LIBRARY OF THE UNIVERSITY OF CALIFORNIA. GIFT OF GEN. CHAS. R. GREENLEAF- BIOLOGY LIBRARY G Class MAKCH, 1880, KIEKES1 HAND-BOOK OF PHYSIOLOGY HAND-BOOK OP PHYSIOLOGY BY W. MOKKANT BAKEE, F.E.O.S. SUEGEON TO ST. BARTHOLOMEW'S HOSPITAL AND CONSULTING SUEGEON TO THE EVELINA HOSPITAL FOE SICK CHILDREN; LECTURER ON PHYSIOLOGY AT ST. BARTHOLOMEW'S HOSPITAL, AND LATE MEMBEE OF THE BOARD OF EXAMINEES OF THE EOYAL COLLEGE OF SURGEONS OF ENGLAND. AND VINCENT DORMER HARRIS, M.D., LOND. DEMONSTEATOE OF PHYSIOLOGY AT ST. BAETHOLOMEW'S HOSPITAL. ELEVENTH EDITION WITH NEARLY SOO ILLUSTRATIONS VOLUME II Of THC UNIVERSITY Of LJ NEW YOEK WILLIAM WOOD & COMPANY 56 & 58 LAFAYETTE PLACE * 1885 BJOLOGY LIBRARY G THE PUBLISHERS' BOOK COMPOSITION AND ELECTROTYPING Co., 39 AND 41 PARK PLACE, NEW YORK. CONTENTS TO VOLUME II. CHAPTER XIV. PAGE THE VASCULAR GLANDS 1 Structure and Functions of the Spleen 2 " Thymus 5 Thyroid .7 Supra-renal capsules 8 Pituitary Body 10 Pineal Gland 10 Functions of the Vascular Glands in general 10 CHAPTER XV. CAUSES AND PHENOMENA OF MOTION 12 Ciliary Motion 12 Amoeboid Motion 13 Muscular Motion 14 Plain or Unstriped Muscle 14 Striated Muscle 15 Development of Muscle 20 Physiology of Muscle at rest 20 " in activity . . .24 Rigor Mortis ............. 37 Actions of the Voluntary Muscles . . . 39 " Involuntary Muscles .44 Sources of Muscular Action 44 Electrical Currents in Nerves 45 CHAPTER XVI. THE VOICE AND SPEECH .50 Mode of Production of the Human Voice 50 The Larynx 51 Application of the Voice in Singing and Speaking 56 Speech ... 60 218840 IV CONTENTS. CHAPTER XVII. PAGE NUTRITION: THE INCOME AND EXPENDITURE OF THE HUMAN BODY . . 63 Nitrogenous Equilibrium and Formation of Fat 66 CHAPTER XVIII. THE NERVOUS SYSTEM 68 Elementary Structures of the Nervous System 68 Structure of Nerve-Fibres 69 Terminations of Nerve-Fibres 74 Structure of Nerve-Centres . 77 Functions of Nerve- Fibres 78 Classification of Nerve-Fibres 80 Laws of Conduction in Nerve- Fibres 81 Functions of Nerve-Centres 83 Laws of Reflex Actions 85 Secondary or Acquired Reflex Actions 87 CEREBRO- SPINAL NERVOUS SYSTEM 88 The Spinal Cord and its Nerves 90 The White Matter of the Spinal Cord 91 The Grey Matter of the Spinal Cord 92 Nerves of the Spinal Cord 94 Functions of the Spinal Cord . 97 THE MEDULLA OBLONGATA 105 Its Structure 105 Distribution of the Fibres of the Medulla Oblongata 106 Functions of the Medulla Oblongata 109 STRUCTURE AND PHYSIOLOGY OF THE PONS VAROLII, CRURA CEREBRI, COR- PORA QUADRIGEMINA, CORPORA GENICULATA, OPTIC THALAMI, AND COR- PORA STRIATA PonsVarolii U2 CruraCerebri 113 Corpora Quadrigemina 114 Corpora Striata and Optic Thakmi 114 THE CEREBELLUM Functions of the Cerebellum 118 THE CEREBRUM • 120 Convolutions of the Cerebrum 120 Structure of the Cerebrum 123 Chemical Composition of the Grey and White Matter 125 Functions of the Cerebrum , . . . 127 Effects of the Removal of the Cerebrum 128 Localization of Functions 129 Experimental Localization of Functions Sleep 135 CONTENTS. V PAGE PHYSIOLOGY OF THE CRANIAL NERVES 186 Physiology of the Third Cranial Nerve 137 Fourth Cranial Nerve 138 " • " Fifth or Trigeminal Nerve 139 »' " Sixth Nerve 143 " " Facial Nerve 144 " " Glosso-Pharyngeal Nerve 145 " " Pneumogastric Nerve 146 Spinal Accessory Nerve 149 " Hypoglossal Nerve . 150 PHYSIOLOGY OF THE SPINAL NERVES 150 PHYSIOLOGY OF THE SYMPATHETIC NERVE 151 Functions of the Sympathetic Nervous System 153 CHAPTER XIX. THE SENSES , 158 Common Sensations 158 Special Sensations 159 THE SENSE OF TOUCH . 162 THE SENSE OF TASTE 168 The Tongue and its Papillae .169 THE SENSE OF SMELL 175 THE SENSE OF HEARING 179 Anatomy of -the Organ of Hearing 179 Physiology of Hearing 186 Functions of the External Ear 186 Functions of the Middle Ear; the Tympanum, Ossicula, and Fenestrce . 187 Functions of the Labyrinth ......... 191 Sensibility of the Auditory Nerve 193 THE SENSE OF SIGHT 196 The Eyelids and Lachrymal Apparatus 196 The Structure of the Eyeball .197 Optical Apparatus 203 Accommodation of the Eye 206 Defects in the Apparatus , . . .211 Spherical Aberration . . , 212 Chromatic Aberration 213 The Blind Spot 215 Visual Purple 218 Color Sensations . . . 223 VI CONTENTS. PAGE Reciprocal Action Of different parts of the Retina 226 Movements of the Eye 228 Simultaneous Action of the two Eyes 228 CHAPTER XX. GENERATION AND DEVELOPMENT 234 Generative Organs of the Female 234 Unimpregnated Ovum 236 Discharge of the Ovum 239 Menstruation 240 Corpus Luteum , 243 IMPREGNATION OP THE OVUM 246 Male Sexual Functions 246 Structure of the Testicle 246 Spermatozoa 247 The Semen ' 251 DEVELOPMENT 252 Changes of the Ovum up to the Formation of the Blastoderm . . . 252 Segmentation of the Ovum ......... 253 Fundamental Layers of the Blastoderm: Epiblast; Mesoblast; Hypoblast. 255 First Rudiments of the Embryo and its Chief Organs .... 256 Fatal Membranes 261 The Umbilical Vesicle 262 The Amnion and Allantois 262 TheChorion . . 264 Changes of the Mucous Membrane of the Uterus and Formation of the Placenta 266 DEVELOPMENT OF ORGANS 270 Development of the Vertebral Column and Cranium .... 270 " Face and Visceral Arches . . . . . . 273 " Extremities 275 " Vascular System 276 Circulation of Blood in the Foetus 286 Development of the Nervous System 287 " Organs of Sense 291 " Alimentary Canal 295 " Respiratory Apparatus 298 " " Wolffian Bodies, Urinary Apparatus, and Sexual Organs 298 CHAPTER XXI. ON THE RELATION OF LIFE TO OTHER FORCES , 306 CONTENTS. Vil APPENDIX A: PAGE THE CHEMICAL BASIS OF THE HUMAN BODY 325 APPENDIX B : ANATOMICAL WEIGHTS AND MEASURES 345 Measures of Weight 345 " Length . 345 Sizes of various Histological Elements and Tissues 346 Specific Gravity of various Fluids and Tissues ..... 347 Table showing the percentage composition of various Articles of Food . 347 CLASSIFICATION OF THE ANIMAL KINGDOM 348 349 INDEX ,351 HAND-BOOK OF PHYSIOLOGY. CHAPTER XIV. THE VASCULAR GLANDS. THE materials separated from the blood by the ordinary process of secretion in glands, are always discharged from the organ in which they are formed, and are either straightway expelled from the body, or if they are again received into the blood, it is only after they have been altered from their original condition, as in the cases of the saliva and bile. There appears, however, to be a modification of the process of secretion, in which certain materials are abstracted from the blood, undergo some change, and are added to the lymph or restored to the blood, without being pre- viously discharged from the secreting organ, or made use of for any second- ary purpose. The bodies in which this modified form of secretion takes place, are usually described as vascular glands, or glands without ducts, and include the spleen, the tliymus and thyroid glands, the supra-renal cap- sules, the pineal gland and pituitary body, the tonsils. The solitary and agminate glands (Peyer's) of the intestine, and lymph-glands in general, also closely resemble them; indeed, both in structure and function, the vascular glands bear a close relation, on the one hand, to the true secret- ing glands, and on the other, to the lymphatic glands. The evidence in favor of the view that these organs exercise a function analogous to that of secreting glands, has been chiefly obtained from investigations into their structure, which have shown that most of the glands without ducts contain the same essential structures as the secreting glands, except the ducts. THE SPLEEN. The Spleen is the largest of the so-called ductless glands; it is situated to the left of the stomach, between it and the diaphragm. It is of a deep red color, of a variable shape, generally oval, somewhat concavo-convex. Vessels enter and leave the spleen at the inner side (hilus). VOL. II.— l. 2 HAND-BOOK OF PHYSIOLOGY. Structure. — The spleen is covered externally almost completely by a serous coat derived from the peritoneum, while within this is the proper fibrous coat or capsule of the organ. The latter, composed of connective tissue, with a large preponderance of elastic fibres, and a certain propor- tion of unstriated muscular tissue, forms the immediate investment of the spleen. Prolonged from its inner surface are fibrous processes or trabeculce, containing much unstriated muscle, which enter the interior of the organ, and, dividing and anastomosing in all parts, form a kind of supporting FIG. 254.— Section of dog's spleen injected: c, capsule; tr, trabeculae; m, two Malpighian bodies with numerous small arteries and capillaries; a, artery; Z, lymphoid tissue, consisting of closely- packed lymphoid cells supported by very delicate retiform tissue; a light space unoccupied by cells is seen all round the trabeculae, which corresponds to the " lymph path11 lymphatic glands. (Schofleld.) framework or stroma, in the interstices of which the proper substance of the spleen (spleen-pulp) is contained (Fig. 254). At the hilus of the spleen, the blood-vessels, nerves, and lymphatics enter, and the fibrous coat is prolonged into the spleen-substance in the form of investing sheaths for the arteries and veins, which sheaths again are continuous with the trabeculce before referred to. The spleen-pulp, which is a dark red or reddish-brown color, is com- posed chiefly of cells, imbedded in a matrix of fibres formed of the branching of large flattened nucleated endotheloid cells. The spaces of the network only partially occupied by cells form a freely communicating THE VASCULAR GLANDS. 6 system. Of the cells some are granular corpuscles resembling the lymph corpuscles, more or less connected with the cells of the meshwork, both in general appearance and in being able to perform amoeboid movements; others are red blood-corpuscles of normal appearance or variously changed ; while there are also large cells containing either a pigment allied to the coloring matter of the blood, or rounded corpuscles like red blood- cells. The splenic artery, after entering the spleen by its concave surface, divides and subdivides, with but little anastomosis between its branches; at the same time its branches are sheathed by the prolongations of fibrous coat, which they, so to speak, carry into the spleen with them. The arteries send off branches into the spleen-pulp which end in capillaries, and these either communicate, as in other parts of the body, with the radicles of the veins, or end in lacunar spaces in the spleen-pulp, from which veins arise (Gray). The walls of the smaller veins are more or less incomplete, and readily allow lymphoid corpuscles to be swept into the blood-current. "The blood traverses the network of the pulp, and interstices of the lymphoid cells contained in the latter, in the same manner as the water of a river finds its way among the pebbles of its bed: the blood from the arterial capillaries is emptied into a system of intermediate passages, which are directly bounded by the cells and fibres of the network of the pulp, and from which the smallest venous radicles with their cribriform walls take origin" (Frey). The veins are large and very distensible: the whole tis- sue of the spleen is highly vascular, and becomes readily engorged with blood: the amount of distension is, however, limited by the fibrous and muscular tissue of its capsule and trabeculse, which forms an investment and support for the pulpy mass within. On the face of a section of the spleen can be usually seen readily with the naked eye, minute, scattered rounded or oval whitish spots, mostly from -gV to ¥V inch in diameter. These are the MalpigMan corpuscles of the spleen, and are situated on the sheaths of the minute splenic arte- ries, of which, indeed, they may be said to be outgrowths (Fig. 254). For while the sheaths of the larger arteries are constructed of ordinary con- nective tissue, this has become modified where it forms an investment for the smaller vessels, so as to be composed of adenoid tissue, with abun- dance of corpuscles, like lymph-corpuscles, contained in its meshes, and the Malpighian corpuscles are but small outgrowths of this cytogenous or cell-bearing connective tissue. They are composed of cylindrical masses of corpuscles, intersected in all parts by a delicate fibrillar tissue, which though it invests the Malpighian bodies, does not form a complete cap- sule. Blood-capillaries traverse the Malpighian corpuscles and form a plexus in their interior. The structure of a Malpighian corpuscle of the spleen is, therefore, very similar to that of lymphatic-gland substance. Functions. — With respect to the office of the spleen, we have the 4 HAND-BOOK OF PHYSIOLOGY. following data. (1.) The large size which it gradually acquires toward the termination of the digestive process, and the great increase observed about this period in the amount of the finely-granular albuminous plasma within its parenchyma, and the subsequent gradual decrease of this mate- rial, seem to indicate that this organ is concerned in elaborating the albu- minous materials of food, and for a time storing them up, to be gradually introduced into the blood, according to the demands of the general system. (2.) It seems probable that the spleen, like the lymphatic glands, is engaged in the formation of blood-corpuscles. For it is quite certain, that the blood of the splenic vein contains an unusually large amount of white corpuscles; and in the disease termed leucocythsemia, in which the pale corpuscles of the blood are remarkably increased in number, there is almost always found an hyper trophied state of the spleen or of the lym- phatic glands. In Kolliker's opinion, the development of colorless and also colored corpuscles of the blood is one of the essential functions of the spleen, into the veins of which the new-formed corpuscles pass, and are thus conveyed into the general current of the circulation. (3.) There is reason to believe, that in the spleen many of the red cor- puscles of the blood, those probably which have discharged their office and are worn out, undergo disintegration; for in the colored portions of the spleen-pulp an abundance of such corpuscles, in various stages of degeneration, are found, while the red corpuscles in the splenic venous blood are said to be relatively diminished. This process appears to be as follows. The blood-corpuscles, becoming smaller and darker, collect to- gether in roundish heaps, which may remain in this condition, or become each surrounded by a cell- wall. The cells thus produced may contain from one to twenty blood-corpuscles in their interior. These corpuscles become smaller and smaller; exchange their red for a golden yellow, brown, or black color; and at length, are converted into pigment- granules, which by degrees become paler and paler, until all color is lost. The corpuscles undergo these changes whether the heaps of them are enveloped by a cell- wall or not. (4.) From the almost constant presence of uric acid, as well as of the nitrogenous bodies, xanthin, hypoxanthin, and leucin, in the spleen, some nitrogenous metabolism may be fairly inferred to occur in it. (5.) Besides these, its supposed direct offices, the spleen is believed to fulfil some purpose in regard to the portal circulation, with which it is in close connection. From the readiness with which it admits of being dis- tended, and from the fact that it is generally small while gastric diges- tion is going on, and enlarges when that act is concluded, it is supposed to act as a kind of vascular reservoir, or diverticulum to the portal system, or more particularly to the vessels of the stomach. That it may serve such a purpose is also made probable by the enlargement which it under- THE VASCULAR GLANDS. goes in certain affections of the heart and liver, attended with obstruction to the passage of blood through the latter organ, and by its diminution when the congestion of the portal system is relieved by discharges from the bowels, or by the effusion of blood into the stomach. This mechani- cal influence on the circulation, however, can hardly be supposed to be more than a very subordinate function. It is only necessary to mention that Schiff believes that the spleen manufactures a substance without which the pancreatic secretion cannot act upon proteids, so that when the spleen is removed the digestive action of the pancreas is stopped. Influence of the Nervous System upon the Spleen.— When the spleen is enlarged after digestion, its enlargement is probably due to two causes, (1) a relaxation of the muscular tissue which forms so large a part of its framework; (2) a dilatation of the vessels. Both these phe- nomena are doubtless under control of the nervous system. It has been found by experiment that when the splenic nerves are cut the spleen enlarges, and that contraction can be brought about (1) by stimulation of the spinal cord (or of the divided nerves); (2) reflexly by stimulation of the central stumps of certain divided nerves, e.g., vagus and sciatic; (3) by local stimulation by an electric current; (4) the exhibition of quinine and some other drugs. It has been shown by means of a modification of the plethysmo- graph (Roy), that the spleen undergoes rhyth- mical contractions and dilatations, due no doubt to the contraction and relaxation of the muscular tissue in its capsule and tra- beculse. The gland also shows the rhythmical alteration of the general blood pressure, but to a less extent than the kidney. THE THYMUS. FIG. 255.— Transverse section of a lobule of an injected infantile thymus S^nd. a, capsule of connective tis- sue surrounding the lobule; 6, mem- brane of the glandular vesicles; c, cavity of the lobule, from which the larger blood-vessels are seen to ex- tend toward and ramify in the sphe- roidal masses of the lobule, x 30. (Kolliker.) This gland must be looked upon as a tem- porary organ, as it attains its greatest size early after birth, and after the second year gradually diminishes, until in adult life hard- ly a vestige remains. At its greatest devel- opment it is a long narrow body, situated in the front of the chest behind the sternum and partly in the lower part of the neck. It is of a reddish or greyish color, distinctly lobulated. Structure. — The gland is surrounded by a fibrous capsule which 6 HAND-BOOK OF PHYSIOLOGY. sends in processes, forming trabeculse, which divide the gland into lobes, and carry the blood and lymph-vessels. The large trabeculas branch into small ones, which divide the lobes into lobules. The gland is encased in a fold of the pleura. The lobules are further subdivided into follicles by fine connective tissue. A follicle (Fig. 256) is more or less polyhedral in shape, and consists of cortical and medullary portions, the structure of both being of adenoid tissue, but in the medullary portion the matrix is coarser, and is not so filled up with lymphoid corpuscles as in the cortex. The adenoid tissue of the cortex, and to a less marked ex- tent in the medulla, consists of two kinds of tissue, one with small meshes formed of fine fibres with thickened nodal points, and the other enclosed within the first, composed of branched connective-tissue cor- Fio.256.— Fromahor- puscles (Watney). Scattered in the adenoid tissue of izontal section through ,-, in J.T / • T ^ TT ^^ superficial part of the the medulla are the concentric corpuscles of Hassall, thymus of a calf, slight- -\ • -\ i • _c ly magnified. showing which are protoplasmic masses of various sizes, con- sisting of a central nucleated granular centre, sur- rounded by flattened nucleated endothelial cells. In the reticulum, especially of the medulla, are large transparent giant cells. In the thymus of the dog and of other animals are to be found cysts, probably derived from the concentric corpuscles, some of which are lined with ciliated epithelium, and others with short columnar cells. Haemoglobin is found in the thymus of all animals, either in these cysts, or in cells near to or. of the concentric corpuscles. In the lymph issuing from the thymus are found cells containing colored blood-corpuscles and haemoglobin granules, and in the lymphatics of the thymus there are more colorless cells than in the lymphatics of the neck. In the blood of the thymic vein, there appears sometimes to be an in- crease in the colorless corpuscles and also masses of granular matter (cor- puscles of Zimmermann) (Watney). The arteries radiate from the centre of the gland. Lymph sinuses may be seen occasionally surrounding a- greater or smaller portion of the periphery of the follicles (Klein). The nerves are very minute. Function. — The thymus appears to take part in producing colored corpuscles, both from the large corpuscles containing haemoglobin, and also indirectly from the colorless corpuscles (Watney). Eespecting the function of the gland in the hybernating animals, in which it exists throughout life; as each successive period of hibernation approaches, the thymus greatly enlarges and becomes laden with fat, which accumulates in it and in fat-glands connected with it, in even larger proportions than it does in the ordinary seats of adipose tissue. Hence it appears to serve for the storing up of materials which, being re-absorbed in inactivity of the hibernating period, may maintain the respiration and THE VASCULAR GLANDS. the temperature of the body in the reduced state to which they fall during that time. THE THYROID. The Thyroid gland is situated in the neck. It consists of two lobes, one on each side of the trachea extending upward to the thyroid cartilage, covering its inferior cornu and part of its body; these lobes are connected FIG. 257.— Part of a section of the human Thyroid, a, fibrous capsule; 6, thyroid vesicles filled with, e, colloid substance; c, supporting fibrous tissue; d, short columnar cells lining vesicles; /, ar- teries; gr, veins filled with blood; /i, lymphatic vessel filled with colloid substance. (S. K. Alcock.) across the middle line oy a middle lobe or isthmus. The thyroid is cov- ered by the muscles of the neck. It is highly vascular, and varies in size in different individuals. Structure. — The gland is encased in a thin transparent layer of dense areolar tissue, free from fot, containing elastic fibres. This capsule sends in strong fibrous trabeculae, which enclose the thyroid vesicles — which are rounded or oblong irregular sacs, consisting of a wall of thin hyaline membrane lined by a single layer of low cylindrical or cubical cells. These vesicles are filled with a coagulable fluid or transparent colloid material. The colloid substance increases with age, and the cavities appear to coalesce. In the interstitial connective tissue is a round meshed 8 HAND-BOOK OF PHYSIOLOGY, capillary plexus and a large number of lymphatics. The nerves adhere closely to the vessels. In the vesicles there are in addition to the yellowish glassy colloid material, epithelium cells, colorless blood corpuscles, and also colored cor- puscles undergoing disintegration. Function. — There is little known definitely about the function of the thyroid body. It, however, produces the colloid material of the vesicles, which is carried off by the lymphatics and discharged into the blood, and so may contribute its share to the elaboration of that fluid. The destruc- tion of red blood-corpuscles is also supposed to go on in the gland. SUPRA-RENAL CAPSULES OR ADRENALS. These are two flattened, more or less triangular or cocked-hat shaped bodies, resting by their lower border upon the upper border of the kidneys. Structure. — The gland is surrounded by an outer sheath of connec- tive tissue, which sometimes consists of two layers, sending in exceedingly FIG. 258.— Vertical section through part of the cortical portion of supra-renal of guinea-pig, a, capsule; 6, zona glomerulosa; c, zona fasciculata; d, connective tissue supporting the columns of the ceDs of the latter, and also indicating the position of the blood-vessels. poor in fat, and occasionally branched; the nerves run through the corti- cal substance, and anastomose over the medullary portion. Function. — Of the function of the supra-renal bodies nothing can be definitely stated, but they are in all probability connected with the lym- phatic system. 10 HAND-BOOK OF PHYSIOLOGY. Addison's Disease. — The collection of large numbers of cases in which the supra-renal capsules have been diseased, has demonstrated the very close relation subsisting between disease of those organs and brown dis- coloration of the skin (Addison's disease); but the explanation of this relation is still involved in obscurity, and consequently does not aid much in determining the functions of the supra-renal capsules. PITUITAKY BODY. This body is a small reddish-grey mass, occupying the sella turcica of the sphenoid bone. Structure. — It consists of two lobes — a small posterior one, consist- ing of nervous tissue; an anterior larger one, resembling the thyroid in structure. A canal lined with flattened or with ciliated epithelium, passes through the anterior lobe; it is connected with the infundibulum. The gland spaces are oval, nearly round at the periphery, spherical toward the centre of the organ; they are filled with nucleated cells of various sizes and shapes not unlike ganglion cells, collected together into rounded masses, filling the vesicles, and contained in a semi-fluid granular sub- stance. The vesicles are enclosed by connective tissue rich in capil- laries. Function. — Nothing is known of the function of the pituitary body. PINEAL GLAND. This gland, which is a small reddish body, is placed beneath the back part of the corpus callosum, and rests upon the corpora quadrigemina (Fig. 327, g). Structure. — It contains a central cavity lined with ciliated epithe- lium. The gland substance proper is divisible into — (1.) An outer corti- cal layer, analogous in structure to the anterior lobe of the pituitary body; and (2) An inner central layer, wholly nervous. The cortical layer con- sists of a number of closed follicles, containing (a) cells of variable shape, rounded, elongated, or stellate; (b) fusiform cells. There is also present a gritty matter (acervulus cerebri), consisting of round particles aggre- gated into small masses. The central substance consists of white and grey matter. The blood-vessels are small, and form a very delicate capillary plexus. Function. — Of this there is nothing known. FUNCTIONS OF THE VASCULAR GLANDS IN GENERAL. The opinion that the vascular glands serve for the higher organization of the blood, is supported by their being all especially active in the dis- charge of their functions during foetal life and childhood, when, for the THE VASCULAR GLANDS. 11 development and growth of the bod}7, the most abundant supply of highly organized blood is necessary. The bulk of the thymus gland, in propor- tion to that of the body, appears to bear almost a direct proportion to the activity of the body's development and growth, and when, at the period of puberty, the development of the body may be said to be complete, the gland wastes, and finally disappears. The thyroid gland and supra-renal capsules, also, though they probably never cease to discharge some amount of function, yet are proportionally much smaller in childhood than in foetal life and infancy; and with the years advancing to the adult period, they diminish yet more in proportionate size and apparent activity of function. The spleen more nearly retains its proportionate size, and enlarges nearly as the whole body does. The vascular glands seem not essential to life, at least not in the adult. The thymus wastes and disappears: no signs of illness attend some of the diseases which wholly destroy the structure of the thyroid gland;- and the spleen has been often removed in animals, and in a few instances in men, without any evident ill-consequence. It is possible that, in such cases, some compensation for the loss of one of the organs may be afforded by an increased activity of function in those that remain. Although the functions of all the vascular glands may be similar, in so far as they may all alike serve for the elaboration and maintenance of the blood, yet each of them probably discharges a peculiar office, in rela- tion either to the whole economy, or to that of some othef organ. Re- specting the special office of the thyroid gland, nothing reasonable can be suggested; nor is there any certain evidence concerning that of the supra- renal capsules. Bergman believed that they formed part of the sympa- thetic nervous system from the richness of their nervous supply. Kolliker states that he is inclined to look upon the two parts as functionally dis- tinct, the cortical part belonging to the blood vascular system, and the medullary to the nervous system. CHAPTER XV. CAUSES AND PHENOMENA OF MOTION. IN" the animal body, motion is produced in these several ways: (1.) The oscillatory or vibratory movement of Cilia. (2.) Amoeboid and certain Molecu lar movements. (3.) The contraction of Muscular fibre. I. CILIARY MOTION. Ciliary, which is closely allied to amoeboid and muscular motion (p. 8, Vol. I.), consists in the incessant vibration of fine, pellucid processes, about -g-^ of an inch long, termed cilia (Figs. 260, 261,) situated on the free extremities of the cells of epithelium covering certain surfaces of the body. The distribution and structure of ciliary epithelium and the micro- scopic appearances of cilia in motion have been already described (pp. 25, 26, Vol. I.). Ciliary motion is alike independent of the will, of the direct influ- ence of the nervous system, and of muscular contraction. It continues for several hours after death, or removal from the body, provided the FIG. 260. FIG. 261. FIG. 260.— Spheroidal ciliated cells from the mouth of the frog; magnified 300 diameters. (Sharpey.) FIG. 261.— Columnar ciliated cells from the human nasal membrane: magnified 300 diameters. (Sharpey.) portion of tissue under examination be kept moist. Its independence of the nervous system is shown also in its occurrence in the lowest inverte- brate animals apparently unprovided with anything analogous to a nervous system, in its persistence in animals killed by prussic acid, by narcotic or other poisons, and after the direct application of narcotics to the ciliary sur- CAUSES AND PHENOMENA OF MOTION. 13 face, or the discharge of a Leyden jar, or of a galvanic shock through it. The vapor of chloroform arrests the motion; but it is renewed on the dis- continuance of the application (Lister). The movement ceases in an at- mosphere deprived of oxygen, but is revised on the admission of this gas. Carbonic acid stops the movement. The contact of various substances will stop the motion altogether; but this seems to depend chiefly on destruction of the delicate substance of which the cilia are composed. Nature of Ciliary Action.— Little or nothing is known with cer- tainty regarding the nature of ciliary action. It is a special manifestation of a similar property to that by which the other motions of animals are effected, namely, by what we term vital contractility (Sharpey). The fact of the more evident movements of the larger animals being effected by a structure apparently different from that of cilia, is no argument against such a supposition. For, if we consider the matter, it will be plain that our prejudices against admitting a relationship to exist between the two structures, muscles and cilia, rests on no definite ground; and for the simple reason, that we know so little of the manner of production of movement in either case. The mere difference of structure is not an argument in point; neither is the presence or absence of nerves. For in the foetus the heart begins to pulsate when it consists of a mass of em- bryonic cells, and long before either muscular or nervous tissue has been differentiated. The movements of both muscles and cilia are manifesta- tions of energy, by certain special structures, which we call respectively muscles and cilia. We know nothing more about the means by which the manifestation is effected by one of these structures than by the other: and the mere fact that one has nerves and the other has not, is no more argument against cilia having what we call a vital power of contraction, than the presence or absence of stripes from voluntary or involuntary muscles respectively, is an argument for or against the contraction of one of them being vital and the other not so. As a special subdivision of ciliary action may be mentioned the motion of spermatozoa (Fig. 403), which may be regarded as cells with a single cilium. II. AMOEBOID MOTION. The remarkable movements observed in colorless blood corpuscles, connective-tissue corpuscles, and many other cells (p. 8, Vol. I.), must be regarded as depending on a kind of contraction of portions of their m£ss very similar to muscular contraction. There is certainly an analogy between the spherical form assumed by a colorless blood-corpuscle on electric stimulation and the condition known as tetanus in muscles. 14 HAND-BOOK OF PHYSIOLOGY. III. MUSCULAR MOTION. Varieties of Muscular Tissue. — There are two chief kinds of muscular tissue: (1.) the plain or non-striated, and (2.) the striated, and they are distinguished by structural peculiarities and mode of action. The striped form of muscular fibre is sometimes called voluntary muscle, because all muscles under the direct control of the will are constructed of it. The plain or unstriped variety is often termed involuntary, because it alone is found in the greater number of the muscles over which the will has no power. (1.) PLAIK OR UNSTRIPED MUSCLE. Distribution. — Involuntary muscle forms the proper muscular coats (1.) of the digestive canal from the middle of the oesophagus to the inter- nal sphincter ani; (2.) of the ureters and urinary bladder; (3.) the trachea and bronchi; (4.) the ducts of glands; (5.) the gall-bladder; (6.) the vesiculae seminales; (7.) the pregnant uterus; (8.) of blood-vessels and lymphatics; (9.) the iris, and some other parts. This form of tissue also FIG. 262.— Vertical section through the scalp with two hair-sacs; a. epidermis; 6, cutis; c, muscles of the hair-follicles. (Kolliker.) enters (10. ) largely into the composition of the tunica dartos, and is the principal cause of the wrinkling and contraction of the scrotum on expo- sure to cold. Unstriped muscular tissue occurs largely also (11.) in the cutis (p. 335, Vol. I.), being especially abundant in the interspaces between the bases of the papillae. Hence when it contracts under the influence of cold, fear, electricity, or any other stimulus, the papillae are made unusually pi#minent, and give rise to the peculiar roughness of the skin termed cutis anserina, or goose skin. It occurs also in the superficial portion of the cutis, in all parts where hairs occur, in the form of flattened roundish bundles, which lie alongside the hair-follicles and sebaceous glands. They pass obliquely from without inward, embrace the sebaceous glands, and are attached to the hair-follicles near their base (Fig. 228). CAUSES AND PHENOMENA OF MOTION. 15 Structure. — The non-striated muscles are made up of elongated, spindle-shaped, nucleated, fibre cells (Fig. 263), which in their perfect form are flat, from about ^-§^5- to j-.1,,-,-,- of an inch broad, and -$fa to -j-J^ of an inch in length, — very clear, granular, and brittle, so that when they FIG. 263. — A, unstriped muscle cells from mesentery of newt, sheath with transverse marking faintly seen. X ISO. B, from similar preparation, showing each muscle cell consists of a central bundle of fibrils (contractile part) connected with the intranuclear network and a sheath with annu- lar thickenings. The cells show varicosities due to local contraction, and on these the annular thick- enings are most marked. X 450. (Klein and Noble Smith.) break they often have abruptly rounded or square extremities. Each muscle cell consists of a fine sheath, probably elastic; of a central bundle of fibrils representing the contractile substance; and of an oblong nucleus which includes within a membrane a fine network anastomosing at the poles of the nucleus with the contractile fibrils. The ends of fibres FIG. 264. — Plexus of bundles of unstriped muscle cells of the pulmonary pleura of the guinea-pig. X 180. (Klein and Noble Smith.) are usually single, sometimes divided. Between the fibres is an albumi- nous cementing material (endomysium) in which are found connective- tissue corpuscles, and a few fibres. Theperimyshim is the fibrous con- nective tissue surrounding and separating the bundles of muscle cells. (2.) STRIATED OR STRIPED MUSCLE. Distribution. — The striated muscles include the whole class of vol- untary muscles, the heart, and those muscles neither completely volun- 16 HAND-BOOK OF PHYSIOLOGY. tary nor involuntary, which form part of the walls of the pharynx, and exist in many other parts of the body, as the internal ear, urethra, etc. Structure. — All these muscles are composed of larger or smaller bundles of muscular fibres called, fasciculi, enclosed in coverings of fibro- cellular tissue (perimysium), by which each is at once connected with and isolated from those adjacent to it (Fig. 265). Supporting the fibres contained in each fasciculus is a scanty amount of fine connective tissue endomysium. Each muscular fibre is thus constructed: — Externally is a fine, trans- parent, structureless membrane, called the sarcolemma (Eig. 266, A), which in the form of a tubular investing sheath forms the outer wall of FIG. 265. FIG. 266. FIG. 265.— A small portion of muscle natural size, consisting of larger and smaller fasciculi, ^en in a transverse section, and the same magnified 5 diameters. (Sharpey.) FIG. 266. — Part of a striped muscle-fibre of a water-beetle (hydrophilus) prepared with absolute alcohol. A, sarcolemma; B, Krause's membrane. Owing to contraction during hardening, the sar- colemma shows regular bulgings. Above and below Krause's membrane are seen the transparent "lateral discs." The chief mass of a muscular compartment is occupied by the contractile disc com- posed of sarcous elements. The substance of the individual sarcous elements has collected more at the extremity than in the centre: hence this latter is more transparent. The optical effect of this is that the contractile disc appears to possess a ''median disc" (Disc of Hensen). Several nuclei of muscle corpuscles, C and D, are shown, and in them a minute netAvork. X 300. (Klein and Noble Smith.) the fibre, and is filled up by the contractile material of which the fibre is chiefly composed. Sometimes, from its comparative toughness, the sarco- lemma will remain untorn, when by extension the contained part can be broken (Eig. 269), and its presence is in this way best demonstrated. The fibres, which are cylindriform or prismatic, with an average diameter of about -g fa of an inch, are of a pale yellow color, and apparently marked b}r fine striae, which pass transversely round them, in slightly curved or wholly parallel lines. Each fibre is found to consist of broad dim bands of highly refractive substance representing the contractile portion of the muscle fibre — the contractile discs (Fig. 267, A, c) — alternating with nar- row bright bands of a less refractive substance — the interstitial discs (Fig. 267, A, i). After hardening, each contractile disc becomes longi- tudinally striated, the thin oblong rods thus formed being the sarcous elements of Bowman. The sarcous elements are not the optical units, since each consists of minute doubly-refracting elements — the disdiaclasts CAUSES AND PHENOMENA OF MOTION. 17 of Briicke. When seen in transverse section the contractile discs appear to be subdivided by clear lines into polygonal areas, Cohnheim's fields (Fig. 271), each corresponding to one sarcous element prism. The clear lines are due to a transparent interstitial fluid substance pressed out of the sarcous elements when they coagulate. There is still some doubt regarding the nature of the fibrils. Each of them appears to be com- posed of a single row of minute dark quadrangular particles, called sarcous elements, which are separated from each other by a bright space formed of a pellucid substance continuous with them. Sharpey believes that, even in a fibril so constituted, the ultimate anatomical element of the fibre has not been isolated. He believes that each fibril with quadrangular FIG. 267.— A. Portion of a medium-sized human muscular fibre. X 800. B. Separated bundles of fibrils equally magnified; a, a, larger, and 6, b, smaller collections; c, still smaller; d, d, the smallest which could be detached, possibly representing a single series of sarcous elements. (Sharpey.) sarcous elements is composed of a number of other fibrils still finer, so that the sarcous element of an ultimate fibril would be not quadrangular, but as a streak. In either case the appearance of striation in the whole fibre would be produced by the arrangement, side by side, of the dark and light portions respectively of the fibrils (Fig. 267, B, d). A fine streak can usually be discerned passing across the interstitial disc between the sarcous elements: this streak is termed Krause's mem- brane: it is continuous at each end with the sarcolemma investing the muscular fibre (Fig. 266, B). Thus the space enclosed by the sarcolemma is divided into a series of compartments by the transverse partitions known as Krause's membranes; these compartments being occupied by the true muscle substance. On VOL. II.— 2. 18 HAND-BOOK OF PHYSIOLOGY. -each side (above and below) of Krause's membrane is a bright border (lateral disc). In the centre of the dark zone of sarcous elements a lighter band can sometimes be dimly discerned: this is termed the middle disc of Hensen (see Fig. 266, A). In some fibres, chiefly those from insects, each lateral disc contains a TOW of bright granules forming the granular layer of Elogel. The fibres FIG. 269. FIG. 268.— Transverse section of a muscle-fibre of water-beetle (hydrophilus pisceus), showing the position of the muscle nuclei. (Walter Pye.) FIG. 269. — Muscular fibre torn across ; the sarcolemma still connecting the two parts of the fibre. (Todd and Bowman.) contain nuclei, which are roundish ovoid, or spindle-shaped in different animals. These nuclei are situated close to the sarcolemma, their long axes being parallel to the fibres which contain them. Each nucleus is composed of a uniform network of fibrils, and is embedded in a thin, FIG. 270. FIG. 271. FIG. 270.— Section through the musculac substance of the tongue, with capillaries injected, their meshes running parallel to the fibres. Three muscular fibres are seen running longitudinally, and two bundles of fibres in transverse section, x 150. (Klein and Noble Smith.) FIG. 271. — Transverse section through muscular fibres of human tongue: the fibres appear in transverse section of different sizes owing to their being more or less spindle-shaped. The muscle- corpuscles are indicated by their deeply -stained nuclei situated at the inside of the sarcolemma. Each muscle-fibre shows the "Cohnheim's fields," that is the sarcous elements in transverse section separated by clear (apparently linear) interstitial substance, x 450. (Klein and Noble Smith.) more or less branched film of protoplasm. The nucleus and protoplasm together form the muscle cell or muscle corpuscle of Max Schultze. The sarcous elements and Krause's membranes are doubly refracting, the rest of the fibre singly refracting (Briicke). CAUSES AND PHENOMENA OF MOTION. 19 According to Schafer, the granules, which have been mentioned on either side of Krause's membrane, are little knobs attached to the ends of "muscle-rods;" and these muscle-rods, knobbed at each end and imbedded in a homogeneous protoplasmic ground-substance, form the substance of the muscles. This view, however, of the structure of muscle requires further confirmation before it can be accepted. Although each muscular fibre may be considered to be formed of a number of longitudinal fibrils, arranged side by side, it is ako true that they are not naturally separate from each other, there being lateral cohesion, if nofc fusion, of each sarcous element with those around and in contact with it; so that it happens that there is a tendency for a fibre to FIG. 272. FIG. 273. FIG. 272. — Muscular fibres from the heart, magnified, showing their qross-striae, divisions, and junctions. (Kolliker.) FIG. 273.— Network of muscular fibres (striated) from the heart of a pig. The nuclei of the mus- cle-corpuscles are well shown, x 450. (Klein and Noble Smith.) split, not only into separate fibrils, but also occasionally into plates or discs, each of which is composed of sarcous elements laterally adherent one to another. Muscular Fibres of the Heart (Figs. 272 and 273) form the chief, though not the only exception to the rule, that involuntary muscles are constructed of plain fibres; but although striated and so far resembling those of the skeletal muscles, they present these distinctions: — Each muscular fibre is made up of elongated, nucleated, and branched cells, the nuclei or muscle-corpuscles being centrally placed in the fibre. The fibres are finer and less distinctly striated than those of the voluntary muscles; and no sarcolemma can be usually discerned. Blood and Nerve Supply. — The voluntary muscles are freely sup- plied with blood-vessels; the capillaries form a network with oblong 20 HAND-BOOK OF PHYSIOLOGY. meshes around the fibres on the outside of the sarcolemma. No vessels penetrate the sarcolemma to enter the interior of the fibre (Fig. 270). Nerves also are supplied freely to muscles (pp. 76, 80, Vol. II. ) ; the volun- tary muscles receiving chiefly nerves from the cerebro-spinal system, and the unstriped muscles from the sympathetic or ganglionic system. FIG. 274.— Muscular fibre cells from the heart. (E. A. Schafer.) Development. — (1.) Unstriped. — The cells of unstriped muscle arc derived directly from embryonic cells, by an elongation of the cell, and its nucleus; the latter changing from a vascular to a rod shape. (2.) Striped. — Formerly it was supposed that striated fibres are formed by the coalescence of several cells, but recently it has been proved, that each fibre is formed from a single cell, the process involving an enormous increase in size, a multiplication of the nucleus by fission, and a differen- tiation of the cell-contents (Remak, Wilson Fox). This view differs but little from that previously taken by Savory, that the muscular fibre is produced, not by multiplication of cells, but by arrangement of nuclei in a growing mass of protoplasm (answering to the cell in the theory just referred to), which becomes gradually differentiated so as to assume the characters of a fully developed muscular fibre. Growth of Muscle. — The growth of muscles, both striated and non- striated, is the result of an increase both in the number and size of the individual elements. In the pregnant uterus the fibre-cells may become enlarged to ten times their original length. In involution of the uterus after parturition the reverse changes occur, accompanied generally by some fatty infil- tration of the tissue and degeneration of the fibres. PHYSIOLOGY OF MUSCLE. Muscle may exist in three different conditions: rest, activity, and rigor. CAUSES AND PHENOMENA OF MOTION. 21 I. EEST. Physical Condition. — During rest or inactivity a muscle has a slight but very perfect elasticity; it admits of being considerably stretched; but returns readily and completely to its normal length. In the living body the muscles are always stretched somewhat beyond their natural length, they are always in a condition of slight tension; an arrangement which enables the whole force of the contraction to be utilized in approximating the points of attachment. It is obvious that if the muscles were lax, the first part of the contraction till the muscle became tight would be wasted. There is no doubt that even in a condition of rest oxygen is being abstracted from the blood and carbonic acid given out by a muscle; for the blood becomes venous in the transit, and since the muscles form by far the largest element in the composition of the body, chemical changes must be constantly going on in them as in other tissues and organs, although not necessarily accompanied by contraction. When cut out of the body such muscles retain their contractility longer in an atmosphere of oxygen than in an atmosphere of hydrogen or carbonic acid, and during life, an amount of oxygen is no doubt necessary to the manifestation of energy as well as for the metabolism going on in the resting condition. Chemical composition. — The reaction of living muscle is neutral or slightly alkaline. The substance or muscle plasma which forms the con- tractile principal element in its composition undergoes coagulation when the muscle is removed from the body, and the process may be observed if the coagulation be delayed by cold. If the muscles of a frog be frozen, minced whilst in that condition, and reduced to a pulp by being rubbed up with a 1 per cent, solution of sodium chloride, the temperature of which must be very low, on filtration in the cold, a colorless, somewhat turbid filtrate separates with difficulty, which is muscle plasma. This fluid at the ordinary temperature of the air undergoes a coagulation or clotting, by which it is separated, as in the case of blood, into muscle- serum and muscle-clot. The latter, however, is not made up of fibrin but of myosin, which is a globulin (p. 328, Vol. II.). Myosin may also be obtained from dead muscle by subjecting it, after all the blood, fat, fibrous tissue, and substances soluble in water, have been removed, to a ten per cent, solution of sodium chloride, filtering and allowing the- filtrate to drop into a large quantity of water; myosin separating out as a white flocculent precipitate. Obtained in either way, viz., from living or dead muscle, myosin is soluble in dilute saline solutions, and the solution undergoes coagulation at a lower temperature than serum-albumin or paraglobulin, viz., at 131°— 140° F. (55°— 60° C.). It is coagulated also by alcohol. It is dissolved and converted into acid-albumin by dilute acid, such as hydrochloric. 22 HAND-BOOK OF PHYSIOLOGY. Muscle-serum is acid in reaction, contains serum-albumin and several other proteids as well as other bodies, among which are fats; free acids, especially sarco-lactic, formic, and acetic; glucose, glycogen and inosite; kreatin, hypoxanthin, or carnin, taurin, and other nitrogenous crystalline bodies; many salts, of which the chief is potassium phosphate; Carbonic acid, and lastly Haemoglobin, on which the color of muscles partially depends. There are also traces of ferments, pepsin among others. Electrical Condition; Natural muscle currents. — In muscles which have been removed from the body, it has been found that electrical cur- rents can be demonstrated for some little time, passing from point to point on their surface; but as soon as the muscles die or enter into rigor mortis, these currents disappear. The method of demonstration usually FIG. 275.— Diagram of Du Bois ReymoruTs non-polarizable electrodes, a, glass tube filled with a saturated solution of zinc sulphate, in the end, c, of which is china clay drawn out to a point; in the solution a well amalgamated zinc rod is immersed and connected by means of the wire which passes through A with the galvanometer. The remainder of the apparatus is simply for convenient applica- tion. The muscle to the end of the second electrode is to the right of the figure. employed is as follows: The frog's muscles are most convenient for ex- periment, and a muscle of regular shape, in which the fibres are parallel, is selected. The ends are cut off by clean vertical cuts, and the resulting piece of muscle is called a regular muscle prism. The muscle prism is in- sulated, and a pair of non-polarizable electrodes connected with a very deli- cate galvanometer are applied to various points of the prism, and by a de- flection of the needle to a greater or less extent in one direction or another, the strength and direction of the currents in the piece of muscle can be estimated. It is necessary to use non-polarizable and not metallic elec- trodes in this experiment, as otherwise there is no certainty that the whole of the current observed is communicated from the muscle and is not derived from the metallic electrodes themselves in consequence of the action of the saline juices of the tissues upon them. The form of the non-polarizable electrodes is a modification of Du Bois Eeymond's appa- CAUSES AND PHENOMENA OF MOTION. 23 ratus (Fig. 275), which consists of a somewhat flattened glass cylinder a, drawn abruptly to a point and fitted to a socket capable of movement and attached to a stand A, so that it can be raised or lowered as required. The lower portion of the cylinder is filled with china clay moistened with saline solution, part of which projects through its drawn-out point, the rest of the cylinder is fitted with a saturated solution of zinc sulphate into which dips a well amalgamated piece of zinc which is connected by means of a wire with the galvanometer. In this way the zinc sulphate forms an homogeneous and non-polarizable conductor between the zinc and the china clay. A second electrode of the same kind is, of course, necessary. In such a regular muscle prism the currents are found to be as follows: — (t e i t J FIG. 276.— Diagram of the currents in a muscle prism. (Du Bois Reymond.) If from a point on the surface a line — the equator — be drawn across the muscle prism equally dividing it, currents pass from this point to points away from it, which are weak if the points are near, and increase in strength as the points are further and further away from the equator; the strongest passing from the equator to a point representing the middle of the cut ends (Fig. 276, 2); currents also pass from points nearer the equator to those more remote (Fig. 276, 1, 3, 4), but not from points equally distant, or iso-electric points (Fig. 276, 6. 7, 8). The cut ends are always negative to the equator. These currents are constant for some time after removal of the muscle from the body, and in fact remain as long as the muscle retains its life. They are in all probability due to chemical change going on in the muscles. The currents are diminished by fatigue and are increased by an in- crease of temperature within natural limits. If the uninjured tendon be used as the end of the muscle, and the muscle be examined without re- moval from the body, the currents are very feeble, but they are at once much increased by injuring the muscle, as by cutting off its tendon. The last observation appears to show that they are right who believe that the currents do not exist in muscles uninjured in situ, but that injury, either 24 HAND-BOOK OF PHYSIOLOGY mechanical, chemical or thermal, will render the injured part electrically negative to other points on the muscle. In a frog's heart it has been shown, too, that no currents exist during its inactivity, but that as soon as it is injured in any way currents are developed, the injured part being negative to the rest of the muscle. The currents which have been above described are called either natural muscle currents or currents of rest, according as they are looked upon as always existing in muscle or as developed when a part of the muscle is subjected to injury; in either case, up to a certain point, it is agreed that the strength of the currents is in direct proportion to the injury. J II. ACTIVITY. The property of muscular tissue, by which its peculiar functions are exercised, is its contractility, which is excited by all kinds of stimuli applied either directly to the muscles, or indirectly to them through the medium of their motor nerves. This property, although commonly brought into action through the nervous system, is inherent in the mus- cular tissue. For — (1). it may be manifested in a muscle which is iso- lated from the influence of the nervous system by division of the nerves supplying it, so long as the natural tissue of the muscle is duly nourished; and (2). it is manifest in a portion of muscular fibre, in which, under the microscope, no nerve-fibre can be traced. (3). Substances such as urari, which paralyze the nerve-endings in muscles, do not at all diminish the irritability of the muscle. (4). When a muscle is fatigued, a, local stimulation is followed by a contraction of a small part of the fibre in the immediate vicinity without any regard to the distribution of nerve -fibres. If the removal of nervous influence be long continued, as by division of the nerves supplying a muscle, or in cases of paralysis of long-standing, the irritability, i.e., the power of both perceiving and responding to a stimulus, may be lost; but probably this is chiefly due to the impaired nutrition of the muscular tissue, which ensues through its inaction. The irritability of muscles is also of course soon lost, unless a supply of arterial blood to them is kept up. Thus, after ligature of the main arterial trunk of a limb, the power of moving the muscles is partially or wholly lost, until the collateral circulation is established; and when, in animals, the abdom- inal aorta is tied, the hind legs are rendered almost powerless. The same fact may be readily shown by compressing the abdominal aorta in a rabbit for about 10 minutes; if the pressure be released and the animal be placed on the ground, it will work itself along with its front legs, while the hind legs sprawl helplessly behind. Gradually the muscles recover their power and become quite as efficient as before. So. also, it is to the imperfect supply of arterial blood to the muscular CAUSES AND PHENOMENA OF MOTION. 25 tissue of the heart, that the cessation of the action of this organ in asphyxia is in some measure due. Sensibility. — Besides the property of contractility, the muscles, especially the striated, possess sensibility by means of the sensory nerve- fibres distributed to them. The amount of common sensibility in muscles is not great; for they may be cut or pricked without giving rise to severe pain, at least in their healthy condition. But they have a peculiar sensi- bility, or at least a peculiar modification of common sensibility, which is shown in that their nerves can communicate to the mind an accurate knowledge of their states and positions when in action. By this sensibil- ity, we are not only made conscious of the morbid sensations of fatigue and cramp in muscles, but acquire, through muscular action, a knowledge of the distance of bodies and their relation to each other, and are enabled to estimate and compare their weight and resistance by the eifort of which we are conscious in measuring, moving, or raising them. Except with such knowledge of the position and state of each muscle, we could not tell how or when to move it for any required action; nor without such a sensation of eifort could we maintain the muscles in contraction for any prolonged exertion. MUSCULAE CONTRACTION. The power which muscles possess of contraction may be called forth by stimuli of various kinds, viz., by Mechanical, Thermal, Chemical, and Electrical means, and these stimuli may also be applied directly to the muscle or indirectly to the nerve supplying it. There are distinct advan- tages, however, in applying the stimulus through the nerves, as it is more convenient, as well as more potent. Mechanical stimuli, as by a blow, pinch, prick of the muscle or its nerve, will produce a contraction, repeated on the repetition of the stim- ulus; but if applied to the same point for a limited number of times only, as such stimuli will soon destroy the irritability of the preparation. Thermal stimuli. — If a needle be heated and applied to a muscle or its nerve, the muscle will contract. A temperature of over 100° F. (37 '8° C.) will cause the muscles of a frog to pass into a condition known as heat rigor. Chemical stimuli. — A great variety of chemical substances will excite the contraction of muscles, some substances being more potent in irrita- ting the muscle itself, and other substances having more effect upon the nerve. Of the former may be mentioned, dilute acids, salts of certain metals, e.g., zinc, copper and iron; to the latter belong strong glycerin, strong acids, ammonia and bile salts in strong solution. Electrical stimuli. — These are most frequently used as muscle stimuli, as the strength of the stimulus may be more conveniently regulated. 26 HAND-BOOK OF PHYSIOLOGY. The kind of current employed may be, for the sake of clearness, treated of under two heads: — (1) The continuous current, and (2) The induced current. (1) The continuous current is supplied by a battery such, as that of Daniell, by which an electrical current which varies but little in intensity is obtained. The battery (Fig. 277) consists of a positive plate of well-amalgamated zinc immersed in a porous cell, containing dilute sul- phuric acid; and this cell is again contained within a larger copper vessel (forming the negative plate), containing besides a saturated solution of copper sulphate. The electrical current is made continuous by the use of the two fluids in the following manner. The action of the dilute sulphuric acid upon the zinc plate partly dissolves it and liberates hydrogen, and this gas passes through the porous vessel and decomposes the copper sul- phate into copper and sulphuric acid. The former is deposited upon the FIQ. 277.— Diagram of a DanielTs Battery. (After Balfour Stewart.) copper plate and the latter passes through the porous vessel to renew the sulphuric acid which is being used up. The copper sulphate solution is renewed by spare crystals of the salt which are kept on a little shelf attached to the copper plate and slightly below the level of the solution in the vessel. The current of electricity supplied by this battery will continue without variation for a considerable time. Other continuous- current batteries such as Grove's may be used in place of Daniell's. The way in which the apparatus is arranged is to attach wires to the copper and zinc plates and to bring them to a key, which is a little apparatus for connecting the wires of a battery. One often employed is Du Bois Keymond's (Fig. 280, D); it consists of two pieces of brass about an inch long, in each of which are two holes for wires and binding screws to fix them tightly; these pieces of brass are fixed upon a vulcanite plate, to the under surface of which is a screw clamp by which it can be secured to the table. The interval between the pieces of brass can be bridged over by means of a third thinner piece of similar metal fixed by a screw to one of the brass pieces and capable of movement by a handle at right angles, so as to touch the other piece of brass. If the wires from the CAUSES AND PHENOMENA OF MOTION. 27 battery are brought to the inner binding screws, and the bridge be brought to connect them, the current passes across it and back to the battery. Wires are connected with the outer binding screws, and the other ends are approximated for about two inches, but, being covered except at their points, are insulated, the uncovered points are about an eighth of an inch apart. These wires are the electrodes, and the electrical stimulus is ap- plied to the muscle, if they are placed behind its nerve and the connection between the two brass plates of the key be broken by depressing the handle of the bridge and so raising the connecting piece of metal. The key is then said to be opened. (2) The induced current. — An induced current is developed by means of an apparatus called an induction coil, and the one employed for physiological purposes is mostly the one (Fig. 278). Wires from a battery are brought to the two binding screws d' and d, FIG. 278.— Du Bois Reymond's induction coil. a key intervening. These binding screws are the ends of a coil of coarse covered wire c, called the primary coil. The ends of a coil of finer cov- ered wire g, are attached to two binding screws to the left of the figure, one only of which is visible. This is the secondary coil and is capable of being moved nearer to c along a grooved and graduated scale. To the binding screws to the left of g, the wires of electrodes used to stimulate the muscle are attached. If the key in the circuit of wires from the bat- tery to the primary coil (primary circuit) be closed, the current from the battery passes through the primary coil and across the key to the battery and continues to pass as long as the key continues closed. At the moment of closure of the key, at the exact instant of the completion of the primary circuit, an instantaneous current of electricity is induced in the secondary coil, g, if it be sufficiently near, and the nearer it is to c, the stronger is the current. The induced current is only momentary in duration and 28 HAND-BOOK OF PHYSIOLOGY. does not continue during the whole of the period when the primary cir- cuit is complete. When, however, the primary current is broken by opening the key, a second, also momentary, current is induced in g. The former induced current is called the making, and the latter the breaking shock; the former is in the opposite to, and the latter in the same direc- tion, as the primary current. The induction coil may be used to produce a rapid series of shocks by means of another and accessory part of the apparatus at the right of the figure. If the wires from a battery are connected with the two pillars by the binding screws, one below c, and the other, «, the course of the cur- rent is indicated in Fig. 279, the direction being indicated by the arrows. FIG. 279.— Diagram of the course of the current in the magnetic interrupter of Du Bois ReymoncTs induction coil. (Helmholz's modification.) The current passes up the pillar from e and along the spring, if the end of d' be close to the spring, and the current passes to the primary coil c, and to wires covering two upright pillars of soft iron, from them to the pillar «, and out by the wires to the battery; in passing along the wire, 1), the soft iron is converted into a magnet and so attracts the hammer,/, of the spring, breaks the connection of the spring with d' and so cuts off the current from the primary coil and also from the electro-magnet. As the pillars, #, are no longer magnetized the spring is released and the current passes in the first direction, and is in like manner interrupted. At each make and break of the primary current, currents corresponding are in- duced in the secondary coil. These currents are, as before, in an opposite direction, but are not equal in intensity, the break shock being greater. In order that the shocks should be about equal at the make and break, a wire (Fig. 279, e') connects e and d', and the screw d' is raised out of reach of the spring, and d is raised (as in Fig. 279), so that part of the current always passes through the primary coil and electro-magnet. When the spring touches d, the current in Z» is diminished, but never entirely with- drawn, and the primary current is altered in intensity at each contact of the spring with d, but never entirely broken. CAUSES AND PHENOMENA OF MOTION. 29 BECORD OF MUSCULAR CONTRACTION UNDER STIMULI. The muscles of the frog are those which can most conveniently be experimented with and their contractions recorded. The frog is pithed, that is to say its central nervous system is entirely destroyed by the inser- tion of a stout needle into the spinal cord and the parts above it. One of its lower extremities is used in the following manner. The large trunk of the sciatic nerve is dissected out at the back of the thigh, and a pair of electrodes is inserted behind it. The tendo-achillis is divided from its FIG. 280. — Arrangement of the apparatus necessary for recording muscle contractions with a revolving cylinder carrying smoked paper. A, revolving cylinder; B, the frog arranged upon a cork- covered board which is capable of being raised or lowered on the upright, which also can be moved along a solid triangular bar of metal attached to the base of the recording apparatus — the tendon of the gastrocnemius is attached to the writing lever properly weighted by a ligature. The electrodes from the secondary coil pass to the apparatus— being, for the sake of convenience, first of all brought to a key. D (Du Bois Reymond's): C, the induction coil; F, " one); E, the key (Morse's) in the primary circuit. the battery (in this figure a bichromate attachment to the os calcis, and a ligature is tightly tied round it. This tendon is part of the broad muscle of the thigh (gastrocnemius) which arises from above the condyles of the femur. The femur is now fixed to a board covered with cork, and the ligature attached to the tendon is tied to the upright of a piece of metal bent at right angles (Fig. 280, B), which is capable of movement about a pivot at its knee, the horizontal portion carrying a writing lever (myograph). When the muscle con- tracts the lever is raised. It is necessary to attach a small weight to the 30 HAND-BOOK OF PHYSIOLOGY. lever. In this arrangement the muscle is in situ, and the nerve disturbed from its relations as little as possible. The muscle may, however, be detached from the body with the lower end of the femur from which it arises, and the nerve going to it may be taken away with it. The femur is divided at about the lower third. The bone is held in a firm clamp, the nerve is placed upon two electrodes con- nected with an induction apparatus, and the lower end of the muscle is connected by means of a ligature attached to its tendon with a lever which can write on a recording apparatus. To prevent evaporation this so-called nerve-muscle preparation is placed under a glass shade, the air in which is kept moist by means of blotting paper saturated with saline solution. EFFECT OF A SINGLE INDUCTION SHOCK. Taking the nerve-muscle preparation in either of these ways, on closing or opening the key in the primary circuit we obtain and can record a contraction, and if we use the clockwork apparatus revolving rapidly, a curve is traced such as is shown in (Fig. 281). Another way of recording the contraction is by the pendulum myo- graph (Fig. 282). Here the movement of the pendulum along a certain FIG. 281.— Muscle-curve obtained by the pendulum myograph. s, indicates the exact instant of the induction shock; c, commencement; and m x, the maximum elevation of lever; t, the line of a vibrating tuning-fork. (M. Foster.) arc is substituted for the clockwork movement of the other apparatus. The pendulum carries a smoked glass plate upon which the writing lever of a. myograph is made to mark. The opening or breaking shock is sent into the nerve-muscle preparation by the pendulum in its swing opening a key (Fig. 282, C. ) in the primary circuit. Single Muscle Contraction.— The tracings obtained in a manner above described and seen in Fig. 281, may be thus explained. The upper line (m) represents the curve traced by the end of the lever CAUSES AND PHENOMENA OF MOTION. 31 after stimulation of the muscle by a single induction-shock: the middle line (/) is that described by the marking-lever, and indicates by a sudden drop the 'exact instant at which the induction-shock was given. The pendulum swings along the arc to D on the left of figure, and is caught by its spring. lower wavy line (t) is traced by a vibrating tuning-fork, and serves to measure precisely the intervals of time occupied in each part of the con- traction. FIG. 283. — Tracing of a double muscle-curve. 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), a second induction -shock was thrown in, at such a 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. (M. Foster.) It will be observed that after the stimulus has been applied, as indi- cated by the vertical line s, there is an interval before the contraction 32 HAND-BOOK OF PHYSIOLOGY. commences, as indicated by the line c. This interval, termed the "latent period" (Helmholtz), when measured by the number of vibrations of the tuning-fork between the lines s and c, is found to be about -^fa sec. The contraction progresses rapidly at first and afterward more slowly to the maximum (the point in the curve through which the line mx is drawn) which takes yf^ sec., and then the muscle elongates again las indicated by the descending curve, at first rapidly, afterward more slowly, till it attains its original length at the point indicated by the line c', occupying T|T sec. The muscle curve obtained from the heart resembles that of unstriped muscles in the long duration of the effect of stimulation; the descending curve is very much prolonged. The greater part of the latent period is taken up by changes in the muscle itself, the rest being occupied in the propagation of the shock along the nerve (M. Foster). Tetanus. — If instead of a single induction-shock through the prepa- ration we pass two, one immediately after the other, when the point of FIG. 284.— Curve of tetanus, obtained from the gastrocnemius of a frog, where the shocks were sent in from an induction coil, about sixteen times a second, by the interruption of the primary cur- rent by means of a vibrating spring, which dipped into a cnp of mercury, and broke the primary current at each vibration. stimulation of the second one corresponds to the maximum of the first, a second curve (Fig. 283) will occur which will commence at the highest point of the first and will rise as high, so that the sum of the height of FIG. 285.— Curve of tetanus, from a series of very rapid shocks from a magnetic interrupter. the two exactly equals twice the height of the first. If a third and a fourth shock be passed, a similar effect will ensue, and curves one above the other CAUSES AND PHENOMENA OF MOTION. 33 will be traced, the third being slightly less than the second, and the fourth than the third. If the shocks be repeated at short intervals, how- ever, the lever after a time ceases to rise any further, and the contraction which has reached its maximum is maintained (Fig. 285), and the lever marks a straight line on the recording cylinder. This condition is called tetanus of muscle. The condition of "an ordinary tetanic muscular movement is essentially a vibratory movement, the apparently rigid and firm muscular mass is really the subject of a whole series of vibrations, a se- ries namely of simple spasms; it will be readily understood why a tetanized muscle, like all other vibrating bodies, gives out a sound" (M. Foster). If the stimuli are not quite so rapidly sent in the line of maximum contraction it becomes somewhat wavy, indicating a slight tendency of the muscles to relax during the intervals between the stimuli (Fig. 284). Muscular Work. — We have seen (p. 124, Vol. I. ) that work is esti- mated by multiplying the weight raised, by the height through which it has been lifted. It has been found that in order to obtain the maximum of work, a muscle must be moderately loaded: if the weight be increased beyond a certain point, the muscle becomes strained and raises the weight through so small a distance that less work is accomplished. If the load is still further increased the muscle is completely overtaxed, cannot raise the weight, and consequently does no work at all. Practical illustrations of these facts must be familiar to every one. The power of a muscle is usually measured by the maximum weight which it will support without stretching. In man this is readily deter- mined by weighting the body to such an extent that it can no longer be raised on tiptoe: thus the power of the calf -muscles is determined (Weber). The power of a muscle thus estimated depends of course upon its cross- section. The power of a human muscle is from two to three times as great as a frog's muscle of the same sectional area. Fatigue of Muscle. — A muscle becomes rapidly exhausted from repeated stimulation, and the more rapidly, the more quickly the induc- tion-shocks succeed each other. This is indicated by the diminished height of contraction in the ac- companying diagrams (Fig. 286). It will be seen that the vertical lines,, which indicate the extent of the muscular contraction, decrease in length from left to right. The line A B drawn along the tops of these lines is; termed the "fatigue curve." It is usually a straight line. In the first diagram the effects of a short rest are shown : there is a pause of three minutes, and when the muscle is again stimulated it con- tracts up to A', but the recovery is only temporary, and i\& fatigue curve? after a few more contractions, becomes continuous with that before the: rest. In the second diagram is represented the effect of a stream of oxygenated VOL. II.— 3. 34 HAND-BOOK OF PHYSIOLOGY. blood. Here we have a sudden restoration of energy: the muscle in this case makes an entirely fresh start from A, and the new fatigue curve is parallel to, and never coincides with the old one. A fatigued muscle has a much longer "latent period" than a fresh one. The slowness with which muscles respond to the will when fatigued must be familiar to every one. In a muscle which is exhausted, stimulation only causes a contraction producing a local bulging near the point irritated. A similar effect may FIG. 286.— Fatigue muscle-curves. (Ray Lankester.) be produced in a fresh muscle by a sharp blow, as in striking the biceps smartly with the edge of the hand, when a hard muscular swelling is in- stantly formed. Accompaniments of Muscular Contraction.— (1.) Heat is de- veloped in the contraction of muscles. Becquerel and Breschet found, with the ther mo-multiplier, about 1° Fahr. of heat produced by each forci- ble contraction of a man's biceps; and when the actions were long con- tinued, the temperature of the muscle increased 2°. This estimate is probably high, as in the frog's muscle a considerable contraction has been found to produce an elevation of temperature equal on an average to less than \° 0. It is not known whether this development of heat is due to chemical changes ensuing in the muscle, or to the friction of its fibres vigorously acting: in either case, we may refer to it a part of the heat developed in active exercise (p. 310, Vol. I.). (2.) Sound is said to be produced when muscles contract forcibly, as mentioned above. Wollaston showed that this sound might be easily heard by placing the tip of the little finger in the ear, and then making- some muscles contract, as those of the ball of the thumb, whose sound may be conducted to the ear through the substance of the hand and finger. CAUSES AND PHENOMENA OF MOTION. 35 A low shaking or rumbling sound is heard, the height and loudness of the note being in direct proportion to the force and quickness of the muscular action, and to the number of fibres that act together, or, as it were, in time. (3.) Changes in shape. — The mode of contraction in the transversely striated muscular tissue has been much disputed. The most probable .account is, that the contraction is effected by an approximation of the constituent parts of the fibrils, which, at the instant of contraction, without any alteration in their general direction, become closer, flatter, and wider; a condition which is rendered evident by the approximation of the trans- verse striae seen on the surface of the fasciculus, and by its increased breadth and thickness. The appearance of the zigzag lines into which it was supposed the fibres are thrown in contraction, is due to the relaxation of a fibre which has been recently contracted, and is not at once stretched again by some antagonist fibre, or whose . extremities are kept close to- gether by the contractions of other fibres. The contraction is therefore a simple, and, according to Ed. Weber, a uniform, simultaneous, and steady shortening of each fibre and its contents. What each fibril or fibre loses in length, it gains in thickness: the contraction is a change of form, not of size; it is, therefore, not attended with any diminution in bulk, from condensation of the tissue. This has been proved for entire muscles, by making a mass of muscle, or many fibres together, contract in a vessel full of water, with which a fine, perpendicular, graduated tube commu- nicates. Any diminution of the bulk of the contracting muscle would he attended by a fall of fluid in the tube; but when the experiment is carefully performed, the level of the water in the tube remains the same, whether the muscle be contracted or not. In thus shortening, muscles appear to swell up, becoming rounder, more prominent, harder, and apparently tougher. But this hardness of muscle in the state of contraction, is not due to increased firmness or condensa- tion of the muscular tissue, but to the increased tension to which the fibres, as well as their tendons and other tissues, are subjected from the resistance ordinarily opposed to their contraction. When no resistance is offered, as when a muscle is cut off from its tendon, not only is no hardness perceived during contraction, but the muscular tissue is even softer, more extensile, and less elastic than in its ordinary uncontracted state. (4.) Chemical changes. — (a) The reaction of the muscle which is nor- mally alkaline or neutral becomes decidedly acid, from the development of sarcolactic acid, (b) The muscle gives out carbonic acid gas and takes up oxygen, the amount of the carbonic acid given out not appearing to be entirely dependent upon the oxygen taken in, and so doubtless in part arising upon some other source. (c) Certain imperfectly understood chemical changes occur, in all probability connected with (a) and (b). 36 HAND-BOOK OF PHYSIOLOGY. Glycogen is diminished, and muscle sugar (inosite) appears; the extrac- tives are increased. (5.) Electrical changes. — When a muscle contracts the natural muscle current or currents of rest undergo a distinct diminution, which is due to the appearance in the actively contracting muscle of currents in an op- posite direction to those existing in the muscle at rest. This causes a, temporary deflection of the needle of a galvanometer in a direction oppo- site to the original current, and is called by some the negative variation of the muscle current, and by others a current of action. Conditions of Contraction. — (a) The irritability of muscle is great- est at a certain mean temperature; (b) after a number of contractions a muscle gradually becomes exhausted; (c) the activity of muscles after a FIG. 287.— Muscle-curves from the gastrocnemius of a frog, illustrating effects of alterations in temperature. time disappears altogether when they are removed from the body or the arteries are tied; (d) oxygen is used up in muscular contraction, but a muscle will act for a time in vacuo or a gas which contains no oxygen: in this case it is of course using up the oxygen already in store (Hermann). Response to Stimuli. — The two kinds of fibres, the striped and unstriped, have characteristic differences in the mode in which they act on the application of the same stimulus; differences which may be ascribed in great part to their respective differences of structure, but to some degree, possibly, to their respective modes of connection with the nervous system. When irritation is applied directly to a muscle with striated fibres, or to the motor nerve supplying it, contraction of the part irri- tated, and of that only, ensues; and this contraction is instantaneous, and ceases on the instant of withdrawing the irritation. But when any part with unstriped muscular fibres, e.g., the intestines or bladder, is irritated, the subsequent contraction ensues more slowly, extends beyond the part irritated, and, with alternating relaxation, continues for some time after the withdrawal of the irritation. The difference in the modes of con- traction of the two kinds of muscular fibres may be particularly illus- trated by the effects of the electro-magnetic stimulus. The rapidly suc- ceeding shocks given by this means to the nerves of muscles excite in all the transversely-striated muscles a fixed state of tetanic contraction as previously described, which lasts as long as the stimulus is continued, and on its withdrawal instantly ceases; but in the muscles with smooth fibres CAUSES AND PHENOMENA OF MOTION. 37 they excite, if any movement, only one that ensues slowly, is compara- tively slight, alternates with rest, and continues for a time after the stimulus is withdrawn. In their mode of responding to these stimuli, all the skeletal muscles, or those with transverse striae, are alike; but among those with plain or unstriped fibres there are many differences, — a fact which tends to con- firm the opinion that their peculiarity depends as well on their connection with nerves and ganglia as on their own properties. The ureters and gall-bladder are the parts least excited by stimuli: they do not act at all till the stimulus has been long applied, and then contract feebly, and to a small extent. The contractions of the caecum and stomach are quicker and wider-spread: still quicker those of the iris, and of the urinary blad- der if it be not too full. The actions of the small and large intestines, of the vas deferens, and pregnant uterus, are yet more" vivid, more regular, and more sustained; and they require no more stimulus than that of the air to excite them. The heart, on account, doubtless, of its striated muscle, is the quickest and most vigorous of all the muscles of organic life in contracting upon irritation, and appears in this, as in nearly all other respects, to be the connecting member of the two classes of muscles. All the muscles retain their property of contracting under the influence of stimuli applied to them or to their nerves for some time after death, the period being longer in cold-blooded than in warm-blooded Verte- brata, and shorter in Birds than in Mammalia. It would seem as if the more active the respiratory process in the living animal, the shorter is the time of duration of the irritability in the muscles after death; and this is confirmed by the comparison of different species in the same order of Yertebrata. But the period during which this irritability lasts, is not the same in all persons, nor in all the muscles of the same persons. In a man it ceases, according to Nysten, in the following order: — first in the left ventricle, then in the intestines and stomach, the urinary bladder, right ventricle, oesophagus, iris; then in the voluntary muscles of the trunk, lower and upper extremities; lastly in the right and left auricle of the heart. III. EIGOE MORTIS. After the muscles of the dead body have lost their irritability or capa- bility of being excited to contraction by the application of a stimulus, they spontaneously pass into a state of contraction, apparently identical with that which ensues during life. It affects all the muscles of the body; and, where external circumstances do not prevent it, commonly fixes the limbs in that which is their natural posture of equilibrium or rest. Hence, and from the simultaneous contraction of all the muscles of the trunk, is produced a general stiffening of the body, constituting the rigor mortis or post-mortem rigidity. 38 HAND-BOOK OF PHYSIOLOGY. When this condition has set in, the muscle becomes acid in reaction, (due to sarco-lactic acid), and gives off carbonic acid in great excess. Its. volume is slightly diminished: the muscular fibres become shortened and opaque, and their substance has set firm. It comes on much more rapidly after muscular activity, and is hastened by warmth. It may be brought on, in muscles exposed for experiment, by the action of distilled water and many acids, also by freezing and thawing again. Cause. — The immediate cause of rigor seems coagulation of the muscle plasma (Briicke, Kuhne, Norris). We may distinguish three main stages. — (1.) Gradual coagulation. (2.) Contraction of coagulated muscle-clot (myosin) and squeezing out of muscle-serum. (3.) Putrefac- tion. After the first stage, restoration is possible through the circulation of arterial blood through the muscles, and even when the second stage has set in, vitality may be restored by dissolving the coagulum of the muscle in salt solution, and passing arterial blood through its vessels. In the third stage recovery is impossible. Order of Occurrence. — The muscles are not affected simultaneously by post-mortem contraction. It affects the neck and lower jaw first; next, the upper extremities, extending from above downward; and lastly, reaches the lower limbs; in some rare instances only, it affects the lower extremities before, or simultaneously with, the upper extremities. It usually ceases in the order in which it began; first at the head, then in the upper extremities, and lastly in the lower extremities. It never com- mences earlier than ten minutes, and never later than seven hours, after death; and its duration is greater in proportion to the lateness of its ac- cession. Heat is developed during the passage of a muscular fibre into- the condition of rigor mortis. Since rigidity does not ensue until muscles have lost the capacity of being excited by external stimuli, it follows that all circumstances which cause a speedy exhaustion of muscular irritability, induce an early occur- rence of the rigidity, while conditions by which the disappearance of the irritability is delayed, are succeeded by a tardy onset of this rigidity. Hence its speedy, occurrence,, and equally speedy departure, in the bodies of persons exhausted by chronic diseases; and its tardy, onset and long- continuance after sudden death from acute diseases. In some cases of sudden death from lightning, violent injuries, or paroxysms of passion, rigor mortis has been said not to occur at all; but this is not always- the case. It may, indeed, be doubted whether there is really a complete absence of the post-mortem rigidity in any such cases; for the experi- ments of Brown-Sequard make it probable that the rigidity may super- vene immediately after death, and then pass away with such rapidity as- to be scarcely observable. Experiments. — Brown-Sequard took five rabbits, and killed them by CAUSES AND PHENOMENA OF MOTION. 39 removing their hearts. In the first, rigidity came on in 10 hours, and lasted 192 hours; in the second, which was feebly electrified, it com- menced in 7 hours, and lasted 144; in the third, which was more strongly electrified, it came on' in two, and lasted 72 hours; in the fourth, which was still more strongly electrified, it came on in one hour, and lasted 20; while, in the last rabbit, which was submitted to a powerful electro -gal- vanic current, the rigidity ensued in seven minutes after death, and passed away in 25 minutes. From this it appears that the more powerful the electric current, the sooner does the rigidity ensue, and the shorter is its duration; and as the lightning shock is so much more powerful than any ordinary electric discharge, the rigidity may ensue so early after death, and pass away so rapidly as to escape detection. The influence exercised upon the onset and duration of post-mortem rigidity by causes which exhaust the irritability of the muscles, was well illustrated in further experiments by the same physiologist, in which he found that the rigor mortis ensued far more rapidly, and lasted for a shorter period in those muscles which had been powerfully electrified just before death than those which had not been thus acted upon. The occurrence of rigor mortis is not prevented by the previous exist- ence of paralysis in a part, provided the paralysis has not been attended with very imperfect nutrition of the muscular tissue. The rigidity affects the involuntary as well as the voluntary muscles, whether they be constructed of striped or unstriped fibres. The rigidity of involuntary muscles with striped fibres is shjown in the contraction of the heart after death. The contraction of the muscles with unstriped fibres is shown by an experiment of Valentin, who found that if a gradu- ated tube connected with a portion of intestine taken from a recently- killed animal, be filled with water, and tied at the opposite end, the water will in a few hours rise to a considerable height in the tube, owing to the contraction of the intestinal walls. It is still better shown in the arteries, of which all that have muscular coats contract after death, and thus pre- sent the roundness and cord-like feel of the arteries of a limb lately removed, or tho?e of a body recently dead. Subsequently they relax, as do all the other muscles, and feel -lax and flabby, and lie as if flattened, and with their walls nearly in contact. ACTIONS OF THE VOLUNTARY MUSCLES. • The greater part of the voluntary muscles of the body act as sources of power for removing levers, — the latter consisting of the various bones to which the muscles are attached. Examples of the three orders of levers in the Human Body. — All levers / have been divided into three kinds, according to the relative position of ' • the power, the weight to be removed, and the axis of motion or fulcrum. In a lever of the first kind the power is at one extremity of the lever, the weight at the other, and the fulcrum between the two. If the initial 40 HAND-BOOK OF PHYSIOLOGY. letters Only of the power, iveiglit, and fulcrum be used, the arrangement will stand thus: — r.F.W. A poker, as ordinarily used, or the bar in Pig. 288, may be cited as an example of this variety of lever; while, as an instance in which the bones of the human skeleton are used as a lever of the same kind, may be mentioned the act of raising the body from the stooping posture by means of the hamstring muscles attached to the tuberosity of the ischium (Fig. 288). FIG. 288. In a lever of the second kind, the arrangement is thus: — P.W.F.; and this leverage is employed in the act of raising the handles of a wheel- barrow, or in stretching an elastic band as in Fig. 289. In the human body the act of opening the mouth by depressing the lower jaw is an example of the same kind, — the tension of the muscles which close the jaw representing the weight (Fig. 289). In a lever of the third kind the arrangement is — F.P.W., and the act of raising a pole, as in Fig. 290, is an example. In the human body FIG. 289. there are numerous examples of the employment of this kind of leverage. The act of bending the fore-arm may be mentioned as an instance (Fig. 290). The act of biting is another example. At the ankle we have examples of all three kinds of lever. 1st kind — Extending the foot. 3rd kind — Flexing the foot. In both these cases the foot represents the weight: the ankle joint the fulcrum, the power being the calf muscles in the first case, and the tibialis anticus in the CAUSES AND PHENOMENA OF MOTION. 41 second case. 2nd kind — When the body is raised on tip-toe. Here the ground is the fulcrum, the weight of the body acting at the ankle joint the weight, and the calf muscles the power. In the human body, levers are most frequently used at a disadvantage as regards power, the latter being sacrificed for the sake of a greater range of motion. Thus in the diagrams of the first and third kinds it is evi- FIG. 290. dent that the power is so close to the fulcrum, that great force must be exercised in order to produce motion. It is also evident, however, from the same diagrams, that by the closeness of the power to the fulcrum a great range of movement can be obtained by means of a comparatively slight shortening of the muscular fibres. The greater number of the more important muscular actions of the human body — those, namely, which are arranged harmoniously so as to subserve some definite purpose or other in the animal economy — are described in various parts of this work, in the sections which treat of the physiology of the processes by which these muscular actions are resisted or carried out. There are, however, one or two very important and some- what complicated muscular acts which may be best described in this place. Walking. — In the act of walking, almost every voluntary muscle in the body is brought into play, either directly for purposes of progression, or indirectly for the proper balancing of the head and trunk. The muscles of the arms are least concerned; but even these are for the most part instinctively in action also to some extent. Among the chief muscles engaged directly in the act of walking are those of the calf, which, by pulling up the heel, pull up also the astraga- lus, and with it, of course, the whole body, the weight of which is trans- mitted through the tibia to this bone (Fig. 291). When starting to walk, say with the left leg, this raising of the body is not left entirely to the muscles of the left calf, but the trunk is thrown forward in such a way that it would fall prostrate were it not that the right foot is brought for- ward and planted on the ground to support it. Thus the muscles of the left calf are assisted in their action by those muscles on the front of the trunk and legs which, by their contraction, pull the body forward; and, of course, if the trunk form a slanting line, with the inclination forward, it is plain that when the heel is raised by the calf-muscles, the whole body will be raised, and pushed obliquely forward and upward. The 42 HAND-BOOK OF PHYSIOLOGY. successive acts in taking the first step in walking are represented in Fig. 291, 1, 2, 3. Now it is evident that by the time the body has assumed the position No. 3, it is time that the right leg should be brought forward to support it and prevent it from falling prostrate. This advance of the other leg (in this case the right) is effected partly by its mechanically swinging for- ward, pendulum-wise, and partly by muscular action; the muscles used being, — 1st, those on the front of the thigh, which bend the thigh for- ward on the pelvis, especially the rectus femoris, with the psoas and the iliacus; %ndly, the hamstring muscles, which slightly bend the leg on the thigh; and Srdly, the muscles on the front of the leg, which raise the front of the foot and toes, and so prevent the latter in swinging forward from hitching in the ground. The second part of the act of walking, which has been just described, is shown in the diagram (4, Fig. 291). When the right foot has reached the ground the action of the left leg has not ceased. The calf -muscles of the latter continue to act, and by pulling up the heel, throw the body still more forward over the right leg, now bearing nearly the whole weight, until it is time that in its turn the left leg should swing forward, and the left foot be planted on the ground to prevent the body from falling prostrate. As at first, while the calf -muscles of one leg and foot are preparing, so to speak, to push the body forward and upward from behind by raising the heel, the muscles on the front of the trunk and of the same leg (and of the other leg, except when it is swinging forward) are helping the act by pulling the legs and trunk, so as to make them incline forward, the rotation in the inclining for- ward being effected mainly at the ankle joint. Two main kinds of lever- age are, therefore, employed in the act of walking, and if this idea be firmly grasped, the detail will be understood with comparative ease. One kind of leverage employed in walking is essentially the same with that employed in pulling forward the pole, as in Fig. 290. And the other, less exactly, is that employed in raising the handles of a wheelbarrow. Now, supposing the lower end of the pole to be placed in the barrow, we should have a very rough and inelegant, but not altogether bad repre- sentation of the two main levers employed in the act of walking. The body is pulled forward by the muscles in front, much in the same way that the pole might be by the force applied at p (Fig. 290), while the raising of the heel and pushing forward of the trunk by the calf -muscles is roughly represented on raising the handles of the barrow. The manner in which these actions are performed alternately by each leg, so that one after the other is swung forward to support the trunk, which is at the same time pushed and pulled forward by the muscles of the other, may be gathered from the previous description. CAUSES AND PHENOMENA OF MOTION. 43 There is one more thing to be noticed especially in the act of walking. Inasmuch as the body is being constantly supported and balanced on each leg alternately, and therefore on only one at the same moment, it is evi- dent that there must be some provision made for throwing the centre of gravity over the line of support formed by the bones of each leg, as, in its turn, it supports the weight of the body. This may be done in various ways, and the manner in which it is effected is one element in the differ- ences which exist in the walking of different people. Thus it may be done by an instinctive slight rotation of the pelvis on the head of each femur in turn, in such a manner that the centre of gravity of the body shall fall over the foot of this side. Thus when the body is pushed on- ward and upward by the raising, say, of the right heel, as in Fig. 291, 3, the pelvis is instinctively by various muscles, made to rotate on the head of the left femur at the acetabulum, to the left side, so that the weight may fall over the line of support formed by the left leg at the time that the right leg is swinging forward, and leaving all the work of support to fall on its fellow. Such a "rocking" movement of the trunk and pelvis, however, is accompanied by a movement of the whole trunk and leg over the foot which is being planted on the ground (Fig. 292)-, the action FIG. 292. being accompanied with a compensatory outward movement at the hip, more easily appreciated by looking at the figure (in which this movement is shown exaggerated) than described. Thus the body in walking is continually rising and swaying alternately from one side to the other, as its centre of gravity has to be brought alter- nately over one or other leg; and the curvatures of the spine are altered in correspondence with the varying position of the weight which it has to support. The extent to which the body is raised or swayed differs much in different people. In walking, one foot or the other is always on the ground. The act of leaping or jumping, consists in so sudden* a raising of the heels by the sharp and strong contraction of the calf-muscles, that the body is jerked 44 HAND-BOOK OF PHYSIOLOGY. off the ground. At the same time the effect is much increased by first bending the thighs on the pelvis, and the legs on the thighs, and then suddenly straightening out the angles thus formed. The share which this action has in producing the effect may be easily known by attempt- ing to leap in the upright posture, with the legs quite straight. Running is performed by a series of rapid low jumps with each leg alternately; so that, during each complete muscular act concerned, there is a moment when both feet are off the ground. In all these cases, however, the description of the manner in which any given effect is produced, can give but a very imperfect idea of the in- finite number of combined and harmoniously arranged muscular contrac- tions which are necessary for even the simplest acts of locomotion. Actions of the Involuntary Muscles.— The involuntary muscles are for the most part not attached to bones arranged to act as levers, but enter into the formation of such hollow parts as require a diminution of their calibre by muscular action, under particular circumstances. Ex- amples of this action are to be found in the intestines, urinary bladder, heart and blood-vessels, gall-bladder, gland-ducts, etc. The difference in the manner of contraction of the striated and non- striated fibres has been already referred to (p. 36, Vol. II.); and the pecu- liar vermicular or peristaltic action of the latter fibres has been described at p. 36, Vol. II. SOURCE OF MUSCULAR ACTION". It was formerly supposed that each act of contraction on the part of a muscle was accompanied by a correlative waste or destruction of its own substance; and that the quantity of the nitrogenous excreta, especially of urea, presumably the expression of this waste, was in exact proportion to the amount of muscular work performed. It has been found, however, both that the theory itself is erroneous, and that the supposed facts on which it was founded do not exist. It is true that in the action of muscles, as of all other parts, there is a certain destruction of tissue, or, in other words, a certain "wear and tear," which may be represented by a slight increase in the quantity of urea excreted: but it is not the correlative expression or only source of the power manifested. The increase in the amount of urea which is excreted after muscular exertion is by no means ^o great as was formerly supposed; indeed, it is very slight. And as there is no reason to believ ethat the waste of muscle-substance can be expressed, with unimportant exceptions, in any other way than by an increased excretion of urea, it is evident that we must look elsewhere than in destruction of muscle, for the source of muscular action. For, it need scarcely be said, all force manifested in the living body must be the correlative expression of force previously latent in the food eaten or the tissue formed; and evidences of force expended in CAUSES AND PHENOMENA OF MOTION. 45 the body must be found in the excreta. If, therefore, the nitrogenous excreta, represented chiefly by urea, are not in sufficient quantity to account for the work done, we must look to the non-nitrogenous excreta as carbonic acid and water, which, presumably, cannot be the expression of wasted muscle- substance. The quantity of these non-nitrogenous excreta is undoubtedly increased by active muscular efforts, and to a considerable extent; and whatever may be the source of the water, the carbonic acid, at least, is the result of chemical action in the system, and especially of the combustion of non- nitrogenous food, although, doubtless, of nitrogenous food also. We are, therefore, driven to the conclusion, — that the substance of muscles is not wasted in proportion to the work they perform; and that the non-nitrog- enous as well as the nitrogenous foods may, in their combustion, afford the requisite conditions for muscular action. The urgent necessity for nitrogenous food, especially after exercise, is probably due more to the need of nutrition by the exhausted muscles and other tissues for which, of course, nitrogen is essential, than to such food being superior to non- nitrogenous substances as a source of muscular power. The electrical condition of Nerves is so closely connected with the phenomena of muscular contraction, that it will be convenient to consider it in the present chapter. Electrical currents in Nerves. — If a piece of nerve be removed from the body and subjected to examination in a way similar to that adopted in the case of muscle which has been described (p. 22, Vol. II.), electrical cur- rents are found to exist which correspond exactly to the natural muscle currents, and which are called natural nerve currents or currents of rest, according as one or other theory of their existence be adopted, as in the case with muscle. One point (corresponding to the equator) on the sur- face being positive to all other points nearer to the cut ends, and the greatest deflection of the needle of the galvanometer taking place when one electrode is applied to the equator and the other to the centre of either cut end. As in the case of muscle, these nerve-currents undergo a negative variation when the nerve is stimulated, the variation being momentary and in the opposite direction to the natural currents; and are similarly known as the currents of action. The currents of action are propagated in both directions from the point of the application of the stimulus, and are of momentary duration. Rheoscopic Frog. — The negative variation of the nerve current may be demonstrated by means of the following experiment.— The new current produced by stimulating the nerve of one nerve -muscle prepara- tion may be used to stimulate the nerve of a second nerve-muscle prepa- ration. The fore-leg of a frog with the nerve going to the gastrocnemius cut long is placed upon a glass plate, and arranged in such a way that its nerve touches in two places the sciatic nerve, exposed but preserved in 46 HAND-BOOK OF PHYSIOLOGY. situ in the thigh of the opposite leg. The electrodes from an induction coil are placed behind the sciatic nerve of the second preparation, high up. On stimulating the nerve with a single induction shock, the muscles not only of the same leg are found to undergo a twitch, but also those of the first preparation, although this is not near the electrodes, and so the stimulation cannot be due to an escape of the current into the first nerve. This experiment is known under the name of the rheoscopic frog. Nerve-stimuli. — Nerve-fibres require to be stimulated before they can manifest any of their properties, since they have no power of them- selves of generating force or of originating impulses. The stimuli which are capable of exciting nerves to action, are, as in the case of muscle, very diverse. They are of very similar nature in each case. The mechanical, chemical, thermal, and electric stimuli which may be used in the one case are also, with certain differences in the methods employed, efficacious in the other. The chemical stimuli are chiefly these: withdrawal of water, as by drying, strong solutions of neutral salts of potassium, sodium, etc., free inorganic acids, except phosphoric;, some organic acids; ether, chloro- form, and bile salts. The electrical stimuli employed are the induction and continuous currents concerning which the observations in reference to muscular contraction should be consulted, p. 26, et seq., Vol. II. Weaker electrical stimuli will excite nerve than will excite muscle; the nerve stimulus appears to gain strength as it descends, and a weaker stimulus applied far from the muscle will have the same effect as a somewhat stronger one applied to the nerve near the muscle. It will be only necessary here to add some account of the effect of a constant electrical current, such as that obtained from Daniell's battery, upon a nerve. This effect may be studied with the apparatus described before. A pair of electrodes are placed behind the nerve of the nerve- muscle preparation, with a Du Bois Keymond's key arranged for short circuiting the battery current, in such a way that when the key is opened the current is sent into the nerve, and when closed the current is cut off. It will be found that with a current of moderate strength there will be a contraction of the muscle both at the opening and at the closing of the key (called respectively making and breaking contractions), but that during the interval between these two events the muscle remains flaccid, provided the battery current continues of constant intensity. If the cur- rent be a very weak or a very strong one the effect is not quite the same; one or other of the contractions may be absent. Which of these con- tractions is absent depends upon another circumstance, viz., the direction of the current. The direction of the current may be ascending or de- scending; if ascending, the anode or positive pole is nearer the muscle than the kathode or negative pole, and the current to return to the bat- tery has to pass up the nerve, — if descending, the position of the electrodes is reversed. It will be necessary before considering this question further CAUSES AND PHENOMENA OF MOTION. 47 to return to the want of apparent effect of the constant current during the interval between the make and break contraction: to all appearance, indeed, no effect is produced at all, but in reality a very important change is brought about in the nerve by the passage of the current. This may be shown in two ways, first of all by the galvanometer. If a piece of nerve be taken, and if at either end an arrangement be made to test the electrical condition of the nerve by means of a pair of non-polarizable electrodes connected with a galvanometer, while to the central portion a pair of electrodes connected with a Daniell's battery be applied, it will be found that the natural nerve-currents are profoundly altered on the passage of the constant current (which is called the polarizing current) in the neighborhood. If the polarizing current be in the same direction as the latter the natural current is increased, but if in the direction oppo- site to it, the natural current is diminished. This change, produced by the continual passage of the battery-current through a portion of the nerve is to be distinguished from the negative variation of the natural cur- rent to which allusion has been already made, and which is a momentary change occurring on the sudden application of the stimulus. The con- dition produced in a nerve by the passage of a constant current is known by the name of electrotonus. The other way of showing the effect of the same polarizing current is by taking a nerve-muscle preparation and applying to the nerves a pair of electrodes from an induction coil whilst at a point further removed from the muscle, electrodes from a Daniell's battery are arranged with a key for short circuiting and an apparatus (reverser) by which the battery cur- rent may be reversed in direction. If the exact point be ascertained to which the secondary coil should be moved from the primary coil in order that a minimum contraction be obtained by the induction shock, and the secondary coil be removed slightly further from the primary, the in- duction current cannot now produce a contraction; but if the polarizing current be sent in a descending direction, that is to say, with the kathode nearest the other electrodes, the induction current, which was before in- sufficient, will prove sufficient to cause a contraction; whereby indicating that with a descending current the irritability of the nerve is increased. By means of a somewhat similar experiment it may be shown that an ascending current will diminish the irritability of a nerve. Similarly, if instead of applying the induction electrodes below the other electrodes they are applied between them, like effects are demonstrated, indicating that in the neighborhood of the kathode the irritability of the nerve is in- creased by a constant current, and in the neighborhood of the anode diminished. This increase in irritability is called katelectrotonus, and similarly the decrease is called anelectrotonus. As there is between the electrodes both an increase and a decrease of irritability on the passage of a polarizing current it must be evident that the increase must shade off 48 HAND-BOOK OF PHYSIOLOGY. into the decrease, and that there must be a neutral point where there is neither increase nor decrease of irritability. The position of this neutral point is found to vary with the intensity of the polarizing current; when the current is weak the point is nearer the anode, when strong nearer the kathode (Fig. 293). When a constant current passes into a nerve, there- fore, if a making contraction result, it may be assumed that it is due to FIG. 293.— Diagram illustrating the effects of various intensities of the polarizing currents, n, nf nerve; a, anode; fc, kathode; the curves above indicate increase, and those below decrease of irrita- bility, and when the current is small the increase^nd decrease are both small, with the neutral point near a, and so on as the current is increased hTstrength. the increased irritability produced in the neighborhood of the kathode, but the breaking contraction must be produced by a rise in irritability from a lowered state to the normal in the neighborhood of the anode. The contractions produced in the muscle of a nerve-muscle preparation by a constant current have been arranged in a table which is known as Pfliiger's Law of Contractions. It is really only a statement as to when a contraction may be expected: — DESCENDING CURRENT. ASCENDING CURRENT. Make. Break. Make. Break. Weak . . . Moderate . Strong . . Yes. Yes. Yes. No. Yes. No. Yes. Yes. No. No. Yes. Yes. The difficulty in this table is chiefly in the effect of a weak current, but the following statement will explain it. The increase of irritability at the kathode is more potent to produce a contraction than the rise of irritability from a lower to a normal condition at the anode. With weak currents the only effect is a contraction at the make of both ascending and descending currents, the descending current being more potent than the ascending (and with still weaker currents is the only one which pro- duces any effect), since the kathode is near the muscle, whereas in the case of the ascending current the stimulus has to pass through a district of diminished irritability, which may either act as an entire block, or may diminish slightly the contraction which follows. As the polarizing CAUSES AND PHENOMENA OF MOTION. 49 current becomes stronger, recovery from anelectrotonus is able to produce a contraction as well as katelectrotonus, and a contraction occurs both at the make and the break of the current. The absence of contraction with a very strong current at the break of the ascending current may be explained by supposing that the region of fall in irritability at the kathode blocks the stimulus of the rise in irritability at the anode. Thus we have seen that two circumstances influence the effect of the constant current upon a nerve, viz., the strength and direction of the current. It is also necessary that the stimulus should be applied sud- denly and not gradually, and that the irritability of the nerve be normal, and not increased or diminished. Sometimes (when the nerve is specially irritable?) instead of a simple contraction a tetanus occurs at the make or break of the constant current. This is especially liable to occur at the break of a strong ascending current which has been passing for some time into the preparation; this is called Ritter's tetanus, and may be increased by passing a current in an opposite direction or stopped by passing a current in the same direction. VOL. II. CHAPTER XVI. THE VOICE AND SPEECH. IK nearly all air-breathing vertebrate animals there are arrangements lor the production of sound, or voice, in some parts of the respiratory apparatus. In many animals, the sound admits of being variously modi- fied and altered during and after its production; and, in man, one such modification occurring in obedience to dictates of the cerebrum, is speech. MODE OF PKODUCTION or THE HUMAK VOICE. t It has been proved by observations on living subjects, by means of the laryngoscope, as well as by experiments on the larynx taken from the dead body, that the sound of the human voice is the result of the inferior laryngeal ligaments, or true vocal cords (A, cv, Fig. 298) which bound the glottis, being thrown into vibration by currents of expired air impelled over their edges. Thus, if a free opening exists in the trachea, the sound of the voice ceases, but returns if the opening is closed. An opening into the air-passages above the glottis, on the contrary, does not prevent the voice being formed. Injury of the laryngeal nerves supplying the muscles which move the vocal cords puts an end to the formation of vocal sounds; and when these nerves are divided on both sides, the loss of voice is complete. Moreover, by forcing a current of air through the larynx in the dead subject, clear vocal sounds are produced, though the epiglottis, the upper ligaments of the larynx or false vocal cords, the ventricles between them and the inferior ligaments or true vocal cords, and the upper part of the arytenoid cartilages, be all removed; provided the true vocal cords remain entire, with their points of attachment, and be kept tense and so approximated that the fissure of the glottis may be narrow. The vocal ligaments or cords, therefore, may be regarded as the proper organs of the mere voice: the modifications of the voice being effected by other parts — tongue, teeth, lips, etc., as well as by them. The structure -of the vocal cords is adapted to enable them to vibrate like tense mem- branes, for they are essentially composed of elastic tissue; and they are so attached to the cartilaginous parts of the larynx that their position .and tension can be variously altered by the contraction of the muscles which act on these parts. THE VOICE AND SPEECH. 51 The Larynx. — The larynx, or organ of voice, consists essentially of the two vocal cords, which are so attached to certain cartilages, and so under the control of certain muscles, that they can be made the means not only of closing the aperture of the larynx (rima glottidis), of which they are the lateral boundaries, against the entrance and exit of air to or FIG. 294. FIG. 295. FIG. 294.— Outline showing the general form of the larynx, trachea, and bronchi, as seen from before, h. the great cornu or the hyoid bone; e, epiglottis; t, superior, and t', inferior cornu of the thyroid cartilage; c, middle of the cricoid cartilage; tr, the trachea, showing sixteen cartilaginous rings; b. the right, and b', the left bronchus, x & (Allen Thomson.) FIG. 295.— Outline showing the general form of the larynx, trachea, and bronchi, as seen from behind, h, great cornu of the hyoid bone; f, superior, andV, the inferior cornu of the thyroid carti- lage; e, the epiglottis; a, points to the back of both the arytenoid cartilages, which are surmounted by the cornicula; c, the middle ridge on the back of the cricoid cartilage; tr, the posterior mem- branous part of the trachea; 6, 6', right and left bronchi, x ^. (Allen Thomson.) from the lungs, but also can be stretched or relaxed, shortened or length- ened, in accordance with the conditions that may be necessary for the air in passing over them, to set them vibrating and produce various sounds. 52 HAND-BOOK OF PHYSIOLOGY. Their action in respiration has been already referred to (p. 189, Vol. I.). In the present chapter the sound produced by the vibration cf the vocal cords is the only part of their function with which we have to deal. Anatomy of the Larynx. — The principal parts entering into the for- mation of the larynx (Figs. 294 and 295) are — (t) the thyroid cartilage; (c) the cricoid cartilage; (a) the two arytenoid cartilages; and the two true vocal cords (A, cv, Fig. 298). The epiglottis (Fig. 298 e), has but little to do with the voice, and is chiefly useful in falling down as a "lid" over the upper part of the larynx, to help in preventing the entrance of food and drink in deglutition. It also guides mucus or other fluids in small amount from the mouth around the sides of the upper opening of «the glottis into the pharynx and oesophagus: thus preventing them from entering the larynx. The false vocal cords (cvs, Fig. 298), and the ven- tricle of the larynx, which is a space between the false and the true cord of either side, need be here only referred to. Cartilages. — The thyroid cartilage (Fig. 296, 1 to 4) does not form a complete ring around the larynx, but only covers the front portion. The FIG. 296. FIG. 297. FIG. 296. — Cartilages of the larynx seen from before. 1 to 4, thyroid cartilage; 1, vertical ridge or pomum Adami; 2, right ala; 3, superior, and 4, inferior cornu of the right side; 5, 6, cricoid carti- lage; 5, inside of the posterior part; 6, anterior narrow part of the ring; 7, arytenoid cartilages. X %. FIG. 297. — Lateral view of exterior of the larynx. 8, thyroid cartilage; 9, cricoid cartilage; 10, crico-thyroid muscle; 11, crico-thyroid ligament; 12, first rings of trachea. (Willis.) cricoid cartilage (Fig. 296, 5, 6), on the other hand, is a complete ring; the back part of the ring being much broader than the front. On the top of this broad portion of the cricoid are the arytenoid cartilages (Fig. 298 a) the connection between the cricoid below and arytenoid cartilages above being a joint with synovial membrane and ligaments, the latter permitting tolerably free motion between them. But although the arytenoid cartilages can move on the cricoid, they of course accompany the latter in all their movements, just as the head may nod or turn on THE VOICE AND SPEECH. 53 the top of the spinal column, but must accompany it in all its movements as a whole. Ligaments. — The thyroid cartilage is also connected with the cricoid, not only by ligaments, but by two joints with synovial membrane (f, [Pigs. 294 and 295); the lower cornua of the thyroid clasping, or nipping, as it were, the cricoid between them, but not so tightly but that the thy- roid can revolve, within a certain range, around an axis passing trans- versely through the two joints at which the cricoid is clasped. The vocal cords are attached (behind) to the front portion of the base of the arytenoid cartilages, and (in front) to the re-entering angle at the back part of the thyroid; it is evident, therefore, that all movements of either of these cartilages must produce an effect on them of some kind or other. Inas- much, too, as the arytenoid cartilages rest on the top of the back portion of the cricoid cartilage (#, Fig. 298), and are connected with it by cap- sular and other ligaments, all movements of the cricoid cartilage must move the arytenoid cartilages, and also produce an effect on the vocal cords. Intrinsic Muscles. — The so-called intrinsic muscles of the larynx, or those which, in their action, have a direct action on the vocal cords, are nine in number — four pairs, and a single muscle; namely, two crico- thyroid muscles, two thyro-arytenoid, two posterior crico-arytenoid, two lateral crico-arytenoid, and one arytenoid muscle. Their actions are as follows: — When the crico-thyroid muscles (10, Fig. 297) contract, they rotate the cricoid on the thyroid cartilage in such a manner that the upper and back part of the former, and of necessity the arytenoid cartilages on the top of it, are tipped backward, while the thyroid is in- clined forward: and thus, of course, the vocal cords being attached in front to one, and behind to the other, are "put on the stretch." The thyro-arytenoid muscles (7, Fig. 300) on the other hand, have an opposite action,— pulling the thyroid backward, and the arytenoid and upper and back part of the cricoid cartilages forward, and thus relaxing the vocal cords. The crico-arytenoidei posticus muscles (Fig. 299, V) dilate the glottis, and separate the vocal cords, the one from the other, by an action on the arytenoid cartilage which will be plain on reference to B' and 0', (Fig. 298). By their contraction they tend to pull together the outer angles of the arytenoid cartilages in such a fashion as to rotate the latter at their joint with the cricoid, and of course to throw asunder their anterior angles to which the vocal cords are attached. These posterior crico-arytenoid muscles are opposed by the crico-anjte- noidei laterales, which, pulling in the opposite direction from the other side of the axis of rotation, have of course exactly the opposite effect, and close the glottis (Fig. 300, 4 and 5). The aperture of the glottis can be also contracted by the an/fenoid muscle (s, Fig. 299, and 6, Fig. 300), which, in its contraction, pulls together the upper parts of the arytenoid cartilages between which it extends. Nerve supply. — In the performance of the functions of the larynx the sensory filaments of the pneumogastric supply that acute sensibility by which the glottis is guarded against the ingress of foreign bodies, or of irrespirable gases. The contact of these stimulates the filaments of the superior laryngeal branch of the pneumogastric; and the impression con- veyed to the medulla oblongata, whether it produce sensation or not, is reflected to the filaments of the recurrent or inferior laryngeal branch, 54 HAND-BOOK OF PHYSIOLOGY. and excites contraction of the muscles that close the glottis. Both these branches of pneumogastric co-operate also in the production and regula- tion of the voice; the inferior laryngeal determining the contraction of the muscles that vary the tension of the vocal cords, and the superior laryngeal conveying to the mind the sensation of the state of these muscles necessary for their continuous guidance. And both the branches co-operate in the actions of the larynx in the ordinary slight dilatation and contraction of the glottis in the acts of expiration and inspiration, and more evidently in those of coughing and other forcible respiratory movements. FIG. 298.— Three laryngoscopic views of the superior aperture of the larynx aud surrounding- parts. A, the glottis during the emission of a high note in singing; B, in easy and quiet inhalation of air; C, in the state of widest possible dilatation, as in inhaling a very deep breath. The diagrams A', B', and C', have been added to Czermak's figures, to show in horizontal sections of the glottis the position of the vocal ligaments and arytenoid cartilages in the three several states represented in the other figures. In all the figures, so far as marked, the letters indicate the parts as follows, viz. : I, the base of the tongue; e, the upper free part of the epiglottis; e', the tubercle or cushion of the epi- glottis; ph, part of the anterior wall of the pharynx behind the larynx; in the margin of the aryteno- epiglottidean fold w, the swelling of the membrane caused by the cartilages of Wrisberg; s, that of the cartilages of Santorini; a, the tip or summit of the arytenoid cartilages; c v, the true vocal cords or lips of the rima glottidis; cvs. the superior or false vocal cords; between them the ventricle of the larynx; in C, tris placed on the anterior wall of the receding trachea, and 6 indicates the com- mencement of the two bronchi beyond the bifurcation which may be brought into view in this state of extreme dilatation. (Czermak.) (From Quain's Anatomy.) Movements of Vocal Cords. — The placing of the vocal cords in a position parallel one with the other, is effected by a combined action of the various little muscles which act on them — the thyro-arytenoidei having, without much reason, the credit of taking the largest share in the pro- duction of this effect. Fig. 298 is intended to show the various positions- THE VOICE AND SPEECH. 55 of the vocal cord under different circumstances. Thus, in ordinary tran- quil breathing, the opening of the glottis is wide and triangular (B) becoming a little wider at each inspiration, and a little narrower at each expiration. On making a rapid and deep inspiration the opening of the glottis is widely dilated (as in c), and somewhat lozenge-shaped. At the moment of the emission of sound, it is narrowed, the margins of the urytenoid cartilages being brought into contact and the edges of the vocal cords approximated and made parallel, at the same time that their tension is much increased. The higher the note produced, the tenser do the cords become (Fig. 298, A) ; and the range of a voice depends, of course, FIG. 299. — View of the larynx and part of the trachea from behind, with the muscles dissected; ft, the body of the hyoid bone; e, epiglottis; f, the posterior borders of the thyroid cartilage; c, the median ridge of the cricoid; a, upper part of the arytenoid; s, placed on one or the oblique fasciculi of the arytenoid muscle ; 6, left posterior crico-arytenoid muscle ; ends of the incomplete c'artilagi- nous rings of the trachea; I, fibrous membrane crossing the back of the trachea; n, muscular fibres exposed in a part (from Quain's Anatomy). in the main, on the extent to which the degree of tension of the vocal cords can be thus altered. In the production of a high note, the vocal cords are brought well within sight, so as to be plainly visible with the help of the laryngoscope. In the utterance of grave tones, on the other hand, the epiglottis is depressed and brought over them, and the arytenoid cartilages look as if they were trying to hide themselves under it (Fig. 391). The epiglottis, by being somewhat pressed down so as to cover the superior cavity of the larynx, serves to render the notes deeper in tone, and at the same time somewhat duller, just as covering the end of a short tube placed in front of caoutchouc tongues lowers the tone. In no other respect does the epiglottis appear to have any effect in modify- ing the vocal sounds. 56 HAND-BOOK OF PHYSIOLOGY. The degree of approximation of the vocal cords also usually corre- sponds with the height of the note produced; but probably not always, for the width of the aperture has no essential influence on the height of the note, as long as the vocal cords have the same tension: only with a wide aperture, the tone is more difficult to produce, and is less perfect, the rushing of the air through the aperture being heard at the same time. No true vocal sound is produced at the posterior part of the aperture of the glottis, that, viz., which is formed by the space between the aryte- FIG. 300. FIG. 301. FIG. 300.— View of the anterior of larynx from above. 1, aperture of glottis; 2, arytenoid car- tilages; 3, vocal cords; 4, posterior crico-arytenoid muscles; 5, lateral crico-arytenoid muscle of right side, that of left side removed ; 6, arytenoid muscle ; 7, thyro-ary tenoid muscle of left side, that of right side removed; 8, thyroid cartilage; 9, cricoid cartilage; 13, posterior crico-arytenoid ligament. (Willis.) FIG. 301.— View of the upper part of the larynx as seen by means of the laryngoscope during the utterance of a grave note, c, epiglottis; s, tubercles of the cartilages of Santorini; a, arytenoid car- tilages; z, base of the tongue; hph, the posterior wall of the pharynx. (Czermak.) noid cartilages. For, as Muller's experiments showed, if the arytenoid cartilages be approximated in such a manner that their anterior processes touch each other, but yet leave an opening behind them as well as in front, no second vocal tone is produced by the passage of the air through the posterior opening, but merely a rustling or bubbling sound; and the height or pitch of the note produced is the same whether the posterior part of the glottis be open or not, provided the vocal cords maintain the same degree of tension. APPLICATION OF THE VOICE IN SINGING AND SPEAKING. Varieties of Vocal Sounds. — The notes of the voice thus produced may observe three different kinds of sequence. The first is the monoto- nous, in which the notes have nearly all the same pitch as in ordinary speaking; the variety of the sounds of speech being due to articulation in the mouth. In speaking, however, occasional syllables generally receive a higher intonation for the sake of accent. The second mode of sequence is the successive transition from high to low notes, and vice versa, with- out intervals; such as is heard in the sounds, which, as expressions of THE VOICE AND SPEECH. 57 passion, accompany crying in men, and in the howling and whining of dogs. The third mode of sequence of the vocal sounds is the musical, in which each sound lias a determinate number of vibrations, and the num- bers of the vibrations in the successive sounds have the same relative pro- portions that characterize the notes of the musical scale. Compass of the Voice. — In different individuals this comprehends one, two, or three octaves. In singers — that is, in persons apt for sing- ing— it extends to two or three octaves. But the male and female voices commence and end at different points of the musical scale. The lowest note of the female voice is about an octave higher than the lowest of the male voice; the highest note of the female voice about an octave higher than the highest of the male. The compass of the male and female voices taken together, or the entire scale of the human voice, includes about four octaves. The principal difference between the male and female voice is, therefore, in their pitch; but they are also distinguished by their tone, — the male voice is not so soft. Pitch^nd Timbre.— The voice presents other varieties besides that of male and female; there are two kinds of male voice, technically called the bass and tenor, and two kinds of female voice, the contralto and soprano, all differing from each other in tone. The bass voice usually reaches lower than the tenor, and its strength lies in the low notes; while the tenor voice extends higher than the bass. The contralto voice has generally lower notes than the soprano, and is strongest in the lower notes of the female voice; while the soprano voice reaches higher in the scale. But the difference of compass, and of power in different parts of the scale, is not the essential distinction between the different voices; for bass singers can sometimes go very high, and the contralto frequently sings the high notes like soprano singers. The essential difference be- tween the bass and tenor voices, and between the contralto and soprano, consists in their tone or "timbre," which distinguishes them even when they are singing the same note. The qualities of the baritone and mezzo- soprano voices are less marked; the baritone being intermediate, between the bass and tenor, the mezzo-soprano between the contralto and soprano. They have also a middle position as to pitch in the scale of the male and female voices. The different pitch of the male and the female voices depends on the different length of the vocal cords in the two sexes; their relative length in men and women being as three to two. The difference of the two voices in tone or "timbre," is owing to the different nature and form of the resounding walls, which in the male larynx are much more extensive, and form a more acute angle anteriorly. The different qualities of the tenor and bass, and of the alto and soprano voices, probably depend on some peculiarities of the ligaments, and the membranous and cartilaginous parietes of the laryngeal cavity, which are not at ^present understood, but 58 HAND-BOOK OF PHYSIOLOGY. of which we may form some idea,, by recollecting that musical instruments made of different materials, e.g., metallic and gut-strings, may be tuned to the same note, but that each will give it with a peculiar tone or "timbre." Varieties of Voices. — The larynx of boys resembles the female larynx; their vocal cords before puberty have not two-thirds the length which they acquire at that period; and the angle of their thyroid cartilage is as little prominent as in the female larynx. Boys' voices are alto and soprano, resembling in pitch those of women, but louder, and differing somewhat from them in tone. But, after the larynx has undergone the change produced during the period of development at puberty, the boy's voice becomes bass or tenor. While the change of form is taking place, the voice is said to "crack;" it becomes imperfect, frequently hoarse and crowing, and is unfitted for singing until the new tones are brought under command by practice. In eunuchs, who have been deprived of the testes before puberty, the voice does not undergo this change. The voice of most old people is deficient in tone, unsteady, and moreflrestricted in extent: the first defect is owing to the ossification of the cartilages of the larynx and the altered condition of the vocal cord; the want of steadi- ness arises from the loss of nervous power and command over the muscles; the result of which is here, as in other parts, a tremulous motion. These two causes combined render the voices of old people void of tone, un- steady, bleating, and weak. In any class of persons arranged, as in an orchestra, according to the character of voices, each would possess, with the general characteristics of a bass, or tenor, or any other kind of voice, some peculiar character by which his voice would be recognized from all the rest. The conditions that determine these distinctions are, however, quite unknown. They are probably inherent in the tissues of the larynx, and are as indiscernible as the minute differences that characterize men's features; one often ob- serves, in like manner, hereditary and family peculiarities of voice, as well marked as those of the limbs or face. Most persons, particularly men, have the power, if at all capable of singing, of modulating their voices through a double series of notes of different character: namely, the notes of the natural voice, or chest-notes, and the falsetto notes: The natural voice, which alone has been hitherto considered, is fuller, and excites a distinct sensation of much stronger vibration and resonance than the falsetto voice, which has more a flute-like character. The deeper notes of the male voice can be produced only with the natural voice, the highest with the falsetto only; the notes of middle pitch can be produced either with the natural or falsetto voice; the two registers of the voice are therefore not limited in such a manner as that one ends when the other begins, but they run in^part side by side. Method of the Production of Notes. — The natural or chest-notes THE VOICE AND SPEECH. 59 are produced by the ordinary vibrations of the vocal cords. The mode of production of the falsetto notes is still obscure. By Miiller the falsetto notes were thought to be due to vibrations of only the inner borders of the vocal cords. In the opinion of Petrequin and Diday, they do not result from vibrations of the vocal cords .at all, but from vibrations of the air passing through the aperture of the glottis, which they believe assumes, at such times, the contour of the embouchure of a flute. Others (considering some degree of similarity which exists between the falsetto notes and the peculiar tones called harmonic, which are produced when, by touching or stopping a harp-string at a particular point, only a portion of its length is allowed to vibrate) have supposed that, in the falsetto notes, portions of the vocal ligaments are thus iso- lated, and made to vibrate while the rest are held still. The question cannot yet be settled; but any one in the habit of singing may assure himself, both by the difficulty of passing smoothly from one set of notes to the other, and by tbe necessity of exercising himself in both registers, lest he should become very deficient in one, that there must be some great difference in the modes in which their respective notes are produced. The strength of the voice depends partly on the degree to which the vocal cords can be made to vibrate; and partly on the fitness for reso- nance of the membranes and cartilages of the larynx, of the parietes of the thorax, lungs, and cavities of the mouth, nostrils, and communicating sinuses. It is diminished by anything which interferes with such capability of vibration. The intensity or loudness of a given note with maintenance of the same "pitch," cannot be rendered greater by merely increasing the force of the current of air through the glottis; for increase of the force of the current of air, cceteris paribus, raises the pitch both of the natural and the falsetto notes. Yet, since a singer possesses the power of increasing the loudness of a note from the faintest "piano" to "fortissimo" without its pitch being altered, there must be some means of compensating the tendency of the vocal cords to emit a higher note when the force of the current of air is increased. This means evidently consists in modifying the tension of the vocal cords. When a note is rendered louder and more intense, the vocal cords must be relaxed by remission of the muscular action, in proportion as the force of the current of the breath through the glottis is increased. When a note is rendered fainter, the reverse of this must occur. The arches of the palate and the uvula become contracted during the formation of the higher notes; but their contraction is the same for a note of given height, whether it be falsetto or not; and in either case the arches of the palate may be touched with the finger, without the note being altered. Their action, therefore, in the production of the higher notes seems to be merely the result of involuntary associate nervous action, excited by the voluntarily increased exertion of the muscles of the 60 HAND-BOOK OF PHYSIOLOGY. larynx. If the palatine arches contribute at all to the production of the higher notes of the natural voice and the falsetto, it can only be by their increased tension strengthening the resonance. The office of the ventricles of the larynx is evidently to afford a free space for the vibrations of the lips of the glottis; they may be compared with the cavity at the commencement of the mouth-piece of trumpets, which allows the free vibration of the lips. SPEECH. • Besides the musical tones formed in the larynx, a great number of other sounds can be produced in the vocal tubes, between the glottis and the external apertures of the air-passages, the combination of which sounds by the agency of the cerebrum into different groups to designate objects, properties, actions, etc., constitutes language. The languages do not employ all the sounds which can be produced in this manner, the com- bination of some with others being often difficult. Those sounds which are easy of combination enter, for the most part, into the formation of the greater number of languages. Each language contains a certain number of such sounds, but in no one are all brought together. On the contrary, different languages are characterized by the prevalence in them of certain classes of these sounds, while others are less frequent or alto- gether absent. Articulate Sounds. — The sounds produced in speech, or articulate sounds, are commonly divided into vowels and consonants: the distinction between which is, that the sounds for the former are generated by the larynx, while those for the latter are produced by interruption of the cur- rent of air in some part of the air-passages above the larynx. The term consonant has been given to these because several of them are not prop- erly sounded, except consonantly with a vowel. Thus, if it be attempted to pronounce aloud the consonants £, d, and g, or their modifications, p, t, k, the intonation only follows them in their combination with a vowel. To recognize the essential properties of the articulate sounds, we must, according to Miiller, first examine them as they are produced in whisper- ing, and then investigate which of them can also be uttered in a modified character conjoined with vocal tone. By this procedure we find two series of sounds: in one the sounds are mute, and cannot be uttered with a vocal tone; the sounds of the other series can be formed independently of voice, but are also capable of being uttered in conjunction \vith it. All the vowels can be expressed in a whisper without vocal tone, that is, mutely. These mute vowel-sounds differ, however, in some measure, as to their mode of production, from the consonants. All the mute con- sonants are formed in the vocal tube above the glottis, or in the cavity of the mouth or nose, by the mere rushing of the air between the surfaces THE VOICE AND SPEECH. 61 differently modified in disposition. But the sound of the vowels, even when mute, has its source in the glottis, though its vocal cords are not thrown into the vibrations necessary for the production of voice; and the sound seems to be produced by the passage of the current of air between the relaxed vocal cords. The same vowel sound can be produced in the larynx when the mouth is closed, the nostrils being open, and the utter- ance of all vocal tone avoided. This sound, when the mouth is open, is so modified by varied forms of the oral cavity, as to assume the characters of the vowels a, e, i, o, u, in all their modifications. The cavity of the mouth assumes the same form for the articulation of each of the mute vowels as for the corresponding vowel when vocal- ized; the only difference in the two cases lies in the kind of sound emitted by the larynx. Krantzenstein and Kempelen have pointed out that the conditions necessary for changing one and the same sound into the differ- ent vowels, are differences in the size of two parts — the oral .canal and the oral opening; and the same is the case with regard to the mute vowels. By oral canal, Kempelen means here the space between the tongue and palate: for the pronunciation of certain vowels both the opening of the mouth and the space just mentioned are widened; for the pronunciation of other vowels both are contracted; and for others one is wide, the other contracted. Admitting five degrees of size, both of the opening of the mouth and of the space between the tongue and palate, Kempelen thus states the dimensions of these parts for the following vowel sounds: — Vowel. Sound. Size of oral opening. Size of oral canal. a as in "far" 5 ... 3 a " "name" 4 ... 2 e " "theme" 3 .... 1 o " "go" 2 ... 4 oo " "cool" 1 ... 5 Another important distinction in articulate sounds is, that the utter- ance of some is only of momentary duration, taking place during a sud- den change in the conformation of the mouth, and being incapable of prolongation by a continued expiration. To this class belong b, p, d, and the hard g. In the utterance of other consonants the sounds may be continuous; they may be prolonged, ad libitum, as long as a particular disposition of the mouth and a constant expiration are maintained. Among these consonants are h, m, n, f, s, r, I. Corresponding differ- ences in respect to the time that may be occupied in their utterance exist in the vowel sounds, and principally constitute the differences of long and short syllables. Thus the a as in "far" and "fate," the o as in "go" and "fort," may be indefinitely prolonged; but the same vowels (or more properly different vowels expressed by the same letters), as in "can" and "fact," in "dog" and "rotten," cannot be prolonged. 62 HAND-BOOK OF PHYSIOLOGY. All sounds of the first or explosive kind are insusceptible of combina- tion with vocal tone ("intonation"), and are absolutely mute; nearly all the consonants of the second or continuous kind may be attended with ' 'intonation." Ventriloquism; — The peculiarity of speaking, to which the term ventriloquism is applied, appears to consist merely in the varied modifi- cation of the sounds produced in the larynx, in imitation of the modifica- tions which voice ordinarily suffers from distance, etc. From the obser- vations of Muller and Colombat, it seems that the essential mechanical parts of the process of ventriloquism consist in taking a full inspiration, then keeping the muscles of the chest and neck fixed, and speaking with the mouth almost closed, and the lips and lower jaw as motionless as possible, while air is very slowly expired through a very narrow glottis; care being taken also, that none of the expired air passes through the nose. But, as observed by Muller, much of the ventriloquist's skill in imitating the voices coming from particular directions, consists in deceiv- ing other senses than hearing. We never distinguish very readily the direction in which sounds reach our ear; and, when our attention is directed to a particular point, our imagination is very apt to refer to that point whatever sounds we may hear. Action of the Tongue in Speech. — The tongue, which is usually credited with the power of speech — language and speech being often employed as synonymous terms — plays only a subordinate, although very important part. This is well shown by cases in which nearly the whole organ has been removed on account of disease. Patients who recover from this operation talk imperfectly, and their voice is considerably mod- ified; but the loss of speech is confined to those letters in the pronuncia- tion of which the tongue is concerned. Stammering depends on a want of harmony between the action of the muscles (chiefly abdominal) which expel air through the larynx, and that of the muscles which guard the orifice (rima glottidis) by which it escapes, and of those (of tongue, palate, etc.) which modulate the sound to the form of speech. Over either of the groups of muscles, by itself, a stammerer may have as much power as other people. But he cannot harmoniously arrange their conjoint actions. CHAPTER XVII. NUTRITION; THE INCOME AND EXPENDITURE OF THE HUMAN BODY. THE various physiological processes which occur in the human body have, with the exception of those in the nervous and generative systems, which will be considered in succeeding chapters, now been dealt with, and it will be as well to give in this chapter on Nutrition a summary of what has been considered more at length before. The subject may be considered under the following heads. (1). The Evidence and Amount of Expenditure. (2). The Sources and Amount of Income. (3). The Sources and Objects of Expenditure. 1. Evidence and Amount of Expenditure. — The evidence of Expenditure by the living body is abundantly complete. From the table (p. 212, Vol. I.) it will be seen how the various amounts of the excreta are calculated. From the Lungs there is exhaled every 24 hours, Of Carbonic Acid, about .... 15,000 grains " Water 5,000 " Traces of organic matter. From the Skin — Water 11,500 grains Solid and gaseous matter .... 250 " From the Kidneys — Water 23,000 grains Organic matter ...... 680 Minerals or salines 420 " From the Intestines — Water 2,000 grains Various organic and mineral substances . 800 " In the account of Expenditure, must be remembered in addition the milk (during the period of suckling), and the products of secretion from the generative organs (ova, menstrual blood, semen); but, from their variable and uncertain amounts, these cannot be reckoned with the pre- ceding. 64 HAND-BOOK OF PHYSIOLOGY. Altogether, the Expenditure of the body represented by the sum of these various excretory products amounts every 24 hours to — Solid and gaseous matter . . . 17,150 grains (1,113 grms.) Water (either fluid or combined with the solids and gaseous matter). . 49,500 (2,695 " ) The matter thus lost by the body is matter the chemical attractions of which have been in great part satisfied; and which remains quite useless as food, until its elements have been again separated and re-arranged by members of the vegetable world (p. 2, Vol. L). It is especially instructive to compare the chemical constitution of the products of expenditure, thus separated by the various excretory organs, with that of the sources of in- come to be immediately considered. It is evident from these facts that if the human body is to maintain its size and composition, there must be added to it matter corresponding in amount with that which is lost. The income must equal the expen- diture, 2. Sources and Amount of Income. — The Income of the body consists partly of Food and Drink, and partly of Oxygen. Into the stomach there is received daily: — Solid (chemically dry) food . . 8, 000 grains (520 grms.) Water (as water, or variously com- bined with, solid food) . . . 35,000-40,000 " (2,444 " ) By the lungs there is absorbed daily: — Oxygen 13,000 " 844 " ) The average total daily receipts, in the shape of food, drink and oxy- gen, correspond, therefore, with the average total daily expenditure, as shown by the following table: 20,000 grains. 11,750 " 24,100 " 2,800 " Income. Expenditu Solid food 8,000 grains Lungs Water 37,650 " Skin Oxygen 13,000 " Kidneys . T"l"i't"OO~f"1T>OC! 58,650 grains Xlllt^otllltlo • • (Generative and mam- (about 3,808 grms., or 8^ Ib.) mary-gland products are supposed to be in- cluded. ) / A U^,,-(- O OAO 58,650 grains These quantities are approximate only. But they may be taken as fair averages for a healthy adult. The absolute identity of the two INCOME AND EXPENDITURE OF BODY. 65 numbers (in grains) in the two tables is of course diagrammatic. No such exactitude in the account occurs in any living body, in the course of any given twenty-four hours. But any difference which exists between the two amounts of income and expenditure at any given period, corresponds merely with the slight variations, in the amount of capital (weight of body), to which the healthiest subject is liable. The chemical composition of the food (p. 213, Vol.1.) may be profitably compared with that of the excreta, as before mentioned. The greater part of our food is composed of matter, which contains much potential energy; and in the chemical changes (combustion and other processes), to which it is subject in the body, active energy is manifested. 3. The Sources and Objects of Expenditure. — The sources of necessary waste and expenditure in the living body are various and ex- tensive. They may be comprehended under the following heads: — (1) Common wear and tear; such as that to which all structures, living and not living, are subjected by exposure and work; but which must be especially large in the soft and easily decaying structures of an animal body. (2) Manifestations of Force in the form either of Heat or Motion. In the former case (Heat), the combustion must be sufficient to maintain a temperature of about 100° F. (37 '8° C.) throughout the whole sub- stance of the body, in all varieties of external temperature, notwithstand- ing the large amount continually lost in the ways previously enumerated (p. 313, Vol. I.). In the case of Motion, there is the expenditure involved , in (a) Ordinary muscular movements, as in Prehension, Mastication, Lo- /y comotion, and numberless other ways: (b) Various involuntary movements, as in Eespiration, Circulation, Digestion, etc. (3) Manifestation of Nerve-force; as in the general regulation of all physiological processes, e.g., Eespiration, Circulation, Digestion; and in Volition and all other manifestations of cerebral activity. (4) The energy expended in all physiological processes, e.g., Nutrition, Secretion, Growth, and the like. The Total expenditure or manifestation of energy by an animal body can be measured, with fair accuracy; the terms used being such as are employed in connection with other than vital operations. All statements however, must be considered for the present approximate only, and es- pecially is this the case with respect to the comparative share of expendi- ture to be assigned to the various objects just enumerated. The amount of energy daily manifested by the adult human body in (a) the maintenance of its temperature; (b) in internal mechanical work, as in the movements of the respiratory muscles, the heart, etc. ; and (c) in external mechanical work, as in locomotion and all other voluntary move- ments, ha^been reckoned at about 3,400 foot-tons (p. 124, Vol. I.). Of this amount only one-tenth is directly expended in internal and external VOL. II.— 5. 66 HAND-BOOK OF PHYSIOLOGY. mechanical work; the remainder being employed in the maintenance of the body's heat. The latter amount represents the heat which would be required to raise 48*4lb. of water from the freezing to the boiling point; or if converted into mechanical power, it would suffice to raise the body of a man weighing about 150 Ib. through a vertical height of 8 J miles. To the foregoing amounts of expenditure must be added the quite un- known quantity expended in the various manifestations of nerve-force, and in the work of nutrition and growth (using these terms in their widest sense). By comparing the amount of energy which should be produced in the body from so much food of a given kind, with that which is actu- ally manifested (as shown by the various products of combustion, in the excretions) attempts have been made, indeed, to estimate, by a process of exclusion, these unknown quantities; but all such calculations must be at present considered only very doubtfully approximate. Sources of Error. — Among the sources of error in any such calcu- lations must be reckoned, as a chief one, the, at present, entirely unknown extent to which forces external to the body (mainly heat) can be utilized by the tissues. We are too apt to think that the heat and light of the sun are directly correlated, as far as living beings are concerned, with the chemico -vital transformations involved in the nutrition and growth of the members of the vegetable world only. But animals, although compara- tively independent of external heat and other forces, probably utilize them, to the degree occasion offers. And although the correlative manifes- tation of energy in the body, due to external heat and light, may still be measured in so far as it may take the form of mechanical work; yet, in so far as it takes the form of expenditure in nutrition or nerve -force, it is evidently impossible to include it by any method of estimation yet dis- covered; and all accounts of it must be matters of the purest theory. These considerations may help to explain the apparent discrepancy be- tween the amount of energy which is capable of being produced by the usual daily amount of food, with that which is actually manifested daily by the body; the former leaving but a small margin for anything beyond the maintenance of heat, and mechanical work. In the foregoing sketch we have supposed that the excreta are exactly replaced by the ingesta. NITROGENOUS EQUILIBRIUM AND FORMATION OF FAT. If an animal, which has undergone a starving period, be fed upon a diet of lean meat, it is found that instead of the greater part of the nitro- gen being stored up, as one would expect, the chief part of it appears in the urine as urea, and on continuing with the diet the excreted nitrogen approximates more and more closely to the ingested nitrogen u^itil at last the amounts are equal in both cases. This is called nitrogenous equili- INCOME AND EXPENDITURE OF BODY. 67 tirium. There may, however, be at the same time an increase Of weight which is due to the putting on of fat. If this is the case it must be ap- parent that the protoplasm of the tissues is able to form fat out of proteid material and to split it up into urea and fat. If fat be given in small quantities with the meat, for a time the carbon of the egesta and in- gesta are equal, but if the fat be increased beyond a certain point the body weight increases from a deposition of fat; not, however, by a mere mechanical deposition or nitration from the blood, but by an actual act of secretion by the protoplasm whereby the fat globules are stored up within itself. In a similar manner as regards carbo-hydrates, if they are in small quantity, the whole of the carbon appears in the excreta, but beyond a certain amount a considerable portion of it is retained in fat, having been by the protoplasm stored up within itself in that material. The amount of proteid material required to produce nitrogenous equi- librium is considerable, but it may be materially diminished by the addition of carbo-hydrate or fatty food or of gelatine to the exclusively meat diet. It is of much interest to consider how the protoplasm aots in convert- ing food into energy and decomposition products, since the substance itself does not undergo much change in the process except a slight amount of wear and tear. We may assume that it is the property of protoplasm to separate from the blood the materials which maj be required to pro- duce secretions, in the case of the protoplasm of secreting glands, or to evolve heat and energy, as in the case of the protoplasm of muscle. The substances are very possibly different for each process, and the decomposi- tion products, too, may be different in quality or quantity. Proteid ma- terials appear to be specially needed, as is shown by the invariable pres- ence of urea in the urine even during starvation; and as in the latter case, there has been no food from which these materials could have been derived, the urea is considered to be derived from the disintegration of the nitrog- enous tissues themselves. The removal of all fat from the body in a star- vation period, as the first apparent change, would lead to the supposition that fat is also a specially necessary pabulum for the production of proto- plasmic energy; and the fact that, as mentioned above, with a diet of I lean meat an enormous amount appears to be required, suggests that in that case protoplasm obtains the fat it needs from the proteid food, which pro- cess must be evidently a source of much waste of nitrogen. The idea that proteid food has two destinations in the economy, viz., to form organ or tissue proteid which builds up organs and tissues, and circulating pro- teid, from which the organs and tissues derive the materials of their secre- tions or for producing their energy, is a convenient one, as it is unlikely that protoplasm would go to the expense of construction simply for the sake of immediate destruction. CHAPTER XVIII. THE NERVOUS SYSTEM. Chief Divisions of the Nervous System. — The Nervous System consists of two portions or systems, the (I.) Cerebro-spinal, and the (II.) Sympathetic. (I.) The Cerebro-spinal system includes the Brain and Spinal cord, with the nerves proceeding from them. Its fibres are chiefly, but not exclusively, distributed to the skin and other organs of the senses, and to- the voluntary muscles. (II.) The Sympathetic Nervous system consists of: — (1) A double chain of ganglia and fibres, which extends from the cranium to the pelvis, along each side of the vertebral column, and from which branches are distributed both to the cerebro-spinal system and to other parts of the sympathetic system. With these may be included the small ganglia in connection with those branches of the fifth cerebral nerve which are . distributed in the neighborhood of the organs of special sense: namely, the ophthalmic, otic, spheno-palatine, and sulmaxillary ganglia. (2) Various ganglia and plexuses of nerve-fibres which give off branches to the thoracic and ab- dominal viscera, the chief of such plexuses being the Cardiac, Solar, and Hypogastric; but in intimate connection with these are many secondary plexuses, as the aortic, spermatic, and renal. To these plexuses, fibres pass from the prgevertebral chain of ganglia, as well as from cerebro-spinal nerves. (3) Various ganglia and plexuses in the substance of many of the viscera, as in the stomach, intestines, and urinary bladder. These, which are, for the most part, microscopic, also freely communicate with other parts of the sympathetic system, as well as, to some extent, with the cerebro-spinal. (4) By many, the ganglia on the posterior roots of the spinal nerves, on the glosso-pharyngeal and vagus, and on the sensory root of the fifth cerebral nerve (Grasserian ganglion), are also included as sym- pathetic-nerve structures. Elementary Structure.— The organs both of the Cerebro-spinal and Sympathetic nervous systems are composed of two structural elements- — -fibres and cells. The cells are collected in masses, and are always min- gled, more or less, with fibres; such a collection of cellular and fibrous nerve-structure being termed a nerve-centre. The fibres, besides entering into the composition of nerve-centres, form by themselves the nerves, THE NERVOUS SYSTEM. 69 which connect the various centres, and are distributed in the several parts of the body. NERVE FIBRES. Structure. — Each nerve-trunk is composed of a variable number of different-sized bundles (funiculi) of nerve-fibres which have a special .sheath (perineurium or neurilemma). The funiculi are enclosed in a firm FIG. 302.— Transverse section of the sciatic nerve of a cat X 100.— It consists of bundles (Funiculi) of nerve-fibres ensheathed in a fibrous supporting capsule, epineurium, A: each bundle has a special sheath (not sufficiently worked out from the epineurium in the figure) or perineurium B; the nerve- fibres N/ are separated from one another by endoneurium; L, lymph spaces; A r, artery: V, vein; F,fat. (V.D.Harris.) fibrous sheath (epineurium)', this sheath also sends in processes of connec- tive tissue which connect the bundles together. In the funiculi between the fibres is a delicate supporting tissue (the endoneurium). There are numerous lymph -spaces both beneath the connective tissue investing individual nerve- fibres, and also beneath that which surrounds the funiculi. Varieties. — In most nerves, two kinds of fibres are mingled; those of one kind being most numerous in, and characteristic of, nerves of. the Cerebro-spinal system; those of the other, most numerous in nerves of the Sympathetic system. These are called (A) medullated or white fibres, and (B) non-medullated or grey fibres. (A) Medullated Fibres. — Each medullated nerve-fibre is made up of the following parts: — (1.) Primitive nerve sheath, or nucleated sheath of Schwann. (2) Medullary sheath, or white substance of Schwann. (3) Axis-cylinder, primitive band, axis band, or axial fibre. Although these parts can be made out in nerves examined some time after death, in a recent specimen the contents of the sheath appear to be homogeneous. But by degrees they undergo changes which show them to be composed of two different materials. The internal or central part, 70 HAND-BOOK OF PHYSIOLOGY. occupying the axis of the tube (axis-cylinder), becomes greyish, while the outer, or cortical portion (white substance of Schwann), becomes opaque and dimly granular or grumous, as if from a kind of coagulation. At the same time, the fine outline of the previously transparent cylindrical tube is exchanged for a dark double Contour (Fig. 303, B), the outer line being formed by the sheath of the fibre, the inner by the margin of curdled or coagulated medullary substance. The granular material shortly collects into little masses, which distend portions of the tubular membrane; while the intermediate spaces collapse, giving the fibres a varicose, or beaded appearance (Fig. 303, c and D), instead of the previous cylindrical form. FIG. 303. FIG. 304. FIG. 303.— Primitive nerve-fibres. A. -A perfectly fresh tubule with a single dark outline. B. A tubule or fibre with a double contour from commencing post-mortem change, c. The changes further advanced, producing a varicose or beaded appearance. D. A tubule or fibre, the central part of which, in consequence of still further changes, has accumulated in separate portions within the sheath. (Wagner.) FIG. 304.— Two nerve-fibres of sciatic nerve. A. Node of Ranvier. B. Axis-cylinders, c. Sheath of Schwann, with nuclei. X 300. (Klein and Noble Smith.) The whole contents of the nerve-tubules are extremely soft, for when sub- jected to pressure they readily pass from one part of the tubular sheath to another, and often cause a bulging at the side of the membrane. They also readily escape, on pressure, from the extremities of the tubule, in the form of a grumous or granular material. The nucleated sheath of Schwann is a pellucid membrane, forming the outer investment of the nerve-fibre. Within this delicate structureless membrane nuclei are seen at intervals, surrounded by a variable amount of protoplasm. The sheath is structureless, like the sarcolemma, and the nuclei appear to be within it: together with the protoplasm which sur- rounds them, they are the relics of embryonic cells, and from their resem- blance to the muscle corpuscles of striated muscle, may be termed nerve- corpuscles. THE NERVOUS SYSTEM. 71 (2.) The medullary sheath or white substance of Sclnvann is the part to which the peculiar white aspect of the cerebro-spinal nerves is princi- pally due. It is a thick, fatty, semi-fluid substance, as we have seen, pos- sessing a double contour. It is said to be made up of a fine reticulum (Stilling, Klein), in the meshes of which is embedded the bright fatty material. According to McCarthy, the medullary sheath is composed of small rods radiating from the axis-cylinder to the sheath of Schwann. Some- times the whole space is occupied by these rods, whilst at other times the rods appear shortened, and compressed laterally into bundles embedded in some homogeneous substance. (3.) The axis-cylinder consists of a large number of primitive fibrillm. This is well shown in the cornea, where the axis-cylinders of nerves break up into minute fibrils which go to form terminal networks (see Cornea), and also in the spinal cord, where these fibrillae form a large part of the grey matter. From various considerations such as its invariable presence and unbroken continuity in all nerves, though the primitive sheath or the medullary sheath may be absent, there can be little doubt that the axis-cylinder is the conductor of nerve-force^ the other parts of the nerve having the subsidiary function of support and possibly of insulation. At regular intervals in most medullated nerves, the nucleated sheath of Schwann possesses annular con- strictions (nodes of Ranvier). At these points (Figs. 304, 305), the continuity of the medullary white sub- stance is interrupted, and the primitive sheath comes into immediate contact with the axis-cylinder. Size. — The size of the nerve-fibres varies, and the same fibres do not preserve the same diameter through their whole length, being largest in their course within the trunks and branches of the nerves, in which the majority measure from -g-^ to -g-^gr of an inch in diameter. As they approach the brain or spinal cord, and generally also in the tissues in which they are dis- tributed, they gradually become smaller. In the grey or vesicular substance of the brain or spinal cord, they generally do not measure more than from YMTS *° TTO~O¥ °^ an inch. (B.) Non-Medullated Fibres. — The fibres of the second kind (Fig. 306), which constitute the whole of the branches of the olfactory and (uulitory nerves, the principal part of the trunk and branches of the sym- pathetic nerves, and are mingled in various proportions in the cerebro- spinal nerves, differ from the preceding, chiefly in their fineness, being FIG. 305.— A node of Ranvier in a medul- 1 a t e d n erve-fibre, viewed from above. The medullary sheath is interrupted, and the primiti ve sheath thickened. Copied from Axel Key and Retzius. X750. (Klein and Noble Smith.) 72 HAND-BOOK OF PHYSIOLOGY. only about \ or \ as large in their course within the trunks and branches of the nerves; in the absence of the double contour; in their contents being apparently uniform; and in their having, when in bundles, a yel- lowish grey hue instead of the whiteness of the cerebro -spinal nerves. These peculiarities depend on their not possessing the outer layer of FIG. 306.— Grey, pale, or gelatinous nerve-fibres. A. From a branch of the olfactory nerve of the sheep; a, a, two dark-bordered or white fibres from the fifth pair, associated with the pale olfactory fibres. B. From the sympathetic nerve. X 450. (Max Schultze.) medullary nerve-substance; their contents being composed exclusively of the axis-cylinder. Yet, since many nerve-fibres may be found which appear intermediate in character between these two kinds, and since the large fibres, as they approach both their central and their peripheral end, gradually diminish in size, and assume many of the other characters of FIG. 307.— Several fibres of a bundle of medullated nerve-fibres acted upon by silver nitrate to show peculiar behavior of nodes of Ranvier toward their reagent. The silver has penetrated at the nodes, and has stained the axis-cylinder for a short distance. (Klein and Noble Smith.) the fine fibres of the sympathetic system, it is not necessary to suppose that there is any material difference in the two kinds of fibres. It is worthy of note, that in the foetus, at an early period of develop- ment, all nerve -fibres are non-medullated. THE NERVOUS SYSTEM. 73 Course. — Every nerve-fibre in its course proceeds uninterruptedly from its origin in a nerve-centre to near its destination, whether this be the periphery of the body, another nervous centre, or the same centre whence it issued. Bundles of fibres run together in the nerve-trunk, but merely lie in apposition with each other; they do not unite: even when they anas- tomose, there is no union of fibres, but only an interchange of fibres between the anastomosing funiculi. Although each nerve-fibre is thus single and undivided through nearly its whole course, yet as it approaches the region in which it terminates, individual fibres break up into several FIG. 308.— Small branch of a muscular nerve of the frog, near its termination, showing divisions of the fibres, a, into two; 6, into three; x 350. (Kolliker.) subdivisions (Fig. 308) before their final ending. The medullated nerve- fibres, moreover, lose their medullary sheath before their final distribution, and acquire the characters more or less of non-medullated fibres. Plexuses. — At certain parts of their course, nerves form plexuses, in which they anastomose with each other, as in the case of the brachial and lumbar plexuses. The objects of such interchange of fibres are, (a}, to give to each nerve passing oif from the plexus, a wider connection with the spinal cord than it would have if it proceeded to its destination with- out such communication with other nerves. Thus, each nerve by the wideness of its connections, is less dependent on the integrity of any single portion, whether of nerve-centre or of nerve-trunk, from which it may spring. (b) Each part supplied from a plexus has wider relations with the nerve-centres, and more extensive sympathies; and, by means of the same arrangement, groups of muscles may be co-ordinated, every member 74 HAND-BOOK OF PHYSIOLOGY. of the group receiving motor filaments from the same parts of the nerve- centre, (c) Any given part, say a limb, is less dependent upon the integ- rity of any one nerve, (d) A plexus is frequently the means by which centripetal and centrifugal fibres are conveniently mingled for distribution, as in the case of the pneumogastric nerve, which receives motor filaments, near its origin, from the spinal accessory. As medullated nerve-fibres approach their terminations they lose their medullary sheath, and consist then merely of axis-cylinder and primitive sheath. They then lose also the latter, and only the axis-cylinder is left, with here and there a nerve-corpuscle partly rolled around it. Finally, even this investment ceases, and the axis-cylinder breaks up into its ele- mentary fibrillas. PERIPHERAL NERVE TERMINATIONS. (a.) Sensory. — (1.) Pacinian Corpuscles. — The Pacinian bodies or corpuscles (Figs. 309 and 310), named after their discoverer Pacini, are little elongated oval bodies, situated on some of the cerebro-spinal and sympathetic nerves, especially the cutaneous nerves of the hands and feet; and on branches of the large sympathetic plexus about the abdominal aorta (Kolliker). They often occur also on the nerves of the mesentery, and are especially well seen in the mesentery of the cat. They have been ob- served also in the pancreas, lymphatic glands and thyroid glands, as well as in the penis of the cat. Each corpuscle is attached by a narrow pedicle to the nerve on which it is situated, and is formed of several concentric layers of fine membrane, consisting of a hyaline ground-membrane with connective-tissue fibres, each layer being lined by en dot helium (Fig. 310); through its pedicle passes a single nerve-fibre, which, after traversing the several concentric layers and their immediate spaces, enters a central cavity, and, gradually losing its dark border, and becoming smaller, terminates at or near the distal end of the cavity, in a knob-like enlargement, or in a bifurcation. The enlargement commonly found at the end of the fibre, is said 'by Pacini to resemble a ganglion corpuscle; but this observation has not been confirmed. In some cases two nerves have been seen entering one Pacinian body, and in others a nerve after passing unaltered through one, has been observed to terminate in a second Pacinian corpuscle. The physiological import of these bodies is still obscure. Closely allied to Pacinian corpuscles, except that they are smaller and longer, with a row of nuclei around the central termination of the nerve in the core, are corpuscles of Herlst, which have been found chiefly in the tongues of ducks. The capsules are nearer together, and toward the centre the en- dothelial sheath appears to be absent. (2.) End-bulbs are found in the conjunctiva, in the penis and clitoris, in the skin, and in tendon; each is composed of a medullated nerve-fibre THE NERVOUS SYSTEM. 75 which terminates in corpuscles of various shapes, with a capsule containing a transparent or striated mass, in the centre of which terminates the axis- cylinder of the nerve-fibre, the ending of which is somewhat clubbed (Fig. 230). (3.) Touch corpuscles (Fig. 229) are found in the papillae of the skin or among its epithelium; they may be simple or compound; when simple they are large and slightly flattened transparent nucleated ganglion cells FIG. 309. FIG. 310. FIG. 309.— Extremities of a nerve of the finger with Pacinian corpuscles attached, about the natural size (adapted from Henle and KollikerX FIG. 310.— Pacinian corpuscle of the cat's mesentery. The stalk consists of a nerve-fibre (N) with its thick outer sheath. The peripheral capsules of the Pacinian corpuscle are continuous with the outer sheath of the stalk. The intermediary part becomes much narrower near the entrance of the axis-cylinder into the clear central mass. A hook-shaped termination with the end-bulb (T) is seen in the upper part. A blood-vessel (V) enters the Pacinian corpuscle, and approaches the end-bulb : it possesses a sheath which is the continuation of the peripheral capsules of the Pacinian corpuscle. X 100. (Klein and Noble Smith.) enclosed in a capsule; when compound the capsule contains several small cells. The corpuscles of Grandry form another variety, and have been noticed in the beaks and tongues of birds. They consist of corpuscles oval or spherical, contained within a delicate nucleated sheath, and containing several cells, two or more compressed vertically. The cells are granular and transparent, with a nucleus. The nerve enters on one side, and laying aside its medullary sheath, terminates in or between the cells. 76 HAND-BOOK OF PHYSIOLOGY. (4.) In plexuses, as in the cornea, both sub-epithelial and also intra- epithelial. (5.) In cells, as in the salivary glands.(p. 228, Vol. I.), and in the special sense organs. To the latter, further allusion will be made in a future chapter. (b.) Motory. — (1.) In unstriped muscle, the nerves first of all form a plexus, called the ground plexus (Arnold), corresponding to each group of muscle bundles; the plexus is made by the anastomosis of the primitive fibrils of the axis-cylinders. From the ground plexus, branches pass off. FIG. 311.— Summit of a Pacinian corpuscle of the human finger, showing the endothelial mem- branes lining the capsules. X 220. (Klein and Noble Smith.) and again anastomosing, form plexuses which correspond to each muscle bundle, — intermediary plexuses. From these plexuses branches consisting of primitive fibrils pass in between the individual fibres and anastomose. These fibrils either send off finer branches, or terminate themselves in the nuclei of the muscle cells. (2.) In striped muscle the nerves end in the so-called "motorial end- plates" having first formed, as in the case of unstriped fibres, ground and intermediary plexuses. The nerves are, however, medullated, and when a branch of the intermediary plexus passes to enter a muscle-fibre, its primitive sheath becomes continuous with the sarcolemma, and the axis-cylinder forms a network of its fibrils on the surface of the fibre. This network lies embedded in a flattened granular mass containing nuclei of several kinds; this is the nwtorial end-plate (Fig. 312). In batrachia, besides end-plates, there is another way in which the nerves end in the muscle-fibres, viz., by rounded extremities, to which oblong nuclei are attached. THE NERVOUS SYSTEM. 77 NERVE CELLS OR CORPUSCLES. The vesicular nervous substance contains, as its name implies, vesi- cles or corpuscles, in addition to fibres; and a structure, thus composed of corpuscles and inter-communicating fibres, constitutes a nerve-centre; the chief nerve-centres being the grey matter of the brain and spinal cord, and the various ganglia. In the brain and spinal cord a fine stroma of FIG. 312.— Two striped muscle-fibres of the hyoglossus of frog, a, Nerve end-plate; 6, nerve fibres leaving the end-plate; c, nerve-fibres, terminating after dividing into branches; d. a nucleus in which two nerve-fibres anastomose. X 600. (Arndt.) neuroglia (p. 34, Vol. I.), extends throughout both the fibrous and vesicular nervous substance, and forms a supporting and investing framework for the whole. The nerve-corpuscles which give to the ganglia and to certain parts of the brain and spinal cord the peculiar greyish or reddish-grey aspect by which these parts are characterized, are large, nucleated cells, filled with a finely granular material, some of which is often dark like pigment: 78 HAND-BOOK OF PHYSIOLOGY. the nucleus containing a nucleolus. Besides varying much in shape, partly in consequence of mutual pressure, they present such other varieties as make it probable either that there are two different kinds, or that, in the stages of their development, they pass through very different forms. Some of them are small, generally spherical or ovoid, and have a regular uninter- rupted outline. These simple nerve-corpuscles are most numerous in the sympathetic ganglia; each is enclosed in a nucleated sheath. Others, which are called caudate or stellate nerve-cor- puscles (Fig. 313), are larger, and have one, two, or more long processes issuing from them, the cells being called respectively uni- polar, bipolar, or multipolar; which pro- cesses often divide and subdivide, and appear tubular, and filled with the same kind of granular material that is contained within the corpuscle. Of these processes some appear to taper to a point and terminate at a greater or less distance from the corpuscle; some ap- pear to anastomose with similar offsets from other corpuscles; while others are continuous with nerve -fibres, the prolongation from the cell by degrees assuming the characters of the nerve-fibre with which it is continuous. Ganglion-cells are each enclosed in a trans- parent membranous capsule similar in appear- ance to the nucleated sheath of Schwann in FIG. 313. — Ganglion nerve-corpus- rn *j_i J.T • i • i j? cies of different shapes (Klein and nerve- fibres: within this capsule is a layer of small flattened cells. That process of a nerve-cell which becomes continuous with a nerve- fibre is always unbranched, as it leaves the cell. It at first has all the characters of an axis-cylinder, but soon acquires a medullary sheath, and then may be termed a nerve-fibre. This continuity of nerve-cells and fibres may be readily traced out in the anterior cornua of the grey matter of the spinal cord. In many large branched nerve-cells a distinctly fibril- lated appearance is observable; the fibrillae are probably continuous with those of the axis-cylinder of a nerve. THE FUNCTIONS OF NERVE FIBRES. It will be evident from the account of nervous action previously given (p. 45 et seq., Vol. II.) that nerve-fibres are stimulated to act by anything which increases their irritability, but that they are incapable of originating of themselves the condition necessary for the manifestation of their own functions. When a cerebro-spinal nerve-fibre is irritated in the living THE NERVOUS SYSTEM. 79 body, as by pinching, or by heat, or by electrifying it, there is, under ordinary circumstances, one of two effects, — either there is pain, or there is twitching of one or more muscles to which the nerve distributes its fibres. From various considerations it is certain that pain is always the result of a change in the nerve-cells of the brain. Therefore, in such an experiment as that referred to, the irritation of the nerve-fibre seems to the experimenter to be conducted in one of two directions, i.e., either to the brain (central termination of the fibre), when there is pain, or to a muscle (peripheral termination) when there is movement. Fio. 314. — An isolated sympathetic ganglion cell of man, showing sheath with nucleated-cell lin- ing, B. A. Ganglion-cell, with nucleus and neucleolus. C. Branched process. D. Unbranched pro- cess. Copied from Key and Retzius. x 750. (Klein and Noble Smith.) The effect of this simple experiment is a type of what always occurs when nerve-fibres are engaged in the performance of their functions. The result of stimulating them, which roughly imitates what happens naturally in the body, is found to occur at one or other of their ex- tremities, central or peripheral, never at both; and in accordance with this fact, and because, for any given nerve-fibre, the result is always the same, nerves are commonly classed as sensory or motor. It may be well to state, in order to avoid confusion, that the apparent conduction in both directions, which seems to occur when a nerve, say the ulnar or median, is irritated, depends on the fact that both motor and sensory fibres are bound up together in the same nerve-trunks — an arrange- 80 HAND-BOOK OF PHYSIOLOGY. ment which, for medium-sized and large nerves, is the rule rather than the exception. Conduction in Nerves. — A nerve when removed from the body will be found to conduct electrical impressions in either direction equally well, and microscopic examination fails to discover the slightest essential differ- ence between motor and sensory nerve-fibres. The question, therefore, naturally arises, whether the conduction of a stimulus in the living body, in one direction only, is not rather apparent than real, the difference in the result being due to the different connections of the two kinds of nerve-fibres respectively at their extremities. In other words, when the stimulation of a nerve-fibre causes pain, the result is due to its central extremity being in connection with structures which alone can give rise to the sensation, while its peripheral extremity, although the stimulus is equally conducted to it, has no connection with a structure which can respond to the irritation in any manner sensible to the observer. So, when motion is the result of a like irritation, it is because the peripheral extremity of the nerve-fibre is in connection with muscles which will re- spond by contracting, while it f central extremity, although equally stimulated, has no means of showing the fact by any evident result. That this is the true explanation is made highly probable, not merely by the absense of any structural differences in the two kinds of nerve -fibre, but also by the fact, proved by direct experiment, that if a centripetal nerve (gustatory) be divided, and its central portion be made to unite with the distal portion of a divided motor nerve (hypoglossal) the effect of irri- tating the former after the parts have healed, is to excite contraction in the muscles supplied by the latter. (Philippeaux and Vulpian. ) Classification of Nerve-Fibres. — 1. Centripetal, afferent, or, 2. Centrifugal, afferent, or motor. 3. Intercentral. Centripetal or afferent, and centrifugal or efferent, are frequently em- ployed in connection with nerve-fibres in lieu of the corresponding terms sensory and motor, because the result of stimulating a nerve of the former kind is not always the production of pain or other form of sensation, nor is motion the invariable result of stimulating the latter. Conduction in centripetal nerves may cause (a) pain, or some other kind of sensation; or (b) reflex action; or (c) inhibition, or restraint of action. Conduction in centrifugal nerves, may cause (a) contraction of muscle (p. 25, Vol. II.), (motor nerves); (b) it may influence nutrition (trophic nerves); or (c) may influence secretion (secretory nerves). The term intercentral is applied to those nerve-fibres which connect more or less distinct nerve-centres, and may, therefore, be said to have no peripheral distribution, in the ordinary sense of the term. It is a law of action in all nerve-fibres, and corresponds with the con- tinuity and simplicity of their course, that an impression made on any THE NERVOUS SYSTEM. 81 fibre, is simply and uninterruptedly transmitted along it, without being imparted or diffused to any of the fibres lying near it. In other words, all nerve-fibres are mere conductors of impressions. Their adaptation to this purpose is, perhaps, due to the contents of each fibre being complete!^ isolated from those of adjacent fibres by the membrane or sheath in which each is enclosed, and which acts, it may be supposed, just as silk or other non-conductors of electricity do, which, when covering a wire, prevent the electric condition of the wire from being conducted into the surrounding medium. Velocity of Nerve-force. — The change which a stimulus sets upon a nerve, of the exact nature of which we are unacquainted, appears to travel along a nerve-fibre in both directions in the form of a wave. Nervous force travels along nerve-fibres with considerable velocity. Helmholtz and Baxt have estimated the average rate of conduction in human motor nerves at 111 feet (nearly 29 metres) per second; this result agreeing very closely with that previously obtained by Hirsch. Kutherford's observations agree with those of Von Wittich, that the rate of transmission in sensory nerves is about 140 feet per second. Conduction in Sensory Nerves. — Centripetal nerves appear (p. 80, Vol. II.) able to convey impressions only from the parts in which they are distributed, toward the nerve-centre from which they arise, or to which they tend. Thus, when a sensitive nerve is divided, and irritation is applied to the end of the proximal portion, i.e., of the portion still con- nected with the nervous centre, sensation is perceived, or a reflex action ensues; but, when the end of the distal portion of the divided nerve is irritated, no effect appears. When an impression is made upon any part of the course of a sensory nerve, the mind may perceive it as if it were made not only upon the point to which the stimulus is applied, but also upon all the points in which the fibres of the irritated nerve are distrib- uted: in other words, the effect is the same as if the irritation were applied to the parts supplied by the branches of the nerve. When the whole trunk of the nerve is irritated, the sensation is felt at all the parts which receive branches from it; but when only individual portions of the trunk are irritated, the sensation is perceived at those parts only which are sup- plied by the several portions. Thus, if we compress the ulnar nerve where it lies at the inner side of the elbow-joint, behind the internal condyle, we have the sensation of "pins and needles," or of a shock, in the parts to which its fibres are distributed, namely, in the palm and back of the hand, and in the fifth and ulna half of the fourth finger. When stronger pressure is made, the sensations are felt in the fore-arm also; and if the mode and direction of the pressure be varied, the sensation is felt by turns in the fourth finger, in the fifth, and in the palm of the hand, or in the back of the hand, according as different fibres or fasciculi of fibres are more pressed upon than others. VOL. II.— 6. 82 HAND-BOOK OF PHYSIOLOGY. Illustrations. -t-li is in accordance with this law, that when parts are deprived of sensibility by compression or division of the nerves supplying them, irritation of the portion of the nerve connected with the brain still excites sensations which are felt as if derived from the parts to which the ^peripheral extremities of the nerve-fibres are distributed. Thus, there are cases of paralysis in which the limbs are totally insensible to external stimuli, yet are the seat of most violent pain, resulting apparently from irritation of the sound part of the trunk of the nerve still in connection with the brain, or from irritation of those parts of the nervous centre from which the sensory nerve or nerves which supply the paralyzed limbs originate. An illustration of the same law is also afforded by the cases in which division of a nerve for the cure of neuralgic pain is found useless, and in which the pain continues or returns, though portions of the nerves be removed. In such cases, the disease is probably seated nearer the nervous centre than the part at which the division of the nerve is made, or it may be in the nervous centre itself. In the same way may be ex- plained the fact, that when part of a limb has been removed by amputation, the remaining portions of the nerves may give rise to sensations which the mind refers to the lost part. When the stump is healed, the sensations which we are accustomed to have in a sound limb are still felt; and tingling and pains are referred to the parts that are lost, or to particular portions of them, as to single toes, to the sole of the foot, to the dorsum of the foot, etc. It must not be assumed, as it often has been, that the mind has no power of discriminating the very point in the length of any nerve-fibre to which an irritation is applied. Even in the instances referred to, the mind perceives the pressure of a nerve at the point of pressure, as well as in the seeming sensations derived from the extremities of the fibres: and in stumps, pain is felt in the stump, as well as, seemingly, in the parts re- moved. It is not quite certain whether those sensations are due to con- duction through the nerve fibres which are on their way to be distributed elsewhere, or through the sentient extremities of nerves which are them- selves distributed to the many trunks of the nerves, the nervi nervorum. The latter is the more probable supposition. When, in a part of the body which receives two sensory nerves, one is paralyzed, the other may or may not be inadequate to maintain the sensi- bility of the entire part; the extent to which the sensibility is preserved corresponding probably with the number of the fibres unaffected by the paralysis. There are instances in which the trunk of the chief sensory nerve supplied to a part having been divided, the sensibility of the part is still preserved by intercommunicating fibres from a neighboring nerve- trunk. Conduction in the Nerves of Special Sense.— The laws of con- duction in the olfactory, optic, auditory, gustatory — resemble in many .aspects those of conduction in the nerves of common sensation, just de- scribed. Thus the effect is always central; stimulation of the trunk of the nerve produces the same effect as that of its extremities, and if the THE NERVOUS SYSTEM. 83 nerve be severed, it is the central and not the peripheral extremity which responds to irritation, although the sensation is referred to the periphery. There are, however, certain peculiarities in the effect. Thus the various stimuli, which might cause, through an ordinary sensitive nerve, the sense of pain, would, if applied to the optic nerve, cause a sensation as of flashes of light; if applied to the olfactory, there would be a sense as of something smelt. And so with the other two. Hence the explanation of so-called subjective sensations. Irritation in the optic nerve, or the part of the brain from which it arises, may cause a patient to believe he sees flashes of light, and among the commonest troubles of the nerves of special sense, is the distressing noise in the head (tinnitus aurium), which depends on some unknown stimulation of the auditory nerve or centre quite unconnected with external sounds. Conduction in Motor Nerves. — Conduction in motor nerves pre- sents a remarkable contrast with the foregoing. Thus — the effect of applying a stimulus to the motor nerve is always noticeable, at the periph- eral extremity, in the contraction of muscles supplied by it. If a motor nerve be severed, irritation of the distal portion causes contraction of muscle, but no effect whatever is produced by stimulating that part of the nerve which is still in direct connection with the nerve-centre. Contractions are excited in all the muscles supplied by the branches given off by the nerve below the point irritated,- and in those muscles alone: the muscles supplied by the branches which come off from the nerve at a higher point than that irritated, are not directly excited to contraction. And it is from the same fact that, when a motor nerve enters a plexus and contributes with other nerves to the formation of a nervous trunk pro- ceeding from the plexus, it does not impart motor power to the whole of that trunk, but only retains it isolated in the fibres which form its con- tinuation in the branches of that trunk. FUNCTIONS OF NERVE-CENTRES. The functions of nerve-centres may be classified as follows: — 1. Conduction. 2. Transference. 3. Reflection. 4. Automatism. 5. Aug- mentation. 6. Inhibition. 1. Conduction. — Conduction in or through nerve-centres may be thus simply illustrated. The food in a given portion of the intestines, acting as a stimulus, produces a certain impression on the nerves in the mucous membrane, which impression is conveyed through them to the adjacent ganglia of the sympathetic. In ordinary cases, the consequence of such an impression on the ganglia is the movement by reflex action (p. 85, Vol. II. ) of the muscular coat of that and the adjacent part of the canal. But if irritant substances be mingled with the food, the sharper stimulus produces a stronger impression, and this is conducted 84 HAND-BOOK OF PHYSIOLOGY. through the nearest ganglia to others more and more distant; and, from all these, reflex motor impulses issuing, excite a wide-extended and more forcible action of the intestines. Or even through the sympathetic ganglia, the impression may be further conducted to the ganglia of the spinal nerves, and through them to the spinal cord, whence may issue motor impulses to the abdominal and other muscles, producing cramp. And yet further, the same morbid impression may be conducted through the spinal cord to the brain, where it may loefeU. In the opposite direc- tion, mental influence may be conducted from the brain through a suc- cession of nervous centres — the spinal cord and ganglia, and one or more ganglia of the sympathetic — to produce the influence of the mind on the digestive and other organs; altering both the quantity and quality of their secretions. 2. Transference. — It has been previously stated that impressions conveyed by any centripetal nerve-fibre travel uninterruptedly through- out its whole length, and are not communicated to adjacent fibres. When such an impression, however, reaches a nerve-centre, it may seem to be communicated to another fibre or fibres; as pain or some other kind of sensation may be felt in apart different altogether from that from which, so to speak, the stimulus started. Thus, in disease of the hip, there may be pain in the knee. This apparent change of place of a sen- sation to a part to which it would not seem properly to belong is termed transference. The transference of impressions may be illustrated by the fact just referred to, — the pain in the knee, which is a common sign of disease of the hip. In this case the impression made by the disease on the nerves of the hip-joint is conveyed to the spinal cord; there it is transferred to the central ends or connections of the nerve-fibres which are distributed about the knee. Through these the transferred impression is conducted to the brain, which, referring the sensation to the part from which it usually through these fibres receives impressions, feels as if the disease and the source of pain were in the knee. At the same time that it is transferred, the primary impression may be also conducted to the brain; and in this case the pain is felt in both the hip and the knee. And so, in whatever part of the respiratory organs an irritation may be seated, the impression it produces, being conducted to the medulla oblongata, is transferred to the central connections of the nerves of the larynx; and thence, being conducted as in the last case to the brain, the latter per- ceives the peculiar sensation of tickling in the glottis, which excites the act of coughing. Or, again, when the sun's light falls strongly on the eye, a tickling may be felt in the nose, exciting sneezing. A variety of transference, which may be termed radiation of impres- sions, is shown when an impression received by a nervous centre is dif- fused to many other parts in the same centre, and produces sensations ex- THE NERVOUS SYSTEM. 85 tending far beyond the part from which the primary impression was derived. Hence, as in the former cases, result various kinds of what have been denominated sympathetic sensations. Sometimes such sensations are referred to almost every part of the body: as in the shock and ting- ling of the skin produced by some startling noise. Sometimes only the parts immediately surrounding the point first irritated participate in the effects of the irritation; thus the aching of a tooth may be accompanied by pain in the adjoining teeth, and in all the surrounding parts of the face; the explanation of such a case being, that the irritation conveyed to the brain by the nerve-fibres of the diseased tooth is radiated to the central ends of adjoining fibres, and that the mind perceives this second- ary impression as if it were derived from the peripheral ends of the fibres. 3. Reflection. — In the cases of transference of nerve-force just described, it has been said that all that need be assumed is a communica- tion of the excited condition of an afferent nerve to other parts of its nerve-centre than that from which it takes its origin. In the case of reflection, on the other hand, the stimulus having been conveyed to a nerve-centre by a centripetal nerve, is conducted away again by a cen- trifugal nerve, and effects some change — motor, secretory or nutritive, at the peripheral extremity of the latter — the difference in effect depending on the variety of centrifugal nerve secondarily affected. As in transfer- ence, the reflection may take place from a certain limited set of cen- tripetal nerves to a corresponding and related set of centrifugal nerves; as when in consequence of the impression of light on the retina, the iris contracts, but no other muscle moves. Or the reflection may extend to widely different parts: as when an irritation in the larynx brings all the muscles engaged in expiration into coincident movement. Reflex move- ments, occurring quite independently of sensation, are generally called excito-motor ; those which are guided or accompanied by sensation, but not to the extent of a distinct perception or intellectual process are termed sensori-motor. Laws of Reflex Action. — (a) For the manifestation of every reflex action, these things are necessary: (1), one or more perfect centripetal nerve-fibres, to convey an impression; (2), a nervous centre for its recep- tion, and by which it may be reflected; (3), one or more centrifugal nerve-fibres, along which the impression may be conducted to (4), the muscular or other tissue by which the effect is manifested (p. 80, Vol. II.). In the absence of any one of these conditions, a proper reflex action could not take place; and whenever, for example, impressions made by external stimuli on sensory nerves give rise, to motions, these are never the result of the direct reaction of the sensory and motor fibres of the nerves on each other; in all such cases the impression is conveyed by the afferent fibres to a nerve-centre, and is therein communicated to the motor fibres. 86 HAND-BOOK OF PHYSIOLOGY. (b) All reflex actions are essentially involuntary, though most of them admit of being modified, controlled, or prevented by a voluntary effort. (c) Keflex actions performed in health have, for the most part, a dis- tinct purpose, and are adapted to secure some end desirable for the well- being of the body; but, in disease, many of them are irregular and pur- poseless. As an illustration of the first point, may be mentioned move- ments of the digestive canal, the respiratory movements, and the con- traction of the eyelids and the pupil to exclude many rays of light, when the retina is exposed to a bright glare. These and all other normal reflex acts afford also examples of the mode in which the nervous centres combine and arrange co-ordinately the actions of the nerve-fibres, so that many muscles may act together for the common end. Another instance of the same kind is furnished by the spasmodic contractions of the glottis on the contact of carbonic acid, or any foreign substance, with the sur- face of the epiglottis or larynx. Examples of the purposeless irregular nature of morbid reflex action are seen in the convulsive movements of epilepsy, and in the spasms of tetanus and hydrophobia. (d) Reflex muscular acts are often more sustained than those produced by the direct stimulus of muscular nerves. The irritation of a muscular organ, or its motor nerve, produces contraction lasting only so long as the irritation continues; but irritation applied to a nervous centre through one of its centripetal nerves, may excite reflex and harmonious contrac- tions, which last some time after the withdrawal of the stimulus (Volk- mann). Classification of Reflex Actions. — Reflex actions maybe classified as follows (Kuss): — 1. Those in which both the centripetal and cen- trifugal nerves concerned are cerebro-spinal; e.g., deglutition, sneezing, coughing, and, in pathological conditions, tetanus, epilepsy. 2. Those in which the centripetal nerve is cerebro- spinal, and the centrifugal is sympathetic, most often vaso-motor; e.g., secretion of saliva, or gastric juice; blushing or pallor of the skin. 3. Those in which the centripetal nerve is of the sympathetic system, and the centrifugal is cerebro-spinal. The majority of these are pathological, as in the case of convulsions pro- duced by intestinal worms, or hysterical convulsions. 4. Those in which both centripetal and centrifugal nerves are of the sympathetic system: as, for example, the obscure actions which preside over the secretion of the intestinal fluids, those which unite the various generative functions and many pathological phenomena. Relations between the Stimulus aud the Resulting" Reflex Action. — Certain rules showing the relation between the resulting reflex action and the stimulus have been drawn up by Pflliger, as follows: — 1. Laiv of unilateral reflection. — A slight irritation of sensory nerves is reflected along the motor nerves of the same region. Thus, if the skin of a frog's foot be tickled on the right side, the right leg is drawn up. THE NERVOUS SYSTEM. 87 2. Law of symmetrical reflection. — A stronger irritation is reflected, not only on one side, but also along the corresponding motor nerves of the opposite side. Thus, if the spinal cord of a man has been severed by a stab in the back, when one foot is tickled both legs will be drawn up. 3. Law of intensity. — In the above case, the contractions will be more violent on the side irritated. 4. Laiv of radiation. — If the irritation (afferent impulse) increases, it is reflected along the motor nerves which spring from points higher up the spinal cord, till at length all the muscles of the body are thrown into action. Simple and Co-ordinated Reflex Actions. — In the simplest form of reflex action a single nerve cell with an afferent and an efferent fibre is concerned, but in the majority of actual actions a number of cells are probably concerned, and the impression is as it were distributed among them, and they act in concert or co-ordination. This co-ordinating power belongs to nerve centres. Primary and Secondary or Acquired Reflex Actions. — We must carefully distinguish between such reflex actions which may be termed primary, and those which are secondary or acquired. As examples \ of the former class we may cite sucking, contraction of the pupil, drawing up the legs when the toes are tickled, and many others which are performed \ as perfectly by the infant as by the adult. • \ The large class of secondary reflex actions consists of acts which re- quire for their first performance and many subsequent repetitions, an effort of will, but which by constant repetition are habitually though not necessarily performed, mechanically, i.e., without the intervention of con- sciousness and volition. As instances we may take reading, writing, walking, etc. In endeavoring to conceive how such complicated actions can be per- formed without consciousness and will, we must suppose that in the first instance the will directs the nerve-force along certain channels causing the performance of certain acts, e.g., the various movements of flexion and extension involved in walking. After a time, by constant repetition, these routes become, to use a metaphor, well worn : there is, as it were, a beaten track along which the nerve-force travels with much greater ease than formerly: so much so that a slight stimulus, such as the pressure of the foot on the ground, is sufficient to start and keep going indefinitely the complex reflex actions of walking during entire mental abstraction, or even during sleep. In such acts as reading, writing, and tlje like, it would appear as if the will set the necessary reflex machinery going, and that the reflex actions go on uninterruptedly until again interfered with by the will. Without this capacity possessed by the nervous system of "organizing conscious actions into more or less unconscious ones," education or training 88 HAND-BOOK OF PHYSIOLOGY. would be impossible. A most important part of the process by which these acquired reflex actions come to be performed automatically consists in what is termed association. If two acts be at first performed voluntarily in succession, and this succession is often repeated, the performance of the first is at once followed mechanically by the second. Instances of this "force of habit" must be within the daily experience of every one. Of course it is only such actions as have become entirely reflex that can be performed during complete unconsciousness, as in sleep. Oases of somnambulism are of course familiar to every one, and authentic instances are on record of persons writing and even playing the piano during sleep. 4. Automatism. — To nerve centres, it is said, belongs the property of originating nerve-impulses, as well as of receiving them and conducting and reflecting them. The term automatism is employed to indicate the origination of nervous impulses in nerve-centres, and their conduction therefrom, independently of previous reception of a stimulus from another part. It is impossible, in the present state of our knowledge, to say definitely what actions in the body are really in this sense automatic. An example of automatic nerve-action has been already referred to, i.e., that of the respiratory centre, but the apparently best examples of automatism are found, however, in the case of the cerebrum, which will be presently considered. 5. and 6. Augmentation and Inhibition.— Nerve cells not only receive and reflect nerve impulses, and also in some cases even originate such impulses, but they are also capable of increasing the impulse, and the result is what is called augmentation; and when a nerve centre is in action its action is also capable of being increased or diminished (inhibi- tion) by afferent impulses. This is the case in whatever way the centre has caused the action, whether of itself or by means of previous afferent impulses. The action, by which a centre is capable of being inhibited or exalted, has been well shown in the case of the vaso-motor centre, before described (p. 155, Vol. I.). This power, which can be exerted from the periphery, is very important in regulating the action even of partially automatic centres such as the respiratory centre. CEKEBKO-SPINAL NEKVOUS SYSTEM. The physiology of the cerebro- spinal nervous system includes that of the Spinal Cord, Medulla Oblongata, and Brain, of the several Nerves given off from each, and of the Ganglia on those nerves. Membranes of the Brain and Spinal Cord.— The Brain and Spinal Cord are enveloped in three membranes — (1) the Dura Mater, (2) the Arachnoid, (3) the Pia Mater. (1.) The Dura Mater, or external covering, is a tough membrane com- THE NERVOUS SYSTEM. 89 posed of bundles of connective tissue which cross at various angles, and in whose interstices branched connective-tissue corpuscles lie: it is lined by a thin elastic membrane, and on the inner surface, and, where it is not FIG. 315.— View of the cerebro- spinal axis of the nervous system. The right half of the cranium and trunk of the body has been removed by a vertical section; the membranes of the brain and spinal marrow have also been removed, and the roots and first part of the fifth and ninth cranial, and of all the spinal nerves of the right side, have been dissected out and laid separately on the wall of the skull and on the several vertebrae opposite to the place of their natural exit from the cranio- spinal cavity. (After Bourgery.) adherent to the bone, on the outer surface also, is a layer of endothelial cells very similar to those found in serous membranes. (2.) The Arach- 90 HAND-BOOK OF PHYSIOLOGY. noid is a much more delicate membrane very similar in structure to the dura mater, and lined on its outer or free surface by an endothelial mem- brane. (3.) The Pia Mater consists of two chief layers between which numerous blood-vessels ramify. Between the arachnoid and pia mater is a network of fibrous-tissue trabeculae sheathed with endothelial cells: these sub-arachnoid trabeculje divide up the sub -arachnoid space into a number of irregular sinuses. There are some similar trabeculae, but much fewer in number, traversing the sub-dural space, i.e., the space between the dura mater and arachnoid. "Pacchionian" bodies are growths from the sub-arachnoid network of connective-tissue trabeculae which project through small holes in the inner layers of the dura mater into the venous sinuses of that membrane. The venous sinuses of the dura mater have been injected from the sub- arachnoidal space through the intermediation of these villous outgrowths known as " Pacchionian bodies." THE SPIRAL COED AND ITS NEEVES. The Spinal cord is a cylindriform column of nerve-substance con- nected above with the brain through the medium of the medulla oblon- gata, and terminating below, about the lower border of the first lumbar vertebra, in a slender filament of grey substance, the filum terminate, which lies in the midst of the roots of many nerves forming the cauda equina. Structure. — The cord is composed of white and grey nervous sub- stance, of which the former is situated externally, and constitutes its chief portion, while the latter occupies its central or axial portion, and is so arranged, that on the surface of a transverse section of the cord it appears like two somewhat crescentic masses connected together by a narrower por- tion or isthmus (Fig. 318). Passing through the centre of this isthmus in a longitudinal direction is a minute canal (central canal), which is continued through the whole length of the cord, and opens above into the space at the back of medulla oblongata and pons Varolii, called the fourth ventricle. It is lined by a layer of columnar ciliated epithelium. The spinal cord consists of two exactly symmetrical halves separated anteriorly and posteriorly by vertical fissures (the posterior fissure being deeper, but less wide and distinct than the anterior), and united in the middle by nervous matter which is usually described as forming two com- missures— an anterior commissure, in front of the central canal, consisting of medullated nerve fibres, and a posterior commissure behind the central canal, consisting also of medullated nerve-fibres, but with more neuroglia, which gives the grey aspect to this commissure (Fig. 316, B). Each half of the spinal cord is marked on the sides (obscurely at the lower part, but distinctly above) by two longitudinal furrows, which divide it into THE NERVOUS SYSTEM. 91 three portions, columns, or tracts, an anterior, lateral, and posterior. From the groove between the interior and lateral columns spring the anterior roots of the spinal nerves (B and c, 5); and just in front of the groove between the lateral and posterior column arise the posterior roots of the same (B, G) : a pair of roots on each side corresponding to each vertebra (Fig. 317). White m after. — The white matter of the cord is made up of medullated nerve fibres, of various sizes, arranged longitudinally around the cord under FIG. 316.— Different views of a portion of the spinal cord from the cervical region, with the roots of the nerves (slightly enlarged). In A, the anterior surface of the specimen is shown; the anterior nerve-root of its right side being divided; in B, a view of the right side is given; in c, the upper sur- face is shown: in D, the nerve-roots and ganglion are shown from below. 1. The anterior median fis- sure; 2. posterior median fissure; 3, anterior lateral depression, over which the anterior nerve-roots are seen to spread; 4, posterior lateral groove, into which the posterior roots are seen to sink; 5, anterior roots passing the ganglion; 5'. in A, the anterior root divided; 6, the posterior roots, the fibres of which pass into the ganglion 6' ; 7, the united or compound nerve ; 7', the posterior primary branch, seen in A and D to be derived in part from the anterior and in part from the posterior root. (Allen Thomson.) the pia mater and passing in to support the individual fibres in the delicate connective tissue or neuroglia made up of a very fine reticulum, with both small cells almost filled up by nuclei and stellate, branching corpuscles. Size. — The general rule respecting the size of different parts of the cord appears to be, that the size of each part bears a direct proportion to the size and number of nerve-roots given off from itself, and has but little relation to the size or number of those given off below it. Thus the cord is very large in the middle and lower part of its cervical portion, whence arise the large nerve-roots for the formation of the brachial plex- uses and the supply of the upper extremities, and again enlarges at the low- est part of its dorsal portion and the upper part of its lumbar, at the origins 92 HAND-BOOK OF PHYSIOLOGY. of the large nerves which, after forming the lumbar and sacral plexuses, are distributed to the lower extremities. The chief cause of the greater size at these parts of the spinal cord is increase in the quantity of grey matter; for there seems reason to believe that the white or fibrous part of the cord becomes gradually and progressively larger from below upward, doubtless from the addition of a certain number of upward passing fibres from each pair of nerves. From careful estimates of the number of nerve-fibres in a transverse section of the cord toward its upper end, and the number entering it by the anterior and posterior roots of each pair of nerves, it has been FIG. 317. — Section of grey matter of anterior cornu of a calf 's spinal cord; n /, nerve-fibres of "white matter in transverse section, showing axis-cylinder in centre of each; a r, anterior roots of spinal nerve passing out though white matter; g c, large stellate nerve-cells with nuclei; they are seen imbedded in neuroglia. (Schofield.) shown that in the numan spinal cord not more than half of the total num- ber of nerve-fibres entering the cord through all the spinal nerves are con- tained in a transverse section near its upper end. It is obvious, therefore, that at least half of the nerve-fibres entering it must terminate in the cord itself. Grey matter. — The grey matter of the cord consists essentially of an extremely delicate network of the primitive fibrillae of axis-cylinders, and which are derived from the ramification of multipolar ganglion c$lls of very large size, containing large round nuclei with nucleoli. This fine plexus is called Gerlach's network, and is mingled with the meshes of neuroglia, which in some parts is chiefly fibrillated, in others mainly granular and punctiform. The neuroglia is prolonged from the surface into the tip of the posterior cornu of grey matter and forms a jelly-like transparent substance, which when hardened is found to be reticular, and is called the substantia gelatinosa of Rolando. THE NERVOUS SYSTEM. 93 The multipolar cells are either scattered singly or arranged in groups, of which the following are to be distinguished: — (a.) In the anterior cormi. The groups found in the anterior cornu are generally two — one at the lateral part near the lateral column, and the other at the tip of the cornu in the middle line — sometimes, as in the lumbar enlargement, there is a third group more posterior. The cells of the anterior group are the largest. Into many of these cells the fibres of the anterior motor nerve- roots can be distinctly traced, (b.) In the tractus inter medio-lateralis. A group of nerve-cells midway between the anterior and posterior cornua, near the external surface of the grey matter. It is especially developed in the dorsal and also in the upper cervical region, (c. ) In the posterior FIG. 318.— Transverse section of half the spinal cord in the lumbar enlargement (semi-diagramma- tic). 1. Anterior median fissure; 2, posterior median fissure; 3, central canal lined with epithelium; 4. posterior commissure ; 5, anterior commissure ; 6, posterior column ; 7, lateral column ; 8, anterior column. The white substance is traversed by radiating trabeculae of pia mater. 9. Fasciculus of posterior nerve-root entering in one bundle ; 10, fasciculi of anterior roots entering in four spreading bundles of fibres ; 6, in the cervix cornu, decussating fibres from the nerve-roots and posterior com- missure ; c, posterior vesicular columns of Lockhart Clarke. About half way between the central canal and 7 are seen the group of nerve-cells forming the tractus intermedio-lateralis ; e, e, fibres of anterior roots; son.) x 7 are seen the group of nerve-cells forming oots; e', fibres of anterior roots which decussate in anterior commissure. (Allen Thom- trvicnlar columns of Lockhart Clark. These are found in the posterior cornua of grey matter toward the inner surface, extending from the cer- vical enlargement to the third lumbar nerves (Fig. 318, c). (d.) Smaller cells are scattered throughout the grey matter, but are found chiefly at the tip (caput cornu) of the posterior cornu, in a finely granular basis, and among the posterior root fibres (substantia gelatinosa cinerea of Rolando). The nerve-cells are connected by their processes immediately with the axis-cylinder of the fibres of the anterior or motor nerve-roots: whereas the nerve-cells of the posterior roots are connected with nerve-fibres, not 94 HAND-BOOK OF PHYSIOLOGY. directly, but only through the intermediation of Gerlach's nerve-network, in which their branching processes lose themselves. Spinal Nerves. — The spinal nerves consist of thirty-one pairs, issuing from the sides of the whole length of the cord, their number corre- sponding with the intervertebral foramina through which they pass. Each nerve arises by two roots, an anterior and posterior, the latter being the larger. The roots emerge through separate apertures of the sheath of dura mater surrounding the cord; and directly after their emergence, where the roots lie in the intervertebral foramen, a ganglion is found on the pos- terior root. The anterior root lies in contact with the anterior surface of the ganglion, but none of its fibres intermingle with those in the gan- glion (5, Fig. 316). But immediately beyond the ganglion the two roots coalesce, and by the mingling of their fibres form a compound or mixed spinal nerve, which, after issuing from the intervertebral canal, divides into an anterior and posterior branch, each containing fibres from both the roots (Fig. 316). The anterior root of each spinal nerve arises by numerous separate and converging bundles from the anterior column of the cord; the posterior root by more numerous parallel bundles, from the posterior column, or, rather, from the posterior part of the lateral column (Fig. 318), for if a fis- sure be directed inward from the groove between the middle and pos- terior columns, the posterior roots will remain attached to the former. The anterior roots of each spinal nerve consist of centrifugal fibres; the posterior as exclusively of centripetal fibres. Course of the Fibres of the Spinal Nerves.— (a) The Anterior roots enter the cord in several bundles which may be called: — (1) Inter- nal; (2) Middle; (3) External; all being more or less connected with the groups of multipolar cells in the anterior cornua. 1. The internal fibres are partly connected with internal group of nerve cells of anterior cornu of the same side; but some fibres pass over, through anterior commissure, to end in the anterior cornu of opposite side, probably in internal group of cells. 2. The middle fibres are partly in connection with the lateral group of cells in anterior cornu, and in part, pass backward to posterior cornu, having no connection with cells. 3. 'The external fibres are partly in connection with the lateral group of cells in the anterior cornu, but some fibres proceed direct into the lateral column without connection with cells and pass upward in it. (£) The Posterior roots enter the posterior cornu in two chief bundles, either at the tip, through or round the substantia gelatinosa, or by the inner side. The former enter the grey matter at once, and as a rule, turn upward or downward for a certain distance and then pass horizontally, some fibres reach the anterior cornua, passing at once horizontally; and the others, the opposite side, through the posterior grey commissure. Of those which enter by the inner side of the cornua the majority pass up THE NERVOUS SYSTEM. 95 (or down) in the white substance of the posterior columns, and enter the grey matter at various heights at the base of the posterior cornu, perhaps some pass directly upward without entering the grey matter. Those that enter the grey matter pass in various directions, some to join the lateral cells in the anterior cornu, some join the cells in the posterior vesicular column, and some pass across to the other side of the cord in the anterior commissure,, whilst others become again longitudinal in the grey matter. It should be here mentioned that the cells in the posterior vesicular column are connected with medullated fibres which pass horizontally to the white matter of the lateral columns and there become longitudinal. Course of the fibres in the cord. The nerve fibres which form the white matter of the cord are nearly all longitudinal fibres. It is, howevjer, a matter of great difficulty to trace these fibres by mere dissection, and so some other methods must be adopted. One method is based upon the fact P.M.C. FIG. 319. — Diagram of the spinal cord at the lower cervical region to show the track of fibres; d. p. t., direct pyramidal tract; c. p. t., crossed pyramidal tract; * direct cerebellar tract; p. M. c., posterior medium column. (Gowers.) that nerve fibres undergo degeneration when they are cut off from the centre with which they are connected, or when the parts to which they are distributed are removed, as in amputation of a limb; and information as to the course of the fibres has been obtained by tracing the course of these degenerated tracts. The second method consists in observing the development of the various tracts; some have their medullary substance later than others, and are to be distinguished by their more grey appear- ance. The chief tracts which have been made out are the following: — (1) The direct pyramidal tract (Fig. 319 d.p.t.), a comparatively small portion of the inner part of the anterior columns, which is traceable from the anterior pyramids of the medulla to the mid-dorsal region of the spinal cord. It consists of the fibres of the pyramids which do not undergo decussation in the medulla. There is reason for believing, however, that these fibres of the direct pyramidal tract undergo decussation through- out their course, and fibres pass over through the anterior commissure to join the lateral pyramidal tract (vide infra); (2) the Crossed pyra- midal tract (Fig. 319, c.p.t.) can be traced from the anterior pyramids 96 HAND-BOOK OF PHYSIOLOGY. of the medulla, and consists of fibres which decussate in the anterior fis- sure arid pass downward in the lateral columns near the posterior cornu of the grey matter to the lower end of the cord;. (3) Direct cerebellar tract (Fig. 319), which corresponds to the peripheral portion of the pos- terior lateral column between the crossed pyramidal tract and the edge of the cord, can be traced up directly to the cerebellum and down to the mid-lumbar region; (4). Posterior medium column, or Fasciculus of Golly is found on either side of the posterior commissure, and is trace- able upward as the fasciculus gracilis of the medulla, the fibres are con- nected with the cells of the posterior vesicular column. It is traceable downward to the mid-dorsal region. As regards the remaining part of the cord unoccupied by the above tracts little can be said. The portion of the posterior column between the posterior median column and the posterior roots of the spinal nerves, known as fasciculus cuneatus or Bur- dach's column, is composed of fibres of the posterior roots on their way to enter the grey substance at different heights. The antero-lateral column contains fibres from the anterior cornua of the same as well as of the op- posite side. Functions of the Spinal Nerves. — The anterior spinal nerve-roots are efferent or motor: the posterior are afferent or sensory (Sir. C. Bell). The fact is proved in various ways. Division of the anterior roots of one or more nerves is followed by complete loss of motion in the parts supplied by the fibres of such roots; but the sensation of the same parts remains perfect. Division of the posterior roots destroys the sensibility of the parts supplied by their fibres, while the power of motion continues unimpaired. Moreover, irritation of the ends of the distal portions of the divided anterior roots of a nerve excites muscular movements; irritation of the ends of the proximal portions, which are still in connection of the cord, is followed by no appreciable effect. Irritation of the distal portions of the divided posterior roots, on the other hand, produces no muscular movements and no manifestations of pain; for, as already stated, sensory nerves convey impressions only toward the nervous centres: but irritation of the proximal portions of these roots elicits signs of intense suffering. Occasionally, under this last irritation, muscular movements also ensue; but these are either voluntary, or the result of the irritation being reflected from the sensory to the motor fibres. Occasionally, too, irritation of the distal ends of divided anterior roots elicits signs of pain, as well as produ- cing muscular movements: the pain thus excited is probably the result either of cramp or of so-called recurrent sensibility (Brown-Sequard). Recurrent Sensibility. — If the anterior root of a spinal nerve be di- vided and the peripheral end be irritated, not only movements of the muscles supplied by the nerve take place, but also of other muscles, in- dicative of pain. If the main trunk of the nerve (after the coalescence of the roots beyond the ganglion) be divided, and the anterior root be irri- THE NERVOUS SYSTEM. 97 tated as before, tin general signs of pain still remain, although the con- traction of the muscles does not occur. The signs of pain disappear when the posterior root is divided. From these experiments it is believed that the stimulus passes down the anterior root to the mixed nerve and returns to the central nervous system through the posterior root by means of cer- tain sensory fibres from the posterior root, which loop back into the ante- rior root, before cont'nuing their course into the mixed nerve-trunk. Functions of the Ganglia on Posterior Roots. — The ganglia act as centres for the nutrition of the nerves, since when the nerves are severed from connection with the ganglia, the parts of the nerves so severed degenerate, whilst the parts which remain in connection with them do not. FUNCTIONS OF THE SPINAL COED. The power of the spinal cord, as a nerve-centre, may be arranged under the heads of (1) Conduction; (2) Transference; (3) Reflex action. (1) Conduction. — The functions of the spinal cord in relation to con- duction may be best remembered by considering its anatomical connections with other parts of the body. From these it is evident that, with the ex- ception of some few filaments of the sympathetic, there is no way by which nerve-impulses can be conveyed from the trunk and extremities to the brain or vice versd, other than that formed by the spinal cord. Through it, the impressions made upon the peripheral extremities or other parts of the spinal sensory nerves are conducted to the brain, where alone they can be perceived. Through it, also, the stimulus of the will, con- ducted from the brain, is capable of exciting the action of the muscles supplied from it with motor nerves. And for all these conductions of impressions to and fro between the brain and the spinal nerves, the per- fect state of the cord is necessary; for when any part of it 4s destroyed, and its communication with the brain is interrupted, impressions on the sensory nerves given off from it below the seat of injury, cease to be propagated to the brain, and the brain loses the power of voluntarily exciting the motor nerves proceeding from the portion of cord isolated from it. Illustrations of this are furnished by various examples of paraly- sis, but by none better than by the common paraplegia, or loss of sensa- tion and voluntary motion in the lower part of the body, in consequence of destructive disease or injury of a portion, including the whole thick- ness, of the spinal cord. Such lesions destroy the communication be- tween the brain and all parts of the spinal cord below the seat of injury, and consequently cut off from their connection with the brain the various organs supplied with nerves issuing from those parts of the cord. It is probable that the conduction of impressions along the cord is effected (at least, for the most part) through the grey substance, i.e., through the nerve -corpuscles and filaments connecting them. But all parts VOL. II.— 7. 98 HAND-BOOK OF PHYSIOLOGY. of the cord are not alike able to conduct all impressions; and as there are separate nerve-fibres for motor and for sensory impressions, so in the cord, separate and determinate parts serve to conduct always the same kind of impression. Experiments (chiefly by Brown-Sequard), point to the following con- clusions regarding the conduction of sensory and motor impressions through the spinal cord. It is important to bear in mind that the grey matter of the cord, though it conducts impressions giving rise to sensation, appears not to be .sensitive when it is directly stimulated. The explanation probably is, FIG. 320.— Diagram of the decussation of the conductors for voluntary movements, and those for sensation: a, r, anterior roots and their continuations in the spinal cord, and decussation at the lower part of the medulla oblongata, m o; p r, the posterior roots and their continuation and decus- sation in the spinal cord; g g, the ganglions of the roots. The arrows indicate the direction of the nervous action; r, the right' side; Z, the left side. 1, 2, 3, indicate places of alteration in a lateral half of the spino-cerebral axis, to show the influence on the two kinds of conduc* resulting from sec- tion of the cord at any one of these three places. (After Brown-Sequard.) that it possesses no apparatus such as exists at the peripheral terminations of sensory nerves, for the reception of sensory impressions. a. Sensory impressions, conveyed to the spinal cord by root-fibres of the posterior nerves are not conducted to the brain only by the posterior columns of the cord, but pass through them in great part into the central grey substance, by which they are transmitted to the brain (p r, Fig. 320). b. The impressions thus conveyed to the grey substance do not pass up to the brain to more than a slight degree, along that half of the cord corresponding to the side from which they have been received, but cross THE NERVOUS SYSTEM. 99 over to the other side almost immediately after entering the cord, and along it are transmitted to the brain. There is thus, in the cord itself, an almost complete decussation of sensory impressions brought to it; so that division or disease of one posterior half of the cord (3, Fig. 320) is followed by loss of sensation, not in parts on the corresponding, but in those of the opposite side of the body. From the same fact it happens that a longitudinal antero-posterior section of the cord, along its whole length, most completely abolishes sensibility on both sides of the body. c. The various sensations of touch, pain, temperature, and muscular contraction, are probably conducted along separate and distinct sets of fibres. All, however, with the exception of the last named, undergo decus- sation in the spinal cord. d. The posterior columns of the cord appear to have a great share in reflex movements. e. Impulses of the will, leading to voluntary contractions of muscles, appear to be transmitted principally along the antero -lateral columns; but if a transverse section of this part be made (the grey matter being in- tact) although at first no voluntary movements of the part below occur, this paralysis is only temporary, indicating that the grey matter may take on the conduction of these impulses. /. Decussation of motor impulses occurs, not in the spinal cord, as is the case with sensory impressions, but at the anterior part of the medulla oblongata (Fig. 321). Hence, motor impulses, having made their decus- sation, first enter the cord by the lateral tracts and adjoining grey matter, and then pass to the anterior columns and to the grey matter associated with them. Accordingly, division of the anterior pyramids, at the point of decussation (2, Fig. 320), is followed by paralysis of motion in all parts below; while division of the olivary bodies which constitute the true con- tinuations of the anterior columns of the cord, appears to produce very little paralysis. Disease or division of any part of the cerebro-spinal axis above the seat of decussation (1, Fig. 320) is followed, as well-known, by impaired or lost power of motion on the opposite side of the body; while a like injury inflicted below this part (3, Fig. 320), induces similar paralysis on the corresponding side. When one half of the spinal cord is cut through, complete anaesthesia of the other side of the body below the point of section results, but there is often greatly increased sensibility (hyperaesthesia) on the same side; so much so that the least touch appears to be agonizing. This condition may persist for several days. Similar effects may, in man, be the result of injury. Thus, in a patient who had sustained a severe lesion of the spinal cord in the cervical region, causing extensive paralysis and loss of sensation in the lower half of the body, there were two circumscribed areas, one on each arm, symmetrically placed, in which the gentlest touch caused extreme pain. 100 HAND-BOOK OF PHYSIOLOGY. In addition to the transmission of ordinary sensory and motor im- pulses, the spinal cord is the medium of conduction also of impulses to and from the vaso-motor centre in the medulla oblongata, and probably also contains special vaso-motor centres. 2. Transference.— Examples of the transference of impressions in the cord have been given (p. 84, Vol. II.); and that 'the transference takes place in the cord, and not in the brain, is nearly proved by the fre- quent cases of pain felt in the knee and not in the hip, in diseases of the hip; of pain felt in the urethra or glans penis, and not in the bladder, in calculus; for, if both the primary and the secondary or transferred im- pression were in the brain, both should be felt. 3. Reflection. — In man the spinal cord is so much under the control of the higher nerve-centres, that its own individual functions in relation to reflex action are apt to be overlooked; so that the result of injury, by which the cord is cut off completely from the influence of the encephalon, is apt to lessen rather than increase our estimate of its importance and individual endowments. Thus, when the human spinal cord is divided, the lower extremities fall into any position that their weight and the resistance of surrounding objects combine to give them; if the body is irritated, they do not move toward the irritation; and if they are touched, the consequent reflex movements are disorderly and purposeless; all power of voluntary movement is absolutely abolished. In other mammals, e.g. , rabbit or dog, after recovery from the shock of the operation, which takes some time, reflex actions in the parts below will occur after the spinal cord has been divided, a very feeble irritation being followed by extensive and co-ordinate movements. In the case of the frog, however, and many other cold-blooded animals, in which experimental and other injuries of the nerve-tissues are better borne, and in which the lower nerve-centres are less subordinate in their action to the higher, the reflex functions of the cord are still more clearly shown. When, for example, a frog's head is cut off, the limbs remain in or assume a natural position; they resume it when disturbed; and when the abdomen or back is irritated, the feet are moved with the manifest purpose of pushing away the irritation. The main difference in the cold-blooded animals, being that the reflex movements are more definite, complicated, and effective, although less energetic than in the case of mammals. It is as if the mind of the animal were still engaged in the acts; and yet all analogy would lead us to the belief that the spinal cord .of the frog has no different endowment, in kind, from those which belong to the cord of the higher vertebrata: the difference is only in degree. And if this be granted, it may be assumed that, in man and the higher animals, many actions are performed as reflex movements occurring through and by means of the spinal cord, although the latter cannot by itself initiate or even direct them independently. Co-ordinate Movement not a proof of Consciousness.— The THE NERVOUS SYSTEM. 1U1 evident adaptation and purpose in the movements of the cold-blooded animals, have led some to think that they must be conscious and capable of will without their brains. But purposive movements are no proof of consciousness or will in the creature manifesting them. The movements of the limbs of headless frogs are not more purposive than the movements of our own respiratory muscles are; in which we know that neither will nor consciousness is at all times concerned. It may not, in- deed, be assumed that the acts of standing, leaping, and other move- ments, which decapitated cold-blooded animals can perform, are also always, in the entire and healthy state, performed involuntarily, and under the sole influence of the cord; but it is probable that such acts may be, and commonly are, so performed, the higher nerve-centres of the animal having only the same kind of influence in modifying and direct- ing them, that those of man have in modifying and directing the move- ments of the respiratory muscles. Inhibition of Reflex Actions. — The fact that such movements as are produced by irritating the skin of the lower extremities in the human subject, after division or disorganization of a part of the spinal cord, do not follow the same irritation when the mind is active and connected with the cord through the brain, is, probably, due to the mind ordinarily perceiving the irritation and instantly controlling the muscles of the irri- tated and other parts; for, even when the cord is perfect, such involun- tary movements will often follow irritation, if it be applied when the mind is wholly occupied. When, for example, one is anxiously thinking, even slight stimuli will produce involuntary and reflex movements. So, also, during sleep, such reflex movements may be observed, when the skin is touched or tickled; for example, when one touches with the finger the palm of the hand of a sleeping child, the finger is grasped — the impres- sion on the skin of the palm producing a reflex movement of the muscles which close the hand. But when the child is awake, no such effect is produced by a similar touch. Further, many reflex actions are capable of being more or less con- trolled or even altogether prevented by the will: thus an inhibitory action may be exercised by the brain over reflex functions of the cord and the other nerve centres. The following may be quoted as familiar examples of this inhibitory action: — To prevent the reflex action of crying out when in pain, it is often sufficient firmly to clench the teeth or to grasp some object and hold it tight. When the feet are tickled we can, by an effort of will, prevent the reflex action of jerking them up. So, too, the involuntary closing of the eyes and starting, when a blow is aimed at the head, can be similarly restrained. Darwin has mentioned an interesting example of the on the other hand, such an instinctive reflex act may/C-foerridfc the 102 HAND-BOOK OF PHYSIOLOGY. strongest effort of the will. He placed his face close against the glass of the cobra's cage in the Reptile House at the Zoological Gardens, and though, of course, thoroughly convinced of his perfect security, could not by any effort of the will prevent himself from starting back when the snake struck with fury at the glass. It has been found by experiment that in a frog the optic lobes and optic thalami have a distinct action in inhibiting or delaying reflex action, and also that more generally any afferent stimulus, if sufficiently strong, may inhibit or modify any reflex action even in the absence of these centres. On the whole, therefore, it may, from these and like facts, be con- cluded that reflex acts, performed under the influence of the reflecting power of the spinal cord, are essentially independent of the brain and may be performed perfectly when the brain is separated from the cord: that these include a much larger number of the natural and purposive movements of the lower animals than of the warm-blooded animals and man: and that over nearly all of them the mind may exercise, through the higher nerve centres, some control; determining, directing, hinder- ing, or modifying them, either by direct action, or by its power over associated muscles. To these instances of spinal reflex action, some add yet many more, in- cluding nearly all the acts which seem to be performed unconsciously, such as those of walking, running, writing, and the like: for these are really involuntary acts. It is true that at their first performances they are voluntary, that they require education for their perfection, and are at all times so constantly performed in obedience to a mandate of the will, that it is difficult to believe in their essentially involuntary nature. But the will really has only a controlling power over their performance; it can hasten or stay them, but it has little or nothing to do with the actual carrying out of the effect. And this is proved by the circumstance that these acts can be performed with complete mental abstraction: and, more than this, that the endeavor to carry them out entirely by the exercise of the will is not only not beneficial, but positively interferes with their harmonious and perfect performance. Any one may convince himself of this fact by trying to take each step as a voluntary act in walking down stairs, or to form each letter or word in writing by a distinct exercise of the will. These actions, however, will be again referred to, when treating of their possible connection with the functions of the so-called sensory gan- yliti, p. 115 et seg., Vol. II. Morbid reflex actions.— -The relation of the reflex action to the strength of the stimulus is the same as was shown generally in the action of gan- glia, a slight stimulus producing a slight (p. 87, Vol. II.) movement, and a greater, a greater movement, and so on; but in instances in which we must THE NERVOUS SYSTEM. 103 assume that the cord is morbidly more irritable, i.e., apt to issue more nerv- ous force than is proportionate to the stimulus applied to it, a slight impres- sion on a sensory nerve produces extensive reflex movements. This appears to be the condition in tetanus, in which a slight touch on the skin may throw the whole body into convulsion. A similar state is induced by the introduction of strychnia and, in frogs, of opium into the blood; and numerous experiments on frogs thus made tetanic, have shown that the tetanus is wholly unconnected with the brain, and depends on the state induced in the spinal cord. Special Centres in Spinal Cord. — It may seem to have been im- plied that the spinal cord, as a single nerve-centre, reflects alike from all parts all the impressions conducted to it. But it is more probable that it should be regarded as a collection of nervous centres united in a con- tinuous column. This is made probable by the fact that segments of the cord may act as distinct nerve-centres, and exeite motions in the parts sup- plied with nerves given off from them; as well as by the analogy of cer- tain cases in which the muscular movements of single organs are under the control of certain circumscribed portions of the cord. Thus, — for the governance of the sphincter-muscles concerned in guarding the orifices respectively of the rectum and urinary bladder there are special nerve- centres in the lower part of the spinal cord (ano-spinal and vesico-spinal centres) ; while the actions of these are temporarily inhibited by stimuli which lead to defsecation and micturition. So, also, there are centres directly concerned in erection of the penis and in the emission of semen (genito-urinary). The emission of semen is a reflex act: the irritation of the glans penis conducted to the spinal cord, and thence reflected, ex- cites the successive and co-ordinate contractions of the muscular fibres of the vasa deferentia and vesiculae seminales, and of the accelerator urinae and other muscles of the urethra; and a forcible expulsion of semen takes place, over which the mind has little or no control, and which, in cases of paraplegia, may be unf elt. The erection of the penis, also, as already explained (p. 169, Vol. I.), appears to be in part the result of a reflex con- traction of the muscles by which the veins returning the blood from the penis are compressed. The involuntary action of the uterus in expelling its contents during parturition, is also of a purely reflex kind, dependent in part upon the spinal cord, though in part also upon the sympathetic system: its independence of the brain being proved by cases of delivery in paraplegic women, and also by the fact that delivery can take place whilst the patient is under the influence of chloroform. But all these spinal nerve-centres are intimately connected, both structurally and physi- ologically, one with another, as well as with those higher encephalic centres, without whose guiding influence their actions may become dis- orderly and purposeless, or altogether abrogated. Centre for Movements of Lymphatic Hearts of Frog. — Volkmann 104 HAND-BOOK OF PHYSIOLOGY. IKIS shown that the rhythmical movements of the anterior pair of lymphatic hearts in the frog depend upon nervous influence derived from the portion of spinal cord corresponding to the third vertebra, and those of the posterior pair on influence supplied by the portion of cord opposite the eighth vertebra. The movements of the heart continue, though the whole of the cord, except the above portions, be destroyed; but on the instant of destroying either of these portions, though all the rest of the cord be untouched, the movements of the corresponding hearts cease. What appears to be thus proved in regard to two portions of the cord, may be inferred to prevail in other portions also; and the inference is reconcilable with most of the facts known concerning the physiology and comparative anatomy of the cord. Tone of Muscles. — The influence of the spinal cord on the sphinc- ter ani (centre for defecation) has been already mentioned (see above). It maintains this muscle in permanent contraction, so that, except in the act of defaecation, the orifice of the anus is always closed. This influence of the cord resembles its common reflex action in being involun- tary, although the will can act on the muscle to make it contract more, or may inhibit the action of the ano-spinal centre so as to permit its dila- tation. The condition of the sphincter ani, however, is not altogether exceptional. It is the same in kind, though it exceeds in degree that condition of muscles which has been called tone, or passive contraction; a state in which they always when not active appear to be during health, and in which, though called inactive, they are in slight contraction, and certainly are not relaxed, as they are long after death, or when the spinal cord is destroyed. This tone of all the muscles of the trunk and limbs depends on the spinal cord, as the contraction of the sphincter ani does. If an animal be killed by injury or removal of the brain the tone of the muscles may be felt and the limbs feel firm as during sleep; but if the spinal cord be destroyed, the sphincter ani relaxes, and all the muscles feel loose, and flabby, and atonic, and remain so till rigor mortis com- mences. This kind of tone must be distinguished from that mere firm- ness and tension which it is customary to ascribe, under the name of tone, to all tissues that feel robust and not flabby, as well as to muscles. The tone peculiar to muscles has in it a degree of vital contraction: that of other tissues is only due to their being well nourished, and therefore com- pact and tense. All the foregoing examples illustrate the fact that the spinal cord is a collection of reflex centres, upon which the higher centres act by sending down impulses to set in motion, to modify or to control them; the movements or other phenomena of reflection being as it were the function of the ganglion cells to set in action, after an afferent impression has been conveyed to them by the posterior nerve-trunks in connection with them. The extent of the resulting movement depends upon the strength of the THE NERVOUS SYSTEM. 105 stimulus, the position at which it was applied as well as upon the condi- tion of the nerve cells; the connection between the cells being so intimate that a series of co-ordinated movements may result from a single stimula- tion, first of all affecting one cell. Whether the cells possess as well the power of originating impulses (automatism) is doubtful, but this is pos- sible in the case of vaso-motor centres which are situated in the cord (p. 154, Vol. I.), and of sweating centres which must be closely related to them, and possibly in the case of the centres for maintaining the tone of muscles. THE MEDULLA OBLONGATA. The medulla oblongata (Figs. 321, 322), is a column of grey and white nervous substance formed by the prolongation upward of the spinal cord and connecting it with the brain. FIG. 321. FIG. 322. FIG. 321.— Anterior surface of the pons Varolii, and medulla oblongata. a, a, anterior pyramids; 6, their decussation; c, c, olivary bodies; d, d, restiform bodies; e, arciform fibres; /, fibres described by Solly as passing from the anterior column of the cord to the cerebellum; gr, anterior column of the spinal cord; ft, lateral column; p, pons Varolii; i, its upper fibres; 5, 5, roots of the fifth pair of nerves. FIG. 322. — Posterior surface of the pons Varolii, corpora quadrigemina, and medulla oblongata. The peduncles of the cerebellum are cut short at the side, a, a, the upper pair of corpora quadri gemma; 6, ft, the lower; /,/, superior peduncles of the cerebellum; c, eminence connected with the nucleus of the hypoglossal nerve ; e, that of the glosso-pharyngeal nerve ; t, that of the vagus nerve ; d, d, restiform bodies; ;>, p, posterior pyramids; v, v, groove in the middle of the fourth ventricle, ending below in the calamus scriptorius; 7, 7, roots of the auditory nerves. Structure. — The grey substance which it contains is situated in the interior, and variously divided into masses and laminae by the white or fibrous substance which is arranged partly in external columns, and partly in fasciculi traversing the central grey matter. The medulla oblongata is larger than any part of the spinal cord. Its columns are pyriform, enlarging as they proceed toward the brain, and are continuous with those 106 HAND-BOOK OF PHYSIOLOGY. of the spinal cord. Each half of the medulla, therefore, may be divided into three columns or tracts of fibres, continuous with the three tracts of which each half of the spinal cord is made up. The columns are more prominent than those of the spinal cord, and separated from each other by deeper grooves. The anterior, continuous with the anterior columns of the cord, are called the anterior pyramids; the posterior, continuous with the posterior columns of the cord, and comprising the funiculus cune- atus, and the funiculus of Rolando (Fig. 323, /.c., /.#.), are called the restiform bodies. On the outer side of the anterior pyramids of each side,* near its upper part, is a small oval mass containing grey matter, and named the olivary body; and at the posterior part of the restiform column, immediately on each side of the posterior median groove, con- tinuous with the posterior median column of the cord, a small tract is marked off by a slight groove from the remainder of the restiform body, and called the posterior pyramid or fasciculus gracilis. The restiform columns, instead of remaining parallel with each other throughout the whole length of the medulla oblongata, diverge near its upper part, and by thus diverging, lay open, so to speak, a space called the fourth ven- tricle, the floor of which is formed by the grey matter of the interior of the medulla, by this divergence exposed. On separating the anterior pyramids, and looking into the groove between them, some decussating fibres of the lateral columns of the cord can be plainly seen. DISTRIBUTION OF THE FIBRES OF THE MEDULLA OBLOXGATA. The anterior pyramid of each side, although mainly composed of con- tinuations of the fibres of the anterior columns of the spinal cord, receives fibres from the lateral columns, both of its own and the opposite side; the latter fibres forming almost entirely the decussating strands which are seen in the groove between the anterior pyramids. Thus composed, the anterior pyramidal fibres proceeding onward to the brain are distributed in the following manner: — 1. The greater part pass on through the Pons to the Cerebrum. A portion of the fibres, however, running apart from the others, joins some fibres from the olivary body, and unites with them to form what is called the olivary fasciculus or fillet. 2. A small tract of fibres proceeds to the cerebellum. The lateral column of the cord on each side of the medulla, in pro- ceeding upward, divides into three parts, outer, inner, and middle, which are thus disposed of: — 1. The outer fibres (direct cerebellar tract) go with the restiform tract to the cerebellum. 2. The middle (crossed pyramidal tract) decussate across the middle line with their fellows, and form a part of the anterior pyramid of the opposite side. 3. The inner pass on to the cerebrum, at first superficially but afterward beneath the olivary body and the arcuate fibres, and then proceed along the floor of the fourth ventricle, on each side, under the name of the fasciculus teres. THE NERVOUS SYSTEM. 107 The posterior column of the cord is represented in the medulla by the posterior pyramid, or fasciculus gracilis, which is a continuation of the posterior median column, and by the restiform body, comprising the funiculus cuneatus and the funiculus of Rolando. The fasciculus gracilis (Fig. 323, f'(/), diverges above as the broader clava to form, one on either side, the lower lateral boundary of the fourth ventricle, then tapers off, and becomes no longer traceable. The funiculus cuneatus, or the rest of the posterior column of the cord, is continued up in the medulla as such (Fig. 323, f.c); but soon, in addition, between this and the continuation of the posterior nerve roots, appears another tract called the funiculus of Rolando (Fig. 323, f. R). High up, the funiculus cuneatus is covered FIG. 323.— Posterior view of the medulla, fourth ventricle, and mesencephalon (natural size). p. n, line of the posterior roots of the spinal nerves; p.m./., posterior median fissure; f.y., funiculus gracilis; cl., its clavis; f.c., funiculus cuneatus; /.J?., funiculus of Rolando; r.b., restiform body; c.s., calamus scriptorius; I., section of ligula or ttenia: part of choroid plexus is seen beneath it; Z.r., lateral recess of the ventricle; str., strige acusticse; t./., inferior fossa; s.f., posterior fossa; between it and the median sulcus is the fasciculus teres; cbl., cut surface of the cerebellar hemisphere; n.d., central or grey matter; s.m.v., superior medullary velum; Ing., ligula; s.c.p., superior cerebellar pedunclecut longitudinally; cr., combined section of the three cerebellar peduncles; c.g.s., e.g.*., cor- pora quadrigemina (superior and inferior); /r., fraenulum; /., fibres of the fillet seen on the surface of the tegmentum; c., crusti; l.g., lateral groove; c.r/.i., corpus geniculum internus; th., posterior part of thalamus; p., pineal body. The roman numbers indicate the corresponding cranial nerves. (E. A. Schafer.) by a set of fibres (arcuate fibres), which issue from the anterior median fissure, turn upward over the anterior pyramids to pass directly into the corresponding hemisphere of the cerebellum, being joined by the fibres of the direct cerebellar tract; the funiculus of Rolando, and the funiculus cuneatus, although appearing to join them, do not actually do so, except to a partial extent. Grey matter of the medulla. — To a considerable extent the, grey matter 108 HAND-BOOK OF PHYSIOLOGY. of the medulla is a continuation of that in the spinal cord, but the ar- rangement is somewhat different. The displacement of the anterior cornu takes place because of the decussation of a large part of the fibres of the lateral columns in the anterior pyramids passing through the grey matter of the anterior cornu, so that the caput cornu is cut off from the rest of the grey matter, and is, moreover, pushed backward by the olivary body, to be mentioned below. It lies in the lateral portion of the medulla, and exists for a time as the nucleus lateralis (Fig. 324, n.l)\ it consists of a reticulum of grey matter, containing ganglion cells intersected by white nerve fibres. The base of the anterior cornu is pushed more from the anterior surface, and when a:m.f. fa. P? FIG. 324.— Section of the medulla oblongata in the region of the superior pyramidal decussation. a.m./., anterior median fissure; /.a., superficial arciform fibres emerging from the fissure; »?/., pyramid; n.a.r., nuclei of arciform fibres; /.a1, deep arciform becoming superficial: o., lower end of olivary nucleus; n.L, nucleus lateralis; f.r., formatio reticularis: /.a2, arciform fibres proceeding from the formatio reticularis; <;., substantia gelatinosa of Rolando; a. F., ascending root of fifth nerve; n.c., nucleus cuneatus; n.c'., external cuneate nucleus; n.g., nucleus gracilis; f.g., nucleus gracilis; ».m./., posterior median fissure; c.c., central canal surrounded by grey matter, in which are n.XL, nucleus of the spinal accessory, and n.XIL, nucleus of the hypoglossal; s.d., superior pyramidal decussation. (Schwalbe.) (Modified from Quain.) the central canal opens out into the fourth ventricle, forms a collection of ganglion cells, producing the eminence of the fasciculus teres; from cer- tain large cells in it arise the hypoglossal nerve (Fig. 325, XII.}, which passes through the medulla, and appears between the olivary body and the anterior pyramids. In the funiculus teres, nearer to the middle line as well as to the sur- face, is a collection of nerve cells called the nucleus of that funiculus (Fig. 325, n.t). The grey matter of the posterior cornu is displaced somewhat by bands of fibres passing through it. The caput cornu appears at the surface as the funiculus of Rolando, whilst the cervix cornu is broken up into a reticulated structure which is displaced laterally, similar in struc- ture to the nucleus lateralis. From the increase of the base of the posterior cornu, the nuclei of the funiculus gracilis and funiculus cuneatus are de- THE NERVOUS SYSTEM. 109 rived (Fig. 324, n.g, n.c), and outside of the latter is an accessory nucleus formed (Fig. 324, n.c'). Internally to these latter, and also derived from the cells of the base of the posterior cornu and appearing in the floor of the fourth ventricle, when the central canal opens are the nuclei of the spinal accessory, vagus, and glosso-pharyngeal nerves. In the upper part of the medulla also, to the outside of these three nuclei, is found the principal auditory nucleus. All the above nuclei appear to be derived from a continuation of the grey matter of the spinal cord, but a fresh col- -/., formatio reticularis; c.r., corpus resti- forme, beginning to be formed, chiefly by arciform fibres, superficial and deep; n.c.. nucleus cunea- tus; ii.o., nucleus gracilis; t., attachment of the ligula; f.s., funiculus solitarius; n.X., nX'., two parts of the vagus nucleus ; n.XIL, hypoglossal nucleus; n.t., nucleus of the funiculus teres: n.am., nucleus ambiguous; r., raphe; A., continuation of the anterior column of cord; o'. o"., accessory olivary nucleus; P.O., pedunculus olivae. (Schwalbe.) (.Modified from Quain.) lection of grey matter not represented is interpolated between the anterior pyramids and the lateral column, contained within the olivary promi- nence, the wavy line of which (corpus dentatum) is doubled upon itself at tin angle with the extremities directed upward and inward (Fig. 325, o). There may also be a smaller collection of grey matter on the outer and inner side of the olivary nucleus known as accessory olivary nuclei. FUNCTIONS OF THE MEDULLA OBLONGATA. The functions of the medulla oblongata, like those of the spinal cord, may be considered under the heads of: 1. Conduction; 2. Transference and Reflection; and, in addition, 3. Automatism. 1. In conducting impressions the medulla oblongata has a wider ex- tent of function than any other part of the nervous system, since it is HO HAND-BOOK OF PHYSIOLOGY. obvious that all impressions passing to and fro between the brain and the spinal cord and all nerves arising below the pons, must be transmitted through it. 2. As a nerve-centre by which impressions are transferred or reflected, the medulla oblongata also resembles the spinal cord; the only difference between them consisting of the fact that many of the reflex actions per- formed by the former are much more important to life than any per- formed by the spinal cord. Demonstration of Functions.— It has been proved by repeated experiments on the lower animals that the entire brain may be gradually cut away in successive portions, and yet life may continue for a consider- able time, and the respiratory movements be uninterrupted. Life may also continue when the spinal cord is cut away in successive portions from below upward as high as the point of origin of the phrenic nerve. In Amphibia, the brain has been all removed from above, and the cord, as far as the medulla oblongata, from below; and so long as the medulla oblongata was intact, respiration and life were maintained. But if, in any animal, the medulla oblongata is wounded, particularly if it is wounded in its central part, opposite the origin of the pneumogastric nerves, the respiratory movements cease, and the animal dies asphyxi- ated. And this effect ensues even when all parts of the nervous system, except the medulla oblongata, are left intact. Injury and disease in men prove the same as these experiments on animals. Numerous instances are recorded in which injury to the me- dulla oblongata has produced instantaneous death; and, indeed, it is through injury of it, or of the part of the cord connecting it with the origin of the phrenic nerve, that death is commonly produced in fractures and diseases with sudden displacement of the upper cervical vertebrae. SPECIAL CENTRES. (1.) Respiratory. — The centre whence the nervous force for the pro- duction of combined respiratory movements appears to issue is in the in- terior of that part of the medulla oblongata from which the pneumo- gastric nerves or Vagi arise. The vagi themselves, indeed, are not essen- tial to the respiratory movements; for both may be divided without more immediate effect than a retardation of these movements. But in this part of the medulla oblongata is the nerve-centre whence the impulses producing the respiratory movements issue, and through which impulses conveyed from distant parts are reflected. The wide extent of connection which belongs to the medulla oblongata as the centre of the respiratory movements, is shown by the fact that impressions by .mechanical and other ordinary stimuli, made on many parts of the external or internal surface of the body, may modify, i.e., in- THE KERVOUS SYSTEM. Ill crease or diminish the rapidity of respiratory movements. Thus involun- tary respirations are induced by the sudden contact of cold with any part of the skin, as in dashing cold water on the face. Irritation of the mucous membrane of the nose produces sneezing. Irritation in the pharynx, oesophagus, stomach, or intestines, excites the concurrence of the respiratory movements to produce vomiting. Violent irritation in the rectum, bladder, or uterus, gives rise to a concurrent action of the respiratory muscles, so as to effect the expulsion of the feeces, urine, or foetus. (2.) Centre for Deglutition. — The medulla oblongata appears to be the centre whence are derived the motor impulses enabling the muscles of the palate, pharynx, and oesophagus to produce the successive co-ordi- nate and adapted movements necessary to the act of deglutition (p. 239, Vol. I.). This is proved by the persistence of swallowing in some of the lower animals after destruction of the cerebral hemispheres and cere- bellum; its existence in anencephalous monsters; the power of swallowing possessed by the marsupial embryo before the brain is developed; and by the complete arrest of the power of swallowing when the medulla ob- longata is injured in experiments. (3) A centre by which the move- ments of mastication are regulated (p. 226, Vol. I.). (4) Through the medulla oblongata, chiefly, are reflected the impressions which excite the secretion of saliva (p. 232, Vol. I.). (5) Cardio-inliibitory centre for the regulation of the action of the heart, through the pneumogastrics and probably also, the accelerating fibres of the sympathetic (p. 127, Vol. I.). (6) The chief vaso-motor centre. From this centre arise fibres which, passing down the spinal cord, issue with the anterior roots of the spinal nerves, and enter the ganglia and branches of the sympathetic system, by which they are conducted to the blood-vessels (p. 154, Vol. I.). (7) Cilio- spinal centre for the regulation of the iris, and other plain-fibred muscles of the eye. (8 and 9) Centres or ganglia of the special senses of hearing and taste. (10) The centre for speech, i.e., the centre by which the various muscular movements concerned in speech are co-ordinated or har- monized. (11) Centre by which the many muscles concerned in vomiting are harmonized. (12) The so-called diabetic centre, or, in other words, the grey matter in the medulla oblongata which, being irritated, causes glycosuria (p. 283, Vol. I.), is probably the vaso-motor centre; and this peculiar result of its stimulation is merely due to vaso-motor changes in the liver. Though respiration and life continue while the medulla oblongata is perfect and in connection with the respiratory nerves, yet, when all the brain above it is removed, there is no more appearance of sensation, or will, or of any mental act in the animal, the subject of the experiment, than there is when only the spinal cord is left. The movements are all involuntary and unfelt; and the medulla oblongata has, therefore, no 112 HAND-BOOK OF PHYSIOLOGY. claim to be considered as an organ of the mind, or as the seat of sensation or voluntary power. These are connected with parts to be afterward described. PONS VABOLII. Structure. — The meso-cephalon, or pons Varolii (vi, Fig. 326), is composed principally of transverse fibres connecting the two hemispheres of the cerebellum, and forming its principal transverse commissure. But it includes, interlacing with these, numerous longitudinal fibres which connect the medulla oblongata with the cerebrum, and transverse fibres which connect it with the cerebellum. Among the fasciculi of nerve- FIG. 326.— Base of the brain. 1. superior longitudinal fissure; 2, 2', 2', anterior cerebral lobe- 3 fissure of Sylvius, between anterior and 4,4',4", middle cerebral lobe; 5, 5', posterior lobe- 6 medulla oblongata; the figure is in the right anterior pyramid: 7.8,9,10, the cerebellum- + the inferior ver- miform process. The figures from I. to IX. are placed against the corresponding cerebral nerves- * *" fibres by which these several parts are connected, the pons also contains abundant grey or vesicular substance, which appears irregularly placed among the fibres, and fills up all the interstices. ^unctions.— The anatomical distribution of the fibres, both trans- verse and longitudinal, of which the pons is composed, is sufficient evi- dence of its functions as a conductor of impressions from one part of the cerebro-spinal axis to another. Concerning its functions as a nerve- centre, little or nothing is certainly known. THE NERVOUS SYSTEM. 113 CRURA CEREBRI. Structure. — The crura cerebri (in, Fig. 326), are principally formed of nerve-fibres, of which the inferior or more superficial (crusta) are con- tinuous with those of the anterior pyramidal tracts of the medulla oblon- gata, and the superior or deeper fibres (tegmentum) with the lateral and posterior pyramidal tracts, and with the olivary fasciculus. Besides these fibres from the medulla oblongata, are others from the cerebellum; and FIG. 327.— Dissection of brain, from above, exposing the lateral fourth and fifth ventricles with the surrounding parts. %— a, anterior part, or genu of corpus callosum; 6; corpus striatum; b', the corpus striatum of left side, dissected so as to expose its grey substance ; c, points by a line to the taenia semicircularis; d, optic thalamus; e, anterior pillars of fornix divided; below they are seen descending in front of the third ventricle, and between them is seen part of the anterior commissure ; in front of the letter e is seen the slit-like fifth ventricle, between the two laminae of the septum luci- dum ; /, soft or middle commissure ; (/, is placed in the posterior part of the third ventricle ; immedi- ately behind the latter are the posterior commissure (just visible) and the pineal gland, the two crura of which extend forward along the inner and upper margins of the optic thalami ; h and z, the cor- pora quadrigemina; fc, superior cms of cerebellum; close to fc is the valve of Vieussens. which has been divided so as to expose the fourth ventricle; I, hippocampus major and corpus fimbriatum, or taenia hippocampi; m, hippocampus minor; n, eminentia collaterals ; o, fourth ventricle; p, posterior surface of medulla oblongata; r, section of cerebellum; s, upper part of left hemisphere or cerebel- lum exposed by the removal of part of the posterior cerebral lobe. (Hirschfeld and Leveille.) some of the latter as well as a part of the fibres derived from the lateral tract of the medulla oblongata, decussate across the middle line. Each cms cerebri contains among its fibres a mass of grey substance, the locus niger. Functions. — With regard to their functions, the crura cerebri may be regarded as, principally, conducting organs: the crusta conducting VOL, II.— 8 114 HAND-BOOK OF PHYSIOLOGY. motor and the tegmentum sensory impressions. As nerve-centres they are probably connected with the functions of the third cerebral nerve, which arises from the locus niger, and through which are directed the chief of the numerous and complicated movements of the eyeball. The crura cerebri are also in all probability connected with the co-ordination of other movements besides those of the eye, as either rotatory (p. 119, Vol. II.) or disorderly movements result after section of either of them. COEPOKA QUADRIGEMIKA. The corpora quadrigemina (from which, in function, the corpora gen- iculata are not distinguishable), are the homologues of the optic lobes in Birds, Amphibia, and Fishes, and may be regarded as the principal nerve-centres for the sense of sight. Functions. — (1) The experiments of Flourens, Longet, and Hert- wig, show that removal of the corpora quadrigemina wholly destroys the power of seeing; and diseases in which they are disorganized are usually accompanied by blindness. Atrophy of them is also often a consequence of atrophy of the eyes. Destruction of one of the corpora quadrigemina (or of one optic lobe in birds), produces blindness of the opposite eye. This loss of sight is the only apparent injury of sensibility sustained by the removal of the corpora quadrigemina. The (2) removal of one of them affects the movements of the body, so that animals rotate, as after division of the crus cerebri, only more slowly: but this may be due to giddiness and partial loss of sight. (3) The more evident and direct in- fluence is that produced on the iris. It contracts when the corpora quad- rigemina are irritated: it is always dilated when they are removed: so that they may be regarded, in some measure at least, as the nervous centres governing its movements, and adapting them to the impressions derived from the retina through the optic nerves and tracts. (4) The centre for the co-ordination of the movements of the eyes is also contained in them. This centre is closely associated with that for contraction of the pupil, and so it follows that contraction or dilatation follows upon certain definite ocular movements. CORPORA STRIATA A^D OPTIC THALAMI. Structure. — (1.) The corpora striata are situated in front of the optic thalami, partly within and partly without the lateral ventricle. Each corpus striatum consists of two parts. (a.) Intraventricular portion (caudate nucleus) is conical in shape, with the base of the cone forward; it consists of grey matter, with white substance in its centre, which comes from the corresponding cerebral peduncle, (b.) Extraventricular portion (lenticular nucleus) is separated THE NERVOUS SYSTEM. 115 from the other portion by a layer of white material. It is seen on section of the hemisphere. Its horizontal section is wider in the centre than at the end. On the outside is the grey lamina (claustrum). Between the corpus striatum and optic thalamus is the tcenia semicir- cularis, a semi-transparent band which is continued back into the white substance of the roof of the descending horn of the ventricle. (2) The Optic Thalami are oval in shape, and rest upon the crura cerebri. The upper surface of each thalamus is free, and of white sub- stance; it projects into the lateral ventricle. The posterior surface is also white. The inner sides of the two optic thalarni are in partial contact, and are composed of grey material uncovered by white, and are, as a rule, connected by a transverse portion. Functions. — The two ganglia, the Corpus Striatum and Optic Thal- amus, are placed between the cerebral convolutions and the crus cerebri of the same side. It is probable that although some of the fibres of the crus pass without interruption into the cerebrum, the majority of the fibres pass into these ganglia; first of all the lower fibres (crusta) into the corpus striatum, and the upper (tegmentum) into the optic thalamus, and then out into the cerebrum. From the position of these bodies, it would be reasonable to suppose that they were interposed in function between the operation of the will on the one hand, and on the other with the sen- sori-motor apparatus below them, and it is believed that this is the case, although the evidence is not exact: the theory that the corpus striatum is the motor ganglion, and that, when injured, the communication be- tween the will ancl the muscles of one half of the body is broken (hemi- plegia), being supported by many pathological facts and physiological ex- periments, and generally received by pathologists. It is found that the cerebral functions are as a rule unimpaired. In the same way the evidence that the optic thalamus is the sensory ganglion depends upon similar observations, that when injured or destroyed, sensation of the opposite side of the body is impaired or lost. In both cases, the parts paralyzed are on the opposite side to the lesions, the decussation of both sets of fibres taking place, as we have seen, below the ganglia. It is a fact, however, that many experiments and pathological observations are op- posed to the above theory, which must therefore be received with caution. THE CEREBELLUM. The Cerebellum (7, 8, 9, 10, Fig. 326), is composed of an elongated central portion called the vermiform processes, and two hemispheres. Each hemisphere is connected with its fellow, not only by means of the vermiform^ processes, but also by a bundle of fibres called the middle crus or peduncle (the latter forming the greater part of the pons Varolii), while the superior crura with the valve of Vieussens connect it with the cere- 116 HAND-BOOK OF PHYSIOLOGY. brum (5, Fig. 328), and the inferior crura (formed by the prolonged res- tiform bodies) connect it with the medulla oblongata (3, Fig. 328). Structure.— The cerebellum is composed of white and grey matter, the latter being external, like that of the cerebrum, and like it, infolded, FIG. 328.— Cerebellum in section and of fourth ventricle, with the neighboring parts. 1, median groove of fourth ventricle, ending below in the calamus scriptorius, with the longitudinal eminences formed by the fasciculi teretes, one on each side; 2, the same groove, at the place where the white streaks of the auditory nerve emerge from it to cross the floor of the ventricle; 3, inferior crus or peduncle of the cerebellum, formed by the restif orm body; 4, posterior pyramid; above this is the calamus scriptorius; 5, superior crus of cerebellum, or processus e cerebello ad cerebrum (or ad testes); 6, 6, fillet to the side of the crura cerebri; 7, 7, lateral grooves of the crura cerebri; 8, cor- pora quadrigeinina. (From Sappey after Hirschfeld and Leveille.) so that a larger area may be contained in a given space. The convolutions of the grey matter, however, are arranged after a different pattern, as shown in Fig. 328. Besides the grey substance on the surface, there is, near the centre of the white substance of each hemisphere, a small capsule FIG. 329. — Outline sketch of a section of the cerebellum, showing the corpus dentatum. The section has been carried through the left lateral part of the pons, so as to divide the superior pedun- cle and pass nearly through the middle of the left cerebellar hemisphere. The olivary body has also been divided longitudinally so as to expose in section its corpus dentatum. c r, crus cerebri: /, fillet; g, corpora quadrigemina; sp, superior peduncle of the cerebellum divided; m p, middle pedun- cle or lateral part of the pons Varolii, with fibres passing from it into the white stem; a v, continu- ation of the white stem radiating toward the arbor vitae of the folia; c d, corpus dentatum; o, olivary body with its corpus dentatum; p, anterior pyramid. (Allen Thomson.) %. of grey matter called the corpus dentatum (Fig. 329, cd) resembling very closely the corpus dentatum of the olivary body of the medulla oblongata (Fig. 324, o). THE NERVOUS SYSTEM. 117 If a section be taken through the cortical portion of the cerebellum, the following distinct layers can be seen (Fig. 330) by microscopic exami- nation. (1.) Immediately beneath the pia mater (p m) is a layer of consider- able thickness, which consists of a delicate connective tissue, in which are iVi ivAVS Bjiwifli FIG. 330.— Vertical section 9f dog's cerebellum; p m. pia mater; p, corpuscles of Purkinje, which are branched nerve-cells lying in a single layer and sending single processes downward and more numerous ones upward, which branch continuously and extend through the deep "molecular layer" toward the free surface; g, dense layer of ganglionic corpuscles, closely resembling nuclear layers of retina; /, layer of nerve-fibres, with a few scattered ganglionic corpuscles. This last layer (f f) constitutes part of the white matter of the cerebellum, while the layers between it and the free sur- face are grey matter. (Klein and Noble Smith.) scattered several spherical corpuscles like those of the granular layer of the retina, and also an immense number of delicate fibres passing up toward the free surface and branching as they go. These fibres are the processes of the cells of Purkinje. (2.) The Cells of Purkinje (p). These are a 118 HAND-BOOK OF PHYSIOLOGY. single layer of branched nerve-cells, which give off a single unbranched process downward, and numerous processes up into the external layer, some of which become continuous with the scattered corpuscles. (3.) The granular layer (g], consisting of immense numbers of corpuscles closely resembling those of the nuclear layers of the retina. (4. ) Nerve fibre layer (/). Bundles of nerve-fibres forming the white matter of the cerebellum, which, from its branched appearance, has been named the "arbor vitae." Functions. — The physiology of the Cerebellum may be considered in its relation to sensation, voluntary motion, and the instincts or higher faculties of the mind. Its supposed functions, like those of every other part of the nervous system, have been determined by physiological experi- ment, by pathological observation, and by its comparative anatomy. (1.) It is itself insensible to irritation, and may be all cut away with- out eliciting signs of pain (Longet). Its removal or disorganization by disease is also generally unaccompanied by loss or disorder of sensibility; animals from which it is removed can smell, see, hear, and feel pain, to all appearance, as perfectly as before (Flourens; Magendie). Yet, if any of its crura be touched, pain is indicated; and, if the restiform tracts of the medulla oblongata be irritated, the most acute suffering appears to be produced. So that, although the restiform tracts of the medulla oblongata, which themselves appear so sensitive, enter the cerebellum, it cannot be regarded as a principal organ of sensation. (2.) Co-ordination of Movements. — In reference to motion, the experi- ments of Longet and many others agree that no irritation of the cerebel- lum produces movement of any kind. Eemarkable results, however, are produced by removing parts of its substance. Flourens (whose experi- ments have been confirmed by those of Bouillaud, Longet, and others) extirpated the cerebellum in birds by successive layers. Feebleness and want of harmony of muscular movements were the consequence of remov- ing the superficial layers. When he reached the middle layers, the ani- mals became restless without being convulsed; their movements were vio- lent and irregular, but their sight and hearing were perfect. By the time that the last portion of the organ was cut away, the animals had entirely lost the powers of springing, flying, walking, standing, and pre- serving their equilibrium. When an animal in this state was laid upon its back, it could not recover its former posture, but it fluttered its wings, and did not lie in a state of stupor; it saw the blow that threatened it, and endeavored to avoid it. Volition and sensation, therefore, were not lost, but merely the faculty of combining the actions of the muscles; and the endeavors of the animal to maintain its balance were like those of a drunken man. The experiments afforded the same results when repeated on all classes of animals; and from them and the others before referred to, Flourens THE NERVOUS SYSTEM. 119 inferred that the cerebellum belongs neither to the sensory nor the intel- lectual apparatus; and that it is not the source of voluntary movements, although it belongs to the motor apparatus; but is the organ for the co- ordination of the voluntary movements, or for the excitement of the combined action of muscles. Such evidence as can be obtained from cases of disease of this organ confirms the view taken by Flour ens; and, on the whole, it gains sup- port from comparative anatomy; animals whose natural movements require most frequent and exact combinations of muscular actions being those whose cerebella are most developed in proportion to the spinal cord. Foville supposed that the cerebellum is the organ of muscular sense, i.e., the organ by which the mind acquires that knowledge of the actual state and position of the muscles which is essential to the exercise of the will upon them; and it must be admitted that all the facts just referred to are as well explained on this hypothesis as on that of the cerebellum being the organ for combining movements. A harmonious combination of muscular actions must depend as much on the capability of appreciating the condition of the muscles with regard to their tension, and to the force with which they are contracting, as on the power which any special nerve-centre may possess of exciting them to contraction. And it is because the power of such harmonious movement would be equally lost, whether the injury to the cerebellum involved injury to the seat of mus- cular sense, or to the centre for combining muscular actions, that experi- ments on the subject afford no proof in one direction more than the other. The theory once believed, that the cerebellum is the organ of sexual passion, has been long disproved. Forced Movements. — The influence of each half of the cerebellum is directed to muscles on the opposite side of the body; and it would appear that for the right ordering of movements, the actions of its two halves must be always mutually balanced and adjusted. For if one of its crura, or if the pons on either side of the middle line, be divided, so as to cut off the medulla oblongata and spinal cord the influence of one of the hemi- spheres of the cerebellum, strangely disordered movements ensue (forced movements). The animals fall down on the side opposite to that on which the crus cerebelli has been divided, and then roll over continuously and repeatedly; the rotation being always round the long axis of their bodies, and generally from the side on which the injury has been inflicted. The rotations sometimes take place with much rapidity; as often, according to Magendie, as sixty times in a minute, and may last for several days. Similar movements have been observed in men; as by Serres in a man in whom there was apoplectic effusion in the right crus cerebelli; and by Belhomme in a woman in whom an exostosis pressed on the left crus. They may, perhaps, be explained by assuming that the division or injury of the crus cerebelli produces paralysis or imperfect and disorderly move- 120 HAND-BOOK OF PHYSIOLOGY. ments of the opposite side of the body; the animal falls, and then, strug- gling with the disordered side on the ground, and striving to rise with the other, pushes itself over; and so again and again, with the same act, rotates itself. Such movements cease when the other crus cerebelli is divided; but probably only because the paralysis of the body is thus made almost com- plete. Other varieties of forced movements have been observed, especially those named "circus movements," when the animal operated upon moves round and round in a circle; and again those in which the animal turns over and over in a series of somersaults. Nearly all these movements may result on section of one or other of the following parts; viz., crura cere- bri, medulla, pons, cerebellum, corpora quadrigemina, corpora striata, optic thalami, and even, it is said, of the cerebral hemispheres. THE CEREBRUM. The Cerebrum (composed of two so-called Cerebral hemispheres) is placed in connection with the Pons and Medulla oblongata by its two crura or peduncles (III., Fig. 326): it is connected with the cerebellum by the processes called superior crura of the cerebellum, or processus a cere- bello adtestes, and by a layer of grey matter, called the valve of Vieussens, which lies between these processes, and extends from the inferior vermiform process of the .cerebellum to the corpora quadrigemina of the cerebrum. These parts, which thus connect the cerebrum with the other principal divisions of the cerebro-spinal system, may, therefore, be regarded as the continuation of the cerebro-spinal axis or column; on which, as a kind of offset from the main nerve-path, the cerebellum is placed; and on the further continuation of which in the direct line, is placed the cerebrum (Fig. 331). The Cerebrum is constructed, like the other chief divisions of the cerebro- spinal system, of grey (vesicular and fibrous) and white (fibrous) matter; and,. as in the case of the Cerebellum (and unlike the spinal cord and medulla oblongata), the grey matter (cortex) is external, and forms a capsule or covering for the white substance. For the evident purpose of increasing its amount without undue occupation of space, the grey matter is variously infolded so as to form the cerebral convolutions. Convolutions of the Cerebrum. — For convenience of description, the surface of the brain has been divided into five lobes (Gratiolet). 1. Frontal (F. , Figs. 332, 333), limited behind by the fissure of Rolando (central fissure), and beneath by the fissure of Sylvius. Its surface con- sists of three main convolutions, which are approximately horizontal in direction and are broken up into numerous secondary gyri. They are teAied the superior, middle, and inferior frontal convolutions. -In addi- tion, the frontal lobe contains, at its posterior part, a convolution which runs upward almost vertically ("ascending frontal"), and is bounded in front by a fissure termed the praecentral, behind by that of Rolando. THE NERVOUS SYSTEM. 121 FIG. 331.— Plan in outline of the encephalon, as seen from the right side, ^. The parts are rep- resented as separated from one another somewhat more than natural, so as to show their connec- tions. A, cerebrum; f, g, h, its anterior, middle, and posterior lobes; e. fissure of Sylvius; B, cere- bellum; C, pons Varolii; D, medulla oblongata; a, peduncles of the cerebrum; 6, c, d, superior mid- dle, and inferior peduncles of the cerebellum. (From Quain.) FIG. 332.— Lateral view of the brain (semi-diagrammatic). F, Frontal lobe; P, Parietal lobe: O, Occipital lobe; T, Temporo-sphenoidal lobe; S, fissure of Sylvius; S', horizontal, S", ascending ramus of the same; c, sulcus centralis (fissure of Rolando); A, ascending frontal; B, ascending parietal convolution; Fl, superior; F2, middle: F3, inferior frontal convolutions: fl, superior; f 3, inferior frontal sulcus; f3, prse-ceutral sulcus; PI, superior parietal lobule ; P2, inferior parietal lobule con- sisting of P2, supramarginal gyms, and P2', angular gyrus; ip, interparietal sulcus; cm, termination of calloso-marginal fissure; Ol, first, O2, second, O3, third occipital convolutions; po, parieto-oeoipi- tal fissure; o, transverse occipital fissure; o2. sulcus occipitalis inferior: Tl. first. T;!. second, T3, third temporo-sphenoidal convolutions; tl, first, t2, second temporo-sphenoidal fissures. (Ecker.) 122 HAND-BOOK OF PHYSIOLOGY. 2. Parietal (P.). This lobe is bounded in front by the fissure of Bo- lando, behind by the external perpendicular fissure (parieto-occipital), and below by the fissure of Sylvius. Behind the fissure of Rolando is the "as- cending" parietal" convolution, which swells out at its upper end into what is termed the superior parietal lobule. The superior parietal lobule is separated from the inferior parietal lobule by the mtra-parietal sulcus. The inferior parietal lobule (pli courbe) is situated at the posterior and upper end of the fissure of Sylvius; it consists of (a) an anterior part (supra- marginal convolution) which hooks round the end of the fissure of Sylvius, and joins the superior temporal convolution, and a posterior part (b) (angu- lar gyrus) which hooks round into the middle temporal convolution. FIG. 383.— View of the brain from above (semi-diagrammatic). SI, end of horizontal ramus of fis- sure of Sylvius. The other letters refer to the same parts as in Fig. 332. (Ecker.) 3. Temporo-splienoidal (T. ), contains three well-marked convolutions, parallel to each other, termed the superior, middle, and inferior temporal. The superior and middle are separated by the parallel fissure. 4. Occipital (0.). This lobe lies behind the external perpendicular or parieto-occipital fissure, and contains three convolutions, termed the supe- rior, middle, and inferior occipital. They are often not well marked. In man, the external parieto-occipital fissure is only to be distinguished as a notch in the inner edge of the hemisphere; below this it is quite obliter- ated by the four annectent gyri (plis de passage) which run nearly hori- zontally. The upper two connect the parietal, and the lower two the tem- poral with the occipital lobe. 5. The central lobe, or island of Eeil, which contains a number of radiating convolutions (gyri operti). The internal surface ^Fig. 334) contains the following gyri and sulci: Gyrus fornicatus, a long curved convolution, parallel to and curving round the corpus callosum, and swelling out at its hinder and upper end THE NERVOUS SYSTEM. 123 into the quadrate lobule (praecuneus), which is continuous with the superior parietal lobule on the external surface. Marginal convolution runs parallel to the preceding, and occupies the space between it and the edge of the longitudinal fissure. The two convolutions are separated by the calloso -marginal fissure. The internal perpendicular fissure is well marked, and runs downward to its junction with the calcarine fissure: the wedge-shaped mass inter- vening between these two is termed the cuneus. The calcarine fissure corresponds to the projection into the posterior cornu of the lateral ven- tricle, termed the Hippocampus minor. The temporo-sphenoidal lobe on its internal aspect is seen to end in a hook (uncinate gyrus). The notch round which it curves is continued up and back as the dentate or hippo- FIG. 334.— View of the right hemisphere in the median aspect (semi-diagrammatic). CC, corpus callosum longitudinally divided; Gf , gyrus fornicatus; H, gyrus hippocampi; h,sulcus hippocampi; U, uncinate gyrus: cm, calloso-margmal fissure ; Fl, median aspect of first frontal convolution; c, terminal portion of sulcus centralis (fissure of Rolando) ; A, ascending frontal ; B, ascending parietal convolution; PI', prsecuneus; Oz, cuneus; po, parieto-occipital fissure; o, sulcus occipitalis transver- sus; oc, calcarine fissure; oc', superior; oc", inferior ramus of the same; D, gyrus descendens; T4, gyrus occipito-temporalis lateralis (lobulus f usiformis) ; T5, gyrus occipito-temporalis medialis (lobulus hngualis). (Ecker.) campal sulcus; this fissure underlies the projection of the hippocampus major within the brain. There are three internal temporo -occipital con- volutions, of which the superior and inferior ones are usually well marked, the middle one generally less so. The collateral fissure (corresponding to the eminentia collateralis) forms the lower boundary of the superior temporo-occipital convolution. All the above details will be found indicated in the diagrams (Fig. 332, 333, 334). Structure. — The cortical grey matter of the brain consists of five layers (Meynert) (Fig. 335). 1. Superficial layer with abundance of neuroglia and a few small multi- polar ganglion-cells. 2. A large number of closely packed small ganglion- cells of pyramidal shape. 3. The most important layer, and the thickest of all : it contains many large pyramidal ganglion-cells, each with a process running off from the apex vertically toward the free surface, and lateral processes at the base which are always branched. Also a median process 124 HAND-BOOK OF PHYSIOLOGY. from the base of each cell which is unbranched and becomes continuous with the axis-cylinder of a nerve-fibre. 4. Numerous ganglion-cells: termed the "granular formation" • by Meynert. 5. Spindle-shaped and branched ganglion-cells of moderate size arranged chiefly parallel to the free surface (vide Fig. 335). FIG. 335. FIG. 336. fc'« FIG. 337. FIG. 335. — The layers of the cortical g;rey matter of the cerebrum. (Meynert.) FIG. 337. — [Drawn by G. Munro Smith from ammonium bichromate preparations by E. C. Bousfield.J According to recent observations by Bousfield, the fibres of the medullary centre become connected with the multipolar ganglion cells of the fourth layer, and, from these latter, branches pass to the angles at the bases of the pyramidal cells of the third layer of the cortex (Fig. 337, a). From the apices of the pyramidal cells, the axis-cylinder processes pass upward for a THE NERVOUS SYSTEM. 125 considerable distance, and finally terminate in ovoid corpuscles (Fig. 336) closely resembling, and homologous with, the corpuscles in which the ulti- mate ramifications of the branched cells of Purkinje in the cerebellum terminate. Thus it would seem that the large pyramidal cells of the third layer are themselves homologous with the cells of Purkinje in the cere- bellum. The white matter of the brain, as of the spinal cord, consists of bundles of medullated, and, in the neighborhood of the grey matter, of non- medullated nerve-fibres, which, however, as is the case in the central nervous system generally, have no external nucleated nerve-sheath, which are held together by delicate connective tissue. The size of the fibres of the brain is usually less than that of the fibres of the. spinal cord: the average diameter of the former being about TO -BOOK OF PHYSIOLOGY. FIG. 348. roots of their nerves. The spinal cord, indeed, appears to be a large source of the fibres of the sympathetic nerve. Through the communi- cating branches between the spinal nerves a"d the prse-vertebral sympathetic ganglia, which have been generally called roots or origins of the sympathetic nerve, an interchange is effected between all the spinal nerves and the sym- pathetic trunks; all the gan- glia, also, which are seated on the cerebral nerves, have roots (as they are called) through which fila- ments of the cerebral nerves are added to their own. So that, probably, all sympa- thetic nerves contain some intermingled cerebral or spinal nerve-fibres; and all cerebral and spinal nerves, some filaments derived from the sympathetic sys- tem or from ganglia. But the proportions in which these filaments are mingled are not uniform. The nerves which arise from the brain and spinal cord retain throughout their course and distribution a prepon- derance of cerelro-spinal fibres, while the nerves im- mediately arising from the so-called sympathetic gan- glia probably contain a ma- jority of sympathetic fibres. But inasmuch as there is THE NERVOUS SYSTEM. 153 no certainty that in structure the branches of cerebral or spinal nerves differ always from those of the sympathetic system, it is impossible in the present state of our knowledge to be sure of" the source of fibres which from their structure might lead the observer to believe that they arose from the brain or spinal cord on the one hand, or from the sym- pathetic ganglia on the other. In other words, although the large white medullated fibres are especially characteristic of cerebro-spinal nerves, and the pale or non-medullated fibres of a sympathetic nerve, in which they largely preponderate, there is no certainty to be obtained in a doubtful case, of whether the nerve-fibre is derived from one or the other, from mere examination of its structure. It may be derived from either source. Functions. — It may be stated generally that the sympathetic nerve- fibres are simple conductors of impressions,, as are those of the Cerebro- spinal system; and that the ganglionic centres have (each in its appropri- ate sphere) the like powers both of conducting, transferring, reflecting, and possibly of augmenting or of inhibiting impressions made on them. The power possessed by the sympathetic ganglia of conducting impres- sions is sufficiently proved in disease, as when any of the viscera, usually unfelt, give rise to sensations of pain, or when a part not commonly sub- ject to mental influence is excited or retarded in its actions by the vari- ous conditions of the mind; for in all these cases impressions must be conducted to and fro through the whole distance between the part and the spinal cord and brain. So, also, in experiments, now more than FIG. 348. — Diagrammatic view of the Sympathetic cord of the right side, showing its connections with the principal cerebro-spinal nerves and the main prseaortic plexuses. 1-4. (From Quain's Anatomy.) Cerebro-spinal nerves. — VI, a portion of the sixth cranial as it passes through the cavernous sinus, receiving two twigs from the carotid plexus of the sympathetic nerve; O, ophthalmic ganglion connected by a twig with the carotid plexus; M, connection of the spheric-palatine ganglion by the Vidian nerve with the carotid plexus; C, cervical j cervical plexus ; Br, brachial plexus ; D 6, sixth intercostal nerve; D 12, twelfth; L 3, third lumbar nerve; S 1, first sacral nerve; S 3, third; S 5, fifth; Cr, an- terior crural nerve; Cr', great sciatic; pn, pneumogastric nerve in the lower part of the neck; r, re- current nerve winding round the subclavian artery. Sympathetic Cord.—c, superior cervical ganglion; c', second or middle; c", inferior: from each of these ganglia cardiac nerves (all deep on this side) are seen descending to the cardiac plexus; d 1, E laced immediately below the first dorsal sympathetic ganglion; d 6, is opposite the sixth; 1 1, first imbar ganglion; c g, the terminal or coccygeal ganglion. P>-ceaortic and Visceral Plexuses.— p p, pharyngeal, and, lower down, laryngeal plexus; pi, pos- terior pulmonary plexus spreading from the vagus on the back of the right bronchus; o a, on the aorta, the cardiac plexus, toward which, in addition to the cardiac nerves from the three cervical ninth dorsal ganglia; +, small splanchnic from the ninth and tenth; + +, smallest or third splanch- nic from the eleventh: the first and second of these are shown joining the solar plexus, s o; the third descending to the renal plexus, r e; connecting branches between the solar plexus and the vagi are also represented; pri, above the place where the right vagus passes to the lower or posterior surf ace of the stomach; pn", the left distributed on the anterior or upper surface of the cardiac portion of the organ: from the solar plexus large branches are seen surrounding the arteries of the cceliac axis. and descending to m s, the superior mesenteric plexus; opposite to this is an indication of the supra- renal plexus; below r e (the renal plexus), the spermatic plexus is also indicated; a o, on the front of the aorta, marks the aortic plexus, formed by nerves descending from the solar and supe- rior mesenteric ' rounding the cor connected above with the aortic plexus, receiving nen below into the right and left pelvic or inferior hypogastric plexuses; pi, the right pelvic plexus: from this the nerves descending are joined by those from the plexus on the superior hemorrhoidal vessels, mi', by sympathetic nerves from the sacral ganglia, and by numerous visceral nerves from the third and fourth sacral spinal nerves, and there are thus formed the rectal, vesical, and other plexuses, which ramify upon the viscera from behind forward and from below upward, as toward ir, and v, the rectum and bladder. 154 HAND-BOOK OF PHYSIOLOGY. sufficiently numerous, irritations of the semilunar ganglia, the splanchnic nerves, the thoracic, hepatic, and other ganglia and nerves, have elicited expressions of pain, and have excited movements in the muscular organs supplied from the irritated part. In the case of pain, or of movements affected by mental conditions, it may be supposed that the conduction of impressions is effected through the cerebro-spinal fibres which are mingled in all, or nearly all, parts of the sympathetic nerves. There are no means of deciding this; but if it be admitted that the conduction is effected through the cerebro-spinal nerve-fibres, then, whether or not they pass uninterruptedly between the brain or spinal cord and the part affected, it must be assumed that their mode of conduction is modified by the ganglia. For, if such cerebro- spinal fibres are conducted in the ordinary manner, the parts should be always sensible and liable to the influence of the will, and impressions should be conveyed to and fro instantaneously. But this is not the case; on the contrary, through the branches of the sympathetic nerve and its ganglia, none but intense impressions, or impressions exaggerated by the morbid excitability of the nerves or ganglia, can be conveyed. Respecting the general action of the ganglia of the sympathetic nerve, in reflex or other Actions, little need be said here, since they may be taken as examples by which to illustrate the common modes of action of all nerve-centres (see p. 83, Vol. II.). Indeed, complex as the sympathetic system, taken as a whole, is, it presents in each of its parts a simplicity not to be found in the cerebro-spinal system: for each ganglion with afferent and efferent nerves forms a simple nervous system, and might serve for the illustration of all the nervous actions with which the mind is unconnected. The parts principally supplied with sympathetic nerves are usually capable of none but involuntary movements, and when the mind acts on them at all, it is only through the strong excitement or depressing influ- ence of some passion, or through some voluntary movement with which the actions of the involuntary part are -commonly associated. The heart, stomach, and intestines are examples of these statements; for the heart and stomach, though supplied in large measure from the pneumogastric nerves, yet probably derive through them few filaments except such as have arisen from their ganglia, and are therefore of the nature of sym- pathetic fibres. The parts which are supplied with motor power by the sympathetic nerve continue to move, though more feebly than before, when they are sepa- rated from their natural connections with the rest of the sympathetic sys- tem, and wholly removed from the body. Thus, the heart, after it is taken from the body, continues- to beat in Mammalia for one or two minutes, in reptiles and Amphibia for hours; and the peristaltic motions of the intestine continue under the same circumstances. Hence the motions of THE NERVOUS SYSTEM. 155 the parts supplied with nerves from the sympathetic are shown to be, in a measure, independent of the brain and spinal cord; this independent maintenance of their action being, without doubt, due to the fact that they contain, in their own substance, the apparatus of ganglia and nerve- fibres by which their motions are immediately governed. It seems to be a general rule, at least in animals that have both cere- bro-spinal and sympathetic nerves much developed, that the involuntary movements excited by stimuli conveyed through ganglia are orderly and like natural movements, while those excited through nerves without ganglia are convulsive and disorderly; and the probability is that, in the natural state, it is through the same ganglia that natural stimuli, impress- ing centripetal nerves, are reflected through centrifugal nerves to the involuntary muscles. As the muscles of respiration are maintained in uniform rhythmic action chiefly by the reflecting and combining power of the medulla oblongata, so are those of the heart, stomach, and intes- tines, by their several ganglia. And as with the ganglia of the sympa- thetic and their nerves, so with the medulla oblongata and its nerves dis- tributed to the respiratory muscles, — if these nerves of the medulla oblongata itself be directly stimulated, the movements that follow are con- vulsive and disorderly; but if the medulla be stimulated through a cen- tripetal nerve, as when cold is applied to the skin, then the impressions are reflected so as to produce movements which, though they may be very quick and almost convulsive, are yet combined in the plan of the proper respiratory acts. Among the ganglia of the sympathetic nerves to which this co-ordina- tion of movements is to be ascribed, must be reckoned, not those alone which are on the principal trunks and branches of the sympathetic ex- ternal to any organ, but those also which lie in the very substance of the organs; such as those of the heart (p. 125, Vol. I.). Those also may be included which have been found in the mesentery close by the intestines, as well as in the muscular and sub-mucous tissue of the stomach and in- testinal canal (pp. 244, 255, Vol. I.)., and in other parts. The extension of discoveries of such ganglia will probably diminish yet further the num- ber of instances in which the involuntary movements appear to be effected independently of nervous influence. Respecting the influence of the sympathetic system on various physi- ological processes, see Heart (p. 127, Vol. I.), Arteries (p. 152, Vol. I.), Animal Heat (p. 316, Vol. I.), Salivary Glands (p. 233, Vol. I.), Stomach (p. 252, Vol. I.), Intestines (p. 255, Vol. I.). These are parts which have been specially investigated. But they are not in any way exceptional. All physiological processes must, of necessity, either directly or through vaso-motor fibres, be under the influence of the Sympathetic system. Influence of the Nervous System on Nutrition. — It has been held that the nervous svstem cannot be essential to a healthy course of 156 HAND-BOOK OF PHYSIOLOGY. nutrition, because in plants and the early embryo, and in the lowest animals, in which no nervous system is developed, nutrition goes on with- out it. But this is no proof that in animals which have a nervous system, nutrition may be independent of it; rather, it may be assumed, that in ascending development, as one system after another is added or in- creased, so the highest (and, highest of all, the nervous system) will always be inserted and blended in a more and more intimate relation with all the rest; according to the general law, that the interdependence of parts augments with their development. The reasonableness of this assumption is proved by many facts show- ing the influence of the nervous system on nutrition, and by the most striking of these facts being observed in the higher animals, and especially in man. The influence of the mind in the production, aggravation, and cure of organic diseases is matter of daily observation, and a sufficient proof of influence exercised on nutrition through the nervous system. Independently of mental influence, injuries either to portions of the nervous centres, or to individual nerves, are frequently followed by de- fective nutrition of the parts supplied by the injured nerves, or deriving their nervous influence from the damaged portions of the nervous centres. Thus, lesions of the spinal cord are sometimes followed by mortification of portions of the paralyzed parts; and this may take place very quickly, as in a case in which the ankle sloughed within twenty-four hours after an injury of the spine. After such lesions also, the repair of injuries in the paralyzed parts may take place less completely than in others; so, in a case in which paraplegia was produced by fracture of the lumbar verte- brae, and, in the same accident, the humerus and tibia were fractured. The former in due time united: the latter did not. The same fact was illustrated by some experiments, in which having, in salamanders, cut off the end of the tail, and then thrust a thin wire some distance up the spinal canal, so as to destroy the cord, it was found that the end of the tail was reproduced more slowly than in other salamanders in whom the spinal cord was left uninjured above the point at which the tail was ampu- tated. Illustrations of the same kind are furnished by the several cases in which division or destruction of the trunk of the trigeminal nerve has been followed by incomplete and morbid nutrition of the corresponding side of the face; ulceration of the cornea being often directly or indirectly one of the consequences of such imperfect nutrition. Part of the wasting and slow degeneration of tissue in paralyzed limbs is probably referable also to the withdrawal of nervous influence from them; though, perhaps, more is due to the want of use of the tissues. Undue irritation of the trunks of nerves, as well as their division or destruction, is sometimes followed by defective or morbid nutrition. To this may be referred the cases in which ulceration of the parts supplied by the irritated nerves occurs frequently, and continues so long as the THE NERVOUS SYSTEM. 157 irritation lasts. Further evidence of the influence of the nervous system upon nutrition is furnished by those cases ir which, from mental anguish, or in severe neuralgic headaches, the hali' becomes grey very quickly, or even in a few hours. So many and varied facts leave little doubt that the nervous system exercises an influence over nutrition as over other organic processes; and they cannot be easily explained by supposing that the changes in the nutritive processes are only due to the variations in the size of the blood- vessels supplying the affected parts, although this is, doubtless, one im- portant element in producing the result. The question remains, through what class of nerves is the influence exerted? When defective nutrition occurs in parts rendered inactive by injury of the motor nerve alone, as in the muscles and other tissues of a paralyzed face or limb, it may appear as if the atrophy were the direct consequence of the loss of power in the motor nerves; but it is more prob- able that the atrophy is the consequence of the want of exercise of the parts; for if the muscles be exercised by artificial irritation of their nerves their nutrition will be less defective. The defect of the nutritive process which ensues in the face and other parts, however, in consequence of destruction of the trigeminal nerve, cannot be referred to loss of influence of any motor nerves; for the motor-nerves of the face and eye, as well as the olfactory and optic, have no share in the defective nutrition which follows injury of the trigeminal nerve; and one or all of them may be destroyed without any direct disturbance of the nutrition of the parts they severally supply. It must be concluded, therefore, that the influence which is exercised by nerves over the nutrition of parts to which they are distributed is to be referred, in part or altogether, either to the nerves of common sensa- tion, or to the vaso-motor nerves, or, as it is by some supposed, to nerve fibres (trophic nerves), which preside specially over the nutrition of the tissues and organs to which they are supplied. It is not at present possible to say whether the influence on nutrition is exercised through the cerebro-spinal or through the sympathetic nerves, which, in the parts on which the observation has been made, are generally combined in the same sheath. The truth perhaps is, that it may be ex- erted through either or both of these nerves. The defect of nutrition which ensues after lesion of the spinal cord alone, the sympathetic nerves being uninjured, and the general atrophy which sometimes occurs in con- sequence of diseases of the brain, seem to prove the influence of the cerebro-spinal system: while the observation that inflammation of the eye is a constant result of ligature of the sympathetic nerve in the neck, and many other observations of a similar kind, exhibit very well the influence of the latter nerve in nutrition. CHAPTER XIX. THE SENSES. THROUGH the medium of the Nervous system the mind obtains a knowledge of the existence both of the various parts of the body, and of the external world. This knowledge is based upon sensations resulting from the stimulation of certain centres in the brain, by irritations con- veyed to them by afferent (sensory) nerves. Under normal circumstances, the following structures are necessary for sensation: (a) A peripheral organ for the reception of the impression; (b) a nerve for conducting it; (c) a nerve-centre for feeling or perceiving it. Classification of Sensations.— Sensations may be conveniently classed as (1) common, and (2) special. (1.) Common Sensations. — Under this head fall all those general sen- sations which cannot be distinctly localized in any particular part of the body, such as Fatigue, Discomfort, Faintness, Satiety, together with Hunger and Thirst, in which, in addition to a general discomfort, there is in many persons a distinct sensation referred to the stomach or fauces. In this class must also be placed the various irritations of the mucous mem- brane of the bronchi, which give rise to coughing, and also the sensations derived from various viscera indicating the necessity of expelling their contents; e.g., the desire to defsecate, to urinate, and, in the female, the sensations which precede the expulsion of the f oatus. We must also include such sensations as itching, creeping, tickling, tingling, burning, aching, etc. , some of which come under the head of pain: they will be again referred to in describing the sense of Touch. It is impossible to draw a very clear line of demarcation between many of the common sensations above men- tioned, and the sense of Touch, whicn forms the connecting link between the general and special sensations. Touch is, indeed, usually classed with the special senses, and will be considered in the same group with them; yet it differs from them in being common to many nerves, e.g., all the sensory spinal nerves, the vagus, glosso-pharyngeal, and fifth cerebral nerves, and in its impressions being communicable through many organs. Among common sensations must also be ranked the muscular sense, which has been already alluded to. It is by means of this sense that we become aware of the condition of contraction or relaxation of the various muscles and groups of muscles, and thus obtain the information necessary THE SENSES. 159 for their adjustment to various purposes — standing, walking, grasping, etc. This muscular sensibility is shown in our power to estimate the dif- ferences between weights by the different muscular efforts necessary to raise them. Considerable delicacy may be attained by practice, and the difference between 19 £ oz. in one hand and 20 oz. in the other is readily appreciated (Weber). This sensibility with whicn the muscles are endowed must be carefully distinguished from the sense of contact and of pressure, of which the skin is the organ. When standing erect, we can feel the ground (con- tact), and further there is a sense of pressure, due to our feet being pressed against the ground by the weight of the body. Both these are derived from the skin of the sole of the foot. If now we raise the body on the toes, we are conscious (muscular sense) of a muscular effort made by the muscles of the calf, which overcomes a certain resistance. (2.) Special Sensations. — Including the sense of touch, the special senses are five in number — Touch, Taste, Smell, Hearing, Sight. Difference between Common and Special Sensations. — The most important distinction between common and special sensations is that by the former we are made aware of certain conditions of various parts of our bodies, while from the latter we gain our knowledge of the external world also. This difference will be clear if we compare the sensations of pain and touch, the former of which is a common, the latter a special sensation. "If we place the edge of a sharp knife on the skin, we feel the edge by means of our sense of touch; we perceive a sensation, and refer it to the object which has caused it. But as soon as we cut the skin with the knife, we feel pain, a feeling which we no longer refer to the cutting knife, but which we feel within ourselves, and which communicates to us the fact of a change of condition in our own body. By the sensation of pain we are neither able to recognize the object which caused it, nor its nature" (Weber). General Characteristics: Seat. — In studying the phenomena of sensation, it is important clearly to understand that the Sensorium, or seat of sensation, is in the Brain, and not in the particular organ (eye, ear, etc.) through which the sensory impression is received. In com- mon parlance we are said to see with the eye, hear with the ear, etc., but in reality these organs are only adapted to receive impressions which are conducted to the sensorium, through the optic and auditory nerves re- spectively, and there give rise to sensation. Hence, if the optic nerve is severed (although the eye itself is per- fectly uninjured), vision is no longer possible; since, although the image falls on the retina as before, the sensory impression can no longer be con- veyed to the sensorium. When any given sensation is felt, all that we can with certainty affirm is that the sensorium in the brain is excited. The exciting cause may be (in the vast majority of cases is), some object of 160 HAND-BOOK OF PHYSIOLOGY. the external world (objective sensation}] or the condition of the sensorium may be due to some excitement within the brain, in which case the sen- sation is termed subjective. The mind habitually refers sensations to external causes; and hence, whenever they are subjective (due to causes within the brain), we can hardly divest ourselves of the idea of an ex- ternal cause, and an illusion is the result. Illusions. — Numberless examples of such illusions might be quoted. As familiar cases may be mentioned, humming and buzzing in the ears caused by some irritation of the auditory nerve or centre, and even musi- cal sounds and voices (sometimes termed auditory spectra); also so-called optical illusions: persons and other objects are described as being seen, although not present. Such illusions are most strikingly exemplified in cases of delirium tremens or other forms of delirium, in which cats, rats, creeping loathsome forms, etc., are described by the patient as seen with great vividness. Causes of Illusions. — One uniform internal cause, which may act on all the nerves of the senses in the same manner, is the accumulation of blood in their capillary vessels, as in congestion and inflammation. This one cause excites in the retina, while the eyes are closed, the sensa- tions of light and luminous flashes; in the auditory nerve, the sensation of humming and ringing sounds; in the olfactory nerve, the sense of odors; and in the nerves of feeling, the sensation of pain. In the same way, also, a narcotic substance, introduced into the blood, excites in the nerves of each sense peculiar symptoms: in the optic nerves, the appear- ance of luminous sparks before the eyes; in the auditory nerves, "tinnitus auriunr'; and in the common sensory nerves, the sensation of creeping over the surface. So, also, among external causes, the stimulus of electricity, or the mechanical influence of a blow, concussion, or pressure, excites in the eye the sensation of light and colors; in the ear, a sense of a loud sound or of ringing; in the tongue, a saline or acid taste; and in the other parts of the body, a perception of peculiar jarring or of the mechan- ical impression, or a shock like it. Sensations and Perceptions. — The habit of constantly referring our sensations to external causes, leads us to interpret the various modifi- cations which external objects produce in our sensations, as properties of the external bodies themselves. Thus we speak of certain substances as possessing a disagreeable taste and smell; whereas, the fact is, their taste and smell are only disagreeable to us. It is evident, however, that on this habit of referring our sensations to causes outside ourselves (percep- tion), depends the reality of the external world to us; and more especially is this the case with the senses of touch and sight. By the co-operation of these two senses aided by the others, we are enabled gradually to attain a knowledge of external objects which daily experience confirms, until we THE SENSES. 161 come to place unbounded confidence in hat is termed the "evidence of the senses." Judgments. — We must draw a distinction between mere sensations, and the judgments based, often unconsciously, upon them. Thus, in looking at a near object, we unconsciously estimate its distance, and say it seems to be ten or twelve feet off: but the estimate of its distance is in reality a judgment based on many things besides the appearance of the object itself; among which may be mentioned the number of intervening objects, the number of steps which from past experience we know we must take before we could touch it, and many others. Symptoms of Irritation of Nerves of Special Sense. — Irritation of the optic nerve, as by cutting it, invariably produces a sensation of light, of the auditory nerve a sensation of some modification of sound. Doubtless these distinct sensations depend not on any specialty in the structure of the nerves of special sense, but on the nature of their con- nections in the sensorium. Experiments seem to have proved that none of these nerves possess the faculty of common sensibility. Thus, Magendie observed that when the olfactory nerves, laid bare in a dog, were pricked, no signs of pain were manifested; and other experiments of his seem to show that both the retina and optic nerve are insusceptible of pain. Further, the optic nerve is insusceptible to the stimulus of light when severed from its con- nection with the retina, which alone is adapted to receive luminous im- pressions. Sensation of Motion is, like motion itself, of two kinds, — progres- sive and vibratory. The faculty of the perception of progressive motion is possessed chiefly by the senses of vision, touch, and taste. Thus an impression is perceived traveling from one part of the retina to another, and the movement of the image is interpreted by the mind as the motion of the object. The same is the case in the sense of touch; so also the movement of a sensation of taste over the surface of the organ of taste, can be recognized. The motion of tremors, or vibrations, is perceived by several senses, but especially by those of hearing and touch. Sensations of Chemical Actions. — We are made acquainted with chemical actions principally by taste, smell, and touch, and by each of these senses in the mode proper to it. Volatile bodies, disturbing the conditions of the nerves by a chemical action, exert the greatest influ- ence upon the organ of smell; and many matters act on that sense which produce no impression upon the organs of taste and touch, — for example, many odorous substances, as the vapor of metals, such as lead, and ths vapor of many minerals. Some volatile substances, however, are per- ceived not only by the sense of smell, but also by the senses of touch and taste. Thus, the vapors of horse-radish and mustard, and acrid suffoca- ting gases, act upon the conjunctiva and the mucous membrane of the VOL. II.— 11. 162 HAND-BOOK OF PHYSIOLOGY. lungs, exciting, through the common sensory nerves, merely modifications of common feeling; and at the same time they excite the sensations of smell and of taste. SPECIAL SENSES — TOUCH. Seat. — The sense of touch is not confined to particular parts of the T^ody of small extent, like the other senses; on the contrary, all parts capa- ble of perceiving the presence of a stimulus by ordinary sensation are, in certain degrees, the seat of this sense; for touch is simply a modifica- tion or exaltation of common sensation or sensibility. The nerves on which the sense of touch depends are, therefore, the same as those which confer ordinary sensation on the different parts of the body, viz., those derived from the posterior roots of the nerves of the spinal cord, and the sensory cerebral nerves. But, although all parts of the body supplied with sensory nerves are thus, in some degree, organs of touch, yet the sense is exercised in per- fection only in those parts the sensibility of which is extremely delicate, e.g., the skin, the tongue, and the lips, which are provided with abun- dant papillae. A peculiar and, of its own kind in each case, a very acute sense of touch is exercised through the medium of the nails and teeth. To a less extent the hair may be reckoned an organ of touch; as in the case of the eyelashes. The sense of touch renders us conscious of the presence of a stimulus, from the slightest to the most intense degree of its action, by that indescribable something which we call feeling, or common sensation. The modifications of this sense often depend on the extent of the parts affected. The sensation of pricking, for example, informs us that the sensitive particles are intensely affected in a small extent; the sensation of pressure indicates a slighter affection of the parts in the greater extent, and to a greater depth. It is by the depth to which the parts are affected that the feeling of pressure is distinguished from that of mere contact. Schiff and Brown -Sequard are of opinion that common sensibility and tactile sensibility manifest themselves to the individual by the aid of different sets of fibres. Sieveking has arrived at the same con- clusion from pathological observation. Varieties. — (a) The sense of touch, strictly so-called (tactile sensi- bility), (b) the sense of pressure, (c) the sense of temperature. These when carried beyond a certain degree are merged in (d) the sensation of pain. ^ Various peculiar sensations, such as tickling, must be classed with pain under the head of common sensations, since they give us no infor- mation as to external objects. Such sensations, whether pleasurable or painful, are in all cases referred by the mind to the part affected, and not to the cause which stimulates the sensory nerves of the part. The THE SENSES. 163 sensation of tickling may be produced in many parts of the body, but with especial intensity in the soles of the feet. Among other sensations belonging to this class, and confined to particular parts of the body, may be mentioned those of the genital organs and nipples. (a) Touch proper. — In almost all parts of the body which have delicate tactile sensibility the epidermis, immediately over the papillae, is moderately thin. When its thickness is much increased, as over the heel, the sense of touch is very much dulled. On the other hand, when it is altogether removed, and the cutis laid bare, the sensation of contact is replaced by one of pain. Further, in all highly sensitive parts, the papillae are numerous and highly vascular, and usually the sensory nerves are connected with special End-organs, such as have been described (p. 337, Vol. L). The acuteness of the sense of touch depends very largely on the cuta- neous circulation, which is of course largely influenced by external temperature. Hence the numbness, familiar to every one, produced by the application of cold to the skin. Special organs of touch are present in most animals, among which may be mentioned the antennae of insects, the "whiskers" (vibrissae) of cats and other carnivora, the wings of bats, the trunk of the elephant, and the hand of man. Judgment of the Form and Size of Bodies. — By the sense of touch the mind is made acquainted with the size, form, and other external characters of bodies. And in order that these characters may be easily ascertained, the sense of touch is especially developed in those parts which can be readily moved over the surface of bodies. Touch, in its more limited sense, or the act of examining a body by the touch, consists merely in a voluntary employment of this sense combined with movement, and stands in the same relation to the sense of touch, or common sensibility, generally, as the act of seeking, following, or examining odors, does to the sense of smell. The hand is best adapted for it, by reason of its peculiarities of structure, — namely, its capability of pronation and supina- tion, which enables it, by the movement of rotation, to examine the whole circumference of the body; the power it possesses of opposing the thumb to the rest of the hand, and the relative mobility of the fingers; and lastly from the abundance of the sensory terminal organs which it pos- sesses. In forming a conception of the figure and extent of a surface, the mind multiplies the size of the hand or fingers used in the inquiry by the number of times which it is contained in the surface traversed; and by repeating this process with regard to the different dimensions of a solid body, acquires a notion of its cubical extent, but, of course, only an imperfect notion, as other senses, e.g., the sight, are required to make it complete. 164 HAND-BOOK OF PHYSIOLOGY. Acuteness of Touch. — The perfection of the sense of touch on different parts of the surface is proportioned to the power which such parts possess of distinguishing and isolating the sensations produced by two points placed close together. This power depends, at least in part, on the number of primitive nerve-fibres distributed to the part; for the fewer the primitive fibres which an organ receives, the more likely is it that several impressions on different contiguous points will act on only one nervous fibre, and hence be confounded, and perhaps produce but one sensation. Experiments have been made to determine the tactile prop- erties of different parts of the skin, as measured by this power of distin- guishing distances. These consist in touching the skin, while the eyes are closed, with the points of a pair of compasses sheathed with cork, and in ascertaining how close the points of compasses might be brought to each other, and still be felt as two bodies. (E. H. "Weber, Valentin.) Table of variations in the tactile sensibility of different parts. — TJie measurement indicates the least distance at which the two Hunted points of a pair of compasses could be separately distin- guished. (E. H. Weber.) Tip of tongue ^ inch Palmar surface of third phalanx of forefinger . . TW " Palmar surface of second phalanges of fingers . . -J- " Red surface of under-lip i ' ' Tip of the nose Middle of dor sum of tongue -J- " Palm of hand T5¥ Centre of hard palate ...... £ Dorsal surface of first phalanges of fingers . . T\- Back of hand . . . . . . . . 1-| Dorsum of foot near toes 1£ Gluteal region 1J- Sacral region ........ 1* Upper and lower parts of forearm . . . . 1J- Back of neck near occiput . . . . . 2 " Upper dorsal and mid-lumbar regions . . . 2 " Middle part of forearm 2J " Middle of thigh ....... 2-J- " Mid-cervical region 2J " Mid-dorsal region 2J " Moreover, in the case of the limbs, it was found that before they were recognized as two, the points of the compasses had to be further separated when the line joining them was in the long axis of the limb, than when in the transverse direction. According to Weber the mind estimates the distance between two points by the number of unexcited nerve-endings which intervene be- tween the two points touched. It would appear that a certain number THE SENSES. 165 of intervening unexcited nerve-endings are necessary before two points touched can be recognized as separate, and the greater this number the more clearly are the points of contact distinguished as separate. By practice the delicacy of a sense of touch may be very much increased. A familiar illustration occurs in the case of the blind, who, by constant practice, can acquire the power of reading raised letters the forms of which are almost if not quite undistinguishable, by the sense of touch, to an ordinary person. The power of correctly localizing sensations of touch is gradually derived from experience. Thus infants when in pain simply cry, but make no effort to remove the cause of irritation, as an older child or adult would, doubtless on account of their imperfect knowledge of its exact situation. By long experience this power of localization becomes perfected, till at length the brain possesses a complete "picture" as it were of the surface of the body, and is able with marvellous exactness to localize each sensation of touch. Illusions of Touch. — The different degrees of sensitiveness pos- sessed by different parts may give rise to errors of judgment in estimating the distance between two points where the skin is touched. Thus, if blunted points of a pair of compasses (maintained at a constant distance apart) be slowly drawn over the skin of the cheek toward the lips, it is almost impossible to resist the conclusion that the distance between the points is gradually increasing. When they reach the lips they seem to be considerably further apart than on the cheek. Thus, too, our estimate of the size of a cavity in a tooth is usually exaggerated when based upon sensation derived from the tongue alone. Another curious illusion may here be mentioned. If we close the eyes, and place a small marble or pea between the crossed fore and middle fingers, we seem to be touching two marbles. This illusion is due to an error of judgment. The marble is touched by two surfaces which, under ordinary circumstances, could only be touched by two separate marbles, hence the mind, taking no cogni- zance of the fact that the fingers are crossed, forms the conclusion that two sensations are due to two marbles. (b) Pressure. — It is extremely difficult to separate touch proper from sensations of pressure, and, indeed, the former may be said to depend upon the latter. If the hand be rested on the table and a very light body such as a small card placed on it, the Only sensation produced is one of contact; if, however, an ounce weight be laid on the card an additional sensation (that of pressure) is experienced, and this becomes more intense as the weight is increased. If now the weight be raised by the hand, we are conscious of overcoming a certain resistance; this consciousness is due to what is termed the "muscular sense" (p. 119, Vol. II.). The estimate of a weight is, therefore, usually based oh two sensations, (1) of pressure on the skin, and (2) the muscular sense. 166 HAND-BOOK OF PHYSIOLOGY. The estimate of weight derived from a combination of these two sensa- tions (as in lifting a weight) is more accurate than that derived from the former alone (as when a weight is laid on the hand) ; thus Weber found that by the former method he could generally distinguish 19J- oz. from 20 oz., but not 19f oz. from 20 oz., while by the latter he could at most only distinguish 14£ oz. from 15 oz. It is not the absolute, but the relative, amount of the difference of weight which we have thus the faculty of perceiving. It is not, however, certain, that our idea of amount of muscular force used is derived solely from sensation in the muscles. We have the power of estimating very accurately beforehand, and of regulating, the amount of nervous influence necessary for the production of a certain de- gree of movement. When we raise a vessel, with the contents of which we are not acquainted, the force we employ is determined by the idea we have conceived of its weight. If it should happen to contain some very heavy substance, as quicksilver, we shall probably let it fall; the amount of muscular action, or of nervous energy, which we had exerted being in- sufficient. The same thing occurs sometimes to a person descending stairs in the dark; he makes the movement for the descent of a step which does not exist. It is possible that in the same way the idea of weight and pressure in raising bodies, or in resisting forces, may in part arise from a consciousness of the amount of nervous energy transmitted from the brain rather than from a sensation in the muscles themselves. The men- tal conviction of the inability longer to support a weight must also be distinguished from the actual sensation of fatigue in the muscles. So, with regard to the ideas derived from sensations of touch combined with movements, it is doubtful how far the consciousness of the extent of muscular movement is obtained from sensations in the muscles them- selves. The sensation of movement attending the motions of the hand is very slight; and persons who do not know that the action of particular muscles is necessary for the production of given movements, do not sus- pect that the movement of the fingers, for example, depends on an action in the forearm. The mind has, nevertheless, a very definite knowledge of the changes of position produced by movements; and it is on this that the ideas which it conceives of the extension and form of a body are in great measure founded. (c) Temperature. — The whole surface of the body is more or less sensitive to differences of temperature. The sensation of heat is distinct from that of touch; and it would seem reasonable to suppose that there are special nerves and nerve-endings for temperature. At any rate the power of discriminating temperature may remain unimpaired when the sense of touch is temporarily in abeyance. Thus if the ulnar nerve be compressed at the elbow till the sense of touch is very much dulled in the fingers which it supplies, the sense of temperature remains quite unaffected (Nothnagel). The sensations of heat and cold are often exceedingly fallacious, and in many cases are no guide at all to the absolute temperature as indicated THE SENSES. 167 by a thermometer. All that we can with safety infer from our sensations of temperature, is that a given object is warmer or cooler than the skin. Thus the temperature of our skin is the standard; and as this varies from hour to hour according to the activity of the cutaneous circulation, our estimate of the absolute temperature of any body must necessarily vary too. If we put the left hand into water at 40° F. and the right into water at 110° F. and then immerse both in water at 80° F., it will feel warm to the left hand but cool to the right. Again, a piece of metal which has really the same temperature as a given piece of wood will feel much colder, since it conducts away the heat much more rapidly. For the same reason air in motion feels very much cooler than air of the same temperature at rest. Perhaps the most striking example of the fallaciousness of our sensa- tions as a measure of temperature is afforded by fever. In a shivering fit of ague the patient feels excessively cold, whereas his actual temperature is several degrees above the normal, while in the sweating stage which succeeds it he feels very warm, whereas really his temperature has fallen several degrees. In the former case the cutaneous circulation is much diminished, in the latter much increased; hence the sensations of cold and heat respectively. In some cases we are able to form a fairly accurate estimate of absolute temperature. Thus, by plunging the elbow into a bath, a practised bath- attendant can tell the temperature sometimes within 1° F. The temperatures which can be readily discriminated are between 50°— 115° F. (10°— 45° C.); very low and very high temperature alike produce a burning sensation. A temperature appears higher according to the extent of cutaneous surface exposed to it. Thus, water of a tem- perature which can be readily borne by the hand, is quite intolerable if the whole body be immersed. So, too, water appears much hotter to the hand than to a single finger. The delicacy of the sense of temperature coincides in the main with that of touch, and appears to depend largely on the thickness of the skin; hence, in the elbow where the skin is thin, the sense of temperature is delicate, though that of touch is not remarkably so. Weber has further ascertained the following facts: two compass points so near together on the skin that they produce but a single impression, at once give rise to two sensations, when one is hotter than the other. Moreover, of two bodies of equal weight, that which is the colder feels heavier than the other. As every sensation is attended with an idea, and leaves behind it an idea in the mind which can be reproduced at will, we are enabled to com- pare the idea of a past sensation with another sensation really present. Thus we can compare the weight of one body with another which we had previously felt, of which the idea is retained in our mind. Weber was 168 HAXD-BOOK OF PHYSIOLOGY. indeed able to distinguish in this manner between temperatures, experi- enced one after the other, better than between temperatures to which the two hands were simultaneously subjected. This power of comparing present with past sensations diminishes, however, in proportion to the time which has elapsed between them. After-sensations left by impres- sions on nerves of common sensibility or touch are very vivid and durable. As long as the condition into which the stimulus has thrown the organ endures, the sensation also remains, though the exciting cause should have long ceased to act. Both painful and pleasurable sensations afford many examples of this fact. Subjective sensations, or sensations dependent on internal causes, are in no sense more frequent than in the sense of touch. All the sensa- tions of pleasure and pain, of heat and cold, of lightness and weight, of fatigue, etc., may be produced by internal causes. Neuralgic pains, the sensation of rigor, formication or the creeping of ants, and the states of the sexual organs occurring during sleep, afford striking examples of sub- jective sensations. The mind has a remarkable power of exciting sensa- tions in the nerves of common sensibility; just as the thought of the nau- seous excites sometimes the sensation of nausea, so the idea of pain gives rise to the actual sensation of pain in a part predisposed to it; numerous examples of this influence might be quoted. TASTE. Conditions Necessary. — The conditions for the perceptions of taste are: — 1, the presence of a nerve and nerve-centre with special endow- ments; 2, the excitation of the nerve by the sapid matters, which for this purpose must be in a state of solution. The nerves concerned in the pro- duction of the sense of taste have been already considered (pp. 142 and 146, Vol. II.). The mode of action of the substances which excite taste con- sists in the production of a change in the condition of the gustatory nerves, and the conduction of the stimulus thus produced to the nerve-centre; and, according to the difference of the substances, an infinite variety of changes of condition of the nerves, and consequently of stimulations of the gustatory centre, may be induced. The matters to be tasted must either be in solution or be soluble in the moisture covering the tongue; hence insoluble substances are usually tasteless, and produce merely sen- sations of touch. Moreover, for the perfect action of a sapid, as of an odorous substance, it is necessary that the sentient surface should be moist. Hence, when the tongue and fauces are dry, sapid substances, even in solution, are with difficulty tasted. The nerves of taste, like the nerves of other special senses, may have their peculiar properties excited by various other kinds of irritation, such % THE SENSES. 169 as electricity and mechanical impressions. Thus, Henle observed that a small current of air directed upon the tongue gives rise to a cool saline taste, like that of saltpetre; and Baly has shown that a distinct sensation of taste, similar to that caused by electricity, may be produced by a smart tap applied to the papillae of the tongue. Moreover, the mechanical irri- tation of the fauces and palate produces the sensation of nausea, which is probably only a modification of taste. Seat of Sensation. — The principal seat of the sense of taste is the tongue. But the results of experiments as well as ordinary experience show that the soft palate and its arches, the uvula, tonsils, and probably the upper part of the pharynx, are endowed with taste. These parts, together with the base and posterior parts of the tongue, are supplied with branches of the glosso-pharyngeal nerve, and evidence has been already adduced that the sense of taste is conferred upon them by this nerve. In most, though not in all persons, the anterior parts of the tongue, especially the edges and tip, are endowed with the sense of taste. The middle of the dorsum is only feebly endowed with this sense, prob- ably because of the density and thickness of the epithelium covering the filiform papillae of this part of the tongue, which will prevent the sapid substances from penetrating to their sensitive parts. The gustatory prop- erty of the anterior part of the tongue is due, as already said (p. 142, Vol. II.), to the lingual or gustatory branch of the fifth nerve. Structure of the Tongue. — The tongue is a muscular organ covered by mucous membrane. The muscles, which form the greater part of the substance of the tongue (intrinsic muscles) are termed linguales; and by these, which are attached to the mucous membrane chiefly, its smaller and more delicate movements are chiefly performed.. By other muscles (extrinsic muscles) as- the genio-hyoglossus, the styloglossus, etc., the tongue is fixed to surrounding parts; and by this group of muscles its larger movements are performed. The mucous membrane of the tongue resembles other mucous mem- branes (p. 322, Vol. I.) in essential points of structure, but contains papillce, more or less peculiar to itself; peculiar, however, in details of structure and arrangement, not in their nature. The tongue is beset with numerous mucous follicles and glands. The use of the tongue in relation to mastication and deglutition has already been considered (pp. 226 and 238, Vol. I.). The larger papillw of the tongue are thickly set over the anterior two- thirds of its upper surface, or dorsum (Fig. 349), and give to it its char- acteristic roughness. In carnivorous animals, especially those of the cat tribe, the papillae attain a large size, and are developed into sharp re- curved horny spines. Such papillae cannot be regarded as sensitive, but they enable the tongue to play the part of a most efficient rasp, as in scraping bones, or of a comb in cleaning their fur. Their greater promi- 170 HAND-BOOK OF PHYSIOLOGY. nence than those of the skin is due to their interspaces not being filled up with epithelium, as the interspaces of the papillae of the skin are. The papillae of the tongue present several diversities of form; but three principal varieties, differing both in seat and general characters, may usually be distinguished, namely, the (1) circumvallate, the (2) fungi- form, and the (3) filiform papillae. Essentially these have all of them lae FIG. 349.— Papillar surf ace of the tongue, with the fauces and tonsils. 1,1, circumvallate papil- , in front of 2, the foramen caecum ; 3, f ungif orm papillae ; 4, filiform and conical papillae ; 5, trans- verse and oblicme rugae; 6, mucous glands at the base of the tongue and in the fauces; 7, tonsils; 8, part of the epiglottis; 9, median glosso-epiglottidean fold (frsenum epiglottidis). (From Sappey.) the same structure, that is to say, they are all formed by a projection of the mucous membrane, and contain special branches of blood-vessels and nerves. In details of structure, however, they differ considerably one from another. The surface of each kind is studded by minute conical processes of mucous membrane, which thus form secondary papillae. THE SENSES. 171 Simple papillae also occur over most other parts of the tongue not occupied by the compound papilla?, and extend for some distance behind the papillae circumvallatae. The mucous membrane immediately in front of the epiglottis is, however, free from them. They are commonly buried beneath the epithelium; hence they are often overlooked. (1.) Circumvallate. — These papillae (Fig. 350), eight or ten in num- ber, are situate in two V-shaped, lines at the base of the tongue (1, 1, FIG. 350.— Vertical section of a circumvallate papilla 10-1.— A, the papillae; B, the surrounding wall; a, the epithelial covering; 6, the nerves of the papilla and wall spreading toward the surface; c, the secondary papillae. (Kolliker.) Fig. 349). They are circular elevations from ^T) to T^th of an inch wide, each with a central depression, and surrounded by a circular fissure, at the outside of which again is a slightly elevated ring, both the central elevation and the ring being formed of close set simple papillae (Fig. 350). (2.) Fungiform. — The fungiform papillae (3, Fig. 349) are scattered chiefly over the sides and tip, and sparingly over the middle of the dor- sum, of the tongue; their name is derived from their being usually nar- FIG. 351.— Surface and section of the fungiform papillae. A, the surface of a fungiform papilla, partially denuded of its epithelium; p, secondary papillae; e, epithelium. B, section of a fungiform papilla with the blood-vessels injected; a, artery; v, vein; c, capillary loops of similar papillae in the neighboring structure of the tongue; d, capillary loops of the secondary papillae; e, epithelium. (From Kolhker, after Todd and Bowman.) rower at their base than at their summit. They also consist of groups of simple papillae (A, Fig. 351), each of which contains in its interior a loop of capillary blood-vessels (B), and a nerve-fibre. (3.) Conical or Filiform. — These, which are the most abundant papillae, are scattered over the whole surface of the tongue, but especially over the middle of the dorsum (Fig. 349). They vary in shape some- what, but for the most part are conical or filiform, and covered by a thick 172 HAND-BOOK OF PHYSIOLOGY. layer of epidermis, which is arranged over them, either in an imbricated manner, or is prolonged from their surface in the form of fine stiff pro- jections, hair-like in appearance, and in some instances in structure also (Fig. 352). From their peculiar structure, it seems likely that these papillae have a mechanical function, or one allied to that of touch rather than of taste; the latter sense being probably seated especially in the ther two varieties of papillae, the circumvallate and ihefungiform. The epithelium of the tongue is stratified with the upper layers of the FIG. 352.— Two filiform papillae, one with epithelium, the other without. 35-1.— p, the substance of the papillae dividing at their upper extremities into secondary papillae; a, artery, and r, vein, dividing into capillary loops; e, epithelial covering, laminated between the papillae, but extended into hair-like processes, /, from the extremities of the secondary papillae. (From Kolliker, after Todd and Bowman.) squamous kind. It covers every part of the surface; but over the fungi- form papillae forms a thinner layer than elsewhere. The epithelium cover- ing the filiform papillae is extremely dense and thick, and, as before men- tioned, projects from their sides and summits in the form of long, stiff, hair-like processes (Fig. 352). Many of these processes bear a close re- semblance to hairs. Blood-vessels and nerves are supplied freely to the papillae. The nerves in the fungiform and circumvallate papillae form a kind of plexus, spreading out brush-wise (Fig. 350), but the exact mode of termination of the nerve-filaments is not certainly known. THE SENSES. 173 7 We Goblets. — In the circumvallate papillae of the tongue of man peculiar structures known as gustatory buds or taste goblets, have been discovered (Loven, Schwalbe). They are of an oval shape, and consist of a number of closely packed, very narrow and fusiform, cells (gustatory cells). This central core of gustatory cells is enclosed in a single layer of broader fusiform cells (encasing cells). The gustatory cells terminate in fine spikes not unlike cilia, which project on the free surface (Fig. 353). These bodies also occur side by side in considerable numbers in the FIG. 353.— Taste-goblet from dog's epiglottis (laryngeal surface near the base), precisely similar in structure to those found in the tongue, a, depression in epithelium over goblet; oelow the letter are seen the fine hair-like processes in which the cells terminate; c, two nuclei of the axial (gustatory) cells. The more superficial nuclei belong to the superficial (encasing) cells; the converging lines in- dicate the fusiform shape of the encasing cells. X 400. (Schofield.) epithelium of the papilla foliata, which is situated near the root of the tongue in the rabbit, and also in man. Similar "taste-goblets" also occur pretty evenly distributed on the posterior (laryngeal) surface of the epi- glottis (Verson, Schofield). It seems probable, from their distribution, that all these so-called taste-goblets are gustatory in function, though no nerves have been distinctly traced into them. Other Functions of the Tongue. — Besides the sense of taste, the tongue, by means also of its papillae, is endued, (2) especially at its sides and tip, with a very delicate and accurate sense of touch (p. 164, Vol. II.), which renders it sensible of the impressions of heat and cold, pain and mechaiicial pressure, and consequently of the form of surfaces. The tongue may lose its common sensibility, and still retain the sense of taste, and vice versa. This fact renders it probable that, although the senses of taste and of touch may be exercised by the same papillae supplied by the same nerves, yet the nervous conductors for these two different sen- sations are distinct, just as the nerves for smell and common sensibility in the nostrils are distinct; and it is quite conceivable that the same nervous trunk may contain fibres differing essentially in their specific properties. Facts already detailed (p. 142, Vol. II.) seem to prove that the lingual branch of the fifth nerve is the conductor of sensations of taste in the anterior part of the tongue; and it is also certain, from the 174 HAND-BOOK OF PHYSIOLOGY. marked manifestations of pain to which its division in animals gives rise, that it is likewise a nerve of common sensibility. The glosso-pharyngeal also seems to contain fibres both of common sensation and of the special sense of taste. The functions of the tongue in connection with (3) speech, (4) masti- tication, (5) deglutition, (6) suction, have been referred to in other chapters. Taste and Smell; Perceptions. — The concurrence of common and special sensibility in the same part makes it sometimes difficult to determine whether the impression produced by a substance is perceived through the ordinary; sensitive fibres, or through those of the sense of taste. In many cases, indeed, it is probable that both sets of nerve-fibres are concerned, as when irritating acrid substances are introduced into the mouth. Much of the perfection of the sense of taste is often due to the sapid substances being also odorous, and exciting the simultaneous action of the sense of smell. This is shown by the imperfection of the taste of such substances when their action on the olfactory nerves is prevented by closing the nostrils. Many fine wines lose much of their apparent excel- lence if the nostrils are held close while they are drunk. Varieties of Tastes. — Among the most clearly defined tastes are the sweet and bitter (which are more or less opposed to each other), the acid, alkaline, and saline tastes. Acid and alkaline taste may be excited by electricity. If a piece of zinc be placed beneath and a piece of copper above the tongue, and their ends brought into contact, an acid taste (due to the feeble galvanic current) is produced. The delicacy of the sense of taste is sufficient to discern 1 part of sulphuric acid in 1000 of water; but it is far surpassed in acuteness by the sense of smell. After-tastes. — Very distinct sensations of taste are frequently left after the substances which excited them have ceased to act on the nerve; and such sensations often endure for a long time, and modify the taste of other substances applied to the tongue afterward. Thus, the taste of sweet substances spoils the flavor of wine, the taste of cheese improves it. There appears, therefore, to exist the same relation between tastes as between colors, of which those that are opposed or complementary render each other more vivid, though no general principles governing this relation have been discovered in the case of tastes. In the art of cooking, however, at- tention has at all times been paid to the consonance or harmony of flavors in their combination or order of succession, just as in painting and music the fundamental principles of harmony have been employed empirically while the theoretical laws were unknown. Frequent and continued repetitions of the same taste render the per- ception of it less and less distinct, in the same way that a color becomes more and more dull and indistinct the longer the eye is fixed upon it. THE SENSES. 175 Thus, after frequently tasting first one and then the other of two kinds of wine, it becomes impossible to discriminate between them. The simple contact of a sapid substance with the surface of the gustatory organ seldom gives rise to a distinct sensation of taste; it needs to be dif- fused over the surface, and brought into intimate contact with the sensi- tive parts by compression, friction, and motion between the tongue and palate. Subjective Sensations of Taste. — The sense of taste seems capa- ble of being excited only by external causes, such as changes in the con- ditions of the nerves or nerve-centres, produced by congestion or other causes, which excite subjective sensations in the other organs of sense. But little is known of the subjective sensations of taste; for it is difficult to distinguish the phenomena from the effects of external causes, such as changes in the nature of the secretions of the mouth. SMELL. Conditions Necessary. — (1.) The first conditions essential to the sense of smell are a special nerve and nerve-centre, the changes in whose condition are perceived in sensations of odor; for no other nervous struc- ture is capable of these sensations, even though acted on by the same causes. The same substance which excites the sensation of smell in the olfactory centre may cause another peculiar sensation through the nerves of taste, and may produce an irritating and burning sensation on the nerves of touch; but the sensation of odor is yet separate and distinct from these, though it may be simultaneously perceived. (2.) The second condition of smell is a peculiar change produced in the olfactory nerve and its centre by the stimulus or odorous substance. (3.) The material causes of odors are, usually, in the case of animals living in the air, either solids suspended in a state of extremely fine division in the atmosphere; or gaseous exhalations often of so subtile a nature that they can be detected by no other re-agent than the sense of smell itself. The matters of odor must, in all cases, be dissolved in the mucus of the mucous membrane before they can be immediately applied to, or affect the olfac- tory nerves; therefore a further condition necessary for the perception of odors is, that the mucous membrane of the nasal cavity be moist. When the Schneiderian membrane is dry, the sense of smell is impaired or lost; in the first stage of catarrh, when the -secretion of mucus within the nostrils is lessened, the faculty of perceiving odor is either lost or rendered very imperfect. (4.) In animals living in the air, it is also requisite that the odorous matter should be transmitted in a current through the nostrils. This is effected by an inspiratory movement, the mouth being closed; hence we have voluntary influence over the sense of smell; for by inter- rupting respiration we prevent the perception of odors, and by repeated 176 HAND-BOOK OF PHYSIOLOGY. quick inspiration, assisted, as in the act of sniffing, by the action of the nostrils, we render the impression more intense (see p. 201, Vol. I.). An odorous substance in a liquid form injected into the nostrils appears in- capable of giving rise to the sensation of smell: thus Weber could not smell the slightest odor when his nostrils were completely filled with water containing a large quantity of eau de Cologne. Seat of the Sense of Smell. — The human organ of smell is formed by the filaments of the olfactory nerves, distributed in the mucous mem- brane covering the upper third of the septum of the nose, the superior turbinated or spongy bone, the upper part of the middle turbinated bone, and the upper wall of the nasal cavities beneath the cribriform plates of the ethmoid bones (Figs. 354 and 355). The olfactory region is covered FIG. 354.— Nerves of the septum nasi, seen from the right side. %.— I, the olfactory bulb; 1, the olfactory nerves passing through the foramina of the cribriform plate, and descending to be dis- tributed on the septum; 2, the internal or septal twig of the nasal branch of the ophthalmic nerve; 3, naso-palatine nerves. (From Sappey, after Hirschfeld and Leveille.) by cells of cylindrical epithelium, prolonged at their deep extremities into fine branched processes, but not ciliated; and interspersed with these are fusiform (olfactory) cells, with both superficial and deep processes (Fig. 356), the latter being probably connected with the terminal fila- ments of the olfactory nerve. The lower, or respiratory part, as it is called, of the nasal fossae is lined by cylindrical ciliated epithelium, ex- cept in the region of the nostrils, where it is squamous. The branches of the olfactory nerves retain much of the same soft and greyish texture which distinguishes those of the olfactory tracts within the cranium. Their filaments, also, are peculiar, more resembling those of the sympa- thetic nerve than the filaments of the other cerebral nerves do, contain- ing no outer white substance, and being finely granular and nucleated. The sense of smell is derived exclusively through those parts of the nasal cavities in which the olfactory nerves are distributed; the accessory cavi- ties or sinuses communicating with the nostrils seem to have no relation THE SENSES. 177 to it. Air impregnated with the vapor of camphor was injected into the frontal sinus through a fistulous opening, and odorous substances have been injected into the antrum of Highmore; but in neither case was any odor perceived by the patient. The purposes of these sinuses appear to be, that the bones, necessarily large for the action of the muscles and other parts connected with them, may be as light as possible, and that there may be more room for the resonance of the air in vocalizing. The former FIG. 355.— Nerves of the outer walls of the nasal fossae. 3-5.— 1, network of the branches of the olfactory nerve, descending upon the region of the superior and middle turbinated bones; 2, external twig of the ethmoidal branch of the nasal nerves ; 3, spheno-palatine ganglion ; 4, ramification of the anterior palatine nerves; 5, posterior, and 6, middle divisions of the palatine nerves; 7, branch to the region of the inferior turbinated bone; 8, branch to the region of the superior and middle turbinated bones; 9, naso-palatine branch to the septum cut short. (From Sappey, after Hirschfeld and Leveille.) purpose, which is in other bones obtained by filling their cavities with fat, is here attained, as it is in many bones of birds, by their being filled with air. Other Functions of the Olfactory Region.— All parts of the nasal cavities, whether or not they can be the seat of the sense of smell, are endowed with common sensibility by the nasal branches of the first and second divisions of the fifth nerve. Hence the sensations of cold, heat, itching, tickling, and pain; and the sensation of tension or pressure in the nostrils. That these nerves cannot perform the function of the olfactory nerves is proved by cases in which the sense of smell is lost, while the mu- cous membrane of the nose remains susceptible of the various modifications of common sensation or touch. But it is often difficult to distinguish the sensation of smell from that of mere feeling, and to ascertain what belongs to each separately. This is the case particularly with the sensations, excited in the nose by acrid vapors, as of ammonia, horse-radish, mustardr etc., which resemble much the sensations of the nerves of touchj and the- difficulty is the greater, when it is remembered that these acrid vapors VOL. II.— 12. 178 HAND-BOOK OF PHYSIOLOGY. have nearly the same action upon the mucous membrane of the eyelids. It was because the common sensibility of the nose to these irritating sub- stances remained after the destruction of the olfactory nerves, that Magen- die was led to the erroneous belief that the fifth nerve might exercise this special sense. Varieties of Odorous Sensations.— Animals do not all equally perceive the same odors; the odors most plainly perceived by an herbiv- orous animal and by a carnivorous animal are different. The Oarnivora have the power of detecting most accurately by the smell the special peculiarities of animal matters, and of tracking other animals by the scent; but have apparently very lit- tle sensibility to the odors of plants and flowers. Herbiv- orous animals are peculiarly sensitive to the latter, and have a narrower sensibility to animal odors, especially to such as proceed from other individuals than their own species. Man is far inferior to many animals of both classes in respect of the acuteness of smell; but his sphere of susceptibility to various odors is more uniform and ex- tended. The cause of this difference lies probably in the endowments of the cerebral parts of the olfactory appa- ratus. The delicacy of the sense of smell is most remark- able; it can discern the presence of bodies in quantities so minute as to be undiscoverable even by spectrum an- alysis; Too"i~o1)~o",o~oo~ °f a grain of musk can be distinctly smelt (Valentin). Opposed to the sensation of an agree- able odor is that of a disagreeable or disgusting odor, which corresponds to the sensations of pain, dazzling and disharmony of colors, and dissonance in the other senses. The cause of this difference in the effect of different (Max odors is unknown: but this much is certain, that odors are pleasant or offensive in a relative sense only, for many animals pass their existence in the midst of odors which to us are highly disagreeable. A great difference in this respect is, indeed, observed amongst men: many odors, generally thought agreeable, are to some per- sons intolerable; and different persons describe differently the sensations that they severally derive from the same odorous substances. There seems also to be in some persons an insensibility to certain odors, comparable with that of the eye to certain colors; and among different persons, as great a difference in the acuteness of the sense of smell as among others in the acuteness of sight. We have no exact proof that a relation of har- mony and disharmony exists between odors as between colors and sounds; though it is probable that such is the case, since it certainly is so with regard to the sense of taste; and since such a relation would account in some measure for the different degrees of perceptive power in different E FIG. 356.— Epithe- lial and olfactory cells of man. The letters are placed on the free surface. E, E, epithelial cells; CM/., olfac- tory cells. Schultze.) THE SENSES. 179 persons; for as some have no ear for music (as it is said), so others have no clear appreciation of the relation of odors, and therefore little pleasure in them. Subjective Sensations of Smell.— The sensations of the olfactory nerves, independent of the external application of odorous substances, have hitherto been little studied. The friction of the electric machine produces a smell like that of phosphorus. Ritter, too, has observed, that when galvanism is applied to the organ of smell, besides the impulse to sneeze, and the tickling sensation excited in the filaments of the fifth nerve, a smell like that of ammonia was excited by the negative pole, and an acid odor by the positive pole; whichever of these sensations were produced, it remained constant as long as the circle was closed, and changed to the other at the moment of the circle being opened. Subjec- tive sensations occur frequently in connection with the sense of smell. Frequently a person smells something which is not present, and which other persons cannot smell; this is very frequent with nervous people, but it occasionally happens to every one. In a man who was constantly con- scious of a bad odor, the arachnoid was found after death to be beset with deposits of bone; and in the middle of the cerebral hemispheres were scrofulous cysts in a state of suppuration. Dubois was acquainted with a man who, ever after a fall from his horse, which occurred several years before his death, believed that he smelt a bad odor. HEARING. Anatomy of the Ear.— For descriptive purposes, the Ear, or Organ of Hearing, is divided into three parts, (1) the external, (2) the middle, and (3) the internal ear. The two first are only accessory to the third or internal ear, which contains the essential parts of an organ of hearing. The accompanying figure shows very well the relation of these divisions, — one to the other (Fig. 357). (1.) External Ear. — The external ear consists of the pinna or auricle, and the external auditory canal or meatus. The principal parts of the pinna (Fig. 358, A) are two prominent rims enclosed one within the other (Helix and antilielix), and enclosing a central hollow named the concha; in front of the concha, a prominence directed backward, the tragus, and opposite to this, one directed forward, the antitragus. From the concha, the auditory canal, with a slight arch di- rected upward, passes inward and a little forward to the membrana tym- pani, to which it thus serves to convey the vibrating air. Its outer part consists of fibro-cartilage continued from the concha; its inner part of bone. Both are lined by skin continuous with that of the pinna, and extending over the outer part of the membrana tympani. Toward the outer part of the canal are fine hairs and sebaceous glands, while deeper in the canal are small glands, resembling the sweat-glands 180 HAND-BOOK OF PHYSIOLOGY. in structure, which, secrete a peculiar yellow substance called cerumen, or ear-wax. (2.) Middle Ear or Tympanum. — The middle ear, or tympanum (3, Fig. 357), is separated by the membrana tympani from the external auditory canal. It is a cavity in the temporal bone, opening through its anterior and inner wall into the Eustachian tube, a cylindriform flattened canal, dilated at both ends, composed partly of bone and partly of carti- lage, and lined with mucous membrane, which forms a communication between the tympanum and the pharynx. It opens into the cavity of the pharynx just behind the posterior aperture of the nostrils. The cavity FIG. 357.— Diagrammatic view from before of the parts composing the organ of hearing of the left side. The temporal bone of the left side, with the accompanying soft parts, has been detached from the head, and a section has been carried through it transversely, so as to remove the front of the meatus externus, half the tympanic membrane, the upper and anterior wall of the tympanum and Eustachian tube. The meatus internus has also been opened, and the bony labyrinth exposed by the removal of the surrounding parts of the petrous bone. 1, the pinna and lobe; 2, 2', meatus externus; 2', membrana tympani; 3, cavity of the tympanum; 3', its opening backward into the mas- toid cells; between 3 and 3', the chain of small bones; 4, Eustachian tube; 5, meatus internus, con- taining the facial (uppermost) and the auditory nerves; 6, placed on the vestibule of the labyrinth above the fenestra ovalis: a, apex of the petrous bone; 6, internal carotid artery; c, styloid process; d, facial nerve issuing from the stylo-mastoid foramen; e, mastoid process; /, squamous part of the bone covered by integument, etc. (Arnold.) of the tympanum communicates posteriorly with air-cavities, the mastoid cells in the mastoid process of the temporal bone; but its only opening to the external air is through the Eustachian tube (4, Fig. 357). The walls of the tympanum are osseous, except where apertures in them are closed with membrane, as at the fenestra rotunda, and fenestra ovalis, and at the outer part where the bone is replaced by the membrana tym- pani. The cavity of the tympanum is lined with mucous membrane, the epithelium of which is ciliated and continuous with that of the pharynx. THE SENSES. 181 It contains a chain of small bones (Ossicula auditus) which extends from the membrana tympani to the fenestra ovalis. The membrana tympani is placed in a slanting direction at the bottom of the external auditory canal, its plane being at an angle of about 45° with the lower wall of the canal. It is formed chiefly of a tough and tense fibrous membrane, the edges of which are set in a bony groove; its outer surface is covered with a continuation of the cutaneous lining of the auditory canal, its inner surface with part of the ciliated mucous membrane of the tympanum. The small bones or ossicles of the ear are three; named malleus, incus, and stapes. The malleus, or hammer-bone, is attached by a long slightly curved process, called its handle, to the membrana tympani; the line of attachment being vertical, including the whole length of the handle, and extending from the upper border to the centre of the membrane. The head of the malleus is irregularly rounded; its neck, or the line of boundary between it and the handle, supports two processes; a short conical one, which receives the insertion of the tensor tympani, and a slender one, processus glacilis, which extends for- ward, and to which the laxator tympani muscle is attached. The incus, or anvil-bone, shaped like a bicuspid molar tooth, is articulated by its broader part, corresponding with the surface of the crown of a tooth, to the malleus. Of its two fang-like pro- cesses, one, directed backward, has a free end lodged in a depression in the mastoid bone; the other, curved downward and more pointed, articulates by means of a roundish tuber- cle, formerly called os orUculare, with the stapes, a little bone shaped exactly like a stirrup, of which the base or bar fits into the fenestra ovalis. To the neck of the stapes, a short process, corresponding with the loop of the stirrup, is attached the stapedius muscle. The Ossicula. — The bones of the ear are covered with mucous membrane reflected over them from the wall of the tympanum; and are movable both altogether and one upon the other. The malleus moves and vibrates with every movement and vibration of the membrana tympani, and its movements are communicated through the incus to the stapes, and through it to the membrane closing the fenestra ovalis. The malleus, also, is movable in its articulation with the incus; and the membrana tympani moving with it is altered in its degree of tension by the laxator and tensor tympani muscles. The stapes is movable on the process of the incus, when the stapedius muscle acting, draws it backward. The axis round which the malleus and incus rotate is the line joining the processus gracilis of the malleus and the posterior (short) process of the incus. (3.) Internal Ear. — The proper organ of hearing is formed by the dis- tribution of the auditory nerve within the internal ear, or labyrinth of the ear, a set of cavities within the petrous portion of the temporal bone. FIG. 358. -Outer surface of the pinna of the right auricle. 1, helix: 2, fossa of the helix; 3, antihelix; 4, fossa of the antihelix ; 5, antitragus; 6, tragus; 7, concha; 8, lobule. %. 182 HAND-BOOK OF PHYSIOLOGY. The bone which forms the walls of these cavities is denser than that around it, and forms the osseous labyrinth; the membrane within the cavities forms the membranous labyrinth. The membranous labyrinth contains a fluid called endolymph; while outside it, between it and the osseous labyrinth, is a fluid called perilymph. The osseous labyrinth consists of three principal parts, namely, the vestibule, the cochlea, and the semicircular canals. The vestibule is the middle cavity of the labyrinth and the central organ of the whole auditory apparatus. It presents, in its inner wall, several openings for the entrance of the divisions of the auditory nerve; in its outer wall, the fenestra ovalis (2, Fig. 359), an opening filled by the base of the stapes, one of the small bones of the ear; in its posterior FIG. 359. FIG. 360. FIG. 359.— Right bony labyrinth, viewed from the outer side. The specimen here represented is prepared by separating piecemeal the looser substance of the petrous bone from the dense walls which immediately enclose the labyrinth. 1, the vestibule; 2, fenestra ovalis; 3, superior semicircu- lar canal; 4, horizontal or external canal; 5, posterior canal; *, ampullae of the semicircular canals; 6, first turn of the cochlea: 7, second turn; 8, apex; 9, fenestra rotunda. The smaller figure in outline below shows the natural size. 2^. (Sommering.) FIG. 360.— View of the interior of the left labyrinth. The bony wall of the labyrinth is removed superiorly and externally. 1, foveahemielliptica; 2, fovea hemispherica: 3, common opening of the superior and posterior semicircular canals; 4, opening of the aqueduct of the vestibule; 5, the supe- rior, 6, the posterior, and 7, the external semicircular canals; 8, spiral tube of the cochlea (scala tympani); 9, opening of the aqueduct of the cochlea; 10, placed on the lamina spiralis in the scala vestibuli. 2& (Sommering.) 1 and superior walls, five openings by which the semicircular canals com- municate with it: in its anterior wall, an opening leading into the cochlea. The hinder part of the inner wall of the vestibule also presents an opening, the orifice of the aquceductus vestibuli, a canal leading to the posterior margin of the petrous bone, with uncertain contents and un- known purpose. The semicircular canals (Figs. 359, 360), are three arched cylin- driform bony canals, set in the substance of the petrous bone. They all open at both ends into the vestibule (two of them first coalescing). The ends of each are dilated just before opening into the vestibule; and one end of each being more dilated than the other is called an ampulla. Two of the canals form nearly vertical arches; of these the superior is also anterior; the posterior is inferior; the third canal is hori- zontal, and lower and shorter than the others. THE SENSES. 183 The cochlea (6, 7, 8, Figs. 359 and 360), a small organ, shaped like a common snail-shell, is seated in front of the vestibule, its base rest- ing on the bottom of the internal meatus, where some apertures transmit to it the cochlear filaments of the auditory nerve. In its axis, the cochlea is traversed by a conical column, the modiolus, around which a spiral canal winds with about two turns and a half from the base to the apex. At the apex of the cochlea the canal is closed; at the base it presents three openings, of which one, already mentioned, communicates with the vestibule; another called fenestra rotunda, is separated by a membrane from the cavity of the tympanum; the third is the orifice of the aquce- duclus cochlea, a canal leading to the jugular fossa of the petrous bone, and corresponding, at least in obscurity of purpose and origin, to the aquseductus vestibuli. The spiral canal is divided into two passages, or FIG. 361. FIG. 362. Fie. 361.— View of the osseous cochlea divided through the middle. 1, central canal of the modio- lus; 2, lamina spiralis ossea; 3, scala tympani; 4. scala vestibuli ; 5, porous substance of the modiolus near one of the sections of the canalis spiralis modioli. 5 . (Arnold.) FIG. 362.— Section through one of the coils of the cochlea (diagrammatic). S T, scala tympani ; 8 V, scala vestibuli; C C, canalis cochleae or canalis membranaceus; R, membrane of Reissner; I s o, lamina spiralis ossea; 1 1 s, limbus laminae spiralis; s s, sulcus spiralis; n c, cochlear nerve; g s, gang- lion spirale; £, membrana tectoria (below the membrana tectoria is the lamina reticularis); 6, mem- brana basilaris; Co, rods of Corti; Isp, ligamentum spirale. (From Quain's Anatomy.) scalae, by a partition of bone and membrane, the lamina spiralis. The osseous part or zone of this lamina is connected with the modiolus; the membranous part, with a muscular zone, according to Todd and Bowman, forming its outer margin, is attached to the outer wall of the canal. Commencing at the base of the cochlea, between its vestibular and tym- panic openings, they form a partition between these apertures; the two scalae are, therefore, in correspondence with this arrangement, named scala vestibuli and scala tympani (Fig. 361). At the apex of the cochlea, the lamina spiralis ends in a small hamulus, the inner and concave part of which, being detached from the summit of the modiolus, leaves a small aperture named helicotrema, by which the two scalae, separated in all the rest of their length, communicate. Besides the ' 'scala vestibuli" and "scala tympani/' there is a third space between them, called scala media or canalis membranaceus (CO, Fig 362). In section it is triangular, its external wall being formed by the wall of the cochlea, its upper wall (separating it from the scala vestibuli) by the membrane of Reissner, and its lower wall (separating it from the scala tympani) by the basilar membrane, these two meeting at the outer 184 HAND-BOOK OF PHYSIOLOGY. (canalis reuniens) uniting it with the sacculus. The scala media (like the rest of the membranous labyrinth) contains "endolymph." Organ of Corti.— Upon the basilar membrane are arranged cells of various shapes. About midway between the outer edge of the lamina spiralis and the outer wall of the cochlea are situated the rods of Corti. Viewed sideways, the rods of Corti are seen to consist of an external and internal pillar, each rising from an expanded foot or base on the basilar membrane. They slant inward toward each other, and each ends in a swelling termed the head; the head of the inner pillar overlying that of the outer (Fig. FIG. 363.— Vertical section of the organ of Corti from the dog. 1 to 2, homogeneous layer of the so-called membrana basilaris; u, vestibular layer; v, tympanal layer, with nuclei and protoplasm; a, prolongation of tympanal periosteum of Jamina spiralis ossea; c, thickened commencement of the membrana basilaris near the point of perforation of the nerves h; d, blood-vessel, (vas spirale); e, blood-vessel; /, nerves; g, the epithelium of the sulcus spiralis internus; i, internal or tufted cell, with basil process fc, surrounded with nuclei and protoplasm (of the granular layer), into which the nerve-fibres radiate; Z, hairs of the internal hair-cell; n, base or foot of inner pillar of organ of Corti; m, head of the same uniting with the corresponding part of an external pillar, whose under half is missing, while the next pillar beyond, o, presents both middle portion and base; r,*,d, three external hair-cells; £, bases of two neighboring hair or tufted cells; x, so-called supporting cell of Hensen; w, nerve fibre terminating in the first of the external hair-cells; II to I, lamina reticularis. X 800. (Waldeyer.) 363). Each pair of pillars forms, as it were, a pointed roof arching over a space, and by a succession of them, a little tunnel is formed. It has been estimated that there are about 3000 of these pairs of pillars, in proceeding from the base of the cochlea toward its apex. They are found progressively to increase in length, and become more oblique; in other words, the tunnel becomes wider, but diminishes in height as we approach- the apex of the cochlea. Leaning, as it were, against these external and internal pillars are certain other cells, of which the external ones terminate in small hair-like processes. Most of the above details are shown in the accompanying figure (Fig. 363). This complicated structure rests, as we have seen, upon the basilar membrane; it is roofed in by a remarkable fenestrated membrane (lamina reticularis of Kolliker), into the fenestrae of which the tops of the various rods and cells are re- ceived. When viewed from above, the organ of Corti shows a remarkable THE SENSES. 185 resemblance to the key-board of a piano. In close relation with the rods of Corti and the cells inside and outside them, and probably projecting by free ends into the little "tunnel" containing fluid (roofed in by them), are filaments of the auditory nerve. Membranous Labyrinth. — This corresponds generally with the form of the osseous labyrinth, so far as regards the vestibule and semi- circular canals, but is separated from the walls of these parts by fluid, except where the nerves enter into connection within it. As already men- tioned, the membranous labyrinth contains a fluid called endolympli; and between its outer surface and the inner surface of the walls of the vesti- bule and semicircular canals is another collection of similar fluid, called perilympli; so that all the sonorous vibrations impressing the auditory nerves on these parts of the internal ear, are conducted through fluid to a membrane suspended in and containing fluid. In the cochlea, the membranous labyrinth completes the septum between the two scales and encloses a spiral canal, previously mentioned, called canalis membranaceus or canalis cochlece (Fig. 362). The fluid in the scales of the cochlea is con- tinuous with the perilympli in the vestibule and semicircular canals, and there is no fluid external to its lining membrane. The vestibular portion of the membranous labyrinth cofnprises two, probably communicating cavities, of which the larger and upper is named the utriculus; the lower, the sacculus. They are lodged in depressions in the bony labyrinth termed respectively "fovea hemielliptica" and "fovea hemispheric^." Into the former open the orifices of the membranous semicircular canals; into the latter the canalis cochlece. The membranous labyrinth of all these parts is laminated, transparent, very vascular, and covered on the inner surface with nucleated cells, of which those that line the ampullae are prolonged into stiff hair-like processes; the same appearance, but to a much less degree, being visible in the utricule and saccule. In the cavities of the utriculus and sacculus are small masses of calcareous particles, otoconia or otoliths; and the same, although in more minute quantities, are to be found in the interior of some other parts of the membranous labyrinth. Auditory Nerve. — For the appropriate exposure of the filaments of the auditory nerve to sonorous vibrations all the organs now described are provided. It is characterized as a nerve of special sense by its softness (whence it derived its name of portio mollis of the seventh pair) and by the fineness of its component fibres. It enters the labyrinth of the ear in two divisions; one for the vestibule and semicircular canals, and the other for the cochlea. The branches for the vestibule spread out and radiate on the inner surface of the membranous labyrinth : their exact termination is unknown. Those for the semicircular canals pass into the ampullae, and form, within each of them, a forked projection which corresponds with a septum in the 186 HAND-BOOK OF PHYSIOLOGY. interior of the ampulla. The branches for the cochlea enter it through orifices at the base of the modiolus, which they ascend, and thence suc- cessively pass into canals in the osseous part of the lamina spiralis. In the canals of this osseous part or zone, the nerves are arranged in a plexus, containing ganglion cells. Their ultimate termination is not known with certainty; but some of them, without doubt, end in the organ of Corti, probably in cells. PHYSIOLOGY OF HEAEING. All the acoustic contrivances of the organ of hearing are means for conducting the sound, just as the optical apparatus of the eye are media for conducting the light. Since all matter is capable of propagating sono- rous vibrations, the simplest conditions must be sufficient for mere hear- ing; for all substances surrounding the auditory nerve would communi- cate sound to it. The whole development of the organ of hearing, there- fore, can have for its object merely the rendering more perfect the propa- gation of the sonorous vibrations, and their multiplication by resonance; and, in fact, all the acoustic apparatus of the organ may be shown to have reference to these two principles. Functions of the External Ear.— The external auditory passage influences the propagation of sound to the tympanum in three ways: — 1, by causing the sonorous undulations, entering directly from the atmos- phere, to be transmitted by the air in the passage immediately to the membrana tympani, and thus preventing them from being dispersed; 2, by the walls of the passage conducting the sonorous undulations imparted to the external ear itself, by the shortest path to the attachment of the membrana tympani, and so to this membrane; 3, by the resonance of the column of air contained within the passage; 4, the external ear, especially when the tragus is provided with hairs, is also, doubtless, of service in protecting the meatus and membrana tympani against dust, insects, and the like. 1. As a conductor of undulations of air, the external auditory passage receives the direct undulations of the atmosphere, of which those that enter in the direction of its axis produce the strongest impressions. The undulations which enter the passage obliquely are reflected by its parietes, and thus by reflexion reach the membrana tympani. 2. The walls of the meatus are also solid conductors of sound; for those vibrations which are communicated to the cartilage of the external ear, and not reflected from it, are propagated by the shortest path through the parietes of the passage to the membrana tympani. Hence, both ears being close stopped, the sound of a pipe is heard more distinctly when its loAver extremity, covered with a membrane, is applied to the cartilage of the external ear itself, than when it is placed in contact with the surface of the head. THE SENSES. 187 3. The external auditory passage is important, inasmuch as the air which it contains, like all insulated masses of air, increases the intensity of sounds by resonance. Regarding the cartilage of the external ear, therefore, as a conductor of sonorous vibrations, all its inequalities, elevations, and depressions, which are useless with regard to reflexion, become of evident importance; for those elevations and depressions upon which the undulations fall per- pendicularly, will be affected by them in the most intense degree; and, in consequence of the various forms and positions of these inequalities, sonorous undulations, in whatever direction they may come, must fall perpendicularly upon the tangent of some one of them. This affords an explanation of the extraordinary form given to this part. Functions of the Middle Ear. — In animals living in the atmos- phere, the sonorous vibrations are conveyed to the auditory nerve by three different media in succession; namely, the air, the solid parts of the body of the animal and of the auditory apparatus, and the fluid of the laby- rinth. Sonorous vibrations are imparted too imperfectly from air to solid bodies, for the propagation of sound to the internal ear to be adequately effected by that means alone; yet already an instance of its being thus propagated has been mentioned. In passing from air directly into water, sonorous vibrations suffer also a considerable diminution of their strength; but if a tense membrane exists between the air and the water, the sono- rous vibrations are communicated from the former to the latter medium with very great intensity. This fact, of which Miiller gives experimental proof, furnishes at once an explanation of the use of the f enestra rotunda, and of the membrane closing it. They are the means of communicating, in full intensity, the vibrations of the air in the tympanum to the fluid of the labyrinth. This peculiar property of membranes is the result, not of their tenuity alone, but of the elasticity and capability of displacement of their particles; and it is not impaired when, like the membrane of the fenestra rotunda, they are not impregnated with moisture. Sonorous vibrations are also communicated without any perceptible loss of intensity from the air to the water, when to the membrane form- ing the medium of communication, there is attached a short, solid body, which occupies the greater part of its surface, and is alone in contact with the water. This fact elucidates the action of the fenestra ovalis, and of the plate of the stapes which occupies it, and, with the preceding fact, shows that both fenestrae — that closed by membrane only, and that with which the movable stapes is connected — transmit very freely the sonorous vibrations from the air to the fluid of the labyrinth. A small, solid body, fixed in an opening by means of a border of mem- brane, so as to be movable, communicates sonorous vibrations from air on the one side, to water, or the fluid of the labyrinth, on the other side, much better than solid media not so constructed. But the propagation 188 HAND-BOOK OF PHYSIOLOGY. of sound to the fluid is rendered much more perfect if the solid conductor thus occupying the opening, or fenestra ovalis, is by its other end fixed to the middle of a tense membrane, which has atmospheric air on both sides. A tense membrane is a much better conductor of the vibrations of air than any other solid body bounded by definite surfaces: and the vibra- tions are also communicated very readily by tense membranes to solid bodies in contact with them. Thus, then, the membrana tympani serves for the transmission of sound from the air to the chain of auditory bones. Stretched tightly in its osseous ring, it vibrates with the air in the audi- tory passage, as any thin tense membrane will, when the air near it is thrown into vibrations by the sounding of a tuning-fork or a musical string. And, from such a tense vibrating membrane, the vibrations are communicated with great intensity to solid bodies which touch it at any point. If, for example, one end of a flat piece of wood be applied to the membrane of a drum, while the other end is held in the hand, vibrations are felt distinctly when the vibrating tuning-fork is held over the mem- brane without touching it; but the wood alone, isolated from the mem- brane, will only very feebly propagate the vibrations of the air to the hand. In comparing the membrana tympani to the membrane of a drum, it is necessary to point out certain important differences. When a drum is struck, a certain definite tone is elicited (fundamental tone) ; similarly a drum is thrown into vibration when certain tones are sounded in its neighborhood, while it is quite unaffected by others. In other words, it can only take up and vibrate in response to those tones whose vibrations nearly correspond in number with those of its own fun- damental tone. The tympanic membrane can take up an immense range of tones produced by vibrations ranging from 30 to 4000 or 5000 per second. This would be clearly impossible if it were an evenly stretched membrane. The fact is, that the tympanic membrane is by no means evenly stretched, and this is due partly to its slightly funnel-like form, and partly to its being connected with the chain of auditory ossicles. Further, if the membrane were quite free in its centre, it would go on vibrating as a drum does some time after it is struck, and each sound would be pro- longed, leading to considerable confusion. This evil is obviated by the ear-bones, which check the continuance of the vibrations like the "dam- pers" in a pianoforte. The ossicula of the ear are the better conductors of the sonorous vibrations communicated to them, on account of being isolated by an atmosphere of air, and not continuous with the bones of the cranium; for every solid body thus isolated by a different medium, propagates vibra- tions with more intensity through its own substance than it communicates them to the surrounding medium, which thus prevents a dispersion of the sound; just as the vibrations of the air in the tubes used for conduct- ing the voice from one apartment to another are prevented from being THE SENSES. 189 dispersed by the solid walls of the tube. The vibrations of the mem- brana tympani are transmitted, therefore, by the chain of ossicula to the fenestra ovalis and fluid of the labyrinth, their dispersion in the tym- panum being prevented by the difficulty of the transition of vibrations from solid to gaseous bodies. The necessity of the presence of air on the inner side of the membrana tympani, in order to enable it and the ossicula auditus to fulfil the objects just described, is obvious. Without this provision, neither would the vibrations of the membrane be free, nor the chain of bones isolated, so as to propagate the sonorous undulations with concentration of their inten- sity. But while the oscillations of the membrana tympani are readily communicated to the air in the cavity of the tympanum, those of the solid ossicula will not be conducted away by the air, but will be propagated to the labyrinth without being dispersed in the tympanum. The propagation of sound through the ossicula of the tympanum to the labyrinth, must be effected either by oscillations of the bones, or by a kind of molecular vibration of their particles, or, most probably, by both these kinds of motion. Movements of the ossicula. — E. Weber has shown that the existence of the membrane over the fenestra rotunda will permit approximation and removal of the stapes to and from the labyrinth. When by the stapes the membrane of the fenestra ovalis is pressed toward the labyrinth, the membrane of the fenestra rotunda may, by the pressure communicated through the fluid of the laby- rinth, be pressed toward the cavity of the tympanum. The long process of the malleus receives the undula- tions of the membrana tympani (Fig. 364, a, a) and of the air in a direction indicated by the arrows, nearly per- pendicular to itself. From the long process of the malleus they are propagated to its head (b) : thence into the incus (c), the long process of which is parallel with the long process of the malleus. From the long process of the incus the undulations are communicated to the stapes (d), which is united to the incus at right angles. The several changes in the direction of the chain of bones ha^ve, however, no influence on that of the undu- Flo 364 lations, which remain the same as it was in the meatus externus and long process of the malleus, so that the undulations are communicated by the stapes to the fenestra ovalis in a perpendicular direction. Increasing tension of the membrana tympani diminishes the facility of transmission of sonorous undulations from the air to it. Savart observed that the dry membrana tympani, on the approach of a body emitting a loud sound, rejected particles of sand strewn upon it more strongly when lax than when very tense; and inferred, therefore, that hearing is rendered less acute by increasing the tension of the mem- 190 HAND-BOOK OF PHYSIOLOGY. brana tympani. Miiller has confirmed this by experiments with small membranes arranged so as to imitate the membrana tympani; and it may be confirmed also by observations on one's self. The pharyngeal orifice of the Eustachian tube is usually shut; during swallowing, however, it is opened; this may be shown as follows: — If the nose and mouth be closed and the cheeks blown out, a sense of pressure is produced in both ears the moment we swallow; this is due, doubtless, to the bulging out of the tympanic membrane by the compressed air which, at that moment, enters the Eustachian tube. Similarly the tympanic membrane may be pressed in by rarefying the air in the tympanum. This can be readily accomplished by closing the mouth and nose, and making an inspiratory effort and at the same time swallowing (Valsalva). In both cases the sense of hearing is temporarily dulled; proving that equality of pressure on both sides of the tympanic membrane is necessary for its full efficiency. Functions of Eustachian Tube. — The principal office of the Eustachian tube, in M tiller's opinion, has relation to the prevention of these effects of increased tension of the membrana tympani. Its exist- ence and openness will provide for the maintenance of the equilibrium between the air within the tympanum and the external air, so as to pre- vent the inordinate tension of the membrana tympani which would be produced by too great or too little pressure on either side. While dis- charging this office, however, it will serve to render sounds clearer, as (Henle suggests) the apertures in violins do; to supply the tympanum with air; and to be an outlet for mucus. If the Eustachian tube were permanently open, the sound of one's own voice would probably be greatly intensified, a condition which would of course interfere with the percep- tion of other sounds. At any rate, it is certain that sonorous vibrations can be propagated up the Eustachian tube to the tympanum by means of a tube inserted into the pharyngeal orifice of the Eustachian tube. Action of Tensor Tympani. — The influence of the tensor tympani muscle in modifying hearing may also be probably explained in connec- tion with the regulation of the tension of the membrana tympani. If, through reflex nervous action, it can be excited to contraction by a very loud sound, just as the iris and orbicularis palpebrarum muscle are by a very intense light, then it is manifest that a very intense sound would, through the action of this muscle, induce a deafening or muffling of the ears. In favor of this supposition we have the fact that a loud sound excites, by reflection, nervous action, winking of the eyelids, and, in per- sons of irritable nervous system, a sudden contraction of many muscles. "The ossicula of aquatic mammalia are very bulky and relatively large, especially in the true seals and the sirenia (Manatee and Dugong). In the cetacea the stapes is generally ankylosed to the fenestra ovalis, the malleus is always ankylosed to the tympanic bone, yet the membrana tym- pani is well formed, and there is a manubrium, often ill-developed, but always attached to the membrane by a long process. In the Otarise or Sea- THE SENSES. 191 lions, where the ossicula are far smaller relatively, and less solid than in whales, manatees, and the earless true seals, there are well-formed, mov- able external ears. The ossicula seem to be vestigial relics utilized for the auditory function. In land animals they vary in shape according to the type of the animal rather than in relation to its acuteness of hearing. I have never found a muscular laxator tympani in any animal, but the tensor exists as a ligament in whales where the malleus is fixed. " (Alban Doran. ) Action of the Stapedius. — The influence of the stapedius muscle in hearing is unknown. It acts upon the stapes in such a manner as to make it rest obliquely in the fenestra ovalis, depressing that side of it on which it acts, and elevating the other side to the same extent. It pre- vents too great a movement of the bone. Functions of the Fluid of the Labyrinth.— The fluid of the laby- rinth is the most general and constant of the acoustic provisions of the labyrinth. In all forms of organs of hearing, the sonorous vibrations affect the auditory nerve through the medium of liquid — the most convenient medium, on many accounts, for such a purpose. The crystalline pulverulent masses (otoliths) in the labryinth would reinforce the sonorous vibrations by their resonance, even if they did not actually touch the membranes upon which the nerves are expanded ; but, inasmuch as these bodies lie in contact with the membranous parts of the labyrinth, and the vestibular nerve-fibres are imbedded in them, they communicate to these membranes and the nerves, vibratory impulses of greater intensity than the fluid of the labyrinth can impart. This appears to be their office. Sonorous undulations in water are not perceived by the hand itself immersed in the water, but are felt distinctly through the medium of a rod held in the hand. The fine hair-like prolongations from the epithelial cells of the ampullae have, probably, the same function. Functions of the Semicircular Canals. — Besides the function of collecting in their fluid contents sonorous undulations from the bones of the cranium, the semicircular canals appear to have another function less directly connected with the sense of hearing. Experiments show that when the horizontal canal is divided in a pigeon a constant movement of the head from side to side occurs, and similarly, when one of the vertical canals is operated upon, up and down movements of the head are ob- served. These movements are associated, also, with loss of co-ordination, as after the operation the bird is unable to fly in an orderly manner, but flutters and falls when thrown into the air, and, moreover, is able to feed with difficulty. Hearing remains unimpaired. It has been suggested, therefore, that as loss of co-ordination results from section of these canals, and as co-ordinate muscular movements appear to depend to a consider- able extent for their due performance upon a correct notion of our equili- brium, that the semicircular canals are connected in some way with this 192 HAND-BOOK OF PHYSIOLOGY. sense, possibly by the constant alterations of the pressure of the fluid within them; the change in the pressure of the fluid in each canal which takes place on any movement of the head, producing sensations which aid in forming an exact judgment of the alteration of position which has occurred. Functions of the Cochlea. — The cochlea seems to be constructed for the spreading out of the nerve-fibres over a wide extent of surface, upon a solid lamina which communicates with the solid walls of the labyrinth and cranium,, at the same time that it is in contact with the fluid of the labyrinth, and which, besides exposing the nerve-fibres to the influence of sonorous undulations, by two media, is itself insulated by fluid on either side. The connection of the lamina spiralis with the solid walls of the laby- rinth, adapts the cochlea for the perception of the sonorous undulations propagated by the solid parts of the head and the walls of the labyrinth. The membranous labyrinth of the vestibule and semicircular canals is suspended free in the perilymph, and is destined more particularly for the perception of sounds through the medium of that fluid, whether the sono- rous undulations be imparted to the fluid through the fenestrae, or by the intervention of the cranial bones, as when sounding bodies are brought into communication with the head or teeth. The spiral lamina on which the nervous fibres are expanded in the cochlea, is, on the contrary, con- tinuous with the solid walls of the labyrinth, and receives directly from them the impulses which they transmit. This is an important advantage; for the impulses imparted by solid bodies have, cceteris par-ibus, a greater absolute intensity than those communicated by water. And, even when a sound is excited in the water, the sonorous undulations are more intense in the water near the surface of the vessel containing it, than in other parts of the water equally distant from the point of origin of the sound; thus we may conclude that, cceteris paribus, the sonorous undulations of solid bodies act with greater intensity than those of water. Hence, we perceive at once an important use of the cochlea. This is not, however, the sole office of the cochlea; the spiral lamina, as well as the membranous labyrinth, receives sonorous impulses through the medium of the fluid of the labyrinth from the cavity of the vestibule, and from the fenestra rotunda. The lamina spiralis is, indeed, much better calculated to render the action of these undulations upon the audi- tory nerve efficient, than the membranous labyrinth is; for as a solid body insulated by a different medium, it is capable of resonance. The rods of Corti are probably arranged so that each is set to vibrate in unison with a particular tone, and thus strike a particular note, the sensation of which is carried to the brain by those filaments of the audi- tory nerve with which the little vibrating rod is connected. The distinc- tive function, therefore, of these minute bodies is, probably, to render THE SENSES. 193 sensible to the brain the various musical notes and tones, one of them answering to one tone, and one to another; while perhaps the other parts of the organ of hearing discriminate between the intensities of different sounds, rather than their qualities. "In the cochlea we have to do with a series of apparatus adapted for performing sympathetic vibrations with wonderful exactness. We have here before us a musical instrument which is designed, not to create musical sounds, but to render them perceptible, and which is similar in construction to artificial musical instruments, but which far surpasses them in the delicacy as well as the simplicity of its execution. For, while in a piano every string must have a separate hammer by means of which it is sounded, the ear possesses a single hammer of an ingenious form in its ear-bones, which can make every string of the organ of Corti sound sepa- rately." (Bernstein.) About 3000 rods of Corti are present in the human ear; this would give about 400 to each of the seven octaves which are within the compass of the ear. Thus about 32 would go to each semi-tone. Weber asserts that accomplished musicians can appreciate differences in pitch as small as -g^h of a tone. Thus on the theory above advanced, the delicacy of discrimination would, in this case, appear to have reached its limits. Sensibility of the Auditory Nerve.— Any elastic body, e.g., air, a membrane, or a string performing a certain number of regular vibrations in the second, gives rise to what is termed a musical sound or tone. We must, however, distinguish between a musical sound and a mere noise; the latter being due to irregular vibrations. Qualities of Musical Sound. — Musical sounds are distinguished from each other by three qualities. 1. Strength or intensity, which is due to the amplitude or length of the vibrations. 2. Pitch, which de- pends upon the number of vibrations in a second. 3. Quality, Color, or Timbre. It is by this property that we distinguish the same note sounded on two instruments, e.g., a piano and a flute. It has been proved by Helmholtz to depend on the number of secondary notes, termed har- monics, which are present with the predominating or fundamental tone. It would appear that two impulses, which are equivalent to four single or half vibrations, are sufficient to produce a definite note, audible as such through the auditory nerve. The note produced by the shocks of the teeth of a revolving wheel, at regular intervals upon a solid body, is still heard when the teeth of the wheel are removed in succession, until two only are left; the second produced by the impulse of these two teeth has still the same definite value in the scale of music. The maximum and minimum of the intervals of successive impulses still appreciable through the auditory nerve as determinate sounds, have been determined by M. Savart. If their intensity is sufficiently great, sounds are still audible which result from the succession of 48,000 half VOL. II.— 13. 194 HAND-BOOK OF PHYSIOLOGY. vibrations, or 24,000 impulses in a second; and this, probably, is not the extreme limit in acuteness of sounds perceptible by the ear. For the op- posite extreme, he has succeeded in rendering sounds audible which were produced by only fourteen or eighteen half vibrations, or seven or eight impulses in a second; and sounds still deeper might probably be heard, if the individual impulses could be sufficiently prolonged. By removing one or several teeth from the toothed wheel the fact has been demonstrated that in the case of the auditory nerve, as in that of the optic nerve, the sensation continues longer than the impression which causes it; for a removal of a tooth from the wheel produced no interrup- tion of the sound. The gradual cessation of the sensation of sound ren- ders it difficult, however, to determine its exact duration beyond that of the impression of the sonorous impulses. Direction of Sounds. — The power of perceiving the direction of sounds is not a faculty of the sense of hearing itself, but is an act of the mind judging on experience previously acquired. From the modifications which the sensation of sound undergoes according to the direction in which the sound reaches us, the mind infers the position of the sounding body. The only true guide for this inference is the more intense action of the sound upon one than upon the other ear. But even here there is room for much deception, by the influence of reflexion or resonance, and by the propagation of sound from a distance, without loss of intensity, through curved conducting tubes filled with air. By means of such tubes, or of solid conductors, which convey the sonorous vibrations from their source to a distant resonant body, sounds may be made to appear to originate in a new situation. The direction of sound may also be judged of by means of one ear only; .the position of the ear and head being varied, so that the sonorous undulations at one moment fall upon the ear in a perpendicular direction, at another moment obliquely. But when neither of these circumstances can guide us in distinguishing the direction of sound, as when it falls equally upon both ears, its source being, for example, either directly in front or behind us, it becomes impossible to determine whence the sound comes. Distance of Sounds. — The distance of the source of sounds is not recognized by the sense itself, but is inferred from their intensity. The sound itself is always seated but in one place, namely, in our ear; but it is interpreted as coming from an exterior soniferous body. When the in- tensity of the voice is modified in imitation of the effect of distance, it excites the idea of its originating at a distance. Ventriloquists take advantage of the difficulty with .which the direction of sound is recognized, and also the influence of the imagination over our judgment, when they direct their voice in a certain direction, and at the same time pretend, themselves, to hear the sounds as coming from thence. The effect of the action of sonorous undulations upon the nerve of THE SENSES. 195 hearing, endures somewhat longer than the period during which the un- dulations are passing through the ear. If, however, the impressions of the same sound be very long continued, or constantly repeated for a long time, then the sensation produced may continue for a very long time, more than twelve or twenty-four hours even, after the original cause of the sound has ceased. Binaural Sensations. — Corresponding to the double vision of the same object with the two eyes, is the double hearing with the two ears; and analogous to the double vision with one eye, dependent on unequal refraction, is the double hearing of a single sound with one ear, owing to the sound coming to the ear through media of unequal conducting power. The first kind of double hearing is very rare; instances of it are recorded, however, by Sauvages and Itard. The second kind, which depends on the unequal conducting power of two media through which the same sound is transmitted to the ear, may easily be experienced. If a small bell be sounded in water, while the ears are closed by plugs, and a solid conductor be interposed between the water and the ear, two sounds will be heard differing in intensity and tone; one being conveyed to the ear through the medium of the atmosphere, the other through the conduct- ing-rod. Subjective Sensations of Sound. — Subjective sounds are the result of a state of irritation or excitement of the auditory nerve produced by other causes than sonorous impulses. A state of excitement of this nerve, however induced, gives rise to the sensation of sound. Hence the ringing and buzzing in the ears heard by persons of irritable and exhausted nervous system, and by patients with cerebral disease, or disease of the auditory nerve itself; hence also the noise in the ears heard for some time after a long journey in a rattling noisy vehicle. Hitter found that electricity also excites a sound in the ears. From the above truly subjec- tive sound we must distinguish those dependent, not 011 a state of the auditory nerve itself merely, but on sonorous vibrations excited in the auditory apparatus. Such are the buzzing sounds attendant on vascular congestion of the head and ear, or on aneurismal dilatation of the vessels. Frequently even the simple pulsatory circulation of the blood in the ear is heard. To the sounds of this class belong also the buzz or hum heard during the contraction of the palatine muscles in the act of yawning; during the forcing of air into the tympanum, so as to make tense the membrana tympani; and in the act of blowing the nose, as well as dur- ing the forcible depression of the lower jaw. Irritation or excitement of the auditory nerve is capable of giving rise to movements in the body, and to sensations in other organs of sense. In both cases it is probable that the laws of reflex action, through the medium of the brain, came into play. An intense and sudden noise ex- cites, in every person, closure of the eyelids, and, in nervous individuals, 196 HAND-BOOK OF PHYSIOLOGY. a start of the whole body or an unpleasant sensation, like that produced by an electric shock, throughout the body, and sometimes a particular feeling in the external ear. Various sounds cause in many people a dis- agreeable feeling in the teeth, or a sensation of cold tickling through the body, and, in some people, intense sounds are said to make the saliva collect. SIGHT. Eyelids and Lachrymal Apparatus. — The eyelids consist of two movable folds of skin, each of which is kept in shape by a thin plate of yellow elastic tissue. Along their free edges are inserted a number of curved hairs (eyelashes), which, when the lids are half closed, serve to protect the eye from dust and other foreign bodies: their tactile sensibil- ity is also very delicate. Ciliary muscle Ciliary Canal of Petit- Cornea — Anterior chamber Iris- Ciliary process- Ciliary muscle FIG. 365. On the inner surface of the elastic tissue are disposed a number of small racemose glands (Meibomian), whose ducts open near the free edge of the lid. The orbital surface of each lid is lined by a dslicate, highly sensitive mucous membrane (conjunctiva), which is continuous with the skin at the free edge of each lid, and after lining the inner surface of the eyelid is reflected on to the eyeball, being somewhat loosely adherent to the sclerotic coat. The epithelial layer is continued over the cornea at its anterior epithelium. At the inner edge of the eye the conjunctiva becomes continuous with the mucous lining of the lachrymal sac and duct, which again is continuous with the mucous membrane of the in- ferior meatus of the nose. THE SENSES. 197 The lachrymal gland is lodged in the upper and outer angle of the orbit. Its secretion, which issues from several ducts on the inner surface of the upper lid, under ordinary circumstances just suffices to keep the conjunctiva moist. It passes out through two small openings (puncta lachrymalia) near the inner angle of the eye, one in each lid, into the lachrymal sac, and thence along the nasal duct into the inferior meatus of the nose. The excessive secretion poured out under the influence of any irritating vapor or pain- ful emotion overflows the lower lid in the form of tears. The eyelids are closed by the contraction of a sphincter muscle (orUcularis) , supplied by the Facial nerve; the upper lid is raised by the Levator palpebrcB superioris, which is supplied by the Third nerve. THE EYEBALL. The eyeball or the organ of vision (Fig. 365) consists of a variety of structures which may be thus enumerated: — The sclerotic, or outermost coat, envelopes about five-sixths of the eyeball: continuous with it, in front, and occupying the remaining sixth, is the cornea. Immediately within the sclerotic is the choroid coat, and within the choroid is the retina. The interior of the eyeball is well-nigh filled by the aqueous and vitreous humors and the crystalline lens; but, also, there is suspended in the interior a contractile and perforated cur- tain,— the iris, for regulating the admission of light, and behind the -junction of the sclerotic delicate sub-epitheiiai plexus, • and sending up fine twigs be- and cornea is a ciliary muscle, the function of twee.n the epithelial ceils to J end in a second plexus on the which is to adapt the eye for seeing objects at various distances. Structure of Sclerotic. — The sclerotic coat is composed of connective tissue, arranged in vari- ously disposed and inter-communicating layers. It is strong, tough, and opaque, and not very elastic. Structure of Cornea. — The cornea is a transparent membrane which forms a segment of a smaller sphere than the rest of the eyeball, and is let in, as it were, into the sclerotic with which it is continuous all round. It is coated with a laminated anterior epithelium (a, Fig. 367) consisting of seven or eight layers of cells, of which the superficial ones are flattened FIG. 366.— Vertical sectionof rabbit's cornea, stained with gold chloride, e, Laminated anterior epithelium. Imme- diately beneath this is the an- terior elastic lamina of Bow- man. n, Nerves forming a free surface; d, Descemefs membrane, consisting of a fine elastic layer, and a single layer of epithelial cells; the substance of the cornea, /, is seen to befibrillated, and con- tains many layers of branched corpuscles, arranged parallel to the free surface, and here seen edgewise. (Schofield.) 198 HATsD-BOOK OF PHYSIOLOGY. and scaly, and the deeper ones more or less columnar. Immediately beneath this is the anterior elastic lamina (Bowman). The cornea tissue proper as well as its epithelium is, in the adult, completely d3stitute of blood-vessels; it consists of an intercellular ground- substance of rather obscurely fibrillated flattened bundles of connective tissue, arranged parallel to the free surface, and forming the boundaries FIG. 367.— Vertical section of rabbit's cornea, a, Anterior epithelium, showing the different shapes of the cells at various depths from the free surface; 6, portion of the substance of cornea. (Klein.) of branched anastomosing spaces in which the cornea-corpuscles lie. These branched cornea-corpuscles have been seen to creep by amoeboid move- ment from one branched space into another. At its posterior surface the cornea is limited by the posterior elastic lamina, or membrane of Descemet, the inner layer of which consists of a single stratum of epithelial cells (Fig. 366, d). Nerves of Cornea. — The nerves of the cornea are both large and numerous: they are derived from the ciliary nerves. They traverse the FIG. 368.— Horizontal preparation of cornea of frog; showing the network of branched cornea corpuscles. The ground substance is completely colorless. X 400. (Klein.) substance of the cornea, in which some of them terminate, in the direc- tion of its anterior surface, near which the axis cylinders break up into bundles of very delicate beaded fibrillge (Fig. 366): these form a plexus immediately beneath the epithelium, from which delicate fibrils pass up THE SENSES. 199 between the cells anastomosing with horizontal branches, and forming a deep intra-epithelial plexus, from which fibres ascend, till near the surface they form a superficial intra-epithelial network. Structure of Choroid (tunica vasculosa). — This coat of the eye- ball is formed by a very rich network of capillaries (chorio-capillaris) out- side which again are connective-tissue layers of stellate pigmented cells (Fig. 25) with numerous arteries and veins. The choroid coat ends in front in what are called the ciliary processes (Fig. 365). Structure of Retina. — The retina (Fig. 370) is a delicate mem- brane, concave, with the concavity directed forward and ending in front, near the outer part of the ciliary processes in a finely notched edge, — the ora serrata. Semi-transparent when fresh, it soon becomes clouded and opaque, with a pinkish tint from the blood in its minute vessels. ' It results from the sudden spreading out or expansion of the optic nerve, of whose terminal fibres, apparently deprived of their external white substance, together with nerve cells, it is essentially composed. Fia. 369.— Surface view of part of lamella of kitten's cornea, prepared first with caustic potash and then with nitrate of silver. (By this method the branched cornea-corpuscles with their granular protoplasm and large oval nuclei are brought out.) x 450. (Klein and Noble Smith.) Exactly in the centre of the retina, and at a point thus corresponding to the axis of the eye in which the sense of vision is most perfect, is a round yellowish elevated spot, about -fa of an inch in diameter, having a minute aperture at its summit, and called after its discoverer the yelloio spot of Scemmering. In its centre is a minute depression called fovea centralis. About -^ of an inch to the inner side of the yellow spot, and consequently of the axis of the eye, is the point at which the optic nerve begins to spread out its fibres to form the retina. This is the only point of the surface of the retina from which the power of vision is absent. . The retina consists of certain nervous elements arranged in several layers, and supported by a very delicate connective tissue. From the nature of the case there is considerable uncertainty as to the character (nervous or connective tissue) of some of the layers of the retina. The following ten layers, from within outward, are usually to be distin- guished in a vertical section (Figs. 370, 373). 200 HAND-BOOK OF PHYSIOLOGY. 1. Membrana limitans internal a delicate membrane in contact with the vitreous humor. 2. Fibres of optic nerve. This layer is of very varying thickness in different parts of the retina: it consists chiefly of non-medullated fibres which interlace, and some of which are continuous with processes of the large nerve-cells forming the next layer. FIG. 370.— Diagram of the retina. A, connective tissue portion; B, nervous portion (the two must be combined to form the complete retina); aa, membrana limitans externa; 6, rods; c, cones: &', rod-granule; c'. cone-granule; both belonging to the external granule layer: e< Mailer's sustentacular fibres, with their nuclei e'; d, intergranular layer;/, internal granule layer; g, molecular layer, con- nective-tissue portion; , deeper layer, corresponding to hypoblast, and probably in part to mesoblast; M, large 'formative cells," filled with yelk granules, and lying on the floor of the segmentation cavity ; A, the white yelk im- mediately underlying the segmentation cavity (Strieker). Beneath the blastoderm there are a few scattered larger cells — "for- mative cells." In the lower of the above two layers, some cells become flattened and unite to form a distinct membrane (hypoblast); the re- maining cells of the lower layer, together with some of the large formative FIG. 408.— Vertical section of blastoderm of chick (1st day of incubation). 8, epiblast, consisting of short columnar cells; Z>, hypoblast, consisting of a single layer of flattened cells; M, "formative cells." They are seen on the right of the figure, passing in between the epiblast and hypoblast to form the mesoblast; A, white yelk granules. Many of the large "formative cells" are seen contain- ing these granules (Strieker). cells, which migrate by amoeboid movement round the edge of the hypo- blast (Fig. 408, M), constitute a third layer (mesoblast). These important changes are among the earliest results of incubation. From the epiblast are ultimately developed the epidermis and its various appendages, also the cerebro-spinal nerve-centres, the sensorial epithelium of the organs of special sense (eye, ear, nose), and the epithelium of the mouth and salivary glands. From the hypoblast is developed the epithelium of the whole digestive canal, together with that lining the ducts of all the glands which open into it; also the glandular parenchyma of the glands (e.g., liver and pancreas) connected with it, and the epithelium of the respiratory track. From the mesoblast are derived all the tissues and organs of the body intervening between these two, the whole group of the connective tissues, 256 HAND-BOOK OF PHYSIOLOGY. the muscles and the cerebro-spinal and sympathetic nerves, with the vas- cular and genito-urinary systems, and all the digestive canal with its various appendages with the exception of the lining epithelium above mentioned. FlKST KUDIMEKTS OF THE EMBRYO AKD ITS CHIEF Germinal Area. — The position in which the embryo is about to appear is early marked out by a central roundish opacity in the blastoderm, due to the accumulation of cells in this region. This germinal area, which is at first circular, changes its shape, becoming pyriform, and finally an elongated oval constricted in the middle like a savoy biscuit. The central portion becomes transparent, and thus we have an area pelludda, sur- rounded by an area opaca (Fig. 409). Primitive Groove. — The first trace of the embryo is a shallow longitudinal groove (primitive groove), which appears toward the posterior part of the area pellucida (Figs. 409, 412). Medullary Groove.— The primitive groove is but transitory, and is soon dis- placed by the medullary groove, which first ap- pears at the anterior extremity of the future embryo, and grows backward, gradually caus- ing the disappearance of the primitive groove. Laminae dorsales. — The medullary canal is bounded by two longitu- dinal elevations (lamina dorsales), which are folds consisting entirely of cells of the epiblast: these grow up and arch over the medullary groove FIG. 409. — Impregnated egg, with commencement of formation of em- bryo : showing the area germinativa or embryonic spot, the area pellu- cida, and the primitive groove or trace (Dalton), FIG. 410.-Transverse section through embryo chick (26 hours), a, epiblast; ft, mesoblast; c, hy- poblast; d, central portion of mesoblast, which is here fused with epiblast- e primitive groove- f dorsal ridge (Klein). (Fig. 411) till they coalesce in the middle line, converting it from an open furrow into a closed tube — the primitive cerebro-spinal axis. Over this closed tube, the walls of which consist of more or less cylindrical cells, the superficial layer of the epiblast is now continued as a distinct membrane. GENERATION AND DEVELOPMENT. 257 The union of the medullary folds or laminae dorsales takes place first about the neck of the future embryo; they soon after unite over the region of the head, while the closing in of the groove progresses much more FIG. 411.— Diagram of transverse section through an embryo before the closing-in of the medul- lary groove, w, cells of epiblast lining the medullary groove which will form the spinal cord; ft, epiblast; d, hypoblast; eft, notochord; w, proto vertebra; sp, mesoblast; w, edge of lamina dorsalis, folding over medullary groove. (Kolliker.) slowly toward the hinder extremity of the embryo. The medullary groove is by no means of uniform diameter throughout, but even before the dorsal laminae have united over it, is seen to be dilated at the anterior extremity and obscurely divided by constrictions into the three primary vesicles of the brain. FIG. 412.— Portion of the germinal membrane, with rudiments of the embryo; from the ovum of a bitch. The primitive groove, A, is not yet closed, and at its upper or cephalic end presents three dilatations, B, which correspond to the three divisions or vesicles of the brain. At its lower extremity the groove presents a lancet-shaped dilatation (sinus rhomboidalis) c. The margins of the groove consist of clear pellucid nerve-substance. Along the bottom of the groove is observed a faint streak, which is probably the chorda dorsalis. D, Vertebral plates. (Bischoff.) The part from which the spinal cord is formed is of nearly uniform calibre, while toward the posterior extremity is a lozenge- shaped dilata- tion, which is the last part to close in (Fig. 412). Notochord. — At the same time there appears in the middle line, im- mediately beneath the floor of the medullary groove, a rod-shaped structure formed by an aggregation of cells of the mesoblast; it soon becomes quite distinct from the remainder of the mesoblasfc, and constitutes an axial cord VOL IT.— 17. 258 HAND-BOOK OF PHYSIOLOGY. (notochprd, chorda dorsalis) (cli, Fig. 414) which extends nearly the whole length of the medullary canal, terminating anteriorly beneath the middle one of the three cerebral vesicles, and occupies the future position of the bodies of the vertebrae and basis cranii. Protovertebrae. — Simultaneously on each side of the notochord appears a longitudinal thickening of the mesoblast. Thus we have two lateral plates which when viewed from above are seen to be divided into a number of squarish segments (protovertebrcB) by the vpl FIG. 413.— Embryo chick (36 hours), viewed from beneath as a transparent object (magnified). pi, outline of pellucid area; FB, fore-brain, or first cerebral vesicle: from its sides project op, the optic vesicles; SO, backward limitof somatopleure fold, "tucked in11 under head; a, headfold of true amnion; a', reflected layer of amnion, sometimes termed "false amnion"; sp, backward limit of splanchnopleure folds, along which run the omphalomesaraic veins uniting to form h, the heart, which is continued forward into 6a, the bulbus arteriosus; d, the fore-gut, lying behind the heart, and having a wide crescentic opening between the splanchnopleure folds; HB, hind-brain; MB, mid- brain; pv, protovertebrse lying behind the fore-gut; me, line of junction of medullary folds and of notochord; ch, front end of notochord; vpl, vertebral plates; pr, the primitive groove at its caudal end. (Foster and Balfour.) formation of transverse clefts. The first three or four of these protoverte- brse make their appearance in the cervical region, while one or two more are formed in front of this point: and the series is continued backward till the whole medullary canal is flanked by them (Fig. 413). Splitting of the Mesoblast.— External to the protovertebrse, the mesoblast now splits into two laminae (parietal and visceral) : of these the former, when traced out from the central axis, is seen to be in close appo- sition with the epiblast and gives origin to the parietes of the trunk, while GENERATION AND DEVELOPMENT. 259 the latter adheres more or less closely to the hypoblast, and gives rise to the serous and muscular walls of the alimentary canal and several other parts (Fig. 414). The united parietal layer of the mesoblast with the epiblast is termed Somatopleure, the united visceral layer and hypoblast, Splanchnopleure. FIG. 414. — Transverse section through dorsal region of embryo chick (45 hours). One half of the section is represented: if completed it would extend as far to the left as to the right of the line of the medullary canal (Me). A, epiblast; C, hypoblast, consisting of a single layer of flattened cells; Me, medullary canal : Pv, protovertebrse ; Wd, Wolffian duct; /So, somatopleure ; Sp, splanchnopleure; pp, pleuro-peritoneal cavity; c/i, notochord; ao, dorsal aorta, containing blood-cells; v. blood-vessels of the yolk-sac. (Foster and ~ Balfour.) The space between them is the pleuro-peritoneal cavity, which becomes subdivided by subsequent partitions into pericardium, pleura, and peri- toneum. Head and Tail Folds. Body Cavity. — Every vertebrate animal consist essentially of a longitudinal axis (vertebral column) with a neural canal above it, and a body-cavity (containing the alimentary canal) beneath. We have seen how the earliest rudiments of the central axis and the neural canal are formed; we must now consider how the general body- cavity is developed. In the earliest stages the embryo lies flat on the sur- face of the yelk, and is not clearly marked off from the rest of the blas- toderm: but gradually a crescentic depression (with its concavity backward) is formed in the blastoderm, limiting the head of the embryo; the blastoderm is, as it were, tucked in under the head, which thus comes to project above the general surface of the membrane: a similar tucking in of blastoderm takes place at the caudal extremity, and thus the head and tail folds are formed (Fig. 415). Similar depressions mark off the embryo laterally, until it is completely surrounded by a sort of moat which it overhangs on all sides, and which clearly defines it from the yelk. This moat runs in further and further all round beneath the over- hanging embryo, till the latter comes to resemble a canoe turned upside- down, the ends and middle being, as it were, decked in by the folding or tucking in of the blastoderm, while on the ventral surface there is still a large communication with the yelk, corresponding to the "well" or un- decked portion of the canoe. 260 HAND-BOOK OF PHYSIOLOGY. This communication between the embryo and the yelk is gradually contracted by the further tucking in of the blastoderm from all sides, The head-fold has fold of the splanchnopleure; the line of reference, FSo, lies outside the embryo in the "moat,11 which marks off the overhanging head from the amnion; Z>, inside the embryo, is that part which is to become the fore-gut; FSo and FSp, are both parts of the head-fold, and travel to the left of the figure as develop- ment proceeds; pp, space between somatopleure and splanchnopleure, pleuro-peritoneal cavity; Am. commencing head-fold of amnion; NC, neural canal; Ch, notochord; Ht, heart; A, B, C, epiblast, mesoblast, hypoblast. (Foster and Balfour.) till it become narrowed down, as by an invisible constricting band, to a mere pedicle which passes out of the body of the embryo at the point of the future umbilicus. FIG. 416.— Diagrammatic section showing the relation in a mammal between the primitive alimen tary canal and the membranes of the ovum. The stage represented in this diagram corresponds tc> that of the fifteenth or seventeenth day in the human embryo, previous to the expansion of the al- lantois; c, the villous chorion; a, the amnion; a', the place of convergence of the amnion and reflex- ion of the false amnion a" a", or outer or corneus layer; e, the head and trunk of the embryo, com- prising the primitive vertebrae and cerebro-spinal axis; t, t, the simple alimentary canal in its upper and lower portions. Immediately beneath the right hand i, is seen the foetal heart, lying in the an- terior part of the pleuro-peritoneal cavity; v, the yolk-sac, or umbilical vesicle; v i, the vitello-intes- tinal opening; it, the allantois connected by a pedicle with the anal portion of the alimentary canal. (From Quainns "Anatomy.") Visceral Plates. — The downwardly folded portions of blastoderm are termed the visceral plates. GENERATION AND DEVELOPMENT. 261 Thus we see that the body-cavity is formed by the downward folding of the visceral plates, just as the neural cavity is produced by the upward growth of the dorsal laminae, the difference being that, in the visceral or ventral laminae, all three layers of the blastoderm are concerned. The folding in of the splanchnopleure, lined by hypoblast, pinches off, as it were, a portion of the yelk-sac, enclosing it in the body-cavity. This forms the rudiment of the alimentary canal, which at this period ends blindly toward the head and tail, while in the centre it communicates freely with the cavity of the yelk-sac through the canal termed vitelline or omphalo-mesenteric duct. The yelk-sac thus becomes divided into two portions which communi- cate through the vitelline duct, that portion within the body giving rise/ as above stated, to the digestive canal, and that outside the body remain- ing for some time as the umbilical vesicle (Fig. 417, ys). The hypoblasfc forming the epithelium of the intestine is of course continuous with the lining membrane of the umbilical vesicle, while the visceral plate of the mesoblast is continuous with the outer layer of the umbilical vesicle. All the above details will be clear on reference to the accompanying diagrams. FCETAL MEMBRANES. Umbilical Vesicle or Yelk-sac. — The splanchnopleure, lined by hypoblast, forms the yelk-sac in Eeptiles, Birds, and Mammals; but in Amphibia and Fishes, since there is neither amnion nor allantois, the wall of the yelk-sac consists of all three layers of the blastoderm, enclosed, of course, by the original vitelline membrane. FIG. 417.— Diagrams, showing three successive stages of development. Transverse vertical sec- tions. The yelk-sac, ys. is seen progressively diminishing in size. In the embryo itself the medul- lary canal and notochord are seen in section, a', in middle figure, the alimentary canal, becoming pinched off, as it were: from the yelk-sac; a', in right hand figure, alimentary canal completely closed ; a, in last two figures, amnion : ac, cavity of amnion filled with amniotic fluid ; pp, space be- tween amnion and chorion, continuous with the pleuro-peritoneal cavity inside the body; vt, vitel- line membrane; ?/s, yelk-sac, or umbilical vesicle. (Foster and Balfour.) The body of the embryo becomes in great measure detached from the yelk-sac or umbilical vesicle, which contains, however, the greater part of the substance of the yelk, and furnishes a source whence nutriment is derived for the embryo. This nutriment is absorbed by the numerous 262 HAND-BOOK OF PHYSIOLOGY. vessels (omphalo-mesenteric) which ramify in the walls of the yelk-sac, forming what in birds is termed the area vasculosa. In Birds, the con- tents of the yelk-sac afford nourishment until the end of incubation, and the omphalo-mesenteric vessels are developed to a corresponding degree; but in Mammalia the office of the umbilical vesicle ceases at a very early period, the quantity of the yelk is small, and the embryo soon becomes independent of it by the connections it forms with the parent. Moreover, in Birds, as the sac is emptied, it is gradually drawn into the abdomen through the umbilical opening, which then closes over it: but in Mam- Fio. 418. FIG. 419. FIG. 418.— Diagram showing vascular area in the chick, a, area pellucida; &, area vasculosa; cy area vitellina. FIG. 419. — Human embryo of fifth week with umbilical vesicle; about natural size (Dalton). The human umbilical vesicle never exceeds the size of a small pea. malia it always remains on the outside; and as it is emptied it contracts (Fig. 419), shrivels up, and together with the part of its duct external to the abdomen, is detached and disappears either before or at the termination of intra-uterine life, the period of its disappearance varying in different orders of Mammalia. When blood-vessels begin to be developed, they ramify largely over the walls of the umbilical vesicle, and are actively concerned in absorbing its contents and conveying them away for the nutrition of the embryo. The Amnion and Allantois. — At an early stage of development of the foetus, and some time before the completion of the changes which have been just described, two important structures, called respectively the amnion and the attantois, begin to be formed. Amnion. — The amnion is produced as follows: — Beyond the head and tail-folds before described (p. 259, Vol. II.), the somatopleure coated by epiblast, is raised into folds, which grow up, arching over the embryo, not only anteriorly and posteriorly but also laterally, and all converg- ing toward one point over its dorsal surface (Fig. 417). The growing up of these folds from all sides and their convergence toward one point very closely resembles the folding inward of the visceral plates already described, and hence, by some, the point at which the amniotic folds meet over the back has been termed the "amniotic umbilicus." GENERATION AND DEVELOPMENT. 263 The folds not only come into contact but coalesce. The inner of the two layers forms the true amnion, while the outer or reflected layer, some- times termed the false amnion, coalesces with the inner surface of the original vitelline membrane to form the chorion. This growth of the amniotic folds must of course be clearly distinguished from the very similar process, already described, by which the walls of the neural canal are formed at a much earlier stage. Amniotic Cavity. — The cavity between the true amnion and the ex- ternal surface of the embryo becomes a closed space, termed the amniotic cavity (ac, Fig. 417). At first, the amnion closely invests the embryo, but it becomes grad- ually distended with fluid (liquor amnii), which, as pregnancy advances, reaches a considerable quantity. This fluid consists of water containing small quantities of albumen and urea. Its chief function during gestation appears to be the mechani- cal one of affording equal support to the embryo on all sides, and of pro- tecting it as far as possible from the effects of blows and other injuries to the abdomen of the mother. The embryo up to the end of pregnancy is thus immersed in fluid, which during parturition serves the important purpose of gradually and evenly dilating the neck of the uterus to allow of the passage of the foetus: when this is accomplished the amniotic sac bursts and the "waters" escape. On referring to the diagrams (Fig. 417), it will be obvious that the cavity outside the amnion (between it and the false amnion) is continu- ous with the pleuro-peritoneal cavity at the umbilicus. This cavity is not entirely obliterated even at birth, and contains a small quantity of fluid ("false waters"), which is discharged during parturition either be- fore, or at the same time, as the amniotic fluid. Allantois. — Into the pleuro-peritoneal space the allantois sprouts out, its formation commencing during the development of the amnion. Growing out from or near the hinder portion of the intestinal canal (c, Fig. 420), with which it communicates, the allantois is at first a solid pear-shaped mass of splanchnopleure; but becoming vesicular by the pro- jection into it of a hollow outgrowth of hypoblast, and very soon simply membranous and vascular, it insinuates itself between the amniotic folds, just described, and comes into close contact and union with the outer of the two folds, which has itself, as before said, become one with the ex- ternal investing membrane of the egg. As it grows, the allantois devel- opes muscular tissue in its external wall and becomes exceedingly vascu- lar; in birds (Fig. 421 ) it envelopes the whole embryo — taking up vessels, so to speak, to the outer investing membrane of the egg, and lining the inner surface of the shell with a vascular membrane, by these means affording an extensive surface in which the blood may be aerated. In the 264 HAND-BOOK OF PHYSIOLOGY. human subject and in other Mammalia, the vessels carried out by the allantois are distributed only to a special part of the outer membrane or chorion, where, by interlacement with the vascular system of the mother, a structure called the placenta is developed. In Mammalia, as the visceral laminae close in the abdominal cavity, the allantois is thereby divided at the umbilicus into two portions; the outer part, extending from the umbilicus to the chorion, soon shriveling; while the inner part, remaining in the abdomen, is in part converted into the urinary bladder; the portion of the inner part not so converted, extending from the bladder to the umbilicus, under the name of the FIG. 420. FIG. 421. Fro. 420.— Diagram of fecundated egg. a, umbilical vesicle; 6, amniotic cavity; c, allantois. (Dalton.) FIG. 421. — Fecundated egg with allantois nearly complete, a, inner layer of amniotic fold; 6, outer layer of ditto; c, point where the amniotic folds come in contact. The allantois is seen pene- trating between the outer and inner layers of the amniotic folds. This figure, which represents only the amniotic folds and the parts within them, should be compared with Figs. 417, 423, in which will be found the structures external to these folds. (Dalton.) uraclms. After birth the umbilical cord, and with it the external and shriveled portion of the allantois, are cast off at the umbilicus, while the urachus remains as an impervious cord stretched from the top of the urinary bladder to the umbilicus, in the middle line of the body, imme- diately beneath the parietal layer of the peritoneum. It is sometimes enumerated among the ligaments of the bladder. It must not be supposed that the phenomena which have been succes- sively described, occur in any regular order one after another. On the contrary, the development of one part is going on side by side with that of another. The Chorion. — It has been already remarked that the allantois is a structure which extends from the body of the foetus to the outer invest- ing membrane of the ovum, that it insinuates itself between the two layers of the amniotic fold, and becomes fused with the outer layer, which has itself become previously fused with the vitelline membrane. By these means the external investing membrane of the ovum, or the chorion, as it is now called, represents three layers, namely, the original vitelline mem- brane, the outer layer of the amniotic fold, and the allantois. Very soon after the entrance of the ovum into the uterus, in the human subject, the outer surface of the chorion is found beset with fine GENERATION AND DEVELOPMENT. 265 processes, the so-called villi of the chorion (Figs. 422, 423), which give it a rough and shaggy appearance. At first only cellular in structure, these little outgrowths subsequently become vascular by the development in them of loops of capillaries (Fig. 423); and the latter at length form the minute extremities of the blood-vessels which are, so to speak, con- FIGS. 422 and 423 (after Todd and Bowman), a, chorion with villi. The villi are shown to be best developed in the part of the chorion to which the allantois is extending; this portion ultimately be- comes the placenta; 6, space between the two layers of the amnion; c, amniotic cavity; d, situation of the intestine, showing its connection with the umbilical vesicle ; e, umbilical vesicle ; /, situation of the heart and vessels; g, allantois. ducted from the foetus to the chorion by the allantois. The function of the villi of the chorion is evidently the absorption of nutrient matter for the foetus; and this is probably supplied to them at first from the fluid matter, secreted by the follicular glands of the uterus, in which they are soaked. Soon, however, the fcetal vessels of the villi come into more intimate relation with the vessels of the uterus. The part at which this relation between the vessels of the foetus and those of the parent ensues, FIG. 424. is not, however, over the whole surface of the chorion : for, although all the villi become vascular, yet they become indistinct or disappear except at one part, where they are greatly developed, and by their branching give rise, with the vessels of the uterus, to the formation of the placenta. 266 HAND-BOOK OF PHYSIOLOGY. To understand the manner in which ihe foetal and maternal blood- vessels come into relation with each other in the placenta, it is necessary briefly to notice the changes which the uterus undergoes after impregna- tion. These changes consist especially of alterations in structure of the superficial part of the mucous membrane which lines the interior of the uterus, and which forms, after a kind of development to be immediately described, the membrana decidua, so called on account of its being dis- charged from the uterus at birth. FOKMATION OF THE PLACENTA. The mucous membrane of the human uterus, which consists of a matrix of connective tissue containing numerous corpuscles (adenoid tissue), and is lined internally by columnar ciliated epithelium, is abun- FIG. 425.— Section of the lining membrane of a human uterus at the period of commencing preg- nancy, showing the arrangement and other peculiarities of the glands, d, d, d, with their orifices, a, a, a, on the internal surface of the organ. Twice the natural size. dantly beset with tubular glands, arranged perpendicularly to the surface (Fig. 425). These follicles are. very small in the unimpregnated uterus; but when examined shortlv after iirmregnation, they are found elongated, FIG. 426.— Two thin segments of human decidua after recent impregnation, viewed on a dark ground; they show the openings on the surface of the membrane. A is magnified six diameters, and » twelve diameters. At 1, the lining of epithelium is seen within the orifices, at 2 it has escaped. enlarged, and much waved and contorted toward their deep and closed extremity, which is implanted at some depth in the tissue of the uterus, and may dilate into two or three closed sacculi (Fig. 425). (JKXK RATION AND DEVELOPMENT. 267 The glands are lined by columnar ciliated epithelium, and they open on the inner surface of the mucous membrane by small round orifices set closely together (a, a, Fig. 420). On the internal surface of the mucous membrane may be seen the cir- cular orifices of the glands, many of which are, in the early period of pregnancy, surrounded by a whitish ring, formed of the epithelium which lines the follicles (Fig. 426). Membrana decidua. — Coincidently with the occurrence of preg- nancy, important changes occur in the structure of the mucous membrane FIG. 427.— Diagrammatic view of a vertical transverse section of the uterus at the seventh or eighth week of pregnancy, c, c, c', cavity of uterus, which becomes the cavity of the decidua, open- ing at c, c, the cornua, into the Fallopian tubes, and at c' into the cavity of the cervix, which is closed by a plug of mucus: d v, decidua vera; d r, decidua reflexa, with the sparser villi imbedded in its substance ; d s, decidua serotina, involving the more developed chorionic villi of the commencing placenta. The foetus is seen lying in the amniotic sac; passing up from the umbilicus is seen the umbilical cord and its vessels/passing to their distribution in the villi of the chorion ; also the pedicle of the yelk-sac, which lies in the cavity between the amnion and chorion. (Allen Thomson.) of the uterus. The epithelium and sub-epithelial connective tissue, to- gether with the tubular glands, increase rapidly, and there is a greatly increased vascularity of the whole mucous membrane, the vessels of the mucous membrane becoming larger and more numerous; while a sub- stance composed chiefly of nucleated cells fills up the interfollicular spaces in which the blood-vessels are contained. The effect of these changes is an increased thickness, softness, and vascularity of the mucous mem- brane, the superficial part of which itself forms the memlrana decidua. 268 HAND-BOOK OF PHYSIOLOGY. The object of this increased development seems to be the production of nutritive materials for the ovum; for the cavity of the uterus shortly becomes filled with secreted fluid, consisting almost entirely of nucleated cells in which the villi of the chorion are imbedded. When the ovum first enters the uterus it becomes imbedded in the structure of the decidua, which is yet quite soft, and in which soon after- ward three portions are distinguishable. These have been named the decidua vera, the decidua reflexa, and the decidua serotina. The first of these, the decidua vera, lines the cavity of the uterus; the second, or decidua reflexa, is a part of the decidua vera which grows up around the ovum, and, wrapping it closely, forms its immediate investment. The third, or decidua serotina, is the part of the decidua vera which becomes especially developed in connection with those villi of the chorion which, instead of disappearing, remain to form the foetal part of the placenta. In connection with these villous processes of the chorion, there are developed depressions or crypts in the decidual mucous membrane, which correspond in shape with the villi they are to lodge; and thus the chori- onic villi become more or less imbedded in the maternal structures. These uterine crypts, it is important to note, are not, as was once supposed, merely the open mouths of the uterine follicles (Turner). As the ovum increases in size, the decidua vera and the decidua reflexa gradually come into contact, and in the third month of pregnancy the cavity between them has quite disappeared. Henceforth it is very diffi- cult, or even impossible, to distinguish the two layers. The Placenta. — During these changes the deeper part of the mucous membrane of the uterus, at and near the region where the placenta is placed, becomes hollowed out by sinuses, or cavernous spaces, which com- municate on the one hand with arteries and on the other with veins of the uterus. Into these sinuses the villi of the chorion protrude, pushing the thin wall of the sinus before them, and so come into intimate relation with the blood contained in them. There is no direct communication between the blood-vessels of the mother and those of the foetus; but the layer or layers of membrane intervening between the blood of the one and of the other offer no obstacle to a free interchange of matters between them. Thus the villi of the chorion containing foetal blood, are bathed or soaked in maternal blood contained in the uterine sinuses. The arrangement may be roughly compared to filling a glove with foetal blood, and dipping its fingers into a vessel containing maternal blood. But in the foetal villi there is a constant stream of blood into and out of the loop of capillary blood-vessels contained in it, as there is also into and out of the maternal sinuses. It would seem from the observations of Goodsir, that, at the villi of the placental tufts, where the foetal and maternal portions of the GENERATION AND DEVELOPMENT. 269 placenta are brought into close relation with each other, the blood in the vessels of the mother is separated from that in the vessels of the foetus by the intervention of two distinct sets of nucleated cells (Fig. 428). One of these (b) belongs to the maternal portion of the placenta, is placed between the membrane of the villus and that of the vascular system of the mother, and is probably designed to separate from the blood of the parent the materials des- tined for the blood of the foetus; the other (/) be- longs to the foetal portion of the placenta, is sit- uated between the membrane of the villus and the loop of vessels contained within, and probably serves for the absorption of the material secreted by the other sets of cells, and for its conveyance FlG 433.— Extremity of a into the blood-vessels of the foetus. Between the two sets of cells with their investing membrane there exists a space (d), into which it is probable that the materials secreted by the one set of cells of the villus are poured in order that they may be ^ t^uu^V cefisnof absorbed by the other set, and thus conveyed into ^^^^i^Soa^)10^ the foetal vessels. Not only, however, is there a passage of materials from the blood of the mother into that of the foetus, but there is a mutual interchange of materials between the blood both of foetus and of parent; the latter sup- plying the former with nutriment, and in turn abstracting from it materials which require to be removed. Alexander Harvey's experiments were very decisive on this point. The view has also received abundant support from Hutchinson's impor- tant observations on the communication of syphilis from the father to the mother, through the instrumentality of the foetus; and still more from Savory's experimental researches, which prove quite clearly that the female parent may be directly inoculated through the foetus. Having opened the abdomen and uterus of a pregnant bitch. Savory injected a solution of strychnia into the abdominal cavity of one foetus, and into the thoracic cavity of another, and then replaced all the parts, every precau- tion being taken to prevent escape of the poison. In less than half an hour the bitch died from tetanic spasms: the foetuses operated on were also found dead, while the others were alive and active. The experi- ments, repeated on other animals with like results, leave no doubt of the rapid and direct transmission of matter from the foetus to the mother, through the blood of the placenta. The placenta, therefore, of the human subject is composed of a foetal part and a maternal part, — the term placenta properly including all that entanglement of foetal villi and maternal sinuses, by means of which the blood of the foetus is enriched and purified after the fashion necessary for the proper growth and development of those parts which it is designed to nourish. 270 HAND-BOOK OF PHYSIOLOGY. The importance of the placenta is at once apparent if we remember that, during the greater portion of intra-uterine life, the maternal blood circulating in its vessels supplies the foetus with both food and oxygen. It thus performs the functions which in later life are discharged by the alimentary canal and lungs. The whole of this structure is not, as might be imagined, thrown off immediately after birth. The greater part, indeed, comes away at that time, as the after-birth; and the separation of this portion takes place by a rending or crushing through of that part at which its cohesion is least strong, namely, where it is most burrowed and undermined by the cav- ernous spaces before referred to. In this way it is cast off with the foetal membrane and the decidua vera and reflexa, together with a part of the decidua serotina. The remaining portion withers, and disappears by being gradually either absorbed, or thrown off in the uterine discharges or the lochia, which occur at this period. A new mucous membrane is of course gradually developed, as the old one, by its peculiar transformation into what is called the decidua, ceases to perform its original functions. The umbilical cord, which in the latter part of foetal life is almost solely composed of the two arteries and the single vein which respectively convey foetal blood to and from the placenta, contains the remnants of other structures which in the early stages of the development of the embryo were, as already related, of great comparative importance. Thus, in early foetal life, it is composed of the following parts: — (1.) Exter- nally, a layer of the amnion, reflected over it from the umbilicus. (2.) The umbilical vesicle with its duct and appertaining omphalo-mesenteric blood-vessels. (3.) The remains of the allantois, and continuous with it the urachus. (4.) The umbilical vessels, which, as just remarked, ultimately form the greater part of the cord. DEVELOPMENT OF ORGANS. It remains now to consider in succession the development of the several organs and systems of organs in the further progress of the embryo. The accompanying figure (Fig. 429) shows the chief organs of the body in a moderately early stage of development. DEVELOPMENT OF THE VERTEBRAL COLUMN AND CRANIUM. The primitive part of the vertebral column in all the Vertebrata is the chorda dorsalis (notochord), which consists entirely of soft cellular cartilage. This cord tapers to a point at the cranial and caudal extremities of the animal. In the progress of its develop- ment, it is found to become enclosed in a membranous sheath, which GENERATION AND DEVELOPMENT. 271 at length acquires a fibrous structure, composed of transverse an- nular fibres. The chorda dorsalis is to be regarded as the azygos axis of the spinal column, and, in particular, of the future bodies of the ver- tebrae, although it never itself passes into the state of hyaline cartilage or bone, but remains enclosed as in a case within the persistent parts of the vertebral column which are developed around it. It is permanent, how- ever, only in a few animals: in the majority only traces of it persist in the adult animal. In many Fish no true vertebrae are developed, and there is every gra- dation from the ampliioxus, in which the notochord persists through life ss FIG. 429.— Embryo chick (4th day), viewed as a transparent object, lying on its left side (magni- fied). C H, cerebral hemispheres ; F -B, fore-brain or vesicle of third ventricle, with P n, pineal gland projecting from its summit; M B, mid-brain; C b, cerebellum; IV V, fourth ventricle; L, lens; chs, choroidal slit; Cen V, auditory vesicle; s m, superior maxillary process; IF, 2F, etc., first, second, third, and fourth visceral folds; V, fifth nerve, sending one branch (ophthalmic) to the eye, and another to the first visceral arch; VII, seventh nerve, passing to the second visceral arch; G Ph, glosso-pharyngeal nerve, passing to the third visceral arch; P g, pneumogastric nerve, passing to- ward the fourth visceral arch; i v, investing mass; e 7i, notochord; its front end cannot be seen in. the living embryo, and it does not end as shown in the figure, but takes a sudden bend downward, and then terminates in a point; H t, heart seen through the walls of the chest; M P, muscle-plates; W, wing, showing commencing differentiation of segments, corresponding to arm, forearm, and hand; H L, hind-limb, as yet a shapeless bud, showing no differentiation. Beneath it is seen the curved tail. (Foster and Balfour.) and there are no vertebral segments, through the lampreys in which there are a few scattered cartilaginous segments, and the sharks, in which many of the vertebrae are partly ossified, to the bony fishes, such as the cod and herring, in which the vertebral column consists of a number of distinct ossified vertebrae, with remnants of the notochord between them. In Amphibia, Eeptiles, Birds, and Mammals, there are distinct vertebrae, which are formed as follows: — Protovertebrae. — The protovertebrcz, which have been already men- tioned (p. 258, Vol. II. }, send processes downward and inward to surround the notochord, and also upward between the medullary canal and the epiblast covering it. In the former situation, the cartilaginous bodies of 272 HAND-BOOK OF PHYSIOLOGY. the vertebrae make their appearance, in the latter their arches, which enclose the neural canal. The vertebrae do not exactly correspond in their position with the pro- tovertebrae: but each permanent vertebra is developed from the contigu- ous halves of two protovertebrae. The original segmentation of the pro- tovertebrae disappears and a fresh subdivision occurs in such a way that a permanent invertebral disc is developed opposite the centre of each pro- tovertebra. Meanwhile the protovertebrae split into a dorsal and ventral portion. The former is termed the musculo-cutaneous plate, and from it are developed all the muscles of the back together with the cutis of the dorsal region (the epidermis being derived from the epiblast). The ven- tral portions of the protovertebrae, as we have already seen, give rise to the vertebrae and heads of the ribs, but the outer part of each also gives rise to a spinal ganglion and nerve-root. The chorda is now enclosed in a case, formed by the bodies of the vertebrae, but it gradually wastes and disappears. Before the disappear- ance of the chorda, the ossification of the bodies and arches of the verte- brae begins at distinct points. The ossification of the body of a vertebra is first observed at the point where the two primitive elements of the vertebrae have united inferiorly. Those vertebrae which do not bear ribs, such as the cervical vertebrae, have generally an additional centre of ossification in the transverse pro- cess, which is to be regarded as an abortive rudiment of a rib. In the foetal bird, these additional ossified portions exist in all the cervical ver- tebrae, and gradually become so much developed in the lower part of the cervical region as to form the upper false ribs of this class of animals. The same parts exist in mammalia and man; those of the last cervical vertebrae are the most developed, and in children may, for a considerable period, be distinguished as a separate part on each side, like the root or head of a rib. The true cranium is a prolongation of the vertebral column, and is developed at a much earlier period than the facial bones. Originally, it is formed of but one mass, a cerebral capsule, the chorda dorsalis being continued into its base, and ending there with a tapering point. At an early period the head is bent downward and forward round the end of the chorda dorsalis in such a way that the middle cerebral vesicle, and not the anterior, comes to occupy the highest position in the head. Pituitary Body.— In connection with this must be mentioned the development of the pituitary body. It is formed by the meeting of two outgrowths, one from the foetal brain, which grows downward, and the other from the epiblast of the buccal cavity, which grows up toward it. The surrounding mesoblast also takes part in its formation. The con- nection of the first process with the brain becomes narrowed, and persists as the infundibulum, while that of the other process with the buccal GENERATION AND DEVELOPMENT. 273 cavity disappears completely at a spot corresponding with the future posi- tion of the body of the sphenoid. The first appearance of a solid support at the hase of the cranium ob- served by Miiller in fish, consists of two elongated bands of cartilage (trabeculae cranii), one on the right and the other on the left side, which are connected with the cartilaginous capsule of the auditory apparatus, and which diverge to enclose the pituitary body, uniting in front to form the septum nasi beneath the anterior end of the cerebral capsule. Hence, in the cranium, as in the spinal column, there are at first developed at the sides of the chorda dorsalis two symmetrical elements, which subse- quently coalesce, and may wholly enclose the chorda. The brain-case consists of three segments: occipital, parietal, and frontal, corresponding in their relative position to the three primitive cer- ebral vesicles; it may also be noted that in front of each segment is devel- oped a sense-organ (auditory, ocular, and olfactory, from behind forward). The basis cranii consists at an early period of an unsegmented cartilagi- nous rod, developed round the notochord, and continued forward beyond its termination into the trabeculce cranii, which bound the pituitary fossa on either side. In this cartilaginous rod three centres of ossification appear: basi- occipital, basi-sphenoid, and pre-sphenoid, one corresponding to each segment. The bones forming the vault of the skull (frontal, parietal, squamous portion of temporal), with the exception of the squamo-occipital, which is pre-formed in cartilage, are ossified in membrane. DEVELOPMENT OF THE FACE AND VISCEKAL ARCHES. It has been said before that at an early period of development of the embryo, there grow up on the sides of the primitive groove the so-called dorsal laminw, which at length coalesce, and complete by their union the spinal canal. The same process essentially takes place in the head, so as to enclose the cranial cavity. Visceral Laminae. — The so-called visceral laminae have been also described as passing forward, and gradually coalescing in front, as the dorsal laminae do behind, and thus enclosing the thoracic and abdominal cavity. An analogous process occurs in the facial and cervical regions, but the enclosing laminae, instead of being simple, as in the former instances, are cleft. In this way the so-called visceral arches and clefts are formed, four on each side (Fig. 430, A). From or in connection with these arches the following parts are de- veloped;— VOL. II.— 18. 274 HAND-BOOK OF PHYSIOLOGY. The first arch (mandibular) contains a cartilaginous rod (Meckel's cartilage), around the distal end of which the lower jaw is developed, while the malleus is ossified from the proximal end. From near the root of this arch the maxillary process grows forward and inward toward the middle line; from it are formed the superior max- illary and malar bones. A pair of cartilaginous rods (ptery go-palatine), parallel to the trabeculae cranii, give origin to the external pterygoid plate of the sphenoid and the palate bones. The cleft between the maxillary process and the mandibular (or first visceral arch) forms the mouth. When the maxillary processes on the two sides fail partially or com- pletely to unite in the middle line, the well-known condition termed cleft palate results. When the integument of the face presents a similar defi- FIG. 430. — A. Magnified view from before of the head and neck of a human embryo of about three weeks (from Ecker). 1, anterior cerebral vesicle or cerebrum; 2, middle ditto; 3, middle or fronto- nasal process : 4, superior maxillary process; 5, eye; 6, inferior maxillary process, or first visceral arch, and below it the first cleft; 7, 8, 9, second, third, and fourth arches and clefts. B. Anterior view of the head of a human foetus of about the fifth week (from Ecker, as before, Fig. IV.). 1, 2, 3, 5, the same parts as in A; 4, the external nasal or lateral frontal pi-ocess; 6, the superior maxillary pro- cess; 7, the lower jaw; x, the tongue; 8, first branchial cleft becoming the meatus auditorius ex- ternus. ciency, we have the deformity known as hare-lip. Though these two deformities frequently co-exist^ they are by no means always necessarily associated. \ The upper part of the face in the middle line is developed from the so-called frontal-nasal process (A, 3, Fig. 430). From the second arch are developed the incus, stapes, and stapedius muscle, the styloid process of the temporal bone, the stylo-hyoid ligament, and the smaller cornu of the hyoid bone. From the third visceral arch, the greater cornu and body of the hyoid bone. In man and other mammalia the fourth visceral arch is indistinct. It occupies, the position where the neck is afterward developed. A distinct connection is traceable between these visceral arches and certain cranial nerves: the trigeminal, the facial, the glosso-pharyngeal, and the pneumogastric. The ophthalmic division of the trigeminal sup- plies the trabecular arch; the superior and inferior maxillary divisions supply the maxillary and mandibular arches respectively. The facial nerve distributes one branch (chorda tympani) to the first visceral arch, and others to the second visceral arch. Thus it divides, enclosing the first visceral cleft. GENERATION AND DEVELOPMENT. 275 Similarly, the glosso-pharyngeal divides to enclose the second visceral cleft, its lingual branch being distributed to the second, and its pharyn- geal branch to the third arch. rr FIG. 431.— For description see Fig. 429. The vagus, too, sends a branch (pharvngeal) along the third arch, and in fishes it gives off paired branches, which divide to enclose several suc- cessive branchial clefts. DEVELOPMENT OF THE EXTREMITIES. The extremities are developed in a uniform manner in all vertebrate animals. They appear in the form of leaf -like elevations from the pari- FIG. 432.— A human embryo of the fourth week; 3}£ lines in length. 1, the chorion; 3, part of the amnion; 4, umbilical vesicle with its long pedicle passing into the abdomen; 7, the heart; 8, the liver; 9, the visceral arch destined to form the lower jaw, beneath which are two other visceral arches separated by the branchial clefts; 10, rudiment of the upper extremity; 11, that of the lower extremi- ty; 12, the umbilical cord; 15, the eye; 16, the ear; 17, cerebral hemispheres; 18, optic lobes, corpora quadrigemina. (.Mliller.) etes of the trunk (see Fig. 432"), at points where more or less of an arch will be produced for them within. The primitive form of the extremity 276 HAND-BOOK OF PHYSIOLOGY. is nearly the same in all Vertebrata, whether it be destined for swim- ming, crawling, walking, or flying. In the human foetus the fingers are at first united, as if webbed for swimming; but this is to be regarded not so much as an approximation to the form of aquatic animals, as the prim- itive form of the hand, the individual parts of which subsequently become more completely isolated. . The fore-limb always appears before the hind-limb and for some time continues in a more advanced state of development. In both limbs alike, the distal segment (hand or foot) is separated by a slight notch from the proximal part of the limb, and this part is subsequently divided again by a second notch (knee or elbow- joint). DEVELOPMENT OF THE VASCULAR SYSTEM. At an early stage in the development of the embryo-chick, the so- called "area vasculosa" begins to make its appearance. A number of branched cells in the mesoblast send out processes which unite so as to form a network of protoplasm with nuclei at the nodal points. A large number of the nuclei acquire a red color; these form the red blood-cells. The protoplasmic processes become hollowed out in the centre so as to form a closed system of branching canals, in the walls of which the rest of the nuclei remain imbedded. In the blood-vessels thus formed, the circulation of the embryonic blood commences. According to Klein's researches, the first blood-vessels in the chick are developed from embryonic cells of the mesoblast, which swell up and become vacuolated, while their nuclei undergo segmentation. These cells send out protoplasmic processes, which unite with corresponding ones from other cells, and become hollowed, give rise to the capillary wall composed of endothelial cells; the blood-corpuscles being budded off from the endothelial wall by a process of gemmation. Heart. — About the same time the heart makes its appearance as a solid mass of cells of the splanchnopleure. At this period the anterior part of the alimentary tube ends blindly beneath the notochord. It is beneath the posterior end of this "fore-gut" (as it may be termed) that the heart begins to be developed. A cavity is hollowed out longitudinally in the mass of cells; the central cells float freely in the fluid, which soon begins to circulate by means of the rhyth- mic pulsations of the embryonic heart. These pulsations take place even before the appearance of a cavity, and immediately after the first "laying down" of the cells from which the heart is formed, and long before muscular fibres or ganglia have been formed in the cardiac walls. At first they seldom exceed from fifteen to eighteen in the minute. The fluid within the cavity of the heart shortly assumes the characters of blood. At the same time the cavity itself GENERATION AND DEVELOPMENT. 277 forms a communication with the great vessels in contact with it, and the cells of which its walls are composed are transformed into fibrous and muscular tissues, and into epithelium. In the developing chick it can he observed with the naked eye as a minute red pulsating point before the end of the second day of incubation. Blood-vessels. — Blood-vessels appear to be developed in two ways, according to the size of the vessels. In the formation of large blood- vessels, masses of embryonic cells similar to those from which the heart FIG. 433.— Capillary blood-vessels of the tail of a young larval frog, a, capillaries permeable to blood; b, fat-granules attached to the walls of the vessels, and concealing the nuclei; c, hollow pro- longation of a capillary, ending in a point; d, a branching cell with nucleus and fat-granules; it com- municates by three branches with prolongation of capillaries already formed; e, e, blood corpuscles still containing granules of fat. x 350 times. (Kolliker.) and other structures of the embryo are developed, arrange themselves in the position, form, and thickness of the developing vessel. Shortly after- ward the cells in the interior of a column of this kind seem to be devel- oped into blood-corpuscles, while the external layer of cells is converted into the walls of the vessel. Capillaries. — In the development of capillaries another plan is pur- sued. This has been well illustrated by Kolliker, as observed in the tails of tadpoles. The first lateral vessels of the tail have the form of simple 278 HAND-BOOK OF PHYSIOLOGY. arches, passing between the main artery and vein, and are produced by the junction of prolongations, sent from both the artery and vein, with certain elongated or star-shaped cells, in the substance of the tail. When these arches are formed and are permeable to blood, new prolongations pass from them, join other radiated cells, and thus form secondary arches FIG. 434. FIG. 434. — Development of capillaries in the regenerating tail of a tadpole cords of protoplasm. (Arnold.) FIG. 435.— The same region after the lapse of 24 hours, have become channeled out into capillaries. (Arnold.) FIG. 435. a, 6, c, d, sprouts and The "sprouts and cords of protoplasm" (Fig. 434). In this manner, the capillary network extends in proportion as the tail increases in length and breadth, and it, at the same time, be- comes more dense by the formation, according to the same plan, of fresh vessels within its meshes. The prolongations by which the vessels com- municate with the star-shaped cells, consist at first of narrow pointed FIG. 436— Capillaries from the vitreous humor of a foetal calf. Two vessels are seen connected by a cord of protoplasm, and clothed with an adventitia, containing numerous nuclei, a, insertion of this "cord" into the primary walls of the vessels. (Frey.) projections from the side of the vessels, which gradually elongate until they come in contact with the radiated processes of the cells. The thick- ness of such a prolongation often does not exceed that of a fibril of fibrous GENERATION AND DEVELOPMENT. 279 tissue, and at first it is perfectly solid; but, by degrees, especially after its junction with a cell, or with another prolongation, or with a vessel already permeable to blood, it enlarges, and a cavity then forms in its interior (see Figs. 434, 435). This tissue is well calculated to illustrate the various steps in the development of blood-vessels from elongating and branching cells. In many cases a whole network of capillaries is developed from a net- work of branched, embryonic connective-tissue corpuscles bv the joining of thair processes, the multiplication of their nuclei, and the vacuolation FIG. 437.— Foetal heart in successive stages of development. 1, venous extremity; 2, arterial ex- tremity; 3, 3, pulmonary branches; 4, ductus arteriosus. (Dalton.) of the cell-substance. The vacuoles gradually coalesce till all the parti- tions are broken down and the originally solid protoplasmic cell-substance is, so to speak, tunneled out into a number of tubes. Capillaries may also be developed from cells which are originally spheroidal, vacuoles form in the interior of the cells, gradually becoming united by fine protoplasmic processes: by the extension of the vacuoles into them, capillary tubes are gradually formed. Morphology. Heart. — When it first appears, the heart is approximate- ly tubular in form. It receives at its two posterior angles the two omphalo- mesenteric veins, and gives off anteriorly the primitive aorta (Fig. 437). It soon, however, becomes curved somewhat in the shape of a horse- shoe, with the convexity toward the right, the venous end being at the same time drawn up toward the head, so that it finally lies behind and somewhat to the right of the arterial. It also becomes partly divided by constrictions into three cavities. Of these three cavities which are developed in all Vertebrata, that at the venous end is the simple auricle, that at the arterial end the bulbus arteriosus, and the middle one is the simple ventricle. These three parts of the heart contract in succession. The auricle and the bulbus arteriosus at this period lie at the extremities of the horseshoe. 280 HAND-BOOK OF PHYSIOLOGY. The bulging out of the middle portion inferiorly gives the first indication of the future form of the ventricle (Fig. 438). The great curvature of the horseshoe by the same means becomes much more developed than the smaller curvature between the auricle and bulbus; and the two extremi- ties, the auricle and bulb, approach each other superiorly, so as to produce a greater resemblance to the later form of the heart, whilst the ventricle becomes more and more developed inferiorly. The heart of Fishes retains these three cavities, no further division by internal septa into right and left chambers taking place. In Amphibia, also, the heart throughout life consists of the three muscular divisions which are so early formed in the embryo; but the auricle is divided internally by a septum into a pulmo- nary and systemic auricle. In Eeptiles, not merely the auricle is thus divided into two cavities, but a similar septum is more or less developed FIG. 438.— Heart of the chick at the 45th, 65th, and 85th hours of incubation. 1, the venous trunks; 2, the auricle; 3, the ventricle; 4, the bulbus arteriosus. (Allen Thomson.) in the ventricle. In Birds and Mammals, both auricle and ventricle undergo complete division by septa; whilst in these animals as well as in reptiles, the bulbus aortas is not permanent, but becomes lost in the ven- tricles. The septum dividing the ventricle commences at the apex and extends upward. The subdivision of the auricles is very early fore- shadowed by the outgrowth of the two auricular appendages, which occurs before any septum is formed externally. The septum of the auricles is developed from a semilunar fold, which extends from above downward. In man, the septum between the ventricles, according to Meckel, begins .to be formed about the fourth week, and at the end of eight weeks is complete. The septum of the auricles, in man and all animals which possess it, remains imperfect throughout foetal life. When the partition of the auricles is first commencing, the two venae cavse have different relations to the two cavities. The superior cava enters, as in the adult, into the right auricle; but the inferior cava is so placed that it appears to enter the left auricle, and the posterior part of the septum of the auri- cles is formed by the Eustachian valve, which extends from the point of entrance of the inferior cava. Subsequently, however, the septum, grow- ing from the anterior wall close to the upper end of the ventricular sep- tum, becomes directed more and more to the left of the vena cava inferior. During the entire period of foetal life, there remains an opening in the septum, which the valve of the foramen ovale, developed in the third month, imperfectly closes. GENERATION AND DEVELOPMENT. 281 Bulbus Arteriosus. — The lulbus arteriosus which is originally a single tube, becomes gradually divided into two by the growth of an in- ternal septum,, which springs from the posterior wall, and extends forward toward the front wall and downward toward the ventricles. This parti- tion takes a somewhat spiral direction, so that the two tubes (aorta and pulmonary artery) which result from its completion, do not run side by side, but are twisted round each other. As the septum grows down toward the ventricles, it meets and coalesces with the upwardly growing ventricular septum, and thus from the right and left ventricles, which are now completely separate, arise respectively the pulmonary artery and aorta, which are also quite distinct. The au- riculo- ventricular and semilunar valves are formed by the growth of folds of the endocardium. At its first appearance the heart is placed just beneath the head of the foetus, and is very large relatively to the whole body: but with the growth of the neck it becomes further and further removed from the head, and lodged in the cavity of the thorax. Up to a certain period the auricular is larger than the ventricular division of the heart; but this relation is gradually reversed as develop- ment proceeds. Moreover, all through foetal life, the walls of the right ventricle are of very much the same thickness as those of the left, which may probably be explained by the fact that in the foetus the right ventri- cle has to propel the blood from the pulmonary artery into the aorta, and thence into the placenta, while in the adult it only drives the blood through the lungs. Arteries. — The primitive aorta arises from the bulbus arteriosus and divides into two branches which arch backward, one on each side of the foregut, and unite again behind it, and in front of the notochord, into a single vessel. This gives off the two omphalo-mesenteric arteries, which distribute branches all over the yolk-sac; this area vasculosa in the chick attaining a large development, and being limited all round by a vessel known as the sinus terminalis. The blood is collected by the venous channels, and returned through the omphalo-mesenteric veins to the heart. Behind this pair of primitive aortic arches, four more pairs make their appearance successively, so that there are five pairs in all, each one run- ning along one of the visceral arches. These five are never all to be seen at once in the embryo of higher animals, for the two anterior pairs gradually disappear, while the pos- terior ones are making their appearance, so that at length only three remain. In Fishes, however, they all persist throughout life as the branchial 282 HAND-BOOK OF PHYSIOLOGY. arteries supplying the gills, while in Amphibia three pairs persist through- out life. In Reptiles, Birds, and Mammals, further transformations occur. In Reptiles the fourth pair remains throughout life as the permanent right and left aorta; in Birds the right one remains as the permanent aorta, curving over the right bronchus instead of the left as in Mammals. In Mammals the left fourth aortic arch develops into the perma- nent aorta, the right one remaining as the subclavian artery of that side. Thus the subclavian artery on the right side corresponds to the aortic arch Cl -pn FIG. 439.— Diagram of the aortic arches in a mammal, showing transformations which give rise to the permanent arterial vessels. A, primitive arterial stem or aortic bulb, now divided into A, the ascending part of the aortic arch, and p, the pulmonary; a a', right and left aortic roots; A', de- scending aorta; 1, 2, 3, 4, 5, the five primitive aortic or branchial arches; /, //, ///, IV, the four branchial clefts which, for the sake of clearness, have been omitted on the right side. The perma- nent systemic vessels are deeply, the pulmonary arteries, lightly shaded ; the parts of the primitive arches which are transitory are simply outlined; c, placed between the permanent common carotid arteries; c e, external carotid arteries; c i, internal carotid arteries; s, right subclavian, rising from the right aortic root beyond the fifth arch; v, right vertebral from the same, opposite the fourth arch; v' s', left vertebral and subclavian arteries rising together from the left, or permanent aortic root, opposite the fourth arch; p, pulmonary arteries rising together from the left fifth arch; d, outer or back part of left fifth arch, forming ductus arteriosus; p n, p n, right and left pneumogas- tric nerves, descending in front of aortic arches, with their recurrent branches represented diagram- matically as passing behind, to illustrate the relations of these nerves respectively to the right sub- clavian artery (4), and the arch of the aorta and ductus arteriosus (d). (Allen Thomson, after Rathke.) on the left, and this homology is further confirmed by the fact that the recurrent laryngeal nerve hooks under the subclavian on the right side, and the aortic arch on the left. The third aortic arch remains as the external carotid artery, while the fifth disappears on the right side, but on the left forms the pulmonary ar- tery. The distal end of this arch originally opens into the descending aorta, and this communication (which is permanent throughout life in many rep- tiles on both sides of the body) remains throughout foetal life under the name of ductus arteriosus: the branches of the pulmonary artery to the GENERATION AND DEVELOPMENT. 283 right and left lung are very small, and most of the blood which is forced into the pulmonary artery passes through the wide ductus arteriosus into the descending aorta. All these points will become clear on reference to the preceding diagram (Fig. 430). As the umbilical vesicle dwindles in size, the portion of the omphalo- mesenteric arteries outside the body gradually disappears, the part inside the body remaining as the mesenteric arteries (Figs. 440, 441). Meanwhile with the growth of the allantois two new arteries (umbilical) appear, and rapidly increase in size till they are the largest branches of FIG. 440.— Diagram of young embryo and its vessels, showing course of circulation in the umbili- cal vesicle; and also that of the allantois (near the caudal extremity), which is iust commencing. (Dalton.) FIG. 441.— Diagram of embryo and its vessels at a later stage, showing the second circulation. The pharynx, oesophagus, and intestinal canal have become further developed, and the mesenteric arteries have enlarged, while the umbilical vesicle and its vascular branches are very much reduced in size. The large umbilical arteries are seen passing out in the placenta. (Dalton.) the aorta: they are given off from the internal iliac arteries, and for a long time are considerably larger than the external iliacs which supply the com- paratively small hind-limbs. Veins. — The chief veins in the early embryo may be divided into two groups, visceral and parietal: the former includes the omphalo-mesenteric and umbilical, the latter the jugular and cardinal veins. The former may be first considered. The earliest veins to appear in the foetus are the omphalo-mesenteric, which return the blood from the yolk-sac to the developing auricle. As soon as the placenta with its umbilical veins is developed, these unite with the omphalo-mesenteric, and thus the blood which reaches the auricle comes partly from the yolk-sac and partly from the placenta. The right omphalo-mesenteric and the right umbilical vein soon disappear, and the united left omphalo-mesenteric and umbilical veins pass through the developing liver on the way to the auricle. Two sets of vessels make their appearance 'in connection with the liver (venae hepaticae advehentes, 284 HAND-BOOK OF PHYSIOLOGY. and revehentes), both opening into the united omphalo-mesenteric and umbilical veins, in such a way that a portion of the venous blood travers- ing the latter is diverted into the developing liver, and, having passed through its capillaries, returns to the umbilical vein through the venae hepaticae revehentes at a point nearer the heart (see Fig. 442). The por- tion of vein between the afferent and efferent veins of the liver becomes the ductus venosus. The venae hepaticae advehentes become the right and left branches of the portal vein, the venae hepaticae revehentes become the hepatic veins, which open just at the junction of the ductus venosus with another large vein (vena cava inferior), which is now being developed. The mesenteric portion of the omphalo-mesenteric vein returning blood from the developing intestines remains as the mesenteric vein, which, by its union with the splenic vein, forms the portal. FIG. 442.— Diagrams illustrating the development of veins about the liver. B, d c, ducts \ f Cuvier, right and left; c a, right and left cardinal veins; o, left omphalo-mesenteric vein; o', rigijt omphalo-mesenteric vein, almost shriveled up; u, u', umbilical veins, of which u', the right one, has almost disappeared. Between the venae cardinales is seen the outline of the rudimentary liver, with its venae hepaticae advehentes, and revehentes; D, ductus venosus; Z', hepatic veins; c i, vena cava inferior; P, portal vein; P' P', venae advehentes; m, mesenteric veins. (Kolliker.) Thus the foetal liver is supplied with venous blood from two sources, through the umbilical and portal vein respectively. At birth the cir- culation through the umbilical vein of course completely ceases and the vessel begins at once to dwindle, so that now the only venous supply of the liver is through the portal vein. The earliest appearance of the parietal system of veins is the formation of two short transverse veins (ducts of Cuvier) opening into the auricle on either side, which result from the union of a jugular vein, collecting blood from the head and neck, and a cardinal vein which returns the blood from the Wolffian bodies, the vertebral column, and the parietes of the trunk. This arrangement persists throughout life in Fishes, but in Mammals the fol- lowing transformations occur. As the kidneys are developing a new vein appears (vena cava inferior), formed by the junction of their efferent veins. It receives branches from the legs (iliac) and increases rapidly in size as they grow: further up it receives the hepatic veins. The heart gradually descends into the thorax, GENERATION AND DEVELOPMENT. 285 causing the ducts of Cuvier to become oblique instead of transverse. As the fore-limbs develop, the subclavian veins are formed. A transverse communicating trunk now unites the two ducts of Cuvier, and gradually increases, while the left duct of Cuvier becomes almost entirely obliterated (all its blood passing by the communicating trunk to the right side) (Fig. 443, c, D). The right duct of Cuvier remains as the right innominate vein, while the communicating branch forms the left innominate. The remnant of the left duct of Cuvier generally re- sv FIG. 443.— Diagrams illustrating the development of the great veins, d c, ducts of Cuvier; j, jugular veins ; /i, hepatic veins; c, cardinal veins; s, subclavian vein; j i, internal jugular vein; j e, external jugular vein; a z, azygos vein; ct, inferior vena cava; r, renal veins; i I, iliac veins; h ij, hypogastric veins. (Gegenbaur.) mains as a fibrous band, running obliquely down to the coronary vein, which is really the proximal part of the left duct of Cuvier. In front of the root of the left lung, another relic may be found in the form of the so-called vestigial fold of Marshall, which is a fold of pericardium running in the same direction. In many of the lower mammals, such as the rat, the left ductus Cuvieri remains as a left superior cava. Meanwhile, a transverse branch carries across most of the blood of the left cardinal vein into the right; and by this union the great azygos vein is formed. The upper portions of the left cardinal vein remain as the left superior intercostal and vena azygos minor (Fig. 443, D). 286 HAND-BOOK OF PHYSIOLOGY. CIRCULATION OF BLOOD IK THE F(ETUS. The circulation of blood in the foetus differs considerably from that of the adult. It will be well, perhaps, to begin its description by tracing the course of the blood, which, after being carried out to the placenta by the two umbilical arteries, has returned, cleansed and replenished, to the foetus by the umbilical vein. It is at first conveyed to the under surface of the liver, and there the stream is divided, — a part of the blood passing straight on to the inferior vena cava, through a venous canal called the ductus venosus, while the remainder passes into the portal vein, and reaches the inferior vena cava only after circulating through the liver. Whether, however, by the direct ronte through the ductus venosus or by the roundabout way through the liver, — all the blood which is returned from the placenta by the umbilical vein reaches the inferior vena cava at last, and is carried by it to the right auricle of the heart, into which cavity is also pouring the blood that has circulated in the head and neck and arms, and has been brought to the auricle by the superior vena cava. It might be naturally expected that the two streams of blood would be mingled in the right auricle, but such is not the case, or only to a slight extent. The blood from the superior vena cava — the less pure fluid of the two — passes almost exclusively into the right ventricle, thrpugh the auriculo- ventricular opening, just as it does in the adult; while the blood of the inferior vena cava is directed by a fold of the lining membrane of the heart, called the Eustacliian valve , through the foramen ovale into the left auricle, whence it passes into the left ventricle, and out of this into the aorta, and thence to all the body. The blood of the superior vena cava, which, as before said, passes into the right ventricle, is sent out thence in small amount through the pul- monary artery to the lungs, and thence to the left auricle, as in the adult. The greater part, however, by far, does not go to the lungs, but instead, passes through a canal, the ductus arteriosus, leading from the pulmo- nary artery into the aorta just below the origin of the three great vessels which supply the upper parts of the body; and there meeting that part of the blood of the inferior vena cava which has not gone into these large vessels, it is distributed with it to the trunk and lower parts, — a portion passing out by way of the two umbilical arteries to the placenta. From the placenta it is returned by the umbilical vein to the under surface of the liver, from which the description started. Changes after Birth.— After birth the foramen ovale closes, and so do the ductus arteriosus and ductus venosus, as well as the umbilical vessels; so that the two streams of blood which arrive at the right auricle by the superior and inferior vena cava respectively, thenceforth GENERATION AND DEVELOPMENT. 287 mingle in this cavity of the heart, and passing into the right ventricle, go by way of the pulmonary artery to the lungs, and through these, after purification, to the left auricle and ventricle, to be distributed over the body. (See Chapter on Circulation.) FIG. 444.— Diagram of the Foetal Circulation. DEVELOPMENT OF THE NERVOUS SYSTEM. Nerves. — All the spinal nerves are derived from the mesoblast; also all the cranial nerves, except the optic and olfactory, which are out- growths of the anterior cerebral vesicles. From the same middle layer of the embryo are also derived the ganglia connected with these nerves, and the whole sympathetic system of nerves and ganglia. Spinal Cord. — Both the brain and spinal cord have a different origin 288 HAND-BOOK OF PHYSIOLOGY. from that of the nerves which arise from them. These nerve-centres are developed entirely from the epiblast (possibly, however, a portion of the spinal cord originates in the mesoblast); while the nerves, as we have seen, are formed from mesoblast. The spinal cord is developed out of the primitive medullary tube which results from the folding in of the dorsal laminae (m, Fig. 411). Soon after it has closed in, this tube is found to be somewhat oval in section, with a central canal, which, in sections, presents the appearance of an elongated slit, slightly expanded at each end. The two opposite sides unite (Fig. 445) in the centre of the slit, dividing it into an anterior portion (the permanent central canal of the cord) and a posterior, which makes its way to the free surface, and persists as the posterior fissure of the cord, lodging a very fine process of pia mater. At this period the cord consists almost entirely of grey matter, but the white matter, which is derived probably from the surrounding mesoblast, becomes deposited around it on all sides, growing up especially on the FIG. 445.— Diagram of development of spinal cord; cc, central canal; a/, anterior fissure; pf, pos- terior fissure; s, secondary optic vesicle containing the rudiment of the vitreous humor, x 100. (Kolliker.) FIG. 452.— Transverse vertical section of the eyeball of a human embryo of four weeks. The an- terior half of the section is represented; pr, the remains of the cavity of the primary optic vesicle; p, the inner part of the outer layer forming the retinal pigment; r, the thickened inner part giving rise to the columnar and other structures of the retina; v, the commencing vitreous humor within the secondary optic vesicle ; i/, the ocular cleft through which the loop of the central blood-vessel, a, projects from below; Z, the lens with a central cavity, x 100. (Kolliker.) the corneal tissue proper is derived from the mesoblast which intervenes between the epiblast and the primitive lens which was originally continu- ous with it. The sclerotic coat is developed round the eyeball from the general mesoblast in which it is imbedded. The iris is formed rather late, as a circular septum projecting inward, from the fore part of the choroid, between the lens and the cornea. In the eye of the foetus of Mammalia, the pupil is closed by a delicate mem- brane, the membrana pupittaris, which forms the front portion of a. highly vascular membrane that, in the foetus, surrounds the lens, and is named the membrana capsulo-pupillaris (Fig. 453). It is supplied with blood by a branch of the arteria centralis retincv, which, passing forward to the back of the lens, there subdivides. The membrana capsulo-pupil- laris withers and disappears in the human subject a short time before birth. The eyelids of the human subject and mammiferous animals, like those of birds, are first developed in the form of a ring. They then extend over the globe of the eye until they meet and become firmly agglutinated 294 HAND-BOOK OF PHYSIOLOGY. to each other. But before birth, or in the Carnivora after birth, they again separate. Ear.— Very early in the development of the embryo a depression or ingrowth of the epiblast occurs on each side of the head which deepens and soon becomes a closed follicle. This primary otic vesicle, which closely corresponds in its formation to the lens follicle in the eye, sinks down to some distance from the free surface; from it are developed the epithe- lial lining of the membranous labyrinth of the internal ear, consisting of the vestibule and its semicircular canals and the scala media of the cochlea. The surrounding mesoblast gives rise to the various fibrous bony and cartilaginous parts which complete and enclose this membran- ous labyrinth, the bony semicircular canals, the walls of the cochlea with FIG. 453.— Blood-vessels of the capsulo-pupillary membrane of anew-born kitten, magnified. The drawing is taken from a preparation injected by Tiersch, and shows in the central part the converg- ence of the network of vessels in the pupillary membrane. (Kolliker.) its scala vestibuli and scala tympani. In the mesoblast, between the primary otic vesicle and the brain, the auditory nerve is gradually differ- entiated and forms its central and peripheral attachments to the brain and internal ear respectively. According to some authorities, however, it is said to take its origin from and grow out of the hind brain. The Eustachian tube, the cavity of the tympanum, and the external auditory passage, are remains of the first branchial cleft. The membrana tympani divides the cavity of this cleft into an internal space, the tym- panum and the external meatus. The mucous membrane of the mouth, which is prolonged in the form of a diverticulum through the Eustachian tube into the tympanum, and the external cutaneous system, come into relation with each other at this point; the two membranes being sepa- rated only by the proper membrane of the tympanum. The pinna or external ear is developed from a process of integument in the neighborhood of the first and second visceral arches, and probably corresponds to the gill-cover (operculum) in fishes. GENERATION AND DEVELOPMENT. 295 Nose. — The nose originates like the eye and ear in a depression of the superficial epiblast at each side of the fronto-nasal process (primary olfactory groove), which is at first completely separated from the cavity of the mouth, and gradually extends backward and downward till it opens into the mouth. The outer angles of the fronto-nasal process, uniting with the maxil- lary process on each side, convert what was at first a groove into a closed canal. DEVELOPMENT OF THE ALIMENTARY CANAL. The alimentary canal in the earliest stages of its development consists of three distinct parts — the fore and hind gut ending blindly at each end of the body, and a middle segment which communicates freely on its FIG. 454.— Outlines of the form and position of the alimentary canal in successive stages of its development. A, alimentary canal, etc., in an embryo of f9ur weeks; B, at six weeks; C, at eight weeks; D, at ten weeks; Z, the primitive lungs connected with the pharynx; «, the stomach; d, the duodenum; i, the small intestine; i', the large; c, the caecum and vermiform appendage; r, the rec- tum; cl, in A, the cloaca; a, in B, the anus distinct from s i, the sinus uro-genitalis; v, the yelk-sac; vi, the vitello-intestinal duct; it, the urinary bladder and urachus leading to the allantois; of power, there can be no doubt, of course, that the changes in any part which is the seat of vital action must be considerable, not only from what may be called "wear and tear," but, also, on account of the great instability of all organized struc- tures. Between such waste as this, however, and that of an inorganic machine there is only the difference in' degree, arising necessarily from diversity of structure, of elemental arrangement, and so forth. But the repair in the two cases is different. The capability of reconstruction in a living body is an inherent quality like that which causes growth in a special shape or to a certain degree. At present we know nothing really of its nature, and we are therefore compelled to express the fact of its existence by such terms as "inherent power," "individual endowment," and the like, and wait for more facts which may ultimately explain it. This special quality is not indeed one of living things alone. The repair of a crystal in definite shape is equally an "individual endowment," or "inherent peculiarity," of the nature of which we are equally ignorant. In the case, however, of an inorganic machine there is nothing of the sort, not even as in a crystal. Faults of structure must be repaired by some means entirely from without. And as our notion of a living being, say a horse, would be entirely altered if flaws in his composition were repaired by external means only; so, in like manner, would our idea of the nature of a steam-engine be completely changed had it the power of ab- sorbing and using part of its fuel as matter wherewith to repair any ordi- nary injury it might sustain. It is this ignorance of the nature of such an act as reconstruction which causes it to be said, with apparent reason, that so long as the term "vital force" is used, so long do we beg the question at issue— What is the nature of life? A little consideration, however, will show that the jus- tice of this criticism depends on the manner in which the word ""vital" is used. If by it we intend to express an idea of something which arises in a totally different manner from other forces — something which, we know not how, depends on a special innate quality of living beings, and owns no THE RELATION OF LIFE TO OTHER FORCES. 321 dependence on ordinary physical force, but is simply stimulated by it, and has no correlation with it — then, indeed, it would be just to say that the whole matter is merely shelved if we retain the term "vital force." But if a distinct correlation be recognized between ordinary physical force and that which in various shapes is manifested by living beings; if it be granted that every act — say, for example, of a brain or muscle — is the exactly correlated expression of a certain quantity of force latent in the food with which an animal is nourished; and that the force produced either in the shape of thought or movement is but the transformed expres- sion of external force, and can no more originate in a living organ with- out supplies of force from without, than can that organ itself be formed or nourished without supplies of matter; — if these facts be recognized, then the term used in speaking of the powers exercised by a living being is not of very much consequence. We have as much right to use the term "vital" as the words galvanic and chemical. All alike are but the expressions of our ignorance concerning the nature of that power of which all that we call "forces" are various manifestations. The differ- ence is in the apparatus by which the force is transformed. It is with this meaning that, for the present, the term "vital force" may still be retained when we wish shortly to name that combination of energies which we call life. For, exult as we may at the discovery of the transformation of physical force into vital action, we must acknowledge not only that, with the exception of some slight details, we are utterly ignorant of the process by which the transformation is effected; but, as well, that the result is in many ways altogether different from that of any other force with which we are acquainted. It is impossible to define in what respects, exactly, vital force differs from any other. For while some of its manifestations are identical with ordinary physical force, others have no parallel whatsoever. And it is this mixed nature which has hitherto baffled all attempts to define life, and, like a Will-o'-the-wisp, has led us floundering on through one defini- tion after another only to escape our grasp and show our impotence to seize it. In examining, therefore, the distinctions between the products of transformations by a living and by an inorganic machine, we have first to recognize the fact, that while in some cases the difference is so faint as to- be nearly or quite imperceptible, in others there seems not a trace of' resemblance to be discovered. In discussing the nature of life's manifestations — birth, growth, devel- opment, and decline — the differences which exist between them and other processes more or less resembling them, but not dependent on life, have: been already briefly considered and need not be here repeated. It may- be well, however, to sum up very shortly the particulars in which life as; a manifestation of force differs from all others. VOL. II.— 21. 322 HAND-BOOK OF PHYSIOLOGY. The mere acquirement of a certain shape by growth is not a pecu- liarity of life. But the power of developing into so composite a mass even as a vegetable cell is a property possessed by an organized being only. In the increase of inorganic matter there is no development. The minutest crystal of any given salt has exactly the same shape and intimate struc- ture as the largest. With the growth there is no development. There is increase of size with retention of the original shape, but nothing more. And if we consider the matter a little we shall see a reason for this. In all force-transformers, whether living or inorganic, with but few ex-, ceptions — and these are, probably, apparent only — something more is required than homogeneity of structure. There seems to be a need for some mutual dependence of one part on another, some distinction of qualities, which cannot happen when all portions are exactly alike. And here lies the resemblance between a living being and an artificial machine. Both are developments, and depend for their power of transforming force on that mutual relation of the several parts of their structure which we call organization. But here, also, lies a great difference. The develop- ment of a living being is due to an inherent tendency to assume a certain form; about which tendency we know absolutely nothing. We recognize the fact, and that is all. The development of an inorganic machine — say an electrical apparatus — is not due to any inherent or individual property. It is the result of a power entirely from without; and we know exactly how to construct it. Here, then, again, we recognize the compound nature of a living being. In structure it is altogether different from a crystal — in inherent capacity of growth into definite shape it resembles it. Again, in the fact of its organization it resembles. a machine made by man: in capacity of growth it entirely differs from it. In regard, therefore, to structure, growth, and development, it has combined in itself qualities which in all other things are more or less completely separated. That modification of ordinary growth and development called gener- ation, which consists in the natural production and separation of a portion of organized structure, with power itself to transform force so as there- with to build up an organism like the being from which it was thrown off, is another distinctive peculiarity of a living being. We know of nothing like it in the inorganic world. And the distinction is the greater because it is the fulfilment of a purpose, toward which life is evidently, from its very beginning, constantly tending. It is as natural a destiny to separate parts which shall form independent beings as it is to develop a limb. Hence it is another instance of that carrying out of certain pro- jects, from the very beginning in view, which is so characteristic of things living and of no other. It is especially in the discharge of what are called the animal func- tions that we see vital force most strangely manifested. It is true that THE RELATION OF LIFE TO OTHER FORCES. 323 one of the actions included in this term — namely, mechanical movement — although one of the most striking, is by no means a distinctive one. For it must be remembered that one of the commonest transformations of physical force with which we are acquainted is that of heat into mechani- cal motion, and that this may be effected by an apparatus having itself nothing whatever to do with life. The peculiarity of the manifestation in an animal or vegetable is that of the organ by which it is effected, and the manner in which the transformation takes place, not in the ultimate result. The mere fact of an animal's possessing capability of movement is not more wonderful than the possession of a similar property by a steam engine. In both cases alike, the motion is the correlative expression of force latent in the food and fuel respectively; but in one case we can trace the transformation in the arrangement of parts, in the other we cannot. The consideration of the products of the transformation of force effected by the nervous system would lead far beyond the limits of the present chapter. But although the relation of mind to matter is so little known that it is impossible to speak with any freedom concerning such correlative expressions of physical force as thought and nerve-products^ still it cannot be doubted that they are as much the results of transfer-' mation of force as the mechanical motion caused by the contraction of a muscle. But here the mystery reaches its climax. We neither know how the change is effected, nor the nature of the product, nor its analo- gies with other forces. It is therefore better, for the present, to confess our ignorance, than, with the knowledge which we have lately gained, to build up rash theories, serving only to cause that confusion which is worse than error. It may be said, with perfect justice, that even if the foregoing conclu- sions be accepted, namely, that all manifestations of force by living beings are -correlative expressions of ordinary physical force, still the argument is based on the assumption of the existence of the apparatus which we call living organized matter, with power not only to use external force for its own use in growth, development, and other vital manifestations, but for that modification of these powers which consists in the separation of a part that shall grow up into the likeness of its parent, and thus con- tinue the race. We are therefore, it may added, as far as ever from any explanation of the origin of life. This is of course quite true. The ob- ject of the present chapter, however, is only to deal with the relations of life, as it now exists, to other forces. The manner of creation of the various kinds of organized matter, and the source of those qualities, belonging to it, which from our ignorance we call inherent, are different questions altogeth To say that of necessity the power to form living organized matter will never be vouchsafed to us, that it is only a mere materialist who 324 HAND-BOOK OF PHYSIOLOGY. would believe in such a possibility, seems almost as absurd as the state- ment that such inquiries lead of necessity to the denial of any higher power than that which in various forms is manifested as "force," on this small portion of the universe. It is almost as absurd, but not quite. For, surely, he who recognizes the doctrine of the mutual convertibility of all forces, vital and physical, who believes in their unity and imperish- ableness, should be the last to doubt the existence of an all-powerful Being, of whose will they are but the various correlative expressions; from whom they all come; to whom they return. APPENDIX A. THE CHEMICAL BASIS OF THE HUMAN BODY. Of the sixty-four known chemical elements no less than seventeen have "been found, in larger or smaller quantities, to form the chemical basis of the animal body. The substances occurring in largest quantities are the non-metallic ele- ments, Oxygen, Carbon, Hydrogen, and Nitrogen — oxygen and carbon making up altogether about 85 per cent, of the whole. The most abun- dant of the metallic elements are Calcium, Sodium, and Potassium. The following table represents the relative proportion of the various elements. — (Marshall. ) Oxygen 72-0 Carbon ....... 13 '5 Hydrogen 9*1 Nitrogen 2 '5 Calcium 1-3 Phosphorus 1'15 Sulphur -1476 Sodium *1 Chlorine -085 Fluorine -08 Potassium -026 Iron -01 Magnesium . • . . . -0012 Silicon -0002 (Traces of copper, lead, and aluminium) . . . 100- Compounds. — The elementary substances above-mentioned seldom occur free or uncombined in the animal body; but are nearly always united among themselves in various numbers, and in variable proportions to form "compounds." Several elements have, however, been detected in small amount free; traces of uncombined Oxygen and Nitrogen have been found in the blood, and of Hydrogen as well as of Oxygen and Nitrogen in the intestinal canal. Organic and Inorganic Compounds. — It was formerly thought that the more complex compounds built up by the animal or vegetable organism were peculiar, and could not be made artificially by chemists from their elements, and under this idea they were formed into a distinct class, termed organic. This idea has been given up, but the name is still in use, with a different signification. The term organic is now applied 326 HAND-BOOK OF PHYSIOLOGY. simply to the compounds of the element Carbon, irrespective of their complexity; chemists having found that these compounds are so numer- ous and important, and that they include all those to which the term organic was in former times exclusively given. Characteristics of Organic Compounds.— The animal organic compounds are characterized as a rule by their complexity, for in the first place many elements enter into their composition, thereby distin- guishing them from bodies such as water (H20), hydrochloric acid (HC1), and ammonia (NH3), which may be taken as types of inorganic com- pounds. And again, because many atoms of the same element occur in each molecule. This latter fact no doubt explains also the reason of the instability of organic compounds. Another great cause of the instability arises from the fact that many such compounds contain the element Nitrogen, which may be called negative or undecided in its affinities, and may be easily separated 'from combination with other elements. « Animal tissues, containing as they do these organic nitrogenous com- pounds, are extremely prone to undergo chemical decomposition, and this is especially the case since they also contain a large quantity of water, a condition most favorable for the breaking up of such substances. It is from this fact that in the consideration of the chemical basis of the body we meet with an extremely large number of decomposition products. In treating of the various substances found in the animal organism it is convenient to adopt the division into — a' Nitroenous. 2. Inorganic. Ornrfnir Organic > Non_Nitrogenous. 1. ORGANIC. (a) Nitrogenous bodies take the chief part in forming the solid tissues of the body, and are found to a considerable extent in the circulating fluids (blood, lymph, chyle), the secretions and excretions. They contain often in addition to Carbon, Hydrogen, Nitrogen, and Oxygen, the ele- ments Sulphur and Phosphorus; but although the composition of most of them is approximately known, no general rational formula can at present be given. Several classes of animal nitrogenous bodies may be distinguished, and it is convenient to consider them under the following heads: — (I- (2. (3. Albuminoids or proteids. Gelatinous substances. Decomposition nitrogenous bodies. (4.) Certain supposed nitrogenous bodies, the exact composition of which has not been made out. APPENDIX. 327 (1.) Albuminoids or Proteids are the most important of the nitroge- nous animal compounds, one or more of them entering as essential parts into the formation of all living tissue. In the lymph, chyle, and blood, they also exist abundantly. Their atomic formula is uncertain. Their composition may be taken as — Carbon . . from 51 -5 to 54 '5 Hydrogen . . " 6-9 " 7 '3 Nitrogen . . " 15 '2 " 17' Oxygen . . " 20-9 " 23 -5 Sulphur . -3 " 2- (Hoppe-Seyler.) Physical Properties. — Proteids are all amorphous and non-crystalliza- ble, so that they possess as a rule no power (or scarcely any) of passing through animal membranes. They are soluble, but undergo alteration in composition in strong acids and alkalies; some are soluble in water, others in neutral saline solutions, some in dilute acids and alkalies, few in alcohol or ether. Their solutions have a left-handed action on polarized light. Chemical Properties. — Certain general reactions are given for proteids. They are a little varied in each particular case: — i. — A solution boiled with strong nitric acid, becomes yellow, and this yellowness gets darker on addition of ammonia (xantho-proteic reaction), ii. — With potassium ferrocyanide and acetic acid, they give a white precipitate, iii. — With a trace of copper sulphate and an excess of potassium or sodium hydrate they give a purple coloration, iv. — With Millon's reagent (mixed nitrate and nitrite of mercury?), they give a white or pinkish precipitate, becoming more pink on boiling. v. — When boiled with sodium sulphate and acetic acid, a white precipitate is thrown down. It is usual to place Proteids into the following sub-classes, thus: — I. II. III. NATIVE ALBUMINS. DEBITED ALBUMINS. GLOBULIN. Egg- Albumin. Acid- Albumin. (a.) Globulin. Serum-Albumin. Alkali- Albumin. (b.) Myosin. Casein. (c. ) Fibrinoplastic Globulin, (d.) Fibrinogen. (e.) Vitellin, etc. IV. — FIBRIN. V.— -PEPTONES. VI.— COAGULATED PKOTEIDS. VII. — LARDACEIN. CLASSES OF PROTEIDS. I. The Native Albumins are soluble in water and in saline solutions coagulable by heating, not precipitated by acetic or normal phosphoric acid. Serum-albumin (p. 85, Vol. I.) is distinguished from egg-albumin 328 HAND-BOOK OF PHYSIOLOGY. in being soluble in ether and in not so easily giving a precipitate with strong hydrochloric acid; the precipitate being easily redissolved in excess of the acid. Serum-albumin is found in the blood, lymph and serous and synovial fluids, and the tissues generally; it appears in the urine in the condition known as albuminuria. Two varieties, metalbumin and paral- lumin have been described as existing in dropsical fluids and ovarian cysts respectively. II. Derived Albumins are made by adding dilute acids or alkalies to solutions of native-albumin. They are insoluble in water or in neutral saline solutions, and are not coagulated by heat. Both the native-albu- mins and the next two classes (iii. and iv.) of proteids generally undergo change into either acid or alkali albumin on the addition of acids or al- kalies, and foods containing either albumins or globulins change first of all into one or other of these compounds, according as they are acted upon by the gastric or pancreatic juices respectively. Acid- albumin is called also syntonin, and is either identical with or akin to it. Casein is very probably natural alkali-albumin, and exists in milk, being kept in solution by the alkaline phosphates; it exists also in the serum and serous fluids in small quantity, and in muscle. It is not coagulable by heat, and so corresponds with the other derived albumins; it is obtainable as a pre- cipitate by neutralizing milk with acid (acetic). Naturally it is precipi- tated in sour milk, on the formation of lactic acid. III. Globulins which comprise the fibrin-forming substances of the blood and the coagulable material in muscle, and also the principal part of the crystalline lens, yelk of egg, etc., are soluble in very dilute saline solutions, but not in distilled water like the native-albumins; on addition of an acid or alkali, they are converted into the corresponding derived- albumin. They are precipitated on heating. The following are the chief varieties of globulins. (a.) Globulin or Crystallin is prepared by rubbing up the crystalline lens with sand, adding water and filtering. On passing a current of car- bonic acid gas through the filtrate, globulin is precipitated. In proper- ties, it resembles fibrino-plastin and fibrinogen, but cannot apparently produce fibrin in fluids containing either. It coagulates at 70° — 75° C. (b.) Myosin can be prepared (1) from dead muscle by removing all fat, tendon, etc., and washing repeatedly in water, until the washing contains no trace of proteids, and then treating with 10 per cent, solution of sodium chloride, which will dissolve a large proportion into a viscid fluid, which filters with difficulty. If the viscid filtrate be dropped little by little into a large quantity of distilled water, a white flocculent pre- cipitate of myosin will occur. (2) Or from living muscle by freezing and rubbing up in a mortar with snow and sodium chloride solution 1 per cent., a fluid is obtained which on filtering is at first liquid, but will finally clot; the clot is myosin. Myosin, on addition of dilute acids, dissolves and forms syntonin or acid-albumin. It is less soluble in dilute saline solutions than (c] and (d). It coagulates at 55°— 60° C. APPENDIX. 329 (c.) Fibriiioplastin or fibrinoplastic globulin or paraglobulin is pre- pared from blood-serum diluted with 10 vols. of water, by passing a cur- rent of carbonic acid gas, and collecting the fine precipitate which is formed, and washing with water containing carbonic acid gas. The current should be strong and not long continued. It may be better pre- pared as a sticky white substance, by saturating serum with crystallized sodium chloride or magnesium sulphate. (See also p. 69, Vol. I.) It coagulates at 68°— 80° C. (d.) Fibrinogen is prepared from hydrocele and other like fluids by diluting and passing a brisk current of carbonic acid gas (COJ through the solution; or by saturation of the nerve fluids with sodium chloride or magnesium sulphate. (See also p. 69, Vol. I.) It coagulates at 55° — 57° C. (e. ) Vitellin can be prepared from yelk of egg, in which it is prob- ably associated with lecithin. IV. Fibrin is a white filamentous body formed in the spontaneous coagulation of certain animal fluids. It is insoluble in water, except at very high temperatures, soluble in dilute acids and alkalies to a slight degree, and in strong neutral saline solutions. Soluble also in strong acids and alkalies. It is prepared by washing blood-clot or by whipping blood with a bundle of twigs. Its formation in the blood has been already fully con- sidered. V. Peptones (or albuminose) are nitrogenous bodies of uncertain composition made in the process of the digestion of other proteids. It is almost certain that there are several distinct forms. The great distinction which exists between peptone and other proteids is their diffusibility and they giving no precipitates with either acids or alkalies, with copper sulphate, ferric chloride, potassium ferrocyanide and acetic acid, or on boiling, and only with picric acid, tannin, mer- curic chloride, silver nitrate, and lead acetate. In addition to this the color which a peptone gives with potassium hydrate and cupric sulphate is reddish instead of violet. Kuhne believes that ordinary albumin splits up under the action of the gastric juice or pancreatic juice into two parts, one called antialbu- mose, and the other h em ialbumose, and further that antialbumose becomes antipeptone and heimalbumose, hemipeptone. The difference between hemipeptone and antipeptone is that the former can be further split up by the action of the pancreatic juice. He believes that antialbumose is closely allied to syntonin, and that the hemialbumose is more like myosin, and if the pepsin be feebly acting, a body which he calls antialbuinate appears, which cannot be converted into peptone by gastric juice, but can by pancreatic juice. Solutions of hydrochloric acid or of sulphuric acid can, under favorable circumstances, partially change albumin into peptone. VI. — Coagulated Proteids. — When a native albumin or a globulin is raised to a certain temperature (varying a little with each substance), 330 HAND-BOOK OF PHYSIOLOGY. about 70° C, it undergoes coagulation and loses most of its original char- acters. It becomes insoluble both in water and in saline solutions, and although soluble in strong acids and alkalies in boiling, partially decom- poses during the process. They are not soluble in dilute acids or alka- lies, but dissolve freely under the action of the gastric or of the pancre- atic secretion, being converted into peptones. VII. Lardacein. — Lardacein or amyloid substance is found in cer- tain organs of the body, chiefly in the liver, as a morbid deposit. It is insoluble in water, and in saline solutions. It is unacted upon by the digestive juices. It is colored red by iodine. It is soluble in acids or in alkalies, thus forming acid or alkali albumin. (2.) Gelatinous principles include: — (1.) Gelatin; (2.) Mucin; (3.) Elastin; (4.) Chondrin; and (5.) Keratin. They are very like the Pro- teid group, but exhibit considerable differences among themselves. (1.) Gelatin is produced by boiling fibrous tissue, or by treating bones with acids, whereby their salts are dissolved, leaving the framework of gelatin, which is soluble in hot water. It is a yellow, amorphous, transparent body, which does not give any of the proteid reactions if pure, insoluble in cold, but soluble in hot water, forming a jelly on cooling. Its solutions are precipitated by tan- nin, by alcohol and by mercuric chloride. (2.) Mucin, contained in mucus. It is a substance of ropy consist- ency. Prepared from ox-gall by precipitation with alcohol, and afterward redissolving in water, and reprecipitating with acetic acid. It may be also prepared from diluting mucus with water, filtering, treating the insoluble portion with weak caustic alkali, and precipitating with acetic acid. It is precipitated by alcohol and mineral acids, but dissolved by excess of the latter^dissolved by alkalies. It gives the proteid reaction with Mil- Ion's reagent, but not with cupric sulphate and potassium hydrate. It is not precipitated by mercuric chloride or by tannic acid. It is a colloid substance. (3.) Elastin is the basis of elastic tissue; it is soluble only in strong alkalies on boiling; strong sulphuric or nitric acid dissolves it in the cold. (4.) Chondrin is contained in the matrix of hyaline cartilage, and may be extracted by boiling with water and precipitating with acetic acid. (5.) Keratin is obtained from hair, nails, and dried skin. It contains sulphur, evidently only loosely combined. % (3.) Decomposition Nitrogenous products. — These are formed by the chemical actions which go on in digestion, secretion, and nutrition. Most of the compounds are amides, Avhich are acids in which amidogen9 NH2, is substituted for liydroxijl, OH. Amides may also be represented as obtained from the ammonium salts by abstraction of water, or as de- rived from one or more molecules of ammonia, JSTH3, by substituting acid radicals for hydrogen. Thus acetamide may be written in any of the following ways: — APPENDIX. 331 CH, CH3 CO NHa CO ONH or H' (C2 H3 0) being the radical of acetic acid. Varieties.— Several of the varieties of amides are represented in the products with which we have to do. (a. ) Monamides which are derived from a monatomic acid — that is to say, an acid which contains the carboxyl group COOH, once, by the sub- stitution of NH2 for OH in this group. In these compounds if only one is the II in NH3 is replaced by an acid radical, a primary monamide of formed; if two, by acid or alcohol radicals, a secondary monamide; if three, by acid or alcohol radicals, a tertiary monamide. Two monamides are also formed from each diatomic acid (i.e., those which contain OH twice, once in the carboxyl group COOH, and once in the alcohol group Cn H2D OH), both by the substitution of NH2 for OH, and therefore having the same composition. They are isomeric and not identical however, the one formed by the substitution of NH2 for the alco- holic OH being acid, while the other formed by the replacement of the basic hydroxyl is neutral. The acid amides are called amic acids, or may form a class by themselves, called alanines. Three amides are obtained from each diatomic and bibasic acid: — (1.) An acid amide or amic acid, derived from the acid ammonium salt by ab- straction of one molecule of water. (2.) A neutral monamide (or imide), derived by abstraction of two molecules of water from the ammonium salts. (3.) A neutral amide or (b) DIAMIDE, derived from the ammonium salt by abstraction of two molecules of water. Thus succinic acid gives: — Succinamic Acid . . . C2 H4 -j Succinimide . . . . C2 H4 j £j£ i NH Succinamide . . . . C2 H4 (CO NH2)2 (a) PEIMAKY MONAMIDES. Glycin, glycocol or glycocin, or amido-acetic acid — O.H.O.n c II O) H' > N or ^ Yr [• 0 occurs in the body in combination, as in H' ) H*> the biliary acids, never free. Glycocholic acid, when treated with weak acids, with alkalies, or with baryta water, splits up into cholic acid and glycin, or amido-acetic acid. Thus: C26 H43 N06 -f- H,0 = C2P H40 06 + C2 H5 N02. Glycocholic acid + water = cholic acid -f glycin, and under similar circumstances Taurocholic acid splits up into cholic acid and taurin:— C26 H4& 03 NS07 + H30 = C26 H40 06 + C2 H7 NS03, or amido-isethionic. Taurocholic acid -f- water = cholic acid and taurin. Glycin occurs also in hippuric acid. It can be prepared from gelatin by the action of acids or alkalies; it can also be obtained from hippuric acid. 332 HAND-BOOK OF PHYSIOLOGY. 6 -^11 ^2 / C1 TT O ) Leucin, or amido-caproic acid, [-ON, or -^-j^1 V- 0 H ) 2 occurs normally in many organs of the body and is a product of the pan- creatic digestion of proteids. It is present in the urine in certain diseases of the liver in which there is loss of substance, especially in acute yellow atrophy. It occurs in circular oily discs or crystallizes in plates, and can be prepared either by boiling horn shavings, or any of the gelatins, with sulphuric acid, or out of the products of pancreatic digestion, 02 H3 02 } Sarcosin may be considered as methyl glycin, CH3 > 1ST. It is a H ) constituent of kreatin, but has never been found free in the human body. Neurin (C6 H13 NO), is an unstable body, which has been found in ox and pig'*s gall. 0, H& ) Taurin, C2H7NS03 or S02 HO >• N; or amido-isethionic acid, is a con- EC ; stituent of the bile acid, taurocholic acid, and is found also in traces in the muscles and lungs. — See above. Cystin, C3 H7 NS02 occurs in a rare form of urinary calculus, which is only formed in a urine of neutral reaction. It can be crystallized in hexagonal laminae of pale yellow color, becoming greenish on exposure to light. C9H9N03,orC2H3OJ Hippuric Acid, C7H50 V N, or benzolglycin, a normal H ) constituent of human urine, the quantity excreted being increased by a vegetable diet, and therefore it is present in greater amount in the urine of herbivora. It may be decomposed by acids into glycin and benzoic acid. It crystallizes in semi-transparent rhombic prisms, almost insoluble in cold water, soluble in boiling water. (See also p. 361, Vol. I.) Tyrosin, C9 Hn N03, is found, generally together with leucin, in certain glands, e.g., pancreas and spleen; and chiefly in the products of pancreatic digestion or of the putrefaction of proteids. It is found in the urine in some diseases of the liver, especially acute yellow atrophy. It crystallizes in fine needles, which collect into feathery masses. It gives the proteid test with Millon's reagent, and heated with strong sulphuric acid, on the addition of ferric chloride gives a violet color. Lecithin, C42 H84 P N09, is a phosphoretted fatty body, which has been found mixed with cerebrin, and oleophosphoric acid in the brain. It is also found in blood, bile and serous fluids, and in larger quantities in nerves, pus, yelk of egg, semen, and white blood-corpuscles. On boiling with acids it yields cholin, glycero-phosphoric acid, palmic and oleic acids. Cerebrin, C1? H33 N03, is found in nerves, pus-corpuscles, and in the brain. Its chemical constitution is not known. It is a light amorphous powder, tasteless and odorless. Swells up like starch when boiled with water, and is converted by acids into a saccharine substance and other bodies. The so-called Protagon is a mixture of lecithin and cerebrin. APPENDIX. 333 (b.) PRIMARY DIAMIDES OR UREAS. Urea, (NH2)2 CO, is the last product of the oxidation of the albu- minous tissues of the body and of the albuminous foods. It occurs as the chief nitrogenous constituent of the urine of man, and of some other animals. It has been found in the blood and serous fluids, lymph, and in the liver. Properties. Crystallizes in thin glittering needles, or in prisms with pyramidal ends. Easily soluble in water and alcohol, insoluble in ether, easily decomposed by strong acids, readily forms compounds with acids and bases, of which the chief are (NH2)2 COHN03, urea nitrate, and (NH2)2 (CO), H2 C2 02 + H2 0, urea oxalate. Constitution. — It is usually considered to be a diamide of carbonic CO N H 2 H2 V acid which may be written H2 N2, or CO N H2 V which is CO (H0)2, H2 ) with (OH)'2, replaced by (NHa)'a. Some think it a monamide of carbamic acid, CO, OH, NH2, thus CO, NH2 NH2, with one atom of NH2, or amidogen in place of one of hydroxyl OH. ) IN" TJrea is isomeric with ammonium cyanate C j- QJSTTT from which it was first artificially prepared. Kreatin, C4 H9 N3 02, is one of the primary products of muscular disintegration. It is always found in the juice of muscle. It is gener- ally decomposed in the blood into urea and kreatinin, and seldom, unless under abnormal circumstances, appears as such in the urine. Treated with either sulphuric or hydrochloric acid, it is converted into kreatinin; thus — C4 II, N. 0, = 0, H, N3 0 + H, O. Kreatinin, C4 H7 N30, is present in human urine, derived from oxi- dation of kreatin. It does not appear to be present in muscle. (c.) UREIDES. Ureides are a third variety of amides, and may be considered as ureas in which part of the hydrogen is replaced by diatomic acid radicals. Honour eides contain one acid radical and one urea residue; and diureides, one acid radical and two urea residues. Uric Acid, C H4 N4 03, occurs in the urine, sparingly in human urine, abundantly in that of birds and reptiles, where it represents the chief, nitrogenous decomposition product. It occurs also in the blood, spleen, liver, and sometimes is the only constituent of urinary calculi. It is probably converted in the blood into urea and some carbon acid. It 334 HAND-BOOK OF PHYSIOLOGY. generally occurs in urine in combination with bases, forming urates, and never free unless under abnormal conditions. A deposit of urates may occur when the urine is concentrated or extremely acid, or when, as during febrile disorders, the conversion of uric acid into urea is incom- pletely performed. Properties. — Crystallizes in many forms, of which the most common are smooth, transparent, rhomboid plates, diamond-shaped plates, hexa- gonal tables, etc. Very insoluble in water, and absolutely so in alcohol and ether. Dried with strong nitric acid in a water-bath, a compound is formed called alloxan, which gives a beautiful violet red with ammo- nium hydrate (murexide), and a blue color with potassium hydrate. It is easily precipitated from its solutions by the addition of a free acid. It forms both acid and neutral salts with bases. The most soluble urate is lithium urate. Composition. — Very uncertain; has been however recently produced artificially, but it is not easily decomposed; it may be regarded as diureide of tartronic acid. The chief product of its decomposition is urea. Guanin, CB H6 N5 0, has been found in the human liver, spleen, and faeces, but does not occur as a constant product. XantMn, C5 H4 N4 02, has been obtained from the liver, spleen, thymus, muscle, and the blood. It is found in normal urine, and is a constituent of certain rare urinary calculi. Hypoxanthin, 05 H4 N4 0, or sarkin, is found in juice of flesh, in the spleen, thymus, and thyroid. Allantoin, C4 H6 N4 03, found in the allantoic fluid of the foetus, and in the urine of animals for a short period after their birth. It is one of the oxidation products of uric acid, which on oxidation gives urea. In addition to the amides and probably related to them, are certain coloring and excrement itious matters, which are also most likely distinct decomposition compounds. PIGMENTS, ETC. BiliruUn, C9H9N02, is the best known of the bile pigments. It is best made by extracting inspissated bile or gall stones with water (which dissolves the salts, etc.), then with alcohol, which takes out cholesterin, fatty, and biliary acids. Hydrochloric acid is then added, which decom- poses the lime salt of bilirubin and removes the lime. After extracting with alcohol and ether, the residue is dried and finally extracted with chloroform. It crystallizes of a bluish-red color. It is allied in compo- sition to haematin. Biliverdin, C8H9N05, is made by passing a current of air through an alkaline solution of bilirubin, and by precipitation with hydrochloric acid. It is a green pigment. Bilifustin, C9HnN03, is made by treating gall stones with ether, then with dilute acid, and extracting with absolute alcohol. It is a non-crys- tallizable brown pigment. APPENDIX. 335 Biliprasin is a pigment of a green color, which can be obtained from gall stones. Bilihumin (Staedeler) is a dark brown earthy-looking substance, of which the formula is unknown. Urobilin occurs in bile and in urine, and is probably identical with stercobilin, which is found in the faeces. Uroerytlirin is one of the coloring matters of the urine. It is orange red, and contains iron. Melanin is a dark brown^or black material containing iron, occurring in the lungs, bronchial glands, the skin, hair, and choroid. HcB-matin has been fully treated of in Chapter IV. Indican is supposed to exist in the sweat and urine. It has not, how- ever, been satisfactorily isolated. Indigo, C8 H5 N9 0, is formed from indican, and gives rise to the bluish color which is occasionally met with in the sweat and urine. Indol, Op H2 N, is found in the faeces, and is formed either by decom- position of indigo, or of the proteid food materials. It gives the charac- teristic disagreeable smell to faeces. (4.) Nitrogenous Bodies of Uncertain Nature. Ferments are bodies which possess the property of exciting chemical changes in matter with which they come in contact. They are at present divided into two classes, called (1) organized, and (2) unorganized or soluble. (1.) Of the organized, yeast may be taken as an example. Its activity depends upon the vitality of the yeast cell, and disappears as soon as the cell dies, neither can any substance be obtained from the yeast by means of precipitation with alcohol or in any other way which has the power of exciting the ordinary change produced by yeast. (2.) Unorganized or soluble ferments are those which are found in secretions of glands, or are produced by chemical changes in animal or vegetable cells in general; when isolated they are colorless, tasteless, amorphous solids soluble in water and glycerin, and precipitated from the aqueous solutions by alcohol and acetate of lead. Chemically many of these are said to contain nitrogen. Mode of action. — Without going into the theories of how these unor- ganized ferments act, it will suffice to mention that: (1.) Their activity does not depend upon the actual amount of the ferment present. (2.) That the activity is destroyed by high tempera- ture, and various concentrated chemical reagents, but increased by moderate heat, about 40° C. and by weak solutions of either an acid or an alkaline fluid. (3.) The ferments themselves appear to undergo no change in their own composition, and waste very slightly during the process. Varieties. — The chief classes of unorganized ferments are: — (1.) Amylolytic, which possess the property of converting starch into 336 HAND-BOOK OF PHYSIOLOGY. glucose. They add a molecule of water, and may be called hydrolytic. The probable reaction is as follows: 3 C6 H10 03 + 3 H20 = C6 H12 06 + 0 H10 0. - 3 0 H12 06 Starch Water Glucose Dextrin Glucose. This shows that there is an intermediate reaction, the starch being first turned only partly into glucose and principally into dextrin, which is afterward further converted into glucose. The principal amylolytic ferments are Ptyalin, found in the saliva, and a ferment, probably dis- tinct in the pancreatic juice, called Amylopsin. These both act in an alkaline medium. Amylolytic ferments have been found in the blood and elsewhere. Conversion of starch into sugar. — With reference to the action of the amylolytic ferments, recent observations have shown that the starch mole- cule is not by any means so simple as it has been represented above. As it is said that starchy materials, in the form of wheat and other cereals, and in the potato or its substitutes, form two-thirds of the total food of man, it is very important that we should note (1) the changes which occur in starch on cooking, and (2) the series of reactions it undergoes during its conversion by the amylolytic ferments into sugar. (1.) The object of this change is to produce gelatinous or soluble starch. A starch granule consists of two parts: an envelope of cellulose, which gives a blue color with iodine on addition of sulphuric acid, and of qranulose, which is contained within it, giving a blue with iodine alone. Briicke states that a third body is contained in the granule, which gives a red with iodine, viz., erytliro-granulose. On boiling, the granulose swells up, bursts the envelope, and the whole granule is more or less completely converted into a paste or into mucilaginous gruel. (2.) Changes which occur on addition of an amylolytic ferment. On the addition of saliva or extract of pancreas to gelatinous starch, the first change noticed is that the paste liquifies very quickly, but the liquid does not give the reaction for dextrin or for sugar; but soon this latter reaction appears, increasing very considerably and quickly, although at first, in addition, a reaction of erethrodextrin, a red on addition of iodine, is found; as the sugar increases, however, this disappears. At first the erythrodextrin is mixed with starch, as the reaction is a reddish purple with iodine, then it is a pure red, and finally a yellowish brown. As the sugar continues to increase the reaction with iodine disappears, but it is said that dextrin is still present in the form of achroo-dextrines, which give no reaction with iodine. However long the reaction goes on, it is unlikely that all the dextrin becomes sugar. Next with regard to the kind of sugar formed, it is, at first at any rate, not glucose but maltose, the formula for which is 01? H22 On. Maltose is allied to saccharose or cane sugar more nearly than to glucose; it is crystalline; its solution has the property of polarizing light to a greater degree than solutions of glucose; is not so sweet, and reduces copper sulphate less easily. It can be converted into glucose by boiling with' dilute acids. According to Brown and Heron the reactions may be represented thus: — APPENDIX. 337 One molecule of gelatinous starch is converted into n molecules of soluble starch. One molecule of soluble starch = 10 (C13 H?0 010)-f 8 (H2 0) = 1 Erythro-dextrin (giving red with iodide) Maltose. 9 (Clf H30 010) + (C12 H22 On) = 2. Erythro-dextrin (giving yellow with iodine) Maltose. 8i r\ TT /i \ | k) / r\ 'TT r\ \ I v^1Q £lQ0v>' ) — ]— \/ (\u „ ij-o vy ) = 3. Achroo-dextrin Maltose. 7 (0,, HJO 010) + 3 (0,, HM OJ And so on; the resultant being: — 10 (0,, H!0 O,.) + 8 (H, 0) = 8 (0,. H« 0M) + 2 (0,, H20 010) Soluble starch Water Maltose Achroo-dextrin. Pancreatic juice and intestinal juice are able to turn the achroo-dex- trin which remains into maltose, and maltose into glucose (dextrose). It is doubtful whether saliva possesses the same power. (2.) Proteolytic convert proteids into peptones. The nature of their action is probably hydrolytic. The proteolytic ferments of the body are called Pepsin, acting in an acid medium from the gastric juice. Trypsin, acting in an alkaline medium from the pancreatic juice. The Succus entericus is said to contain a third such ferment. (3.) Inversive, which convert cane sugar or saccharose into grape sugar or glucose. Such a ferment was found by Claude Bernard in the Succus entericus; and probably exists also in the stomach mucus. 2 Cia H22 On + 2 H2 0 = C12 H24 012 + C12 H24 013 Saccharose Water Dextrose Laevulose. (4.) Ferments which act upon fats; such a body called Steapsin has been found in pancreatic juice. The ferments Amylopsin, Trypsin, and Steapsin, are said to exist separately in pancreatic juice, and if so, make up what was formerly called Pancreatin and which was said to have the functions of the three. (5.) Milk-curdling ferments. It has been long known that rennet, a decoction of the fourth stomach of a calf, in brine, possessed the power of curdling milk. This power does not depend upon the acidity of the gas- tric juice, since the curdling will take place in a neutral or alkaline medium; neither does it depend upon the pepsin, as pure pepsin scarcely curdles milk at all, and the rennet which rapidly curdles milk has a very feeble proteolytic action. From this and other evidence it is believed that a distinct milk-curdling ferment exists in the stomach. W. Roberts has shown that a similar but distinct ferment exists in pancreatic extract, which acts best in an alkaline medium, next best in an acid medium, and worst in a neutral medium. The ferment of rennet acts best in an acid medium, and worst in an alkaline, the reaction ceasing if the alka- linity be more than slight. VOL. II.— 22. 338 HAND-BOOK OF PHYSIOLOGY. In addition to the above ferments, many others most likely exist in the body, of which the following are the most important: 6. Fibrin-forming ferment (Schmidt), (see p. 69, et seg., Vol. I.) found in the blood, lymph and chyle. 7. A ferment which converts glycogen into glucose in the liver; being therefore an amylolytic ferment. 8. Urinary ferments. (b.) Organic non-nitrogenous bodies consist of — (1.) Oils and fats. (2.) Amyloids. (3.) Acids. (1.) OILS AND FATS. Saponifiable. Palmitin C51H90 06 Stearin C57H11006 Olein ...... 0° Non-saponifiable. Cholesterin .... 020H44 0 Stercorin ? Excretin 078H160SOa Constitution. Tlie Saponifiable fats are formed by the union of fatty acid radicals with the triatomic alcohol, Glycerin 03 H5 (OH)3. The radicals are 0IS H350, 016 H18 0, and CJ8 H33 0, respectively. Human fat consists of a mixture of palmitin, stearin, and olein, of which the two former con- tribute three-quarters of the whole. Olein is the only liquid constituent. General characteristics. — Insoluble in water and in cold alcohol; sol- uble in hot alcohol, ether, and chloroform. Colorless and tasteless; easily decomposed or saponified by alkalies or superheated steam into glycerin and the fatty acids. Non- Saponifiable. — CJiolesterin, 026 H44 O, is the only alcohol which has been found in the body in a free state. It occurs in small quantities in the blood and various tissues, and forms the principal constituent of gall-stones. It is found in dropsical fluids, especially in the contents of cysts, in disorganized eyes, and in plants (especially peas and beans). It is soluble in ether, chloroform, or benzol. It crystallizes in white feathery needles. See also under the head of the constituents of the bile. Excretin (Marcet), and Stercorin (Flint), are crystalline fatty bodies which have been isolated from the faeces. (2.) AMYLOIDS. Amyloids.— Under this head are included both starch and sugar. The substances, like the fats, contain carbon, hydrogen, and oxygen; but the last-named element is present in much larger relative amount, the hydro- gen and oxygen being in the proportion to form water. The following varieties of these substances are found in health in the body. APPENDIX. 339 (a) Glycogen (C6 H10 06). — This substance, which is identical in com- position with starch, and like it, is readily converted into sugar by fer- ments, is found in many embryonic tissues and in all new formations where active cell-growth is proceeding. It is present also in the pla- centa. After birth it is found almost exclusively in the liver and muscles. Glycogen is formed chiefly from the saccharine matters of the food; but although its amount is much increased when the diet largely consists of starch and sugar, these are not its only source. It is still formed when the diet is flesh only, by the decomposition, probably, of albumin ID to glycogen and urea. The destination of glycogen has been considered in a former chapter. (Seep. 282, Vol. I.) (b) Glucose or grape sugar (C6 H12 06 -J- H2 0) is found in minute quantities in the blood and liver, and occasionally in other parts of the body. It is derived directly from the starches and sugars in the food, or from the glycogen which has been formed in the body from these or other matters. However formed, it is in health quickly burnt off in the blood by union with oxygen, and thus helps in the maintenance of the body's temperature. Like other amyloids it is one source whence fat is derived. (c) Lactose or sugar of milk (C12 H22 Ou -}- H2 0), is formed in large quantity when the mammary glands are in a condition of physiological activity, — human milk containing 5 or 6 per cent, of it. Like other sugars it is a valuable nutritive material, and hence is only discharged from the body when required for the maintenance of the offspring. The same remark is applicable to the other organic nutrient constituents of the milk, albumin and saponifiable fats, which, if we except what is preseni in the secretions of the generative organs, are discharged from the body only under the same conditions and in the same secretion. (d) Inosite (C6HJ2 06 -f- 2 H2 0), a variety of sugar, identical in com- position with glucose, but differing in some of its proparties, is found constantly in small amount in muscle, and occasionally in other tissues. Its origin and uses in the economy are, presumably, similar to those of glycogen. (e) Maltose (C12 H22 On), is formed in the conversion of starch into glucose (see p. 336, Vol. II. j. (3.) ORGANIC ACIDS. Group I. — Monatomic Fatty Acids. Formic 0 HO OH Acetic C2 H3 0 OH Propionic . . . . C3 Hr 0 OH Butyric . . . . C4 H^ 0 OH Valerianic . C. HQ 0 OH Caproic . . . -. C6 Hn 0 OH Capric . . . . C8 H 0 OH Palmitic . . . . 016 H31 0 OH Stearic .... C18 H3B 0 OH Oleic CL H,, 0 OH 340 HAND-BOOK OF PHYSIOLOGY. Formic, acetic, and propionic acids are present in sweat, but normally in no other human secretion. They have been found elsewhere in dis- eased conditions. Butyric acid is found in sweat. Various others of these acids have been obtained from blood, muscular juice, faeces, and urine. Group II. — Diatomic Fatty Acids. Monobasic. Glycolic C2 H4 03 Lactic C3H6 03 Leucic C6H1203 Bibasic. Oxalic C2 H2 O4 Succinic C4 H6 O4 Sebacic 010 H10O4 Lactic acid exists in a free state in muscular plasma, and is increased in quantity by muscular contraction, is never contained in healthy blood, and when present in abnormal amount seems to produce rheumatism. Oxalates are present in the urine in certain diseases, and after drink- ing certain carbonated beverages, and after eating rhubarb, etc. AROMATIC SERIES. Benzoic C7 H6 02 Phenol . . . . C6H60 Benzoic acid is always found in the urine of herbivora, and can be obtained from stale human urine. It does not exist free elsewhere. Phenol. — Plienyl alcohol or carbolic acid exists in minute quantity in human urine. It is an alcohof of the aromatic series. 2. INORGANIC PRINCIPLES. The inorganic proximate principles of the human body are numerous. They are derived, for the most part, directly from food and drink, and pass through the system unaltered. Some are, however, decomposed on their way, as chloride of sodium, of which only four-fifths of the quantity ingested are excreted in the same form; and some are newly formed within the body, — as for example, a part of the sulphates and carbonates, and some of the water. Much of the inorganic saline matter found in the body is a necessary constituent of its structure, — as necessary in its way as albumin or any other organic principle; another part is important in regulating or modify- ing various physical processes, as absorption, solution, and the like; while a part must be reckoned only as matter, which is, so to speak, accident- ally present, whether derived from the food or the tissues, and which will, at the first opportunity, be excreted from the body. Gases. — The gaseous matters found in the body are Oxygen, Hydro- APPENDIX. 341 gen, Nitrogen, Carburetted and Sulphuretted hydrogen, and Carbonic acid. The first three have been referred to (p. 325, Vol. II.). Car- buretted and sulphuretted hydrogen are found in the intestinal canal. Carbonic acid is present in the blood and other fluids, and is excreted in large quantities by the lungs, and in very minute amount by the skin. It will be specially considered in the chapter on Respiration. Water, the most abundant of the proximate principles, forms a large proportion, — more than two- thirds of the weight of the whole body. Its relative amount in some of the principal solids and fluids of the body is shown in the following table (quoted by Dalton, from Robin and Ver- deiFs table, compiled from various authors) : — QUANTITY OF WATER IK 1000 PARTS. Teeth 100 Bones 130 Cartilage 550 Muscles 750 Ligament • . 768 Brain 789 Blood 795 Synovia 805 Bile 880 Milk 887 Pancreatic juice 900 Urine 936 Lymph 960 Gastric juice 975 Perspiration 986 Saliva 995 Uses of the Water of the Body.— The importance of water as a constituent of the animal body may be assumed from the preceding table, and is shown in a still more striking manner by its withdrawal. If any tissue — as muscle, cartilage, or tendon — be subjected to heat sufficient to drive off the greater part of its water, all its characteristic physical prop- erties are destroyed; and what was previously soft, elastic, and flexible, becomes hard and brittle, and horny, so as to be scarcely recognizable. In all the fluids of the body — blood, lymph, etc., water acts the part of a general solvent, and by its means alone circulation of nutrient matter is possible. It is the medium also in which all fluid and solid aliments are dissolved before absorption, as well as the means by which all, except gaseous, excretory products are removed. All the various processes of secretion, transudation, and nutrition, depend of necessity on its presence for their performance. Source. — The greater part, by far, of the water present in the body is taken into it as such from without, in the food and drink. A small amount, however, is the result of the chemical union of hydrogen with oxygen in the blood and tissues. The total amount taken into the body every day is about 4J- Ibs. ; while an uncertain quantity (perhaps J- to f Ib.) is formed by chemical action within it. (Dalton.) Loss. — The loss of water from the body is intimately connected with excretion from the lungs, skin, and kidneys, and, to a less extent, from 342 HAND-BOOK OF PHYSIOLOGY. the alimentary canal. The loss from these various organs may be thus apportioned (quoted by Dalton from various observers). From the Alimentary Canal (faeces) . 4 per cent. Lungs 20 " Skin (perspiration) ... 30 Kidneys (urine) 46 " 100 Sodium and Potassium Chlorides are present in nearly all parts of the body. The former seems to be especially necessary, judging from the instinctive craving for it on the part of animals in whose food it is deficient, and from the diseased condition which is consequent on its with- drawal. In the blood, the quantity of chloride of sodium is greater than that of all its other saline ingredients taken together. In the muscles, on the other hand, the quantity of chloride of sodium is less than that of the chloride of potassium. Calcium Fluoride, in minute amount, is present in the bones and teeth, and traces have been found in the blood and some other fluids. Calcium, Potassium, Sodium, and Magnesium Phosphates are found in nearly every tissue and fluid. In some tissues — the bones and teeth — the phosphate of calcium exists in very large amount, and is the principal source of that hardness of texture on which the proper per- formance of their functions so much depends. The phosphate of calcium is intimately incorporated with the organic basis or matrix, but it can be removed by acids without destroying the general shape of the bone; and, after the removal of its inorganic salts, a bone is left soft, tough, and flexible. Potassium and sodium phosphates with the carbonates, maintain th& alkalinity of the blood. Calcium Carbonate occurs in bones and teeth, but in much smaller quantity than the phosphate. It is found also in some other parts. The small concretions of the internal ear (otoliths) are composed of crystalline carbonate of calcium, and form the only example of inorganic crystalline matter existing as such in the body. Potassium and Sodium Carbonates are found in the blood, and some other fluids and tissues. Potassium, Sodium, and Calcium Sulphates are met with in small amount in most of the solids and fluids. Silicon. — A very minute quantity of silica exists in the urine, and in the blood. Traces of it have been found also in bones, hair, and some other parts. Iron. — The especial place of iron is in haemoglobin, the coloring- matter of the blood, of which a further account has been given with the APPENDIX. 343 chemistry of the blood. Peroxide of iron is found, in very small quanti- ties, in the ashes of bones, muscles, and many tissues, and in lymph and chyle, albumin of serum, fibrin, bile, and other fluids; and a salt of iron, probably a phosphate, exists in the hair, black pigment, and other deeply colored epithelial or horny substances. Aluminium, Manganese, Copper, and Lead.— It seems most likely that in the human body, copper, manganesium, aluminium and lead are merely accidental elements, which, being taken in minute quan- tities with the food, and not excreted at once with the faeces, are absorbed and deposited in some tissue or organ, of which, however, they forfci no necessary part. In the same manner, arsenic, being absorbed, may be deposited in the liver and other parts. APPENDIX B. MEASURES OF WEIGHT (Avoirdupois). Ibs. 21 77 Recent Skeleton Muscles and Tendons Skin and Subcutaneous tissue . . . .16 Blood . . . . 11 to 14 T Cerebrum . . 2 I Cerebellum . . - I Pons and Medulla (^ oblongata . . - Brain Encephalon Eyes .... Heart .... Intestines, small large Kidneys (both) Larynx, Trachea, and larger Bronchi ozs. 8 Ibs. Liver .... 3 ozs. 8 8 Lungs (both) ... 2 10 5 (Esophagus - Ovaries (both) . J- to - If _ Pancreas . . . - 3* 12 Salivary Glands (both 5J sides) . . . 1| to - 2 Stomach . . . . - 7 1 Spinal Cord, divested of its nerves and membranes . - li 2± Spleen - 7 i Suprarenal Capsules (both), 10 i' ^° ~ i llj Testicles (both) . H to - 1 Thyroid body and remains 10i of Thymus gland . . - f Tongue and Hyoid bone . - Uterus (virgin) . £ to 3 3 4 MEASURES OF LENGTH (Average). ft. in. 6 Appendix vermiformis 3 to Bronchus, right . . - 11 left . . . - 2i Caecum . . . . - 2% Duct, common bile . . - 3 ejaculatory, to - 1 of Cowper's gland " hepatic . . " nasal . . " parotid . . " sub-maxillary . Epididymis . . unraveled. Eustachian tube . . - Fallopian tube . . . - Intestine, large . . 5 to 6 small . . . 20 Ligament, round, of uterus - - 2 - -} - 2$ - 2 - If 20 - ft. in. Ligament of ovary Meatus auditorius externus - l|- Medulla oblongata . . - 1£ (Esophagus . . . - 10 Pancreas . . . . - 7 Pharynx . . . . - 4J Rectum . . . . - 8 Spinal cord . . .15 Tubulus seminiferus . .23 Urethra, male . . . - 8 female . . - 1J Ureter . . . .14 Vagina . . . 4 to - 6 Vas deferens . . .2 Vesicula seminalis . . - 2 " " unraveled/ 4 to - 6 Vocal cord - -4 346 HAND-BOOK OF PHYSIOLOGY. SIZES OF VARIOUS HISTOLOGICAL ELEMENTS AND TISSUES. Air-cells, ^ to Blood-cells (red), -g-g Average size infractions of an inch, Lacunas (bone), (breadth). -nrioir (thickness). • (colorless), YgVir- _ Canaliculus of bone, T ^Vo- (width). Capillary blood-vessels, to TgW (bone). Cartilage-cells (nuclei of), Chyle-molecules, -g^-onr Cilia, ToW to nW (length). Cones of retina (at yellow spot), Tdnro-.to Tinhnr (width). Connective-tissue fibrils, g 0 i 0 0 to (width). Dentine-tubules, ^faj (width). Enamel-fibres, g0100 (width). End-bulbs, ^fa. Epithelium columnar (intestine), (length). spheroidal (hepatic), r oVo to ¥ or- squamous (peritoneum) (width). squamous (mouth), (skin), Elastic (yel.) fibres, (wide). Fat-cells, ^ to Germinal vesicle, spot, Glands gastric, ^ to ^ (length). ^to,^ (width). Lieberkuhns (small intestines), -^ (width). (width).' to to jfo- (length). Lieberkuhn's (small intestine), to (width). Peyer's (follicles), Sweat, ^5- (width). " in axilla, -^- to -J- (width). Haversian canals, ToVo- to ( width). (length). Macula lutea, -g1 Malpighian bodies (kidney), T$-g " corpuscles (spleen), .to A* Muscle (striated), T-J-g- to ( width). Muscle-cell (plain), -^ to length). Muscle-cell (plain), T-gVo- to (width). Nerve-corpuscles (brain), -g-jj^rr to 300* Nerve-fibres (medullated) y^-J-o^ to y^or (width). Nerve- fibres (non-medullated) 80J00 to 5oVo (width). Ovum, T^. Pacinian bodies, y1^ to yV (length). " A to A- (width). Papillaa of skin (palm), -^ to y^-g- (length). " (face), ^ to T^. tongue (circumvallate), fa- to TV (width). " " (fungiform), ^ to fa (width). m " " ffiliform), TV (length). Pigment-cells of choroid (hexa- gonal), y^Vo-. Pigment-granules, ^J^nr. Spermatozoon, -g^ to -^ (length). head, F5Vo S " ToicH) (Width). Touch-corpuscle, y^g- (length). Tubuli seminiferi, -^ to y^-g- ( width). Tubuli uriniferi, -$!-$. ViUi, A to i (length). TV (Width). APPENDIX. 347 SPECIFIC GRAVITY OF VARIOUS FLUIDS AND TISSUES. (Water = 1'OOO.f Adipose tissue . Bile .... Blood " corpuscles (red) Body (entire) . Bone . . 1-870 Brain " grey matter " white Cartilage . Cerebro-spinal fluid . Chyle. Gastric juice Intestinal juice . Kidney Liquor amnii . 0-932 to 020 055 088 065 970 036 034 1-040 1-150 1-006 1-024 1-0023 1.011 1-052 1-008 Liver . Lymph Lungs when fully distended ordinary condition, post mortem . 0*345 when deprived of air Muscle ... Milk . Pancreatic juice . Saliva . Serum . Spleen . . Sweat . Urine 1.055 1-020 , 0-126 to 0.746 056 020 030 012 006 026 060 004 020 TABLE SHOWING THE PERCENTAGE COMPOSITION OF VARIOUS ARTICLES OF FOOD. (LETHEBY.) Bread Oatmeal . Indian corn meal Rice Arrowroot Potatoes . Carrots . Turnips . Sugar Treacle . Milk Cream Cheddar cheese Lean beef Fat beef . Lean mutton . Fat mutton Veal Fat pork . Poultry . White fish Eels Salmon . White of egg . Yelk of egg Butter and Fat Beer and porter Water. Albumin. Starch. Sugar. Fat. Salts. 37 8-1 47-4 3-6 1-6 2-3 15 12-6 58-4 5-4 5-6 3- 14 11-1 64-7 0-4 8-1 1-7 13 6-3 79-1 0-4 0-7 0-5 18 — 82- — — — 75 2-1 18-8 3-2 0-2 0-7 83 1-3 8-4 6-1 0-2 1-0 91 1-2 5-1 2-1 — 0-6 5 — — 95-0 — — 23 — — 77-0 — — 86 4-1 — 5-2 3-9 0-8 66 2-7 — 2-8 26-7 1-8 36 28-4 -^ — 31-1 4-5 72 19-3 — — 3-6 5-1 51 14-8 — — 29-8 4-4 72 18-3 — — 4-9 - 4-8 53 12-4 — — 31-1 3-5 63 16-5 — — 15-8 4-7 39 9-8 — — 48-9 2-3 74 21-0 — 3-8 1-2 78 18-1 — - 2-9 1-0 75 9-9 — — 13-8 1-3 77 16-1 — — 5-5 1-4 78 20-4 — — — 1-6 52 16-0 — — 30-7 1-3 15 — — 83-0 2-0 91 0-1 — 8-7 — 0-2 348 HAND-BOOK OF PHYSIOLOGY. CLASSIFICATION OF THE ANIMAL KINGDOM. Vertebrata. MAMMALIA Primates t i Chiroptera . Iiisectivora . Carnivora . Proboscidea Hyracoidea . Ungulata: Perissodactyla Artiodaciyla Sirenia Cetacea Rodentia » Edentata Marsupiata . Monotremata BIRDS CARINAT.E Eaptores (Birds of Prey} Typical Examples. Man. Ape, baboon. Bat, flying fox. Mole, hedgehog. Lion, dog, bear, seal. Elephant. Hyrax Tapir, rhinoceros, horse. Hippopotamus, pig, camel, chevrotain, deer, ox, sheep, goat, giraffe. Dugong, manatee. Whale, porpoise, narwhal. Hare, porcupine, guinea pig, rat, beaver, squirrel, dormouse. Armadillo, pangolin, true anteater, Cape anteater, sloth. Opossum, bandicoot, Thylacinus, pha- langer, wombat, kangaroo. Ornithorhynchus, or duck-billed platy- pus, Echidna or spiny anteater. Vulture, hawk, owl. Woodpecker, parrot. Crow, finch, swallow. Fowl, pheasant, grouse. Scansores ( Climbing Birds) . Passeres (Perching Birds) . Rasores (Scratching Birds) . Grallatores ( Wading Birds) : Heron, stork, snipe, crane. N&tsitoTeB (Swimming Birds) Penguin, duck, pelican, gull. RATIT^E Cursores (Running Birds) REPTILES Crocodilia Lacertilia Chelonia Ophidia AMPHIBIA Anura Urodela FISH Dipnoi Teleostei Placoidei Ganoidei Cyclostomi Leptocardii Ostrich, emeu, apteryx. Crocodile, alligator, Iguana, chameleon, gecko, lizard, slow- worm, flying dragon. Tortoise, turtle Snake, viper. Frog, toad. Newt, salamander. Lepidosiren. Perch, mackerel, cod, herring. Shark, ray. Sturgeon, bony pike. Lamprey, hag. Amphioxus lanceolatus. APPENDIX. 349 CLASSIFICATION OP THE ANIMAL KINGDOM. MOLLUSCA Cephalopoda Pteropoda . Gasteropoda: Pulmonigasteropoda Branchiogasteropoda Lamellibranchiata Brachiopoda Tunicata, or Ascidioidea Bryozoa or Polyzoa ARTHROPODA Insecta Arachnida Myriopoda Crustacea Invertebrata. Typical Examples. . Octopus, argonaut, squid, cuttle-fish, nautilus. . Clio, Cleodora. Snail, slug. . Whelk, limpet, periwinkle. . Oyster, mussel, cockle. . Terebratula, Lingula. . Salpa, Pyrosoma. Sea mat. Beetle, bee, ant, locust, grasshopper, cockroach, earwig, moth, butterfly, fly, flea, bug. £ Scorpion, spider, mite. Centipede, millipede. Crab, lobster, crayfish, prawn, barnacle. Annulate Scolecida Echinodermata CCELENTERATA Ctenophora . Anthozoa . Hydrozoa . Spongida Sea-mouse, leech, earthworm. Hair-worm, thread- worm, round-worm, fluke, tape-worm, guinea- worm. Sea- cucumber, sea-urchin, star-fish, sand-star, feather-star. Beroe. Sea anemone, coral, sea-pen. Hydra, Sertularia, Velella, Portuguese man-of-war. Sponges. PROTOZOA Rhizopoda . Infusoria Foraminifera, Amoeba. Paramoecium, Vorticella. INDEX ABDOMINAL muscles, action of in respi- ration, i, 187 Aberration, chromatic, ii, 213 spherical, ii, 213 Abomasum, i, 240 Absorbents. See Lymphatics. Absorption, i, 291 by blood-vessels, i, 305 by lacteal vessels, i, 303 by lymphatics, i, 303 conditions for, i, 307 by the skin, i, 345 oxygen by lungs, i, 195 process of osmosis, i, 305 rapidity of, i, 306. See Chyle, Lymph, Lymphatics, Lacteals. Accessory nerve, ii, 149 Accidental elements in human body, ii, 860 Accommodation of eye, ii, 206 Acids, organic, ii, 339 acetic, ii, 339 Acid-albumin, i, 247; ii, 846 Acini of secreting glands, i, 323 Actinic rays, ii, 224 Addison's disease, ii, 10 Adenoid tissue, i, 34 Adipose tissue, i, 35. See Fat. development, i, 36 situations of, i, 36 structure of, i, 36 Adrenals, ii, 8 After-birth, ii, 270 Aftei-sensatfons, taste, ii, 174 touch, ii, 168 vision, ii, 216 Aggregate glands, i, 323 Agminate glands, i, 258 Air, atmospheric, composition of, i, 192 breathing, i, 189 complemental, i, 189 reserve, i, 189 residual, i, 189 tidal, i, 189 changes by breathing, i, 193 quantity breathed, i, 189 Air, transmission of sonorous vibrations through, ii, 186 in tympanum, for hearing, ii, 188 undulations of, conducted by external ear, ii, 186 Air-cells, i, 180 Air-tubes, i, 177. See Bronchi. Alanines, ii, 331 Albino-rabbits, i, 21 Albumin, ii, 327 acid, i, 247 4 action of gastric fluid on, i, 247 alkali, ii, 327, 328 characters of, ii, 328 chemical composition of, ii, 327 derived, ii, 328 egg, ii, 328 native, ii, 328 serum, i, 85; ii, 327 tissues and secretion in which it ex- ists, ii, 327 of blood, i, 83 Albuminoids, ii, 327 Albuminose, ii, 329 Albuminous substances, absorption of, i, 285 action of gastric fluid on, i, 247 of liver on, i, 280 of pancreas on, i, 266 Alcoholic drinks, effect on respiratory changes, i, 194 Alimentary canal, i, 224 development of, ii, 294 length in different animals, i, 284 Allantoin, ii, 334 Allantois, ii, 262, 263 Alloxan, ii, 334 Aluminium, ii, 343 Amic acids, ii, 331 Amides, ii. 330 Ammonia, cyanate, of, identical with urea, i, 359; ii, 333 exhaled from lungs, i, 196 urate of, i, 360 Amnion, ii, 262 fluid of, ii, 263 Amoeba, i, 7 Amoeboid movements, i, 8; ii, 213 352 INDEX. Amoeboid cells, i, 29 colorless corpuscles, i, 80 cornea-cells, i, 29 ovum, ii, 253 protoplasm, i, 7 Tradescantia, i, 7 Amphioxus, ii, 271 Ampulla, ii, 182 Amputation, sensations after, ii, 82 Amyloids or Starches, ii, 338 action of pancreas and intestinal glands, i, 267, 283 of saliva on, i, 231 Amylopsin, i, 267 Anacrotic wave, i, 146 Anastomoses of muscular fibres of heart, •i, 107 of nerves, ii, 73 of veins, i, 161 in erectile tissues, i, 169 Anelectrotonus, ii, 47 Angle, optical, ii, 221 Angulus opticus seu visorius, ii, 220 Animal heat, i, 309. Sec Heat and Tem- perature. Animals, distinctive characters, i, 3 Antiulhumatc, ii, 329 AntiallMmose, ii, 329 Antihelix, ii, 179 Antipeptone, ii, 329 Antitragus, ii, 179 Anus, i, 224 Aorta, i, 128 development, 281 pressure of blood in, i, 151 valves of, i, 110 action of, i, 114 Aphasia, ii, 130 Apncea, i, 209. See Asphyxia. Appendices epiploica?, i, 262 Appendix vermiformis, i, 262 Aqureductus, cochlea, ii, 183 vestibuli, ii, 182 Aqueous humor, ii, 204 Arches, visceral, ii 273 Area germinativa, ii, 256 opaca, ii, 256 pellucida, ii, 256 vasculosa, ii, 262 Areolar tissue, i, 31. See Connective Tissue. Arsenic, ii, 343 Arterial tension, i, 148 Arteries, i, 128 circulation in, i, 138 velocity of, i, 164 distribution, i, 128 muscular contraction of, i, 141 effect of cold on, i, 142 of division, i, 142 elasticity, i, 138 purposes of, i, 138 muscularity, i, 130 governed by nervous system, i, 153 Arteries, purposes of, i, 141 nerves of, i, 132 nervous system, influence of, i, 152 office of, i, 153 pressure of blood in, i, 148 pulse, i, 142. See Puise. rhythmic contraction, i, 140 structure, i, 129 distinctions in large and small arte- ries, i, 130 systemic, i, 102 tone of, i, 153 umbilical, 793 velocity of blood in, i, 264 Articulate sounds, classification of, ii, 60. See Vowels and Consonants. Arytenoid cartilages, ii, 52 effect of approximation, ii, 55 movements of, ii, 54 muscle, ii, 52 Asphyxia, i, 209 causes of death in, i, 210 experiments on, i, 211 Astigmatism, ii, 212 Atmospheric air, i, 192. See Air. pressure in relation to respiration, i, 193 Auditory canal, ii, 179 function, ii, 186 Auditory nerve, ii, 185 distribution, ii, 185 effects of irritation of, ii, 193 Auricle of ear, ii, 179 Auricles of heart, i, 104, 106 action, i, 111 capacity, i, 107 development, ii. 279 dilatation, i, 123 force of contraction, i, 123 Automatic action, ii, 88 cerebrum, ii, 127 medulla oblongata, ii, 110 respiratory, ii, 110 Axis-cylinder of nerve-fibre, ii, 70 B. Barytone voice, ii, 57 Basement-membrane, of mucous membranes, i, 322 of secreting membranes, i, 319 Bass voice, ii, 57 Battery, Darnell's, ii, 26 Benzoic acid, i, 372 Bicuspid valve, i, 109 Bile, i, 273 antiseptic power, i, 279 coloring matter, i, 274 composition of, i, 273 digestive properties, i, 279 exorementitious. i, 277 fat made capable of absorption by, i, 279 INDEX. 353 Bile, functions in digestion, i, 279 mixture with chyme, i, 279 mucus in, i, 275 natural purgative, i, 279 process of secretion of, i, 276 quantity, i, 277 re-absorption, i, 276, 280 salts, i, 273 secretion and flow, i, 276 secretion in fretus, i, 277 tests for, i, 274, 275 uses, i, 277 Bilifulvin, Biliprasin, Bilirubin, Biliver- din, i, 274 Bilin, i, 273 preparation of, i, 273 re-absorption of, i, 265, 280 Bioplasm, i, 6. See Protoplasm. Birth, i, 1 Bladder, urinary, i, 349. See Urinary Bladder. Blastema, i, 5. See Protoplasm. Blastodermic membrane, ii, 254 Bleeding, effects of, on blood, i, 87 Blind spot, ii, 215 Blood, i, 63 albumin, i, 85 use of, i, 99 arterial and venous, i, 87 assimilation, i, 99 buffy coat, i, 66 chemical composition, i, 82 coagulation, i, 65 color, i, 63, 87 changed by respiration, i, 198 coloring matter, i, 83, 90 coloring matter, relation to that of bile, i, 275 composition, chemical, i, 82 variations in, i, 87 corpuscles or cells of, i, 74. See Blood corpuscles, red, i, 75 white, i, 79 crystals, i, 91 cupped clot, i, 66 development, i, 96 extractive matters, i, 86 fatty matters, i, 86 use of, i. 99 fibrin, i, 65, 84 separation of, 1, 66 use of, i, 99 formation in liver, i, 82 in spleen, ii, 4 gases of, i, 88 haemoglobin or cruorin, i, 83, 91 hepatic, i, 87 menstrual, ii, 242 odor or halitus of, i, 63 portal, characters of, i, 87 purification of, by liver, i, 277 quantity, i, 63 reaction, i, 63 relation of, to lymph, i, 302 VOL. II.— 20. Blood, saline constituents, i, 86 uses of, i, 99 serum of, i, 85 compared with secretion of serous membrane, i, 320 specific gravity, i, 63 splenic, i, 88 structural composition, i, 75 temperature, i, 63 uses, i, 99 of various constituents, i, 99 variations of, in different circum- stances, i, 86 in different parts of body, i, 87 Blood-corpuscles, red, i, 75 action of reagents on, i, 75 chemical composition, i, 83 development, i, 96, 97 disintegration and removal, i, 99 method of ^ counting, i, 81 rouleaux, i, 76 sinking of, i, 66 specific gravity, i, 75 stroma, i, 75 tendency to adhere, i, 75 uses, i, 100 varieties, i, 75 vertebrate, various, i, 76 Blood-corpuscles, white, i, 79 amoeboid movements of, i, 80 derivation of, i, 99 formation of, in spleen, i, 99; ii, 4 locomotion, i, 80 Blood-crystals, i, 91 Blood-pressure, i, 148 influence of vaso-motor system of, i, 155 variations, i, 152 Blood-vessels, 'absorption by, i, 305 circumstances influencing, i, 307 difference from lymphatic absorp- tion, i, 305 osmotic character of, i, 306 rapidity of, i, 306 development, ii, 277 influence of nervous system on, i, 153 relation to secretion, i, 326 Bone, i, 42 canaliculi, i, 44 cancellous, i, 42 chemical composition, i, 42 compact, i, 42 development, i, 46 functions, i, 55 Haversian canals, i, 45 lacunae, i; 44 lamella?, i, 46 medullary canal, i, 43 periosteum, i, 43 structure, i, 42 growth, i, 54 Brain. See Cerebellum, Cerebrum, Pons, etc. adult, ii, 126 354 INDEX. Brain, amphibia, ii, 125 apes, ii, 126 birds, ii, 126 capillaries of, i, 135, 167 child, ii, 126 circulation of blood in, i, 167 convolutions, ii, 120 development, ii, 288 female, ii, 126 fish, ii, 125 gorilla, ii, 126 idiots, ii, 126 lobes, ii, 122 male, ii, 126^ mammalia, ii, 126 orang, ii, 127 proportion of water in, ii, 341 quantity of blood in, i, 167, et seq. rabbit, ii, 126 reptiles, ii, 126 weight, ii, 126 relative, ii, 126 Breathing, i, 172. See Respiration. Breathing-air, i, 189 Bronchi, arrangement and structure of, i, 177 Bronchial arteries and veins, i, 182 Brownian movement, i, 7 Brunner's glands, i, 257 Buffy coat, formation of, i, 66 Bulbus arteriosus, ii, 281 Burdach's column, ii, 96 Bursae mucosae, i, 320 C. Caecum, i, 261 Calcification, compared with ossification, i, 51 Calcium, ii, 342 fluoride, ii, 342 phosphate, ii, 342 carbonate, ii, 342 Calculi, biliary, containing cholesterin, ii, 338 containing copper, i, 276 Calyces of the kidney, i, 347 Canal, alimentary, i, 224. See Stomach, Intestine, etc. external auditory, ii, 179 function of, ii, 186 spiral, of cochlea, ii, 185 Canaliculi of bone, i, 44 Canalis membranaceus, ii, 185 Canals, Haversian, i, 45 portal, i, 269 semicircular, ii, 182 function of, ii, 191 Cancellous texture of bone, i, 42 Capacity of chest, vital, i, 189 of heart, i, 107 Capillaries, i, 132 circulation in, i, 158 rate of, i, 165 Capillaries, contraction of, i, 161 development, ii, 277 diameter of, i, 133 influence of on circulation, i, 161 lymphatic, i, 292 network of. i, 134 number, i, 135 passage of corpuscles through walls of, i, 159 resistance to flow of blood in, i, 158 still layer in, i, 158 structure of, i, 133 of lunirs, i, 134 of stomach, i, 244 Capric acid, ii, 339 Caproic acid, ii, 339 Capsule of Glisson, i, 268 Capsules, Malpighian, i, 348, 352, Carbonic acid in atmosphere, i, 192 in blood, i, 88 effect of, i, 204 _ exhaled from skin, i, 345 increase of in breathed air, i, 193 in lungs, i, 197 in relation to heat of body, i, 311 Carbonates, ii, 342 Cardiac orifice of stomach, action of, i, 250 sphincter of, i, 251 relaxation in vomiting, i, 251 Cardiac revolution, i, 117 Cardiograph, i, 119 Carnivorous animals, food of, i, 221 sense of smell in, ii, 178 Cartilage, i, 38 articular, i, 38 cellular, i, 40 chondrin obtained from, ii, 330 classification, i, 38 development, i, 42 elastic, i, 40 fibrous, i, 41. See Fibro-cartilage. hyaline, i, 38 matrix, i. 39 ossification, i, 51 perichondrium of, i, 52 structure, i, 38 temporary, i, 40 uses, i, 42 varieties, i, 38 Cartilage of external ear, used in hear- ing, ii, 186 Cartilages of larynx, ii, 52 Casein, ii, 327, 328. See Milk. Cauda equina, ii, 90 Caudate ganglion corpuscles, ii, 78 Cause of fluidity of living blood, ii, 72 Cells, i, 9 abrasion, i, 14 amoeboid, i, 29 blood, i, 74. See Blood-corpuscles. cartilage, i, 38 chemical transformation, i, 14 ciliated, i, 25 classification, i. 16 INDEX. 355 Cells, contents of, i, 9 decay and death, i, 14 definition of, i, 9 epithelium, i, 19. See Epithelium, fission, i, 12 formative, ii, 255 functions, i, 14 gemmation, i, 11 gustatory, ii, 173 lacunar of bone, i, 44 modes of connection, i, 16 nutrition, i, 9 action of, in secretion, i, 235 olfactory, ii, 176 pigment, i, 21 reproduction, i, 11 segmentation, i, 12 structure of, i, 9 transformation, i, 14 varieties, i, 15, 16 vegetable, i, 7 distinctions from animal cells, i, 3 Cellular cartilage, i, 40 Cement of teeth, i, 58 Centres, nervous, i, 154, 155, etc. See Nerve-centres, of ossification, i, 54 Centrifugal nerve- fibres, ii, 80 Centripetal nerve-fibres, ii, 80 Cerebellum, ii, 115 co-ordinating function of, ii, 118 cross-action of, ii, 119 effects of injury of crura, ii, 119 of removal of, ii, 118 functions of, ii, 118 in relation to sensation, ii, 118 to motion, ii, 118 to muscular sense, ii, 119 to sexual passion, ii, 119 structure of, ii, 116 Cerebral circulation, i, 167 hemispheres, ii, 120. See Cerebrum. Cerebral nerves, ii, 136 • third, ii, 137 effects of irritation and injury of, ii, 137 relation of to iris, ii, 137 fourth, ii. 138 fifth, ii, 139 distribution of, ii, 139 effect of division of, ii, 139 influence of on iris, ii. 141 on muscles of mastication, ii, 139 on organs of special sense, ii, 141, relation of, to nutrition, ii, 142 resemblance to spinal nerves, ii, 139 sensory function of greater division of fifth, ii, 139 sixth, ii, 143 communication of, with sympa- thetic, ii, 144 seventh, ii, 144. See Auditory Nerve and Facial Nerve, eighth, ii, 145, et seq. See Glosso- pharyngeal, Pneumogastric, and Spinal Accessory Nerves. ninth, ii, 150 Cerebration, unconscious, ii, 130 Cerebrin, ii, 332 Cerebro-spinal fluid, relation to circula- tion, i, 168 Cerebro-spinal nervous system, ii, 88, et seq. See Brain, Spinal Cord, etc. Cerebrum, its structure, ii, 120, 123 chemical composition, ii, 125 convolutions of, ii, 120, et seq. crura of, ii, 113. development, ii, 288 distinctive character in man, ii, 126 effects of injury, ii, 128 electrical stimulation, ii, 131 functions of, ii, 127 grey matter, ii, 123 in relation to speech, ii, 131 localization of functions, ii, 129 structure, ii, 123, et seq. unilateral action of, ii, 129 white matter, ii, 125 Cerumen, or ear-wax, i, 339 Chalk-stones, i, 360 Characteristics of organic compound, 326 Charcoal, absorption of, i, 307 Chemical composition of the human body, ii, 326-343 Chest, its capacity, i, 189 contraction of in expiration, i, 259 enlargement of in inspiration, i, 183 Chest-notes, ii, 58 Cheyne-Stokes' breathing, i, 209 Chlorine, ii, 342 in human body, ii, 342 in urine, i, 364 Cholesterin, ii, 338 in bile, i, 275 Chondrin, ii, 804 Chorda dorsalis, ii, 258 Chorda tympani, i, 232, et seq, Chordae tendineas, i, 110 action of, i, 113 Chorion, ii, 264 villi of, ii, 265 Choroid coat of eye, ii, 199 blood-vessels, ii, 203 Choroidal fissure, ii, 292 Chromatic aberration, ii, 213 Chyle, i, 301 absorption of, i, 303 analysis of, i, 302 coagulation of, i, 302 compared with lymph, i, 301 corpuscles of, i, 301. See Chyle-cor- puscles. course of, i, 291 fibrin of, i, 302 forces propelling, i, 303 molecular base of, i, 301 quantity found, i, 302 relation of, to blood, i, 302 Chyle-corpuscles, i, 301 356 INDEX. Chyme, i, 247 absorption of digested parts of, i, 285 changes of in intestines, i, 285, et seq. Cilia, i, 25; ii, 12 Ciliary epithelium, i, 25 of air-passages, i, 177 function of, i, 26 Ciliary motion, i, 26; ii, 12 nature of, ii, 13 Ciliary -muscles, ii, 206 action of in adaptation to distances, ii, 209 Ciliary processes, ii, 199 Circulation of blood, i, 101 action of heart, i, 111 agents concerned in, i, 170 arteries, i, 188 brain, i, 167 capillaries, i, 158 course of, i, 100, et seq. discovery, i, 170 erectile structures, i, 168 foetal, ii, 286 forces acting in, i, 103 influence of respiration on, i, 205 peculiarities of, in different parts, i, 167 portal, i, 269 proofs, i, 170 pulmonary, i, 198 systemic, i, 102 in veins, i, 161 velocity of, i, 163 Circumvallate papillae, ii, 169 Claviculi of Gagliardi, i, 46 Cleft, ocular, ii, 292 Clefts, visceral, ii, 273 Clitoris, ii, 239 development of, ii, 305 Cloaca, ii, 303 Clot or coagulum of blood, i, 65. See Coagulation. of chyle, i, 301 Coagulation of blood, i, 65 absent or retarded, i, 71 conditions affecting, i, 71 influence of respiration on, i, 198 theories of, i, 70 of chyle, i, 301 of lymph, i, 302 Coat, buffy, i, 66 Coats of arteries, i, 81 Cochlea of the ear, i, 179 office of, i, 188 Cold-blooded animals, i, 311 extent of reflex movements in, ii, 100 retention of muscular irritability in, ii, 37 Colloids, i, 306 Colon, i, 261 Colostrum, i, 331 Color-blindness, ii, 226 Coloring matter, i, 274 of bile, i, 274 of blood, i, 83, 90 Coloring matter of urine, i, 362 Colors, optical phenomena of, ii, 223, et seq. Columnae carneae, 105 action of, i, 110 Columnar epithelium, i, 24 Complemental air, i, 189 colors, ii, 225 Compounds, ii, 325 inorganic, ii, 340 organic, ii, 325 Concha, ii, 179 use of, ii, 186 Cones of retina, ii, 201 Coni vasculosi, ii, 247 Conjunctiva, ii, 196 Connective tissues, i, 28 corpuscles of, i, 28 fibrous, i, 31 gelatinous, i, 33 retiform, i, 34 varieties, i, 32 Consonants, i, 61 varieties of, i, 61 Contralto voice, ii, 57 Convolutions, cerebral, ii, 120, et seq. Co-ordination of movements, office of cerebellum in, ii, 118 office of sympathetic ganglia in, ii, 155 Copper, an accidental element in the body, ii, 343 in bile, i, 276. Cord, spinal, ii, 90. See Spinal Cord. umbilical, ii, 270 Cords, tendinous, in heart, i, 110 vocal, ii, 52. See Vocal Cords. Corium, i, 335 Cornea, ii, 197 action of on rays of light, ii, 204 corpuscles, ii, 198 nerves, ii, 198 structure, ii, 197 after injury of fifth nerve, ii, 143 Corpora Arantii, i, 111 geniculata, ii, 114 quadrigemina, ii, 114 their function, ii, 114 striata, ii, 114 their function, ii, 115 Corpus callosum, office of, ii, 134 cavernosum penis, i, 168 dentatum of cerebellum, ii, 116 of olivary body, ii, 109 luteum, ii, 243 of human female, ii, 243 of mammalian animals, ii, 243 of menstruation and pregnancy com- pared, ii, 245 spongiosum urethrae, i, 169 Corpuscles of blood, i, 74. See Blood- corpuscles. of chyle, i, 301 of connective tissue, i, 28 of cornea, ii, 198 INDEX. 357 Corpuscles of lymph, i, 301 Pacinian, ii, 74 Correlation of life with other forces, ii, 305 Cortical substance of kidney, i, 347 of lymphatic glands, i, 298 Corti's rods, ii, 184 office of, ii, 192 Costal typos of respiration, i, 187 Coughing, influence 011 circulation in veins, i, 207 mechanism of, i, 200 sensation in larynx before, ii, 84 Cowper's glands, ii, 246 office uncertain, ii, 251 Cranial nerves, ii, 136. See Cerebral nerves. Cranium, development of, ii, 288 Oassamentum, i, 65 Crescents of Gianuzzi, i, 228. See Semi- • lunes of Heidenhain. Crico-arytenoid muscles, ii, 52 Cricoid cartilages, ii, 52 Crossed pyramidal tract, ii, 95 Crura cerebelli, effect of dividing, ii, 118, et seq. of irritating, ii, 118 cerebri, ii, 113 their office, ii, 113 Crusta petrosa, i, 58 Cryptogamic plants, movements of spores of, i, 4 Crystal growth of, i, 1 Crystallin, ii, 328 Crystalline lens, ii, 204 in relation to vision at different dis- tances, ii, 207 Crystalloids, i, 306 blood, i, 91 Cubic feet of air for rooms, i, 205 Cupped appearance of blood-clot, i, 66 Curdling ferments, i, 248 Currents of action, ii, 36 ascending, ii, 46 continuous, ii, 26 descending, ii, 46 induced, ii, 27 muscle, ii, 23 natural, ii, 24 negative variation, ii, 36 nerve, ii, 45 polarizing, ii, 47 rest, ii, 24, 45 Curves, Traube-Hering's, i, 209 Cuticle, i, 333. See Epidermis, Epithe- lium of hair, i, 340 Cutis anserina, ii, 14 vera, i, 335 Cyanate of ammonium, i, 359 Cylindrical or columnar epithelium, i, 24 Cystic duct, i, 268 Cystin in urine, i, 365 D. Daltonism, ii, 226 Daniell's battery, ii, 26 Decidua, menstrual is, ii, 242 reflexa, ii, 268 serotina, ii, 268 vera, ii, 268 Decline, i, 2 Decomposition, tendency of animal com- pounds to, ii, 326 Decomposition-products, ii, 330 Decussation of fibres in medulla oblon- gata, ii, 107 in spinal cord, ii, 99 of optic nerves, ii, 231 Defecation, mechanism of, i, 288 influence of spinal cord on, ii, 102 Deglutition, i, 236. See Swallowing. Dentine, i, 55 Depqfessor nerve, i, 154 Derived albumins, ii, 328 Derma, i, 335 Descendens noni nerve, ii, 150 Descemet's membrane, ii, 198 Development, i, 3; ii, 252 • of organs, ii, 270 alimentary canal, ii, 294 arteries, ii, 281 blood, i, 96, et seq. blood-vessels, ii, 277 bone, i, 46 brain, ii, 288 capillaries, ii, 277 cranium, ii, 288 ear, ii, 294 embryo, ii, 260 extremities, ii, 275 eye, ii, 291 face and visceral arches, ii, 273 heart, ii, 276 liver, ii, 297 lungs, ii. 297 medulla oblongata, ii, 290 muscle, ii, 20 nerves, ii, 287 nervous system, ii, 287 nose, ii, 295 organs of sense, ii, 291 pancreas, ii, 297 pituitary body, ii, 272 respiratory apparalus, ii. 298 salivary glands, ii, 296 spinal cord, ii, 287 teeth, i, 58 vascular system, ii, 276 veins, ii, 283 vertebral column and cranium, ii, 270 visceral arches and clefts, ii, ',??:} of Wolffian bodies, urinary apparatus and sexual organs, ii, 298 Dextrin, i, 231 Diabetes, i, 283 Diamides, ii, 331 Diapedesis of blood-corpuscles, i, 159 Diaphragm, action of, on abdominal viscera, i, 175 358 INDEX. Diaphragm in inspiration, i, 183 in various respiratory acts, i, 198 in vomiting, i, 251 Diaphysis, i, 54 Diastole of heart, i, 111 Dicrotous pulse, i, 146 Diet- daily, i, 221 influence on blood, i, 87 mixed, necessity of, i, 213, et seg. Diffusion of gases in respiration, i, 197 Digestion, i, 224 in the intestines, i, 284, 286 in the stomach, i, 247 influence of nervous system on, i, 290 of stomach after death, i, 253. See Gastric fluid, Food, Stomach. Diplopia, ii, 229 Direct cerebellar tract, ii, 96 pyramidal tract, ii, 95 Direction of sounds, perception of, ii, 194 Discus proligerus, ii, 236 Disdiaclasts, ii, 16 Distance, adaptation of eye to, ii, 207 of sounds, how judged of, ii, 194 Distinctness of vision, how secured, ii, 203, et seq. Dormant vitality, ii, 308 Dorsal laminae, ii, 256, 273 Double hearing, ii, 195 vision, ii, 229 Dreams, ii, 136 Drowning, cause of death in, i, 211 Duct, cystic, i, 268 hepatic, i, 271 thoracic, i, 291 vitelline, ii, 261 Ductless glands, ii, 1 Ducts of Cuvier, ii, 285 Ductus arteriosus, ii, 282 venosus, ii, 284, 286 closure of, ii, 286 Duodenum, i, 254 Duration of impressions on retina, ii, 216 Duverney's glands, ii, 283 Dyspjiagia, absorption from nutritive baths in, i, 346 Dyspnoea, i, 209 E. Ear, ii, 179 bones or ossicles of, ii, 180 function of, ii, 188 development of, ii, 294 external, ii, 179 function of, ii, 186 internal, ii, 181 function of, ii, 191 middle, ii, 180 function of, ii, 187 Ectopia vesicse, i, 372 Efferent nerve-fibres, ii, 80 Efferent lymphatics, i, 300 vessels of kidney, i, 352 Egg- albumin, ii, 327 Eighth cranial nerve, ii, 145 Elastic cartilage, i, 40 fibres, i, 30 tissue, i, 33 Elastin, ii, 330 Electricity, in muscle, ii, 21 nerve, ii, 45 retina, ii, 218 Electrodes, ii, 22 Electrotonus, ii, 47 Elementary substances in the human body, ii, 325 accidental, ii, 343 Embryo, ii, 255. See Development and Foetus, formation of blood in, i, 96 Emmetropic eye, ii, 211 Emotions, connection of with cerebral hemispheres, ii, 127 Enamel of teeth, i, 57 Enamel organ, i, 58 End-bulbs, i, 337 End-plates, motorial, ii, 76 Endocardium, i, 108 Endolymph, ii, 182 function of, ii, 191 Endomysium, ii, 15 Endoneurium, ii, 69 Endosmometer, i, 305 Endotheliiim, i, 21 distinctive characters, i, 21 germinating, i, 23 Energy, ii, 65 relations of vital to physical, chap, xx, daily amount expended in body, ii, 65 Epencephalon, ii, 290 Epiblast, ii, 255 Epidermis, i, 333 development, etc., of, i, 334 functions of, i, 342 hinders absorption, i, 335 pigment of, i, 334 relation to sensibility, i, 342 structure of, i, 333 thickening of, i, 334 Epididymis, ii, 247 Epiglottis, ii, 52 action in swallowing, i, 238 influence of on voice, ii, 55 Epineurium, ii, 69 Epiphysis, i, 54 Epithelium, i, 19 air-cells, i, 182 arteries, i, 130 bronchi, i, 177 bronchial tubes, i, 177 ciliated, i, 25 cogged, i, 21 columnar, i, 24 cylindrical, i, 24 development, i, 27 * glandular, i, 24 INDEX. 359 Epithelium, goblet-shaped, i, 25 growth, i, 28 mucous membranes, i, 322 . olfactory region, ii, 176 secreting glands, i, 323 serous membranes, i, 319 spheroidal, i, 23 squamous or tessellated, i, 20 transitional, i, 26 Erect position of objects, perception of, ii, 219 Erectile structures, circulation in, i, 168 Erection, i, 168 cause of, i, 168 influence of muscular tissue in, i, 169 a reflex act, ii, 103 Erythro-granulose, ii, 105 Erythro-dextrin, ii, 336 Eunuchs, voice of, ii, 58 Eustachian tube, ii, 180 development, ii, 294 function of, ii, 190 Eustachian valve, i, 105 Excito-motor and sensori-motor acts, ii, 85 Excreta in relation to muscular action, ii, 44, et seq. Excretin, i, 287 Excretion, i, 347 Excretoleic acid, i, 287 Exercise, effects of, on production of carbonic acid, i, 194 on temperature of body, i, 310 on venous circulation, i, 162 Expenditure of body, ii, 63 amount, ii, 63 compared with income, ii, 64 evidences, ii, 63 objects, ii, 65 sources, ii, 65 Expiration, i, 186 influence of, on circulation, i, 207 mechanism of, i, 186 muscles concerned in, i, 187 relative duration of, i, 188 Expired air, properties of, i, 193, et seq. Extractive matters, i, 193 in blood, i, 86 in urine, i, 363 Extremities, development of, ii, 275 Eye, ii, 196 adaptation of vision at different dis- tances, ii, 203, et seq, blood-vessels, ii, 203 capillary vessels of, ii, 199 development of, ii, 291 effect on, of injury of facial nerve, ii, 144 of fifth nerve, ii, 141, 143 effect of pressure on, ii, 229 nerves, supplying muscles of, ii, 137, 138, 143 optical apparatus of, ii, 302 refracting media of, ii, 204 Eye, resemblance to camera, ii, 214 structure of, ii, 197 Eyelids, i, 196 development of, ii, 293 Eyes, simultaneous action of in vision, ii, 228 F. Face, development of, ii, 273 effect of injury of seventh nerveVm, ii, 144 Facial nerve, ii, 144 effects of paralysis of, ii, 144 relation of, to expression, ii, 144 Faeces, composition of, i, 287 quantity of, i, 287 Fallopian tubes, ii, 238 opening into abdomen, ii, 238 Falsetto notes, ii, 59 Fasciculus, cuneatus, ii, 96 olivary, ii, 96 teres, ii, 96 Fasting, influence on secretion of bile, i, 276 Fat. See Adipose tissue. action of bile on, i, 279 of pancreatic secretion on, i, 267 of small intestine on, i, 284 absorbed by laci eals, i, 303 formation of, ii, 66 in blood, i, 86 in relation to heat of body, i, 315 of bile, i, 275 of chyle, i, 301 situations where found, i, 35 uses of, i, 37 Feclmer's law, ii, 217 Female generative organs, ii, 234 Fenestra ovalis, ii, 182 rotunda, ii, 183 Ferments, i, 69, 231, 246, 266, 267. Fibres, i, 17 of Milller, ii, 203 Fibrils or filaments, i, 17 Fibrin, ii, 329, in blood, i, 65 use of, i, 99 in chyle, i, 302 formation of, i, 65 in lymph, i, 302 sources and properties of, ii, 329 vegetable, i, 216 Fibrinogen, i, 68, et seq. Fibrinoplastin, i, 68 Fibro-cartilage, i, 49 classification, i, 41 development, i, 41 uses, i, 41 white, i, 41 yellow, i, 40 Fibrous tissue, i, 31 white, i, 31 yellow, i, 32 360 INDEX. Fibrous development, i, 34 Field of vision, actual and ideal size of, ii, 220 Fifth nerve, ii, 139. See Cerebral Nerves. Fillet, ii, 106 Filtration, i, 325 Filum terminale, ii, 90 Fimbria3 of Fallopian tube, ii, 238 Fingers, development of, ii, 275 Fish, temperature of, i, 311 Fissures, of brain, ii, 120, et seq. of spinal cord, ii, 90 Fistula, gastric, experiments in cases of, i, 245, 246 Flesh, of animals, i, 214 Fluids, passage of, through membranes, i, 305 Fluoride of calcium, ii, 342 Focal distance, ii, 206 Foetus, blood of, i, 96 circulation in, ii, 286 communication with mother, ii, 268 faeces of, i, 277 membranes, ii, 261 office of bile in, ii, 261 pulse in, i, 122 Folds, head and tail, ii, 259 Follicles, Graafian, ii, 235. See Graafian Vesicles. Food, i, 212-215 albuminous, changes of, i, 247 amyloid, changes of, i, 231, 267, 285. of animals, i, 220 of carnivorous animals, i, 221 classification of, i, 213 composition of many, ii, 845, et seq. digestibility of articles of, i, 248 value dependent on, i, 223 digestion of, in intestines, i, 284, et seq. in stomach, i, 284, et seq. improper, i, 221, of man, i, 213 mixed, the best for man, i, 213 mixture of, necessary, i, 214 relation of, to carbonic acid, produced i,194 to heat of body, i, 311 to muscular action, ii, 44 relation of, to urea, i, 370 to urine, i, 357 phosphates in, i, 363 table of, i, 223 too little, i, 168 1 too much, i, 222 vegetable, contains nitrogenous prin- ciples, i, 216 Foot-pound, i, 124 Foot-ton, i, 124 Foramen ovale, i, 106 Forced movements, ii, 119 Form of bodies, how estimated, ii, 222 Formation of fat, ii, 66 Formic acid, ii, 339 Fornix, office of, ii, 134 Fourth cranial nerve, ii, 138 ventricle, ii, 106 Fovea centralis, ii, 215 Fundus of bladder, i, 354 Fundus of uterus, ii, 238 Fungiform papilke of tongue, ii, 171 G. Galactophorous ducts, i, 328 Gall-bladder, i, 272 functions, i, 273 passage of bile into and from, i, 276 structure, i, 272 Ganglia. See Nerve centres, of spinal nerves, ii, 94 of the sympathetic, ii, 151 action of, ii, 153, et fteq. as co-ordinators of involuntary move- ments, ii, 155 structure of, ii, 151 in heart, i, 125 in substance of organs, ii, 155 Ganglion, Gasserian, ii, 139 corpuscles, ii, 77 See Nerve-corpuscles. Gases, ii, 325 in bile, i, 275 in blood, i, 88 extraction of, i, 88 extraction from blood, i, 88 in stomach and intestines, i, 296 in urine, i, 365 Gastric glands, i, 242 Gastric juice, i, 245 acid in, i, 246 action of, on nitrogenous food, i, 247 on non-nitrogenous food, i, 2^8 on saccharine and amyloid princi- ples, i, 248 artificial, i, 247 preparation of, i, 247 characters of, i, 245 composition of, i, 246 digestive power of, i, 247 experiments with, i, 247 pepsin of, i, 246 quantity of, i, 246 secretion of, i, 245 how excited, i, 245 influence of nervous system on, i, 252 Gelatin, ii, 330 as food, i, 221 action of gastric juice on, i, 248 action of pancreatic juice on, i, 267 Gelatinous substances, ii, 330 Generation and development, i, 234 Generative organs of the female, i, 234 of the male, i, 246 Genito-urinary tract of mucous mem- brane, i, 321 INDEX. 361 Gerlach's network, ii, 92 Germinal area, ii, 255 epithelium, ii, 235 matter, i, 6. See Protoplasm. Germinal membrane, ii, 254 spot, ii, 2:57 development, ii, 238 vesicle, ii, 238 development of, ii, 238 disappearance of, ii, 253 Gill, i, 172 Gizzard, action of, i, 241 Gland, pineal, ii, 10 pituitary, ii, 10 prostate, ii, 246, 251 Gland-cells, agents of secretion, i, 326 changes in during secretion, i, 234, . 244, 264 relation to epithelium, i, 322 Gland-ducts, arrangement of, i, 326 contractions of, i, 326 Glands, aggregate, i, 323 Brunner's, i, 257 ceruminous, i, 339 Cowper's, ii, 246 ductless, ii, 1. See Vascular. Duverney's, ii, 239 of large intestine, i, 263 of Lieberkuhu, i, 256 lymphatic, i, 297. See Lymphatic Glands. mammary, i, 328 of Peyer, i, 258 salivary, i, 226 sebaceous, i, 339 secreting, i, 322. See Secreting Glands. of small intestines, i, 257 of stomach, i, 242 sudoriferous, i, 337 tubular, i, 323 vascular, ii, 1. See Vascular Glands. vulvo vaginal, ii, 239 Glandula Nabothi, ii, 239 Glisson's capsule, i, 268 Globulin, i, 86; ii, 328 distinctions from albumin, ii, 328 Globus major and minor, ii, 247 development, ii, 300 Glosso-pharyngeal nerve, i, 232; ii, 145 communications of, ii, 145 motor filaments in, ii, 146 a nerve of common sensation and of taste, ii, 146 Glottis, action of laryngeal muscles on, ii, 54 closed in vomiting, ii, 251 effect of division of pneumogastric nerves on, ii, 149 forms assumed by, ii, 55 narrowing of, proportioned to height of note, ii, 55 respiratory movements of, i, 188 Glucose, ii, 339 in liver, i, 282 test for, i, 230 Gluten in vegetables, i, 216 Glycerin extract, i; 247, 266 Glycin, ii, 331 Glycocholic acid, ii, 331 Glycogen, i, 282; ii, 339 characters, i, 282 destination, i, 282 preparation, i, 282 quantity formed, i, 281 variation with diet, i, 281 Glycosuria, i, 283 artificial production of, i, 283 Goll's column, ii, 96 Graafian vesicles, ii, 236 formation and development of, ii, 236, et seq. relation of ovum to, ii, 237 rupture of, changes following, ii, 240 Granular layers of retina, ii, 199 Grape-sugar, ii, 339. See Glucose. Grey matter of cerebellum, ii, 116 of cerebrum, ii, 124 of cruri cerebri, ii, 112 of medulla oblpngata, ii, 109 of pons Varolii, ii, 112 of spinal cord, ii, 92 Groove, primitive, ii, 256 Growth, i, 1 coincident with development, i, 3 of bone, i, 54 not peculiar to living beings, i, 2 Guanin, ii, 334 Gubernaculum testis, ii, 302 Gullet, i, 236 Gustatory nerves, ii, 169 cells, ii, 173 H. Habitual movements, ii, 87 Haematin, i, 89 hydrochlorate of, i, 94 Hsemadynamometer, i, 150 Haematochometer, i, 165 Haematoidin, i, 94 Haemin, i, 94 Haemacytometer, i 81 Haemoglobin, i, 90, et seq. action of gases on, i, 93 distribution, i, 95 estimation of, i, 95 spectrum, i, 92 Hair-follicles, i, 340 their secretion, i, 343 Hairs, i, 339 chemical composition of, ii, 330 structure of, i, 339 Hamulus, ii, 183 Hare-lip, ii, 274 Hassall, concentric corpuscles of, ii, 6 Haversian canals, i, 45 Hearing, anatomy of organ of, ii, 179 double, ii, 195 impaired by lesion of facial nerve, ii, 144 362 INDEX. Hearing, influence of external ear on, ii, 179 of labyrinth, ii, 191 of middle ear, ii, 187 physiology of, ii, 185 See Sound, Vibrations, etc. Heart, i, 103-129 action of, i, 111 accelerated, i, 127 effects of, i, 124 force of, i, 122 frequency of, i, 122 inhibited, i, 126 after removal, i, 126 rhythmic, i, 125 work of, i, 124 auricles of, i, 105, 111. See Auricles, capacity, i, 107 chambers, i, 104 chordae tendineae of, i, 110 columnse carneae of, i, 105, 110 course of blood in, i, 108 development, ii, 276 endocardium, i, 105 force, i, 146 frog's, i, 124 ganglia of, i, 125 impulse of, i, 119 tracing by cardiograph, i, 119, etseq. influence of pneumogastric nerve, i, 126 of sympathetic nerve, i, 127 investing sac, i, 103 muscular fibres of, i, 107 musculi papillares, i, 109, 113 nervous connections with other organs, i, 127 rhythm, i, 126 nervous system, influence on, i, 124 revolution of, i, 117 situation, i, 103 sounds of, i, 117 causes, i, 118 structure of, i, 107 tendinous cords of, i, 109 tubercle of Lower in, i, 105 valves, i, 109 arterial or semilunar, i, 110 function of, i, 114 auriculo-ventricular, i. 109 function of, i, 112 ventricles, their action, i, 112 capacity, i, 107 weight of, i, 107 work of, i, 124 Heat, animal, i, 309. See Temperature. influence of nervous system, i, 316 of various circumstances on, i, 309, et seq. losses by radiation, etc., i, 313 in relation to bile, i, 278 sources and modes of production, i, 312 developed in contraction of muscles, i 309, 312 perception of, ii, 166 Heat centres, i, 316 Heat-producing tissues, i, 312 Heat or rut, ii, 240 analogous to menstruation, ii, 240 Height, relation to respiratory capacity, i. 189 Helicotrema, ii, 183 Helix of ear, ii, 179 Hemipeptone, ii, 329 Hemispheres, Cerebral, ii, 120. See Cere- brum. Hepatic cells, i, 268 ducts, i, 271 veins, i, 270 characters of blood in, i, 87 vessels, arrangement of, i, 269, et seq. Herbivorous animals, perception of odors by, ii, 178 Hering's theory, ii, 224 Hermaphroditism, apparent, ii, 305 Hibernati n, state of thymus in, ii, 6 Hiccough, mechanism of, i, 200 Hip-joi t, pain in its diseases, ii, 84 Hippuric acid, i, 361, 372; ii, 332 Horse's blood, peculiar coagulation of, i, 66 Howship's lacunae, i, 44 Hunger, sensation of, i, 218 Hya ine cartilage, i, 38 Hydrogen, ii, 325 Hydrolytic ferments, i, 230; ii, 335 Hvmen, ii, 239 Hyperaesthesia, resuit of injury to spinal cord, ii, 99 Hypermetropia, ii, 212 Hypoblast, ii, 255 Hypoglossal nerve, ii, 150 Hypospadias, ii, 305 Hypoxanthin, ii, 334 I. Ideas, connection of, with cerebrum, ii, 128 Ileurn, i, 254 Jleo-caecai valve, i, 263 Illusions of touch, i, 165 Image, formation of, on retina, ii, 204 distinctness of, ii, 211 inversion of, ii, 218 Impulse of heart, i, 119 Income of body, ii, 64 compared with expenditure, ii, 64 Incus, function of, ii, 181 Indican, i, 362 Indigo, ii, 335 Indol, i, 267 Induction coil, ii, 27 current, ii, 27 Tnfundibulum, i, 180 Inhibitory influence - f pneumogastric nerve, i, 126 INDEX. 363 Inhibitory action of brain, ii, 102 nerves, ii, 80 action of, on heart,(i, 126 on blood-vessels, i, 155 on blood-vessels of salivary glands, i, 232, el seq. o.i gastric blood-vessels, i, 252, et seq. on intestinal movements, i, 289 on respiratory movements, i, 201 Inhibitory heat-centre, i, 316 Inorgani • matter, distinction from or- ganized, ii, 326, et seq. pri ciples, ii, 340 Inosite, ii, 339 Insalivatiou, i, 226 Inspiration, i, 183 e astic resistance overcome by, i, 191 extraordinary, i, 186 force employed in, i, 191 during dyspnoea, i, 209 influence or, on circulation, i, 205 mechanism of, i, 183 Intercellular substance, i, 17 Intercostal muscles, action in inspiration, i, 185, et seq. in expiration, i, 186 Interlobular veins, i, 271 Intestinal juice, i, 283 Intestines digestion in, i, 284, 286 development, ii, 295 fatty discharges from, i, 267 gases, i, 296 large, digestion in, i, 286 structure, i, 262 length in different animals, i, 284 ' movements, i, 289 small, changes of food in, i, 284 structure of, i, 254 Intonation, ii, 57, et seq. Intralobular veins, i, 271 Inversive \\ rments, i, 284 Involuntary muscles, acti« >ns < f , i, 251 s ructure of, ii, 14 Iris, ii, 205 action of, ii, 205, et seq. in adaptation to distances, ii, 209 blood-vessels, ii, 205 development of, ii, 293 influence of fifth nerve on, ii, 206 of third nerve, ii, 206 relation of, to optic nerve, ii, 206 Iron, ii, 342 Irradiation, ii, 214 Ivory of teeth, i, 57 J. Jacob's membrane, ii, 201 Jacobson's nerve, ii, 145 Jaw, interarticular cartilage, i, 226 Jejunum, i, 254 Juice, gastric, i, 245 Juice, pancreatic, i, 266 Jumping, ii, 43 K. Karyokinesis, i, 13 Katacrotic wave, i, 146 Katelectrotonus, ii, 47 Ker tin, i, 248 Key, ii, 27 Kidneys, their structure, i, 347 blood-vessels of, how distributed, i, 352 capillaries of, i, 343 development of, ii, 299 function of, i, 355. See Urine. Malpighian corpuscles of, i, 348 nerves, i, 353 tubules of, i, 348 Knee, pain of, in diseased hip, ii, 84 Krause's membrane, ii, 17 Kreatinin, i, 363 Kymograph, i, 150 tracings, i, 149, et seq. spring, i, 150 L. Labia externa and interna, ii, 239 Labyrinth of the ear, ii, 182, et seq. membranous, ii, 185 osseous, ii, 182 function of, ii, 191 Lachrymal apparatus, ii, 196 gland, ii, 196 Lactation, i, 329 Lacteals, i, 291 absorption by, i, 303 contain lymph in fasting, i, 301 origin of, i, 292 structure of, i, 293 in villi, i, 259 Lactic acid, ii, 340 in gastric fluid, i, 246 Lactiferous ducts, i, 329 Lactose, i, 215, 331 Lacunae of bone, i, 44 Lamellae of bone, i, 46 Lamina spiralis, ii, 183 use of, ii, 192 Laminae dorsales, ii, 256 viscerales or ventrales, ii, 261 Language, how produced, ii, 60 Large intestine, i, 261. See Intestine. Larynx, construction of, ii, 51 muscles of, ii, 53 nerves of, ii, 53 variations in, according to sex and age, ii, 58 ventricles of, ii, 60 vocal cords of, ii, 52 Latent period, ii, 32 Laughing, i, 201 Laxator tympani muscle, ii, 191 364 INDEX. Lead an accidental element, ii, 343 Leaping, i, 44 Lecithin, i, 275 Legumen identical with casein, i, 216 Lens, crystalline, ii, 204 Lenticular ganglion, relation of third nerve to, ii, 141 Leucic acid, ii, 340 Leucin, i, 266 Leucocytes, of blood, i, 79 amoeboid movements, i, 80 chyle, i, 301 lymph, i, 300 origin of, i, 99 Leucocythaemia, state of vascular glands in, ii, 3 Levers, different kinds of, ii, 39 Lieberkilhn's glands, in large intestines, i, 263 in small intestines, i, 256 Life, ii, 320 relation to other forces, ii, 306 simplest manifestations of, i, 7 Ligamentum nuchse, i, 33 Lightning, condition of blood after death by?i, 72 Lime, salts of, in human body, ii, 342 Lingual branch of flftn nerve, i, 231 Lips, influence of fifth nerve on move- ments of, ii, 141 Liquor amnii, ii, 263 Liquor sanguinis, or plasma, i, 63 lymph derived from, i, 302 still layer in capillaries, i, 158 Liver, i, 268 action of, on albuminous matters, i, 280 on saccharine matters, i, 281 blood-elaborating organ, i, 280 blood-making organ, i, 97 blood-vessels of, i, 271 capillaries of, i, 271 cells of, i, 269 circulation in, i, 269 development of, ii, 297 ducts of, i, 271 functions of, i, 273 in foetus, i, 277 glycogenic function of, i, 280 secretion of, i, 273. See Bile. structure of, i, 268 sugar formed by, i, 282, et seq. Locus niger, ii, 113 Loss of water, ii, 341 Ludwig's air pump, i, 89 Lungs, i, 178 blood supply, i, 182 capillaries of, i, 134 cells of, i, 179 changes of air in, i, 192 changes of blood in, i, 197 circulation in, i. 182 contraction of, i, 192 coverings of, i, 179 development of, ii, 298 Lungs, elasticity of, i, 187 lobes of, i, 179 lobules of, i, 179 lymphatics, i, 182 muscular tissue of, i, 192 nerves, i, 182 nutrition of, i, 182 position of, i, 173 structure of, i, 179 Luxus consumption, i, 222 Lymph, i, 301 compared with chyle, i, 301 with blood, i, 302 current of, i, 297 quantity formed, i, 302 source of, i, 303 Lymph-corpuscles, i, 301 in blood, i, 99 development of into red blood-corpus- cles, i, 99 origin of, i, 99 Lymph- hearts, structure and action of, i, 304 relation of to spinal cord, i, 305 Lymphatic glands, i, 297 Lymphatic vessels, i, 291 absorption by, i, 303 communication with serous cavities, i, 293 communication with blood-vessels, i, 293 contraction of, i, 297 course of fluid in, i, 297 distribution of, i, 291 origin of, i, 292 propulsion of lymph by, i, 297 structure of, i, 297, et seq. valves of, i, 297 Lymphoid or retiform tissue, i, 34. See Adenoid Tissue. M. Macula germinativa, ii, 237 Magnesium, ii, 342 Male sexual functions, ii, 246 Malleus, ii, 180 function of, ii, 188 Malpighian bodies or corpuscles of kid- ney, i, 349 capsules, i, 350 corpuscles of spleen, ii, 4 Maltose, i, 231; ii, 336 Mammalia, blood corpuscles of, i, 77 brain of, ii, 126 Mammary glands, i, 328 evolution, i, 330 involution, i, 330 lactation, i, 329 Mandibular arch, ii, 274 .Manganese, ii, 343 Manometer, i, 149 experiments on respiratory power with, i, 192 INDEX. 305 Marrow of bone, i, 43 Mastication, i, 225 fifth nerve supplies muscles of, i, 226 muscles of, i, 226 Mastoid cells, ii, 180 Matrix of cartilage, i, 38 of nails, i, 341 Mature corpuscles, origin of, i, 97 Meatus of ear, ii, 179 urinarius, opening of in female, ii, 239 Meckel's cartilage, ii, 274 Meconium, i, 277 Medulla of bone, i, 43 of hair, i, 340 Medulla oblougala, ii, 105 columns of, ii, 105 conduction of impressions, ii, 109 decussation of fibres, ii, 106 development, ii, 289 effects of injury and disease of, ii, 110 fibres of, how distributed, ii, 106 functions of, ii, 109, et seq. important to life, ii, 110 nerve centres in, ii, 110 pyramids of, anterior, ii, 106 posterior ii, 107 structure of, ii, 106 Medullary portion of kidney, i, 349 substance of lymphatic glands, i, 297 substance of nerve fibre, ii, 71 Melanin, ii, 335 Membrana decidua, ii, 242 granulosa, ii, 236 development of into corpus luteum, ii, 243 limitans externa, ii, 201 interna, ii, 200 Membrana propria or basement mem- brane, i, 322. See Basement Mem- brane, pupillaris, ii, 293 capsulo-pupillaris, ii, 293 tympani, ii, 180 office of, ii, 187 Membrane, blastodermic, ii, 254 Jacob's, ii, 201 of the brain and spinal cord, ii, 88 ossification in, i, 47 primary or basement, i, 319. See Base- ment membrane, vitelline. ii, 237 Membranes, mucous, i, 321. See Mucous membranes. Membranes, passage of fluids through, i, 296 secreting, i, 322 Membranes, serous, i, 319. See Serous membranes. Membranous labyrinth, ii, 185 Memory, relation to cerebral hemispheres, ii, 127, et seq. Menstrual discharge, composition of, ii, 242 Menstruation, ii, 240 coincident with discharge of ova, ii, 241 corpus luteum of, ii, 243 time of appearance and cessation, ii, 243 Mental derangement, ii, 128 exertion, effect on heat of body, i, 316 on phosphates in urine, i, 363 faculties, development of in proportion to brain, ii, 128 theory of special localization of, ii, 129, et seq field of vision, ii, 220 Mercurial air-pump, i, 89 Mercurial manometer, i, 148 Mercury, absorption of, i, 345 Mesencephalon, ii, 290 Mesenteric veins, blood of, i, 88 Mesoblast, ii, 255 Mesocephalon, ii, 112 Metalbumin, ii, 328 Metallic substances, absorption of by skin, i, 345 Metencephalon, ii, 290 Metbsemoglobin, i, 93 Mezzo-soprano voice, ii, 57 Micturition, i, 373 Milk, as food, i, 248 chemical composition, i, 331 secretion of, i, 329 Milk- curdling ferments, i, 267, 332 Milk-globules, i, 331 Milk-teeth, i, 62, et seq. Millon's re- agent, ii, 327 Mind, cerebral hemisphere the organs of, ii, 127 influence on action of heart, i, 124 influence on animal heat, i, 316 on digestion, i, 290 on hearing, ii, 194 on movements of intestines, i, 290 on secretion, i, 327 on secretion of saliva, i, 232 in vision, ii, 220, et seq. power of concentration on the senses, ii, 223 of exciting sensations, ii, 160 Mitral valve, i, 107 Modiolus, ii, 183 Molecules, or granules, i, 7 in blood, i, 75 in milk, i, 332 movement of in cells, i, 7 Molars, i, 61 Molecular base of chyle, i, 301 motion, i, 7 Monamides, ii, 331 Motion, causes and phenomena of. ii, 12 amoeboid, i, 7, 80; ii, 13 ciliary, i, 7; ii, 12 molecular, i, 7 muscular, ii, 24, et seq. of objects, how judged, ii, 223 power of, not essentially distinctive of animals, i, 3 366 INDEX. Motion, sensation of, ii, 161 Motor impulses, transmission of in cord, ii, 99 nerve-fibres, ii, 80 laws of action of, ii, 83 Motor linguae nerve, ii, 150 oculi, or third nerve, ii, 137 Motorial end-plates, ii, 76 Mouth, changes of food in, i, 224, et seq. Movements, of eyes, ii, 228 of intestines, i, 290 of voluntary muscles, ii, 39 produced by irritation of auditory nerve, ii, 195 Mucigen, i, 235 Mucin, i, 235 Mucous membrane, i, 321 basement membrane of, i, 322 capillaries of, i, 134 epithelium-cells of, i, 322. See Epithe- lium. digestive tract, i, 321 gastro-pulmonary tract, i, 321 genfto- urinary tract, i, 321 gland-cells of, i, 322 of intestines, i, 254, 261 of stomach, i, 241 of tongue, ii, 169 of uterus, changes of in pregnancy, ii, 265 respiratory tract, i, 321 Muco-salivary glands, ii, 229 Mucus, i, 322 in bile, i, 275 in urine, i, 362 of mouth, mixed with saliva, i, 229 Muller's fibres, ii, 203 Murexide, i, 361; ii, 334 Muscles, activity, ii, 24 changes in, by exercise, ii, 34 chemical constitution, ii, 21, 35 clot, ii, 21 contractility, ii, 24 contraction, mode of, ii, 29 corpuscles, ii, 18 curves, ii, 32, et seq. ; ii, 36 development, ii, 20 disc of Hensen, ii, 18 effect of pressure of, on veins, i, 162 elasticity, ii, 20 electric currents in, ii, 22, 35 fatigue, ii, 33 curves, ii, 33 growth, ii, 20 heart, ii, 19 heat developed in contraction of, ii, 34 involuntary, ii, 14 actions of, ii, 36, 44 Krause's membrane, ii, 17 muscle-rods, ii, 19 natural currents, ii, 22. nerves of, ii, 20 Muscles, non-striated, ii, 14 nutrition of, ii, 19 physiology of, ii, 20 plain, ii, 14 plasma, ii, 21 reaction, ii, 21 response to stimuli, ii, 36 rest of, ii, 20 rigor, ii, 37 sarcolemma, ii, 16 sensibility of, ii, 25 serum, ii, 22 shape, changes in, ii, 35 sound developed in contraction of, ii, 34 source of action of, ii, 44 stimuli, ii, 25 striated, ii, 15 str cture, ii, 16, et seq. tetanus, ii, 32 unstriped, ii, 14 voluntary, ii, 15 actions of, ii, 39 blood-vessels and nerves of, ii, 19 work of, ii, 33 Muscular action, ii, 36 conditions of, ii, 36 force, ii, 33 source, ii, 44 Muscular irritability, ii, 36 duration of, after death, ii, 37 Muscular motion, ii, 14 sense, ii, 164 cerebellum the organ of, ii, 119 tone, ii, 104 Muscularis mucosae, i, 237, 242, 255 Museuli papillares, i, 110 Musculo-cutaneous plate, ii, 272 Musical sounds, ii, 193 Myograph, ii. 30 pendulum, ii, 30 Myopia, or short-sight, ii, 212 Myosin, ii, 21 N. Nabothi glandulae, ii, 239 Nails, i, 341 growth of, i, 341 structure of, i, 341 Naphthilamine, i, 267 Nasal cavities in relation to smell, ii, 176, et seq. Native albumins, ii, 327 Natural organic compounds, ii, 326 classification of, ii, 326 Nerve-centre, ii, 74. -See Cer bellum, Cerebrum, etc. ano-spinal, ii, 103 automatic action, ii, 88 car io-inhibitory, i, 127; ii, 111 cilio-spinal, ii, 109 conduction in, ii, 83 deglutition, i, 240; ii, 111 INDEX 367 Nerve-centre, diabetic, ii, 111 diffusion in, ii, 84 functions of, ii, 83 genito-urinary, ii,.103 m tstication, i, 226; ii, 111 radiation in, ii, 85 reflexion in, ii, 85 laws and conditions of, ii, 85 respiratory, i, 202; ii, 110 secretion of saliva, i, 232; ii, 111 transference of impressions, ii, 84 vaso-motor, i, 154; ii, 111 vesico-spinui, ii, 103 Nerve-corpuscles, caudate or stellate, ii, 78 polar, ii, 78 Nerves, ii, 68 accelerator, i, 128 action of stimuli on, ii, 46 currents of, ii, 45 affe ent, ii, 80 axis-cylinder of, ii, 70 centrifugal, ii, 80 centripetal, ii, 80 cen-bro-spinal, ii, 68 classification, ii, 70, 80 conduction by, ii, 80, et seq. rate of, ii, 81 continuity, ii, 73 course of, ii, 73 cranial, ii, 136. See Cerebral Nerves, depressor, i, 154 efferent, ii, 80 electrical currents of, ii, 45 functions of, ii, 78 effect of chemical stimuli on, ii, 46 of mechanical irritation, ii, 46 of temperature, ii, 46 funiculi of, ii, 69 grey, ii, 71 impressions on, referred to periphery, ii, 81 inhibitory, ii, 80. See Inhibitory Action. intercentral, ii, 80 laws of conduction, ii, 81 of motor nerves, ii, 83 of sensory nerves, ii, 81 medullary sheath, ii, 69 medullated, ii, 69 motor, ii, 80 laws of action in, ii, 82 natural currents, ii, 45 neurilemma, ii, 69 nodes of Ranvier, ii, 71 non-medullated, ii, 71 nuclei, ii, 70 of special sense, ii, 82 plexuses of, ii, 73 primitive nerve sheath, ii, 70 sensory, ii, 80 laws of action in, ii, 81 size of, ii, 80 spinal, ii, 94, 96, 150, et seq. See Spinal Nerves. Nerves, stimuli, ii, 46 structure, ii, 69 sympathetic, ii, 68, 151. See Sympa- thetic Nerve, terminations of, ii, 76 central, ii, 77 in cells, ii, 76 in end-bulbs, ii, 74 in motorial end-plates, ii, 76 in networks or plexuse-, ii, 76 in Pacinian coipuscles, ii, 74 in touc-.i. -corpuscles, ii, 75 trophic, ii, 142, 157 ulnar, effect of compression of, ii, 81 varieties of, ii, 69 vaso-constrictor, i, 156 vaso-dilator, i, 156 vaso-inhibitory, i, 156 vaso-motor, i, 156 white, ii, 46 Nervi nervo um, ii, 82 Nervi vasorum, i, 132 Nervous force, velocity of, ii, 80 Nervous system, ii, 68 cerebro spinal, ii, 68 development, ii, 287 elementary structure of, ii, 68 influence of on animal heat, i, 316 on arteries, i, 154, et seq. on contractility, ii, 24 on contraction of blood-vessels, i, 152 on erection, i, 169 on gastric digestion, i, 252 on the heart's action, i, 124 on movements of intestines, i, 289 of stomach, i, 252 on nutrition, ii, 157 on respiration, i, 201 on secretion, i, 231 on sphincter ani, i, 288 sympathetic, ii, 151. Network, intracellular, i, 10 nuclear, i, 11 Neurilemma, ii, 69 Neurin, ii, 332 Neuroglia, i, 34 Nipple, an erectile organ, i, 168 structure of, i, 329 Nitrogen, in blood, i, 96 influence of, in decomposition, ii, 326 in relation to food, i, 213, et seq. in respiration, i, 195 Nitrogenous compounds, i, 213 non-nitrogenous compounds, i, 213 Nitrogenous equilibrium, ii, 66 Nitrogenous food, i, 214 in relation to muscular work, i, 370, et seq. in relation to urea, i, 370 to uric acid, i, 372 Nodes of Ranvier, ii, 71 Noises in ears, ii, 83 368 INDEX. Non-azotized or Non-nitrogenous food, i, 213 organic principles, ii, 335 Nose, ii, 175. See Smell. irritation referred to, ii, 85 Notochord, ii, 257 Nucleus, i, 10 position, i, 11 staining of, i, 11 Nutrition, ii, 63 general nature, of nervous system, ii, 155 of trophic nerves, ii, 157 in paralyzed parts, ii, 157 of cells, i, 9 Nymphse, ii, 239 O. Ocular cleft, ii, 292 spectrum, ii, 225, et seq. Odontoblasts, i, 59 Odors, causes of, ii, 77, et seq different kinds of, ii, 178 perception of, ii, 178 varies in different classes, ii, 178 relation to taste, ii, 174 (Esophagus, i, 236 Oil, absorption of, i, 303 Oleaginous principles, digestion of, i, 331 Oleic acid, ii, 339 Olfactory cells, ii, 176 nerve,' ii, 175 subjective sensations of, ii, 179 Olivary body, ii, 106 fasciculus, ii, 106 Omphalo-mesenteric, arteries, ii, 281 duct, ii, 270 veins, ii, 281 Oncograph, i, 367 Oncometer, i, 366 Ophthalmic ganglion, relation of third nerve, ii, 137 Ophthalmoscope, ii, 217 Optic, lobes, corpora quadrigemina, homo- logues of, ii, 114 functions of, ii, 114 nerve, decussation of, ii, 231 point of entrance insensible to light, ii, 215 thalamus, function of, ii, 115 vesicle, primary, ii, 291 secondary, ii, 292 Optical angle, ii, 220 apparatus of eye, ii, 203 Ora serrata of retina, ii, 199 Orang, brain of, ii, 127 Organ of Corti, ii, 184 Organic compounds in body, ii, 325 instability of, ii, 326 Organs, plurality of cerebral, ii, 129 Organs of sense,* development of, ii, 291 Osmosis, i, 306 Os orbiculare, ii, 181 Os uteri, ii, 239 Osseous labyrinth, ii, 182 Ossicles of the ear, ii, 181 office of, ii, 188 Ossicula auditis, ii, 181 Ossification, i, 47, et seq. Osteoblasts, i, 48 Osteoclasts, i, 51 Otoconia or Otoliths, ii, 185 use of, ii, 191 Ovaries, ii, 235 enlargement of, at puberty, ii, 238 Graafian vesicles in, ii, 236 Ovisacs, ii, 236 Ovum, ii, 236 action of seminal fluid on, ii, 253 changes of, in ovary, ii, 238 previous to formation of embryo, ii, 253 subsequent to cleavage, ii, 255, et seq. in uterus, ii, 254, et seq. cleaving of yelk, ii, 253 connection of with uterus, ii, 235 discharge of from ovary, ii, 239 formation of, ii, 238 germinal membrane of, ii, 254 germinal vesicle and spot of, ii, 237 impregnation of, ii, 253 structure of, ii, 236 unimpregnated, ii, 236 Oviduct, or Fallopian tube, ii, 238 Oxalic acid, i, 365 Oxalic acid in urine, i, 365 Oxygen, ii, 325 in blood, i, 89 consumed in breathing, i, 195 effects of on color of blood, i, 88 proportion of to carbonic acid, i, 192, et seq. Oxyhasmoglobin, i, 92 spectrum, i, 92 P. Pacinian bodies or corpuscles, ii, 74 Palate and uvula in relation to voice, ii. 59 cleft, ii, 274 Palmitin, ii, 338 Pancreas, i, 264 development of, ii, 297 functions of, i, 264 structure, i, 264 Pancreatic fluid, i, 265 Pancreatin, ii, 337 Papilla foliata, ii, 173 Papillae of the kidney, i, 348 of skin, distribution of, i, 335 INDEX. 369 Papillffi, end-bulbs in, i, 337 epithelium of, i, 335 nerve-fibres in, i, 336 supply of blood to, i, 336 touch corpuscles in, i, 337 of teeth, i, 59 of tongue, ii, 169, et seq. circumvallate or calyciform, ii, 176 conical or filiform, ii, 171 fungiform, ii, 171 Paraglobulin, i, 70 Paralbumin, ii, 328 Par vagurn, ii, 146. See Pneumogastric nerve. Paralyzed parts, nutrition of, ii, 157 pain in, ii, 82 limbs, temperature of, i, 316 preservation of sensibility in, ii, 99 Paralysis, cross, ii, 99 Parapeptone, i, 248 Paraplegia, delivery in, ii, 103 reflex movements in, ii, 103 state of intestines in, i, 290 Parotid gland, saliva from, i, 226, 234 nerves influencing secretion by, i, 234 Pause in heart's action, i, 117 respiratory, i, 188 Pecten of birds, ii, 292 Peduncles, of the cerebellum, ii, 118 of the cerebrum, or Crura Cerebri, ii, 113 Pelvis of the kidney, i, 348 Penis, corpus cavernosum of, i, 168 development of, ii, 305 _ erection of, explained, i, 169 reflex action in, ii, 103 Pepsin, i, 244 Pepsinogen, i, 244 Peptic cells, i, 242 Peptones, i, 247, et seq. Perceptions of sensations by cerebral hemispheres, ii, 128 Pericardium, i, 103 Perichondrium, i, 49 Perilymph, or fluid of labyrinth of ear, ii, 182 use of, ii, 191 Perimysium, ii, 15 Perineurium, ii, 69 Periosteum, i, 43 Peristaltic movements of intestines, i, 289 of stomach, i, 249 Perivascular lymphatic sheaths, i, 139 Permanent teeth, i, 62. See Teeth. Perspiration, cutaneous, i, 343 insensible and sensible, i, 343 ordinary constituents of, i, 343 Peyer's glands, i, 258 patches, i, 258 resemblance to vascular glands, ii, 1 structure of, i, 259 VOL. II.— 24. Pfluger's law, ii, 48 Phakoscope, ii, 208 Pharynx, i, 236 action of in swallowing, i, 239 influence of glosso-pharyngeal nerve on, i, 239 of pneumogastric nerve on, i. 239 Phenol, ii, 340 Phosphates, ii, 342 Phosphates in tissues, ii, 343 Phosphorus in the human body, ii, 342 Pia mater, circulation in, i, 167 Pigment, i, 21 of hair, i, 339 of retina, ii, 202 of skin, i, 334 Pigment cells, forms of, i, 21 movements of granules in, i, 21 Pineal gland, ii, 10 Pinna of ear, ii, 179 Pituitary body, ii, 10 development, ii, 272 Placenta, ii, 265, et seq. foetal and maternal, ii, 265 Plants, distinctions from animals, i, 3. See also Vegetables. Plasma of blood, i, 65 salts of, i, 85 Plasmine, i, 68 composition, i, 69 nature of, i, 68 Plethysmograph, i, 153 Pleura, i, 178 Plexus, terminal, ii, 76 of spinal nerves, relation to cord, ii, 73 myentericus, i, 255 Auerbach's, i, 255 Meissner's, i, 255 Pneumogastric nerve, ii, 146 distribution of, ii, 146 influence on action of heart, i, 126 deglutition, i, 239 gastric digestion, i, 252 larynx, i, 239 lungs, i, 202 oesophagus, ii, 147 pharynx, ii, 146 respiration, i, 202 secretion of gastric fluid, i, 252 sensation of hunger, i, 218 stomach, i, 252 mixed function of, ii, 146 origin from medulla oblongata, ii, 108 Poisoned wounds, absorption from, i, 318 Pons Varolii, its structure, ii, 112 functions, ii, 112 Portal, blood, characters of, i, 87 canals, i, 271 circulation, i, 269 function of spleen with regard to, ii,4 veins, arrangement of, i, 271, et seq. 370 INDEX. Portio dura, of seventh nerve, ii, 344 mollis, of seventh nerve, ii, 185 Post mortem digestion, i, 253 Potassium, ii, 342 sulphocyanate, i, 229 Pregnancy, absence of menstruation dur- ing, ii, 243 corpus luteum of, ii, 245 influence on blood, i, 86 Presbyopia, or long-sight, ii, 214 Primitive groove, ii, 256 Primitive nerve-sheath, or Schwann's sheath, ii, 71 Processus gracilis, ii, 181 Propionic acid, ii, 339 Prosencephalon, ii, 289 Prostate gland, ii, 246 Proteids, i, 247 chemical properties, ii, 327, et seg. physical properties, ii, 327 tests for, ii, 327 varieties of, ii, 328 Proteolytic ferments, i, 248 Protoplasm, i, 6 chemical characters, i, 6 movement, i, 6 nutrition, i, 9 physical characters, i, 6 physiological characters, i, 6 reproduction, i, 11 transformation of, i, 14 Proto-vertebrse, ii, 258 Pseudoscope, ii, 233 Ptyalin, i, 229 action of, i, 229 Puberty, changes at period of, ii, 243 indicated by menstruation, ii, 243 Pulmonary artery, valves of, i, 110 capillaries, i, 134 circulation, i, 182 Pulse, arterial, i, 142 cause of, i, 142 dicrotus, i, 146 difference of time in different parts, i, 143 frequency of, i, 122 influence of age on, i, 122 of food, posture, etc., i, 122 relation of to respiration, i, 123 sphygmographic tracings, i, 146, et seq. variations, i, 146, et seq. in capillaries, i, 159 Purkinje's figures, ii, 215 Pylorus, structure of, i, 242 action of, i, 250 Pyramidal portion of kidney, i, 348 Pyramids of medulla oblongata, ii, 106 Quadrupeds, retinas of, ii, 230 Quantity of air breathed, i, 189 Quantity of blood, i, 63 saliva, i, 229 R. Racemose glands, ii, 323 Radiation of impressions, ii, 85 Rectum, ii, 261 Recurrent sensibility, ii, 96 Reflex actions, ii, 85 acquired, ii, 87 augmentation, ii, 88 classification, ii, 86 compound, ii, 87 conditions necessary to, ii, 85 in disease, ii, 102 examples of, ii, 88 exci to-motor and sensori-motor, ii, 85 inhibition of, ii, 88, 101 irregular in disease, ii, 102 after separation of cord from brain ii, 100 laws of, i, 373 morbid, ii, 102 of medulla oblongata, ii, 109, et seq. of spinal cord, ii, 100 purposive in health, ii, 86 relation between a stimulus and, ii, 86 secondary, ii, 87 simple, ii, 87 Refracting media of eye, ii, 204 Refraction, laws of, ii, 204 Regions of body, See Frontispiece. Registering apparatus, cardiograph, ii, 119 kymograph, i, 150 sphygmograph, i, 143 Relations between secretions, i, 327 Reptiles, blood-corpuscles, i, 76 Drain, ii, 125 Reserve air, i, 189 Residual air, i, 189 Respiration, i, 172 abdominal type, i, 186 changes of air, i, 194 of blood, i, 197 costal type, i, 186 force, i, 191 frequency, i, 190 influence of nervous system, i, 201 mechanism, i, 183, et seq. movements, i, 184. See Respiratory Movements. nitrogen in relation to, i, 195 organic matter excreted, i, 196 quantity of air changed, i, 189 relation to the pulse, i, 123, 213 suspension and arrest, i, 209 types of, i, 186 Respiratory capacity of chest, i, 189 cells, i, 180 functions of skin, i, 345 INDEX. 371 Respiratory movements, i, 184 axes of rotation, i, 184, etseq. of air tubes, i, 175 of glottis, i, 188 influence on amount of carbonic acid, i, 193 on arterial tension, i, 213 rate, i, 190 relation to pulse rate, i, 190 size of animal, i, 190 relation to will, i, 201 various mechanism, i, 198 muscles, i, 183, et seq. daily work, i, 189 power of, i, 191 nerve-centre, i, 202 rhythm, i, 188 sounds, i, 188 Restiform bodies, ii, 107 Rete mucosum, i, 333 testis, ii, 247 Retif orm or adenoid, or lymphoid tissue, i 34 Retina,' ii, 199 blind-spot, ii, 215 blood-vessels, ii, 203 duration of impressions on, ii, 216 of after-sensations, ii, 216 effect of pressure on, ii, 229 excitation of, ii, 215 focal distance, ii, 206 fovea centralis, ii, 199, 215 functions of, ii, 215 image on, how formed distinctly, ii, 203 inversion of, how corrected, ii, 218 insensible at entrance of optic nerve, ii, 215 layers, ii, 199 in quadrupeds, ii, 230 reciprocal action of parts of, ii, 226 in relation to direction of vision, ii, 222 to motion of bodies, ii, 222 to single vision, ii, 229 to size of field of vision, ii, 220 reflection of light from, ii, 217 structure of, ii, 199 vessels, ii, 203 visual purple, ii, 218 Rheoscopic frog, ii, 46 Rhinencephalon, ii, 289 Ribs, axes of rotation, i, 184, et seq. Rigor mortis, ii, 37 affects all classes of muscles, ii, 37 phenomena and causes of, ii, 38 Rima glottidis, movements of in respira- tion, i, 188 Ritter's tetanus, ii, 49 Rods of Corti, ii, 184 use of, ii, 192 Rouleaux, formation of in telood, i, 76 Ruminants stomach of, i, 240 Rumination, i, 240 Running, mechanism of, ii, 44 Rut or heat, ii, 240 S. Saccharine principles of food, digestion of, i, 284 Sacculus, ii, 185 Saliva, i, 229 composition, i, 229 process of secretion, i, 235 quantity, i, 230 rate of secretion, i, 230 uses, i, 230 Salivary glands, i, 226 development of, ii, 297 influence of nervous system, i, 231 mixed, i, 229 nerves, i, 229 secretion, i, 228 structure, i, 226 true, i, 227 varieties, i, 227 Sarcode, i, 5. See Protoplasm. Sarcolemma, ii, 16 Sarcosin, ii, 332 Sarcous elements, ii, 17 Scala media, ii, 183 tympani, ii, 183 vestibuli, ii, 183 Sclerotic, ii, 197 blood-vessels, ii, 203 Scurvy from want of vegetables, i, 217 Sebaceous glands, i, 337 their secretion, i, 343 Sebacic acid, ii, 340 Secreting glands, i, 322 aggregated, ii, 323 convoluted tubular, ii, 323 tubular or simple, ii, 323 Secreting membranes, i, 319. See Mu- cous and Serous membranes. Secretion, i, 318 apparatus necessary for, i, 318, et seq. changes in gland- cells during, i, 326 " " pancreas, i, 265 " " stomach, i, 244. 1 " " salivary glands, i, 234 circumstances influencing, i, 326 discharge of, i, 326 general nature of, i, 318 influence of nervous system, i, 327 process of physical and chemical, i, 324, 325 serous, i, 320 synovial, i, 321 Segmentation of cells, ii, 252 ovum, ii, 252 Semen, ii, 251 composition of, ii, 251 emission of, a reflex act, ii, 103 filaments or spermatozoa, ii, 247 purpose of, ii, 251 tubes, ii, 247 372 INDEX. Semicircular canals of ear, ii, 182 development of, ii, 294, et seq. use of, ii, 191 Semilunar valves, i, 106 functions of, i, 114 Semilunes of Heidenhain, i, 228 Sensation, ii, 158 color, ii, 223 common, ii, 158 conditions necessary to, ii, 159 excited by mind, ii, 159 by internal causes, ii, 160 of motion, ii, 161 nerves of, ii, 136, et seq. impressions on referred to periphery, ii, 79 laws of action, ii, 80 objective, ii, 160 of pain, ii, 162 of pressure, ii, 165 special, ii, 159 nerves of, ii, 137 stimuli of, ii, 82 of special, ii, 82 subjective, ii, 83, 168. See also Special Senses, ii, 160 tactile, ii, 166 temperature, ii, 168 tickling, ii, 162 touch, ii, 162 transference and radiation of, ii, 83, et seq. of weight, ii, 166 Sense, special, ii, 158 of hearing, ii, 179. See Hearing, Sound, of sight, ii, 196. See Vision, of smell, ii, 175. See Smell, of taste, ii, 168. See Taste, of touch, ii, 162. See Touch, muscular, ii, 165 organs of, development of, ii, 291 Sensory impressions, conduction of, ii,81 by spinal cord, ii, 97 nerves, ii, 81 Septum between auricles, formation of, ii, 280 between ventricles, formation of, ii, 280 Serous fluid, i, 320 Serous membranes, i, 319 arrangement of, i, 319 communication of lymphatics with, i, 294 epithelium, i, 319 fluid secreted by, i, 320 functions, i, 320 lining joints, etc., i, 320 visceral cavities, i, 320 stomata, i, 294 structure of, i, 319 Serum, of blood, i, 93 separation of, i, 66, 93 Seventh cerebral nerve, auditory portion, ii, 185 I Seventh cerebral nerve, facial portion, ii, 144 Sex, influence on blood, i, 87 influence on production of carbonic acid, i, 193 relation to respiratory movements, i, 186 Sexual organs and functions in the fe- male, ii, 234 in the male, ii, 246 Sexual passion, connection of with cere- bellum, ii, 119 Sighing, mechanism of, ii, 199 Sight, ii, 196. See Vision. Silica, parts in which found, ii, 342 Silicon, ii, 342 Singing, mechanism of, i, 201; ii, 56, et seq. Single vision, conditions of, ii, 229 Sinus pocularis, ii, 304 urogenitalis, ii, 304 Sinuses of dura mater, i, 167 Sixth cerebral nerve, ii, 143 Size of field of vision, ii, 220 Skeleton. See Frontispiece. Skin, i, 333 absorption by, i, 345 of metallic substances, i, 345 of water, i, 346 cutis vera of, i, 335 epidermis of, i, 333 evaporation from, i, 313 excretion by, i, 344 exhalation of carbonic acid from, i, 344 of watery vapor from, i, 344 functions of, i, 342 respiratory, i, 345 papillae of, i, 335 perspiration of, i, 343 rete mucosum of, i, 334 sebaceous glands of, i, 336 structure of, i, 333 sudoriparous glands of, i, 337 Sleep, ii, 135 ; Smell, sense of, ii, 175 conditions of, ii, 175 delicacy, ii, 177 different kinds of odors, ii, 178 impaired by lesion of facial nerve, ii, -L^tTC impaired by lesion of fifth nerve, ii, 141 internal excitants of, ii, 179 limited to olfactory region, i, 176 relation to common sensibility, ii, 178 structure of organ of, ii, 176 subjective sensations, ii, 179 varies in different animals, ii, 178 Sneezing, caused by sun's light, ii, 84 mechanism of, i, 200 I Sniffing, mechanism of, i, 201 smell, aided by, ii, 176 Sobbing, i, 201 Sodium, ii, 342 i in human body, ii, 342 INDEX. ' 373 Sodium, salts of in blood, i, 85 Solitary glands, i, 25s Soluble ferments, ii, :>:>5 Somatopleure, ii, 259 Somnambulism, ii, 87 Sonorous vibrations, how communicated in ear, ii, 186, et .vy. in air and in water, ii, ISO. A'Vr Sound. Soprano voice, ii, 57 Sound, binaural sensations, ii, 195 conduction of by ear, ii, 186 by external ear, ii, 186 by internal ear, ii, 191 movements and sensations produced by, ii, 196 perception, of direction of, ii, 194 of distance of, ii, 194 permanence of sensation of, ii, 195 produced by contraction of muscle, ii, 35 production of, ii, 193 subjective, ii, 195 Source of water, ii, 341 Spasms, reflex acts, ii, 103 Speaking, ii, 60 mechanism of, i, 200; ii, 60 Special senses, ii, 159 Spectrum-analysis of blood, i, 92 Spectrum or ocular after-sensation, ii, 225 Speech, ii, 60 function of tongue in, ii, 62 influence of medulla oblongata on, ii, 111 Spermatozoa, development of, ii, 247 form and structure of, ii, 248 function of, ii, 251 motion of, ii, 251 Spherical aberration, ii. 212 correction of, ii, 213 Spheroidal epithelium, i, 23 Sphincter ani, i, 263, 288 external, i, 288 internal, i, 263 influence of spinal cord on, i, 288 Sphygmograph, i, 143 tracings, i, 145, et seq. Spinal accessory nerve, ii, 149 Spinal cord, ii, 90 automatism, i, 105 canal of, ii, 90 centres in, ii, 103 a collection of nervous centres, ii, 103 columns of, ii, 91 commissures of, ii, 91 conduction of impressions by, ii, 97, et seq. course of fibres in, ii, 95 decussation of sensory impressions in, ii, 99 effects of injuries of, on conduction of impressions, ii, 99, et seq. on nutrition, ii, 157 fissures and furrows of, ii, 90 Signal cord, functions of, ii, 97 of columns, ii, 99 influence on lymph- hearts, ii, 103 on sphincter ani, ii, 103 on tone, ii, 104 morbid irritability of, ii, 103 nerves of, ii, 93 reflex action of, ii, 100 in disease, ii, 102 inhibition of, ii, 101 size of different parts, ii, 91 special centres in, ii, 103 structure of, ii, 90, et seq. transference, ii, 100 weight, ii, 126 relative, ii, 126 white matter, ii, 91 grey matter, ii, 92 Spinal nerves, ii, 94, 150 origin of, ii, 94 physiology of, ii, 96 Spiral canal of cochlea, ii, 182 lamina of cochlea, ii, 182 function of, ii, 188 Spirometer, i, 189 Splanchnic nerve, i, 154, 252 Splanchnopleure, ii, 259 Spleen, ii, 1 functions, ii, 4 hilus of, ii, 1 influence of nervous system, ii, 5 Malpighian corpuscles of, ii, 3 pulp, ii, 2 stroma of, ii, 2 structure of, ii, 2 trabeculae of, ii, 2 Splenic vein, blood of, i, 88 Spot, germinal, ii, 237 Squamous epithelium, i, 20 Stammering, ii, 62 Stapedius muscle, ii, 181 function of, ii, 191 Stapes, ii, 181 Starch, i, 231 digestion of in small intestine, i, 267, 285 in mouth, i, 231 in stomach, i, 248, 285 Starvation, i, 219 appearances after death, i, 220 effect on temperature, i, 220 loss of weight in, i, 219 period of death in, i, 220 symptoms, i, 220 Bteapam, i, 267 Stearic acid, ii, 339 Stearin, ii, 338 Stercorin, i, 278 allied to cholesterin, i, 278 Stereoscope, ii, ~~~ St. Martin, Alexis, case of, ii, 245 Stomach, i, 240 blood- vessels, i, 244 development, ii, 295, et seq. digestion in, i, 245 374 INDEX. Stomach, circumstances favoring diges- tion in, i, 248 products of, i, 247 digestion after death, i, 253 glands, i, 242 lymphatics, i, 244 movements, i, 249 influence of nervous system, i, 252 mucous membrane, i, 241 muscular coat, i, 241 nerves, i, 248 ruminant, i, 240 secretion of, i, 245. See Gastric fluid. structure, i, 241 temperature, i, 245 Stomata, i, 160, 295 Stratum intermedium (Hannover), i, 60 Striated muscle, ii, 15 Stromtlhr, i, 164 Structural basis of human body, i, 5 Stumps, sensations in, ii, 82 Succinic acid, ii, 340 Succus entericus, i, 283 functions of, i, 283 Sucking, mechanism of, i, 201 Sudoriferous glands, i, 337 their distribution, i, 338 number of, i, 338 their secretion, i, 343 Suffocation, i, 208, et seg. Sugar, ii, 339 as food, experiments with, i,-221 digestion of, i, 284, 286 formation of in liver, i, 280, 282 Sulphates, ii, 342 in tissues, ii, 342 in urine, i, 163 Sulphuretted hydrogen, ii, 341 Suprarenal capsules, ii, 8 development of, ii, 302 disease of, relation to discoloration of skin, ii, 10 Structure, ii, 8 Sun, a source of energy, ii, 310 Swallowing, i, 238 nerves engaged, i, 239 Sweat, i, 343 Sympathetic nervous system, ii, 151 character of movements executed through, ii, 154 conduction of impressions by, ii, 153 diagrammatic view, ii, 152 distribution, ii, 151 divisions of, ii, 68 fibres, differences of from cerebro- spinal fibres, ii, 72 mixture with cerebro-spinal fibres, ii, 151 functions, ii, 153 ganglia of, ii, 154 action of, ii, 154, et seq. co-ordination of movements by, ii, 155 structure, ii, 151 in substance of organs, ii, 155 Sympathetic nervous system, influence on animal heat of, ii, 316 blood-vessels, i, 153, et seq. heart, i, 128 intestines, i, 289 involuntary motion, ii, 154, et seq. salivary glands, i, 231, et seq. secretion, i, 231 stomach, i, 252 structure of, ii, 151 Synovial fluid, secretion of, i, 321 membranes, i, 321* Syntonin, i, 248; ii, 328 Systemic circulation, i, 101. See Circu- lation. vessels, i, 101 Systole of heart, i, 119 T. Taste, ii, 168 after-tastes, ii, 174 conditions for perception of, ii, 168 connection with smell, ii, 174 impaired by injury of facial nerve, ii, 145 of fifth nerve, ii, 142 nerves of, ii, 142, 146 seat of, ii, 168 subjective sensations, ii, 175 varieties, ii, 174 Taste-goblets, ii, 173 Taurin, ii, 332 Taurocholic acid, i, 274 Teeth, i, 55 development, ii, 58 eruption, times of, i, 62 structure of, i, 55, et seq. temporary and permanent, i, 61, et seq. Temperament, influence on blood, i. 87 Temperature, i, 309 average of body, i, 309 changes of, effects of, i, 310, et seq. circumstances modifying, i, 312 of cold-blooded and warm-blooded ani- mals, i, 311 in disease, i, 311 influence on amount of carbonic acid produced, i, 194 loss of, i, 313 maintenance of, i, 313 of Mammalia, Birds, etc., i, 311 of paralyzed parts, i, 316 regulation of, i, 313 of respired air, i, 196 sensation of variation of, ii, 166. See Heat. Tendons, structure of, i, 32 cells of, i, 32 Tenor voice, ii, 57 Tension, arterial, i, 148 Tension of gases in lungs, i, 197 Tensor tympani muscle, ii, 181 office of, ii, 190 INDEX. 375 Tessellated epithelium, i, 19 Testicle, ii, 246 development, ii, 300 descent of, ii, 302 structure of, ii, 246, el seq. Tetanus, ii, 32 Thalamencephalon, ii, 289 Thalami optici, functions of, ii, 115 Thermogenic nerves and nerve-centres, i, 316 Thirst, i, 219 allayed by cutaneous absorption, i, 345 Thoracic duct, i, 291 contents, i, 302 Thymus gland, ii, 5 function of, ii, 6 structure, ii, 5 Thyro-arytenoid muscles, ii, 58 Thyroid cartilase, structure and connec- tions of, ii, 52 Thyroid-gland, ii, 7 function of, ii, 8 structure, ii, 7 Timbre of voice, ii, 57 Tissue, adipose, i, 35 areolar, cellular, or connective, i, 31 elastic, i, 32 fatty, i, 35 fibrous, i, 32 gelatinous, i, 33 retiform, i, 34 Tissues, connective, i, 28 elementary structure of, i, 28, et 8€q. erectile, i, 168 Tone of blood-vessels, i, 153 of muscles, ii, 104 of voice, ii, 57 Tongue, ii, 169 action of in deglutition, i, 238 in sucking, i, 201 action of in speech, ii, 62 epithelium of, ii, 72 influence of facial nerve on muscles of, ii, 145 motor nerve of, ii, 150 an organ of touch, ii, 173 papillae of, ii, 169 parts most sensitive to taste, ii, 174 structure of, ii, 169 Tonsils, i, 236 Tooth, i, 55. See Teeth. Tooth-ache, radiation of, sensation in, ii, 85 Tooth-pulp, i, 55 Touch, ii, 162 after sensation, ii, 168 conditions for perfection of, ii, 163 connection of with muscular sense, ii, 165 co-operation of mind with, ii, 167 function of cuticle with regard to, i, 333 of papillae of skin with regard to, i, 333 Touch, hand an organ of, ii, 163 illusions, ii, 165 modifications of, ii, 162 a modification of common sensation, ii, 162 special organs, ii, 163 subjective sensations, ii, 168 the 'tongue an organ of, ii, 164 various degrees of in different parts, ii, 164 Touch-corpuscles, i, 336 Tiabecula? cranii, ii, 273 Trachea, i, 175 Tradescantia Virginica, movements in cells of, i, 7 Tragus, ii, 179 Transference of impressions, ii, 84 Traube-Hering's curves, i, 209 Tricuspid valve, i, 109 safety-valve action of, i, 113 Trigeminal or fifth nerve, ii, 139 effects of injury of, ii, 140 Trophic nerves, ii, 142 Trypsin, i, 267 Trypsinogen, i, 266 Tube, Eu-tachian, ii, 180 Tubercle of Lower, i, 105 Tubes, Fallopian, ii, 238. See Fallopian Tubes. looped, of Henle, i, 350 Tubular glands, i, 323 convoluted, i, 323 simple, i, 323 of intestines, i, 257, 263 of stomach, i, 242 Tubules, i, 17 Tubuli seminiferi, ii, 247 uriniferi, i, 348, et seq. Tunica albuginea of testicle, ii, 246 Tympanum or middle ear, ii, 180 development of, ii, 293 functions of, ii, 187 membrane of, ii, 180 structure of, ii, 180 use of air in, ii, 189 Types of respiration, i, 186 Tyrosin, i, 266 U. Ulceration of parts attending injuries of nerves, ii, 156 Ulnar nerve, effects of compression of, ii, 81 Umbilical arteries, ii, 270 contraction of, i, 142 cord, ii, 270 vesicle, ii, 254, 261 Unconscious cerebration, ii, 130 Unorganized ferments, ii, 335 Unstriped muscular fibre, ii, 14 development, ii, 20 distribution, ii, 14 structure, ii, 15 376 INDEX. Uraclms, ii, 264 Urate of ammonium, i, 360 of sodium, i, 360 Urea, i, 358 apparatus for estimating quantity, i, 359 chemical composition of, i, 395 identical with cyanate of ammonium, i, 359 properties, i, 358 quantity, i, 359 in relation to muscular exertion, i, 371 sources, i, 370 Ureides, ii, 333 Ureter, i, 354 Urethra, development of, ii, 305 Uric acid, i, 360 condition in which it exists in urine, i, 360 forms in which it is deposited, i, 361 proportionate quantity of, i, 360 source of, i, 372 tests, i, 361 variations in quantity, i, 360 Urina sanguinis, potus, et cibi, i, 357 Urinary bladder, i, 349 development, ii, 302 nerves, i, 353 regurgitation from prevented, i, 373 structure, i, 349 Urinary ferments, i, 355; ii, 338 abnormal, i, 358 analysis of, i, 355 chemical composition, i, 355 coloring matter of, i, 362 cystin in, i, 365 decomposition by mucus, i, 356 effect of blood pressure on, i, 367 expulsion, i, 373 extractives, i, 363 flow of into bladder, i, 372 gases, i, 365 bippuric acid in, i, 561 mucus in, i, 362 oxalic acid in, i, 365 physical characters, i, 355 pigments, i, 362 quantity of chief constituents, i, 356 reaction of, i, 355 in different animals, i. 356 made alkaline by diet, i, 356 saline matter, i, 363 secretion, i, 370 effects of posture, etc., on, i, 373 rate of, i, 373 solids, i, 358 variations of, i, 356 specific gravity of,i, 357 variations of, i, 357 urates, i, 360, 361 urea, i, 358 uric acid in, i, 860 variations of specific gravity, i 357 of water, i, 357 Urobilin, i, 362 Urochrome, i, 362 Uroerythrin, i, 362 Uses of blood, i, 91 Uterus, ii, 238 change of mucous membrane of, ii, 242 development of in pregnancy, ii, 242 follicular glands of, ii, 239 masculinus, ii, 304 reflex action of, ii, 103 structure, ii, 238 Utriculus of labyrinth, ii, 185 Uvula in relation to voice, ii, 59 V. Vagina, structure of, ii, 239 Vagus nerve, i, 232. See Pneumogastric. Valerianic acid, ii, 339 Valve, ilio-caecal, structure of, i, 263 of Vieussens, ii, 115 Valves of heart, i, 109 action of, i, 112, et seq. bicuspid or mitral, i, 109 semilunar, i, 110, 114 tricuspid, i, 109, 110 of lymphatic vessels, i, 297 of veins, i, 137, et seq. Valvulse conniventes, i, 255 Vas deferens, ii, 246 development, ii, 300 Vasa eff erentia of testicle, ii, 247 of kidney, i, 353 recta of kiidney, i, 353 of testicle, ii, 247 vasorum, i, 131 Vascular area, ii, 262 Vascular glands, ii, 461 in relation to blood, ii, 11 several offices of, ii, 11 Vascular system, development of, ii, 276 Vaso-constrictor nerves, i, 156 Vaso-dilator nerves, i, 156 Vaso-motor influence on blood-pressure i, 154, et seq. Vaso-motor nerves, i, 154 effect of section, i, 154, et seq. influence upon blood-pressure, i, 154 Vaso-motor nerve-centres, i, 154 reflection by, i, 154 Vegetables and animals, distinctions be- tween, i, 8 Veins, i, 135 anastomoses of, i, 162 blood-pressure in, i, 162 circulation in, i, 161, et seq, rate of, i, 166 cardinal, ii, 284 collateral circulation in, i, 161 cranium, i, 167 development, ii, 283 distribution, ii, 135 effects of muscular pressure on, i, 162 of respiration on, i, 206 force of heart's action remaining in, i, 162 IND.KX. 377 Veins, influence of expiration on, i, 2(>? inspiration, i, 206 influence of gravitation in, i, 163 parietal system of, ii, 283, et seq. pressure in, i, 162 rhythmical action in, i, 162 structure of, i, 136 systemic, i, 102 umbilical, ii, 270 valves of, i, 137 velocity of blood in, i, 165 visceral system of, ii, 283, et seq. Velocity of blood in arteries, i, 164 in capillaries, i, 165 in veins, i, 165 of circulation, i, 163 of nervous force, ii, 81 Venaportaa.i, 88,269 Venae hepatica? advehentes, ii, 283 revehentes, ii, 284 Ventilation, i, 204 Ventricles of heart, i, 112 capacity of, i, 107 contraction of, i, 112 effect on blood-current in veins, i, 124 dilatation of, i, 124 force of, i, 124 of larynx, office of, ii, 60 Ventriloquism, ii, 62, 194 Vermicular movement of intestines, i, 289 Vermiform process, i, 262 Vertebrae, development of, ii, 270 Vesicle, germinal, ii, 237 Graafian, ii, 235 bursting of, ii, 240 umbilical', ii, 254, 261 Vesicula germinativa, ii, 237 Vesiculae seminales, ii, 250 functions of, ii, 250 reflex movements of, ii, 103 structure, ii, 250 Vestibule of the ear, ii, 182 Vestigial fold of Marshall, ii, 285 Vibrations, conveyance of to auditory nerve, ii, 185, et seq. perception of, ii, 194 of vocal cords, ii, 52 Vidian nerve, ii, 144 Villi inchorion,ii,265 in placenta, ii, 268 Villi of intestines, i, 259 action in digestion, i, 260 Visceral arches, development of, ii, 273 connection with cranial nerves, ii, 274 laniinse or plates, ii, 260 Vision, ii,196 angle of, ii, 221 at different distances, adaptation of eye to, ii, 207, et seq. contrasted with touch, ii, 221 corpora quadrigemina, the principal nerve-centres of, ii, 114 correction of aberration, ii, 213, et seq. of inversion of image in, ii, 218 Vision, defects of, ii, 211, et seq. distinctness of, how secured, ii, 203, et seq. double, ii, 229 duration of sensation in, ii, 216 estimation of the form of objects, ii, 222 of their direction, ii, 222 of their motion, ii, 222 of their size, ii, 221 field of, size of, ii, 220 focal distance of, ii, 206 impaired by lesion of fifth nerve, ii, 140 influence of attention on, ii, 223 modified by different parts of the ret- ina, ii, 226 purple, ii, 218 in quadrupeds, ii, 230 single, with two eyes, ii, 231 Visual direction, ii, 222 Vital or respiratory capacity of chest, i, 189 Vital capillary force, i, 161 Vital force, ii", 321 Vitellin, ii, 329 Vitelline duct, ii, 261 membrane, ii, 237 spheres, ii, 253 - Vitreous humor, ii, 205 Vocal cords, ii, 52 action of in respiratory actions, i, 188, et xeq. approximation of, effect on height of note, ii, 56 elastic tissue in, i, 33 longer in males than in females, ii, 57 position of, how modified, ii, 56 vibrations of, cause voice, ii, 51 Voice, ii, 50/57 of boys, ii, 58 compass of, ii, 57 conditions on which strength depends, ii, 58 Voice, human, produced by vibration of vocal cords, ii, 50, 55 in eunuchs, ii, 58 influence of age on, ii, 58 of arches of palate and uvula, ii, 59 of epiglottis, ii, 55 of sex, ii, 57 influence of ventricles of larynx, ii, 60 of vocal cords, ii, 56 in male and female, ii, 57 cause of different pitch, ii, 57 modulations of, ii, 57 natural and falsetto, ii, 58 peculiar characters of, ii, 57 varieties of, ii, 58 Vomiting, i, 251 action of stomach in, i, 251 nerve actions in, i, 252 voluntary and acquired, i, 252 Vowels and consonants, ii, 60 Vulvo- vaginal or Duverney's glands, ii, 239 378 INDEX. W. Walking, ii, 41 Water, ii, 341 absorbed by skin, i, 345 by stomach, i, 284 amount, in blood, variations in, 82, 87 exhaled from lungs, i, 195 from skin, i, 345 forms large part of human body, ii, 341 influence of on coagulation of blood, i, 71 influence of on decomposition, ii, 326 in urine, excretion of, i, 365 variations in, i, 357 loss of from body, ii, 341 uses, ii, 341 quantity in various tissues, ii, 341 source, ii, 341 vapor of in atmosphere, i, 192 Wave of blood causing the pulse, i, 142 velocity of, i, 143 White corpuscles, i, 79. See Blood cor- puscles, white; and Lymph-cor- puscles. White fibro- cartilage, i, 41 fibrous tissue, i, 31 Willis, circle of, i, 167 Wolflian bodies, ii, 398, et seq. Work of heart, i, 124 X. Xanthin, i, 363 Xantbo-proteic reaction, ii, 327 Yawning, i, 201 Yelk, or vitellus, ii, 252 changes of, in Fallopian tube, ii, 253 cleaving of, ii, 253 constriction of, by ventral lamina, ii, 260 Yelk-sac, ii, 260, et seq. Yellow elastic fibre, i, 30, 33 fibro-cartilage, i, 40 spot of S5mmering, ii, 199 Young-Helmholtz theory, ii, 224 * Z. Zimmermann, corpuscles of, ii, 6 Zona pellucida, ii, 237 THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW AN INITIAL FINE OF 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO SO CENTS ON THE FOURTH DAY AND TO $1.OO ON THE SEVENTH DAY OVERDUE. _, ... « *TJ* I nlniV^l i lAttl Q IQfil JlW o jyot -ffaZJ ulJ m DEC 31963 i££? (iPR 26 1967 LD 21-95m-7,'37 THE UNIVERSITY OF CALIFORNIA LIBRARY