liHf iiil USiJiii: •w&'k'' ■•'■■■ V CORNELL UNIVERSITY. THE THE GIFT OF ROSWELL P. FLOWER FOR THE USE OF THE N. Y. STATE VETERINARY COLLEGE 1897 i '^(.:^iitif^^ ,.vy CornePI University Library QP 34.089 A text-book of physiology. 3 1924 001 045 164 mf A TEXT-BOOK OF PHYSIOLOGY OTT Cornell University Library The original of tiiis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924001045164 A Text-book '^tl,^;:|.;' OF PHYSIOLOGY BY Isaac Ott. A.M., M.D. FiiOFSBSOB OF PHYSI0L09T IN THE MEDIOO-CHIBUBSICAL COI.I.EOE OF PHILADELPHIA WITH 137 ILLTJSTEATIOIS'S PHILADELPHIA F. A. DAVIS COMPANY, Publishers 1904 ' 3 »^ ,. ^I^hf^ 34- Ho. ^.jj-o r\ jH o COPYRIGHT. ¥04, F. A. DAVIS COMPANY. [Registered at Stationers' Hall, London, Eng.] Philadelphia, Pa., U. S. A. The Medical Bulletin Printing-house. 1914-16 Cherry Street. PEEFACE. This book has been written at the solicitation of students who have attended my lectures for the past eight years. The aim has not been to write a treatise on the subject, but rather an elementary work containing the chief facts of physiology which are necessary to the student who wishes to apply them in the practice of his profession. Physiology is the bs^sis of medicine, and its understanding is requisite to the study of pathology. With this idea in mind, small space has been given to the subject of electro-physiology. The technique of the laboratory has been omitted for similar reasons. In the preparation of this book it was found impossible to give due credit to all the sources from which information has been derived. The illustrations have been selected from various authorities, to whom credit has been given. Isaac Ott. Afsu., 1901. (V) COI^'TEE'TS, chapter i. page The Cell 1 CHAPTER n. Chemical Constituents of the Body and Foods 34 CHAPTER ni. Digestion 42 CHAPTER IV. Absokption 108 CHAPTER V. The Blood 124 CHAPTER VT. The Cieculation 163 CHAPTER VII. Eespihation 237 CHAPTER VIII. Seceetion 277 chapter ix. Metabolism 328 CHAPTER X. Animal Heat 338 chapter xi. The Muscles 358 chapter xii. Voice and Speech 384 chapter xiii. Electeo-physiology 394 (vii) viii CONTENTS. CHAPTER XIV. PAGE Nektous System 398 CHAPTER XV. Tactile Sense 477 chapter xvi. Taste 488 CHAPTER XVII. Smell 493 CHAPTER XVIII. Heaeing 496 CHAPTER XIX. Vision 509 chapter xx. Ceanial Neeves 530 chapter xxi. Eepbodttction 547 Index 557 LIST OF ILLUSTEATIOIfrS. FIG. PAGE 1. Vegetable Cell. (Dtjval) 6 2. Cell with Reticulum of Protoplasm Radially Disposed. From Intes- tinal Epithelium of a Worm. (Cabnot) 8 3. Amoeba Proteus. (Leidt) 14 4. Specimens of Milk, viewed through the Microscope. (Landois) 38 5. Dog's Stomach. (Pawlow) 66 6. Liver of Maa. (DxrvAi,) 85 7. Taurin. (Duval) 89 8. Glycocholic Acid. (Duval) 89 9. Crystals of Cholesterin. (Duval) 91 10. Inhibitory Apparatus of Ano-spinal Center 102 11. Section of Dog's Intestine showing the Villi. (Cadiat) 103 12. Diagram of the Relation of the Epithelium to the Lacteal in a Villus. (Punke) 104 13. Lacteals of a Dog during Digestion. (Colin) 105 14. Osmometer. (Cohen) 110 15. Blood-corpusdes of Different Animals. (THANHorrEE) 128 16. Himian and Amphibian Blood-corpuscles. (Landois) 129 17. Hsemacytometer of Thoma-Zeiss. (Lahousse) 131 18. Bed Blood-corpuscles. (Landois) 133 19. Leucocytes of Man, showing Amceboid Movement. (Landois) 135 20. Blood-plates and tbedr Derivatives. (Landois) 138 21. Blood-crystals of Man and Different AnimaJs. (Thanhoffeb and Feet) 144 22. Teichmann's Hsemin-crystals. (Lahousse) 145 23. Sorby-Browning Microapectroscope 147 24. Spectra of Oxyhsemoglobiij, Reduced Haemoglobin, and CO Haemo- globin. (Gamgejb) 148 25. Von Fleischl Hsemometer. (Lahousse) 150 26. Heart of the Cow, with Left Auricle and Ventricle Laid Open. (MiJLLEE) 166 27. Diagram of Mammalian Heart. (Beclaed) 1G7 28. Course of Muscular Fibers of Heart. (Landois) 168 29. Course of the Ventricular Muscular Fibers. (Landois) 169 30. Diagram of the Circulation. (Duval) 172 31. Sanderson Cardiograph 176 32. Record Obtained with the Cardiograph when the Button is Placed at the Apex-beat of the Human Heart. (Sandeeson) 177 33. Heart of the Frog. (Livon) 186 34. Schema of Ligatures of Stannius. (Hbdon) 188 35. Cardiac Plexus and Stellate Ganglion of the Cat. (Landois).. 190 36. Course of Vagus Nerve in Frog. (Stieling) igi (ix) X LIST OF ILLUSTRATIONS. no. PAGE 37. Tracing by Lever Attached to Frog's Heart on Stimulation of the Pneumogastrlc Nerve. (Fostee) ^^^ 38. Manometer Tracing from Rabbit, on Stimulation of the Pneumogas- trie Nerve. (Fosteb) 193 39. Scheme of the Cardiac Nerves in the Rabbit. (Landois) 194 40. Blood-pressure Tracing Obtained by Stimulating the Depressor Nerve in a Rabbit. (Fosteb) ■ 195 41. Weber's Schema 201 42. Marey's Intermittent Afflux Apparatus. (Lahousse) 204 43. Marey's Sphygmograph. (Yeo) 207 44. Tracings Recorded by Marey's Sphygmograph. (Yeo) 208 45. Frog's Web, Highly Magnified. (Yeo, after Huxley) 210 46. Showing the Relative Heights of Blood-pressure in Different Blood- vessels. (Yeo) 213 47. Variations in Pressure. (Landois) 214 48. Manometer of Mercury for Measuring and Registering Blood-pressure. (Yeo) , 216 49. Ludwig's Kymograph. (Yeo) 217 50. Blood-pressure Curve Recorded by the Mercurial Manometer. (Yeo). 218 51. Ludwig's Stromuhr. (Landois) 223 52. Human Respiratory Apparatus. (Duval) 241 53. Termination of a Bronchus in an Alveolus '. 244 54. Diagrammatic Representation of the Action of the Diaphragm. (Bbclabd) 247 55. The Action of the Ribs in Man in Inspiration. (Bbclabd) 248 56. Schema of Action of Intercostal Muscles. (Landois) 249 57. Tracing of a Respiratory Movement. (Fosteb) 251 58. Marey's Tympanum and Lever. (Sandeeson) 252 59. Scheme of Chief Respirotory Nerves. (LANDi)is, after Rutherford) 259 60. Arrest of Respiration in State of Expiration. (Hedon) 260 61. Apparatus for Taking Tracings of the Movements of the Column of Air in Respiration. (Fosteb) 262 62. Tracing of an Experiment with Splenic Extract upon a Dog 284 63. I, Dog. Arrest of Peristalsis by 30 Drops of Adrenalin. II, Dog. ' Arrest of Peristalsis for a Minute and a Half by 20 Drops of Adrenalin Solution 286 64. Dog's Mammary Gland in First Stage of Secretion. (Heidenhain) . . 291 65. Mammary Gland of Dog, Second Stage of Secretion. (Heidenhain).. 292 66. Section of Sweat-glands of Cat. (Colored) 295 67. Relations of the Kidney. (After Sappey) 300 68. Section of Kidney. (Landois) 302 69. Diagram of the Course of Two Uriniferous Tubules. (Landois) 303 70. Bowman's Capsule and Glomerulus, "Rodded Cells" from a Convo- luted Tubule, Cells lining Henle's Looped Tubule, Cells of a Col- lecting Tube, and Section of an Excretory Tube. (Landois) .... 304 71. Blood-vessels and Uriniferous Tubules of the Kidney (Semidiagram- matic) . (Landois) 306 72. Longitudinal Section of a Malpighian Pyramid. (Landois) 307 LIST OF ILLUSTRATIONS. xi FIG. PAGE 73. Uric-Acid Crystals with Amorphous Urates. (PuEDT, after Peyer.) (Colored) 312 74. Leucin in Balls ; Tyrosin in Sheaves. (Peyee) 315 75. Crystals of AmmoBio-magnesium Phosphate. (After Ultzmann) . . 320 76. Crystals of Phenylglucosazone. (Pubdy, after v. Jaksch.) (Colored) 323 77. Human Calorimeter 345 78. Bilateral Puncture of the Tuher Cinereum of Babbit Through Eoof of Mouth 350 79. Cortex of Cat's Brain , 351 80. Lesions of Cortex in Man Causing Elevations of Temperature 352 81. Curves of Temperature and Respiration when Cortex is Removed and the Animal is Artificially Heated 353 82. Curve of Temperature and Respiration when the Tuber Cinereum is Destroyed and the Animal is Artificially Heated 354 83. Heat Production and Heat Dissipation in Man during a Paroxysm of Malao-ial Fever — a Great Increase of Heat Production 355 84. Histology of Muscular Tissue. (ElIaENBERGEr) 3S1 85. Unstriped Muscular Tissue. (Ellenberqee) 368 86. The Pendulum Myograph. (Foster) 374 87. Muscle-curve Obtained by Means of Pendulum Myograph. (Foster). 376 88. Arrangement of Apparatus in Conducting Experiments on Nerve and Muscle. (Stirling) 377 89. Apparatus for Measuring the Velocity of the Wave of Muscular Con- tractions. (Mahey) 378 90. Tracing of a Double Muscle-curve. (Foster) 379 91. Tetanus Produced with the Ordinary Magnetic Interrupter of an Induction Machine. (Foster) 380 92. Muscle Thrown into Tetanus, when the Primary Current of an Induc- tion Machine is Repeatedly Broken at the Rate of Sixteen Times per Second. (Foster) 381 93. The Larynx as Seen with the Laryngoscope. (Landois^ 385 94. Action of the Muscles of the Larynx. (Beaunis) 386 95. Schematic Horizontal Section of Larynx. (Landois) 387 96. Schematic Closure of the Glottis by the Thyro-arytenoid Muscles. (Landois) .' 388 97. Position of Vocal Cords on Uttering a High Note. (Landois) 390 98. The Nerve-muscle Preparation. (Stirling) 395 99. The Structure of Nervous Tissue. (Landois) 399 100. Transverse Section of the Spinal Cord 416 101. Medulla Oblongata, Pons, Cerebellum, and Pes Pedunculi. Anterior View, to Demonstrate Exits of Cranial Nerves. (Edingee) 421 102. The Three Pairs of Cerebellar Peduncles. (After Hirschfeld and Leteill]6) 423 103. Cross-section of the Oblongata through the Decussation of the Pyramids. (After Henle) 427 104. The Base of the Brain. The Left Lobus Temporalis is in Part Repre- sented as Transparent in order that the Entire Course of the Optic Tract might be Seen. (Edingee) 429 xii LIST OF ILLUSTRATIONS. FIG. PAGE 105. The Fillet, Ending Chiefly in the Ventral Nucleus of the Optic Thal- amus and then United by New Neuraxons (Upper Fillet) to Parietal Cortex 434 106. Section through the Cerebral Cortex of a Mammal. (Edingek and Cajal) 437 107. Curves Illustrating the Measurement of the Velocity of a Nervous Impulse (Diagrammatic) . (Foster) 446 108. Scheme of Electrotonic Excitability 447 109. Diagram of the Roots of a Spinal Nerve Showing Effect of Section. (Landois) 454 110. Horizontal Section through the Cerebellum. (After B. Stirling) . . 463 111. Effects of Removal of Cerebellum. (Dalton) 468 112. Left Cerebral Hemisphere in Man, Showing Areas of Localization . . . 470 113. Left Cerebral Hemisphere in Man, Showing Areas of Localization ... 471 114. Effects of Ablation of Cerebrum. (Dalton) 473 115. Structure of the Taste-organs. (Landois) 490 116. Diagram of the External Surface of the Left Tympanic Membrane. (Hensen) 497 117. Tympanic Membrane and Auditory Ossicles, seen from the Tympanic Cavity. (Landois) 498 118. Left Tympammi and Auditory Ossicles. (Landois) 499 119. Scheme of the Organ of Hearing. (Landois) 500 120. Scheme of the Labyrinth and Terminations of the Auditory Nerve. (Landois) 501 121. Section through the Uncoiled Cochlea (I) and through the Terminal Nerve Apparatus of the Cochlea (II). (Munk, after Eensen) . . . 502 122. Section of the Ductus Cochlearis ajnd the Organ of Corti. (After (Landois) - 503 123. I. The Mechanics of the Auditory Ossicles. (After Helmholtz. ) II. Section of the Middle Ear. (Munk, after Hensen) 505 124. Diagram of a Horizontal Section through the Human Eye. (Yeo) . . 510 125. Vertical Section of Human Retina. (Landois) 514 126. Diagram lUusti-ating Spherical Aberrations. (Ganot) 519 127. Scheme of Accommodation for Near and Distant Objects. (Landois, after Helmholtm) 520 128. Myopic Eye. (Landois) 521 129. Hypermetropic Eye. (Landois) 521 130. Different Kinds of Lenses. (Ganot) 522 131. Diagram Showing Refraction by a Double Convex Lens. (Ganot) . . 523 132. Diagram Illustrating the Decomposition of White Light into the Seven Colors of the Spectrum in Passing Through a Priam. (Beclaed) .■ 524 133. Diagram Illustrating Irradiation. (Stirling) 528 134. Diagram Illustrating Binocular Vision. (Beclaed) 528 135. Position of the Nuclei of the Cranial Nerves. (After EdinGiE. } (Colored) 533 136. Human Spermatozoa. (Manton) 549 137. Ovum of Rabbit. (Manton) 55O CHAPTER I. THE CELL. Obsertation and experience tell us that all tangible or material things about us are either dead or alive; that is, matter is either life- less or living. The conception of life in its simplicity is limited to a few ele- mentary phenomena, as nutrition^ evolution, reproduction, sensibility, and motion. These properties taken together distinguish the living from every form of lifeless substance. Combinations of these simple, elementary phenomena give us every complex occupation of our present life. If the study of life is the study of these elementary phenomena, it is necessary that our ■working force be brought to their seat and home — the cell. Everywhere there is a sharp line or division between living and lifeless matters, although the two are frequently so closely allied that first observations seem to show no distinctions. This is particularly true of those things that are not seen with the naked eye — micro- scopical things. When one's attention is brought to such materials as quartz, iron, the earthworm, or the dog, the distinction is very evident. On the other hand, long and tireless observation and investi- gation are required to determine whether some of the bodies found in water are dead or alive. And although so closely associated, scientists have found that living substance never comes of its own accord from the lifeless, but only through the influence of some other living matter. For example, no vegetation springs up from the soil until the seed (a form of dormant life) becomes buried in it; no colony appears for the bacteriologist on the sterilized medium until the surface is impreg- nated with the germ. Although the sharp distinction exists, nevertheless the two mate- rials are very closely associated, as is shown by a little observation. Plants and animals are kept alive and nourished by the food they con- sume, which consists, in the main, of lifeless matter. While in the body it seems to be transformed, as it were, to a living state, as it forms part of the body. After it has served the needs of the economy of the plant or animal it dies, and is gotten rid of as waste-matter. (1) / 2 . PHYSIOLOGY. A living plant or animal is like a fountain into which and out of which material is constantly passing, but the fountain maintains its form and general appearance. Huxley's simile of a whirlpool in a stream is very striking. The pool remains the same in the stream, but water enters it, being part of it as it is being whirled around, and then as it passes out gives place for other water. The pool retains its identity all the while that its elememts are being changed. The contrast between living matter and lifeless matter forms the basis of the separation of the natural sciences into two divisions : the biological and physical sciences, biology dealing with liviag and physics with lifeless matter. Biology is the science that treats of living things, whether animal or vegetable, normal or abnormal. It deals with the forms, structures, and origin, together with the functions and activities of the whole animal or plant or its various parts. In fact, its scope is so wide and comprehensive that it becomes necessary to divide it into two branches : morphology and physiology. Morphology is that part of the science that deals with the form and structure of living things, together with their arrangements. Physiology is the science that treats of the functions or work of the various parts o:^ the liviag organism and what each one does toward the economy of the whole. For instance, the study of the form, growth, and development of the different parts of the brain, beginning with the lamper-eel, then the higher fishes, birds, and mam- mals, belongs to the science of morphology. By the comparisons we see that in the lamper there is merely the semblance of a brain in its crudest form, showing no development as compared with the brain of the higher fishes and birds. In them we notice a stronger develop- ment in one department — ^the optic lobes. The cerebral portion is very weak. In mammals the reverse is true, and reaches its most striking size in man, in whom the cerfebral portions are extremely large and well developed and the optic lobes relatively very small. The study of the functions, for instance, of the heart and kidneys belongs to the science of physiology; how the heart by its alternate contractions and relaxations forces the blood through the circulatory system to the peripheral parts of the body for its sustenance and nutri- tion and to the lungs for its purification by the elimination of the carbonic acid and the absorption of the oxygen; how the kidneys by means of their mass of tubes and cells take from the blood those parts that are no longer of any use and fit only to be expelled from the body. When physiology is applied to man it is called human physiology, for THE CELL. 3 the understanding of the functions of ourselves is the great and ulti- mate end and aim of all physiological studies. Morphology and physiology are treated as though they were absolutely distinct sciences, yet they are so closely related that the division is made only for con- venience. Morphology includes in its category such subdivisions as anatomy, histology, and embryology. Anatomy is the science that treats of the situation, form, and structure of the various parts of the organism. Anatomy from its root keeps in miad the idea of cutting or dissection, and as commonly used at the present time deals with the grosser work done upon the more common and apparent structures. of the body with scalpel and forceps. When we describe in all their detail the different organs of the body and the position of the organs to one another we call it descriptive anatomy. Contrasted with anatomy is histology, sometimes called micro- scopical anatomy. Histology is the science that deals with the inti- mate structure of the various tissues of an organism. It takes up the work where anatomy stops, as it briugs to its aid the microscope and so can delve down deeper and deeper until it gives us knowledge of the component parts of the various organs. Histology is a tissue-study. Its division from anatomy is only one for convenience, and is not absolute. Embryology is the science of the development of the adult from the ovum or germ. It gives a history from the moment of impregna- tion of the ovum, through the various stages of development until the adult is reached. Its field is more closely associated with morphology than physiology. Living things are usually found in separate masses which have peculiarities and structures of their own which give to them the name "organisms." This is true equally of the large masses, as the elephant or whale, as of the small bodies found in water or the bacteria of dis- ease. The structures of the latter have as yet not all been discovered and dissected, as it were, since the microscope is not powerful enough and our supply of reagents not adequate enough to lay bare all of their properties and forms. When we examine some of the contrivances found in the mechan- icEtl world, such as a watch or machine, they at first sight appear to us, as regards their identity, single individual units; that is, one watch or one machine, each capable of doing its own peculiar work. Upon closer investigation we perceive that each is composed of a variety of 4 PHYSIOLOGY. individual parts, each of which has its own peculiar share of the work to do and bears an essential relation to the working of the whole. In the watch, the springs, pinions, levers, and numerous little wheels all bear certain relations to one another and assist in the running of the watch. Similarly we find that it is characteristic of any living body or organism — say, a dog or a rose — that it should be made up of a num- ber of different and distinct parts which are so constructed that they may assist in the life of the whole organism. The animal has a head, trunk, limbs, eyes, ears, etc., externally; heart, lungs, liver, stomach, intestines, brain, etc., internally. To these parts the name organs has been applied. Thus, the organism is composed of distinct parts called organs. The division of the body into organs is purely arti- ficial. An org(f,n is a particular part of the organism that has a certain specified work to do. For example, the liver is a certain structure found in a particular situation in the animal and which has assigned as its share of the work of the general economy the manufacture of the bile to aid digestion. So, also, the eye and the stomach are organs. They are particular parts of the organism concerned in particular work ; the eye in sight, or vision ; the stomach in digestion. The work which any organ does is called its function. Since the appearance and structure of the various organs of a living body are so varied, we do not expect, therefore, that their functions are any more the same than the functions of the watch and locoinotive. Thus, the function of the heart is to pump the blood to all parts of the body, of the blood itself to carry nutritious food to all parts and at the same time carry away certain waste-products, of the kidneys to excrete waste-matters from the blood, the brain to have a general oversight and govern the functions of the whole organism, etc. Anatomy is the forerunner of physiology and must pave the way for it. For how are we to study the functiofis of the various organs and their relations to one another unless we are acquainted with the structure, form, and position in the body of the various organs ? Even while studying physiology anatomy must run hand in hand with it, particularly that modified form of anatomy — histology, or micro- scopical anatomy — which deals with the minute structures and their components — the cells. We have learned that the various portions of the living body are called organs. As we know, each organ has its own particular work to do. By careful dissection, we find that an organza human arm, for THE CELL. 5 instance — is made up of a variety' of substances called tissues. There are bone-tissues, cartilaginous tissues, muscle-tissues, nerve-tissues, etc., all different in structure, yet all bundled up in the member called the arm and essential to it to perform its various functions. The brain is composed of two distinct parts — the gray and white tissues. So, in like manner, any of the organs of the body may be resolved into various parts known as tissues. Thus far anatomy has aided us in our analysis of the various parts of the body, for it has to deal with only the grosser and more coarse and obvious forms of the body. So for a long time physiology was the study of those large and more evident organs. Physiology could not go further until it had more exact and intimate knowledge of the organs. How can we gain correct knowledge of the working of any machine unless we first know and understand the construction of the parts of the machine ? Chemistry and physics teach us that matter is made up of simple forms, called elements and molecules, respectively. It is assumed that the units, ultimately, of these elements and molecules are definite, though exceedingly small, material particles. These particles are called atoms — the word meaning that the particles are unable to be divided without losing their identity. The atom of the chemist and the cell of the phj'siologist are the final divisions of matter. In the physical world it was found that all phenomena were due to the movements of these small particles — the atoms. The fact that animals and plants, although very different ex- ternally, are made up of the same anatomical units was not brought to light until the invention of the microscope. These structural units were called cells. The theory that organisms were made up of cells was suggested by the study of plant-structure. At the end of the seventeenth century scientists, by means of their low-power micro- scopes, discovered in plants small, roomlike spaces, provided with firm walls and filled with fluid. Because of their similarity to the large cells of the honeycomb these small structures received the name of cells. To their minds, however, the principal feature seemed to be the firm walls. By study they found that the cell absorbed nutrient material, assimilated it, and produced new material. Although plants were composed of a mass of cells or even a single cell, it was found that each cell was an isolated whole; that it nourished itself and built itself up. The cell-theory was also applied to animal tissues. By its use it was found that many of the tissues were formed also of cells and that these cells appeared to be of similar construction to those in plant 6 PHYSIOLOGY. life. Thus we find that every tissue is composed of minute parts known as cells and which in a particular tissue are nearly or quite similar. Por instance, in examining a muscular fiber we find that it is composed of very small, ribbonlike units called muscle-cells. Although differing somewhat in size and development, yet they are otherwise similar. That is, muscular tissue is composed of muscular units, or cells. Cartilage is composed of oystershell-shaped cells; mucous- membrane cells are gobletlike, and secrete, or give off, mucus. Even though these cells are self-supporting and grow and form other cells, in the higher animals they are grouped and held together by means of a kind of cement, spoken of as "intercellular material." Hence a tissue may be defined as a group of similar cells having a similar function. Tissues are different only because they are com- Kg. 1.— Vegetable Cell. (Dtjval.) up, CeU-waU of cellulose, n. Nucleus, eft, Chlorophyll bodies. posed of different kinds of cells having functions peculiar to them- selves. An aggregation of cartilage- and muscle- cells give us, respec- tively, cartilage- and muscle- tissues. As the result of this knowledge, physiology is beginning to develop from a science of the organ and its functions to that of the cell and its functions. But this is only natural as a form of development, since we first consider the greater and more active functions of the organs and then delve down deeper and deeper until we reach the functions of the cell. Cells are characterized by the presence of the elementary functions or phenomena of nutrition, growth, reproduction, etc. If physiology has to deal with them, it can do it most successfully by studying them in their seat — the cell. THE CELL. 7 The vegetable cell is known from the animal cell by the presence of cellulose. The cell of the vegetable kingdom takes in oxygen and gives off carbonic acid, as we do, but the action of the sim's rays upon the chlorophyll causes it to break up the carbon, fix it in the tissues, and give off oxygen. This fixation of carbon overshadows ia daylight the ordinary respiration of the plant, which goes on both by day and by night. Yeast-cells break up sugar into alcohol and carbonic acid. . Besides this action they have in them a ferment, invertin, which changes cane-sugar into invert-sugar, which is a mixture of dextrose and laevulose. CELLS. We have learned that the higher forms of life, whether plants or animals, may be resolved into a vast number of very small, structural units, called cells. The skin, muscles, bone, brain, etc., appear to the naked eye to be composed of one kind of substance respectively. The microscope, however, has told us that each tissue is composed of colonies of units, held together by intercellular cement, and that the units or cells of a particular tissue are similar in structure and func- tions. Por example, upon examination we find that muscular tissue is made up of ribbonUke fibers, similar in appearance and structure and all engaged in the same function — contraction. Thus, the cell is not only the unit of structure, but also of function, diseased or normal. Animal cells are of various sizes. Although differing very much in shape and appearance in various parts of the body, nevertheless every cell consists of the following parts : (1) protoplasm, (3) nucleus, (3) centrosomeSj and (4) various matters commonly called "special cell-constituents." Max Schultze's definition of a cell, enlarged by later research, is : "A mass of protoplasm containing a nucleus." The term cell as employed to-day is a misnomer, but from its constant use since the seventeenth century it has gained such a hold upon the minds of those engaged in the study of science that the attempt to supersede it with a more appropriate term has been unsuc- cessful. However, the idea that it originally conveyed has been modi- fied somewhat. The term originated among the botanists of the seventeenth and eighteenth centuries, and was applied to chamberlike elements, separated from one another and containing a fluid. The characteristic and most important feature of them was the wall or 8 PHYSIOLOGY. membrane, and in it were supposed to lie active properties of the cell. The liquid, originally called plant-slime, was named protoplasm by von Mohl, and was thought to be a waste-product. That the wall or membrane was not of vital importance was clearly demonstrated by later researches. The study of the amoeba and white blood-corpuscle, one-celled organisms, was the chief means. These organisms are capable of extending their bodies into processes — fine threads and networks — as they move about from place to place, taking up and giving ofE matter as they go. They possess all the • elementary vital functions, and yet at no time do they possess a cell- membrane, showing that the protoplasm, not the membrane, was the Cell-inenibrane. Reticulnm of cell • | Membrane of nucleus Nuclear achromatic substance Nuclear chromatic substance rig. 2. — Cell with Reticulum of Protoplasm Radially Disposed. Intestinal Epithelium of a Worm. (Caenoy.) From seat of the functions. An immense number of other unicellular organisms was examined, together with the development of other plants and animals, and many cells devoid of a membrane were found. PROTOPLASM. The protoplasm of unicellular organisms appears as a viscid sub- stance, which is almost always colorless and will not mix readily with water. The name of protoplasm is constantly in the mouths of the physiologists, and it is difficult to give a rigid definition of the word, as it is used in so many different senses. Hence, we commonly describe protoplasm as a living substance surrounding a nucleus, which substance may or may not be limited by a cell-wall. THE CELL. 9 Its refractive power is greater than that of water and in it as a medium very delicate threading of protoplasm may be distinguished. It was formerly supposed to be composed of a homogeneous material, destitute of any structure and containing a number of minute granules of a solid nature. Under the high powers of the microscope, when properly stained with reagents, it has been found that the protoplasm consists of two parts : (1) a fine network of fibers, like a sponge, called the reticulum, or spongioplasmj and (3) the more fluid portion in the meshes, called the enchylema, or hyaloplasm. However, it must be mentioned that the views concerning the structure of protoplasm are divided, several theories being offered. According to the first idea, the protoplasm forms the network, the nodal points of which appear as individual granules. It is very probable that many of the larger and more obvious of them are inert bodies, such as glycogen, mucin, fat-globules, albuminous substances, etc., suspended in the network. The glycogen granules are foimd in the liver-cells, the fat-globules in the cells of the lacteal glands, and the pigment-granules in the skin-cells of many colored animals. Sometimes in unicellular animals are found cal- careous matters, although those most uniformly found are of the same general nature as the protoplasm. All these particles or granules are termed microsomes. Besides, there are occasionally found indigestible bodies, such as grains of sand, indigestible residue of foodstuffs and excretory substances, waiting to be expelled from the body. Other substances found within the protoplasm and supposed to be of great importance to cell-life are drops of liquid — vacuoles, as they are commonly called. Specific Gravity of Living Protoplasm. Living protoplasm has the physical property of having a greater specific gravity than water. When cells of the most varied kinds are allowed to fall into water they sink to the bottom. In some cases the protoplasm contains a considerable quantity of fat; so that, although the substratum of protoplasm is heavier than water, the floating of the cell is due to the lighter specific gravity of the fat-particles overcom- ing the heavier specific gravity of the protoplasm. The chemical composition of protoplasm (a living substance) can be obtained only after it has been killed. However paradoxical this may seem, it is found impossible to apply the methods of chemistry without killing it. Every reagent that comes in contact with it dis- turbs and changes it and eventually kills it. Thus, our ideas of the 10 PHYSIOLOGY. chemical composition of living protoplasm are the ideas we get from the chemical composition of dead protoplasm. The substances of which it is composed are : — 1. Water. — ^Water is that element in living substance that gives it its liquid nature, allowing its particles to move about with a certain degree of freedom. In the cell, water occurs, either chemically com- bined with other constituents or in the free state. Salts occur dis- solved in the water. Protoplasm is semifluid, and about three-fourths of its weight is due to water. The molecules of protoplasm are thought to be separated from one another by layers of water. 2. Proteids. — The proteids take a very active and essential part in the functions of all cells. The proteids consist of the elements carbon, hydrogen, sulphur, nitrogen, and oxygen. Proteids occur both in the protoplasm and in the nucleus, but with this difference : that found in the nucleus has combined with it phosphoric acid, forming the so-called nucleins. To show this fact is very easy, for the nuclein of cells resists the action of digestion by the gastric juice. All kinds of cells in artificial gastric juice have their protoplasm digested and only the nuclei remain; that is, nuclein. If, now, this nucleus is treated with stains, it shows that the nuclear bodies consist of nuclein, while the protoplasm of the cell is constructed from other albuminous bodies. Protoplasm is composed principally, then, of simple proteids and compound proteids that lack phosphorus. Our most common and typical type of an albuminous substance, or proteid, is the white of an egg. This contains 12 per cent, of actual proteid substance, the remainder being chiefly water. The albumins are the only bodies that can safely be said to be found in all cells. Although the albumins contain only five elements, — C, H, N, S, and 0, — yet the number of their atoms often exceeds a thousand. 3. Various Other Substances occur in smaller proportions as car- lohydrates; as glycogen in protoplasm of liver-cells; fats, seen in protoplasm as fats or oil-drops ; and simpler substances which are the result of decomposition of the, proteids or are concerned in its forma- tion. Also, inorganic salts, such as phosphates, and chlorides of cal- cium, sodium, and potassium. NUCLEUS. Prom an examination of the protoplasm we pass on to the nucleus. As we have said before, "a cell is a mass of protoplasm containing a nucleus." Various properties and functions of an important nature THE CELL. 11 have been assigned to protoplasm, but it is found that the nucleus is equally as important. The classical experiments of the old observers upon protoplasm gave them the belief that the protoplasm was the embodiment of all the functions of life. To them the nucleus was unessential as regards the activities of life. The ruling power of the protoplasm was dismissed when it was found that the nucleus in repro- duction of cells by division or impregnation underwent extraordinary changes, while the protoplasm remained passive and quiet. Within recent years there has set in a reaction, and the happy mean 'twixt the two extremes is now held to be correct: the two are of equal importance. By extended research and with staining reagents such as carmin, hsematoxylin, etc., a distinct nucleus was found imbedded in the pro- toplasm of most animal cells. For a long time, and until the micro- scope was greatly improved, two classes of organisms appeared to be the. exceptions. They were : monera, the lowest and simplest organ- isms, and bacteria. Gradually the number of each class was reduced until at the present day it may safely be said that every cell contains a distinct nucleus. Every cell may thus be said to be characterized by two general cell-constituents, protoplasm, and at least one nucleus, sometimes more. The form of the nucleus is different in various cells. Usually it is a round or oval body situated in the middle of the cell. Its rounded form is considerably expanded in young cells, as the ovaries in their evolution. Very frequently the form of the element influences that of the nucleus. Thus, in muscle- and nerve- cells the nucleus is generally elongated. In the lower organisms it sometimes assumes the shape of a horseshoe or a twisted strand, or is very much branched, the processes running out in every direction into the surrounding proto- plasm. The size of the nucleus is usually in proportion to the mass of protoplasm enveloping it. Thus, in the large ganglion-cells of the spinal cord the nuclei are correspondingly large. Also in cells en- gaged in active work the nuclei are generally of good size, as the secreting cells of the salivary and mucous glands. As to the number of nuclei present in a cell the general condition seems to prevail of the presence of but one in a cell. There are excep- tions, however, as liver-cells "very frequently contain two, and the immense cells of bone-marrow many. 13 PHYSIOLOGY. General Substance, or Structure. The nucleus is no more of a homogeneous nature than the proto- plasm and presents several distinct substances and structures. The different constituents that are known are not always present in all cells at all times or in the same proportions. Among some cells one element may be very conspicuous, while in some others it is scarcely to be found. According to Verworn, the following substances occur most constantly: (1) nuclear sap, (2) achromatic nuclear substance, (3) chromatic nuclear substance, and (4) the nucleolus. The nuclear sap may be present in large or smaller quantities and is the liquid ground-substance which fills up the interstices left among the solid nuclear constituents. In many cells under the influence of certain reagents and even in life it is known to be of a very fine granular nature. The achromatic nuclear substance is a structure of fine threads found in the nuclear sap and is characterized, as is also the latter, by not staining with the usual reagents : carmin, heematoxylin, etc. It contains aehromatin. The chromatic nuclear substance, as its name implies, has an affinity for coloring-matter in the form of different stains, li is usually in the form of a continuous network, but sometimes appears in small granules, or particles. It contains chromatin. t The nucleolus, if it appears at all, is found in the network of the nucleus as a rounded or irregularly shaped body. It contains para- nuclein and has an especial afBnity for color and stains more deeply than the network. The nucleoli are thought to be passive bodies that hold in reserve different constituents which are essential to the life of the nucleus. Sometimes the nucleus is enveloped in a membrane, called the nuclear membrane, which marks it distinctly from the protoplasm. This, however, as with the cell-membrane, is not universal and is not classed as a general constituent of the nucleus. The sharpness of the contour which distinguishes the nucleus in the midst of protoplasm led many histologists firmly to believe that the nucleus always does possess a membrane. The truth is between the two extreme opinions. The nucleus can very readily exist without one. A portion of a cell deprived of its nucleus may live for a time, but it evinces no activities or functions other than that of movement. It neither absorbs food nor grows or reproduces, but seems gradually to dwindle away and die. From this it is believed that the nucleus exer- THE CELL. 13 cises some powers with regard to the building up or constructive meta- morphosis. Eegarded chemically, the nucleus is composed principally of proteid and a substance like proteid which contains as much as 10 per cent, of phosphorus. No doubt there are others, but even the most delicate chemical reagents kill the constituents and so lessen the oppor- tunities for careful investigation. CENTROSOME. About twenty years ago, when nuclear cell-division was being investigated, a small body other than the nucleus was noticed during the division of the cell and which was called by various names : polar corpuscle^ central corpuscle, or centrosome. The last name seems to be more generally used at the present time. The centrosome in its simplest form is a body of extreme minute- ness, frequently not larger than a microsome, but which exerts an active influence on the protoplasmic structure during cell-division. Because of its influence in the cell it has aroused more interest among investigators than any other component of the cell. By some it is considered to be a part of the nucleus and by others of the proto- plasm. As a rule, it lies in the protoplasm just outside of the nucleus, even during the resting stage, and in certain conditions of the cell is clearly indicated by a radiation of protoplasm, the fibers of which are arranged in the form of a star, the centrosome being at the center. In size the centrosome ranges between that of the ordinary micro- some and the smallest micro-organism. No structure has been as yet discovered in it. It cannot be classed as a general cell-constituent, since many forms of the cell and unicellular organisms have been examined and no centrosome found, due probably to the inadequacy of the microscope. The centrosome does not absorb the ordinary stains suitable for the nucleus, but requires acid aniline dyes, as acid fuchsin and orange. By them it is colored vividly. As a rule, there is one centrosome in a cell, lying close to the nucleus and surrounded by a raylike or rodlike structure of the proto- plasm. As the cell prepares for division, the centrosome divides into two distinct parts, both lying passively within the starlike network. When the daughter-cells are examined each is found to possess one of the centrosomes, which, as the cell grows, passes through the same process as its antecedents. The centrosome is regarded as the par- ticular organ of cell-division. 14: PHYSIOLOGY. PROTOPLASMIC MOVEMENT. The movements of protoplasm are movements in currents and the amoeboid movement. In certaia vegetable cells protoplasm moves and causes a true rotation of its substance, as in ehara; or the move- ment may be ia opposite direction and the paths even cross over each other. In this movement all parts of the protoplasm do not move with the same rapidity. The rate iu protoplasm is about Vbo i^^^ per minute. Movements differ according to whether the protoplasm is naked — without any enveloping membrane — or inclosed within a firm wall, or membrane. rig. 3. — Amoeba Proteus. (Leidt.) n. Nucleus, ov. Contractile vacuole. N, Food-vacuoles. en, Eudoplasm. ek. Ectoplasm. 1. Movement of the Naked Protoplasm. Probably our most common and typical form of naked protoplasm is presented to us by the fresh-water amosia^ found in stagnant water. The amoeba is a unicellular organism, about Viooo ^^^ in diameter, possessing one or more nuclei, and which is almost continually in motion, due to its extending numerous protoplasmic projections, called pseudopodia (false feet) . It then rolls its entire mass into the pseudo- podium, or fingerlike projection, only to continue the same operation repeatedly during its life. The pseudopodia assume different forms and shapes in the differ- ent kiuds of cells, and iu this way the identity of a cell is frequently THE CELL. 15 aided by an observation of the processes. For example, most of the fresh-water amoeba possess broad, lobate or finger-shaped pseudopodia ; leucocytes, white blood-corpuscles, divided and pointed pseudopodia; some of the rhizopods and pigment-cells, threadlike and reticular pseudopodia which flow into one another. In the human body some of the cells — such as white blood- corpuscles, lymph-corpuscles and connective-tissue cells — ^possess move- ments, which, because of their likeness to those of the amoeba, are called amaboid. 2. Ciliary Movement. There have been discovered cells and unicellular organisms which possess delicate, hairlike processes which extend in greater or less numbers from their surfaces. They are called flagella, or dlia. These resemble very thin pseudopodia when they are composed of hyaloplasm alone, as the cilia and flagella are homogeneous and nongranular in nature. However, they differ from pseudopodia in that their movements are very energetic and always definite, and also that, unlike pseudopodia, their structures are not temporary, but permanent, beiug neither protruded nor withdrawn. The ciliary cells lining the trachea are subjects for exanunation. The deep back part of the throat of a frog is gently scraped and the scrapings placed upon a warm stage ia a drop of water. When we examine the cells under the microscope we see upon their surface a constant rapid movement, but the movement is so rapid that we see only the motion, and not the vibrating cilia. If, however, the vibrations be lowered to about a dozen per second, we are then able to see the cilia themselves. Ciliary movements are of various kinds. Most often it is a movement of elevation and depression of the cilia ; some- times it is like the extension and flexion of our fingers, at other times a sort of wave or whirlpool-like movement. In these movements all the cilia on the surface move m. the same direction like a field of grain before the wind. Bach completed movement of the cilia is composed of two movements of unequal duration, the longer correspondiug to contraction and the shorter to relaxation of the cilia. Ciliary move- ments may be of a high rapidity, as many as 960 to about 1000 per minute, and entirely independent of the circulation and the nervous system. These movements are able to continue after death as long as a day, while in frogs they have been observed for many days. Cilia are about Vsooo i^^h in length and are able to perform some work. By their movements they are able to float a cell in a liquid. 16 PHYSIOLOGY. such as water, even though the cell and the cilia are composed, in a great part, of protoplasm, whose specific gravity is heavier than water and naturally inclined to sink, and at the same time they propel the cell in some definite direction at a much faster speed than that obtained by the protrusion and retraction of pseudopodia. The func- tion of the ciliated cells does not appear to be of any particular importance in man except that in the trachea their movements bring to the larynx foreign substances that have been inhaled into the lungs, such as dust, etc., and to bring up for expectoration the thickened mucus that is formed during the stages of a cold. A practical illustration of the effects of the protoplasmic move- ments of leucocytes (white blood-corpuscles) can be observed when an injury occurs to any part of the body. As a result of the injury and as an attempt at repair, more blood is sent to the injured part. This, called congestion, gives to it its red color. With the additional quantity of blood comes an additional number of leucocytes. They by protoplasmic movements, pass through the walls of the capillaries to the seat of the injury to take up dead portions. Sometimes bac- teria lodge in the wound, which the leucocytes approach and kill by ii^gestion, as it were, thus rendering them harmless. This process of ingesting bacteria and other foreign substances is called phagocytosis, and hence the leucocytes are sometimes termed phagocytes. Chemotaxis is the phenomenon of a leucocyte in active movement, which by one-sided action of the chemical products of bacteria, as toxins, moves toward (positive) or away (negative) from the bacteria. CELL=DIVISION. We have learned that organs are composed of various structures, called tissues. A tissue may be defined as "a group of similar cells having a similar function." Por example, muscular tissue is made up of ribbonlike muscle-cells; mucous tissue of secreting, goblet-shaped cells; nervous tissue of ganglion-cells, with their numerous • projecting dendrons, etc. By observation we notice a variety of tissues due to a diversity of •kinds of cells; also that all tissues of a kind are not necessarily of the same bulk, size, or weight. The chick shortly after its exit from the shell contains in its body a number of organs of a definite size and consistency. It has a head, limbs, muscles, heart, lungs, intestines, liver, etc. We see that these organs, of course, are of a size and weight in proportion to its THE CELL. 17 age — none of them large or heavy. Upon examination; the tissues of the various organs would be found to be composed of cells such as we would expect them to contain ; that is, the muscles of muscle-cells, the bones of osseous cells, the brain of gangUon-ceUs, etc. Further- more, although cells are of different sizes and forms, yet there is very little difference between the cells of a particular tissue as compared with one another or with those of the adult animal in respect to size, for the size of every cell is definite. When we observe the same animal one year from its birth, we notice some striking differences: it is much larger and heavier, the various organs are fuller, more compact, and show the effects of the development which took place as it approached maturity. The head, brain, muscles, heart, lungs, intestines, etc., are all much larger and better developed than those found in the small chick. However, if a microscopical examination be made of the various tissues in this, the adult animal, what do we find and how do the cells compare with those of the chick? Nothing remarkable in the iadividual cells themselves. The liver-cells of the adult are no larger than those of the chick, nor the ganglion-, muscle-, or other cells. What we do perceive is a great increase in the number of the cells in any particular tissue. The liver and brain of the adult animal contain many more cells than the same respective organs of the chick. Thus we see that there has been a growth due, not to larger cells, but a greater number of cells. That is, the cells have multiplied. Similarly, as the infant passes through the various stages of boy- hood, youth, and manhood, we say that he grows, for there is an increase in the size and weight of the various organs of his body. This means that there is a greater number of cells composing the tissues of his various organs. The power to multiply — that is, producing new forms similar to itself — is one of the most important and characteristic functions of the cell. By this attribute it not only is able to maintain its own particular kind or species, but also can undergo constructive metamorphosis: building up or growing until any part or organ is matured. A cell multiplies by dividing into two or more parts. Each part is, of course, smaller than the original or mother-cell, but by assimilat- ing nutrient material from the surrounding tissues it grows until each part is the size of the mother-cell, when it also is r^ady for division, or reproduction. No cell exists but that had its origin in some pre-existing cell. In animals whose tissues are composed of many cells those same tissues 18 PHYSIOLOGY. can be traced back to single cells of which they are developments. The animal itself, with all its many and various parts and structures, originated from a single cell, the germ-cell, or ovum, which is also part of a cell having existed in the parent-body. Schleiden, the botanist and accredited discoverer of the cell- theory among plants, and Schwann, to whom Schleiden confided his views and ideas of plant-structure and who then reduced animal tissues to their structural units, the cells, were anxious to know the origin of the cells. To them the presence of the nucleus was known and even the nucleolus, but their instruments were not powerful enough to allow of their penetrating deeper and getting the correct ideas of cell-division. It was proved in 1858 that cells multiplied as a result of the divi- sion of the two equally essential parts of the cell, the nucleus and protoplasm. Our present conception that the two are of equal im- portance and value dates from this time. It was asserted that the division began within and proceeded to the outer parts of the cell. That is, the nucleolus was divided, its division was followed by separa- tion of the nucleus, and this in turn followed by constriction and division of the protoplasm with its enveloping membrane. These views were confirmed by Virchow, who formulated the doctrine "Omnis cellula 6 cellula" (every cell from a cell). Later it was discovered by the investigation of some of the tissue-cells that the process of division was not so simple as expected. In some cases it was found that the nucleus became star-shaped, or lobed, or even seemed to disappear altogether before cell-division. A few years later it was seen that the process of division was complicated in the extreme and that the cell-nucleus underwent a variety of trans- formations, assuming different shapes and figures until two daughter- cells were formed from the mother-cell. This process was afterward named haryoMnesis. By experiment it was denionstrated that, if a cell in a living organism or tissue was so divided that one of the parts was composed of protoplasm only, none of the nucleus being present, the protoplasmic part continued to live for a considerable time, but that, of the vital phenomena exhibited by the normal cell, it possessed only that of movement. It was unable to take up from the surrounding tissues a proper amount of nutrition and that growth and reproduction never occurred. After a time it died. Thus it was concerned only in destructive, not constructive, metamorphosis. It was totally unable to build itself up, grow, and reproduce others of its species. On the THE CELL. 19 other hand, the part containing the nucleus grew and reproduced its kind, forming daughter-cells, who in turn formed other cells, etc. Thus, in order that the daughter-cells may possess the same properties, form, and functions of the mother-cell, — in fact, in order that it may live^ — it becomes necessary in the division that both the nucleus and the protoplasm must divide. The disposition of any cell to divide or reproduce is usually announced by changes in its nucleus, both physical and chemical. In fact, the division of any cell is pre- ceded by division of the nucleus. This process in the cells of most organisms is very complicated, whereas the division of the protoplasm is most simple, consisting of the appearance of a constriction, which becomes deeper and deeper, forming a groove, or fissure, until event- ually the mass is divided into two parts. The evident importance of the relation of the nucleus to cell- division has led to extended study of the nucleus and its transforma- tions during the process of reproduction, with the result that upon its functions in this respect three forms of division are recognized: (1) direct cell-division, (2) indirect cell-division, and (3) endogenous nuclear multiplication. 1. Direct Cell-division (Amitosis). Direct cell-division is very rare and present in only some of the unicellular organisms and leucocytes. In pathological formations, however, such as tumors, this form of division occurs very frequently. To get a better conception of the direct form of division we will study one of the infusorians, the tjrpical amoeba, and the changes occurring in it during reproduction. The first intimation of a division is noted in the spherical nucleus, which becomes elongated, the middle por- tion of it being indented by a constriction which gives to the nucleus a dumb-bell shape. The constricted portion becomes gradually nar- rower and slenderer until the two heads of the ball separate and each assumes the same shape as its mother — spherical. The cell thus contains two distinct nuclei. Following the division of the nucleus is that of the protoplasm by constriction also. The indentation always appears between the two nuclei. Eventually two cells are thus formed, each with a separate nucleus; each daughter-cell is, of course, smaller than its mother, but by the assimilation of the nutrient material sur- rounding it it soon grows to the normal, definite size. This process often requires several hours for its completion, the various stages fre- quently being accomplished in an uncertain manner. 20 PHYSIOLOGY. 2. Indirect CelI=division (Mitosis, or Karyolcinesis). By far the greater mimber of animal and plant- cells folbw the more complicated and intricate method of indirect, or karyolcinetic, form of division. The division of the protoplasm is simple enough, following only the laws of constriction until the mass is completely separated into two parts by means of a furrow, or fissure. It is the nucleus which undergoes very remarkable and typical changes, very complicated in their nature, but which in plants and animals are con- stant and agree very much in regard to essentials. Thus the indirect method is very nearly, though not quite, universal. As a cell prepares for division the most evident and important fact noticed is a change in its nucleus, both physical and chemical. The nucleus becomes somewhat enlarged and its chromatic nuclear substance, or chromoplasm, — so called because it has an affinity for stains, — ^begins to become changed little by little from the netlike arrangements of its minute granules and particles until the substance is arranged in the form of threads loosely rolled up, like a coil or convolution, called the shein, or spirem. These consist principally of nuclein, and stain more deeply than the surrounding parts, and are, hence, more easily discerned. It is the presence of these threads that gives to the process the name mitosis. In most cases there is but a single thread that is coiled or convoluted throughout its entire length; occasionally there occur several such threads. The threads are somewhat thicker than before and more separated than during the resting stage. With the formation of the spirem, or wreath, the nucleoli and membrane, if any, disappear. In some cases the nucleoli are dissolved and cast into the hyaloplasm, where they degenerate and have no further function. The thread of the spirem becomes divided transversely into nearly equal parts, or bodies, known as chromosomes, which i^ most cases are in the form of rods, straight or curved. The ground- substance of the nucleus now becomes a part of the surrounding hyal- oplasm. The chromosomes at first are placed rather irregularly, but they soon begin to arrange themselves into a more definite form, that of a rosette. The curved chromosomes now become more angular and V-shaped, the angle pointing toward the center of the nuclear space while the free ends are directed toward the circumference, this figure being called the aster, or garland. While in the form of the aster each chromosome splits longitudinally into halves, so that we have just again as many, though thinner, chromosomes. THE CELL. 21 Before the membrane has been dissolved there appear in the pro- toplasm, but very near the nuclear membrane, two small granules lying side by side. These are the centrosomes. They are of a sub- stance that stains with difficulty. Gradually they begin to separate from one another, moving in a semicircle, until they are diametrically opposite one another, or at the nuclear poles. As they have been in motion the nuclear membrane has been dissolving, so that by the time they are again at rest the membrane has disappeared. The achromatic nuclear spindle develops between the centrosomes. When they begin to separate the spindle is small, scarcely discernible, and like a band ia form. As the centrosomes separate more, the fibers become more plainly visible and assume the form of a spindle — ^broad in the middle and converging at either end, toward and ending in the centrosomes. The protoplasm now arranges itself around the centrosomes in the form of rays as a star, as though the filaments of protoplasm were attracted by the centrosomes in the manner of iron filings by a magnet. At first these fibers are small, but increase in length and numbers as the division of the cell progress.es until they run throughout the entire protoplasmic mass. The V-shaped filaments, called chromosomes, are now collected in the plane of the equator, called the equatorial plate. While the chromosomes have been arranging themselves in the plane of this plate, they have been growing somewhat shorter and thicker, their angles pointing to the axis of the spindle and their ends to the cir- cumference. By the contraction of the spindle fibers the daughter- chromosomes (the result of the original chromosomes being divided longitudinally into two separate halves by means of fission) are divided iato two equal groups, which are moved toward the poLats, or poles, of the spindle, but never reach it absolutely. Between these groups fine "connecting fibrils" stretch. This figure is called the double star, or diaster. The star shape is formed by the angles of the chromosomes being arranged next to the centrosomes with their free ends extending out radially. There now follows a retransforming of the daughter-chromosomes arranged in the form of a star into a genuine resting nucleus. The angles begin to disappear, the threads draw more closely to one an- other, becoming more bent and roughened at the same time that little processes appear on their surfaces. A very delicate nuclear membrane develops and surrounds the group of threads. The radiating fibers of protoplasm around the centrosomes become more and more indis- tinct until they finally disappear. The same thing occurs with the "connecting fibrils." 22 PHYSIOLOGY. When the two daughter-stars were separated as far as possible there appeared on the surface of the cell-body a fissure, cutting into the protoplasm in the line of the equatorial plate, until the cell was completely divided into two parts, each containing a nucleus. The duration of this process has been seen to take place in man in half an hour, while in the larvm of the salamander it has been known to take as long as -five hours. The difEerent stages are very neatly and correctly summarized and tabulated as they appear in Quain's "Anatomy" : — Network, or reticulum 1. Resting condition of mother -nucleus. C 2. Close skein of fine convoluted filaments. Skein, or splrem J 3. Open skein of thicker filaments. Spindle 1 appears. C 4. Movement of V-shaped chromosomes to Cleavage J middle of nucleus, and each splits into I ' two sister-threads. i equator Of spindle. 6. Separation of cleft filaments and move- ,5. Stellate arransement of V filaments at Star, or monaster. ' Divergence, or metakinesis . . J ('■ ment along fibers of spindle. Convergence of V filaments toward poles Double star, or diaster » , ... ' of spindle. _ , , , . ... f 8. Open skein in daughter-nuclei. Double skein, or dispirem ... J „ _, , . . , , . 19. Close skein m daughter-nuclei. Network, or reticulum 10. B-esting condition of daughter-nuclei. 3. Endogenous Nuclear Multiplication. A third rare mode of nuclear multiplication, to which is given the above-named title, was discovered in the thalassicola. The thalassicola, which is the largest in size of the radiolarians and the diameter of whoge central capsule is nearly equal to that of the frog's egg, has durjng the major portion of its life one single, highly differentiated, giant nucleus, called the internal vesicle. This nucleus, or internal vesicle, usually attains to ^/^^ inch in diameter, and possesses a thieji:, porous, nuclear membrane. It is very similar to the multinucleated germinal vesicle of the ovum of an amphibian. Simultaneously with the advent of the centrosome into the proto- plasm there appeared in the latter, which heretofore has been entirely free and clear, a large number of very small nuclei. These act as centers, arounij each one of which there develop nucleated zoospores. THE CELL. 23 which may amount finally to as many as some hundreds of thousands of separate cells. Fatigue of Cells. — Hodge, of Clark University, has found changes in the cell corresponding to rest or activity. Thus the nerve-cell in the morning has a clear, round nucleus, while in the evening, beiag tired from work, the nucleus has an irregular contour. LiTERATUBE CONStTLTBD. Verworn, "General Physiology," 1899. Hertwig, " The Cell," 1895. CHAPTER II. (a) CHEMICAL CONSTITUENTS OF BODY AND FOOD. (b) ALIMENTARY SUBSTANCES. Digestion' has been described as the physical and chemical altera- tion of the foodstuffs into forms better fitted for absorption by the action of certain soluble ferments, the digestive enzymes. The animal organism had its birth in a single ovum or cell, which, under certain favoring circumstances and conditions, developed into a mass of simple cells. As development proceeded this aggregation became differentiated into tissues by the grouping of the cells, altered by chemical changes in the substance of the cells themselves, by altera- tions in their shapes, and by deposits of intercellular substances. As the organism continued to grow, the various parts became more and more complex by use and development until it presented a highly com- plex unit. In the metabolism of the cell it was learned that the various cells while performing their various vital phenomena must constantly maiatain a very nice balance in respect to waste and repair. That is, the various kinds of cells took out from their environments those sub- stances that were necessary for their economy to build themselves up and grow, while the waste-products were excreted. A distinctive property of the cells was the selective power exercised in regard to different nutrient materials with which they came into contact. Al- though the surrounding media might contain many kinds of food, yet cells of a particular kind took only that for themselves which was best adapted to their wants, disregarding entirely all the others. As there was a great variety of cells, there must necessarily be a corresponding variety of foodstuffs. What is true of the cells is true of that of which they are but components or units: the body. Among the phenomena produced by the waste of the solid constituents of the body and the loss of the fluid or watery parts of the tfesues are the sensations of hunger and thirst. These sensations of appetite excite the desire to take food, which by the processes of digestion is prepared for absorption and cir- culation in the blood to supply the various needs of the organism. The term food includes all those substances received into the (34) CHEMICAL CONSTITUENTS OP BODY AND FOOD. 85 alimentary canal and used for the support of life by supplying the waste continually occurring in the living animal tissues, and also weight, heat, and energy. Food contains substances that have a cer- tain chemical relation to the tissues which it supports. The substances out of which the complex adult tissues are constructed or built up are chemical elements^ chemical compounds, or unions of these elements. The food taken in by the animal consists of the same or similar com- position, in its nature very complex. Animals are either carnivorous or herbivorous. The carnivora, or flesh-eating species, consume food possessing apparently the same chemical components as the tissues and fluids of their own bodies. The food of the herbivora, or vegetable-eating species, contains principles resembling very closely those found in the animal body. No matter what the source or nature of the food for animals might be, their chemical constituents or principles are similar, since it is through the agency of the vegetable kingdom with the aid of light and heat from the sun that the simpler combinations of inorganic nature are woven together and elaborated to form the complex organisms in the shape of plants and vegetables. Thus, the animal kingdom is dependent on the vegetable for its existence, as nimierous experiments have proven that the animal organism does not possess the power to any great extent of constructing complex from simple materials. Yet complex foods it must have to supply its own complex constituents. However, it is also necessary that the food should possess, besides the complex constituents, a proper proportion of the various principles, and these must be in a digestible form. It is well known that beans, peas, and other vegetables contain a very considerable percentage of proteid, but it is in such indigestible form that much of it passes off in the faeces. The various digestive juices had been unable properly to dissolve their nutritious elements. Of the 74 elements known to the chemist, but 20 are found in the body. They are: carbon, hydrogen, nitrogen, oxygen, sulphur, phos- phorus, fluorin, chlorine, iodine, silicon, sodium, potassium, calcium, magnesium, lithium, iron, and occasionally manganese, copper, and lead. These elements are rarely foimd in the free state, being usually in the form of compounds. The compounds, or, as they ate sometimes termed, proximate prindpleSj are divided into: (1) mineral, or inorganic, compounds; (2) organic compounds, or compounds of carbon. The organic com- pounds may again be divided very conveniently into two groups : the nitrogenous and nonnitrogenous. 26 PHYSIOLOGY. The inorganic compounds are water; the various acids, such as the hydrochloric acid of the gastric juice; and numerous salts. Since the proximate principles of both food and the body are the same, mention of them will be known to refer to both. A very con- venient method of grouping the principles of both food and the body is that by Halliburton, as follows : — f Water. Inorganic -i ^^^g^ ^^ chlorides and phosphates of sodium and calcium. r Proteids: albumin, myosin, etc. Nitrogenous... J Alhuminoids : gelatin, keratin, etc. I Simpler nitrogenous bodies: lecithin, urea, etc. r Fats: butter, adipose tissue. Nonnitrogenous J Carbohydrates: sugar, starch. 1 Simple organic bodies: alcohol, lactic acid. Although all of these elements are present, yet not all are of equal importance or occur in the same proportions. Among the inor- ganic group, water and salts are prominent; among the organic, carbo- hydrates, fats, and proteids. WATER. Water forms more than one-half of the body-weight. The value of water to the economy can be readily appreciated by the student when he considers that the various processes and stages of digestion, absorption, and assimilation are dependent upon hydration and dehy- dration. About fifty ounces of urine are excreted daily, this being the main avenue for the escape of watery elements from the body. In addition, considerable water is given ofE by the skin as sensible and insensible perspiration, while expired air is heavily laden with moisture. With so much water making its escape from the body, at least as much must find its way into the economy. About two and a half quarts of water are ingested daily as food. The water we drink ought to be fresh, limpid, without smell, and of an agreeable taste. When complete and exact analysis is impossible, the taste is the only safe criterion or judge as to its fitness. Drinking-water should always con- tain a certain percentage of air. The palatability is due to the pres- ence of carbonic acid gas in the water. Besides gaseous constituents, solid substances are also present. These are both mineral and or- ganic, and should be present in but very small amount. Somewhat more water is excreted daily than is ingested, since some water is formed in the tissues by the oxidation of hydrogen. CHEMICAL CONSTITUENTS OF BODY AND FOOD. 37 SALTS. The most important salts found are the sulphates and chlorides of sodium; the phosphates of sodium, potassium, calcium, and mag- nesium ; and the carbonates of sodium and calcium. Of these various salts, sodium chloride is the most important and the most common one found. In the fluids — ^blood, serum, lymph, and urine — ^this salt is high in percentage. While in the body it favors absorption by increasing the endosmosis of the tissues and so aids metabolic processes, the absence of sodium chloride for an extended time causes disturbances and disorders in the constitution. There are about 3000 grains of common salt present in the body. About 325 grains are excreted daily in the urine, while some finds its exit as a component of the faeces, sweat, and tears. A practical illustration of its value to animal life may be gained by noticing how wild animals repair to the so-called "salt-licks" at various times, traveling for many miles to procure it. Calcium phosphate is a very prominent factor of the mineral solids of the body. It forms about one-half of the bony skeleton, where it is most abundant, although it occurs to some extent in all other solids and fluids. This salt is particularly conspicuous in milk. Iron is an important element of hasmoglobin. It is this iron in the red blood-corpuscles that is the means of holding the oxygen without being itself oxidized. A want of it causes the pathological condition called anemia. In the blood of an adult are found forty- five grains. In small proportions it is found in the liquids of the body, — as the chyle, lymph, bile, urine, etc., — in the fseces, and traces in the liver and spleen. CARBOHYDRATES. The carbohydrates are found principally in the vegetable king- dom. They are, however, not indigenous to the vegetable kingdom, but are found and formed in animal tissues; notably, glycogen, or animal starch ; dextrose ; and lactose, or milk-sugar. For the sake of a clearer conception of the term carbohydrate the components of the name are used when it is defined as a compound of carbon, hydrogen, and oxygen, the last two in the proportion occurring in the formation of water, two to one. The carbohydrates are: — Glucoses (CaHjjOj), or monosaccharides. Saccharoses (CisHojOn), or disaccharides. Amyloses (C|,HioOj)„ or polysaccharides. 28 PHYSIOLOGY. The Glucoses are glucose; dextrose, or grape-sugar; laevulose, and galactose. The glucoses have three properties which are im- portant for the physiologist to know: physical, chemical, and bio- logical. From the fact that it deviates the plane of polarization to the right, its physical property is demonstrated, whence its name, dextrose. Its chemical property is the reducing of certain metallic salts in the presence of alkalies. Biologically, it ferments under the influence of yeast to form carbonic acid and ethylie alcohol. Saccharoses. — The saccharoses are saccharose, or cane-sugar ; lac- tose, or milk-sugar ; and maltose. When saccharose, or cane-sugar, is boiled with a dilute mineral acid, the right-handed polarizing solution of saccharose is transformed into invert-sugar, or is said to be inverted. Invert-sugar is a mixture of equal weights of glucose, a right-handed polarizing agent, and IsBvulose, which is a left-handed polarizing body. The saccharoses do not reduce the copper salts. The saccharoses are not directly fermentable by yeast except in this way: (1) when yeast is added the saccharoses take up water and the soluble ferment of yeast, invertin, changes the saccharoses into glucose and lEevulose; then (2) the vital fermentation of the glucose and Isevulose by the yeast-cell. Lactose, or sugar of milk, is a right-handed polarizing sugar. It reduces the copper salts, but is not fermentable either directly or in- directly by the yeast-ferment. Lactose ferments in the presence of the lactic acid bacillus to form lactic acid. Maltose is a right-handed polarizing sugar, reduces copper salts, and ferments by yeast. Maltose has the same properties as glucose, but is distinguished in two ways: (1) the light-rotating power of glucose is 56 degrees, while maltose is 150 degrees; (2) the reducing of metallic salts by glucose is equal to 100, while that of maltose is but 66. The sugar in blood is a glucose. By moistening barley and germinating it in heaps at a constant temperature, the starch of the barley is converted into dextrose and maltose. This change is brought about by the ferment called diastase, which is found in barley. This product when dried is denominated malt, which when it is acted upon by yeast produces the malted bever- ages, beer and ale. Maltose by invertin of yeast is changed into glucose. Amyloses, or Polysaccharides.— Under the influence of dilute mineral acids the amyloses are changed by boiling or are transformed into glucose. Starch presents a polarizing cross : a black cross upon a white ground or a white cross upon a black ground. Starch does not CHEMICAL CONSTITUENTS OF BODY AND FOOD. 39 reduce copper solution nor is it fermentable by yeast. When iodine is added to starch it gives a blue color. Glycogen, or animal starch, does not reduce copper salts nor is it fermentable by yeast. During the hydrolysis of starch dextrin is formed as an intermediate product. Dextrins colored red by iodine are called erythrodextrins ; those not colored by iodine are called achroodextrins. FATS. Fats form a more or less variable proportion of the animal economy. They come to us principally in the form of animal articles of food, but to some extent in vegetable food also, especially in seeds, nuts, fruit, and roots. The fats contain in their substances a fatty principle having acid properties — a sort of fatty acid. When acted upon by alkalies and ferments this acid becomes separated and a sweet principle known as glycerin makes its appearance. Thus fats may be said to be com- pounds of fatty acids with glycerin. It would seem, however, that the glycerin had not pre-existed in the fats, as the united weight of the glycerin and fatty acid produced exceeds that of the fat originally employed. In bone-marrow, adipose tissue, and milk the fats are very promi- nent components. The adipose tissue consists of nucleated vesicles filled with fatty matter. The vesicles are closely packed together and surrounded by a network of blood-vessels which draw out from this source a supply for nutrition. This fatty tissue is found between the muscles, bones, vessels, etc., and by its accumulation under the skin gives to the surface of the body its full and regular outliae. By reason of its bad conducting power it helps to keep the various structures of the body warm by a coating of it lying under the skin. This fact is best illustrated in the warm-blooded aquatic ani- mals, as the seal, porpoise, and whale. The normal fats found in the body and used for food are divided into three compounds : stearin, palmitin, and olein. Stearin is the most solid of the three. It is typically illustrated in mutton suet, and is the element which makes this fat so hard and firm and characterizes it at once. Its melting-point is 145° F., so that at ordinary temperatures it is solid. Palmitin occupies a position midway between stearin and olein as regards consistency. It is the principal constituent of most animal fats and occurs largely in vegetable fats also. . 30 PHYSIOLOGY. Olein is always found in a fluid state unless the temperature be very low. When the olein ingredients predominate in a body it is then in a liquid state, as in the case of the oils. Olein is found in both animal and vegetable fats, but the vegetable fats are richer ia it than the animal. The oils used in food — olive-oil, oil of sweet almonds, etc. — are derived from the vegetable kingdom. Human fat contains about 75 per cent, of olein plus a small quan- tity of fatty acids ia a free state. All are soluble in hot alcohol, ether, and chloroform, but insoluble in water. Saponification. When fat is boiled with alcoholic soda or potash, the particles of fat are broken up into a small quantity of glyceria and a larger quan- tity of fatty acid. The fatty acid imites with the soda or potash, form- ing, as a result, soap. This process of soap-forming is known as saponification. Emulsification. If oil and water are well shaken together the fatty particles do not form a part of the water, but are held in suspension and come to the surface in the form of small globules. A mixture of an oil, a soap, and water is spoken of as an emulsion. No eniulsion is per- manent, for even in milk, the most perfect of emulsions, the fatty particles in the form of cream rise to the surface in a few hours. Emulsification is a physical or mechanical rather than a chemical change. Both soaps and emulsions are continually being formed in the body during the digestion of fats. PROTEIDS. The principal constituents forming the muscular, nervous, and glandular tissues, as well as the serum, blood, and lymph, are proteids. In normal urine there are found no proteids, or, if any, only traces. In a great measure the various phenomena of life are present and due to the protoplasm in the cells. On analyzing protoplasm chemically its substance is, of course, killed by the reagents used, but "there invariably result in the process proteids. Whether the proteids exist as such in the protoplasm or occur only after the death of the proto- plasm has not been fully established, but are believed to be the con- stituents of it. However, none of the phenomena of life occur without their presence. Proteids are very complex, comprising compounds of carbon. CHEMICAL CONSTITUENTS OF BODY AND FOOD. 31 hydrogen, jiitrogen, oxygen^ and sulphur. They may be either solid or liquid, as they are found in the different tissues of the body. 'The different classes of proteids present both physical and chemical pecul- iarities, although all have certain common reactions. Some are soluble, others are insoluble, ia water, while nearly all are soluble in ether and alcohol. Strong acids and alkalies are also capable of dis- solving the proteids, but in the process of dissolution decomposition almost invariably occurs. The supply of proteids in our bodies is obtained from the vege- table kingdom, being taken in as vegetables directly, or indirectly in the form of meat which is derived from animals that live on vegetables. Thus the proteids are built up from the simpler inorganic compounds taken from the soil and air and elaborated in plant-structure. The chemical composition of the proteids is variable, depending upon the products analyzed by the different investigators, as the purity of the substances cannot be definitely determined. From investiga- tions we have the following average percentages: 0, 21.50 to 33.50; H, 6.5 to 7.3; N, 15.0 to .17.6; C, 50.6 to 54.5; S, 0.3 to -2.3. The nitrogen and sulphur are each contained in the molecule in two forms, the one loosely combined, the other firmly combined. The basis of construction of all proteids is, according to Kossel, a body called protamin (CjoHg^Ni^Oj), which on hydrolysis gives three basic substances each containing six carbon atoms, hence called hexone bases, lysia, histidin, and arginin. Protamin has been found loosely combined with nucleic acid in the spermatozoa of fishes. In the pro- teid molecule it is firmly combined with the amido acids, like leucin, glycin, and usually with aromatic bodies, like tyrosin, etc., and inor- ganic elements, like sulphur and phosphorus.^ Classification of Proteids. For the sake of convenience and study the proteids have been divided into various groups and classes by different authorities. They are almost universally divided into the two main groups of animal and vegetable origin. The amount of proteid matter in plants, particu- larly the full-grown ones, is less than in animals. It is found dis- solved in their juices, in the protoplasm, or deposited in the form of grains called aleuron granules. Vegetable proteids are divisible into the same classes as the animal, but, since human physiology deals with animal proteids, the vegetables are disregarded. 'Beddard, "Practical Physiology." 33 PHYSIOLOGY. A convenient classification is into: (1) native albumins, (3) derived albumins, ov albuminates, (3) compound proteids, (4) globu- lins, (5) peptones, and (6) albuminoids. 1. Native Albumins. The proteids of this class are those that are found in an unaltered, natural state or condition in the solids of the body. They are soluble in water and are not precipitated by the dilute acids. The two main forms are egg-albumin and serum-albumin. The egg-albumin occurs in the part of the egg known as the white. The serum-albumin is found not only in the blood-serum, but also in the lymph as it is found in its proper lymphatic channels and diffused throughout the tissues, in the chyle, milk, and transudations. 2. Derived Albumins, or Albuminates. To this class belong two divisions: acid-albumin and alkali- albumin. The derived albumins are formed from the native albumins by the action of weak alkalies or acids. Thus, when a native albumia, such as serum-albumin, is treated for a while with dilute hydrochloric acid its properties become entirely changed. The solution is no longer able to be coagulated by heat, and when the solution is carefully neu- tralized the whole of the proteid is thrown down as a precipitate. The substance into which the native albumin was changed by the action of an acid is called an add-albumin, or syntonin. This acid- albumin is insoluble in distilled water and neutral saline solutions, but readily soluble in dilute acids and alkalies. This is the process through which albumins pass when undergoing gastric digestion and when acted upon by the HCl of the gastric juice. If serum-albumin, egg-albumin, or washed muscle is acted on by an alkali, instead of an acid, the proteid undergoes changes similar to those produced by the acid, except that the product formed is an alkali-albumin instead of an acid one. 3. Compound Proteids. These are native proteids with another organic substance, in con- trast to albuminates, which are compounds of native proteids with inorganic substances. The compound proteids include (1) gluco- proteids, like mucin, consisting of a proteid combined with a carbo- hydrate group; (3) pseudonuclein, like casein of milk, nuclein of cell nuclei and a nucleo-proteid, vitellin of yelk of eggs; (3) histones. CHEMICAL CONSTITUENTS OF BODY AND FOOD. 33 made up of albumin and protamin. To the histones belong globin, the proteid which is separated from hsemoglobiii by decomposing it with acids and alkalies, and a pigment called heematin, which contains 0.4 per cent, of iron. 4. Globulins. The globulins are quite abundant. The globulins differ from the albumins in that they are not soluble ia distilled water. There must be present an appreciable amount of sodium chloride or magnesium sulphate. The different members of this group are : Serum-globulin (para- glohulin), and -fibrinogen in bloody myosinogen in muscle, etc. Paraglobulin is a precipitate that can be formed from blood- serum by diluting it tenfold with water and passing through it a current of carbon anhydride. A flocculent and finally a granular precipitate results, which is the paraglobulin. The coagulated proteids are fibrta, myosin, and casein. The coagulation is produced by ferments. Fibrinogen is present in the blood, chyle, serous fluids, and transudations. Myosinogen is the principal proteid found in muscle. 5. Peptones. In the body peptones are the final results of the action of the gas- tric and pancreatic juices upon the native proteids, and as peptones are ready for absorption by the cells. Although formed in large quan- tities in the stomach and intestine, they are quickly absorbed as soon as formed, since none is left in these organs. Peptones can, however, be produced outside the body by the action of dilute acids at medium temperatures. The peptones are soluble in water, not coagulated by the presence of heat, can be precipitated by the usual proteid precipitants, and diffused very readily through membranous tissues. Intermediate products between the native proteids and peptones are the proteoses. True peptones are not found in the circulating juices of plants, but the product found is very likely proteose. The proteoses are only slightly diffusible, are not coagulated by heat, but can be precipitated. A characteristic feature of their precipitates is that they can be dissolved by heating, but reappear when the solution cools. 34 PHYSIOLOGY. 6. Nitrogenous bodies Allied to Proteids, or Albuminoids. Besides the proteids there are othei* nitrogenous, noncrystalline bodies that are allied to the former, having many general points in common. Gelatin is the substance produced by heating the collagen, of connective-tissue fibers, in dilute acetic acid for several days. It pos- sesses the property of setting into a jelly when its concentration is greater than 1 per cent. When digested it is converted into a peptone, and, although readily absorbed, is not able to take the place of a true proteid, since it cannot build up nitrogenous tissue, being valuable only as a means of storing up energy. Keratin is the horny material forming the outer layer of the epidermis, hair, wool, nails, hoofs, etc. Blastin of elastic tissue belongs to this group. ALIMENTARY SUBSTANCES. We have learned that the body is composed of the chemical con- stituents or proximate principles, carbohydrates, fats, and proteids comprising the organic group, and water and salts the inorganic class. In order that the nutrition of the body may proceed normally, it is very apparent that those principles must be supplied in the food, in the proper proportions and quantities. So, a proper diet for man is one containing the proximate principles in their proper proportions, the value of it depending mainly on the amount of carbon and nitro- gen present. The elements, as elements, are not valuable; it is only when they are in combination that they serve their proper ends as foods. Por the elements must be united previously by some liviag organism to constitute an organic product. It is not often that the alimentary substances are used by us as N^ature furnishes them, even though they contain the proper ingredients. One requisite is that they should be presented in a digestible form. Water, heat, and condiments are the three agents used to make food more palatable and digestible. Water helps to soften the insoluble substances and to dissolve the principal substances. Heat modifies the foods still more, so that they acquire different characters. The condiments give physical satisfac- tion and enjoyment, and at the same time they please the taste. A diet to be sufficient must be adapted to the particular indi- vidual's need, keeping in mind, also, the climate, age of person, and the amount of work done by him. ALIMENTARY SUBSTANCES. 35 Although we make changes of clothing to suit the weather condi- tions in order that the body may not suffer iu regard to the surrounding temperature, yet our diet is also regulated with the same ends ia view. In cold weather we eat more, to furnish an extra amount of heat ; in warm weather we eat less than usual. A growiug youth's body must not only repair the daily waste, but also assist in constructive meta- morphosis, or growth, so that he requires relatively more food per diem than the adult. Because of the waste attending action, the workingman requires more than the ordinary supply of food. There are some single foods which contain all the necessary proxi- mate priuciples in proper proportions, but they are the exceptions rather than the rule. Thus, milk and eggs are classed as perfect foods. It is usually necessary for a proper diet to contain a variety of sub- stances in this list. For a man doing a moderate amount of work, it has been com- puted that it is necessary that the daily diet should contain the fol- lowing amounts: — - Proteid 125 grama. Eat 50 grams. Carbohydrates 500 grams. Alimentary substances comprise products of both animal and vegetable kingdoms. The principal ones are animal substances, with cereals, potatoes, drinks, condiments, cocoa, coflEee, tea, etc. The animal substances, or foods, comprise: (1) meat, (3). eggs, and (3) milk, with its derivatives — cream, butter, and cheese. The parts of animals used for food are the various portions of their muscular system. They comprise the general term meat. Ani- mal food, being identical with the body structures, requires nothing to be added or detracted to make it fit to give proper nourishment. MEAT. The more compact the fiber, the less digestible the meat. Hence ham is much less digestible than other meats. The more fat that is combined intimately with the fibers, so much less is the digestibility of the meat, because the fat melts and coats the fibers of the meat with a layer of oil which prevents the ferment from acting upon it. Meat is noted for the large quantity of nitrogenous matter which it contains, having four times the amount of proteid compared with the same weight of milk. The proteid in meat is myosin, the main constituent. Beef-tea is a solution of gelatin, salts, extracted matters, a little albumin, together with some fat. The value of beef-tea as an all- 36 PHYSIOLOGY. mentary substance has been much disputed, some claiming great results from it, others none. However, one thing is certain : it possesses a stimulant and restorative value, though it must not be depended upon as a food and administered as such. The process of cooking meat loosens up the various fasciae and enveloping membranes, thereby separating the fibers; at the same time parasitic growths are killed. Thus the digestive juices are given a greater opportunity for acting upon all parts of the foods, even penetrating into the innermost parts. EGGS. The white of an egg is a faint-yellowish, albuminous fluid inclosed in a framework of thin membranes, and this fluid itself is very liquid, but seems viscid because the membranes are entangled. Ovalbumin, or the egg-albumin of the egg-white, is the chief constituent. The mineral bodies in the white of egg are potash, soda, lime, magnesia, iron, chlorine, phosphoric acid, and sulphuric acid. The principal part of the yelk is an orange-yellow, alkaline emul- sion of a mild taste. The yelk contains vitellin as its principal con- stituent. Besides vitellin, the yelk contains alkali albuminate and albumin. The yelk, besides vitellin, contains a phosphorized fat (leci- thin) with cholesterin, fats, and a small quantity of sugar and of mineral bodies, chiefly lime and phosphoric acid. As the egg is so easily digested it is prized highly as a food. However, the more that an egg is boiled, the more insoluble do the proteids become and so are more indigestible. In cases where eggs are difficult of digestion the white of egg may be given. The yelks of eggs make some persons have headache and drowsiness. The caloric value of two eggs is about twenty calories, equal about to the heat-value of a tumbler of milk. MILK. Like eggs, milk contains all the elements necessary for the main- tenance of life, and hence it is regarded as a type of alimentary sub- stances and classed as a perfect food. It serves very well as an infant-food. The quantitative composition of cows' milk and human milk is as follows, according to Bunge : — Proteid. Cows' milk 3.5 Human milk 1.7 Pat. Caebo- HYDEATE. Salt. 3.7 4.9 0.7 3.4 6.2 0.23 ALIMENTARY SUBSTANCES. 37 The amount of fat and carbohydrate is nearly the same in both, there being, however, twice as much proteid and nearly three times as much salt in cows' as in human millc. To bring cows' milk to the same condition as human milk it is necessary to dilute with an equal amount of water and at the same time to add some cream and sugar. Milk is a watery solution of various proteids, a carbohydrate and salt, containing in suspension emulsified fat. Cows' milk is an opalescent solution with a characteristic taste and an amphoteric reac- tion. The specific gravity varies between 1.028 and 1.034. Micro- scopically, it consists, like blood, of plasma and corpuscles, or globules, of fat. Boiling does not coagulate fresh milk, but forms a skin on its surface which is chiefly composed of caseinogen inmeshing some fat- particles. This film is formed by the drying of proteid at the surface of the milk. The chief proteid of milk is a pseudonuclein called caseinogen, and can be precipitated by adding to the diluted milk a weak acid or by saturating it with a neutral salt. The chief pecul- iarity of caseinogen is its coagulating power when treated with a fer- ment, renniQ, iu the presence of lime salts. The coagulation of milk depends upon the ,change of a soluble proteid, caseinogen, into an insoluble body, casein, by means of the enzyme, rennin, and the pres- ence of lime salts is necessary. It is probable that the rennin first splits the caseinogen into two bodies, the more important being soluble casein, which then combines with the calcium salts to form a caseinate of calcium, while the other passes into solution in the whey as whey proteid, or lactoserum proteose. The casein thus generated inmeshes the fat-granules and forms milk-curd. This curd, like the blood-clot, shrinks after a few hours and an opalescent fluid, or serum, called whey, is expressed. This whey contains, besides the whey-proteid, or lactoserum pro- teose, traces of other proteids and also lactose and milk salts. The casein, of cows' milk forms large masses on coagulation, while women's milk forms very fine flakes. The lactose, or sugar of milk, does not readily ferment with yeast, but is capable of undergoing a special fermentation, by which it is changed by the lactic acid bacillus into lactic acid, and this lactic acid is further split up into butyric acid. These two acids, lactic and butyric, precipitate the caseinogen and produce the curd in sour milk ; but this curd is quite a different body from that produced by rennin, for it can be dissolved by a weak alkali, and then the rennin. will clot it. Potassium oxalate, which precipitates the calcium in the milk, prevents the clotting of milk. The other proteids in milk besides caseinogen are lactalbumin and lactoglobulin. 38 PHYSIOLOGY. Kumyss is mares' milk fermented. It contains 10 per cent, of solids, 3 per cent, of alcohol, 2 per cent, of fat, 2 per cent, of sugar, 1 per cent, of lactic acid, 1 to 3 per cent, of casein, and 1 volume per cent, of carbonic acid. Kepliir is cows' milk fermented by kephyr grains. Matzoon is prepared by adding to milk a ferment consisting of some form of yeast and the lactic acid bacilli. It, however, contains very much less alcohol and carbonic acid than kumyss. Plasmon is prepared by precipitating casein from fresh milk. Then it is dis- solved in sodium bicarbonate in the presence of free carbon dioxide, which prevents the alkali from decomposing the casein. It is then Fig. 4. — Specimens of Milk, viewed through the Microscope. (IiANDOIS.) M, Milk. C, Colostrum, dried, and is a yellowish-white body. It contains 2 per cent._ of fat and milk-sugar and 7 per cent, of salts. It is used as a substitute for milk when a large amount of water is not desirable. The fats of milk are olein, palmitin, stearin, caproin, and butyrin. The milk of women contains twice as much olein as palmitin and stearin, but they are about the same in quantity in cows' milk. In cows' milk two-fifths is olein, one-third is palmitin, one-sixth stearin and butyrin, and caproia one-fourteenth of the total fat. Buttermilk contains about 10 per cent, of solids, including casein ; lactose ; and about 1 per cent, of fats. Butter is formed by the fatty portions in churning making the fat-particles adhere to each other, forming a yellow, fatty mass. ALIMENTARY SUBSTANCES. 39 The salts of milk average 0.6 per cent, and they consist chiefly of phosphate of lime with calcium chloride, magnesium phosphate, and traces of iron. Milk also contains about 7.6 per cent, of carbonic acid and traces of oxygen and nitrogen. The quantity of milk daily secreted by a woman is about one quart. The quantity of milk changes during lactation, which lasts in the woman about ten months. In the case of the woman the percentage of casein and fat increase to the end of the second month, but sugar lessens even in the first month. During the fifth to the seventh month there is a diminution of fat, and between the ninth and tenth months a decrease of casein. In the first five months the salts increase ; after that they diminish. Colostrum is the milk secreted for a few days after parturition, and it has peculiar characters. It contains large corpuscles . called colostrumrcorpuscles, which are large cells full of colorless, fatty par- ticles. A poisonous principle is sometimes generated in milk by microbes. It is called tyrotoxicon. VEGETABLE FOODS. Vegetable substances differ very much from animal bodies in their physical appearances and in. some respects also chemically. The vege- table matters are capable of being transformed into the various animal components and thereby nourish the animal body, since they contain aU the elements, or proximate principles, that are necessary for the maintenance of life. They need a more complex apparatus for their transformation, and as a consequence the 'digestive organs of the herbivora are better developed and more complex than those of the carnivora. The cereals have the same general composition, all containing the same proximate principles, but not all possess the same relative amounts, because of which some are more valuable as food than others. The most important of the cereals is wheat. Wheat, as a source of food, occupies a very important place and is one of the most widely cultivated of the cereals. The wheat-grains by grinding have their cellulose coats burst, and the resulting powder is called flour. This contains, on an average, 70 per cent, of carbo- hydrates, 8 per cent, of proteid, and 1 per cent, of fat. The coverings of the grain still contain some albumin and starch and thus form 40 PHYSIOLOGY. bran, a substance used for feeding the herbivora. Bread is made by a mixture of wheat-flour and water, forming dough. The body which, on the addition of water, becomes viscid is called gluten, and is a tough, sticky mass. This is made more porous by carbonic acid, which is generated in the dough by the action of the yeast-plant on sugar. The sugar is produced by the diastase in the flour, which hydrates the starch into sugar. Baking kills the yeast-action and makes the vesicles filled with carbonic acid expand, so the dough is filled with little cavities. The crust of bread is formed by the heat coagulating the gluten, and at the same time the heat transforms the starch into dextrin and solu- ble starch. The glazing of the crust is due to dextrin. The different color of the crust and its taste is due to a caramel generated by the action of heat on the sugar produced by the diastase. ACCESSORY FOODS. In addition to the ordinary foods there is a series of articles which are not necessary to the maintenance of life, but which are fre- quently used. They are: alcohol, tea, coffee, and cocoa. Of these accessory foods, alcohol is the predominant one and is used in a variety of drinks. Alcohol. — Beer contains from 3 to 5 per cent, of alcohol. It also has from 5 to 7 per cent, of extractives, which consist mainly of dextrin and maltose, with albumose, which give it nutrient properties. Bach ounce usually holds about two cubic inches of carbon dioxide. It is an infusion of malt fermented, to which a bitter principle found in hops is added. It is frequently adulterated with salicylic acid and benzoic acid to preserve it. In excess it gives rise to rheu- matism, gout, and bilious attacks, due to diminished excretion of waste-materials from the economy. Wines contain from 6 to 35 per cent, of alcohol. Port holds 10 per cent, and sherry 16 to 35 per cent. of alcohol. Besides, the aroma is due to ethers. Champagnes con- tain, in addition, 10 per cent, of sugar, which upsets the stomach. Wines also have free acids, especially tartaric, which also disagree with certain stomachs. Spirits contain about 50 per cent., of alcohol. Alcohol is a nutrient and heat-generator. One gram of alcohol produces more heat than one gram of proteid or carbohydrate. Ordinarily the system can oxidize daily about one and one-half ounces of alcohol. When alcohol is oxidized it spares the fats and carbohydrates and probably the pro- teids. It is well known that the continuous drinking of alcohol makes a person fat. The persistent use of alcohol also increases ALIMENTARY SUBSTANCES. 41 the dangers of infection from infections diseases. In fevers its use prevents the loss of fat and stimulates the secretion of gastric juice. It dilates the capillaries of the skin either by a local or central action. Its habitual use gives rise to chronic gastritis and cirrhosis of the liver. The odor of spirits in the breath is due to fusel-oil. Alcohol in the blood is changed into carbonic acid and water. Coffee. — Each cup of coffee contains about two grains of caffeine. Coffee also contains a volatile substance called coffeon, which resem- bles an oil. The exhilaration after the drinking of coffee and the increased peristalsis is due to the coffeon. Tea. — Tea contains caffeine and theophylline and about 7 per cent, of tannin. Tea induces constipation and chronic gastritis when used in excess. Neither tea nor coffee diminishes metabolic changes. Cocoa. — This body is a nutrient because it contains fat (50 per cent.) and an albuminous substance. It contains theobromine. Caf- feine and theobromine belong to the purin group. CHAPTER III. DIGESTION. Anatomy and Structure of the Mouth, Pharynx, and (Esophagus, together with the Digestive Processes Occurring in Them. Digestion has for its aim the separation of the principles of growth and repair from the aliments and fitting them for absorption into the circulation. The process is both mechanical and chemical, accomplished mainly through the action of certain soluble ferments called digestive enzymes. Some form of digestion is found to take place in all animal organ- isms no matter how low we proceed in the zoological scale. It is essential to every one of them that they be able to take from their environments those elements that are necessary to maintain their economy and give off those substances that are no longer fit for use and termed waste-products, for only by this exchange of the elements outside of their own organisms are they able to live, grow, and produce others of their kind. In the higher grades of animal life, as the articulata and verte- brata, the number of organs concerned in digestion is increased, and, of course, in direct ratio the various stages and acts in the whole process are multiplied. In them is a long tube, in some parts much, folded on itself; in and along the outside of it are numerous glands which empty their products, called secretions, into the long tube ; and at the beginning of which there is an apparatus for crushing and grinding the solid parts of the food. Intimately connected with this apparatus is the system of blood- and chyle- vessels for absorbing the digested products and thus allowing them to circulate through the entire body and come into contact with every part of the organism. In the vertebrata there are modifications and forms of develop- ment dependent upon the class, and even in mammalia there are differ- ences as the animal may be insectivorous, carnivorous, herbivorous, or omnivorous. Man, the highest of the mammalia, is the real and intimate study upon which all our physiological researches bear. He is omnivorous, and naturally we expect to find his digestive apparatus suited to dis- integrating and dissolving all kinds of food. (42) DIGESTION. 43 In him the digestive apparatus consists of a long tube, called the alimentary canal, about thirty feet in length, with its accessories of teeth and the various glands which empty their products into the tube by means of little ducts. The alimentary canal is the long tube beginning with the mouth and ending with the anus., composed of muscle and mucous membrane, the latter liuing it throughout its entire length and giving to the interior of the canal its characteristic smoothness and redness. In this lining membrane, as also in the submucosa, are located some of the glands whose secretions aid digestion. The alimentary canal in its extent of about thirty feet has received various names for its several parts. They are: mouth, pharynx, (esophagus, stomach, small and large intestines. The mouth is the oval box, situated at the commencement of the canal, in which, by the action of the jaws with their two rows of teeth, the hard parts of the food are masticated, as it is called. While the food is being masticated it is at the same time being mixed with a watery fluid, the saliva, the secretion of the salivary glands; this mix- ing of food and saliva has been termed insalivation. In the pharynx and oesophagus occurs the act of deglutition, or swallowing of the masticated mouthful in the form of a large, moist bolus. It is by the contraction of the muscles in these parts that the food is quickly passed on to the stomach. The course of the tube beginning with the mouth and ending at the opening of the stomach is comparatively straight and measures about fifteen or eighteen inches in length. This part of the tube is found in the head, neck, and thorax, ending just below the transverse "muscular wall of the trunk, the diaphragm. The stomach is the muscular pouch in which occurs some of the chemical changes of the food, converting it into a grayish-brown soup- like mass. From thence it passes on to the small intestine, where the nutrient materials are separated from the waste-residue; the latter is passed on to the large intestine to be later expelled from the body. The stomach, large and srruM intestines are Ideated in the ab- domen and pelvis, diilering from that part of the canal above the diaphragm iu that the iatestines are much folded and convoluted in their course; so that the major portion of the entire length of the canal is contained here. In the mucous membrane and submucosa are located microscopical glands whose ducts open directly upon the lining, interior surface. Outside the canal, their secretions emptying into the canal by small 44 PHYSIOLOGY. duets, are the larger glands : salivary, liver, and pancreas. The ducts of the salivary glands open into the mouth ; the common duct of the liver and pancreas into the first fold of the small intestine, the duo- denum. Although digestion in its entirety, as it occurs in the alimentary canal, is in its nature very complex, yet there are three natural divi- sions of the whole process based upon the changes as they occur (1) in the mouth (including the pharynx and oesophagus), (2) in the stomach, and (3) in the intestines. It is the intention to consider the changes and alterations of the foodstuffs, whether mechanical or chemical, in each, together with the anatomy of the parts of each division and the structure of the accessory glands, with their secretions and the functions they bear to the com- pletion of the entire work. However, the fact must not be lost sight of that these divisions are only arbitrary and for convenience, as no real line can be drawn at the various stages, siace all parts, structures, and functions work in harmony, on the plan of division of labor: having in mind one common end — the dissolving of the food so that it can become a part of the circulation. PREHENSION, Before the processes of digestion can begin, it is essential that the food should be brought to and placed in the mouth, the beginning of the alimentary canal, for only in some of the infusoria does diges- tion of the food take place outside the organism, due to the influence of ferments secreted by the organism to be nourished. The act of bringing the food to the mouth has been termed prehension. Nature has admirable contrivances for this act wherever we look among the lower animals. The monkey, squirrel, rat, etc., usually make use of their anterior extremities for grasping and bringing to their mouths the food, while they sit upon their haunches. The horse makes use of his teeth and lips; indeed, his upper lip is very movable, long, and endowed with extreme sensibility. It is his means of gathering together his grain and bringing it to the incisors which cut it up, then to be passed along by the tongue to the molars for grinding. In the cow the tongue, in the cat and dog the teeth and jaws, are the main organs of prehension. The frog, by protruding his long, thin tongue, the surface of which is covered with a viscid mucus, catches insects as they fly. By far the most complicated and best developed prehensile instru- ment in animal mechanics is that employed by man — the human DIGESTION. 45 upper limb. The extreme perfection of all its parts, and particularly of its terminal portion, the hand, makes it admirably fitted, not only for the prehension of food, but also for the execution of all the various caprices and designs of the human will. Thus it not only simply raises the food to the mouth (prehension), but also, with the human intelli- gence as the real potent factor, aids in the preparation of food by means of fire (cooking). Thus we learn that the first real step in digestion is prehension : bringing the food to the mouth. THE MOUTH. The space included between the lips in front, the pharynx behind, and the cheeks at the side is the mouth. Above the roof of the mouth we have the palate ; below, its floor, upon which rests the tongue. The cavity of the mouth, excepting the teeth, is everywhere invested with a highly vascular mucous membrane, with an investment of squamous epithelium. Conical papillae, for the larger part minute and con- cealed beneath the epithelium, are found. The lips are separated by the oral fissure. They are composed of various muscles converging to and surrounding the oral fissure. The cheeks have a composition similar to the lips, and their principal muscle is the buccinator. At their back part they include the ramus of the jaw and its muscles, and usually between these and the buccinator muscle is a mass of soft, adi- pose tissue. Beneath the mucous membrane of the lips and cheeks there are a number of small, racemose glands, with ducts which open into the mouth. These glands are, in the lips, called labial and, iu the cheeks, buccal. They secrete mucus. There are two parts to the palate : a hard and a soft palate. The hard palate is deeply vaulted and lined with a smooth mucous mem- brane, except at its anterior part, where it is roughened by transverse ridges. The soft palate is a doubling of the mucous membrane in- closing a fibromuscular layer, also containing racemose glands. It hangs down obliquely from the hard palate between the mouth and posterior nasal orifices. It is a freely movable partition. The uvula is an appendage like a tongue projecting from the middle of the soft palate, and consists of a pair of muscles inclosed in a pouch of mucous membrane. Palate. — The palate has two crescentic folds of mucous mem- brane inclosing muscular fasciculi and diverging from the base of the uvula, on each side of the palate outward and downward, one to the 46 PHYSIOLOGY. side of the tongue, the other to the side of the pharynx. These folds are known as the half -arches of the palate. The one in. front is known as the anterior palatine arch, the one posterior as the posterior palatine arch. The Fauces. — The fauces are the straits, or passages, leading from the mouth to the pharynx, and correspond with the space included between the half-arches of the palate. Tongue. — The tongue is composed of muscle and covered with a mucous membrane. It is composed of two symmetrical halves joined in the middle liue. By the freedom of its movements it aids in mastication and deglutition, and it is also a great help in articula- tion, and by the papillae on its surface forms an organ of taste. The root, or base, is the posterior part, where it is attached to the hyoid bone and inferior maxilla. The body is the great bulk of the organ. Its tip is the anterior free extremity. On the anterior two-thirds of the upper surface of the tongue we find a mucous membrane which ad- heres most intimately to the muscles beneath. Its surface is roughened by the presence of a number of little papillse. On the surface of the tongue there are many mucous glands. Papillse. — The papillae are the fungiform, filiform, and circum- vallate. These are more minutely described in the section on the sense of taste. Nerves. — The nerves of the tongue are the lingual of the fifth pair, the glosso-pharyngeal, and the hypoglossal. THE TEETH. In form, structure, and number the teeth vary very considerably among different animals, which is markedly shown in the classes, carnivora and herbivora. In most animals the teeth are worn down by use and eventually decay. The exception is found in that class of animals that constantly nibble; their incisors are peculiar in that there are deposits of fresh dentine within and upon the pulp and of enamel upon the anterior surface, thus giving a continuous growth. They are the rodentia. Among mammalia, and particularly in man, the teeth are devel- oped in two sets: (1) the fiist, less numerous and smaller set, called the temporary, or milk, teeth; and (2) a second set, larger and more numerous, called the permanent teeth. The temporary, or milTc, teeth are usually £0 in number, JO in each jaw. In each jaw there are ^ incisors, 2 canines, and J^ molars. When the milk teeth drop out they are followed by the permanent teeth. DIGESTION. 47 The permanent teeth are 32 in mimber, 16 in each jaw, consisting of 4 incisors, 2 canines, ^ iicuspids, and 6 molars. There are three distinct parts in a tooth: crown, root, and neck. The crown, or body, is the protruding portion of the tooth; the portion inserted in the alveoli of the jaws is the root, or fang. The slightly constricted part enveloped by the gum is the neck. The fang is firmly fastened to the sides of the alveolus, in which it is inserted by fibrous tissue) which is continuous with the periosteum of the jaws. When the jaws are closed the under incisors are inclosed by the upper ones, but the grinding surface of the molars is in contact. Temporary Teeth. — Ttere are 30 milk teeth, 10 in each jaw, or 5 on each side of the jaw; that is, 2 incisors, 1 canine, and 2 molars. The temporary set resembles the permanent in form and structure. The teeth are, however, fewer in number, smaller in size, and charac- terized by the bulging out of the crown close to the neck, making the latter very sharply defined. The milk teeth die off and so give room for the second and more permanent set. They die partly in accordance with the rule of epi- thelial tissues and drop off, since all such tissues are expelled after their death; then, too, the jaws grow as the being passes from infancy to adult life, when larger and more numerous teeth must replace the smaller ones, so as not to impair the efficiency necessary to masticate quantities of food proportionate to the demands of the growing body. Permanent Teeth. — There are 8 incisors, and they form the 4 front teeth in each jaw, and are named incisors because they divide the food. The upper incisors are the larger. The canine teeth are 4 in number, larger than the incisors. The upper canines are usually called the eye teeih, and they are longer and larger than the canine teeth in the lower jaw. In the carnivorous animals, like the dog, the canine teeth are usually large; hence the name of canine. The lower canines are popularly known by the. name of stomach teeth. There are 4 premolars, or bicuspids, in each jaw. They are shorter and smaller than the canines. The bicuspids of the upper jaw are larger than those of the lower jaw. The function of the bicuspids is to cut and grind the food. The molars are 12 in number, 3 on each side above and below. Their large crown and their great width are the chief distinguishing characteristics. The upper molars have 3 conical fangs, the lower ones 2. The last molar is the wisdom tooth, so called because it appears about the twentieth year, when the individual is assumed to have acquired wisdom. The molars are intended for the grinding of food. 48 PHYSIOLOGY. Structure of the Teeth. — If a tooth is split in its long axis the surface exhibits, besides the pulp-cavity, three different kinds of mate- rials Dentine forms the greater part of the yellowish-white sub- stance; the capping of the crown is enamel; and the translucent, thin investment on the fang is cement, or crusta petrosa. The main bulk of the tooth is composed of dentine, giving it shape and containing the pulp-cavity. It consists of about 28 parts of organic matter and 73 of earthy material. Dentine resembles bone both physically and in chemical constitution. When subjected to microscopical examination we find the dentine penetrated throughout by fine tubes called dentinal tubules. The inner end of these tubules open into the pulp-cavity, whence they radiate in every part of the dentine toward the surface of the tooth. They have a direction gen- erally parallel, with a wavy, undulating course. In the pathway toward the periphery they subdivide into several parallel branches which anastomose with each other. The average diameter of the tubule is Visoo inch. Near the end of the tubule the arrangement is in globular spaces which communicate with each other and are known as the interglobular spaces of Purkinje. Enamel. — The hardest of all organized substances is known as enamel. It is a bluish-white material capping the crown of the tooth. It is thickest on the triturating surface of the tooth. Chemically it consists of 3 parts of organic matter and 97 of earthy matters, prin- cipally calcium phosphate. Under the microscope the enamel appears in the form of hexagonal columns about ^Aooo inch in diameter. The Cement, oh Ckdsta Petrosa. — This substance covers the fang of the tooth, gradually becoming thicker toward its extremity. It is like true bone, and contains lacunae and canaliculi. Externally it is covered by dental periosteum. In old age the cement grows thicker and may close up the entrance to the pulp-cavity. THE SALIVARY GLANDS. The parotid gland is named from its position near the ear. It is the largest of the salivary glands. It extends upward as far as the zygoma, as far down as the angle of the lower jaw, and inwardly between the ramus of the jaw and the mastoid process. The duct of the parotid, called Stenos, has the diameter of a crow-quill, is two inches in length, and runs across the masseter to open into the mouth opposite the second molar tooth. The parotid has a full supply of blood-vessels, which run through it. The nerves of the parotid are the auriculo-temporal and the DIGESTION. 49 cervical sympathetic. In the dog and cat the parotid derives its nerve-supply from the glosso-pharyngeal through the small petrosal and the otic ganglion, the fibers finally running in a branch of the auriculo-temporal. The submaxillary gland is separated from the parotid by a process of the deep cervical fascia. It is beneath the mylohyoid muscle, is below the curve of the digastric muscle, and on the outside covered by the subcutaneous cervical muscle and skin. It is about one-third the size of the parotid, and its duct of Wharton is about two inches in length. The duct opens on the side of the lingual fraenum. The blood-vessels are branches of the facial and lingual. The nerves are those from the submaxillary ganglion and through this from the chorda tympani. The sympathetic also supplies this gland. The sublingual gland rests on the floor of the mouth and is seen beneath the side of the tongue as a ridge. It has a half-dozen ducts called the Eivinian, which open on the ridge which marks the position of the gland on the side of the fraenum. STRUCTURE OF THE SALIVARY GLANDS. These glands are of the compound racemose variety. The alveo- lus has a duct ending in it. The alveoli are united by the blood- vessels and a small amount of loose connective tissue with lobules. The alveoli of the salivary glands are divided into two classes, according to the kind of secretion, one kind giving a secretion containing mucin, the other kind secreting a more watery fluid containing a large amount of serum-albumin; hence the alveoli are mucous or serous. The sublingual chiefly secretes' mucus, the parotid chiefly serum-albumin. The submaxillary secretes both kinds. In most of the alveoli of the glands there are found cells of a kind differing frorii the mucin-cells, as in the submaxillary of the cat, where they form an almost complete outer layer next to the basement membrane, inclose the mucin-eells, and are called "marginal cells." In the dog's submaxillary they are only seen as semilunar masses known as the half-moons of Gianuzzi. The lymphatics lie closer to the alveoli than the capillary network of blood-vessels. The lymphatics begin in the form of lacunae between and around the alveoli. The nerves pierce the basement membrane and arborize between and around the cells of the alveoli. PHARYNX. The pharynx is a funnel-like cavity running from the under sur- face of the skull down to the levSl of the fifth cervical vertebra, where 50 PHYSIOLOGY. it ends in the oesophagus. There are 7 openings communicating with it: the 2 posterior nares, the 3 Eustachian tubes, the mouth, the larynx, and the CESophagus. The walls of the pharynx are musculo- membranous. The interior is lined with a soft, red, mucous mem- brane containing many glands. Squamous cells are the chief variety of epithelium lining the mucous membrane. Next is a fibrous coat, then a muscular coat, and outside of this a fibrous investment which attaches it to the skull. The muscular coat includes the superior, middle, and inferior constrictors of the pharynx, which are concerned in deglutition. Lymphoid tissue is very abundant at the upper back part of the pharynx, and a number of lymph-follicles lie between the orifices of the Eustachian tubes, forming the pharyngeal tonsil. (ESOPHAGUS. This tube extends from the Mtlp. cervical down to the ninth dorsal vertebra. It is about nine inches long and less than an inch in diameter. It is narrowest at its commencement and gradually en- larges. It has three coats: from the outside, muscular; a middle coat, fibrous; and an internal, or mucous, coat. The muscular coat has a liyer of longitudinal fibers and a circular layer, the upper end of the oesophagus has striated fibers, while the lower half has plain, unstriped fibers. The mucous coat is paler than that of the pharynx and mouth. In ordinary circumstances the mucous membrane is in longitudinal folds. It contains minute papillse and a squamous epi- thelium. The nerves of the oesophagus are the vagus and the sym- pathetic. THE MECHANICAL PROCESSES OF DIQESTIOINJ OCCURRING IN THE MOUTH, PHARYNX, AND CESOPHAGUS. MASTICATION. This is a voluntary act whereby the food is comminuted by the teeth, jaws, and muscles concerned in this act, aided by the tongue, palate, cheeks, and lips. The bulk of the work is accomplished by the biting and grinding movements of the lower teeth against the upper ones. From the manner of its articulation with the skull the lower jaw is capable of performing three primary movements, together with combinations of these same, viz. : up and down, side to side, with projection and retraction. The muscles concerned in producing these movements are the masseter, temporal, and internal pterygoids, which DIGESTION. 51 raise the lower jaw; the inferior maxillary division of the fifth nerve innervates them. The depression of the jaw is accomplished mainly through the action of the digastric, aided considerably by gravity. The side-to-side, or lateral, movements are due to the separate action of the external pterygoids. Their united contraction gives projection of the lower mandible, to be retracted by a part of the temporal muscle. The innervation of the pterygoids is also by the inferior division of the fifth. Mastication is particularly important when solid and fibrous foods are eaten, to prepare them by comminution for the fermentative action of the various digestive fluids. When improperly performed repeat- edly a severe form of dyspepsia ensues. During mastication there is performed a separate and distinct act, insalivation, or the mixiug of the food with saliva. By means of it, the dry, hard portions of food are moistened and softened better to fit them for swallowing; at the same time the mucous membrane is lubricated to allow free movement of the food over its surface and the surfaces of the teeth are freed from accumulations of food during mastication which otherwise would collect and impede its progress. A fever patient attempting to swallow a dry cracker affords ample illus- tration of the mechanical value of the saliva duriag mastication. DEGLUTITION. The swallowing of the food, which has been named the act of deglutition, is performed by the aid of the tongue, fauces, pharynx, ahd the oesophagus or gullet. For the purpose of description only, since the process in reality admits of no lines of distinction, this act is usually said to comprise three stages: first, that in which the food is forced baelcward from the mouth, through the fauces, into the pharynx. This act is voluntary, though usually performed uncon- sciously, being ascribed to the movements of the tongue itself. The second stage is that in which the bolus is made to travel along the middle and lower part of the pharynx to the oesophagus. This second act is more complicated and requires quicker movements, because the nasal and laryngeal orifices are open, but past which the food must go without entering. The main motive power for this performance is gained by the contractions of the three constrictors, aided by the synchronous action of other muscles, whose duty is to occlude tem- porarily the nasal and laryngeal openings. The opening into the nasal cavity is closed by the elevation of the soft palate, uvula, and the contraction of the posterior pillars of the fauces. Just above the 52 PHYSIOLOGY. laryngeal opening and at the base of the tongue is a small, leaf -shaped piece of cartilage, the epiglottis. It was formerly believed that the laryngeal orifice was guarded during deglutition by the retraction of the tongue pressing down the epiglottis to fit it firmly. But, as re- moval of the epiglottis did not interfere with normal swallowing, it was learned that the real safeguard was the contraction of the aryteno- epiglottic folds. The third stage is that in which the bolus descends along the oesophagus to enter the stomach. This stage is performed by the intrinsic contractions of the muscular fibers of the cesophagusT walls. As is known, its muscular fibers are arranged in two layers: one circular, the other longitudinal. The upper third is composed- of striated muscle-fibers, the lower two-thirds of the plain, or unstriped, variety. Accordingly in the upper third the movement of the bolus is more rapid than in the lower two-thirds. The movement through the oesophagus is that known as peristaltic, or vermicular. The sec- ond and third stages of deglutition are involuntary. When the death-rattle occurs it is caused by the pharynx not contracting around the bolus. Swallowing of Fluids. From what has been said previously it will be readily perceived that the act of deglutition of both liquids and solids is a muscular act, and not, therefore, dependent upon gravity. Thus, horses and many other animals drink with their heads low, so that the fluid must needs be forced up an inclined plane to reach their stomachs. Sometimes jugglers, while standing upon their heads, perform the feat of drinking. The deglutition of boli or food was, for convenience, -divided into three stages, but so quickly is the passage of liquids accomplished that physiologists are able to recognize but one movement when they are swallowed. We are indebted to the experiments and observations of Kronecker and Meltzer for an explanation of this process ; accord- ing to them, there is an action resembling, in the main, that of a force- pump, whereby the mass of liquid is propelled with extreme rapidity through the pharynx and oesophagus. It is by the contraction of the two mylo-hyoids that the liquid is put under high pressure and shot along in the direction of least resistance: through the pharynx and oesophagus. This pair of mus- cles is greatly aided by the simultaneous action of the two hyoglossi muscles. These two pairs of muscles, by acting in unison, form a sort of diaphragm to push the root of the tongue backward and down- ward, at the same time performing a force-pump action upon the DIGESTION. 53 liquid to be swallowed. So quickly is the passage of the liquid aecom- plished that the pharyngeal and oesophageal muscles have not time to contract about the mass of liquid; in fact, they are inhibited during the passage of liquids through their respective channels. After the liquids arrive in the stomach the act of deglutition ensues for the pur- pose of removing the liquids. adhering to the walls of the oesophagus. This statement is substantiated very strikingly in cases of poison- ing by carbolic acid and other corrosive substances. The mouth and tongue, from longer contact, are always burned, while the pharynx and oesophagus may escape altogether, or, at most, are but slightly burned. The escape of the latter is due to the rapid transit of the cor- rosive substance through them. However, the cardiac entrance of the stomach is always very much corroded before the sphincter relaxes for admission into the stomach. When the ingested food has been thoroughly insalivated or is semisolid, there begins to be a departure from the three-stage act toward the force-pump action of liquids. When the food is very much liquefied the latter action is very prominent; so that any fixed line for the swallowing of food or liquids does not exist. Nervous Control of Deglutition. Deglutition is a reflex act. Every reflex act requires an afferent set of sensory nerves, a reflex center, and an efferent set of motor nerves, that of swallowing no less so than any other. The sensory nerves have their terminations in the mucous membrane of the pharynx and oesophagus, including branches of the glosso-pharyngeal to the tongue and pharynx, branches of the fifth to the soft palate, and the superior laryngeal branch of the vagus innervating the glottis and epiglottis. The reflex center lies somewhere forward in the medulla. The efferent nerves are : Branches of the fifth, which sup- ply the digastric, mylo-hyoid, and muscles of mastication; the facial, which supplies the levator palati; the glosso-pharyngeal supplies the muscles of the pharynx. Stimulation of the central end of the superior laryngeal calls out an act of deglutition. Stimulation of the central end of the glosso-pharyngeal arrests it. The inferior laryngeal branch of the vagus innervates the muscles of the larynx, while the hypo- glossal is distributed to the intrinsic muscles of the tongue. Division of the two vagi is followed by paralysis of both oesophagus and stomach, with a very firm contraction of the circular band of fibers guarding the cardiac orifice. Therefore these nerves send motor fibers to the oesophagus and stomach, but inhibitory ones to the cardiac 54 PHYSIOLOGY. sphincter. So firm is the tetanic contraction of the sphincter that if food, is swallowed after division of the vagi it accumulates within the oesophagus, no part of it passing into the stomach. The act of swallowing inhibits the vagus center, for a single act of deglutition increases the pulse-rate. This influence upon the heart- beat is dependent upon neither the amount, character, nor temperature of the bolus swallowed. It is influenced only by the reflex act and the summation of other acts. It also has an inhibitory influence upon the respiration. This is very evident during rapid drinking in an animal with a tracheotomy tube. For increasing the activity of the heart's action a tablespoonful of water taken in a large number of swallows is more beneficial than a glass of wine taken in one swallow. THE CHEMICAL CHANGES OCCURRING IN THE MOUTH DURING DIGESTION. As before stated, the chief aim of digestion in the animal economy is the reduction of the alimentary substances into a soluble and ab- sorbable condition before they can pass through the various animal membranes and so become components of the tissues and blood of the body. No matter how soft, through the influence of insalivation, or finely divided and triturated by reason of mastication, the food may be, it cannot become a constituent of the body until it has been acted upon chemically and dissolved by the various ferments present in the different digestive fluids. When food enters the mouth, the commencement of the digestive tract, the first digestive fluid that it comes in contact with is the saliva. Besides its mechanical functions of moistening and softening the food to render easier the task of swallowing it in the form of boli, it per- forms other duties of a chemical nature. First, by reason of its watery base, it has the power to dissolve , saline substances, the organic acids, alcohols, sugars, and a few other substances soluble in water. Secondly, it has the power to transform certain materials, as starches, into maltose, a form of sugar. The starch must have its cellulose coat dissolved by boiling, however, for the ferment in saliva will not act readily upon cellulose. The active, transforming prin- ciple in saliva is an unorganized ferment, or enzyme, to which the name ptyalin has been given. The conversion of starch into sugar by it is known as the amylolytic action of saliva. Its action is by mere contact, for no appreciable change in quantity or character is noted in DIGESTION. 55 it after its functions are performed, and so active is it that it is able to convert two thousand times its own weight of starch into sugar. Ferments do not initiate a chemical action, but alter the velocity of reaction, which occurs in their absence, only then much more slowly or much more quickly. Saliva, as it appears in the mouth, is a thick, glairy, generally frothy and turbid fluid. It is a mixed fluid, its secretions being de- rived from the parotid, submaxillary, and sublingual salivary glands, and contains mucin procured from the labial, lingual, and buccal glands. Then, too, it contains some debris of food, bacteria, and the so-called salivary corpuscles. Its thick, ropy nature is due to the pres- ence of the mucin in it. Normal saliva is- alkaline in reaction, al- though in some forms of dyspepsia it becomes somewhat acid. The specific gravity ranges from 1.002 to 1.006. The amylolytic action of saliva is sensitive to changes of tem- perature, a low temperature either retarding its action or stopping it altogether, while increased temperature causes greater activity until 40° C. is reached, which is considered the optimum point. Above that mark the heat becomes injurious. During the proper mastication and insalivation of a mouthful of food there occurs to the starches present a splitting up into dextrin and maltose; the dextrin is later converted into maltose also. This occurs more quickly with erythrodextrin, which gives a characteristic red color with iodine, than with achroodextrin, which gives no color with iodine. The amylolytic action of saliva is best favored by a neutral medium, although it can take place when the environment is slightly alkaline or acid. The slightest quantity of free acid in excess stops its action at once. Its normal condition in the mouth is slightly alkaline or neutral. In these media the splitting-up process takes place quickly ; but, since the food is usually teld in the mouth for so short a time, all the starches cannot be transformed during the period of mastication. As the gastric juice contains free hydrochloric acid, it has been generally thought that immediately the bolus of food comes in contact with the gastric juice the ptyalin of the saliva is killed and its amylolytic action stopped. Eecent researches have proved that the transforming continues in the stomach for some time after its entry, the time ranging from fifteen to thirty minutes. That is, until (a) the alkalinity of the saliva has been neutralized and (b) until a trace of free hydrochloric acid remains in excess. According to Veldin, free hydrochloric acid does not occur in the stomach until about three- fourths of an hour after a meal. 56 PHYSIOLOGY. The action of saliva upon starch is very readily seen by test-tube experimentation. In a tube is placed a quantity of boiled starchy which is viscid and gelatinous in nature and rather turbid in appear- ance. That it is true starch may be shown by the iodine test, a blue color resulting. With the starch in the tube is mixed a quantity of saliva. Soon there is a marked change: the solution becomes more watery and thinner and the turbidity disappears. On boiling a por- tion of this transparent solution with Pehling's - solution a cuprous oxide is precipitated, showing the presence of sugar in the form of dextrose or maltose. The saliva also contains traces of an inorganic substance, potassium sulphocyanide. Tincture of iron stains it red. In the resting serous gland when stained with carmin it is found that the cells are pale, with but little color, and containing a few minute granules. The nucleus is small sized, without a nucleolus; in shape, irregular, and red stained. The shrinking of the nucleus is well marked. In the active stage the cells are smaller, the nuclei are round, with sharp walls containing nucleoli. The contents of the cell are turbid, due to the lessening of the clear substance and an increase of granules. The carmin stains the cells more profoundly. The salivary glands are greatly influenced by nervous activity. The submaxillary is supplied by the chorda tympani, which contains two kinds of fibers : the secretory and the vasodilator. If you give atropine you can paralyze the endings of the secretory fibers while the vasodilator still continue their activity. Injection of sodium bicarbonate into the duct of Wharton arrests the action of the secretory fibers and leaves intact the vasodilators. Pilocarpine and muscarine increase the flow of saliva by stimulating the endings of the chorda tympani and will remove the paralysis of them by atropine. Opium makes the mouth dry by acting on the center of salivation. The salivation by mercury is due to excessive metabolism of the gland-cells themselves. When the chorda is stimulated by electricity the pressure in the excretory duct is greater than the blood-pressure of the animal. During this stimulation the temperature is elevated. When the chorda tympani is stimulated the blood-vessels of the gland dilate and the veins are red and pulsate because the arterial blood rushes rapidly through them. The antagonistic nerve which slows the secretion of saliva, both in the submaxillary and parotid gland, is the cervical sympathetic. At the same time, owing to its vasoconstrictors, the blood-vessels are contracted. Hence in the submaxillary we have as a secretory nerve the chorda tympani; in the parotid the auriculo- temporal. The nerve playing against them both is the cervical sympa- DIGESTION. 57 thetic. The reflex center for the salivary secretion is situated in the medulla oblongata, near the origin of the niath and seventh cranial nerves. The afEerent nerves are the nerves of taste, the chorda tympani and the glosso-pharjmgeal and sensory branches of the tri- gemirius; the efferent nerves are the auriculo-temporal and chorda tympani. GASTRIC DIGESTION (DIGESTION IN THE STOMACH). The stomach is the principal organ of digestion. As we know, digestion has for its aim the rendition of the organic and inorganic substances ingested from the external world into such a condition that they can readily mix with the blood and so be introduced into the living tissues of the body. For no animal can exist which does not receive materials for its support from the environing media. To accomplish this aim both chemical and mechanical changes are closely interwoven. In the stomach, as one of the principal organs, is per- formed a large and important share of the whole digestive process ; as it were, it is one of the large departments of a mechanical and chem- ical laboratory or establishment in which every department is working toward a definite end : the digestion of the food. Unlike the amylo- lytic changes of the saliva which best occur in an alkaline solution, stomachic digestion is an acid digestion. The stomach is the first organ into which the food passes as it leaves the oesophagus. It is the most enlarged or dilated portion of the entire alimentary canal, being located in the left hypochondriac, epigastric, and right hypochondriac regions. It is a large muscular pouch, and extends from the oesophagus to the small intestine. The greater extremity of the stomach is to the left and communicates with the oesophagus by the cardiac orifice. The pyloric end is the lesser extremity, and at the right communicates with the small intestine by the pyloric orifice. The fundus is the greater extremity of the stomach, and projects several inches to the left of the oesophagus. The lesser extremity for about two LQches of its length is slightly constricted, and is called the pyloric antrum. The pyloric orifice is the entrance to the duodenum, and is about a half-inch in diameter. It contains the pyloric sphincter, or valve. STRUCTURE OF THE STOMACH. The stomach has four coats : from the outside, serous, muscular, fibrous, and mucous. The serous coat is derived from the peritoneum. 58 PHYSIOLOGY. I The miiscular eoat contains three layers of unstriped muscular fibers. The layer of longitudinal fibers is continuous with that of the oesophagus, from which it radiates over the stomach. The middle layer is composed of circular fibers. These circular fibers gradually accumulate toward the pyloric extremity and form a thick band known as the pyloric sphincter. The internal layer con- sists of oblique fibers. The submucous coat is made up of areolar tissue and forms an extensible layer upon which the strength of the stomach maialy depends. The mucous membrane of the stomach is soft to the touch and of a pale-pinkish color. Under excitement it becomes reddened. During digestion and when inflamed it has a deep-red hue, It is thin at the fundus and gradually thickens toward the pyloric extremity. In this place it ordinarily is in a state of wrinkles or rugse, which are longitudinal ia great part. At the pyloric orifice a thick circular fold acts as a part of a valve called the pyloric valve. Structure of Mucous Membrane. Upon an examination with a feeble magnifying power there is found on the mucous membrane a great number of depressions about ^/joo inch in diameter, which are the openings of the glands of the stomach. The mucous membrane is lined with a columnar epithelium. The tubular glands of the stomach are placed side by side and number several millions. These glands have a basement membrane, which separates the glands from one another and in which the capillaries spread a fine network over the tubules. They have also a blind end. They are two kinds of gastric glands: the cardiac and the pyloric. The pyloric glands have at their mouth an epithelium which is a con- tinuation of the columnar epithelium of the stomach. In the tubules the epithelium is shorter and more cubical and granular. In the fundus glands and cardiac glands the epithelium is composed of short columnar cells, and these cells have coarser granules than the pyloric glands. These are the central, or adelomorphous, cells. Between these cells and the basement membrane there are other cells, oval in shape, with distinct oval granular nuclei, called the parietal, or delo- morphous or oxyntic, cells. The blood-vessels of the stomach are derived from the three divi- sions of the coeliac axis. The veins are the tributaries of the portal vein, and contain numerous valves. The nerves are the vagus and sympathetic. Numerous small gangliated plexuses are found: those of Meissner in the submucous coat, like those in the intestine; and Auerbach's, between the muscular fibers, also found in the intestine. DIGESTION. 59 Movements of the Stomach. Dr. Bftaumont, upon a human stomach, ascertained that a very feeble peristaltic contraction begins at the cardiac orifice, to proceed toward the pylorus by way of the greater curvature, for only along it is any movement apparent. The wave grows stronger until the special band separating the antrimi from the fundus is reached, when the contraction becomes so strong that the stomach presents an hour- glass appearance. Immediately the entire antrum contracts at one time as a unit ; so that, if the contents are properly acted upon by the gastric secretion, they are propelled by this movement through the pylorus into the duodenp.m. If, as very frequently happens, the semi- liquid mass contains solid portions of too great bulk to pass through the opening, a muscular wave is set up in the opposite direction. The dirtect result of this is to force into the fundus through the now relax- ing temporary sphincter the food-mass, from where the whole process is begun again. These movements occur with a certain degree of regularity and jhythm, once in about every two or three minutes ; the time and regularity are, however, much influenced by the quantity and quality of the food ingested. As a result of these combined movements, not only is the chymified food propelled into the duo- denum, but there are set up regular currents among the contents. Dr. Cannon has studied the movements of the stomach in cats by means of the Eoentgen rays. He states that the stomach consists of two physiologically distinct parts : the pyloric part and the fundus. Over the pyloric part while food is present constriction waves are seen continually coursing toward the pylorus. The fundus is an active reservoir for the food, and squeezes out its contents gradually into the pyloric part. The stomach is emptied by the formation between the fundus and the antrum of a tube along which the constrictions pass. The contents of the fundus are pressed into the tube and the tube and antrum slowly cleared of food by the waves of constriction. The constriction waves have three functions : the mixing, trituration, and expulsion of the food. The stomach movements are inhibited when the cat shows anxiety, rage, or distress. Cannon has observed in cats that carbohydrate food appeared in the intestine in ten minutes, while proteid did not leave for an hour. Proteids also remained in the stomach twice as long as the fats. CLOSURE OF THE PYLORUS. Each time the acid chyme escapes it sets up a reflex act which temporarily occludes the pyloric orifice and at the same time inhibits 60 PHYSIOLOGY. the propulsive movements of the organ. The acid mass of chyme escaping the pylorus excites an increased secretion of pancreatic juice and the acid is gradually neutralized. When this is accomplished the escape of further acid chyme is permitted. This regulatory action prevents disorder in the progress of digestion and at the same time insures regularity in the transition from the acid gastric digestion to the alkaline intestinal one. THE NERVOUS CONTROL OF THE STOMACH. As known to-day, the nerve-supply to the stomach is from both the cerebro-spinal system and the sympathetic; its connection with the former is through the medium of the vagi, with the latter by the splanchnics through the solar plexus. The fibers of both systems as distributed to the gastric muscles are nonmeduUated. The functions of the vagi have been conclusively proved to be motor, for when they are stimulated by chemical, thermal, or other irritants there results a peristalsis throughout the whole viscus. On the contrary, the fibers from the sympathetic system are inhibitory ; when they are stimulated, peristalsis is stopped and there is dilatation of the sphincter pylori. The stomach also has movements of its own independent of the central nervous system. THE GASTRIC JUICE. Gastric juice mixed with food and water can readily be obtained by the gastric sound or stomach-pump. Pure gastric juice cannot be procured thus, for when the stomach is empty the flow of gastric juice ceases and any surplus remaining in the stomach seems to be reab- sorbed. Its flow is begun again only as the result of stimuli; the natural ones and those, producing what alone may be termed normal gastric juice are food and drink. Normal gastric juice has been procured by feeding an animal a fictitious meal. In this process the foo'd swallowed does not reach the stomach, but passes out of the oesophagus through a fistula. The eating has the power to excite refiexly the flow of the secretion. Gastric juice thus obtained from a dog is "a clear, colorless, limpid fluid, very acid, and peptic in nature. The liquid is practically odorless ; if there is any odor at all present it is characteristic of the animal. Its specific gravity differs very little from that of water." The.largest constituent of the gastric juice is water. In man and animals it is remarkable to note the small quantities of solid matters present and then view the immense amount of work done by them in the digestive processes. Of the solids present, about half are inorganic DIGESTION. 61 salts; the remaining portion comprises the organic ferment, or enzyme, present in gastric juice — ^pepsin. The reaction of gastric juice is undoubtedly acid, caused by the presence of free hydrochloric acid (0.2 per cent.). In the pure secre- tion, free from food, it has been demonstrated that the only acid is hydrochloric. Acid is necessary, for the active ferment of gastric juice, pepsin, can act onlj"^ in an acid medium. During digestion, lactic, acetic, butyric, and other acids are often present, due to putre- factive changes and the presence of bacteria. Pepsin can act in the presence of these acids as media, but not very well. Schmidt's analysis of the composition of gastric juice is as follows : — Water 994.40 Solid residue 5.60 1000.00 Organic matter: Pepsin 3.19 Inorganic matter: Chloride of sodium 1.46 Chloride of potassium 0.55 Chloride of ca.lcium 0.06 Free hydrochloric acid 0.20 Phosphate of calcium Prosphate of magnesium ^ 0.12 Phosphate of iron Secretion of the Gastric Juice. Imbedded in the mucous membrane of the walls of the stomach are two sets of secretory apparatuses : the cardiac and pyloric glands. Naturally, the products of these glands differ somewhat in their char- acters ; so that the gastric secretion as a unit is a mixed body, or solu- tion. This "mixed" gastric juice is a secretion compound of a very small percentage of free hydrochloric acid together with the proteolytic ferment, pepsin, in a rather saline solution. We know that the pepsin, for instance, of the gastric juice, is not found as such in the blood and requiring only to be filtered from the same for use, but that it is the result of the activity of the cells and yielded by them. A characteristic microscopical feature of the cells of- secretory glands in general is that the protoplasmic portions are crowded with fine granular bodies before secretion, but that during and particularly after secretion their numbers are very perceptibly diminished. From 62 PHYSIOLOGY. this it was inferred that, while the granules might not in themselves represent the important ingredients of the various secretions, yet they were responsible and directly concerned in their manufacture. The cardiac glands are composed of two distinctive types of cells : columnar epithelium lining the lumen and the large spherical or oval cells located on the periphery. The former are termed chief, or central, the latter parietal, cells. The pyloric glands are constructed of but the one kind, epithelial in nature, similar to those found in the cardiac cells and termed chief., or central. The central cells of both the cardiac and pyloric glands are found to be heavily charged with minute granules before digestion ; in fact, such numbers are present as to interfere with the staining of the cells with aniline dyes because of the protoplasm being obscured. During secretion some of the granules are discharged into the lumen, pre- sumably through the protoplasmic movements of the cells as agents or media. After digestion, therefore, the cells show a difference, principally in that there is a decrease in the number of granules present, manifested by either a clear path along the periphery or by a shrunken appearance of the cells with fewer granules. The materials for the formation of these granules is taken by the cells from the lymph which constantly bathes them and through the influence of the protoplasm manufactured into granules. The central are the cells which are directly concerned in yielding the very important and proteolytic element of the gastric juice, the pepsin. Without its presence in an acidulated medium, the normal processes of proteolysis are unable to be accomplished in the stomach. These granules are not pure pepsin to be passed along the lumen and so enter the composition of the gastric juice, but are, rather, a zymo- gen substance acting as a precursor -and which is readily converted into pepsin through the influence of the acid. To this intermediate substance has been given the name pepsinogen. The large oval or parietal cells also contain granules which are very few in number and small in size, though quite distinct. These are very constant in quantity, the cells showing mainly differences in size. Thus, before secretion they are swollen, afterward shrunken. They are frequently termed oxyntic, as they are thought to secrete hydrochloric acid, one of the essential compounds of the gastric secre- tion. The exact process, however, is still shrouded in mystery. It is thought to result from a simple process of diffusion in the parietal cells of chlorides taken from the blood, for during secretion the DIGESTION. 63 quantity- of chlorides leaving the blood through the kidneys is dimin- ished. Maly's theory with regard to this is very satisfactory. In it he claims that the acid originates by the interaction of the calcium chloride with the disodium hydrogen phosphate of the blood. The interaction is simplified by the following equation of Maly's : — gNa^HPO, + SCaCl^ = Csl^{T?0^)^ + 4NaCl + 3HC1 Disodium Calcium Calcium Sodium Hydro- hydrogen chloride. phosphate. chloride. chloric phosphate. acid. Permed in the central cells is another zymogen than pepsinogen, which, when mixed with acid, produces an enzyme, or ferment, known as rennin. This ferment has the power to coagulate milk, forming casein. Eennin is found wherever pepsin is manufactured, although distinctly different in character and action. There are vegetable pep- sins, like papain of Carica papaya and bromelin of the pineapple. The fluid is not poured out at the same rate from the beginning to the end of digestion. The Mett method of preparing the proteid is to fill a glass tube, one to two millimeters in diameter, with egg- albumin and coagulate it at 95° C. The tube is then cut into small pieces and placed in 1 or 3 cubic centimeters of the juice to be investi- gated. The law of Schuetz is as follows : The quantity of pepsin in the compared liquids is proportionate to the square of the rapidity of digestion; that is, the square of the column of proteid in a Mett tube expressed in millimeters which the juices are capable of digesting in the same period of time. If one of the fluids digest a column of 3 millimeters of proteid and the other a column of 3 millimeters, the relative quantity of pepsin in each is not expressed by the figures 3 and 3, respectively, but by the squares of them ; that is, 4 and 9 ; so that the second liquid is two and one-fourth times stronger than the first. Not only the quantity of the secretion varies, but the secretion varies in composition with a greater or less quantity of ferment. Other properties of the juice are likewise varied. In one and the same juice the different ferments may suffer variations, running courses independently of each other, a fact which undoubtedly shows that the pancreas, which has a complex chemical activity, is able to furnish, during given periods of its secretory work, now one prod- uct and now another. That which may be said of the ferments may also be applied to the quantities of the salts in the juices. The gastric juice always has the same acidity as poured out by the glands, but on running over the walls of the stomach the mucus can neu- tralize 35 per cent, of it. The food also neutralizes the acid. 64 PHYSIOLOGY. At the beginning of digestion, when the quantity of food is large and its external structure still coarse, the strongest juice should be poured out when most needed. The greatest digestive power belongs to the juice poured out on bread, which might, for brevity, be called "bread- juice"; the next strongest is "flesh- juice," and then comes "milk-juice." In other words, "bread-juice" contains four times as much ferment as "milk- juice." Not alone the digestive power, but likewise the total acidity, varied according to the nature of the diet. Coniparing equivalent weight, flesh requires the most and milk the least gastric juice; but taking equivalents of nitrogen, bread needs the most and flesh the least. The hourly intensity of gland work is almost equal in the case of milk and flesh diets, but far less with bread. The bread, however, exceeds all others in the time required for its digestion, and the duration of the secretion is correspondingly protracted. Bach separate kind of food corresponds to a definite hourly rate of secretion, and calls forth a characteristic alteration of the properties of the juice. Thus, with flesh diet the maximum of secretion occurs during the first or second hour, and in both the quantity of juice furnished is approximately the same. With bread diet we have always a sharply indicated maximum in the first hour, and with milk a simi- lar one during the second or third hour. On the other hand, the most active juice occurs with flesh in the first hour, with bread in the' second and third hours, and with milk in the last hour of secretion. The point of maximum outflow as well as the whole curve of secretion is always characteristic for each diet. On proteid in the form of bread flve times more pepsin is poured out than on the same quantity of proteid in the form of milk, and the flesh-nitrogen requires 25 per cent, more pepsin than that of milkr. These different kinds of proteid receive, therefore, quantities of ferment corresponding to the differ- ences in their digestibility, which we already know from experiments in physiological chemistry. Excitants of Flow of Gastric Juice. In his dog adapted for sham feeding Pawlow cut up meat and sausage before the dog, when he obtained a great flow of gastric juice, more so than when he fed the dog with them and they escaped by the oesophagus. Here is a psychic excitation of the gastric secretion, which plays a considerable part in the production of gastric juice in the sham feeding experiment. The appetite is then the first and mightiest exciter of the secre- DIGESTION. 65 tory nerves of the stomaeli. A good appetite in eating is equivalent from the outset to a vigorous secretion of the strongest gastric juice. Sham feeding of five minutes does not call forth a secretion for longer than three to four hours. Mechanical excitation of' the mucous membrane of the stomach does not cause the. flow of gastric juice. Sodium bicarbonate in the stomach inhibits its secretion. Liebig's extract or meat-broth intro- duced into the stomach increases the secretion of gastric juice. Fat in the stomach inhibits the psychic secretory action of the stomfich upon meat. The fat of milk can inhibit its digestion to a certain extent. The secretory activity of the stomach depends on nervous proc- esses. In the immense majority of cases gastric digestion begins by a strong central excitation of the secretory and trophic fibers of the glands. Secretory Nerves of the Stomach. In a dog with a cannula in the stomach and the oesophagus opened so that food leaving the mouth goes through the opening in the oesophagus, and not into the stomach ("sham feeding"), the swallow- ing of food caused a great increase of flow of gastric juice. If, now, the pulmonary and abdominal vagi are divided on both sides, then sham feeding causes no flow of gastric juice. These experiments show that the gastric glands receive their normal impulses to activity by means of nerve-fibers in the vagi. Pawlow believes that secretory nerves of the stomach run in the vagi. Pawlow also excited the vagi after a previous section for some days and obtained an increase of gastric secretion. Atropine paralyzes the secretory nerves of the stomach. By the secretory fibers we mean those, according to Hei- denhain, which stir up the secretion of water and inorganic salts of the gastric juice. The trophic fibers are concerned in the secretion of the ferment of the gastric juice. Sooner or later after the taking of food the influence of the reflex excitant comes into play, while the psychic effect dies out. If meat has been eaten the secretory center will still be strongly excited in a reflex manner from the stomach and intestine, while at the same time the trophic center receives only weak impulses from the peripheral terminations of the nerves in question. When bread is eaten the reverse happens. After the cessation of the psychical stimulus the secretory fibers are now only weakly excited through the end-apparatus ; the trophic, on the other hand, are strongly influenced. In the case of fat foods reflex inhibitory impulses proceed to the centers which affect the activity of both secretory and trophic nerves. 66 PHYSIOLOGY. ACTION OF AGENTS ON THE STOMACH. When absolute alcohol or a strong emulsion of oil of mustard is introduced in the small stomach (Pawlow) there was an enormous secretion of mucus. Ice-cold water in the large stomach (Pawlow) causes the secre- tion, which is subsequently produced by an ordinary meal, to be less Fig. 5. — ^Dog's Stomach. (Pawlow.) I, A-B, Line of incision. C, Plap for forming stomach-poucli of Pawlow. II. V^ Cavity of large stomach. S, Pawlow's pouch, or small stomach. A^ A, Abdominal wall. than normal, more especially in the first hour; here is a special inhibitory reflex. When alcohol is poured into the large stomach (Pawlow) an extremely free secretion of gastric juice begins in the small stomach (Pawlow). The secretion in the small stomach was compensatory for the arrested secretion in the large stomach. DIGESTION. 67 In hypersecretion of the stomachs of dogs he found sodium bicar- bonate to have a good effect. In hyposecretion he found water a good agent. Bitters act in promoting gastric secretion by exciting a change of the taste, an appetite. TJie unpleasant taste-impressions of bitters by contrast awakens the idea of pleasant ones. Hydrochloric acid, when secreted in considerable quantity, .pre- vents further secretion of gastric juice. Phosphoric acid does not inhibit. Butyric acid excites strongly gastric secretion. ACTION OF THE GASTRIC JUICE. The amylolytic action of the saliva, conversion of starch into maltose, was dependent upon the presence of ptyalin, an organic fer- ment whose action is best carried on in a neutral or alkaline medium. The proteolytic action of the gastric juice is due to the presence of its organic ferment, or enzyme, — pepsin, — in an acid medium. A par- tial digestion of certain foodstuffs can be accomplished in an acid solution, if given sufficient time and the proper temperature. There is, however, a strong tendency toward putrefaction during the process. On the other hand, pepsin alone is unable to perform any dissolution or digestion of the foods with which it comes into contact. But, if to it a 0.2-per-cent. solution of hydrochloric acid is added, proteolysis proceeds quickly and energetically. The powers of the gastric juice cannot be attributed to the presence, then, of its acid or pepsin alone, but to a combination which may be termed pepsin-acid. Thus gastric digestion is an acid digestion, and demands a knowledge of chemistry, for it is in many respects a chemical act. The result of the action of gastric juice on food is essentially the same whether the act takes place within the body or outside of it. Life has nothing to do with it, for it is a chemical action on the proteids of the food. In the stomach, then, the main process of digestion is the conversion of the proteids, through intermediate stages, into peptones, for proteids are incapable of diffusion through animal membranes in the act of absorption. Thus it can safely be stated that the prime and essential func- tion of the gastric secretion is to dissolve the proteids present and convert them into peptones. Gastric juice exercises no amylolytic influences upon any starch present; in fact, three-fourths of an hour after a meal, the action going on due to the saliva swallowed with the food is stopped alto- gether by reason of traces of free hydrochloric acid secreted by the oxyntic cells. 68 PHYSIOLOGY. There is a fat-splitting ferment in the gastric juice of the fundus. Those mineral matters which can be dissolved in hydrochloric acid of the strength of that found in the gastric juice are also dis- solved in the stomach. The degree of solubility and efficiency at- tained by the gastric secretion far surpasses that of simple, diluted acid, probably because of the pepsin found in the former. Although the amylolytic action of the saliva on starch takes place for a definite interval, the gelatinous envelopes of the fat-globules and mineral substances are dissolved within the receptacle of the stomach, yet the essential and characteristic feature of the work to be done there is on the proteids: converting them into peptone through the action of proteolysis. The proteids found in Nature are very complex and as yet not thoroughly known. However much they, as individuals, may difEer in composition, reactions, etc., yet they all possess an inherent tendency to undergo hydrolytic decomposition when conditions are favorable. Hydration and cleavage can be induced by simple heating in water alone raised to the temperature of 100° C, for there results partial solution of the proteids during the process. The proteolytic process of the gastric secretion in its converting proteids into peptones is also one of hydration and cleavage. The final products are not the. result of one simple step, not the formation of one simple body or substance, as when the proteids are acted on by heated water alone. The acid in gastric digestion induces a row of chemical changes and products, each separate and distinct, and capable of being recognized by certain reagents. By the action of pepsin-acid the proteid is first changed into (1) syntonin, or acid-albumin. By further action of the ferment the acid- albumins are changed into (2) proteoses j with their divisions into primary and secondary proteose. The proteoses are the intermediate products between acid-albumins and peptones. These are found un- der various names in this group; as, the proteoses may be derived from albumin, when they are called albumoses; or from globulin, when the name globuloses is used. The proteoses are soluble in warm water, acids, and the alkalies. They are only slightly diffusible and coagulated by the action of heat. Nitric acid produces a white pre- cipitate, which is colored yellow by heat and dissolved again. When cool, the precipitate occurs again; this recurrence of the precipitate upon cooling is a distinctive feature of proteoses. By the continued proteolytic action of the gastric juice, the proteoses are changed into (3) peptones, the final, diffusible products DIGESTION. G9 of gastric digestion. They are simply the result of a process of hydration. The peptones are very diffusible, particularly in acid solution. The utility and benefit to be derived from that characteristic is very evident when we keep in mind the chief aim of digestion: to render foodstuffs into soluble conditions so that they may be readily absorbed and so become a component of the blood and eventually of the tissues. The peptones are soluble in water, but not precipitated from their aqueous solutions by the addition of acids or alkalies, or by boil- ing. In fact, peptones are never coagulated by heat. They are not precipitated by nitric acid, copper sulphate, ammonium sulphate, and a number of other reagents usually held as preeipitants of proteids. A cold mixture of peptones with a strong solution of caustic potash will give, on adding only a trace of cupric sulphate, a decided pinh color. Other proteids give a violet color. However, the chief and striking feature of peptones is their great diffusibility. Other forms of proteid matter pass through animal membranes with yery great difBculty, if at all. When the proteids have been reduced to peptones, they are ready for absorption into the blood through the capillary walls. However, proteoses, the intermediate products, although less diffusible than pep- tones, find their way, to some extent, also, through the capillary walls. Experiment has demonstrated that pure proteoses or even peptones introduced directly into the blood are more or less toxic, and the system behaves toward them as foreign bodies, striving to get rid of them as speedily as possible. From this it is evident that there must be some transformation in the very act of diffusion through the capillary walls, else the nutritious proteid matters are not used in constructive metamorphosis, but expelled as foreign matters. The agencies which act upon these proteoses and peptones in some manner destroy their toxic tendencies and probably convert them into the serum-albumin, or globulin, of the blood. The fact that peptones are not found in the blood and lymph during or directly after digestion confirms this idea, since peptones are absorbed as soon as manu- factured. An excess of peptone in the stomach-contents would have the power to arrest proteolysis by its mere presence. A preparation on the market is somatose, a mixture of albumoses produced by the action of a ferment on meat. It is a predigested beef, and readily absorbed. It dispenses with so much fluid as is necessary in pep- tonized milk. 70 PHYSIOLOGY. Antiseptic Action of the Hydrochloric Acid in Gastric Juice. Besides the function which hydrochloric acid exercises as a com- ponent of the gastric secretion, — namely: of rendering the pepsin in it active, — it possesses another very powerful property as a dis- infectant and germicide in that it can kill many bacteria that are taken in with the food. By means of it the bacteria producing putrefaction are killed, and thus disorders in the entire constitution as a result of abnormal digestion are prevented. Even when putre- faction has occurred in the food previous to its entrance into the stomach, upon reaching this receptacle it is stopped. Many pathological bacteria are likewise destroyed by the acid in the juice, although some, as the bacillus of tuberculosis and that of splenic fever, are unaffected. It is interesting to note that experi- ment has shown that just about the amount and strength of hydro- chloric acid as that in the stomach is needed outside the body to accomplish the death of putrefactive and many pathological germs. Acetic and lactic fermentations are arrested by mere traces of hydro- chloric acid. To epitomize: The general action of gastric juice is to convert the proteids into peptones by various stages. The fats are split up. Starch is unaffected. The general result is a souplike mass in the stomach, which undigested food is passed through the pylorus into the duodenum of the small intestine, and is called chyme. The average time that food remains in the stomach is about three hours. Giinzberg's Test for Hydrochloric Acid. — "With a solution of phloroglucin and vanillin in alcohol mix. a drop of a 0.2-per-cent. solu- tion of hydrochloric acid; evaporate slowly in a porcelain capsiile, when a red color vidll appear. Uffelmann's Test for Lactic Acid. — Add a trace of a solution of ferric chloride to a 1-per-cent. solution of carbolic acid. This ame- thyst-colored solution will change to canary yellow on the addition of lactic acid. VOMITINQ. Vomiting is a spasmodic rejection of food from the stomach, and is usually a sign of some malady. The ease with which animals vomit is dependent upon the conformation of the stomach, particularly with regard to the fundus, as well as the condition of its contents. Thus, a child vomits easily, since its fundus is not very well developed; with tb,e adult the act is one of great difficulty. DIGESTION. 71 When the person is conscious, vomiting is usually preceded by a sensation of nausea, during which the saliva flows very freely into the mouth. While the food is being swallowed considerable air enters the stomach and later assists actual vomiting by helping to dilate the cardiac orifice. Before the real expulsion occurs and during the efforts to accomplish the same a very deep inspiration is taken jnst as in the act of coughing. Immediately the glottis closes and the muscles of the abdomen commence to contract very actively. In- stead of the glottis opening to permit an expiration, it remains tightly closed, thereby holding the diaphragm immovably fixed and so furnishing an unresisting plate against which the stomach is pressed. Immediately preceding the pressure brought to bear upon the stomach by the contraction of the abdominal muscles, there occurs a shortening of the longitudinal fibers of the oesophagus, thereby bringing the cardiac orifice of the stomach nearer the diaphragm, to form a straight passageway for the vomit to the pharynx. The muscles of the sphincter at the cardiac orifice are rather suddenly dilated, forming a funnel-shaped opening at the beginning of escape, since the pylorus usually remains closed. By the abdominal con- tractions and slightly assisted by gastric movements also, some of the contents of the stomach is forced into the opening of the oesophagus, where its movement toward the pharynx and mouth is aided by con- tractions of the oesophageal circular fibers : the reverse of what occurs when a bolus of food is swallowed. Thus there are two separate and distinct acts occurring during vomiting: (a) the dilating of the cardiac sphincter and (h) the expulsive movements of the abdominal muscles. The absence of either act is detrimental to the accomplishment of vomiting. The pyloric gate is usually closed during vomiting; so that little or no substances find their way into the duodenum. However, when the gall-bladder is very full, the movements of the surrounding organs force its contents into the duodenum and very frequently some of the bile finds its way into the stomach, from whence it passes out through the oesophagus, pharynx, and mouth in bilious vomiting. That the expulsive impetus is mainly given by the contractions of the abdominal walls and not the gastric movements alone has been proved by experiment. The stomach of an animal was excised and replaced with a bladder filled with water and attached to the oesoph- agus by means of a rubber tube. When the wound was closed and an emetic injected, the contents of the bladder were immediately expelled through the mouth. 73 PHYSIOLOGY. Vomiting is normally considered to be a re-flex action, although in some instances vomiting may proceed at will or be acquired after some practice. The afferent nerves are principally the -fifih, the glosso-pharyngeal, and the vagus. The center of- vomiting is located in the medulla oblongata. The efferent impulses are conveyed by the vagi to the stomach, phrenics to the diaphragm, and various spinal nerves to the abdominal muscles. Thus vomiting may arise: — 1. From irritation of the stomach, as when this organ is too full. 2. Prom tickling the vault of the palate. 3. Prom intestinal irritation by worms. 4. From irritation of the. uterine mucous membrane during the first three months of pregnancy. 5. The remembrance or sight of disgusting sights, or patho- logical disorders of the brain may cause it, which proves that the brain is united to a vomiting center. 6. The use of emetics, which do not all act alike. Thus, some emetics, as copper sulphate, mustard, etc., produce emesis because of their irritating effects upon the peripheral nerves in the mucous membrane lining the stomach. Others, like tartar emetic, apomorphine, etc., attain the same results by reason of their stimulat- ing the vomiting center in the medulla. DIGESTION IN THE INTESTINES. When the food is converted into chyme and partially dissolved by the gastric Juice, it passes into the small intestine, where it is subjected to new reagents: the bile, pancreatic juice, and intestinal juices. Here the food is prepared for absorption, forming what is called chyle, which is rapidly taken up by the chyliferous vessels. Because of the small and large calibers of the two parts of the intestinal tract, the portions have received the names of small and large intestines, respectively. The small intestine, the continuation of the stomach, opens into the large intestine by an orifice which is guarded by the ileo-ccecal valve. Under ordinary and normal condi- tions this valve allows the passage of the remnants of active digestion to pass through from the small into the large intestine; very rarely does the reverse occur, except in some cases of hernia and other ob- structions in the large intestine. THE SMALL INTESTINE. This tube is cylindrical and much convoluted. It occupies the umbilical region and is suspended from the vertebral column by the DIGESTION. 73 mesentery. It measures about twenty-five feet in length, and its diam- eter is about one and three-fourths inches. As it continues to join the large intestine it becomes slightly narrower. It consists of three parts : the duodenum, jejunum, and ileum. The duodenum is twelve fingers' breadth in length, and it is the widest part of the small intestine. It commences at the pyloric end of the stomach and opposite the second lumbar vertebra; it terminates in the jejunum. The common bile-duct and the pan- creatic duet perforate the inner side of the duodenum. The jejunum constitutes two-fifths of the small intestine. It is wider than the ileum and is characterized by the absence of the agminated glands. The ileum constitutes three-fifths of the small in- testine, and terminates in the right iliac region by joining the large intestine at a right angle. Structure of Small Intestine. Like the stomach, the intestine has four coats: (1) the external serous, (2) the muscular, (3) the submucous, and (4) the mucous coat. The serous coat is furnished by the peritoneum. The muscular coat is composed of two layers of pale, unstriped fibers, the external layer of longitudinal fibers, and the internal layer of circular fibers. The submucous coat is thinner than that in the stomach, but is also extensible. The mucous coat is thinner and redder than that of the stomach, and, like it, has a columnar epithelium. It has folds of mucous and submucous tissue, running in a transverse direction and in the shape of a crescent, which are called the valvulse eonniventes. These valv- ulse are more abundant in the upper part of the small- intestine, where they overlap the edges. As you go down the small intestine you find the number of the valvule gradually lessen, and in the ileum they disappear. These folds are permanent. The minute elevations called villi beset the mucous membrane of the small intestine and even the valvulse eonniventes. They give a velvety appearance to the surface of the small intestine. In the upper part of the small in- testine the villi appear as fine folds, but farther down the intestine they appear as flattened, conical projections. The villi are V40 ^'^^ in height and in structure are appendages of the intestinal mucous membrane. They are covered with a columnar epithelium and com- posed of lymphoid tissue. Inside of the villi are found the lacteal blood-vessels and a few unstriped muscular fibers. In the center of the villus the lacteal begins very near its extremity as a blind end. 74 PHYSIOLOGY. The imstriped iniiscular fibers in the villus run in a longitudinal direction. The number of the villi has been estimated to be about four millions. Glands of the Small Intestine. There are four kinds of glands in the mucous membrane of the small intestine. They are : duodenal, or Brunner's ; glands of Lieber- kiihn; solitary; and agmiuated glands, or Peyer's patches. Brunner's glands are small, racemose glands situated in the sub- mucous tissue of the duodenum. Toward the end of the duodenum they gradually disappear. The glands of Lieberkiihn are the most numerous of all the glands of the small iatestine, and they exist from the pyloric end to the ileo-csecal valve. They are placed in a vertical direction in the thick- ness of the mucous membrane and open between the villi. They are about ^/loo inch in length. They have thin walls lined with a co- lumnar epithelium. The solitary glands are found in all parts of the mucous mem- brane of the small intestine. They are minute, whitish, oval or rounded bodies scattered singly ia the intestine. They are closed vesicles, and are situated in the submucous tissue. They are lymph- nodules composed of retiform tissue and lymphocytes. The agminated glands (Peyer's) are formed of solitary glands, disposed ia oval patches. Usually there are fifteen to thirty of these patches, from one-half to two inches in length, and one-half inch in breadth. The ileum is their usual habitat, and they are seated opposite the attachment of the mesentery. In the neighborhood of the ileo- csecal valve they are larger and more numerous. As the duodenum is approached they are smaller and fewer. In youth they are distinct, less so in adult life, and in old age may disappear. They are the seat of ulceration in typhoid fever. The arteries of the small intestine are the superior mesenteric and pyloric. The lymphatics are numer- ous. The nerves are given off by the solar plexus. Beneath the mucous coat in the areolar tissue of the small intestine are Meissner's ganglia. Between the muscular coats the ganglia of Auerbach can be found. THE LARGE INTESTINE. This is a cylindrical tube differing from the small intestine in having a greater capacity and a sacculated appearance. It is about five feet in length and extends from the ileo-csecal valve to the anus. It encircles the abdomen in its course. Like the small intestine, it DIGESTION. 75 is divided into three parts : the cascum, colon, and rectum. The head of the colon, the csecum, is a wide, blind pouch, or cul-de-sac, about two and one-half inches in length and breadth. Toward its bottom it curves inwardly and backward and is abruptly reduced to a wormlike prolongation — the vermiform appendix. The small intestine opens into the csecum, the orifice being guarded by the ileo-csecal valve. The second and largest part of the large intestine is the colon, and it ex- tends from the csecum to the rectum. It consists of four parts, the ascending, transverse, and descending colon, with the sigmoid flexure. Its diameter is greatest at its commencement, being about two and one- half inches ; but it gradually lessens to an inch. The sigmoid flexure is shaped like the letter S. It is the narrowest part of the colon. The rectum extends from the sigmoid flexure to the anus. It is about seven inches in length. When distended the rectum is club-shaped, being narrow above and expanded just before it contracts to the anus. The anus is completely surrounded by a sphincter muscle. Structure of Large Intestine. The caecum and colon, like the small intestine, have four coats : the (1) serous, (2) muscular, (3) submucous, and (4) mucous. The mucous membrane contains two kinds of glands : the glands of Lieber- kiihn and the solitary glands. The glands of Lieberkiihn are closely set together and give a peculiar sievelike appearance to the surface of the mucous membrane. Experiments upon the csecum of the cadaver prove that the action of the ileo-csecal valve is not dependent upon muscular contraction, for fluid forced through the large intestine rarely passes into the ileum. When the caecum is fllled the dilatation of the same presses upon the folds of the valve so as to squeeze them tightly together and thus prevent any reflux into the small intestine. MOVEMENTS OF THE INTESTINES. As was the ease with the oesophagus, the intestines are composed of two muscular coats, an outer longitudinal one and an inner circular one. Movements in them are caused by alternate contractions and relaxations of adjoining portions of the tube. To the characteristic movements of the intestines two names have been given to describe two separate forms : (1) peristaltic and (2) pendular. Peristalsis. — By this term is implied the alternate contractions and dilatations of adjoining segments to produce a wavelike motion which proceeds from its point of origin anywhere along the intestinal 76 PHYSIOLOGY. tract away from the stomach. "Antiperistalsis" is the term used to designate the movements running in an exactly opposite direction: that is, toward the stomach. This is said never to occur under normal conditions. Pendular Movements. — These are the very slight swinging to-and- fro oscillations, probably caused by the contractions of the longitudinal fibers. NERVE-SUPPLY OF THE INTESTINES, The intestines are supplied with nerves from the sympathetic system mainly, with a few filaments from the vagus. The sympathetic ganglia of Auerbach lie between the two muscular coats and extend from the oesophagus down throughout the small and large intestine. Meissner's ganglia, also belonging to the sympathetic system, lie in the submucous coat. The vagi convey motor impulses to the intestine, while the sympathetics mainly convey inhibitory, although they also carry motor, impulses. Slight stimulation of the splanchnic calls out motion, strong stimulation inhibition of the intestinal movements. I have found that, when the vagus is divided in a rabbit and the cardio- inhibitory fibers are allowed to degenerate for five days, electric stimu- lation of the cut vagus slows the pendular movement. I have found, also, that eserine, nicotine, and muscarine act on the intestino-motor ganglia, while atropine and opium act on the intestino-inhibitory ganglia. Salines are supposed to act as aperients by their presence in the blood, causing an increased secretion to be poured out by the blood- vessels into the intestinal canal. The theory of endosmosis has been abandoned. PANCREAS. The pancreas is a long gland of a reddish-cream color, and situ- ated behind the stomach. Its pointlike extremity comes in contact with the spleen. It closely adheres to the duodenum. It is about seven inches in length, its width about one and' one-half inches, and its thickness about one-half inch. The right and large end is the head ; its left free end is its tail. The duct of Wirsimg, or the pan- creatic duet, the size of a goose-quill, runs the entire length of the gland. Upon leaving the pancreas the duct penetrates the wall of the duodenum, opening, in conjunction with the common biliary duct, about three inches from the pylorus. Structure. In structure the pancreas is a compound tubular gland, resem- bling the salivary glands. In fact, it has very frequently been called DIGESTION. 77 the abdominal salivary gland. The lobes are composed of ducts which have been convoluted, terminating in alveoli or sacs and which unite with other tubules so as to communicate with the main duct. The small ducts are lined with short columnar epithelial cells which are smaller than those of the salivary glands. The secretory cells of the pancreas are large and rounded, being distinctive in that they possess an outer portion which is nearly or quite homogeneous, staining readily with dyes, and an inner portion, very granular, which does not stain easily. The latter forms about two-thirds of the cell. When the gland is inactive the cells are heavily charged with granules and the lumen is almost invisible. When active, the cells first swell up and press outward against the basement membrane, later diminish in size as the granules pass out through the now opened lumen, and so leave a large, clear zone. The presence of these numerous small granules mark the presence in the cells of a zymogen, termed trypsinogen, which is the precursor of trypsin, the active ferment of the pancreatic juice. In the interalveolar tissue are islets of small cells permeated with a close network of convoluted capillaries. These cells are also met vfith in the carotid and coccygeal glands. In the pancreas they are called cells of Langerhans, and are often degenerated in pancreatic diabetes. The pancreatic blood-vessels are derived from the splenic and branches of the hepatic and superior mesenteric. Its nervous supply comprises networks of fibers from the splenic plexus. Pancreatic Secretion (Pawlow). Each kind of food determines the secretion of a definite quantity of pancreatic juice, while the result as regards ferments is truly strik- ing. The greatest amount of proteid ferment is found in "milk- juice," less in "bread-juice" and "flesh-juice." The most amylolytic ferment occurs in "bread- juice," less in "milk-juice" and "flesh-juice." On the other hand, "bread-juice" is extraordinarily poor in fat- splitting ferment; "milk-juice," on the contrary, is very rich, "flesh- juice" taking an intermediate position. It is clear that as regards the two latter ferments the properties of the juice correspond with the requirements of the food. The starch-holding diet receives a juice rich in amylolytic ferment, and the fat a juice rich in fat-splitting ferment. The behavior of the proteid ferment may puzzle. In the work of the gastric glands we saw the weakest, here in pancreatic juice the strongest, ferment poured out on milk. When, however, we take 78 PHYSIOLOGY. the quantity of juice into consideration, we find here also that adminis- tration of like quantities of proteid in the form of bread, flesh, and milk calls forth a secretion as regards the first of 1978, as regards the second of 1502, and as regards the third of 1085 ferment units; that is to say, vegetable proteid likewise demands from the pancreas the most, milk and milk proteid the least, ferment. The difference be- tween the stomach and the pancreas is limited to this : that the former pours out its ferment in very concentrated form upon bread, the latter in a very dilute condition. This fact strengthens the supposition that in the digestion of bread a large accumulation of hydrochloric acid has to be avoided. When in feeding animals the kind of food is altered and the new diet maintained for a length of time, it is found that the ferment-con- tent of the juice becomes from day to day more and more adapted to the requirements of the food. If, for example, a dog has been fed for weeks on nothing but milk and bread and is then put on an exclusive fiesh diet, which contains more proteid, but scarcely any carbohydrate, a continuous increase of the proteid ferment in the juice is to be observed. The capability of digesting proteid waxes from day to day, while, on the contrary, the amylolytic power of the juice continuously wanes. When under the influence of a given diet this or that condition of the pancreas 'had been established in experiment-animals in charac- teristic form, Pawlow was able, by altering the feeding, to reverse it several times in the same animal. It seems then that the gastric and pancreatic glands have what may be called a form of instinct. They pour out their juice in a manner which exactly corresponds both quali- tatively and quantitatively to the amount and kind of food partaken of. Besides, they secrete precisely that quantity of fluid which is most advantageous for the digestion of the meal. . Hydrochloric acid of gastric juice acts on epithelium of duodenal mucous membrane, producing secretin^ which, when absorbed, greatly • excites pancreatic secretion. Pats in the stomach retard stomachic secretion, but increase pancreatic secretion, chiefly by a reflex action through the duodenum, and not from the mucous membrane of the stomach. Sleep does not arrest pancreatic secretion. Psychical effect, strong- craving .for food and water, are common excitants for both gastric and pancreatic secretion. The extractives of meat excite the gastric secretion, while acids and fats excite the pancreas. Sodium bicarbonate and alkalies inhibit pancreatic secretion. DIGESTION. 79 Secretory Nerves of Pancreas. In nonnarcotized dogs whose vagus was divided four days pre- viously and whose eardio-inhibitory fibers had lost their irritability, Pawlow irritated the vagus without pain and obtained an increased pancreatic secretion. He found that vasoconstriction of the pan- creatic vessels prevented the action of the vagus on the pancreas, as did compression of the aorta and pain. He also found in the vagus inhibitory fibers of the secretion, as well as secretory. He believes that secretory fibers also run in the sympathetic, not only for the pancreas, but also for the stomach. The usual method of obtaining pancreatic juice for experimental purposes is by insertion of a cannula or fistula into the duct of Wirsung. By this method practically normal secretion is procured whose composition is variable at difierent times, depending upon whether the fluid is collected three or four hours or two or three days after the operation. The secretion examined shortly after the opera- tion is meager in quantity, though rich in solids ; that collected a day or two later is more copious, but contains a smaller proportion of solid constituents. This is probably due to inflammatory changes in the pancreas as a result of the operation. The pancreatic Juice examined is usually obtained from dogs, human secretions of the gland having been but rarely analyzed and it has never been obtained under quite normal conditions. Most experiments are performed with the aid of an artificial juice made by mixing a weak alkaline solution (1 per cent, sodium carbonate) with a glycerin extract of pancreas. It is usual to treat the pancreas with a dilute acid several hours previous to its being mixed with glycerin to convert the zymogen or mother-substance, trypsinogen, into the ferment, trypsin. Normally, the pancreatic juice is colorless, viscid, and gummy ; it fiows in large, pearl-like drops, which become foamy on agitation. The fiuid is without odor, and gives to the tongue an impression of a viscid liquid and a taste like that of salt. The reaction is always alkaline; its specific gravity about 1.030. In consequence of the removal of a pancreatic tumor Zawadski obtained human pancreatic juice through the fistula remaining, which possessed powerful digestive properties, and found it to be made up of the following composition in a thousand parts: 135.9 parts were of solid nature, the remaining ones being water. Of the solid portions, 92 were proteids, 3.4 parts were inorganic in nature, while the re- mainder were organic substances soluble in alcohol. The figures rep- 80 PHYSIOLOGY. resenting the quantities of secretion in twenty-four hours vary con- siderably as given by different observers, but it has been roughly esti- mated to average about 8 ounces. The flovir of pancreatic juice is somewhat as follows : Before the meal is finished there begins the secretion, which reaches its maximum point at about the third hour. After this the secretion sinks till about- the sixth or seventh hour, when it increases to the ninth or- eleventh hour, only to sink gradually to the eighteenth or twentieth. When the quantity is greatest the quality is poorest, and vice versa. Thus the function of the pancreas in man is intermittent. During secretion the gland is very red, its vessels dilated, and the venous blood red. During repose the gland is flat and of a pale-yellow color, while its blood-vessels are contracted. The secretion is probably caused by secretin and the reflex action due to the contact of the foods. The pancreatic secretion can be moderated or suppressed equally by reflex action, notably in vomiting. Of the 3.4 parts of an inorganic nature, the most abundant is sodium chloride, with alkaline and earthy phosphates and alkaline carbonates. The alkalinity of the juice is due principally to the phos- phates of sodium. Pilocarpine increases the secretion, while atropine diminishes it. The organic matters of the pancreatic juice comprise four principal enzymes or ferments. They are: (1) trypsin, (3) amylopsin, (3) steapsin, and (4) a milk-curdling ferment. Trypsin, a very important constituent of the pancreatic secretion, is much like pepsin of the gastric juice, in that it is a proteolytic enzyme acting on the proteids and transforming them into peptones through intermediate stages. However, its fermentative powers are much stronger and its range of activity extends over more space than do those of pepsin. Although pepsin and trypsin, possess many prop- erties in common, yet they are distinctly different and separate bodies. The main, characteristic difference is that pepsin requires an acid medium for its activity, while trypsin acts and performs its functions best in an alkaline solution whose strength ranges from 0.5 to 1 per cent. Experiment has proved that trypsin can act in a neutral or very slightly acid medium. A remarkable feature of trypsin is the large and rapid transfor- mation of proteid matter of any kind into peptone which it produces by means of only a moderately strong solution. Thus, it is a very capable body to take up the work of proteolysis where the pepsin of the gastric juice left it, since it is particularly a peptone-forming ferment. DIGESTION. 81 As the final products of pepsin-proteolysis, there resulted peptones. When these come into contact with the pancreatic juice, they were quickly broken down into simple, crystalline bodies, as leucin, tyrosine aspartic acid, and arginin. Like pepsin, the proteolytic action of trypsin is one of contact also, only it displays its powers more remarkably and energetically, in that it needs no enTironing bodies to set it in action other than water, the proteid matters, and temperature equal to that of the body. Trypsin displays no digestive powers on nuclein, keratin, or starches. Hydrochloric acid quickly destroys trypsin unless there is great excess of proteid substances present, which means that the acid is com- bined with them and rendered less active. When a filled pancreas-cell is examined the little granules within are found not to be active trypsin, but the precursor or mother of the ferment. This zymogen, trypsin- ogen, is readily converted into the ferment by the presence of a trace of, acid, since a great quantity will immediately kill the newly formed ferment as soon as generated. Amylopsin. — This starch-splitting ferment converts starch partly into dextrin, but chiefly into isomaltose and maltose. During the first month of life it is thought that no amylopsin is formed; hence chil- dren of that age should not be fed starches. Amylopsin differs from ptyalin in that it can digest cellulose, so that it is capable of acting on unboiled starch. In many cases the failure of digestion of the carbo- hydrates by the amylopsin is associated with drowsiness after meals and slight headache. The Steapsin, or Fat-splitting Ferment, decomposes the neutral fats into fatty acid and glycerin. It also emulsifies the fats: an activity which is assisted by the bile. One part of the fatty acids set free by the steapsin combines with alkalies in the intestine to form soap. This soap favors the emulsification of the fats. Another part of the fatty acid is absorbed as such and combines with glycerin in the intestinal wall again to form a fat. The steapsin acts best in an alkaline medium, for acids stop it. Glycerin does not dissolve steapsin; so that a glycerin extract is not suitable for an experiment. The Fourth Ferment present in the pancreatic juice is an un- named one, which, like rennin, has the power to coagulate milk. It is hardly possible that its powers are exercised extensively, if at all, since the milk is probably coagulated in the stomach by the rennin found there tefore it ever reaches the duodenum. The so-called "pepton- izing powders" are composed of pancreatin and sodium bicarbonate. 83 PHYSIOLOGY. From the nature of the resulting precipitates in the transforma- tion of the caseinogen into casein, it is evident that the two ferments — rennin of the stomach and that found in pancreatic juice — are markedly distinct and dare not be confounded. Eennin seems to re- quire the presence of calcium salts before it can produce coagula- tion, which, when it does occur, presents the casein in the form of a coherent clot entangling in it the fats present. There is squeezed out, as it were, from the closely formed curd a clear, yellowish liquid, known as the whey, containing some proteids with the salts and sugar of the milk. On the other hand, experimentation shows that the ferment in pan- creatic juice does not require the presence of the calcium salts for precipitation of caseinogen; further, that the precipitate which does occur is very finely granular in nature; at the same time the milk seems to undergo no change in its fluidity as far as can be dis- tinguished by the naked eye. The presence of certain salts, which entirely check the action of rennin, but slightly hinder the action of the pancreatic ferment. It is believed that this pancreatic casein is not a true casein, for rennin placed in its presence has the power to change it still further, the resultant product being identical with true casein. Effects Resulting Upon Removal of Pancreas. It was in 1889 that von Mering and Minkowski by experiment upon the lower animals proved that removal of the pancreas was in every case followed by the appearance of dextrose in the urine, a con- dition known as diabetes, plus those nymptoms marking the absence of pancreatic secretion in the intestinal canal during digestion. In the blood there was as much as O.o per cent., while in the urine the 8-per-cent. mark was reached. These investigators found that animals presented the identical characteristics as do human beings suffering from the same disease, namely : an abnormal excretion of water with the appearance in the urine of dextrose, acetone, and aceto-acetic acid. Another step was determining that this condition is not due to want of the pancreatic secretion in the intestine by tying the duct of Wir- sung or else plugging it and its branches with paraffin, but allowing the organ to remain in its proper position in the body. The presence of a certain 'proportion of the whole gland, even though its secretion be not allowed to reach the intestines, will prevent diabetes; absence of this diseased condition is still maintained though a portion of the gland be removed from its normal position to be transplanted elsewhere. DIGESTION. 83 From these data it would seem that the pancreas possesses virtues in the general economy other than that of merely producing pancre- atic juice. Any disturbance to these functions is felt, not only in the gland itself, but throughout the entire body, since then its metabolism is disturbed. Thus is very clearly established one other instance showing the intimate relation that each and every organ or part bears to the general mechanism of the entire body as a unit and the consequent general disturbances following its disease. The transfusion of diabetic blood into a normal animal fails to produce within the recipient any diabetic symptoms. Prom this we learn that there was no accumulation in the blood of poisonous matter which the pancreas was supposed to remove. From the facts noted it is apparent that removal of the pancreas produces diabetes not from any influence upon surrounding sympathetic ganglia or hindrance to passage of its secretions into the intestinal canal, but is caused by the removal from the system of something, as yet undetermined, which something possesses powers aside from those employed in digestion. The salivary glands, whose structure is similar to that of the pan- creas, when removed give no untoward results. When the struc- tures of these two- glands are minutely and carefully examined, it is found that there is but one difference : in the parenchyma of the pan- creas there are present little cells, — of Langerhans, — epithelial in appearance, richly supplied with blood-vessels, but having no connec- tion with the alveoli or ducts of the gland. . It is now believed that there is some internal secretion manufactured by these patches of Langerhans cells in the pancreas which is a very powerful factor in the disintegration of carbohydrates, but whose removal allows the abnor- mal production in the blood and urine of dextrose. The sugar present has been shown by Dr. Lusk to be in a proportion which bears a fixed relation to the nitrogen found in the urine; hence the sugar must arise from the breaking down of the proteid molecule of cells. Leucin, Tyrosin, and Arginin. The continued action of the ferment trypsin produces a chain of simple crystalline bodies of a nitrogenous nature. The crystalline bodies formed are leucin and tyrosin. Leucin crystallizes in the form of spheroidal crystals; tyrosin in the form of fine, silky needles. A body called arginin is also formed at the same time. This body by hydration is changed into urea in the intestine and absorbed. Dreehsel has estimated that about one-ninth of the urea excreted could arise 84 PHYSIOLOGY. from this source alone. Arginin has also been found in the helianthus : a product of vegetable proteid metabolism. Leucin (CgHialSrOa) is an a-amido-isobutylacetic acid, belonging to the fatty acid series. It is always formed in any profound decom- position of p'roteid, such as boiling with dilute acids or alkalies, in tryptic digestion, or putrefaction. It has been found in nearly every tissue of the body in some proportion or other, being particularly com- mon in pathological conditions of the tissues. It may be produced synthetically in the chemical laboratory. Tyrosin (CgHnNOa) belongs to the aromatic group, and is known as oxyphenyl-amido-propionic acid. It is a constant associate of leu- cin. It is from tyrosin, however, that cresol and phenol are formed. I have found an infusion of the pancreas, when injected per jugular, decrease the pulse and the arterial tension; afterward the tension rose. LIVER. The largest gland in the body is the liver. Its shape is that of a triangular prism or ovoidal, with its long diameter transverse. Its convex surface is against the diaphragm. Its concave surface is in contact with the stomach, colon, and right kidney. The right and left lateral ligaments, with the suspensory ligament, hold it in position. It weighs from three to four pounds. The right portion of the liver is much larger than the left. It is also thicker and extends lower in the abdomen and higher in the thorax. It is of a firm structure, smooth on the surface, and of a reddish-brown color. The liver has five lobes, five fissures, five ligaments, and five vessels. The chief fissure to remember is the transverse, and is the point where the blood- vessels and nerves enter the liver and where the lymphatics and excre- tory duct emerge. The lobes are the quadrate, caudate, right and left, and lobus Spigelii, the most important being the right and left. The vessels are the hepatic artery, vein, and duct, the portal vein, and lymphatics. The nerves are derived from the solar plexus, and the left vagus has some fibers going to it. The whole organ is insheathed in a very fine coat of areolar tissue known as Glisson's capsule. Structure. The hepatic substance is readily torn and has a granular appear- ance ; these coarse granules, corresponding with the - distinct one hundred and five spots seen on the surface, are polyhedral, and are the lobules of the liver. These lobules are ^/^ inch in diameter. In studying the relation of these lobules to the blood-vessels and ducts of DIGESTION. 85 the liver it is found that an extreme branch of the hepatic vein com- mences in the axis of every lobule and emerges at its base to join a larger branch. This connection of veins and lobules reminds one of the attachment of the leaves by their midribs and stems to the branches of trees. The capsule of Glisson divides the liver-substance into these lobules, for the areolar tissue enters the transverse fissure of the liver. Microscopically, each lobule is made up of epithelial cells, natu- rally spheroidal, but because of compression are more or less polyg- Fig. 6. — Liver of Man. (DrvAL.) 1, lieft lobe. 2, Right lobe. 6, Lobus quadratus. 7, Lobus Spigelii. 9, Gall-bladder. 10, Cystic duct. 11, Hepatic duct. 12, Common biliary duct. 13, Portal vein. 14, 15, Hepatic veins. 16, Inferior vena cava. 19, Hepatic artery. onal. These, the true liver-cells, are about Viooo i'lch in diameter, containing protoplasm with large, round nuclei vt^hieh have one or more nucleoli. The cells are held together by an albuminous cement- substance; in it are fine channels containing the bile-capillaries. The portal vein also has its course in the portal canals, where it divides and subdivides. By its division between the lobules in the interlobular connective tissue it forms the interlobular vein. From this vein fine capillary branches are given off, which pierce the envelop- 86 PHYSIOLOGY. mg membrane of the lobule to find their way toward its center in a converging manner. In their course to its center they pass in close proximity to the hepatic cells, and it is here that the real secretion of the bile takes place. From the point of union of the capillaries in the center of the lobule there proijeeds a single, straight vein, called the intralobular vein. Arrived at the base of the lobule, this vein empties its contents into the sublohular vein, a radicle of the hepatic vein, which empties into the inferior vena cava. The hepatic artery does not furnish the blood for the secretion of bile. Its function is to furnish a blood-supply to Glisson's capsule and to the investment of the lobules and the walls of the bile-ducts. The course of the tile-ducts is very similar to that of the portal vein and hepatic artery. They have their origin as a very fine inter- cellular plexus formed within the lobule in the cement-substance join- ing the hepatic cells. All cells, except those in contact with capillary blood-vessels, are completely girdled with bile-capillaries. Intracellu- lar passages pass from the bile-capillaries into the interior of the liver- cells. After numerous anastomoses the bile-ducts form larger ones, to leave the liver through the hepatic fissure as two main branches. Toward the exit the bile-ducts become correspondingly larger, with increase in the thickness of their walls. These are found to contain fibrous tissue with bundles of nonstriped muscle-fibers plus small mucus-secreting glands. Within each lobule are three networks: a network of blood-capillaries, a network of liver-cells, and a network of bile-capillaries. The Gallbladder. The gall-bladder acts as the natural reservoir for storage of the bile. It is a pear-shaped bag of a musculo-membranous texture, capable of containing rather more than a fluidounce and situated upon the under side of the liver in a fissure fashioned for it. It is about four inches long, one inch at its fundus, or base. The structure of the gall-bladder consists of three coats : an outer, serous coat; a middle, fibrous; and an inner, mucous coat. The fibrous coat contains both circular and longitudinal fibers. The inner surface of the bladder is lined with mucous membrane, which is of a yellowish-brown color. The hepatic duct, formed by union of two bile-ducts issuing from the liver, is about one and one-half inches long. By its joining the cystic, also about one and one-half inches in length, is formed the common bile-duct, known as the ductus communis choledochus. This, DIGESTION. 87 the largest of the three, is three inches long, with the diameter of a goose-quill, emptying with the pancreatic duct into the duodenum through a common opening. Functions of the Liver. The liver, being such an important gland, naturally occupies a very prominent position in the general metabolism of the economy. Its principal functions are: the formation of an internal secretion, glycogen; the formation of urea; and, last, the production of the bile, in which as a vehicle many poisonous products within the body are expelled. Bile is a thick, golden-colored liquid of a very bitter taste. Its secretion byj;he liver represents only one subsidiary function of the many performed by this important gland. It represents waste al- buminous matters, together with coloring pigments and mineral salts dissolved in water. Though primarily an excrementitious substance performing the necessary functions of such, it, however, possesses some powers to aid intestinal digestion, both directly and indirectly. These will be discussed under the head of "Uses of Bile." The secretion of bile is a continuous process, for a supply, though scanty, is constantly passing into the duodenum. The arrival of chyme in the duodenum immediately calls forth an increased amount, to be followed by a second increase some hours later. It is in the intermission between meals that the liver is least active, and it is then that only a small supply reaches the duodenum. It continues during pains the most violent, in intestinal congestion, and in peritoneal inflammations. Contrary to the plan of all- the other secreting and excreting organs, the main supply of blood to the liver, and from which its secretion, the bile, is formed, is venous: from the portal vein. The function of the hepatic artery is to supply structures and membranes only. Since the portal vein furnishes the supply, the bile is secreted at a very much lower pressure and therefore more slowly than those secretions from glands whose supply is arterial, as the pancreas and salivary glands. It is quite natural that a fluid so complex as the bile demands for its preparation a much longer period of time than one which contains only water, salts, and certain principles of the blood. Though not directly governed by nerve-influences upon the portal vein, the supply to the liver is varied. Compared with the size of the liver, the secretion is small and slow and holds but little relation to the mass of blood traversing it. 88 PHYSIOLOGY. The quantity secreted per diem has been variously computed at two pounds. Its specific gravity in man averages 1.026 ; reaction, neutral or slightly alkaline. Chemical Properties and Constituents of the Bile. Bile mixes with water, producing no turbidity ; heat produces no coagulation because of the absence of any coagulable proteids. Alcohol precipitates mucin, diastase, and bilirubin, if the latter is present. Acetic acid precipitates mucus ; lead acetates, the biliary salts. When in contact, bile rapidly destroys the red blood-corpuscles. Bile contains both organic and inorganic materials. Those or- ganic are mucin, biliary pigments, biliary salts, cholesterin, lecithin, neutral fats, soap, urea, and diastase. In organic matters are water, chloride of sodium, and phosphates of iron, calcium, and magnesium. The means by which the various components of the bile are formed is as yet not thoroughly understood. Some of its constituents may exist in the portal blood; thus the pigment is produced by the decomposition of the blood. If haemoglobin itself or substances which are capable of separating the coloring matter from the red corpuscles be injected into the portal blood, there is a proportionate increase in bile-pigment. Biliary acids are not preformed in the blood, for upon extirpation of the liver there follows no appearance of them in the blood. Evidently the hepatic cells must exert some functions as yet not understood. The composition of human bile is approximately as follows : — Water . . .... . .982 Solids < Mucin and pigments . . . 1.5 Bile-salts .... 7.5 Lecithin and soaps . 1.0 Cholesterin . . 0.5 Inorganic salts 7.5 18 - parts in 1000. Bile-mucin. The latest investigations show that human bile contains real mucin. Bile-salts. There are two salts of bile, both having sodium as a base. These are glycocholate and taurocholate. These two acids are very closely related to each other, for on boiling with stronger acids' a common nonnitrogenous body is obtained called cholalic acid, and an amido- acid which contains nitrogen. The glycocholic acid gives glycin and 'I DIGESTION. 89 the taurocholic acid gives tauria, which contains sulphur. In man these acids exist in variable proportions. The bacteria of the intes- tinal canal break up the bile-salts. Fig. 7. — Taurin. (DtrvAL.) Glycocholie acid is a monobasic acid, crystallizing in long, fine needles. Taurocholic is also monobasic; it crystallizes with great difficulty, forming fine, deliquescent needles, which in solution have a bitter-sweet taste. Proteid is the source of glycin and taurin. Fig. 8. — Glycocholie Acid. (DtrVAL.) Subcutaneous and venous injection of bile-salts cause coma and depression. Hay's Sulphur Test for Bile-salts. — On the surface of bile or a solution holding bile-salts sprinkle flowers of sulphur, which will sink to the bottom of the tube, while on most other liquids they will float. 90 PHYSIOLOGY. The bile-salts lower the surface tension of fluids in which they are dissolved. Pettenkofer's Test for Bile-acids. — Take a small quantity of cane- sugar with sulphuric acid and add to the bile, when on slight heating a purple color is produced which shows absorption bands in the spec- trum. The acid on the cane-sugar produces a body called furfuralde- hyde, which sets up a reaction with the cholalic acid to produce the color. The Bile^pigments. Normally, the color of the bile is due to the presence of but two bile-pigments: bilirubin and biliverdin. When pathological, other characteristic ones have been described. Depending upon the propor- tion of each present, the color may range from reddish brown to grass-green. They are formed from the haemoglobin of the blood — the mother of all the bile-pigments. In man and camivora bilirubin predominates and gives to the bile its yellow color; the green color of that of herbivora is due to biliverdin. Bilirubin, being identical with hsematoporphyrin, represents the iron-free pigment of the bile ; its formula is CisHisNaOa. This is the permanent pigment of the bile and may also appear as a calcium com- pound in red gall-stones. When exposed to the air and in an alkaline solution, it oxidizes very readily, changing into biliverdin; because of this, bile, when standing, assumes a greenish tint. Biliverdin is present in all biles of a greenish color. It occurs as such in the liver-secretion of herbivora, but may be obtained by allowing human and carnivorous bile to oxidize slowly by exposure to the air. Its formula is CieHuN^Oi, having one more atom of oxj'gen than bilirubin. When bilirubin arrives in the intestine the bacteria generate nascent hydrogen, which reduces it and generates another pigment, the coloring matter of the faeces, called stercobilin. This stercobilin when absorbed and excreted in the urine is called urobilin. Gmelin's Test for Bile-pigments. — ^Add to some bile some nitric acid containing nitrous acid, when there will be a play of colors: green, blue, purple, and yellow. These tints are due to the oxidation of bile-pigments. The green is biliverdin; the blue, bilicyanin; the purple, bilipurpurin ; and the yellow, choletelin. Cholesterin. Cholesterin is a monovalent alcohol. It is present to some extent in all protoplasmic structures, — ^blood-corpuscles, — but particularly in DIGESTION. 91 bile and nervous tissues. In the latter it forms a very important part of myelin. In the bile it forms but a small proportion of its contents — from 1 to 5 per cent. It is insoluble in water and dilute saline solutions, but readily soluble in ether, chloroform, alcohol, etc. ; in this respect it resembles fat, though not a true fat. In bile it is readily dis- solved, because of the presence of bile-salts. If for any reason the latter should be iQsufBcient, the cholesterin passes out of solution to form concretions around any foreign particles or previously hardened concretions, forming a gall-stone combined with bilirubin. Besides its characteristic crystals, cholesteria is also detected by various color- reactions in the presence of iodtae and sulphuric acid. The general presence of cholesterin in so many parts and cells of the body leads to the impression that it is a cleavage product of Fig. 9. — Crystals of Cholesterin. (Duval.) metabolism, being one of the waste-elements in the life of the cell, especially the nerve-cell. Beiag absorbed by the blood, it finds its way to the liver, there to be elaborated and so appear in the bile. Being an excrement, it is not reabsorbed, but is expelled from the economy as a part of the faeces. Pathological changes in tissues are always marked by an increased quantity, which may be accounted for by loss of vitality in the diseased cells so that they are unable to break down the cholesterin. Cholesterin is not poisonous to animals. Like lecithin, choles- terin is held in solution in the bile by the bile-salts. Lecithin is found chiefly in nervous tissues, red corpuscles, and the bile. When lecithin is taken by the mouth it is broken up in the intestine into cholin, a poisonous alkaloid ; but the intestinal bacteria destroy it a once, producing methane, carbonic acid, and ammonia. 93 PHYSIOLOGY. Uses of Bile. In fasting not a drop of bile enters the intestine. Fat, meat extractives, and the products of digestion of egg-albumin set up a free discharge of the fluid. Bile accentuates the activity of the pancreatic enzymes, especially the fat-splitting ones, the action of which was in- creased twofold. The pancreatic secretion in its hourly rate corre- sponds closely with the entry of bile into the intestine under the same conditions of diet. The similarity is most striking. Bile arrests the action of pepsin, which is injurious to ferments of pancreatic Juice, and favors the ferments of the latter, especially the fat-splitting one. Bile is principally excrementitious. It partly emulsifies the fats and contributes to their solution by the soap which the alkalies of the bile produce. By thus rendering the fats alkaline in part they are able to come in closer touch with the intestinal mucous membrane, to be absorbed by it. Endosmotie experiments have proved that the fats are imbibed and traverse more easily membranes that are impregnated with an alkaline solution than those simply wet with water. Experi- mentally, when the bile is turned out of its course, the chyliferous vessels are not filled with white, milky fluid, only one-seventh of the normal amount of chyle being absorbed. As an excrementitious substance, the bile may serve as a medium for the separation of the excess of carbon and hydrogen from the blood, particularly during intra-uterine life. When the chyme passes into the duodenum, the glycocholate and taurocholate of sodium are broken up by the acid in the chyme to form sodium chloride, at the same time setting the bile-acids free. Imme- diately they are precipitated, carrying down with them the pepsin, making the chyme alkaline and more turbid, due to the precipitation of the unpeptonized proteids. This thickening of the stomach con- tents aids very materially in slowing the movements of the digested products through the intestines, thus giving the villi and blood-vessels more ample time to absorb nutritious substances. By rendering the chyme alkaline it aids the action of the pan- creatic juice, which is most effective as a digestive agent in an alkaline medium, at the same time favoring absorption, since alkaline liquids permit of more ready osmosis. To the bile has been given the credit of being a natural antiseptic in that it hinders putrefaction in the intestine. The bile itself easily becomes putrid on standing. How can it prevent the putrescence, then, of the intestinal contents? That it does in some way diminish this DIGESTION. 93 degenerative process is very evident, for, when the common biliary canal is ligated the fasces are more foetid and the intestinal gases more abundant. The bile's so-called antiseptic powers must be accounted for by its hastening absorption and assisting it to such an extent that the quantity of matter capable of putrefaction is greatly diminished in quantity. It has been found that bile stimulates muscles when in contact with them, throwing them into a violent state of tetanus, while at the same time it irritates the nerves. By this action the economy possesses a natural purgative. By it as a stimulus the secretion of the intestinal mucous membrane glands is increased and more rapid peri- staltic movements of the intestinal muscles induced to aid in the propulsion of their contents. Reabsorption of Bile=salts. When it was ascertained that the bile-salts were the product of the hepatic cells, that only a small proportion appeared in the faeces, with a still smaller proportion in the urine, the question arose: Is the remainder reabsorbed by the intestines to be again secreted from the blood by the hepatic cells ? Bile-salts taken by the mouth produce an increased flow of the bile, which is at the same time higher in its percentage of proteids. Dogs' bile, containing normally only tauroeholate of sodium, has been found to contain glycocholate when that salt had been injected into the animal's blood. Again when bile has been taken from an animal for some time by a fistula, its quantity of solids diminishes, showing that the hepatic cells cannot give back these salts to it when the portal blood does not convey to them the materials for their formation. Prom these and other facts it was deduced that there must exist in the body reabsorption of bile-salts. Antitoxic Function of the liver. — It was found that nicotine added to the portal blood of an experimental circulation through the liver soon vanishes. Similar experiments with strychnine, morphine, and quinine resulted in the same way. These alkaloids are not only deposited in the liver-cells, but they experience a change in their chem- ical constitution by which they lose their poisonous properties. It is well known that the liver is a storage for the metallic poisons mercury, arsenic, iodine, and antimony for long periods. The liver also trans- forms the bodies developed by action of intestinal bacteria on proteid. I refer to indol and phenol. Here the liver exerts a protective action against poisoning by these bodies. 94 PHYSIOLOGY. The liver also reduces the poisonous activity of poisons generated by specific bacteria, as by the typhoid bacilli and tetanus organism. The liver is probably the seat of most active oxidations, and it is by these chemical activities that it acts as a protective agent against poisons. Internal Secretion of the Liver (Glycogen). — Besides secreting the bile to be partly used in digestion, but mainly as an excrementitious substance, the liver possesses still another remarkable function, namely: separation from the portal blood by its cells of a substance known as glycogen, or animal starch. Glycogen exists constantly, though in very small proportions, in protoplasm and animal membranes in general; also in vrhite blood- corpuscles and pus. It occurs in more considerable quantities in liver, muscle, and embryonic tissues after the third month. Glycogen is a white, tasteless powder, soluble in water, but producing an opaque solution. Glycogen possesses the property of being readily trans- formed into glucose, to be ready for easy oxidation. Glycogen with iodine in solution gives a port-wine color, which disappears upon heating. Naturally during absorptive processes following active digestion portal blood contains more than the normal quantity — 1 per 1000. At the very same time the blood in the hepatic vein during the in- tervals of absorption of carbohydrates contains 2 parts per 1000. Within the hepatic-cell protoplasm glycogen is deposited. When an excess of carbohydrates are taken, not all of the glycogen can be absorbed, but passes through into the general circulation, to be depos- ited in the muscles and other tissues. Muscles may contain as much as 1 or 2 per cent. That sugar should appear in both portal and hepatic blood is not to be wondered at when carbohydrates are fed, but that it should still be present when but meats are given or when the portal vein is ligated at the transverse fissure, goes far to prove that glycogen, or sugar- forming animal starch, must be manufactured within the parenchyma of the liver. Even when an animal is made to fast and at the same time perform very severe muscular work so that glycogen disappears in muscles and liver, its presence in the liver is soon ascertained again though the animal be fed but gelatin. Since neither glycogen nor sugar appear in the bile, it follows that it, or some transformed product of it, must be absorbed into the blood before it can serve any needs in the economy. From our data we are led to believe that the glycogen is formed and stored up DIGESTION. 95 in the liver-cell protoplasm and the appearance of sugar is due to its transformation by liver diastase, to be absorbed into the hepatic veins. Glycogen is formed most abundantly from carbohydrate food, next from proteids, but not from fats, except glycerin, which causes glycogen to be produced. On a diet rich in carbohydrates the gly- cogen of the liver reaches 15 per cent., while in a state of starvation it may be so small as to escape the tests. Uses. The liver is the chief storehouse of the carbohydrate material. Thus the use of the 'glycogenic function of the liver is supposed to be that of continuously supplying material which may be easily oxidized for the purpose of maintaining animal heat and motion. Sugar is a very unstable article in the presence of oxygen with albuminoid sub- stances. The sugar becomes oxidized, both in the blood during respira- tion as well as in the tissues supplied by the blood. DIABETES. Diabetes is a chronic affection characterized by the constant pres- ence of grape-sugar in the urine, an excessive urinary discharge, and progressive loss of flesh and strength. Its exact pathology is as yet unknown, but seems to be intimately associated with certain nervous afiections, disturbed hepatic and pancreatic functions, sexual excesses, while heredity also seems to play an important r61e. Simple Glycosuria must be differentiated from the disease dia- betes (mellitus), since the former is but a temporary condition, and not a disease. When excessive quantities of sugar, maltose, etc., are eaten by a perfectly healthy individual, sugar appears in the urine, due to the fact that all of the absorbed sugar cannot be carried into the portal circulation fast enough, so that some finds its way into the thoracic duct and by it emptied at once into the general circulation. Before reaching the liver, where it would be stored up as glycogen, it passes through the kidneys, there to be promptly eliminated. This temporary condition has been termed simple, or alimentary, glycosuria. Dietary conditions ia the way of abstaining from starchy and sac- charine foods will promptly eradicate this condition. Simple gly- cosuria may also result from the inhalation of chloroform, turpentine, use of chloral, etc. ; it may be one of the conditions following injury to the head. Diabetic glycosuria differs in that sugar is constant and is not made more significant by quantities present. We know from our study of the glycogenic function of the liver 9G PHYSIOLOGY. that glycogen can be produced from proteids by synthesis after the proteid molecule has been first broken down. If from any cause, nervous or otherwise, the metabolism of the liver is interfered with, the function of glycogenesis is disturbed, the balance broken, with the result- of the appearance of sugar in the urine. Experimental diabetes may be produced in animals in various ways : — 1. By Diabetic Puncture. — By Bernard was it discovered that certain lesions to the eerebro-spinal axis, as puncture of the floor of the fourth ventricle, is capable of producing diabetic conditions. After puncture the glycogen of the liver is so rapidly converted into sugar that it raises the percentage of sugar in the blood to such a degree that there is more present than the tissues can use up, and thus some of it finds its way to the kidneys, there to be eliminated. The increased activity of the hepatic cells in transforming the glycogen is believed to be due to stimulation of the vasomotor center in the medulla caused by the puncture, for other means of stimulating this center have always produced temporary diabetes. In man, some dis- eases of the brain, particularly those in the medullary region, are characterized by diabetic symptoms. 2. Adrenalin produces glycosuria by increasing the changes of glycogen in the liver into sugar. lodotliyrin when given to animals for a considerable time occasionally produces glycosuria. The removal of the pancreas also causes diabetes. 3. Phloridzin. — This drug is a glueoside obtained from the root- bark of cherry-trees. Powerful results are obtained after its admiais- tration either by the stomach or by subcutaneous or intravenous injection. With the appearance of the sugar in the urine there is a diminution in the quantity of glycogen in the liver. If the drug be administered repeatedly so that all of the glycogen from the liver and other tissues is entirely used up, and then an additional dose be admin- istered, dextrose will promptly appear. Phloridzin glycosuria is caused by an injury to the renal epi- thelium, allowing it to become permeable to the sugar iu the blood. In phloridzin diabetes the blood shows a decrease of sugar in it, while in other cases of diabetes there is always an excess of sugar. In diabetes the failure of the cells of the body to bum sugar is so great that the organism not only fails to bum the starches and sugars of the food, but is unable to burn completely the carbohydrate moiety of the proteids of the body itself. To epitomize: Diabetes appears (1) after the use of certain agents, adrenalin, iodothyrin, and particularly phloridzin; (3) after DIGESTION. 97 inhalation of chloroform and amyl nitrite; (3) after puncture of the medulla oblongata.; (4) by section of the spinal cord above the exit of the hepatic nerves, probably by a paralysis of the vasoconstrictors of the liver; (5) by irritation of the central ends of the vagus and depressor; (6) by extirpation of the pancreas. The majority of cases of true diabetes terminate fatally. Death is due to exhaustion and blood poisoning, producing just previous to the end a condition of complete coma called acetonsemia. Oxybutyric acid is the chief acid in diabetic coma. It is believed to be produced by the excessive metabolism of proteid. Whenever a patient passes more than five grains of oxybutyric acid daily then the danger of acid intoxication must be watched. As to the estimation of the oxybutyric acid, it can be made by ascertaining the amount of ammonia excreted, as it gives a rough index of the excretiop of the acid. Thus, a daily output of ammonia of two grams corresponds to about six grams of the acid. The treatment of this diabetic coma is by sodium bicarbonate by intravenous injection and by mouth. CONJUGATED SULPHATES. The aromatic products which are formed in the intestines — as indol, skatol, phenol, and cresol — are eliminated by the kidneys in the form of sulphates. The aromatic bodies are absorbed by the portal vein and in the liver unite with sulphuric acid produced by the oxida- tion of the sulphur of the proteids. ^ UREA AND URIC ACID. The liver receives products from the muscles, as ammonia car- bonate, and builds them into urea. It also forms uric acid. In addi- tion it receives the urea absorbed by the portal vein from a hydration of arginin in the intestinal canal. Jaundice is a discoloration of the skin due to the reabsorption of bile by the lymphatics of the liver. This is usually due to obstruction of the bile-ducts by a catarrh, calculus, or tumor. Arsenureted hydro- gen and toluylendiamin will produce jaundice. Influence of Drugs on Secretion of Bile. — Podophyllin, aloes, nitrohydrochloric acid, ipecacuanha, euonymin, and sodium phosphate stimulate the bile-secreting apparatus. Other substances, like calomel, etc., stimulate the intestinal glands, but not the liver-cells. The best stimulant of the liver is ox-^all, but it is important to remember that bile in the intestine is liable to be absorbed ; hence it is best to combine a purgative with it to carry it down the intestinal canal. 98 PHYSIOLOGY. THE SUCCUS ENTERICUS. By most physiologists the presence of a certain liquid product occurring upon the surface of the intestinal mucous membrane is attributed to the ' secretory powers of the crypts of Lieberkiihn and the glands of Brunner, presumably due to their columnar cells, al- though the real mechanism of its secretion is still unknown. To this secretion the name succus entericus has been commonly given. As described by Thiry, it is "a limpid, opalescent, light-yellow-colored fluid, strongly alkaline in reaction, and possessing a specific gravity of 1.010." It contains proteid and mucin, while its great alkalinity is due to the presence of a considerable quantity of carbonate; the latter's presence is easily detected by the effervescence resulting upon mixture^ with dilute acids. The amount secreted daily is perhaps about two pounds. Erepsin, a ferment found in the succus entericus, does not act on albumins, but breaks up albumoses, peptones, casein, protamin, and histon, changing them into leucin, tyrosin, and am- monia. The succus entericus also contains a ferment like that in yeast — invertin. This body inverts cane-sugar into dextrose and laevulose, and maltose into two molecules of dextrose. This inversion is necessary for the absorption of these sugars. The succus also contains another ferment known as enterokinase — a ferment of ferments. This ferment augments the activity of the pancreatic ferments, especially the trypsin, by converting the trypsinogen of the pancreatic juice into trypsin. When dogs are fed only on starch and fatty foods, then the pancreatic juice contains only trypsinogen with the object of protecting the amylopsin and steapsin. If the dogs were fed on meat exclusively, then the pancreatic juice contained mainly the fer- ment in the shape of trypsin. Unlike the stomach, mechanical irrita- tion of the intestine calls out increased secretion of the succus entericus. But the intestine has a special stimulus, and that is the pancreatic juice. If a little pancreatic juice is inserted into a loop of the intes- tine for half an hour, then a fluid will be secreted containing much enterokinase. Every cannula introduced into an intestine acts as a foreign body and excites a secretion of water, with the object of wash- ing it out of the intestine, and the amount of enterokinase becomes steadily less and less. Hence a mechanical stimulus calls out only water, and explains the severe diarrhoea of acute enteritis, while the ferment enterokinase is called out by the pancreatic juice. DIGESTION. 99 DIGESTION IN THE LARGE INTESTINE. Besides the changes wrought upon the foodstuffs in the mouth, stomach, and small intestine by the various digestive secretions with their powerful enzymes, there is still another more or less active agency in the form of certain bacteria which occur normally in health in varying amounts. They are swallowed by the mouth with the food, drinks, and saliva. The bacteria are one-celled organisms and are produced with marvelous rapidity. Prom a physiological point of view we are able to classify them into three groups: (1) ferment, (2) chromogenic, and (3) pathogenic bacteria. However, only the ferment bacteria interest us. Bacteria of different kinds have been noticed at various times throughout the entire alimentary canal from mouth to anus, but are more numerous in the intestines, particularly in the large one, where their action is very marked upon matters reaching it, so as to give rise to the term "bacterial digestion." In the stomach, under normal conditions, the putrefactive activity of the bacteria is neutralized and the germs themselves killed by the free hydrochloric acid of the gastric Juice. It is in the intestines, where the secretions are alkaline, that the best media are found for their culture and development. It has been suggested that bacterial digestion was necessary to the economy, because it accomplishes so many things. But it has been shown by Nuttall that, by removing guinea-pig foetuses directly by incision from the uterus and with antiseptic care, and then keeping them in a sterile chamber receiving sterilized air and fed on sterile milk, they grew. When their intestinal contents were examined no bacteria were found. Hence the inference that bacteria are not neces- sary for good digestion. The two chief bacteria are the lactic acid bacillus and the colon bacillus. The former is found in the stomach at times and the upper part of the small intestine. The colon bacillus chiefly lives in the colon. These bacteria are aerobic; that is, they consume oxygen in their action. Hence they are powerful reducing agents. Thus they take oxygen from bilirubin and form stercobilin. But, although these •microbes use oxygen, they can also live without it. On proteids the bacteria produce by their action proteoses and peptones, and from tjTosin the aromatic bodies : phenol and cresol. Indol and skatol are derived from tyrosin. On carbohydrates the bacteria act like ptyalin and amylopsin ; on fats they act like steapsin, breaking up lecithin into cholin. Bacteria in the stomach and intestine can set up five kinds of 100 PHYSIOLOGY. fermentation: (1) alcoholic; (2) acetic; (3) lactic; (4) butyric; and (5) a form of fermentation discovered by Drs. Herter and Bald- win — the oxalic acid variety. These fermentations may give rise to acute and chronic gastritis. In the intestine the fermentations will give rise to excessive distension, diarrhcEa, colic, and a loss of weight and strength. The remote effects of these fermentations will be an increase of uric and oxalic acid in the urine and of tlie acidity of the urine itself, causing frequent urinations, especially at night. The best indication of intestinal putrefaction is the aromatic or ethereal sulphates which appear in the urine. The easiest test to detect the indoxyl sulphate of potassium is the indican reaction.^ These bac- teria also help form the gases of the intestine by a fermentation of the food. THE F/ECES. The foods that have failed to be absorbed, after having remained about three hours in the small intestine, pass into the large intestine, where they remain for about twelve hours. The quantity and con- sistency of that secreted daily by an adult varies within wide marks, depending upon the kind of diet and the length of time the foodstuffs remain within the intestine. The adult eliminates about 8 ounces of moist excrement per diem. Prom a vegetable diet the faeces are both softer and contain a higher percentage of solids than from a meat diet ; sbfter because their irritations to the intestinal walls heighten mucous secretion and increase peristalsis, thereby hastening its passage, to the detriment of absorption. In a meat diet j:he want of this stimulation retards defecation to such an extent that it may occur but once in several days. The stools are then small in amount and dark in color. The stimulating action of vegetables is what makes them so valuable in mixed diets, although they are inferior in nutritive value, bulk for bulk. Although the faeces are so variable quantitatively, they are more consistent qualitatively, and present the following substances : — I. Water. — In health about 75 per cent.; this becomes much greater during diarrhcea. II. Indigestible Residue of different foodstuffs, as nuclein, keratin from epidermic structures, hsematin from haemoglobin, ligaments of meat, cellulose from vegetables, mucin, wood-fibers, gums^ resins, and cholesterin. III. Undigested Food. — The quantity of food ingested has an effect. The more one eats, the more likely he is to have a quantity 'Herter, "Chemical Pathology." DIGESTION. 101 of undigested matters in the stool. These undissolved substances are usually pieces of vegetables, muscle-fibers, connective tissue, and small quantities of casein -and fat. These materials help to accelerate peri- stalsis and so interfere with a proper absorption of those foods that would otherwise be readily taken up. IV. Mucous Epithelial Cells. — The microscope shows these as present from the intestinal surface. V. Derivatives of Bile-salts and Bile-pigments. — These are sterco- bilin, cholesterin, traces of bile-acids, and lecithin. VI. Number of Putrid Products, as skatol, indol, phenol, volatile fatty acids, ammonia, sulphureted hydrogen, and methane. VII. Inorganic Salts. — These are salts of sodium, potassium, cal- cium, magnesium, and iron. VIII. Micro-organisms. — Bacteria of numerous kinds are present in the fseces. The Color depends upon the kind of food ingested; meat gives dark-brown or black, and vegetables light-yellow, fseees. The reaction is normally alkaline in adults, while in infants it may be acid and yet not pathological. Meconium is the name given to the greenish-black contents of the large intestine of the fcetus which is expelled at or after birth. It is chiefly concentrated bile with intestinal epithelium. The coloring matter is a mixture of bilirubin and biliverdin, not stercobilin. Defecation. — The act of defecation is to a slight extent voluntary, but in the main involuntary. In order that the ffeces may not stimu- late mechanically the sphincter reflexes so that they relax at any time, volition plays a role. For there is a center, having its seat in the brain, which is inhibitory and by voluntary impulses the individual is capable of relaxing or increasing the contraction of the external sphincter ani. ' The inhibitory apparatus of the ano-spinal center arises, accord- ing to the latest researches that I have made upon the subject, from the locus niger of the crura cerebri. Erom this point inhibitory fibers descend, some of which commence to decussate at a point in the pons down to the nib of the calamus scriptorius and then pass down the lateral columns. Some of the fibers not decussating also pass down the lateral column. This inhibitory apparatus is under the control of a center in the cortex. I might add here that the same inhibitory apparatus presides over the sphincter vaginse. When a sufficient quantity of faces has arrived in the lower part of the rectum there is felt a need of expelling them. During defeca- 102 PHYSIOLOGY. tion all the organs situated in the abdomen are compressed so that the intestinal contents may be expelled, but the anal sphincter, like the cardiac sphincter of the stomach, offers a resistance, and during the violent efforts the vesical sphincter is relaxed, allowing the urine to escape. The sensory nerve-endings in the mucous membrane of the rectum carry impressions to the ano-spinal center in the lumbar cord, which sends out motor impulses to the muscles of the intestine. At A., B, M, Fig. 10. — Inhibitory Apparatus of Ano-spinal Center. Locus niger of cerebral crura. E, F, Inhibitory fibers. P, Pons. Medulla oblongata. C, C, Sensory fibers. S, Ano-spinal center. the same time the glottis is closed, the diaphragm and abdominal muscles are set in action, and the act of defecation is accomplished. ABSORPTION OF FOOD IN THE STOMACH. The absorption of the stomach is much more limited than one might at iirst imagine, at the same time attended with mueh slowness. Water is practically not at all, or with extreme slowness, absorbed in the stomach, even though the blood-vessels are dilated, as during the time that food is ingested. Experiments show that when water is ingested it is almost immediately passed through the pylorus in little DIGESTION. 103 squirts Tsy reason of the peristaltic movements before any, practically, has disappeared into the vessels. The stomach does not behave thus to all fluids, for alcohol is very rapidly taken up. Drugs mixed with the latter, such as chloral hydrate, are far more rapidly absorbed than when presented to the stomach in other vehicles. Concentration plays a very prominent part here, for absorption increases proportionately until 20 per cent, is reached; the reverse is true of the intestines. Salts are absorbed very slowly. FatSj in their stay within the stomach, are split up. Fig. 11, — Section of Dog's Intestine showing the Villi. (Cadiat.) I, Blood-vessels, injected, d, Lacteals, injected. Blind end of villi enveloped in a capillary network of blood-vessels. ABSORPTION IN THE SMALL INTESTINE. The soluble end-products of the digestion of the three main foods — carbohydrates, fats, and proteids — appear in the small intestines as glucose, emulsified fats, and peptones, ready for absorption. It is here (the lower two-thirds, since the upper third is the site of main digestion) that the chief absorption of nutriment takes place. The presence of the almost innumerable villi, with their network of capil- lary blood-vessels and lacteals, the valvules conniventes to add more 104 PHYSIOLOGY. surface and at the same time to slow the progress of the partially digested mass, all help to make the intestine an ideal abode for this most important process. The passage of the food along the small intestine, though slow, is yet rapid compared to the progress in the large intestine. Two to five hours are consumed from the time food is ingested until the first portion passes through the ileo-csecal valve, but nine to twenty-three hours until the last vestige has made its exit. That fats are absorbed here has been demonstrated microscop- ically; the sugars and peptones are known to be very rapidly taken up even though the solutions are very weak. It is known that 85 per cent, of proteids disappear; that is, have been absorbed in passage through only the small intestine. rig. 12. — Diagram of the Relation of the Epithelium to the Lacteal in a Villus. (Funke.) The central axis is the lacteal surrounded by adenoid tissue. ABSORPTION IN THE LARGE INTESTINE. That considerable absorption takes place within the large intes- tine is vividly impressed when one considers for a moment the con- sistency of the contents as they enter it through the ileo-csecal valve and their density as they are ejected as faeces. As they enter they are of the nature of a somewhat thickened chyme ; as they leave they are a soft solid. By this alone we recognize the amount of water that has been extracted. From an intestinal fistula it was ascertained that about 14 per cent, of proteids enter the large intestine, while the faeces contain but a very small percentage. This rather extensive power of the large intestine is made use of clinically by the medical profession, who inject into the large intestine enemata of various substances for the nutrition of the patient who may be unable to take nourishment by the mouth. All in all, the DIGESTION. 105 results have been satisfactory; proteids in solution, eggs beaten, or peptone to which is added a little salt, are absorbed per rectum. Fig. 13. — Lactcals of a Dog during Digestion. (Colin.) A, Lacteals of meaentery. B, Mesenteric glands. C, Efferent chyle-ducts. D, Reoeptaculum chyli. The steapsin of the pancreatic juice splits up the neutral fats into fatty acids and glycerin. The fatty acids then unite with the alkaline salts of the intestinal secretions to form alkaline soaps, which 106 PHYSIOLOGY. are soluble in water. These two products, soap and glycerin, are ab- sorbed by the epithelial cells to be, in their protoplasm, so built up and constructed that neutral fats are again in evidence. These fats appear in the form of small droplets surrounding or becoming mixed with the protoplasmic granules of the cells. It has been learned that in feeding with fatty acids or with soaps, they were not only absorbed, but also converted into fats, which appeared in the thoracic duct. Bile also aids the absorption of fat, since it is a typical solvent medium for fatty acids and glycerin, and at the same time membranes (and the mucous membrane is no exception) moistened by it allow the more ready passage of fats, very probably because of its alkalinity. Absorption of Carbohydrates. — This is sometimes considered a "sugar absorption," for it has been learned that the carbohydrates are mainly converted into maltose and other forms of sugar by the enzymes ptyalin and amylopsin. Thus it can be said that carbohydrates are taken up by the epi- thelial cells mainly as maltose and other forms of sugar; but these products are by their action and the aid of the succus entericus con- verted into dextrose to appear as such in the blood. Absorption of Proteids. — Proteids may be absorbed by the stom- ach and small and large intestines, but their main seat of absorption is in the small intestine. The end-products of proteolysis (proteoses and peptones) differ from the ingested proteids mainly in that they are more diffusible. Numerous and extended experiments all go to prove that these end-products of proteolytic digestion (proteoses and peptones) are transformed, in their passage through the epithelial cells, by virtue of their living protoplasm, bach again into native, coagulable proteids in the form of globulins and albumins. To the vital properties of the living epithelial cell of the villi is the economy indebted, not only for absorption, but because it protects it from those toxic effects at- tending the presence of peptones in the blood by its converting them into useful bodies. The proteoses and peptones are taken up directly by the blood- capillaries to enter the systemic circulation directly, the lymphatics taking little or no part in their absorption. Absorption of Water and Salts. — In the intestines the (absorption of water and inorganic salts is both very extensive and very rapid. The following resume of Moore's,, somewhat changed, gives a re- view of the action of the ferments : — DIGESTION. lor Class op Ekzxme. Name of Enzyme. Digestive Fluid IN Which Found. Concise Description OP Specipic Action. Amylolytic. 1. Ptyalin. Saliva. Convert amy loses ( starch and glycogen) into dextrin, maltose, and isomaltose, accom- panied by glucose. 2. Amylopsin. Pancreatic juice. 1. Pepsin. GaBtr:c juice. 1. Converts proteids into proteoses and peptones. Proteolytic. 2. Trypsin. ■Pancreatic juice. 2. Converts proteids into proteoses, peptones, and amido-acids. 3. Erepsin. Succus entericus. 3. Converts peptones intoleucin, tyrosin, and ammonia. Fat-splitting, or steatolytic. Steapsin. Pancreatic juice. Splits up neutral fats into fatty acids and glycerin. Coagulating. 1. Bennin. Gastric juice. 1. Coagulates milk, con- verting caseinogen in presence of calcium salts into casein. 2. Eennin. Pancreatic juice. 2. Coagulates milk. Inverting. Invertin. Succus entericus. Inverts maltose into dex- trose and laevulose. Ferment increas- ing power of other ferments, Enterokinase. Succus entericus. Increases the power of the pancreatic ferments, especially the proteo- lytic, by converting trypsin ogen into tryp- sin. CHAPTER IV. ABSORPTION. According to some authors, the absorption of the economy in its entirety consists of two processes, the first of which has for its purpose and aim the introduction into the blood-stream of fresh material for the nutrition of the various tissues of the body. It is called absorption from without, and has its seat in the alimentary canal chiefly, aided, to some extent, by the skin and lungs. The second process endeavors to remove from the numerous tissues of the body, by very gradual meas- ures, the waste-products that would otherwise accrue everywhere within the body as a resultant of the use of its various tissues. This second process is known as the absorption that takes place from within, and has its seat everywhere within the tissues of the body. For consideration of the first process, or absorption from without, the reader is referred to absorption of food under the general head of "Digestion" (in the preceding chapter). It was there noted that the ingested foodstuffs in their passage through the alimentary canal were subjected to various and numerous enzymic and bacterial actions until the major portion of them was reduced to certain soluble and well-defined end-products. Until these latter were produced they were incapable of serving the needs of the body, since they were unable to be absorbed. It is only after absorption that the different nutrient products can be assimilated to become components of the living mate- rials of the economy for growth and repair. It was also learned that, though some absorption occurred in the mouth, oesophagus, and large intestine, yet the main seat of this function is in the small intestines, where the end-products enter the circulation by the villi and the so- called lacteals. In turn we noted the manner and principal seats of absorption of the fats, carbohydrates, proteids, water, and salts. For many years the old physiologists entertained the view that absorption of the end- products of digestion from the alimentary canal was purely phys- ical; that is, that the same laws governed this bodily function that do the passage of any liquid with its contained dissolved substances (108) ABSORPTION. 109 through a dead membrane placed outside of the body. These proc- esses of osmosis and filtration, as they were known to the physicist, are to a small extent responsible for some of the intestinal absorption. But to-day the newer view concerniag this absorption is accepted, whereby it is believed that the living epithelial cells of the lining mucous membrane of the small intestine possess in themselves, as living beings, the power to exert a selective action during absorption; at the same time they modify the end-products during their passage through them. They change the peptones into albumins and unite the fatty acids to glycerin. That the process was selective, and not due to purely physical laws, was proved by the more rapid absorption of grape- sugar than sodium sulphate, though the latter is many times more diffusible than the former. OSMOSIS. An electrolyte is a chemical compound which when molten or in solution conducts an electrical current. When such a current passes through its solution the latter undergoes certain changes that are grouped under the name of electrolysis. The places at which the electrical current enters or leaves the electrolyte are called electrodes: the anode and cathode. The electrically charged particles, the aggre- gation of which constitutes a molecule of the electrolyte, are called the ions of the electrolyte. The ions which under the influence of the electrical current migrate to the anode are anions; those which wander to the cathode, cathions. Thus, for example, NaCl is an elec- trolyte ; Na and CI are its ions ; Na is the cathion, CI the anion ; in the electrolysis of an NaCl solution the cathion, Na, wanders to the cathode, the anion to the anode. According to Clausius, the con- stituents of a greater or less number of dissolved molecules exist in a free state and move in all directions through the solution even before the passage of an electrical current. Only the presence of the free ions makes it possible that such a solution can at all conduct electricity. If we dissolve crystals of sodium chloride in water, a part of the NaCl molecules split into ions : Na and CI. If an electrical current is passed through such a solution the ions which at first were moving in, all directions are arrested and drawn to the poles. An ion is the electro- lytic representative of an atom, but is theoretically much smaller in size. The function of ions is by their presence in definite proportion in each tissue to preserve the "labile equilibrium" of the colloid mate- rials of the protoplasm on which its activities depend. 110 PHYSIOLOGY. Osmotic Pressure/ Saw a Pasteur-Chamberland filter in half. The cylinder is then dipped in dilute hydrochloric acid, which is sucked through the wall of the cylinder by a hydraulic airpump ia order to remove any caolin dust that might choke its pores; then rinse with water in a similar way. A beaker is now filled with a solution of potassium ferrocyanide (139 grams per liter), the cylinder is dipped into it, and the solution is sucked through its wall. After the cylinder has been again rinsed in water it is dipped into a second beaker containing a copper solution Water Sugar solu- tion Water Water G Fig. 14. — Osmometer. (Cohek.) (249 grams of the salt per liter), the inside of the cylinder being also filled with the solution. A layer of copper ferrocyanide is deposited within the wall of the cylinder, and this precipitate constitutes the semipermeable precipitation membrane which is permeable for water, but impermeable for salts. If we introduce a sugar solution into cell C prepared in this man- ner and close it with the stopper of rubber (S), which is perforated by the tube AB, then when C is dipped into pure water the sugar en- » Literature consulted: Cohen's "Physical Chemistry," 1903. ABSORPTION. Ill deavors to pass from the place of higher concentration (the solution) to that of lower concentration (the water without the cell) . But this movement is opposed by the semipermeable membrane, and in conse- quence the sugar exerts a pressure upon the membrane. Since this wall, however, is unyielding and so resists the pressure, a pull is exerted upon the water by the solution which tends to dilute the latter. This comes to pass when the solution enters the tube and the water from G streams through the membrane into the cell and dilutes the solution. This process goes on until the resulting hydrostatic pressure in AB prevents the further entrance of the water. When equilibrium has been established this hydrostatic pressure is equal to the osmotic pressure of the solution. Conversely, however, the latter may be measured by ascertaining the hydrostatic pressure which exists when equilibrium is established ; with 100 grams of water, containing 6 grams of sugar, the osmotic pressure was 3075 millimeters of mercury. Boyle-Van't Hoflf Law. — At constant temperature the osmotic pressure of dilute solutions is proportional to the concentration of the dissolved substance. Gay-Lussac-Van't Hoff law for dilute solutions is as follows : At constant volume the osmotic pressure of dilute solu- tions increases as the temperature; or, also, the osmotic pressure of dilute solutions is proportional to the absolute temperature. Law of Avogadro-Van't Hoff. — At the same osmotic pressure and the same temperature equal volumes of dilute solutions contain the same number of molecules. The same laws have been applied to gases. The great importance for the biologist of the freezing-point determina- tion lies in the fact that they enable him to ascertain the number of molecules dissolved in a given volume of any body fluid. A depression of the freezing-point of Viooo degree corresponds to an osmotic pressure equal to 0.012 atmosphere. While chemical analysis can tell us much concerning the composition of physiological fluids, it cannot yield us anything definite concerning the osmotic behavior of such solutions. This becomes intelligible when we remember that the osmotic pressure of a solution is dependent upon the number of molecules (+ ions) it contains, and that this cannot be determined by chemical analysis. By the determination of the lowering of the freezing-point (cryoscopy) we have a direct means of accomplishing our end. By finding out the freezing-point of blood and of urine it is possible to discover a les- sened permeability of the kidneys for dissolved molecules and disturb- ances in the secretion of water. The freezing-point is determined by Beckman's differential ther- mometer. Thus, the freezing-point of blood-serum of mammals is 112 PHYSIOLOGY. 0.56° C. lower than water. It is usually expressed by the Greek delta ( A) .* A solution of NaCl of 0.95-per-cent. strength gives the same A ; hence the two solutions have the same osmotic pressure and 0.95 per cent, of NaCl is isotonic with mammals' serum. The osmotic pressure of urine has the highest isotonic coefficient of any fluid in the body, and its A is equal to 1.85° C. The most important electrolytes present in bkod-serum are the inorganic salts NaCl and NajCOj. The freezing-point of defibrinated blood is the same as that of serum; in other words, the presence of blood-corpuscles has no effect upon the freezing-point. This ensues because proteids have an ex- ceedingly low osmotic pressure, although a high molecular weight. The freezing-point of blood does not change during haemorrhage. In metabolism the large proteid molecules which in solution exert an exceedingly low osmotic pressure are split into smaller ones. In consequence the number of dissolved molecules in the tissue fluids and in the blood is increased, which causes an increase in the depression of the freezing-point of these fluids. The loss of water by the body through evaporation has a similar effect. It is the function of the kidneys to rid the body of this excessive number of molecules and so keep the osmotic pressure of the blood and of the other fluids con- stant. If the activity of the kidneys is decreased, the depression of the freezing-point of the blood will become greater. A beginning renal insufficiency will therefore be manifested by an abnormally great de- pression of the freezing-point of the blood. The work done by the secretory cells of the kidneys in secreting the urine, the osmotic pres- sure of which is much higher than that of the blood, can be calculated by utilizing the laws of osmotic pressure. If the kidneys secrete 200 cubic centimeters of urine, the energy required amounts to 37 kilo- grammeters; that is, the energy required is equal to that expended in raising a weight of 37 kilograms to the height of 1 meter. The freezing-point of a solution of any substance in water is lower than that of the water alone. The kidney-cells separate urine from the blood against a pressure of a force about six times greater than the maximum force of muscle. The molecular weight of a body can be determined by the depression of the freezing-point. Another theory has been proposed to explain the low freezing- point of urine. Ludwig proved that the glomerulus filters a nearly pure solution of sodium chloride and that in the urinary tubules the water is in part reabsorbed. The theory of Koranyi is that in the urinary tubules there is a molecular exchange in such a manner that for ABSORPTION. 113 each molecule of urinary constituents coming from the blood there is a molecule of sodium chloride passing from the tubules into the blood. Loeb has shown that rhythmical contractions can be produced at will in striped muscles of the frog by a single salt solution. This is not produced by the salt itself, but the ions, because it occurs only in solutions of electrolytes ; that is, substances which dissociate. Among the ions found in the blood he thinks those of sodium are the pro- ducers of rhythmical activity. Pure sodium chloride he regards as a poison. If rhythmical activity begun by it is to persist, these poi- sonous properties must be neutralized by calcium salts. Loeb thinks calcium and potassium salts prevent rhythmical activity, but that they in conjunction with sodium chloride bring about a sustained rhythm. He believes the sodium ion acts by migrating into the muscle-substance and combining with some part of it. Hence, when too many sodium ions have combined and taken the place of a number of calcium ions in the muscle, rhythmical beats cease. The poisonous effects of Na ions are antagonized by the addition of a small amount of Ca and K ions. Muscles contract only as long as they contain all three classes of ions (Na, Ca, and K) in a certain proportion, which may vary to a certain extent. Numerous substances have been classified on the basis of the degree which they possess of passing through a membrane while in aqueous solution. Those which pass through freely have been found to be capable of crystallization as- a rule, so are termed crystalloids; those which are more tardy in their osmosis through a separating mem- brane have been ascertained to be noncrystallizable, but gluelike in nature, hence are known as colloids. The colloids are very feeble in all chemical relations, the reverse being true of the crystalloids. Ex- amples of colloids are seen in albumins, gelatin, and starch, while alcohol, sugar, and ordinary saline substances form good examples of crystalloids. Filtration. — Filtration, synonymous with transudation, is the passage of fluid or fluids through the pores and interstices of a mem- brane while subjected to pressure. The amount of filtration is pro- portional to the extent and quantity of pressure ; thus, the greater the pressure, the greater is the amount of fluid made to pass through the separating membrane. The rapidity and duration of filtration is strongly modified by the nature of the fluids used and the kinds of membrane through which the various fluids are made to pass under pressure. Colloids can be made to filter, but their passage is much less free than is that of crystalloids. In the pathological condition 114 PHYSIOLOGY. known as dropsy, there is presented a partial example of filtration. It is cHaracterized by a transudation of the watery portion of the blood through the membranous walls of the capillaries and small veins into the surrounding connective tissues, producing oedema. This watery element has been literally squeezed through the vessel-walls because of increased intravascular pressure within the capillaries and small veins. The causes of this increased pressure are numerous and need not be dealt with here. Loeb explains this oedema by a greater osmotic pressure in the tissues than in the blood or lymph. Chemical changes in the muscle take place which increase the osmotic pressure. These chemical con- ditions are the result of a diminished supply of oxygen caused by deficient circulation. Rapidity of Absorption. — The rapidity of absorption has been determined by experiment. Thus it was found that lithium chloride may be diffused throughout all of the vascular structures and even into some of the nonvascular ones, as the cartilage of the hip-joint and aqueous humor of the eye, within a quarter of an hour after having been given on an empty stomach. When lithium carbonate is taken in 5- or 10-grain doses, its presence may be detected in the urine within five or ten minutes; the time for appearance is doubled or even trebled when the substance is taken on a full stomach. It is interesting as well as curious to note that some of the mineral and vegetable poisons are more readily absorbed from the rectum than the stomach. Thus, it has been ascertained that strychnine in solu- tion will produce toxic effects very much sooner when injected into the rectum than when administered by the stomach. When adminis- tered in solid form the reverse is true. THE LYMPHATIC SYSTEM. Having previously dwelt upon -absorption as it occurs in the alimentary tract, it remains to turn our attention to the next important process in the general absorption of the body. It is the absorption from within as accomplished by the lymphatic system. By it as an in- strument those materials of the alimentary end-products that were not taken up by the lacteals are collected and transported back into the regular blood-stream, while, on the other hand, fluid which has escaped from the blood-vessels and has not been used by the tissues is gathered up and again carried back into the blood-stream. Very frequently this fluid gathered from the tissues of the body after it has given up much of its nutriment to the tissues contains numerous bacteria, ABSORPTION. 115 pathogenic and otherwise, as well as particles of waste-matter from the tissues. These are normally destroyed by the lymphocytes ; if the foreign particles are too numerous for immediate destruction, they are stored up in the lymphatic glands, or, more properly, nodes, until the lymphocytes are able to dispose of them. The watery fluid which transudes from the vessels, particularly the capillaries, is known as the lymph. It is this fluid which bathes every cell of all the tissues to give them nutriment, while it carries away from these same tissues the products of their activity. It is col- lected by a system of channels and vessels which unite to form one main trunk — ^the thoracic duet — and a second, shorter and smaller duct, and both empty into the subclavian veins: the thoracic duct into the left and the shorter lymphatic duct into the right subclavian. By this means the lymph once more enters the blood-stream to be -again used and perform perhaps identical functions. The vessels with their adnexa which convey the lymph back to the blood-stream again comprise a system known as the lymphatic system. Lymphatic Vessels. In order to nourish the tissues of the body, the plasma of the blood is constantly being osmosed through the capillary walls into spaces between the cells of the tissues. Each cell is thus bathed in a plentiful supply of plasma, from which it absorbs what is needed for its nourishment. This escaped blood-plasma, together with some white cells which have found their way into the spaces, constitute the lymph. To prevent oedema from its accumulation, as well as to have it with its contained impurities reach the blood from which it may be excreted, Nature makes use of a set of tubes, the lymphatics. These vessels are found within the body generally, even in those struc- tures which contain no blood-vessels, as the cornea of the eye. The fluid within them always moves in one direction only: toward the heart. These vessels, whose sources may be very different, unite in their course to form larger vessels until, by continual union, they terminate in two large trunks which empty into the subclavian veins at their junction with the internal jugulars. The one emptying into the left side is the thoracic duct, that into the right side is the right lymphatic trunTc. Structure of the Lymphatics. When the agriculturist wishes to drain his wet lowlands he resorts to the use of pipes of great porosity. These are buried and so arranged that the moisture of the soil very readily finds its way into the pipes. 116 PHYSIOLOGY. to flow along them and so be conveyed away. When the arrangement of the pipes is suitable, the excess of water is carried off. Should the drain-pipes become defective, or should their capacity be less than that demanded of them, there at once results a stagnation with inun- dation of the land. For the water to find its way from between the particles of earth and sand into the pipes it is necessary that the latter be very porous and permeable— a most essential factor. The principle underlying the structure of the lymphatics is very similar to that of the system of drain-pipes of the agriculturist, — namely: porosity, — for the aim of each is to collect the excess of their respective fluids and convey the same to certain desired channels. This principle being kept in mind, the student can readily con- ceive the nature of the lymphatics. They must be vessels of thin walls — walls which allow of the easy osmosis of plasma through them. In fact, the lymphatic vessel- walls are similar in structure to those of veins, differing mainly in the fact that the former are thinner. Like the larger veins, the larger lymphatics consist of three coats. The inner is made of endothelium (tunica intima), the middle coat contains some muscular fibers (tunica media) , while the external coat is connective tissue (tunica adventitia) . The small lymphatics have walls composed of but a single layer of endothelial cells, whose, edges are usually sinuous. So thin and translucent are the walls of many that the clear lymph contained in them can be clearly defined. Like some veins, the larger lymphatics contain valves of a fibrous nature lined with endothelium. In form, structure, and attachments they are identical with those of the veins. Usually two valves of equal size are found opposite one another; these, by their functions, prevent reflux of the lymph when pressure or other disturbance is brought to bear upon their course. Where Nature has vessels with thin walls and which vessels con- tain fluids propelled by very weak vis a tergo, she must needs resort to numerous valves. So numerous are these little safeguards that when tha lymphatics are injected they present the appearance of a string of beads. While dealing with lymphatics, mention must be made of those modified lymphatics known from ancient times as the lacteals. These vessels take their origin from the intestines to empty their contents via the thoracic duct into the left subclavian vein for admixture with the systemic blood. The lacteals were so named from their white color at certain times; that is, during active digestion, when the ABSORPTION. 117 lymph-stream is overwhelmed by the absorbed fatty granules, which give to it its milky hue. The milky-colored fluid has been termed chyle. During the intermission between active digestion the lacteals carry pure lymph, and, from their functions and structure being identical with that of true lymphatics, they deserve to be classed with the latter. Origin of the Lymphatics. Though many features of this system are yet obscure and open for investigation, it seems very probable that, as stated by Landois, the lymphatics arise as follows: — 1. Connective-Tissue Spaces. — These are very numerous, star- shaped or irregularly branched spaces which communicate with one another by fine tubular processes. They are lined with endothelium and contain lymph and a few "wandering cells." 2. Within the Villi. — This mode has been discussed under the subject of "Digestion." 3. In Perivascular Spaces. — The small blood-vessels which supply bone, central nervous tissue, retina, and the liver are themselves surrounded by lymphatic tubes which in many instances are larger than the blood-vessels. Between these tubes and the blood-vessels there exists a space called the perivascular space of His. These are believed to be one source of lymphatics, for, when they exist, the passage of lymph-corpuscles into the lymphatic vessels is greatly facilitated. 4. In the Form of Interstitial Slits Within Organs. — Within the testicle and certain other organs there exist long, slitlike spaces between the various cells and network of tubules. They are all, however, lined with endothelium. Into these spaces there is poured lymph from the blood-capillaries for the maintenance of the glandular cells, and at the same time it furnishes material for secretion. From these little slits lymphatics take their origin, but receive independent walls after their exit from the gland-substance. 5. By Means of Free Stomata. — These occur, for the most part, upon the walls of the larger serous cavities. Lymph is pumped here by the alternate dilatation and contraction of the serous surface, due to the movements of respiration and circulation; so that serous sacs may be regarded in a certain sense as large lymph-cavities. Fluids placed within these cavities readily find their way into the lymphatics. The cavities referred to are those of the peritoneum, pleura, peri- cardium, aqueous chamber of the eye, and labyrinth of the ear. 118 PHYSIOLOGY. 6. In the mucous membrane of the nose, larynx, trachea, and bronchi there have been noticed open pores which are in communica- tion with the lymphatics. Lymphatic vessels of moderate size are supplied with nutrient vessels (vasa vasorum), which are distributed to the external and middle coats of their walls; up to the present time no nerve-supply has as yet been ascertained except for the thoracic duct. Lymphatic glands are hard, pinkish bodies varying in size, and are principally ovoidal. They are generally situated along the course of the larger blood-vessels. The afferent vessels enter the gland at various points on its surface. The efferent vessels emerge from a slight concavity on one side of the gland called the hilura. In this hilum the blood-vessels course. There are two parts in a lymphatic gland: the outer, lighter part, called the cortex; and the darker interior, called the medulla. A fibrous covering envelops the lymph-gland and sends partitions into the gland, cutting it up into spaces called alveoli. These alveoli communicate freely with each other, and are filled with a lymphoid tissue where the leucocytes are undergoing division. They are genera- tors of lymphocytes. Flow of Lymph and Chyle. The lymph and chyle always run in a centripetal direction from the periphery to the center under the influence of various forces. The villi contract and push their contents in a centripetal course, aided by the contractions of the intestinal muscles. The dilatation of the blood-vessels at each contraction of the heart pushes the lymph out of the perivascular spaces. Although the lymphatic cells by their proper activity are the principal cause of the passage of the plasma from the blood-vessels into the lymphatic capillaries, yet it is necessary to admit that the arterial blood-pressure contributes in a marked manner. By this exudation the interstitial pressure always tends to the same height as the intracapillary pressure — ^the stronger the intracapillary pressure, the stronger the interstitial pressure. On the other hand, the stronger the interstitial pressure, the more easily the lymph will be absorbed by the lymphatic capillaries. We must admit with Ludwig that the pressure of the blood is a powerful cause in the circulation of the lymph, and this can be easily shown by sec- tion and irritation of the spinal cord, after a cannula has been intro- duced into the thoracic duct, where the lymph-flow decreases with the dilatation of blood-vessels on section of the cord and increases on irri- ABSORPTION. 119 tation of the cut section. Once the lymph and chyle are in the vessels it continues to move by the muscular contraction of the walls of these vessels, and this movement can only take place in a centripetal direction by reason of the arrangement of the valves. The lymphatic ganglia, by their structure, ofEer a resistance to the circulation of the lymph, but their fibrous covering and unstriped muscles favor the flov?^. Cold-blooded animals have lymphatic hearts which act as motors in circulating the lymph. The valves in the lymphatic vessels are powerful adjuvants in propelling the lymph in a central direction. The respiratory movements have an influence. At the time of inspira- tion the flow of lymph, like the blood, rushes into the chest, owing to the partial vacuum in the chest. The pressure by muscular action on the lymphatics also greatly aids in the propulsion of the lymph. Lymph moves at the rate of about ten inches per minute, and its pressure is fifteen millimeters of soda solution. The nervous system bears a direct relation to the lymph-stream in so far as it governs the musculature of the lymph-trunks and capsule and trabeculae of the lymph-glands. A solution of common salt injected beneath the skin of a frog will be rapidly absorbed, unless the central nervous system be destroyed, when no absorption takes place. Composition of the Lymph. Lymph is an albuminous, colorless fluid which contains lymph- corpuscles; these are identical with the colorless blood-corpuscles. Lymph is alkaline, has a specific gravity of about 1.015, and when drawn from its vessels it clots, forming a colorless coagulum of fibrin. The watery part of the lymph is known as the lymph-plasma, which contains the three elements necessary for coagulation: fibrinogen, fibrin-ferment, and calcium salts. It is very similar to blood-plasma, only diluted so far as its proteid constituents are concerned. The proteids present are fibrinogen^ serum-globulin, and serum-albumin. The salts contained in solution are present in smaller proportion than those found in blood-plasma. The waste-products — urea, carbonic acid, leucin, etc. — are more abundant in the lymph than in blood; the solids herein contained reach 4 per cent., of which 3 ^/^ per cent, are proteid in nature. The amount of glucose is about the same as in blood-plasma. The lymphocytes contain glycogen. The apparently transparent lymph is found to contain corpuscles when examined under the microscope; to them the name lymphocytes has been applied. They have a large nucleus with comparatively little protoplasm. In some places — the thoracic duct, for example — a few 120 PHYSIOLOGY. colored blood-corpuscles are found and are believed to have found their way into this distinct system by reason of diapedesis. The regular lymphocytes find their way into the blood-stream, where they multiply and are known as leucocytes. The real manufactories of these lymphocytes are the lymphatic glands, whose alveoli contain adenoid tissue. The number of lym- phocytes is much greater in the lymph after it has passed through a gland, and we find that lymph collected from regions where there are few glands, as the lower extremities, is always poorer in albumin and richer in water than the lymph in the large lymphatic vessels. For purposes of analysis, lymph can be obtained from the limbs, thoracic duct, and serous cavities. Accidental lymphatic fistulae in man as well as experimental ones in animals have been the source of much lymph for analytical purposes. The pericardial fluid and aqueous humor are forms of lymph which are not coagulable except upon the addition of fibrin-ferment. Cerebro-spinal fluid has the identical appearance of lymph, but differs from it in chemical properties and composition. Synovial fluid of joints differs from true lymph in that it contains mucin or mucinlike bodies and a high percentage of solids. Chyle is the term used to designate the fluid of the lacteal system during active digestion, particularly of fats. It is an opaque, whitish, milky fluid, neutral or slightly alkaline in reaction. The color of the chyle is due to the presence in it of numerous fatty granules, each surrounded by an albuminous envelope, very minute, though uniform in size. Their fatty nature becomes evident when they are treated with ether, for they are immediately dissolved. Varying quantities of the fat give different shades of whiteness to the chyle. Thus, in addition to the constituents of the lymph, the chyle contains a large amount of fat, which is its characteristic feature. During fasting the chyle in the lacteals resembles ordinary lymph. As the chyle passes on toward the thoracic duct, especially when traversing some of the mesenteric glands, it is elaborated. As a result there are fewer fat-particles, but there now begin to appear corpuscles to which the name chyle-corpuscles is applied. Further, it now gains the ability to coagulate spontaneously. As the chyle advances in the thoracic duct the corpuscles become more numerous, and the larger and firmer becomes the clot when the chyle is withdrawn from its vessels. The clot is like that of blood when only white corpuscles are present. Its ability to coagulate is due to the disintegration of the lymph-corpuscles which supply it with the necessary fibrin-factors. ABSORPTION. 121 Quantity of Lymph and Chyle. It may be roughly stated that the amount of lymph and chyle combined passing through the large vessels in twenty-four hours is about twelve pounds. The formation of lymph in the tissues takes place continually and without interruption. It must be remembered that the total quantity of the lymph and chyle is not a constant factor, but may become affected by different conditions. Thus, the amount of chyle becomes very much increased during digestion; is diminished during hunger. The amount of lymph increases with the activity of the organ from which it proceeds, while active or even passive movements of the muscles greatly increase its amount. Conditions which increase the pressure of the vascular supply of the tissues increase the amount of lymph, and vice versa. Formation of Lymph. Ludwig thought the lymph was regulated by differences between the arterial tension and the interstitial pressure, and to chemical dif- ferences between the two liquids resulting in an osmosis through the wall of the blood-vessel. Heidenhain has sought to prove that the lymph is a true secretory product. The quantity and composition of this liquid was regulated by the elective activity of the cells of the capillaries. He considers the force developed by the cells as one of the principal causes of the flow of the lymph. He based his con- clusions on the fact that the quantity of lymph produced is not always exactly parallel in the value of the arterial tension. Lymph can flow for many hours after death when a fistula has been made in the thoracic duct. He also found that certain substances, as glucose, is larger in amount in the lymph than the blood, due, as he believes, to the selective action of the endothelial cells of the lymphatics. Heidenhain makes two classes of lymphagogues. In his first class a decoction of crayfish, leeches, or mussels in the blood increases the flow of lymph from the thoracic duct, acting upon the endothelial cells of the capillaries. They cause a slight injury to the capillary wall, thus increasing its permeability, so that a slight rise of pressure greatly increases the transudation. They chiefly affect the capillaries of the liver. Curare has a specific action on the endothelial cells of the capillaries, causing an increase of lymph. The second class of lymphagogues — ^like sugar, salt, potassium iodide, and peptone — abstract water from the tissues into the blood, thus raising arterial tension and increasing the flow of lymph. 123 PHYSIOLOGY. Skin and Lungs. It remains to consider the nature of the absorption that takes place through the skin and lungs. These avenues are but subsidiary ones to the two greater ones just mentioned: intestinal absorption and that along the lymphatic system. Absorption through one of. them takes place from without; so that it is usually classed with the first of the two processes of absorption mentioned at the beginning of this chapter. For a long time it was a subject for much discussion whether water was absorbed by the skin with the epidermis still intact. It was a rather difficult matter to ascertain, since the skin is constantly giving off water in the form of perspiration, sensible or insensible. The absorption of water through the skin covering the body takes place very rapidly in the lower animals. It has been finally ascer- tained that absorption of water does take place through the skin of man, but to a much less degree than occurs in animals. Aqueous solu- tions of various drugs when in simple contact with the skin are only slightly active. It is believed that the great hindrance to their ab- sorption is the presence of the fat that is normally present upon the skin and in its pores and interstices. If this be removed by the appli- cation of alcohol, ether, or chloroform, physiological effects of the drugs are soon manifested. Inunction. — When ointments are ruhhed into the skin so as to press the substance in, absorption will take place. Mercury when applied in this manner exerts its specific effect upon syphilis and ex- cites salivation; tartar emetic so applied may produce vomiting or an eruption extending over the entire body. Voit found globules of mer- cury between the layers of the epidermis and even in the corium of a person who had been executed and into whose skin mercurial ointment had previously been rubbed. An abraded or inflamed surface absorbs very rapidly. Under normal conditions minute traces of are absorbed from the air ; CO, COj, vapor of chloroform, and ether may also be absorbed. In dysphagia, when the condition is so severe that even fluids cannot be taken into the stomach, immersion of the patient into a bath of warm water or water and milk may quench the thirst. It is well known that sailors, when destitute of fresh water, assuage their thirst by wetting their clothing with salt water and wearing them until dry. It is very probable that the effects produced are in a great measure attributed to hindrance to the evaporation of water from the skin. ABSORPTION. 123 Throug^h the Lungs. — It is interesting to note that not only do gases pass through the epithelium of the pulmonary air-vesicles, but that fluids, such as water, may be absorbed when they have found their way into the air-passages. The presence of particles of carbon in the bronchial glands and other tissues of the respiratory apparatus is accounted for only by reason of the open pores : one of the origins of the lymphatic system. CHAPTER V. THE BLOOD. Blood is a red, somewhat viscid fluid, denser than water, and apparently composed of but one substance. This liquid, which is usually spoken of as the nutritive fluid of the body, serves as an in- ternal medium of exchange existing between the foodstuffs found in the outer world and the cells composing the various tissues of the body. It was constantly kept before the student's attention that the main and ultimate end of digestion was the absorption of the food- stuffs into the blood-stream, not as proteoses and peptones, but as native albumins and globulins — these latter the results of the living, vital activity of the epithelial cells of the villi through which pass the proteoses and peptones. Thus, into the blood are poured new products (the work of digestion), which are carried by its circulation to all parts of the body, to be given up to the various tissues having need of them. By this means every cell receives the nutriment neces- sary for carrying on its own metabolic processes, either directly or indirectly. For the student will remember that each cell possesses an inherent selective capability. Prom the pabulum contained in the enveloping lymph it is able to take up those factors which it can work up into its own constitution to form an integral part of itself. These constituents, having served their respective purposes, are no longer of any value to the cell — they are waste-products, and as such must be gotten rid of. Passing out from the cell-substance, they find themselves in the same enveloping lymph, to be eventually carried again into the blood-stream for elimination through the excretory activities of the lungs, kidneys, and skin. Thus, indirectly the blood is a medium of elimination of such deleterious products as urea, uric acid, water, carbon dioxide, etc. However, the afferent function of the blood is not simply single, for it conveys to the tissues in addition that material, all-important for successful combustion,— namely, oxygen, — which has been ob- tained from the respired air of the lungs. Among warm-blooded animals another office served by the blood is to equalize to a certain degree the temperature of the body. (124) THE BLOOD. 125 Color. — There are certain characteristics which distinctly mark blood from other fluids. The color of the blood of vertebrata is gen- erally red. Its shade is, however, not fixed. As the blood-stream passes through a variety of tissues and is subjected to many different conditions, its color varies from a scarlet red in the arteries to a bluish red found within the veins. It is the presence of the oxygen in combination with haemoglobin that gives to the arterial blood its bright color. Lessened oxygen means excess of carbon dioxide, and it is the presence of the latter which gives to venous blood its char- acteristic bluish-red color. When normal blood is drawn from a blood-vessel to be placed upon a glass slide as a very thin film, it is found to be opaque, and printed matter cannot be read through it. This opacity is produced by difEerences of refraction possessed by its several components. The healthy red color of the nails, conjunctiva, lips, ears, and mucous membranes in general is due to the presence of the blood. When there is insufficient supply to these parts, — temporarily in fainting or for a longer period, as in anaemia, — they become pale and waxy in color. In asphyxia and certain heart affections there is a want of proper oxidation, with a resultant bluish color to the above-named parts. Eeaction. — The reaction of blood is alkaline. This alkalinity is variable in amount. Thus, it is diminished after great muscular ex- ertion, owing to the formation and presence in it of a large quantity of sarco-lactic acid. After long-continued ingestion of soda the alka- linity is increased; after the use of acids it is diminished. In no case, however, does it become distinctly acid. To test the alkalinity of the blood, dry, faintly reddened glazed litmus-paper is used. Upon it is placed a drop of blood, which is allowed to remain for half a minute, to be then wiped off with a weak salt solution. The result is a blue spot upon a red background. Blood possesses a distinctly salty taste. It owes this property to the presence of disodic phosphate and bicarbonate of soda. Specific Gravity. — The specific gravity of normal, healthy blood varies within certain limits: for men, about 1.057 to 1.066; for women, 1.054 to 1.061. Its density is influenced by various factors and conditions. If fluids be used sparingly and a dry diet eaten, the density is increased. It is also increased by exercise and profuse sweating. It falls when fluid is injected into the vessels, but for a short time only. The temperature of the blood varies between 97.7° and 100° F. The cutaneous blood-supply is slightly lower in temperature, while 126 PHYSIOLOGY. the warmest blood is that in the hepatic vein; the coldest in the tip of the nose. Fresh blood imparts a decided odor, peculiar to the animal from which it is drawn. The odor of blood is due to volatile fatty acids held in solution. The effect becomes more striking upon the addition of concentrated sulphuric acid to the blood. Quantity of Blood. — From very early times the theme of the quantity of blood circulating within the body has been uppermost in the minds of physiologists and investigators. By reason of the methods then employed the results were inaccurate and difficult of at- tainment. Simple bleeding was resorted to, but deductions depended upon the rapidity with which the blood was lost. If the animal were bled very rapidly, then considerable of blood remained in the vessels. If the blood was extracted very slowly, not only blood, but serum from the lymphatic vessels, spaces, and glands was obtained. These factors very materially altered the calculations. The accepted, though not very simple, method, for determina- tion of quantity is that of Welcker's. It is as follows: The specific gravity of the blood as well as weight of the animal are first noted. A cannula is placed in the animal's carotid through which is extracted a quantity of blood to serve as a sample. This is defibrinated, where- upon portions of it are diluted at different known strengths. The remainder of the blood in the body is then allowed to escape, and is collected and defibrinated. A normal salt solution is next run through the vessels and likewise collected. The entire body, minus the stomach and intestines, is then cut into very fine pieces and extracted with water for one or two days, at the end of which time the bloody water is expressed and added to the drawn blood and washings. The entire amount is carefully measured. The experimenter compares this diluted blood with the pre- viously prepared samples of the diluted blood of known strength until he finds tints of two that are exactly alike. From the total quantity of diluted blood and the knowledge of what the sample contains it is comparatively easy to calculate the amount of blood contained in the body. To this must be added the blood drawn at first to make the various samples. The weight of the animal compared with the above results gives the proportionate amount. By this and similar computations it has been ascertained that the blood is equal to from one-eleventh to one-fourteenth of the body-weight. Approximately, it may be said to be one-thirteenth of the body-weight. THE BLOOD. 137 "Koughly, it may be said that the lungs, heart, large arteries, and veins contain one-fourth ; the muscles of the skeleton one-fourth ; the liver one-fourth; and other organs one-fourth." (Eanke.) Arterial and Venous Blood Compared. — At this point the stu- dent's attention is called to but a few main points wherein the arte- rial and venous bloods differ. Very conspicuously stands out the marked difference in color: the scarlet of arterial, the bluish red of venous blood. These color-differences depend primarily upon the amount of oxygen-gas contained in the blood. It unites with the iron of the blood-corpuscles (little bodies) to form a very unstable compound, known. as oxy haemoglobin. When carbon-dioxide gas is present it also forms an unstable compound. Its color is dark. When oxyhaemoglobin is in excess, as it is in arterial blood, the color is a bright red. When carbon dioxide is in the ascendancy, the blood is bluish red and the oxygen-gas is present in diminished amounts. Arterial blood contains more of the assimilable products of the digestive processes, so that it is better fitted to supply the cells with their proper nutrition and materials to the various glands for their secretions. It also contains greater quantities of salts, fats, and sugars. Venous blood contains less nutriment, but more waste-prod- ucts resulting from eatabolic processes, particularly urea and carbonic acid. Composition of the Blood. — Apparently the blood-stream, as viewed by the naked eye, is composed of one homogeneous, red sub- stance; but when examined histologically with the microscope this impression becomes entirely dispelled. It is then found to be com- posed in reality of a transparent liquid portion, known as the plasma, or ligiwr sangvdnis, in which, as a medium, float an immense number of blood-corpuscles. The great majority of these latter are colored, and it is due to them that the blood owes its color. There are at least three different kinds of blood-corpuscles, commonly known as the red corpuscles; the white corpuscles, or leucocytes; and, last, hlood-plates. The red corpuscles of mammalia — the camel and others of the group of CamelidcB alone being excepted — are circular plates, bicon- cave, and without nuclei. Those of the camel, birds, and reptiles are elliptical and biconvex. Human red blood-corpuscles are biconcave, disc-shaped bodies with rounded edges and slight central depressions. They have been tersely described by one author as "circular, biconcave, nonnucleated discs." 1-28 PHYSIOLOGY. The corpuscles are formed of a semisolid, homogeneous, iron- holding mass which appears to have no membrane or nucleus; for a nucleus is normally met with in them only during embryonic life of mammals and in the blood of the lower vertebrates, as the amphibia. In size, they are about Vjjoo inch in diameter and V12000 i^ich in thick- ness. Various causes and conditions may, however, slightly increase or decrease their size. Blood-corpuscles of Different Animals. (Thanhofpeb.) 1, Proteus. 2, Bana escul&nta: ii, upper view of same; 6, white blood- corpuscles; c, side-view of red corpuscles. 3, Triton. 4, Snake. 5, Camel. 6, Turtle. 7, Salamander. 8, Carp. 9, Cobilis fossilia. 10, Cuckoo. 11, Chicken. 12, Canary bird. 13, Lion. 14, Elephant. 15, Man: a, upper view of same; 6, crenated form; c, white blood-corpuscles. 16, Horse's cells in rouleaux. 17, Hippopotamus. Because of their extremely small size the corpuscles are not really red when viewed singly with the microscope, but rather of a pale yellow or even greenish tinge. It is only when millions of them are en masse that the characteristic red color becomes apparent: scarlet red in arterial blood, purplish red in venous blood. These shades of red are occasioned by the varying proportion of oxygen in combination with the haemoglobin, with which the gas unites very readUy. Because of this fact it falls to the lot of these little bodies to perform a very important function for the economy, viz. : to con- THE BLOOD. 129 vey oxygen from the lungs to the tissues to he distributed to them. The is held hy the haemoglobin so lightly and unstable that it can be very readily extracted from the corpuscles hy the cells of the tis- sues. Upon the blood depends the internal respiration of the tissues and all oxidation processes. While there is undoubted active oxida- tion occurring in the blood itself, yet the blood is not the place of the oxidation in the body. The cause is in the living cells of the tissues. In addition to an inherent affinity possessed by the tissues for oxygen, its passage from the blood to the tissue-cells, as also the passage' of carbon dioxide from the cells back to the blood-stream. B Fig. 16. — Human and Amphibian Blood-corpuscles. (Landois.) A, Human red blood-corpuscles: 1, on the flat; 2, on tlie edge; 3, rouleaux of red corpuscles. B, Amphibian red corpuscle: 1, on the flat; 2, on edge. C, Ideal transverse section of a. human red corpuscle, magnified 5000 times. a~b, linear diameter; c-d, thickness. depend very materially upon differences of pressure of these two gases in the blood and tissues. The direction is always from a higher pressure to a lower one. A peculiar inherent power and property of red corpuscles is to arrange themselves, when withdrawn from their retaining vessels, in the form of rolls of coin, adhering to one another by some peculiar afSnity. To describe this condition the term rouleaux has been used. This peculiarity becomes particularly marked when there is an in- flammatory state of the system.- Formation of rouleaux can be pre- vented by the injection of physiological saline solution. Parasites of Blood-corpuscles. — In the red corpuscles of some birds and fishes the microscopist frequently notices small, transparent 130 PHYSIOLOGY. spots. These are " pseudovaeuoles," in which may be developed and later shed into the blood-stream small parasites. Within the red corpuscles of man, when affected by malaria, are developed the Plas- modium malarice. Their passage into the patient's blood-plasma marks a paroxysm. The number of the corpuscles is usually spoken of in terms of cubic millimeters; thus, in man there are about 5,000,000 per cubic millimeter; in woman, about 4,500,000. These figures represent the average number per cubic millimeter, but even in health and in the same individual there may be wide variations from this standard given, to say nothing of the extreme diminution experienced in cer- tain pathological conditions. As the corpuscles are small bodies floating in a liquid medium, the student can easily understand why their number should be in inverse ratio to the quantity of plasma, when the unit, cubic milli- meter, is considered. Copious sweating and the loss of much water by way of the bowels and kidneys occasion a temporary increase in their number. Normally, there is no difference as to the number of corpuscles in arteries and veins, provided there be no congestion in the latter. A most interesting variation is that produced by habitation in high altitudes. A two weeks' sojourn in a high mountain has been known to show an increase from 5,000,000 to 7,000,000 per cubic millimeter. This is accounted for not because of any real increase in the manufacture of corpuscles, but to increased evaporation with con- sequent loss of larger amounts of water. In chlorosis and pernicious anemia the corpuscular count falls considerably. A decrease to half a million per cubic millimeter is the lowest limit compatible with life. life-cycle of the Red Corpuscles. — The life of the red corpuscle is unknown. In experimental transfusion the red corpuscles disap- pear at the end of a variable period. The destruction of blood-cor- puscles in extravasations does not give us any precise results. Ob- serving the differences in color, consistency, and dhemical reaction, it is found that they correspond to the different degrees of development. This shows that in the blood there is a constant destruction and renewal of the corpuscles. As to the place of destruction of the red corpuscles, certain facts show that the liver and spleen seem to be places for the accomplish- ment of it. Counting Red Corpuscles. — Various methods have been devised for counting the number of corpuscles, the instruments used receiv-. THE BLOOD. 131 ing the name hcemacytometers. Modifications are numerous, but un- derlying all of them is one main principle, namely: the actual count- ing of the corpuscles within a certain measured bulk. To preserve the shape and integrity of these little bodies during the technique it is necessary to dUute the sample of blood with some solution whose specific gravity exactly equals that of the blood-serum. Some of this blood-solution is then placed upon a graduated slide beneath a micro- Fig. 17. — Haemacytometer of Thoma-Zeiss. (LAHOrssE.) A, Capillary- glass tube. B, A glass slide upon whicli is a covered disc accurately ruled so as to present 1 square millimeter divided into 100 squares of Vm millimeter each. 1, Blood is drawn up to this point. 101 represents normal saline-solution drawn up the tube, mixed with the blood drawn up to 1. In 101 parts the blood forms 1 part. scope for counting, when the number per cubic mUlimeter is easily computed. At this point the attention of the student will be directed to but two instruments: (1) the Thoma-Zeiss apparatus and (2) the Daland hasmatocrit. 1. Thoma-Zeiss Appaeatus. — The apparatus consists of two separate and distinct parts : a capillary tube and a counting chamber. 132 PHYSIOLOGY. The tube is for the purpose of measuring the amount of blood whose corpuscles are to be counted. By it also is accomplished the proper dilution in the upper, bulbed chamber. The capillary portion of the tube is graduated to 0.5 and 1.0 marks. Just above the capillary portion of the instrument is the bulbous portion containing a small glass ball to assist in the thorough mixing of blood and diluting nor- mal saline fluid. Just above the bulb is the 101 mark. For drawing both blood and the diluting saline into the apparatus there is at- tached a piece of rubber tubing with a suitable mouthpiece. AVith the blood up to the 1.0 mark and enough diluting saline to bring the whole quantity of liquid to 101, the dilution is 1 to 100. The second portion of the instrument, known as the counting chamber, is constructed so as to enable one to count under the micro- scope all the cells in a known bulk of the diluted blood. In the center of a thick glass slide is cemented a cover-glass of accurately measured thickness with a hole in the center about 1 centimeter in diameter. In the central area of this cover-glass is also cemented to the glass slide a glass disc about 2 millimeters smallfer in diameter and exactly ^/lo millimeter thinner than the. cover-glass. The glass shelf being exactly ^/i„ millimeter thinner than the cover-glass, it will readily be seen that if a second loose cover-glass be laid upon the first, the under surface of this loose cover-glass will be exactly Vio millimeter above the upper surface of the glass disc. In this way there is secured a layer of fluid ^/m millimeter in depth. Furthermore, 1 square millimeter of the surface of the disc is outlined and subdivided by intersecting lines into 400 small squares. For convenience in counting, every fifth row of squares is divided into two by an addi- tional line. The volume of diluted blood above each square of the micrometer will be V4000 cubic millimeter. The average of 10 or more squares is then ascertained, which result is multiplied by 4000 times 100 to give the number of corpuscles in a cubic millimeter of undi- luted blood. The H^matoceit. — A rapid approximate determination of the relative percentage of the corpuscles may be made by Daland's instru- ment. The blood is sucked up the graduated tube without dilution and then centrifuged. The corpuscles rapidly accumulate at the end of the tube in an almost solid mass and their collective volume can be directly read off. The estimate can be made with a small quantity of blood, and is, therefore, capable of being used for clinical purposes. Daland found that 50 on the scale was normal; this, multiplied by 100,000, gives the number of corpuscles in 1 cubic millimeter. THE BLOOD. 133 Experiments Upon the Blood. — Points of interest to ihe physiol- ogist particularly and the clinician incidentally have been disclosed as the results of some simple experimental work upon the blood- corpuscles. Each red corpuscle is seen to be composed of a fine meshwork, or stroma, consisting of noncolored, homogeneous proto- toplasm. Scattered throughout this framework is the iron-holding pigment, which gives color to the corpuscle and is the substance with which the oxygen-gas enters into loose combination. Any reagent which is able to sever the union between stroma and haemoglobin causes the latter to pass into solution in the plasma. The once-red corpuscles then appear as transparent bodies. This makes the blood dark red, but transparent, since the coloring matter is in solution. When the blood is in this condition it is said to be "lake-colored." Fig. 18. — Red Blood-corpuscles. (Landois.) a, b, Normal human red corpuscles with the central depression more or less in focus, u, d, e, Mulberry forms, g, h, Crenated corpuscles, ft, Pale, decolored corpuscles, i, Stroma, f, Frog's corpuscles acted upon by a strong saline solution. Laky blood may also be produced upon the injection of the blood- serum of one animal into the blood of another kind, the serum having the power to destroy the red corpuscles. The term " globulicidal action " covers this property of the serum. The first effect of pv/re water upon red corpuscles is to produce a very obvious change in shape. From being d^pcoid in form, they become spherical, or nearly so. After some time the haemoglobin becomes dissolved out, leaving the corpuscles transparent: shadow- corpuscles. The knowledge thus gained led to further research to find some solution which will not affect the corpuscles. Isotonic Solutions. — To prevent " laking " of the blood normally there must be a certain degree of concentration of the medium im- mediately surrounding the corpuscles so that just sufficient water is maintained within the corpuscles as is needed. If by the addition 134 PHYSIOLOGY. of distilled water or other reagents this degree of concentration is changed so that the balance is broken, theii too much water enters the corpuscle. There immediately follows a change in shape, with forcing out of the pigment. A solution containing just enough of salts so that the corpuscles are neither altered in shape nor lose their haemoglobin is said to be "isotonic." The percentage of NaCl neces- sary to generate such a solution is, for frogs' blood, 0.65 per cent. ; for blood of man, 0.95 per cent. The action of certain organic svhstances is of considerable im- portance. Thus, bile and the alkaline salts of the biliarj' acids hare the power to dissolve and destroy the red corpuscles with phenomena which resemble those produced by the action of chloroform. Urea in solution also destroys them. As to vitality, it is known that the corpuscles of blood that have escaped from the circulatory system, as well as those from defibrin- ated blood, when reintroduced into the living blood-stream, retain their vitality. THE WHITE CORPUSCLES. The white corpuscles are colorless, spherical little bodies which are a little larger than the red ones and much less numerous. Each is about V2500 iiich in diameter and is composed of granular proto- plasm that is highly refractUe a,nd without any enveloping membrane. In striking contrast to the erythrocytes, the leucocytes possess not only one, but usually three nuclei ; even four are not uncommon. Within the nuclei may be defined several distinct nucleoli. When examining a section of blood, it is at once a striking fea- ture how few are the white as compared with the red corpuscles. In the average field but three or four are found, while at the same time hundreds of erythrocytes are noticed. The average is but 1 white for every 500 or 600 red ones. This proportion does not pretend to convey an accurate idea of their relationship because of the frequent fluctuations of the white corpuscles even in a single day. They increase during digestion and diminish during abstinence. Bleeding, lactation, quinine, local suppuration, and leucocythse- mia increase the white corpuscles; their number is diminished by large doses of mercury. The proportionate number of leucocytes that is found in blood drawn from its containing vessels is no criterion of the number found within the blood-stream. As soon as blood is drawn from the body. THE BLOOD. 135 for no accountable reason as yet known, an immense number of white corpuscles disappears. It is stated that there remain but one-tenth of the number previously found in circulation. Colorless corpuscles are not essentially peculiar to the blood- stream nor to be found only in it, for similar corpuscles are found in lymph, chyle, adenoid tissue, the marrow ot the long bones, and also as wandering cells in connective tissue, drawn thither by inflamma- tion and bacteria. Fig. 19. — Leucocytes of Man, showing Amoeboid Movement. (Landois.) Varieties. — According to Ehrlich, they may be separated into three groups, the basis of classification depending upon the staining proclivities of the granules held within the cytoplasm. To the first group he gave the name eosinophiles, because the granules of this class of corpuscles stain best with acid aniline dyes. The hasophiles comprise the second group and include those staining best with basic dyes. Last come the neutropMlesj their granules are capable of being colored only by the presence of neutral dyes. This classification is a 136 PHYSIOLOGY. very popular one and one that holds a very prominent position in pathological circles. Another and perhaps easier classification is into (1) lymphocytes, (3) mononuclear leucocytes, and (3) polymorphonuclear leucocytes. 1. Lymphocytes. — These contain a single, round, vesicular nucleus enveloped in a scanty supply of rather granular cytoplasm. They are derived from the cells of the lymphatic glands. 2. The Mononuclear Leucocytes, as the term implies, hold but a single nucleus. They are large, adult-sized cells, with a vesic- ular nucleus surrounded hy a liberal supply of cytoplasm. They possess certain amoeboid movements. 3. The Polymoephonucleah Leucocytes are especially con- spicuous because of the number and curious forms in which their nuclei are found. There may be as many as four or five distinct nuclei ' or but one divided entirely or partially into separate lobes. As to shapes, the horseshoe and crescent are very prominent. These are the cells that are particularly active in their amoeboid movements. These latter classes may represent but various stages in the life- history of a single leucocyte, the lymphocyte representing the embryo, the polymorphonuclear the adult cell. Amoeboid Movement. — All the leucocytes, with the exception of the lymphocytes, have in common a very remarkable attribute of spontaneously changing their shape and thereby executing certain movements, which, from their great similarity to those performed by the micro-organism amoeba, have been termed amcehoid. When the conditions of temperature and moisture are maintained at the proper standard, the leucocytes will be seen slowly to alter their shapes and to send out from their cytoplasm little processes into which the remainder of the leucocytes seems to fiow, thereby causing a slight movement with change of position. This process repeated successively gives to the cell its power slowly to move from place to place, after having worked its way through the vessel-walls into the surrounding connective tissues. This locomotion is frequently termed the " wandering " of the cell. To their sticky exteriors there are fre- quently seen adhering fine pieces of broken-down cells, bacteria, and other foreign particles. By reason of certain internal circulatory movements in the -protoplasm of the leucocytes, these adherent for- eign particles may be drawn into the interior of the cell, where some are absorbed, others excreted as effete matters. Functions of the leucocytes. — It is definitely known that the leucocytes play an important role in the process of blood-coagulation. THE BLOOD. 137 Their relation to this most important process will be discussed under the head of " Coagulation." They are believed to help maintain the needed proportion of proteids. Their most evident function is the protection of the economy from both harmless and pathogenic bacteria. This they accomplish by two methods. The first is by generating adefensive proteid which, when imbibed by the bacteria, kills them. The second and more usual method is that of drawing into their interiors the various bacteria, together with the debris resulting from lesions, and, as it were, eating them. From this apparent consumption of foreign par- ticles they have gained for themselves the name of phagocytes, and the act is known as phagocytosis. The seat of the presence of the bacteria mark a miniature battlefield, with the hosts of bacteria drawn up on one side in battle array against the leucocytes, the two armies to become engaged in a death-struggle. If the leucocytes, now termed phagocytes, are victorious, they not only kill their adversaries, but even remove every vestige of the combat, aided by the fixed con- nective-tissue cells. Those leucocytes which come out of the affray unharmed, and are no longer needed, find their way back into the blood-stream. If, however, the bacteria with their toxic secretions and excre- tions are too powerful for the phagocytes, the latter succumb, to be- come pus-corpuscles. When the pus has been removed by drainage and the action of other leucocytes; the broken-down tissues are re- placed by regenerating connective tissues. Bacteria are not alone the provocation for attack by the phago- cytes, for the presence of other foreign matters will also call out an assault. It is well known that surgical ligatures of gut and silk that are allowed to remain within the body-cavity and tissues are grad- ually removed, particle by particle, by the phagocytic action of the leucoc3rtes. The absorption of the tails of tadpoles and other batrachians is due to phagocytic action. Diapedesis. — By reason of their locomotive tendencies the leuco- cytes and red corpuscles are able to make their way through the walls of the capillaries ; this emigration has been styled diapedesis. There are several stages before the leucocyte finally makes its exit, namely: slowing of the current with the adherence of the cell to the side of the blood-vessel, and projection of processes, to be followed by the gradual exit of the entire leucocyte. This process occurs to some extent in health, but is greatly exaggerated by inflammation, presence of bac- 138 PHYSIOLOGY. teria, etc. Circumscribed collections outside of the .vessels often form abscesses,' the leucocytes then receiving the name pus-corpuscles. The leucocytes in this condition usually are dead and show signs of fatty degeneration. Frequently red corpuscles -follow iu the' wake of the white ones, passing through the openings in the vessel-walls made by the former. In acute fevers and septic processes, as the temperature rises there follows a decrease in the number of erythrocytes, with a corre- sponding increase of leucocytes. Origin of Leucocytes. — The source of the colorless corpuscles seems to be rather extended. They originate in the bone-marrow and I « 2 I Fig. 20. — Blood-plates and their Derivatives. (Landois.) 1, Red corpuscle on the flat. 2, On the side. 3, Unchanged blood-plates. 4, Lymph-corpuscle surrounded by blood-plates. 5, Altered blood-plates. 6, Lymph-corpuscle with two heaps of blood-plates and threads of fibrin. 7, Group of fused blood-plates. 8, Small group of partially, dissolved blood- plates with fibrils of fibrin. spleen, but the credit for greatest production belongs to the lymphoid tissues and lymphatic glands. From these latter sources the leuco- cytes enter the lymph-circulation, from thence to be emptied into the blood-stream. After having once gained entrance to the blood-circu- lation there is rapid multiplication to keep up the proper supply, since many succumb to the poisons secreted and excreted by the various bacteria. Blood-plates and Elementary Granules. — In addition to the eryth- rocytes and leucocytes found floating in the liquor sanguinis, there have been discovered other numerous, smaller bodies, termed blood- plates and elementary granules. THE BLOOD. 139 The hlood-plaies are pale yellow or colorless discs; round, oval, or crescentic in shape; and varying within wide ranges as to size, although always smaller than red corpuscles. In blood that has been drawn from the vessels they diminish very rapidly both in numbers and size, becoming gradually dissolved in the plasma and are believed to assist in coagulation. As to their nature, there is some diversity of opinion, but the consensus of thought seems to be in favor of the "plates being formed bodies, and not precipitates. They have been found to contain the same elements chemically as do the nuclei of the leucocytes, so that they are probably fragments of the nuclei of dis- integrated leucocytes. In number, their range is very extensive: from 15,000 to 300,000 in a cubic millimeter of blood. The elementary granules are smaller than the blood-plates and appear to be composed of portions of the protoplasm of leucocytes. They contain proteid and fatty matters. FORMATION OF RED' BLOOD-CORPUSCLES. The red corpuscles, as every other portion of the economy, per- form their allotted task and round of existence, to finally die and disappear. Just how long the red corpuscle lives is yet unknown, but that it cannot be very long lived is probable when we consider that its haemoglobin is the parent-body of the bile-pigments which are constantly being expelled from the body as a portion of" the fseees. Hence there must constantly be manufactured a new supply of cor- puscles to replace those that die. The origin of the red corpuscle as to time may be spoken of as that which occurs during intra-uterine life and that occurring during extra-uterine life. During Intra-uterine life. — The corpuscles which first appear in the human embryo owe their existence to a very simple origin. They differ in some respects from those that appear later during intra-uterine life, and very materially from those formed during life outside of the uterus. The wall of the yelk-sac, situated entirely outside of the body of the embryo, is the seat of the first vessels and blood. In the chick the corpuscles appear during the first days of incubation and before the appearance of a heart. At the end of the first day, surrounding the early embryo there appears a circular, vascular area made up of cords of cells in which are developed the first evidences of the ves- sels and corpuscles. The corpuscles appear in groups within this branched network of mesoblastic cells, where they form the "blood- 140 PHYSIOLOGY. islands " of Pander. Presently the cords of mesoblastic cells which compose this network begin to become vacuolated and hollowed out to constitute a system of branching canals, at the same time that their cells acquire the endothelial type. The small, nucleated masses of protoplasm, known as the " blood-islands," undergo disintegration, whereby their nuclei are set free to soon collect around themselves a thin envelope of protoplasm. These constitute the primitive red corpuscles, and are the only bodies contained within the blood during the iirst month. In the meantime they have been acquiring a reddish hue, which marks the advent of the haemoglobin. As the canals be- come extended and branched eventiiaUy to connect with the heart as its system of vessels, there appears within them a fluid into which are emptied the red corpuscles. Thus is completed the circulation. According to Klein, the nuclei of the protoplasmic vessel-walls multi- ply to form new cells. The primitive corpuscles are spherical in shape, nucleated, and possess amoeboid movements. They undergo multiplication by karyokinesis. During the foetal period the protoplasm of the connective-tissue corpuscles, derived from the mesoblast, contains cells of the size and appearance of blood-corpuscles. The mother-cells elongate, throw out pi-ocesses which become hollowed out and branched untU they reach the regular circulatory vessels, with which they unite to empty into them their fluid and cells. During this period also they seem to be developed from the liver, spleen, and red bone-marrow. During Extra-uterine Life. — ^For some time after the birth of the mammal, nonnucleated corpuscles are still formed in the spleen, liver, and connective-tissue cells, but by far the most important and prolific seat is in the red marrow of bones. It is in the bones of the skull and trunk and ends of the long bones that blood-formation is most extensive ; the shafts of these bones contain a yellow, fatty sub- stance which is nonproductive. Within the marrow is seen numbers of nucleated, red cells, which are very similar to the corpuscles of the embryo, and, like them, multiply by karyokinesis. From these repeated divisions there result nonnucleated red corpuscles which are washed into the circulation. The blood-forming cells have received the name of erythrohlasts, or hcematoUasts, and are particularly numer- ous after copious hsemorrhage, when the loss of blood is being re- placed by more active formation. At such times some erythrohlasts may appear in the blood-stream, having been forced out prematurely, so active is the function of the red marrow in striving to repair the damage done. These soon lose their nuclei while in the blood-stream. THE BLOOD. 141 If the loss by hsemorrliage has been particularly severe, the yellow- bone-marrow and spleen assist in blood -manufacture, for in the latter and in the splenic vein are found nucleated, red corpuscles identical with those of the red marrow of bone. DESTRUCTION OF THE RED CORPUSCLES. No exact time can be given as the life-period of an erythrocyte, but it is usually estimated to be in the neighborhood of three or four weeks. The student can gain some comprehension of the number of corpuscles which must constantly be undergoing disintegration when he recalls the fact that all of the pigmentary matters in the body owe their existence, directly or indirectly, to the hemoglobin of these little bodies. The quantities of urinary and biliary pigments alone that are excreted from the economy are considerable. Physiologists have proved that there are fewer red corpuscles in the hepatic than in the portal vein. The bile-pigments are formed by the liver-cells ; these coloring matters contain only traces of iron, while the hepatic cells are rich with it. They give the characteristic test for iron when treated with hydrochloric acid and potassium ferroeyanide. Traces only of the iron are excreted as a constituent of the bile. The presence of iron in the spleen has long made this organ seem a cradle to many physiologists where erythrocytes are born and nour- ished. But the presence of this same element advances an argument equally as strong in favor of the spleen being the grave for these same little bodies. Pathologically, masses of iron substances are found within the spleen, liver, and red bone-marrow when abnormal disintegration occurs, as in ancemia. CHEMISTRY OF THE CORPUSCLES. The red corpuscles consist of a stroma containing in its meshes a peculiar proteid haemoglobin.. Chemically they are made of 60 per cent, of water and 36 per cent, of hsemoglobin, the remaining 4 per cent, representing the stroma, which is made up of lecithin, choles- terin, and nucleo-proteid. The white corpuscles consist of solids and water. The solids are gluco-proteids and nueleo-proteids and a small amount of albumin and globulin. The protoplasm may also contain glycogen and fat. The nucleus is made up of nueleo-proteids, nuclein, and nucleic acid. The phosphorus content of the nucleus is greater than that of the protoplasm. 14:2 PHYSIOLOGY. The following table is the result of the analyses reported by Halliburton : — Chkmical Composition of Blood. TI KVUUl. • Serum- . . \i\J.(^\i W Average, 52% Maximum, 56.7% Minimum, 45.6% ' Take 100 parts - Oiganio (8.86%)" ' Proteids < albumin Serum- globulin Fibrin - . 7.9 % . 0.4 % _ Extractives : Fats, etc. . 0.56% - Solids C9.71%)" Soluble ' NaCl KCl salts . NaHCOa Inorganic ^ - (0.85%) ' Insoluble salts NajHPOi ' CaHPOi CaSOi - . 0.85% 100.00% COEPUSCLES. Water ...--- . . 68.80% Average, 48% Maximum, 54.4% Minimum, 43.3% Organio (30.4%) Proteids (29.79%) Haemoglobin (27%) Globulin . . Hsematin (Fe) ■ Globulin - . 27.36% . . 2.43% Take 100 parts Solids Fats fLecithin \ ^ \CholesterinJ . . . . . 0.61% (31.2%) KCl Inorganic (0.8%) NaCl MaClj CaHPOt 0.80% .Mg3(PO,)3 Fe (see Hser natin). 100.00% The other named constituents are common to the two kinds of corpuscles. The mineral components are principally the chlorides of potassium and sodium and the phosphates of calcium and magnesium, THE BLOOD. 143 f the phosphates heing in greater proportion. Water forms 90 per cent, of the corpuscular contents. It wUl be remembered that the sodium salts assume greater proportions in the plasma. The nucleo- proteid obtained from the white corpuscles is the precursor of the fibrin-ferment of coagulation. It is believed that the proteid is con- verted into fibrin-ferment through the activity of the calcium salts of the plasma. Hsemoglobiu. — This is the pigment matter of the red corpuscles. Haemoglobin is a proteid composed of globin, a histon, and hasmatin. Its principal characteristics are : (1) its ability to combine chemically with oxygen and other gases, (3) its spectroscopic phenomena, (3) its crystallization, and (4) the fact of its containing iron. It is by virtue of the presence of this haemoglobin that the red corpuscles are capable of performiag the function of oxygen-carrying — carrying it from the external respiration in the lungs to the internal respiration in the cells of the tissues. The haemoglobin molecule possesses the property of linking to itself an oxygen molecule, form- ing a compound known as oxyhcemogldbm. The union of the two molecules is so unstable that the presence of an easily oxidized body, or an atmosphere with a lower oxygen pressure, separates the two, the oxidizable body and the atmosphere taking up the oxygen. Oxy- haemoglobin minus oxygen is usually termed reduced hwmogldbin; bet- ter, however, simply hsemoglobin. Oxyhasmoglobin is most abundant in arterial blood; that is, blood that has received its oxygen from the lungs during respiration and is then on its way to supply the needs of the cells of the tissues. Oxyhemoglobin behaves as an acid. Ordi- nary venous blood upon exposure to the air for a considerable length of time becomes bright red because of the union of the oxygen of the air with the haemoglobin of the blood. Crystallization of Hsemoglobin. — The haemoglobin is contained within the stroma of the corpuscles. In form, the crystals of the blood of man and the great majority of animals is that of rhombic prisms or needles which belong to the rhombic system ; in the squirrel there is produced six-sided plates. Haemoglobin crystals are readily broken up by the addition of an acid or alkali into two parts: hcematin and globin. Hcematin is a brown pigment, representing the cleavage product of haemoglobin in the presence of oxygen. It contains all of the iron of the decomposed ciystals, and is not crystallizable. In addition to the iron, it con- tains the four chief elements of proteid bodies: Carbon, hydrogen, oxygen, and nitrogen. Globin is the proteid element of the hsemo- 144 PHYSIOLOGY. globin. It contains all of the sulphur, and constitutes the major proportion of the hsemoglobin molecule, which is 16,000 times heavier than a molecule of hydrogen. Fig. 21. — Blood-crystsuls of Man and Different Animals. (Than- HOFFER and Fbey.) 1, Haemoglobin crystals: Mo, squirrel; Tr, guinea-pig; M, groundmole; L, horse; Em, man; S, marmot; Ma, cat; T, cow; mv, from venous blood of a cat. 2, Hsematin crystals: E, man; Tb, sparrow; M, cat. 3, Hffimatoidin crystals from an old extravas.ation of blood in man. Hsemin. — Haemin is the decomposition-product that results from the action of hydrochloric acid upon hsematin. The hsemin crystals THE BLOOD. 145 are small rhombic plates and prisms. The finding of these crystals of Teichmann constitutes the best-known clinical test for the detec- tion of blood. The crystals are prepared by adding a small crystal of common salt to dry blood on a glass slide, and then an excess of glacial acetic acid. The preparation is then gently heated until bubbles of gas are given off. Upon cooling, the characteristic hsemin crystals are formed. By transmitted light the crystals appear as mahogany-brown, but by reflected light they are bluish black. Chemical Phopeeties. — Hsemin crystals are insoluble in water, alcohol, ether, and chloroform. Very strong sulphuric acid is capable of dissolving them. Should the solution be evaporated to dryness and the residue properly treated, there will be produced a brown, amorphous powder. This product is known as hcematoporphyrin. Fig. 22. — Teichmann's Hsemin-crystals. (Lahoussk) Hsematoporphyrin is iron-free hsematin. It is frequently found in pathological urines, while traces of it are to be found in normal urine. It is identical with bilirubin in composition. Methsemoglobin. — Methsemoglobin is prepared chemically by adding amyl nitrite to blood. In large doses amyl nitrite is poisonous by reason of arrest of tissue-respiration. With carbon-monoxide gas (CO) hsemoglobin forms a compound similar to oxyhaemoglobin, but known as carbon-monoxide hwrnoglohin. This union is much more stable than the preceding, so that when carbon-monoxide gas is breathed in excess death results from as- phyxia, since the tissues are prevented from receiving their proper supply of oxygen. Carbon-monoxide results from the incomplete combustion of carbon in coal and charcoal stoves. Its poisonous properties are caused by its combining so strongly with the haemoglobin of the cor- 146 PHYSIOLOGY. puscles that it prevents union with oxygen^ and so produces asphyxia. The blood of both veins and arteries is bright, cherry-red in color. In poisoning from this gas, artificial respiration is sometimes of avail, with saline transfusion. For a better understanding of the import of the absorption bands of the coloring matters in the blood, a brief description wUl be given of the instrument whereby they are studied. THE SPECTROSCOPE. When white light, or that which reaches us from the sun, passes from one medium into another more dense, it is decomposed into sev- eral kinds of light, a phenomenon to which the name dispersion is given. Thus, when a pencil of the sun's rays is passed through a prism of flint glass, it is broken up into the seven colors of the spec- trum. This band of colors may be seen naturally in the form of the rainbow. These colors are violet, indigo, blue, green, yellow, orange, and red. The colors of the solar spectrum are not continuous. Several grades of refrangibility of rays are wanting, and, in consequence, throughout the whole extent of the spectrum there is a great number of very narrow, dark lines which run at right angles to the longi- tudinal axis of this band of light. They are generally known as Praunhofer's lines, since the most marked ones were first mapped and indicated by him. They are designated by the letters A, B, and C, in the red; D, in the yellow; E, b, and F, in the green; G and E, in the violet. If the light produced from burning common salt (sodium chlo- ride) be decomposed by means of a prism, it will be found to give one broad yellow line. Artificial light wUl not give Praunhofer's lines. The D line in the solar spectrum is due to the volatilizing of the metal sodium in the sun. Other elements account for the remaining dark lines of the spectrum. The spectroscope is combined with the microscope when making a medico-legal analysis of a small amount of coloring matter resem- bling blood. The mierospeetroseope used is generally the Sorby- Browning instrument. As will be seen from the figure opposite, it is a very compact piece of apparatus, very ingenious in construction, and consisting of several parts. The prism is contained in a small tube, which can be removed at pleasure. Below the prism is an achromatic eyepiece, having an adjustable slit between the two lenses, the upper lens THE BLOOD. 147 being fumislied with a screw motion to focus the slit. A side slit, capable of adjustment, admits, when required, a second beam of light from any object whose spectrum it is desired to compare with that of the object placed on the stage of the microscope. This second beam of light strikes against a very small prism suitably placed inside the apparatus, and is reflected up through the compound prism, forming a spectrum ia the same field with that obtained from the object on the stage. Fig. 23. — Sorby-Browning Microspectroscope. A is a brass tube carrying the compound direct-vision prism, and has a sliding arrangement for roughly focusing. B, a milled head, with screw motion to adjust finally the focus of the achromatic eye- lens. G, milled head, with screw motion to open and shut slit ver- tically. Another screw, H, at right angles to G, regulates the slit horizontally. This screw has a larger head, and when once recognized cannot be mistaken for the other. D, D, an apparatus for holding 148 PHYSIOLOGY. ei tn -^ la THE BLOOD. 149 a small tube, that the spectntm given by its contents may be com- pared with that from any other object on the stage. E, a screw opening and shutting a slit to admit the quantity of light required to form the second spectrum. Light entering the aperture near E strikes against the right-angled prism which I have mentioned as being placed inside the apparatus and is reflected- up through the slit belonging to the compound prism. If any incandescent object is placed in a suitable position with reference to the aperture its spec- trum will be obtained and will be seen on looking through it. F shows the position of the field-lens of the eyepiece. (? is a tube made to fit the microscope to which the instrument is applied. To use this instrument insert G like an eyepiece in the microscope tube, taking care that the slit at the top of the eyepiece is in the same direction as the slit below the prism. Screw on to the microscope the object- glass required and place the object whose spectrum is to be viewed on the stage. Illuminate with stage mirror if transparent. Eemove A and open the slit by means of the milled head H at right angles to D, D. When the slit is sufficiently open the rest of the apparatus acts like an ordinary eyepiece, and any object can be focused in the usual way. Having focused the object, replace A and gradually close the slit till a good spectrum is obtained. The spectrum will be much improved by throwing the object a little out of focus. Every part of the spectrum differs a little from adjacent parts in refrangibility, and delicate bands or lines can only be brought out by accurately focusing their own parts of the spectrum. This can be done by the milled head B. When spectra of very small objects are viewed, powers of V2 inch to y^o may be employed. These bands represent the light absorbed by the colored medium. For the same substance the bands are always identical and similarly placed. Thus, a solution of oxyhaemoglobin of a certain strength gives two hands, reduced hsBmoglobin gives only one. The other de- rivatives, methsemoglobin, hsematin, hsemin, etc., though similar to hasmoglobin when viewed with the naked eye, yet each gives charac- teristic absorption bands in various positions. The amount of haemoglobin as calculated by various methods and instruments has been found to be in man, 13.77 per cent. ; in woman, 12.59 per cent. Pregnancy reduces the quantity to from 9 to 13 per cent. Normally there are two periods in a person's life when the amount of haemoglobin attains maximum limits — in the blood of the newborn and again between the years twenty-one and forty-five. Pathologically there follows a decrease during recovery from febrUe 150 PHYSIOLOGY. coDditions, as also during phthisis, cancer, cardiac disease, chlorosis, anaemia, etc. It is kaown that dry haemoglobin contains 0.4 per cent, of iron, and that all of the iron of the blood is held by the haemoglobin of the red corpuscles. The amount of iron in the blood is about 45 grains. Colorimetric methods consist in making comparisons between a standard solution of a known strength and the test solution of blood to be examined, water being added to the latter until the exact shade of the standard solution is obtained. Kg. 25. — Von Fleischl Haemometer. (Lahottsse.) A, Mixing vessel with two compartments: B, for diluted blood; C, for pure water, reposes over the colored prism of glass. D. E, Scale to read off amount of haemoglobin. M, A mirror to reflect light. H. Milled wheel that moves D. Von Fleischl's Haemometer. — This instrument consists of A, a cylindrical cell for holding the prepared blood j D, a graduated wedge-shaped piece of colored glass with which to compare the solu- tion of blood ; H, a stand with a rack and pinion ; J/., a capillary tube for measuring the quantity of blood required. 1. The cell (A) is a cylindrical metallic chamber divided by a fixed partition into two equal compartments, open at the top, but closed at the bottom by a base of glass. One of these compartments is to be filled with distiUed water, the other with the proper quantity of blood dissolved in distilled water. THE BLOOD. 151 2. The colored glass wedge (D) is fitted to a metal frame so that it can be adjusted in the stand and moved from side to side by the rack and pinion. When in position the glass wedge moves directly beneath that part of the cell which contains the distilled water, thus enabling one to compare the color of the glass with that of the dis- solved blood which fills the adjoining compartment of the cell. The wedge is graduated at E from 1 to 100, the figures representing the percentage of hsemoglobin in the specimen of blood as compared to normal blood containing 13.7 per cent, of haemoglobia. 3. Besides the support for the glass wedge and frame, there is a white plaster mirror (M) which furnishes the diffused light re- quired in the test. 4. The capillary tubes are carefully prepared to hold the proper quantity of blood. The size of these tubes varies, and on the handle of each is stamped a number indicating its capacity. PHYSICAL PROPERTIES OF THE PLASMA. Plasma is the fluid part of the blood as it occurs in a healthy condition within the circulatory system. However, upon its removal from the body there is formed in it a solid substance, called fibrin, from elements which it previously held in solution. The fluid which surrounds the clot is termed serum; it is plasma minus fibrin. Plasma is described as a clear, somewhat viscid fluid; that of man, when strata are examined, is colorless; when in bulk it is slightly yellow because of the presence of a pigment. CHEMICAL PROPERTIES OF PLASMA AND SERUM. In order to examine plasma, a very great amount of caution is necessary to prevent its coagulation, even after separating the cor- puscles. The most common methods for obtaining it in a liquid state are by the use of the " living test-tube " — an excised piece of jugular of a horse filled with blood — and cold as an environment. It has been found that serum differs from plasma only in respect to certain pro- teids, and, as it is so much easier to handle the serum, the latter is principally used for ex.perimentation. Chemically the plasma is composed of inorganic and organic sub- stances, with certain gases. Inorganic Constituents. — The plasma's greatest factor is water. It is this which gives it fiuidity and is present to the extent of 90 per cent. There are present many salts : sodium chloride, carbonate of soda, chloride of potassium, sulphate of potassium, phosphate of 153 PHYSIOLOGY. calcium, phosphate of sodium, and phosphate of magnesiiim. The first two occur in the greatest amounts, the remaining ones only as traces. It is carbonate of soda that gives to plasma its ability to absorb carbonic acid and also contributes much to its alkalinity. Organic Constituents. — These components are readily divisible into proteid and nonproteid groups. The Photeids are: — 1. One albumin (serum-albumin). 2. Two globulins, termed serum-globulin and fibrinogen. 3. A nucleo-proteid. The classes of proteids present various solubilities in neutral salt solutions, by appreciation of which they are able to be separated from one another. The albumins upon half -saturation with ammonium sulphate re- main in solution, whUe the globulins and nucleo-proteids are pre- cipitated. The precipitate is removed by filtration, or the albumins may themselves be precipitated by saturation with ammonium sul- phate. The globulins almost universally possess the characteristic of coagulating when heat of 75° C. is applied to them. In man the globulins make up about 3 per cent, of the total serum. Fibrinogen is also a globulin. It is precipitated by half-satura- tion with NaCl, thus making its differentiation from serum-globulin a comparatively easy task. Upon precipitating with NaCl, if a lime salt be added, the precipitate partakes of the nature of a fibrin-clot or coagulum, but is not true fibrin, since it is a combination of fibrin- ogen with lime. Nucleo-proteid of Plasma. — About the only characteristic that is known in connection with the nucleo-proteid is that it is very essential to the formation of fibrin during coagulation. It is formed by the dissolution of the leucocytes and blood-plates after the blood is shed from the body. When hydrocele, pericardial, and ascitic fluids contain no leucocytes, it has been noticed that they lack power of spontaneous coagulation. The nucleo-proteids in the presence of calcium salts form a substance which is identical in every respect with the fibrin-ferment of Alexander Schmidt. This new substance possesses the power of converting fibrinogen into fibrin. The Nonproteids oe the Plasma. — The nonproteids comprise both nitrogenous and nonnitrogenous elements. The nonnitrogenous consist of carbohydrates and fats, with small amounts of lipochrome and sarco-lactic acid. THE BLOOD. 153 The nitrogenous elements comprise in their category urea, uric acid, hippuric acid, creatin, and some ferments. Urea, which represents the end-product of nitrogenous com- bustion of either the tissues or the blood itself, and which must be includjed among the normal elements of this fluid, is found in the blood in weak proportion. But it can accumulate in an abnormal manner within the blood and give rise to the disorder known as urjemia. It is in this way that ablation of the kidneys, acute nephri- tis, and the terminal feverish period of cholera, in which the urinary secretion is suppressed, permit the accumulation of urea in the blood. Uric acid, which is regarded as the product of a work of com- bustion less advanced than for urea, doubtless owes its existence to an incomplete oxidation of the true, immediate principles of the blood. It may occur in greater proportion than usual in combination with soda, with the urea, in the blood of gouty persons, and in that of albuminuric persons. Gases of the Plasma. — Present knowledge af&rms the presence of oxygen, nitrogen, and carbonic anhydride. The first two are simply dissolved in the plasma, but the carbonic anhydride occurs in from 43 to 57 volumes and then combines chemically with soda to form carbonates and bicarbonates. COAGULATION OF THE BLOOD. Normal blood contained within the body-vessels is a fluid. For a very brief period after it makes its exit from a wounded vessel it remains in a liquid state, but within two or three minutes its viscidity increases until there is formed a solid of the consistency of jelly; to this has been given the name llood-clot. The process whereby the clot is formed is termed coagulation, and is caused by the presence of a body called fibrin. To observe best the process of coagulation, the blood is drawn into an open vessel as a beaker, care being taken that the atmospheric and other conditions are favorable. The initial change to occur within the first two or three minutes is the formation of a jellylike layer over the surface of the blood; during the next three or four minutes this layer extends to such a degree that the entire blood-mass becomes enveloped. If at this time the contents of the vessel be turned out, they form a mold of the exact shape of the containing vessel, or the vessel may be inverted without the escape of the con- tents. This jellylike mass is the clot. Within it are imprisoned the serum and corpuscles. 154: PHYSIOLOGY. A straw-colored fluid, the serum, is expressed, appearing upon the surface to form finally a transparent layer of liquid around the clot. The retraction is complete at the end of from twelve to twenty hours, at which time all of the serum has been expressed and the corpuscles enmeshed within the network of fibrin. The clot, so dense that it may readily be cut with a knife, being heavier than the serum, is found at the bottom of the vessel. It is now just about one-half of its original size. The serum, when examined, is found to be prac- tically free from corpuscles. The character of the clot varies ac- cording to the state of the blood. It is large, soft, and tears easily at times. At other times it is small, resistant, and from the energetic contraction of the fibrin the edges of the upper surface of the clot curve over so as to form a sort of cup. The clotting of the blood is due to the development in it of fibrin, whose fibrils arrange themselves in the form of a network. In blood within its vessels there are found no such fibrils of fibrin ; therefore normally no . coagulation occurs within the body. These fibrils then must have been formed by some change, chemical or otherwise, of one or more constituents of the blood. That the corpuscles themselves cannot form a clot excludes them, so that our attention is turned to the plasma. In it is formed the fibrin, for pure plasma from which the corpuscles have been removed very readily coagulates. When blood is vigorously beaten with twigs, long shreds of a nearly transparent substance are found adhering to them. These are fibrin-fibers, free, or nearly so, from corpuscles. Its structure consists of very delicate, doubly-refractive fibrils of micro- scopical size. Many theories have been propounded to account for the forma- tion of fibrin and the coagulation of the blood, but the one most widely received is that of Hammersten, a Swedish investigator. In the study of plasma it was learned that one of its constitu- ents was a proteid of the globulin class, to which had been given the name fibrinogen. It is held in solution by the plasma and believed to be an end-product of the disintegration of useless white corpus- cles. Within the circulating fluid there is an immense number of these white cells; when blood is withdrawn from the living vessel there is a large and very sudden destruction of them; according to Alexander Schmidt, 71.7 per cent, are dissolved. When these little bodies are disintegrated in the laboratory they yield nucleo- proteids ; so that it is very probable that practically the same prod- ucts result upon disintegration in the shed blood. To this nucleo- THE BLOOD. 155 proteid has been given the name prothrombin. By the action of the calcium salts dissolved in the blood-plasma the prothrombin is con- verted into fibrin- ferment, or thrombin. When thrombin comes into contact with the fibrinogen molecule dissolved in the plasma it splits it into two parts : one is a globulin, which is very small in proportion and equally unimportant; it remains in solution. The other is the insoluble substance fibrin, which entangles the corpuscles and is so essential to the formation of the blood-clot. The process of fibrin-formation has been neatly tabulated by Dr. J. J. E. Macleod,^ as follows : — Living blood Plasma Albumin Globulin CJorpuscles White Eed Ca salts + Prothrombin Fibrinogen -\- Fibrin ferment Second globulin Fibrin Serum Clot Dead blood To epitomize, it may be said that coagulation depends upon three factors, according to Hammersten's theory: (1) calcium salts to con- vert the nucleo-proteids in the form of prothrombin into thrombin, "Practical Physiology." 156 PHYSIOLOGY. or (3) fibrin-ferment J this latter breaks up the (3) fiirinogen in solu- tion into an unimportant globulin and the all-important fibrin. Fibrin-ferment is a term used simply for convenience and prob- ably is a misnomer. It is a proteid of the globulin group whose substance does not seem to be used up in the process nor to enter into the fibrin formed; a small quantity of it serves to break up an immense amount of fibrinogen. In the peculiar hereditary disease of males only, known as haemophilia, it sometimes happens that diminished coagulability is due to a deficiency of the calcium salts. Consequently the tendency to bleed may in some cases be lessened by the internal administration of calcium chloride, or the actual haemorrhage may be stopped upon its local application or of adrenalin. A condition known as buffy coat occurs when blood coagulates very slowly. It is most readily seen in horses' blood, being caused by the moT6 rapid sinking of the red corpuscles in slow coagulation, thus leaving the upper stratum to consist of a layer of fibrin and white corpuscles. This whitish layer is elastic, has some resistance, is more or less opaque, and has therefore been designated the bufEy coat. The shape of the vessel is also a factor in the production of " bufEy coat." If the vessel be long and straight, the fall of the corpuscles is facilitated. The buffy coat then appears. No buffiness, however, is seen if the vessel be large and low, and if the blood be received in a vessel which is shaken from time to time. The blood of different parts of the vascular system shows differences as to the time required for complete coagulation. Arterial blood coagulates more quickly than venous; blood of the hepatic veins coagulates very little, and the same is' true of menstrual blood — ^probably due in the latter to mixture with the alkaline vaginal secretions, for, when menstruation is so abundant that this alkalinity is overcome, then clotting may ensue. Certain conditions favor the rapidity of coagulation. Clotting is accelerated by these factors : 1. Calcium salts. 2. A temperature a little higher than that of the body (102° to 107° P.). 3. Presence of foreign bodies. If a needle be made to penetrate the wall of a vessel, fibrin is deposited upon it and so produces coagulation. It seems to be a sort of phenomenon analogous to that which occurs when a thread is suspended in a solution of sugar, when the crystals of sugar are deposited upon it. Injections of laky blood, biliary salts, fibrin-ferment, and rapid venous injection of a strong alkaline solu- tion of a nucleo-proteid also hasten coagulation. 4.^ Injury to the THE BLOOD. 157 vessel-walls. 5. Agitation, probably because there is then a more free mixture with oxygen. Gelatia increases the coagulating power of blood, and has been used in haemophilia. Coagulation is retarded by: 1. Oxalates, which combine with calcium. 2. A very low temperature. 3. The saturation of blood with CO2 (thus in asphyxia the blood does not coagulate). 4. Blood received into a vessel filled with oil does not coagulate. 5. Coagula- tion is prevente.) The shaded parts represent the positions of the rihs in repose. The line A-B represents a horizontal plane passing through the sternal extremity of the seventh rib; the line C-D represents a horizontal plane touching the superior extremity of the sternum; the line B-0 indicates the linear direc- tion of the sternum. When the ribs are elevated as indicated by the dotted lines, the line A-B becomes the plane a-b, the line 0-D^ the line c-d, and the line H-G becomes the line h-g, the projection of the sternum being more marked interiorly. The distance which separates the line M-N from the line m-n measures the increase in the antero-pbsterior diameter of the thorax. posterior diameter. At the same time that the ribs are raised they undergo a movement of rotation, by virtue of which they separate from the median line of the chest. It is this movement which pro- . duces an enlargement of the thorax in its lg,teral diameter at the same time the antero-posterior diameter is slightly increased. RESPIRATION. 249 During inspiration the ribs are raised, when the breathing is ordinary, by the external intercostals. The sealeni and costal elevators also are of service. When respiration is governed by the latter muscles, the lower part of the chest possesses the greater expansion. The reverse is true when inspiration is forced, for then the upper antero- posterior diameter becomes the greater. 1 Nv e i Fig. 56. — Schema of Action of Intercostal Muscles. (Landois.) I. When the rods a and 6 which represent the ribs are raised, the inter- costal space must be widened (e, f — c, d). On the opposite side when the rods are raised the line g-h is shortened (4, k — g, ft), the direction of the external intercostal, l-m, is lengthened (J, m — o, ») in the direction of the internal intercostals. II. When the ribs are raised the Intercartilaginei indicated by g-h and the external intercostals indicated by l-h are shortened. When the ribs are raised the position of the muscular fibers is indicated by the diagonals of the rhombs becoming shorter. During extraordinary inspiration — as that caused by violent mus- cular exercise or when some pathological condition is present so that air finds its way into the chest only as the result of strong muscular effort — ^the other muscles are called into service. These, the emergency muscles, are very probably the stemo-cleido- mastoids, the serrati magni, the pectorals, and the trapezii. 250 PHYSIOLOGY. Expiration. — Expiration, when it is effected with the aid of muscular powers, has as its causative agents the internal intercostals, the triangularis sterni, the two oblique and transverse muscles of the abdomen, and quadratus lumborum. It is in complex expiration — as crying, coughing, singing, expectoration, sneezing, etc. — ^that the pre- ceding muscles enter into contraction. The abdominal muscles are the most powerful in the above-named group. In general, it may be said that any and all muscles concerned in the depression of the ribs belong to the expiratory set of muscles. On the contrary, ordinary expiration can be effected by the mere ' relaxation of those factors concerned in the production of inspiration. During this relaxation the thoracic and abdominal walls, by reason of their elasticity, compress the air-distended lungs, and by so doing compel expiration. The lung-tissue itself helps to the extent of its own elasticity. The expenditure of that power and energy necessary to produce inspiration now becomes the expiratory exponent. During ordinary and tranquil breathing this elastic recoil of the stretched components is amply, sufficient to expel the air from the lungs. Thus no muscular energy is required to perform expiration. A normal lung is never able to contract to its fullest ability, since it is always distended to some extent by reason of its cohesive attraction with the interior of the chest-walls, as well as because of the presence of a certaia proportion of air within the vesicles which exerts an expansive pressure. It is interesting to note that, though the expiratory muscles be more numerous and powerful than the inspiratory ones, it is because the former are intended especially for complex expiration; that is to sgj^, violent actions, since ordinary expiration is able to be effected by the mere elasticity of the parts. During expiration the lungs, which were dilated, return upon themselves, so that they let out a quantity of air nearly corresponding to that which entered at first. The lungs, which are seen to be entirely passive during inspiration, can participate actively in expiration, particularly in such complex acts as expectora- tion, coughing, etc. There are various modes of respiration among man and mammals which are usually classed under three principal types. In the abdom- inal type, characteristic among children, the ribs remain motionless and the respiratory action is revealed only by the movements of the abdominal wall ; this becomes projecting during inspiration and sinks during expiration. In the inferior costal type, man's type, the respira- tory movements take place especially at the level of the lower ribs. RESPIRATION". 251 beginning with the seventh. Finally, in the superior costal, or clavicu- lar, type, the respiratory movements are very manifest only about the upper ribs, especially the first, vrhich are carried upward and for- ward. The clavicle also participates in this movement. This last type is the mode of respiration peculiar to woman, who presents it very early. The state of pregnancy, which would greatly interfere with the other types of respiration, does not hinder breathing very much in this last type, since the movements take place naturally at the upper part of the chest. The use of the corset counts for nothing in the development of this made of respiration peculiar to women ; it tends merely to exag- gerate it. The superior costal type is found perfectly established in girls and women who have never worn this kind of garment. Among animals the abdominal type of respiration is found in the horse, cat, and rabbit, and the inferior costal type in the dog. Kg. 57. — Tracing of a Respiratory Movement. (Foster.) A whole respiratory moTement is comprised between a and a, inspiration extending from a to 6 and expiration from & to a. The waves at c are caused by heart-beats. The Stethograph, or PneTimograph. — To gain an exact idea of the time occupied in the various phases of respiration it becomes necessary to obtain its curve, or pneumatogram. The apparatus for recording these respiratory movements is termed a stethograph, or pneumograph. The simplest form of stethograph is that of Brondgeest. It con- sists of a brass saucer-shaped vessel covered with a double layer of rubber membrane. The air is forced in between the two layers until the external layer bulges outward. This is placed in position on the chest by means of tapes. The cavity of the saucer-shaped apparatus communicates with a recording tambour, which writes down the move- ments on a revolving smoked drum. The resultant curve, known as the pneumatogram, shows that the acts of , expansion and contraction of the chest-wall consume nearly equal times. The ascending limb (inspiration) is begun with mod- 252 PHYSIOLOGY. A ag Fig, 58. — Marey's Ty m- p a n u m and Lever. {Sandebsoh. ) A, Lever. B, Tympa- num. F, Tube Tfh oh communicates with cavity of thetympanuiu and con- nects with the tracheal cannula or the card o- graph. erate rapidity, becomes accelerated in the middle of its course, to be again slowed at its end. The descending limb (expiration) shows the same characteristics as to its construction, thereby giving a gradual fall to the curve. Inspiration is Slightly Shoetek than Bxpiha- TiON. — For all practical purposes it may be stated that the average respiratory rhythm is : Inspiration : Expira- tion : : 5 : 6. However, it is known that various authors give different ratios, and in women, children, and old people 6 to 8 or 6 to 9 may be found. Immediately fol- lowing expiration there is a slight pause. Cases are rather rare in which the duration of in- spiration and expiration are equal, or that of expiration shorter than inspiration. When the respiratory move- ments are studied as depicted on the pneumatogram, it is found that there is practically no pause between the end of inspiration and the beginning of expiration. RESPIRATORY SOUNDS, If a stethoscope is placed over a portion of a lung at some. distance away from the trachea and larger bronchi, a sound will be heard the character of which is variously described as soft or sighing, resembling the rustling of leaves in a slight wind. The sound is heard during the whole of inspiration and is followed by a short expiratory sound. The inspiratory sound is three times the length of the expiratory. It must be remem- bered that the movements of inspiration are to those of expiration in point of time as 5 to 6, while the vesicular sounds of inspiration is to expiration as 3 to 1. The cause of vesicular sound, according to one theory, is supposed to arise from the passing of air into and out of the alveoli and infundibula, the friction here gen- erating a sound, aided by the sudden dilatation of the air-vesicles. If now the stethoscope is placed over the trachea just above the suprasternal notch, two sounds are heard: one during inspiration, the other during expiration. They are of equal RESPIRATIOlSr. 253 length, or, if anything, the expiratory is the longer. The quality of both sounds may be described as blowing, tubular, or bronchial. The expiratory part is more intense and frequently of higher pitch. This bronchial sound is produced by air, in passing through the chink of the glottis, being thrown in Tibration and imparting its motion to the columns of air in the trachea and bronchi. In practical medicine it is inferred that, when the vesicular mur- mur is heard over any portion of the lung-tissue, this area being prop- erly distended, the lung is in a healthy condition. If, however, the expiratory portion of it becomes loud and prolonged, it excites inquiry. QUANTITY OF AIR BREATHED. The determination of the volume of air necessary to the needs of human respiration is a problem that has received much attention. Because of a multitude of circumstances, both external as well as those that are proper to the individual himself, the figures representing the quantity of air that enters the lungs at each inspiration and the quan- tity that leaves them at each corresponding expiration can scarcely have more than an approximate value. Nevertheless, results agreeing sufficiently to permit of establishing an average of the quantity of air put in circulation during each normal respiratory movement has been arrived at. It is very generally admitted that, in an adult and healthy man, each inspiration introduces into the pulmonary apparatus about 20 cubic inches of air. Among the numerous observers who have occupied themselves with the study of the quantity of air put into circulation, Herbst and Hutch- inson may be cited in particular. The latter's spirometer is the instru- ment which has been most frequently used to secure data in experiments along this line. It represents essentially a gasometer. It is furnished with a fixed scale and movable indicator ; the latter follows the move- ments of the air-receiver to indicate them on the graduated scale. The receiver dips into a reservoir filled with water and communicates with the chest of the experimenter by means of a rubber tube ending in a glass or metal funnel. To measure the volume of air concerned in exaggerated respira- tion, the experimenter is made to stand up, care being exercised that his chest is free from any restraint that would hinder its mobility. After several forceful inspirations and expirations, he inhales the greatest quantity of air that he can draw into his lungs. With the tube of the spirometer between his lips he then makes the fullest possible expiration. 254 PHYSIOLOGY. By subjecting about two thousand persons to this test Hutchinson recognized that the quantity of air which a maximum inspiration and expiration can put into circulation varies according to the individual. It is 230 cubic inches for a man 5 feet 8 inches in stature. According to this observer, the prime factor in producing variance in pulmonary capacity is mainly the size of the individual. For every inch of height from 5 feet to 6 feet, 8 additional cubic inches are given out by a forceful expiration after a full inspiration. Vice versa, for every inch below the 5-foot mark the capacity is diminished by the same amount. The mobility of the thoracic walls has here a real influence. Persons with narrow chests are sometimes found who can dilate the thorax much more than those in whom the circumference of that part of the body is greater. With equal dimensions, the number indicated by the spirometer increases with the dilatability of the thorax. The individual's capacity appears to be greatest in the period from the twenty-fifth to the fortieth year, showing a gradual increase until the latter mark is reached. From this point it begins to diminish, to become, in old age, less than it was even in youth. Observers agree in admitting that, in woman, the maximum vol- ume expired is perceptibly less than in man. The difference is usually represented by 50 cubic inches. Abdominal tumors, whatever their nature and the organ affected, have the constant effect of diminishing the volume of air expired ; pregnancy alone has not that consequence. If a lung from an animal be thrown into a vessel of water, it floats. If it be forcibly submerged and then squeezed, bubbles of air will find their way to the water's surface. Prom this little experi- ment the student knows that, even though the lungs be collapsed, yet they contain a certain amount of air which is not very readily expelled. This is the air which is held within the confines of the small alveoli and cannot very easily find its way through the small passageways opening into them. It follows, then, that all of the air in the lungs cannot possibly be changed during each respiration, and the amount that is changed bears a very close relationship to the type of respiration, whether it be forced or ordinary. 1. Tidal Air. — The volume of air that is introduced into the lungs during ordinary iaspiration and by an adult in good health is termed tidal air. It is 20 cubic inches. The tidal air finds its way into and out of only the larger bronchial vessels, where it comes into contact with the nearly stationary columns of air which extend through the smaller bronchial tubes. RESPIRATION. 255 The interchange between the two eolumns is by a process of diffusion. By this means does the oxygen find its way to the blood flowing through the capillaries, while the carbonic acid makes its way into the larger bronchial tubes to be finally expelled from the body. 2. Complemental Air is the quantity of air wjiich we are able to inspire with the greatest effort over and above that of ordinary breath- ing. The average is estimated by volume as 110 cubic inches. 3. Reserved Air, or supplemental air, is the quantity of air re- maining in the lungs after an ordinary expiration which would be expelled by the fullest effort. It is considered to be about 100 cubic inches. 4. Eesidual Air is that which remains in the lungs after the fullest possible expiration and cannot be expelled by any voluntary effort. Its volume is also 100 cubic inches. 5. The Vital Capacity is the tidal, complemental, and reserved airs added together, and is 2S0 cubic inches. It represents the amount of air which a person is able to expel from his lungs after the deepest possible inspiration. One-sixth of the air in the lungs is renewed at each ordinary respiration. NUMBER OF RESPIRATIONS. In an adult, the number of respirations per minute may vary from 16 to 24. It is usually stated that 4 pulse-beats occur during each respiration. The number is varied by the position of the body ; thus, there may be counted 13 while recumbent, 19 in the sitting posture, and 22 respirations per minute while standing. During infancy and childhood the number of respirations is always greater than in the adult. Exercise temporarily increases res- piration both as to number and depth. It is believed that there is some product derived from the metabolism of muscles which acts as the respiratory stimulant. Every athlete knows of that condition popularly termed "second wind." . At the beginning of severe exercise there is a marked dyspnoea which passes away after a short time, even though the exercise be unin- terrupted. It cannot be explained physiologically, but is believed to be in a very great measure cardiac. Fathological. — Eespirations may be increased by reason of fever, pleurisy, pneumonia, some heart diseases, and anaemia. Diminution is occasioned by pressure upon the respiratory center in the medulla; this occurs in coma. 25G PHYSIOLOGY. PRESSURE IN THE AIR=PASSAQES DURING RESPIRATION. It has been previously stated that even after the deepest expiration the lungs are never completely collapsed. They are still "on the stretch" by reason of the elastic fibers contained in them. These fibers, acting in direct opposition to the external atmospheric pressure, diminish the amount of pressure within the thoracic cavity. It has been found that in man the elasticity of the lungs themselves equals 6 millimeters of mercury. The reason for the collapsing of the lungs when the chest is opened is that the pressure upon the pleural and alveolar surfaces is now equal, being that of the pressure of the atmosphere. The pressure of the residual air was sufficient to overcome the elasticity of the muscular fibers of the lungs. As long as the chest-wall was un- opened the lungs contracted only until their elasticity was just balanced by the outward pressure of the contained air. In intra-uterine life, and in stillborn children who have never breathed, the lungs are com- pletely collapsed (atelectasis). If the lungs be once inflated they never completely collapse so long as the thoracic walls be not pierced. When a manometer was attached to the trachea of an animal so that its respirations proceeded unchecked, every inspiration showed a negative pressure, every expiration a positive pressure. An observer placed a U-shaped manometer tube in one of his nostrils, closed his mouth, let the other nostril open, and then respired quietly. During every inspiration there was a negative pressure of 1 millimeter of mercury, and during expiration a positive pressure of from 3 to 3 millimeters. Forced respirations produce great variations from the above fig- ures. The greatest negative pressure averaged — 57 millimeters of mercury during inspiration; the maximum positive pressure during expiration averaged + 87 millimeters. The greater part of the force exerted in deep inspiration is used in overcoming the resistance offered by the elasticity of the lungs, the raising of the weight of the chest, and depressing the abdominal contents. These resisting forces acting during expiration aid the expiratory muscles; from this it follows that the forces concerned in inspiration are much greater than those of expiration. Expiration is longer and stronger than inspiration, but the sound of inspiration is longer than that of expiration. RESPIRATION. 257 THE FUNCTION OF THE UNSTRIPED MUSCLE OF THE BRONCHIAL SYSTEM. If a dog be curarized, the interior of a small bronchus be con- nected with a recording instrument (the chest being opened), and a va;gus be divided, there will be a marked expansion of the bronchi. If the peripheral end of the vagus be stimulated, then a strong con- traction of the bronchus will ensue. It is evident here that the smooth muscles of the bronchi are under the iafluence of the pneumogastrics. These effects could also be called out in a reflex manner. This ex- plains asthmas due to reflex irritations transmitted to the centers of the vagi. Atropine and lobelina paralyze the vagus ending in the bronchial muscles, which explains their utility in spasmodic asthma. VARIOUS FEATURES OF RESPIRATION. Nasal Breathing. — During ordinary, quiet breathing most people breathe through the nostrils, keeping the mouth closed. This is very proper and there are certain advantages to be derived by so doing. Thus, in the passage of the air through the nostrils, whose walls are narrow and somewhat tortuous, the air is not only warmed, but ren- dered moist as well. By this means there is prevented the irritation occasioned by cold, dry air upon the lining mucous membrane. In addition, the smaller foreign particles are caught by the mucous lining and carried outward by the instrumentality of the ciliated epithelium. Pathological. — Pulmonary oedema, which is a transudation of lymph into the pulmonary alveoli, occurs (1) when there is very great resistance to the blood-stream in the aorta and its branches; (3) when the pulmonary veins are occluded; (3) when the left ventricle, owing to mechanical injury, ceases to beat, while the right ventricle continues in its contraction. Injection of muscarine rapidly produces pulmonary oedema by reason of increased pressure and slowing of the blood-stream in the pulmonary capillaries. The effects of this drug are counteracted by atropine. Relation of Respiration to the Nervous System. — Movements of respiration are entirely dependent upon the nervous system. They are nicely balanced actions, performed by voluntary muscles under the guidance of a special presiding nerve-center, namely : the respira- tory center. Through its influence the muscles of inspiration and expiration are kept working rhythmically and regularly, whether the 258 , PHYSIOLOGY. individual be awake or sleeping. There -are constantly proceeding from the center co-ordinated impulses to the muscles involved. How- ever, the muscles being voluntary, they may be controlled momentarily by the will, and respiration be made entirely to cease for a minute or two. Soon Nature's cry for oxygen becomes so strong that the will is overcome and respiration is begun again under the supervision of the respiratory center. The Respiratory Center. — This center is located in the medulla oblongata, in the formatio reticularis, behind the superficial origin of the vagi and on both sides of the posterior aspect of the apex of the calamus seriptorius. Plourens, its discoverer, found that, when destroyed, respiration ceases at once and the animal dies. Hence he termed it "the vital knot." It is a bilateral center; that is, it has two functionally symmetrical halves, one on each side of the median raphe. If separated by means of a longitudinal incision, the respiratory move- ments continue symmetrically on both sides. Destruction of one-half of the medulla is attended with paralysis of respiration only on that side, seeming to prove that each half of the center is particularly con- cerned in the respiratory muscles of its own side. During ordinary breathing impulses are sent from the respiratory center along the phrenics to the diaphragm and along the intercostal nerves to those muscles which elevate the ribs. Impulses and mes- sages to the center find their way along the fibers of the vagi nerves. While it seems to be undisputed that the principal respiratory center lies in the medulla and upon it depends the rhythm of the respiratory movements, yet there have been found other and sub- ordinate centers located in the cord. These, however, are reinforced by the main one in the medulla. The cutaneous nerves also exercise some effect upon respiration. The most marked influence is exerted by those of the face (trigem- inus), abdomen, and chest. Both thermal and mechanical stimuli easily excite them. Mechanical stimulation of the sensory nerves is sometimes resorted to by midwives. It is well known that to arouse a sluggish respiratory center they resort to slapping the buttocks of a newborn child. During the act of deglutition there is a very necessary cessation of breathing for a short period. This is caused by stimulation of the central end of the glosso-pharyngeal nerve. Section of the cord just below the medulla produces an arrest in the movements of not only the intercostals, but even the diaphragm. Section of one phrenic nerve paralyzes the corresponding half of the RESPIRATION. 259 diaphragm; division of both nerves causes entire cessation of move- ment of the diaphragm. The phrenic nerves take an active part in the- function of respiration. When these nerves are bared and irritated there is noticed a rapid movement of the abdomen produced by con- traction of the diaphragm. The spasmodic movement is repeated at each irritation so long as the tissue of the nerve remains uninjured. If instead of mechanical, an electrical irritant be applied, the dia- phragm is thrown into a state of tetanic contraction and produces Fig. 59. — Scheme of the Chief Respiratory Nerves. (Landois, after RutJwrford.) INS, Inspiratory center. EXP, Expiratory center. Motor nerves are in unbroken lines; expiratory motor nerves to abdominal muscles, AB; to muscles of back, DO; inspiratory motor nerves, phrenics to diaphragm, D. lyiT, Intercostal nerves. RL, Recurrent laryngeal; CX, pulmonary fibers of vagus that excite inspiratory center. GX', Pulmonary fibers that excite expiratory center. OX", Fibers of superior laryngeal that excite expiratory center. INH, Fibers of superior laryngeal that inhibit inspiratory center. death from asphyxia. As the irritability of the phrenic nerve remains a long time after death, it becomes easy to demonstrate these phe- nomena without causing any pain. After section of the vagi the heart's movements become more rapid and the respirations slower. At the end of some minutes the nares dilate a little, inspiration is accompanied with a slight noise, an indefinite restlessness seems to seize upon the animal from head to foot; it moves about frequently, and raises and lowers the head as if there were a constriction of the throat. At length the anxiety 260 PHYSIOLOGY. of the animal disappears; it is calm and t}uiet; respiration is slow and the beats of the heart augment in frequency. Finally the animal dies from an affection of the lungs known as vagus pneumonia. For a time after the section the amount of carbonic acid exhaled and of oxygen taken in remain the same, but finally they are much changed. The animals usually live seven days, but Pawlow has succeeded, by dividing one vagus and then waiting some time before dividing the next one, in keeping them alive. Instead of tying or dividing the vagi, a galvanic current may be sent through them. There will follow disturbances of the vascular system, particularly the heart; so that death follows in a short time. If the central end of a divided vagus be irritated by a strong induction current, there is produced a strong degree of excitation in the medulla oblongata. It sends out impulses along motor nerves which arrest respiration in a state of inspiration, due to tetanus of the diaphragm. Fig. 60. — ^Arrest of Respiration in State of Expiration. (Hedon.] By irritation of the central end of the vagus in a chloralized dog. Stimulation of the central end of the superior laryngeal calls out an expiratory arrest. Each half of the respiratory district, termed a center, consists of two minor centers, which are in an alternate state of activity. The one center is inspiratory; the other, expiratory. Each one forms the motor central point for the acts of inspiration and expiration. The co-ordinated impulses proceed from these centers in the medulla along the nerves which supply the muscles of respiration and the associated muscles of the face, nose, and larynx. The activity of the respiratory center is excited by irritation of the sensory nerves, either cutaneous or pulmonary. It may also be stimu- lated by the accumulation of carbonic acid in the blood, producing dyspnoea; diminution of oxygen and the presence of heat are also noticeable factors. According to some observers, the acid substance formed in the blood when the muscles are greatly exercised also stimu- lates ,the inspiratory center. RESPIRATION. 261 The functions of the expiratory center, on the contrary, are diminished or even paralyzed by a strong excitation of the sensory nerves. Excess of oxygen and carbonic acid in the blood, or increased intracranial pressure, produce similar effects. The consensus of opinion among physiologists now seems to be in favor of considering the activities of the respiratory center as purely reflex, and that the vagus is the principal nerve concerned in the reflex activities. Hering and Breuer put animals in a state of apncea by repeatedly filling the lungs with air by a bellows. Then when the chest was greatly distended the tracheal cannula was cbsed and the thorax kept in that position. The first movement with a distended chest was one of expiration. Then after the animal was again made apnoeic by re- peated insufilations, the air was sucked out of the chest, the tracheal canniila closed, and the chest kept in that position. The first move- ment to be made was one of inspiration. These two kinds of experi- ments show that dilatation of the chest irritates the fiber-ends of the vagus in the lung, which carry impulses to the expiratory center to call out an expiration. The collapse of the lungs shows that this act excites the fiber-ends of the vagus, which carry impulses to the inspira- tory center to call out an inspiration. Hence the knowledge that in the vagus we have fibers of two kinds : one calling out expiration when an ordinary inspiration is made, the other calling out inspiration when an ordinary expiration is made. So that every act of inspiration calls out an expiration and every act of expiration calls out an inspiration. Apnoea. — When a dog has frequent insufflations of air through a tracheal cannula by means of a bellows, there ensues an arrest of respiratory movements for a short time. Eosenthal believed this to be due to an excess of oxygen in the blood and that the respiration centers were not excited because of this excess in the tissues. Fred- ericque lately, by cross-circulation in the head of one dog with blood from another dog, has been able to produce apnoea which remains a long time if the other dog continues to receive exaggerated pulmonary insufflations. This apnoea is not due to an augmentation of the oxygen, but to a deficiency of carbonic acid. The arrest that ensues in a dog by frequent insufflation of hydrogen instead of oxygen is, accord- ing to Fredericque, due to irritation of the vagus fibers, which call out an expiration-arrest and which is a simulated apncea. Asphyxia. — In considering the phenomena of asphyxia, it is nec- essary to distinguish between rapid asphyxia, produced by complete obstruction to the entrance of air, and slow asphyxia, which is grad- 2G2 PHYSIOLOGY. .a I si a^fsg •aai-!3.9gi£ S .k^J73.£a ^ Sfc^l .•saS'3 -a S^^'ge j£;"S.S^ a; 1 >• . 2"?"M . rH o^ Sa EESPIEATION. 263 ually established. The phenomena of asphyxia are divisible into three stages, which are easily observed in animals, especially in the dog. In the -first stage, which lasts about a minute, the phenomena of dyspnoea appear in the beginning, the forced inspiratory movements are very marked, especially for the thoracic muscles; the abdominal muscles then contract forcibly. At the end of the first minute con- vulsions appear, which at first are purely expiratory and afterward accompanied by spasms, more or less irregular, of the limbs, especially the flexor muscles. In the second stage, which lasts about the same length of time, the convulsive actions cease, sometimes quite suddenly; the expiratory movements at the same time are scarcely perceptible, the pupil is dilated, the eyelids do not close when the cornea is touched, reflex actions have ceased, all the muscles except the inspiratory are in a state of relaxation, and the arterial pressure is elevated. In fact, a state of general calm ensues, which contrasts forcibly with the agitation of the first stage. In the third stage, which lasts from two to three minutes, the inspiratory movements become more feeble and widely separated, the extraordinary muscles of inspiration contract spasmodically, stretching convulsions ensue, and opisthotonos is present. The nostrils are di- lated; convulsive, yawning movements take place; and death closes the scene. The phenomena of slow asphyxiation follow the same course, but with less rapidity. CiRCULATOHT Effect OF AspHYXiA. — The circulation does not change until the second period of asphyxia. During the convulsive stage, and particularly toward its close, the heart enlarges to double its former dimensions. This enlargement is due to the lengthening of the diastolic interval and to the quantity of blood contained in the great veins, which, in fact, are so distended that, if cut, they spurt like an artery. The arterial pressure at first rises and. then fajjs from 160 millimeters to 20 millimeters. These changes are expUmpd as follows : The increase of carbonic acid stimulates the vasoconstrictor center and thus causes general contraction of the arterioles. The immediate result is the filling of the venous system, in the production of which result the contraction of the expiratory muscles of the trunk and extremities co-operate powerfully. The heart, being abundantly supplied with blood, fills rapidly during diastole and contracts vigor- ously. In consequence of these conditions and the vasomotor con- striction, the arterial pressure rises. But the last effect is only tern- 264 PHYSIOLOGY. porary; the diastolic intervals are lengthened by the excitation of the vagus center by the carbon dioxide, the vasomotor center is paralyzed, and the weakness of the heart is due to a deficit of oxygen in the blood. Then the heart soon passes into a state of diastolic relaxation and greatly enlarges. Its contractions become more and more inef- fectual until they finally cease, leaving the arteries empty, the veins fuU, and the right side of the heart engorged with blood. In slow asphyxia, as in death by membranous croup, there is a feeling of painful constriction around the larynx and sternum, yawns, gapings, and vain efforts to breathe, with dimness of sight, buzzing in ears, and vertigo, soon followed by loss of consciousness. The face and lips are tumefied and livid; the eyes watery and projecting; the con- junctiva injected; the jugular veins distended with blood; the nose, ears, hands, and feet have a violet color ; the whole skin presents spots like bruises; the heart movements are uneven and intermittent, and grow weaker and weaker; finally the respiratory movements be- come less and less frequent, soon cease altogether, and almost at once the heart stops and the body is motionless in death. As regards mammals particularly the age affects the rapidity of death from suffocation. In fact, the newborn of this class of animals resist the suppression of respiration very much longer than adults. This accords with the instances of newborn infants which, having been foimd in pools of water, or even in water-closets, have been pre- served alive, although the time passed since their immersion permitted but little hope of saving them. Aktipicial Eespieatioit in Asphyxia. — In cases of suspended animation artificial respiration must be performed. Care should be taken first to remove any foreign bodies or froth from the mouth and nose. Draw forward the patient's tongue and keep it projecting beyond the teeth. Eemove all tight clothing from about the neck and chest. Por relieving asphyxia by dilating and compressing the chest so as to cause an exchange of gases there are several methods. Chief among these are Sylvester's and Marshall Hall's. In the Sylvester method the tongue is pulled forward to prevent any hindrance to the entrance of the air into the windpipe. Expan- sion of the chest is produced by drawing the arms from the sides of the body and then upward until they almost meet over the head. Bringing the arms down to the sides again, causing the elbows almost to meet over the pit of the stomach, produces contraction of the chest. The rate of elevation and depression of the arms should be about sixteen times per minute. RESPIRATION. 265 In the Marshall Hall method the person is placed flat upon his face, gentle intermittent pressure being made upon the back with one's hands. The body is then turned on the side and a little beyond, then upon the face agata, and the same pressure continued as at first. The entire body must be worked simultaneously, the same number and frequency of these artificial processes of respiration being employed as in the Sylvester method. In the Laborde method rhythmical trac- tion of the tongue is made. In artificial respiration a bellows may be employed in a gentle manner so as not to rupture the lung. Iffodlfied Respiratory Movements. — As to breathe is to live, the modes of breathing indicate' the modes of life. We see unfolded ia a series of modifications of the respiratory act many of the sensations and emotions which man experiences in the course of his existence. His birth is announced by a cry, which seems the expression of a first pain; his death is revealed by a sigh ia which his last suffering is breathed out. In the number of his days there are very few devoted to laughter. There are more for sobs. .Yawning often expresses his weariness; straining, the severity of his labor; sneezing, coughing, and expectoration are so many means that Nature employs to struggle against imcomfortable or painful sensations. All of these result from modifications of respiration. Hiccough is only manifested with their aid. Voice or speech, the supreme attribute of man, is only a par- ticular mode of respiration. Sighing. — A large inspiration, slowly executed and followed by a rapid and sonorous expiration, constitutes the sigh. In normal condi- tions of respiration, in about every five or six inspirations there is one which is longer than the others ; it is really a slight sigh. It is sup- posed that this longer inspiration supervenes whenever oxidation of blood needs to be accelerated. It takes place without participation of the will; in fact, it is one of those movements called reflex. The nervous center reacts spontaneously by reason of a painful impression received because of the aceumidation of the venous blood in the right cavities of the heart. The unpleasant effect of sad emotions upon oxidation of blood explains why sighs are given at such times. Their contagious nature is due entirely to sympathy. The Yawn differs from the sigh more by its mechanism thaji by its causes or effects. The needs of oxidation of blood call it forth in the same manner as the sigh is elicited. But, whereas the sigh may be voluntary, the yawn is always involuntary. It is not easy of imita- tion, since it is purely reflex; a person usually will not yawn if the 2G6 PHYSIOLOGY. need of doing it does not exist. Besides its relation to oxidation, it also expresses painful sensations in the stomach, hunger, or a feeling of torpor at the approach of sleep. The Hiccough cannot be compared with the acts connected with respiration, except by the noise accompanying it. It is a spasmodic contraction, abrupt and involuntary, of the diaphragm with coincident contraction of the glottis. The air, drawn rapidly into the chest by the convulsive contraction of the diaphragm, breaks upon the out- stretched lips of the glottis, where is produced the sound characteristic of hiccough. The ordinary causes for this phenomenon are engendered in the stomach by the too rapid introduction of alimentary substances, by alcoholic drinks or those charged with carbonic acid, and by certain foods. It can also result from a special state of the nervous centers. Coughing usually arises from an irritation in the laryngeal pas- sage ; the irritating effect of the sensory filaments of the larynx reaches a certain intensity ; there is then a deep inspiration, which is followed by a sudden and strong expiration. Coughing can be produced voluntarily, but it is more often caused by reflex action, which it is generally impossible to resist. A cold draught on the skin or a tickling of the external auditory meatus will provoke a cough iu some people. Laughing and Sobbing have this feature in common : they have their seat in the chest and face at the same time. They act especially upon the same muscle: the diaphragm. In the face they differ in that one has its own particular seat in the region of the eye, the other around the mouth. The same muscles, the same nerves, produce sobs and laughter. Their movements of inspiration and expiration are, however, accompanied by their own characteristic sounds. Snohing is due to vibration of the soft palate. Chetne-Stokes Eespiration. — This is a peculiar modification of the respiratory movements which is seen in certain pathological con- ditions, as in fatty heart, atheroma of the aorta, certain apoplexies, and in uraemia. It has even been noted in healthy children during sleep. It consists of respiratory pauses alternating with a series of respira- tions till a maximum depth and rapidity is reached ; after this climax they gradually diminish till they end in another pause. Certain drugs— chloral is one — ^may cause Cheyne- Stokes respiration. Cheyne-Stokes respiration rhythm is to the respiratory system what the Traube-Heriug rhythm is to the circulatory system. Both arise in their respective centers in the medulla oblongata. The pause in Cheyne-Stokes respiration is somewhat less than RESPIRATION. 267 half of the duration of the active period. During the pause the pupils are contracted and inaetitive; when respiration begins again they become dilated and sensitive to light. The eyeball is usually moved at the same time. CHEMISTRY OF RESPIRATION. Looked at from a chemical point of view, respiration presents the following phenomena: (1) absorption of oxygen; (2) exhalation of carbon dioxide; (3) release of a certain quantity of nitrogen; (4) exhalation of vapor of water. It has been previously stated that at each normal respiration of atmospheric air but one-sixth of the air within the lungs is changed. This current does not actually penetrate beyond the largest bronchial tubes. The air which finds its way into the bronchioles and air- vesicles does so by dijfusion. The student has already learned that the normal lung contains within it a certain quantity of air which cannot be expelled by the strongest expiration: residual air. This air is contained within the alveolar air-spaces; its exchange with the atmospheric air is accom- plished by the slower processes of gaseous diffusion. The difference in the amount and pressure of the two gases — oxygen and cartlonic- acid gas — is the real explanation of the current-movement of the two. The COj moves outward, the inward. The interchange is aided by the heart-movements, also. When the heart contracts (systole) it occupies less space in the thorax than it does during relaxation (diastole). Hence, ait is sucked in or pushed outward through the open glottis by these movements. A glanc^ at the anatomy of lung-structure reveals the fact that the alveoli are surrounded by a dense network of capillaries. Some of the capillaries even 'project into the air-spaces. .These conditions make more easy the processes of diffusion. Some of the oxygen from the respired air passes into the blood to form a loose, chemical combination with the hEemoglobin of the red corpuscles : oxyhsemoglobin. This gives to the blood its red color, making it arterial. At the same time there is diffusion of carbonic acid from the impure, venous blood into the alveolar compartments. Gradually it rises in the air-vesicles and bronchioles until it finds its way into the current of air in the larger bronchioles, by which it is expelled from the system. With this rise of carbonic acid in the alveolar air there is a corresponding descent of oxygen for purposes of oxygenation. The oxyhemoglobin of the blood is carried along 268 PHYSIOLOGY. by the blood-stream to the tissues (the real seats of respiration), where it becomes disengaged to unite with the tissue-cells. In the produc- tion of heat and energy it has united with the carbon of the tissues to form carbonic acid and with the hydrogen to form water. That which is not used up at once constitutes a reserve supply in the tissue to be used as occasion demands. It has been ascertained that the quantity of oxygen absorbed within a given time is not found entirely in the carbonic acid exhaled by the animal during the same time. Consequently one can scarcely consider the oxygen as employed solely in burning carbon or in form- ing carbonic acid. Thus, animals draw from the surrounding atmos- pheric medium a quantity of free oxygen which attacks the ternary and quaternary materials of the organisms. These then exhale car- bonic acid and water as the result of the respiratory combustion, together with a small quantity of nitrogen. The latter proceeds from the destruction of a certain proportion of the nitrogenized substances of the blood and tissues. As an animal can keep its weight the same during these combustive changes, it must be admitted that the carbon, hydrogen, and nitrogen thus lost must be unceasingly renewed by the food it ingests and digests. It is impossible to observe any constancy in the quantity of the products consumed or exhaled while searching into the amounts of oxygen absorbed and carbonic acid given off by man in a certain time. The chemical phenomena of respiration are, in fact, of such extreme changeableness, due to the variety of causes, that physiologists can scarcely know them all. The expired air is richer in COj than inspired. It contains 4.38 volumes per cent, of this gas, and consequently a hundred times more CO2 than the air inspired. The air expired is poorer in oxygen. It contains 16.03 volumes per cent, of this gas, which is about 4.78 volumes per cent, less than the inspired air. These iigures show that the absorption or loss of oxygen is greater than the elimination of COj. This further sub- stantiates the statement that all of the oxygen absorbed does not appear in the form of carbonic acid. So often in the study of physiology the student's attention is called to the fact that the movements of the fluids of the body are always in the direction of higher to lower pressure. The explana- tion of the exchange of gases held in loose combination in the blood and those comprising the atmospheric air in the lungs is another inter- esting study of difference of pressure. RESPIRATION. 269 The exchange depends upon the law of "dissociation of gases," and is as follows: "Many gases form true chemical compounds with other bodies when the contact of these bodies is effected under such con- ditions that the partial pressure of the gases is high. The chemical compound formed under these conditions is broken up whenever the partial pressure is diminished, or when it reaches a certain minimum ' level, which varies with the nature of the bodies forming the com- pound. Thus, by alternately increasing and decreasing the partial pressure, a chemical compound of the gas may be formed and again broken up." (Landois.) The CO2 and the in the blood form certain loose combinations which follow this law exactly. These gaseous compounds, as they cir- culate with the blood-stream, find conditions of high and low pressure enveloping them, whence they take up and give off their respective gases. As the pressures vary, so does the dissociation of the gases. Thus, the oxygen-carrying elements of the blood, the haemoglobin of the red corpuscles, as it reaches the pulmoliary capillaries is poor in 0. The air adjoining them in the pulmonary alveoli is rich with 0. The low-pressure hemoglobin unites with the high-pressure to form the loose compound oxyhsemoglobin. Later, the oxyhsemoglobin meets with tissues poor in oxygen and which need this element for their combustion. There is a dissociation from a higher to a lower pressure whereby the tissues receive their needed supply. The corpuscles must needs receive replenishment again from the alveolar , oxygen, and in this way the circle is completed. On the other hand, the blood in contact with the body-tissues meets a high pressure of CO2. By reason of which compounds are formed containing CO2, in which form they reach the air-vesicles in the lungs. The inspired air contained within the air-vesicles has a much lower partial of COj than that contained in the venous blood coming from the tissues. Hence, the dissociation of the COj from the blood to the vesicular air, finally to make its exit along the bronchioles, bronchi, trachea, etc., to the atmosphere. Bohr, of Copenhagen, be- lieves the epithelial cells of the air-cells have the power to excrete carbonic acid and absorb oxygen independent of the differences in tension of the gases. The temperature of the air expired is greater than that of the air inspired, and is but a trifle lower than the body-temperature. Though the temperature of the surrounding atmosphere vary, that of the ex- pired air remains nearly the same. 270 PHYSIOLOGY. The volume of the air expired is greater than that of the air inspired, by reason of the increase in temperature and the contained watery vapor. If, however, it be dried and reduced to the same tem- perature as the inspired air, there will be a diminution of volume: about one-fiftieth. The respiratory quotient is the relation between the- volume of oxygen absorbed and the volume of carbonic acid eliminated. That is :— volume of COj given off The respiratory quotient = . Normally it is volume of absorbed , J. 4-38 about = 0.9. 4.78 This quotient varies, however, with the nature of the chemical composition of the foods ingested. With the hydrocarbons the quotient approaches unity. The carbohydrates contain in their molecules enough oxygen to oxidize their hydrogen; all that remains for the inspired oxygen is to burn up the carbon. The fats and albumins, on the contrary, possess too little oxygen to burn all of the hydrogen and nitrogen they contain. Hence all of the oxygen is not found in the CO2 eliminated, and the respiratory quotient falls to 0.75. On a mixed diet the quotient is intermediate between 0.9 and 0.75. In plants the respiratory quotient, especially in starchy ones, is equal to 1.0. In fatty seeds the respiratory quotient is 0.6 to 0.8. Muscular activity augments the gaseous exchanges and so makes the respiratory quotient approach a unit. All things being equal, a man absorbs more oxygen and exhales more carbonic acid than a woman. The exchanges are increased in the latter during pregnancy. During sleep the consumption of oxygen and the elimination of CO2 diminish about one-fourth. This decrease depends upon mus- cular and intellectual repose, darkness, etc. The cells of the tissues determine the amount of oxygen needed, and not an excess of the oxygen present. The intramolecular changes take place in the cells of the tissue, and not in the blood. The amount of water thrown off daily is about a pound; of oxygen taken in, about a pound and one-half; and of carbonic acid thrown off, a little more than a pound and a half. In human blood the average total gases are estimated to be, in round numbers, 60 volumes per cent, at 0° C. and 760 millimeters' pressure, made up as follows: — • EESPIRATION. 371 Artekial 'Vknous Blood. Blood. Oxygen 20 8 to 12 Nitrogen 1.4 1.4 Carbonic acid 39 46 The above table represents the average composition of the gases contained in man's blood. A considerable attraction exists betweeil the particles of solid, porous bodies and gases, whereby the latter are condensed within the pores of the solid bodies ; that is, the gases are absorbed. Fluids can also absorb gases. One of the functions of the blood is to carry oxygen from the lungs to the tissues and carbon dioxide from the tissues back to the lungs for expulsion from the economy. These two gases, to- gether with nitrogen, present themselves in two different states in the blood. The blood, a fluid, must very naturally absorb gases also. Hence one wotild expect to find 0, COj, and N held in solution, and that these gases should behave according to Dalton's law : the amount of gas dissolved in a liquid varies with the pressure of the gas; the higher the pressure, the greater the amount of gas dissolved. But oxygen held in the blood disregards Dalton's law, since its proportions in the blood in various parts of the body remain fairly constant no matter what the pressure. Hence, it owes its presence in and obeys laws dependent upon its being in the form of loose chemical combina- tions. If the oxygen were mainly held in solution, then would the blood give it up in a forming vacuum in direct proportion to the falling oxygen-pressure. That these conditions do not follow tends to (estab- lish the fact that the oxygen is held by some chemical union. Experi- mental physiologists also tell us that in their work they notice that very little is given off in a forming vacuum until a very much re- duced pressure is reached, when there is a sudden evolution of the gas, just as though it had been freed from some restraining influence. The restraint is now generally accepted to be the chemical union before mentioned. Physiologists admit to-day that the major portion of the oxygen of the blood is contained in the red corpuscles, which are the special messengers for carrying it to the different tissues. Their capacity for holding oxygen is nicfely demonstrated by the following simple experiment : Serum, without corpuscles, is agitated in the presence of oxygen. The amount of oxygen absorbed is found to be less than half what would be taken up by the same amount of serum containing red corpuscles. .272 PHYSIOLOGY. The oxygen, being preferably united with the corpuscles, is joined to them in a very unstable combination. The affinity is just strong enough to facilitate the conveyance of the gas in the circulatory system, yet not so strong but that it may attack the combustible materials of the tissues. Oxygen united chemically with hsemoglobin forms oxy- haemoglobin. However, it must be kept in mind that some of the oxygen is con- tained in the blood-plasma, where it is in simple solution and obeys the laws of Dalton. There can scarcely be any doubt of the source of the oxygen con- tained in the blood, for it evidently comes from the atmospheric air, of which it forms one of the elements. It represents the indispensable agent of most of the transformations which take place in the heart of the general economy. Ehrlich's experiments with methylene blue and other similar pig- ments show the intense affinity of the tissues for oxygen. Belation of COj in the Blood. — Carbonic acid must be regarded, on the contrary, as one of the final products of the nutritive transmu- tations. It is destined to be eliminated with the vapor of water and free nitrogen, especially through the respiratory passages. When the very small proportion of this gas in ordinary atmospheric air and its considerable amount in expired air are considered, it is easy to be con- vinced that carbonic acid is indeed a product of the organism. The gas, therefore, comes from the tissues and liquids themselves of ani- mals, and not from outside media. It is very generally admitted that the greater part of the carbonic acid is in a condition of chemical combination. The principal com- pound is bicarbonate of sodium. The tension of the carbonic acid in the tissues is high. It is less in the alveolar air. Hence we find it working its way along the respiratory passages to be expelled by the movements of respiration. The movement of the oxygen was found to be toward the tissues ; the direction of carbon dioxide is the reverse: away from the seats of tissue- combustion. It has been found that, when the lung is distended, the heart beats faster, this increased action being caused by an irritation of the sensory nerves in the lungs, which, in a reflex manner, inhibits the cardio-inhibitory center and allows the heart to beat faster as the brake is taken off. Dr. Da Costa, in his examination of twenty-four glass-blowers, found that in eleven the pulse ranged from 90 to 116 per minute. EESPIEATIOK. 273 I have shown elsewhere that this is due to the irritation of the sensory fibers by the great distension of the lungs diminishing the irritability of the cardio-inhibitory center, since the great lung-distension occurs daily for years. Now, it is well known that the inhibitory power of the vagus in man is very great, and its power varies in different individuals, which would explain why the thirteen other glass-blowers showed no habitual acceleration of the heart. As this performance is kept up many hours daily for a series of years, it is easy to conceive that the cardio- inhibitory power of the vagus centers receives such a diminution of irritability so often that it would at length remain constantly weak. The vasomotor center also sends out rhythmical impulses by which undulations of blood-pressure are produced. That this center is capable of producing such undulations has been amply verified by the existence of the Traube-Hering curves. Bespiration of Different Gases. — Eespiration is essentially the intaking of oxygen and the output of carbon dioxide by the living cells. Among the higher orders of animals two phases of respiration are distinguished — ^the external, the exchange of gases between the air or water and the blood; and the interrml, the exchange between the blood, lymph, and the tissues. The usual and normal medium inspired is ordinary atmospheric air, from which there is derived the needful supply of oxygen. The open atmosphere is a mixture of gases in the following approximate proportions : — Atmosphere Nitrogen, including argon, etc 79.00 "] O^^ygei 20.96 Ln 100 parts. Carbon dioxide 0.04 I NH„ H2O, and organic matter in small variable quantities. Though the quantity of water in the air is marked, — over 1 per cent., — it is not customary to reckon it in the gaseous constituents. Some gases, as hydrogen and nitrogen, produce no specific effects from any toxic powers in themselves when they are breathed; they produce results simply because they exclude the proper s,upply of oxygen for the animal. On the other hand, gases such as carbon dioxide, carbon monoxide, nitrous oxide, and hydrogen sulphide, when respired in sufBcient bulk, are absorbed and so produce specific, toxic effects. A third class of gases, as ammonia and nitric oxide, are not respirable because of their highly irritant action upon the respiratory apparatus, spasm of the glottis being produced. 274 PHYSIOLOGY. Carbon dioxide, when undiluted, is irrespirable by reason of the spasm of the glottis occasioned. Properly diluted it can be respired, but produces headache, dizziness, drowsiness, and dypsnoea by an action on the nervous system. Nitrous oxide acts directly upon the nervous system, partly by a special action and partly by producing an excess of COj in the blood. Nitrogen and hydrogen gases produce their fatal effects by asphyxia, due to exclusion of the oxygen and thereby preventing oxygenation of the blood-corpuscles. Differing from these gases are the effects produced by inhalation of carbon monoxide. It was long known that this gas was poisonous, but it has only been within recent years that its mode of producing asphyxia has been learned. Instead of excluding the oxygen, it displaces the latter in the blood, forming a very stable compound with the haemo- globin of the red corpuscles. It is interesting to note that the color of the blood after death from asphyxia from carbon monoxide is cherry-red; in other forms of asphyxia the blood is almost black. The action of this gas is of practical importance, since every year it is the cause of many deaths. They occur from poisoning with coal-gas (especially where charcoal stoves are used in small rooms), the fumes of kilns and coke-fires, and from inhaling the air of coal-mines, espe- cially after explosions. Caissons and the Effect of Compressed Air. — Men are able in caissons to support during some moments a pressure of five to ten atmospheres when they proceed with caution. If the pressure is too rapid there is great danger. If an animal who resists a pressure of ten atmospheres dies instantly from a rapid change to ordinary pres- sure, the autopsy shows that the heart and large vessels are filled with bubbles of gas, especially of nitrogen. Under the influence of double or treble pressure the blood absorbs a double or triple pro- portion of air, especially the nitrogen. If the animal is submitted to a rapid diminution- of pressure, the nitrogen, not being kept in solu- tion in the blood, is disengaged in a gaseous state in the form of bubbles, which produces emholism in the capillaries of the brain, lungs, and heart, and which arrests the circulation. To avoid the disen- gagement of bubbles of nitrogen it is necessary to let the atmospheric compression down in a very gradual manner. Operatives in leaving the tubes in which compressed air exists must remain a quarter to a half hour in the closed chambers, where the pressure is reduced little by little. The excess of gas absorbed is slowly eliminated by the lungs without producing an accident. Four atmospheres is about the amount that operative? can work in with safety. Every ten meters in depth of RESPIRATION. 275 water roughly equals one .atmosphere. By itself compressed oxygen is a toxic agent, for it lowers the output of carbonic acid and the tem- perature of the body. The cure for caisson-paralysis is recompression and slow decompression. Rarefied Air. — All travelers who have climbed the Alps speak of the same troubles experienced by them at nearly the same altitude : a considerable diminution of appetite, a disgust for food, nausea and even vomiting, palpitations, headache, lassitude, sleepiness, and buzzing in the ears. This state is known as anoxyhssmia, or want of oxygen in the blood. Dyspnoea takes place not only because the air inspired con- tains oxygen in a given volume, but the dissolution of this gas in the blood is less easy under feeble pressure. Muscular work in the ascent also uses up considerable of the oxygen taken in. At 10 per cent, of an atmosphere there ensues restlessness and dyspnoea, and, at about 7 per cent., death. A partial pressure, like 7 per cent, of an atmosphere, corresponds to an altitude of 30,000 feet. Men in a balloon have ascended about 28,500 feet. People who live on high mountains have a disease known as the mal de montagne. In mountain sickness Kronecker holds that there is an increased amount of blood in the pulmonary vessels, due to an increase in their capacity and to a stagnation of blood arising from an equalization of the atmospheric and intrathoracic pressure, causing a passive oedema resulting in dyspnoea and asphyxia. Ventilation. — Let it suffice here to recall that the problem of ventilation consists in maintaining, in more or less closed spaces, the normal composition of the atmospheric air. Not only this, but to counteract the incessant modifications the respiration of man or of ani- mals makes this medium undergo. For these purposes it is important that the ventilation should be very active. It has been established that, for closed spaces intended to receive healthy persons, it suffices that the ventilation furnish 1000 cubic feet of new air per person per hour. This is not sufficient for hospitals which contain sick persons, where more abundant and vitiated emana- tions are received by organisms less fitted to react against their infiu- ence. Those hospitals which receive 3000 cubic feet of fresh air for each sick person hourly are free from odor. A healthy adult gives off about 0.6 cubic feet of carbonic acid per hour. If he be supplied with 1000 cubic feet of fresh air per hour he will add 0.6 to the 0.4 cubic feet of carbonic acid it already contains. That is, he raises the percentage to 1.0. 276 PHYSIOLOGY. Pharmacological. — The increase of pressure in the pulmonary circulation and a simultaneous decrease of arterial tension in the systemic circulation by amyl nitrite is due either to a contraction of the pulmonary vessels or to a weakness of the left ventricle and as a consequence a backing up of blood in the left auricle. Nitro- glycerin acts like nitrite of amyl. Aconite lowers the pressure in both the pulmonary and systemic cireulations^ due to a weakening of both sides of the heart. Ergot constantly causes a marked increase of pulmonary tension with a primary decrease of aortic pressure. Digitalis, strophanthin, and adrenal extract increase the tension in the systemic circulation, leaving the pressure in the pulmonary circu- lation unchanged. It is singular that the adrenal extract should so greatly affect the systemic pressure and not the pulmonary, while ergot acts reversely — augments the pulmonary pressure more than that of the aortic system. These facts show the independence of the pulmonary vessels to the vessels of the systemic circulation.^ The blood-pressure in the pulmonary artery is about one-third that in the aorta. As to the vasomotor nerves of the lungs, we do not know if they have a tonus, or under what circumstances they are called into activity. It is natural to conclude, since pulmonary vasomotor nerves exist, that they are excited when the left heart has difiBculty in emptying itself; in this case they could contract and diminish the afflux of blood to the left side of the heart. ' Tigerstedt, "Ergebnisse der Physiologie," 1903. CHAPTER VIII. SECRETION. INTERNAL SECRETION. The tissue-activity of the organism may be conveniently classed under three groups : (a) muscular activity, manifesting itself in heat and motion; (b) nervous activity, including all nervous acts, from sensation to reason ; (c) glandular activity, which is the general f unc* tion of epithelial and lymphoid tissues. It includes all those changes of metabolism whereby there follows, as a result of elaboration, a special mixture. It is with the last of the three — glandular activity — ^that we are now to deal. However, the human economy being such a complex organism, it must be borne in mind that disturbance or lack of activity of one kind may have a very marked influence upon other metabolic functions. It is well known, especially among animal fan- ciers, what a great effect the removal of the ovaries and testicles may occasion in the development of other organs and in the general nutri- tion of the body. Proteid waste of increased proportion follows the removal of a considerable portion of renal tissue. The liver is most intimately connected with the metabolism of carbohydrates and pro- teids as well as those food-constituents which contain iron. The gland-cells perform an essential role in secretion. These cells are applied upon the basement membrane of the glandular acini in such a fashion that each cul-de-sac is surrounded by a network of capillaries. Ludwig and Tomsa have shown that between the blood- capillaries and acinus are found lymphatic spaces. The cells of the acinus, surrounded by the lymph in the spaces, take from it the ele- ments needed for the production of its own peculiar secretion. Dependent upon the nature of the activity of the epithelium of the glands, the general process of secretion may be said to comprise four distinct modes : — 1. Secretion by Filtration. — In this case the glandular epithelium does not manufacture any material; it utilizes the principles pre- existing in the blood and lymph. This kind of secretion is related to serous transudation, as of the pleura? and peritoneum, but it is not a (277) 278 PHYSIOLOGY. simple filtration. The selective action of the epithelium acts upon the transit of the secretion and varies the proportion of the constituents of the secretion according to the composition of the lymphatic and blood-plasma. To this style of secretion belongs the water of the urine, sweat, and tears. The most important principles filtered are water, salts of the plasma, chlorides of potassium, sodium phosphates, lime, magnesia, and carbonic acid. 2. Secretion Proper — Production of New Principles. — Here glandular activity especially intervenes; the epithelial cell does not act as a simple filter. It modifies the nature of those products passing through it, or creates from them new products. In this class may be put the digestive secretion. The products thus formed by gland- cells vary for each gland, neither is physiology nor histology able to explain their manner of production. Thus, we are not able to explain in a satisfactory manner the chemical changes which make hydro- chloric acid appear in the gastric juice, sulphocyanide of potassium in the saliva, bile-acids in the bile, etc. 3. Secretion by Glandular Desquamation. — In the preceding types of secretion the gland-cell preserves its integrity; it does not do any- thing else except allow the external materials to pass through it, changed or unchanged. However, in this type the cell itself falls and is eliminated to contribute to form the product of secretion. This glandular desquamation is comparable to the epithelial desquamation which occurs during the life-history of the epidermis. Generally this desquamation is preceded by a chemical change of the gland-cells. This change is fatty, as in sebaceous secretion. The sebaceous fats and mucin form the special products of this group of secretions'. 4. Morpholog^ical Secretion. — In this type the essential element of the secretion is a formed element. It is a specialized cell derived from a cell, together with a liquid which holds this anatomical element in suspension. Such is the spermatic fluid. Secretion Defined.- — The term secretion has been defined as the special activity of the glandular tissues. It is the elaboration of fluid or semifluid mixtures by selection and formation from the fluids which surround the active cells, as well as from the substances of the cells themselves. Up to a certain point secretion is composed of two acts which are separated by a distinct line of .demarcation. 1. A filtration of blood-plasma passes through the wall of the capillary. This plasma spreads into the lymph-spaces which surround the acini, and it is from this lymph that the elements are taken out for the production of the secretory products. The filtration is under SECRETION. 279 the influence of the blood-pressure, and varies in its intensity as the arterial tension varies. It, properly speaking, is an accessory act of secretion. 2. The second feature is the activity of the gland-cells, which take from the lymph the materials necessary for secretion, to change them more or less. This phase is the essential act of secretion. It is dependent upon filtration to the extent that filtration furnishes the liquid which the glandular cells need and renews- it when exhausted. The activity of the gland-cells attains its maximum in general during the apparent repose of the gland. When the gland is not secreting, its cells are preparing substances peculiar to each secretion. This is true particularly of the ferments, as pepsinogen, trypsin- ogen, etc. The two processes — filtration and gland-cell activity — may be separated from one another without producing any interference. Thus, secretion can continue when the head is amputated and even if the cir- culation of the gland be arrested. Salivation can continue after both these events have occurred. On the other hand, the injection of carbonate of soda into the salivary duct destroys the gland activity without affecting the circula- tion, of the gland. Should the chorda tympani be stimulated filtra- tion from the blood continues, but the gland does not secrete. There is an accumulation of lymph in the lymph-spaces until the gland becomes oedematous. NATURE OF INTERNAL SECRETION. This is not the same for all of the glands. The secreted product may be destined to destroy the noxious principles resulting from the functions of the organ, as of the liver and suprarenal capsules. Its aim may be to break up the excess of sugar, as is the case with the pancreas ; or to prevent excess of a colloid material, as with the thyroid gland. The enrichment of the blood with useful principles is accom- plished by the sugar of the liver. The testicle extract supplies more nervous energy. THE THYROID. The thyroid gland, when fully developed, has no excretory duct; so, with the spleen, suprarenal bodies, and thymus, it is usually classed under the head of • ductless glands. The thyroid is a soft, reddish body embracing the front and sides of the upper extremity of the trachea. It consists of a pair of lateral 280 PHYSIOLOGY. lobes united at their lower part by a transverse isthmus. The lateral lobes are oblong oval, thicker below than above, and usually of un- equal length. The weight of the thyroid is usually from one to two ounces, but is larger in the female. It is very liable to become hyper- trophied, especially in the female : a condition called goiter. The thyroid is a highly vascular organ, invested with a thin, fibrous membrane, and composed of a fibrous stroma, in the meshes of which a multitude of minute closed vesicles exist. Each little lobule seems to be a completely closed sac — at least, no tubule is noticed emanating from it. The little sacs are filled with a transparent, amber-colored, viscid, nucleo-albuminous fluid. In the connective tissue surrounding each lobule there is a plexus of capillaries. With them there is found an abundant supply of lymphatics. Vessels and Nerves. — The arterial supply for the thyroid body is gained from the superior and inferior thyroid arteries. These ar- teries are remarkable for their large size and numerous anastomoses. The veins form a plexus upon the front of the trachea and surface of the gland. From the plexus arises the superior, middle, and inferior veins. The lymphatics terminate in the thoracic and right lymphatic duets. The nerve-supply to the thyroid body is derived from the mid- dle and inferior cervical ganglia of the sympathetic and the pneumo- gastric. Their nonmedullated fibers adhere very closely to the vessels. Function. — It was shown by one observer that gentle pressure upon the lobes of the gland caused the contents of the gland-acini, or vesicles, to flow into the peripheral lymphatics. This was later con- firmed by the work of microscopists, and the colloid nature of the secretion was also recognized. The vesicular epithelium is a true secretory gland-tissue which separates the colloid material from the blood. The secretory character of the epithelium has been furtiier shown by the injection of pilocarpine. Following its administration there results a remarkable increase in secretion of the colloid sub- stance. It has been demonstrated that the expressed juice of a thyroid gland of a dog produced coma in another animal three hours after its administration. Hence it must be concluded that the thyroid gland is a structure essentially connected with the metabolism of the blood and tissues. In performing its functions it is a blood-agent, both directly and in- directly. In the human fcetus the gland-tubes, or rather cylinders of epithelium, commence their secretory activity during the interval from the sixth to the eighth month. In proportion to the body-weight, the SECEKTION. 281 gland is heaviest at birth and diminishes notably toward the end of life. Therefore the thyroid gland is in functional activity before birth, and is of special metabolic importance in early extra-uterine life. Its value falls as the general vital processes decrease. The thyroid body is one of those organs of great metabolic im- portance, since its removal or disease is followed by general disturb- ances. Experimental thyroidectomy is very much more fatal in young animals than in adults. The removal of the gland in aged carnivora is followed by the usual cachexia. Cachexia Stkumipeiva has been found by all observers to occur with greater frequency when thyroidectomy has been performed on young individuals. The classification of symptoms from removal of the thyroid are either (a) tetany, (b) myxoedema, and (c) cretinism. According to the violence of the cachexia, death may occur in any of these stages. The nervous symptoms appear early and are well marked. The first indication is fibrillary muscular tremor or twitching, resembling very closely the disease called tetany ; next tremor occurs ; and finally rigidity makes its appearance. Some experimentalists hold that it is the removal of parathyroids which cause tetany, and not the removal of the thyroid. When the thyroid body is diseased or removed from children so that its functions are obliterated, there is produced a species of idiocy called cretinism. A like condition in adults receives the name of myxwdema. Noticeable symptoms of this disease are slowness of both body and mind, associated with tremors and twitchings. There is also a peculiar condition of the skin wherein there is overgrowth of the subcutaneous tissue. In time this becomes replaced by fat. Myxoedema was ba- lieved to be an cedematous condition characterized by the presence of a large amount of mucin. That there is an excess of mucin has been determined, but it is not in proportion to produce this patho- logical condition. The disease is rather a hyperplasia of the con- nective tissue. The integument especially swells and the eyelids become pufiy. At the same time the surface becomes dry and there is a tendency to shed hairs and superficial epithelium. The hyper- plastic change is followed by atrophic changes, accompanied at first by slight fever; later the temperature becomes subnormal. All of these various effects' of thyroidectomy can be temporarily prevented by a graft of thyroid ; they may also be caused to disappear either by injection of thyroid juice into a vein or under the skin. The 283 PHYSIOLOGY. same results may be attained by raw thyroid or thyroid juice by the mouth. If a graft can be made to "take," the effects are permanent. Eemoval of a permanent graft will be followed by all the symptoms of thyroidectomy. The phenomena attending extirpation are due to the absence of a secretion which is formed within the thyroid, passing from it into the blood. This secretion is necessary for certain of the metabolic proc- esses of the animal economy, especially for those connected with the nutrition of the central nervous system and connective tissues. Ex- tracts of thyroid gland produce distinct pathological effects in the normal subject. An injection into a vein of the decoction of the gland lowers the blood-pressure and increases the caliber of the radial artery. From this it would seem that the juice has a. distinct action upon the vascular system. Whether the gland possesses the function of destroying toxic products of metabolism which would otherwise tend to accumulate in the blood is a point not as yet understood. Because of the extreme vascularity of this organ and its direct connection with the vessels which supply blood to the head, the thy- roid has been regarded as exercising a regulatory function on the blood-supply to the brain — short-circuiting the cerebral flow, as it were. Experiments have showed that at least a part of the thyroid gland must be allowed to remain after operations' upon this gland. Other- wise cachexia will follow. The occurrence of thyroid tissue in other parts than the lobes of the glands is a matter of more than embryological interest. These glandular masses have been termed accessory thyroid glands, or para- thyroids. The parathyroids lie in the immediate neighborhood of the lobes of the thyroid gland. It has been observed, after complete thyroidectomy in man, that these islands, or parathyroids, become enlarged. Also, where temporary symptoms of cachexia have ap- peared, they improve in proportion to the degree of swelling of the parathyroids. The thyroid contains two albuminous bodies, the one containing iodine, the other having phosphorus. The first one has the character of a globulin I and has received the name of thyreoglobulin and by reagents is changed into iodothyrin. Hutchinson states that "if the presence of iodine in iodothyrin is essential to the activity of this substance, it is not so in virtue of its being iodine, but owing to the form of organic combination in which SECRETION. 283 it occurs." It is estimated that the normal thyroid gland contains approximately ten times as much iodine as do the hypertrophied glands of patients sufEering from exophthalmic goiter. The thyroid seems to possess a peculiar afiBnity for iodine. While our knowledge of the thyroid has been considerably ex- tended by reason of modern research, there yet remains much that is very obscure. Thus, the accessory thyroid glands, or parathyroids, are free masses of tissue located in the vicinity of the thyroid and which seem to contain no colloid material. Nevertheless, their removal, although the bulk be small, produces identical results with the com- plete removal Of the thyroid gland. Eegarding the function of the parathyroids, it is probable that they are concerned in removing some- thing from the blood rather than adding anything to it. Thyroid by the mouth reduces weight by an increase of the intake of oxygen and the output of carbon dioxide. This excessive burning of fat produces water, thus causing increased secretion of urine. It also increases the urinary nitrogen, probably due to proteid changes. It acts best in the pale, fat person. Von Cyon has made a study of the relation of the thyroid to the heart. He states that suppression of the activity of the thyroid or an injection of iodothyrin has an immense influence upon the entire nervous system of the heart and blood-vessels. He proves that the vagus participates in the innervation of the thyroid gland, or is at least closely connected with it. The function of the thyroid is to render harmless the salts of iodine, which have a toxic effect upon the vagi and sympathetic nerves by converting them into an organic com- pound, the iodothyrin. The latter compound has a stimulating effect upon these same nerves and at the same time increases their power. The thyroid acts mechanically as a safeguard of the brain against en- gorgement. In a sudden increase of blood-pressure, whether from increased activity of the heart or from increased capillary resistance, the thyroid is capable of passing through its vessels a large amount of blood within a very short time, so as to turn it directly from the arterial into the venous system and thus prevent its entrance into the cerebral circulation. THE SPLEEN. The spleen is deeply placed in the left hypochrondium. Its shape is a half-ovoid. Its consistency is comparatively soft, and its color is purplish. Its external convex surface is in contact with the dia- ■ phragm opposite the three or four lower ribs. Its internal surface is 284 PHYSIOLOGY. applied to the fundus of the stomach, to which it adheres by the gastro- splenic omentum. In the middle of the internal surface of the spleen there is a slight groove, the hilus, where the artery and nerves enter. The spleen usually is five inches in length, four inches in breadth, and from one to one and one-half inches thick. It has two coats: the outer serous and the inner fibro-elastic. The spleen when torn has a deep reddish-black, pulpy appearance, resembling coagulated blood. This splenic pulp may be removed from the spleen by maceration, leaving a spongy mass composed of splenic blood-vessels associated with numerous trabeculae of fibro-elastic tissue. Adhering to the side of the smallest arteries of the spleen are small, rounded, whitish bodies, the corpuscles of Malpighi, one-thirtieth to one-sixtieth of an inch in diameter. The splenic pulp contains red blood-corpuscles, granular corpuscles resembling lymphocytes in ap- pearance and having an amoeboid movement, and red corpuscles under- going disintegration. Function. — The extirpation of the spleen leaves life and health intact in animals and in man. All that results is a more or less Fig. 62. — Tracing of an Experiment with Splenic Extract upon a Dog. Read from left to right. pronounced hypertrophy in all the lymphatic ganglia of the body. Direct irritation of the spleen, the direct or reflex irritation of the medulla oblongata, the application of ice-water to the left hypo- gastrium, and quinine cause a diminution of the spleen by contraction of the muscles of the capsule and trabeeula. The spleen is congested during digestion, and when the portal circulation is interfered with, and in a great number of infectious diseases, notably typhoid and malarial fevers. The spleen is supposed by some to manufacture white blood-corpuscles, and this manufacturing reaches a pronounced activ- ity when the organ is hypertrophied, as in leueocythsemia. The spleen, from its power to dilate, serves as a reservoir of blood for the portal system, especially for the blood-vessels of the stomach. Many of the purin bodies are found in the spleen, as xanthin, hypoxanthin, and uric acid. ilnfluence of the Nervous System Upon the Spleen. — The nerves that supply the spleen have their center in the medulla oblongata. Section of these nerves is followed by an increase in the size of the organ. SECRETION. 285 It has been shown by the oncometer that the spleen undergoes rhythmical contractions and dilatations by virtue of the regular con- traction and relaxation of the muscular fibers found in its capsule and trabeculse. I have demonstrated experimentally that extract made from the spleen when injected into an animal will excite active peristaltic move- ments (Fig. 62). THE ADRENALS. The adrenals are a pair of flattened triangular organs, one being situated upon the upper end of each kidney and inclined inwardly toward the vertebral column. Their posterior surface, moderately convex, rests against the crura of the diaphragm; their anterior sur- face, flatter than the posterior, on the right side is in contact with the liver, on the left side with the pancreas and spleen. The surfaces present vascular furrows, the largest of which at the base is dis- tinguished as the hilus. These adrenals are in color brownish yellow, of moderately firm consistence, and vary in size in different individuals and slightly on the two sides. Usually they are about one and one-half inches in breadth and height, and about one-fourth of an inch in thickness. On section we find an external layer, the cortex, and an internal layer of softer substance, the medulla. The cortical layer is yellow in color, of firm consistence, and pre- sents a columnar appearance at right angles to the surfaces of the layer. Microscopically, it contains oblong receptacles occupying a ■fibrous stroma continuous with the fibrous coat of the body. In these receptacles are nucleated, transparent cells often containing oil- globules and a yellowish-brown pigment. Beneath the capsule is the zona glomerulosa, with cells in round groups; the next is the zona fasciculata, with cells in columns; and the last the zona reticularis. The medullary substance is composed of very irregularly shaped cells, rather closely, but irregularly, packed into a meshwork of fibrous tissue. In the interstices lie masses of multinucleated protoplasm, blood-vessels, and an abundance of nerve-- fibers and cells. The cells of the medulla are conspicuous in that they contain certain reducing agents. The agent which gives color-reactions has been termed chromogen. Just what this agent is chemically is not known, but it is believed to be the principle which raises blood-pressure when suprarenal extracts are injected subcutaneously. The active principle is, according to Abel, epinephrin; according to Takamine, adrenalin. 286 PHYSIOLOGY. Blood-supply. — The blood-vessels of these suprarenal bodies are numerous. Each is supplied by the suprarenal artery from the aorta, together with branches from the contiguous phrenic and renal arteries. When the arteries enter the organ they ramify through the fibrous stroma and terminate in capillaries surrounding the receptacles of the, granular cell-contents. The nerves are chiefly derived from the solar and renal plexuses of the sympathetic system, and are very numerous for the size of the organ. Function. — The function of the suprarenal bodies is still very obscure. The discovery that a relation existed between the bronzing of the skin of Addison's disease and a diseased condition of the supra- renals was a signal-point. It was learned that these small bodies are indispensable to life. The phenomena ensuing, from their extirpa- tion are due to a chemical alteration of the blood, and not to trauma. ^ 6^d'a^4yn,a^^yCy^ ' ,f J 7^ II Fig. 63. — I. Dog. Arrest of Peristalsis by 30 Drops of Adrenalin. II. Dog. Arrest of Peristalsis for a Minute and a Half by 20 Drops of Adrenalin Solution. Read from left to right. The minute curves are cardiac pulsations. The ablation of one capsule is not necessarily mortal, but the destruc- tion of both produces death very quickly. In the rabbit (death follows in nine hours; in the guinea-pig, in three hours. Death is preceded by a considerable weakness, true paralysis of the members and respira- tory muscles, and epileptiform convulsions. If the blood of animals dying from removal of the capsules be transfused into an animal that has just undergone the operation, there is produced a very rapid paralysis and death. Injecting an extract of the capsules into an animal from whom the capsules have been removed slowed the symptoms and prolonged life. Hence, it has been con- cluded that the chief function of the suprarenal capsules is the neu- tralization of a poison analogous to curare. The means by which this is accomplished is a poison-destroying secretion in their cells. The poison to be neutralized is manufactured in the organism and accumu- lates in the blood in instances of lesion or removal of the suprarenals. SECRETION. 287 I have shown that adrenalin, the active prinaiple, arrests peri- stalsis in diastole. This has been confirmed by Prof. Pal, of Vienna. Dr. Pal believes that the arrest of the intestinal peristalsis is due to vasoconstriction by the adrenals, while the after-increase of peristalsis is caused by a return of a full irrigation by the blood. We have, then, two glands, one of which arrests peristalsis — the adrenal; the other, which excites it — ^the spleen. Blum has shown that adrenalin causes glycosuria. Oliver and Schafer found that when extracts of the suprarenals were injected into the circulation very noticeable phenomena resulted. Thus, the arteries become greatly contracted, the blood-pressure rises very rapidly, and the action of the heart is greatly augmented. This vasoconstrictor action is independent of the main, vasomotor center, which I have confirmed. These two observers conclude that the cap- sules secrete a substance to maintain the tonicity of the muscular tis- sues in general and the heart and arteries in particular. Nearly all the adrenalin is destroyed in the body, but I have shown that a minute quantity is excreted by the kidneys. One one- millionth of a gram of the dried gland will elevate the arterial tension. The splanchnics are supposed to contain the secretory nerves of the adrenals. THE THYMUS. The thymus body is a temporary organ which increases in size from the embryo up to two years after birth, and subsequently dwindles away. It occupies the upper part of the anterior mediastinal cavity behind the sternum and extends into the neck frequently to the thyroid gland. It rests upon the pericardium, aorta, and the trachea. It is a flat, triangular body, consisting of a pair of lateral and unequal lobes. It is of a pinkish-cream color, and varies in size and weight not only according to age, but also in different persons. At birth it is about two inches long and one and one-half inches wide at the lower part and two to three lines thick. It is composed of numerous angular lobules mixed with connective tissue. The lobules are subdivided into follicles, and each follicle has a cortex and medulla. In the medulla are spherelike bodies known as the concentric corpuscles of Hassall. Chemical Composition. — The thymus is principally a lymph- gland. Nothing special is Imown of the concentric corpuscles. The presence of extractives, like xanthin, hypoxanthin, leuein, and adenin has been noted. The alkaline reaction of life becomes rapidly acid after death. The acid is sarco-lactie acid. 288 PHYSIOLOGY. The main constituent of the cells is proteid, especially nucleo- proteid. The total percentage in the thymus gland is about 13.29 per cent. When it is desired to produce experimental tntravaseular clotting, the thymus is usually employed as the source for the nucleo- proteid. This property is not characteristic of the thymus, for it is found in all protoplasm. Function. — Extirpation gives few positive results, but chemical investigation shows that the parenchyma of the gland contains a- large number of products that indicate that it possesses very considerable metabolic activity. As long as the thymus gland exists, it seems to take part in the production of white corpuscles like other varieties of lymphatic tissue. Some authors claim for it the production of red corpuscles in early life. Extracts of the thymus, when injected subcutaneously, have been shown by Ott to increase the pulse-rate, with a momentary rise of pressure, followed by a fall. This has been confirmed by Svehla and Swale Vincent. Svehla found that extirpation of the thymus of the frog Jcills it. Swale Vincent, however, did not find that removal of the gland of the frog was necessarily fatal, as his frogs lived thirty- six days after the operation. According to Vincent, extirpation of the gland of guinea-pigs did not affect the animal in any way. PITUITARY BODY. The pituitary body (hypophysis cerebri) is a small, reddish-gray, vascular mass, weighing from five to ten grains. It is oval in shape, situated in the pituitary fossa of the sphenoid bone, and is connected with the end of the infundibulum. The body is retained in position by a process of dura mater derived from the inner wall of the cav- ernous sinus. Structure. — This little pituitary body is very vascular, and con- sists of two lobes, separated from one another by a fibrous stroma. The two lobes differ both in development and structure. The anterior lobe is of a dark yellowish-gray color and resembles in microscopical structure the thyroid body and suprarenal bodies. A canal passes through the anterior lobe to connect it with the infun- dibulum. The posterior lobe is entirely different in that it is developed from an outgrowth from the embryonic brain, and therefore is nervous in its structure. Ablation of this body in the cat produces death in about two weeks. The symptoms resemble very much those that follow thy- SECRETION. 289 roidectomy. Extracts of the infundibular part elevate the arterial tension by a constriction of the arteries and slow the heart. This substance is not soluble in alcohol. Prom a saline decoction of the gland there was obtained an alcoholic precipitate which produced a fall of arterial tension; so that there seems to be two substances in this gland antagonizing each other as regards arterial tension. Dis- ease of this gland produces the condition known as acromegaly, in which the bones of the face and limbs become hypertrophied. It is also connected with giantism. EXTERNAL SECRETION. THE MAMMARY GLANDS. The mammae, or breasts, are accessory organs of the generative system. They secrete the milk. They exist in the male as well as in the female, but only in a rudimentary condition in the former. In the female they are two large, hemispherical eminences situated toward the lateral aspect of the pectoral region. They range between the third and seventh ribs. Before puberty they are of small size, but enlarge as the generative organs become more fully developed. They enlarge during pregnancy, especially after delivery. In old age they become atrophied. The outer surface of the mammae is convex, with just below the center a small, conical eminence: the nipple. The surface of the nipple is dark-colored, and surrounded by an areola of a colored tint. In the virgin the areola is of a delicate, rosy hue; about the second month after impregnation it enlarges and also acquires a darker shade of color. The color deepens as pregnancy advances; in some cases it becomes dark brown or even black. After cessation of lactation there is a diminution in the quantity of pigment, but the original hue is never regained. Change in the color of the areola is of importance in determining an opinion in cases of suspected first pregnancy. The nipple is a conical eminence that is capable of erection from mechanical excitement. This is mainly produced by the contraction of its unstriped, muscular tissue, aided by its numerous blood-vessels. All tend to give it an erectile structure. The nipple is perforated by numerous orifices : the apertures of the lactiferous ducts. On its sur- face are very sensitive papillae. Near the base of the nipple and upon the surface of the areola are numerous sebaceous glands. These be- come enlarged during lactation, their fatty secretion serving as a means of protection during the act of sucking. 290 PHYSIOLOGY. The nipple is made up of areolar tissue interspersed with numerous blood-vessels and plain muscular fibers. The fibers are arranged chiefly in a circular manner around the base, some fibers, however, radiating from the base to the apex. Structure of the Mammae. — The mammae consist of gland-tissue. Like other glands, they are composed of large divisions, or lobes^ which in turn are subdivided into lobules. The lobules and lobes are held together by means of fibrous tissue, while between the lobes are septa. The mammary gland-tissue, in general, when free from fibrous tissue and fat, is of a pale-reddish color, firm in texture, and circular in form. The smallest lobules consist of a cluster of rounded vesicles, which open into the smallest branches of the lactiferous ducts. These small ducts unite to form larger ducts, which later terminate in a single canal. This latter corresponds with one of the chief sub- divisions of the gland. These main excretory ducts, about fifteen or twenty in number, are termed tubuli lactiferi. These present in their course a general convergence tcfward the areola, beneath which they form dilata- tions: ampullcB. These dilatations serve as small reservoirs for the ' milk. During active secretion by the gland the milk collecting in them distends them. Each lactiferous duct is of an average diameter of one seventy-fifth of an inch, expanding into the ampulla, whose average caliber is one-fourth of an inch. At the base of the nipple the am- pullae become contracted again to pursue a straight course to its sum- mit. Each duct pierces the nipple by a separate orifice, whose opening is about one-fiftieth of an inch. The ducts are composed of areolar tissue with elastic fibers and longitudinal muscular fibers. Their mucous lining is continuous at the point of the nipple with the integu- ment. They are lined internally by short columnar, and, near the nipple, by fiattened epithelium. With the exception of the nipple, the general surface of the mamma is covered with fat. The latter is lobulated by sheaths and processes of connective tissue, which bind the skin and the gland together loosely. It is by this same manner that the gland is fastened to the great pectoral muscle beneath it. Blood-vessels, nerves, and lymphatics are plentifully supplied to the mammary glands. The arteries are derived from the thoracic branches of the axillary, the inter costals, and internal mammary. The veins describe, by their frequent anastomoses, a circle around the base of the nipple. This has been called by Haller the circulus venosus. Prom this branches SECRETION. 291 run to the circumference of the gland. The caliber of the contained vessels, as well as the size of the glands, may be increased during preg- nancy and lactation. The lymphatics principally run along the lower border of the pectoralis major muscle to the axillary glands. The nerves are derived from the supraclavicular and the intercostals. No secretory nerves of the mammse exist. Bach gland-acinus, or vesicle, consists of a membrana propria, surrounded externally with a network of branched connective-tissue corpuscles. Internally there is a somewhat flattened polyhedral layer of nucleated secretory cells. The size of the lumen of the acini de- pends upon the secretory activity of the glands; when it is large the vesicle is filled with milk containing numerous refractive, fatty granules. Fig. 64. — Dog's Mammary Gland in First Stage of Secretion. (Heidenhain.) a, 6, Section through the center of two alveoli of the mammary gland, the epithelial cells seen in profile, i!. Surface view of the epithelial cells. In the gland of a woman who is not pregnant or suckling the alveoli are very small and solid. They are filled with a mass of granular, polyhedral cells. During pregnancy the alveoli enlarge while the cells undergo rapid multiplication. With the beginning of lactation the cells in the center of the alveolus undergo fatty degenera- tion and are eliminated in the first milk as colostrum-corpuscles. The lining cells of the alveolus remain to form a single layer of granular, short, columnar cells. Each possesses a spherical nucleus, and is at- tached to the limiting membrana propria. By means of metabolic processes within the protoplasm of the cells the fats, salts, milk-sugar, etc., are formed. During glandular activity, instead of one, two or more nuclei are seen; the well-formed one is near the base, the other nearer the free end of the cell. Near the border of the cell are seen numerous oil-globules and granules. Some of the larger oil-globules are seen projecting from the surface of the cell as if about to be ex- truded from it. 292 PHYSIOLOGY. In addition to this, a division of the cell itself takes place: a parting of the cell-substance with a nucleus in it. The daughter-cell thus cast off passes into the alveolus to form a part of the milk. The secretion of milk is an example of a secretion that is eminently the result of the metabolic activity of the secreting cell. The blood is the original source of the milk, but it becomes milk only by the action of the cells of the mammary gland : a metabolism of those cells. Ottolenghi has found in the active mammary gland of guinea- pigs the presence of "Ninsen's globules," which are due to two causes : first, an increase of the nuclei of the epithelium of the gland; and second, an infiltration of the gland-cells with leucocytes. This theory is opposed to that of Heidenhain, and makes the milk secretion chiefly a disintegration of the nuclei of the epithelium of the gland rather than a breaking up of the protoplasm. Fig. 65. — Mammary Gland of the Dog, Second Stage of Secretion. (Heidenhain.) Ottolenghi also saw in the milk-glands, with islands of active gland-tissue, other islands of a colostrum type — a type of relative rest. Colostrum. — At the beginning of the period of lactation milk has peculiar characters and has received the name of colostrum. This term is applied to the milk appearing during the first week after delivery. Colostrum is acid, possesses a yellow color, which becomes white toward the fourth day. It is viscid and has a mean density of 1.056. It contains, in addition to the fat-globules, colostrum-corpus- cles. These are degenerating polyhedral cells which filled the vesicles previous to lactation. I have found that infusion of dried mammary gland decreases the pulse and increases arterial tension. The blood-pressure rises after removal of the main vasomotor center. Functional Variations in Milk. — A substantial amount of nour- ishment augments the quantity of milk. Drinks have the same effect. An exclusive meat diet augments the proportion of fat in the milk; a small meat allowance in a mixed diet increases casein and diminishes SECRETION. 293 the sugar. A vegetable diet diminishes the total quantity, lowers the amount of casein and butter, but augments the proportion of sugar of milk. A diet rich in fats does not augment the quantity of butter, but if kept up too long it diminishes it. Atropine dries up the milk secretion; antipjTin is said to have a similar effect. Jaborandi in- creases it. Alcohol, frequently given in the shape of porter, increases the secretion of milk. THE SWEAT-GLANDS. The sweat-glands are the organs which furnish the means for the elimination of a large portion of the aqueous and gaseous materials excreted by the skin. They are found in almost every part of the integument, being particularly numerous where hairs are absent, as upon the palms and soles. Krause foimd the smallest number of them (400 for each square inch) upon the back and buttocks; the greatest number (2800 per square inch) on the surface of the palm of the hand and the sole of the foot. By this observer it was calculated that the total number of them is 2,400,000. These glands may be- come hypertrophic (in elephantiasis), thereby producing sudoriparous tumors upon the cheek. Atrophy also occurs. In structure the sweat-glands are small, lobular, reddish bodies. Each one consists of a single, convoluted tube, from which mass the efferent duct proceeds upward through the corium and cuticle. It is somewhat dilated at its extremity and opens upon the surface of the cuticle by an oblique valvelike aperture. The efferent part of the duct in its course through the skin presents a corkscrew arrangement in those places where the epidermis is thick. The convoluted or coiled portion of the tube is the place where secretion takes place, and is usually known as the secretory part of the sweat-apparatus. Here the tube is lined by a single layer of clear, nucleated, cylindrical epithelium. Smooth muscular fibers are ar- ranged longitudinally along the tube in the larger glands. Beyond the muscular coat is the basement-membrane ; so that the duct has a definite outline and exists as an entity that is distinct from the sur- rounding tissues. The distal portion of the tube serves the simple purpose of a conduit for the passage of the sweat-secretion to the skin surface. It contains no muscular fibers or basement-membrane. There is, how- ever, a; distinct lumen surrounded by several layers of cubical cells ; so that by some authorities this portion of the apparatus is considered to be but an opening between epidermal cells. 294 PHYSIOLOGY. Glands which are constantly active, as are the sweat-glands, must necessarily require a very liberal blood-supply. Each coil (the real seat of secretion) is surrounded by a network of capillaries, whose arrangement is such that the secretory cells are easily enabled to ob- tain th6 watery secretion from the blood-stream. Nerves. — A plentiful supply of nerve-fibers in the form of a nerve-plexus ends in the glandular substance. That the secretion of sweat is not a mere filtration that varies according to the blood- pressure, but a process dependent upon a direct action of the nerve upon the gland-cell has been demonstrated by Ott. In experiments upon cats certain changes were produced in the cell-protoplasm by changes in the activity of the nerve. In the cat the sciatic was cut and the animal kept until the fifth day. At this time the pads of the feet were excised, placed in absolute alcohol, and when hard enough were cut into sections, stained with carmine solution, and mounted in glycerin. In another cat the sciatic was exposed and the nerve feebly irri- tated for a period of two and one-half hours, when the pads of the feet were treated in the same manner. Sections of the pads of the feet of each cat were then examined microscopically. It was found that the irritated cells were smaller than the resting cells, that their protoplasmic contents were more granular and more highly tinged with carmine solution, although left in it the same length of time as the resting cell. These facts have been confirmed by Eenaut in the horse's glands. Sweat is the secretory product of the sudoriferous glands. It is discharged in a continuous fashion upon the surface of the skin, there to be gotten rid of as vapor. As long as the secretion is small in amount it is evaporated from the surface at once. Because of this feature it is termed insensible perspiration. The skin is supple, fresh, and without any appreciable humidity. When, however, the secretion of the glands is increased in quan- tity or its evaporation arrested, drops appear upon the skin. These drops of water form what is commonly known as sweat. During this condition the skin is also supple and soft, but is humid. There often, is, in fact, a visible liquid. Sweat is a more or less transparent liquid^ of a salty flavor. It is constantly acid in reaction and has a specific gravity of 1.004. The acidity of the sweat is due to acid sodium phosphate. From its being very readily contaminated it is impossible to obtain sweat in a pure state. SECRETION. 395 WW Fiff.3. Fig. 66. — Section of Sweat-glands of Cat. 1, Section of gland five days after section of sciatic nerve. 2, Gland with sciatic irritated two and a half hours. 3, Sweat-gland in normal condition. 296 PHYSIOLOGY. The relation of the sensible and insensible perspirations varies considerably with the temperature of the air. In round numbers, the total amount of sweat secreted by a man is two pounds in twenty- four hours. The quantity of solid components of sweat is, on the average, 1.0 per cent. It may descend to 0.8 per cent, when there is an increase in the rapidity of the secretion. That means that in profuse perspira- tion it is the water which acquires the predominance. However, no matter what the celerity of the perspiration, there is a minimum of solid components: 0.8 per cent. This remains unchanged, showing that the sweat is a primitive secretion in character. Sweat contains many and different members of the series of fat acids, neutral fats, alkaline sulphates and phosphates, lactic acid, and urea. Horse's sweat contains albumin. The different strength and odor peculiar to the sweat of different animals is due to the variety and abundance of the volatile fatty acids. Of these, acetic, formic, and bTityric prevail in general, with capronic and caprillic. To their prevalence in the armpits and feet is due the corresponding intensity of odor. It has been calculated that about 0.08 per cent, of the sweat is urea. It may be increased greatly in cholera, by reason of its sup- pressed passage through the kidneys. There is often observed a crys- talline deposit of this substance upon the surface of the body in death by cholera. Carbonic acid and traces of nitrogen are found diffused in the sweat and so eliminated from the organism: Perspiration is especially favored by the elevation of the body- temperature; by the wateriness of the blood; by the energetic action of the vessels of the heart; by increase of pressure in the cutaneous vessels, as during muscular exercise, etc. Drugs. — Certain drugs favor sweating. Such are pilocarpine. Calabar bean, strychnine, picrotoxine, muscarine, nicotine, camphor, and the ammonias. Atropine, and morphine in large doses, diminish the secretion. I have foim.d that muscarine and pilocarpine act on the peripheral end of the sudorific nerves. Quinine, iodine, arsenic, and mercury, when introduced into the body, reappear in the sweat. Although the nerves of the sweat-glands are not anatomically separated from others, yet their concurrence in the secretion is evident. In cutting the cervical sympathetic in a horse there is produced uni- lateral sweating (Dupuy) . According to the increased intensity with SECRETION. 397 which the cervical sympathetic is galvanically excited through the skin of man, there follows a lowered or increased perspiration of the corre- sponding side of the face. These facts, together with the known dila- tation of the cutaneous vessels in profuse perspiration, show the influ- ence of the vasomotor nerves. Goltz and others have shown that hy exciting the nerve of a limb the perspiration of it can be increased through the action of sudorific nerve-fibers. The same results have been attained even though the limb has been previously amputated and therefore no longer subject to circulation. It appears that the vasomotor and sudorific nerve-fibers run in the nerves by themselves. Stimulating in man a motor nerve, — such as the tibial, median, or facial, — the part corresponding to the active mtiscles would perspire, even upon the side not excited. The excretion of sweat takes place through vis a tergo, aided by the concurring contraction of the interlaced muscular fibers in the glandular glomerules. Besides, a kind of aspiration is exercised at the mouth of the gland by the evaporation of the liquid which arrives there. It is for this latter reason that air saturated with vapor slack- ' ens perspiration, especially when the other causes of transpiration do not act very strongly. In the normal state the sweat and urine vary in quantity with the season; in the spring the sweat predominates over the urine, in winter the reverse is true. There is an inverse relation between the sweat and intestinal secretions. There is a very noticeable balancing between the sweats and diarrhoea of phthisis. By varnishing the body death is caused. This does not occur by retention of poisonous principles in the blood. There are functional troubles, the most remarkable of which is the cooling of the body. This cooling is due to vasodilation, and is the cause of death. There seems to be a very steady relation between the amount of moisture exhaled from the lungs and the secretion of sweat. It is cal- culated in general that the perspiration is double that of the water from the lungs and, on an average, one sixty-fourth of the weight of the body. Suppression of Sweat by Cold.— All pathologists recognize cold as the cause of many lesions of an inflammatory nature. If this be true, it is produced not by suppression of sweat alone. It is prob- able that there is a transmission of impressions by the skin-nerves to the nerve-centers. These impressions generate, by an obscure patho- genic mechanism, the inflammations of the viscera. 298 PHYSIOLOGY. Role of Sweat-secretions. — The sweat is an important means for the elimination of water and alkalies. It is also of very great use in the excretion of fatty volatile acids introduced into, or formed in, the organism. It is able to supplement the urinary secretion, for the skin is vicarious for the kidneys. It also carries off medicines and poisonous principles. It regulates animal heat, since the evaporation of the water of sweat cools the body. The secretion of sweat is independent of the circulation; however, there exists a relationship between them.- Thus, an abundance of sweat requires a full, free circulation. As the salivary glands need a flow of blood to furnish materials for secretion, so do the sweat-glands. I have shown elsewhere that the sudorific centers are in the spinal cord and that their fibers run in the lateral columns. The sweat-centers are excited by an excess of CO2 in the blood and by over- heated blood. Camphor, acetate of ammonium, and pilocarpine excite sweat by a direct action on the centers. Muscarine excites sweat by a local action; atropine arrests it. Pathological. — Besides the components mentioned, biliary pig- I ment is also found in the sweat of persons having Jaundice; sweat becomes bitter after strong doses of quinine from its appearing in this medium during its elimination from the body. The sweat of diabetes is found to be sweetish, although the presence of glucose in it has not been definitely determined. The red pigmentation some- times found is attributed to the blood-globules, crystals of which were found in the sweat. Hebra saw it succeed menstruation; but it may also occur in serious nervous disease and in yellow fever. In the offensive sweat of feet there is found leucin, tyrosin, baldrianic acid, and ammonia. THE SECRETION OF THE URINE. In a perfectly normal being the problems of waste and repair are balanced to a nicety. This equilibrium owes its maintenance to the proper action of the various glands of the economy, whether secre- tory or excretory. As we know, the tissues of the body are bathed in lymph containing the compounds in solution that are necessary for their nourishment: proteids, carbohydrates, fats, salts, and gases. By reason of the organism exercising its various functions, waste follows in direct proportion to the activity of the tissues. The worn- out and effete materials first find their way into the lymph and from it into the blood-stream, to be later eliminated from the economy, else deleterious results will follow their retention in the body. It is by the SECRETION. 299 selective action of the cells of the various glands of the body that these useless substances are removed from the blood : that is, secreted by them and converted into such form as to be readily removed to the exterior of the organism by excretory processes. In the main, the products to be removed are urea and allied nitrogenous bodies, carbon dioxide, salts, and water. Most of the water, salts, urea, and allied substances are eliminated as components of the urine by those most important organs, the kidneys. These organs are of vital importance, since nearly all of those waste-products containing nitrogen are elim- inated in the urine. The kidneys secrete the urine. Their excretory functions, a mat- ter of everyday observation, represent the extent of their external secretion ; although not yet definitely settled, the consensus of opinion leans toward the kidneys possessing an internal secretion as well. Morphology of the Urinary Apparatus. — The secretory organs of the urine are the kidneys. They, two in number, are compound tubu- lar glands, situated in the back part of the abdomen. The kidneys fje extraperitoneal organs, lying behind the peritoneum and resting upon the lumbar portion of the diaphragm and anterior layer of the lumbar fascia. The upper borders of the kidneys touch a plane that is on a level with the upper border of the twelfth dorsal vertebra ; their lower extremities are on a level with the third lumbar vertebra. The right kidney is usually somewhat lower than the left, probably because of the pressure exerted by the liver, against whose lower surface the kidney rests. In front it is in relation with the liver, the descending portion of the duodenum, and the hepatic flexure of the colon; the left kidney lies ia relation with the fundus of the stomach, the tail of the pancreas, and the descending colon. Superiorly lie the supra- renal bodies. The kidneys are incased in a variable quantity of fat and loose areolar tissue, to which has been given the name perirenal fat. The kidneys are firm organs, of variable color,' between light red and bluish, according to the degree of congestion; each kidney weighs about four and one-half ounces. In shape they resemble a bean, their length being double their vridth ; each kidney is about four inches in length, two inches in width, and one inch in thickness. The internal border of each kidney is concave, the concavity being directed slightly forward and downward. This portion of the kidney is divided by a deep, longitudinal fissure, bounded by a prominent an- terior and posterior lip. The fissure is known as the hilus, and allows of the passage of the vessels, nerves, and ureter to and from the sub- stance of the kidney. Just within the hilus is a dilated fossa known 300 PHYSIOLOGY. as the sinus, which contains the renal artery, vein, and pelvis of the iddney. The relation of the structures passing in and out of the hilus from before backward are : vein in front, artery in the middle, and the duct, or ureter, behind and toward the lower part. By keeping in mind these relations one will be able to distinguish the* right from the left kidney after their removal from the body. Fig. 67. — Relations of the Kidney. (After Sappey.) 1, 1, The two kidneys. 2, 2, Fibrous capsules. 3, Pelvis of the kidney. 4, Ureter. 5, Renal artery. 6, Renal vein. 7, Suprarenal body. 8, 8, Liver raised to show relation of its lower surface to right kidney. 9, Gall-bladder. 10, Terminus of portal vein. 11, Origin of common bile-duct. 12, Spleen turned outward to show relations with left kidney. IS, Semicircular pouch on which the lower end of the spleen rests. 14, Abdominal aorta. 15, Vena cava inferior. 16, Left spermatic vein and artery.. 17, Right spermatic vein opening into vena cava inferior. IS, Subperitoneal fibrous layer or fascia propria dividing to form renal sheath. 19, Lower end of quadratus lumborum muscle. In the funnel-shaped cavity of the renal pelvis is the ureter. From the kidney it passes over the psoas muscle, converging toward that of the opposite side to cross the external iliac artery and vein. It opens obliquely into the base of the urinary bladder. In females the ureter embraces the neck of the uterus. The ureters have an average length of eighteen inches and a lumen which averages that of a goose- quill. Just before piercing the bladder-wall the lumen of the ureter becomes appreciably smaller. SECRETION. 301 The urinary bladder, situated between the symphysis pubis and the rectum in man, between the sjrmphysis and the uterus in woman, is held in position by the urachus and lateral ligaments. Its base rests upon the perineum and anterior wall of the rectum in man, upon the anterior wall of the vagina in woman. From the base of the blad- der the urethra takes its origin. The opening for the latter bears such a relation to the entrance into the bladder of the two ureters that there is formed the vesical triangle. The openings for the ureters are about sixty millimeters apart. The capacity of the bladder varies with its extensibility, so that it is possible for the viscus to be so distended that its upper border may reach the umbilicus or even the epigastric region. Ordinarily the capacity in both sexes is about a pint. The bladder receives its Mood-supply from the branches of the anterior trunk of the internal iliac. The lymphatic vessels communi- cate with the lumbar ganglia. The nerves are derived from the sympathetic, the sacral, and probably some fibers from the pneumo- gastric also. General Structure of the Kidney. — Beneath the perirenal fat lies the proper tunic, or covering, of the kidney, commonly called the capsule. In health it is a smooth, thin, but tough, fibrous covering, closely adherent to the organ, but from which it can be readily stripped. By reason of this separation, however, fine connective-tissue processes and minute blood-vessels are torn which have served as a means of attachment for the capsule. The denuded kidney presents a smooth, even surface of a deep-red color. For a proper naked-eye study of the kidney the organ must be divided longitudinally from the hilus to its outer border, and the fat and areolar tissue must be removed from the vessels and ureter. It will at once be seen that the kidney is composed of a cavity, somewhat centrally located, and the parenchyma of the organ, nearly surrounding the central cavity. This compartment, as before stated, is termed the sinu^, and is lined by a continuation of the fibrous covering of the kidney. It is through the hilus that this fibrous covering passes, as do the renal vessels and ureter. i The ureter, upon entering the sinus, is expanded into a funnel- shaped sac, the pelvis. The pelvis soon divides into several branches of smaller size, and these immediately subdivide into from eight to twelve infundibula, or calyces, from their resemblance to cups. Into each calyx there projects the point or extremity of a renal pyramid. 302 PHYSIOLOGY. The blood-vessels lie within the sinus, between its wall and the exterior of the pelvis, before subdividing and entering the parenchyma of the organ. The parenchyma is seen to be composed of two portions, an external, investing cortical portion, and an inner, medullary, or pyram- idal portion. Fig. 68.— Section of Kidney. (Landois.) 1, Cortex. 1', Medullary rays. 1", Labyrinth. 3, Medulla. 2', Papillary portion of medulla. 2", Boundary layer of medulla. 4, Fat of renal sinus 5, Artery. A, Branch of renal artery. TJ, Ureter. C, Renal calyx. The cortex is light brown in color, granular, and very friable. The granular aspect is due to the presence of Malpighian corpuscles, which are separated at regular distances by medullary rays, or striae, which give to the cortex a radiate appearance. The boundary zone is darker, and also striated from blood-vessels and uriniferous tubules. It is through this portion that arteries and nerves enter and veins and lymphatics pass from the kidney. SECRETION. 303 The medulla is composed of from eight to twelve pyramids, or cones, of pale-red, striated tissue, known as the pyramids of Malpighi; Fig. 69. — ^Diagram of the Course of Two Uriniferous Tubules. (Landois.) 1, Malpighian tutt surrounded by Bowman's capsule. 2, Constriction on neck. 3, Proximal convoluted tubule. 4, Spiral tubule. 5, Descending limb of Henle's loop-tube. 6, Henle's loop. 9, Wavy part of ascending limb. 10, Irregular tubule. 11. Distal convoluted tubule. 12, First part of collecting tube. 13, Straight part of collecting tube. A, Cortex. B, Boundary zone. V, Papillary zone. their number depends upon the number of lobes composing the organ during the foetal state. It is the apices of these cones which dip down into the calyces of the pelvis. 304 PHYSIOLOGY. Minute Anatomy.^— The kidneys consist of numerous tubular glands intimately united together. The tubes, known as tubuli uri- niferi, take their origin in the labyrinth of the cortex as distinct globular dilatations, each of which is known as Bowman's capsule. The capsule surrounds a small, red, spherical body known as the glomerulus, or Malpighian corpuscle, after Malpighi, its discoverer. The capsule, about one one-hundredth of an inch in diameter, is con- stricted at its neck to form a tube. Beyond this constriction the tube pursues a very convoluted course through a considerable extent of the cortical area, as the tubulus contortus, which is about one six- Mr r Fig. 70. (Landois.) II. Bowman's capsule and glomerulus, a, Vas afferens. e, Vas effereng. Ti, Endothelium of the capsule, c, Capillary network of the cortex, ft. Origin of a convoluted tubule. III. " Redded cells " from a convoluted tubule. 2, Seen from the side, with g, inner granular zone. 1, Seen from the surface. IV. Cells lining Henle's looped ti^bule. V. Cells of a collecting tube. VI. Section of an excretory tube. hundredth of an inch in diameter. Soon the convolutions disappear to give place to a more or less spiral tube as it approaches the medulla : spiral tuie of Schachowa. At the boundary-line between cortex and medulla the tube be- comes suddenly smaller and is now perfectly straight, forming the descending limb of Henle's loop, dipping down for a considerable distance into the pyramid. By the sudden changing of its course backward, but still parallel with its original course, there is formed the loop of Henle, which, continued upward to the cortex, constitutes the ascending limb of Henle's loop. Ascending into the cortex it be- SECRETION. 305 comes dilated, irregular, and angular, — zigzag, — ^which ends in the distal convoluted tube, finally to terminate in a short curved tube, which empties into the straight, or collecting, tube. The collecting tubes, as they run toward the medulla of the kid- ney, unite with other distal convoluted tubules. They also unite at acute angles with adjacent collecting tubes finally to pass to the papillae. The loops of Henle and the collecting tubes constitute the tubuli recti. Each uxiniferous tubule is thus completely isolated as far as the junction of the distal contorted tubes with the collect- iug tube. A portion of the loops of Henle and the upper part of the collect- ing tubes form the little cones in the cortex, visible to the eye and known as the pyramids of Ferrein. The Malpighian corpuscle consists of a spherical plexus or knot of blood-vessels, the glomerulus, which is inclosed in the dilated end of the urinary tubule, known as the capsule of Bowman. As the capsule has been infolded by the glomerulus being pushed into it (as one would iafold the end of the finger of a glove by the tip of one's finger), it follows that the capsule consists of two layers. The internal one, covering the glomerulus closely, is formed of cubical cells, while the external one, formed of flat, polygonal cells, passes on into the neck and thence forms the wall of the convoluted tubule. The cells in this portion of the tube are shaped like a cone, the narrow end be- ing directed toward the lumen of the vessel; owing to the fine, longi- tudinal lines upon each cell, it has a rodlike appearance : rodded cell. The Blood-vessels. — The reaal artery divides at the hilus into four or five branches. The four or five main branches continue to divide and subdivide and so pass into the parenchyma of the organ. They course between the papillas to run up to the boundary between the medulla and cortex. Here the vessels bend at right angles to form a series of loops or arches, their convexity toward the cortex of the kidney. From the convex sides of the arches there spring ves- sels at regular intervals termed interlobular, or radiate, arteries. They sometimes run up so as to divide the cortex into small lobules, coursing singly between each two medullary rays. These radiate arteries give off numerous small branches which run at right angles, each one enter- ing a Malpighian corpuscle. It is usual for the point of entrance of the artery to be diametrically opposite the point of origiu of the urinary tubule. These last-named vessels, the vasa efferentia, break up into very fine vessels within the capsule to constitute the glomerulus. They are supported by connective tissue, and form a veritable tuft of 306 PHYSIOLOGY. capillary vessels. It is of interest to note that each glomerulus is covered by a single layer of flat, nucleated, epithelial cells, these even dipping down between the capillaries. s Fig. 71. — Blood-vessels and Urmiferous Tubules of the Kidney (Semidiagrammatic). (Landois.) A, CapiUaries of the cortex. B, Of medulla, a. Interlobular artery. 1, Vas afferens. 2, Vas eflerens. r, e, Vasa recta, c. Venae rectae. ■», v, Inter- lobular vein. », i. Bowman's capsule and glomerulus, m, a;. Convoluted tubules, t, t, Henle's loop. 0, 0, Collecting tubes. O, Excretory tube. SECRETION. 307 From the center of the glomerulus there proceeds a vessel that is somewhat smaller than the afferent vessel, known as the efferent vessel; it is a vein, and leaves the capsule very close to the point of entrance of the vas afferens. The efferent vessel also divides to form a secondary capillary network, the renal portal system, with elongated meshes in the situa- tion of the pyramids of Ferrein ; from this plexus arise the interlobular veins which run parallel to the interlobular arteries. Fig. 72. — Longitudinal Section of a Malpighian Pyramid. (Landois.) . h, Oortex. i, Boundary or marginal zone, fc, Papillary zone. PF, Pyra- mids of Ferrein. RA, Branch of renal artery. RV, Lumen of renal vein receiving an interlobular vein. VR, Vasa recta. PA, ^pez of renal papilla. b, b, Embrace the bases of the renal lobules. The medulla of 'the kidney receives its arterial supply from the artericB rectm; these .latter are vessels which spring either from the arterial arches or from the interlobular arteries. According ta some authors, they may be derived from the afferent vessels of the deepest and largest glomeruli. Within the pyramids the arterise rectse divide and subdivide to form a plexus of capillaries which eventually merge into the vence rectce, to empty into the venous trunks at the boundary between the medulla and cortex. 308 PHYSIOLOGY. The renal veins arise from three sources: (1) the venous plexus beneath the capsule, (3) the plexus around the tubuli contorti, and (3) the plexus located near the apices of the pyramids. Within the sinus the larger branches from these plexuses inosculate to form the renal veins, which pass through the hilus to empty into the inferior vena cava. The vasa recta circulation is of prime importance in that it forms a sidestream through which much blood may pass without being compelled to traverse the glomerulus. It is very apparent that this circulation is highly useful in conditions of kidney congestion as a sidestream. Three kinds of capillaries are found within the kidney: (1) glomerular^ (2) efferent capillaries, and (3) capillaries of the vasce rectce. The kidney, for its size, is abundantly supplied with blood. Lymphatics. — The kidneys are richly supplied with lymphatics, occurring as slits. The renal lymphatics terminate in the lumbar lymphatic glands. Nerves. — The nerves of the kidney accompany its blood-vessels, ganglionic plexuses being numerous. They are from the renal plexus, coming originally from the solar plexus. Physical Properties and Chemical Composition of the Urine. The analytical study of the urine is of great value to the physi- cian and surgeon because of the knowledge which it gives concerning the processes of metabolism occurring within the body. The nature and amount of the various end-products of metabolism are carefully investigated as they occur in the urine, whether they be normal or pathological. From these investigations corresponding conclusions are drawn. Neutral substances are, normally, either absent or present in but minutest quantities. All of the important and more abimdant constituents of normal urine are either basic or acid in reaction. These bases and acids must, therefore, enter into various combinations, making the urine a solution of salts. The quantity of separate in- gredients found analytically might lead the observer to consider the metabolic processes as pathological, yet in solution perfectly normal compounds are forpied by these same components. The error is due to the inability to study the properties of the urine as a complex unit : the efEects certain components have on others, their avidity for one another, and the consequent equilibrium established. SECRETION. 309 The Urine. — The normal human urine, recently passed, is a clear liquid of a straw color. It has an average specific gravity of 1.020, is of aromatic odor, and a salty bitter flavor. In reaction it is acid; only in pathological conditions does it become neutral or alkaline. Eeceding from the temperature of about 100° F., which is proper to it in the act of passing, it loses its aromatic odor and acquires a peculiar odor, described as urinous. In healthy persons it has been seen to be phosphorescent during micturition, probably from the liberation of phosphorus by its salts. In cooling, urine becomes tur- bid, with a small cloud suspended in the thickness of the liquid, formed from the epithelium of the uriniferous tubules. It leaves, besides, especially if very much colored, sediments of different appearance, according to the varying composition. The quantity of urine secreted by the kidneys of a healthy adult man in twenty-four hours ranges from 1200 to 1700 cubic centimeters, or about 50 ounces ; in females the quantity is less. During sleep the amount secreted is less than at other times, so that the minimum secre- tion is placed between 2 and 4 a.m. and the maximum from 2 to 4 p.m. While the average daily secretion is placed at 50 ounces, yet it must be borne in mind that this quantity is not fijced, but may be very variable, dependent upon numerous conditions. The amount of urine is diminished by reason of profuse sweating, extensive diarrhoea, thirst, diminution in blood-pressure, after severe haemorrhage, and in some forms of kidney disease. Increase in urinary secretion (polyuria) is produced by an in- crease in blood-pressure, by imbibing excessive draughts of liquids, by any condition whereby the cutaneous blood-supply is diminished (cold will do this). Polyuria is likewise produced by the administration of drugs which i;aise arterial tension, as digitalis and alcohol, and caffeine and sparteine, which stimulate the renal cells. The influence of the nervous system upon the secretion of urine is very clearly demonstrated by cases of hysteria. Hysterical patients void excessive amounts of a very pale, watery urine. The specific gravity, as previously stated, averages 1.030; that is, the mean between 1.015 and 1.020. The specific gravity varies inversely to the quantity excreted. When, for any reason not patho- logical, there is polyuria, the mark drops proportionately, registering as low as 1.002. As a result of profuse sweating and abstinence from liquids, the mark may reach 1.035 in healthy individuals. Acidity. — The acidity of the urine is chiefly due to acid phosphate of sodium. There are two tides in the acidity of the urine. During 310 PHYSIOLOGY. digestion the formation of the hydrochloric acid in the stomach frees certain bases in the blood, which, when excreted, diminish the acid reaction of the urine. This is called the alkaline tide. The acid tide is after a fast, and hence occurs early in the morning. Ordinarily it should be remembered, when taking the specific gravity of urine, that anything below 1.010 should at once excite sus- picion of polyuria, with probably albumin ; when above 1.030, diabetes mellitus or some febrile condition may be present. The urinometer is the instrument used to ascertain the density of any given sample of urine, and is so graduated that, when floating in distilled water, it registers degree, by which is meant 1000. The urine is placed in a tall, cylindrical glass of proper width so that the urinometer will not adhere to its sides. After cessation of the oscillations of the instrument, the observer carefully sights along the surface of the urine to note the number registered. This precaution is taken because the capillarity along the stem of the instrument causes the urine to rise. The urine is composed of water in the average proportion of 96 per cent., and of substances dissolved in it in the proportion of 4 per cent. Among the "substances 'dissolved" in urine we find: urea, uric, hippurie, lactic, and oxalic acids, and ammonia; also creatin, chlorides, sulphates, phosphates, with the bases — potassium, sodium, calcium, and magnesium. Urea (C0[N'H2]2) is the diamide of COj; that is, a carbamide. Urea greatly prevails over the other constituents of the urine, since in normal urine it forms nearly one-half of the solids. Nearly one-half of urea is nitrogen. It is the principal representative of the waste of the nitrogenous tissues. Urea is inodorous, fresh, bitter, neutral, very soluble in water and alcohol, but almost insoluble in ether. It crystallizes quickly into needles; slowly, into quadrangular prisms of the rhombic sys- tem. Urea fuses and decomposes at 248° F., with the development of ammonia. Urea is very rich in nitrogen. The nitrogen that finds its way from the body through the urine as a vehicle amounts to about 15 grams in twenty-four hours. This represents practically all of the nitrogenous waste of the economy, since less than 1 gram finds egress from all other channels taken collectively. The total amount of nitrogen is estimated by the KJeldahl process. Among the combinations with acids and bases of which urea is capable, those with nitric and oxalic acids are important. It is SECRETION. 311 precisely these which are most commonly employed in the extraction of urea. With nitric acid, nitrate of urea is formed, which crystal- lizes in lozenge-shaped crystals. With oxalic acid, nrea forms urea oxalate, and crystallizes into flat or prismatic bodies. Both types of crystals may yery readily be demonstrated by placing drops of urea beneath cover-glasses and allow drops of nitric and oxalic acids, respectively, to flow beneath the cover-glasses. After some little time crystals of the respective types will be seen to form. Besides being free, urea is also found combined in the urine with sodium chloride. Deoomposition of Urea. — When urea is heated, vapors of am- monia are evolved. Urine is also subject to an alkaline fermentation, due to the micrococcus ureae. This generally follows the acid fer- mentation, but may take place without it, in the bladder as well as outside. This fermentation is accomplished by" decomposition of the urea into carbonate of ammonia. By virtue of this the urine is strongly darkened, becomes alkaline, putrescent, and forms a film of bacteria on its surface. Urinals always have an ammoniacal odor. Hypobromite of soda decomposes urea as follows : — CO<^NH^ + 3NaBrO ^ CO, -f N, + 2H,0 -\- 3NaBr Upon this reaction- depends an estimation of the amount of urea present in a sample of urine. The calculation is made in units of nitrogen-gas, which gas rises in small bubbles to be collected and measured. The constituents of urine are not actually formed in the kidney itself, as bile is formed in the liver, but are formed elsewhere. The kidney is simply the place where the constituents are picked out from the blood and eliminated from the body. Muscular exercise has but a slight effect on the amount of urea excreted; this is in striking contrast to the quantity of carbonic acid that accompanies muscular exertion to find exit in the expired air. Muscle-work falls upon the carbon rather than upon the nitrogen of the muscle-substance. Quantity op Ueea. — The quantity of urea excreted daily varies, but may be averaged as 500 grains. According to Tschlenoff, after a meal rich in proteids, which stimulate proteid metabolism, there are two maxima in its excretion. The first takes place at the third or 312 PHYSIOLOGY. fourth hour and the second at the sixth or seventh hour. The urea comes from proteid metabolism, and not from the food. Labor greatly increases the exhalation of carbonic acid, but does not affect to any great' extent the excretion of urea. Formation op Urea. — The chief source of urea is from the metabolism of the muscles. The ingestion of a large amount of pro- teid food stimulates metabolism. Muscles contain in their mass over 70 grams of creatin, while the amoimt of creatin excreted is only about 1 gram. Urine contains about 30 grams of urea and muscles I Kg. 73. — Uric- Acid Crystals with Amorphous Urates. (PuKDY, 0/ter Peyer.) only a trace. But all experiments to prove an actual relation between creatin and urea have been failures. The other alloxuric bodies — xanthin, hypoxanthin, and uric acid — are also to be regarded. They are members of a group of bodies having as their base of formation the so-called purin-ring which con- sists of two urea radicles linked together by a central chain of carbon atoms. They are probably split up iu part into urea. I have already alluded to arginiu as a source of urea. All the proteids are probably split up into bodies which form ammonia. Now, if we give by the mouth ammonia salts we find an increase of urea. Further, if ammonia salts are perfused through the liver we find urea SECRETION. 313 is generated. This and various other facts lead ns to believe that the liver is the chief manufactory of urea. Uric Acid (C5H4N4O3). — This constituent is scarce in human urine, hardly reaching 0.03 per cent, of its component solids. Next to urea, it is the product of excretion richest in nitrogen. It is very preponderant and perhaps altogether the chief excretion in birds, rep- tiles, and insects. Uric acid, or lithic acid, is colorless, inodorous, and insipid; it usually crystallizes in whetstone crystals, which have for a fundamental type the vertical rhombic prism. It is insoluble in alcohol and ether, only very slightly soluble in water. The rhombic crystals are charac- teristic of uric acid. If HCl be added to urine, there will be deposited on the bottom of the vessel after several hours a deposit resembling Cayenne pepper. Uric acid occurs in the urine as acid sodium urate. The HCl de- composes the urates, setting free the acid, which does not crystallize at once, by reason of the presence of phosphates. According to Liebig, it is especially by the phosphates that the acid is dissolved, under the form of urate. Uric acid is dibasic^ so that there are two classes of urates : the normal urates and the acid urates. The amorphous urates are quad- riurates; acid urates are crystalline. Uric acid is trioxy-purin. The purin bases are hypoxanthin, xanthin, adenin, guanin, and uric acid. All these bodies are derived from a substance called purin. The elimination of nitrogen in the urine can be augmented by the food. Thus, nuclein (of which the thymus contains a large amount), coffee, cocoa, and meat (veal and ham especially), cheese, atid beer are rich in purins. The bodies poor in purins are milk, potatoes, white bread, rice, eggs, salads, and cabbage. Formation of the Uric Acid. — Like with urea, the liver also forms uric acid from ammonia and lactic acid. It is a result of pro- teid metabolism, especially of the nuclein of the cells. Large draughts of water, quinine, and common salt diminish the quantity of uric acid. In gout the amount excreted in the urine is small, while it ac- cumulates in the blood and tissues. Uric acid and lithic acid are the same. Lateritious, or brick-dust, sediment in the urine is composed of urates, and is chieily sodium urate. The average daily quantity of uric acid passed in the urine of man might be calculated at about 7 grains. When the quantity is excessive, it very frequently happens that the acid is deposited in the form of urinary calculi and gravel. 314 PHYSIOLOGY. MuEEXiDE Test. — Slowly and gently heat some urine and nitric acid in a porcelain dish to the point of dryness. Decomposition has taken place, the color changing to yellow, and N and COj are given off. After allowing the yellow stain to cool, add a drop of dilute ammonia-water to it, when will be formed with the uric acid a purplish- red color of murexide. On the addition of caustic potash the color becomes a marked blue. Hippuric Acid (CgllgNOg), which is the principal representative of nitrogenized regression in the herbivora, is scarce in human urine. In the latter it appears chiefly after the use of some fruits, such as apples, plums, and grapes. Hippuric acid is the product of the coupling of glyeocin with benzoic acid. It may also be formed in the kidney itself. It is mono- basic, very slightly soluble in cold water and ether, and readily sol- uble in warm water and alcohol. It crystallizes in vertical rhombic prisms, is of a bitterish flavor, and is acid in reaction. When decom- posed by heating with acids and alkalies, or when transformed by ' animal ferments, hippuric acid resolves itself into its components : benzoic acid and glyeocin. Ingested benzoic acid and oil of bitter almonds are eliminated with the urine as hippuric acid. Some of the hippuric acid, at least, is the product of the activity of the secreting cells of the renal tubules, as is demonstrated by per- fusing. If arterial blood containing benzoic acid and glyeocin be forced through the blood-vessels of a freshly excised kidney, hippuric acid will be found in the perfused blood. The food of herbivora seems to be an important factor in the manufacture of hippuric acid. When fed upon grain without the husk, hippuric acid is absent. Crystals of hippuric acid can be readily precipitated from the fresh urine of horses and cows. Lactic Acid is a constant component of the urine. Its quantity is increased when it abounds in the blood from deficiency of oxidation, or from free derivation from the aliments, or from gastric fer- mentations. Oxalic Acid is an inconstant component; it occurs with calcium in the crystalline form of octahedrons. The crystals are insoluble in acetic acid, but are readily dissolved by hydrochloric and nitric acids. The " envelope '"-shaped crystals are very characteristic. Oxalic acid appears to be derived from outside the economy, principally from the ingestion of vegetable foods, such as sorrel, lemons, rhubarb, etc. It may also result from incomplete oxidative processes. SECRETION. 315 Creatinin occurs in the urine in the average daily amount of 0.9 gram. Its sources are believed to be: (1) the creatin of muscles formed by the subtraction of a molecule of water and (3) flesh foods. If creatin be fed to animals it appears as creatinin in the urine; however, if it be injected intravenously it appears in the urine as creatin; so that it is very improbable that the kidneys are concerned in its manufacture. Xanthin, hypoxanthin, leucin and tyrosin, and traces of allantoin are sometimes formed in the urine where they represent nitrogenized bases of albuminoid retrogression. Glycuronic and homogentisinic Fig. 74.— Leucin in Balls; Tyrosin in Sheaves. (Peter.) acids are found in the urine occasionally. Children of first cousins almost invariably have in their urine homogentisinic acid. Coloring Matters of the Urine. — The two main coloring matters of the urine are urochrome and urobilin. Under normal physiological conditions, urine may range from an almost colorless or pale straw- yellow through intermediate shades until reddish brown is reached. The commonest condition is yellow. Pale urine is usually of low density; high-colored, of high density, dependent upon the constituents excreted by the renal epithelium. In addition to the two main color- ing matters may be mentioned uroerytlirin and hcematoporphyrinj 316 PHYSIOLOGY. these four are not the only chromogenic factors in the urine, but are the ones that are best known to us to-day. Urobilin, like bile-pigment, is an iron-free derivative of hsemo- globin. In normal urine it occurs in very small amounts and almost always as a chromogen; only rarely is it found free in physiological urine. In diseases it is commonly increased, especially in the highly colored urines of feverish patients. It gives to the urine a peculiar reddish color. Urobilin is identical with stercobilin. The theory usually ac- cepted concerning its mode of origin is that bile-pigment is converted in the intestines into stertiobilin ; while the major portion of the ster- cobilin leaves the body combined with the fseces, nevertheless some is reabsorbed, and excreted in the urine as urobilin. Some observers state that intestinal micro-organisms can reduce bilirubin to urobilin. Urochrome is regarded as the proper pigment of the urine, giving to this secretion its familiar yellow color. When removed from this medium the urine loses nearly all of its color. It is separable into yellow scales. Urochrome may decompose to produce uromelanin, among other products. The last-named constituent gives a blackish tinge to the urine. UROEEYTHRiisr. — Aqucous solutions of urochrome, when exposed to the air and so oxidized, turn red (uroerythrin). This coloring matter is familiarly known by reason of its association with the acid , sodium urates, which it colors red to form the popularly known "brick- dust" sediment. Normally, it occurs in but small quantities, but by reason of its strong coloring properties is intimately concerned in the coloring of the urine. Three properties are characteristic of uroery- thrin: (1) its remarkable affinity for uric-acid compounds, (2) the ease with which its solutions are decolored by light, and (3) its color-reactions with caustic alkalies and mineral acids. H^MATOPOEPHTRiN cxists in but very small amounts in the urine normally; pathologically and after the ingestion of certain drugs, as sulphonal, it may be greatly increased. Indican, or Indoxyl. — This is another pigment which colors the urine intensely yellow. It is an indigo substance represented by a dense, yellow -brown acid, nauseatingly bitter and very soluble in water, alcohol, and ether. Indican is derived from indol, which is formed in the intestines as a product of putrid decomposition of the pancreo-peptones. It is in direct relation to the quantity of bacterial putrefaction of albumins. Indican is really a conjugated sulphate. SECRETION. 317 Test. — ^When urine is mixed with an equal bulk of strong HCl, indoxyl is liberated from the sulphate. A solution of hypochlorite is now added, drop by drop, when indigo-blue will be formed by oxida- tion of the indoxyl. Upon the addition of chloroform the blue matter is precipitated, forming a layer at the bottom of the liquid. Pathological Pigments. — Blood-pigments. — Blood in the urine (hsematuria) may result from injury or disease anywhere along the urinary tract. In this urine the red blood-corpuscles are found in the deposit. An idea as to the probable source of the hsemorrhage may be gotten by careful analysis. Thus, blood from the kidney is usually small in amount, gives urine a "smoky" appearance, and is well mixed. Large coagula are never found in this urine. In hsemorrhage from the ureter it is common to find long, wormlike coagula. Bladder hsemorrhage is known by its numerous clots and shriveled-up leuco- cytes. If the urine be alkaline, crystals of triple phosphate will likely be found. In hcemoglobinuria, the pigments exist in solution, no corpuscles being found. It is caused by the excretion of hemoglobin by the kidneys when it exists as a free body in the blood-stream. Free hsemoglobin is due to active hsemocytolysis, as injection of foreign blood, severe burns, etc. Bile-pigments in the Ueine. — It is usually in cases of icterus that this condition exists when the urine becomes of a decided yellow color. The pigment usually found is bilirubin. Bile-pigment is readily detected by Gmelin's reaction, performed by gently pouring the urine upon the surface of fuming nitric acid, when a green-colored ring appears. Caeboluria. — In this condition the urine is greenish brown, be- coming darker upon exposure to the air. It occurs either after poison- ing by carbolic acid or when the acid has been administered as a drug. Deug-pigments. — After the administration of certain drugs the urine is sure to be colored differently from normal. Those which do this are rhubarb, hsematoxylin, santonin, and methylene blue. The Inorganic Constituents. — These are derived either from the aliments with which they are introduced into the body or they are formed in the organism by combination with bases of the oxidized sulphur and alimentary phosphorus. They are eliminated with the urine in daily amounts from 16 to 24 grams. To these components belong: chlorine, combined chiefly with sodium; phosphoric acid, uniting with potassa, soda, calcium, and magnesia to form basic, neutral, and acid salts ; sulphuric acid, in part 318 PHYSIOLOGY. combined with alkalies and in part united to iiidol and phenol m the form of aromatic substances (Baumann) . The chlorides and the major portion of the phosphates come from the blood; the sulphates and the remainder of the phosphates come from the activities of metabolism. Chlorides occur in the form of sodic chloride. The average quantity excreted is 180 grains daily. If the chlorides be in excess in the food, not so much is given out in the urine as has been introduced, since part passes off through the skin and rectum, while another part accumulates in the tissues. Some is decomposed to form the HCl of the gastric Juice. Sodium chloride is absent in early stages of pneumonia. Phosphoric Acid. — This acid, combined to form the alkaline and earthy phosphates, appears in the urine in the daily quantity of about 2 grams. The phosphoric acid of the urine is derived princi- pally from the alimentary phosphates. Hence there is an increase of phosphates after a meal composed principally of meat, after muscular and nervous labor. There is pathological increase in diseases of the brain and in osteomalacia; there is diminution in pregnancy by reason of deposition of phosphate within the foetal bones. The Sulphueic Acid is derived from the liberation and oxi- dation of tissue sulphur. Sulphuric acid occurs in the urine in combination with alkalies, principally sodium and potassium. The sulphur introduced into the system medically finds egress mainly in the fseces, as it does not easily pass into the blood. From this it is inferred that the sulphur eliminated is derived especially from the transformation of the tissue-proteids. It runs parallel with urea ex- cretion. The daily quantity of sulphates excreted is 3 grams. Proteid contains 1 per cent, of sulphur and 16 per cent, of nitrogen. The aromatic sulphates form one-tenth of the total sulphates, and arise from bacterial putrefaction within the intestinal canal, in intes- tinal obstruction, typhoid fever, etc. The chief aromatic (ethereal) sulphates are phenol sulphate of potassium and indoxyl sulphate of pgtassium. Carbonic Acid in a state of combination is scarce ia the urine and only increases there after the use of alkaline carbonates and of vegetable acids, which latter are transformed into carbonic acid by oxi- dation. To sum up in an approximate average the very variable propor- tions of the principal, normal constituents of the urine, it may be said SECRETION. 319 that with a mixed diet and moderate bodily movement there are in every 100 cubic centimeters of daily urine: — Water 96.00 grams. Solid components 4.00 " Urea 2.30 " Uric acid 0.03 gram. Sodium chloride 0.80 Phosphoric acid 0.15 " Sulphuric acid 0.20 " Earthy phosphates 0.08 " Ammonia 0.04 " Fermentation of Urine. — We have seen that the reaction of urine is generally acid ; but it can become alkaline, even in the physiological state, from abundant ingestion of alkalies, or of salts with organic acid. The intensity of the acid or alkaline reaction of urine must necessarily vary, not only with the proportion of the components that determine it, but also with the degree of dilution. The acidity of the urine may, however, be further increased by a process of acid fermentation due to bacteria, in the presence, perhaps, of vesical mucus. This fermentation may take place outside of the bladder as well, for we see the acidity of the urine continue to increase from the time of emission. The process of acid fermentation is finally accompanied with development of a mycelium whose spore is smaller than that of torula. It appears that with the initiation of this process the urine absorbs oxygen much more actively (Pasteur). The urine is also subject to an allcaline fermentation due to an enzyme, urease, of the micrococcus ureae. It generally follows the acid fermentation, but may occur without it, in the bladder as well as outside. The urine, after prolonged exposure, especially in a warm atmosphere, has been found to become neutral and then gradually alka- line. This fermentation is accompanied with decomposition of the urea into ammonium carbonate, by which the urine is strongly dark- ened and becomes alkaline and of a strong, putrid, ammoniacal odor. In disease of the urinary apparatus, and especially in vesical inflammation and catarrhs, the process of ammoniacal fermentation is already advanced in the urine at the time of its passage. In this case, epithelial mucus and purulent elements aid in making it turbid. On the basis of the preponderance of one group of combinations over another, they are divided into uric, oxalic, and phosphoric sedi- ments. 320 PHYSIOLOGY. Ueic Sediments. — These, composed of uric acid and the alkaline and earthy urates, increase the acidity of the urine, render it muddy, and impart to it a brick-red color, which is made more intense by exposure to the air. With the microscope the observer recognizes in the sediment the characteristic crystals of uric acid. The precipitation of urates within the bladder is very probably caused by concentration from the absorption of water from the urine. The common belief that holding the urine predisposes to stone is, therefore, justified. Another and more frequent cause of uric sedi- ments in the bladder is the acid fermentation which may occur there Fig. 75. — Crystals of Ammonio-magnesium Phosphate. (After Ultzmann.) 1, Crystals in rosette shape. 2, Crystals in coffln-lid shape. from the presence of mucus, as in vesical catarrh. These are strong predisposing causes to uric calculi. Oxalic Sediments. — These accompany the uric sediments, but there may be a predominance of oxalic acid combined with lime. This sediment is recognized by its crystals of calcium oxalate, the "envelope" crystals. They are insoluble in acetic acid. They are chiefly observed in deficient respiration, in rickets, in epileptiform convulsions, and in convalescence from serious diseases. The crystals are precipitated by neutralizing the acid urine. This explains why uric calculi are often mixed with oxalic sediments. The acid urine, with its uric sediment, readily becomes neutral and alkaliue SECRETION. 321 by reason of purulent catarrh with, therefore, succeeding precipita- tion of the oxalates. Phosphoric Sediments. — The phosphoric sediments consist chiefly of crystallized ammonio-magnesium phosphate, coffin-lid shaped crystals, and of calcium phosphate. • The phosphoric sediments are readily distinguished by the alkaline reaction of the urine and by their insolubility by heat (by which the urates are dissolved), and phosphoric crystals are distinguished from oxalic by their solubility in acetic acid. The phosphoric sediments acquire importance only when they are formed within the bladder, either by purulent products or by excessive retention of urine, as in paralysis. Exceptional or Pathological Components. — Besides the ordinary constituents of the urine, there may at times be found in it exceptional ones of pathological significance. Albumin. — Albumin, and more properly albumin of blood-serum, is an abnormal component of the urine which has great importance for the physician. Its presence in this secretion gives the clinical condition commonly termed albuminuria. Its presence is due to a great number and variety of causes, a few of which are: (1) temporary or lasting increase of pressure of the blood within the renal system, especially in hypersemia from cardiac defect; (2) in exanthemata (scarlatina) and other febrile diseases in general (pneumonitis, typhus, pyaemia) ; (3) inflammation and degeneration of the kidneys, as well as in dis- turbances and inflammation of the brain and in epilepsy; (4) any substance which acts upon the vascular system of the kidneys, as diu- retics, mercurials, and cantharides. The recognition of albumin in the urine requires care, and, above all, it is necessary to remember some of the reactions that occu^ in the urine. If the urine be acid, the albumin accidentally contained there coagulates at temperatures above 70° C, the coagulation first showing as an opacity upon the surface of the liquid. Again, if the urine be alkaline and then subjected to heat, there may result a marked opacity without the presence of albumin, the darkening being caused by precipitation of phosphates. To differ- entiate from phosphates, a few drops of acetic acid are added, which immediately dissolve them. Heller's Nitric-Acid Test. — Albumin is also recognized by means of adding one-fourth of the proper volume of HNOj. The reaction, a ring of white precipitate occurring at the junction of the two liquids, is evident when there is much albumin. If, instead, the quantity 322 PHYSIOLOGY, should be small and the urine concentrated, nitrate of urea will be precipitated, giving an erroneous impression to the observer. If the urine be diluted one-fourth with water, the urea precipitate disappears. A method of measuring the quantity of albumin present in urine is easily accomplished by the method devised by Esbach. The essen- tial principle is precipitation of the albumin by means of Esbach's reagent, which in 1000 cubic centimeters of water contains 10 grams of picric acid and 30 grams of citric acid. This is performed in a test-tube so graduated that the figures represent grams of dried albumin in a liter of urine. It is essential that the reaction be allowed to proceed for twenty-four hours before any readings are taken. Proteoses are detected by the precipitates produced by nitric and salicyl-sulphonic acids clearing up on heating the urine and returning when it is cooled. Sugar. — While it is known that normal urine may contain traces of sugar, attention is required with the sugar that occurs in excess, especially from the disease known as diabetes mellitus. In the first place, diabetic urine is abnormal in amount, even reaching 10 liters a day. It has a high specific gravity, and is of a pale and greenish yellow, so that sugar may be suspected at once; when the increased density is due to urea the urine is intensely red- dish. However, it must be remembered that the nitrogenous excreta are also increased. The sugar present is in the form of dextrose^ or grape-sugar. It is increased with a carbohydrate diet and diminished with one that is nitrogenous. Upon standing, there are developed in diabetic urine torulcB. Fehling's Test. — Results are obtained by the use of Fehling's solution. This is an alkaline solution of copper sulphate to which Eochelle salt has been added. The latter holds the cupric hydrate in solution. The presence of sugar is denoted by the reduction on boil- ing of yellow precipitate of cuprous oxide. Phenylhydrazin Test. — This is, perhaps, the most trustworthy of all the sugar tests. It depends upon the formation of a very charac- teristic body from phenylhydrazin hydrochloride and sodium acetate: phenylglucosazone. The resultant body is found as yellow crystals, for the most part arranged in rosettes and clusters. They are only sparingly soluble in water. The characteristic crystals are readily detected under the microscope. The phenylhydrazin test takes place with glucose, laevulose, and glycuronic acid^ SECRETION. 323 Fermentation Test for Sugar. — With an Einhorn saccharometer tube introduce a definite quantity of urine and a piece of Fleischman's yeast about the size of a pea; then stand in a warm place. Next morning read off the percentage of glucose on the instrument. The fermentation test of glucose excludes glycuronic acid, as it will not ferment. BiLB and Blood in the urine have been previously discussed. Tube-casts. — Cylinders, or casts, of the uriniferous tubules are of prime importance to the physician in his diagnosis of soihe forms .*'v (; Fig. 76. — Crystals of Phenylglucosazone. (Pubdt, after v. Jaksch.) of renal disease. Those which are straight may be said to be casts of the collecting tubes; the more curved and twisted ones are probably from the convoluted tubules. Various kinds of casts, or cylinders, are distinguished. Theory of the Urinary Secretion. The theory of the urinary secretion is summed up by regarding the water (which determines the quantity of the uriae) and its salts as a product of filtration from the renal glomerules ; the dissolved com- ponents (as urea, uric acid, etc.) as products of the special activity of the elements of the epithelium of the contorted tubules. 334 PHYSIOLOGY. That the passage of the water takes place chiefly by filtration is shown by the fact that the quickness of this passage is kept in direct relation with the pressure of the blood in the renal arteries, and the glomerules in particular, from whose vessels the watery element of the urine is chiefly derived. Nevertheless, hydrostatic pressure is not the only factor at work in the glomerules, for their epithelium exerts both a positive and a negative influence: positive in that some of the salts of the urine are here secreted ; negative, in that the serum-albumin of the blood is prevented from passing through. In support of the part that blood-pressure bears to secretion it has been noted that, when the total contents of the vascular apparatus are increased so that blood-pressure also increases, there follows an increased secretion; that increased action of the heart increases the amount of urihe; and that variations in the caliber of the renal artery give proportionate urinary secretions. The diuretics made use of by the physicians owe their efficiency mainly to the foregoing principles. Digitalis increases the quantity of urine by raising the blood-pressure, whereas urea, potassium ni- trate, caffeine, and other drugs act upon the rodded epithelium of the tubuli eontorti. It must not be forgotten that at all times there is glomerular pressure by reason of the vasa efferentia being of smaller lumen than that of the afferentia. Colheim and Eoy, in their experiments with the oncometer, have noted that the curve representing the volume of the kidneys runs parallel with the curve of arterial pressure ; it has smaller oscillations, both respiratory and cardiac. The nervous influences acting upon the renal secretion are vasomotor; existence of the so-called secretory nerves has not yet been definitely demonstrated. Toxicity of the Urine. — After the ablation of the two kidneys the animal dies from urjemia ; that is, there is an accumulation of the urinary products in the blood. The removal of one kidney i^ not necessarily fatal. The urine of daytime is more toxic than at night; it is especially narcotic, while night urine is more convulsivant. A man excretes enough poisonous material by the kidneys in two days to cause death. When there is an excess of urea in the blood, the disease is termed uraemia. The toxic substance is probably not urea, but some other organic body. The usual cause of ursemia is Bright's disease. Uric acid in excess is supposed to be the cause of rheumatism and gout. SECRETION. 335 Influence of the Nerves Upon the Secretion of Urine. — As has been elsewhere stated, the nerves of the kidneys are derived from the renal plexns and are composed of both medullated and nonmedullated fibers with nerve-cells. These are both vasodilator and vasoconstrictor in function. As yet, no true secretory nerves are known, so that it is by the influence of the vasomotor nerves distributed along the course of the renal vessels that variations in the amount of urine secreted occur. Thus, the amount of urine secreted depends upon the pressure of the blood circulating through the capillaries. Frequent and small urinations, under mental apprehension, show a very probable nervous influence upon the excretion of the urine. Polyuria and the peculiar aspect of the urines of hysteria are also known ; whether these peculiarities are dependent upon direct nervous influence upon the secretion is not Icnown. Ludwig believes that the cause lies in the increased pressure in the renal arteries from spastic contraction of other vascular regions. Injury by puncture of the vasomotor center in the floor of the fourth ventricle likewise is followed by polyuria, accompanied by hsematuria and albuminuria. By this experiment it is demonstrated that variations in urinary secretion are, for the most part, very inti- mately concerned with vasomotor innervation. If, while the renal vasomotors are paralyzed, the majority of the vasomotor nerves of the entire body be also paralyzed (as by section of the medulla), there follows a general dilatation of the arterioles and capillaries of the body. This causes such a decided fall in the blood- pressure that the amount of urine secreted is much diminished or entirely absent. However, secretion is not suspended by removal of ,the brain, nor destruction of the spinal cord below the cervical portion, provided that the medulla is intact and with it the respiration and circulation. (Krimer.) Urinary Excretory Apparatus. — After the urine has been secreted by the kidneys, it must needs be carried away from the body, so that the economy may not suffer from resorption of contained toxic prin- ciples, as well as not to interfere with the renal action by equalizing pressure within that organ from damming back of the urine. The excretory apparatus comprises the ureters, bladder, and urethra. The Ueeters are two cylindrical membranous tubes of the diam- eter of a goose-quill and about twelve inches long. They extend from the pelvis of the kidney to the bladder, to which viscus runs the urine 326 PHYSIOLOGY. from the kidneys. The general course of each ureter is downward and inward toward the median line, to empty into the base of the bladder by a constricted, slitlike orifice. The ureter runs for nearly an inch between the muscular and mucous coats of the bladder before it makes its exit upon the inner wall of the organ. Structure. — The ureter is composed of three coats, or layers: serous, or adventitia; muscular j and mixous. The adventitia is continuous with the capsule of the kidney at one end and with the fibrous layer of the bladder at the other. In it are found its larger vessels and nerves. The muscular coat comprises the two usually distinct muscular layers: an external longitudinal; an internal, circular one. The mucous coat, continuous with that of the bladder, lines the ureter. It is composed of stratified epithelial cells. Movement of the Urine. — The urine flows into the tubules by the vis-a-tergo pressure of the blood in the afferent capillaries. This averages from 120 to 140 millimeters of mercury. This force, which is capable of making the urine flow through the tubules, is incapable of forcing the urine through the ureters. By reason of the ureters taking a diagonal course through the vesical wall, the weight of the urine already in the bladder must exert a certain amount of pressure upon this portion of each ureter. To overcome this some auxiliary force must be called into action, which is the peristaltic contraction of the ureters. This movement begins at the kidneys and is trans- mitted (with a speed of from 20 to 30 millimeters per second) down- ward into the bladder. With the completion of each peristaltic move- ment there exudes into the bladder a drop of urine. The movements of the two ureters are not synchronous ; they are reflex, being caused by the presence of urine in the lumen of the ureter. In a case of Dr. W. Easterly Ashton's, where the ureters opened on the abdominal surface, I counted an emission of urine by the ureter every twenty-four seconds. The greater the distension of the lumen of the ureter, the more rapid will the number of peristaltic movements become. Experimentally, peristaltic movements may be aroused by elec- trical or n).echanical excitation ; movements always begin at the point excited and proceed toward both ends. The Ukiitart Bladder. — The bladder is a musculo-membra- nous pouch which serves as a temporary reservoir for the urine. It lies behind the pubis and within the pelvic cavity while the viscus is SECRETION. 327 empty, but when distended protrudes into the hypogastric region, in extreme cases even up to the umbilicus. In the cat, two days after section of the spinal cord above the vesieo-spinal center I found that a pressure of 140 millimeters of water was required to overcome the tonus of the sphincter when a cannula was bound in the urethra. Iffictiixitioii. — When the act of micturition takes place the spinal detrusor center is excited into activity bx the pressure of the urine; the sphincter reflex center is also independently excited by the pressure of the urine, and opens to expel the secretion. The spinal detrusor and spinal sphincter are under the control of a cerebral detrusor center which I have shown to be seated in the locus niger, which is set in activity by the cerebral hemisphere in voluntary micturition. Voluntary micturition is materially aided by the action of the abdominal and respiratory muscles. CHAPTER IX. METABOLISM. The food that has been properly digested within the stomach and intestines is absorbed by the chyle vessels and the small capil- laries by whose union is formed the portal vein. When once in the blood-stream, it circulates with the blood-current, which carries it to all of the various organs and tissues of the body. The absorbed iiutritive products are held in solution within the plasma of the blood. In order to nourish the structures outside of the vessel-walls, the plasma with its contained nourishment is constantly being dia- lyzed through the capillary walls into the spaces between the living cells. By this provision each cell is bathed in a plentiful supply of plasma, from which medium it absorbs its nutriment. The various stages of the nutritive process — viz. : the transudar tion of the nutritive plasma from the blood, the assimilation of parts of this by the tissues under repair, the absorption of the other portion by the lymphatics, and, last, the reabsorption of the final residue together with that of the waste-products of the tissues by the veins — are performed simultaneously and continuously in the living body. With the entire organism in a healthy condition there is a perfect balance of action. Action and use are always followed by a corresponding amount of waste. The machinist must be making repairs to the locomotive or other machine that is in use. So the tissues of the body are con- tinually being destroyed, to pass away as effete matters due to exer- cise and action of the various organs and parts of the economy. Thus, the simple movement of the finger, our very thoughts and reasonings, are productive of waste in the tissues concerned. It is due to the repair by the machinist that the machine is kept in normal running order; likewise it is due to the proper absorption, assimilation, and elimination of foodstuffs taken into our own econ- omies that the body owes its normal function and health. The digested products, having arrived at their destination in the organs and tissues, undergo two kinds of chemical processes in the presence of oxygen and under the peculiar activity of the cells. (328) METABOLISM. 329 The one is anaboUsm, or upbuilding; the other catabolism, or de- struction. These two processes are diametrically opposite to one another, so that by virtue of the one the organism increases in bulk ; by reason of the other its bulk is diminished. By reason of the anabolic processes the nonUving materials of the food are converted into the complex molecules of the living tissues, where they are stored up to form a store of potential energy. At any time the organism is capable of transforming this potential energy into hinetic, which is usually most conspicuous to the observer as heat and motion. By the transformation the complex tissues are broken do^vn into excretory products whose structure is simple. The waste-materials leave the cells to be carried by the lymphatics into the blood-stream, ultimately to reach the exterior of the body as excreta or as compo- nents of some secretions. The two processes, anabolism and catabolism, taken conjointly constitute what is known as metabolism : an exchange of material. Normal metabolism thus requires the ingestion of suitable qual- ity and quantity of food, which must be absorbed, assimilated, and stored within the tissues. In the latter place there must occur the necessary transformation of the food in its now complex form into simpler products of effete nature, evolving, at the same time, those functions and activities which are common to the organism. In short, all of the physiological phenomena demonstrable in the econ- omy are the result, either directly or indirectly, of anabolic or cata- bolic changes. Equilibrium of Metabolism. — By this term is meant that, ordi- narily, just as much foodstuffs are stored up within the tissues as effete matters and excretions find egress from the economy. For the organism to remain normal there must exist a balance between in- come and output. So long as this condition lasts the body maintains its bulk, while at the same time it is capable of performing its neces- sary functions. Should this equilibrium be disturbed, there will occur marked changes dependent upon whether anabolic or catabolic processes are in the ascendancy. Anabolic Processes become visible during (1) the growth of the bo^dy in infancy and adolescence, and (3) during convalescence from a serious and debilitating disease. Catabolic Processes become evident during old age and in the course of malignant diseases. Catabolism is the destruction of tis- sue, from which process result the numerous manifestations of life. 330 PHYSIOLOGY. Catabolism is carried on by means of different chemical forces : — 1. Duplication: that is, the decomposition of an organic sub- stance into two or more products whose sum represents exactly the primitive substance. 2. Dehtdhation. — This is a particular form of duplication in which one of the products is water. 3. Oxidation. — This is the most important part of the chemical processes. By this means the decomposition is accomplished with fixation of oxygen, such as the decomposition of albumin, sugars, and fats. 4. , Synthesis. — This is the combination of two or more sub- stances whereby result a third, new substance. Syntheses are char- acteristic of anabolism, but yet they do occur in ccUdbolism. Thus, with the disintegration of the tissue-elements into benzoic acid and glycocoU there follows hippuric acid; urea is formed from carbonic acid and ammonia. THE AIM OF ALIMENTATION. Alimentation has for its end (1) to furnish materials for catab- olism and (2) to furnish suitable products for anabolism. That is, to replace and rejuvenate the organized substances which are de- stroyed in the former process. To know what are the foods which the body needs, it becomes necessary to study the substances which undergo anabolism and catabolism. It is these substances which must enter into our daily nourishment. These two processes ensue in all of the substances, without any exception, which compose the organism. Hence, all the principles of which the economy is composed are indispensable in food : water, proteids, fat, carbohydrates, and salts. Foods. — Each one of these principles taken in an isolated man- ner is not a complete food, since it is not able to replace its neighbor. Thus, water is as necessary a food as is proteid, but yet neither is a complete food. A food is any product which is capable of being transformed into a proximate principle of the organism, or capable of at least dimin- ishing or preventing the destruction of this principle. Hence, a complete food is the sum of the food-products capable of preserving or augmenting the sum of the proximate principles of which the organism is composed. The fundamental principles which enter into the chemical com- position of the human body — water, proteids, fats, carbohydrates, METABOMSM. 331 and salts — aree in themselves composed of simple elements : 0, Tj., G, S, N, P, CI, K, Xa, Ca, Mg, Pe, silicon, and finorin. Will these simple elements, upon ingestion, become converted into complex principles and so constitute foods ? They will in the case of the plant, for it is able to form a com- plex frame by the aid of simple elements. The plant is a synthetic laboratory of chemistry. But this is not true of the animal organiza- tion. The latter is incapable of anabolism and life except by the aid of complex food-combinations such as have been formed by the plant. Contrary to the plant, the animal is a laboratory of analytical chemistry. The animal can only form by synthesis combinations of a low degree, as water, benzoic acid, and ammonia, which cannot be built up in the animal. But the plant can take H, 0, CO2, and N, and from them make complex and elevated combinations. BALANCE OF NUTRITIVE EXCHANGE. To ascertain the balance of nutritive exchange, a comparison is made between the ingesta and egesta: between the gains and losses. The ingesta consist of food and oxygen; the egesta of various excreta and of the carbon dioxide and water lost by the lungs and skin. When the ingesta equal the egesta and the organism neither gains nor loses weight, there is a complete nutritive equilibrium. A balance of water is made by giving, upon the one side, the quan- tity of water ingested by the foods and drinks ; upon the other, the quantity of water eliminated by the stools, urine, skin, and lungs. As the hydrogen contained in the food is oxidized and transformed into water, it is evident that in a state of equilibrium the quantity of water eliminated will be much greater than that ingested. By comparing the water ingested with the water egested, it is found how much oxygen serves to burn the hydrogen. Definite enough information is obtained regarding the balance of metabolism if the nitrogen and carbon only are determined in the ingesta and egesta. The balance of proteid is made by a comparison of the nitrogen ingested with that egested, for the amount of nitrogen permits us to know the quantity of proteid, since 100 parts of proteid contain 16 parts of nitrogen. The nitrogen eliminated is found in the urine. Nearly all of the proteid that is destroyed is found in the form of urea, uric acid, creatinin, and hippuric acid in the urine. There is also found in the stools proteid which has not been digested or absorbed along the digestive tract. A part of the nitrogen is elimi- 332 PHYSIOLOGY. nated by the desquamation of hairs, nails, and epidermis. But it usually sufEees to determine the amount of nitrogen in the stools and urine. If, in making up the balance, it be found that the ingesta have more than equaled the egesta, it is concluded that there has been an anabolism of nitrogen. On the other hand, should the egesta contain more nitrogen than the ingesta, then there has been a catabolism of proteid. Should the income and output be equal, it is concluded that there is a state of nitrogenous equilibrium. The carbon contained in the foods and organized tissues and which is destroyed by catabolie phenomena is eliminated by the skin and lungs under the form of 00^, by the urine and stools under the form of carbonated organic compounds. From the comparisons of the ingesta and egesta it is ascertained whether there be carbon anab- olism, catabolism, or equilibrium. The proteids, fats, and carbohydrates all contain carbon; so that if there be a gain or loss of carbon it may be from the proteids, fats, and carbohydrates. To arrive at some solution, it becomes necessary to calculate the quantity of nitrogen eliminated. Every hundred parts of proteid contain 53.6 parts of carbon and 16 parts of nitro- gen. If it be known how much proteid be destroyed, nothing is easier than to calculate the quantity of carbon which belongs to it. The remaining carbon that is eliminated must belong to the fats and carbohydrates. All of the carbohydrates ingested, except those stored up as glycogen, are burned up in the metabolism of the tissues and their carbon found in the excreta. Hence, by calculating the quantity of carbon which is found in the ingested carbohydrates, one finds what quantity of carbon eliminated belongs to the decomposition of the carbohydrates. If there be an excess of carbon it must come from the fats, since the latter contain, as a mean, 76.5 per cent, of carbon. By multiplying the surplus of carbon by 1.3, there is found the quantity of fat which is gained or lost. EFFECTS OF STARVATION UPON THE DESTRUCTION OF PROTEID. The influence of starvation upon the catabolism of the proteids has been studied upoij animals and in man. During starvation the organized proteid continues to be destroyed and death ensues more or less quickly. The loss of proteid is greater on the first day, and is in proportion as the food has been rich ia proteid and the animal METABOLISM. 333 has drawn from and stored np a large quantity from the circulation. The more fat that an animal has, the less proteid is destroyed. Dur- ing starvation the body-fat is rapidly diminished. The fat-cells give up their fat, becoming smaller, but yet retaining their envelopes. The reabsorbed fat is thus capable of taking the place of a diet for a considerable length of time. Work. — The researches of many observers have demonstrated that muscular work, however exaggerated it may be, does not influ- ence the destruction of proteids, except to a small extent. Varia- tions of the temperature of the air do not influence the destruction of proteids. Should there be fever, the destruction of proteid and fat increases. METABOLISM. Catabolism varies according to the age and weight of the animal; the younger and lighter the animal, the greater is the relative de- struction of proteid. Peptones and albumoses have about the same caloric and nutri- tive value as the proteids. Most of, if not all, the proteids contain sulphur, and the nueleo-proteids contain phosphorus. An increase of sulphates in the urine indicates proteid metabolism. As agents to spare proteid metabolism, gelatin ranks first, then carbohydrates, and next fats. Gelatin, however, cannot be built up into tissue, nor even into gelatin. Fats. The quantity of fats in healthy persons may vary greatly : from 2.5 to 23 per cent. Fats are encountered in two forms in the organ- ism : (a) as an emulsion in the nutritive fluids ; (h) in drops in small particular cells or in the interior of tissue-cells. While in the emul- sion state the fats are in circulation, in the second state they are at rest. The combustion of fats produces water and COj. Origin of Fats. — Fats are deposited within the body from the fats, proteids, and carbohydrates absorbed in the digestion of food. Proteids may be decomposed to produce fat. Thus, if a lean animal be poisoned by phosphorus, large quantities of fat will be found in its liver. The carbohydrates i6rm one of the principal sources of fat. While muscular exercise has hardly any ipfluenee upon proteid, it is not so with fats. The latter are rapidly used up. Hence, a man who works has need of more fat than one who pursues a seden- tary life. 334 PHYSIOLOGY. Carbohydrates. The carbohydrates are fouiid in small proportion in flesh-foods, as glycogen, and in milk in the form of lactose. By far the greater proportions of carbohydrates are obtained from the vegetable king- dom. In vegetable foods they occur as starches and sugars. An animal that is fed upon carbohydrates exclusively dies of starvation on account of want of proteid. The saving of proteid increases proportionately with the quantity of carbohydrates in- gested. This is an important fact, since the digestive juices are capable of digesting them in large quantities. The fatigue of muscle is slowed by the use of sugar. Dr. Lee gave animals phloridzin for four days, which sweeps the greater part of the carbohydrate material, or glycogen, out of the muscles. Then he irritated the tibialis anticus, and, while it gave 1000 contractions per minute on electrical stimulation normally, after the removal of glycogen by the phloridzin the contractions were only from 300 to 400 per minute. These experiments proved that carbohydrates as- sisted the muscle in its contraction. He made another series of experiments upon the muscles which had their glycogen removed by phloridzin, and then gave 50 grams of dextrose. Then electrical irritations were used on the muscles, which gave 650 contractions per minute. Here the glucose restored the muscle. Water. Among the inorganic compounds, the most important, without exception, is water. It is even more important than proteid and fat, since it forms about three-fifths of the weight of the body. Water has an important function within the organism. When proteid is insufficient, water accumulates in the tissues. Among the poorer classes, whose nourishment is insufficient, infectious diseases flourish, since their nutritive liquids are excellent media for the cultivation of micro-organisms. Excess of water causes an augmentation of urea; hence the success of mineral waters in Bright's disease. This increase of urea is due to the abundant washing out gf the retarded metabolic acts through the kidneys. Salts. There is not any liquid nor any tissue which does not produce an ash upon calcination. The inorganic salts are either in solution METABOLISM. 335 or combined with organic substances^ notably proteid. The combina- tion of the various needful salts with protoplasm, the substratum of life, is of the highest importance. Of the various salts found within the tissues, sodium chloride is the most important. Lime and Magnesia Salts. — The alkaline earths, if in too great quantity, may precipitate to form hepatic calculi. The phosphate of lime forms the greater part of bone. Bone depends upon the salts of lime found in the food. Lime occurs in large amount in milk. The only other food which has the same amount as milk is the yelk of egg. This latter should be given to children when milk is not at hand or not readily digested. Withholding lime is favorable to the production of rickets. Calcium is excreted with the suecus entericus chiefly. Animals from whose food the salts have been extracted very frequently die more rapidly than aniinals from whom food has been entirely withheld. There is caused a train of symptoms indicating a disturbance of the central nervous apparatus and the digestive sys- tem. This untoward result is due to chronic sulphuric-acid poisoning from oxidation of the sulphur of the proteids. Now, the bases in the blood which neutralize are the sodium carbonate and sodium phosphate, and it has been estimated that the amount of this alkaline reacting alkali or native alkali in the entire body is equivalent to 60 grams of sodium hydroxide (NaOH). This amount of alkali is so small that it would be quickly exhausted by a persistent acid intoxication with a persistent formation of only small amounts of acid. Certain diabetic patients pass, daily for long periods a large amount of acids which are excreted by the urine in combina- tion with bases, it being understood that the urine does not contain free acid. As the native alkali of the body is not sufficient to neu- tralize so much acid, it is necessary that there must be another and more enduring source of alkali than the native. For this ammonia is generated by proteid metabolism of the cells and especially of meat. The acids in diabetes are the aceto-acetic and the oxybutyric, which can be detected in the urine. Acetone is also present in the urine of severely diseased diabetics.^ Iron. — Such compounds of iron as are contained in nuclein as found in the yelk of egg have been termed by Bunge hcematogms. In the chick the developing red corpuscles obtain their iron from it. Iron is absorbed through the duodenum and excreted mainly through 'Herter: "Chemical Pathology," 1902. 336 PHYSIOLOGY. the mueoiis membrane of the colon. Inorganic and organic combina- tions of iron are absorbed. Iron is deposited in lymph-ganglia, spleen, and liver. Diet. The diet of a healthy man has for its aim not only to cover any deficit without catabolism ceasing and of maintaining the system in a state of integrity indispensable to its physiological functions, but also to furnish to the organism a certain food-reserve so that the body will not lose its own proper tissue. To ascertain exactly the quantity of nourishment necessary to keep the body-weight the same it is necessary to have recourse to experiments. Example of a Metabolism Investigation. I have selected as an example one given by Beddard.^ It is desired to know whether a diet containing 125 grams of proteid, 50 grams of fat, and 500 grams of carbohydrate is sufficient for a man doing a moderate amount of work. Intake. CARBON. NITROGEN. CALORIES. Proteid ' 62 grams. 200 " 38 " 300 " 20 grams. 00 00 20 grams. 512.5 2050.0 Fat 465 3027.5 Output. CAKBOK. BITROOEN. In urme In faeces . . 11 grams ( 16.5 X. 0.67) 5 " 2.';4 " 16.5 grams. 1.0 gram. In hreatli 270 " 17 5 grams. Ketained in body, 30 grams of carbon and 3.5 grams of nitrogen. This amount of nitrogen represents 2.5 X 6.25 = 15.6 grams proteid, or 75 grams of muscle. Now, this amount of proteid will account for 8.25 grams of carbon; so that 30 — 8.25 = 21.75 grams of carbon •"Practical Physiology." METABOLISM. 337 represents 21.75 X 1-3 = 28.3 grains of fat. On this diet, therefore, the subject retains in his tissues 15.6 grams proteid and 28.3 grams fat per diem. To express this result in terms of energy liberated, we know that 3027.5 calories were supplied, and that all these have been used except 15.6 X 4.1 = 64 retained as proteid and 28.3 X 9-3 == 263.2 retained as fat, or, in toto, 327.2 C. We find, therefore, that 3027.5 — 327.2 = 2700 C. have been required. One gram of fat when burned produces 9.5 Calories. One gram of proteid when burned produces about 4.1 Calories. One gram of carbohydrate when burned produces 4.1 Calories. One gram of alcohol when burned produces 7 Calories. One large Calorie equals 1000 small calories. The large Calorie is written with a capital C ; the small calories with a small c. Obesity is produced by all the causes which slow the organic oxi- dations, as sedentary life, absence of work or locomotion, and insuf- ficiency of air and light. Predisposing causes are heredity, anaemia, and sexual influences. .Development and Growth. When the anabolic and catabolic processes are balanced in adult life, the body remains the same in weight. The progressive development of the body in height is made in an uneven manner, dependent upon different ages. In the first year the growth is about twenty centimeters. From the fourth and fifth years up to puberty there is each year an increase of one twenty-first of the total height. On the contrary, the development in thickness and breadth is slower during the first years than at puberty; toward the fortieth and fiftieth years it attains its maximum. The tissues of the organs may increase in two ways : by increase in volume of existing elements or by the multiplication of new cells. Bones present certain physiological properties of great interest, for they grow in both length and thickness. The increase in length is at each end of the bone at the junction of the epiphysis with the diaphysis. The increase in thickness is made by means of the peri- osteum adding new layers of bone on the surface. CHAPTER X. ANIMAL HEAT. Inorganic bodies have a constant tendency, either by losing or gaining heat, to adapt themselves to the temperature of surrounding media or objects. They may be artificially cooled or artificially heated to all possible degrees. Living plants and animals also receive and give off heat physic- ally; but, in addition, they possess a common power of resisting external temperatures. With plants this power is very feeble in degree ; with animals it is more marked. Among the higher animals, especially, is there an inherent power to maintain a temperature that differs from that of the surrounding media. Since living animals, like dead ones and inorganic bodies, exhibit the same physical plie- nomena of absorption, conduction, and radiation of heat, they un- dergo constant changes; these are usually in the direction of loss of heat. Hence there must exist within them a power of constant renewal or production of heat to take the place of that lost. This function of producing heat is universal with the warm-blooded ani- mals, and all of the processes of life are influenced by it. Certainly the higher animals have within their bodies not only some means to produce heat, but some mechanism whereby the production and loss are regulated. Thus, though the temperature of the surrounding atmosphere be very high, as in midsummer, or very low, as in mid- winter, yet the standard temperature of the animal's body remains uniform and constant. The energy necessary to accomplish this is known as animal heat. Physical Heat. — Heat is a form of energy exhibited by matter. We cannot create or destroy either. Energy is the power to do work. Any agent that is capable of doing work is said to possess this property. The quantity of energy that it possesses is measured by the amount of work it can do. When a body is hot it possesses a store of energy which may be exhibited by the heated matter. Energy is known in two forms: 1. The energy possessed by a body in consequence of its velocity is known as energy of motion^ or Mnetic energy. The body in motion wbich has this kinetic energy communi- (338) ANIMAL HEAT-. 339 cates it to some other body during the process of bringing it to rest. This is the fundamental form of energy. 2. The other form of energy which a body may have depends not upon its own state, but upon its position with respect to other bodies. It is the energy possessed by a mass in consequence of its having been raised from the ground. Potential energy can exist in a body all of whose parts are at rest. Radiant heat is one and the same thing as that which we call light. When detected by the thermometer or by the sensation of heat, it is called radiant heat. When equal weights of quicksilver and water are mixed together, the resulting temperature is not the mean of the temperature of the ingredients, The effect of the same quantity of heat in raising the temperature of two bodies depends not only on the amount of matter in the bodies, but also upon the kind of matter of which each is formed. This is called capacity of heat, or specific heat. The capacity of a body for heat is the number of units required to raise that body one degree of temperature. The specific heat of a body is the ratio of the quantity of heat required to raise that body one degree to the qiiantity required to raise an equal weight of water one degree. Latent heat is the quantity of heat that must be communicated to the body in a given state to convert it into another state without changing the temperature. The higher the temperature of a body, the greater is its radia- tion. When the temperature of bodies is unequal, the hotter bodies will emit more heat by radiation than they receive from the colder. Therefore, on the whole, heat will be lost by hotter and gained by colder bodies until thermal equilibrium is attained. The cause of heat is popularly explained to-day by what is known as the "undulatory theory." According to its doctrines, the heat of a body is caused by an extremely rapid oscillating or vibratory motion of its molecules. The hottest bodies are those in which the vibra- tions have both the greatest velocity and the greatest amplitude. Hence, heat is not a substance, but a condition of matter. It is a condition which can be transferred from one body to another. When a heated body is placed in contact with a cooler one, the former gives more molecular motion than it receives; but the loss of the former is the equivalent of gain of the latter. Animal Heat. — Within the organs of the human body, as well as those of all animals, processes of oxidation are continually going on. 340 PHYSIOLOGY. Oxygen passes through the lungs into the blood to be thus carried to all parts of the body. In like manner the oxidizable bodies, which are principally foods, pass by the processes of digestion into the blood finally to reach every part of the body. The gases, liquids, and solids which enter the body are loaded with energy. These various bodies are intimately concerned in the different chemical processes which sum up metabolism: that is, those phenomena whereby living organisms are capable of incorporating substances obtained from their food into their tissues. Metabolism is also con- cerned in the formation of a store of potential energy which may readily be transformed into kinetic energy, as manifested in muscular work and heat. Within the body the assimilable substances undergo many chemical changes, and finally leave it in forms quite different from those entering it. The oxygen inspired combines mainly with carbon and hydrogen to form carbon anhydride and water, while the more complicated compounds are reduced to simple bodies, to be excreted as such. In the process of disintegrating these compounds — in fact, in catabolism in general — one of the most important re- sults is the production of lieat. The energy enters the body as poten- tial energy stored up in the food. By chemical processes it becomes evolved into kinetic energy and heat. Animal heat is the accompani- ment of the formation of carbonic acid, urea, and other excreted products. According to our theory of heat, the animal heat due to metabolic processes must represent to us vibrations of the corporeal atoms. Other Sources. — Eoughly speaking, the muscles constitute about one-half of the whole mass of the body, the bones the other half. As but little oxidation occurs in the bones, the muscles must be the chief seat of heat production. Muscular exercise greatly increases the metabolism and the CO2 excreted, but there is an accompanying increase in heat production. In health the muscles yield four-fifths of the body-heat. The secreting glands are kno\\Ti to be centers of thermogenesis as well. The alimentary canal during digestion and also the liver are very marked sources. In fact, the blood in the hepatic veins is the warmest part of the body. The function of the muscles, tendons, ligaments, and bones is not a very slight source of warmth. It must be borne in mind by the student that the processes of oxidation are concerned not only in the combustion of the digested foodstuffs, but also of the cells of the body. It is the oxidation of their protoplasm that evolves warmth. ANIMAL HEAT. 341 Warm-blooded and Gold-blooded Animals. — Depending upon the relationship of the temperature of the animal^s body and that of the enveloping media there are two great classes: homothermal and poihiloihermal. The homofhermal, or warm-blooded, animals include the higher orders of the animal kingdom, in whom the temperature remains fairly constant despite variations in temperature of the enveloping media. The temperature of this class of animals is high, but uni- form. Should homothermal animals remain a considerable length of time in a cold medium, their heat-producing organs become more ac- tive in order to compensate for that lost rapidly by radiation. When they remain in very warm media, heat production is diminished. PoiMlothermal, or cold-blooded, animals constitute that class of lower animals whose temperature bears a very intimate relationship and is dependent upon that of the enveloping media. Their tem- perature is thus subject to very considerable variations, although it is always slightly above that of its surroundings. When the tempera- ture of the surrounding medium is raised, the amount of heat pro- duced within poikilothermal animals is increased. Inversely, when the enveloping temperature falls, the heat production within the ani- mal is diminished. This class includes reptiles, amphibians, fish, and most invertebrates. However, the line of demarcation between the two classes of animals is not a very clear and decisive one. For there are some animals, as the bat and dormouse, which seem to be intermediary. In summertime they possess a high temperature that is independent of their surroundings; in winter they become dormant and hibernate. While in this latter condition their temperature varies with that of the enveloping medium. Temperature of Man. — Although the blood in circulation tends to distribute the heat of the body uniformly, yet there are found slight variations in different regions. These regions are principally upon the surface, where exposure is such that the leveling function of the blood is hindered. The mean, daily temperature of a healthy man varies between 98° and 99° F. In the rectum it is 98.96° F.; in the axilla, 98.45° F.; in the mouth, 98.36° F. These figures repre- sent the averages obtained from various observations, but they, too, are subject to many variations from exercise, rapid respiration, food within the alimentary tract, etc. From frequent observations and numerous tables it will be found that the mean rectal "temperature of other mammals is, for the 342 PHYSIOLOGY. most part, higher than that of man. In the case with birds, the temperature averages from two to three degrees higher than that of mammals. In securing these observations it is always necessary that the animal should not struggle either before insertion or during the time that the thermometer is in position. A faulty reading of as much as three degrees may occur when the animal struggles or has been previously chased. Hibernation. — Many animals regularly at the approach of cold weather gradually lose their activities until they apparently have lost all of their functions and are dormant. Such a state is known as hibernation. The temperature of the animal's body is but a trifle above that of the surrounding atmosphere. The respirations are greatly decreased in number, while the rhythm is of the Cheyne- Stokes type. The heart's action in point of force and frequency is much reduced during hibernation. Animals whose hearts during active life beat one hundred or more now register but fourteen or sixteen, per minute. The digestive powers are at a very low ebb, while as to its nervous sensibilities the animal is very markedly depressed. The awakening from hibernation is a most interesting phenom- enon in so far as the rise of the animal's temperature is very sudden. So sudden is the rise and in so short a time is it accomplished that it surpasses the most rapid rise in temperature of any fever. With proportionate celerity are the vital functions spurred on to activity. Modifying Influences. — Close observation shows that there occur slight variations in man's daily temperature. It is found to rise during the late morning and afternoon; to fall during the evening and early morning. Because of differences in age of subjects, modes of living, climate, etc., observers are not agreed as to the maximum and minimum temperatures. However, it may be safe to say that the maximum temperature is attained about from 5 to 5 o'clock in the afternoon, while the minimum is registered at from 5 to 5 o'clock in the morning. The range of difference averages about 1° C. Causes. — Probably the two most important causes for these nor- mal variations are mibscular activity and food-ingestion. It is during the day that man, as a rule, is most active and it is then that he usually replenishes the waste of his body by the consumption of a proper amount of food. Naturally he will be most inactive during the night; his bodily functions will be depressed at that time so that just so much heat will be generated as the economy needs. It has been found that the maximum and minimum points of temperature in man can be inverted. Thus, if a man change his ANIMAL, HEAT. 343 mode of life so that he contimie to worh for a considerable length of time at night and sleep in the daytime, after a week's time there will be noted a gradual change toward inversion. It is well to note also that the high and low points of temperature of the body correspond to those times when the external temperature is high and low, re- spectively. Eadiation may thus be a not inconsiderable factor. Age. — Just before birth the infant's temperature is generally somewhat higher than that of its mother's uterus. After birth and during the first few weeks the temperature remains fairly constant, but still a little high. There is a fall of one-tenth or two-tenths from infancy to puberty; a like amount from the latter period to middle life, when there occurs a slight rise. During muscular work the temperature rises rapidly, but, by reason of compensatory measures, the loss by radiation and con- duction is almost proportionately increased. So nearly are the gen- eration and loss balanced that during actual work there is registered but a rise of a degree and a fraction. With the conclusion of the muscular activity the temperature very rapidly falls to normal. Mental worh causes a rise of both the general as well as local tem- perature of the brain and head. The increase registered is usually about 0.1° C. Food causes a very slight rise in temperature; sleep, in itself, has no effect. Inactivity is a very marked factor in producing a fall. As inaction is very prominent during sleep, the latter has been erro- neously given the credit for causing the drop in temperature. Lying perfectly quiet will produce identical results. Because of the heat, the inhabitants of tropical countries possess a slightly higher tem- perature. The difference is less than 1° C. Extremes of Temperature. — During excessively hot spells in sum- mertime when the temperature of the enveloping atmosphere is con- siderably above that of the normal body-temperature, it is remarkable to iind that the temperature of the body has not been raised one degree. This result is mainly accomplished by reason of the heat extracted from the body's surface during evaporation. The limit of extreme cold is reached when the Ijnnph within the animal's tissues is frozen. Fishes have been incased within ice and then found completely to recover upon being thawed out and placed in a warmer medium. Normally, the range of temperature in a man is about 1° C. However, drunkards have been known, after exposure to extreme cold, to have a body-temperature as low as 24° C. without fatality. 344 PHYSIOLOGY. Cases of temperature as high as 45° C. have been noted and yet recovery has taken place. Experimentally, Bernard found that, when the internal temperature of rabbits was raised to 45° C, they died. According to his view, death occurred as the result of stoppage of the heart from the hot, circulating blood, causing rigor mortis of the musculature of this organ. Temperature of the Blood. — The average temperature of the blood is 39° C, but there are found numerous variations in diiferent regions. The blood of the superficial veins is cooler than that of the internal veins, due to prolonged exposure while traversing the course of the former. The warmest blood of the body is that of the hepatic veins. The blood in the veins is cooler than the blood in the cor- responding arteries, due to the more superficial position of the former. The temperature of the blood of the left heart is some- what lower than that of the right. This has been explained on the ground that the right heart is in closer proximity to the warm liver ; also, that the blood going to the left heart has been cooled from its passage through the lungs during respiration. Estimation of Temperature. — Our knowledge as to difference in d^ree of the heat of the same or different bodies is gained by ther- mometry. Thermometers are instruments for measuring tempera- tures. Their principle is based upon the physical phenomenon of expansion of bodies by heat. Liquids are best suited for this purpose. Mercury and alcohol are the only two liquids used.- The mercurial thermometer is the one most extensively used. It consists of a capillary glass tube, at the end of which is blown the bulb. Both the bulb and a portion of the tube are filled with mer- cury. The expansion of the mercury is registered by a scale, which is graduated either upon the stem itself or upon a frame to which it iS attached. On the Continent, and more especially in Prance, the stem is divided into one hundred parts, or degrees ; this division is known as the Centigrade scale. In England, in Holland, and in ISTorth Amer- ica the Fahrenheit scale is used. Its stem is divided into two hundred and twelve degrees between zero and the boiling-point of water. Estimation of Heat. — Calorimetry is the measure of the quantity of heat which results from the transformation of energy. By it is learned the amount of heat possessed by any body, and what amount of heat the latter is capable of producing. Calorimetric measurements are expressed in thermal units. A certain quantity of heat with which all other quantities are compared is Jcnown as a thermal, or heat, unit. ANIMAL HEAT. 345 A thermal unit is the quantity of heat required to raise a pound of water from one defined temperature to another defined temperature. A particular thermal unit has been called by some authors a Calorie. It is the quantity of heat necessary to raise a kilogram (3.3 pounds) of water 1° C. An English heat unit is the quantity of heat re- quired to elevate one pound of water 1° P. One Calorie equals 3.96 English heat units. In Germany scientists frequently use the word calorie, but mean the gram-calorie. It represents the quantity of heat that is required to elevate the temperature of 1 gram of water 1° C. The whole science of animal heat is founded upon thermometry and calorimetry, as well as the indirect method of caleulating the quantity of heat produced from the quantity of nutritive materials that have been consumed. There are various types of calorimeters Fig. 77. — Human Calorimetei*. in existence, but it has only been within the past few years that re- sults at all exact have been attained. The calorimeter employed by the author in his laboratory ex- periments is constructed as follows: It is composed of two cylinders of galvanized iron — one smaller than the other and inclosed within the larger. The space in which the man lies upon a mattress is six feet long and two feet in diameter. Air is conveyed to him through the tube (H) which traverses the whole length of the apparatus to enter the hollow tube of lead at F; it finally emerges at B, after having given off its heat to the water between the two cylinders. The meter (M) is run by the water-wheel (N), which aspirates the air through the entire apparatus by means of a hose (R) connecting it with the lead tube at B. 346 PHYSIOLOGY. The space between the cylinders is filled with about 484 pounds of water. This water is kept thoroughly mixed by means of the agi- tator (0), which has two arms. The arms are pushing the water back and forth thirty times a minute, the motion being caused by the electrical motor (X), whose wheel (S), with its eccentric, drives the agitator. The thermometer (A) gives the temperature of the water; because of the thorough mixing of the water by the agitator it gives an accurate record of the temperature of the water throughout the apparatus. The thermometer is pushed down farther than is repre- sented in the illustration. It usually lies aside of the tube (H). The air-tube (B) also has a thermometer to denote the temperature of the air as it is heated by the man. The thermometer at B is grad- uated into tenths, while that at A is graduated into fiftieths. The markings are so far apart that one one-hundredth of a degree Fah- renheit can be read. The temperature of the mouth is taken by a thermometer grad- uated into tenths. The rectal temperature is preferable because of accuracy. The bucket (I) receives the water from the motor (X), and so conveys it to the water-wheel (H) that runs the meter as an aspirator. The meter is filled with water, and belongs to Voit's little respiration apparatus. The quantity of air that is aspirated within an hour is from 5000 to 6000 liters, which is ample for respiratory pur- poses. The instrument is made air-tight by means of the door (K), which is lined at its outer edge with rubber. The whole apparatus is inclosed in over six inches of sawdust, the door (K) having against it a sawdust mattress. The door is bound by -eight powerful screw-clamps. The air enters the tube (H), then passes through a leaden tube that is coiled upon itself before it reaches the person lying upon the mattress. I have tested the calorimeter before and after the performance of my experiments. The interior of the instrument is lighted up by an Edison incandescent light of one-candle power. The patient is thus enabled to spend his time in reading a book while the experimenter is making his observations. By placing a pulley outside the calorimeter and attaching to a leather rope a fourteen-pound weight, the man within the instrument is able to exercise. The leather band enters one of the air-holes of the instrument. Of the entire amount of heat dissipated, about IJf per cent, is thrown off by the lungs. My little calorimeter is constructed upon the same plan as the ANIMAL HEAT. " 347 instrument for men. In this — the animal calorimeter — the agitator sits astride the inner cylinder, outside of the leaden coils, and is run at the rate of sixty to seventy movements per minute by means of a water-motor. In other instruments the water is occasionally agitated by means of a hand-contrivance. Instead of the air entering the inner chamber by a straight tube, it traverses a tube coiled upon itself in the water reservoir of the instrument to enter the inclosure at its base. The air emerges through the opening at the top to be carried out through the serpentine coil and thence through the aspirating meter. The latter records at the same time the amount of air. The constant activity of the agitator causes the heat to be equally diffused through the water and so permits none to be given to the air. The door swings upon a hinge. In its center is a glass through which one can readily see the state of the animal or the apparatus connected with it. At its edge it is lined with rubber and closed by powerful iron screw clamps. In front of the door is a mat- tress of sawdust several inches thick. Over and around the calorime- ter, instead of the usual sawdust or felt, I used the packing material of wood-fiber known as excelsior. The whole instrument is inclosed within a box which has a door. The calorimeter is sixteen inches in length and twelve inches in diameter. The instrument has a circular opening through which a thermometer graduated to one-fiftieth of a degree Fahrenheit passes into the water. An opening is also provided in the air-tube . into which a thermometer can be inserted. This instrument is fairly exact. By calculation it is found that the error is 5.4 per cent. After the performance of numerous experi- ments it was found that the variations from this number were within 1 per cent. Hence it may be assumed that this is an instrument of precision. For absolute accuracy the moisture of the air and the barometric correction should be made, but they would not alter the result very perceptibly. The instrument is always used with the air a degree or so above the temperature of the calorimeter. The agi- tator is set in motion for a half-hour before the observation is com- menced. The room temperature for twenty-four hours previously is kept the same. With these precautions the instrument works ac- curately. By the calorimeter we are enabled to measure the transforma- tion of the potential energy of the food into heat and, at the same time, measure the number of heat units produced. The total amount of energy present in the human body might be measured by com- 348 ' PHYSIOLOGY. pletelj"^ burning an entire human body in a calorimeter. By this means it may be determined how many heat units are produced when it is reduced to ashes. If a man were not supplied with food he would lose fifty grams of his body-weight every hour. This is due to the constant oxidation which occurs, whereby the materials of the body unite with the in- spired and circulating oxygen to produce combustion and heat. It is known that any given oxidation will always produce the same amount of heat. Thus, if a gram of fat be burned in a calorim- eter there will be produced a certain and almost unvarying number of heat imits. By numerous experiments upon foodstuffs it has been determined by the calorimeter just the number of heat units a gram of each will yield. Just as in the calorimeter, only far more slowly, are the foodstuffs within our bodies burned up. That is, the presence of oxygen transforms the potential energy within them into kinetic. Should the voluntary activities be at rest, the major portion of this energy is transformed into heat. The same number of heat units would be produced within the body as within the calorimeter, pro- vided the foodstuffs were completely oxidized. However, we know that every gram of proteid yields one-third of a gram of urea during combustion within the body. The urea has a heat value of its own, so that the real number of heat units obtained by body-combustion is considerably less than that of calorimeter combustion of proteids. The. units obtained from body or tissue combustion represent a "physiological heat value"; those gained from the calorimeter, a "physical heat value." Thermotaxic Centers. — These centers compose the thermogenic, thermo-inhibitory, and thermolytic centers, as the aim of all is to regulate the temperature. Thermogenic Centers. — Spinal Cord. — Destruction of the spinal cord from the fifth dorsal vertebra down permits the animal to generate as much heat as before -the operation. A drug, beta- tetrahydronaphthylamin, when injected by the vein causes a great in- crease of temperature, but after a section behind the tuber cinereum it fails to cause any rise of temperature. These facts lead to the conclusion that there are no special thermogenic centers in the spinal cord, but that the basal thermogenic centers act through the trophic centers in the anterior cornua. Brain. — ^When a normal animal is subjected to heat or cold it regulates its temperature and keeps it at a fixed point. If, however, the spinal cord is separated from the brain, the spinal cord is not ANIMAL HEAT. 349 able to regulate the temperature at a given degree, but its tempera- ture changes with the temperature of the surrounding air. ^hese facts also show the importance of the thermotaxic centers in the brain in the regulation of temperature. As to the medulla oblongata and pons, numerous punctures by a probe two millimeters in width and one millimeter in thickness caused a very slight rise of temperature, which was of a very fugitive nature. Cross-section of the pons is an operation which cuts off the afferent and efferent fibers from the thermotaxic centers anterior to it and permits heat-production to increase without any regulation. If there are any thermogenic centers in the pons, puncture ought to bring out the fact, as it has done for the thermogenic centers located in the basal ganglia. x\ny transverse section behind the crura cerebri or pons simply cuts out the thermogenic and thermo-inhibitory centers in front of the section and permits the thermic apparatus behind the section to elevate the temperature. That a greater rise of temperature should ensue after pontal than after crural section is quite in accord with the well-known fact that successive sections from before backward cause a greater activity of the spinal-cord centers behind the section, and also of the trophic centers. Now, I have shown that after the intravenous injection of beta- tetrahydronaphthylamin in the normal animal a great rise of tem- perature ensues. But after section through the crura cerebri this drug is powerless to raise the temperature. A needle-point thrust into the pons or crura causes a fugitive rise, and a feeble one. But if the needle goes into the corpora striata or tuber cinereum there is a quite permanent and considerable elevation of temperature. To as- sume that a different kind of thermogenic center exists in the pons is begging the question. In April, 1884, I was the first to make a transverse section of the corpora striata in the cat, which was followed by the temperature rising to 110 Vj" F. Afterward Drs. Sachs and Aronsohn more exactly localized the center in the caudate nucleus. I also located another thermogenic center in the optic thalami, a bilateral puncture of their anterior ends causing a rapid rise of temperature to 109° F. Von Tangl, of Budapest, has confirmed this fact by experiment upon the brain of a horse. Upon more exact localization this thalamic thermogenic center was found to be located in the tuber cinereum. Hence the conclusion that the thermogenic centers are located in the corpus striatum and tuber cinereum. 330 PHYSIOLOGY. The tuber cinereum is also connected with the vasomotor appa- ratus. In experiments to find vasotonic centers in the thalami I have located them in their anterior part. Later experiments have led to more exact data. After puncture of the tuber with a fine probe a gradual fall of arterial tension ensued. In about forty minutes it amounted to one-fourth the absolute pressure. This fall invariably ensued in six experiments; so that there seemed little doubt that vasotonic centers exist in the thalami. Theemo-inhibitort Cbntees. — Eulenberg and Landois discov- ered about the cruciate sulcus a center whose ablation was followed R.T. loS' 1 06° to s6o 300 340 Minutes, first day. Fig. 78. — Bilateral Puncture of the Tuber Cinereum of Rabbit Through Roof of Mouth. by an increase of temperature. Prof. H. C. Wood has shown that the increase is due to augmented production of heat. I have also shown in the eat that at the juncture of the suprasylvian and post- sylvian fissures is another center whose removal is followed by an increase of temperature. This has been confirmed by White. The increased heat-production after injury to the Sylvian and cruciate centers, the fall to normal, and the subsequent rise in some cases indicate that there is a conflict between these centers and those ANIMAL HEAT. 351 that lie beneath in an effort to gain the mastery. This state of things is seen in the temperature of patients afSicted with fever. Puncture, like fever poison, excites the thermogenic centers. Antipyretics act as sedatives to them and so reduce their excitability. Albumoses, peptones, and neurin have been shown by Ott to pro- duce fever. Dr. W. Hale White reports a case in which a bullet from a pistol caused an injury of the anterior extremity of the middle lobe of the Fig. 79.— Cortex of Cat's Brain. g, Cruciate thermo-inhibitory center of Bulenberg and Landolg. S, Sylvian thermo-inhibitory center of Ott. right hemisphere and also the third frontal convolution, which was followed by a temperature of 104.4° F. in less than twelve hours after the accident. Dr. Page also reported a case of depressed fracture of the skull which was about the posterior part of the temporo-sphenoidal lobe and which was followed by a temperature of 105° ¥. This tempera- ture fell after trephining, and it did not rise again. Pig. 80 shows 353 PHYSIOLOGY. the position of these lesions in man, and they correspond roughly to the position of the cruciate and Sylvian centers in the cat. Theemolttio Centers. — These centers include the cooling appa- ratus of the body: the polypnoeic, the sudorific, and the vasomotor centers. Polypnoea. — Professor Eiehet found that with the elevation of the body-heat of an animal its respirations suddenly increased to 350 or 400 per minute. This form of respiration he termed polypnoea. It was found that the animal did not do this from want of oxygen. An animal pants to cool himself, while a man perspires for the same purpose. The role of polypnoea is exclusively to regulate the tem- perature of the body. Fig. 80. — ^Lesions of Cortex in Man Causing Elevations of Temperature. I have made numerous experiments to determine the exact seat of the polypnoeic center. To establish a center three things are necessary: (1) that its abolition causes the phenomena to disappear, (2) that irritation — mechanical, chemical, or electrical — causes the phenomena to be present, and (3) that the part of the nervous system exhibiting these peculiarities be circumscribed in extent. After nu- merous observations and experiments it was found that pressure upon the tuber cinereum with a pledget of cotton, or even slight puncture, increased the normal respirations to the point of polypnoea. Complete puncture in a normal animal was followed by a rise to 106° F. within two hours, even though the animal were bound down and had been subjected to considerable shock. If now the animal be heated in whom the tuber is punctured, there AKIMAL HEAT. 353 will result no polypnoea, even though a temperature of 107° P. be reached. I am convinced that the tuher cinereum is a center of polyp- noea and thermotaxis. When heat is thrown on the body the polypnoeic center telegraphs the respiratory center to work more rapidly to throw off more moisture by the expired air. The afferent nerves of the thermotaxie apparatus are probably those nerves in the skin administering to the "hot"' and "cold" spots. Regulation of Loss of Heat, or Thermolysis. — Heat is lost by an animal in various ways. It may be by direct radiation and conduction from the skin, by the extraction of heat during the process of evapo- 1 1 \ \ 1 1 1 "Vjm i 1 m.itt \\ nt.at S 1 H 1 1 1 1 1 g s 1 Fig. 81. — Curves of Temperature and Respiration when Cortex is Removed and the Animal is Artifteially Heated. rating perspiration, by warming the respired air, and by the discharge of urine and faeces. Skin Eadiation and Conduction. — The skin is the main means of escape of the bodily heat. Nearly three-fourths of the heat which escapes from the economy does so through the skin as a means. A marked difference between the temperature of the skin and that of the surrounding atmosphere constitutes a prime factor in radiation. When the enveloping mediubi is very cold radiation from the skin's surface is very rapid. The cutaneous circulation has considerable to do with the dissi- pation of heat. The caliber of the peripheral vessels is governed by the vasomotor system, which is itself under the guidance of the central nervous system. 354 PHYSIOLOGY. External heat refiexly causes dilatation of the cutaneous vessels, so that at such times the skin becomes red and engorged. It contains more fluids and thus is a better conductor of heat. More blood being at the body surface allows of greater and more rapid loss through radiation. External cold reflexly causes a contracting of the peripheral ves- sels; so that their lumin a are narrowed. In consequence there is less blood circulating in the skin, which appears pale and contains less fluid; so that the radiation of heat is markedly hindered. By reason of nervous stimulation the sweat-glands are at times made to functionate very freely; whereupon the skin's surface be- fL^m avffi d^ a ffi ^ ? iK i |i ^ \M § ff ■ 1 1 f' i I't \ : t 1 1 i i |i m '" 1 it 1 r i * s iw m //^ppm m 1 1 a FT s T. ^i If i tf m "* i 3 II 1 1 1 \ ti m 1 [ i u l| m f T 'Di \ \ t 'm' f! ^ j ( Its j w \ \ § k t 1 1 i! m V«./>3^^^^ M 11' m ^ s m i^Ki 1 f 1 1 i j, i 1 £Ar#/||! 1 1 mm 1 m m Fig. 82. — Cun'e of Temperature and Respiration when the Tuber Cinereum is Destroyed and the Animal is Artificially Heated. comes bathed in a sensible perspiration. For the conversion of this moisture into vapor heat is necessary. It is by the abstraction of this heat from the underlying tissues that the body owes much of its loss when its parts are hyperpyrexial. The covering pf the body by clothing during the various seasons of the year contributes a great deal to the proper regulation of loss of heat, so that the mean temperature may be maintained fairly constant. Fevbk. — The process of fever is one of absorbing interest during every period of a physician's life. The constant level of temperature in man is accounted for by two theories i One that it is due to changes in heat production ; the other, held by a minority, that it is NOE.nAL li- S S DAY AFTER.. CHllJL Periods. 1 ry^5 560 J B25 rnsoo H475 450 ^425 r400 H G> 375 350 325 300 102 H < 101 3 C 100 ■^I 99 98 ^5 O O m m 0) ^140 2139 I H137 136 110 2ioo r 90 m 80 70 ^ i^fe W^ :i:i#i 4i • tji ffl^' ^B 1 Pni^ ^t iififH^ \^--M^ : Mi? ^1 h4 %! 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T H n^ fl 1: ^ ii '1 ; : ^ ±tt : i ^1 ii^^l mii 'Is lilii3 liliTuIj • Fig. 83. — Heat Production and Heat Dissipation in Man during a Paroxysm of Malarial Fever — a Great Increase of Heat Production. 356 PHYSIOLOGY. kept so by changes in heat dissipation under the varying conditions of external temperatiire. In a case of fever generated by the malarial parasite I found with the human calorimeter an increased production of heat as the primary cause of the fever. In the case of fever generated by the subcutaneous injection of putrid blood I found a fever caused by an increased production of heat in the animal. As a rule, it is true that fever is set u^p by an increase of heat production beyond that of heat dissipation. But when this is once established the fever continues, not from an excessive production, but from an altered relation between heat production and heat dissipation. That the basal thermogenic centers, the corpus striatum and tuber cinereum, play a prominent part in the production of fever is proved by the fact that putrid blood and betatetrahydronaphthylamin both produce a rise of temperature. After a section behind the tuber cinereum they are powerless to elevate the temperature. Antipyrin reduces the temperature by an action upon the cor- pora striata. Experiments in my laboratory by Dr. W. S. Carter proved that while the temperature of the body has a rhythm, there was no rhythm in either heat production or heat dissipation. All recent researches go to show that fever is not a fire that is continuously kept up by an excessive oxidation of the constituents of the human body. For instance, if the amount of water flowing into a vessel partly filled with water is equal to 2, and the amount going out is equal to 2, the level of the water will be the same. But if the amount of water going into the vessel is equal to 3 and the amount going out equal to 2, the level of the water will rise. If, however, the amount going into the vessel should suddenly fall to 1 and the amount going out should do the same, the level of the water would be nearly the same as before. If, now, you substitute for the amoimt of water going in the amount of heat produced, and for the water going out the amount of heat dissipated, and the level of the water as the height of temperature, it is easy to see how a diminished pro- duction and dissipation of heat due to want of food and the waste of the body by the fever process, may still keep up a high fever, al- though both are diminished below what is generated and dissipated in a state of health." Postmortem Temperature.— Usually ati&f death the body cools gradually, depending upon the temperature of the external atmos- ANIMAL HEAT. 357 phere and the body-surface. The body of a child or emaciated sub- ject cools more rapidly than does that of a well-developed and well- nourished adult body. A temporary increase of postmortem temperature is due to the change of myosinogen into myosin and to those series of chemical changes immediately succeeding death. When death has occurred from tetanus, acute rheumatism, ty- phoid, small-pox, cholera, or injuries to the brain, there is noted a marked postmortem rise in temperature. CHAPTER XI. THE MUSCLES. CovEKiNG up the bones and attached to their surfaces at certain definite places is the soft, red, flesh}' portion of the body: the muscular substance. This consists of not one homogeneous environing mass, but a great number of distinct fleshy masses, called muscles. These are of various forms and sizes ; number about four hundred ; and are, for the most part, arranged in pairs. It is mainly to the shape and disposition of these muscles that the body owes the regularity of its contour. It is by the power of these skeletal muscles that the animal U able to move about, procure means of sustenance, care for its young, etc. ; but it must be borne in mind that muscles — not so powerful as are the skeletal muscles, but muscles, nevertheless — are contained within the viscera and blood-vessel walls. These muscles have very important functions to perform in aiding the processes of metab- olism: that balance which when disturbed produces, not health, but disease. Any animal motion means muscle. Muscular tissue is empowered with contractility; that is, an ability to shorten itself when acted upon by any stimulus. By its shortening it produces movement to parts to which one or both of its ends are attached. The resultant motions may be the very common ones of walking, running, various manual employments, etc., or the peristaltic movements of stomach and in- testines, or the variations in the sizes of the lumen of the blood- vessels. Any animal movement should at once recall to the mind of the student that it is the resultant of some muscular contractility produced by the influence of a stimulus to it, whether that be nerv- ous, electrical, mechanical, or thermal. Muscular tissue consists of fibers bound together into those dis- tinct organs already mentioned aS muscles, and in this condition is known as the meat of animals. In the fine anatomy of the muscles I have followed the writings of Professor Shaefer, as appears in Quain's "Anatomy," of which this is an abstract. (358) THE MUSCLEy. 359 Varieties. — When seen under the microscope, these fibers are found to be cross-striped, or striated; as many of them are under the control of the will, they are usually spoken of as being voluntary. In the coats of the blood-vessels and the hollow viscera is another variety of muscular fibers often making a distinct layer or layers to these organs. In this kind the fibers do not have the cross- striped appearance, but are plain, or unstriped. Nearly all of these are not under the control of the will, and are, hence, involuntary. It must here be noted,' however, that the muscle of the heart — ^which, as everyone knows, is an involuntary muscle — is exceptional to this class of muscle in that its fibers are very plainly cross-striped. Never- theless, it presents differences from the striped fibers of skeletal muscles; so that it has become customary with very many authors to class it under the separate title cardiac miiscular tissue. The muscular fibers of the skeleton are generally collected into distinct organs of various sizes and shapes which have at each end a tendon by which they are attached to the skeleton. The fibers of the muscles are collected together into bundles, called fasciculi. In the fasciculi the fibers are parallel, so that the fasciculi wind from one tendinous end to the other, except in a few muscles like the rectus abdominis. In this instance the body of the muscle is interrupted by interposed tendinous tissue. The fas- ciculi themselves do not mingle with one another and, for the most part, run parallel, although in many cases they converge to their tendinous endings. The covering of the entire muscle is termed the epimysium, and is a connective-tissue envelope. The covering of areolar tissue which insheathes the fasciculi of the muscle is spoken of as the perimysium. The latter, a septum from the epimysium, furnishes to each fascicu- lus a special covering as well as furnishing it with blood-vessels and nerves. Within each compartment lie a number of muscle-fibers which are usually parallel to one another and held together by a very delicate reticular connective tissue. This areolar network is called the endomysium, but does not make a continuous covering and so cannot be said to form sheaths for them. Each fiber of the muscle, however, has a tubular sheath, but this sheath is not composed of the areolar tissue just mentioned. The special function of the areolar tissue seems to be to connect the fasciculi and fibers, and to support and conduct the blood-vessels and nerves in their ramifications be- tween the various parts. 360 PHYSIOLOGY. Fasciculi in form are prismatic, so that a transverse section shows an angular, outline. The thickness of a fasciculus, as well as the number of fibers of which it is composed, varies. The texture of a muscle, whether coarse or fine, depends upon the large or small fasciculi contained within it ; thus, the glutei are coarse, the muscles of the eye fine. The length of the fasciculi is not always the same as the length of the muscle ; this characteristic .depends upon the arrangement of the tendons to' which the muscle is attached. When the tendons are attached to the ends of a long muscle, as the sartorius, the fasciculi run from one end of the muscle to the other and so are of consid- erable length. However, a long muscle may be made up of a series of short fasciculi attached obliquely to one another by beveled ends. Short fasciculi thus attached, as in the rectus muscle of the thigh, have stronger action than where they run the extent of the muscle. PiBEES. — The form of the muscle-fibers is cylindrical or prismatic with rounded angles^ Their diameter varies very considerably, even in each muscle, although a certain standard is found to exist in every muscle. The largest human fibers average one-tenth of an inch in diameter, and from that size to one two-hundred-and-fiftieth of an inch fibers may be found. Between the size of the muscle and that of its fibers there is no constant relation. The length of the muscular fibers does not generally exceed one and one-half inches. Thus, in a long fasciculus, the fibers do not reach its whole length, but end in a rounded or tapering end invested with sarcolemma and cohering with neighboring fibers. There is, as a rule, no anastomosis or division of the fibers of a muscle, except in the tongue of a frog, where they branch beneath the mucous mem- brane to which they are attached. The same thing has been observed in the tongue of man. Saecolemma. — The sarcolemma is a tubular sheath inclosing the soft substance of the muscle. It is an elastic, transparent, homoge- neous membrane; it is rather tough and can remain intact even though the muscle be ruptured. Upon its inner side are found nuclei which, however, belong to the muscle rather than to the inclosing membrane. Structure. — With a low magnifying power, the muscle presents clear pellucid fibers which are cross-striped with bands alternately dark and light. That this striation is not on the surface alone, but extends throughout the substance of the muscle, is readily demon- strated by altering the focus of the microscope. The stripes do not THE MUSCLES. 361 Fig. 84. — Histology of Muscular Tissue. (Ellenberger.) 1. Diagram of part of a striped muscular fiber. 8, Sarcolemma. Q, Transverse stripes. F, Fibrillse. K, Muscle nuclei. Ny Nerve-fibers entering it with A., its axis cylinder, and Kilbnes motorial end-plate, E, seen in profile. 2. Transverse section of part of a muscular fiber, showing Cohnheim's areas, C. 3. Isolated muscular fibrillse. 4. Part of an insect's muscle, greatly magnified. A, Krause-Amici's line limiting the muscular cases. B, The doubly refractive substance. C, Hen- sen's disc. D, Singly refractive substance. 5. Fibers cleaving transversely into discs. 6. Muscular fiber from the heart of a frog. 7. Development of a striped muscle from a human foetus at the third month. 8. 9. Muscular fibers of the heart. C, Capillaries. S, Connective tissue corpuscles. 10. Smooth muscular fibers. 11. Transverse section of smooth muscular fibers. 12. Muscular fibers with tendon. 13. Interfibrillary muscular nerves. 363 PHYSIOLOGY. occur on the sarcolemma, but throughout the sarcous substance in- closed by the former. The breadth of the bands is about ^/jtoo'o inch, so that eight or nine dark bands may be counted in ^/looo inch. While this is the common breadth in human 'muscle, yet they are much narrower in different parts; so that there may be twice as many bands existing in the space just mentioned. ' This striation is found in all muscles attached to the skeleton, in the heart, pharynx, upper oesophagus, diaphragm, urethral sphincter, external anal sphincter, as well as in the muscles of the middle ear. When a muscle is deeply focused, the appearance of the striae is somewhat altered; a finely dotted line is seen to pass across the middle of each light band. This is supposed to represent Krause's membrane stretching across the fiber and attached to the surface of the sarcolemma. However, there is reason to believe that the ap- pearance of a dotted line in this position in the fresh fiber is due to the peculiar optical condition of the tissue. A fine, clear line is sometimes seen in the middle of each dark band, and is known as the line, or disc, of Hensen. Since there seems to be such variance as to muscle-structure and so many different names are met with in text-books, it might be well to call the student's attention to the fact that Dobie's line, Amici's line, and Krause's membrane are terras used to describe the same condition. They designate the dark line in the white band. Hen- sen's line occurs in the dark bands. In addition to the cross-striping, the fiber of the muscle has longitudinal striation. When a muscle has been very carefully teased with fine needles after having been previously hardened in spirits, an interesting result follows. The muscle-fibers break up into fine, longitudinal elements of a rounded or angular section and which run from end to end of the fiber. These have been very aptly termed mtiscle-columns, or sarcostyles. Bach sareostyle appears to consist of a row of elongated pris- matic particles with clear "intervals. These particles are termed sarcous elements. The sarcostyles in some muscles are striated longi- tudinally. This appearance has led some authors to believe that they are composed of still finer elements, or fibrils. Under some conditions, the fibers show a tendency to cleave across in a direction parallel to the bands, and even to break up into transverse plates, or discs. The latter are made up by the lateral cohesion of the sarcous elements of adjacent sarcostyles. To the for- THE MUSCLES. 363 mation of such discs, therefore, every sarcostyle furnishes a particle, which coheres with its neighbors on each side, and this with perfect regularity. Sarcoplasm is the intercolumnar substance by which the sarco- styles are united into the muscle-fibers. It is the protoplasm of the muscle-corpuscles, and forms a fine network throughout the whole muscular fiber. From an examination of the aforementioned facts, Bowman was induced to believe that the division of the fiber into fibrils, or sarco- styles, was merely a phenomenon of the same kind as the separation into discs, only a more common occurrence. Coi-inheim's Areas. — If a transverse section be made of a mus- cular fiber, or the surface of a separated disc be examined with a strong objective, there appear in the field small polygonal areas separated by fine lines. In acid preparations they give the appear- ance of a network. These areas represent sections of the muscle- columns, and are usually designated as Cohnlmm's areas. The line between them represents the sarcoplasm, or intercolumnar substance. When a muscle-fiber placed in fresh serum is examined, fine, longitudinal lines are seen running through the cross-striping. If, now, a weak acid is added to swell the muscular substance and render it more transparent, these lines can be traced from end to end of the fiber. By careful management of the microscope, it is found that these lines are really the optical section of the planes of separation between the sarcostyles; that is to say, the optical effect of the sarcoplasm, or intercolumnar substance. The sarcoplasm, in transverse section, pre- sents the aspect of network ; in longitudinal optical section it has the appearance of fine, parallel lines. The student can readily imagine how these effects can be produced by the presence of a small amount of interstitial substance between closely packed prismatic columns. In most muscular fibers the sarcoplaspi exhibits a peculiarity of arrangement which has a very characteristic influence upon the op- tical appearance of the fiber. In a longitudinal view of fresh muscle, the lines representing intercolumnar sarcoplasm present at regular intervals along their course rather marked enlargements. Tliese en- largements lie in the bright cross-strise, either in their middle or near their junction with the dim cross-stripes. These sarcoplasm nodules have the appearance of dots upon fine longitudinal lines which run through the muscle; in the more extended fibers these dots are in double rows. In less extended parts they are thicker and blend together in the middle of the bright striae. 364 PHYSIOLOGY. Structure of the Wing-muscles of Insects. — The study of these muscles has furnished the key to the comprehension of the intimate structure of muscle. As to their structure, the wing-fibers are in complete agreement with ordinary muscles. Wing-fibers occur in large bundles of muscle-cplumns or sarco- styles imbedded in a considerable amount of granular sarcoplasm, while the whole of the structure is inclosed within a sareolemma. The nuclei are scattered here and there. The qiiantity of sarco- plasm in wing-muscle is relatively far greater than in the ordinary muscle. When wing-muscle has been carefully teased into muscle-col- umns, or sarcostyles, it is found that they contract while the sarco- plasm is quiescent. The muscle-columns can then be very carefully studied, when they show, like other muscles, the alternate bright and dark cross-striping. Each bright stria is bisected by a line which.is- the optical section of a transverse membrane: the membrane of Krause. These membranes divide the fibers into a series of seg- ments, called sarcomeres. In a muscle hardened by spirits each sarcomere is seen to contain : (1) in its middle, a strongly refracting, disklike sarcous element; (3) at either end (next the membrane of Krause) a clear interval occu- pied by hyaline substance. With strong lenses the sarcous elements can be made out to be composed of a sarcous substance which stains with logwood; it is pierced by short, tubular canals which extend from the clear interval as far as the middle of the disc. It is these canals which give to the sarcous element its longitudinal striping. If, for any reason, the sarcostyle becomes extended, the sarcous elements tend to separate into two parts with an interval between them; vice versa, if the muscle be contracted or retracted the sarcous elements tend to encroach upon the clear intervals. At the same time the sarcous elements become swollen, so that the sarcomeres are bulged out at their middle and contracted at their ends. Changes in Contraction.- — When these muscles contract, the sar- cous elements become bulged out and shortened, while the fluid of the clear interval becomes relatively diminished in amount. The ends of the sarcomeres are thereby contracted opposite the mem- branes of Krause, so that the sarcostyles become moniliform. This alteration in the shape of the sarcostyle necessarily affects the sarco- plasm which lies in their interstices. It must become squeezed out of the parts which are opposite the bulgings of the sarcostyles and into those parts which are opposite their constrictions. In other words. THE MUSCLES. 365 the sarcoplasm must accumulate in greater quantity opposite the clear bands and the membranes of Krause, and must necessarily diminish in amount opposite the sarcous elements. In the living muscle this change in the position of the sarcoplasm during contraction can be observed; the muscle-columns tend to cause the contracted parts to appear dark, the bulged parts bright, in comparison. Appearance of Muscle under Polarized Light. — Briicke was the first to point out that the fiber is not composed entirely of a double refracting, or anisotropous, substance. In addition there is a cer- tain amount of singly refracting, or isotropous, material. This investigator points out that there is a difference between the ap- pearances presented by living muscle examined ia its own plasma and those of dead and hardened muscle examined in glycerin. In living muscle nearly the entire fiber is doubly refracting, the isotropous substance occurring only as fine transverse lines or as rows of rhom- boidal dots which are united to one another across the anisotropous substance by fine longitudinal lines. Sarcous element is anisotropic ; sarcoplasm is isotropic. Nuclei. — In muscles that are cross-striped are found a number of clear, oval nuclei. They are sometimes spoken of as muscle-cor- puscles. In mammalian muscle they usually lie upon the inner sur- face of the sarcolemma. In the muscles of the frog and reptiles the nuclei lie in the substance of the fiber surrounded by a small amount of protoplasm. When the nuclei lie immediately beneath the sarco- lemma they are more or less flattened. Each nucleus contains one or two nuclei. Mitotic figures, denoting division of the nuclei, have been observed. The nuclei are not very readily seen in fresh muscle, due to their being of the same refractive index as the sarcous sub- stance. Only after they have undergone some spontaneous change or acetic acid has been added to the specimen can they be readily dis- cerned. In the rabbit and rays of fishes some of the voluntary muscles present differences from others, both as to appearance and mode of action. Thus, while most of the voluntary muscles are pale and con- tract forcibly when irritated, the soleus and semitendinosus show different characteristics. They are of deeper color and respond with slow, prolonged contractions when stimulated. Thus, in these ani- mals there are red and white muscles. In other animals, this distinction of muscles is not found as re- gards a whole muscle, but may affect individual fibers. Thus, in the 366 physiology: diai^agm many of the fibers have numerous nuclei imbedded within the protoplasm so as to form an almost continuous layer beneath the sareolemma. Eelation to Tendons. — When a muscle terminates in a tendon, it is found that the muscular fibers either run in the same direction as the fibers of the tendon or join with the tendon at an acute angle. According to Toldt, the delicate connective-tissue elements covering the several miiscular fibers pass from the latter directly into the con- nective-tissue elements of the tendon. According to another author, the ends of the muscular fibers are believed to be fastened to the smooth tendons by means of a special cement. However, it is probable that the areolar tissue which lies between the tendon-fibers passes between the ends of the muscular fibers to be gradually lost in the interstitial connective tissue. Blood-vessels of Muscle. — The blood-vessels to the muscles are very numerous. The average muscle leads such an active life that its nourishment and repair material must be in proportionate rela- tion. Unlike the organs, as the kidney and spleen, >vhich visually are supplied by one artery and vein, muscles receive several branches from various arteries which pierce the muscle at different points along its course. The artery and vein usually are in close proximity, being held in position by the connective tissue upon the perimysium. The capil- laries lie between the muscle-fibers in the endomysium, but outside of the sareolemma. Here the capillaries are small, and form a fine net- work with narrow, oblong meshes, which are stretched out in the direction of the fibers. The capillaries have both longitudinal and transverse vessels. The lymph that is destined to support the sarcous substance must pass through the sareolemma to reach the same. Muscle Nerve-supply. — The nerve-supply to muscles is both motor and sensory. Each muscle-fiber receives a motor nerve-fiber. The trunk of the motor nerve, as a rule, enters the muscle at its geometrical center (Schwalbe) ; thus, the point of entrance in a long, spindle-shaped muscle lies near its middle. At this ''geometrical center" there is the point of least disturbance during contraction of the muscle. After the trunk of the nerve pierces the muscle it proceeds to divide dichotomously until there are Just as many nerve- fibers as muscle-fibers. A nerve-fiber now enters each muscle-fiber, to do which, of course, it must pierce the sareolemma. The point of entrance forms an eminence known as Doyere's eminence, or motorial end-plate. At this point the sheath of the nerve-fiber becomes con- THE MUSCLES. 367 tinuous with the sarcolemma. The eminence itself consists of a mass of protoplasm (sarcoplasm) containing granules and nuclei. Beneath the sarcolemma the original nerve-liber is broken up into a number of divisions, spoken of as nerve-endings. These are divisions of the axis-cylinder which are spread over the sarcous substance without piercing it. To this branched arrangement of the nerve- endings Kiihne gave the name motor spray. The nerve-endings are thus confined to very small areas on the muscle-fibers which have been termed ,by the same author fields of innervation. As a rule, each muscle-fiber has but one such area; it is the exception to find more than one, but as many as eight have been found in very long fibers. Sensory fibers are also found in muscles, for it is through their presence that we obtain muscle sensibility. They seem to be dis- tributed upon the outer surface of the sarcolemma, where there is formed a plexus. This plexus winds around the muscle-fiber. Cardiac Muscle. — Some mention has previously been made con- cerning cardiac muscle, so that at this point only its most striking peculiarities will be mentioned, and that cursorily, (a) It is a striped muscle. However, its striations are not nearly so distinctly marked as are those of voluntary muscle. Occasionally it is seen to be marked longitudinally, (h) Cardiac muscle-fibers possess no sarcolemma. (c) Its fibers branch and anastomose, (d) The nucleus is placed in the center of each cell. One author says that cardiac muscle stands, physiologically, midway between striped and unstriped muscle. When stimulated, its contractions occur slowly, but last for a considerable length of time. Nonstriped Uuscle. — These muscles are made up of a number of contractile fiber-cells of an elongated, fusiform shape, and usually pointed at the end. These fiber-cells may be readily demonstrated by placing the tissue in a strong alkaline solution or a solution of strong nitric acid. Upon transverse section they are generally prismatic, but some- times are more flattened. Their muscle-substance is doubly refract- ing. Bach cell has a nucleus which is either elongated or oval. It may contain one or more nucleoli. The nucleus is brought into view by means of dilute acetic acid or staining reagents. The involuntary fiber-cells have a delicate sheath, which, like the sarcolemma of voluntary muscle-fiber, is very apt to become wrinkled when the fiber is contracted. By reason of this an indis- tinctly striated appearance may be produced. 368 PHYSIOLOGY. While fiber-cells do occur singly, yet it is more common for them to be found in groups. Thus, muscular sheets, or bundles, are pro- duced which may cross one another and interlace, being held in position by enveloping connective tissue. The individual cells are united by the presence of a very delicate cement. The average length of the fiber-cells ranges from Vioo to ^/joo inch ; those forming the middle coat of the arteries are shorter, those Fig. 85. — Unstriped Muscular Tissue. (Ellenbekger.) A and B, Foetal cells. C, B, Fully formed fiber. /, Bundle of fibers. K, Cross-section of bundle of pale muscular fibers. in the intestinal tract and the pregnant uterus are considerably longer. Where Pound. — The unstriped muscular tissue is more generally distributed within the body than one would suppose. It is found in the lower part of the oesophagus, in the stomach, small and large intestines ; in arteries, veins, and lymphatics ; in the ureters, bladder, and urethra; in the internal female generative organs, etc. THE MUSCLES. 369 Blood-supply. — The blood-supply to imstriped muscle is very free, but not nearly so liberal as that to voluntary muscle. Th^erve- supply is from the sympathetic system, and comprises both mediillated and nonmedullated fibers. The fibers form a maia plexus, lying in the connective tissue of the perimysium. From this plexus of fibers there come off numerous fibrils, which traverse the fiber and nucleus. Irritability of Muscle. — Contractility, elasticity, tonicity, and irritability are terms used to designate various properties of muscles. Thus, contractility is the property the muscle possesses of short- eniag and of giving a contraction when it is excited. Elasticity is the general property, common to muscles and many other bodies, of stretching under the infiuence of a weight and of theh returning, more or less perfectly, to the first shape. Tonicity is the state midway between extreme contraction and relaxation. It is a condition depending upon the central nervous system. In addition, muscle possesses a property that is common to all live tissues and which is of fundamental importance in general physiology. It is irritability. By irritability is meant that property of a living element to act according to its nature under the stimulus of an excitant. Paralyses have been observed which have lasted for several months or even several years and, although the nerves were abso- lutely unexcitable, yet the muscles had retained their irritability. This may be readily demonstrated in cases of paralysis of the seventh pair of nerves. The independence of muscle irritability is formally demonstrated by experiment iu which the known action of the drug, curare, upon muscles is taken advantage of. A watery extract of this drug, when injected into the blood of an animal or introduced beneath its skin, acts chiefly upon the motor nerve-endings. It does not, however, affect muscular contractility. Curare is an agent which separates the muscle-element from the nerve-element by a physiological dissection much superior to the coarse anatomical dissections which we could make. When a few milligrams of this drug are injected into the dorsal lymph-sac of a frog, the poison is absorbed within a few minutes. The animal soon ceases to support itself, but lies in any position ia which it may be placed by the experimenter. It is paralyzed, produc- ing neither voluntary nor reflex movements. Now, should the brain be destroyed, the skin removed, and the sciatic nerve stimulated by 370 PHYSIOLOGY. electricity, no movenieiits of the muscles of the limb follow. On the other Aand, should the stimulus be applied directly to the muscles, they immediately contract. Therefore the muscle is irritable by itself. By this it -would seem to be clearly demonstrated that irritability belongs to the muscle, and does not depend upon the nerve-fibers mingled with those of the muscle. In addition to this classical experiment there may be mentioned several other facts which go to corroborate what has been stated concerning irritability : — 1. The chemical excitants of the muscle are not the same as the chemical excitants of the nerves. Thus, glycerin excites the nerve, but has no effect upon the muscle. 2. Isolated muscle-fibers have been seen which, according to microscopical examination, contained no nervous elements and which, notwithstanding, were contractile. 3. If the decreasing progress of irritability be followed after death, in the muscle as well as in the nerve, it will be found that the nerve dies long before the muscle. When the nerves have lost all irritability, the muscle is still alive, and can contract under the infla- ence of excitations directly applied to its tissue. It is at that very moment when the nerves have lost all excitability that the muscle is at its maximum of irritability. Influence of Blood Upon Iebitabilitt. — It has been demon- strated by experiment upon the frog that when the artery of a mem- ber is ligated the muscle contraction is less high and less strong than if the artery had been left intact. Stenon's experiment of ligating the abdomiaal aorta of a dog is worthy of mention. In twenty to thirty minutes after the ligation the dog seems paraplegic. He is unable to stand upon his hind limbs. Eeflex and voluntary movements are completely lost; muscle irrita- tility, however, persists for nearly three hours. When the ligature is removed movement does not return to the limbs at once, but within a very short time the dog is able to stand upon his four feet. Stimuli. — Those extreme forces which bring into play the irrita- bility of the muscle are simply various forms of energy. To them the name stimuli has been applied. By their action the muscle is thrown into a state of excitement whereby the chemical energy of the muscle is transformed into heat and work. These muscle excitants, or stimuli, are of five varieties: (a) nervous, (b) electrical, (c) thermal, (d) mechanical, and (e) chemical. THE MUSCLES. 371 Nekvous Stimuli. — The most important of all the excitatory forces of the muscle is ianervation. In the normal state there is scarcely any other than this to produce muscle contraction. Our mus- cles, as well as those of all other animals, contract because the motor nerve transmits to them the spontaneous or reflex excitation of the nervous centers. The nerve impulses average about ten per second. The stimulus is exactly proportioned to the effect which must be obtained. Electeical Stimuli. — Electricity is employed as a stimulus in preference to any other external agent to bring into play the irrita- bUity of muscle. Thermal Stimuli. — Thermic excitations also provoke muscular movements. The stomach and intestines are viscera whose muscles are very readily excited by heat and cold. They contract very ener- getically when very cold drinks are taken and their temperature sud- denly modified. On the contrary, striated muscles hardly react to thermic excitants. If heat or cold be applied gradually, there is not produced any muscle contraction. Excitants act only when they are applied suddenly. Mechanical Stimuli. — Mechanical excitants that are capable of producing muscular contraction are rather common. Thus, the surgeon, whUe performing an operation, notices slight fibrillary tremblings following each stroke of his scalpel. Chemical Stimuli. — It can be stated as a rule that all the sub- stances which are fatal to the life of the muscle are excitants of the muscle. On this ground, distilled water is an excitant, for when it is injected into the arterial system of a frog its muscles show fibrillary twitchings. Not only does the water excite the muscle, but it also kills rapidly. Chemical Constitution of Muscle-tissue. — The chemical study of muscle is one of the most difficult of physiological chemistry. There are in the muscle proteid matters which are very like one another and which can be distinguished only by superficial characters. This ren- ders results far from being satisfactory or reliable. Besides, it is necessary, in order to know chemical reactions of muscles, to study only living muscle. But from previous study it will be recalled that even the weakest chemical actions produce very de- cided changes in the muscle, with consequent alteration of its chem- ical functions. Then, too, muscle-fiber is mingled with many other tissues, ar- teries, veins, nerves, connective tissue, etc.; the separation of the 373 PHYSIOLOGY. muscular fiber from its enveloping media is almost impossible com- pletely to effect. Reaction. — Living muscle is alkaline; however, after extreme activity and after death its reaction is found to be acid. This is due to the development of sarco-lactie acid. The postmortem change in muscular constitution is due to spontaneous coagulation of a proteid within the muscle-fibers. Among the constituent substances of the muscle-fiber are dis- tinguished: (1) proteids — myosinogen, myo-albumin, myogldbulin; (3) glycogen; (3) ferments and mineral salts; (4) extractives. Peoteids. — The sarcolemma of the muscular fiber resembles elastin very closely as to its solubilities. Within the soft, contracting portion, the sarcous substance, is a large percentage of proteids and smaller proportions of extractives and salts. Myosin is formed from myosinogen, myosin ferment, and calcium salts. Syntonin. — ^When a solution of myosin is heated it is altered in such a manner that it can no longer be dissolved in NaCl as before. If it be treated with dilute HCl, it becomes altered in still another manner, and produces an important substance which is called syntonin. If syntonin in HCl solution have pepsin added to it, the syntonin is transformed into peptone. Muscle-serum. — It will be remembered that in the coagulation of blood two principal components were noted : the clot and the serum floating upon the clot. Also, after coagulation of the muscular juice, myosin and serum must be distinguished. The muscle-serum which floats upon the surface of the myosin contains several substances. Among them the chemist points out two principal ones: myo-alhumin and myoglobulin. In that part of the muscle which does not yield muscle-]uice there are insoluble albumins. They are rich in nuclein. The amount of proteid matters contained in the muscular tissues is very variable. It is usually stated that in 100 parts, by weight, of muscle, there are 20 parts of proteid matters. Myohwmatin. — Another proteid found within the muscle is myo- haematin. It is the coloring matter of muscle. Extractives. — Creatinin is found in nearly all muscles. Cre- atinin is derived from creatin by dehydration. The amount of creatinin in muscle is small, being but 0.3 per cent. Muscle also contains the purin bodies : hypoxanthin and xanthin. These bodies occur to the extent of about 0.03 per cent. THE MUSCLES. 373 There is in nmscle-juice a STibstance analogous to pepsin. When a muscle becomes acid in reaction and the temperature is suitable, the pepsin acts upon the proteids to convert them into albumoses and peptones. Halliburton found a myosin-ferment. Its presence would seem to explain the coagulation of myosin. Glycogeit. — ^Among the nonnitrogenized substances must first be classed the sugars and their analogues. Glycogen is the principal muscle-starch. The glycogen in the muscles -was discovered by Claude Bernard while looking for the glycogen in the liver of the foetus and newborn. He found in the muscles of the embryo quantities of glycogen that were relatively enormous. Glycogen exists in all of the muscles. The more active the state of a muscle, the less glycogen it con- tains. Therefore, much of it is found in those muscles which contract but little. Muscle extract and pancreatic extract obtained by expression when mixed together rapidly destroy sugar, probably by the formation of a ferment. Either extract alone is powerless to break up glucose. These two extracts resemble the action of enterokinase upon trypsin- ogen and explain the diabetes due to removal of the pancreas. Inosite. — Another sugarlike matter has been found in the mus- cle-fiber. It is inosite. It is a sort of crystallizable body that is un- fermentable. That is, it does not ferment to form alcohol, but lactic acid. It is found in the vegetable kingdom also, where it is usually extracted from peas or beans. It is identical with the inosite of muscle. It is not a sugar, but belongs to the aromatic series. Pats. — Muscle also contains fats. Mineral Substances. — Alkaline phosphates predominate. In 100 parts of ash there are about 90 parts of phosphates. The metals found in muscle are : Potassium, sodium, and calcium ; there is also a small quantity of magnesium and iron. Phosphoric acid exists in muscle as inorganic phosphates, phosphorus of phospho- camic acid, and phosphorus of inosinic acid. Carnic acid is identical with antipeptone. When a muscle works it increases the phosphates in the urine. The gases found in muscle are carbonic-acid gas and oxygen. Adipocere is a waxy substance which replaces muscular tissue if bodies be buried in damp soil. It consists principally of a soap made of calcium with palmitic and stearic acids. 374 PHYSIOLOGY. The Pendulum Myograph. (Fosteb.) A, Smoked glass plate, swings on the "seconds" pendulum, B, by means of carefully adjusted bearings at 0. The contriyances by whicli the glass plate can be moved and replaced at pleasure are not shown. A second glass plate, so arranged that the first glass plate may be moved up and down without altering the swing of the pendulum, THE MUSCLES. 375 Kigor Mortis. — That state of firmness, of retraction, and of stiff- ness in which the limbs of an animal are found some time after death is called rigor mortis. It is caused by the coagulation of the myo- sinogen. In man it is generally four hours after death that cadaveric rigid- ity becomes complete. As a rule, it may be said that rigidity begins two hours after death, reaching its maximum two hours later. A particular kind of rigor mortis has been observed by military surgeons. Soldiers while in full activity have been struck by pro- jectiles and have been seen to become stiff instantaneously. It is a sort of rigor mortis which seizes all of the muscles of the body im- mediately after death. Influence of Temperature. — Animals which have died in heated chambers become rigid very quickly and the rigidity disappears as quickly. Gold, which retards chemical phenomena, retards the appearance of cadaveric rigidity and prolongs it enormously. Influence of Fatigue. — The influence of prolonged labor of the muscle upon the premature appearance of rigidity is an indisputable fact. MuscTTLAE Labok AND Ueba Exceetion. — The amount of urea excreted from the body is not markedly increased during muscular labor. Lactic Acid. — The production of lactic acid is the more abun- dant as the muscle has been longer and more strongly excited. Myograph. — The du Bois-Eeymond induction coil is the one most commonly employed in physiological experiments. When it is neces- sary to use very rapid breaking of the current, some instrument must is also omitted. Before commencing an experiment tlie pendulum is raised up (in the figure to the right) and is kept in that position by the tooth (a) catching on the spring- catch (6). On depressing the catch (6) the glass plate is set Iree, swings into the new position indicated by the dotted lines, and is held in that position by the tooth (o') catching o-n the catch (60. In the course of its swing the tooth (a'), coming into con- tact with the projecting steel rod (c), knocks it on one side into the position indicated by the dotted line (c'). The rod (c) is in electrical continuity with the wire (a?) of the primary coil of an induction-machine. The screw (d) Is similarly in electrical continuity with the wire (|/) of the same primary coil. The screw id) and the rod (c) are armed with platinum at the points at which they are in contact, and both are insulated by means of the ebonite block (e). As long as c and d are in contact the circuit of the primary coil to which x and y belong is closed. When in its swing the tooth {a') knocks c away from d, at that instant the circuit is broken, and a " breaking " shock is sent through the electrodes connected with the secondary coil of the machine and so through the nerve. The lever (,1), the end only of which Is shown in the figure, is brought to bear on the glass plate, and when at rest describes a straight line, or more exactly an arc of a circle of large radius. The tuning-fork (f), the ends only of the two limbs of which are shown in the figure placed immediately below the lever, serves to mark the time. 376 PHYSIOLOGY. be employed for that purpose. The first instrument used in making myograms -was that of Helmholtz. Simple Contraction. — If a single induction shock be applied to a muscle there will result a simple muscular contraction ; that is, the muscle responded by a quick contraction, with return to its former relaxed condition. This contraction, when graphically shown, is termed a simple muscle-curve. Muscle-curve^ or Myogram. — If the muscle-curve of a single stimulus be analyzed, it will be seen to be composed of various ele- ments, as follows: (1) period of latent stimulation^ (3) period of contraction, and (3) period of relaxation. Fig. 87. — ^A Muscle-eurve Obtained by Means of the Pendulum Myograph. (Fostbb.) To be read from left to right. a indicates the moment at which the induction-shock is sent into the nerve. 6, The commencement; c, the maximum; and d, the close of the contraction. The two smaller curves succeeding the larger one are due to oscillations of the lever. Below the muscle-curve is the curve drawn by a tuning-fork making 180 double vibrations a second, each complete curve therefore representing Viso of a second. It will be observed that the plate of the myograph was traveling more rapidly toward the close than at the beginning of the contraction, as shown by the greater length of the vibration-curves. Latent Period. — The significance of this term is that the muscle experimented with does not respond at the precise moment when the stimulus is applied to it. The response comes later — about Vioo oi a second. During the latent period there is no apparent change oc- curring within the muscle. The latent period may be modified by increased stimulus and heat, when it becomes shortened ; fatigue and cold lengthen the time. .The latent period of unstriped muscle may be as long as one or two seconds. Contraction Period. — The muscle-curve comprises two periods: that of the ascent and that of the descent of the muscle. The ascent of the curve represents the contraction of the muscle until it has THE MUSCLES. 377 reached its maximimi. The rate of contraction is at first a trifle sIotv, then more rapid and more slow a second time. The extent is Vioo of a second. Relaxation Period. — ^After the muscle has contracted to its max- imum, it begins to relax — at first slowly, then more quickly, and finally more slowly again. Its duration is °/ioo of a second. It is shorter with a weak stimulus and longer with a strong stimulus. In the myograph we use a light lever and a weight as near its axis as possible to record the contraction. Here the tension of the Z^^^jt^ Fig. 88. — ^Arrangement of Apparatus in Conducting Eixperiments on Nerve and Muscle. (Stirling.) B, Galvanic battery. K, Electric key in primary circuit. P, primary coil ot Induction macliine. iS, Secondary coil of induction apparatus, from whicli the current is conducted when the key (K') is open to the electrode (E) on which rests the nerve (»). The muscle {M) is supported by a clamp under a glass shade, its tendon being connected by a thread with a lever (L) writ- ing on the smoked surface of a revolving drum. The time-marker ITM) is included In the primary circuit so that when the current passes through P by closing the key (K) it also traverses the electromagnet of the time-marker and causes a record of th» instant of stimulation to be made on the surface of the drum. B, Stand supporting moist chamber. W, Weight by which muscle Is stretched and which is lifted in the contraction of the muscle. muscle in its contraction and relaxation remains nearly the same. This contraction is called an isotonic contraction. The isometric contraction is produced when the muscle pulls against a spring. Here the muscle undergoes slight change in length and the energy of change of form is transformed into tension and stored in the spring. An examination of isometric and isotonic curves proves that a muscle which has shortened to a given length will be making a far greater pull when its effort to shorten has been resisted than when it has 378 PHYSIOLOGY. reached the same during a contraction without resistance, which is an isotonic contraction. O I ^ % CuKVB OF Fatigue. — ^When a muscle has become fatigued and its myogram studied, at first the contractions improve for a short time. This is shown by the successive contractions being higher. THE MUSCLES. 379 Afterward the latent period increases, the curve hecomes less high, while the contraction becomes slower and lasts longer. The resultant myogram gives the picture spoken of as the "staircase." Veratrine and adrenalin greatly prolong the stage of relaxation in a muscle. Eesting and Acting Muscle. — The chief differences between resting and acting muscle are: (1) the acting muscle forms more CO2; (3) more oxygen is consumed; (3) sarco-lactic acid is formed; (4) glycogen is made use of; (5) the substances soluble in water diminish in amount, while those soluble in alcohol increase. Changes in the Volume of the Muscle during Conteac- TiON. — Muscular contraction can be defined by its apparent ejBEects: a shortening of the muscle. By experiment it has been shown that Pig. 90. — Tracing of a Double Muscle-curve. (Foster.) To be read from left to right. While the muscle was engaged in the first contraction (whose complete course, had nothing intervened, is indicated by the dotted line), u. second induction shock was thrown in at such time that the second contraction began just as the first was beginning to decline. The second curve is seen to start from the first as does the first from the base line. the muscle on contracting simply shifts its muscular units when it shortens, for the volume of the muscle remains the same. The velocity of a contraction-wave in muscle can be measured ; in the frog it is from three to four meters per second; in man, about forty feet per second. The Effects of Two Successive Stimuli. — Let the student imagine two successive momentary stimuli applied successively to a muscle. The stimuli may be either maximal or submuximal; that is, either the greatest possible contraction the muscle is able to accomplish or only a medium contraction from the applied stimulus. If each of the two stimuli be maximal, the effects produced will vary according to the time of application of the two excitants. Thus, (1) if the second stimulus be applied after the relaxation following the effect of the first stimulus, then the myogram shows two maximal 380 PHYSIOLOG'i^t contractions; (8) if the second stimulus follow the first with such rapidity that the two occur during the latent period of the muscle- curve, then the recording instrument shows but one maximal con- traction. If the two stimuli be nonmaximal, the effects of the two separate stimuli will be superimposed; that is, there will be a summation of the contractions. This summation occurs regardless of the time of application of the stimuli. Summation of Stimuli. — As the second stimulation was just seen to add its curve to the first, so does the third add itself to the second, the fourth to the third, etc. If the excitations occur with a rhythm that is not too rapid, the various shocks are nearly equal, as shown by the myogram, but yet they do not mingle. These isolated shocks are seen when the rhythm does not exceed six per second. a- Fig. 91.— Tetanus Produced with the Ordinary Magnetic Interrupter of an Induction Machine. (Recording surface traveling slowly.) (Fostee.) To be read from left to right. The interrupted current being thrown in at a, the lever rises rapidly; but at T> the muscle reaches the maximum of contraction. This is continued till c, when the current is shut oft and relaxation commences. If, now, these same excitations be repeated with a frequency of twenty per second, isolated shocks will not be seen. Bach stimulus, lasting but V^o of a second, does not allow the muscle completely to relax; thus, the second contraction encroaches upon the first, the third upon the second, etc. Prom the rapid succession of the stimuli, the muscle remains in a condition of continued vibratory contraction. That is, in a state of tetanus. Complete Tetanus. — If the excitation rhythm be more frequent, — say, fifty of them per second, — there wiU no longer be any trace of the primitive shocks. The ascent of the muscle-curve mil be abrupt and decided; the contraction due to the first shock will not be fol- lowed by any relaxation. There will be no oscillation recorded upon the myogram'. The upper straight line due to the complete contrac- tion of the muscle is called the plateau. When the muscle is in this condition the tetanus is said to be perfect or complete. THE MUSCLES. 381 The tetanus is spoken of as incomplete wlien there are still relax- ations and vibrations which indicate the incomplete mingling of the shocks. The number of stimuli that 'are required to produce tetanus may be very variable. Fifteen to twenty stimuli per second suffice to throw a frog's muscle into tetanus. Fig. 92. — ^Muscle Thrown into Tetanus, when the Primary Current of an Induction Machinei is Repeatedly Broken at the Rate of Sixteen Times per Second. (Foster.) To be read from left to right. The upper line is that described by the muscle. The lower marks time, the intervals between the elevations indicating seconds. The intermediate line shows when the shocks were sent in, each mark on it corresponding to a shock. The lever, which describes a straight line before the shocks are allowed to fall Into the nerve, rises almost vertically (the recording surface traveling in this case slowly) as soon as the first shock enters the nerve at a. Having risen to a certain height, It begins to fall again, but in its fall is raised once more by the second shock, and that to a greater height than be- fore. The third and succeeding shocks have similar effects, the muscle con-_ tinuing to become shorter, though the shortening at each shock is less. After a while the increase in the total shortening of the muscle, though the individual contractions are still visible, almost ceases. At & the shocks cease to be sent into the nerve; the contractions almost immediately disappear, and the lever forthwith commences to descend. The muscle being lightly loaded, the descent is very gradual; the muscle had not regained its natural length when the tracing was stopped. DuEATiON OF Tetanus. — A tetanized muscle cannot be kept con- tracted for a considerable length of time, even though the stimuli be kept constant. The muscle begins to elongate — at first somewhat quickly, but later more slowly. This change is produced by fatigue of the muscle. MTiscle-soTind. — Helmholtz said that 36 vibrations per second formed the average for the production of muscular tones. To-day this is considered an overtone, and the requisite number of necessary vibrations is placed at 19 per second. 383 PHYSIOLOGY. First Heakt-sound. — It is probable that the first sound of the heart is partly a nmscle-sound. It is a duU sound, persisting when the thorax is taken away and the aurieulo-ventrieular valves are de- stroyed. The sound could not in such an instance be produced by the vibration of the valves. Voluntary Contraction. — The number of single impulses sent to our muscles during voluntary movements are somewhat variable. There are from 8 to 13 impulses for a slow movement and from 18 to 20 impulses per second for a rapid movement. Ten vibrations per second may be taken as the average. Elasticity of the Muscle. — Of all the properties of muscle, elas- ticity is the one least well known, the one which is most difficult to explain and understand. Physicists say that a body is perfectly elastic when, after having been removed from its first position, it returns exactly to the orig- inal position. Thus, an ivory ball is perfectly elastic; after it has been fiattened by an external force it returns exactly to its original shape. If a piece of rubber is stretched by adding successive weights it is found that the series of elongations are nearly proportional to the weights. When the weights are successively removed it will be found that the elasticity of the rubber is nearly perfect. But if over- weighted for a long time it does not return completely to its original length, and the elasticity disappears gradually. If now you take a frog's fresh muscle and successively load it, the extension of the muscle for each weight is not proportional to the weight used, but with each increase in weight the muscle stretches rather less, the greater the previous extension. On removing the weights the muscle shortens, but it does not return to its original length. A contracted muscle is more extensible than a resting one, which prevents a rupture of the muscle in a sudden contraction. Muscular Work. — ^While treating of elasticity and its modifica- tion, tonicity, it might be well to give a brief discussion upon muscular work. The amount of mechanical work which a muscle performs equals the product of the weight lifted and the height to which the weight is lifted. Thus, the work =: height X the weight. When a muscle begins to contract, it is then that it lifts the greatest load; as the contraction continues, the muscle is capable of lifting less and less. If the height be expressed in feet and the weight in pounds, then the work performed is measured in units of foot-pounds. Likewise, THE MUSCLES. 383 should the height be measured in meters and the weight in grams, then the work done is expressed in grammeters. In studying the heights of contraction in a loaded muscle it is found that the heights of lift continuously diminish, but the actual work done by the muscle increases rapidly and then more slowly until it reaches its maximum with a load of 200 grams. After that point the work done slowly decreases and then more rapidly until it receives a load of 700 grams, when the muscle is unable to contract. Dynamometer. — The common, clinical form of dynamometer is much used to determine the absolute force of certain muscles. The instrument is very useful to determine the difference in grip between the two hands in cases of paralysis. The patient grasps the instru- ment in his hand and squeezes upon it; the power exerted is regis- tered in. kilograms. Muscles axe Most Perfect Machines. — They take the best ad- vantage of the fuel supplied to them and give in return a very high percentage of energy in the form of work. They, by legitimate exer- cise, increase in strength and power so that they progressively per- form more work. The steam engine, to which muscles are frequently compared, is inferior in every respect. The best made steam engine shows as work only about 12 per cent, of the total energy supplied to it by the oxidation of the coal, whUe about 88 per cent, is transformed into heat. Muscle transforms 25 per cent, of its energy into work and 75 per cent, into heat to warm itself. CHAPTER XII. VOICE AND SPEECH. It has long been established that the sounds of the voice in man and mammalia are produced by the vibratory action of the vocal cords. It is usually the blast of expired air — ^under certain circumstances the inspiratory blast also — ^in its passage through the glottis that causes the tense vocal cords to vibrate. These cords vibrate according to the laws which regulate the vibration of stretched membranous tongues. As a result of these vibrations sound is produced which, iu man, is capable of being so modified as to constitute articulate speech. Experiments upon living animals show that the vocal cords are alone the essential factors in the production of sound. For, so long as these remaiu untouched, although all other parts in the interior of the larynx are destroyed, the animal is still able to emit vocal sounds. The existence of an opening in the larynx of a living animal, or of man, above the glottis in no way prevents the formation of vocal sounds; however, should such an opening occur in the trachea, it causes total loss of voice. By simply closing the opening sounds can be again produced. Such openings in man are usually met with as the result of accident, of suicidal attempts, or of operations performed upon the larynx or trachea for the relief of disease. Production and Modification of Sounds. — Whenever a solid body surrounded by air is thrown into vibration the sensation of sound is carried to the ear. The vibrations must, however, be of certain strength and follow one another with certain rapidity. It is usually stated that if the vibrations be fewer than 32 or exceed 33,768 per second no effect is produced upon the nerve of hearing. For the production of a musical sound the vibrations must suc- ceed each other at regular intervals; if the vibrations occur at irregular intervals, only a noise results. The pitch of a sound depends upon the number of vibrations withia a given period of time. The pitch becomes higher in direct proportion to the rate of increase in the rapidity of the vibrations. The strength^ or intensity, of the sound depends upon the extent of the vibratory action of the sonorous body. (384) VOICE AND SPEECH. 385 Tone, or timbre, is that peculiar character of a musical note whereby it can at once be distinguished from another note of exactly the same pitch and strength. THE ORGAN OF VOICE. The special organ of voice in man is that portion of the air- passages called the larynx. It is a sort of hollow chamber which extends from near the root of the tongue to the first ring of the trachea. It is placed in the middle line of the neck, where it forms a considerable projection, larger above than below. Although the larynx is the proper organ of voice, yet the lungs and the moving parts of the thorax serve to propel the air through this Fig. 93. — The Larynx as Seen with the Laryngoscope. (Landois.) L., Tongue. E., Epiglottis. 7., Vallecula. B., Glottis. L. v.. True vocal cords. S. M., Sinus Morgagni. L. ». s., False vocal cords. P., Position of pharynx. S., Cartilage of Santorini. W., Cartilage of Wrisberg. S.p., Sinus pyriforniis. organ. The cavities above it, including the pharynx, mouth, and nasal cavities, assist in modifying the vocal sounds. They are, there- fore, adjunct organs of voice. Anatomy of the Larynx. — The larynx consists of a cartilaginous skeleton which constitutes its walls ; also vocal cords ; muscles which move directly the cartilaginous pieces, and influence indirectly the tension of the cords; and, finally, a mucous membrane which lines the internal cavity. Cahtilages. — The cartilages of the larynx are four in number : two unlike and two alike. One of the former is iaferior and exists in the form of a signet-ring. It is the cricoid. This cartilage is continuous with the rings of the trachea. Its narrower portion is situated anteriorly; its wider portion is placed posteriorly. It ar- 386 PHYSIOLOGY. ticulates with the inferior comua of the thyroid cartilage, forming the crico-thyroid articulation. The other odd cartilage, the superior one, is 'called the thyroid. It is composed of two quadrilateral laminse which meet in front at an angle. This projection is popularly known as Adam's apple. Each thyroid lamina terminates posteriorly in two horns : one superior, the other inferior. The two cartilages which are alike are the arytenoids. -Each one is in the form of a triangular pyramid, whose base is movably articulated at the back on the cricoid cartilage. The apex of each arytenoid cartilage has attached to it, in the shape of a movable point, a cartilage of Santorini. Fig. 94.— Action of the Muscles of the Larynx. (Beaunis.) The dotted line indicates the new positions assumed by the thyroid carti- lage in the action of the crico-thyroid muscle. 1, Cricoid cartilage. 2, Arytenoid cartilage. 3, Thyroid cartilage. 4, True vocal cord. 5, New posi- tion of the thyroid cartilage. 6, New position of vocal cords. The true vocal cords are attached to the anterior angles, or vocal processes, of the arytenoids; the erieo-arytenoid muscles are inserted into the external angles. The cartilages of Wrisberg are found in the ^jgfteno-epiglottic folds. V "■" - The epiglottis is attached to the inner surface of the anterior portion of the thyroid cartilage. It projects upward behind the base of the tongue. The epiglottis is attached to the tongue by the three glosso-epiglottic folds. The false vocal cords are two folds of the laryngeal mucous mem- brane which pass from the anterior surfaces of the arytenoids to the thyroid cartilage. They are located above the true vocal cords. VOICE AND SPEECH. 387 The true vocal cords extend from the anterior angles of the bases of the arytenoids to the thyroid cartilage. The glottis is the chink between the true vocal cords. The ventricle of the larynx is the pouch between the true and false vocal cords. The Muscles. — All of the laryngeal cartilages, joined together by ligaments, are moved by five pairs of muscles. The muscles of the larynx are divided into two groups: intrinsic and extrinsic. To the former group belong those muscles which are attached to the various cartilages. The latter collection comprises the musculature connect- ing the larynx to other parts like the hyoid bone. Fig. 95.— Schematic Horizontal Section of La,rynx. (Lahdois.) /, Position of horizontally divided arytenoid cartilages during respiration. From their anterior processes run the converging vocal cords. The arrows show the line of traction of the posterior crico-arytenoid muscles. II, II, Position of the arytenoid muscles as a result of this action. Inteinsios. — Of these there are five pairs. 1. The Grico-thyroid Muscles. — These, which are iix the anterior part of the larjm^ originate in the front and sides of the cricoid car- tilage below. Outwardly they are attached on each side to the lower edge of the thyroid cartilage. They become fixed by the action of the thyro-hyoid, sterno-thyroid, and laryngo-pharyngeal muscles. Action. — They incline the cricoid cartilage upward and backward and so elongate and stretch the vocal cords, >atjjthe same time contract- ing the openiag of the glottis. 2. The Posterior Crico-arytenoid Muscles. — These take their de- parture from the posterior surface of the shield of the cricoid cartilage. 388 PHYSIOLOGY. They then converge and are fastened to the base of the corresponding arytenoid cartilage. ^ Action. — In contractiag they turn the anterior ends of the aryte- noids outward, whereby they separate the vocal cords from each other and give a rhomboid form to the glottis. Thus it is materially widened. S. The Lateral Crico-arytenoids. — These muscles are found upon the inner side of the cricoid. They are carried backward and upward and are fastened to the outside of the posterior ends of the bases of the arytenoid cartilages. Action. — In contracting they rotate the arytenoid cartilage in- ward. They are antagonists of the posterior crico-arytenoid muscles; they narrow the vocal part of the glottis. Fig. 96. — Schematic Closure of tke Glottis by^ the Thyro-ai-ytenoiji Muscles. (Landois.) //, II, Position ot tlic arytenoid cartilages during quiet respiration. The arrows indicate the direction of muscular traction. /, /, Position of the arytenoid cartilages after the muscles contract. J/.. The Thyro-arytenoid Muscles. — This pair of muscles is inserted at the anterior end in the middle of the angle of the thyroid cartilage, and at the posterior end is fastened to the inside of the anterior end of the base of the arytenoid cartilages. Each muscle of the pair runs its entire length parallel with the corresponding vocal cord. This muscle has two bundles: an internal and external bundle. The muscle draws the arytenoids toward the thyroid and relaxes the cords. By the internal bundle the anterior part of the vocal cord can be tightened while relaxing the posterior part. It is the muscle concerned in the production of the high notes in the singing voice. VOICE AND SFEECH. 389 5. The Arytenoid constitutes an odd muscle. It extends pos- teriorly between the two arytenoid cartilages. The muscle is divided into two layers: one posterior, of oblique fibers disposed like an X; and one anterior, of transverse fibers. Its action is, in contracting, to draw the arytenoid cartilages together so that the respiratory part of the glottis is closed. If the contraction be simultaneous with that of the lateral crico-arytenoid muscles, respiration is entirely interrupted. The Extrinsic Muscles are those of the anterior region of the neck : those in the suprahyoid as well as those in the subhyoid region. By the action of these muscles the entire larynx is moved upward and downward. The Cavity of the larynx is lined with a mucous membrane. The mucous membrane is continuous with that of the trachea. It is covered with the prismatic or ciliated epithelium in all places ex- cept over the vocal cords and epiglottis. In these special areas it is stratified. The Vocal Coeds comprise two sets, as was previously men- tioned; the upper, false cords, composed of folds of mucous mem- brane, take no part in voice production; the lower, true cords, are composed of a mucous membrane with pavement epithelium, a lamina of elastic fibers, and the thyro-arytenoid muscle. Opening the cavity of the pharynx and raising the epiglottis, the whole extent of the glottis is seen; that is, the slit left by the two superior cords. This has the shape of a much elongated triangle — apex in front, base at the back. The limited anterior part of the triangle is called the vocal part of the glottis; whereas the posterior part is called the respiratory portion. It does not participate in phonation, but only in the passage of air. Nerve-supply. — The nerves which are distributed to the larynx come from the pneumogastric. The superior laryngeal nerve supplies the mucous membrane of the larynx and gives the external laryngeal branch to the crico-thyroid muscle. The inferior, or recurrent, laryn- geal nerve supplies all of the muscles except the crico-thyroid. The ganglia which preside over the motor innervation of the larynx are seated in the floor of the fourth ventricle. Laryngfoscopy. — The laryngoscope is an instrument that is used to bring to the user's view various parts of the pharynx, larynx, and trachea. It consists of a small mirror fastened to a long handle. The angle that the mirror makes with its handle is from 125 to 130 degrees. 390 PHYSIOLOGY. Condition of the Vocal Coeds. — By observations made with the laryngoscope it has been determined that, while in respiration the vocal cords are inclined from each other, and the glottis is wide open, in speaking or vocalization the cords are seen to approximate and vibrate. In ordinary quiet breathing there is a wide, triangular- shaped opening in the glottis. On the other hand, durihg the produc- tion of vocal sounds the triangular posterior opening is completely closed, while the anterior portion of the rima glottidis becomes a very fine fissure, or slit. VOICE. It is the vibration of the edges of this fissure by the passage of air through it that produces sound : the voice. The air expelled from the lungs acquires a maximum of tension in the narrow tracheal Fig. 97. — Position of Vocal Cords on Uttering a High Note. (Landois.) , tube, causing it to strike underneath the true vocal cords and put them into the proper vibrations. But the tone produced will not always be of the same caliber and height, since the expired air may iind the vocal cords in different states, the result of muscular con- tractions. The Height of the sound produced in the larynx depends upon the number of vibrations of the vocal cords during a given time. The number of vibrations would then depend upon the state of tension and the length of the cords themselves. The greater the number of vibrations during a second, the higher will be the tone, and vice' versa. The range of the human voice, as regards height, is usually be- tween 87 and 768 vibrations per second. Not all persons have such a range. Bach type of voice includes about two octaves. When a man speaks — ^that is, when he uses the articulate voice — ^his voice does not exceed a height of a half-octave. When he sings his vocal range is more extended. VOICE AND SPEECH. 391 The Intensity of sound depends upon the extent of the vibrations of the vocal cords, produced especially by the force of the current of air. The height of the voice depends, to a considerable extent, upon different lengths of the vocal cords. The result is that in adult man the 6ass, baritone^ and tenor voices are found, because of the greater length of the vocal cords in man. On the contrary, the contralto, mezzosoprano, and soprano voices belong to -women and boys, for they have cords shorter in length. Timbre of sound depends upon the nature of the vibrating body and of the other means vibrating at the same time with it for the production of harmonious sounds. Resonance. — The normal voice of man is sonorous; that is, it is composed of vibrations regular in extent and isochronous. Its resonance comes either from the air-tube or from the resonators. By the former is understood the trachea, bronchi, walls of the liings, and thoracic ease ; by the latter, the ventricles, pharynx, mouth, and nasal cavities. The resonance within the thorax in an adult causes a fremitus of the thoracic wall. This is greatly increased in low sounds and diminishes until it disappears in high sounds. Ordinarily, in speaking and singing, the air put in vibration in the larynx issues from the mouth while the nostrils are open. If they be closed, the air which is held there vibrates with the air issuing through the oral cavity and gives the voice a nasal tone. The human voice can assume two different registers. The one is strong and sonorous and accompanied with vibrations of the thoracic wall (chest-voice). The other is weak, without resonance, and of higher pitch (head-voice, or falsetto). Ventriloquy, which by practice can reach great perfection, con- sists only in the possibility of changing the register of the voice. The name derived its origiu from the erroneous interpretation of it by the ancients. They claimed that the ventriloquists spoke from the stom- ach. The performer is able to conduct dialogues in which two persons appear to take part. Speech. — If man had the faculty of making only sounds with the larynx, his vocal organ would not differ greatly from ordinary musical instruments. The voice in such case would but serve to make others aware of his presence and to call them for the various wants of life, as happens in animals and ia the child itself when just bom. But man i^ endowed with an important means by which he can communicate to his fellows the state of his mind. It forms one of man's noblest characteristics, a distinctive one. 392 PHYSIOLOGY. The infant at first expresses the state of his mind by cries accom- panied by gestures. Then little by little it learns and tries to imitate those sounds which the parents always make corresponding to given objects and persons. It pronounces them without understanding their meaning. In later years it learns of the correspondence of given sounds to given objects and ideas. Speech is articulate voice. It is an ensemble of sounds and noises harmonized by the will and co-ordinated by a particular cortico-motor nervous center. Its aim is the making known to the listener the pres- ent state of mind of the speaker as well as recollections of the past and tendencies toward the future. Vowels and Consonants. — Speech is composed of two elements, namely : vowels and consonants. The former consist of sounds gen- erated in the larynx and slightly modified in the pharynx and mouth- cavity. The consonants result from noises variously produced by the obstacles encountered by the air in its passage through the pharynx and mouth-cavity. Vowels are produced in the larynx, pharynx, and mouth; consonants not in the larynx, but in the mouth. The vowels are produced by the different form of the cavity of the pharynx and mouth during the expiration of air through them. The principal change in form consists in the lengthening and shorten- ing of the mouth. The vowels are a, e, i, o, and u. The consonants consist of sounds emitted by the larynx, but which become noises by reason of obstacles they encounter. According to the obstructions met with, consonants are termed gutturals (h, Tc, q), Unguals (c, d, g, t, s, n, I, r), and labials (h, f, m, p, v). The Unguals are subdivided into palatals and dentals. The very varied union of the vowels with the consonants consti- tutes syllables; union of the latter forms words. Stammerings is due to a continued spasmodic contraction of the diaphragm and to the muscles of the larynx not harmonizing the chink of the glottis. Stuttering is due to a want of ability to form the proper sounds by the laryngeal muscles; the breathing and diaphragm are both normal. Pathology. — Paralysis of the motor nerves of the larynx from the pressure of tumors, causes aphonia, or loss of voice. In aneurism of the aortic arch the left recurrent nerve may be paralyzed from pressure. The laryngeal nerves may be temporarily paralyzed by overexertion and hysteria. VOICE AND SPEECH. 393 If one vocal cord be paralyzed, the voice is impure in tone and falsettolike. Hoarseness may be caused by mucus upon the vocal cords or by roughness or laxness of the cords. Disease of the pharynx or naso- pharjmx and uvula may, iu a reflex manner, produce a change in the voice. CHAPTER XIII. ELECTRO-PHYSIOLOGY. To lEKiTATE nerves we employ the du Bois-Eeymond induction apparatus. It consists of a primaiy spiral of some 130 coils of wire and a secondary spiral of 6000 coils of wire. The core inside the primary spiral is formed of a number of thin iron wires. To graduate the current the secondary spiral is moved in a groove to and from the primary, or, following Bowditch, it can be rotated at an angle to the primary spiral. A wooden scale at the side shows the separa- tion of the coils in millimeters. The strength of the current at the different separations of the coils can also be graduated by means of the galvanometer. To break the current Neef's automatic hammer is used. The break shock is stronger than the make shock. To equalize the shocks, Helmholtz used a side wire to make an accessory current. To study the currents of muscles or nerves it is necessary to use various kinds of apparatus devised by du Bois-Eeymond. To use the galvanometer (instead of the usual wire electrodes) we make use of nonpolarizable electrodes. They are formed of flat, glass tubes and their lower end is closed water-tight by means of common salt clay (kaolin), which externally is molded into a hooklike shape for the nerve to rest on. A strip of amalgamated zinc plate is inserted into the glass tube filled with a concentrated solution of sulphate of zinc. The zinc is fastened to a piece of brass which has a screw for the attachment of the wire to lead off the current to the galvanometer. Instead of the galvanometer the capillary electrometer may be used. The current of the muscle or nerve traverses the muscle or nerve and produces a deflection of the needle of the galvanometer, which indicates the direction of the current. Physiological Bheoscope. — This name has been given to the nerve- muscle preparation of the frog where the greatest possible length of the sciatic nerve attached may be used. The preparation of the nerve requires special care, for the nerve must be removed by a little seeker of glass or bone. No metal must touch it. It is removed from below (394) ELECTRO-PHYSIOLOGY. ^ 395 upward, and if properly done there should be no contraction of the muscle during the operation. If the nerve of this preparation be brought into contact with- a segment of separated muscle so as to touch simultaneously the longitudinal and transverse surfaces, a contraction instantly follows. If a piece of the muscle be placed on the electrodes of du Bois-Keymond so that the transverse section corresponds to one and the longitudinal surface to the other, the deflection of the needle of the galvanometer indicates the existence of a current in the muscle which passes from the transverse to the longitudinal surface. The surface of the muscle is positive and that of the transversely divided segment negative. Instead of a transverse section of a muscle its tendon may be taken, which is also negative and has been called the Fig. 98. — The Nerve-musele Preparation. (Stirling.) S, The Nerve-muscle. F, Lower third of femur. I, Tendon of gastrocnemius muscle. natural transverse surface. The cut surface of a longitudinal section of muscle presents positive electrization. The laws of electrical cur- rents of muscle have been fully determined by du Bois-Eeymond : — 1. When the conductor unites the longitudinal to the transverse surface there is a well-marked deviation of the needle, and the greatest deviation occurs when the middle of the longitudinal surface is con- nected with the middle of the transverse. 2. When two points are connected on a longitudinal or transverse surface which are unequally distant from the middle, or two points unequally distant on opposed surfaces, then there is a slight deflection of the needle. In the case of the longitudinal surfaces the current passes along the conductor from the point nearer the center to the one farther ofE. The reverse is the case for the transverse. 396 PHYSIOLOGY. 3. When two points are connected on the same or on opposed surfaces equally distant from the center, or when the centers of two opposite surfaces are joined, there is no movement of the needle of the galvanometer. The parelectronomic part of the muscle is the tendinous part of the muscle, which is negative instead of being positive, as is the rule. Here it is necessary to make an artificial section for the purpose of demonstrating the electrical phenomena of muscle. Hermann has shown that the muscle-currents are the result of the preparation, and do not exist in the normal, intact fibers when in a state of repose. These galvanometrical deviations are due to the traumatic action of air, cold, or chemicals. Electrical Phenomena of Contracting Muscle. — If upon the elec- trodes c6nnecting the poles of the galvanometer a muscle is so placed that the needle deflects, and then tetanize the muscle by stimulating its nerve, the needle will be seen to retrace its movement of deflection. This reverse of the natural current is Icnown as negative deviation. This has been shown to be due to a weakening of the natural nerve- current, and not to the production of a new one contrary to the current of rest. This negative variation can stimulate the nerve of another muscle if the nerve of the physiological rheoscope be placed on the nerve of a contracting muscle in such, a manner that the first touches both the cut surface and another point on the second nerve ; then each contraction of the muscle is followed by a contraction of frog's nerve- muscle preparation (secondary contraction) . This negative variation lasts about 0.004 second and is propagated along the muscle with the same velocity as -^he wave of contraction it precedes, vanishing even before the arrival of the latter. Hermann calls the negative variation by the name of current activity. Negative Variation of the Nerve-eurrent. — If you place upon the electrodes connected with the galvanometer a piece of nerve, the devia- tion of the needle shows the existence of the nerve-current already described so long. as the nerve is at rest. If you tetanize the nerve the needle is seen to run back toward zero, and sometimes even beyond it. This takes place in every kind of nerve and in the whole length of the nerve. It can be produced by mechanical or chemical stimuli as readily as with electricity. The greater the stimulus, the greater the negative variation, but there is not a definite proportion between them. Hermann has shown that neither in the nerve nor muscle do any of these currents exist so long as the structures are uninjured. To generate a nerve-current in repose it is necessary to make a transverse ELECTRO-PHYSIOLOGY. 397 section. This produces death of the superiicial layer of a segment next the cut surface. The dead tissue behaves negatively with regard to the living, and the electromotor forces accordingly have their seat at the plane of demarcation between the dead and living. As to the currents of activity, they are explained by admitting that during stimulation the active parts are negative with regard to the parts at rest. CHAPTER XIV. THE ANATOMY AND PHYSIOLOGY OF THE NERVOU5 SYSTEM. ANATOMY OF THE NERVOUS SYSTEM (EXCEPT THE CEREBELLUM).^ STRUCTURE OF NERVE=TISSUE. Nerve-tissues present themselves in two varieties : some as white substance and some as gray substance. These two substances are dif- ferent, not only in color, but also in physical and chemical properties and in anatomical arrangement. The gray substance contains as characteristic elements the nerve- cells; the white substance, the nerve-fibers. These latter emerge from the gray nervous substance to branch out toward the peripheral organs. These two substances, gray and white, possess a common element known as neuroglia; in addition, each contains blood-vessels. The Nerve-cell. — The nerve-cell is the characteristic funda- mental element of the gray substance: it is the unit of the nervous system. It is the element which gives to this kind of nervous tissue its gray color. When these units are charged with a strong portion of pigment, they are black, as in the locus niger of the cerebral peduncles. When a little less pigmented they present a grayish color: the color that is characteristic of the brain and the central portion of the spinal cord. They may be charged with red pigment, then the cells are reddish; such cells constitute the red nucleus of the head of the cerebral crura. Steuctuee of the Neeve-cell. — The nerve-cell is composed of (1) a mass of protoplasm inclosing a nucleus with its nucleolus; (2) of simple or branched prolongations. The protoplasm of a nerve- cell, like that of many other cells, is formed of a very delicate network of bands whose meshes are filled with a clear or finely granular albuminoid substance. The network has been designated by the name of spongioplasm and the intermediate substance is generally tenned =• For anatomy of the cerebellum see subsequent pages. (398) ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 399 Kg. 99. — The Structure of Nervous Tissue. (Laitdois.) 1, Primitive fibril. 2, Axis-cylinder. 3, Remak's fiber. 4, Medullated varicose fiber. 5, 6, MeduUated fiber with Schwann's sheath. 0, Neuri- lemma, t, t, Ranvier's nodes. 6, White substance of Schwann, d. Cells of the endoneurium. a, Axis-cylinder, x, Myelin drops. 7, Transverse section of nerve-fiber. 8, Nerve-fiber acted on with silver nitrate. /, Multipolar nerve- cell from spinal cord, z, Axial cylinder process, y. Protoplasmic processes; to the right of it u bipolar cell. II, Peripheral ganglionic cell with a con- nective-tissue capsule. ///, Ganglionic cell, with o, a spiral, and n, straight process, m, Sheath. 400 PHYSIOLOGY. hyaloplasm. As to these two components, the protoplasm of nerve- cells is like that of most other cells. Fibrils. — One peculiarity is the presence in it of fibrils which run through its substance. Granules. — The other characteristic feature of nerve-protoplasm is the existence within it of angular granules. These show a special liking for basic aniline dyes, as methylene blue. By many authors they are spoken of as Nissl bodies, after their discoverer and the man who has demonstrated their physiological worth. The granules are found scattered throughout the cell-body and its dendrons, but not in the axis-cylinder and the adjacent area of the cell to which it is attached. The most important relations that these granules bear physio- logically to the cell is as follows : Under either normal or abnormal activity of the nerve-cell the granules undergo a change which has been termed chromatolysis. It is a slow dissolution of the granules with diffusion of the degenerated product into the protoplasm. At first the cell swells, pushing its nucleus to one side; later the cell diminishes in size, due to loss of its chromatophilic substance. It is in the hyaloplasm that the pigment substance which gives to the cell its particular color is deposited. Nucleus. — The nucleus of the nerve-cell forms a small, rounded or oval mass. It is characterized by its relatively large size. This nucleus is strongly colored by all the reagents, as carmine, methylene blue, etc. Around the nucleus the chromatin forms a sort of cell-wall called the nuclear membrane. Within the nucleus is seen a small refracting body called the nucleolus. Its chromatin is relatively great in amount. Cell-prolongations. — From the researches of Deiters it has been learned that nearly every nerve-cell has protruding from its periphery a greater or less number of prolongations. These are of two varieties : one is unique, nonbranching, and prolonged under the form of a cylinder-axis of a nerve. It is known by the various terms, axis- cylinder, neuraxon, and neurite. The other variety of prolongations is composed of many, though an uncertain number of, processes. This new set of prolongations bears the name of protoplasmic processes, dendrons, dendrites, or the poles of the cells. Some cells possess no ■dendrons, others very many. However, it is believed that no cell is without its neuraxon. According to Cajal, the communications of the prolongations of the cells among themselves is no more than that of simple contact. It is analogous to the contact which permits of the ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 401 passage of the electrical current when the two electrodes of an electrical battery are in contact. Further, the nervous impulses are transmitted only along the neuraxons from cell to cell. Bach neuraxon, by branch- ing and coming in contact with the dendrons of other and neighboring cells, conveys its impulse to them. They in turn transmit it cen- tripetally to the axis-cylinders of their own cells, to be further trans- mitted to other cells. According to this doctrine the nerve-cell would be physiologically unipolar. To denote this close contact exist- ing between the axis-cylinder and dendrons of various cells, Foster has used the term "synapsis." The nerve-cells of the gray matter are of various sizes and shapes, the branched, stellate, or multipolar form being predominant. Some are more or less bipolar or spindle-shaped ; however, at each extremity there is usually a fine plexus of branches. Some are ovoid or pyri- form, as in the cortex of the cerebellum, where they have received the name of cells of Purkinje. The cells of the ganglia of the spinal nerves are, in great part, unipolar. The dimensions of the nerve-cells are very variable ; the smallest are about ^/looo i^^ch in diameter, the cells of the posterior horns of the spinal cord are from ^/jioo to ^/i2oo inch, and the giant cells of the anterior horns of the spinal cord are about ^/i^o inch in diameter. By employing Golgi's silver-nitrate method of staining, the nerve-cells, with their processes, are stained black from a deposition of the silver. By reason of this, the nerve-prolongations may be traced to their ultimate terminations. This method beautifully dem- onstrates the distribution of the dendrites, their branching, and man- ner of contact with dendrites of contiguous cells ; also, how, as a rule, the neuraxon does no very immediate branching. It must be stated, though, that there usually proceed from the neuraxon numerous fine fibrils to which the term collaterals is applied. These are in com- munication with the dendrites of neighboring cells. The neuraxon in nerve-centers after proceeding for some distance does really branch to form arborizations to come into contact with nerve-dendrites. The Neete-fibees. — Every nerve-fiber is a process of a nerve- ceU. It is the neuraxon of some particular cell. It is the medium which conducts impulses to or from the tissues and organs, on the one hand, and the nerve-centers, on the other. In the majority of cells the neuraxon acquires a sheath to be thus converted into a medul- lated nerve-fiber. Thus, there are two kinds of nerve-fibers: medul- lated, or those with myelin; and nonmedullated, or those without myelin. 402 PHYSIOLOGY. Medullated Fibers in the fresh condition are bright, glistening cylinders showing a dark, double contour. The essential part of it is the axis-cylinder. This is a soft, transparent rod, or thread, which runs from one end of the fiber to the other. It does not anastomose with its neighbors, and in the average nerve is about ^Aaoo ^^^^ ™ diameter. After the employment of certain reagents the axis-cylinder shows itself to be composed of very fine, homogeneous or more or less beaded fibrillse. The latter are the elementary, or primitive, fibrillce. They are held together by a small amount of a faintly granular, inter- stitial substance. The thickness of the axis-cylinder is in direct pro- portion to the thickness of the whole nerve-fiber. The axis-cylinder is enveloped in its own, more or less elastic, hyaline sheath. The axis-cylinder is not regularly cylindrical, but is slightly narrowed in places. Under the influence of silver nitrate applied to its surface there appear alternate obscure and clear transverse strise. They are the so-called lines of Frommann. Myelin. — Surrounding the axis-cylinder is the myelin, medullary sheath, or the white substance of Schwann. It is a layer of fatty substance, strongly refracting, and of homogeneous aspect. It is colored black by osmic acid. It is the myelin which gives to the nerve its double contour. It is composed of a network of fibrils of a chemical substance called neurokeratin, which incloses the semi- fluid, fatty substance. The latter contains, among other substances, a complex, phosphorized fat. The sheath of myelin envelops the axis-cylinder everywhere, ex- cept at its termination and at the nodes of Eanvier. In its arrangement the myelin is imbricated in the fashion of tiles on a roof by reason of a series of segments one above the other. They are separated one from the other by clear lines. The lines are known as the incisures of Lantermann, and the segments as those of Schmidt. Neurilemma. — The neurilemma, or sheath of Schwann, surrounds the medullary sheath to form the outer boundary of the nerve-fiber. It is a thin, elastic, very delicate, hyaline, and transparent membrane. It is comparable to the cell-wall of a cell. Between the neurilemma and medullary sheath there are irregularly scattered ovoid nuclei. They are the nerve-corpv^cles, and are analogous to the muscle- corpuscles previously mentioned. Each nerve-corpuscle is surrounded by a thia zone of protoplasm. Between the myelin layer and the neurilemma is a thin zone of protoplasm. When this arrives at the level of the annular constric- tions it is reflected upon itself to line the internal surface of the ANATOMY AXD PHYSIOLOGY OF NERVOUS SYSTEM. 403 myelin laj'er. The protoplasm is also insinuated into the incisures of Lantermann and decomposes the layer of myelin into the superposed segments of Schmidt. Nodes of Ranvier. — At intervals of about one millimeter along the course of the nerve there appear constrictions: the nodes of Eanvier. At these points the myelin sheath is interrupted so that the neurilemma appears to do the constricting. That portion of the nerve-fiber between any two constrictions is termed an internodal seg- ment. At about' the center of each internodal segment is located one, sometimes more, nerve-corpuscles. Such is the composition of a meduUated nerve-fiber. This type of nerve is found chiefly in the white matter of the nerve-centers and in the cerebro-spinal nerves, with the exception of the olfactory nerve. NoNMEDULLATED Neeve-hbehs. — Thfey occur especially in the sympathetic system, but are also present in the cerebro-spinal nerves to a slight extent. Each fiber consists of a bundle of fibrils — primitive fibrils — which are inclosed in a delicate, transparent, and elastic sheath. The fibrils are very delicate and somewhat flatteiied. Here and there along the course of the fibrils will be found oval nuclei. These latter lie between the axis-cylinders and their enveloping neurilemma. As these fibrils contain no myelin, they are not blackened by osmie acid. This allows of a differentiation between meduUated and nonmeduUated nerves when examining the nerve-supply of a tissue. Nerve-tkunks consist of bundles of nerve-fibers. Each bundle, of course, contains a greater or less number of fibrils.' Several bundles are held together by a common connective-tissue sheath: the epi- neurium. Delicate fibrils lie between the nerve-fibers to constitute the endoneurium. The larger blood- and lymph- vessels lie in the epineurium; the few capillaries of the nerve-fibers lie supported in the endoneurium. Termination of the Nerve. — After a certain course in the trunk of the nerve the nerve-fiber divides at the periphery into a terminal plaque, the motor plaque of muscles; or into a sense-cell, as in the retinal cells or organ of Corti; or into a sense-corpuscle, as a tactile corpuscle; or into numerous fibrils which anastomose to form a terminal plexus, as in the cornea. NONMEDULLATED FiBERS— that is, thosc that are naked, pale or gray, and reduced to an axis-cylinder and sheath — branch and form networks : their peripheral terminations. This mode of termination occurs in the nerve-fibers of common sensation, as in many of the 404 PHYSIOLOGY. nerve-fibers of the skin, cornea, and mucous membrane. In all of these cases the peripheral termination fibrils are intra-epithelial : that is, they are situated in the epithelial portions of cornea, mucous membrane, etc. Neuroglia. — In the gray, as well as ia the white, substance of the nerve-centers there exists between the cells and nerve-fibers an intervening substance which has been termed neuroglia. It must not be confounded with the true connective-tissue along the course of the blood-vessels in the nerve-centers. Its chemical nature is wholly different from the latter, which is always derived from the mesoblast. Eanvier has shown that neuroglia is derived from the primitive neuro- blast or epiblast. Neuroglia sometimes presents itself in the shape of very fine fila- ments assembled in a very close network, as in the gray substance. Sometimes, again, it is seen under the aspect of reticulated plates bounding the space in which the nerve-fibers pass. This is beautifully demonstrated in the white substance of the columns of the spinal cord. Elsewhere the neuroglia is found to be a homogeneous, gelatini- f orm substance, as in the ependyma of the spinal cord or in the gelat- inous substance of Eolando in the postero-lateral groove of the same structure. Besides the fibers and plates already mentioned, neuroglia con- tains cells. "These are star-shaped, flat, and nucleated. They have numerous prolongations. By the aid of these prolongations the cells of the neuroglia are freely in contact with one another to form a very complicated network. This incloses in its meshes the nerve-elements. Neuroglia enjoys the role of a true cement which unites all of the fibers and nerve-cells. Classification of Nerve-cells. — According to Schafer, nerve-cells are broadly classified into : "1. Afferent cells, which receive impressions at the periphery to convert them into impulses. The latter then pass toward the central nervous system. 2. Efferent cells, which send out nervous impressions toward the periphery. 3. Intermediary cells, which receive impressions from afferent cells to transmit them directly or indirectly to efferent cells. 4. Distributing cells, which occur near the periphery, and, receiving impulses from efferent cells, distribute them to involuntary muscles and secreting cells. The cells of this class belong to the so-called sympathetic system. "The afferent and efferent cells are known as root-cells. The greater number of the nerve-cells of the brain and cord belong to the intermediate class. They serve the purposes of association and co- ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 405 ordination and afford a physical basis for psychical phenomena." Efferent, fibers are also called cellulifugal. Afferent fibers are also called cellulipetal. Structure of the Gray Substance. — The gray matter is formed (1) of nerve-cells, (2) of neuroglia-cells, (3) of fibril elements repre- senting the prolongations of nerve- and neuroglia- cells, (4) of an intervening network formed by the branching fibrils, and (5) of blood-vessels. Elements 1, 2, and 3 (here enumerated) of the struc- ture have been treated previously in detail. The blood-vessels penetrate the gray substance, and are sur- rounded with a layer of connective tissue coming from the pia mater, which they have received in their passage along and through this membrane. The connective tissue forms sheaths around the capillary network, arterioles, and little veins, in which the vessels seem to float. These have been termed the perivascular sheaths of His. Between them and the vessels exists a lymph-space: one of the origins of the lymphatics. White-Substance Formation. — The white matter is formed by the bundles of white fibers covered by a lamellar investment of neuroglia. These bundles are separated from one another by tracts of connective tissue detached from the pia mater. Axis-cylinders are also found, which come from the gray matter. Blood-vessels anastomose and run in a course parallel with the nerve- fibers. This circulatory network likewise has a perivascular sheath as has that in the gray substance. Chemical Properties of Nervous Substance. — The following table of Landois gives the percentage of the various components of both gray and white matters: — CHKMicAL Composition of Water Solids The solids consist of : — Proteids (globulins) . . Lecithin Cholesterin and fats .... Cerebrin ... Substances insoluble in ether Salts Gray Matter. White Matter. 81.6 percent. 68.4 per cent. 18.4 " 31.6 55.4 per cent. 24.7 rer cent. 17.2 " 9.9 18.7 52.1 0.5 9.5 6.7 3.3 1.5 0.5 406 PHYSIOLOGY. In 100 parts of ash. Breed found potash, S2; soda, 11 ; magnesia, 2; lime, 0.7; NaCl, 5; iron phosphate, 1.3; fixed phosphoric acid, 39; sulphuric acid, 0.1; and silicic acid, 0.4. Proteids occur chiefly as albumin. They are found in the axis- cylinder and in the substance of the nerve-cells. Halliburton finds that the proteids exist as globulins and nucleo-proteids. Nuclein oc- curs especially in gray matter because of the presence there of its units : the nerve-cells. Neurokeratin is a body which contains a rela- tively large amount of sulphur. It occurs in the corneous sheath of nerve-fibers. In the sheath of Schvirann is found a substance which is very similar to elastin. From the connective tissue of nerves may be obtained gelatin. Pats and Other Substances Soluble in Ether are found more particularly in the white matter. Cerebrin is a white powder composed of spherical granules. These are soluble in hot alcohol and ether, but are insoluble in cold water. Haitai has shown that lecithin, when administered to white rats^ caused a gain of 60 per cent, in body-weight compared with the nor- mal animal. Hence lecithin is a stimulant of normal growth. Lecithin consists of glycerin, two of the hydroxyl radicles, of which are combined with a fatty acid and the third one with phos- phoric acid, and this latter is combined with a body called cholin. Cerebrin is a nitrogenized body and yields on hydration with an acid a carbohydrate which has been identified as galactose. Cerebrin and lecithin when combined form a body called protagon. Halliburton has found cholin in the cerebro-spinal fluid and in the blood in inflam- mations of the nervous system. Eeaction. — When passive, nerve-tissue is neutral or feebly alka- line. When active or dead it is said to be acid. It is found that after death nerves have a more solid consistence. Probably some coagulation occurs which is to be compared to the stiffening of muscle. Simultaneously there is generated and liberated a free acid. Mechanical Properties. — A remarkable property of nerve-fibers is the absence of elastic tension according to the varying positions of the body. Divided nerves do not retract. The cohesion of a nerve is an important property. Oftentimes when a limb is forcibly torn from the body the nerve still remains intact (though considerably stretched), while the other soft tissues are completely severed. The sciatic nerve at the level of the popliteal ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 407 space requires a force equal to one hundred and ten or one hundred and twelve pounds to rupture it; the median or ulnar require forces equal to forty or fifty pounds. The latter nerves will stretch six to eight inches before the point of rupture is reached. It is upon the knowledge of this fact that the method of nefve-stretching is em- ployed in some forms of neuralgia. Nerve-metabolism. — Some extractives are obtained which are be- lieved to be decomposition products of the nerve. The Nerve-centers. — The nerve-fibers and nerve-cells comprise the essentials from which the nerve-centers are formed; the elements must, of course, be held together by enveloping neuroglia. The term center is merely applied to. an aggreg'ation of nerve-cells which are so related to one another as to subserve a certain function. These cells give off numerous processes whereby they are brought into direct communication with one another as well as other parts of the body. These masses thus form structural integrations which perform cor- responding integral functions. If at any time the structure suffers, the function must of necessity suffer also. The nerve-centers comprise the spinal cord, medulla oblongata, pons Varolii, cerebrum, and cerebellum. Common Properties. — There are certain properties which all nerve-centers seem to possess in common and which are of interest to the student: — 1. They all contain nerve-cells. These are the real centers of activity. They both originate and conduct impulses. Nerve-fibers are almost exclusively conductors. 2. Nerve-centers are capable of discharging reflexes. They are motor, secretory, and inhibitory reflexes. 3. They are the seat of automatic excitement when phenomena are manifested without the application of any apparent external stimulus. 4. The nerve-centers are trophic centers for both their nerves and the tissues supplied by them. THE SPINAL CORD. , Structure of the Spinal Cord. "The key to the study of the central nervous system is to remem- ber that it begins as an involution of the epiblast. It is originally tubular with a central canal whose brain-end is dilated into ventricles. In the spinal cord there are three concentrated parts: First, the 408 PHYSIOLOGY. columnar, ciliated epithelium ; outside of this is the central gray tube ; and, covering all, the outer white, conducting fibers." (Hill.) The spinal cord is that portion of the cerebro-spinal axis which is inclosed within the vertebral canal. It extends in the form of a large, cylindrical cord from the upper level of the atlas to the first or second lumbar vertebra. Above it is continuous with the medulla ob- longata. Below it becomes conical, to terminate finally in a slender filament: the fllum terminale. It is attached to the base of the coccyx. The filum terminale passes through and is partly concealed by the conical extremity of the spinal cord. The cone is a mass of nerve-roots which, from its striking resemblance to a horse's tail, has been termed the cauda equina. The average length of the spinal cord is eighteen inches. In the foetus the cord extends the whole length of the vertebral canal. The difference in relative length of the cord in the foetus and in the adult is due to the unequal and more rapid growth of the spinal canal than the cord. The cord thus seems to ascend in its canal. In- stead of the spinal nerves of the lower portion of the cord leaving their points of emergence horizontally, they sweep down like the hairs in the tail of a horse to form the aforementioned cauda equina. Coverings. — Not only is the cord protected by the spinal canal in which it is suspended, but in addition is enveloped by a triple membranous container. The cord does not more than half fill the lumen of the spinal canal. It is suspended in this cavity surrounded by an aqueous medium : the cerebro-spinal fluid. The investing membranes have been termed, from within outward, pia mater, arachnoid, and dura mater. They form a sheath, or theca, which is considerably larger than the cord. It is separated from the bony wall of the spinal canal by venous plexuses and loose areolar tissue. The pia mater is a very delicate eoveriug which is closely adherent to the cord. It sends numerous septa into the substance of the cord as well as into its anterior and posterior median fissures. It is composed of blood-vessels and connective tissue. The arachnoid (spider's web) is, as its names implies, a very deli- cate, reticular membrane. It is nonvascular. Hanging like a curtain between the innermost and outermost membranes, it forms two spaces which are termed subdural and subarachnoid. The outermost and toughest membrane is the dura mater. It is a very dense sheath and lies indirectly in contact with the canal-wall. However, unlike the dura of the brain, it does not form the periosteum ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 409 for the portions of the vertebrae constituting the walls of the spinal canal. Diameter of the Cord. — The volume of the cord is not the same throughout its whole extent. Although of a mean diameter of half an inch, yet it presents two decided enlargements. The one enlargement is at the level of the inferior portion of the cervical region; the other at the lower portion of the dorsal region. The first one is the cervical enlargement from which emerge the nerves of the upper extremities. The name brachial enlargement has been given to it. From the lower enlargement arise the nerves which proceed to the lower extremities. It is known as the lumbar enlargement. At the site of each enlargement the cord loses its cylindrical form to become somewhat flattened from before backward. The formation of the enlargements is in intimate relation with the development of the members. In fishes, which have only rudi- mentary members, the cord is of uniform diameter throughout. In steelworkers the cervical swelling is considerable. The weight of the cord is about one and one-fourth ounces; it is equa,l to about one-fortieth of the weight of the brain. The suspension of the spinal cord within the canal is maintained antero-posteriorly by irregular fibrous tracts which form the liga- mentum denticulatum. Laterally the roots of the spinal cord give support ; below the filum terminale fastens it to the coccyx ; above its continuation as the medulla furnishes the most important support. Exterior Form of the Cord. — Externally the cord has two longi- tudinal median grooves: one anterior, the other posterior. They traverse the entire length of the cord to divide it into two halves which are usually perfectly symmetrical. The origins of the spinal nerves are situated upon each side of these two parallel, longitudinal lines. The anterior median groove divides the anterior surface of the cord into two perfectly equal parts. It extends from the decussation of the pyramids to the caudal extremity of the cord. In depth it occupies nearly a third of the thickness of this organ. In this groove is folded a layer of pia mater ; at its base is seen a layer which passes from one-half of the cord to the other — the white, or anterior, com- . missure. The posterior median fissure, deeper and more narrow than the anterior, extends from the nib of the calamus scriptorius to the termi- nation of the spinal cord. Into this groove the pia mater sends but 410 PHYSIOLOGY. a simple partition ; but it is very adherent to the walls of the grooVe. The depth of the fissure is bounded by a commissure analogous to that which is furnished to the anterior median groove, but of a gray color. This is the gray, or posterior, commissure. Upon each side of the cord are seen two lateral grooves which represent the lines of implantation of the anterior and posterior roots. They are known as the antero- and postero- lateral grooves. The lat- ter is the more apparent of the two, showing itself in the form of a dotted, longitudinal line. The antero-lateral groove corresponds to the line of insertion of the anterior roots of the spinal nerves. The two lateral grooves may be regarded as purely artificial : seen only after the spinal nerves are torn from the cord. By virtue of the median and lateral fissures the cord is divided into columns, paired and symmetrical. The portion comprised be- tween the anterior median and the antero-lateral fissures is known as the anterior column. That portion between the two lateral fissures bears the name of lateral column. That part between the postero- lateral and posterior median groove is the posterior column. Anatomy and physiology demonstrate that the separation of the anterior from the lateral column is not complete; hence it is cus- tomary to reunite these two columns under the name of antero-lateral columns. Internal Conformation of the Spinal Cord.— The texture of the cord is best studied by means of transverse section. These sections show that the cord is composed throughout its whole extent of two substances: one, the cortical, white substance; and the other, the central, gray substance. The white substance is located peripherally and covers all of the gray substance except at the base of the posterior median groove. It forms the columns which have just been pointed out. The gray substance forms in each half of the cord a longitudinal column whose transverse section appears in the form of a crescent with its concavity directed externally. The crescent terminates in two swollen extremities, the anterior one having the name of anterior horn; the posterior one, that of the posterior horn. The two crescents are bound to one another at their convexity by the aid of a transverse band of gray substance, the gray commissure. This band is pierced centrally by a canal, the central canal of the cord. It runs down the central axis of the cofd and is accompanied on each side by a vein, the central veins of the cord. In all sections the gray AKATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 411 matter is vaguely represented by the letter H; perhaps better by the two wings of a butterfly united by a transverse bar. The column of gray matter is not exactly of the same form in its whole length. It is thicker in the cervical and lumbar regions than in the thoracic. The white matter is likewise thicker at the level of the cervico-dorsal and lumbar enlargements. At the level of the cauda equina the white substance forms but an enveloping layer for the gray matter. In the cervical and lumbar regions the anterior cornua are re- markable for their volume; toward the dorso-lumbar enlargements the posterior cornua increase in size. The anterior cornu of the crescent is swollen. The posterior is more slender and reaches to the surface of the cord. Each cornu possesses a swelling (head) and a somewhat restricted portion (cervix). The head of the posterior cornu is remarkable in that it is capped with a layer of neuroglia to which has been given the name of gelatinous substance of Rolando. It is nearly amorphous, and, in section, gives an appearance very similar to the small letter u. The substantia contains a few neuroglia cells, with some fusiform nerve- cells along its margin. In the inferior cervical and superior thoracic region the most lateral portion of the anterior cornu is shaped in a special fashion so as to constitute a particular prolongation. This is known as the lateral cornu, or intermedio-lateml column. The cells of this column are ar- ranged in groups of from eight to twelve bipolar cells whose long axes are vertical or more or less oblique. It is believed that these give origin to those fine meduUated fibers which form the splanchnic efferent fibers. On examination of sections it is seen that the anterior cornua do not reach to the surface of the cord. Hence that portion of the white substance which surrounds the anterior cornua reaches from the anterior median groove to the posterior cornua. It seems to form a homogeneous column : the antero-lateral column. In the rear, on the contrary, the posterior cornua sharply sepa- rate the preceding to form posterior columns. They lie between the posterior median groove and the posterior cornua. In the cervical region the posterior column is sharply divided into two secondary columns by the posterior intermediate groove. These are the columns of Goll (next to the posterior median groove) and Burdach (in appo- sition with the posterior cornu). From measurements by Stilling it seems that the cervical swell- ing results from a localization of superdevelopment of both the gray 412 PHYSIOLOGY. and the white matter of the cord. The lumbar enlargement is almost exclusively formed by a localized superdevelopment of gray substance. This is readily explained by the constitution of the columns them- selves. Excepting the fibers forming the roots of the spinal nerves, the columns of white matter are formed of descending, or motor, and . ascending, or sensory, fibers. The motor bundle successively gives off fibers to the motor roots of the spinal nerves to such a degree that in their descent their volume proportionately diminishes. The sensory, or ascending, bundle, receiving fibers from each posterior root which comes from a sensory nerve, enlarges as it ascends. Hence it results that at the level of the lumbar enlarge- ment the bundles are at a minimum, the ascending JDundle just com- mencing, while the descending bundle is nearly spent. Minute Constitution of the Cord. — The spinal cord is composed of fibers, nerve-cells, neuroglia, and blood-vessels. In the white . sub- stance there are found only nerve-fibers and neuroglia; in the gray substance, nerve-cells and fibers plunged in a stroma of neuroglia. White Substance.— The white matter is composed principally of medullaied fibers without the sheath of Schwann. The fibers in the white substance are, for the most part, arranged longitudiaally ; those which pass to the nerve-roots, as well as those fibers which proceed from the gray matter into the columns, possess an oblique course. In addi- tion there are decussating fibers in the white commissure. On cross-section the fibers (which are of different sizes) present the appearance of small circles with a rounded dark spot in their centers. This latter represents the axis-cylinder of the fiber. The diameter of the fibers varies from V5000 to ^Aaoo i^^h in diameter. The most voluminous are the motor parts of the antero- lateral column and direct cerebellar tract; the finest are in the posterior median column. Classification. — The fibers of the cord are classified into two great classes : intrinsic-ajid, extrinsic. Intrinsic. — This class of fibers originates in and terminates in the cord, thereby uniting the levels of gray matter. Fixed by their lower extremity upon a given point of gray substance, they follow an ascending course, to become lost by their extremity in a more or less elevated part of the gray column. Thus they are fibers of union or association for the purpose of establishing communication between the different levels of the gray substance of the cord. Extrinsic. — These fibers in the gray matter proceed to the gan- glia of the brain after having traversed the medulla oblongata. ANATOMY AND PHYSIOI-OGY OF NERVOUS SYSTEM. 413 pons, and crura. They unite the cells of the gray substance of the spinal cord to the upper nerve-centers. They are long and gradually diminish in number from the top to the bottom of the cord. Degeneration occupies their whole extent. Some are centripetal and undergo an ascending degeneration. They are contained in the column of GoU, the direct cerebellar bundle, and Gowers's tract. The others are centrifugal fibers, and undergo a descending degeneration. They are localized in the crossed pyramidal and bundle of Tiirck. They are the last ones to appear in the foetus. The roots of the nerves arrive at the central gray substance and plunge into it after having passed between the fibers of the peripheral white substance. But few of them take part in the constitution of the cortical white matter. Neuroglia. — In addition to the fibers just discussed the white matter of the cord contains neuroglia. From the neuroglia project extremely fine prolongations. These penetrate the cord to form within its thickness an infinity of partitions of extreme tliickness. These are united to the adventitious tissue of the vessels and to the tissue which serves as a basement membrane to the epithelium of the ependyma. Thus there is formed (on transverse section) a polygonal network which isolates little colonies of nerve elements one from the other. This sort of framework has been compared to a sponge in whose interstices are found the fibers and cells of the cord. Neuroglia does not belong to the category of connective tissues. It is a special formation which is derived from the primitive epi- blast. In the central gray substance the neuroglia does not seem any more than amorphous matter with some few cellular elements. The gelatinous substance of Eolando is composed of abundant neurog- lia in the form of amorphous matter. The only connective tissue present in the cord is carried in by the blood-vessels. Geat Matter of the Coed. — The gray substance of the cord is composed of neuroglia, fibrils, and nerve-cells. The cells of the cord are formed by a small mass of protoplasm in which is plunged a nucleus surrounded by pigment-granules. These cells, whose volume varies with the groups, have a certain number of prolongations. Cell-arrangement. — The cells of the cord are not disseminated in the gray substance in a disorderly way. They are grouped at certain points to form nuclei — nuclei of nerves; these are situated one above the other in a fashion to form columns parallel with the long axis of the cord. 414 PHYSIOLOGY. There are distinguished three groups in the anterior horns: an interior internal group, an anterior external group, and a posterior external group. In the posterior horns the cells are fewer in number; it is only at the internal part of the neck of these horns that there is found a grouping. It is known as the dorsal nucleus of Stilling or the vesicular colv/mn of Clarke. The ganglionic cells of the anterior horns are very large, star-shaped, and from '^/^^^ to ^/aoo ""^^^ ™ diameter. That is, they are nearly large enough to be visible to the naked eye. Degeneration. — The nuclei of origin of the anterior roots are seized with degeneration in the various forms of muscular atrophy. The cells, by reason of their function, are known as rmtor cells. They are motors for the muscles to which their nerves go, and trophic for the same nerves and muscles. Progressive muscular atrophy is fina- tomically characterized by a general atrophy of the motor cells of the anterior horns of the cord. Children's palsy is also characterized by an inflammation of these cells. The cells of the posterior horns, irregularly distributed in the neuroglia, are fewer in number and smaller in size than are those of the anterior horns. Their diameters average about '/1200 inch. Anatomically, the column of Clarke exists only from the second lumbar to the eighth dorsal pair of nerves. However, there are small erratic groups of cells and two restiform nuclei at the level of the medulla which are analogous to the two columns of Clarke. The cells of the column of Clarke are very large, star-shaped, and* only very meagerly branched. The intermedio-lateral gray column is in the outermost portion of gray matter, midway between the anterior and posterior horns. It lies in what is known as the lateral horn. It is the spinal origin of the great sympathetic. The greater part of the posterior root-fibers are said to end in these columns. From this as a source fibers pass into the column of 60II and the direct cerebellar tract; other fibers pass into the columns of Burdach and Gowers. To the degenerative changes within the cells of the column of Clarke have been attributed the vasomotor troubles of paralysis agitans. Sclerosis of the lateral columns explains the exaggerated trembling in the reflexes. The fibers of the cells of the gray matter form a spongy sub- stance which unites the two halves of the gray axis of the cord to one another. This, the gray commissure, passes in front of and behind the central canal of the cord. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 415 Neuroglia. — The neuroglia of the gray matter has a structure analogous to that of the neuroglia of the white substance of the cord. It is found in particular abundance at the extremity of the posterior horns (gelatinous substance of Rolando) and at the periphery of the central canal. The Central Canal. — This is a canal of very fine caliber located within the center of the gray commissure. It traverses the entire length of the cord and, at the level of the nib of the calamus scrip- torius, is continuous with the fourth ventricle ; by means of the latter it communicates with the ventricles of the brain. The wall of this canal, known as the ependyma, is composed — from within outward — of: (1) a ciliated epithelium, (2) an amor- phous basal membrane, and (3) a substratum of neuroglia which unites the wall of the canal to the body of the cord. The canal is flanked on each side by a longitudinal vein; the two constitute the central veins. Systemization in the Spinal Cord. — The spinal cord may be con- sidered as formed of a series of segments superposed. They are metameres corresponding to each pair of spinal nerves. Bach one of these is a complete center, being supplied with nerve-cells and motor and sensory nerves. Each one is different from its neighbor, since it innervates a particular area of the surface of the body, whether it be tactile surface or muscular group. The nerve-cells are grouped in motor and sensory fields. They are all in perfect comm.unication with one another by reason of nimierous fibers; some are longitudinal (longitudinal commissures) which unite the various levels of the cord; others are transverse (transverse commissures^ whose function seems to be to unite the cells of the right side to those of the left side of each segment. The transverse commissures are but from one to three centimeters in extent. In addition to the spinal commissures just mentioned, there are two other kinds formed by the long fibers uniting the spinal cord either to the cerebrum or cerebellum. They are known as the cerebrospinal and cerebellospinal fibers. Experimental physiology, pathological anatomy, and embryology all agree very admirably in demonstrating that the apparently homo- geneous cord is composed of distinct and specialized parts. These parts are called systems, which, in the white substance, form sec- ondary columns, or bundles. 416 PHYSIOLOGY. White Columns of the Cord. Flechsig ascertained that in the fcetlis the different bundles oi nerve-fibers did not all take on myelin layers at the same time. By taking advantage of this fact he was able to trace the bundles of fibers with myelin and thus map out the different tracts of the spinal cord and brain. Gudden extirpated an organ of sense and after waiting a sufficient length of time was able to trace the course of the atro- phied nerve-fibers. The nerve-fibers of the cord enveloping the central gray axis are distributed in different bundles or columns. These have previously been mentioned cursorily, but wUl now be discussed in detail. Anterior Coliimn.-^The anterior column comprises that area be- tween the anterior median groove and the line of implantation of the Fig. 100. — Transverse Section of the Spinal Cord. T. B., Burdaeh's tract. T. G., Goll's tract. T. P. C, Crossed pyramidal tract. T. C. D., Direct cerebellar tract. T. G., Gowers's tract. T. P. D., Direct pyramidal tract, or Tiirck's. T. L. P., Deep lateral tract. Straight lines are motor tracts. Little crosses are sensory tracts. Dotted spaces are cerebellar tracts. T. I., T. R., Root tracts. anterior roots of the spinal nerves. Its most internal fibers are com- missural ; they cross throughout the whole extent of the cord and so contribute in the formation of the white commissure. Other fibers run across at the same level to connect the large cells of the anterior horns of the two halves of the spinal cord. The anterior column comprehends two bundles: one, internal (next to the median groove), is known as Turch's bundle, or direct pyramidal bundle; the other, external, comprises the remainder of the anterior column and is known as the root-bundle of the anterior^ column, or antero-lateral ground-bundle. The bundle of Tiirck (pyramidal bundle, direct cerebral, direct motor) is formed of centrifugal fibers which descend from the brain into the cord without decussating at the level of the medulla ob- ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 417 longata. Its fibers are longitudinal and travel along and through the brain, the anterior pyramid of the medulla, and the same side of the corresponding half of the spinal cord. Yet, having arrived in the cord, some of its fibers cross to the opposite side along the path of the white commissure. They finally terminate in the cells of the anterior cornua. This bundle usually terminates about the second lumbar nerve. It undergoes descending degeneration. The antero-lateral ground-bundle (root-bundle of the anterior col- umn) occupies the territory between the preceding and the antero- lateral groove. It is formed in part by the anterior roots which descend in a certain course within its interior ; but especially by the more or less long, longitudinal fibers. The latter unite between themselves the successive levels of the anterior horns. It is thus in part a system of longitudinal commissural fibers. Lateral Column. — The lateral column is bounded between the line of implantation of the anterior roots and the line of insertion of the posterior roots. It is formed of fibers which are larger on the surface and much finer in the depths. This column comprises five different systems of bundles. They are : (1) the direct cerebellar; (3) the bundle of Gowers, or ascending antero-lateral cerebellar tract; (3) the crossed pyramidal tract; (4) tract of Loewenthalj or descending antero-lateral cerebellar tract; (5) deep lateral, or lateral marginal, zone. The direct cerebellar bundle, or tract, is situated at the posterior and superficial part of the lateral column in the form of a very thin band. It extends from the second lumbar upward to the restiform bodies, into the vermis of the cerebellum. It is formed of a collec- tion of centripetal fibers which unite the cerebellum to different levels of the vesicular column of Clarke. It develops ascending de- generation. About the cells of Clarke arborize the collaterals of the posterior root so that there is an indirect communication between the posterior roots and the cerebellum. The bundle of Gowers, or ascending antero-lateral tract, occupies the anterior superficial zone of the lateral column. This bundle com- mences at its inferior part in the lumbar swelling, increasing in size as it ascends by two orders of toots, some fine, others large. It termi- nates by its fine fibers in the lateral nucleus of the medulla; by its larger fibers in the cerebellum by way of the superior peduncle. This tract undergoes ascending degeneration. The crossed pyramidal tract (motor tract or cerebral crossed tract) is situated inside the cerebellar tract. The term has been 418 PHYSIOLOGY. applied to that which is contained within the pyramids of the medulla, and which decussates at this level with the opposite tract. It decreases in volume from above downward to terminate in from the second to the fourth lumbar pair. It is composed of long, centrifugal fibers which unite the motor regions of the cortex of the brain with the motor cells of the anterior horns of the cord. It undergoes descending degeneration as the re- sult of lesions which seize the cortex, internal capsule, or cerebral peduncle. A lesion of the pyramidal tract in the cord produces hemiplegia or monoplegia below the lesion and on the same side. Its degenera- tion, as a result of lesion of the brain, gives place to a crossed hemi- plegia, whose clinical mark, is a spasmodic contracture. It is well to remember that there is a double decussation of the motor fibers: one at the level of the neck of the medulla oblongata, the other much lower — the length of the white commissure. From this the student can comprehend why in the majority of hemiplegias the nonparalyzed member has, nevertheless, lost its muscular energy; also why a unilateral cerebral lesion is able to cause permanent con- tracture of the two inferior members or an exaggeration of the re- flexes of the side not paralyzed. The bundle of Loewenthal and Marchi, or antero-lateral de- scending cerebellar tract, comes from the cerebellum of the same side by the inferior cerebellar peduncle. The fibers form an extensive circumferential tract in the anterior three-fourths of the antero- lateral column, spreading inward to the intermedio-lateral column of gray matter, and run down to the sacral cord, gradually decreasing in their descent. Its fibers are mingled with those of Gowers's column. The deep lateral tracts lateral mixed tract, or lateral marginal zone, is molded upon the lateral concavity of the gray matter. It incloses at the same time the fibers coming from the anterior motor horns, the gray column of Clarke, and the gray intermedio-lateral column. Posterior Columns. — The posterior columns comprise that area of the spinal cord lying between the postero-lateral groove and the posterior median groove. It is composed of fine fibers in that portion nearest the median groove, and is remarkable for its abundance of neuroglia. This large tract is divided into two tracts : one internal, the other external. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 419 - The internal one, br column of GoU, is especially apparent in the upper part of the cord. Here it occurs in the form of a triangular pyramid whose base is turned toward the central gray commissure. It is formed by long commissural fibers which arch so as to unite the posterior horns. They proceed from the level of one posterior horn to that of a higher level. It incloses the posterior root-fibers which compose the major portion of it. The fibers of the column of GoU are very long, ascending from the cauda equina to the nucleus of this tract in the medulla. Its trophic centers are in the cells of the pos- terior horns. The more external and cuneiform tract, column of Burdach, con- tains short, commissural, longitudinal fibers which have the same dis- tribution as those of GroU, and sensory fliers, which also spring from the posterior horns, but do not sojourn there. Almost immediately they pass into the mixed lateral column of the same side, or, travers- ing the commissure, cross into the opposite tract. At the level of the medulla oblongata these fibers go to form the lemniscus, or fillet, which itself terminates in the corpora quadrigemina, optic thalami, and the sensorj^ convolutions. In transverse section of the cord there is ascending degeneration. The comma tract is composed of a few fibers in the column of Burdach. After lesions of the cord they undergo descending de- generation. These fibers originate from the descending fibers of the posterior roots. The posterior columns, and particularly the columns of Burdach, are the seat of the sclerosis known as tabes dorsalis, or locomotor ataxia. Clinically this disease is characterized by progressive aboli- tion of co-ordination, loss of equilibrium, paralysis of eye-muscles, loss of tendon reflexes, etc. Tracts of lissauer. — About the entrance of the posterior roots into the postero-lateral groove of the cord are found two small, cuneiform colimans. They are the root-zones of Lissauer. The one is internal, the other external. The two zones are formed by the posterior root-fibers at their entrance into the cord. They have the same properties as the posterior roots and undergo ascending de- ( generation under the same conditions that produce it in the latter. Roots of Nerves. The spinal nerves, thirty-one pairs in number, exist throughout the entire length of the cord. 430 , PHYSIOLOGY. The anterior root-fibers are composed of large nerve-tubes which lose themselves, for the most part, in the ganglionic cells of the anterior horns of the same or opposite sides. The posterior root-fibers are composed of fine tubes. After having arisen in the intervertebral ganglia they go toward the postero-lateral groove, where they enter the cord. There are here two groups of fibers : one external, the other internal. The external root-fibers penetrate into the gelatinous substance of Eolando, where they become ascending. After a more or less lengthy course they pass into the ganglionic cells of the posterior horn. The internal root-fibers, which pass into the posterior column, be- come lost either in the cells of the posterior horn or in the vesicular column of Clarke. Some very long fibers ascend to the nuclei of Goll and Burdach in the medulla, where they terminate. Some of the fibers traverse the posterior commissure to pass either into the anterior horn of the opposite side (and so belong to reflex motor actions) or into the posterior horn or descend in the cord as fibers of the comma tract. Commissures of the Cord. The white, anterior commissure is formed by a body of fibers which decussate upon the median line to pass into the lateral half of the cord opposite to that from which they came. It forms the major portion of the fibers of the direct pyramidal tract. This tract in its long course in the cord gives oil fibers in succession which go- either into the cells of the anterior horn or into the crossed pyramidal tract of the opposite side. The commissure also contains fibers which unite transversely the anterior horns of the two sides. The gray, or posterior, commissure is likewise formed by decussa- tions upon the median line both in front of and back of the central canal. The fibers comprising this decussation are : some of the fibers from the posterior roots on one side to terminate in the opposite posterior horn; al^o, fibers of the posterior horn which go into the deep lateral tract. MEDULLA OBLONGATA. The medulla oblongata is a continuation of the spinal cord which crowns its upper part in the form of a capital. It reaches from the cord to the pons Varolii. The medulla is an enlargement ^ in the form of a truncated cone, a little flattened from before back- ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 421 ward. It measures an inch in length, about three-fourths in width, and about one-half inch in thickness. Commencing toward the mid- dle part of the odontoid process, it inclines forward, to recline upon the basilar process of the occipital bone. The medulla forms with the cord an obtuse angle open in front. The back and sides of the medulla are embraced by the cerebellum. In front, the medulla is bounded anteriorly by the pons Varolii, posteriorly by a transverse iN.cerv, Fig. 101. — Medulla Oblongata, Pons, Cerebellum, and Pes Peduneuli. Anterior View, to Demonstrate Exits of Cranial Nerves. (Edinger.) line which unites the lateral angles of the fourth ventricle to divide its floor into two triangles. The anterior and posterior median fissures of the cord are con- tinued up into the medulla. The anterior fissure becomes somewhat indistinct at one poiat by reason of the decussation of the bundles forming the pyramids. The posterior median fissure terminates at the lower end of the fourth ventricle. The weight of the medulla is about one hundred grains. From the front and sides of the medulla arise the sixth to the twelfth cranial nerves, inclusive. 422 PHYSIOLOGY. External Form of the Medulla Oblongata. — Inspection of the inferior surface of the medulla brings to view first along the median line the anterior median groove. This, as before mentioned, is a con- tinuation of a similar groove belonging to the cord. In one area the crossing of the white fibers from side to side (decussation of the pyramids) renders this more shallow. At the base of the groove is seen a continuation of the white, anterior commissure of the cord. This layer unites the two pyramids of the medulla and is known as the raphe of Stilling. Anteeige Pyeamids. — On each side of the median groove are located two white columns, which are slightly enlarged at their upper ends and have the appearance of clubs. These columns are the an- terior pyramids. Olives. — Just outside of the upper portion of the pyramids are two prominent, oval masses whose longer axes are vertical. These bodies measure about one-half inch in length and one-fourth in breadth. They are the inferior olives. They are prominences added to the medulla, and do not have any similar portions in the spiaal cord. The olives are separated from the pyramid in front by a groove; in this latter is embodied the continuation of the false antero-lateral groove. In it is found the apparent origin of the hypoglossal nerve. Behind, the olives are separated from the resti- f orm bodies by another groove : a continuation of the postero-lateral groove of the spinal cord. From it emerge the glosso-pharyngeal, vagus, and spinal accessory. At their lower edge these grooves are somewhat effaced by the white arcuate fibers of the olive; these latter ascend in the restiform bodies. Eestifoem Body. — Back of the postero-lateral groove of the medulla, and therefore on its posterior surface, is found a large column of white substance : the restiform body. It seems to be con- tinuous below with the posterior columns of the cord; above with the inferior peduncle of the cerebellum. These columns form part of the anterior as well as lateral aspects of this organ. Posteriorly it is seen that the inferior third of the medulla is very different to the upper two-thirds. The inferior third is similar to the cord in that it possesses a posterior median groove continuous with that of the cord; on each side of it are two white columns. They are continuations of the posterior columns of the cord. At the base of the groove is foimd the gray commissure. In the upper two-thirds of the medulla this form is much changed. Here the posterior columns take the name of restiform ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 423 bodies, or inferior peduncles of the cerebelliim. Instead of pursuing a parallel course, they diverge from one another in such a manner as to leave between them at their upper end a V-shaped surface. The surface included within this angular space comprises gray matter. It forms the lower half of the floor of the fourth ventricle. The upper, angular portion is formed by the posterior face of the pons. The beginning of divergence of the restiform bodies presents an appearance analogous to that of a writing pen; hence its name: calamus scriptarius. The space between the restiform bodies presents a median groove. Above it passes over the posterior face of the pons; Fig. 102.— The Three Pairs of Cerebellar Peduncles. HlESCHFELD and LiEVEILLi;.) (After 1, Fossa rbomboidalis. 2, Strife acusticse. 3, Posterior cerebeUar pedun- cle. 5, Anterior cerebellar peduncle. 6, Fillet. 7, Middle cerebellar peduncle, or Bracbium pontis. 8, Corpora quadrigemina. below it is arrested by the point of divergence of the restiform bodies. This is known as the groove of the calamus scriptorium. From each side of this groove there proceed white transverse fibers whose direc- tion is at right angles to that of the groove. They are knovm as the harbce of the calamus, or auditory strim. These fibers are the posterior roots of the auditory nerve. The restiform bodies, which seem to form the limits of the floor of the fourth ventricle on each side of the calamus scriptorius, come up from the posterior columns of the cord. They ascend upward and outward toward the cerebellum. 434 PHYSIOLOGY. The columns of Goll and Burdaeh of the spinal cord as they enter the lower portion of the posterior aspect of the medulla seem to be divided into several distinct tracts. Bordering upon the pos- terior median fissure is the funiculus gracilis (column of Goll). As the tract approaches the fourth ventricle it broadens out to form the expansion known as the clava. The two clavse diverge to form the nib of the calamus scriptorius. Lying external, but adjacent, to the funiculus gracilis is another tract which is a continuation of the column of Burdaeh. It is the funiculus cuneaius. As previously stated, the upper, expanded portion of the gracilis has been termed the clava; the upper portion of the cuneatus is known as the cuneate tubercle. Both prominences are caused by underlyiag masses of gray matter. The scriptorial half of the floor of the fourth ventricle is divided into two lateral halves by a longitudinal groove. In each half can be seen three small prominences whose general shape is somewhat triangular. The first one, a triangle of white color, is the trigonum hypoglossi; it covers the nucleus of origin of the hypoglossus nerve. The second one, the trigonmn vagi and the continuation of the head of the anterior horn, corresponds to the nuclei of the ninth, tenth, and eleventh cranial nerves. It is the ala cinerea. The third emi- nence, the trigonum aeustici, covers the nucleus of the eighth nerve. Internal Structure of the Medulla. — The medulla oblongata, like the spinal cord, is formed of nerve-cells, nerve-fibers,vand a meshwork of neuroglia. As it is a continuation of the cord, one ought to find the white columns and central axis common to the spinal cord. As a matter of fact, the constituent elements of the cord are found in the medulla, but their position is changed very much. The cells forming the nuclei of nerves are analogous to those of the cord, but are more isolated. They also give exit to fibrils which unite them to other cells in the opposite half of the medulla and in the brain proper, and to nerves of which they are the seat of origin. In the medulla the grouping of these nuclei is quite different to that found in the spinal cord. However, it is always the same central gray sub- stance, but modified in its form and arrangement. The gray matter is cut here and there by white columns and their fragments. To understand this new disposition of the gray matter it is necessary to recall that at the level of the medulla the central gray substance of the cord has been pushed backward by reason of several factors. These are : the separation of the restif orm bodies, the pas- ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 425 sage outward of the posterior columns, and the formation of the rhomboid sinus. The latter is so arranged as to form the floor of the fourth ventricle. The posterior horns have become separated and are so rotated upon themselves as to be thrown outward and so placed at the external part of the fourth ventricle. The anterior cornua have their bases placed upon the floor of the fourth ventricle on each side of the median raphe. The isolated horn of gray matter is afterward known as the nucleus lateralis. Further, the crossed pyramidal tracts of fibers are carried for- ward, outward, and upward. By the oblique passage of these numer- ous white fibers through the gray matter of the anterior horn the anterior horn is broken up so that the caput is entirely separated from the remainder of the gray matter. The fibers in passing through the base of the anterior horns to decussate upon the median line with those of the opposite side give rise to \he reticulated formation of Deiters and to the raphe of Stilling. PoKMATio Eeticulaeis. — The formatio reticularis is an asso- ciated system of the short fibers with nerve-cells which is to be met with at any point between the spinal cord and the optic thalamus. These fibers run at right angles to one another. It is the result of the decussa- tion of the crossed pyramidal and arcif orm fibers which, in their march forward and upward, travel through the base of the anterior horns in the form of a multitude of small bundles. These arch and decussate from side to side. Still higher up the fillet decapitates, as it were, the posterior horns. The caput comes close to the surface, where it forms the distinct projection known as the gelatinous substance of Rolando. The cervix of the cornu becomes broken up in a manner similar to that of the anterior base. ' White Substance of the Medulla. — This is formed by the pro- longation of the columns of the spinal cord and by an additional white mass, the olive. White Columns. — The direct pyramidal tract, whose fibers decussate the length of the cord by traversing the white commissure, do not cross at the level of the medulla. They pass directly into this organ, to be placed in the anterior pyramid of the corresponding side. At the level of the medulla the two principal anterior columns, those of the right and left, which heretofore pursued a parallel course, now separate from the median line. They carry themselves outward and backward for a little distance, then bend inward to pursue a parallel 426 PHYSIOLOGY. course again. By this course there is formed a sort of elliptical but- tonhole which is ineiined obliquely from bottom to top. TraTersing this buttparfiole are found the crossed pyramidal bundles; both are carried toward the median line, where they decussate with their similars of the opposite side to produce the pyramidal decussation. Thus, the two principal bundles of the anterior columns have become posterior in the medulla, where they are placed in the deepest part of the pyramids. Lateral Columns. — The crossed pyramidal bundle in the medulla bends toward the median line. Here it meets its fellow of the opposite side, with which it decussates in the manner of a twist to arrive in the opposite side of the medulla. At this level, in the same pyramid of the medulla, there exist side by side the direct pyramidal column of the same side of the cord and the crossed pyram-. idal bundle of the opposite side. These two bundles now form one and the same group of nerve-fibers. This type of fibers forms the pyramidal, or cerebral motor, tract. Along this course descend, motor messages to the voluntary muscles from the brain to the an- terior horns of the cord, and then along axis-cylinders to the motor plates in muscles. An act incited by an impulse traveling along this course is always crossed, since the left hemisphere of the brain, for example, carries the order of motor power to the right half of the spinal cord by the crossed pyramidal fibers and to the left half of the spinal cord by the direct pyramidal tract. The latter tract decussates throughout the length of the cord with its fellow of the opposite side. Thus, the result is that the decussation is total for the pyramidal tract in its complete action, and that all of the voluntary parts excited from some part of the cerebral hemisphere end in muscles of the opposite side of the body. Prom this the student will deduce that lesions which affect the pyramidal tract above the medulla oblongata have as their direct result a motor paralysis opposite to the lesion; in other words, a crossed hemiplegia. PosTEBiOE CoLTfMNS. — The columns of GoU ascend to the me- dulla, where they pass, without decussation, into the postpyramidal nucleus, or nucleus of GoU. By this nucleus it is carried into the cerebellum, following part of the restiform body; another part is placed in relation with the nuclei of the pons. The column of Burdach comprises the longitudinal commissural fibers, the root-fibers of the posterior roots, and the sensory fibers issuing from the column of Clarke. The root fibers and commissural ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 437 fibers pass, without decussation, into the restiform nucleus, or nucleus of Burdaeh. Parts added to the medulla oblongata, which are not found in the cord, are : arcuate fibers and olives. Arcuate fibers are the curved fibers which are seen in transverse section of the medulla. By reason of their position they have been termed superficial and deep, or external and internal. Fig. 103. — Cross-section of the Oblongata through the Decussation of the Pyramids. (After Henlb.) PPV, Pyramidal tract. Cga, Anterior horn. Fa', Remnant of anterior column. Ng, Nucleus funiculi gracilis, g. Substantia gelatinosa. XI, Nervus acces^orius. The superficial arcuate fibers form a more or less voluminous ribbon. They are fibers which come from the cells ia Goll's and Burdach's nuclei. They proceed to the restiform body of the same side ajid thence to the cerebellum. The internal arcuate fibers likewise proceed from the cells of the nuclei of Goll and Burdaeh. The hindmost fibers form the sensory decussation of the fillet. Other fibers cross the median raphe in the substance of the medulla, then to pass upward into the brain. 438 PHYSIOLOGY. The olivary body is formed by a portion of the white cortical substance which belongs to the lateral column, by a layer of inter- vening gray matter folded upon itself, the corpus dentatum, in such a manner as to represent an oblong purse. This is open at its internal aspect, and is known as the hilus of the olive. The corpus dentatum of the olive is formed by a great quantity of small, multipolar cells. The fibers which emanate from it go to the olive of the opposite side, traversing the raph6 or mounting toward the pons. PONS VAROLII. The pons is a mass of nervous tissue placed transversely and in the form of a half -ring. It is situated between the medulla oblongata and cerebral peduncles, which limit it below and -above, respectively. The cerebellar hemispheres bound it laterally. Its weight is sixteen or seventeen grams. Por examination microscopically the pons presents six surfaces or faces. 1. The anterior face is free, convex, and rounded, and rests upon the basilar gutter of the occipital bone. It presents an antero-pos- terior median depression: the basilar groove. On each side of this are two parallel prominences due to the heaving up of the annular fibers by reason of the anterior pyramids which pass through it. Upon this face are seen the transverse fibers which pass laterally to penetrate into the corresponding hemisphere of the cerebellum. They thus form a large column upon each side, known as the middle cerebellar peduncles. 3. The posterior face forms part of the floor of the fourth ventricle, and is continuous with the corresponding face of the medulla oblongata. It forms a triangle whose apex, turned upward, is placed at the level of the lower orifice of the aqueduct of Sylvius. The sides of this triangle are formed by the superior cerebellar pe- dimcles. Upon the median line it has a groove which follows that of the calamus seriptorius. Upon each side there are two slight depres- sions : one known as the superior fovea, the other the locus cwruleus. 3. A superior face. 4. The inferior face is continuous with the base of the medulla oblongata. The annular fibers of the pons embrace as a half-circle the anterior pyramids of the medulla oblongata. The two lateral faces (5 and 6) are mingled with the origin of the middle cerebellar peduncles. The peduncles sink into the hemi- spheres of the cerebellum, where they are lost. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 439 Stnicture of the Pons. — The pons is composed of nerve-fibers and scattered nerve-cells. It forms a kind of knot into whicli con- verge the fibers coming from the cerebellum, as ■well as those passing to and fro from the mednlla into the cerebral peduncles. Fig. 104. — The Base of the Brain. The Left Lobus Temporalis is in pajt Repre- sented as Transparent in order that the Entire Course of the Optic Tract might be Seen. (Edingek.) The transverse fibers which form the cortex of this organ go in great part to the middle cerebellar peduncles. They are the com- missural fibers which unite one cerebellar hemisphere to the other. 430 PHYSIOLOGY. Some fibers emanate from the middle cerebellar peduncles and decussate on the median line with those of the opposite side. They thus form the median raph6. They terminate in the. gray masses of the pons. Other fibers, having decussated, bend upward and ascend into the cerebral peduncles. All of the yarious fibers — semi-annular, horizontal, and oblique — cover in the longitudinal fibers which unite the medulla oblongata to the cerebral peduncles. In them various planes are formed : (1) there is a superficial plane, or stratum zonale, which covers the two pyramidal columns; (2) the stratum profundvm, which separates the pyramids from the fillet and upper part of the pons; (3) the third plane, stratum complexiwn, separates the cerebral tracts. It is this separation which gives rise to the formatio reticu- laris of the pons and which is continuous with the formatio reticularis of the medulla. Between the superior, or pontal, olives there is a system of fibers which envelops and covers the olivary nuclei to decussate upon the median line back of the pyramids. It is to this system of fibers which unite the nuclei of the auditory nerves and the olives that Edinger has given the name of trapezoid body. The longitudinal fibers are in three grotips: 1. The anterior bundle, which contains the middle fibers of the cerebral peduncle. It is continuous with the superficial motor fibers of the anterior pyramids of the medulla; farther down it is still in connection with the pyramidal column of the opposite side of the spinal cord. 2. The middle column, or fillet. 3. The third group, the posterior longitudinal column, passes along the floor of the fourth ventricle, from which it is separated by . a plane of transverse fibers. It is continuous with the anterior column of the cord to form, consequently, the longitudinal com- missural column. Some of the fibers of this bundle decussate with their fellows of the opposite side to unite among themselves the nuclei of the motor nerves of the eye and the gray mass of the aqueduct of Sylvius. Each bundle is separated from its fellow by a plane of trans- verse fibers : the strata zonale and profundum. The gray substance of the pons is found isolated in small islands (nuclei of the pons), which are located between the various white layers which have just been mentioned. One of these nuclei, the most voluminous of all, is situated near the median raph6 at the site of the Junction of the inferior and ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 43 1 middle thirds of the pons. It bears the name of reticulated nucleus of the pons. At a slightly higher level is found another, known as the central nucleus. To these two nuclei are joined the root-bundles of the antero-lateral column of the cord. In addition, as a continuation of the posterior horns of the cord, there exists a nucleus which gives origin to the trigeminus. Inward and somewhat to the front is found a gray mass composed of large multipolar cells. These represent the caput of the anterior horn. It forms the nucleus of origin of the motor root of the trigeminus. Upon each side of the raphe and very close to the surface of the floor of the fourth ventricle are found other gray nuclei, as of the facial and oculomotor ; also a yellow mass of an S-shape which forms the superior olive of the pons. This latter is connected with the auditory apparatus. The gray substance of the medulla is prolonged into the pons to form the origin of the cranial nerves. CEREBRAL PEDUNCLES. The peduncles of the brain are two white cords which extend from the superior face of the pons in a divergent manner up in the optic thalami. They are somewhat flattened from top to base. Their volume is in direct relation to that of the brain. The peduncles are much larger than the columns of the cord reunited; they con- tain fibers coming from the gray matter of the meduUa, pons, corpora quadrigemina, locus niger, and masses of gray matter lying in a line along the aqueduct of Sylvius. In length the peduncles measure about three-fourths of an inch. Immediately after their emergence from the pons they separate, each one making its way toward its corresponding hemisphere of the cerebrum. Between them there remains a triangular space, the interpeduncular space, filled in its back part by a cribiform white layer containing a great number of vascular openings. The latter is known as the posterior perforated space. This space, bounded in front by the optic chiasm, is occupied by the mammillary eminences and tuber cinereum. Texture of the Peduncles. — A transverse section of the cerebral peduncles gives an idea of the architecture of the large nerve-trunks. In a cut of this kind it is seen that the peduncles are separated into two white, superposed layers by a black line : the locus niger. The inferior level, or crusta, of the peduncle is formed in great part by a large, flat, white bundle which is a prolongation of the motor fibers extending to the spinal cord. The crusta extends from 433 PHYSIOLOGY. the internal capsule through the pons to the ventral portion of the medulla oblongata. From the internal capsule its fibers become lost in the cortical layer of the hemisphere of its own side. The crusta is composed of two bundles, the internal, or cortico-pontal, and the external, or voluntary motor, bundle. The cortico-pontal bundle acts as a commissure between the cerebrum and cerebellum. It passes from the anterior region of the cerebrum through the peduncles to the pons and medulla, to end in the cerebellum. The voluntary motor bundle descends from the motor regions of the cortex to end in the nuclei of origin of the cranial and spinal nerves. Tegmentum. — The superior layer of the cerebral peduncle, known as the tegmentum, consists of masses of gray matter and fibers which extend through the posterior end of the medulla ob- longata, pons, and crura up to the optic thalami. At the height of the corpora quadrigemina is a reddish column formed of multipolar cells. It is the red nucleus of the tegmentum. In the tegmentum, between the fillet and the red nucleus, is found the formatio reticu- laris. The Locus Niger, which separates the pes, or crusta, from the tegmentum, consists of highly pigmented cells. They are like the cells of the motor regions of the cortex. Thus, the locus niger might be considered as a sort of motor ganglion whose cells are charged with black pigment. THE FOURTH VENTRICLE. The fourth ventricle is a rhomboid cavity (sinus rhomboidalis) imbedded upon the posterior surface of the medulla oblongata, and pons. It is the space into which the central canal of the cord opens superiorly. It is flattened from top, to base; and has an inferior wall, or floor; a superior wall, or vault; and four angles. Floor of the Ventricle. — The floor of the fourth ventricle is lozenge-shaped, being formed by two triangles placed in contiguity at their bases. It is lined by a layer of gray matter, which is but a continuation of that of the cord. The inferior triangle (calamus scriptorius) belongs to the pos- terior face of the medulla; the superior triangle to the posterior face of the pons. Upon the median line of the floor there is a slight groove: the handle of the calamus. On each side of this groove the surface of the floor presents small, rounded, and elongated prominences. These have been described at some length previously, so that now they will ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 433 be but mentioned. In the inferior triangle, from the handle of the calamus to the restiform body, they are: (1) trigonum hypoglossi; (3) ala cinerea, or trigonum vagi; (3) trigonum acustici. In the superior triangle, upon each side of the median groove and near the base of the triangle, are seen two rounded eminences: (1) eminentia teres and (2) the locU:S cceruleus. The various eminences correspond to the origin of the cranial nerves. Thus, in the locus cceruleus is located the origin of the small root of the trigeminus ; in the teres eminentia the common ori- gin of the facial and oculomotor; in the trigonum hypoglossi is the origin of the hypoglossal nerve ; in the ala cinerea, or trigonum vagi, occurs the origin of the motor roots of the glosso-pharyngeal nerves, pneumogastric, and spinal accessory; in the trigonum acustici are found the fibers of the auditory and the sensory fibers of the mixed nerves, glosso-pharyngeal, vagus, and spinal accessory. The trigo- num hypoglossi corresponds to the funiculus teres; the ala cinerea to a depression : posterior fovea. At the level of the middle of the floor of the fourth ventricle a variable number of striae go out from the median groove toward the lateral angles. Here they converge somewhat and form, according to some authors, the posterior root of the auditory nerve. The striations constitute the barhce of the calamus. The gray matter of the spinal cord, when it penetrates into the medulla, exposes itself upon the floor of the fourth ventricle. The horns of the central gray column of the cord are found broken up into many parts by the decussation of the pyramids and flUet. By reason of this, the gray matter in the floor of the ventricle repre- sents four irregular, discontinuous longitudinal columns; two are central, with a superficial one on each side. These columns are pro- duced by the bases and detached heads of the anterior and posterior horns of the central gray column. From the anterior gray matter proceed motor cranial nerves; from the posterior gray matter spring sensory cranial nerves. The lateral loundaries of the ventricle are, in the lower half, the elavae of the funiculi graciles, the cuneati, and the restiform bodies. In its upper half the superior peduncles of the cerebellum form the limits. AQUEDUCT OF SYLVIUS. The aqueduct of Sylvius is a canal a centimeter and a half long. It is hollowed out beneath the corpora quadrigemina; By means of 434 PHYSIOLOGY. this aqueduct the fourth ventricle communicates with the third. It is derived from the middle cerebral vesicle. Its walls are formed above by the valve of Vieussens, the corpora quadrigemina, and the white, posterior commissure. Its base, or floor, is formed by the tegmentum. Its floor is grooved by the continuation of the median groove of the fourth ventricle. Its walls are composed of gray matter continued from the spinal cord. Pig. 105.— The Fillet, Ending Chiefly in the Ventral Nucleus of the Optic Thalamus and then United by New Neuraxons (Upper Fillet) to Parietal Cortex. FILLETS. The chief fillet consists of the axis-cylinders from Goll's and Burdach's nuclei, which decussate under the floor of the fourth ventricle, then pass up through the tegmentum, and chiefly end in the ventral nucleus of the optic thalamus. From new neuraxons it goes through the posterior part of the internal capsule to the ascend- ing frontal and ascending parietal convolutions. It is a continuation of the sensory tract. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 435 The lateral fillet also starts from the nuclei of GoU and Bnrdach and is chiefly composed of axis-eyUnders from the end nuclei of the auditory nuclei and the superior olivary body; it then passes into the posterior corpora quadrigemina, and thence hy means of the brachium posterioris of the corpora quadrigemina through the pos- terior limb of the internal capsule to the first and second temporal convolutions. It is made-up mainly of auditory fibers. THE BRAIN. The weight of the brain is about fifty ounces. However, the weight of the braia may be, as in the case of Couvier, sixty-five ounces. It is greater in civilized persons than in savage tribes; it is ' likewise greater in the male than in the female; in an eminent man ' than in an ordinary man. But what really shows the superiority of the brain is not so much its size nor the exuberance of its convolutions, but the well-balanced development, the harmony, of -all of its parts. External Form. — The brain is composed of two symmetrical halves, or hemispheres. These are nearly entirely separated from one another by the great longitudinal fissure. The parts which are intact are located at the center and base and comprise the corpus callosum and floor of the fowrth ventricle. The surfaces of the hemispheres are separated into lobes and convolutions by various fissures. The con- volutions appear to be infoldings of the gray matter of the brain within its rigid confines, the cranial vault. The mode of spreading of the fibers of the peduncle may have something to do with their conformation also. The end obtained by their presence is to lodge a much larger gray mass within a given space. There are five principal fi^swes in the brain : (1) the great longi- tudinal; (3) the great transverse fissv/re between the cerebrum and cerebellum; (3) the fissv/re of Sylvius; (4) fissure of Rolando; (5) parieto-occipital fissure. As previously stated, the great longitudinal fissure runs antero- posteriorly to separate the two hemispheres of the brain. At its posterior end and at right angles to it lies the great transverse fissure. By it the posterior portion of the cerebrum is separated from the cerebellum. The fissure of Sylvius begins at the base of the brain at the anterior perforated space. It passes outward to the external sur- face of the hemispheres, where it divides into two branches. The one branch passes upward (ascending limb) ; the other, a larger one, runs nearly horizontally backward (horizontal limb). 436 PHYSIOLOGY. The fissure of Eolando commences at the great longitudinal fissure, half an inch behind its middle, measuring from the glabella to the external occipital protuberance. It runs down and forward to terminate a little above the horizontal limb of the fissure of Sylvius. The parieto-oceipital fissure commences about midway between the posterior extremity of the brain and the fissure of Rolando to run down and forward for a variable distance. The fissures which have just been mentioned are made use of to map out the surface of the hemispheres into regions to which the term lohes has been applied. This mapping is purely artificial and has no clinical or pathological bearing; in many instances the lines dividing the lobes are purely imaginary. However, anatomists are accustomed to speak of six lobes: (1) frontal; (3) parietal; (3) occipital; (4) temporal; (5) limbic, and (6) island of Reil. The island of Reil, or central lobe, is located at the bottom of the fissure of Sylvius. It is a portion of the cerebral cortex which is overhung by the operculum. The convolution of Broca is that portion of the inferior frontal convolution which winds around the ends of the anterior and ascending limbs of the fissure of Sylvius. It is characteristic in that it is the speech-center and also that it is better developed upon the left side in right-handed people. On the internal, or mesial, aspect of the hemispheres are the following fissures and convolutions: The convolution immediately bounding the corpus callosum is termed the gyrus fornieatus; the hippoeampal gyrus ends inferiorly in a crochetlike extremity, termed the uncus. The gyri fornieatus and hippocampus together form the great limbic lobe; the marginal convolution is merely the internal aspect of the convolutions of the frontal and parietal lobes. That portion which forms the mesial aspect of the ascending frontal con- volution is known as the paracentral lobule. Upon the mesial aspect of the postero-parietal lobule is a quadrilateral lobule: the praecuneus. Between the parieto-oceipital and calearine fissures is a wedge- shaped lobule called the cuneus. Structure of the Cerebral Convolutions. — The gray matter of the cerebral cortex has been divided into four layers : — 1. The superficial layer. 2. The layer of small pyramidal cells. 3. The layer of large pyramidal cells. 4. The layer of polymorphous cells. Fig. 106. — Section through the Cerebral Cortex of a Mammal. (Edingee and Cajal.) 1, Superficial, or molecular, layer. 2, Layer of small pyramidal cells. 3, Layer of large pyramidal cells. 4, Layer of pclymorplious cells, a, b, c. Ganglionic cells, d. Fusiform cells, e. Fibers. /, Pyramidal cells, p. Multipolar cells. 438 PHYSIOLOGY. The first layer contains the cells of Cajal. In this layer termi- nate many of the fibers coming from the spinal cord, medulla, and cerebellum. The second layer contains the small pyramidal cells, whose axons run into the superficial layer. The third layer contains the cells of Martinotti, with the large pyramidal cells. The fourth layer is made up of triangular, small pyramidal, and spindle cells. The white matter of the hemispheres consists of meduUated fibers whose size is varied. As a rule, however, they are smaller than those of the cord and bulb. For the most part, they are arranged in bundles separated by layers of neuroglia. Central Ganglia of the Brain. — At the level of the hilus of the brain the cerebral peduncles sink into the body of the two herai- i spheres. They contain fibers which proceed from the cord, pons, and cerebrum to the brain, as well as those fibers from the brain to the cord, pons, and cerebellum. There are also direct fibers which reach from the peduncles to the brain cortex. However, there are other indirect or ganglionic fibers which communicate previously in the nuclei or ganglia of the gray substance. The ganglia referred to are : the optic thalami and the corpora striata. The optic thalami are two oval bodies placed upon the tract of the cerebral peduncles. At the posterior part of the thalamus are the external and internal geniculate bodies. Between the pulvinar and origin of the pineal gland is found a small surface, slightly depressed and of triangular form; it is the triangle of the hahenula. Within this triangle is a small prominence known as the nucleus of the habenula. The haben- ula is the peduncle of the pineal gland. The inferior surface of the thalamus rests upon the cerebral peduncle, from which it receives some fibers. In the rear it remains free, and presents two nipplelike swellings: the geniculate bodies. One lies internal; the other external. ; Monakow divides the nuclei of the thalamus as follows : (1) an- 'terior, (2) median, (3) ventral, (4) posterior, and (5) pulvinar. The posterior root-fibers arborize about the nuclei of GoU and Burdach. Prom there they are continued by a second neuraxon to end in the ventral nucleus of the thalamus. Each thalamus has a double con- nection with all parts of the cerebral cortex by neuraxons from its various nuclei to the cortex, and by neuraxons from the pyramidal cells of all parts of the cortex. The neuraxons of the ganglionic ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 439 eell-layer of the retina end about the cells of the pulvinar and ex- ternal geniculate body, thus connecting it with the primary division of the optic tract. It has also a double connection with the occipital lobes by nenraxons from the pulvinar cells (optic radiations), which terminate in the pyramidal cells of the occipital cortex and by neu- raxons from the pyramidal cells of that lobe which end in the cells of the pulvinar. Corpora Striata. — The corpora exist as two large ovoid gray masses lodged within the thickness of the frontal lobe. They are situated in front of and slightly outward from the optic thalami. The outer surfaces of the corpora are in relation with the island of Eeil and the centrum ovale of the hemispheres. Internally, they are in apposition with the optic thalami and the gray layer of the third ventricle. They are formed of two large nuclei: the caudate and lenticular. The nucleus caudatus is so named from its resemblance to a pear in shape. It lies inside the lateral ventricle upon its floor. The cells of -this nucleus are of two types — sensory and motor; the cells of the motor type seem to be more abundant. The nucleus lenticularis, a part of the. corpus striatum, is sepa- rated from the caudate nucleus by the internal capsule. By reason of its situation near the center of the body of the hemisphere and outside of the ventricle it is called the extraventriciilar nucleus of the corpus striatum. The lenticular nucleus is divided into three segments by two layers of white matter placed within its thickness. The segments are distinguished from one another by their color, which is most pronounced in the external segment. The latter has received the name of putamen. The two other segments are known as the in- ternal and external segments of the globus palUdus. Hence it ensues that the corpus striatum has the general char- acter of the letter c, its upper extremity, or branch, being repre- sented by the caudate nucleus; its lower branch by the lenticular nucleus. The point of union of the two forms the knee. The corpora striata are of cortical origin, and not of central origin, as is the thalamus. That is to say, the nerve-impulses of voluntary move- ment ordered by the cortex descend to the corpora striata, where they undergo transformation before appearing as muscular move- ments. The Claustrum. — To the corpora striata is attached a thin layer of gray substance, so placed that it occupies the field between the 440 PHYSIOLOGY. lenticular nucleus and the island of Eeil. This band, derived from the cortex in a manner similar to those fibers of the corpora striata just mentioned, is the claustrum. It is separated from the external surface of the lenticular nucleus by a band of white substance: the external capsule. The claustrum is composed of spindle cells, quite like those found in the deep layer of the cortex. The claustrum should be con- sidered as a part of the cortex that has been detached by reason of the passage of a bundle of fibers of association. These fibers unite the various convolutions among themselves. The corpora quadrigemina are four small bodies or rounded emi- nences. They are composed, for the greater part, of gray matter, although covered externally by and containing in their interior some white fibers. They lie beneath the pulvinar of the optic thalamus. The corpora are arranged in two pairs: one anterior, the other posterior. The upper, or anterior, pair is broader, longer, and darker than the posterior pair. Laterally the corpora extend into distinct and prominent tracts of white substance. The lower, or posterior, corpora are composed almost entirely of gray matter. Internal Capsule. — The name of internal capsule is given to a thick band of white fibers situated between the optic thalamus and caudate nucleus on one side and the lenticular nucleus on the other. In a frontal section of the brain the tract is seen to follow a course upward and outward in an oblique manner between the preceding nuclei. Downward it is continuous with the cerebral peduncle. Where the capsule enters the lenticular-striate defile it expands like a bundle of stalks to form the corona radiata of Eeil. If studied horizontally, the internal capsule is seen to present the shape of an angle opening outward and embracing the lenticular nucleus. The capsule seems to be composed of two parts or segments and a hend, or genu. The anterior segment is placed between the lenticular and caudate nuclei; it bears the name of arm, or lenticulo-striate segment. The posterior segment, situated between the optic thalamus and lenticular nucleus, for this reason takes the name of lenticulo-optic segment. • The point of union of the two segments is called the Icnee, or genu. Its position is exactly at the center of the three nuclei just mentioned. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 441^ Capsular Structuee. — ^With the naked eye or even a microscope the internal capsule presents itself as a homogeneous structure, composed of white fibers. There is nothing in its appearance to let anyone suppose that there are diflEerent tracts or bundles. How- ever, pathological anatomy, with its secondary degeneration, and embryology, by reason of the myelin appearing in the bundles at different stages of development of the foetus, reveal a number of segments perfectly separated either from a functional or pathological point of view. The three bundles of fibers are distributed somewhat as follows in the capsule: — 1. The Cortico-Pontal-Cerebellar Tract is composed of neuraxons coming from the pyramidal cells of the frontal lobes. Then the neu- raxons pass through the anterior two-thirds of the anterior segment of the internal capsule, then through the crusta, ending in some of the pontal nuclei. These pontal nuclei are joined by neuraxons to the fibers chiefiy from half of the cerebellum of the opposite side, al- though some fibers are from the cerebellar half of the same side. Hence the frontal lobes are anatomically connected with the oppo- site cerebellar hemisphere. 2. The Motor Tract, which arises from the neuraxons of the large pyramidal cells of the ascending parietal and ascending frontal convolutions and paracentral convolutions; then go through the an- terior two-thirds of the posterior segment of the internal capsule; then through the crusta to the anterior pyramids of the medulla oblongata, where they partly decussate, becoming the crossed pyramidal tract of the opposite side of the spinal cord, ending in the cells of the anterior horns. Part of the motor tract passes dovm on the side upon which it originated as the tract of Tiirck, then through the anterior white commissure into the cells of the anterior horn of the opposite side of the cord. Here we have a long neuraxon or axon from the motor convolution to the anterior horns of the oppo- site side of the spinal cord. From here a second axon starts out to supply the muscles, making only two axons in the motor tract. The motor tract includes a band of fibers running from the cortex to the nucleus of the various motor cranial nerves. Thus the cortex sends motor fibers to the nucleus of the third, fourth, motor division of fifth, the sixth, the seventh, the motor divisions of the ninth and tenth, and the eleventh and twelfth pairs. We only know the cortical origin of the seventh, the motor branch of the fifth, and the hypoglossal, and these originate from the lowest third of the 442 PHYSIOLOGY. ascending frontal and ascending parietal convolutions; then they pass through the knee, or genu, of the internal capsule and continue through the crusta until they end in the nuclei of the various cranial motor nerves. As this tract passes through the genu of the capsule it is known as the geniculate tract : a part of the main motor tract. 8. The Sensory Tract. — Its axons arise in the ganglion of the posterior root and extend from the skin and muscles to the spinal cord, where they divide into an ascending and descending branch. The descending branches arborize about the cells in the gray matter of the cord. The ascending branches in great part ascend in the columns of GroU and Burdach and arborize in the cells of the nuclei of GoU and Burdach. From the nuclei of GoU and Burdach a second series of axons pass under the name of the fillet or lemniscus or inter- olivary tract, decussating under the floor of the fourth ventricle and chiefly arborize about the cells of the ventral nucleus of the thalamus. From the ventral nucleus a third set of neuraxons arise and go through the posterior part of the posterior segment of the internal capsule, to the ascending frontal and ascending parietal convolutions. This tract also receives the neuraxons of the sensory nuclei of the cranial nerves running to the cortex excepting the auditory nucleus. In the internal capsule the motor fibers going to the face are in front; next the arm- and then the leg- fibers. Hence lesions occur- ring in the anterior two^thirds of the posterior limb of the capsule cause motor troubles; lesions in the posterior third cause sensory troubles. The sensory tract is composed of three neuraxons: one from the skin to GolPs and Burdach's nuclei, the second from these nuclei to the ventral nucleus of the thalamus, and the third from this ventral nucleus to the cortex. Pain and temperature sensations travel through the gray matter. Blood-supply of the Brain. — The brain is freely supplied with arteries. The brain with its enveloping membrane is said to receive fully one-fifth of the entire quantity of blood within the body. The brain with its adnexa is supplied by the two vertebrals and the two internal carotids, with their numerous branches. These principal vessels form a free anastomosis at the base of the brain, known as the circle of Willis. The circle is composed of the tip of the basilar, the two posterior cerebrals, the two posterior communi- cating, the tips of the two internal carotids, the two anterior cere- brals, and the anterior communicating, which connects the two anterior cerebrals. The nucleus eaudatus and the nucleus lenticularis are almost ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 443 exclusively supplied by the middle cerebral artery, whose branches pass through the foramina of the anterior perforated space. The branches are subdivided into the lenticular, lenticulo-striate, and Imticulo-thalamic arteries. These vessels pass to their terminations without anastomosing with one another. One of the lenticulo-striate arteries which passes through the outer part of the putamen is very frequently the seat of haemorrhage. By Charcot it was named the artery of cerebral haemorrhage. The lymph finds its way out of the various areas of the brain by means of perivascular spaces in the tunica adventitia of the blood- vessels. These spaces communicate with the subarachnoid space at the surface of the brain. PHYSIOLOGY OF THE NERVOUS SYSTEM.^ Comparison of Nerve and Muscle. — In the study of the general physiology of muscle there was first analyzed its most apparent phe- nomenon: muscular contraction. Then was considered the forces which provoke muscular contraction, with modifications of muscular excitability. Practically the same course will be adopted in treating of the general physiology of the nerves. First there will be considered that property comparable to the muscular contraction; in turn will follow a study of the forces which produce the nerve-wave, with modifications also of the nervous excitability. Thus, there will be established a sort of parallel between nerv- ous and muscular functions; muscular contraction and nerve-wave; muscular irritability and nervous irritability; muscular excitability and nervous excitability. When a nerve is separated from its nervous centers and no force intervenes to modify its state, then it will remain inert. There will be neither movement nor sensibility. Neither will the nerve come into action unless it be stimulated or excited. Nerve Excitability. — When a stimulus is applied to a nerve it enters into activity. There are various ways in which this activity is manifested, as by modification of motion or sensation, and besides these external manifestations a latent property in the nerve itself, known as negative variation, which it undergoes during activity. The most striking exhibit of nerve activity is the contraction of the muscle supplied by the nerve. If we would estimate the irritabUity ' For anatomy of the cerebellum and mesencephalon see subsequent pages. 444 PHYSIOLOGY. of a nerve it is necessary to know accurately both the intensity of the stimulus and the result produced. Irritability requires for its due manifestation the integrity of the nerve and an unimpaired cir- culation and nutrition. But even in a normal state the irritability of the nerve is extremely variable and in a constant state of instability. Intervals of repose alternating with activity are the most favor- able conditions for the maintenance of irritability. When a nerve ■ remains at rest for a long time the irritability diminishes and may even be abrogated, conducing to degeneration of the nerve. Ex- cessive stimulation has a similar tendency to destroy the nerve. For a proper appreciation of so delicate a structure as the nervous tissue and the changes of a fundamental order occurring within it, the student should picture to himself the physical condi- tion of the nerve; how it is composed of molecules in a state of stable eqtdlibrium. With this conception he will readily see how any ex- ternal stimulus may produce molecular movement in one direction and hold them in said position for any variable time. With cessation of the exciting cause the molecules will be re- leased from their rigid condition and immediately return to their previous normal state* This "return" is the occasion of changes in the opposite direction. Thus, any power that is capable of pro- ducing movement in any one direction is sure to be succeeded by movement in the opposite direction as the molecules of the nerve resume their normal, gtable equilibrium. This fundamental principle must constantly be kept before the student's mind, since many of the physiological phenomena of ihe nervous system are dependent upon it, or their conception is materi- ally aided by remembering it. Ieeitability of Different Points of the Same Nerve. — The farther from the muscle the nerve is stimulated, the lower will be the original irritability. It was upon this fact that Pfliiger predicated his erroneous avalanche hypothesis : that a nerve-wave gathers force as it passes along the nerve-fiber. The true theory about the fact is that the irritability of the nerve is elevated in the neighborhood of the cross- section by the passage of the demarcation current through that por- tion. It has been shown by mechanical stimuli that the uninjured nerve has an equal irritability throughout its whole length. Effect of Heat on Nerves. — Any sudden change of temperature acts as an excitant of a nerve. A temperature below 34.8° F. or above 95° F. applied to a motor nerve of a frog calls out a contrac- tion of the muscle. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 445 If, however, a nerve be gradually frozen it will regain its excita- bility upon thawing. When a nerve is cooled in the case of the frog the irritability persists for a long time. If a nerve of a frog is heated to 113° F. its excitability is- increased and then diminished. In the case of a man who plunged his elbow into a freezing mixture, so as to greatly cool the ulnar nerve, there was no contraction, but pain in the parts innervated by the nerve. The Transmission of the Nerve-wave. — This demands that the nerve-fiber stimulated be entirely sound. It has the following phe- nomena: The nerve-wave passes in both directions in both sensory and motor nerves. When a nerve is irritated by an electrical current the electromotive phenomenon of negative variation is seen in botli ends of the nerve. In Bert's experiment of fixing the end of a rat's tail in a wound in the back and dividing the tail at its root after union had ensued shows that the stimulus is transmitted both ways in the case of sensory nerves. When the root of the divided tail was irritated there followed symptoms of pain, showing that the nerve impulse of sensation was transmitted in a direction opposite to the normal one. This fact is somewhat difiBcult of explanation, but in support of it comes Kiihne's classical experiment. This investigator takes the sartorius muscle of a frog and separates it lengthwise, beginning at its extremity, so that two small tongues are formed. Bach tongue receives nervous filaments from the same peripheral branch. If one of these small tongues be mechanically stimulated the exciting state of the motor nervous fiber is found to be communicated to the other small tongue. Since the second small tongue was excited by a motor stimulus to the first one, it follows that the conduction occurred in a centripetal direction along the course of a motor nerve. This direc- tion is different from that of normal conduction, for the nerve which has been thus excited is a centrifugal motor nerve. Therefore, since the motor nerve has played the role of a centripetal conductor in this experiment, it follows that a motor nerve can conduct an excitation in both directions. Swiftness of the Nerve-wave. — Compared with the rapidity of an electrical current, the nerve-current is immeasurably slower. In the motor nerves of a frog Helmholtz made it about 88 feet per second. In the horse Chauveau found it to be about 227 feet per second in the motor nerves of the larynx and only 24 feet in the motor nerves of the oesophagus. In sensory nerves the velocity of the nerve-wave is variable, but may be put down as 150 feet per second. Cold dimin- 446 PHYSIOLOGY. ishes the swiftness of the nerve-wave. If the intensity of the elec- trical stimulus is increased the swiftness is increased. The part of a nerve in a state of an eleetrotonus slows the rapidity of the nerve- current, and this is more perceptible as the duration and intensity of the polarizing current increases. Catelectrotonus favors the rapidity of the nerve-wave, except for very strong currents, where the rapidity of the nerve-current is arrested. I have found that stretching a nerve lowers the rate of transmission of nerve-force. The method of Helmholtz to measure the velocity of the nerve-wave is as follows : He stimulated a motor nerve of a muscle and registered Kg. 107. — Curves Illustrating the Measurement of the Velocity of a Nervbus Impulse (Diagrammatic). (Foster.) To be read from left to right. The same muscle-nerve preparation is stimulated (1) as far as possible from the muscle and (2) as near as possible to the muscle; both contractions are registered by the pendulum myograph exactly in the same way. In 1 the stimulus enters the nerve at the time indicated by the line a, the contraction, shown by the dotted line, begins at 6'; the whole latent period therefore is indicated by the distance from a to V. In 2 the stimulus enters the nerve at exactly the same time (a) ; the con- traction, shown by the unbroken line, begins at 6; the latent period there- fore is Indicated by the distance between a and h, ' The time taken up by the nervous impulse in passing along the length of nerve between 1 and 2 is therefore indicated by the distance between & and V, which may be measured by the tuning-fork curve below. N. B. — No value is given in the figure for the vibrations of the tuning- fork, since the figure is diagrammatic, the distance between the two curves, as compared with the length of either, having been purposely exaggerated for the sake of simplicity. the time of its' contraction after excitation. After a while the same nerve was stimulated at a point nearer its distribution with the muscle. Its time was also registered. The second time was found to be shorter than the first, so that the difference between it and the preceding must represent the time required between the two excita- tion points for the transmission of the nerve-wave. The distance between the two stimulated areas being known, one can very readily calculate the swiftness of the nervous action. Excitability and Conductivity. — ^Excitability of a nerve is its ability to react to the irritations received by it, not only at one spot, ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 447 but through its whole length. Conductivity is the property of trans- mitting its whole length, up to terminal extremity, a nerve-wave which has been called out by an irritant. If a part of a trunk of a sciatic nerve of a frog is submitted to the action of carbon dioxide and you stimulate that part, no contraction ensues. But if you stimulate the nerve above this point a tetanus ensues. Here the nerve-wave must travel through the part affected by the carbon dioxide. Hence it is inferred that conductivity and irritability are separate properties in a nerve. Excitants of the Nerve. — Nerve-excitants are all those forces which modify its. state. There are electrical, thermal, mechanical, and chemical excitants. From the fact that they may act upon a N f Fig. 108. — Scheme of Electrotonic Excitability. The nerve (??-») is traversed by a constant current in the direction of the arrow. The curve shows the degree of increased excitability in the neighbor- hood of the cathode (B) as an elevation above the nerve; diminution at the anode (A) as a depression. The curve i-h-g shows the degree of excitability with a strong current; the curve f-e-d with a medium current, and the curve c-i-a with a weali current. A, is anode. B, is cathode. nerve in any part of its course, they are frequently designated as general stimuli. The above are the excitants of the sensory and motor nerve. However, it must not be forgotten that in the normal being it is not these forces which come into play to stimulate to activity the motor nerve. The normal excitant is the physiological stimulus; it is the will. It originates within the nerve-centers, from where it is trans- mitted to the motor nerve. Any stimulus when applied to a nerve causes the molecules in that localized area to vibrate and so produce certain electromotive changes. By the changes set up in this par- ticular area of nerve, the contiguous parts are necessarily also brought into activity by reason of nerve-conduction. By many authors this transmission of changes along the course of the nerve so as to act as excitants is known as the true physiological stimulus. 448 PHYSIOLOGY. Thus, the vibrations in each segment perform the function of excitant for each succeeding segment. Electrical Excitants. — This form of stimulus is surely the most important to study and is, perhaps, the one that is most com- plex. The electrical stimulus may consist of either the constant or interrupted current. The stimulation of the nerve may be direct, as when the electrodes are applied to the nerve. There are two kinds of currents used: the induction current and the galvanic cur- rent. I shall take up the constant current. The passage of a con- stant current through a nerve changes its irritability and conduc- tivity and the nerve is said to be in a state of electrotonus ; the positive pole is the anode and the negative pole is the cathode. The nerve about the positive pole is said to be in a state of anelectrotonus, the parts about the cathode are said to be in a state of cateleetro- tonus. , When the current runs up the nerve, the anode nearest the muscle, then the current is said to be ascending. In the descending current the anode is farthest away from the muscle. The parts at the anode are decreased and at the cathode increased in excitability. When a constant current passes through the motor nerve a £ontraction takes -place only at the closing and at the opening of the current. These opening and closing contractions occur, according to Pfliiger, as follows ("No" means rest for muscle; "Yes" means contraction of muscle) : — CUHBENT. Descending. Ascending. MAKE. BREAK. MAKE. BREAK. Weak. . Yes. No. Yes. No. Medium ... Yes. Yes. Yes. Yes. Strong Yes. No. No. Yes. These laws are explained as follows : — With Ascending Current. — 1. If the current is strong the anelec- trotonic part of the nerve loses its conductivity, the stimulus of the closing is not transmitted to the nerve and no contraction follows. At the opening of the current the anelectrotonus disappears, stimu- ktion is produced at the anode, and the muscle contracts. 2. If the current is moderate the conductivity of the aneleetro- tonic part is not affected and the stimulation produced at the open- ing and closing of the current is transmitted to the muscle, which contracts. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 449 3. With weak currents the stinmlation is only active at the point farthest from the muscle, and the closing produces contraction. With Desceniiing Cwrrent. — 1. With strong currents the stimulus of closing produces a contraction, but the stimulation of opening acting on the anelectrotonic part has no effect. 3. With moderate current contraction ensues on the opening and closing of the current for the same reasons as in the case of the ascending current. 3. With weak current the onset of catelectrotonus is a more powerful stimulant than the disappearance of the anelectrotonus; the effect of the latter is too slight to manifest any action. Mechaitioal Iksitants. — Nerves respond to mechanical stimu- lants only when the disturbance which reaches them possesses a certain suddenness. By this suddenness there is produced a change in the form of the nerve-particles. Thus, the blow, pressure, pinch- ing, or section must be accomplished quickly; if a nerve be squeezed slowly it may be completely destroyed without having provoked move- ment in the muscle innervated by the same. Chemical Excitants of the Neeve. — Certain substances which act with a certain degree of rapidity upon a nerve-fiber are capable of acting as nerve-stimuli. Nearly all' chemical substances, other than very dilute salts and very weak acid solution, excite the nerves. Glycerin is a very energetic nervous stimulant. This fact is interest- ing, since glycerin is not a chemical excitant of muscular tissues. It owes its function to its dehydrating properties. Seat of Reflex Action. — Experiments prove that the transforma- tion of feeling into movement takes place in the spinal cord. This doctrine is universally accepted to-day. The fundamental experiment is as follows: A frog is decapi- tated. When one of its feet is touched the same is at once with- drawn and movements of escape are made. As a probe is passed into the spinal cord to destroy the same, convulsive movements of all the muscles are immediately provoked. The aspect of the frog is now altogether different. It has become flabby, inert, and it no longer reacts to the different excitants. Nevertheless, its muscles and nerves in themselves are irritable. Muscles contract when an elec- trical irritant is applied either to the muscle (direct excitation) or to the nerve (indirect excitation). What was destroyed in the frog and prevented the transforma- tion of feeling into movement was the nert)e-ceZL- an anatomical ele- ment which becomes absolutely necessary for such transformation. 29 450 PHYSIOLOGY. Reflex Action. — A motor reflex act is the transmission of an irritation by the neuraxon of a sensory neuron to the dendrons of a motor neuron and hy its neuraxon in turn to the muscle. The functions of the gray substance of the nervous centers can be known only through reflex movements; so that, to study reflex action is to study the nervous centers. From a knowledge of the principles of a reflex action it will be seen that three stages must be considered : 1. The external excitation which goes to excite the nervous centers through the sensitive nerves as a medium. 2. The excitation of the nervous centers which re- ceive the irritation and then transform and modify it; through the medium of the motor nerves it is communicated to the muscles. 3. The contraction of the muscle thus innervated. Othee Seats. — It is not only in the spinal cord properly so called that there are reflex acts. There are some in the meikilla oblongata, in the pons, and in the gray parts of the brain. The physiological study of strychnine shows what intimate con- nections exist between the different parts of the spinal cord. The irritation of any point whatever of the periphery, being transmitted to the spinal cord by a sensitive nerve, goes to provoke at once the activity of the whole organ. The initial stimulation for a reflex action may arise from any sensory nerve, whether of special sense, touch, or visceral supply. But there are some which generate a more active reflex movement, among which may be mentioned those of the palm of the hand and the sole of the foot. The quality and nature of the stimulus used has an influence on the reflex. Thus, tickling the auditory meatus produces cough; excessive sunlight acting on the retina causes sneezing. Stimulation of a sensory nerve-trunk in any part of its course calls out a reflex action, but the movement in this case is much less energetic and its character altered. In such a case the stimulation causes movement in one or more muscles, while stimulation of the skin surface innervated by the same nerve produces movements "which have a peculiar character of co-ordination. To produce a reflex action the application of the stimulus must be sufficiently rapid. Any agent which produces a slow and gradual change in the nerve is without effect. Some experimentalists have found a differ- ence between the reflex of chemical and mechanical stimulation. When the reflex center has a greater or less excitability, then the stimulation produces greater or less results. Every center which ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 45I gives origin to a motor nerve may be looked upon as a reflex center. The excitability of the reflex centers is increased when their connec- tion with the cerebrum is cut off or when the latter centers are inactive. Hence after decapitation, removal of the brain!, section of the oblong medulla, or section of the spinal cord, the centers below the section have greatly increased activity in their reflexes. Set- schenow has shown that mainly in the optic thalami and corpora striata are seated centers inhibiting the activity of the spinal reflex centers. Eeflex excitability is much greater in young animals than in adults. This explains the quickness with which slight causes pro- duce convulsions in the infant. Eeflex activity is greater in the summer than in the winter. Certain toxic agents have an effect on the reflexes. Thus, atropine, bromides, chloral, chloroform, and ether reduce reflex activity, while strychnine greatly excites it. Chloro- form is poisonous to every living cell, whether of plant or animal life. Strychnine is only poisonous to the nerve-cell, not to the plant-cell. Every time that intellectual action is suppressed then are the reflexes more manifest. A person asleep has more energetic reflex actions than a person who is awake. In somnambulism the action of the will is nearly suppressed, while the reflex excitability of the cord is enormously increased. On the other hand, a person by exercising a strong will can arrest certain reflexes. Thus, the conjunctival reflex can be pre- vented by the will of a courageous person. Up to a certain point a person is able to resist sneezing or coughing, which are certainly typical reflex movements. Swiftness of Eeflex Actions. — Helmholtz succeeded in meas- uring by the graphic method the swiftness of the spinal actions. By him it was ascertained that the excitation travels in the spinal cord at the rate of about twenty-four feet per second. Laws of Eeflex Actions. — They are the law of localimtien and that of irradiation. One other accessory law will be added : the law of co-ordination. Law of Localization. — If any sensitive region be excited, the first reflex movement which will be produced will bear upon the muscles near the sensitive region excited. Thus, if the foot of a frog bp very lightly touched, the muscles of that foot will respond reflexly. If the conjunctiva be touched, the reflex movement will be in the orbicular muscles. 452 PHYSIOLOGY. Law of Irradiation. — When an excitation has produced a reflex movement in the muscles of one side by a first degree of irradiation, there will be reflex movements in the corresponding muscles of the opposite side. Cutaneous constriction by cold applied to the right hand determines constriction of the vasomotors of the left hand as ■well. These are examples of the type known as transverse irradiation. If the excitation be more intense, the movement is spread into the muscles situated above and below the point of excitation. This represents the longitudinal irradiation. Law of Co-ordination. — The law of co-ordination or adaptation of the reflex actions in decapitated animals is very striking. If a drop of acetic acid be placed upon the back of a decapitated frog the animal will make such movements with the feet as will show that it seems to want to free itself from the substance which irritates it. They are not blind movements, but such as seem to be adapted to an end and are co-ordinated. Tonus of Spinal Cord. — It cannot be denied that, in the normal state, there is always a certain spinal tonus. That is to say, an active state of the cord which is not provoked by any immediate excitation. All of the muscles of the organism, striated as well as smooth, are always in a state intermediate between relaxation and con- traction. This state of semiconstriction, of semi-activity, is governed by the spinal cord. When the spinal cord is destroyed, immediately all of the muscles of the body relax and their tonus ceases. Influence of the Blood. — If a limb be separated from the rest of the organism, and, consequently, receives no nutritive blood-current, nevertheless the function of tTie nerve persists. By making Stenon's experiment (tying the abdominal aorta), at the end of twenty minutes, or an hour at the most, it will be found that sensibility and motility disappear in the abdominal members. Yet, though the deprivation of blood be complete, still there is preservation of the nervous activity for some time. By using on man the ligature and then compressing the limb by an Esmareh bandage interesting observations upon the influence of aneemia are made. During the first twenty minutes the arm is sensi- tive and the cutaneous excitations are plainly perceived. Likewise the motor nerves can still command the movements of the muscles. Soon, however, the sensibility becomes obtuse; the voluntary movements take place only incompletely, without force, and slowly. Kext the sensibility disappears so completely that the strongest elec- trical excitations are not felt. Because of the powerlessness of the ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 453 motor nerves, the limb feels limp and inert as if it were completely paralyzed. This state of death of the nerves, from anaemia, contrasts with the survival of the muscles. The nerve dies before the muscle, but much later than the nervous centers. Exciting Effects of An^^emia. — ^However it may be, anaemia, which makes the functions of the nerve finally disappear, begins at first by overexciting it. Thus, the first effects of anaemia are marked by an increase of excitability. If it be a sensory member, anaemia of it provokes extremely lively pains. Physicians have long been ac- quainted with painful anaemiae. It is anaemia, not absolute, but rela- tive, which is often the cause of intense peripheral pains. Thus, in symmetrical gangrene of the extremities (Raynaud's disease), which is characterized by complete cessation of the circulation in the affected areas, the pain is very acute. There is extreme hyperaesthesia, prob- ably due to nervous anaemia. Physiology of the Spinal Cord and its Nerves. The spinal cord represents: 1, A great conductor whose extent lies between the brain and periphery of the body. Along it are transmitted centrifugal as well as centripetal actions; the former carry volitional impulses to the muscles, the latter impressions from the sensitive surfaces to the brain. By reason of the spinal cord having in its composition ianumerable nervous cells, it becomes a co-ordinator of the actions which pass over it. 2. The spinal cord represents a true nervous center. It may be either an important center of reflex phenomena in that its cells unite centripetal fibers with centrifugal ones, or it may possess the r61e of acting as a special center of the special functions. Cord as a Conductor. — The law of Bell is enunciated as follows : "Of the roots which issue from the spinal cordj the anterior are those of motion and the posterior those of sensation." This law is very clearly demonstrated by the so-called Miiller frog. If the last four anterior spinal roots in the cauda equina of a frog are cut off at the rights and the four last posterior roots are cut off at the left, the animal after recovering from the operation will present interesting conditions. The right lower leg will be para- lyzed; that is, deprived of voluntary motion. The left lower leg will be ancesthetic instead. It will be deprived of sensation, but still possess motion. Therefore, the anterior spinal roots are motor and the posterior ones sensory. 454 PHYSIOLOGY. Irritation of the posterior roots, or of their central stumps, determines sensations. These sensations are sharp pains in the regions innervated hy the particular nerve. Excitation of the peripheral stump is without any effect. Irritation of the anterior roots, or of their peripheral stumps, determines movements. These movements are of the nature of con- vulsive cramps in the particular muscles innervated. Excitation of the central stumps is not followed by any effect. ' Cutting off, or the complete destruction, of the posterior roots causes the loss of tactile, thermal, and painful sensibilities; also of muscular sensation in the parts where they are distributed. Sec- tion of the anterior roots wholly paralyzes the muscles innervated by them. Kg. 109. — Diagram of the Roots of a Spinal Nerve Showing Effect of Section. (Landois.) The black represents the degenerated parts. A^ Section of the nerve- trunk beyond the ganglion. B, Section of the anterior root. C, Section of the posterior root. D, Excision of the ganglion, a. Anterior root, p, Pos- terior root, g, Granglion. Appaeent Contbabiction.— In demonstrating Bell's law there occasionally are seen results which seem to contradict that law, but instead they really confirm it. It is found that in stimulating the anterior (motor) root with electricity the animal sometimes gives evidences of pain. This same thing may occur also after cutting it in the middle and then stimulating, not the central, but the peripheral stump. Bernard has explained the sensibility of the anterior root by admitting that the recurrent sensitive fibers, which, taking their departure from the posterior roots, run back from the periphery to the center on the anterior root. If the posterior root be cut near to the spinal cord, sensibility in the corresponding anterior root wholly disappears. The spinal roots united, those of sensation with those of motion, constitute the mixed spinal nerves. They furnish the different parts ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 455 of the body in which they are distributed with both sensibility and motion. Consequently the section of many spinal nerves leads to anaesthesia and paralysis of the parts innervated. In the recently cut nerves, the central as well as peripheral stumps are excitable by stimulants, the former causing pain, the latter contractions. Ganglion. — The posterior root, before joining the anterior, forms the ganglion. The function of this ganglion is its trophic influ- ence, discovered by Waller and afterward proved by Bernard and others. When an anterior root is cut the peripheral stump becomes atrophied, whereas the central stump remains entire. The latter retains its vitality, since it is still in connection with its trophic center in the cells of the anterior horn of the gray matter. On the contrary, when a posterior root is cut between the spinal cord and the ganglion the peripheral stump remains entire, while the central ^tump becomes atrophied. The ganglia of the posterior spinal roots have, therefore, the office of trophic centers over the sensory nerves; the trophic centers for the motor nerves lie within the cord itself and are none other than the large, multipolar cells of the anterior horns. The anterior roots contain different centrifugal iibers — motor fibers, vasomotor fibers, sweat, and inhibitory fibers of the splanch- nics. The motor fibers take^ their origin in the cells of the anterior horns, while other centrifugal fibers are united to the cerebral cortex. As to the vasomotor fibers, they have their centers of origin in the medulla oblongata and cord to penetrate the anterior roots. They probably do this without entering into communication with the cells of the anterior horns. The posterior roots have centripetal refiex fibers. These leave the skin, muscles, and other organs; penetrate the spinal cord; and are in direct connection with the reflex centers located partly in the cord itself and partly in the medulla oblongata, pons, corpora quadri- gemina, cerebellum, and optic thalami. The other sensory and sense- fibers enter the cord by way of the posterior roots to ascend toward the cerebral cortex. Here are received the several conscious sensations : touch, pressure, temperature, pain, and muscular sense. Path of Transmission of Voluntary Motion. — Volimtary motor excitation is transmitted from the cerebral cortelx to the nerve-cells of the anterior horns by way of the anterior and lateral columns. These columns, as a whole, do not participate in conduction, but only the anterior pyramidal tracts of the anterior columns and the crossed pyramidal tracts of the lateral columns. 456 PHYSIOLOGY. As the student knows, the crossed pyramidal tracts do not decus- sate in the cord, but in the medulla oblongata. The direct pyramidal tract does not decussate in the medulla, but in the spinal cord by the anterior commissure. When the spinal cord is completely severed the voluntary move- ments for all of the muscles below the point of section are absolutely abolished. Path of Conscious Sensations. — The sensations of touch and muscular sense are transmitted by the posterior roots and traverse the posterior columns to the brain. Muscular sense is transmitted mainly by the posterior columns. The cerebellar tract also contains fibers which conduct muscle-sense. Tactile and muscular sensations are abolished by locomotor ataxia. One-sided section of the posterior and lateral columns causes: (a) suppression of skin sensations, or ansesthesia, in the whole half of the body innervated by nerves which enter the cord on the side of section; (b) loss of motion on side of section. There is very fre- quently observed on the side of hemisection a zone of hypersesthesia; this is due either to removal of inhibition on that side or inflamma- tory irritation of the central extremity of the cut cord. It has been shown by Worosehilofl in Ludwig's laboratory that the lateral columns are a pathway for sensory impulses. I have shown with Dr. Eobert M. Smith similar results in a series of sections of the lumbar part of the spinal cord. Section of the posterior and lateral columns does not exercise any influence upon sensibility to pain and temperature. But this is not the case when the gray matter is cut;, so that it must be inferred that these impulses ascend through the gray substance to the brain. Syringomyelia is the term applied to that condition when there is complete abolition of the conduction of pain and temperature. It is due to vacuolation of the gray matter of the cord. PiBEES FROM THE CeNTEES OF THE MeDDLLA ObLOITGATA. The vasomotor nerves, which come from a center ■ seated in the medulla oblongata, run down the lateral column to penetrate into the gray substance and anterior roots. Hence, section of the lateral columns produces a dilatation of the arterioles innervated by vasoconstrictors, which leave the cord below the point of section. The nerves leaving the respiratory center also run through the lateral columns and enter the gray substance, to communicate with it and leave by the anterior roots. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 457 In the middle third of the lateral columns I have found running both sweat and inhibitory fibers. Both sets of fibers I have discovered decussate : the former in the spinal cord, the latter in the medulla. Skin Reflexes. — The most important shin reflexes in man are : — 1. The Plantae Eeflex, which is caused by tickling the sole of the foot. The involved center lies in the lumbar cord. 2. The Cremasteric Eeflex. — If the skin of the upper and inner surface of the thigh in man be excited the corresponding testicle will be seen suddenly to rise by contraction of the cremaster muscle. Its center lies between the first and second lumbar nerves. 3. The Abdominal Eeflex is a contraction of the abdominal muscles caused by a sharp push of the finger. Its center lies between the eighth and twelfth dorsal. 4. The Epigastric Eeflex. — If the skin between the fourth, fifth, and sixth intercostal spaces be irritated, contractions of the rectus abdominis of the same side will follow. The center is between the fourth and eighth dorsal. 5. Scapular Eeflex. — An irritation of the skin covering the scapulse may cause contraction of the shoulder-muscles. Its center is between the seventh cervical and second dorsal nerves. Tendon Reflexes. — 1. Ankle-clonus. — When the sole of the foot is pressed upon by the hand, then the gastrocnemius contracts, and if the pressure is continued there may be several clonic contrac- tions. Ankle-clonus is never found in health. 2. Patellar Eeflex. — When a tap is made on the tendon of the quadriceps just below the patella, the foot jumps upward. The tendon refiexes are not true reflexes, but are due to a direct stimulant action on the muscle itself. But a reflex arc is necessary to keep the muscles in a state of tonus that the tendon reflexes may take place. Centers in the Spinal Cord. — The spinal cord presides over the movements of the anus, bladder, and genital apparatus by means of three centers located one above the other. The ano-spinal center is found in the dog near the fifth lumbar vertebra. From this center emanate fibers which, with the sacral nerves, go to animate the sphincter of the anus. Irritation of this center, especially by disease, brings on spasm of the sphincter, with difficulty in passing the faeces. Destruction of the center causes paralysis of the sphincter and incontinence of fseces. In paraplegics (those affected with paralysis of the lower limbs from cord lesion), spinal incontinence or the involuntary passage of 458 PHYSIOLOGY. the faeces may be observed. In addition, there is a protracted and invincible constipation. The former condition depends upon the destruction of the spinal center, while the latter comes from paresis of the intestine in the region of the colon and rectum. The vesicospinal center in dogs is found between the third and fifth lumbar vertebrae. When it or the nerves which take their de- parture from it are stimulated there are energetic and painful contrac- tions of the body and neck of the bladder. In apoplectics there is often, first, ischuria (retention of urine), which seldom comes from irritative or nervous spasm of the sphincter, but more frequently from paralysis limited to the detrusor nerves only. Afterward there is enuresis (incontinence of urine), from paralysis also of the nerves of the sphincter. The genito-spinal center is to be found in the spinal cord at the level of the fourth lumbar vertebra. If excited by stimuli it pro- duces contractions of the lower part of the rectum, bladder, and, if the animal be a female, the uterus. In addition, if the spinal cord be cut between the dorsal and limibar parts, tickling of the mucous membrane of the glans penis of the dog determines by reflex action an erection. Erection is no longer obtained if the lumbar cord be destroyed. Goltz and Freusberg have observed in a bitch, whose spinal cord was cut at the level of the last lumbar vertebra, the mani- festations of desire, conception, gestation, delivery, and lactation to take place just as in a sound bitch. In obstetrical wards women are delivered while in the anses- thetie sleep produced by ether, chloroform, or other anaesthetics. These various facts show that the center of the movements of the uterus is found in the spinal cord, and not in the brain. The sudorific centers are seated in the spinal cord. The spinal cord has minor vasomotor centers for the vessels of the parts it inner- vates. In fact, cutting of the cord produces hypersemia and eleva- tion of temperature in the paralyzed parts. This is due to the paralysis of the vessels there. The constrictors are paralyzed. Electrical excitations of the peripheral stump lowers the tem- perature in the parts innervated by constricting the lumen of the corresponding arterioles. The vasomotor fibers, emanating from the spinal column, rejoin the vessels either directly or, more commonly, by means of branches of the sympathetic. The cilio-spinal center is seated in the lower cervical cord and down the dorsal cord to the third dorsal vertebra. There fibers emerge by the anterior root of the two lower cervical and the two ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 459 upper dorsal nerves and go into the cervical sympathetic to the dilat- ing fibers of the iris. Pinching the skin of the neck will dilate the pupils : another skin reflex. Physiology of the Medulla and its Nerves. The medulla oblongata, or bulb, like the spinal cord, is an organ • of transmission, or conduction, but at the same time it is a center of particular and very important functions. Double Conduction. — Like the spinal cord, the medulla carries centripetal, or sensory actions, and centrifugal, or motor actions. The former are conveyed by means of its posterior part; the latter by the anterior part. The centripetal, sensory conduction is crossed or decussated along the floor of the fourth ventricle. The centrifugal, motor conduction accomplishes, instead, its decussation in the pyramids of the medulla, where the right, lateral fibers pass to the left, and vice versa. This decussation of the fibers is much more complete in man than in animals. So much is this so that in man a lesion which destroys one-half of the medulla brings on complete hemi- plegia of the opposite side; in animals a similar lesion never pro- duces hemiplegia, but only paresis. Equally, in animals this same lesion does not entirely abolish sensibility in the opposite side of the body. The gray substance of the opposite side connects the parts lying over and under the lesion, and so conducts the sensory im- pressions. Bulbar Nerves. — From the medulla oblongata take their origin and departure ten pairs of nerves: the bulbar nerves. Each nerve has a gray nucleus. The nuclei on the right side are connected with those on the left and all have their location along the gray substance of the floor of the fourth ventricle. The fibers which connect these nuclei of origin with the superior cranial centers are also crossed on the way. Centers. — The medulla, with its gray substance and especially with the gray nuclei of the nerves which issue from it, becomes a center of very important functions. First, it is a respiratory center. This center is found toward the inferior angle of the fourth ventricle, a little back of and lateral to the source of the vagi nerves. It is composed of two lateral halves, each of which can take the place of the other in function. This center is about two and one-half millimeters in size. 460 PHYSIOLOGY. A lesion affecting both respiratory centers causes the sudden death of a warm-blooded animal. Therefore this region of the fourth ventricle has been called the vital hnot. In fact, a blow from a stick upon the back part of the head or upon the nape of the neck, also a thrust from a sharp stUetto between the back of the head and the first vertebra, suffices to cause even a large mammal to fall to the ground instantly. Butchers inflict a blow on the nape of the neck to injure the vital knot. Components of the CENTEE.^The center of respiration in the medulla is composed of an inspiratory center and an expiratory center. From the inspiratory center the excitation for the nerves, and therefore for the muscles of inspiration, takes its departure rhyth- mically. These excitations always decussate in the cervical cord. The inspiratory excitation reaches the center by means of the pneumo gastric nerves, having been carried along their sensory pul- monary fibers. The excitation is originated either by reason of an accumulation of CO2 in the blood or the absence of 0. On the con- trary, an excess of oxygen in the blood abolishes excitation of the inspiratory center. The expiratory center, on the other hand, gives excitation to the nerves and muscles of forced expiration (normal expiration is accom- plished by reason of the elasticity of the thoracic case). Experimentally it is observed that exciting the vagus nerves or their central stumps provokes very deep inspirations until the thorax stops in the inspiratory movement. Stimulating the superior laryngeal nerves or their stumps provokes violent and forced expirations until the thorax stops in the expiratory movement. It is said that when a lesion affects the bilateral respiratory center there follows immediate suspension of breathing, and, therefore, death. The medulla oblongata is a moderating center of the movements of the heart. By irritating the medulla near the originating nucleus of the vagus nerve there is caused a stoppage of the cardiac move- ments. The heart first slackens its systole and afterward stops in diastole. The medulla exercises this moderating action upon the heart through the vagus nerve as a medium. Some of its centrifugal fibers put themselves in relation with its inhibitory ganglia. Hence, moderation and suspension of the heart movements are obtained by irritating the peripheral stump of the vagus in the neck. According to Traube, the normal stimulus, capable of exciting this moderating action, is the accumulation of CO2 in the blood. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 461 In the medulla is found this moderating center, -which is antago- nistic to that other center seated in the medulla oblongata: the accelerator center of the heart. The medulla contains the principal vasomotor center, which is of the utmost importance to the economy. This general vasomotor center in the medulla may become stimulated directly from the Irain. In short, an emotion or irritation to the cerebral cortex readily brings on ischsemia or hypersemia either in the skin or in the internal organs. Thus, there may be pallor from fear or diarrhcsa from fright. This organ of the nervous system is a secretory center for the saliva. In the floor of the fourth ventricle at the level of the origin of the facial nerve, and somewhat posteriorly to it, is found the originating nucleus of the fibers of the intermediary nerve of Wris- berg. This, through the chorda tympani of the facial nerve, is car- ried to the submaxillary gland. Pricldng the center or stimulating it electrically provokes a copious secretion of saliva. Certain patho- logical lesions may produce the same thing. Glucose Secketion. — Concerning this secretion, Bernard dem- onstrated that puncture of the floor of the fourth ventricle in its median line above the sources of the vagi nerves will determine within an hour the condition known as diabetes mellitus: glucose in the urine. The diabetes ceases if the liver be extirpated, and is not produced if the liver has been previously taken away, or its vessels have previously been tied. In the liver of animals rendered diabetic in such manner there is found an intense vasomotor paralysis. This appears to be the cause of the increased production of glucose. The action of the medulla upon the liver is exercised by means of the spinal cord through the intervention of the great sympathetic. The oblongata centers are: (1) respiratory, (2) vasoconstrictor and vasodilator, (3) cardio-inhibitory, (4) cardio-accelerator, (5) diabetic center, (6) vomiting center, (7) deglutition, (8) salivation, and (9) mastication. ANATOMY OF THE CEREBELLUM. The cerebellum is situated at the posterior and inferior portion of the brain. It is bounded anteriorly by the cerebrum, which is separated from it by the tentorium of the cerebellum. At the posterior face of the cerebellum are the pons and medulla oblongata, from which structures it is separated by the fourth ventricle. The cerebellum is 463 PHYSIOLOGY. entirely covered by the occipital lobes of the cerebrum in man, but only incompletely so in monkeys. It is united by the cerebellar peduncles to the cerebrum, pons, and medulla. The peduncles are six in number — three on each side. They are known as the superior, niiddle, and inferior cerebellar peduncles. Surface Form. — The cerebellum consists of a median lobe (the vermis) and two lateral lobes (the cerebellar hemispheres). The supe- rior vermiform process extends from the notch on the anterior to the one on the posterior border. The under surface of the cerebellum is subdivided into two lateral hemispheres by a depression (the valley). It extends from before backward in the median line. On the floor of the median lobe is the inferior vermiform process. Internal Structure of the Cerebellum. — The cerebellum, like the spinal cord, is composed of both white and gray substances. The gray is the most abundant, and occupies the periphery of the organ in the form of a thin layer which is from two to three millimeters in thickness. The white substance is placed in the center of the organ and is enveloped in all of its parts by the gray matter. The white represents nearly one-third of the whole cerebellar mass. Its consistency is greater than that of the gray matter. The central nucleus of the white matter sends out an infinity of arborescent prolongations which terminate in the cells of the gray sub- stance of the lamellae. It is this formation which the student knows under the name of arbor vitee. Bach one of the leaflike divisions of the white arbor vitse forma- tion is enveloped by a very thin plate of yellowish substance, while above this is the cortical gray substance. The latter sinks into the white substance at the level of the grooves which separate the plates from one another. A horizontal section of the cerebellum shows in the center of each half of the organ an ovoid body. It is very similar to the olive of the bulb in size and structure. This is the corpus dentatum. Corpus Dentatum. — The corpus dentatum is formed by a yellow layer folded upon itself in the form of a purse which opens in front. Within the interior of this purse is found the tissue proper of the corpus dentatum. It is formed of a matter which seems to be a mixture of the white and gray substances. Under the name of accessory nucleus dentatus Meynert has de- scribed two small leaves of gray substance located in front and inward ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 463 from the corpus dentatum. They are the nucleus fflobosus and nucleus fastigii. Stilling has discovered two clear gray nuclei at the lower border of the vermis near the median line and roof of the fourth ventricle. He calls them the nuclei emboli formes. Part of the fibers of the inferior cerebellar peduncles end within these nuclei. Hence, there are here four gray nuclei: dentate, glohosus, fas- tigU, and emholiformes. The last three are in pairs, but the dentate is single. Fig. 110. — Horizontal Section through the Cerebellum. (After B. Stilling.) The section passes through the region under the corpora quadrigemina (I"), then through the anterior cerebellar peduncle (B), and between these through the lingula (A). Above this lies the nucleus tegmentl, nucleus fastigii (m), to the left of the nucleus globosus QJg), the embolus (Emh), and still farther to the side within the hemisphere the corpus dentatum (Cdc). The central white substance passes toward the lateral angles of the sinus rhomboideus in three prolongations on each side. They are the cerebellar peduncles. The superior cerebellar peduncles go forward, pass under the cor- pora quadrigemina, where they decussate with one another in the upper level of the cerebral peduncles. They end in the optic thalamus and cortex of the brain. The middle cerebral peduncles pass forward and inward to form the superficial annular fibers of the pons. These fibers form a true 464 PHYSIOLOGY. commissure between the two hemispheres of the cerebellum; other fibers decussate in the pons to terminate in the islands of gray sub- stance ; a last category ascends into the brain after decussating in the pons Varolii. The inferior cerebellar peduncles (corpus restiformis) pass down- ward and inward to the level of the medulla, where the fibers which form them separate into three groups: the first form the external arcuate fibers of the medulla; the second are thrown into the post- pyramidal bodies (nuclei of Goll and Burdach) ; and the third are prolonged directly into the cord under the name of direct cerebellar tract. The cortex of the cerebellum is divided into two layers: the external layer, or molecular layer; and the internal granular layer, the rust-colored layer, or nuclear layer. The external layer is made up of two kinds of cells : star-shaped and basket cells. The neuraxons of the stellate cells enter the upper part of the molecular, or external, layer, forming a network of fibers. The basket cells have their den- drons extending into the inner part of the molecular layer, while their neuraxons arborize in a tuftlike manner, forming a "basket-work" about the cells of Purkinje. The internal layer is made up of multi- polar cells whose neuraxons form the horizontal fibers ia the external, or molecular, layer. These horizontal fibers divide in a T-shaped manner, arborizing about the dendrons of the cells of Purkinje. In the granular layer are relatively large cells known as the cells of Golgi; their neuraxon end is in the nuclear layer, while their dendrons lie in the molecular layer. Between the external and the internal layers we have the cells of Purkiaje, which are supposed to be the cells concerned in the pres- ervation of equilibrium. The dendrons of the Purkinje cells occupy the chief part of the external layer, and have little, clublike projections on them. The neuraxons of the Purkinje cells go into the internal layer, enter the external layer, and arborize about the dendrons of the cells of the latter layer. Prom the white matter come fibers, perhaps from the spinal cord, which on entering the granular and molecular layers have at their terminations irregular thickenings; hence called moss-fibers by Cajal, who believes that they conduct impulses to the granular cells. Another kind of fiber from the white matter, perhaps from the spinal cord, goes through the granular layer into the molecular layer, and, like a climbing plant, clings around the dendrons of the cells of Purkinje, and is called the tendril fiber. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 465 ' Poster holds that impulses froiii the spinal cord or other parts pass along the tendril fibers to the dendrons of the Purkinje cells and by its neuraxons from the cerebellum to other parts, or other impulses may be caused by the moss-fibers, which would go to the cells of the granular layer. From here the impulse would be carried to the molec- ular layer and spread along the bifurcating fibrils a long distance which would carry them to the dendrons of Purkinje cells. At the same time the arborizations of the just-mentioned bifurcating fibrils running in longitudinal directions about the basket cell? would affect the Purkinje cells in an indirect manner, and, since the neuraxon of each basket cell bears baskets for several Purkinje cells, a number of these Purkinje cells would be "associated" in the same event. The cerebellum has a threefold grasp on the cerebro-spinal axis: 1. By the direct cerebellar tract and the tract of Marchi and Loewen- thal; by the restiform bodies and inferior cerebellar peduncles. 2. By the middle cerebellar peduncles connecting the nuclei of the pons and indirectly by these nuclei with the frontal lobes. 3. By the superior cerebellar peduncles where the corpus dentatum is connected with the red nucleus and where the cerebellum is connected with the nuclei of the optic thalamus, and through new neuraxons of the optic thalamus to the parietal, ascending frontal, and ascending parietal of the opposite side. In the red nucleus we have a point of union for impulses from the cerebellum on one side, and, on the other side, from the cerebrum. PHYSIOLOGY OF THE CEREBELLUM AND MESENCEPHALON. Cerebellum. — Mechanical irritation applied to the cortical sub- stance of the cerebellum does not cause the animal to cry out nor are contractions of his members provoked. Even a prick or a wound that is not very deep in the cerebellar cortex does not cause any noticeable or constant disturbances, particularly in movements. Most often the only movements are those of the ocular globes. However, a deep lesion of the cerebellum— a large compressioii, a tumor, haemorrhage, the removal of all or a large portion of the cerebellum — determines a peculiar ataxia which shows the loss of equilibration. The animal, desiring to move, shows great uncertainty, irregularity, and want of co-ordination of movement. Often when it wishes to take some steps, it falls backward, slipping with the feet foremost. The experiment succeeds best in birds. After removal of the cerebellum they can no longer keep their balance. This is known as 466 PHYSIOLOGY. cerebellar tottering. Sometimes after several efforts they succeed in remaining upon their feet for a little while, but they soon fall and always in a particular manner. They slip either with the feet spread wide apart laterally, so as to touch the ground with the breast, or else, slipping with the legs extended forward, they support themselves with the wings behind. The head is folded with more or less twisting upon the back. When these animals continue to live for some time with such a lesion, they end by presenting characteristic obstructions with the feet, especially in the disposal of the toes. A man with deep lesions of the cerebellum has very noticeably disordered movements in walking and standing erect. He cannot bal- ance himself well. While walking he appears like one who is drunk. He suffers intense vertigo, with loss of balance, which renders all of his movements ataxic. This is especially so of motions of locomotion. Fig. 111.— Effects of Removal of Cerebellum. (Dalton.) From this it would seem that the cerebellum is the center of the co-ordination of movements. With the cerebellum destroyed, the ani- mal can no longer balance itself. Atrophy of one cerebellar hemi- sphere follows atrophy of the opposite cerebral hemisphere, showing a close relation between them. The function of equilibration is regulated by the cerebellum, which receives afferent impulses as follows : — 1. Tactile impressions by the posterior columns to the nuclei of Goll and Burdach and from them by the restiform body to the cere- bellum. To prove that tactile impressions are necessary to co-ordina- tion it is simply necessary to remove the skin from a frog, when it will not be able to leap, swim, or resume its natural position when placed on its back. In locomotor ataxia where we have a scl^osis of the posterior columns there is great difficulty in walking. ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 467 2. Visual impressions by optic nerve conveyed by the superior cerebellar peduncle. Ataxics are able to walk much better when they fix their eyes on the ground, and when they close their eyes walking becomes impossible. 3. Muscular-sense impulse through the direct cerebellar tract by the restiform body to the vermis. 4. Impressions from the semicircular canals, which will be con- sidered under the " Semicircular Canals." Here the vestibular nerve carries impressions from the semicircular canals by the restiform body to the nucleus fastigii and nucleus globosus of the cerebellum. The motor tract from the cerebellum is possibly the tract of Loewenthal and Marchi, which arises in the cerebellum and runs down by the inferior cerebellar peduncle to the antero-lateral column. In addition to the tottering walk and vertigo, deep lesions of the cerebellum in man produce a tendency to vomiting. This is probably due to the irritation which spreads to the center of the origin of the vagus nerve in the underlying medulla oblongata. Sometimes there is found a disposition to dyspncea and syncope for the same reason. Frequently there are changes in the organ of sight, as amaurosis, strabismus, and astigmatism. Middle Peduncles. — Deep lesion of the middle peduncles of the cerebellum (those which pass to the pons Varolii), if made upon one side only produces in the animal a tendency to turn or rotate upon the principal axis of its body. If the lesion occur in the pos- terior part of the peduncle the rotation is toward the side where the peduncle is cut. The animal may make as many as sixty or more revolutions per minute. The rotation will be toward the opposite side when the anterior portion of the peduncle has been injured. This rotation is explained by SchifE, who admits paralysis of the rotaxy muscles of the head and one side of the spinal column. Cutting the middle cerebellar peduncle brings on internal strabis- mus in the eye on the side operated upon, but external superior stra- bismus in the eye upon the opposite side. Lesion of the inferior peduncle of the cerebellum or of the bulb becomes painful. Also the animal falls upon the opposite side and is imable to keep itself erect. The animal's body is presented curved in the form of an arch toward the side of the lesion. Lesion of the superior peduncle does not give characteristic and precise phenomena. The Pons. — The pons represents a crossed way of conductibility between the periphery of the body and the brain, and vice versa. Be- 468 PHYSIOLOGY. sides, it is a co-ordinating center of the actions that pass through. The pons Varolii, at its anterior surface, shows itself to be but very little or not at all irritable. Posteriorly, there are signs of great pain and agitation in the animal under stimulation. Deep irritation causes convulsions and pains according to the kind of fibers irritated. The facial nerve is often found paralyzed upon the same side as the lesion and so opposite to the paralysis of the members and trunk. This condition is spoken of as alternate hemiplegia. The pons Varolii is the center of epileptiform convulsions. Deep irritation with electricity to the substance of the pons causes general epileptiform movements in the animal. Nothnagel, by irritating with the needle, has defined the limits of the spasmodic territory, or region of cramps. This convulsive center is irritated by excess of COj in the blood, or else by absence of the proper proportion of oxygen. Oil of absinthe is capable of irritating this center. Cerebral Peduncles. — The cerebral peduncles contain all of the fibers of sensation and motion in the body and direct them (except a few) toward the large ganglia at the base of the brain. Stimulation of a peduncle produces pain and contractions in the opposite half of the body; section or deep lesion from disease produces paralysis and anaesthesia in the opposite half of the body. The cerebral peduncles, therefore, carry: (1) the voluntary exci- tations to the nerves of motion and so to the muscles; and (3) the sensitive impressions made upon the peripheral extremities of the centripetal nerves up to the brain. I have found in the cat that mechanical irritation of the locus niger will cause the bladder to contract, indicating a high detrusor center. Mechanical irritation to any part of brain in front of this point has no efliect on the bladder. In the greater number of unilateral lesions of the cerebral pe- duncle the so-called movement in a circle is observed. That is, the animal walks or flies, but always follows the curve of circumference. This is usually to the side opposite the lesion. Corpora Quadrigemina. — In man atrophy of the opposite anterior quadrigeminal body follows removal of an eye. The anterior quad- rigemina are also centers for the reflex movements of the iris. As the student already, knows, the pupil contracts in the presence of strong light, but enlarges in a faint light or darkness. If the anterior quad- rigeminal bodies be destroyed, the pupil remains immovable and dilated even in the presence of a strong light. Besides the^e functions for the eye, the quadrigeminal bodies are ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 469 believed to serve other reflex actions. The posterior quadrigeminal bodies are pathways of auditory fibers. They are also regarded as centers of co-ordination of movements; their destruction is accom- panied by disturbances of mobility. PHYSIOLOGY OF THE OPTIC THALAMI AND STRIATED BODIES. The optic thalami, if deeply stimulated or injured, appear to be but slightly irritable and little or not at all sensitive. The animal has shocks or shrinkings, but does not cry out. A deep lesion, made in the posterior third of the optic thalamus, determines in the animal movements in a circle from the injured side toward the sound side. If, however, the lesion be made in the anterior part of the thalamus, the circular movement is reversed. Opinion seems to be divided as to the effect produced by lesion of the optic thalamu's upon the visual function. It is concluded, how- ever, that the surface of the thalamus (in conjunction with the corpora quadrigemina) is connected with sight. In addition to the functions just mentioned, the optic thalami have an influence upon the sensibility of the opposite side of the body. That is, not conscious sensibility, but that tactile and muscular sensi- bility necessary for the execution of extended and co-ordinate move- ments. This is especially so for locomotion without the aid of the will. These movements, then, are none else than reflex. They respond to the impressions made upon the sensory surface of the body and reflected in the large, exeitomotor centers, viz., the thalami. The thalami are relay centers for the sensory tract. Thus, while a normal individual walks along a clear street, per- haps he thinks of his movements but once. During that short time his will directs his volitional impulses; the rest of his walk, on the contrary, is executed almost automatically. In this case the excita- tions take their departure from impressions upon the body by the ground, space, weight of the body, etc. These impressions are all summed up in the optic thalami, from which they return, co-ordi- nated, along the nerves of motion. When the striated bodies are irritated they do not provoke any signs of pain. Though the animal remains relatively quiet under ablation of the hemispheres, yet it is seized with violent and con- vulsive contractions in the opposite half of the body when the striated body is hardly reached. This response is especially marked in the lenticulo-striate part of the internal capsule. By stimulating a stri- 470 PHYSIOLOGY. ated body with electricity, tetanus in the opposite half of the body has been obtained. The corpora striata are motor relay centers. They also contain a thermogenic center. EXPERIMENTAL PHYSIOLOGY OF CEREBRAL HEMISPHERES. There are two great means that experimental physiology has at its disposal, viz. : stimulation (electrical, mechanical, chemical, and thermal) and removal. These are likewise applied to the most im- portant and noble part of the nervous apparatus: the cerebral hemi- spheres. The experimental results are then compared with those Fig. 112. — Left Cerebral Hemisphere in Man, Showing Areas of Localization. observed in clinics from pathological lesions located and circumscribed in various points of the same hemispheres. Some years ago all physiologists admitted the complete inexcita- bility of the cortical substance of the cerebral hemispheres. Accord- ing to the view then held, mechanical, thermal, chemical, and electrical irritation of the convolutions did not determine phenomena of any kind. Later, however, it was demonstrated that very slight electrical currents apj)lied to the cerebral convolutions in dogs determined vari- ous movements in the head, limbs, eyes, etc. By this means the operator can cause the execution of various movements to suit his ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 471 will, as, for example, closing the iist, extending the arm, moving the leg, eyes, face muscles, etc. These results were best demonstrated in experiments upon apes. By experiments along this line it has become feasible to fix the seat of various cortical motor centers of the brain. In man himself experiments with electricity have been made upon the convolutions exposed from various causes. Fig. 113. — Left Cerebral Hemisphere in Man, Showing Areas of Localization. Motor and Sensory Centers. The motor centers are located in the ascending frontal, ascend- ing parietal, and paracentral convolutions. The foot of the third left frontal convolution contains the center of speech. The tactile centers have been located by the neurologist in the same area as the motor centers. The physiologist places them in the gyrus fornicatus. The visual area corresponds to the occipital lobe. Its unilateral destruction produces bilateral, but passing, hemianopsia. Bilateral 472 PHYSIOLOGY. destruction produces complete blindness at first, but later only ambly- opia with impossibility of distinguishing objects. Excitation of this region on one side produces a sidewise movement of the eye toward the side of the lesion, with a contraction of the pupils, and kaown as conjugate deviation. Lesions of the cuneus are usually the cause of hemianopsia, or half-blindness. The auditory area is found in the superior temporo-sphenoidal region. Its unilateral removal causes temporary deafness on the oppo- site side. Bilateral removal causes complete deafness on both sides. Excitation of this region determines movements in the eyes, pupils, head, and ears as if the animal had heard a loud sound. The centers for taste and smell are localized in the uncus. The motor speech center is located in the posterior part of the inferior left frontal gyrus and the island of Eeil. When this center is destroyed there is produced a defect in speech known as aphasia, which is an inability to give correct utterance to thought. Another condition — inability correctly to write one's thoughts, and often asso- ciated with aphasia — is known as agraphia. A lesion of the base of the second left frontal convolution is probably the motor writing center. The tactile area, according to the physiologists, is found in the gyrus fornieatus; according to the neurologists, in the ascending parietal and parietal convolutions. To conclude, it may be said that the normal, physiological sig- nificance of these cortical centers cannot be other than that they are primitive motor and sensory centers. The motor centers may be con- sidered as the origin of primitive impulses which produce volimtary movements. They are, then, psychical motor centers or even centers of motor ideation. The sensory areas would be centers of conscious sensation, or cen- ters of perception. These various centers, by means of definite bundles of nervous fibers, are in relation with particular muscular groups or else with special organs and sensory regions. PHENOMENA FOLLOWING THE DESTRUCTION OF ONE OR BOTH OF THE CEREBRAL HEMISPHERES. Ablation of the cerebral hemispheres is generally performed in frogs or fowls, who seem to endure the operation sufficiently well. Mammals easily succumb. The skin of the head being cut and the thin cap Of the skull removed, the brain is reached. The incision of the meninges is pain- ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 473 fulj but, after gradually removing the mass of the hemispheres from above downward, the bird shows itself indifferent. In fact, it be- comes more stupid and apathetic the more of the cerebral tissue is removed. The removal of the hemispheres completed without injur- ing the peduncular system, with its ganglia, and the haemorrhage stopped as well as possible, the bird remains in a sleepy state. It has a tendency to bury the head and close its eyes ; it breathes slowly, but does not walk away. Under stimulation the bird reopens its eyes, raises the head, takes a few steps, then suddenly returns to its former position. The bird, having recovered from its traumatism, the following phenomena are observed within a few days: The bird has become an automaton. It does not eat, so that it becomes necessary to put the food into its mouth. It moves not at all of its own volition; if pur- Fig. 114. — Effects of Ablation of Cerebrum. (Dalton.) sued it takes some steps; its pupil contracts under the influence of the light, cries or tries to flee when the skin is irritated. It is startled by loud noises. Por the rest there are no longer voluntary movements, and the few movements observed are aroused by external excitement, or some internal need. The movements are rubbing the skin with the beak, scratching the head with the foot, etc. The vegetative functions (once that care is taken to nourish the birds and clean them) are performed without disturbances. If the bird lives for some time it shows a general deposit of fat. The skin and muscles in particular are seen to be infiltrated with adipose tissue. In these birds there are only movements of a reflex nature. Sensibility is blunted since the stimuli are not able to reach the cortical centers. Hence, they cannot provoke volitional acts in them, as Kliss says, these birds live, but do not perceive; they hear, but do not listen; they are aware of stimuli upon the tongue, but do not taste them. They are just as a human being who is asleep or absorbed 474 PHYSIOLOGY. in contemplation. He may drive a fly from the face without being conscious of it. When but one cerebral hemisphere is removed without in the least injuring the other and the animal recovers, it does not show positive disturbances of intelligence or conscious sensibility or of voluntary motion. However, the opposite side shows weakness. Should the lesion extend to the underlying basal ganglia or to the peduncular system, there will be complete hemiplegia in the opposite side of the body. The same manifestations are observed in a man who has lost an entire hemisphere from a wound or from disease. There is no positive lesion of intelligence, but there is manifested very marked fatigue from intellectual labors. If the lesion has extended toward the peduncular base of the hemisphere, there is hemiplegia in the opposite side of the body. The crowbar case is a much-cited instance. A workman twenty- five years of age was engaged in charging a blast in a rock. The instrument he used was a sharp-pointed bar, forty inches long, one and one-fourth inches in diameter and weighing twelve pounds. The charge was suddenly exploded, driving the bar so that it entered the man's lower jaw and came out at the top of the head close to the sagittal suture in the frontal region. It fell at some distance, covered with blood and brains. For the moment the victim remained uncon- scious. An hour after the accident he walked to the house of a sur- geon, where he gave an intelligent account of the accident. For a long time his life was despaired of, but he finally recovered to live twelve and one-half years longer. It may be concluded, therefore, that one cerebral hemisphere only is sufficient for the mobility and sensibility of the two sides of the body, as well as the performance of psychical functions. The individual with one hemisphere destroyed remains like one who has lost an eye. That is to say, the brain continues to perform its functions, animal as well as psychical, but with noticeable weakness, greater effort, and fatigue. The frontal lobes are the chief seat of the will, memory, and intellectual functions. The irritability of the cerebral cortex may be diminished or ex- aggerated by various circumstances. Thus, opium, ether, chloroform, chloral, the bromides, cold, asphyxia, etc., diminish it. Inflamma- tion, urea, uric acid, atropine, strychnine, etc., increase its excitability. Action of Brain Extracts. — In 1898 I found that infusions of dried brain reduced the heart's frequency and the arterial tension. Section of the vagus or its paralysis by atropine did not prevent this ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 475 action. Halliburton did not obtain the same results after the use of atropine, but my experiments have been confirmed by Swale Vincent and Sheen. Quite recently Swale Vincent and Cramer have found two substances in brain, both depressing the heart even after the previous use of atropine. They also obtained another substance depressing the circulation, but its effects are abolished by atropine. THE GREAT SYMPATHETIC. The great sympathetic is composed of a double chain of ganglia, situated at the sides of the vertebral column upon its visceral surface and known as the lateral or vertebral ganglia. This chain may be divided into four parts, viz. : cervical, thoracic, abdominal, and pelvic. In addition to these main ganglia others are found either along the course of the cranial nerves (submaxillary, optic, spheno-palatine, ciliary, etc.) or interspersed among the splanchnic organs. These latter are found in the heart, lungs, mesentery, the intestines, bladder, vessels, etc., and are known as the prevertebral ganglia. The ganglia of the two cords of the sympathetic are in relation with the cerebro-spinal axis by means of the communicating tranches. These proceed from the anterior and posterior roots of the spinal nerves. They are constituted, for the most part, of delicate medullary tubes : centripetal and centrifugal. They come from the mixed nerves of animal life to enter the ganglia and so put themselves in relation with the ganglionic cells. From these cells, then, issue bundles of fibers known as Remak's gray fibers. These, joined to the medullary fibers of the communicating branches, go to make up the sO-called plexuses of the great sympathetic around each organ of the neck, thorax, abdomen, and pelvis, consisting of the prevertebral ganglia. The preganglionic sympathetic fibers which are concerned in the nerve- supply of vessels, glands, or the visceral muscles pass through the chain of lateral or vertebral ganglia to end in some of the prevertebral ganglia. Here they arborize, making a sort of contact. From the prevertebral ganglia run fibers to the tissues concerned and these fibers are the postganglionic fibers. A portion of the fibers issuing from the ganglionic cells retrocede into the communicating branches. They either distribute themselves to the mixed spinal nerves or else penetrate the spinal cord. The plexuses of the sympathetic are inseparable companions of the arterial branches; their centrifugal branches go to the muscles with smooth fibers, while the centripetal branches are distributed, lor the most part, to the mucous memhranes. 476 PHYSIOLOGY. The cervical part of the great sympathetic is composed of three ganglia with certain vasomotor branches which follow some of the neighboring large vessels. The thoracic portion is composed of twelve ganglia upon each side. Prom this part issues the cardiac plexus. The inferior thoracic ganglia give off the splanchnic nerves, which are distributed to the plexuses of the abdominal viscera. Unlike the branches of the sym- pathetic, they are white and hard, like the spinal branches. The abdominal, or lumbar, part consists of four ganglia whose branches, together with the splanchnic nerves, branches of the aortic plexus, and the right vagus nerve constitute the solar, or cceliac, plexus. The pelvic portion consists of five or six ganglia, including the coccygeal ganglion. As regards the general physiology of the great sympathetic, it can be said that this system gives to the mucous membranes and the in- nervated splanchnic organs an obtuse sensibility. That is, a sensibility which does not make the individual notice the normal stimuli (ali- ment, air, blood, liquids of secretion, etc.), but purely the abnormal stimuli. The latter produce a pain which is dull, not very well defined, and not localized. For this reason it is called general sen- sibility. Furthermore, the sympathetic, with its centrifugal branches, gives to the smooth muscular fibers a mobility: that is, a mobility which never comes into play by volitional impulse. It is always aroused by reflex actions which give reflex phenomena. Contraction of smooth muscles, from excitation of the sympathetic, requires a long time of latent irritation; it is established slowly, and also disappears slowly- The actions, instead of being instantaneous and intense, become rela- tively unconscious, lasting, and weak. If the spinal cord be wholly destroyed, stimulus to the intestinal mucous membrane is followed by peristalsis. This occurs from reflex action in the cells of the sympathetic plexuses existing between the layers of the intestine itself. Finally, with the sympathetic run many vasomotor, secretory, and trophic nerves. Literature Consulted. Quain's "Anatomy." Debierre, "La Moelle." CHAPTER XV. SPECIAL SENSES. TACTILE SENSE. The organs of special sense constitute the peripheral portion of the centripetal part of the nervous system. The nervous system is open to receive the impressions from the external world according to the nature of the different agents which must impress the organs of the special senses. The various kinds of sense-organs have each a different con- struction. They are always adapted to receive an impression of a given agent. Thus, the eye is an organ that is particularly adapted to receive impressions from rays of light; the ear receives sound- waves ; the skin is responsive to touch, etc. Man is endowed with five senses. That is, he possesses five kinds of organs which are destined to give him notice of the impressions upon his nervous system from five different agents. To these agents man has assigned special names which recall their relations to the organs of sense, and without which they could not be conceived of. These agents, with the corresponding organs of sense, are (1) contact, which is perceived through the sense of touch, whose highest devel- opment is in the skin; (3) taste, a modification of touch is perceived through the setise of taste, embodied in the tongue ; (3) odor is recog- nized through the sense of smell as located in the nose; (4) sound- waves are made Iniown to the economy through the sense of hearing, whose peripheral organ is the ear; and (5) light is perceived through sight by reason of the respopse produced in the eye from the excita- tion of rays of light. The various peripheral organs of special sense respond best and give the clearest centripetal impulses when they are stimulated by excitations peculiarly their own. Thus, waves of light are best re- ceived by the eye, sound-waves by the ear, and so on. However, the fact must not be lost sight of that any other excitation than the proper one acting upon these organs will always be perceived by the indi- vidual in the same way as an appropriate impression. An induction current upon the skin will produce unpleasant tactile sensations. (477) 478 PHYSIOLOGY. Upon the eye it provokes Iwminous sensations, upon the ear noise sensations, and upon the tongue there is produced a sensation of taste. Yet in each case the stimulus is always the same. In order that the impressions caused by the external excitants may be able to reach the consciousness of the individual, it becomes necessary that each organ of sense be furnished with centripetal nerves. These are in direct anatomical relation with the central nervous system. By means of these nerves the cortical portion of the cerebrum, endowed with consciousness, perceives the impressions com- ing from the external world. These are the so-called special, external, and objective sensations. Among the parts furnisJied with nerves of general sensibility are the mucous membrane of the digestive^ respiratory, and genito-urinary tracts, and the sheletal muscles. In the digestive tract, the mouth, pharynx, and anus are endowed with tactile nerves; the rest of the tract is furnished with nerves of general sensibility. The mucous membrane of the oesophagus gives us the sensation of thirst, the gastric mucous membrane the sensation of hunger and satiety, while the rectal membrane notifies the individual of the need of defecation. Pulmonary tissue in itself has but very little sensibility; but ab- normal irritations cause cough and painful sensations. The pleura, when invaded by disease,_ produces very painful sensations. The genito-urinary membrane, besides its exquisite tactile sensi- bility, is also the seat of general sensibility that is doubly modified: in the need of urination and the sexual sense. The kidneys, ureters, testes, Fallopian tubes, and the uterus are endowed only with nerves of general sensibility. The sheletal muscles are furnished with the so-called muscular sense. This is none other than, general sensibility. It conveys disa- greeable sensations only, when the stimulus becomes intense or ab- normal. When a muscle is irritated or lacerated it gives rise to pain. Fatigue is generally localized as an unpleasant sensation in the muscles. A proof of muscular sense is the employment of enough force to overcome resistance. Consciousness is a large factor in this last function, for by it the individual judges the amount of resistance. He then voluntarily regulates the amount of muscular effort. It is by the sum of all the sensations from the nerves of general sensibility, as well as the sensation produced by muscular movement, that individuals feel that they exist. With these data the individual recognizes the state of different parts of his body, whether in repose or activity. TACTILE SENSE. 479 Laws of Sensations. — Special sensations are subject to the fol- lowing laws : — 1. For every nerve of sense there is a nominal degree or limit of stimulus which gives no sensation whatever. There is also a max- imum degree beyond which an increase of the intensity of the stim- ulus brings on pain or an unpleasant sensation. 2. The minimum limit varies for the separate sensations, or, . rather, the single specific agents. Thus, the minimum for excitation of touch is a pressure of 0.002 milligram; for temperature, ^/g° - C. ; for sensation of movement, a shortening to the extent of 0,044 millimeter of the internal rectus of the eye; for hearing, the noise made by a ball of pith 1 milligram in weight falling 1 millimeter in height upon a glass plate heard at a distance of 91 millimeters from the ear ; for sight, an intensity of" light about one three-hundredth as strong as that of the full moon. 3. The intensity of the sensation is proportional to the intensity of the stimulus and the degree of irritability of the nerve at the moment of excitation. As the strength of the stimulus increases, so do the sensations. But the sensations increase equally when the strength of the stimulus increases in relative proportions. Thus, small noises will be distinguished in the silence, not in the midst of loud noises; a slight difiEerence will be noticed between small weights, not between heavy ones. A burning candle in the daytime makes little impression. 4. Sensations do not increase in the same proportion as the stimulus. If the stimulus increase in geometrical progression, then the sensation increases in simple arithmetical progression. Eather, it increases as the logarithm of the strength of the stimulus. (This is Fechner's psycho-physical law.) 5. For the single, specific sense apparatuses, wherever a stimulus takes place, whether at the peripheral terminations of a nerve or in its course, or at its central point, the individual always localizes with his perception the stimulus at the place where the normal stimulus operates. That is, for sight and hearing he refers it to space ; for the nerves of taste, smell, or touch, he refers it to the peripheral regions of his body, even if these be lacking. Thus, in an amputated leg, pain in the stump is referred to the toes. This is the law of eccentric projection of sensation. Touch. The organ of touch is represented by the skin and mucous mem- branes in proximity to the natural orifices of the body. 480 PHYSIOLOGY. The skin, or common integument, is composed of the following layers: (1) the epidermis; (2) the corium, or cutis vera, with its papillffi; and (3) the subcutaneous tissue with the adipose tissue. 1. The Epidermis belongs to the tissues which are composed of simple cells united to each other by cement-substance. It in itself consists of several layers : — (a) Stratum corneum. This is the superficial ho;rny layer and consists of several layers of homy scales, without any nucleus. The layers are separated from one another by narrow clefts containing air. They are in a process of desquamation. The variable thickness of the epidermis is chiefly dependent upon the thickness of this outer layer. The stratum corneum is of greater thickness on the palm of the hand and fingers, and sole of the foot. (l) The stratum lucidum is clear and transparent and consists of a few layers of clear cells which contain but the remains of nuclei. (c) Stratum Granulosum. — Under this is the (d) rete muco- surri, or rete Malpighii. This layer consists of strata of nucleated, protoplasmic, epithelial cells. In the colored races these contain pigment. Among the fair races this layer of the skin of the scrotum and anus contains pigment-granules. The deeper cells are more or less" polyhedral, while the deepest ones are columnar. These last are placed vertically upon the papillae and are provided with spherical nuclei. Granular leucocytes or wandering cells are occasionally found between these cells. The superficial layers of the epidermis are continually being thrown off, while new cells are just as rapidly being formed in the deep layers. Within them there occurs a proliferation of the cells of the rete Malpighii. Many of the cells exhibit the changes of karyo- kinesis. No pigment is formed within the epidermis itself. But in brunettes and colored races pigment granules of melanin exist within the cells of the Ipwermost layers of the stratum Malpighii. The pigment-granules present here have been carried thither by leucocytes from the subcutaneous tissue. This explains how a piece of white skin transplanted to a colored person becomes black. 2. The Corium, or cutis vera, is a dense network of fibrous con- nective tissue admixed with elastic fibers. Its entire surface is studded with numerous papillce, the largest of which are upon the volar surface of the hand and foot. The majority of the papillae contain a looped capillary. In some regions of the surface of the body they contain touch-corpuscles. The papillae are arranged in groups whose disposi- tion varies in the several parts of the body. TACTILE SENSE. 481 The lowermost connective-tissue layers of the corium gradually merge into the subcutaneous tissue. Its arrangement is such as to leave spaces which contain, for the most part, cells of fat. The sub- cutaneous connective tissue composed of ordinary connective tissue, is soft, and is rich in adipose cells, vessels, nerves, and lymphatics. Tactile Corpuscles. — The student well knows that in the epithe- lium of the skin and mucous membranes the nerves of common sen- sation are arranged, for the most part, in networks of fibrillffi. In addition to these there are other special terminal organs of sensory nerves. These are variously known as tactile corpuscles. These are concerned in the perception of some special quality or quantity of sensory impulses. They have their site, not in the surface of the epidermis, but deeper within the tissues. The principal ones among them are the corpuscles of Pacini, the end-bulbs of Krause, and the corpuscles of Meissner. The tactile corpuscles of Meissner in the papilla of the cutis vera are oval bodies ^/go inch in length and nearly the same width. These are the corpuscles of the palm of the hand and sole of the foot. One or two medullated nerve-fibers are spirally twisted around it, and near the top of the corpuscles the nerves lose their white substance and the axis-cylinders end in ilat bodies penetrating the surface of the corpuscle. The corpuscle is composed of flattened cells, which give it a striated appearance. These corpuscles are built up of a great number of tactile discs and of tactile cells. There are about twenty tactile corpuscles to a square millimeter of the skin. The Pacinian or Vater's corpuscles are attached in greatest num- ber along the digital nerves of the fingers and toes and occasionally on other nerves. These bodies are oval or pyriform, about Vj inch in length and '/12 inch in thickness. They have a pearly luster and consist of a series of capsules or concentric layers of fibrous tissue, with here and there a nucleus. The outer capsules are separated more widely than the inner ones and the interspaces are filled with a colorless liquid. Each corpuscle is attached to a nerve by a pedicle of fibrous tissue through which exetends a single nerve-fiber, which, penetrating the series of capsules, terminates by sending its neuraxon into the central cavity of the corpuscle, at the top of which it ends in a simple extremity. Bach corpuscle is covered with forty or fifty capsular layers. Krause's End-bulbs. — The tactile corpuscles of Krause are elon- gated, oval bodies, into one end of which a nerve-fiber penetrates. Externally they have a covering of connective tissue, a continuation 482 PHYSIOLOGY. of the perineurium, and an internal knob of granular matter dis- posed in concentric layers with a few nuclei. In the center of this knob is found the axis-cylinder which runs through it like a ribbon to the upper pole and then ends in a slight thickening. These bulbs are found in the basement membrane of certain mucous membranes, as in the corneal conjunctiva, in the mucous membrane of the mouth, in the clitoris, and in the glans penis. They are also to be found in the skin. Corpuscles of Grandry or Merkel consist of two or more flattened cells, each larger than a simple tactile cell. Each cell is nucleated, and the nerve-fiber, before entering the corpuscle, loses its white sheath, and the axis-cylinder ends as a flat disc lying between the two tactile cells. These tactile cells are piled one upon the other so as to form a heap of cells. They are found chiefly in the beak and tongue of the duck and in the epiderm of man. Other Modes of Ending. — ^In addition to sensory nerves ending by special structures as those just described, there are some which do not possess such elaborate apparatus. In the case of many nerves, the axis-cylinder splits up into fibrils which are arranged in the form of a network. From this somewhat deeply placed network very fine fibrils or fibrUlse are given off to terminate in the tissues to be sup- plied. The fibrilliB have their terminus in free ends lying between the epithelial cells. In many cases the free ends are seen to be pro- vided with small enlargements. These latter are known as tactile Knowledge Gained. — By the sense of touch one feels the contact of bodies and their temperature, whether these bodies be solid, liquid, or gaseous. This special sense also defines at the same time the locality of the impression made by the external agent. The judgment of locality is not, however, free from error. It is really exact for but a few points; that is, wherever the touch is delicate. On the other parts of the skin the individual never exactly divines the point pressed upon; so that he makes mistakes of millimeters, centimeters, and even decimeters. In sensory nerve-trunks there exist different kinds of nerve-fibers ; , some administer to painful impressions and others to tactile impres- sions. Sensations of temperature and muscular sense belong to the latter group. Sense Spots. — The surface of the skin is found by experimenta- tion to be composed of very small sensorial areas. Between these areas are found little fields which are insensitive and which are relatively TACTILE SENSE. 483 much larger than the sensitive areas, or "spots." It has been dem- onstrated that each " spot " has its own specific function to perform, whether that be touch, cold, warmth, or pain. Each little sensitive area no doubt marks the site of single or groups of sensory corpuscles, end-organs, or bulbs, of the terminations of various nerves. Where the nerves terminate, there are the sense-spots represented upon the skin's surface. Some one has very aptly likened the skin with its sense-spots to a pond upon whose surface, as well as Just below the same, are seen lily leaves floating. The leaves represent the sense-spots. A pebble thrown into the pond may strike one or more leaves, depending upon how close, together they are growing. The pebble represents a stim- ulus, and by its presence temporarily stirs up or throws into a state of excitation the leaves struck as well as some of those adjacent. Upon the skin's surface may be demonstrated "touch-spots," "cold-spots," "warmth-spots," and "pain-spots." These are all mixed up, though those of one kind may be more strongly in evi- dence in certain areas. As a rule, " pain-spots " are found to be the most numerous ; " warmth-spots " are the least likely to be found. Solids. — These act upon the sense of touch either by pressure or by traction. Pressure may be from zero to a maximum whose limit is the disorganization of the tissues. Up to a certain minimum, which depends upon the sensibility of the region, the application of pressure excites no sensation. The minimum pressure corresponds to the sensation of simple contact; this by degrees gives way to the sensa- tion of pressure. When the pressure is sufficiently increased there results pain. This in turn disappears when the pressure is increased to disorganization of the tissues. ' > Pressure varies not only. in intensity, but in extent. No matter how the latter may be limited, the pressure always affects at least more than one peripheral nerve-ending. When tactile sensations are very light and succeed one another rapidly, a large number of nerves is stimulated. The sensation ex- cited is a peculiar one : that of tickling: Traction upon the hair and nails determines pain much more rapidly than does pressure. Liquids. — Liquids applied at the temperature of the skin exercise a uniform pressure upon all parts of the cutaneous surface excepting those at the level of the surface of the fluid. If a finger be plunged into a heavy fiuid, as metallic mercury, the part submerged bears a pressure which decreases from below upward 484 PHYSIOLOGY. uniformly. It is only at th'e surface of the liquid that a marked inequality of pressure exists. It follows a circular line which sur- rounds the finger at this level and can be plainly felt by the indi- vidual. If a lighter fluid, as water, be used, the pressure sensation is but very slight. Compound Tactile Sensations. — These may be simultaneous or successive. Simultaneous tactile sensation may be either double or multiple. Double sensations, whether of contact, pressure, or traction, are shown only when the stimuli are applied at a certain distance from one another. If the stimuli be near enough, the sensa- tion remains single even though the stimulus has been applied to the skin in two places. The earliest systematic experiments upon this subject were by Weber. He touched the various points of the skin's surface with a pair of carpenter's compasses and then observed the distance of separation necessary to give a distinct impression of two points of contact. The instrument now used for this purpose is the cesthesiometer. From the table compiled by Weber it is foimd that the tip of the tongue is most sensitive, while the thigh and arm are least so. In the case of the tongue, the minimum separation neces- sary for the impression of double contact is but 1.1 millimeters; 67.6 millimeters are necessary in the ease of the thigh and arm. The connection between the mental and physical conditions explains cer- tain illusions of tactile sensations. Of these, the best known is the so-called experiment of Aristotle. When a pea or small ball is rolled between the crossed index and middle fingers of a blindfolded person there results a sensation of two halls being present instead of one. There are spots of temperature which have been worked out by Goldscheider. They are found to be arranged in a linear manner and generally radiate from certain points of the skin, usually the hair-roots. The chain of " cold-spots " does not coincide with those of "warmth-spots." The sensation of cold occurs at once; that of heat develops gradually. As a rule, the cold-spots are more abund- ant over the entire body surface. The hot-spots may be quite absent. The minimal distance on the forehead for cold-spots is 0.8 milli- meter, while for warmth-spots it is 5 millimeters. Protection of the Organs of Touch. The means are the cutaneous oil and the Jiorny appendages. The cutaneous oil is the product of the sebaceous glands of the skin. They are found in every area of the skin, but are less numerous than the sudorific glands except- in the palms of the hands and soles of the TACTILE SEKSE. 485 ■feet. They may be large, as in the nose; these usually have fine, downy hairs near their mouths. The sebaceous glands are situated more superficially than the sweat-glands. They are white granules annexed to the hair-follicle, in which their excretory duct ends. Their size is, in general, in- verse to the volume of the corresponding hair-follicle. Where the hairs are large the sebaceous glands seem to be appendages, and when the hairs are small its hair-folliele seems to be an appendage of the sebaceous gland. The glands are aeiniform, surrounded by a thin, connective tissue with a basement membrane studded with epithelial cells infiltrated with fat, and the cells are more fatty in the direction of the excreting duct, where is found free fat, due to the destruction of the cells. When the sebaceous secretion stagnates, it forms a fat- like mass which, when expressed, as in the nose, forms the comedo, a wormlike body. The black-heads, as they are called, consist of dirt in the surface of the gland. When the comedo is expressed the duct has been mistaken as the head of the worm. The sebaceous matter contains, even in healthy individuals, the pimple-mite, or Demodex folliculorum. There are three varieties of sebaceous secretions : (1) that of the skin, (3) the vernix caseosa of the newborn child, and (3) the smegma of Tyson's glands of the prepuce. Function. — The sebaceous matter anoints the hairs with oil in their progress of growth from the skin. The greasiness of the surface of the skin caused by this secretion permits the dust readUy to adhere, which makes soap necessary to remove its excess. Seba- ceous secretion is made up of olein, pahnitin, cholesterin, and earthy phosphates. The organ of touch is also protected by the homy layer of the epidermis, whose cells are being constantly removed by friction and as constantly renewed by proliferation of the cells of the cutis vera. The modifications of the epidermis in man are the hair and nails. Hair. — The hairs are threadlike appendages to the skin project- ing from almost every part of its surface except the palms and soles. They are flexible, elastic, and shining, but vary in degree of develop- ment, fineness, color, and form in different races and the sexes as well as in different persons. The color of the hair varies from a light color to a black. The black hairs are found in all parts of the globe and in all latitudes, as in the Esquimaux, negro, Indian, and Malay. All the colored races have black hair, and this is true in some groups of the white race. Eed hair is represented in all races. The hair is 486 • PHYSIOLOGY. composed of a projecting part, the stem, terminated by the point, or end. The portion inserted into the skin is the root, which begins in a clnblike expansion. The hairs generally project obliquely from the fekin. The hairs of the white race are cylindrical; the hair of the negro flattened cylindrical. In structure the hairs consist of an ex- terior cuticle, a cortex, and an interior medulla. The cuticle consists of a single layer of thin, colorless, quadrilateral scales which overlap like the shingles of a roof. The edges of the scales are directed up- ward and outward along the shaft. The cortex makes the chief part of the hair, and it is that iipon which the color of the hair mainly depends in different individuals. The cortical layer is made up of elongated, fusiform cells containing a lineal nucleus. When the color- ing matter disappears in the cortex the hair becomes white. The medulla is frequently absent, especially in the dark-colored hairs. It occupies the axis of the hair. It consists of cuboidal cells with gran- ular contents and an indistinct nucleus. The medullary substance is generally mingled with more or less air, in small bubbles, which pene- trates from the ends of the hairs and gives to these when white the characteristic silver luster. The root of the hair is lodged in a flask- shaped receptacle of the skin called the hair-follicle, at the bottom of which is a papilla from which the hair grows. " Goose-flesh " is due to minute muscles contracting and causing the hair-follicles to become erect. At the same time the sebaceous glands are compressed, favor- ing the exudation of the sebaceous secretion. Chemically, the hairs are mainly composed of an albuminoid de- rivative, keratin, in which, a notable quantity of sulphur is present : about 5 per cent. In the ashes are found the phosphates, earthy sulphates, oxide of iron, and pigment. PuNOTioisr. — The large hairs serve to protect the skin, breaking shocks and preventing a considerable loss of heat. In other places, like the armpits, they prevent friction and attrition of the skin layers. The downlike hairs render the touch more delicate. Nails. — The nails are hard appendages of the skin, and corre- spond to the claws of other animals. They are flexible, translucent, square-shaped plates continuous with the epiderm and resting on a depressed surface of the dermis called the matrix, or bed. The exposed part of the nail is the body and its anterior end is its free border. The root of the naU is lodged in a deep groove of the matrix and the lateral borders are received into shallow grooves. The half -moon, or lunule, of the nail is due to a less degree of vascu- larity of the matrix at the root defined by a semicircular line. The TACTILE SENSE. 487 horny layer corresponds to the cuticle of the epiderm, and is com- posed of flattened, nucleated cells. The soft layer of the nails, the stratum mucosum, corresponds to that layer of the epiderm. The nails grow in length by new cells at the root, in thickness by additions beneath the nail. The nails serve to protect the skin at the tips of the phalanges, and, at the same time, perfect the touch of the fleshy parts of the fingers. The average growth of the nails is about one-eighth of an inch per month. CHAPTER XVI. SPECIAL SENSES (Continued). THE SENSE OF TASTE. Taste is an organ of special sense, by which as a medium the individual perceives savory impressions. Its principal uses to the economy are two: First, it acts as a guide to the individual in his choice of food, at the same time, rendering its mastication a matter of some pleasure. Secondly, it excites the salivary glands reflexly, so that they pour out their juices into the mouth. The organ of taste is seated in the oral cavity and in the mucous membrane of the tongue. Its limits are not well defined. The diflB- culty in their determination depends upon the double fact that these organs of taste are endowed with a very delicate sensibility of a tactile nature, and that the gustatory sensibility and the organ of smell are in very close proximity to one another. For these reasons one may very easily believe that certain regions of his mouth are gustatory, when in reality the substances which have touched them have only produced tactile or olfactory impressions. Still it has been shown that the principal regions of the oral mucous membrane designed to perceive taste-impressions are at the base and edges of the tongue. In a secondary degree, also, gustatory impressions are perceived in the anterior surface and edge of the soft palate, and the anterior portion of the tongue. All other portions of the mouth are incapable of taste-impressions. The Tongue. — The principal organ of the sense of taste is un- doubtedly the tongue; Its anatomical structure as a muscular organ has already been described when discussing deglutition and the part it played in the r&le of that important function. At this time it remains but to review such portions as have a direct bearing upon its role as a gustatory member. There are three kinds of papillse in the mucous membrane of the tongue : the circumvallate, fungiform, and filiform. They extend from the tip of the tongue to the foramen csecum. The papillas consist of elevations, visible to the naked eye and covered with stratified, squamous epithelium. The central body of each papilla contains connective tissue, blood- and lymph- vessels, and nerves. (488) THE SENSE OF TASTE. 489 The cirenmvallate papillae, the largest of the varieties and about a dozen in number, form a V-like row, defining the papillary layer at the posterior third of the tongue. They have the form of an inverted cone surrounded by a ringlike wall-elevation. The fungiform are next in size, and more numerous than the cireumvallate. They are small, red eminences scattered over the sur- face of the tongue, but are especially numerous at and near the tip. They are rounded at the free extremity and narrower at the point of attachment to the tongue. The filiform papillae, smaller and more numerous than the others, are crowded in the spaces between the others, but are arranged in rows diverging from the median line of the tongue. Nerves. — The tongue receives three nerves : one of motion, the hypoglossal, which animates the muscles; and two other sensory branches — the lingual branch of the glosso-pharyngeal and the lingual branch of the trigeminus. The former of the latter two branches spreads in the mucous membrane at the base and edges of the tongue ; the latter is distributed to the mucous membrane of the anterior two- thirds of the tongue. The branches of the glosso-pharyngeal are espe- cially concerned in sensations of bitterness, while the branches of the trigeminus are affected principally by sweet and add tastes. Section of the hypoglossal upon both sides causes paralysis of the tongue without injuring its tactile or gustatory sensibilities. Section of the lingual branch of the trigeminus causes only loss of fine tactile sensibility and gustatory sensibility of the anterior two-thirds of the tongue. Section of the glosso-pharyngeal causes loss of tactile and gusta- tory sensibility in the mucous membrane at the base of the tongue. Such an animal can swallow bitter and nauseous substances, like coloeynth, with impunity. The gustatory action of the lingual branch of the trigeminus comes from the chorda tympani. The latter is a small nerve which begins in the facial and traverses the middle ear to join the lingual branch at the level of the pterygoid muscles. The chorda tympani nerve passes from the tongue to the nerve- centers through the lingual nerve, the facial, and finally through the intermediate nerve of Wrisberg. Taste-organs. — The terminal branches of the glosso-pharyngeal nerve end in the taste-bulbs. The taste-bulbs are oval bodies imbedded in the epithelial layer. Each taste-bulb is formed of two kinds of elongated epithelial cells, and their whole outline is barrel-shaped. 490 PHYSIOLOGY. The taste-cells are narrow and slightly thickened in the middle, where the nucleus is situated. The taste-bulbs occur chiefly on the sides of the circumvallate papilla, although a small number of them are on the fungiform and the soft palate. The end of the taste-bulbs near the surface have a minute, funnel-like opening called the taste-pore. The number of taste-bodies is very great. If the glosso-pharyngeal nerve is cut, the taste-bodies degenerate. The proper stimuli for the end-bulbs of the gustatory nerves are the savory substances. These must be dissolved in the liquids of the mouth before they can penetrate the outer cells of the mucous mem- brane to come into contact with the nerve-filaments in the imbedded Fig. 115. — structure of the. Taste-organs. (Landois.) I. Transverse section of a circumvallate papilla. W, the papilla, v, v, The wall in sections. R, B, The circular slit, or fossa. K, K, The taste-bulbs in position. N, N, The nerves. II. Isolated taste-bulbs. D, Supporting, or protective, cells. K, Lower end. E, Free end, open, with the projecting apices of the taste-cells. III. Isolated protective cell id) with a taste-cell (e). bulbs. The most suitable temperature for the thorough testing of liquids is 100° F. The intensity of the gustatory impression depends upon various factors : the nature of the substance, the duration of the impression, sensibility -of the region touched, and the stimulating action of the substance upon the mucous membrane. The flavor of a substance does not depend upon its chemical properties, for both quinine and sulphate of magnesia are bitter; sugar, chloroform, and glycerin are sweet. Improper stimuli give gustatory impressions. Thus, the galvanic current applied to the tongue gives an acid taste at the positive pole and a weaker, alkaline taste at the negative pole. THE SENSE 01' TASTE. 491 Varieties of Substances. — Of the gustatory substances there are four: (1) sweet, (3) hitter, (3) acid, and (4) saline. In addition to these fundamental substances there are compound gustatory im- pressions, or a confusion of gustatory sensations with those which are tactile or olfactory. Thus, there is known the piquant taste of cheese, the caustic taste of mustard, and the aromatic taste of strawberries. The acid and sweet tastes are best perceived at the tip and edges of the tongue; the salty and hitter tastes are comprehended at the hose. This leads to the result that some substances have a different taste, dependent upon whether they touch the tip or the base of the tongue. Thus, acetate of potassium at the tip of the tongue is acid, and at the base it is bitter. The four primitive tastes are not all perceived at the exact time of their impression upon the tongue. The salty is first perceived, then the sweet, next the acid, and last the bitter. Tactile sensations by astringents (tannic acid) or thermal sensa- tions (mustard) are usually confounded with taste proper. The taste of vanilla is but an olfactory impression. Drugs. — By the action of drugs one is able to abolish certain tastes more readily than others. Cocaine upon the tongue abolishes tactile sensations and the taste for bitter things, but does not interfere with voluntary movement. The leaves of Gymnema' sylvestre, when chewed, destroy the sense of taste for bitters and sweets, while that for salts and acids remains. The Taste-center, to which the gustatory nerves send their im- pressions, lies in the uncinate gyrus. CHAPTER XVII. SPECIAL SENSES (Continued). THE SENSE OF SMELL. The seat of the sense of smell resides in the cavities of the nose. Kant has very aptly spoken of smell as "taste at a distance." The organ of smell resembles those of sight and hearing in that it consists of a special nerve which ends in a specialized epithelium. In this case the special nerve is the olfactory; the specialized epithe- lium is the mucous membrane of the upper portion of the nasal cavity. It is in this portion of the mucous membrane that the fila- ments of the olfactory nerve are distributed. For that reason it has been termed the regio olfactoria, and comprises the upper portion of the septum, the upper turbinated, and part of the middle turbinated regions. All other portions of the nasal-cavity covering is known as the regio respiratoria, or simply the Schneiderian membrane. During ordinary respiration the currents of air in their passage in and out are, for the most part, confined to this latter region. The mucous, membrane which covers this portion of the nasal cavity is, in struc- ture and appearance, very similar to that of the trachea. It is com- posed of layers of ciliated epithelium which rest upon a basement membrane rich in blood-vessels and lymphatics. Among the ciliated cells are found numerous goblet and mucous cells whose secretions keep the surface of the mucous membrane soft and moist. In it are numerous filaments of the trigeminus which endow it with tactile sensibility. There are no filaments of the olfactory nerve in this region. The olfactory mucous memhrane is thicker than that of the respiratory portion. To the naked eye it presents a yellow or brown- yellow color because of the pigment contained within it. By reason of its color it is very readily distinguished from that of the Schneide- rian membrane. Its surface is covered by a single layer of cylindrical ■ epithelium whose cells are often branched at their lower ends. The olfactory region contains the olfactory cells. These possess a body of spindle shape with a large nucleus containing nucleoli. In the deeper part the olfactory cells pass into and become continuous with fine fibers. These last pass into the olfactory nerve. (492) THE SENSE OF SMELL. 493 The olfactory, the nerve of smell, issues by two roots, each from the corresponding hemisphere. The fibers are composed of medullated and nonmedullated fibers. These latter fibers proceed from the olfactory bnlb. The olfactory bulb is a part of the cerebral cortex and is an oval or club-shaped mass of gray matter which rests on the cribriform plate of the ethmoid bone, through the foramen of which it is con- nected with the olfactory nerves. The olfactory nerves are twenty in number and are the central coursing of the neuraxons of the rod- shaped olfactory nerve-cells in the olfactory region of the nose. They pass through the openings in the cribriform plate and terminate in arborizations about the dendrons of the mitral cells of the olfactory glomeruli. These bipolar cells greatly resemble the cells of a ganglion of a posterior root of the spinal cord, one neuraxon going to the olfactory mucous menibrane and the central neuraxon connecting with the olfactory bulb. The olfactory bulb from without inward consists of four layers : — 1. The nerve-fibers. 3. Stratum glomerulosum. 3. Stratum gelatinosum. 4. Layer of central nerve-fibers. In the first layer each fibril is a central neuraxon of a rod-shaped nerve-cell from the olfactory mucous membrane. The fibers of the olfactory nerves pass into the glomeruli lying beneath. Within the glomerulus the endings of the olfactory fibril come in contact with an olfactory end-brush of an apical dendron of a mitral cell. In the stratum glomerulosum each glomerulus consists of the terminal arborizations of an olfactory nerve-fiber, together with the olfactory end-brushes from the apical dendrons of the mitral cells. The stratum gelalinosum in its inner part contains two chief forms of cells: the deep and superficial layers of mitral cells which correspond to the pyramidal cells of the cerebral cortex. The fourth layer in its outer part has a large number of very small granular cells between which pass the descending neuraxons of the mitral cells. The nerve-fibers of the olfactory bulbs collect at their posterior extremities into two bundles: the olfactory tracts. The outer root-fibers of the olfactory tract come into relation with the gyrus hippocampus, the uncus, and cornu ammonis. The inner root- fibers pass into the gyrus fornicatus. Olfactory Sensations. — The student, in order to obtain clear-cut ideas as to the mechanism of the special sense of smell, should bear 494 PHYSIOLOGY. in mind the principle of the arrangement of the olfactory nerve- terminations. It is recalled that within the mucous membrane lie the olfactory cells. Prom the peripheral end of each cell project seven or eight ciliumlike processes. These not only project to the surface of the mucous membrane, but even to the surface of the serous fluid moistening the membrane. Thus, the terminal filaments are placed in an exposed position so that they may very readily respond to any irritant. The proper stimulus for olfactory-nerve filaments are odorous substances which reach the regio olfaetoria through the air and must be in a volatile state. Hence, olfactory sensations are produced by volatile, odorous particles coming into direct contact with the exposed nerve-filaments during the act of inspiration. As the regio olfaetoria is located in the highest portion of the nasal cavity, it becomes nec- essary for the individual to cause the inspired air forcibly to reach this area. This is accomplished by the act ordinarily known as "snifiing." During ordinary respiration the inspired and expired air courses along close to the septum and below the inferior turbinated bone. Should the respired air be heavily charged with odorous particles, of course some will find their way into the regio olfaetoria, as the air in this compartment is gradually changed. There will then result a sensation of smell, but it will be faint and not so sharply defined as when the person sniffs. By the latter process the air is changed more quickly, and a greater number of volatile particles irritate the exposed nerve-endings, with the result of a sharply defined sensation. The sensation seems to occur at the first moment of contact of the odorous particles with the mucous membrane. The olfactory nerve tires very quickly when an odor acts for a certain time; the effect becomes weaker and weaker little by little, until the odor is finally unperceived. Should the free movement of the air be prevented, — as, for example, when nasal catarrh brings on a tumefaction of the mucous membrane of the inferior turbinate, — the odorous impression cannot take place. In case many different odors act simultaneously upon one nasal cavity, the individual receives a mixed sensation. Should but two odors act, the one is perceived on the right half of the mucous mem- brane of the cavity, the other upon the left half. There is not a true mixture, for the person perceives slightly the one odor and slightly the other. THE SENSE OF SMELL. 495 Secondary Sensation. — The olfactory impression having been made, the secondary aftersensation often remains for a long time. This is particularly the case with strong, disagreeable odors. This phenomenon is explained on the supposition that the odorous particles remain in the cavity of the nose, even in the air. It is not believed that the manifestation is due to persistence of excitation of the olfac- tory nerve-fibers after the stimulus has been removed. There are subjective olfactory sensations which are true hallucina- tions. They are often met with in demented, hysterical, or pregnant women. These sensations owe their existence to some material altera- tion of the nervous apparatus. Prom impressions truly olfactory it becomes necessary to dis- tinguish the gustatory as well as tactile or irritative sensations upon the nasal mucous membrane. The irritation and even pain produced by the vapors of ammonia often lead it to be improperly classed as "having a bad odor." Experimentally, a dog with both olfactories divided always starts from the odor of ammonia or of acetic acid. This ^ is due to painful stimulation of his Sehneiderian membrane, which gets its sensory nerve-filaments from the second branch of the trigeminus. Uses. — The organ of smell represents an advance sentinel for the functions of respiration and alimentation. Among the lower animals it serves for the recognition of sex. Hyperosmia and Anosmia. — Hyperosmia,. or increased sensitive- ness of smell, is a common condition. It is very apt to be found in hysteria and in many other nervous disorders. Strychnine is one of the drugs which is capable of producing this condition when it is applied locally in solution. Anosmia is a term used to designate a condition which is the reverse of the one before mentioned. It may be complete, when it is usually congenital. In such a case the olfactory nerves are absent. It is more usual, however, to find the condition partial. Its causes may be stenosis of the nasal cavities, disease of the olfactory mucous membrane, or nervous diseases. Strychnine often relieves the con- dition. The Center of Smell lies in the tip of the uncinate gyrus upon the inner surface of the cerebral hemisphere. CHAPTER XVIII. SPECIAL SENSES (Continued). THE SENSE OF HEARING. Bx means of the special sense of hearing the individual gains knowledge of a kind differing from the just-mentioned senses. It does not tell him what is going on in the outer world by actual con- tact, as in touch or taste; nor yet by particles of matter impinging upon the exposed end of nerve-filaments, as in the sense of smell. In the special sense of hearing the impressions conveyed to the central nervous system are produced by wavelike vibrations in the surrounding air. For the reception of these vibrations, so that they may be properly interpreted and the corresponding impressions conveyed to the brain, it becomes necessary to have a special sense- organ : the ear. The Ear. The organ of hearing ia its greatest simplicity may be repre- sented by a small membrane stretched like a drumhead over the bottom of a funnel-shaped tube. The tube opens upon the surface of the body so that it is in direct communication with the enveloping atmos- phere. The membrane is so disposed that it is readily thrown into vibrations when the external air becomes undulatory as the result of vibrations of some body. Its vibrations are communicated to an inner vesicle that is filled with a liquid. The liquid is likewise thrown into waves whose undulations stimulate the ramifications of the audi- tory nerve which are spread out upon the walls of the vibrating vesicle. Anatomy. — The apparatus for hearing is composed of three parts : external ear, middle ear, and internal ear. External Ear. — The external ear is composed of the auricle and external auditory meatus. The auricle has the form of an irregularly shaped shell. It is composed of yellow, elastic cartilage which is covered over with skin. Prom its shape one might readily believe that the function of the auricle is to collect and reflect sound-waves into the auricle: that is, to behave in the capacity of an ear-trumpet. But it is found that hearing is perfectly normal in those persons from whom the external ear has been removed by accident or otherwise. (496) THE SENSE OF HEARING. 497 The external auditory meatus and canal extend from the concha of the auricle to the tympanum. The canal is composed partly of cartilage and partly of bone ; the bony portion belongs to the temporal bone. The canal is lined by skin, which contains modified sebaceous and sudoriferous' glands. By the glands is secreted the cerumen, or earwax. The internal end of the auditory canal is bounded by an ellipsoid structure which is composed of three layers of tissue: the tympanic membrane. The functions of the external auditory canal are twofold: (1) to conduct waves of sound to the membrana tympani, and (3) to insure Fig. 116. — ^Diagram of the External Surface of the Left Tympanic Membrane. (Hensen.) a, Head of maUeus. b. Incus, e, Joint between maUeus and incus. Be- tween c and d is tlie flaccid portion of the membrane, ax. Axis of rotation of ossicles. Tlie umbo is ttie deeply shaded part. this membrane, as well as the delicate structure of the middle ear, from injury. Middle Eak^ or Tympanum. — The tympanum is a space situated within the substance of the petrous portion of the temporal bone. It is composed of two bony and four soft parts. The two bony parts comprise the walls of the cavity, with the mastoid cells and Eustachian tube ; also the ossicles or bones of the ear. The soft structures are: (1) the ligaments and muscles of the little ossicles, (2) the mucous membrane of the tympanic cavity, (3) the Iftiing of the Eustachian tube, and (4) the membrana tympani and membrane of the round window. 498 PHYSIOLOGY. In otitis media pus may cause a disintegration of the mastoid cells, from which it frequently extends to the membranes of the brain. The cavity of the tympanum forms a dilatation added to the auditory canal. It has an internal wall, an external wall, and the Eustachian tube. The mastoid cells communicate by a large orifice with the upper, back part of the tympanum. They are lined through- out with a delicate mucous membrane. The external wall is occupied in its greatest extent by an opening which is nearly circular and closed by the membrana tympani. The latter is semitransparent, concave externally and convex internally. Kg. 117. — Tympanic Membrane and Auditory Ossicles,. seen from the Tympanic Cavity. (Lanuois.) M, Manubrium, or handle of the malleus. T, Insertion of the tensor tympani. h. Head. IF, long process of the malleus, or incus-tooth. The short (E) and the long (l) process. B, Plate of the stapes. Ax is the common axis of rotation of auditory ossicles. 8, The pinion-wheel arrangement be- tween the malleus and incus. To its inner surface is attached the malleus, one of the three ear ossicles. The internal wall is convex and has in its central portion a tubercle known as the promontory. Its base corresponds to the origin of the cochlea. The most prominent of the grooves upon its surface marks the position of the nerve of Jacobson. Above the promontory is found the oval window. Its shape is really reniform; it leads to the vestibule. The round window ig situated just beneath the oval window. It- is closed by a membrane. The ossicles, which form an articulated chain, reach from the membrana tympani to the oval window. In number they are three: THE SENSE OP HEARING. 499 the malleus, or mallet ; the incus, or anvil ; and the stapes, or stirrup. The three ossicles form a chaia suspended across the cavity of the tympanum. The handle of the malleus is inserted into the tympanic membrane; the base of the stirrup is applied to the oval ■window. Between these two ossicles is suspended the incus. The ossicles have joints which are lined with synovial membrane; there are present suitable ligaments. The mucous membrane of the tympanum is very thia, and either white or rose-colored. It envelops the chain of ossicles. Kg. 118. — ^Left Tympanum and Auditory Ossicles. (Landois.) A.G., External meatus. M, Membrana tympanl, whioli is attaohefl to the handle of the malleus (») and near its short process (p). ft. Head of the malleus, a. Incus. K, Its short process, with its ligament. I, Long process. S, Stapes. The Eustachian tube is composed of a bony and a cartilaginous part. The canal opens at the anterior upper part of the tympanum; its. pharyngeal orifice is situated ten millimeters behind the posterior extremity of the nasal fossa. The walls of the tube open at each move- ment pf deglutition by reason of the action of the tensor palati. The Bony Labyrinth, or Internal Ear. — This structure is imbedded within the substance of the petrous portion of the temporal bone. Its long axis lies in a position parallel with that of the bone. The labyrinth is composed of three portions: vestibule, semicircular canals, and cochlea. 500 PHYSIOLOGY. The vestibule is an oval, irregular cavity, lying between the tym- panum and the bottom of the internal auditory meatus. The semi- circular canals open from it posteriorly and the cochlea opens from it anteriorly. Through its outer wall it communicates with the tym- panum by the oval window. The fovea hemispherica and fovea hemi- elliptica are two depressions upon the inner and superior walls of the vestibule, respectively. They are pierced by numerous foramina ; through the former pass the filaments of the cochlear branch of the auditory nerve ; through the latter foramina pass the branches of the n^*" Kg. 119. — Scheme of the Organ of Hearing. (Landois.) A&, External auditory meatus. T, Tympanic membrane. E, MaUeus with its head (ft), short process (fcfl, and handle (m). a, Incus, with its short process (.x) and long process; the latter is united to the stapes (s). P, Middle ear. o, Oval window, r. Round window, x, Beginning of the lamina spiralis of the cochlea, pt. Its scala tympani. vt, Its scala vestihuli. V^ Vestibule. (8, Saccule. V, Tubercle. B, Semicircular canals. TE, Eustachian tube. The long arrow indicates the line of traction of the tensor tympani; the short curved one that of the stapedius. vestibular branch. Through the latter also pass small veins which ■communicate with the inferior petrosal sinus. The semicircular canals are three in number. They are located above the inner and back part of the tympanum. From their location "they are named superior, posterior, and external. The canals lie in three distinct planes: the first two are vertical, but nearly at right angles to one another; the last is horizontal. Each canal is rather more than half of a circle, and forms at one extremity a dilatation called the ampulla. The canals communicate THE SENSE OF HEARING. 501 with the vestibule by -five openings, one of which belongs to both the superior and horizontal canal. The interior of the vestibule and semicircular canals is lined with a delicate membrane. The cavity formed by this membrane contains a fluid of serous nature. It is known as the perilymph, by reason of its surrounding a secondary structure, the labyrinth. This last struc- ture consists of a pair of saccules in the vestibule, and three semi- circular saccules whose form is the same as the osseous canals contain- ing them. This membranous labyrinth comprising the saccules just mentioned itself contains a serous fluid, the endolymph. Fig. 120.^Scheme of the Labyrinth and Terminations of the Auditory Nerve. (Landois.) I. Transverse section of a turn of the cochlea. II. Ampulla of a semicircular canal, a, p. Auditory cells, p. Cell pro- vided with a fine hair. T, Otoliths. III. Scheme of the human labyrinth. IV. Scheme of a bird's labyrinth. V. Scheme of a fish's labyrinth. The inner portion of the bony labyrinth is the cochlea: so named from its resemblance to a shell. Its base is attached to the internal auditory meatus, while its apex is directed forward and outward. The axis of the cochlea is nearly at right angles to that of the petrous portion of the temporal bone in which it lies. The cochlea is a tube of bone wound around a central axis, each turn successively rising. This bony tube is about one and one-half inches long. Its beginning is connected with the fore part of the vestibule to produce the prom- ontory of the tympanum; it ends in a closed extremity called the infundibulum. The central axis just spoken of is termed the modiolus. The apex of the cochlea is often called the cupola. 502 PHYSIOLOGY. The bony canal is divided into two passages, or scalm, by a septum known as the lamina spiralis, which projects from the modiolus. The two scalse communicate with one another only at the top of the cochlea, by an opening: the hiatus, or helicotrema. That portion of the cochlear canal that is above the septum terminates in the vestibule; hence scdla vestibuli. The lower portion opens into the tympanum through the round window; hence scala tympani. The membranous portion of the septum, or lamina spiralis, con- Fig. 121. — Section through the Uncoiled Cochlea (I) and through the Terminal Nerve Apparatus of the Cochlea, (II). (Munk, after Hensen.) I. F.r., Round window. S, Helicoterma. St., Stapes. II. IS, Huschke's process. 6', Basilar membrane, e, Corti's arch, g, Sup- porting cells, h. Cylindrical cells, i, Deiters's hair-cells, c, Membrana teo- toria. », Nerve-fibers. »', NonmeduUated nerve-fibers. sists of two layers: The superior layer is the membrane of Corti, or membrana tectoriaj the other is the membrana basilaris. These two membranes are placed parallel with one another to contain between them the organ of Corti. The latter rests upon the basilar membrane. The bony portion of the septum has, upon its superior external surface, a denticulated, cartilaginous substance called the lamina den- ticulata. From the superior surface of the lamina spiralis, and in- ternal to the lamina denticulata, exists a delicate membrane, the THE SENSE OF HEARING. 503 membrane of Beissner. This membrane divides the scala vestibuli into two passageways, one of which is the ductus cochlearis. It con- tains the essential portion of the auditory apparatus of the cochlea: the organ of Corti. It forms part of the membranous labyrinth. The membranous labyrinth is a closed sac consisting of semi- circular canals, a vestibular portion, and the membranous part of the lamina spiralis. The vestibular portion consists of an expanded body, the utricle, and a smaller body, the saccule. Within these compart- ments are two calcareous bodies: the otoliths. The vestibular fila- Fig. 122. — Section of the Ductus Cochlearis and the Organ of Corti. (After IiA.NDOis.) N, Cochlear nerve. K, Inner, and P, outer, halr-oells. n, Nerve-flbrils terminating In P. a, a. Supporting cells, d. Cells in the sulcus spiralis. «, Inner rod of Corti. Mt, Corti, membrane of Corti, or the membrana tectoria. o. The membrana reticularis. B, Cf, Cells filling up the space near the outer wall. ments of the cochlear nerve are distributed to the ampullse, utricle, and saccule. In the first, the fibers terminate in elevations called crista acusticcBj in the last two they end as oval plates, — maculae, — colored by yellow pigment. Organ of Corti. — The organ of Corti contains the following elements : — 1. Arches of Corti. — They are formed of an internal and ex- ternal pillar whose pedestals rest upon the basilar membrane. The arches intercept the canal of Corti. 504 PHYSIOLOGY. 2. Internal Auditory Cells. — Inward from the internal pillar of Corti is found a layer of auditory cells. These cells contain nuclei, while their superior extremities terminate in a plateau having long ciliated prolongations; their inferior extremities are in relation with the basilar membrane and axis-cylinder of the terminal cochlear branches of the auditory nerve. S. A Granular Layer composed of rounded cells. J^. Cells in the sulcus spiralis which are cubical in shape. 5. The External Auditory Cells, whose structure and arrangement is very similar to the internal cells Just mentioned. 6. The Cells of Deiters, Hensen, and Claudius, which make a prominence upon the interior of the cochlear canal. 7. Reticular Membrane. — The membrana reticularis is formed by the superior extremity of the cells of Deiters. It possesses lacunae which allow the passage of cilia of the cells. 8. The Membrane of Corti, or membrana tectoria, is a soft, thick membrane which covers the spiral groove and organ of Corti. Be- neath it adheres to the cilia of the auditory cells. Auditory Nerve. — The auditory nerve consists of two parts : the cochlear, the hearing part, and the vestibular, the tonus part. The cochlear part arises in the, spiral ganglion of the cochlea, and, like a posterior root ganglion, sends a branch to the auditory cells in the organ of Corti and a central branch to the cochlear nucleus in the medulla. The cochlear nucleus consists of two parts: the accessory nucleus and the tuberculum aeusticum. Hence the first neuron ex- tends from the spiral ganglion to the cochlear nucleus; then the two divisions of the cochlear nucleus — ^the accessory nucleus and tuberculum aeusticum — send out neuraxons to the superior olive ; here they are second neurons. The superior olive sends out neuraxons to the lateral fillet ; here the third neuraxons make up chiefly the lateral- fillet fibers. These go to the posterior quadrigemina and finally are connected with the seat of hearing in the first temporal convolution. The vestibular root arises in Scarpa's ganglion-cells of the laby- rinth and goes to the auditory nucleus. Prom here neuraxons go up by the restiform body to the nucleus of the roof (nucleus fastigii) and nucleus globosus of the opposite side of the cerebellum. The cochlear nerve is the nerve concerned in hearing. The vestibular nerve is the nerve concerned in equilibration. It does not have anything to do with hearing. The functions of the auricle and external auditory meatus and canal have been mentioned above. The membrana tympani, like all THE SENSE OF HEARING. 505 elastic and stretched bodies, enters into vibrations when it is directly struck or when a body produces a sound that is capable of setting this membrane into a vibration of unison. The contact of the hammer pos- sesses the role of a damper ; it arrests the vibrations of the membrane and to a certain measure makes the different vibrations follow each other in a regular, noninterfering manner. It is probably a function of the tensor tympani to relax the membrane in case of violent noises, as with cannon-shots. By this means rupture of the membrane is prevented. The vibrations of the membrana tympani are transmitted to the internal ear by the chain of ossicles as well as by the air in the middle ear. II. Fig. 123. — I. The Mechanics of the Auditory Ossicles. (After Helmholtz.) II. Section of the Middle Ear. (Mttnk, after Bensen.) I. a, Malleus, h, Incus, am, Long process of incus, s, Stapes. The arrows show the direction of motion. II. G, External auditory canal. M.t., Membrana tympani. 0, Tympanum. H, Malleus. L.8., Superior ligament. S, Stapes. The Eustachian tube is closed at its pharyngeal end except during deglutition. Thus, if one closes the mouth and nose and then expires forcibly at the moment of deglutition, there is heard a dry crackling in the ear from the entrance of air into the middle ear with depression of the tympanum. The tube thus acts as a medium whereby there is established an equilibrium between the intratympanic pressure and the pressure of the atmosphere. Should the pressure be not equal upon each side, as in closure of the Eustachian tube, then the vibra- tions of the membrane are made with difficulty. In making descent 506 PHYSIOLOGY. in a deep mine where the atmosphere is considerably more dense than that on the surface, the uninitiated is instructed to swallow every few minutes. By so doing he maintains an equable pressure upon both sides of the membrana tympani. It will be recalled by the student that all of the spaces and com- partments of the internal ear, or labyrinth, are filled with fluid, and that in this fluid float saccules also containing serous fluid. So intimately are all of the parts of the labyrinth associated that any vibration of its contained fluid at one part is promptly propagated to every other portion. The vibrations of the fluid striking upon the tiny nerve-filaments act as stimulants whose impressions are carried to the center of hearing, where the impressions are recognized as sound. To epitomize : The sonorous waves collected by the auricle to pass through the external auditory meatus and along its canal strike the surface of the membrane of the tympanum. It becomes tense, vibrates in unison, and then commimicates its vibrations through the ossicles and contained air in the tympanum to the oval window. From here the vibrations are carried over the vestibule, semicircu- lar canals, and labyrinth to the perilymph.- Prom this last the vibra- tions are transmitted through the membranous walls of the sacculus to the endolymph. Vibrations also pass from the vestibule to the scala vestibuli of the cochlea, and, descending the scala tympani, end as an impulse against the membrane of the round window. Most of the organs of special sense contain a "specially modified epithelium" for the reception of the particular kind of stimulus peculiar to each other. Nor is the sense of hearing different from the others. It also has its tissues representing " specially modified epithelium" in which lie the terminal filaments of the auditory nerve. These tissues are so constituted that they receive the "waves of sound" which generate in the auditory nerve : auditory impulses. These last, when conveyed to the brain, are developed into auditor}' sensations. The vibrations of elastic bodies produce condensation and rare- faction of the enveloping atmosphere. That is, there are developed waves whose particles vibrate longitudinally. These waves are usually spoken of as sound-waves. Normally, then, the auditory nerve may be stimulated by sonorous vibrations which set into motion the end-filaments of the acoustic nerve. The filaments are distributed over the inner surface of the membranous labyrinth, upon the membranous expansions of the coch- lea, and in the semicircular canals. The excitement of the filaments THE SENSE OF HEARING. 507 is really mechanical in nature, due to the wavelike motion of the serous fluid of the membranous labyrinth. Conduction through the iones of the head occurs very readily when the vibrating solid body is applied directly to some part of the head. This is exemplified by placing a tuning fork upon the head, or by the striking together of stones when the head is submerged beneath the surface of water. It is common to divide auditory stimuli into those which are caused by noises and those caused by musical sounds. It is a feature peculiar to musical sounds that the vibrations which form them are periodical and that they recur at regular intervals. When neither of these two conditions is present, there results a noise. Prom the sensory impulses to which the several vibrations give rise are generated our sensations of noise or of sound. To produce a sensation certain conditions in the excitation of the auditory nerve are necessary. The sound-wave must exist for a certain length of time ; it must not be less than Yjo nor greater than '/40000 second. In the piano the lowest base (C, 33 vibrations) and the highest treble (C, 4224 vibrations) exist. A certain number of impulses must be made within a given interval of time to excite a sensation of tone. The lower limit is about 30 vibrations, the upper limit about 40,000, per second. Visual sensations separated by less than a tenth of a second are fused, but auditory sensations separated by V134 second remain distinct. Theory of Hearing. — If you sing a note into a piano, the cords of the piano tuned for this note only respond. Now the basilar mem- brane is supposed, like a harp, to represent a series of cords which, like the piano-strings, respond to the sounds • striking them. This membrana basilaris is striated in a radiating direction, and these striations increase as it ascends toward the helicotrema. Unlike the harp, the cords are joined together by their edges; but, as they are stretched only in a radiating direction, they can vibrate as though they were separate cords. Now, the cords are very short, being at most not over V12 inch in length ; so that they would be expected only to vibrate for high sounds; but it must be remembered that these cords are weighted with the arches and cells of Corti, which lower their sound. Hence we have a series of cords in. the basilar membrane vibrating separately to musical sounds. We know that there is in man about 3000 arches of Corti, and as at least two of the cords correspond to an arch of Corti, we have 6000 cords. Now, the scale of musical sounds extends to seven octaves, and we have 400 arches of Corti to 1 octave. 508 PHYSIOLOGY. In 1 octave there are 12 semitones, and we have 66 cords correspond- ing to a semitone ; so that we have sufficient cords to vibrate in unison with all possible musical sounds. When the sound-waves vibrate the cells of Corti they make the terminal filaments of the cochlear nerve vibrate, because they are in relation with the cells of Corti. The differentiation of sounds takes place in the brain. Binaural Audition. — The hearing of a single sound with both ears may be due to habit or to the connection in the nerve-centers of the fibers connected with both ears. Undoubtedly binaural audition facili- tates our knowledge of the direction of sound, since each ear has its own axis and direction. The semicircular canals are, through the vestibular nerve and the cerebellum, the most important agents in the preservation of equi- librium. When in a pigeon the horizontal canals are divided the head moves from left to right and from right to left, with nystagmus and a tendency to revolve on its vertical axis. When the inferior vertical or posterior canals are divided, the head oscillates from front to rear; the animal has a tendency to fall backward. A section of the superior vertical canal causes the head to oscillate from front to rear, with a tendency to fall forward. A section of all the canals is followed by , contortions of the most bizarre nature. After a destruction of all the canals the animal cannot maintain his equilibrium. Similar phenomena have been observed in man in disease of the semicircular canals, known as Meniere's vertigo. In the fixed position of the head there is equilibrium, but with each movement the tension of the liquid in the ampulla changes and irritates the vestibular nerve. These ampulla and canals are then sensory organs, and give the animal an idea of the position of his head in space. Now, as the canals are at right angles to each other according to the three dimensions in space, their section makes the animal unable to know the position of his head and thus produces vertigo. Cyon's theory is that the semi- circular canals give us a series of unconscious sensations as to the position of our heads in space. CHAPTER XIX. SPECIAL SENSES (Concluded). VISION. Those bodies are said to be luminous which especially affect the organ of vision. Some are luminous in themselves, others become so by reflection. Since there is no direct contact between the visual apparatus and the object which makes the impression, and since the distance which separates them is often infinite, it is impossible not to admit the existence of a particular intervening agent between the center of radiation and the eye. This agent is ether. How Does Light Transmit Itself? — The accepted theory to-day with regard to its propagation is the undulatory, or wave-, theory. Its doctrines make light, like heat and ^ound, a mode of motion. A luminous body is one whose particles are in a state of vibration. That they may give rise to a luminous impression it is necessary that they be transmitted to the eye. Ordinarily the atmospheric air is the usual medium for the transmission of the vibrations of a sounding body to our ears. However, a luminous body does not become invisible in a vacuum, as does a sounding body become inaudible. Hence, there must be supposed the existence of a highly elastic medium that per- vades all space and all bodies. To this especial medium luminous bodies communicate their vibrations to be transmitted with enormous velocity. This medium is known to physicists as ether. Suppose a luminous body isolated in a gas or suspended in a vacuum ; it will be visible in all directions. Imagine, also, a point of space lighted up by its radiations. The line which joins this point to one of the elements of the luminous body represents the direction of a ray of light. So long as no obstruction intervenes the ray of light pursues an even, straight course. Should, however, a mirror inter- cept its path, the greater portion of it will be bent out of its regular course. That is, it is reflected. In all cases of reflection it is well to remember that "the angle of reflection always equals the angle of in- cidence." Again, the passage of light through transparent media of various densities presents peculiarities: its straight course is modified — broken. To convey a conception of this phenomenon the term re- fraction is used. (509) 510 PHYSIOLOGY. Visual Apparatus. The organ of sight, the eye, is construeted upon the principles of the camera obscura. In the latter the collecting lens unites the light impressions at the hack of the apparatus to form upon the groilnd- glass plate a diminished and reversed image of external objects. . Structure. — The eye is composed of three concentric coats (scle- rotic, choroid, and retina), the aqueous and vitreous humors, and the crystalline lens. Fig. 124. — Diagram of a Horizontal Section, through the Human Eye. (Yeo.) 1, Cornea. 2, Sclerotic. 3, Choroid, i, Ciliary processes. 5, Suspensory ligament of lens. 6, So-called posterior chamber between iris and lens. 7, Iris. 8, Optic nerve. 8', Entrance of cerebral artery of retina. 8", Central depression of retina, or yellow spot. 9, Anterior limit of retina. 10, Hyaline membrane. 11, Aqueous chamber. 12, Crystalline lens. 13, Vitreous humor. 14, Circular venous sinus which lies around the cornea, a-a, Antero-posterior axis of bulb. 6-6, Transverse axis of bulb. ' The first, or outside, coat of the eye is opaque in all of its parts except a small anterior segment. This area, which is about one-sixth of the entire circumference, is perfectly transparent. The dense opaque part is known as the sclerotic; the transparent portion is the cornea, which is the most anterior portion of the sclerotic. The Scleeotio is composed of iibrous connective tissues whose bundles are woven together both circularly and longitudinally. It contains a few blood-vessels in the form of a wide-meshed capillary plexus. VISION. oil The Cornea represents a cap of a smaller sphere attached to the larger, sclerotic sphere. It is transparent and resembles very much a watch-glass in form. The cornea is thicker at its periphery than in its center. This little, transparent window is composed of five dif- ferent layers. In the third layer the connective-tissue fibers are arranged in thin plates. Between the plates are series of spaces which communicate with each other and which are lined with endothelium. These — called the lymph-spaces — communicate with the lymphatics of the conjunctiva. Within, but not quite filling, the lymph-spaces lie the fixed corpuscles of the cornea, which are connective-tissue corpuscles. Leu- cocytes also pass into these lymph-spaces. The membrane of Descemet constitutes the fourth layer from the outside. Long and short ciliary nerves supply branches to the cornea. They penetrate it from the periphery, divide, and subdivide, some of them terminating in the corneal corpuscles. Others end within small knobs placed between the deep and middle epithelial cells. The blood-vessels are at the margia of the cornea, there beiag none within its substance. The Choeoid is the vascular coat of the eye, containing some pigment-granules. Its external layer is composed principally of blood-vessels and nerves. Between the vessels are found numerous stellate pigment-cells which form a fibrous network. That portion of the internal surface which is joined to the retina also contains pigment-cells. Posteriorly it is penetrated by the optic nerve; an- teriorly it is continuous with the ciliary processes and iris. The choroid lies beneath the sclerotic, covering the posterior five-sixths of the eyeball. The ciliary arteries furnish an abundant supply of blood to this coat of the eye. The ciliary veins collect the deoxygenated blood. They perforate the sclerotic just behind the equator of the globe of the eye. 7m. — The anterior one-sixth of the choroid is composed of a muscular curtain known as the iris. It is practically a diaphragm with a central opening, called the pupil. The iris is separated from the cornea by the anterior chamber of the eye. The musculature of the iris comprises both circular and radiating fibers. The pupil is made smaller- by contraction of its circular fibers. These belong to the smooth type of muscle-fibers and are innervated by the oculomotor through the medium of its ciliary branches. 513 PHYSIOLOGY. The pupil enlarges through contraction of the radiating fibers of the iris. It is innervated by the ciliary branches derived from the great sympathetic. Sensory nerves are. present, coming from the first branch of the fifth, or trigeminus. Hence, stimulation of the oculomotor and trigeminus, as well as cutting the sympathetic nerve in the neck, produces contraction of the pupil. Irritation of the sympathetic causes the pupil to dilate. The ncJrmaJ contraction and dilatation of the pupil are reflex movements that are caused by the rays of a very strong or very faint light striking the retina. From the retina the impression is conveyed to the an- terior corpora quadrigemina and then to the oculomotor nucleus and its nerve to the iris. It is not due to the direct action of light upon the iris itself. The iris is composed of several layers, in the posterior one of which is the pigmentary epithelium. In brunettes the color is due to pigmented connective-tissue corpuscles. The artery and veins of the iris lie at its periphery. In the ciliary portion of the choroid is located the ciliary muscle : the muscle of accommodation. It contains two layers : one radiating, the other circular. The ciliary processes^ about sixty in number, are conical bodies which project inward from the ciliary ring into the posterior chamber of the eye. They are the most important part of the choroid coat. > Uses. — ^By reason of its vascularity the choroid is destined to nourish the all-important and underlying retina. By reason of its elasticity and contained musculature the choroid maintains intra- ocular pressure. The pigment of the choroid is believed to serve a dioptric purpose: that of absorbing the superfiuous rays of light which pass through the eyeball on their way to the retina. Their absorption prevents dazzling and interference with vision. The Eetina. — The optic nerve pierces the eye a little to the inner side of the center of the eyeball. It soon divides into numerous small bundles of ultimate fibers which appear to spread themselves out so as to inosculate with one another and thus form a network. It is this plexus which constitutes the inner layer of the retina. The most anterior portion of the retina is the ora serrata. The retina is composed of two main portions: the pigmentary membrane and the terminal elements of the optic nerve.^ The pigmentary layer has been called the uvea. It covers the entire inner surface of the ciliary processes, the iris, and the choroid. It is composed of a layer of nucleated, hexagonal pigment-cells. VISION. 513 The nervous layer of the retina is composed principally of the terminal nerve-elements of the optic nerve. Externally, it is coated with a pigment-layer; internally, it is lined with a homogeneous, transparent structure, the hyaloid membrane. Histological Structure. — The histological structure of the retina is very complicated. The retina is really an outward expansion of the original f orebraiu. The retina is usually divided into eight layers : — 1. The layer of nerve-fibers. 2. The layer of ganglionic cells. 3. The inner molecular layer. 4. The inner nuclear layer. 5. The outer molecular layer. 6. The outer nuclear layer. 7. The layer of rods and cones. 8. The hexagonal pigment-layer. The first layer consists of neuraxons from the ganglionic cells of the second layer. The second layer consists of a lot of multipolar nerve-cells, and their neuraxons run iaward to form most of the fibers of the optic nerve. The dendrons of these multipolar cells are branched and terminate in the inner molecular layer, of which this third layer is chiefly composed. The fourth inner nuclear layer is made up chiefly of round and oval cells with a peripheral neuraxon and a central neuraxon. The peripheral neuraxon arborizes around the dendrons of a gan- glionic cell in the inner molecular layer. The fifth outer molecular layer is made up of the arborizations of the neuraxons of the visual cells of the outer nuclear layer. The sixth layer, the outer nuclear layer, is the layer of bipolar visual cells. Their central neuraxons end in arborizations in the outer molecular layer about the dendrons of the bipolar cells of the inner nuclear layer. The peripheral processes of these cells are the rods and cones of the retina, which are similar to the dendrons of other nerve-cells. The seventh layer of rods and cones are the dendrons of the visual cells. The eighth layer is the pigment-layer of the retina. The retina is essentially formed by a number of nerve-cell chains, the elements of which are arranged in three series from without in. The first is the rod and cone; the second is the bipolar cell, which interlaces with the peripheral dendrons of the ganglionic cells. The third element is the ganglion-cell. 514 PHYSIOLOGY. The optic tract arises in the retinal cells, which is its trophic cen- ter. These retinal cells send in fibers which arborize around the cells of the anterior corpora quadrigemina, pulvinar, and the lateral corpus geniculatum. liTow, from the lateral corpus geniculatum and pulvinar we have a second set of neuraxons running to the occipital cortex, the center of vision. Here the lateral corpus geniculatum and pulvinar are the relay centers in the path of visual impulses. Fig. 125. — Vertical Section of Human Retina. (Landois.) a, Rods and cones. 6, External limiting membrane, c, External nu- clear layer, e, External granular layer. /, Internal nuclear layer, g, In- ternal granular layer, j, Internal limiting membrane. Rods and Cones. — The rods are cylindrical bodies, each of which ends externally in a truncated, flattened extremity. The cones, as their name iudieates, are conical bodies. It has been demonstrated that the rods and cones consist of two segments, or limbs, which are composed of fibers and granular matter. Continued strong light produces swelling of the rods; they shrink again in darkness. The rods and cones show that their outer, granular VISION. 515 matter breaks up into transverse plates. The inner segments are stri- ated by reason of fibers prolonged into them from the external limit- ing 'membrane. Number. — In man and mammals the number of rods far exceeds that of the cones. The reverse is true in birds. Macula Luiea. — The yellow spot of Soemmering is an oval depres- sion in the center of the retina. It measures one-twentieth of an inch across and is one-tenth of an inch to the outer side of the point of entrance of the optic nerve. Its center is the fovea centralis. In the fovea there are no rods; cones only are present, and these are longer and narrower than those of the other parts of the retina. When the optic nerve penetrates the eye it projects somewhat be- yond the inner surface of the eyeball as a papilla. In this papilla there are none of the essential nerve-elements of the retina, so that rays of light cannot be perceived by this particular area ; hence the name of blind spot. Cbtstalline Lens. — The lens is a biconvex, solid, transparent body, located behind the iris and in front of the vitreous body. Its greater convexity is on the posterior surface. The transverse and vertical diameters are about one-thitd of an inch ; the antero-posterior one is but one-sixth. The lens is enveloped in a capsule of fibrous membrane. The substance of the lens is made up of fibers which were originally cells. The fibers are in concentric layers traceable from the posterior sur- face to the anterior. The suspensory ligament of the lens is derived from the hyaloid membrane of the vitreous body. Cataract. — Normally the lens is transparent. When it becomes opaque for any reason then there results the condition known as cataract. This condition is artificially produced in frogs by the in- jection of grape-sugar. Cataract in diabetes is from the same cause. Aqueous Humor. — This fluid contains about 3 per cent, of solids, chiefly in the form of sodium chloride. It occupies the anterior chamber in the space back of the cornea and in front of the iris. The so-called posterior chamber lies between the back of the iris and in, front of the lens. ViTEEOUS HuMOE. — The vitreous humor is a gelatinous body which is held in its position posterior to the crystalline lens by the hyaloid membrane. At. the ora serrata the membrane splits into two layers : one, the hyaloid membrane proper, passes over the front of the vitreous body; the other, a fibrous structure, is much firmer than the true hyaloid. It extends over the ciliary processes to be attached to 516 PHYSIOLOGY. the capsule of the lens, forming for it a suspensory apparatus: the zonule of Zinn. The lymphatic canal of Petit is formed by the splitting of the two layers of the hyaloid membrane. In the center of the vitreous body is the canal of Stilling. Dur- ing fcetal life it transmitted the artery of Zinn to the back of the capsule of the lens. When by ulceration of the cornea or accident the aqueous humor escapes, it is found to be regenerated very rapidly. The secretion of the aqueous humor has been studied by fluorescin instilled into the fluids of the eyebaU. It has been found that the humor is secreted by the posterior surface of the iris and ciliary body. It passes through the pupil into the anterior chamber. The globe of the eye is filled with fluids during life and is con- stantly under a certain pressure: the intra-ocular. This pressure depends mainly upon the arterial pressure of the retinal arteries, and so rises and falls with their variations of pressure. Eetinal Epithelium. — Puscin, a variety of melanin, is found in the hexagonal cells of the retinal epithelium. The cells send down processes between the rods and cones like the hairs of a brush. It has been found that light exerts a marked efEect upon these processes. The protoplasm of the pigment-cells of a frog that has been kept in the dark for several hours is found to be retracted and the pigment lies chiefly in the body of the cell. When exposed to the light the proc- esses filled with pigment dip down between the rods and cones as far as the external limiting membrane. Lymphatics. — The lymphatics of the eye comprise an anterior and posterior set. The former is located in the anterior and posterior chambers of the eye and have communication with the lymphatics of the iris, ciliary processes, cornea, and conjunctiva. The posterior set consists of the perichoroidal spaces lying between the choroid and sclerotic coats of the eyeball. Optic Nerve. The optic nerve-apparatus comprises (1) the optic tracts j (2) tl}^e optic commissure, and (3) the optic nerves. The centripetal fibers of the optic nerve are the neuraxons of the ganglionic cells of the second layer of the retina. The dendrons ■of these cells receive arborizations from the neuraxons of the bipolar cells of the retina. The dendrons of the bipolar cells end about the neuraxons of the visual cells, whose dendrons are the rods and cones. VISION. 517 Hence there is a conducting path through the retina continuous with the optic nerve which decussates in part and connects with the ex- ternal geniculate body, the. pulvinar of the optic thalamus, and the anterior corpora quadrigemina. From these parts new neuraxons arise which issue from the outer side of the thalamus, and run through the extreme end of the thalamus, ending chiefly in the cuneus and occipital lobes. These are the optic radiations of Gratiolet. The union of the two tracts produces the optic commissure, or optic chiasma. It is in the commissure that there occurs a partial decussation of the fibers of the two tracts. More than one-half of the fibers of the one tract cross over to those of the opposite tract. That is, the left tract sends fibers to the left half of both eyes ; the right tract ia turn supplies the right half of each eye. Destruction of the optic tract, then, produces homonymous hemianopsia; that is, the outer half of one eye and the inner half of the other is blind. In owls there is complete decussation, so that destruction of one tract back of the decussation produces blindness in the whole eye of the side opposite to the lesion. From the optic commissure proceed the two optic nerves: one to each eyeball. Bach optic nerve is inclosed within a sheath of its own, composed of dura mater and arachnoid. Perception of Light. Light is due to vibrations of ether; a proper conception of them gives the sensation of sight. Transmission of light, with air as a medium, is 186,000 miles per second. The rapidity of the vibrations influences the sensation produced, for color is for luminous sensation what height is for sound. The inferior limit of visible vibrations is represented by the color red ; the superior limit is exemplified in violet. For light to be perceived physiologically by any individual it must make an impression upon the retina. The light falling upon the retina immediately stirs up certain changes in it which in turn give rise to nervous changes in the fibers of the optic nerve. This last change, or "visual impulse," produces a further series of events within the brain, one effect of which is a change in our consciousness ; that is, there is a sensation. The point upon the retina at which the impressions are strongest and most exact is the macula lutea and its fovea centralis. The anatomical layer designed to be impinged upon by a distinct image is the membrane of Jacobson, the layer of rods and cones. As only the 518 PHYSIOLOGY. cones, and no rods, are found in the fovea centralis, it is the point where objects are fixed. Hence it must be held ttat the cones are the specific elements of the retina that are designed to make the indi- vidual perceive a luminous impression precisely. Nevertheless, the field of vision, though indistinct toward its periphery, is very much enlarged. The luminous impression consists of the vibrations of the lumi- nous ether, which stimulate the outer portion of the rods and cones. In them there is produced a molecular, mechanical change, or dis- turbance. Whenever the layer of rods and cones is stimulated, the excitation is propagated from without inward to all of the retinal ele- ments. The various elements are connected by fibers, and, finally, by the optic nerve with the brain. Physiology of the Eye. The study of the phenomena of the eye may be divided into four parts: (1) dioptrics ^ (2) accommodation, (3) imperfections and cor- rections, and (4) vision with both eyes. Dioptrics. — The eye has previously been mentioned as being like a camera obscura. If a small opening exist in the shutter of a dark room the rays of light from the outside passing through the opening will form an inverted image of the external object upon the opposite wall of the chamber. However, unless the opening be very small, the image will be blurred and indistinct. These latter qualities will be due to overlapping of rays of light from various points of the object. If the opening be small enough the overlapping rays will be cut off and a distinct image be formed. Should a convex lens be interposed in the path of the rays of light the opening may be very considerably enlarged and yet the various rays be brought to a focus so that diffused images will be prevented. The camera obscura is popularly laiown to-day in the form of the photographic camera. The latter consists of a box blackened on the interior to prevent reflection from the walls. In front is a short tube which contains achromatic lenses. In the back wall of the camera is found a ground-glass plate upon which the image formed by the lens is focused. If the camera be so adapted that parallel rays falling upon the lens are focused upon the ground-glass plate, then divergent rays must have their focal point behind the plate. Should the plate be moved backward or forward it can be made to coincide with the conjugate focus of the rays diverging from the object. VISION. 519 Sphekical AsEKKATioisr, which interferes with distinctness, is gotten rid of by cutting off outside rays. In the camera this point is accomplished by the insertion of a diaphragm through a slit in the lens-tube. The diaphragm is pierced by holes — a larger or smaller one being used according as the light is feeble or strong. The eye may be very aptly compared to the camera. It has a small opening in front through which pass the rays of light. The sclerotic and choroid coats form its walls. The refracting lenses are the cornea, aqueous humor, crystalline lens, and vitreous humor. They all tend toward the accomplishment of the same end : to bring parallel rays of light to a focus upon a sensitive plate (the retina), Fig. 126. — Diagram Illustrating Spherical Aberrations. (Ganot.) The rays passing through the edge of the lens have a shorter focal distance than those passing neai er to the center. there to form a real inverted image of the object. Last, the iris with its pupil acts as a diaphragm. Chromatic Abeeeation. — The edge of the lens of a camera rep- resents the outer angle of a prism. White light falling upon it is decomposed into its spectral components. Objects seen upon the ground-glass plate have an iridescent hue. In the eye this trouble is obviated by the presence of the iris and the fact of the edge of the lens being more angular and less curved. Visual Angle. — It has been stated by Helmholtz that the visual angle is really the angle inclosed by visual lines, which are lines from a point in space which pass through the center of the image of the pupil formed by the cornea and pass to the center of the macula lutea. The apparent size of the object depends upon the visual angle. Acute- ness of vision is inverse as the size of the visual angle. The test-types 520 PHYSIOLOGY. of Snellen are constructed on this principle. They are adjusted to be seen under an angle of five miuutes. Accommodation of Eye for Distance. — The refractive media of the eye are such that parallel rays are brought to a focus upon the retina. Such an eye is said to be emmetropic. It is evident that, if divergent rays fall upon the eye, — ^that is, rays from a finite distance, — ^they will not be brought to a focus upon the retina, but behind it if the eye remain in its emmetropic condition. The result of this would be circles of diffusion and a blurred and indistinct image. Kg. 127. — Scheme of Aeeommodation for Near and Distant Objects. (iiANDOis, after Eelmholts.) The right side of the figure represents the condition of the lens during accommoda- tion for a near object and the left side when at rest. The letters indicate the same parts on both sides ; those on the right side are marked with a stroke (of minute mark. ^, Left half of lens, jj, Eight half of lens. C, Cornea. S, Sclerotic. CS, Canal of Schlemm. VK^ Anterior chamber. J, Iris. P, Margin of pupil, V, Anterior sur- face. JET, Posterior surface of lens. Ji, Margin of the lens. F^ Margin of ciliary proc- esses, a, &, Space between the two former. The line Z-X indicates the thickness of the lens during accommodation for a near object ; Z~Y, the thickness of the lens when the eye is passive. Should the refractive power of the media be increased, then the focal point would be brought forward. Such increase might be accom- plished by the addition of another convex lens in front of the crystal- line lens. The effect is practically accomplished by reason of the lens being able to adjust its capacity to suit varying distances. This capacity is termed the power of accommodation. It is an ability to alter the con- vexity of the lens, due to contraction of the ciliary muscles which relax the zonule of Zinn of the lens. By reason of its own elasticity the lens bulges forward, thus increasing its convexity. In what may be regarded as the normal, or so-called emmetropic eye, the near point of accommodation is about five inches. The far VISION. 531 limit, for all practical purposes, is from two hundred feet up to an infinite distance. In this eye the range of distinct vision has wide latitudes. In the myopic, or short-sighted, eye the near point is two and one-half inches from the cornea. The far limit is at a variable, but not very great distance. The range of vision in this eye is very lim- ited. In this the rays of light are brought to a focus in front of the retina. Kg. 128. — ^Myopic Eye. (Landois.) In the hypermetropic, or far-sighted, eye rays of light coming from an infinite distance are, in the passive state of the eye, brought to a focus behind the retina. The near point is some distance away. The presbyopic, or long-sighted, eye of aged persons resembles the hypermetropic eye, but- differs in so far that the former is an essentially defective condition of the mechanism of accommodation. --/ Fig. 129. — Hypermetropic Eye. (Landois.) There are two changes which occur when we accommodate for near objects: one is that the pupil contracts to cut off divergent rays; the other is a change of curvature of the lens. The ciliary muscle is the motive power of accommodation. Its paralysis renders accommo- dation impossible. The oculomotor innervates the ciliary muscle. Its paralysis by atropine produces both dilatation of the pupil and inability to accommodate. 522 PHYSIOLOGY. To correct anomalies of refraction it" is necessary to use lenses. These are transparent media which seem to refract rays of light passing through them. They have curved surfaces. The direction which the rays take on emerging from the medium depends upon the nature of the curvature. The chief forms of lenses are convex and concave; convex lenses may be doubly convex, plano-convex, or con- cavo-convex. A concave lens may have equivalent features. A con- vex lens converges the rays of light; a concave lens diverges the rays of light. In myopia a concave lens is used; in hypermetropia and presbyopia a convex lens. Astigmatism is a defect of refraction due to a want of symmetry in the refracting media of the eye. The result of this is that the rays of light passing through the lens are not brought to a focus at the same point. This want of symmetry is usually in the cornea, but may be in the lens. To remedy this defect we use a lens called a s A J Fig. 130.— Different Kinds of Lenses. (Ganot.) ^, Double convex. ^, Plano-convex. C, Converging concavo-convex. D, Double concave, ^E", Plano-concave. J^, Diverging concavo-convex. C and i^ are also called meniscus lenses. cylinder to level up the curvature of one of the meridians of the cornea to correspond to the curvature of the others. Cylinders have no curvature in one axis, but more or less considerable curvature in the opposite axis in correspondence with the degree of astigmatism that has to be corrected. Lenses. — Lenses are arranged accordiug to their focal distance in inches, and, as the unit was taken as one inch, all weaker lenses were expressed in fractions of an inch. However, Bonders made the standard in lenses of a focal distance of one meter, and this unit he called a dioptre. Thus the standard in a weak lens and, the stronger lens are multiples of these. Hence a lens of two dioptres equals one of about twenty inches' focus. Entoptic Phenomena. — When in the vitreous there exist cel- lular elements which in the field of vision appear as strings of beads, circles, and stripes, they are called muscse volitantes. They move when the eye is moved. If the eye is strongly illuminated at the side. VISION, 533 branching figures are seen in the fieldr of vision, ■which are called Purkinje's figures. They are due to shadows of the blood-vessels of the retina which fall upon the rods and cones. DtJKATiON OF Eetinal STIMULATION. — Light impresses the ret- ina, but the excitation of it does not cease immediately with the disappearance of the luminous vibrations. Indeed, they persist for a certain time, about one-eighth of a second : that is, proportional to the intensity of the excitation. Upon a disc black and white sections are alternately painted. When the disc is made to rotate rapidly the disc appears neither black nor white, but gray. Visual Purple, ok Rhodopsin. — The outer part of the rods eon- tains a reddish coloring matter which is called visual purple. This coloring matter must be kept in the dark, for it bleaches the moment light strikes it. But the color will return if the eye is again brought Kg. 131. — Diagram Showing Refraction by a Double Convex Lens. (Ganot.) The incident ray, L-B, is refracted at the points of incidence, 5, and emergence, D, toward the axis, M-N-A, which it cuts at F. into a dark chamber. The bile acids extract the coloring matter from the retina. The visual purple is a product of the melanin or fuscin. Color-vision. — White light is composed of rays of different re- frangibUity by reason of the different length and duration of the luminous rays. These various rays falling upon the retina determines in the individual different sensations which correspond to the colors. To decompose white light into its different colors, the prism is used. A ray of white light upon issuing from the prism presents the spec- trum. That is, there emerge the principal simple colors from the most to the least refrangible. They are violet, indigo, blue, green, yellow, orange, and red. Each primary color cannot be further de- composed, but all can be reunited by a biconvex lens so that white light will result again. The ultra-red (thermal) and ultraviolet (chemical) rays do not make any impression upon the retina. The former do not pass through the media of the eye, since to vibration- rates beneath 435,000,000,000 per second the retina is not stimu- 524 PHYSIOLOGY. lated; the latter color produces no sensation, since to vibration-rates above 764,000,000,000 per second thie retina is insensible. Sensations of Color. — In the production of the sensations of color there are three chief factors: tone, saturation, and intensity. The tone of the color depends upon the number of vibrations of the ether. A color is said to be saturated when it does not contain any white light. The simple colors of the spectrum are saturated. The intensity of color depends upon the amplitude of the vibrations. Loss of Color-vision, or Daltonism. — Young stated, as the ex- planation of color-vision, that all the colors were referable to three fundamental sensations: those of red, green, and violet. Corre- Fig. 132. — ^Diagram Illustrating the Decomposition of White Light into the Seven Colors of the Spectrum in Passing Through a Prism. (Beclaed.) ■/•, Red. 0, Orange, j. Yellow, -ii, Green. &, Blue, i, Indigo, vi, Violet. spending to the three sensations excited by these three colors were three kinds of retinal fibers, stimulation of which gives rise to sen- sations of red, green, and violet. It is also supposed that white light stimulates these fibers with different degrees of activity according to the length of the wave. The longest wave acts most on the fibers which respond to the red color, the medium wave on the fibers which respond to green, and the shortest wave on the violet. Helmholtz adopted the theory of Young. It is also supported by the facts of color-blindness, in which there is an inability to distinguish one or more of the fundamental colors. The commonest form of color- blindness is that in which red is the invisible color, and in the com- ^'ISION. 535 pound colors in which red enters the complementary color alone is visible, white appearing as bluish green. Another theory of color- vision is that of Hering. The six sensations of color readily fall iato three pairs, the members of each pair having similar relationship. White and black naturally go together, the one being antagonistic of the other. According to Hering, the retina is undergoing meta- bolic changes, and he supposes there are three distinct visual sub- stances which are undergoing anabolism and eatabolism. When breaking down, or eatabolism, is in excess of the building up, or anabolism, we have a sensation of white; when upbuilding predomi- nates, we have black. Anabolism of the visual substances by the rays of light produces green, blue, and black; eatabolism of these visual substances pro- duces white, red, and yellow. f White is catabolic f Red is catabolic I. J and 2. J and I Black is anabolic. I Green is anabolic. Yellow is catabolic and Blue is anabolic. In applying this theory to color-blindness it must be assumed that those who are red-blind want the red-green visual substance; they have only the black-white and yellow-blue visual substance in the retina. According to the Young-Helmholtz theory, there is a defect cor- responding to the three color-perceiving fibers. According to this theory color-blindness is of four kinds : red, green, and violet, and complete blindness to colors. In the Hering theory the kinds are: (1) complete, (2) blue-yeUow, (3) red-green, and (4) incomplete color- blindness. Color-blindness is also called Daltonism, after Dalton, a Quaker, who first described it. The percentage of color-blindness among persons is about 3, and among Quakers about 3 Vg, because for gen- erations they have worn drabs. The disease is hereditary. CoMPLEMENTAKT CoLOSS. — Those colors are complementary which when mixed together produce white. The following table gives the complementary colors of the spectrum : — Red — ^greenish blue. Greenish yeUow — violet. Orange — Prussian blue. Green — purple. Yellow — indigo-blue. 526 PHYSIOLOGY. Green alone has no complementary color in the spectrum. It gives a white color with the componnd color purple. Irradiation. — This is a phenomenon which is observed when look- ing at a strongly illuminated object upon a dark background; the object appears larger than it really is. Thus, of two rings of eqaal size, one white on black, the other black on white, the former appears larger than the latter. Irradiation is due to imperfect accommoda- tion. Here the margins of an object are projected upon the retina in circles of diffusion and the brain tends to increase the ill-defined margin to those parts of the visual image which are most prominent in the image itself. What is bright seems larger and overcomes what is dark. Black clothes make one appear to be much smaller than light clothes. After-images. — When a bright light is thrown on the eye and then suddenly put out, there remains for a short time an impression Fig. 133. — Diagram Illustrating Irradiation. (Stielikg.) If this diagram is held some distance from the eye especially if not exactly focused, the white dot will appear larger than the black, though both iire of exactly the same size. of the same light, as though the retinal molecules still continued to vibrate from the light stimulus. This is a positive after-image. When the eye has received a stimulus for some time, the sensation which follows the withdrawal is of a diif erent kind, and you have a negative after-image, which is due to exhaustion of the retinal cells. For instance, if you look at a red color for some time and the eye afterward is focused on a white ground, the negative after-image is a greenish-blue; that is, the color of the negative image is comple- mentary to that of the object. Phosphenes. — If the retina be pricked, compressed, or twitched by any sudden movement, an impression of light will be produced. The same effect follows the use of electricity. Hence the retina is an essentially sensitive membrane. No matter by what cause its sensibility be excited, it always gives rise to the subjective phe- nomenon of a luminous sensation. VISION. 527 Vision with Both Eyes. — The study of phenomena bearing upon this subject comprises : (1) movements of the eyes, (2) Mnocular vision, and (3) the advantages of sight with hath eyes. Movements of the Eyes. — The eyeball may be considered as an articulated spherical globe which turns upon three axes that cross each other. Six voluntary muscles affect the tliree rotations of the eye. The rectus internus and externus, when acting alone, turn the eye from side to side. The superior and inferior recti give to the ocular sphere an up-and-down movement. The superior or inferior oblique muscle, acting alone, gives the eye an oblique movement. Co-ordinated Movements. — The two eyes always present co-ordi- nated movements in order to maintain the parallelism or convergence of the two visual lines. The visual line is that line which passes be- tween the object, center of the pupil, and center of rotation of the ocular globe. For accommodation at a distance the two visual lines are parallel. In accommodation for near objects the lines are con- vergent. So long as the muscles of the eyeball are normal in function their movements are in co-ordination. Should one or more become para- lyzed or seized with spasm, then proper parallelism and convergence are lost. Straiismus will then be present and the object looked at will appear double : diplopia. The innervation of the muscles of the eye is derived from the third, fourth, and sixth pairs of cranial nerves. BiNOCULAK. Vision. — Looking into space with one eye, one sees an almost circular field. With the one eye he can look toward the opposite side as far as the root of the nose permits. If he opens the other eye the visual space becomes much more extended in a trans- verse direction, but corresponding to the monocular field, since the two monocular fields are superposed. Why should any point or object be seen single and not double, when the point forms not one, but two images upon the retinse? The explanation, accepted is that the images are as two corresponding identical points. These points are so related to one another that the sensations from each are blended into one perception. The move- ments of the eyeballs are also adapted to bring the image of the object to fall upon identical parts. The law results that if one luminous point simultaneously impresses two identical points, it must be seen as single and not double. The two images are referred to one point in space and they produce in the individual only one im- pression. 528 PHYSIOLOGY. lacrymal Secretion. — Lately it has been shown by Landolt that in the rabbit and the monkey secretory nerves of the lacrymal gland run in the facial nerve. These nerves leave the geniculate ganglion and enter the superficial petrosal. We then find them in the supe- rior maxillary and occasionally in the ophthalmic. He believes these fibers run in the glosso-pharyngeal and then in the facial, but he did not locate the nucleus from -whieh they arise. Ophthalmoscope. — This is a small concave mirror by means of which rays of light are directed through the pupil of the eye so that Kg. 134. — ^DiagTEun Illustrating Binocular Vision. (Beclakd.) The lines from the object indicate that rays from the back of the book fall on coincident points of the retina, while each eye further has a special field of vision. the deep parts are illuminated and made visible. There is a hole in the center of the mirror through which the examiner looks. But the ophthalmoscope may be used with or without lenses. Without lenses the ophthalmoscope gives an erect image. If, however, we use a convex lens over the central aperture of the ophthalmoscopic mirror the observer sees a reinverted image. If a concave lens is used over the aperture of the ophthalmoscopic mirror there is seen an erect image considerably magnified. The instrument is usually fitted with a series of concave and convex mirrors, which can be re- volved in front of the central aperture of the mirror. VISION. 529 If the observer is myopic he can use the concave lenses to correct ■ his myopia. If he is long-sighted, he corrects it hy means of one of the convex lenses. If the eye examined be short- or long- sighted, the retinal image could not be brought into focus with the mirror alone, but the ex- aminer can adjust his concave or convex disc, as the case may be, and find a lens to correct the short or long sight of the eye examined. In this way the ophthalmoscope may be used to measure the degree of myopia or hypermetropia of the eye examined. Perimeter. — ^It has been noted that by the peripheral parts of the retina a person can observe pretty definitely the form and color of objects. To determine just how far this field of indirect vision ex- tends in every direction from the visual axis is to locate, by the perimeter, the field of indirect vision. The instrument devised for this purpose is called the perimeter. With the perimeter the eye is made to view a fixed point from which a quadrant proceeds so that the eye lies in the center of it. Around the fixed point the quadrant rotates, and this circumscribes the surface of a hemisphere in the center of which the eye is located. From this fixed point objects are slid on semicircular arms and are gradually placed more toward the periphery of the field of vision until the object is no longer noticed. Then by moving the semi- circular arm in different meridians of the field of vision we obtain what is called the field of vision. The field of vision is more extended below and to the outer side. It is narrowed above by the brow; below by the cheek and the nose. _ CHAPTER XX. CRANIAL NERVES. The cranial nerves are twelve pairs of nerves which reach their respective terminations after passage through foramina located in the base of the cranium. They are designated numerically, beginning from the anterior portion of the base of the brain backward, as well as by narries dependent upon their functions and distribution. They are as follows : — 1. Olfactory. 5. Trifacial. 9. Glosso-pharyngeal. 2. Optic. 6. Abducent. 10. Pneumogastric. 3. Motor oculi. 7. Facial. 11. Spinal accessory. 4. Pathetic. 8. Auditory. 12. Hypoglossal. Origfin of the Cranial Nerves. — Upon examination, each cranial nerve is found to possess a point of superficial origin as well as a nucleus of deep origin. The superficial origin is that point upon the brain's surface where each nerve emerges. This is but the apparent origin of each pair of nerves, since their individual fibers may be traced more deeply. Each cranial nerve has a special nucleus of gray matter lying deeply vdthin the brain-substance. The nucleus consists of a collec- tion of cells from whose prolongations spring the axis-cylinders which constitute the fibers of the nerves. The gray masses which represent the prolongations of the anterior horns of the cord into the medulla oblongata form the nuclei of origin of the cranial motor nerves. The base, separated from the head of the horn by decussation of the pyramidal columns, remains contiguous to the central canal. It is prolonged in its entirety upon the fioor of the fourth ventricle, lying upon each side of the raphe. Beneath the trigonum hypoglossi lies the nucleus of the hypoglossal; beneath the eminentia teres is found the common nucleus of the facial and motor oculi; the nuclei of the abducent and pathetic lie upon each side of the aqueduct. Tlie head of the anterior horn, cut into fragments by the motor decussation, forms that which is known as the antero-lateral nucleus. This is the motor nucleus of the mixed nerves. By its most internal parts it represents the accessory or anterior nucleus of the hypo- (530) CiRANIAL NERVES. 531 glossus; farther up, the proper niieleus of the facial; and in the pons there is found the motor root of the trigeminus. The gray masses of the posterior horns of the cord, prolonged ■ into the medulla oblongata and cut by the sensory decussation or fillet, form the sensitive nuclei of the cranial nerves. The base of the poste- rior horn forms the sensory nucleus of the mixed nerves, namely: glosso-pharyngeal, vagus, and spinal accessory. Above these nuclei there is a gray layer which represents the oblongata center of the internal root of the auditory; higher still arises the sensory nucleus of the trigeminus. The head of this horn, under the name of gray nucleus of Eolando, ascends in the pons to form the ascending root of the trigeminus. Among the twelve pairs of cranial nerves, ten have their points of origin in cells of the gray matter of the cord. This latter has been prolonged into the medulla oblongata and pons in the form of four motor and sensory columns. Thus these cranial nerves are com- parable to spinal nerves. Comparison with Spinal Nerves. — The law of double root is as applicable here as to the spinal nerves. Those nerves destined for movement originate in the prolongations of the anterior horns, while those which preside over sensibility take their origin in gray matter of the medulla and pons which has sprung from the posterior horns of the spinal cord. Point of Diffeeence. — There is this difference, however, be- tween cranial and spinal nerves : In the spinal nerves the two roots are intimately united just outside of the spinal-cord substance to form a mixed nerve. In the ease of the cranial nerves the posterior sensory roots and the anterior motor roots remain, for the most part, sepa- rated to form nerves that are either exclusively motor or exclusively sensory. In other words, the cranial nerves represent the dissociated spinal nerves in which the anterior and posterior roots remain habit- ually isolated to form nerves which are either fine conductors of motion or sensation, dependent upon their source. In the hypoglossal alone are fulfilled the true characteristics, for in numerous eases it is found to have a ganglion upon its posterior root. The mesencephalon has been considered to possess parallel fea- tures with the spinal cord, in that it is formed of a series of segments corresponding to the cranial nerves. As the student already knows, each spinal nucleus has peripheral conductors which bring to the cord its sensory impressions, and motor nerves to conduct to the muscles 532 PHYSIOLOGY. the motor reactions. In the same way the central conductors of the brain bring to it sensory impressions and by its motor fibers carry out motion. Hence it results that all of the sensory fibers of cen- tripetal course have their origin, not in the gray nuclei of the medulla oblongata, but in the ganglia annexed to the dorsal roots of the cranial nerves. The oblongata nuclei are but terminal nuclei, for in them the sensory fibers terminate' by fine arborizations which surround the central cells without penetrating them. The termination is identical with that of the sensory roots of the spinal nerve. The sensory fibers of the tenth, ninth, seventh, and fifth pairs of cranial nerves, as well as that of the auditory, originate in their re- spective ganglia. Thus, there is the jugular for the tenth pair, the petrosal for the ninth pair, the geniculate for the seventh, G-asserian for the fifth, and vestibular ganglion for the eighth pair. On the contrary, the motor fibers of the cranial nerves arise in the central cells of the medulla and pons, just like the motor fibers of the spinal cord. Thus, fine anatomy demonstrates that the cranial, like the spinal, nerves have double roots. Decussations. — The afferent or sensory cranial nerves do not decussate. Of the motor cranial nerves, the third and fourth, the motor root of the fifth, the seventh, the motor root of the vagus, the glosso-pharyngeal, and the hypoglossal decussate partially. The pathetic decussates completely in the valve of Vieussens. The last- named nerve springs from the oculomotor nucleus united with that of the pathetic. These portions of gray matter are a direct part of the anterior horn of the spinal cord lying beneath the aqueduct of Sylvius. In Chapters XVII and XIX were considered the olfactory, or first pair of cranial nerves, and the optic, or second pair; so that in this chapter there will be taken up, first, the motor oculi, or third pair of cranial nerves. THIRD PAIR, OR MOTOR OCULI NERVE. This nerve arises from a nucleus situated between the corpora quadrigemina and beneath the floor of the aqueduct of Sylvius. Beneath its posterior end, the corpus quadrigeminum, it becomes continuous with the nucleus of the trochlearis or patheticus. The oculo-motor nuclei consist (1) of a group of cells concerned in ac- commodation; (2) those concerned in the reflex action of the iris to light; (3) the innervation of all the muscles of the eye except the CRANIAL NERVES. 533 external rectus and superior oblique. The neuraxons of these cells pass by and through the red nucleus and emerge at the inner side of the cerebral crura, to pass through the interpeduncular space along the. outer boundary of the cavernous sinus, enter the sphenoidal fissure, and go to the muscles of the eyeball, except the external rectus and superior oblique. It also gives fibers to the ciliary muscle and the sphincter of the pupil and a branch to the elevators of the upper lid. The posterior longitudinal bundle is also connected with the nuclei of the third, fourth, and sixth nerves. The oculomotor nucleus also has a connection with the optic neurons in the anterior corpora quadrigemina. In the cavernous sinus it receives filaments coming Jiad- cutter tores ,EK M.TI. Pig. 135. — Position of the Nuclei of the Cranial Nerves. (After Edingeb.) The medulla oblongata and pons are imagined as transparent. The nuclei of origin (motor), black ; the end nuclei (sensory), red. from the carotid branches of the great sympathetic nerve and also a branch from the ophthalmic of the trigeminus. Functions. — From a functional point of view, it may be said that the motor oculi is devoted exclusively, in conjunction with the fourth and sixth pairs of nerves, to making the sight perfect. With these nerves it concurs to regulate the varied movements which allow the eye to act as a telescope upon a support that is furnished with numer- ous articulations. By means of these muscles and nerves of the orbit the individual is enabled to remove the visual field from place to place and in all directions to any objects which he might wish to examine. For its part, the motor oculi allows the eye to see particularly objects that are situated high or low or at one side. However, it has a most important function in the harmony of the associated move- 534 PHYSIOLOGY. " ments by which two images fall upon identical points of the retinae of the two eyes, thus causing but one and the same impression. The third pair of nerves manages to regulate the amount of light which falls upon the retinse. Its function in this capacity is to pro- tect the optic nerve against a too intense excitement from excessive light. By contracting the pupil it lessens the peiicil of light which penetrates into the depths of the ocular globe. On the contrary, it is the sympathetic which produces dilatation of the pupil so that the retina may receive all of the light which can be reflected from obscure objects. For the accomplishment of con- traction and dilatation of the pupil the iris comprises two kinds of muscular fibers : circular and radiating. The former are connected with the motor oculi; the latter with the sympathetic. Finally, the third nerve is considered to have an important func- tion in the act of accommodation. Pathology. — The motor oculi is frequently a sufferer by reason of its situation and course. It is often compressed by tumors at the base of the brain. In its passage through the sinus cavernosus it is exposed to compression by a thrombosis of this venous canal. The course of the third nerve through the interpeduncular space makes it play a considerable part in pathology. This is the place of predilection for meningitic deposits. This segment of the nerve is most frequently compressed in the exudates of tubercular meningitis. It is also the point of attack of constitutional syphilis, partictilarly during the tertiary period; this is a chronic meningitis which has its principal focus at the interpeduncular space as an exudate. Diph- theritic infection often attacks the third pair of cranial nerves. Paralysis of the oculomotor gives rise to external squint. Its irritation causes internp,l squint, and also contraction of the pupil, or myosis. The eye deviates outward, due to the action of the ex- ternal rectus not being antagonized by the internal rectus. Diplopia. — The deviation of one of the eyes does not .permit the maintenance of parallelism of the visual axes. "Without this coinci- dence the two images will not fall upon identical points in the retina. Hence aU objects seen will be double. This symptom, known as diplopia, renders the sight very uncertain and often produces vertigo. Should the paralysis be general, so that it comprises the elevator of the lid, Nature brings for itself a remedy for the defect of diplopia by suppressing the vision of one eye. It does this by letting the lid fall aver the deviating eye. This drooping of the lid gives the con- dition known as ptosis. CRANIAL NERVES. 535 Stimulation of the motor fibers of the third can be produced re- flexly by teething or intestinal irritations of children; hence their squint. Chronic spasms of the eye-muscles which are involuntary are called by the name nystagmus. Drugs. — Atropine paralyzes the intra-ocular ends of the motor oculi; Calabar bean stimulates them and paralyzes the sympathetic. FOURTH PAIR, OR PATHETIC NERVE. Distribution. — The pathetic supplies the superior oblique muscle. Physiology. — If the peripheral end of the pathetic be electrically irritated, the superior oblique muscle contracts and turns the eyeball downward and outward. The pathetic is a nerve that is especially endowed for the realiza- tion of simple vision with the two eyes in inclined positions of the head. It is impossible for an individual to carry one eye downward and outward. That is, he cannot make a movement directed by the superior oblique and still keep the head perfectly vertical. It be- comes necessary that the head be inclined to one side, and at the time this inclination is produced the rotation of the eyeball occurs without the will having the power to prevent it. By the very act of inclination of the head the necessary parallelism of the two eyes is positively destroyed; hence this involuntary action of the superior oblique to place the visual axes upon the same plane. The fourth pair of cranial nerves arise from a collection of cells beneath the anterior part of the posterior corpus quadrigeminum. It completely decussates in the superior medullary velum. It starts behind the quadrigeminal body and then appears like a white thread winding around the outer 'side of the crus of the cerebrum. It then pierces the dura mater, runs along the outer waU of the cavernous sinus, and enters the sphenoidal foramen with the oculomotor and abducent. It supplies the superior oblique muscle of the eye. Pathology. — Usually the first sign of any disorder of the pathetic is a giddiness when ascending or descending a stairs, owing to the double vision that occurs when the patient, in going down, looks at his steps. To overcome this diplopia he gives to his head a position that is quite characteristic. He holds his head bent forward and directed to the ground. This position overcomes the necessity of moving the eyeballs from above downward and so minimizes the liability to diplopia. 536 PHYSIOLOGY. SIXTH PAIR, OR ABDUCENT NERVE. This nerve arises from a eoUeetion of cells seated beneath the floor of the fourth ventricle below the strise acusticse. The loop of the facial incloses it. The abducent emerges between the summits of the pyramidal bodies of the medulla oblongata and the pons. As a threadlike nerve it goes through the cavernous sinus and through the sphenoidal foramen to the external rectus. The nucleus of the abducent has a connection with the posterior longitudinal bundle of fibers to the opposite oculomotor nucleus, thus permitting associated movements of the eyeball. The pontal olives are connected by fibers with the oculomotor nucleus. These olives are also connected with the auditory nuclei, and these nuclei are connected with the cere- bellum; so that there is an association between the motor nerves of the eye, the auditory nerves, and the cerebellum. Physiology. — The sixth nerve is exclusively motor. It has for its only aim to excite the external rectus. When the nerve is strongly galvanized the eyeball deviates outward. Its section, on the contrary, produces an internal strabismus. It is especially adapted for seeing objects placed to one side. In general, the abducent is b^^t one of the elements for the exercise of perfect vision. Pathology.— Paralysis is the most common manifestation in the sixth pair. A considerable concussion of the orbital cavity, espe- cially when it is upon the external side, will particularly paralyze the abducent. Unilateral paralyses of this nerve are usually of peripheral origin. Bilateral paralysis is generally due to central disturbance. The most prominent symptom of this affection is an internal or con- vergent strabismus. The eye is held inward by the tenacity of the rectus internus, so that not more than one part of the cornea is per- ceived. CONJUGATE DEVIATION. Waller explains this as follows: The two eyes are exactly equal and parallel for different directions of distant vision. Both eyes are turned to the right or to the left, up or down, so that the object fixed gives images on corresponding parts of both retinse. In movements directly upward or downward muscles of the same name in each eye are associated in action; but in lateral movements the association is asymmetrical: e.g., the external rectus of one eye acts with the in- ternal rectus of the other, and the peculiarity of this associated action seems still more striking when it is remembered that the external rectus is supplied by the sixth nerve, while the internal rectus is CRANIAL NERVES. 537 supplied by the third. A similar, if less striking, association of asymmetrical muscles on the two sides occurs in the rotation of the head and neck, which are turned to the right by the right inferior oblique and the left stemo-mastoid muscles, and to the left by the left inferior oblique and the right stemo-mastoid. In looking to the right we contract the right external and left internal rectus: i.e., impulses pass through the right sixth nerve and the left third, pos- sibly from the left and from the right side, respectively, of the motor cortex, but more probably from only the left motor cortex, in which case we must suppose that certain nerve-fibers cross twice: once between the cortex and bulbar nucleus and a second time between the nucleus and nerve-termination. Unilateral convulsions of cor- tical origin are accompanied by rotation of the head and eyes toward the convulsed side: i.e., away from the cerebral lesion. Thus a discharging lesion of the right motor cortex causes convulsions of the left side of the body, with rotation of the eyes to the left. This is a " conjugate deviation." A destructive lesion of the right motor cortex causes paralysis of the left side of the body, with rotation of the eyes to the right. The peculiarity in this ease is that there is a cessation of action along the left sixth nerve (external rectus) and the right third nerve (internal rectus), the deviation of the eyes to the right being caused by the unbalanced action of the muscles, which rotate the eyes to the right. FIFTH PAIR, TRIGEMINUS, OR TRIFACIAL NERVE. The fifth pair of nerves, like a spinal nerve, has two roots : an anterior motor one and a posterior sensory one. The neuraxons of the motor nucleus in the pons make up the motor root. The sensory arises in the Gasserian ganglion, and, like a posterior-root ganglion, its neuraxons are divided, one part going to the skin of the face and the other, running toward the pons, also divides into two parts, one going upward and the other downward. The gelatinous substance of Eolando on the posterior horn receives the fibers running upward, which arborize around the cells. The descending part of the trigeminus, known as the ascending root, extends down to the second cervical vertebra, continually giving off collaterals as it descends, which arborize around the gelatinous substance of Rolando of the posterior horn, thus making the lower trigeminal nucleus a long one. The descending branch also has col- laterals, which arborize around the motor nuclei of the hypoglossal, facial, and trifacial. The neuraxons of the sensory nuclei in which 538 EHYSIOLOGY. the trigeminus ends decussate and go to the cortex in the fillet. The nucleus of the motor root lies in the pons, near the sensory nucleus of the trigeminus and back of the nucleus of the facial, of which it is probably a part. There is another nucleus, the accessory nucleus of the motor nucleus, which is situated beneath the aqueduct of Sylvius, and which sends descending fibers to the motor nucleus. The trigeminus emerges from the pons by two roots: a large sensory root and a small motor root. The large root has the Gas- serian, or semilunar, ganglion, while the small root runs beneath it. Prom the semilunar ganglion emanate the ophthalmic, superior max- illary, and a third branch, which joins the small root of the trifacial to form the inferior maxillary nerve. The nasal branch of the ophthalmic, ciliary, or lenticular, ganglion, gives off the ciliary nerves for the ciliary muscle and iris. This ganglion receives motor fibers from the oculomotor nerve and branches from the sympathetic. The superior maxillary branch passes through the rotund foramen of the sphenoid bone and gives off dental and spheno-palatine nerves which go to Meckel's, or the spheno-palatine, ganglion. It gives off nasal, palatine, and pterygoid nerves. The pterygoid nerve gives off a branch, the great petrosal, which enters the cranial cavity through the cavity of the foramen lacerum and enters a canal on the front of the petrous portion of the temporal bone to join the facial nerve. The inferior maxillary nerve is formed of the small motor root of the trigeminus and a third branch of the semilunar ganglion, and makes its exit from the skull by the oval foramen. It gives off the auriculo-temporal and the lingual nerve, which in its course is joined by the chorda tympani of the facial and the inferior dental nerves. On the sensory division of the inferior maxillary nerve is seated the otic, or ganglion of Arnold. From it emanates the small petrosal nerve, which enters the cranium through a fine canal in the spinous process of the sphenoid bone and then courses along a canal in front of the petrous portion of the temporal bone to join the facial. The otic ganglion gives out filaments to the tensor palati and tensor tympani muscles. Physiology. — From the point of view of general sensibility the trigeminus possesses a considerable domain. To it alone is intrusted the giving of general sensibility to nearly all parts which enter into the composition of the head. In the external covering of the head but one region escapes it, which is the lateral and posterior part of the hairy scalp, the innervation for the latter coming from the cer- vical nerves. CRANIAL NERVES. 539 As to mucous-membrane sensibility, trifacial innervation comes only to the posterior third of the tongue, where the glosso-pharyngeal innervates the palate, with the middle and inferior parts of the pharjmx. These points being eliminated, it gives tactile sensibility not only to the skin, but also to all of the tissues of the head, comprising the glands, meninges, organs of sense, bone, and dental pulp. Eeflex Relations. — By reason of the ciliary filaments the trigem- inus is in particular reflex relation with the motor oeuli and sympa- thetic. Because of the ramifications of the trifacial branches in the mucous membrane of the nose there is established a very intimate relation with the expiratory muscles and nerves. Even the slightest touch may occasion a sudden and violent sneeze. A close relationship exists between this nerve and the muscles and nerves of deglutition. A remarkable fact in connection with the trigeminus is its great functional resistance to various poisons which are capable of paralyz- ing nerves of sensation. While all other regions of the body show the effects of anaesthetics, those under the dominion of the trigem- inus still preserve a high degree of sensibility. Even though a patient be anaesthetized with chloroform, yet will he perceive punctures in the temples and frontal regions. This occurs in spite of the fact that sensations are not perceived elsewhere. Motor Functions. — By its short root the trigeminus holds under its power the movements of elevation, depression, and rotation of the lower jaw. If this root be cut, it is found that the muscles concerned in the performance of the, above-mentioned movements are paralyzed. The lower jaw remains passively separated from the upper. Trophic Function. — Within twenty-four hours after intracranial section of the trigeminus, the cornea becomes opaque. At the end of five or six days the cornea becomes very white in color. The iris becomes inflamed and covered with false membranes. In about eight days the cornea becomes detached and the contents of the eye escape. The suppression of the fifth pair is followed by remarkable alterations in the Sehneiderian membrane. It becomes spongy and bleeds upon the least touch. The place where the olfactory bulbs lie is completely changed. Thus the acts of olfaction and vision are indirectly affected. Pathology. — -By reason of the intimate association of the tri- geminus, and its Gasserian ganglion, with the petrous portion of the temporal bone, it is exposed to all of the shocks and blows that are able to fracture this bone. 540 PHYSIOLOGY. The relations of the trigemimis with its meninges are very apt to he disturbed seriousty by the presence of tumors. The false mem- branes which are found in meningitis compress it and so produce atrophy. The exudates of tubercular meningitis very often produce antesthesia of the face. The fifth pair is most often the seat of either excessive sensibil- ity or paralysis. It is, perhaps, the one nerve which is the most frequently affected in neuralgia. The relative nearness of the tri- geminus to its sensory center probably explains the aeuteness of the pains in neuralgia. SEVENTH PAIR, FACIAL NERVE, OR PORTIO DURA. The facial nerve arises from a nucleus beneath the floor of the fourth ventricle. This nerve contains a motor and a sensory root. The sensory root comes from the cells of the geniculate ganglion, and is called the nerve of Wrisberg. The motor pontal nucleus gives off the neuraxons of the motor root. The motor nucleus is thought to be the upward part of the nucleus ambiguus, which originates the motor iibers in the vagus and glosso-pharyngeal nerves. The neuraxons of the motor nucleus form a distinct knee, which, uprising on the floor of the fourth ventricle, is known as the eminentia teres. The facial nerve in its course to the periphery makes a peculiar loop, or knee, inclosing the nucleus of the abducent, and emerges from a depression back of the pons between the olivary and restiform bodies, enters the internal auditory meatus with the auditory nerve, leaves the auditory nerve, enters the Fallopian canal, and makes its exit by the stylo- mastoid foramen to go. to the muscles of the face. The nerve of Wris- berg, or the sensory part of the facial, is made up of neuraxons from the cells of the geniculate ganglion seated in the Fallopian canal. The auditory nerve is also called portio mollis, and it lies to the outer side of the facial,-^the portio dura, — and between the two is the pars intermedia portio inter duram et moUem of Wrisberg, which extends from the medulla to Join the facial in the internal auditory meatus. It is connected with both auditory and facial nerves, be- tween which it lies. The central neuraxons of the geniculate gan- glion or the nerve of Wrisberg go to the fasciculus solitarius or the vagus and glosso-pharyngeal roots. The peripheral neuraxons of the geniculate ganglion join the facial, and Duval states that they go to form the nerve of taste : the chorda tympani. In the hiatus Fallopii the great petrosal nerve branches off from the facial. It, in conjunction with a filament from the glosso-pharyn- CRANIAL NER^'ES. 541 geal and another from the sympathetic, passes over to Join the gan- glion of Meckel. The small petrosal leaves the aqueduct by a particular opening to end in the otic ganglion. Chorda Tympani. — A few millimeters above the stylo-mastoid foramen the facial gives o£E a branch of very considerable size : the chorda tympani. It ascends into the cavity of the tympanum. It passes between the malleus and incus, giving a branch to the lat- ter, and then enters the zygomatic fossa. The chorda tympani then descends between the two pterygoid muscles to meet the nerve of taste. After communicating with the latter it accompanies it to the submaxillary gland. There it joins the submaxillary ganglion to terminate in the lingual nerve. Physiology. — While the trigeminus is responsible for the sensory actions of the face, the facial presides over the contraction of the facial muscles of expression. The facial nerve is purely motor, and so has nothing to do with the transmission of sensory impressions developed upon the face. After its section the skin still preserves all of its sensibility. On the other hand, after section of the trifacial it completely disappears. Though the facial does not transmit sensory impressions, yet in itself it is sensitive because of the branches which it receives from the trigeminus. If the nerve be pinched, the animal shows signs of pain. Pathologfy. — The facial is the motor nerve which suffers most easily from the influence of cold. Facial paralysis, or Bell's palsy, may occur very easily when draughts from a window blow upon the face. When the paralysis is unilateral, the face is drawn toward the sound side. The labial commissure on the paralyzed side is lower than the other, thus giving to the mouth an oblique direction. Bell's paralysis is usually due to a cold draught of air striking the nerve at its exit from the stylo-mastoid foramen. When the cause is seated in the brain the external rectus is usually affected, because its nerve is also involved and usually there is paralysis of the opposite half of the body, or crossed paralysis. Here the lesion is iu the pons. If the lesion is seated in the petrous portion of the tem- poral bone, there is not only facial palsy, but also loss of taste from an involvement of the chorda tympani. EIGHTH PAIR, OR AUDITORY NERVE. The anatomy and function of this nerve have been discussed in Chapter XVIII. 542 PHYSIOLOGY. NINTH PAIR, OR QLOSSO^PHARYNOEAL NERVE. The glosso-pharyngeal nerve is a nerve of both motion and sen- sation. The nucleus ambiguus gives off neuraxons_to form its motor root. The sensory neuraxons arise from the Jugular and petrosal ganglions and arborize about two sensory nuclei in the medulla ob- longata. The lower sensory end nucleus produces an elevation on the floor of the fourth ventricle, and is called the ala cinerea. The upper nucleus is also connected with sensory neuraxons of glosso- pharyngeal nerves, while the lower portion of this nucleus is in relation with the vagus. The second nucleus is called the vertical nucleus, the fasciculus solitarius, the combined descending root of the pneumogastrie and glosso-pharyngeal nerves, or the respiratory bundle. This respiratory tract extends from the olive down the spine to the eighth cervical nerve. This respiratory bundle of Gierke may associate the nuclei co-ordinating the various respiratory muscles. The glosso-pharyngeal nerve arises by a half-dozen cords from the restiform body and goes through the jugular foramen into the vagus, where it has a small ganglion : the jugular. As it emerges from the jugular foramen there is developed the petrosal ganglion, or ganglion of Anderseh. Nerve of Jacobson. — This same ganglion gives origin to the nerve of Jacobson. It enters the cavity of the tympanum by way of an opening in its floor, where it divides into three filaments. These are distributed: one to the round window, one to the oval window, the third to the lining membrane of the Eustachian tube and tympanum. Physiology. — The ninth is a mixed nerve. Its motor properties are distributed to the middle constrictors of the pharynx and the stylo-pharyngeus muscle. The most important sensory function of the glosso-pharyngeal is the part which it plays in the role of the sense of taste. The ninth nerve has an action upon the blood-vessels of the tongue identical with that of the chorda tympani. If the glosso- pharyngeal be cut and its peripheral end stimulated, the tongue becomes of a livid red. Pathology. — In man there are no clear cases recorded where there have been uncomplicated affections of the glosso-pharyngeal. TENTH PAIR, PNEUMOGASTRIC, OR VAQUS. Of all of the cranial nerves, the vagus is the most important and has the most functions of a varied nature in clinical study. It is a CRANIAL NERVES. 543 nerve of motion and sensation. The motor neuraxons arise from the nucleus ambiguus. The sensory roots come from the neuraxons of the jugular and petrosal ganglions. The sensory neuraxons have been described ujider the preceding nerve: the glosso-pharyngeal. The vagus springs by means of from ten to fifteen cords from the groove behind the olivary body and passes through the jugular fora- men with the glosso-pharyngeal and spinal accessory nerves. In the jugular foramen it has a ganglion: the jugular ganglion. After it emerges from the foramen it has an enlargement, the gangliform plexus, or ganglion nodosum. The plexus gives o£E the pharyngeal and superior laryngeal nerves. The pharyngeal nerves, three in number, go dovm the side of the pharynx to supply the mucous membrane and muscles of the pharynx. The superior laryngeal goes down the side of the larynx. This nerve also furnishes a collateral branch, important from a physiological standpoint, to the crico-thyroid muscle. It then loses itself in the mucous membrane of the larynx. At the base of the neck the vagus gives off another branch, the recurrentj or inferior laryngeal. The, nerve upon the right side de- scends in front of the subclavian artery and winds around it pos- teriorly from beneath. Upon the left side the nerve winds around the arch of the aorta in the same manner. As collateral branches, the vagus furnishes cardiac fibers, which form the cardiac plexus and are destined to innervate the heart. There are also oesophageal fibers whose terminations are distributed to the oesophagus and trachea. In the cervical region the tenth pair gives rise to a branch, the nervus depressor. It results by the fusion of two fibers: one from the superior laryngeal and the other from the vagus itself. The nervus depressor loses itself in the cardiac tissue of the heart at the level of the aortic and pulmonary orifices. During the first portion of its course the vagus forms numerous a-nastomoses. These are with the spinal accessory, the facial, and hypoglossal cranial nerves, and with a great number of branches from the various ganglia of the sjonpathetic system. In the thorax the vagus gives off cardiac and pulmonary branches. These also anastomose with the sympathetics to form numerous plexuses. The terminal tranches of the vagus are distributed to the stom- ach, to the solar plexus, and also to the hepatic plexus of the sympa- thetic. 544 PHYSIOLOGY. The most striking feature with regard to the vagus is the great number of its anastomoses. It is a very complex nerve and in no part of its course is it exclusively itself. Physiology. — The relationship existing between the vagus and spinal accessory nerves is a very intimate one by reason of their anastomoses. This makes the determination of the true nature of the vagus one of the difficult problems of physiology. It is certain that the vagus is endowed with sensibility, for the suppression of the spinal accessory does not deprive the parts of any sensibility in any portion of their common distribution. But, as the spinal accessory is motor and the vagus sensory, it does not neces- sarily follow that the latter nerve is exclusively sensory and that all movements realized by association should be the special work of the spinal accessory. It was Bernard who first demonstrated that the vagus in itself is a mixed nerve. After he had torn out all of the root- fibers of the spinal accessory in animals he found that the motor acts of the larynx persisted in the phenomena of respiration. How- ever, while the vagus in itself is a mixed nerve and has a certain amount of motor functions, yet its principal role is of a sensory nature. The mode of distribution of the vagus indicates that the nerve exercises some action upon (1) the digestive apparatus ^ (2) the respira- tory apparatus, (3) the circulation^ (4) the hepatic apparatus, and (5) an indirect action upon the kidneys and suprarenal glands. Pathology. — The recurrent is more liable to be pressed upon by reason of its peculiar course and its direct relations with the great vessels and body of the thyroid. As the vagus is a mixed nerve, it is very evident that compression causes troubles in motion and sensi- bility, either isolated or conjointly. Any lesions located at the origin of the vagus cause phenomena of irritation in the whole sphere of distribution of this nerve. Re- flexly the vagus is capable of afffecting the chorda tympani and in- creasing the flow of saliva. It is for this reason that intestinal parasites often cause ptyalism. The sensibility of the branches of the vagus in the stomach re- mains unconscious during the normal physiological state, when it does not seem to be any greater than that of the sympathetic. Dur- ing pathological conditions, however, it acquires a high degree of intensity. Thus, in simple wounds of the stomach, without haemor- rhage or peritonitis, the impression carried to the medullary center may be of such a nature as to cause rapid death. CRANIAL NERVES. 545 The great frequency of gastralgia is due to an affection of the terminal branches of the tenth pair. At its cranial end this same nerve is found to be in direct relation with the trigeminus through the intervention of the gray tubercle of Eolando. This fact un- doubtedly furnishes the key to the headache which so often accom- panies gastralgia. The vagus is the chief sensory carrier of the reflex movements of circulation and respiration. Thus, irritation of the renal and hepatic plexuses can produce vomiting. Angina pectoris has its seat in the cardiac plexus. The sensation experienced is like that seen in the renal and hepatic plexuses after renal and hepatic colic. ELEVENTH PAIR, OR SPINAL ACCESSORY NERVE. The eleventh pair of cranial nerves, the spinal accessory, is com- posed of two distinct parts : a spinal portion and an accessory portion. A group of cells in the anterior horns of the spinal cord and extend- ing downward to the sixth cervical segment is called the accessory nucleus. There is another group of cells at the exit of the first cervical nerve which extends into the medulla oblongata and is the origin of the hypoglossal nerve. The medulla-oblongata root arises from the nucleus ambiguus, which is connected vnth the vagus nucleus in the medulla. The superficial origin of the accessory portion is from the groove between the inferior olive and the restiform body. Fear the Jugular foramen both portions come together, but do not exchange fi.bers. Very soon both roots separate from one another to form the two distinct branches. The accessory portion of the nerve passes entirely into the plexus gangliformis of the vagus. This branch supplies the vagus with the major portion of its motor fibers and also with its cardio-inhibitory fibers. The spinal portion enters the cavity of the cranium by passing through the foramen magnum. The two portions of the spinal accessory leave the cranium together by passing through the middle compartment of the jugular foramen. The spinal portion then pierces the sterno-mastoid to supply it and the trapezius. This por- tion of the nerve communicates with several cervical nerves. Physiology. — The eleventh nerve is generally considered to be motor. Any observable sensibility must be due to anastomosis with^ the cervical nerves. 546 PHYSIOLOGY. From experimentation it has been found that the accessory branch presides, through branches in the vagus, over the formation of sound and its tone. The spinal branch is concerned in the duration, in- tensity, and modulation of the vocal sound. Hence it regulates the rhythm of speech and song. Aphonia is often due to hysteria, but may be due to lead poisoning, syphilis, or to such reflex causes as intestinal worms. The reflex that is established between the vocal and genital organs is also shown by troubles in the spinal branch of the spinal accessory. The voice may be lost at times during menstruation. TWELFTH PAIR, OR HYPOGLOSSAL NERVE. The nuclei of the hypoglossal nerve are under the floor of the fourth ventricle, on each side of the raphe. Beneath the main nucleus of the hypoglossal nerve is a collection of cells in the formatio reticularis called the hypoglossal nucleus of EoUer. ' Anastomoses. — The connections of the hypoglossal are : 1. With the superior cervical ganglion of the sympathetic, which supplies vasomotor fibers to the vessels of the tongue. 3. The plexus gangli- formis vagi gives a small lingual branch which supplies the tongue with sensory fibers. 3. The hypoglossal is also connected with the upper cervical nerves. Physiology. — The hypoglossus, by itself, is purely motor. It moves the muscles of the tongue. When its original filaments are torn out there is never any pain. Sensibility of its terminal branches is due to anastomoses with the lingual. When the hypoglossus is cut, the tongue remains quiescent in the mouth. In unilateral paralysis of the hypoglossus the tongue, when pro- truded, passes over to the paralyzed side. This phenomenon is occa- sioned by the action of the genio-hyoglossus of the sound side. LiTEKATTJEE COJSTSTJLTED. Gordinier, "Nervous System." CHAPTER XXI. REPRODUCTION. Eephoduction, with the aim to maintain the species, is one of Nature's foremost laws. On every side of us does biology demon- strate this to the student. It is foremost in all the varying stages of both animal and vegetable life: from the lowest organisms to the highest. Among the amoebae and other forms of lower life are their own definite laws of reproduction adhered to and carried out as per- fectly as among the highest order of the vertebrata. THE LOWER ORDERS. Among the lower orders of creation there is not present that great complexity and amount of detail seen in the reproduction of the higher orders. The individuals of -the lowest orders, whether plant or animal, seem to possess in their every part and component the general plan of that particular species of plant or animal. And, furthermore, each part and component is capable of building up for itself a perfect plant or animal. It is not necessary for its propaga- tion that there be specialized cells present, or that it be aided by other and perfect individiials of its own species. It has long been known that, should a portion of a hydra be separated from the living animal, it wiU develop into a complete hydra. The agriculturist makes use of the fact that from a cutting, branch, tuber, or even a leaf of a plant there may spring a perfect plant of the exact species from which the parts were taken. Among the lowest organisms there is no need for sex or special- ized cells by whose union there emanates an entirely new individual. There are present in every part, and, in fact, within the cells of every part, those inherent principles which are the essentials for the proper reproduction of the individual. AMONG HIGHER ANIMALS. Among the higher animals the plan of the entire organism is not latent in each and every portion of its economy. Any portion that is severed from the individual promptly dies, unless it be properly nourished and cared for. Among these higher spheres of life sex (547) 548 PHYSIOLOGY. is a most important factor in reproduction. The two sexes are sepa- rate. In order that a new being be brought into existence, it becomes necessary that specialized cells of the male be brought into conjunc- tion with specialized cells of the female: that is, fecundation, or impregnation, must occur. Fractional Reproduction. By the term " reproduction " is generally conveyed the idea that there is propagation of the species by the formation of an entirely new individual. However, the fact must not be lost sight of that, among the higher orders, there occurs a reproduction, to a certain limited extent, of the various components of the organism: a frac- tional reproduction, so to speak. Prom the incessant wear and tear incident to almost constant usage, the various components of the economy are losing many of their cells by death. These dead cells, no longer able properly to functionate, find egress from the body. To maintain a normal and ' Tvell-balaneed body it is necessary that the wasted, ejected cells be renewed. Hence, during the natural cycle of the animal's life there is constantly occurring a partial, or fractional^ reproduction of the economy's organs. When the tissues of any organ are not too highly specialized this reproduction is very evident, as new skin covering an ulcerous area by means of granulation tissue. On the other hand, nerve-cells, which are representatives of the highest type of spe- cialized tissue, are not believed to be reproduced. Lesions among these cells are healed by granulation and cicatricial tissue. Among some animals this partial reproduction is more marked than in men and other high types of animal life. It is said that in the hydra an amputated part is replaced, not by cicatricial tissue, but by the regular specialized tissues as they occur in the animal. Fecundation. As just stated, it is necessary that the male elements enter into conjunction with the female element before fecundation takes place among the higher animals. The male specialized element is the spermatozoon; the female, the ovum. Both of these sexual cells are the results or products of a series of changes which have taken place in certain epithelial cells. Spermatozoon. — That portion of the seminal fluid which comes from the testis contains myriads of microscopical cells : the sperma- tozoa. These little bodies, or sexual cells, are derivatives of the walls REHRODUCTION. 549 of the seminiferous tubuies. The tubules are lined with low-euboidal cells which become broken up so as to form spermatdblasts. Each spermatoblast by further metamorphosis becomes a spermatozoon. ' Structure. — The spermatozoa of various animals present diiler- ences as to shape and size. The human spermatozoon is an elongated, ciliarylike body. It is about one-fiTe-hundredth of an inch long and presents three portions : headj middle piece, arid tail. The head is the most prominent portion of the body and repre- sents the nucleus of the spermatozoon. It is the essential portion of the spermatozoon as regards sexual function. ' Fig. 136. — Human Spermatozoa. (Maxtou.) The tail is a slender, albuminous filament whose chief function seems to be to propel the cell in its search for the female element: the ovum. Ovum. — The ovum is a small, sphenoidal body lodged in a Graaf- ian follicle within the ovary of the female. It is the female sexual cell. In size the human ovum measures about one one-hundred-and- twentieth of an inch in diameter. Not only the human ovum, but ova of other animals are remarkable in that they are larger than any other cell within the body of the female. The ovum is a typical cell, containing cell-wall, cell-contents, nucleus, and nucleolus. Like other cells, it undergoes division and produces cells which iiltimately form the various tissues of the future. 550 PHYSIOLOGY. but not before the ovum has been fertilized by union with the sper- matozoon. The ovum is the final product of a series of metamorphic changes occurring in cells -which have been derived from the germinal epithe- lium of the ovary. Each ovum develops within its own compartment, a Graafian follicle; as the ovum nears completion the follicle moves to the surface of the ovary. The fluid contained within, the follicle then gradually thins its own wall as well as the germinal epithelium of the ovary until there occurs a rupture of the sac. The ovum, with the escape of the fluid, also passes out upon the surface of the ovary. During sexual excitement the fimbriated end of the Fallopian tube grasps the ovary, and the ovum is conducted to the tube by the Mg. 137.— Ovum of Rabbit. (Manton.) fimbria ovarica, and is then carried through the tube down into the uterus by the instrumentality of the ciliated epithelium lining the tube. This escape of the ovum from its Graafian follicle is known by the term ovulation. Should the ovum not be impregnated, it dies and passes out of the uterus as a constituent of its secretions. On the other hand, should it become fecundated, the ovum becomes at- tached to the mucous membrane of the uterus, usually occupjing the bottom of some little cleft or pouch. The investigations of Peters, of Vienna, and of Webster, of Chicago, show that the uterine mucosa does not fold up around the ovum, but that the mucosa at the site of implantation is eroded; so that the ovum eats its way, as it were, into the mucosa, sinidng into its depths until the edge of the swollen mucosa closes over it, thus . forming the deeidua reflexa. REPRODUCTION. 551 Matueation. — Before the ovum leaves its follicle and before it is possible for it to be impregnated, the ovum must pass through the process of maturation, or ripening. In short, the process is the expul- sion of a portion of the nucleus and protoplasm of the ovum. The nucleus then undergoes changes which seem to be the same as those occurring during ordinary karyokinesis. The significance of matura- tion is believed by some observers to be to furnish room in the ovum for the entrance of the male pronucleus, which is to occupy the place of the portion lost. Menstruation. — In the adult female during certain age-limits there occurs a discharge from the genitalia once about every twenty- eight days. This periodical discharge consists of blood, dead and disintegrated epithelium from the uterus, and mucus from the glands of the uterus. With the discharge of the above-named materials there is usually expelled at the same time one or more ova from their follicles. How- ever, ovulation and menstruation may be and very often are inde- pendent of one another. The onset of menstruation is usually her- alded and then accompanied by certain constitutional signs of fullness and pain in the pelvic region. There is a real congestion of all of the pelvic organs; in particular the uterine mucous membrane is swollen and congested. Prom it are derived the blood and epithelium of the menstrual flux. By some authorities it is claimed that the entire uterine mucous membrane is exfoliated at every flux, to be regenerated in the interim. It has been found by observers that congestion of the ovary coincident with sexual intercourse is capable of rupturing Graafian follicles and so liberating ova. From this it is reasonable to suppose that the congestion and high tension of the generative organs during the time of menstruation would surely accomplish the same end. The usual period of a female's life during which she menstruates is from puberty (from the thirteenth to the fifteenth year) to the climacteric, or menopause (about the forty-fifth year.) Its cessation at the latter period denotes the end of the childbearing period. Fertilization. — This is the proper union of the male and female sexual cells after the ovum has been previously matured, or ripened. The act is consummated when the head of the spermatozoon (now known as the male pronucleus) becomes permanently fused with the remnant of the nucleus of the ovum (the female pronucleus). Segmentation. — The unimpregnated ovum soon perishes; not so with one that is fertilized. The latter immediately begins to show 553 PHYSIOLOGY. karyokinetie changes, segmentation following segmentation until the ovum has become a mass of cells : the morula. These are the prim- itive cells from which all of the tissues of the future embryo are formed. They are known as Uastomeres. During segmentation the ovum is enlarging by the absorption of fluid into its interior and the formation of a cleavage-cavity in the center of the morula. From pressure upon one another the cells become polyhedral in shape and are so arranged as to form a cellular envelope just inside of the vitelline membrane, — the blastoderm, — and a central mass of cells projecting from the wall into the cleavage- cavity. The cells forming the wall of the cleavage-cavity, known as the outer cell-mass, thin out and are known as the cells of Eauber; they subsequently disappear, while the cells of the inner cell-mass, which later projects into the cleavage-cavity, become rearranged in a man- ner at present inexplicable, to form two layers: the entoderm and the ectoderm, respectively. The outer layer is known as the ectoderm, or epiblastj the inner, as the entoderm, or hypoblast. Embryonal Area. — At the beginning of the stage of gastrulation there appears upon the delicate vitelline membrane a round, whitish spot. It is the emibryonal area, or shield. The area becomes oval and then pear-shaped. At the narrow end there appears an elongated narrow thickening: the primitive streak. Later the streak develops a furrow : the primitive groove. At the same time there appears in the region of the front end of the primitive streak several layers of new cells. As they occupy a position between the ectoderm and entoderm, they have been desig- nated the mesoderm. While the mesoderm is pushing its way over the germinal area and into the blastoderm, the, epiblast in front of the primitive streak rises up so as to form two lateral ridges. These inclose within them the medullary groove. Very soon the edges of these two ridges begin to curl up, to produce the medullary canal by their final union. The canal is the foundation of the entire adult nervous system. Beneath and parallel with the canal is found the notochord, the forerunner of the spinal column. The brain and spinal cord are gradually evolved from the medullary canal by reason of the specialization of some of the cells constituting the walls of the canal. The mesoderm takes its origin from a double source; most of its cells come from the entoderm, but yet some are derived from the ectoderm. REPRODUCTION. 553 After its formation the mesoderm grows by reason of its own cell-proliferation, and is independent of its dual source. Along either side of the median line the mesoderm presents a thickening of cells (vertebral plate), which becomes laminated laterally (lateral plate). From the vertebral plate develop the somites; the lateral plate splits into two lamellae, of which the outer is the somatic mesoderm; the inner, the splanchnic mesoderm. The former unites with the ectoderm to form the somatopleure, while the latter unites with the entoderm to form the splanchnopleure. Between the somatopleure and the splanchnopleure there is an opening, the body-cavity, from which arise the serous cavities of the adult. Derivatives from the Layers. Epiblast. — ^From the epiblast are developed the central nervous system and the epidermal tissues. Mesoblast. — From the mesoblast arise most of the organs of the body. These include the vascular, muscular, and skeletal systems; also the generative and excretory organs; but not the bladder, the first part of the male urethra, nor the female urethra. Hypoblast. — The hypoblast is the secretory layer. From it spring the intestinal epithelium and that of the glands which open into the intestines; also the epithelium of the respiratory system, the bladder, the prostatic part of the male urethra, and the entire female urethra. Up to this point the cavity of the germ is one undivided compart- ment bounded by splanchnopleure. By infolding of the splanchno- pleure this cavity is divided into two smaller compartments of unequal size. The smaller one is the gut-tract; the larger, the yelk-sac, or umbilical vesicle. The communication between the two cavities is the vitelline duct. With the unfolding of the splanchnopleure the somatopleure also follows to form the body-walls of the embryo. Part of the somatopleure becomes so lifted Up as eventually to curl up and over the embryo until the fold of one side fuses with that of the other. That is, there is formed the amniotic membrane and cavity. The amnion is a membranous sac consisting of two layers of embryonal cells. The inner layer is composed of ectodermic cells, the outer layer of mesodermic cells. The false amnion, or serosa, comprises all that part of the somatopleure which does not go to form the body- wall and the true amnion. It is also called the primitive chorion and by some authors the chorion. The allantois growing forth from the 554 PHYSIOLOGY. gut-tract unites with its ianer surface and thus gives it vascularity. It is the outermost envelope of the germ. The amniotic sac is filled with a fluid in which floats the foetus. The function of the yelk-sac is to furnish nutrition to the embryo for a certain length of time, but is very rudimentary in man. As the yelk-sac disappears by degrees, its place is taken by the allantois. The latter then serves as a medium of nutrition and respiration until the formation of the placenta at the end of the third month. Chorion. — The chorion is the membrane which envelops the ovum subsequent to the appearance of the amnion. It results from the fusion of the allantois and false amnion. Upon the surface of the chorion are numerous villi. At first they are uniform in size, but at the latter half of the first month there de- velops an area the villi of which are noted for their long prolonga- tions : the chorion frondosum. This eventually becomes, a portion of the placenta. The remaining villi atrophy and finally disappear. Placenta, — The placenta is the nutritive-, excretory, and respir- atory organ of the fcetus from the third month to the end of preg- nancy. It is discoid in shape, one side being attached to the uterine wall, the other becoming attenuated, to end in the umbilical cord, which is the medium of exchange between the placenta and the foetus. The villi of the chorion f rondosimi dip down into the mucous membrane of the uterus, to push against the walls' of the large vessels found there and whose structure is similar to that of capillaries. The cells comprising the villi act as an osmotic membrane through which osmosis occurs. By this means oxygen and nutritive lyinph pass from the mother's blood to that of the foetus. On the other hand, the foetal blood gives off carbon dioxide and probably urea. There is no intermingling of the two blood-currents, since there is always a layer of epithelium to act as a limiting membrane. Foetal Circulation. — The blood is brought to the body of the foetus by the umbilical vein. Some of this oxygenated blood passes through the liver to the hepatic veins, to be emptied into the inferior vena cava. The remainder of the umbilical blood passes into the inferior vena cava through the ductus venosus. The blood, mixed with that which is returned from the lower extremities, enters the right auricle. Guided by the Eustachian valve, it passes over into the left auricle through the foramen ovale. The blood now courses through the left ventricle, aorta, the hypogas- tric and umbilical arteries to the placenta. REPRODUCTION. 555 The blood is returned from the head and the upper extremities to the right auricle by the superior vena cava. This stream of blood passes through the auricle and aurieulo-ventricular opening directly into the right ventricle, guided by the tubercle of Lower. The blood next passes into the pulmonary artery. Some of it (enough to nour- ish the solid lung-substance) passes to the lungs, but the major por- tion passes into the aorta through the ductus arteriosus. When in the aorta it takes the course of the blood from the left ventricle to finally reach the placenta. The blood to the lungs returns to the left auricle through the pulmonary veins. After hirth the umbilical arteries are obliterated with the excep- tion of their lower portions, which remain as the superior vesical arteries. The umbilical vein becomes obliterated and remains as the round ligament of the liver. Thfe umbilicals become impervious soon after cessation of the placental circulation. The foramen ovale closes, thereby cutting off communication between the right and left hearts. By the second or third day the ductus arteriosus has also become obliterated, to be present in adult life as the ligamentum arteriosum. These changes in the circulatory apparatus are dependent upon the establishment of pulmonary respiration at birth. The first in- spiration is said to be due to a sensory reflex from the colder air striking the sensory skin filaments of the chest and abdomen. ACter the cord is tied there soon follows an increase of COj in the blood. By its presence the activities of the respiratory center of the medulla are instigated. However, the various centers are but feebly irritable at birth and require somewhat heroic stimulation to bring out their activities. This feebleness accounts for the remarkable vitality of the infant and its intense resistance to asphyxiation. Literature Consulted. Heisler's "Embryology." INDEX. Absorption, 102, 103 by skin and lungs, 122 in large intestine, 104 in small intestine, 103 in stomacli, 102 of carbohydrates, 106 of proteids, 106 of salts, 106 of water, 106 rapidity of, 114 Acetic fermentation, 100 Achromatic nuclear substance, 12 Action of brain extract, 474 Adipocere, 373 Adrenalin, 93 Afferent impulses, 466, 467 Air, 273 complemental, 255 -passages, 241 quantity of, breathed, 253 reserved, 255 residual, 255 tidal, 254 Albuminates, 32 Albuminoids, 34 Albumins, 32 Alcohol, 40 Alcoholic fermentation, 100 Alimentary canal, 43 substances, 24, 34 Amoeba, 14 movements of, 15 Amylopsin, 80 Amyloses, 27 Animal heat, 338, 339 estimation of, 344 extremes of temperature, 343 postmortem temperature, rise of, 357 Animals, 341 cold-blooded, 341 temperature of, 341 warm-blooded, 341 Anosmia, 495 Anterior pyramids, 422 Antipyrin, 356 Aphonia, 392 Apnraa, 261 Aqueduct of Sylvius, 433 Aqueous humor, 515 Arcuate fibers, 427 Arginin, 83 Arterial blood, 127 Arteries, 196 elasticity of, 203 rate of movement of blood in, 222 structure of, 197 Artery of cerebral haemorrhage, 443 Artificial respiration, 264 Asphyxia, 261 effect on circulation, 263 . Auditory nerve, 504 Auditory striae, 423 Auricles of heart, 171 Avogadro-Van't Hoff law. 111 Bacteeial digestion, 99 Beckman's differential thermometer. 111 Beef-tea, 35 Beer, 40 Bell's palsy, 541 Betatetrahydronaphthylamin, 349 Bile, 88 acids of, 89 action of drugs on, 97 cholesterin, 91 composition of, 88 mucin, 88 pigments, 90 salts, 88 test for, Gmelln's, 90 Hay's, 89 Pettenkofer's, 90 uses of, 92 Biology, 2 Bladder, 326, 299 Blood, 124, 142 arterial, 127 cause of movement, 212 color of, 125 composition of, 127 plates of, 138 quantity of, 126 reaction of, 125 specific gravity of, 125 temperature of, 344 estimation of, 344 venous, 127 Blood-corpuscles, 128 chemistry of, 141, 142 count of, 131, 132 destruction of, 141 experiment upon, 133 formation of red, 139 life-cycle of, 130 parasites of, 129 Blood-gases, 271 Blood-pressure, 212, 213 effect of vagus on, 220 extremes of, 219 in man, 21S measurement of, 216, 217 respiratory wave. 220 cause of, 220 Traube-Hering curve of, 220 variations of, 213, 214 Boyle-Van't Hoff law. 111 Brain, 435 aqueduct of Sylvius, 433 artery of haemorrhage, 443 blood-supply of, 442 claustrum, 439 corpora quadrigemina, 440 corpora striata, 439 ■external form, 435 fissures, 435, 436 ganglia of, 438. 439 internal capsule, 440 optic thalamus, 438 structure of convolutions, 436, 437, 438 tract, cortico-pontal-cerebellar, 441 motor, 441 sensory, 442 (557) 558 INDEX. Bread, 40 Bread-juice, 64 Bromelin, 63 . Bronclii, 241 Buffy coat, 156 Bulbar nerves, 459 Butter, 38 Buttermilk, 33 Butyric fermentation, 100 Cachexia strumipriva, 287 CaHeine, 41 Caisson paralysis, 275 Calamus scriptorius, 423 Calorie, 345 Calorimeter, 346, 347 Capillaries, 199 Capillary circulation, 209, 210, 211 blood-pressure ol, 221 swiftness of, 212 Carbohydrates, 27, 35 Carbon monoxide, 145 Carbonic acid, 318 Cardiac impulse, 175 Cardiac pathology, 175 Cardiac revolution, 173 Cardiograms, 177 Cardiographs, 176 Caseinogen, 37 Cell, 1 achromatic nuclear substance, 12 constituent of, 10 definition of, 7 fatigue of, 23 nuclear sap, 12 nucleolus, 12 nucleus, 12 vegetable, 6 Cell-division, 16 direct, 19 indirect, 20 Cement, 48 Center of smell, 495 Centrosome, 13 Cereals, 39 Cerebellum, 461 afferent impulses, 466, 467 corpus dentatum, 462 cortex, structure of, 464 efferent impulses, 467 function of, 465 internal structure, 462 nuclei of, 463 peduncles, 464 Purkinje cells, 464 section of, 467 spinal-cord connections, 465 surface form, 462 Cerebral cortex, 437, 470 ablation of, 472, 473, 474 action of brain extract on, 474 motor centers in, 470, 472 sensory centers of, 470, 472 Cerebral peduncles, 431, 468 crusta, 432 locus niger, 432 tegmentum, 432 texture of, 431 Cheyne- Stokes respiration, 266 Chlorides, 318 Cholesterin, 91 Chorda tympani, 541 Chorion, 554 Chromatic aberration, 519 Chromatic nuclear substance, 12 Chyle, 118 Ciliary movement, 15 Circulation, 163, 164 course of, 172 in brain, 226 system of, 165 Circulation of blood, 199, 200, 201, 202 duration of, 224 rapidity of, 221 Claustrum, 439 Coagulation of blood, 153, 154, 155 condition affecting, 157 rapidity of, 156 Cocoa, 41 Coffee, 41 Cpffeon, 41 Cold-blooded animals, 341 Colloids, 111 Colon bacillus, 99 Color-vision, 523, 524 Colostrum, 38, 291 Complemental air, 255 Complementary colors, 525 Compressed air of caisson, 274 Conjugate deviation, 636, 537 Conjugated sulphates, 97 Coronary arteries, 182 Corpora quadrigemina, 440, 468 Corpora striata, 439 Corpus dentatum, 462 Corpus striatum, 356, 469 Cortico-pontal-c%rebellar tract, 441 Coughing, 266 Cranial nerves, 530 decussations of, 532 origin of, 530, 531 Creatinin, 315 Cresol, 99 Cretinism, 281 Cruciate centers, 351 Crusta, 432 Cryoscopy, 111 Crystalline lens, 515 Crystalloids, 113 Daltonism, 525 Defecation, 101, 102 Deglutition, 50, 51 of fluids, '52 of solids, 51 Dendrons, 400 Development, 337 Diabetes, 95 * Diabetic puncture, 96 Diapedesis, 137 Diet, 336 Digestion, 42 Dioptrics, 518 Diplopia, 634 Dubois-Reymond induction coil, 394 Dynamometer, 383 Eab, 496 Eggs, 36 Electrolytes, 109 Electro-physiology, 394 Dubois-Reymond induction coil, 394 electrical phenomena of contracting muscle, 396 negative variation of nerve-current, 396, 397 nerve-muscle preparation, 394 physiological rheoscope, 394 Electrotonus, 448 Embryonal area, 652 Emulsiflcation, 30 Enamel, 48 Endocardiac pressure, 127 Enterokinase, 98 Entoptic phenomena, 522 Enzymes, 107 classification, 107 Epiblast, 553 Erepsin, 98 Eustachian tube, 505 Expiration, 250, 252 INDEX. 559 Facial nerve, 540 Bell's palsy, 541 cborda tympani, 641 pathology of, 541 pbyslology of, 541 Faeces, 100 amount of, 100 color of, 101 composition of, 100, 101 Fats, 29, 50 Fauces, 46 Feohner's law, 479 Fecundation, 548 Fehling's test, 322 Ferment, 55 definition of, 55 Fermentation, 99 acetic, 100 alcoholic, 100 butyric, 100 lactic, 100 oxalic, 100 Fermentation test, 323 Fertilization, 551 Fever, 354 Fibrin, 154 Fibrin-ferment, 156 Fillets, 434 Filtration, 113 Flesh-juice, 64 Fcetal circulation, 565 Foods, 330 caloric value of, 337 Fourth ventricle, 432, 433 Fractional reproduction, 548 Preezina-point, 112 Function of eye, 518 Gall-bladder, 83 Ganglia of heart, 185 Gastric digestion, 67 Gastric juice, 60 action of, 67, 68 composition, 61 flow of, 64 secretion of, 61 Gay-Lussac-Van't Hoff law. 111 Glands of the intestine, 73 Globulins, 33 Glomerules of kidney, 340 Glosso-pharyngeal, 642 nerve of Jacobson, 542 pathology of, 542 physiology of, 642 Glucoses, 27 Glycocholic acid, 89 Glycogen, 373 Gmelin's test for bile, 90 Growth, 337 Guaiac test, 160 Giinsberg's test for hydrochloric acid, 75 H;ematocrit, 132 Haematoporpbyrin, 145 Haemin, 144 Haemoglobin, 143 amount of, 149 Haemometer, 150 Haemorrhage, 157 Hair. 485 Hay's test for bile, 89 Hearing, 496 anatomy, 496, 497, 498, 499 auditory nerve, 504 - binaural audition, 508 ear, 496 Eustachian tube, 505 organ of Corti, 602, 603, 504 semicircular canals, 600, 601 theory of hearing, 507 Heart, 165 areas of audibility, 181 auricles, 171 cause of sounds, 179, 180 effects of drugs on, 195 frequency, 183, 184 ganglia of, 185 innervation of, 185 movements of, 175 nerves of, 189, 190, 192, 193, 194 nutrition of, 196 persistence of movements, 178 position of valves, 181 rhythm of, 186 sounds of, 178, 179 stimuli of, 196 structure of, 166, 167, 168, 170 valves of, 169 ventricles of, 171 work of, 184 Heat unit, 345 calorie, 345 calorimeter, 346, 347 Heller's nitric-acid test, 321 Hibernation, 342 Hippuric acid, 314 Hoarseness, 393 Hyaloplasm, 9 Hydrochloric acid, 69, 70 test for (Gtinsberg), 76 Hypermetropia, 521 Hyperosmia, 495 Hypoblast, 653 Hypoglossal, 546 physiology of, 546 INDICAN, 316 Indol, 99 Inspiration, 246, 247, 248, 262 Intermittent aSlux apparatus, 203 Internal capsule, 440 Intestinal digestion, 72 Intestine, 43, 72 glands of, 73 large, 99 movements of, 75 nerve-supply of, 76 structure of, 74, 75 Invertin, 99 Ions, 109 Iron, 335 Irradiation, 526 Isotonic solution, 133 Jaundice, 97 Karyokinesis, 20 stages of, 22 Kephyr, 38 Kidney, 299 blood-vessels of, 306, 306, 307 capillaries of, 308 glomerules of, 340 lymphatics of, 305 Malpighian corpuscles of, 305 position of, 299, 300 structure of, 301, 302, 303 urinary tubules of, 304 Krause's end-bulbs, 481, 482 Kumyss, 38 Kymograph, 217 Lacrymal secretion, 628 Lacteals, 103, 104, 117 Lactic acid, 70, 314 test for (Uftelmann's), 70 Lactic-acid bacillus, 37 Lactic fermentation, 100 Lactose, 37 Large intestine, 99 Laryngoscopy, 389 560 INDEX. Larynx, 385 condition ot, 390 muscles of, 387 nerves of, 389 vocal cords, 387, 3S9 Lateral columns, 426 Laughing, 266 Law of Fechner, 479 Laws of sensation, 479 Lecithin, 91, 406 Lenses, 522 Leucin, 83 Liver, 84 antitoxic function ot, 93 function of, 87 gall-bladder, 86 internal secretion of, 94 structure of, 84 Locus niger, 101, 432 Lungs, 242 Lymph, 118 composition of, 119 formation of, 121 quantity of, 121 Lymphatic system, 114 Lymphatic vessels, 115 origin of, 117 structure of, 115 Mammary glands, 291 effects on circulation of dried, 292 Marey's tympanum, 252 Mastication, 50 Matzoon, 38 Meat, 35 Meconium, 101 Medico-legal tests for blood, 161 Medulla oblongata, 421 anterior pyramids, 422 arcuate fibers, 427 auditory, 423 bulbar nerves, 459 calamus scriptorius, 423 centers in, 459, 460, 461 external form of, 422 fillets, 434 fourth ventricle, 432, 433 internal structure of, 424 lateral columns, 426 olives, 422, 427 posterior columns, 426 restiform body, 422, 423 white columns, 425 white substance, 424 Menstruation, 651 Mesoblast, 553 Metabolism, 328, 332, 333 anabolic process, 329 balance of, 331 catabolic process, 329 effect of starvation on, 332 effect of work on, 333 of carbohydrates, 334 of fats, 333 of salts, 334 of water, 334 Methsemoglobin, 145 Micturition, 327 Milk, 36, 292 clotting ot, 37 colostrum ot, 292 fats ot, 38 functional variations of, 293 matzoon, 38 quantity secreted, 39 specific gravity of, 37 theory of Ottolenghi, 292 Milk-juice, 64 Morphology, 64 Motor centers, 471, 472 Motor tract, 441 Mouth, 43, 48 Mucin, 88 Muscle-X!urve, 376 effect of stimuli, 379 summation of, 380 tetanus curve, 380 Muscles, 358 appearance under polarized light, 365 blood-vessels of, 366 cardiac, 367 chemistry of, 371 contractility of, 369 elasticity of, 382 fibers of, 360 infiuence of blood on, 370 irritability of, 369 nerve-supply ot, 366 nervous stimuli of, 371 chemical, 371 electrical, 371 mechanical, 371 thermal, 371 reaction ot, 372 rigor mortis, 375 sound ot, 381 structure of, 360, 361, 362, 364 unstriped, 367 • varieties of, 359 work ot, 382 Myograph, 375 Myopia, 521 Myxoedema, 281 Nails, 487 Nerve, 443 electrotonus, 448 excitability, 443 v excitability and conductivity, 447 excitants, 447 chemical, 449 electrical, 448 mechanical, 449 irritability, 444 of Jacobson, 542 Pfluger's contraction laws, 448 \ transmission of nerve-wave, 445, 446 Nerve-cell, 398 dendrons, 400 neurite, 400 Nissl granules of, 400 nucleus of, 400 structure of, 399 Nerve-fibers, 401 medullated, 402 myelin of, 402 neurilemma of, 402 nodes ot Ranvier, 403 nonmedullated, 402 terminations of, 403 Nerve-muscle preparation, 394 Nerves of deglutition, 53 of heart, 189, 190, 192, 193, 194 ot intestine, 76 ot larynx, 385 ot respiration, 245, 257 ot salivary glands, 66 ot sweat-glands, 293 ot taste, 489 of tongue, 46 ot vasomotor system, 228 Nervous system, 398 anatomy of, 398 chemistry of, 405 lecithin, 406 metabolism ot, 407 neuroglia, 404 Neurites, 400 Nodes of Ranvier, 403 Nuclear sap, 12 Nuclei of cerebellum, 463 Nucleolus, 12 I INDEX. 561 Nucleus, 12 Obesity, 337 Oculomotor, 532 diplopia, 534 effect of drugs on, 635 function of, 533 pathology of, 534 CBsophaguB, 43, 50 Olein, 30 Olfactory organ, 493 Olfactory sensation, 493 Olives, 422, 427 Ophthalmoscope, 628 Optic nerve, 516 thalamus, 438, 469 Organ of Corti, 502, 503, 504 of taste, 489, 490 of voice, 385 Osmosis, 109 Osmotic pressure, 110 Ovum, 649 maturation of, 551 Oxalic acid, 314 fermentation, 100 Oxybutyric acid, 97 Oxyntic glands, 62 Palate, 45 Falmitin, 29 Pancreas, 76 removal of, 82 secretion of, 77, 78 secretory nerves of, 79 structure of, 76 Pancreatic juice, 79 composition of, 79 ferments of, 80 quantity of, 80 reaction of, 78 specific gravity of, 78 Papain, 63 Papilla of tongue, 46 Path of motion, 466 Path of sensation, 466 Pathetic nerve, 535 function of, 635 pathology of, 636 Pawlow's stomach, 66 Peduncles, 464 Pepsin, 63 Pepsinogen, 62 Peptone, 33, 69 Perimeter, 529 Peristalsis, 76 pendular movement, 76 Pettenkofer's test for bile, 90 Pfliiger's contraction laws, 448 Pharynx, 43, 49 Phenol, 99 Phenylhydrazin test, 322 Phloridzln, 96 Phosphenes, 526 Phosphoric acid, 318 Physiological rheoscope, 394 Physiology, 2 Placenta, 554 Plasma of blood, 161 chemical properties of, 151 gases of, 153 inorganic constituents of, 151 organic constituents of, 162 physical properties of, 161 Plasmon, 38 Plethora, 160 Pleura, 245 Fneumogastric, 543 branches of, 543 pathology of, 644, 545 physiology of, 644 Pons Varolii, 428, 467, 468 structure of, 429 Posterior columns, 426 Prehension, 44 Presbyopia, 521 Proteid compounds, 32 Proteids, 30, 35 classification of, 31 Proteoses, 68 Protoplasm, 8 constituents of, 10 movements of, 14 specific gravity of, 10 Proximate principles, 26 Pulmonary artery, pressure, 276 action of drugs on, 276 Pulse, 205, 206, 208 dicrotic,208 Purkinje cells, 464 Pylorus, 59 Quotient of gases, respiratory, 273 Rareflesd air, 275 Reflex action, 460 forms of, 452 laws of, 461, 462 swiftness of, 461 Rennin, 63, 80 Reproduction, 647 among higher animals, 647 among lower animals, 547 chorion, 664 embryonal area, 552 epiblast, 663 fecundation, 648 fertilization, 661 foetal circulation, 665 fractional reproduction, 648 hypoblast, 553 menstruation, 661 mesoblast, 663 ovum, 649 maturation of, 651 placenta, 664 segmentation, 551 spermatozoon, 648 structure of, 649 Reserved air, 255 Residual air, 265 Respiration, 237, 238, 239 air-passages, 241 alveoli, 244 apparatus, 240 artiScial, 264 bronchi, 243 carbon monoxide, 274 center of, 268 chemistry of, 267 Gheyne-Stokes respiration, 266 compressed air, 274 expiration, 260, 252 function of unstriped muscle bronchi, 267 inspiration, 246, 247, 248, 262 lungs, 242 lymphatics, 246 mechanism of, 246 nasal, 257 nerves of, 245, 257 number ot^ 266 pressure, 255 quotient of gases, 273 rarefied air, 275 trachea, 241 Restitorm body, 422, 423 Retina, 612, 613, 614, 616 Retinal epithelium, 516 Rhodopsin, 623 Rigor mortis, 376 of 563 INDEX. Saccharoses, 27 Saliva, B4 ferment of, 54, 55 reaction of, 55 reflex centers, 57 specific gravity of, 56 Salivary glands, 48 action of drugs on, 56 structure of^ 49 Salts, 27 Saponification, 30 Schuetz's law, 60 Sebaceous glands, 485 function of, 485 Secretin, 78 Secretion, 277 adrenal, 286, 286 internal, 279 mammary, 289, 290 pituitary, 288 spleen, 283 thymus, 287, 288 thyroid, 279, 280 Segmentation, 551 Semicircular canals, 500, 501 Sensation of color, 524 Sensory centers, 471, 472 Sensory tract, 442 Sighing, 265 Skatol, 98 Skin, 480 action of liquids on, 483 of solids on, 483 cold spots, 483, 484 hot spots, 483, 484 Krause's end-hulbs, 481, 482 layers of, 480 touch-corpuscles, 481 Skin radiation of heat, 353 Skin-reflexes, 457 Smell, 492 anosmia, 495 center of smell, 495 hyperosmia, 495 olfactory organ, 493 sensation, 493 uses of, 495 Snoring, 266 Sobbing, 266 Somatose, 69 Sound, 390 height of, 390 intensity of, 391 resonance of, 391 timbre, 391 Sounds of heart, 181 variation in, 182 Special senses, 477 Spectra of blood, 148 Spectroscope, 147 Speech, 391 aphonia, 392 hoarseness, 393 stammering, 392 'stuttering, 392 ventriloquy, 391 Spermatozoon, 548 structure of, 549 Spherical aberration, 519 Sphygmograph, 207 Spinal accessory, 545, 546 Spinal cord, 407, 420, 449 anterior roots, 453 blood-supply, effect of, 452 centers in, 457, 458 central canal, 415 columns of, 416 commissures, 420, 449, 450 coverings of, 408 diameter of, 409 ependyma of, 415 Spinal cord, exterior form of, 409 fibers of, 412, 413 gray matter of, 413 internal conformation of, 401, 411 minute structure of, 412 neuroglia of, 413 path of motion, 455 of sensation, 456 posterior roots, 453 recurrent sensibility, 454 reflex action, 450 forms of, 452 laws of, 451, 452 swiftness of, 461 skin-refiex, 467 systemization of, 415 tendon-reflexes, 457 tract, comma, 419 tracts of anterior column, 416 of lateral column, 417 of Lissauer, 419 posterior columns, 418 trophic centers, 455 Spirits, 40 Spongioplasm, 9 Stammering, 392 Stannius's experiment, 18S Steapsin, 80 Stearin, 29 Stethograph, 251 Stomach, 43, 57 action of agents on, 65 of alcohol on, 66 of bitters on, 66 movements of, 59 nervous control of, 60 Schuetz's law, 60 secretory nerves of, 65 structure of, 57, 58 Stuttering, 392 Succus entericus, 98 ferments of, 98 Sulphuric acid, 318 Swallowing of fluids, 191 Sweat, 294 acidity of, 294 composition of, 296 effect of drugs on, 296 function of, 298 pathological findings in, 298 suppression by cold, 297 Sweat-glands, 293 nerves of, 294 structure of, 293, 295 Sylvian center, 351 Sympathetic, the,, 475, 476 Tactile sense, 477, 478 law of Fechner, 479 laws of sensation, 479 Taste, 488 center for, 491 effects of drugs on, 491 organs of, 489, 490 variety of substances to be tasted, 491 Tea, 41 Teeth, 46 milk, 47 permanent, 47 structure of, 48 Tegmentum, 432 Teichmann's crystals, 145, 160 Tendon-reflexes, 457 Tetanus of muscle, 380 Tetany, 2»i Thermogenic center, 348 Thermo-inhibitory center, 350 Thermolytic center, 352 Thermotaxio center, 348 Thoma-Zeiss apparatus, 131 INDEX. 563 Thrombosis, 155 Tidal air, 254 Tongue, 46, 488 Touch, 479 Touch-corpuscles, 481 Trachea, 241 Transfusion, 158 Trifacial, 537, 538 motor function of, 539 pathology of, 539 physiology of, 538 reflex relations, 539 trophic function of, 539 Trophic centers, 465 Trypsin, 80 Tuber cinereum, 350, 352 Tyrosin, 83 Tyrotoxicon, 3d UffbIiMANN's test for lactic acid, 70 Uhlenhuth's test for blood, 161 Urea, 97, 312 ■ decomposition of, 311 formation of, 311 quantity of, 311 Ureters, 225 Uric acid, 97, 312 murexide test for, 314 Urinary tubules, 304 Urine, 308 acidity of, 309 albumin in, 321 Heller's nitric-acid test, 321 bile-pigments, 316 coloring matters of, 315, 316 composition of, 301 drug-pigments, 317 fermentation of, 319 inorganic constituents, 317 movements of urine, 326 nerves, influence of, on, 325 quantity of, 309 reaction of, 309 sediment of, 320 oxalic, 320 phosphoric, 321 specific gravity of, 309 sugar in, 322 Fehling's test for, 322 fermentation test for, 323 phenylhydrazin test for, 322 temperature of, 309 theory of secretion of, 323 toxicity of, 324 tube-casts, 323 Urobilin, 316 Urochrome, 316 Uroerytherin, 316 Valves of heart, 169 Vasoconstrictors, 230 Vasodilators, 231 Vasomotor reflex, 235 system, 227 centers of, 233, 234 functions of, 288 nerves of, 288 Vegetable cell, 6 Vegetable foods, 39 Veins, 198 blood-pressure in, 221 Veins, rate of movement of blood in, valves of, 198 Venous blood, 127 Venous circulation, 225 Ventilation, 275 Ventricles of heart, 171 , Ventriloquy, 391 Vision, 509 accommodation, 520 after-images, 526 aqueous humor, 615 binocular vision, 527, 628 chromatic aberration, 519 color-vision, 523, 524 complementary colors, 525 crystalline lens, 515 Daltonism, 525 dioptrics, 518 entoptic phenomena, 522 function of the eye, 518 hypermetropia, 521 irradiation, 526 lacrymal secretion, 528 lenses, 522 lymphatics, 516 movements of eyes, 527 myopia, 521 ophthalmoscope, 528 optic nerve, 516 perception of light, 517 perimeter, 529 phosphenes, 526 presbyopia, 621 retina, 612, 513, 614, 515 retinal epithelium, 616 rhodopsin, 623 sensation of color, 624 spherical aberration, 619 transmission of light, 509 visual angle, 519 apparatus, 610 structure of, 610, 511, 512 purple, 523 Visual angle, 519 Visual apparatus, 510 structure of, 610, 611, 512 Visual purple, 523 Vital capacity, 256 Vitellin, 36 Vocal cords, 387, 389 Voice, 384, 390 organ of, 385 Vomiting, 70 Warm-blooded animals, 341 Water, 26 Wheat, 39 Whey, 37 White columns, 425 White corpuscles, 134 amceboid movement of, 136 diapedesis of, 137 function of, 136 number of, 134 origih of,. 138 varieties of, 136 substance, 424 Wine, 40 YAVlfN, 265