HUMAN PHYSIOLOGY PREPARED WITH SPECIAL REFERENCE TO STUDENTS OF MEDICINE BY JOSEPH HOWARD RAYMOND, A.M., M.D. V I N Professor of Physiology and Hygiene in the Long Island College Hospital, New York City THIRD EDITION, THOROUGHLY REVISED 444 Illustrations, some of them in Colors, and 4 full-page Lithographic Plates PHILADELPHIA AND LONDON . B. SAUNDERS & COMPANY J905 rs 3IOLOGY LIBRARY 8 Set up, electrotyped, printed, and copyrighted September, 1894. Reprinted March, 1895. Revised, entirely reset, reprinted, and recopyrighted September, 1901. Revised, reprinted, and recopyrighted April, 1905. Copyright, 1905, by W. B. Saunders & Company. 7 PRESS OF W. B. SAUNDERS & COMPANY, TO THE MEMORY ALEXANDER JOHNSTON CHALMERS SKENE, M.D., LL.D. COLLEAGUE AND FRIEND FOR MORE THAN A QUARTER OF A CENTURY This Volume is Affectionately Inscribed by THE AUTHOR PREFACE TO THE THIRD EDITION. IN the present edition the author has availed himself of the valuable contribution of Chittenden, under the title of " Physi- ological Economy of Nutrition," to this portion of Human Physiology. The results of the experiments therein reported he regards as among the most important additions to the physi- ology of nutrition made during the present decade. The completion of the work of Atwater and others, as recorded in the publication entitled " Physiological Aspects of the Liquor Problem/ 7 has enabled the author to discuss more fully the nutritive value of alcohol. Among other topics, either more fully elaborated or introduced for the first time, are : Vegetarianism ; The Identity of Human and Bovine Tuberculosis in connection with the subject of Food ; The Experiments of Cannon and others on the Movements of the Stomach and Intestines ; The Influence of Alcohol and Alco- holic Fluids on the Excretion of Uric Acid ; Hemolysis and Bacteriolysis ; The Effect of Cold on Bacteria with reference to the purification of water in freezing ; and Ovarian and Ab- dominal Pregnancy. Many other minor changes have been made in the text, rendered necessary by the advance in Physiology since the publi- cation of the previous edition. The author desires to extend his thanks to critics who have pointed out defects in the former edition, which might otherwise have escaped detection, and all of which he hopes have been cor- rected in the present edition. APRIL 15, 1905. 9 PREFACE. THE author's experience of twenty years as a teacher of Physiology to medical students has brought him to the con- clusion that in the short time allotted to the study of physi- ology in medical schools students can assimilate only the main facts and principles of this branch of medicine, which lies at the very foundation of a sound knowledge of the healing art; and that even if there were time to investigate the more recondite and abstruse parts of the subject, such an investiga- tion would be profitless during this formative period. In his teaching the author has kept this thought constantly in mind, and in this manual has endeavored to put into a concrete and available form the results of his experience. 11 CONTENTS. PAGE INTRODUCTION 17 Definitions, 17 Branches of Physiology, 19 Human Physiology Defined, 20 Classification of Functions, 21 Histology of the Human Body, 21 Physiologic Chemistry, 21 Arrangement of Topics, 22. I. HISTOLOGY OF THE HUMAN BODY 23 Cells, 23 Division of Cells, 28. Elementary Tissues, 30 Epithelial Tissue, 30 Connective Tissue, 34 Areolar Tissue, 34 Adipose Tissue, 35 Ketiform Tissue, 37 Lymphoid Tissue, 37 Elastic Tissue, 37 Fibrous Tissue, 38 Jelly- like Tissue, 38 Cartilage, 38 Bone, 41 Dentin, 50 Muscular Tissue, 5G Voluntary Muscle, 56 Involuntary Muscle, 61 Nervous Tissue, 63 Nerve-fibers, 63 Nerve-cells, 69 Neuroglia, 72 Development of Nerve-cells and Nerve-fibers, 73 Chemistry of Nervous Tissue, 74. H. PHYSIOLOGIC CHEMISTRY .' . .\ 76 Inorganic Ingredients, 77 Carbohydrates, 87 Fats, 99 Proteids, 102 Albumins, 107 Albuminates, 109 Globulins, 110 Nucleopro- teids, 111 Proteoses and Peptones, 113 Coagulated Proteids, 113 Poisonous Proteids, 113 Albuminoids, 115 Enzymes, 117 Metabo- lism, 120 Food, 121 Milk, 141 Mammary Glands, 144 Eggs, 148 Meat, 150 Cereals, 153 Vegetables, 155 Beverages, 156 Effects of Alcohol upon the Human Body, 158. in. NUTRITIVE FUNCTIONS ... . > . . . 167 DIGESTION 167 Mouth Digestion, 169 Stomach Digestion, 191 Coats of the Stom- ach, 192 Quantity of Gastric Juice, 194 Composition of Human Gastric Juice Mixed with Saliva, 195 Action of the Gastric Juice, 199 Movements of the Stomach, 200 Vomiting, 205 Excretory Function of the Stomach, 208 Effect of Nervous Disturbances upon Gastric Digestion, 208 Self-digestion of the Stomach, 208 Duration of Stomach Digestion, 209 Removal of the Human Stomach, 211 Achylia Gastrica, 219 Artificial Gastric Juice, 220 Effect of Alcohol on Di- gestion, 220 Intestinal Digestion, 221 Structure of the Small Intes- tine, 221 Structure of the Large Intestine, 227 Succus Entericus, or Intestinal Juice, 228 The Pancreas, 229 Structure of the Pancreas, 229 Pancreatic Juice, 232 Innervation of the Pancreas, 238 Internal Secretion of the Pancreas, 239 The Liver, 239 Chemical Composition, 239 Structure, 240 Hepatic Artery, 241 Portal Vein, 241 Hepatic 13 14 CONTEXTS. DIGESTION (Continued) PAGE Duct, 242 Gall-bladder, 242 Bile, 244 Innervation, 250 Movements of the Small Intestine, 250 Digestion in the Large Intestine, 251 Movements of the Large Intestine, 252 Bacterial Digestion, 253. ABSORPTION OF THE FOOD ; 254 Mouth Absorption, 254 Gastric Absorption, 254 Absorption by the Small Intestine, 255 Glycogenic Function of the Liver, 256 Formation of Glycogen from Carbohydrates, 257 Formation of Gly- cogen from Proteids, 257 Formation of Glycogen from Fats, 257 Glycogenic Theory, 257 Diabetes, 259 Absorption of Proteids, 260 Absorption of Vegetable and Animal Proteids, 261 Absorption of Fat, 261 Absorption by the Large Intestine, 261. FECES AND DEFECATION 265 Quantity of Feces, 265 Color of Feces, 266 Eeaction of Feces, 266 Composition of Feces, 266 Meconium, 266 Defecation, 266. BLOOD 268 Physical Properties of Blood, 268 Distribution, 270 Microscopic Structure, 270 Blood-serum, 291 Coagulation of Blood, 294 Regen- eration of Blood, 299 Hemolysis and Bacteriolysis, 300. LYMPH 302 Chemical Composition, 302 Histologic Composition, 303 Origin, 303 Chyle, 305. CIRCULATORY SYSTEM 305 The Heart, 305 The Arteries, 308 The Capillaries, 310 The Veins, 310 Circulation of the Blood, 311 Blood-pressure, 319 Rate of Blood-flow in the Vessels, 323 The Pulse, 326 The Plethysmo- graph, 329 Circulation in the Veins, 329. LYMPHATIC SYSTEM ,...".. 330 Lymphatic Vessels, 330 Lymphatic Glands, 332 Cavities of Serous Membranes, 333 Circulating Lymph, 334. DUCTLESS GLANDS t 334 The Spleen, 335 The Thyroid and Parathyroid, 339 The Thymus, 346 The Suprarenal Capsules or Adrenal Bodies, 347 The Pineal Gland, 351 The Pituitary Body, 351 The Carotid and the Coccygeal Glands, 352. RESPIRATION 352 The Nose, 353 The Larynx, 354 The Trachea, 361 The Bronchi, 362 The Lungs, 362 The Pleura, 365 The Thorax, 365 Respiratory Movements, 372 Capacity of the Lungs, 374 Types of Respiration, 375 Chemistry of Respiration, 376. VOICE AND SPEECH V .... ?.,. 389 Laryngoscope, 390 Resonance, 391 Intensity, 392 Pitch, 392 Quality, 393 Registers, 393 Speech, 393 Vowels, 394 Consonants, 394 Photography of the Larynx, 394. VITAL HEAT / - . \ 406 Warm-blooded Animals, 406 Homoiothermal Animals, 407 Poikilo- thermal Animals, 407 Temperatures of Different Animals, 407 Tern- CONTENTS. 15 VITAL HEAT Continued) PAGE perature of Different Parts of the Body, 407 Temperature at Different Ages, 408 Daily Variations in Temperature, 408 Remarkable Instances of High and Low Temperature, 408 Heat Unit, 409 Sources of Vital Heat, 409 Channels Through which Vital Heat is Lost, 410 Calor- imetry, 410 Regulation of Temperature, 413. THE SKIN 413 Corium, 413 Epidermis, 413 Perspiratory Glands, 413 Sebaceous Glands, 416 Cerumen, 417 Hairs and Nails, 417 Functions of the Skin, 418 Care of the Skin, 419. THE URINARY APPARATUS 421 The Kidneys, 421 Ureters, 428 Bladder, 429 -Urethra, 430. THE URINE 431 Quantity, 431 Color, 431 Reaction, 431 Specific Gravity, 432 Composition, 432 Inorganic Constituents, 440. IRRITABILITY; CONTRACTILITY; ELECTRIC PHENOMENA OF MUSCLE . 442 IV. NERVOUS FUNCTIONS 460 General Considerations, 460 Nerves, 461 Nerve-impulses, 465 The Nervous System, 468 Spinal Cord, 468 Functions of the Spinal Cord, 477 Reflex Time, 479 Reflexes in Man, 479 Special Centers in the Cord, 481 Functions of Spinal Nerves, 482. THE BRAIN 483 The Medulla Oblongata, 484 The Cerebellum, 491 The Cerebrum, 495 Cranial Nerves, 513. THE SENSES 527 General Sensibility, 527 Sense of Touch, 527 Sense of Pressure, 529 Muscular Sense, 529 Sense of Temperature, 529 Sense of Pain, 530 Sense of Smell, 530 Olfactory Nerves, 531 Olfactory Bulb, 531 Olfactory Tract, 533 Functions of the Olfactory Nerves, 533 Sense of Taste, 535 Circumvallate Papillae, 536 Conical Papilla?, 537 Fungi- form Papillae, 537 Taste-buds, 537 Conditions of the Sense of Taste, 540 Sense of Sight, 541 Coats or Tunics, 541 Sclerotic Coat, 541 Cornea, 541 Choroid, 544 Ciliary Processes, 545 Iris, 545 Ciliary Body, 547 Retina, 547 Anterior and Posterior Chambers, 554 Vitreous Body, 554 Crystalline Lens, 554 Suspensory Ligament, 555 Chemistry of the Eye, 555 Ocular Muscles, 556 Physiology of Vision, 560 Defects in the Visual Apparatus, 570 The Iris, 575 The Retina, 575 Light, 581 Form, 583 Identical Points, 583 Size, 583 Distance, 584 Color, 587 Color-blindness or Daltonism, 593 Fatigue of Retina, 594 After-images, 594 Visual Judgment, 595 Appendages of the Eye, 597 Lacrimal Apparatus, 597 Meibomian Glands, 597 The Sense of Hearing, 598 External Ear, 598 Middle Ear, 600 Membrana Tympani, 600 Tympanic Cavity, 602 Ossicles, 602 Eustachian Tubes, 604 Mastoid Anti-urn, 605 Fenestra Ovalis, 605 Fenestra Rotunda, 606 Internal Ear, 615 Physiology of Hear- ing. 616 Theories of Hearing, 618 Period, 620 Amplitude, 620 Frequency, 620 Noises, 620 Musical Sounds, 620 Intensity, 621 Loudness, 621 Pitch, 621 Quality, 621. 16 CONTENTS. PAGE V. REPRODUCTIVE FUNCTIONS 624 Reproductive Organs, 624 Genital Organs of the Male, 625 Testes, 625 Penis, 630 Genital Organs of the Female, 631 Ovary, 631 Fallopian Tubes, 640 Uterus, 640 Ovulation, 642 Menstrua- tion, 645 Formation of the Corpus Luteum, 649 Maturation of the Ovum, 651 Impregnation, 651 Erection of the Penis, 651 Ejacu- lation, 652 Ovarian and Abdominal Pregnancy, 654 Method of Fertilization, 656 Segmentation, 657 Formation of the Embryo, 657 Development of the Chick, 658 Membranes of the Embryo, 659 Amnion, 659 Yolk-sac, 660 Allantois, 660 Chorion, 660 Placenta, 660 Circulation in the Embryo, 661 Changes in the Circulation at Birth, 663. INDEX ... . 665 HUMAN PHYSIOLOGY. INTRODUCTION. Definitions. Physiology is the science which treats of func- tiom. By the term function is meant the characteristic work performed by an organ. An organ may be defined as a structure which performs a function or functions, for the special or char- acteristic work of an organ may not be limited to a single function : thus the pancreas secretes not only pancreatic juice, which is its external secretion^ but also another product, which is its internal secretion (p. 239). Lifeless things perform no functions, hence physiology has no dealings with inanimate things. Rocks, stones, and other members of the mineral kingdom at no time possess life ; consequently they perform no functions, and with them physiology has no concern : we cannot speak of the physi- ology of minerals. Plants and animals are sometimes living and sometimes dead : when living they perform functions, when dead they perform no functions ; in the latter condition they are like the rocks so far as function is concerned, and with them physiology has nothing whatever to do. It is only when they are living that they perform functions, and it is then and only then that with them physiology concerns itself. Another definition which might be given of physiology is, that it is the science which treate of vital phenomena. A brief consideration of this definition will bring us to the same conclu- sion as did that of the preceding definition. Of life in its essence we know nothing. Metaphysicians have endeavored to explain life, and some have even ventured to point out its seat, but the fact remains that we are utterly ignorant of its nature. We only know that it exists by certain manifestations which it presents. When we see a growing plant or a moving animal, we say of each that it is alive. In the higher forms of animals and plants it is easy, under ordinary circumstances, to determine whether they are living or not ; but in the lower forms this determination is some- times a most difficult task. The evidences upon which reliance is placed to determine the presence or the absence of life are spoken of as vital phenomena. Thus, if in examining an animal we find that its heart beats, we say that the animal is alive ; but 2 17 18 INTRODUCTION. if the heart is motionless, we say that the animal is dead. This beating of the heart, therefore, is a vital phenomenon that is, a manifestation of life. We speak also of this beating of the heart as its function ; hence the first definition of physiology, that it is the science which treats of functions, and the second definition, that it is the science which treats of vital phenomena, amount to the same thing. Definition of "Organ." An organ has already been defined as a structure which performs a function or functions. In speaking of the organs of an animal reference is usually had to such struct- ures as the heart, the lungs, and the stomach, inasmuch as their size and the important work they perform force them upon our attention. These are indeed organs, for they perform functions ; thus the function of the heart is to receive blood in one portion and to propel it from another portion, that of the lungs is to aerate the blood, and that of the stomach is to digest certain kinds of food ; but the term organ, as used in physiology, has a much broader signification. A muscle, a nerve, and a blood-vessel are as truly organs as are the greater ones above spoken of, for each has its own function. Thus the function of a muscle is to contract, that of a nerve is to transfer nervous impulses, and that of a blood- vessel is to convey blood. At first sight it might seem that these functions were unimportant, and that the structures which per- formed them were hardly worthy of so dignified a name as organs ; but a moment's reflection will show that without the contraction of muscles, the transference of nervous impulses, or the carrying of blood the life of an animal would as certainly cease as if it was deprived of its heart, of its lungs, or of its stomach. Inasmuch as minerals, on the one hand, possess no organs, they perform no work that is, they have no functions ; therefore we do not speak of the physiology of a mineral. Plants and ani- mals, on the other hand, possess organs, each of which performs its special function ; and it is with them, as has been said, that physiology has to do. As we find organs in the animal, so do we find them in the plant ; not the same organs, it is true, but struct- ures which are as truly organs, for they respond to the same test. The roots of a plant absorb moisture and nourishment from the soil, this being their function ; the green leaves take up from the air carbonic acid, with which and with water they form starch that is utilized by the plant, while oxygen is set free, this being the function of the leaves ; the anthers and the ovaries of flowers are concerned in reproducing plants by forming new ones, this being their function. Thus we might continue to show that as in animals, so in plants, the different organs have their respective functions. Definition of 'Organic" and "Inorganic." We can now under- stand the meaning of two very important terms organic and BRANCHES OF PHYSIOLOGY. 19 inorganic. These terms are used in* two senses : first, as to struct- ure, and, second, as to product. When we say that a plant or an animal is organic, we mean that it is made up of organs that is, of structures which perform functions. The plant or the animal may be simple or may be complex, but, however simple or however complex, its parts do something, that something being the function of the part which acts. We say, therefore, that the plant or animal is organic, meaning that it is composed of organs organic, then, as to structure. The rock has no organs, therefore it is non-organic, or is inorganic. These terms are used also in another sense. Thus we speak of honey as organic. Mani- festly, we do not mean organic as to structure, for honey has no organs, that is, no parts which perform functions, but it is the product of the bee, which is an organic structure ; hence honey is an organic product. The nectary of a flower is organic as to structure, and the nectar which it produces is also organic, inasmuch as it is the product of the nectary. But organs do not act each for itself: they are, as a rule, associated in the performance of a common function, and thus associated form a system. Thus the group of organs which, are concerned in digestion forms the digestive system ; those which together accomplish the circulation of the blood, the circulatory system. An attempt has been made to distinguish an apparatus from a system; the former being defined as a group of organs concerned in the performance of a common function, no matter how dissimilar their structure, while organs similar in structure irrespective of their function would be regarded as a system. Similarity of function, under this definition, would characterize an apparatus, and similarity of structure a system. The organs whose functions are to digest food would be regarded as an appa- ratus, constituting the digestive apparatus ; the bones, on the other hand, would form the osseous system. Practically, however, such a differentiation is of no use, and the two terms apparatus and system may therefore be used interchangeably. Branches of Physiology. From these elementary con- siderations it is evident that physiology has to do with living plants and animals only that is, with organic structures and inci- dentally with their products. That branch of the science which treats of the functions of plants is denominated Vegetable Physi- ology, and that which deals with the functions of animals is called AnimaL Physiology. Vegetable Physiology. We are concerned but indirectly with vegetable physiology, or so far only as its study helps us to under- stand some of the more obscure processes in animals. Some of these processes, being simpler in plants, are more easily studied in them, and what is there learned is of great assistance in understanding analogous processes in man. Thus a knowledge of fertilization as 20 INTRODUCTION. it occurs in the vegetable kingdom aids very much in elucidating the process of reproduction in the human species. Animal Physiology. The same organs in different animals per- form their functions in different ways. Thus the stomach of the cow and that of the dog act very dissimilarly, and a knowledge of the one would aid very little in acquiring a knowledge of the other. What is true of the stomach is true of other organs to a greater or lesser degree. Each class of animals has its own peculi- arities as to function that is, has its own physiology. One who intends to devote his life to the treatment of the diseases of the lower animals must study the functions of those animals, while one who is preparing himself for the cure of human diseases must understand the functions of the organs of the human body, or Human Physiology. Many hints, it is true, may be obtained by the student of human physiology from a study of the processes which take place in the lower animals, and many of the most valuable contributions made to physiologic science have been based upon such a study ; but it must ever be borne in mind that specific differences exist, and that we cannot infer too much from such observations. Thus one who studies the process of stomach digestion in a ruminant, such as the cow, will make a most serious blunder should he sup- pose that the process is the same in man. Errors of a similar character, though perhaps less glaring, have been made, notably in the process of reproduction. This process is so obscure that many opportunities which have presented tnemselves for investi- gation, both in the lower and in the higher animals, have been seized upon ; but theories which have been accepted as proved, and which have largely depended on such observations, are now, in the light of more recent study, being questioned. Notwith- . standing this disadvantage, had it not been for such studies many of the most important facts of medical science would have re- mained undiscovered. Inasmuch as functions cease with life, these observations can only be made upon living animals. Vivi- section, therefore, has been of the greatest benefit to the human race, and those who decry it are daily reaping the results which it has attained, and which could never have been attained with- out it. Wanton and unnecessary experiments are to be condemned, but no terms of praise are too exalted to bestow upon those patient investigators who, through many long years, have laboriously and zealously pursued their studies and experiments, with no other end in view than to add to the sum of human knowledge and to contribute to the relief of human suffering. Human Physiology Defined. Human physiology is the science which treats of the human functions. This science, together with anatomy, which treats of structure, and with chemistry, which treats of composition, lies at the foundation of rational medicine. PHYSIOLOGIC CHEMISTRY. 21 No one can be a successful physician who does not understand at least the more important functions of the human body, and the greater the knowledge he possesses of physiology, the broader will be the scientific groundwork on which he has to build. Disease is a departure from the normal or physiologic condition. A dis- eased organ performs its function in an abnormal manner, and to succeed in correcting the diseased condition one must first be able to recognize this abnormal action, which can only be done by knowing how the organ acts in health that is, by understanding its physiology. Even with this knowledge one may be unable to accomplish the desired object, for the structure of the organ may be so changed that no means can be applied which will restore it to its normal condition ; but one is certainly more likely to succeed if possessed of a knowledge of its physiology than if ignorant of it. The study of human physiology is but the study of the human functions, and when these functions are thoroughly understood the science is mastered. Classification of Functions. The functions of the body may be classified as follows : 1. Nutritive Functions, which include those concerned directly with the maintenance of the individual, such as digestion, respiration, circulation, etc. ; 2. Nervous Func- tions, which include those that bring the different organs of the body into harmonious relations with one another, and, in addition, bring the individual, through the special senses sight, hearing, etc. into relation with the world outside him ; and 3. Reproductive Functions, which are concerned not with the individual, but with the species, which they perpetuate. Histology of the Human Body. Anatomy, as we have already learned, is the science which treats of structure ; and this is true as well of the minute or microscopic as of the gross or macroscopic structure ; but it will be of advantage to the student of physiology to have distinctly in mind so much of the histology or minute structure of the body as is necessary to a full under- standing of its functions, and to appreciate the discussion of them. With this end in view, the histology of each organ will be given in connection with its function, but preliminary to all this we shall discuss the tissues of the body which go to make up these organs. For fuller details the student is referred to the many excellent treatises on human histology. Physiologic Chemistry. Although physiology, strictly speaking, has nothing to do with composition, still, as a matter of necessity as well as of convenience, it is usual to preface the study of the functions of the human body with a greater or lesser consideration of its composition. This consideration is necessary, because, as a rule, medical students have an insufficient knowledge of this branch of chemistry physiologic chemistry to take up at once the study of the functions with profit, and should the 22 INTRODUCTION. attempt be made confusion and loss of time would inevitably result. As an illustration we may refer to the function or series of functions by which the food is prepared for absorption that is, digestion. Food is the material which is taken into the body to supply the waste of its tissues, and it must be of such a composi- tion as will meet this want. To select the proper food-materials we must know of what the body is composed, and what are the changes which take place in its composition what parts are wasted. For these reasons a study of physiologic chemistry must precede a study of the functions of digestion. This is but one of many illustrations which might be given to show the importance of prefacing the study of physiology proper with a study of the chemistry of the body and of the food. Arrangement of Topics. The topics treated of in this work will therefore be arranged in the following order : I. Histology of the Human Body.; II. Physiologic Chemistry ; III. Nutritive Functions; IV. Nervous Functions; V. Reproductive Functions. I. HISTOLOGY OF THE HUMAN BODY. ORGANS on minute examination are found to be made up of tissues, or elementary tissues as they are sometimes called. Of elementary tissues there are four: 1. Epithelial; 2. Con- nective ; 3. Muscular ; and 4. Nervous. Some organs . contain all four kinds of tissues, while others, more simple in their structure, contain but one or two. If these tissues are still further analyzed, they are seen to con- sist of cells or fibers, or of both together in varying proportions : thus the epithelial tissues are made up of cells alone ; the con- nective tissue, principally of fibers ; and the nervous, of both cells and fibers. Cells (Fig. 1). A cell consists of protoplasm, a nucleus, and a centrosome and attraction-sphere. A cell-membrane enclos- Vacuoles. Chromatin network Linin network Nuclear fluid Nuclear membrane. _Li Cell-membrane, 'i. Exoplasm. _ _ Spongioplasm. Hyaloplasm. Nucleolus, Chromatin net-knot. entrosome. Centrosphere. Foreign mclosures. Metaplasm. FIG. 1. Diagram of a cell (Huber). ing the protoplasm may or may not be present; it is not an essential part of a cell as are the other structures. A centrosome 23 24 CELLS. and attraction-sphere have been found in so many cells that they may be regarded as essential constituents of every cell. Protoplasm. This is the principal part of a cell, and is of an albuminous nature. Chemically it consists of water (75 per cent, or more), proteids, lecithin, cholesterin, and phosphates and chlo- rids of sodium, potassium, and calcium, and sometimes fat and glycogen. Microscopically examined it is found to be made up of spongioplasrn and hyaloplasm. Spongioplasm. Under high powers of the microscope the pro- toplasm of a cell presents the appearance of a fine network, called reticulum, spongework, or spongioplasrn. This network has in it knots, which give to it a granular appearance. These knots or granules are of the same chemic nature as the network that is, are albuminous or proteid. It is still undecided whether these granules are constituent parts of the protoplasm or are its products. Collectively they are denominated granuloplasm. Other granules may be present which are not connected with the network, and which are not proteid in character, but fatty or starchy or con- tain coloring-matter. In some instances they are of an inor- ganic nature. Granules of this latter kind constitute paraplasm ; by which is meant any and all material contained in a cell, not being an actual part of it, whether there as pabulum or food for the cell, or as waste material to be excreted. Hyaloplasm. In the meshes of the spongioplasm is the hyalo- plasm, a clear substance differing but slightly in its consistence from the spongioplasm, although it is less solid. Ameboid Movement. Protoplasm is endowed with the power of motion, which from its resemblance to the motion of the ameba, a minute animal, which is but a mass of protoplasm, is called ameboid. .Examined under the microscope the ameba puts out from its sides projections of its protoplasm pseudopodia ; and later the whole mass flows into one or more of these projections, thus changing its position and its shape. This ameboid movement takes place in the white blood-corpuscle, and in some other cells as well as in the ameba. The pseudopodia are frequently drawn back into the protoplasm, or retract, thus illustrating the posses- sion by the protoplasm of contractility. Their formation is due to an outflowing of the hyaloplasm, and their retraction to return of the hyaloplasm to the interstices of the reticulum. Ameboid movement is said to be spontaneous ; but if so, it can also be pro- duced by the action of heat, by dilute solutions of salt, by mod- erate currents of electricity, and by many other agents, all of which are called stimuli, because of their power to stimulate this movement. On the other hand, certain agents have the power of stopping or inhibiting the movement if it has begun. Thus a temperature above 40 C. or below C. acts as an inhibitant, while if the high temperature is continued the protoplasm is coag- CENTROSOME. 25 ulated and its life destroyed. Acids and strong alkalies have the power of destroying the movement altogether, while chloroform inhibits it temporarily. This property of responding to a stimulus is known as irritability, and the fact that a stimulus applied to one part of a mass of protoplasm will produce results in other and distant parts demonstrates the presence of conductivity. Nutrition. Another property possessed by living protoplasm is that of nutrition ; by which is meant the power to absorb mate- rial, to convert it into protoplasm, and to get rid of such waste products as have served their purpose or are formed as a result of the activity of the protoplasm. That portion of the process which is concerned in the building up of the protoplasm is assimilation or anabolism, while that concerned with its breaking down or destruction is disassimilation or katabolism. A fourth property of protoplasm is that of reproduction, which will be treated of under the heading Division of Cells. Nucleus. Embedded in the protoplasm is a vesicle of various shapes spherical, oval, or irregular which is to be regarded as of great importance, especially in the process of cell-subdivision by which new cells are formed and growth thus brought about. It consists of an external enveloping membrane, the nuclear membrane, enclosing the chromoplasm or intranuclear network, a material resembling spongioplasm, and in the interstices of this is the nuclear matrix. In addition to these there are nucleoli, some of which are thickenings of the network like the knots in the spongioplasm, and are called pseudonucleolij while others are free, the latter being the nucleoli proper, or the true nucleoli. A single true nucleolus is usually found, although this is not always the case. Chromatin and Achromatin. When cells are stained with hema- toxylin the nuclear membrane, the chromoplasm, and the nucleoli take up the staining-fluid readily, while the nuclear matrix does not ; hence the former are said to be made up of chromatin, or to be chromatic ; while the latter is achromatin, or is said to be achro- matic. Other dyes, such as safranin, methyl-green, and carmine, produce the same effect: Chromatin is but another name for nuclein, which is the principal constituent of the nucleus. It is closely allied to the proteids, but is characterized by containing a considerable percentage of phosphorus ; some analyses give as much as 8 per cent. Nuclein is a compound of nucleic acid with proteids, and it is to the affinity of this acid for the coloring- matter that the staining of chromatin is due. It is more correct to speak of nucleins rather than of a single substance, as the compo- sition of nuclein is not always the same. For a further discussion of this subject the reader is referred to the chapter dealing with Proteids. Centrosome. As already stated, this is probably to be regarded 26 CELLS. -Centrosome. -Centrosphere. -Chromosomes. , Central spindle. -Nucleolus. Centrosome. Crown of ' chromo- some. x Crown of chromo- some. FIG. 5. FIG. 6. FIG. 7. FIGS. 2-7. Diagrammatic representation of the processes of mitotic cell- and nuclear division (Bohm and Davidoff). FIGS. 2-4, Prophases ; FIGS. 6, 7, metaphases. FIG. 2, Eesting nucleus ; FIG. 3, coarse skein or spirem ; FIG. 4, fine skein or spirem ; FIG. 5, segmentation of the spirem into single chromosomes ; FIG. 6, longi- tudinal division of the chromosomes ; FIG. 7, bipolar arrangement of the separated chromosomes. DIVISION OF CELLS. 27 Uniting filaments. FIG. 8. FIG. 9. FIG. FIGS. 8-12. Diagrammatie representation of the processes of mitotic cell- and nuclear division (Bohm and Davidoff). FIGS. 8-11, Anaphases ; FIG. 12, telophases. FIG. 8, wandering of the chromosomes toward the poles; FIG. 9, diaster; FIGS. 10 and 11, formation of the dispirem ; FIG. 12, two daughter-cells with resting nuclei. To simplify the figures 5-10, we have sketched in only a few chromosomes. In Fig. 9 it is seen that the cell-body is also beginning to divide. 28 CELLS. as an essential element of the cell, inasmuch as the more the sub- ject is investigated the more frequently is this structure found. It is also known by the name of attraction-particle. Radiating from it as a center are fine fibers, which together with it constitute the centrosphere (Fig. 2). Usually there are two of these spheres in a cell ; especially is this the case when the cell is about to divide, and they are connected by fibers forming an achromatic or central spindle. Division of Cells. Cells divide and then multiply in two ways : 1. By direct division ; 2. By indirect division. Direct Division of Cells. This may be either by gemmation or by fission. In the former a portion of the nucleus and proto- plasm forms a bud-like projection from the parent cell, from which it subsequently separates. The bud develops into a cell similar in all respects to that from which it had its origin. In fission the original nucleus divides into two, and then the protoplasm divides in such manner that each half shall possess its own nucleus, and two new cells are thus produced. Direct division is, however, not the method by which cells, as a rule, reproduce their kind ; indeed, it is regarded as very infrequent. Indirect Division, Karyokinesis, Karyomitosis, Mitosis (Figs. 2-17). It is to this method of division that we must look for the com- prehension of the processes by which the tissues produce and re- produce themselves. It has been studied in them all epithelial, connective, muscular, and nervous. While in direct division the nucleus divides into two equal halves, in karyokinesis the changes which take place in the nucleus are complicated, and it is only after a long series that new cells are produced. The statement is made by some authors that the division of a cell is preceded by the division of its attraction-sphere, and that the division of the nucleus follows ; indeed, some regard the change taking place in the attraction-sphere as determining or causing the division of the nucleus ; but inasmuch as instances have been observed in which the nuclear changes preceded, they are evidently not under all circumstances dependent upon the influence of the attracti on -sphere . The changes which take place in the process of karyokinesis may be concisely described as follows : Prior to the beginning of the process the cell consists of protoplasm containing a nucleus, with one or more contained nucleoli, and enclosed by the nuclear membrane, and a centrosome and attraction-sphere. A close ex- amination of the chromoplasm of the nucleus shows it to be made up of some fibers which form loops at the ends or poles of the nucleus, and are the primary loops, while others less prominent and which help to give to the chromoplasm its reticular or net- work form are secondary fibers. When indirect division begins the first change usually, though INDIRECT DIVISION. 29 not always, consists in the division of the centrosome and of the attraction-sphere into two ; then the following changes take place in the nucleus : The nucleoli and the secondary fibers disappear, while the primary loops remain as chromosomes. These latter become less twisted, forming a spirem or skein, and split into two sets, forming a dispirem or double skein, thus doubling the number FIG. 13. FIG. 14. FIG. 15. FIG. 16. FIG. FIGS. 13-17. Mitotic cell-division of fertilized whitefish eggs Coregonus albus (Huber). FIG. 13, Cell with resting nucleus, centrosome, and centrosphere to the right of the nucleus; FIG. 14, cell with two centrospheres, with polar rays at opposite poles of nucleus ; FIG. 15, spirem ; FIG. 16, monaster ; FIG. 17, metakinesis stage. of chromosomes (Fig. 10, 11). The number of chromosomes is subject to considerable variation in different animal cells. In some, four have been seen, in others as many as twenty-four. The achromatic spindle (Fig. 6) now appears. This consists of a spindle-shaped structure, at each end of which is a centro- some, the two having been formed from the original centrosome of the cell. These are connected by achromatin fibers i. e., fibers which are not colored by the staining-material used in the study 30 EPITHELIAL TISSUE. of the karyokinetic process. Whether these fibers are formed from the attraction-sphere or from the achromatin of the nucleus is unknown. Each of these centrosomes forms a pole of the spindle. The nuclear membrane now disappears, and there is nothing between the protoplasm of the cell and the nuclear matrix. The protoplasm in contact with the nucleus is clear, while that outside of this clear space is granular. In some cells these gran- ules have the appearance of fine fibers radiating from the centro- somes or poles, and constitute the amphiaster. The next stage is characterized by the settling of the chromo- somes to the equator of the spindle, where they form a star or aster, which being single is called monaster : this is known as the equatorial stage. The chromosomes now separate so as to form two distinct groups, constituting the stage of metakinesis. One group passes to one end or pole and the other to the other, thus forming a star at each end and giving rise to the term diaster or double star. This passage of the chromosome from the equator to the poles is believed to be accomplished by the contraction of the achromatin fibers of the spindle. Thus from the chromoplasm of the nucleus two new nuclei, or daughter-nuclei, are formed, each aster passing into a resting nucleus by a process the reverse of that by which it was formed, through the dispirem stage. A nuclear membrane forms around each new nucleus, and the protoplasm of the original cell subdivides into two, each half enclosing a new nucleus : at the same time the spindle disappears. ELEMENTARY TISSUES. EPITHELIAL TISSUE, Distributed over the surface of the body, lining its many cavities and canals, and in the ducts of glands, epithelium is found of several varieties and arrangement. The varieties are as follows : Pavement or scaly, cubical, columnar, goblet-cell, spheroidal or glandular, and ciliated. Pavement or Scaly Epithelium (Fig. 18). As its name implies, the cells of this variety of epithelium are thin and flat, and are arranged like the stones of a pavement. They are bound together by a small amount of cement-substance. They are found in the lung-alveoli, in the ducts of the mammary glands, and in the kidney in the tubes of Henle, and lining Bowman's capsules. These cells are also found covering serous membranes, as the peri- cardium, and lining blood-vessels and lymphatics, and in that case receive the name of endothelium. Cubical Epithelium. This kind of epithelium is of a COLUMNAR EPITHELIUM. 31 cubical shape, and occurs in the tubules of the testis and in the alveoli of the thyroid gland. FIG. 18. Isolated cells of squamous epithelium (surface cells of the stratified squamous epithelium lining the mouth) : a, a, cells presenting under surface ; 6, cell with two nuclei (Huber). Columnar Epithelium (Fig. 20). Columnar epithelium is sometimes described as cylindrie epithelium. The cells are of a prismatic shape, and usually rest upon a basement-membrane. When looked at from the free end, they present the appearance of a mosaic ; when ob- served from the side, the free edge is seen to be striated. This variety of epithelium lines the stomach and intestines, and the glands which open into these cavi- ties. It covers the mucous mem- brane of most of the urethra, the vas FlG - i9;-Surface view of squa- -, f, ,-* i j mous epithelium from skin of a deferens, prostate, Cowper's glands, frog; x400(B6hm and Davidoff). and the ducts of most glands. The germinal epithelium which covers the ovary is of this type. Goblet-cell (Fig. 22). A peculiar modification of columnar Goblet-cell. Cuticular border. FIG. 20. Simple columnar epithelium from the small intestine of man : o, isolated cells ; b, surface view ; c, longitudinal section (Huber). 32 EPITHELIAL TISSUE. epithelium is seen in the goblet-cell. This occurs in the intestine, for example ; the mucin, which is the product of the cell, distends the upper part of it, and the cell bursts (Fig. 22). The mucin is discharged as mucus, and the open, cup-like end of the cell gives to it the peculiar appearance characteristic of the goblet-cell. Goblet-cell. Cilia. FIG. 21. Cross-section of stratified ciliated columnar epithelium from the trachea of a rabbit (Huber). Formerly regarded as a simple modification of the columnar cell, these goblet-cells are probably more properly to be considered as a special kind of epithelium which is of a permanent nature, and whose function is to secrete mucus; hence they are sometimes called mucus-secreting cells. Spheroidal or Glandular Epithelium. This is charac- terized by its polyhedral or spheroidal shape, and occurs in secreting Nucleus... Basal process - FIG. 22. Goblet-cells from the bronchus of a dog: the middle cell still pos- sesses its cilia : that to the right has already emptied its mucous contents (collapsed goblet-cell) ; X 600 (Bohm and Davidoff). glands ; as, the salivary glands, liver, and pancreas. The secretion of these glands is the product of the protoplasm of the glandular epithelium. Ciliated Epithelium (Fig. 23). The characteristic of this variety is the cilia or hair-like or eyelash-like appendages attached CILIARY MOTION. 33 -Cilia. Cell-body. .Nucleus. FIG. 23. Ciliated cells from the bron- chus of the dog, the left cell with two nuclei ; X 600 (Bohm and Davidoff ). to the free surface of the cells. The cells which bear the cilia are usually of the cokimnar variety. Ciliated epithelium covers the mucous membrane of the respir- atory tract, which begins with the nose and ends in the alveoli of the lung, with the following exceptions : The olfactory membrane (that part of the/tnucous mem- brane of the nose to which the olfactory nerves^are distributed), the lower partf of the pharynx, the surfape of the vocal cords, the ultimate bronchi, and the lung-alveoli. It covers also the mucpus membrane of the tympanum, except the roof, promontory, ossicles, and mem- brana tympani, where the epi- thelium is of the pavement variety and non-ciliated. Cil- iated epithelium occurs also in the Eustachian tube, the Fal- lopian tube, the cavity of the body of the uteVus and of the upper two-thirds of the cervix, the vasa eiferentia and coni vasculosi of the testicle, the ventricles of the brain, and the central canal of the spinal cord. Some observers have seen ciliated epithelium in the convoluted tubules of the kidney. Ciliary Motion. Cilia are composed of protoplasm, and, like other protoplasm, have the power of motion ; but ciliary motion, though in some respects like that known as ameboid, is in other respects quite different. Instead of being slow, it is very rapid ten times and more a second so much so that when active, the individual cilia which produce it are indistinguishable. It has been likened to the movement of a field of wheat over which a breeze is passing. The effect of this movement is to produce a current always in one direction, and this current is often of con- siderable physiologic importance : thus it is to its influence that the ovum is carried down the Fallopian tube in the human female ; and, according to some authors, were it not for the ciliated epithe- lium in this canal the ovum would not find its way into the tube, but at the time it escapes from the ovary would fall into the peritoneal cavity and degenerate. Various explanations have been given to account for ciliary motion. One wl\ich seems reasonable is that it is due to the same cause which produces ameboid movement, namely, the flow of the hyaloplasm into and out of the spongioplasm. It is a well-known fact that if cilia are severed from the cells of which they form a part, this motion ceases, so that intimate connection with the 34 CONNECTIVE TISSUE. cells is essential. The protoplasm composing the cilia being thus in direct communication with that of the epithelium, being in fact a prolongation of it, the hyaloplasm can flow in and out without hindrance ; the inflow causing them to straighten, the outflow causing them to resume their original condition, which is curved ; this rapid inflow and outflow produce the characteristic motion. External agencies affect this motion as they do that of other protoplasm. Chloroform inhibits it, as do temperatures above 40 C. or below C. ; while dilute alkalies favor it. Simple Epithelium. When epithelium of either of these varieties is arranged in a single layer it is known as simple epi- thelium. Stratified Epithelium (Fig. 21). When the epithelial cells are arranged in many layers they form stratified epithelium, the cells of each layer differing in shape. Thus in the epidermis, the epithelium of which is of this variety, the deepest layer is columnar in character ; next to this is a granular layer of spindle-shaped cells ; then one of closely packed cells ; and, most superficial of all, are several layers of dry, horny scales'. Stratified epithelium is also found covering the mucous mem- brane of the mouth, the lower part of the pharynx, the esophagus, vagina, and outer third of the cavity of the cervix uteri, and the conjunctiva. Transitional Epithelium. This term is applied to epithe- lium which is arranged in a few layers two, three, or four. The line of demarcation between stratified and transitional epithelium is not very distinct. This variety exists in the ureters and bladder in three layers. The inner layer is composed of cuboidal cells, the next of pear-shaped cells, between the lower elongated ends of which is a third layer of small cells. The hair, the nails, and the enamel of the teeth are of an epithelial nature, though in a much modified form. Epithelium is nourished by lymph, and with few rare exceptions is not sup- plied with nerves : such exceptions are the epithelium covering the cornea and that in the deep layers of the epidermis. CONNECTIVE TISSUE. The term " connective " as applied to this large group of tissues implies that they are concerned in binding the body together into one organic whole, without which the tissues would be disconnected and the body lack the support which these structures afford. The following are the varieties : 1. Areolar ; 2. Adipose ; 3. Retiform ; 4. Lymphoid ; 5. Elastic ; 6. Fibrous ; 7. Jelly-lfke ; 8. Cartilage ; 9. Bone; 10. Dentin. Areolar Tissue. Areolar tissue consists of bundles of fibers presenting a wavy appearance (Fig. 24) running in various direc- ADIPOSE TISSUE. 35 tions, together with elastic fibers (Fig. 25) which do not form bundles and are not wavy. These fibers are bound together by a cementing-material or ground-substance. The irregular crossing of the fibers leaves spaces, called areolse, which give the name to the tissue. In these are connective-tissue cells or corpuscles, of which there are several varieties, the protoplasm of which pro- duces the fibers and the ground-substance. These varieties are : FIG. 24. Cell-spaces in the ground-sub- stance of areolar connective tissue (subcu- taneous) of a young rat; stained in silver nitrate (Huber). FIG. 25. Elastic fibers from the ligamentum nuchae of the ox, teased fresh ; X 500. At a the fiber is curved in a characteristic manner (Bohm and Davidoff). 1. Lamellar cells; 2. Plasma-cells of Waldeyer; 3. Granule-cells. Lymph-corpuscles are not infrequently seen, and in some places, as in the choroid coat of the eye, the corpuscles contain coloring- matter or pigment. Areolar tissue occurs under the skin as subcutaneous tissue, beneath serous membranes as subserous, and beneath mucous mem- ---. Nucleus. L"" Protoplasm. Fat-drop. Cell-membrane. FIG. 26. Scheme of a fat-cell (Bohm and Davidoff). branes as submucous, connecting these membranes loosely to the structures upon which they lie. Enclosing muscle, blood-vessels, and nerves, it forms their sheaths. It is also found in glands con- necting the various parts with one another. Adipose Tissue (Fig. 27). When the areolae of areolar tissue contain fat-cells, the tissue is called adipose. These fat- cells or adipose vesicles consist of an envelope or sac, protoplasmic 36 CONNECTIVE TISSUE. in character, within which is the fat in a fluid form. The tem- perature of the body during life is believed to keep this fat fluid ; FIG. 27. Adipose tissue (Leroy ; : a, fibrous tissue ; 6, fat-cells ; c, nucleus of fat-cells ; d, fatty acid crystals in fat-cells. but after death, when the temperature falls, the fat becomes solid. Free adipose vesicles would doubtless assume a spheroidal 4- ^ & . BfliSl Li-' Reticulum. Nucleus of connec- tive-tissue cell. Blood- vessel. FIG. 28. Eeticular connective tissue from lymph-gland of man ; Brush prepara- tion (Bohrn and Davidoffj. shape, but by compression, either of contiguous vesicles or other structures, they assume various shapes, oval or polyhedral. ELASTIC TISSUE. 37 Adipose tissue is widely distributed through the body; indeed, it is an exception to find areolar tissue without some fat in its areolse. The principal exceptions are the areolar tissue beneath the skin of the eyelids t the penis, the scrotum, and the labia minora. There is also no adipose tissue within the cranium, in the. liver, or in the lung, except near its root. It is to be understood that this statement does not apply to fat, but to adipose tissue, which is characterized by the fact that the fat is enclosed in a protoplasmic envelope. The fat is formed from the protoplasmic connective-tissue corpuscles, the cell-wall of which forms the wall of the vesicle. The nucleus of the cell remains, although it is not always readily discernible. Retiform Tissue (Fig. 28). This may be defined as areolar tissue whose ground-substance is fluid, and in which but few, if any, elastic fibers exist, and the white fibers form a close network. Authorities differ as to the identity of the white fibers of areolar and those of retiform tissue ; some claim that their different be- havior to certain reagents demonstrates them not to be the same. Retiform tissue exists in mucous membranes. I/ymphoid Tissue. When the areolae of retiform tissue contain lymph-corpuscles, which will be described in connection with the blood, the tis- sue is lympkoid or ade- noid. It is found in lym- phatic glands, the thy- mus gland, the tonsils, solitary glands, patches of Peyer, and Malpigh- ian corpuscles of the spleen. Elastic Tissue (Fig. 25). This tissue is composed of fibers or membranes which are characterized by their elasticity and a yellow color. By elasticity is defined "that property of matter by virtue of which a body tends to return to a former or nnrm-il :^^.s--"' Inner circum- ferential lamellae. FIG. 33. Segment of a transversely ground section from the shaft of a long bone, showing all the lamellar systems ; metacarpus of man ; X 56 (Bohni and Davidoff). with it, and the lacunae with one another by means of fine canals, canaliculi, into which project processes of the bone-corpuscles. A Haversian canal (Fig. 34) with its lamellae, lacunae, bone- BONE. 43 corpuscles, and canaliculi form a Haversian system. In a section of bone several of these systems may be seen, the spaces between them being occupied by interstitial lamellce. Lamellae which are on the surface of the bone, parallel with its circumference, are circumferential lamellce. A longitudinal section of bone shows the Haversian canals to be what their name indicates, channels running through the bone. Their communication with one another is also seen. In each canal are an artery and a vein. If a piece of bone is treated with dilute nitric acid, so as to dissolve the lime salts which it contains, or by some other method of decalcification, a small portion may be torn off, which upon examination shows the fibrous structure of the lamellae. Such specimens also show the perforating fibers of Sharpey, which hold the lamellae together; elastic fibers may also be observed. Lacuna." Canaliculi. Haversian canal. FIG. 34. Portion of a transversely ground disk from the shaft of a human femur; X 400 (Bohm and David off). Periosteum. This is a fibrous membrane which encloses the bones except where covered by cartilage. It is made up of an outer layer of connective tissue, in which there are blood-vessels which give off branches that go to the Haversian canals ; and an inner layer, in which elastic fibers are present. Between the peri- osteum and the bone in young animals are nucleated cells, the osteoblasts or bone-forming cells. Bone-marrow. Marrow is of two kinds, yellow and red. The yellow marrow is found in the interior of the shafts of long bones, in the medullary canal, and consists of fibrous tissue in which are blood-vessels and cells, fat-cells principally, although some marrow- cells and myeloplaxes also occur. The composition of yellow mar- row is : fat, 96 per cent, (no other structure of the body containing so much, adipose tissue containing but 82.7 per cent.) ; areolar tissue, 1 per cent. ; and 3 per cent, of fluid. Red marrow (Fig. 35) occurs in flat and short bones, the articular ends of long bones, bodies of vertebrae, cranial diploe, sternum, and ribs. In structure it resembles yellow marrow, except that fat-cells are few, while marrow-cells are very abundant. Chemically it is composed of 44 CONNECTIVE TISSUE. 75 per cent, water and 25 per cent, solids ; the latter consisting of salts, a very small amount of fat, and two proteids, one a cell- globulin coagulating at 47-50 C. and a nucleoproteid containing 1.6 per cent, of phosphorus. Hemoglobin is also present. Marrow-cells (Fig. 36). The cells of red marrow are of four kinds : 1. True marrow-cells, which are round, nucleated cells like white blood-corpuscles, but larger, and exhibiting ameboid motion. 2. Erythroblasts, pinkish in color, and in appearance like the nucle- ated red blood-corpuscles of the embryo. Some authorities regard these latter as cells which are originally true marrow-cells and afterward become red blood- corpuscles; while others hold that they are never marrow-cells, but have come directly from the nucleated blood-cells of the embryo and become red blood- corpuscles, the nuclei disappearing. In the erythroblasts the process of karyokinesis may often be observed. 3. Myeloplaxes ; these cells are also called giant cells, myeloplagues, and osteoclasts* These are very large nucleated cells, which are also found in the yellow marrow of the adult. 4. Cells which contain red blood- corpuscles in various stages of transformation into pigment, resem- bling the large cells found in the spleen, and called splenic cells. Blood-vessels of Bone. The periosteum sends branches of its blood-vessels into the compact tissue, some passing into the Haver- sian canals, while others continue on and supply the cancellous tissue in the interior. In the middle of the long bones is an opening, the nutrient foramen, through which passes the medullary or nutrient artery, with one or two veins, traversing the compact tissue to reach the medullary canal, where it supplies the tissue contained therein. Similar openings exist in other bones for the transmission of blood-vessels to their interior. It is claimed by some that the walls of the capillaries in the marrow are imperfect, and that through the openings which exist the red blood-corpuscles produced in the marrow find their way into the blood-circulation. Lymphatic Vessels of Bone. These are found in the periosteum and the bone-substance, and also in the Haversian canals. Nerves of Bone. The periosteum is supplied with nerves, and they also pass into bones through the nutrient foramina, Espe- cially rich in nerves are the articular extremities of long bones, the vertebrae, and the larger flat bones. Chemical Composition of Bone. Hoppe-Seyler gives the follow- ing analysis of undried bone without separation of marrow or blood : Water 50.00 per cent. Ossein (or collagen ). . 11.40 per cent. Fat . ... . 15.75 Bone earth 21.85 The following is Zalesky's analysis of human dried macerated bone : Organic constituents 34.56 per cent. Inorganic " , . . . 65.44 " " 100.00 BONE. 45 Gray states that the organic constituent of bone forms about 33 per cent., and the inorganic 66.7 per cent. He quotes the fol- lowing analysis of Berzelius : Organic matter ... . Gelatin and blood-vessels . (Phosphate of lime . . . . Carbonate " .... Fluorid of calcium ... Phosphate of magnesium . Soda and chlorid of sodium, 33.30 per cent. 51.04 11.30 2.00 1.16 1.20 The organic constituents are ossein, also called collagen ; elas- tin, proteids, and nuclein form the bone-corpuscles, with a small quantity of fat. The inorganic constituents are calcium phosphate, \ 4 - FIG. 35. From a section through human red bone-marrow : a, /, normoblasts ; 6, reticulum ; c, mitosis in giant cell ; d, giant cell ; e, h, myelocytes ; g, mitosis ; i, space containing fat-cells ; X 680 (Bohm and Davidoff ). carbonate, chlorid, and fluorid ; magnesium phosphate, sodium chlorid, and some sulphates. Of these inorganic constituents, calcium phosphate exists to the amount of 83.88 per cent., and calcium carbonate to the amount of 13 per cent. Development of Bone. Ossification, the process by which bone is formed, occurs in two forms : intramembranous and intracarti- laginous or endochondral. The subperiosteal variety described by some authors is, in all essential particulars, identical with the intramembranous. By the intramembranous are formed the parietal, frontal, and upper portions of the tabular surface of the 46 CONNECTIVE TISSUE. occipital bone ; while by the intracartilaginous, the humerus, femur, and other long bones are formed. Intramembranous Ossification (Fig. 37). This process may be studied in the parietal bone, which, prior to the beginning of ossification, about the seventh or eighth week of fetal life, is a fibrous membrane containing blood-vessels and osteoblasts (Fig. 37). The process begins in the center of ossification, which, in the parietal bone, is single, at the parietal eminence. The number of these centers varies in different bones ; in the frontal there are two. The embryonic membrane is composed of bundles of fibers, osteogenic fibers, with a granular matrix between them. Both the t- FIG. 36. Cover-glass preparation from the bone-marrow of dog ; X 1200 (from preparation of H. F. Miiller) (Bohm and Davidoff) : a, mast-cell; 6, lymphocyte; c, eosinophile cell ; d, red blood-cell ; e, erythroblast in process of division ; /, /, nor- moblast ; g, erythroblast. Myelocyte not shown in this figure. fibers and the matrix become calcified by the deposition in them of lime salts, and there is produced in them a calcareous mass enclosing blood-vessels and osteoblasts, which latter become bone- corpuscles, and the spaces in which they lie form the lacunae. The blood-vessels permeate the whole, the channels which they form being Haversian canals. It will be observed that in this variety of ossification a membranous structure precedes the bone ; hence the bone is said to Reformed in membrane. Intracartilaginous or Endochondral Ossification (Fig. 37). In this form cartilage precedes the bone, and the changes which result in bone-formation take place within it and practically convert it into bone. First Stage. In the first stage the cartilage-cells at the center BONE. 47 Connective tissue. Marrow space. Blood- ves- sel. Osteobla Osteoblasts. FIG. 37. From a cross-section of a shaft (tibia of a sheep) ; X 550 (Bohm and Davidoff) : in the lower part of the figure is endochondral bone-formation (the black cords are the remains of the cartilaginous matrix) ; in the upper portion is bone developed from the periosteum. of ossification become larger and arranged in rows ; in the matrix or ground-substance, between these rows of cells, lime salts are deposited in such manner as to form longitudinal rows of cells, separated by the calcified matrix ; in the matrix, between 48 CONNECTIVE TISSUE. adjacent cells, at right angles to these calcareous columns, lime salts are also deposited, thus forming spaces containing cartilage- cells, the boundaries of which are composed of the calcified matrix. These spaces or cavities are primary areolce. While this process is taking place at the center of the cartilage, beneath the mem- brane which envelops the cartilage, the perichondrium, or, as it is subsequently called, the periosteum, the osteoblasts form fibrous Vesicular cartilage- cells. Primary periosteal bone-lamella. _ Periosteal bud. Periosteum. Unaltered hyaline cartilage FIG. 38. Longitudinal section through a long bone (phalanx) of a lizard embryo (Bohm and Davidoff). The primary bone-lamella originating from the periosteum is broken through by the periosteal bud. Connected with the bud is a periosteal blood-vessel containing red blood-corpuscles. lamellae on the surface of the bone, which become calcified by the deposit in them of lime salts. Some osteoblasts are closed in by the lamellae and become bone-corpuscles. These changes which take place on the surface beneath the periosteum constitute sub- periosteal or intramembranous ossification, which has already been described ; thus, both kinds of ossification take place in the long bones. BONE. 49 Second Stage or Stage of Irruption. In this stage the blood- vessels and osteoblasts of the periosteum form processes which absorb portions of the bone recently made by intramembranous ossification, and of the walls of the primary areolae, thus pro- ducing larger spaces or cavities, sec- ondary areolce or medullary spaces; these contain osteoblasts and blood- vessels, which constitute embryonic marrow. Authorities differ as to the ultimate fate of the cartilage-cells; some think they become osteoblasts, while others teach that they are ab- sorbed. Third Stage. The osteoblasts of the embryonic matrix, increased in num- ber by division, form a layer of bone on the surfaces of the walls of the secondary areolse. On this bony wall another layer of osteoblasts forms a second layer of bone, and thus the process continues until only a small canal remains, the Haversian canal. The layers of bone, produced in the manner described, are the lamellae; while such of the osteoblasts as remain between the lamellae become the bone- corpuscles. No satisfactory explanation has been given of the method of pro- duction of the canaliculi. During this stage the process of ossification which began in the center of the bone extends toward the extremities, and thus the en- tire shaft becomes ossified. Histologists describe the multinucleated cells (sim- iliar to the myeloplaxes of the marrow) which are concerned in the absorption of the calcified matrix and bone under the name osteoclasts, reserving the term osteoblasts for the cells which form the bone. The shaft of the bone and its ex- tremities remain separated for a period of time which varies in different bones, and increase in length takes place by a growth of cartilage between the shaft and its epiphyses. This intermediate cartilage later ossi- fies, and the union of shaft and extremities is complete. Cartilagi- nous at first like the shaft, the epiphyses undergo ossification in FIG. 39. Longitudinal sec- tion through area of ossifica- tion from long bone of human embryo (Huber). 50 CONNECTIVE TISSUE. / Enamel. SHI- Pulp-cavity. the same manner. The bone becomes of greater circumference by the deposits made by the periosteum externally, and the medul- lary canal is made larger by the absorption of a portion of its walls. In the repair of bones, as after fractures, the periosteum performs the same office as in "\ the original formation \ of bone. \ Dentin. Thecon- \ sideration of this sub- /\ \ stance calls for a de- scription of the teeth, of which it forms an important part. A tooth (Fig. 40) is divided anatomically into the crown, the vis- ible portion, which pro- jects above the gum ; the root, the portion out of sight within the alveolus or socket ; and the neck, the constricted portion joining the crown and the root. In the center of the crown and extending into the roots is the pulp-chamber, the openings of which, at the tip of the roots, are apical foramina, through which pass b 1 o o d-v e s s e 1 s and nerves into the pulp- chamber, which con- tains dental pulp. This latter is com- posed of a gelatinous connective tissue with branched cells, to- gether with the blood- vessels and nerves just mentioned ; lymphatic vessels are absent. Some of the cells are in contact with the dentin of the tooth, and having been concerned in its formation are called dentin-forming cells or odontoblasts. The solid part of a tooth, excluding the pulp-chamber and its FIG. 40. Scheme of a longitudinal section through a human tooth ; in the enamel are seen the "lines of Retzius" (Bohm and Davidoif). DENTIN. 51 contents, is made up of dentin or ivory, enamel, and cement or crusta petrosa. Dentin. The main portion of a tooth is composed of dentin, which forms the walls of the pulp-chamber. It bears some resem- blance to bone, though the Haversian canals and lacunae, which characterize the latter, are not present ; it is, however, regarded as modified bone. Chemically it consists of 10 per cent, water and 90 per cent, solids, of which latter 27.70 per cent, is organic, collagen and elastin, and 72.30 per cent, inorganic. Of this, calcium carbonate and phosphate form 72 per cent., and magne- sium phosphate and calcium fluorid the rest. Microscopically, dentin is made up of dentinal tubuli, hollow tubes, which present a wavy appearance, between which is inter- tubular tissue. In general, the tubules are parallel with one Cementum. < Dentin. FIG. 41. Cross-section of human tooth, showing cement and dentin ; X 212 (Bohm and Davidoff ). At a are seen small interglobular spaces (Tomes' granular layer). another, although in the upper part of the crown they are arranged vertically, while in the neck and root they are oblique. They extend from the enamel and cement to the pulp-chamber, into which they open, and from the odontoblasts of which they receive processes ; the dentin thus resembling bone in which bone- corpuscles send processes into the canaliculi. At the ends, which open into the pulp-chamber, the tubules are unbranched, but as they extend toward the enamel and cement they divide dicho- tomously i. e., into two branches, each of which again divides in the same manner. They terminate beneath the enamel and cement in irregular communicating spaces, interglobular spaces or the granular layer. The intertubular tissue contains the greater portion of the inorganic constituents of the dentin. FIG. 43. v '&a*S8K :p Fio. 42. FIG. 44. FIG. 45. FIGS. 42-45. Four stages in the development of a tooth in a sheep embryo (from the lower jaw) (Bohm and Davidoff). FIG. 42, anlage of the enamel-germ connected with the oral epithelium by the enamel-edge ; FIG. 43, first trace of the dentinal papilla ; FIG. 44, advanced stage with larger papilla and differentiating enamel-pulp; FIG. 45, budding from the enamel-edge of the anlage of the enamel- germ, which later goes to form the enamel of a permanent tooth ; at the periphery of the papilla the odontoblasts are beginning to differentiate. FIGS. 42, 43, and 44, X 110; FIG. 45, X 40. a, a, a. a, Epithelium of the oral cavity; 6, 6, 6, 6, its basal layer ; c, c, c, the superficial cells of the enamel-organ ; d, d, d, d, enamel-pulp ; p, p, p, dentinal papilla; -s, a, enamel-forming elements (enamel-cells); o, odonto- blasts; 8, enamel-germ of the permanent tooth; r, part of the enamel-edge of a temporary tooth ; u, surrounding connective tissue. DENTIN. 53 Enamel. This covers the crown and extends to the root. It is the hardest part of a tooth indeed, it is the hardest tissue in the human body and protects the softer and more sensitive portion beneath in the process of mastication or chewing. It is made up of elongated hexagonal prisms, enamel-prisms, which are placed at right angles to the dentin (Fig. 46). Chemical analyses of enamel vary to a considerable extent. Hoppe-Seyler gives the following : Calcium carbonate and phos- phate, 96 per cent. ; magnesium phosphate, 1 per cent. ; and organic substances, 3 per cent. Other chemists state the amount of organic matter to be from 2 to 10 per cent. ; but the most recent - Enamel. - Branching of the dentinal tubules. Dentinal tubules. Interglobular J space. FIG. 46. A portion of a ground tooth from man, showing enamel and dentin ; X 170 (Bohin and Davidoff). analyses seem to show that the organic matter present in the enamel of a fully formed tooth is too minute to be weighed. Cement or Crusta Petrosa. At the point where the enamel ends the cement begins, and forms a covering of the dentin as far as the tip of the root. It is both structurally and chemically identical with bone, possessing both lacunae and canaliculi. The presence of Haversian canals is claimed by some histologists, es- pecially in the thicker portions ; while others deny it in normal teeth. Like bone, the cement is covered with periosteum, which 54 CONNECTIVE TISSUE. lines the alveolus and -holds the tooth in its place. It is here called pericementum. Development of Teeth (Figs. 42-45). About the seventh week of fetal life the germinal epithelium which covers the mucous mem- brane of the gums of the embryo, grows so as to form an elevated ridge, the maxillary rampart. A similar growth occurs downward into the tissue of the mucous membrane, forming the common dental germ or dental lamina. From this lamina ten cellular proc- esses, the special dental germs, are given off in each jaw, corre- sponding to the number of teeth. Each special germ becomes 21 Enamel-cells. Mi rF ""Odontoblasts. FIG. 47. A portion of a cross-section through a developing tooth (later stage than in Fig. 45) ; X 720 (Bohm and Davidoff). The den tin is formed, but has become homogeneous from calcification. Bleu de Lyon differentiates it into zones (a and 6). At c is seen the intimate relationship of the odontoblasts to the tissue of the dental pulp. flask -shaped, and later flattened, and still later indented on its under side. The special germ becomes the enamel-organ of the future tooth, as from it the enamel is produced. From the corium of the mucous membrane grows a vascular papilla, the dental papilla, which, as it grows, increases the indentation of the special germ and is covered by it. This papilla becomes the dentin and pulp of the tooth, the odontoblasts which cover it forming the dentin and the other portion the pulp. From the tissue which produces the papilla a vascular sac, the dental sac, is formed, which surrounds the special germ and its papilla. The dental sac and all the structures within it constitute the dental follicle. DENTIN. 55 The epithelial cells of the special dental germ become changed into three kinds of cells : (1) Columnar cells, adamantoblasts or ameloblasts. These are the deepest layer next the papilla, and therefore next the future dentin. The adamantoblasts form the enamel-prisms (Fig. 46), at first fibrous in character, later becoming calcified. (2) The outer cells, those adjoining the dental sac, be- come arranged into a single layer of cubical epithelium. Between the two the cells form a spongy network of (3) branching cells, whose processes communicate, forming the stellate reticulum or enamel-jelly or enamel-pulp. The name enamel-organ is now applied to this structure. The cement, which, as already stated, is identical with bone, is formed by the dental sac, whose internal tissue is in all respects the same as the osteogenetic layer of periosteum. The outer layer of this sac is the dental periosteum. The above description is that of the development or formation of the temporary or milk-teeth (p. 56). The permanent teeth are formed in the same manner. The process from which each of these latter is developed is an offshoot of the special dental germ, which produces a temporary tooth, and this offshoot undergoes the same changes. The milk-teeth are shed by the action of the osteoclasts of the dental periosteum, here called odontoclasts, which cause absorption of the roots of these teeth. While there are but ten temporary teeth in each jaw, there are, on the other hand, sixteen permanent ones, or six more ; the perma- nent molars, three on each side of the jaw, the first and secondmolars y and the wisdom-teeth. These arise from a backward extension of the dental germ, for which additional special germs are developed. The eruption or cutting of the teeth is due to the absorption of the gum about them by the pressure of the growing teeth. The alveoli or sockets are formed by the ossification of the tissue between the dental sacs. The ten teeth which replace the ten temporary are called succes- sional permanent teeth ; the other six, superadded permanent teeth. The molars of the temporary set are replaced by the pre molars or bicuspids of the permanent set, while the superadded teeth are the molars of the permanent set, and have no representatives in the temporary set. While the formation of the milk-teeth begins at about the seventh week of fetal life, that of the successional permanent teeth commences at about the sixteenth week, the second molars at the third month, and the wisdom teeth at the third year. Temporary, Milk-, or Deciduous Teeth. The first set of teeth, ten in number in each jaw, twenty in all, constitute the temporary, milk-, or deciduous teeth. Four of these are incisors, two canines, and four molars. The following table gives their arrangement and approximate time of eruption or cutting. 56 MUSCULAR TISSUE. TEMPORARY TEETH. Arrangement and Time of Eruption. One-half only of each jaw is represented, the arrangement and time of erup- tion being the same in the corresponding halves. Molars. Canine. Incisor. Middle line Second. First. Lateral. Central. of jaw. Upper jaw 1 1 1 1 Time of eruption ) in months after I . 20-24 15-21 16-20 15-21 8-10 birth . . . . J Lower jaw 1 1 1 1 Time of eruption ) in months after \ . 20-24 12 16-20 15-21 6-9 birth . . . . J Permanent Teeth. The second or permanent set consists of thirty-two teeth, sixteen in each jaw. The third molars or wis- dom teeth do not always appear. The following table gives the arrangement of these teeth and the approximate time of their eruption : PERMANENT TEETH. Arrangement and Time of Eruption. One-half only of the jaw is represented, the other half corresponding in all particulars ; and as the time of eruption of the permanent teeth of the lower jaw differs from that of the upper only in that it precedes it slightly, the upper jaw is alone represented. Bicuspid or Third or Molar. 1'remolar. Canine. Incisor. Middle line Wisdom. Second. First. Second. First. Lateral. Central, of jaw. Upper jaw .... 1 1 1 1 111 1 | Time of eruption ) in years after 1 17-25 12 6 10 9 11 8 7 birth . . . . J MUSCULAR TISSUE. The muscular tissue of the human body is of two kinds, volun- tary and involuntary r , both being possessed of contractility or the power to shorten. Voluntary Muscle (Fig. 49). This is composed of fibers having a length of 2.5 cm. or more, and a diameter of 0.05 mm., enclosed in a sheath, the sarcolemma (Fig. 48). The material possessed of contractile power, contractile substance, when viewed under the microscope presents the appearance of alternating dark and light stripes, strive, crossing it, giving to this variety the name of striated muscle. These striae are not superficial markings, but are in reality the edges of dark and light disks (Fig. 49). At the boundaries of the light striae are seen rows of granules, and run- ning through the dark striae lines connecting the granules. These lines mark longitudinally the subdivisions of the muscle, which VOLUNTARY MUSCLE. 57 are called muscle-columns, sarcostyles, or fibrils. When stained with chlorid of gold transverse lines are also seen uniting the granules, the whole arrangement of lines presenting a reticular appearance, FIG. 43. Striated muscle-fiber of frog, showing sarcoleinma (Huber). which, however, Schafer regards as in reality not a network, but only the optical expression of the interstitial substance between the muscle-columns, and which is called sarcoplasm. If a muscle-fiber is examined in cross-section, it is found to be divided into angular areas, Cohnheim's areas (Fig. 51). These are FIG. 49. Voluntary muscle (Leroy). A, Three voluntary fibers in long sections: a, three voluntary muscle-fibers; b, nuclei of same; c, fibrous tissue between the fibers (endomysium) ; d, fibers separated into sarcostyles. B, Fiber (diagrammatic): a, dark band ; 6, light band ; c, median line of Hensen ; d, membrane of Krause ; e, sarcolemma; /, nucleus. C: a, Light band ; b, dark band; c, contracting ele- ments ; d, row of dots composing the membrane of Krause ; e, slight narrowing of contracting element aiding in production of median line of Hensen. the cross-sections of the muscle-columns or sarcostyles, between which is the sarcoplasm. Hensen's line is a line crossing a muscle-fiber in the middle of 58 MUSCULAR TISSUE. a dark stripe, while Dobie's line crosses each light stripe. This latter is regarded by Schafer as not an actual structure, but an effect produced by the transmitted light. One authority, Hay- croft, regards the striated appearance of muscle as a refractive effect simply ; but the evidence of this is not convincing, and the difference in reaction to stain ing-agents seems to prove that the light and dark stripes of muscle-fibers are different structures. *Sarcoplasm. FIG. 50. Diagram of the struct- ure of the fibrils of a striated muscle-fiber ; the light spaces be- tween the fibrils may represent the sarcoplasin (Huber). Sarcoplasm. Fibrils. -Sarcolemma. FIG. 51. Transverse section through stri- ated muscle-fibers of a rabbit (Bohm and Davidoff). 1 and 3, from a muscle of the lower extremity; 2, from a lingual muscle; X900. In 2, Cohnheim's fields are distinct; in 1, less clearly shown ; in 3, the muscle- fibrils are more evenly distributed. Nuclei are to be seen under the sarcolemma of the muscular tissue presenting the usual appearance of cell-nuclei, often with spiral chromoplasm. Endomysium is the areolar tissue between the individual fibers, which are bound together by connective tissue, perimysium, into bundles, fasciculi; these in turn, united by the perimysium, con- stitute what is commonly called a muscle, whose investment or sheath is the epimysium. The muscles of insects are characterized by broad stripes whose VOLUNTARY MUSCLE. 59 structure is very distinct, and the following description from Schafer is very instructive. He says : " The wing-muscles of insects are easily broken up into sarco- styles (fibrils), which also show alternate dark and light striae. " The sarcostyles are subdivided at regular intervals by thin transverse disks (membranes of Krause) into successive portions, which may be termed sarcomeres. Each sarcomere is occupied by a portion of the dark stria of the whole fiber (sarcous element) : the sarcous element is really double, and in the stretched fiber separates into two at the line of Hensen. At either end of the sarcous element is a clear interval separating it from the mem- brane of Krause ; this clear interval is more evident the more the sarcostyle is extended, but diminishes to complete disappearance in the contracted muscle. The cause of this is to be found in the Nucleus. Muscle- substance. Sarcolemma. FIG. 52. Cross-section of striated muscle-fibers : 1, of man ; 2, of the frog ; the relations of the nuclei to the muscle-substance and sarcolemma are clearly visible ; X 670 (Bohm and Davidoff ). structure of the sarcous element. Each sarcous element is per- vaded with longitudinal canals or pores, which are open in the direction of Krause' s membranes, but closed at the middle of the sarcous element. In the contracted or retracted muscle the clear part of the muscle-substance has passed into these pores, and has therefore disappeared from view, but swells up the sarcous element and shortens the sarcomere in the extended muscle ; on the other hand, the clear part has passed out from the pores of the sarcous element, and now lies between this and the membrane of Krause, the sarcomere being thereby lengthened and narrowed. The sar- cous element does not lie free in the middle of the sarcomere, but is attached laterally to a fine enclosing envelope, and at either end to Krause's membrane by very fine lines, which may represent fine septa running through the clear substance." Schafer regards the sarcomere as similar to the protoplasm of an ameboid cell, the substance of the sarcous element being repre- 60 MUSCULAR TISSUE. sented by the spongioplasm, and the clear substance by the hyalo- plasm. When stimulated, the clear substance passes into the pores as the hyalo- plasm does into the spongio- plasm, thus producing con- traction ; and in the absence FIG. 53. Diagrams of the transverse stria- tion in the muscle of an arthropod ; to the right with the objective above ; to the left with the objective below its normal focal distance (after Rollet, 85) : Q, transverse disk; h, median disk (Hensen); E, terminal disk (Merkel) ; N, accessory disk (Engel- mann) ; J, isotropic substance (Bohm and David off). FIG. 54. Cardiac muscle, semidiagrammatic: a, nu- cleus; b, branch of fibers; c, cross-striation . of stimulation it passes out, as in the case of the ameba, causing in it the formation of pseudopodia, and in the muscle its extension. - Nucleus Contractile substance. Contractile substance. -Nucleus. FIG. 55. FIG. &>. Longitudinal and cross-section of muscle-fibers from the human myocardium, hardened in alcohol ; x640. The muscle-cells in the longitudinal section are not sharply defined, and appear as polynuclear fibers blending with one another : between them lie, here and there, connective-tissue nuclei (Bohm and Davidoff). INVOLUNTARY MUSCLE. 61 Nucleus. - Protoplasm. He calls attention to the similarity of the movements of the ameba, muscle, and cilia. Muscles are well supplied with blood-vessels, which run lengthwise of the muscle with transverse branches ; they do not penetrate the sarcolemma. The motor nerves of striated muscle terminate in motor end-organs, and the sensory nerves in muscle- spindles, which are further referred to in the discussion of Nerve- endings (p. 64). Besides the muscle- fibers, muscles contain connective tissue with some fat. Striated muscle is found in all the muscles of the body which are attached to bone, and is sometimes described un- der the name skeletal muscle. Although this variety is said to be voluntary, it is not in all places under control of the will, as, for instance, in the pharynx, esophagus, and the internal ear. Development of Striated Muscular Tissue. Embryonic cells of the meso- blast become elongated, and the nuclei form long fibers, which later become striated ; some of the nuclei remain beneath the sarcolemma as the nuclei of the muscle. Cardiac Muscle (F\g. 54). The mus- cle of which the heart consists differs from that just described in having its strise less marked, in being without sar- colemma, and in the fact that its fibers are short, each possessing a nucleus, and that they branch and join the fiber- cells contiguous to them. The nerves supplying cardiac muscle end in plexuses or networks. Involuntary Muscle (Fig. 57). This is also called plain and non-striated. It consists of flat, fusiform cells, contrac- tile fiber-cells, having lengths varying considerably, each possessing a nucleus and one or two nucleoli, and having longitudinal striae. The cells are joined together by means of an intercellular material. Involuntary muscular tissue is widely disseminated over the body ; it is found in the following locations : esophagus, muscular and mucous coats of the alimentary canal, bladder, ureter, uterus, Fallopian tubes, spleen, ciliary muscle, iris, ducts of glands, arte- FIG. 57. Smooth muscle- cells from the intestine of a cat : in 1, isolated ; in 2 and 3, in cross-section ; X 300. At a the cell is cut in the plane of the nucleus ; at c, in the neigh- borhood of the pointed end. In 3 (from Barfurth) is seen the manner in which neigh- boring cells are joined to one another by intercellular bridges (Bohm and Davidoff). 62 MUSCULAR TISSUE. ries, veins, lymphatics, sweat-glands connected with hair-follicles, scrotum, and areola of the nipple of the breast. The nerves of involuntary muscle end in plexuses or networks, as in the cardiac muscle. Development of Involuntary Muscular Tissue. The contractile fiber-cells which compose this tissue are formed from cells of the mesoblast, which elongate, the nuclei also elongating. The muscular tissue of the sweat-glands is formed from the epiblast. When new muscular tissue of the plain variety is formed, as when the uterus enlarges in pregnancy, growing from an organ weighing from 30 to 40 grams to one weighing from 900 to 1100 grams, this is accomplished by an increase in the size of the original fibers, and by the formation of new fibers from small cells which lie between the original ones. In the process of involution, that process by which the uterus returns to its original size, the fibers become fatty and are absorbed. Chemical Composition of Striated Muscular Tissue. The sarco- lemma resembles elastin. When the contractile substance is pressed, a fluid is expressed, the muscle-plasma, which coagulates, the clot being myosin. A similar change takes place after death, producing rigor mortis or cadaveric rigidity. During life muscular tissue has an alkaline reaction ; while after death, owing par- tially, at least, to the formation of sarcolactic acid, it becomes acid. This also occurs after the muscles have been very active. PERCENTAGE COMPOSITION OF HUMAN MUSCLES. Water 73.5 Proteids, including the sarcolemma, proteids of connective tissue, vessels, and pigments 18.02 Gelatin 1.99 Fat 2.27 Extractives 0.22 Inorganic salts 3.12 The proteids in muscle-plasma are three in number: 1. Para- myosinogen, which coagulates at 47-50 C., constituting 17 to 22 per cent, of the total proteid ; 2. Myosinogen or Myogen, coag- ulating at 56 C., 77 to 83 per cent. ; and traces of an albumin, Myo-albumin. Both paramyosinogen and myosinogen enter into the clot which forms when the plasma coagulates. This clot is called myogen-fibrin or myosin-fibrin. The extractives are very numerous, creatin, creatinin, xan- thin, hypoxanthin, earn in, carnic acid, uric acid, tannin, and inosinic acid, all containing nitrogen and fats, glycogen, inosit, dextrose, and sarcolactic acid. This acid is attributed by some authorities to the glycogen, while others trace it to the proteids. The presence of urea in mammalian muscular tissue is still a matter of dispute. Muscular tissue always contains fat, and there is excellent authority for believing that, while some of this comes NERVE-FIBERS. 63 from the adipose tissue which cannot be separated from the true muscular tissue, fat is also a constituent part of muscle-plasma. The coloring-matter of the red muscle is myohematin, which is probably produced from the hemoglobin of the blood. The inorganic salts are principally those of potassium, the most abundant being potassium phosphate. Composition of the Cardiac Muscle. This variety of muscular tissue contains paramyosinogen and myosiuogen, and undergoes cadaveric rigidity. Composition of Involuntary Muscular Tissue. Cadaveric rigidity has been observed in the stomach and uterus ; and from plain muscular tissue a proteid has been obtained which resembles myosinogen. NERVOUS TISSUE. The nervous tissue of the body is made up of nerve-fibers, nerve-cells, and neuroglia. Nerve-fibers (Fig. 58). This kind of nervous tissue is also called fibrous and white nervous matter. Fibrous nervous matter should not be confounded with fibrous connective tis- sue ; the term " fibrous" simply implies that the nervous substance is arranged in fibers. Nerve-fibers are medullated and non- medullated. Medullated Nerve-fibers (Fig. 58) are Medullary sheath. Fibrils of axial cord. -- Neurilemma. Segment of Lantermann. Axis-cylin- der. FIG. 58. FIG. 59. FIG. 58. Longitudinal section through a nerve-fiber from the sciatic nerve of a frog ; X 830 (Bohm and Davidoff ). FIG. 59. Medullate nerve-fiber from sciatic nerve of a frog; in two places the medullary sheath has been pulled away by teasing, showing the "naked axis- cylinder"; X212 (Bohm and Davidoff). 64 NERVOUS TISSUE. characterized by possessing a medullary sheath or white substance of Schivann, which gives the white color to the nerve-fiber. This is a protective covering to the essential part of a nerve, the axis- cylinder. The space inside the medullary sheath is the axial space, which is filled by the axial cord. This consists of axis-fibrils em- bedded in the neuroplasm, a material of semi-fluid consistency, both fibrils and neuroplasm being covered by a delicate mem- brane, the axolemma. When nerve-fibers have been prepared for microscopic examination the axial cord changes its appearance by the coagulation of the neuroplasm, and the altered cord is what is commonly called the axis-cylinder. The primitive sheath, nucleated sheath of Schwann, or neurilemma, is a membrane which encloses the white substance of the nerves, except- ing those within the nerve-center. Neuri- lemma (also written neurolemma) is a term formerly applied to what is now called peri- neurium. The medullary sheath is not continuous ; at regular intervals it is absent, and only the primitive sheath and axis-cylinder are present. This gives to the nerve the ap- pearance of constrictions, known also as the nodes of Ranvier. The portion of nerve between these constrictions is an internode, in the middle of which is a nu- cleus. Medullated fibers make up the white part of the brain and spinal cord, and the nerves that have their origin in these struct- ures, the cerebrospinal nerves. In size they vary from 2 p to 19 p.. This variety never branches except near the termination. Nonmedullated Nerve-fibers (Fig. 60). These are also known as gray, gelatinous, and fibers of Remak. These have no white sub- stance, but are composed of fibrillae, which are probably enclosed in a sheath, the neurilemma, in which are nuclei. Nonmedullated fibers, unlike those that are medullated, fre- quently branch. Nerve-fibers are associated together in bundles, funiculi (Fig. 61), each of which bundles is enclosed in a sheath of connective tissue, perineurium. The funiculi are surrounded by a similar sheath, the epineurium, which binds them together and in which are the blood-vessels, lymphatics, and nerves of the nerves, the last being the nervi nervorum. Within the funiculi is connective tissue, embedded in which are the nerve-fibers. Modes of Termination of Nerve-fibers. The nerves which supply striated muscle subdivide near their ends, and one of the - Nucleus. FIG. 60. Remak' s fibers (nonmedullated fibers) from the pneutnogastric nerve of a rabbit ; X 360 (Bohm and Davidoff). NERVE-FIBERS. 65 branches goes to a muscular fiber. Its primitive sheath is con- tinuous with the sarcolemma, and the medullary sheath terminates. The axis-cylinder breaks up into fine ramifications, which are em- bedded in granular nucleated protoplasm ; this is a motor end-organ or end-plate (Figs. 62-65). In involuntary muscle the nerve-fibers end in plexuses, from which fine branches pass to the contractile fiber-cells. Nerve-fibers also end in special organs, of which there are various kinds : End-bulbs of Krause, tactile corpuscles, Pacinian corpuscles, organs of Golgi, and muscle-spindles. End-bulbs (Fig. 67). An end-bulb consists of a cylindrical, oblong, or spheroidal body formed from the connective- tissue sheath of a medullated nerve-fiber. Within this is a core with many nucleated cells, in which the axis-cylinder terminates. End- Connective - tissue. Fibrils of axial ^ Wm&^ZS&ZMll Wm^?-~ Fibrils, cord. Medullary sheath. FIG. 61. Transverse section through the sciatic nerve of a frog ; X 820; at a and 6 is a diagonal fissure between two Lantermann segments ; as a result, the medullary sheath here appears double (Bohm and Davidoff). (Compare Fig. 60.) bulbs are found in the conjunctiva, in the papillae of the lips and tongue, the skin and mucous membrane of the penis, the clitoris, vagina, epineurium of nerve-trunks, and in tendon. In the synovial membrane of some joints, as in the fingers, end-bulbs also occur, and are here called articular end-bulbs. Tactile Corpuscles. These consist of connective tissue which forms a capsule, from which are given off membranous partitions or septa. After winding around the corpuscle the axis-cylinder enters it, and terminates in an enlargement. Tactile corpuscles occur in the papillae of the skirt of the hand, foot, front of the forearm, lips, and nipple ; also in the mucous membrane of the tip of the tongue and the conjunctiva lining the eyelids. Pacinian Corpuscles (Fig. 70). These are also called corpuscles of Vater. Each corpuscle consists of concentrically arranged layers of connective tissue, with nucleated cells. A medullary NERVOUS TISSUE. -So-called granular sole. == 1=:^=?=-- -Nerve. FIG. 63. Nerve. So-called 'i granular sole. I End-brush. 'Muscle- fiber. FIGS. 64 and 65. So-called - granular sole. End-brush. Sarco- lemma. FIGS. 62-65. Motor endings in striated voluntary muscles. FlG. 62, from Pseudopus Pallasii ; X 160. FIG. 63, from Lacerta viridis ; X 160,, FIGS. 64 and 65, from a guinea-pig ; X 700. FIG. 66, from a hedgehog ; x 1200. As a consequence of the treatment (T. 182, I) the arborescence is shrunken and in- terrupted in its continuity. In Figs. 62 and 63 the end-plate is considerably larger than in Figs. 64 and 65. In Fig. 62 it is in connection with two nerve-branches. Fig. 66 shows a section through an end-plate. The latter is bounded externally by a sharply defined line, which can be traced along the surface of the muscle-fiber. This is to be regarded as the sarcolemma (Bohm and Davidoff). NERVE-FIBERS. 67 nerve-fiber enters at one end and passes into an interior space which contains a transparent substance ; here only the axis- FIG. 67. End-bulb of Krause from conjunctiva of man ; methylene-blue stain (Dogiel). FIG. 68. Cylindric end-bulb of Krause from intermuscular fibrous tissue septum of cat ; methylene-blue stain (Huber). cylinder is present. This terminates at the end of the corpuscles in an enlargement or in minute branches, an arborization. These corpuscles exist in the subcutaneous tissue of the palm -- Nucleus of lamellae. End-cell of core. Lamellae. Axis-cylinder in core. Cubic cells of core. - Termination of medul- lary sheath. Axis-cylinder of nerve- fiber. Medullary sheath of nerve-fiber. Neurilemma and sheath of Henle. FIG. 69. Corpuscle of Herbst from bill of duck ; x 600 (Bohm and Davidoff). of the hand and sole of the foot, and in the penis. Observers have also found them in the pancreas, lymphatic glands, and thyroid. 68 NERVOUS TISSUE. FIG. 70. Pacinian corpuscles from mesorectum of kitten: A, showing the fine branches on central nerve-fiber ; B, the network of fine nerve-fibers about the cen- tral fiber ; methylene-blue preparation (Sala). FIG. 71. Genital corpuscle from the glans penis of man ; methylene-blue stain (Dogiel). FIG. 72. Meissner's tactile corpus- cle ; methylene-blue stain (Dogiel). NERVE-CELLS. 69 Organ of Golgi (Fig. 73). At the point where muscles and their tendons join, the tendon-bundles present an enlargement, between the fasciculi of which one, two, or more nerve-fibers enter to terminate in an arborization which is characterized by varicosities. The term " organ of Golgi " includes the enlargement and the arborizations. Muscle-spindles. These are de- scribed under the name neuro-mus- cular spindles. A spindle is a fusi- form body having a length of from 0.75 mm. to 4 mm. Externally is a sheath of connective tissue within which is the interposed bundle, con- sisting of from ten to twelve muscle- fibers, resembling embryonic fibers. The nerve-fibers distributed to these spindles divide, and the axis-cylin- ders clasp the fibers by flattened ex- pansion. None of these spindles has been found in either the muscles of the eye or the tongue. They are con- sidered to be sensory nerve-endings in the muscles. Nerve-cells (Figs. 75-78). This kind of nervous tissue is also called gray, cineritious, cellular, vesicular, nervous matter. Nerve-cells are of different sizes, varying from 4 p. to 150 /j>. Their shape also varies greatly, some being ovoid, while others are very irregular in outline. Each cell contains a large, distinct, and spheroidal nucleus, with a single nucleolus, and fibrillated pro- toplasm. In the protoplasm are some- times angular granules, Nissl's gran- ules, which are stained by methylene- blue. From nerve-cells are given off two kinds of processes : axis-cylinder pro- cesses or neuraxe,, and protoplasmic processes or dendrites. These are the preparation of tissue stained in principal elements in nerve-fibers, methyiene-blue (Huber and De ,, r Witt, Jour, of Comp. A enrol., vol. Ine number 01 these processes or x .). 70 NERVOUS TISSUE. poles determines the name of the cell : thus a cell with one pole * * Sfc- ' m%mm&. p FIG. 74. Cross-section of neurotendinous nerve end-organ of rabbit, from tissue stained in methylene-blue : m, muscle-fibers ; t, tendon ; c, capsule of neurotendi- nous end-organ ; m n, medullated nerve-fiber (Huber and DeWitt, Jour, of Comp. Neurol., vol. x..). is unipolar ; one with two poles, bipolar ; and one with three or more, multipolar. Nucleus. r , Nucleolus. Fibrillar structure. Medullary sheath. FIG. 75. Bipolar ganglion-cell from the ganglion acusticum of a teleost (longi- tudinal section) ; the. medullary sheath of the neuraxis and dendrite is continued over the ganglion-cell ; X 800 (Bohm and Davidoff). The process in a so-called " unipolar" cell is, in reality, two processes which have become united. Such cells occur in the spinal ganglia (Fig. 78). NERVE-CELLS. 71 Axis-cylinder Process. Every nerve-cell has an axis-cylinder process, which, in the medullated nerve-fiber, becomes the axis- cylinder, and in the non-medullated is the nerve-fiber itself. This ,. Dendrite. Neuraxis. FIG. 76. A ganglion-cell from anterior horn of the spinal cord of calf; teased preparation ; X 140 ; by this method only the coarsest ramifications of the dendrites are preserved ; the rest are torn off (Bohm and Davidoff ). process is characterized by the fact that it gives off a few side-shoots, collaterals in its course ; thus its branching is very limited. To this process some histologists apply the term neuronj -Dendrite. Neuraxis. Neuraxis. Dendrite.-" FIG. 77. Motor neurones from the anterior horn of the spinal cord of a newborn cat; chrome-silver method (Huber). while others call it neuraxon, or axon, and reserve the term "neuron* 1 for the whole nerve-unit that is, the cell and all its processes, for which the term neurone is more commonly used. 72 NERVOUS TISSUE. Cells which have but one axis-cylinder process are mononeuric ; those having two such processes are dineuric ; and trineuric is applied to those having three. Most nerve-cells are mononeuric. Ganglia. A ganglion is a collection or group of nerve-cells. These occur upon the posterior roots of the spinal nerves (Fig. 78), upon some of the cranial nerves, and in connection with the sympathetic nervous system. In these structures the cells have a nucleated sheath continuous with that of the nerve-fibers con- nected with them. From each cell in the ganglion, upon the roots of the spinal cord, and among the cranial nerves is given off but one process, the axis-cylinder process. Passing in a convoluted form from the cell, this process, before it leaves the ganglion, divides into two, one going to the nerve-center, the other to the periphery. From this descrip- tion it will be seen that these cells have no dendrons. In the cells of the sympathetic ganglion, besides the axis-cylin- der process, there are also sev- eral dendrons. Protoplasmic Process. Unlike the axis-cylinder process, this va- riety is characterized by its fre- quent branching. The larger branches are called dendrons, and the finer ones dendrites. FIG. 78. Ganglion-cell with a pro- mi i ,1 ,1 T cess dividing at a (T-shaped process); I he idea that the axiS-cylm- from a spinal ganglion of the frog; J er process alone COnvevS lier- X230 (Bohm and Davidoff). . -, j ,1 , .1 i vous impulses, and that the den- drons and dendrites are nutritive organs exclusively, is at the present time replaced by the belief that nervous impulses also travel along the branches of the protoplasmic process. The anatomic fact that the fibrils of the axis-cylinder have been traced through the body of the cell into the dendrons, seems to substantiate this theory. It is a most important fact that the nerve-unit, or the " neu- rone" of some writers that is, the nerve-cell and its branches does not anastomose or join with any other nerve-unit, but the terminal twigs or arborizations of one intertwine with those of another, and nerve-impulses may thus pass from one to the other. This inter- twining is called synapse, a word literally meaning a clasping. This subject will be again referred to when the physiology of nerves is discussed. Neuroglia (Fig. 79). This is sometimes spoken of as a con- nective tissue, but it is in structure unlike connective tissue as we have studied it. It is also unlike it chemically, consisting of NEUROGLIA. 73 neurokeratin. Its origin from fhe epiblast also differentiates it from connective tissue, which arises from the mesoblast. Neuroglia is the supporting tissue of the nerve-cells and nerve- fibers of the brain and spinal cord. It consists of cells and fibers. In describing ciliated epithelium it will be remembered that among the locations in which it was found the ventricles of the brain and the central canal of the spinal cord were mentioned. From the attached ends of these cells branching neuroglia-fibers pass to the surface of the brain and the cord, and terminate at the pia mater in enlargements. Other fibers of the neuroglia arise from cells, neuroglia, glia- or spider-cells, which are stellate in shape. These fibers aid in supporting the nerve-cells and nerve-fibers. Development of Nerve-cells and Nerve-fibers. The following description is from Schafer: "All nerve-cells in the body are developed from the cells of the neural groove and neural crest of the early embryo; the neural groove closing to form the neural canal, the cells of which form the spinal cord and brain, and the neural crest giving off, at intervals, sprouts which become the rudiments of the ganglia. The cells which line the neural canal are at first all long, columnar cells, but among these, and probably produced by a metamorphosis of some of these, rounded cells (neuroblasts) make their appearance, and presently from each one a process begins to grow out. This is the axis-cylinder process (neuron) and is char- acterized by its enlarged ex- tremity. As it grows, it may emerge from the anterolateral regions of the canal and be- come a motor neuron or ante- rior root-fiber. The dendrons appear somewhat later than the neuron. The axis-cylinder processes of some of the neu- roblasts remain Avithin the nerve-centers, and are devel- oped into association or intra- central fibers. "The sprouts from the neural crest contain the neu- roblasts from which the pos- terior root-fibers are devel- oped. Neurons grow out from these neuroblasts in two directions, so that the cells become bipo- lar, one set, forming the posterior root-fibers, grow into the pos- terolateral portion of the spinal cord, and ramify in the develop- ing gray matter ; the other set, containing the afferent fibers of the FIG. 79. Neurogliar cells : a, from spinal cord of embryo of cat ; 6, from brain of adult cat ; stained in chrome silver (Huber). 74 NER VO US TISSUE. mixed nerves, grow toward the developing anterior roots, and eventually mingle with them to form the mixed nerves. As development proceeds, the bipolar ganglion-cells become gradu- ally transformed in most vertebrates by the shifting of the two neurons, into unipolar cells ; but in many fibers the cells remain permanently bipolar. "The ganglia on the sympathetic and on other peripheral nerves are formed from small masses of neuroblast-cells, which separate off from the rudiments of the spinal ganglia and give origin to neurons and dendrons much in the same way as do the neuroblasts within the central nervous system. " The manner in which the medullary sheath and neurolemma of the nerve-fibers are formed is not well understood. The neuroglia- cells appear to be developed from cells which are at first similar to the neuroblasts, but, in place of giving off a neuron and den- drons, a number of fine processes grow out from the cell in all directions, forming the fibers of the neuroglia." Chemistry of Nervous Tissue. The following is the analysis of the brain of an ox by Petrowsky : Gray Matter. White Matter. Water 81.60 per cent. 68. 30 per cent. Solids 18.40 " 31.70 " " 100.00 100.00 The percentage composition of the solids is as follows : Gray Matter. White Matter. Proteids 55.37 24.72 Lecithin 17.24 9.90 Cholesterin and fat 18.68 51.91 Cerebrins 0.53 9.55 Other organic compounds (including neurokera- tin and protagon) 6.71 3.34 Salts 1.45 0.57 Halliburton divides the solid constituents of the nervous tissues into the following classes : a. Proteids. These comprise a very considerable percentage of the solids, especially in the gray matter (over 50 per cent.). 6. Neurokeratin and nuclein. c. Phosphorized constituents, especially protagon and lecithin. d. Cerebrins. Nitrogenous substances of unknown constitu- tion. e. Cholesterin. Especially abundant in white matter. f. Extractives. Creatin, xanthin, hypoxanthin, inosit, lactic acid, leucin, uric acid, and urea. g. Gelatin and Fat. From the adherent connective tissue. h. Inorganic Salts. The total mineral matter varies, according to different writers, from 0.1 to 1 per cent. CHEMISTRY OF NERVOUS TISSUE. 75 Geoghegan gives the following as representing parts per 1000 of brain : Total ash . . 2.9 to 7.1 , Chlorin . . 0.4 to 1.2 Potassium 0.6 "1.7 Sodium 0.4 "1.1 Magnesium 0.0 " 0.07 Calcium . 0.005" 0.02 PO 4 0.9 "2.0 CO 3 0.2 "0.7 SO 4 0.1 "0.2 Fe(POJ, 0.01 " 0.09 Halliburton gives the following table, which shows the propor- tion of water, solids, and proteids in different portions of the nervous system. The table represents mean analyses of the organs of adult human beings, dogs, cats, and monkeys : Percentage of Water. Solids. proteids in solids. Gray matter of cerebrum 83.467 16.533 51 White " " 69.912 30.088 33 Cerebellum 79.809 20.191 42 Spinal cord as a whole 71.641 28.354 31 Cervical cord 72.529 27.471 31 Dorsal " 69.755 30.245 28 Lumbar " 72.639 27.631 33 Sciatic nerves 61.316 38.684 29 The percentage of neurokeratin is in gray matter 0.3 ; in white matter, 2.2 to 2.9 ; and in nerve, 0.3 to 0.6. Proteids of Nervous Tissue. The proteids are : 1. A globulin, coagulated by heat at 47 C., analogous to the cell-globulin derivable from cellular tissues generally ; 2. Nucleoproteid, which coagulates at 56-60 C. and contains 0.5 per cent, of phosphorus ; and 3. A globulin coagulating at 70-75 C., analogous to a glob- ulin obtained from the liver. Protagon. It was for some time undecided whether this sub- stance, which was separated from the brain by Liebreich, was a definite substance or a mechanical mixture of lecithin and cerebrin; but the evidence now at hand seems conclusive in favor of its definiteness of chemic composition. Its percentage composition, as given by Garngee and Blankenhorn is C, 66.39 ; H, 10.69 ; N, 2.39; P, 1.068; and O, 19.462. The empirical formula is C^H^NgPO^. It is probable that there are more than one pro- tagon. Cerebrin. This constituent of nervous tissue should be spoken of as cerebrins, as there are more than one. The constitution of them is not known. They contain nitrogen and yield galactose on hydration. They are also called cerebrosides, and are constitu- ents of the medullary sheaths, and are also found in the yolk of egg, pus-corpuscles, and spleen-cells. II. PHYSIOLOGIC CHEMISTRY. PHYSIOLOGIC chemistry, as applied to the human body, may be defined as the science which treats of the ingredients of the human body and of the human food. These ingredients are spoken of by some writers as " proximate principles," by others as the " chemical basis/' and by still others as " physiologic ingredients." The latter term is the one which will be adopted, as it is the most expressive. If the human body is analyzed into its ultimate chemical ele- ments, it will be found that of the sixty-nine elements known to chemists no less than fifteen are constantly present. These elements are oxygen, carbon, hydrogen, nitrogen, calcium, sodium, potas- sium, iron, phosphorus, sulphur, magnesium, chlorin, fluorin, sil- icon, and iodin. Some authorities place lithium also in this list. As fluorin and silicon occur in such small proportions, they may be omitted from consideration altogether. To obtain most of these substances in their elementary form such processes must be adopted as will utterly destroy the tissues. In the body, in its living state, most of these substances do not exist in their elementary condition ; and, however interesting it may be to know all the facts about them, still a knowledge of the properties of these elements does not help to an understanding of their offices in the human body. What is really desired to be known is, under what forms these elements exist in the body during life, and not what can be obtained by the analytic chemist. Chemical elements and physiologic ingredients are not inter- changeable terms. A physiologic ingredient may be defined as a substance which exists in the body under its own form. To deter- mine, then, whether a given substance is or is not a physiologic ingredient of the human body, it must be ascertained whether it does or does not exist there under its own form. For instance, if it is asked if carbon is a physiologic ingredient, before the question could be answered we should have to determine whether carbon exists in the body under its own form that is, as carbon. Chemistry demonstrates that carbon, as an element, is found in nature in but three forms, namely, as coal, as the diamond, and as graphite or plumbago. In the human body none of these sub- stances is found ; therefore carbon does not exist under its own form, and consequently is not a physiologic ingredient, although 76 CLASSIFICATION OF PHYSIOLOGIC INGREDIENTS. 77 more than one-eighth of the body is made up of carbon, and this amount can be obtained from it. But this carbon does not exist under its own form that is, free or uncombined but it is all in a state of combination, as carbonates or in carbohydrates or other forms of combination, and when we obtain the carbon as an ele- ment these combinations are broken up and the carbon is set free. Water is a physiologic ingredient, because it exists in the body under its own form, and can be obtained therefrom without the use of such violent means as are necessary to destroy chemical combinations. It is exceedingly important to have a clear conception of what are and what are not physiologic ingredients : all that can be learned of them and their properties will be of assistance ; but a knowledge of the properties of their chemical elements will be of no special aid in our physiologic studies, for the properties of a com- pound are not the sum of the properties of its component parts. One might be thoroughly conversant with the properties of oxygen and hydrogen, and yet have no possible conception of the proper- ties of water, which their combination forms. Classification of Physiologic Ingredients. The physio- logic ingredients of the human body may be -classified as fol- lows : Inorganic ; Carbohydrates ; Fats ; Proteids ; Albuminoids ; Enzymes. Other ingredients will be discussed in connection with the solids or liquids in which they occur. Water. INORGANIC INGREDIENTS. Salts Sodium Potassium . . Calcium . . Magnesium . Ammonium . Chlorid. Phosphate. Biphosphate. Sulphate. Carbonate. Bicarbonate. C Chlorid. j Phosphate. } Sulphate. (^ Carbonate. T Phosphate. < Carbonate. ( Fluorid. f Phosphate. ( Carbonate. Chlorid. 78 INORGANIC INGREDIENTS. aSL }** I lodin. Oxygen. Hydrogen. Nitrogen. Marsh-gas. Ammonia. Sulphuretted Hydrogen. Hydrochloric Acid. Carbon Dioxid. Water (H 2 O). Water is one of the most important of the physiologic ingredients. Its quantity in the human body is vari- ously stated by different authorities : Halliburton placing it at 58.5 per cent, of the body- weight of an adult, and 66.4 per cent, of that of infants, while others give it as 68 per cent. It is found in all the tissues, both solid and fluid. Quantity of Water in the Body. The percentage of water in some of the solids and fluids of the body is as follows : Enamel of teeth 0.2 Dentin . . 10. Bones (undried) 50. Costal cartilage 67.66 Corpuscles of venous blood 68.16 Muscles 73. Human milk 87. Plasma of venous blood 90.15 Urine 93. Gastric juice 98. Perspiration . 98. Saliva 99. Pulmonary vapor 99. From this table it will be seen that while water makes up but a small part of the enamel of the teeth, it constitutes almost the whole of the saliva. Between these two extremes it is present in different tissues in varying proportions. It should be said of these, and of most other quantities given in physiologic tables, that they are not invariable, hence the analyses of different author- ities will vary. The composition of the milk, for instance, is not always the same ; therefore there will not invariably be 87 per cent, of water present; but the normal variations from this figure, either above or below, will not be very great, and the percentages given in the above table may be regarded as averages. Offices of Water. We should naturally infer from the large quantity of water present in the body, and from its universal presence in all the solids and liquids, that its offices must be important ; and a study of these demonstrates that this is a fact. It is the water which gives to fluids their fluidity. Without this property the blood could not circulate through the blood-vessels, WATER. 79 nor dissolve and hold in solution the nutritive materials which it supplies to the tissues, nor carry the waste materials to the vari- ous organs whose duty it is to eliminate them. Without water the saliva would cease to be the important agent it is in softening the food in the mouth preparatory to its being swallowed. In short, without water as an integral part of the fluids of the body these fluids w r ould cease to be fluids, and the many and varied offices which they subserve would at once be abolished, and life could no longer be maintained. Equally important, though less apparent, are the various offices which are subserved by water in the solids of the body. From the above table it is seen that water exists in the muscles to the amount of 73 per cent. The striking property of muscles is their power of contractility, or ability to shorten. By the exercise of this property all the movements of the different parts of the body are accomplished : without this power locomotion would be impos- sible, the movements of the heart would cease, and death would quickly supervene. A muscle deprived of its water would cease to possess this contractile power in other words, would lose its characteristic function. It must not be inferred from this, how- ever, that it is to the water that muscles owe their contractility, but simply that its presence is one of the conditions essential to the exercise of this power. As will be seen later, the skin pos- sesses most important functions those, for instance, of sensation, of excretion, and of protection. All these functions would be destroyed if the water in the skin was expelled. Perhaps this fact is nowhere more strikingly evident than in studying the func- tions of the skin of the palm of the hand. The pliability of this portion of the skin, by which objects are grasped, and the sense of touch, by which it can be determined whether they are hard or soft, whether rough or smooth, whether hot or cold, are both dependent on the presence of water in the skin, and the mere evaporation of the water would at once make the skin hard and rigid, its pliability would vanishj and its functions would cease. Sources of Water. The water which exists in the body is derived from two principal sources : First, from the food, and second, from its formation in the interior of the body, the former being the main source of supply. As water is a constituent part of every tissue of the human body, so it is of all the varieties of food, both solid and liquid, taken into the body. The quantity of water in food (percentage) is as follows : Wheat bread (fresh) 33 Mackerel 70 Lean beef 70 Potato 76 Human milk 87 Cows' milk 87 Green vegetables 88 80 INORGANIC INGREDIENTS. From this table it will be seen that the greater part of potato and of green vegetables is water, and that even of bread, water con- stitutes a third. In other words, three of every four pounds of potatoes and one of every three pounds of bread are water. In some vegetables, such as the turnip, about 90 per cent, is water. In liquid food, as milk, tea, and coffee, the proportion of water is, of course, still greater. The amount of water daily taken into the body in solid and liquid food aggregates 2000 c.c. In addition to this there is a small amount actually formed within the body. One of the important ingredients of food is the class of carbo- hydrates. A study of their composition shows that hydrogen and oxygen exist in these substances in such proportion as to form water. In the various changes which these elements undergo in the body water is formed. Besides this source there is reason to believe that a small quantity of water is formed by the action of free oxygen on some organic substances. The amount of water daily formed in these two ways is not far from 500 c.c., which makes, with the water taken in with the food, a total of 2500 c.c. Avenues of Discharge from the Body. The water which has been shown to form so essential a part of the body is not, how- ever, a permanent ingredient that is, while water is always pres- ent, it is not the same water : that which at one time exists in the tissues is soon replaced by other water. The amount daily dis- charged is equal to the amount taken in with the food and formed in the body that is, about 2500 c.c. The avenues by which it passes out, and the proportion by each, are as follows : Large intestine, as feces 4 per cent. Lungs, as watery vapor 20 " Skin, as perspiration 30 u Kidneys, as urine 46 u When discharged it is not pure water, but contains ingredients that vary according to the channel by which it is eliminated. The composition of these ingredients respectively will be studied in the appropriate places. Salts. Sodium chlorid or common salt (NaCl) is present in all the solids and fluids of the body, except in the enamel of the teeth. The quantity (percentage) in different solids and fluids is as follows : Milk 0.03 Saliva 0.15 Gastric juice 0.17 Perspiration ] 0.22 Blood t . o^33 Urine 0.55 Bones / 0.70 The total quantity of common salt in the human body is 110 grams. Offices of Sodium Chlorid. The most important office which SALTS. 81 sodium chlorid subserves is in connection with the process known as " osmosis," or the diffusion of liquids' through animal membranes, a subject which will be discussed in connection with the process of absorption. A second office which it pos- sesses is to hold in solution the globulins. TJie globulins are proteids which are not soluble in distilled water, as are the native albumins, but are soluble in dilute solutions of sodium chlorid (1 per cent.). The so-called " normal" or " physiologic" salt-solu- tion is made by dissolving 6 grams of sodium chlorid in a liter of water. The importance of this office of common salt will be more fully appreciated in the study of the plasma of the blood, of which the globulins form an essential part. A third office which is attributable to it is to aid in the excretion of waste matter. The sodium chlorid of the blood is the source of the hydrochloric acid of the gastric juice. Source of Sodium Chlorid. The food taken into the body is the principal source of the sodium chlorid which the body con- tains. The quantity (percentage) of this salt in some articles of food is as follows : Oats 0.01 Turnip 0.03 Potato 0.04 Cabbage 0.04 Beet 0.06 It has been the opinion of physiologists that sodium chlorid is not present in sufficient amount in human food to satisfy the demands of the body ; consequently, that an additional amount must be taken in as a condiment at the table or be added to the food during the process of cooking. But Dr. F. A. Cook, surgeon to the first Peary North-Greenland Expedition, states that the Eskimos who dwell between the seventy-sixth and seventy-ninth parallels use no salt or condiment of any kind in their food, which is entirely of meat and blubber only one-third cooked. This cooking is done in order that there may be obtained the blood of the meat, and this blood the Eskimos drink. How- ever this may be with the Eskimos, it is the general experience that by the addition of salt the food is not only made more pala- table, but the digestive juices are also increased and digestion im- proved. This insufficiency of salt in the food of man is seen also in that of some of the lower animals. While carnivora or flesh- eating animals find in their food all the salt they need, it is differ- ent with the herbivora or vegetable-eaters. Especially noticeable is this fact in the ruminants. Boussingault many years ago demon- strated this by a series of experiments which he conducted. He selected two sets of bullocks as nearly as possible in the same condition of health, and to both sets he gave the same food, except 82 INORGANIC INGREDIENTS. that to one he gave salt, while to the other he gave none. Several months elapsed before any very marked difference could be detected, but at the end of a year, during which time the experiment con- tinued, there were striking differences in the two sets. The bul- locks that received the salt were in excellent physical condition, while those deprived of it were much inferior in every respect : their hide was rough, their hair tangled, and they were dull and apathetic. Experiments of a similar nature upon sheep have pro- duced like results. A venues of Discharge. Sodium chlorid is daily discharged from the body through the following excretions and in the given amounts : Urine, 13 grams ; perspiration, 2 grams. There is a small amount also in mucous secretions. Sodium Phosphate (Na 2 HPO 4 ) and Potassium Phosphate (K 2 - HPO 4 ). These salts are so intimately associated that they may be described together. They are frequently spoken of as the " alka- line phosphates," and exist in all the solids and fluids of the body. Offices of Alkaline Phosphates. The most important office which these salts perform is to assist in giving alkalinity to the alkaline fluids a property which, in the blood at least, is essential to life, and in some of the other fluids is necessary to the per- formance of their offices. The fluids of the body are, with but four exceptions, alkaline in reaction : these exceptions are gastric juice, perspiration, urine, and vaginal mucus. The following fluids are alkaline : plasma of the blood, lymph, aqueous humor, cephalorachidian fluid, pericardial fluid, synovia, mucus (except that of vagina), milk, spermatic fluid, tears, saliva, bile, pancreatic juice, and intestinal juice. The alkalinity of the plasma of the blood is not an accidental property. The fact that the blood of all animals hitherto ex- amined has invariably been found alkaline would seem to indicate that this condition is an important one. Bernard has shown that if an acid is injected into the blood of an animal, death will be produced even though the amount injected is not enough to make the blood itself acid. One of the properties of the blood is to carry carbonic acid gas one of the products of the waste of the tissues to the lungs, where it is eliminated ; and experiment has shown that the alkalescence of the blood enables it to carry more of this gas than it could were it neutral in action. In discussing the alkaline carbonates it will be seen that they take part in rendering alkaline the fluids in which they occur. Source of Alkaline Phosphates. The alkaline phosphates are taken into the body in the food, of which they form a constituent part. Avenues of Discharge. After fulfilling their offices in the body these alkaline salts are discharged in the perspiration, the mucus, and the urine. In the urine a portion of the sodium phosphate SALTS. 83 is converted into sodium biphosphate, or, as it is sometimes called, " acid sodium phosphate," which gives to the urine its acid reaction. In this fluid are discharged daily 4.5 grams of the alkaline phosphates and the sodium biphosphate. Sulphates. Sodium sulphate (NajS0 4 ) and potassium sulphate (K 2 SO 4 ) are found in the blood, lymph, aqueous humor, milk, saliva, mucus, perspiration, urine, and feces. Their quantity is small, however, except in the urine, by which fluid they are dis- charged daily to the amount of 4 grams. Source of Sulphates. These sulphates are taken in as part of the solid food we eat and also in the water we drink. They are present in flesh, in eggs, in the cereals, and in other animal and vegetable foods. Drinking-water often contains these sulphates, and calcium sulphate as well. Sulphates are undoubtedly formed to some extent within the body. In discussing the constitution of the albuminous ingredients of the food it will be seen that one of their elements is sulphur. Some of this sulphur becomes oxidized, forming sulphuric acid, which, being a stronger acid than carbonic, displaces it from the carbonates and unites with the alkaline bases, forming sulphates. Carbonates. Sodium carbonate (Na 2 CO 3 ), sodium bicarbonate (NaHCOj), and potassium carbonate (K 2 CO 3 ) are salts which are known as the " alkaline carbonates/' and are intimately associated with the alkaline phosphates. Source of Carbonates. These salts are, to some extent, intro- duced with the food, but are principally formed by the decom- position of the salts of the vegetable acids. In fruits, such as apples and cherries, and in vegetables, such as potatoes and carrots, are found malic, tartaric, and citric acids, united with sodium and potassium to form malates, tartrates, and citrates of sodium and potassium. When these fruits or vegetables are eaten, these salts are taken up by the blood, and while in the blood the organic acids are decomposed, and the bases uniting with carbonic acid, alkaline carbonates are formed, which are discharged in the urine. This accounts for the fact that after eating sufficient of such fruits or vegetables the urine becomes alkaline. Office of Carbonates. The alkalinity of the blood and of other alkaline fluids is, as has been stated, only partially due to the alkaline phosphates. In causing this reaction the alkaline car- bonates have a share. In the blood of flesh-eating animals the phosphates are more abundant, this being due to the predominance of phosphates in muscular tissue, while in that of the herbivora the carbonates are in excess of the phosphates. Remembering, then, what has been said of the formation of the carbonates from the salts in fruits and vegetables, this difference in the blood is readily understood. In human blood there are both phosphates and carbonates to account for its alkalinity. 84 INORGANIC INGREDIENTS. Potassium Chlorid. Potassium chlorid (KC1) is found in many of the tissues, especially in the muscles, in blood-corpuscles, and in milk. This salt occurs also in gastric juice, in urine, and in perspiration. Like sodium chlorid, it is neutral in reaction and is soluble in water. Source of Potassium Chlorid. Potassium chlorid is contained in both animal and vegetable foods. Avenues of Discharge. Potassium chlorid is discharged in mucus, in urine, and in perspiration. Calcium Salts Calcium Phosphate, Lime Phosphate, or Phosphate of Lime (Ca 3 (PO 4 ) 2 ). Next to water, calcium phosphate is the most abundant physiologic ingredient of the human body. Its total amount is 2400 grams in a man weighing 65 kilograms. The quantity (percentage) of calcium phosphate is as follows : Blood 0.03 Urine 0.07 Milk , 0.27 Bone 57.6 Enamel of teeth 88.5 The greater part of the calcium phosphate in the body is in the bones. It is estimated that 6.4 per cent, of the body is bone, and in a man weighing 65 kilograms, an average weight, there would therefore be 2400 grams of this salt. Its presence in the fluids of the body is not in noteworthy amount, except in the milk. Office of Calcium Phosphate. The principal office of calcium phosphate is to give to the bones their rigidity. During early life this salt is in small amount in the bones, and at this time the bones are soft and yielding. Later, as the phosphate and other inorganic ingredients are deposited in greater amount, these structures become more rigid and better adapted to sustain weight. In old age the inorganic constituents are in excess of the organic, and besides this difference in the proportion of organic and inorganic constituents there is the further difference that the bones of the old are lighter in weight and more porous. This is due to an increase in the size of the medullary canal and the cancel Ions spaces, brought about by absorp- tion ; this is especially marked at the 'articular head. There is also sometimes a fatty change in the bone-tissue. These changes constitute senile atrophy of the bones. At an advanced period of life the bones are easily bro- ken ; while in infancy they bend but do not break, or if they do break, the fracture is not complete, but is similar to that which occurs in a green stick, and is known as the "green-stick fracture" FIG. 80. Par- tial or " green - stick " fracture (Stimson). SALTS. 85 (Fig. 80). The flexible condition of the bones may be artificially produced by putting a long bone, like the fibula, into a jar contain- ing dilute hydrochloric acid. The acid dissolves the inorganic salts, and, although in appearance the bone is much the same as before, it will now be found so flexible as to permit its being tied in a knot (Fig. 81). In the blood, calcium phos- phate, which is insoluble in alkaline fluids, is held in solution by the albuminous constituents. Were these withdrawn the calcium phosphate would at once be rendered insoluble, and would be precipitated. Source of Calcium Phosphate. Calcium phosphate is an important ingredient of the animal and vegetable food of man. It is contained in flesh, in eggs, in milk, in wheat, in oats, in rice, in peas, in beans, in potatoes, in apples, in cherries, and in some other ali- mentary substances. Its presence in milk needs especial comment. As has been stated, during early life calcium phosphate is in the bones in small amount. The milk, upon which the growing child relies for its nour- ishment, supplies the necessary amount of this salt to give the bones their firmness and rigidity. From this statement it will be seen that the adulteration of milk with water, even though the water is pure, may be of great in- jury to the child. To obtain the necessary amount of calcium phosphate a certain amount of milk must be taken. If half this amount is water, the quantity of the lime-salt present will be but one-half of what it should be, and the child is consequently defrauded. Of course, if impure water is used in the adul- teration, there is the additional danger of introducing the germs of disease with the milk. A venues of Discharge. A very small amount of calcium phosphate is discharged from the body a fact which shows its permanent character. It is discharged in the urine, in the feces, and in the perspiration. Calcium Carbonate (CaCO 3 ). This salt exists in the bones to the amount of about 300 grams, in the teeth, in the blood, in lymph, in chyle, in the saliva, and sometimes in the urine. Like calcium phosphate, with which it is usually associated, it is insolu- ble in water ; and when it exists in solution its solubility is due either to alkaline chlorids or to free carbonic acid. FIG. 81. Bone tied in knot. 86 INORGANIC INGREDIENTS. Calcium Fluorid (CaFl 2 ) exists in the bones and in the teeth, and is of little importance. Magnesium Salts. Magnesium phosphate (Mg 3 PO 4 ) is found wherever calcium phosphate is found, and the two together are frequently spoken of as the " earthy phosphates." It is discharged by the urine. Magnesium Carbonate (MgCO 3 ). A trace of this salt is found in the blood. Ammonium Salts. Traces of ammonium chlorid (NH 4 C1) are found in the gastric juice and in the urine. Iron. Iron is present in the hemoglobin of the blood, in the hair, the bile, and the urine. Its presence in the coloring-matter of the blood is its most striking characteristic. It exists in the blood combined with the other chemical elements, and not as an oxid. The total amount of iron in the blood of the body of a man weighing 65 kilograms is about 2.71 grams. Office of Iron. The office of iron is not understood. It is re- garded as a remarkable fact that without iron chlorophyll, the green coloring-matter of plants, cannot be formed in other words, that vegetable life is interfered with ; and it is believed that its pres- ence in the coloring-matter of the blood of an animal is equally necessary for its nutrition. Source of Iron. All animal food containing blood contains iron. In addition to this, iron is taken into the body in rye, barley, oats, wheat, peas, and strawberries. Avenues of Discharge. A small amount only of iron is dis- charged in the bile and the urine. After serving its purpose in the blood it is probably deposited in the hair. lodin (I). This element occurs in the thyroid gland. Silicon (S). It is not known in exactly what form silicon exists in the body, possibly as silicic acid. Oxygen (O). This gas is absorbed from the air, and exists in the blood principally in loose combination with the hemoglobin, though some of it is doubtless free. Hydrogen (H). Hydrogen is found in the alimentary canal and in the expired air, having been absorbed by the blood from the intestine. Nitrogen (N). Nitrogen is absorbed from the air by the blood, in which it exists in a dissolved state. Some nitrogen is formed also within the body. Marsh-gas (CH 4 ). This gas is found in the expired air, like hydrogen, having been absorbed from the intestines. Reiset found that thirty liters were expired in twenty-four hours. Ammonia (NH 3 ). A small amount of ammonia is found in the expired air, probably derived from the blood. Sulphuretted Hydrogen (H 2 S). This gas is found in the intestines. CARBOHYDRATES. 87 Hydrochloric Acid (HC1). Hydrochloric acid exists in the gastric juice. Carbon Dioxid (CO 2 ). This gas exists in many of the fluids, having been absorbed by them from the tissues. It is also present in blood and in expired air. CARBOHYDRATES. This class is so called because its members contain hydrogen and oxygen in the proportion to form water, united with carbon. All substances, however, which have this composition are not carbohydrates, e. g., acetic acid (C 2 H 3 OOH), nor is it to be inferred that a carbohydrate is a compound in which water is simply joined to carbon ; on the contrary its constitution is quite complex. Most of the members of this class which are of physiologic interest contain six atoms of carbon or a multiple of that number, and are, therefore, hexoses. Carbohydrates are classified as Monosaccharids or Glucoses, Disaccharids or Saccharoses, and Polysaccharids or Amyloses. Monosaccharids or Glucoses. The members of this group have the chemical formula C 6 H 12 O 6 . Those which are^of special interest are Dextrose, Levulose, and Galactose. Dextrose (glucose, grape-sugar, diabetic sugar) is normally found in the blood, chyle, lymph, and in very small amount in the urine. It occurs in grapes and some other fruits, and also in honey. Dextrose and levulose usually occur together. In the disease known as " diabetes mellitus " the quantity of dextrose in the blood and urine is very much increased. It is a substance of much interest, as it is in the form of dextrose that the carbo- hydrates of the food find their way into the blood. In its pure state dextrose is colorless and readily crystallizes ; it is soluble in cold, more so in hot water. It is dextrorotatory, whence it derives its name. In alkaline solutions dextrose reduces metallic oxids, a property which is made use of in determining its pres- ence and in measuring its quantity. Various tests are employed for the detection of dextrose ; among these are Trommer's, the fermentation-test, and Fehling's. Trommer's Test. The method of applying this test is as follows : If the presence of dextrose in an organ is to be ascertained, this should be cut into small pieces and boiled with water and sulphate of sodium, and the mixture filtered in order to have a clear solu- tion, which is essential. Some of this should be poured into a test-tube, and a few drops of a solution of sulphate of copper added. To this a solution of caustic potash should be added, so as to make the contents of the tube distinctly alkaline. The tube should now be heated, when, if dextrose is present, just before the 88 CARBOHYDRATES. boiling-point is reached, a reddish precipitate, consisting of cup- rous oxide, will form. Levulose, galactose, lactose, and maltose have reducing power similar to that of dextrose, but differing in degree ; thus, the power of lactose as compared with dextrose is but that of 7 to 10, while maltose has one-third less power than dextrose. Cane-, maple-, and beet-sugar have no reducing power, and must first be converted into dextrose before the reaction will take place. Fermentation-test. This test depends upon the fact that under the influence of yeast dextrose is decomposed into ethyl alcohol and carbonic anhydrid. Fehling's Test. This test is based on the same principle as that of Trommer, namely, the property possessed by dextrose to reduce metallic oxids. It is employed not only to determine the presence of dextrose, but also to measure the quantity present. The test- solution is liable to undergo changes which invalidate the result ; it should, therefore, be freshly prepared, or at least be boiled be- fore it is used. The principal change which takes place is the formation of racemic acid from the tartaric acid of the solution, and this has the same reducing action as the sugar. If after boiling the solution is clear, it may be inferred that decomposition has not taken place, and it may be used. The solution is prepared in the following manner : 34.639 grams of pure recrystallized copper sulphate are dis- solved in distilled water, which is made up to 500 c.c. This solu- tion should be kept separate from the second solution, which is made by dissolving 175 grams of crystallized Rochelle salts and 60 grams of sodium hydroxid in distilled water, and likewise made up to 500 c.c. It is found by experience that when these two solutions are mixed the resulting mixture does not keep well. When the test is to be made equal quantities of the two solu- tions are mixed. Prof. Bartley's method of applying this test in urine is as follows : 10 c.c. of the solution are measured into a suitable flask. To this 10 c.c. of a freshly prepared 10 per cent, solution of potassium ferrocyanid are added, and about 30 c.c. of water. The mixture is heated on a water-bath, and the urine, previously diluted with water if it contains much sugar, is run in from a faucet, drop by drop, until the blue color just dis- appears. The addition of the slightest excess of sugar shows itself by the solution becoming quickly brown. By careful com- parative tests Prof. Bartley has found this method to be reliable and accurate provided the solution is not boiled during the reduc- tion. The best temperature he finds to be between 80 and 90 C. Polariscope. This is also known as a polarimeter. It may be employed to determine the presence of dextrose. In order to understand the use of this instrument it will be necessary to con- sider briefly the subject of the polarization of light. MONOSACCHARIDS OR GLUCOSES. 89 Common light is due to vibratory disturbances in the ether, which are propagated through it as waves, the direction of the vibrations being transverse to that of propagation. In all places where light is polarized its vibrations, still trans verse to the direc- tion of the ray, are all in one plane. Light may be polarized by transmitting it through most crystals, and if it is then transmitted through another crystal it will be observed that when this is in certain positions it will pass most easily, and that in positions at right angles to these it will be quenched entirely. It is supposed that the molecular structure of these crystals is such as to make them transparent for vibrations in one plane and opaque to those in the plane at right angles. The rotation of the plane of polarization by passing the polarized light through a crystal constitutes rotary polarization, and is the principle upon which the polariscope is constructed. The crystal which polarizes the light is the polarizer, and that which distinguishes it is the analyzer. This power to rotate the plane of polarization is possessed by other substances than crystals, such as solutions of various sub- stances, among them being sugar ; and as each of these substances rotates the plane through a different number of degrees of a circle, this fact enables the investigator to determine with what substance he is dealing. Substances having this power of rotating the plane of the polarized ray are said to be optically active; and those which rotate it to the right are dextrorotatory, and those that rotate it to the left, levorotatory. Inasmuch as the rotation is different for each of the component parts of white light, this kind of light cannot be used, but in its stead light of a single color, monochromatic light, must be used. This is usually the yellow light produced by burning a salt of sodium in the flame of a Bunsen burner. A polariscope or polari meter which is specially adapted to the estimation of the amount of sugar in a given solution is called a saccharimeter. Of these, there are various kinds, the one most commonly used being Laurent's. Laurent's Polarimeter. This and its use are described by Prof. Bartley in his Medical Chemistry in the following language : " Laurent's polarimeter (Fig. 82) is one of the simplest and best. In this instrument one-half of the field of vision is covered by a very thin plate of quartz, which slightly rotates the plane of the light passing through it, and causes some light to pass even when the polarizer and analyzer, both of which are Nicol prisms, are crossed. If the analyzer (h) is rotated so as to cause the quartz plate to become dark, the light passes through the uncovered half of the field. In an intermediate position the two halves of the field appear equally illuminated. The scale (c) is so graduated that this position of the analyzer is made the zero point of the instru- 90 CARBOHYDRATES. ment. The slightest deviation of the analyzer from this position causes one-half of the field to appear darker and the other half lighter. There are thus presented to the eye two lights to be compared, and the instrument is thus very sensitive. Monochro- matic light must be used. In some instruments the circle is divided both into degrees and sugar units, or percentages. The scale is read by means of a vernier and lens (n). Before using the instrument the observation tube is filled with water and placed in position between the analyzer and polarizer. If the instrument is properly adjusted, the zero mark on the vernier will correspond with the zero point of the scale when the two halves of the field are equally illuminated. The tube is then filled with the solution FIG. 82. The Laurent shadow polarizing sacchari meter. to be tested and again placed between the analyzer and polarizer, when, if it is an active substance, the plane of the polarized ray coming from the analyzer will be turned to the right or to the left in passing through the solution, and one-half of the field will be lighter than the other. The amount of rotation of the plane of the polarized ray will be proportioned to the amount of the active substance in the solution. It will now be necessary to rotate the analyzer (h) to the right or to the left, so that the two halves of the field will again appear equally illuminated. When this has been accomplished we may read oflf on the vernier the degrees of the circle through which the analyzer has been rotated. In this way the amount of rotation of the polarized ray is deter- mined. MONOSACCHAEIDS OR GLUCOSES. 91 " The specific rotatory power of any substance is the amount of rotation of the plane of polarized light in degrees of a circle, produced by 1 gram of the substance dissolved in 1 c.c. of the liquid, examined in a tube one decimeter in length. The specific rotatory power of a substance is obtained by dividing the angular rotation observed in the polarimeter (a) by the length of the tube in decimeters (1) and by the number of grams in 1 c.c. of the liquid (w). If a sodium flame is used as a source of light, the specific rotation of the substance is that of light with wave- lengths corresponding to the D line of the solar spectrum, and is usually denoted by (a) d . Then the above statement may be ex- pressed as follows : In this formula plus indicates that the substance is dextrorotatory, and minus that the substance is levorotatory. If in this formula the specific rotatory power of the substance under examination is known, and we wish to find the value of (w), the weight of the substance, then the formula becomes, In this formula a is the observed rotation, I the length of the tube in decimeters, which is known, and (a) d the specific rotatory power, which has been determined for all well-known optically active substances ; w can easily, therefore, be calculated. The specific rotatory powers of a few of the most important optically active substances are as follows : Cane-sugar, (a) d = + 73.8 Milk-sugar " = + 59.3 Dextrin" " =+130.8 Levulose (a) d = 106 Egg-albumin " =- 33.5 Serum-albumin " = - 56 Dextrose " = + 56 I Gelatin =-130." Other tests for the presence of dextrose are Pavy's modification of Fehling's, Moore's, picric acid, and phenylhydrazin ; for the methods of their use the reader is referred to special manuals on chemistry and urine-analysis. Fermentations of Dextrose. Dextrose undergoes various fer- mentations : (1) Alcoholic ; (2) Lactic ; and (3) Butyric. 1. Alcoholic Fermentation. In alcoholic fermentation, under the influence of yeast, the dextrose is decomposed and ethyl alcohol and carbonic anhydrid are produced (C 6 H 12 O 6 = 2C 2 H 6 O -f 2CO 2 ).' This process is at the height of its activity when the temperature is 25 C. ; when above 45 C. or below 5 C. it ceases. When sugar is present in the solution to the extent of more than 15 per cent, the process of fermentation will be 92 CARBOHYDRATES. arrested by the alcohol produced, before all the sugar has been decomposed. 2. Lactic Fermentation. When milk sours, the sugar which it contains is converted into lactic acid, constituting the lactic fer- mentation : C 12 H 22 U + H 2 ---- 4 C 3 H 6 3 Lactose. Water. Lactic acid. This fermentation is not confined to milk-sugar, but may occur also with dextrose. The change is brought about by the presence of specific micro-organisms. It is stated that there exists also in the mucous membrane of the stomach an enzyme which can change lactose, and possibly dextrose, into lactic acid. 3. Butyric Fermentation. When the lactic fermentation is con- tinued for some time it is liable to pass into the butyric. This change is due to the action of a ferment (organized) upon the lactic acid. In the change, hydrogen and carbonic anhydrid are given off. 4C 3 H 6 3 2C 4 H 8 2 + 4C0 2 + 4H 2 Lactic acid. Butyric acid. Carbonic Hydrogen, anhydrid. The optimum (most favorable) temperature for the lactic and butyric fermentations is from 35 C. to 40 C. When the diet consists largely of carbohydrates both these fermentations may occur in the alimentary canal. Levulose (left-rotating sugar, fruit-sugar, or mucin-sugar) is found in many fruits and in honey, and occurs in small quantity in blood, urine, and muscle. It is crystallizable, but with diffi- culty. When cane-sugar is treated with dilute mineral acids it is decomposed into equal parts of dextrose and levulose. Cane- sugar has a dextrorotatory action on polarized light, but when changed by the acid the solution becomes levorotatory, the levo- rotatory power of the levulose being greater than the dextro- rotatory power of the dextrose, and the cane-sugar is said to be " inverted ;" hence the mixture of dextrose and levulose is some- times spoken of as " invert-sugar." As will be seen in the con- sideration of cane-sugar, " inversion" takes place in the alimentary canal. Although in many respects levulose is very similar to dextrose, still its action on polarized light serves to distinguish the two. Galactose. When lactose is boiled with dilute mineral acids it is changed into dextrose and galactose : C^O,, + H 2 = C 6 H 12 6 + C 6 H 12 6 Lactose. Water. Dextrose. Galactose. A similar change takes place under the influence of certain enzymes. DISACCHARIDS OR SACCHAROSES. 93 Inosit or muscle-sugar has been found in the muscles, lungs, liver, spleen, kidneys, and brain, and pathologically in urine. It occurs also in beans and grape-juice. Because of its sweet taste and its chemical composition it was formerly regarded as a carbo- hydrate, but as it has no rotatory action on polarized light, does not reduce metallic salts, and does not undergo the alcoholic fermen- tation, it is now regarded as belonging te the aromatic series, and not as being a carbohydrate. Disaccharids or Saccharoses. The chemical formula representing this group is C 12 H 22 O n . They are regarded as a con- densation-product of two molecules of the monosaccharids, in which a molecule of water is lost. This may be expressed as follows : C 6 H 12 6 + C 6 H 12 6 - C^H^A, + H 2 Mono- Mono- Disaccharid. Water, saccharid. saccharid. This process is known as reversion. The members of this group which are of physiologic impor- tance are Cane-sugar, Lactose, Maltose, and Isomaltose. Cane-sugar or Saccharose. This sugar is not found in the human body, but it nevertheless plays an important part in the food of man. It occurs in sugar-cane, beet-root, and sugar-maple. It does not reduce metallic salts, is soluble in water, dextrorotatory, and does not undergo alcoholic, but does readily undergo lactic fermentation in presence of sour milk to which zinc oxid is added to fix the acid as formed. One of the interesting facts connected with cane-sugar is its property of " inversion," which consists in its decomposition into equal parts of dextrose and levulose, and to this mixture the name of " invert-sugar" has been given. This change is represented chemically as follows : C^E^Ai + H 2 = C 6 H 12 6 -f- C 6 H 12 6 Cane-sugar. Water. Dextrose. Levulose. and may be produced by the action of acid, as has been described under Levulose. It takes place also in the small intestine under the influence of an enzyme of the intestinal juice, namely, invertin. A similar inversion takes place in lactose and maltose ; thus maltose + water = dextrose 4- dextrose ; and lactose + water = dextrose -f galactose. Invertin exists also in yeast, in w r hich it has the same power as in the intestinal juice. Cane-sugar cannot be taken up as such by the blood, and when injected into an animal it is eliminated unaltered in the urine. When taken in as food it is absorbed, not as cane-sugar, but as invert-sugar, into which it has been changed. T^his inversion is most pronounced in the small intestine ; it is claimed that it may take place also in the stomach, and that there exists in the gastric juice an enzyme which has this power. 94 CARBOHYDRATES. Lactose (milk-sugar, sugar of milk) is found only in milk, although it may occur in the urine of lying-in women and of suck- lings during the early days of lactation. It is crystallizable, less soluble in water than dextrose, and insoluble in alcohol. It is dextrorotatory, its power in this respect being the same as that of dextrose. As above noted in speaking of galactose, lactose is changed into equal parts of galactose and dextrose by boiling it with dilute mineral acids. Lactose by itself does not undergo alcoholic fermentation with yeast, but an alcoholic fermentation does take place in milk, as when mare's milk is used for the preparation of kumyss and kephir. This fermentation is due to special ferments, the nature of which is not fully understood. In Russia kephir ferment may be purchased. Lactose readily undergoes the lactic fermentation (see Lactic Fermentation, p. 92). It is this change which takes place in the souring of milk due to the action of certain micro- organisms. The character of the change in the case of lactose is the same as in dextrose and saccharose. Lactose injected into the blood is eliminated by the urine, as are saccharose and maltose, and like them must therefore be changed in the alimentary canal during the process of absorption. This conversion, which is into dextrose and galactose, takes place under the influence of the sugar- splitting enzyme, lactase (p. 119). Maltose. When starch-paste or glycogen is treated with saliva, maltose is the principal sugar formed ; prolonged treatment with pancreatic juice will produce, besides the maltose, some dextrose. Although pancreatic juice, on the one hand, acts in this manner, still the tissue of the small intestine or an extract of it has but slight action on the paste. On the other hand, the pancreatic juice rapidly changes maltose into dextrose. Maltose, like cane-sugar, injected into the blood is eliminated as maltose in the urine. From this fact it would appear that maltose is not absorbed as such in the intestine, but as dextrose. Recent researches show the presence in the succus entericus of lambs, and in the mucous membrane of the jejunum of dogs and new-born children, of an enzyme glucase which changes maltose into glucose, so that the conversion of the maltose may take place both in the cavity of the intestine and while it is passing through the intestinal walls. The action of pancreatic juice on starch in the intestine will be further discussed in the consideration of the enzymes of this fluid. Maltose is soluble in water, but it is less soluble in alcohol than dextrose. It is crystallizable, dextrorotatory, and reduces metallic salts. Maltose is distinguished from dextrose (1) by the difference in its rotatory power on polarized light, that of maltose being greater; (2) by having a less reducing power, as when boiled with Fehling's solution only two-thirds as much cuprous oxide is separated out with maltose as with dextrose ; (3) by Barfoed's reagent, which, consisting of a solution of cupric acetate in water POLYSACCHARIDS OR AMYLOSES. 95 to which acetic acid has been added, is reduced by dextrose, but not by maltose. Isomaltose. When starch is acted on by any of the enzymes which produce maltose isomaltose is also formed ; unlike maltose, it is not directly fermentable by yeast. It is very soluble in water, and is sweet in taste. It occurs in small quantity in the urine. Polysaccharids or Amyloses. The formula of this group is (C 6 H 10 5 X, The exact formula is not determined. Chemists agree that it is not C 6 H 10 O 5 , but some multiple of this, as indicated by " n" and that " n" is not less than five. The members of the group are : Starch, Amylodextrin, Erythrodextrin, Achroodextrin, Maltodex- trin, Glycogen, and Cellulose. Starch. Starch is not found in the human body except when it is taken in as food. It is very abundant in vegetable food. In- deed, it is said that starch exists in every chlorophyll-containing plant at some period of its existence. Starch is a substance of great interest, from the fact that it is the first organic substance produced by vegetables from inorganic matter. Animals have not the power to produce organic substances directly from mem- bers of the inorganic kingdom, but plants have this power, and they exercise it, and from the organic materials thus produced animals are nourished. Animals may change the organic matter from one form to another, as starch to sugar, but were inorganic substances alone supplied to animals they would starve. The inorganic substances out of which the plant forms the starch are carbonic acid and water, these being taken from the atmosphere and the soil. This process is represented by the fol- lowing formula : (6C0 2 + 5H 2 0) n = (C 6 H 10 5 ) + O n Carbonic acid. Water. Starch. Oxygen. That is, the carbonic acid and the water are decomposed, the car- bon and hydrogen, with some of the oxygen, unite and form starch, while the rest of the oxygen is set free. To bring about this change there must be present solar light and the green color- ing-matter, chlorophyll. If chlorophyll is absent, this change does not take place, nor does it when solar light is absent. Starch exists in plants in the form of grains, known as " starch-grains" or " starch-granules" (Fig. 83). They present a characteristic appearance under the microscope by which they may at once be recognized. Each granule presents a number of concentric markings and varies in size and shape in different plants ; by these points of difference the plant from which the granules are derived may be identified. This fact is made use of in detecting adulterations, in which cheaper kinds of starch are mixed with more expensive kinds and sold for the latter at a 96 CARBOHYDRATES. higher price. The markings are caused by the arrangement of the material composing the granule in alternate layers of cellulose and granulose. Quantity of Starch. The quantity of starch (percentage) in the following food-plants is Sweet potato . 16.05 Potato 20.00 Beans 33.00 Peas 49.30 Wheat 57.88 Oats 60.59 Eye 64.65 Indian corn 67.55 Kice ...'.. 88.65 The presence of starch is determined by the addition of a little tincture of iodin, which gives a blue color. This reaction is due to the granulose, and not to the cel- lulose. Starch cellulose differs in some respects from ordinary cellu- lose, as is demonstrated by its solu- bility in some reagents which do not dissolve the latter* Starch is insoluble in cold water. When boiling water is added to it in an amount twenty times its weight the granules swell and burst, and there is formed a gelatinous mass which is called " starch-paste." This paste will respond to the iodin test, showing it to be, principally at least, granulose. If the amount of water added should be one hundred times the weight of the starch, a solution of granulose is made, the insoluble cellulose falling to the bottom of the vessel. This starch solution will likewise respond to the iodin test. Amylodextrin (Soluble Starch, Amidulin). When starch-paste, produced in the manner above described, is heated to a temperature of 40 C. on a water-bath, and saliva is then added, the paste changes from a gelatinous to a watery condition, and in this fluid soluble starch now exists. This soluble starch gives also a blue color with iodin. It filters readily, whereas starch-paste, even in dilute solution, filters with difficulty. Soluble starch is dextro- rotatory that is, it rotates the ray of polarized light to the right. This substance is the first product of the conversion of starch into sugar by saliva ; and if the action is not stopped, as it may be by boiling, the stage of soluble starch is only a temporary one, it pass- ing quickly into that of dextrin. As will be seen hereafter, the ingredient of the saliva that changes starch into soluble starch is FIG. 83. Starch-grains. POLYSACCHAEIDS OR AMYLOSES. 97 an enzyme ptyalin the action being one of hydrolysis. Pancreatic juice produces the same change as does saliva ; and as the action of saliva is due to the enzyme ptyalin, so is the action of pancreatic juice due to an enzyme, amylopsin. Erythrodextrin. If the action of either of these enzymes upon starch is not arrested in the soluble-starch stage, erythrodextrin is formed. The blue color caused by the action of iodin on starch gradually changes into violet, reddish violet, and then to reddish brown as the starch gradually changes to erythrodextrin. This reddish-brown color produced by iodin is the test for erythro- dextrin. Achrobdextrin. If the action of these enzymes is continued, a still further change in the starch takes place. It passes into the condition of achroodextrin, and iodin fails to produce any color. A further change into maltose follows the formation of achroo- dextrin. In the action of these enzymes upon starch outside the body the first product is a mixture of dextrin with the sugar, but within the body there is little doubt that all the starch is converted into sugar, and as such is absorbed. If starch is treated with boiling dilute acids instead of with these enzymes, the changes just described take place with far greater rapidity, and dextrose results. Maltodextrin. If diastase, the enzyme contained in malt extract, is used instead of saliva or pancreatic juice, maltodextrin is formed ; and indeed it is not certain that the latter substance is not formed in addition to the erythrodextrin and achroodextrin when saliva and pancreatic juice are employed. Maltodextrin differs from the dextrins already described in being more soluble in alcohol, in being diffusible, and in responding to Fehling's test. It also passes over into maltose by the continued action of the diastase. Glycogen. The similarity between glycogen and starch has led to the term "animal starch" being applied to the former. Glycogen was first discovered in the liver, where it is normally found to the amount of between 1.5 and 4 per cent, of the weight of the organ, which may in man be increased to 10 per cent. It also exists in muscles to the amount of from 0.5 to 0.9 per cent., and it is estimated that all the muscles of the body contain as much glyco- gen as does the liver. It occurs also in the integument and the mucous membranes of the human embryo, in the placenta and the amnion, in white blood-corpuscles and in pus-corpuscles, in oysters and in other mollusca. For purposes of study it is usu- ally obtained from the liver of an animal (a rabbit or a dog), in which it is stored up in amorphous granules around the nuclei of the liver-cells. Glycogen is soluble in water, and with iodin gives a port-wine color. This color does not distinguish it from erythro- dextrin ; but when it exists pure, as ordinarily it does not, it is 7 98 CARBOHYDRATES. precipitated by 60 per cent, alcohol, while the dextrins are not precipitated. Watery solutions are dextrorotatory. In general it may be said that the action of the enzymes and of boiling acids upon glycogen is the same as upon starch. The glycogen of the liver becomes converted, by physiologic processes, into liver-sugar, which is regarded as identical with dextrose. In this process probably no maltose is formed, such as occurs in the artificial hydrolysis already described. This difference would seem to indicate that in the liver-cells there is no enzyme to which this action can be attributed ; for, so far as can be judged, most enzymes produce maltose, and not dextrose, and up to the present time no dextrose-producing enzyme has been obtained from the liver. Cellulose. Nowhere in the animal body is cellulose found, but it exists in many of the vegetable alimentary principles upon which man relies for his nutrition. As has already been stated, it is a constituent of the starch-granule, and so covers the granulose that the digestive fluids cannot reach it. When starch is boiled the granules burst, and thus access to the granulose is given. It has recently been suggested that there is in the intestinal canal, formed by the epithelial cells, an enzyme which has the power of causing a digestion of the cellulose. But the evidence of the existence of such an enzyme is very meagre. The disappearance of the cellulose is probably due to the action of bacteria, all the products being unknown, though marsh-gas, acetic and butyric acids are among them. This change takes place especially when vegetables, such as celery and lettuce, and fruits are eaten whose cell-walls are tender and have not yet become lignified or woody in character. Lignin is the name applied to cellulose in this advanced stage. In the human intestine from 4 to 60 per cent, of the cellulose taken in is dissolved. It doubtless has very little nutritive value, but is regarded as increasing by its local action intestinal peristalsis and keeping the bowels free. In the rabbit its absence from the food results in death, inflammation of the intestine being caused thereby ; but if horn-shavings, which are excreted unchanged, are substituted for cellulose, the animal maintains its health. The cellulose of some plants, such as the date, is regarded as a reserve material to be made use of in germination. The presence of cellulose is recognized by the fact that when treated with strong sulphuric acid it becomes converted into a sub- stance that is colored blue by iodin. Schulze's reagent is another test for its presence. This test consists in the production of a blue color when the substance is treated with iodin dissolved to satura- tion in a solution of chlorid of zinc to which potassium iodid has been added. ADIPOCERE. 99 THE FATS. The chemical elements entering into the composition of the fats are carbon, hydrogen, and oxygen. The fats are widely dis- tributed throughout the human body. The percentage in the solids and fluids is as follows : Sweat 0.001 Vitreous humor 0.002 Saliva 0.02 Lymph 0.05 Synovia 0.06 Liquor amnii ..." 0.06 Clfc'le 0.2 Mlcus 0.3 Blood 0.4 BUe 1.4 Milk -^:3 Cartilage 1.3 Bone 1.4 Crystalline lens 2.0 Liver 2.4 Muscles 3.3 Hair 4.2 Brain 8.0 Nerves 22.1 Adipose tissue 82.7 Marrow . .96.0 Fats are regarded by chemists as composed of fatty acids and glycerin, and are called glycerids or glyceric ethers. When treated with superheated steam and mineral acids, and in the human body under the influence of steapsin, the lipolytic enzyme of the pancreatic juice, the fats are decomposed into glycerin and the respective fatty acid. This change is expressed by the follow- ing formula, palmitin being taken as an example : C 3 H 5 (O.C 15 H 31 CO) 3 Palmitin. 3H 2 O = C 3 H 5 (OH) 3 Water. Glycerin. 3C 15 H 31 CO.OH Palmitic acid. There are three varieties of fats: Olein, C 3 H 5 (OC 17 H <33 CO) 3 ; palmitin, C 3 H 5 (OC 15 H 31 CO) 3 ; and stea7uTpC 3 H 5 (OC 17 H 35 CO) 3 . These differ in several particulars, one of the most important being their melting-points : Olein melts at 5 C. ; palmitin, at 45 C. ; and stearin, at from 53 to 66 C. Their respective acids are oleic, palmitic, and stearic. Fats are characterized by being insoluble in water, slightly soluble in alcohol, and very soluble in ether and chloroform. All fats are mixtures of the three varieties, the difference in the con- sistency of any given fat depending upon the proportion in which the neutral fats are present. Thus in the more solid fats, such as suet, stearin predominates, while in the fluid fats it is olein which is in excess. The latter exists in human fat to the amount of from 67 to 80 per cent. When fats decompose or become " rancid/' propionic, acetic, and formic acids are produced. Adipocere. It sometimes happens that when bodies are dis- interred, instead of being found in a condition of putrefaction, they are discovered to have been changed into adipocere or grave- wax. This is a peculiar substance of a waxy nature, and consists of calcium soaps, of which the fatty acids are palmitic and stearic. Acid ammonium soap has been found in some cases. This change 100 THE FATS. occurs in bodies which have been interred in moist soils, or have been in water for a considerable time after death. Source of Fat in the Human Body. Human fat is de- rived from the fats, the carbohydrates, and the proteids of the food. In fatty meats, nuts, eggs, milk, and other foods more or less fat exists as a constituent, and undoubtedly contributes to the forma- tion of the fat of the body. That the fat of the food can be deposited as such in the tissues was for a time denied, but it has been shown by feeding starved dogs upon such fatty foods as rape- seed oil, linseed oil, or mutton tallow, that they will not only take on fat, but that some of the kind of fat which enters into their food is deposited as such in their tissues. Food containing starch and sugar is also fattening in its nature, and persons who have an excess of fat are placed upon a diet containing a minimum of these ingredients. Herbivorous animals the cow, for instance rely entirely upon vegetable food for their support, and it is the carbo- hydrates which this contains that are converted into the fat of their milk and that which covers their muscles. It is doubtless from the carbohydrates that most of the fat is produced. That proteid food will also produce fat is shown by the amount of the latter which carnivorous animals put on. Offices of Fat. The offices which fat subserves in the human body are manifold : (1) It protects the underlying parts from in- jury, as in the palm of the hand and the sole of the foot ; (2) it serves as a lubricator, as in the sebaceous matter poured out upon the skin, which it keeps soft and pliable ; (3) it acts as a non- conductor of heat, aiding in the retention within the body of the vital heat which would otherwise be lost so rapidly as to produce injurious results; (4) it serves as a reservoir when the supply of food is cut off or diminished ; thus in wasting diseases the fat deposited in various parts of the body is absorbed and contributes to its nutrition ; (5) it is a source of energy and of heat through its oxidation, the final products of which are CO 2 and H 2 O. Important properties of fats, besides those already men- tioned, which deserve special consideration, are two that of form- ing a soap and that of forming an emulsion. Saponification. Fats are saponifiable i. e., capable of being converted into a soap. Thus when heated with a caustic alkali the fat is split up as already described, into glycerin and a fatty acid, and the latter unites with the base, the compound resulting being a soap. Thus if palmitin and potassium hydrate are the fat and alkali used, the product is a soap whose chemical composi- tion is potassium palmitate. This is expressed in the following formula : C 3 H 5 (O.C 15 H 31 CO) 3 + 3KHO C 3 H 5 (OH) 3 + 3C 15 H 31 CO.OK Talmitin. Potassium hydrate. Glycerin. Potassium palmitate. CHOLESTERIN. 101 In like manner stearin would form i ^teaite^ and 'oljein an oleate. The sodium soaps are "hard/ 7 a^nd those of potassium are " soft/ 7 In the discussion of intestinal digestion it yviti ha. seoil thitt the process of saponification takes place in the small intestine, and that the soap there formed aids in the important functions of that portion of the alimentary canal (p. 236). Emulsification. Besides being saponifiable, fats are also emul- sifiable capable of forming an emulsion. If oil and water are poured into a test-tube, they will at once separate, the oil floating on the water. If the mouth of the tube is closed by the thumb and the tube firmly shaken, the oil and water will form a milky mixture, but will separate again when the agitation ceases ; if a small amount of an alkali is added and the tube is again shaken, separation will not take place as before, but the milky appear- ance will continue for some considerable time. If a drop of the mixture is placed under the microscope, it will be found that the oil-globules have been broken up into an exceedingly fine state of subdivision, some of the particles being too small to measure even with a very high magnifying power. This more or less permanent subdivision and suspension of the oil-globules constitutes an emul- sion. The change is not a chemical one, but purely physical. A similar process takes place in the small intestine during intestinal digestion (p. 237) and is regarded by some as a necessary prelimi- nary to the absorption of fat (p. 261). The fat in milk is in an emulsified condition ; consequently milk may be regarded as a natural emulsion. lecithin. This substance may be regarded as a fat, and from the fact that it contains phosphorus it has been spoken of as " phos- phorized fat. v Its formula is C 42 H 84 NPO 9 . It is decomposable into glycerin, stearic acid, phosphoric acid, and an alkaloid, cholin. Lecithin occurs in the brain and other nervous tissues, consid- ered by some authorities as here produced by decomposition of protagon, in yolk of eggs, blood-corpuscles, semen, bile, and milk. It is also one of the constituents of protoplasm. Cholesterin. This substance bears some resemblance to the fats in that it is insoluble in water, but soluble in ether, hot alco- hol, and chloroform. It is a constituent of protoplasm, and is also found in blood-corpuscles, bile, serum, and white substance of Schwann. In the blood it is in combination with oleic and pal- mitic acids. It forms esters with fatty acids, and as such exists in the fatty secretions of the skin. Lanolin, the fat obtained from sheeps' wool, is said to be rich in esters, and these are very resist- ant to the action of bacteria. 102 PROTEIDS. * ^PROTEIDS. .' \ 33te^s6- ingr^p ents/a-re the most important constituents of mus- cles, glands, nervous tissue, and blood ; indeed, it has been said of them that none of the phenomena of life occurs without their presence. Of them Gamgee says : " They are highly complex, and, for the most part, uncrystallizable compounds of carbon, hydrogen, oxygen, nitrogen, and sulphur (phosphorus is also some- times present), occurring in a solid, viscous condition, or in solu- tion in nearly all the solids and liquids of the organism. The different members of the group present differences in physical, and to a certain extent even in chemical properties. They all pos- sess, however, certain common chemical reactions, and are united by a close genetic relationship." Their percentage-composition is as follows : Carbon . 50 to 55 Nitrogen 15 "18 Hydrogen 6.9 " 7.3 Oxygen 20 " 23.5 Sulphur 0.3 " 2 qu chl When proteids are burned there is found in the ash a certain uantity of salts ; from the ignition of egg-albumin, for instance, chlorids of sodium and potassium result, and salts of calcium, magnesium, and iron. It is still undecided whether these salts are integral parts of proteids or impurities, probably the latter. The percentage of proteids in some of the solids and liquids of the body, and their wide distribution, are shown by the follow- ing table : Cerebrospinal fluid ....... 0.09 Aqueous humor 0.14 Liquor amnii 0.70 Intestinal juice 0.95 Pericardia! fluid 2.36 Lymph 2.46 Pancreatic juice 3.33 Synovia 3.91 Milk 3.94 Chyle 4.09 Blood 8.56 Spinal cord 7.49 Brain 8.63 Liver .....; 11.64 Thymus 12.29 Muscle 16.18 Tunica media of arteries .... 27.38 Crystalline lens 38.30 Various attempts have been made to ascertain the constitution of the proteids and give a formula for them, but the differences in the results obtained by equally competent chemists have been so great that practically nothing worthy of quoting is on record. There is no doubt, however, that the molecules are very large. General Properties of Proteids. All are insoluble in alcohol and ether. They are also said to be soluble with the aid of heat in concentrated mineral acids and caustic alkalies ; but inasmuch as this is accompanied with decompositien of the pro- COLOR-REACTIONS. 103 teids it is a question whether it can be regarded as a true solu- tion. Action on Polarised I/ight. All proteids are levorotatory (see p. 89), but the degree of rotation varies considerably. The following table gives the specific rotatory power of several of the proteids : Proteid. Value of (d)d. Serum-albumin 56 to - 68 Egg-albumin - 35.5 " - 38.08 Lactalbumin - 36 " - 37 Serum-globulin - 59.75 Fibrinogen - 43 Alkali-albumin - 62.2 Syntonin (from myosin) 72 Casein (dissolved in MgSO 4 solution) .... -80 Various proteoses 70 to 80 Color-reactions. Certain color-changes which take place when proteids are treated with various reagents have been made use of to detect their presence or absence. Although chemists have determined the elements which go to make up proteids, they have not as yet determined their constitution. They have ascer- tained that proteids undergo changes or decomposition in the body, as a result of which carbonic acid, water, and urea are finally formed, and that there are various intermediate products, such as leucin, creatin, uric acid, and ammonia. It has also been deter- mined that by chemical means proteids can be decomposed into a great variety of substances : some of these are ammonia, carbonic acid, amins, leucin, and aromatic compounds. Of this last class, the aromatic compounds, there are three groups: 1. The phenol group, including tyrosin, phenol, and cresol ; 2. The phenyl group, including phenylacetic and phenylpropionic acids ; and 3. The indol group, in which are indol and skatol. It is upon this class of substances, the aromatic compounds or radicles, that the color- reactions of proteids depend. Xanthoproteic Reaction. When a solution of proteid, to which a few drops of nitric acid have been added, is boiled, it becomes yel- low, and if ammonia is added the yellow color changes to orange. Millon's Reaction. Proteids when heated with Millon's reagent give a white precipitate which becomes brick red on cooling. This reagent is prepared by dissolving mercury in nitric acid and add- ing water. The precipitate which forms is allowed to settle, and the fluid is the reagent. Very small amounts of proteids give the red color without the precipitate. Piotrowski's or Biuret Reaction. When many proteids are mixed with an excess of concentrated solution of sodium hydrate and one or two drops of a dilute solution of cupric sulphate, a violet color is produced which becomes deeper on boiling ; with peptones and proteoses the color produced is rose red. Biuret is the substance 104 PROTEIDS. formed when urea is heated, ammonia being given off in the process. The following formula expresses the change which takes place : 2CON 2 H 4 - NH 3 = C 2 O 2 N 3 H 5 Urea. Ammonia. Biuret. Since the rose-red color is produced by biuret, the reaction is also called by this name. Crystallization. While it is true that proteids as a class are not crystallizable, or perhaps it would be more correct to say have never been crystallized, still there are exceptions to this rule, inasmuch as crystals of globulin or vitellin have been seen in the aleurone grains of seeds and in the yolk of the egg of fishes and amphibians. Egg-albumin, serum^albumin, and caseinogen have also been made to crystallize. This may be demonstrated in the following way : To a solution of egg-albumin, white of egg, add half its volume of a saturated solution of sodium sulphate, pre- cipitating the globulin, which is removed by filtration. In the filtrate, exposed to the air for some days, during which evapora- tion takes place, minute spheroidal globules and needles will form, which are the crystals of the proteid. Acetic acid hastens the crystallization and produces better crystals. Non-diffiisibility. As a class, proteids are not diffusible ; to this rule peptones are the exception. In order that this prop- erty of proteids may be understood, it will be advantageous to the student to describe the processes of diffusion and osmosis. If a solution of common salt is placed in a vessel and water is care- fully poured on the surface of the salt solution, the salt will pass into the water, and in a short time the contents of the vessel will be of the same composition throughout. This passage of the salt into the water is diffusion, and in this instance the process takes place very quickly. Not so, however, would be the case if a solution of albumin was substituted for the solution of salt ; the same phenomenon would occur, but would require a much longer time. When liquids are separated by a membrane the diffusion which takes place through it is osmosis. It is important to understand osmosis and the conditions under which it takes place, as without this knowledge many of the proc- esses which occur in the human body would be unintelligible ; at the same time it must be said that osmosis does not occupy the prominent place it once did in explaining phenomena connected with absorption ; investigations have shown that the passage of the products of digestion from the alimentary canal into the blood is not a simple diffusion through a passive membrane, but that cell-activity must be largely taken into account. Fig. 84 represents a jar, A, which contains distilled water. Within this, resting on a tripod, is an osmometer, an expanded glass vessel, B, closed by a piece of parchment, C, from the top NON-DIFFUSIBILITY. 105 of which rises a graduated tube. The osmometer is supposed to contain a solution of some salt ; sulphate of copper, for instance. In a short time after the apparatus has been put in the condition described, the water in the jar will become bluish from the pas- sage into it of some of the sulphate of copper from the osmometer. This outward passage of the salt is exosmosis. In the graduated tube the fluid in the osmometer will be seen to rise higher and higher, due to the passage of the distilled water from the jar through the parchment into the osmometer, lowering the level of the water in the jar. This inward passage con- stitutes endosmosis. This continues until the proportion of sulphate of copper is the same in both jar and osmometer; in the mean- time, however, the amount of water in the osmometer is greater than at the beginning of the experiment. If different solutions are used than those mentioned, the results as to time, amount of endosmosis, etc., will vary materially from those described. This subject was exhaustively studied by Graham, who objected to the use of the terms " endosmosis " and " exosmosis," be- lieving that there was in reality but one current, the inward one; and he therefore used only the terms osmosis and osmotic. In the outward passage of the salt he held that it was the particles of salt which passed, but not the water holding them in solution. A second experiment may be performed which illustrates another phase of osmosis. From one end of a hen's egg the shell is to be carefully removed so as to leave the membrane uninjured. Through the other end, into the interior of the egg, a glass tube is to be passed, and the place at which it enters the egg closed with sealing-wax. The egg is then to be placed in a wine-glass containing distilled water. The water in the wine-glass passes through the membrane into the egg, and the yolk will be seen to rise in the glass tube ; at the same time it will be noted that the water in the wine-glass is diminished. After a time a solution of nitrate of silver may be dropped into the wine-glass, and immediately a whitish precipitate forms, consisting of silver chlorid. This is a proof that the chlorid of sodium, or common salt, which was a constituent of the egg, has passed through the membrane into the water. Other tests will show that the other salts have also passed out, but that little of the albumin has come through. From this experiment it will be seen that substances act FIG. 84. Graham's os- mometer. 106 PROTEIDS. differently with reference to passing through membranes ; those which pass through readily Graham denominated crystalloids; while those that pass not at all or with difficulty, he called col- loids, a term which does not necessarily imply that the substances which are called by that name do not crystallize, for, as we have seen, egg-albumin does crystallize, though salts are crystalloids and egg-albumin a colloid. This principle is the same as dialysis, or the separation of crystalloids from colloids in a dialyzer, an apparatus constructed like the osmometer, already described. As already stated, proteids, except proteoses and peptones, are not diffusible, or, to put the statement affirmatively, are colloids i. e., they do not readily pass through animal membranes ; and this principle of dialysis is employed to separate them from crystal- loids, such as sugar and salts. This may be demonstrated by putting a saline solution of albumin and globulin, as, for instance, blood-serum, in a dialyzer, the vessel outside containing distilled water ; the salts diffuse, leaving the albumin and globulin behind. The albumin, being soluble in water, remains in solution, and, being colloid, does not diffuse ; the globulin, requiring the salts to hold it in solution, is precipitated because the salts have diffused. Proteoses are diffusible, but less so than peptones ; protoproteose more than deuteroproteose, and this more than heteroproteose, so that the order of diffusibility would be peptones, protoproteose, deuteroproteose, and heteroproteose. It is to be borne in mind that diffusibility is a relative term, and that when peptones are said to be readily diffusible the idea intended to be conveyed is, that when compared with other proteids they exhibit this prop- erty. If, however, they are compared with salts, their diffusibility is low. The explanation formerly given to account for the non-diffusi- bility of proteids was that they were not crystallizable ; but since the discovery of the fact that some of them do crystallize, this explanation is abandoned, and for it is substituted that of the great size of their molecule. The molecular weight of some of these proteids has been determined, and this confirms the theory just enunciated: thus peptone, very diffusible, has a molecular weight of 400 or less ; protoproteose, less diffusible, of 2467 to 2600 ; and deuteroproteose, still less diffusible, of 3200. Precipitation. As a class, proteids in solution are precipit- able by certain reagents, of which the number is considerable. Some of the principal precipitants are : Nitric acid, picric acid, acetic acid with potassium ferrocyanid, acetic acid with excess of sodium or magnesium sulphate or sodium chlorid, when boiled with the solution of the proteid, mercuric chlorid, silver nitrate, lead acetate, tannin, and alcohol. Tannin and alcohol will pre- cipitate peptone, but most of the others will not. ALBUMINS. 107 Classification of Proteids. The proteids are classified as follows : C Serum-albumin. AH- Egg-albumin. Albumms . ..... , llctalbumin. (^ Myo-albumin. f Acid-albumin. j Alkali-albumin. f Serum-globulin (paraglobulin). Fibrinogen. Albummates Nucleoproteids Proteoses Pe P tones Coagulated Proteids . . Poisonous Proteids. Lactoglobulin. Crystallin. f Albumoses. Globuloses. . 1 3 d CO J2J CO' T}= ^ D l^ O O t cNd^id r-l r-l rH d ^ ^v *-S c *- ^ a 50 3 SE Amou Protein. o CN S o cq 111 in co d co' O O t- s n s oo rH Is ^ 00 i -es aJTS to co oc ^H r^ OS O i-^ iO co 1! . OT . "? * 5 8 2 |^ c >.S ' +j -3 2 sS 5. h^ t^ eo r c<> en o o -ii d to os -r d co' COO-^OS dos^joo eoooi-n CN rH OS GO Oi :ll* = J P.. ia JD I i 30 CN CO I> asaa CN^fXOS sssd os oq o S S 'S3 iO S O '"O g i. Is GOflOO O swsw D o ' < (M 'Sb '5c S 1 p "* s 8 I o '"5$ '* i 3 ' i ! Oj ^ S3 ft o 3 n ' i 5 i""^ fl o ^ ^ r "S > i "i - Biel. 88.8 j (5.4 6.6 0.34 1 89.1 - 1.79 3.3 5.4 0.42 Gerter. 87.24 1.9 4.3 5.9 0.28 Christenn. 89.29 89.06 1.6 1.72 3.2 2.9 5.8 6.0 0.16 0.2 Woman 20-30 years old. " 30-40 " | Pfeiffer. 87.79 2.53 3.9 5.5 0.25 Mendus de Leon. Cows' Milk. The following analysis of cows' milk may be regarded as a sample of many analyses which have been recorded, and will enable a comparison to be made with human milk. Analysis of Cows' Milk (Simon). Water 86.95 (Win \ Albumin / Fat (butter) 3.65 Lactose 4.25 Inorganic salts 0.75 COWS' MILK. 143 Comparative Analyses of Human Milk and Cows' Milk. Human Milk. Cows' Milk. Water . . . 88.05 .86.95 Casein and albumin 2.45 4.40 Fat (butter) 3.40 3.65 Lactose 5.75 4.25 Inorganic salts 0.35 0.75 If a comparison is made between the milk of the human being and that of the cow it will be seen that cows' milk contains more proteid, 4.40 as compared with 2.45 ; more fat, 3.65 to 3.40 ; and more inorganic salts, 0.75 to 0.35 ; but, on the other hand, less sugar, 4.25 to 5.75. It results from this that in substituting cows' milk for mother's milk in the feeding of infants the milk should be diluted and sugar added. In the consideration of the carbohydrates lactose or sugar of milk was discussed, so that here we need only refer to it. As we then learned, this variety does not undergo the alcoholic fermen- tation with yeast, but does with some other ferments. The fat of cows' milk is a mixture of palmitin, stearin, and olein, together with triglycerids of butyric, caproic, and other acids. It also contains lecithin, cholesterin, and a yellow lipochrome. The fats of human milk differ somewhat from those of cows' milk, but these differences are not important. The proteids of milk are, as already stated, caseinogen, which is by far the most important, and lactalbumin and lactoglobulin, which two are present in but minute quantities. Of caseinogen and its properties we have already spoken. It is this constituent which, when milk coagulates, becomes casein, forming with fat the coagulum or curd; the liquid portion, which contains whey-proteid, lactalbumin, lactose, and salts, being whey. Milk is almost entirely free from purin in any form (p. 434). Cows' milk is a fluid which is very prone to undergo fermen- tative changes ; one of these, the formation of lactic acid from lactose, has already been described ; but there are others, which are perhaps more harmful, being especially irritating to the delicate mucous membrane of the alimentary canal of the young infant. These changes are brought about by various bacteria which find their way into the milk at the dairy, where the milk is produced, or subsequently, either during transportation or after it has been delivered to the customer. Great pains should be taken to keep the surroundings of dairy and home in a cleanly condition. Milk may be the transmitter of specific disease if taken from a diseased animal as, for instance, one suffering from tubercu- losis ; and it may also become infected after coming from the cow and before it is used as food. Numerous epidemics of enteric or typhoid fever have been traced to infection of the milk-supply 144 MAMMARY GLANDS. by polluted water used either to dilute the milk or to wash the cans which contained it ; scarlet fever, also, has been contracted by those who have drunk milk which had become infected by the hands of milkers who were recovering from the disease. Diph- theria has also been transmitted through infected milk. In order to prevent the fermentation of milk, the bacteria con- tained in it should be destroyed. This may be done either by sterilization or pasteurization. Sterilization consists in heating the milk to 100 C., the boiling- point, by which the milk becomes " sterile" that is, all organisms which would produce fermentative changes in the milk are killed. The objections to this process are that the taste of the milk is altered to that of boiled milk, the casein is not so easily digested, the ernulsification of the fat and its absorption are not so readily brought about, and the amylolytic enzyme is destroyed. If the exposure to the heat continues too long, the milk becomes brown- ish in color, due to the conversion of lactose into caramel. In pasteurization the milk is exposed to a temperature of only 71 C. to 76 C. for fifteen to twenty minutes; milk thus treated is not changed as in sterilization, but will keep only a short time a day or two. Human milk is the product of the mammary glands, the structure of which may here be concisely described. MAMMARY GLANDS. The mammary glands or mamma3 (Fig. 87) are two in number, situated one in each pectoral region. They are compound racemose glands, and consist of gland-tissue which is made up of lobes, and these again of lobules (Fig. 88). The lobes are connected by fibrous tissue, and between them is fat. Each lobule is composed of sacculated alveoli and a duct, the lobular duct. The lobular ducts discharge into larger ducts, which in turn discharge into a lactiferous duct, which may be regarded as the excretory duct of a lobe. Of these ducts, tubuli lactiferi, there are from fifteen to twenty. They open at the surface of the prominent point of the breast, the mammilla or nipple, surrounding which is the areola, which in the virgin is of a pinkish color, becoming darker during pregnancy and almost black at its termination. Under the areola the tubuli lactiferi are dilated, forming ampullce, in which, during the period of lactation, the milk accumulates in the intervals of nursing. When these reservoirs are full the tension of the gland stops the process until they are emptied by the sucking child, when the cells again take on their function and the milk is secreted and flows into the ampullae through the ducts, there to accumulate until the next nursing. MAMMARY GLANDS. 145 The walls of the alveoli consist of a basement-membrane, covered, during the period when the gland is not active, by a single layer of flat or cuboidal cells (Fig. 90) with one nucleus and presenting a granular appearance. There are at this time no fat- globules. When, however, the gland begins to take on an active condition (Fig. 91) these cells become higher and project into the interior of the alveoli, and the single nucleus divides, thus becom- ing two. In the cytoplasm drops of fat appear, especially at the ends of the cells nearest the interior of the alveoli, and at the same time the nucleus which is nearer to this end of the cell becomes fatty. This end of the cell then breaks down, and the FIG. 87. Arrangement of glandular tissue of breast, the fat having been removed to show the ducts and acini (Astley Cooper). material forms the albuminous ingredients of the milk and the lactose, while the drops of fat become the milk-globules. The portion of the cell which remains forms new cytoplasm, and the same process is repeated over and over again. The cells also secrete water and the salts which are found in the milk. There is some difference of opinion as to the origin of the corpuscles found in the colostrum, and which are known as colostrum-corpuscles. One view is that they are epithelial cells of the alveoli, which become rounded and in which fat is devel- oped, and that in this condition they become detached and are discharged into the cavity of the alveolus. Another view is that 10 146 MAMMARY GLANDS. they are emigrated lymph-corpuscles ; while still a third regards them as derived from the wandering cells of the connective tissue. When the period of lactation is over the glands return approxi- mately to their original condition, thus undergoing the process of involution. Clavicle- Greater pectoral - muscle. Integument- Fibrous septa con- nected with in- tegument. Glandular tissue. Mass of adipose tissue. Areola.., Interlobular adi-- pose tissue. Nipple. Lactiferous duct.J Ampulla. Intcrlobular adi- pose tissue. Glandular tissue. Peripheral acini Mass of adipose tissue. Fibrous septa. Integument. First rib. Second rib. Lesser pectoral muscle. Intercostal mus- cles. Third rib. Deep fascia. Superficial fas- cia. Fourth rib. Horizontal axis of nipple. Fifth rib. Sixth rib. External oblique muscle. ' FIG. 88. Longitudinal section of mammary gland in situ; frozen subject of twenty years (Testut). That the secretion of milk is under the control of the nervous system there is no doubt, for the instances are numerous in which strong emotions of grief or anger have caused the secretion to cease, but just what the relation is remains still undecided. It may be that secretory nerves are involved in the activity of these glands, or that it is through the influence of vasomotor fibers that MAMMARY GLANDS. 147 their secretion is produced ; but experiments have as yet not de- termined the question. That the glands may act automatically is Duct and alveoli. Adipose tissue. FIG. 89. From section of mammary gland of nullipara (from Nagel's "Die weib- lichen Geschlechtsorgane,*' in Handbuch der Anatomic des Menschen, 1896). proved by the fact that when all the nerves which supply them are divided, the secretion still continues to be formed. FIG. 90. Section through the middle of two alveoli of the mammary gland of the dog ; condition of rest (after Heidenhain). The table on page 149 gives the composition of milk and other food-materials, together with their nutritive value. It is from one of the Farmers' Bulletins, " Milk as Food," issued by the United 148 EGGS. States Department of Agriculture. Incidentally we would call attention to these publications, which are issued free or at a FIG. 91. Mammary gland of dog, showing the formation of the secretion: A, medium condition of growth of the epithelial cells ; B, a later condition (after Heideuhain). . nominal cost by the Government, and are full of practical value, not alone to farmers, but to all students of economics. EGGS. Eggs in various forms enter largely into the common dietary. So far as birds are concerned, eggs may be regarded as a perfect food, inasmuch as until the young leaves the shell all its nutrition has been obtained from the shell and its contents, together with what it has obtained from the atmosphere. The egg of the hen is the one commonly used as food, although ducks' eggs are eaten to a considerable extent. In a hen's egg weighing 50 grams there are 7 grams of shell, 27 grams of the white, and 16 grams of yolk. The yolk and white are made up of water, 73.5; proteids, 13.5; fats, 11.6 ; and salts, 1 per cent. The white of egg consists of egg-albumin, egg-globulin, and ovomucoid, with some sugar, fat, lecithin, cholesterin, and salts. The yolk is composed of two kinds of material, one yellow, containing fat and the yellow coloring-matter lipochrome, and the other nearly white in color in which is found the nucleoproteid, vitellin, together with sugar, lecithin, cholesterin, and salts, as in the white. The white of the egg in its raw state is more digestible than when cooked, but there are few persons to whom raw eggs are palatable. Egg-albumin is coagulated at a temperature of 73 C., and vitellin at 75 C. When the temperature reaches 100 C., the boiling-point, and is kept there for some time, the albumin is so thoroughly and densely coagulated as to be difficult of digestion. Eggs have a high nutritive value, being so rich in proteid con- stituents, but must be supplemented by carbohydrates, in which they are very deficient. They contain no free purin or purin- yielding bodies (p. 434), and are therefore useful when a diet free EGGS. 149 COMPOSITION OF MILK AND OTHEE FOOD-MATERIALS. . Nutritive ingredients, refuse, and fuel-value. Protein. Fats. Carbo- Mineral hydrates, matters. Non-nutrients. Water. Refuse. Fuel-value. Protein compounds, e. g., lean of meat, white of egg, casein (curd) of milk, and gluten of wheat, make muscle, blood, bone, etc. Fats, e. g., fat of meat, butter, and oil, I serve as fuel to yield heat and muscular Carbohydrates, e. g., starch and sugar, j power. Nutrients, etc., p. ct Fuel-value of 1 lb......... 400 800 1200 1600 2000 2400 2800 3ZOO 3600 4 150 MEAT. from purin is desired. Eggs with milk in which the amount of purin is very small, together with butter and cheese, makes a diet almost entirely free from purin free or bound. MEAT. Meat is the flesh of such vertebrate animals as are used for food, though the term is perhaps commonly restricted to the mus- cular tissue of mammals. It is the kind of food from which the nitrogen necessary for nutrition is chiefly obtained. In meat there are not only connective and adipose tissue, in addition to muscular fiber, but even in the leanest meat there are fat-cells between the muscular fibers. In the following table (Munk) are given the percentages in which the various constituents occur in the meats of the common mammals used as food, together with those of fowl and pike. Constituents. Ox. Calf. Pig. Horse. Fowl. Pike. Water 76.7 75.6 72.6 74.3 70.8 79.3 Solids Proteids and Gelatin Fat Carbohydrates ; . Salts 23.3 20.0 1.5 0.6 1.2 24.4 19.4 2.9 0.8 1.3 27.4 19.9 6.2 0.6 1.1 25.7 21.6 2.5 0.6 1 29.2 22.7 4.1 1.3 1.1 20.7 18.3 0.7 0.9 0.8 We have already discussed the chemical composition of muscle (p. 62), and therefore need simply refer to it here. Liebig states that the flesh of young animals contains more gelatin than that of old ones ; in 1000 parts of beef there are 6 parts of gelatin, while in veal there are 50 parts. It is a matter of common belief that veal is less digestible than beef. This is, perhaps, true to some extent, but not to such an extent as is generally thought. Veal is more tender than some other meats, and is therefore not usually well masticated, and hence not sufficiently prepared for the action of the digestive juices. This renders its digestion difficult and leads to the inference that its digestibility is low. When very young, veal has a gelatinous consistency and is regarded as being unfit for food. The cooking of meat has the effect of making it more digesti- ble by changing its collagen into gelatin, and also more palatable. Besides this, if the temperature is carried sufficiently high, any animal parasites or pathogenic bacteria which the meat may con- tain are killed. Whenever meat is eaten which is raw or in- sufficiently cooked, there is always danger of contracting disease. Meat which contains the Trichina spiralis may in this condition produce trichinosis; and that which contains cyslicerci may cause tapeworm in those who eat it. There is also great danger from eating the meat of a tuberculous animal. This is denied by some, but the evidence in its favor seems conclusive to the author. MEAT. 151 Until the year 1901 it was the general consensus of opinion among those who had made a study of the subject that bovine and human tuberculosis were identical. In 1895, the Royal Commis- sion on Tuberculosis said : " We find the present to be a conven- ient occasion for stating explicitly that we regard the disease as being the same disease in man and the food animals, no matter though there are differences in the one and the other in their manifestations of the disease ; and that we consider the bacilli of tubercle to form an integral part of disease in each, and (whatever be its origin) to be transmissible from man to animals, and from animals to animals." In 1901, Koch announced that he felt "justified in maintaining that human tuberculosis differs from bovine, and cannot be trans- mitted to cattle." He also expressed the opinion that bovine tuber- culosis was scarcely, if at all, transmissible to man. Since this announcement of Koch was made, the matter has been investigated all over the world by experienced and competent men, and the practical result of such inquiry is to leave the subject where it was prior to Koch's announcement. The infection may not be directly due to the ingestion of the meat itself that is to say, the muscular tissue may not contain the bacilli but to the tuberculous matter from glands with which in the cutting of the meat the butcher smears it. The Bacillus tuber- culosis is killed in a few minutes at a temperature of 100 C., the boiling-point, in five minutes at 80 C., and in four hours at 55 C., but the bacillus itself must be exposed to these temperatures. Experiment has demonstrated that in ordinary cooking both by boiling and roasting, the temperature in the interior of the joint of meat, unless it is under six pounds in weight, seldom reaches 60 C. ; and that rolled meat, in the center of which is tuber- culous matter, is not sterilized by any process of cooking if it is over four pounds in weight. It follows from this that the greatest care and supervision should be exercised by health author- ities at the slaughter-house, so as to prevent the possibility of infected meat finding its way into the market. To minimize still further the danger, all meat which may contain infection should be thoroughly cooked. The cysticerci which develop tapeworm in man are not destroyed by the simple processes of salting and smoking, so that for their destruction meat should be exposed to a temperature of at least 66 C., while for the destruction of the trichina the temperature should be even higher, say 70 C., inasmuch as the trichina is enclosed in a capsule which serves as an obstacle to the entrance of heat. The common methods of cooking meat are, roasting, boiling, broiling, and frying. These all have their proper places, but should be employed with discrimination. In roasting, the meat is exposed to a great heat, so as to coagulate the proteids on the 152 MEAT. surface in as short a time as possible, thus retaining the juices of the meat in the interior. The temperature is then reduced to 93 C. or 88 C., and maintained at that point, the general rule being to allow fifteen minutes for every pound of meat, otherwise the coagulating process will extend to the interior and make the muscular fibers tough. This temperature is high enough to cook thoroughly the whole piece, but not so high as to dry up the juices. Broiling is allied to the process of roasting. In boiling meat the same object is accomplished by plunging it into boiling water, which coagulates the exterior as in the roasting process. If, however, the object to be attained is to make soup or broth, then the meat, having been cut into small pieces, is placed for some time in cold water and the temperature gradually raised to 71 C. By this treatment the juices of the meat are extracted and the soluble parts are dissolved out from the meat, before the heat has time to coagulate the proteid. It should be remembered, however, that such soups are not very nutritious, but are stimulating. They contain very little proteid or fat, but do contain salts and the ex- tractives of muscles, such as creatin, creatinin, etc. It is for the reasons thus given that beef-tea is of little value as food. Prof. Halliburton, in a recent address before the American Chemical Society, called attention to the valueless character of beef tea in the following language : " Beef tea, or ' beef extract/ as it is generally termed in the United States, is in no sense a food, but merely a palatable and stimulating drink, ordinarily harmless, though possibly harmful in gouty conditions. " I have looked in vain among your advertisements for one which is familiar to us in England, representing an ox in a teacup. Another advertisement on a similar line shows an ox looking at a bottle of meat extract and saying, < Alas ! my poor brother/ the inference being that all that is of nutritive value in the ox was con- tained in the little bottle he is contemplating. The absurdity of these advertisements must be apparent to all who have any know- ledge of the chemistry of foods, and it is the province of the physiologist and the chemist to teach the public and the medical profession how erroneous such views are. Instead of an ox in a teacup, the ox's urine in a teacup would be much nearer the fact, for the meat extract consists largely of products on the way to urea, which much more nearly resemble in constitution the urine than they do the flesh of the ox. The manner in which meat extracts have been pushed in the market will, I fear, stand for a long time in the way of the recognition of the simple truth, that the best way of getting all the available benefit from a mutton chop is just to eat it. "Some of the manufacturers of meat extracts have lately awakened to the fact that the general public is learning something CEREALS. 153 of the real value, or lack of value, of their wares, and, with a view to meeting the criticisms which have been raised, they have added greater or less quantities of powdered meat fibers. Even if it is granted that the powdered fibers are digestible, and that the meat extracts are composed wholly of them, which they are not, how much nutriment would the patient receive from teaspoonful doses given through the twenty-four hours ? Certainly not an appreciable amount." If vegetables are added to meat extracts, making a vegetable soup, the nutritive value is correspondingly increased. If bones are used in the soup-making process, the amount of gelatin may be increased to such an extent that when cold the soup gelatinizes and becomes solid. Frying is a method of cooking which should never be applied to meat such as beef, as it makes it indigestible by reason of its toughness, and also by reason of the fat with which it becomes soaked. If meats are fried by immersion in boiling fat, the process is not so objectionable ; but the fat should not be allowed to permeate the tissue, as it would do if the process was continued too long. Frying is well adapted to the cooking of fish. CEREALS. The cereals are the farinaceous seeds used as food, such as wheat, Indian corn or maize, rice, rye, oats, and barley. They all contain proteids, fat, starch, and mineral salts, though the pro- portion of these ingredients varies considerably in the different cereals, as is shown by the following table (Halliburton) : Constituents. Wheat. Barley. Oats. Rice. Water Proteid 13.6 12.4 13.8 11.1 13.4 10.4 13.1 7.9 Fat 1 4 2.2 5.2 0.9 Starch Cellulose 67.9 2.5 64.9 5.3 57.8 11.2 76.5 0.6 Mineral Salts . ... 1.8 2.7 3.0 1.0 The proteids in the flour of cereals are not identical. Some writers regard those in wheat-flour as being a vegetable myosin and a soluble proteose called phytalbumose. Gluten, which is considered by some authorities as a proteid constituent of wheat, is regarded by others as a mixture of gluten-fibrin, which is formed from the vegetable myosin, and a proteose insoluble in water, which is formed from the phytalbumose, and which gives to the gluten its sticky consistency. According to this theory, the gluten as such does not exist until water is added, when by the action of an enzyme gluten is produced. This enzyme has, how- ever, never been isolated, and until this theory is better sustained by proofs we shall regard gluten as a constituent of wheat-flour. 154 CEREALS. The proteids of oats are three in number: One soluble in alcohol, one a globulin, and the third a proteid soluble in alkali. Jn maize there are two globulins, one a vitellin and the other a myosin ; one or more albumins ; and zein, a proteid soluble in alcohol. The proteids of rye are gliadin, leucosin, edestin, and proteose ; and those of barley are leukosin, proteose, edestin, and hordein. The cereal most commonly used is, perhaps, wheat, the flour of which is made into bread. Bread. The cereal most used for bread-making is wheat, though bread is also made from rye and cornmeal. Wheat-flour contains approximately 14 per cent, of water, 12 of proteids, and 70 of carbohydrates. The amount of fat and salts is small. In the making of flour the wheat-grains are ground, and the result is sifted, or " bolted " as it is termed, into fine flour, coarse flour, and bran. The bran is the extreme outer covering of the grain, and is so tough and silicious that it is of no nutritive value, while the other coverings contain so much of proteid, fat, and salts as to give them considerable food-value. The process of making flour just described is known as the old process, and results in heating the flour, which, if not properly cooled, is liable to spoil. In the new process the grains are cut with knives or crushed between iron rollers which do not produce heat. Flour is made by another process, in which the grains are moistened and the extreme outer covering or husks removed by rubbing. The grains after being dried are exposed to blasts of air which have force enough to thor- oughly disintegrate them. When pulverized this is known as whole-wheat flour, and contains all that is nutritive in the wheat. In making bread the flour is moistened with water or milk to which yeast has been added, and when thoroughly mixed this becomes dough. Salt is also added, and some breadmakers add sugar and butter as well. After thorough kneading, the dough is exposed to a temperature of about 24 C. The starch is con- verted by an enzyme which exists in the wheat into dextrin and sugar, and this, under the influence of the yeast, then undergoes the alcoholic fermentation, alcohol and carbonic-acid gas resulting. This gas rises up through the dough, expanding it to more than double its original volume, making it thereby very spongy. When the dough has risen sufficiently, it is put into an oven and baked. This results in killing the yeast-cells, and thus prevents any further fermentation, and at the same time the carbonic acid and alcohol are expelled and the crust is formed. Wheat bread con- tains 7 to 10 per cent, of proteids, 55 of carbohydrates, 1 of fat. 2 of salts, and 32 to 35 of water. VEGETABLE PROTEIDS. 155 VEGETABLES, The green vegetables form a very important part of the food of man. It is true that they contain a large amount of water, varying from 75 to 95 per cent. ; still, they also contain carbo- hydrates, and are one of the principal sources from which these food-stuffs are derived. Thus in potatoes, while there is but 2 per cent, of proteids, and only 0.2 per cent, of fat, there is 20 per cent, of starch. The pulses or leguminous plants, such as peas, beans, and lentils, supply man in their seeds with food which is rich in proteids as well as in carbohydrates ; thus in peas there are 23.7 per cent, of proteid and 49.3 per cent, of starch ; in lentils, 24.8 per cent, of proteid and 54.8 per cent, of starch. The pro- teids of the pulses are of the nature of vitellin and globulin. In the kidney-bean two globulins, phaseolin and phaselin, besides proteose have been found. Vegetable Proteids. The proteids in vegetables may exist in three forms: (1) In solution in the juices of the plant; (2) in the protoplasm ; or (3) in aleurone grains. They are classified, as are the animal proteids, into albumins, globulins, albuminates, pro- teoses and peptones, and coagulated proteids. What was formerly spoken of as legumin or vegetable casein, or simply vegetable proteid, is now held to be an alkali-albumin produced by the action of the alkali used in the extraction on the globulins which exist normally in the plant. Proteoses have been found in the various varieties of flour, as well as in the circulating fluids of plants, and in the latter also occur hemi-albumose, leucin, tyrosin, and asparagin. Enzymes also exist in plants, and to those of a proteolytic character these proteoses are probably due. Some of these proteolytic enzymes have been carefully investigated, notably papain in the papaw plant, and bromelin in pineapple- juice. In the juice of the papaw are a number of proteids : a globulin resembling serum-globulin, an albumin, and two pro- teoses, with one of which papain is associated. This enzyme is very much like trypsin. Bromelin acts in neutral, acid, or alkaline media, acting particu- larly well at 60 C. It produces proteoses and peptones, and is used to prepare artificially digested foods. Enzymes are very abundant in the vegetable kingdom, and have for their office the conversion of the insoluble proteid of the seed into the soluble nitrogenous substances of the sap. They are, however, not all of a proteolytic nature. There are also those that are amylolytic, as the diastase in barley, and these enzymes change the starch of seeds into sugar. Such a conversion we have already referred to in the process of bread-making when the wheat- starch first becomes sugar, and then undergoes alcoholic fermenta- tion under the influence of yeast. 156 BEVERAGES. The nutritious value of fruits is not to be overlooked. When fresh and ripe they are easily digested, and serve besides a useful purpose in keeping the bowels in regular action. BEVERAGES. Under this general head are included tea, coffee, cocoa, and alcoholic beverages. Some of these have a distinct food-value, others are stimulants only, while the opinions held by authorities as to some of the others are so diverse and the results of experi- ments so differently interpreted, that it is difficult with our present knowledge to classify them with precision. Tea. Tea is an infusion made from the leaves or leaf-buds of the tea plant, the principal constituents of which are an aro- matic oil, an alkaloid, thein (C 8 H 10 N 4 O 2 ) 1.8 per cent., tannin about 15 per cent., albuminous compounds, dextrin, and salts con- taining potash and phosphoric acid. Tea is a stimulant by virtue of the thein which it contains, and an astringent because of the presence of tannin. Tea should be made with boiling water, and in about five minutes the infusion should be poured into another vessel ; if left longer, it becomes bitter and unwholesome because of the large amount of tannin dissolved. Coffee. This beverage is an infusion made from the seeds of the coffee plant. The seeds or berries contain fat, legumin or vegetable casein, sugar, dextrin, salts, an aromatic oil, and an alka- loid caffein (C 8 H 10 N 4 O 2 ) about 0.75 per cent., and caffeo-tannic or caffeic acid, a variety of tannic acid. Thein and caffein are isomeric, and their effects are similar. While tea is astringent, coffee has a laxative action on the bowels and acts as a stomachic tonic. It has also been claimed that both tea and coffee act indirectly as foods by retarding the waste of the tissues ; whether this is true or not, they certainly have their uses in removing the sense of fatigue, and they also allay the sensation of hunger. If used to excess, however, both coffee and tea disturb the digestive organs and produce nervous disturbances, such as headache, trembling, and wakefulness. This condition is most commonly observed in the confirmed tea-drinker, who is as intemperate as anyone addicted to the excessive use of alcohol. Black coffee increases the heart action, and is given by physicians when the circulation is depressed. It is also given in cases of poisoning by opium. For its relation to uric acid see page 434. Cocoa. This is prepared from the seeds of Theobroma cacao, which are roasted, husked, and crushed. Cocoa-nibs, as the crushed seeds are called, contain about 50 per cent, of oil or cocoa- butter, 15 per cent, of proteids, and an alkaloid, theobromin, 0.5 ALCOHOLIC BEVERAGES. 157 to 1.2 per cent. This alkaloid is very similar in all respects to thein and caffein. Cocoa is supposed to possess inuch more nutritive value than either tea or coffee, and that it is, therefore, especially useful in wasting diseases, during which it is frequently prescribed, but the small amount of proteid and fat contained in a single tea- spoonful of cocoa can hardly entitle it to a very high place among foods. Alcoholic Beverages. Under this head are included spirits, or those that are distilled ; wines, those that are fermented ; and beers or malt liquors. Spirits or distilled liquors include whiskey, brandy, rum, and gin. Whiskey is produced by distilling fermented grain, such as corn or rye. It contains by volume 28.90 to 60.30 per cent., and by weight 23.75 to 52.58 per cent., of alcohol. Brandy is the product of the distillation of fermented grapes, and has an alco- holic strength of 30.80 to 50.40 per cent, by volume and 25.39 to 42.96 per cent, by weight. Brandy contains enanthic and other ethers which whiskey does not. These percentages are the results of actual analyses made by the Board of Health of the State of New York, and differ very markedly from those given by most authorities. Thus we have before us one excellent authority, who states that whiskey contains 44 to 50 per cent, by weight, or 50 to 58 per cent, by volume, of alcohol ; and brandy 39 to 47 per cent, by weight, or 45 to 55 per cent, by volume ; while another makes the statement that brandy contains from 50 to 60 per cent, of alcohol. It is evident from these figures that the alcoholic strength of different whiskeys and brandies varies to a considerable degree so much so, indeed, that in using alcohol medicinally physicians are recommended to prescribe " alcohol of a known strength, flavored with ethereal essences, and softened with glycerin or syrup" (Bartley). Wines differ also greatly in alcoholic strength, the "lighter" wines containing less, the "stronger" wines more. Of the lighter wines, champagne contains from 5.8 to 13 per cent., and red Bordeaux 6.85 to 13 per cent. ; while of the stronger wines, port contains from 16.62 to 23.2 per cent., and sherry from 16 to 25 per cent. Wines contain besides alcohol various aromatic com- pound ethers enanthic, citric, malic, racemic, etc. which give to them their " bouquet," also sugar, tannic acid, various other acids, and potassium salts. Beers contain on an average from 3 to 6 per cent, of alcohol by volume ; although there is here, as in the distilled beverages, a great variation. They also contain dextrin, sugar, lupulin, free organic acids and salts. Purin-bodies (p. 434) have been found in beer and porter. Hall obtained on analysis 0.1250 grams per liter from lager beer and 0.1550 from porter. He remarks that 158 EFFECTS OF ALCOHOL UPON THE HUMAN BODY. their presence may account for the harmful influence of these bev- erages in gout, and for some of the pathologic changes which occur in chronic alcoholism. In claret, sherry, and port no trace of purin-bodies is found. The following table gives the per- centages of alcohol and solid matter or extract in some of the common beers and ales (Allen) : Alcohol. Solid matter or extract. Munich Lae^er . . . 4.75 7 08 Pilsen Laa;er . 3.55 5 15 American La^er (average of 19 samples) 2 78 6 05 Bass's Pale Ale 6 25 6 98 Alsop's Pale Ale .... 6 37 4 44 Guinness 's Stout . 6 66 7 24 Value of Alcoholic Beverages as Food. It will be seen that by virtue of the carbohydrates and salts which wines and beers con- tain they certainly have a food-value entirely irrespective of the alcohol, which is also one of their constituents. The compound ethers are regarded as assisting digestion by promoting the secre- tion of the digestive fluids, while the bitter principles are well- recognized stomachic tonics. Used in moderation they are there- fore not injurious, but used to excess there is danger of their producing fat in excess, imperfect oxidation, and a resulting plethoric and perhaps gouty diathesis. EFFECTS OF ALCOHOL UPON THE HUMAN BODY. We come now to consider a subject about which volumes have been written, and one which has, perhaps, excited more discussion in both scientific and lay organizations than any other i. e., the eifects of alcohol upon the human body. The warfare has raged long and fierce around the question, "Is alcohol a food?" In a discussion of any subject it is very important that there should be no misunderstanding about the meaning of the terms employed, and, therefore, before entering upon this discussion we must have a distinct understanding as to what is meant by a food. For this purpose we quote the following definitions : Definitions of Food. " That which is eaten or drunk for nourishment; aliment; nutriment in the scientific sense; any substance that, being taken into the body of animal or plant, serves, through organic action, to build up normal structure or supply the waste of tissue ; nutriment, as distinguished from condi ment." Standard Dictionary. " Anything which, when taken into the body, serves to nourish or build up the tissues or to supply heat." Borland's Illustrated Medical Dictionary. " Any substance, inorganic or organic, solid or liquid, that will INFLUENCE OF ALCOHOL UPON GASTRIC DIGESTION. 159 nourish the body, renew the materials consumed in producing those forms of energy called vital." Chapman's Human Physi- ology. " The use of food is to repair the waste of the tissues, and through combustion in the economy to liberate energy." Ibid. These quotations might be increased indefinitely, but those given will answer our purpose. A food serves one or more of four purposes: 1. To build up normal structure; 2. To dimmish the waste of tissue ; 3. To supply the waste of tissue ; 4. Through combustion (oxidation) to liberate energy. Any substance, there- fore, which performs any one or more of these four offices is a food. It may do it to a considerable extent, and consequently have great food-value ; or it may do it to but a slight extent, and have but little food-value ; but in so far as it does it at all it is a food. Influence of Alcohol upon Secretion of Saliva. When strong alcohol or an alcoholic beverage is taken into the mouth there is produced an increase in the secretion of saliva, not only as to volume, but also as to its organic and inorganic constituents. The same effect is produced by vinegar, ether-vapor, and other similar substances. This stimulating effect, however, lasts only while the liquid is in the mouth. Alcohol in the stomach has no effect upon the secretion of saliva. Influence of Alcohol upon Secretion of Gastric Juice. The evidence is overwhelming that alcohol, whether taken as alcohol or in the form of alcoholic beverages, such as whiskey, wine, or beer, increases the amount of gastric juice se- creted, and that this is more acid and contains more of its normal constituents. The action of this gastric juice upon proteids is also very pronounced. That this is not entirely due to direct stimulation of the glands of the stomach by the alcohol is shown by the fact that when alcohol is introduced into the small intes- tine, and then this latter is ligated so that none of the alcohol can enter the stomach, an increased secretion of gastric juice is still produced. It is as yet not determined just how this is brought about, whether by action on the cells of the gastric glands through the medium of the blood, or upon secretory nerve-fibers. It is to be borne in mind that other constituents than alcohol are to be found in wines and malted liquors ; and experiments show that these, especially the organic acids, produce also a stimu- lating effect upon the gastric glands, so that the alcohol is not the only factor concerned in causing increased secretion and acidity. Influence of Alcohol upon Gastric Digestion. In a paper on " Influence of Alcoholic Drinks upon Digestion," by Chittenden, Mendel, and Jackson, published in the American Journal of Physiology, and to which we are indebted for much information, is a synopsis of the opinions and results of experiments 160 EFFECTS OF ALCOHOL UPON THE HUMAN BODY. of different physiologists on this part of the subject. Kretschy observed in a woman with gastric fistula that alcohol retarded digestion. Buchner found that in the human stomach alcohol, wine, and beer retarded digestion, but less so than in artificial digestion. Bikfavi observed in dogs a retardation of digestion with even small quantities of alcohol. Beer and wine showed no favorable influence, the latter retarding digestion in large quanti- ties. Ogata states that beer, wine, and brandy retard digestion noticeably. Schelhaas observed that in the living stomach wine did not retard digestion so long as there was free HC1 present. Gluzinski found that alcohol retarded proteid digestion and brought about the secretion of a very active, strongly acid gastric juice. Henczincki observed no bad effect on digestion with the use of beer. Blumenau found that 25-50 per cent, alcohol dimin- ishes stomach digestion during the first two or three hours. Wolff- hardt observed in a healthy man that 15-20 grams of absolute alcohol interfered with proteid digestion ; that the effect of cognac varied with the period of digestion during which it was taken ; and that wines tended to promote digestion. Brunton states that alcohol increases the movements and the secretion of the stomach, and by mixing its contents more thoroughly with gastric juice accelerates digestion. Gluzinski on the other hand, finds that alcohol diminishes the mechanical action of the stomach to a moderate degree. Chittenden and his associates experimented upon a dog to ascer- tain the effect of alcohol upon (1) variations in acidity and (2) time of digestion. The results are very interesting and in- structive. In these experiments 50 grams of meat were given in each, sometimes alone, sometimes with water, and sometimes with alcohol of varying strengths, and sometimes with various alcoholic beverages. When meat alone was given the stomach was empty (end of gastric digestion) in 2 hours and 55 minutes. When water was given with the meat, the time of digestion varied from 2 hours and 15 minutes to 3 hours ; an average of 2 hours and 40 minutes. With alcohol, varying from 22 to 30 per cent., the time was from 3 hours to 3 hours and 45 minutes ; average, 3 hours and 20 minutes. With weak alcoholic beverages, wine and beer, the time of digestion was from 3 hours to 3 hours and 15 minutes ; average, 3 hours and 10 minutes. With strong alcoholic beverages, it was with whiskey, 2 hours in one experiment and 3 hours in another; with gin, 3 hours ; with brandy, 2 hours and 40 minutes ; an average of 2 hours and 40 minutes. " The conclusions to be drawn from these experiments would seem to be that alcohol does not retard proteid digestion to any great degree ; taking the set of experiments quoted in connection with another set, there is a slight retardation, and that more marked with malted beverages. ABSORPTION OF ALCOHOL FROM THE STOMACH. 161 Inasmuch, however, as we have already seen, an increased amount of an active gastric juice is produced by the alcohol, it is more than probable that this makes up for any retardation in the pro- teolytic processes. The great care with which these experiments of Chittenden and his associates have been made seems to the writer to entitle their conclusions to great consideration, which may be briefly summed up in the statement that " gastric digestion in the broad- est sense is not markedly varied under the influence of alcohol or alcoholic fluids. This conclusion, it may be mentioned, stands in perfect harmony with the results of the investigations of Zuntz and Magnus-Lenz regarding the influence of alcohol (beer) on the digestibility and utilization of food in the body. These investi- gators found by a series of metabolic experiments on men with diets largely made up of milk and bread, and on individuals accustomed and unaccustomed to the use of alcoholic beverages, that the latter did not in any way diminish the utilization of the food by the body." Influence of Alcohol and Alcoholic Fluids upon the Excretion of Uric Acid. Beebe has conducted a series of experiments reported by Chittenden in the American Journal of Physiology, with : 1, Absolute alcohol suitably diluted ; 2, whisky ; 3, beer ; and 4, port wine. The quantity used in twenty-four hours represented between 75 and 80 c.c. of absolute alcohol. The result was a marked increase in the uric-acid excretion, the increase in most cases beginning in the second hour after the meal and reaching its height at the fifth hour ; this increase was not due to a hastening of the normal output, but was an actual increase in the amount produced. The effect, Chittenden believes, is doubtless due to a disturbance in the metabolism of the purin-bases of the food (p. 434). As already stated (p. 157) Hall has obtained purin- bodies from beer and porter. Absorption of Alcohol from the Stomach. Chittenden's experiments, in which 200 c.c. of 37 per cent, alcohol were intro- duced into the stomach of a dog with the duodenum ligated at the pylorus, resulted in the complete disappearance of the alcohol in 3-3^- hours by absorption through the stomach-walls into the blood. When the intestine is open the absorption is more rapid. When 68 grams of alcohol, as wine or beer, are taken into the stomach, 8090 per cent, will have disappeared from the aliment- ary tract within ^ hour. In one of Chittenden's experiments 50 c.c. of 20 per cent, alcohol were absorbed within -J- hour. His conclusion is that, " in view of this rapid disappearance of alcohol from the alimentary tract, it is plain that alcoholic fluids cannot have much, if any, direct influence upon the secretion of either pancreatic or intestinal juice." We have seen that when alcohol is taken into the stomach it 11 162 EFFECTS OF ALCOHOL UPON THE HUMAN BODY. produces an increased secretion of an active gastric juice. When this stimulation is excessive changes are set up in the mucous membrane, as a result of which the gland tissue becomes less, and the secretion is correspondingly diminished. Up to the point where the stimulation resulting in increase of the normal secre- tion ends and the pathologic changes begin, alcohol is not in- jurious, but manifestly in health no such artificial stimulus is needed. So long as the individual is well, the natural food is a sufficient stimulus to the gastric glands and the additional stimu- lation of alcohol is uncalled for, and inasmuch as the exact line of demarcation between the amount of alcohol that does good and that which does harm has not as yet been absolutely determined, there is always a possibility that an excess may be taken and in- jury result. So far as the stomach is concerned, then, there is in a condition of health no useful purpose served by alcohol, but there are conditions in which this property of alcohol of exciting the gastric glands to increased activity may be availed of under medical advice. Alcohol being a very diffusible substance, is mostly absorbed by the blood-vessels of the stomach, which carry it into the portal vein, and by this channel it reaches the liver, where its stimulating action is again exercised upon the cells of that organ, and an in- creased production of bile is the result. If, however, this stimu- lation is excessive and long continued, degenerative changes take place by which the organ ultimately becomes diminished in size and incapable of performing its function. From the liver the blood carries the alcohol to the heart, which is quickened in action, and to the brain, whose activity is also in- creased. If the quantity of alcohol is excessive, the cells of gray matter in the braiii are over-stimulated and great excitement re- sults, and this may, if the quantity is sufficient, result in a suspen- sion of the functions of the brain and a condition of unconscious- ness, passing on in extreme cases to a fatal termination. But if the quantity of alcohol which reaches the brain is not enough to produce the fatal result, but still enough to maintain the condition of over-stimulation, there result changes in the structure of the brain, as there do in that of the stomach and liver, which weaken the mental activities and produce the irregular and inco-ordinated muscular movements so familiar to all who have observed in- dividuals who have for years been addicted to drink. From this necessarily incomplete recital of the effects of alcohol we now turn to some experimental evidence bearing upon the subject. These experiments have been carried on by various experimenters, and some of the results are well summarized in the following quotation from An American Text-Book of Physiology under the title " Alcohol in the Body." " Alcohol in the stomach at first prevents the gelatinization necessary in proteid for peptic ABSORPTION OF ALCOHOL FROM THE STOMACH. 163 digestion, but this difficulty is of no great moment because the absorption of alcohol is rapid and complete. It makes the mucous membrane hypereinic, promotes the absorption of accom- panying substances (sugar, peptone, potassium iodid), and stim- ulates the flow of the gastric juice. In this matter it acts as do other condiments (salt, pepper, mustard, peppermint), but if there be too great an irritation of the mucous membrane there is less activity (dyspepsia). The rapid absorption gives to al- cohol its quick recuperative effect after collapse, and its value in administering drugs, especially antidotes. Alcoholic beverages combining alcohol and flavor promote gastric digestion and absorp- tion, but often stimulate the appetite in excess of normal require- ments. Alcohol is burned in the body, but may also be found in the breath, perspiration, urine, and milk. Alcohol has no effect on proteid decomposition, but acts to spare fat from combustion. The addition of 50 to 80 grams of alcohol to the food has no apparent effect on the nitrogenous equilibrium. Alcohol in the body acts as a paralyzant on certain portions of the brain, destroy- ing the more delicate degrees of attention, judgment, and reflective thought, diminishing the sense of weariness (use after great exer- tion furnished to armies in the last hours of battle), and raising the self-esteem ; it paralyzes the vasoconstrictor nerves, producing turgescence of the skin with accompanying feeling of warmth, and thereby indirectly aiding the heart. Alcohol acts to stimulate the respiration, especially in the tired and weak, wine with a rich bouquet, like sherry, being more effective than plain alcohol. The higher alcohols, propyl, butyl, amyl, are more poisonous as the series ascends, and are less volatile, less easily burned, and therefore more tenaciously retained by the body, with more pernicious results." The most complete and the most recent knowledge which we possess on the subject of alcohol and its effects upon the human body is contained in a publication entitled " Physiological Aspects of the Liquor Problem, Investigations made under the Direction of W. O. Atwater, John S. Billings, H. P. Bowditch, R. H. Chit- tenden, and W. H. Welch, Sub-Committee of the Committee of Fifty to Investigate the Liquor Problem," which was issued from the press in 1903. The only portion of this report to which it is our purpose to here refer is that which treats of " The Nutritive Value of Alcohol," by Prof. W. O. Atwater. The author states at the outset that no one doubts that the continued and excessive use of alcohol is injurious to body, mind, and character, and that in large enough quantities it is really a poison. He, however, makes the broad statement that the great majority of physiologists and hygienists hold to the opinion that alcohol, taken in small quantities, may serve the body for nutriment, that it is at some times valuable, at others harmful. The two chief functions of food are, Prof. Atwater states, to 164 EFFECTS OF ALCOHOL UPON THE HUMAN BODY. furnish materials for the growth and repair of the tissues and fluids of the body and to yield energy for maintaining the healthful bodily temperature and for its muscular work. The proteids in the main perform the former function, and while they also yield energy, yet this is principally due to the fats and carbohydrates. Alcohol, containing no nitrogen, is not a tissue builder, its value to the body, therefore, if it possesses any, must be that of a fuel, sup- plying energy. Food serves as fuel by being oxidized in the body ; in this oxidation potential energy becomes kinetic; part of this kinetic energy appears as heat and another part as muscular work. Besides, in supplying energy the foods protect the body from con- sumption, for energy must be produced, and if there is nothing else to produce it from, the body tissues must undergo oxidation. The question, then, which Prof. Atwater proposed to settle was : " Is the energy of alcohol transformed like that of ordinary food materials ?" In determining this question a respiration calorimeter was used ; this served to measure the materials received and given off from the body, including the products of respiration, and also to measure the heat given off by the body. In conducting the experiments pure ethyl alcohol was used, generally to the amount of two and one-half ounces a day, about as much as would be contained in a bottle of wine with 10 per cent, alcohol, or three or four glasses (6 or 8 ounces) of whisky. In some of the experiments whisky or brandy was used. The alcohol given was divided into six doses three given with meals and three between meals the object being to avoid any special influence of the alcohol upon the nerves, and thus test its action as food under normal bodily conditions. Without dwelling further upon the experiments we will quote the results : 1. Alcohol in moderate amounts tended to very slightly increase the digestibility of the protein, but did not materially alter the digestibility of the other nutrients. While this is the statistical result of these experiments, the extent to which it would be true in general experience is by no means certain. 2. In the average of the experiments at least 98 per cent, of the alcohol taken was actually oxidized in the body. Other experi- ments show that in ordinary diet about 98 per cent, of the carbo- hydrates, 95 per cent, of tlie fats, and 93 per cent, of the protein are burned in the body. Accordingly, the alcohol is more com- pletely oxidized than are the nutrients of an ordinary mixed diet, 3. The law of the conservation of energy obtained with the alcohol diet as with the ordinary diet. The potential energy of the alcohol oxidized in the body was transformed completely into kinetic energy and appeared either as heat or as muscular work, or both. To this extent, at any rate, it was used like the energy of the pro- tein, fats, and carbohydrates of the food. ABSORPTION OF ALCOHOL FROM THE STOMACH. 165 4. Fat protection in the alcohol rations was very slightly dif- ferent from that with the ordinary rations ; in other words, the alcohol was practically as efficient in the protection of body fat from consumption as the fats or carbohydrates of the food which it re- placed. 5. The power of alcohol to protect the protein of food or body tissue, or both, from consumption is clearly demonstrated. Its action in this respect appears to be similar to that of the carbo- hydrates and fats ; that is to say, in its oxidation it yields energy needed by the body, and thus saves other substances from oxidation. 6. Alcohol appears to exert at times a special action as a drug. In large quantities it is positively toxic and may retard or even prevent metabolism in general, and proteid metabolism in particular. In small doses it seems at times to increase the disintegration of protein. The only justification for calling alcohol a proteid poison is found in this disintegrating tendency. 7. In some of the experiments alcohol was administered with coffee, in others with water. There was no direct evidence that the coffee interfered with the action of the alcohol ; if any effect was produced, it was to' increase rather than retard proteid met- abolism. 8. When 72 grams of alcohol, given in six doses and furnishing 500 calories of energy, replaced the isodynamic amounts of fats and carbohydrates, the alcohol caused no considerable increase, in the amount of heat radiated from the body. If the alcohol had all been taken at one dose, it might have caused the cutaneous vessels to dilate, possibly stimulated the sweat-glands, increased the cir- culation, and thus increased the heat radiation. If enough alcohol had been taken to induce the comatose condition called " dead drunk/' and if the men experimented upon had been exposed at the same time to severe cold, the production of heat in the body might have been retarded and the radiation increased so as to lower the body temperature by several degrees. 9. In the experiments alcohol was not suddenly or /rapidly oxidized, or if there was such rapid oxidation, there was a correspond- ing decrease in the oxidation of carbohydrates, fats, or protein. The alcohol, carbohydrates, and fats replace one another as sources of energy ; as either was oxidixed, the others were proportionately spared. 10. In all the test experiments alcohol was certainly, and in the work experiments it was in all probability, a source of heat for the body. 11. The hypothesis that alcohol contributed its share of energy for muscular work is natural and extremely probable, but not ab- solutely proved. Even with the small doses in these experiments there were indications that the subjects worked to slightly better advantage with the ordinary rations than with the alcohol. The 166 EFFECTS OF ALCOHOL UPON THE HUMAN BODY. results of practical tests on a large scale elsewhere coincide with those of general observation in implying that the use of any con- siderable quantity of alcoholic beverages as part of the diet for muscular labor is generally of doubtful value and often positively injurious. In closing the consideration of the question " Is alcohol food ?" Prof. Atwater says : " If I may be permitted the expression of a personal opinion it is that people in health, and especially young people, act most wisely in abstaining from alcoholic beverages, but I cannot believe that the cause of temperance in general, or the welfare of the individual, is promoted by basing the physiologic argument against the use of alcohol on anything more or less than attested fact." If, with the results of these experiments in mind, we now turn back to the definition of food, we shall see that alcohol is a food. We have dwelt to a considerable extent upon this subject for the reason that many of the text-books used in the grammar and high- schools of the country deal with the effects of alcohol upon the human body by reason of laws which have been enacted requiring them so to do. Unfortunately, many of these books do not repre- sent the physiologic facts as we believe them to be. The ten- dency of these books, to say the least, is to teach that alcohol is not a food, but a poison. That it is a food we think has been abundantly proved ; that it is a poison is also true, but whether it is the one or the other depends upon the amount taken. There are many things which, in certain quantities, are not only not harmful, but are absolutely essential. The process of stomach digestion requires that the gastric juice should contain hydrochloric acid, and normally this is present to the amount of 0.2 per cent., and yet given in a sufficiently large quantity it would produce death. The experiments of Prof. Atwater and his colleagues mark a new era in the history of this most important subject, the effect of alcohol upon the human body ; and in all future discussions arguments should not be based upon the experiments which pre- ceded theirs, unless they were conducted with similar precaution?. III. NUTRITIVE FUNCTIONS. DIGESTION. HAVING considered the composition of the body and food, there may now be taken up the study of the nutritive functions. As has been noted already, the body is constantly producing energy and undergoing waste, both of which require the taking of food. But food is of absolutely no use to the body until it reaches the blood and by this fluid is conveyed to the tissues. So long as the food remains within the alimentary canal it is as much out- side the body, so far as nutrition is concerned, as if it had never been taken inside. To be of any service the food must enter the blood, and it does this by being absorbed. In some forms of animal life the food is of such a nature that it readily and without further change undergoes absorption that is, passes through the walls of the absorbing vessels. In other forms of animal life this is not the case : in the latter, unless certain changes take place, the food passes out of the alimentary canal as waste material, without having contributed to the nutri- tion of the body in the slightest degree. Unless, therefore, some provision was made to obviate this, such animals would die of starvation. The provision which has been made consists in the presence of certain organs whose duty is to change the form of the food-substances from that in which they will not, into that in which they will, be absorbed ; and into such forms that when they reach the tissues they can be utilized by them. It is this prepara- tion for absorption which constitutes digestion, and the organs concerned in bringing about the necessary changes in the food are the digestive organs. Manifestly, these organs will be simple or complex according to the amount of change which it is necessary to bring about in the food in order that absorption may take place. Thus, if the food on which an animal relies for its sustentation is already in a proper form, no change will be needed, and the animal will therefore have no digestive organs. If the requisite change is a slight one, the number of the digestive organs will be few and their structure 167 168 DIGESTION will be simple. But if the food is varied in its composition, and largely made up of food-stuffs that require many changes before they are fitted for absorption or before they can be utilized by the Nose. Submaxillary and sublingual glands. Trachea. Liver. Gall-bladder. Duodenum. Large intestine. Vermiform appendix Parotid gland. Pharynx. Vein. Thoracic or chyle duct. Esophagus. Small intestine. Anus. FIG. 92. General scheme of the digestive tract, with the chief glands opening into it. tissues after they are absorbed, then the digestive apparatus that is, the group of organs concerned in digestion will be complex. Such is the character of the food of man, and, consequently, such is the character of his digestive apparatus (Fig. 92). The human digestive apparatus consists of the alimentary canal and the other digestive organs, which, although outside, still com- municate with this canal by ducts through which their secretion is poured. The alimentary canal consists of the mouth, the esophagus, the stomach, and the small intestine. The digestive organs which are outside, but which discharge their secretion MOUTH DIGESTION. 169 into this canal, are the salivary glands, the liver, and the pan- creas. The digestive process is subdivided into three parts : That which takes place in the mouth mouth digestion; that which takes place in the stomach stomach or gastric digestion ; and that which takes place in the small intestine intestinal digestion. For- merly, when digestion was spoken of it was always stomach diges- tion which was referred to, because it was supposed that the entire process took place in that organ ; and when digestion was impaired the remedies which physicians employed were directed to the stomach alone. There is, unfortunately, too much of this kind of practice even now ; but the study of physiology has taught that indigestion may be due quite as much to the improper per- formance of mouth and intestinal digestion as to that which takes place in the stomach, and unless this is recognized many cases will be unsuccessfully treated. When food is taken into the mouth it has, presumably, been as fully prepared as possible by the removal of those portions which are of no nutritive value. No one eats the husks of corn, the shells of nuts, the gristle of meat, or similar substances, be- cause experience has shown that they are of little or no nutritive value, and that their digestion is practically impossible. Such extraneous matters, therefore, are removed, and the food is further prepared, provided this preparation is necessary, by the process of cooking. In the form, then, in which the food is taken in it is as fully prepared as it can be outside the body. Whatever remains to be done in order that the food may be prepared for absorption must be effected after it enters the alimentary canal. Some of the ingredients of human food are already in a con- dition to be absorbed by the blood-vessels of the alimentary canal, and therefore they need to undergo no change. Such ingredients are water, salts, and dextrose ; and were they the only constituents of the food, no digestive organs would.be needed ; but, as already said, this is not the fact. The greater part of the food must be changed before it can be absorbed. The first step in this conver- sion is that which takes place in the mouth. MOUTH DIGESTION. When food enters the mouth it consists of a mixture of vari- ous food-stuffs. In order that the changes which these food-stuffs undergo may be traced thoroughly, let it be supposed that repre- sentatives of all classes of food-stuffs are present, namely, (1) inorganic, salts and water ; (2) carbohydrates, starch and sugar ; (3) fats, or oils ; and (4) proteids. All the food of a fluid nature, no matter what classes of food- 170 MOUTH DIGESTION. stuffs it comprises, passes immediately from the mouth into the pharynx, and thence through the esophagus into the stomach. FIG. 93. Schema showing the temporary and permanent teeth in a child five years old (right side): 1, temporary teeth of the upper jaw; 2, the five temporary teeth of the lower jaw ; 3, 3', permanent median incisors; 4, 4', permanent lateral incisors; 5, 5', permanent canines; 6, 6', the four permanent bicuspids; 7, 7', first molar; 8, second molar of lower jaw in its alveolus (in the upper jaw the second molar is not yet formed) ; 9, inferior dental canal ; 10, orifice of inferior dental canal (after Testut). Such food undergoes no chemical changes whatever during this time ; thus, milk, chocolate, and beverages of various kinds are unchanged. If, however, fluids are taken into the mouth when it contains solid food, the latter will be softened by them, and the Bicuspids Canine Incis Bicuspids Canine Incisors FIG. 94. Schema of the two dental arches ; view of their external faces, showing their natural relations. two will be mixed, and will come under the influence of the agents concerned in carrying on mouth digestion. These agents are the teeth and the salivary glands. MASTICATION. 171 Mastication. The chewing of the food or mastication is performed by the teeth. The first set of teeth, which are known as temporary, decidu- ous, or milk-teeth (Fig. 93), and which exist during early child- hood are twenty in number, and the second or permanent set (Fig. 95), which begin to take the place of the first set at about the sixth year of life, remain to a greater or lesser extent until old age. The latter set is composed of thirty-two teeth four incisors, two canines, four bicus- pids, and six molars in each jaw (Fig. 95). The incisors, or cut- ting teeth, are adapted to bite the food ; the molar teeth, or grinders, are adapted to grind the food, while the canines and bicuspids in man aid the incisors and molars. In the carnivora, the canines or tushes as they are called are very long and pointed, and are admirably adapted to pierce the body of their prey, even to the vitals, thus killing and subse- quently tearing the animal pre- paratory to feeding upon it. The herbivora need no such aggres- sive weapons, and in them the molars are so constructed as to grind the food, their teeth resem- bling the grindstones of the mil- ler. The teeth of man have char- acters which resemble those of both carnivora and herbivora, and from this fact it may be inferred that it was designed that man should have a mixed diet. Movements of Mastication. The movements concerned in mastication are those of the lower jaw upon the upper, produced by the action of the following muscles : Masseter, temporal, internal and external pterygoids, digastric, mi/lohi/oid, and genio- hyoid. The lower jaw is brought against the upper by the con- traction of the masseters, temporals, and internal pterygoid mus- cles. The action of the external pterygoids, when both are acting, is to draw the lower jaw forward, causing it to project beyond the upper. If but one external pterygoid acts, that side of the jaw is drawn forward and the chin deviates to the oppo- site side. FIG. 95. The palate and superior dental arch (right side) : 1, median incisors ; 2, lateral incisors ; 3, canine ; 4, first bicuspid; 5. second bicuspid; 6, first molar; 7, second molar; 8, wisdom-tooth ; 9, mucous membrane of the hard palate continuous behind with that of the soft palate ; 10, the anteroposterior raphe of palate ; 11, pits on each side of the raphe per- forated with the orifices of glands; 12, anterior rugosities of the mucous membrane (after Testut). 172 MOUTH DIGESTION. The digastric, rnylohyoid, and geniohyoid muscles depress the lower jaw, and this is an essential part of mastication, for the jaws must be separated as well as brought together to make the act complete. The movements of the jaw are a combination in which these muscles act, sometimes grouped in one way and sometimes in another. The buccinator muscles in the cheeks and the muscles of the tongue assist very materially by keeping the food between the teeth, where it may be comminuted and triturated. The function of the teeth in man is to subdivide and com- minute thoroughly the food ; and this function is an essential part of the process of digestion. As will be seen later, during diges- tion certain fluids are poured into the alimentary canal to contrib- ute their part toward the process. These fluids cannot act properly on large, compact masses of food. While their action is not that of solution, still, in order to fulfil perfectly their office, they must come in direct contact with every portion of the food. This contact is the more essential because the given time in which to act is not unlimited, and if the process is not completed within the allotted time, digestion will be performed incompletely. When a chemist desires to dissolve a substance quickly and com- pletely, he first pulverizes it in a mortar. Likewise, in digestion one of the most important steps is this process of comminution or mastication. If mastication is insufficiently performed, the succeeding steps in the process of digestion are seriously interfered with, and indigestion or dyspepsia results. f Insufficient mastication is one of the commonest causes of in- digestion, and many dyspeptics are drugged with remedies pre- scribed to overcome some fancied trouble in the stomach, wjien they should be sent to a dentist. Defective mastication may be due to various causes. The teeth may be so decayed as to expose sensitive surfaces, and when food which is at all hard is taken into the mouth the discomfort, or sometimes the pain, caused their possessor in chewing it makes the performance of the act incom- plete, and the food is swallowed half-masticated ; or the eater may be in too great a hurry and not give enough time to this important act. Whatever the cause, the result is the same; therefore too much attention cannot be given to this process, which is so simple as often to be overlooked. Insalivation. Coincident with mastication is the act of in- salivation or the incorporation of saliva with the food. Saliva is the mixed secretion of the salivary glands, which comprise the two parotids, the two submaxillaries, and the two sublinyuals, together with the buccal glands of the mucous membrane of the mouth (Fig. 96). Physiologic Anatomy of the Salivary Glands. The parotid gland is the largest of all the salivary glands, and is named from INSALIVATION. 173 its proximity to the ear, lying below and in front of it. Inflam- mation of this gland is parotitis or mumps. Its secretion passes out by Stenson's duct, which is about 6 cm. long and the size of a crowquill, and is discharged into the mouth on the inner surface of the cheek, opposite the second molar tooth of the upper jaw. FIG. 96. View of the salivary glands (right side) (the inferior maxilla has been removed from the symphysis to the ascending ramus) : A, parotid gland, with A' its anterior prolongation ; B, submaxillary gland ; C, sublingual gland ; 7), gland of Niihn or of Blandin ; E, gland of Weber, a, duct of Steno ; 6, duct of Wharton with b' its orifice on the floor of the mouth ; c, excretory ducts of the sub- lingual gland. 1, sternocleidomastoid ; 2, posterior belly of the digastric; 3, 3', mylohyoid, right and left ; 4, hyoglossus ; 5, genioglossus ; 6, pharyngoglossus ; 7, geniohyoid muscle; 8, masseter ; 9, buccinator; 10, middle constrictor of the pharynx; 11, primitive carotid; 12, internal jugular vein; 13, external carotid artery ;' 14, lingual artery ; 15, facial artery ; 16, facial vein ; 17, superficial tem- poral artery ; 18, transverse facial artery ; 19, facial nerve ; 20, auriculotemporal nerve ; 21, lingual nerve, displaced slightly upward on account of the position of the tongue. The nerves which supply this gland are branches of the carotid plexus of the sympathetic, the facial, the auriculotemporal, and the great auricular nerve. The submaxillary gland is situated beneath the lower jaw. Its secretion is discharged by Wharton' *s duct, which is about 5 cm. 174 MOUTH DIGESTION. long and opens at the side of the frenum of the tongue. Its nerves come from the submaxillary ganglion, and consist of fila- ments of the chorda tympani of the facial and lingual branch of the inferior maxillary, of the mylohyoid branch of the inferior dental, and of the sympathetic. The sublingual gland lies under the mucous membrane, at the side of the frenum of the tongue. Its secretion is discharged through from eight to twenty ducts, ducts of Rivinus, which open on the prominence of the mucous membrane made by the gland beneath. Sometimes two or more of these ducts join, and form the duct of Bartholin, which opens into Wharton's duct. The nerves of this gland are branches of the lingual. Besides these three sets of glands there are numerous mucous glands on the dorsum and the edges of the tongue, in the tonsil, and the soft palate, whose secretion is a constituent of the saliva. The salivary glands belong to the class ordinarily described as compound racemose glands. Inasmuch, however, as the secreting portions are not sacs, which are characteristic of racemose glands, but tubes, this variety of gland is perhaps better denominated compound tubular. It consists of lobes, which in turn are made up of lobules, each of which is composed of tubular alveoli or acini connected with a duct. The ducts from different lobules join together to form larger ducts, and finally all combine to form the main duct of the gland. Mucous (Fig. 97) and Albuminous Glands. Two types of glands are recognized by histologists accord- ing to the product and the appearance of the cells within the alveoli of the salivary glands : mucous and albuminous or serous. The mucous gland secretes a tenacious fluid containing mucin, and the cells are relatively large and clear, and have been described as resembling ground glass ; their granules are ordinarily indistinct. The sublingual and the mucous glands of the mouth are repre- sentatives of this type. These glands also contain demilunes of Heidenhain or crescentic cells, which are placed between the mucous cells and the base- ment-membrane (Fig. 97). Heidenhain, whose name they bear, FIG. 97. Mucous gland : submaxillary of dog resting stage. INSALIVAT10N. 175 considers them to be undeveloped mucous cells, destined to replace the secreting cells when they shall have ceased to perform their function and have disappeared ; while other opinions are that they are a distinct type of albuminous cell, or are due to a post-mortem change. Some observers claim to have demonstrated that the lumen of the albuminous glands is continued as fine capillary spaces between the cells of these glands, and that from these pass off smaller branches which penetrate the cells themselves, and that in the mucous glands these same capillaries exist only in con- nection with the demilunes. If this is confirmed, it would seem to be more than probable that the demilunes have distinct secre- tory functions. The albuminous gland secretes a watery or serous fluid, which FIG. 98. Parotid of the rabbit, in tbe resting condition (after Heidenhain). contains, besides water, inorganic salts, some albumin, and may also contain enzymes. The cells of this variety are small and compactly fill the alveoli, leaving but little lumen (Fig. 98). They contain albuminous granules which are very distinct. The parotid gland represents the serous or albuminous type. The human submaxillary gland is a mixed type containing both mucous and albuminous alveoli, the latter, however, in greater number. It is a fact that in mucous glands some cells are found which are regarded as characteristic of the albuminous type, and vice 176 MOUTH DIGESTION. versa; so that it has been suggested that it would be better to apply the terms mucous and albuminous to the cells, rather than to the glands. Secretory Nerves of the Salivary Glands. The relation existing D FIG. 99. Parotid gland of the rabbit in a fresh state, showing portions of the secreting tubules: A, in a resting condition; B, after secretion caused by pilo- carpin ; C, after stronger secretion pilocarpin and stimulation of sympathetic ; D, after long-continued stimulation of sympathetic (after Langley). between nerves and the secretion of saliva has been more carefully investigated in dogs and rabbits than in man, and it is to the result of these investigations that we shall especially refer. Con nee- . tive tissue. Gland-cell -, of acinus. -- Intralobu- lar duct. FIG. 100. Section from parotid gland of man (Bohm and Davidoff). The nervous supply of the parotid gland is derived from : (1) The glossopharyngeal nerve, through its tympanic branch of the nerve of Jacobson, the small superficial petrosal nerve, the otic INSALIVATION. 177 ganglion, and finally the auriculotemporal branch of the inferior maxillary division of the fifth nerve or trigeminus. This is shown in Fig. 101. (2) The cervical sympathetic, which is dis- tributed principally to the walls of the blood-vessels, although some of its fibers, in some animals at least, are secretory. The nervous supply of the submaxillary and sublingual glands, like that of the parotid, is also double, the chorda tympani, a branch of the seventh or facial, and branches of the sympathetic plexus around the facial artery, being the nerves supplying these glands. There is excellent authority for the statement that the chorda tympani is in reality a branch of the glos- sopharyngeal which joins the facial in the tympanum. The chorda tympani joins the lingual nerve for a part of its course, and . then leaves it to pass through the so-called submaxillary ganglion to the glands. It has been suggested that this would be more properly called the sublingual ganglion, inasmuch as only those fibers which are distributed to the sublingual gland are in communication with the nerve-cells of this ganglion, while those which pass to the submaxillary gland connect with a collection of nerve-cells in that gland, Langley's ganglion. The course of the chorda tympani is shown in Fig. 102. Effect of Stimulation of the Chorda Tympani and Sympathetic Nerves. If the chorda tympani of a dog is stimulated bv passing through it weak induction shocks, the submaxillary gland secretes more saliva. The small arteries of the gland are dilated and a larger amount of blood passes through the gland, giving it a dis- tinctly reddish appearance. Stimulation of the sympathetic fibers produces a diminution in the secretion, and the reddish color dis- appears, leaving the gland pale, a change evidently due to a con- striction of the blood-vessels. It might at first seem that the increase in the amount of blood caused by the stimulation of the chorda tympani would explain the increased secretion of saliva by filtration of the fluid of the blood through the vessel-walls, but experiments have shown that there are in this nerve true secretory fibers i. e., fibers which carry impulses to the secretory structure of the gland, and that the cells are directly stimulated to increased action. We may briefly refer to three of these experiments : 1. If the blood-supply of the gland is cut off, and the chorda tvm- pani stimulated, the secretion of saliva will still be increased. 2. If atropin is injected into the animal and the chorda tympani then stimulated, the blood-vessels will be dilated, but there will be no secretion. 3. If hydrochlorate of quinin is injected into the gland, the blood-vessels dilate, but no secretion follows. It will be seen from these experiments that two effects are produced by stimulation of the chorda tympani : 1. A dilatation of the blood-vessels ; and 2. A direct stimulation of the cells. From this it is evident that there are two sets of fibers in this nerve, 12 178 MOUTH DIGESTION. each having a distinct function ; one vasodilator and the other secretory. There are also two sets of fibers in the sympathetic nerves which supply these glands : One vasoconstrictor i. e., when FIG. 101. Schematic representation of the course of the cerebral fibers to the parotid gland. stimulated the blood-vessels are constricted ; and the other secre- tory. It is, however, mainly through the chorda tympani that the impulses pass which cause secretion. FIG. 102. Schematic representation of the course of the chorda tympani nerve to the submaxillary gland. The glossopharyngeal fibers, which have already been traced to the parotid gland, convey the impulses which cause secretion in this gland. The sympathetic nerves are vasoconstrictor in func- tion. 1NSALIVATION. 179 FIG. 103. A number of alveoli from the submaxillary gland of dog, stained in chrome-silver, showing some of the fine intercellular tubules (Huber). From the mass of evidence which has been accumulated, to only a small part of which have we made reference, it is indis- putably proved that there are true secretory fibers distributed to the salivary glands ; and the same is true of other glands as well, such as the lachrymal, perspiratory, and gastric glands ; but the method by which these fibers terminate is not so certain, though it appears probable that it is by forming plexuses between and around the secreting cells. Further than this, it is more than probable that there are two kinds of se- cretory fibers : One which transmits impulses that cause the secretion of the organic constituents of the saliva, and called trophic; the impulses conveyed by the other, the secretory fibers proper, pro- ducing the secretion of the water and the inorganic salts of the saliva. Paralytic Secretion. If the chorda tympani is cut, there is no immediate effect, but after a day or two the gland begins to secrete a very watery saliva which continues for several weeks, and then it atrophies. This secretion is called paralytic. Although the sec- tion is made on but one side, both glands are similarly af- fected, and the secretion on the opposite side to the section is called antiparalytic or antilytic. There are two explanations given to account for this phenomenon. One is that the continuous secretion is due to an increased irritability of the secretion-center in the medulla oblongata and of the nerve-cells in the gland, by which the venous condition of the blood is alone sufficient to cause them to send out continuous impulses to the secreting cells. The , other theory is based upon the fact that katabolic changes are going on in the cells of the gland which are inhibited by impulses coming through the chorda tympani ; if, therefore, this nerve is cut, such impulses no longer restrain the katabolic changes, and they go on without interference, with the result of atrophy of the gland and the formation of the paralytic secretion. Secretion of Saliva. The secretion of saliva is normally a reflex act. It is ordinarily brought about by the stimulation of the mucous membrane of the mouth by sapid substances that is, those which excite the sense of taste, although chemical and even mechanical stimuli will produce the same result. The chewing of a piece of rubber will cause a profuse flow of saliva. The 180 MOUTH DIGESTION. glossopharyngeal and lingual nerves serve as the afferent nerves in this act, carrying the impulses to a center in the medulla, from which efferent impulses pass out through the secretory nerves to the glands. This center may be stimulated by afferent impulses reaching it through other nerves ; thus salivary secretion may be increased, or " the mouth made to water," by the smell or even the thought of food. This center may also be inhibited from sending out secretory impulses, as through fright or other nervous disturbance, thus diminishing the secretion of saliva and causing the dry mouth and throat which so commonly accompany such conditions. Changes in the Salivary Cells. Certain changes take place in the salivary cells as a result of their activity. When a rabbit is fasting, the cells of the parotid gland are granular throughout, their outlines being faintly marked by light lines. If it is fed, or pilocarpin injected, or the sympathetic stimulated, the granules disappear from the outer portion of the cells, so that there is an external clear border surrounding the granular in- terior. If the stimulation continues, the granules diminish and are collected near the lumen of the alveoli and at the margin of the cells, the clear border becomes enlarged, and the cells become smaller. The explanation of this is that the granules contain a substance which is or which becomes the ptyalin of the saliva. If it should be demonstrated hereafter that there is a zymogen which precedes the ptyalin, it would receive the name of ptyalinogen, but this has not as yet been proved to occur. These granules in the cells are called zymogen granules. While these granules are being used up to form the ptyalin new material is being deposited by the blood at the base of the cells, which in turn will later form the zymogen or ptyalin. Similar changes take place in the mucous glands, in the cells of which are granules (125 to 250 to a cell) composed of mucin- ogen, which becomes mucin, and is in this form discharged into the lumen of the alveoli. The demilunes, before referred to, are situated outside these cells which produce the mucinogen. Properties and Composition of the Saliva. The secretion of the human parotid gland is a clear fluid, though sometimes turbid, and contains some epithelial cells. It is alkaline in reaction, but less so than the saliva of the submaxillary gland. Its specific gravity is very variable, as is shoAvn by the following figures : Mitscherlich gives it as 1.006 to 1.008 ; Oehl, 1.010 to 1.012 with scanty, and 1.0035 to 1.0039 with plentiful secretion ; Hoppe- Seyler, 1.0061 to 1.0088 ; the solids being from 5 to 16 parts per 1000. It contains ptyalin and potassium sulphocyanate, but no mucin. The secretion of the human submaxillary gland is clear and watery, always alkaline, and has a specific gravity between 1.0026 INSALIVATION. 181 and 1.0033. The solids are from 3.6 to 4.6 parts per 1000. It contains ptyalin, but authorities differ as to its containing potas- sium sulphocyanate. The existence of such ducts as those of Stenson and Wharton makes it easy to obtain the pure secretions of the parotid and submaxillary glands by the introduction into them of caimulse ; but this is not true of the sublingaal gland, hence the secretion from this gland in man has never been obtained in sufficient quantity to make a thorough analysis of it, but it is known to be more alkaline than that of the submaxillary, to contain mucin, a dias- tatic enzyme, and potassium sulphocyanate. The secretion of the mucous glands of the human mouth has never been obtained pure, or in quantity sufficient to analyze. It is a tenacious and viscid secretion and alkaline in reaction. Mixed saliva i. e., the saliva as found in the mouth the product of all the salivary glands, is a clear fluid, viscid in con- sistency, with a specific gravity between 1.002 and 1.008, alkaline in reaction, and containing from 5 to 10 parts per 1000 of total solids. It is secreted to the amount of between 300 and 1500 grams daily. Moore states that when it is acid this reaction is commonly due to fermentation of particles of food in the mouth. Many authorities state that it contains sodium carbonate, but Chittenden and Richards make the following statement : " Human mixed saliva contains normally no sodium carbonate whatever ; the alkalinity indicated by litmus, lacmoid, etc., is due to hy- drogen alkali phosphates, with possibly some alkali bicarbonate. Mixed saliva invariably acts acid to phenolphthalein. " The alkalinity of mixed saliva, as indicated by lacmoid, is greater before breakfast than after the morning meal ; a conclusion which stands in direct opposition to the statement frequently made that ' the alkalinity (of mixed saliva) is least when fasting, as in the morning before breakfast, and reaches its maximum with the height of secretion during or immediately after eating. 7 r ' When saliva is examined under the microscope there are seen epithelial scales from the mucous membrane of the mouth, and leukocytes, probably from the tonsils and elsewhere, described usually as salivary corpuscles. Bacteria and portions of food are commonly found in saliva, but they are not constituent parts, but rather impurities. Examined chemically the saliva is found to contain the enzyme ptyalin, mucin, and traces of proteid, probably of the nature of a flobulin, but too little in amount to be quantitatively determined. t contains also, though not invariably, potassium sulphocyanate, which is regarded as a product of proteid metabolism ; but with our present knowledge the physiologic value of this constituent is still undetermined. The inorganic constituents of saliva are sodium chlorid, cal- 182 MOUTH DIGESTION. ciura phosphate and carbonate, magnesium phosphate, and potas- sium chlorid. Although it is commonly stated that it contains also sodium carbonate, yet, as we have seen, this is denied by Chittenden and Richards, whose investigations are the most recent on this subject. Calcium carbonate and phosphate occasionally form salivary calculi in the glands or their ducts, and may require removal by the surgeon. These salts also contribute to the forma- tion of the tartar on the teeth. The following table gives four analyses of human mixed saliva, by as many chemists. It should be remembered, however, that even in the same individual the composition of this secretion varies during the day, and that, too, independently of the taking of food. Observation has shown that between 7 and 11 A.M., provided no food is taken, its composition is very constant. Mixed Human Saliva. I. II. III. IV. Water 992 9 995 10 994 10 994 20 Total solids 7 1 4 84 5 90 5 80 Suspended solids (epithelium, mucus, etc ) . . . . 1.4 1.62 2.13 2.20 Soluble organic mutter (ptyaliu and albumin) Potassium sulphocvanate 3.8 1.34 0.00 1.42 0.10 1.40 0.04 Inorganic salts 1 9 1 82 2 19 2 20 Office of Saliva. This is twofold : (1) chemical and (2) mechan- ical. The chemical action of saliva is due to the enzyme ptyalin, which is undoubtedly the most important constituent of the mixed saliva. This ingredient exists in the human parotid gland at birth, but does not appear in the submaxillary gland until the age of two months. It is an amylolytic or diastatic enzyme /. ,1 . e , . . , small intestine, laid open to show the Ulterior OI tile intestine at right V alvula> conniventes (Brinton). angles to its long axis. They do not completely encircle it like a ring, but vary in length, some extending about two-thirds and others only one-third the distance around. The widest of them is not more than 1.5 cm. in width, projecting into the caliber of the intestine to this extent. Each is a double fold of mucous membrane with connective tissue be- tween, which so binds the folds together that even in the condi- tion of distention the valvulse conniventes are not obliterated, as FIG 117.-MUCOUS membrane of the jejunum, highly magnified (schematic): 11 intestinal yilh ; 2, 2, closed or solitary follicles; 3, 3, orifices of the follicles of Lieberkuhn (Testut). is the case with the rugae of the stomach. By means of these foldings the extent of the mucous membrane is greatly increased over what it would be did it simply line the intestine. Vilii. Projecting from the mucous membrane including the STRUCTURE OF THE SMALL INTESTINE. 223 valvulse conniventes are the mill (Fig. 117), which are so numerous as to give to it a velvety appearance. Between them open the glands of Lieberkiihn. The villi are prominences, some triangular, some conical, and some filiform in shape, and in length are about 0.5 to 0.7 mm., and in width at their base about one-fourth their length (Fig. 118). They are most numerous in the duodenum and the jejunum, although present throughout the whole extent of the Epithelium of villus. Epithelium of villus. Goblet-cell. Gland (crypt) of Lieber- kiihn. Mucosa. Muscularis mucosae. FIG. 118. Section through mucous membrane of human small intestine ; X88: at a is a collapsed chyle-vessel in the axis of the villus (Bohm and Davidoff ). small intestine. It has been estimated that there are no less than 4,000,000 of these villi in an intestine. Each villus is composed of retiform tissue, and is covered with a single layer of columnar epithelium resting upon a basement- membrane consisting of a layer of endothelial cells. Between the cells of columnar epithelium, at their bases and in the retiform tissue, are numerous lymph-corpuscles. Between adjoining epithe- lial cells and also between the endothelial cells is interstitial 224 INTESTINAL DIGESTION. cement-substance, and the reticulum of the matrix of the villus is continuous from the interior of the villus through this interstitial substance to its exterior. Next the basement-membrane is a plexus of capillary blood-vessels. Still more interior is muscular tissue, a part of the muscularis mucosae, while the central structure of all is a lacteal. The capillary plexus, muscular tissue, and lacteal are sur- rounded by reticular tissue constituting the matrix of the villus, and in the interstices of this are lymph-corpuscles and the cells of FiG. 119. Longitudinal section through summit of villus from human small intestine ; X 900 (Flemming's solution) : at a is the tissue of the villus axis ; &, epithelial cells; c, goblet-cell; d, cuticular zone (Bohm and Davidoff). the villus ; large, flat cells with oval nuclei. If the components of a villus are named in the reverse order to that just given, we shall have, starting from the center, (1) lacteal, (2) muscular tissue, (3) capillary plexus, (4) basement-membrane, (5) columnar epi- thelium. The lacteals are single in some of the villi and in others double. Their walls consist of a single layer of endothelium, and the cement-substance between the cells is continuous with the reticular tissue composing the matrix. It will be seen, therefore, that from the lacteal to the surface of the villus there is continuous reticular tissue. This is regarded by Dr. Watney as the path STRUCTURE OF THE SMALL INTESTINE. 225 which the particles of fat take when they are undergoing the process of absorption (p. 261) i. e., from the lumen of the in- testine (1) through the interstitial or cement-substance of the columnar epithelium ; (2) through the same substance in the basement-membrane; (3) through the reticulum of the matrix; (4) through the interstitial substance of the lacteals into the inte- rior of this structure. The lacteals are the lymphatic vessels of the small intestine, ~|Er Central chyle-vessel of villus. hyle-vesseL -Mucosa. Muscularis mucosse. S Submucosa. Plexus of " lymph-ves- sels. Circular mus- ~ cular layer. ^^ Plexus of Sc? Ivmph-ves- - . . orr-fT^T ~ ~~ f*r~*' . , >= 'TVT^T^ -*L".~T' l - ^-"~v ctlc &%ffi#2^^ ' '"*' "- 1 s ' -= - layer with Vein. serous coat. FIG. 120. Schematic transverse section of the human small intestine (after F. P. Mall). which, on leaving the villi, form a plexus in the mucous and sub- mucous tissue, and discharge into larger lymphatic vessels, and theii contents finally pass into the thoracic duct. Brunner's Glands (Fig. 121). In the submucous coat of the upper part of the duodenum, and to a less extent in that of the lower part, and in the beginning of the jejunum, are certain glands known as the glands of Brunner, or the duodenal glands. These are tubulo-racemose glands, similar to the lobules of a salivary gland. They discharge through ducts which open upon the sur- 15 226 INTESTINAL DIGESTION. face of the mucous membrane of the intestine. Their secretion is mucus having a slightly alkaline reaction, but it has never been successfully obtained so pure as to admit of its being analyzed. These glands are so few in number, comparatively, that their prod- uct cannot be very abundant nor very important in its action upon the food, although an enzyme has been described as one of its constituents which has the power of converting maltose into glucose. The secretion of the glands, together with that of the follicles of Lieberklihn, constitutes the intestinal juice. These glands are inflamed and ulcerate whenever the body is burned to any great extent. Follicles of Lieberkuhn. The folli- cles or crypts of Lieberkuhn, which are found throughout the entire length of the small intestine, are simple tubu- lar glands in the mucous membrane, and not beneath it, as is the case with the glands of Brunner. They are lined with a layer of columnar epithe- lium similar to that which covers the surface of the mucous membrane and the villi (Fig. 122). Solitary and Anminated Glands. The solitary glands are found in the mucous membrane of the whole small intestine, in greater number, however, in the lower part of the ileum. They have a diameter of from 3 to 6 mm., and present a round and somewhat prominent appearance. They are composed of lymphoid tissue, and contain many lymph-corpuscles. They have no duct, and their product probably oozes through the walls of the glands and contributes something to the in- testinal juice. When these glands are aggregated they form patches, and are called agminated glands or Peyer's patches (Fig. 123). These are about twenty-five in number, though in youth as many as forty-five have been seen, while in old age they are absent. They occur principally in the ileum, though they are also found in the lower part of the jejunum, where they are much smaller and circular, and sometimes in the lower part of the duodenum. These patches vary in length from 1.5 cm. to 10 cm., and in width from 4 cm. to 5 cm. Like the solitary glands, they are with- FIQ. 121. Vertical section of duodenum, showing villi (a) ; crypts of Lieberkuhn (b), and Brunner's glands (c) in the sub- mucosa (s), with ducts (d) ; mus- cularis mucosse (m), and circular muscular coat (/) (Schofield). STRUCTURE OF THE LARGE INTESTINE. 227 out ducts, and their secretion finds an exit in the same manner. In typhoid fever they become inflamed and often undergo ulcera- tion. Structure of the I/arge Intestine. The coats of this portion of the alimentary canal are the same in number and kind as those of the small intestine, although the arrangement of the longitudinal fibers of the muscular coat is in some portions in the Intestinal epithe- lium. Lumen of gland. Goblet-cell. Mucosa. Mucosa. Muscularis mucosae. FIG. 122. From colon of man, showing glands of Lieberkiilm ; X 200 (Bohm and Davidoff). form of bands, a quite different arrangement from that in the small intestine. At the anus the circular fibers constitute the internal sphincter. The mucous membrane contains both solitary glands (Fig. 117) and glands which resemble the follicles of Lieberkiilm, and indeed are called by that name by some writers (Fig. 122); still the secretion differs very materially, not containing any enzymes 228 INTESTINAL DIGESTION. possessing digestive powers. The epithelium contains mucus- secreting or goblet-cells, and their product is principally mucus. Succus Entericus or Intestinal Juice. This is the secre- tion of all the glands of the small intestine ; but the follicles of Lieberkiihn, being vastly more numerous than the others, con- tribute by far the greater part of the fluid. It is obtained from animals by making a " Thiry-Vella fistula." This consists in cutting out a piece of intestine, from 10 to 30 cm. long, without interfering with its nerves or blood-supply, and sewing the open ends to two openings in the abdominal wall. The severed ends of the intestine, from which the piece has been isolated, are also sewn together. The fluid ob- tained from the portion thus iso- lated is pure intestinal juice, with- out admixture with food or other substances. This operation has been performed on the dog, and the juice obtained is described as being limpid, yellowish, having a specific gravity of 1010, and a strongly alkaline reaction, due to the presence of sodium carbonate. The fluid has also been ob- tained from a human being, from a piece of intestine 9 cm. long, situated about 20 cm. above the ileocecal valve. The daily prod- uct averaged 27 c.c. The spe- cific gravity averaged about 1007. The fluid was opalescent and often of a brownish color. It was always alkaline, and when treated with acids carbonic acid gas was evolved. It gave all the proteid reactions, but did not reduce Fehling's solution or change the color of a solution of iodine. Action of Intestinal Juice. Although the chemical composition of this fluid is not well understood, it is, nevertheless, known to possess several enzymes : amylolytic, sugar-splitting, and activating (p. 119). The amylolytic enzyme changes starch to maltose, and possibly some dextrose. It has been claimed that the maltose is converted into glucose by the product of Peyer's patches. Another enzyme, invertin or invertase, changes saccharose into dextrose and levulose. The changes undergone in this process have been already described (p. 93). The succus entericus contains no pro- teolytic enzyme, nor is fat split up by it. Its alkalinity aids in the em unification of fats. The activating enzyme is enterokinase, which changes trypsinogen into trypsin. FIG. 123. Mucous membrane of the jejunum (Testut) : 1, Peyer's patch; 2. its border ; 3, solitary follicles ; 4, 4, valvulse conniventes. STRUCTURE OF THE PANCREAS. 229 From the above considerations the intestinal juice must be regarded as possessing some digestive action upon the food-stuffs, its most marked property being its power of inversion. Ti : It is Epithelium of intes- tine. Gland. ^ Submu- cosa. FIG. 124. A solitary lymph-nodule from the human colon : at a is seen the pro- nounced concentric arrangement of the lymph-cells (Bohm and Davidoff). not an abundant secretion, and one of its important offices is, doubtless, to lubricate the mucous membrane of the small in- testine. THE PANCREAS, Structure of the Pancreas. This organ is a gland of the tubulo-racemose type, and, from its resemblance to the salivary glands, is described as the abdominal salivary gland ; the pancre- atic alveoli are, however, longer and more tubular. Its location is in the abdominal cavity, behind the stomach and between the duodenum and the spleen. Its length is from 15 to 23 cm., its width about 4.5 cm., and its thickness 2.8 cm. The alveoli are lined with columnar or polyhedral cells, which, in the fresh con- dition, contain small granules in the protoplasm of their inner two-thirds, while that of the outer third is clear. This clear portion becomes larger, encroaching upon the granular part, when the gland is active. The changes which these cells undergo may be more distinctly shown by means of carmine, which acts as a staining agent. Thus Fig. 125 represents the appearance of the cells of a -pancreas which was removed from a dog that had fasted for twenty-four hours. 230 THE PANCREAS. The gland was hardened in alcohol and a section of it was stained with carmine. The clear portion at the base of the cells takes the stain better than the more granular, internal portion. Fig. FIG. 125. Pancreas of dog during hunger; preserved in alcohol and stained in carmine (after Heidenhain). 126 represents a section from a dog that had been fed from six to ten hours before the gland was removed ; the encroachment of the clear upon the granular portion is shown by the greater width of FlQ. 126. Pancreas of dog during first stage of digestion ; alcohol, carmine (after Heidenhain). the stained zone. In other words, the granules are being used up to form these products, the enzymes. Fig. 128 represents the cells when they have returned to a condition of rest. STRUCTURE OF THE PANCREAS. 231 FIG. 127. Pancreas of dog during second stage of digestion; alcohol, carmine (after Heidenhain). In the connective tissue are groups or islets of epithelium-like cells (Figs. 129, 130), which are supposed to produce the internal secretion of the pancreas (p. 239). Outer zone of ^ a secretory cell. Connective tissue. Larger gland- duct. Centro-acinal cell. ntro-acinal cell. Intermediate tubule. Inner granu- lar zone of secretory cells. FIG. 128. From section through human pancreas; X 450 (sublimate) (Bohm and Davidoff). 232 THE PANCREAS. Pancreatic Juice. The most important changes which the food undergoes in the process of intestinal digestion are those which are due to the action of the pancreatic juice. This is the Alveolus. Intermedi- ary duct. Centro-acinal - cell. Intermediary - duct. Intralobular - duct. FIG. 129. From section through human pancreas : X about 200 (sublimate) (Bohm and Davidoff). product of the pancreas, and reaches the intestine by means of the pancreatic duct which, together with the common bile-duct, opens into the duodenum about 8 to 10 cm. below the pylorus. Connective tissue. Centro-acinal cell. Secretory cell. Intermediate duct. FlG. 130. Scheme showing relation of three adjoining alveoli to excretory duct, illustrating origin of centro-acinal cells (Bohm and Davidoff). Quantity of Pancreatic Juice. The amount of this fluid secreted daily in the human being is not known, but it has been found that in the dog it is 2.5 grams per kilo of body-weight. This would give in a man weighing 70 kilos, 175 grams daily. PANCREATIC JUICE. 233 Composition of Pancreatic Juice. The pancreatic juice has been obtained repeatedly from the dog and the rabbit by the operation of establishing a permanent pancreatic fistula. For this purpose that portion of the duodenum of a rabbit into which the main duct discharges, which in this animal is about 35 cm. below the FIG. 131. Stomach in place after removal of liver and mass of intestines: A, diaphragm; B, B', thoraco-abdominal wall; C, right kidney with c, its ureter; D, right suprarenal capsule ; E, left kidney with e, its ureter ; F. , spleen ; G, apon- euroses of transversales : H, H', quadrati lumborum ; /, /', psoas muscles; K, esoph- agus ; /,, stomach ; M, duodenum. 1, cardia ; 2, greater curvature ; 3, lesser curvature ; 4, great tuberosity or fundus; 5, small tuberosity or antrum of pylorus ; 6, pylorus; 7, right vagus ; left vagus ; 9, thoracic aorta ; 9', abdominal aorta ; 10, inferior dia- phragmatic arteries; 11, celiac axis; 12, hepatic artery; 13, right gastro-epiploic ; 14, coronary artery ; 15, splenic artery ; 16, 16', superior mesenteric artery and vein ; 17, inferior mesenteric artery; 18, spermatic artery; 19, gall-bladder; 20, cystic duct; 21, hepatic duct; 22, inferior vena cava ; 23, portal vein; 24, great sympa- thetic (Testut). opening of the bile-duct, is opened and a glass cannula is intro- duced into the duct and the secretion collected as it escapes. The amount thus obtained from rabbits is very small ; it is clear, color- less, alkaline, and does not clot. That obtained from fistulse in dogs is thicker, and coagulates on standing, although it is less thick after the h'stulse have existed for some time. The specific gravity, 234 THE PANCREAS. FIG. 132. Excretory ducts of the pancreas: A, pancreas, with a, its head; B, duodenum; C, jejunum; D, gall-bladder. 1, main pancreatic duct of Wirsung; 2, accessory duct with 2', its opening upon the postero-internal wall of the duo- denum; 3, ampulla of Vater; 4, common bile-duct; 5, cystic duct; 6, hepatic duct; 7, aorta ; 8, superior mesenteric vessels ; 9, celiac axis with its three branches(Testut). too, falls from 1030 to 1010. The following table gives its com- position : Pancreatic Juice of Dog (C. Schmidt). CONSTITUENTS. Immediately after establishing fistula. From permanent fistula. Water 900.76 980.45 Solids 99.24 19.55 Organic substances 90 44 12 71 Ash ... ... 8.80 6 84 Sodium carbonate ... ... 0.58 3 31 Sodium chlorid Calcium, magnesium, and sodium phos- phates 7.35 53 2.50 08 Less is known as to the chemical composition of human pancre- atic juice. Herter obtained the fluid from an enlarged duct caused by carcinoma of the duodenum. In 1000 parts of this there were 24.1 parts of total solids, 17.8 parts of organic matter, and 6.2 parts of ash. Zadawsky obtained the juice from a young woman PANCREATIC JUICE. 235 from whom a tumor of the pancreas had been removed. The analysis of this was as follows : Water 864.05 Proteids 92.05 Other organic substances 40.46 Salts 3.44 Enzymes of Pancreatic Juice. It is a remarkable fact that the pancreatic juice of all vertebrates, so far as examined, contains four enzymes : (1) amylolytic, (2) proteolytic, (3) fat-splitting, and (4) milk-curdling. Amylopsin. This is the amylolytic enzyme of the pancreatic juice, and is regarded as identical with ptyalih of the saliva, although pancreatic juice has much greater amylolytic power than saliva, and acts upon uncooked starch ; but whether this is due to a difference in the enzymes or because in pancreatic juice the enzyme is more concentrated, has not been determined. Some authorities include them both under the name of ptyalin. Amylopsin appears in the pancreatic juice for the first time about one month after birth, while ptyalin is present in the human parotid gland at birth, but in the submaxillary gland not until about two months subsequently. The optimum temperature for amylopsin is from 30 C. to 45 C., while between 60 C. and 70 C. it is destroyed. Its activity is greatest when the reaction is neutral or when a minute trace of acid is present, such as, for instance, 0.01 per .cent, of hydrochloric acid. Its action on starch is to change it to maltose and dextrose, or, under some circumstances, to maltose alone. Authorities who regard the action of saliva upon starch as being of comparatively little importance look to amylopsin and to the amylolytic enzyme of the intestinal juice as the principal agents in starch conversion. This we regard as a mistake, and are in- clined to place a much higher value upon salivary digestion than do these, but at the same time would give pre-eminence to the pancreatic juice as a starch converter. Trypsin. This is the proteolytic enzyme of the pancreatic juice, and its power in this regard is greater than that of pepsin. It has been found in the pancreatic juice during the last third of fetal life. Its activity is greatest when sodium carbonate is present to the amount of about 1 per cent., although it acts when the reac- tion is neutral or very slightly acid. When hydrochloric acid is present to any considerable extent the enzyme is destroyed, and this is hastened when pepsin is also present. Trypsin has never been isolated, so that its chemical com- position has not as yet been determined. In the action of the cells of the pancreas, the zymogen trypsinogen is first formed, and this later becomes trypsin. In studying its action, a pancreas 236 THE PANCREAS. may be cut up finely and the enzyme extracted with glycerin, to which extract a solution of sodium carbonate of from 0.2 to 0.5 per cent, is added. Inasmuch as the pancreas and its extracts undergo putrefaction very readily, the glycerin preparation may be preserved by the addition of a few drops of an alcoholic solution of thymol. Tryptic Digestion. The differences between peptic and tryptic digestion are quite marked. Pepsin requires an acid medium ; trypsin acts best in one that is alkaline. When peptic digestion of a solid proteid occurs, this first swells up and then gradually dis- solves, while in tryptic digestion there is no preliminary swelling of the proteid, but the erosion begins at once. In peptic diges- tion the proteid first becomes acid-albumin, then passes into the stage of primary proteoses, followed by that of secondary proteoses, and finally becomes peptones. In tryptic digestion it passes at once into the stage of secondary proteoses, and then on into peptones. These peptones are spoken of as ampho- peptones, because there are at least two of them, anti-peptone and hemi-peptone. The action of pepsin stops when these are formed, but trypsin can act still further by splitting up the hemi- peptone into a number of substances, among them leucin, tyrosin, aspartic acid, tryptophan, and lysatinin. What office these sub- stances have in the body, if any, is as yet undetermined, though it is probable that a portion of the urea found in the body is derived from lysatinin, and Halliburton states that " recent research indicates that even the simple cleavage products (leucin, tyrosin, etc.) may also be utilized for the synthetic production of proteids. The changes which proteids undergo in tryptic digestion are well shown in the following scheme of Neumeister : Proteid. Deutero-albumoses (proteoses). Ampho-peptones. .1 . ! Anti-peptone. Hemi-peptone, I.I. I I Leucin. Tyrosin. Aspartic Acid. Tryptophan. Lysatinin. Steapsin. The fat-splitting or lipolytic enzyme of the pancre- atic juice, steapsin, is sometimes termed pialyn. Its action has already been described in connection with saponification (p. 100), and consists in the taking up of water by the neutral fats, which then " split up," glycerin and a free fatty acid being the result. PANCREATIC JUICE. 237 The evidence that the pancreatic juice has this power is unques- tioned, and that it is due to the presence of an enzyme is proved by the fact that boiling destroys this power, and by the further fact that it cannot be due to bacteria, for antiseptics do not affect it ; nevertheless, the knowledge as to its properties is very meager. Its action upon fats is very rapid, and it is probable that " it is capable of splitting up all the fat of a full meal in the ordinary time of digestion within the body." The presence of bile, ^ by virtue of its contained bile-salts or bile-acids, increases its activity, and this is still greater when hydrochloric acid is present. An interesting fact in connection with the secretion of the pan- creatic juice is that its composition varies according to the nature of the food ingested. Thus, if fat is present in considerable quan- tity, there will be produced a corresponding amount of the lipolytic enzyme, whereas if the diet consists largely of muscular tissue, trypsin will preponderate. There is no reason to believe that this variation in the composition of digestive juices is confined to the pancreas ; it is doubtless equally true of other digestive organs that their products vary with the character of the food. Emulsifying Power of Pancreatic Juice. One of the offices performed by the pancreatic juice is to make an emulsion of fats which form an important part of the food. This action is not due to any enzyme, but to the formation of fatty acids by the steapsin ; indeed, this is regarded by some authorities as the chief office of the lipolytic enzyme. The splitting, up of fat is in and of itself, according to this theory, of no great physiologic impor- tance, inasmuch as only a part of the fat is thus split up, but the fatty acids which result, together with the fatty acids which the fats themselves contain, bring about the emulsification of the main por- tion of the fat, which process is, according to some authorities, so essential in preparing it for absorption. Of the theories propounded to explain fat absorption, we shall speak later (p. 261). The fatty acids resulting from the decomposition of the fat unite with the alkaline salts in the small intestine, probably those of the bile and the intestinal juice rather than those of the pancreatic juice, and form soaps, which, aided by the peristaltic movements of the intestine, convert the fat into an emulsion. The proteids of the pancreatic juice take no part in this emulsifying process, but it is very materially aided by the presence of the bile, inas- much as bile and pancreatic juice acting together split up fat much more quickly than the juice alone. In what manner soaps act to emulsify fats is not known. Some have supposed that the soap forms a film around the fat-globules after they have been finely divided, which prevents their uniting ; but the formation of such a film has never been demonstrated. Moore, in Schafer's Physiology, says that the very fine subdivision of the fat and the increased viscosity of the menstruum occasioned 238 THE PANCREAS. by the dissolved soap, are quite sufficient to explain the per- manency of emulsions of fat. Milk-curdling Enzyme of the Pancreatic Juice. Milk, to which an extract of the pancreas has been added, coagulates, and the term pancreatic casein lias been applied to this precipitate. It is probably a substance intermediate between casein and caseinogen. The coagulating agent is considered to be an enzyme, though nothing definite is known about it. Innervation of the Pancreas. The nerves which supply this organ are from the celiac plexus of the sympathetic, together with some fibers from the right vagus, and are non-medullated and gangliated. When food enters the stomach of a dog, almost immediately the secretion of pancreatic juice begins, and is at a maximum in from one to three hours. It then diminishes until about five or six hours after the meal is taken, when it again increases until the ninth or eleventh hour, and again diminishes until the sixteenth or seventeenth hour, when it is practically niL Fig. 133 shows this in the dog. Just what the facts are in man is unknown, although it is believed that the secretion begins about the time of entrance of food into the stomach ; but its increase and 13 1.Z 11 1.0 03 08 a 7 O.d 0.5 a 03. 41 N \ \ . J.-""* --* \\ \\ i \ a \ \ \ / I \ - / / "7 / | \ \ / . / V 10 II 1Z 1$ 15 16 // 18 FIG. 133. Curve of the secretion of pancreatic juice during digestion. The figures along the abscissa represent hours after the beginning of digestion : the figures along the ordinate represent the quantity of this secretion in cubic centi- meters. Curves of two experiments are given (after Heideuhain). diminution would, doubtless, vary very materially from those of the dog, which was fed but once during the day. THE LIVER. 239 Formerly it was considered that the secretion of pancreatic juice is a reflex act brought about by stimulation of the afferent fibers of the mucous membrane of the stomach or intestine, or both, by the gastric juice, but, according to Bayliss and Sterling, it is due to the production by the duodenal glands, as a result of the action of the gastric juice, of a substance termed by them secretin, which is taken up by the blood and, being carried to the pancreas, stimu- lates that gland to the secretion of the pancreatic juice. Fleig claims that the soaps formed in the small intestine as a result of the saponification of the fats of the food, produce by their action on the mucous membrane sapokrinin, which is absorbed and carried to the pancreas by the blood, where it stimulates that gland, thus aiding in the secretion of pancreatic juice. Internal Secretion of the Pancreas. This organ has been removed from animals without producing an immediately fatal result, but in every such case sugar has appeared in the urine, producing a condition denominated glycosuria, and this, too, when no carbohydrate was present in the food. The urine has also been increased in quantity, thirst and hunger have been marked, and emaciation and muscular weakness have set in, with death resulting in one or two weeks. If the gland is not entirely removed, so little as one-fourth or one-fifth being left, glycosuria does not occur, and, what is still more remarkable is, that after the removal of the gland, if a portion of it is grafted under the skin, or if the ducts are closed so as to prevent the secretion from entering the duodenum, glycosuria is also absent. All of which goes to prove thai besides the pancreatic juice, which may be re- garded as the external secretion of the pancreas, it also produces an internal secretion which, taken up by the blood or lymph, either aids in destroying the sugar produced by the liver or muscles, or else inhibits the glycogenic function of these organs. The cells which are believed to form this secretion have been described in connection with the pancreas (p. 231). THE LIVER. This organ is situated in the abdominal cavity, and is as large as all the other glands of the body taken together. Its transverse diameter is 28 cm., anteroposterior diameter, 20 cm., and vertical diameter, 6 cm. (Fig. 134). Its blood-supply is from the portal vein and hepatic artery, while its nervous supply is from the left vagus and celiac plexus. It is covered by the peritoneum, and beneath this is the fibrous coat, which, at the transverse fissure, is continuous with Glisson's capsule. This connective-tissue envelope covers the hepatic artery, portal vein, and hepatic duct, and accom- panies them through passages in the liver, the portal canals. Chemical Composition. The liver during life is alkaline, L/.v/ 240 THE LIVER. but after death becomes acid, owing to the formation of sarcolactic acid. Its percentage-analysis is as follows (von Bibra) : Gelatin 3.37 Extractives 2.40 Fats . 2.50 Water Insoluble tissues . . . Proteids ...... Inorganic constituents 76.17 9.44 2.40 1.10 Proteids. These are a globulin (cell-globulin) coagulating at 45 to 50 C. ; another globulin, coagulating at 70 C. ; a nucleo- proteid coagulating at about 60 C., which, when injected into the blood-vessels, causes coagulation of the blood ; and an albumin. Gastric sur- face. Tuber papilla re. Tuber omentale. \ Non-peritoneal \ \ surface. X^ - -\ Imp. supra-ren. - ^ ; -HT i i nnTi-norit^ -^ (non-perit). r- ~- ip Imp. supra-ren. 5T~"T" Impressio renalis. -?-j~ Imp. duodenalis. Impressio celica. Impressio pylorica. FIG. 134. Posterior and inferior surfaces of the liver. Extractives. These are urea, uric acid, xanthin, hypoxan- thin, and jecorin. This last constituent contains phosphorus, and has the following formula : C 105 H 186 N 5 SP 3 O 45 . It resembles lecithin, but, unlike that substance, reduces Fehling's solution. It is not confined to the liver, but is also found in the spleen, muscle, and brain. The liver also contains a nuclein, with which iron is in combination, called Zaleski's hepatin and also Schmiedeberg's fer- ratin. Iron is present in the. liver of young animals in greater proportion than in. old ones, and it is stated that animals are born with iron in both liver and spleen. This iron meets the demand of the body until the use of milk is given up, this fluid being poor in iron. Structure. The liver is made up of five lobes, which are composed of lobules each having a diameter of about 1 mm., and these in turn contain hepatic cells, polyhedral in shape, the secret- ing elements of the liver, each having a diameter of about ^ mm., and containing a nucleus. The protoplasm contains glycogen and iron-containing pigment-granules, and may also contain fat. Nerve-fibers are described by some histologists as terminating between the cells, but not passing into their interior. The lobules are separated by connective tissue, which is abundant in the pig, but much less so in man. PORTAL VEIS. 241 Hepatic Artery. The hepatic artery is a branch of the celiac axis, and enters the liver at the transverse fissure, dividing here into two branches, right and left, which go to the correspond- ing lobes. This artery furnishes nutrition to the coats of the large blood-vessels, the ducts, the membranes of the liver, and to Glis- son's capsule. It also gives off branches, interlobular branches, which pass between the lobules and give off lobular branches. These enter the lobules and end in a capillary network between the cells. Whether, however, any blood is carried by these vessels directly to the network is in dispute. Portal Vein. This vessel also enters the liver at the trans- verse fissure, dividing into two, each branch going to the corre- sponding lobe, and following the course already described as being taken by the hepatic artery and its branches. The termination Portal in- __ terlobular branch, cut longi- tudinally. The same, - cut trans- versely. Anasto- moses be- tween ves- sels of several lobules. FIG. 135. Section through injected liver of rabbit. The houndaries of the lobules are indistinct ; X about 35 (Bohrn and Davidoff). of the portal vein forms the interlobular plexus, which, as its name implies, is in the connective tissue, between the lobules. From this go off vessels which run to the center of the lobule, being connected by transverse vessels, the whole forming a capillary network, in the meshes of which are the hepatic cells. The blood which passes through this network is discharged at the center of the lobule into the intralobular or central vein, which, at the base of the lobule, enters the sublobular vein. In a similar 16 242 THE LIVER. manner all the intralobular veins discharge, and the sublobular veins unite to form larger veins, which terminate in the hepatic veins, which, as three large trunks and some small ones, discharge into the vena cava, at the back of the liver. Hepatic Duct. Between adjoining hepatic cells are small passages, intercellular biliary passages or bile-canaliculi, which are the beginnings of the hepatic duct (Fig. 137). It would be more correct to say that the beginnings of the hepatic duct are within the hepatic cells themselves, for it has been demonstrated that in the interior of these cells are vacuoles which communicate with the bile-canaliculi (Fig. 137). The canaliculi pass outward to the interlobular spaces, where they form an interlobular biliary plexus, from which ducts are given off that enter the portal canals, and, covered with Glisson's capsule, in company with the branches of Tntralobular vein. Branch of portal vein. Bile-duct. Branch of hepatic artery. Interlobular connective tissue. FIG. 136. Section through liver of pig, showing chains of liver-cells; x 70 (Bohm and Davidoff). the portal vein and hepatic artery, they emerge from the liver at the transverse fissure as two trunks, right and left, which unite to form the hepatic duct. This is from 3 to 5 cm. in length and has a diameter of about 4 mm. The bile-canaliculi have no wall save such as is made by the hepatic cells. The interlobular ducts have a wall of connective tissue lined with columnar epithelium. In the larger duct is fibrous and plain muscular tissue. The ducts in the portal canals have opening into them cecal diverticula, which are regarded by Sappey as mucous glands. Gall-bladder. The gall-bladder lies on the under surface of the liver in the fossa vesicalis, being attached thereto by vessels and connective tissue. The neck of the gall-bladder terminates in the cystic duct, which is spiral in form, and unites with the GALL-BLADDER. 243 hepatic duct to form the ductus choledochus or common bile-duct. The cystic duct, from the neck of the gall-bladder to its union with the hepatic duct, is 3 to 7 cm. long, and has a diameter of 2.3 mm. The length of the common bile-duct depends upon the point at which the cystic and hepatic ducts unite, which is not FIG. 137. Diagram of a segment of an hepatic lobule: 1,1, interlobular portal vein ; 2, central vein ; 3, 3, intralobular capillaries ; 4, 4, interlobular hepatic artery ; 5, 5, ramifications of hepatic artery, contributing to the formation of the intralobular capillaries : 6, 6, interlobular bile-duct; 7, 7, its ramifications in the lobule, forming a plexus of intercellular canaliculi ; 8, 8, section of biliary canal- iculi with their intercellular capillaries; 9. 9, hepatic cells; 10, 10, interlobular lymphatics, receiving the intralobular lymphatics; 11, 11, 12, intralobular con- nective tissue (Testut). uniform. The following measurements are given : 7 to 8 cm. (Sappey) ; 2 to 4.5 cm. (Luschka) ; 6 to 7 cm. (Joessel). Its diameter is from 5.6 mm. to 7.5 mm. The coats of the gall-bladder are three : serous or peritoneal ; fbro-muscularj made up of fibrous tissue with plain muscular fibers arranged both longitudinally and transversely, the former greatly predominating ; and mucous. This last, which forms the 244 THE LIVER. internal coat, presents a honey-comb appearance. It is covered with columnar epithelium. The mucous membrane of the cystic duct forms folds which bear some resemblance to the valvulse conniventes of the small intestine. These folds are called valvula Heisteri or the valve of Heister. The mucous membrane is con- tinuous with that lining the hepatic and common bile-duct. Bile. This is one of the products of the cells of the liver ; as it is secreted it passes through the hepatic and cystic ducts into the gall-bladder, where it is stored until needed at the time of intestinal digestion, when it is discharged through the common bile-duct into the duodenum by an opening common to it and the pancreatic duct. Properties of Bile. The bile is a constant secretion i. e., the liver-cells are constantly producing it, although it leaves the liver FIG. 138. View of duodenum and pancreas. The part of stomach removed is indicated by dotted lines: A, quadrate lobe: B, right kidney; C, C", right and left suprarenal capsules; D, left kidney; E, pancreas; F, upper part of stomach; (?, spleen; H, duodenum, with a, b, c, d, e. its five parts; /, jejunum; K, duodeno- jejunal angle. 1, lower end of esophagus; 2. pyloric orifice; 3, celiac axis; 4, coronary artery; 5, hepatic artery; 6, Spigelian lobe of liver; 7, 7', splenic ves- sels; 8, left gastro-epiploic artery; 9, right gastro-epiploic artery; 10, superior mesenteric vessels; 11, portal vein; 12, hepatic duct; 13, cystic duct; 14, gall- bladder; 15, left crus of diaphragm; 16. aorta; 17, vena cava inferior; 18. inferior mesenteric vessels; 19, spermatic vessels (Testut). intermittently, being forced out by the contraction of the muscular tissue in the walls of the bile-ducts. Some authorities state that it flows continuously into the intestine. But whether this is so or not. the greater part is stored up in the gall-bladder during the BILE. 245 intervals of digestion, to be expelled therefrom during the diges- tive process. When the bile leaves the liver it is a clear fluid with a specific gravity of 1010. During its stay in the gall-bladder it becomes viscid, and loses some of its water and inorganic salts, certainly some of the chlorids, which are absorbed by the gall-bladder, and its specific gravity is increased to 1030 or 1040. The viscidity in human bile is due to mucin, but that of ox's bile is due to an in- gredient which was formerly thought to be mucin, but is now regarded as a nucleoproteid. That it is not mncin is shown by several facts : the nitrogen is from 14 to 16 per cent, higher than in mucin, and when boiled with a mineral acid it does not yield a reducing sugar. This substance is formed by the epithelial cells lining the gall-bladder. FIG. 139. Portion of gall-bladder and bile-ducts: 1, cavity of gall-bladder; 2, cavity of calyx; 3, groove separating the calyx from the bladder; 4, promontory; 5. superior valve of calyx ; 6, cystic canal ; 7, common bile-duct ; 8, hepatic duct (Testut). The bile is alkaline in reaction, sodium carbonate and alkaline sodium phosphate being present to the extent of about 0.2 per 1000. Its color varies: in herbivorous animals it is green; in carnivorous animals golden yellow or golden red ; while in man it is of a golden yellow, though often green. Constituents of the Bile. The chemical composition of the bile varies in the same individual at different times, and this differ- ence depends, to a considerable extent, upon the length of time 246 THE LIVER. it remains in the gall-bladder. Analysis will, therefore, vary materially, according as the secretion is removed through a fistula of the bile-duct, in which case it would come directly from the liver or from the gall-bladder after having been stored there for some time. The table on page 246 gives the results of various analyses of bile which have been made by competent chemists. Bile-pigments. These are two : bilirubin and biliverdin. Both of these are present in bile, but if the color is of a reddish brown, as in the carnivora, the bilirubin predominates, while the predomi- nance of the biliverdin gives the greenish hue, the characteristic color of the bile of the herbivora. The formula for bilirubin is C 16 H 18 N 2 O 3 , or, as given by some writers, C 32 H3 6 N 4 O 6 ; that of biliverdin, CJ 6 H 18 N 2 O 4 or C 32 H 36 N 4 O 8 i. e., the former passes into Composition of Normal Human Bile. Bile from fistula. Bile from gall-bladder immediately after death. Copeman and Winston. Frerichs. Gorup-Besanez. Water Total solids ... 985.77 14.23 6.28 ) 0.99 1.72 4.51 860. 140. 102.2 1.6 822.7 177.3 107.09 47.3 22.1* 10.8 Sodium glycocholate . . Sodium taurocholate Cholesterin Lecithin Fats Soaps 3.2 26.6 6.5 Mucin, pigment, etc. Inorganic salts .... the latter by oxidation. It is because of a reduction in the bili- verdin that the greenish color of fresh human bile becomes red- dish after it has remained for some time in the gall-bladder. In clots of blood that are old, crystals are found to which the name fiematoidin was given by Virchow. This is identical with bilirubin. Indeed, it is now conceded that the pigments of the bile are derived from hemoglobin, the coloring-matter of the blood. Thus one of the functions of the liver-cells is to change the hemoglobin which comes from broken-down red blood-corpuscles to bile-pigment, separating from it the iron and preserving it for future blood-making. Neither bilirubin nor biliverdin shows any absorption-bands with the spectroscope. Gmelin's Test for Bile-pigment. If diluted bile, or a solution containing bile-pigment, is poured into fuming nitric acid i. e., nitric acid containing nitrous acid, which is a powerful oxidizing agent there will be produced a set of rings or zones of different colors, according to the amount of oxidation of the bilirubin. The BILE. 247 zone next to the acid will be the most oxidized, and will be of a yellow-red color : the product is choletelin, C 16 H 18 N 2 O 6 . Above this will be a zone of red or purple, becoming blue : this product is called bilicyanm ; above all will be a green zone, biliverdin, which being farthest from the acid has undergone the least oxi- dation. This constitutes Gmelin's reaction, arid is employed to detect the presence of bile-pigments, as in the urine. A modified form of applying this test consists in wetting a piece of filter-paper with bile, or the solution which is suspected to contain bile, and dropping the fuming nitric acid upon it, when the character- istic colors will appear. Biliary urine gives an absorption spectrum showing a wide band beginning at the red side of D and ending between D and E. Choletelin gives a band between C and F. Hydrobilirubin. This substance has the formula C 32 H 40 N 4 O 7 . It is a reduction-product of bilirubin, and is obtained by the action of nascent hydrogen, from sodium amalgam, in an alkaline solution of bilirubin. It gives an absorption spectrum, a dark band between C and F. It is with difficulty oxidized to bilirubin or biliverdin. Although bilirubin and biliverdin as constituents of the bile enter the intestine, still neither is found in the feces, but hydrobilirubin is there found, which is undoubtedly derived from the bile-pigments. This pigment of the feces has been described as stercobilin. A similar pigment in the urine is uro- bilin, and it is now claimed that hydrobilirubin, stercobilin, and urobilin are one and the same substance. As already stated, it is believed that bilirubin comes from hemoglobin, the coloring-matter of the blood. In the liver this is decomposed into a proteid and hematin, the latter containing iron. The hematin takes up water, the liver-cells remove the iron, and bilirubin is formed. This may be expressed by the fol- lowing equation : + 2H 2 - Fe = C 32 H 36 N 4 O 6 or 2(C 16 H 18 N 2 O 3 ). Hematin. Water. Iron. Bilirubin. Bile-salts. These are sodium glycocholate and sodium tauro- cholate i. e., sodium united with glycocholic acid, C^H^NOg, and taurocholic acid, C 26 H 45 NSO 7 . These acids are known as bile-acids. Both occur in human bile, as a rule, though taurocholic acid may be absent. When glycocholic or taurocholic acid is boiled with an acid or an alkali, it takes up water and then splits up, or, as it is expressed, " undergoes hydrolytic cleavage/' into cholic or chola- lic acid, and an amido-acid i. e., an organic acid, one or more of whose hydrogen atoms is replaced by amidogen (NH 2 ). Glyco- cholic acid produces glycocoll or amido-acetic acid, and cholic acid ; while taurocholic acid yields taurin or amido-ethylsulphonic acid. This is represented by the following equations : 248 THE LIVER. .C 26 H 43 N0 6 + H 2 6 = C^H^O, + C 2 H 5 M) 2 . Glycocholic acid. Water. Cholic acid. Glycocoll. C^NSO, + H 2 = C 24 H 40 5 4- C 2 H 7 NSO 3 . Taurocholic acid. Water. Cholic acid. Taurin. A similar decomposition of the bile-acids is believed to take place in the intestine, with the production of cholic acid. Pettenkofer's Test. When cane-sugar and strong sulphuric acid are added to bile or a solution of bile-salts a purplish or red- . dish-violet color is produced. This is due to the action of the sulphuric acid on the cane-sugar, producing furfural or furfur- aldehyd, and this acting upon the cholic acid gives the characteris- tic color. In applying this test the temperature should be kept below 70 C., and not too much cane-sugar added, otherwise it will undergo carbonization. The usual way of performing this test is to add to a few drops of the fluid in a porcelain capsule a drop of strong sulphuric acid, and spread out the mixture ; then add to this a drop of a 10 per cent, solution of cane-sugar. If the color does not appear, the capsule should be warmed. Inas- much as the test depends upon the reaction between furfural and cholic acid, instead of using cane-sugar, a drop of a 1 : 1000 solu- tion of furfural may be added to 1 c.c. of an alcoholic solution of bile-salts, and to this 1 c.c. of concentrated sulphuric acid, care being taken as before to keep down the temperature. It is said that the presence of -^V ^ "sV ^ a milligram of cholic acid may be recognized by the furfural test. Unfortunately, Pettenkofer's reaction alone cannot be relied upon as a test for the bile-salts, inasmuch as proteids and other substances to the number of forty will give the same color. The color produced by cholic acid may, however, be distinguished from that produced by all other substances by its spectrum ; two bands, one between the solar lines D and E near to E, and the other at F. The bile-acids are formed by the cells of the liver ; probably from some albuminoid or proteid constituent. They are absorbed by the intestine and are not excretory products, but have various offices to perform and for which they are produced; just what these are has not been definitely determined, but it is regarded as probable that among other offices is that of dissolv- ing the cholesterin, which would otherwise be insoluble. Other offices will be referred to in connection with the discussion of the offices of the bile as a whole. Cholesterin. The formula for this substance is C^H^O. It is found not only in bile, but also in nervous tissue and in the cells of plants and animals (p. 101), where it results from the kata- bolic processes taking place in them. It is brought to the liver by the blood, and is not formed in that organ. It is an excretory BILK 249 product, and the function of the liver, so far as this substance is concerned, is to eliminate it. It undergoes no changes in the intestine, but is excreted as cholesterin in the feces. Lecithin. This is another of the constituents of the bile which, like cholesterin, is derived from nervous tissue, and whose elimina- tion from the blood is brought about by the liver-cells. Offices of the Bile. The amount of bile which is daily secreted, being about 800 or 900 grams in the human subject, would indicate that its offices in the body must be important. It is a remarkable fact that a single anatomic element can perform so many varied functions as does the liver-cell. (1) It secretes the water of the bile; not alone, for the cells of the bile-ducts and possibly those covering the lining of the gall-bladder aid in this process. (2) It forms the bile-salts. (3) It forms the bile-pig- ments. (4) It separates cholesterin and lecithin from the blood. Besides these functions, all of which are related to the bile, it has others no less important in connection with the formation of gly- cogen and urea, both of which are discussed elsewhere. That the passage of bile into the intestine is not essential to life, even in man, is conclusively proved by the results of the establishment of fistulse of the gall-bladder through which all the bile that is formed is removed ; indeed, under these circumstances the health is not greatly impaired. If, however, the common bile-duct is tied, the bile which is formed is absorbed by the lymphatics, an exit from the bile- duct being due to rupture of their walls. That this absorption is not into the blood-vessels is demonstrated by detecting the bile- pigments and the bile-acids in the lymph as it is discharged from the thoracic duct into the venous system at the junction of the left internal jugular vein with the left subclavian vein ; the result of this absorption 'is to produce jaundice. Its most important office is probably the part which it plays in serving as the medium through which cholesterin, lecithin, and other results of katabolic metabolism are removed. Its bile-acids are to a certain extent absorbed from the intestines and serve as carriers of cholesterin. Its pigments are to a certain extent also absorbed from the intestine, though what advantage results there- from is not known. Its amylolytic action, if it possesses any, is exceedingly slight, and it has no proteolytic power. It aids the steapsin of the pancreatic juice in splitting up fat into its fatty acids and glycerin, and it furnishes, as we have seen, alkaline salts to unite with fatty acids in the small intestine and form soaps, thereby assisting materially in the em unification of the fats which are not split up. The bile aids also, probably by virtue of the bile-salts, in the absorption of fats. The theory that the bile-acids dissolve the fat and that the intestinal walls moistened thereby absorb the fat more 250 THE LIVER. readily because the contact of fat and membrane is closer than it otherwise would be, i's abandoned. This theory was based on the reputed facts that oil would rise higher in a capillary tube which had been moistened with bile than in one which had been moistened with water, and that a filtering medium wet with bile would permit oil to pass through more readily than one wet with water. Experiment, however, demonstrates that these are not facts.j In view of the present belief that absorption depends not upon osmosis, but upon the activity of lining epithelium, it is not improbable that the cells covering the mucous membrane of the intestine are stimulated by the bile-acids to increased absorption of fat. The antiseptic property of bile is very small ; still, when bile is not permitted to enter the intestine putrefaction of the intestinal contents takes place more readily than is normal. The explana- tion of this is not satisfactory. Another purpose which bile subserves is to precipitate the pro- teids of the chyme which are not peptonized, or only partially so, as, for instance, syntonin, as that mixture comes into the intes- tine from the stomach. With this precipitated matter is also some mucin from the bile. The result of this precipitation is a tenacious mass which adheres to the intestinal wall, and which is therefore longer exposed to the action of the digestive fluids of the intestine, and, therefore, more perfectly digested than it otherwise would be. Innervation. So far as the formation of bile is concerned, the liver-cells do not-appear to be supplied with secretory nerves. There is great difficulty in determining this question with cer- tainty, for the reason that in stimulating the nerves to the liver vasomotor fibers are stimulated, and this, of course, affects the blood-supply to the organ, so that it is impossible to say whether what occurs is the result of stimulating secretory nerves or of an increased supply of blood. There is no doubt, however, that it is to the blood of the portal vein that the secretion of bile must be ascribed, and that when this supply is increased the bile secre- tion will be correspondingly augmented. This occurs during digestion, and it is, therefore, at this time that the amount of bile is increased. It is probable that the muscular tissue of the gall-bladder and bile-ducts is supplied with nerves, so that when the mucous mem- brane of the stomach or intestine is stimulated afferent impulses reach a nerve-center through the vagus, and efferent impulses pass out and are carried to this muscular tissue through the splanchnics ; the action is, in other words, reflex. Movements of the Small Intestine. When the food enters the small intestine through the relaxed sphincter pylori, the free hydrochloric acid present brings about, by contact with the duodenal mucous membrane through reflex action, a closure of the pyloric sphincter, and thus the quantity of food material DIGESTION IN THE LARGE INTESTINE. 251 passed into the intestine is limited and the power of the intes- tine not overtaxed. Later, the acidity is neutralized by the bile and pancreatic juice, and the free acid in the stomach causes a relaxation of the sphincter and another portion of the stomach- contents enters the small intestine. Cannon states that the manner in which the food is mixed with the digestive secretions, exposed to the absorbing wall, and carried forward in the small intestine is considerably different from the process observed in the large in- testine and in the stomach. To the admirable process by which these functions are performed in the small intestine he has given the name " rhythmic segmentation." This activity of the muscular wall is first seen in the duodenum when a mass of food has accu- mulated there after repeated relaxations of the pylorus. The mass of food is observed at first to be wholly quiet. Suddenly irregular movements take place about it, and then at regular intervals along its length constrictions of the circular musculature separate the mass into a number of segments of equal size. Hardly have the constrictions thus taken place when similar constrictions begin to appear about the middle of each segment. As these new constric- tions deepen, the first constrictions begin to relax. Finally, when the new constrictions have completely divided the segments, the first constrictions have entirely relaxed and the neighboring halves of the divided segments unite to form new segments in the region of the first constriction. Now these new segments are again divided by circular constrictions about their middle, and neighboring halves of these divided segments unite to make a third series, and so on. This process of rhythmic segmentation of the food may go on for several minutes in the duodenum (at the rate of thirty divisions per minute in the cat), so that the food, coming from the stomach, becomes thoroughly mixed with the out-pouring secretions of the liver and the pancreas. It is usual for the process to be brought to an abrupt end in the duodenum by active peristalsis. A peri- staltic wave forms behind the mass of food and sweeps it swiftly forward through several coils of the intestine. The movements of the small intestine, like those of the stomach (p. 208) and large intestine, are inhibited whenever the animal experimented upon manifests signs of anxiety, rage, or distress. DIGESTION IN THE LARGE INTESTINE, Undoubtedly, the process of intestinal digestion, which is mainly carried on in the small intestine, is continued to some extent in the large intestine, as the conditions there existing are favorable to a continuance of this process, but the enzymes, which are the efficient agents, are those of the fluids which have come with the food into the large intestine, the mucous membrane here producing no enzymes with digestive powers. In studying the process of absorption we shall see that, although the large intes- 252 DIGESTION /JV THE LARGE INTESTINE. tine possesses no digestive power, it has considerable power of absorption. Movements of the I/arge Intestine. In the cecum, as- cending and transverse colon, the normal activity, according to Cannon, is an antiperistalsis. Constriction waves start in the transverse colon and pass backward toward the cecum. These waves, unlike those of the stomach, do not run in continuous rhythm ; they occur usually in periods lasting about five minutes, and recur every fifteen or thirty minutes. He says : " The anti- peristalsis in this part of the large intestine seems, indeed, to give a reason for the presence of a valvular structure at the en- trance of the small intestine into the large. Hundreds of anti- peristaltic waves have been seen coursing toward the cecum, and only twice has food been observed to be pressed back into the ileum through the ileocolic valve. Inasmuch as the valve is com- petent for the food which has gone from the small into the large intestine, the antiperistaltic waves have the same effect here as the peristaltic waves have in the stomach when the pylorus remains closed. For, when a constriction occurs, some of the mucous sur- face of the colon becomes enclosed by the narrowed muscular ring ; and, as this constriction passes on, fresh areas of this surface are continually pressed inward around the narrow orifice, while a thin stream of food is passing in the opposite direction. As waves recur about five times a minute, twenty-five waves or more affect every particle of food in the cecum and in the ascending colon in this churning manner during each normal period of antiperistalsis. The result must be again a thorough mixing of the contents with the digestive secretions brought from the small intestine and an exposure of the digested food to the absorbing wall. " Immediately after food passes from the ileum into the large intestine a strong tonic contraction of the cecum and the ascending colon is commonly observed, which serves to press onward to- ward the rectum the contents of these parts. Antiperistaltic waves follow at once the general contraction, so that much of the food which has been pressed onward is returned into the cecum. With the repetition of this process, however, more and more material appears at the end of the transverse colon, and on its appearance there a persistent ring of contraction cuts it off from the region of antiperistalsis ; as still more food appears in the large intestine this ring moves slowly Onward toward the rectum, pressing a mass before it, and is followed by other similar rings carrying onward similar masses by very slow peristalsis. " Thus, in the large intestine the function of mixing the food with the digestive secretions and of exposing this food to the absorbing walls is performed by an antiperistalsis at the beginning of the large intestine. It is here that the last valuable constituents of the food are worked over and taken into the body. The remnant of unused material is propelled onward by occasional strong contrac- BACTERIAL DIGESTION. tions of the whole region of antiperistalsis. These contractions squeeze the material toward the end of the transverse colon where slowly-moving peristaltic waves force it to the rectum." These movements, as in the case with the stomach and small intestine, are inhibited by rage, anxiety, or distress. BACTERIAL DIGESTION. Bacteria are found in considerable numbers in the mouth, stomach, and intestine ; more than sixty species are recorded by Sternberg as having been found in the mouth ; and seventy- four have been isolated from feces and the intestines of cadavers. Those which occur in the stomach consist of mouth-bacteria which have been swallowed together with bacteria which are in the food and drink. We have already referred to some of the pathogenic or disease-producing bacteria, and the effect of hydrochloric acid upon them (p. 196). But besides these there are others which have a true digestive action on the food-stuffs. Inasmuch as there is no free hydrochloric acid in the stomach for about half an hour after food has entered it, the antiseptic action of this acid is not exerted for that length of time, and the conditions are favorable for bacterial action. During this time some of the carbohydrates may be decom- posed, with the result of producing lactic and other acids and set- ting free hydrogen gas. Proteids do not, however, appear to be acted upon by bacteria in the stomach. In the small intestine there is some decomposition of proteids, but not to any considerable extent. Lactic and other organic acids are, however, produced from carbohydrates. These changes in both proteids and carbo- hydrates are due to the action of bacteria. The action of the intestinal bacteria upon proteids has been likened to that of trypsin. The proteid is dissolved, and then changed into albumoses and peptones. A part goes on to the stage of tyrosin, which becomes still further decomposed into paraoxyphenylpropionic acid, paraoxyphenylacetic acid, phenol, and parakresol. From another portion of the proteid are formed indol, skatol, and skatolcarbonic acid. These substances are not derived from tyrosin nor, indeed, from peptones, but from some unknown intermediate substance derived from the proteid itself. All of the carbohydrates of the food seem to be subject to bacterial action. Thus starch and even cellulose may be decom- posed by the appropriate bacteria. As results of carbohydrate decomposition are produced ethyl alcohol, lactic, butyric, and succinic acids, together with carbon dioxid and hydrogen. The fats are normally unchanged by bacterial action ; in the absence of bile or pancreatic juice they are decomposed, with the formation or fatty acids. It is claimed that one important office performed by the intesti- nal bacteria is to prevent putrefaction. 254 ABSORPTION OF THE FOOD. From all the facts known in connection with bacteria, the con- clusion is inevitable that they serve a useful purpose in the econ- omy ; they may, however, when in excess, produce such amounts of harmful substances as to be injurious when these are absorbed. ABSORPTION OF THE FOOD. Attention has already been called to the fact that a large part of the food-stuffs taken into the body are not .in a condition to be absorbed by the blood, nor to be utilized by the tissues when brought to them by that fluid (p. 167), and that digestion consists in bringing about the changes in them necessary to effect this result. It is these changes which we have studied, and which will prepare us to understand the process of absorption. Manifestly, absorption might take place anywhere in the alir mentary tract from the mouth to the anus, but it has been demon- strated that in some portions of this canal very little absorption, if any, takes place, and that in others the greater part of the proc- ess is carried on. Mouth-absorption. Under ordinary circumstances there is no absorption while substances are in the buccal cavity. This is certainly true for the food-stuffs, though that it may occur for some other substances is proved by the fact that cyanid of potassium taken into the mouth and retained there will produce death. There is likewise no absorption while food is passing through the esophagus ; the time occupied in the transit is altogether too brief, and the conditions generally are unfavorable. Gastric Absorption. The food-stuffs which enter the stom- ach are: (1) inorganic, water and salts; (2) carbohydrates, starch and sugars ; (3) fats or oils ; and (4) proteids. Inorganic Food-stuffs. Water taken into the stomach by itself is not absorbed to any extent by that organ. Von Mering demon- strated this in a dog in which he first established a fistula in the duodenum, and then gave it by the mouth 500 c.c. of water. Almost as soon as it reached the stomach it was forced out by contraction of the muscular coat into the duodenum in spirts, and in twenty-five minutes 495 c.c. passed out through the fistulous opening in the intestine. When water contains in solution sub- stances which are absorbed by the stomach-walls, some of the water is also absorbed with them. The evidence as to the absorption of salts is very incomplete. Sodium iodid in 3 per cent, solution is absorbed, but to a slight extent if the solution is more dilute. Many substances, such as mustard or alcohol, hasten its absorption, probably by stimulating the epithelium. Carbohydrates. Starch is not absorbed as such, but must be changed into maltose, which process, as we have seen, does take ABSORPTION BY THE SMALL INTESTINE. 255 place to no inconsiderable extent in the stomach ; although it also is carried on more energetically in the small intestine. All varie- ties of sugar dextrose, lactose, saccharose, and maltose are absorbed in the stomach, and this is also true of dextrin. Some of the saccharose is inverted to dextrose and levulose in the stomach, and doubtless absorbed in this form to some extent, while the rest of it undergoes the same change in the small intes- tine. It is essential, however, that the solution should be concen- trated ; at least this is true of dextrose, of which very little is absorbed until the concentration equals 5 per cent., and the rate of absorption increases up to a concentration of 20 per cent. Alcohol causes increased absorption of sugar, as it does of sodium iodid, and doubtless for the same reason. Taken as a whole, the amount of the sugars absorbed from the stomach is probably not great. Peptones. These are also absorbed from the stomach, though, as in the case of dextrose, only when the concentration reaches 5 per cent., so that the absorption of peptones from the stomach is relatively small. Fats and Oils. With the exception of the physical change, due to the temperature of the stomach, by which the fats and oils are rendered more fluid, and their probable splitting up into fatty acids (p. 199), no change takes place in them, nor are they absorbed to any extent whatever. Alcohol. The fact that alcohol is readily absorbed from the stomach has been sufficiently dwelt upon (p. 161). From the above considerations it will be seen that gastric ab- sorption is not a process of much importance ; indeed, the cases of the entire removal of this organ, to which we have referred, demonstrate that the exercise of what little absorptive power it possesses, is unnecessary. We desire to direct special attention to the fact that sodium iodid, dextrose, and peptones are more readily absorbed when alcohol is also present. This empha- sizes the view now held as to absorption, that it is not a mere matter of osmosis, but is due to an actual selective power of the epithelial cells, and that this is more actively exercised under the stimulating action of alcohol or other substances having like power. Absorption by the Small Intestine. It is from the cavity of the small intestine that the greater part of absorption takes place, the products of digestion passing into the villi, a part entering the capillary blood-vessels and reaching the liver through the portal vein ; while another part enters the lacteals, and passes on into the thoracic duct, from which it is discharged into the blood-vascular circulation. While osmosis is doubtless one of the factors in this process, still the selective power of living cells is much more potent. 256 ABSORPTION OF THE FOOD.. The materials to be absorbed are : (1) water, salts ; (2) carbo- hydrates ; (3) fats ; (4) proteids. Absorption of Water. As was stated in connection with gastric absorption (p. 254), water is not absorbed to any extent from that organ, most of that taken in being passed on into the small intes- tine. Experiments have shown that the water which enters the small intestine is absorbed by the capillaries of the villi ; and yet even when large quantities are absorbed, an analysis of the blood shows no change, as might be expected, the excess being elimi- nated by the kidneys. Absorption of Carbohydrates. The dextrose and levulose, formed by the action of the enzymes, are absorbed by the veins and carried by the portal vein to the liver, but there is evidence that saccharose, and even dextrin and starch, can be taken up by the cells; although, as we have seen, the action of the intestinal enzymes is very powerful, and doubtless the amount of carbo- hydrates remaining in any other condition than that of dextrose or levulose is very small. But, even if carbohydrates should be absorbed in any form but these, they would be inverted while 1 passing through the cells. It is a remarkable fact that lactose, which forms so important a part of the milk, the sole food of the growing child, is unaffected by the enzymes ; however, in its pass- age through the epithelial cells it is inverted, the product being probably dextrose and galactose. Maltose, also, may be inverted by the columnar epithelium. It is, then, mostly in the form of dextrose and levulose that the carbohydrates of the food enter the blood and are carried to the liver, and from these glycogen is formed. Saccharose and maltose cannot be thus changed by the liver-cells. It sometimes happens that very large quantities of sugar are taken in with the food ; if the amount is so great that the liver and muscles can- not convert it all into glycogen, the overplus is eliminated by the kidney, and appears in the urine, constituting alimentary glycosuria. Glycogenic Function of the I/iver. As we have seen, the result of the digestion of starch is its conversion into mal- tose, or maltose and dextrin, which later becomes dextrose, in which form, for the most part, the carbohydrates of the food reach the liver. Some levulose may accompany it to the liver, where, according to some authorities, it becomes dextrose. If during the time of the absorption of sugar the blood going to the liver through the portal vein and that coming from it by the hepatic vein are analyzed, it will be found that the former contains much more sugar than the latter ; from this fact the inference is inevitable that some change takes place in the sugar during its passage through the liver. This change consists in its conversion by the hepatic cells into glycogen, which is a process of dehydration, the reverse of what takes place when the starch or glycogen of the food is converted into sugar. GLYCOGENIC THEORY. 257 Formation of Glycogen from Carbohydrates. The liver weighs between 1500 and 1900 grams, and as the amount of glycogen in this organ may reach 10 per cent, of its weight, 150 to 190 grams, it is manifest that the carbohydrates of a single meal, which would ordinarily amount to about 100 or 150 grams, could be stored as glycogen in the liver, provided that before the next meal this was all reconverted into liver-sugar, and as such passed out into the blood, leaving the liver free from glycogen ; but this does not occur, so that we may conclude that all the carbohydrates are not deposited in the liver. As has been stated (p. 62), the muscles contain glycogen, sometimes to the amount of 1 per cent., and this undoubtedly comes from the carbohydrates of the food. If, however, all the glycogen in the liver and the muscles is taken into account, together with the dextrose in the blood, about 0.12 per cent., there still remains an overplus unaccounted for, and this is believed to enter into the formation of proteids and other substances ; indeed, it is not by any means certain but that some of the absorbed dextrose may exist in the blood as dextrose and never undergo conversion into glycogen, but perform the same office as the dextrose which does result from liver or muscle glycogen i. e., serve as a source of energy. Formation of Glycogen from Proteids. It has been abundantly demonstrated that feeding animals on proteids alone, without any admixture with carbohydrates, results in the forma- tion of glycogen in both liver and muscles. It follows from this that there exists in the body the power of decomposing proteids, and from the carbon, hydrogen, and oxygen which enter into their composition to form glycogen. By this statement it is not in- tended to convey the idea that the proteid is broken up into its chemical elements, but rather that it is decomposed into a non- nitrogenous and a nitrogenous portion ; the non-nitrogenous portion becoming ultimately glycogen, possibly passing through a prelimi- nary stage of dextrose, some of which may remain as dextrose, and not undergo conversion into glycogen. Formation of Glycogen from Fats. It is generally accepted that no glycogen is formed from fat. There are authori- ties, however, who hold the contrary opinion, basing this upon cer- tain experiments, and upon the fact that in germinating seeds such a change does take place. It may be regarded as an unsettled question. It is an interesting fact that liver-glycogen is increased upon the administration of glycerin. While glycerin is not convertible into glycogen, it seems to prevent the change of the glycogen in the liver into dextrose, and hence causes its retention, which has the same effect upon the total amount in the liver as if more had been formed. Glycogenic Theory. The carbohydrates serve as sources of energy i. e., they are oxidized to CO 2 and HoO in the body, 17 258 ABSORPTION OF THE FOOD. and heat and work are the result of this oxidation. The various stages through which they pass are not all known, but as to some there seems little doubt. Thus the formation of dextrose and levulose, during digestion and absorption, and the deposition of the greater part of these in the liver and muscles as glycogen, are generally accepted; but as to what changes take place in the glycogen there is a difference of opinion. " Theory of Claude Bernard. The opinion advanced by this distinguished physiologist, who, in the year 1848, discovered that sugar'was formed in the liver, and in 1857 that it had its origin in glycogen, was that the dehydration of the dextrose by the liver- cells, by which glycogen is deposited in that organ, is a provision for the storage of the carbohydrates of the food ; otherwise the dex- trose, after it had reached a percentage above that which normally exists in the blood, 0.1 to 0.2 per cent., would be of no use to the body, inasmuch as it would be eliminated by the kidneys. But, being stored up in the liver at the time of its absorption, it is, in the intervals of digestion, gradually converted into dextrose, which passes out in the blood of the hepatic veins and serves the body as a source of energy. It is a matter which is still in doubt whether this conversion is a zymolytic action i. e., whether it is produced by an enzyme or by the liver-cells as one of their peculiar functions. The argument against the change being due to an enzyme is, that while amylolytic enzymes have been found in the liver, which change glycogen to maltose, here is a change to dextrose ; but, on the other hand, a ferment has been obtained from the liver which does convert glycogen into dextrose, so that this argument has but little weight. That the power to change glycogen into dextrose resides in tissues independently of the pres- ence of enzymes is shown by the fact that the muscles of the body, during the entire life of an individual, and other organs, such as the placenta, during fetal life, have the same power as the liver to form glycogen from the dextrose of the blood. While Bernard's theory has been generally accepted by physiologists, there are those who oppose it, and among these the most promi- nent is Pavy. Theory of Pavy. Pavy regards the dextrose which Bernard and others have found in the hepatic vein as due to a change brought about by the action upon the glycogen of an enzyme formed in the liver after death. His analyses of the blood of the ascending vena cava, which carries the blood coming from the liver, show no increase of sugar over the blood obtained from other portions of the circulation, provided that it is examined before post-mortem changes have set in. For this purpose he kills the animal by a blow upon the head, and immediately withdraws the blood. [According to this theory, during life the glycogen of the liver * does not become converted into dextrose, but is a source of fat and (of proteid. That fat is formed in th,e body in considerable amount "* J DIA BETES. 259 on a carbohydrate diet is a well-known fact, and one of the re- strictions placed upon obese individuals who are endeavoring; to reduce their fat is to abstain from sugar as much as possible. The glycogen of the muscles may also serve for the purpose of fat formation. That glycogen serves also as a source of energy there is no doubt. It may seem to the student a strange fact that what appears so simple a matter to determine as this which is in dispute between the adherents of the two theories referred to cannot be definitely settled ; but it is to be borne in mind that the blood is a very complex fluid, and the methods for detecting with certainty the amount of sugar in the blood are not sufficiently exact to warrant a positive statement, for in this fluid there are other reducing substances than sugar. Then, too, it must be remembered that the entire blood of the body passes through the liver every two minutes, so that while the total amount of sugar passed out from that organ in twenty-four hours might be considerable, yet the difference in amount found at any given moment in the blood of the hepatic vein, over and above that found in other parts of the circulation, would be so small as not to be within the possibility of determination. In view of the conflicting evidence we must, therefore, acknowledge that the question is still an open one, with the weight of evidence at the present time in favor of the theory of Bernard. Diabetes. This is " an affection characterized by an immoder- ate and morbid flow of urine." When there is no sugar in such urine the condition is called diabetes insipidus ; but when the urine contains an abnormal amount of sugar, diabetes mellitus, or simply diabetes. The term glycosuria refers to the excessive amount of sugar in the urine, and this condition may exist, tem- porarily, in other affections than diabetes. The form in which the sugar exists is principally that of dextrose, though there is doubt- less some maltose also present. The source of this sugar may be from glycogen or from proteids. If from the former, it may be caused by excessive conversion of glycogen into dextrose (Ber- nard), or from a failure on the part of the liver to convert into glycogen as much of the absorbed sugar as occurs normally (Pavy). Whichever view is taken, the treatment consists, among other things, in depriving the patient of all foods which make sugar. In some cases, however, even after this is done, the glycosuria continues, and the only possible explanation is that the sugar is produced from proteids. Artificial Diabetes. The condition of glycosuria may be arti- ficially produced : (1) Puncture-diabetes. Puncture in the floor of the fourth ventricle of the brain, the region in which is situated the vaso- motor center, will cause glycosuria. This center is stimulated by the puncture, the arterioles of the liver are constricted^, thus 260 ABSORPTION OF THE FOOD. reducing the amount of arterial blood in that organ, which results in an increased activity of the liver-cells, thereby causing an excessive conversion of glycogen into sugar. This is one expla- nation which has been given to account for the phenomenon. Another is that the glycosuria is due to a direct action upon the secretory nerves of the liver. (2) Phlorizin-dlabetes. Glycosuria may also be produced by the administration of a number of different substances; among these are phosphoric and lactic acids, strychnin, arsenic, phosphorus, and especially phloridzin or phlorizin, a bitter substance, having the chemical formula Cg^^O^, obtained from the bark of the root of the apple-, pear-, and cherry-tree. Phlorizin is a glucosicl. A glucosid is a vegetable principle which, when treated with acids and some other substances, yields glucose and another sub- stance which is characteristic of the particular plant from which the glucosid was obtained. There are many glucosids which have been isolated ; among these are, amygdalin, from bitter almonds ; digitalin, from digitalis ; esculin, from the horse-chestnut, etc. It was thought at one time that the glycosuria which follows the administration of phlorizin was due to the glucose which it con- tains, but it is now known that phloretin, which is a crystalline substance formed by the action of an acid on phlorizin, and which contains no glucose, will have the same effect as the phlorizin itself. (3) A diabetic condition may also be produced by removing the pancreas. Of this form of glycosuria we have already spoken (p. 239). Absorption of Proteids. The theory that the digestion of proteids consists in their being changed into a more diffusi- ble form, and that in this condition they are absorbed by the physical process of osmosis, has been to a considerable degree abandoned. For while it is true that proteoses and peptones are diffusible, while native albumins are not, still it has been shown that egg-albumin is absorbed as such, although it is non-diffusible. This absorption takes place in both the small and large intestine ; in the former, under circumstaaces which demonstrate that it could not have been previously peptonized, and in the latter, of course, there is no peptonizing enzyme. We must, therefore, attribute the absorption of proteids to the epithe- lial cells, to whose efficiency in the process of absorption we have so frequently had occasion to refer. Not only is egg-albumin absorbed, but the same is true of syntonin as well. There is this difference, however, that when egg-albumin is absorbed in such quantity that it cannot be changed into an assimilable form while passing through the cells of the villi, it is carried by the blood to the kidneys, where it is eliminated, producing an "alimentary alburninuria," while syntonin is utilized by the tissues. There is little doubt that it is in the form of proteoses and peptones ABSORPTION OF FAT. 261 that the proteids are absorbed, and that the capillary blood-vessels of the villi are the efficient agents in this process. Some recent experimenters, Asher and Barbera, claim that some proteid is absorbed by the lacteals, but Mendel conducted an investigation as a result of which he concludes that " under ordinary circum- stances by far the greater share in the process must still be dele- gated to the capillaries of the villi." Although proteids are mainly absorbed as proteoses and pep- tones, yet during this act they lose their identity. In other words, while passing through the epithelial cells which cover the villi they are so changed that neither proteose nor peptone can be found in the blood, and if these substances are directly injected into the blood they are eliminated by the kidneys and are found in the urine. Indeed, if the amount is sufficient they act as poisons, causing insensibility, lowering blood-pressure, diminishing or destroying the coagulability of the blood, and producing death. Although the power to convert proteoses and peptones into a form which can be assimilated is claimed for the leukocytes present in the intestinal wall, the evidence seems conclusive that this claim is without substantial foundation, and that it is to the columnar epithelial cells covering the villi that the change is to be attrib- uted. Up to the present time the form of proteid into which these substances are changed has not been determined, though it is doubtless a coagulable proteid, and probably serum-albumin or globulin. Absorption of Vegetable and Animal Proteids. The products of vegetable proteolysis are not so completely absorbed as are those of animal origin. It is stated by Moore that this is in part due to their envelopes of indigestible cellulose, in part to their shorter stay in the intestine because of their action in causing increased peristalsis, and in part to their less digestible character. He further states that the proteids of some legumin- ous plants and cereals are absorbed nearly as perfectly as those of animal origin, while in most others (potato, lentil) it is much less complete (22 to 48 per cent. less). The percentage of the nitrogen of meat or egg appearing again in the feces in man amounts to but 2.5 to 2.8 per cent. ; that of milk, to but 6 to 12 per cent. Absorption of Fat. There is no dispute as to the lacteals being the channels through which the fat reaches the blood-vascular circulation by way of the thoracic duct ; the presence qf fat in the vessels has been observed too often to admit of any doubt on this point. Indeed, it is the milky appearance given by the fat-particles to the contents of these vessels which has given to them the name of lacteals (Fig. 120), but as to the manner and form in which fat passes into the villus to reach the lacteals two theories are held : (1) the emulsion theory and (2) the solution theory, or, more correctly, solution theories. Emulsion Theory. This theory is the older, and explains the 262 ABSORPTION OF THE FOOD. absorption of fat by supposing that the greater part of it is emul- sified by the action of the pancreatic juice, and, being thus broken up into a state of extremely minute subdivision, the particles pass into the villi, reach the lacteals, and by way of the thoracic duct enter the blood-vascular circulation, in this theory the splitting up of the fat plays the important part of aiding in the emulsifying process (p. 101).* Although fat-particles have often been observed in the interior of the epithelial cells, they have never been seen in the striated borders of these cells, which is a remarkable fact if as fat they pass through these borders to reach the interior. Nor is there any special reason why fat should be taken up by the columnar epithelium more than any of the products of digestion. It has been supposed that the lymph-corpuscles, already described as existing between the epithelial cells of the villi, put out pseudo- podia and take in the fat-particles, passing them on through the reticular tissue of the villi (p. 223) ; but, as already stated, it is in the columnar epithelial cells that the fat is seen during the FIG. 140. Longitudinal section through summit of villus from human small intestine; X 900 (Flemming's solution): at a is the tissue of the villus axis; b, epithelial cells; c, goblet-cell; d, cutieular zone (Bohm and Davidoff). time of its absorption, and these are entirely distinct from the lymph-corpuscles. - ' or ABSORPTION OF FAT. 263 -v- Solution Theories. Of these there are two : (1) the soap theory and (2) the fatty-acid theory. Soap Theory. This theory takes cognizance of the fact that soaps are formed in the small intestine by the action of steapsin on the neutral fats, by which they are split up into fatty acids and glycerin, the fatty acids uniting with some of the alkali of the intestinal fluids/ with the result of forming soluble alkaline soaps. The theory' under consideration supposes that these soaps, together with the glycerin, are absorbed by the columnar epithe- lium, and that when within the protoplasm the acids and glycerin again unite by virtue of cell-action to form neutral fat, which is seen in the interior of the cells. We have already referred to the fact that pancreatic juice has the power of decomposing all the fat of an ordinary meal into fatty acids and glycerin during the time that it remains in the small intestine. The objection to the soap theory, that there is not enough alkali in the body to com- bine with the fatty acids which would result from the decomposi- tion of the fat which is taken in as food, is met by the explanation that only a small amount is needed at a given time to form a soap, and that as soon as the soap has entered the cells it is again decom- posed into fatty acids and alkali, the latter returning to the blood and being again available for use, while the acids unite with the glycerin to form neutral fat. 'Fatty Acid Theory. The other theory is that fatty acids, formed in the manner stated, are dissolved by the bile, and in this form are absorbed, the fatty acids uniting with the glycerin which was absorbed at the same time and forming neutral fat. There is evidence showing that when fatty acids alone are absorbed, glycerin is formed, probably by the columnar epithelium, and that by the union of the two neutral fat is produced. The evidence seems conclusive that fats are absorbed as soaps and fatty acids, and not as emulsified fat, the fatty acids being dissolved by the bile, the salts and pseudomucin of which are the efficient factors in causing this solution. In summing up this portion of the section on the a Chemistry of the Digestive Processes," in Schafer's Text-Book of Physiology, Moore says : "It is probable, then, that in all animals a great part of the fat is absorbed and dissolved in the form of soaps ; but in some animals a part is also absorbed as dissolved fatty acids, while in others the entire quantity leaves the intestine in the form of soaps." Course of Fat from Columnar Epithelium to the Lacteals. Although fat is not absorbed as an emulsion, it is in this form that it exists in the interior of the epithelial cells after its re-formation from the fatty acids and glycerin. We have already referred to the large number of lymph-corpuscles, or leukocytes, in the tissues composing the villi. During the absorption of fat these cells contain fat, and they doubtless carry this to the lacteals, there 264 ABSORPTION OF THE FOOD. either depositing it while still maintaining their integrity, or set- ting it free by themselves breaking up and disintegrating. Some authorities hold the opinion that the contractions of the proto- plasm of the columnar epithelial cells forces out the fat, and that the particles pass through the spaces between the cells and thus reach the lacteals. Final Disposition of the Absorbed Fat. Inasmuch as no more than 60 per cent, of the fat absorbed finds its way into the thoracic duct, it might be inferred that the lacteals were not the only channels of absorption, and that the capillary blood-vessels of the villi had a part in this process, but there is no more fat found in the blood of the portal vein during the period of fat absorption than in the blood of the rest of the body, and even this is not increased if the contents of the thoracic duct are not permitted to enter the venous circulation. Just what becomes of the 40 per cent, unaccounted for is not known. It was long regarded as impossible for the absorbed fat to be deposited in the tissues unaltered, and it was supposed that it all underwent such changes as to destroy its integrity, and that the fat which existed in adipose tissue and elsewhere was entirely a new formation. In reference to this Liebig said : " In hay or the other fodder of oxen no beef- suet exists, and no hog's lard can be found in the potato-refuse given to swine." While it is true that some of the fat of the body is produced from other substances than the absorbed fat, still, the evidence is conclusive that under certain circumstances this is deposited in the tissues without undergoing any change whatsoever. If a dog is starved until the reserve supply of fat has been exhausted, and it is then fed with rape-seed or linseed oil or mutton tallow, fat will be again deposited in the tissues and in it some of the fat given as food will be recognizable. It is, however, a question whether this occurs except under the exceptional conditions here mentioned, although some of the best authorities state that the fat in the blood after a meal is eventually stored up in the connective-tissue cells of adipose tissue. Others claim that the fat of the food is completely oxidized, and that the body-fat is formed from proteids or carbohydrates, or both. The probabilities are that proteids and carbohydrates are the principal sources of the body-fat, and that fat itself is sometimes a contributory factor, although its main office is to supply the body with heat or other form of energy. Absorption by the Ith of 1- mm. and divided on the bottom into y 1 ^ mm. squares, the cell in use being covered by a cover-glass ; a jar, in which the blood to be examined is diluted ; a glass rod, for staining ; and a needle, for pricking the finger to obtain blood. A solution of sodium sulphate is made having a specific gravity of 1025, which corresponds to the specific gravity of blood-plasma, and this is sucked up into the pipet to the mark indicating 995 cu.mm. This is then deposited in the jar. The finger is pricked with the needle, the amount of projection of which can be regulated by a screw, and 5 cu.mm. of blood sucked up into the capillary tube, and this is then deposited in the jar with the saline solution, and the mixture thoroughly stirred with the glass rod. A drop of the mixture is then placed in the cell and a cover-glass 272 THE BLOOD. placed over it. The brass plate is placed on the microscope, with a magnifying power of 400 diameters. In a short time the red corpuscles settle to the bottom of the cell, and the number con- S o o (J o o o o o D O c FIG. 145. Thoma-Zeiss hemacytometer. 1. Mixing apparatus: a, capillary tube in which the blood is taken ; 6, chamber for mixing the blood with the diluting solution ; c, glass ball to aid in mixing the blood with the diluting solu- tion. 2. Cross-section of the chamber in which the blood is counted. 3. Section of the field on which the blood is counted, showing thirty-six squares. tained in 10 squares are counted, added together, and multiplied by 10,000; the product is the number in 1 cu.mm. of blood. Thoma-Zeiss Hemacytometer (Fig. 145). This is quite simple to use, inasmuch as the blood is drawn and diluted in one in- MICROSCOPIC STRUCTURE OF THE BLOOD. 273 strument. It consists of a pipet with mouthpiece and tubing connecting the two. It is carefully graduated, and has a bulb which contains 100 times as much as the capillary tube when filled to mark 1. In this bulb is a glass bulb which aids in the mixing of the blood and saline solution. There is also a glass slide (Fig. 145, 2) having a covered disk. On the surface of this 1 cu.mm. is divided into 400 squares, each -fa mm. This is surrounded by a cell of such height that when a cover-glass is placed upon it its under surface will be -fa mm. above the disk. The linger being pricked, the blood is drawn into the capillary tube as far as 1 on the scale ; the saline solution, Hay em's fluid (see below) or 3 per cent, sodium chlorid solution, is then drawn up to 101. The pipet is then shaken so as to mix the blood and solution thoroughly, and a drop of the mixture placed on ra and covered with a cover- glass. The volume of blood above each of the squares will be ffa^ cu.mm. The corpuscles in from 10 to 20 squares are counted, and by dividing this number by the number of squares taken, the average per square will be obtained. This multiplied by 4000 X 100 equals the number of corpuscles in a cubic millimeter of blood. For the depth of the cell being -fa mm., and the area of each square being j^- - sq.mm., the volume of blood on each square would be ffaq cu.mm. Inasmuch as the blood has been diluted 100 times, 1 cu.mm. of blood withdrawn from the vessels would contain 400,000 times the corpuscles in 1 square. Hayem's fluid consists cf sulphate of sodium, 5 grams ; sodium chlorid, 1 gram ; corrosive sublimate, 0.5 gram ; dissolved in 200 c.c. of distilled water. Oliver's Hemacytometer (Fig. 146). This apparatus consists of a measuring pipet, a ; a dropper, b ; a mixing tube, c. A small amount of blood is measured in the measuring pipet and mixed in the mixing tube with Hayem's fluid. The tube is then held between the fingers, and the light of a wax candle, held about 2^- meters from the eye, in a dark room, is looked at, the tube being held edgeways. Enough fluid is added to make the flame appear as a bright line through the mixture. If the red corpuscles are present to the number of 5,000,000 to the cubic millimeter, the surface of the mixture will stand at 100. If the number is less, it will not require so much of the fluid to make the mixture trans- parent ; while if the number is in excess of normal it will require more. The graduations on the tube are percentages of the normal standard; thus if 100 represents 5,000,000 corpuscles, 80 would represent 4,000,000. Many observations have shown that the number of red corpus- cles is subject to considerable variation even in the same individual. Muscular exercise, and even massage, which is passive exercise, increase the number ; while food diminishes it. The blood of persons living in high altitudes has shown the 18 274 THE BLOOD. presence of red corpuscles to the number of 8,000,000 per cu.mm. It does not necessarily follow, however, that this is an absolute increase, for it may be due to loss of the water of the blood, caused by increased evaporation from the body, and to increased FIG. 146. Oliver's hemacy tometer : a, measuring pipet: 6, dropper to contain Hayem's fluid; c, mixing tube graduated in percentages; d, mode of making the observation (this must be done in a dark room) ; a, b, and c are natural size. arterial tension, by which the amount of lymph is increased. In conditions of apparent health so small a number as 1,600,000 has been found. In newborn children, 5,000,000 per cu.mm. have been estimated. Color of the Red Corpuscles. A single corpuscle is of a MICROSCOPIC STRUCTURE OF THE BLOOD. 275 yellowish or amber color, and the red color of the blood appears only when the corpuscles are in thick layers or in masses. ^Structure of Red Corpuscles. There is a difference of opinion among histologists as to the minute structure of these bodies. Schafer describes it as follows : " Each red corpuscle is formed of two parts, a colored and a colorless, the former being a solution of hemoglobin ; the latter, the so-called stroma, which is by far the smaller quantity, being composed of various substances, chief among these being lecithin and cholesterin, together with a small amount of cell-globulin." According to this view, the colorless stroma serves as an envelope to contain the hemoglobin in solution. By other authorities, of whom Rollett may be regarded as an exponent, the entire corpuscle is made up of an elastic structure, the stroma, the outer portion of which is denser than the inner, and having in its interstices the coloring- matter together with lecithin, cholesterin, and globulin. In discussing this subject, Gamgee, in Schafer's Text-Book of Physiology, says : " Without attempting to speculate beyond the facts which we possess, it may, however, be assumed that hemo- globin exists in the blood-corpuscles in the form of a compound with a yet unknown constituent of the corpuscle. This compound, the existence of which we are forced to assume, is characterized by remarkable instability, for it is decomposed, setting free the hemo- globin, which then passes into solution (1) when the blood-plasma or serum, in which the corpuscles are suspended, is diluted; (2) when certain substances act upon the corpuscles (ether, chloro- form, salts of the bile-acids, certain products of putrefaction) ; (3) by the action of heat, by alternate freezing and thawing, by induction shocks, etc." The red corpuscles are exceedingly flexible, as may readily be seen by watching them in the circulation of the web of a frog's foot. At times they will be so stretched out as to pass through a vessel whose diameter is -smaller than is theirs when in a circular shape ; or sometimes they may be seen bent over the projection made by the junction of two vessels, one portion being within each, until, one current being the stronger, they are carried for- ward by it, resuming their circular shape as soon as the size of the vessel permits. The human red corpuscles possess in adult life no nuclei. This is true of all mammals. Up to the fourth month of fetal life the blood of the human embryo contains nucleated red corpuscles. It is uncertain, however, whether these develop into the non-nucleated forms. In other vertebrates the corpuscles are nucleated. Chemical Composition of Red Corpuscles. An analysis of the red corpuscles of human blood shows the presence of both organic and inorganic compounds. The percentage of organic ingredients in dried human corpuscles in one analysis was as follows : Proteids 276 THE BLOOD. and nuclein, 12.24 ; hemoglobin, 86.79 ; lecithin, 0.72 ; cholesterin, 0.25. The nucleoproteid is called by some writers cell-globulin. The inorganic substances are potassium and sodium salts ; potas- sium constituting 40.89 per cent, of the total ash, while of sodium there is only 9.71 per cent. Hemoglobin. This is the term applied to the highly complex, iron-containing, crystalline coloring-matter, which forms the most important constituent of the colored corpuscles of the blood, and by virtue of which they perform their function as the oxygen- carriers of the organism (Gamgee). It constitutes 95 per cent, of the solid matter of the red corpuscles, and in the adult male there are about 14 grams for each 100 grams of blood, or in all about 750 grams. When united with a molecule of oxygen it forms oxyhemoglobin ; when it exists by itself, without this molecule, it bears the name of hemoglobin or reduced hemoglobin. Because of its property of serving as an oxygen-carrier it is spoken of as a respiratory pigment. The hemoglobin in the blood of different animals varies both physically and chemically, so that some writers speak of the hemoglobins; but Gamgee thinks this is unnecessary and misleading, inasmuch as the proportion in which iron, the characteristic element in the blood coloring-matter, occurs, is absolutely the same in many animals ; and, besides, there is abun- dant evidence in favor of the view that the optical and physiologic properties of hemoglobin depend upon the identical " typical nucleus" in all animals. When hemoglobin is decomposed in the presence of oxygen, it breaks up into a proteid, globulin, which constitutes 96 per cent, of it, and hematin, of which there is 4 per cent. If this decomposition takes place without oxygen, instead of hematin, hemochromogen re produced. It is to this latter substance that hemoglobin owes its characteristic property of taking up oxygen. The exact percentage-composition of the hemoglobin of human blood has not been determined ; that of the dog, as analyzed by Jaquet, is as follows : C, 53.91 ; H, 6.62 ; N, 15.98; 8,0.542; FeO, 0.333 ; O, 22.62. The molecular formula is C 758 H 1203 N 195 - 833, FeO 218 , making the molecular weight 16.669. Gamgee has calculated for the hemoglobin of the ox the following : C 759 H 1208 - N 2lo S 2 FeO 204 . Bunge says, in reference to the molecular weight of hemoglobin : " The enormous size of the hemoglobin-molecule finds a teleological explanation, if we consider that iron is eight times as heavy as water. A compound of iron which would float easily along with the blood-current through the vessels could only be secured by the iron being taken up by so large an organic molecule." Hemoglobin forms crystals in the absence of oxygen. Hemoglobinometers. There have been various methods devised to determine the amount of hemoglobin in the blood. Those which are commonly used are sufficiently exact for clinical purposes, MICROSCOPIC STRUCTURE OF THE -BLOOD. 277 though undoubtedly the determination of the amount of iron would give more precise results; the ordinary methods depend upon the color. 1 a* FIG. 147. Oliver's hemoglobinometer : e, glass cell for receiving the blood from the pipet (the dilution is effected within the cell itself) ; a, standard graduations made of tinted glass. To avoid multiplying these unduly, they are furnished in tens per cent., the intermediate divisions of the scale being obtained by superposing tinted glass riders in a graduated series from 1 to 9. (These riders are not repre- sented in the figure.) The apparatus is shown of the natural size. Oliver's Hemoglobinometer (Fig. 147). Some of the blood, the amount of whose hemoglobin is to be determined, is diluted and placed in the glass cell e ; the color of this diluted blood is then compared with the series of tinted glasses, the color of each 278 THE BLOOD. of which corresponds to a known percentage of hemoglobin. The one that corresponds to the color of the sample of blood determines the percentage of hemoglobin in the blood under ex- amination. Goners' Hemoglobinometer (Fig. 148). This apparatus consists of two glass tubes having the same diameter, d contains glycerin- jelly colored with carmine, so that the color represents that of blood diluted one hundred times with water. The finger is pricked with the needle/, and the blood is sucked up into the pipet b to the 20 cu.mm. mark, and then blown out into the tube c, distilled water being added in drops from a until the color of the diluted blood corresponds with the color in d. The tube c is so graduated that when filled to 100 with diluted blood its color corresponds to FIG. 148. Gowers' hemoglobinometer : a, pipet bottle for distilled water; b, capillary pipet ; c, graduated tube ; d, tube with standard dilution ; /, lancet for pricking the finger. that of d, which would consequently represent the color of normal blood. If, therefore, in order to produce a color corresponding to that in d, water must be added to fill the tube to a higher level than 100, the hemoglobin is above normal ; while if, on the other hand, the color is produced below 100, then the graduation at that point represents the percentage of the normal. Thus if at 75 the corresponding color is reached, only 75 per cent, of the normal amount is present. Von FleischVs Hemometer (Fig. 149). This consists of a stand carrying a white reflecting surface, e, and having a platform below upon which slides a glass wedge colored red, 6. On the platform is a compartment, J, divided into two by a vertical partition. The one which is directly above the colored wedge is filled with distilled water. Into the other, a small amount of distilled water is placed. MICROSCOPIC STRUCTURE OF THE BLOOD. 279 The finger is pricked and the blood which is to be examined is drawn up into a tube provided for that purpose. The blood is then put into the second compartment, which is afterward filled with distilled water. The milled head /is then turned, and this carries along with it the wedge of glass. W nen tne colors, as seen by transmitted artificial light, in the contents of both com- partments correspond, the percentage of hemoglobin in the blood FIG. 149. Von Fleischl's hemometer: a, stand;. 6, narrow wedge-shaped piece of colored glass fitted into a frame (c), which passes under the chamber ; d, hollow metal cylinder, divided into two compartments, which hold the blood and water ; e, white plate from which the light is reflected through the chamber; /, screw by which the frame containing the colored glass is moved ; g, capillary tube to collect the blood ; h, pipet for adding the water ; i, opening through which may be seen the scale indicating percentage of hemoglobin. may be ascertained by reading the scale at i. This instrument should be used in a dark room. Oxy hemoglobin. It is this substance which gives to arterial blood the scarlet color which is so characteristic of it ; here, how- ever, it occurs, not by itself, but together with hemoglobin (re- duced hemoglobin) and in excess of the latter. In venous blood the two also coexist, but the hemoglobin is in excess, while in the blood of asphyxia the coloring-matter is almost entirely hemoglobin. 280 THE BLOOD. The hemoglobin of some animals, as the guinea-pig, cat, and dog, crystallizes very readily, while that of man, and the mammal? generally, forms crystals with more difficulty. To obtain crystals of oxyhemoglobin, the blood should be mixed in a test-tube with one- sixteenth its volume of ether and the tube shaken with consid- erable force. The coloring-matter passes into the plasma, and the blood becomes lakey. If the tube is then placed on ice, in a short time the crystals will form and can be examined under the micro- scope. The form of the crys- tals varies in different animals (Fig. 1 50). In the guinea-pig, the blood of which is easily obtained, and whose oxyhe- moglobin crystallizes readily, they are rhombic tetrahedra. Derivatives of Hemoglobin. Besides oxyhemoglobin, the properties of which have al- w 1 ^ % ready been given, there are jP \jfyl - 0y various derivatives of hemo- MJi/ A^^^^ * globin ; among them are the ^^^| ^Br^ ^^^1^^ following : T^E^^c Carbon-monoxid Hemoglo- ^^^-^^ bin. As one molecule of ^5^ A hemoglobin combined with /j^ one of oxygen forms oxyhem- f oglobin, so one molecule of hemoglobin united with one of carbon monoxid forms Carbon-monoxid hemoglobin. There is, however, one strik- ing difference in the two com- binations. In the former the oxygen is readily displaceable, while in the latter the com- pound is a very stable one, although Gamgee has shown that by the long-continued passage of neutral gases through solu- tions of CO-hemoglobin the CO is gradually driven out, and reduced hemoglobin is obtained. Carbon monoxid is the gas formed when combustion is incomplete, such as is produced by the charcoal fur- nace used in France for suicidal purposes ; the charcoal fumes when inhaled in sufficient quantity produce fatal results. It is also a con- stituent of illuminating-gas, where it exists in proportions ranging from 7.9 to 28.25 per cent., and is not infrequently the cause of death. The gas displaces the oxygen and unites so firmly with the hemoglobin that even with artificial respiration it cannot be dis- FIG. 150. Crystallized hemoglobin: a, b, crystals from venous blood of man ; c, from the blood of a cat ; rf, from the blood of a guinea-pig ; e, from the blood of a hamster ; /, from the blood of a squirrel (after Frey). MICROSCOPIC STRUCTURE OF THE BLOOD. 281 placed. The color of carbon-monoxid hemoglobin is a cherry red, and the blood in persons poisoned with it has this color. Nitric-oxid Hemoglobin. Nitric oxid will also displace the oxygen from oxyhemoglobin, and the nitric-oxid hemoglobin which results is a more stable compound than carbon-monoxid hemo- globin. It consists of one molecule of hemoglobin and one of nitric oxid. Carbo-hemoglobin. Hemoglobin will also unite with carbon dioxid, and it has been demonstrated that each gas acts with refer- ence to hemoglobin independently of the others i. e., that even when a solution of hemoglobin is nearly saturated with oxygen, it can still take up as much carbon dioxid as when no oxygen is present. It has been suggested that the explanation of this is that the oxygen unites with the portion which gives the color, hemochro- mogen, and the CO 2 with the proteid portion. Methemoglobin. This is regarded as being chemically the same as oxyhemoglobin, except that the union of the hemoglobin and oxygen is more stable. Oxyhemoglobin may be converted into methemoglobin by the action of many substances, among which may be mentioned potassium ferricyanid, nitrites, potassium permanganate, etc. It has been demonstrated that when this con- version takes place the whole of its oxygen passes into such inti- mate relationship with the hemoglobin that it cannot be displaced by carbon monoxid. Methemoglobin also crystallizes, the form of the crystals being the same as that of oxyhemoglobin. Methemo- globin is the form in which the blood-coloring matter exists when blood has been for a considerable time exposed to the air. Jt is also known as reduced hematin. Hematin. Various formulae have been given to represent this substance. That of Hoppe-Seyler is C^H^^FeOg. When oxy- hemoglobin is decomposed by acids or alkalies in the presence of oxygen hematin results. Hemin. This is chemically hematin hydrochlorid, C 34 H^ 5 N 4 - FeO 5 HCl. If to a drop of blood on a glass microscopic slide is added a drop or two of glacial acetic acid and the mixture is boiled, after evaporation there will be found, if examined by the micro- scope, brownish prismatic crystals of hemin. These were discovered 'by Teichmann, and are also known by his name (Fig. 151). These crystals are so characteristic that this method of producing them is very much used to determine whether colored spots or stains are blood or not. The explanation of the changes which take place is as follows : The hemoglobin is decomposed by the action of the acetic acid into hematin and a proteid ; and at the same time the sodium chlorid is decomposed, and the hydrochloric acid which is set free unites with the hematin. If this test is used in the case of old blood-stains, from which the sodium chlorid may 282 THE BLOOD. have been washed out, it is necessary to add a small crystal of the salt to the acid before boiling. Hemochromoyen. This is also called reduced hematin, and re- sults when hemoglobin is decomposed by alkalies, or acids, in the absence of all oxygen. Its crystallizability has not been demon- strated. Gamgee questions whether hemochromogen exists pre- formed in hemoglobin and its compounds. Hematoporphyrin. If to hematin strong sulphuric acid is added, the iron is dissolved out, making ferrous sulphate, and hematoporphyrin or iron-free hematin re- mains. It is regarded by some as iso- meric with bilirubin. The formula as given by Hoppe-Seyler is C 34 H 3 gN 4 O 6 . It has in acidulated alcoholic solutions a pur- ple color, assuming a bluish-violet tint when made strongly acid; but alkaline solutions \are red. Solutions of this substance " ex- ^g^gg-J 8 * 8 *' hibit a magnificent fluorescence " (Gamgee). It is found in small amount in normal urine, FIG. 151. Hemiu, or and in large quantity in chronic poisoning Teichmann's crystals, from f rom t ] ie uge Q f gulphonal. blood-stains on a cloth TT . . -,. TIT iij i (Huber). Hematoiain. In blood-clots, such a^ form in apoplexy, where a blood-vessel of the brain ruptures, a crystalline substance is found, to which Virchow gave the n|ime hematoidin. It is beyond question a deriv- ative of hemoglobin. Its formula is given as C 16 H 18 N 2 O 3 , and it is identical with bilirubin. Histohematins. In the muscles and other tissues of the body coloring-matters are found which are called histohematins, which may be related to hemoglobin, but the relationship has not as yet been established. Spectra of Hemoglobin and its Derivatives. Before discussing the spectra of hemoglobin and its derivatives, it will not be inap- propriate to describe the spectroscope and its application to the differentiation of the coloring-matters of the blood in the varied forms in which we have found them to occur. For a more de- tailed description of spectrum analysis our readers are referred to the many excellent treatises on physics. The wonderful adapta-* bility of spectrum analysis to the solution of many physiologic problems may be illustrated by the statement that by its means 31700000 f a milligram of sodium can be detected, and a corre- sponding delicacy of analysis is true of other substances ; thus the rapid absorption and diffusion of certain substances have been de- termined by the spectroscope. Roscoe, in his Spectrum Analysis, states that twenty-four minutes after injecting 3 grains of lithium salt under the skin of a guinea-pig the lithium is found to be present in the crystalline lens and every part of the body, it only B C 1. Solar spectrum with Fraunlibfer lines. 2. Absorption spectrum of a concentrated solution of oxyhemo- globin ; all the light is absorbed except in the red and orange. 3. Absorption spectrum of a less concentrated solution of oxyhemoglobin. 4. Absorption spectrum of a dilute solution of oxyhemoglobin, showing the two characteristic'bands. 5. Absorption spectrum of a very dilute solution of oxyhemoglobin, showing only the a-band. 6. Absorption spectrum of a dilute solution of reduced hemoglobin, showing the characteristic single band (to be compared with spectrum 4). 7. Absorption spectrum of a dilute solution of carbon-monoxid- hemoglobin (to be compared with spectrum 4). 8. Absorption spectrum of.methemoglobin. 9. Absorption spectrum of acid hematin (alcoholic solution). 10. Absorption spectrum of alkaline hematin (alcoholic solu- tion) (modified from MacMunn, The Spectroscope in Medicine). MICROSCOPIC STRUCTURE OF THE BLOOD. 283 being necessary to burn a portion of the animal tissue in a colorless flame in order to see the bright-red line of lithium : ten minutes after the injection it is found in small quantities in the lens, but plentifully elsewhere ; while four minutes after the injection lithium is not found in the lens, but plentifully in the aqueous humor of the eye, and in the bile. The same rapid diffusion occurs in the human body. The crystalline lenses of per- sons who have been operated upon for cataract have been examined, these persons having previously to the removal of the lens been given by the stomach 20 grains of carbonate of lithium ; in three and a half hours it was detected in each particle of the lens. When a sunbeam passes through a glass prism, the differently FIG. 152. Spectroscope : P, the glass prism ; A, the collimator tube, showing the slit (s) through which the light is admitted ; B, the telescope for observing the spectrum. colored rays which compose it are separated, and if, after emerging from the prism, the beam falls upon a screen, it will appear as a band of different colors, beginning with red and ending with violet; this band is the solar spectrum (Plate 1, Fig. 1). A spectroscope is an instrument for producing and observing spectra (Fig. 152). The beam of light which is to be studied, from what- ever source it may come, passes into the collimator tube A, through the slit s, and its rays, being made parallel by a lens in this tube, are separated or dispersed by the prism p ; the spectrum which results may then be examined by an observer through the telescope B. If the source of the light is an incandescent body, the spec- trum will be a continuous one i. e., there will be nothing but a band of colors, in which the red passes on to violet through 284 THE BLOOD. orange, yellow, green, blue, and indigo ; but if it is the sun which is the source of light, though this is an incandescent body, still its light passes through an atmosphere which absorbs certain portions of the light, and the spectrum is, therefore, crossed by dark lines, Fraunhofer lines. These lines are fixed, and the more distinct ones are designated by letters of the alphabet; thus in the red are A, B, and C ; in the yellow D, etc. As the atmosphere of the sun absorbs certain parts of the light which is transmitted through it, so do many transparent substances, and the spectra of such substances are known as absorbent spectra, in contradistinction to continuous spectra, in which no lines or bands appear. If, there- fore, the light of the sun or that from any other source of illumi- FIG. 153. The hematinometer. FIG. 154. The hematoscope. nation is passed through a solution of one of these substances, in its spectrum dark bands will be seen at definite places and in definite numbers, and the identity of such substances can thus be determined. The positions occupied by these bands may be designated either by stating their relation to the Fraunhofer lines, or the wave-length of the portions of the spectrum between which absorption takes place, this being determined by a scale which is provided for this purpose. For the description of the spectra of hemoglobin and its derivatives, and the use of the spectroscope in their differentiation, we are especially indebted to the section on " Hemoglobin," by Gamgee, in Schiifer's Physiology. MICROSCOPIC STRUCTURE OF THE BLOOD. 285 For studying the visible spectrum of hemoglobin, Gamgee recommends a spectroscope of the ordinary Bunsen type, provided with a single good flint-gfass prism, or direct vision spectroscopes of the Browning or Hofmann patterns. If minute quantities of coloring-matter are to be 'investigated, microspectroscopes may be used i. e., direct vision spectroscopes adapted to the eye-piece of a compound microscope. As the source of light, he recommends a gas lamp, furnished with the Auer incandescent burner. It is convenient to have the solutions, whose absorption-spectra are to be examined, in cells with perfectly parallel sides, and a defi- nite width apart ; such an apparatus is the hematinometer (Fig. 153). The hematoscope or hemoscope of Hermann (Fig. 154) is also used for this purpose. In this apparatus the thickness of a layer of fluid can be regulated by sliding c toward F, and measured by a scale on c. F and c are glass plates through which and the intervening fluid light is transmitted for spectroscopic examina- tion. Spectrum of Oxyhemoglobin (Fig. 155). Dilute solutions of 70 65 6O 55 50 4-5 I 1 1 1 ll 1 BCD E b F G FIG. 155. Diagrammatic representation of the absorption -spectrum of oxyhemo- globin. The numerals give the wave-lengths in hundred-thousandths of a milli- meter; the letters show the positions of the more prominent Fraunhofer lines of the solar spectrum. The red end of the spectrum is to the left. The a-band is to the right of D, the /3-band to the left of K (after Eollett). oxyhemoglobin give two absorption-bands between D and E. The band nearer D i. e., the red end of the spectrum is known as the " a-band "; the one near E is the " /3-band," and is broader, lighter, and less clearly defined than the a-band. The center of the a-band corresponds to a wave-length of 579 millionths of a milli- meter (/I 579) ; while the center of the /3-band corresponds to A 553.8. Spectrum of Hemoglobin (Reduced Hemoglobin) (Fig. 156). Oxyhemoglobin may be reduced to hemoglobin by adding to its solutions Stokes' reagent, which is made by dissolving 2 parts by weight of ferrous sulphate, adding 3 parts of tartaric acid, and then adding ammonia until the reaction is distinctly alkaline. When thus reduced the a- and /9-bands disappear, and the " /-band ' appears ; this is a single band between D and E, its darkest part being nearer D than E, and corresponding to about I 550. If the solution is shaken with air, the appearance of the - and /9-bands shows that oxyhemoglobin has been formed. 286 THE BLOOD. Carbon-monoxid Hemoglobin. This derivative of hemoglobin presents two bands resembling those of oxyhemoglobin, except that they are nearer the violet end of the spectrum. Methemoglobin and hematin have each a characteristic spec- trum. Development of Red Corpuscles. This is described by Schafer as taking place in the following manner : In the developing embryo some cells of the mesoblast become united, forming a protoplasmic network. These cells are nucleated, and their nuclei multiply, colored protoplasm forming an aggregation around them. The protoplasm of this network is hollowed out by an accumulation of fluid ; in this manner the capillary blood-vessels are formed. The nuclei with their colored protoplasm are set free, becoming embryonic blood-corpuscles. The blood-corpuscles are at this period, therefore, nucleated cells. The corpuscles at this time have a diameter of from 10 /jt to 16 /JL, and are spherical. They possess the power of ameboid movement, and thus resemble 70 65 60 55 E b FIG. 156. Diagrammatic representation of the absorption-spectrum of hemo- globin (reduced hemoglobin). The numerals give the wave-lengths in hundred- thousandths of a millimeter; the letters show the positions of the more prominent Fraunhofer lines of the solar spectrum. The red end of the spectrum is to the left. The single diffuse absorption-band lies between D and E (after Rollett). the white corpuscles. It has been suggested that these should be called blood-cells rather than blood-corpuscles. The liver begins to be formed about the third week of em- bryonic life, and about the third month occupies most of the abdominal cavity. This organ, together with the spleen, thymus, and lymphatic glands, also produces blood-cells which are nucle- ated, are at first colorless, and afterward acquire the characteristic color. At a later period of embryonic life, about the second month, non-nucleated disk-shaped corpuscles make their appearance. These originate to some extent in connective-tissue cells, a portion of the cell becoming colored, and separate into globular particles, which subsequently become the discoid corpuscles. The connec- tive-tissue cells afterward become hollowed out, and, joining with other cells which have gone through the same process, blood- vessels are formed. This later embryonic formation of blood- corpuscles does not involve 'the cell-nuclei, as does that of the earlier period. The nucleated cells are replaced by the non- MICROSCOPIC STRUCTURE OF THE BLOOD. 287 nucleated about the end of the fourth month, but it is still a moot question whether any of the nucleated cells are actually concerned in the formation of the non-nucleated. Non-nucleated blood-corpuscles are also formed in the medulla or marrow of bones, and in the spleen. In the red marrow of bones are found nucleated cells possessing the power of ameboid movement, the true "marrow-cells" of Kolliker. In the proto- plasm of these cells hemoglobin is formed, and this portion of the protoplasm becomes converted into the non-nucleated corpuscle. There are, besides these marrow-cells, others of smaller size, erythroblasts, likewise ameboid, nucleated, and colorless, which later undergo karyokinesis ; the daughter-cells become colored, lose their nuclei, and are converted into the mature non-nucleated red blood-corpuscles. It is to the red marrow that is to be principally attributed the formation of the red corpuscles in adult life. This process is called hematopoiesis, and is a constant process, new corpuscles taking the place of the old which have outlived their usefulness. It occurs to a much greater extent than usual after hemorrhages. In the spleen are to be found cells somewhat resembling the erythroblasts just described, and it is the opinion of some authori- ties that these are also sources of the red blood-corpuscles. Destruction of Red Corpuscles. The duration of a red blood- corpuscle is undetermined, but it is doubtless limited. Some authorities place its life at from three to four weeks. Old corpus- cles constantly undergo disintegration and new ones appear. The fact that fewer corpuscles are found in the blood of the hepatic than in that of the portal vein, and the additional fact that biliary pigment is formed from the coloring-matter of the blood, indicate that in the liver a part, at least, of these destructive changes takes place. The spleen is also regarded by some authorities as being an organ in which red corpuscles are destroyed. The argument advanced in favor of this theory is that some of the susten- tacular or supporting cells of the splenic pulp contain colored granules which resemble the hematin of the blood ; in others red corpuscles are found in various stages of disintegration. The explanation is that these large cells are engaged in the process of destroying used-up corpuscles. Opposed to this theory is the fact that the blood coming from the spleen contains no hemoglobin in solution, which it certainly would do if red corpuscles were destroyed in that organ ; besides, after removal of the spleen the destruction of corpuscles apparently goes on much the same as before. There seems to have been an idea in the minds of some that it w r as essential that some organ or organs should be charged with the duty of destroying the red corpuscles. This does not, how- 288 THE BLOOD. ever, follow. There is no reason why many of the corpuscles may not undergo, disintegration in any part of the circulatory system, wherever they happen to be at the time the change takes place. The large extent of blood-vessels in the liver would account for the destruction that takes place there, without regard to any special function of this organ connected with such destruc- tion. If, as there is reason to believe, the pigment of the bile and the urine are formed from that of the blood, the number of corpus- cles daily destroyed must be very great. Function of Red Corpuscles. The red corpuscles are the carriers of oxygen from the lungs, where it is received, to the tissues, which appropriate it. This function is due to the hemo- globin, which has a great affinity for oxygen. Diapedesis. In inflammatory conditions the red corpuscles pass through the walls of the capillaries, constituting diapedesis (p. 290). This is not an active process, as in the case of the leukocytes, but a passive one ; for while the latter can make their way through uninjured walls, it is only after these have thus migrated that through the same opening the red corpuscles can pass. Colorless Blood-corpuscles. These are also called white cor- puscles and leukocytes. They consist of granular protoplasm, and contain one nucleus or more. When in a condition of rest they are spheroidal in shape, with a diameter of about 10 /^, and possess the power of ameboid movement ; their shape is constantly changing. The number of leukocytes in the blood is commonly said to be, compared with the red corpuscles, as 1 to 350 or 1 to 750, or, as others state it, about 10,000 in a cubic millimeter of blood ; but these figures are of very little value, so greatly do the propor- tions vary under different conditions. Thus Hirst found before breakfast, 1 to 1800; one hour after, 1 to 700; before dinner, 1 to 1500; after dinner (1 o'clock), 1 to 400 ; two hours later, 1 to 1475; after supper (8 o'clock), 1 to 550; 12 p. M., 1 to 1200. After eating the number is much increased. This increase also occurs after the loss of blood, during suppurative processes, and after the use of bitter tonics ; while in a state of hunger or defi- cient nourishment the number is diminished. The proportion also varies in different parts of the circulatory system ; thus in the splenic vein it has been found to be as 1 to 60 ; in the splenic artery, 1 to 2260 ; hepatic vein, 1 to 170 ; and portal vein, 1 to 740. Leukocytosis is defined as a temporary increase in the number of leukocytes in the blood. It occurs normally during digestion and in pregnancy, and is seen as a pathologic condition in inflam- mation, traumatic anemia, various fevers, etc. Leukocythemia or leukemia, on the other hand, is a fatal disease with marked MICROSCOPIC STRUCTURE OF THE BLOOD. 289 increase in the number of leukocytes in the blood, together with enlargement and proliferation of the lymphoid tissue of the spleen, lymphatic glands, and bone-marrow. The disease is distinguished as lymphatic, splenic, lymphaticosplenic, medullary or myelogenic, and lienomyelogenous, according as the disease involves the lymphatics, the spleen, both the spleen and the lymphatics, the bone-marrow, or both the spleen and bone-marrow. It may be due to disorder of the intestines (intestinal leukemia}, of the liver (hepatic leukemia), or to disease of the tonsils (amygdaline leukemia) Dorland's Medical Dictionary. If peptones or leech extract are injected into the blood-vessels, there is at first a diminution in the number of the leukocytes, especially the poly nuclear variety ; this is termed the leukocyto- penic phase ; afterward the number is increased, constituting the leukocytotic phase. Acute local inflammation causes similar changes as do these injections, but the diminution in the number of leukocytes in this case largely affects the coarsely granular variety, while the after- increase is found mainly in the finely granular corpuscles (Schafer). It has been observed that the blood clots more readily when the coarsely granular cells are relatively few in number, and Schafer thinks this may explain the more ready clotting of blood in in- flammatory conditions. Varieties of Colorless Corpuscles. Ehrlich classifies the color- less cells according to the kind of anilin stain which the majority of the contained granules take ; thus cells whose granules are stained by basic dyes, as methylene-blue, he terms basophil ; while those whose granules are stained by acid dyes, such as eosin, he calls oxyphil or eosinophil. These terms are also written basophile, oxyphile, and eosinophile. Still another classification divides the colorless corpuscles into (1) lymphocytes, which are characterized by being small, having a round vesicular nucleus, and named from their resemblance to the leukocytes of lymph-glands, but not possessing ameboid movement; (2) mononuclear leukocytes, cells with a single nucleus ; and (3) polymorphous or polynucleated leukocytes, characterized by having more than one nucleus or else a divided nucleus, the divisions being connected by protoplasm. Nos. 2 and 3 possess ameboid movement. It is believed by some authorities (Howell) that these varieties are simply different stages in the development of a single type of cell, the lymphocytes being the youngest and the polynu- cleated leukocytes the oldest. The granules of the mononuclear variety are coarser and stain more deeply with eosin than do those of the polynuclear, but constitute only about 5 per cent, of the total colorless corpuscles ; while the basophil cells are not often found. Still another variety, called hyalin, is described ; these have no granules. It should be borne in mind that it is the kind 19 290 THE BLOOD. of dye which the protoplasm takes which determines the variety of the corpuscles ; the nuclei of all the leukocytes is basophil. Composition of Leukocytes. The chemical composition of leukocytes is given (Lilienfeld) as follows : Water . . I . 88.51 Solids 11-49 The solids are : Proteid 1.76 Nuclein 68.78 Histon (i. e., proteid part of the nucleoproteid ) 8.67 100.00 Lecithin 7 51 Fat 4.02 Cholesterin 4.40 Glycogen . 0.80 This analysis of the cells is of those from the thymus, but we are justified in concluding that the colorless corpuscles of the blood which originate from lymphoid structures have a similar composition. It is, however, impossible to investigate the color- less blood-corpuscles by macrochemical methods. Micro-chem- ically they can be shown to contain fat and glycogen (Halli- burton). Functions of the Colorless Corpuscles. The movements which occur in protoplasm, known as ameboid movements, have been already described (p. 24). This power is possessed by the leuko- cytes, by virtue of which they pass through the walls of the capil- lary blood-vessels, this power being diapedesis or migration. There is no doubt that this occurs normally to a certain extent, but to a much greater extent under abnormal conditions, as in in- flammations. When these migrated leukocytes accumulate out- side the blood-vessels, and have lost their vitality, they consti- tute pus. Phagocytosis. Metschnikoff has advanced the theory that one of the important functions of the leukocytes is to ingest and digest bacteria ; this constitutes phagocytosis. In this process the polynucleated cells are the most active. There is no doubt that by virtue of their ameboid movement the leukocytes do surround and take into their protoplasm foreign matter, and if bacteria are present they are likewise ingested, but whether they are thus taken in while in a living state and destroyed, or only after their vitality has left them, is a question. Those who favor the theory look upon the leukocytes as the protectors of the human race against the incursions of infectious diseases, if their vitality is sufficient to overcome and destroy the bacteria of these diseases ; whereas if the bacteria are the more powerful, then the disease obtains a foothold. A person is said to be immune when on ex- posure to a communicable disease, such as scarlet fever, measles, etc., he does not contract it, and the explanations which have been MICROSCOPIC STRUCTURE OF THE BLOOD. 291 given to account for this immunity are many and various. One of these is the " phagocytosis theory of Metschnikoff " : That " immunity against infection is essentially a matter between the invading bacteria on the one hand and the leukocytes of the tissues on the other ; that during the first attack of the disease the white blood-corpuscles gain a tolerance to the poisons of the bacteria, and so are able to resist the next incursion of the enemy." At the present time, however, the theory of immunity which is most gen- erally accepted is that known as " the lateral-chain theory " of Ehrlich, for the explanation of which the reader is referred to text- books on Pathology. The phagocytotic power of the leukocytes is also manifested in their destruction of the products of inflammation. It is believed that the colorless corpuscles are concerned in the process of coagulation of the blood (p. 294). For the consideration of other properties of the leukocytes, the reader is referred to pages 24, 25, 293, and 300. Development of Colorless Corpuscles. The first leukocytes are formed from the embryonic cells of the mesoblast, and afterward from lymphatic glands and lymphatic tissues generally. They pass into the lymphatics and thence into the blood-vessels. Plaques. These are also known as blood-plates, blood-platelet^^ and hematoblasts. They are circular or elliptical in shape, and smaller than the red corpuscles, but vary very much in size, from 0.5 p. to 5.5 fly and are colorless. Their number is said to vary from 180,000 to more than 600,000. Various theories have been propounded to explain their occur- rence in blood. One of these is that they are not formed struct- ures, but simply precipitates of nucleoproteid from the plasma. This theory is, we think, no longer held. There is little doubt that they are formed elements existing normally in the blood, although the theory of Hayem, who discovered them, that red corpuscles are formed from them, is no longer maintained. Lilienfeld has obtained from them a nucleo-albumin, called by him nucleohiston, which is also found in the nuclei of the leuko- cytes, and it is believed by many that the blood-plates are nothing more than the nuclei of the polynucleated colorless corpuscles, which are set free when these corpuscles disintegrate, and that these plates also disintegrate, and are dissolved in the plasma. Their possible relation to the coagulation of the blood is discussed in connection with that subject (p. 294). Blood-plasma. The plasma or liquor sanguinis is yellowish in color and alkaline in reaction, having a specific gravity of 1027 to 1031. It contains the following ingredients : Water, inorganic salts, extractives, enzymes, proteids, and gases. Water and Inorganic Salts. Water exists in plasma to the approximate amount of 90 per cent., so that 10 per cent, consists of solids. Of these solids, about 0.85 per cent, are inorganic 292 THE BLOOD salts ; and of these, sodium chlorid is the most abundant, being present to the amount of 0.55 per cent. Sodium carbonate is present to the amount of 0.15 per cent. ; and this salt is the principal cause of the alkalinity of the plasma, and gives it its power to absorb carbon dioxid. The salts of the plasma have not been exactly determined, but, according to Schmidt, the following table gives those that probably occur, with their percentages : Potassium sulphate 0.0281 Potassium chlorid 0.0359 Sodium chlorid 0.5546 Sodium phosphate 0.0271 Sodium carbonate 0.1532 Calcium phosphate 0298 Magnesium phosphate 0.0218 Calcium chlorid is probably also present, and traces of a fluorid have likewise been found. Extractives. These include carbohydrates, of which there are three : Glyc6gen, probably derived from the leukocytes ; an animal gum; and dextrose. This last, we have seen, is always present in human blood to the amount of about 0.12 per cent., being much more abundant in portal blood during the digestion of carbohydrates. Fat is also a constituent of the plasma, the amount being increased by its absorption after a meal containing it. Lecithin, cholesterin, lipochrome (which gives the plasma its yellow color), urea, uric acid, kreatin, kreatinin, and occasionally hippuric acid are also present. Enzymes. Plasma contains at least five enzymes : (1) An amyl- olytic, which is, according to some authorities, produced by the red cells, while others attribute it to the leukocytes ; (2) a glycolytic, causing a destruction of some of the dextrose in the blood. Al- though the existence of this enzyme is denied, there is strong evi- dence in favor of its existence. According to Spitzer, it exists in both red and white blood-cells and, indeed, in all tissue-cells. It acts only in the presence of oxygen ; (3) a lipolytic, called lipase; (4) a coagulating thrombin or prothrombin, which causes coagula- tion of the blood under some circumstances (p. 293) ; (5) a proteolytic. The destruction of the exudate of pneumonia is attributed to this enzyme. Proteids. These are : (1) Serum-albumins, a, ft, and y (p. 108) ; (2) serum-globulin or paraglobulin (p. 110); (3) fibrinogen (p. 110); (4) nucleoproteid. The total proteids in human plasma are 7.62 per cent., of which 3.10 per cent, are globulins, and 4.52 per cent, albumins. The proteids of the plasma have been already discussed in dealing with this class of physiologic ingredients (p. 126), but one of them, fibrinogen, deserves special notice at this time because of its relation to the process of blood-coagulation. MICROSCOPIC STRUCTURE OF THE BLOOD. 293 Fibrinogen. Although it is customary to speak of fibrinogen as if it was a simple substance, yet the fact that when it is dis- solved in salt solution and heated to a temperature between 52 C. and 55 C. only a part of the proteid is coagulated, and that when the temperature reaches 65 C. another portion is thrown down, has led Hammarsten to regard it as made up of fibrinogen proper, which coagulates at the lower temperature, and a globulin, fibrin-globulin, which is coagulated at the higher temperature. It is believed that a nucleoproteid is also combined with these two proteids to make up what is commonly termed fibrinogen. Origin of Fibrinogen. Matthews, after a very elaborate study of the subject, reported in the American Journal of Physiology, concludes that the decomposing leukocytes of the blood, and chiefly those of the intestinal area, are the sources of the blood fibrinogen, and supports this opinion : u (l) By the increase in the per cent, of fibrinogen in all cases of prolonged leukocytosis accompanying suppuration ; (2) by the increase in fibrinogen during leukocythemia ; (3) by the increase in fibrinogen in pneu- monia, erysipelas, acute rheumatism, peritonitis, and similar in- flammatory conditions; (4) by the fact that fibriuogen is not simply transformed proteid of the food, as indicated by its con- tinued formation during fasting, and its failure to increase during proteid digestion ; (5) by the observation that neither the spleen, muscles, kidneys, pancreas, nor brain appears to be essential to its formation ; (6) by the well-known fact that there is present in the cell-body of the leukocyte a substance which, by the action of a substance coming from the nucleus or arising in its neighbor- hood, is thrown into a fibrillar form closely resembling fibrin- fibrils, and like them contractile ; (7) by the fact that the leuko- cytes are constantly going to pieces in the body, hence must be adding constantly to the proteid constituents of the blood ; (8) by the close correspondence existing between the fibrinogen-content of the blood and the excretion of uric acid ; and (9) by the fact that the intestine, which is rich in leukocytes, appears to be the chief source of the fibrinogen of the body." In this article Matthews makes the following statement, which is, to say the least, suggestive, although, of course, as yet not demonstrated : " If fibrinogen is derived from the leukocytes, as the preceding considerations indicate, and if Schmidt's and Morner's observations on paraglobulin indicating its origin in the leukocyte prove well founded, the conclusion would seem obvious that the proteids of the blood are derived from the leukocytes. This would strongly confirm Hoifrneister's view that the leukocytes are pre-eminently active in proteid absorption and assimilation. It would lead to the interesting conclusion that the organism lives on its leukocytes much as the egg-cells of some forms live on their follicle-cells. If this were so, it would explain (1) the true 294 THE BLOOD. function of the leukocytes and the elaborate arrangements for their production in the body ; (2) their congregation and great reproduction in the intestinal area during a proteid meal ; (3) the positive chemotaxis they exhibit toward the proteids, albumoses, and other products of digestion ; (4) the maintenance of the pro- teid constituents of the blood during fasting ; (5) the fate of the bodies of the leukocytes w.hen they disintegrate ; (6) the fact that no products of digested proteids are found in the blood during proteid digestion. It would make the leukocyte, in fact, a store- house of the surplus proteid food of the body, just as the liver- cell is a storehouse of surplus carbohydrate food.' 7 Nucleoproteid. In regard to this constituent of plasma, Schafer says that it is doubtful if it exists in the plasma of circulating blood, and that beyond^ the fact of its appearing to be one of the essential factors in the formation of fibrin, very little is known about it. It is regarded as being derived from the leukocytes and plaques at the time the blood is withdrawn from the vessels. A small amount comes from the red corpuscles. The reasons for this belief as given by Schiifer are : 1. White blood-corpuscles and similar cells (lymph-cells, thy- mus-cells, etc.) always contain a considerable amount of nucleo- proteid. 2. In plasma obtained by subsidence of the corpuscles there is most nucleoproteid in the lower layers, which contain most leuko- cytes ; and least in the upper, which contain very few. 3. Fluids which collect in the serous cavities of the body (pericardial fluid, hydrocele fluid, ascitic fluid) frequently contain no leukocytes. When this is the case they are also devoid of nucleoproteid and of the property of spontaneous coagulability, although they contain fibriuogen. Solutions of this nucleoproteid are coagulated at 65 C., and at 60C., if free alkali is present, it is split into nucleiu and a proteid. If soluble salts of lime are present, the nucleoproteid unites with the lime, and the product has the property of converting fibrinogen into fibrin, and is identical with fibrin-ferment or thrombi n ; inasmuch as the nucleo- proteid precedes and becomes changed into thrombin, it is termed prothrombin. Gases. The plasma contains oxygen and nitrogen in solution, and carbon anhydrid both in solution and also in combination as sodium carbonate and bicarbonate. The amount of oxygen in the plasma is very small : in the dog, 0.25 per cent. Coagulation of Blood. When blood is withdrawn from the circulation it undergoes coagulation, consisting in the produc- tion of a clot from which is subsequently expressed a fluid the serum. The length of time required for coagulation varies in the blood of different animals. In human blood the change manifests itself in about two or three minutes. When the blood is withdrawn COAGULATION OF BLOOD. 295 from the vessel it is fluid, but at the end of two or three minutes its fluidity is so much diminished that it will not flow ; this consis- tency increases until at the end of eight or ten minutes the entire quantity of blood becomes a mass resembling currant-jelly in color and consistency. This jelly-like mass becomes more and more consistent, squeezing out upon its surface a few drops of a straw- colored fluid the serum. As the shrinking of this gelatinous mass the dot continues, it separates from the sides of the vessel in which the blood was received, and the serum is squeezed out on all sides, until at length there is a more or less solid clot floating in a considerable quantity of serum. The entire process requires from ten to forty-eight hours. When examined, the clot is found to be made up of fibrin and corpuscles, the red corpuscles giving to it the red color. The white corpuscles may at first be entangled in the meshes of the fibrin, but by virtue of their ameboid move- ment they soon escape into the serum. The serum has the same composition as the plasma minus the fibrinogen. Although the corpuscles are denser than the plasma, still the difference is so slight and the process of coagulation so rapid that before they can settle they are entangled in the meshes of the fibrin as it forms, and thus become a part of the clot. If any- thing occurs to delay coagulation, the corpuscles settle, and the clot is then less red and more yellowish. This delay may be brought about by the addition of a 27 per cent, solution of magnesium sulphate or other neutral salt, the plasma being then termed salted plasma ; it occurs also in inflammatory processes, and hence in the olden time, when venesection or '"bleeding" was commonly practised, this crusta phlogistica, or " bufly coat," was always looked for by the physician, and when it formed was considered as evidence that the bleeding was justifiable. That the physicians of that period were not always right in this judgment is now known, for a bufly coat will form in blood which is hydremic, a condition in which bleeding is contraindicated. In horses' blood, which normally coagulates very slowly, this " bufly coat " always forms. It is simply the fibrin without the corpuscles, or at least without enough of them to give the red color which the clot usually possesses. Influences which Retard Coagulation. Coagulation is retarded by cold, by solutions of sodium or magnesium sulphate, by a diminished amount of oxygen, by an increased amount of carbon dioxid, by acids or alkalies, by egg-albumin, by oil, by a solution of albumose, and by extract of the head of the leech. It is well known that the blood drawn from the vessels by this animal does not coagulate within its body. It is supposed that its saliva contains an albumose which prevents clotting of the blood. Solutions of potassium or sodium oxalate also prevent coagulation. The explanation of this action is that the calcium which is required for the process is precipitated as calcium oxalate. Venous blood 296 THE BLOOD. coagulates more slowly than arterial, because of the lessened amount of oxygen and the increased amount of carbon dioxid. It is said that blood from the capillaries does not coagulate at all. It is the prevalent opinion that menstrual blood does not clot ; this, strictly speaking, is not true. If the blood was collected as it comes from the uterine vessels, it would doubtless coagulate as does other blood ; but when it is mixed with the acid vaginal mucus its coagulation is then impeded. Then, too, during the menstrual period some of the blood undergoes clotting within the uterine cavity or in the vagina : that which escapes and which is regarded as menstrual blood is for the most part only serum, which, of course, does not coagulate. Influences which Hasten Coagulation. Heat hastens coagulation, as does agitation of the blood, as in whipping it with twigs or rods. In general, anything which tends to break down the leukocytes or plaques from which the nucleoproteid prothrombin is derived will cause the latter to be set free and favor coagulation. Causes of Coagulation. Perhaps no physiologic question has excited more controversy than that which deals with the cause of blood-coagulation. Normally, blood remains fluid within the blood-vessels, but within a few minutes after withdrawal it begins to undergo coagulation. What is the explanation ? It has been suggested that blood-coagulation is due to exposure to the air. It is true that contact with the air hastens coagula- tion, but that this is unnecessary to the process is shown by the fact that coagulation will take place under mercury when all air is excluded. Nor can it be due to the cooling the blood undergoes when it is exposed to the air, for, as already noted, cold retards coagulation, while heat aids it. It has also been suggested that the fluid condition of the blood in the circulation is due to its motion, and that it clots when it comes to a state of rest. But experiment shows that motion, such as the beating of blood with wires, hastens coagulation. Experiments demonstrate that the fluidity of the blood is main- tained only when the blood is in contact with the normal lining membrane of the blood-vessels : when this relation is interrupted, either by disease, or by death or injury of the membrane, or by withdrawal of the blood from the vessel, the fluidity ceases and the blood coagulates. The property of coagulation possessed by blood is of great service in arresting hemorrhage. There are individuals in whom bleeding, which in most people would be only slight, amounts to a dangerous hemorrhage, often requiring surgical skill for its arrest, and in some instances being so uncontrollable, even by the most skilful treatment, that death results. Such persons are called bleeders, and on them surgeons hesitate to perform any opera- tion, however trivial, the extraction of a tooth even being often COAGULATION OF BLOOD. 297 followed by an alarming loss of blood. This condition is spoken of as hemophilia or hemorrhagic diathesis. It is probable that in such cases the fibrinogen is very deficient. Theories of Blood-coagulation. From the many theories which have from time to time been advanced to explain this process, we shall select a few, each of which, although perhaps not now held in its entirety, still has elements in it which, combined with those of other theories, enter into the opinions held by the best authorities in regard to this as yet unsolved problem. All explanations have as their basis the production of insoluble fibrin from soluble fibrinogen, but as to how this change comes about, or the agencies which cause it, there is great disagreement. Theory of Schmidt. The proteid now known as paraglobulin Schmidt termed fibrinoplastin, and in his theory this substance, under the influence of fibrin-ferment, which he later called thrombin, enters into combination with fibrinogen, the result being fibrin. This ferment was obtained by adding alcohol to blood-serum, and extracting it from the precipitate by water; it was destroyed by a temperature of 65 C., and had the power of coagulating a considerable amount of fibrinogen ; it resembled, therefore, the ferments or enzymes, and was considered by Schmidt to belong to that class. He later considered that fibrinogen was derived from paraglobulin. Theory of Hammarsten. This experimenter demonstrated that paraglobulin takes no part in the process of coagulation, so that at the present time it does not enter as a factor into any of the theories of blood-coagulation. In Hammarsten's theory there are but two factors : fibrinogen and fibrin-ferment. The action of the ferment splits the fibrinogen into fibrin, which is insoluble, and fibrin-globulin, which remains in solution. Schmidt, Hammarsten, Freund, Page's, and others have shown that salts of calcium play a very important part in the coagulation process. Theory of Pekelharing. This theory supposes that the fibrin- ferment of Schmidt is composed of nucleo-albumin and calcium, and that the calcium leaves the nucleoproteid and unites with fibrinogen, the compound of the two being fibrin. The nucleo- albumin comes from the leukocytes and plaques, but does not exist in normal blood. As soon, however, as blood is shed, these cells disintegrate, with the result of setting free the nucleoproteid. As has already been stated, analyses show the same amount of lime in fibrinogen as in fibrin, so that this theory cannot be sustained. Theory of Lilienfeld. The originator of this theory attributes to the nucleoproteid the power of splitting the fibrinogen into a globulin and thrombosin, which latter unites with lime to form fibrin. He regards this power as due to the nucleic acid, and 298 THE BLOOD. states that acetic or any other weak acid will effect the same change in fibrinogen. This theory has also its weak points, and there is great doubt whether the clot is fibrin in any true sense of the term. Perhaps we can in no better way present to our readers the present status of this subject, which is at best unsatisfactory, than by giving the views of Schafer in his Text-book of Physi- ology. The evidence seems fairly conclusive that three factors are essential to bring about coagulation of the blood. These are fibrinogen, the nucleoproteid prothrombin, and soluble lime salts, the two latter acting in combination, and forming Schmidt's fibrin- ferment or thrombin. In the normal blood-vessels the prothrom- bin and lime have not entered into the necessary combination or interaction which enables them to act as a ferment upon the fibrinogen. This nucleoproteid prothrombin cannot by itself act as a ferment, but must be exposed to the acting soluble lime salts ; it does not follow, however, that the thrombin is a compound of the nucleoproteid and lime ; nor is there any certainty as to just what the interaction is. The prothrombin doubtless comes from the leukocytes and plaques ; but it is not necessary to suppose that they always undergo disintegration to produce it. It is also probable that the red corpuscles may contribute to this production of nucleoproteids, for they contain them, and the same is also true of the epithelial cells of the blood-vessels, which are doubt- less composed of living protoplasm. Schafer, in his text-book, sums up the evidence as to coagulation as follows : 1. That the coagulation of blood i. e., the transformation of fibrinogen into fibrin requires for its consummation the inter- action of a nucleoproteid (prothrombin) and soluble lime salts, and the consequent production of a ferment (thrombin). 2. That either nucleoproteid is not present in appreciable amount in the plasma of circulating blood, or that the interaction in question is prevented from occurring within the blood-vessels by some means at present not understood. 3. That the nucleoproteid (prothrombin) appears and the inter- action occurs as soon as the blood is drawn and is allowed to come into contact with a foreign surface, the source of the nucleoproteid being in all probability mainly the leukocytes (and blood-platelets). 4. That under certain circumstances and conditions either the nucleoproteid does not appear in the plasma of drawn blood or it appears, but the interaction between it and lime salts is prevented or delayed. 5. That the nucleoproteid (prothrombin) appears in the plasma of circulating blood under certain conditions, being in all probabil- ity shed out from the white corpuscles and blood-platelets, or in some cases even from the red corpuscles ; and that when shed out under these conditions from the corpuscles, or when artificially injected into the vessels,, it tends at once to interact with the lime REGENERATION OF BLOOD. 299 salts of the plasma and to form fibrin-ferment (thrombin), intra- vascular coagulation being the result. 6. That under other conditions either the shedding out of nucleoproteid from the corpuscles or its interaction with the lime salts of the plasma may be altogether prevented and the blood rendered incoagulable, unless nucleoproteid is artificially added, or unless a modification of the conditions is introduced which will permit of the interaction of the nucleoproteid with lime to form ferment. 7. That the nucleoproteid (prothrombin) is incompetent, in the entire absence of lime salts, to promote the transformation of fibrinogen into fibrin ; but, as a result of its interaction with lime salts, it becomes transformed into a ferment (thrombin), which, under suitable conditions of temperature, and the like, produces fibrin. 8. That either the place of nucleoproteid in coagulation may be taken by certain albumoses, such as those found in snake-venom, and by certain colloidal substances, such as those prepared by Grimaux ; or that such substances may act by setting free nucleo- proteid from the leukocytes and other elements in the blood, or from the cells of blood-vessels, and thus indirectly promote coagu- lation. The colloidal substances referred to in paragraph 8 were three in number, and were artificially prepared by Grimaux, and presented many of the characteristics of proteids. They all gave the xantho- proteic reaction and in other ways resembled the proteid class. Thus when injected into the veins of animals, as the dog, cat, or guinea-pig, they caused intravascular coagulation, resembling in this respect nucleoproteid. It is suggested by Schafer that they produce this effect not directly, but by setting free the nucleo- proteid from the leukocytes, inasmuch as there is no disintegration of the red or white corpuscles, nor any apparent change in the epithelium of the vessels. Regeneration of Blood. One of the striking peculiarities of the blood is the rapidity with which it is renewed after hemor- rhages. The blood constitutes about 7.7 per cent, of the weight of an adult ; and it is estimated that a hemorrhage in which no more than 3 per cent, of the weight is lost will not be fatal, and that the plasma will be renewed in such cases within forty-eight hours, although it may require weeks for a renewal of the red corpuscles. In the treatment of severe hemorrhages it is now the practice to inject into the veins physiologic salt solution (p. 81). The rationale of this is stated by Howell to be that in normal blood the number of red corpuscles is greater than that necessary for a barely sufficient supply of oxygen, and that if after a hemor- rhage the quantity of fluid in the vessels is increased, the circula- tion is made more rapid, and the remaining corpuscles are made 300 THE BLOOD. more effective as oxygen-carriers ; this office is made still more effective by keeping the corpuscles from becoming stagnant in the capillary areas. In proportion as intravenous transfusion of salt solution has come into favor for the treatment of hemorrhages, in a similar proportion has transfusion of blood been abandoned. From what has been said, it will readily be understood that in the withdrawal of blood from the vessels of a lower animal or man the conditions are most favorable for bringing about the destruction of leuko- cytes, and the consequent setting free of the nucleoproteid pro- thrombin. To throw this material into the circulation of a living animal is to invite coagulation within the vessels, a condition which is dangerous in the extreme, inasmuch as clots would be inevitably carried into the smaller arteries of the brain, causing embolism., and producing a fatal result. It has also been demonstrated that the injection of the serum of the blood of some animals into the circulation of others, as that of man into the vascular system of a rabbit, destroys the red corpuscles. This is the globuliddal action of serum. Such a result might follow in the case of blood-transfusion, unless special care was taken to select an animal whose blood did not possess this action upon the blood of the animal on which the operation was to be performed. Hemolysis and Bacteriolysis. The fresh normal serum of the blood of a goat, an ox, a dog, etc., has the power to dissolve the red blood-cells of a rabbit or guinea-pig. This is. described as the normal globuliddal property of serum. Such serum has also the power of dissolving many species of bacteria ; this is its bacte- ricidal property. Buchner attributed both of these to a substance existing in all normal serum, to which he gave the name alexin. In transfusing blood, therefore, in the treatment of hemorrhage, the danger of destroying the red blood-cells exists, in addition to the danger already mentioned. It should be said that Buchner's idea of alexin has been much modified by recent researches ; it has been shown that the action of two substances is necessary to bring about hemolysis : an inter-body and a complement, the latter corre- sponding to Buchner's alexin. This was shown by Ehrlich and Morgenroth, who treated the blood of a guinea-pig with the serum of a dog, the complement existing in the guinea-pig and the inter- body in the dog. These authorities carried their observations still further and found that normal goat serum would dissolve the red cells of both guinea-pigs and rabbits, and that in this serum there were two inter-bodies, one for the red cells of the rabbit and the other for those of the dog, and that there were also two complements. Ehr- lich believes that there are many substances of similar character existing in the normal serum which have a hemolytic action. HEMOLYSIS AND BACTERIOLYSIS. 301 Metchnikoff and Buchner regard the leukocytes as being the source of the complements or alexins, the former considering them as due to the breaking down of the corpuscles, the latter as true secretory products. Other authorities regard the connection between these complements apd the leukocytes as not established. Wasser- man believes the leukocytes to be one source, but not the only one, while Ehrlich and Morgenroth claim that the production of the complements is one of the functions of the liver. Hemagglutinins and Bacterial Agglutinins. The normal serum of the goat possesses also the power of agglutinating the red cells of the human being, the pigeon, and the rabbit i. e., causing them to adhere, forming clumps. The normal serum of a rabbit will agglutinate the bacilli of typhoid fever. This property is due to substances in the serum called agglutinins ; those which agglutin- ate the red cells being distinguished as hemagglutinins. It is believed that there is a separate agglutinin for each species of blood-cells. The hemolysins and the agglutinins are not identical substances, for a serum can retain its agglutinating power after its hemolytic power is lost. Cytotoxins. If an animal is injected with white blood-cells, spermatozoa, etc., substances are produced in its serum which bring about a dissolving action in the cells used for the injection. These substances are termed cytotoxins. Thus, if the leukocytes of a rab- bit are injected into a guinea-pig, the serum of the guinea-pig will dissolve the leukocytes of a rabbit ; in this instance the cytotoxin is called leukotoxim. The action of such serum is believed to be due to interacting substances, as in the case of hemolysis. If sper- matozoa are injected, a cytotoxin is produced, called spermatoxin. Precipitins. If, instead of injecting cells, the dissolved albu- minous bodies of one species of animal are injected into another, there is a precipitation of albumin. Thus, if a rabbit is injected with the serum of a horse, and subsequently the rabbit serum is mixed with that of a horse, the mixture becomes cloudy, owing to the precipitation of the horse's albumin. The substances which produce this precipitation are termed precipitins. A practical application has been made of the knowledge obtained by this research into the nature of precipitins in the identification of blood-stains. For the details of the method the reader is referred to text-books treating of the subject. Ewing states that the reaction does not fail with very old specimens of blood, although it becomes less distinct the older the specimen. Ziemke obtained a cloudiness in three hours from a blood-stain twenty-five years old ; from blood mixed with earth three years old ; from decomposed blood ; and from human blood highly diluted with six other kinds of blood. A solution of iron rust gave no reaction. Uhlenmuth secured positive results with blood of a three months 7 decomposed cadaver. Stern obtained the characteristic reaction in solutions of 1 of serum to 50,000 of blood. Ewing 302 LYMPH. concludes his discussion of the subject, in his Clinical Pathology of the Blood, as follows : " From the foregoing discussion it is evident that full medicolegal requirements for the positive identification of blood-stains may be met, under some conditions, by the biologic test. These conditions are the positive proof by the hemin test that the material is blood, and the occurrence of a flocculent pre- cipitate appearing within one to three hours in the suspected speci- men and in no other of the controls when a potent serum is added in proportion of 1 : 50 of blood. " While these conditions can usually be secured when dealing with fresh blood in considerable quantities, in the writer's opinion and experience the material submitted for medicolegal examination is more apt to be old, scanty, and impure, and the difficulty of securing a fully satisfactory test by this method is thereby greatly increased. With such material one has often to be content with faint turbidities instead of flocculent precipitates, and in such cases it would appear, as Stoenesco maintains, that a guarded opinion be given and the claim made only that the specimen is probably human blood. It should be added that an absolutely faultless technic is required, and that this can be obtained only after considerable experience." LYMPH. Lymph is an alkaline fluid which is derived from the blood, and while, generally speaking, its constituents are the same as those of the plasma, still these differ in amount to a considerable degree ; nor is the lymph obtained from all parts of the body uniform in composition. Chemical Composition of I/ymph. The following anal- ysis is of lymph obtained from a case of fistula of the thoracic duct in man, and is reported by Munk and Rosenstein. In 100 parts of lymph there are : Total solids 3.7 to 5.5 Proteids 3.4 "4.1 Substances soluble in ether 0.046" 0.13 Sugar (dextrose) 0.1 Salts 0.8 "0.9 In another specimen the inorganic constituents were found by Hensler and Danhardt to be : Nad 0.614 Na 2 O 0.057 K 2 O 0.049 CaO 0.013 MgO Fe 2 3 So . traces 0.033 From lymph only 0.1 per cent, of fibrinogen can be obtained, while from plasma the amount obtainable is 0.4 per cent. Besides fibrinogen, paraglobulin and serum-albumin are also present. ORIGIN OF LYMPH. 303 Lymph coagulates more slowly than the blood, and the clot is less firm. Urea is present to a greater amount than in plasma. Histologic Composition of I/ymph. Examined under the microscope lymph is found to contain colorless cells, lympho- cytes, which pass into the blood with the lymph and there become leukocytes (p. 291). Fat-globules are also found, especially after a meal, and in the lymph from the thoracic duct. Origin of I/ymph. While there is no doubt that the source of the lymph is the blood, still there is a difference of opinion as to the manner in which it escapes from the blood-vessels. Theory of Ludwig. Ludwig believed that the pressure of the blood in the capillaries was sufficient to cause the plasma to filter through their walls, thus forming the lymph. He also believed that diffusion played a part in lymph-formation. He expressed his views as follows : " The blood which is contained in the vessels must always tend to equalize its pressure and its chemical con- stitution with those of the extravascular fluids, which are only separated from it by the porous blood-vessel walls. If, for ex- ample, the quantity of blood in the vessels has increased, the mean blood-press.ure is also increased, and at once a portion of the blood is driven out into the tissues by a mere process of filtration. The same result is brought about when the constitution of the blood is altered by the absorption of food or by increased excretion by the kidneys, blood, or skin, or when the composition of the tissue- fluids is altered in consequence of increased metabolic changes taking place in the tissues. In the latter case the changes brought about in the lymph are effected by processes of diffusion." This theory of Ludwig may, therefore, be termed that of filtration and diffusion. Theory of Heidenhain. This experimenter studied the subject of lymph-formation by examining the flow from the thoracic duct. He found that if the thoracic aorta was obstructed, there would follow a fall of arterial blood-pressure below the obstruc- tion, and yet there was no diminution in the flow of lymph in the thoracic duct, and in some cases it was increased. If lymph was formed by filtration from the blood, a diminution of blood-pressure should have been followed by a corresponding lessening of lymph- production. Other experiments demonstrated that the flow of lymph might be increased without correspondingly increasing the blood-pressure. He also found that if commercial peptone and some other substances were injected into the blood-circulation, the amount and concentration of the lymph would be increased, al- though blood -pressure might be reduced ; also that if concentrated solutions of sodium chlorid or sugar were injected, the flow of lymph would be increased and its concentration diminished. If blood-pressure was increased, it was so but slightly. Heidenhain terms substances having the power of increasing the flow of lymph lymphagogues. These experiments demonstrated that the lymph 304 LYMPH. may contain more of injected substances than the blood-plasma, while at the same time there is no increase in blood-pressure. From these experiments Heidenhain formed the opinion that filtration and diffusion cannot explain all the facts connected with the formation of lymph, but that it is to be attributed to a selective power of the endothelial cells of the walls of the capillaries, and that lymphagogues act by stimulating these cells. This subject has been investigated by Starling, who finds many reasons for upholding the theory of Ludwig as against that of Heidenhain. For a full discussion of the subject we must refer our readers to Schafer's Physiology, but it will not be out of place to quote Starling's conclusions. He says : " Thus a renewed investigation of the facts discussed by Heiden- hain has shown that they are not irreconcilable with the filtration hypothesis, but rather serve to support it. At the same time they prove the extreme importance of the factor upon which so much stress was laid by Cohnheim, namely, the nature of the filtering- membrane. In fact, we may say that the formation of lymph and its composition, apart from the changes brought about by diffusion and osmosis between it and the tissues it bathes, depend entirely upon two factors : 1. The permeability of the vessel- wall. 2. The intracapillary blood-pressure. " So far as our experimental data go, we have no sufficient evidence to conclude that the endothelial cells of the capillary walls take any active part in the formation of lymph. It seems rather that the vital activities of these cells are devoted entirely to maintaining their integrity as a filtering-membrane, differing in permeability according to the region of the body in which they may be situated. Any injury, whether from within or without, leads to a failure of this their one function, and therefore to an increased permeability, with the production of an increased flow of a more concentrated lymph. "We have no evidence that the nervous system has any in- fluence on the production of lymph in any part, except an indirect one by altering the capillary pressures in the part through the intermediation of vasoconstrictor or dilator fibers. This action is better marked in situations where the capillaries are normally very permeable or where the permeability has been increased by local injury to the vessels, or by the circulation of poisons in the blood -stream." The lymph-corpuscles enter the lymph as it passes through the lymphatic glands or other lymphoid tissue, such as the tonsils and the thymus gland, and become constituents of the lymph. Office of the Lymph. The lymph after it passes out from the blood-vessels bathes the tissues, and is one of their sources of nutrition, but not the only one, for there is abundant evidence that tissues may receive their nutritive supply directly from the blood and pass into that fluid their waste-products. This muscles will PLATE n. A, aorta, with left vagus and phrenic nerves crossing its transverse arch ; B, root of pulmonary artery ;' C, right ventricle ; D, right auricle ; E, vena cava superior, with right phrenic nerve on its outer border; F,' F, right and left lungs collapsed, and turned outward to show the heart's outline; G, inferior vena cava ; H, celiac axis, dividing into the gastric, splenic, and hepatic arteries (Maclise). THE HEART. 305 do, while at the time no lymph is flowing in the lymphatic vessels of the part. When lymph accumulates, whether in a serous cavity or in the cellular tissue beneath the skin, it constitutes dropsy or edema. The lymph is collected by the lymphatic vessels and ultimately reaches the blood-circulation again (p. 330). CHYLE. The term chyle is applied to that portion of the lymph which comes from the small intestine during the period of digestion. The tissues of this portion of the body are, like all others, bathed in lymph ; but during digestion such products as enter the lacteals change its composition to a considerable extent, and the fat gives to it a milky appearance. The following is an analysis of chyle taken from a fistula of the thoracic duct in man (Paton) : Water 95.34- Proteids 1.37 Fats 2.40 Cholesterin , 0.06 Lecithin . . . , 0.03 Inorganic constituents 0.56 CIRCULATORY SYSTEM. The blood in carrying nutrition to, and in carrying waste products from, the tissues passes through the entire circulatory system, and this constitutes the circulation of the blood. Before studying this process in detail it is essential to have a knowledge of the organs concerned in carrying it on-^i. e., the circulatory organs. These are (1) the heart, (2) the arteries, (3) the capillaries, and (4) the veins. THE HEART. The heart, together with the great blood-vessels at its base, is enclosed in the pericardium, a fibroserous membrane having an external fibrous and an internal serous layer. The serous layer not only lines the inner surface of the sac, forming the parietal portion, but it also covers the heart itself; this portion is the visceral portion or epicarditim ; its structure is similar to that of other serous membranes, being composed of connective tissue and elastic fibers, beneath which are the blood-vessels, nerves, and lymphatics of the heart. The myocardium, or muscular structure of the heart, is composed of transversely striated muscular fiber-cells, each' con- taining a single nucleus. They differ from voluntary muscle in possessing no sarcolemma, in branching and uniting with adjoining cells, and in having their striae less pronounced (p. 61). The endocardium, which lines the heart and takes part in the formation of the valves, resembles the epicardium in struct- ure, and is covered by endothelium. 306 CIRCULATORY SYSTEM. The heart (Figs. 157, 158) is a hollow muscular organ whose functions consist in acting as a reservoir and also as a pump, the auricles being the reservoir and the ventricles being the pump (Plate 2). It is about 12.5 cm. long, 8 cm. wide in its widest part, and 6.3 cm. thick at its thickest part ; its weight is about 300 grams in the adult. It has a conical form, its base being above and to the right, and its apex below and to the left. It is divided longitudinally by a partition or septum into a right and a left half, which are sometimes denominated the right heart and the left heart. Each half is com- posed of an auricle and a ventricle ; thus there are four cavities the right au- ricle, the right ventricle, the left auricle, and the left ven- tricle. The right auricle (Fig. 157) is somewhat larger than the left, and has the thinnest walls of the four cavities, measuring about 2 mm. in thickness. Discharging into this cavity are the superior and inferior venae cavae, at the mouths of which there are no valves. Within the cavity is the Eustachian valve, which will further be described when discussing the fetal cir- culation, This valve is sit- uated between the opening of the inferior vena cava and the auriculoventricular orifice. The right ventricle (Fig. FIG. 157. Interior of right auricle and ventricle, exposed by the removal of a part of their walls : 1, superior vena cava ; 2, in- ferior vena cava ; 2', hepatic veins ; 3, 3', 3". inner wall of right auricle ; 4, 4, cavity of right ventricle ; 4', papillary muscle ; 5, 5', 5", flaps of tricuspid valve; 6, pulmonary ar- tery, in the wall of which a window has been cut ; 7, on aorta near the ductus arte- riosus ; 8, 9, aorta and its branches ; 10, 11, left auricle and ventricle (Allen Thomson). 1 57) has walls whose thickness is greater than that of either auricle, but less than that of the left ventricle. The cavity of the right ventricle communicates with that of the right auricle by the right auriculoventricular orifice, at which is situated the tricuspid valve. It ordinarily contains, when filled, 87 grams of blood (p. 314). Connected with this ventricle is the pulmonary artery, at whose point of junction with the ventricle is the pulmonary orifice, at which is situated the pul- monary valve. The left auricle (Fig. 158) is not so large as the right, but its walls are thicker. Discharging into it are the two right and the THE HEART. 307 two left pulmonary veins, the former coming from the right and the latter from the left lung. The left veins sometimes join, and have but a single opening, in which case there would, of course, be but three openings instead of four. At these openings there are no valves. The left ventricle (Fig. 158) is by far the most powerful of the four subdivisions of the heart. Its walls are three times as thick as those of the right ventricle. The capacity of its cavity is the same as that of the right. The left auricle and ventricle communicate by the left auriculoventricular orifice, at which is situated the mitral valve. Connected with this ventricle is the aorta, the opening of communication being the aortic orifice, at which is situated the aortic valve. On the inner surface of the ventri- cles the muscular tissue projects, and forms the eolunmce camece, or fleshy columns ; some of these are ridges only, while others are attached at both ends, but are unattached in the middle, while still others project into the cavity and are attached at one ex- tremity only ; the latter are the mus- culi papillares, or papillary muscles. Cardiac Valves. There are four sets of valves in the heart : (1) The tricuspid ; (2) the pulmonary ; (3) the mitral ; and (4) the aortic. The pulmo- nary and aortic valves are sometimes spoken of as the semilunar valves. The tricuspid valve (Fig. 159) is situatrd at the right auriculoventric- ular orifice, and, as its name implies, consists of three cusps or segments. The bases of these cusps are attached to the opening, while the other edges are free, and to them are attached the chordae tendinece, or tendinous cords, the other ends being connected with the free extremities of the musculi papillares to which reference has been made. This valve, when shut, closes the right auriculoventricular orifice ; when open the segments are in the cavity of the right ventricle. The tendinous cords prevent these segments from passing into the cav- ity of the auricle at the time of the valve's closure, while the papil- lary muscles by their shortening keep the cords taut at the time of the ventricle's contraction, as will be seen later. FIG. 15S. Left auricle and ven- tricle, opened and part of their walls removed to show their cavi- ties ; 1, right pulmonary vein cut short; 1', cavity of left auricle; 3, 3", thick wall of left ventricle ; 4, portion of the same with papil- lary muscle attached ; 5, the other papillary muscles; 6, 6', the seg- ments of the mitral valve ; 7, the figure in aorta is placed over the semilunar valves; 8, pulmonary artery ; 10, aorta and its branches (Allen Thomson). 308 CIRCULATORY SYSTEM. The pulmonary valve is sometimes spoken of as the pulmonary semilunar valve or valves. It is composed of three, occasionally two, segments, and is situated at the beginning of the pulmonary artery. These segments are at- tached at their bases to the wall of the artery, and on the free edge of each is a projection, the corpus Arantii. When the valve is open the segments lie against the walls of the artery ; when it is shut they are in contact, and thus close the orifice of the pulmonary artery. The mitral valve is sometimes described as the bicuspid, because it consists of two cusps. The attachments of the segments, the FIG. 159.-0rifice of the heart, seen pregence of cho rdse, and the other points referred to in from above, both the auricles and the great vessels being removed : PA, pul- anatomic monary artery and its semilunar spea ki ng o f t h e tricuspid Valve valves; AO, aorta and its valves; " & . * . . . RA V, tricuspid, and LAV, bicuspid are to be seen in connection with valves; MV, segments of mitral valve ; t ^ e m itral. It closes the auricu- LV, segments of tricuspid valve , , . , . (Huxley). loventncular orifice. The aortic valve resembles in all essential particulars the pulmonary ; it likewise is sometimes called the semilunar valve, and closes the aortic orifice. The ventricular septum is the partition between the right and left ventricles. It is closed at all periods of life. The auricular septum, between the auricles, is closed from the tenth day after birth ; prior to this time and during fetal life it has an opening, the foramen ovale, which serves as a means of communi- cation between the right and the left auricles. Structure of the Valves. The valves consist of reduplications of endocardium, between which is fibrous tissue. THE ARTERIES, Arteries are composed of three coats : (1) An internal, tunica intima; (2) a middle, tunica media; and (3) an external, tunica adventitia. The tunica intima consists of a layer of pavement-epithelium (Fig. 160), the cells being polygonal, oval, or fusiform, termed endothelium, and of a network of elastic fibers or a fenestrated membrane (Fig. 161). Between these two layers is a subepithelial layer consisting of connective tissue. The tunica media has a special physiologic interest. In the large arteries that is, those larger than the carotids this coat is principally yellow elastic tissue, only about one-fourth being mus- cular tissue. Vessels of this size are therefore characterized by THE ARTERIES. 309 their elasticity. In the arteries of medium size that is, those between the carotids and those having a diameter of about 2 mm. the amount of muscular tissue is very much increased, while the Endothelium of the intima. " Intima. Media. Adventitia with non-striated mug- cle-fibers in cross- section. FIG. 160. Section through human artery, one of the smaller of the medium-sized ; X 640 (Bohm and Davidoff ). elastic tissue is also well represented. Such arteries possess, there- fore, both contractility and elasticity. In the small arteries that is, those less than 2 mm. in diameter the external coat gradually Intima. Elastica in- v terna. Endothelium of the intima. m. > Media. Fenestrated ?? | elastic mem- brane. Elastica ex- terna. Inner layer of adventitia. Outer layer of adventitia. ~- Vasa vasorum. FiG. 161. Cross-section of the human carotid artery ; X 150 (Bohm and Davidoff). disappears until in the arterioles there remains only muscular tissue, representing the middle coat and the internal coat. These vessels are endowed with the property of contractility. 310 CIRCULATORY SYSTEM. The tunica adventitia consists of bundles of white connective tissue and elastic fibers, and gives to the artery its strength. This coat merges with the sheath of the artery, which is composed of fibro-areolar tissue, and in this are the blood-vessels which supply the arteries, the vasa vasorum. THE CAPILLARIES, The capillaries are minute vessels, having in general a diameter of 12 f2j though this differs very considerably in the different organs of the body. They are smallest in the brain and intestinal mucous membrane, and largest in the skin and bone-marrow, where they have a diameter of about 20 //. Their arrangement is also subject to great variation ; thus in the lungs and mucous membranes they form rounded meshes, while in muscles and nerves the form of the mesh is elongated. In some organs they are very close together, as in the lungs, while else- where they are separated to a considerable extent, as, for instance, in the external coats of arteries. In general, where an organ is active, as is the kidney, there the number of capillaries is the FIG. 162. Endothelial cells of capillary (a) and precapillary (b) from the mesentery of a rabbit; stained in silver nitrate (Huber). greatest ; and where it is inactive, as is the case with bone, the capillaries are correspondingly lacking. The walls of the capillaries consist of endothelial cells joined edge to edge by a cement-material. From a physiologic standpoint this portion of the circulatory apparatus is the most important, as all the changes between the blood and the tissues take place while the blood is passing through the capillaries. THE VEINS. The structure of the veins is in many respects similar to that of the arteries. They are likewise composed of three coats, but CIRCULATION OF THE BLOOD. 311 the middle coat is the thinnest so much so, indeed, that, while the arteries when cut remain patulous, the veins collapse. This coat contains both elastic and fibrous tissue : the former gives the vessels some elasticity, while to the latter is attributable the greater strength of the veins as compared with the arteries. The greater thickness of the arterial wall would seem calculated to make these vessels the stronger, but, although possessed of thin walls, still the white fibrous tissue which aids in their formation gives the veins greater resisting power. Valves are to be found in most of the veins, but are absent in those whose diameter is less than 2 mm. ; also from the vena cava, hepatic, portal, renal, uterine, ovarian, cerebral, spinal, pulmonary, and umbilical veins. The valves are so arranged that they permit the blood to flow in the direction of the heart, but prevent its flow in the opposite direction. They consist of a reduplication of the internal coat, together with connective and elastic tissue to give them strength. Like the arteries, they are supplied with vasa vasorum to nourish their walls. CIRCULATION OF THE BLOOD. The course of the blood, starting from any point, may be traced through the circulatory apparatus. The circulation from the right ventricle through the lungs and back to the left side of the heart is the lesser or pulmonary circulation ; that from the left ventricle through the rest of the body other than the lungs and back to the right side of the heart is the greater or systemic circu- lation. Beginning with the right auricle, the blood flows into this cavity from the venae cavse (inferior and superior) ; thence through the right auriculoventricular orifice into the right ventricle ; thence into and through the pulmonary artery to the lungs ; thence by the pulmonary veins into the left auricle ; thence through the left auric- uloventricular orifice into the left ventricle ; thence into and through the aorta and the arterial system to the capillaries; through these vessels to the vein^, by which, through the venae cava3, it returns to the right auricle, the place of beginning. Cardiac Movements. If the heart is exposed in a living animal a dog, for example it will be seen that the ventricles are at one time in motion and at another time at rest. Each period of motion and rest constitutes a pulsation or a cardiac cycle, and these pulsations recur very rapidly, so much so that the inter- vals are recognized with difficulty. These different states of the heart are better detected by the sense of touch than by that of sight. If the ventricles are grasped by the hand, it will be found that, corresponding with the resting stage, the muscular tissue composing them is soft and flaccid, while during the active stage it is hard and resisting. If these movements are studied still more carefully and analyzed, it will be found that the beginning of the 312 CIRCULATORY SYSTEM. cardiac movement, which immediately follows the stage of rest, occurs in the auricles, in the region of the openings of the vense cavae on the right side, and of the pulmonary veins on the left ; that this movement is propagated along the auricles in the direc- tion of the ventricles ; and that by the time it has reached the auriculo ventricular orifices it has ceased at the orifices of the veins, and the muscular tissue in this region has begun to relax. It is to be noted that the auricles act synchronously, so that whatever is the condition of one auricle as to relaxation or con- traction of its muscular tissue, the same condition exists in the other. This contraction of the auricles is spoken of as the auricular systole, and has something of a peristaltic character, which has already been studied in connection with the stomach and small intestine, although differing materially in that it is much more rapid. Up to this time the ventricles are relaxed, or in a condition of diastole; but as soon as the auricular contraction reaches the ventricles these organs take it up, although in a different manner. For, while in the auricles one portion is contracting while another is relaxing, in the ventricles the whole mass of muscle contracts at once with a degree of suddenness and vigor which might be expected of so large a mass of striped muscular tissue. This contraction is the ventricular systole, and while it is taking place the auricles are relaxing throughout ; this relaxation constitutes the auricular diastole. Thus the auricular systole and ventricular diastole, and the auricular diastole and ventricular systole, are respectively synchronous. Immediately after the systole of the ventricles these structures relax, and for a brief period the whole heart, both auricles and both ventricles, is in a state of relaxation ; this is the pause of the heart. The work performed by the ventricles is so much more important than that of the auricles that when the terms systole and diastole are used, reference is always had to these states of the ventricles, the auricles being practically ignored. To designate the corresponding states of the auricles it is always necessary to speak of the auricular systole and diastole. Cardiograph. The cardiograph is an instrument for recording the movements of the heart, the record itself being a cardiogram. The form most used is that of Marey. It consists of a metal box, over the mouth of which an elastic membrane is stretched, to which a knob is attached (Fig. 163). This knob, in another form of this instrument, is attached to a spring (Fig. 164). This box or tympanum is in connection with another box, the recording tambour, by means of a tube, and upon the elastic membrane of this rests a lever. The first tambour is so fixed in place against the chest wall as to bring the knob over the point where the cardiac impulse is felt, and the movement of the knob is com- CIRCULATION OF THE BLOOD. 313 municated to the membrane, sending a wave of air through the tube and causing the lever to move at every impulse ; the point of the lever makes its record on a revolving drum or kymograph, covered with smoked paper (Fig. 1 66). This may be varnished with shellac for preservation. Fig. 164 shows a cardiogram taken in this way. The same instrument in a modified form is used to obtain a record of the endocardiac pressure. In this case India-rubber bags communicating with the recording tambours are introduced through the jugular vein into the cavities of the right auricle and ventricle. This method is of service only in an animal with large vessels, such as the horse. Movements of Blood during Systole and Diastole. Before con- sidering other movements of the heart it will be well to study the course of the blood while contraction and relaxation of the mus- cular tissue of this organ are taking place. The venous blood, returning from the head and upper extrem- ities by the superior or descending vena cava, and from the portion of the body below the heart by the inferior or ascending vena FIG. 163. Diagram of Marey's cardiograph : A, knob attached to flexible membrane tied over end of metal box ; the knob is placed over the apex-beat ; c, folded edge of membrane; Bis the tube commu- nicating with a recording tambour. FIG. 164. Cardiogram taken with Marey's cardiograph : a, auricular systole ; v, ventricular systole ; d, diastole. The arrow shows the di- rection in which the tracing is to be read (Stewart). cava, flows into and through the right auricle, passing into the right ventricle through the right auriculoventricular orifice. The tricuspid valve at this time is open, and offers no obstacle to the passage of the blood. Blood is also at the same time flowing into the left auricle and ventricle from the lungs. More blood enters the auricles than can at once pass out into the ventricles ; conse- quently some blood accumulates in, and gradually fills, the auricles, although at the same time as much blood is flowing into the ven- tricles as the auriculoventricular orifices will permit to pass, nearly filling these cavities, and floating up the segments of the mitral and tricuspid valves until they are nearly closed. This is the condition at the end of the pause. At this moment begins the auricular systole. Near the ends of the veins which discharge 314 CIRCULATORY SYSTEM. into the auricles that is, the venae cavae and pulmonary veins are muscular fibers ; these fibers contract, diminishing the size of the orifices of the veins, thus taking the place of valves, and par- tially preventing a back-flow of blood into these vessels. Then the muscular fibers of the auricles in contiguity with these fibers contract, the movement spreading to the adjoining fibers until the wave of contraction has reached the ventricles. This auricular contraction forces more blood into the ventricles, and as the fibers relax the blood enters the auricles again from the veins. It will thus be seen that the interval of time during which the venous flow is arrested is the briefest possible. The principal office of the auricles is to serve as reservoirs to supply the ventricles; the work they do in completing the filling of these cavities is com- paratively unimportant. The auricular systole is followed by the systole of the ventri- cles. These cavities are at this time filled with blood, and the auriculoventricular valves are nearly closed, the segments having been raised up by the blood from the auricles. The ventricles, as has been stated, contract en masse, and the blood which they con- tain is compressed with great force. Under the pressure it tends to escape from the ventricles through all outlets on the right side through the right auriculoventricular orifice back into the right auricle, and through the pulmonary orifice into the pulmonary artery ; on the left side through the left auriculoventricular orifice into the left auricle, and through the aortic orifice into the aorta. The pressure of the blood instantly closes the tricuspid valve, and thus prevents the blood from going back into the right auricle. The same force closes the mitral valve, and regurgitation of blood into the left auricle is made impossible. The pulmonary and aortic valves, as has been stated, open from the ventricles into the arteries. At the beginning of the ventricular systole these valves are closed, but when systole occurs the pressure of the blood forces them open, and the contents of the ventricles, 70 c.c. for each, are propelled into the pulmonary artery and the aorta respectively. Authorities differ as to the amount of blood which is expelled from the ventricle at each pulsation, and which is termed the pulse volume ; some place it as low as 50 c.c., and others as high as 190 c.c. Stewart gives it as his opinion that the average amount of blood thrown out by each ventricle at each beat is not more than 70 c.c. or 80 c.c. (87 grams). This agrees closely with Tiger- stedt's calculation, which places the amount at 69 c.c. If the average amount is 70 c.c., the whole blood of the body would pass through the heart in about a minute. In accomplishing this the ventricles have to overcome the pressure which the blood already in the arteries is exerting on the other side of the valves to keep them closed. This pressure in the arteries is equal to a column of mercury, approximately, 150 mm. high, and in the pulmonary CIRCULATION OF THE BLOOD. 315 artery is one-third as much. The amount of work done by the ventricles daily in thus forcing blood into the arteries is equal to that which is performed by an individual weighing 75 kilograms in climbing a mountain 806 meters in height. As soon as the ventricles cease their contraction the pressure of the blood in the arteries closes the pulmonary and aortic valves, the ventricles begin their diastole, and the pause of the heart commences. As it was at this point that the consideration of the changes which take place was begun, the study of a cardiac cycle, cardiac period, or heart-beat is now completed. If the time occupied by such a period is divided into one hundred parts, it will be found that the auricular systole lasts during nine of the parts, the ventricular systole during thirty, and the pause during sixty-one ; or, in other words, the heart is at rest six-tenths and at work four-tenths of the time. Shortening of the Heart. At the time of the systole of the heart (ventricular systole) the organ becomes shorter, yet the apex does not change its place, for the lengthening of the aorta which occurs compensates for the shortening, so that while the apex and base approximate the whole heart is lowered, the result being to keep the apex in its original position with reference to the chest wall. Cardiac Impulse. The situation of the heart in the thoracic cavity is such that its apex is against the chest wall at the fifth intercostal space, the space between the fifth and sixth ribs, and about 3 cm. below and 1 cm. within the left nipple. The apex of the heart is the extreme point of the left ventricle. If the finger is placed in this region during the ventricular systole, there will be felt a tap as if something was gently striking it. This tap is known as the apex-beat. It is so called because it was formerly supposed that during the systole the heart was raised up and car- ried forward so as to cause the apex to strike against the chest wall and thus produce the sensation.. A more careful study of the changes which the heart undergoes during systole has, however, demonstrated that the apex of the heart is always in contact with the chest wall, and that this supposed striking does not take place. Indeed, the tap is not due to the apex at all. The term apex- beat is a misnomer : it should rather be called cardiac impulse, the sensation being produced by the anterior surface of the con- tracting ventricles swelling out and hardening. The location at which this impulse is felt most pronouncedly is not over the apex, but higher up. If a long needle was to be introduced deeply here, it would penetrate the left ventricle at a point where the middle and lower thirds unite. The cardiac impulse is not always, even in health, detected at the same place : it changes somewhat with respiration and also with changes in the position of the body. 316 CIRCULATORY SYSTEM. Papillary Muscles. It has been stated that during the ven- tricular systole the heart shortens. It is manifest that unless some provision was made this change in the shape of the heart would permit of regurgitation of the blood into the auricles, and thus would result a damming back of the blood in the venae cavse and pulmonary veins ; for if the chordae tendinese were of just the right length at the beginning of the ventricular systole to keep the segments of the mitral and tricuspid valves so exactly in place as not to permit a leakage, then when the ventricles shortened these cords would be too long, and would permit the segments to enter the cavity of the auricles and there separate, leaving a considerable gap through which the blood could pass. That this does not occur is due to the papillary muscles. As the ventricles shorten, these structures contract sufficiently to take up the slack in the cords, and keep them just long enough to main- tain the proper approximation of the segments of the valves. Cardiac Sounds. When the ear is placed against the chest wall in the region of the heart two sounds are heard during each cardiac period. The first of these sounds is heard loudest that is, at its maximum of intensity over the apex, and is by some writers called the apex-sound. For the reason that it is the first sound heard after the pause it is called the first sound, and because it occurs at the beginning of the systole of the heart (ventricular systole) it is called the systolic sound. The second sound is heard loudest over the base of the heart, and is therefore sometimes de- scribed as the basic sound; inasmuch as it occurs during the diastole, it has received the name of the diastolic sound. More commonly, however, it is spoken of as the second sound. Characteristics of the Cardiac Sounds. The first sound, as com- pared with the second, is lower in pitch and longer in duration, and has been likened to the sound of the word liibb. The second sound is higher in pitch and shorter in duration than the first, and has been likened to the sound of diip. These sounds occur suc- cessively, without any interval between them ; in the pause which follows no sound is heard. Causes of the Cardiac Sounds. The cause of the second sound is undoubtedly the closure of the aortic and pulmonary valves. This has been demonstrated by hooking back the segments of the valves, when the sound disappears, to reappear when the seg- ments are set free. The causation of the first sound is not so simple; indeed, authorities are not at one on this point. The closure of the mitral and tricuspid valves contributes something to it, but the closing of the valves is not the sole factor, for in a heart in which there is no blood the sound may still be heard, although modified, and in such a heart the valves would not close. The contraction of the muscular tissue of the heart gives forth a sound, as does indeed the contraction of other muscles, and this CIRCULATION OF THE BLOOD. 317 is also an element in producing the first sound. The striking of the apex against the chest-wall, the so-called apex-beat, formerly regarded as one of the factors of the first sound, can take no part in its production, because:, as has been pointed out, this action does not take place. Every student should familiarize himself with the cardiac sounds, not simply by reading about them, but by listening to the human chest. A thorough knowledge of their character is essential to a comprehension of the diseases of the heart. It is important to remember that the impulse of the heart, the systole of the ventricles, the first sound, and the closure of the mitral and tricuspid valves are synchronous, and that when the second sound is heard the ventricles are beginning their diastole and the aortic and pulmonary valves have just closed. Cardiac Innervation. The cause of the beat of the heart has not been definitely ascertained. The fact that it beats when removed from the body shows that this action is dependent upon some power within itself. The length of time that a heart so iso- lated will continue to beat varies in different animals, being longer in the poikilothermal than in the homoiothermal ; thus, it may con- tinue for days in the former, w r hile in the latter it may cease after a few hours or even minutes. Landois states that in hearts that have been excised " the last vestige of cardiac action has been observed in the rabbit after 15J hours, in the mouse after 46 J hours, in the dog after 96J hours, and in a three-month s'-old human embryo after 4 hours." Two theories have been advanced to explain the beat of the heart: (1) That it is due to stimuli having their origin in nerve- ganglia which exist in the heart ; and (2) that it is due to an in- herent power of contraction residing in the cardiac muscle-cells, a power independent of any nervous connection whatsoever, and that this is due to the action upon the heart muscle of chemical sub- stances in the blood, as calcium, sodium, and potassium salts; the first being apparently essential for the chemical stimulation, while a certain proportion of potassium is also necessary (Ho well). The effect of the sodium chlorid is to maintain the osmotic equilibrium between the muscle-cells and the surrounding liquid. The first of these theories is supported by the fact that there are numerous ganglion-cells in the heart, and that where these are most abundant, as in the auricle, there the power of contraction is greater than in the part (the ventricle) where the cells are fewer ; and, further, that when the apex of the heart i. e., the point of the ventricle in which there are no cells is cut away, it no longer beats. The second theory derives its support from the fact that a piece of the apex of the ventricle of a tortoise, in which there are no ganglion-cells, when suspended in a moist chamber, will beat for hours. The apex of a dog's heart, in which there are no cells, 318 CIRCULATORY SYSTEM. will beat for hours, provided it is supplied with defibrinated blood through its nutrient artery (Porter). This second theory is rapidly gaining favor among physiologists. Cardiac Nerves. Whatever may be the cause of the heart-beat, its regulation is brought about by the central nervous system. The cardiac nerves are derived from two sources, the vagus and the sympathetic, through the cardiac plexuses, of which there are four : 1, the superficial, situated in the concavity of the arch of the aorta ; 2, the deep, or great ; 3, the right coronary, and, 4, the left coronary ; the last two being derived from the superficial and the deep. The impulses which reach the heart through the vagus are of an inhibitory nature, while those passing through the sympa- thetic are accelerating or augmenting (pp. 487 and 523). Circulation in the Arteries. Each time that the ven- tricles contract they send into the arteries about 140 c.c. of blood, each ventricle expelling 70 c.c. (p. 314). The arterial system is always overdistended that is, even when the heart is at rest the amount of blood in the arteries is sufficient to stretch their walls a little. When an additional amount of blood is forced into them by the muscular contraction of the heart, these vessels are distended still more, for the blood already in them cannot at once flow on in an amount equal to that which comes from the heart. If an artery at this time should be felt with the finger, it would beat against the latter, this beat being called the pulse. As soon as the systole ceases the elastic coats of the arteries squeeze the blood that is within them, and this blood tends to flow away from the point of pressure in two directions back toward the heart and onward toward the capillaries. Its backward flow at once closes the pulmonary and aortic valves, and in this direction, therefore, its progress is barred. The blood then can go only forward. Before the onward flow of the blood has ceased another systole occurs, and again the ventricles are emptied into the arteries, and thus this action continues during the life of the individual. If a cannula is inserted into the cavity of the ventri- cle, it will be seen that at each systole the blood spurts out in a jet, which ceases at the end of the systole that is, the flow from the heart is intermittent. If the cannula is inserted into the aorta, the blood will jet out at each systole of the heart, but, instead of ceasing to flow during diastole, it will not entirely cease, but will continue to flow a little under the influence of the elastic force of the aorta. If the cannula is inserted into successive portions of the arterial system farther and farther from the heart, the blood will come out in jets as before under the influ- ence of the heart's contraction, but it will continue to flow in the intervals, the difference between the jet and the continuous flow being less and less marked the greater is the distance of the inser- tion of the cannula from the heart. In the capillaries the flow is regular and continuous, unaffected by the action of the heart. EL OD-PRESS URE. 319 Internal Friction. If the blood is studied as it is flowing through a small artery in the web of a frog's foot, it will be seen that in the center of the current it is flowing much faster than at the sides ; this is the axial stream, and in it will be observed the red corpuscles. That portion of the current which is between the axial stream and the walls of the vessel moves more slowly, the rate diminishing from the center outward, until at the walls themselves it is at the minimum. This outer portion is known as the inert layer. It should be stated that this arrangement of the current is not due to any peculiarity of the blood or of the vessels through which it flows, but is present in every fluid while flowing through a tube. Between the different layers of fluid there is friction, called internal friction. The smaller the tubes the greater the internal friction, so that the amount of friction in the sub- divisions of the aorta and its numerous ramifications is very great, and this friction acts as an obstacle to the outflow of the blood, constituting peripheral resistance. BLOOD-PRESSURE. The systemic circulation of the blood i. e., its flow from the left ventricle through the arteries and capillaries ; and back by the veins to the right ventricle again is a movement from a point of high pressure, the left ventricle, to one of low pressure, the right FIG. 165. Height of blood-pressure (b.p.) in left ventricle (l.v.) : a, arteries; c, capillaries ; r, veins ; r.a., right auricle ; o 0, line of no pressure (after Starling). auricle. This is shown in Fig. 165, where the pressure is greatest at the left ventricle, gradually diminishing in the large arteries, until at the end of the arterial system the fall is abrupt ; it falls gradually throughout the capillaries and veins until the large veins in proximity to the heart are reached, where it is negative (p. 323). The fact that the blood within the vessels is under varying degrees of pressure may be demonstrated by repeating the classic experiment performed by Stephen Hales, an English Episcopal clergyman, and described by him in u Statical Essays, Containing Hsemostaticks." This was published in London in 1733. He in- 320 CIRCULATORY SYSTEM. FIG. 166. Diagram of the recording mercurial manometer and the kymo- graph ; the mercury is indicated in deep black : M, the manometer, connected by the leaden pipe L with a glass cannula tied into the proximal stump of the left common carotid artery of a dog; A, the aorta ; C, the stop-cock, by opening which the manometer may be made to communicate through ET, the rubber tube, with a pressure-bottle of solution of sodium carbonate ; F, the float of ivory and hard rubber; R, the light steel rod, kept perpendicular by B, the steel bearing; P, the glass capillary pen charged with quickly drying ink ; T, a thread which is caused, by the weight of a light ring of metal suspended from it, to press the pen obliquely and gently against the paper with which is covered D, the brass "drum" of the kymograph, which drum revolves in the direction of the arrow. The supports of the manometer and the body and clock-work of the kymograph are omitted for the sake of simplicity. The aorta and its branches are drawn disproportionately large for the sake of clearness (Curtis). troduced into the femoral artery of a horse a brass-pipe whose bore was one-sixth of an inch in diameter, to that, by means of BLOOD-PRESSURE. 321 another brass-pipe which was fitly adapted to it, " was attached a glass tube of nearly the same diameter, which was nine feet in length"; the blood rose to a height of 2.44 meters, and at each in- spiration of the animal the column rose and at each expiration it fell ; besides this movement due to respiration, there was a smaller rise at each systole and a corresponding fall at each diastole. This pressure under which the blood is in the artery which causes it to rise so high in the tube is arterial pressure, or the blood- pressure in the arteries. Such an instrument for measuring pressure is a manometer. It is manifest that a glass tube 2^ meters in height is not a very convenient instrument to manipu- late, and besides the blood soon clots. To obviate both of these difficulties the mercurial manometer was devised, together with the use of a solution of sodium carbonate ; the latter preventing the coagulation of the blood. Later a drum or kymograph was added to the apparatus, on which a record could be made for study and preservation (Fig. 166). The legend beneath the illustration is sufficiently descriptive of the complete apparatus. The curve P BL FIG. 167. The trace of arterial blood -pressure from a dog anesthetized with morphia and ether. The cannula was in the proximal stump of the common carot- id artery. The curve is to be read from left to right: P, the pressure-trace written by the recording mercurial manometer ; B L, the base-line or abscissa, representing the pressure of the atmosphere. The distance between the base-line and the press- ure-curve varies, in the original trace, between 62 and 77 millimeters, therefore the pressure varies between 124 and 154 millimeters of mercury, less a small correction for the weight of the sodium-carbonate solution ; T, the time-trace, made up of intervals of two seconds each, aud written by an electro-magnetic chronograph (Curtis). made by the pen is shown in Fig. 167. The longer waves are due to respiration, the smaller ones to the heart-beat. By the term mean pressure is meant the average pressure throughout the observation. The mean arterial pressure in man is approximately 150 mm., an increase of 5 mm. occurring at the time of systole. The figures here given for the mean aortic pressure may be too high ; it has, of course, never been measured in man. The following table (Starling) gives the approximate heights in differ- ent portions of the vascular system, calculated largely from obser- vations in lower animals : 21 322 CIRCULATORY SYSTEM. Large arteries (e.g., carotid) -f 140 mm. of mercury. Medium arteries (e. g., radial) +110 Capillaries -f 15 to -f 20 Small veins of arm +9 Portal vein -f 10 Inferior vena cava -j- 3 Large veins of neck from to 8 The Sphygmometer (Fig. 168). The sphygmometer is an instrument for ascertaining the blood-pressure in the human subject. It consists of a rubber bag, containing a colored fluid, connected with a graduated glass tube, the top of which is expanded into a bulb and closed with a stopcock. The instru- ment is so attached to the body that the rubber bag is on the artery whose blood-pressure . is to be ascertained. The bag being pressed down upon the artery, the fluid rises in the tube, and the air in the bulb, being compressed, acts as an elastic spring. The top of the fluid is watched carefully, and when its pulsation is greatest, which is known as the maximal pulsation, its height is read off on the scale ; this is so graduated as to correspond to millimeters of mercury pressure, and represents the arterial press- ure. By this instrument the radial pressure of an adult has FIG. 168. Hill and Barnard's sphygmometer. been found to be from 110 to 120 mm. of mercury. The instru- ment can also be used to obtain venous pressure. Stewart states that the blood-pressure in the radial artery of a healthy man may average 150 mm. of mercury. In the anterior tibial artery of a boy whose leg was to be amputated, it was found to vary from 100 mm. to 160 mm. according to the position of the body and other circumstances. The pressure in the pulmo- nary artery is about one-third that in the aorta. The mean press- RATE OF BLOOD-FLOW IN THE VESSELS. 323 ure in the veins is perhaps 5 mm. and in the great veins near the heart negative, so that a cannula introduced into this part of the circulatory system would show a depression of the mercury in the distal limb of the manometer, indicating that there was a suction from \vithin the vein ; this constitutes negative pressure. It is the pressure under which the blood is in the arteries that causes it to spurt or jet when the vessel is cut, while the flow from a wounded vein or capillary is continuous. Pick's spring myograph is another form of this instrument, in which the movements of a hollow spring are communicated to a writing lever. RATE OF BLOOD-FLOW IN THE VESSELS. The caliber of the blood-vessels is constantly changing, and the rate of the flow of blood through them is subject to great variations, so that any estimate of the velocity of the flow can at best be but approximate. There are two factors which enter into the problem : (1 ) the caliber of the vessel at the point where the velocity is to be ascertained, and (2) the amount of blood passing that point in a given time, for the velocity is inversely pro- portional to the sectional area. Rate of Flow in the Arte- ries. It is in these vessels that the velocity is the greatest, begin- ning at the heart and gradually diminishing along the course of the arterial system. Its maximum is at the time of the systole. The Stromuhr. One of the in- struments used to determine the rate of speed is the stromuhr of Ludwig (Fig. 169). This consists of a U-shaped tube, glass above and metal below, expanded into two bulbs, A and B, which can be filled from the top. The lower extremities of these tubes are con- nected with the ends of a divided artery, so that the channel between the two is continuous through the stromuhr. The instrument is so constructed that while in place the upper portion, including the bulbs, can be so rotated at c as to bring A in connection with 6, and B with CT-, and this process repeated as often as desired, the flow through the instrument not. being interrupted. The tubes and the bulb B are filled with defibrinated blood, which in A a FIG. 169. Diagram of longitudi- nal section of Ludwig's "stromuhr." The arrows mark the direction of the blood-stream. For further descrip- tion see the text (Curtis). - . 324 CIRCULATORY SYSTEM. reaches only up to the mark e; and the bulb A is filled with oil. The clamps which close the ends of the vessel are now removed, the time being noted, and the blood from a expels the oil in A into B. When A is filled with blood to the point c?, the time is again noted, and the capacity of A, and the caliber of the vessel being known, the velocity of the flow may be calculated. A single measurement would not be sufficient to give results of much value ; but if at the moment the blood reaches d the instru- ment is rotated, the bulb B into which the oil has been driven by the blood will be brought into relation with a, and will be filled with blood from the vessel, as A originally was, the oil being forced into A, and the blood contained in that bulb will be driven on into the vessel 6, thus entering the circulation again. When the oil emerging from the bulb reaches the mark, the time is again noted, and the bulb again rotated ; thus the blood which is meas- ured is always the volume be- tween e and d in A. The time between the rotations is the time occupied in filling the bulb, and this may be recorded on a kymo- graph. The Dromograph (Fig. 170). This consists of a metal tube, which is inserted into a divided artery ; in the side of the tube is an opening, closed by rubber, through which a lever passes, one end being inside the vessel, FIG. 170. Chauveau's dromograph : the other outside, and so ar- A, tube connected with blood-vessel f B, ranged that its movements are metal cylinder in communication with indicated on a dial. The num- A. The upper end of B has a hole in i r> j , T the center, which is covered by a mem- ber of graduations corresponding brane, ro, through which a lever, (7, to a given Velocity is known by - C_ has a small disk, j>, at its lower observing the deflection of the end, which projects into the lumen of A, and is deflected in the direction of the blood -stream is registered lever when it is inserted into a tube communication by the tube E with a flowing at a known rate IS pass- tambour Z>, the flexible membrane of which is connected with the lever of the pendulum C. ing. Various observations have been made on lower animals to determine the velocity of the blood-flow in the arteries. In the dog's carotid it is found to be from 205 mm. to 350 mm. per second ; in the same vessel of a horse, 306 mm. ; and in the metatarsal artery of the horse, 56 mm. When an artery divides, the sectional area of the branches is more than that of the original vessel, and this consequently results in a gradually in- creasing sectional area, and a .corresponding diminution in the velocity of the flow, so that in the smaller artery the speed is RATE OF BLOOD-FLOW IN THE VESSELS. 325 greatly reduced. The velocity in the large arteries may be con- sidered as approximately 3 dcm. a second. Rate of Flow in the Capillaries. The sectional area of the capillaries is 700 times greater than that of the aorta, where the velocity is, perhaps, 500 mm. per second ; when this portion of the circulatory apparatus is reached the rate of flow is greatly reduced, being in the dog from 0.5 mm. to 0.75 mm. per second. The rate of flow through the capillaries of the retina has been ascertained by Vierordt in his own eye to be from 0.6 mm. to 0.9 mm. per second. The length of any given capillary through which a specified portion of the blood passes is only 0.5 mm., so that the length of time such portion would remain in the capillary system would be less than a second, and yet during this brief time important interchanges take place between the blood and the tissues. It is here that the tissues receive from the blood the materials they require for their nutrition, and in the case of glands for their secretion ; and it is likewise here that the blood receives from the tissues their waste products. The thin walls of the capillaries are admirably adapted for this interchange. In fact, it is within bounds to say that the heart, the arteries, and the veins are simply subsidiary to the capillaries, the arteries carrying to these vessels the blood which the heart pumps into them, while the veins return the blood to the heart. Rate of Flow in the Veins. It is estimated that the sectional area of the veins is at least twice as great as that of the arteries, and therefore the velocity would be twice as great in the arteries as in the veins. Some estimate the area of the veins as three times that of the arteries. Inasmuch as the sectional area of the veins decreases as the heart is approached, the rate of flow in these vessels gradually increases. The Circulation-time. The length of time which the blood takes to make the entire round of the body was first ascer- tained by dividing the jugular vein and injecting a solution of potassium ferrocyanid into the end nearest the heart ; the blood was collected from the vein of the other side and tested by adding a solution of ferric chlorid to the serum ; as soon as the Prussian- blue reaction appeared it was demonstrated that the blood had completed the circulation of the body. These observations con- ducted on different animals gave the following results : In the horse, 31.5 seconds; dog, 16.7 seconds; cat, 6.69 seconds; and goose, 10.89 seconds. It was also found that this represented the time occupied by 27 heart-beats in each animal. If 72 times a minute are considered as representing the average number of beats in man, it will be seen that the blood requires 22.5 seconds to complete the entire circula- tion. Stewart has devised a method for ascertaining the circulation- 326 CIRCULATORY SYSTEM. time by injecting into the vessels methylene-blue, the color of which shows through the blood-vessels. By this means he has been able to study the circulation-time in the lungs, kidney, stom- ach, and other organs of lower animals. He thinks that the pulmonary circulation-time i. e., the time occupied by the blood in passing through the pulmonary circulation is not usually much less than 12 seconds nor more than 15 seconds ; the circulation-time of the kidney, spleen, and liver is relatively long and much more variable than that of the lungs, these organs being easily affected by exposure and changes of temperature (increased by cold, diminished by warmth), and that of the retina and heart is the shortest of all. The total circulation -time in man he thinks is not much less than a minute, nor more than a minute and a quarter. THE PULSE. As has been seen, the left ventricle expels at each beat about 70 c.c. of blood, pumping it into the elastic arteries ; these being already filled, are still further distended by this additional amount, and the elastic coat of the artery recoils upon the blood within the vessel, driving it still further along. If a finger is placed upon an artery, this distention can be recognized, and constitutes the pulse. When the ventricle ceases its systole and begins its diastole, although blood ceases to be expelled from it, still the current in the arteries does not cease, for the elastic force of the vessels is sufficient to keep up a continuous movement of the fluid, which while it is in the arterial system is affected by the pulsation of the heart, but which in the capillary and venous systems, is uniform in rate. If it was possible to place a finger upon the carotid, another on the radial, and still another on the dorsal artery of the foot, it would be found that the pulse would first be felt in the artery nearest the heart, then in that at the wrist, and finally in the most distant one. Thus the pulse-wave starting at the left ventricle is felt in 0.159 second at the wrist, and in 0.193 second at the foot. It travels at the rate of about 9 meters per second. The number of pulsations varies in different conditions, increas- ing in activity and diminishing during rest ; it also varies at dif- ferent ages : At birth it is 140 to the minute ; atone year, 120; two years, 110; three years, 90; seven years, 85; puberty, 80; adult age, 70 ; old age, 60. These figures are approximate only. Any artery which is accessible may be used to obtain the pulse, but physicians have selected the radial as the most convenient be- cause of its accessibility and also because it lies upon an unyield- ing bony bed, and can be readily compressed by the finger and its character studied. The heart is one of the vital organs of the body, and a knowledge as to how it is performing its functions is very important for the physician to possess. Situated as it is within the thorax, he cannot examine it directly, and is therefore THE PUL8&. 327 compelled to resort to other means to ascertain its condition. One of the best sources of information is the pulse. This he studies to learn : (1) The frequency of the heart-beats, for each time the FIG. 171. Scheme of Marey's sphygmograph : a, toothed wheel connected with axle h, and gearing into toothed upright 6 ; c, ivory pad which rests over blood- vessel and is pressed on it by moving g, a screw passing through the spring j ; e, writing-lever attached to axle h, and moved by its rotation ; e writes on d, a travel- ling surface moved by clockwork /. ventricle contracts there is a corresponding beat of the pulse ; (2) the force with which the heart is acting, for the strength of the pulse is an indication of that of the heart ; (3) its regularity; and FIG. 172. Sphygmogram from a normal human radial pulse beating from 58 to 60 times a minute. To be read from left to right (Burdon-Sanderson). (4) its tension i. e., whether it is compressible or not, whether a slight pressure will obliterate it, or whether it requires a greater amount of pressure. Low tension implies low arterial pressure, and high pressure denotes high blood-pressure. FIG. 173. Pulse-tracings : 1, primary elevation ; 2, predicrotic or first tidal wave ; 3, dicrotic wave. The depression between 2 and 3 is the dicrotic or aortic notch ; 3 is better marked in B than in A. C, dicrotic pulse with low arterial pressure. D, pulse with high arterial pressure-summit of primary elevation in the form of an ascending plateau. E, systolic anacrotic pulse ; the secondary wavelet a occurs during the upstroke corresponding to the ventricular systole. F, presystolic ana- crotic pulse; a occurs just before the systole of the ventricle. In this rarer form of anacrotism a may sometimes be due to the auricular systole when the aortic valves are incompetent (Stewart). The Sphygmograph (Fig. 171). This instrument makes a record, sphygmogram or pulse-trace, of the pressure in the 328 CIRCULATORY SYSTEM. arteries. It is attached to the wrist, and the point of the lever makes a sphygrnogram upon the card previously smoked. It is an instrument which needs great care in its use in order to make its records of practical value. Fig. 172 shows a sphygmo- gram of the radial pulse. It represents five complete pulsa- tions of the artery and the beginning of a sixth. The upstroke is caused by the expansion of the artery due to the arrival of the pulse-wave, while the downstroke is due to the retraction of the vessel. The upstroke, the primary or percussion-wave, is abrupt, because the systole of the left ventricle is abrupt, but the down- FIG. 174. Plethysmograph for arm: p, float attached by A to a lever which records variations of level of the water in B, and therefore variations in the vol- ume of the arm in the glass vessel c. Or the plethysmograph may be connected to a recording tambour. The tubulure at the upper part of C is closed when the tracing is being taken (Stewart). stroke is gradual, because of the fact that the return of the artery to its former condition is gradual by virtue of its elas- ticity. The downstroke is seen to be made up of a number of waves: First, the predicrotic or tidal wave; second, the dicrotic wave; and third, the post-dicrotic wave. These sec- FIG. 175. Plethysmograph tracing from arm. The tracing was taken by means of a tambour connected with the plethysmograph ; the dicrotic wave is distinctly marked (Stewart). ondary waves of the downstroke are termed katacrotic. There is sometimes a secondary wave in the upstroke, called anacrotic. The predicrotic and post-dicrotic waves are supposed to be due CIRCULATION IN THE VEINS. 329 to the elastic tension of the arteries, and are therefore more marked when this is at its highest. They are also caused to some extent by oscillation of the sphygmograph. Their causes are not thoroughly understood. The dicrotic wave is, on the other hand, a very constant and valuable feature of the sphygmogram. It is probably caused by a second wave, which is produced by the closure of the aortic valve, although on this point opinions are at variance. The arteries are already filled when the left ventricle throws in its contents, causing the expansion of the aorta and putting its elastic coat upon the stretch ; when the systole is at an end the elastic recoil upon the blood drives this fluid both forward and backward ; the backward flow closes the aortic valve, and, being suddenly brought to a standstill, a wave of blood is produced which is propagated along the arterial system closely following the pri- mary wave and causing, the dicrotic wave. This is sometimes so marked that it can be felt by the finger, constituting the dicrotic pulse; thus each pulsation of the heart produces 2 pulse-beats. The sphygmograph shows this condition much better than the finger. The Plethysmograph (Fig. 174). This is an instrument for recording the volume-pulse i. e. y the increase in the volume of an artery caused by the pulse-wave. It consists of a chamber into which the organ to be experimented upon is inserted and filled with fluid, the opening being closed with a rubber baud. At the other end is a rubber tube communicating with a vessel, in which is also fluid, and on its surface a float with a writing-point attached, which is so arranged as to record on a drum. If the arm is placed in the chamber in the manner illustrated, at every contrac- tion of the ventricle the volume of blood in the arteries will be increased, and a movement be set up in the fluid which will cause the float to rise ; when the diastole occurs the float will sink. The record made is called a plethysmogram (Fig. 175). CIRCULATION IN THE VEINS. The forces which propel the blood through the arteries and capillaries i. e., the contractile force of the ventricles and the elastic force of the arteries, collectively called the vis a tergo are sufficient to carry the blood back to the heart through the veins ; for, as has been stated, the pressure in the aorta is equal to a column of mercury 200 mm. in height, while in the veins it is at most only 5 mm., and sometimes actually negative, so that there is a difference in pressure of 195 mm. of mercury. This visa tergo is, however, aided by two other forces : (1) compression of the veins and (2) aspiration of the thorax. Compression of the Veins. It will be remembered that in the veins there are, at different points along their course, valves 330 LYMPHATIC SYSTEM. which are so arranged as to permit the blood to flow in but one direction that is, toward the heart. Many of these veins are so situated with reference to muscles that when the muscles contract the contiguous veins are compressed. This compression forces the contained blood away from the points of pressure, and as the closure of the valves prevents the blood from flowing backward, it must go forward. Aspiration of the Thorax. At each inspiration the cavity of the chest is enlarged and the pressure on its contents is dimin- ished. One of the results of this inspiration is the inflowing of air. Another result is the inflowing of blood into the venae cavse and right auricle, for while the intrathoracic pressure is dimin- ished, that upon the blood-vessels outside remains the same. A similar tendency exists for the blood in the aorta to flow back into the left ventricle, but this is prevented by the aortic valve. This subject will be again discussed in connection with respiration. Force of Gravity. The force of gravity assists in the return of the blood to the heart from the upper portions of the body, but retards its return from the lower portions, so that as a factor in aiding the circulation as a whole it may be ignored. This force may, however, be utilized whenever for any reason there is congestion in a part as, for instance, in a foot the seat of inflam- mation. In such a case the elevation of the lower extremity facilitates the flow of blood in the veins and proves beneficial. Also, when by reason of an imperfect performance of its function the heart fails to send enough blood to the brain, and fainting occurs, relief will come more promptly if the patient is at once placed on the back, with the head lower than the heart, thus assisting that organ in sending blood to the anemic brain. LYMPHATIC SYSTEM. The lymphatic system is composed of lymphatic vessels, lymphatic glands, and the cavities of the serous membranes. I/ymphatic Vessels. The larger lymphatic vessels struct- urally are like the veins, being composed of three coats, the middle coat containing both muscular and elastic fibers. Unlike the veins, however, muscular fibers are found in the external coat. The smaller vessels have only a connective-tissue coat lined with endothelium. In the lymphatic vessels, as in the veins, are valves opening toward the heart, but they are nearer together than are those of the venous system. The origin of these vessels in the tissues, as a rule, is by plexuses or by stomata, as in serous mem- branes ; by blind extremities, as in the lacteals ; or by lacunar interstices, as in some viscera and glands. They ultimately dis- charge into the venous system on the right side through the right lymphatic duct, and on the left side through the thoracic duct. LYMPHATIC VESSELS. 331 Right Lymphatic Duct. The lymphatic vessels of the right side of the head, neck, and thorax, and of the right arm, right lung, right side of the heart, and a portion of the convex surface of the liver, discharge into the right lymphatic duct, which in turn discharges into the right subclavian vein, at its junction with the right internal jugular vein. It is about 1.25 cm. in length and about 2 mm. in diameter. At its junction with the venous system there are two semilunar valves, to prevent regurgi- tation of the blood. Thoracic Duct. All the lymphatics not connected with the right lymphatic duct discharge into the thoracic duct. This vessel Scalenusanticus. Brachial plexus. Superficial cer- vical vein. Axillary lym- phatic trunk. Esophagus Vertebral vein. FIG. 176. Topography of the thoracic duct (Zuckerkandl). begins at the receptaculum chyli or reservoir or cistern of Pecquet, which is situated upon the body of the second lumbar vertebra, and terminates in the left subclavian vein, where it joins the left internal jugular vein. The duct is from 38 cm. to 45 cm. long, about the size of a goose-quill at commencement and termination, and somewhat smaller in the middle of its course. Structure of the Thoracic Duct (Figs. 176, 177). The thoracic duct is composed of three coats : an internal, composed of a single 332 LYMPHATIC SYSTEM. layer of endothelium, a subendothelial layer, and an elastic fibrous layer ; a middle, consisting of connective, elastic, and muscular tissues; and an external, also containing connective, elastic, and muscular tissues. I/ymphatic Glands (Fig. 178). The lymphatic glands are bodies of a pale reddish color, and are oval in shape. Their diameter is from 2 mm. to 20 mm. Lymphatic vessels run into the glands the afferent; and out of them the efferent; and through them pass the lymph and the chyle. They consist of a capsule of connective tissue, from which are given off trabeculce Longus colli muscle. Thyroid gland. Thyrocervi- cal artery. - Costocervi- cal artery. Esophagus Trachea. Axillary lymphatic trunk. Internal jugular vein. FIG. 177. Topography of the thoracic duct (Zuckerkandl). made up of connective tissue with some muscular fiber-cells ; these pass into the gland toward the center or medullary portion (M) for about one-fourth of the distance, dividing this outer or cortical portion into alveoli (C). The trabeculse then divide and subdivide, forming a network in the medullary portion, the spaces between these smaller trabeculae being also alveoli. The alveoli contain gland-pulp or lymphoid tissue, which consists of retiform tissue with lymph-corpuscles, with numerous capillary blood- vessels. Between the gland-pulp and the trabeculse in the cortical portion there is a space (l.s), which is termed a lymph-path or lymph- CAVITIES OF SEROUS MEMBRANES. 333 sinm. The afferent vessel a.l. loses all its coats, save the endo- thelial, as it enters the gland, and this is continuous with that lining the lymph-sinus ; the same is true of the efferent vessel, which emerges at the hilum. The structure of the lymphatic gland is such that the lymph in its flow passes through the pulp and takes up lymphocytes. It may also deposit any poisonous matter which it has absorbed, and thus prevent its entrance into the blood. The arteries supplying blood to the gland enter at the hilum, and the veins emerge at the same point. FIG. 178. Diagram of a lymphatic gland, showing afferent (a.l.) and efferent (e.l.) lymphatic vessels ; cortical substance ((7)*; medullary substance (M) ; fibrous coat (c), sending trabeculse (tr) into the substance of the gland, where they branch, and in the medullary part form a reticulum ; the trabeculse are surrounded by the lymph-path or sinus (Is), which separates them from the adenoid tissue (Ik) (Sharpey). Cavities of Serous Membanes. The serous membranes are closed lymph-sacs, made up of connective tissue lined inter- nally with pavement-epithelial cells, termed endothelium. Be- tween some of these cells are openings stomata which are surrounded by small protoplasmic cells. They are very distinct in the peritoneal covering of the rabbit's diaphragm. The stomata are openings into the lymphatic vessels through which lymph is pumped by the contraction and dilatation of the serous cavities, brought about by respiration and circulation. The serous membranes are: (1) peritoneum ; (2) pleura; (3) 334 DUCTLESS GLANDS. pericardium, which on account of its fibrous layer is termed fibro- serous ; (4) tunica vaginalis testis. CIRCULATING LYMPH. The lymph and its source having been discussed (p. 302), need not again be referred to. It is taken up by the lymphatic capil- laries in the tissues by endosmosis, and, as it accumulates there, gradually fills the larger vessels, and, as it is readily discharged into the venous system, there is set up a current which constitutes the lymphatic circulation. It is to be noted, however, that there is no true circulation, as in the case of the blood. The blood goes out from the heart and returns again, completing a circuit, but here the flow is always in one direction, toward the heart. Additional aids to the endosmotic force in producing the move- ment of the lymph are the contractions of the muscles of the body, by which, as in the veins, the lymphatics are compressed, and the lymph, being prevented by the valves from flowing back, is pro- pelled toward the heart. The pressure exerted by the walls of the aorta in its pulsations compresses the thoracic duct in a similar manner, and, as this possesses valves, the onflow of the lymph and chyle is favored. The force of aspiration of the thorax is FIG. 179. Endothelial cells from small artery of the mesentery of a rabbit : stained with silver nitrate and hematoxyliu (Huber). also a factor in the movement of the lymph, acting as was stated in the case of the venous blood. It has been estimated that the amount of lymph absorbed daily in a human adult is about 2000 grams, and of lymph and chyle together 3000 grams. DUCTLESS GLANDS* This term includes the spleen, the thyroid and parathyroids, the thymus, the suprarenal capsules, the pineal gland, the pituitary body, the carotid and coccygeal glands, and the lymphatic glands, the last of which we have already considered. They have re- ceived this name because they lack secretory ducts. For -the reason that they are believed by some to have important relations to the blood they are sometimes described as blood-glands or vas- cular glands. We have seen that although the lymphatic glands have no THE SPLEEN. 335 proper duct, still there are added to the lymph during its passa through the glands the lymphocytes, which are a product of the gland, and it is now held that in a similar manner while the blood is passing through the ductless glands their product is added to it This product is regarded as an internal secretion. THE SPLEEN, The spleen is the largest of the ductless glands, and its func- tion is, doubtless, the most important. Its location is in the left '** %,v^ 3fe -'- - '^*?^?'* ''iM^;^: ';/ '*"" ': V, V'l-.-.vS x ;-." /~/- '.'-^ '/. -S ( y " ' $vl?*:Mi fe^>3i?V *l3 Blood-vessel. Trabecula. -Spleen pulp. ft Artery. |^- Malpighian cor- fe. puscle with m germ center. ^'' "*^ : S^ftl*p FIG. 180. Part of a section through the human spleen : X 75 (sublimate fixation). At a is an oblong Malpighian body with a blood-vessel (Bohm and Davidoff). hypochondrium between the stomach and diaphragm. Instances are on record in which the organ was absent, while sometimes it is so divided as to present the appearance of a considerable number of small spleens. Weight. The weight of the spleen varies at different periods of life, being at birth to the entire body as 1 is to 350 ; in adult life, as 1 to 320 and 400 ; and in old age, as 1 to 700, while in 336 DUCTLESS GLANDS. certain diseased conditions, such as ague, syphilis, or heart disease, it may be enormously increased, in some cases as much as 1 to 7, or 9 kilograms, the average normal weight being about 176 grams in the cadaver, or about 225 grams during life, on account of the contained blood. Its color is dark red. The size of the spleen is greatest during digestion, and least during starvation. Chemical Composition. The spleen consists of about 75 per cent, water and 25 per cent, solids, of which only about 1 per cent, is inorganic, a part being iron. The organic ingredients are proteids, among them being a cell-globulin and a nucleo- proteid ; whether peptones exist or not is still undecided ; hemo- globin, xanthin, uric acid, glycogen, cholesterin, lecithin, and the fatty acids, formic, acetic, and butyric. The reaction of the gland Intr^lobular trabec ula. Artery to one of the ten compartments. Intralobular artery Interlobular trabec- - - ula. Intralobular trabec- * ula. Man cor- puscle. Capsule. Intralobular venous i spaces. "Intralobular vein. | ""Ampulla of Thoma. I - - Spleen pulp cord. -L ----- Interlobular vein. Intralobular vein. FIG. 181. Diagram of lobule of the spleen (Mall, Johns Hopkins Hospital Bulletin, Sept., Oct., 1898). is alkaline during life, becoming acid after death, due to the forma- tion of sarcolactic acid. Structure. The outer covering is peritoneal, and is closely adherent to the nbro-elastic coat or tunica propria, the two form- ing practically one. From it are given off trabeculce, which form the framework of the organ, in the interspaces of which, areolce, is the splenic pulp, a soft material with a reddish-brown color, within which are whitish bodies, Malpighian corpuscles (Figs. 180, 181), composed of lymphoid tissue, and having a diameter of from % mm. to 1 mm. The spleen-pulp, when examined under the microscope, is seen to be made up of connective-tissue corpuscles, the sustentacular cells, from which are given off processes that form by their union a network in the areolse of which is blood, characterized by a large number of white corpuscles. The THE SPLEEN. 337 sustentacular cells possess ameboid movement, and in some of them reddish granules, resembling hematin, are seen ; also red cor- puscles in various stages of disintegration. In young spleens Klein has seen these cells each with a large nucleus from which project bud-like processes, and it has been suggested that these are possibly white corpuscles in the process of formation. The splenic artery enters the spleen at the hilum, after having divided into a number of branches (Fig. 181) and being covered by sheaths from the fibro-elastic coat. These arteries divide and subdivide and finally end in the pulp in small arterioles, their external coat gradually changing from connective tissue to lyrnphoid tissue in which enlargements occur the Malpighian corpuscles. These consist of a delicate reticulum enclosing lymph- corpuscles. The cells which make up the reticulum possess ame- boid movement. The arterioles end in capillaries, which later cease to be distinct vessels, the cells making up their walls becoming branched and the branches uniting with the processes of the sustentacular cells. The blood which reaches the pulp through these vessels is by this means brought into direct relation with it. It is again collected into vessels which ultimately become veins that emerge from the hilum as the splenic vein. Innervation of the Spleen The nerves which are dis- tributed to the spleen are derived from the celiac plexus and right vagus. Functions. The spleen has been frequently removed from lower animals and from man. In the human being this operation, splenectomy, is performed for wounds of the organ, " wandering spleen " and enlargement due to malaria, and that accompanied with anemia. Splenectomy, for enlargement associated with leuke- mia, is accompanied with so much hemorrhage that it is, by excel- lent authority, regarded as unjustifiable. In the chapter on " Surgery of the Lymphatic System," by Prof. Warren in the International Text-Book of Surgery, the author says that the results of the many operations already reported show that the spleen is not an organ in any way essential to healthy existence. A diminution in hemoglobin and in the number of red corpuscles is a constant sequel to splenectomy in animals as in man. This diminution reaches its height two to three weeks after the operation, and then gradually disappears. There is also a temporary leukocytosis, including the polynuclear form, the lym- phocytes, and the eosinophiles. In some instances the lymph- glands and the thyroid are enlarged, and an increased vascularity of the bone-marrow occurs in animals. One of the most striking phenomena presented by the spleen is the change in size which occurs during digestion. This begins after a meal has been taken, and continues for about five hours, when the maximum is reached, after which its decrease begins. This has 22 338 DUCTLESS GLANDS. been supposed to indicate that the spleen serves as a reservoir for the blood which is needed during the time of digestion, and especially for that taking place in the stomach. The enlargement is caused by relaxation of its muscular tissue and a dilatation of the blood-vessels. A peculiar movement of contraction and expansion has been found by Roy to occur in this organ at intervals of about a minute. This he demonstrated by the use of an oneometer (Fig. 182). The principle on which this is constructed is the same as that of the plethysmograph (p. 329). It is a metal box made up of two halves, fitted together in such manner that they can be tightly closed, openings being left for the vessels of the organ which is enclosed, be it spleen or kidney. To each half is attached a membrane between which and the metal is a space filled with oil. Any increase in the size of the contained organ is accom- panied by an expulsion of the oil, which returns when the organ becomes smaller. These changes are recorded by the oncograph. While the functions of the spleen have not as yet been satis- factorily determined, still they are doubtless comprehended in the various theories which have from time to time been formulated. FIG. 182. Roy's oncometer for spleen : A, open ; B, closed. (1) It is a producer of white blood-corpuscles. As to this func- tion there is great unanimity of opinion. The blood emerging by the splenic vein contains more of these cells than that which enters the gland, and this number is greatly increased in leuko- cythemia or leukemia, in which the spleen and the Malpighian cor- puscles especially are hypertrophied. This disease may also be due to affections of other organs, as the bone-marrow and lymphatics. (2) It destroys red blood-corpuscles. This theory is based upon the fact that red blood-cells are found in the pulp in different THE THYROID AND PARATHYROID. 339 degrees of disintegration, and this is supposed to be brought about by the ameboid cells hitherto described (p. 336). It is stated that in the cells of the spleen hemoglobin is found in different degrees of transformation into other pigments, and a considerable amount of iron is also found in the splenic tissue. It is rather remarkable that if hemoglobin is set free or changed into bile-pigment, one or the other of these substances is not found in the blood of the splenic vein, and yet this is the fact. (3) It is a producer of red blood-cot*puscles. The formation of red blood -corpuscles does, doubtless, take place during fetal life and for a short time after birth in man, but there is no evidence that this function exists in the human adult, though it does in some animals, as the rabbit. Laudenbach found that in this animal after an extensive hemorrhage nucleated erythroblasts or hematoblasts are found in the splenic pulp and in the blood of the splenic vein, arid that if the spleen is removed the number of red corpuscles is diminished, as is also the hemoglobin. In an animal whose spleen has been removed the return of the red corpuscles to- their normal number is much delayed. (4) It is a producer of uric acid. From the fact that uric acid, as also xanthin, has been found in the spleen, it has been inferred that this is one of its functions. The same is true of lymphoid tissue generally, so that this function cannot be considered as one of the characteristic functions of the spleen. (5) It is an enzyme producer. Some experimenters have found that an enzyme is produced by the spleen which when carried by the blood to the pancreas converts the trypsinogen into trypsin. This theory lacks confirmation. Schafer sums up his views on the functions of this organ in the following language : " Whatever may be the nature of its functions in relation to the blood, it is certain that the organ is in no way essential to the normal nutrition of the body. It is, on the other hand, not at all improbable that the main function of the spleen is to serve a mechanical purpose, answering as a reservoir at certain periods of digestion for the blood which has to pass through the portal system ; and the fact that, as was first shown by Roy, the spleen normally exhibits regular rhythmic contrac- tions and dilatations, seems to point to its exercising an influence in assisting the flow of blood through the portal vein, and thus through the liver." THE THYROID AND PARATHYROID. The thyroid gland is also called the thyroid body ; it is situated in front of the trachea or windpipe, and consists of the lobes united by an isthmus. It weighs from 30 to 60 grams, and is larger in females than males, and is said to be larger during men- struation. 340 DUCTLESS GLANDS. Chemical Composition. An analysis of an adult thyroid gives a percentage of 82.24 of water, 17.66 of organic and 0.1 of inorganic constituents ; in that of an infant the figures were, 77.21, 22.35, and 0.44 respectively. Like the spleen, it is alkaline during life and acid after death, the acidity being due to the same cause the formation of sarcolactic acid. Fatty acids, xanthin, hypoxanthin, and other extractives have also been obtained from it. The constituents which possess the greatest importance are those of a proteid nature, for upon them it is believed depend some of the remarkable powers with which this gland is endowed. Among these are thyreoproteid and thyreo-antitoxin (C 6 H U N 3 O 5 ). A substance has also been found in the thyroid, principally com- bined with a proteid, although also free, called thyro-iodin and iodo-thyrin, containing 9.3 per cent, of iodin and 0.56 per cent, of phosphorus. The amount of iodin in each gram of the human adult thyroid varies from 0.3 to 0.9. Structure. The thyroid has a capsule of connective tissue which sends off septa or trabeculce that enclose the thyroid vesicles --- Lumen of follicle. Connective tissne. 1 Epithelium of follicle. J FIG. 183. From section through thyroid gland of child (Bohm and Davidoff). (Fig. 183), each of which is lined by cubical epithelium and con- tains viscid, colloid liquid, yellowish in color, which is coagulated by alcohol and stained with hematoxylin, and is doubtless secreted by these cells. Red blood-corpuscles in various stages of disinte- gration and white corpuscles are also found in these vesicles. The color of the colloid material is probably due to hemoglobin. Around the vesicles is a plexus of capillary blood-vessels, which is also found between the vesicular epithelium and the endothelium of the lymph-spaces, which latter surround the vesi- cles and communicate with lymphatic vessels. Colloid material, THE THYROID AND PARATHYROID. 341 identical with that contained in the vesicles, has been found in the lymphatics. The arteries which supply the thyroid body are the superior and inferior thyroid, and sometimes the thyroidea media or ima, an occasional branch of the innominate or aorta. The nerves are from the middle and inferior cervical ganglia of the sympathetic. Functions. In recent years the physiology of the thyroid body has received a great deal of attention, and important addi- tions have been made to the knowledge of its function by a study of (1) the effects of its disease and (2) of its removal. Cretinism. In some parts of Switzerland and elsewhere on the Continent there exists a disease characterized by a swelling of the thyroid, termed goiter, together with "stunted growth, swelled abdomen, wrinkled skin, wan complexion, vacant and stupid countenance, misshapen cranium, idiocy, and comparative insensi- bility." This disease is cretinism, and those suffering from it are cretins. This condition is accompanied by disease of the thyroid, as manifested by the goiter. Myxedema. A similar condition is sometimes seen in which the striking characteristic is the appearance of the skin, which resembles edema ; and the material which is deposited in the con- nective tissue was thought to be mucin, hence the name myxedema. Although there is more mucin than in ordinary connective tissue, still the material here is not altogether mucin, nor is it true edema /. v: o FIG. 202. From longitudinal section of human trachea, stained in orcein (Huber). ated within the two layers of an elastic fibrous membrane. In the spaces between the rings these layers unite, thus forming a single membrane. The membrane behind is also single. Be- tween the ends of the cartilaginous rings is also a transverse layer of unstriped muscular tissue, trachealis muscle, and posterior to this are some longitudinal fibers of the same kind. The trachea is lined with mucous membrane covered with columnar ciliated epithelium, and in it are mucous glands, tracheal glands, whose secretion lubricates the membrane, and there are elastic fibers arranged longitudinally. Blood-vessels. The artery supplying the trachea is the inferior thyroid, and its veins terminate in the thyroid venous plexus. Nerves. The nerves are branches of the vagus and sympa- thetic. % 362 RESPIRATION. THE BRONCHI. These are two in number : the right bronchus, which is more horizontal than the left and is about 2.5 cm. in length, divides into three subdivisions which go to the right lung, which has three lobes. The left bronchus is about 5 cm. long, and divides into two branches, one for the upper, and the other for the lower lobe of the left lung. The bronchi are, like the trachea, made up of cartilaginous rings or plates with intervening membrane. THE LUNGS. There are two lungs, right and left, situated in corresponding sides of the thorax ; each being divided by fissures into lobes the right into three, superior, middle,. and inferior, and the left into two, superior and inferior. The root of the lung, where this organ is connected with the heart and trachea, is composed of bronchus, pulmonary artery, pulmonary veins, bronchial arteries, bronchial veins, pulmonary plexus of nerves, lymphatics, bronchial glands, and areolar tissue, all covered by a serous membrane the pleura. Structure. Each lung is covered by the visceral layer of the pleura, beneath which is areolar tissue containing elastic fibers. This coat exists not only on the outside, but also penetrates into the interior between the lobules. The lobules form the parenchyma of the lung. Lobules. A lobule consists of a terminal or ultimate bronchial tube and the air-cells or alveoli, into which it opens, together with such pulmonary and bronchial vessels, lymphatics, and nerves as are associated therewith. Each lobule may be regarded as a miniature lung, a lobe being made up of many lobules. Their form and size vary, those which are on the exterior of the lung being pyramidal in shape, the base forming a polygonal figure ; while those more deeply seated present considerable variations from this. To obtain a clearer idea of the minute structure of the lung than can be obtained from the above description, it will be profitable to approach the lobule from the direction of the bronchi. After entering the lung the bronchi divide and subdivide into two branches, or dichotomously, occasionally into three. The cartilages become plates or lamince, between them being mem- brane. When the bronchial tubes become as small as 0.5 mm. the cartilage disappears and the walls are membranous ; the fibrous tissue and the longitudinal elastic fibers continue throughout, while the muscular tissue, equally extensive, is arranged around the tubes. The mucous membrane continues to be covered with ciliated epithelium of the columnar variety, until the lobule is reached. At this point each subdivision of a bronchus becomes PLATE III. A, upper bone of sternum; B, B, two first ribs ; <7, (7, second pair of ribs ; D, D, right and left lungs; E, lower end of sternum; F, F, right and left halves of the diaphragm in sections: the right half separating the right lung from the liver, the left half separating the left lung from the broad cardiac end of the stomach ; G, G, eighth pair of ribs; K, K, ninth pair of ribs (Maclise). THE LUNGS. 363 a tabular bronchial tube or bronchiole or ultimate bronchial tube, and on one side dilatations exist, air-cells or pulmonary alveoli. Respiratory bronchiole. Alveolar duct. Artery. Lung- tissue. Bronchiole. Fio. 203. Lung-tissue. FIG. 204. FIGS. 203 and 204. Two sections of cat's lung: Fig. 203, X 52; Fig. 204, X 35 (Bohm and Davidoff). These increase in number, and, although at first limited to one side of each bronchiole, they subsequently surround the tube, and the 364 RESPIRATION. bronchiole becomes enlarged, forming the atrium, which opens into sac-like cavities, infundibula, each infundibulum being about 1 mm. in diameter, and these open into air-cells or pulmonary alveoli, which latter have a diameter of from 0.1 mm. to 0.3 mm. At the infundibula the muscular tissue is less abundant and the elastic fibers are arranged around the openings of the air-cells. The epithelium in the bronchioles is both columnar ciliated and cubical non-ciliated ; but in the infundibula and alveoli it is of the pavement variety, with some cubical. Blood-vessels. Branches of the pulmonary artery pass into the lung with the bronchial tubes and terminate in the pulmonary capillaries (Fig. 205), which as plexuses lie under the mucous mem- brane of the walls of the infundibula and alveoli and of the par- titions or septa between them. The capillaries have very thin Blood-capillaries seen in surface "" Alveolus in cross- section. FIG. 205. Section through injected lung of rabbit (Bohm and Davidoff). walls and a diameter of about 8 p, while the spaces between them are even smaller. Small veins collect the blood, and these uni- ting with others finally discharge into the pulmonary veins, which bring the blood back to the left auricle. Some of the blood brought to the lungs by the bronchial arteries returns to the venous circula- tion through these veins. The bronchial arteries, branches of the aorta, supply the blood necessary to nourish the lung tissue, and the bronchial veins carry most of it back to the venous circulation, by the way of the vena azygos major on the right side, and by the superior intercostal or left azygos vein on the left side. Nerves. The innervation of the lungs is supplied through the pulmonary plexuses from the sympathetic and vagus. The nerves accompany the bronchial tubes. THE THORAX. 365 THE PLEURA, The pleura is a serous membrane which covers the lung, pleura pulmonalis or serous layer of the pleura, being at its root reflected so as to line the thorax, forming the pleura costalis or parietal layer of the pleura. The theoretical space between the two layers is the pleural cavity. Inasmuch as these layers are normally always in contact, there is no actual space or cavity between them, although they are moistened by a small amount of secretion for lubricating purposes. When fluid collects here, as it does in some forms of pleuritis or inflammation of the pleura, the layers are then separated. Blood-vessels. The arteries which supply the pleura have their origin in the intercostal, internal mammary, musculophrenic, thymic, pericardiac, and bronchial arteries. The veins are similar in their anatomic relations. Nerves. The nerves are of phrenic and sympathetic origin, and accompany the branches of the bronchial artery. THE THORAX. The thorax or chest is the structure which contains the lungs, heart, and great blood-vessels. The thoracic cavity is the space within the thorax in which these organs are located. The thorax is formed by the vertebral column and the ribs posteriorly, the sternum and the costal cartilages anteriorly, and by the ribs laterally. The spaces between the ribs, intercostal spaces, are filled by the intercostal muscles. These muscles and others which are attached to the thorax are concerned in the movements of respira- tion. Vertebral Column. This portion of the thorax is rigid and takes no part in any of the movements connected with respiration. The vertebrae which are concerned in the formation of the thorax are the 12 dorsal (Figs. 206, 207), and the anatomic points of interest are the facets and demifacets on their bodies, which form articulating surfaces for the heads of the ribs, and the facets on the transverse processes for articulation with the tubercles of the ribs. Between the vertebrae are intervertebral disks of fibrocartilage, which under the microscope present the appearance of fibrous tissue with articular cartilage (Fig. 31, page 39). Ribs. All the ribs, from the first to the twelfth, enter into the formation of the thorax, and articulate posteriorly with the vertebrae. The first seven, the true ribs, are attached anteriorly to the ster- num, not directly, but by means of the costal cartilages ; while of the others, the false ribs, 3, the eighth, ninth, and tenth, are attached to the cartilage of the seventh rib, and, 2, the eleventh and twelfth, the floating ribs$ are free at their anterior extremities. 366 RESPIRATION. The ribs differ very materially in their general relations ; thus the upper ones are less oblique than the lower ones, the obliquity in- FIG. 206. a, Vertebral column; b, clavicle; d, ribs; e, sternum. creasing as far down as the ninth rib, when it becomes less (Fig. 206). Axis of rotation. FIG. 207. First dorsal vertebra and rib. FIG. 208. Sixth dorsal vertebra and rib. Costal Cartilages. These are characterized by their elas- ticity, which is greater in early life, and in the false ribs than in THE THORAX. 367 the true. The elasticity diminishes as years go on, until, at an advanced age, they are calcified. Rib-cartilage is not infrequently fibrous in character, and the cells are, as a rule, larger and collected into groups of greater size than those of articular cartilage (Fig. 209). Respiratory Muscles. The muscles which are concerned in the respiratory movements of the thorax may be divided into three groups: (1) Of ordinary inspiration; (2) of forced inspira- Matrix. ir^t: ' il FIG. 209. Hyaline cartilage (costal cartilage of the ox). Alcohol preparation ; X 300. The cells are seen inclosed in their capsules. In the figure a are repre- sented frequent but by no means characteristic radiate structures (Bohm and Davidoff). tion; (3) of forced expiration. There are no muscles concerned in ordinary expiration. Muscles of Ordinary Inspiration. These are diaphragm, scaleni, external intercostals, internal intercostals (anterior portion), leva- tores costarum. Th.e Diaphragm. This forms the lower boundary of the thoracic cavity, separating it from that of the abdomen. It arises from the whole interior surface of the thorax, and the fibers which compose its muscular portion are inserted into the central or cordiform tendon. Through the diaphragm pass the vena cava, the esophagus, and the aorta. Nerve-supply. The phrenic nerves and the phrenic plexus of the sympathetic. Scaleni. The scalenus anticus is a muscle which arises from the anterior tubercles of the transverse processes of the third, fourth, fifth, and sixth cervical vertebrae, and is inserted into the 368 RESPIRATION. first rib. The scalenus medius arises from the posterior tuber- cles of the transverse processes of the cervical vertebrae from the second to the seventh, both inclusive, and is also inserted into the first rib. The scalenus posticus arises from the posterior tuber- cles of the transverse processes of the fifth, sixth, and seventh cervical vertebrae, and is inserted into the second rib. Nerve-supply. Branches of the anterior divisions of the fifth, sixth, seventh, and eighth cervical nerves. The scalenus medius receives an additional supply from the deep external branches of the cervical plexus. Intercostal Muscles. These fill up the intercostal spaces, and consist of muscular and tendinous fibers, the combination of the two kinds of tissue giving both contractility and strength. There are two sets of these muscles, external and internal. External Intercostal Muscles. These fill the intercostal spaces from the tubercles of the ribs to the costal cartilages, from which point to the sternum there is no muscular tissue. They arise from the lower borders of the ribs, and are inserted into the upper borders of the ribs below them. The direction of their fibers is obliquely downward and forward. Nerve-supply. The intercostal nerves. Internal Intercostals. Those Avhich are attached to the true ribs extend 'from the sternum to the angles of the ribs, where the muscular tissue ceases to exist and a membranous structure takes its place as far as the vertebrae. Those which are attached to the false ribs extend from their cartilages backward in a manner similar to that just described. The fibers of this group arise from the ridge on the inner surface of the ribs and from the costal cartilages, and are inserted into the upper borders of the ribs below. The direction is obliquely downward and forward, the external and internal intercostals, therefore, cross each other. Nerve-supply. The intercostal nerves. Levatores Costarum. These muscles arise from the extremities of the transverse processes of the vertebrae from the seventh cervical to the eleventh dorsal, and are inserted into the upper borders of the ribs between the tubercles and the angle. Nerve-supply. The intercostal nerves. Action. The first rib on each side is raised and held in a fixed position by the scaleni muscles ; the external intercostals now contracting, all the ribs are raised. This elevation of the ribs is assisted by the contraction of that portion of the internal inter- costals which is situated in the front of the thorax, and by that of the levatores costarum. These are, therefore, all muscles of ordi- nary inspiration. All authorities are not agreed as to the action of the inter- costals. Haller regarded both external and internal intercostals as muscles of inspiration ; Keen considers the external intercostals THE THORAX. 369 as being depressors of the ribs, hence muscles of expiration ; while the function of the internal set he considers to be that of elevating the ribs, and therefore regards them as muscles of inspiration. The form of the diaphragm, when its muscular tissue is re- laxed, is that of a dome with its convexity upward. When the muscular fibers contract they pull down the central tendon, and at the same time become themselves less convex and straighter. This movement constitutes the descent of the diaphragm, and results in increasing the capacity of the thorax ; therefore the diaphragm is a muscle of inspiration indeed, it is the most important of all the inspiratory muscles. The abdominal cavity contains the abdominal organs liver, stomach, spleen, intestines, etc. and in its descent the diaphragm depresses these structures, which under the pressure yield to a cer- tain extent, the protrusion of the abdominal walls aiding by allowing this displacement to take place to a greater degree than it would were they rigid. There is, however, a limit to the amount that the central tendon can descend, and when this limit is reached the tendon becomes a fixed point from which the mus- cular tissue can act, and the effect is to raise the lower ribs to which it is attached ; thus the capacity of the thorax is still more increased. This descent amounts to from 5.5 mm. to 11.5 mm. in quiet breathing and 42 during forced inspiration. Not only are the abdominal organs depressed, but they are also compressed, and their attachments put upon the stretch ; when, therefore, the mus- cular tissue of the diaphragm ceases its contraction and begins to relax, the elasticity of the depressed and compressed abdominal contents and the abdominal walls tends to raise the diaphragm into the position it occupied at the beginning of the respiratory act. This ascent of the diaphragm is, therefore, a phenomenon of expiration. Muscles of Forced Inspiration. Trapezius, latissimus dorsi, rhomboideus minor, rhomboideus major, serratus posticus superior, serratus posticus inferior, iliocostalis, quadratus lumborum, sterno- mastoid, pectoralis major, pectoralis minor, subclavius. Trapezius. This muscle arises from the superior curved line of the occipital bone, the ligamentum nuchse, spinous process of seventh cervical, and the spinous processes of all the dorsal vertebrae, and the supraspinous ligament, and is inserted into the clavicle, acromion process, and spine of the scapula. Nerve-supply. The muscular branch of the spinal accessory and branches from the anterior divisions of the third and fourth cervical nerves. Latissimus Dorsi. It arises from the spinous processes of the six lower dorsal and those of the lumbar and sacral vertebrae, the supraspinous ligament, crest of the ilium, and 3 or 4 lower ribs, and is inserted into the bicipital groove of the humerus. 24 370 RESPIRATION. Nerve-supply. Middle or long subscapular nerve. Rhomboideus Minor. It arises from the ligamentum nuchae and spinous processes of the seventh cervical and first dorsal vertebrae, and is inserted into the scapula at the root of the spine. Nerve-supply. The anterior division of the fifth cervical nerve. , Rhomboideus Major. This arises from the spinotis processes of the 4 or 5 upper dorsal vertebrae and the supraspinous ligament, and is inserted into the tendinous arch extending from the scapula at the root of its spine to its inferior angle. Nerve-supply. The anterior division of the fifth cervical nerve. Serratus Posticus Superior. This muscle arises from the liga- mentum nuchae and the spinous processes of the seventh cervical and 2 or 3 upper dorsal vertebrae and the supraspinous ligament, and is inserted into the second, third, fourth, and fifth ribs beyond their angles. Nerve-supply. The external branches of the posterior divisions of the upper dorsal nerve. Serratus Posticus Inferior. It arises from the spinous processes of the eleventh and twelfth dorsal and the 2 or 3 upper lumbar vertebrae and supraspinous ligament, and is inserted into the four lower ribs beyond their angles. Nerve-supply. The external branches of the posterior division of the lower dorsal nerves. lliocostalis. This is sometimes called sacrolumbalis. It is the outer part of the erector spinae which arises from the sacro-iliae groove, and forms a broad tendon attached to the sacrum, lumbar vertebrae, supraspinous ligament, and that of the ilium and the sacrum. It is inserted into the angles of the 6 or 7 lower ribs. Nerve-supply comes through the external branches of the pos- terior divisions of the lumbar and dorsal nerves. Quadratus iMmborum. It arises from the iliolumbar ligament and the crest of the ilium, and is inserted into the last rib and the transverse processes of the 4 upper lumbar vertebrae. Nerve-supply. The anterior branches of the lumbar nerves. Sternomastoid. It arises from the sternum and clavicle, and is inserted into the mastoid process of the temporal bone and the occipital bone. Nervous Supply. The spinal accessory and deep branches of the cervical plexus. Pectoralis Major. It arises from the clavicle, sternum, carti- lage of the true ribs, aponeurosis of the obliquus externus, and is inserted into the anterior bicipital ridge of the humerus. Nervous Supply. The anterior thoracic nerve. Pectoralis Minor. It arises from the third, fourth, and fifth ribs, and from the aponeurosis covering the intercostal muscles, and is inserted into the coracoid process of the scapula. THE THORAX 371 Nervous Supply. The anterior thoracic nerves. Subclavius. It arises from the first rib and its cartilage, and is inserted into the clavicle. Nervous Supply. A filament from the cord formed by the union of the fifth and sixth nerves. * - Serratus Magnus. It arises from the 8 upper ribs and the aponeurosis covering the intercostal muscles, and is inserted into the scapula. Nervous Supply. The posterior thoracic nerve. Action. The trapezius and rhomboidei fix the scapula, and the serratus magnus, contracting, raises the ribs. The arm being fixed, the latissimus dorsi also raises the ribs. The ribs are like- wise elevated by the action of the serratus posticus superior, while the serratus posticus inferior draws downward and backward the lower ribs, increasing thereby the capacity of the thorax. Some authorities regard the serratus posticus superior as being brought into action in ordinary respiration. When the ribs are drawn downward they are held there by the serratus posticus inferior, thus overcoming the upward lifting of the ribs by the diaphragm. The iliocostalis and quadratus lumborum fix the last rib and oppose the tendency of the diaphragm to raise it. The head being fixed, the sternomastoid elevates the thorax. The group of muscles consisting of the pectoralis major and minor and the subclavius draw the ribs upward when the head is fixed. In this manner all the muscles mentioned, some to a greater and some to a lesser degree, aid in the process of forced inspira- tion. Muscles of Forced Expiration. Internal intercostals, triangularis sterni, obliquus externus, obliquus internus, transversalis, rectus. Internal Intercostals (p. 368). Triangularis Sterni. This muscle is situated on the back of the sternum and anterior portion of the ribs. It arises from the sternum, ensiform cartilage, and costal cartilages of the 3 or 4 lower true ribs, and is usually inserted into the costal cartilages of the second, third, fourth, and fifth ribs. Nerve-supply. The intercostal nerves. Obliquus Externus. This muscle is more familiarly known as the external oblique. It arises from the 8 lower ribs, and is inserted into the crest of the ilium and into tendinous fibers which form a broad aponeurosis. Nerve-supply. The lower intercostal nerves. Obliquus Internus. This is also called the internal oblique. It arises from Poupart's ligament, the crest of the ilium, and the posterior lamella of the lumbar fascia, and is inserted into the os pubis, linea alba, through an aponeurosis to the cartilages of the seventh, eighth, and ninth ribs, and into the cartilages of the tenth, eleventh, and twelfth ribs. 372 RESPIRATION. Nerve-supply. The lower intercostal nerves and the ilio- inguinal nerve. Transversalis. It arises from Poupart's ligament, the crest of the ilium, cartilages of the 6 lower ribs, and transverse processes of the lumbar vertebrae, and is inserted into the linea alba or pubes. Nerve-supply. The lower intercostal nerves. Rectus Abdominis. It arises from the os pubis, and is inserted into the cartilages of the fifth, sixth, and seventh ribs. Nerve-*supply. The lower intercostal nerves. Action. The internal intercostal muscles, except the anterior portion (p. 368), depress the ribs, at the same time inverting their lower borders, thus diminishing the size of the thoracic cavity. The triangularis sterni draws down the costal cartilages, thus aiding in the expelling of air from the lungs. When the pelvis and the spine are fixed, the external and in- ternal oblique, trans versalis, and the rectus compress the thorax at its lower part, and thus assist in the expiratory process. RESPIRATORY MOVEMENTS, The respiratory movements are of two kinds inspiratory and expiratory. Inspiratory Movements. By virtue of the inspiratory movements the air passes into the lungs. During their perform- ance the thorax expands under the influence of the diaphragm and the inspiratory muscles (p. 367). In inspiration all the diam- eters of the chest are increased. The descent of the diaphragm increases the vertical diameter (Plate 1). At the same time the transverse and anteroposterior diameters are also increased. The shape and direction of the ribs are such that when they are raised their convexities are carried outward, and thus the transverse diameter of the thorax is increased. But this movement also carries the sternum forward, thereby increasing the anteroposterior diam- eter. Under some circumstances, as when there is some obstruc- tion to the entrance of air, additional muscles, called extraordinary muscles of inspiration or muscles of forced inspiration (p. 369), are brought into action. In this way most of the muscles about the thorax may be called upon. It should be noted that inspiration is an active process that is, one that requires for its performance the action of muscles. Expiratory movements are for the most part passive in their nature that is, are not due to muscular contraction. During the descent of the diaphragm, referred to in describing the inspi- ratory movements, the elastic abdominal organs and their attach- ments and the abdominal walls are put upon the stretch. At the end of the inspiratory act the diaphragm ceases to contract, and RESPIRATORY MOVEMENTS. 373 by virtue of the elasticity of these structures the contents of the abdomen return to the position they occupied at the beginning of the diaphragm's descent, and in so doing this structure is carried back to its original position. The elevation of the ribs by the contraction of the external intercostals during inspiration twists the elastic costal cartilages which join the ribs to the sternum : as soon as these muscles cease to contract these cartilages untwist, and in so doing aid in the return of the ribs. In describing the structure of the lungs it was stated that the walls of the lobules are rich in elastic tissue : in inspiration these lobules are greatly distended, their walls being put on the stretch. When the inspira- tory forces cease to act, then this tissue, by virtue of its elasticity, returns to its former condition, and in so doing expels the air, constituting expiration. Contractility may be said to be the inspiratory force ; elasticity, the expiratory force. As in inspiration, so in expiration, there are occasions when obstruction to the outgoing air exists, and forced expiration be- comes necessary. The muscles concerned in this act* are known FIG. 210. The larynx in gentle breathing : L, epiglottis ; V, vocal cords ; 8, cartilages of Santorini, which sur- mount the arytenoid cartilages ; P, P, ventricular bands (Lennox-Browne). FIG. 211. The larynx in deep breath- ing : W, P, tracheal rings ; B, openings of bronchi ; P, P, ventricular bands (Lennox-Browne) . as extraordinary muscles of expiration or muscles of forced expira- tion, whose arrangement is such that in their contraction the capacity of the thorax is diminished. They have been already described (p. 371). The abdominal walls, by exerting pressure on the abdominal viscera, and thus on the diaphragm, still further diminish the thoracic cavity and force out the contained air. Movements of the Glottis. There are in connection with the process of respiration certain movements of the glottis which are important. On examination of the interior of the larynx it will be seen that during inspiration the vocal cords separate, and during expiration approach each other. During deep breathing (Fig. 211) the separation of the cords is greater than in quiet breathing (Figs. 210, 219). The area of the trachea is nearly three times that of the space between the cords at the beginning of inspiration. The separation of these cords is effected by the contraction of the posterior crico- arytenoid muscles, which, by their attachment to the arytenoid cartilages, rotate these outward, and thus separate the posterior 374 RESPIRATION. ends of the cords which are attached to them, increasing the area nearly twofold. When these muscles cease their contraction, as they do at the end of the inspiratory act, then the elasticity of the cartilages brings the muscles back to the position they occupied at the beginning of inspiration. These movements of the glottis occur synchronously with the respiratory movements of the thorax. The muscles of the larynx have already been described (p. 355). CAPACITY OF THE LUNGS, At the beginning of an ordinary inspiration the lungs contain air, which so distends them that the visceral layer of the pleura is in contact with the parietal layer. As the thorax enlarges the air in the lungs distends them still more, so that they are still kept in contact with the thoracic walls. This contact between the visceral and parietal layers of the pleura is constant, irrespective of the amount of distention of the lungs. The expansion of the air in the lungs makes it of less density than the external air with which it is in communication through the air-passages, and immediately there is a flow of external air into these passages to establish an equilibrium : this inflow constitutes inspiration. Immediately following air is expelled from the lungs, and this outflow constitutes expiration. To this volume of air which flows in and out during ordinary respiration the name of tidal air is given, from the resemblance which the process bears to the flow and ebb of the tide. The amount of this tidal air is variously stated by different authorities; some place it as low as 49 c.c., and others as high as 1640 c.c. It varies greatly in different individuals, and in the same individual according to the manner and frequency of his breathing. Hutchinson has made 80 deter- minations on different individuals, and obtained from 114 c.c. to 196 c.c. in a condition of rest, and from 262 c.c. to 360 c.c. during exercise. One observation was as high as 1262 c.c. In newborn children it is 35 c.c. Each individual has the power, however, of taking into the lungs an additional amount of air over and above the tidal air, by a deep or forced inspiration. To this additional amount the term complemental air is applied, and it may be regarded as averaging about 1500 c.c. As more air is taken in by forced inspiration than is usually inhaled during an ordinary inspiration, so by a forced expiration more air is expelled than is ordinarily exhaled during an ordinary expiration. To the air thus expelled during a forced expiration the name of reserve or supplemental air is given. Hutchinson states the amount to vary from 1148 c.c. to 1804 c.c., while by some it has been placed at 2624 c.c. But even after all the air has been expelled that can be by TYPES OF RESPIRATION. 375 bringing into play all the muscles and other forces available, there still remains a volume of air which cannot be forced out ; this is the residual air, and has been estimated by Sir Humphrey Davy to be 674 c.c. It has been measured by different observers upon both the living and the dead body. In one set of observations upon 9 corpses, the minimum was 640 c.c., the maximum, 1231 c.c., the mean, 981 c.c. In another series of observations on living males the results were 440 c.c. minimum, 1250 c.c. maximum, and 796 c.c. mean ; and in still another upon living females, 347 c.c. minimum, 526 maximum, and 478 c.c. mean. Neupauer determined the amount of residual air in a living subject to be very much greater. Vital capacity is the volume of air over which an individual can exert control. It is the amount which he can expel by a forced expiration after having taken a forced inspiration ; it is, therefore, the sum of the tidal, complemented, and supplemental air ; it excludes the residual air. Hutchinson gives it as 3558 c.c., basing his estimate on 1923 observations. The vital capacity of the newborn child is about 120 c.c. Although it is impossible to give any figures which will repre- sent measurements that are necessarily so variable as those just given, still it may be of use to have an approximate estimate for purposes of reference ; and we may place the amount of tidal air at 300 c.c., complemental air at 1500 c.c., reserve air at 1500 c.c., and residual air at 1000 c.c. Frequency of Respiration. In the newborn child the number of respirations per minute is 44 ; at five years of age, 26 ; at twenty years, 20 ; at thirty years, 1 6 ; and at fifty years, 18. These figures represent an average during a quiescent condition. Should the respirations be counted during sleep, they would be 1 or 2 less per minute ; during great activity they would be increased con- siderably, in the adult running up to 30 or more. TYPES OF RESPIRATION. It has been the practice among writers on physiology to speak of the superior costal or female type of respiration and the abdominal, inferior costal, or male type. The following condensed statement from one of the best text-books on this subject represents the views of these writers : " In children, as well as in the adult male, under ordinary conditions, the diaphragm performs most of the work, and the movements of the abdomen are the only ones especially noticeable .... In the female the movements of the chest, particularly of its upper half, are habitually more prominent than those of the abdomen, and this difference in the mechanism of respiration is characteristic of the sexes." The protrusion of the abdominal wall, caused by the descent of the 376 RESPIRATION. diaphragm, is very marked in children, and produces the ab- dominal type of respiration. The costal type spoken of above as characteristic of the female was supposed to be a wise provision of nature, in order that when pregnancy should occur the respira- tory movements would not be interfered with, as they would be did the female possess the inferior costal type of respiration seen in the male. Very careful and complete studies of women in and out of civilization, the lower portions of whose chests have never been compressed with corsets or with other devices calculated to pre- vent expansion of these parts, have demonstrated that the supposed respiratory difference in male and female does not exist naturally, and that when it is found it is due to the corset, and not to any peculiarity of sex. Indeed, if the male chest is encased in a corset, the inferior costal type becomes changed at once into the superior costal. It is also of interest to note that in one case at least the observation was made in which the inferior costal type of respiration was well marked in a pregnant woman within one week of her confinement. CHEMISTRY OF RESPIRATION. The air, when dry and measured at C. and 760 mm. press- ure, contains 20.96 parts by volume of oxygen, 79.02 parts of nitrogen, and 0.03 part of carbon dioxid. About 1 per cent, of what is given as nitrogen is argon. Watery vapor is also present, the amount varying under different circumstances, being greater the higher the temperature of the air. The term absolute humidity has reference to the total amount of watery vapor which a volume of air contains, irrespective of the question of tem- perature ; the term relative humidity is used to express the pro- portion of watery vapor present in the air at certain temperatures as compared with air fully saturated, saturation being expressed by 100. Absolute humidity is expressed in grams per cubic meter or in grains per cubic foot, while relative humidity is expressed in percentages. Thus if the temperature of the air is 4 C., and it is saturated with watery vapor, its relative humidity would be said to be 100; if, now, its temperature was raised to 27 C. its relative humidity would be only 24, because the higher the temperature the more vapor can a given volume of air contain, and the air at 27 C. would hold a much greater amount than when its temperature was 4 C. The amount of moisture present in air is an important factor in the preservation of health. If it is too dry, the air-passages are irritated ; while if too moist, there is produced a feeling of oppression. A relative humidity of 70 is, as a rule, very agree- able. Traces of ammonia, some ozone, and sodium chlorid are CHEMISTRY OF RESPIRATION. 377 also found in the atmospheric air. Besides these constituents, which are universal, there are many others that may or may not be present as the result of processes of manufacture. Expired Air. When the atmospheric air has been breathed its composition is markedly changed in the following particulars : 1. It has gained carbon dioxid, the amount being increased from 0.03 or 0.04 part per cent, to 4.38. 2. It has lost oxygen, the 20.96 volumes per cent, being reduced to 16.03, or about 5 per cent. It should be noted that the loss of oxygen is greater than can be accounted for by the amount of that gas returned in the carbon dioxid, the difference representing the amount used up in processes of oxidation constantly going on in the body. 3. It has gained watery vapor, the expired air being saturated. The actual amount of vapor which it receives while in the lungs will, of course, vary. If the air when inspired is cool and dry, it will absorb more moisture from the body than if it is moist and warm. The daily loss from this source is about 540 grams. 4. The expired air is, as a rule, warmer than the inspired. Thus in a series of obser- vations it was found that when the inspired air had a temperature of from 15 to 20 C., when expired its temperature was 37.3 C. ; when the inspired air was 6.3 C., it was 29.80 C. when expired; and when 41.9 C. at inspiration, it was 38.1 C. at expiration. The inspired air is warmed from 1 to 2 degrees more when taken in by the nose than by the mouth. 5. The actual volume of expired as compared with inspired air is less by about 2 per cent. 6. The expired air contains certain volatile organic matters, whose presence is at once recognized by the sense of smell, among them crowd-poison, although chemists have not yet made us acquainted with their exact composition. The following table represents the average composition and temperature of inspired and expired air : Inspired Air. Expired Air. Oxygen 20.96 16.03 Nitrogen 78.00 78.00 Argon 1.00 1.00 Carbon dioxid 0.04 4.38 Watery vapor variable saturated Temperature '. " about 37 C. Respiratory Quotient. This is a term employed to express the ratio between the carbon dioxid given off and the oxygen ab- sorbed, and is obtained by dividing the former by the latter i. e., CO 4.34 O 4 93 = 0-88, so *^at there is gained 0.88 volume of CO 2 for every volume of O absorbed. This ratio is an exceedingly vari- able one, differing in different animals, and even in the same indi- vidual with age, food, temperature of the air, during exercise, etc. There are various reasons which account for these differences. 378 RESPIRATION. It is to be borne in mind, in the first place, that the sources of carbon dioxid in the animal body are numerous. The oxygen which is absorbed at any given time does not immediately appear in the carbon dioxid given off ; it may be absorbed and enter into combinations, which may retain it for a considerable time ; so that at any given time the amount of oxygen absorbed may be greater than that given off in the carbon dioxid, or vice versa. Then, too, more CO 2 is formed in proportion to the amount of oxygen absorbed by the decomposition of some substances than others. Thus when carbohydrates constitute the diet the amount of oxygen which they contain is enough to satisfy their hydrogen, but fats and proteids need more, and in the formation of water they use up oxygen ; from this it follows that more oxygen is absorbed during an animal than during a vegetable diet. When the amount of carbon dioxid given off equals the amount of oxygen absorbed, the respiratory quotient is 1. The quotient will be higher in herbivora, where it is from 0.9 to 1.0, than in carnivora, where it is from 0.75 to 0.8. It is interesting to note that when an her- bivorous animal is fasting that is, at a time when it is taking in no food, but is living on its own tissues, and is therefore for the time being a carnivorous animal the quotient is that of the car- nivora, 0.75. In observations upon man it is found that before feeding the quotient is 0.84 to 0.89 ; when meat or fat is given, 0.76 ; with potatoes, 0.93 ; and with glucose, 1.03. The respiratory quotient is higher in adults than in children ; during the day than at night ; during wakefulness than during sleep ; during activity than during rest. Ventilation.- It is manifest that if at each inspiration oxygen is extracted from the air, in the course of time the amount of this gas will be so reduced as to make its want seriously felt. It is necessary, therefore, in order to keep the amount of oxygen up to the standard, that some provision should be made to supply it. Besides the removal of the oxygen, the air is still further rendered unsuited for respiratory purposes by the carbon dioxid, and especially by the organic matter thrown off by the expired air ; the oxygen being still further diminished by stoves and lights, and the air being vitiated by the products of combustion. Another and no less important source of vitiation of the air is the organic matter thrown off from the skin, particularly in those of uncleanly habits. Decayed teeth and foul mouths add to the contamination. To supply oxygen and to remove these impurities are the objects of ventilation. A common test to determine whether the air of an enclosed space contains sufficient oxygen for respiratory purposes is to see if a candle will burn in it. This test is used to determine whether the air in vaults or in excavations is fit for respiration. A candle will not burn if the air contains only 17 volumes per cent, of oxygen ; CHEMISTRY OF RESPIRATION. 379 a man can breathe without difficulty if there are but 15 volumes per cent. So far, then, as the question of oxygen is concerned, a man could breathe where a candle would not -burn, but it does not necessarily follow that it is always safe for a man to venture where a candle will burn, for sometimes, although there may be oxygen sufficient to sustain life, poisonous gases may also be present in an amount sufficient to produce a fatal result. It would be a surer test to place a dog in the suspected place and leave him there for twenty minutes. If it survives, it will be safe for a man to enter. It is a matter of common experience that injury to health follows confinement in badly ventilated apartments, but the cause thereof has never been satisfactorily determined. The generally accepted theory is that it is not due to the carbon dioxid which is given oif by the lungs, but to the organic matter crowd-poison exhaled in the expired air and also given off from the surface of the body, especially of those who are not cleanly in their habits, and who resort to bathing the body too infrequently. Those who maintain these views state that an air which contains respiratory CO 2 i. e.j CO 2 produced by respiration to the amount of more than 0.07 per cent, is unwholesome air to breathe, and yet that CO 2 may be present to the extent of 2 per cent, provided that its presence is due to 'chemical processes, as in soda-water factories, and may be breathed without inconvenience or any injurious conse- quences resulting. Indeed, so reliable observers as Brown^S^quacd and (PArsony^l have breathed air in which CO 2 was present to the amount of 20 per cent, for two hours without marked distress. When, therefore, injurious effects follow from breathing air con- taining 0.8 per cent, of CO 2 , which represents that present in a very badly ventilated lecture-hall, it must be due to something else than the CO 2 , and they attribute it to the organic matter already referred to. Brown^Se^iiard and d'Arsonval, who believed that it was the organic matter from the lungs wKTch was the poison- ous matter, injected into rabbits the condensed vapor of the ex- pired air with fatal results. On the other side of the question are those who maintain that the injurious consequences of breathing vitiated air are due to the excessive amount of CO 2 and the deficiency of oxygen, and not to organic matter. In support of this theory we have the following observations : Haldane and Lorraine Smith found that in breathing air containing 18.6 per cent, of CO 2 , within a minute or two they suffered from hyperpnea, distress, flushing, cyanosis, and mental confusion ; and the injections of condensed vapor-breath into rabbits, practised by Brown-Sequard and d f Arson val, have been repeated by several experimenters with negative results. Besides these, other experiments have been performed, showing that no volatile poisons are exhaled with the expired air. Among recent investigations on this subject are those of Haldane and Lorraine Smith. From these they conclude as follows : 380 RESPIRATION. " 1. The immediate dangers from breathing air highly vitiated by respiration arise entirely from the excess of carbon dioxid and deficiency of oxygen, .and not from any special poison. " 2. The hyperpnea is due to excess of carbon dioxid, and is not appreciably affected by the corresponding deficiency of oxygen. The hyperpnea begins to appear when the carbon dioxid rises to from 3 to 4 per cent. At about 10 per cent, there is extreme distress. " 3. Excess of carbon dioxid is likewise the cause, or at least one cause, of the frontal headache produced by highly vitiated air. " 4. Hyperpnea from defect of oxygen begins to be appreciable when the oxygen in the air breathed has fallen to a point which seems to differ in different individuals. In one case the hyperp- nea became appreciable at about 12 per cent., and excessive at about 6 per cent." Haldane and Smith also regard the odorous substances present in rooms due to a want of cleanliness as contributing to the dis- comfort caused by breathing the air of such rooms. It must be remembered that the oxygen of the air is consumed and carbon dioxid and other impurities produced by stoves, gas- burners, and lamps, as well as by respiration. Thus a large gas- burner will in one hour consume as much oxygen as a human being will in five hours, and at the same time will be produced carbon dioxid and monoxid, sulphur compounds, and other gaseous impurities, all of which vitiate the air to a considerable degree. At the same time the air is heated. Perhaps one of the most important advantages which has accrued from the introduction of electricity as applied to illuminating-purposes is the entire absence of heat and of those impurities which so impoverish the air of inhabited rooms. It is generally conceded that if the respiratory CO 2 in the air does not exceed 0.02 per cent, above that which is ordinarily present in all air 0.03 or 0.04 per cent. bringing it up to 0.06 or 0.07 per cent., no harm will result, and adequate ventilation will be secured i. e., keeping the CO 2 from increasing beyond 0.06 or 0.07 per cent. To bring this about will require as a minimum 60,000 liters (2000 cubic feet) per hour per individual, but this should be increased by at least one^half (making it 3000 cubic feet) to provide for the increased production of CO 2 caused by active exercise ; and in factories and workshops where all the operatives are men, and all actively at work, this amount often needs to be as much as 6000 cubic feet. For hospitals, where the emanations from the sick are more likely to vitiate the air than are those from the well, at least 6000 cubic feet should be pro- vided. These figures take no account of gas-burners or lamps, and for these there should be allowed not less than 1800 cubic CHEMISTRY OF RESPIRATION. 381 feet of air for each cubic foot of gas consumed, and 18,000 cubic feet for each pound of oil burned. The cubic space allotted to each individual must also be taken into account, for experience has proved that unless the ventilating arrangements are very perfect, the air of an inhabited room can- not be changed oftener than three times an hour without causing draughts, which are uncomfortable, and it may be dangerous to health. It becomes necessary, therefore, to provide at least 1000 cubic feet of air-space per individual. In the dormitories of workhouses the amount allowed does not often exceed 300 cubic feet ; in military barracks, 600 cubic feet, and in hospitals, 1 200 cubic feet. It has also been found by practical experience that in rooms that have a height of more than 12 feet the conditions are not favorable for proper ventilation, for the reason that organic matters have a tendency to remain in the lower parts of rooms. A room 50 feet high, with 20 square feet of floor-space, would give 1000 cubic feet of air-space, but it would not be the same from a sani- tary point of view as a room 10 feet in all its dimensions. Atten- tion must, therefore, be paid to the amount of floor-space allotted to each individual ; this varies according to circumstances. It should be at least 100 square feet. Of course, where rooms are occupied for but a short time, as in theaters, churches, etc., where after the audiences are dismissed the buildings can be thoroughly aired by the admission of external air, all these restrictions do not apply. It seems hardly necessary to say that due attention must be paid to the source from which the introduced air is drawn. If it is obtained from filthy cellars or from dirty streets, it may be as impure as that which it is designed to replace. For any further discussion of this subject our readers are re- ferred to text-books on liygiene. Changes in the Blood due to Respiration. When the blood reaches the lungs from the heart it is venous, and when it leaves the lungs to return to the heart it is arterial. The con- version, then, of the venous blood into arterial takes place while it is traversing the pulmonary capillaries. In its passage the bluish-red color which characterizes venous blood becomes changed to the scarlet color of arterial blood, and at the same time the venous blood gives up a portion of its CO 2 to the air, and takes O from it. From 100 volumes of blood, whether arterial or venous, approximately 60 volumes of both gases can be obtained ; the proportion, however, varying. Thus in human arterial blood there is O, 21.6; CO 2 , 40.3; and N, 16. The amount of nitrogen is practically the same in both varieties of blood. It is impossible to give figures which represent accurately the composition of venous blood, for while analyses of arterial 382 RESPIRATION. blood taken from the different arteries vary but little, those of venous blood from different parts of the venous system vary to a considerable degree; and even the blood from the same vein will have a different composition at different times, as, for instance, that coming from a gland when active or at rest. In general, venous blood may be said to contain O from 8 to 12 per cent., and CO 2 about 46 per cent. Zuntz has made many analyses, and concludes, as a result, that venous blood, as compared with arterial, contains 7.15 volumes per cent, less of O, and 8.2 volumes per cent, of CO 2 . Although arterial blood contains but 21.6 per cent, of O, still it can be made to take up as much as 23 per cent., which would about saturate it. But even the 2] .6 per cent, is more than is needed by the tissues in their metabolic processes. Unless, there- fore, the blood contains less oxygen than normal, there is no advan- tage to be derived from inhaling oxygen gas. If, however, the venous condition is marked, then oxygen inhaled under pressure may do good. While the arterial blood is nearly saturated with oxygen, experiments have shown that it can take up nearly four times as much CO 2 as it ordinarily contains. Causes of the Interchange between O and CO 2 in the I/ungfS. The trachea and bronchi can contain about 140 c.c. of air, so that at each inspiration, when 300 c.c. or more of tidal air are taken in, the difference between these two figures, 160 c.c. or more, must represent the amount which passes at each inspiration into the alveoli of the lungs. When expiration occurs an equal volume is exhaled; thus by the repeated alternation of inspiration and expiration the air in the lungs is being constantly changed. But the most potent factor in bringing about this interchange is the diffusion of the gases, which depends upon their partial pressure L e., the part of the total pressure of the air which is exerted by each of its different components. This is also spoken of as tension by some writers ; although others use the term partial pressure with reference to gases in a mechanical mixture, as in atmospheric air ; and that of tension with reference to gases in solution, meaning thereby "the pressure required to keep the gas in solution." If we regard 760 mm. of mercury as representing the pressure of the atmosphere, and 20.96 as the percentage of the total volume 20.96 X 760 represented by oxygen, then - - will equal the pressure exerted by the oxygen, or its partial pressure or tension, which is 159.29 mm. The partial pressure of the CO 2 = ~]~00~ 0.30 mm. If now we ascertain the partial pressure of these gases in the alveoli, we shall have the principal conditions affecting their diffusion. The partial pressure of O in the alveoli is estimated at about 114 mm. and of C0 9 at 36 mm. The O then in the air CHEMISTRY OF RESPIRATION. 383 as it enters the respiratory passages has a partial pressure of 159.29 mm., while in the alveoli it is only 122 mm. ; therefore it will diffuse inward until it reaches the point of lowest pressure. On the other hand, the partial pressure of CO 2 is greatest in the alveoli 38 mm. as compared with 0.30 mm. ; this gas will therefore diffuse outward. There is a third force causing diffusion which is regarded as possessing different value by different authorities ; this is the cardiopneumatic movements. Each time the heart contracts it becomes smaller, and the pressure within the thorax, but outside the lungs the intrathoracic pressure is diminished, with the re- sult of causing the lungs to expand slightly, and air consequently to enter them. When diastole occurs and the volume of the heart becomes larger, the intrathoracic pressure is relatively increased, and the air is forced out of the lungs. Besides, therefore, the en- trance and exit of air due to the inspiratory and expiratory move- ments, there is a corresponding movement of the air due to the contraction and dilatation of the ventricles. Causes of the Interchange of O and CO 2 between the Air and the Blood. The fact that the amount of O and CO 2 in the blood does not follow the general law that the amount of gas which a liquid absorbs depends to a great extent upon its pressure, is conclusive proof that these gases are not to any great extent in solution in the blood. O is in solution in the plasma, but to the extent of less than one volume, and in venous blood only about 5 per cent, of the CO 2 present is in solution. Inas- much as the amount of both of these gases is greatly in excess of these figures, we must look for some other explanation of their presence in the blood in the quantities in which they there exist than to solution. When the gases are extracted from the blood, as they may be by the use of a pump devised for this purpose (Fig. 212), the oxygen which is in solution is given off gradually as the pressure is reduced, but it is not until the pressure has been reduced to from one-thirtieth to one-tenth of an atmosphere that most of it comes off, and this it does suddenly when this low pressure is reached. From this it is evident that most of the oxygen is in chemical combination, and this pressure at which the gas is given off is the tension of dissociation. From various observations and experiments we know that the combination is one between oxygen and hemoglobin, forming oxyhemoglobin. It has been ascertained that theoretically oxyhemoglobin can contain 23.38 volumes per cent, of O, although it never does, but only about 20 per cent., because the hemoglobin is not saturated ; still, blood from which the red corpuscles and consequently the hemoglobin have been re- moved, as in plasma or serum, can take up only 0.26 volume per cent. The tension of O in arterial blood is 29.64 mm. of mercury, and in venous blood 22.04 mm. 384 RESPIRATION. The tension of CO 2 in the blood is as follows : In arterial blood 21.28 mm., and in venous blood 41.04 mm. CO 2 exists in venous blood in solution to the amount of about 5 per cent.; in loose chemical combination, 75 to 85 per cent.; and in firm chemi- cal combination, 10 to 20 per cent. or about 45 volume per cent, in all. The CO 2 is in solution in the plasma, in combination with globulin and alkali, and with sodium in the form of carbonates and bicarbonates. About one-third of the carbon dioxid of the FIG. 212. Kemp's gas pump. (For detailed description see American Text-BooTc of Physiology, vol. i., p. 420.) blood exists in the blood-corpuscles, both white and red, but prin- cipally in the latter, where it is in combination with the alkaline phosphates, with globulin and hemoglobin. We have seen that by various forces the oxygen in the outside air reaches the alveoli, while in turn the carbon dioxid in the latter situation reaches the exterior ; we have now to consider how the interchange between the CO 2 in the blood and the O in the alveoli is effected. We have learned that the tension of the O CHEMISTRY OF RESPIRATION. 385 in the alveolar air is about 114 mm., although one observer at least places it as low as 99 mm. This has never been accurately de- termined. The tension of CO 2 in the alveolar air is about 36 mm. In order to ascertain why the O of the air goes to the blood and the CO 2 of the blood to the air, we must first know the tension of O and CO 2 in the blood. For this purpose an instrument known as an aerotonometer is used. The principle underlying this instrument is thus described by Pembrey in Schafer's Physi- ology : " Blood in contact with a mixture of oxygen, nitrogen, and carbon dioxid gives up some of its gases if their partial pressures are greater than those of the corresponding gases in the mixture ; on the other hand, if the tensions of the gases in the blood be lower than the respective tensions of the gases in the mixture, the blood takes up gas. These interchanges persist until equilibrium is established, until the tension or partial pressure of the gas in the blood is equal to that of the corresponding gas in the mixture. In the aerotonometer the blood is made to pass in a thin layer through a glass tube or tubes containing mixtures of gases of known quantity and tension, and it is arranged by prac- tice that the tension of the gases shall in the one case be greater, in the other case smaller, than the tensions of the corresponding gases in the blood. The gases in these tubes, after the blood has passed through them, are analyzed, and from the alteration in the proportion in the two tubes it is possible to calculate the partial pressure of the gases in the blood. The aerotonometer is sur- rounded by a water-jacket with a temperature of 39 C." Another aerotonometer is that of Fredericq, and Bohr has devised one known as an hemato-aerometer. The results obtained by these different instruments vary con- siderably. Strassburg gives the tension of CO 2 in venous blood of the right side of a dog's heart as 5.4 per cent, of an atmosphere ; and 2.2 to 3.8 per cent, in arterial blood. Herter gives the ten- sion of O in arterial blood as 10 per cent, of an atmosphere. Bohr has obtained quite different results : 101 to 104 mm. of mercury for the tension of O in arterial blood higher than that of the air in the trachea. He also found that when the dog, the subject of the experiment, breathed pure air, the tension of the CO 2 in arterial blood rises from nothing to 28 mm. of mercury, and when the dog breathed air containing CO 2 the tension varied between 0.9 and 57.8 mm. That is to say, the tension of CO 2 was greater in the tracheal air than in the blood. If this is so, it is manifest that the passage of the CO 2 of the blood outward to the air could not be due to diffusion ; so that to explain the actual facts Bohr concludes that the tissues of the lungs play an active part in the absorption of oxygen and the elimination of carbon dioxid. Haldane and Lorraine Smith have substituted for the aerotonometer a method by which " the tension of O in the 25 386 RESPIRATION. arterial blood is calculated from the percentage of carbon monoxid breathed by the subject of the experiment, and from the final saturation of his blood with carbon monoxid " (Pembrey). Their results are 26.2 per cent, of an atmosphere, or 200 rum. of mercury, about twice that of oxygen in the alveoli, which would confirm Bohr's views that diffusion cannot account for the absorption of oxygen by the blood while flowing through the pulmonary cap- illaries, but that it is to be attributed to the epithelial cells of the alveoli. Notwithstanding these results, which need further investiga- tion, diffusion is usually regarded as the principal factor in de- termining the gaseous interchanges between the air and the blood. Causes of the Interchange , of O and CO 2 between the Blood and the Tissues. This process constitutes in- ternal respiration. Oxygen when it reaches the tissues by the blood is immediately taken up by them and enters into chemical combination, so that as oxygen it may be said not to exist, except momentarily. On the other hand, the tension of oxygen in arterial blood is rela- tively high, so that its passage from the blood to the tissues is readily accounted for. The tension of CO 2 in the tissues is about 58 mm. of mercury higher than in the blood ; hence its passage outward from the tissues to the blood. Innervation of the Respiratory Apparatus. The nerv- ous supply to the respiratory apparatus comes from the respiratory center, a collection of nerve-cells in the lower part of the medulla oblongata, though its exact location is not yet determined. Other centers, subsidiary centers, have been described, but their inde- pendence of the principal center is questioned. The respiratory center is in reality made up of two centers, one for each side, so that, although anatomically connected and ordinarily acting together, yet if one center is broken up, while the respiratory movements on that side cease, those on the other side continue. Besides this double character of the center, each half is made up of an inspiratory and an expiratory center i. f. tbc^ R. Freneh is if the voices with exceptional QUIT- there are loor cient evidence has not yet been obtained 10 table.' 9 Speech. Phooatku or vi^-|Nr^h>rrii(. is a to all animals havinr vocal bands, while the farahv of to an anuuais navmg vocai oanosw wn peculiar to man. Channin^ says : - A up his mind in itsehu but to give it w _^^ _- __^_J,=. ^> m. _^ oiner nnnns* cipeecn E one en brute."" It is possible that this attnbiHe of man maty not be 394 VOICE AND SPEECH. made which would lead to the conclusion that they can communi- cate to a certain extent with their fellows. Vowels. These are sounds produced by vibrations of the vocal bands, but modified by the resonating cavities, to which modification the difference in their quality is due : and if the variations in the cavity of the mouth together with those of the tongue and soft palate are observed while different vowels are sounded, this fact will be readily understood (Fig. 216). Consonants. These are not produced by the vocal bands as are the vowels, but by obstructions placed in the way of an out- going blast of air; and places where these obstructions are placed are positions of articulation. " The consonants are classified ac- cording to (1) their places of closure ; (2) the completeness of the closure ; (3) their utterance with breath or voice. The first dis- tributes them into (a) labials, or lip-consonants p, f, b, v, m, w ; (6) dentals, or tooth-consonants t, d, th, dh ; (c) palatab, or palate- \ \ FIG. 216. Section of the parts concerned in phonation, and the changes in'their relations m sounding the vowels A (), /(), U (<") ; T, tongue -, p, soft palate ; e, epiglottis; g, glottis; *, hyoid bone ; 1, thyroid ; 2, 3, cricoid; 4, arytenoid cartilage (after Landois and Stirling). consonants, including sibilants s, z, sh, zh, and liquids, 1, v, n, y ; (d) gutturals, or throat-consonants c-k, ch (Scottish lock), g, gh, (Irish lough), h, ng. " The second division gives mutes, having tight closure p, b, t, d, c-k, g ; the other consonants are continuous. "The third division gives : (1) Surds p, t, ch, c (k), f, th (as in thin) s sh, h. (2) Sonants--*, d, j, g, v, dh, z, zh, w, 1, r, y, m, n, ng (Standard Dictionary). Photography of the Xarynx. Prof. Thomas R. French, of the Long Island College Hospital, has brought larvngeal pho- tography to a high state of perfection, and has demonstrated most thoroughly the changes which take place in the vocal bands during the act of singing. The results of his observations are recorded m the New York Medical Journal. To him we are indebted for our present knowledge of this important subject, and from his articles m this publication we quote freely ; the illustrations are also taken from the same source. PHOTOGRAPHY OF THE LARYNX. 395 In photographing the larynx, Prof. French uses the electric arc light. The apparatus is shown in Fig. 217. It consists of an automatic 2000-candle-power lamp partly inclosed in a metal box. The front face of the box carries a condensing lens which, when placed 9 inches from the arc, gives a focal distance of 20 inches. This relation of light and lens is found to give the most satisfac- tory illumination. The lamp and accessories are fitted to a narrow board which is placed upon a table of sufficient height. The light can be raised or lowered by means of a device designed for that purpose. The rheostat is placed upon a shelf beneath the table top. The whole light outfit is but a modification of the electric stereopticon. This one is so arranged that by adding a second FIG. 217. Showing the manner in which photographs of the larynx and posterior uares are secured with the aid of the arc light. condensing lens and an objective lens to the end of the cone- shaped tube in front it can be used as a projecting lantern. In speaking of the action of the glottis, Prof. French says that with all his experience he has not yet permitted himself to formu- late a theory of the action of the glottis in singing, for even now, after a large number of studies have been made, the camera is con- stantly revealing new surprises in the action of the vocal bands in every part of the scale. The movements of the larynx in a much larger number of subjects must be revealed, grouped, and recorded before definite conclusions can be drawn. Most of our past knowledge on the subject of the changes in the larynx during singing has been obtained from inspection of this organ through the laryngoscope. As these changes follow each other too rapidly to be appreciated by the eye, much of this knowledge has been found to be erroneous. The photographic 396 VOICE AND SPEECH. plate, however, is so sensitive that every detail can be recorded, and as a result of its application to the physiology of the larynx, ranch that was regarded as established has been demonstrated to be false : just as the older ideas of the form of a lightning-flash have been entirely changed by instantaneous photography. The difficulties to be overcome in photographing the larynx so as to show the changes during voice-production are many, among FIG. 218. Apparatus used in photographing the larynx. them being the fact that it is only in certain individuals that the vocal bands can be seen throughout their whole length. This is very well shown in Fig. 220. In No. 1 the insertions of the vocal bands into the thyroid cartilage are so exposed as to be sus- ceptible of being photographed ; in No. 2 these are covered by the anterior wall of the larynx, and it would therefore be impos- sible to determine in such a larynx whether the vocal bands were lengthened or shortened in passing from one register to another, PHOTOGRAPHY OF THE LARYNX 397 or during a change in the pitch of the voice. In some individuals the bands will be exposed throughout their length while some notes are being sung, while during the singing of others they will be covered. Fig. 221 shows this ; while singing F sharp and D, the bands are exposed, but covered when E is being sung. The number of persons whose larynges are so constructed as to permit photographing to determine the changes taking place in the glottis FIG. 219. Photograph taken by Prof. French of a normal larynx in quiet respiration. throughout all the registers is, it will be seen, limited, and who they are can only be ascertained by careful inspection. Nor are the changes which take place the same in all individuals. The following photographs show these changes in the larynx of a well-known professional contralto singer, and their explana- tion will be given in Prof. French's words : No.l. No. 2. FIG. 220. PAIR 1. " The voice in this singer is of excellent quality. The first of the pair (Fig. 222, No. 1) was taken while F sharp, treble clef, third line below staff, was being sung, and the second (No. 2) while she was singing E above. All notes in this and the following series were sung in the key of A. These are one of the lowest and the highest notes of her lower register. In the photograph represent- ing the lowest note it can be seen that the vocal bands are quite 398 VOICE AND SPEECH. short and wide, and that, with the exception of the anterior fourth, the ligaraentous and a part of the cartilaginous glottis is open and the slit between the vocal bands is linear in shape. As the voice ascends the scale the vocal bands increase in length and decrease in width, until at the highest note of the register they can be seen to have become considerably longer. It can also be observed that the ligamentous portion of the glottis is still open to the same relative extent, and that the cartilaginous portion has opened to its full ex- tent. In the photograph representing the lower note the anterior faces of the arytenoid cartilages can be seen. As the voice ascended, the capitula Santorini were tilted forward. This seems to be proved E FIG. 221. by the change in the position of these structures as seen in the photograph representing the upper note, as well as a similar change to be seen in nearly all the series showing the registers which I have taken. The epiglottis, though not well illuminated, seems to have risen as the voice ascended" the scale. The light upon the epiglottis is so weak that the structure does not appear at all in the photo-engraving. The vocal bands have increased in length at least inch in 7 notes. The compass of the voice of this sub- PHOTOGRAPHY OF THE LARYNX. 399 ject is about 2-J octaves. Therefore, at that rate of lengthening, the vocal bauds would increase nearly ^ inch if their length was progressively increased while singing up the scale from the lowest to the highest note. This progressive increase in length does not, No. 1. FIG. 222. PAIR 2. No. 2. however, occur, and the reason is apparent in Fig. 223, which shows the changes which took place in the larynx at the lower break in the voice, which, in this subject, occurs at F sharp, treble clef, first space. No. 1. FIG. 223. PAIR 3. No. 2. " The changes which occur at this point are extremely inter- esting and instructive. In the transition from the lower to the middle register, from E to F sharp, in the voice of this subject, the vibratory portions of the vocal bands are shortened about ^ 400 VOICE AND SPEECH. inch. The anterior insertions of the vocal bands can be seen in both photographs ; therefore the actual difference in the length of the bands can be appreciated. The vocal bands have not only become shorter, but they appear to be subjected to a much higher degree of tension. The cartilaginous glottis is closed and the aperture in the ligamentous portion has been much reduced in size. The laws which govern the pitch in both string and reed instruments will aid us in explaining these changes. Though the tone is higher and the degree of stretching less than in the note below, the tension is increased, and the aperture through which the air passes is much narrower. It seems to me that this clearly defined change in the mechanism of the vocal bands which, so far as my investigations permit me to judge, are at this point in the scale the rule will assist us to a clear understanding of the action of the laryngeal muscles in singing when we reach that part of the study. " In the first photograph, which was taken while the subject was singing the note immediately preceding that on which the break occurred, the vocal bands can be seen to be long and wide and the posterior three-fourths of the chink of the glottis is open. By open, I mean that the edges of the vocal bands are not in actual contact. The anterior fourth or fifth of the ligamentous portion of the glottis is closed. The space between the vocal bands is widest in the cartilaginous portion of the glottis. In the production of the next note higher, F sharp, the second of the pair, a marked change in the size of the larynx and in the length of the vocal bands is seen to have occurred. The cavity of the larynx has been suddenly reduced in size and the vocal bands have been shortened. The cartilaginous portion of the glottis is closed and the ligamentous portion is open in a linear slit from the posterior vocal process to within a short distance of the an- terior insertions of the vocal bands. The decrease in the length of the vibratory portions of the vocal bands is due to the closure of the cartilaginous glottis, for the ligamentous glottis remains about the same as in the note before the break. The arytenoid cartilages have been brought much closer together and occupy a more posterior position. These pictures were taken one after the other in quick succession, the conditions in every respect, except the note sung, being the same. The anteroposterior and lateral dimensions of the cavity of the larynx are shown to have been considerably decreased when the voice broke into the register above. When the mechanism of the larynx was changed the voice acquired a very different quality, which continued, in grad- ual elevation of pitch, throughout the register. As marked a change as this in the mechanism of the vocal bands in females is, I believe, found only in the larynges of contralto singers. " It is believed by many writers on the voice that with the PHOTOGRAPHY OF THE LARYNX. 401 change in the mechanism of the vocal bands the epiglottis is raised higher than in the register below. I am of the opinion that it is usually depressed. The reason for this belief is that, with very few exceptions, I have found it lower in the photo- graphs showing the change than in those representing the note preceding it. When the voice of this subject broke into the middle register it was with difficulty that T could get the epiglottis to rise as high as it is shown here, which, though high enough to show the anterior insertions, is not so high as it was before the break. There does not seem to be any difference in the width of the vocal bands, but in this particular the appearances vary, the variation being due to the position of the ventricular bands. The entire upper surfaces of the vocal bands are rarely exposed to view during the production of the middle and upper notes. No. 1. No. 2. FIG. 224. PAIR 4. " As this singer ascends the scale above the break at F sharp, the vocal bands are increased in length and the chink gradually enlarges, as shown in Fig. 224. The first photograph is of the larynx while singing F sharp, treble clef, first space, the note on which the lower break occurred, and the second while singing D, treble clef, fourth line, which is the highest note in the middle register of the voice of this singer. The difference in the length of the vocal bands and width of the chink of the glottis, as the voice mounts from the lowest to the highest note of the middle register, is clearly shown. Not only is it shown that the vocal bands increase in length as the voice ascends the scale, but the cartilaginous portion of the glottis which, while producing the lowest note of this register, is seen to be tightly closed has begun to open again, as shown by the small triangular opening which has appeared between the arytenoids in the second of this 26 402 VOICE AND SPEECH. pair. Again, as the vocal bands increase in length in this register their tension is apparently decreased. The capitula Santorini, which in the photograph representing the lowest note in the middle register are seen to be close together and occupy a position well backward in the laryngeal image, become more and more separated and are tilted more and more forward in the ascent of the scale. " Now the voice mounts one note higher that is, to E, treble clef, fourth space and as it does so a distinct change in the qual- ity of the voice is heard, and the second change in the mechan- ism of the vocal bands occurs. The changes which take place in the larynx at the upper break in the voice of this singer are shown in Fig. 225. The first of the pair represents the larynx while sing- ing D, treble clef, fourth line, the note immediately preceding the No. 1. No. 2. FIG. 225. PAIR 5. break, and the second shows the change which occurred while singing E, the next note above. A very decided change in the mechanism of the vocal bands is apparent. These ligaments have grown shorter and narrower, and the chink, which in the note before the break can be seen to be linear in shape and quite wide, after the break becomes considerably reduced in both length and width. Not only is the cartilaginous portion of the glottis closed in the note after the break, but also a small portion of the liga- mentous glottis adjoining it. The chink appears to be closed to the same extent in front as it was while producing the note immediately preceding. There is, therefore, stop-closure in front and behind, which leaves a slit in the middle of the glottis measuring a little more than half the length of the vocal bands. In addition to these changes it may be observed that the epiglottis is depressed and the arytenoid cartilages have again receded. As PHOTOGRAPHY OF THE LARYNX. 403 this is the highest note which this subject is capable of singing with ease, we cannot study the action of the vocal bands in the production of tones in the upper register. " It may be remembered that in this larynx the vocal bands increased in length from the low F sharp to the E above. At the next note above they were suddenly shortened. At the next note higher they began to increase in length again, until D, above, was reached, and at E, the note next above, they were again sud- denly shortened. It will be instructive to determine the degree to which the vocal bands were lengthened and at what point in the scale they were longest. We saw that in the lower register the vocal bands were longest in the production of the highest note, and in the middle register they were also longest while the highest note was being sung. By comparing the photographs representing these notes (Fig. 226) it can be seen that the vocal bands were as long, if not the longest, while the highest note of the lower register was being sung. In this subject the vocal bands increase in length in each register, but they attain as great a length in the lower as in either of the registers above, if not greater. It is generally thought that the pitch is raised by the vocal bands increasing progressively in tension and length. In regard to length this is true in some cases, while in others it is only true as applied to a register, not to the whole of the voice. " The next series of photographs (not here reproduced) are of a professional singer who possesses a rich contralto voice of large range and good volume. The photographs of the larynx of this subject are strong enough for satisfactory exhibition upon the screen, but too weak for reproduction by the photo-engraving process. Though this singer has as large a range as she whose larynx we have just investigated, the pitch of her speaking voice is several tones higher. Here we shall find that the larynx acts in a very different way from that just examined. The first photograph of this pair was taken while F sharp, treble clef, third line below staff, was being sung ; the second, while she was singing D, treble clef, first space below staff. The right aryten- oid cartilage overlaps its fellow. In the production of the low note the anterior insertions are covered, and we cannot, therefore, see how long the vocal bands really are. The ligamentous portion of the glottis is well open, the chink being much wider behind than in front. The cartilaginous glottis appears to be closed, but I do not think that it really is, but, because of the somewhat unusual setting of the arytenoid cartilages, the cleft between them cannot be seen. As the voice ascends the scale the epiglottis is raised, the vocal bands increase in length, and the chink of the glottis gradually narrowed until at D, the highest note of the lower register, we find that the vocal bands appear to be consid- erably elongated, the chink considerably reduced in width, and the 404 VOICE AND SPEECH. epiglottis raised considerably higher. The cartilaginous portion of the glottis still appears to be closed, and there is no evidence of a forward movement of the capitula Santorini. When the next note higher was sung, a very noticeable change in the quality of the voice was heard, and, by examining the photographs taken while that note was being sung with that representing the note below it, it can be seen that a slight change in the mechanism occurred. The epiglottis is depressed. The vocal bands are longer and narrower, their edges are straighter, and the chink of the glottis, which in the note before the break was closed in front, has opened from the anterior to the posterior commissure, and is considerably increased in size. The cartilaginous glottis still appears to be closed. The arytenoid cartilage on the right side D No. 1. No. 2. FIG. 226. PAIR 6. occupies the same position as before the break, but the left has moved a little backward. " The voice now ascends the scale until D, treble clef, fourth line, is reached, when it can be seen that the epiglottis is slightly raised, the vocal bands appear to be increased in length and de- creased in width, and the arytenoid cartilages are turned further forward and brought closer together. The chink of* the glottis is still open from front to back, and is altogether larger than in the lower note of this register. The apparent increase in the length of the vocal bands is partly due to the fact that the cartilaginous portion of the glottis is now beginning to open. This note is as high as this subject can sing with ease. " In many particulars the action of this larynx is the reverse of that just examined. In this the cartilaginous glottis does not appear to begin to open until the highest notes are reached. In the lower register the chink of the glottis decreases instead of in- creases in size as the voice ascends. At the lower break the vocal PHOTOGRAPHY OF THE LARYNX. 405 bands are increased instead of decreased in length, and the chink of the glottis is increased instead of decreased in size. In the larynx before examined the chink of the glottis increased in size and the vocal bands increased in length as the voice ascended in each register, attaining their greatest length at the highest note of the middle register ; but in this the vocal bands attained their greatest length at the highest note in the voice of this subject, which corresponds to about the highest note of the middle regis- ter." Figs. 227 and 228 are from photographs of the larynx of the contralto singer referred to on page 397, showing the same mechanism of the vocal bands in passing from the lower to the middle register, from E to F sharp, as is shown in Fig. 223, but on a different occasion. FIG. 227. FIG. 228. In concluding his Berlin address, Prof. French says : " Though the number of series of photographs which have been taken of the larynx in singing is quite large, I do not yet feel justified in drawing definite conclusions from them regarding many of the movements of the glottis at different points in the scale, but from the study made thus far the following conclusions regarding the glottis of the female may, I think, be safely drawn : " 1. The larynx may act in a variety of ways in the production of the same tones or registers in different individuals. " 2. The rule which, however, has many exceptions is that the vocal bands are short and wide and the ligamentous and car- tilaginous portions of the glottis are open in the production of the lower tones; that, as the voice ascends the scale, the vocal bands increase in length and decrease in width, the aperture between the 406 VITAL HEAT. posterior portions of the vocal bands increases in size, the capitula Santorini are tilted more and more forward, and the epiglottis rises until a note in the neighborhood of E, treble clef, first line, is reached. The cartilaginous glottis is then closed. The glottic chink becomes much narrower and linear in shape, the capitula Santorini are tilted backward, and the epiglottis is depressed. " When the vocal bands are shortened in the change at the lower break in the voice, it is mainly due to closure of the carti- laginous portion of the glottis, the ligamentous portion not usually being affected. If, therefore, the cartilaginous glottis is not closed, there is usually no material change in the length of the vocal bands. " As the voice ascends from the lower break, the vocal bands increase in length and diminish in width, the posterior portion of the glottic chink opens more and more, the capitula Santorini are tilted forward, and the epiglottis rises until, in the neighborhood of E, treble clef, fourth space, another change occurs. " The glottic chink is then reduced to a very narrow slit, in some subjects extending the whole length of the glottis. In others, closing in front, or behind, or both. Not only is the cartilaginous glottis always closed, but the ligamentous glottis is, I believe, invariably shortened. The arytenoid cartilages are tilted back- ward and the epiglottis is depressed. As the voice ascends in the head register the cavity of the larynx is reduced in size, the aryte- noid cartilages are tilted forward and brought closer together, the epiglottis is depressed, and the vocal bands decrease in length and breadth. If the posterior part of the ligamentous portion of the glottis is not closed in the lower, it is likely to be in the upper notes of the head register." VITAL HEAT. The temperature of a lifeless object is approximately that of the air which surrounds it ; the temperature of a living object is independent of the temperature of the air, although it may be modified by it. This difference is due to the fact that living things produce heat within themselves ; this is called " vital heat." Many, perhaps most, authorities speak of it as " animal heat," but, though it is most striking in members of the animal kingdom, yet inas- much as its production is not confined to animals, but also occurs in plants, the writer prefers the term vital heat as indicating that the phenomenon is peculiar to the living condition, irrespective of the question whether it occurs in an animal or in a vegetable. Warm-blooded Animals. The term warm-blooded was ap- plied to certain animals because their temperature was so high as to make them warm to the touch, while others were spoken of as cold-blooded because they were cold to the touch. Thus, man, with TEMPERATURE OF DIFFERENT PARTS OF THE BODY. 407 a temperature of 37 C., the dog, 39, the cat, 39, the swallow, 44 or 'even higher, are among the warm-blooded, while reptiles and fishes, whose temperature is from 1.7 degrees to 4.5 degrees C. above that of the medium in which they exist, are cold-blooded. The terms warm-blooded and cold-blooded are, however, now not so frequently used as formerly, but in their stead are used the terms homoiothermal and poikilothermal. Homoiothermal animals are animals of uniform heat or those whose temperature is unvarying. The thermometer if in- troduced into the rectum of a man, whether he is in the tropics or in the frozen regions of the North, will register about 38 C. The temperature of the surface of his body varies with that of the air a fact with which all are familiar but the internal temperature is the same irrespective of whether it is winter or summer. What is true of man is true also of other mammals and of birds that is, of those animals commonly denominated warm-blooded. Poikilothermal animals are animals of varying heat, or those whose temperature varies according to that of the medium air or water in which they live. The frog's temperature is slightly above that of the water, and if this is warm, the temperature in the frog will rise, to fall again when the temperature of the water is lowered. Thus a frog with a temperature of 20.7 C. in water at 20.6 C. will have a temperature of 38 C. when that of the water is raised to 41 C. Fishes, reptiles, amphibia, and insects also exhibit this same variation of temperature, so that cold- blooded and poikilothermal are practically interchangeable terms. A study of insects shows that these creatures produce heat, the thermometer registering, in some experiments on butterflies in active motion, a temperature of 5 degrees C. above that of the air. These insects are poikilothermal. The same power of generating heat is observed also in plants. The amount of heat varies under different circumstances, being especially marked at the time of germination and flowering, sometimes from 5 degrees to 10 degrees C. above that of the air. Temperatures of Different Animals. The following table gives the temperatures of some of the more common animals : Poikilothermal animals. Temperature above surrounding medium. . 0.32- 2.44 degrees C. . 2.50-12.0 degrees C. .0.50- 3.0 degrees C. Temperature of Different Parts of the Human Body. The temperature of the skin at the middle of the upper arm is 35.4 C., while in the sole of the foot it is but 32.26 C. In the Mammals. Birds. Poi Centigrade. Centigrade. Sheep . Ape Dog . . Horse . Ox . . 37.3-40.5 35.5-39.7 37.4-39.6 3f>.8-37.5 37.5 Duck . . . 42.5-43.9 Turkey . . 42.7 Chicken . 43.0 Frog . Snakes Fish . 408 VITAL HEAT. axilla it is about 37.1 C., although some observers have placed it as low as 36.25 C., and others as high as 37.5 C. ; under the tongue, about 37.5 C. ; and in the rectum about 38 C. The temperature of the liver, about 41.39 C. in the sheep, is regarded as the highest in the body : and higher here during digestion than in the inter- vals. The mean temperature of the blood may be stated as 39 C. The temperature of the muscles is increased in contraction 1 degree C. Mental exertion also increases the production of heat. After such exertion the temperature of the body has been found to be 0.3 degree C. higher than before. Temperature at Different Ages. The temperature of the child just born is 37.86 C. (rectum) ; in twenty-four hours, 37.45 C. (rectum). From five to nine years of age it is 37.72 C. (rec- tum); from twenty-five to thirty, 36.91 C. (axilla); from fifty-one to sixty, 36.83 C. (axilla); and at eighty, 37.46 C. (mouth). The amount of heat produced in old people is less than that in the mid- dle-aged, and they therefore need greater protection from the cold. Daily Variations in Temperature. The temperature of an individual is not the same at all times of the day. His lowest temperature is between 2 and 6 o'clock A. M.; it rises during the day, and at about 4 to 8 P. M. is at its height, falling again until it reaches the minimum in the early morning. Thus, in one set of observations, at 5 A. M. the thermometer registered 36.6 C.; at 8 P. M. 37.7 C.; and at 2 A. M. the following day, 36.7 C., and, as shown by recent experiments of Benedict, a chart representing these variations undergoes but slight changes under varying con- ditions, the temperature reaching the minimum at 2 to 6 A. M., " in- dependent of whether the subject is sleeping soundly and in the recumbent position, or whether he is awake and sitting, or even standing and walking." In these experiments no tendency to an in- version of the temperature-curve by inverting the daily routine of life was observed. If the temperature is taken every hour during a day, the mean of the readings is called the " daily mean," and is about 37.13 C. in the rectum. Remarkable Instances of High and I/ow Tempera- ture. The lowest temperature which the writer has been able to find was 24 C. This was in a drunken person who recovered from his debauch. A case of myxedema is reported in the Lon- don Lancet in which, on the day previous to death, the tempera- ture varied from 19 C. to 25 C. In the same journal is recorded a case of shock produced by a fall on the spine, in which the tem- perature fluctuated between 47 C. and 50 C., and for seven weeks did not fall below 42 C. The following case, recorded in the Brooklyn Medical Journal, illustrates the remarkable variations of temperature which may take place in a few hours. The patient was a man aged forty- eight ; the diagnosis of the case was intermittent fever. He had been treated two or three months before for delirium tremens. SOURCES OF VITAL HEAT. 409 He left the hospital, became partially paralyzed, and then devel- oped fever, his temperature rising to 42 and 45 C.; May 1, at night, it was 44 C.; May 2, in the morning, 37 C.; May 4, 2 A. M., 44 C. He had chills, and was treated for malaria. After May 17, he had no rise of temperature. He was a wreck from alcohol. Heat-unit. The standard of measure of heat is the heat-unit or calorie. It is the amount necessary to raise the temperature of 1 gram of water 1 C. This is called the small calorie, to distin- guish it from the kilocalorie or kilogramdegree, which is equal to 1000 small calories, and represents the amount of heat necessary to raise the temperature of 1 kilogram (liter) 1 degree C. It is estimated that an average man produces daily from 2200 to 3000 kilocalories, which is about 100 kilocalories per hour. During active exercise this amount is greatly increased, even to the amount of 3000 kilocalories hourly, while during sleep it may be but 40 kilocalories. Sources of Vital Heat. The sources from which the heat of the body is derived are numerous. Among them are : 1. The Oxidation of the Food-stuffs. The oxidation of carbohy- drates and fats results in the production of CO 2 by the oxidation of the carbon, and of H 2 O by that of the hydrogen ; while from the proteids are formed by the same process CO 2 , H 2 O, urea, and certain extractives. This oxidation may take place with the result of pro- ducing heat, or it may result in the production of some other form of energy, as the contraction of muscles ; but whatever form it may take, the ultimate products of oxidation are the same. Fat burned outside the body and fat burned (oxidized) inside the body will produce the same amount of heat. If, therefore, the chemical composition of the food-stuffs is known, and also that of the products of their oxidation when eliminated from the body, it is a simple matter to calculate the heat-value of any food. Chemists have ascertained that the oxidation of 1 Gm. of carbon to CO 2 produces 8080 calories ; and of the same amount of hydrogen to H 2 O, 34,460 calories. The oxidation of 1 gram of carbohydrate, as starch, to CO 2 and H 2 O results in the production of 41 16 calories, and of fat, 9312 calories. Carbohydrates and fats are completely oxidized in the body, not with the direct and immediate production of CO 2 and H 2 O ; but though there are many intermediate stages, still the ultimate results are the same as when the oxidation takes place outside the body. Proteids, on the other hand, are not completely oxidized in the body, for, as we have seen, the products of their oxidation are mainly CO 2 , H 2 O, and urea ; but urea is still further oxidizable. This oxidation does not occur in the body, as urea is eliminated as such ; hence in estimating the heat-value of proteids we must deduct that of urea. The complete oxidation of 1 gram of proteid to CO 2 and H 2 O produces 5778 calories, but we must deduct from this the heat- value of the urea produced in their oxidation. One 410 VITAL HEAT. gram of urea oxidized gives 2523 calories; the oxidation of 1 gram of proteid produces ^ gram of urea ; hence from the 5778 calories produced by the complete oxidation of the proteid we must deduct 841 calories, which gives 4937 calories as the actual heat- value of 1 gram of proteid. If now we recall the adequate diet of Moleschott (p. 130), we shall find that the amount of heat-production in twenty-four hours with such a diet is 2,801,148 calories, calculated as follows : Grams. Calories. Calories. Proteids 120 x 4937 = 592,440 Fats 90 x 9312 = 838,080 Carbohydrates 333 x 4116 = 1,370,628 2,801,148 It must not be inferred from the above statement that all the food taken into the body is oxidized and reappears in the form of energy, for, as we have seen, a not inconsiderable part passes out from the body without having undergone the digestive process. Although oxidation is the great source of the heat produced in the body, there are doubtless contributory causes, such as (2) the various movements which take place, producing heat by friction ; also (3) electricity generated in muscles and nerves ; but of the amount produced! by these and other physical causes we know but little. Channels through which Vital Heat is I/ost. Helm- holtz estimates that 7 per cent, of the total heat produced in the body is expended in the form of mechanical work ; that 78 per cent, is discharged through the skin by evaporation and radia- tion ; and 15 per cent, by the lungs, urine, and feces. Vierordt calculates that the heat discharged from the body is distributed as follows : Calories. 1.8 per cent, in urine and feces = 47,500 3.5 per cent, in expired air = 84,500 7.2 percent, in evaporation of water from lungs . = 182,120 14.5 per cent, in evaporation of water from skin = 364,120 73.0 per cent, in radiation and conduction from skin --= 1,791,820 2,470,060 Calorimetry. A calorimeter is an apparatus for determining the amount of heat dissipated or disengaged from any substance or from a living animal. Those used for animals consist of a chamber adapted to hold the animal, surrounded by some medium which will absorb the heat, such as ice, air, or water. Dulong's Calorimeter consists of a chamber in which the animal is placed ; this is contained in a larger chamber holding water. Outside of this is a layer of some non-conducting material, like wool, and outside of all is a box. Air from a gasometer is ad- mitted on one side, and the expired air passes out on the other. Reichert's water calorimeter (Fig. 229) is described by its in- CALORIMETRY. 411 ventor as consisting of "two concentric boxes of sheet metal which are fastened together so that there is a space of about 1J inches between them, filled with water. The water box is 15 inches in height and width, and 18 inches in length. An opening (h) 9 inches in diameter is made in one end for the entrance and exit of the animal. It is also perforated with three small holes in the top corners, and a slit-like opening in the top on one side. Two of the holes are for the tubes for the entrance and exit of air (JEN 9 EX\ the entrance tube being carried close to the bottom, while the exit tube extends only to the top of the box, and is placed in the opposite diagonal corner, thus ensuring adequate ventilation. In the third hole a thermometer (CT) is inserted, by means of which the temperature of the calorimeter (jacket of metal and water) is obtained. The opening in the side is for the insertion of a stirrer ($), which is for the purpose of thoroughly mixing the EXT FIG. 229. Reichert's water calorimeter. water and thus equalizing the temperature of both water and metal in other words, of the calorimeter." Before using the apparatus to determine the heat dissipated by an animal, the calorimetric equivalent is determined i. e., the amount of heat necessary to raise the temperature of the calorimeter 1 degree C. One gram of alcohol burned produces 9000 calories of heat. If the burning of 10 grams raises the temperature of the calorimeter 1 degree C., then the calorimetric equivalent will be 412 VITAL HEAT. 90,000 calories or 90 ktlogramdeyrees i. 6., for each degree of increase in the temperature of the apparatus 90 kilogramdegrees are absorbed. Besides the heat which is absorbed by the calorimeter, addi- tional amounts are given off by the subject of the experiment in its expired air, and expended in evaporation of the water from its lungs and skin. To ascertain these, the amount of air supplied and its temperature on entering and leaving the instrument must be determined, also the amount of water in the air. Air calorimeters are also used, such as that of Haldane, Hale White, and Washbourn (Fig. 230). In this instrument the animal is placed in the chamber C, and hydrogen is burnt in H. The tubes A A and A' A' being closed, the heat dissipated by the animal expands the air in the air-space between the walls of the chamber, and increases the pressure on that side of the fluid in the manometer M, causing it to move toward H. The flame of hydrogen is regulated so that the amount of heat which is pro- duced by its combustion counterbalances that of the animal and keeps the fluid in the manometer stationary. From the amount of water produced the amount of hydrogen burnt is calculated, and FIG. 230. Diagram of air calorimeter : F, layer of felt ; A, tubes for ventilation - r V, cage; H, hydrogen flame ; M, manometer (Haldane, Hale White, and Washbourn). the number of calories produced by its burning is determined, which equals that given off from the animal. Although there are produced in the adult human body between 2000 and 3000 kilocalories of heat daily (p. 409), still this is very materially affected by various conditions. Thus, children produce proportionately more than adults ; strong, than weak persons ; fleshy persons, than those who are thin. Diet is another very important factor, as shown by the follow- ing table (Danilewsky), giving the amount of heat produced under different diets : On a minimum diet 1800 kilogramdegrees. On a reduced diet (absolute rest) .... 1989 On a non-nitrogenous diet 2480 On a mixed diet (moderate work) .... 3210 On an abundant diet (hard work) .... 3646 On an abundant diet (very laborious work) 3780 PERSPIRATORY GLANDS. 413 Regulation of Temperature. When the temperature of the muscles is raised to 49 C. they lose their contractility. This figure has been regarded as the highest that can be reached by a living human being ; indeed, much below this, 45 C., has long been considered as fatal, although a temperature of nearly 52 C. has been recorded. When the temperature falls to 19 C. a fatal result will follow. To prevent the body from becoming too hot is one of the functions of the skin. This it accomplishes by radiation, con- duction, and evaporation. Of the total heat given off from the body, 73 per cent, is by radiation and conduction from the skin, and* 14.5 per cent, is by evaporation. Thus there is carried off by the skin nearly 88 per cent, of the total heat. This topic will again be discussed in the consideration of the skin and its functions. The prevention of the reduction of the temperature of the body to an extent that would be harmful is accomplished by wear- ing proper clothing, by the ingestion of food, both solid and liquid, by warming the air which comes in contact with the body, and by increased muscular activity. The use of alcohol for this purpose is, as previously stated, delusive. THE SKIN. The skin is composed of a deep portion, the corium, derma, or true skin ; and of a superficial portion, the epidermis or cuticle. Corium. The corium makes up by far the greater part of the skin, and within it are the perspiratory glands, the sebaceous glands, the hairs, together with both blood- and lymphatic vessels. The upper surface, where it joins the epidermis, is irregular, being composed of elevations papillae and intervening depres- sions. In some of these papillae are the tactile corpuscles, in which nerve-fibers end. Epidermis. The epidermis is made up of a deep and a superficial layer. The deep layer (rete mucosum or rete Malpighii) covers the papillae of the corium and fills the depressions between them. It is composed of cells, round or of different shapes due to pressure of contiguous cells, the material of which they are com- posed yielding readily. It is in this layer that the pigment is deposited which characterizes the dark races. The superficial layer of the epidermis is composed of cells which are flat and dry or horny. Perspiratory Glands. The perspiratory glands, also de- scribed as sweat- and sudoriparous glands, are very numerous, it being estimated that in the entire skin there are not less than 2,400,000. They are more abundant in some parts of the body than in others : in the palm of the hand there are 42 to the square centimeter; on the forehead, 190; and on the cheek,, 85. If all 414 THE SKIN. these glands in the body were straightened out and put end to end, they would extend a distance of 4 kilometers. This brief consideration of the perspiratory glands suggests that their function must be very important. They are constantly at work pouring out their secretion upon the surface of the skin. Ordinarily this secretion is not perceptible, and it is then called u insensible perspiration." Upon active exercise or when the temperature of the air is high this secretion becomes visible, and it is then called " sweat " or " perspiration." The average total amount daily formed is 900 grams. This amount is subject to FIG. 231. Vertical section of the skin, diagrammatic (after Heitzmann). considerable variations, being increased in summer and diminished in winter. During violent exercise the amount may be as much as 380 grams per hour, and during exposure to very high tempera- tures it has been known to reach 1814 grams in the same time. Sweat has a salty taste, a specific gravity of 1003 to 1005, and is acid in reaction. It is claimed by some writers that its true reaction is alkaline, and that its acidity is in reality due to the PERSPIRATORY GLANDS. 415 presence of fatty acids resulting from the decomposition of the sebum. In uremia the amount of urea may be so great as to crystallize on the skin ; in diabetes sugar may be found in the sweat ; and in cases of gout uric acid has been detected. The following table shows the composition of sweat : Water. 99.00 per cent. Urea 0.15 " Neutral fats, fatty acids, cholesterin, sodium and potassium chlorids, and other salts . . . 0.85 " 100.00 Office of Perspiration. One of the important means of regulat- ing the temperature of the body is the perspiration. Without it, FIG. 232. c, Corneous (horny) layer ; g, granular layer; m, mucous layer (rete Malpighii). The stratum lucidum is the layer just above the granular layer. .Nerve-terminations : n, afferent nerve ; b, terminal nerve-bulbs ; I, cell of Lang- erhans (after Ranvier). exposure to high temperatures would be injurious, and in some cases would even be fatal. An external temperature of 52 C. is not infrequently met with in the southern part of the United States ; to this heat human beings are exposed without suffering from its effects. The evaporation of the perspiration abstracts heat from the body. Of the heat given off from the body, 88 per cent, passes off by the skin ; of this amount, 73 per cent, is by radia- tion and conduction, and 14.5 per cent, by evaporation. 416 THE SKIN. Sebaceous Glands. The sebaceous glands are racemose glands, and discharge their product sebum into the hair-folli- cles of large hairs, as upon the scalp, while in other portions of the body, as the forehead, where the hairs are small, the hair pro- jects from the mouth of the sebaceous gland, and is more like an appendage than a separate structure. C-. FIG. 233. (7, Epidermis; D, corium; P, papillae; 8, sweat-gland duct; v, arterial and venous capillaries (superficial or papillary plexus) of the papillae (deep plexus is partly shown at lower margin of the diagram) ; vs, an intermediate plexus, an outgrowth from the deep plexus, supplying sweat-glands and giving a loop to hair- papilla (after Eanvier). Composition of Sebum. The sebum, or sebaceous matter, is of an oily nature. It contains albumin, fat, and cholesterin. The vernix caseosa which covers the infant during the latter part of fetal life is of the same character, consisting principally of fat with epithelium. At the temperature of the body the sebum is fluid, but it solidifies on the surface of the skin. Its office is HAIRS AND NAILS. 417 mainly to keep the skin and the hairs soft and pliable. Besides this, it is probably excrementitious to a certain extent. Cerumen, commonly called " ear-wax," is the product of the sebaceous and perspiratory glands of the external auditory meatus, and is composed principally of fat with some soap. It is a reddish substance having a sweetish-bitter taste. Hairs and Nails. These structures are modified epidermis. The hair grows from the hair-papilla, in the interior of which FIG. 234. A normal sweat-gland, highly magnified : a, sweat-coil, with secreting epithelial cells; 6, sweat-duct; c, lumen of duct; d, connective-tissue capsule : e and /, arterial trunk and capillaries supplying the gland (after Neumann). FIG. 235. A normal sebaceous gland in connection with a lanugo- hair ; greatly magnified : a, con- nective-tissue capsule ; 6, fatty secretion ; c, h, fat-secreting cells ; d, root of a lanugo-hair; e, hair-sac ; /, hair shaft ; p, acini of sebaceous gland (after Neumann). there is a blood-vessel. The integrity of this papilla is essential to the existence of the hair ; when destroyed, the hair can never be reproduced. It should be noted that the hair-papillae and the papillae already described in connection with the corium are very different structures, and should not be confounded. It has been estimated that there are, on an average, 120,000 hairs in the scalp. As a rule, the lighter the color of the hair the finer it is ; in the female it is coarser than in the male. 27 418 THE SKIN. Functions of the Skin. The functions of the skin are numerous and very important. (1) Protection. The tissues which lie beneath the skin are delicate and sensitive, and are protected from injury by it. The epidermis, by reason of its hard and tough character, especially in the palms of the hands and on the soles of the feet, is peculiarly adapted to this end. (2) Excretion. It has already been noted that by the skin a liter of fluid is daily eliminated from the body. In this fluid are FIG. 236.A, Shaft of the hair; B, root of the hair; C, cuticle of the hair; D, medullary substance of the hair ; E, external layer of the hair-follicle ; F, middle layer of the hair-follicle; G, internal layer of the hair-follicle; H, papilla of the hair ; I, external root-sheath ; J, outer layer of the internal root-sheath : K, internal layer of the internal root-sheath (after Duhring). dissolved materials representing the waste of the tissues. There is a reciprocal relation between the skin and the kidneys : in summer, when the skin is active, the amount of fluid passed off by the kidneys is reduced, while in winter, when the skin is inactive, the work of the kidneys is much increased. In diseased conditions of the kidneys, the retention in the blood of poisonous materials which are eliminated by them in health is prevented by causing the perspiratory glands of the skin to assume this function. (3) Sensation. The skin, especially at the tips of the fingers, CARE OF THE SKIN. 419 is very sensitive, and gives knowledge of the consistency of objects, also whether they are rough or smooth, sharp or dull, etc. This subject of general sensibility will be fully discussed in connection with the Nervous Functions. (4) Respiration. Interchanges are constantly' taking place in the skin analogous to those which take place in the lungs, although to a much less extent. Oxygen is absorbed from the air by the blood in the cutaneous blood-vessels, and at the same time carbon dioxid is given off. In frogs these interchanges are much more extensive than in man. FIG. 237. a, A vascular papilla ; b, a nervous papilla ; c, a blood-vessel ; d, a nerve- fiber; e, a tactile corpuscle (after Biesiadecki). (5) Regulation of temperature, which has already been dis- cussed (page 415). Care of the Skin. That the skin may perform its functions properly it must be taken care of. The orifices of the ducts of the perspiratory and sebaceous glands must be kept free, so that they may not become clogged. If the skin of an animal is covered with varnish, it speedily dies. This is not due to the retention of waste-materials, which act as poisons, but to the great loss of heat, in the rabbit the temperature falling to 20 C. Ex- periment has shown that if an animal that has been varnished is packed in cotton and kept in a temperature of 30 C., it will survive. Gerlach covered a horse and a rabbit with linseed oil, with the following results : 420 THE SKIN. Temperature before. Temperature after. Animal. Rectal. Cutaneous. Rectal. Cutaneous. Remarks. Eabbit. . . 39. 7 C. 38 C. 28 C. 26 C. f At time of death, thirty \ hours after varnishing. {On the sixth day after Horse . . . 38 35 32 29 varnishing ; death oc- curred on eighth day. Reference is frequently made to the gilding of a child's body to make it represent an angel at the coronation ceremonies of Pope Leo X., which resulted in the speedy death of the child. Inasmuch as the whole human body has been covered by an impermeable layer for eight or ten days without producing any disturbance whatever, even in the body -temperature, it is probable that there was something in the gilding material which acted as a poison. The ability of the human being to regulate his temperature ex- plains the different result in man arid in the horse and rabbit. The skin requires both friction and bathing to maintain it in a physiologic condition. The process of rubbing removes the useless epidermic scales and any obstructions which tend to clog the mouths of the glands. The oily nature of the sebaceous matter, which is always present and which retains the dust and dirt coming in contact with it, requires that the skin be washed with water and soap. But the soap must be free from irritating in- gredients, such as rancid fat, and from too large an amount of alkali and coloring-matter, and from drugs of various kinds. If the skin is diseased, medication by means of soap may be needed, but it should be prescribed by a physician. If the skin is not diseased, medicated soaps are harmful. Old white Castile soap meets all the indications in health. Baths. Baths may be classified as follows : Cold hath to 24 C. Temperate bath 24 to 26 C. Tepid bath 26 to 32 C. Warm bath 32 to 37 C. Hot bath 37 to 44 C. As a rule, hot baths are relaxing, and should not, therefore, be indulged in too frequently ; indeed, in persons suffering with disease of the heart they may actually endanger life. The Turkish bath, taken under competent medical supervision, is often of great benefit, and many persons take it weekly, and even oftener, with the effect of toning up the system and making them more com- petent to endure both physical and mental fatigue. Cold baths, except for the very robust, are also to be taken with great caution. If afterward there is reaction and if the skin becomes warm and pink, they are beneficial, but if the skin becomes cold and blue, they are injurious. In fact, this should be the test for each indi- KIDNEYS. 421 vidual to apply to his own case. Bathing, except a sponge- or plunge-bath, should not be practised when the vital powers are low, as early in the morning, nor after a long fast, nor should it be indulged in too soon after eating ; eleven o'clock in the morning is, for the average person, a proper time for a bath of considerable duration. THE URINARY APPARATUS. The kidneys (Fig. 238) are situated in the lumbar region of the abdominal cavity, one on each side of the spinal column, with the upper border on a level with the twelfth dorsal, and the FIG. 238. Longitudinal section through the kidney : 1, cortex ; 1', medullary rays; 1", labyrinth; 2, medulla; 2', papillary portion of medulla; 2", boundary layer of medulla ; 3, transverse section of tubules in the boundary layer ; 4, fat of renal sinus; 5, artery; *, transverse medullary rays; A, branch of renal artery; C, renal calyx ; U, ureter (after Tyson and Henle). lower opposite the third lumbar vertebra. The dimensions of each are approximately : Length, 10 cm. ; breadth, 5 cm. ; thickness, 2.5 cm. The weight is from 125 to 180 grams. The shape of the kidney is like that of a bean, the internal 422 THE URINARY APPARATUS. border being concave and presenting a fissure the hilum at which the vessels, the nerves, and the ureter enter the organ. When the kidney is longitudinally cut in two, it is seen to be made up of an external or cortical portion cortex and an in- ternal or medullary portion medulla. The medullary portion is made up of numerous pyramids (those of Malpighi), from 8 to 18 in number, and, dipping down between them, as well as forming the outer part of the kidney, is the cortical portion. Each pyra- mid terminates in a papilla pro- jecting into a calyx, which, with the calices of other pyramids, forms the pelvis, the upper dilated cavity of the ureter. Tubuli Uriniferi (Figs. 239, 240). At each papilla there open about 20 uriniferous tubules, which can be traced to the base of the pyramid. Each tubule continues into the cortical portion of the kidney, where it is larger and becomes convoluted, narrowing again and entering the pyramid, in which it again becomes straight, forms a loop, and re-enters the cortical portion, again becomes convoluted, and finally terminates in a spherical body, the Malpigh- ian capsule or capsule of Bowman. This complicated structure may, perhaps, be traced more easily in the opposite direction. Beginning with the Malpighian capsule in the cortical portion, there is next the convoluted tubule, which, as it passes into the medullary portion, becomes straight and is known as the "descending limb of Henle's loop." This bends on itself, forming the ascending limb, like- wise straight, passes back into the cortex, becomes convoluted, and enters a straight collecting tube which opens at the apex of a pyramid. The uriniferous tubules are lined with epithelium, which varies at different parts of their course. The epithelium which lines the capsules and the neck, and which covers the glomerulus, is flattened, FIG. 239. Diagram of two urinif- erous tubules: 1, Malpighian tuft surrounded by Bowman's capsule; 2, constriction or neck ; 3, proximal convoluted tubule ; 4, spiral tubule ; 5, descending limb of Henle's loop; 6, Henle's loop ; 7 and 8, ascending limb of Henle's loop ; 9, wavy part of ascending limb of Henle's loop; 10, irregular tubule ; 11, distal convoluted tubule ; 12, first part of collecting tube ; 13 and 14, straight part of col- lecting tube ; 15, excretory duct of Bellini (Tyson and Brunton, after Klein and Noble Smith). PLATE IV, A, A, right and left kidneys; B. urinary bladder; C, C, right and left ureters; d, d, renal arteries (Maclise). KIDNEYS. 423 and the cells have an oval nucleus (Fig. 241). This changes to a thick polyhedral epithelium, with a fibrillar or striated structure, in the proximal convoluted tubule and spiral tubule of Schachona. It is again flat in the descending limb of Henle's loop, while in the ascending limb it resembles that of the spiral tubule. The epithelium in the irregular or zigzag tubule is angular and markedly --"Artery of capsule. Arched collect- - ing tubule. . Straight col- lecting tu- " bule. Distal convo- - luted tu- bule. Malpighian corpuscle. Proximal con- t voluted tu- C, bule. Loop of Henle. ( ~ Collecting tubule. Arteria arcua- ta. Large collect- - ing tubule. Glomer- ulus. arcuata. Papillary duct. m FIG. 240. Diagrammatic scheme of uriniferous tubules and blood-vessels of kidney ; drawn in part from the descriptions of Golubew (Bohni and Davidoff). striated ; in the second convoluted tube it is like that in the first ; in the junctional tubes, flat and cubical ; in the straight or collecting tubes, clear cubical and columnar; and in the ducts of Bellini, clear columnar. The following table, from Schafer's Essentials of Histology, exhibits the differences in the epithelium of the tubules in a manner very useful for reference : 424 THE URINARY APPARATUS. Portion of tubule. Nature of epithelium. Position of tubule. Capsule First convoluted tube . Spiral tube Small or descending) tube of Henle. . . . j Loop of Henle Larger or ascending \ tube of Henle. . . . j Zigzag tube Second convoluted tube Junctional tube . . . . Straight or collecting) tube j Duct of Bellini . / Flattened, reflected over glom- ) 1 erulus. j f Cubical, fibrillated, the cells > \ interlocking. j Cubical, fibrillated (like the last). Clear flattened cells. Like the last. f Cubical, fibrillated, sometimes ) \ imbricated. f (Cells strongly fibrillated;) < varying height ; lumen > ( small. f Similar to first convoluted tube, but cells are longer, with larger nuclei, and they have a more refractive as- pect. Clear, flattened, and cubical cells. /Clear cubical and columnar) \ cells. j Clear columnar cells. Labyrinth of cortex. Labyrinth of cortex. Medullary ray of cortex. / Boundary zone and partly | papillary zone of medulla. Papillary zone of medulla. /Medulla and medullary ray I of cortex. Labyrinth of cortex. Labyrinth of cortex. f Labyrinth passing to medul- \ lary ray. Medullary ray and medulla. Opens at apex of papilla. Blood-vessels. The renal artery (Fig. 238), which supplies the kidney, is a branch of the abdominal aorta, which before entering FIG. 241. From section of cortical substance of human kidney : a, epithelium of Bowman's capsule ; 6 and d, membrana propria ; c, glomerular epithelium ; e, blood-vessels; /, lobe of the glomerulus; g, commencement of uriniferous tubule; h, epithelium of the neck ; i, epithelium of proximal convoluted tubule ; X 240 (Bohm and Davidoff). KIDNEYS. 425 the organ subdivides into 4 or 5 vessels. It is from these vessels that the suprarenal capsules and the ureter also receive their blood-supply. When, as frequently happens, there is a second artery, it is called the inferior renal artery. The branches of the renal artery pass toward the cortex and end as proper renal arteries, arterice proprice renales, from which are given off the interlobular arteries in the direction of the cortical substance, and the arteriolw redce toward the medullary pyramids. From the interlobular arteries are given off the afferent Nuclei of en- dothelial cells of blood capillaries. Lumen of uri- niferous tu- bule. Striated bor- der. FIG. 242. Section of proximal convoluted tubules from man ; X 580 (Bohm and Davidoff). vessels, which pierce the capsules and end in the Malpighian tufts. From the capsules emerge the efferent vessels, which form a venous plexus about the uriniferous tubes, and the blood ultimately leaves the kidney by the renal vein. Nerve-supply of the Kidney. The nerves of the kidney, from 15 to 20 in number, have ganglia upon them, and are from the renal plexus. This plexus is formed from the solar plexus, semi- lunar ganglion, lesser and smallest splanchnic nerves. So far as known, the nerves are distributed to the arterioles principally, 426 THE URINARY APPARATUS. though nerve-fibrils are described as ramifying among the epithe- lium of the tubules. Function of the Kidneys. The function of the kidneys is to form urine. This is sometimes spoken of as a secretion, but inas- much as its constituents pre-exist in the blood when that fluid comes to the kidneys, and these organs simply remove these sub- stances from the blood, urine is more properly an excretion. The ingredients composing the urine may, from a physiologic stand- point, be divided into two groups : (1) Water and some of the salts ; and (2) urea, uric acid, and allied substances. The first group, consisting of water and salts, is eliminated from the blood while that fluid is passing through the glomerulus within Bowman's capsule, the beginning of the uriniferous tubules ; while the urea group is excreted while the blood is passing through the venous plexus surrounding the convoluted portions of the tubule. Excretion of Water and Salts. While all authorities agree that it is at the glomeruli that water and some of the inorganic salts are eliminated from the blood, there is a diversity of opinion as to the factors engaged in this process ; some regarding it as a simple filtration in which the glomerular epithelium plays a passive part, while others attribute to these cells a very important part in the process. Whenever the renal blood-supply is increased, the quantity of urine is also increased, and it has therefore been assumed that this increase was due to the heightened blood-press- ure within the glomerulus, and this is the basis of the filtration theory ; but it has been pointed out that under these circumstances there is an increased blood-flow through the organ, and it is to this that Heidenhain attributes the increased secretion, rather than to the simple increase of pressure within the glomeruli. This authority is one of the principal exponents of the theory that the glomerular epithelium is the efficient agent in the elimination which takes place within Bowman's capsule. Bowman, in 1842, advanced the opinion that "the Malpighian bodies might be an apparatus destined to separate from the blood the watery portion " of the urine. On the other hand, he held that " the tubes and their plexus of capillaries were probably the parts concerned in the secretion of that portion of the urine to which its characteristic properties are due." In 1884 Ludwig expressed the opinion that all the constituents of the urine escape from the blood while passing through the glomeruli, and that this separation is due to the high pressure under which the blood is within these structures. Heidenhain combated the view of Ludwig on various grounds : Among others, that a rise of arterial pressure elsewhere in the body, as in the salivary glands, does not cause increased transuda- tion through the walls of the blood-vessels ; that the epithelium KIDNEYS. 427 covering the glomeruli would offer great resistance to filtration ; that if the renal vein is ligated and the pressure within the glomeruli thereby increased, not only is the flow of urine not in- creased, but it is actually abolished; and, finally, that filtration will not explain the increased flow of urine when water and crys- talloid substances are increased in the blood. Heidenhain, as already stated, believes that the cells of the glomerular epithelium act as secretory cells do elsewhere, and by the power which they possess as living cells eliminate water and inorganic salts, espe- cially sodium chlorid, from the blood. In commenting on these opinions, Starling, to whose admirable article on " The Mechanism of the Secretion of the Urine/ 7 in Schafer's Text-book of Physiology, we are much indebted, says : " It seems probable that in the glomeruli the process is largely if not exclusively physical," and that " we have at present no evi- dence that the cellular covering of the glomeruli acts otherwise than passively in the production of the glomerular part of the secre- tion." He also refers to the researches of Munk and Senator, who have reached the conclusion that water and part of the urinary salts, especially sodium chlorid, are transuded through the glomeruli iii direct consequence of the blood-pressure i. e., by a process of fil- tration, although the rapidity of the blood-flow is equally important. It is also generally accepted that when serum-albumin, hemo- globin, or dextrose escapes from the blood and becomes a constitu- ent part of the urine, this takes place while the blood is passing through the glomeruli. The oncometer (p. 338) has been largely used in connection with the various experiments which have been conducted to deter- mine the effects of increased and diminished blood-pressure on the excretion of urine by the kidney. Excretion of Urea, Uric Acid, etc. Bowman, in his views as to the manner of the formation of urine, expressed the opinion that the tubes and their plexus of capillaries were probably the parts concerned in the secretion of the substances forming this second group of urinary constituents, and this is the generally accepted view of the authorities of the present day. It is also probably true that some water, sodium chlorid, sulphates, and phosphates are eliminated from the blood in this part of its course through the kidney. The efficient agents in this elimination are the cells lining the tubules, and especially those in the convoluted portions. Effects of Removal of the Kidneys. Removal of a single kidney for a diseased condition of that organ, constituting nephrectomy, is not an uncommon operation at the present day. After the operation the remaining kidney enlarges and performs the func- tions of both. Removal of both kidneys is followed by a fatal result. 428 THE URINARY APPARATUS. Ureters. From each kidney passes a ureter, a tube which connects the kidney with the bladder, and through which the urine is discharged. It has a diameter about that of a goose-quill and a length of about 40.6 cm. It has 3 coats : External or fibrous; middle or muscular; and internal or mucous. The muscular tissue is of the plain variety and arranged in 2 layers: longitudinal and circular ; a third layer, also longitudinal, is found near the bladder. The mucous membrane is covered with transi- tional epithelium (p. 34). When the ureters reach the base of the bladder, they pass for about 2 cm. between the muscular and mucous coats, and then open by a constricted orifice in the bladder. Function of the Ureters. The urine which is being constantly formed by the kidneys passes into their pelves, and by peristaltic action of the muscular coat of the ureters is carried to the bladder, into which it flows intermittently. The actual entrance of the urine has been observed in a case of ectopia vesicce in a boy. This condition consists in a deficiency in the abdominal wall and in the front wall of the bladder, so that the openings of the ureters FIG. 243. Casper's ureter cystoscope : li, movable lid covering groove in which moves c, the ureteral catheter ; d, handle of lid ; o, ocular end ; p, prism ; I, lamp, , screw for making and breaking connection with the battery ; m, mandril. can be inspected. In this case the flow of urine into the blad- der was intermittent, and about the same in amount "for each ureter. By means of the cystoscope (Fig. 243) it has been determined that the peristaltic action of the ureters is both intermittent and alternate ; exceptionally it may be synchronous. At intervals of a minute or more urine is discharged from the ureters into the bladder, the amount varying; but averaging, perhaps, from 15 to 30 drops. The cause of this peristaltic contraction is not definitely deter- mined. Some authorities attribute it to the direct stimulation of the muscular tissue by the accumulated urine, which results in a wave which is propagated from one muscle-cell to another ; while others think that this contractility of the musculature of the r ' ureters is a power possessed by it independent of any direct stim- ulation, either mechanical or nervous. Experiments upon the rat have demonstrated that when the ureter is cut into several pieces, each section will contract peristaltically. BLADDER. 429 Bladder (Fig. 244). This is not infrequently spoken of as the urinary bladder, and when moderately distended will contain about ^ liter ; though it may be so distended as to contain very much more than this. It has 4 coats : peritoneal or serous, muscular, submucous, and mucous. The muscular coat is made up of 3 layers of plain muscular fiber : External or longitudinal, middle or circular, and internal, which is also longitudinal. The external longitudinal layer is also described as the detrusor urince muscle, and the aggre- FIG. 244. Section of penis, bladder, etc. : 1, symphysis puhis ; 2, prevesical space; 3, abdominal wall; 4, bladder; 5, urachus; 6, seminal vesicle and vas deferens ; 7, prostate ; 8, plexus of Santorini ; 9, sphincter vesicse ; 10, suspensory ligament of penis; 11, penis in flaccid condition; 12, penis in state of erection ; 13, glans penis ; 14, bulb of urethra ; 15, cul-de-sac of bulb, a, Prostatic urethra ; b, membranous urethra; c, spongy urethra (Testut). gation of the fibers of the circular layer around the neck of the bladder and the beginning of the urethra, as the sphincter vesicce. The mucous coat or mucous membrane is covered with transitional epithelium, and contains racemose glands. Nerve-supply. The nerves supplying the bladder are, according to Langley and Anderson, derived from (1) the second to the fifth lumbar nerves, reaching the organ through the sympathetic chain, the inferior mesenteric ganglion, and the hypogastric nerves ; (2) the second and third sacral spinal nerves. Stimulation of the 430 THE URINARY APPARATUS. first group causes feeble, and of the second strong, contraction of the bladder. Function of the Bladder. The bladder acts as a reservoir for the urine until such time as it is passed in the act of urination or micturition. The urine is retained within the bladder by the tonic contraction of the sphincter vesicse in the same manner as feces are retained in the rectum by the sphincter ani. The pressure of the urine when the bladder is full is equal to only 1 cm. of mer- cury, while it takes a pressure of at least 3 cm. to overcome the elasticity of the sphincter. When the bladder is about to be emptied, as the result of an inhibitory impulse, the sphincter vesicse becomes relaxed. At the same time the muscular coat of the bladder and the abdominal muscles contract, and the urine begins to flow. The pressure which is thus exerted equals 10 cm. of mercury. Although the starting of the act is voluntary, when once it has begun it continues under the influence of the vesico- spinal center situated in the lumbar part of the cord until the bladder is empty. Up to a certain point the brain is able to inhibit the center and postpone the evacuation of the bladder, but after a time, if too long delayed, the resistance of the sphincter is overcome and urine will flow. It is more difficult to stop the act after it has once begun than to delay its beginning, for the urine, flowing over the mucous membrane of the urethra, stimulates the vesicospinal center, and the efferent impulses to the contracting muscles are increased. If the mucous membrane of the bladder is inflamed, as in cystitis, the stimulation of the center may be so great as to pre- vent the brain from inhibiting the evacuation, and this may occur when only a small quantity of urine is accumulated. Or it may happen that the spinal cord is injured or diseased in the upper or middle portion, and thus all sensation caused by a full bladder may be abolished. Under these circumstances the bladder, when full, will be emptied by the reflex action of the vesicospinal center. Or, again, if the lesion of the cord is such as to disorganize this center, then there will be no reflex action of the cord, and the elasticity of the tissues about the neck of the bladder will keep the urine in that viscus until the elasticity is overcome by the disten- tion, when the urine will flow in drops as fast as it comes from the kidneys; but the bladder will not empty itself. Inexperi- enced persons are often deceived by this dribbling of the urine, thinking that its discharge is evidence that the bladder is perform- ing its duty, while the fact is that it is evidence of paralysis and retention. Urethra (Fig. 244). This canal extends from the neck of the bladder to the meatus urinarim, and in the male is about 20.4 cm. and in the female about 3.7 cm. in length. It is lined with REACTION OF THE URINE. 431 mucous membrane, in which are mucous glands, glands of Littre, and opening into it in the male are two compound racemose glands, Cowper's glands. In the female urethra the epithelium is stratified. In the male urethra it is stratified near the meatus, transitional in the prostatic portion, and elsewhere columnar. THE URINE. Quantity. The amount of urine voided by an adult' in twenty-four hours is about 1500 c.c., although it may vary within normal limits from 1200 c.c. to 1700 c.c. In health the increased drinking of fluids and lessened formation of the perspiration will increase the amount of urine excreted, while the excretion will be diminished if the quantity of liquids drank is lessened or if the perspiratory glands are more active. It is a matter of common observation that in summer the urinary flow is less than it is in winter. Color. The color is ordinarily yellow, though it may be, even in health, almost colorless or reddish brown. The urinary pigments are urochrome, urobilin, uroerythrin, and hematopor- phyrin. Urochrome. This is the essential pigment to which the yellow color is due. It has been demonstrated that when alcoholic solu- tions of pure urochrome are treated with aldehyd a reducing action is produced on the pigment and urobilin is produced. This would indicate that urochrome is an oxidation-product of urobilin. Urobilin. This is the same as stercobilin of the feces, and is probably formed from the bilirubin of the bile. Urobilin exists in small amount in the urine, and principally in the form of a chromogen, to which the name urobilinogen has been given. Uro- bilin and hydrobilirubin are regarded by some as identical. Hop- kins states that the origin of urinary bilirubin is probably three- fold from absorption of the ready-formed pigment in the bowel ; from direct production in the liver ; and from reduction of the blood-pigment in the organ, independently of hepatic agency. Uroerythrin. This coloring-matter is that which gives the characteristic color to the pinkish deposits of urates. It exists in small amount, but it is always present in normal urine. Hematoporphyrin. Although normally present in but small amount, this substance may exist pathologically in considerable quantity. Reaction. The reaction of the mixed urine passed in twenty- four hours is acid to litmus, due to the presence of sodium dihy- drogen phosphate, NaH 2 PO 4 , or, as it is more commonly called, acid sodium phosphate. The acidity of the urine is subject to considerable variation. It is increased after exercise and after the consumption of animal 432 THE UEINE. food ; it is decreased after the ingestion of vegetable food, because this contains compounds of organic acids which by oxidation form carbonates, and these latter may be so plentiful as to make the urine alkaline. The alkaline tide is a term applied to the condition in which during the period when hydrochloric acid is being set free as a constituent of the gastric juice the urine, through the elimination from the blood of the bases, becomes less acid and sometimes even alkaline. There is also a difference in the degree of acidity of the urine at different times of the day, without regard to the food taken. Specific Gravity. This varies from 1015 to 1025, being lower when the quantity of urine is increased, and higher when it is diminished. It may, in extreme cases, as after the drinking of large quantities of fluid, be as low as 1005. In diseased condi- tions, as in diabetes mellitus, the quantity is greatly increased and this is accompanied by a high specific gravity. Composition. In the following table are given two analyses by Bunge of the twenty-four hours 7 mixed urine of a young man : The "meat diet 77 consisted of beef with a little salt and spring- water ; the " bread diet " consisted of bread, butter, and water : Total quantity in twenty-four hours Urea . . . . Meat diet. 1672 c.c. 67.2 rams Creatinin ............. 2.163 Uric acid ............ 1.398 Sulphuric acid (total) ...... 4.674 Phosphoric acid ......... 3.4/37 Lime .............. 0.328 Magnesia ............ 0.294 Potash .............. 3.308 Soda .............. 3.391 Chlorin . . ........... 3.817 Bread diet. 1920 c.c. 20.3 grams 0.961 9.253 1.265 1.658 0.339 0.139 1.314 3.923. 4.996 The urine of an adult living upon an ordinary mixed diet and amounting in the twenty -four hours to 1500 c.c. would contain approximately 1440 c.c. of water and 60 grams of solids, of which 35 grams would be urea. Urea, CO(NH 2 ) 2 . Chemically this substance is an amid of carbonic acid, and is also described under the name carbamid. It is isomeric with ammonium cyanate, (NH 4 )CNO, and was pre- pared therefrom by Wohler in 1828. It crystallizes in the form of colorless needles or rhombic prisms ; is soluble in water and alcohol, but is insoluble in ether and chloroform. With nitric acid, urea becomes urea nitrate, CO(NH 2 ) 2 NO 2 OH, which forms in its crystallization rhombic tables; the angles of these are usually cut off, making six-sided crystals, which fre- quently overlap one another. The formation of these crystals is used as a test for urea. COMPOSITION OF THE URINE. 433 With oxalic acid urea forms urea oxalate, CO(NH 2 ) 2 (COOH) a which crystallizes as short rhombic prisms. Urea is converted into ammonium carbonate by the action of the ferment Micrococcus urece; this change which takes place in urine declares itself by the ammoniacal odor which is developed. It is represented by the following equation : CO(NH 2 ) 2 + 2H 2 = (NH 4 ) 2 C0 3 Urea. Water. Ammonium carbonate. Urea is the end-product of the proteid metabolism of the body and of the albuminoids of the food. When a meal containing considerable proteids has been ingested, and the urea determined, the amount will be at a maximum at the third or fourth hour ; this is supposed to indicate the absorption of peptones from the stomach. A second maximum occurs at the sixth or seventh hour, and this is attributed to the absorption of peptones from the intestine. Formation of Urea. Urea exists in the blood when that fluid reaches the kidney, and the function of this organ is, so far as urea is concerned, simply to eliminate it. Without recounting the experimental evidence, which is ample and satisfactory, it is enough to say that urea is formed by the cells of the liver. The most satisfactory explanation of the manner of this formation is that given by Dreehsel, and is substantially as follows : Proteids undergo hydrolytic cleavage, and leucin, tyrosin, aspartic acid, and other amido-bodies are formed : these undergo oxidation, forming NH 3 , CO 2 , and H 2 O ; NH 3 and CO 2 unite to form ammonium NH carbonate, COlo of the Ivitterv with r (Fig. 2oi>), and the other with A, and A and r with a short and thick wire. On account of the wire between r and .1. the primary current is never opened, but passes through the primary coil, anil when the vibrating spring and r come into contact, the current is short -circuited. ^fatHMtorimftfc Ettctmlcs. When a muscle or other tissue is placed upon metal electrodes through which a current is passing, the electrodes hoeome polamed as a result of the decomposition taking place in the tissue, and consequent!? currents are set up which materially interfere with a proper interpretation of the effects of the current from the battery or from the induced cur- rent, as the ease may bo. To avoid this, special forms of electrodes have boon devised which are known as HnpoliirizaMt or MOH- polarisabl* dectrod(& Fig. -M shows such electrodes. Kaeh one 448 MUSCLE PHENOMENA. consists of a glass tube, at one end of which is an opening ; the lower part of this tube is filled with China clay, mixed with normal saline solution, which projects a little through the open- ing so that it may come into contact with the tissue to be in- vestigated. The portion of the tube above the clay is filled with a saturated solution of zinc sulphate, into which dips an amalga- mated zinc wire. When the experiment is of long duration the form represented by the middle figure in the illustration is best adapted; the U-shaped tube is filled with the zinc sulphate solu- FIG. 254. Method of recording muscular contraction (Lombard). tion, and into one end dips the wire, and into the other a glass tube filled with clay, on which the tissue rests. PohVs Commutator (Fig. 252). In order to reverse the direction of the current, PohPs mercury commutator is used. This consists of a block of some insulating material, as paraffin or wood, with six cups containing mercury, each of which is connected to a binding-post In Fig. 253, A, it will be seen that a and b are con- nected with the battery, c and d with the electrodes, and e and / with movable wires in such manner that c connects with / and d with e. Above the block is a bridge of some insulating mate- rial, glass or vulcanite, to which two semicircles of wire are attached, one of which is connected with a wire dipping into the cup a, and the other with a wire dipping into the cup b. This bridge can be rocked back and forth, so that if the ends dip into the cups c and d, a will be connected with c, and b with d ; while IRRITABILITY. 449 if they dip into e and /, a will be connected with e, and through the cross-wire with d, and b will be connected with/, and through the cross-wire with c. This arrangement permits the battery- current to pass by way of a and e down the nerve, and back to the battery by way of d and b ; or from the battery through a, e, and d, and up the nerve and back to the battery by way of c, /, and b. In Fig. 253, jB, the cross-wires have been removed, and, as shown by the diagram, the current can be sent through c and d to one part of the nerve, or through e and / to another, by rocking the bridge back and forth. Myographs. --In order properly to study the effects of the FIG. 255. Spring myograph : A, B, iron uprights, between which are stretched the guide-wires on which the travelling plate a runs ; fc, pieces of cork on the guides to check gradually the plate at the end of its excursion and prevent jarring ; 6, spring, the release of which shoots the plate along ; h, trigger-key, which is opened by the pin d on the frame of the plate (Stewart). induction shocks upon the nerves and muscles it is necessary to have some method of recording the movements of the muscles which these shocks produce. Such an instrument is the myograph. The nerve-muscle preparation has already been described. The tendon of the muscle is attached to a lever, and to this latter is attached a writing-point, which rests against a piece of paper wrapped around a revolving drum, the paper revolving with the drum. When the muscle contracts, it raises the lever and an upward line is made by the point on the paper ; when the muscle relaxes, the lever falls and the point makes a descending line. Inasmuch as this drum is revolving all the time, these lines take the form of curves. Such a record is a myogram or muscle-curve, and may be preserved 29 450 MUSCLE PHENOMENA. for the purpose of study. Fig. 254 represents the method of recording muscular contraction. Other forms of the myograph are the spring myograph (Fig. 255) and the pendulum myograph (Fig. 256). FIG. 256. Pendulum myograph ; at the left, as seen from the front : A, bearings on which the pendulum swings ; P, pendulum ; G, G', glass plates carried in the frames T, T ; a, pin which opens the trigger-key. The key, when closed, is in con- tact with c, and so completes the circuit of the primary coil (Stewart). Time-markers or Chronographs. In order to know and record the length of time consumed by various phenomena which are the subject of investigation, various forms of time-markers are used which make a record on the drum at the same time that the myo- IRRITABILITY. 451 gram is being made. Such an one is the electric signal of Deprez (Fig. 258), which is an electromagnet whose circuit is closed and opened by the second pendulum of a clock or a metronome. Or for this purpose a tuning-fork may be used which vibrates FIG. 257. Time-marker; arrangement for marking two intervals: D, seconds pendulum, with platinum point, E, soldered on ; A, mercury trough, into which E dips at the end of its swing ; B, Daniell cell ; C, electromagnets, which draw down writing-lever F when the current is closed by E dipping into A ; G, spring (or piece of India rubber), which raises .Fas soon as current is broken (Stewart). FIG. 258. Electromagnetic time-marker connected with metronome. The pen- dulum of the metronome carries a wire which closes the circuit when it dips into either of the mercury cups, Hg (Stewart). one hundred times in a second, the writing-point being attached to one of its prongs. Moist Chamber. In order to preserve the preparation in as normal condition as possible during an experiment, it is enclosed in a chamber the air of which is kept moist. Simple Muscular Contraction. When the muscle-nerve prep- aration is stimulated by a single induction shock, a single con- traction of the muscle results ; this is a twitch or a simple muscular 452 MUSCLE PHENOMENA. contraction, and its myogram is shown in Fig. 259. This is a simple muscle-curve. Latent Period. The moment that the stimulus reaches the muscle is represented by a in the illustration, but the upward FIG. 259. Myogram from gastrocnemius muscle of frog; beneath, the time is re- corded in 0.005 second : a, moment of excitation ; ft, beginning of contraction : c, height of contraction ; d, end of contraction (Lombard). curve begins at 6. So that between these events there is an interval of 0.006 second, as shown by the lowest line, in which the curves are made by a time-marker. This interval is the latent period. At 6 the curve begins rapidly to rise, then more slowly, FIG. 260. Superposition of contractions: 1 is the curve when only one stimulus is thrown in ; 2, when a second stimulus acts at the time when curve 1 has nearly reached its maximum height (Stewart). when it reaches its highest point, c. Then, as the muscle begins to relax, there is a downward curve until the line is reached from which the curve started, this line being the abscissa; the descend- ing curve shows that the relaxation is at first rapid, then becomes slower, and occupies a longer time than the contraction. From a to b occupies about 0.006 second ; from b to c, about 0.05 second ; from c to d, about 0.07 second. Helmholtz, in his experiments IRRITABILITY. 453 upon the frog's gastrocnemius, found that the latent period occupied yj-g- second ; the rise of the curve, or the stage of contraction proper, I ^- second; and the fall or stage of elongation, Y^-Q : or FIG. 261. Development of incomplete tetanus and contracture, by indirect stimulation. A gastrocnemius muscle of a frog was indirectly stimulated by breaking induction-shocks, of medium strength, applied to the sciatic nerve. The rate was about 8 per second, as shown by comparison of the seconds traced at the bottom of the figure with the oscillations caused by the separate contractions. -jig- second in all. A close inspection of the myogram will show a slight rise after d ; this is due to the elasticity of the muscle, and constitutes the stage of elastic after-vibration or contraction-remain- der. Sometimes more than one of these curves are produced. Since the time of Helmholtz's experiments other observers have found that the true latent period is much shorter, certainly not more than ^Vo" second, and probably even shorter than this, for FIG. 262. Effect of rapid excitations to produce tetanus. Experiment with a gastrocnemius muscle of a frog, excited directly with breaking induction-shocks of medium strength, at the rate of 33 per second. The weight was about 15 grams. The time record gives fiftieths of a second (Lombard). it is highly probable that changes begin immediately in the muscle upon the receipt of the stimulus, although these changes are not at once apparent. The muscle-curve differs in the muscles of different animals and also in those of the same animal. Summation of Stimuli. If a muscle which has been stimulated is again stimulated before the effect of the first stimulation has 454 MUSCLE PHENOMENA. passed, a second curve will be produced, which will be higher than the first (Fig. 260), due to the addition of the second stimu- lation to the first. This is the summation of stimulation, summa- tion of effects, or superposition of contraction. Tetanus. When a series of stimuli are added one to another before the effects of the preceding ones have passed, so that the muscle at no time becomes completely relaxed, the condition of tetanus is produced : incomplete tetanus, if the effect of each stimu- lation can be seen in the separate curves (Fig. 261), and complete tetanus, where these have disappeared and their place is taken by a TOO 800 900 1000 1100 1200 1300 1400 1500 1600 1700 FIG. 263. Effect of fatigue on the height of muscular contractions. The figure is a reproduction of parts of a record of over 1700 contractions made by an isolated gastrocnemius muscle of a frog. The contractions were isotonic, the weight being about 20 grams. The stimuli were maximal breaking induction-shocks, and were applied directly to the muscle at the rate of 25 per minute. Between the first group of 66 contractions and the following groups a rest of five minutes was given ; after this rest the work was continued without interruption for about one and a half hours. The second group of contractions, that immediately following the period of rest, contains the first 20 contractions of the new series: the next group the 100th to the 110th ; the next the 200th to the 210th, and so on (Lombard). continuous line (Fig. 262). Voluntary tetanus is the term applied to the normal voluntary contraction of a muscle. The impulses sent out by the nerve-cells are generated and emitted with such frequency as to produce tetanus, and not a simple contraction. The character of the simple muscle-curve is modified by : IRRITABILITY. 455 1. The load ; 2. The temperature ; 3. Previous stimulation ; 4. The character of the muscle itself; and 5. Drugs. 1. Effect of the Load. The extent to which a muscle contracts is increased up to a certain point with the increase of the load ; but when this point is reached it diminishes, and if the load is sufficiently increased, its power to lift it at all ceases. 2. Effect of Temperature. Up to a certain point cold increases the contraction ; beyond this point it diminishes it ; moderate warmth also increases the height of the contraction, but excessive heat (exceeding 40 C.) coagulates the proteids of the muscle, producing heat-rigor. 3. Effect of Previous Stimulation. When a muscle is stimu- lated, each curve is a little higher than the preceding one for a time, the curve being called a staircase; then, as the stimulation is continued, the curve falls, and finally there is no response to the stimulation the muscle is fatigued. Cause of Fatigue of Muscles. This is explained in the case of the muscle-nerve preparation by the fact that the destruction or katabolism of the muscular tissue predominates over its anabolism or building up, and after a time its contractile power is lost. FIG. 264. Myogram of muscle poisoned with veratrin and that of a normal muscle : a, myogram from a normal gastrocnemius muscle of a frog the waves at the close are due to the recoil of the recording lever ; 6, myogram from a gastroc- nemius muscle poisoned with veratriii, recorded at the same part of the drum (Lombard). Fatigue also occurs as a result of the .accumulation of the prod- ucts of contraction, sarcolactic acid anji acid potassium phosphate, which to a certain extent act to prevent contraction, and when these are removed by the circulating blood during a period of rest following muscular activity, the contractile power is restored. In the fatigue of muscles which follows their use as the result of volition, the cause is chiefly in the nerve-cells in which the voluntary impulses are generated. 4. Effect Due to the Character of the Muscle. Some muscles contract more slowly than others, even in the same individual ; as, 456 MUSCLE PHENOMENA. for instance, those of the leg than those of the arm. The same difference is seen in the corresponding muscles of different animals. 5. Effect of Drugs. The effect of drugs upon muscular contrac- tion is well illustrated by injecting veratrin under the skin of a frog: the principal characteristic of the muscle-curve produced being the extreme prolongation of the period of relaxation (Fig. 264). Rigor Mortis. It has already been stated (p. 62) that the coagulation of the muscle-plasma is the cause of rigor mortis or cadaveric rigidity, in which the muscle becomes opaque and stiff, and loses its elasticity and extensibility ; at the same time it becomes warmer and acid in reaction. Rigor usually appears in from one hour to five hours after death, although this is subject to great variation, coming on more rapidly in muscles that are feeble than in those that are strong and vigorous. Thus in per- sons who have been in good health, dying suddenly, it comes on slowly ; while when death occurs after protracted illness it comes on quickly, and remains but a short time. Animals which have been hunted, and whose muscles are consequently exhausted by fatigue, are the subjects of early rigor mortis. There are, how- ever, instances in which rigor has come on very early in those who were presumably in health at the time, although it is pos- sible that these were not exceptions, and that the cause of the early appearance was due to muscular exhaustion ; as, for instance, soldiers killed in battle being found with one eye closed and the other open in the act of taking aim. It has been said that after death from lightning or in the heat of passion, rigor mortis is entirely absent ; but it is more than probable that in such cases it comes on early and disappears without having been ob- served. Rigor mortis, as a rule, is first observed in the neck and lower jaw, then in the upper, and later in the lower extremities, passing off in the same order. There are, however, exceptions to this. It may remain for from one to six days. Little is known about rigor mortis of involuntary muscle, although this condition has been seen in the heart, stomach, and uterus. Muscular Tone. If a relaxed muscle is divided, the t\vo ends separate i. e., each portion of the divided muscle contracts, so that even in a so-called relaxed muscle this is in a state of tonic con- traction, and this condition is muscular tone or muscular tonus. The advantage which accrues from this is that when the muscles are called upon to perform any work they are already in a posi- tion to effect results quickly, which would not be the case if it were necessary to bring them from a state of complete relaxa- tion to one of effective contraction. It is as if one desired to IRRITABILITY. 457 move a boat by a rope, and before exerting any influence on the boat was compelled to take up a considerable amount of slack. Muscular tone is a reflex action depending upon the reception by the cord of afferent impulses, under which stimulation motor impulses are sent out to the muscles ; and if the afferent nerve are cut, the tone disappears. Peristalsis. The difference in the manner of contraction of voluntary muscle, as the skeletal muscles, as compared with that of involuntary muscle, as that of the intestines, is very marked, for while the action of the former takes place rapidly and throughout the entire muscle, the action of the latter is slow, and moves from point to point as a wave, at a rate of about 30 mm. per second, the contraction occurring at one part of the intestines while it has disappeared at another, the circular coat being especially active in the movement. It is called also vermicular contraction. When the movement is in the direction opposite to the normal, as in the intestine from below upward, or in the stomach from the pylorus toward the cardia, it is reversed peristalsis. ^ ^ CL c 4 & - b d \ FIG. 265. Schema to show the direction of currents to be obtained from muscle. The schema represents a cylindric piece of muscle with normal longitudinal surface (o c and 6 d), and two artificial cross sections (a 6 and c d). The position of the equator is shown by line e. The unbroken lines connect points of different potential, and the arrows show the direction which the currents would take were these points connected with a galvanometer. The broken lines connect points of equal potential from which no current would be obtained (Lombard). Rhythmicality. Involuntary muscular tissue exhibits the prop- erty of contracting and relaxing with a certain degree of regu- larity or rhythm, as in the spleen, where there are a true systole and a diastole, recurring about once each minute, as demonstrated by the oncometer (p. 338). Electric Phenomena (Fig. 265). A normal muscle in a condi- tion of rest is iso-electric i. e., it is " equally electric throughout, and hence has no electric current " ; the same is true of dead muscle. If, however, the muscle is cut, the electrical condition is changed, and if the part that is cut and the normal part are connected to a galvanometer, the movement of the magnet at once 458 MUSCLE PHENOMENA. demonstrates the existence of an electric current flowing from the normal to the cut portion. If the muscle is caused to contract, the needle of the galvanometer will return to the position of rest. The first current was formerly called the current of rest, but is now known as the current of injury or demarcation current ; while the second is the current of action, or negative variation current. Du Bois Reymond explained the current of rest by supposing that in the normal muscle at rest there were electric currents due to the fact that muscle was made up of electromotive molecules, and that each of these molecules is positive at the center and negative at the ends, and this difference of electric tension be- comes manifest when the muscle is cut and the negative ends are exposed. Hermann, however, denies the existence of currents in FIG. 266. Secondary tetanus (Lombard). normal muscle, and attributes their generation to the injury to the muscle caused by its action, chemic changes being thus brought about. Other injury than cutting will produce the same result, and as these changes take place at the point between the normal and injured tissue the term " demarcation" has been applied to the current thus produced. It should be said, however, that there are authorities who hold with Du Bois Reymond that normal muscle in a condition of rest is the seat of electromotive forces, which require changed condi- tions in muscle to bring them forth. It has been already stated that dead muscle is iso-electric ; dead muscular tissue is, however, electrically negative to normal living muscle. Secondary Contraction (Fig. 266). To demonstrate secondary contraction two nerve-muscle preparations are made, and the nerve of one is placed upon the muscle of the other. Such an arrangement constitutes a physiologic rheoscope or rheoscopic frog. When the nerve of the first preparation is stimulated, not only its muscle, but also that of the second preparation, contracts. If the stimulation is single, a secondary contraction or twitch results ; while if the stimuli cause tetanus of the first muscle, there will be secondary tetanus of the second muscle. IRRITABILITY. 459 The explanation of these secondary contractions would seem to be that the current passes through the first preparation into the second ; but if the nerve of the second is tied, the secondary con- traction does not take place, so that this explanation is not a true one. Du Bois Raymond's explanation is that each stimulus applied to the first nerve causes a contraction of its muscle and a current of action, which stimulates the nerve of the second preparation, and a contraction of its muscle follows. IV. NERVOUS FUNCTIONS. GENERAL CONSIDERATIONS. THERE is a most intimate relationship existing between the different organs of the body so intimate, indeed, that not one of the whole number can be 'said to be entirely independent of the others. Many illustrations of this dependency might be given, but one will suffice. The respirations of an individual at rest are not far from 16 per minute, and the pulsations of the radial artery are, under the same condition, about 70. If, now, he exercises violently, the respirations will be found to have greatly increased, amounting perhaps to 30 per minute, while at the same time the pulsations of the artery will have reached 120 per minute. Is this change from the quiescent condition a mere coincidence, or is there a reason for it? If the latter, how has the change been brought about? During a resting condition the muscles of the body do not make great demand upon the blood, and with the heart beating 70 times per minute the muscles, as well as the other tissues, are receiving all the material they need for the performance of their functions. The 16 respirations a minute are also sufficient to supply the blood with all the oxygen required and to remove from it the necessary amount of carbon dioxid. When, however, the muscles are called upon for the increased exertion above referred to, they must have a greater supply of the necessary materials, to furnish which a larger amount of blood must be sent to them. Then, too, as a result of the extra work, more muscular tissue is wasted, and the waste must be taken away rapidly to the organs whose duty it is to eliminate it. To send the larger supply of blood the heart must beat faster, and to provide the increased oxygen and to remove the additional carbon dioxid the respiratory movements must be more rapid. The muscles of the body have not the power within themselves to increase their activity, but when acted upon properly from without they have. Neither has the heart-muscle the power to beat more quickly until influenced thereto by some influence outside itself. Equally powerless are the agencies which produce the respiratory movements. These outside influences, by which the muscles contract and by which the heart and the respiratory apparatus act in harmony, are 460 NERVES. 461 derived from the nervous system, a collection of organs one of whose functions is to cause the different organs to act harmo- niously. The effect of a want of harmony under the circumstances just supposed would be most disastrous. If the nervous force was not at command to make the muscles respond when their increased action was desired, there would be a condition of paral- ysis, or if, when the muscles attempted to perform this added task, the heart should fail to respond, the effort would be fruitless ; and equally unavailing would be the attempt if at the crucial moment the lungs and other respiratory organs should be unresponsive. Many other illustrations of the interdependence of the organs might be given, but a little reflection will suggest them almost ad infinitum. The simplest movements that are made require for their per- formance the conjoint action of several, often many muscles, and were it not for the exciting and controlling power of the nervous system, instead of the harmony which is everywhere and at all times apparent, there would result the utmost confusion. In what has been said thus far reference has been had only to the individual, as if he was alone on the face of the earth and interested only in himself; but there are other human beings with whom he is constantly brought into relation, and a world of other animate objects as well as an infinite amount of inanimate matter. This relationship is also accomplished through the nervous system, principally "by means of the special senses. It will, therefore, be seen that the nervous functions are those which bring the different organs of the body into harmonious relations with one another, and, in addition, bring the individual, through the special senses sight, hearing, etc. into relation with the world outside. him. The nervous system is made up of collections of nervous tissue, which is composed of two kinds of matter nerve-fibers and nerve-cells, with neuroglia ; these have been already de- scribed (p. 63). NERVES. Nerve-fibers associated together form nerves, and these con- duct impulses from within outward, from without inward or from one nerve-center to another. Whether it is the function of a given nerve to do the one or the other does not depend upon any- thing in the nerve itself, but upon its relations ; and there is every reason to believe that were it possible to separate a nerve from its anatomic connections and attach it to different structures, it would be just as capable of acting in its new relations as it did in the old ; just as a copper wire will carry equally well a current of electricity to ring a bell or to supply a motor or to turn a hand on a dial : The result depends not upon the wire, but upon the mechanism with which it is in connection. 462 NERVES. .*. Classification of Nerves. There are three kinds of nerves, classified according to the direction in which they carry impulses : 1. Efferent; 2. Afferent; and 3. Intercentral. Efferent Nerves. Inasmuch as nerves of this kind carry im- pulses away from nerve-centers, they are also called centrifugal nerves. They were formerly spoken of as motor nerves. All motor nerves are efferent, for they carry impulses outward, but all efferent nerves are not motor. A nerve which carries an impulse to a muscle, and thus brings about motion, is properly called a " motor nerve " ; but one that conducts an impulse to a gland, the results of which are the activity of its cells and the production of a secretion, is improperly named a motor nerve, although it is un- questionably an efferent nerve. Secretory is a much more appro- priate name. Efferent nerves may be divided as follows : (1) motor ; (2) vasomotor ; (3) accelerator ; (4) secretory ; (5) trophic ; and (6) inhibitory. Motor nerves terminate in muscles, and convey to them im- pulses which cause and regulate their contraction. Vasomotor nerves, although distributed to the muscular tissue of blood-vessels, and thus act as motor nerves, regulate the amount of blood supplied to a part, and it seems wise to separate them from the purely motor nerves and put them in a class by themselves. Accelerator nerves are nerves which carry impulses that increase the rhythmic action of an organ, as the sympathetic nerves to the heart. Secretory Nerves. The impulses which these nerves carry to glands bring about their secretion. The chorda tympani is a striking example. Trophic nerves are supposed by some to govern the nutrition of the structures to which they are distributed, entirely independently of the regulation of the blood-supply. It is still a mooted ques- tion whether such nerves exist. Efferent inhibitory nerves carry impulses which restrain or inhibit the action of the organs to which they are distributed. The pneumogastric, so far as the heart is concerned, is such a nerve. Without its restraining influence the heart would beat much faster. Afferent Nerves. The fact that these nerves carry impulses to the nerve-centers has led to their being called also centripetal nerves. They were formerly called sensory nerves, but there is the same impropriety in using these terms synonymously as in the case of efferent and motor nerves. All sensory nerves are afferent, but all afferent nerves are not sensory. Afferent nerves may be divided as follows, although the distinction is by no means so well marked as in the efferent nerves : (1) Sensory ; (2) nerves of special sense ; (3) thermic nerves ; (4) excitoreflex ; and (5) inhibitory. DETERMINATION OF THE FUNCTION OF A NERVE. 463 Sensory Nerves. When these nerves are stimulated an impulse is carried to a nerve-center ; if this center is the brain, the sen- sation may be a conscious one, and may or may not be painful. Nerves of Special Sense. The impulses carried by these nerves do not give rise to pain, but with each nerve is connected a special sensation : With the olfactory, the sense of smell ; with the optic, the sense of light ; and with the auditory, the sense of hearing. Thermic Nerves. It is believed by some writers that there are special nerves which convey the sense of temperature only ; but this is still an unsettled question. Exeitoreflex Nerves. In these nerves there is an impulse car- ried to a nerve-center without producing a conscious sensation : this center is excited, and from it or from another center with .which it is in communication there goes out an impulse that, if it is a gland to which it is distributed, produces secretion : such a nerve would be an excitosecretory nerve. Or if it is distributed to a muscle, it produces motion, and would in that case be considered an excitomotor nerve. Afferent Inhibitory Nerves. The afferent inhibitory nerves are also called centro-inhibitory, to distinguish them from the efferent inhibitory nerves. The centro-inhibitory nerves carry impulses to nerve-centers, which are so affected as to prevent them from send- ing out impulses. A familiar instance is that of pinching the lip to prevent sneezing. It is, however, doubtful whether there exists a separate class of nerves performing this function, rather than ordinary sensory fibers which act in this peculiar manner for the moment. Intercentral Nerves. The nerve-centers are intimately con- nected with one another by nerves which are neither afferent nor efferent, and which are called intercentral. As has been said, even the simplest movements of the body bring into action several, and sometimes many muscles ; of course, this action is more obvious in complex movements. To accomplish this, various nerve-centers must be at work ; and that they may act harmoniously and pro- duce coordinated movements it is essential that they should be in intimate relationship. Study for a moment the intricate mechanism brought into play in the ordinary act of picking up a pin from the floor, and it will be readily understood how essential it is that the nerve-centers responsible for these movements should act in the most perfect harmony, sending to each muscle just the right amount of nerve-force and at exactly the right moment ; other- wise the act could not be accomplished in the perfect manner that it is. Determination of the Function of a Nerve. The func- tion of a nerve may be determined by (1) dividing it, and observ- ing what function has been lost ; or (2) stimulating it, and observing the effect of the stimulation. Thus when a motor nerve is divided, 464 NERVES. there is a loss of power, or paralysis of motion, in the muscle sup- plied by the nerve. If, on the other hand, a galvanic current is passed through the nerve, there will follow contraction of the muscle. Similarly a paralysis of sensation will follow division of a sensory nerve ; and when such a nerve is stimulated, sensation will result. When a nerve is thus divided, one portion will remain in communication with the nerve-center, and is called the central or proximal end ; while the other, which remains in communica- tion with the periphery, is the distal or peripheral end. Stimu- lation of the central end of a motor nerve produces no effect ; while the motion referred to above results from stimulation of its peripheral end. In the case of a sensory nerve, it is the reverse. Wallerian Degeneration. When a nerve is divided the first result is a loss of its function. Afterward the nerve under- goes Wallerian degeneration, which results in changes in its structure that can readily be seen. Inasmuch as each nerve-fiber develops from a cell which later nourishes it, if the connection between the two is severed, the nerve-fiber undergoes Wallerian degeneration, and in the case of a nerve which is made up of nerve-fibers the whole nerve undergoes this change. This degener- ation consists, in the case of medullated nerves, in the death of the axis- cylinder, the breaking up of the medullary sheath into drops of myelin, which are later absorbed, and the multiplication of the nuclei of the primitive sheath. In non-medullated nerves the only result is the death of the axis-cylinder. Degeneration begins very soon after the section within a day or two and throughout the entire severed portion of the nerve at the same time. Thus the course of a nerve, or a collection of nerves, may be traced throughout its entire extent. These changes are believed to be due to the severance of the nerve from its trophic center. If an anterior root of a spinal nerve is divided, the distal end, being separated from the gray matter of the cord which is its center of nutrition, undergoes degeneration, while the end which remains connected with the cord retains its integrity. If a posterior root is divided between the cord and the ganglion, the degeneration takes place between the cord and the ganglion ; while if divided below the ganglion, the degeneration takes place in that portion separated from the ganglion, showing that the ganglion is the nutritive center for the posterior root. Regeneration of Nerves. If the two ends of a divided nerve are brought together and retained there, a regeneration may take place, and the new structure has all the properties of the original nerve. It will be remembered that in the degeneration which follows division of a nerve there is an increase in the nuclei of the sheath. These form a continuous thread of pro- toplasm within the old sheath, and around this protoplasm a new sheath develops, the whole forming an embryonic nerve-fiber, ELECTROTONUS. 465 which unites with the proximal portion of the old fiber still in connection with its nutritive center, and hence has undergone no degenerative change. Such a regenerated fiber has both conduc- tivity and irritability, the former appearing as early as the third week, but the latter not manifesting itself until afterward. At this period of the regeneration there is neither myelin nor axis- cylinder, and the fiber is responsive to mechanical stimuli, but not to induction shocks, which latter property returns only after the axis-cylinder is developed. The medullary substance later appears and forms a tube ; and still later the axis-cylinder is formed, having its origin in the central end of the nerve i. e. y the portion which is still in communication with the cell from which the original axis-cylinder was developed. The complete regeneration of a nerve may take months. So far as known, regeneration does not occur in the central nervous system. NERVE-IMPULSES. The function of nerve-fibers is to conduct impulses, and this from centers to the periphery, from the periphery to centers, or from one center to another. Although much study has been given to the subject, exactly what a nerve-impulse is has never been determined. Except an electrical change in the nerve itself, and the results of the reception of the impulses at the termination of the nerve, as motion in a motor nerve, secretion in a secretory nerve, etc., there is no evidence of the fact that impulses have travelled over the nerve. Chemical, mechanical, or thermic changes, if they occur, have never been demonstrated. The stimuli which excite muscle will also stimulate nerves ; these are electrical, mechanical, chemical, and thermic ; and what has been said of these applies in general to nerves. It should be called to mind, however, that induction-shocks stimulate nerves more powerfully than a voltaic current j while in the case of muscle it is the voltaic current which is the more powerful stimulus. Velocity of Nerve-impulses (Fig. 267). In the motor nerves of human beings nervous impulses travel at the rate of 33 meters a second, and in sensory nerves, from 30 to 33 meters in the same length of time. Electrotonus. Although contraction of a muscle takes place at the make and break of a constant current which is passed through the nerve distributed to it, and although no apparent change takes place in the nerve at either of these moments, or indeed while the current is passing;, still during the latter period important changes are actually taking place, though they are not visible ; these are changes in the electrical condition of the nerve, in its excitability and also in its conductivity, and are collectively 30 466 NEE VE-IMP ULSES. called electrotonus. This has been concisely denned as "a change of condition in nerves traversed by an electric current." It also occurs in muscles. FIG. 267. Arrangement for measuring the velocity of the nerve-impulse: A, travelling plate of spring myograph: M, muscle lying on a myograph plate; N, nerve lying on two pairs of electrodes, E and E' ; C, Pohl's commutator without cross-wires; K, knock-over key of spring myograph (only the binding screws shown); K', simple key in primary circuit; B, battery; P, primary coil; 8, secondary coil (Stewart). That an electrical change is produced in a nerve by passing a constant current through it, the polarizing current, may be demon- strated by connecting the nerve with a galvanometer. The FIG. 268. Electrotonic alterations of irritability caused by weak, medium, and strong battery currents : A and E indicate the points of application of the elec- trodes to the nerve, A being the anode, B the kathode. The horizontal line repre- sents the nerve at normal irritability ; the curved lines illustrate how the irrita- bility is altered at different parts of the nerve with currents of different strengths. Curve y l shows the effect of a weak current, the part below the line indicating de- creased, and that above the line increased irritability ; at x l the curve crosses the line, this being the indifferent point at which the katelectrotouic effects are com- pensated for by anelectrotonic effects; y 1 gives the effect of a stronger current, and y 3 , of a still stronger current. As the strength of the current is increased the effect becomes greater and extends farther into the extrapolar regions. In the intrapolar region the indifferent point is seen to advance with increasing strengths of current from the anode toward the kathode. current near the kathode is the katelectrotonic current, while that near the anode is the anelectrotonic current. These currents occur only as the result of passing a constant current through a nerve, ELECTROTONUS. 467 and cease when the current ceases. They exist in living medul- lated nerves only, or if at all in degenerated nerves but to a slight degree. At the time of the passage of the current there is an increase in the excitability or irritability of the nerve in the kathodic region, and a decrease in the anodic region ; the increase is katelec- trotonus, and the decrease, anelectrotonus. After the opening of the current the conditions are reversed, the excitability being temporarily increased in the anodic, and decreased in the kathodic FIG. 269. Diagram of changes of excitability and conductivity produced in a nerve by a voltaic current: E, changes of excitability during the flow of the current, according to Pfliiger. The ordinates drawn from the abscissa axis to cut the curve represent the amount of the change. C (1), changes of conductivity during the flow of a moderately strong current; conductivity greatly reduced around kathode; little affected at anode. C (2), changes of conductivity during flow of a very strong current ; conductivity reduced both in anodic and kathodic regions, but less in the former. C', changes of conductivity just after opening a moderately strong current ; conductivity greatly reduced in region which was formerly anodic; little affected in region formerly kathodic (Stewart). area. The indifferent point is the point at which there is no change in the excitability of the nerve, where the katelectro- tonic and anelectrotonic effects counteract each other; this will change its position according to the intensity of the current, approaching the kathode as the intensity increases. Fig. 268 shows the changes which take place according as the intensity of the current is increased. The conductivity of a nerve is also affected by the constant current, the changes being shown in Fig. 269. 468 THE NERVOUS SYSTEM. THE NERVOUS SYSTEM. The nervous system is divided into two subdivisions : the cerebrospinal system and the sympathetic system. The cerebrospinal system includes the brain and spinal cord, which together form the cerebrospinal axis, and the nerves which come from them, namely, the cranial and spinal nerves. SPINAL CORD. The spinal cord is situated in the vertebral canal, and is covered by three membranes the dura mater, arachnoid, and pia mater. It is about 0.43 meter in length, and, in general, is of a cylindrical shape ; it weighs 42.5 grams. It extends from the medulla oblongata above to the first lumbar vertebra below, where it ends in the filum terminate, although in fetal life it extends to the bottom of the sacral canal. Enlargements of the Spinal Cord. Two enlargements along the course of the spinal cord are noteworthy. The cervical FIG. 270. Different views of a portion of the spinal cord from the cervical region, with the roots of the nerves. 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 surface is shown ; in D the nerve-roots and gang- lion are shown from below : 1, the anterior median fissure ; 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 fibers of which pass into the ganglion, 6 ; 7, the united or compound nerve; 7', the posterior primary branch, seen in A and I) to be derived in part from the anterior and in part from the posterior root (Allen Thomson). enlargement extends from the third cervical to the first or the second dorsal vertebra, and the lumbar enlargement is at the eleventh and twelfth dorsal vertebrae. From the cervical en- largement go off the nerves which supply the upper, and from the lumbar those which supply the lower, extremities. SPINAL CORD. 469 470 THE NERVOUS SYSTEM. C D FIG. 272. Four cross-sections of the human spinal cord: A, cervical region; in the plane of the sixth spinal nerve-root ; B, lumbar region ; (7, thoracic region j D, sacral region; X 7 (from preparations of H. Schmaus) (Bohm and Davidoff). SPINAL CORD. 471 Fissures (Fig. 270). On the anterior surface of the spinal cord is a groove, the anterior median fissure, which extends to the anterior white commissure. On the posterior surface is also a so- called fissure, the posterior median fissure, which is filled with connective tissue and blood-vessels, and extends to the posterior gray commissure. It will thus be seen that the anterior and posterior fissures nearly divide the cord into two symmetrical halves, which are connected by the commissures. At a little distance from the anterior median fissure on each side is the anterolateral fissure. Strictly speaking, this is not a fissure, being rather a line of small openings at which emerge the anterior roots of the spinal nerves. In front of the posterior median fissure and on either side is the posterolateral fissure. Here emerge the posterior roots of the nerves. The posterior intermedi- ate furrow is between the posterior median and posterolateral fissures. Columns. The anterior and posterior median fissures divide the cord into two symmetrical halves, and the anterolateral and posterolateral fissures subdivide each half into three columns called main columns: anterolateral, posterolateral, and posterior median. . Anterolateral Column. This includes that portion of the cord between the anterior median and the posterolateral fissure. It is divided by some anatomists into an anterior, situated between the anterior median fissure and the anterior nerve-roots, and a lateral, the portion between these roots and the posterolateral fissure (Fig. 271). Posterolateral Column. This is the portion between the postero- lateral fissure and the posterior intermediate furrow. Posterior Median Column. This is also called posteromedial column. It is situated between the intermediate furrow and the posterior median fissure. The posterolateral and posterior median are sometimes described together as the posterior column. Section of the Spinal Cord (Fig." 273). A cross-section of the spinal cord shows a central gray substance and an external white substance. The gray matter presents the appearance of two crescents, with the concavities outward, joined together by a band of gray matter, the gray commissure. The points of the crescents are the horns or cornua, two anterior and two posterior. The posterior cornua come nearly to the surface of the cord at the posterolateral fissure, while between the surface and the extremi- ties of the anterior cornua there is considerable white matter. The arrangement of the white matter into columns is readily discerned in this section. In the gray commissure is a small canal the central canal which communicates with the fourth ventricle of the brain, and contains cerebrospinal fluid. This is a colorless alkaline fluid containing sodium chlorid and other 472 THE NERVOUS SYSTEM. inorganic salts, and about 0.1 per cent, of" proteids, principally proto-albumose, with some serum-globulin, and rarely peptone. Serum-albumin, fibriuogen, and nucleoproteid are absent. It also contains a non-nitrogenous reducing substance considered by Claude Bernard to be sugar, but by Halliburton to be pyrocatechin derived from the proteids. The central canal is lined with columnar epithelium, which in fetal life is ciliated, but the cilia are often absent in the adult. The canal is of special interest in connection with the develop- ment of the cord. Sections of the cord at different levels show that the white substance is most abundant in the upper part, and FIG. 273. Transverse section of half the spinal cord, in the lumbar enlargement (semi-diagrammatic) : 1, anterior median fissure ; 2, posterior median fissure ; 3, cen- tral 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 trabeculse of pia mater) ; 9, fasciculus of posterior nerve-root, entering in one bundle ; 10, fasciculi of anterior roots, entering in four spreading bundles of fibers ; b, in the cervix cornu, decussating fibers from the nerve-roots and posterior commissure ; c, posterior vesicular columns. About half-way between the central canal and 7 is seen the group of nerve-cells forming the tractus inter- mediolateralis ; e, e, fibers of anterior roots; e', fibers of anterior roots which decussate in anterior commissure (Allen Thomson). gradually becomes less abundant as the examination is made down the cord. The cervical and lumbar enlargements are due to the increased amount of gray matter at these points. Minute Structure of the Cord. Neuroglia supports both the white and the gray matter of the spinal cord, and occurs also under the pia mater, around the central canal, forming the sub- stantia gelatinosa centralis, and at the apex of the posterior horn, forming the substantia cinerea gelatinosa of Rolando or substantia gelatinosa lateralis. The white substance is made up of medullated nerve-fibers and blood-vessels, in addition to neuroglia. The medullated nerve- SPINAL CORD. 473 fibers in sections stained with carrnin or anilin blue-black appear as clear areas with the stained axis-cylinder in the center, the clear space being the medullary substance. The gray matter consists of nerve-fibers, of nerve-cells and their processes, together with neuroglia and blood-vessels. Tracts Of the Cord. The course which the nerve-fibers take in the columns of the cord has been determined by two methods: the embryologic and the degenerative. The embryologic method, or method of Flechsig, consists in studying the cord at different stages of its development ; and as in some tracts the medullary substance forms at an earlier period than in others, these can be thus differentiated or distinguished from one another. The degenerative, or Wallerian, method consists in studying the degeneration which occurs in nerve-fibers when separated from their nutritive or trophic centers (p. 464). Sections of the cord in which the degeneration has taken place are stained with Marches solution, consisting of Miiller's fluid 2 parts, and 1 per cent, osmic acid 1 part : the degenerated fibers stain black, while the other portion remains practically unstained. A tract in which this degeneration takes place belo\v the injury or point of section is a descending tract, and the degeneration is a descending degenera- tion ; while a tract in which the process occurs above the lesion is an Ascending tract, and the change, an ascending degeneration. These methods have demonstrated the following tracts in the cord (Fig. 271), into which the main columns may be considered as divided. Each tract or fasciculus may be considered, Gray says, as a distinct anatomic system and endowed with special functions : 1. Direct Pyramidal Tract. This is also called fasciculus of Turck, and is situated in the anterolateral column next to the anterior median fissure. It is continuous with the non-decussating fibers of the pyramid of the medulla. Besides this tract, the anterolateral column contains : 2. Crossed Pyramidal Tract. The fibers of this tract are con- tinuous with those forming the decussation of the pyramid of the medulla. 3. Direct Cerebellar Tract. Continuous with the restiform body. % 4. Anterolateral Ground-bundle. Continuous with the forma- tio reticularis of the medulla. 5. Anterolateral Descending Cerebellar Tract (Lowenthal). 6. Anterolateral Ascending Cerebellar Tract (Gowers). 7. Tract of Lissauer. The posterior column contains : 8. Poster omedian, also called posteromesial and column of Goll, which is continuous with the funiculus gracilis of the medulla. 474 THE NERVOUS SYSTEM. 9. Poster olateralj also called column of 33urdach, which is con- tinuous with the fuiiiculus cuneatus. 10. Comma tract. The position and relation of these tracts can be better under- stood by reference to the illustrations than by any verbal descrip- tion. Grouping of the Nerve-cells (Fig. 274). Some of the nerve-cells of the cord are distributed through the gray matter, while others are arranged in groups, the latter being larger, and characterized by their branching ; they are multipolar nerve-cells. Cells of the Anterior Horn. In the anterior cornu are three of these groups: 1. Near the tip on the inner side; 2. At the base on the inner side ; and 3. On the outer side of the gray matter. Posterior horn T~ cell. Crossed pyram- idal column. Golgi cell of posterior horn. Direct cerebel lar column. Column cells. Golgi's com mis- sural cells. Gowers' col-*.-' umn. Motor cells. N Collaterals ending in the gray matter. Direct pyramidal column. FIG. 274. Schematic diagram of the spinal cord in cross-section, after von Lenhossek, showing in the left half the cells of the gray matter, in the right half the collateral branches ending in the gray matter (Bohm and Davidoff ). Each cell of the anterior cornu gives off an axis-cylinder process which passes out into the anterior nerve-roots. Cells of the Posterior Horn. These are smaller than those of the anterior cornu, but their axis-cylinder processes do not pass into the posterior nerve-roots. Clarke's Column. This group of cells is most marked in the thoracic region, and is situated at the base of the posterior cornu. Their axis-cylinder processes pass into the direct cerebellar tract. Intermediolateral Tract. This group is situated on the outer side of the gray matter in what is called the lateral horn between the anterior and posterior cornua. Middle Cell-group. These He in the middle of the crescent. Nerve-fibers of the Gray Matter. These are, as a rule, smaller than those in the white substance. In the posterior cornu SPINAL COED. 475 they form Gerlach's nerve-network, in which small and larget nerve-fibers exist together. These fibers can be traced to the medullated fibers of the posterior nerve-roots, and also to the processes of the ganglion-cells, thus bringing these cells into con- nection with the posterior nerve-roots through the network. The fibers of the anterior horn are directly continuous with the axis-cylinder processes of the ganglion-cells. The following illustration (Fig. 275) represents the relations between the nerve-cells, the skin, and a muscle. Spinal Nerves. There are thirty-one pairs of spinal nerves, which are distributed to the neck, trunk, and extremities. Each FIG. 275. Schematic diagram of a sensorimotor reflex arc according to the modern neuron theory ; transverse section of spinal cord ; mN, motor neuron ; sN, sensory neuron; C 1 , nerve-cell of the motor neuron; C 2 , nerve-cell of the sensory neuron ; d, dendrite; n, neuraxis of both neurons ; t, telodendrons ; M, muscle-fiber; h, skin with peripheral telodendron of sensory neuron (Bohm and Davidoff). of these arises by two roots ; an anterior or motor, and a posterior or sensory root. Anterior Roots. These are traced through the anterolateral column to the cells df the gray matter of the anterior cornu. Around the cells is an interlacement of ramified nerve-endings, which come especially from the collaterals of the posterior root- fibers and from those of the fibers of the white substance of the cord. Posterior Roots. These are characterized by the presence upon each of a ganglion, except the posterior root of the first cervical nerve, which frequently possesses no ganglion. These roots have their origin in the cells of the ganglion, and pass into the postero- lateral column, some entering the marginal bundle of Lissauer, 476 THE NERVOUS SYSTEM. and some passing into the posterior cornu. When the fibers of the posterior root enter the cord they bifurcate, one branch passing upward, the other downward. From the main fiber, and also from the branches, pass collaterals, which end in the gray matter in arborization, and in the nerve-cells of the anterior and posterior cornua. In the same manner end the main fiber and its branches ; some, however, pass upward in the posterolateral and posteromesial FIG. 276. Transverse section through half the spinal cord, showing the ganglia : A, anterior cornual cells; B, axis-cylinder process of one of these going to posterior root ; c, anterior (motor) root ; D, posterior (sensory) root ; E, spinal ganglion on posterior root ; F, sympathetic ganglion ; G, ramus communicans ; H, posterior branch of spinal nerve ; 7, anterior branch of spinal nerve ; a, long collaterals from posterior root-fibers reaching to anterior horn ; 6, short collaterals passing to Clarke's column ; c, cell in Clarke's column sending an axis-cylinder (d) process to the direct cerebellar tract: e, fiber of the anterior root; /, axis-cylinder from sympathetic ganglion cell, dividing into two branches, one to the periphery 7 , the other toward the cord ; g, fiber of the anterior root terminating by an arborization in the sympa- thetic ganglion ; h, sympathetic fiber passing to periphery (Ramon y Cajal). columns, and end in the medulla by arborizing around the cells of the nucleus gracilis and cuneatus. Spinal Ganglia. The structure of these ganglia has been already described. Beyond the ganglion the two roots unite to form the trunk of the spinal nerve, which passes out through the inter vertebral foramen, and gives off a recurrent branch to the dura mater of the cord. It then divides into a posterior division, which is distributed to the posterior part of the body., and an ante- SPINAL CORD. 477 rior division which goes to the anterior part ; each division contains fibers from both roots. Functions of the Spinal Cord. The functions of the spinal cord are of two kinds : 1. A conductor of impulses, by virtue of the fibrous nervous matter which it contains ; and 2. A nerve-center, by virtue of its nerve-cells. As a Conductor of Impulses. The spinal cord is the principal channel through which all impulses from the trunk and the extremities pass to the brain, and all im- pulses to the trunk and extremities pass from the brain. If through disease "or injury the cord is disor- ganized at any point, all power to produce volun- tary motion in the parts below the injury is lost, and conscious sensation in these parts is from that moment abolished. The cord therefore acts as a conductor of impulses, both motor and sensory, between the brain and the trunk and extremities ; the different kinds of impulse follow different paths in the cord. Concluding-paths in the Cord. The paths by which voluntary motor impulses traverse the cord are fairly well ascertained. These im- pulses originate in the pyr- amidal cells of the cerebral cortex, and pass through the pyramids in the medulla, crossing principally at the FIG. 277. Schema showing pathway of the sensory impulses. On the left side, S, &, repre- sent afferent spinal nerve-fibers ; C, an afferent cranial nerve-fiber. This fiber in each case ter- minates near a central cell, the neuron of which " . * p 1 , " crosses the middle line and ends in the opposite decussation OI the pyra- hemisphere (van Gehuchten). mids, and to a less degree in the upper part of the cord, to the opposite side, whence they follow the course of the pyramidal tracts, direct and crossed, arbo- rizing around the cells of the anterior cornua ; from which the anterior roots arise to be distributed to the muscles. The course pursued by the sensory impulses (Fig. 277) is not 478 THE NERVOUS SYSTEM. so well understood as is that of the motor. Bat the best opinions may be summarized as follows : Tactile and muscular sense-impressions pass up the posterior columns to the nucleus gracilis and nucleus cuneatus, by the internal arcuate fibers and fillet to the optic thalamus, by the posterior part of the internal capsule to the Kolandic area of the opposite side. Painful impressions, and those of heat and cold, pass up the gray matter of the cord from cell to cell to the optic thalamus, and by the fibers of the corona radiata to the cortex. Afferent impulses reach the cerebellum by Clarke's column, direct cerebellar tract, restiform body, and inferior peduncles. The fibers composing the tract of Gowers have their origin in cells at the base of the anterior cornu, on the opposite side, and its cerebellar fibers pass to the middle lobe by the superior peduncles. There are other fibers in the cord, which have their origin in the cerebellum ; but although their existence has been ascertained their destination is not certainly determined, though it is thought by some that they arborize around cells in the anterior cornua. As a Nerve-center. Besides the function which the cord per- forms as a conductor of motor and sensory impulses, it also acts as a nerve-center in which, by virtue of its nerve-cells, afferent impulses are received and motor impulses are generated. Voluntary motion in the extremities, which motion originates in the brain, is abolished when the cord is divided and its ana- tomic connection with the brain cut off; but there still remains the power of exciting muscular contractions in these muscles, due to the cells of the cord itself. Reflex Action. If a frog is decapitated, it has no longer the power of producing voluntary movements ; but if the skin of a foot is irritated by pinching, the foot is pulled away from the source of irritation. This is an instance of reflex action. A slight pinch will cause only the one foot to be withdrawn ; but if it is stronger, the other foot may also be withdrawn. This is known as a spreading of reflexes. Such movements are not spontaneous, but they require the application of a stimulus for their production. The irritation does not act upon the muscles directly, but through the medium of nerves, an afferent nerve carrying the sensory impulse inward to the cord, and an efferent nerve conducting a motor impulse outward to the muscles. If either of these nerves is divided, the action does not take place ; nor does it if the gray matter is broken up. For the performance of a reflex act, there- fore, three things are necessary an afferent nerve, a nerve-center, and an efferent nerve, all in a physiologic condition. This can be readily understood by reference to Fig. 275, where h represents the skin, from which passes an afferent nerve to the SPINAL COED. 479 center, and C 1 represents a cell in the anterior cornu of the cord, from which passes a motor impulse to the muscle M. In the human subject, when the cord is injured or diseased at any point, so as to cut off communication between the brain and extremities, but is still intact below this point, tickling of the soles of the feet will be followed by their withdrawal, although the individual will be entirely unconscious of any sensation. This is also an instance of reflex action. As in the frog, so in man, the three structures mentioned must exist in a state of integrity for the performance of this act. It is not essential, however, that the cord be diseased in order to have it manifest reflex action : this property is one which normally resides in the cord. Thus if the hand comes in contact with a flame, it is immediately withdrawn. This is not a voluntary act, for the act of withdrawal takes place before the sensation of pain is felt in the brain. It is a purely reflex act, in which the gray matter of the cord, after being stimulated by an impulse carried to it by an afferent nerve, generates an impulse which is conveyed by an efferent nerve to the muscles concerned in with- drawing the arm. The afferent nerve, nerve-center, and efferent nerve form a reflex arc. If the attention was fixed upon the subject at the time the burn was received, it might be possible to prevent the withdrawal. This would be an instance of inhibi- tion of reflex action. Reflex Time. From the moment when the stimulus is applied to the moment when the reflex action takes place is an appreciable interval of time, part of which is occupied by the passage of the afferent impulse to the center, part by the passage of the efferent nerve to the muscle, part by the latent period of the muscular contraction, and part by the reception of the afferent impulse and the generation of the efferent impulse in the center itself; this latter is the reflex time. In the frog it varies from 0.008 to 0.015 second. Heat and an increase in the strength of the stimulation lessen it. Reflexes in Man. The presence or absence of certain reflexes is made use of to determine the presence or absence of certain diseases in the human subject. They are included in two groups, superficial and deep. Superficial Reflexes. Of these, there are many, but the princi- pal ones are : 1. Plantar. Tickling the sole of the foot causes its with- drawal. 2. Gluteal. Pricking of the skin over the gluteus causes a contraction of that muscle. 3. Cremasteric. Stimulating the skin on the inner side of the thigh causes a retraction of the testicle. 480 THE NERVOUS SYSTEM. 4. Abdominal. Stimulating the skin of the abdomen causes a contraction of muscles in this region : when this occurs in the epigastric region it constitutes the epigastric reflex. 5. Nasal. Stimulation of the nasal mucous membrane causes sneezing. 6. Conjunctival. Touching the eyeball causes closure of the eyelids. Deep Reflexes. These are called also tendon reflexes, but are not true reflexes as are the superficial ones, being caused by direct stimulation of the muscles or their tendons. 1. Tendo Achillis Reflex. If while the extended leg is sup- ported at the knee a hand is firmly pressed against the ball of the foot, a tap on the tendo Achillis causes the gastrocnemius and soleus to contract and draw the heel up quickly. This may exist or not during health. 2. Ankle-clonus. The leg being supported, the ball of the foot is suddenly pressed so as to put the muscles of the calf on the stretch, and there results a series of clonic contractions of these muscles which cease when the pressure is removed. This is absent in health. 3. Patellar Reflex or Knee-jerk. If one thigh is crossed over the other, a tap on the tendon below the patella causes a forward movement of the leg. This is present in health, but may be in- creased or abolished in disease. Other Functions of the Cord as a Nerve-center. The power of the spinal cord to respond to afferent impulses independently of the will is of great advantage in preserving the body from injury. The attempt to retain one's equilibrium after slipping on a side- walk, and the raising of the arms in front of the face to ward off an unexpected blow, are both instances of this action. Walking r , playing on musical instruments, and similar acts are all performed under the influence of the gray matter of the cord. To start them requires the action of the brain, but when once they are begun their continuance is accomplished by the cord, and the brain can be busy about other things without interfering in the slightest degree with the perfection of their performance. Indeed, any attempt to control them is more apt to hinder than to help them. Thus in coming rapidly down a flight of steps, if the spinal cord is permitted to take charge of the act the descent will be made with ease and safety, but if each step is made as the result of volition, the chances of stumbling or of tripping are very much increased. The reflex action of the cord may be diminished by shock to the nervous system ; thus in the frog immediately after decapita- tion the reflex power cannot be excited, but after a short time it manifests itself under the influence of a stimulus. A similar SPINAL CORD. 481 diminution of the reflex power of the cord may be caused by opium, by chloroform, and by some other substances, while the reflex action is increased by strychnin. If under the skin of the decapitated frog a solution of strychnin is injected, the cord in a short time becomes so irritable that a stimulus which before would have had no effect will now produce the most marked results, a slight blow upon the skin sufficing to throw the animal into a con- vulsive state. In tetanus the same irritable condition of the cord exists, and in this state the patient may be thrown into convulsions by the simple opening and closing of a door. Special Centers in the Cord. It is the practice to speak of certain centers as existing in the spinal cord that is, of definite collections of cells which preside over definite functions. Among these centers the following have been described : Musculo- tonic, respiratory, cardio-accelerator, vasomotor, sudorific, cilio- spinal, genitospinal, anospinal, vesicospinal, trophic, for erection of the penis, for parturition, and others. Musculotonic Center. This center is continually discharging impulses which keep the muscular system in a condition of slight contraction : this is called muscular tone. It is questionable whether this condition is to be attributed to any special center rather than to the action of all those cells whose function it is to send out motor impulses. Respiratory Center. The respiratory center is in the medulla, but experiments in which this structure has been destroyed while some respiratory movements persisted demonstrate that to a cer- tain extent, doubtless very slight, the spinal cord controls the respiratory processes. Cardio-accelerator Center. The spinal cord through the cardiac nerves and plexus sends impulses to the heart, causing it to beat more rapidly that is, they accelerate its movements. These impulses are not constantly emitted as are the inhibitory impulses, which travel by the pneumogastric. Vasomotor Center. The vasomotor center in the cord is entirely subsidiary to that in the medulla. Sudorific Center. The existence of special nerves controlling the secretion of sweat seems to be demonstrated. These nerves come from the spinal cord, being a part of the anterior roots. Ciliospinal Center. Nerve-fibers pass from this center to the iris, and they are concerned in the dilatation of the pupil. These fibers come out from the cord through the anterior roots of the spinal nerves, from the fifth cervical to the fifth thoracic, and join the cervical sympathetic. Genitospinal Center. The genitospinal is the center which governs the emission of semen, and is situated in the lumbar region of the cord. Sensory impulses from the glans penis reach this center through afferent nerves and stimulate it, and from it 482 THE NERVOUS SYSTEM. go out efferent impulses which cause contraction of the muscular fibers of the vasa deferentia, seminal vesicles, and accelerator urinae, the result of which is to produce an ejection of semen. Anospinal Center. The act of defecation is governed by the anospinal center and has been already described (p. 266). Vesicospinal Center. The act of micturition is under the in- fluence of the vesicospinal center. This act has been already described (p. 430). Trophic Centers. It has already been seen that when nerve- fibers are divided they undergo degeneration, and that this is ex- plained by the fact that under these circumstances their connection with certain nerve-cells is severed, and that they are thus deprived of the nutritive influence which such centers exert. Such centers are called trophic centers, and the cells of the anterior cornua of the cord and the ganglia on the posterior roots of the spinal nerves are familiar illustrations. That these are true trophic centers for nerves seems to be beyond dispute, but this is an entirely different question from that which deals with trophic nerves as regulating the nutrition of tissues other than nerves. About the existence of such nerves there is considerable doubt. Other Centers. Some writers describe a center for erection of the penis, and locate it in the lumbar enlargement. The afferent nerves from the penis cause this center to send out efferent im- pulses by which the blood-vessels are dilated and the muscles are compressed, thus preventing the return of the venous blood from the penis and bringing about erection. A center for parturition is described as being located in the lumbar region of the cord, above the centers already mentioned ; under the influence of this the muscular tissue of the uterus contracts at the proper time and expels the fetus. Other reflex centers are described, but the tendency to extend the number of such centers seems to be beyond what the actual facts warrant. However, enough has been said to show the great importance of the spinal cord as a nervous center, independently of its function as a conductor of nervous impulses to and from the brain. Functions of Spinal Nerves. Stimulation of an anterior root causes contraction in the muscle to which it is distributed, while its division is followed by a loss of motion in the same muscle. In neither instance is sensation affected. If after the division the distal portion of the nerve is stimulated, muscular contraction will follow, while stimulation of the proximal end, that which is in connection with the cord, will produce no effect. The anterior roots are therefore efferent and motor, and are dis- tributed to muscles. Stimulation of a posterior root causes a sensation of pain in the part to which the nerve is distributed. Division of the root causes a loss of sensation in that part. If after division the THE BRAIN. 483 distal portion of the nerve is stimulated, no effect is produced, while stimulation of the proximal portion produces sensation. The posterior roots are therefore afferent and sensory and are dis- tributed to the skin. The two roots uniting form a mixed nerve that is, one in which there are both motor and sensory fibers. Recurrent Sensibility. When the distal end of a divided an- terior root is stimulated, besides the muscular contraction which follows there is also some pain produced. If the trunk of the nerve beyond the ganglion is divided, and then the anterior root is stimulated, no muscular contraction results, but the pain is felt as before. If, however, the posterior root is divided, no sensation is produced. The sensation experienced when the anterior root is stimulated is accounted for by the presence in this root of some sensory fibers which pass up into it for a short distance and form a loop, returning to the junction of the two roots, and then pur- suing their course in the posterior root. These are called recurrent sensory fibers. The impulse passes along these fibers to the point of junction of the two roots, and then along the posterior root to the nerve-center. Function of the Spinal Ganglia. As has already been stated, upon each posterior root of a spinal nerve, with one exception, is a ganglion. When examined under the microscope, the root-fibers spread out, passing between groups of large cells having promi- nent nuclei and a diameter of about 100 p. With one of these ganglion-cells a root-fiber is in communication, and the function of these cells is to form the^ fibers and to regulate their nutrition ; they are true trophic centers. THE BRAIN. The 6mm, or encephalon (Figs. 278, 279), is that part of the cerebrospinal axis situated within the cranium or skull. Its divisions are sometimes described as the forebrain, including the hemispheres, with the olfactory lobe, the corpora striata, and the optic thalami ; the midbrain, being the corpora quadrigemina and the crura cerebri ; and the hindbraintfiat is, the cerebellum, the pons Varolii, and the medulla oblongata. In the adult male the brain weighs, on an average, 1415 grams ; its weight in the female is about 1245 grams. In 278 cases of males in which the brain was weighed the maximum was 1841 grams and the minimum 963 grams. In 191 cases of females the max- imum Avas 1586 grams and the minimum 878 grams. The brain of Cuvier, the great naturalist, weighed 1815 grams; that of an idiot weighed 651 grams. The brain of a mulatto not remarkable for intelligence weighed 1927 grams. The forebrain weighs about 1245 grams in the adult male. The gray matter of the brain is in some parts on the surface, 484 THE NERVOUS SYSTEM. as in the convolutions of the cerebrum ; in other parts it is deeply situated, as in the basal ganglia i. e., the corpora striata, optic thalami, etc. (p. 499) ; while in still other parts it is scattered about without any fixed arrangement, as in the pons Varolii. The white matter is made up of fibers which come from the spinal cord ; of fibers having their origin in the gray matter, and which, escaping from the skull, go to their points of distribution as the FIG. 278. Base of brain : i; 2, 3, cerebrum ; 4 and 5. longitudinal fissure ; 6, fissure of Sylvius; 7, anterior perforated spaces; 8, infundibulum ; 9, corpora albi- cautia ; 10, posterior perforated space ; 11, cruri cerebri ; 12, pons Varolii ; 13, junc- tion of spinal cord and medulla oblongata ; 14, anterior pyramid ; 14 X , decussation of anterior pyramid; 15, olivary body; 16, restiform body; 17, cerebellum; 19, crura cerebelli; 21, olfactory, sulcus; 22, olfactory- tract; 23, olfactory bulbs; 24, optic commissure; 25, motor oculi nerve: 26, patheticus nerve; 27,' trigeminus nerve ; 28, abducens nerve ; 29, facial nerve ; 30, auditory nerve ; 31, glossopharyn- geal nerve; 32, pneumogastric nerve; 33, spinal accessory nerve; 34, hypoglossal nerve. cranial nerves ; and of still other fibers connecting the ganglia with one another, forming commissures. The Medulla Oblongata. The medulla oblongata, or bulb, is the continuation of the spinal cord, and is about 2.5 cm. long, 2 cm. broad, and 1.2 cm. thick. It is composed of gray and white matter. The gray matter, which in the cord has the characteristic double crescentic shape, approaches more and more the posterior surface THE BRAIN. 485 of the cord as the region of the medulla is reached, and the pos- terior cornua become more and more external, the whole mass of gray matter flattening out, until in the medulla it forms a layer the outer portions of which represent the posterior horns and the middle portions the anterior. The posterior columns separate in the medulla, the central canal coming to the surface posteriorly and end- ing in the fourth ventricle, the floor of which is the gray matter above referred to, which is, however, not limited to this site, but is pres- ent also about the aqueduct of Sylvius. From this gray matter arise all the cranial nerves except- ing the olfactory and optic. The medulla, like the cord, has an anterior and a posterior median fissure. At the lower part of the anterior fissure are fibers that cross from side to side, the decussation of the anterior pyramids. The pos- terior fissure of the cord widens out and forms the fourth ventricle. Some of the cranial nerves come out from the medulla, and serve as boundaries to describe the different portions of the medulla. That por- tion of white matter between the anterior median fissure and the roots of the hypoglossal nerve is the anterior pyramid. The lat- prnl pommn is hpfwppii flip rnnt^ OI the hypoglossal and those OI the glossopharyngeal, the pneu- / P . , mogaStriC, and the Spinal acces- and 3, the inferior maxillary divi- SOry. At the upper portion the sions ; VI, the left abducens nerve; ! . J i J v i ,1 i VII. VIII, the facial and auditory olivary body lies between the col- ner ; es . jx-xi, the glossopharyngeal, limn and the pyramid. The pOS- pneumogastric, and spinal accessory terior column is between the lat- ^^K^ci eral column or tract and the pOS- cervical nerve (Nancrede). terior median fissure. It is com- posed of three smaller columns separated by shallow grooves, the most external being the funiculus of Rolando, next the funiculus cuneatus, and the most internal the funiculus gracilis, the first two being joined in the upper part of the medulla to form the restiform body. The outer portion of .the pyramid is derived FIG. 279. View, from below, of the connection of the principal nerves with the brain : I', the right olfactory tract ; II, the left optic nerve ; II', the right optic tract (the left tract is seen III, the left oculomotor nerve ; IV, the trochlear; V,V, the large roots of the trifacial nerves: + +, the lesser roots (the + of the right side is placed on the Gasserian ganglion) ; 1, the oph- thalmic; 2, the superior maxillary; 486 THE NERVOUS SYSTEM. from the direct pyramidal tracts of the same side, while the decus- sation consists of the libers of the crossed pyramidal tract of the lateral column. In the restiform bodies are to be found, besides the funiculus of Rolando and the funiculus cuneatus, fibers of the direct cere- bellar tract of the lateral column. These bodies form the inferior peduncles of the cerebellum. The funiculus of Rolando is the enlarged head of the posterior cornu of the cord, and is therefore gray matter. The funiculus cuneatus is the continuation of Burdach's column of the cord, and the funiculus gracilis is the continuation of GolPs column. Functions of the Medulla Oblongata. Conduction. All the impulses, whether afferent or efferent, passing between the brain and the cord must pass through the medulla. Nerve-centers. Experiments have demonstrated that all the brain above the medulla and all the spinal cord may be removed and yet life be maintained, provided that the origin of the phrenic nerves is left intact; while if all these structures are undisturbed and the medulla is destroyed, death will result. The centers in the medulla are both reflex and automatic. Reflex Centers. One of the most important of these centers is that which presides over deglutition. As has been seen in dis- cussing this process, the first stage of the act is voluntary ; but as soon as the food has passed into the pharynx, the act becomes involuntary. The mucous membrane of the pharynx is stimu- lated by the food, and the afferent fibers of the glossopharyngeal transmit the impulse to the medulla, in which a motor impulse is generated, and out along the efferent fibers comes the impulse to the constrictors of the pharynx. Centers for vomiting, coughing, sucking, and for other movements are described. The act of vomiting is a reflex one, in which the fibers of the pneumogastric serve as afferent fibers, the impulses stimulating the center in the medulla, from which emanate motor impulses to the respiratory and other muscles concerned in the act. If the act of vomiting is brought on by stimulating the pharynx with a feather or with a finger, the glossopharyngeal is the carrier of the afferent impulses. Afferent impulses producing vomiting may also come from other organs, such as the kidneys, or the testicles when injured. Central Vomiting. In central vomiting the center is stimu- lated by impulses which come from the cerebrum. ^ Merycism, or Rumination. The power to ruminate, by virtue of which animals chew the cud, is possessed by some human in- dividuals, who can regurgitate the food whenever they feel so disposed, and chew it again. Automatic Centers. Besides reflex centers, which require a stimulus from without to bring them into action, the medulla THE BRAIN. 487 possesses automatic centers which generate and emit impulses independently of stimuli from without. Respiratory Center. This center is situated in the floor of the fourth ventricle, and when injured, respiration ceases immediately. Some authorities place it among the reflex centers. It may, in- deed, be excited reflexly, but there are reasons for believing it to possess automatic powers as well. If the spinal cord is divided below the medulla, although the respiratory movements of the thorax cease, those of the nose and larynx continue. Under these circumstances no afferent impulses can be transmitted through the spinal nerves, and the only channel is the cranial nerves ; but if, while the medulla and cord are left undisturbed, the cranial nerves are cut, respiration continues. These two series of experiments show that respiration will continue independently of stimuli from without that is, automatically. The principal nerves that transmit the efferent impulses pro- ducing the respiratory movements are the intercostals to the inter- costal muscles, and the phrenics to the diaphragm. The respiratory center is double, so that one side may act after the other is injured. Division of one phrenic paralyzes only the side of the diaphragm to which it is distributed. The respiratory center may also be ex- cited reflexly. The afferent fibers under these circumstances are those of the pneumogastric. Cardio-inhibitory Center. In the cardio-inhibitory center are generated those impulses which, travelling to the heart by the vagus nerve, inhibit or restrain the action of that organ. These fibers convey impulses to the heart and to the muscular fibers of the superior vena cava, some of which diminish the frequency of the heart's action,. while others lessen the strength of its contrac- tions. This center can be stimulated directly, as when the blood is very venous or when the blood-pressure in the cerebral arteries is increased. It may also be stimulated reflexly, as when the sensory nerves of the abdominal viscera are irritated, as is shown in Goltz's percussion experiment, by percussion of the abdomen of a frog. Cardio-accelerator Center. Fibers from this center, whose ex- istence is not absolutely demonstrated, convey impulses to the heart which increase the frequency of its beats, and there are also fibers which transmit impulses that increase the force of the systole. These fibers pass down the spinal cord and thence into the sympathetic through the communicating branches of the in- ferior cervical and the six upper thoracic nerves. Vasomotor Center. The principal vasomotor center is situated in the medulla, in the floor of the fourth ventricle, extending from its upper part to a point about 4 mm. from the calamus scriptorius. When the center is destroyed there is a marked fall in arterial blood-pressure, due to the loss of tone in the small blood-vessels. After a while the pressure is increased under the' influence of stimuli sent out from the subsidiarv vasomotor centers in the oord. 488 THE NERVOUS SYSTEM. When the center is stimulated, arterial pressure is increased on account of the constriction of the vessels. Vasomotor Nerves. The vasomotor nerves, which originate in the cells of the vasomotor center in the bulb, pass down the lateral column of the spinal cord, and it is believed that they arborize around the cells of the subsidiary centers in the spinal cord, although the precise location of these centers has not been deter- mined. The cells in these subsidiary centers give rise to axis- cylinders which form a part of medullated nerve-fibers that enter as component parts of the anterior roots of the spinal nerves. Vasoconstrictor Nerves. These nerves carry impulses which cause constriction of the arterioles. They pass out from the cord in the anterior roots of the spinal nerves from the second thoracic to the second lumbar, which they leave by the white rami com- municantes, passing into the sympathetic ganglia situated along the vertebral column. These ganglia contain cells around which the nerve-fibers arborize, and they are spoken of as cell stations. From these cells axis-cylinder processes are given off which are continued as non-medullated fibers and which carry the impulses that orig- inate in the vasomotor centers. Vasodilator Nerves. The description of the vasoconstrictor fibers just given applies in general to the vasodilator, though there are some marked exceptions, for while, as a rule, they pass out together, still some do not. A striking example of this is the chorda tympani, which is given off from the facial. Nor do the dilator nerves arborize around the cells of the ganglia of the sympathetic chain, but pass through these and lose their medullary sheaths in the collateral ganglia, such as the semilunar, around whose cells they arborize. Depressor Nerve-fibers. Between the heart and the medulla are nerve-fibers which carry impulses from the heart to the vaso- motor nerve-center, which impulses inhibit the center, and thus diminish the impulses to the muscular coat of the arteries, thereby causing the arteries to dilate and reducing arterial pressure. In the rabbit these fibers are together and form the depressor nerve, but in most animals they are joined with the fibers of the pneumo- gastric. By means of these fibers the nerve-center can be inhibited and arterial pressure lessened, thus reducing the work of the heart. Pons Varolii. The pons Varolii (tuber annulare or meso- cephalon) is situated just above the medulla, and is composed of three sets of fibers and of some gray matter. The first set consists of superficial transverse fibers which cross the upper part of the medulla and connect the two hemispheres of the cere- bellum, forming at the sides the crura cerebelli or middle peduncles. The second is made up of longitudinal fibers which come from the pyramids of the medulla and pass on to help form the crura cere_bri. The third set is also transverse and is deeply THE BRAIN. 489 situated, connecting the middle peduncles of the cerebellum. Among its fibers are collections of gray matter. Functions of the Pons Varolii. The anatomic relations of the pons show that it must serve as a conductor of impulses both to and from the centers above. As to the function of its gray matter, comparatively little is known, save that from a portion of it some of the cranial nerves arise. If it is stimulated or divided, pain and spasms are produced. When a lesion is situated in the lower half of the pons, there result facial paralysis on the same side as the lesion, and motor and sensory paralysis on the opposite side of the body. This is called alternate paralysis. If the lesion is in the upper half of the pons, the facial paralysis and that of the body are on the same side. When the pons is suddenly and ex- tensively injured, a condition of hyperpyrexia is often produced, the temperature rising rapidly within an hour. This is probably M)endrite. Blood-vessel. -V ^ : - ' -f- r ..- c .- ? -o^ . Nerve-fiber ^ layer. 4; -~*-"" "-i- j FIG. 280. Section through the human cerebellar cortex vertical to the surface of the convolution; treatment with Miiller's fluid; x 115 (Bohrn and Davidoff). due to the influence of the gray matter in the floor of the fourth ventricle, or possibly to the involvement of some special heat- regulating center. I THE BRAIN. 491 The Cerebellum. The cerebellum (Figs. 280, 281) is com- posed externally of gray matter, which also penetrates into the substance of the organ, forming with the white matter the laminae. In the central part of the cerebellum is white matter, in which is imbedded a collection of gray matter, the corpus 'dentatum. The cerebellum is connected with the rest of the encephalon by the superior, the middle, and the inferior peduncles. The superior peduncles (processus e cerebello ad testes) connect the cerebellum with the cerebrum ; the middle peduncles (crura cerebelli) con- nect the two cerebellar hemispheres; the inferior (processus ad medullam) connect the cerebellum and medulla oblongata. The gray matter consists of two layers, an inner or granular layer, composed of nerve-cells, principally small in size, and neuroglia ; and an outer or molecular layer, composed of fine nerve- fibers and nerve-cells. Between these two layers are the cells of Purkinje, which are flask-shaped, and from the base of each of which is given off a neuron, which is continued as an axis-cylinder Dendrite. Cell-bod v. Neuraxis. Neuraxis. FIG. 282. Cell of Purkinje from the human cerebellar cortex ; chrome-silver method ; X 120 (Bohm and Davidoff). Claw-like telo- dendron of dendrite. FIG. 283. Granular cell from the granular layer of the human cerebellar cortex ; chrome-silver method; x 100 (Bohm and Davidoff). of a medullated nerve-fiber of the white center. From the opposite side are given off dendrons which pass into the gray matter. In discussing the structure of the cerebellum, Schafer says : " The dendrons of the cells of Purkinje spread out in planes trans- verse to the lamellae of the organ, so that they present a different appearance according to whether the section is taken across the 492 THE NERVOUS SYSTEM. lamellae or along them. These dendrons are invested at their attachment to the cell, and to some extent along their branchings, by basketworks formed by the terminal arborizations of certain fibers of the medullary center. The body of the cell of Purkinje is further invested by a feltwork of fibrils formed by the arboriza- tion of axis-cylinder processes of the same nerve-cells in the outer layer of the gray matter. Each cell has therefore a double invest- ment of this nature, one covering the dendrons, the other the body of the cell. Ramifying among the granule-layer are peculiar fibers derived from the white center, and characterized by having pencils of fine short branches at t intervals like tufts of moss. These are termed by Cajal the moss-fibers; they end partly in the granule-layer, partly in the molecular layer." Functions of the Cerebellum. If the surface of the cerebellum is irritated, no muscular movements are produced, nor is there any evidence of sensation ; if, however, the irritation is applied near the medulla or inferior peduncles, both pain and muscular contrac- tion result. If the cerebellum is removed wholly or partially, sensation is not diminished in the part of the body below, nor is there any impairment of the power of producing muscular move- ments, nor of the special senses, nor of the intelligence ; but there is a marked want of harmony in the muscular movements a lack of co-ordination. Attention has already been called to the fact that even the simplest movements that are made require the harmonious action of different muscles, and when these move- ments are more complex, they require different sets of muscles. If these movements do not occur at just the right time and are not produced in the right manner, the result is disorder instead of harmony ; or, as it is expressed, there is a want of co-ordina- tion, or a condition of inco-ordination or cerebellar ataxy. This is the effect of removing the cerebellum. Thus, if the cerebellum of a pigeon is removed, and an attempt is then made by it to fly, it is unsuccessful, for this act requires the consentaneous action of both wings, which action is absent. In walking the bird reels like a person intoxicated, and cannot go to the spot for which it apparently set out. It should be borne in mind that there is no paralysis either of motion or of sensation in this condition, but the^ voluntary movements which originate in the cerebrum, and which are in the normal condition co-ordinated by the cerebellum, pass to the muscles without this regulating influence, and the result is a series of disordered movements. Especially marked is this inco-ordination in connection with the maintenance of the equilibrium* of the body and locomotion. Indeed, some authorities are inclined to limit the functions of the cerebellum to this, and to regard it as not being the con- trolling organ of co-ordination in general, quoting experiments upon animals in which, after the first effects of its removal had passed away, there was a return of the co-oHinating power, THE BRAIN. 493 and also instances in the human subject in which during life the movements had been co-ordinated, yet after death the cere- bellum had been found completely disorganized. It is interesting to know that in animals that produce complex movements {he cerebellum is considerably developed, while in those whose movements are simple, such as the frog, this organ is exceedingly small. Sources of Impressions that reach the Cerebellum. The ana- tomic relations of the cerebellum are so intimate that impressions of many kinds can reach it and thus enable it to preside over this most important function of co-ordination, especially as regards equilibration and locomotion. Equilibration. Sewall defines equilibrium as "a state in which all the skeletal muscles are under control of nerve-centers, so that they combine, when required, to resist the effect of gravity or to execute some co-ordinated motion." In order that these centers may send to the muscles of the body impulses that are adapted to produce the desired result, it is absolutely essential that they should receive impressions which will give them cognizance of the exact position of the body and of the condition of the muscles at the moment as to contraction or relaxation. These impressions or sensations taken as a whole constitute the sense of equilibrium, and while it is doubtless true that all sensations contribute to bring about this result, yet there are some which are more directly concerned than others. These are impulses received from the skin, from the muscles, and from the semicircular canals, the last being doubtless the most important. Impressions from the Semicircular Canals. These are some- times described under the name labyrinthine impressions. For a description of the labyrinth, the reader is referred to page 607. Although in intimate anatomic relationship with the organs of hearing, there is still no doubt that the semicircular canals bear no physiologic relationship with that special sense, for removal of these structures leaves hearing unimpaired, provided, of course, the cochlea? are uninjured. On the other hand, serious disturbances of equilibrium do result, and these vary according as one or another of the canals is destroyed. Thus, if in a pigeon the horizontal canal is destroyed, the bird moves its head from side to side around a vertical axis : whereas if the injury is to the superior canal, the movements are vertical around a horizontal axis. When a pigeon whose semicircular canals have been injured is in a resting posture, it stands with its head turned backward or forward or to one side, never in a natural position ; and when dis- turbed, its movements are irregular, accompanied by rolling of the eyes and an inability to fly. If the injury is limited to one side, recovery soon takes place ; while if the canals on both sides are destroyed, the condition is a more persistent one. Different ani- mals act somewhat differently after injury to the canals ; in mam- 494 THE NERVOUS SYSTEM. rnals the movements described affect the eyes rather than the head. The explanation of the manner in which the canals are con- cerned with equilibrium is that any change in the pressure of the eudolymph upon the hair-cells of the cristae acusticse in the am- pullae of the semicircular canals will produce a change in the sen- sations which reach the center presiding over equilibration L e., probably the middle lobe of the cerebellum. It will be seen by a reference to Fig. 284 that the canals are FIG. 284. Diagram of semicircular canals to show their positions in three planes at right angles to one another. It will be seen that the two horizontal canals (H) lie in the same plane, and that the superior vertical of one side (S) lies in a plane parallel to that of the posterior vertical (P) of the other (after Ewald). at right angles to one another and thus occupy the three planes of space : the horizontal canal of one side being in the same plane with the corresponding canal of the other, and one anterior vertical canal practically parallel with the opposite posterior vertical canal. Thus movements of the head cause an increase of the pressure of the endolymph in one ampulla and a decrease in that of its parallel canal on the other side, and the sensory impressions thus produced are at once transmitted to the center. When a canal is injured, its endo- lymph is drained off, and at once there is an interference with the pressure upon the hair-cells, to- gether with a consequent modifica- tion of the normal impressions. FIG. 285. Diagrammatic hori- ^x, . zontal section through the head to Observation upon man connrms illustrate the planes occupied by these experiments upon the lower ": 'jSUXrM H, P ho animals. _ Thus a man with his eyes zontal canal (after Waller). closed lying upon a table which IS rotated, can tell that he is being moved, in what direction, and to some extent through how great an angle ; and when the rotation ceases the sensation of rotation in the opposite direction is experienced. In deaf-mutes, in whom THE BRAIN. 495 this condition is due to a defect in the internal ear, there is an absence of the dizziness experienced by normal individuals when rapidly rotated in a swing. The vertigo of MeniZre's disease is accompanied by changes in the internal ear. It has also been observed that defects of locomotion and equilibration are more common in deaf and dumb children than in those that are normal. Static Equilibrium. By this term is meant the equilibrium of rest, and Lee regards the utricle and saccule as being the organs concerned in this function. That is, that the knowledge of the position of the head while at rest is communicated to the co-ordi- nating center in the cerebellum by the pressure of the endo- FIG. 286. View of the brain from above : A, anterior central or ascending frontal convolution ; B, posterior central or ascending parietal convolution ; C, cen- tral fissure, or fissure of Rolando ; cm, callosomarginal sulcus ; F, frontal lobe ; Fi, upper, Fz, middle, Fs, lower frontal convolution ; f\, superior frontal sulcus ; /2, inferior frontal sulcus ; /s, vertical fissure (sulcus prsecentralis) ; ip, interparietal sulcus ; 0, occipital lobe ; o, sulcus occipitalis transversus ; Oi, first occipital convo- lution ; 02, second occipital convolution ; P, parietal lobe ; po, parieto-occipital fissure ; Pi, upper or posteroparietal lobule ; PJ, lower parietal lobule, constituted by PJ, gyrus supramarginalis ; P-j , gyrus angularis; 81, end of the horizontal branch of the fissura Sylvii ; ti, upper temporal fissure. lymph upon the otoliths, and these in turn upon the hair-cells of the maculae acusticae. Dynamic Equilibrium. This is the equilibrium of motion, and, as already stated, is presided over by the semicircular canals, from which impressions pass to the cerebellum. v The Cerebrum. The cerebrum, which in man makes up about four-fifths of the encephalon, is divided into two hemi- spheres which are separated by the great longitudinal fissure (Figs. 286-289), but are connected by a white commissure, the corpus 496 THE NERVOUS SYSTEM. callosum. The surface presents depressions, fissures and sulci, and prominences, convolutions or gyri. The external portion of the hemispheres is gray nervous matter about 3 mm. in thickness, beneath which is white matter. The fissures are not numerous, but are quite constant ; they are folds of the brain-matter both gray and white. The sulci are depressions of the gray matter alone ; they are very numerous and inconstant. As gray matter is present on both sides of the fissures and sulci, this arrangement permits of a larger amount of gray matter than could exist were it only upon the surface of the convolutions. In a brain, therefore, where the sulci are deep and numerous the amount of gray matter FIG. 287. Outer surface of the left hemisphere : A, anterior central or ascending frontal convolution ; B, posterior central or ascending parietal convolution ; c, sulcus centralis or fissure of Eolando ; cm, termination of the callosomarginal fissure ; F, frontal lobe ; F\, superior, l^Vniddle, and Fz, inferior frontal convolution ; /i, supe- rior, and /2, inferior frontal sulcus ; /a, sulciu prsecentralis ; ip, sulcus intraparietalis ; 0, occipital lobe ; Oi, first, Oz, second, Os, third occipital convolutions ; 01, sulcus occipitalis transversus ; 02, sulcus occipitalis longitudinalis inferior ; P, parietal lobe ; po, parieto-occipital fissure ; Pi, superior parietal or posteroparietal lobule ; Pz, infe- rior parietal lobule, viz., P 2 , gyrus supramarginalis ; P{, gyrus angularis ; S, fissure of Sylvius ; S', horizontal, S", ascending ramus of the same ; T, temporosphenoidal lobe: Tij first, Tz, second, Ts, third temporosphenoidal convolutions; ti, first, tz, second temporosphenoidal fissures. exceeds that in a brain where they are more shallow and less abundant. This gray matter is the cortical substance. Fissures of the Cerebrum. The fissures serve as landmarks in the description of the diiferent parts of the hemispheres. Besides the great longitudinal fissure, there are (1) the fissure of Sylvius ; (2) that of Rolando ; and (3) the parieto-occipital fissure. These fissures divide each hemisphere into 5 lobes. (1) The fissure of Sylvius is, next to the great longitudinal fissure, the most important. It is found in all animals whose brains have any fissures. It exists in the human brain in the THE BRAIN. 497 third . month of intra-uterine life. It commences at the base of the brain, and runs .outward, backward, and upward, giving off a short anterior branch or limb. The continuation of the fissure backward from where this branch is given off is the posterior branch or horizontal limb, which ends in the parietal lobe. The fissure of Sylvius is the boundary between the frontal and parietal lobes on the one hand and the temporosphenoidal on the other. At the middle and anterior part of this fissure, deeply situated, is the island of Reil, or insula, or central lobe. (2) The fissure of Rolando starts near the median line, and runs downward and forward nearly to the fissure of Sylvius. It is the boundary between the frontal and parietal lobes. FIG. 288. Inner surface of right hemisphere : A, ascending frontal ; B, ascend- ing parietal convolution ; c, terminal portion of the sulcus centralis, or fissure of Eolaudo; (7(7, corpus callosum, longitudinally divided; Cf, collateral or occipito- temporal fissure (Ecker) ; cm, sulcus callosomarginalis ; D, gyrus descendens ; Fi, median aspect of the first frontal convolution ; (?/, gyrus fornicatus ; H, gyrus hip- pocampi ; h, sulcus hippocampi, or dentate fissure; 0, sulcus occipitalis transversus; oc, calcarine fissure ; oc', superior, oc", inferior ramus of the same ; Oz, cuneus ; po, parieto-occipital fissure; Pi", precuneus ; Tt, gyrus occipitotemporalis lateralis (lobulus fusiformis) ; Ts, gyrus occipitotemporalis medialis (lobulus lingualis) ; U, uncinate gyrus. (3) The parieto-occipital fissure is about half-way between the fissure of Rolando and the posterior extremity of the brain, and is the boundary between the parietal and occipital lobes. Lobes of the Cerebrum. The lobes of the cerebrum are (1) the frontal, (2) the parietal, (3) the occipital, (4) the temporosphen- oidal, and (5) the central, or island of Reil. (1) The frontal lobe is above the fissure of Sylvius and in front of the fissure of Rolando. It is divided into 4 convolutions by 3 sulci, or fissures as they are sometimes called. The precentral fissure or sulcus is in front of the fissure of Rolando, and the convolution between the two is the ascending frontal. From the upper extremity of this sulcus the superior frontal sulcus runs downward and forward between the superior and middle frontal 32 498 THE NERVOUS SYSTEM. convolutions, while from the lower extremity extends the inferior frontal sulcus, separating the middle and inferior frontal convolu- tions. Thus the frontal lobe is divided into the ascending, superior, middle, and inferior frontal convolutions. (2) The parietal lobe is behind the frontal and in front of the occipital lobe, the fissure of Rolando being its anterior, and the parieto-occipital fissure its posterior boundary. Its inferior boundary is the fissure of Sylvius and the imaginary continuation of it to the superior occipital sulcus. It has 2 sulci, the intra- parietal and the post-central, and 3 convolutions, the ascending, superior, and inferior parietal. (3) The occipital lobe is posterior to the parietal, and has 2 Lobulus paracentralis, FIG. 289. Lateral view of the brain : gyri and lobuli marked with antique type, the sulci and fissures with italic type (combined from Ecker). sulci, the superior and middle, and 3 convolutions, the superior, middle, and inferior occipital, the latter being subdivided into the supramarginal and the angular. (4) The Temporosphenoidal Lobe. The fissure of Sylvius forms the anterior and superior boundaries of this lobe, while its posterior boundary is the imaginary continuation of the occipitoparietal fissure. It presents 2 sulci, the superior temporosphenoidal or parallel, and the middle temporosphenoidal. Its convolutions are 3, the superior, middle, and inferior temporosphenoidal. (5) The central lobe, or island of Reil, is situated at the base of the brain, in the fissure of Sylvius. It consists of 6 convolutions, the gyri operti. THE BRAIN. 499 Crura cerebri, also called the peduncles of the cerebrum, are made up of white matter, nerves which are continuous with those already studied in the medulla and pons, together with nerves from the cerebellum, the superior peduncles. Between the super- ficial fibers of the crura, the crusta, and the deeper ones, the teg- mentum f is the locus niger, a collection of gray matter. The fibers of the crura on their way upward to the gray matter of the hemispheres pass through the corpora striata and the optic thalami. Basal Ganglia. At the base of the hemisphere are certain bodies, the basal ganglia, which are the corpora striata, the optic co. FIG. 290. Vertical section through the cerebrum and basal ganglia to show the relations of the latter: co., cerebral convolutions; c.c., corpus callosum; v.l., lateral ventricle ; 6., fornix ; vIIL, third ventricle ; n.c., caudate nucleus ; th, optic thala- mus; n.l., lenticular nucleus; c.L, internal capsule; cl, claustrum; c.e., external capsule ; m, corpus mammillare ; t.o., optic tract ; s.t.t., stria terminalis ; n.a., nucleus amygdalae; cm, soft commissure ; co.i, island of Reil (Schwalbe). > thalami, the tubercula quadrigemina or corpora quadrigemina, the corpora geniculata, and the locus niger. Corpora striata, with the optic thalami, are called the cerebral ganglia. The corpora striata present a striped appearance, which is due to a mixture of gray and white matter, the latter being bundles of fibers which have come from below and within-. Although at the lowest part each corpus striatum is a single body, at the upper part it is divided into two portions, the caudate nucleus and lenticular nucleus. The lenticular nucleus, the more posterior, is separated from the optic thalamus by white matter, the internal capsule, which is the continuation of the crus cerebri. Outside the lenticular nucleus is white matter, the external cap- sule, beyond which is a layer of gray matter, the claustrum, and 500 THE NERVOUS SYSTEM. external to all these structures is the island of Reil. The cortical substance is at this point very near the gray matter of the basal ganglia. The fibers of the internal capsule, passing upward, radiate forward, upward, and backward, forming the corona radiata, the fibers of which pass to the cortex, each one being the continuation of the axis-cylinder process of a pyramidal cell. The fibers of the internal capsule give off collaterals which pass to the optic thalamus, and the nucleus caudatus and nucleus lenticularis of PCI. AP FIG. 291. Diagram to show the connection of the frontal occipital lobes with the cerebellum: ec., the dotted lines passing in the crusta (TOO), outside the motor fibers, indicate the connection between the temporo-occipital lobe and the cerebel- lum ; F. C., the frontocerebellar fibers, which pass internally to the motor tract in the crusta ; I.F., fibers from the caudate nucleus to the pons ; Fr., frontal lobe ; Oc., occipital lobe ; AF., ascending frontal ; AP., ascending parietal convolutions ; PCF., precentral fissure in front of the ascending frontal convolution ; FR., fissure of Rolando ; IFF., interparietal fissure. A section of cms is lettered on the left side : S.IV., substantia nigra ; PY., pyramidal motor fibers, which on the right are shown as continuous lines converging to pass through the posterior limb of /. C., internal capsule (the knee or elbow of which is shown thus (*) ) upward into the hemisphere and downward through the pons to cross at the medulla in the pyramidal decussa- tion ; Ipt., crossed pyramidal tract; apt., direct pyramidal tract (Gowers). the corpus striatum. These ganglia give off fibers which pass into the internal capsule and corona radiata. There are, there- fore, fibers passing into these ganglia and others passing out from them, the latter being the more numerous. The pyramidal fibers in their downward course thus give off collaterals which arborize around the cells of the corpus striatum and optic thala- mus, and from these ganglia axis-cylinder processes pass out to form a part of the pyramidal tract. So, also, the sensory fibers, particularly those of the fillet, arborize around the cells of the optic thalamus and the subthalamic region. THE BRAIN. 501 It is in this locality that hemorrhage produces such serious consequences. The blood-vessels supplying the basal ganglia may rupture on account of a diseased condition, and as a result of this apoplexy or paralysis may occur, or the hemorrhage may prove fatal. When the hemorrhage takes place into the anterior portion of the internal capsule, hemiplegia, or paralysis of motion in the opposite side of the body, will -result ; while if it is into the poste- rior part, paralysis of sensation will occur on the opposite side. Optic Thalami (Fig. 290). Each of. these bodies is covered by a layer of white fibers, which is especially prominent in the internal capsule. From the capsule it enters the thalamus, con- necting it with the hemisphere. The gray matter of the thalamus, of which it is principally composed, is aggregated into two masses, an outer and an inner nucleus, separated by a white lamina, the internal medullary lamina. In the anterior portion there is a third portion of gray matter, in which the nerve-cells are quite large. The cells of the thalamus are multipolar and fusiform. Corpora Quadrigemina. These bodies, 4 in number, the ante- rior pair being the testes, and the posterior the nates, are situated behind the third ventricle and posterior commissure and under the posterior border of the corpus callosum. They consist principally of gray matter. Each gives off a bundle of white fibers to the corpora geniculata, which joins the optic tract of the same side, and each receives fibers of the fillet which can be traced to nuclei of the opposite funiculus gracilis and cuneatus. Thus the fillet serves as a channel for afferent impulses which have traversed the fibers of the posterior roots of the spinal nerves. These nerves arborize around the cells of the nuclei, from which the fibers of the fillet arise. Over the gray matter of the superior corpora quadrigemina is a layer of nerve-fibers which have their origin in the nerve-cells of the retina, coming by way of the optic tract, and which pass into the corpora quadrigemina and arborize around the cells of the gray matter. Schafer says that these cells "are very various in form and size, and are dis- posed in several layers, which are better seen in the optic lobe of the bird (Fig. 292) than in mammals. Most of their processes pass ventralward. Their destination is not certainly known, but some appear to pass downward with the fillet, others probably turn upward and run in the tegmentum toward the higher parts of the brain ; while others, perhaps most, probably form terminal arborizations around the motor cells of the oculomotor and other motor nuclei. All the nerve-fibers of the optic nerve and optic tract do not enter the corpora quadrigemina. Some pass into the lateral geniculate bodies and form arborizations there. On the other hand, from the cells of these geniculate bodies the axis- cylinder processes appear to pass to the cortex of the brain (occipital region)." 502 THE NERVOUS SYSTEM. Functions of the Cerebral Ganglia. A marked change has taken place within comparatively recent times as to the functions and importance of the corpora striata and the optic thalami. The former were for a long period of time considered important motor centers, and the latter as performing the same role with reference to sensation. This was doubtless largely due to the fact, to which Kirkes calls attention, that when a hemorrhage took place in the FIG. 292. Sections of optic lobe of bird taken in planes at right angles to one another (S. Ramon y Cajal) (Golgi method). A. Anteroposterior section : a, optic fibers cut across. The other letters indicate differ- ent kinds of cells, of which it will be noticed that some have their axis-cylinder processes extending outward toward the optic fiber layer, and others have their axis-cylinder processes extending inward toward a deep layer of nerve-fibers ; s, some have only short neurons ramifying in adjacent layers. B. Transverse section : a, optic fibers cut longitudinally; b, c, d, e, their terminal ramifications in different layers of the gray matter. region of the corpora striata, motor paralysis was the result ; and that when it occurred in the region of the optic thalamus, sensory paral- ysis followed. It was, therefore, natural to attribute motion and sensation to these ganglia respectively. It is now known that ?d to these i when the hemorrhage is limited to these ganglia paralysis is slight, or even absent altogether, and that the effects of cerebral hemor- rhage ordinarily observed are due to injury of the internal capsule ; and hemorrhage into the anterior portion is followed by motor paralysis, because it is here that the fibers pass which carry motor impulses from the cortex to the cord ; and that hemorrhage THE BRAIN. 503 into the posterior part is followed by paralysis of sensation, because in this part of the capsule are the fibers which carry the sensory impulses from the cord to the cortex. The cerebral ganglia are subordinate centers : the corpus striatum with regard to motion ; the optic thalamus with regard to sensation, particu- larly to vision. Microscopic Structure of the Cerebrum (Figs. 293, 294). The FIG. 293. The layers of the cortical gray matter of the cere- brum (Meynert). llitl mmw . d FIG. 294. Schematic diagram of the cerebral cortex: a, molecular layer with superficial (tangential) fibers ; &, striation of Bechtereff- Kaes ; c, layer of small pyramidal cells ; d, stripe of Baillarger ; e, radial bundles of the medullary substance ; /, layer of polymor- phous cells (Bohm and Davidoff). Gray Matter. The gray matter on the external surface of the cere- brum, the cortex, is divisible into five layers, whose distinctness varies in different regions, being perhaps most marked in the parietal lobe ; but in the posterior portion of the occipital lobe, in the gray portion of the hippocampus major, in the wall of 504 THE NERVOUS SYSTEM. the fissure of Sylvius, and in the olfactory bulb this arrangement does not exist. These layers are : 1. Molecular Layer. This is the most superficial, and consists of neuroglia, a few small ganglion-cells, and a network of non- medullated and medullated nerve-fibers, the latter forming a delicate white lamina absent in contact with the pia mater. Layer of small pyr- amidal cells. FIG. 295. Schematic diagram of the cerebral cortex, after Golgi and Eam6n y Cajal (Bohmand Davidoff). FIG, 296. Large pyramidal cell from the human cerebral cortex ; chrome-silver method ; x 150 (Bohm and Davidoff). The non-medullated fibers have their origin principally in the small pyramidal cells of the second layer, but also come from the dendrites and axis-cylinder processes of the cells of the first layer. The nerve-cells of this layer have two or three axis-cylinder processes arranged horizontally, which terminate by arborization in this superficial layer. 2. Smalt Pyramid-cell Layer. The cells of this layer are small THE BRAIN. 505 and pyramidal, having a diameter of about 10 //, with their long axes vertical to the surface of the convolutions. Their dendrites pass into the first layer; their axis-cylinder processes passing off from the base give off collaterals and form projection- fibers which go to the corpus striatum. 3. Large Pyramid-cell Layer. This layer is characterized by being made up of pyramidal cells larger than those of the second layer, and increasing in size from above downward, reach- ing a diameter of 40 /JL. The breadth of this layer is shown in the illustration. The axis- cylinder processes of these cells give off collaterals and pass into the white substance of the brain, where they be- come medullated. 4. Polymorphous-cell Layer (Fig. 295). The cells of this layer are irregular in shape, each giving off several den- drites and an axis-cylinder process. Some of these proc- esses pass into the white cen- ter, while others pass to the first layer and are contained in one of its fibers. 5. Fusiform-cell Layer. In this layer are spindle- shaped or fusiform cells. In the inner half thev are nu- FIG. 297. Principal types of cells in the cerebral cortex : A, medium-sized pyrami- meroilS and arranged parallel dal cell of the second layer ; B, large pyram- to the snrfarp Thp rlni/tfri/m idal cel1 of third la y er "> ^ polymorphous ,ce. ine ciaustrum cell of fourth layer; D cell of wnich the IS made Up OI this layer, sepa- axis-cylinder process is ascending ; E, neu- rated by white substance from rg lia c / n ; ^ cel1 ? f the & *> or molecular, layer, forming an intermediate cell-station between sensory fibers and motor cells. Notice the tangential direction of the nerve- the other gray matter. The different varieties of -.-,. fibers ; G, sensory fibers from the white cells are well shown m Fig. matt er; H, white matter; J, collateral of 297. The number of cells in * h e white matter (Ramon y Cajal). the cortex has been estimated at 1,200,000,000 by Donaldson, and 9,200,000,000 by Thompson : the latter regards 1 59,960 of these as motor ; this number would therefore represent the largest pyramidal cells or " giant-cells." White Matter. The medullated nerve-fibers of the white center are traced through the deeper layers of the gray matter. Some are continuous with the axis-cylinder processes of the pyramidal and polymorphous cells; others arborize around the 506 THE NERVOUS SYSTEM. cells of the various layers without being anatomically in connection with them. If the axis-cylinder processes of tbe pyramidal cells are traced, it will be found that they take various courses. Some, commissural fibers, pass either directly or by collaterals through the corpus callosum from one hemisphere to the other ; some join association fibers, and pass into the gray matter of other parts of the same hemisphere as that in which they originated ; while others, projection fibers and this is the course particularly of those having their origin in the largest pyramidal cells pass downward through the corona radiata, internal capsule, and pyramidal tract. The number of pyramidal fibers has been estimated at 158,222 by Blocq and Ozanoif. The white matter of the cerebrum, consisting of medullated nerve-fibers, may then be divided into three groups : 1. Those fibers that connect the cerebrum with the medulla oblongata, pons Varolii, and spinal cord. These are the crura cerebri or cerebral peduncles; hence the group is described as peduncular or projection fibers. It will be remembered that the crura cerebri consist of the crusta and tegmentum. The fibers which come from the pyramids of the medulla and are continued through the pons aid in forming the crusta. To these fibers are added others which originate in the gray matter of the aqueduct of Sylvius and in the locus niger. After forming the crura cerebri the fibers pass upward : some of them go directly to the gray matter of the cortex : these form the corona radiata ; others go to the internal capsule, and thence to the corpora striata, where they terminate ; while some of the others continue on, receiving fibers from these bodies, and together they assist in forming the corona radiata. More fibers come from the corpora striata than end there, so that the number of those which emerge is greater than the number of those which enter. The tegmentum of the crus is made up of fibers from the anterior and lateral columns of the cord, the olivary body, funiculus cuneatus, funiculus gracilis, corpora quadrigemina, corpora genicu- lata, and the superior peduncles of the cerebellum. These fibers pass into the optic thalami, some terminating there, while others pass through. To these latter are added fibers having their origin in the optic thalami, and together they assist in forming the corona radiata, being traced to the cells in the cortical sub- stance of the temporosphenoidal and occipital lobes. 2. The second group of fibers in the cerebrum consists of those which connect the hemispheres and the basal ganglia, and are the transverse or commissural fibers. They compose the corpus callo- sum and the anterior and posterior commissures. The fibers of the corpus callosum connect the hemispheres, being traced into the convolutions and intersecting those of the corona radiata. The anterior commissure connects the corpora striata, and then passes through these bodies into the temporosphenoidal lobe. Some of THE BRAIN. 507 the fibers of the posterior commissure connect the optic thalami, while some come from the tegmentum of one side, traverse the optic thalamus, and terminate in the white matter of the temporo- sphenoidal lobe of the other side. 3. The third group, association fibers, connect different struct- ures in the same hemisphere ; as the short association fibers, which connect adjacent convolutions, and the long association fibers, which connect more distant parts. Functions of the Cerebrum. That the cerebrum is not essential to life has been demonstrated experimentally many times in birds, fishes, rats, and other animals. Of course, the same kind of proof is not available in man, but there are instances on record in which FIG. 298. Dr. Harlow's case of recovery after the passage of an iron bar through the head. the destruction of cerebral tissue has been so great as to warrant the statement that in man, as well as in lower animals, life may be maintained without the influence of the cerebrum. A remark- able instance is that of a man who was injured by a premature blast, an iron bar, one inch in diameter, being driven through the skull and brain. Although delirious and unconscious for several weeks, he finally recovered, with but the loss of one eye. He lived more than twenty years after the injury, and performed the work of a coachman and a farm-laborer. The cerebrum is undoubtedly the seat of the intellectual faculties. A study of the lower animals reveals the fact that according as the hemispheres are developed the signs of intelli- gence are increased : when these structures are destroyed there is an absence of these manifestations. When the hemispheres are removed, spontaneous action ceases. In studying the reflex action of the spinal cord in a decapi- tated frog it was seen that the animal made no attempt to move 508 THE NERVOUS SYSTEM. f or change its position unless some stimulus was applied, and that as soon as this stimulus was withdrawn it lapsed into its original position, remaining therein until again disturbed. If the hemispheres are removed from a pigeon, it will act very much as does the frog. If disturbed, it may fly for a short distance, but at once lapses into a state of apparent unconsciousness, with eyes closed. When the foot is pinched, it will be withdrawn. If a pistol is discharged, the bird will open its eyes and show unmistakably that the report was heard, but the discharge seems to produce no other effect. The fact that there is danger is not appreciated. It seems, therefore, that the faculty is absent by which the bird in health associates danger with such sounds. When the human brain is diseased or injured, something of the same kind is witnessed, and in idiots, whose brains are imperfectly developed, the intellectual faculties are very deficient. Human intelligence is manifested through memory, reason, and judgment. Memory is the basis for the action of the other two faculties ; without it there could be neither reason nor judgment. It is the faculty of the mind by which it retains the knowledge of previous thoughts or events, the actual and distinct retention and recogni- tion of past ideas in the mind. Afferent impulses are continually reaching the cells of the cortex of the brain, and these impulses produce impressions more or less permanent. If they were evanes- cent, passing away almost as soon as received, memory would be impossible ; but it is this retention which constitutes memory. If the ideas produced by these impulses come again into existence spontaneously and without effort, this is remembrance; if this requires an effort, this is recollection, a re-collecting of the im- pressions originally produced on the cells by afferent impulses. Reason is the faculty of the mind by which is appreciated the nature of nervous impulses, and by which they are referred to their external source by which an effect is referred to its cause. This reference an idiot cannot make ; hence he is said to be " un-reasonable." Judgment is the faculty of the mind by which a selection is made of the proper means to be used in the attainment of a par- ticular end. Thus if one selects inadequate means for the accom- plishment of a given object, it is said that one " lacks judgment." The cerebrum is the seat of conscious sensation, as opposed to sensation alone. The gray matter of the spinal cord is said to be sensitive that is, it responds to stimuli. If the finger is burned, the afferent impulse is received by the gray matter of the cord and a motor impulse passes out to the muscles. But if the impulse travels no farther than the cord, there is no conscious sensation. To excite this sensation it must proceed to the gray matter of the cerebral cortex. It is in the cells of the cortex that volitional impulses have their origin. The gray matter, then, is the seat of THE BRAIN. 509 the will as well as the conscious center, and when largely diseased or destroyed, the only movements made are involuntary, depending on other nerve-centers. Cerebral Localization. Although the study of the intellectual faculties is both difficult and abstruse, much advance has in late years been made in the knowledge of the physiology of the cere- brum, so far as relates to the production of voluntary movements and the reception of sensation. Observations upon both man and the lower animals have led to the belief that the power of pro- ducing certain movements is limited to certain restricted areas of the brain, and that other areas are connected with sensation. Lobulus paracentralis, FIG. 299. Lateral view of the brain : gyri and lobuli marked with antique type, the sulci and fissures with italic type (from Ecker). These are known respectively as motor, sensorimotor, or Icinesthetic or Rolandic areas, and sensory areas. The localizing of these functions is cerebral localization. These observations had their beginning in 1870. It was found that when galvanic currents were applied to certain parts of the cerebral convolutions movements of particular muscles followed, and that in order to excite these muscles these parts or areas must be stimulated. Although the dog was first experimented upon, other animals (cat, rabbit, and monkey) have furnished like results. In the application of these experiments the animal is put under ether, the skull is trephined, and the poles of a galvanic battery are applied to the convolutions. When on such stimulation of a 510 THE NERVOUS SYSTEM. given spot or area contractions of certain muscles or groups of muscles follow, and when its extirpation causes paralysis of these muscles, such spot or area is said to be the motor area for these muscles. The following statement summarizes in a general way what is known with reference to cerebral localization in the human subject : Motor Areas (Figs. 300, 301). It has been noted that the FIG. 300. The motor areas on the outer surface of the brain. FIG. 301. The motor areas on the median surface of the brain. Rolandic area is also called sensorimotor and kinesthetic. This is because it has been determined that the sensory fibers from the skin and also from muscles terminate in the Rolandic area, as well as that the motor fibers have their origin here. The motor areas are grouped about the fissure of Rolando and are as follows : THE BRAIN. 511 Head, neck, and face: Lower two-thirds of the ascending frontal and the bases of the lower and middle transverse frontal convolutions. Upper limb : Upper third of the ascending frontal, base of upper transverse frontal, ascending parietal, and part of the mar- ginal convolutions. Lower limb : Parietal lobule and posterior part of marginal. Trunk : Marginal convolution between the leg and arm. It is to be understood that the action is in all cases crossed that is, excitation of one side of the cerebrum causes the move- ments spoken of to occur on the opposite side of the body, and the same is true of the paralysis which follows disease or injury. As a result of destruction of the Rolandic area degeneration 'Filltt F MID BRAIN FIG. 302. Degeneration after destruction of the Eolandic area of the right hemi- sphere (after Gowers). occurs, and its course is well shown in the illustration (Fig. 302), in which the shaded portions represent the parts that have under- gone degeneration. Speech-center. Articulate speech requires the exercise of memory and the power of producing certain voluntary move- ments. Inability to produce articulate speech is known as aphasia. If the memory of words is absent while the power to produce the movements remains, it is amnesic aphasia, and if the reverse condition exists, it is ataxic aphasia. It is believed that the center which presides over language is in the frontal lobe on the left side, and has received from its discoverer the name of Broca's convolution. Some localize it in the third frontal convo- lution ; others regard it as being more diffused, and locate the center in the convolutions surrounding the lower end of the fissure 512 THE NERVOUS SYSTEM. of Sylvius. It is on the left side in persons that are right- handed, and on the right side in those that are left-handed. Sensory Areas. When a sensory area is stimulated., the move- ment which results is reflex. Thus, if the auditory area, which was localized, perhaps incorrectly, by Ferrier in the superior temporosphenoidal convolution, is stimulated, the animal pricks up its ears and turns its head to the opposite side. If a sensory FIG. 303. Base of brain : 1, 2, 3, cerebrum ; 4 and 5, longitudinal fissure ; 6, fissure of Sylvius ; 7, anterior perforated spaces ; 8, infundibulum ; 9, corpora albi- cautia ; 10, posterior perforated space ; 11, crura cerebri ; 12, pons Varolii ; 13, junc- tion of spinal cord and medulla oblongata ; 14, anterior pyramid ; 14 X , decussation of anterior pyramid ; 15, olivary body ; 16, restiform body ; 17, , cerebellum ; 19, crura cerebelli ; 21, olfactory sulcus; 22, olfactory tract; 23, olfactory bulbs; 24, optic commissure; 25, motor oculi nerve: 26, patheticus nerve; 27, trigeminus nerve ; 28, abducens nerve ; 29, facial nerve ; 30, auditory nerve ; 31, glossopbaryn- geal nerve ; 32, pneumogastric nerve ; 33, spinal accessory nerve ; 34, hypoglossal nerve. area is extirpated, there is a loss of the sense presided over by this area. Visual Area. This is located in the occipital lobe and the angular gyrus. Auditory Area. Ferrier located this in the superior temporo- sphenoidal convolution. The location of other areas is a matter of considerable doubt. THE BRAIN. 513 Cranial Nerves (Fig. 303). The cranial nerves have their origin in the gray matter at the base of the brain, and they escape from the skull by various openings, or foramina, to reach the parts to which they are distributed. The only exception to this is the spinal accessory, a part of which arises from the gray matter of the cord. Among the cranial nerves are those of special sense, of motion, and nerves having both motor and sensory properties. The points at which they leave the brain are spoken of as their apparent origin, but this is only apparent, for they can be traced into the brain-substance, to collections of nerve-cells, nerve- centers, to which the name nuclei has been given. The nucleus of a nerve is its real origin. Of cranial nerves there are 12 pairs, the number of each indicat- ing the order, from before backward, in which it escapes from the cavity of the cranium: 1. Olfactory; 2. Optic; 3. Motor oculi communis ; 4. Patheticus or trochlearis ; 5. Trigeminus ; 6. Ab- dticens ; 7. Facial ; 8. Auditory ; 9. Glossopharyngeal ; 10. Pneu- mogastric; 11. Spinal accessory; 12. Hypoglossal. The first two nerves, the olfactory and the optic, will be considered in connection with the senses of smell and sight. Motor Oculi. The third nerve, motor oculi, motor oculi com- munis, or oculomotorius, leaves the surface of the brain at the inner surface of the crus cerebri, just in front of the pons Varolii. Its real origin is, however, a nucleus in the floor of the aqueduct of Sylvius. It escapes from the cranium through the sphenoidal fissure, and is distributed to the superior, internal, and inferior recti and to the inferior oblique. It also supplies the levator palpebrae superioris, and sends a branch to the ophthalmic, lenticular, or .ciliary gang- lion. Another way to describe its distribution is to say that it supplies the levator palpebrae and all the muscles that move the eyeball, except the superior oblique and external rectus. The action of these muscles is largely indicated by their names. The levator palpebrae by its contraction raises the upper eyelid. The internal rectus turns the eyeball inward toward the nose, and the external rectus turns it outward. The direction of action and the point of attachment of the superior rectus are such that when it con- tracts the eyeball is not only turned upward, but it is also rotated slightly inward ; this is corrected by the action of the inferior oblique, so that the two acting together produce a movement directly upward. The same deviation inward follows when the eye is turned downward by the inferior rectus, and a similar cor- rection is made by the action of the superior oblique. If the external and superior recti act together, the movement of the eyeball is in the direction of the diagonal that is, outward and upward ; the conjoint action of the external and inferior recti causes the eyeball to move outward and downward, and a corre- sponding action results when the other adjacent recti are brought 33 514 THE NERVOUS SYSTEM. into play. If the recti act alternately, the eyeball will be rotated completely, as in looking around a room from one side to the other and back again, from the floor to the ceiling. The motor oculi is purely a motor nerve. When stimulated, contraction is produced in the muscles to which it is distributed ; when the nerve is divided, these muscles are paralyzed. Paralysis of the Motor Oculi. When the motor oculi is par- alyzed, the following are the results : (a) External strabismus, which consists in a turning of the eye outward. The retention of the eye in its normal position requires the conjoint action of the internal and external recti. In paralysis of the motor oculi the internal rectus has lost its innervation, and therefore its power to contract, and the external rectus, which receives its nervous supply from another nerve (the ab- ducens), having lost its antagonist, turns the eye outward. (6) Luscitas. After external strabismus has'been produced the eye remains in that condition, for the muscles which could move it in any other direction have been paralyzed. This immobility is called " luscitas." (c) Ptosis. The levator palpebrse superioris is also paralyzed, and the upper eyelid droops, constituting ptosis. The ability to close the eye still remains, as this is the act of the orbicularis palpebrarum, which is not innervated by the third, but by the seventh, nerve. (d) Mydriasis. A branch of the motor oculi goes to the ciliary ganglion, which gives off the ciliary nerves that supply the iris. Accompanying the manifestations of paralysis of the motor oculi already mentioned there is in addition a dilatation of the pupil, or mydriasis. The diminution of the size of the pupil following the action of light upon the retina does not take place when this nerve is paralyzed. The contraction of the pupil is a reflex act requiring the integrity of the optic nerve, which serves as a carrier of the luminous impressions to the brain, and of the motor oculi, which is the efferent nerve in this act. (e) Inability to Focus. The muscle concerned in focusing the eye for short distances is the ciliary. The power to focus is lost in paralysis of the motor oculi. Paralysis of the motor oculi may be due to disease of the brain or to pressure on the nerve. If the trunk of the nerve is affected, all the physical signs mentioned may be observed, while if a single branch only is involved, the effect will be limited to the part to which that branch is dis- tributed. Trochlearis. The apparent origin of the trochlearis or patheti- cus is on the outer side of the crus cerebri, in front of the pons, and its real origin is a nucleus continuous with that of the motor oculi. The trochlearis leaves the cranium by the sphenoidal fissure, and is distributed to but one muscle, the superior oblique. THE BRAIN. 515 When this nerve is paralyzed the patient cannot turn the eye out- ward and downward ; the action of the superior oblique is, there- fore, to turn the eye outward and downward. If the head is not turned toward either side when this nerve is paralyzed, the only thing observable is that the patient sees double when he looks downward, and the image perceived by the affected eye is oblique and below that seen by the eye that is affected. For a further discussion of the ocular muscles see p. 556. Trigeminus. This nerve, which is also called " trifacial," has received its names from the fact that it has three subdivisions, and its latter name from the fact that is distributed in the main to FIG. 304. General plan of the branches of the fifth pair : 1, lesser root of the fifth pair : 2, greater root, passing forward into the Gasserian ganglion ; 3, placed on the bone above the ophthalmic division, which is seen dividing into the supra- orbital, lacrimal, and nasal branches, the latter connected with the ophthalmic ganglion ; 4, placed on the bone close to the foramen rotundum, marks the superior maxillary division ; 5, placed on the bone over the foramen ovale, marks the inferior maxillary division (after a sketch by Charles Bell). the parts about the face. It arises by two roots, anterior and posterior. The anterior root, the smaller, is purely motor; the posterior root, the larger, is sensory, and is characterized anatomi- cally by having upon it the Gasserian ganglion. The nerve leaves the brain at the side of the pons Varolii. The real origin of the motor root is a nucleus in the floor of the fourth ventricle ; the sensory root arises from a nucleus on a level with the middle of the superior peduncle of the cerebellum, just internal to the margin of the fourth ventricle. Some authorities give it a more extensive origin, from the pons through the medulla and as far as the posterior cornua of the gray matter of the spinal cord. 516 THE NERVOUS SYSTEM. The motor root passes beneath the Gasserian ganglion, and takes no part in its formation. Beyond the ganglion the fifth nerve divides into three parts : (1) ophthalmic; (2) superior maxillary; and (3) inferior maxil- lary. *(1) Ophthalmic Division. This division, which leaves the cranium by the sphenoidal fissure, is distributed to the tentorium cerebelli, the eyeball, the Schneiderian membrane, the lacrimal gland, and the skin about the forehead and nose ; and also supplies branches to the ciliary ganglion. It contains fibers from the posterior root only ; none from the anterior. (2) Superior Maxillary Division. This division of the fifth pair leaves the cranial cavity by the foramen rotundum. It is distributed to the dura mater, the sphenopalatine ganglion (Meckel's), the skin of the temple and cheek, the teeth, the gums, the mucous membrane of the upper jaw and upper lip, the mucous membrane of the lower part of the nasal passages, and the skin of the lower eyelid, side of nose, and upper lip. There are no fibers of the anterior root in this division. (3) Inferior Maxillary Division. As has already been stated, there is no anatomic connection between the motor root of the fifth nerve and the Gasserian ganglion. From this ganglion are given off nerve-fibers which join the motor root, together making the inferior maxillary division, which escapes through the foramen ovale. It is distributed to the dura mater, the otic ganglion, the mucous membrane of the cheek and skin, the mucous membrane of the lower lip, the anterior wall of the external auditory meatus, the front of the external ear and the skin of the adjacent temporal region, the submaxillary gland and ganglion, the mucous mem- brane of the mouth and tongue ; to the papillae at the tip, the edges, and anterior two-thirds of the tongue, and to the teeth and gums of the lower jaw. It also supplies the following muscles : Temporal, masseter, pterygoid, mylohyoid, and anterior belly of the digastric. Physiologic Properties of the Trigeminus. The trigeminus is the largest of the cranial nerves, and its functions are many and important. It supplies the parts to which it is distributed with the general sensibility they possess. If it is divided, there is complete absence of sensation (anesthesia) of the face on the cor- responding side. So pronounced is this anesthesia that no amount of irritation applied to such ordinarily sensitive parts as the cornea will produce any effect. An animal thus experimented upon seems entirely unconscious of the irritation. Experimenters have gone so far as to exsect the eyeball and apply hot irons to the skin without causing pain to the animal experimented upon. Neuralgia of the face, headache, and toothache are all due to some interference with the normal functions of this nerve. It is THE BRAIN. 517 not an uncommon thing to hear patients complain of headaches which seem to them to be in the brain itself. These deep-seated headaches may be due to affections of one or more of the recurrent branches which come off from the divisions of the nerve, and which are distributed to the dura mater and bones of the skull. Lingual (Gustatory) Nerve. This nerve is sometimes called the " lingual branch of the fifth nerve." It is the branch which is distributed to the mucous membrane of the mouth and the gums, and to the mucous membrane and papillae of the tongue. It sup- plies the tongue with tactile sensibility, a quality of great advan- tage in enabling one to detect the physical properties of food, to FIGS. 305, 306. Distribution of the cutaneous sensitive nerves upon the head : owa, orni, the occiput, ma j. and minor (from the N. cervical II. and III.) ; am, N. auricular magn. (from X. cervic. III.) ; cs, N. cervical superfic. (from N. cervic. III.) ; Fi, first branch of the fifth (so, N. supraorbit. ; st. N. supratrochl. ; it, N. infra- trochl. ; e, N. ethmoid. ; I, N. lacrimal.) ; Vi, second branch of the fifth (sm, N. subcutan. malfe sen zygomaticus) ; Fs, third branch of fifth (at, N. auriculotempor. ; b, N. buccinator ; m, N. mental.) ; B, posterior branches of the cervical nerve. recognize in it the presence of hard objects which it would be injurious to swallow, and to determine when it is ready for deglutition. Besides this tactile sensibility the lingual nerve, according to some authorities, suppli'es the anterior two-thirds of the tongue with the sense of taste, a special sense, and this power is lost when the fifth pair or the lingual branch is divided. For a further consideration of this nerve see p. 535. Mastication. The muscles that have been mentioned as receiv- ing branches of the inferior maxillary division are those concerned in the act of mastication. In this act the temporal and masseter close the mouth, the mylohyoid and digastric open it, while the pterygoids produce the lateral movement of the lower jaw. Division of the inferior maxillary division paralyzes, therefore, all 518 THE NERVOUS SYSTEM. these muscles. If it is divided on one side, the muscles on the other side can still perform the act, but in an imperfect manner ; if divided on both sides, all masticatory movements will be abolished. Anastomosis of the Fifth Pair. Besides the branches already mentioned, there are others which are termed anastomotic branches. Although the upper, middle, and lower parts of the face are sup- plied with sensation by the ophthalmic, superior maxillary, and inferior maxillary divisions respectively, still the boundaries of each are not absolute. Thus the skin of the nose is supplied by fibers from the ophthalmic and superior maxillary, and the skin of the temporal region is supplied from both the superior and inferior maxillary divisions. In addition to these branches, there are some which unite with other nerves and give a certain amount of sensibility to the parts to which these nerves are distributed. A striking instance of this is the branch which anastomoses with the facial nerve. This nerve is at its origin purely motor, and is distributed to the muscles of the face. These muscles are endowed with sensibility ; but this is not due to fibers of the facial nerve, but to those of the fifth nerve, which anastomose with the facial and go with it to its termination in the muscles. Connection of the Fifth Pair with the Special Senses. After division of the fifth nerve the special senses of smell, sight, taste, and hearing are seriously affected. The Schneiderian membrane becomes swollen, and later assumes a fungous condition and bleeds readily when touched. There is besides an accumulation of altered mucus in the nasal passages. The eye also undergoes marked changes : The conjunctiva becomes congested and the cornea opaque ; later, most of the structures of the eye suffer from inflam- matory changes to the degree of destruction. The sense of taste may likewise be lost, not only in the anterior two-thirds of the tongue, but also in the posterior third as well. Besides, the sense of hearing may also be greatly impaired. The explanation of these changes is not an easy one. Some authorities regard them as due to disturbance of trophic in- fluences. The nerve-fibers which form the posterior or sensory root of the fifth pair in passing through the Gasserian ganglion are reinforced by fibers which have their origin in this collection of nerve-cells. Each of the three divisions of the trigeminus contains, therefore, fibers of the posterior root, and in addition fibers from the ganglion. The latter fibers are distributed to the structures to which the accessory fibers are distributed, and they are regarded as trophic nerves that is, as nerves which regulate the nutrition of the parts to which they go. Among these parts are the mucous membrane of the nose, the cornea, the conjunctiva, and the tongue, and the loss of the special senses is believed to be due to altered nutrition of the affected parts. The sense of sight THE BRAIN. 519 is resident in the retina and optic nerve, but it may be as perfectly abolished by rendering opaque the tissues through which light reaches these structures as by dividing the optic nerve. Thus in cases where a tumor presses upon the trigeminus in front of the ganglion, not only may there be an alteration of the nutrition of the skin of the face, as evidenced by an herpetic eruption, but there may be also the corneal ulceration already referred to. In like manner the olfactory nerves are the nerves of smell, but if the nasal mucous membrane is so aifected in its nutrition as to render the function of the nerves impossible, the sense of smell is as certainly abolished as if the olfactory bulb was broken up. This interference with the normal action of the nerves is seen in catarrhs! affections of the nose, in which the sense of smell is much obtunded and sometimes even lost. Some authorities, however, question the existence of specific trophic nerves. Stewart says that up to the present " no unequivo- cal proof, experimental or clinical, has ever been given of the existence of specific trophic nerves." These authorities consider that the inflammatory changes occurring in the eye, for instance, are due to the presence of foreign bodies lodging on the eyeball, which has lost its sensibility ; that if the eye is so protected that irritating substances cannot injure it, the degenerative changes take place only after a considerable time ; and that when they do occur it is probably even then due to injury, for it is a most difficult thing to protect the eye for a long time from all sources of irritation. Thus in a case reported by Shaw T , in which both the fifth and the third nerves were paralyzed, due to the pressure of a tumor at the base of the brain, no change took place in the nutrition of the eye. The orbicularis could still close the eye, and the protection which this gave was augmented by the ptosis. After many months the growth of the tumor involved the facial nerve, and as the eye could then not be closed, inflammatory changes soon set in and sight was destroyed. Gowers also reports a case in which the patient lived for seven years with complete paralysis of the fifth nerve, yet the eye re- mained free from disease and the sight was unimpaired. Kirkes, on the other hand, is an advocate of the existence of the " trophic influence of nerves/' although he states that the proof that there are distinct trophic nerve-fibers anatomically is not very conclusive. He thinks that the division or disease of the fifth nerve, for instance, acts as a predisposing cause, and the dust which falls on the cornea as the exciting cause. He gives one instance of disturbance of nutrition which it is difficult to account for except on the theory of trophic nerves. He says : " Many bed-sores are due to prolonged confinement in bed with bad nursing ; these are of slow onset. But there is one class of bed- sores which are acute : these are especially met with in cases of 520 THE NERVOUS SYSTEM. paralysis due to disease of the spinal cord ; they come on in three or four days after the onset of the paralysis in spite of the most careful attention ; they cannot be explained by vasomotor dis- turbance nor by loss of sensation ; there is, in fact, no doubt they are of trophic origin ; the nutrition of the skin is so greatly im- paired that the mere contact of it with the bed for a few days is sufficient to act as' the exciting cause of the sore." The subject is one of great importance, but must be regarded as still unsettled. Ganglia of the Trigeminus. Besides the Gasserian ganglion, there are, in connection with the fifth nerve, four ganglia which are by some writers described as a part of the sympathetic system. They are the ciliary or ophthalmic, the sphenopalatine or MeckePs, the otic or Arnold's, and the submaxillary. The ciliary ganglion belongs, according to some authorities, to the third rather than to the fifth nerve. It is not larger than the head of an ordinary pin, and is situated in the orbit. The branches by which other nerves communicate with it are called its " roots " ; of these there are three : The sensory, from the ophthal- mic division of the fifth ; the motor, from the motor oculi ; and the sympathetic, from the cavernous plexus of the sympathetic. The nerves that go off from it are the short ciliary nerves, which, joining with the long ciliary nerves, form the nasal branch of the ophthalmic division, and together they are distributed to the ciliary muscle, the iris, and the cornea. These nerves supply motion to the sphincter and dilator pupillse, sensibility to the iris, choroid, and sclerotic, and vasomotor influences to the blood-vessels of the iris, choroid, and retina. If the trophic influerfce already spoken of exists, it must be conveyed to the eye through the ciliary nerves. The sphenopalatine or Meckel's ganglion, which is the largest of the four, is situated in the sphenomaxillary fossa. This gang- lion also has three roots : The sensory, sphenopalatine, from the superior maxillary division of the fifth ; the motor, large superficial petrosal nerve from the facial ; and the sympathetic, large deep petrosal nerve from the carotid plexus of the sympathetic. The Vidian nerve is made by the union of these two latter nerves. The nerves from this ganglion are distributed to the posterior por- tion of the nasal passages and the hard and soft palate, giving them sensibility ; to the levator palati and azygos uvulae, giving them the power of motion ; and to the blood-vessels of this region. The otic or Arnold's ganglion is situated on the inner side of the inferior maxillary division of the fifth, just below the foramen ovale. It likewise has three roots : The sensory, from the inferior maxillary and glossopharyngeal ; the motor, from the facial and inferior maxillary ; and the sympathetic, from the plexus around THE BRAIN. 521 the meningeal artery. Its branches of distribution are to the tensor tympani, the tensor palati, and a small one to the chorda tympani. The mucous membrane of the tympanum and the Eustachian tube is also supplied by this ganglion. The submaxillary ganglion, which is situated near the sub- maxillary gland, receives branches of communication from the lingual branch of the fifth, chorda tympani, and sympathetic plexus around the facial artery. Its branches of distribution are to the mucous membrane of the mouth and Wharton's duct, also to the submaxillary gland. Abducens. This nerve, which has its real origin in the floor of the fourth ventricle, emerges from the cranium by the sphe- noidal fissure, and is distributed to the external rectus muscle. It is a motor nerve, as is shown by the contraction of this muscle when the nerve is stimulated, and by its paralysis when the nerve is divided. Paralysis of Abducens. When from any cause this nerve is so injured as to deprive it of its function, the internal rectus, having lost its antagonist, the external rectus, turns the eye inward toward the nose, producing internal strabismus. There may also be some contraction of the pupil, because the radiating fibers of the iris, which cause dilatation of the pupil, are to a certain extent deprived of their innervation, this being supplied from the sympathetic, some of the nerves of which system run along with the abducens, and when this nerve is injured, these sympathetic fibers may also be involved. It is said that the abducens is more frequently im- plicated in fractures at the base of the skull than any other cranial nerve. Facial Nerve. The facial nerve leaves the medulla oblongata at the groove between the olivary and the restiform bodies. Its real origin is a nucleus in the floor of the fourth ventricle. It leaves the cranium by the internal auditory meatus, through which and the aqueduct of Fallopius it passes to emerge at the stylo- mastoid foramen. In the older nomenclature, in which there were but nine pairs of nerves, the facial was associated under the name of seventh nerve with the auditory nerve, in company with which it enters the auditory meatus ; the facial, from its firm consistency, being called the portio dura, and the auditory, on account of its opposite quality, being called the portio mollis. The facial has a very extensive distribution the muscles of the face and external ear, the stylohyoid, posterior belly of the digastric, the platysma myoides, and the stapedius. It also gives off the chorda tympani, which is distributed to the submaxillary gland and ganglion, to the inferior lingualis muscle, and to the sublingual gland. Besides these it has most important branches of communication with the sympathetic system and with the glossopharyngeal, pneumogastric, and trigeminus nerves. 522 THE NERVOUS SYSTEM. Physiologic Properties of the Facial. The facial is, origi- nally, a purely motor nerve, and whatever sensibility is possessed by the parts to which it is distributed is not due to facial fibers, but to anastomotic fibers from other nerves, principally the fifth. The most pronounced function of the facial is its relation to ex- pression. The so-called " expression " of the face is caused by different degrees of contraction of the facial muscles, and the different expressions, such as of fear, of anger, etc., are due to con- traction of different muscles. The facial is therefore said to be the " nerve of expression," and when it is divided and the muscles paralyzed, the reason for this title is readily understood. Facial Paralysis. When the facial nerve is divided or its functions otherwise abolished, the following are the results : (1) Effect of Facial Paralysis on Facial Expression. A com- plete loss of expression follows on the affected side ; the wrinkles on that side are obliterated and the face is flattened. (2) Effect of Facial Paralysis on the Eye. The muscle which closes the eye is the orbicularis palpebrarum ; this muscle is inner- vated by the facial nerve, and in paralysis, therefore, the eye remains permanently open, the power to close it being lost. Inas- much as the act of winking is but a rapid partial closing of the eye, this act is also abolished and the eyeball is liable to become dry. The act of winking spreads the tears which keep the eye moist. Unless provided against, this exposure of the eye may result in injury (p. 519). (3) Effect of Facial Paralysis on the Mouth. The mouth is drawn by the unparalyzed muscles to the unaffected side. It is impossible to approximate the lips of the affected side to a tumbler or cup ; consequently in drinking therefrom, unless the head is thrown back, fluids will dribble from the corners of the mouth. The buccinator muscle being paralyzed, food finds its way into the space between the cheek and the gum, and mastication is seriously impeded. The lips being paralyzed, the consonants b and p cannot be pronounced distinctly. If the tongue is protruded, it seems to be deviated toward the affected side ; but this is only ap- parent, for if the mouth is placed in the normal position it will be seen that the tongue is unaffected. (4) Effect of Facial Paralysis on Taste. Accompanying facial paralysis may be impairment or abolition of the sense of taste. Authorities are not agreed as to the explanation of this result, but it is doubtless due to interference with the chorda tympani. Some attribute it to the influence which this nerve exercises over the circulation in the tongue and on the secretion of saliva : others regard the chorda tympani as the nerve of taste to the anterior two-thirds of the tongue, and as taking part in forming the gusta- tory nerve or lingual branch of the trigeminus. Indeed, there is a difference of opinion among anatomists as to the true source of the chorda tympani, at least so far as concerns those fibers which THE BRAIN. 523 are connected with the sense of taste ; some look upon it as a part of the fifth, some as a part of the seventh, and still others as a part of the ninth or glossopharyngeal. Auditory. The auditory nerve has its apparent origin from the lower border of the pons, in the groove between the olivary and restiform bodies. Its real origin is in the floor of the fourth ventricle. As already stated, the auditory nerve enters the in- ternal auditory meatus with the facial nerve. It is distributed to the internal ear, and is the special nerve of the sense of hearing. It will further be discussed in connection with that special sense. Glossopharyngeal. The superficial origin of the glossopharyn- geal nerve is from the upper part of the medulla, in the groove between the olivary and restiform bodies. Its real origin is a nucleus in the lower part of the floor of the fourth ventricle. It escapes from the cranium through the jugular foramen, together with the pneumogastric and spinal accessory nerves. Its branches of communication are with the pneumogastric, facial, and sympa- thetic nerves. The glossopharyngeal gives off the tympanic branch, the nerve of Jacobson, which is distributed to the fenestra rotunda, the fenestra ovalis, and the lining membrane of the tym- panum and Eustachian tube. As its name implies, the glosso- pharyngeal is distributed to the tongue and pharynx. The glossal portion supplies the mucous membrane of the posterior third of the tongue, the tonsils, and the pillars of the fauces and soft palate, while the pharyngeal portion is distributed to the pharyn- geal mucous membrane and to the muscles concerned in a part of the act of deglutition namely, the styloglossus, digastric, and stylopharyngeus, and the superior and middle constrictors. Physiologic Properties. The sensibility of the parts to which the glossopharyngeal nerve is distributed is due to this nerve. It is also a nerve of special sense, supplying the posterior third of the tongue and the palate with the sense of taste ; and, finally, it is the motor nerve for the muscles enumerated which are con- cerned in passing the food from the back of the mouth into and through the pharynx to the esophagus in the act of deglutition. Vagus. This nerve is also called pneumogastric, from two of the important organs, the lungs and stomach, to which it is dis- tributed. Its apparent origin is by eight or ten filaments from the groove below the glossopharyngeal, while its deep origin is from a nucleus in the floor of the fourth ventricle, below and con- tinuous with that of the same nerve. At the jugular foramen, by which it escapes from the cranium, is found the ganglion of the pneumogastric or the jugular ganglion. The pneumogastric receives branches from the spinal accessory, facial, hypoglossal, and anterior branches of the first and second cervical nerves. It assists in forming the pharyngeal, laryngeal, pulmonary, and esophageal plexuses. Among its important branches are the superior and inferior laryngeal nerves, the cardiac 524 THE NERVOUS SYSTEM. FIG. 307. View of the glossopharyngeal, pneumogastric, spinal accessory, and hypoglossal nerves of the left side : 1, pneumogastric nerve in the neck ; 2, ganglion of its trunk ; 3, its union with the spinal accessory ; 4, its union with the hypoglossal ; 5, pharyngeal branch : 6, superior laryngeal nerve ; 7, external laryngeal ; 8, laryn- geal plexus; 9, inferior or recurrent laryngeal; 10, superior cardiac branch; 11, middle cardiac; 12, plexiform part of the nerve in the thorax; 13, posterior pul- monary plexus; 14, lingual or gustatory nerve of the inferior maxillary; 15, hypo- glossal, passing into the muscles of the tongue, giving its thyrohyoid branch, and uniting with twigs of the lingual ; 16, glossopharyngeal nerve ; 17, spinal accessory nerve, uniting by its inner branch with the pneumogastric, and by its outer passing into the sternomastoid muscle ; 18, second cervical nerve ; 19, third ; 20, fourth ; 21, origin of the phrenic nerve ; 22, 23, fifth, sixth, seventh, and eighth cervical nerves, forming with the first dorsal the brachial plexus; 24, superior cervical ganglion of the sympathetic ; 25, middle cervical ganglion : 26, inferior cervical ganglion united with the first dorsal ganglion ; 27, 28, 29, 30, second, third, fourth, and fifth dorsal ganglia (from Sappey, after Hirschfeld and Leveille). and the gastric branches. The pharyngeal branch is distributed to the mucous membrane and muscles of the pharynx and to the THE BRAIN. 525 muscles of the soft palate. Its esophageal branches supply the mucous membrane and muscular coat of the esophagus, so that the act of deglutition, which begins in the mouth and is continued in the pharynx, is completed by the esophagus. The superior laryngeal nerve is distributed to the cricothyroid muscle and to the inferior constrictor, and communicates with the superior cardiac nerve. Its further distribution is to the mucous membrane of the epiglottis and larynx as far as the vocal cords. The superior laryngeal nerve is the sensitive nerve of the larynx. This sensibility is of great importance as a protection of the larynx and the respiratory organs below it from the entrance of foreign bodies, which would set up dangerous inflammatory processes. The instant such a substance touches the surfaces sup- plied by this nerve a violent expulsive cough occurs which ejects it. If the nerve is paralyzed, as it may be after diphtheria or in con- nection with brain disease, this protection is absent, and, owing to paralysis of the cricothyroid, the ability to make tense the vocal cords is lost and the voice is hoarse. The inferior or recurrent laryngeal nerve is distributed to all the muscles of the larynx except the cricothyroid. It sends branches to the mucous membrane and muscular coat of the esophagus, to similar structures of the trachea, and to the inferior constrictor. It is the motor nerve of the larynx, and may be paralyzed under the same conditions as were mentioned in con- nection with the superior laryngeal, and all motion of the vocal cords is abolished. One nerve may alone be paralyzed, as when pressed upon by a tumor, when the corresponding vocal cord would alone be motionless. The cardiac branches of the pneumogastric terminate in the superficial and deep cardiac plexuses. The pulmonary branches assist in forming the pulmonary plexuses, the branches of which are distributed to the lungs. The esophageal branches form the esophageal plexus or plexus guise. The gastric branches, which are the terminal filaments of the nerve, are distributed to the stomach and to the celiac, splenic, and hepatic plexuses, the latter two supplying the liver and spleen. In mentioning some of the branches of the pneumogastric, their functions have also been referred to. In addition to these func- tions the movements of the stomach and the intestines are also performed under the influence of this nerve. It is through the cardiac branches that the inhibitory impulses from the medulla are sent to the heart. Through the pulmonary branches impulses reach the respiratory center and influence respiration. Reference has previously been made to the depressor fibers, which run in the pneumogastric to the vasomotor center, inhibiting its action and thus diminishing the work of the heart. Spinal Accessory Nerve. This nerve has two parts one arising 526 THE NERVOUS SYSTEM. from a nucleus in the medulla below that of the pneumogastric, and the other from the intermediolateral tract of the cord. The former is the accessory, and the latter the spinal, portion. The accessory portion joins the pneumogastric, and is distributed through the pharyngeal and superior laryngeal branches of that nerve. It is also probable that the fibers of the pharyngeal branch going to the muscles of the soft palate are fibers of this portion of the spinal accessory. The inferior laryngeal nerve also contains fibers from this nerve, probably from the internal, anastomotic, or accessory por- tion, and experiments demonstrate that the power which the larynx possesses to produce vocal sounds is due to these fibers, for when the spinal accessory is torn out this power is lost. The other move- ments of the larynx, those which take place during respiration, are not interfered with under these circumstances, but only those of phonation- The inferior laryngeal nerve is, then, only par- tially made up of spinal accessory fibers : these fibers preside over phonation. The other fibers, which are probably derived from the facial, hypoglossal, or cervical, or all of them, provide the nervous influence for the other movements. If the entire nerve is divided, the laryngeal movements of both phonation and respiration will cease. The spinal or external portion is distributed to the trapezius and sternomastoid muscles; it is therefore sometimes called the " muscular branch." This branch is believed to be brought into requisition when these muscles are needed for more than their ordinary activity, for the nervous force to supply the latter is fur- nished by cervical nerves. In unusual straining or in lifting, or in the production of prolonged cries, these muscles are brought into action, and to supply the additional innervatiou which these acts seem to require is believed to be the office of the muscular branch of the eleventh nerve. The spinal accessory is, then, a motor nerve, although some writers regard a portion of the fibers of the accessory part as being sensory. Hypoglossal. The apparent origin of this nerve is by filaments, from 10 to 15 in number, from the groove between the pyramidal and olivary bodies : its real origin is in a nucleus in the floor of the fourth ventricle. It sends branches of communication to the pneumogastric, the sympathetic, the first and second cervical, and the gustatory. It is distributed to the sternohyoid, stern othyroid, omohyoid, thyrohyoid, styloglossus, hyoglossus, geniohyoid, and geniohyoglossus muscles. It is a motor nerve to the tongue, so much so that it has been called the " motor linguae." The move- ments over which it presides are those concerned in mastication and deglutition and in the production of articulate speech. When this nerve is paralyzed on one side, the tongue, when protruded, is directed toward the paralyzed side. When both nerves are involved in the paralysis all motion of the tongue ceases. THE SENSES. 527 THE SENSES. It is by the senses that the individual is brought into relation with the world outside him. The senses are five in number : (1) General sensibility; (2) Smell; (3) Taste; (4) Sight; and (5) Hearing. General Sensibility. This kind of sensibility is so called because it is generally distributed over the entire body in the skin, and in those parts of mucous membrane adjacent to the skin. It is composed of a variety of sensations which are excited by a variety of stimuli, but it is still an unsettled question whether the nerves which conduct the impulses that excite these sensations are in all instances the ordinary sensory nerves of the skin, or whether they are special nerves, each one conducting only its own special stimulus. In treating of the subdivisions of general sensibility this question will again be referred to. Sense of Touch. The sense of touch, or tactile sensibility, de- pends upon the existence of nerves and nerve-endings (p. 64) in the skin and other portions of the body in which the function exists. It gives knowledge of such qualities as hardness or soft- ness, roughness or smoothness, sharpness or dulness, etc. ; by it we become acquainted with the shape and consistency of objects, and are made aware of the presence or absence of irritating quali- ties in certain substances. The pungent vapors of some gases excite in the nose the ultimate fibers of distribution of the fifth pair of nerves, and not those of the first pair, and it is incorrect to describe this sensation as a smell. It is as truly a tactile sensa- tion as when a sharp-pointed instrument is brought in contact with the skin. The same is true of pungent liquids applied to the tongue, which are commonly, but erroneously, said to be tasted. The difference in the tactile sensibility of different portions of the body is shown in the following table : TABLE or VARIATIONS IN THE TACTILE SENSIBILITY or DIFFERENT PARTS. The measurement indicates the least distance at which the two points of a pair of compasses can be separately distinguished (E. H. Weber). Tip of tongue 1 mm. Palmar surface of third phalanx of forefinger ..... 2 Palmar surface of second phalanges of fingers 4 Red surface of under lip 4 Tip of the nose ' 6 Middle of dorsum of tongue 8 Palm of hand 10 Center of hard palate 12 Dorsal surface of first phalanges of fingers 14 Back of hand 25 Dorsum of foot near toes 37 Gluteal region 37 Sacral region 37 528 THE NERVOUS SYSTEM. * TABLE OF VARIATIONS, ETC. Continued. Upper and lower parts of forearm 37 mm. Back of neck near occiput ... 50 ' Upper dorsal and mid-lumbar regions 50 Middle part of forearm 62 Middle of thigh 62 Mid-cervical region 62 Mid-dorsal region 62 Weber, who has investigated thoroughly the subject of tactile sensibility, says that in order to distinguish the two points of the compasses as such, there must be unexcited nerve-endings between the points of the skin that are touched by them, and the greater the number of these, the more distinctly are they recognized as being separate. Tactile sensibility is a function which can be educated to a high degree. Case of Laura D. Bridgman. No better illustration could be given of the degree of perfection to which this sense can be brought than that of the deaf, dumb, and blind girl, Laura Dewey Bridgman. When about two years old this child had scarlet fever, as a result of which she lost the senses of sight, hearing, taste, and smell. Although, about eleven years after, the sense of smell returned to a slight degree, the other senses mentioned were permanently absent. In describing her case, Prof. Musscy, Prof, of Anatomy and Surgery at Dartmouth College, Hanover, N. H., where Laura lived, states that she possessed not merely " touch proper," but the capacity for " acute " sensations, pleasant or pain- ful ; the sensations of pressure, weight, temperature, and " mus- cular sensations." In speaking of this girl, her instructor said : " With regard to the sense of touch, it is very acute, even for a blind person. It is shown remarkably in the readiness with which she distinguishes persons. There are forty inmates in the female wing, with all of whom, of course, Laura is acquainted ; whenever she is walking through the passageways, she perceives by the jar of the floor or the agitation of the air that some one is near her, and it is exceed- ingly difficult to pass her without being recognized. Her little arms are stretched out, and the instant she grasps a hand, a sleeve, or even a part of the dress, she knows the person, and lets them pass on with some sign of recognition. Her judgment of dis- tances and of relations of place is very accurate ; she will rise from her seat, go straight toward a door, put out her hand just at the right time, and grasp the handle with precision." From her Life and Education it is impossible to ascertain what ability Laura possessed of distinguishing colors. Her historian says that it has been stated that she could tell the color of every- thing by feeling, but that this is not true. He further says that fabulous stories have been told of the power of the blind to dis- tinguish color, but such statements could not be made of those in GENERAL SENSIBILITY. 529 the institution with which she was connected. " It is true of many totally blind that, if a number of balls of worsted of various colors are given them, and they are obliged to notice them care- fully in order to use them in their proper places in work, they will rarely make a mistake. So we may give them pieces of silk, with the same result ; but this does not prove that, having been told the colors in one material or fabric, they will recognize them in any other. " We have no evidence that there is any inherent property in the color red, or blue, or yellow, which will enable the most sensi- tive touch to detect each in all materials offered." Sense of Pressure. When objects are laid upon the hand there is a sensation produced, which is that of pressure, and by the exer- cise of this sense we are able to distinguish differences in the weights of objects. This is true of other portions of the body as well as of the hand. Sense of pressure and tactile sensibility are not identical ; indeed, portions of the body in which the latter is very acute are nevertheless very insensitive to pressure. Thus the tactile sensibility of the tip of the tongue is very highly devel- oped, but its sense of pressure is very deficient. Kirkes says that with the tip of the tongue one cannot detect the radial pulse. While there is a marked difference between the tongue and the finger in their ability to distinguish the pulse-beats, still the writer is positive that the statement that these cannot be felt by the tongue is not true for all individuals. It is to be borne in mind that in the investigation of the sense of pressure the muscles must not be brought into play, otherwise a new factor is involved the muscular sense. Muscular Sense. This sense is brought into action in lifting weights, and the estimation of the weight of an object depends upon the amount of nervous energy (efferent impulses) necessary to accomplish the result. Some authorities regard it as a modifica- tion of the sense of pressure ; but the two senses are undoubtedly distinct. Sense of Temperature. By this sense the difference in tem- perature of bodies is recognized, and it is a well-known fact that the various portions of the body are endowed with different degrees of sensibility in this regard : The hand will bear a degree of heat which would cause great pain to some other parts of the body. The sense of temperature and that of touch are entirely distinct, and this fact may readily be demonstrated by pressing firmly on a sensitive nerve* until the part to which it is distributed is almost devoid of the sense of touch, when it will be found that the sense of temperature is unaffected. Not only is the sense of temperature distinct from other sensa- tion, but even this is so subdivided that there are heat spots and cold spots that is, portions of the skin which are excited by heat 34 530 THE NERVOUS SYSTEM. and cold respectively. Thus if a heated object is moved about over the skin, at some points tactile sensibility alone will be excited, while at others the object will feel distinctly hot. In like manner cold spots will be recognized by the application of a cold object. This test applied to the skin of the forearm has resulted in such a chart as is shown in Fig. 308. Sense of Pain. When the stimuli that call out the sense of touch or of temperature are excessive, the sense of pain is pro- duced, and the other sensations are abolished ; thus when a piece HI!!* wfepilililBF P^^^iiiilliWTllPil!!! ::; . '! , i '... >M* HiiHiiiJii ::: FIG. 308. Cold and hot spots from the same part of the anterior surface of the forearm : o, cold-spots ; 6, hot-spots. The dark parts are the more sensitive ; the hatched the medium ; the dotted the feehle ; and the vacant spaces the non- sensitive. of iron very much heated burns the hand, the sensation is the same as when the iron is very cold. Some authorities regard the sense of pain as being a distinct sensation, others as simply an exaggeration of other sensations. Sense of Smell. In the consideration of the respiratory processes the nose was described as being a part of the respiratory tract (p. 353). This is true of the lower portion of the nasal cavity, the entrance or regio vestibularis and the regio respiratoria, the rest of the lower part of the nasal cavity; the upper part, however, is more especially concerned with the function of smell, and is therefore called regio olfactoria. This portion of the mucous membrane is sometimes denominated olfactory membrane, and may be defined as that portion of the Schneiderian membrane which covers the superior and middle turbinated bones and the upper part of the septum nasi. The Schneiderian membrane lines the nasal fossae. Before the time of Schneider, from whom the mem- SENSE OF SMELL. 531 brane was named, it was thought that the secretion it forms came from the brain : he demonstrated that it came from the membrane itself. It is covered by epithelium, which, near the orifice of the nostril in the vestibule, is pavement, but elsewhere, except on the olfactory membrane, this epithelium is columnar and ciliated. In man the olfactory membrane is soft, vascular, and of a yellow color. It is covered by epithelium composed of two varieties of cells, with a superficial lamina through which the ends of the cells pro- ject. One variety, olfactory or olfactorial celts, is spindle-shaped and bipolar (Fig. 309), having a nu- &*fs*&&ss ll! ^^ cleus. One of the poles extends to the ***^ 3 f^Y* t f^ surface, its extremity passing through i [,, j jj i the lamina, and in amphibia, reptiles, and birds terminates in fine, hair-like filaments. It is uncertain whether these filaments exist in mammals. The other pole extends downward and is connected with one of the fibrils of the olfactory nerve, and passes through the cribriform plate of the ethmoid bone, and arborizes within one of the olfactory glomeruli (Fig. 310). The other variety of cells is the columnar or sustentacular cell. These are columnar epithelium-cells with nucleated cell-bodies at the free surface of the mucous membranes and branching processes extending down- ward : they are supporting cells. The corium of the olfactory membrane is very thick and vascular, with bundles of olfactory nerve-fibers and a large number of serous glands, Bow- man's glands, whose ducts open upon the surface of the membrane between the epithelial cells. Olfactory Nerves. These are about twenty in number, non-medullated, and are given off from the olfactory bulb. They pass through the cribriform plate of the ethmoid bone and are distributed to the olfactory membrane. Olfactory Bulb. This is in reality a portion of the hemispheres, and is described as " a cap superimposed upon a conical process of the cerebrum." It consists of gray and white matter, and is thus described by Schafer : " Dorsally there is a flattened ring of longitudinal white bundles enclosing neuroglia, as in the olfactory tract ; but below this ring several layers are recognized, as follows : FIG. 309. Olfactory mucous membrane : a, sustentacular cells ; 6, olfactory cells ; c, basal cells; d, submucous fibrous tis- sue ; e, glands of Bowman ; I, nerve-fibers (Leroy). 532 THE NERVOUS SYSTEM. " 1. A white or medullary layer, characterized by the presence of a large number of small cells (' granules') with reticulating bundles of medullated nerve-fibers running longitudinally between them. " 2. A layer of large nerve-cells, with smaller ones intermingled, the whole embedded in an interlacement of fibrils which are mostly derived from the cell-dendrons. From the shape of most of the large cells of this layer it has been termed the i mitral ' layer. These cells send their neurons upward into the next layer, olf.c. FIG. 310. Diagram of the connections of cells and fibers in the olfactory bulb: olf.c, cells of the olfactory mucous membrane; olf.n, deepest layer of the bulb, composed of the olfactory nerve-fibers which are prolonged from the olfactory cells ; gl, olfactory glomeruli, containing arborization of the olfactory nerve-fibers and of the dendrons of the mitral cells ; m.c, mitral cells ; a, thin axis-cylinder process passing toward the nerve-fiber layer, n.tr, of the bulb to become continuous with fibers of the olfactory tract ; these axis-cylinder processes are seen to give off collaterals, some of which pass again into the deeper layers of the bulb ; n', a nerve- fiber from the olfactory tract ramifying in the gray matter of the bulb (Schafer). and they eventually become fibers of the olfactory tract and pass along this to the base of the brain, giving off numerous collaterals in the bulb as they pass backward. " 3. The layer of olfactory glomeruli consists of rounded nest- like interlacements of fibrils which are derived on the one hand from the terminal arborizations of the non-medullated fibers which form the subjacent layer, and on the other hand from arborizations of descending processes of the large i mitral ' cells of the layer above. "4. The Layer of Olfactory Nerve-fibers. These are all non- SENSE OF SMELL. 533 medullated, and are continued from the olfactory fibers of the Schneiderian or olfactory mucous membrane of the nasal fossae. In this mucous membrane they take origin from the bipolar olfactory cells which are characteristic of the membrane, and they end in arborizations within the olfactory glomeruli, where they come in contact with the arborizations of the mitral cells." Olfactory Tract. This structure is an outgrowth from the brain, which is in man at one period of development hollow, but later the cavity is filled with neuroglia, outside of which are bundles of white fibers, and still more external is a layer of neuroglia. There Mitral cells. f Large i nerve- cell Small nerve- cell. Layer of olfactory glomeruli. Peripheral nerve- fibers. FIG. 311. The olfactory bulb, after Golgi and Eamon y Cajal. The granular layer is not shown. are no nerve-cells in the tract. It lies in the olfactory sulcus, a depression in the under surface of the frontal lobe of the cere- brum, and terminates in the olfactory bulb. Traced backward, the tract is found to be made up of two roots, external and in- ternal ; between these is the trigonum ol/actorium, which is some- times called the middle or gray root, but which is in reality cortical gray matter. The external root is connected with the end of the hippocampal gyrus, and the internal with the beginning of the gyrus fornicatus. Functions of the Olfactory Nerves. The olfactory nerves are beyond all doubt the channels by which olfactory impressions reach the brain (Fig. 312). They are nerves of the special sense 534 THE NERVOUS SYSTEM. of smell. The whole mucous membrane of the nose is not sup- plied with olfactory fibers ; hence only in that part where they are present, the olfactory membrane, does the sense of smell reside. The proof that the function of these nerves is that of smell is derived from experiments upon lower animals and from observa- tions upon man. Animals whose sense of smell is very acute have the olfactory bulbs and tracts more highly developed that is, these structures are larger than in those animals in which the acuteness of the sense of smell is not marked. If the tracts are destroyed, the sense of smell is abolished. Although this experi- FIG. 312 . Nerves of the outer walls of the nasal fossse : 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, sphenopalatine 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, nasopalatine branch to the septum cut short (from Sappey, after Hirschfeld and LeveillS). mental proof is not applicable in man, still there are cases on record in which an absence of the sense of smell during life has been found after death to have accompanied an absence of the olfactory tracts ; and there are cases also of individuals whose sense of smell has been seriously impaired after injury to the tracts. During ordinary respiration the inspired air does not pass over the olfactory membrane, but only over the lower part of the Schneiderian membrane, the respiratory portion. Hence if odors are faint, they are not detected, unless by a strong inspiration the air is carried up to and over that portion to which the olfactory nerves are distributed. If the nasal passages are closed by a catarrhal condition, the sense of smell is obtunded or may even be abolished temporarily. SENSE OF TASTE. 535 ' It is important to distinguish between the sense of smell and general sensibility. The mucous membrane of the nose has, in common with other mucous membranes and the skin, th$ power to recognize such physical properties in objects as consistency, temperature, etc. Thus if a sharp instrument was to be brought in contact with this membrane, it would be recognized as sharp, but this recognition is not due to the excitation of the olfactory nerves, but to the fibers of the trigeminus. The mucous mem- brane is therefore supplied by two nerves, the olfactory and the fifth. One is not liable to confound sharpness with odor, but the irritating effects of certain substances are often confounded with the sense of smell, when, as a matter of fact, it is not the olfactory, but the fifth pair, which is excited. Thus if acetic acid is brought in contact with the mucous membrane of the nose, it will excite the fibers of the fifth pair and will produce an irritating effect, but it would be incorrect to say that we smelled it. If, however, vinegar was substituted for the acetic acid, we should have the irritating effect of the acetic acid it contains, and in addition the olfactory nerves would be excited by the aromatic ingredients which, with the acid, form vinegar ; and it would therefore be cor- rect to say that we smelled the vinegar. The acuteness of the sense of smell differs in different indi- viduals, but in most it is well marked. It has been estimated that -g-Q of a milligram of musk may be detected by this sense, le emanations from objects which excite the sense of smell pro- duce this effect by stimulating the olfactory cells, and the impulses are carried by the olfactory nerves to the brain. Case of Julia Brace. A remarkable instance of the acuteness of the sense of smell is that of Julia Brace, an inmate of the Hartford Asylum, who became entirely deaf and blind at the age of four years and five months. The history of this case is given in the Life and Education of Laura D. Bridgman, by M. S. Lamson. This girl could select by the sense of smell her own clothes from a mass of dresses belonging to a hundred and thirty or forty persons. "She could discriminate, merely by smelling them, the recently washed stockings of the boys at the asylum from those of the girls. Among a hundred and twenty or thirty teaspoons used at the asylum she could distinguish those of the steward from those of the pupils." Her sense of touch was also acute. " By putting the eye of a cambric needle upon the tip of her tongue, she could feel the thread as it entered the eye and pressed upon her tongue, and she would thus thread the needle." Sense of Taste. The sense of taste exists to a slight degree in the middle of the dorsum of the tongue,, but is especially de- veloped in the posterior third of the dorsum. It is also present in its tip and edges and in the soft palate, but the exact area in which it resides has never been determined. ' :.,-- : ..:,- .-- --- 538 THE NERVOUS SYSTEM. branch of the glossopharyngeal nerve ; the apex is narrow and communicates with the cavity of the mouth by a small pore in the superficial epithelium gustatory pore. " The cells which compose the taste-buds are of two kinds, viz.: 1. The gustatory cells, which are delicate fusiform or bipolar cells composed of the cell-body or nucleated enlargement, and of two processes, one distal, the other proximal. The distal process is nearly straight, and passes toward the apex of the taste-bud, Papilla filiformis. ' y e&v-r- Tongue epithe- lium. ,v_ _ Connective-tissue papilla. *Ur- Mucosa. ilV-J , Basal epithelial layer. FlO. 315. From a cross-section of the human tongue, showing short, thread-like papillae (filiform) ; x 140 (Bohm and Davidoff). where it terminates in a small, highly refracting cilium-like appendage which projects into the bottom of the pore above mentioned. The proximal process is more delicate than the other, and is often branched and varicose. The nerve-fibers take origin in ramifications among the gustatory cells (Retzius). " 2. The sustentacular cells (Fig. 318). These are elongated cells, mostly flattened, and pointed at their ends ; they lie between the gustatory cells, which they thus appear to support, and in addition they form a sort of envelope or covering to the taste-bud. SENSE OF TASTE. 539 Between the cells of the taste-buds lymph-corpuscles are often seen, having probably wandered hither from the subjacent mucous membrane." H J^Bi oftSPR FlG. 316. Fungiform papilla from human tongue (Huber). Fig. 319 shows the nerve-endings in the taste-buds. The fact that the general sensibility of the tongue may be lost and the sense of taste remain indicates that the channels for the FIG. 317. Longitudinal section of foliate papilla of rabbit, showing taste-buds (Huber). transmission of these two sensations are different. It may be well again to call attention to the necessity for making a distinction between what may be tasted and what may be smelled, between savors and flavors. The sense of taste gives cognizance of the 540 THE NERVOUS SYSTEM. Epithe- lium. Process of neuro-epi- Nerve- thelial Taste- fibrils, cell. pore. .Tegmental cell. .Neuro-epithe- lial cell. Sustentacular cell. Terminal 1 branches of nerves. FlG. 318. Schematic representation of a taste-goblet (partly after Hermann). qualities sweet, acid, bitter, and saline; but to speak of an oily taste is incorrect: such a quality appeals to general sensibility only. The tip of the tongue is most sen- sitive to sweet tastes, the sides to acid, and the back to bitter. Conditions of the Sense of Taste. That the sense of taste may be exercised requires the presence of certain conditions, one of which is that the substance must be in a state of solution or be soluble in the saliva. Insoluble substances are tasteless : for this reason calomel is especially suitable as a cathartic for children. Another condition is that the mucous membrane of the mouth must be moist. When the mouth is dry and substances not already in a state of solution are taken in, there is no saliva present to dissolve them ; consequently they are not tasted. This absence of taste is very marked in the parched con- dition of the mouth occurring during fevers. To excite the sense of taste, sapid sub- stances must pass by osmosis into the pa- pillae of the mucous membrane and there stimulate the terminal filaments of the nerves which preside over this sense. An important agent in causing this absorption is the FIG. 319. Nerve-endings in taste-buds : n, nerve-fibers of taste-buds, 6; i, ending of fibrils within taste-bud ; p, ending in epithelium be- tween taste-buds; s, surface epithelium (G. Eetzius). SENSE OF SIGHT. 541 movement of the tongue. It is a matter of common observation that if sapid substances are simply placed on the tongue, the sense of taste is not excited ; but if the tongue is pressed against the roof of the mouth, absorption is promoted and the gustatory qual- ities are at once recognized. It is to be noted also that a savor persists for a certain length of time, and that if it is desired to determine the comparative qualities of different substances by the sense of taste, there must either be intervals between the tests or something must be used to obliterate the taste of the first before the second is taken into the mouth. It is also noteworthy that some savors so powerfully impress the taste-organs that others subsequently fail to make any impression. This principle is made practical use of in rendering disagreeable medicines tasteless. Thus a few cloves eaten before taking a dose of castor oil will render the latter far less nauseous ; a mouthful of brandy will have the same effect. Sense of Sight. The eyes are situated in the orbits, cavities formed by the frontal, sphenoid, ethmoid, superior maxillary, malar, lacrimal, and palate bones. Each eye is embedded in fat and enclosed in a serous sac, the capsule of Tenon or tunica vaginalis oculi. The transverse diameter of the eye 'is about 2.5 cm., while the anteroposterior and vertical diameters are about 2.25 cm. each. Coats or Tunics (Fig. 320). These are 3 in number : (1) Scle- rotic and cornea ; (2) choroid, ciliary processes, iris, and ciliary muscle ; and (3) retina. Sclerotic. This tunic forms the external coat of the eye for its posterior five-sixths, the anterior sixth being formed by the cornea. The sclerotic is opaque, and is made up of dense fibrous tissue with elastic fibers and connective-tissue corpuscles, and the white color of its visible external surface covered by conjunctiva causes this portion to be known as the white of the eye. The internal surface is lined by connective tissue, in which are brown pigment- cells, lamina fusca. This inner surface is grooved, and in these grooves lie the ciliary nerves. Posteriorly and on the nasal side the optic nerve pierces the sclerotic, which in this part is charac- terized by small openings, through which the fibers composing the optic nerve pass. This sieve-like structure has given to the scle- rotic at this point the name lamina cribrosa. The largest of these openings, porus options, is in the middle of the lamina, and through it passes the arteria centralis retinae (Fig. 328, A). En- circling the lamina cribrosa are openings in the sclerotic through which pass the ciliary vessels and nerves. Supplying the sclerotic itself, nerves have not been demonstrated. Cornea. This structure is transparent, and its relation to the sclerotic has been compared to that of a watch-crystal to the 542 THE NERVOUS SYSTEM. watch itself. It is the segment of a smaller sphere than the sclerotic. Its anterior surface is convex and covered by conjunc- tiva, its posterior surface concave, the curvature being less in old age. It is composed of four layers (Fig. 321) : (1) Stratified epi- thelium, next to the conjunctiva. (2) A thin layer of connective tissue, membrane of Bowman. (3) Fibrous connective tissue, proper substance of the cornea, which is made up of fibers arranged in lamellse, those of each of the sixty bundles being at right angles with those of the lamellae above and below it. Between the Blood-vessels Sphincter Vein. Canal of Petit, of the iris. Cornea, papillae. Iris. \ I -...- / Fontana's spaces. Ciliary Physiologic excavation. Macula lutea. Pigmenl layer, ~a \-b -- Sclera. '" Choroid ^Rectus muscle. Adipose tissue. FIG. 320. Schematic diagram of the eye : a, vena vorticosa ; 6, choroid ; I, lens (after Leber and Flemmiug). lamellae, and connecting them, is a cement substance, and in this are the stellate corneal spaces, each of which contains a corneal corpuscle, which gives oif branches that form with the processes of other corpuscles a continuous network. This third layer is of the same character as the sclerotic coat, and is continuous with it. (4) Membrane of Descemet or Demours', an elastic layer which, near the junction of the cornea with the iris, separates into fibers, ligamentum pectinatum. Some of these exist in the iris as its pillars. The fourth layer is covered by pavement epithelium, epithelium of Descemet' s membrane. This epithelium forms, there- SENSE OF SIGHT. 543 fore, the most posterior portion of the cornea, and inasmuch as the space directly behind the cornea is the anterior chamber, this epi- thelium forms the anterior boundary of this space. These epithelial Corneal epithelium, Basal cells. Anterior elastic membrane Substantia propria. FIG. 321. Section through the anterior portion of human cornea ; X 500 (Bohm and Davidoff). cells are continuous with those covering the anterior surface of the iris. The cornea contains no blood-vessels, these ending in the form Sclera. < Lamina supra- choroidea. Lamina vascu- losa Halleri. Lamina chorio- capillaris. Glassy layer. " FIG. 322. Section through the human choroid ; X 130 (Bohm and Davidoff). of loops at its circumference. Nor are there distinct lymphatics, though the channels which lodge the nerves are believed to serve this purpose. Branches of the ciliary nerves are supplied to it, 544 THE NERVOUS SYSTEM. varying in number from twenty-four to forty-five, according to different authorities. These nerves terminate in the subepitheliat plexus, beneath the superficial epithelium, from which fibers pass to the cells themselves, forming the intra-epithelial plexus. Choroid. This vascular and pigmented structure forms the posterior five-sixths of the second tunic of the eye. Its anterior boundary is the ciliary ligament formerly so called, but also known as the ring muscle of Mutter ; it is composed of the circular fibers of the ciliary muscle. Anterior to this is the iris. At the anterior margin of the choroid are the ciliary processes. The inner sur- face of the choroid is in contact with the retina. The choroid is composed of three layers: (1) lamina supra- choroidea (Fig. 322), the most external, consisting of connective tissue, elastic fibers, pigment-cells, and lymph-corpuscles. It is Corneal epithe- lium. Substantia pro- 1 pria. Deseemet's membrane. Canal of "" Schlemm. llris. ; Pigment-layer. -- Meridional fibers.") -^~ Radial fibers. h Miiller's fibers. { Sclera. Processus ciliares. FIG. 323. Meridional section of the human ciliary body; X20 (Bohm and Davidoff). in contact with the lamina fusca of the sclerotic. (2) Vascular layer; this is spoken of as the choroid proper; here are the blood-vessels of the choroid, consisting externally of branches of the short ciliary arteries, and veins arranged in a vorticose, whorled, or star-like form, constituting the vence vorticosce, which converge to form four or five main veins ; between these vessels are stellate pigment-cells. The inner portion of the vascular layer is the choriocapillaris or tunica Ruyschiana, a plexus of fine capillaries from the short ciliary vessels. (3) The most internal portion of the choroid is the lamina vitrea, glassy layer, or membrane of Bruch, a thin membrane, transparent, and ordinarily described as structureless, although Kolliker considers it to have a fibrous structure. This is in contact with the pigmentary layer of the retina. The arteries of the choroid are the short ciliary and the recur- SENSE OF SIGHT. 545 rent branches of the long and the anterior ciliary. Its nervous supply is the long and short ciliary nerves. Ciliary Processes (Fig. 323). The vascular layer of the choroid with the lamina vitrea is arranged anteriorly in folds the ciliary processes. These fit into corresponding folds of the suspensory ligament of the crystalline lens. Their number varies from sixty to eighty ; some being about 0.25 cm. in length, others shorter. In structure they are like the choroid, except that their blood-vessels are larger and are longitudinally arranged. On their posterior surface are pigment-cells, as there are also in the processes them- selves. Iris. This is a muscular and vascular structure in front of the crystalline lens and behind the cornea. In its center is a circular opening the pupil. Its structure is not unlike that of the choroid, and on its anterior surface are pigment-cells, the color of FIG: 324. Crystalline lens and suspensory ligament or zonula: 1, lens; 2, poste- rior, and 3, anterior portion of zonula ; 4, its insertion into the pre-equatorial region. The black rays are lines of pigment torn from the ciliary processes, and belong in reality to the ciliary portion of the retina (Testut). whose pigment differs in different individuals. Its posterior sur- face is covered with a layer of pigmented epithelial cells, the uvea, which is continuous with those of the pars ciliaris retinse. The iris is composed of four layers : (1) Most anteriorly is a layer of cells which is continuous with the epithelium of Desce- met's membrane, and in these there is pigment. (2) The stroma ; this consists of fibrous tissue, the fibers of which at the margin of the pupil are circular, elsewhere, and for the most part, radiating. Among these fibers are branched cells, containing pigment in persons whose eyes are dark, while in light eyes the pigment is absent. (3) A muscular layer consisting of the sphincter pupillce, which is composed of involuntary fibers circularly arranged around the pupil, and having a width of about 0.08 cm., and of the dilator pupillce, composed of fibers arranged in a radiating direction. (4) The pigmentary layer on the posterior surface of the 35 546 THE NERVOUS SYSTEM. Margin of pupil. iris. It is this pigment which, as seen through the layers of the iris anterior to it, gives the color to light eyes, while in those having dark eyes there is, besides, pigment in the fibrous tissue of the stroma and on the anterior surface of the iris. The albino is characterized by the colorless iris, in which no pigment is present. The arteries which supply the iris are branches of the long and anterior ciliary, which together form the circulus iridis major and minor, the former being an anastomotic ring at the outer margin of the iris ; the latter, a similar one near the pupil. The nervous supply of the iris is derived from the ciliary ganglion and from the nasal branch of the ophthalmic division of the fifth nerve through the long ciliary. The branches from the cil- iary ganglion contain fibers of the third nerve, which supply the circular muscular fibers or sphincter pupillse, and also sympathetic fibers, which are distributed to the radiating fibers or dilator pu- pillae. Membrana Pupillaris. The pupil during fetal life, until about the seventh or eighth month, is closed by a membrane. At this time it begins to be absorbed, and the absorption is almost en- tirely complete at birth. Ciliary Muscle (Fig. 323). Like the muscular fibers of the iris, this muscle is also of the unstriped variety. Its width is about 0.3 cm., and it consists of two parts, a ra- diating and a circular. The radiating or radial fibers are the more numerous, and have their origin at the junction of the cornea and sclerotic, sclerocorneal junction, and passing backward are attached to the choroid opposite the ciliary processes. Waldeyer states that one bundle is attached to the sclerotic. Internal to these are the circular fibers, running around the attachment of the iris, called circular ciliary muscle, ring muscle of Mutter, and formerly ciliary ligament. These fibers are said to be most marked in hyperme- tropic eyes. Choroid. FIG. 325. Injected blood-vessels of the human choroid and iris; X 7 (Bohm and Davidoff). SENSE OF SIGHT. 547 Ciliary Body. In this term are included the ciliary muscle and the ciliary processes. Retina. This is the most internal of the tunics of the eye, FIG. 326. The normal eye-ground as seen with the ophthalmoscope : n, optic nerve? head ; m, macula ; a, retinal artery ; v, retinal vein (Pyle). and is divided into two parts: (1) Pars optica retince, which extends as far forward as the ciliary body, where it ends in an Layer of nerve-fibers. Gangliou-cell- layer. Inner molecu- lar layer. Inner nuclear layer. Outer molecu- lar layer. Outer fibrous layer. Outer nuclear layer. Cones. Fovea centralis. FIG. 327. Section through human macula lutea and fovea centralis ; X 150. As a result of treatment with certain reagents, the fovea centralis is deeper and the margin more precipitous than during life (Bohm and Davidoff). irregular margin, ora serrata ; (2) pars ciliaris retince, composed of the fibrous stroma of the retina with the pigment-layer, with- 548 THE NERVOUS SYSTEM. out the nervous elements present in the pars optica. This portion passes forward as far as the outer margin of the iris. Macula Lutea (Figs. 326, 327). At the center of the retina posteriorly, and at the posterior extremity of the axis of the eye, FIG. 328. Diagrammatic representation of the retina. is the macula lutea, yellow spot of Sommerring, or limbus luteus, having a diameter of from 1 to 2 mm., an elevated spot in the retina where the sense of sight is most acute ; in its center is a depression, the fovea centralis, whose diameter is from 0.2 mm. FIG. 329. Schematic diagram of the retina, according to Ramon y Cajal: the line a, after passing through a Mailer's fiber, crosses a bipolar rod-cell, then two bipolar cone-cells, and finally ends in the body of a bipolar cone-cell, a', Nerve- fiber layer ; 6, ganglion-cell layer ; c, inner molecular layer ; d, spongioblast ; e, nucleus of Miiller's fiber ; /, inner nuclear layer ; g, bipolar cone-cell ; h, outer molecular layer ; i, outer nuclear layer ; fc, cone ; Z, rod ; m, centrifugal nerve-fiber ; n, impressions on Miiller's fiber of elements of outer nuclear layer ; o, fiber basket of Miiller's fiber; p, diffuse spongioblast ; q, large horizontal cell ; r, bipolar cell. to 0.4 mm. At the fovea the retina is so thin that the color of the choroid can be seen through it, and hence it has somewhat the appearance of an opening, and was formerly called foramen of Sommerring. For further discussion of the macula the reader is referred to p. 553. SENSE OF SIGHT. 549 Porus Opticus (Fig. 328). About 3 mm. to the nasal side of the macula lutea, and about 1 mm. below its level, is the optic disk, the entrance of the optic nerve ; inasmuch as vision is absent at Layer of nerve- fibers. Ganglion-cell layer. -- Inner molecular layer. Inner nuclear layer. Outer molecular -- layer. Outer nuclear layer. < Ext. limiting mem- brane. Inner segment of rod. Inner segment of cone. Outer segment of cone. Outer segment of rod. FIG. 330. Section of the human retina; X 700 (Bohm and Davidoff). this point, it is called the blind spot. At its center, through the porus opticus, enters the arteria centralis retince. As the retina is somewhat elevated at the blind spot, this portion of it has also re- ceived the name of colliculus nervi optici. . Lamina cribrosa. Pigment-layer, and cones. er nuclea er roolecu Layer of ner ayer. ar 'aver, layer, ar 'layer, e- fibers. Blood-vessels. Physiologic excavation. FIG. 331. Section through point of entrance of human optic nerve ; X 40 (Bohm and Davidoff). The arteria centralis retinae is a branch of the ophthalmid artery, and, after piercing the porus opticus, it divides into four or five branches which run between the hyaloid membrane and the 550 THE NERVOUS SYSTEM. nervous layer of the retina, later passing into the retina and ending in a capillary plexus external to the inner nuclear layer. During fetal life a small artery passes forward through the vitreous to the posterior surface of the capsule of the lens. In the fovea centralis there are no blood-vessels, and very few in the rest of the macula lutea. Minute Structure of the Pars Optica Retince (Figs. 329, 330, 331). The pars optica of the retina consists of ten layers, arranged in the following order, beginning with the most internal L e., with the layer next to the hyaloid membrane which encloses the vitreous humor and ending with the most external, the pigmentary layer which is contiguous to the lamina vitrea of the choroid : 1. Membrana limitans interna; 2. Nerve-fiber layer ; 3. Ganglionic layer ; 4. Inner molecular layer ; 5. Inner nuclear layer ; 6. Outer molecular layer ; 7. Outer nuclear layer ; 8. Membrana limitans externa ; 9. Layer of rods and cones ; 10. Pigmentary layer. 1. Membrana Limitans Interna. This is a transparent mem- brane, and a part of the supporting connective tissue of the retina, or the fibers of Miiller, in connection with which it is again referred to (p. 553). 2. Nerve-fiber Layer. This is sometimes described as the fibrous layer. It is composed, however, of nerve-fibers, and not of so-called fibrous tissue. The fibers of which it is composed are those of the optic nerve, and, as this enters the eye from behind, these fibers must pass through all the layers, excepting the membrana limitans interna, in order to reach the nerve-fiber layer. It will be re- membered that the fibers of the optic nerve pass through the lamina cribrosa of the sclerotic ; at this part of their course their medullary sheaths disappear and they become simple axis-cyl- inders, and as such they traverse the choroid and the retina until they reach the nerve-fiber layer, where they radiate from the point of entrance and terminate, some in the cells of the third or gan- glionic layer, while others pass through the third and fourth layers and terminate in the fifth or inner nuclear layer. The nerve-fiber layer is thickest at the point of entrance of the optic nerve, and, gradually becoming thinner, ends at the ora serrata i. e., anterior to this, nerve-fibers are not found in the retina. Or this may be stated in another way, by saying that nerve-fibers are found in the pars optica retinae, but not in the pars ciliaris retinae. 3. Ganglionic Layer. This is called also vesicular layer and layer of nerve-cells, and consists of a single layer of large ganglion- SENSE OF SIGHT. 551 cells. In the macula lutea the cells are smaller, and lie in several layers. The shape of these ganglion-cells- is peculiar, resembling somewhat those of Purkinje in the cerebellum. The portion which is in contact with the nerve-fiber layer is rounded, and from it is given off an axis-cylinder process which is continuous with one of the axis-cylinders which make up the nerve-fiber layer. From the opposite side of each cell is given off a thick process which branches, the branches ending in arborizations at different levels in the fourth or inner molecular layer. 4. Inner Molecular Layer. This is called also inner granular layer, by reason of its granular appearance, and also reticular layer. It is relatively thick, and consists of a reticulum of nerve-fibers with interspersed granules, of processes of the cells of the gan- glionic layer, and of those of the inner nuclear layer. 5. Inner Nuclear Layer. The characteristic elements of this layer are bipolar nerve-cells in which are large nuclei; these cells are called inner granules. , The process of each of these cells which passes inward terminates in arborizations in the inner molecular layer ; the process that passes outward terminates in a similar manner in the outer molecular' layer. There are two kinds of these bipolar cells : (1) Rod-bipolars and (2) cone-bipolars. The rod-bipolars are connected externally with the rods of the retina, and internally with the rods of the ganglionic layer. The cone-bipolars are connected with the cones of the retina exter- nally, while internally they ramify in the middle of the inner molecular layer. In addition to bipolar cells there are amacrine-cells, so called because they lack long processes, although from some of them axis-cylinder processes are given off which may extend into the nerve-fiber layer. The bodies of these cells are often partly in the inner molecular layer, and they are sometimes called sportgio- blasts of the inner molecular layer. From them are given off branching processes or dendrons which pass into the inner molec- ular layer. Horizontal cells of Cajal or spongioblasts of outer molecular layer are cells in this layer which send processes into the outer molecular layer. 6. Outer Molecular Layer. This is a thin layer, and consists of the arborizations of the inner nuclear layer, of the rod- and cone-fibers, and of the horizontal cells of Cajal. Schafer states that up to this point i. e., including the outer molecular layer the retina may be regarded as composed of nervous elements, but beyond it is to be considered as formed of modified epithe- lium-cells. 7. Outer Nuclear Layer. In this layer are found cells charac- terized by transverse striations, passing off from which externally are processes connected with the rods of the ninth layer, by reason 552 THE NERVOUS SYSTEM. of which arrangement they are called rod-granules. These gran- ules also give off processes which pass in an inward direction and terminate in the outer molecular layer. In the outer nuclear layer are also cone-granules ; these are connected with the cones of the ninth layer externally, and internally by a thick process which becomes bulbous, the so-called cone-foot; they terminate in fine fibers in the outer molecular layer. 8. Membrana Limitans Externa. This is, together with the membrana limitans interna and the fibers of Muller, a part of the supporting structure of the retina. Indeed, some authorities include neither of these membranes in the list of layers which compose the retina, and hence describe it as made up of eight rather than of ten layers. 9. Layer of Rods and Cones. This is called also Jacob 's mem- brane and bacillary layer. It is characterized by the presence of rods and cones, of which the former are much more numerous 1 , taking the retina as a whole. Relatively the cones are more numerous at the back of the retina, but less so in the anterior part. Rods. A rod is a solid body set perpendicularly to the sur- face at whatever part of the retina it may be. It is made up of an outer and an inner portion, the two being cemented together. The outer portion is cylindrical and characterized by transverse striae ; it has during life a purplish-red color. The inner portion has striae longitudinally arranged. This portion is slightly bulged, and becomes stained with carmine or iodin, while the outer portion does not take the stain. Cones. Each is conical in form, with its base lying on the membrana limitans externa. The apex is tapering. Like the rods, each cone is made up of an outer and an inner portion ; the outer conical apex presenting transverse striae, the inner portion being striated longitudinally. Both rods and cones present a granular appearance near the membrana limitans externa. Schafer describes the outer nuclear layer and the layer of rods and cones as one, under the name sensory or nerve-epithelium of the retina, inasmuch as their elements are continuous through the two layers. He says : " The elements of which this nerve- epithelium consists are elongated, nucleated cells of two kinds. The most numerous, which we may term the rod-elements, consist of peculiar rod-like structures (rods proper) set closely side by side, and each of which is prolonged internally in a fine varicose fiber (rod-fiber) which swells out at one part of its course into a nucleated enlargement, and ultimately ends (in mammals) in a minute knob within the outer molecular layer, where it is embedded in the ramifications of the dendrons of the rod-bipolars. The rod proper consists of two segments, an outer cylindrical and transversely striated segment, which during life SENSE OF SIGHT. 553 has a purplish-red color, and an inner slightly bulged segment, which in part of its length is longitudinally striated. The nucleus of the rod-element often has, in the fresh condition, a transversely shaded aspect. The cone-elements are formed of a conical tapering external part, the cone proper, which is directly prolonged into a nucleated enlargement, from the farther side of which the cone- fiber, considerably thicker than the rod-fiber, passes inward, to terminate by an expanded arborization in the outer molecular layer ; here it comes into relation with a similar arborization of dendrons of a cone-bipolar. The cone proper, like the rod, is formed of two segments, the outer of which, much the smaller, is transversely striated, the inner, bulged segment being longitudi- nally striated. The inner ends of the rod- and cone-fibers come, as already stated, in contact with the peripheral arborizations of the inner granules, and through these elements and their arbori- zations in the inner molecular layer a connection is brought about with the ganglionic cells and nerve-fibers of the innermost layers. There appears, however, to be no anatomic continuity between the several elements, but merely an interlacement of ramified fibrils. 10. Pigmentary Layer. This layer is called also tapetum nigrum, and consists of a single layer of hexagonal, pigmented cells in contact with the choroid. These cells send offsets inward be- tween the rods. The pigment is in the form of minute crystals, and when the cells have been exposed to light for a considerable time they are found in the filaments just described as extending between the rods. It is supposed that the function of these pig- ment-granules is to restore the purple coloring-matter which has been bleached by prolonged exposure to light. In the horse and many carnivora these cells contain no pigment. Fibers of Mutter. The layers of the retina between the in- ternal and external limiting membranes are traversed by long, stiff cells, the fibers of Mutter. At their bases they expand, and the tissue joining these expanded bases forms the membrana limitans interna. At the outer nuclear layer the fibers branch and form a fenestrated tissue supporting the fibers and nuclei of the rod- and cone-elements. At the junction of the outer nuclear and bacillary layers the fibers form the membrana limitans externa, from which sheaths pass around the bases of the rods and cones. In that portion of the fiber which lies in the inner nuclear layer is an oval nucleus. The arrangement of these fibers of Muller and the limiting membranes has been well described " as columns between a floor and a ceiling." Macula Lutea (Figs. 326, 327). The retina at the yellow spot, except at the fovea centralis, a part of the macula lutea, is thicker than elsewhere ; the middle of the fovea is the thinnest part of the retina. The ganglion-cells are more numerous in the macula, as are the cones when compared with the rods. In the fovea the rods 554 THE NERVOUS SYSTEM. are absent, and the cones are long and slender. This portion of the retina consists of but little else than cones and the outer nuclear layer ; the cone-fibers are very distinct and nearly horizontal. Pars Ciliaris Retince. At the ora serrata the pars optica retinae terminates, and the pars ciliaris retinae begins. It consists of two layers : An external layer of pigment-cells which are the continuation of the tapetum nigrum, and an internal, of columnar cells with oval nuclei, modified fibers of Miiller. The pigmented epithelium is continuous with the uvea of the iris. The sensory epithelium receives its nourishment from the blood-vessels of the choroid. Anterior and Posterior Chambers. The anterior chamber is that portion of the cavity of the eye situated between the cornea and the iris ; the posterior chamber, the space between the iris in front ; and the capsule of the lens, the suspensory ligament and the ciliary processes behind. Inasmuch as the iris is in contact with the capsule for the greater part of its extent, this " chamber " is ex- ceedingly small, and hardly deserves the name. In fetal life these two chambers are separated by the membrana pupillaris, but about the seventh or eighth month, when the membrane begins to be absorbed, they become one cavity, and are filled with aqueous humor (p. 556). Some authorities describe the cavity containing the vitreous under the name " posterior chamber." Vitreous Body. This is called also vitreous humor. It is a transparent, jelly-like material which fills the cavity of the retina and is enclosed in a delicate membrane, the hyaloid membrane. At the pars ciliaris retinae this membrane splits into two layers, an anterior and a posterior. The anterior layer becomes the suspen- sory ligament of the lens, while the posterior passes behind the lens and covers the anterior portion of the vitreous ; at this part there is a depression in the vitreous in which the lens lies. In the vitreous are found fibers and some cells, the bodies of which con- tain large vacuoles and give off long and varicose processes. Through its center in fetal life runs a small artery from the arteria centralis retinae to the capsule of the lens, but in the adult this is a simple channel, canal of Stilling, which is lined by a portion of the hyaloid membrane. Crystalline Lens (Fig. 332). The lens is a transparent body, biconvex in form, the convexity being greater posteriorly than anteriorly. Its transverse diameter is about 0.8 cm., and its anteroposterior diameter about 0.6 cm. It consists of concentric layers or lamina? ; those that are centrally situated form the nucleus, and are harder than the external, which are relatively soft. If the lens is boiled or hardened in alcohol, these laminae may be peeled off like the coats of an onion. The laminae are composed of long fibers with serrated edges, which fit into corre- sponding serrations of adjoining fibers. When cut transversely, SENSE OF SIGHT. 555 the fiber is seen to be a hexagonal prism. The superficial fibers contain nuclei, giving to the external layer the name nucleated layer. The fibers are developed from epithelium-cells. The centers of the anterior and posterior surfaces are the poles, and the margin of the lens, where these surfaces meet, is the equator. During fetal life the lens is nearly spherical, not very trans- parent, and quite soft in consist- ence ; in adult life its posterior surface is more convex than the anterior, and it is transparent. Its consistence has already been described. In old age its con- vexity and transparency are diminished and its density in- creased. Capsule .of the Lens. This, like the lens, is transparent ; it is structureless and elastic. At the front and the sides of the capsule on its inner surface is a layer of cubical epithelium, the epithelium of the capsule. These cells are elongated at the margin of the lens and become lens-fibers. This epithelium is absent from the posterior sur- face. The suspensory ligament is attached to the capsule around its circumference. Anteriorly the capsule and the border of the iris are in contact; at the circumference they are slightly separated, the space thus left being the posterior chamber. Suspensory Ligament. This is the anterior part of the hyaloid membrane which divides into two layers at the pars ciliaris retinae. Its anterior surface is arranged in folds, in the depressions of which the ciliary processes lie. From these processes the liga- ment passes to the capsule of the lens. Its function is to assist in retaining the lens in position. Chemistry of the Eye. Cornea. An analysis of the cornea shows that it consists of the following ingredients : Water, 75.8 per cent. ; collagen, 20.4 per cent. ; other organic matter, 2.8 per cent. ; and ash, 1 per cent. Retina. This tunic has been analyzed in geese, with the fol- lowing result : FIG. 332. Crystalline lens : A, longi- tudinal fibers ; a, anterior capsule ; 6, anterior epithelium; c, lens-fibers. B, posterior surface view of anterior epithe- lium (Leroy). 556 THE NERVOUS SYSTEM. Water 86 to 89 per cent. Solids 14 "11 " Proteids (globulin coagulating at 50 per cent., albumin, and mucin) 4 6 Gelatin 13 17 Cholesterin 0.3 0.8 Lecithin 1 2.9 Fat 0.05 0.5 Salts 0.7 1.2 Retinal Pigments. The black retinal pigment is fuscin, and is Practically identical with the pigment of the iris and choroid. t belongs to the group of pigments called melanins, and differs but little if at all from the coloring-matter in the skin of negroes and in melanotic tumors. Fuscin contains iron, but it is still undecided whether it is derived from hemoglobin or not. Rhodopsin or visual purple is the pigment in the outer portion of the retinal rods ; it bleaches out when exposed to light, and is supposed to be derived from fuscin. The chemistry of this pig- ment is undetermined. Of the yellow pigment characteristic of the macula lutea but little is known. Aqueous Humor. This fluid is lymph. Its analysis is as follows : Water 98.687 per cent. Solids 1.313 " {Fibrinogen ^ Serum-albumin L 0.122 " Serum-globulin J Extractives 0.421 " Inorganic salts 0.77 " Sodium chlorid 0.689 " Vitreous Humor. From the hyaloid membrane gelatin may be obtained, also mucoid and a small amount of proteid. Crystalline Lens. The following is the analysis of the lens : Water ' 63.5 percent. Solids Proteids . Lecithin . Cholesterin Fats . . . Salts 36.5 34.93 0.23 0.22 0.29 0.82 The proteid is a globulin called crystallin or, rather, a-crys- tallin and ^-crystallin ; there is also a small amount of albumin in the lens. In the " proteids " is a considerable amount about 48 per cent. of an albuminoid substance, insoluble in water and saline solutions. Ocular Muscles (Figs. 333, 334). The muscles which move the eyeball are 6 in number : (1) Superior rectus ; (2) inferior rectus ; internal rectus ; (4) external rectus ; (5) superior oblique ; inferior oblique. SENSE OF SIGHT. 557 Superior Rectus. Its origin is from the upper margin of the optic foramen and the fibrous sheath of the optic nerve ; its inser- tion is into the sclerotic, about 0.6 cm. from the margin of the cornea. Nerve-supply is from the oculomotorius. Inferior Rectus. Its origin is, in common with the internal rectus, from the ligament or tendon ofZinn; this is an aponeurosis which is attached around the circumference of the optic foramen, with the exception of the upper and lower parts ; its insertion is FIG. 333. Ocular muscles viewed after removal of lateral wall of orbit : a, eye- ball; 6, optic nerve; c, c', eyelids; d, maxillary sinus; e, pterygoid plate; /, fora- men rotundum ; g, roof of orbit ; h, frontal sinus ; i, supra-orbital nerve ; k, septum orbitale ; 1, levator palpebrse superioris; 2, 3, superior and inferior recti ; 4,4', por- tions of the cut external rectus ; 5, internal rectus ; 6, inferior oblique ; 7, insertion of superior oblique; 8, annular ligament of tendon of Zinn (Testut). into the sclerotic, about 0.6 cm. from the cornea. Nerve-supply is from the oculomotorius. Internal Rectus. Its origin is from the ligament of Zinn ; its insertion, into the sclerotic, about 0.6 cm. from the cornea. Nerve- supply is from the oculomotorius. External Rectus. Its origin is by two heads, the upper from the outer margin of the optic foramen, and the lower from the ligament of Zinn and a bony process at the lower margin of the sphenoidal fissure ; its insertion is into the sclerotic, about 0.6 cm. 558 THE NERVOUS SYSTEM. from the margin of the cornea. Nerve-supply is from the ab- ducens. Superior Oblique. Its origin is from above the inner margin of the optic foramen ; thence it passes to the inner angle of the orbit, where it terminates in a rounded tendon which plays through a fibrocartilaginous ring. It passes under the superior rectus, and FIG. 334. Ocular muscles of right side, viewed from above, after removal of roof of orbit: A, frontal bone ; B, section of great wing of sphenoid ; C, section of malar bone ; D, anterior clinoid process ; E, optic nerve ; 1, superior rectus ; 2, superior oblique muscle with its pulley (2') and its insertion into the eyeball (2") ; 3, inter- nal rectus ; 4, external rectus ; 5, common origin (ligament of Zinn) of muscles ; 6, cut tendon of levator palpebrse; 7, 7', 7", palpebral expansion of same; 8, inser- tion of inferior oblique ; 9, intra-orbital cushion of fat ; 10, orbicularis palpebrarum (Testut). its insertion is into the sclerotic, between the superior rectus and the external rectus, midway between the cornea and the optic nerve. Nerve-supply is from the trochlearis. Inferior Oblique. Its origin is from the orbital plate of the superior maxilla, external to the lacrimal groove for the nasal duct ; its insertion is into the sclerotic, between the superior rectus SENSE OF SIGHT. 559 and the external rectus, behind the insertion of the superior oblique. Nerve-supply is from the oculomotorius. Functions of the Ocular Muscles (Figs. 335, 336). The supe- rior rectus turns the eye upward and inward ; when the eye is turned directly upward this is brought about by the conjoint 4 4 6 6 FIG. 335. Movements of the eyeballs: 1, inferior oblique; 2, superior rectus; 3, external rectus ; 4, internal rectus ; 5, superior oblique ; 6, inferior rectus. action of the superior rectus and the inferior oblique. The in- ferior rectus turns the eye downward and inward ; when the eye is turned directly downward, this is effected by the conjoint action of the inferior rectus and the superior oblique. The internal FIG. 336. Horizontal section of left eye. Arrows show direction of pull of the muscles. The axis of rotation of the external and internal recti would pass through the intersection of a and at right angles to the plane of the paper (Stewart). rectus turns the eye inward ; the external rectus turns it outward. The superior oblique rotates the eye outward on its anteroposterior axis, and corrects the inward deviation of the inferior rectus. The inferior oblique rotates the eyeball outward on its anteroposterior axis, and corrects the inward deviation of the superior rectus. 560 THE NERVOUS SYSTEM. Physiology of Vision. The eye has very aptly been compared to a photographic camera, the transparent structure, through which pass the rays of light, representing the lenses, and the retina representing the sensitive plate on which the image is received, while the pigmented choroid coat is the representative of the lampblack with which the photographer darkens the interior of the camera-box to prevent any reflected light striking the plate and interfering with the sharpness of the picture. In the camera, in order to bring to a focus upon the plate the rays of light coming from objects at different distances, the photographer uses a focus- sing screw, by which the lens may be moved nearer to or farther from the object he wishes to photograph ; and in order that clear images may be obtained by the eye it is necessary to accomplish the same result, for when the eye is focussed for near objects, those at a distance are blurred, and vice versd.^ This fact may readily be demonstrated by looking through a piece of mosquito-netting at the windows of a house on the opposite side of a street. When FIG. 337. Principal focus of a lens. The parallel rays, a, 6, c, d, are refracted by the lens so as to unite at the point F on the axis P; the ray P undergoes no refraction. F is the principal focus. the threads of the net can be seen distinctly, the bars of the window will be indistinct, and when the bars of the window are clear and distinct, then the threads are blurred. In the optical apparatus of the eye there is no provision for altering the position of the lenses, but there is one which answers the same purpose, and which is called accommodation. In connection with every camera there is an arrangement of openings or diaphragms by which a greater or lesser amount of light may be admitted, according to circum- stances. In the eye the iris serves a similar purpose. In many cameras it is necessary to have a number of such diaphragms, each having an opening of a different size, but some are provided with a single one, the size of whose opening can be altered ; this is called an " iris diaphragm," and is a rude contrivance compared with the natural iris from which it derives its name, and which by means of its muscular fibers can alter in a moment the size of the pupil. Rays of light coming from an object, in order to produce a distinct image of that object, must be brought to a focus upon the retina (Fig. 337). If the media through which the light from an SENSE OF SIGHT. 561 object passes to reach the retina were all of the same density as the air, and were also plane surfaces, an impression would be produced, but there would be no distinct image. Actually, before such rays do reach the retina they pass through certain media which, by reason of both density and shape, refract them and bring them to a focus, thus producing a sharp and distinct image of the object looked at. These media are the cornea covered with a layer of tears, aqueous humor, crystalline lens with its anterior and poste- rior capsule, and vitreous humor, seven in all. The amount of refraction is determined by the radius of curvature of the surface through which the rays pass, the refraction being greater as the radius becomes smaller, and by the difference between the refrac- tive indices of the media, refraction increasing as the difference increases. The radii of curvature are as follows : When accommodated for Far vision. Near vision. Cornea 8mm. 8 mm. Anterior surface of lens 10 " 6 " Posterior " " " 6 " 5.5 " The refractive indices of the various media through which the light passes are as follows : Tears l.J Cornea 1.337 Aqueous humor 1.3365 Vitreous " 1.3365 Lens (mean for all layers) 1.437 The refractive index of air is 1.000, and of water 1.335. From this table it will be seen that the tears, cornea, and aqueous humor have practically the same indices of refraction, and we may there- fore regard the media through which light passes to reach the retina as three in number: 1, tears, cornea, and aqueous humor, with a refractive index of 1.33; 2, crystalline lens, with a re- fractive index of 1.43; and 3, vitreous humor, with a refractive index of 1.33. The following table gives the distances between the various points mentioned therein : When accommodated for Far vision. Near vision. Anterior surface of cornea and anterior surface of lens . . 3.6 mm. 3.2 mm. " " " " posterior " " . . 7.2 " 7.2 " " lens " " " " . . 3.6 " Posterior " " retina " . . 14.6 " 14.6 " The anteroposterior diameter of an em me tropic eye along the axis is 21.8 mm. 36 562 THE NERVOUS SYSTEM. The data here given are known as optical constants, and the figures may be regarded as averages, individual eyes differing, as would naturally be expected. Reduced Eye (Fig. 338). For purposes of calculation, an imaginary eye, the reduced or schematic eye, has been proposed, FIG. 338. The reduced eye: S, the single spherical refracting surface, 1.8 mm. behind the anterior surface of the cornea; N, the nodal point, 5 mm. behind S ; F, the principal focus (on the retina), 20 mm. behind S. The cornea and lens are put in in dotted lines in the position which they occupy in the normal eye (Stewart). whose refractive medium is a single one, representing, approxi- mately enough for practical purposes, the natural eye. This eye has the following characteristics (Listing) : From anterior surface of cornea to the principal point From nodal point to the posterior surface of lens Posterior principal focus behind cornea . . . . Anterior principal focus in front of cornea . . Kadius of curvature of single refracting surface Index of refraction of single refractive medium . 2.3448 mm. . 0.4764 . 22.8237 . 12.8326 . 5.1248 1.33 The optical and visual axes may be regarded as identical, and as represented by a line which passes through the centers of cur- vature of the cornea and lens directly backward until it terminates FIG. 339. Diagram of the formation of a retinal image (after Foster). in the fovea centralis. Rays of light falling upon the cornea are refracted and made convergent, and this effect is increased by the SENSE OF SIGHT. 563 lens and vitreous, so that when the rays reach the retina they are brought to a focus. This is shown in Fig. 339, where the arrow XY is projected upon the retina, forming the inverted image YX. The angle xnY is the visual or optical angle, also called the angle of vision, and determines the size of the image upon the retina. If an object subtends an angle less than 50 seconds, it cannot be seen, because the size of the image upon the retina would be less than 3.65 p. ; the distance between the centers of two adjacent cones being about 4 //, each cone having a diameter of about 3 fi. Retinal Images are Inverted. By reference to Fig. 339 it will be seen that the retinal image is inverted the question nat- urally arises, therefore, Why are not the objects which form these images seen in an inverted position ? The answer to this question is that objects are "seen" by the brain, and not by the retina; that certain impressions are produced by the light upon the retina ; and that these impressions are transmitted to the brain by the optic nerve, and are there interpreted in the form of what is A FIG. 340. Diagram illustrating the projection of a shadow on the retina. called " sight." The brain has by long experience come to asso- ciate the top of an object with the image which the top of the object produces on the retina, so that although the upper end of an object as the point of an arrow, for instance makes its image below, and the lower end or, in the supposed instance, the head of the arrow forms its image above, the brain sees the arrow with its point up and the head down. Light which reaches the retina is always referred by the brain to an object situated on the opposite side. Thus light which reaches the right side of the retina comes from the left, and that which reaches its left side comes from the right. It is a curious fact that when an upright object makes an upright image on the retina, the brain inverts the object, so that it is seen in an inverted position. This is illustrated in Fig. 340, for which and for the recital of the fact we are indebted to the American Text-book of Physiology. If a card with a small pin- hole in it is placed in front of a source of light and about three or 564 THE NERVOUS SYSTEM. .4 four centimeters from the eye, and the head of a pin is held as close as possible to the cornea, the pinhole becomes a source of light, and the shadow of the pin, not the image for the pin is too near the eye to form an image falls on the retina. This shadow is an upright one, and yet the pinhead appears inverted, for the reason that the brain has become accustomed to interpret all im- pressions made upon the retina as corresponding to objects in the opposite portion of the field of vision. In the illustration, AB is the card with the pinhole, P the pin, and p' its upright shadow on the retina. Accommodation (Figs. 341, 342). The eye possesses the capa- bility of adjusting itself to seeing objects at varying distances ; this is accommodation. If the entire optical apparatus of the eye was rigid and immovable, it would be necessary, in order to obtain FIG. 341. Anterior quadrant of a horizontal section of the eyeball, cornea and lens cut in the middle of their vertical diameter: a, substantia propria of the cornea; 6, Bowman's membrane; c, anterior corneal epithelium; d, Descemet's membrane; e, its epithelium; /, conjunctiva; g, sclera ; h, iris; i, sphincter muscle of the iris ; j, pectinate ligament of the iris with the adjacent fenestrated tissue ; k, canal of Schlemm ; I, longitudinal, m, circular fibers of the ciliary muscle ; n, cil- iary process ; o, ciliary portion of the retina ; q, canal of Petit, with the zonule of Zinn (Z) in front of it, the posterior leaflet of the hyaloid membrane (P) behind it ; r, anterior, s, posterior, capsule of the lens ; <, choroid ; n, perichoroidal space ; T, pigment epithelium of the iris; x, margin (equator) of the lens. (Landois). a clear image of an object, either for the individual to approach or to recede from the object, or to cause the object to do the same with reference to him, for only parallel rays, namely, rays coming from objects at a distance of two to three meters or more, are brought to a focus in the normal eye unless some change is brought about in SENSE OF SIGHT. 565 the refractive media. If an object is within that distance, the rays of light coming from it are brought to a focus by altering the shape of the crystalline lens ; this is positive accommodation. As already stated, the optical apparatus of the eye is in a state of rest when it is looking at objects more than two to three meters CS 1 FIG. 342. Diagrammatic representation of accommodation for near and far ob- jects. On the right the condition during positive accommodation is shown, on the left the condition during rest (negative accommodation). On both sides one-half of the contour of the lens is drawn as a continuous line, the other half as a dotted line. The letters appearing twice on both the right and left sides have the same sig- nificance ; those on the right side are primed A, left, B, right half of the lens; C, cornea ; i -r>/ ^ At B and E' there are two prisms, in front of which a candle-flame is placed. The eye of the observer at A sees two sets of the three reflected images, each image being a square spot of light ; those reflected from the ante- rior surface of the lens approach those reflected from the cornea, as already explained, and also approach each other (Fig. 346). Tscherning's Theory of Accommodation. This authority ex- plains positive accommodation by supposing that by the contrac- tion of the anterior part of both the radiating and circular fibers of the ciliary muscle the ciliary processes are drawn backward, and that this pulls the zonule of Zinn (suspensory ligament) backward and outward. This increases the tension of the ligament and the pressure upon the lens, the external or softer portion of which is caused to bulge out, this change being especially marked on its anterior surface. The contraction of the posterior portion of the ciliary muscle pulls forward the choroid, and thus makes tense, so to speak, the vitreous, preventing it from yielding when the lens is pressed against it by the anterior portion ; thus the pressure of SENSE OF SIGHT. 569 the anterior portion of the muscle causes the increased con- vexity of the lens, and not its displacement backward. Schoen's Theory of Accommodation (Fig. 347). This writer explains the increased convexity of the lens by assuming that the contraction of the ciliary muscle produces the same effect on the lens as is produced upon a rubber ball when held in both hands and com- pressed by the fingers. The theories of Tscher- ning and Schoen presupposes a stretching of the zonule of Zinn, while that of Helmholtz is based on its relaxation. Recent observations of Hess seem to demonstrate that the change in this structure is one of relaxation rather than increased tension, so that at the present time the theory of Helmholtz may be accepted as the true explanation of accommodation. Range of Accommodation. The point nearest to the eye to which objects can be brought and be seen distinctly is the near- point ; while the point farthest from the eye at which distinct vision exists is the far-point FIG. 347. To illus- trate Schoen' s theory of accommodation. intervening space is the range of accommodation. the length of the FIG. 348. Scheiner's experiment. In the upper figure the eye is focussed for a point farther away than the needle ; in the lower, for a nearer point. The continuous lines represent rays from the needle, the interrupted lines rays from the point in focus. Near-point. This is also called punctum proximum, and is ex- pressed by p.p. It varies in different individuals, but for a normal adult eye is about 12 cm. Objects brought nearer to the eye than this cannot be seen with distinctness, for the refractive media cannot bring the image of such objects to a focus upon the retina. The near-point for any given eye may be determined by Scheiner's 570 THE NERVOUS SYSTEM. experiment (Fig. 348). In a "card two pinholes are made whose distance from each other must not exceed the diameter of the pupil, about 2 mm. Through these holes, with the card held close to the eye, a needle is looked at. It will appear single ; if the needle is brought near to the eye, a point will be reached at which it appears double, or it may be blurred ; this is the near-point for the eye in question. Far-point. This is also known as punctum remotum, or p. r. It is the farthest point at which objects can be seen distinctly by a normal eye, and is infinitely distant ; so that the range of accom- modation in the normal eye is from about 12 cm. to infinity. Asj a matter of fact, rays of light which reach the retina from any object not more than two meters distant from the eye are practi- cally parallel, so that in looking at objects at any distance greater than this there is no change in the accommodative apparatus i. e.j the eye is in a state of accommodative rest ; while as objects are brought nearer than two meters there is necessitated an increase in the convexity of the lens in order that. they may be seen dis- tinctly until the near-point is reached, within which their images become blurred by reason of the fact that the lens has reached the limit to which its convexity can be increased. Convergence of the Eyes during Accommodation. If, as an object is brought nearer to the eyes of an observer, his eyes are inspected by another, it will be seen that, as the accommodative apparatus is brought into action to focus the image on the retina, the eyes are at the same time turned inward i. e., made to converge. When it is remembered that in order to produce distinct vision the image must be formed in the fovea centralis, it will be seen that as the object is brought nearer to the eyes each eye must be turned in- ward, otherwise the image would not fall upon the fovea. Contraction of the Pupil during Accommodation. When a dis- tant object is observed, the pupil is relatively large ; but when the eye is accommodated for near objects, the pupil becomes smaller. By this contraction of the iris the very divergent rays which come from the object, and which, by reason of their extreme divergence, would not be brought to a focus on the retina, are excluded, and thus a sharpness of the image is secured which would not be the case if the pupil was large enough to admit these rays. Defects in the Visual Apparatus. Emmetropia (Fig. 349, A). The emmetropic or normal eye is one in which parallel rays are brought to a focus upon the retina when the eye is in a state of accommodative rest. In such an eye the near-point is about 12 cm. distant from the eye, the far-point at infinity, and from about two meters distant to an infinite distance objects can be distinctly seen without any change in the accommodative apparatus. SENSE OF SIGHT. 571 Ametropia. Whenever the permanent condition of an eye is not as described above, it is one of ametropia. Of this condition, there are several varieties. Myopia (Fig. 349, B). A myopic eye is one that is abnormally elongated, and some au- thorities regard an in- creased convexity -of the lens as constituting an essential part of this con- dition. The retina is so far from the lens that parallel rays are focussed in front of it, and, cross- ing, do not form distinct images on the retina, the images being blurred. To correct this,concave glasses are used, which cause these rays to diverge as they en- ter the eye, and by adjust- ing the concavity to the amount of myopia, par- allel rays are brought to a focus on the retina as they are in the emme- tropic eye without glasses. A myopic eye is commonly said to be a " near-sighted " one. The near-point in myopia may be 5 or 6 cm. from the eye, while the far- point is comparatively near FIG. 349. Diagram showing the difference between (.4) emmetropic, (B) myopic, and (C) hypermetropic eyes. the eye, never at an infinite distance, so that the range of accom- modation is extremely limited. Hypermetropia (Fig. 349, C). In this condition the eye is shorter than normal, and the retina is too near the lens, so that parallel rays are brought to a focus behind the retina and indis- tinct vision is produced, as in the myopic eye. In the endeavor to overcome this defect the ciliary muscle is liable to overstrain in order to converge the rays to a focus upon the retina, and the constant effort is painful and injurious. The condition is corrected by the use of convex glasses. The near-point in the hypermetropic eye is farther than in the normal eye. The far-point does not exist, for objects would of necessity have to be removed to a greater distance than infinity, which is, of course, impossible, in order that the rays coming from them might be converging, and 572 THE NERVOUS SYSTEM. thus these rays be brought to a focus upon the retina when the eye was in a state of accommodative rest. Presbyopia, which is sometimes called " old sight," sometimes " long sight," is the condition of the eye present in elderly people. In this condition it is difficult to see near objects, although the vision for those at a distance is unaffected. It is usually attrib- uted to a lessened elasticity of the lens, though the ciliary muscle is also less strong ; some writers state that it depends on dimi- nution of the convexity of the cornea. To aid in correcting it convex glasses are used. Presbyopia may begin as early in life as the fifteenth year, although it commonly does not until about the fortieth year. The ability to see objects nearer by in advanced age, when pre- viously spectacles were required, is explained by an increased refractive power which sometimes occurs under such conditions. FIG. 350. Lines for the detection of astigmatism. Astigmatism (Fig. 350). In this condition the cornea is usually at fault, its curvature being greater in one meridian than in another, and consequently the rays of light from an object are not all brought to the same focus, and the image, therefore, is not distinct. Astigmatism is regular when the curvature in any given meridian is regular in that meridian, although the meridian may differ in respect to curvature when compared with the one at right angles to it : the cornea is ellipsoidal and not spherical. Astigmatism is irregular when in any given meridian or meridians the curva- ture of the cornea is not an arc of a circle or an ellipse. It is irregular astigmatism which causes the stars to look as though rays projected from them. For the correction of regular astigma- tism glasses are worn which are segments of a cylinder that is, curved in but one direction and are known as " cylindrical " glasses. Irregular astigmatism cannot be corrected by any glasses. The crystalline lens may also be at fault in astigmatism. Regular astigmatism is detected by the observation of con- centric rings or radiating lines, as in Fig. 350. In the former SENSE OF SIGHT. 573 some portions will be blacker and more distinct than others, while in the latter the lines will present the same differences. Spherical Aberration (Fig. 351). When rays of light are refracted, those which are incident near the edge of the lens are refracted more than those near the principal axis, and will, therefore, come to a -focus in front of them, and produce an indistinctness of the image. This indefiniteness of focus is spherical aberration. To reduce this, a diaphragm is used in optical instruments, by which these marginal rays are excluded, or, as in large telescopic lenses, the same result is accomplished by diminishing the curvature of the lens at its margin. This FIG. 351. Diagram showing the effect of a diaphragm in reducing the amount of spherical aberration. defect exists in the eye, and is lessened by the iris, which serves as a diaphragm to cut off the marginal rays, and also by the diminished refractive power of the marginal portions of the lens as compared with its center. Spherical aberration is more marked with divergent than with parallel rays, and as rays are more divergent the nearer the object from which they come is to the eye, this is corrected by the greater contraction of the iris i. e., the greater diminution of the pupil which results in cutting off more of the marginal incident rays. In the human eye spherical aberration is not an important defect. Chromatic Aberration. White light being a mixture of rays of different colors, and these differing in refrangibility, the red being the least and the violet the most refrangible, when white light passes through a lens it is broken up into its component rays 574 THE NERVOUS SYSTEM. i. e., undergoes dispersion and the most refrangible or violet rays will be brought to a focus nearer the lens (Fig. 352) than the least refrangible or red rays, and between will be the various intermediate colors. When these rays fall upon a screen there will be produced a series of circles of the different colors. In Fig. 352 it will be seen that if the screen was placed at x, the outer color would be red, and the inner violet ; while if it was FIG. 352. Chromatic aberra- FIG. 353. Achromatic combination tion (Carhart and Chute). of lenses (Carhart and Chute). placed at y, the colors would be reversed. This defect in lenses is chromatic aberration, and is overcome by combining a biconvex lens of crown glass with a planoconcave lens of flint glass (Fig. 353). Inasmuch as images formed by rays which have passed through such a combination are not fringed with color, the combination is achromatic. It is a rather curious fact that the eye was at one time sup- posed to be free from this defect, and its absence was explained by the fact that the different media through which light passes to reach the retina differ so in their refracting power as to over- come dispersion ; and it is said that it was this which led to the combination just described of the crown and flint glass to make the achromatic lens. The media of the eye, however, do not form an achromatic combination, but the violet rays are actually FIG. 354. To show dispersion in the eye, view the figure from a distance too small for accommodation. Approach the eye toward it : the white rings appear bluish, owing to circles of dispersion falling on them. A little closer, and the black rings become white or yellowish-white, being covered by circles of dispersion and diffusion. brought to a focus about 0.5 mm. in front of the red. Under ordinary circumstances this produces no confusion ; and yet that this defect is inherent in the human eye may be readily demon- strated. If Fig. 354 is brought very close to the eyes so close that the two crystalline lenses cannot accommodate for it the white rings become bluish on account of circles of dispersion fall- ing on them, and if brought a little closer, the black rings become of a yellowish-white color. This dispersion also explains irradia- tion. SENSE OF SIGHT. 575 The Iris. The iris possesses two sets of muscular fibers, the circular and the radiating. Some authorities question the existence of the radiating muscular fibers, regarding them as elastic rather than contractile, and explain dilatation of the pupil by supposing that the circular fibers cease to contract, and that by the elasticity of the radiating fibers the pupillary margin of the iris is drawn outward. It seems to us, however, that the existence of contrac- tile radiating fibers has been sufficiently demon- strated. By the enlarge- ment or diminution of the size of the pupil the amount of light which is permitted to pass into the eye is regulated. The pigment in the iris makes it opaque, and thus only such light as enters the pupil can reach the retina. We have seen that it is the iris which, excluding the marginal rays, mini- mizes spherical aberra- tion ; and that contrac- tion of the pupil takes place during accommo- dation. The three func- tions of the iris may, therefore, be regarded as (1) to regulate the amount ^/ ' \ |-|_ Vophth of light which falls upon the retina ; (2) to minimize spherical aberration ; and Course of constrictor nerve-fibers (3) to assist the accom- Course of dilator nerve-fibers - modative apparatus in the FIG. 355. Diagrammatic representation of the production of distinct vi- ^f. v _ es governing the pupil : //, optic nerve ; Lg, le sion for near objects. ciliary ganglion ; r.b, its short root from JIT, motor oculi nerve ; sym, its sympathetic root ; In the changes which r -l> ^ ts l n g ro * from V, ophthalmonasal branch , i i ' , i of ophthalmic division of fifth nerve ; s.c, short take place in the iris, two c ni a ry nerves ; sets of nerves are involved ; I.e., long ciliary nerves (Foster). (Fig. 355) : (1) Those of the third nerve or oculomotorius ; and (2) those of sympathetic origin. The third nerve supplies the circular fibers, and consequently section of this nerve paralyzes these fibers, and dilatation of the pupil occurs. When the third nerve is stimu- lated, the circular fibers contract, causing a diminution in the size of the pupil. The sympathetic supplies the radiating fibers, and 576 THE NERVOUS SYSTEM. its section paralyzes these fibers, causing contraction of the pupil, while its stimulation produces dilatation. Mydriatics are drugs which cause the pupil to dilate ; atropin is a well-known mydriatic. Cocain, daturin, and hyoscyamin likewise produce dilatation of the pupil, and are therefore mydri- atics. Myotics are drugs which produce contraction of the pupil. Prominent in the list of myotics are eserin, pilocarpin, and morphin. The mydriatics probably act by paralyzing the oculo- motorius and stimulating the sympathetic. When large doses are used, the circular fibers may be paralyzed directly. Myotics paralyze the sympathetic and stimulate the oculomotorius. In addition to producing dilatation of the pupil, the mydriatics paralyze the accommodation, so that as long as their effect lasts it is impossible to focus the eye for near objects. Myotics, besides contracting the pupil, cause a contraction of the ciliary muscle, and thus the lens is adjusted for near objects. When light falls upon the retina this portion of the eye is stimulated, and the impression is carried by the optic nerve to the brain, and there motor impulses are generated which are trans- mitted through the third nerve to, the sphincter of the iris, causing it to contract ; this is, therefore, a reflex act. When one goes from the dark into the light, the pupil contracts, but this contrac- tion lasts only a short time, and is followed by dilatation, and in a few minutes the size of the pupil is about the same as at first. If, on the other hand, one goes from the light into the dark, there is at first a dilatation of the pupil, then a contraction, and in about twenty minutes the pupil is as it was before the dilatation. These observations demonstrate that there are other influences than the incidence of light upon the retina to produce the changes in the pupil. The Retina. As odors excite the olfactory apparatus and savors excite the gustatory, so does light excite the retina. As neither odors nor savors reach the brain, where smell and taste are pro- duced, but only the nerve-impulses which they excite and which the olfactory and gustatory nerves transmit, so when the light- waves fall upon the retina they go no farther ; but the nerve-im- pulses which they there excite are carried to the brain by the optic nerve and produce the sensation called " light." Thus it is that a blow upon the eye or an injury to the optic nerve produces in the brain the impression of a flash of light, although the room in which the blow or injury was received may be absolutely dark. That the optic nerve is itself insensitive to light is shown by the fact that at the point where it enters the eye, forming the optic disk, is the "blind spot/' at which there is an entire absence of sight. This fact may be demonstrated in the following simple SENSE OF SIGHT. 577 way: Look with the right eye at the round black spot here printed, closing the left eye, and holding the book six inches from it. The spot and the cross can both be seen. Now carry the book away from the face farther and farther, still looking at the spot. A point will be reached where the cross will at once disappear, and when this occurs the light from the cross falls upon the optic disk. If the book is carried still farther, the cross will again come in sight. There is no doubt that the portion of the retina which reacts to the stimulus of light is the layer of rods and cones, and of this layer the cones are especially sensitive. This is shown by the fact that the macula lutea (yellow spot) is the portion of the retina which is the most sensitive, and here there are no nerve-libers, but rods and cones, and in the fovea centralis, which is the most sensi- tive portion of the macula, only cones are found. Purkinje's Figures. It may also be shown by the following experiments : 1. If in a dark room a small candle-flame is moved to and fro, close to and at the side of the eye, while the latter is directed toward the dark, an outline of the blood-vessels of the retina will be seen. 2. Or, if after the eyes have been closed for FIG. 356. Method of rendering the retinal blood-vessels visible by concentrating a beam of light on the sclerotic. From the brightly illuminated point of the scle- rotic, a, rays issue, and a shadow of a vessel, r, is cast at a'. It is referred to an ex- ternal point, a", in the direction of the straight line joining a' with the nodal point. When the light is shifted so as to be focussed at b, the shadow cast at b' is referred to b" i. e., it appears to move in the same direction as the illuminated point of the sclerotic (Stewart). some time, as upon awaking from sleep, the eyes are directed for an instant to a white ceiling, an outline of the retinal blood-vessels 37 578 THE NERVOUS SYSTEM. may be seen. If the eye is quickly closed and again opened, this outline may be again seen, and this may be repeated several times. 3. A third method of demonstrating the retinal vessels is by con- centrating a strong light on the sclerotic, at a part as distant as possible from the cornea, by means of a lens, as is shown in Fig. 356. 4. If a card is perforated with a pin, and then held close to the cornea, and through the pinhole light from a lamp or other source of illumination is allowed to fall on the retina, when the card is moved rapidly up and down or from side to side, but not so much as to prevent the light from entering the pupil, FIG. 357 Figure to illustrate the principle of the ophthalmoscope. Kays of light from a point, P, are reflected by a glass plate, M (several plates together in Helmholtz's original form), into the observed eye E'. Their focus would fall, as shown in the figure, at P 7 , a little behind the retina of E'. The portion of the retina A B is therefore illuminated by diffusion circles ; and the rays from a point of it, F will, if E' is emmetropic and unaccommodated, issue parallel from E' and be brought to a focus at F' on the retina of the (emmetropic and unaccommodated) observing eye E. a shadow of the blood-vessels of the retina will be seen. These shadows of the retinal blood-vessels are Purkinje's figures. The retinal blood-vessels do not extend beyond the inner nuclear layer, and the fact that these vessels cast a shadow when light is admitted to the eye, as in the experiments just referred to, demonstrates that the sensitive portion of the retina lies behind the blood-vessels, and the distance behind can be calculated by measuring the amount of change of position the shadows undergo when the light is moved about. This has been done, and the distance has been ascertained to be about 0.2 mm. to 0.3 mm. behind the vessels, which corresponds to the layer of rods and cones. SENSE OF SIGHT. 579 Circulation of Blood in the Retina. Not only is it possible to see the shadow of the retinal blood-vessels, but the movement of FIG. 358. Diagram of the direct method with the formation of an upright image. Rays from the source of light L are received upon the concave mirror M, and con- verged upon the observed eye Obd., within which they cross and illuminate an area of its fundus. From an area A B thus lighted, rays pass out of the pupil (parallel if it he emmetropic, as here represented) through the sight-hole of the mirror, and, entering the observer's eye, Obr., are fociissed upon the retina. An image is there formed as though the object seen was at a great distance, and the perceptive centers project it into space as though the object was at some arbitrary distance (e. g., 25 cm.). By the laws of magnification by a simple" lens the image is embraced between the lines passing from the optical center of the magnifying-lens (the refracting system of the observed eye), through the extremities of the object, and has the size A' B', A" B", etc., according to the distance of projection (Randall). the corpuscles within these vessels can also be seen if the eye is directed toward the sky. They appear as bright little bodies, FIG. 359. Diagram of the indirect method, giving an inverted image : rays from the source of light L, converged toward the observed eye Obd by the concave mirror M, are intercepted by the lens Obj, and after coming to a focus diverge again and light up the fundus. From a part of the illuminated fundus A B rays pass out of the pupil to be again intercepted by the lens 0, and form an inverted real image at its anterior focus A' B'. This real image is viewed by the observer's eye behind the sight-hole of the mirror with the aid of a magnify ing-lens Oc, and is seen enlarged, as at A" B" (Randall). moving rapidly and uniformly through the field. If cobalt glass is held in front of the eyes, the corpuscles are more readily dis- 580 THE NERVOUS SYSTEM. Jf " * cernible. The velocity of the flow of blood in the capillaries of the retina is from 0.5 mm. to 0.9 mm. per second. Intra-ocular Images. In addition to the blood-vessels and blood-corpuscles, other objects within the eye may throw shadows upon the retina ; indeed, any opacity iii the media of the eye through which the rays of light pass would do this, as, for in- stance, the muscce volitantes. These are little bodies floating in the vitreous, which are supposed to be the remains of cells or fibers which exist during fetal life, and which have not become converted into the vitreous humor, as have most of the cells and fibers. They assume various shapes in different individuals, but the shape is invariable in the same person. They may appear as a string of beads, or in the form of streaks or granules. The Ophthalmoscope. This is an instrument by means of which one person can examine the eye of another and obtain a view of the retina. Inasmuch as some of the rays of light which enter the eye and fall upon the retina are reflected from the surface and are brought to a focus again at the source of illumination, it is mani- fest that without some special device it would be impossible to see the image which these reflected rays make, for to have the eye of the observer in the path of these reflected rays would cut off the light which caused them. To overcome this obstacle, Helmholtz devised the ophthalmoscope, which consisted of several plates of glass, one upon another (Fig. 357), that reflect rays of light from a lamp or other source of illumination into an eye to be examined ; these rays illuminate the retina, and those that are reflected issue from the observed eye and are brought to a focus on the retina of the observer. The observed eye and that of the observer are con- sidered to be emmetropic and in a condition of negative accommo- dation or accommodative rest. A reference to Fig. 357 will render this explanation clearer. At the present time glass plates are not used, but in their place a concave mirror, with an opening in it, through which the observer can look. There are two methods of using the ophthalmoscope : the direct (Fig. 358) and the indirect (Fig. 359). These will be readily understood after an examination of the illustrations and their respective legends. It is customary, though not absolutely necessary, before making an ophthalmoscopic examination to drop into the eye a solution of atropin of a strength of two grains to the ounce. This paralyzes the accommodation and dilates the pupil. The examination is conducted in a dark room. The illuminated retina produces a red glare, the reflex, which, as the observed turns his eye slightly inward, becomes lighter in color, because of the white surface, the optic disc, from which the light is reflected when the eye is in this position ; in its center is the porus opticus, with the arteria centralis retince, and radiating from this are its branches ; veins also are seen. The macula lutea and thefovea centralis may likewise be discerned. SENSE OF SIGHT. 581 The ophthalmoscope is used to detect changes in the retina, as in Bright' s disease of the kidneys, and also for testing errors of refraction, as in myopia and hypermetropia. For this latter purpose skiascopy also is employed, which is defined as " a method of determining the refraction of the eye by examining the move- ments of light and shadow across the pupil when the retina is illuminated by light thrown into the eye from a moving mirror." Light. The word " light" is used in two senses: 1. With reference cO the sensation produced in the brain ; and 2. With reference to the cause of that sensation. Light, the cause, is defined as " the form of radiant energy that acts on the retina of the eye, and renders visible the objects from which it comes ; the illumination or radiance that is apprehended by the sense of vision" (Standard Dictionary). It is " a periodic disturbance in a very subtle and highly elastic medium which is supposed to exist everywhere in space, even pervading the inter- molecular spaces in matter. This medium is known as the ether, and vibrating disturbances in it give rise to all the phenomena of radiant energy. These disturbances are propagated through it as waves, not of compression and rarefaction, but more like those of the rope, the direction of vibration being transverse to that of propagation " (Carhart and Chute). The reference to " the rope " is to an experiment of laying a soft-cotton rope, about 5 feet long, on a floor, and then, holding one end of the rope in the hand, setting up vibrations in it by a quick up-and-down movement of the hand. When these waves in the ether reach the retina they produce the sensation of sight, and, as has been stated, the portion of the retina which is sensitive to light is the layer of rods and cones. Just how this is accomplished is not known. Various theories have been advanced to explain it : (1) That the waves of light be- come waves of heat and thus act as thermic stimuli to the rods and cones ; (2) that the waves of light become waves of electricity, and that the stimuli are electric; and (3) that these waves produce certain chemical changes, so that the stimuli are chemical. The first and second theories may be passed by with a mere men- tion, and, although the third is far from proved, yet there are facts which make the theory worthy of attention and continued investiga- tion, as a result of which the true explanation may be forthcoming. In the outer portions of the rods of the retina is a pigment, rhodopsin or visual purple, which, when the retina is exposed to light, becomes red, then orange, then yellow, and finally fades away. When the eye is exposed to light, the pigmented epithe- lium of the retina sends pigmented processes between the rods and cones, and this pigment, fuscin, forms visual purple again, and this reappears in the rods. If the pigmentary layer is sepa- rated from the other layers of the retina, the formation of the rhodopsin, after it has been bleached by light, does not occur. If an eye, after having been protected from the light for a con- 582 THE NERVOUS SYSTEM. siderable time, is then exposed so as to receive the image of a window upon the retina for a time varying from several seconds to several minutes, according to the intensity of the light, and the retina is then removed and inspected in a red light, the image of the window will be seen in it. Such an image is an optogram, and is due to the action of the light on the visual purple, bleaching it in some places, and but little affecting it in others. This image may be preserved, or, as photographers say, " fixed," by putting the retina in a 4 per cent, solution of alum. While it might at first seem as if these changes in the rhodopsin explained what actually took place in the eye when the waves of the luminiferous ether reached the retina and produced the sensa- FIG. 360. Model to illustrate astigmatism. tion of light, still the absence of this coloring-matter from the cones, which exist without the rods in the fovea centralis, where sight is most acute, would alone be sufficient proof that the visual purple is not essential to vision. Some animals possessing sight have no visual purple even in the rods. Engelmann has described a shortening and a thickening of the cones of frogs and fishes under the stimulation of light, and a lengthening in the absence of light, but as to the connection be- tween these changes in the cones and sight, nothing is known. The eye is able not only to see objects, but to take cognizance of certain facts in connection with them, such as their form, size, distance, and color. SENSE OF SIGHT. 583 Form. Plane surfaces can be seen with either eye alone, but solid bodies require the combined use of bofch eyes, or binocular vision, in order that their solidity may be appreciated. If a solid object is looked at with the left eye, while the right eye is closed, and then with the right eye while the left is closed, it will be ob- served that with the left eye more of the left side of the object is seen than with the right eye, and with the right eye more of the right side of the object than with the left eye. The two images produce the effect in the brain of a single solid body. This principle is made use of in the stereoscope (Fig. 361). The picture which is seen with this instrument is double, each having been taken with a separate lens, so that when their images are thrown on the retina the effect is as if both eyes were looking at the scene represented in the pho- tographs. Identical Points. It would seem a priori that each retinal image would produce its own ef- fect upon the brain, and that, in- stead of seeing a single object, it would appear double. The theory of identical or corresponding points has been advanced to explain what actually takes place. If one retina is in imagination placed upon the other, the foveae centrales super- imposed the one upon the other, all the other points of the retinae similarly 'superimposed are iden- The prisms refract the rays coming tioil or oorresnondino* noints and from the points c ' r of the P ictures ab ing po nis, anc and a ^ so that they appear to come images formed upon such points from a single point, q. Similarly the will in the brain produce the ef- points a and a appear to be situated at J ... , . . r , T7 , , , /, and the points 6 and ft at <<>. feet or single vision. When the images of an object are not formed upon identical points, double vision or diplopia results. If, therefore, while looking at an object we press with the finger upon the outer side of one eye so as to turn it a little inward, we see the object double. Size. The size of objects is determined by two factors : The size of the visual angle which they subtend, and their distance from the observer. Helmholtz has demonstrated that an object which subtends a visual angle of less than 50" cannot be seen by the unaided emmetropic eye. This corresponds to an image on the retina of 3.65 p.. The diameter of each cone in the macula lutea is about 3 p. Kolliker gives it as 4 p. to 5 p. In other words, if an object does not make an image on the retina large FIG. 361. Brewster's stereoscope: 584 THE NERVOUS SYSTEM. enough to stimulate a cone, it does not come within the range of vision. Distance. It is impossible to judge of the distance of objects except by experience ; thus a child reaches for everything it sees, irrespective of the distance from it the objects may be ; and persons who, having been blind from birth, are in maturer years endowed with sight by operation, for instance bear testimony that every- thing seems to be immediately in front of them. If, however, the size of an object is known, then the size of its image on the retina determines our estimate of its distance. Conversely, if we know the distance of an object, then the image which that object produces on the retina is the determining factor in our judgment of its actual size. If, therefore, our judgment of the distance of an object from us is erroneous, so will be our judgment of its size, and vice versa. If, for instance, a ship is seen through a fog, we suppose that, being indistinctly seen, it is at a considerable dis- tance from us, although, as a matter of fact, it may be quite near, and making an image of considerable size upon the retina, we judge the ship to be larger than it actually is. It is a well-known fact that the moon seems larger to an observer when near the horizon than when near the zenith, although, as a matter of fact, it is nearer by about 4000 miles, half the diameter of the earth, when in the zenith, and should therefore a priori seem larger, but when it is near the horizon we have terrestrial objects to compare it with, while when in the zenith there is nothing with which to com- pare it. The correctness of this explanation has been questioned by a critic, who says : " The moon looks large when rising on Salisbury Plain, on which there is no conspicuous terrestrial object with which it can be compared, and looks small at its zenith when close to the vane of the spire of Salisbury Cathedral, the size and dis- tance of which are well known. It is probably an affair of re- ft ,, A J fraction." As this illusion is almost universal, and one of great interest, the writer deemed it worth while to obtain the views of several well-known physicists. Among those written to was Prof. Spice, of Cooper Union, New York. In commenting on the criticism above quoted, he says : " Though it is true that there is no l con- spicuous ' object in sight, still there is at least the Plain and this would give one an idea of distance. With reference to the prox- imity to the vane on the cathedral spire, I would suggest that unless an observer were on the spire the vane itself would (of necessity) look small, and therefore would not tend to make the moon look large. As to the idea of refraction increasing the ap- parent size : The refraction at the horizon is about 34*' + ; the apparent diameter of the moon is about 31' + so if the moon SENSE OF SIGHT. 585 were just below the horizon it would appear just on the horizon. Further, if the moon were just on the horizon the lower part of the moon would be raised (by refraction) more than the upper pirt, because refraction diminishes rapidly after leaving the hori- zon, so the vertical (apparent) diameter of the moon would be less, but the horizontal diameter would not change i. e., the area (size) of the moon at the horizon would be smaller by refraction. "As to the apparent greater size of the moon when near the horizon, I believe that as stated in most astronomy books, say Charles Young's or Todd's New Astronomy it is due to the fact that in looking at the moon in that position we see many well- known objects as well : houses, trees, etc. ; and as we have a rough idea of the size of these objects and also know they are nearer us than the moon is, we get the idea of largeness. In the zenith we have no objects for comparison, and as angular magnitude alone conveys no meaning, we have nothing to guide (or misguide) our judgment. Of course, when in the zenith, the moon's angular size is very slightly greater, as we are nearly 4000 miles nearer i. e., by the radius of the earth. I may remark that the common notions as to .the moon's size are curious : one person may say it looks as 4 big as a dinner-plate/ and another, ( as big as a half-dollar/ but in no case which I have examined have these thoughtful people made any mention of how far from them the dinner-plate was sup- posed to be at the time." Prof. C. A. Young, the well-known astronomer, of Princeton University, was written to for his explanation of the phenomenon ; his answer is as follows : "As to the phenomenon to which you refer, the apparent enlargement of celestial objects near the horizon, I am satisfied with the generally received explanation that it is due to the fact that while the angular diameter of the object re- mains practically the same as at the zenith (really a little less), the object is instinctively referred to a greater distance because of the number of intervening objects by which we judge of distance. " If the sun or moon be looked at through a smoked glass, which leaves the disc visible while hiding the horizon and inter- vening objects, the sun or moon immediately shrinks to the same apparent diameter as if higher up. At least it is so with me, and with most persons whom I have seen try the experiment. Look- ing through a tube like a piece of gas-pipe 12 inches long is just as effectual; what is necessary is to cut out all objects and the horizon line while still leaving the moon (or sun) visible. But some persons say they do not get the effect. In their case I judge that the habitual sense of the horizon as distant comes in to main- tain the illusion, even though they cannot actually see it, but I am aware that some physiologic psychologists decline to accept the explanation" 586 THE NERVOUS SYSTEM. . The New International Encyclopaedia regards the apparent enlargement as due to an illusion of distance. The distance be- tween the observing eye and the horizon seems to be longer than the distance between the eye and the zenith, owing to the haziness of the air, the number of intervening objects, etc. The retinal image being practically the same in both instances, the object which the mind refers to a greater distance appears to be larger. Prof. Pickering, of Harvard College Observatory, in his book, The Moon, in treating of this subject, says : " The true angular size of the moon is about half a degree ; it can, therefore, always be concealed behind a lead-pencil held at arm's length. The sun and moon when rising or setting appear to most persons of from two to three times the diameter that they have when near the meridian. The cause of this phenomenon has been a source of speculation from the earliest times. Before optical science was thoroughly developed some thought that the image was really magnified by the vapors near the horizon. Not only is this incorrect, but in point of fact the sun is slightly and the moon measurably smaller when near the horizon, because they are farther off than when overhead. " The true explanation is twofold. Human estimates of angular dimensions are dependent not merely on the angular dimensions themselves, but also on several extraneous circumstances. The case is analogous to our estimates of height, which are dependent primarily on the real height of the object, but secondarily upon its bulk. Thus, a pound of lead feels much heavier than a pound of feathers. " One circumstance affecting our estimates of angular dimension is the linear dimension of the object itself. It was pointed out by Alhazen about nine hundred years ago that if we hold the hand at arm's length and notice what space it apparently covers on a dis- tant wall, and then move the hand well to one side so that it is in front of some very near object, we shall find that it will appear to us decidedly smaller than the part of the wall which it previously covered. ^ It is an analogous effect which makes the full moon when rising or setting appear larger than when it is well up in the sky. On the horizon we can compare it with trees and houses, and see how large it really is ; overhead we have no linear scale of comparison. " It is certain that this is not the only reason, however, nor even the chief one, that makes the moon appear larger when near the horizon. The same optical illusion appears when at sea, and it applies also to the constellations for example, to Orion. When rising they appear decidedly larger than when near the meridian, and yet no comparison of their size with that of terrestrial objects is usually possible. There is evidently another circumstance SENSE OF SIGHT. 587 affecting our estimates of angular diameter. The explanation of this was first given by Clausius about thirty years ago, . . . but it has not as yet got into the text-books. The circumstance chiefly affecting our estimates of size depends on the angular altitude of the object under consideration. " When we pass under an archway or under the limb of a tree we know that we are nearer to the object than we are when we see it under a lower altitude ; at the same time it appears just as large to the average person angularly as it does when we are several feet farther away. We are, in fact, used, all our lives as we walk about, to see objects rapidly shifting their angular positions, yet not appearing as we pass them any larger than they do when we are slightly more distant from them. We thus always uncon- sciously make some compensation in our minds for the real changes in angular size that actually occur. " If, now, the limb of the tree that we passed under, instead of really growing angularly smaller at the low altitude than it was when overhead, should remain of the same angular size in all posi- tions, we should say that it looked larger at the low altitude. This is exactly what happens in the case of the heavenly bodies. Unlike all terrestrial objects, they are practically of the same real angular dimensions when on the horizon that they are in the zenith. We involuntarily apply to them the same compensation that we are accustomed to apply to terrestrial objects, and are thus naturally surprised to see that they appear larger at the lower altitude." FIG. 362. Formation of solar spectrum. Color. When a beam of sunlight passes through a prism it is separated by dispersion into its component colors, forming a solar spectrum (Fig. 362), the red rays being the least refracted, and the violet rays the most. The color depends upon the rapidity of vibration or the length of the waves ; thus the red waves are the longest and the vibrations the least rapid, while the violet are the shortest and the vibrations the most rapid. In the following 588 THE NERVOUS SYSTEM. table are given the wave-lengths for the center of each color in ten-millionths of a millimeter. Red 7000 Orange 5972 Yellow 5808 Green . 5271 Blue . . ...'.>- 4960 Indigo 4383 Violet . . 4059 There are rays, calorific rays, beyond the red rays whose wave- lengths are longer than the red, and others beyond the violet whose wave-lengths are shorter than those of the violet ; these latter are the actinic rays ; neither the calorific nor the actinic rays are visi- ble. If, after the dispersion, a second prism in reversed position (Fig. 363) is placed in the path of the colored rays, these will be FIG. 363. Reunion of colored rays to form white light. reunited, and will emerge from the second prism as white light. This synthesis of light, or the composition of white light by the union of all the colors of the spectrum, may be brought about by the union of certain colors without using all of them ; thus red and bluish green will produce white light, as will also orange and light blue. Colors which when mixed produce white light are complementary. In the color diagram (Fig. 364) this relation is FIG. 364. Color diagram. made evident, the form of a triangle being selected around which to arrange the colors, rather than a circle, for the reason that they do not act equally as stimuli. Red, green, and violet are placed at the angles on the Young-Helmholtz theory of these being the primary colors i. e., the theory thaf the other colors are mixtures of these three colors. A reference to this diagram shows that red, green, and violet, represented by R, G, and v, make white, repre- SENSE OF SIGHT. 589 sented by w. The colors at the extremities of straight lines are complementary colors ; orange and blue, o and B, make white, w. But neither B nor o is at the extremities of the line from n, but, if this line was continued, it would strike the curved line between B and G i. e., red and bluish green are complementary colors. One can see also from this diagram what color results from the union of two others. Thus red and yellow will produce the inter- mediate color, orange ; red and violet will produce purple, and this and green will produce white. If complementary colors are put beside each other, both colors are more pronounced ; on the other hand, if colors which are not complementary are so placed, the colors are subdued. It may be well here to refer to some of the fundamental facts in connection with colors, and for this purpose we shall quote statements and experiments from Elements of Physics, by Carhart and Chute. Color is not a property inherent in objects i. e., bodies have no color of their own. Thus in the case of opaque bodies, the color which they appear to have depends upon the kind of light which they reflect. A red body is red because it absorbs the other colors of the spectrum than the red and reflects this color from its surface. If all the colors are reflected in proper proportion, the body appears white. This can be proved by looking through a glass prism at a piece of white paper 3 cm. long and 2 mm. wide, pasted on a piece of black cardboard several times larger, the edges of the prism being held parallel to the length of the strip. The image seen through the prism will be a spectrum similar to the solar spectrum. If a piece of red paper is substituted for the white paper, on looking through the prism the red end of the spectrum will be seen, but the other colors will be dim or absent. If a blue strip is looked at, the spectral image will show the blue, the other colors being lacking. In other words, white paper is white because it reflects all the colors in due proportion, while red paper reflects only red, and blue, only blue. If in the red of the solar spectrum a piece of red paper or ribbon is held, it will appear brilliantly red ; else- where it will be nearly black ; a piece of blue will appear blue in the blue of the spectrum, and there only. The color of opaque bodies varies as the light which falls upon them varies ; thus if any fabric into which blue or violet enters, as purple and pink, is examined by artificial lights, all of which are deficient in blue and violet rays, its color will vary from that which it has in sun- light. It is on this account that matching colors by artificial light is so difficult. Transparent bodies, on the other hand, are colorless when they absorb no light i. e., transmit it all ; or when they absorb all the colors in like proportion. It is the color or colors which are trans- mitted that give the color to transparent bodies. If one color is 590 THE NERVOUS SYSTEM. absorbed, the color of the object will be the sum of the colors that are transmitted. We are now prepared to discuss some of the facts which have been established in connection with the sensation of color. The union of the spectral colors to produce white light may be demon- strated by cutting out disks of colored paper (Fig. 365) and attaching them to a whirling machine (Fig. 366), or complemen- tary colors may be combined in the same way with the same result ; or, again, by using different colors various combinations may be made. This may be called a physiologic mixture of colors, and is thus explained : When the retina is exposed to a color, this produces a certain effect which remains even after the color which produced it has been removed ; if, before the sensation caused by this color has, disappeared, the retina is exposed to another color, the second color is superimposed upon the first, and if the two are complementary, the effect is that of white light, as when these FIG. 365 Disks of colored paper. FIG. 366. Whirling machine. colors are combined by a prism. If the revolving disks contain all the spectral colors in due proportion, and are revolved rapidly enough, so that all the colors produce their effect on the retina before the sensation produced by any one has faded away, the effect of white light is produced, as when these colors are united by a prism. Mixing of Pigments. The effects just described as being pro- duced by the physiologic mixture of colors cannot be produced by the mechanical mixture of pigments. Although blue and yellow when mixed upon the retina produce white, yet when blue and yellow pigments are mechanically mixed the resulting color is green and not white. If a broad' line is drawn on a blackboard with a yellow crayon, and over this is drawn another line with a blue crayon, the resulting color will be green. This effect is ex- plained in the following manner : The yellow crayon reflects not only yellow light, but also green light, and absorbs all the other colors. The blue crayon reflects not only blue, but also green, and SENSE OF SIGHT. 591 absorbs all the others. So that when the two are mixed, the only color which is not absorbed by the crayon is green, and therefore the line appears green. Nor can the colors which are transmitted through transparent bodies be united to produce white light, or the combination which the mixture of colored lights produces on the retina, any more than can the pigments mentioned above, and the reason for this is obvious. If, for instance, sunlight is transmitted through red glass, all the rays which produce other colors than red are absorbed, and the red only being transmitted, gives the red color to the glass. If the same is done with green glass, only the green rays will be transmitted, all the other rays being absorbed. If now white light is transmitted through red glass, only the red will remain, and if this is transmitted through green glass, no light will come through, for green glass will not transmit the red rays, and the green rays have already been absorbed by the red glass. To pro- duce white light or the various combinations of the spectral colors, the rays must fall upon the retina and the colors be mixed phy- siologically, the mixture producing effects which are interpreted by the brain. Young-Helmholtz Theory of Color. Inasmuch as this theory was advanced by both Young and Helmholtz, it bears the name of both. It is based on the view that there are in the retina three substances which are stimulated by the three primary colors, re- spectively, of red, green, and violet, and that when all three fall upon the retina in proper proportion the sensation of white is produced ; and when any two of the three stimulate the retina, the effect is to produce some intermediate color, as, for instance, violet and green produce blue ; red and green, yellow and orange ; red and violet, purple. That such substances actually exist, there is no proof; the term " substance " is used for want of a better one. The term " fiber " is used by Helmholtz, and " red fibers," " green fibers," and " violet fibers'" are spoken of. This theory supposes, also, that each of the primary colors stimulates to some extent all the three substances, but one is stimulated so much more than the others that the effect upon the others is not noticed. Especially marked is this differentiation of the red, green, and violet near the fovea centralis, and when the light is not too intense. If the light falls upon the portions of the retina near the ora serrata, or if that which falls on the retina in the neighborhood of the fovea is of very little or of very great inten- sity, all the rays seem to stimulate the three substances alike, for, under such circumstances, the colors of objects are not readily made out. The theory has been advanced that the power to dis- tinguish colors resides in the cones, and that the stimulation of the rods by light gives the sensation of luminosity without color. Von Kries states that the rods are color-blind, their stimulation re- 592 THE NERVOUS SYSTEM. suiting in the sensation of luminosity only ; that they are more easily stimulated than the cones, and are particularly responsive to waves of short wave-lengths ; and that they adapt themselves to light of varying intensity. Hering Theory of Color. This theory supposes the existence of three substances in the retina, and of six primary color sensa- tions, arranged in pairs, white and black forming one pair, red and green another, and yellow and blue the third. These corre- spond, it will be noticed, to complementary color sensations. The three substances are the white-black, the red-green, and the yellow- blue. These substances are supposed to be susceptible of being affected in two opposite ways : In one a constructive or anabolic change is produced, and in the other a disintegrate ve or katabolic change. If, for example, all the spectral colors fall upon the white-black substance, katabolic changes occur in this substance producing the sensation of luminosity ; while if no light enters the eye, anabolic changes occur, with the effect of producing blackness. The red rays falling upon the retina produce katabolic changes in the red-green substance, producing the sensation of red, while the green produces anabolic changes, and the resulting sensation is that of green. Blue rays cause anabolic changes in the yellow- blue substance, and yellow rays cause katabolic changes in the same substance. These changes in the retinal substances produce the sensations of color when transmitted through the fibers of the optic nerve to the brain. Franklin Theory of Color-sensation. This theory supposes that the eye, in the early periods of development, possesses only the white-black or gray visual substance, and is therefore sensitive to luminosity only, and not to color. Later this substance becomes modified into the blue and yellow substance, and then into the red and green. For a further account of this theory the reader is referred to the American Text-book of Physiology, vol. ii., p. 337. Birch Modification of the Young-Helmholtz Theory. This ex- perimenter has exposed the eye to sunlight in the focus of a burn- ing-glass behind transparent screens of different colors, with the result of producing a temporary color-blindness. If a red screen is used, the eye is red-blind i. e., cannot distinguish the color, so that if scarlet is looked at, it appears black, while yellow appears green and purple appears violet. If a violet-colored screen is used, violet appears black ; purple appears crimson ; and green, a bright green. These effects are due to fatigue of the retina, so that the color to which the retina is exposed for a time ceases to stimulate, and that color ceases to be recognized while the other colors con- tinue to stimulate. Birch found that after exposure to yellow the eye was blind not only to yellow, but to red and green also, which primary colors in the Young-Helmholtz theory produce yellow. He concludes that there are not only the three primary SENSE OF SIGHT. 595 sun, but not long enough to produce fatigue, and then closed, a bright spot of light is seen : this is a positive after-image. It remains bright for but a short time and then changes color, becoming greenish blue or bluish green, blue, violet, purple, and red, and then fading away entirely. It may be followed by a negative after- image. Visual Judgment. -We have al- ready referred to some visual judg- ments as to form, size, distance, etc. (p. 584). It is a common say- ing that " seeing is believing," and yet not one of the senses is more liable to deceive its possessor than that of sight. For instance, if the vertical and horizontal lines in Fig. 367 are compared, the vertical will immediately be pronounced the longer, and yet when accurately measured it will be found that each is exactly 4 cm. in length. This tendency to overestimate vertical lines is attributed to the relative weakness of the superior rectus muscle as compared with the muscles that move the eyeball horizontally. The difference is said to be from 30 to 50 per cent, in height and 40 to 53 per FIG. 367. To illustrate the overesti- mation of vertical lines. FIG. 368. To illustrate the illusion of subdivided space. cent, in area of cross-section ; owing to this weakness a greater effort is required to turn the eyeball upward, and the effect upon the mind is that of turning it through a greater distance ; hence vertical lines seem to be longer than they really are. 596 THE NERVOUS SYSTEM. In Fig. 368 the space between A and B seems to be greater than that between B and c, and yet they are exactly the same. Any space like that between A and B which is subdivided seems larger than that which is undivided, as that between B and c. In Fig. 368 D appears to be higher than it is broad, and E broader than it is high. So, too, Zollner's lines (Fig. 369) are very illusory. The hori- zontal lines appear to be far from parallel, and yet if they are looked at from their ends, by turning the page sidewise, their / / / 7 /////// \ \ \ \ \ \ v v v v v \ \ \ \ \ \ \ \ \ \ \ FIG. 369. Zollner's lines. parallelism is at once apparent. This is explained by the fact that acute angles are apt to be overestimated and obtuse angles underestimated. In Fig. 370 the straight line A appears shorter than the straight line B, though it is of exactly the same length. Similar illusions might be multiplied almost indefinitely, and yet with all its imperfections the human eye is a wonderful organ. Some one has said that it is so defective from an optical standpoint that, had he ordered such a piece of apparatus from an optician FIG. 370. Illusion of space-perception (Bowditch). and it had been delivered with as many defects, he would have returned it and refused to pay for it. It has also been said, in speaking of the crystalline lens, that an optician could make a better lens than Nature has furnished ; but it has also been said that he could not make so good an eye. And finally, Dr. Bow- ditch, in his excellent discussion of "Vision," in the American Text-book of Physiology, well says : " When we reflect upon the difficulty of the problem which Nature has solved, of constructing an optical instrument out of living and growing animal tissue, we cannot fail to be struck by the perfection of the dioptric apparatus SENSE OF SIGHT. 597 of the eye as well as by its adaptation to the needs of the organism of which it forms a part." Appendages of the Eye. Lacrimal Apparatus. To keep the conjunctiva (the mucous membrane covering the anterior seg- FIG. 371. Lacrimal and Meibomian glands, the latter viewed from the posterior surface of the eyelids. (The conjunction of the upper lid has been partially dis- sected off, and is raised so as to show the Meibomian glands beneath.) Jf, free border of upper, and 2, free border of lower lid, with openings of the Meibomian glands; 5, Meibomian glands exposed, and 6, as seen through conjunctiva ; 7, 8, lacrimal gland ; 9, its excretory ducts, with 10, their openings in the conjunctival cul-de-sac; 11, conjunctiva (Testut). ment of the sclerotic and the cornea and lining the lids) moist and in normal condition is the function of the tears. They are secreted by the lacrimal gland, a compound racemose gland lodged in a depression at the upper and outer portion of the orbit. Its ducts, about seven in number, open on the upper and outer half of the conjunctiva near its reflection over the eyeball. At the edge of the upper and lower eyelids, at their inner ex- tremities, are openings, puncta lacrimalia, into which the tears pass after performing their function. These openings are the beginnings of the canaliculi (Fig. 372), which open into the lacrimal sac, or the dilated upper extremity of the nasal duct, which discharges at the inferior meatus of the nose, the open- ing here being partially closed by a fold of mucous membrane, the valve of Hasner. Meibomian Glands. On the posterior surface of the eyelids, FIG. 372. 1, Canaliculus ; 2, lacrimal sac ; 3, nasal duct ; 4, plica semilunaris ; 5, car- uncula lacrimalis. 598 THE NERVOUS SYSTEM. beneath the conjunctiva, are the Meibomian glands (Fig. 371), thirty in number on the upper, and fewer on the lower lid. Their ducts open on the edges of the lids, and their secretion prevents the adhesion of the lids and the tears from running over them on to the cheeks. The Sense of Hearing. The ear (Fig. 373), the organ of hearing, consists of three subdivisions : (1) External ; (2) middle ; and (3) internal. External Ear. The external ear consists of the pinna or auricle, and the external auditory canal or meatus. The function of the FIG. 373. Diagram of organ of hearing of left side : 1, the pinna ; 2, bottom of concha; 2, 2', meatus externus; 3, tympanum ; above 3, the chain of ossicles; 3', opening into the mastoid cells : 4, Eustachian tube ; 5, meatus internus. containing the facial (uppermost) and auditory nerves ; 6, placed on the vestibule of the laby- rinth above the fenestra ovalis ; a, apex of the petrous bone ; b, internal carotid artery ; c, styloid process ; d, facial nerve, issuing from the stylomastoid foramen ; , mastoid process; /, squamous part of the bone (Quain, after Arnold). pinna is to collect the sound-waves and direct them to the external auditory canal, which they traverse to reach the membrana tym- pani. In some animals, such as the horse, the auricles are very important, enabling the animal to detect the direction from which sounds come, and they are capable of considerable movement ; but in man they are not so important, although when the hearing is defective they are of assistance. That they are not essential to hearing is shown by the fact that when removed, hearing is not affected, and also by the fact that in birds, where they are absent, the sense of hearing is well marked. SENSE OF HEARING. 599 The pinna (Fig. 375) is composed of yellow fibrocartilage covered by skin, although in some parts, as the lobule, the cartilage is absent. It is attached to the meatus and other parts by liga- ments and muscles. FIG. 374. Semidiagrammatic section through the right ear : G, external audi- tory meatus ; T, membrana tympani ; P, tympanic cavity ; o, fenestra ovalis ; r, fenestra rotunda ; B, semicircular canal ; S, cochlea ; Vt, scala vestibuli ; Pt, scala tympani (Czermak). External Auditory Meatus. This canal, extending from the pinna to the membrana tympani, is about 3.2 cm. in length, the outer 1.3 cm. being of cartilage, except at the upper and back Fossa of helix. Anthelix. Concha. Antitragus. Helix. f Fossa of anthelix. Tragus. Lobule. FIG. 375. External ear. part, where its place is taken by fibrous membrane. The inner 2 cm. is osseous. The entire canal is lined with skin, which in the cartilaginous portion of the canal contains sebaceous and perspiratory glands, their product being cerumen or ear-wax (p. 417). The skin lining the meatus also contains hair-follicles. 600 THE NERVOUS SYSTEM. Inasmuch as in the examination of the ear and the treatment of its diseases it is necessary to introduce an aural speculum (Fig. 377), a knowledge of the direction and shape of the canal is essen- tial. Its greatest diameter is at the external orifice and is vertical ; FIG. 376. Muscles of the auricle : 1, attollens aurem ; 2, attrahens aurem ; 3, Tetrahens aurem; 4, helicis major; 5, helicis minor; 6, tragicus, with 6', its acces- sory portion ; 7, an ti tragicus ; a, spine of helix; b, concha (Testutj. its smallest diameter is in the middle. At the tympanic end the greatest diameter is horizontal. The direction of the canal is obliquely forward, inward, and downward. Before introducing the speculum the helix of the ear is raised upward and backward so as to straighten the canal as much as possible. Middle Ear. This is called also the tympa- num (Fig. 378). Membrana Tympani (Fig. 379). This mem- branous structure separates the tympanic cavity from the external auditory canal. Its shape is oval, and the direction of its long axis is down- ward and inward ; its diameter along this axis is about 9 mm. It is composed of three layers : An external or cuticular, which is an extension of the integument that lines the external audi- f j I'll tory canal ; an internal, mucous, a continuation of the mucous membrane lining the tympanic cavity ; and a middle, fibrous, made up of both fibrous and elastic tissues. There are two vari- eties of these fibers radiating, which radiate from the center to the circumference ; and circular, which form a ring at the circum- ference. The membrana tympani is set into a groove in a ring of bone, except at the upper part, where it is attached to the wall of the canal. This portion of the membrane is not so tense as FiG. 377.-Aural speculum. SENSE OF HEARING. 601 .& .{t F ^m FIG. 378. Tympanum of left ear, with ossicles in situ : 1, suspensory ligament of malleus ; 2, head of malleus ; 3, epitympanic region ; 4, external ligament of malleus ; 5, processus longus of incus ; 6, base of stapes ; 7, processus brevis of mal- leus; 8, head of stapes; 9, os orbicular e ; 10, manubrium ; 11, Eustachian tube; 12, external auditory meatus ; 13, membrana tympani ; 14, lower part of tympanum (Morris). FIG. 379. Otoscopic view of left membrana tympani : 1, membrana fiaccida : 2, 2', folds bounding the former ; 3, reflection from processus brevis of malleus ; 4, pro- cessus longus of incus (occasionally seen) ; 5, membrana tympani ; 6, umbo and end of manubrium; 7, pyramid of light (Morris). 602 THE NERVOUS SYSTEM. the rest, and has therefore received the name membrana flacdda. It is called also Shrapnett's membrane. When a normal membrana tympani is viewed through an aural speculum, there is seen a triangular spot or CQne or pyramid of light, whose apex is at the end of the manubrium or handle of the malleus, and whose base is at the circumference. The membrane is funnel-shaped, with the concavity toward the meatus, at the apex being attached the tip of the manubrium, and at this point on the outer surface is the umbo (Fig. 379). Tympanic Cavity (Fig. 378). In this cavity, which is situated in the petrous portion of the temporal bone, are the chains of bones, the ossicles, serving as a means of communication between the membrana tympani and the internal * ear. It communicates posteriorly with the mas- toid antrum and the mas- orfaculc FIG. 380. The ossicles of the left ear, external view (enlarged) (after Gray). FIG. 381. Malleus of the right side : A, anterior face ; B, internal face ; 1, capitulum or head of malleus ; 2, cervix or neck ; 3, processus brevis; 4, processus gracilis; 5, manubrium ; 6, grooved articular surface for incus ; 7, tendon of musculus tensor tympani (after Testut). toid cells, and anteriorly with the pharynx by means of the Eusta- chian tube. Two openings, the fenestra ovalis and fenestra rotunda, give it communication with the internal ear. The roof of the tym- panic cavity, the tegmen, is a very thin plate of bone, the only struc- ture separating this cavity from that in which lies the brain. It is on account of this slight separation that inflammation of the middle ear sometimes extends to the brain. The tympanic cavity is lined by mucous membrane, which is covered with ciliated epithelium except over the ossicles and the membrana tympani. Ossicles (Fig. 380). These are three in number : the malleus, the incus, and the stapes. Malleus (Fig. 381). The malleus is about 18 mm. long, and consists of head, neck, manubrium, processus gracilis, and processus brevis. The head has a general surface for articulation with the incus. SENSE OF HEARING. 603 The manubrium or handle is attached to the membrana tympani. The processus gracilis is attached to the Gasserian fissure by bone and ligament. The processus brevis presses against the membrana flaccida, and its location is visible by inspection of the external FIG. 382. The incus of the right side: A, anterior face; B, internal face: 1, body of incus; 2, processus brevis; 3, processus longus; 4, articular surface for the malleus ; 5, a convex tubercle, processus lenticularis, for articulation with stapes ; 6, rough surface for attachment of the ligament of the incus (after Testut). surface of the membrana tympani, through which it shows (Fig. 379). The malleus is held in place by ligaments (Fig. 384). Incus (Fig. 381). This is called also ambos and anvil-bone. The body is characterized by the presence of an articular surface for articulation with the malleus. It has two processes processus brevis and processus longus. The processus brevis is attached by ligament to the margin of the opening that leads into the mastoid cells. The processus longus is nearly parallel with the handle FIG. 383. The stapes: 1, base ; 2, anterior crus ; 3, pos- terior crus ; 4, articulating surface of head of the bone ; 5, cervix or neck (after Tes- tut). f FIG. 384. Ligaments of the ossicles and their axis of rotation. The figure represents a nearly horizontal section of the tympanum, carried through the heads of the malleus and incus : M, malleus ; I, incus ; t, articular tooth of incus ; Ig.a. and Ig.e, external ligament of malleus; Ig.inc, ligament of the incus; the line a-x represents the axis of rotation of the two ossicles (from Foster, after Testut). of the malleus and ends in a round projection, os orbicular e or lenticular process, which articulates with the head of the stapes. During fetal life the os orbiculare exists as a separate bone. Stapes (Fig. 383). This bone is so called from its resemblance 604 THE NERVOUS SYSTEM. to a stirrup. It consists of a head, which articulates with the os orbiculare ; a neck, into which the stapedius muscle is inserted ; and two crura, which are connected with the base, this being attached by ligamentous tissue so as to close. the fenestra ovalis. Ligaments of the Ossicles. The ossicles are connected with one another, and also with the walls of the tympanum, by ligaments (Fig. 384). One of these, the anterior ligament of the malleus, was at one time supposed to be a muscle and was described under the name levator tympani. Muscles of the Ossicles. These are two in number tensor tympani and stapedius. Tensor Tympani. This muscle lies in a bony canal which is above the canal containing the Eustachian tube, and sepa- rated from it by the processus cochleariformis, a thin plate of bone. It has its origin from the petrous bone, the cartilaginous portion of the Eustachian tube, and the bony canal in which it lies. Its tendon enters the tympanum and bends at almost a right angle around the end of the processus cochleariformis, and is inserted into the mauubrium near the neck. Its nervous supply is a branch from the otic ganglion. When this muscle contracts, the membrana tympani is drawn inward and made more tense. Stapedius. This muscle arises from the interior of the pyramid which is situated just behind the fenestra ovalis, and just below the opening of the mastoid antrum, and its tendon passes out at an opening in the apex ; it is inserted into the neck of the stapes. Authorities do not agree as to the effect of the contrac- tion of this muscle. Gray says that "it draws the head of the stapes backward, and thus causes the base of the bone to rotate on a vertical axis drawn through its own center ; in doing this the back part of the base would be pressed inward toward the vestibule, while the fore part would be drawn from it. It probably compresses the contents of the vestibule." Sewall, in the American Text-Book of Physiology, says : " Con- traction of the muscle would cause a slight rotation of the stapes round a vertical axis, so that the hinder part of the foot of the ossicle would be pressed more deeply into the fenestra, while the remaining portion would be drawn out of it. Its action probably reduces the pressure in the cavity of the perilymph, and thus is antagonistic to that of the tensor tympani." The nervous supply of this muscle is the tympanic branch of the facial, which reaches the muscle through a canal in the pyramid which communicates with the aquseductus Fallopii. Eustachian Tube (Fig. 385). Through this channel the tym- panum is in communication with the pharynx. It is about 36 mm. in length, and passes downward, forward, and inward. It begins in the lower part of the anterior wall of the tympanum, and is bony for about 12 mm. It then becomes cartilaginous, and SENSE OF HEARING. 605 remains so throughout the rest of its course. It is lined by mucous membrane, the epithelium of which is ciliated. The direc- tion of the motion of these cilia is from the tympanum to the mouth, holding the nostrils closed with the thumb and finger, and forcibly blowing. The pharyngeal opening is at the upper lateral part of the pharynx behind the inferior turbinated bone. There Portion of Elista chian tube fret from glands. Cartilage Mucosa of the pharynx. Glands. Glands. -K- FIG. 385. Cross-section of the Eustachian tube with its surrounding parts ; X 12 (from a preparation by Professor Eiidinger). is a band of muscular tissue, the dilatator tubce, which joins the tensor palati. Mastoid Antrum. This is a cavity which opens into the attic or epitympanic recess, an extension upward and backward of the tympanic cavity. It is in this recess that the head of the malleus and a part of the incus are situated. The antrum communicates with the mastoid cells in the mastoid process. Antrum and cells are lined by mucous membrane which is continuous with that of the tympanum. This extension of the mucous membrane explains how inflammation of the middle ear may extend to the mastoid cells. Fenestra Ovalis (Fig. 386). This is an oval opening in the internal wall of the tympanum into the vestibule of the internal 606 THE NERVOUS SYSTEM. ear, and is closed by the stapes, an annular ligament uniting the bone to the fenestra. Fenestra Eotunda. This opening, also on the internal wall of the tympanum, leads into the cochlea of the internal ear. It is FIG. 386. Eight bony labyrinth, viewed from outer side: the figure represents the appearance produced by removing the petrous bone down to the denser layer immediately surrounding the labyrinth : 1, 2, 3, the superior, posterior, and external or horizontal semicircular canals ; 4, 5, 6, the ampullse of the same ; 7, the vestibule ; 8, the fenestra ovalis ; 9, fenestra rotunda ; 10, first turn of the cochlea ; 11, second turn ; 12, apex (from Quain., after Sommerring). FIG. 387. Interior view of left bony labyrinth after removal of the superior and external walls : 1, 2, 3, the superior, posterior, and external or horizontal semicir- cular canals ; 4, fovea hemi-elliptica ; 5, fovea hemispherica ; 6, common opening of the superior and posterior semicircular canals ; 7, opening of the aqueduct of the vestibule ; 8, opening of the aqueduct of the cochlea ; 9, the scala vestibuli ; 10, scala tympani ; the lamina spiralis separating 9 and 10 (from Quain, after Som- merring). closed by the membrana tympani secundaria, which is made up of an external or mucous layer, a continuation of that lining the tympanum ; and an internal or serous, a continuation of that lining the cochlea ; between these two is a third or fibrous layer. Be- SENSE OF HEARING. 607 tween the two fenestra} is the promontory, a prominence caused by the projection of the first turn of the cochlea. Internal Ear (Figs. 386, 387). This is called also the labyrinth. It consists of a bony part, the osseous labyrinth, in which is con- tained the membranous labyrinth. Osseous Labyrinth. This is made up of three parts : The vestibule, the semicircular canals, and the cochlea, all of which are connecting cavities in the petrous bone. These cavities not only communicate with one another, but through the fenestra ovalis and fenestra rotunda the osseous labyrinth is in communica- tion with the tympanum ; and through the meatus auditorius internus with the cranial cavity. Vestibule. This cavity is at the inner side of the tympanum, and opens anteriorly into the cochlea and posteriorly into the semicircular canals. It is about 5 mm. in diameter, and on its outer wall communicates with the tympanum through the fenestra ovalis, which is closed by the stapes and its annular ligament. The fovea or fossa hemispherica is a depression on the anterior wall. This is perforated anteriorly, forming the macula cribrosa, and through these perforations the auditory nerves pass to the saccule. Behind the fovea hemispherica is a vertical ridge, the crista vestibuli. The aquceductus vestibuli communicates with the vestibule by an opening at the posterior part of the inner wall. Through this canal pass a vein and the ductus endolymphaticus. The fovea or fossa hemi-elliptica is an oval depression on the roof of the vestibule. Between it and the fovea hemispherica is the crista vestibuli. Posteriorly the semicircular canals open into the vesti- bule, while the opening into the cochlea, apertura scalce vestibuli cochlece, is situated anteriorly. Semicircular Canals. These are three in number, situated behind the vestibule and above it. Each has a diameter of about 1.5 mm., except at one end, the ampulla, where the diameter is 2.5 mm., and each canal is so arranged as to be at right angles to the others. The superior is vertical and at right angles to the posterior surface of the petrous bone ; its ampullated extremity opens into the vestibule, while its other extremity joins with the non-ampullated extremity of the posterior canal, and these open into the vestibule by one common opening. The posterior canal is also vertical, but parallel with the posterior suriace of the petrous bone. Its ampullated extremity opens into the vestibule. The external canal is horizontal, and both its extremities open into the vestibule. It will be seen that the three canals have but five openings into the vestibule, one opening being common to two canals. Cochlea (Fig. 388). The cochlea is situated in front of the vestibule, with its apex directed outward, forward, and downward, its base corresponding to the internal auditory meatus. It is 5 608 THE NERVOUS SYSTEM. mm, long and 9 mm. broad at its base. It consists of an axis, the modiolus or columella, which runs through the entire structure, from the base to the apex ; around the modiolus runs the spiral canal. At the base the raodiolus is perforated to transmit filaments of the cochlear branch of the auditory nerve, and through it ex- tends the canalis centralis modioli, which transmits a nerve and an artery. The spiral canal is about 2 mm. in diameter and 3.3 cm. in length. It makes two and three-fourth turns, clockwise i. e., FIG. 388. The cochlea and vestibule as seen from above: A, cochlea; B, vesti- bule ; (7, internal auditory canal ; D, tympanum. 1, Lower border of fenestra ovalis ; 2, vestibulotympanic cleft; 3, fossa hemispherica ; 4, fossa hemi-elliptica ; 5, fossa cochlearis ; 6, orifice of aqueduct of vestibule ; 7, lower orifice of posterior semi- circular canal ; 8, non-amp ullary orifice of the external semicircular canal ; 9, scala tympani ; 10, scala vestibuli ; 11, cupola ; 12, lamina spiralis, with 12', its vestibulary origin ; 12", its external border ; 13, helicotrema (Testut). in the direction taken by the hands of a clock around the modiolus. At the apex the canal terminates in the cupola. This canal is partially divided into two by a bony septum, the lamina spiralis, which consists of two thin plates of bone between which are minute canals for the transmission of nerve-fibers. The lamina spiralis extends from the modiolus only about half-way toward the outer wall of the spiral canal. In the recent state there is a membrane, the membrana basilaris, extending from the edge of the lamina spiralis to the outer wall, dividing the canal into two parts, the lower being the scala tympani, while the SENSE OF HEARING. 609 upper is again subdivided by a membrane, the membrane ofReissner, into two canals : that between the inner wall of the cochlea and this membrane being the scala vestibuli; and that between the outer wall and the membrane of Reissner, having the membrana basilaris as its base, the scala media, ductus cochlece, or canalis cochlece. This latter is in reality a part of the membranous labyrinth, not of the osseous, but it is somewhat more convenient to describe it at this point. At the apex of the cochlea the lamina spiralis ends in the hamulas, a hook-like process, and here the scala vestibuli and scala tympani communicate, the opening being the helicotrema. At the junction of the lamina spiralis and the modiolus, and winding around the latter, is the canalis spiralis modioli, which lodges the ganglion spirale, an enlargement of the cochlear nerve containing ganglion-cells. From this are given off the nerves to the organ of Corti. The scala vestibuli communicate,s with the vestibule at its lower end. The scala tympani at its lower end terminates at the fenestra rotunda, which is closed by the membrana tympani secundaria. Aquceductus Cochlece. This is a small canal running from the scala tympani to the basilar surface, of the petrous bone which transmits a vein from the cochlea that joins the internal jugular vein. Lining of Osseous Labyrinth. All the cavities of the osseous labyrinth are lined by a fibroserous membrane, regarded by some as periosteum ; this membrane also covers the fenestra ovalis and fenestra rotunda. On its inner surface is a layer of epithe- lium which secretes the perilymph, a watery fluid containing niucin, which fills so much of the osseous labyrinth as is not occupied by the membranous labyrinth. Membranous Labyrinth (Fig. 391). The membranous labyrinth is contained within the osseous, and is, to a certain extent, a dupli- cation of it. Its walls consist of three layers : ] . An external, which is made up of fibrous tissue, rather loose in structure, in which are blood-vessels and pigment-cells similar to those in the retinal pigmentary layer ; 2. A middle layer, thicker than the external, and somewhat like the hyaloid membrane of the eye ; and 3. An internal, composed of polygonal nucleated epithelium which secretes the endolymph or liquor Scarpce, a fluid similar in composition to the perilymph, and contained within the membra- nous labyrinth, as the perilymph is within the osseous. The membranous labyrinth consists of the utricle and saccule, which are contained in the vestibule ; the three membranous semi- circular canals, and the canal of the cochlea or scala media. The utricle, saccule, and membranous semicircular canals are attached on one side to the wall of the osseous labyrinth, and from the opposite side are given off bands of fibrous tissue which hold 39 610 THE NERVOUS SYSTEM. them to the corresponding wall of the osseous labyrinth. In these bands are the blood-vessels and the fibers of the auditory nerve which are distributed to the utricle, saccule, and membranous semicircular canals. Utricle. The utricle or utriculus is situated in the upper and back part of the vestibule at the fovea hemi-elliptica, and is oblong in shape. It communicates posteriorly with the membranous semi- circular canals by five openings, and from it passes a small canal which unites with one from the saccule, the two forming the ductus endolymphaticus. Branches of the auditory nerve pierce the wall of the utricle at one point, and here the tunica propria is thick- ened, and the epithelium consists of columnar cells upon which are long, stiff", tapering hairs, around which the axis-cylinders of the auditory nerve-fibers ramify. Schafer, to Whom we are indebted for this description, says that these are like the rod- and cone-elements of the retina, the bipolar cells of the olfactory membrane, and the gustatory cells of the taste-buds sensory or nerve-epithelium cells. Between the hairs are nucleated cells, FIG. 389. Section of macula of utricle, human : n. utr., bundles of the utricular branch of the eighth nerve; h, auditory hairs; p.l.s., perilymphatic space (G. Betzius). fiber-cells of Retzius, which rest upon the basement-membrane, and are connected at their free extremity with a cuticular mem- brane through which the auditory hairs project. The auditory hairs do not project free into the endolymph, but into a soft, mucus-like substance of a dome-like form in the ampullae, and which in the saccule and utricle has a mass of calcareous particles, otoliths, embedded in it. The otoliths are also called otoconia and ear-stones, and are minute crystals of calcium carbonate. The thickening of the tunica propria with the modified cells, etc., just described, forms the macula acustica in the utricle and saccule (Figs. 389, 390). In the ampullae of the semicircular canals the columnar cells and auditory hairs are upon a ridge, and here the structure is called crista acustica. The cristse of the ampullae have essentially the same structure as the maculae of the utricle and saccule, save that the otoliths are absent. Saccule. The saccule or sacculus is globular, smaller than the utricle, being about 3 mm. by 2 mm. in diameter, and lies in the fovea hemispherica. It receives nervous filaments derived from SENSE OF HEARING. 611 the auditory nerve, which terminate, as already described, in a macula acustica in which are otoliths, and it gives off a small canal which, uniting with that coming from the utricle, forms the FIG. 390. Nerve terminations in macula ; Golgi method (G. Retzius). ductus endolymphaticus. On the opposite side is a similar canal, 1 mm. long and 0.5 mm. wide, the canalis reuniens (Fig. 391), by FIG. 391. Diagram of right membranous labyrinth seen from the external side : 1, utricle; 2, 3, 4, superior, posterior, and horizontal semicircular canals; 5, saccule; 6, ductus endolymphaticus, with 7, 7', its twigs of origin ; 8, saccus endolymphaticus ; 9, canalis cochlearis, with 9', its vestibular cul-de-sac, and 9", its blind extremity; 10, canalis reuniens (after Testut). which it is in communication with the scala media or canalis cochlearis. Ductus Endolymphaticus. This canal, formed by the union of the canals from the utricle and saccule, is lodged in the aquseducttis 612 THE NERVOUS SYSTEM. vestibuli. It terminates in a dilated and flattened cul-de-sac, which lies within the cranial cavity between the layers of the dura mater. Membranous Semicircular Canals. These are three in number, in shape like the osseous canals, but are only about one-third their diameter ; they open by five apertures into the utricle. The lining of the canals forms papilliform elevations (Fig. 392). In each ampulla is the ridge, crista acustica, already described (p. 610). Membranous semicircular canal. Blood-vessel. Wall of mem- branous canal. Epithelium of the membranous canal. Ligament of canal. Bone. Perilymphatic V spaces. Blood-vessel. FIG. 392. Transverse section through an osseous and membranous semicircular canal of an adult human being : a, connective-tissue strand representing a remnant of the embryonic gelatinous connective tissue. Such strands serve to connect the membranous canal with the osseous wall ; X 50 (after a preparation by Dr. Scheibe) (Bohm and Davidoff ). Canal of the Cochlea. For the following description we are indebted to Schafer's Essentials of Histology: "The periosteum, a peculiar kind of connective tissue which covers the upper surface of the lamina spiralis, is thickened, forming the limbus, also called limbus lamince spiralis, and denticulate lamina by Todd and Bow- man, and the edge is grooved, somewhat resembling the letter C, the upper part of which is the labium tympanieum ; between these labia is the sulcus spiralis (Fig. 393). The membrana basilaris, already referred to (p. 608), extends from the labium tympanieum SENSE OF HEARING. 613 to the outer bony wall of the cochlea, where it is enlarged, forming the ligamentum spirale. From the base of the labium vestibulare a membrane (Reissner's membrane) extends to the outer wall, above and nearly parallel with the membrana basilaris. Between this membrane and the membrana basilaris is the ductus cochlearis or ductus auditorius, and in this, situated upon the membrana basilaris, FIG. 393. Section through one of the turns of the osseous and membranous cochlear ducts of the cochlea of a guinea-pig : I, scala vestibuli ; m, labium vestibu- lare of the limbus ; n, sulcus spiralis internus ; o, nerve-fibers lying in the lamina spiralis; p, ganglion -cells ; g, blood-vessels; , bone; 6, Eeissner's membrane; DC, ductus cochlearis; d, Corti's membrane; /, prominentia spiralis; <7, organ of Corti : ft, ligamentum spirale ; i, crista basilaris ; fc, scala tympani ; X 90 (Bohm and Davidoff). is the organ of Corti. The membraua basilaris is composed of stiff, straight fibers, estimated at 24,000 in number, which are embedded in a homogeneous stratum. It is much broader in the uppermost turns of the cochlea than in the lowest ; the width being at the bottom, 0.21 mm. ; in the middle, 0.34 mm. ; and at the top, 0.36 mm." THE NERVOUS SYSTEM. Organ of Corti (Figs. 394, 395). This consists of (1) the rods of Corti ; (2) a reticular lamina ; (3) outer hair-cells ; (4) inner hair-cells. V t' n*' * FIG. 394. Organ of Corti : at x the tectorial membrane is raised ; e, outer sus- tentacular cells ; d, outer auditory cells ; /, outer pillar cells : g, tectorial membrane ; h, inner sustentacular cells; i,p, epithelium of the sulcus spiralis internus; k, labium vestibulare ; e, tympanic investing layer ; m, outer auditory cells ; n, n, nerve-fibers which extend through the tunnel of Corti ; o, inner pillar cell; q, nerve-fibers; 6, 6, basilar membrane ; a, epithelium of the sulcus spiralis externus ; r, cells of Hensen ; s, inner auditory cell ; I, ligamentum spirale (after Eetzius). Rods of Corti. These are of two kinds, the inner, of which there are 5600, and the outer, 3850 in number. They are both FIG. 395. Section of Corti's organ from guinea-pig's cochlea : 8T, scala tympani : TC, tunnel of Corti ; a, bony tissue or spiral lamina ; 6, 6, fibrous tissue covering same continued as substantia propria of basilar membrane ; c, c, protoplasmic envelope of Corti's pillars (e, e) d, endothelial plates ; /, heads of pillars containing oval areas ; g, head plates of pillars ; h, h', inner and outer hair-cells ; m, membrana reticularis ; fc, I, cells of Hensen and Claudius ; n, n, nerve-fibers ; L cells of Deiters (after Piersol). stiff, striated cells ; the shape of the inner has been compared to that of the human ulna, with a depression like the sigmoid cavity and processes like the coronoid and olecranon ; the shape of the SENSE OF HEARING. 615 outer, to the head and neck of a swan. The feet of the rods rest on the basilar membrane, and here may be seen the cells from which they are derived ; their heads are joined together, the head of the outer fitting into the depression of the inner. Inasmuch as the rods are arranged in a series by the side of one another, this arrangement makes a tunnel, the floor of which is the basilar membrane, while the sloping sides are made by the inclined rods. From each outer rod projects a phalangeal process. Reticular Lamina. This is also described under the name membrane of Kolliker, and consists of a network in which are perforations. It is made up of u minute fiddle-shaped cuticular structures," phalanges, and through the perforations which are between these phalanges project the cilia of the outer hair-cells. Outer Hair-cells. These are 12,000 in number, and are arranged in three or four rows external to the outer rods, each cell being surmounted by a bundle of short auditory hairs which projects through one of the perforations of the reticular lamina. From the. other extremity is given off a fine process which is attached to the membrana basilaris. Between the rows of hair- cells are the cells of Deitws, regarded as supporting cells, with their bases on the membrana basilaris and their tapering processes attached to the reticular lamina. Inner Hair-cells. These, 3500 in number, are arranged in a single row, internal to the internal rods, and, like the outer hair- cells, possess auditory hairs. The epithelial cells next to the outer hair-cells are long and columnar, but cubical over the outer wall of the canal of the cochlea ; they are much the same on the inner side of the inner hair-cells, but are of the pavement variety on the membrane of Reissner. Membrana Tectoria. This structure, called also the membrane of Corti, is soft and fibrillated. It extends from the limbus, and " lies like a pad over the organ of Corti," probably resting on the auditory hairs. Retzius states that it is attached to the reticular lamina. Gray says that it is blended with the ligamentum spirale on the outer wall of the spiral canal. Auditory Nerve. The auditory nerve divides into two branches at the bottom of the meatus auditorius internus ; these are the cochlear and vestibular. Cochlear Branch of Auditoi*y Nerve. This is called also cochlear nerve. At the base of the columella or modiolus of the cochlea it subdivides into filaments, which run through it in canals. When they reach the lamina spiralis they form at its base the ganglion spirale, composed of a plexus of the nervous filaments with ganglion-cells. From the ganglion spirale delicate filaments are given off, which pass between the plates of the lamina spiralis until they reach the sulcus spiralis, where they pass out to the organ of Corti. Waldeyer states that here they divide 616 THE NERVOUS SYSTEM. into two groups one going to the inner hair-cells, the other to the outer. Schafer says that " after traversing the spiral lamina they emerge in bundles, and the fibers then, having lost their medullary sheath, pass into the epithelium of the inner hair-cell region. Here some of them course at right angles, and are directly applied to the inner hair-cells, whilst others cross the tunnel of Corti, to become applied in like manner to the outer hair-cells and the cells of Deiters ; but there does not appear to be any continuity between the nerve-fibrils and the cell-substance." Vestibular Branch of Auditory Nerve. This is often spoken of as the vestibular nerve. It divides into three branches : 1, supe- rior, which is distributed to the utricle and the ampullae of the external and superior semicircular canal ; 2, middle, which is dis- tributed to the saccule ; and 3, inferior, which is distributed to the ampulla of the posterior semicircular canal. Physiology of Hearing. Sound is defined by the Standard Dictionary as : "1. The sensation produced through the organs of hearing. 2. The physical cause of this sensation ; waves of alter- nate condensation and rarefaction passing through an elastic body, whether solid, liquid, or gaseous, but especially through the atmo- sphere." Bodies which emit sound are called sonorous bodies, and are at the time in a state of vibration. Thus a tuning-fork when set in vibration produces in the air around it a series of condensations and rarefactions which form " concentric spherical shells of air of different densities. Each air particle swings to and fro in a very short path along the radius of the sphere that is, the vibrations are longitudinal " (Carhart and Chute). These waves are sound-waves, and when they enter the external auditory meatus they set up vibrations in the membrana tympani. . Through the ossicles these vibrations are transmitted to the peri- lymph. The base of the stapes, which, with its annular membrane, closes the fenestra ovalis, communicates these vibrations to the perilymph in the scala vestibuli, along which waves of the fluid travel, passing through the helicotrema and down the scala tympani to the fenestra rotunda, the membrana tympani secun- daria being pressed out as each wave reaches it. In this course the waves of perilymph pass over the membrane of Reissner as they travel up the scala vestibuli, and under the membrana basilaris as they return down the scala tympani, thus setting up corresponding vibrations in the endolymph which fills the membra- nous cochlea. The external ear collects the sound-waves, and in some animals, as in the horse, is very useful in determining the direction from which sounds come ; these animals, by virtue of muscles attached to the ear, can move it in all directions. In man such muscles exist, but in a relatively undeveloped form, and are not under the SENSE OF HEARING. 617 control of the will to any extent, although some individuals can produce a slight to-and-fro motion of the auricle. When the hearing is imperfect the hand is sometimes applied to the ear in such manner as to increase its projection from the side of the head and to supplement it, so as to collect more sound-waves than would otherwise enter the meatus. In order that the membrana tympani should respond to the many tones and shades of tones which reach it, it is important that the pressure upon the internal and external surfaces should be the same, and this is effected by the passage of air through the Eus- tachian tube, so that in going from an atmosphere of one density into that of another the equilibrium is thus maintained. The pharyngeal aperture of the tube, ordinarily closed, is opened by the action of the tensor palati at each act of swallowing. When the membrana tympani moves inward, the manubrium of the malleus moves inward also, and with it the incus, the articulation between these two ossicles being such that in tjiis in- ward movement they move as one. In speaking of this articula- tion Helinholtz says : " In its action it may be compared with the joints of the well-known Breguet watch-keys, which have rows of interlocking teeth, offering scarcely any resistance to revolution in one direction, but allowing no revolution whatever in the other/' When the membrana tympani is forced strongly outward, the manu- brium glides in the joint, and the incus follows it for but a short distance ; if this was not so, in such movements of the membrana tympani the stapes would be pulled out of the fenestra ovalis, and severe, if not irretrievable, injury would result. This extreme outward movement of the membrana tympani might result from increased pressure within the tympanum or diminished pressure in the external -auditory meatus. These movements of the drum- membrane and the stapes are at most but limited ; the maximum for the membrane being only from y 1 ^ to ^ mm., and of the stapes from about ^ to ^ mm. The amplitude of movement of the latter may be only Y^STF mm - Thus is accomplished the conversion of sound-waves into waves of perilymph. Helmholtz says : " The mechanical problem which the apparatus within the drum of the ear had to solve was to transform a motion of great amplitude and little force, such as impinges on the drum-skin, into a motion of small amplitude and great force, such as had to be communicated to the fluid in the labyrinth." A study of the ossicles (Fig. 396) shows that their movement is around the axis of rotation, a-x in Fig. 397. If the distance from this axis to the tip of the manubrium is measured, it will be found to be one and one-half times that from the axis to the end of the long process of the incus, with which the stapes articulates, so that the amplitude of the movement of the stapes 618 THE NERVOUS SYSTEM. will be but two-thirds that of the tip of 'the manubrium, but will have one and one-half times its force. The action of the tensor tympani and that of the stapedius have been already described (p. 604). It is interesting to note that sound may be* conducted to the in- ternal ear through the bones of the skull so as to cause the sensa- tion of hearing. Thus if a vibrating body, as a tuning-fork, is held between the teeth, it can be heard though the ears are closed ; indeed, it sounds more loudly when the ears are closed than when they are open. The sound is conducted by the bones to the internal ear, and also, doubtless, some of the sound is due to vibrations of the membrana tympani. This fact is made use of in the audiphone, a fan-like device held in the teeth by the deaf. If the essential portions of the auditory apparatus are so diseased as to cause deafness, no such device as the audiphone will be of any use. Tlveories of Hearing. Two theories have been advanced to FIG. 396. The chain of auditory ossicles, anterior view: 1, head of malleus; 2, long process of incus; 3, stapes (after Testut). FIG. 397. Ligaments of the ossicles and their axis of rotation. The figure represents a nearly horizontal section of the tympanum, carried through the heads of the malleus and incus : M, malleus ; /, incus ; t, articular tooth of incus ; Ig.a. and Ig.e, external ligament of malleus; Ig.inc, ligament of the incus; the line a-x represents the axis of rotation of the two ossicles (from Foster, after Testut). explain the physiology of hearing : (1) The piano theory and (2) the telephone theory. The Piano Theory. This is by far the older, and may be 'regarded as the theory usually held to explain what takes place in the cochlea. The cochlear division of the auditory nerve sends into the modiolus of the cochlea branches that pass in between the plates of the lamina spiralis, where they form a plexus in which are ganglion-cells, from which the nerve-filaments pass to the organ of Corti, terminating, it is believed, in the hair-cells. The waves already referred to as being set in motion in the endolymph pass over and under these cells, with which the nerve- filaments are connected, and cause the basilar membrane on which they rest to vibrate. This motion is communicated to the outer rods of Corti, which in turn pass it to the hairs of the special audi- tory cells through the medium of the perforated membrane, and from SENSE OF HEARING. 619 there it passes to the nerves. Here it is converted into impulses which are transmitted to the brain, where sound is produced. It has been supposed that the rods of Corti are so arranged as to vibrate with particular tones, one rod for each tone, but it is doubtful whether such a differentiation can be made out in the auditory apparatus. The rods are not present in the ears of birds, and there is no reason to believe that birds cannot appreciate musical tones. In the basilar membrane there are' fibers enough to respond to all the notes that can be appreciated that is, from 33 waves to 38,000 waves in a second. It is more probable that the rods simply act as levers to communicate the vibrations of the fibers of the basilar membrane to the terminal nerve-filaments in the auditory cells. Just how one is able to distinguish the differences in the in- tensity (loudness), pitch, and quality of sounds is not understood. The explanation most generally accepted at the present time, as to pitch at least, is that as when a tone is sung over the strings of a piano, certain strings are set in vibration sympathetically, so in the basilar membrane, where, as in the piano, there are fibers of different lengths, these respond to different tones, and that in con- nection with each tone there is a separate filament of the auditory nerve, so that if the note is a high one a certain fiber is set in vibration, and the nerve-filament in communication with it transmits an impulse to certain cells in the brain, which when excited give the impression of a high note, and so with other notes and other nerve-cells. The Telephone Theory. The introduction of the telephone and a study of its mechanism have led some writers to question the explanation which is generally accepted of the mechanism of hearing, and to suggest that as the single telephone wire transmits the complex sounds produced by an orchestra to a distance where they are reproduced in all their variety of intensity, pitch, and quality, so " the cochlea does not act on the principle of sympa- thetic vibration, but that the hairs of all its auditory cells vibrate to every tone, just as the drum of the ear does ; that there is no analysis of complex vibration in the cochlea or elsewhere in the peripheral mechanism of the ear ; that the hair-cells transform sound-vibrations into nerve-vibrations similar in frequency and amplitude to the sound-vibrations ; that simple and complex vibra- tions of nerve-molecules arrive in the sensory cells of the brain, and there produce, not sound again, of course, but the sensations of sound, the nature of which depends not upon the stimulation of different sensory cells, but on the frequency, the amplitude, and the form of the vibrations coming into the cells, probably through all the fibers of the auditory nerve." This explanation has been put forth by Prof. William Rutherford under the title of the " Telephone Theory of the Sense of Hearing." 620 THE NERVOUS SYSTEM. In referring to this subject, Waller compares the basilar mem- brane to the rnembrana tympani in the following language : " It is the internal drum-head, repeating the complex vibrations of the membrana tympani, and vibrating in its entire area to all sounds although more in some parts than in others ^giving what we may designate as acoustic pressure patterns between the membrana tectoria and the subjacent field of hair-cells. In place of an analysis by sympathetic vibration of particular radial fibers, it may be imagined that varying combinations of sound give vary- ing pressure patterns, comparable to the varying retinal images of external objects." There are several terms used in the discussion of the subject of sound which it is important to understand ; especially is this true for the medical student, for he will constantly meet them in his study of physical diagnosis. Period; Amplitude; Frequency. If a weight attached to a rubber cord (Fig. 398) is pulled down and then released, the weight and the particles composing the cord will vibrate, and any particle, as a, will oscillate between two extreme points, as b and c, which are equidistant from a. The motion of a from c to b and back again to c is one vibration or one complete vibration, and the time this FIG. 398. Weight and cord. xi_ j /> ,r -u x- occupies is the period ot the vibration. The distance from a, when the particle is in equilibrium, to b or to c is the amplitude of the vibration, and the number of complete vibrations in one second is the fre- quency. Noises. These are sounds produced by irregular vibrations i. e. y wanting in periodicity ; or by discordant or dissonant sounds i. e., sounds which differ from one another in pitch ; or they may be single, sudden sounds, as the report of a cannon. Noises are disagreeable sounds. Musical Sounds. These are sounds produced by regular vibra- tions, and they produce a pleasing effect upon the ear. It should be said, however, that what may under some circum- stances be a noise may, under others, produce the effect of a musical tone. Haughton says : " Nothing can be imagined more purely a noise or less musical than the jolt of the rim of a cab wheel against a projecting stone ; yet if a regularly repeated succession of such jolts takes place, the result is a soft, deep, musical sound that will bear comparison with notes derived from more sentimental sources." And Zahm says : " With a sufficient number of properly tuned bottles a skilful performer could, by SENSE OF HEARING. 621 merely withdrawing the corks, easily evoke a simple melody that every one would recognize." Musical sounds differ in intensity, pitch, and quality. . Intensity. This depends upon the energy with which the particles of air in vibration strike upon the air, and : (1) Varies directly as the square of the amplitude of vibration of the sound- ing body ; (2) varies inversely as the square of its distance ; and (3) diminishes with the density of the air. Loudness is oftentimes spoken of as synonymous with intensity, but it depends somewhat upon the condition of the ear and upon the rate of vibration, all sounds not affecting the ear alike, as well as upon the energy of vibration. Pitch. This depends upon the frequency of vibration or vibra- tion frequency, as it is called ; the more vibrations per second, the higher is the pitch. There must be at least 30 vibrations in a second to produce a continuous sound, and when these are more frequent than 38,000 in a second they become inaudible, at least to the human ear, although other creatures than man may still hear them. These limits are those assigned by Helmholtz ; others give the lowest number as 16 and the highest as 41,000. Most musical sounds are produced by vibrations between 27 and 4000 a second. Quality. This is called also timbre and tone-color. As it is a property of sound which is difficult to understand, and even to define, we will quote some of the definitions which are given of it. Thus the Standard Dictionary defines " quality" as "That which distinguishes sounds of the same pitch and intensity from different sources, as from different instruments." And this same authority defines " timbre" as "The special peculiarity of a continuous sound or musical tone, or that common to all tones from the same source, as the human voice or some particular instrument, dis- tinguishing them from notes from different sources, due to the special form of the sound-waves ; the quality of a tone, as distin- guished from intensity and pitch, called sometimes tone-color." This sentence is quoted by the Standard from Silliman's Physics : " The essential difference between the bass and tenor voices, and between the contralto and soprano, consists in the tone or timbre which distinguishes them even when they are singing the same note." Quality is, then, concisely, that which enables us to distinguish one sonorous body from another as, a piano from a violin, or a flute from a harp, etc. ; and Helmholtz has demonstrated that "the quality of a sound is determined by the number, order, and relative intensity of the partial tones into which it can be decom- posed" To understand this it will be necessary to consider briefly the compound character of musical sounds. Compound, Fundamental, and Partial Tones. When a string 622 THE NERVOUS SYSTEM. stretched between two points is set in' vibration, as by drawing the bow of a violin over it, it will vibrate as a whole (Fig. 399, a-b) and emit a tone which, being the lowest that it can emit, is its fundamental or prime tone. If now this string is held at its middle point, c, and either half is bowed, that half of the string will vibrate, and after the finger has been removed the other half will also vibrate, and the tone emitted will be an octave higher ; in a similar manner the string may be held at one-third, one- fourth, etc., of its length, and the string when bowed will divide into three or four segments, and the frequency of the emitted tones will be three or four times that emitted by the string when it vibrated as a whole. Such a series of tones is a harmonic series, and all the tones above the fundamental are har- monic overtones , or upper partial tones, or simply partial tones. To demonstrate this more effectively, a sonometer may be used, which con- sists of a wire stretched over a sounding-box (Fig. 400) with a graduated scale, so that the divisions of the wire may be accurately determined. In order to produce these overtones it is not neces- sary to divide the string with the finger, or, in the case of the sonom- eter, the wire with the bridge ; for in the vibration of the string or wire as a whole it divides itself, so that it may vibrate as a whole and also in segments ; and consequently, while the whole vibrat- ing string or wire emits the fundamental tone, the subdivided seg- ments emit each its own partial tone, producing therefore compound tones, the fundamental tone determining the pitch. As a rule, the FIG. 399. Vibrating strings. FIG. 400. Sonometer. sounds of musical instruments are compound tones, and, as Helm- holtz has shown, it is the partial tones which determine their quality by which they are differentiated from one another, there being no difference in the fundamental tones. Thus if a key on a piano, say "middle C," is struck, the string will vibrate^ as a whole 1 32 times in a second, producing one fundamental tone, C, and it will also break up into segments which will vibrate respectively 264 times, producing the octave C f ; 396 times, producing the fifth above this ; 528 times, producing the second octave C" ; 660 times, producing the third above this, etc. SENSE OF HEARING. 623 These tones are believed to form a composite wave, and as such to strike the membrana tympani ; and, according to the " piano theory," this wave is analyzed into its component tones by the basilar membrane, each of whose fibers is caused to vibrate by a partial tone ; while according to the " telephone theory" this analysis takes place in the brain. Resonators. That musical sounds possess this compound char- acter Helmholtz demonstrated by means of resonators (Fig. 401), which consist of metallic globes of various sizes having two openings of unequal diam- eter. If one of these is held with its small opening to the ear, and the large one is held toward a source of sound, the resonator will resound when a tone is emitted which corresponds to the vibration- rate of its contained air, and to no other, and by using a series of these the various overtones may be identified. To sum up the properties of sounds and their causes, we may say that the amplitude of a wave determines its intensity ; its vibration-frequency, its pitch ; its form, its quality. Semicircular Canals, Utricle, and Saccule. The utricle and saccule have been regarded by some authorities as having the function of responding to irregular vibrations, and as being connected, therefore, with the perception of noises, while the perception of musical sounds depends upon the cochlea ; but the consensus of opinion now is that, together with the semicir- cular canals, they are connected with the important function of the preservation of the equilibrium of the body, the utricle and saccule with static equilibrium i. e., when the body is in a state of rest ; the semicircular canals with dynamic equilibrium i. e., when the body is in motion. This subject is discussed in connection with the cerebellum (p. 493). FIG. 401. Resonator. V. REPRODUCTIVE FUNCTIONS. THE reproductive functions are those concerned in the perpetua- tion of the species. In the lower forms of animal life, where the individual consists of a- single cell, this process of reproduction is very simple, consisting of the division of the cell into two, each of which has the power of dividing to form new individuals in the same manner as it was formed. This is asexual reproduc- tion. In the higher animals the reproduction is sexual that is, it requires the union of two elements produced in the organs of two individuals, the male and the female, neither of which can accomplish the process alone. REPRODUCTIVE ORGANS. These organs, which are also called the genital or generative organs, are in the male the testes, each with its duct, the vas FIG. 402. Diagram representing the male genital apparatus of right side : A, bladder ; B, prostatic urethra ; C, membranous urethra ; I), spongy urethra. 1, Eight testicle ; 2. epididymis ; 3, vas deferens, with 3', its ampulla ; 4, seminal vesicle ; 5, ejaculatory duct opening at the verumontanum ; 6, Cowper's gland; 7, its excre- tory duct (Testut). deferens, the vesiculae seminales, and the penis (Fig. 402) ; and in the female, the ovaries, Fallopian tubes, uterus, and vagina. 624 GENITAL ORGANS OF THE MALE. 625 Genital Organs of the Male. Testes. The testes or testicles (Fig. 403), two in number, are situated in the scrotum. They are composed of lobules, the number of which in each testis is variously estimated at from two hundred and fifty to four hundred. In each lobule are convoluted seminiferous tubules, tubuli seminiferi, varying in number from one to three. These tubules contain epithelial cells of two varieties, susten- tacular cells, or Sartoli's columns, and spermatogenic cells, the latter being related only to the formation of spermatozoa. These two varieties of cells are sometimes described as the parietal cells. Internal to these are the mother-cells, which are derived from the spermatogenic cells by the process of mitosis or karyokinesis Globm Major Vaga Efferentia Globus Minor FIG. 403. Vertical section of the testicle to show the arrangement of the ducts (Leroy). (p. 28). These give rise to a third and more internal layer of daughter-cells, from whose nuclei, by the disappearance of the cell-body, the spermatoblasts are developed. These in turn become spermatozoa. This process by which spermatozoa are formed is known as spermatogenesis. Spermatozoa (Fig. 404). A human spermatozoon is about 50 /JL in length, and consists of a head from 3 p to 5 // long, a body and a tail, the last terminating in the end-piece of Retzius, which is the end of the axial fiber which runs through the center of the body and tail. The tail during the living condition is in rapid motion, by virtue of which the spermatozoon can travel quite rapidly. The vitality of spermatozoa is considerable, as they can live for several 40 626 REPRODUCTIVE ORGANS. days outside the body, and they are also very resistant to low temperatures. They appear at the a/"\ time of puberty, and have been f r found in individuals ninety years ^^ * of age, though they are not com- FIG. 404. Human spermatozoa. The two at the left after Retzius; the one at the extreme left is seen in profile ; the others in surface view ; the one at the right is drawn as de- scribed by Jensen : a, head ; b, ter- minal nodule; c, middle piece; d, tail ; e, end-piece of Eetzius (Bohm and Davidoff). FIG. 405. Spermatozoa : a, human ; 6, of the rat; c, of menobranchus (X 480). Epithelium. Inner longi- tudinal muscular layer. uter longi- tudinal muscular layer. FIG. 406. Cross-section of vas deferens near the epididymis (human) (Huber). GENITAL ORGANS OF THE MALE. 627 monly found in semen after the age of seventy or seventy-five years is past. The spermatozoa of different animals vary in size, though their general appearance is much the same (Fig. 405). Their number is very great ; some writers state that in a single ejaculation as many as 25,000,000 may be discharged, while one has placed their number as high as 412,500,000. Both figures may be correct, inasmuch as the amount of semen ejaculated varies at each emission. The seminiferous tubules terminate at the apices of the lobules B FIG. 407. Vas deferens and seminal vesicle, A, seen in longitudinal and, J?, in horizontal section : 1, vas deferens ; 2, its terminal or ampullary portion ; 3, semi- nal vesicle with, 3', its partitions; 4, its terminal portion ; 5, ejaculatory duct (Testut). FIG. 408. Eight seminal vesicle, unfolded and seen on its posterior aspect (subject of forty years, previous injection of tallow) : 1, vas deferens, with, 1', its ampulla ; 2, seminal vesicle with, 3, its lateral prolongation ; 4, its enlargements in form of cecum ; 5, protuberances of its wall ; 6, junction of the vesicle and vas deferens ; 7, ejaculatory duct (the dotted line, x x, indicates the level of the upper extremity of the vesicle before its unfolding) (Testut). in the vasa recta (straight tubes), about thirty in number. In the mediastinum these tubes form a network, the rete testis, the vessels of which end in the vasa efferentia, about fifteen in number. These vessels connect the testicles with the epididymis, the con- tinuation of which is the vas deferens. The canals of the rete testis are lined by non-ciliated epithelium ; the vas aberrans, how- 628 REPRODUCTIVE ORGANS. ever, which is connected with it, has ciliated epithelium. Ciliated columnar and non-ciliated cubical epithelium line the vasa efferentia. Vas Deferens (Fig. 406). This duct, the excretory duct of the 'frrs"- FIG. 409. Sagittal section through the ampulla of the right vas deferens and ejaculatory duct : 1, ampulla of vas deferens ; 2, ejaculatory duct : 3, seminal vesicle dissected away in its middle portion; 4, its opening into the ejaculatory duct ; 5, bladder ; 6, urethra ; 7, prostate ; 8, verumontanum. testis, has a thick muscular wall. Its lining epithelium is partly simple ciliated columnar, and partly stratified ciliated columnar, FIG. 410. Seminal vesicles and vasa deferentia, posterior view: 1, bladder; 2, prostate; 3, 3', seminal vesicles; 4, 4', vasa deferentia; 5, ejaculatory ducts; 6, 6', ureters; 7, 7, peri vesicular cul-de-sac of peritoneum; 8, interdeferential triangle, in direct relation with the rectum, from which it is separated only by the prostato- peritoneal aponeurosis. The two crosses (+ -f ) indicate the points at which the ureters disappear in the vesical wall (Testut). though the cilia are sometimes absent. At the base of the bladder this duct lies between it and the rectum, and here presents an GENITAL ORGANS OF THE MALE. 629 enlargement, the ampulla (Figs. 407, 408), beyond which, at the base of the prostate, it narrows and joins with the duct of the vesicula seminalis, thus forming the ejaculatory duct (Fig. 409). The total length of the duct is about 60 cm. Vesicula Seminalis (Fig. 410). This structure is a diverticulum from the vas deferens, and glands exist in its mucous membrane which is covered with non-ciliated columnar epithelium. Some authorities regard it as a storehouse for the semen, while others do not regard this as one of its functions. Bohm and Davidoff state that " spermatozoa are, as a rule, not met with in the seminal FIG. 411. Section of penis, bladder, etc. : 1, symphysis pubis ; 2, prevesical space ; 3, abdominal wall ; 4, bladder ; 5, urachus ; 6, seminal vesicle and vas deferens ; 7, prostate ; 8, plexus of Santorini ; 9, sphincter vesicae ; 10, suspensory ligament of penis; 11, penis in flaccid condition; 12, penis in state of erection ; 13, glans penis; 14, bulb of urethra,; 15, cul-de-sac of bulb. ' a, Prostatic urethra; 6, membranous urethra; c, spongy urethra (Testut). vesicles." The vas deferens and especially its ampulla serve to retain the semen until ejaculated. A considerable amount of fluid is added to the semen by the secretion of the mucous membrane lining the vesicula seminalis, and this is probably its most im- portant function. The ejaculatory ducts discharge into the urethra at its prostatic part. The prostate gland and Cowper's glands contribute also to the formation of the semen. Semen. The semen or seminal fluid consists of secretions from 630 REPRODUCTIVE ORGANS. the testes, vasa deferentia, vesiculae seminales, prostate, Cowper's glands, and the muciparous glands of the urethra. It is whitish in color, viscid in consistency, alkaline in reaction, and possesses a characteristic odor. The amount ejaculated varies from 0.5 c.c. to 6 c.c. It contains from 82 to 90 per cent, of water, nuclein, protamin, proteids, xanthin, lecithin, cholesterin, fat, sodium and potassium chlorids, sulphates, and phosphates. From it may be obtained Charcot's crystals, which are a phosphate of the nitrogen- ous base, spermin, and which have their origin in the portion of the semen which is contributed by the prostate; to the decomposition of the substance which produces these crystals the odor of the semen is at- tributable. While the spermatozoa are the essential fertilizing agents, the presence of the fluid portion of the semen is important as giving to them their mobility, without which they could not travel in the genera- tive passages. Penis (Fig. 411). The penis serves a double purpose, inasmuch as it is the organ of copulation and also the termination of the urinary passages. The former function is undoubtedly the essential one, for thefe !s DO I ^ Bon wh ^ ! he urin "7 passages could not terminate at the surface of the body ; it is, however, manifestly advantageous in provid- ing for the perpetuation of the spe- cies that the semen should be ex- pelled as near as possible to the mouth of the uterus, a result which is obtained by the intromission of the penis. The penis consists of erectile tissue arranged in three subdi- visions, two above, corpora cavernosa, and one below, corpus spongiosum, which latter terminates in the glans penis. The corpora cavernosa are surrounded by fibro-elastic sheaths from which are given off trabeculce. These pass inward, and between them are spaces which contain venous blood. A similar structure characterizes the corpus spongiosum which encloses the urethra. The arteries which supply the penis are derived from the internal pudic (Fig. 413). Sensory nerves are distributed to the FIG. 412. Sagittal section of the anterior extremity of the penis : 1, glans penis ; 2, corpus cavernosum ; 3, 3, spongy portion of urethra; 4, meatus urinarius ; 5, fossa uavicularis ; 6, left half of the valve of Guerin ; 7, sinus of Guerin between the valve and the anterior wall of the urethra ; 8, left lateral border of urethra; 9, its lower surface ; 10, prepuce pushed back behind the glans ; 11, frenum ; 12, integument ; 13, dorsal vein ; 14, fibrous partition between the corpus cavernosum and corpus spongiosum (Testut). GENITAL ORGANS OF THE FEMALE. 631 skin of the penis, and especially to the glans penis, where they terminate in Meissner's corpuscles, Krause's spheric end-bulbs, and genital corpuscles (Fig. 414). FIG. 413. Diagram of the arterial circulation of the penis : 1, corpus cavernosum, with 1', its root ; 2, suspensory ligament ; 3, corpus spongiosum with 4, bulb ; 5, glans; 6, internal pudic artery; 7, bulbo-urethral artery, with 7', itsbulbar branch, 7", its anterior branch going to the frenum; 8, arteria cavernosa, with 8', its recur- rent branch ; 9, dorsal artery ; 10, 10, its lateral branches ; 11, its termination in the glans (Testut). Sensory nerves are distributed also to the verumontanum, in the urethra, and the pleasurable sensations connected with coitus are due to the excitation of the nerves here distributed, as well as to those supplying the glans penis. In addition to sensory nerves there are also distrib- uted to the penis e x c i t o r nerves, nervi erigentes, which are derived from the first and second, and sometimes from the third, sacral nerves ; they are vasodilator nerves, and have their origin in the sex- ual center of the spinal cord. Genital Organs of the Female. Ovary. The ova- ries (Fig. 415), two in num- ber, are attached to the pos- terior surface of the broad ligament, one on each side of the uterus, with which they are connected by the ova- rian ligament, a fibromuscular structure. They are covered by peritoneum, except at the hilum, which is, however, somewhat modified, its mesothelial cells form- ing the germinal epithelium (Fig. 416), the cells of which are FIG. 414. Genital corpuscle from the glans penis of man ; methylene-blue stain (Dogiel, Arch. f. mile. Anat., vol. xli.). 632 REPRODUCTIVE ORGANS. FIG. 415. Posterior view of left uterine appendages: 1, uterus ; 2, Fallopian tubes; 3, fimbriated extremity and opening of the Fallopian tube ; 4, parovarium ; 5, ovary ; 6, broad ligament; 7, ovarian ligament; infundibulopelvic ligament (Henle). FIG. 416. Section through part of ovary of adult bitch : a, germinal epithelium ; 6, 6, ingrowths (egg-tubes) from the germinal epithelium, seen in cross-section ; c, c, young Graafian follicles in the cortical layer ; d, a more mature follicle, containing two ova (this is rare) ; e and /, ova surrounded by cells of discus proligerus ; g, h, outer and inner capsules of the follicle; i, membrana granulosa; I, blood-vessels; m, m, parovarium ; g, germinal epithelium commencing to grow in and form an egg- tube ; z, transition from peritoneal to germinal epithelium (from Waldeyer). GENITAL OEGANS OF THE FEMALE. 633 cubical or cylindrical and higher than those of the rest of the peritoneum. At the hilum the connective tissue of the ovarian ligament passes into the ovary, forming the stroma (Fig. 417), which constitutes the greater part of the organ. The spindle- shaped cells of the stroma are regarded by His as unstriped muscle-cells, while Waldeyer, Henle, and others consider them to be connective-tissue cells. Beneath the germinal epithelium is a condensed portion of the stroma, which was formerly described under the name of tunica albuginea, and was regarded as a cover- ing or coat of the ovary. The outer third of the ovary is the cortex, while the inner or deeper two-thirds is the medulla, in FIG. 417. Part of the same section as represented in Fig. 415, more highly enlarged : 1, small Graafian follicles near the surface ; 2, fibrous stroma ; 3, 3', less fibrous, more superficial stroma ; 4, blood-vessels ; 5, a follicle still further advanced ; 6, one or two more deeply placed; 7, one further developed, enclosed by a prolonga- tion of the fibrous stroma ; 8, part of the largest follicle ; a, membrana granulosa ; b, discus proligerus; c, ovum; d, germinal vesicle; e, germinal spot (Schron). which are the blood-vessels giving to this medullary portion another name by which it is sometimes known, zona vasculosa. In the cortex above are the Graafian follicles, the medulla con- taining none of them. These are sacs varying in size according to the stage of their development. In the Graafian follicles are the ova, the least developed of which are covered by a single layer of cells, those further advanced, by several layers, constituting the membrana grannlosa. The ova and the cells are derived from the germinal epithelium. A mature Graafian follicle (Fig. 418) has a diameter of from 8 to 19 mm., and extends from the medulla to the surface of the ovary and projects therefrom (Fig. 419), rupturing at the most 634 REPRODUCTIVE ORGANS. projecting part and permitting the escape of the ovum. The wall of the follicle, theca folliculi, is a condensed layer of the stroma, Membrana granulosa. Discus proligerus. Ovtun. Germinal vesicle. Blood-vessel. FIG. 418. Section of fully developed Graafian follicle from injected ovary of pig; X 50 (Bohm and Davidoff ). and is itself divisible into an outer layer of fibrous connective tissue, tunica externa, and an inner, tunica internet, which is charac- _, terized by the presence of ^~x -'l^i^L blood-vessels and of cells. Within the theca is the mem- brana granulosa or stratum granulosum, which is com- posed of several layers of small polyhedral cells. In one portion of the membrana granulosa the cells are very numerous, constituting the discus proligerus, in which the ovum lies embedded. The cells of the discus pro- ligerus which are in contact with the ovum are arranged radially, constituting the corona radiata (Fig. 422). Between the discus proligerus and the membrana granulosa, except at the point where the two are in contact, is a cavity, the antrum, which is filled with FIG. 419. Ovary with mature Graafian follicle about ready to burst (Ribemont- GENITAL ORGANS OF THE FEMALE. 635 a Ruid, liquor folliculi, formed by a secretion of the cells and by the destruction of some of them. Graafian follicles continue to be formed in the ovary for a short time after birth, and have been estimated to number, in both ovaries, more than 70,000 ; but a small proportion of these, however, become mature, the rest undergoing degeneration. During the development of Graafian follicles the ova which they contain also become developed in the following manner (Nagel, Bohm and Davidoff). In the early period of the develop- ment of the ovary the germinal epithelium pushes into the sub- jacent connective tissue in solid projections (Fig. 416); these form the primary egg-tubes of Pfluger, some of the cells of which become ova, while others become Graafian follicles. The differentiation FIG. 420. Mature ovuin of rabbit: a, cells from the discus proligerus (epithe- lium of cvum) ; 6, zona pellucida ; c, vitellus ; d, germinal vesicle ; e, germinal spot ; /, large globules with dull luster in the germinal vesicle. of the cells of the germinal epithelium into ova and follicles may occur in the epithelium itself, in which case the larger cells con- stitute primitive or primordial ova. " In the further development of the ovarian cortex the primitive egg-tubes are penetrated throughout by connective tissue, so that each egg-tube is separated into a number of irregular divisions. In this way a number of distinct epithelial nests are formed, which lose their continuity with the germinal epithelium and finally lie embedded in the con- nective tissue. According to the shape and other characteristics of these epithelial nests, we may distinguish several different groups : (1) The primitive egg-tubes of Pfliiger ; (2) the typical primitive follicles i. e., those which contain only a single egg-cell (present in the twenty-eighth week of fetal life) ; (3) the atypical follicles i. e., FIG. 424. FIGS. 421-424. From sections of cat's ovary, showing ova and follicles in different stages of development: a, a, a, a, germinal spots; 6, 6, 6, 6 germinal vesicles ; c, e, c, c, ova ; d, d, d, zonse pellucidse ; e, e, e, e, corona radiata ; /, /, /, /, thecae folliculorum ; g, beginning of formation of the cavity of the follicle- X*225 (Bohm and Davidoff). 636 GENITAL ORGANS OF THE FEMALE. 637 those containing two or three egg-cells ; (4) the so-called nests of follicles, in which a large number of follicles possess only a single connective-tissue envelope ; (5) follicles of the last-named type, which may assume the form of an elongated tube, and which are then known as the constricted tubes of Pfl tiger. The fourth, fifth, and possibly the third types are further divided by connective- tissue septa, until they finally form distinct and typical follicles (Schottlander). " In the adult ovary true egg-tubes are no longer developed. Isolated invaginations of the germinal epithelium sometimes occur, but apparently lead merely to the formation of epithelial cysts (Schottlander). The theories as to when the formation of new epithelial nests or follicles ceases are, however, very conflict- ing, some authors believing that cessation takes place at birth, others that it continues into childhood and even into middle age. " The ova of the primitive or primordial follicles attain a size (in fresh tissue teased in normal salt solution) varying from 48 fj. to 69 //. They possess a nucleus varying in size from 20 -/JL to 32 p., presenting a doubly contoured nuclear membrane, and containing a distinct chromatin network with a nucleolus and several accessory nucleoli. The protoplasm shows a distinct spongioplastic network containing a clear hyaloplasm. The primitive ova, until they undergo development, retain this size and structure, irrespective of the age of the individual. They are numerous in embryonic life and early childhood, always found during the ovulation period, but not observed in the ovaries of the aged. Changes in the size and structure of the ova accompany the proliferation of the foilicular cells in the growing follicles. As soon as the follicular cells of a primitive follicle proliferate, as above described, the ovum of the follicle increases in size until it has attained the size of a fully developed ovum. The zona pellucida now makes its appearance, and after this has reached a certain thickness, yolk granules (deutoplastic granules) develop in the protoplasm of the ovum. In a fully developed Graafian follicle the ovum presents an outer clearer protoplasmic zone and an inner fine granular zone containing yolk-granules ; in the former lies the germinal vesicle. Between the protoplasm of the ovum and the zona pellucida is found a narrow space known as the perivitelline space. The germinal vesicle (nucleus), which is usually of spherical shape, possesses a doubly contoured membrane and a large germinal spot (nucleolus), which shows ameboid movements. " The origin of the zona pellucida has not as yet been fully determined. It probably represents a product of the egg-epithe- lium, and may be regarded in general as a cuticular formation of these cells. At all events it contains numerous small canals or pores into which the processes of the cells composing the corona 638 REPRODUCTIVE ORGANS. radiata extend. These processes are to be regarded as inter- cellular bridges (Retzius) ; and, according to Palladino, they occur not only between the ovum and the corona radiata, but also between the follicular cells themselves. In the ripe human ovum the pores are apparently absent (Nagel), and it is very probable that they have to do with the passage of nourishment to the grow- ing egg. Retzius believes that the zona pellucida is derived from the processes of the cells composing the corona radiata, which at first interlace and form a network around the ovum. Later, the matrix of the membrane is deposited in the meshes of the net- work, very probably by the egg itself." Ovum. The human ovum has a diameter of from 0.22 to 0.32 mm. The external envelope is the zona pellucida, the origin of which, as has been stated, is uncertain. Within this is the vitellus with its nucleus, the germinal vesicle, whose diameter is from 30 p to 40 //. The vitellus consists of a protoplasmic network, in the FIG. 425. Portion of broad ligament stretched to show the parovarium (p) lying between the folds and consisting of the head-tube and cross-tubules (Gegenbaur). meshes of which are embedded highly refractive oval bodies, the yolk-globules. The germinal vesicle has a distinct enveloping membrane, and within it is a scanty framework with a small amount of chromatin, and one or two false nucleoli, germinal spots, due to the thickening of the chromatin. These structures have a diameter of from 7 JJL to 10 p. Parovarium (Fig. 425). This structure is known also as the epoophoron and the organ of Rosenmutter. It lies within the b^oad ligament, between the Fallopian tube and the ovary, and represents what remains of the Wolffian body of the fetus. The tubules of that organ being the short canals of the parovarium, and the upper part of the Wolffian duct being represented by the head-tube. This latter sometimes persists as a patent canal, con- stituting Gartner** duct, which is the homologue of the vas deferens. The paroophoron is a structure sometimes observed GENITAL ORGANS OF THE FEMALE. 639 within the broad ligament near the ovary, ordinarily closer to the uterus than the parovarium. It appears also as tubules, and these FIG. 426. Dissection of the pelvic organs, showing the relation of the abdominal parietes to the round ligaments and the bladder : 1, 3, the obliterated hypogastric arteries; the urachus (Bourgery arid Jacob). correspond to the transverse tubules of the lowest part of the fetal Wolffian bodv. The tubules in adult life sometimes be- FIG. 427. Fallopian tube laid open : a, 6, uterine portion of tube ; c, d, folds of mucous membrane ; e, tubo-ovarian ligament or fimbria ovarica ; /, ovary ; g, round ligament (from Playfair). come distended, forming cysts which require operative interference for their removal. 640 REPRODUCTIVE ORGANS. Fallopian Tubes (Figs. 427, 428). Tnese tubes are each about 10 cm. in length, and extend from the angles of the uterus to the vicinity of the ovaries. The ovarian extremity of each tube expands into a funnel-shaped opening, the pavilion or infundi- bulum, which is surrounded by fringed processes, the fimbrise. At the uterine extremity its lumen will scarcely admit a bristle, while at the ostium abdominale, the outer opening where the tube expands into the infundibulum, its diameter is about 4 mm. The tube is composed of three coats, an internal mucous, next to this a muscular, and, most external, a serous or peritoneal. The FiG. 428, Transverse section of Fallopian tube, showing the complicated arrange- ment of the longitudinal plications which are here cut across (Martin). mucous membrane is arranged in longitudinal folds (Figs. 427, 428) and covered by a single layer of ciliated columnar epithe- lium. There are no distinct glands in the duct, though some writers regard the crypts as fulfilling the function of glands. The muscular coat consists of an inner circular and an outer longitu- dinal layer. Uterus (Fig. 429). This organ in the virgin condition has a length of about 7.5 cm., a width of 4 cm. at its widest part, and a thickness of 2.5 cm. It is divided into a body or corpus and a neck or cervix, and is composed of three coats mucous, muscular, and peritoneal. The mucous, which is the internal coat, is covered GENITAL ORGANS OF THE FEMALE. 641 by a single layer of columnar ciliated epithelium, that extends to the external os, where the epithelium is of the stratified Tube. Reflection of. peritoneum. FIG. 429. Anterior view of virgin uterus, showing relations of cervix to corpus uteri and reflection of peritoneum at isthmus. squamous variety. Some authorities describe this latter variety of epithelium as covering the lower third of the cervical mucous FIG. 430. Section of human uterus, including mucosa (a) and adjacent mus- cular tissue (6) ; c, epithelium of free surface and tubular uterine glands (d) ; /, deepest layer of mucosa, containing fundi of glands; h, strands of non-striped muscle penetrating within the mucosa (Piersol). membrane. In the mucous membrane are numerous uterine glands (Fig. 430), into which the ciliated epithelium extends. The 41 642 REPRODUCTIVE ORGANS. motion of the cilia of the uterine mucous membrane is toward the vagina. In the mucous membrane of the cervix are closed sacs lined by cylindrical or ciliated epithelium ; these are the ovula Nabothi, and are regarded as cystic formations. The muscular coat (Fig. 431) consists of three layers : An inner and an outer, both longitudinal ; and a middle circular, which is more highly developed than the other two. The muscular tissue is of the unstriped variety (Fig. 432). Ovtllation. The formation of ova in the human female is FIG. 431. Arrangement of uterine muscle, as seen from in front after removal of serous coat (Helie). probably complete two years after birth. Although during this period, and, indeed, even before birth, some ova may undergo development to some extent, still it is not until the period of puberty that there is any approach to regularity in the develop- ment of either the Graafian follicles or the ova. At undetermined periods Graafian follicles rupture and mature ova are discharged, together with the cells of the discus proligerus. This ripening and discharge of ova constitute ovula tion. The cause of the OVULATION. 643 rupture of the follicle is still an unsettled question. In discussing this subject Bohm and Davidoff say : "The manner in which the fully developed Graafian follicle bursts and its ovum is freed is still a subject of controversy ; the following may be said regarding it : By a softening of the cells forming the pedicle of the discus proligerus, the latter, together with the ovum, are separated from the remaining granulosa, and lie free in the liquor folliculi. At the point where the follicle comes in contact with the tunica albuginea of the ovary the latter, with the theca folliculi, becomes thin, and in this region, known as the stigma, the blood-vessels are obliterated and the entire tissue gradually atrophies; thus a point of least resistance is FIG. 432. A, isolated muscle-elements of the non-pregnant uterus ; B, cells from the organ shortly after delivery (Sappey). formed which gives way at the slightest increase in pressure within the follicle, or in its neighborhood. "The increase of pressure within the follicle, leading to its rupture, is, according to Nagel, due to a thickening of the tunica mterna of the theca of the follicle. The cells of this layer pro- liferate and increase in size and show yellowish colored granules. This cell-proliferation leads to a folding of the tunica interna, the folds encroaching on the cavity of the follicle, and causing its contents to be pushed toward the stigma." Piersol states that the liberation of the ova usually takes place at definite times, which in general coincide with the men- strual epochs, one or more ova being set free at each period. This 644 REPRODUCTIVE ORGANS. t coincidence, however, is by no means necessary or invariable, since ovulation undoubtedly proceeds independently of menstruation. Other authorities regard the intervals between periods of ovula- tion as very irregular. J. Bland Button, in his Surgical Diseases of the Ovaries and Fallopian Tubes, says : " In the ovary of the human fetus ova ripen, form follicles, and undergo suppression during the last month of Ultra-uterine life. The life of the human ovary may be divided into the following periods of activity and repose : The first period extends from the seventh month of intra- uterine life to the end of the first year. Ova ripen in such abund- ance that in some cases a marked diminution in the number of the ova is appreciable at the second year after birth. To this succeeds a period of comparative repose, terminating at the tenth or twelfth year ; then the ripening of the ova is again easily detected, and goes on independently of menstruation, even after the accession of the climacteric." In an uncertain proportion of instances the ova find their way into the Fallopian tube. The mechanism by which this is accom- plished is still a matter of doubt. One theory maintains that the fimbriated extremity is so approximated to the ovary as to bring the ostium abdominale against the part at which the Graafian vesicle is about to rupture, and that the escaping ovum thus enters the tube. This approximation is by some writers supposed to be due to an engorgement of the fimbriated extremity by blood, thus causing its erection and approximation, but the absence of erectile tissue disproves this theory. Tait found, in certain cases upon which he operated, the tube grasping the ovary, and he attributed this action to muscular fibers in the tube which develop at the period of puberty and which atrophy at the menopause, so that ova can enter the tube only during the active life of these fibers, and then, and then only, can pregnancy take place, though both before puberty and after the menopause ovulation may occur, fhe ova under these circumstances falling into the abdominal cavity, where they disintegrate. According to this theory, if ovulation takes place and the tube does not grasp the ovary, the ovum when dis- charged does not enter the tube, but falls into the abdominal cavity. The second theory is that this grasping of the ovary by the tube does not occur, but that the ovum is carried into the ostium abdominale by the current created by the ciliated epithelium lining the fimbrise. This latter theory is the one generally accepted at the present time. Indeed, facts are accumulating to show that this current is sufficiently powerful to carry an ovum from one ovary to the tube of the opposite side. Kelly removed a diseased left ovary and right tube from a woman who, fifteen months later, was delivered of a child at term. In this instance the ovum must have come from the right ovary and been carried to the uterus through the MENSTRUATION. 645 left tube. This passage of an ovum from one ovary to the tube of the opposite side is external migration, and is perhaps not as infrequent as would at first be thought. Internal migration is the passing of an ovum from an ovary down the tube of the same side, through the uterine cavity, and to a greater or less extent up the tube of the opposite side. Internal migration is supposed to account for some tubal pregnancies. It is doubtful if it ever occurs. It is to be remembered that the ovum is but 0.25 mm. in diameter, and there seems no reason to question the power of the current to draw so small a body into the tube. Once in the tube, it is carried on to the uterus by the ciliated epithelium. Menstruation. At about the age of fourteen years a bloody discharge takes place from the vagina at intervals of about four weeks. This is the menses, and the process is menstruation. It should be noted that the period of life at which menstruation appears is by no means uniform in all individuals. Byron Robinson, in the Medical Brief, says that " the influ- ences which change the individual age of beginning are : Climate, race, residence, altitude, latitude and longitude, environments, food, and disease. Climate (atmospheric and geographical rela- tions) exercises the chief influence among the various factors. In general, the hotter the climate the earlier the menstruation begins. The average age for the beginning of menstruation is : Chicago, fourteen ; Sweden, eighteen ; Norway, sixteen and one- half; Denmark, sixteen and three-fourths; Russia, fourteen; Germany, fifteen ; Great Britain, fifteen ; Austria, sixteen ; Pales- tine, thirteen ; Turkey, eleven ; Syria, twelve ; Ceylon, Siam, and Japan, thirteen." Prof. Skene, in his Diseases of Women, lays down the follow- ing rules : 1. Menstruation should begin at puberty that is, when the woman is maturely developed, no matter what the age may be. 2. It should recur at regular intervals : about every twenty- eight days is the average time. A regular periodicity is normal, but the duration of the periods often differs in different persons. 3. The discharge should always be fluid in consistence and sanguineous in color. 4. The flow should continue a definite length of time, the duration depending upon the habit of each case ; at least there should not be any great deviation from this rule. The duration is usually from three to five days, and the total amount is about four or five ounces. At about the age of forty-five years menstruation ceases : this is the menopause, or climacteric, or change of life. The cessation is not abrupt, but gradual. The menstruation becomes irregular, and finally ceases altogether. The changes which take place in the mucous membrane of 646 REPRODUCTIVE ORGANS. the body of the uterus during menstruation are not agreed upon by authorities. Webster says that "the latest evidence points clearly to the view that there is but a slight denudation, irregular in distribution in the superficial layers of the mucosa." The complete menstrual cycle is, according to Marshall, as quoted by the American Text-book of Obstetrics, divisible into four stages : (1) The first or constructive stage is one of prepara- tion for the reception of an ovum, and is characterized by the formation of a menstrual decidua, in the preparation of which swelling of the mucous membrane, enlargement of the uterine glands, and increase of the connective tissue, all take place. This stage probably lasts one week, and is followed, when pregnancy has not occurred, by degenerative changes. (2) The second or destructive stage is marked by the destruc- tive processes which give rise to the usual phenomena of the FIG. 433. Uterus during menstruation, cut open to show the swelling of the whole organ, and particularly the mucous membrane : A, mucous membrane of cervix; B, C, mucous membrane of corpus, much thickened; D, muscular layer; E, uterine opening of tube; F, os internum (the mucous membrane tapers down to these openings) (Courty). menstrual period, including the discharge of mucus, blood, and disintegrated uterine mucous membrane. Five days constitute the average duration of the menstrual flow, although its continuance may be extended or curtailed, owing to individual peculiarities. MENSTR UA TION. 647 (3) The third or reparative stage is one of repair, during which the deeper and unaffected parts of the uterine mucous membrane institute constructive processes, which within the short period of from three to four days result in the formation of a new mucosa. (4) The fourth or quiescent stage includes the remaining twelve or fourteen days of the menstrual cycle, and represents the qui- escent period preceding the initiative changes marking the begin- ning of the next period. Cause of Menstruation. The cause of menstruation is still undetermined. Lawson Tait held that menstruation was dependent upon the oviducts, but that ovulation and menstruation were independent functions. Johnstone believed that menstruation is regulated by a nerve which passes through the broad ligament. Byron Kobinson holds that menstruation is due to ganglia located in the walls of the uterus and oviducts, which he terms " automatic menstrual ganglia." He considers it to be independent of ovulation. He calls the ovary the chief central sexual organ of woman, and the uterus and oviducts appendages of the ovary. According to this writer (loo. cit.) menstruation is due to a nervous mechanism termed automatic menstrual ganglia, located in the walls of the uterus and oviducts. Its utility is the secre- tion of fluid to float an egg into the uterus. Its design is repro- duction. "Among the lower animals menstruation and ovulation are concomitant, but as the scale of life ascends they become separate processes. Man and monkey are probably the only animals with a distinct rhythmical or periodical menstrual discharge independent of ovulation. This process in lower animals is called cestrus or ' rut.' Menstruation is limited to a certain period of life, seed- time and harvest, generally from the fifteenth to the forty-fifth year. It is due to automatic menstrual ganglia, small nerve- ganglia situated in the walls of the uterus and tubes. It is a manifestation of the nervous system. It must be remembered that a nerve-ganglion is a small brain ; it receives sensation and sends out motion ; it assimilates food, and is a trophic center ; it reproduces itself, and controls secretion and vermicular action ; it is a physiological center, and has all the elements of a brain. These little ganglia are situated along the uterus and oviducts passing through a monthly rhythm, rising and sinking between the extremes of functional activity and repose, and corresponding in these states to the menstrual congestion and intermenstrual quietude of the uterus and oviducts. The oviducts at the monthly periods assume peristaltic motion, a vermicular or tortuous action, so that an ovum may be carried to the uterus by their movements. It may be observed that when the ganglia along the oviducts are 648 REPRODUCTIVE ORGANS. in the slightest action, the oviducts become filled with fluid secreted from the blood, which is whipped in a stream toward the uterus by the cilia that always move in that direction. This oviductal fluid furnishes a canal in which the ovum can float to the uterus ; for in a dry, contracted oviduct an egg could pass only with difficulty. The automatic menstrual ganglia are similar to the other visceral ganglia, such as the cardiac and those of the digestive tract, and the renal ganglia." Christopher Martin states his views on the subject as follows : Menstruation is a process directly controlled by a special nerve-center situated in the lumbar part of the spinal cord, and the changes in the uterine mucosa during the period are brought about by katabolic nerves, and during the interval by anabolic nerves. The menstrual impulses reach the uterus either through the pelvic splanchnic or the ovarian plexus, possibly through both. And, finally, removal of the uterine appendages arrests menstrua- tion by severing the menstrual nerves. Relation between Ovulation and Menstruation. The relation between these two processes is as yet undetermined, although physiologists in the main hold that at the time of the discharge of an ovum from an ovary there is such a condition of the uterus as brings about its increased vascularity and the oozing from its ves- sels of the menstrual blood. They believe that at each menstru- ation there is discharge of an ovum. Other writers and these are principally surgeons who have devoted much time to the study of diseases of women, and who have had large experience in opera- tions for the removal of the ovaries differ very materially from the physiologists. One of the number (A. Reeves Jackson, in an article entitled " Ovular Theory of Menstruation : Will it Stand ? " in the American Journal of Obstetrics) says : " Menstruation may occur without accompanying ovulation ; ovulation may occur without accompanying menstruation ; and ovulation is the irreg- ular but constant function of the ovaries, while menstruation is the regular rhythmical function of the uterus." Lawson Tait, the celebrated surgeon, says that " ovulation and menstruation are not only not concurrent, but ovulation is much less frequent than menstruation." J. Bland Button, already referred to, says : " It is very difficult to uproot ancient tradition, especially one so ancient as the belief in the intimate association of ovulation and men- struation, but evidence is rapidly accumulating which will show that the two processes are not so intimately connected as was formerly supposed. " Leopold and Mironoff state, as their opinion, that " Ovulation usually accompanies menstruation, though not always. Menstru- ation depends upon the presence of the ovaries and a well-formed uterine mucosa. Ovulation usually coincides with menstruation ; it rarely occurs in normal conditions between the menstrual periods." MENSTR UA TION. 649 Manton, in Jewett's Practice of Obstetrics, says : " Although menstruation and ovulation should not be considered as necessarily coincident processes, it is altogether probable that the conditions which influence the one have also an effect upon the other, and that, as a rule, the two functions occur simultaneously and are, to a greater or less extent, interdependent." Williams concludes, from all the available evidence, " that the two processes usually occur about the same time, but that one not infrequently antedates the other by a few days ; while in exceptional cases they may occur quite independently." In discussing the relation between menstruation and ovulation, Edgar says that " they occur about the same time, although ovulation often follows menstruation and may occur between the menses ; that the ovarian changes which precede ovulation by producing ovarian tension, reflexly excite the uterus and cause menstruation ; that both processes are under some nervous control, yet either may occur independently." It would appear, then, that the relation existing between ovula- tion and menstruation is not definitely determined, but that they are intimately associated cannot be questioned, for the removal of the ovaries, as a rule, is followed by a discontinuance of men- struation. As to the relation between a particular menstrual period and the process of ovulation, Marshall says, that the decidua of a particular menstrual period is related not to the ovum discharged at that period, but to the ovum discharged at the preceding period, and which takes, probably, a week in its passage from the ovary to the uterus. Formation of Corpus Luteum. After an ovum has been dis- charged from a Graafian follicle certain changes take place in the latter structure which result in the formation of a corpus luteum. The cavity of the follicle is filled with blood from the lacerated blood-vessels of the walls of the follicle, and this under- goes coagulation, the serum being expressed and absorbed, and the clot, at first red, later becomes decolorized. Into this penetrates the tunica interna of the theca folliculi, which undergoes proliferation. In this proliferated tissue are lutein cells containing lutein, which gives the characteristic yellow color from which the corpus luteum derives its name, and fibrous connective tissue with blood-vessels whose capillaries penetrate between the lutein cells. The inner wall of the corpus luteum becomes folded in or convoluted, and the cen- tral portion of this body undergoes degeneration and is absorbed. Afterward the corpus luteum undergoes hyaloid degeneration, and the corpus albicans results, so called because of the white color which replaces the yellow. This is ultimately absorbed, and there remains but a small amount of connective tissue. While a corpus luteum which occurs during menstruation exists 650 REPRODUCTIVE ORGANS. for but a few weeks, that which occurs in connection with preg- nancy remains for a much longer period, even until after child- FIG. 434. Portions of ova of Asterias glacialis, showing changes affecting the germinal vesicle at the beginning of maturation : a, germinal vesicle ; b, germinal spot, composed of nuclein and paranuclein (c) ; d, nuclear spindle in process of formation (Hertwig). V , pv FIG. 435. Formation of polar bodies in ova of Asterias glacialis: ps, polar spindle ; pb f , first polar body ; pb", second polar body ; n, nucleus returning to con- dition of rest (Hertwig). FIG. 436. A, mature ovum of echinus : n, female pronucleus ; B, immature ovarian ovum of echinus (Hertwig). birth. The manner of formation is, however, the same in both, only under the stimulus of pregnancy the corpus luteum which ERECTION OF THE PENIS. 651 occurs at this time becomes much larger, having a diameter of from 12 to 20 mm. The two varieties are known respectively as the corpus luteum spurium or of menstruation, and the corpus luteum verum or of pregnancy. There is, however, no essential difference between the two. It was supposed at one time that the existence of pregnancy could be determined by the presence of a corpus luteum in the ovary, but the existence of such bodies in undoubted virgins has overthrown that theory absolutely. Is is said that in the mouse there is no difference as to structure or size between corpora lutea derived from follicles whose ova have been impreg- nated and those whose ova have not been fertilized. Maturation of the Ovum. This process takes place in all ova, and is necessary for their preparation for fertilization. In other words, an immature ovum is not susceptible of being fertilized. These changes take place while the Graafian follicle is also be- coming mature, and are complete by the time the ovum is dis- charged from the follicle. To understand the process thoroughly one must be familiar with karyokinesis (p. 28). It may, how- ever, here be briefly described as beginning with the migration of the germinal vesicle to the periphery (Fig. 434), the rupture of the nucleus, the formation of the spindle, etc., and the extrusion of the polar bodies (Fig. 435) ; and thus is formed a new nucleus, the female pronucleus (Fig. 436). If the ovum is unfertilized, it undergoes disintegration, probably within eight days from the time it left the ovary : but if fertilized, the female and male pro- nuclei, the latter being derived from a spermatozoon, fuse and form a new nucleus, the segmentation nucleus. Impregnation. In order that the ovum may be impregnated or fertilized the spermatozoa must come in contact with it in the generative passage of the female ; or, more properly speaking, one spermatozoon must, for in the process of fertilization but one of these structures is involved. This is preceded by erection of the penis and ejaculation of the semen. Erection of the Penis. Any influence brought to bear upon the sexual center, which is situated in the lumbar region of the spinal cord, by which it is stimulated, results in the emission of impulses through the nervi erigentes. This influence may come from the brain in the form of mental impressions, or from stimu- lation of the sensory nerve-endings in the penis. The efferent impulses which reach the penis cause a relaxation of the muscular structure of the trabecula?, thus increasing the capacity of their interspaces, and also a dilatation of the arterial vessels, so that an increased amount of blood is supplied to the organ. The veins (Fig. 437) which return the blood from the penis are relatively small, and are unable to return quickly the blood supplied by the relaxed arteries ; this obstacle to the free return of the blood is augmented by the compression of the veins produced by the con- 652 REPRODUCTIVE ORGANS. traction of the erector penis and bulbocavernosus muscles. The result is the distention of the penis with blood, producing the rigid condition of that organ called erec- tion. The verumontanum, which like- wise contains erectile tissue, becomes at the same time rigid, and assisted by the contraction of the sphincter vesicse, closes the passage to the bladder. The clitoris of the female pos- sesses an erectile structure, and during coitus undergoes a change analogous to that of erection in the male. Ejaculation. Some writers de- scribe an ejaculatory center that is, a special center in the spinal cord that presides over the emission of semen which constitutes ejaculation, while others deny its existence. As a result of the excitation produced by the act of copulation the testicles become very active in the formation of their secre- tion, and this is carried to the ampullae of the vasa deferentia by the muscular action of the various portions of the canal which it traverses. The mus- cular coat of the seminal vesicles, and that of the ampullations by their con- traction expel their contents, the semen, into the ejaculatory ducts, through which it is discharged into the prostatic portion of the urethra (Fig. 438). Here are added to it the secretion of the prostate, expelled by the muscular tissue of that gland, and the secretion of the glands of Cowper. By the combined rhythmic action of the ischio- and bulbocavernosi, constrictor urethra, external sphincter ani, and levator ani muscles, the semen is forced through the remaining part of the urethra and out of the meatus. During copulation the glands of Bartholin, situated on each side of the commencement of the vagina and behind the hymen, and which are regarded as the analogues of Cowper's glands in the male, secrete a mucous fluid which is poured out upon the vulva. By the vibratile movement of their tails or flagella the sper- matozoa penetrate the os uteri, passing into the interior of the FIG. 437. Deep dorsal vein and its tributaries : A, glaus ; B, B', corpus cavern osum ; (7, section of pubis, made slightly below the symphysis. 1, Deep dorsal vein ; 2, its origin behind the glans ; 3, 3, its tributaries coming from the corpus cavernosum and corpus spongiosum ; 4, dorsal vein, bifurcated and arranged in a sort of plexus, subpubic plexus ; 5, plexus of Santorini ; 6, 7, an- astomosis of superficial dorsal vein with external pudic and obturator (Testut). EJACULATION. 653 uterus. According to Litzmann and others, at the time of coitus the uterine muscular tissue contracts, thus compressing the cavity of that organ ; subsequently relaxation occurs and by aspiration, the spermatozoa are drawn into the cavity. Kristeller believes that at the time of the completion of coitus, when the orgasm occurs, the plug of mucus in the cervical canal is forced down into the vagina, and that the spermatozoa, discharged at the same moment, attach themselves to it and are drawn back with it into the FIG. 438. Posterior portion of urethra, seen after median incision of the ante- rior wall of the canal ; 1, vesical neck ; 2, section of prostate and urethral sphincters ; 3, section of membranous urethra; 4, section of spongy urethra; 4', bulb; 5, 5', cor- pora cavernosa ; 6, verumontanum with orifice of utricle ; 7, posterior wall of prostatic urethra with its glandular openings ; 8, right ejaculatory duct laid bare, with, 8', its opening; 9, Cowper's gland; 10, its excretory duct laid bare; 1CX, opening of this duct; 11, longitudinal fold of mucous membrane of urethra; 12, cul-de-sac of bulb; 13, collar of bulb (Testut). uterus. Whether either of these theories is, in the main, the cor- rect one has not been determined. That the spermatozoa can, by the vibratile motion alone of their tails or flagella, penetrate the os uteri is proved by the fact that impregnation has occurred when the woman was unconscious. The rate at which spermatozoa travel in the human female passages is one centimeter in three minutes ; in the rabbit two and three-quarter hours are sufficient for them to reach the ovary. Their vitality is retained in the human passages 654 REPRODUCTIVE ORGANS. probably for several days and sometimes longer, after which they undergo disintegration. Diihrssen found living spermatozoa in a tube which he removed from a woman whose statement, if true, would show that they had been there for fully a month. Ovarian and Abdominal Pregnancy. The portion of the female generative passages in which the spermatozoa and the ovum ordinarily meet is probably the Fallopian tube in the major- ity of instances. It may, however, also be the uterus. That the place of meeting may also be the ovary is proved by the occurrence of ovarian pregnancy, which is one form of ectopic gestation. The proportion of ectopic to uterine gestations is vari- ously estimated ; some writers placing it at 1 in 500, and others at 1 in 10,000. Of ectopic pregnancies, Edgar thinks 4.8 per cent, are ovarian. Williams regards only 5 reported cases of primary ova- rian pregnancy as having been conclusively demonstrated, 30 cases as highly probable, and 25 as fairly probable. Four cases are reported by such competent authorities as Leopold, Patenko, and Martin. It may be interesting in this connection to say that in Patenko's case the right ovary, which was about the size of a hen's egg, contained a cyst within which was a yellow body consisting of cylindrical and flat bones, which upon examination were found to be fetal, and not such as are found in dermoid cysts. In the wall around the cyst were found corpora lutea and Graafian follicles, showing that the tissue was true ovarian tissue. Martin reports 2 cases which he regards as undoubtedly primary ovarian pregnancies ; 1 of these is shown in Fig. 439. He believes that in cases of ova- rian pregnancy the spermatozoon finds its way through the fimbri- ated extremity of the Fallopian tube into one of the small, recently ruptured, cysts so often seen on the surface of the ovary, and there fertilizes the contained ovum. As to the occurrence of primary abdominal or peritoneal preg- nancy, there is great difference of opinion. Some writers, while recognizing its possibility, doubt that it has ever actually occurred. When the impregnated ovum is implanted upon the fimbria ovarica the subsequent growth would make it appear to be a peritoneal or abdominal pregnancy. SchlechtendahFs case would, however, appear to have been an instance of primary abdominal pregnancy. In this case a fetus 15 cm. long was found attached to the abdomi- nal wall, near the spleen, of a woman who had died from hemor- rhage. Should this form of pregnancy occur, it would be explained by the meeting of the spermatozoa and the ovum at the time of the escape of the latter from the Graafian follicle, which, instead of entering the Fallopian tube, falls into the peritoneal cavity, where it would subsequently become developed. Webster, in his Ectopic Pregnancy, in which he considers the subject most exhaustively, states it as " extremely probable that OVARIAN AND ABDOMINAL PREGNANCY. 655 no gestation can begin its development, except in some part of the genital tract derived from the Miillerian ducts which form the uterus and tubes." This, of course, rules out both abdominal and ovarian pregnancy. Of the latter, Webster says : " Supposed cases of ovarian pregnancy require to be studied carefully, and in every instance must be distinguished from the following condi- tions, which may be mistaken for it, viz., pregnancy in the outer FIG. 439. Prof. August Martin's case of ovarian pregnancy. The intact tube is seen lying above the ovarian sac containing the fetal envelopes. end of the tube which has become intimately connected with the ovary ; pregnancy in an accessory tube-end which has become attached to it ; pregnancy in the ovarian fimbria, which may be hollow sometimes, representing the extreme outer end of the tube ; pregnancy in the tube which has extended into the ovarian sac of peritoneum, which occasionally occurs in women." The terms " extra-uterine pregnancy " and " ectopic pregnancy " are ordinarily used synonymously, but there is really a distinction. The term "ectopic" implies that the gestation is outside the uterine cavity. A gestation may occur in that part of the Fallo- pian tube which is situated in the uterine wall. Such an one, described under the name " interstitial" would not be " extra- uterine," for it is within the uterus. It would, however, be " ec- topic." If the view of Webster is correct, all ectopic gestations must be of tubal origin. He divides them into five subdivisions : 1. Ampullar, in which the gestation begins in the ampulla or mid- dle portion of the tube, and he regards this as by far the most common. 2. Interstitial, in which the gestation develops in that 656 REPRODUCTIVE ORGANS. portion of the tube situated in the wall of the uterus. 3. Infundib- ular, in which the gestation develops in the outer end of the tube- lumen or among the fimbriae. 4. Anomalous Varieties. Among these Webster places those that develop in accessory fimbriated extremities or in tubal diverticula, and also those that develop in detached portions of Mullerian tissue i. e., those attached to or embedded in the ovary. In this class, he thinks, are some of the recently described cases of ovarian pregnancy. 5. Cornual preg- nancy, in which the ovum develops in the undeveloped horn of a bicornate uterus. FIG. 440. Sections of the ovum of a rabbit, showing the formation of the blasio- dermic vesicle : a, 6, c, d, are ova in successive stages of development ; sp, zona pel- lucida ; ect, ectomeres, or outer cells ; ent, entomeres, or inner cells (E. Van Beneden). Method of Fertilisation. In the vitelline membrane of the ova of some animals there is a minute opening, the micropyle, by which a spermatozoon gains access to the interior. Such an opening does not exist in the human ovum. Some histologists have described the vitelline membrane as possessing a porous structure, and it has been suggested that through one of these FORMATION OF EMBRYO. 657 pores a spermatozoon might pass. It is by no means established that such pores exist. However, in some way the spermatozoon passes through the membrane into the protoplasm ; here its tail disappears and the head assumes a spherical form, and to it the name of " male pronucleus " is given. The male and female pro- nuclei then unite to produce the fecundation nucleus. After this occurs the ovum consists of a mass of protoplasm with a nucleus, and is spoken of as the " segmentation sphere," because it under- goes segmentation. Segmentation. This consists in the production of two seg- ments by the same process of indirect division which takes place in the germinal vesicle ; these again divide, forming four, and, the same process continuing, the entire ovum is broken up into a mass of spherical cells which, from the resemblance to a mulberry, is named morula. These cells separate into two layers, with fluid between them, except at one place where the layers are in con- tact. The blastodermic vesicle is now formed. It is probable that development has reached this stage at about the tenth day, by which time the ovum has entered the uterus. The albuminous secretion of the Fallopian tube serves as pabulum or food to the cells in this process. Formation of Embryo. The next change which takes place is the formation of three layers from the two just described. They are termed the epiblazt, the mesoblast, and the hypoblast; together they form the blastoderm. The epiblast is most external, in con- tact with the vitelline membrane, which takes no part in the changes thus far described. It would, perhaps, be too much to say that the embryo is now formed, yet the subsequent changes are but the modification and differentiation of the cells which compose these three layers. The epiblast forms the brain and spinal cord, portions of the organs of special sense, and the epidermis, and also takes part in the for- mation of the chorion and amnion. The mesoblast forms the vascular, osseous, and muscular systems, and the endothelium which lines the serous cavities. The hypoblast forms the lungs, the epithelium of the alimentary canal and of the glands which are offshoots from this canal. The membrane which lines the allantois and the yolk-sac is also formed from the hypoblast. The segmentation just described is such as takes place in the human ovum and that of other mammalia. It is a process in which the entire mass of protoplasm undergoes division : such ova are said to be holoblastic. In the ova of birds and of reptiles only a portion undergoes this segmentation, the rest serv- ing as food. Such ova are meroblastic. As an illustration of the latter may be mentioned the fowl's egg, in which the processes of development have been most thoroughly studied. In this egg only a minute portion, the cicatricula, becomes converted into 42 658 REPRODUCTIVE ORGANS. the chick, while the great body of material nourishes the growing embryo until it leaves the shell and is able to gain its own liveli- hood. As such an embryo is never attached to the parent, it must have within itself, supplemented by what it receives from the air, all the material necessary for its development and maintenance until freed from its enclosing shell, hence the large size of the ovum ; while in the mammal this supply is not necessary, for the attachment to the maternal structures is made at an early period of its history, and from the parent all necessary sustenance is obtained. Inasmuch as development has been so much more thoroughly studied in the hen's egg than in any other, and inasmuch as the processes are in many respects probably the same as in the human ovum, the development of the chick will be described, referring to the principal points of difference as they are reached in the description, giving, however, only a general view of the subject, which is much too extensive and complicated to discuss in any other manner in this connection, and referring our readers for fuller details to monographs on embryology. Development of Chick. If the shell of a hen's egg is broken during the first day of its incubation and the blastoderm is examined, it will be seen that there is a clear central portion, the area pellucida, and a portion outside of this, the area opaca, which is much less clear. The embryo forms in the area pellu- cida, and the membranes and structures which are to nourish it form in the area opaca. On the second day, the area opaca having meanwhile extended, within it are formed red blood-corpuscles and vessels, and during the same time in the area pellucida the heart is formed. These structures arise, as has been stated, from the cells of the mesoblast. At one extremity of the area pellucida a fold forms in the blas- toderm, and, as this is the anterior end, it is called the cephalic fold. A similar fold, the tail fold, forms at the other extremity of the area pellucida. In the same manner lateral folds form on the sides. All these folds, which include the three layers of the blastoderm, approach one another below, and by so doing form a canal, the embryonal sac. This sac is bounded above by the blastoderm, anteriorly by the cephalic fold, posteriorly by the tail fold, and laterally by the lateral folds, while below it is in com- munication with the vitellus. This embryonal sac subsequently becomes divided into two, one division forming the alimentary tract, and the other the body-walls, the umbilicus being the point at which the folds all unite. These folds just described are to be carefully distinguished from the membranes, the amnion, the cho- rion, etc. The folds, as stated, involve the epiblast, the mesoblast, and the hypoblast, while in the formation of the membranes the various layers play different parts. MEMBRANES OF THE EMBRYO- AMNION. 659 Membranes of the Embryo. Amnion. The mesoblast about the embryo splits into two laminae, the parietal and the visceral. The parietal (external) joins with the epiblast to form the somatopleure, from which the amnion and the body-walls are developed, while the visceral lamina unites with the hypoblast to JVC F.So. FIG. 441. Diagrammatic longitudinal section through the axis of an embryo chick : N. C., neural canal ; Ch, notochord ; D, foregut ; F. So, somatopleure ; F. 8p, splanchnopleure ; Sp, splanchnopleure forming the lower wall of the foregut; Ht, heart ; pp, pleuroperitoneal cavity ; Am, amniotic fold ; A, epiblast ; B, mesoblast ; C, hypoblast (Foster and Balfour). form the splcmchnopleure. From this structure are developed the walls of the allantois, the yolk-sac, and the alimentary canal. Between the somatopleure and the splanchnopleure is the pleuro- peritoneal cavity, which later is divided by partitions into peri- cardial, pleural, and peritoneal cavities. From the somatopleure folds form which rise above the embryo on all sides, meeting over hy FIG. 442. Diagrammatic longitudinal section of a chick on the fourth day: ep, epiblast ; hy, hypoblast ; sm, somatopleure ; vm, splanchnopleure ; af, pf, folds of the amnion; pp, pleuroperitoneal cavity; am, cavity of the amnion; ai, allantois; a, position of the future anus: h, heart; i, intestine; vi, vitelline duct; ys, yolk; s, foregut ; m, position of the mouth ; me, the mesentery (Allen Thomson). its back and fusing together. These are the amniotic folds. As each fold is double, when they unite two membranes result : the inner, next the embryo, is the amnion, and the outer, toward the vitelline membrane, is the false amnion (Fig. 442). The latter and the vitelline membrane fuse together, forming the chorion. 660 REPRODUCTIVE ORGANS. The true amnion has epiblast for its inner, and mesoblast for its outer, layer, and the space between it and the embryo is the araniotic cavity, in which the liquor amnii accumulates. Yolk-sac. The yolk-sac is a very, important structure in the fowl and in birds generally, as it is upon the yolk that the nutri- tion of the embryo depends ; but in mammals it is of little impor- tance, as the nutritive material in the vitellus is insignificant in amount. Allantois. The allantois is a projection of the splanch- nopleure into the pleuroperitoneal cavity. It subsequently com- municates with the posterior portion of the intestinal canal, and its lining is hypoblast. This structure projects more and more into the pleuroperitoneal cavity, following up the folds that have been described as forming the true and the false amnion. The allantois at last comes in contact with the chorion, which, it will be remembered, \vas formed by the fusion of the false amnion with the vitelline membrane, and into the villi of that structure it sends processes. It is especially developed in that part corre- sponding to the attachment of the ovum to the uterine wall. The allantois has two layers, a mesoblastic and a hypoblastic. In the former are blood-vessels which come from the vascular system of the embryo, the connecting vessels becoming the umbilical arteries. At a later stage of development the character of the allantois dis- appears, except in that portion which is to be included within the body of the fetus, and which becomes the urinary bladder, and in that portion between the bladder and the umbilicus, which becomes the urachus. Chorion. This membrane, as already stated, is formed by the union of the vitelline membrane and the false amnion. When first formed, it is smooth, but becomes shaggy by the growth from it of processes called villi. These villi are at first scattered over the whole exterior of the ovum, but later they are found only at the point of attachment of the ovum to the uterus, where 'the placenta is to be formed. In these villi are blood-vessels from the fetal vascular system. Placenta. When the impregnated ovum reaches the cavity of the uterus the mucous membrane of that organ is prepared to receive it, and it finds a lodgment there. Under the stimulus of impregnation the whole mucous membrane becomes thickened, and at the termination of uterogestation the entire mucous membrane of the body is cast off; it is called the decidua vera. Especially marked is this thickening at the point of attachment of the ovum, and to this part the name decidua serotina is applied (Fig. 443). As a result of this stimulus the mucous membrane increases around the ovum, finally completely enclosing it. This new formation is the decidua reflexa. The villi of the chorion find their way into the depressions of CIRCULATION IN THE EMBRYO. 661 the decidua serotina, and their walls become atrophied, being finally represented only by epithelial cells covering the capillary blood- vessels which have come from the allantois. The blood-vessels in the decidua serotina become converted into blood-spaces, sinuses, to which the uterine arteries carry blood, and from which the uterine veins carry the blood away. It will be seen, therefore, that the fetal blood- vessels are surrounded by the maternal blood in the uterine sinuses, the two fluids being separated only by the thin wall of the fetal capillaries, through which the interchanges of oxygen and carbon dioxid take place, and also the passage of the nutri- tious material to supply the growing fetus, and in the reverse direction pass the effete products to be eliminated. The structure which performs all these im- portant offices is the placenta, made up of both maternal and fetal tissues. It seems hardly necessary to say that the blood of the mother and that of the child never come in contact, but are always separated by the walls of the fetal capillaries. At birth the placenta is cast off, arid by the contraction of the uterine muscular tissue the mouths of the maternal blood-vessels are closed, and thus hemorrhage is prevented. The blood which escapes during a normal labor is that which was in the sinuses. The functions of the placenta are thus seen to be threefold nutri- tive, respiratory, and excretory. Circulation in the Embryo. Vitelline Circulation. During the earliest part of human fetal life the contents of the ovum supply the growing embryo with nutrition. This is done by means of vessels which compose the vitelline circulation, but, im- portant as this circulation is in the fowl's egg, it is of very brief duration in the human subject, for the supply of nutritious material is soon exhausted, probably at the sixth week. Placental or Fetal Circulation (Fig. 444). By the sixth week the placenta is formed and the connection has been made by which the embryo receives its nourishment from the maternal blood. 4 5 FIG. 443. Series of diagrams repre- senting the relationship of the decidua to the ovum at different periods. The decidua are colored black, and the ovum is shaded transversely. In 4 and 5 the vascular processes of the chorion are figured. 1, Ovum entering the con- gested mucous membrane of the fundus decidua serotina; 2, decidua reflexa growing around the ovum ; 3, comple- tion of the decidua around the ovum ; 4, general growth of villi of the chorion ; 5, special growth of villi at placental attachment, and atrophy of the rest (copied from Dalton). 662 REPRODUCTIVE ORGANS. From this time until birth the fetus depends upon the piacental or fetal circulation for its nourishment and maintenance. The blood of the fetus is freed from much of its impurities in the placenta, and there likewise it receives oxygen and nutritive materials. It returns to the fetus through the umbilical vein, passing to the liver. In this organ the current is divided : the Vmbilicus- Placenta, FIG. 444. Diagram of the fetal circulation. greater part joins with the venous blood of the portal vein ; a second portion goes directly into the hepatic circulation ; while a third part goes through the ductus venosns into the ascending vena cava without passing through the liver. The currents all meet again in the ascending vena cava, here mixing with the blood returning from the lower extremities. The ascending vena cava CHANGES IN THE CIRCULATION AT BIRTH. 663 discharges its blood into the right auricle of the heart, where, guided by the Eustachian valve, it is directed into the left auricle through the foramen ovale. From this cavity it passes into the left ventricle, thence into the aorta, which distributes it to the head and upper extremities. It will be seen from this description that to these three portions of the body the blood from the placenta is distributed. This blood is not very pure, for it is deteriorated by admixture with the impure blood returning from the lower extremities, with which it mingles in the ascending vena cava; but it is the purest and most nutritious blood the fetus receives, and this accounts for the greater development of the upper portion of the body as compared with the lower, which is so striking a feature in the newborn babe. The blood returns from the head and upper extremities through the descending vena cava to the right auricle, and thence passes into the right ventricle. There is probably always a slight mixing of the currents in the right auricle, that returning from the placenta and that from the descending vena cava, but at first this is very slight ; later, it is doubtless greater. From the right ventricle the blood passes into the pulmonary artery, a very small portion going through the capillaries of the lungs, the larger part passing through the cluctus arteriosus into the aorta, passing down this vessel to the common and internal iliacs, from which latter are given off the hypogastric or umbilical arteries by which the blood is conveyed to the placenta. By comparing this description with that of the circulation in the adult the points of difference will be seen. It may be well to note here that there are six principal points of difference be- tween the fetal and the adult circulatory apparatus, besides less important ones of size and shape. These points of difference are the presence in the fetal heart of the Eustachian valve and the foramen ovale, in the venous system of the umbilical vein and the ductus venosus, and in the arterial system of the umbilical arteries and the ductus arteriosus. Changes in the Circulation at Birth. During intra- uterine life the respiratory center in the medulla is supplied with blood containing sufficient oxygen to prevent any inspiratory im- pulse, and there is therefore during this period no attempt at respiration on the part of the fetus. As soon, however, as the connection between the parent and the child is severed, whether by separation of the placenta or by tying of the umbilical cord, the respiratory center, being no longer supplied with oxygen, sends out impulses to the respiratory muscles, and respiration begins. This may be hastened or assisted by slapping the skin or dashing water upon it, but under ordinary circumstances these measures are not called for. The fact that respiration will take place while the fetus is still enclosed in its membranes, without the reflex in- 664 REPRODUCTIVE ORGANS. fluence of exposure to the air, shows that this is not the essential, but only a contributing, cause. It is the stoppage of the placenta! circulation which starts the respiratory movements. Although during fetal life some blood flows through the pulmo- nary capillaries, still the amount is small, and, there being no air in the pulmonary alveoli, the lungs will sink if placed in water. The first respiratory movement causes an enlargement of the thoracic cavity and a consequent distention of the lungs, the air passing h to the alveoli, and the blood, which is at the time in the pulmonary capillaries, becomes oxygenated and returns to the left auricle as arterial blood. The expansion of the thorax reduces the resistance to the flow of the blood through the pulmo- nary circulation, and as a result a large amount of blood goes to the lungs ; this means a lessened amount through the ductus arteriosus, and, following the law that a diminution of function is followed by atrophy, this vessel begins to diminish in size, and becomes closed between the fourth and tenth days, and in later life is to be found as a fibrous cord between the left pulmonary artery and the aorta. With the termination of the placental circulation the flow through the ductus venosus ceases, and within a few days this vessel closes, and remains only as a fibrous cord in the fissure of the same name in the liver : that portion of the umbilical vein which is within the body of the child becomes the round ligament of the liver. The blood flowing into the right auricle from the inferior vena cava finds it easier to pass into the right ventricle than into the left auricle, which is now filled with blood from the lungs, and hence takes this course, while the blood cannot flow into the right auricle through the foramen ovale by reason of the valve which has been forming in the left auricle during the latter part of intra-uterine life to close this opening. The opening is not permanently closed for a considerable time after birth, in some cases a year, and sometimes not at all. As a result of these various changes the fetal circulation becomes converted into that of the adult. INDEX. ABDOMFSJJL reflex, 480 Abducens, 521 paralysis of, 521 Aberration, chromatic, 573 spherical, 573 Abrin, 113 Abscissa, 452 Absolute humidity, 376 Absorption of food, 167, 254 Accommodation, 560, 564 convergence in, 570 negative, 565 positive, 565 pupil contraction in, 570 range of, 569 Schoen's theory of, 569 Tseherning's theory of, 568 Accommodative rest, 564 Acenrulus cerebri, 351 Achromatic spindle, 28, 29 Achromatic. _ Achroodextrin, 97 Achylia gastrica, 219 Acid sodium phosphate in urine, 83 Acid-albumin, 109 Acromegaly, Actinic rays, 538 Adamantoblast-. Adam's apple, 354 Addison's disease, 349 Adenoid tissue, 37 Adipocere, 99 Adipose tissue, 35 vesicles, 35 Adrenal bodies, 347 Adrenalin, 349 Aerotonometer, 385 Afferent nerves, 462 vessels, 425 After-images, 596 After-vibration, elastic, 453 Agglutinins, 301 bacterial, 301 Agminated glands, 226 Air. amount of moisture in, 376 and blood, interchange of oxygen and carbon dioxid between, 383 calorimeters, 412 expired. vitiated, breathing of, 379 Air-cells, 363 Air-space, 381 Albumin, 107 acid-, 109 alkali-, 109 coagulation of, 107 derived, 109 egg-, 108 nucleo-, 112 precipitation of, 107 serum-, 108 Albuminates, 109 Albuminoids, 115 action of gastric juice on, 199 Albuminous glands, 174 Albuminuria, 438 alimentary, 260 Albumosuria, 438 Alcohol, absorption of, from stomach, 161 as food, 166 effect on body, 158 on brain, 162 on digestion, 159 on excretion of uric acid, 161 on gastric acidity, 160 digestion, 159* on liver, 162 on secretion of gastric juice, 159 of saliva, 159 on temperature, 165 gastric absorption of, 255 Alcoholic beverages, 157 influence on excretion of uric acid. 161 purin-bodies in, 157 Alexin, 300 Alimentary album in uria, 260 bolus, 186 canal, 168 walls of, 659 glycosuria, 256, 438 Alkali-albumin, 109 Alkaline carbonates, 83 phosphates, 82 tide, 432 Allantois, 660 walls of, 659 Alloxuric substances in urine, 437 Amacrine-cells, 551 Ambon, 603 Ameba, 24 665 666 INDEX. Ameboid movements, 24 Ameloblasts, 55 Ametropia, 571 Amido-acetic acid, 247 Amido-ethylsulphonic acid, 247 Amidulin, 96 Ammonia, 86 Ammonium salts, 86 Amnion, 659 Amphiaster, 30 Ampho-peptones, 199 Amplitude, 623 definition of, 622 Ampulla, 628 Ampullae, 144 Amygdaline leukemia, 289 Amylodextrin, 96 Amylopsin, 97, 235 A my loses, 95 Anabolism, 120 definition of, 25 Anacrotic wave, 328 Anatomy, definition of, 20, 21 Anelectrotonic current, 466 Anelectrotonus, 467 Angle of vision, 563 Animal gum, 112 Ankle-clonus, 480 Anode, 444 Anospinal center, 482 Anterior chamber of eye, 554 horn, cells of, 474 median fissure, 471 white commissure, 471 Anterolateral fissure, 471 Antrum , 634 pylori, 194 Anvil- bone, 703 Aortic pressure, mean, 321 valve, 308 Apertura scalse vestibuli cochleae, 607 Apex-beat, 315, 317 Aphasia, 511 Apical foramina, 50 Apnea, 388 Apoplexy, 501 Apparatus, definition of, 19 Aquseductus cochleae, 609 vestibuli, 607 Aqueous humor, 554 chemistry of, 556 Arborization, 67, 72 Areolae, 144 primary, 48 secondary, 49 Areolar tissue, 34 Arnold's ganglion, 520 Aromatic substances in urine, 439 Arterial pressure, 321 Arteries, 308 bronchial, 364 circulation of, 318 Arteries, rate of flow in, 323 Aryteno-epiglottic fold, 354, 358 Arytenoid cartilages, 354 Arytenoideus muscle, 356 Ascending tract, 473 Asphyxia, 389 Assimilation, 120 definition of, 25 Association-fibers, 506, 507 Aster, 30 Astigmatism, 572 Ataxy, cerebellar, 492 Atrium of lungs, 364 Atrophy, senile, 84 Attic recess, 605 Attraction-particle, 28 Audi phone, 618 Auditory area, 512 canal, external, 598, 599 nerve, 523, 615 Auricle, 598 left, 306 right, 306 Auricular diastole, 312 septum, 308 systole, 312 Automatic centers, 486 Axial cord, 64 space, 64 stream, 319 Axis-cylinder, 64 process, 71, 72, 73 Axis-fibrils, 64 Axolemma, 64 Axon, 71 Azygos vein, 364 BACILLARY layer of retina, 552 Bacterial agglutinins, 301 digestion, 253 poison, 114 Bactericidal property of serum, 300 Bacteriolysis, 300 Bartholin's duct, 174, 654 Bartley's use of Fehling's test, 88 Basal ganglia, 499 functions of, 502 Basic sound of heart, 316 Basophils, 289 Baths, 420 Battery, 444 Beer, 157 Belly-sweetbread, 346 Bernard's experiment to prove irrita- bility of muscle, 442 glycogenic theory, 258 Beverages, 156 as food, 158 Bicuspids, 171 Bile, 244 antiseptic powers of, 250 constituents of, 245 INDEX. 667 Bile, offices of, 249 properties of, 244 Bile-acids, 247 Bile-canaliculi, 242 Bile-duct, common, 243 Bile-pigments, 246 Gmelin's test for, 246 Bile-salts, 247 tests for, 248 Biliary passages, intercellular, 242 plexus, interlobular, 242 Bilicyanin, 247 Bilirubin, 246 Biliverdin, 246 Binocular vision, 583 Birch-modification of Young-Helm holtz color theory, 592 Birth, circulation t, 663 Biuret reaction, 103 Bladder, 429 Blastoderm, 657 folds of, 658 Bleeders, 296 Blind spot, 549, 576 Blindness, color-, 593 Blood, 268 amount expelled from ventricle, 314 and air, interchange of oxygen and carbon dioxid between, 383 and tissues, oxygen and carbon dioxid interchange between, 386 changes in, from respiration, 381 circulation of, 305, 311 time for, 325 coagulation of, 294 causes, 296 influences hastening, 296 retarding, 295 theories, 297 distribution of, 270 gravity and, 330 inert layer of, 319 internal friction of, 319 lakey, 269 menstrual, power to clot, 296 microscopic structure of, 270 movements of, in diastole, 313 in systole, 313 peripheral resistance to, 319 physical properties of, 268 regeneration of, 299 serum, 294 specific gravity of, 268 Blood-cells, 286 Blood-corpuscles, 270 colorless, 288. See also Leukocytes. red, 270. See also Red Corpuscl-es. white, 288. See also Leukocytes. Blood-flow, rate of, 323 Blood-glands, 334 Blood-plasma, 291 enzymes of, 292 extractives of, 292 gases in, 294 inorganic salts in, 294 proteids of, 292 water of, 291 Blood-plates, 291 Blood-pressure, 319 aortic, 321 arterial, 321 measuring of, 321 negative, 323 venous, 323 Blood-stains, precipitins in identifying, 301 Bolus, alimentary, 186 Bone, 41 blood-vessels of, 44 calcium phosphate in, 84 cancellated, 41 chemical composition of, 44 compact, 41 development of, 45 lacuna?, 42 lamella?, 42 lymphatic vessels of, 44 ' nerves of, 44 Bone-corpuscles, 42 Bone-marrow, 43 Bowman's capsule, 422 glands, 531 membrane, 542 Brace, Julia, case of, 535 Brain, 483 columns of, 485 effect of alcohol on, 162 gray matter of, 483 pyramids of, 485 weight of, 483 Brain-sand, 351 Bran, 154 Brandy, 157 Bread, 154 Break of current, 447 Bridgman, Laura D., case of, 528 Brigham's case of esophago-duodenos- tomy, 217 Broca's convolution, 511 Bromelin, 155 Bronchi, 362 Bronchial arteries, 364 tube, lobular, 363 veins, 364 Bronchiole, 363 Broth, meat, 152 Bruch's membrane, 544 Brunner's glands, 225 Buffy coat, 295 Bulb, 484 Burdach's column, 474 668 INDEX. CADAVERIC rigidity, 62, 456 Caflein, 156 Caffeo-tannic acid, 156 Cajal's cells, 551 Calcification, 40 Calcium carbonate, 85 fluorid in body, 86 phosphate in body, 84 salt in body, 84 Calculi, salivary, 182 Calorie, 409 Calorific rays, 588 Calorimetry, 410 Canaliculi/42, 597 Cane-sugar, 93 action of gastric juice on, 199 as food, 123 Canines, 55, 171 Capillaries, 310 pulmonary, 364 rate of flow in, 325 Carbamid, 432 Carbo-hemoglobin, 281 Carbohydrates, 87 action of gastric juice on, 199 as food, 123 gastric absorption of, 254 glycogen formation from, 257 intestinal absorption of, 255 Carbon dioxid in body, 87 and oxygen interchange. See Oxy- gen and Carbon Dioxid. tension of, in blood, 384 Carbonates in body, 83. See also Cal- cium, Sodium, etc. Carbon-monoxid hemoglobin, 280 spectrum of, 286 Cardia, 191 Cardiac cycle, 311 glands, 193 impulse, 315 innervation, 317 muscle, 61 composition of, 63 nerves, 318, 525 . orifice, 191 portion of stomach, movements of, 203 Cardio-accelerator center, 481, 487 Cardiogram, 312 Cardiograph, 312 Cardioinhibitory center, 487 Cardiopneumatic movements, 383 Carotid gland, 352 Cartilage, 38 articular, 39 cellular, 41 chemical composition of, 41 costal, 40 hyaline, 38 inorganic solids of, 41 intermediate, 49 organic solids of, 41 Cartilage, transitional, 39 true, 38 white fibrous, 40 yellow elastic, 41 Casein, 112 pancreatic, 238 vegetable, 155 Caseinogen, 109, 112 Casper's cystoscope, 428 Caudate nucleus, 499 Cell stations, 488 Cell-group, middle, 474 Cells, 23 air-, 363, 364 amacrine-, 551 bipolar, 70 blood, 286. See also Red, Corpuscles and Leukocytes. bone-forming, 43 central, 193 chief, 193 columnar, 531 connective-tissue, 35 crescentic, 175 daughter-, 625 dentin-forming, 50 division of, 28 fat-, 35 fiber-, of Eetzius, 610 giant-, 44 glia-, 73 goblet-, 31 granule, 35 gustatory, 538 hair-, of ear, 615 lamellar, 35 marrow-, 44, 287 mastoid, 605 mother-, 625 mucus-secreting, 32 multipolar, 70 nerve-, 69 neuroglia, 73 of anterior horn, 474 of Cajal, 551 of Deiter 5 , 615 of gray matter of cerebrum, 504 of posterior horn, 474 of Purkinje, 491 olfactory, 531 oxyntic, 193 parietal, 193 plasma-, 35 salivary, changes in, 180 spermatogenic, 625 spider-, 73 splenic, 44 sustentacular, 336, 538, 625 tendon-, 38 unipolar, 70 villi, 224 Cellulose, 98 IXDEX. 669 Cellulose, action of ptyalin on, 183 Cement, tooth, 53 Central canal, 471 cells, 193 lobe, 498 of cerebrum, 487 spindle, 28 vein, 241 Centrifugalization, 270 Centrosome, 25 Centrosphere, 28 Cephalic fold, 658 Cereals as food, 153 Cerebellar ataxy, 492 tracts, 473 Cerebellum, 491 effect of removal of, 492 functions of, 492 gray matter of, 491 impressions of, sources of, 493 inferior peduncles of, 486 laminse of, 491 white matter of, 491 Cerebral localization, 509 Cerebrin, 75 Cerebrosides, 75 Cerebrospinal fluid, 471 Cerebrum, 495 convolutions of, 496 fibers of, 506 fissures of, 496 functions of, 507 gray matter of, 496 microscopy of, 503 gyri of, 496 lobes of, 497 microscopy of, 503 peduncles of, 499 sulci of, 496 vital importance of, 507 white matter of, 505 Cerumen, 417, 599 Charcot's crystals, 630 Chemistry, definition of, 20 physiologic, 21, 76 Cheyne-Stokes respiration, 387 Chick, development of, 658 Chief cells, 193 Cholalic acid, 247 Cholesterin, 101, 248, 266 Choletelin, 247 Cholic acid, 247 Chondrigen, 115 Chondrin, 41 Chorda tympaui, 177 Chordse tendinese, 307 Choriocapillaris, 544 Chorion, 660 Choroid, 544 Chromatin, 25 Chromogen, 348 Chromoplasm, 25 hronographs, 450 Chyle, 305 Chymosin, 112 Cilia, 33 Ciliary body, 547 ganglion, 520 ligament, 544, 546 motion, 33 muscle, 546 processes, 545 Ciliospinal center, 481 Cineritious matter, 69 Circulation, 311 pulmonary, 311 systemic, 311 time required for, 325 Circulatory system, 305 Circulus iridis major, 546 minor, 546 Circumvallate papillae, 536 Clarke's column, 474 Claustrum, 499, 505 Climacteric, 645 Climate, menstruation and, 645 Clitoris, erection of, 652 Coagulated proteid, 108, 113 Coagulum, 143* Coccygeal gland, 352 Cochlea, 607 canals of, 609, 612 duct of, 609 nerve of, 615 spiral canal of, 608 Cocoa, 156 Coffee, 156 Coffin-lid crystals, 441 Cohnheim's areas, 57 Cold-blooded animals, 406, 407 Collagen, 115 Colliculus nervi optici, 549 Colloids, 106 Color, 587 diagram, 588 theories, 591, 592 Color-blindness, 593 Colorimetric equivalent, 411 Colors, complementary, 588 physiologic mixture of, 590 Colostrum, 141 Colostrum-corpuscles, 145 Columella, 608 Columnar carneee, 307 Columnar cells, 529 Columns, Burdach's, 474 Clarke's, 474 Goll's, 473 of brain, 485 spinal, 471 Comma tract, 474 Cornmissural fibers, 506 Commissures, 471 Commutator, 448 670 INDEX. Complement, 300 Complementul air, 374 Conduction-paths in cord, 477 Cone proper, 553 Cone-bipolars, 551 Cone-elements, 553 Cone-fiber, 553 Cone-foot, 552 Cone-granules, .552 Cones, 552 Conical papillae, 537 Conjunctiva, 597 Conjunctiva! reflex, 480 Connective tissue, 34 jelly-like, 38 Consonants, 394 Continuous spectrum, 283 Contractile substance, 56 Contractility, 442 Contraction, secondary, 458 superposition of, 454 vermicular, 457 Contraction-remainder, 453 Corium, 413 Cornea, 541 chemistry of, 555 proper, substance of, 542 vascular system of, 542 Corneal corpuscle, 542 spaces, 542 Cornicula laryngis, 354 Cornua, 471 Corona radiata, 500, 634 Corpora cavernosa, 630 quadrigemina, 501 striata, 499 Corpus albicans, 649 Arantii, 308 callosum, 495 dentatum, 491 luteum, formation of, 651 spongiosum, 630 Corpuscles, bone-, 42 colostrum-, 145 connective-tissue, 35 corneal, 542 Pacinian, 65 salivary, 181 tactile, 65 Vater's, 65 Corresponding points, 583 Coil ex. microscopy of, 503 Cortical substance, 496 Corti's membrane, 615 organ, 613, 614 rods, 614 Costal cartilages, 366 Coughing center, 486 ( 'owner's glands, 431 Cowrf milk, 142 ( ninial nerves, 513 Creatinin in urine, 438 Cremasteric reflex, 479 Cretinism, 341 Crico-arytenoideus lateralis muscle, 356 posticus muscle, 356 Cridoid cartilage, 354 Cricothyroid muscle, 356 Crista acustica, 610, 612 vestibuli, 607 Crotalin, 114 Crowd-poison, 377 Crura cerebelli, 491 cerebri, 499 Crusta, 499 petrosa, 53 ' phlogistica, 295 Crystallin, 111, 556 Crystalline lens, 554 capsule of, 555 chemistry of, 556 Crystalloids, 106 Cubic space allotment, 381 Cuneiform cartilages, 354 Cupola, 608 Curd, 112, 143 Current of action, 458 of injury, 458 of rest, 458 Cuticle, 413 Cylindrical glasses, 572 Cystic duct, 242 Cystoscope, 428 Cytotoxins, 301 DALTONISM, 593 Daniell cell, 444 Daughter-cells, 625 Decidua reflex a, 660 serotina, 660 veia, 660 Defecation, 265-268 Degeneration, 473 Deglutition, 186-190 center, 486 Deiters' cells, 615 phalanges, 615 Demarcation current, 458 Demilunes of Heidenhain, 174 Demours' membrane, 542 Dendrites, 69, 72 Dendrons", 72 Dental follicle, 54 germ, common, 54 lamina, 54 papilla, 54 pulp, 50 sac, 54 Denticulate lamina, 612 Dentin, 50, 51 Dentinal tubuli, 51 Deprez electric signal, 451 Derma, 413 Descemet's membrane, 542 INDEX. 671 Descending tract, 473 Detrusor urinae muscle, 429 Deutero-proteoses, 19V) Deutoplastic granules, 637 Dextrose, 87 fermentation of, 91 in urine, 439 Diabetes, 459 mellitus, 259, 439 Dialysis, 106 Diapedesis, 288, 290 Diaphragm, 367 iris, 560 (Master, 30 Diastole, 312 Diastolic sound, 316 Diathesis, hemorrhagic, 297 Dicrotic pulse, 329 wave, 328, 329 Diet, age and, 140 meat, vegetable, 128 proper, 127 tropical, 135 Diffusion, 104 Digastric muscle, 355 Digestion, 167 apparatus of, 168 bacterial, 253 effect of alcohol on, 159 inlarge intestine, 251 intestinal, 221 mouth, 169 stomach, 191. See also Stomach Diges- tion. tryptic, 236 Diplopia, 583 Direct cell division, 28 Disaccharids, 93 Disassimilation, definition of, 25 Discus proligerus, 634 Dispersion, 574 Dispirem, 29 Distance, judgment of, 584 Dobie's line, 58 Dromograph, 324 Dropsy, 305 Drugs, effect on muscle-curve, 456 DuBois-Reymond key, 445 inductorium, 447 Ductless glands, 334 Ductus auditorius, cochlearis, 613 choledochus, 243 endolymphaticus, 607, 610, 611 Dulong's calorimeter, 410 Duodenal glands, 225 Duodenum, 221 Dysentery from drinking water, 122, 123 Dyspnea, 389 EAR, 598 external, 598 hair-cells of, 615 Ear, internal, 607 labyrinth of, 607 middle, 600 ossicles of, 602. See also Ossicles. vestibule of, 607 Ear-stones, 610 Ear-wax, 417, 599 Ebner's glands, 537 Ectopia vesicse, 428 Edema, 305 Efferent nerves, 462 vessels, 425 Egg-albumin, 108 Eggs as food, 149 Egg-tubes, 635 Ehrlich's lateral-chain theory, 291 Ejaculation, 652 Elastic tissue, 37 Elasticity, definition of, 37 Elastin, 116 Electric keys, 444 phenomena of muscle, 442, 457 signal of Deprez, 451 Electrodes, 444 non-polarizable, 447 Electrotonus, 465 Eleidin, 117 Elementary tissues, 23 Embolism,' 300 Embryo, circulation of, 661 formation of, 657 membranes of, 659 Embryologic method of determining course of nerve-fibers, 473 Emergency ration, 131 Emmetropia, 570 Emulsification, 101 Emulsion theory of fat-absorption, 261 Enamel, 53 Enamel-jelly, 55 Enamel-organ, 54, 55 Enamel-prisms, 53 Enamel-pulp, 55 Encephalon, 483 End-bulbs, 65 Endocardiac pressure, recording of, 313 Endocardium, 305 Endolymph, 609 i Endomysium, 58 j End-organs, motor, 61, 65 j Endosmosis, 102 Endothelium, 30 End-plate, 65 English ration, 131 Enterokinase, 119, 228 Enzymes, 117-119, 292 spleen as producer of, 339 Eosinophiles, 289 Epiblast, 657 Epicardium, 305 Epidermis, 413 Epiglottis, 354 672 INDEX. Epiglottis in deglutition, 188 Epimysium, 58 Epinephrin, 349 Epineurium, 04 Epiphysis cerebri, 351 Epithelium, 30 ciliated, 32 columnar, cylindric, 31 cubical, 30 ' germinal, 31, 631 glandular, 32 pavement, scaly, 30 simple, stratified, 34 spheroidal, 32 transitional, 34 Epitympanic recess, 605 Epoophoron, 638 Equilibrium, 493-495 Erectile center, 482 Erection, 651 Erythroblasts, 44, 287 Erythrodextrin, 97, 183 Esophageal glands, 188 Esophago-duodenostomy, 217 Esophago-enterostomy, 212 Esophagus, 188 Ether, 581 glyceric, 99 Eupnea, 388 Eustachian tube, 306, 604 Excretin, 266 Excretoleic acid, 266 Exophthalmic goiter, 341 Exosmosis, 105 Expiration, 371-374 Expiratory center, 386 Expired, air, 377 External capsule, 499 oblique, 371 rectus, 557 functions of, 559 Extrinsic muscles of tongue, 186 Eye, 541 accommodation of, 560, 564 anterior chamber of, 554 appendages of, 597 chemistry of, 555 effects of facial paralysis on, 522 near-sighted, 571 normal, 570 posterior chamber of, 554 reduced, 562 schematic, 562 tunics of, 541 white of, 541 Eyeball, muscles of, 556 Eyes, convergence of, during accommo- dation, 570 FACIAL expression, 522 nerve, 521 paralysis, 522 Fallopian tubes, 640 ova in, 644 Falsetto, 393 Far-point, 569, 570 Fasciculi, 58 Fasciculus of Tiirck, 473 Fat-cells, 35 Fatigue of muscles, cause of, 455 Fats, 99 absorption of, 261 action of gastric juice on, 199 as food, 125 course of from columnar epithelium to lacteals, 263 disposition of, 264 gastric absorption of, 255 glycogen formation from, 257 Fatty-acid theory of fat absorption, 263 Feces, 265 after stomach removal, 214 color of, 266 composition of, 266 quantity of, 265 reaction of, 266 Fecundation nucleus, 657 Fehling's test for dextrose, 88 Female genital organs, 631 Fenestra ovalis, 605 rotunda, 606 Fermentation, 91, 117 Fermentation-test for dextrose, 88 Ferments, 117-119 Ferratin, Schmiedeberg's, 240 Fertilization, 651 method of, 656 Fetus, circulation of, 661 at birth, 663 Fibrils, 57 Fibrin, 110 Fibrin-ferment, 297 Fibrin-globulin, 293 Fibrinogen, 110, 293 Fibrinoplastin, 110, 297 Fibrocartilage, 40 Fibrous nervous matter, 63 tissue, 38 Field ration, 132 Filiform papillae, 537 Filtration-and-difl'usion theory of lymph origin, 303 Filum terminale, 478 First sound, 316 Fission, 28 Fissures of spinal cord, 471 Floor-space, allotment of, 381 Flour, processes of making, 154 Focus, inability to, 514 Focussing, 560 Food, 121 absorption of, 167, 254 definitions of, 158 digestibility of, 130, 209 INDEX. 673 Food for soldiers, 131 quantity required, 130 of water in, 79 sodium chlorid in, 81 starch in, 96 Food-stuffs, 121 composition of, 148 inorganic, absorption of, in stomach, 254 oxidation of, 409 Foramen of Sommering, 548 ovale, 308 Forebrain, 483 Form, appreciation of, 583 Fossa vesicalis, 242 Fovea centralis, 548 hemi-elliptica, 607 hemispherica, 607 Fracture, green-stick, 84 Franklin color theory, 592 Fraunhofer lines, 284 Frick's spring myograph, 323 Frontal lobe, 497 Function, definition of, 17 Functions, classification of, 21 Fungiform papillae, 537 Funiculi, 64 Funiculus cuneatus, 485, 486 gracilis, 485, 486 of Rolando, 485, 486 Furfur-aldehyd, 248 Furfurol, 248 Fuscin, 556 GALACTOSE, 88, 92 Gall-bladder, 242 Gamgee's theory of HC1 in gastric juice, 196 Ganglia, 72 automatic menstrual, 647 basal, 499 functions of, 500 cerebral, 499 of trigeminus, 520 spinal, 476 function of, 483 Ganglion spirale, 609, 615 Garrison ration, 133 Giirtner's duct, 638 Gastric acidity, intestinal contents and, 214 juice, action of, 199 artificial, 220 gerrnicidal powers of, 197 hydrochloric acid in, 195 mixed with saliva, 195 pepsin in, 198 pepsin-hydrochloric acid in, 198 quantity of, 194 rennin in, 198 secretion of alcohol and, 159 nerves, 524 Gastritis glandularis atrophicans, 219 Gelatin, 115 Gelatoses, 200 Gemmation, 28 Geniohyoid muscle, 356 Genital organs, 624 female, 631 male, 625 Genitospinal center, 481 Gerlach's nerve-network, 475 German ration, 131 Germinal epithelium, 631 spots, 638 vesicle, 637, 638 Giant-cells, 44 Gland-pulp, 332 Glans penis, 630 Glia-cells, 73 Glisson's capsule, 239 Globulicidal action of serum, 292, 300 Globulins, 81, 110, 276 Glossopharyngeal nerve, 388, 523 Glottis, 358, 360 in singing, 395 movements of, 373 Glucoses, 87 Glucosid, 260 Gluteal reflex, 479 Gluten, 153 Glycerids, 99 Glycocoll, 247 Glycogen, 97, 257 action of ptyalin on, 183 Glycogenic theory, 257 Glycosuria, 259 alimentary, 256, 439 from pancreas, removal, 239 Gmelin's reaction, 247 Goblet-cell, 31 Goiter, 341 Golgi's organ, 69 Goll's column, 473 Gowers' hemacytometer, 271 hemoglobinometer, 278 Graafian follicles, 633 bursting of, 643 ova in, 635 Granule-cells, 35 Granuloplasm, 24 Grape-sugar, 87 Graves' disease, 341 Grave-wax, 99 Gravity, circulation and, 330 Gray commissure, 471 fibers, 64 matter, 69 nerve-fibers of, 474 of brain, 483 of cerebellum, 491 of cerebrum, 496 microscopy of, 503 of cord, 473 674 INDEX. Green-stick fracture, 84 Ground-bundle, anterolateral, 473 Gum, animal, 112 Gustatory cells, 538 nerve, 517 pore, 538 Gyri, 496 operti, 498 HAIR-CELLS of ear, 615 Hairs, 417 Hammarsten's blood-coagulation theory, 297 Hamulus, 609 Harmonic series, 622 Hasner's valve, 597 Hassal's corpuscles, 347 Haversian canals, 41,43 Head, motor area of, 511 Hearing, 598 physiology of, 616 theories of, 618 Heart, 305 apex-beat of, 315, 317 beat of, explanation of, 317 impulse of, 315 movements of, 311 papillary muscles of, 307 parietal portion, 305 pause of, 312 septum of, 306 shortening of, 315 sounds, 316 valves of, 307 visceral portion, 305 Heat-rigor, 111 Heat-unit, 409 Heidenhain's demilunes, 175 lymph theory, 303 Heister's valve, 244 Helicotrema, 609 Heller's test, 438 Helmholtz phakoscope, 568 Hemacytometer, 271-273 Hemagglutinins, 301 Hematin, 276, 281, 282 hydrochlorid, 281 Hemato-aerometer, 385 Hematoblasts, 291 Hematocrit, 270, 271 Hematoidin, 246, 282 Hematopoiesis, 287 Hematoporphyrin, 282, 431 Hematoscope, 285 Hemm, 281 Hemiplegia, 491 Hemochromogen, 276, 282 Hemoglobin, 286 carbon-monoxid, 280 spectrum of, 286 derivatives of, 280 spectra of, 282 Hemoglobin, nitric-oxid, 281 spectra of, 282-285 Hemoglobinometer, 276-278 Hemolysis, 300 Hemophilia, 297 Hemorrhagic diathesis, 297 Hemoscope, 285 Henle's loop, 422 Hensen's line, 57 Hepatic artery, 241 duct, 242 Hepatin, Zaleski's, 240 Hering color theory, 588 Hermann's hematoscope, 285 Hetero-proteose, 199 Hindbrain, 483 Hippuric acid in urine, 437 Histohematins, 282 Histology of body, definition of, 21 Holmgren test, 590 Homoiothermal animals, 407 Horns of cord, 474 Human milk, 141 Humidity, 376 Humor, aqueous, 554 chemistry of, 556 vitreous, 554 chemistry of, 556 Hyaloid membrane, 554 Hyaloplasm, 24 Hydrobilirubin, 247, 431 Hydrochloric acid in body, 87 Hydrogen, 86 sulphuretted, 86 Hydrolysis, 119 Hypermetropia, 571 Hyperpnea, 389 Hypoblast, 657 Hypoglossal nerve, 526 Hypophysis cerebri, 351 IDENTICAL point?, 583 Iliocostalis muscle, 370 Immunity, 290 Ehrlich's lateral-chain theory of, 291 Impregnation, 651 method of, 656 Incisors, 53, 171 Inco-ordination, 492 Incus, 603 Indifferent point, 467 Indirect cell-division, 28 Indol, 266 Indoxyl in urine, 439 Induced current, 446 Induction apparatus, 447 Inferior maxillary nerve, 516 oblique, 558 rectus, 557 functions of, 559 Infundibula of lungs, 364 Infundibulum, 640 INDEX. 675 Inhibition of reflex action, 479 Inorganic, definition of, 18 ingredients, 77 Inosit, 93 Insalivation, 172 Inspiration, 372, 374 extraordinary muscles of, 369, 372 forced, 374 muscles of, 369, 372 ordinary, muscles of, 367 [nspiratory center, 386 spasm, 389 Insula, 497, 498, 500 Intensity, 621, 623 Interarytenoid fold, 359 Intercentral nerves, 463 Intercostal muscles, 368 spaces, 365 Interlobular arteries, 425 plexus, 241 vein, 241 Intermediolateral tract, 474 Internal capsule, 499 medullary lamina, 501 oblique, 371 rectus, 557 functions of, 559 secretion, 335 sphincter, 227 Internodes, 64 Interposed bundle, 69 Intervertebral disks, 365 Intestinal contents, gastric acidity and, 214 digestion, 221 juice, 228 Intestine, large, absorption by, 264' digestion in, 253 movements of, 250 structure of, 227 small, 221 absorption by, 255 movements of, 250 villi of, 22-2 Intra-epithelial plexus, 544 Intranuclear network, 25 Intraocular images, 580 Intrinsic muscles of tongue, 186 Invertin, 93, 228 Invert-sugar, 92, 93 Involuntary muscle, 61-63 Involution, definition of, 62 lodin in body, 86 test for starch, 96 lodo-thyrin, 340 Iris, 545, 575 arteries of, 546 diaphragm, o60 Iron in body, 86 Irradiation, 574 Irritability, 442 Irritants, 442, 443 Island of Keil, 497, 498, 500 Iso-electric, definition of, 457 Isomaltose, 95 Isotonic solution, 269 Isthmus of fauces, constrictors, of, 187 Ivory of tooth, 41 JACOB'S membrane, 558 Jecorin, 240 Jelly-like connective tissue, 38 Judgment, 508 KARYOKINESIS, 28 Karyomitosis, 28 Katabolism, 120 definition of, 25 Katacrotic wave, 328 Katelectrotonic current, 466 Katelectrotonus, 467 Kathode, 444 Keratin, 117 Keys, electric, 444 Kidney, 421 blood-vessels of, 424 effects of removal of, 427 function of, 426 nerve-supply of, 425 Kilocalorie, 409 Kilogramdegree, 409 Kinases, 119 Kinesthetic area, 509, 510 Knee-jerk, 480 Kolliker's membrane, 615 Kra use's end-bulbs, 65 membrane, 49 Kymograph, 313 LABIUM tympanicum, 612 Labyrinth, 607-609 Labyrinthine impressions, 493 Lacrimal apparatus, 597 Lactalbumin, 109 Lacteals, 224 Lactoglobulin, 109, 111 Lactose, 88, 94 in urine, 439 Lactosuria, 439 Lacuna?, bone, 42 Lakey blood, 269 LamelUe, 42, 43 Lamina cribrosa, 541 fusca, 541 spiralis, 608 suprachoroidea, 544 vitrea, 544 Langley's ganglion, 177 Lanolin, 101 Laryngeal nerves, 388, 523 pouch, 359 Laryngoscope, 390 Larynx, 354 blood-supply of, 360 676 ISDEX. Larynx, cartilages of, 354 cavity of, 358 depressors of, 355 elevators of, 355 in singing, 395-406 interior of, 358 muscles of, 355 nerves of, 360 photography of, 394 Latent period, 452 Lateral horn, 474 Lateral-chain theory of Ehrlich, 291 Latissimus dorsi, 369 Laurent's polarimeter, 89 Lecithin, 101, 249 Legs, motor area of, 510 Legumin, 155 Lens, crystalline, 554. See also (7h/s- talline. Lenticular nucleus, 499 Leukemia, 288, 338 Leukocytes, 288 composition of, 290 development of, 291 functions of, 290 spleen in production of, 338 varieties of, 289 Leukocythemia, 288, 338 Leukocytopenic phase, 289 Leukocytosis, 288 Leukocytotic phase, 289 Leukornains, 115 Leukotoxin, 301 Leva tores costarum, 368 Levulose, 88, 92 Lieberkuhn, follicles of, 226 Ligamentum pectinatum, 542 spirale, 613 Light, 576, 581 polarization of, 88 synthesis of, 588 Lignin, 98 Lilienfeld's blood-coagulation theorv, 297 Limbus, 612 luteus, 548 Lime phosphate in body, 84 Lingual nerve, 517 papilla, 536 Lipase, 292 Liquor folliculi, 635 sanguinis, 291 Scarpse, 609 Lissauer's tract, 473 Littre"'s glands 431 Liver, 239, 240 effect of alcohol on, 162 extractives of, 240 glycogenic action of, 256 innervation of, 253 iron in, 240 proteids, 240 Load, effect on muscle-curve, 455 Lobules, 362 Locus niger, 499 Loudness, 621 Ludwig's theory of origin of lymph, 303 Lungs, 362 blood-vessels of, 364 capacity of, 374 causes of oxygen and carbon dioxid interchange in, 382 nerves of, 364 Lupino-toxin, 113 Luschka's gland, 352 Luscitas, 514 Lymph, 302 circulation of, 334 office of, 304 origin of, 303 Lymphagogues, 303 Lymphatic duct, 331 glands, 332, 333 ' system, 330 Lymphocytes, 289, 303 Lymphoid tissue, 37, 332 Lymph-path, 332 Lymph-sinus, 332 _ *- MACULA acustica, 610 cribrosa, 607 lutea, 548, 553, 577 Magnesium salts, 86 Make of current, 447 Male genital organs, 625 Malleus, 602 Malpighian capsule. 422 corpuscles, 336, 337 Maltodextrin, 97 Maltose, 88, 94 Maly's theory of origin of HC1 in gastric juice, *196 Mammse, 144 Mammary glands, 144 Mammilla, 144 Manometer, 321 Marey's cardiograph, 312 Marrow, bone-, 43 embryonic, 49 red, 43 yellow, 43 Marrow-cells, 44. 287 Marsh-gas, 86 Mastication, 171, 517 Mastoid antrum, 605 cells, 605 Maxillary nerves, 516 rampart, 54 Maximal pulsation, 322 Mean blood-pressure, 321 Meat as food, 150 cooking of, 150, 151 Meatus, auditory, external, 598, 599 internal, 607 INDEX. 677 Meatus urinarius, 430 Mecke!' s ganglion, 520 Meconium, 266 Medulla oblongata, 484-486 Medullary artery, 44 canal, 43 sheath, 64 spaces, 49 Meibomian glands, 597 Membrana basilaris, 598 flaccida, 602 granulosa, 634 limitans externa, 552 interna, 550 pupillaris, 546 tectoria, 615 tympani, 600 in hearing, 617 secundaria, 606 Memory, 508 Meniere's disease, vertigo of, 495 Menopause, 645 Menses, 645 Menstrual ganglia, automatic, 647 Menstruation, 645 and ovulation, relation between, 648 cause of, 647 corpus luteum of, 649 cycle of, 646 Mercurial manometer, 321 Merycism, 486 Mesoblast, 657 Mesocephalon, 488 Metabolism, 120 Metakinesis, 30 Methemoglobin, 281 Metschnikoff's phagocytosis theory, 290 Micropyle, 656 Micturition, 430 Midbrain, 483 Middle cell-group, 474 Migration, external, 645 internal, 645 of leukocytes, 290 Milk as food, 141 composition of, 149 cows', 143 human, 144 formation of, 145 secretion of, nervous control of, 146 transmission of disease by, 143 Milk-curdling enzyme of pancreatic .juice, 238 Milk-sugar, 94 Milk-teeth, 55, 171 Millon's reaction, 103 Mitosis, 28 Mitral valve, 308 Modiolus, 608 central canal of, 608 spiral canal of, 609 Moist chamber, 451 Molars, 55, 171 Monaster, 30 Monosaccharids, 87 Morgagni's ventricle, 359 Morula, 657 Moss-fibers, 492 Mother-cells, 625 Motion, paralysis of, 464 Motor area, 509, 510 end-organs, 61, 65 lingual nerve, 526 oculi, 513 Mouth, absorption in, 254 digestion, 169 effects of facial paralysis on, 522 floor of, 186 Mouth-breathing, 353 Mucinogen, 180 Mucins, 117 Mucin-sugar, 92 Mucous glands, 174 of mouth, secretion of, 181 of stomach, 193 Mucus-secreting cells, 32 Mailer's fibers, 553 ring muscle, 544, 546 Mumps, 173 Murexid test for uric acid, 434 Muscse volitantes, 580 Muscle, blood-vessels of, 61 cardiac, 61, 63 character of, effect on curve, 455 electric phenomena of, 442, 457 fatigue, cause of, 455 involuntary, 61-63 non-striated, 61 nuclei of, 58 of insects, 58 phenomena, 442 plain, 61 skeletal, 61 striated, 56, 61, 62 voluntary, 56 Muscle-clot, 11 Muscle-columns, 57 Muscle-curve, 449, 452, 454 Muscle-nerve preparation, 443 Muscle-plasma, 62 Muscles, ocular, 556 Muscle-spindles, 61, 69 Muscle-sugar, 93 Muscular contraction, simple, 451 sense, 529 tissue, 56 tone, 456, 481 Musciili papillares, 307, 316 Musculotonic center, 481 Mydriasis, 512 Mydriatics, 576 Myeloplaques, 44 Myeloplaxes, 44 Mylohyoid muscle, 355 678 Myo-albumin, 109 Myocardium, 305 Myogen-fibrin, 62 Myogram, 449 Myograph, 449 Trick's spring, 323 Myoheraatin, 63 Myopia, 571 Myosin, 62, 111 Myosin-fibrin, 62 Myosinogen, 111 Myotics, 576 Mytilotoxin, 115 Myxedema, 341 NAILS, 417 Nasal duct, 597 reflex, 480 Nates, 501 Near-point, 565, 569 Near-sightedness, 571 Neck, motor area of, 511 Neck-sweetbread, 346 Negative accommodation, 565 blood-pressure, 323 variation current, 458 Nephrectomy, effects of, 427 Nerve-cells, 69 development of, 73 of spinal cord, 474 Nerve-center, cord as, 478, 480 Nerve-centers of medulla, 486 Nerve-fibers, 63 depressor, 488 development of, 73 Nerve-impulses, 465 Nerves, 461-464 cardiac, 318, 525 cranial, 513 olfactory, 531 functions of, 533 spinal, 475 functions of, 482 trophic, 519 vasoconstrictor, 488 vasodilator, 488 vasomotor, 462, 488 Nervi erigentes, 631 nervorum, 64 Nervous functions, 460 system, 468 tissue, 63 chemistry of, 74 proteids of, 75 Neu raxes, 69 Neuraxon, 71 Nt-urilemma, 64 Neuroblasts, 73 Neuroglia, 72 Neurokeratin, 117 Neurolemma, 64 Neuron, 71, 73 INDEX. Neuroplasm, 64 Nipple, 144 Nissl's granules, 69 Nitric-oxid hemoglobin, 281 Nitrogen in body, 86 Nitrogenous foods, 126 Nodes of Ranvier, 64 Noises, 620 Normal salt solution, 81 Nose, 353 Nuclear matrix^ 25 membrane, 25 Nucleic acid, 111 Nuclein, 25 Nucleins, 111 Nucleo-albumins, 112 Nucleohiston, 291 Nucleolus, 25, 637 true, 25 Nucleoproteids, 111, 112, 294 in urine, 438 poisonous property of, 113 Nucleus, 25 fecundation, 657 Nutrient artery, 44 foramen, 44 Nutritive functions, 167 OBLIQUE muscles, 558 Obliquus externus, 371 internus, 371 Occipital lobe, 498 Ocular muscles, 556 functions of, 559 Odontoblasts, 50 Odontoclasts, 55 OEstrus, 647 Oils as food, 125 gastric absorption of, 255 Old sight, 572 Olein, 99 Olfactory bulb, 531 cells, 531 glomeruli, 532 membrane, 530 nerve-fibers, 532 nerves, 531 function of, 533 sulcus, 533 tract, 533 Olivary body, 485 Oliver's hemacytometer, 273 hemoglobinometer, 277 Omohyoid muscle, 355 Oncometer, 338 Opaque bodies, 589 Ophthalmic nerve, 516 Ophthalmoscope, 580 Optic angle, 563 constants, 561 disk, 549 thalami, 501 INDEX. 679 Optogram, 582 Ora serrata, 547 Orbits, 541 Organ, definition of, 17, 18 of Corti, 613, 614 of Golgi, 69 Organic, definition of, 18 Organs of body, relations between, 460 Os orbiculare, 603 Osmometer, 104 Osmosis, 81, 104 Ossein, 115 Ossicles of ear, 602 ligaments of, 604 muscles of, 604 Ossification, 40, 45 center of, 46 endochondral, 46 intracartilaginous, 46 intramembranous, 46 superiosteal, 45 Osteoblasts, 43 Osteoclasts, 44, 49 Osteogenic fibers, 46 Ostiurn abdominale, 640 Otic ganglion, 520 Otoconia, 610 Otoliths, "610 Ova, 638 holoblastic, 657 in Fallopian tubes, 644 in Graafian follicles, 635 liberation, 642 maturation of, 651 meroblastic, 657 nucleolus of, 637 nucleus of, 637, 638 primitive, 635, 637 Ovarian ligament, 631 pregnancy, 654 Ovary, 631 * cortex of, 633 medulla of, 633 Overtones, harmonic, 622 Ovula Nabothi, 642 Ov ulation, 642 and menstruation, relation between, 648 Oxygen and carbon dioxid, interchange of, between air and blood, 383 between blood and tissues, 386 in lungs, 382 in body, 86 tension of, in blood, 383 Oxyhemoglobin, 276, 279 spectrum of, 285 Oxyntic cells, 193 Oxyphils, 289 PACINIAN corpuscles, 65 Pain, sense of, 530 Palmitin, 99 Pancreas, 229 innervation of, 238 removal of, 239 secretion of, 232 internal, 239 structure of, 229 Pancreatic fistula, 233 juice, 233 emulsifying powers of, 237 enzymes of, 235 milk-curdling enzyme of, 238 secretion of, 239 Papain, 113 Papillae, circumvallate, 536 conical, 537 filiform, 537 fungiform, 537 lingual, 536 Papillary muscles, 316 of heart, 307 Paraglobulin, 110 Paralysis, cerebral, 501 of motion, 464, 501 of sensation, 464 Paranucleins, 112 Para plasm, 24 Parathyroid, 339, 345 Parietal cells, 193 lobe, 498 Parieto-occipital fissure, 497 Paroophoron, 638 Parotid gland, anatomy of, 172 nervous supply of, 176 secretion of, 180 Parotitis, 173 Parovarium, 638 Pars ciliaris retinae, 547, 554 optica retinse, 547 minute structure of, 550 Parturition, center for, 482 Pasteurization, 144 Patellar reflex, 480 Patheticus, 514 Pavilion, 640 Pavy's glycogenic theory, 258 Pecquet's cistern, 331 Pectoralis major and minor, 370 Peduncular fibers, 506 Pekelharing's blood-coagulation theory, 297 Penis, 630 erection of, 651 Pepsin in gastric juice, 198 Pepsin-hydrochloric acid, 198 Pepsinogen, 198 Peptones, gastric absorption of, 255 gelatin, 200 poisonous property of, 113 Peptonuria, 438 Percussion-wave, 328 Pericardium, 305 Pericementum, 54 080 INDEX. Perichondrium, 41 Peri lymph- waves, conversion of sound- waves into, 616 Perimysium, 58 Perineurium, 64 Period of vibration, 620 Periosteum, 43 dental, 55 Peripheral resistance, 319 Peristalsis, 457 of esophagus, 189 Perivitelline space, 637 Perspiration, 414 Perspiratory glands, 413 Pettenkofer's test, 248 Peyer's patches, 226 Pfliiger, primary egg-tubes of, 635 Phagocytosis, 290 Phakoscope, Helmholtz, 568 Phalanges, Deiters', 615 Phloridzin, 260 Phlorizin-diabetes, 260 Phonation, 393 laryngoscopic image during, 391 Phosphates, earthy, 86 in body, 82. See also Calcium, Mag- nesium, etc. Phospho-glucoproteids, 112 Phosphorized fat, 101 Phrenic nerves, 388 Physiologic chemistry, 76 ingredients, 76 salt solution, 81 Physiology, animal, 20 branches of, 19 definition of, 17 human, defined, 20 vegetable, 19 Phytalbumose, 153 Pialyn, 236 Piano theory of hearing, 618 Pigeon-breast, 353 Pigmentary layers of retina, 553 Pigments, mixing of, 590 respiratory, 276 retinal, 566 Pineal gland, 351 Pinna, 598 Piotrowski's reaction, 103 Pitch, 392, 621, 623 Pituitary body, 351 Placenta, 660 circulation of, 661 Plantar reflex, 479 Plaques, 291 Plasma, 108 blood, 291. See also Blood-plawia. muscle-, 62 salted, 295 Plasma-cells, 35 Plethysmograph, 329 Pleura, 362, 365 | Plenral cavity, 365 Plexus, intra-epithelial, 544 subepithelial, 544 Pneumogastric nerve, 523 Pohl's commutator, 447 Poikil'othermal animals, 407' Polarimeter, 88 Polariscope, 88 Polarization, 88, 444 Polarizing current, 466 Poles of cells, 70 Polysaccharids, 95 Pomum Adami, 354 Pons Varolii, 488 Portal canals, 239 vein, 241 Portio dura of facial, 521 mollis of facial, 521 Porus opticus, 541 , 549 positive accommodation, 565 Post-dicrotic wave, 328 Posterior chamber of eye, 554 gray commissure, 471 horn, cells of, 474 intermediate furrow, 471 median fissure, 471 Posterolateral column, 474 fissure, 471 Posteromedian column, 473 Potassium carbonate, 83 chlorid, 84 phosphate, 82 sulphate, 63 Pre-antral constriction, 200 Precipitins, 301 in identifying blood-stains, 301 Predicrotic wave, 328 Pregnancy, abdominal, 654 ampullar, 655 anomalous varieties, 656 cornual, 656 corpus luteum of, 651 ectopic, 655 extra-uterine, 655 infundibular, 656 interstitial, 655 ovarian, 654 peritoneal, 654 Presbyopia, 572 Pressure sense, 529 Primary pulse wave, 328 Primitive sheath, 64 Processus ad medullam, 491 cochleariformis, 604 e cerebello ad testes, 491 Projection-fibers, 505, 506 Pronucleus, female, 651 male, 657 Protagon, 75 Proteids, 102 absorption of, 260 action of gastric juice on, 199 INDEX. 681 Proteids, action of, on polarized light, 103 as food, 125 classification of, 107 coagulated, 108, 113 color-reactions of, 103 crystallization of, 104 glycogen formation from, 257 in urine, 438 non-diffusibility of, 104 of liver, 240 poisonous, 113 precipitation of, 106 vegetable, 155 Protein, 110 Proteoses, poisonous property of, 113 primary, 199 secondary, 199 Prothrombin, 292, 294 Protoplasm, 24 Protoplasmic process, 72 Proto-proteose, 199 Pseudonucleins, 112 Pseudonucleoli, 25 Pseudopodia, 24 Ptomain, 114 Ptosis, 514 Ptyalin, 97, 182 Ptyalinogen, 180 Pulmonary alveoli, 363 artery, 364 capillaries, 364 circulation, 311 nerves, 525 valve, 308 veins, 364 Pulsation, 311 maximal, 322 Pulse, 318, 326 dicrotie, 329 record of, 327 volume, 314, 329 waves, 328 Pulse-trace, 327 Puncta lacrimalia, 597 Punctum pioximum, 565, 569 remotum, 570 Puncture-diabetes, 259 Pupil, 545 contraction of, during accommoda- tion, 570 membrane of, 546 Purin, 435 bases and uric acid, 434 Purin-bodies in alcoholic beverages, 157 Purkinje's cells, 491 figures, 577 Purkinje-Sanson images, 567 Purple, visual, 556, 581 Pyloric glands, 193 muscle, 192 orifice, 191 Pylorus, movements of, 201 Pyramidal tracts, 473 Pyramids of brain, 485 QUADRATUS lumborum, 371 Quality of sound, 621, 623 RACEMOSE glands, compound, 174 Kami communicantes, 488 Ranvier's nodes, 64 Rations, 30 Reason, 508 Receptaculum chyli, 331 Recollection, 508 Rectus abdominalis, 372 muscles, 557 functions of, 559 Recurrent sensibility, 483 Red corpuscles, 270 chemical composition of, 275 color of, 274 destruction of, 287 development of, 286 function of, 288 number of, 271 spleen and, 338 structure of, 275 Reflex action, 478-481 arc, 479 centers of medulla, 486 deep, 480- in man, 479 * superficial, 479 time, 479 Regio olfactoria, 530 respiratoria, 530 vestibularis, 530 Reichert's water calorimeter, 410 ReiFs island, 497, 498, 500 Reissner's membrane, 609, 613 Relative humidity, 376 Remak's fibers, 64 Remembrance, 508 Renal arteries, 424, 425 Rennin, 112 in gastric juice, 198 Reproduction, 624 organs of, 624. See also Genital Or- gans. Residual air, 375 Resonance, 391 Resonators, 623 Respiration, 352 apparatus of, 353 at birth, 663 blood-changes from, 381 chemistry of, 376 Cheyne-Stokes, 387 efferent nerves, 388 female type, 375 frequency of, 375 innervation of, 386-388 682 L\DEX. Respiration, internal, 386 t&rvngOBOOpic image during, 391 male type, 375 movements of, 372 rhythm of % 386 muscles of, 367 of skin, 419 Respiration-calorimeter, 164 Respiratory center, 386, 481 pigment, 276 quotient, 377 Restiform body, 485 Eete mueosum, 413 test is, 627 Retieular lamina, 615 Reiieulin, 116 Retieulum, 24 Retiform tissue, 37 Retina, 547, 576 central artery of, 541, 549 chemistry of, 555 circulation in, 579 epithelium of, 552 fatigue of, 594 layers of, 550-553 pars optica of, minute structure of, 550 pigmentary layer of, 553 n-ilexof, 580 * Retinal image, 562, 563 Retzius' fiber-cells, 610 Reunions, canalis, 611 Reverse air, 374 Rheoseope, physiologic, 458 Rhodopsin, 556, 581 Khomhoidei, 370 Rhythmieality, 457 Ribs, 365 Ricin, 113 Rigor mortis, 62, 111, 456 Ring muscle of Miiller, 544, 546 Rima glottidis, 359 Rivinus' ducts, 174 Rod-bipolars, 551 Rod-elements, 552 Rod -fiber, Rod-granules, 552 R..ds :>.vj Rolandic area, 509, 510 Rolando's lissure, 497 funieulus, 485, 486 Rontgen rays in examination of stom- ach, 201 Root-fiber, anterior, 73 Routs of spinal nerves, 475 Rope, the, 581 Rosenmiiller's organ, 638 Rotatory power, specific, 91 Riiira' 01 stomai-h, 192 Rumination, 486 Rut, 647 SACCHARTMETER, 89 Saccharoses, 93 Sacrule, 610, 623 Sacculus laryngis, 359 Sacrolumbalis, 370 Saliva, alkalinity of, 181 amylolytic action of, 183 celte of, changes in, 180 chemical action of, 182 examination of, 187 composition of, 180 corpuscles of, 181 effect of alcohol on secretion of, 159 of nerve-stimulation on, 176 mixed, 181 with gastric juice, 195 offices of, 182-185 properties of, 180 secretion of, 179 taste and, 185 Salivary calculi, 182 glands, anatomy of, 172 secretory nerves of, 176 Salted plasma, 295 Salts as food, 123 excretion of, 426 in body, 80 Santorini's cartilages, 354 Sapokrinin, 239 Saponification, 100 Sarcolemma, 56 Sarcomeres, 59 Sarcoplasm, 57 Sarcostyles, 57 Sarcous element of muscle, 59 Sartoli's columns, 625 Scala media, 609 tyrnpani, 608 vestibuli, 609 Scaleni, 367 Schemer's experiment, 569 Schlatter's case of stomach extirpation, 212 Schmidt's theory of blood-coagulation, 297 Schmiedeberg's ferratin, 240 Schoen's theory of accommodation, 569 Schulze's tests for glycogen, 98 Schwann's nucleated* sheath, 64 white substance, 64 Sclerocorneal junction, 546 Sclerotic tunic of eye, 541 Sebaceous glands, 416 Sebum, 416 Second sound, 316 Secretin, 239 Segmentation, 657 Semen, 629 ejaculation of, 652 Semicircular canals, 607, 623 impressions from, 493 membranous, 612 positions of, 494 result of injury to, 493 INDEX. 683 Semilunar valves, 307, 308 Seminiferous tubules, 625 Senile atrophy, 84 Sensation, paralysis of, 464 Senses, 527 special, trigeminus and, 518 Sensibility, general, 527 recurrent, 483 tactile, 527 Sensorimotor area, 509, 510 Sensory area, 509, 512 fibers, recurrent, 483 Septum, auricular, 308 ventricular, 308 Serous glands, 174 membranes, 333 Serrati muscles, 370, 371 Serum, 108 bactericidal property of, 300 blood, 294 globulicidal action of, 300 Serum-albumin, 108 Serum-globulin, 110 Sharpey's perforating fibers, 43 Shock, reflex action and, 480 Shrapnell's membrane, 602 Sight, 563 long, 572 old, 572 sense of, 541 Silicon, 86 Singing, resonance chamber in, 395-406 Size, appreciation of, 583 Skatol, 266 Skatoxyl in urine, 439 Skein, 29 Skeletal muscle, 61 Skin, 413' care of, 419 excretion of, 418 functions of, 418 nerves of, in respiration, 388 protection furnished by, 418 respiration by, 419 sensation in, 418 temperature and, 419 Smell, sense of, 530 acuteness of, 535 Snake-poison, 113, 114 Soap, 100 emulsification and, 237 theory of fat-absorption, 263 Sodium carbonate, 83 chlorid, 80 in osmosis, 81 glycocholate, 247 phosphate, 82 sulphate, 83 taurocholate, 247 Solar spectrum, 283, 587 Solitary glands, 226 Soluble starch, 96 Solution theories of fat-absorption, 263 Somatopleure, 659 Sum men-ing's foramen, 548 yellow spot, 548, 553J 577 Sonometer, 622 Sonorous bodies, 616 Sound conduction through skull bones, 618 definition of, 616 Sounds, 620 Sound-waves, 616 Spectroscope, 283 Spectrum, 283, 587 Speculum, aural, 600 Speech, 389, 393 Speech-center, 511 Spcnnatoblasts, 625 Spermatogenesis, 625 Spermatoxin, 301 Spermatozoa, 625 passage of, 652 Sphenopalatine ganglion, 520 Sphincter antri pylorici, 194 internal, 227 pupillae, 545 pyloricus, 192 movements of, 201 vesicae, 429 Sphygmograph, 327 Sphygmometer, 322 Spider-cells, 73 Spinal accessory nerve, 525 columns, 471 cord, 468 as nerve-center, 478, 480 conduction-paths in, 477 enlargements of, 468 fissures in, 471 functions of, 477 gray matter of, 473 minute structure of, 472 nerve- cells of, 474 reflex action of, 478 section of, 471 special centers of, 481 tracts of, 473 white substance of, 472 ganglia, 476 functions of, 483 nerves, 475 functions of, 482 in respiration, 388 Spiral canal of ear, 608 Spirem, 29 Spirits as food, 157 Splanchnopleure, 659 Spleen, 335 contraction and expansion of, 338 corpuscles and, 338, 339 during digestion, 337 enzymes and, 339 684 INDEX. Spleen, uric acid and, 339 Splenic arterv, 337 cells, 44 pulp, 336 Spongework, 24 Spongioblasts of retinal molecular layer, 551 Spongioplasm, 24 Spreading of reflexes. 478 Stains, blood-, precipitins in identifying, 301 Staircase curve, 455 Stapedius, 604 Stapes, 603 Starch, 95-97 Starch-grains, 95 Starch-paste, 96 Steapsin, 236 Stearin, 99 Stellar phosphates, 441 Stellate reticulum, 55 Stenson's duct, 173 Stercobilin, 247, 266 Stereoscope, 583 Sterilization of milk, 144 Sternohybid muscle, 355 Sternomastoid, 370 Sternothyroid muscle, 355 Stilling's canal, 554 Stimulation, 443, 444 previous, effect on muscle-curve, 455 Stimuli, 442, 443 protoplasmic, 24 summation of, 453 Stomach, 191 absorption in, 254 of alcohol from, 161 changes in, in digestion, 204 digestion, 191, 208 excretory function of, 209 movements of, 200 effect on food, 205 progressive atrophy of, 219 removal of. 211, 214 Rontgen rays in examination of, 201 ruga? of, 192 self-digestion of, 208 Stomata, 333 Strabismus, external, 514 Straight tubes, 627 Stratum granulosum, 634 Stria?, 56 Striated muscle, 56 Stroma, 545, 633 Stromuhr, 323 Stylohyoid muscle, 355 Subclavius, 371 Sul>epithelial plexus, 544 Sublingual gland, 174 iK-rve-supply of, 177 secretion of, 181 Sublobular vein, 241 Submaxillary ganglion, 521 gland, 173 nerve-supply of, 177 secretion of, 180 Subsidiary centers, 386 Substantia cinerea gelatinosa, 472 gelatinosa centralis, 472 lateralis, 472 Succus entericus, 228 Sucking center, 486 Sudorific center, 481 Sudoriparous glands, 413 Sugar, composition of, 124 Sulci, 496 Sulphates, 83 Sulphuretted hydrogen, 86 Superior intercostal vein, 364 maxillary nerve, 516 oblique, 558 rectus, 557 Supplemental air, 374 Suprarenal capsules, 347-349 Suspensory ligament, 555 Sustentacular cells, 336, 537, 625 Swallowing, 189, 190 Sweat, 414 Sweat-gland, 413 Sweetbread, 346 Sylvius' fissure, 496 Sympathetic nerve, effect of stimulation of, 177 Synaptase, 72 Syntonin, 109 System, definition of, 19 Systemic circulation, 311 Systole, 312 Systolic sound, 316 TAIL fold of blastoderm, 658 Tapetum nigrum, 553 Tartar, 182 Taste, facial paralysis and, 522 saliva and, 185 sense of, 535 conditions of, 540 Taste-buds, 537 Taurin, 247 Tea, 156 Tears, 597 Teeth, 50, 55, 171 development of, 54 in mastication, 171 Tegmen, 592 Tegmentum, 499 Telephone theory of hearing, 619 Temperature, 406, 407 effect on muscle-curve, 455 regulation of, 413 sense, 529 skin as regulator, 419 Temporosphenoidal lobe, 498 Tendo A chillis reflex, 480 INDEX. 685 Tendon reflexes, 480 Tendon-cells, 38 Tenon's capsule, 541 Tension of dissociation, 383 Tensor tympani, 604 Testes, 601, 625 Test-meals, 210 Tetanin, 115 Tetanus, 454 secondary, 458 Theca folliculi, 634 Them, 156 Thiry-Vella fistula, 228 Thoma-Zeiss hemacytometer, 272 Thoracic cavity, 365 duct, 331 Thorax, 365 aspiration of, 330 respiratory muscles of, 367 Throat-sweetbread, 346 Thrombin, 292 Thrombosin, 297 Thymus, 346 Thyreo-antitoxin, 340 Thyreoproteid, 340 Thyro-arytenoideus muscle, 357 Thyro-ep'iglottideus muscles, 357 Thyrohyoid muscle, 355 Thyroid, 339 arteries, 341 cartilage, 354 colloid liquid of, 340 extract, 342 innervation of, 341 internal secretion of, 342 removal of, 341 treatment, 343 venous plexus, 361 vesicles, 340 Thyroidectomy, 341 Thyro-iodin, 340 Tidal air, 374 wave, 328 Timbre, 393, 621, 623 Time-markers, 450 Tissues, elementary, 30 epithelial, 30. See also Epithelium. Tone-color, 621, 623 Tones, 621, 622 Tongue, 186 mucous membrane of, 536 nerves of, 536 Ton us, muscular, 456, 481 Touch, sense of, 527 Toxalbumins, 114 Trachea, 361 Tracheal glands, 361 Trachealis muscle, 361 Transparent bodies, 589 Transversalis, 372 Transverse band, 194 fibers, 506 Trapezius, 369 Travel ration, 132 Trial-meals, 210 Triangularis sterni, 371 Tri cuspid valve, 307 Trifacial nerve, 515 Trigeminus, 515 anastomosis of, 518 ganglia of, 520 nerve, 388 special senses and, 518 trophic influence of, 519 Trigonum olfactorium, 533 Trochlearis, 514 Trommels test for dextrose, 87 Trophic centers, 482 Tropical diet, 135 Trunk, motor area of, 511 Trypsin, 235 Tryptic digestion, 236 Tscherningfs theorv of accommodation, 568 Tuberculosis from eating raw meat, 150 Tubular glands, compound, 174 Tubuli lactiferi, 144 uriniferi, 422 Tunica advehtitia, 310 albuginea, 633 externa, 634 interna, 634 intima, 308 media, 308 propria, 336 Ruyschiana, 544 vaginalis oculi, 541 Tiirck's fasciculus, 473 Twitch, 451 Tympanic cavity, 600, 602 Tympanum, 600 muscle of, 604 Typhoid fever from drinking-water, 122 Typhotoxin, 115 Tyrotoxicon, 115 UMBO, 602 United States' ration, 133, 134 Unpolarizable electrodes, 447 Urea, 432 excretion of, 427 Ureters, 428 Urethra, 430 Uric acid, 433 excretion of, 427 influence of alcohol on, 161 purin bases and, 434 spleen as producer of, 339 test for, 434 Urinary apparatus, 421 Urination, 430 Urine, 431 after stomach removal, 214 Albumin in, 438 686 INDEX. Urine, albumoses in, 438 alloxuric substances in, 437 aromatic substances in, 439 carbonates in, 441 chlorids in, 440 color of, 431 composition of, 426, 432 creatinin in, 438 dextrose in, 439 formation of, 426 hippuric acid in, 437 inorganic constituents of, 440 lactose in, 439 peptone in. 438 phosphates in, 440 proteids in, 438 specific gravity of, 432 sulphates in, 441 sulphur in, 441 urea in, 432 uric acid in, 433 xanthin bases in, 437 Urobilin, 247, 431 Urobilinogen, 431 Urochrome, 431 Uroerythrin, 431 Uterine glands, 641 Uterus, 640 Utricle, 610, 623 Utriculus, 610, 623 VAGI nerves, 388 Vagus, 523 Valvula Heisteri, 244 Valvuke conniventes, 222 Vas aberrans, 627 deferens, 628 Vasa recta, 627 vasorum, 310 Vascular glands, 334 Vasomotor center, 481 of medulla, 487 Vater's corpuscles, 65 Vegetable proteids, absorption of, 261 Vegetables as food, 155 Vegetarianism, 128 Veins, 310 bronchial, 364 circulation in, 329 compression of, 329 pulmonary, 364 rate of flow in, 325 Vena azygos major, 364 Vena? vorticose, 544 Ventilation, 378 positive, 387, 388 Ventricles, 306, 307 blood expelled from, 314 work done by, 315 Ventricular septum, 308 systole, 312 Vernix caseosa, 416 Vertebra, 365 Vertebral column, 365 Verumontanum, 631 Vesicospinal center, 482 Vesicula seminalis, 629 Vestibular nerve, 616 Vestibule of ear, 607 Vibration, period of, 620 Vibration-frequency, 620, 623 Villi cells, 224 intestinal, 222 of chorion, 660 Viperin, 114 Vis a tergo, 329 Vision, binocular, 583 physiology of, 560 Visual angle, 563 apparatus, defects of, 570 area, 512 judgment, 595 purple, 566, 581 Vital capacity, 375 heat, 406 losing of, 410 sources of, 409 phenomena, 17 Vitellin, 113 Vitelline circulation, 661 Vitellus, 638 Vitreous body, 554, 556 humor, 554, 556 Vocal cords, 358, 360 in change of register, 400 in singing, 398 Voice, 389, 392 Volume-pulse, 329 Voluntary muscle, 56 Vomiting, 205 after stomach removal, 214 center, 486 Von Fleisch's hemometer, 278 Vowels, 394 WALKING, cord and, 480 Wallerian degeneration, 464 method of determining course of nerve-fibers, 473 Warm-blooded animals, 406, 407 Water, 121 absorption of, in stomach, 254 excretion of, 80, 426 in body, 78 intestinal absorption of, 256, 265 quantity of, in food, 79 Weidel's reaction, 434 Welcker's method of blood estimation. 269 Wharton's duct, 173 Wheat-flour, 154 Whey, 112, 143 Whey-proteid, 112 Whirling machine, 590. INDEX. 687 Whiskey as food, 157 White corpuscles, 288. See also Leuko- cytes. fibrous tissue, 38 matter of cerebrum, 505 nervous matter, 63 of egg, 149 of eye, 541 substance, 472 Whole-wheat-flour, 154 Windpipe, 361 Wines, 157 Wisdom-teeth, 55 Wrisberg's cartilages, 354 XANTHIN bases, 437 Xanthoproteic reaction, 103 YELLOW spot of Sommerring, 548, 553, 577 Yolk of egg, 149 Yolk-sac, 660 walls of, 659 Young-Helmholtz color theory, 591 Birch modification of, 592 ZALESKI'S hepatin, 240 Zinn's tendon, 557 Zollner's lines, 596 Zona fasciculata, 348 pellucida, 637, 638 reticularis, 348 vasculosa, 633 Zymogen, 119 Zymolysis, 118 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. JBEO. MAY 2 1933 APR 19 1934 JAN 2 1934 SFP 201935 logy Lfeary- EC 16 1937 ffrrr 3 1964 to Recall Immediately LD 21-50m-l,'3 BIOLOSY LIBRARY UNIVERSITY OF CALIFORNIA LIBRARY