the product of 
 two factors: first, the pulling forward of the choroid coat 
 and with it the hyaloid membrane next to it, and the conse- 
 quent production of a slack of the suspensory ligament and 
 capsule. Second, the elasticity of the lens which enables it 
 to take advantage of this slack to return, to some extent at 
 least, to its more rounded form. Hither the paralysis of the 
 muscles or the loss of elasticity of the lens would at once 
 make the accommodation of the eye impossible. 
 
 This explanation is the one advanced by Helmholtz, and 
 is the one which is now almost universally accepted as cor- 
 rect. Recently there has been advanced, on not very good 
 grounds, however, a second explanation. According to 
 this second explanation the increase in the convexity of the 
 lens is brought about by the contraction of some circular 
 fibers which seem to lie among the radial fibers of the cili- 
 ary muscles, by the contraction of which circular fibers the 
 lens is rounded. As these circular fibers are said to sur- 
 round the lens like a rubber band, it is clear how a flat- 
 tened object would have its convexity increased by a 
 circular pressure exerted upon it in the manner indicated, 
 but as most of the fibers of the ciliary muscles are radial 
 fibers, and as even the few circular fibers do not lie suf- 
 ficiently close to the margin of the lens, this explanation 
 does not seem satisfactory, especially so in view of the 
 completeness of the other explanation. 
 
 It will be remembered in the chapter on the distribu- 
 tion of nerves that the ciliary muscles are innervated with 
 branches from the oculi motores. 
 
 With the process of accommodation are associated 
 changes in the size of the pupil. The enlarging of the 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 565 
 
 pupil is accomplished by the radial fibers of the iris, its 
 contraction by the circular ones. The pupil changes its 
 caliber under the following circumstances: 
 
 First. Very strong light thrown into the eye causes a 
 contraction of both pupils, even when the strong light is 
 admitted to one eye only. 
 
 Second. Under a constant light the pupil contracts 
 when the eye is accommodated for objects near by. 
 
 Third. A contraction of the pupil seems to accompany 
 the movements of the eyes inwards. This is probably but 
 a special case of number two, as ordinarily the eyes are 
 turned inward when they are accommodated for near ob- 
 jects. 
 
 Fourth. The pupil is contracted in sleep. 
 
 Fifth. The pupil is much dilated in cases of asphyxia- 
 tion. A dilation also usually follows a strong stimulation 
 of any large region of the skin of the body. 
 
 Sixth. Various drugs have a decided effect upon the 
 pupil. Thus, atropin and belladonna dilate the pupil, 
 while nicotine and morphine cause it to contract. 
 
 THE DIOPTRICS OF THE ETE. 
 
 In a general way the passage of rays of light through 
 the media of the eye has been pointed out, and while it 
 would be out of place here to go into the detailed mathe- 
 matical considerations of the various foci and indices of re- 
 fraction a few elementary considerations of this nature seem 
 appropriate. Although the eye consists of several refract- 
 ing media, these three media may mathematically be re- 
 solved into one, and the cardinal points for such a com- 
 posite medium be determined. In Figure 178 the line // 
 actually indicates the curvature of a lens of the density of 
 the vitreous humor which would have the same refracting 
 power as the entire eye. To determine at what point on 
 the retina the refracting media of the eye will throw an 
 image it is necessary that several determining points of 
 these media be established. These have, with considerable 
 
566 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 accuracy, been made out on the human eye and are given 
 approximately correct in Figure 178. 
 
 It will be noticed that in the lens itself not far from its 
 posterior portion there are indicated two points marked k' 
 and k". These are called the nodal points of the eye. A 
 ray of light entering in any direction through the pupil and 
 passing through point k' will proceed from k' to k", and at 
 k" be bent parallel to its direction of entrance. As,. how- 
 ever, for practical purposes k' and k" are very close to- 
 gether we may imagine them as one point, and that any ray 
 of light which passes through k' will be continued to the 
 retina without suffering any bending 
 
 Fig. 178. SEMI-DIAGRAMMATIC SECTION OK THE EYE-BALL. 
 The explanation of lines and letters is given in the text. 
 
 To know, therefore, where on the retina a certain lum- 
 inous point will be imaged, it is necessary to draw a straight 
 
THE: EYE AND THE PHYSIOLOGY OF VISION. 567 
 
 line from the luminous point in question through the nodal 
 point of the eye to the retina. If the eye be a normal one 
 and focussed properly all the other rays of light from this 
 same luminous point will fall at the same point on the retina 
 as the straight unbent one passing through the nodal point. 
 
 In Figure 178 two directions of light are indicated. 
 One, F' F" passes through the horizontal axis of the eye, 
 and passing through the point k' k" suffers no bending. 
 The line G' G" is a second direction of light passing 
 through the point k' k" and so is continued straight back 
 to the retina. 
 
 The line of light G' G'' is the common path of light fall- 
 ing on the yellow spot. It is apparent, therefore, that the 
 geometric axis of the eye is not the path which the light 
 usually takes in entering it, but that the yellow spot is 
 slightly above the axis, thus necessitating in ordinary vision 
 a constant, although slight rotation of the eyeball upwards. 
 
 It may be pointed out once more that all the refracting 
 media of the eye reduced to a single medium would in its 
 optical action be that of a spherical surface of vitreous 
 humor of a little over 5 mm. radius, as indicated by the 
 line // in the figure, which surface would have as its central 
 point the nodal point indicated by the letter H". 
 
 THE LUMINOSITY OF EYES. 
 
 On account of the black choroid which lines the inside 
 of the eye, very little light indeed is reflected back out of 
 the eye, it being all absorbed by this coat. For this reason 
 the pupil looks black. It is true, though, that even in the 
 human eye a little light is reflected out of the pupil, enabling 
 an observer by means of proper instruments to see the 
 retina. In many of the lower animals, on the other hand, 
 a very much increased amount of light is reflected through 
 the pupil, sometimes to such an extent as to make the eyes 
 luminous, as for instance, those of a dog, cat, or tiger. 
 This is brought about by the presence of a reflecting mem- 
 brane in the back of the eyes of these animals, called the 
 
568 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 tapetum. This luminosity of the eyes is most readily ob- 
 servable if such an animal be placed in a darkened room 
 and light admitted through a door in which the observer 
 himself stands. In that case it is frequently possible to see 
 the two eyes luminous enough to shine in the dark, the ex- 
 planation being, as just pointed out, the light which is 
 actually reflected out of the eye by the shining tapetum 
 within. 
 
 THE PHYSIOLOGY OF COLOR SENSATION. 
 
 Up to this point the eye has been treated almost exclu- 
 sively as a purely physical instrument, unless we except the 
 nerves and muscles by means of which it accommodates 
 itself. But all these physical arrangements in the eye are 
 intended to make possible the physiological perception of 
 color in the retina. It has been pointed out how the image 
 is spread upon the retina, and there arises now the question 
 how this physical image is translated into physiological 
 phenomena. In other words, how do we see colors? 
 
 It is well to note that it is color and color alone that we 
 observe with the eyes. Distance, solidity, form, size, etc. , are 
 all inferences which we draw from the arrangement of colors 
 before us. The eye sees color or absence of color, and ar- 
 rangement of colors, and nothing more. 
 
 The physiology of vision pure and simple, therefore, 
 narrows itself down to the perception of these colors. Un- 
 fortunately we are yet far removed from a complete under- 
 standing of this question, and the theories that have been 
 advanced have left so much still unexplained that they have 
 scarcely the dignity of scientific theories. They are, how- 
 ever, the best attempts, in the light of what we now know, 
 towards the explanation of these phenomena. 
 
 Two fairly distinct theories are proposed. These are 
 the Young-Helmholtz theory, as suggested by Young early 
 in this century, and later on materially modified by Helm- 
 holtz. It seems to offer the most plausible explanation and 
 is the one probably most generally accepted. The other 
 theory is that of Ewald Hering, which explains colors upon 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 569 
 
 an. entirely different basis. Both theories, however, start 
 from facts and observations which are afforded by instances 
 of color blindness, and so before giving these theories it 
 may be desirable to describe somewhat in detail the various 
 kinds of color blindness observed. Two distinct kinds of 
 color blindness are found called respectively monochro- 
 matic, and dichromatic colorblindness. Of the dichromatic 
 blindness two varieties occur called red blindness and green 
 blindness. More correctly, however, the terms monochro- 
 matics and dichromatics are applied to the persons them- 
 selves showing these defects. 
 
 COLOE BLINDNESS. 
 
 Monochromatics . As the name indicates, these are per- 
 sons who see but one color. This color seems to be a bluish 
 white. Such monochromatics see the world, about as we 
 do, as far as distinctness is concerned. They can recognize 
 objects readily. The world appears to them about as it 
 appears to us in a photograph or an etching. It will be 
 remembered that in photographs and etchings but shades 
 of white and dark, as a rule, are used. Yet so true may a 
 photograph be, using only these two colors, that we fail to 
 notice frequently the absence of the spectral tints. It is 
 even possible for such monochromatics to live for some 
 time without really suspecting their defect, attributing their 
 lack of color perception frequently to stupidity in that di- 
 rection rather than a real optical disability. Such mono- 
 chromatics show when they are looking at objects a pecu- 
 liar habit of squinting the eye, as if they were focussing 
 with effort. They seem to have some difficulty to turn 
 their point of acutest vision on the object in question. 
 Strange as it may seem, such monochromatics may some- 
 times successfully recognize colors, but when they do so it 
 is for the same reason that a photographer may recognize 
 colors on his photograph, having learned by experience 
 what the appearance of red or yellow in the photograph will 
 be, and so these monochromatics having red pointed out 
 
570 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 to them repeatedly they are sometimes enabled to recognize 
 Ihe red by a slightly different appearance which it shows to 
 them in their single color. 
 
 Monochromatic color-blindness is not very general. Rel- 
 atively few cases have been scientifically noted. The ex- 
 planation of the phenomena of monochromatic eyes will be 
 explained in terms of each theory further on. 
 
 Dichromatics . Dichromatic eyes see but two colors. 
 These are blue and yellow. Of course black is not counted 
 as a color in any of the eyes, black being simply the absence 
 of light, and in this sense it would be correct to say that a 
 totally blind individual could still see black. These dichro- 
 matic eyes see the blue about as we do, but instead of green, 
 yellow and red, they see but yellow alone. 
 
 1. Green- Blindness. Two distinct varieties of dichro- 
 matic eyes occur. The varieties are so marked off, that 
 gradations from one into the other do not seem to exist. 
 One variety of dichromatic eyes sees yellow where we see 
 red, but sees no definite tint where we see green. Such per- 
 sons are called green-blind. They seem to their friends to 
 be perfectly able to recognize the red, but the red is to them 
 really an intense yellow, which they have learned to call red 
 because it has always been pointed out to them as red, 
 while green they are not able to recognize except as a paler 
 yellow, and this inability to readily pick out green objects 
 has given them the name of green-blind persons. 
 
 2. Red- Blindness. In the second variety of dichro- 
 matic eyes (a variety which is more numerous than either 
 of the others) the yellow is seen most intense where we see 
 green, while our red is to them a very indistinct color some- 
 thing like a pale yellow. They readily pick out green ob- 
 jects, because these appear to them a bright yellow, calling 
 them green, however, for reasons explained above. Such 
 persons not being able to clearly distinguish the red are 
 called red-blind persons. 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 571 
 
 It is said that about one female in twenty-five is affected 
 with color blindness of one variety or another, and about 
 one male in every eight or ten. Red-blindness is the more 
 frequent defect. It is hard to explain the relatively higher 
 per cent, of color-blindness in men, unless it is due to the 
 fact that they pay relatively less attention to colors and that 
 this neglect in their visual education has contributed to this 
 defect. 
 
 What we call green-blindness and red-blindness are, after 
 all, varieties of the same defect, for red-blind and green- 
 blind alike see blue and yellow only. In the green-blind 
 people our red seems a most intense yellow, while in red- 
 blind people our green seems most intense. As it is ex- 
 ceedingly necessary in many professions, especially that of 
 navigation and railroading, that employes shall be able to 
 readily distinguish between a green signal and a red danger 
 signal, such corporations now very generally subject their 
 employes to a very careful color test in order to preclude 
 as much as possible an accident from such a lack of dis- 
 crimination. 
 
 With a general description of these three varieties of 
 color-blindness we are enabled to understand possibly a 
 little more readily each of the two attempts made to explain 
 them, as well as the color sensations of the normal eye. 
 
 THE YOUNG-HELMHOLTZ THEORY. 
 
 According to this theory there are found in the retina 
 three kinds of nerve fibers, physiologically considered. To 
 these three different kinds of fibers are attributed respect- 
 ively sensations of red, green and blue. The sensation of 
 blue is attributed to the rods. It will be remembered that 
 the rods are scattered over the entire retina but are wanting 
 in the yellow spot, for which reason, if this theory be true, 
 the yellow spot should be blind to sensations of blue. And 
 such seems really to be the case. If with proper apparatus 
 one arranges a blue point in such a way that it shall fall 
 right in the fovea centralis, it seems to disappear, while red 
 
572 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 and green points persist. In the author's own experience 
 such a disappearance of the blue when falling right in the 
 fovea centralis seems unquestionable from repeated experi- 
 ments. There is, however, a cause that might produce the 
 disappearance of the blue point apart from the absence of 
 the cones. It will be remembered that the fovea centralis 
 lies in the yellow spot, and we know that yellow light very 
 rapidly absorbs blue light. Blue light does not readily pass 
 through a yellow window pane, and so the disappearance of 
 a blue point on the retina may be due to the fact that the 
 yellow pigment of the yellow spot absorbs the blue light and 
 so prevents it from affecting the retina. 
 
 According to the Helmholtz theory, however, the blind- 
 ness of the yellow spot with reference to blue is due to the 
 absence of the rods. The rods being distributed over all 
 other portions of the retina explains why blue is thus gen- 
 erally present. It will also be remembered that the vision 
 purple found in the eye occurs only in the rods, and so this 
 theory goes a point further suggesting that it is a chemical 
 action of the vision purple produced by the light that irri- 
 tates the rods and so occasions a nervous impulse leading 
 to the perception of blue. 
 
 Monochromatic eyes are upon this theory explained as 
 eyes in which the rods alone are functional. The yellow 
 spot is then entirely blind, and to this blindness of the yel- 
 low spot is attributed the difficulty in focussing and the 
 habitual squinting which marks monochromatic persons. 
 The points of acute vision in these monochromatics not be- 
 ing a definite spot, but a circle around that spot, the at- 
 tempt to keep the focus on this circle occasions their extra 
 efforts in looking closely. 
 
 But even normal eyes are monochromatic at times. 
 When the ordinary light of day is very much reduced, as it 
 is some time after sunset, we notice how the sensation red 
 disappears first, then green, while blue is the last sensation 
 to go. Every one must have noticed that a night scene has 
 a bluish cast. Pictures of night scenes are purposely tinted 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 573 
 
 blue. A moonlight scene in a picture is readily distin- 
 guished from a view by day in the absence of all reds, and 
 the prevailing tint of blue. In subdued light red and green 
 disappear, and things before they shade into blackness 
 seem to pass through gradations of deeper and deeper blue. 
 According to this theory we have lost the use of the cones 
 and our vision is limited to the rods. Therefore, we, too, 
 ought to be blind in the yellow spot, as this possesses no 
 rods, and the holders of this theory in support of this, point 
 out the difficulty we have in distinct vision even when the 
 light would still be strong enough to permit the details to 
 be seen carefully. 
 
 Dichromatic eyes are explained by supposing that in ad- 
 dition to the rods which see blue, there are cones which 
 see yellow, and the two varieties of dichromatic eyes are 
 explained by the relative ease with which these yellow 
 cones are stimulated. In red-blind individuals they are 
 stimulated most readily by green objects; in green-blind 
 persons the yellow cones are stimulated most readily by 
 red objects. 
 
 NORMAL OR TRICHROMATIC EYES. 
 
 In the normal eye this theory supposes, as was stated, 
 three sensations: blue, green and red. A grievous fault of 
 this theory is its inability to explain why the second color 
 in dichromatic eyes should be yellow, and why this color 
 should not be represented at all in the trichromatic eyes. 
 One would naturally suspect that in normal eyes the ad- 
 dition would be made to the blue and yellow of partially 
 color-blind eyes. It was, in fact, this difficulty to explain 
 how the yellow of dichromatic eyes was replaced by green 
 and red of the trichromatic eyes that led to the proposal of 
 the Hering theory, which explains this point at least satis- 
 factorily. 
 
 It will be noticed that a normal eye might be derived 
 from the composition of a green-blind eye and a red-blind 
 eye. Thus dichromatics see blue just as we do. This is 
 
574 
 
 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 one color. The green-blind people see our red, although it 
 is yellow to them. In other words, their sense of sight is 
 aroused by what we call red. This is the second color. 
 
 Fig. 179. DIAGRAMMATIC REPRESENTATION OF THE STRENGTHS OF THE THREE FUNDA- 
 
 " MENTAL SENSATIONS IN THE DIFFERENT PARTS OF THE SPECTRUM. 
 
 J, curve for color red; #, curve for green; 3, curve for blue. The red curve should 
 show a small added elevation at the violet end, since the stronger reappearance of the 
 red there causes with the blue the production of the violet. 
 
 In red-blind persons the sensation of yellow is produced by 
 what we call green. Such a composition of two dichro- 
 matic eyes would therefore be (1) blue, (2) yellow where 
 we see green, (3) and yellow where we see red. Now, it 
 is just possible that for psychological reasons this primitive 
 yellow sensation has been divided into two separate sensa- 
 tions which we have learned to call red and green. One 
 can easily understand how by having two colors, even if 
 they are somewhat alike, side by side before the eye,, that 
 it would tend to make distinctions which would otherwise 
 go unnoticed. 
 
 The normal eye is usually spoken of as a trichromatic 
 eye because of its ability to perceive three, different sensa- 
 tions. By the varying compositions of these different sen- 
 sations all the shades and tints, and intermediate colors 
 may easily be derived. When all three fibers in the eye 
 are stimulated in the proper proportion, white is the result. 
 This may be shown to be true by taking a card on which 
 the red, green and blue are put in the proper proportion 
 and then whirling it rapidly. The three colors melt to- 
 gether and the sensation of white results. The red and the 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 575 
 
 blue produce purple. Red and white a sensation in which 
 the red nerves are more stimulated than in the proportion 
 of white, produces pink. Violet, although usually indi- 
 cated in elementary books as one of the fundamental color 
 sensations, is in reality not one, but is a mixture of the blue 
 and red, for it will be remembered when the number of 
 vibrations of the various colors was given that it was pointed 
 out that the violet was just an octave above the red, and 
 that the red seemed to appear again there mixed with the 
 blue. It was pointed out in the case of sound that a string 
 set in vibration by a certain sound would be readily affected 
 by its octave. So a nerve in the retina that is affected by 
 red seems also affected by an octave of red, and for that 
 reason blue will gradually "shade into the violet as the 
 octave of the red is there approached. As the sensation of 
 blue was attributed to the rods, yellow and green sensa- 
 tions and the colors into which they enter are attributed to 
 the cones. 
 
 R Y Gr Bl V 
 
 Fig. 180. GRAPHIC REPRESENTATION OF THE COMPOSITION OF COLOR SENSATIONS IN 
 
 TERMS OF THK YOUNG-HELMHOLTZ THEORY. THE CURVES FOR RED. GREEN AND 
 BLUE ARE HERE SUPERIMPOSED. 
 
 THE BERING THEORY. 
 
 According to the theory of Hering there are in the retina 
 three different color substances which are either in process 
 of being made, assimilation, or in process of destruction, 
 dissimilation. One of these color substances he calls his 
 white-black substance. When this substance is being pro- 
 duced in the eye the sensation of black results; when it is 
 being destroyed in the eye the sensation of white results. 
 Hence, objects appear white when the light falling into 
 the eye causes this white-black substance to disintegrate. 
 Things appear black when on that point of the retina this 
 white-black substance is being formed. 
 
576 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 Hering explains monochromatic eyes as eyes that pos- 
 sess but this white-black substance. He questions the 
 bluish tint which many monochromatics have and explains 
 the appearance of the world as monochromatics see it as 
 that of a black and white steel engraving. As this white- 
 black substance is produced when no light enters the eye 
 things seem black in the absence of light. 
 
 Dichromatics possess in addition to this white-black 
 substance a blue-yellow substance. This substance when 
 it is being destroyed in the eye produces blue ; when it is 
 being re-formed in the eye produces yellow sensations. 
 Looking at a blue object according to this theory would 
 produce a disintegration of this substance, which would 
 occasion the sensation blue, while looking at a yellow ob- 
 ject would cause the production of some of this substance 
 and in this way the retina be affected to see yellow. 
 
 Finally, in normal eyes there is, in addition to the 
 white-black substance and the blue-yellow substance, a red- 
 green substance. Here, too, a disintegration of the same 
 produces red, a production of it, green sensations. While 
 this theory seems very fanciful at first, it explains the 
 dichromatic eyes and further gives us a reason for many of 
 the phenomena which may be observed in studying after- 
 images and color contrasts. 
 
 AFTER-IMAGES. 
 
 An after-image is, as the name suggests, an image re- 
 tained on the retina after the stimulus producing it has 
 ended. Such after-images may be of two kinds: positive, 
 when they have the same color as the object, or negative, 
 when they have the complementary color. 
 
 1. Positive After- Images. The forming and dis- 
 appearance of an image on the retina is, from a physical 
 standpoint, as instantaneous as the changes of light, but 
 the sensation which this image produces will sometimes 
 continue after the stimulus is gone. Thus, a sky rocket 
 seems to leave a trail of fire after it ; a red-hot coal swung 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 577 
 
 around on a string looks like a luminous circle ; a point of 
 light moving rapidly up and down looks like a luminous 
 stick. All this is explained on the ground that the sensa- 
 tions linger and that we therefore see the rocket in a cer- 
 tain position after it has left it and attained a new one. 
 We see a rapidly moving luminous object in the position in 
 which it is at the moment, together with quite a number 
 of positions through which it has just passed, and in that 
 way its path becomes luminous. A rapidly rotating wheel 
 shows none of the spokes distinctly for similar reasons. 
 If, in a room lighted by a gas jet, the gas be suddenly 
 turned off while one is looking at it, an image of the flame 
 remains an instant or two after that on the retina. Pos- 
 sibly the most familiar illustration of this fact is in the 
 lightning, a stroke of which seems to us to extend in a 
 continuous although zig-zag line from the cloud to the 
 earth. 
 
 Positive after-images retain not only the shape, but also 
 the color of the object and offer no serious difficulty in their 
 explanation. It is not so easy with negative after-images. 
 
 2. Negative After- Images. If one glances at the sun 
 just an instant and then looks up into the sky in a differ- 
 ent direction one sees a round black disk. If one looks in- 
 tently with the eyes fixed on a red light and then shifts 
 his view to a white wall an image of the light looked at is 
 projected against the wall but in different colors, usually 
 bluish or greenish. Or, if one looks out of the window 
 intently for some time, then turns the look to the wall, 
 the white window panes are black, the black window 
 frames somewhat light in the negative after-image. An 
 after-image retains the form and size of the real image, but 
 in its complementary colors. A very clear illustration of 
 this on a wider scale is afforded by placing close before the 
 eye an intensely red light and looking at the same for some 
 time, even at the risk of tiring the eye. Upon turning now 
 to a room lighted with electricity or gas light, or even ordi- 
 nary day light, the objects possess an intensely bluish tint, 
 37 
 
578 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 which only gradually fades and disappears. Here the entire 
 retina having been stimulated with red, everything later pic- 
 tured upon it is clothed with bluish tints the complementary 
 color of red. We have now to consider how these negative 
 after-images are accounted for by Young's theory and by 
 Hering's. 
 
 EXPLANATION OF NEGATIVE AFTER-IMAGES. 
 
 These negative after-images are explained by the Young- 
 Helmholtz theory as due to the fatigue of the retina. If 
 one looks intently for some time at a red light evidently the 
 red nerves of that part of the retina on which this image 
 falls will be stimulated, while the green and the blue nerves 
 are resting. If this stimulation continues it is evident that 
 these red nerves will become fatigued. There will be a 
 tendency for the red object to become paler and paler as this 
 effect proceeds. If, now, the eye be turned upon a white 
 wall the entire retina is flooded with white light. In that 
 part of the retina where the red image was the red nerves are 
 fatigued and so do not respond; at least not fully. The con- 
 sequence is that the green and blue nerves react alone and 
 so that area appears a greenish-blue or a bluish-green. As 
 the red nerves gradually recover from their fatigue their 
 stimulation is mixed with the blue and green, which of 
 course produces white. This explains very satisfactorily the 
 complementary color of the negative after-image and how it 
 is gradually transformed back into white. 
 
 But not only may one nerve be thus fatigued; two or 
 even three may be so affected. If one, for instance, gazes 
 at the sun an instant the image of the sun falling on the 
 retina and strongly stimulating that portion, fatigues it. 
 When, now, the view is turned in another direction this por- 
 tion of the retina which the sun's image had fatigued fails 
 to be fully excited, and so there arises the sensation of 
 black, or, if the excitation is only a partial one, shades of 
 gray. 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 579 
 
 This theory also explains why looking from one color to 
 a complementary one seems to increase the brightness of 
 the second. An animal grazing in the field and seeing prac- 
 tically nothing all day except the green grass and the green 
 foliage, has a much more vivid impression of a red object 
 when this is suddenly presented, than it would otherwise 
 have, the explanation being that the red nerves have been 
 resting all day, and then suddenly stimulated they react 
 with great energy. The offense which certain animals seem 
 to take at such bright objects flared at them may be to a 
 slight extent at least accounted for in this way. Every 
 stroller through the woods must have been struck with the 
 intense redness of a summer redbird or a cardinal as it 
 darted in among the green leaves. 
 
 In terms of the Hering theory negative after-images are 
 explained as follows: 
 
 Taking, for instance, the supposed red-green substance 
 of the eye which when it is being destroyed produces red 
 sensations, when it is being regenerated produces green, it 
 seems entirely possible that the excessive destruction of it 
 might induce its regeneration. Just like an active destruc- 
 tion of muscle tissue is the occasion for a corresponding 
 active regeneration of it. An increased use of any product 
 of the body very naturally brings about an increased pro- 
 duction. 
 
 Turning now to the first illustration, it is supposed that 
 while the eye is looking intently at a red object this red- 
 green substance is in that part of the retina where the image 
 falls being used up, and if the look continues, is being ex- 
 hausted rapidly. If, now, the eye is turned away there is 
 naturally induced an attempt of the eye to produce some 
 new substance of this kind, and this regeneration acting as 
 a stimulus gives us the sensation of green. So with the 
 other two substances. If the white-black substance had at 
 some point of the retina been almost exhausted by staring 
 an instant at the sun, say, there would occur at that point 
 in the retina as soon as the eye was turned away a regener- 
 
580 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 ation of this substance, and so a sensation of black. It is 
 unnecessary to carry this further with the yellow-blue sub- 
 stance. 
 
 If two substances were simultaneously being exhausted 
 then there would be induced the regeneration of both, and 
 in this way there would arise in the eye various intermedi- 
 ate colors corresponding to the intermediate colors first 
 looked at. It is apparent that the negative after-image 
 will be not far from the complementary color of the object 
 looked at. 
 
 It will thus be seen that both theories account more or 
 less satisfactorily for many of the phenomena of color sen- 
 sation, and each reader will have to decide for himself the 
 relative probability of these two views. A point, very much 
 in favor apparently of the Young-Helmholtz theory lies in 
 the fact that owls and bats, which from their habits would 
 naturally be suspected of being monochromatics, possess 
 rods only, the cones being entirely absent. A second 
 point in its favor is the observation that we are not able to 
 see red towards the periphery of the retina. For instance, 
 if one take a red object, such as a stick of red sealing-wax, 
 and move it from behind the head forwards it does not ap- 
 pear red at first, and must be moved some distance .further 
 even after its outline is recognizable, when suddenly the 
 sensation red flashes into consciousness. Blue and green, 
 however, are more readily recognized at the periphery. 
 Now, in terms of the Hering theory it would be impossible 
 to see green where one cannot see red, since one substance 
 is the cause of both. The explanation that suggests itself 
 is that green and blue nerves occur here only, the red 
 ones being absent. 
 
 DOUBLE VISION. 
 
 So far everything that has been said would apply if we 
 had but one eye, but, as a matter of fact, we use two eyes 
 in looking at objects and the question naturally arises, why 
 vision with two eyes should result in an apparently simple 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 581 
 
 visual sensation. Every normal individual when looking 
 directly at an object sees It as one object. It is possible, 
 however, to see objects double, of the truth of which one 
 may easily satisfy himself by holding a pencil before his 
 eyes and then looking past the pencil into the distance. 
 He will perceive two pencils. Of course if he turns his 
 focus upon the pencil before him the two pencils will melt 
 into one and the object appear single. But in that case 
 the objects in the distance appear more or less double. 
 There are on the retinas corresponding points, the simul- 
 taneous stimulation of which produces in the mind but a 
 ^single sensation, and we ordinarily see objects single be- 
 cause we turn to the object, corresponding points. If, on 
 the other hand, the image of anything should fall on points 
 which do not correspond, each image will produce its own 
 sensation and so we see double. 
 
 To determine which are corresponding points of the ret- 
 ina it is only necessary to imagine the retina of one eye 
 laid right over the retina of the other eye in such a way 
 that the yellow spots would coincide as well as the merid- 
 ians passing through the yellow spots. In that case the 
 points lying immediately above and below each other are 
 corresponding points. For a point in the upper and outer 
 part of the retina of the right eye, the corresponding point 
 of the left eye would be found in the upper inner portion. 
 Reference to Figures 181 and 182 will help to clarify this. 
 Thus, in Figure 181 the gaze is directed for the point/", 
 which is seen as a single point because its images at c and 
 c fall on corresponding points, but the point g is seen 
 double at G and G 2 because the images of it fall on points 
 g and g 2 which do not correspond. The corresponding 
 point to g is of course g' A . Turning now to the next fig- 
 ure in which the point G is seen single because its images 
 at c and c fall on corresponding points, f is seen double at 
 F' and F~ , because the images of point f fall at f and/"', 
 which are not corresponding points, the corresponding 
 point to f being/" 3 . 
 
582 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 From these figures it will be seen that only one point 
 can be seen single at one time; all other points appear 
 
 C 9, 92" " . T3 
 
 Fig. 181. Fig. 182. 
 
 Figs. 181 and 182. DIAGRAMS TO SHOW THE ORIGIN OF DOUBLE VISION. 
 
 more or less distinctly double. We are not aware of the 
 doubleness of these outside-lying points for the following 
 reasons: 
 
 First. To see an object clearly we turn to it the yellow 
 spots of both eyes, which are corresponding points. Hence 
 all objects seen distinctly, that is, with the yellow spot, 
 appear single. 
 
 Second. The other portions of the retina are not so sen- 
 sitive as the yellow spot, and so the doubleness of the 
 image does not press itself into the field of consciousness. 
 
 Third . Attention is usually riveted to those objects only 
 which fall in or very close to the yellow spot, and we do 
 not take cognizance of objects falling on the periphery of 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 
 
 583 
 
 the retina. A somewhat curious exception to this rule of 
 double vision is found in viewing the starry heavens. Here 
 all the stars appear as single stars, whether the image falls 
 close to the yellow spot or on the periphery. This arises 
 from the fact that owing to the immense distances of these 
 objects the rays coming from them are practically parallel, 
 and entering the eye in parallel lines all the images must 
 naturally fall upon corresponding points. Reference to 
 Figure 183, in which the rays of light from one star are 
 given as lines 1 and 7, and rays from the second star given 
 as lines 2 and 2, it will be seen that c and c and a and a 
 are corresponding points. 
 
 c * c, 
 
 Fig. 183 DIAGRAM SHOWING THE COMPLETE CORRESPONDENCE OF RETINAL POINTS IN 
 
 LOOKING AT VERY DISTANT OBJECTS, SUCH AS STARS. 
 
 THE ADVANTAGES OF TWO EYES. 
 
 Even if one eye were able to see all colors as perfectly 
 as two, one or two decided advantages arise from the pos- 
 session of two eyes. 
 
 First. The defect in the retina caused by the blind spot 
 is remedied by the opposite eye, as the corresponding points 
 
584 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 for the blind spot of one eye are very sensitive points of the 
 other. In a similar way smaller pathological defects in the 
 retina of one eye are more or less fully counteracted by the 
 other. 
 
 Second. We are enabled to look at the same object from 
 two different points of view, and so can see more of the ob- 
 ject than with one eye alone. This vision from two differ- 
 ent points gives rise to the perception of solidity. One may 
 easily satisfy himself that notions of the solidity of objects 
 are very materially dependent upon one's seeing them with 
 both eyes. The stereoscope is based upon this principle. 
 Two views are taken of the same scene from points some 
 distance apart. These two figures are then mounted in 
 such a way that one eye sees one photograph, the other eye 
 the photograph from the other corresponding position. In 
 this way there arises the sensation of solidity to such an ex- 
 tent that we actually seem to see certain portions of the pic- 
 ture projecting in front of the others. Of course the two 
 views taken must not be from remotely removed points. In 
 that case the mind is unable to blend the two pictures into 
 one, and recognizes them as two distinct pictures. 
 
 When two entirely distinct scenes or objects are brought 
 one to one eye and one to the other, the two eyes seem to 
 strive for the mastery, and sometimes we see one picture, 
 then suddenly the other. This contest of the two pictures 
 is not really a process of the eye ; possibly each eye sends 
 the image of the picture before it to the brain, but the brain, 
 unable to look at two different things at the same time, 
 takes cognizance of one, then of the other, and so on. 
 Such a result naturally occurs in persons who are cross- 
 eyed. . In such individuals the corresponding points of the 
 retina are placed entirely awry, and each eye produces its 
 own picture. Only one of these pictures rises into full con- 
 sciousness, or, as we say, cross-eyed persons select one eye 
 to look with. This frequently remains the same. Some- 
 times the attention is shifted to the other eye, which then 
 becomes the seeing one. 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 585 
 
 Third. By determining the amount of motion neces- 
 sary to move the view of the eyeballs from one point to an- 
 other we make inferences as to the distance absolute and 
 relative of the objects seen. If an individual closes one 
 eye and then with his arm and finger extended forward, 
 moves towards the wall with the intention of halting when 
 his finger is, say just an inch from the wall, he will find 
 himself quite unable to do this satisfactorily, sometimes 
 touching the wall while he thinks he is still several inches 
 away, at other times suspecting the distance from his finger 
 tip to the wall to be about an inch, when it is five or six times 
 that amount. His inability to form correct judgments of dis- 
 tance in this case arises from the lack of using both eyes. 
 
 OPTICAL ILLUSIONS. 
 
 It has been pointed out that the eye is enabled to give 
 us sensations of color only. All knowledge of form, size, 
 distance, solidity, etc., are inferences made by the mind. 
 One would naturally suspect, therefore, that these infer- 
 ences would occasionally prove faulty and so give rise to il- 
 lusions, a deception which we then attribute to our physical 
 senses instead of holding our own minds responsible for 
 them. 
 
 Several of the more striking forms of illusions are men- 
 tioned here. 
 
 1. Irradiation. A light area on a dark background 
 seems larger than a black area on a black background, 
 even when these areas are mathematically alike. A hole 
 through an object, such as a wall, or even a piece of card- 
 board, seems larger than the solid piece that entirely fills 
 the hole. A person in light attire seems larger than in dark 
 attire. The explanation of this lies in the lack of sharp 
 focussing in the eye. When the focus of an object does not 
 fall directly on the retina, but the rays of light strike the 
 retina before meeting at a point, it is evident that a larger 
 area of the retina is affected. Turning to Figure 184 it is 
 readily seen that the image of the point a is a correspond- 
 
586 
 
 STUDIES IN ADVAXCKD PHYSIOLOGY. 
 
 ing point on the retina ;/ n at c. If the focussing were not 
 distinct and the rays of light should strike the retina as they 
 
 Fig. 184. DIAGRAM TO SHOW THK EFFECTS OF IMPERFECT FOCUSSING IN PRODUCING 
 
 THE PHENOMENA OF IRRADIATION. 
 
 At either m, m, or I, I, there is a circular field of light instead of a point as at , n. 
 
 do at m m or at / /, a much larger portion of the retina would 
 be covered. The image instead of being a point would be 
 a disk. This disk covering a larger portion of the retina 
 than it would do if it were exactly focussed, produces a sen- 
 sation which is interpreted as much larger in extent. Thus, 
 also, a black area in a light background would seem larger 
 than it naturally is, because now the black area would not 
 be sharply focussed, would spread over more retina and give 
 rise to a sensation of larger extent. For this reason a per- 
 son in dark attire would seem larger when projected against 
 a white background just as a person in light attire seems 
 larger when projected against the usual dark background. 
 
 2. Parallelism. While we are usually able to distin- 
 guish with considerable accuracy the parallelism of two 
 lines, there arises a deception when these lines are crossed 
 with diagonal lines, as indicated in Figure 185, where the 
 long lines are parallel, but seem not to be. 
 
 3. Distance. We judge distance in several ways; by 
 the size which the object appears to us to have when its 
 actual size is known ; by the distinctness with which we see 
 it, and by the number of objects which lie between us and 
 it. Unbroken distances are as a rule entirely under-judged. 
 This is due to the fact that distances in which many objects 
 are found seem longer than distances in which no objects 
 
THE EYK AND THK PHYSIOLOGY OF VISION. 
 
 587 
 
 occur. For this reason ten miles on a level prairie with a 
 clear view seem much shorter than when the intervening 
 
 Fig. 185. OPTICAL ILLUSION. THE PARALLELISM OF THE LONG LINES is DESTROYED BY 
 
 THE CROSS-LINES. 
 
 space is filled with a multitude of striking objects. So in 
 Figure 186 the distance from a to b seems longer than the 
 distance from b to c. For a similar reason the first square 
 in Figure 187 seems higher and narrower than the second. 
 In Figure 188 the distance from a to b seems greater than 
 the distance from c to d. 
 
 ViZ> 186. Fig. 187. 
 
 Fififs. 186 and 187-7-OPTiCAL ILLUSIONS. 
 
 4. Size. Primarily, the size of an object depends upon 
 the size of its image in the eye, but we have learned by ex- 
 perience that the size of this image will depend upon the 
 distance of the object. Therefore, when we know the dis- 
 tance we infer the size. It is the opposite, in short, of the 
 inference of distance. When we are ignorant of the dis- 
 tance we are unable to judge size closely, our inferences 
 being then based wholly upon the clearness with which it 
 
588 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 can be seen and a comparison with objects lying near it. 
 These inferences are frequently deceptive. A mountain 
 which on account of its immense size stands out so clearly 
 seems for that reason to be very close, and many a deceived 
 tourist has walked miles to find that his mountain remained 
 about as far away as ever. A person unaccustomed to the 
 sea seems helpless in judging distance, and therefore size, 
 and the guesses made by a group of passengers on board of 
 an ocean steamer as to the distance and size of a certain 
 vessel on the horizon will sometimes vary from one mile to 
 twenty-five in the matter of distance, and from a small fish- 
 ing smack to an ocean steamer in size. 
 
 Fig:. 188. OPTICAL ILLUSION OF LENGTH. 
 
 A rather interesting deception occurs in connection with 
 the moon. The moon seems larger near the horizon than 
 near its zenith. Very frequently the comparison is made as 
 between a wagon wheel at the horizon and a cheese-box at 
 the zenith. This apparent change in the size of the moon 
 arises for two reasons. First, we imagine the moon to be 
 farther away when near the horizon that when directly 
 overhead. The globe of the heavens seems to us in fact, 
 a flattened inverted bowl. The moon, however, having the 
 same size at the horizon but being judged by us farther 
 away, we think it larger. It is like the boy in the fable 
 who projected a spider hanging from his hat rim against 
 the distant heavens, and imagined it therefore a spectre 
 reaching from the earth to the skies. The spider appeared 
 no larger than it really was, but under the belief that it 
 
THE EYE AND THE PHYSIOLOGY OF VISION. 589 
 
 was miles away it seemed to reach into the clouds. A 
 second reason for the increased size of the moon lies in the 
 comparison which we make of the size of the same with the 
 objects in its range. We see for instance the moon about 
 twice as wide as a certain chimney, the dimensions of which 
 we know, and in an unconscious way we make calculations 
 as to the moon's size. When the moon is overhead there 
 are no intervening objects and the comparison does not 
 occur. 
 
 5. Shine or Brilliancy. It was pointed out in the dis- 
 cussion of the reflection of light that a perfectly smooth 
 surface reflected the light in an unbroken way and would 
 appear even to a single eye polished or shiny. But the 
 sensation of the shine or brilliancy of a surface is very 
 much increased when we look at it with both eyes. This 
 seems to be due to the fact that the same amount of light 
 is not reflected into both eyes. It is apparent that the 
 reflection from a shining surface is not the same for differ- 
 ent directions. Especially is this true if that surface should 
 move slightly as, for instance, a surface of water. This 
 slight disagreement between the sensations of brightness 
 in the two eyes is interpreted by the mind as increased 
 shine or brilliancy. It is possible experimentally to take 
 two surfaces, neither of which when seen alone appearing 
 polished, and, placing one before each eye and then illu- 
 minating them with different intensities, to produce a sen- 
 sation of shine or brilliancy. The mind seems to combine 
 the non-agreement of intensity of light reported by the two 
 eyes into a new sensation. In this way arises, for instance, 
 the brilliancy of reflected moonbeams from a rippling sur- 
 face of water. 
 
 6. Entopic Illusions. These are illusions which arise 
 from a cause lying within the eye itself. They are: 
 
 (a) Musccz volitantes. These are commonly called the 
 flying motes, and appear as little black spots which we pro- 
 ject into space. These black spots are due to shadows which 
 
590 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 small opaque bodies in the vitreous humor throw against 
 the retina, which shadows we by mistake project outside of 
 the eye. These opaque bodies in the vitreous humor are 
 remnants of embryonic blood-vessels. 
 
 (b) The figures of Piirkinje. These are figures pro- 
 duced by the shadows which the blood-vessels of the retina 
 throw against the retina. The blood-vessels lie in the outer 
 coats of the retina, and so whenever light enters the eye 
 they cast a shadow on the deeper sensitive layers. Ordi- 
 narily we do not notice this shadow because we have been 
 accustomed to it, as the shadows always fall on the same 
 points of the retina, the light entering always at the pupil. 
 In the same way we might become insensible to an object 
 resting on a certain portion of the skin if it should remain 
 there for any great length of time. When, however, the 
 object is suddenly placed on a new bit of skin it produces a 
 distinct sensation, so when the shadows of these blood- 
 vessels fall on a new part of the retina we at once distinctly 
 see them, and as usual project these shadows out into space. 
 If an individual go into a room lighted only with a lamp and 
 then move the lamp at one side of his head in such a way 
 that the light of the lamp pass through the white portion of 
 the eye on that side instead of through the pupil, he will 
 suddenly see, especially if he look against a white wall, a 
 branched system of vessels, and if the experiment is very 
 successful may even note the translation of the individual 
 corpuscles through these blood-vessels. The explanation 
 is apparent. The light entering through the sclerotic por- 
 tion of the eye causes the blood-vessels to cast a shadow in 
 a different direction than when the light normally enters 
 the pupil, and this shadow falling upon a new portion pro- 
 duces a sensation. These Purkinje figures may be pro- 
 duced upon suddenly emerging into the light after having 
 been confined for some time in a dark space, or after a 
 night's sleep upon suddenly opening the eyes. In this case 
 the retina where the shadow normally falls has been resting 
 
THE EYE AND THE PHYSIOLOGY OK VISION. 591 
 
 during the night and becomes sensitive when the shadow is 
 suddenly projected against it. 
 
 From this long chapter on the eye it will be noted that 
 while our knowledge is very satisfactory in certain direc- 
 tions there is much that needs further study and investiga- 
 tion. We understand the eye fairly well as a physical m r 
 strument, but the gap in our knowledge is in the physi- 
 ology of the retina. Unfortunately it must be granted that 
 neither the Young-Helmholtz theory nor the Hering theory 
 explain satisfactorily all the phenomena. In conclusion 
 there may be mentioned some observations made upon the 
 eyes of birds which may lead in the. future to important 
 results. 
 
 There occur in the rods and cones of the retina of birds 
 small, fatty globules, some of which are red, others yellow, 
 and still others colorless. These globules are so situated 
 that the light must pass through them before reaching the 
 sensitive endings of the rods and cones in question. One 
 can hardly resist the suggestion that -these colored globules 
 of fat determine to some extent, if not wholly, the sensation 
 which the rod in which it is imbedded shall give. It is 
 evident that the red globule, for instance, will absorb all 
 the other colors and permit only the red to pass through, 
 and so stimulate the end of the rod or cone. Similarly the 
 yellow globules will permit only yellow light to pass through. 
 One feels tempted to believe that there may be globules 
 answering to the entire scale of simple colors and thus the 
 retina become a veritable color sounding-box, its physiology 
 somewhat analagous to the basilar membrane of the ear, 
 with its strings attuned to the various vibrations. The 
 many individual rods and cones might each be provided 
 with some contained colored globule to permit only that 
 light in question to pass through it and affect the retina. 
 In fact, it would be as if each rod and cone had a little 
 colored plate of glass spread before it which permitted only 
 the light of that color to penetrate it, and consequently to 
 stimulate it to a sensation. May it not be possible that in 
 
592 STUDIES IN ADVANCED PHYSIOLOGY. 
 
 the human retina there are such colors which we are, how- 
 ever, not able to see because these small globules might so 
 blend their light as to appear white, just as the individual 
 colors of the spectrum blend into ordinary white? This, 
 however, takes us into the domain of guessing, a procedure 
 which is not always scientific. 
 
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