feed's Series of Pocket 
 
 01 i 
 
 v/ 
 
 PHYSIOLOGY; 
 
 A MANUAL FOR STUDENTS AND PRACTITIONERS, 
 
 BY 
 
 HOWARD D. COLLINS, M.D., 
 
 Assistant to the Attending Surgeon of the Roosevelt Hospital ; Assistant Demonstrator of 
 Anatomy, College of Physicians and Surgeons (Columbia University), New York. 
 
 WM. H. ROCKWELL, JR., M. D., 
 
 Assistant Demonstrator of Anatomy, College of Physicians and Surgeons (Columbia 
 University), New York; Member of Association of American Anatomists. 
 
 SERIES EDITED BY 
 
 BERN B. GALLAUDET, M.D., 
 
 Demonstrator of Anatomy and Instructor in Surgery, College of Physicians and Surgeons, 
 Columbia University, New York; Visiting Surgeon, Bellevue Hospital, New York. 
 
 ILLUSTRATED WITH ONE HUNDRED AND FIFTY-THREE ENGRAVINGS. 
 
 LEA BROTHERS & CO., 
 PHILADELPHIA AND NEW YORK. 
 
Entered according to Act of Congress, in the year 1899, by 
 
 LEA BROTHERS & CO., 
 In the Office of the Librarian of Congress, at Washington. All rights reserved. 
 
 
 WESTCOTT 4 THOMSON, 
 ELECTROTYPFRS. PHILADA. 
 
PREFACE. 
 
 IN preparing the present volume the authors make no claim 
 to original research. Their purpose is, frankly, not only to 
 help the student acquire a knowledge of physiology such as 
 will enable him to read with better understanding the larger 
 works on the subject ; but also to give him actually fuller and 
 more accurate information than can be obtained from the 
 various and popular quiz-compends. 
 
 Thus, in each section, in addition to the purely physiologi- 
 cal aspects, histological considerations are discussed, such as 
 those of the cell in general and of the neuron in the nervous 
 system ; and, wherever practicable, the application of physio- 
 logical principles to pathological conditions is also dealt with. 
 
 Acknowledgment as to source of material is made to the 
 larger works of Chapman, Kirke, and Foster, to the manual 
 by Dr. F. A. Manning, and to the lectures delivered at the 
 College of Physicians and Surgeons of New York. 
 
 HOWARD D. COLLINS, 
 WM. H. KOCKWELL, JR. 
 

 
CONTENTS. 
 
 PAGE 
 
 GENERAL CONSIDERATIONS: Physiology; life; living body com- 
 pared to a machine ; metabolism 17,18 
 
 CELLS : Structure ; gemmation ; karyokinesis ; development ; 
 
 amoeba ; classification of tissues 18-24 
 
 CHEMISTRY OF THE BODY : Proximate principles ; inorganic ; 
 
 organic 24-30 
 
 THE BLOOD: Gross appearance ; quantity; red corpuscles ; func- 
 tion; globulin; hsematin ; leukocytes; lymphocytes; func- 
 tion ; blood-plates ; plasma ; serum ; gases ; coagulation . . . 30-46 
 
 THE LYMPH: Composition; sources; uses 46-48 
 
 CIRCULATION OF THE BLOOD: Apparatus; course; heart; action 
 of auricles and ventricles ; capillaries ; veins ; arteries ; speed ; 
 blood-pressure; arterial tension; the blood in circulation; 
 action of heart ; systole ; diastole ; arterial tension ; heart- 
 sounds ; heart-innervation ; vaso-motor nerves ; pulse ; sphyg- 
 mograph 48-70 
 
 "CIRCULATION" OF THE LYMPH: Lymphatics; stomata and 
 pseudostomata ; flow of lymph ; sources ; pressure ; lymph- 
 ganglia 70-75 
 
 RESPIRATION : Respiratory act ; movements ; tract ; larynx ; 
 trachea ; bronchi ; lungs ; muscles : of inspiration ; of expira- 
 tion ; forced inspiration; forced expiration ; sounds; tidal air; 
 reserve air ; residual air ; complementary air ; expired air ; 
 external respiration ; internal respiration ; nervous mechan- 
 ism ; centres ; section of vagi ; vitiated atmosphere ; effect of 
 
 respiration on circulation ; special respiratory acts 75-90 
 
 5 
 
6 CONTENTS. 
 
 PAGE 
 
 DIGESTION: Mouth; mastication; teeth; saliva; ptyalin; deglu- 
 tition; stomach; gastric juice ; peptones; gastric digestion ; 
 vomiting; small intestine; intestinal digestion; intestinal 
 juice; the pancreas ; pancreatic juice ; trypsin ; amylopein; 
 steapsin ; the liver; secretion of the liver; bile; bile-salts; 
 bile-pigments ; cholesterin ; excretion of the liver ; glycogenic 
 function ; large intestine ; defecation . 90-108 
 
 ABSORPTION: Dialysis; sites of absorption; villi of intestine; 
 changes in the products of digestion on being absorbed ; des- 
 tination of absorbed food 109-112 
 
 SECRETION : Secretions ; excretions ; apparatus ; glands ; dis- 
 charge ; correlation of secretions ; serous; mucous; mammary 
 glands ; milk ; secretions of skin ; structure of skin ; seba- 
 ceous glands ; sweat-glands; hair; nails; sweat; perspiration; 
 absorption by skin; kidneys; structure of kidneys; blood- 
 supply; ureters; bladder; urine; secretion of urine ; compo- 
 sition ; acidity of urine ; course of urine ; amount ; micturi- 
 tion ; urea; uric acid ; vascular glands ; table of secretions . . 113-134 
 
 NUTRITION : Sources of income to the body ; expenditures of the 
 body; energy of the body: starvation; diet; overfeeding; 
 nitrogenous equilibrium ; assimilation 134-138 
 
 ANIMAL HEAT: Normal temperature; sources of heat; loss of 
 heat ; regulation of heat ; centres for heat-regulation ; limits 
 of body-temperature . 138-140 
 
 MUSCLE : Varieties ; microscopic appearances ; general properties ; 
 chemistry; physiology; muscles as levers; oxygen-supply; 
 fatigue ; latent period ; contractility ; stimuli ; electrical cur- 
 rents ; effect of galvanic shock ; electrical state ; excitability 
 and conductivity ; Pfliiger's law of contraction ; ascending and 
 descending currents ; nerve-muscle preparation ; rigor mortis . 140-159 
 
 NERVOUS SYSTEM: Fibres and cells; varieties of fibres; nerve- 
 trnnks ; function of fibres ; nerve-cells ; varieties ; nerve-end- 
 ing : nerve-impulse ; neuron; speed of nerve-impulses; 
 degeneration ; regeneration 159-169 
 
 Sympathetic System : Fibres; communication with cerebro-spinal 
 >y-trin ; iranylia ; pelvic plexuses ; function; vaso-motor fibres ; 
 relation to secreting glands 169-173 
 

 CONTENTS. 7 
 
 PAGE 
 
 Spinal Cord: Gross anatomy; nerves; white substance; gray 
 matter ; nerve-roots ; trophic centres ; functions ; conduction ; 
 motor fibres ; sensory fibres ; transference ; reflex action ; 
 augmentation; automatic acts; coordination; inhibition. . . 174-185 
 
 Medulla Oblongata: Anatomy; columns; gray matter ; function; 
 
 special centres 185-191 
 
 Pons, Crura Cerebri, Corpora Quadrigemina: Paralysis following 
 
 lesions; functions 191,192 
 
 Cerebrum : Hemispheres ; fissures; convolutions; regions; lobes; 
 gray matter ; chemistry of brain-tissue ; weight of brain ; 
 course of fibres ; corpora striata ; optic thalami ; functions of 
 cerebrum ; localization of brain -function ; motor areas ; sen- 
 sory areas: paralysis 192-201 
 
 Cerebellum: Gray matter ; function 201-203 
 
 Tracts in Brain and Cord : Motor tract ; sensory tract ; lesions . 203, 204 
 Mutilations: Brain; cord; cerebellum; hemispheres 204-206 
 
 Cranial Nerves: III nerve; IV nerve; V nerve; VI nerve; 
 VII nerve; IX nerve; X nerve; XI nerve ; XII nerve . . . 206-220 
 
 THE SEXSES : Sensations ; special ; common ; pain ; hallucina- 
 tions ; perceptions; judgments 220-222 
 
 Touch : Organ ; varieties ; acuteness ; measure of ; pressure-sen- 
 sation ; muscular sense ; temperature-sense 222-225 
 
 Taste : Tongue ; papillae ; taste-globlets ; association of smell ; 
 after-taste . . . 225-229 
 
 Smell: Odors; olfactory nerves ; acuteness of; sneezing .... 229-232 
 
 Hearing : Auditory apparatus ; external ear ; middle ear ; inter- 
 nal ear; membrana tympani ; ossicles; Eustachian tube; 
 semicircular canals ; sense of equilibrium ; cochlea ; canalis 
 cochlearis ; sacculi ; utricle ; organ of Corti ; auditory nerve ; 
 course of sound-waves; localization of hearing; distance; 
 subjective hearing ; musical range 232-241 
 
 Voice or Speech : Larynx ; production of voice ; articulate 
 speech ; musical range of the voice . 241-243 
 
8 CONTENTS. 
 
 PAGE 
 
 Sight: Visual apparatus; accessory organs of eye; eyelids; 
 lachrymal gland; Meibomian glands; extrinsic muscles of the 
 eye; eyeball; cornea; sclera; aqueous humor; crystalline 
 lens; ciliary muscle; iris; vitreous humor; refraction; 
 accommodation ; retina ; rods and cones ; area of most acute 
 vision ; blind spot ; optic nerve ; optic tracts ; nervous mechan- 
 ism of vision ; binocular vision ; stereoscope ; inversion of 
 the image ; visual sensations and perceptions ; retinal red ; 
 optograms ; achromatism ; after-images ; near-point ; emme- 
 tropic eye; myopia; hypermetropia; presbyopia; astig- 
 matism; diplopia; color-blindness; theories of normal color- 
 perception ; causes of color-blindness ; in sexes ; test for color- 
 blindness 243-265 
 
 EMBRYOLOGY: Reproduction; Species; heredity; methods of 
 reproduction ; asexual ; sexual ; theory ; fecundation ; copula- 
 tion ; female organs of generation ; ovaries ; Fallopian tubes ; 
 uterus ; vagina ; ovulatiou ; menstruation ; puberty ; meno- 
 pause; corpus luteum; male generative organs; testicles; 
 spermatozoa ; seminal vesicles ; prostate gland ; penis ; urethra ; 
 impregnation ; coitus ; details of impregnation 267-283 
 
 Development: Segmentation; germinal membrane; changes in 
 uterine lining; blastoderm; medullary groove; changes in 
 the mesoblast ; structures derived from : the epiblast, the 
 mesoblast, the hypoblast ;sp lanchnopleure ; umbilical vesicle ; 
 vitelline duct; amnion ; allantois ; chorion ; placenta; foetal 
 and maternal blood ; umbilical cord ; foetal circulation ; vitel- 
 line circulation; placental circulation ; area vasculosa ; forma- 
 tion of heart ; change from foetal to adult circulation ; vertebral 
 column ; cranium ; face ; extremities ; spinal cord ; nerves ; 
 brain; vesicles; folding of brain axis ; eye; auditory appa- 
 ratus ; olfactory apparatus ; alimentary canal ; salivary glands ; 
 pancreas; liver; lungs; Wolffian duct; Miiller's duct ; testicle; 
 ovary; Gartner's duct ; external genitals 283-306 
 
 Parturition: Expulsion of the foetus ; uterine contractions ; char- 
 acter of uterine contractions 306, 307 
 
 APPENDIX : Table of development of an embryo ; chemical tests 
 
 used commonly in physiological analysis; metric system . . . 309-311 
 
PHYSIOLOGY. 
 
 GENERAL CONSIDERATIONS. 
 
 Physiology, from the Greek yuaiz, and /oyo^, literally means 
 a discourse on nature. At present, however, the word has a 
 more limited significance, meaning that branch of science 
 which treats of the workings of the healthy living body. 
 
 That portion of physiology discussed in the following 
 pages is the physiology of the healthy living human being. 
 From the very nature of things it is evident that every detail 
 of physiology cannot be studied on the human subject, and 
 the deficiency has been supplied by analogous study on the 
 lower animals. In order properly to understand physiology, 
 it is essential that the student be somewhat familiar with 
 anatomy, or that branch of science which teaches the gross 
 structure of the body. To appreciate the workings of a 
 machine, at least a superficial knowledge of its component 
 parts is necessary. 
 
 Life : Our definition of physiology assumes the body to be 
 alive ; but what life is, is a very difficult subject to explain. 
 It may be described as the stimulus which keeps active the 
 functions of the body, the characteristic phenomena exhibited 
 by living beings. It is really indefinable ; for while it is 
 readily possible to state the differences between living and 
 dead things, it is impossible to define these differences. 
 
 Living body compared to a machine : The living body 
 may be compared to any piece of complex machinery, the 
 parts being carefully adjusted to one another and performing 
 their work as long as the proper stimulus is applied. When 
 the stimulus fails and in the case of animals and plants the 
 stimulus is called life the machine stops. 
 
 2 Phys. 17 
 
 
18 CELLS. 
 
 Still another comparison may be drawn between the body 
 and a piece of machinery say, a steam engine. There is for 
 both the need of fuel that can be oxidized by burning, and 
 of resultant energy, liberated in the form of heat and visible 
 motion. Also, as the parts arc subject to wear and tear, new 
 parts must be supplied. In the case of a steam engine, the 
 fuel is the coal fed to the boiler and oxidized by burning. In 
 man the fuel is the food we eat, burned up in the presence of 
 the oxygen we breathe. But here the analogy ceases, for 
 whereas the coal supplied to a steam boiler never forms an 
 integral part of the boiler, in man the food-stuffs are absorbed 
 and go to form part of the individual himself before they are 
 broken down by the oxidizing agent. 
 
 Metabolism: The process of building up the food-stuffs, 
 already properly digested, into a part of the body is called 
 anabolism. The breaking down is the kataboiie process, 
 or katabolism. Both together are called metabolism. 
 
 To make the simile between man and a steam boiler perfect, 
 we should have to imagine a boiler made of coal, instead of 
 iron, which being ignited on its inner surface generated heat 
 which caused the contained water to boil. And further, we 
 should have to imagine that as fast as the inner layers of coal 
 were consumed fresh coal was placed on the outside to make 
 up for the loss. 
 
 Thus we see that food is digested, absorbed, and incor- 
 porated into the body, only to be broken down again by oxi- 
 dation. 
 
 This oxidation, or burning, is the source of the <//ov/// of 
 the body, manifested as heat and visible motion; and also of 
 certain waste-products, comparable to the smoke and noxious 
 gases of a steam boiler. 
 
 These waste-products are eliminated by the body through 
 four great channels the breath, sweat, urine, and faeces. 
 
 CELLS. 
 
 General structure : The fundamental element or unit of 
 structure of all living bodies is the cell. Some bodies, for 
 example the amoeba, are so small and so simple in structure 
 as to consist of only a single cell. On the other hand, the 
 
ESSENTIAL FEATURES OF A CELL. 19 
 
 higher animals have millions of cells, highly differentiated 
 for the different functions they are called upon to perform. 
 Let us examine a cell, and see what it looks like and of what 
 it consists. 
 
 A cell (Fig. 1) is a mass of living matter, known as proto- 
 plasm, varying from ^-oVo^h to T2"o tn f an ^ ncn ' n diameter, 
 which may or may not have a limiting membrane or capsule. 
 As a general rule, animal cells do not have a capsule, while 
 vegetable cells usually do. The contents of the cells may be 
 liquid, semi-liquid, or granular in character. The granules 
 
 FIG. 1. 
 
 Buccal and glandular epithelium. 
 
 in some cells, according to many histologists, are united by 
 filaments, the cell-contents consisting then of a network. 
 
 The nucleus: Usually amidst the cell-contents may be seen 
 a still smaller cell, the nucleus ; and within this the nucleo- 
 lus. Though in some kinds of cells no nucleus can be found, 
 it may be assumed as true that at some period of its life every 
 cell had one, though it may have been lost in the course of 
 development. 
 
 Essential features of a cell : Great difference still prevails 
 among histologists as to the relative importance of the nucleus 
 
20 CELLS. 
 
 and nucleolus; of the cell-contents and cell-wall. Some hold 
 that the nucleus is the all-important element in cell-life ; 
 others maintain that the cell-contents hold this position. As 
 yet their relative significance is not definitely understood. 
 
 Importance of the cell : Though there is some doubt as to 
 the exact use of the different parts of the cell, no doubt 
 exists that the life of the organism resides in the cells com- 
 posing it. Among reasons for this belief may be mentioned 
 the fact that the life of human beings begins as the ovum, a 
 cell ; and that the tissues of the embryo consist of modified 
 cells, the lineal descendants of this primitive cell or ovum. 
 
 Cells gemmation: If one watches the career of a cell, it 
 will be seen to give out a little bud or sprout from one side ; 
 this bud or sprout grows in size, and the band connecting it 
 with the original mass becomes more and more constricted 
 until the offshoot is separated from the 
 FIG. 2. parent-mass. Thus a new cell is born, 
 
 and after its full growth is attained it 
 shows all the characteristics of the 
 parent-cell. Such a process of birth 
 is called " gemmation " (Fig. 2). 
 
 Karyokinesis : This (Fig. 3) is the 
 indirect or mitotic division of the 
 nucleus, hence also called karyomi- 
 tosis. The cell-nucleus is enlarged, 
 and its net-like arrangement dis- 
 appears and is changed into a skeiu of 
 filaments of chromoplasm, into which 
 Div embryo 0f of slagl^ey). In the uudeoli are merged (convolution). 
 Now appears another set of filaments, 
 
 arranged like a spindle, which grows until equal to the diam- 
 eter of the nucleus. By this time the filaments of the first- 
 named skein of filaments have become shorter and V-shaped, 
 and radiate from the equator of the spindle (aster stage). 
 Then each chromoplasmic filament splits longitudinally into 
 two others, and separation, beginning at the V, is soon distinct. 
 The apices of all these loops of filaments now swing away from 
 the equator of the spindle and point toward the poles of the 
 spindle, so that their ends look toward the equator (diaster 
 
DECAY AND DEATH OF CELLS. 
 
 21 
 
 stage). There are thus two groups of filaments, the apices of 
 one pointing to one pole and those of the other group pointing 
 to the opposite pole of the spindle. Each group becomes con- 
 verted into a daughter-nucleus, and the process is completed 
 by a complete constriction and division across the equator of 
 
 FIG. 3. 
 
 Karyokinesis. A, ordinary nucleus or a columnar epithelial cell; B, c, the same 
 nucleus in the stage of convolution ; D, the wreath or rosette form ; E, the aster 
 or single star ; p, a nuclear spindle from Descemet's endothelium of the frog's 
 cornea ; G, H, i, diaster ; K, two daughter-nuclei (Klein). 
 
 the spindle, two nuclei being thus produced, as the cell-pro- 
 toplasm soon divides also. 
 
 Development of cells : The daughter-cells, whether produced 
 by the direct or the indirect form of cell-division, grow until 
 they reach maturity. They then in turn subdivide and give 
 origin to more cells. Thus it will be seen that every cell 
 owes its origin to some preexisting cell. 
 
 As to the question of the origin of the original parent-cell 
 f all living matter, we have no answer. The whole process 
 f cell-division and cell-structure is far more complex than 
 as been given above ; and for further details the student is 
 referred to more exhaustive works on the subject. 
 
 Decay and death of cells : The comparatively brief life of 
 cells is brought to an end either through mechanical abrasion 
 or by chemical transformation. Epithelial cells give frequent 
 
 ; 
 
22 CELLS. 
 
 examples of the former method. As the coll approaches the 
 surface it becomes more and more flattened and scaly, till tit 
 last it is simply rubbed off. Hence epithelial cells are found 
 in the mucus of the mouth, intestine, etc. In the case of 
 chemical transformation the cell degenerates in various ways, 
 the process being frequently normal, though it may 1><- patho- 
 logical. Thus fatty degeneration of the cells in the breast 
 produces the oil-globules in the secretion of milk. 
 
 The protoplasm of which all cells are made up has been 
 called the basis of life. Protoplasm is an unstable albuminoid 
 substance of more or less gelatinous consistency. Its reactions 
 are those of albumin (coagulation by heat and mineral acids), 
 and its chemical composition is in varying proportions of the 
 elements C, H, O, N, and S. Protoplasm is living albumin, 
 or proteid. Besides proteid, every cell contains water. 
 
 The amoeba is a microscopic animal that consists of but 
 one cell ; yet this one cell performs all the animal functions. 
 
 FIG. 4. 
 
 Protamoeba (Haeckel). 
 
 (1) It is capable of motion (Fig. 4), the cell sending out a 
 small branch or arm of the protoplasm. This branch, or 
 pseudopod as it is called, attaches itself to some part ^ of the 
 environment, and then the rest of the cell is drawn forward 
 until the whole cell seems to flow to and into its branch. The 
 process is then repeated, the cell advancing steadily forward. 
 
 (2) It has the power of food-absorption ; the cell flowing 
 around and completely enveloping any particle of food it may 
 meet, Later on, such of the rood as has not been absorbed is 
 excreted, by a process of flowing away, on the part of the 
 protoplasm. 
 
EPITHELIUM. 23 
 
 (3) It also absorbs oxygen from the surrounding atmos- 
 phere. 
 
 (4) It is irritable to stimuli; and is capable of (5) repro- 
 duction and (6) growth. 
 
 Thus we see that the amoeba presents in its single cell all 
 the main functions of the higher animals. But the individual 
 cells of the human body are by no means so well endowed 
 with functions as the amoaba. 
 
 Differences between plants and animals : The most essential 
 difference lies in the fact that vegetable protoplasm can build 
 up new albuminous compounds out of such chemical bodies 
 as water, carbonic acid gas, and inorganic mineral salts. 
 Animal protoplasm, on the other hand, must have ready- 
 formed albuminous food in order to live. Vegetables exhale 
 oxygen, but inhale carbonic acid gas ; while animals do the 
 reverse. 
 
 Specialization of cells : As a rule the body-cells are highly 
 specialized for the fulfilment of one or more functions, to the 
 exclusion of all others. Where we find two or more cells of 
 the same kind aggregated together, the mass is called a tissue. 
 
 Two or more tissues of different kinds are spoken of as 
 organs. 
 
 By apparatus is meant an association of organs for the per- 
 formance of a common function. Thus the stomach, intes- 
 tines, and pancreas may be spoken of as a collection of organs, 
 forming an apparatus for the common function of digestion. 
 
 In ordinary parlance an organ is " the instrument of func- 
 tion, the performer of a function." 
 
 Classification of tissues: The cells in man are, roughly 
 speaking, found to make four main classes of tissues : epithe- 
 lial, connective-tissue, blood-cells, and nerve-cells. 
 
 Epithelium : The name " epithelium " is given to the cells 
 which cover the skin, and the mucous and serous membranes 
 )f the body ; and which also enter into the formation of the 
 ;lands. Its varieties are (1) simple, a layer of flat (squarn- 
 >us), cubical (spheroidal), or cylindrical (columnar) cells, as 
 in the serous and mucous surfaces ; (2) stratified, when it 
 occurs in layers, as in the skin ; (3) transitional, where it has 
 the characteristics of both in situations where the other two 
 
 
24 
 
 CHEMISTRY OF THE BODY. 
 
 FIG. 5. 
 
 forms approach one another, as in the bladder. (4) In the 
 "lands are (\n\i\d functional cell*, which partake of the charac- 
 ter of the epithelium of the surface. They are arranged in 
 groups about the ducts. Such cells are often known as 
 secreting or glandular epithelial cells. 
 
 Simple epithelium possesses hair-like processes in certain 
 locations, and this is known as viliutctl epithelium (Fig. 5). 
 The hairs are endowed with motion, and 
 wave in such a manner as to throw for- 
 ward small particles which fall upon 
 them. 
 
 The principal uses of epithelium are: 
 protection, as skin, serous surfaces; 
 motion, ciliated epithelium of air-pas- 
 sages and Fallopian tubes ; secretion, in 
 glands e. </., gastric juice; sensation, 
 in the cones of the retina, olfactory 
 cells of the nose, etc. 
 
 Endothelium is a simple form of 
 squamous or scale-like, flat epithelial 
 cells which line the serous membranes and the bloodvessels. 
 The cells arc very delicate, and are not stratified. They are 
 of various forms, usually irregularly polygonal, and are 
 joined at the edges so as to form a sort of mosaic. 
 
 Connective tissues form the frame and supports of the body 
 and of the organs of the body. The ligaments, tendons, 
 fasciae, cartilages, and bones are examples of them. The 
 fibrous connective-tissue cells are found in all organs in 
 greater or less amount. In the organs whose use is the sup- 
 port of the body or one of its members these cells predomi- 
 nate. In other organs the fibrous cells serve to hold in place 
 the functional cells and to maintain the shape of the organs. 
 
 Columnar ciliated epithe- 
 lium-cells, from the 
 human nasal membrane ; 
 magnified 300 diameters 
 (Quain and Sharpey). - 
 
 CHEMISTRY OF THE BODY. 
 
 The ultimate analysis of the human body shows it to con- 
 sist of the following elements: carbon, hydrogen, oxygen, 
 nitrogen, magnesium, calcium, sodium, potassium, sulphur, 
 phosphorus, manganese, silica, iron, chlorine, fluorine, and 
 
PROXIMATE PRINCIPLES. 25 
 
 iodine. Of these, only oxygen and nitrogen are found free, 
 the other elements existing as compounds. 
 
 By proximate principles we mean those elements or com- 
 pounds that exist as such in the body. Thus sodium chloride 
 is a proximate principle, as it is found as such in the human 
 body. Neither the metal sodium nor the gas chlorine, how- 
 ever, can be considered as belonging to this class, as they do 
 not exist or act as such in the body. The proximate princi- 
 ples are subdivided into two great classes organic and 
 inorganic. It will be wise to attempt at this point to 
 draw a clear distinction bet\veen organic and inorganic sub- 
 stances. 
 
 Organic substances are nearly always highly complex bodies 
 containing many elements. Two particular elements carbon 
 and hydrogen enter into all organic bodies. Some organic 
 substances are very simple chemically and may contain no 
 elements except carbon and hydrogen. It was formerly 
 supposed that any substance must, in order to be included in 
 this class, have been at some time either an intimate part of, 
 or a product of the activity of, a living body ; or else either 
 an intimate part of, or a product of the decomposition of, a 
 body that had lived. Of recent years, however, many of 
 these principles have been prepared in the laboratory from 
 inorganic elements without invoking the aid of a so-called 
 " vital force " ; and there is every reason to suppose that in 
 time all will be. Such being the case, the distinction between 
 organic and inorganic substances regarded at one time as being 
 so essential, is without philosophical significance, and is only 
 made use of as a matter of convenience. Organic substances 
 are further subdivided into those containing nitrogen and 
 those not containing it. 
 
 Inorganic substances are best defined by negativing the 
 above conditions that is to say, if a chemical body fails to 
 fulfil every condition given above, it cannot be classed as 
 "organic," but is u inorganic." Carbon dioxide (CO 2 ) is a 
 body that fulfils all the conditions for being organic to a marked 
 degree, except that there is no hydrogen present ; hence 
 breaking the rule that both carbon and hydrogen must be 
 present in order that a body be organic. Nevertheless carbon 
 
26 CHEMISTRY OF THE BODY. 
 
 dioxide is the one exception allowed, and is classed among 
 both organic and inorganic substances. 
 
 With few exceptions the inorganic principles are so firmly 
 combined with the organic that, as the latter become effete 
 and are eliminated, the inorganic substances are cast out with 
 them. Some of them play a more important role than others 
 and are found in greater quantities. 
 
 List of inorganic proximate principles : The inorganic prin- 
 ciples found in the human body are: oxygen; nitrogen; 
 water ; hydrochloric acid ; chlorides of sodium and potassium ; 
 sulphates of sodium and potassium ; carbonates of sodium, 
 potassium, calcium, and magnesium ; phosphates of sodium, 
 potassium, calcium, and magnesium; also small amounts of 
 compounds containing iron, silica, fluorine, iodine, and man- 
 ganese. To complete the list we must add carbon dioxide. 
 
 Uses of inorganic proximate principles: The uses to which 
 these principles are put by the body are not well understood ; 
 but they are necessary in making the structure of the body or 
 in aiding chemical work. They are not sources of chemical 
 potential energy. Many of the inorganic proximate principles 
 are taken into the body and excreted unchanged. Others 
 not only are taken into the body, but are also manufactured 
 in the body as the result of oxidation and breaking up of 
 more complex organic bodies. As a result of this manu- 
 facture we should expect to find that certain of the inorganic 
 proximate principles are excreted in greater amounts than 
 they are ingested. Such is proven to be the case, for water, 
 and the sulphates, phosphates, and carbonates leave the body 
 in greater amount than that in which they enter. 
 
 Distribution: The inorganic proximate principles are found 
 distributed in various parts of the body. Water and sodium 
 chloride are omnipresent. Oxygen and nitrogen are found in 
 the blood and tissues. Potassium chloride is found generally, 
 but not so omnipresent as the chloride of sodium. The phos- 
 phates and the carbonates of the alkaline metals are found in 
 the blood, rendering the latter alkaline. The phosphates and 
 carbonates of the alkaline earths are neutral, and give rigidity 
 to the bones. Hydrochloric acid is present in the gastric 
 juice. The less important salts are found elsewhere, and 
 
PROXIMATE PRINCIPLES. 27 
 
 play but an insignificant part. Water constitutes more than 
 two-thirds of the weight of the body. 
 
 Organic proximate principles are divided into two great 
 classes : (1) nitrogenous and (2) non-nitrogenous. 
 
 (1) The former take the principal part in the formation of 
 the solid constituents of the body, and occur in all the body- 
 tissues and -fluids. They make up the protoplasm of cells 
 and essential ingredients of the fluids, both circulatory and 
 excretory. Chemically, they are compounds of C, H, O, N, 
 sometimes with sulphur or phosphorus. These, with few 
 exceptions, are not crystallizable. 
 
 (2) The latter (non-nitrogenous) class of bodies are made 
 up of the fats and carbohydrates. With the exception of 
 starch, all of this class are crystallizable. 
 
 In striking contrast with the inorganic proximate princi- 
 ples, none of those belonging to the organic division, with the 
 exception of butter and sugar of milk among the non-nitrog- 
 enous ; and of casein of milk, mucus, epithelium, and epider- 
 mis, among the nitrogenous principles, ever appear among 
 the excretions or secretions of the healthy human body. 
 
 Uses of organic proximate principles : All our vital manifes- 
 tations depend on the energy derived from the organic matter 
 of the body. This organic matter is constantly being used 
 up, and to supply its place the body must acquire fresh organic 
 matter. The essence of life is in change, and in this change 
 the element nitrogen plays a very important part because of 
 the readiness with which the nitrogenized proximate princi- 
 ples break down. This liability to breaking down is not only 
 due to the presence of nitrogen, but also to the great number 
 of molecules which all organic principles contain. Through 
 this breaking down is derived the energy required for life. 
 
 Source of organic supply: Green plants have the power, by 
 virtue of the chlorophyl in their substance, to convert the in- 
 organic compounds, that are the food for plants, into simple 
 organic bodies. Animals, on the other hand, cannot convert 
 their inorganic foods into organic substances, but are com- 
 pelled to eat organic bodies in order to have the necessary 
 fuel on which they live. To illustrate : green plants live on 
 water, nitrite and nitrate of potassium, sulphates of calcium 
 
28 
 
 CHEMISTRY OF THE BODY. 
 
 3 ^ 
 
 8,5 
 
 ^S G 15 !l 
 
 w.l K |S g8 
 
 2.S- c -^ ^"3 
 
 g S go og^ 
 
 ^ QPM> 
 
 ODIES, 
 
 33 
 
 3 
 
 02 C 
 
 A 
 
 = -3 *> g tc 
 
 OQ t-l 
 , > . v~*-^ 
 
 , * 
 
 t^ 
 
 
 Icj 
 
 g 
 
 0) 
 
 bio 
 
 PQ 
 
 B 
 
 
 
 
 | 
 
 
 d 
 
 '~c t 
 
 rr* 
 
 ,GANIC 
 
 PRINC 
 
 g 
 
 fll .2 
 
 I 
 
 .si 
 
 il 
 
 % 
 
 T3 
 
 3 
 
 I 
 
 I 
 
 1 
 
 5 c ' 
 B aS 
 
 'SSs 
 
 3sJ 
 
 milk-cur< 
 
 n 
 
 
 
 i 
 
 IMATE 
 
 I 
 
 ! 
 
 
 
 
 
 "S. 
 
 <S 
 ' s ' 
 
 o x 
 
 tp o> 
 
 = "E 
 
 i 
 
 o> . 
 C ^ - 
 
 .si 
 
 ^.Sc 
 
 ^ 
 ^^ 0) 
 
 s'c'S 
 
 oteolytic, 
 
 
 
 Y 
 
 NITROGEN 
 
 M 
 
 
 
 P4 
 O 
 
 1. Native albumins found in 
 nature, 
 
 2. Globulins found in nature, 
 
 3. Derived albumins, derived 
 from Class 1 by action of 
 acids, alkalies, or ferments. 
 4. Fibrin, from Class 1 by ac- 
 tion of " fibrin-ferment," 
 
 5. Coagulated albumin, by 
 heat, etc., from Class 1, 
 
 6. Peptones, by action of di- 
 gestive ferments on Class 1. 
 
 f Gelatin, soluble in hot water. 
 Mucin, soluble in weak alkali 
 Elastin, insoluble. 
 Chondrin, soluble in hot wate 
 1 Keratin, insoluble ; probably 
 
 ' Crystallizable acids e. g., give 
 Urea and its allies e. q\, kre'at 
 [ Pigments e. g., bile-pigments, 
 
 Ferments e. g., amylolytic, pi 
 
 
 
 
 
 
 
 
 
 
 
 y 
 
 S.2 
 
 
 
 
 
 
 
 
 
 
 ^ S 
 
 si 
 
 
 
 
 
 
 
 
 
 ^ci 
 
 |i 
 
PROXIMATE PRINCIPLES. 
 
 29 
 
 
 
 
 ORGANIC BOD] 
 
 3 PRINCIPLES. 
 
 j. ) 
 
 (melts at 113 F. ^ 
 ( " 140 F. j 
 
 at closely allied to the 
 
 - s itl l| 
 
 ^'"SflS c 
 ^- 3 *o S -rH ** "" 
 
 2 *lli'a > 
 
 d 
 _o 
 
 ENOUS 
 CIMATI 
 
 o> 
 J5 
 
 g 
 
 ,Q 
 
 "o 
 
 J3 
 
 Or^H-u'CSdO S 
 
 1 ir g 
 
 i| 
 
 a perspira 
 
 
 
 3 
 
 5 
 
 IS 
 
 s 
 
 E-I 
 
 03 
 
 "3 
 
 
 
 
 
 ^5~ - 
 
 .2 
 
 J3 .5, 
 
 o 
 
 O 
 
 O 
 
 5 
 
 fl 0> 
 
 o 
 
 g 
 
 
 ^3 
 
 5^ 
 
 , - 
 
 O 
 
 g-S- 
 
 - 
 
 o" " - 
 
 
 w 
 
 o- M - 
 
 c 
 
 1 e . 
 
 OJ~ 
 
 S || I H 1 I-H.2 
 S OQ 3 $& 5 ^-<3 
 
 
30 THE BLOOD. 
 
 and magnesium, the phosphates of calcium, and some soluble 
 salts of iron, all of which exist in the earth ; also on the 
 oxygen and carbon dioxide of the air. By various chemical 
 combinations and changes these inorganic compounds are con- 
 verted by the green plant under the influence of sunlight into 
 simple organic substances. 
 
 Non-chLorophyl-bearinfj plants, such as fungi, have not the 
 property of absorbing inorganic substances and converting 
 them into organic substances, but must receive their food 
 in the form of organic compounds; hence the fungi live on 
 other plants. So too with animals ; they must live on plants 
 and other animals. From these plants and animals we cat 
 we obtain, besides a number of inorganic salts, water, etc., 
 the three great classes of food-stuffs which are eventually to be 
 digested, altered, and assimilated into the body, then " burned " 
 with the liberation of energy, and finally to be cast off as 
 waste-products by means of the sweat, breath, urine, and 
 faeces. These three classes of food-stuffs are protei^, c<ti-l><>- 
 hydrates, and fats. How these foods are absorbed and assim- 
 ilated will be studied later in the chapter on Digestion. To 
 be sources of energy, the tissues of the body must be oxidized ; 
 this is accomplished by the oxygen conveyed from the lungs 
 to the tissues by the blood. 
 
 THE BLOOD. 
 
 General observations : Since the earliest times it has been 
 recognized that the blood is the most important fluid in the 
 human body ; that it is, indeed, indispensable to life. Its 
 loss prostrates and enfeebles the body. With excessive 
 hemorrhage life itself ebbs away. This is readily evident 
 when it is known that the blood, circulating through the sys- 
 tem, carries to the tissues and the cells composing them 
 material for their growth, renewal, and repair; and removes 
 from them that which has become effete. It also tends to 
 equalize more or less the temperature throughout the body. 
 
 Gross appearance: Freshly drawn blood is a somesvhat 
 viscid opaque fluid of a more or less pronounced red color. 
 This color, which depends entirely on the amount of oxygen 
 present in the blood, varies according as the blood is drawn 
 
PHYSICAL CHARACTERISTICS. 
 
 31 
 
 from the arterial or the venous system. That drawn from 
 the arteries or pulmonary veins is of a bright scarlet, and 
 contains a large amount of oxygen ; while that from the 
 systemic veins is bluish-red to reddish- black, and has far 
 less oxygen. The opacity is due to the fact that blood is not 
 a homogeneous liquid, but consists, as we shall see later, of 
 two elements corpuscles and plasma. These, differing in 
 their refractive power, oppose the transmission of light, thus 
 causing the opacity. 
 
 FIG. 6. 
 
 Human blood as seen on the warm stage. Magnified about 1000 diameters, c, c, 
 crenated red corpuscles; p, a finely granular ; g, a coarsely granular pale cor- 
 puscle ; both exhibit two or three vacuoles. In g & nucleus also is visible. 
 r, r, single red corpuscles, flat; r', r', the same on edge; r", r", the same in 
 rouleaux (Quain). 
 
 Physical characteristics : The specific gravity of the blood 
 at ordinary temperature varies between 1045 and 1062. It 
 is of a slightly alkaline reaction, due to the phosphates and 
 carbonates of the alkaline metals, and has a salty taste and a 
 peculiar characteristic odor. The degree of alkalinity, esti- 
 mated as Na,CO 3 , corresponds in human blood to 0.35 per 
 cent, of this salt. 
 
32 
 
 THE BLOOD. 
 
 If examined under the microscope, the blood will be seen to 
 consist of a fluid, called plasma or liquor sanguinis, in which 
 are suspended small particles called blood-corpuscles. The 
 corpuscles are of three types, known as red corpuscles, white 
 corpuscles or leukocytes, and blood-plates or microcytcx. 
 
 The temperature of the blood in man is, on the average, 
 98.9 F. ; but it is very probable that in certain parts of the 
 body it is several degrees higher. 
 
 Quantity of blood : The total amount of blood is estimated 
 as being one- thirteenth of the body-weight. Thus in an in- 
 dividual weighing one hundred and seventy pounds, the 
 
 FIG. 7. 
 
 Red globules of the blood, seen a little beyond the focus of the microscope (Dalton). 
 
 amount of blood in his body would weigh about thirteen 
 pounds and would measure about six quarts. The corpuscle* 
 weigh about one-third of the total blood- weight. 
 
 Corpuscles : The corpuscles (Fig. 6) exist in large numbers 
 in the blood, it being estimated that in every cubic millimetre 1 
 of blood there are 10,000 leukocytes, 250,000 blood-plates, 
 and 5,000,000 red corpuscles. 
 
 Red corpuscles: Human colored blood-corpuscles (Figs. 
 7 and 8) are circular, biconcave disks with rounded edp- : in 
 
RED CORPUSCLES. 
 
 33 
 
 diameter they are about s^nj-th in. ; in thickness about 
 in. In water they swell and become flat or convex. When 
 seen singly they appear yellow, but their color is red when 
 seen in groups. Microscopic examination shows that they 
 have no nucleus and no limiting membrane ; but they have 
 an elastic framework, or stroma, which retains an individ- 
 
 FIG. 
 
 Red globules of the blood, seen a little within the focus (Dalton). 
 
 uality for each corpuscle, and allows changes of shape to adapt 
 them for capillary circulation, and brings them back to the 
 original form after such distortion. 
 
 The color is due to a chemical body, called haemoglobin, 
 which is held within the stroma. The red corpuscles have a 
 specific gravity of 1088, and are the heaviest of the compo- 
 nent parts of the blood. 
 
 In all mammals, with the exception of the camel family, 
 the c/encrdl character of the corpuscles is the same as in man ; 
 but their size varies in the different animals (Fig. 9). The 
 camel family have the same corpuscles as other mammals, 
 except that the discs are oval instead of circular. 
 
 In reptiles, fishes (except a few species), and birds the red 
 corpuscles are oval, nucleated, and usually larger than those 
 of mammals. 
 
34 THE BLOOD. 
 
 Red corpuscles origin : Like all the other cellular elements 
 of the body, there must be a birth of new blood-cells to take 
 
 Mainnjiils. Birds. Reptiles. 
 
 Amphibia. 
 
 the place of those whose life-work is done. The ancestors 
 of the red blood-corpuscles are the large, irregular, polyn->- 
 
RED CORPUSCLES. 35 
 
 nal marrow-cells. These marrow-cells are found, as their 
 name implies, in the marrow of the long bones. They are 
 found in layers or phalanxes, each phalanx a little more 
 highly developed than the layer underlying it. The most 
 highly developed divide by karyokinesis, and are pushed oif 
 from the mass of cells by the growth of the cells below. The 
 detached cells, after undergoing certain changes in shape, enter 
 the blood-current and become the ordinary red blood-corpus- 
 cle. The marrow-cell is polygonal, nucleated, and only very 
 slightly colored. To become a red blood-cell the marrow- 
 cell loses its nucleus, assumes the biconcave disc-shape, and 
 acquires a greater amount of coloring-matter, or haemoglobin. 
 Such changes have been observed to take place in the mar- 
 row-cells; and also in cases in which individuals have suf- 
 fered severely from hemorrhage, during the recuperation, 
 numbers of only partially transformed marrow-cells have 
 been found circulating in the blood-current, not having had 
 time to be fully altered, as the demand for new cells was so 
 urgent. 
 
 What becomes of the nuclei which the marrow-cells cast 
 oif is not known. Suggestions have been made that these 
 nuclei may become the blood-plates or else be destroyed by 
 the leukocytes. These are merely suggestions, and not to be 
 accepted as proven. Where the increase in coloring-matter 
 which the marrow-cell acquires comes from, is also a source 
 of speculation. 
 
 Red corpuscles function: The one important and funda- 
 mental purpose of the red blood-corpuscles is to convey 
 o.i't/f/cii. from the lungs to the tissues. As has been said, the 
 red corpuscles consist of an elastic network or stroma, which 
 holds, probably both mechanically and chemically, a highly 
 complex protcid body called haemoglobin, which, although 
 cry stall izable, is non-diffusible. The form of the crystals 
 of haemoglobin varies in different animals. In man they are 
 prismatic, in the guinea-pig they are tetrahedral, in the 
 squirrel they are hexagonal, and so on. 
 
 Hamoglobin can be subdivided into two bodies globulin 
 (96 per cent.) and hsematin (4 per cent.). 
 
 Hcemin (Fig. 10), the hydrochlorate of haematin, is formed 
 
36 
 
 THE BLOOD. 
 
 by adding muriatic acid to haemoglobin. It is of especial 
 iui. rest from u medico-legal point of view, as it can be 
 obtained, by proper manipulation, from a very minute 
 <juantity of blood. It forms characteristic crystals, rhombic 
 
 Fio. 10. 
 
 Rhombic crystals of hsemin, or hydrochlorate of haematiu. 
 
 tablets, which are sometimes disposed as stars or crosses, 
 of a red or brown color. If oxygen be added, the crystals 
 assume a violet hue, while under the influence of carbon 
 dioxide the crystals lose their transparency. Unfortunately, 
 however, (here is no characteristic form of these crystals for 
 the different animals. We can prove that a certain material 
 is or is not blood, but not that it is or is not human blood. 
 
 Globulin is composed of the elements C, H, N, O, and S. 
 Ihriiuifin is composed of the elements C, H, N, O, and Fe. 
 The iron \< the important element; for the oxygen from the 
 lungs forms a very loose chemical combination with the 
 iron in the haemoglobin. 
 
 When the red corpuscle rich in haemoglobin reaches the 
 lungs the oxygen absorbed from the air is rapidly taken up 
 in lo<-c chemical combination by the haemoglobin. The 
 corpuscle is now hurried with it.- load of oxygen to the dis- 
 
RED CORPUSCLES. 
 
 37 
 
 tant tissues, where the oxygen is absorbed by the tissues, and 
 the red corpuscle is carried back to the lungs for a fresh 
 supply. Besides this, the red corpuscle has no other func- 
 tion except diapedesis i. e., a passive ability to pass through 
 capillary walls. The student must bear in mind that the 
 oxygen which enters into the chemical compound called 
 
 Red. Orauge. Yellow. G 
 
 O xy haemoglobin and 
 NO 2 -haemoglobin. 
 
 CO-hsemoglobin. 
 
 Reduced haemoglobin. 
 
 Hsematin in acid solu- 
 tion. 
 
 Haematin in alkaline 
 solution. 
 
 Reduced hsematin. 
 
 Solar spectrum with 
 Fraunhofer's lines. 
 
 haemoglobin (see formula above) is not the oxygen which 
 unites with the iron, and which is taken into the hsemoglobin- 
 molecule in the lungs, only to be given up in the tissues. 
 The first " oxygen " spoken of is an essential of the haemo- 
 globin, and is retained as long as the molecule retains its 
 chemical identity. Haemoglobin rich with the oxygen of 
 respiration is called oxyhcemoglobin. When this oxygen is 
 entirely removed the proteid is called reduced hemoglobin. 
 Both reduced haemoglobin and oxyhaemoglobin give perfectly 
 
38 THE BLOOD. 
 
 characteristic spectra (Fig. 11). This point has been of some 
 value in medico-legal cases in determining the presence of 
 blood in suspected stains. 
 
 Red corpuscles death : After a period of functional activity 
 the red blood-cell has outlived its utility and dies. Other 
 red cell- are lost from the circulation by hemorrhages of all 
 kinds. These dead and lost red corpuscles are replaced 
 by new cells from the bone-marrow, as has been already 
 shown. Just what conditions determine the death of a red 
 corpuscle, or just how the dead body is disposed of, is not 
 accurately determined. The evidence points toward the 
 assumption that the stroma of the corpuscle is chemically 
 destroyed and absorbed by the tissues as proteid material. 
 The haemoglobin, after the destruction of the framework, is 
 liberated and eventually eliminated as a part of the bile- 
 pigment. 
 
 Leukocytes, or white blood-corpuscles, are spherical, granular 
 masses of protoplasm, each having a nucleus, but no cell- 
 walls. They are about Y^Vir tn ll} - * n diameter. Some appear 
 to be much smaller, and probably this diminution in size is he- 
 cause these corpuscles have not yet attained full development. 
 It has been said above that the leukocytes are spherical. 
 This is true when the leukocytes are being carried along by the 
 blood-current ; but when the leukocytes exercise their power 
 of locomotion, which permits them to emigrate (^igration) 
 from the blood-current into the surrounding tissues, each 
 leukocyte changes its shape and behaves in a manner iden- 
 tical with that of the amoeba (Fig. 12). The properties and 
 animal functions of leukocytes are the same as those of the 
 amoeba. 
 
 The white corpuscles differ in many respects, other than 
 H/e and appearance, from the red ones. They are differently 
 affected by the various reagents. They keep close to and 
 even seem to adhere to the walls of the vessels in which they 
 are circulating, while the red corpuscles keep in the middle of 
 the stream. The white corpuscles arc found in lymph, chyle, 
 pus and other fluids as well as in the blood; the more 
 general name of leukocytes is often, therefore, given to 
 them. 
 
LEUKOCYTES. 
 
 39 
 
 Leukocytes varieties : Three varieties of leukocytes have 
 been noted in the blood. The most marked physical differ- 
 ence is in the nuclei. The properties are the same, except 
 in the amount of amoeboid movement exhibited. 
 
 1. Lymphocytes, large single nucleus, very little cytoplasm, 
 practically no amoeboid movement. Most commonly found 
 in the lymph. 
 
 2. Mononuclear leukocytes, large corpuscles with single 
 nucleus, relatively small to size of the cell, free amoeboid 
 movement. 
 
 3. Poly nuclear leukocytes are large corpuscles with a par- 
 tially divided nucleus or even several distinct nuclei. The 
 amoeboid movement is particularly well marked. 
 
 FIG. 12. 
 
 Various forms assumed by the white corpuscles of the blood. The upper row repre- 
 sents the white corpuscles of man : the lower row, white corpuscles from the 
 newt, showing changes effected in fifteen minutes (Carpenter). 
 
 Undoubtedly these three types are merely three stages in 
 the development, the lymphocytes being the youngest. 
 
 Leukocytes chemical composition : Leukocytes consist of 
 water, inorganic salts (largely potassium salts), proteids, 
 glycogen, nuclein, fat, lecithin, cerebrin, cholesterin. 
 
 Origin : The leukocyte owes its origin to the splitting up 
 by karyokinesis of some previous leukocyte into two second- 
 ary cells. This birth takes place in most instances in the 
 
40 THE BLOOD. 
 
 lymphatic or adenoid tissue, and the new cells are poured into 
 the blood-current by lymphatic channels. 
 
 Function : Leukocytes act as protecting agents for the body, 
 by destroying bacteria that may get into the blood-current, 
 lymph- or tissue-spaces into which the leukocyte can enter. 
 The method of destroying the bacteria is supposed to he 
 either by a process in which the leukocyte ing< MS the bac- 
 terium (phagocytosis), or else the leukocyte surrounds the 
 bacterium with some substance that destroys it. The leuko- 
 cytes act as agents in assisting the absorption of flits and pep- 
 tones from the intestines. 
 
 Leukocytes are poured out in large numbers in any wound 
 in the body, and by their presence act as barriers to infection. 
 In such a wound some of the leukocytes may eventually be- 
 come converted into granulation-tissue. 
 
 Among other uses, it has been suggested that leukocytes, 
 when disintegrated, help keep up the necessary amount of pro- 
 teid in the blood-plasma. 
 
 Death: The natural ending for the leukocyte is to be divided 
 into two daughter-cells by karyokinesis. Other leukocytes 
 are disintegrated in the blood-current. Again, other leuko- 
 cytes are destroyed in the battle waged against bacteria. 
 Others are lost by hemorrhage. Still others may be con- 
 verted into granulation-tissue in wounds. 
 
 Blood-plates : The blood-plates, or miarocytes, are small 
 rounded masses of which little is known. They arc much 
 smaller than the red corpuscles. The blood-plates arc sup- 
 posed to assist in the coagulation of blood ; but all we know 
 at present is that the fibrin-fibrillae seem to start from the 
 microcytes. The microcytes may be the source of the fibrin, 
 or may merely serve as mechanical anchors. 
 
 Blood-plasma: The flu id portion of the blood in which the 
 corpuscles float is called plasma. The corpuscles can be fil- 
 tered out under certain conditions, leaving the plasma fr 
 further examination. The chief method is by filtration at 
 a temperature of to 3 C. ; but equally tr<><l results may 
 be obtained by the addition to the blood of neutral salts in 
 certain proportions, or by the use of the centrifugal machine. 
 It differs from the serum in containing fibrinogen, but closely 
 
CHEMICAL COMPOSITION OF BLOOD-PLASMA. 41 
 
 resembles that fluid in reaction and appearance, its alkalinity, 
 however, being somewhat less. 
 
 Blood-serum : The serum is the liquid part of the blood 
 left after the separation of the clot. It is alkaline, trans- 
 parent, of a yellow color, and of a specific gravity of about 
 1030. During the ordinary process of coagulation part of 
 the serum remains in the clot and the rest is squeezed out. 
 As the clot keeps on contracting for thirty-six hours or more, 
 the amount of serum cannot be estimated till this time has 
 elapsed. There is nearly as much serum by weight as there 
 is clot in coagulated blood. As the chemical composition of 
 serum is merely that of plasma less the fibrinogen, one de- 
 scription will suffice for both. 
 
 Properties and chemical composition of blood-plasma : Blood- 
 plasma is a straw-colored, slightly viscid fluid, of a specific 
 gravity of 1030, and alkaline (slight) reaction. Another 
 property of plasma is that of dotting, to be discussed later. 
 
 Chemically, plasma consists of a large percentage of water, 
 holding in solution a number of inorganic salts, of which 
 sodium chloride and sodium carbonate are the most abundant. 
 
 Besides the inorganic compounds, the plasma is rich in 
 three proteids serum-albumin, fibrinogen, and paraglobulin. 
 
 Serum-albumin is one of the so-called groups of native al- 
 bumins, and represents the proteid portion of our food-supply 
 after digestion and absorption into the blood have taken place. 
 
 Fibrinogcn and paraglobulin belong to the group of globu- 
 lins. Their source of origin is unknown. Their purpose in 
 circulating blood is also doubtful ; but they may be a source 
 of nitrogenous food. At any rate, they play an important 
 part in the coagulation of blood, as will be seen. 
 
 Carbohydrates in solution and/afe in suspension or saponi- 
 fication are also present in the plasma. These, too, have been 
 absorbed from the alimentary tract. 
 
 Other organic bodies, such as urea, lecithin, and cholesterin, 
 representing waste-products, are held in solution by the plasma. 
 
 Carbon dioxide is found in solution in the plasma, repre- 
 senting the result of oxidation in the tissues. This gas is 
 found in both arterial and venous blood, but in greater 
 amount in the latter. 
 
42 THE BLOOD. 
 
 Small amounts of oxygen and nit rot/en are also found in 
 solution in the plasma. There is also probably a yellow pig- 
 ment, independent of the haemoglobin, which has not yet been 
 exactly determined, though it is probably e/tofcsferm. Similarly 
 the odoroua matter which gives the characteristic smell to the 
 blood of different animals has not yet been discovered. 
 
 Gases of the blood : In the blood as a whole are found car- 
 bonic acid, oxygen, and nitrogen gases, there being from 50 to 
 60 volumes of these gases collectively in 100 volumes of 
 blood. There are relatively more oxygen and less carbonic acid 
 gas in arterial than in venous blood ; but in both kinds of 
 blood the carbonic acid exceeds the oxygen in amount. In 
 arterial blood there is about 20 per cent, of oxygen, 40 per 
 cent, of carbonic acid, and 1 to 2 per cent, of nitrogen ; while 
 in venous blood the oxygen forms from 8 to 12 per cent., the 
 
 FIG. 13. FIG. 14. 
 
 Bowl of recently coagulated blood, show- Bowl of coagulated blood after t welvo 
 ing the whole 'mass uniformly solidified hours, showing the clot contracted 
 
 (Dalton). and floating in the fluid serum 
 
 t Dalton). 
 
 carbonic acid about 45 per cent., and the nitrogen the same 
 percentage as in the arterial. Part of both the oxygen and 
 the carbonic acid is in solution, and the rest in weak chemi- 
 cal combination. Probably all the nitrogen is in solution. 
 
 Coagulation of blood: If blood be drawn into a shallow 
 vessel and exposed to the air, it will become semisolid at the 
 surface in two or three minutes. This jelly-like condition 
 will extend to the sides of the vessel, and then throughout 
 the entire mass, so that if the vessel be inverted the blood 
 will not flow at the end of ten to fifteen minutes (Fig. 13). 
 
COAGULATION OF BLOOD. 
 
 43 
 
 Then drops of pale fluid (serum) begin to appear at the sur- 
 face, and these unite to form an amount of fluid sufficient 
 in an hour to float the clot, which meanwhile is contracting 
 from the sides of the vessel. The serum continues to exude 
 and the clot to contract for twenty-four to thirty-six hours. 
 The color of the clot remains red, while the serum has a pale 
 straw color (Fig. 14). 
 
 Clotting is due to the formation of a substance called fibrin, 
 which appears as a mesh of fine fibrils and soon entangles the 
 corpuscles. This mesh of fibrin contracts and squeezes out 
 the watery elements of the blood to form serum, and holds 
 the solid compounds, as shown by diagram as follows : 
 
 Blood. 
 
 Plasma. 
 
 Corpuscles. 
 
 Serum. 
 
 Fibrin. 
 
 I 
 
 Clot. 
 
 Clotted blood. 
 
 Conditions affecting coagulation : It has been found that 
 some conditions hasten and others retard the time of coagu- 
 lation. 
 
 Retard. 
 
 Greater heat or extreme cold re- 
 tard or entirely check. 
 
 Contact with living tissues, espe- 
 cially bloodvessels. 
 
 Absence of air retards. After 
 death by asphyxia blood remains 
 fluid. 
 
 Agitation of vessel retards. 
 
 More than twice the bulk of water. 
 
 Hasten. 
 Moderate warmth, 100-120 F. 
 
 Contact with foreign matters. 
 Access of air. 
 
 Kest. 
 
 Addition of moderate amounts of 
 water. 
 
 Addition of viscid substances 
 i. e., glycerin, syrup. 
 
 Addition of neutral salts, about 2 
 per cent, solution. 
 
 Digestive ferments. 
 
 Strong acids or alkalies. 
 
44 THE BLOOD. 
 
 Coagulation of blood explanation : There are many theories 
 to explain why the blood clots, but no one theory is perfectly 
 satisfactory. The best we can do is to state such facts as are 
 proven. As has been already stated, in the plasma of the 
 blood there exists a proteid, called fibrinogen ; there is also in 
 the plasma a true, unorganized, organic ferment, called filn-in- 
 ferment. When the blood is withdrawn from the living 
 bloodvessels the fibrin-ferment acts on the fibrinogen and 
 converts it into fibrin, the fibrin-ferment, like all true fer- 
 ments, remaining unchanged. If the process were as simple 
 as described, there would be no difficulty ; but the change 
 from fibrinogen to fibrin under the action of fibrin-ferment 
 does not take place unless a third substance is present. The 
 third ingredient is paraglobulin, already mentioned as exist- 
 ing in the blood-plasma. What part the paraglobulin plays 
 is unknown. It is merely a proteid, and not a ferment, and 
 yet is unchanged by the act of clotting. A possible expla- 
 nation is that the paraglobulin unites with and renders inert 
 some substance (unknown) which prevents the formation of 
 fibrin in the living condition. After clotting has occurred 
 the unchanged fibrin-ferment and the paraglobulin are found 
 in the serum ; the fibrinogen, now converted into fibrin, is 
 the clot. The fibrin-ferment and paraglobulin are capable of 
 still further activity if brought into contact with a fresh 
 supply of fibrinogen. As to the origin of these three factors 
 of coagulation there is no good explanation. It has been 
 suggested that the leukocytes are the source of supply of one 
 or more of the three substances, particularly fibrin-ferment. 
 Certainly coagulation is more active in the presence of leuko- 
 cytes. 
 
 In addition to the three factors given, the very important 
 presence of calcium salts must not be forgotten. Although 
 not an organic agent, in the process of coagulation the calcium 
 salts blend with the fibrinogen, which under the influence of 
 the fibrin-ferment becomes the fibrin. 
 
 Blood-coagulum />'(//// coat: If we examine under the 
 microscope the blood-clot which has formed under ordinary 
 circumstances, it is seen that the red corpuscles arc caught by 
 the meshes of fibrin and are uniformly distributed through- 
 
BL OD-COA G UL UM. 
 
 45 
 
 out the clot. Many of the leukocytes have made good their 
 escape into the serum. If we take a quantity of blood (Figs. 
 15 and 16) and retard the time of coagulation (horse's blood 
 coagulates more slowly than human blood), we note that the 
 upper part of the clot is much lighter in color. This is called 
 the " buify coat." The explanation of its formation is very 
 simple. Owing to retardation of the coagulation, the red cor- 
 puscles have had a chance to settle toward the bottom. When 
 seen under the microscope the upper layer, or buify coat, of 
 the clot is found almost free from red corpuscles. 
 
 FIG. 15. 
 
 FIG. 16. 
 
 Vertical section of a recent coagulum, 
 showing the greater accumulation of 
 blood-globules at the bottom (Dalton). 
 
 Bowl of coagulated blood, showing 
 the clot buffed and cupped. 
 
 Why blood does not clot in the blood-vessels : As long as the 
 endothelial lining of the blood-vessels is intact the blood does 
 not clot ; but if the endothelium is injured, a clot is formed at 
 the site of the injury. Just what check on coagulation the 
 endothelium plays is unknown, but it is none the less 
 positive. 
 
 If a vein of some animal, preferably a horse, be carefully 
 ligated in two places some inches apart, the blood within it 
 will not coagulate for a long time, provided the endothelium 
 is uninjured. This is not due to occlusion from the air sim- 
 ply. If such ligated vein with its contained blood be re- 
 moved from the body and carefully opened, the blood may be 
 poured from it into another vein similarly prepared, just as 
 we pour fluid from one test-tube to another. Though the 
 blood is thus exposed to the air, it will not coagulate till the 
 endothelium is injured or loses its vitality. 
 
-10 THE LYMPH. 
 
 If one accepts the theory that the fibrin-ferment is the re- 
 sult of disintegration of leukocytes, it is clear why Mood does 
 not clot within the bloodvc^els, lor then- is no ferment unless 
 a leukocyte disintegrates, the " normal " destruction of leuko- 
 oytes being disregarded as a possible factor, owing to the 
 small Dumber so destroyed at any given time. On the other 
 hand, if the endothelium be wounded, the leukocytes rush to 
 the breach and are broken up; also, if the blood is shed, 
 many leukocytes disintegrate in mass; thus in both instances 
 a large amount of fibrin-ferment is liberated and clotting 
 begins. 
 
 Blood resume of its uses : The red corpuscles convey oxygen 
 from the lungs to the tissues. 
 
 The platnna conveys the food, after absorption from the 
 alimentary canal, to the tissues. The pla.-ma also holds in 
 solution the carbon dioxide and water (the result of oxidation) 
 which it receives from the tissues, and carries these products 
 to be eliminated by the skin, lungs, and kidneys. The 
 plasma also holds in solution the urea and other nitrogenous 
 bodies that are carried to and excreted by the liver and 
 kidneys. 
 
 The leukocytes are protectors against the invasion of bac- 
 teria. 
 
 Thus it is seen that the various factors of the blood make 
 up a whole that is, a conveyor of supplies, a remover of 
 waste, and a protector from invasion. 
 
 THE LYMPH. 
 
 Lymph is a pale straw-colored fluid that bathes all the tiny 
 tissue-spaces of the body and is conveyed by lymph-vessels 
 
 from the lymph-spaces to the blood. It is slightly alkaline, 
 <>f a salty taste, and has no odor. 
 
 Composition : Lymph may be compared to a dilute blood 
 free from r<-d corpuscles, but rich in leukocytes. "When the 
 lymph-vessels of the lower animals, such MS tadpole-, are ex- 
 amined under the microscope, it is found that the leukocytes 
 are only present in the larger Trunks; the smallest channels 
 rarely contain particles >r corpuscles of any kind. It is not 
 
 
THE LYMPH. 47 
 
 meant that all the constituents of blood are equally reduced 
 when lymph is spoken of as a dilute form of blood. About 
 the same proportions of salts, urea, and sugar are present in 
 blood and lymph. Only about one-half as much serum- 
 albumin and paraglobulin, and about one-quarter as much 
 fibrinogen, are in lymph as are present in blood. Dnrin(/ 
 digestion there is a marked increase in fats and at such times 
 the appearance of the lymph from the intestines is like milk, 
 instead of being straw-colored. This form of lymph, known 
 as chyle, owes its opacity to the distribution of this fatty 
 matter in innumerable particles of very minute though 
 nearly uniform size, measuring about -g-o-jyo^oth ^ an i ncn 
 Each particle is coated over with albumin. 
 
 Lymph coagulates in the same manner as blood, but more 
 slowly and more feebly ; a difference readily explained by 
 the marked difference in amount of fibrinogen present. This 
 property of coagulation is not possessed by the lymph in the 
 smallest lymph-spaces nor by the chyle in the villi or lacteals 
 near them. It is only developed as the fluids near the tho- 
 racic duct. 
 
 Lymph sources: Between the individual capillaries of the 
 blood-system there exist small intercellular spaces, into 
 which the fluid portions of the blood are exuded owing to the 
 differences in pressure. This exudate, plus the leukocytes 
 that have left the bloodvessels by emigration, makes up the 
 lymph proper. In addition to the lymph proper, the lymph 
 that fills the lacteals of the intestinal villi absorbs some of 
 the products of digestion, especially the fats. This portion 
 of the lymph that has absorbed the fats is milky in appear- 
 ance, and is called " chyle.' 7 The chyle and lymph proper 
 are carried along in their respective channels and are min- 
 gled together just before the entire fluid is poured into the 
 vein at the root of the neck. 
 
 Uses: The lymph bathes all portions of the body not 
 reached by the blood. Hence the lymph conveys the nu- 
 trient ingredients of the blood to all cells not directly bathed 
 by the blood. The " chyle/' or lymph of digestion, absorbs 
 nutrient materials (mostly fat) from the intestines and pours 
 this food into the blood-current, to be universally distributed. 
 
48 
 
 CIRCULATION OF THK JlLOOh. 
 
 The lymph gathers up the waste-materials of the cells sur- 
 rounding the lymph-spaces and pours this waste into the 
 blood, to be eliminated by the skin, lungs, and urine. 
 
 CIRCULATION OF THE BLOOD. 
 
 The circulation of the blood is the course which the blood, 
 as a transporting medium, follows in taking food and air to 
 the tissues and bringing away the used-up material for ex- 
 cretion, and returning when freshly charged with oxygen and 
 food. 
 
 FIG. 17. 
 
 J. V. 
 
 Subcl. 
 artery. 
 
 Lungs. 
 
 Lungs. 
 
 Heart and lungs of man (Milne Edwards), r. a., right auricle; v., vena mv.i in- 
 ferior; a., right ventricle ; r., aorta ; I. v., left ventricle ; j. v., jugular vein ; c. a., 
 trachea and carotid artery. 
 
 The circulatory apparatus consists of: 
 
 (1) The heart, which propels the blood ; 
 
 (2) The arteries, which convey it from the heart to the 
 different parts of the body ; 
 
COURSE OF THE BLOOD. 
 
 49 
 
 (3) The capillaries, a 
 network of inosculating 
 tubules interwoven with 
 the substance of the tis- 
 sues and bringing the 
 blood into intimate con- 
 tact with it ; 
 
 (4) The veins, which 
 collect the blood from the 
 capillaries and return it 
 to the heart. 
 
 Course of the blood : As 
 the motion of the blood 
 is in a circle, it is imma- 
 terial at what part of the 
 vascular system we begin 
 its study. Starting, for 
 convenience, with the 
 blood as it leaves' the 
 lungs, we find that the 
 blood enters into the left 
 auricle from the pulmon- 
 ary veins, thence passing 
 the open mitral valve into 
 the left ventricle (Figs. 
 17 and 18). Upon con- 
 traction of the ventricle 
 the mitral valve is closed 
 and the aortic valves 
 thrown open, so that the 
 blood is thrown into the 
 aorta, and thence through 
 the systemic arterial cir- 
 culation into capillaries 
 and on into veins, the 
 systemic veins finally 
 joining to fill the venae 
 cavre, and from them the 
 right auricle. From the 
 
 4 Phys, 
 
 
50 
 
 CIRCULATION OF THE BLOOD. 
 
 right auricle the blood passes the tricuspid valve into the 
 right ventricle, whence it is thrown through the pulmonary 
 artery (guarded by the .pulmonary semilunar valves) into the 
 pulmonary capillaries, and thence into the pulmonary veins, 
 whence it started. Thus we have in reality two circulations, 
 the systemic and the pulmonary. 
 
 Also we see that the blood goes through one set of capil- 
 laries the lungs to be purified of waste-products and re- 
 
 FIG. 19. 
 
 
 Anterior view of heart (Quain). 
 
 oxygenated ; and another set the systemic capillaries where 
 the oxygen is lost and the waste-products gathered up. 
 
 Furthermore, the student will take note that the blood 
 which enters the splenic and intestinal arteries from the aorta 
 passes through fim ,sv7x of capillaries before returning to the 
 general venous circulation: the Jirxf *<t of capillaries is in 
 the (t/iiiH-iiftirif caiid/ and .vyVro/, whence the blood return-, is 
 jin the portal vein, and carried to the liver. In 
 
THE HEART. 
 
 51 
 
 FIG. 20. 
 
 the latter organ the blood passes through a second set of 
 capillaries, to be gathered into the hepatic veins, and finally 
 emptied into the inferior vena cava. While in the first set 
 (intestinal) of capillaries the blood gives up its oxygen to 
 nourish the walls of the intestine, and takes up in exchange 
 the carbon dioxide (waste of intestinal activity) and certain 
 of the nourishing products of digestion. On passing through 
 the hepatic capillaries some of the food-products are left be- 
 hind in the liver for storage, while others are carried on into 
 the circulation. 
 
 The heart (Fig. 19) is a muscular organ situated in the 
 thorax, where it lies between the lungs within the pericardial 
 sac, and rests upon the diaphragm, its larger portion lying 
 somewhat to the left of the midline of the body. It is coni- 
 cal in form, and is so suspended by the great vessels that the 
 apex points to the left and downward. Its size is about 
 that of the closed fist (weight, in adults, about ten ounces). 
 
 It is divided by a septum 
 into two cavities, not con- 
 nected, the right and the left 
 (Fig. 20). Each of these in 
 turn is subdivided into two 
 parts, the auricle and the 
 ventricle. 
 
 The auricles are thin- 
 walled cavities, whose func- 
 tion is to receive the blood 
 from the veins and pour it 
 into the ventricles. 
 
 The ventricles are sur- 
 rounded by the most power- 
 ful portions of the heart-muscle, the walls of the left being 
 much stronger and thicker than those of the right ventricle. 
 The auricles contain about four ounces, the ventricles about 
 six ounces. 
 
 Action of the auricles : During the period of rest of the 
 heart, blood flows freely from the veins into the auricles and 
 thence into the ventricles, the auriculo-ventricular valves 
 offering no resistance ; but the influx is so strong that by the 
 
 Transverse section of a bullock's heart 
 in the state of cadaveric rigidity, a, 
 cavity of the left ventricle ; b, cavi'ty of 
 the right ventricle. 
 
52 
 
 CIRCULATION OF THE BLOOD. 
 
 time the heart begins to contract the auricle is quite filled and 
 the ventricle partially. The contraction of the auricle is sud- 
 den and very quick, commencing at the great veins aixl ex- 
 tending toward the ventricular opening. Both auricle.- con- 
 tract simultaneously. There are no valves at the openings of 
 the venae cavse into the auricles, but the blood r/orx not r<(/nr</i- 
 tate for the following reasons : 
 
 FIG. 22. 
 
 Course of blood through the heart. Valves of the heart, 
 
 a, a, venn cava, superior and infe- 
 rior ; b, ritfht ventricle ; c, pulmonary 
 artery ; <7, pulmonary vein ; e, left 
 ventricle ; / aorta. 
 
 (1) The power of the auricular contraction is not sufficient 
 to cause a reflux. 
 
 (2) The muscular coat of the great veins near the heart 
 contracts, and helps to prevent this regurgitation. 
 
 (3) The weight of the incoming blood opposes. 
 
 (4) Valves in the veins oppose, and the Eustachian valve 
 partially guards the inferior vena cava. 
 
 Action of the ventricles: The ventricle is distended during 
 its period of rest by the flow of the blond from the veins and 
 by the auricular contraction; and its contraction seems con- 
 tinuous with that of the auricle, so immediately dors it sue- 
 
THE VALVES. 53 
 
 ceed. The ventricular contraction is slower and probably 
 completely empties the cavity. The ventricles contract si- 
 multaneously. The shape of the ventricles is changed : as the 
 heart-muscle becomes hard and rigid in contraction the section 
 of its base becomes circular, instead of elliptical, as it is dur- 
 ing repose ; the ventricles shorten and twist to the right, and 
 the form is conical. As the organ relaxes it returns to its 
 former position and shape, that of a cone with elliptical base. 
 This shortening of the ventricles in contraction is compen- 
 sated by the lengthening of the great vessels at the base as 
 they become distended by the load of blood. 
 
 The valves : In considering the functions of the valves of 
 the heart one must bear in mind constantly that the organ is 
 a pump whose office is to force the blood in one direction. 
 There are four principal valves two auriculo- ventricular, 
 and two in the great arteries, the aorta and the pulmonary 
 artery : (1) As the ventricle fills the auriculo-ventricular valves 
 are floated up from the sides of the ventricle in such manner 
 that their edges are in contact, cusp to cusp. As the ventricle 
 contracts more violently, pressure is brought upon the valve, 
 so that not only is the edge in contact, but also portions of 
 the surfaces of the cusps. These valves are of considerable 
 area, and are guyed in position by the chordce tendinece, which 
 spring from the papillary muscles, so that e version of the 
 valve into the auricle is impossible. (2) The semilunar valves 
 form a guard against the return of the blood to the ventricle 
 at the pulmonary and aortic openings of the ventricles. These 
 valves are forced open by the ventricular contraction, and 
 through them the blood rushes to distend the elastic walls of 
 the large arteries. The pressure of the blood under this 
 elastic grasp is sufficient to throw the cusps of the valves into 
 action. The corpora Arantii are useful in making a perfect 
 closure of the valve, though not absolutely essential. A part 
 of the weight of this pressure is borne by the thick ventricu- 
 lar wall, which forms a ring, from the outer edge of which 
 the artery springs, while the valves are attached to the inner 
 edge. 
 
 Under some circumstances the tricuspid valve does not en- 
 tirely close, but allows a certain amount of regurgitation of 
 
54 CIRCULATION OF THE BLOOD. 
 
 blood. This occurs in conditions of disease or of violent ex- 
 ertion, in which the lung-capillaries are overcharged with 
 blond. The leakage of the valve is conservative, and relieves 
 the prcs-urc upon the delicate capillaries of the pulmonary 
 alveolae. Pulsation in the jugular veins indicates this re- 
 gurgitation. The condition is not pathological, and with 
 altered conditions disappears. 
 
 The arteries are continuous hollow tubes leading from the 
 heart. They are surrounded by a dense fibrous coat exter- 
 nally, and are lined internally by a smooth endothelial lining; 
 between these is an elastic layer of fibrous tissue, which has 
 interlaced in its structure muscle-cells arranged transversely 
 around the vessel. Each artery has its own vasa vasorum, 
 or nutrient vessels, and is usually enmeshed in a plexus of 
 sympathetic nerves, "vaso-motor" nerves. Owing to the 
 various branches given off from the arteries, the calibre 
 of these vessels diminishes as we leave the heart. The 
 smallest arteries have been designated artei'ioles, and at 
 their distal ends the arterioles cease and the capillaries 
 begin. 
 
 In the large arteries the elastic tissue is in excess of the 
 muscle-tissue, whereas the reverse holds true in the arterioles. 
 The principal difference between the larger and the sm a 1 lei- 
 arteries is in the structure of their middle coat. In the 
 smaller arteries this is composed exclusively of muscular 
 fibres. In arteries of medium size it contains both muscular 
 and elastic tissue ; while in those of the largest calibre it 
 consists of elastic tissue alone. The larger arteries, accord- 
 ingly, have much elasticity and but little contractility ; while 
 the smaller are contractile and less elastic. The variation in 
 thickness of this middle coat is chiefly responsible for t In- 
 differences in the thickness of the walls of the larger and 
 smaller arteries. 
 
 The capillaries : The capillary blood-vessels (Fig. 23) are 
 channels of very small but variable size, but usually of about 
 sufficient calibre to permit just the passage of the red and 
 white corpuscles. They are usually composed of a single 
 layer of endothelial cells joined at the edges, though near the 
 arteries and veins there is sometimes an elastic fibrous coat. 
 
SIZE OF THE BLOODVESSELS. 
 
 55 
 
 A sympathetic nerve-plexus surrounds these vessels. The 
 capillaries form a complicated network in the tissues, and the 
 mesh of the net varies in shape and size greatly with the vas- 
 cularity and function of the tissue. 
 
 The veins : In structure the veins are similar to the arteries, 
 being composed of three coats an inner, a middle, and an 
 exterior of similar nature ; but they contain a smaller quan- 
 tity of muscular and elastic fibres and a larger portion of 
 condensed connective tissue. 
 That is, their inner and middle FIG. 24. 
 
 FIG. 23. 
 
 Fine capillaries from the mesen- 
 tery. 
 
 Diagram showing valves of veins. A, 
 part of a vein laid open and spread 
 out, with two pairs of valves. B, 
 longitudinal section of a vein, 
 showing the apposition of the edges 
 of the valves in their closed state. 
 C, portion of a distended vein, ex- 
 hibiting a swelling in the situation 
 of a pair of valves (Quain). 
 
 coats are thin, while the outer coat is relatively thick. Con- 
 sequently they are less elastic and contractile, but more com- 
 pressible than arteries. Veins collapse, while arteries remain 
 open when not distended by blood. Valves (Fig. 24) occur 
 in most of the veins ; these are so placed as to prevent the 
 blood from tending to flow backward. The valves are so 
 placed as to aid the onward progress of the blood in the veins, 
 the pressure of neighboring muscles forcing forward the blood, 
 which cannot regurgitate past the valves. 
 
 Size of the bloodvessels : With the division of the arteries 
 
56 CIRCULATION OF THE BLOOD. 
 
 into branches the sectional area of the branches is greater than 
 that of the stem. Of the veins the same is true, while the 
 total sectional area of the capillary system is much greater 
 than that of either. For purposes of simile the comparison 
 may be made of two funnels placed base to base. In numbers 
 one may consider the sectional area of the aorta as 1 ; of the 
 venae cavae, 2 or 3 ; of the capillaries, (about) 500. An in- 
 dividual capillary has been estimated as being i mm. long, 
 and from 5 to 20 /n in diameter. 
 
 Forces maintaining circulation: The heart, as has been 
 shown, is a force-pump, and at each contraction injects a 
 fresh volume of blood into the arteries ; during the repo^- <>f' 
 the heart it fills up with blood from the veins which has 
 already travelled the circuit. 
 
 The heart is the prime and important factor in maintaining 
 circulation, and is capable of forcing, unaided, the blood 
 through the entire circuit ; but in addition we find suh^'ulitirii 
 forces assisting the outward flow of blood : 
 
 (1) Arterial resiliency : At each beat the ventricles inject a 
 fresh quantity of blood into the already filled arteries. To 
 make room for this surcharge of blood the large arteries, 
 owing to their elasticity, are dilated by the increased amount 
 of blood. During the repose of the heart the arteries con- 
 tract by virtue of the recoil of their elastic fibres and drive 
 the blood on. This action of the arteries converts the inter- 
 mittent character of the blood-stream into a steady flow by 
 the time the capillaries are reached. 
 
 (2) Contraction of muscles: The skeletal muscles, during 
 the ordinary activities of the body, contract, and so compress 
 the veins lying between them. This compression drives the 
 blood out of the veins, but only in the proper direction, as 
 the valves of the veins prevent the reverse flow. 
 
 (3) Cardiac suction : During the period of repose the open- 
 ing out of the heart-cavity is sufficiently strong to exert a 
 decided suction on the blood in the veins. 
 
 (4) Thoracic suction: During the expansion of the chest 
 in inspiration a tendency to a vacuum is produced, which ex- 
 erts a suction on the large veins within the thoracic cavity. 
 This fact must always be borne in mind by the surgeon 
 
BLOOD-PRESSURE. 57 
 
 when operating on the neck. Should a large vein be wounded, 
 it must be instantly closed, lest by reason of this suction 
 air be drawn into the vein. If air should in this way 
 enter the proximal part of a wounded vein, it would be hur- 
 ried along to the heart, and, there expanding, cause serious 
 trouble or even death. 
 
 (5) A slight rhythmical contraction of the veins. 
 
 Speed of the blood : In the arteries it has been estimated 
 that the blood in the large arteries travels at the rate of about 
 300 to 500 mm. per second. As the blood advances in the 
 arteries the speed decreases gradually. 
 
 In the capillaries, owing to their much larger aggregate 
 diameter (500 : 1), the speed falls very low, and is estimated 
 to be f of a mm. per second. 
 
 In the veins the speed increases as we approach the heart, 
 and in the venae cavse is found to be from 125 to 200 mm. 
 per second. 
 
 With these figures as a basis, it has been calculated that a 
 given particle of blood occupies about a half minute of time 
 in going the round of the body. One second of the half min- 
 ute is used in passing the systemic capillaries, another second 
 in traversing the pulmonary capillaries. 
 
 It has been found by experiment on animals that there is 
 a ratio between the blood-speed and -pressure which may be 
 direct or inverse. Any influence which increases or dimin- 
 ishes the force of the heart will at the same time increase or 
 diminish both the velocity and the pressure of the blood ; 
 while any influence which increases or diminishes the re- 
 sistance to the arterial flow will make the velocity and the 
 blood-pressure vary in an inverse ratio to each other. Other 
 things being equal, both the pressure and the velocity in the 
 large arteries increase markedly during systole and diminish 
 greatly during diastole. Very near the heart the velocity is 
 greatest at the beginning of systole, then drops to almost 
 nothing toward the end of systole, and then, regaining speed, 
 flows at an almost even pace during diastole (Fig. 25). 
 
 Blood-pressure : By means of manometers the blood-pressure 
 has been determined. It is greatest in the arteries nearest 
 the heart, and gradually diminishes, until in the veins empty- 
 
58 
 
 CIRCULATION OF THE BLOOD. 
 
 ing into the heart it is found to be zero ; or even a slight 
 negative pressure or suction may be present. 
 
 The figures are as follows : pressure in the large arteries 
 supports a column of mercury 150200 mm. Iiiirh (about four 
 pounds to the square inch). In the capillaries, 3050 mm. 
 of mercury. In the distal veins, 20 mm. of mercury, gradu- 
 ally falling as we approach the heart. 
 
 1 234 
 
 1 23 4 
 
 1 234 
 
 Tracings of variations of rapidity and of pressure of blood in the carotid of a horse, 
 obtained by Chauveau and Lortet. The line v represents tin- curve of the ra- 
 pidity of the blood ; and p the curve of arterial pressure. The h'gun < aixl vi -r- 
 tical lines represent corresponding periods in the tracings (McKnidrirk i. 
 
 The cause of the high pressure in the arteries is due to the 
 force of the blood injected from the heart behind, and the re- 
 sistance of the capillaries in front. Although the blood is 
 pumped into the arteries in intermittent jets, when a *//>"// 
 artery is cut the blood spurts from it in a continuous jet. The 
 reason for this is the elasticity of the arterial walls, these 1 
 being put on the stretch by the blood forced into them at con- 
 siderable pressure, and contracting again during the period of 
 heart-rest, thus enabling the arteries to keep the blood under 
 elastic compression. The capillaries, though collectively of 
 much greater area than the arteries, by reason of the friction 
 they offer to the blood-stream maintain a less degree of ten- 
 sion. 
 
THE BLOOD IN CIRCULATION. 59 
 
 Conditions modifying arterial tension : (1) The rate of the 
 heart-beats, by keeping the arteries fuller or less full, will 
 modify the blood-pressure in the arteries. 
 
 (2) Vaso-motor changes, by increasing or decreasing the 
 friction offered the arterial blood, vary the tension in the 
 arteries. 
 
 (3) The amount of blood in the system must to a great 
 extent determine the limits of arterial pressure. In great 
 exsanguination the arterial pressure is quite low. 
 
 (4) Motion of the thoracic walls in breathing necessarily 
 changes the arterial tension by the pumping force exerted by 
 this motion. 
 
 The blood in circulation : While circulating in the arteries 
 and veins the blood travels at too great a speed to admit of 
 careful examination ; the leukocytes in spherical form and 
 the red corpuscles, bowled along indiscriminately, pass the eye 
 too rapidly for any peculiarities to be noticed. 
 
 The capillaries of the web of a frog's foot can be easily 
 examined with a microscope. In these the speed of the blood 
 is slow, and ample time is given to study the particular cor- 
 puscles. 
 
 On entering the capillaries the red cells are seen to occupy 
 the central portion of the stream of plasma. That portion 
 of the plasma in contact with the capillary walls is seen to 
 travel much slower than the central portion, owing to the 
 friction presented by the capillaries. This is known as the 
 " inert layer " of plasma. The corpuscles, being compara- 
 tively heavy, are crowded in the centre of the stream. That 
 the centre of the stream travels faster than the periphery is 
 shown by the fact that if we watch three corpuscles floating 
 abreast, in a moment or two the centre corpuscle forges ahead 
 and leaves its companions behind. 
 
 Some of the capillaries are so small that the red corpuscles 
 pass in single file ; some may even be so small that the cor- 
 puscle is squeezed up and elongated that it may glide through 
 the constriction ; on entering a vessel of larger calibre the 
 corpuscle, owing to its elasticity, resumes its shape. 
 
 The leukocytes in the arteries are carried along passively in 
 spherical shape, but on entering the capillaries are crowded 
 
60 
 
 CIRCULATION OF THE BLOOD. 
 
 into the inert layer by the heavier red corpuscles. In the 
 inert layer they change their shape and flatten out against 
 the capillary-wall. They now exhibit their am<eboid move- 
 ment, and perchance one may be seen sending its pseudo- 
 podia through the cement-substance between the endothelial 
 cells of the capillary-wall in other words, puncturing the 
 capillary. Having projected a pseudopod through the capil- 
 
 FIG. 26. 
 
 Capillary plexus in a portion of the web of a frog's foot (magnified 110 diameters). 
 1, trunk of vein; 2, 2, 2, its branches ; 3, 3, pigment-cells. 
 
 lary-wall, the leukocyte proceeds to draw the rest of its body 
 through, and then escapes into the tissue-spaces. The cement- 
 si ibstance closes spontaneously and no leak occurs. 
 
 Of course, it must not be supposed that all the leukocytes 
 escape from the capillaries. Only a small portion undergo 
 this " emigration," the majority going on with the blood- 
 current into the veins (Fig. 26). 
 
ACTION OF HEART. 
 
 61 
 
 The Heart (see also p. 51). 
 
 Action of heart: During ordinary average life the heart 
 beats about 72 times per minute. During muscular activity 
 and after eating or under excitement the rate increases ; 
 
 FIG. 27. 
 
 FIG. 28. 
 
 Projection of a dog's heart. Shaded portion indicates appearance of diastole; 
 white portion, of systole. A, anterior surface; L, lateral surface; P, poste- 
 rior surface (McKendrick). 
 
 during sleep it is lowered. At birth it is about 130 per min- 
 ute ; at three years, 100 ; in adult life, 72 ; in old age, 65. 
 
 This rate is varied from time to time 
 by conditions of bodily health and by 
 environment. The heart-beat in women 
 is somewhat more rapid than in men. 
 The relative frequency of heart and 
 respiratory action is about three or four 
 heart-beats to one respiratory act. 
 
 The heart-beat^ is made up of a con- 
 traction systole and a repose dias- 
 tole. During systole the heart becomes 
 
 hard and diminishes in size not only Converging spiral fibres at 
 transversely, but longitudinally (Fig. 
 27), thus resembling voluntary muscle. 
 This can be proved by experiment, 
 though it seems false to any one who 
 has examined a heart while in place in a living animal. In 
 such cases there is an apparent elongation of the heart during 
 systole, due, however, to the forward motion of the whole 
 heart during systole. This forward motion is a result of 
 
 the apex of the heart. The 
 direction of the arrows in- 
 dicates that of the rotat- 
 ing movement of the heart 
 at the ventricular systole. 
 
62 CIRCULATION OF THE BLOOD. 
 
 the twisting of the apex of the heart upon itself during sys- 
 tole (Fig. 28) from left to right, returning during diastole. 
 It i- caused by the spiral arrangement of the muscular fibres 
 at the apex. 
 
 The combined systole and diastole is called the <-ftr<//<ic 
 <//</,, and consists of four factors : (1) systole of the auricles, 
 (2) diastole of the auricles, (3) systole of the ventricles, and 
 (4) diastole of the ventricles. 
 
 The auricular systole is rapid, and forces the blood into 
 the still quiescent ventricles. On completion of the au- 
 ricular systole the auricles expand and remain quiet during 
 the systole of the ventricles, which begins the moment the 
 auricles cease contracting. 
 
 The ventricular systole is more forcible than that of the 
 auricles, but the ventricles remain in contraction longer than 
 do the auricles. During ventricular systole the blood is 
 forced into the arteries. At the close of the ventricular 
 systole the ventricles dilate. The auricles do not take up 
 work again at once, but there is a period during which the 
 entire heart is in repose. After this repose the auricles again 
 contract and a new cycle is begun. 
 
 Time of cycle : If we assume the average heart-beats to be 
 72 per minute, each cardiac cycle occupies 0.8 of a second. 
 The contraction of the auricles lasts 0.1 of a second. The 
 contraction of the ventricles lasts 0.3 of a second ; and the 
 repose of the entire heart, 0.4 of a second. Thus of the en- 
 tire 0.8 of a second, the auricular systole lasts 0.1 of a second 
 and the diastole 0.7 of a second ; the ventricular systole 0.-'5 of 
 a second and the diastole of the ventricles 0.5 of a second. 
 The combined systole of the auricles and ventricles, 0.4 of a 
 second ; and the total repose of the whole heart, 0.4 of a 
 second. If the heart-rate be increased, the ventricular 
 systole remains about 0.3 of a second : so we see that an in- 
 crease in the heart-rate is made at the expense of the dias- 
 tole. 
 
 Heart-iounds : The first sound is heard best over the apex 
 of the heart. It is of a dull, prolonged, booming character. 
 The second sound is heard immediately after the first, and is 
 a sharp, quick, almost clicking sound ; it is heard most clearly 
 
FORCE OF THE HEART. 63 
 
 over the base. The sounds are said somewhat to resemble 
 that expressed by lubb-dup. 
 
 The first sound is synchronous with the ventricular sys- 
 tole and with the closure of the auriculo-ventricular valves ; 
 it is supposed to be made up in reality of two sounds a val- 
 vular one, caused by closure of the auriculo-ventricular 
 valves, and a muffled one, due to contraction of the muscular 
 fibres of the ventricles. That it is due in part to the action 
 of the valves is proved by the fact that the sound is altered 
 when the valves are diseased or are artificially prevented 
 from closing. That muscular contraction of the heart pro- 
 duces a sound can be demonstrated by the cardiophone. This 
 is the only way of accounting for the sound, though of an 
 altered character it is true, which is produced at the begin- 
 ning of systole by a heart from which the auriculo-ventricu- 
 lar valves have been experimentally removed. 
 
 The second sound is synchronous with the closure of the 
 semilunar valves, and is caused by this action. It is heard 
 most distinctly opposite these valves, and is propagated upward 
 along the great vessels to which they are attached. There is 
 no doubt that it is caused solely by their closure. 
 
 Blood-supply of the heart : By the coronary arteries, which 
 arise in the sinuses of Valsalva circumferential to the leaves 
 of the semilunar valves. They do not receive blood during 
 systole ; but during diastole from pressure of the blood due 
 to the elasticity of the arteries, especially that of the aorta. 
 The blood is returned to the right auricle through the coro- 
 nary sinus and cardiac veins. 
 
 Force of the heart : The left ventricle exerts more than 
 twice as much power as the right. The exact intra ventricu- 
 lar pressure in man has not been ascertained. The expansion 
 of the heart exerts a negative (or suction) pressure which aids 
 the onflow of the blood, especially from the lungs to the left 
 auricle and ventricle. The intra-auricular pressure is very 
 much less than the intraventricular, and there is a negative 
 pressure during diastole in the auricles. 
 
 Estimated in foot-pounds, each ventricular contraction rep- 
 resents three and a half to four and a half foot-pounds. In 
 twenty-four hours this is estimated to equal more than one 
 
64 
 
 CIRCULATION OF THE BLOOD. 
 
 hundred and twenty foot-tons. In another light, if the blood 
 is one-twelfth of the body-weight, and if the amount of blood 
 
 FIG. 29. 
 
 Diagrammatic view of the nerves influencing the action of the heart. The right 
 half repri'.si-iits the course of the inhibitory, and the left the course of the 
 accelerating nerves of the heart; the arrows >h<;win^ tin- direction in \\hiHi 
 impressions are conveyed. The ellipse :it tin- upper extremity of the vat-us, 
 looking like a section of the nerre, u intended to represent the va^al nucleus 
 or centre. In this diagram the nerves are incorrectly made to cross, instead of 
 passing behind, the m.rta. 
 
 pumj^ed with each ventricular contraction is six ounces, in 
 an ordinary man an amount of blood equal to the total blood 
 
INNERVATION OF THE HEART. 65 
 
 of the body will pass through the heart in about half a 
 minute. 
 
 The amount of blood poured out by the systole of the ven- 
 tricles is called the " pulse-volume." 
 
 Innervation of the heart : This matter is somewhat unde- 
 cided at present, for the reason that many of the results must 
 be obtained from experiments upon the hearts of cold- 
 blooded animals. We do know that the mechanism of rhyth- 
 mical contraction is contained within the heart itself. Nerve- 
 ganglia are demonstrated in the frog's heart which are essen- 
 tial to its action ; similar ganglia exist in the human heart. 
 These ganglia are connected with fibres from the pneumo- 
 gastric (or vagus) nerve and with the sympathetic system 
 (Fig. 29). 
 
 The eardiac inhibitory nerve is a branch from the pneumo- 
 gastric nerve running to the heart. It has an inhibitory or 
 slowing effect upon the heart ; for if we cut the nerve the 
 heart becomes more rapid, and if we stimulate (Fig. 30) the 
 
 FIG. 30. 
 
 Effect of stimulation of the pneumogastric nerve upon the action of the 
 heart in a frog. To be read from right to left. 
 
 peripheral end of the nerve we slow the heart again. This 
 action may be traced to the medulla oblongata, where a cardio- 
 inhibitory centre is located. That the inhibitory influence of 
 the cardiac fibres of the vagus is not directly exerted upon 
 the heart is proven by the length of time elapsing between 
 the application of the stimulus and the appearance of the in- 
 hibitory effect. In some cases even two entire heart-beats 
 occur after a strong stimulus is applied before the heart stops, 
 indicating that some resistance must be overcome, the inhib- 
 itory fibres acting upon inhibitory centres in the heart itself. 
 Stimulation of the vagus not only slows the heart's action, 
 but modifies it. Systole and diastole are lengthened ; the 
 input and output of the ventricle are diminished ; the dias- 
 tole pressure and volume of blood in the ventricles are in- 
 
 5 Phys. 
 
66 
 
 CIRCULATION OF THE BLOOD. 
 
 i 
 
 1* 
 
 8 a 
 
 II 
 
 creased, and ventricular become less frequent than auricular 
 ((niti-actions, the latter being often twice as numerous. 
 
 ( 'crtaiu fibres of the sympathetic from the cervical and up- 
 per dorsal spinal cord pass to the heart. 
 If these fibres are left after all other 
 nerve-connections of the heart are cut 
 away, stimulation of the spinal cord will 
 cause the heart to become rapid. These 
 are known as accelerator nerves. These 
 accelerating nerves act less powerfully 
 than the inhibitory ones. They not only 
 accelerate the heart's action, but in- 
 crease the force of the beat and the out- 
 put (Fig. 31). 
 
 The cardiac depressor nerve is a cen- 
 tripetal nerve running from the heart to 
 the vaso-motor centre in the medulla. 
 Its purpose is to stimulate the vas- 
 motor centre to dilate the peripheral 
 arteries. The nerve is "stimulating" 
 only when the heart is laboring against 
 too high tension produced by unusually 
 high peripheral resistance. 
 
 Vaso-motor Nerves. 
 
 Arterial contraction and dilatation : 
 The muscular coats of the peripheral 
 arteries do not undergo a rhythmical 
 contraction and dilatation, but only con- 
 tract so as to diminish the calibre of the 
 arteries and thus limit the supply of 
 blood to a given part of the body. On 
 the other hand, the muscle-fibres relax 
 and allow the arteries to dilate when 
 the given part demands more blood to 
 satisfy its activities. Hence it is a per- 
 fectly normal condition to have the arteries of one part of 
 the body dilated, while the arteries supplying another part 
 
ACTION OF VASO-MOTOR NERVES. 67 
 
 are contracted, depending on which part of the body is func- 
 tionating. 
 
 By tone of the arteries is meant their average normal state 
 of contraction. 
 
 The nerve-supply of the muscular coats of the arteries is 
 through the " vaso-motor " nerves. They are of two varie- 
 ties according to their function, vaso-constrictor and vaso- 
 dilator. These nerves (vaso-constrictor and vaso-dilator) run 
 together in the same sheath, and are part of the sympathetic 
 system. 
 
 They have their origin in the vaso-motor centre in the 
 medulla. They pass down the spinal cord to emerge at dif- 
 ferent levels, thence to be distributed to all the different ar- 
 teries. Just before leaving the spinal cord there are second- 
 ary vaso-motor centres in the course of these nerves. Close 
 to the wall of the artery to be supplied there is a third (gan- 
 glionic) centre for vaso-motor action. On emerging from this 
 third centre the vaso-motor nerve breaks up into its terminal 
 filaments which are distributed to each muscle-fibre. 
 
 Action of vaso-motor nerves : It must not be supposed that 
 contraction and dilatation of the muscle-fibres are active 
 acts on their part depending upon whether the vaso-con- 
 strictor or the vaso-dilator fibres are stimulated. It is true 
 that contraction of the muscle-fibre is an active act depend- 
 ing on stimulation from the vaso-constrictors ; but were this 
 stimulus removed the muscle-fibres would relax and the artery 
 dilate passively, owing to the presence of blood within it. 
 
 We find that the vaso-constrictors act continuously with 
 more 0r less intensity. The action of the vaso-dilators is 
 only occasionally called into play, when marked dilatation of 
 the bloodvessels is called for. Also the dilators do not 
 directly act upon the muscle-fibres, causing them to dilate ; 
 but act upon and inhibit the action of the vaso-constrictors, 
 thus allowing a passive dilatation of the arteries because the 
 constrictor action is removed. 
 
 The vaso-motor centre in the medulla is the prime centre, 
 and the only one acting during normal life. The secondary 
 centres in the cord only assume control if the primary centre 
 is destroyed or its connection severed. The third centres 
 
68 CIRCULATION OF THE BLOOD. 
 
 (close to the artery) only act if the secondary centres are de- 
 stroyed or cut off. 
 
 Pulse. 
 
 The pulse is the alternate expansion and contraction of the 
 artery ("excursion of the wall of the artery ") resulting from 
 the fresh injection of blood at each ventricular systole. Of 
 course, the pulse-rate is the same as the number of heart- 
 beats. 
 
 A number of various terms are used to describe the char- 
 acter of the pulse : 
 
 Frequent or infrequent^=uumber of beats per minute ; 
 Regular or irregular whether beats follow successively or 
 not; 
 
 Intermittent beats skipped at regular intervals ; 
 Large or srnall=amplitude of excursion of wall of artery ; 
 Quick or slow^whether wall of artery rises rapidly or not. 
 , ir . ( are synonymous terms ^ 
 
 f Ir - v ' denoting a high-ten- S aseous > ... 
 
 Incompr esS ,ble, i g . & S Their "P"*Mi 
 Hard, soft. 
 
 ^ opposites are J 
 
 The sphygmograph : While an experienced physician can 
 appreciate slight variations in the character of the pulse, it 
 
 FIG. 32. 
 
 Marey's sphygniograph applied to the arm (Marey). 
 
 is only by means of the graphic method that the different 
 kinds of pulse can be successfully investigated and records 
 kept. The sphygmograph (Fig. 32) is an instrument which 
 
VENOUS PULSE. 69 
 
 measures the succession of the alternate dilatation and con- 
 traction of an artery, known as the pulse ; and, magnifying 
 these movements, registers them on a surface moving at a 
 uniform rate by clockwork. The resultant tracings are in 
 the form of a wavy line, the irregularities of which show 
 variations of the pulse too slight to be appreciated by the 
 most experienced fingers (Figs. 33 and 34). 
 
 FIG. 33. 
 
 Trace of the radial pulse, taken by the sphygmograph. 
 FIG. 34. 
 
 Dicrotic pulse of typhoid fever (Marey). 
 
 Extinction of pulse : In health the pulse gradually lessens 
 as we get further from the heart, and is entirely lost where 
 the arteries break up into capillaries. There is no pulse in 
 the capillaries nor a true pulse in the veins. 
 
 Venous pulse : Were the venous walls rigid, there would be a 
 respiratory pulse in the veins. In deep and infrequent respi- 
 ration, as in partial asphyxiation, the jugular veins may be seen 
 to be distended in expiration and collapsed during inspiration, 
 thus forming an abnormal venous pulse. The cause is the 
 pressure of the atmosphere upon the flaccid vein, it being easier 
 to empty the vein than to fill it under the sudden vacuum 
 produced by the act of inspiration drawing the blood from the 
 surface veins into the thorax. The veins are thus emptied, 
 and, being flaccid, are depressed by atmospheric pressure. 
 
 This suction power of the inspiratory vacuum in the thorax 
 extends over a small region only ; roughly speaking, the neck 
 and axilla. This is the so-called " dangerous surgical region ;" 
 for if a vein is punctured, air enters the blood-current and 
 is carried to the heart, and death results. But the flaccidity 
 
70 "CIRCULATION" OF THE LYMPH. 
 
 of the vein naturally causes a collapse of the wall, and air 
 will not rea< lily enter unless the wall remains ri^-id from arti- 
 ficial or abnormal causes. If the vein can collapse, not being 
 held open by connective tissue or fascia, or artificially or as a 
 result of calcareous infiltration, no air will be allowed to 
 enter the vessel, and the only sign will be an expiratory inter- 
 mittent hemorrhage. 
 
 "CIRCULATION" OF THE LYMPH. 
 
 The lymphatics : The blood-capillaries as they pass through 
 the various tissues of the body are surrounded by small open 
 spaces, called lymph-spaces. These spaces are the interstices 
 between the various component parts of the body-tissues. 
 The lymph-spaces form the open mouths of microscopic 
 lymph-capillaries, that closely resemble the blood-capillaries 
 in structure. The lymph-capillaries run together and go to 
 form larger channels, known as the "lymphatics n r " lym- 
 phatic vessels"; this arrangement is comparable to the for- 
 mation of veins from blood-capillaries (Fig. 35). These lym- 
 phatic vessels converge finally into two main channels- 
 thoracic duct and right lymphatic duct that pour their con- 
 tents into the venous system at the junction of the internal 
 jugular and subclavian veins on the left and right sides of the 
 neck respectively. 
 
 The lymphatic radicles (Fig. 36) of the intestine, although 
 not differing in structure from lymphatics elsewhere in the 
 body, are called " lacteals," because of the milk-like appear- 
 ance of the lymph they contain. 
 
 The lymphatics of the lower extremities, the trunk of the 
 body, and the intestinal tract, go to form a long channel, the 
 thoracic duct, which ascends along the front of the vertebral 
 column 1o the root of the neck on the left side. Here the 
 thoracic duct is joined by lymphatics draining the left side of 
 the head and left upper extremity. The combined channel 
 empties into the left innominate vein at the point of junction 
 of the left internal jugular and left snbelaviau vein. 
 
 The lymphatics of the right side of the head and right 
 upper extremity join to form the rif/lit lymphatic duct a .-hort 
 
STOMATA AND PSEUDOSTOMATA. 
 
 11 
 
 structure, one and a half inches long, emptying into the right 
 innominate vein. 
 
 Stomata and pseudostomata : In certain parts of the body 
 
 FIG. 35. Fro. 36. 
 
 Lacteals and lymphatics, during digestion. 
 
 Diagrammatic representation 
 of the origin of the lacteals 
 in a villus. e, central lac- 
 teal ; d, lymph -channels; 
 c, columnar epithelial cells, 
 the attached extremities of 
 which are directly continu- 
 ous with the lymph-chan- 
 nels. 
 
 there have been found 
 openings, or stomata, by 
 which a direct communi- 
 cation exists between the 
 lymphatic capillaries and 
 certain cavities previously 
 supposed to be entirely 
 closed. We say that 
 absorption takes place 
 through pseudostomata 
 when fluids pass into the 
 lymphatic system through 
 the intercellular cement- 
 substance of the epithe- 
 lium or endothelium 
 covering membranes. 
 
 Stomata have been found in the peritoneum and pleura. 
 
72 "CIRCULATION" OF THE LYMPH. 
 
 Flow of lymph : Thus we see that the lymph flows from 
 the tissue-spaces into the veins at the root of 
 FIG. 37. t j ie 1R , e k . 80 it is not justifiable to speak of 
 the " circulation of the lymph," as there is no 
 return-current. The lymph is formed in the 
 lymph-radicles, and ceases to be lymph proper 
 aV soon as it enters the venous blood. But 
 new lymph is constantly formed, and so there 
 is a steady onward flow. 
 
 Structure of lymphatics : The lymphatic 
 channels closely resemble the veins in struct- 
 ure, but are much thinner walled and pos- 
 sess a much larger number of valves (Fig. 
 37). 
 
 Sources of lymph: The lymph present in 
 the lymph-spaces is made up of the exudation 
 of a certain amount of blood-plasma through 
 the walls of the capillaries, together with the 
 leukocytes that have emigrated from the capil- 
 laries. It is probable also that certain por- 
 tions of the body-tissues may be found in the 
 lymph, which, though they have fulfilled their 
 functions and have to be removed, are not 
 entirely waste-products. They may be capa- 
 ble of reorganization in the lymph-glands ;:nd 
 V phatics f (sSpplyr ma y be absorbed by the lymphatics for this 
 
 purpose. 
 
 The lymph in the radicles of the intestines is composed of 
 the blood-plasma and leukocytes that have left the intestinal 
 capillaries, plus an innumerable number of microscopic 
 globules of fat that have been absorbed from the digesting 
 food. These particles of fat render the lymph milky in 
 appearance, hence the name "lacteals" for the intestinal 
 lymphatic radicles. This milky fluid is called clii//c. The 
 lymph proper and the chyle mingle in the thoracic duet to be 
 poured into the venous system. 
 
 I.i/nifili IH'<>I><I- is a pale >t raw-colored fluid ; after the ad- 
 mixture of chyle it is milky. 
 
 Pressure of lymph : The blood in the capillaries has been 
 
LYMPH-GANGLIA. 73 
 
 stated as being under a pressure equal to 2050 mm. of mer- 
 cury. In exuding through the capillary- walls the blood loses 
 about one-half its pressure ; hence we find that the lymph in 
 the tissue-spaces is under a pressure of 1025 mm. of mer- 
 cury. At the veins of the neck the lymph is under very low 
 pressure, or is at zero, or even under a negative pressure due 
 to the suction of the chest. 
 
 Factors producing lymph-flow; In some of the lower ani- 
 mals there is a distinct separate lymph-heart, the purpose of 
 which is to act as a force-pump to drive on the lymph, just 
 as the human heart drives on the blood. In man there is no 
 such lymph-heart, but the flow of lymph depends on other 
 causes. They are as follows : 
 
 (1) The positive pressure (1025 mm. of mercury) in the 
 lymph-spaces, as opposed to the zero or negative pressure at 
 the other end of the lymph-channel, drives the lymph on. 
 
 (2) The muscular movements of the body compressing the 
 lymphatics force the lymph on in the proper direction, the 
 reverse flow being prevented by the valves. The chyle is 
 aided in its flow by the actions of the muscular fibres of 
 the small intestine, and possibly by the layer of unstriped 
 muscle-fibre found in each intestinal villus. In the small in- 
 testine of the mouse the chyle has been seen to flow with 
 intermittent movements, corresponding to the peristaltic 
 movements. The contractility of the walls of the lymph- 
 vessels themselves, due to the muscle-fibres they contain, 
 probably supplies some of the force. 
 
 (3) The thoracic aspiration of the chest on inspiration 
 sucks on the lymph in the same manner as it does the venous 
 blood. 
 
 Lymph-ganglia : The lymph-ganglia, or lymph-nodes, are 
 innumerable small masses, varying in size from 1 mm. to 2 
 cm. in diameter, interposed in the course of the lymphatics. 
 They are found in great numbers in -the neck, thorax, axilla, 
 groin, and mesentery, and along the great vessels of the ab- 
 domen. A few are found in the popliteal space and in the 
 arm as far as the elbow, but none further down the leg or 
 forearm. 
 
 The lymph-ganglia consist of a mass of cellular pulp-sub- 
 
74 
 
 "CIRCULATION" OF THE LYMPH. 
 
 Fro. 38. 
 
 stance, through which run many open channels, the whole 
 being enclosed in a capsule. If a particular lymph- vessel be 
 
 examined, it will be seen to 
 empty directly at some point 
 into a lymph-ganglion. The 
 lymph flows through the open 
 channels in the substance of 
 the ganglion and emerges on 
 the opposite side, to be again 
 collected into a lymph-vessel, 
 and so on to its destination 
 (Fig. 38). 
 
 A lymph-ganglion is com- 
 parable to a sponge placed in a 
 snug-fitting rubber bag. The 
 
 cap- 
 ics, 
 
 Sim nle lymphatic gland, a, the c 
 
 suk', with sections of lymph;it 
 <l, (I, conning through it; b, la- 
 cunarand intercommunicating pas- 
 sages, permeated by the lymph, and 
 forming the superficial lymph-paths 
 nt' Frry ; c, nucleus or medullary 
 p >rtioii of the gland, in the centre 
 of which the section of a bloodvessel 
 may be seen. The path pursued by 
 the lymph through the medullary 
 portion constitutes the deep or sec- 
 ondary lymph-path of Frey (Car- 
 penter). 
 
 rubber bag connects on one 
 side with a rubber tube repre- 
 senting the afferent lymph- 
 vessel, and from the opposite 
 side there leads away from the 
 rubber bag another tube repre 
 sc 11 ting the efferent lymph- 
 vessel. The rubber bag is the 
 representative of the capsule of the ganglion, the meshwork 
 of the sponge is comparable to the framework of the ganglion, 
 ;s ml the holes in the sponge to the open channels. The sub- 
 stance of a lymphatic ganglion is adenoid tissue. 
 
 Purpose of lymphatic ganglia : The lymphatic ganglia serve 
 as filters for the lymph. Also the cell-division of leukocytes 
 occurs in their channels. An important attribute is the way 
 iu which they serve to retard the spread of infection through 
 the body, thus acting as safety-valves. If any portion of the 
 body is infected, the poison is carried by the lymphatics to 
 their especial glands. There its course is stopped till the 
 opposition of the glands is overcome, when it proceeds to 
 the next ones. As a result of this we uet at first en- 
 largement of the glands ; later, if the process continues, 
 they lireak down and are destroyed. If it were not for 
 their action in this way, an infected wound might often 
 
MOVEMENTS OF RESPIRATION. 75 
 
 prove rapidly fatal before surgical treatment had time to be 
 of value. 
 
 EESPIRATION. 
 
 By the respiratory act we mean the process by which oxy- 
 gen is introduced into the system and by which carbonic ox- 
 ide is excreted. This function is performed by the lungs, and 
 the transfer is effected by the agency of the blood. 
 
 The respiratory act is subdivided into (1) the "movements 
 of respiration," by which term is meant those movements that 
 cause the thorax alternately to expand and collapse, thus fill- 
 ing and emptying the lungs of air ; and (2) " respiration " 
 used to designate the interchange of oxygen and carbon 
 dioxide between the blood and the air in the lungs (external 
 respiration) ; also the exchange of oxygen and carbon dioxide 
 between the blood and the tissues of the body (internal respi- 
 ration). 
 
 Movements of respiration : The action by which the lungs 
 are filled with air (inspiration) is as follows : The thoracic 
 cavity is expanded by muscular action ; this expansion draws 
 on the walls of the lungs through the intervention of the 
 pleurae, thus enlarging the cavity of the lungs. To prevent 
 a vacuum in the lungs, air is taken through the nose or mouth, 
 and passes through the pharynx to the larynx ; entering the 
 rima glottidis, it passes through the larynx to the trachea and 
 bronchi. The air is somewhat warmed and moistened in its 
 passage. The trachea and bronchi are lined with ciliated 
 epithelium, which serves to sweep particles of dust and the 
 like out of the air-passages. After the lungs have been filled 
 with air the thoracic wall is made to collapse and the air is 
 expelled from the lungs. 
 
 The respiratory tract : In all vertebrates and in many in- 
 vertebrates certain specialized structures, either lungs or gills, 
 are specially adapted for allowing the blood to come into close 
 proximity with the air or water which contains air. A lung 
 or gill in its simplest form consists of a thin membrane, on 
 one side of which is a network of thin-walled bloodvessels, 
 while the other side is in contact with the air or water. 
 There is a difference of degree only between the most com- 
 
76 
 
 RESPIRATION. 
 
 plex and the simplest forms. In man the respiratory tract is 
 highly complex, and includes essentially the larynx, trachea, 
 bronchi, and lungs (Fig. 39). 
 
 FIG. 39. 
 
 Human larynx, trachea, bronchi, and lungs; showing the ramification of the 
 bronchi and the division of the lungs into lobules (Dalton). 
 
 The larynx : The air enters the body through the mouth or 
 nares. It first passes through the larynx, the upper part of 
 tin- respiratory passage. This is a short tube, triangular on 
 section, formed of hyaline cartilage, which contains the 
 voral cords. At its lower extremity the larynx joins the 
 trachea. 
 
 The trachea : The trachea, or windpipe, is a hollow tube, 
 four to four and a half inches long, composed of fibro-elas- 
 
MINUTE ANATOMY OF THE LUNG. 
 
 77 
 
 tic membrane, in which are enclosed a series of from sixteen 
 to twenty cartilaginous rings. These latter serve to stiffen it. 
 At its lower extremity it divides into two bronchi, one for 
 each lung, named respectively the right and the left. 
 
 The bronchi : These are merely smaller editions of the 
 trachea and of a similar structure. They divide, enter the sub- 
 stance of the lungs, and, subdividing, penetrate every part till 
 they end in the lobules. As they get smaller the walls 
 become thinner and the cartilaginous rings disappear. 
 
 The lungs : These occupy the larger part of the thorax. 
 They are of a spongy, elastic texture, and on section appear 
 to be solid organs for the greater part. In reality they are 
 hollow. The lungs are two in number, the right and the 
 left, of which the former is partially subdivided into three 
 lobes ; the latter into two. 
 
 Covering each lung separately is a serous membrane, the 
 pleura, which in the form of a sac envelops the outer sur- 
 
 FIG. 40. 
 
 Diagrammatic view of the pleural sacs with the heart and lungs interposed. A, in- 
 ternal mammary artery ; N, phrenic nerve. 
 
 face of the lung and the inner surface of the chest-wall. The 
 pericardium containing the heart is interposed between the 
 two lungs (Fig. 40). 
 
 Minute anatomy of the lung : Each lobe of the lung is 
 
78 RESPIRATION. 
 
 composed of numerous lobules, into each of which a small 
 bronchiole enters, and the minute terminal branches of these 
 bronchioles (infimdibula] widen into a .sort of irregular funnel 
 having pouched or sacculated dilatations, known as air-cc//*. 
 These air-cells are supported by numerous elastic fibres, and 
 are lined with a very thin layer of flat (not ciliated) epi- 
 thelium. Outside the epithelial lining is a very close mesh 
 of capillaries, which are often exposed to air on both sides In- 
 lying in a partition between two of the air-cells. The air- 
 cells or vesicles are about one-sixtieth of an inch in diameter, 
 and the space between the capillaries is often less than the 
 diameter of a capillary (Figs. 41 and 42). The total surface 
 in the lungs bathed by the air is about two hundred square 
 metres. 
 
 FK;. 41. FIG. 42. 
 
 Single lohule of human lung, a, ulti- Network of capillary blood-vossi-ls in the 
 
 mate bronchial tube; h, cavity of pulmonary vesicles .f thr hone, n 
 
 :>bule; c,, c, c, pulmonary cells, or cavity of vesicle, with capillary plexus : 
 
 vesicles (Dalton). ft, pulmonary blood-vesaels, supplying 
 
 capillary plexus (Frey). 
 
 Muscles of inspiration: During <|iiiet inspiration the cavity 
 of the chest is increased in all three diameters vertical, 
 anteri-jM)>trri.r, and lateral. The upper part of the thoracic 
 ba-Ui-t being fixed, the vertical diameter is increased by the 
 d'-mit of the diaphragm in contracting ( Fig. 4:5). Th<> ex- 
 ternal intercostals, together with other muscles, act on the 
 
MUSCLES OF INSPIRATION, 
 
 79 
 
 ribs so that they turn on their axes, with the result that the 
 sternal ends are raised up and carried forward ; at the same 
 time the peculiar curve that exists in the rib at its angle 
 
 FIG. 43. 
 
 TT 
 
 Si 
 
 A 
 
 Diagrammatic sections of the body in inspiration and expiration. A, inspiration; 
 B, expiration ; Tr, trachea ; St, sternum ; D, diaphragm ; Ab, abdominal 
 walls. The shading roughly indicates the stationary air (Huxley). 
 
 causes an eversion of the lateral aspect of the rib when the 
 sternal end is brought upward and forward. This eversion 
 increases the lateral diameter. 
 
 The axis of a rib is a line running through the centre of 
 the head (vertebral end) of the rib and through the articula- 
 tion of the rib with the transverse process of the vertebra. 
 
 The muscles producing these changes in the diameters of 
 the chest are the muscles of " quiet inspiration/' and are as 
 follows : 
 
 Diaphragm increases the vertical diameter 
 
80 
 
 RESPIRATION. 
 
 Scaleni fix upper part of the thorax ; 
 External intercostals ] 
 
 and > draw the ribs upward ; 
 
 Interchondrals J 
 
 C fix the second rib and raise 
 Serrati postici stiperiores< the third, fourth, and fifth 
 
 ( ribs; 
 Levatores costarum breves raise the upper ten ribs. 
 
 It is stated that of the two types of respiration, " thoracic " 
 and " abdominal/' the former is more marked in women and 
 the latter in men. This is true in the sense that women in- 
 crease the antero-posterior and the lateral diameter of the 
 chest more than do men, owing to the functional differences 
 between the sexes, and also due to habits of dress, etc. On 
 
 FIG. 44. 
 
 FIG. 45. 
 
 The changes of the thoracic and abdominal The same in the female (Hutchinson). 
 walls of the male during respiration. 
 
 tin 1 other hand, adult males and children of both sexes use 
 tin- diaphragm almost exclusively in quiet inspiration (Fiir>. 
 44 and 45). 
 
MUSCLES OF EXPIRATION. 81 
 
 During forced inspiration additional muscles are brought 
 into play to permit of a more powerful inspiratory act. Be- 
 side the muscles already enumerated, the muscles of forced 
 inspiration are as follows : 
 
 Trapezei and rhomboidei fix the shoulders ; 
 
 Pectorales majores and minores, acting from the fixed 
 shoulders, draw the sternum and ribs upward ; 
 
 Sterno-mastoidei fix the upper part of the chest ; 
 
 Erector sphue stiffen the vertebral column ; 
 
 Serrati postici inferiores. ^ ^ -IT 
 
 QuadJi lu.bo,,, U a-k^rt- Downward 
 
 oacro-lum bales, ) 
 
 Muscles of expiration : At the close of inspiration the va- 
 rious muscles that raised the thorax relax, and by its own 
 weight the thorax drops, thus compressing the lungs and ex- 
 pelling the air. In addition there is an active collapse of 
 the lungs due to the recoil of the elastic tissue in the sub- 
 stance of the lung, the elastic fibres having been put on the 
 stretch during inspiration. Also during inspiration the inter- 
 osseous portions of the internal intercostal muscles were put 
 upon the stretch ; when expiration begins these muscles con- 
 tract, but their contraction is not sufficiently forcible to pull 
 the ribs down, and the only purpose of this contraction seems 
 to be to keep the intercostal tissues tense and thus prevent 
 bulging of the intercostal spaces. 
 
 Also during inspiration each costal cartilage was twisted 
 in the direction of its long axis, due to the eversion of the rib 
 twisting the rib-end of the cartilage, the sternal end being 
 fixed. During expiration the costal cartilage tends to un- 
 twist itself. So we may justly say there are no muscles for 
 quiet expiration, as the act is performed by the weight of the 
 thorax, elastic recoil of the lungs, and untwisting of the 
 cartilage. 
 
 Forced expiration is accomplished by the intervention of 
 many muscles as follows : 
 
 Interosseous internal intercostals act forcibly in drawing 
 down the ribs, when the lower part of the thorax is fixed ; 
 
 Abdominal muscles fix the lower part of the thorax and 
 press the abdominal contents upward; 
 
 6 Phys. 
 
82 RESPIRATION. 
 
 Levatores ani and perineal muscles, hold the floor of the 
 pelvis rigid against abdominal pressure. 
 
 Triangtilaris sterni draws the costal cartilages down. 
 
 Frequency of respiration : In normal adult life, with the body 
 in repose, there are about eighteen respiratory cycles to the 
 minute. Inspiration and expiration alternate without any 
 appreciable pause between the two. The inspiration is some- 
 what shorter than the expiration ; the ratio being about 5 to 
 6. In infants and invalids the rate is often much more rapid. 
 The ratio to the pulse-rate is about 1 to 4 in the healthy in- 
 dividual. During violent activity both the respiratory- and 
 pulse-rates increase, but the ratio remains about the same. 
 
 Respiratory sounds : When the ear is placed in contact with 
 the chest-wall, or a stethoscope is used, a respiratory murmur 
 will be heard, fairly marked during inspiration ; short and 
 faint during expiration, in a healthy subject. It varies in 
 diiferent parts of the chest-wall, being loudest over the large 
 bronchi. The changes in these murmurs incident to disease 
 of the respiratory tract are just as characteristic of the differ- 
 ent pathological processes as are changes in the heart- sounds 
 depending on disease of the heart ; and it is upon the recog- 
 nition of these changes that the value of auscultation depends. 
 
 Associated respiratory movements : With every inspiration 
 (especially if rapid) there is dilatation of the nostrils; and a 
 partial closure during expiration. The rima glottidis is in 
 the same way opened for the ingress of air. This is like the 
 respiratory act, in that the opening is a muscular act during 
 inspiration, and the recoil, elastic, in ordinary breathing. 
 
 Capacity of the lungs: The lungs, if filled to their utmost, 
 can hold about 4500 c.c. of air. This total of air is divided 
 as follows: (1) tidal air, (2) reserve air, (3) residual air, and 
 (4) complementary air. 
 
 Tidal air is the ordinary amount of air that passes in and 
 <>ut during each quiet respiration. It seldom goes lower than 
 the large bronchi. Its amount is 500 c.c. 
 
 Reserve air is the amount of air in addition to the tidal air 
 one can expel from the lungs in a forced expiration. It is 
 ordinarily lodged in the bronchi and bronchioles. Its amount 
 is 1600 c.c. 
 
EXPIRED AIR. 83 
 
 Residual air is found in the alveoli of the lungs, and remains 
 even after the most violent expirations. Amount, 800 c.c. 
 
 Complementary air is the air taken in, in addition to the 
 tidal air, in the most forced inspiration. Amount, 1600 c.c. 
 
 The complementary, tidal, and reserve airs have been 
 called the vital capacity of the lungs. 
 
 Force of the inspiratory and expiratory muscles : The force 
 of the inspiratory muscles is greatest in people of about five 
 feet seven and a half inches in height, being equivalent, on 
 the average, to a column of mercury three inches high. It 
 diminishes in people above and below this height. The force 
 of expiration is about one-third greater; but the variations 
 are not so regular, as there are many variations due to the 
 fact that the expiratory muscles are used for other purposes, 
 hence becoming stronger. 
 
 Composition of inspired air : Pure air has a nearly uniform 
 composition : 
 
 By volume. By weight. 
 
 Nitrogen, 79 parts 75 parts 
 
 Oxygen, 21 " 25 " 
 
 Carbonic acid, 04 part 
 
 Ammonia and impurities, trace. 
 
 Expired air : After its sojourn in the lungs there are 
 marked changes in the respired air. Its temperature is 
 changed to nearly that of the body, regardless of the tempera- 
 ture of the atmosphere. The oxygen is decreased, carbon 
 dioxide and aqueous vapor are increased ; also there are 
 present many minute particles of volatile organic bodies. 
 Nitrogen is unchanged. The composition of expired air is 
 about as follows : 
 
 By volume. 
 
 Nitrogen, 79 parts 
 
 Oxygen, 16 " 
 
 Carbon dioxide, 4 " 
 
 Water increased (from 6 to 30 ounces per day). 
 Volatile organic bodies are added. 
 
 The total weight of expired air is somewhat heavier than 
 
84 RESPIRATION. 
 
 that of inspired air, because the amount of carbon dioxide 
 gained weighs more than the amount of oxygen lost. 
 
 In temperate atmospheres the volume of expired air is 
 greater than that of the inspired air, because the air has been 
 expanded by being heated. If, however, the expired air lie 
 reduced to the temperature of that inspired, the volume of 
 expired air will be found less than that inspired, as the car- 
 bon dioxide gained is less bulky than the oxygen lost. 
 
 Value of nitrogen: The nitrogen in the atmosphere serves 
 merely as a diluent ; pure oxygen would be too powerful to 
 serve for respiration. We do find a little nitrogen in solu- 
 tion in the blood-plasma, but it probably serves no purpose 
 in the body economy. 
 
 External respiration : By external respiration is meant the 
 interchange of gases in the respired air and the gases of the 
 blood while in the pulmonary capillaries. It is true the 
 ordinary tidal air of respiration, lodged as it is in the upper 
 air-passages, does not come into actual contact with the pul- 
 monary capillaries, but by virtue of the physical laws of diffu- 
 sion of gases the oxygen in the tidal air is diffused into the 
 reserve air, and carbon dioxide and other wastes of the re- 
 serve air are diffused into the tidal air. A similar exchange 
 takes place between the reserve air and the residual air. 
 Thus it comes about that the residual air, while never leaving 
 the air-cells of the lungs, is constantly revivified with fresh 
 oxygen and constantly gets rid of its carbon dioxide and 
 other impurities. The blood coming to the pulmonary capil- 
 laries through the pulmonary arteries is rich in carbon diox- 
 ide and other wastes, but poor in oxygen ; on the other hand, 
 the air in the alveoli is rich in oxygen, but poor in carbon 
 dioxide. Hence the oxygen in the air is under high tension 
 as compared with the oxygen in the blood; and likewise the 
 carbon dioxide of the blood is under higher tension than the 
 carbon dioxide of the air. Owing to these ditlcivnces in 
 pressures, interchanges of the gases readily take place, so as 
 to equal i/e the pressures. 
 
 In the blood oxygen is in loose chemical combination with 
 the haemoglobin (<>x\ -h \ moglobin). The amount of oxygen 
 in the residual air of the pulmonary alveoli is estimated at 
 
NERVOUS MECHANISM OF RESPIRATION. 85 
 
 about 10 per cent., that of expired air being 16 per cent. It 
 is found that unless there is present about 4 per cent, of oxy- 
 gen there is no tendency for the blood of the pulmonary 
 arteries (venous) to take up fresh oxygen ; or, the tension of 
 the oxygen in the reduced hemoglobin of venous blood is 
 about 4 per cent., and unless the oxygen-tension in the lungs 
 is greater there is no absorption of oxygen. But, as we have 
 seen, the amount of oxygen amounts to at least 10 per cent., 
 and therefore the excess is sufficient to exceed the demands, 
 and the exchange is readily made by diffusion through the 
 thin capillary walls of the alveoli. On the other hand, the 
 tension of the carbonic acid in the pulmonary arteries is much 
 higher than in the alveoli, and hence the extrusion of this gas 
 by diffusion is accomplished. 
 
 The following changes in the blood are noted after passing 
 through the pulmonary capillaries : (1) Color, deep purple to 
 bright scarlet by oxidization of the reduced haemoglobin 
 i. e., from venous becoming arterial blood ; (2) gains oxygen ; 
 (3) loses carbonic acid ; (4) becomes cooler ; (5) coagulates 
 more readily. 
 
 Internal respiration : Internal respiration means the ex- 
 change of gases between the arterial blood and the tissues of 
 the body. This interchange takes place through the walls 
 of the systemic capillaries, and depends on the same physical 
 laws (differences in pressure) as already described for the 
 pulmonary exchange. 
 
 The arterial blood, rich in oxygen, gives oxygen to the 
 needy tissues, and in return relieves the tissues of their 
 burden of carbon dioxide and other wastes. In the systemic 
 capillaries the blood changes from arterial to venous. 
 
 Nervous mechanism of respiration : Respiration is described 
 as one of the so-called automatic acts, but is profoundly modi- 
 fied by the reflexes and partially controlled by the will. 
 
 Throughout our lives we continue to breathe unconscious 
 of the fact, unless our attention is called to it. A dash of 
 cold water on the skin or a disagreeable mental or visual pict- 
 ure will produce an uncontrollable gasp ; these are examples 
 of reflex influences on respiration. One may so exert will as 
 to increase or decrease the rate of respiration, but only up to 
 
86 RESPIRATION. 
 
 certain limits. It is impossible to commit suicide by " hold- 
 ing the breath." 
 
 Centres for respiration : In the medulla oblongata arc cen- 
 tres for each half of the body, from which arise automatically 
 the rhythmical impulses for the inspiratory act*. These so- 
 called automatic impulses are generated by the presence or 
 absence of oxygen in the blood (not presence of carbon 
 dioxide) bathing the medulla. If the blood in the medulla 
 is rich in oxygen, there is no impulse for an inspiratory act ; 
 but as soon as the oxygen is diminished to a given point the 
 respiratory centre is stimulated to make an inspiratory effort. 
 The nerves which convey to the muscles of inspiration their 
 impulse are the phrenics (to the diaphragm) and the intercos- 
 tals (to the intercostal muscles). In addition to the auto- 
 matic impulses from the centres, there are certain regular 
 reflex impulses (other than the unusual ones mentioned 
 above cutaneous reflexes, etc.) that are conveyed to the 
 centres by the pneumogastric nerves. 
 
 The pneumogastric nerves arising in the medulla scud 
 branches to the lungs that terminate in filaments distributed 
 to the walls of the air-cells. These fibres are afferent, and 
 are stimulated by two factors : (1) The lack of oxygen in the 
 air of the alveoli after expiration ; (2) During the partial col- 
 lapse of the lung at the end of expiration these filaments are 
 mechanically pinched by the walls of the air-cells. 
 
 The stimuli thus generated in the terminal filaments of the 
 pulmonary branches of the pneumogastric nerves convey 
 their impulses to the centres of respiration, producing an ad- 
 ditional impulse for inspiration. 
 
 The condition (amount of oxygen) of the blood bathing the 
 respiratory centre is, however, the prime factor, the afferent 
 impulses of the pneumogastrics being only secondary. 
 
 While there are distinct expiratory centres in the me- 
 dulla for expiration, they act to produce forced expiration 
 only when properly stimulated by afferent nerves as, for 
 example, if the superior laryngeal nerve be stimulated, the 
 result is a forced explosive expiration, or cough. 
 
 Under <>/-(f innri/ oircurngtance* when the inspiratory act is 
 accomplished, the condition of the blood no longer calls for 
 
 
SECTION OF VAGI. 87 
 
 more oxygen, and, the inspiratory impulse ceasing, the mus- 
 cles of inspiration relax and expiration is a purely passive 
 act. 
 
 In dyspnoea, however, the expiratory centres are stimu- 
 lated. 
 
 Synchronism of respiratory centres : Although there is a 
 respiratory centre for each half of the body, nevertheless, 
 owing to their association-fibres, the two centres work syn- 
 chronously. By making a median section of the medulla, the 
 centres are disassociated, so that, if proper artificial stimuli be 
 applied, one half of the chest may be made to inspire, while 
 the other half expires. 
 
 Lack of oxygen in the blood : If the need be only moderate, 
 there will be increased effort of both expiration and inspira- 
 tion, and the respirations will be rapid a condition known 
 as hyperpnoea. As the oxygen becomes less and less abundant 
 the symptoms become more severe, and the condition is known 
 as dyspnoea. The dyspnoea increasing, the respiratory efforts 
 become very violent, and the condition of asphyxia is seen. 
 In this the face is blue, eyes staring, face anxious, and respir- 
 ations very rapid and strident. Then follows a convulsive 
 condition which is brief, the convulsions being very violent 
 and involving the whole body. After this the patient lapses 
 into a state of exhaustion, in which the respirations are slow 
 and very feeble, and the general condition is one of collapse. 
 Death ensues very soon. 
 
 Apncea is absence of breathing. 
 
 Section of vagi : If one pneurnogastric nerve be divided 
 below the offshoot of the inferior laryngeal nerve, there is a 
 temporary excitation of the respiratory rate, due to the mechan- 
 ical stimulus of cutting ; but soon the respirations return to 
 normal, .the other vagus taking up the work of both. 
 
 If both vagi be divided below the inferior laryngeal nerve, 
 there is an excitation of respiration due to the stimulus of 
 cutting, soon followed by slower and deeper inspirations and 
 active expirations. Stimulation of the central ends of cut vagi 
 will bring the rate and character back to the normal. 
 
 If the superior laryngeals be divided, a cough or expiratory 
 sniff follows the act of cutting ; later on the subject dies of 
 
88 RESPIRATION. 
 
 ' foreign-body pneumonia," because the sensation of the lar- 
 VMX being lost foreign particles pass the. larynx without being 
 coughed out, enter the lungs, and give rise to a fatal pneu- 
 monia. 
 
 Section of the inferior laryngeals gives the same result ; for 
 although sensations in the larynx are present if the superior 
 laryngeals are intact, all motion in the larynx is lost and 
 coughing is ineffectual. 
 
 Vitiated atmosphere : In ill-ventilated rooms the air of the 
 room is used repeatedly, and, besides becoming partial!} de- 
 prived of its oxygen, is charged with carbonic acid and with 
 putrescible nitrogenous organic matters. This gives rise to an 
 atmosphere which is intolerable to one who enters from fresh 
 air. That such a condition is unsanitary needs no argument. 
 The mere presence of the excess of carbonic acid is not in 
 itself injurious; but the amount of carbon dioxide is indica- 
 tive of the amount of organic matter present, and it is the 
 latter that are highly poisonous. It is generally accepted as 
 a fact that about 1000 cubic feet of air-space per head must 
 be allowed in sleeping-quarters, and sufficient facilities for 
 exchange of air to allow complete change in each hour. This 
 ventilation must be accomplished without exposure to 
 draughts. 
 
 Effect of respiration on the circulation : As the heart and its 
 great vessels are contained together with the lungs in the 
 thorax, an air-tight cavity, there naturally results a certain 
 alteration in pressure on the heart when the capacity of the 
 thorax changes. Though the expansion of the lungs during 
 inspiration tends to compensate for this increased capacity, it 
 never does so fully, as part of the atmospheric pressure is 
 expended in overcoming the elasticity of the lungs. There- 
 fore, during inspiration the pressure on the heart become.- 
 considerably less than the atmospheric pressure exerted on 
 the bloodvessels outside of the thoracic cavity. This differ- 
 ence varies from 5 to 8 mm. of mercury during the pause, 
 up to 25 or 30 mm. at the end of a deep inspiration. The 
 result of this is to draw more blood through the veins into 
 the heart during inspiration, and consequently to increase ar- 
 terial tension. The relative values of intrathoracic press- 
 
SPECIAL RESPIRATORY ACTS. 
 
 89 
 
 ure and arterial tension may be graphically expressed as in 
 Fig. 46. 
 
 Special respiratory acts : There are a number of involun- 
 tary and voluntary special respiratory acts, largely reflex, 
 which are dependent upon modifications of inspiration and 
 
 FIG. 46. 
 
 i e i 
 
 J 
 
 Comparison of blood-pressure curve with curve of intrathoracic pressure. To be 
 read from left to right, a is the blood-pressure curve, with its respiratory undu- 
 lations, the slower beats on the descent being very marked ; bis the curve of 
 intrathoracic pressure obtained by connecting one limb of a manometer with 
 the pleura! cavity. Inspiration begins at i, expirati9n at e. The intrathoracic 
 pressure rises very rapidly after the cessation of the inspiratory effort, and then 
 slowly falls as the air issues from the chest ; at the beginning of the inspiratory 
 effort the fall becomes more rapid (Foster). 
 
 expiration e. g., sighing, hiccough, cough, sneezing, speaking, 
 singing, sniffing, sobbing, laughing, yawning. 
 
 Sighing : This results from a prolonged inspiration, the air 
 passing noiselessly through the larynx and being rather sud- 
 denly expelled. 
 
 Hiccough: This resembles sighing, but the inspiration is 
 sudden, due to spasmodic action of the diaphragm. 
 
 Cough : This results from a deep inspiration followed by a 
 forced and sudden expiration, during which the glottis is 
 momentarily closed by spasmodic action of the vocal cords. 
 
 Sneezing : In this case, following on a deep inspiration, by 
 a sudden and forced expiration the air is directed through the 
 nasal passages. 
 
 Speaking : In this case there is a voluntary expiration, and 
 the vocal cords, being rendered tense by their muscles, vibrate 
 as the air passes over them, producing sound. 
 
90 DIGESTION. 
 
 Singing : This only varies from speaking in the differing 
 tension and position of the vocal cords and the consequently 
 different sounds produced, 
 
 Sniffing: This results from rapidly repeated but incom- 
 plete nasal inspirations. 
 
 Snhltiny: This consists of a series of convulsive inspira- 
 tions, during which the glottis is more or less closed. 
 
 Laughing: This results from a series of short and rapid 
 expirations. 
 
 Yawning : This is an act of inspiration, more or less in- 
 voluntary, accompanied by a stretching of various facial 
 muscles. 
 
 Sucking: This is not really a respiratory act. It is caused 
 chiefly by the depressor muscle of the os hyoides, which, by 
 drawing down and back the floor of the mouth, produce a 
 partial vacuum in it. 
 
 DIGESTION. 
 
 By digestion we indicate the process by which food is in- 
 troduced into the body and prepared in such way that it 
 becomes suitable for absorption and tissue-nutrition. The 
 process may be divided logically and conveniently into masti- 
 cation, insalivation, deglutition, stomach digestion, intestinal 
 digestion, and defecation. 
 
 The mouth : The first portion of the alimentary tract is the 
 mouth. In this is received the food destined to support the 
 body. It is a cavity contained between the jaws and bounded 
 laterally by the cheeks. Its roof is formed by the hard and 
 soft palate, and its floor by the tongue. It is lined through- 
 out with mucous membrane, which is provided with numer- 
 ous mucous glands, and into it open the ducts of the salivary 
 glands. The tongue is both a prehensile organ and also the 
 chief seat of the sensation of taste. In this cavity occurs the 
 process of mastication. 
 
 Mastication : When a mass of food enters the mouth it is 
 caught by the tongue and moved to a position such that it 
 may he erushed and ground between the upper and lower 
 teeth. This process is favored by the action of the tongue 
 and of the cheeks, which not only crush the softer food- 
 
MASTICATION. 
 
 91 
 
 masses, but bring the less tractable portions repeatedly under 
 the action of the teeth. 
 
 There are during life two sets of teeth, temporary and per- 
 manent. In the first set are twenty teeth , and in the second 
 thirty-two. The permanent set are arranged as follows : 
 
 Upper. 
 
 Lower. 
 
 Molar. Bicuspid. Canine. Incisor. Canine. Bicuspid. Molar. 
 3214123 
 
 A tooth may be roughly described as consisting of a crown, 
 neck, and fang or fangs. The crown is the portion which pro- 
 jects above the margin of the gum ; the neck is the con- 
 stricted part below the crown which is covered by the free 
 
 FIG. 47. 
 
 Section of human molar tooth, magnified (Owen). 
 
 edges of the gum ; while the fang or root includes all below 
 this. On making a section of a tooth, for instance a molar 
 (Fig. 47), it will be seen that there is a cavity within the 
 
92 DIGESTION. 
 
 crown which extends into and through the fangs, opening by 
 a small aperture at their apices. This is the pu/jt-rdrify, and 
 contains in the living tooth the pulp. A portion of the tooth- 
 structure resembles bone, anatomically as well as chemically. 
 The crusta petrosa, or cement, is true bone, and covers in the 
 <!< ntine of the fang, while outside the dentine of the crown is 
 a very dense layer of enamel (of epithelial origin). 
 
 Muscles of mastication : Biting movements are produced by 
 the action of the temporal, masseter, and internal pterygoid 
 muscles, opposing the depressors of the jaw ; grinding move- 
 ments are produced by the alternate action of the external 
 pterygoids. The action is to some extent reflex, though largely 
 voluntary, and is controlled in the medulla through branches 
 of the cranial nerves, motor impulses coming through branches 
 of the trigeminus and (to the tongue) hypoglossal nerves. 
 
 Insalivation : The mixing and thorough moistening of the 
 food-mass with the saliva and mucus in the mouth during the 
 act of chewing are called insalivation. 
 
 Saliva: The saliva is derived almost entirely from the 
 parotid, submaxillary, and sublingual glands, and is secreted 
 most abundantly during the mastication of food. Of the 
 glands, the parotid secretes pure saliva containing ptyalin ; the 
 sublingual secretes only mucus ; while the submaxillary is a 
 mixed gland, secreting both saliva and mucus. The resultant 
 mixture of the secretions of these and the other glands of the 
 mucous membrane constitutes what is ordinarily known as 
 saliva, though really it should be called mixed saliva. It is a 
 transparent watery fluid, and is somewhat viscid from the 
 mixture of mucus. This viscidity allows it to retain air- 
 bubbles when churned by the action of the tongue and checks. 
 It has a specific gravity of about 1006 and an alkaline reac- 
 tion. Chemically, it is mostly (99J per cent.) water, holding 
 in solution very small amounts of salts and proteids, with the 
 addition of a ferment called ptyalin. The amount secreted 
 in twenty-four hours is estimated to be one to two quarts ; 
 most abundant secretion occurring during mastication. 
 
 It keeps the mouth in a moist condition, and so lubricates 
 the tongue in speaking and in chewing ; dissolves the soluble 
 portions of the food, and in this way brings them in contact 
 
 
NERVE-CONTROL OF SALIVARY SECRETION. 93 
 
 with the organs of taste ; mixes with the food, and forms a 
 soft and slippery bolus suitable for swallowing. Saliva from 
 the front of the mouth, containing more water, softens the 
 bolus, while the tonsillar and pharyngeal secretions, being 
 mucous, coat it with a slippery surface. The saliva has a 
 special digestive function by the action of its ferment, ptyalin. 
 
 Ptyalin : Ptyalin is a ferment (a non-nitrogenous body hav- 
 ing an uncertain chemical composition), with the special prop- 
 erty of converting cooked starch into maltose. While the fer- 
 ment itself cannot be isolated and analyzed, a glycerin solu- 
 tion may be obtained from the parotid and submaxillary glands, 
 which have been dehydrated by alcohol. This ferment does not 
 act upon any other body than starch. The action of the ferment 
 in changing starch to sugar is known as an amylolytic action, 
 and such a ferment is called an amylolytic ferment. The 
 kind of sugar resulting from the action of ptyalin is maltose. 
 
 Ptyalin works most actively at a temperature of 40 C. and 
 in a neutral solution. Its action is suspended in an acid solu- 
 tion, but continues in a slightly alkaline medium. At C. 
 its action is suspended, and if raised to 65 C. is destroyed. 
 Most of the ptyalin (in man) is found in the saliva secreted 
 by the parotid glands. The sublingual glands secrete very 
 little ptyalin (if any), the submaxillary glands being midway 
 between the other two in the amount of ptyalin formed. 
 
 The salivary glands do not become active until the subject 
 is from four to six months old ; hence the reason for avoiding 
 starchy food for young infants. 
 
 Nerve-control of salivary secretion : Saliva is secreted more 
 abundantly upon the application of a stimulus. It is there- 
 fore increased by reflex nerve-force. The stimuli may be 
 mechanical or chemical or mental ; thus the flow of saliva is 
 increased by taking food into the mouth or by irritating the 
 inside of the mouth by scratching or burning, or by looking 
 at or smelling or even thinking about food. 
 
 In the submaxillary gland the chorda tympani nerve is said 
 to have a double function to increase the vascularity of the 
 gland by one portion of its fibres, and to excite the secreting 
 function by another set of fibres, the sympathetic nerves of 
 the gland acting as the vaso-constrictors. 
 
94 DIGESTION. 
 
 In the parotid the vasodilator impulse comes also from the 
 facial nerve through the fifth by the communication of the 
 lesser petrosal nerve. The vaso-constrictor impulse comes 
 from the sympathetic. 
 
 There is found a medullary centre which controls this func- 
 tion. 
 
 Deglutition: Deglutition, or swallowing, is the process by 
 which we convey food from the mouth to the stomach, and 
 may be divided for the purpose of analysis into three actions : 
 1st. The food after mastication is pushed by the tongue 
 against the palate, and so forced on toward the fauces. (The 
 importance of the tongue should be remembered by the sur- 
 geon when operating on it. Enough of the base must bo left 
 to press against the palate, otherwise deglutition will become 
 very difficult or impossible.) 2d. As soon as the bolus enters 
 the pharynx it is pushed on by the tongue and by the con- 
 traction of the pillars of the fauces and the constrictors of 
 the pharynx toward the cesophageal opening. The pharyngeal 
 vault is guarded from invasion by solid or liquid food by the 
 valve-action of the soft palate, while the opening of the 
 glottis is protected by the simultaneous intrinsic muscular 
 closure of the rima glottidis and by the partial covering of 
 the epiglottis. When the muscles of the fauces and tongue 
 push on the food-mass, they also draw up the larynx and 
 dilate the resophageal opening. 3d. The oesophagus grasps 
 the food, and a peristaltic wave-series carries it rapidly on to 
 the cardiac opening of the stomach. The time involved in 
 the whole act of deglutition is about six seconds. The be- 
 ginning (1st) of the act of swallowing is voluntary, the re- 
 mainder reflex, and is governed by centres in the medulla 
 oblongata acting through the cranial nerves which supply 
 the parts. The trigeminus, glosso-pharyngeus, and vagus by 
 their sensory and motor functions act both in the capacity of 
 afferent and efferent communication with the medullary centre. 
 
 The Stomach. 
 
 Structure: The stomach (Fig. 48) is an organ which re- 
 in structure the rest of the intestinal tract; it is 
 
STRUCTURE. 
 FIG. 48. 
 
 95 
 
 Human alimentary canal, n, oesophagus ; b, stomach ; c, cardiac orifice ; d, pylorus ; 
 e, small intestine ;/, biliary duct; <?, pancreatic duct; h, ascending colon; i, 
 transverse colon ; j, descending colon ; k, rectum, 
 
96 DIGESTION. 
 
 hollow, having a peritoneal covering and a mucous membrane 
 lining, with a muscular layer between. It is in this mucous 
 membrane that the special function of the stomach lies, for 
 here are found glands which secrete the gastric juice. The 
 active peristaltic motion churns the food about after degluti- 
 tion, and exposes it thoroughly to the action of the digestive 
 agents. The function of the stomach is the digestion of ]>r<>- 
 teids. When distended it measures about fifteen inches from 
 end to end, and about five inches antero-posteriorly. 
 
 Glands of the stomach : If one looks closely at the mucous 
 surface of the stomach, it is seen to present a sort of reticu- 
 lated (Fig. 49) appearance, the meshes being larger at the 
 
 FIG. 49. 
 
 Free surface of the gastric mucous membrane, viewed from above, from pig's 
 stomach ; cardiac portion ; moderately magnified. 
 
 pyloric than at the cardiac end of the stomach. It is in the 
 interstices of this mesh that the glands open. The openings 
 are smaller at the cardiac than at the pyloric end, and the 
 character of the glands changes: we therefore speak of \\\<> 
 varieties of gastric glands (1) peptic ; (2) pyloric. 
 
 (1) The peptic glands are arranged in groups throughout 
 the stomach, but not so abundantly at the pyloric end. They 
 often consist of a simple tube dipping into the surface and 
 lined with columnar epithelium (Fig. 50), but they may be 
 
GASTRIC JUICE. 
 
 97 
 
 branched^, e., several glands may empty into a common 
 duct. The columnar epithe- 
 lium in the deeper portion Fro. 50. 
 of the gland contains large, 
 almost globular, cells, which 
 are known as peptic cells. 
 
 (2) The pyloric glands, or 
 mucous glands, like the peptic, 
 may be simple or compound. 
 The ducts are larger, and the 
 large cells are wanting (Fig. 
 51). During digestion the 
 cells of both varieties of 
 glands become swollen, and 
 in them are found granules 
 which are supposed to be pep- 
 sin, or that from which pepsin 
 is formed. 
 
 Gastric juice : When the 
 stomach is not at work it con- 
 tains no gastric juice, but is 
 bathed in an alkaline mucus. 
 As soon as food enters the 
 organ, however, it immediately 
 begins to secrete considerable 
 
 nnantitios nf nn 'irirl fliiirl Compound gastric follicle, from the car- 
 
 1Cl > diac Dortion of the human stomach. 
 
 which soaks into and mingles 
 with the food. The cele- 
 brated case of Alexis St. Mar- 
 tin, who had a gunshot-wound resulting in gastric fistula, 
 enabled Beaumont, surgeon U. S. A., to investigate accu- 
 rately its composition. It is a limpid, colorless fluid of 
 specific gravity 10011010 and acid reaction. It contains 
 about \ per cent, solid matter. Its composition is nearly 
 
 Water 99.50 
 
 Pepsin .25 
 
 Hydrochloric acid .05 
 
 Salts (alkaline chlorides and phosphates) .20 
 
 7-Phys. 100.00 
 
 diac portion of the human stomach. 
 1, excretory tubes leading to the sur- 
 face ; 2, tubular follicles containing 
 spheroidal cells (Kolliker). 
 
98 
 
 DIGESTION. 
 
 This composition is not constant, as the proportions vary 
 considerably, HC1, for example, being present much more 
 abundantly in some cases. 
 
 Secretion of gastric juice: The stomach secretes about 
 fifteen pints of gastric juice per diem. 
 
 The hydrochloric acid is probably secreted by the cubical 
 parietal cells of the peptic glands. Very little seems to be 
 formed by the pyloric glands. 
 
 FIG. 51. 
 
 Tubular follicles, from pyloric portion of pig's stomach, showing their csecal ex- 
 tremities and epithelial lining; at a is the torn end of a follicle, showing its 
 cavity more highly magnified. 
 
 The pepsin comes from the globular cells in the peptic 
 glands. These cells are supposed to form a subst:mr<- 
 called pepsinogen, from which pepsin is derived. Pepsin is 
 derived for commercial or for experimental purposes from 
 fresh stomachs by scraping the surface and dissolving out the 
 ferment with cold water, or by mincing the mucous mem- 
 brane and extracting the ferment with glycerin after dehydrat- 
 ing with alcohol. 
 
 Functions of the gastric juice : The principal function of 
 the gastric juice is the transforming of proteids into peptones. 
 
CHARACTERISTICS OF PEPTONES. 99 
 
 This action depends upon the presence of both pepsin and 
 acid. The first change which occurs is the formation of acid 
 albumin, but as the action of the ferment continues the acid 
 albumin is transformed to peptone. The presence of acid al- 
 bumin is demonstrated by the addition of an alkali, which 
 precipitates it. 
 
 The action of the pepsin in converting proteids to peptones 
 is called a proteolytic action, and chemically its action is to 
 cause a hydration of the proteid molecules. 
 
 Milk is curdled in the stomach by a ferment, aside from 
 pepsin, which is derived from t the gastric juice. This action 
 takes place in the absence of hydrochloric acid. Rennet (de- 
 rived from the fourth stomach of calves) is used for this pur- 
 pose in cheese manufacture. 
 
 Fats are unaffected, except that the albuminous capsules 
 of fat-cells in adipose tissues are digested and the oil set free 
 in globules. 
 
 Carbohydrates are unaffected. 
 
 In conclusion, therefore, it can be said that gastric diges- 
 tion is of a preparatory character, fitting the food for further 
 digestion in the intestines. Not only the carbohydrates and 
 fats pass the stomach practically unchanged, but part of the 
 proteids, the hemipeptones, are not completely digested. 
 That it is not indispensable is proven by the fact that re- 
 cently the entire stomach was removed from a woman, yet 
 she showed no ill effects, but lived for a year or more, and 
 finally died from another cause. 
 
 Characteristics of peptones: (1) They are diffusible i. e., 
 have the property of osmosis, or passing through an animal 
 membrane. This is of great importance in digestion, for if 
 this property were absent no animal food could be absorbed 
 from the intestines. (2) They are very freely soluble in 
 water and neutral solutions. (3) They do not respond to the 
 chemical tests for other proteid substances. They are not 
 precipitated by heat and the mineral acids, but are precipi- 
 tated by tannic and picric acids and by the bichloride of 
 mercury. 
 
 Muscular action of the stomach : The stomach is elastic, 
 and is supplied with circular and longitudinal muscles in its 
 
100 DIGESTION. 
 
 middle coat. These muscular fibres are capable of producing 
 peristaltic movements of the organ, which turn the food over 
 and over during the process of digestion. This elastic pouch 
 is closed at each end by strong, sphincter-like, circular bands 
 of muscles at the cardiac and pyloric openings, and until the 
 stomach digestion is well advanced none of the contents 
 escapes; but as the peptone-making advances the pyloric 
 opening permits the escape of the digested food, and this is 
 aided by strong peristaltic efforts on the part of the stomach 
 at its pyloric end. Toward the end of digestion the pylorus 
 permits the escape of undigested as well as of digested mat- 
 ter. The circulation of the stomach-contents is circumfer- 
 entially toward the pylorus, but centrally toward the cardiac 
 opening. 
 
 The digested food as it leaves the stomach is called 
 chyme. 
 
 Time required for digestion : The time varies with the kind 
 and amount of food from one to five or six hours. Digestion 
 is favored by rest of the stomach before eating, by gentle ex- 
 ercise of the mind or body, by an undisturbed mental condi- 
 tion, and by a healthy condition of the body. 
 
 Conditions favoring gastric digestion : The temperature of 
 the body is most favorable, and the presence of acid prefer- 
 ably HC1 is essential. For the best results the percentage 
 of HC1 should be about -^th of 1 percent. Excess of acid, 
 or neutralization, will stop the process. The movements of 
 the stomach assist digestion by thoroughly mixing the food 
 and the gastric juice. Digestive secretion does not continue 
 except during the presence of food. Also the removal of 
 completed products assists in the conversion of the re- 
 mainder. 
 
 Capacity of the stomach : About a quart in the adult, but 
 its muscular walls enable it to contract so as to fit its con- 
 tents if much or little. When empty the stomach is tightly 
 contracted. 
 
 Nervous mechanism of gastric digestion: The pncumo-as- 
 trie and sympathetic (splanchnic from the solar plexus) are 
 the nerves which supply the stomach, and besides then- there 
 lerous ganglia in the stomach-walls. The ordinary 
 
INTESTINAL DIGESTION. 101 
 
 motion-stimulus of the organ lies in the intrinsic ganglia. 
 Irritation of the pneumogastric nerve causes contraction ; its 
 division, cessation of peristalsis. But, further than this, the 
 vagus has control to a considerable degree over secretion in 
 the stomach. 
 
 Digestion of the stomach after death : When death occurs 
 at a time when the stomach contains food and gastric diges- 
 tion is going on the walls of the stomach are often partially 
 digested, even to such an extent that a perforation occurs. 
 This condition is often found in post-mortems on the human 
 body. Many reasons have been brought forward as to why 
 this does not occur during life, but no entirely satisfactory 
 theory has yet been propounded. Some have thought that- 
 gastric ulcers were merely an example of localized self-di- 
 gestion. 
 
 Vomiting: The regurgitation of food from the stomach 
 through the cardiac orifice, and thence through the mouth, 
 may occur when the cardiac opening is free and the pylorus 
 is closed. This is usually a reflex act, and is performed by 
 the contraction of the stomach, aided by the pressure of the 
 abdominal muscles opposing the fixed diaphragm. It may 
 be described as a reversed peristalsis. The stimuli which ex- 
 cite the reflex may be either local in the stomach or periphe- 
 ral. Violent irritation of the gastric mucous membrane will 
 excite it; also mental impulses, from ocular, auditory, or 
 olfactory sources; injury or irritation of the testis, ovary, 
 kidney, etc.; unusual motion, as swinging ; certain diseases ; 
 and effort of will in some is sufficient. There is a vomiting- 
 centre in the medulla acting through the pneumogastric 
 nerve. 
 
 Absorption from the stomach: Although the stomach is not 
 designed as an organ of absorption, nevertheless probably 
 some water and peptones are absorbed by the capillaries of 
 the stomach-wall. 
 
 Small Intestine. 
 
 Intestinal ( digestion : By the peristaltic action of the gut 
 the food is carried on through the length of the organ, but its 
 
102 DIGESTION. 
 
 progress is more or less impeded by the vahruke conniventes, 
 which are folds of the mucous membrane extending trans- 
 versely across the intestine at right angles to its long axis, 
 and occupying usually one-third or one-half of the circum- 
 ference, but sometimes extending all the way around. They 
 commence close to the stomach, and are well developed in the 
 upper two-fifths of the small intestine. They then gradually 
 diminish in size and number, and finally disappear at the 
 commencement of the lower fourth. These folds of the mu- 
 cous coat not only retard the too rapid advance of food, but 
 cause it to be thoroughly exposed to the action of the diges- 
 tive fluids (Fig. 52). Soon after passing the pylorus food 
 
 FIG. 52. 
 
 Portion of small intestine laid open to show valvulse conniventes (Brinton). 
 
 comes in contact with the alkaline secretions of the small in- 
 testine and of the liver and pancreas. In the small intestine 
 the food is still further prepared for absorption, and from this 
 part of the alimentary tract the digested food is taken up for 
 body-nutrition. The peristaltic action is controlled by Un- 
 sympathetic system of nerves. Auerbach's plexus lies be- 
 tween the circular and longitudinal muscular coats. It is 
 also known as the plexus mesentericus. The blood-supply is 
 also controlled by the sympathetic system. Meissner's plexus 
 lies beneath the mucous coat, and is regarded as the source 
 of control of the blood-supply and of the function of absorp- 
 tion. 
 
 Glands of the small intestine: There are three types of 
 irland- peculiar to the small intestine: (1) Lieberk film's, 
 (2) Brunner's, and (3) Fever's glands. 
 
GLANDS OF THE SMALL INTESTINE. 
 
 103 
 
 FIG. 
 
 Glands of Lieberkiihn : These glands (or follicles or crypts) 
 are thickly distributed over the whole surface of the small 
 and large intestine, being 
 larger in the large intes- 
 tine. They are simply tu- 
 bular depressions in the 
 mucous membrane, lined 
 with columnar epithelium, 
 which contains occasional 
 large " goblet "-cells. 
 
 Brunner's glands are 
 found in the duodenum 
 alone, and are situated in 
 the submucous tissue. 
 They resemble the pylo- 
 ric glands of the stomach, 
 and, like them, are usually 
 compound glands. The 
 duct of the gland passes up through the mucous membrane 
 and opens at its surface (Fig. 53). 
 
 Peyer's glands: These are of two varieties (1) solitary 
 and (2) agminate. 
 
 (1) The solitary glands consist of a rounded mass of whit- 
 ish adenoid tissue about ^-th to y^th in. in diameter, situated in 
 the submucous tissue, but often projecting to the surface of 
 the intestine. Each lymphoid mass is surrounded by Lieber- 
 kuhn's follicles (Fig. 54). 
 
 FIG. 54. 
 
 A vertical section of the dvwdenum highly 
 magnified. 1, a fold-like villas; 2, epithe- 
 lium of the mucous membrane ; 3, orifices 
 of the tubular glands ; 4-5, orifice of a duo- 
 denal gland ; 6-7, two vesicles of the latter, 
 more highly magnified, exhibiting the epi- 
 thelial cells lining their internal surface 
 (Leidy). 
 
 Portions of the mucous membrane from the ileum. moderately magnified, exhibit- 
 ing the villi on its free surface, and between them the orifices of the tubular 
 glands. 1, portion of an agminated gland ; 2, a solitary gland ; 3, fibrous tissue 
 (Leidy). 
 
104 DIGESTION. 
 
 (2) The agminate glands (Peyer's patches) consist of 
 groups of these adenoid masses, making " patches " in the 
 mucous membrane \ to 3 in. long and about \ in. wide. 
 
 Intestinal juice: The intestinal juice, or succus cuff-rim*, 
 is the secretion of the intestinal glands. This secretion is 
 yellow in color and is markedly alkaline. Its effect upon diges- 
 tion is not fully understood, but it probably has some effect 
 upon saccharose. However, its chief function seems to be to 
 supply loss of fluid L e., to take the place of that which is 
 absorbed as digestion progresses. At any rate, the contents 
 of the small intestine as they enter the colon are about as 
 fluid as when they leave the stomach. 
 
 Other digestive secretions: The most important digestive 
 fluids that act upon the food while in the intestines are not 
 derived from the intestines, but are poured into the small in- 
 testine near its beginning. These secretions are two in num- 
 ber, and are formed respectively by the pancreas and the 
 liver. 
 
 The Pancreas. 
 
 The pancreas is an organ lying in the upper part of the 
 abdomen in contact with the duodenum : in length it is about 
 six inches, and is thicker at its right or duodenal end. It is 
 a conglomerate gland, resembling in structure the salivary 
 glands. During digestion it is active, but is quiescent iu the 
 intervals. Its secretion, pancreatic fluid, is discharged into 
 a main duct which receives branches from the lobes of the 
 gland, and is emptied with the bile through a common open- 
 ing about two or three inches beyond the pylorus. During 
 digestion the cells of the organ become granular, and the 
 granules are thought to consist of the substance from which 
 the ferments of the pancreas are derived, -i/ntoyen, rather than 
 of the ferments themselves. 
 
 Pancreatic juice : The pancreatic juice is a clear, colorless 
 fluid, having an alkaline reaction and a notably viscid con- 
 sistency. It coagulates with heat, and is made quite gelat- 
 inous by cold. Specific gravity, 1015. Its composition 
 varies. 
 
DIFFERENCE IN ACTION OF TRYPSIN AND PEPSIN. 105 
 
 Composition of pancreatic juice : 
 
 Water 90 
 
 Organic matter: 
 
 Ferments, ") 
 
 Serum-albumin, I 
 
 Alkali-albumin, ( 
 
 Fats, soaps, etc.,J 
 
 Inorganic salts (chiefly sodium chloride) . . 1 
 
 100 
 
 Pancreatic ferments: (1) Trypsin, a peptone-forming (pro- 
 teolytic) ferment, which continues the digestion of proteids 
 begun in the stomach. It forms a peptone which resembles 
 the stomach peptone in its reactions. This ferment, unlike 
 pepsin, only acts in an alkaline medium. It acts less vigor- 
 ously upon gelatins and other nitrogenous bodies. 
 
 (2) Amylopsin, a starch-changing (amylolytic) ferment, by 
 which starch is converted to maltose, as by the ptyalin in the 
 saliva. 
 
 (3) Steapsin, a ferment by which fats are broken up from 
 the large globules and emulsified or saponified in alkaline 
 media. It is claimed by some that this is not a ferment- 
 action, but is the result of the action of the alkaline intestinal 
 contents upon the fat. 
 
 Of these processes the emulsifi,cation, or breaking the fat- 
 globules into minute particles, is by far the more important, 
 as it allows this form of food to be absorbed from the gut. 
 Milk is an excellent example of a natural emulsion. 
 
 Sapon i fixation (or soap-making) results from the fatty acid 
 combining with an alkali, forming the corresponding salt and 
 glycerin e. g. : 
 
 Stearin 4- Potassium hydrate = Potassium stearate + Glycerin. 
 
 Difference in action of trypsin and pepsin : These two fer- 
 ments act on proteids in different ways. Under the influence 
 of pepsin the proteid first swells, then gradually becomes 
 softer, changes in color, and breaks down into a grumous 
 
106 DIGESTION. 
 
 mass. When exposed to the action of trypsin, however, pro- 
 teids do not swell up, but are eroded or oaten away, seeming 
 at times as though they were full of worm-holes. lYp.Mu 
 cmi verts proteids iiitohemi-albumose and anti-albumose, which 
 it later converts into hemipeptone and antipeptone. Tryp- 
 sin splits the proteids at once into deutero-albumose, and alni 
 carries the process a step further than pepsin, splitting the 
 hemipeptones into leucin and ty rosin. 
 
 Function of pancreatic juice : It is most active during diges- 
 tion, and is peculiar in having an effect upon all forms of food 
 which require preparation for absorption upon proteids, 
 starches, and fats. 
 
 Conditions favoring pancreatic digestion : Moderate heat 
 (100 F.), an alkaline medium, and the removal of the prod- 
 ucts of the ferment-action as soon as the change is com- 
 pleted. 
 
 The Liver. 
 
 The liver is the largest gland in the body, and is situated 
 in the upper part of the abdominal cavity. It secretes a fluid 
 known as the Itilc or gall, which is stored in a bladder lying 
 attached to its lower surface. The functions of the organ 
 are : (1) secretion, (2) excretion, (3) glycogenic function, and 
 (4) elaboration of urea. 
 
 Secretion of the liver: The secretion of the liver is stored 
 in the f/df/-M<i<t<1<'r until its flow is excited by the acid dis- 
 charge of the stomach-contents into the duodenum. It is an 
 active secretion, and not a passive filtration from the blood, 
 for if a manometer-tube be fastened in the duct it will indi- 
 cate a pressure greater than that of the blood. While the 
 gall-bladder acts as a storage reservoir, the bile does not 
 -arily enter it, but may discharge directly from the 
 hepatic into the common duct. The opening of the common 
 duct into the duodenum is guarded bv a sphincter-like arrange- 
 ment of the muscular fibres in the gut-wall. The gall-blad- 
 der and the nail-duet are provided with unstriped muscular 
 fibres, so that they may empty themselves. Inspiration and 
 expiration bring alternating pressure upon the gall-bladder, 
 ami aid in emptying it. 
 
BILE-SALTS. 107 
 
 Amount of bile : The quantity varies with the amount of 
 food taken, but is estimated to vary between twenty and 
 forty ounces, or, approximately, from a pint to a quart, in 
 twenty-four hours. 
 
 Character of the bile : It is a viscid, almost ropy fluid, of a 
 yellow or red or greenish color and bitter taste. It is faintly 
 alkaline or neutral in reaction, and has a specific gravity of 
 about 1020. Its composition is, approximately : 
 
 Water .86 
 
 ( Bile salts, 9 ^ 
 
 Organic matter, < Fat and cholesterin, 1 V . 13 
 ( Mucus and pigments, 3 j 
 
 Inorganic salts 1 
 
 Too 
 
 Bile-salts : The bile-salts are sodium glycocholate (Fig. 
 55) and sodium taurocholate. They may be isolated in crys- 
 
 FIG. 55. 
 
 Sodium glycocholate from ox-bile, after two days' crystallization. At the lower 
 part of the figure the crystals are melting into drops, from the evaporation of 
 the ether and absorption of moisture (Dalton). 
 
 talline form from bile, and are present in human bile in about 
 equal proportions. They are soluble and very deliquescent 
 
108 
 
 DIGESTION. 
 
 colorless crystals, which have the bitter taste of bile. 7Vx/ 
 by Pettenkofer's method: add to a solution of bile a small 
 amount of a solution of cane-sugar. On treating this solu- 
 tion with pure sulphuric acid drop by drop there is first a 
 precipitation of a turbid sediment (cholic acid) ; this is cleared 
 by a further addition of sulphuric acid, and the solution 
 a nines a bright cherry color, changing to violet, and, if much 
 bile be present, to deep purple. 
 
 Bile-pigments : The bile-pigments are biliverdin and bili- 
 rubin. Both pigments are found in human l>ile, but the 
 former is characteristic of the bile of herbivora, and the lat- 
 ter, bilirubin, of the bile of carnivora. The pigments are 
 
 FIG. 56. 
 
 Cholesterin from the contents of an encysted tumor. 
 
 orygtallizable, and are insoluble in water. The crystals have 
 the "Teen ; in <l red colors of the pigments. Qmdin's hilc //>/.- 
 add fuming nitric (nitroso-nitric) acid, and there results a 
 play of colors which is best seen when the bile solution is in 
 thin layer on a white plate. The presence of the bile-pig- 
 ments is shown also by absorption-bands in the spectrum. 
 Bilirubin is derived from haemoglobin, and biliverdin from 
 the bilirubin, as they are chemically closely allied. 
 
GLYCOGENIC FUNCTION OF THE LIVER. 109 
 
 In considering the death of the red blood-corpuscle, it has 
 been already stated in the chapter on the Blood that the haemo- 
 globin from the disintegrated red corpuscle is eliminated by 
 the liver. This is the haemoglobin that makes the bile- 
 pigment. 
 
 Cholesterin is a crystallizable, insoluble substance which 
 belongs to the alcohol group in chemical composition. Best 
 recognized by microscopic appearance of the crystals (Fig. 
 56), though it may be tested chemically by the addition of 
 sulphuric acid, which gives a red reaction. 
 
 Use of bile in digestion: (1) The alkaline reaction of the 
 bile aids the pancreatic and checks the pepsin digestion ; it 
 aids in the emulsion of the fats, and is probably very active 
 in this process. (2) It moistens the mucous membrane and 
 favors the absorption of digested food. (3) It acts as a 
 natural purgative and as a natural antiseptic, and in this 
 way is very essential to the proper performance of the diges- 
 tive process. As a purgative bile acts by stimulating peri- 
 stalsis. 
 
 Excretion of the liver : The bile for the most part, in nor- 
 mal conditions, is a sort of circulating fluid : it is secreted by 
 the liver, poured into the intestines, and reabsorbed from 
 them, to be returned through the portal vein to the liver for 
 recirculation. There is, however, a small proportion of biliary 
 matter, about one-sixteenth, which is not absorbed, and this 
 consists chiefly of the pigments of the bile. The salts are 
 nearly all reabsorbed in the assimilation. Further than this, 
 the liver is found, so to speak, to filter materials which would 
 be poisonous if circulating in the general system, and either 
 to reject them at once, or to store them up and return them 
 slowly back to the intestine. The excrementitious material 
 from the liver is known as stercobilin. Stercorin is found in 
 the fa3ces, and is thought to be an excretion of the liver : it 
 closely resembles cholesterin, and is supposed to be a modifi- 
 cation of cholesterin by digestion. Whether or not the ster- 
 corin (cholesterin) is an excretion of the liver corresponding 
 to the urea of the kidney is somewhat uncertain. 
 
 Glycogenic function of *the liver : The liver normally forms 
 a substance resembling starch in its chemical composition. 
 
110 DIGESTION. 
 
 This is known as glycogen, and is formed from glucose taken 
 up by the portal circulation. Its chemical formula is that of 
 starch (C 6 H 10 O 5 ), and it is derived from glucose (C 6 H 12 O 6 ) by 
 dehydration, and is rapidly changed by diastatic ferments to 
 glucose. This process is known as the glycogenic function 
 of the liver : its use is the storage of a fund of carbohydrate 
 mail-rial (an "animal starch") to maintain a steady supply to 
 the system. 
 
 Elaboration of urea : This subject will be discussed under 
 the Urine. 
 
 Large Intestine. 
 
 Structure : While the villi and valvulse are absent, yet 
 throughout its whole extent there are found tubular and soli- 
 tary glands which closely resemble 
 FIG. 57. those of the small intestine. The 
 
 tubular glands, however, are more 
 numerous, longer, and more closely 
 set together (Fig. 57). 
 
 Digestion : The chyme which enters 
 the large intestine still continues 
 under the influence of the ferments, 
 and the process of digestion continues. 
 
 section of the mucous mem- The food ma 7 "ndergo acid fermon- 
 brane of the colon, i, free tation here, but there is no new diges- 
 
 surface exhibiting the onh- . . ~, 
 
 ces of the tubular elands; tive action. Inat the large intestine 
 m^Sr' 88 "^' 1 ' may have the power of acting upon 
 food is shown by the absorption of 
 fats, proteids, etc., which are taken in nutrient enemata. 
 
 Defecation : The expulsion of the refuse of digestion from 
 the intestine is partly a voluntary act, but more especially re- 
 flex. The voluntary act is the pressure of the abdominal 
 muscles upon the contained viscera, while the reflex is an in- 
 creased peristalsis in the sigmoid flexure and rectum and the 
 relaxation of the sphincter. The centre which governs this 
 act, so far as it is reflex, lies in the lumbar region of the 
 spinal cord. 
 
FACTORS FAVORING ABSORPTION. Ill 
 
 ABSORPTION. 
 
 Absorption is the process by which the digested food is 
 taken from the intestines and carried into the blood, whence 
 it is taken to nourish the cells. The same term is applied to 
 the removal of worn-out material from the tissues. Chyme is 
 the name given to food after digestion. By digestion, 
 the proteids, starches, arid fats, which were not dialyz- 
 able, have become peptones, sugars, and emulsified fat. 
 All these products of digestion are readily capable of di- 
 alysis, and therefore ready for absorption. The absorption 
 takes place through the bloodvessels and lymphatics of the 
 intestine. 
 
 By dialysis we mean the property of fluids which enables 
 them to pass through animal membranes osmosis. This 
 we have seen is possessed in a high degree by the ingredi- 
 ents of chyle. The reverse process may occur, and fluids 
 (serum) from the blood may similarly be drawn into the 
 intestinal canal, as is seen when the salines are used as purga- 
 tives. 
 
 Too much importance must not, however, be attached to 
 osmosis as accounting for the phenomena of absorption. 
 Under certain circumstances substances are absorbed inde- 
 pendently of this principle. For example, when tested ex- 
 perimentally outside the body, sugar is less diffusible than 
 sodium sulphate, yet it is absorbed more rapidly from the 
 intestine. Certain coloring-matters are not absorbed at 
 all, the cells appearing to exert some selective action. It 
 is also difficult to explain by osmosis the absorption of 
 emulsified fats. It is probable that the protoplasm of the 
 living cells on the walls of the intestine has some specific 
 action. 
 
 Sites of absorption : In the stomach and large intestine 
 the absorption is very much less than in the small intestine, 
 but there is reason to think that there is considerable ac- 
 tivity to absorption from the entire gut so long as digestion 
 continues. 
 
 Factors favoring absorption: (1) The valvulse conniventes 
 greatly increase the area of the intestinal surface, and by their 
 
112 
 
 ABSORPTION. 
 
 shelf-like formation delay the advance of chyme. (2) The 
 villi of the intestine not only increase the area, but are the 
 special organs of the function of absorption. (3) The con- 
 traction of the intestine upon its fluid contents also favors, 
 mechanically, the filtration of the contents through its walls. 
 Villi of the intestine: The villi are almost innumerable, 
 minute, teat-like projections from the surface of the wall of 
 the intestine. They are very numerous in the small intestine, 
 but none is found in the large gut. Each villus is covered by 
 
 an epithelial layer, and within, 
 FIG. 58. supported by areolar tissue, is a 
 
 delicate capillary network of 
 bloodvessels, a muscular layer 
 (muscularis mucosse), and a more 
 or less branched ending of a lac- 
 teal vessel (Figs. 58 and 59). 
 
 FIG. 59. 
 
 a 
 
 An intestinal villus. a, 
 layer of cylindrical epi- 
 thelium, with its exter- 
 nal transparent striated 
 portion ; hb. blood vr>sHs 
 enterlngftnd leaving the 
 villus ; c, lymphatic ves- 
 sels, occupying its cen- 
 tral axis (Leydig). 
 
 Patch of Peyer's plands, tVom the lower 
 part of the ileuin, showing villi (mag- 
 nified). 
 
 The ileo-Cffical valve slio\v> tlie abs<lu1<- alteration which is 
 apparent in the mucous membrane of the small as compared 
 with the large intestine. On the side toward the ileuin are 
 found villi in great numbers, while its ea-cal side shows none. 
 
DESTINATION OF ABSORBED FOOD. 
 
 113 
 
 FIG. 60. 
 
 The lacteals are similar to the lymph-capillaries found in 
 other parts of the body. 
 
 Changes in the products of digestion on being absorbed : The 
 proteids that have been eaten are changed by the digestive 
 fluids, as already explained, into 
 peptones. These peptones are 
 largely absorbed by the blood- 
 capillaries of the digestive tract. 
 In passing through the mucous 
 membrane of the intestine the 
 peptones are converted, in some 
 unexplained manner, into serum- 
 albumin. Hence we find that ab- 
 sorbed proteids exist in the blood 
 as serum-albumin. Unconverted 
 peptones would, if injected into 
 the blood, act as a poison. 
 
 The carbohydrates are con- 
 verted by digestion into maltose. 
 On being absorbed by the blood- 
 vessels maltose is converted into 
 dextrose. 
 
 The fats are highly emulsified 
 and saponified. They are ab- 
 sorbed by the lacteals. 
 
 Water and inorganic salts are 
 absorbed as such by the blood- 
 vessels of the intestinal villi. 
 
 Peptones and sugars then are 
 absorbed by the blood-capillaries 
 of the stomach and of the small 
 and large intestines, principally 
 of the small intestine. Fats are 
 absorbed only by the lacteals, hence only in the small intes- 
 tine ; water and inorganic salts, principally in the large and 
 small intestines. 
 
 Destination of absorbed food : The food absorbed by the 
 lacteals is collected from all the lymph-spaces in the villi and 
 about the glandular structure of the intestines, and is taken 
 
 8 Phys. 
 
 Lacteals and lymphatics during 
 digestion. 
 
114 ABSORPTION. 
 
 thence into the larger lacteals, whence it passes through the 
 mesenteric lymphatic glands and into the receptaculum chyli 
 of the thoracic duct (Fig. 60). Hence it passes on into the 
 blood-vascular system, which it joins at the root of the neck 
 at the union of the left internal jugular and subclavian 
 veins. 
 
 The food absorbed by the blood-capillaries is brought to the 
 liver by the portal veins. 
 
 On entering the liver the portal vein breaks up into capil- 
 laries, and thus the serum-albumin and dextrose are brought 
 under the direct influence of the liver-cells. 
 
 The liver-cells allow only a small part of the carbohydrates 
 (dextrose) to pass on and enter the general circulation. The 
 remainder of the dextrose is acted upon by a ferment in the 
 liver-cells, converting it into glycogen. The glycogen is then 
 stored up in the liver until such time as the body needs more 
 carbohydrates than the food eaten furnishes. When such 
 demand is made upon it the liver reconverts some of the 
 stored-up glycogen into dextrose and pours it into the general 
 circulation. 
 
 The scrum-albumin representing the proteid food-stuffs 
 passes through the liver and into the general circulation. 
 
 Ultimate use of absorbed food: The absorbed food has now 
 been followed into the general circulation. By the arteries 
 the food-products are carried all over the body, to be used in 
 building up the tissues. These same tissues ultimately, as 
 the result of their lifework, are oxidized, broken up into 
 carbon dioxide, water, and other wastes, to be finally elimi- 
 nated from the body. 
 
 Conditions favoring food-absorption : To be absorbed by the 
 bloodvessels or lacteals we must have substances in a Jlnid 
 .v/ff/r, and the more dilute in solution the more ready the ab- 
 sorption ; insoluble substances are not appreciably affected 
 by this process, nor are any dense solutions readily taken up. 
 The rapid removal of the absorbed matter and the rcm-iml of 
 fresh blood in the capillaries are of importance. Thus, if 
 the portal circulation is obstructed, so that the blood is cir- 
 culated slowly or the capillaries are tense from intravascular 
 pressure, absorption will be slow. 
 
PROCESSES OF SECRETION AND EXCRETION. 115 
 
 SECRETION. 
 
 Secretions are materials separated from the blood by the 
 cells to serve some further purpose in the animal economy. 
 These secretions, for the most part, consist of substances 
 which probably do not exist as such in the blood itself, but 
 require special cells for their formation ; for example, the 
 liver-cells for the formation of bile, the stomach-cells for the 
 formation of gastric juice, etc. The mucous and serous 
 membranes also act in this capacity as well as the glands. 
 Examples of secretions are found in milk, bile, gastric juice, 
 tears, etc. 
 
 Excretions are materials which are separated from the blood 
 by cell-activity and discharged from the body, being either 
 
 FIG. 61. 
 
 Follicles of Lieberkiihn, from small intestine of dog. 
 
 useless or harmful if retained e. g., urine, sweat. They con- 
 tain materials which exist in the blood in the same form, and 
 are merely abstracted from it. 
 
 Processes of secretion and excretion : Secretion and excretion 
 are carried on by means of the activity of the cells set aside 
 for that purpose. In most cases the cells are grouped in 
 organs which are known as glands. The serous fluids are the 
 
1 hi 
 
 SKCRKTrON 
 
 only notahle exception to lliis ml*-, the endolhelial cells secret 
 
 iiiii- without ilic intervention of complex anatomical 
 
 Structure of a secreting apparatus : The essentials of 
 secreting apparatus ;irc the primary or basement UK inl>r<tn< , a 
 simple Mild nearly le\l ureless si rue! lire ; cerlain x^/vw/ IT//X, 
 ami AAW/rxxr/x. Those essentials mai I" 1 continued in \:iri 
 oils \v:iys, hill :ill \ :irid ics ;ire divided inlo t//,ui<lx :ind IIKID- 
 
 Forms of secreting glands: (I) SimpU u6utM, or 
 
 t/fttmls, \vhieli are pits or depressions in epithelial surface- 
 lined with epithelial cells. The mucous surfaces furnish the 
 BIO i numerous examples of this form of ^land, follicles of 
 Liehcrkidm (Kit:. <!l). and Inhnlar (mucous) o-himU of ihe 
 slomach ; hut the skin, in the sweat glands, sho>\s a more 
 Complicated form of tnhnlar inland in that it is convoluted 
 and tortuous. 
 
 ("2) Compound tulmtnr <jfttints consist of a Inhnlar ^land 
 which suhdivides the main tnhnle, so as to have icveral 
 
 branching tnhules leading inlo 
 
 1 1<; 62. it. Often these hranehes 
 
 a^-ain snhdi\ ide so as to form 
 a TOUJ> of nllimale glandular 
 elements grouped ahoul the 
 main tulmle, which acts 
 duct. This form of inland is 
 found in kidncN . testlS. -nli 
 \arv and mammarx j-land-. 
 lirnnner's o-lands ( Ki^-. 
 and in maiix of ihe other ^lan 
 dnlar structures. 
 
 glands, in which 1 lie ^landnlar 
 structure is diviled inlo lol> 
 ulcs, or tifiin'. These "-hinds 
 in i\ he regarded as a relineinenl of the compound luhiilar 
 VarietV, and example^ are found in (he sali\ar\ -dand and in 
 the Mi-ihoiniaii follicles 
 
 Processes of secretion : ( 1 i P.y /*A//.v/V^/ procc e \ iz., Ultra 
 ti"ii and dialysis the cells are aide to separate from the 
 
 .( un,. o| Itiiiniii-r's 
 II.MII IMIIIIMM ml. vim,. 
 
v . vs u N N U7 
 
 . n(-. xxhu-h uuk Up 
 
 u-mW (hat (ho t\uw of dialysis may 
 
 uv> ami K tH>itsH|iioittlYft twt & 
 
 I 1 * . m^a^ain, i ho taot that tho oomlitmii 
 
 ot <lu I-KHH! as i- x .iml salim> iogfftdtatl makos 
 
 din i MU (ho jwnnanonoy uf tht> 
 
 ,i wmlil 
 
 I'vx .'At*mi\M/ iwnnvsst- ill,- vUs of glamls 
 
 -.nui MI iiu- hi.s-ii pltimt Mid tidd 
 u il i jmHHsss^ av jnvuli 
 
 in iiu- iniiuMii produdnf f laodi idivtiy) ptptlo^ tod \*\\\- 
 
 Dlsohrtrgo of soaottons : Tlu> Mvifiions max 
 
 tVMi ilu- i'l.iu.l-. M loon M ilu-x .uv' t,MMi-l. as iu tho 
 '1,1-. riu-x in.i\ IT lottg ^^aimnl in au 
 
 x-I,|>,-l (.Mm ui du- >,. - d ill---' -l.inJ u KOM M i'^ ^ 
 M>U ,sv.i i.Mi.il , ,-r in .1 fiilK ( lr\rl,.|u-,l furm in thoir 
 
 ;n :!. in.l- , -n,li .1- liir Li, lux m.l 1 , \\ hioh hdiUI^ ( 
 
 !,-(> small iu>Miu(-,. IMK inoinni^ 
 jini.Mitn \\ lirn itimukted 
 Oonditloiui ffiotUif flMidulMr Activity : (M) I f tin* Minono/ */' 
 
 A/MM/ MtwiHtf M^H//A (I f/All(/ IT i n, I r.i- r, I , (li,-ir will |>o |Q. 
 I MX in Crf & lun, u, MI . .iii,l, , ,MIX, i , U , .i-. .1 ml,-. 
 
 during functional iotiv)^j it"- |knd \\iii Inoi^Me in vas- 
 
 rul.MKv I iu- - 1, .in. i, li. I,M r\.iin|.l t -, ilnrin^ tli^vstiou || 
 
 .jinh- .MI- -,.i ; -, ,1, IMK \\ lirn ulh- i-. ii|.plir,l \\ ill. inn. li 1, 
 
 blood . ' i i'x Hi.- eoloi l--|iMiinu dnnn^its \wv\w\ uf 
 
 'M 
 
 (A) An luwwtw m M^ md^id/ i^w*i wA*VA M*^ //Aim/ uo^ 
 
 inuul.Kr ili,- ; .|.iM.l (o gmitvr .'il-Mt .nui InoTMMI (l>^ }UH>- 
 
 dyotion frf ii- -i.n.,1 rim-.. di- uoounl oi mva is inoh^a^nl 
 
 l\ -Ml Ml.1,.1 ,- ,.| Ill(l,.,' t -Il,.ll U.I (,-, .1-. hx |XtfOlM| Of ^ I" 
 
 ret -I nUrogenoui matter ". d.,- bl^ad, as h t v a f\ll mt] 
 oi animal UwL 
 
 I -<VMV iit//r*niv upon 
 
 (I. Ml I i U ll.llK |Vll,-\ III , ll.ll .1, 1,1 . .111,1 11, ,,ll,-|lll\ I . 
 
 .1, (IX .' llir,MI:'ll ill,- \ .1 ,. IIU.l.M U, I \ , i S\ ll.-ll ill.' : .;ll\ 11 V 
 
 .m.l -M in, , , retlon ", M,, i,-., ,-,i i.\ HI,- - n-i.i ... -.in, -ii ,.i' 
 
 fnl. .1 X\fll .1 |.\ l( .1, (ll.ll ;l,lllllll|-.lr : lll,MI. I'll, I.' I .ll -,. .1 
 
118 SECRETION. 
 
 so-called trophic influence of the nervous system, which di- 
 rectly affects the secreting power of a gland : this is especially 
 well shown in the case of the chorda tympani in its relation 
 to the secretion of the snbniaxillary gland. 
 
 Correlation of secretions : There often seems to be a relation 
 in the amount of one secretion to that of some of the others ; 
 thus in a diseased condition of the intestinal mucous mem- 
 brane, with increased secretion, there will often be an in- 
 crease of the bile secreted, and perhaps a diminution of 
 other secretions, as salivary or urinary. And, again, unusual 
 perspiration is followed by decrease in the activity of the 
 kidneys. 
 
 Having studied the general subject of secretion, the matter 
 will be best pursued if we study the individual secreting and 
 excreting glands. 
 
 Serous Secretions. 
 
 The serous secretions are the products of the activity of the 
 cells of the pleura, peritoneum, pia mater, and tunica vaginalis ; 
 also of the synovial membrane of joints, tendon-sheaths, etc. 
 The secretion of the synovial membranes is far more glairy 
 and viscid than is that of the true serous membrane. 
 
 The purpose of serous secretion is to lubricate surfaces in 
 which friction is undesirable. The serous membranes are 
 characterized by having a single layer of polygonal endothe- 
 lial cells covering their free surface. The fluid secreted ap- 
 pears to be identical with very dilute liquor sanguinis It is 
 pale yellow or straw color, alkaline, slightly viscid, and, be- 
 cause it contains albumin, is coagulable by heat. 
 
 Mucous Secretions. 
 
 Mucus is secreted by the mucus-cells of glands opening 
 onto mucous membrane. It is a more or less viscid, semi- 
 tran-parent, alkaline fluid of high specific gravity, contain- 
 in- epithelium and leukocytes. It consists of a large amount 
 of mucinj a little albumin, water, salts, and traces of fats and 
 
COMPOSITION OF MILK. 119 
 
 extractives. The object of the secreted mucus is to keep 
 moist and soft the delicate cells of the mucous membrane ; also 
 at the same time the mucus acts as a lubricant. Mucous tracts 
 which are so protected are the digestive, respiratory, and 
 genito-urinary. 
 
 Mammary Glands. 
 
 The mammary glands are large structures which are made up 
 of several distinct lobes. Each lobe has its duct, which leads 
 to the nipple, and there are about twenty such lobes and ducts. 
 The lobes are subdivided, and the small lobes, or lobules, 
 are made up of the terminal tubules of the duct, which lie in 
 a mesh of fibrous areolar tissue containing considerable fat in 
 its reticulum. The ultimate divisions (alveoli) of the termi- 
 nal tubules are lined with columnar epithelial cells, as are 
 the ducts and their branches, but the epithelium of the ducts 
 becomes flat (squamous) near the nipple. The main ducts 
 (lactiferous ducts) are sacculated, and during lactation the 
 secretion of the alveoli collects in them, and is drawn from 
 them through their small orifices in the nipple. The flow of 
 milk is also aided by the presence of a small amount of un- 
 striped muscular fibre in the wall of the ducts. 
 
 The mammae are abundantly supplied with bloodvessels, 
 lymphatics, and nerves, and during pregnancy and lactation 
 the vessels, as well as the gland, undergo considerable increase 
 in size. 
 
 Milk: The secretion of the mammary gland is a bluish- 
 white fluid. It is opaque, and this opacity is caused by the 
 presence of minute fat-globules which are held suspended 
 an emulsion. Besides the fat-globules the microscope shows 
 in milk from a newly active gland certain albuminous bodies 
 which are known as colostrum-corpuscles. They are proba- 
 bly cells from the gland which are undergoing fatty degene- 
 ration. Milk is alkaline in reaction, and has a specific gravity 
 of about 1030. 
 
 Composition of milk : The ingredients of milk are water, 
 containing in suspension fats and in solution casein, serum- 
 albumin, milk-sugar, and salts. Human milk differs from 
 
120 SECRETION. 
 
 cows' milk in containing less proteids and fats and more 
 sugar: 
 
 Human milk. Cows' milk. 
 
 Water 890 858 
 
 Proteids 35 68 
 
 Fats 25 38 
 
 Sugar 48 30 
 
 Salts _2 _6 
 
 1000 1000 
 
 Cream : The fat-globules rise to the top if milk is allowed 
 to stand, and are called cream. By agitating or " churning " 
 the cream the albuminous envelopes of the fat-globules arc 
 broken, and they coalesce to form a fat mass known as 
 butter. 
 
 Secretion of milk: The activity of the mammary glands 
 does not begin until the individual has become pregnant in 
 fact, the secreting alveoli are not fully formed until the first 
 pregnancy. During the period of gestation there is no true 
 milk secreted, but the cells are developing and preparing for 
 their functions. There is formed during the latter part of 
 pregnancy a secretion somewhat similar to milk, called colos- 
 trum. It differs from ordinary milk in containing a larger 
 quantity of solid matter. Under the microscope are to bo seen 
 certain granular masses, called colostrum-corpuscle* , which have 
 been seen to exhibit contractile movements. Its chief value 
 lies in the fact that it acts as a laxative, thus insuring an 
 emptying of the infant's intestinal canal. The formation of 
 colostrum is marked during the first two or three days after 
 labor, followed by secretion of true milk. 
 
 The continued secretion of milk is only kept up by the 
 stimulus of the nursing infant. If the child be weaned, tlie 
 milk-producing cells rapidly cease to secrete. The nerve- 
 supply regulating secretion of milk has not been definitely 
 proven. 
 
 Milk as a food: As the food of all young animals it must 
 be considered of the greatest importance; besides this, as a 
 direct food, both in the natural state and in the derived forms 
 
EPIDERMIS. 121 
 
 of butter and cheese, it is one of the most used articles of 
 adult diet. The causes which lead to its choice in the dietary 
 are easily seen : it contains all the elements necessary to sus- 
 tain life water, proteids, carbohydrates, and fats. As an 
 exclusive diet it will probably sustain life better than any 
 other substance. 
 
 Digestion of milk : When milk taken as food enters the 
 stomach it is first acted upon by rennin. 
 
 Kennin is a milk-curdling ferment, its property being to 
 convert the soluble proteid casein into an insoluble curd. 
 The digestion of the curd is by the hydrochloric acid and 
 pepsin. The digestion of the remaining elements of milk is 
 the same as that of other proteids, carbohydrates, and fats. 
 
 Besides rennin of the stomach, there are other milk-curd- 
 ling ferments that will act upon milk so as to cause its sepa- 
 ration into curds and whey. They are found in the pancreas 
 and intestine. 
 
 " Souring " of milk : There is also a curdling of milk pro- 
 duced when an acid is added to milk. This is called " sour- 
 ing." In nature the acid is made by the breaking up of 
 milk-sugar (lactose) to form lactic and butyric acids, through 
 the action of a micro-organism, the " bacterium lactis." 
 
 Secretions of the Skin. 
 
 The skin : The skin acts as a general protective and sensory 
 covering for the outer surface of the body. It also acts to a 
 certain extent as an absorbing surface. As we shall see later, it- 
 acts as an excretory organ and as an important heat-regulator. 
 There are two layers of tissue which form the entire thick- 
 ness of the skin. The superficial epithelial layer is known as 
 the epidermis or cuticle ; the deeper stratum, in which lie the 
 active functional elements, is called the cutis vera, corium, 
 or derma. 
 
 Epidermis : The epidermis is a stratification of epithelial 
 cells, of varying thickness. The epithelium is flat and horny 
 at the surface ; in the deeper portions are flattened and poly- 
 hedral cells ; and it is closely adapted to the surface of the 
 corium beneath it (Fig. 63). In its deeper layer is found the 
 
122 
 
 SECRETION. 
 
 FIG. <;;-;. 
 
 pigment which characterizes the complexion of individuals and 
 of races. Its function is purely one of protection. The growth 
 
 to replace worn-out cells is verv 
 rapid, and in cases of consider- 
 able use of a part, with inter- 
 rupted pressure upon the skin, 
 the cuticle becomes very thick 
 and horny, as is often seen upon 
 the hands and feet. The hair 
 and nails are modifications of 
 the epidermal epithelium. 
 
 Corium : The true skin is a 
 tough, elastic tissue composed 
 of interlacing bundles of con- 
 nective-tissue cells containing 
 spaces between the fasciculi. 
 These spaces are known as 
 areolce. There are also numerous 
 unstriped muscular fibres. This 
 structure lies upon a more or less 
 thick layer of fatty or loose eel 1 1 1- 
 lar tissue. In thecutis are found 
 the active organs of the skin 
 papillae, sweat- and sebaceous 
 glands, and the hairs (Fig. 64). 
 
 Papillae : Upon the superficial surface of the cutis vera 
 Are innumerable minute elevations which project into the 
 epithelium. They are very vascular, and contain the nerve- 
 endings which give to the skin its sensibility, the sense of 
 touch. The papillae are especially abundant upon the parts 
 in which this sense is most acute palms, finger-tips, soles. 
 
 Sweat-glands : Each gland lies in the subcutaneous fat, and 
 consists of a convoluted mass of tubules which terminates in 
 a duct leading up through the derma and epidermis, discharg- 
 ing the secretion of the gland through a minute opening. 
 This secretion is known as perxjtinifion, or sweat. 
 
 Sebaceous glands : The sebaceous glands occur everywhere 
 over the entire skin surface with the except ion of the palms 
 and soles, and most abundantly in the hairy parts. They are 
 
 Skin of the negro, vertical section, 
 magnified 250 diameters, a, a, cuta- 
 neous papilla. 1 ; 6, undermost and 
 dark-colored layer of oblong vertical 
 epidermis-cell* ; c, mucous or Mal- 
 pighian layer; d, horny layer (K61- 
 liker). 
 
HAIR. 
 
 123 
 
 intimately connected with the hair- follicles ; and their ducts, 
 as a rule, open into the follicles, though sometimes they dis- 
 charge separately. The glands are aggregate glands that is, 
 
 FIG. 64. 
 
 Epidermis 
 
 or 
 Cuticle 
 
 Fibrous^ 
 tissue : 
 
 Sebaceous 
 Glands 
 
 -Glands 
 
 Nutrient Artery 
 
 Sectional view of the skin, magnified. 
 
 are formed by the subdivision of the duct to make up the 
 lobules of the gland. There is a delicate plexus of capillary 
 vessels about the sacculi. 
 
 Hair : A hair is produced by a peculiar growth and modi- 
 
124 
 
 SECRETION. 
 
 FIG. 65. 
 10 9 
 
 fication of the epidermis, especially of the rete mucosum. It 
 consists of a bulb or root imbedded in the skin and of a pro- 
 jecting shaft. It is composed of a central medullary sub- 
 stance, around which is dis- 
 posed a thick layer of elongated 
 horny cells the cortex. On the 
 outside is a layer of fine scales, 
 closely overlapping with the 
 edges turned upward, known as 
 the cuticle. The root of each 
 hair is lodged in the follicle, a 
 tubular depression of the skin 
 descending into the subcutane- 
 ous fat. At the bottom of the 
 follicle is a small papilla of true 
 skin, by the projection and out- 
 growth of whose cells the hair 
 is formed (Fig. 65). 
 
 Nails : A nail, like a hair, is 
 produced by modified skin. It 
 consists of two layers, a super- 
 ficial horny one, composed of 
 flattened nucleated cells or scales, 
 and a deeper soft layer, corre- 
 sponding to the rete mucosum 
 of the epidermis. The back 
 edge of the nail the root is 
 received in the groove of the 
 matrix, a specially modified part 
 of the corium. The growth of 
 the nail, like that of the hair, 
 is due to a constant production 
 of cells from beneath and behind in the matrix. 
 
 The sweat is a watery fluid, colorless, slightly turbid, 
 slightly salty to the taste, of acid reaction, and possessing a 
 peculiar odor. It is an excrement. Its composition is some- 
 what variable, but in general it may be said to contain about 
 J per cent, of solids suspended and dissolved in water. These 
 solids are fats and fatty acids, sodium chloride, epithelium, 
 
 Diagram of structure of the root of a 
 hair within its follicle. 1, hair-pa- 
 pilla ; 2, capillary vessel ; 3, nerve- 
 fibres ; 4, fibrous wall of the hair- 
 follicle; 5, basement-membrane : 6, 
 soft epidermis lining the folli- 
 cle ; 7, its elastic cutieular layer ; 8, 
 cuticle of the hair: 9, cortical sub- 
 stance ; 10, medullary substance ; 
 11, bulb of the hair composed of 
 soft polyhedral cells; 12, transition 
 of the latter into the cortical sub- 
 stance, medullary substance, and 
 cuticle of the hair (Leidy). 
 
SECRETION OF SEBACEOUS GLANDS, 125 
 
 and a trace of urea. Besides these there is a considerable 
 amount of carbonic dioxide (CO 2 ) excreted by the skin. 
 
 Nervous mechanism of perspiration : It is probable that the 
 sweat-glands are under the reflex control of centres in the 
 medulla and in the spinal cord, and that these centres regu- 
 late this function of the skin through the vaso-motor 
 system. 
 
 Amount of sweat : The amount of sweat excreted depends 
 on the condition of the atmosphere, the nature and quantity of 
 the food, the amount of fluids consumed, the exercise taken, 
 and the relative activity of the other glands, especially of the 
 kidneys. Certain mental conditions, some diseases, and drugs 
 also interfere with sweat- secretion. In general, we may say 
 the amount is about a quart in twenty-four 'hours. 
 
 Odor of sweat : The odor of sweat varies for different parts 
 of the body, and markedly for different races of mankind. 
 The odor is due to various acids found in the sweat formic, 
 acetic, butyric, propionic, caproic, and caprylic. 
 
 Purpose of sweat : The sweat is an excrement, and so we 
 consider the skin as an excretory organ. The principal sub- 
 stances excreted in the sweat are water, carbon dioxide, and 
 urea. 
 
 In addition to being a means of excretion, the sweat is of 
 great value as a regulator of body-heat. By evaporating from 
 the surface the sweat cools the body. 
 
 Insensible perspiration : When the secretion of the sweat- 
 glands forms in drops upon the skin we speak of this as 
 sensible perspiration, or sweat. However, since the glands are 
 continuously active, there are times when the fluid evaporates 
 so rapidly that no moisture is noticeable upon the surface ; 
 this is called insensible perspiration. 
 
 Secretion of sebaceous glands : The secretion of the seba- 
 ceous glands is a soft, oily, white material, and has, besides 
 other fats, stearin for basis. Its use seems to be to lubricate 
 the skin, keeping it soft and flexible, and at the same time, by 
 its oily nature, to prevent maceration of the skin from con- 
 tinued exposure to moisture ; and to check undue absorption 
 from the surface. Sebaceous matter is not excrementitious, 
 but is a secretion. 
 
126 SECRETION. 
 
 Absorption by the skin : In addition to its excretory and 
 secretory properties, the skin has the power of absorption. 
 This function admits of the application to and absorption by 
 the skin of certain medicines, food, and drink. 
 
 In frogs, for example, the skin has the power, if kept 
 moist, of absorbing oxygen ; it is by virtue of this property 
 that a frog can oxygenate its blood under water. 
 
 Necessity of sweat: Sweating is an absolute necessity to 
 life, in order to assist the other excretory organs in removing 
 the wastes of the body. The symptoms of complete sup- 
 pression of the insensible sweat are those of an acute poison- 
 ing, together with pyrexia and exhaustion. This can be 
 proven by varnishing the skin of animals, which causes 
 death. A celebrated instance of this is the case of a 
 child who, being covered with gold-leaf to personate an 
 angel at the coronation of Leo X., died a few hours after- 
 ward. 
 
 Kidneys and Urine. 
 
 The kidneys are glandular organs having somewhat the 
 form of a bean. In size they are somewhat more than 4 
 inches in length, somewhat more than 2 inches wide, and 
 about 1 inch thick. The weight of each organ is about 4 to 6 
 ounces. A thin but rather tough capsule invests the kidney 
 (Fig. 66). This may be pulled off readily, leaving the sur- 
 face of the organ smooth and even and of a deep-red color. 
 If a vertical section of the organ be made, the central cavity 
 (sinus) will be noticed, and about it the kidney-tissue. Within 
 the sinus are the apices of pyramidal projections, about ten in 
 number ; and if the cut surface be examined closely, it may 
 be noted that the outer (cortical) portion differs in appear- 
 ance from the more central (medullary) portion. The blood- 
 supply is from the renal artery, and the nerve-supply is from 
 the sympathetic system through the solar plexus. The kidney 
 is a compound tubular gland. The medullary portion of the 
 organ is almost entirely made up of tubules, which take 
 origin in the cortex and empty upon the apices of the pyra- 
 mids of Malpighi of the medullary portion (see below). 
 
URINIFEROUS TUBULES. 
 
 127 
 
 FIG. 66. 
 
 Malpighian bodies : In the cortical portion of the kidneys 
 are found minute tufts of capillaries which are surrounded 
 
 by a capsule lined with epi- 
 thelial cells (Fig. 67) ; and 
 here it is that the tirinifer- 
 ous tubules arise, the tuft of 
 capillary vessels being, as it 
 were, built into the end of 
 the tubule. 
 
 Uriniferous tubules : Be- 
 ginning in the cortex of the 
 kidney at one of the bodies 
 of Malpighi, the minute se- 
 
 FIG. 67. 
 
 Vertical section of a kidney. 
 
 Malpighian body. 
 
 creting ducts pursue a tortuous course to the larger collecting 
 tubules, which empty at the apices of the pyramids of Mal- 
 pighi into the calyces of the kidney (see Ureters). Without 
 entering minutely upon the course of the tubules, it is impor- 
 tant to remember that they form a loop (of Henle) which 
 dips into the pyramid, and that they pursue a somewhat tortu- 
 ous course both before entering into the loop of Henle and 
 upon returning to the cortical portion of the kidney, where 
 they empty into the straight collecting tubules. The straight 
 course of the arms of Henle's loop and of the collecting 
 
128 
 
 SECRETION. 
 
 tubules gives to the pyramids a finely striated appearance 
 (Fig. 68). These collecting tubules en masse, together with 
 interstitial tissue, bloodvessels, and lymphatics, make a " pyra- 
 mid." 
 
 FIG. 
 
 Diagram of the tubules ami vascular supply of the kidney. <>n the left is a tubule 
 alone; in the middle is a tubule along with the bloodvessels ; on the right an- 
 bloodvessels only. v. r., venae rectae; a. r., arterise rectse. 
 
 Blood-supply of kidney : On entering the kidney the renal 
 artery bivaks up into several brandies, which pass into the 
 ti ne proper of the organ. Branches from these arteries 
 
URINE. 129 
 
 (arteria propria renales) have two determinations (1) into 
 the cortex and (2) into the pyramids. 
 
 (1) Those branches (interlobular) which pass into the cortex 
 divide to become the afferent vessels to the Malpighian bodies, 
 and, after there passing through the capillary tuft, the blood 
 is re-collected and goes out by an efferent vessel. This effer- 
 ent vessel in its turn is broken into a minute capillary plexus 
 which surrounds the uriniferous tubules in the cortex of the 
 kidney, and these capillaries unite to form the venous return- 
 circulation (interlobular veins). Thus, this system has, it is 
 to be noted, two capillary divisions, in the Malpighian tuft, 
 and again about the tubules of the cortex. There is also a 
 sub-capsular capillary division, derived from certain of the 
 interlobular vessels that do not go to nor come from the 
 Malpighian bodies. 
 
 (2) Numerous minute branches (arterise recta?) are given 
 off, which pass into the pyramids as far as their apices, and 
 there form capillary divisions from which the venae recta3 
 return to join the branches from the cortex and form the 
 venaB proprise of the kidney. 
 
 The ureters : Leading from each kidney to the bladder is a 
 duct the ureter about the size of a goose-quill and from 
 twelve to sixteen inches in length. The ureters are lined 
 with mucous membrane, continuous above with that of the 
 pelvis of the kidney, and below with that of the bladder. The 
 " pelvis of the kidney " is the upper dilated end of the ureter ; 
 and, in its turn, is made up of the conjoined calyces (see 
 Uriniferous Tubules). 
 
 The bladder : This, which forms a temporary receptacle for 
 the urine, is a hollow muscular organ of a pyriform shape, 
 lined with mucous membrane, and situated in the pelvic por- 
 tion of the abdominal cavity. The widest part is called the 
 fuiHJH*, and the narrowed part, whence leads the urethra, is 
 sometimes known as the cervix. 
 
 Urine : It is a clear, amber-colored fluid of slightly acid 
 reaction. It may develop a flocculent precipitate of a light 
 cloud of mucus upon standing. It has a characteristic odor 
 and a salty-bitter taste. 
 
 Urine has a specific gravity of about 1020 ; but under con- 
 
 9 Phys. 
 
130 SECRETION. 
 
 ditions of health it may vary from 1010 to 1030, or even be- 
 yond these limits. 
 
 ( 'otwing-matter of urine: The coloring-matter of the urine 
 appears to be identical with hydrobilirubin. It is derived 
 from the bilirubin of the bile, which, being absorbed, passes 
 out of the body in the urine rather than in the faeces. The 
 varying tints are probably due to oxidation of this sub- 
 stance. 
 
 Composition of urine : The urine is an excrementitious fluid, 
 and may be considered as a watery solution of the excrementi- 
 tious products of the retrograde metamorphosis of nitrogenous 
 bodies, resulting from the processes of life and action. Chem- 
 ically, it is a solution of urea and urates with a small per- 
 centage of organic salts. 
 
 Table of the Chemical Composition of the Urine. 
 
 Water . . . 967 
 
 Crystallizable nitrogenous bodies : 
 
 Urea 14 
 
 Uric acid, free (trace), 
 
 Uric acid in form of alkaline urates, 
 
 Hippuric acid and hippurates, !> . 11 
 
 Pigments, extractives, and mucus, 
 
 (All in small and constant amounts). 
 
 Salts: 
 
 Inorganic 
 
 Chlorides of sodium and potassium, 
 Sulphates and phosphates of sodium and 
 
 potassium, 
 
 Phosphates of magnesium and calcium, 
 Silicates (trace), 
 Organic 
 Lactates, acetates, and formates, which 
 
 only appear occasionally. 
 Sugar (occasionally), a trace, 
 Gases, nitrogen, and carbonic acid. 
 
 1000 
 
 Acidity of urine : The acidity of the urine is due to the 
 
AMOUNT OF URINE. 131 
 
 presence of acid sodium phosphate. There is no free acid 
 present, as is shown by the fact that no precipitate is formed 
 upon the addition of sodium hyposulphite. The degree of 
 acidity varies, being less during active digestion and less after 
 vegetable food. Herbivora have alkaline urine, while car- 
 nivora have strongly acid urine ; but the herbivorous animal 
 during fasting has acid urine, because it is then living from 
 its own tissues and is for the time a carnivore. After excre- 
 tion, however, the urine soon becomes more acid (probably 
 because of the presence of some fermentation), and at this 
 time uric acid and urates may precipitate. Upon further ex- 
 posure it is attacked by micro-organisms, and the urea is 
 changed to ammonium carbonate, the reaction becoming alka- 
 line, and there is a precipitation of triple phosphates and 
 alkaline urates. In the body these conditions do not occur in 
 conditions of health. 
 
 Secretion of urine : The kidneys secrete urine in two ways : 
 (1) by filtration and (2) by real functional action of the epi- 
 thelium. 
 
 (1) In the circulation of the blood through the Malpighian 
 tuft there seems to be no active separation of the urinary in- 
 gredients by cell-power, but the water and saline elements are 
 given off here by the blood by a process of simple filtration. 
 The amount of fluid which passes here is governed by the 
 blood-pressure in the arteries of the kidney and by the fluid- 
 ity of the blood. 
 
 (2) The epithelium of the uriniferous tubules has secreting 
 function, and is able to separate from the blood foreign sub- 
 stances (e. g. 9 urea or indigo-carmine) and eject them into the 
 tubules, and to manufacture from material taken from the 
 blood new substances not found there (e. g. y pigments). 
 
 Amount of urine : The average amount of urine secreted 
 daily is fifty-two fluidounces, though as little as thirty-five 
 ounces, or as much as eighty-one, may be voided within the 
 limits of health. The quantity varies greatly in health with 
 the amount of fluid taken, of food consumed, of the activity 
 of the skin evaporation, and somewhat with the character of 
 the food. In a more general way it may be said to depend 
 upon the condition of the blood, an excess of fluids demand- 
 
132 SECRETION. 
 
 ing increase of functional activity on the part of the kidneys. 
 In conditions of disease or under the stimulus of drugs the 
 limits mentioned are by no means final, for in certain patho- 
 logical conditions the secretion may be almost wholly sus- 
 pended or very greatly increased. 
 
 Conditions affecting urinary secretion : The facto is that favor 
 the increase of urine are those conditions which favor filtra- 
 tion of water by the glomeruli of Malpighi that is, the 
 presentation of a larger amount of blood to the action of these 
 bodies. This is accomplished 
 
 (1) By increasing the force of the heart. 
 
 (2) Through the nervous system by its action upon the 
 vascular, so as to produce local congestion. The effect of the 
 nervous system in increasing the urine by reflex vaso-motor 
 impulses is felt most in the glomeruli, and the urine is there- 
 fore very watery. 
 
 (3) By conditions which cause anemia of other parts, thus 
 producing a greater determination of blood to the kidneys, 
 and so increasing the urinary flow. So marked is this that 
 the skin and kidneys may almost be said to be complementary 
 in their action in eliminating water from the system ; and in 
 this regard their relative activity may be said to be inversely 
 proportional to one another. 
 
 Kirke gives the following table (modified from Foster), 
 which is useful for reference : 
 
 Table of the Relation of the Secretion of Urine to Arterial 
 
 Pressure (Kirke). 
 A. Secretion of urine may be increased 
 
 a. Ry increasing the general blood-pressure by 
 
 1. Increase of the force or frequency of the heart-beat. 
 
 2. Constriction of the small arteries of areas other than 
 
 that of the kidney. 
 
 b. By increasing the local blood-pressure by relaxation <>f flu' 
 
 renal artery, without compensating relaxation < /*< - 
 where by 
 
 1. Division of the renal nerves (causing polyuria). 
 
 2. Division of the renal nerves and stimulation of the 
 
 cord below the medulla (causing greater polyuria). 
 
MICTURITION. 133 
 
 3. Division of the splanchnic nerves ; but the polyuria 
 
 produced is less than in 1 or 2, as these nerves are 
 distributed to a wider area, and the dilatation of 
 the renal artery is accompanied by dilatation of 
 other vessels, and therefore with a somewhat di- 
 minished general blood-supply. 
 
 4. Puncture of the floor of the fourth ventricle or me- 
 
 chanical irritation of the superior cervical ganglion 
 of the sympathetic, possibly from the production 
 of dilatation of the renal arteries. 
 B. Secretion of urine may be diminished 
 
 ft. By diminishing the general blood-pressure by 
 
 1. Diminution of the force or frequency of the heart- 
 
 beats. 
 
 2. Dilatation of capillary areas other than that of the 
 
 kidney. 
 
 3. Division of the spinal cord below the medulla, which 
 
 causes dilatation of the general abdominal area, and 
 urine generally ceases being secreted. 
 
 b. By increasing the blood-pressure by stimulation of the 
 
 spinal cord below the medulla, the constriction of 
 the renal artery which follows not being compen- 
 sated for by the increase of the general blood- 
 pressure. 
 
 c. By constriction of the renal artery by stimulating the 
 
 renal or splanchnic nerves or the spinal cord. 
 
 Course of the urine : The urine collected in the tubules of 
 the kidney passes into the pelvis of the kidney, and is carried 
 to the urinary bladder in irregular quantities by the ureter. 
 The ureters simply act as ducts, and do not store up urine, 
 nor do they usually actively eject it into the bladder. As a 
 few drops of urine collect in the pelvis of the kidney, they 
 run into the bladder, the action of the two kidneys not being 
 in alternation nor absolutely regular in point of time. Re- 
 gurgitation from the bladder is prevented by the oblique 
 course of the ureter through the muscular wall of the blad- 
 der. 
 
 Micturition : When the bladder is filled the act of emptying 
 
134 
 
 SECRETION. 
 
 it is called micturition. It is a voluntary act, aided by the 
 involuntary reflex contraction of the muscular coat of the 
 oriran itself. The voluntary muscles involved are those of 
 respiration the diaphragm and the abdominal muscles. So 
 far as micturition is involuntary, it is a reflex depending upon 
 a centre in the lumbar spinal cord. 
 
 Urea is a chemical body, the formula being CH 4 N 2 O (Fig. 
 69). The nitrogen atom is derived from the "combustion. 
 
 FIG. 69. 
 
 Urea, prepared from urine, and crystallized by slow evaporation (Lehmann). 
 
 of proteid material. Hence we infer that the amount of urea 
 excreted gives us an index of the amount of proteid material 
 consumed by the body. The used-up nitrogenous matters of 
 the body may be derived from : (1) the food (urea being 
 greatly increased by a nitrogenous meal) ; (2) the metabolism 
 of the tissues. 
 
 The result of the " combustion " of nitrogenous material is 
 not at once found in the blood, but exists as some antecedent 
 of urea (probably carbonate of ammonium) until the blood 
 reaches the liver. Under the action of the liver-cells the an- 
 tecedent of urea is converted into urea. The urea thus formed 
 remains in the circulation until the blood reaches the kidney ; 
 here the urea is excreted. Thus it is seen that the kidncv- 
 
VASCULAR GLANDS. 135 
 
 cells play no part in the formation of urea, but merely exert 
 a selective action upon it for excretory purposes. 
 
 Amount of urea excreted : The amount varies, but it may be 
 considered to be about one-half the solid constituents of the 
 urine. Roughly speaking, the urinary solids may be regarded 
 as 4 per cent, of the total, and the urea (including the uric 
 acid and urates) about 1.5 to 5 per cent. This proportion is 
 very variable, and there may be urea in healthy urine to 
 exceed 2J per cent., or in a much less ratio than 5 per 
 cent. 
 
 Method of estimating solids : A useful rule for approxi- 
 mately estimating the total solids in any given specimen of 
 healthy urine is to multiply the last two figures representing 
 the specific gravity by 2.33. Thus, in urine of specific grav- 
 ity 1025, 25' X 2.33 = 58.25 gr. of solids in 1000 gr. of urine. 
 In using this method it must be remembered that the limits 
 of error are much wider in diseased than in healthy urine. 
 
 Urea as a waste : Urea is capable of still further oxidation, 
 and so would be a source of further chemical potential energy ; 
 but urea is excreted before it is fully oxidized, and so is a real 
 waste. 
 
 Uric acid : Of the other constituents of urine, uric acid 
 is the most important, it being one of the forms in which 
 nitrogen is eliminated. It usually exists in the urine in the 
 form of urate of ammonium or sodium. It probably comes, 
 like urea, from food-disintegration. Some consider it to be 
 an imperfectly oxidized form of urea. The amount found in 
 the blood is especially increased in gout. 
 
 Hippuric acid : This is one of the few important constitu- 
 ents of urine which is produced in the kidneys themselves, 
 being formed from benzoic and amido-acetic acids. It is also 
 formed in the liver. It is another form of nitrogenous elim- 
 ination, but may come from tissue-waste as well as food-dis- 
 integration. It exists in slightly larger quantity than does 
 uric acid. 
 
 Vascular Glands. 
 
 The vascular glands, or ductless glands, are a collection of 
 glandular structures that possess no ducts and apparently do 
 
136 
 
 NUTRITION. 
 
 not seem to be associated in either secretion or excretion. 
 Ductless glands include the spleen, thyroid, thymus, and 
 tonsils. 
 
 Purpose of ductless glands : No definite function has l><<n 
 asi-ribed to the ductless glands ; but we do know that the ex- 
 tirpation of certain of these structures is attended with 
 serious results to the subjects. For example, congenital de- 
 fects of the thyroid produce the condition known as cretin- 
 ism. 
 
 Table of Secretions. 
 
 Secretion : 
 
 Secreting organ : 
 
 Reaction : 
 
 Main Purpose : 
 
 Sebum; 
 
 Sebaceous glands of 
 
 Acid; 
 
 To oil the skin. 
 
 
 the skin ; 
 
 
 
 Mucus; 
 
 Mucous cells of mu- 
 
 Alkaline ; 
 
 Lubricant and diluent. 
 
 
 cous membranes ; 
 
 
 
 Serous secretion; 
 
 Serous membranes ; 
 
 Alkaline; 
 
 Lubricant and diluent. 
 
 Tears; 
 Saliva; 
 
 Lachrymal glands ; 
 Salivary glands; 
 
 Alkaline; 
 Alkaline; 
 
 To moisten conjunctive. 
 To moisten food mid di- 
 
 (inatrir juice; 
 f<iicni.<< nit riciis; 
 
 Stomach; 
 Intestines; 
 
 Acid; 
 Alkaline; 
 
 gest carbohydrates. 
 To digest proteids. 
 To dilute the divine. 
 
 1'niKicatic juice: 
 
 Pancreas ; 
 
 Alkaline ; 
 
 To digest proteids, fats. 
 
 
 
 
 and carbohydrates. 
 
 Bile; 
 
 Liver; 
 
 Alkaline; Part of the bile is used in 
 
 
 
 
 digestion and reab- 
 
 
 
 
 sorbed. Part is a true 
 
 
 
 
 excretion ; bile-pig- 
 
 
 
 
 ments). 
 
 Milk; 
 
 Mammary glands ; 
 
 Alkaline; 
 
 Food. 
 
 Sweat ; 
 
 Sweat-glands of skin ; 
 
 Acid; 
 
 Elimination of water, car- 
 
 
 
 
 bon dioxide, and urea. 
 
 
 
 
 Regulates body-temper- 
 
 
 
 
 ature. 
 
 Urine; 
 
 Kidneys; 
 
 Acid; 
 
 Elimination of water and 
 
 
 
 
 urea. 
 
 NUTRITION. 
 
 By nutrition we mean the physiological principles which 
 preserve the normal conditions of the structure and function 
 of the body, so far as refers to the balance between the in- 
 come and out<ro of material. While it is almost an impos.-i- 
 bility to study this subject exactly, yet an idea of the modes of 
 expense and income may he gained by consideration of data 
 which are fairly well settled. In considering the income and 
 expenditure of the body it is always necessary to bear in mind 
 thai all the factors are variable and the results inconstant, for 
 the income often exceeds the expense, and viceversti, in life. 
 
RESULTS OF BODY-EXPENDITURE. 137 
 
 Sources of income to the body : Food and drink and oxygen 
 are the factors of the income, and may be calculated about as 
 follows for twenty-four hours : 
 
 Food (chemically dry) 16 ounces. 
 
 Water (as drink and as combined with solid 
 
 food) 80 " 
 
 Oxygen (absorbed by lungs) 26 " 
 
 Total, 122 ounces. 
 
 Expenditures of the body : The more important are those 
 by the ordinary excretory channels lungs, skin, kidneys, and 
 intestines. 
 
 From the lungs there are exhaled every twenty-four hours 
 
 Of carbonic acid, about ... 30 ounces. 
 
 Of water 10 " 40 ounces. 
 
 Traces of organic matter. 
 From the skin 
 
 Water 23 " 
 
 Solid and gaseous matter ... 1 ounce. 24 " 
 From the kidneys 
 
 Water 50 ounces. 
 
 Organic matter 1-J. " 
 
 Minerals and salines Jounce. 52 " 
 
 From the intestines 
 
 Water 4 ounces. 
 
 Various organic and mineral 
 
 substances 2 " 6 " 
 
 Total, 122 ounces. 
 
 Thus we may represent the schematic plan of income and 
 expense as about equal ; but it must be borne in mind that 
 the plan only represents an average result of both. 
 
 Variation* in the rate of income and expenditures are 
 shown by changes in the body- weight. 
 
 Results of body-expenditure : In return for the amount of 
 food, drink, and oxygen the body has consumed, we have to 
 show for it : 
 
138 NUTRITION. 
 
 (1) The growth of the body and secretion of its necessary 
 materials, as well as the maintenance of the tissues, subjected 
 as they are to the wear incident to the continuance of life 
 and function. 
 
 (2) The continuance of physical conditions suitable to life 
 in the form of heat and motion. The actual combustion of 
 carbon (/. e., oxidation) must be sufficient to maintain the ani- 
 mal heat and the nourishment of the muscles upon which the 
 continuance of life depend. 
 
 (3) Net-roil* energy, as in the regulation of all physiologi- 
 cal processes by the reflexes, as well as in voluntary mental 
 and nervous action. 
 
 Energy of the body : The daily work of the body has been 
 calculated to be about 3400 foot-tons. Of this about one- 
 tenth has been considered to be exhausted in involuntary 
 muscular action (circulation, respiration, etc.) and in volun- 
 tary motion, while the remainder (nine-tenths) is expended 
 in maintaining the body-heat. Another method of consider- 
 ing this enormous force may be of use : it is equivalent in 
 heat to that required to raise nearly fifty pounds of water 
 from the freezing- to the boiling-point ; or in mechanical force 
 it is sufficient to raise the body of a man weighing one hun- 
 dred and fifty pounds to a height of eight and one-half miles. 
 
 Effect of starvation : There is a loss of weight in all the 
 tissues, but it is in the loss of the fat that the change is most 
 marked : the fat almost entirely (93 per cent.) disappears after 
 death from starvation. The sense of hunger gives way to a 
 sense of pain ; thirst is excessive ; sleep is absent ; progressive 
 weakness accompanies increasing emaciation ; the exhalations 
 of the skin and lungs are foetid; and diarrhoea with convul- 
 sions or delirium often precedes death. Death occurs with 
 absolute deprivation of both food and drink at the end of 
 about a week (six to ten days), though life may be considera- 
 bly prolonged by small quantities of food or water. The 
 temperature of the body falls before death very considerably 
 (30 C.), and it has been considered that death results from 
 cold, no fuel being furnished to maintain animal heat. The 
 body decays rapidly after death from starvation. 
 
 " Exclusive " diet : The result of feeding animals exclu- 
 
NITROGENOUS EQUILIBRIUM. 139 
 
 sively on a single article of diet (sugar, gum, oil, etc.) is 
 practically the same as that of starvation, except that death 
 does not occur until the end of four or five weeks. In man 
 the exclusive diet of isolated communities often results in the 
 breaking down of tissue and general malnutrition. 
 
 Effect of over-feeding: An excess of nitrogenous food, if 
 digested, increases the metabolic work of the glanular organs 
 (especially of liver and kidneys), and induces disease in those 
 organs and faulty excretion of nitrogenous matter. This 
 may be obviated or delayed by active physical exercise. Car- 
 bohydrate food in excess is stored up in the form of fat, 
 which may be excessive, with resulting fatty infiltration of 
 the viscera, or it may show as glycosuria. 
 
 An excess of any food is apt to pass undigested through the 
 intestines and undergo putrefactive changes, with resulting 
 gaseous distention : the carbohydrates are especially apt to 
 give rise to this disturbance. 
 
 Normal diet : There should be a general diet of well-cooked 
 food, and it should contain about the amount of carbon and 
 nitrogen which is excreted ; that is, it should maintain an 
 equilibrium. This is, commonly, about two pounds of solid 
 food and two quarts of fluid. The proportion of the various 
 kinds of food varies considerably, but in a general way for a 
 healthy man, one may divide the solid food somewhat in this 
 way : nitrogenous food (meat), about -| pound ; hydrocarbon 
 and fat-food (bread, vegetables, and butter), about 1^ pounds. 
 Besides this, the food will contain from 1 to 2 ounces of salts 
 and a varying amount of sugar. 
 
 " Nitrogenous equilibrium " : When an animal is fed exclu- 
 sively upon a nitrogenous diet, it is found that after a time 
 the egested nitrogen approaches and finally balances that 
 taken in as food. This is known as the " nitrogenous equilib- 
 rium." But at the same time the animal may increase in 
 weight, and this occurs by the formation of fat which is 
 stored up in the tissues. The nitrogenous equilibrium is 
 more easily maintained by the addition of carbohydrates to 
 the food. 
 
 It is also known that the fat of the body not only comes 
 from the fat we eat, but is also made from carbohydrates and 
 
140 ANIMAL HEAT. 
 
 proteids. So, too, carbohydrates may be manufactured from 
 proteids. Hence the animal fed on nitrogenous diet exclu- 
 sively may store up some fat that has been manufactured in 
 its body from the proteids. 
 
 Assimilation : It seems almost needless in closing the sub- 
 ject of nutrition, to remind the student that the body derives 
 no benefit from the food ingested unless the food is asMini- 
 lated. 
 
 To be assimilated the food must be properly digested, then 
 properly absorbed by the blood and lymph, and finally become 
 part of the body-tissues. Then, too, to be a source of chemi- 
 cal potential energy, the absorbed food must be capable of 
 further oxidation. 
 
 ANIMAL HEAT. 
 
 The normal temperature of the body is about 98.5 F. (37 
 C.). This temperature is not invariable, but in the superfi- 
 cial cavities, mouth, and axilla, which are convenient for as- 
 certaining the body-temperature, this is nearly exact. In the 
 internal organs the thermometer may indicate as high as 100 
 F. in normal conditions. In the rectum the temperature is 
 about 1 F. higher than in the mouth or armpit. In health the 
 temperature is maintained constantly with but slight varia- 
 tions, due to marked changes in surrounding air temperature, 
 age, exercise, sex, etc. The temperature in health varies to 
 the extent of 1 to 1.5 F., according to the time of day or 
 night, being lowest late at night or in the early morn ing, 
 while it is highest late in the afternoon. This correspond- to 
 the usual temperature-ranges in fever, when the minimum is 
 in the early morning, the maximum in the late afternoon. 
 
 Sources of heat: (1) Principally from the oxidation of the 
 tissues during katabolism of the body-structure. The tissues 
 of the body, as has been previously mentioned, are derived 
 fnm the organic food-stuffs. Hence we owe our main supply 
 of body-heat to the oxygen of the air and the organic food- 
 stuffs. 
 
 (2) Chemical action going on during digestion of food is 
 also productive of some heat. 
 
REGULATION OF HEAT. 141 
 
 (3) Friction of muscles upon one another, friction of blood 
 in capillaries, and all forms of friction, are productive of a 
 little heat. 
 
 (4) Warm media about the body, warm drinks and foods. 
 Of these various sources only the oxidizing of body-tissue 
 
 generates enough heat to keep the body-temperature up to the 
 standard. The main seat of this oxidizing is in the muscles, 
 which form so large a part of the organism. Therefore, we 
 can say that the principal part of the total heat produced 
 within the body is generated by muscular activity. Active 
 exercise may raise the body-temperature from 1 to 2 F. 
 
 Loss of heat: (1) Blood circulating at the surface of the 
 body is cooled by the colder air. Although in ordinary health 
 the external application of cold, as by baths, has only a slight 
 effect on the temperature, it is otherwise in the case of high 
 fever. In these cases a tepid bath may reduce the tempera- 
 ture several degrees, the effect lasting in some cases for many 
 hours. This method of reducing high temperature is success- 
 fully applied in cases of sunstroke and certain fevers, espe- 
 cially typhoid. 
 
 (2) The evaporation of sweat dissipates a vast amount of 
 heat. 
 
 (3) Loss of heat is considerable by the lungs, though less 
 than that from the skin : the air is warmer, in usual condi- 
 tions, after leaving the lungs than before it has entered them. 
 
 (4) Warming the excretions of the body (faBces, sweat, and 
 urine) is another factor in loss of heat. 
 
 Regulation of heat : The amount of heat generated can be 
 regulated by diminishing the source or increasing the elimina- 
 tion of heat, and vice versd. The loss of heat is principally 
 regulated by : 
 
 (1) The amount of blood sent to the surface to be cooled ; 
 this is regulated by the vaso-motor nerves; (2) the in- 
 crease or decrease in sweat secretions. The supply of heat 
 depends on the activity of tissue-metabolism, resulting from 
 exercise, mental activity, etc. 
 
 Diseases, such as fevers, that are accompanied by a rise of 
 temperature, owe that rise to either a marked increase in 
 katabolism or diminished elimination power, or to both. 
 
142 
 
 MUSCLE. 
 
 Centres for heat-regulation : There are reasons for believing 
 that there are nerve-centres exciting the heat-production in the 
 tissues (thermogenic centres), and centres which check the 
 metabolism of tissue, and thus control the temperature (in- 
 hibitory heat-centres). This is not entirely proven, nor are 
 these centres exactly localized. We do know that the inner- 
 vation of a part is necessary for the main- 
 FIG. 70. tenance of its warmth, aside from vaso- 
 
 motor causes for alteration of temperature. 
 Limits of body-temperature : In ordinary 
 pathological conditions the temperature 
 does not remain long at a point below 
 95 F. nor above 105 F. without fatal 
 results. Under extreme conditions of pro- 
 longed exposure to cold and the algid stage 
 of cholera, recovery has occurred after a 
 bodily temperature as low as 75 F. On 
 the other hand, in some cases of extreme 
 fever, as from sunstroke, recovery has been 
 noted after a temperature of 110-112 F. 
 
 MUSCLE. 
 
 Varieties : Muscle-tissue consists of 
 three distinct types: 1. Nou-xtr'uttnl, or 
 plain muscle-fibre. This is " involuntary/ 7 
 or not under the control of the will. 
 
 2. Striated muscle, which is under the 
 control of the will, or "voluntary." 
 
 3. Striated muscle, but not under the 
 control of the will, hence " inrn/Htifttri/" 
 
 Examples of the first class are the mus- 
 cles of the intestines, walls of the arteries, 
 etc. The skeletal muscles make up the second class. The 
 heart-muscle is the only example of the third class. 
 
 Microscopic appearances : Ao/*-.s7/vV/AW /////xrA-//.vxm is made 
 Op df bundles of elongated, spindle-shaped cells. Kadi cell has 
 an oblong nucleus and is flattened (Fig. 70). In length they 
 are about ^J-^th to ^th inch, and about ^Vu^ 1 " K ' n ' n 
 
 Nnn-st rinted element- 
 ary fibres, from the 
 human colon, a, 
 treated with ^acetic 
 acid, showing the 
 corpuscle's ; l>, frag- 
 ment of a detached 
 fibre not touched 
 with acid. 
 
MICROSCOPIC APPEARANCES. 
 
 143 
 
 width. The cells are bound into bundles by an albuminous 
 cement, and these again into larger bundles by areolar tissue. 
 Striated voluntary muscle-tissue consists of bundles of long 
 muscle-cells or fibres. Each fibre is completely enveloped in 
 a sheath, the sarcolemma, and the whole bundle of fibres is 
 bound together by a delicate connective-tissue framework. 
 
 FIG. 71. 
 
 A, portion of a medium-sized human muscular fibre (magnified nearly 800 diame- 
 ters). B, separated bundles of fibrils, equally magnified: a, a, larger, and b, b, 
 smaller collections ; c, still smaller ; d, d, the smallest which could be detached. 
 
 A number of these fasciculi are joined together to make up 
 the gross anatomical muscle. On examining the muscle-fibre 
 itself, it will be seen to consist of alternate segments of light 
 and dark matter, giving the fibre a striped appearance (Fig. 
 
 These fibres are about an inch in length and ^poth inch in 
 diameter. They join the connective-tissue cells of a tendon 
 
144 
 
 MUSCLE. 
 
 FIG. 72. 
 
 or aponenrosis or another muscle-fibre by adhesion of the 
 sarcolerama at the ends, and thus unite the muscle-bundles 
 in a firm mass ; and this union is further strengthened by the 
 cohesion of the fibres. 
 
 The st nation of the heart-muscle fibres is not so marked as 
 in ordinary muscle, and the form of the fibres is different, 
 for they are branched and more slender. Each fibre is nucle- 
 ated, a large oval nucleus occurring at the centre. The appear- 
 ance of the heart-fibres indicates that they occupy an internu- 
 diate position between typical plain and striped fibres (Fig.72). 
 
 Muscle general properties : (<t) 
 Un striated muscle-tissue acts 
 slowly, is not under the control 
 of the will, acts continuously for 
 quite long periods of time, and 
 is slowly exhausted. 
 
 (6) Involuntary striated muscle 
 (heart) acts quickly, is not under 
 control of the will, acts for a 
 short period, and recuperates 
 rapidly. Under this condition 
 of rapidly alternating periods of 
 activity and repose, the heart- 
 muscle does its work throughout 
 the life of the individual. 
 
 (c) Voluntary striated MH *</< 
 (skeletal) acts rapidly, is under 
 control of the will, and recuper- 
 ates quickly (but not so rapidly 
 as heart-muscle). 
 Chemistry of muscle: About 75 per cent, of muscle-tissue 
 is water. Proteids make up about 15 per cent. Of these, 
 the chief constituent is myosinogen, which appears t<> bear 
 the snne relation to living muscle as fibrinogen does to blood. 
 It' 1>\ cold \ve delay the coagulation of muscles removed from 
 animals immediately after death, we can express a viscid fluid 
 of slightlv alkaline reaction, known as muscle-plasma. This 
 muM'le-plasma, when exposed to ordinary temperatures, coag- 
 ulates much in the same way as docs blood-plasma, inyosin 
 
 Muscular fibres of the heart (Quain) 
 
PHYSIOLOGY OF MUSCLE. 145 
 
 being formed. In a short time the clot will contract and 
 squeeze out a fluid resembling blood-serum. Myosin differs 
 from fibrin in many of its reactions. It belongs to the glob 
 ulin class of proteids. Fat, glyeogen, organic and inorganic 
 salts (chiefly potassium) make up the remaining 10 per cent. 
 The fat exists as minute strips between the fasciculi. The 
 glyeogen is stored up to serve as a supply of chemical poten- 
 tial energy. The amount of glyeogen present in resting mus- 
 cle is about -J- per cent. 
 
 Physiology of muscle : Muscle may exist in three different 
 conditions : those of rest, activity, and rigor. 
 
 Muscle-rest: During rest a muscle has a slight but very 
 perfect elasticity. It can be stretched to a considerable ex- 
 tent, but always returns at once to its former condition. In 
 the living body the muscles are always in a condition of sligkt 
 tension, which gives mechanical advantages. Even during a 
 state of rest the muscle takes oxygen from the blood and 
 gives up carbon dioxide to it. The reaction of a resting 
 muscle is neutral or faintly alkaline. 
 
 Muscle during activity : The peculiar property of muscle- 
 fibre is its contractility, which is excited by all kinds of stim- 
 uli direct and indirect. This property is soon lost, unless the 
 supply of arterial blood is kept up. Muscles, especially the 
 striated, possess a certain kind of sensibility due to the sen- 
 sory nerve-fibres which end in them. They are but slightly 
 sensible to pain, the sensations produced being rather those 
 of the condition of the muscle, as to fatigue, cramp, etc.; or 
 else of muscular sense, as to position of the muscles, com- 
 parison of weights, etc. 
 
 After activity the reaction is acid, due to the development 
 of sarcolactic acid or lactates by the breaking up of the gly- 
 eogen in the muscle. There is also an increase in water and 
 carbon dioxide. 
 
 Only a little proteid material is oxidized during muscular 
 activity. This is shown by the fact that after severe exercise 
 the amount of urea excreted, although increased somewhat, 
 is not increased commensurately with what would have been 
 the case had the proteid furnished the chemical potential 
 energy. 
 
 10 Phys. 
 
146 
 
 MUSCLE 
 
 Actions of muscles as levers : Most of the voluntary mus- 
 cles in the body may be regarded as sources of power for 
 moving the bones viewed as levers. All levers are divided 
 into three classes, according to the relative position of the 
 power, the weight to be moved, and the axis of motion or 
 fulcrum. The different movements of the foot offer an illus- 
 tration of all three kinds of levers : The first kind (Fig. 73), 
 
 FIG. 73. 
 
 i ii in 
 
 Illustration of levers of all three orders (Huxley). 
 W, weight of resistance ; F, fulcrum ; P, power. 
 
 where the fulcrum, F, is between the source of power, P, and 
 the weight or resistance, ,W, is illustrated when the foot is 
 raised and the toe tapped upon the ground, the ankle-joint 
 being the fulcrum. The second kind of lever, where W is 
 between F and P, is illustrated when the body is raised upon 
 the toes, the ground being the fulcrum. The third kind of 
 lever, where P is between F and W, is illustrated when a 
 weight is held up by the toes, the ankle being the fulcrum 
 and the anterior group of muscles on the leg the source of 
 power. The forearm also acts as a lever of this sort when 
 a weight is lifted in the hand. 
 
 Oxygen-supply : Muscle receives its oxidizing agent oxy- 
 gen from the blood coursing through the vessels contained 
 in the muscle. Even during repose the muscle takes up 
 oxygen from the blood and gives back carbon dioxide. The 
 muscle also stores up within itself a certain amount of oxy- 
 gen, which can be called upon to do work even if the blood- 
 supply be stopped. To prove this it is only necessary to cut 
 a muscle out of the body and cause it to contract in a cham- 
 ber of nitrogen. As a result of these contractions the muscle 
 
LATENT PERIOD. 147 
 
 throws off a quantity of CO 2 as a product of oxidation. The 
 oxygen necessary for this oxidation comes from the supply 
 stored up in the muscle as the only source, there being no 
 blood-supply and the atmosphere of the chamber in which 
 the experiment is conducted consisting only of nitrogen. 
 
 During muscular activity a greater supply of oxygen is 
 needed, and this is supplied by a dilatation of the bloodves- 
 sels of the part. Systematic exercise of a muscle educates 
 the arterioles supplying that muscle to remain in a condition 
 of dilatation. This increase in the blood-supply not only 
 provides an increase of oxygen during activity, but during 
 repose carries an increased amount of nourishment to the 
 muscle, with the result that the muscle increases in size and 
 power. Hence the value of " training." 
 
 Muscle-fatigue : After performing its function of contraction 
 for a certain length of time the muscle is less active in its 
 response to stimuli, and finally, in spite of the strongest im- 
 pulses, fails altogether to act. This is " fatigue " of a muscle, 
 a phenomenon with which we are all familiar. After a suit- 
 able rest the muscle recuperates and is as active as ever. 
 
 The reason for this fatigue is that during the muscle's 
 activity a number of effete poisonous products, the result of 
 the active katabolism, have been formed more rapidly than 
 the power of removal by the outgoing blood. After a time 
 the accumulation of poison is so great as to paralyze the mus- 
 cle, so that no further activity takes place until the excess 
 has been removed. 
 
 The first effect of fatigue is seen in the increased latent 
 period and decrease in the strength of the contraction. 
 
 Muscle latent period : By latent period is meant the time 
 that elapses after a stimulus has been applied to a muscle and 
 before the muscle acts. 
 
 We speak of the " apparent " latent period and the 
 "true" latent period. 
 
 By " apparent " latent period is meant not only the time 
 consumed by the impulse in awakening the muscle into 
 activity, but also the time consumed by the impulse in reach- 
 ing the muscle (say in travelling along the nerve). 
 
 " True " latent period is the actual time consumed between 
 
148 
 
 MUSCLE. 
 
 the arrival of the impulse at the muscle and the beginning 
 
 contraction. The time lor 
 
 FIG. 74. the true latent period is 
 
 about one one-hundredth 
 of a second. 
 
 Contractility : The im- 
 portant use of this power 
 is to do " work " /. e., the 
 conversion of the potential 
 chemical energy of the 
 muscle into heat and visi- 
 ble motion. 
 
 If one watches a muscle 
 contract, he will see that 
 the muscle becomes much 
 thicker and shorter; but 
 the volume does not 
 change. The fact that 
 there is no chaiiyc of 
 volume during contraction 
 may be proved by placing 
 a muscle in a vessel filled 
 with fluid to a given mark. 
 The muscle is now made 
 to contract, and it is noted 
 that the level of the fluid 
 remains unchanged. 
 
 Owing to the increased 
 metabolism during func- 
 tional activity, there is 
 heat liberated, hence an 
 increase of temperature. 
 
 Path of stimulus for con- 
 traction : In the living 
 body the impulse causing contraction of a muscle arises in the 
 centres of brain or spinal cord, and travels thence by 
 means of anterior nerve-roots and the somatic nerves going to 
 the particular muscle (Fig. 74). The nerve that supplies 
 a given mii-cle as it enters that muscle breaks up into a num- 
 
 representation of cerebral 
 and spinal motor cells with axons. 1, 
 cerebral cell ; 2, axon ; 3, 4, collaterals ; 4', 
 end-tufts; 5, spinal cells; 6, axon; 7, 
 limit of spinal cord ; A7. motor-nerve; S, 
 muscle ; 9, muscle end-plate (Kauber). 
 
CONTRACTILITY OF MUSCLE. 
 
 149 
 
 her of branches that are distributed to all parts of the mus- 
 cle. The terminal ends of the nerve-fibres are small cellular 
 elements called nerve end-plates or end-organs (Fig. 75). As 
 a rule, these end-organs are scattered in great numbers 
 throughout the muscle. By means of these end-plates the 
 impulse from the nerve is transmitted to the muscle-fibres. 
 Contractility an inherent property of muscle : Although 
 under ordinary circumstances an impulse to contract is sent to 
 a muscle through the intervention of its nerve and end-plates, 
 nevertheless the impulse may be administered directly to the 
 muscle itself and the result be a contraction. 
 
 FIG. 75. 
 
 Nerve-ending in muscular fibre of a lizard (lacerta viridis). a, end-plate seen edge- 
 ways ; b, from the surface ; s, s, sarcolemma ; p, p, expansion of the axis-cylinder. 
 In b the expansion of the axis-cylinder appears as a clear network branching 
 from the divisions of the medullated fibre. Highly magnified (Kuhne). 
 
 To prove that a stimulus may be administered directly to 
 muscle-fibre with a resulting contraction the following exper- 
 iment will be described : 
 
 Liberate the sciatic nerve from the surrounding tissues in 
 the thigh (say the right) of a frog ; but do not destroy the 
 connection of this exposed nerve with the gastrocnemius mus- 
 cle or the spinal cord. Pass a ligature about the right thigh 
 so as to include all the tissues except the sciatic nerve. Tie 
 the ligature tightly. The purpose of this ligature is to shut 
 
150 MUSCLE. 
 
 off all blood-supply to the lower part of the limb. Xow 
 poison the frog with curare. Curare is the Indian arrow- 
 poison, and kills by paralyzing the end-plates in all the mus- 
 cles. In the frog experimented upon, the poison is carried to 
 all parts of the body except to the right leg below the liga- 
 ture. The frog lies as though completely paralyzed. 
 
 Now, with an electrical battery stimulate the right sciatic 
 nerve ; the right gastrocnemius contracts. Stimulate the left 
 sciatic ; no result. During the stimulation of both the right 
 and the left sciatics the nerves showed that they were carry- 
 ing impulses (proven by a galvanometer) ; hence the lack 
 of activity in the left leg is due to the curare having affected 
 either the muscle itself or the end-organs. On the right side 
 the blood carrying the curare has been prevented (by the lig- 
 ature) from reaching the muscle or its end-plates. 
 
 Now apply the electrical stimulus directly to each gastroc- 
 nemius in turn ; both will be found to contract and with 
 equal vigor. 
 
 This experiment proves the following facts : (1) Curare 
 paralyzes a muscle by inhibiting the end-plates of the nerves ; 
 hence" (2) the nerve-endings in the left gastrocnemius being 
 paralyzed, the stimulus that made the left gastrocnemius con- 
 tract necessarily exerted its influence on the muscle direct, and 
 not by the intervention of the end-plates. 
 
 Another proof may be offered to the same end, as follows : 
 the gracilis muscle in the frog is practically free from nerve 
 end-organs in its lower part, and yet the lower part of the 
 muscle contracts as readily to direct stimulation as does any 
 other muscle. An additional proof is that the heart of the em- 
 bryo begins to beat some time before the nerve end-organ* 
 have developed within the heart-muscle. 
 
 Artificial stimuli: A muscle may be stimulated to activity 
 either by irritating the muscle itself, or by sending impulses 
 to the muscle through the intervention of its motor nerve. 
 
 The stimuli employed are : (1) chemical, (2) mechanical, 
 (3) thermal, (4) electrical. The last (electrical) is the most 
 practical and most frequently used. 
 
 To study the effects of muscular contraction a myograph is 
 necessary. A myograph consist of a drum or cylinder cov- 
 
EFFECT OF GALVANIC SHOCK. 151 
 
 ered with smoked paper. The drum is made to revolve by 
 clockwork at a definite rate. The nerve-muscle preparation 
 is so arranged that when the muscle contracts a lever is made 
 to trace a curve on the smoked paper. This curve is called 
 a myogram, and by studying the curve one can learn the 
 amount and character of the contraction. 
 
 Galvanic, faradic, and interrupted currents : A galvanic cur- 
 rent is a continuous flow of electricity directly from the bat- 
 tery. 
 
 A faradic current consists of a direct current passing 
 through a coil of wire ; about this coil is wrapped a second 
 coil, carefully insulated from the first coil. The current pass- 
 ing through the primary coil, induces a current in the second- 
 ary coil. It is the secondary current that is applied to the 
 nerve to be experimented upon. 
 
 An interrupted or alternating current is a faradic current in 
 which the primary current is rapidly made and broken by an 
 automatic interrupter. 
 
 Response to stimuli : It has been found that striped and 
 unstriped muscles react to stimuli in a somewhat different 
 manner. This difference is probably due, for the most part, 
 to their differing structure, but may possibly be due in some 
 degree to their differing modes of connection with the nervous 
 system. When a stimulus is applied to a striped voluntary 
 muscle there is an instantaneous contraction of the part irri- 
 tated, and of that only. This contraction ceases the moment 
 the stimulus is withdrawn. If, on the other hand, any part 
 having involuntary muscle for instance, the bladder or in- 
 testines is stimulated, the contraction comes on more slowly, 
 extends beyond the part stimulated, and continues for some 
 time, with alternating relaxation, after the stimulus is with- 
 drawn. 
 
 Effect of galvanic shock : The instantaneous application and 
 removal of a galvanic shock to a nerve-muscle preparation 
 result in a single twitch of the muscle. Although it is stated 
 above that the application is " instantaneous," it is shown by 
 experiment that the impulse is not appreciated by the nerve 
 unless the flow of current lasts at least 0.0015 of a second. 
 On examining the curve traced by the muscle on the myo- 
 
152 
 
 MUSCLE. 
 
 graph, there are noted : (a) the latent period i. e., the time 
 elapsed after the application of the current before the con- 
 
 Base-line. 
 
 Diagram of muscle-curve, a, point of application of current ; b, point of beginning 
 contraction ; c, maximum ; d, return to normal. 
 
 traction commenced ; (b) a gradual rise in the curve until the 
 maximum is reached, and then a gradual curve down to the 
 base-line (Fig. 76). 
 
 Fio. 77. 
 
 Opening shock. 
 
 The time a-b is the latent period, and in the case of a frog's 
 rust rocnemius is about y^th of a second. The total curve in 
 the same muscle lasts about -t^th of a second. 
 
 If, instead of applying and removing the galvanic current 
 in close succession, the current be allowed to flow for some 
 
INTERRUPTED CURRENT. 153 
 
 time through the nerve-muscle preparation, two contractions 
 and relaxations are noted. One contraction and relaxation 
 takes place when the current is applied, but during the rest 
 of the flow of the current the muscle remains in a state of 
 repose. The second contraction and relaxation occurs when 
 the current is broken. The ' contraction at the "make" of 
 current is greater than that at the " break " (Figs. 77 and 78). 
 
 From the fact that the muscle remains quiescent during the 
 flow of the current after the first shock, the theory is deduced 
 that it is not the change in 
 
 state, but the rapidity of FIG. 78. 
 
 the change in state, which 
 irritates the muscle into con- 
 traction. This is proven 
 by the fact that a large 
 amount of electrical cur- 
 rent can be poured into a 
 nerve-muscle preparation 
 without exciting a contrac- closing shock, 
 
 tion, provided the current 
 
 be gradually applied and very slowly increased. On the other 
 hand, a small amount of electricity if rapidly administered 
 will produce a sharp contraction. 
 
 Induced current : A single shock from an induced current 
 produces the same result as that of a galvanic current of in- 
 stantaneous duration. 
 
 A prolonged application of the induced current produces the 
 contraction on the " make " and a contraction on the " break " 
 similar to that of the galvanic current, except that the " break " 
 contraction is greater than the " make " contraction. 
 
 Interrupted current: The interrupted current, consisting 
 as it does of rapidly alternating " makes " and " breaks," 
 produces a series of rapidly succeeding shocks on the nerve- 
 muscle preparation. The result is that the muscle, after the 
 period of contraction is over, has no time to relax before a 
 second shock is received, which tends to a fresh contraction. 
 Hence the muscle remains in a state of continuous contraction 
 until the stimulus is removed or the muscle wears out. This 
 condition of continuous contraction is called tetanus (Fig. 79). 
 
154 
 
 MUSCLE. 
 
 7 
 
 Muscle electrical state : By a rise in electrical state is 
 meant an increase in the height of the curve in succeeding 
 contractions, on the application of single shocks. It is as 
 
 though the muscle became more 
 FIG. 79. sensitive and more responsive to 
 
 the second shock than to the first, 
 and more so to the third than to 
 the second, etc. This rise in elec- 
 trical state is observed for the 
 first six to ten shocks. It is as 
 though the muscle "limbered 
 up " in the first few shocks by a 
 little preliminary exercise until it 
 reached its power of doing its best. 
 Currents of rest : When a living 
 curve of tetanus. muscle is tested by means of the 
 
 galvanometer after removal from 
 
 the body, it is found to develop certain electrical currents 
 known as muscle-currents or currents of rest. They are 
 strongest from the centre of the muscle toward the cut end, 
 though certain minor currents are developed with the elec- 
 trodes in closer proximity. The cut ends of a muscle are 
 always electro-negative to its equator. This phenomenon 
 cannot be observed in uninjured muscle when in the bodv, 
 but any injury will render the injured portion electro-nega- 
 tive to the rest of the muscle. This condition ceases with 
 the power of contraction, and cannot be demonstrated in dead 
 muscle. 
 
 When the muscle is made to contract, the galvanometer- 
 needle, which has indicated the passage of an electri- 
 cal current during rest, flies quickly back toward the /ero, 
 indicating the cessation of the current of rest. This 
 action is known as the negative variation of the galvanom- 
 eter, and as soon as the contraction of the muscle has ceased 
 the instrument again indicates the presence of the current 
 of rest. 
 
 The causes are not yet fully determined, but these cur- 
 rents are probably due to chemical changes resulting from 
 physiological degeneration. It has been held that such 
 
PFLUGER'S LAW OF CONTRACTION. 155 
 
 currents occur naturally in muscle as the result of certain of 
 the cells exciting electro-motive forces, but the former theory 
 seems the more plausible. 
 
 Excitability and conductivity : These terms, although similar 
 as to the results, really mean very different things. 
 
 Excitability, or irritability, refers to the activity of response 
 a nerve may show to a given electrical shock ; whereas conduc- 
 tivity means the power of one part of a nerve to conduct an 
 impulse generated at another part of the nerve. 
 
 A moderate current while passing through a nerve pro- 
 duces no shock, but the excitability of the nerve at the point 
 where the kathode is placed is increased (this increase at the 
 kathodic area is called katelectrotonus) ; at the same time the 
 excitability of the anodic area is lessened (anelectrotonus). 
 On removing the current the excitability at the kathodic area 
 falls, and the excitability at the anodic area rises. 
 
 Ou the other hand, during the flow of a moderate current 
 there is a marked diminution in the conductivity of the nerve 
 at the kathodic area, even to the extent of rendering the 
 kathodic area impervious to conduction, without seriously 
 affecting the anodic area. On removing the moderately strong 
 current the nerve instantly returns to its normal conductivity. 
 If very strong currents be used, conduction is completely lost 
 at both the anodic area and the kathodic area during the flow 
 of the current ; and when the current is removed the nerve 
 does not at once return to a normal state of conductivity, but 
 remains impaired for a little while. 
 
 Pfluger's law of contraction : It has already been shown that 
 the stimulation of a nerve-muscle preparation by a galvanic 
 current will result in a contraction only at the "make" and 
 at the " break " of the current ; this is true only if the 
 current be of medium strength, regardless of whether the 
 current be " ascending" or "descending." But the results 
 are different if the current be very weak or very strong. 
 
 The following table, known as Pfluger's table, shows the 
 effects at a glance : 
 
156 
 
 MUSCLE. 
 
 Current-strength. 
 
 Ascending current. 
 
 Descending current. 
 
 "Make." 
 
 "Break." 
 
 " Make." 
 
 "Break." 
 
 Weak current .... 
 Medium current . . 
 Strong current . . . 
 
 Contraction. 
 Contraction. 
 
 
 Contraction. 
 Contraction. 
 Contraction. 
 
 Contraction. 
 
 Contraction. 
 Contraction. 
 
 Ascending and descending currents : By an ascending cur- 
 rent we mean a position of the electrodes such that the elec- 
 trical flow is from the periphery (muscle) to the centre (brain) 
 i. e.j the anode or positive pole is nearer the muscle and the 
 kathode or negative pole is nearer the nerve-cell. The de- 
 scending current is the reverse and the poles are transposed. 
 
 The explanation of the results is simple, if we hear in mind 
 the' effects on the nerve of the various strengths of currents. 
 
 A galvanic current is stronger on the " make " than on the 
 " break." Hence if we reduce the strength of our current 
 so that the " break " shock is so weak as to fail to give 
 any result, our " make/ 7 being somewhat stronger, would still 
 influence the muscle so as to cause a contraction. This, too, 
 would be regardless of the direction of the current. This 
 explains the first part of the " law," namely, that regarding 
 weak currents. 
 
 In explaining the second part of the law, it is necessary to 
 bear in mind that the nerve-vibrations start from the region 
 of the kathode on closing the current; but on opening tin- 
 current the nerve-vibrations start at the anodic area; also to 
 bear in mind that moderate currents diminish the conductivity 
 at the kathodic area without affecting the anodic region, anil 
 on removing the current the nerve at once returns to normal. 
 
 So we find on closing a descending current of moderate 
 strength, the excitation starting at the kathode can readily 
 pass to the muscle and produce a contraction. On opening 
 the current, the excitation starts at the anode and readily 
 travels along the nerve past the kathodic area (which, on 
 opening the current, returned to normal conductivity), and 
 so on to the muscle. 
 
 If we take an ascending current, on closing, the impulse 
 
NERVE-MUSCLE PREPARATION. 157 
 
 goes from the kathode down the nerve, past the unaffected 
 anodic area, to the muscle. On opening the current, the im- 
 pulse passes from, the anode directly to the muscle. 
 
 For the third part of the law we must remember that very 
 strong currents reduce conductivity at both anode and kathode, 
 and on removing the current the loss of conductivity does not 
 at once disappear. So, to study it in detail, let us assume 
 a strong ascending current. On making the current we re- 
 move the conductivity of the anodic area, and the impulse 
 starting at the kathode cannot travel by the impervious anodic 
 area, and hence no contraction results. On opening the current 
 the impulse from the anode passes to the muscle and a contrac- 
 tion follows. With a descending current, we find on closing 
 that the impulse starting from the kathode travels to the mus- 
 cle unhindered and a contraction results ; but on opening the 
 current the impulse starting at the anode travels along the 
 nerve until it reaches the area where the kathode was. This 
 area the impulse cannot pass (for the conductivity does not 
 return for some time) and no contraction results. 
 
 Position in the body: During repose a muscle is not in a 
 state of complete relaxation, but in an intermediate condition 
 between relaxation and contraction. The object of this is to 
 save time ; for the muscle can at once exert its power, as it 
 has no " slack " to gather in before it exerts its pull. Also 
 there is no jerk or jar in the motion. 
 
 Results of contraction : (a) heat ; (6) motion ; (c) sound ; (d) 
 change of shape ; (e) fatigue ; (/) chemical changes ; (</) rise 
 of electrical state. 
 
 Nerve-muscle preparation conditions influencing the results : 
 (a) freshness of the nerve-muscle preparation ; (6) suitable 
 temperature (98.6 F.) and moisture ; (c) suitable stimulus 
 interrupted electrical current ; (d) moderate weight for the 
 muscle to act on ; (e) duration of stimulus not less than 
 0.0015 of a second; (/) position of electrodes they must be 
 applied to the nerve obliquely and not at right angles ; (g) a 
 suitable length of nerve must intervene between the two 
 electrodes. 
 
 Nerve-muscle preparation order of fatigue : Fatigue ap- 
 pears in a nerve-muscle preparation : first, in the nerve- 
 
158 MUSCLE. 
 
 endings ; second, in the muscle-fibres ; third, in the nerve 
 proper (practically untiring). 
 
 The following experiments are offered in proof of the 
 above statement : 
 
 Stimulate a nerve-muscle preparation through the nerve 
 until the muscle no longer contracts. Then apply the stimulus 
 to the muscle-substance directly ; it is noted that the mus- 
 cle is excited to still further activity. This shows that 
 either the nerve or the nerve-endings were exhausted before 
 the muscle itself. To determine which is more liable to 
 give out, nerve or nerve-endings, perform the following 
 experiment : 
 
 Poison a nerve-muscle preparation with curare, which, as 
 has been shown elsewhere, inhibits the action of the nerve- 
 endings. Now, while the nerve-endings are paralyzed, apply 
 a continuous stimulation to the nerve-fibre. No muscular 
 activity is seen, for the stimulus cannot pass from the nerve 
 to the muscle across the bridge of poisoned end-plates. 
 Nevertheless the nerve is being constantly stimulated. After 
 a time the effects of the poison pass off and the end-plates 
 recover their activity, and the stimulus which is applied to 
 the nerve is transmitted to the muscle and active contractions 
 follow. This shows that the nerve outlasts either the end- 
 plates or muscle, for the nerve has been receiving and has 
 been capable of transmitting stimuli during the entire stimula- 
 tion, a period of time far greater than that during which either 
 the end-plates or muscle-fibre would have been capable of 
 such activity. 
 
 From these two experiments we deduce the order of fatigue 
 (1) nerve-endings, (2) muscle, (3) nerve-fibre. It is also 
 shown that nerve-fibre is practically untiring. 
 
 Rigor mortis: When an animal dies the muscles of the 
 body do not die at once, but remain alive for a variable time. 
 In man, if the individual be wasted and enfeebled by luiiir 
 illness and disease, the muscles may die in about ten minutes 
 after the death <>f the individual. In robust, healthy people 
 >ii(lleuly killed, the muscles may live for six or eight hours 
 longer. All the intermediate stages have been noted. The 
 death of the muscle is characterized by a contraction, fixing 
 
MEDULLATED FIBRES. 159 
 
 the limbs and body in a rigid condition. This post-mortem 
 rigidity constitutes rigor mortis. The muscles of the jaw 
 and neck are usually first affected, and then the arm, trunk, 
 thighs, and legs in the order named. All muscles are 
 affected, both the voluntary and involuntary. 
 
 The condition of rigor mortis lasts from ten to twenty- 
 four hours, and passes off in the inverse order from its ap- 
 pearance. First the legs relax, then the thighs, etc., and 
 lastly the jaw. 
 
 Cause of rigor mortis : Rigor mortis is caused by a fermen- 
 tative change which produces a coagulation of the blood- 
 plasma in the muscles. During this coagulation-process 
 there is a development of heat, which causes a rise in the 
 temperature of the body. It may amount to 5 or 10 F., 
 or even more. 
 
 Cause of disappearance of rigor mortis : After the fermenta- 
 tive change which causes the coagulation of the muscle- 
 plasma has ceased, a putrefactive process is set up which 
 destroys the coagulum and the muscles become soft and 
 flabby. 
 
 NERVOUS SYSTEM. 
 
 Fibres and Cells. 
 
 The nervous system is an aggregation of tissues so arranged 
 as to adjust the workings of all the parts of the body to one 
 another and to suit the body to its environment. 
 
 The elementary tissues of the nervous system are of two 
 forms : nerve-fibres and nerve-cells. 
 
 The nerve-fibres are of two kinds : (1) medullated or white 
 fibres ; (2) non-medullated or gray fibres. The fibres are 
 united in bundles to form nerve-trunks or " nerves/' 
 
 The cells are in groups to form nerve-ganglia, but nerve- 
 fibres are also found in the ganglia. 
 
 Medullated fibres consist of (1) an external nucleated 
 sheath, or neurilemma ; (2) an inner protective medullary 
 sheath (the white matter of Schwann) ; and (3) internally the 
 axis-cylinder (Fig. 80). 
 
160 
 
 NERVOUS SYSTEM. 
 
 The neurilemma is a pellucid structureless mem- 
 brane. Within are seen at inter- 
 vals nuclei surrounded by more FIG. 80. 
 or less protoplasm. These nuclei 
 and their protoplasm are relics 
 of embryonic cells. 
 
 The medullary sheath is a thick 
 fatty semifluid substance. It is 
 this substance which produces the 
 peculiar white appearance of some 
 nerves. Some authorities have 
 claimed that it is made up of a 
 fine network, in the meshes of 
 which is embedded the bright 
 fatty material. 
 
 The axis-cylinder consists of a 
 
 large number of primitive fibrill* Medullatcd ncr " librc . 
 which vary considerably in size, A, node of 
 but on the average may be said 
 to be about Y^j-ytn inch in diam- 
 eter. There is little doubt that 
 the axis-cylinder is the essential 
 part of the fibre, the other parts 
 being merely for support or pro- 
 tection. 
 
 Nodes of Panvicr: Here and 
 there at short intervals along the 
 course of medu Hated fibres are 
 found notches or constriction in 
 the medullary sheath. These con- 
 strictions are called the nodes of Ranvier. At these 
 points there is no loss of continuity of the axis- 
 cylinder nor of the neurilemma, but the medullary 
 sheath is deficient and allows the neurilemma to dip 
 in and touch the axis-cylinder. 
 
 The nodes apparently divide the nerve-fibre off 
 into histological units, for there is a nucleus for each 
 segment marked off by the nodes. 
 
 As the medullated nerves near their terminations, 
 
 B, nucleus beloiii:in 
 to the neurileinma : ('. 
 axis-cylinder ; J'. neu- 
 rilemma rendered dis- 
 tinct by the retraction 
 of the myelin of the 
 medullary sheath. In 
 the right-hand figure 
 the clefts of LimtLT- 
 mann arc shown as 
 while lines in the 
 dark myelin. The fi^r- 
 arefl are taken from spe- 
 cimens treated with 
 osmic acid, which 
 colors the tatty con- 
 stituents of the myelin 
 a dark brown or black 
 (Key and Retzius). 
 
FUNCTION OF NERVE-FIBRES. 
 
 161 
 
 FIG. 81. 
 
 the medullary sheath disappears and the axis-cylinder con- 
 tinues with the neurilemma ; but this latter also disappears 
 before the final ending of the fibre (axis-cylinder) in the 
 tissues. The fibre then splits into two or more terminal 
 branches. Thus white fibre becomes non-medullated fibre. 
 
 Non-medullated fibres: They consist of the axis-cylinder 
 alone, without the medullary sheath. They do not differ in 
 any other regard from the white fibres. When collected 
 in bundles to form nerves they have a yellowish or grayish 
 color. They are found in the olfactory and auditory nerves 
 and in the nerves of the sympathetic system, and they occur 
 in greater or less number in the nerves of the cerebro-spinal 
 system. In size these fibres are about one-third to one-half 
 the diameter of the medullated. They 
 are sometimes spoken of as the fibres of 
 Remak (Fig. 81). 
 
 Formation of nerve-trunks : To build 
 up a nerve-trunk, whether from medul- 
 lated or non-medullated fibres, the fibres 
 are joined in bundles which are enclosed 
 in a thin fibrous sheath (perineurium), 
 and these bundles of nerve -fibres are 
 bound in a firm connective-tissue which 
 serves to protect and to unite them 
 strongly. So far as we can see, the 
 individual nerve-fibres, as a rule, are 
 continuous and independent from their 
 origin in the nervous centres to within a 
 short distance of their peripheral termi- 
 nation. When a nerve divides into 
 several branches, or when adjacent nerves 
 communicate, it is because certain fibres 
 leave those with which they are associ- 
 ated and pursue a different course. There 
 is no real union of nerve-fibres. 
 
 Function of nerve-fibres : The function 
 of a nerve-fibres is the transmission of a 
 stimulus. The axis-cylinder connects the centre and pe- 
 riphery cells, and conveys between them the stimuli. This 
 
 11 Phys. 
 
 Fibres of Remak; mag- 
 nified 300 diameters. 
 With the gelatinous 
 fibres are seen two of 
 the ordinary, dark 
 bordered nerve-fibres 
 (Robin). 
 
102 NERVOUS SYSTEM. 
 
 transmission for any particular fibre is in one direction 
 
 only. 
 
 Depending on the direction the impulse is carried, the 
 nerve-fibres are classified into afferent (or centripetal), effer- 
 ent (or centrifugal), and intercentral fibres. 
 
 The former are those by which impressions are taken from 
 the periphery to the brain, and are commonly called sensory 
 fibres. 
 
 Conduction in these nerves may cause (1) a sensation as of 
 pain, heat, etc. ; (2) special sensation ; (3) reflex action of 
 some kind ; or (4) inhibition or restraint of action. 
 
 The second class conduct stimuli to the periphery, and are 
 known as motor fibres. Conduction in these nerves may 
 cause : (1) contraction of muscles (motor nerves) ; (2) control 
 of nutrition (trophic nerves) ; (3) control of secretion (secre- 
 tory nerves ; or (4) inhibition, augmentation, or checking of 
 other efferent impulses. 
 
 The last class includes nerve-fibres which connect more or 
 less distinct nerve-centres, and may therefore be said to have 
 no peripheral distribution. Nerve-fibres are mere conductors 
 of impressions. An impulse started in any fibre is trans- 
 mitted unchanged to its termination without being imparted 
 to any of the fibres lying near it. 
 
 Nerve-cells : As has been shown, the nerve-fibres are the 
 conveyors of impulses, either from the brain to the periphery, 
 or from the periphery to the brain. It is now in order to 
 study the termination or starting-points of these impulses. 
 Every nerve-fibre starts or ends in a nerve-cell, which is the 
 origin of the impulse in the case of an efferent nerve-fibre, or 
 the recipient of the sensation in afferent nerves. 
 
 Nerve-cells or ganglion-cells present a great variety of 
 shapes, and yet have common characteristics. The cell-body 
 is granular, and contains a large nucleus which contain- a 
 prominent nucleolus. The cells have at least one pncos, 
 and often more (Fig. 82), and the cells are classified as uni- 
 polar, bipolar, or multipolar. These processes are of two kinds 
 one kind dividing and subdividing (branching or proto- 
 plasmic processes ; or dendrites) until they become very deli- 
 cate and seem to interlace with, but without joining, the 
 
NERVE-ENDINGS AT PERIPHERY. 
 
 163 
 
 equally fine processes from other cells ; another kind (axis- 
 cylinder processes or axons) pass on without division and be- 
 come axis-cylinders of medullated nerve-fibres. 
 
 The nerve-cells vary greatly in size, and are very diverse 
 in form, but the presence of a nucleus, a nucleolus and the 
 processes is characteristic of nerve-cells. They may be 
 
 FIG. 82. 
 
 Is from the anterior horn of the gray substance of the spinal cord. 
 
 enclosed in a delicate capsule, which becomes continuous with 
 the netiri lemma (Fig. 83). 
 
 Nerve-endings at periphery : Efferent nerves, as has been 
 stated previously, on nearing their terminations undergo a 
 loss of the neurilemma and the sheath of Schwann, the axis- 
 cylinder itself splitting into several subdivisions. Each of 
 these subdivisions ends directly in the substance of a cell be- 
 longing to the organ supplied, by means of end- plates. 
 
 Sensory nerves " ending" in the skin find their way to or 
 take origin from certain bodies (sense-organs) which are essen- 
 tial to the conduction of the sensory impression to the central 
 nerve-ending. These sense-organs are of several kinds. In 
 
NERVOUS SYSTEM. 
 
 the fingers and toes are found two kinds of sense-organs 
 which may be especially mentioned : 1, touch-corpuscles 
 
 FIG. 83. 
 
 Nerve-cells, from spinal and sympathetic ganglia of man, enclosed in their cap- 
 sular sheaths from hardened preparations (Key and Rctzius). 
 
 (Fig. 85); 2, Pacinian corpuscles (Fig. 84). The exact 
 anatomy and physiological use of these bodies are still some- 
 what obscure; and, indeed, the whole subject of sensorv 
 nerve-terminations is but ill understood. We may regard 
 the fibres of sensory nerves, as a majority, as forming a 
 minute plexus in the corium and to terminate in sense- 
 organs in a way not always known. Some of the speeial 
 sense-organs are possessed of nerve-endings which are more 
 clearly observed. 
 
 Neuron : By the term neuron (Fig. 80) is meant a nervous 
 
NATURE OF NERVE-JM PULSE. 
 
 165 
 
 entity that is, a nerve-cell, its axis-cylinder process, dendrites, 
 and the terminals. 
 
 Nature of nerve-impulse : The nature of the impulse that 
 travels along the nerve is hard to determine. Nerve-fibres 
 
 FIG. 84. 
 
 FIG. 85. 
 
 A, tactile corpuscle ; b, nerve (Quain). 
 
 may be stimulated by any- 
 thing which increases their 
 irritability with sufficient 
 suddenness, but they cannot 
 of themselves originate such 
 a condition. The stimulus 
 produces its effect upon the 
 nerve-termination. The re- 
 sult, therefore, of any stimu- 
 lation of a nerve depends 
 solely on the character of the 
 end-organ, and not upon the 
 character of the stimulus. 
 
 Artificially in a nerve-mus- 
 cle preparation the impulse 
 can be aroused by four meth- 
 ods : chemical, thermal, electrical, and mechanical means. 
 The impulse passing along the nerve is not chemical, be- 
 cause there is no heat liberated ; nor is there an expansion 
 of nerve-fibre, even after prolonged activity, and naturally 
 one would expect heat and expansion as the result of chemi- 
 
 Vater's or Pacini's corpuscle, a, stalk ; 
 b, nerve-fibre entering it ; a, d, con- 
 nective-tissue envelope ; e, axis- 
 cylinder, with its end divided at / 
 
 S 
 
 (Quain). 
 
166 
 
 NERVOUS SYSTEM. 
 
 Fro. 86. 
 
 Neuron with long axon proceeding as an 
 uxis-cyliiiderof a nerve-fibre, n, nerve- 
 cell proper ; r/,dendrites ; x, axon ; d. g., 
 dendrite showing gemmulee; c, collutt r 
 als; /. nui tut'ts or terminals. Pyram- 
 i<lul cell of the cerebral cortex (S. 
 Ramon y Cajal). 
 
 cal changes. The fact that 
 the nerve does not change 
 its temperature excludes 
 the thermal theory. 
 
 The impulse cannot be 
 an electrical one, because 
 there is no insulation for 
 the conductors (the nerves). 
 
 The best explanation of 
 the impulse is that prob- 
 ably it is a physical molec- 
 ular vibration. 
 
 Direction of nerve - im- 
 pulse : A nerve - impulse 
 may travel in either direc- 
 tion in a given nerve, be 
 it either afferent or effer- 
 ent ; but the impulse trav- 
 elling in the physiological 
 direction alone is manifest, 
 because the impulse travel- 
 ling in the physiological di- 
 rection is the only one that 
 finds suitable terminals 
 through which to become 
 manifest. 
 
 It can be shown that a 
 nerve-fibre is capable of 
 transmitting its impulse in 
 either direction by the fol- 
 lowing experiments : 
 
 1. Take a fresh nerve 
 of considerable length, and 
 apply near its middle tin- 
 two polos of a galvanom- 
 eter. Apply a suitable 
 stimulus to one end of the 
 nerv<- ; an impulse will be 
 generated which will travel 
 

 DEGENERATION. 167 
 
 along the nerve. The presence of the impulse will be de- 
 tected by the galvanometer. This change of electrical state, 
 due to the physical molecular vibrations and shown by the 
 ^alvanometer, is called the "current of action." The gal- 
 vanometer has now shown that the nerve has carried an im- 
 pulse in one direction. If now we apply the stimulus to the 
 opposite end of the nerve, the galvanometer again will record 
 a " current of action," thus showing an impulse travelling in 
 the opposite direction to that taken by the first impulse. 
 
 2. If one were to stimulate one of the terminal branches 
 f an efferent axis-cylinder, not only would the impulse 
 travel in the physiological direction toward the end-organ, 
 but the impulse would travel up the branch of the axis- 
 cylinder until it reached the point where the axis-cylinder 
 had divided, and then travel down the other branches to 
 their respective end-organs. 
 
 Speed of nerve-impulses : Efferent impulses are somewhat 
 slower than afferent, the rate for the former being about 110 
 feet per second ; for the latter, about 150 feet. 
 
 The time occupied in executing a voluntary movement at 
 a given signal for instance, the recording the time of a 
 transit in an astronomical observation is found to be suffi- 
 cient to demand a correction for an accurate result. This 
 amounts to ^ to -fa of one second with different individuals. 
 The time lost in this way is known as the personal error of 
 the observer. When this has been ascertained by experi- 
 ment, the allowance to be made for the personal error is his 
 personal equation. This remains nearly constant for each 
 person. 
 
 Degeneration : When a nerve is divided its function, of 
 course, ceases. It is no longer capable of carrying impulses 
 throughout its length, owing to the loss of continuity. But 
 by applying proper artificial stimulation to the nerve at a 
 point distal to the point of division in the case of an efferent 
 nerve, or proximal to the cut in an afferent nerve, a response 
 is obtained similar to the normal action. For example, 
 certain muscles may be made to contract by applying an 
 electric shock to the distal end of a cut motor nerve ; or 
 sensation of pain may be produced by stimulating the proxi- 
 
 O\^llk5Cl 
 
168 NERVOUS SYSTEM. 
 
 mal end of a sensory nerve. Furthermore, it is noticed that 
 for the first few hours after division the irritability of a 
 divided nerve is heightened ; after this period of heightened 
 irritability the nerve begins to lose its power of conductivity, 
 and in three or four days the process of degeneration is com- 
 plete and the nerve fails to convey any impulses. 
 
 Microscopic examination: When examined under the micro- 
 scope a divided nerve-fibre presents certain changes. At the 
 point of division, degeneration takes place in but one direc- 
 tion, and that away from the " nutrient cell," or cell of which 
 it was an outgrowth. The degeneration of the fibre extends 
 to its final distribution. In the case of a medullated nerve- 
 fibre, if the section is at a point between two nodes of 1 Jan- 
 vier, the degeneration in that portion of the nerve still in 
 continuity with its trophic cells extends up as far as the first 
 node of Ranvier from the point of section. 
 
 The histological changes during the period of degeneration 
 are as follows : During the period of increased irritability the 
 axis-cylinder is slightly granular, and the medullary sub- 
 stance somewhat cloudy. Soon a complete fragmentation of 
 the axis-cylinder takes place, the myelin-substance is de- 
 stroyed, the axis-cylinder is absorbed, and in place of the 
 normal nerve only the neurilemma is left. 
 
 Non-mod ul lated fibres have not been studied with such 
 great care, but the process of degeneration is the same as 
 that described, except for the absence of a medullary 
 substance. 
 
 The degeneration occurs practically simultaneously through- 
 out the entire portion of the nerve involved. 
 
 Nerve-regeneration: If, under proper precautions, the sev- 
 ered ends of a divided nerve are put in apposition, they may 
 be made to unite and regenerate, with a return of function. 
 1 1 is noticed that sensory fibres regenerate more rapidly than 
 motor i.e., in the ease of an ordinary mixed somatic nerve 
 during regeneration pain is felt before motion is present. 
 
 Microscopic examination shows an extension of the axis- 
 cylinder from the normal part of the nerve into the empty 
 neurilemma of the degenerated portion. The regenerating 
 :i\i cylinder extends along until it reaches the final distrilm- 
 
SYMPATHETIC SYSTEM. 169 
 
 tion of the nerve, the medullary substance gradually being 
 reformed, until the nerve is again intact. 
 
 Although the nervous system throughout the body is con- 
 nected with the brain and forms an integral whole, neverthe- 
 less it has always been the custom to speak of a certain por- 
 tion of the nervous system as a separate part, to which the 
 name " sympathetic system " has been given, the rest of the 
 nervous system being designated as the cerebro-spinal. 
 
 The cerebro-spinal system consists of the brain, the medulla 
 oblongata, and the spinal cord, with the nerves proceeding 
 from them. 
 
 Sympathetic System. 
 
 Primarily, the sympathetic system (Fig. 87) consists of a 
 double chain of ganglia and communicating nerves which lie 
 on either side of the vertebral column and extend throughout 
 its entire length. Other ganglia occur in connection with 
 some of the cranial nerves, more especially the vagus and 
 trigeminus. There are ganglia and plexuses connected with 
 the various organs (e. </., cardiac and solar), and still others 
 in the substance of some of the organs (e. g., stomach and 
 intestines) ; still others in connection with the bloodvessels. 
 The sympathetic system has numerous communications with 
 the cerebro-spinal system. 
 
 The fibres of the sympathetic nerves are often smaller than 
 those of the cerebro-spinal system, and among them are a large 
 number of non-medullated fibres. The sympathetic nerves do 
 not differ materially from the cerebro-spinal. They are very 
 similar. The occurrence of ganglia upon the sensory branches 
 of the spinal nerves and upon the sensory cranial nerves 
 (pneumogastric, glosso-pharyngeal, and trigeminus) adds to 
 the similarity. Then, too, the frequent communications be- 
 tween the two systems practically make one system of them, 
 and the division is largely one for convenience. 
 
 Communication of cerebro-spinal and sympathetic systems : 
 From each spinal nerve is given off a communicating branch 
 to a neighboring sympathetic ganglion. These branches con- 
 tain both motor and sensory fibres. Thus it is seen that all 
 
170 
 
 NERVOUS SYSTEM. 
 FIG. 87. 
 
 Ganglia and nerves of the sympathetic system. 
 
 impulses travelling alon^ the sympathetic system may cither 
 start or terminate in the cerebro-spinal. 
 
CEPHALIC GANGLIA. 171 
 
 By the term ganglion is meant a collection of gray and 
 white nerve-substance, which is usually oval in outline, and 
 is frequently found in the course of a nerve-trunk. In the 
 sympathetic system the ganglia contain numerous nerve-cells, 
 smaller than those of the brain and spinal cord, and from 
 these cells arise nerve-fibres which distribute themselves in 
 the plexuses. 
 
 Ganglia of the sympathetic. The long chain of ganglia, 
 with the various plexuses, of the sympathetic system are 
 classified regionally as cephalic, cervical, thoracic, abdominal, 
 and pelvic ganglia and plexuses. 
 
 Cephalic ganglia : In the head the sympathetic ganglia are 
 four iu number ophthalmic, spheno-palatine, submaxillary, 
 and otic ganglia. Each has communications from the general 
 sympathetic; and from the cranial nerves both motor and sen- 
 sory fibres. 
 
 Ophthalmic ganglion: It is a small ganglion situated in the 
 orbit, and receives communications from the sympathetic and 
 from the motor oculi (third) nerve, a motor branch, and from 
 the trigeminus (fifth) nerve a sensory branch. Its branches 
 pass into the eyeball (ciliary nerves), and are distributed in 
 the iris. Their function is the control of the pupil, of the 
 apparatus of accommodation, and of the vaso-motor function 
 in the vessels of the eye. 
 
 Spheno-palatine ganglion : It is situated in the spheno-max- 
 illary fossa, and receives branches from the cervical sympa- 
 thetic system and motor fibres from the facial (seventh) nerve, 
 and sensory from the fifth. Its branches are distributed to 
 the mucous membrane and muscles of the palate and uvula, 
 and to the naso-pharynx. They are both sensory and motor. 
 
 The submaxillary ganglion lies in close proximity to the 
 submaxillary gland. It receives branches from the superior 
 cervical ganglion by way of the plexus on the facial artery, 
 and a sensory branch from the lingual branch of the fifth 
 nerve. Its motor branch is through the chorda tympani 
 nerve from the seventh or facial nerve. Its branches are 
 distributed to the submaxillary gland and control its 
 function. 
 
 The otic ganglion is a small ganglion lying upon the third 
 
 
172 NERVOUS SYSTEM. 
 
 division of the fifth nerve as it emerges from the foramen 
 ovale. It has branches from the sympathetic on the middle 
 meningeal artery, and both a motor and a sensory communi- 
 cation from the fifth, as well as a branch from the glosso- 
 pharyngeal through Jacobson's nerve. Its branches are 
 motor, to the tensor palati and tensor tympani muscles ; and 
 sensory, to the mucous membrane of the tympanum and 
 Eustachian tube. 
 
 Cervical ganglia: There are two a superior and an in- 
 ferior (with sometimes a third, middle) ganglia on each side 
 (Fig. 87). These ganglia receive communications from each 
 of the cervical spinal nerves and from each other. Their 
 branches are given off: (1) to form the carotid plexus, which 
 follows the carotid artery and its branches, forming by its 
 inosculations the vaso-motor plexuses of the carotid system. 
 (2) To furnish branches for distribution to the thyroid gland, 
 larynx, trachea, pharynx, and oesophagus. (3) To form the 
 cardiac nerves, which are distributed in the cardiac plexus. 
 
 Thoracic ganglia : In the chest the ganglia are numerous 
 (Fig. 87), and each ganglion receives two branches of com- 
 munication from the intercostal nerve above it, while the 
 relationship of the ganglia is maintained by the intercommu- 
 nicating chain. The nerves originating here are distributed 
 to the plexuses on the thoracic aorta, and to those of the 
 lungs and oesophagus. 
 
 Abdominal ganglia : In the abdomen there is an aggrega- 
 tion of ganglionic enlargements situated upon the co-liae 
 artery, known as the semilunar or cceliac ganglion. It com- 
 municates with the thoracic ganglia and with all the lumbar 
 nerves. From this centre proceed a multitude of diverging 
 and inosculating fibres, which, from their common origin and 
 radiating course, are called the solar plexus. Its secondary 
 plexuses, accompanying the branches of the abdominal aorta, 
 are distributed to 'the stomach, intestines, spleen, pancreas, 
 liver, kidney, and internal organs of generation. 
 
 Pelvic plexuses: The plexuses of the pelvis are derived 
 from four or five pairs of ganglia situated on the anterior 
 portion of the sacrum and terminating in the ganglion i))i}><tr, 
 lying upon the coccyx. Its fibres join those from the solar 
 
VASO-MOTOR FIBRES. 173 
 
 plexus, and are distributed with them along the course of 
 the branches of the internal iliac arteries. 
 
 Sympathetic system function: The action of the sympa- 
 thetic is principally shown in the organs of nutrition and 
 secretion and in the vascular system. The sympathetic also 
 plays an important part in the special senses e. g., dilatation 
 of the pupil is effected through it, and probably accommoda- 
 tion is acted upon by fibres, other than the oculomotorius, 
 which come through the lenticular ganglion. The tensor tym- 
 pani muscle is supplied, indirectly, from the otic ganglion. 
 The efferent nerve-fibres of the sympathetic system send to 
 the muscles of the vascular system vaso-motor (i. e., vaso- 
 constrictor and cardiac accelerator) and also vaso-inhibitory 
 fibres (i. e., vaso-dilator and cardiac inhibitory). To the 
 muscles of the viscera they send both vaso-motor and vaso- 
 inhibitory fibres. 
 
 Sensory and motor influence of the sympathetic : It will be 
 remembered that the spinal nerves, both afferent and efferent, 
 act very quickly upon the tissues supplied by them; the 
 sympathetic nerves act more slowly. Thus, if the afferent 
 nerve of a ganglion or its efferent nerve be stimulated, there 
 is a slow wave-like series of motions set up in the parts sup- 
 plied, which continue for some time after the stimulus is with- 
 drawn. This is particularly well seen in intestinal peristalsis, 
 which may be excited by stimulation of the intestine or of 
 the semilunar ganglion or of the branches of the solar 
 plexus. 
 
 Relation of the sympathetic to the secreting glands : There 
 has been demonstrated in some of the secreting glands and 
 it is probably true for all that functional stimuli, distinct 
 from the vaso-motor, come through the sympathetic nerves, 
 and that these fibres are closely associated with the vaso- 
 motor fibres. Thus, in the stomach the secretion of the 
 gastric juice is only temporarily suspended by the section of 
 the vagi, and is resumed by the action of the sympathetic, 
 showing that the control is by the sympathetic. Thus it is 
 seen that there are true " secretory " nerve-fibres. 
 
 Vaso-motor fibres : The vaso-motor function of the sympa- 
 thetic has been discussed under the section on Circulation. 
 
174 
 
 NERVOUS SYSTEM. 
 
 Transverse sections of 
 the sjiiiiiil cord in man. 
 I, upper cervical re- 
 gion : II, lower cervical 
 region; III. dorsal re- 
 gion : IV, lumbar en- 
 largement ; V, lower ex- 
 tremity. 
 
 Spinal Cord. 
 
 Gross anatomy : The spinal cord is 
 that portion of the cerebro-spinal nerv- 
 ous system contained within the spinal 
 canal. It connects with the medulla 
 oblongata, and terminates in a fine 
 thread of gray matter (the filum termi- 
 nale) at about the second lumbar ver- 
 tebra. In form it is irregularly cylin- 
 drical, and varies in the size and shape; 
 of its cross-section at various levels, as 
 is shown in Fig. 88. It is incompletely 
 divided into symmetrical halves, and its 
 mid-line is indicated in front by a fissure 
 (anterior median fissure) which extends 
 for about one-third its antero-posterior 
 diameter; behind by a deeper but nar- 
 rower fissure (posterior median fissure), 
 which involves about one-half of the 
 same diameter. It is composed of white 
 and gray substance. 
 
 Issuing from the cord along its course 
 are thirty-one pairs of nerves. Each of 
 
 FIG. 89. 
 
 Transverse section of tin- spinal cord, a, t>, 
 spinal nerves of tin- right and left sides; 
 (I, origin of the anterior rout : e, origin 
 of the posterior root ; c, ganglion of the 
 posterior root.' 
 
 these spinal nerves is made up of an an- 
 terior and a posterior root (Fig. 89), of 
 which the latter is the larger. The ante- 
 rior root arises between the anterior and 
 lateral white columns, the posterior be- 
 
SPINAL CORD. 175 
 
 tween the posterior and lateral columns. On each pos- 
 terior nerve-root is found a ganglion immediately beyond 
 its point of emergence. The function of this seems to be 
 trophic. 
 
 The white substance is arranged externally to the gray in 
 each half of the cord, and is so disposed as to be conve- 
 niently divided for purposes of description into three columns, 
 known respectively as the anterior, lateral, and posterior 
 columns of the cord. There is also a thin band of white 
 substance at the base of the anterior median fissure (the 
 white commissure). The gray matter fills in the central 
 portion of the cord, and is variable in its amount, the calibre 
 of the cord at its enlargements being increased by the in- 
 crease in the amount of gray matter at these points (Fig. 88). 
 The white substance will be noticed to diminish quite regu- 
 larly in the sections of the cord from above downward, as 
 seen in this series. The gray substance is not completely 
 halved by the anterior and posterior fissures of the cord, but 
 is continuous across the mid-line (gray commissure) ; and in 
 it at the centre is a minute canal communicating with the 
 ventricles of the brain. The gray matter is more abundant 
 between the lateral and anterior and between the lateral and 
 posterior columns of the white substance ; the names anterior 
 and posterior horns (cornua) are given to these regions re- 
 spectively. 
 
 Spinal cord microscopic examination: Under minute ex- 
 amination the white matter is found to be made up of medul- 
 lated nerve-fibres, which collect to form the anterior and 
 posterior nerve-roots, and communicate with other regions 
 of the cord. 
 
 The gray matter contains multipolar cells of varying size 
 and shape, with axis-cylinders and " branching 77 processes 
 lying in the neuroglia (" connective tissue "). The multi- 
 polar cells are some of them quite large. In the anterior 
 horn of the gray substance the axis-cylinder-processes of the 
 nerve-cells connect directly with fibres forming the anterior 
 nerve-roots (Fig. 90) ; but in the posterior cornu the com- 
 munication is indirect i. e., through the branching processes 
 and the divided axis-cylinders of the collaterals of the pos- 
 
176 
 
 NERVOUS SYSTEM. 
 
 terior nerve-roots, forming thus by contiguity what are known 
 as end-arborization^. 
 
 Origin and course of nerve-roots : (a) Anterior nerve-roots 
 are derived from (1) the anterior columns of the cord, but 
 some fibres come through the commissure from (2) the oppo- 
 site side, and some come from (3) the lateral tract. Still 
 other fibres arise from (4) the multipolar cells in the anterior 
 cornu of the gray matter. The fibres of the anterior nerve- 
 
 Fio. 90. 
 
 Transverse section of the spinal cord in man (lumbar region). 
 
 roots are efferent i. e., they carry impulses from the centre 
 (brain) to the periphery. 
 
 (/>) Posterior nerve-roots give off collaterals which enter the 
 posterior horn of the gray matter, and the ultimate fibres 
 break up and form "indirect" communication with the 
 branching processes of the large multipolar cells, but some 
 fibres cross through the gray commissure to the opposite side. 
 The fibres of the posterior roots arc afferent i. e., they cnrry 
 impulses from the periphery to the centre in the cord, 
 medulla, or brain. 
 
 The course of all the fibres through the cord itself has not 
 been determined with absolute accuracy. Certain fibres, how- 
 

 TROPHIC CENTRES OF NERVE-ROOTS. Ill 
 
 ever, have been traced through their length, notably the fibres 
 of the pyramidal tracts, in the anterior and lateral columns. 
 
 It has been calculated that only about one-half as many 
 fibres enter the spinal cord from the brain as leave it through 
 the nerves ; therefore it must follow that some fibres originate 
 from the corcl. The increase in gray matter in the cervical 
 and lumbar enlargements, where the fibres for the large plex- 
 uses of the nerves (branchial and lumbar) are given off, con- 
 firms this view. 
 
 Spinal cord recurrent sensibility fibres : Certain afferent 
 fibres in the nerve-trunks of the body do not pass directly into 
 the posterior nerve-roots and so to the spinal cord, but take an 
 erratic course as follows : After leaving the nerve-trunk these 
 fibres, known as the recurrent sensibility fibres, pass into the 
 anterior nerve-root, being mingled with the efferent fibres fora 
 short distance ; then these fibres double on their course, return 
 to the point of junction between the anterior and posterior 
 nerve-roots, to follow by way of the posterior root the normal 
 course to the cord. These fibres form but a small proportion 
 of the afferent fibres, and the purpose of their erratic course 
 is not easily explainable. 
 
 Trophic centres of nerve-roots degeneration : The posterior 
 nerve-roots seem to be dependent upon the ganglia which are 
 found upon them for trophic influence. The anterior root in 
 a similar way seems to depend upon a trophic centre in the 
 gray matter in the anterior horn. 
 
 Division of a nerve is followed by a degeneration or break- 
 ing down of the axis-cylinders of its fibres within a day or 
 two, the loss of function being an earlier and immediate 
 manifestation. This degeneration is centrifugal that is, does 
 not proceed toward the spine, but to the periphery. If the 
 posterior root be cut, however, between its ganglion and its 
 emergence from the cord, the degeneration is toward the cord 
 i. c., centripetal and the nerve beyond the ganglion does 
 not degenerate. The anterior root cannot, however, be 
 divided at any point beyond its emergence without centrifugal 
 degeneration of the fibres (Fig. 91). The regeneration takes 
 place slowly if the continuity of the nerve is at once restored, 
 and may even follow after the nerve has degenerated for some 
 
 12 Phys. 
 
178 
 
 NERVOUS SYSTEM. 
 
 months and a complete loss of function has affected the part 
 supplied by it. The fact that the axis-cylinders are restored 
 only in this way is of interest, as showing the influence of the 
 trophic centres on the nerve-growth. 
 
 FIG. 91. 
 
 Degeneration of spinal nerves and nerve-roots after section. A, section of nerve- 
 trunk beyond the ganglion ; B, section of anterior root ; C, section of posterior 
 root ; D, excision of ganglion ; a, anterior root ; p, posterior root ; g, ganglion. 
 
 The functions of the spinal cord may be tabulated as fol- 
 lows : 
 
 (a) Conduction, or carrying impulses between centre and 
 periphery ; 
 
 (b) Transference i. e., an apparent transferring of im- 
 pression from one set of fibres to another ; 
 
 (c) Reflex action i. e., the origination of action in response 
 to stimuli from the periphery ; 
 
 (d) Augmentation, or a resulting effect in excess of the 
 exciting cause; 
 
 (e) Automatic acts, from corresponding centres ; 
 
 (/) Coordination, or the adjustment of the workings of 
 different parts of the body to one another; 
 
 (g) In hi /tit ion of reflex acts. 
 
 Conduction : Than by the spinal cord there is practically no 
 other nervous communication between the brain and the 
 musculo-cutaneous system; hence through it must conic nil 
 the nerve-impulses which pass to or from the brain. In 
 other words, every sensory impulse that is felt and every 
 motion that is willed, perception and volition being attributes 
 
CONDUCTION. 179 
 
 of the brain, must be conducted through the nerve-fibres of 
 the spinal cord to the brain, and vice versa. 
 
 The student must not suppose that in all instances a con- 
 tinuous nerve-fibre runs from the central cell in the brain to 
 the peripheral end-organ, and vice versa. The nerve-fibre is 
 often broken at one or more places along its course, the end 
 of the fibre terminating in a brush-like ending which " articu- 
 lates " with the dendrites of a secondary or relay cell. The 
 impulse is thus communicated to the second cell, which in 
 turn transmits the impulse along its own nerve-fibre and 
 so on. 
 
 The conducting fibres in the cord lie chiefly in the white 
 matter; whereas the gray substance represents the cell-ele- 
 ments as well. 
 
 The conducting fibres have definite positions in the cord, 
 and each portion has fibres which always conduct the same 
 kind of impressions. 
 
 Most of the motor fibres cross to the opposite side in the 
 medulla oblongata (decussation of the pyramids), and the im- 
 pulses pass down by the lateral columns in the crossed or lat- 
 eral pyramidal tract on the side opposite to that in which they 
 originate. There is also a set of motor fibres which does not 
 cross, but passes directly to the same side in the anterior col- 
 umns, and decussates in the anterior or white commissure near 
 the point of distribution. The destination of these fibres is 
 variable, for the reason that the amount of decussation in the 
 medulla is not constant ; but, as a rule, the fibres in the direct 
 tract go to the upper portion of the body. The cells in the 
 anterior cornu of the gray matter of the cord originate many 
 of the fibres which go to the nerves. This is demonstrated 
 after division of the cord by stimulating these fibres : a series 
 of coordinated motions follows, and this stimulus may be ap- 
 plied direct to the fibres or through the sensory nerves. 
 
 The course of the sensory fibres (Fig. 92) is somewhat 
 problematical, but certainly these impulses enter the cord by 
 the posterior nerve-roots. The fibres conducting them break 
 up as described, and cross to the opposite side of the cord 
 through the gray commissure. It is probable that after decus- 
 sating the fibres communicate with multipolar cells, and thus 
 
180 
 
 NERVOUS SYSTEM. 
 
 pass on as white fibres in the lateral columns. These fibres 
 after entering the lateral columns (of the opposite side) pass 
 to the medulla as a distinct tract the antero-lateral ascending 
 
 FIG. 92. 
 
 Diagram showing pathway of the sensory impulses. On the left side SS' represent 
 afferent spinal nerve-fihres ; C, an afferent cranial nerve-fibre. These fibres ter- 
 minate near central cells, the neurons of which cross the middle line and end 
 in the opposite hemisphere (Van Gehuchten). 
 
 tract at the periphery of the lateral, extending into the 
 anterior column. 
 

 REFLEX ACTION. 181 
 
 It is by this tract that sensations of pain and of tempera- 
 ture are supposed to pass. There are also afferent fibres in 
 the posterior columns the posterior median by which the 
 sensations of touch and weight (or muscular sensation) are be- 
 lieved to pass ; the latter, however, does not decussate. To 
 recapitulate : sensations of pain and temperature are trans- 
 mitted through the lateral columns, and those of touch and 
 weight through the posterior columns. 
 
 Transference : Impressions conveyed by a centripetal nerve- 
 fibre, it has been stated, pass uninterruptedly throughout 
 its whole length without being communicated to adjacent 
 fibres. When such an impression reaches a nerve-centre in 
 the cord, it may seem to pass to another fibre or set of fibres, 
 so that the pain or other sensation is felt in an entirely differ- 
 ent part from that in which the stimulus started. At the 
 same time the primary impression may also be conducted to the 
 brain, so that the sensation seems to come from two different 
 places. This phenomenon, known as transference, cannot be 
 well explained, yet instances of it are very frequent. In dis- 
 ease of the hip the pain is frequently felt in the knee alone, 
 yet the latter may be perfectly sound. A biliary calculus 
 will often cause pain in the glans penis. 
 
 Reflex action : Certain sensory stimuli are received, pass up 
 the nerve-trunks to the posterior nerve-roots, and thus to the 
 spinal cord. In the cord the impulse may be sent to the brain, 
 producing the consciousness of pain, etc.; or else the impulse 
 in the cord may be transmitted directly to some motor cell in 
 the anterior horn, stirring it to activity, with the result that 
 there is some muscular action. For example, a person may 
 be tickled with a feather : the subject brushes away the offend- 
 ing object either with or without consciousness of what he is 
 doing. If he does it unconsciously, the reflex act takes place 
 in the cord ; if he brushes away the feather as a result of 
 the impression received in his brain, the reflex act took place 
 in the brain. Furthermore, a person may perform a reflex 
 act through the reflex centres in the cord, and yet after 
 the act is completed he may receive the sensory impulse 
 in the brain. From this we may deduce the following 
 rule : 
 
182 NERVOUS SYSTEM. 
 
 A reflex act taking place through the cord, may or may not 
 be accompanied by conscious sensation ; but if it is accompa- 
 nied by conscious sensation, the consciousness is always later 
 in point of time than the act. Thus we may say a reflex ac- 
 tion is an action which results from a centripetal nerve-im- 
 pulse passing to a nerve-centre in a ganglion, and there trans- 
 forming to a centrifugal impulse passing to a muscle. Such 
 an action may be simple and involve a single muscle, or com- 
 plex and involve many : thus, a ray of light falling upon the 
 retina causes a simple reflex contraction of a single muscle, 
 and the iris contracts. As an illustration of a complex reflex 
 action, however, irritation of the larynx causes not only a 
 closing of the glottis, but a contraction of all the muscles in- 
 volved in forced expiration or coughing. 
 
 Reflex acts are more noticeable in the cerebro-spinal sys- 
 tem ; but they may belong to either, or may be mixed, the 
 impulse going by the one system and returning by the other. 
 Examples: sneezing, coughing, swallowing are cerebro-spinal 
 reflexes ; the vaso-motor reflexes are largely sympathetic, but 
 the centripetal nerve is often cerebro-spinal, as in the secre- 
 tion of saliva or in blushing. 
 
 The spinal cord in man is so much under the control of 
 the higher centres that its capabilities for reflex action nro 
 often overlooked. After injury to the spinal cord the reflex 
 acts are apt to be purposeless and fruitless. In many lower 
 animals reflex actions, after the cord has been divided, are 
 often followed by extensive and coordinated movements. In 
 the frog this is especially marked. Yet the difference is 
 one of degree only. In man many minor acts are per- 
 formed as reflex movements occurring through the aid of the 
 spinal cord, although the cord is incapable of initiating them 
 of itself. 
 
 Special reflexes of the cord : Under this heading we may 
 enumerate the micturition, defecation, and genital centres : 
 
 (1) Micturition: Here the sphincter of the bladder is kept 
 in a normal state of contraction, until such time as afferent 
 impulses are sent to the cord from the neck of the bladder 
 owing to pressure of urine; an efferent impulse is then 
 aroused which releases the sphincter and at the same time 
 
SPECIAL REFLEXES OP THE CORD. 
 
 183 
 
 FIG. 93. 
 
 causes the wall of the bladder to contract (Fig. 93). 
 though this act is a reflex one, it is 
 under the control of the will to a 
 large extent. 
 
 (2) Defecation : The nature of the 
 act is identical with that of micturi- 
 tion : the impulse arising from the 
 presence of flatus or faeces, with the re- 
 sultant relaxation of the sphincter ani 
 and contraction of the lower bowel. 
 
 (3) Genital: Controls the erection of 
 the penis and the ejaculation of semen. 
 Under this heading we may also in- 
 clude the centre for parturition. 
 Stimulation of the interior of the 
 uterus by its contents may excite the 
 centre enough to cause it to send out 
 impulses producing uterine contrac- 
 tions and expulsion of its contents. 
 That delivery can take place in a 
 person under the influence of chloro- 
 form shows that the centre is inde- 
 pendent of the will. As in the case 
 of micturition or defecation, there is 
 an accessory action of the abdominal 
 muscles, for the most part reflex and 
 involuntary. 
 
 Al- 
 
 Schema of micturition. AC, 
 EC, C, automatic, reflex, 
 and cerebral centres; B, 
 bladder ; S, sensory centre 
 acted on by afferent im- 
 pulses (Landois). 
 
 All these reflexes have their seat in the lumbar enlarge- 
 ment of the cord. 
 
 Varieties of reflex acts : Reflex actions may be simple or 
 coordinated, primary or secondary. In the simplest reflex act 
 only a single nerve-cell with an afferent and an efferent fibre 
 is concerned. In most reflexes, however, it is probable that 
 several cells are involved and act in concert. Primary reflex 
 acts are those such as sucking, which the infant can perform 
 as well as the adult. Secondary or acquired reflexes are 
 those which require an effort of the will for their first per- 
 formance, but which become habitual after frequent repeti- 
 tion. They are described under Coordination. 
 
184 NERVOUS SYSTEM. 
 
 Augmentation : The resultant reflex act of a stimulation 
 may be far in excess of the amount of stimulation received. 
 For example : a tiny drop of acetic acid applied to the skin 
 of a decapitated frog may result in most frantic efforts on the 
 part of the animal to rub off the offending fluid, although 
 the irritation can be but slight. The explanation lies in the 
 fact that the sensory nerve- fibres, as they enter the cord, in- 
 dividually break up into an ascending and a descending limb. 
 These two limbs in turn give out, at several points along 
 their course, collaterals, which break up into sets of brush- 
 endings. These " brush-endings " connect with the demlrites 
 of motor cells. Thus it is seen that one sensory fibre may 
 stir into activity several motor fibres, so that the resultant act 
 is augmented. 
 
 Automatic acts : In normal subjects the cord is not tho scat 
 of many automatic acts. But if the brain be destroyed or 
 severed from the cord, certain centres which normally are 
 secondary assume primary importance and are capable of au- 
 tomatic activity. The best examples are the vaso-motor 
 centres of the cord. 
 
 Under the capitulation of normal automatic coifrcx we 
 may include those governing the sweat and general mus- 
 cular tone. 
 
 The student must bear in mind that there are many auto- 
 matic acts whose centres are outside of the cord, their origin 
 being in local centres. Thus, there are certain actions which 
 continue, and, while they are closely related to reflex action, 
 do not seem to be true reflexes, but to originate in the part. 
 Thus, the peristaltic action of the alimentary tract is not de- 
 pendent upon the presence of food in the intestines, but may 
 be excited in the absence of food or checked when it is pres- 
 ent. This action has been referred to small ganglia and 
 nerve-plexuses found there (Auerbaeh's and Meissner's), and 
 is considered to originate in the local nerve-centres. This is 
 what is known as automatism or automatic nerve-action. 
 
 Coordination: The coordination of the cord is nothing but 
 a repetition of ordinary reflex acts for our daily lives. F<>r 
 example, we look upon walking as a coordinate movement. 
 It is performed unconsciously and depends on reflex activity 
 
GROSS ANATOMY. 185 
 
 resulting from cutaneous and muscular sensations, or the 
 sense of position in space. 
 
 Inhibition of reflex acts : This function does not originate in 
 the cord, but in the brain ; but the transference of the impulse 
 takes place in the reflex centres of the cord. It is the ability to 
 control or modify reflex action by an effort of the will or by 
 mental action which is not consciously voluntary. As an ex- 
 ample of this, if the palm of a sleeping child be touched by the 
 finger, the baby's hand will grasp the finger ; but if the child 
 is awake, no such reflex occurs : it is checked by mental 
 action. Again : one may avoid crying out when in pain by 
 an effort of the will, or may hold the feet still when the soles 
 are tickled. An example of this inhibition of reflex action 
 is offered in the knee-jerk, an important sympton in the diag- 
 nosis of certain nervous diseases. When the patellar tendon 
 is tapped sharply with the tips of the fingers the foot and leg 
 are suddenly jerked forward. If the patient is ignorant of 
 what is to be done, the amount of motion obtained is diag- 
 nostic ; but if he knows what is expected, the result is apt to 
 be deceptive, as this reflex can be entirely prevented by the 
 will. For this reason, if the patient knows the symptom, it 
 is always tried when he is off his guard. 
 
 The object of reflex acts is to save time, suffering, and 
 wear and tear on the body ; but if we had no check on reflex 
 activities, we should spend all our time making efforts to 
 escape outside stimuli. 
 
 Medulla Oblongata. 
 
 Gross anatomy : The medulla oblongata, or bulb, is a column 
 of white and gray nerve-substance, the lowermost portion of 
 the brain, and connecting with the spinal cord below. 
 
 The white substance is composed of the medullary fibres 
 continued up from the cord, and the gray matter is arranged 
 variously between the bands of white fibres. It has an an- 
 terior and a posterior fissure, corresponding to those of the 
 cord, and the central canal of the cord here opens into the 
 fourth ventricle. 
 
 The medulla continues in a general way the arrangement 
 
186 NERVOUS SYSTEM. 
 
 of the fibres in tracts of the cord below ; but as the diameter 
 is greater, the general shape is pyriform and the shape of the 
 columns is changed (Fig. 94). The anterior columns of the 
 cord correspond in position to the pyramids of the medulla ; 
 the posterior columns, to the restiform bodies ; and the lateral 
 columns correspond to the lateral tract of the medulla with 
 the olivary bodies. The fibres, however, do not follow this 
 
 FIG. 94. 
 
 Middle 
 peduncle of 
 cerebellum. 
 
 Medulla oblongata and pons Varolii, anterior surface. 
 
 arrangement so closely, but are distributed variously in the 
 medulla. 
 
 The anterior columns of the cord send some of their fibres 
 (the direct pyramidal tract) into the pyramids, forming con- 
 tinuous tracts. Fibres from the lateral columns also enter 
 the pyramids, but cross in bundles to the opposite side. These 
 fibres may be seen crossing the anterior fissure between the 
 pyramids by gently separating them. This is known as the 
 decussation of the pyramids. The fibres which cross in this 
 way belong in the cord to the portion of the lateral column 
 known as the crossed or lateral pyramidal tract. 
 
MEDULLA. 187 
 
 Further course of the fibres of the pyramids : Almost all of 
 the fibres pass on through the pons Varolii and crusta of the 
 mid-brain, to be distributed to the cortex of the hemispheres 
 by way of the internal capsule and corona radiata. A few 
 of the fibres (external arciform) pass to the cerebellum by 
 way of the restiform body. 
 
 Lateral columns : The lateral column of the cord is broken 
 into three tracts in the medulla : one, we have just seen, joins 
 the anterior pyramid of the opposite side by the decussation ; 
 a second joins the restiform body on its way to distribution 
 in the cerebellum ; while the third set of fibres passes through 
 the deeper part of the medulla (formatio reticularis) and 
 tegmentum of the mid-brain, and reaches the ganglia at the 
 base of the brain ; some of these go to the fillet. 
 
 Posterior columns : The fibres of the posterior column con- 
 tinue on as the funiculi cuneatus and gracilis of the medulla. 
 These in turn terminate in their own nuclei, from which new 
 fibres arise and pass to the fillet of the opposite side. The 
 restiform body, just above the ends of these funiculi, for the 
 most part reaches the cerebellum. 1 
 
 Olivary bodies : Each is a mass of white nerve-substance 
 containing a central gray nucleus. There are communications 
 between it and some of the tracts from the cord, especially 
 from those tracts of the anterior and lateral columns which 
 go to the ganglia at the base of the brain. 
 
 Medulla arrangement of the gray matter: As the fibres 
 which form the crossed pyramidal tract pass from the lateral 
 column to decussate into the pyramid of the opposite side, 
 they push the anterior cornu of the gray matter backward ; 
 and this is still further accomplished by the olivary body, 
 until the gray matter is spread out toward the posterior sur- 
 face of the medulla at its upper part. Here the central canal 
 of the cord has widened out to form the lower part of the 
 
 1 In speaking of these fibres it has been convenient to say that they "pass" 
 in certain directions or " are distributed" in some situation. It must not 
 be forgotten that they are afferent and efferent medullated nerve-fibres, and 
 that such terms must be considered as somewhat figurative. In reality, it 
 would not seem proper to speak of an efferent fibre as being " distributed " 
 at its origin, but convenience and usage permit the use of these and similar 
 expressions. 
 
188 NERVOUS SYSTEM. 
 
 fourth ventricle, and the gray substance is aggregated just 
 under the floor of the ventricle. There are also sonic other 
 collections of gray matter for example, in the olivary bodies. 
 
 In this gray substance are the nuclei of origin of some of 
 the cranial nerves : the spinal accessory, hypoglossal, pneu- 
 mogastric, and glosso-pharyngeal nerves ; and roots of the 
 auditory, of the facial, and of the trigeminus nerves, arise in 
 this important collection of gray matter. Of the smaller col- 
 lections of gray substance, probably none has the peculiar 
 interest which the floor of the fourth ventricle possesses for 
 this reason. 
 
 Function of the medulla : The functions of the medulla are 
 practically of the same kind as those possessed by the spinal 
 cord, but of a higher degree. They are as follows : (a) con- 
 duction ; (6) reflex action ; (c) automatic action ; (d) inhibition. 
 
 Conduction: As the medulla is the sole connecting link 
 between the upper parts of the brain and the cord, it neces- 
 sarily contains all fibres passing between these limits. Thus 
 it conducts all impulses and transmits all sensations. 
 
 Reflex action: The medulla resembles the spinal cord in 
 being the seat of reflex acts; the only difference between 
 them being in the fact that many of the reflexes performed 
 by the former are of much greater importance to life than 
 any performed by the latter. Of the many reflex acts arising 
 from the medulla, the following are examples : 
 
 (1) That part of digestion which is performed in the mouth 
 is dependent upon medullary reflexes mastication, degluti- 
 tion, and the secretion of saliva; and, probably, the secretion 
 of the pancreatic and other digestive juices. In this con- 
 nection the so-called vomiting-centre may be noted. 
 
 (2) The respiratory functions are so-called automatic func- 
 tions of the medulla, and are capable of being sustained by 
 the nerve-force derived from the medulla alone. The centres 
 for coughing and sneezing are also here. The pneumogastrie 
 and phrenic nerves convey the afferent and efferent stimuli, 
 though there may be communications with other nerves 
 whereby sensory stimuli are applied. 
 
 (3) " Cardiac depressor" is the name given to a bundle of 
 nerve-fibres running from the heart to the medulla, which i< 
 

 SPECIAL CENTRES. 189 
 
 stimulated when the heart is overworking against a high ten- 
 sion in the bloodvessels. The result of the stimulation of 
 this " cardiac depressor " is a stimulus to the vaso-motor nerves 
 which results in a dilatation of the arterioles, and conse- 
 quently the tension is diminished and the overwork of the 
 heart ceases. This reflex act takes place in the medulla. 
 
 Automatic action : The impulses which are sent out to 
 muscles without apparent afferent stimuli, and without an 
 effort of the will, are called automatic. Such rhythmic im- 
 pulses as those which maintain the respiratory function be- 
 long to this class. It is not to be doubted that such actions 
 are reflex, and in response to stimuli. In the case of the 
 lungs, for example, the presence of deoxygenated blood may 
 serve to excite an afferent impulse. Nevertheless, some 
 authors distinguish between automatism and reflex action. 
 This automatic action cannot be considered as at all the same 
 as an action of the brain proper, like volition, but rather as 
 a high grade of reflex action. On the other hand, some 
 authorities claim that it is truly automatic in some of its acts, 
 in that it is capable of direct stimulation by the condition 
 of the blood circulating through the environment. It is 
 bilateral, and probably consists of both an inspiratory and 
 an expiratory part. It may be influenced to a certain extent 
 by voluntary impulses. 
 
 Inhibition: This is the control or inhibition of action 
 through the nerves which are distributed from this region 
 and through the communications with other centres in the 
 cord. Besides, there are supposed to lie in the medulla 
 centres which maintain the nutrition and tone of the muscles. 
 These are known as control and tonic centres. 
 
 Special centres : In addition to the centres already given 
 there is a considerable number of centres in the medulla which 
 control many important and complicated coordinated muscular 
 actions. These are centres of reflex action for the most part- 
 that is, are called upon to act in response to stimuli derived 
 from an afferent impulse or to a voluntary effort. 
 
 The following are examples : 
 
 (1) Regulation of the heart's action is found here, both inhib- 
 itory and accelerator centres communicating through the vagus. 
 
190 NERVOUS SYSTh'M. 
 
 (2) Vaso-motor regulation of the unstriped muscular fibre 
 of the arteries is al>o accomplished by the medulla. A 
 peculiar vaso-motor disturbance is brought about by injury of 
 one centre of the medulla namely, the interference with the 
 glycogen-function of the liver and the appearance of sugar 
 in the urine the diabetic centre. 
 
 (3) Various centres which have to do with the regulation 
 of the body-temperature. The vaso-motor centres we have 
 already mentioned. There are also found special wct- 
 centres ; and, furthermore, a control of the special sweat- 
 centres found in the cord is here maintained. Upon plausible 
 theoretical grounds there is also assumed to be a licut-iiiliibi- 
 tory centre, by which the heat-production is controlled without 
 reference to vaso-motor conditions. 
 
 (4) Also see example under " Reflex action." 
 
 Other functions : The origin of the roots of certain of the 
 cranial nerves here has caused the special senses of hearing 
 and of taste to be referred to this region ; and the connection 
 with the sympathetic system through the cord has caused the 
 centre for the dilatation of the pupil to be located in the 
 medulla. Phonation is also dependent upon the action of 
 nerves arising in this focus of gray matter, and no voluntary 
 or reflex sound can be produced by an animal in which the 
 speech-centre in the medulla is destroyed. The origin here 
 of the hypoglossal and pneumogastric nerves, involving as 
 they do the movements of the tongue and glottis, controls 
 both the acts of phonation and articulation. 
 
 Demonstration of respiratory functions of the medulla : For 
 this purpose we select an active, healthy frog : If the spinal 
 cord be removed up to the medulla, the respirations continue, 
 and in the same way they do not cease if the hemispheres be 
 removed without disturbing this organ ; or, if both cord and 
 hemispheres be removed without disturbing the medulla, the 
 movements of breathing will continue. If the medulla is 
 injured at the origin of the pneumogastric nerve, however, 
 the movements of respiration cease and the animal dies. 
 The same occurs when a similar injury happens in the higher 
 animals and in man. Death occurs instantaneously in this 
 way when the medulla is broken near the axis in executions 
 
CEUEA CEREBRL 191 
 
 by hanging " the neck is broken " or when an animal is 
 killed by "pithing" in laboratory experiments. 
 
 Glosso-labio-laryngeal paralysis : It may be of interest at 
 this point to observe the pathological changes that occur in 
 the medulla in producing the disease known as glosso-labio- 
 laryngeal or bulbar paralysis : It is a progressive degenera- 
 tion of the gray matter of the medulla, and it shows itself 
 first in a paralysis of the tongue, which renders articulation 
 of certain sounds indistinct : as the degeneration progresses 
 in the medulla articulation becomes more and more im- 
 possible and deglutition is affected. The disease continues to 
 aifect more and more of the functions dependent upon the 
 medulla, until death ensues as a result of involvement of the 
 cardiac and respiratory centres or of inability to take food. 
 
 Pons, Crura Cerebri, and Corpora Quadrigemina. 
 
 The pons Varolii is a collection of nervous tissue lying 
 immediately above the medulla. It consists of white fibres, 
 with areas of gray matter filling in the intervals between the 
 fasciculi of white fibres. The white fibres connect the mid- 
 brain with the medulla, and also pass between the hemi- 
 spheres of the cerebellum. What is the function of the gray 
 matter is little known ; but some of it is directly continuous 
 with that of the medulla, and, like it, active as a centre of 
 nervous force. In the pons is the decussation of many nerve- 
 fibres, among which are some of the fibres of the facial nerve 
 arising in the floor of the fourth ventricle. 
 
 Paralysis following lesions of the pons : The so-called crossed 
 paralysis may follow lesions in the lower portion of the pons 
 that is, paralysis of sensation and motion, more or less 
 complete, of the opposite side of the body, with paralysis of 
 the facial muscles of the same side as the lesion. 
 
 Crura cerebri : The crura are formed of fibres passing from 
 the medulla through the pons Varolii, to the hemispheres of 
 the cerebrum. They divide so as to form two sets of fibres : 
 the more superficial (crustse) are mostly motor or efferent fibres 
 which are continuous with the pyramidal tracts in the cord; 
 while the deeper (tegmentum) layer of fibres are afferent or 
 
192 NERVOUS SYSTEM. 
 
 sensory, and are derived largely from the lateral and posterior 
 tracts of the cord. Lying between these bands of fibre.- i- a 
 mass of gray substance (locus nigcr) whose function as a 
 nerve-centre is not understood, though it has to do with 
 coordination of the muscles, and especially with regulation 
 of the muscles controlled by the motor oculi nerve. 
 
 Paralysis following lesions in the crura : This is paralysis 
 of the opposite side of the body, both of sensation and motion, 
 and of a degree of intensity depending upon the size of the 
 lesion ; and, besides this, paralysis of the motor oculi nerve 
 of the same side as the lesion. There is a derangement of the 
 coordination of motions which follows lesions of this region 
 beyond that which belongs to the motor paralysis; this is 
 often shown in rotary movements when the subject attempts 
 to walk. It is inferred that there are coordinating influences 
 derived from the crura. 
 
 The corpora quadrigemina are four rounded eminences 
 placed in pairs, two anterior, two posterior. They are situ- 
 ated on the dorsal aspect of the mid-brain below the posterior 
 lobes of the cerebral hemispheres and between the optic 
 thalami and third ventricle in front and the cerebellum 
 behind. 
 
 Functions: The anterior corpora quadrigemina are the 
 homologues of the optic lobes in some of the lower animals, 
 and the anterior pair may be regarded as important centres 
 for the visual and motor functions of the eyes. The posterior 
 pair are more intimately associated with the sense of hearing. 
 The special functions of the corpora quadrigemina will be 
 more fully discussed under the special senses. Not only doe- 
 blindness follow lesions of the anterior corpora quadrigemina, 
 but there is often atrophy of them when the eyes are de- 
 stroyed.. 
 
 Cerebrum. 
 
 The cerebrum is composed of two hemispheres, connected by 
 a commissure of white fibres, the corpus callow m, and of the 
 third ventricle and optic thalami (di- or thalamencephalon). 
 
 The two hemisphere* are separated by a deep fissure ex- 
 tending from before backward, and in the interior of each is 
 
REGIONS OF THE CEREBRUM. 193 
 
 found a cavity known as the lateral ventricle. The hemi- 
 spheres are connected directly with the spinal system by the 
 crura cerebri and medulla, and with each other by the corpus 
 callosum. They are composed of white and gray nerve- 
 substance, and the latter is arranged largely at the periphery 
 of the hemispheres ; the former being made up of communi- 
 cating nerve-fibres which connect the various portions of the 
 hemispheres with each other, and the hemispheres with other 
 parts of the cerebro-spinal system, thus allowing a free 
 control of the impulses arising from one cell or set of cells 
 by other cells in the gray matter. 
 
 The surface of the cerebrum is divided into regions by 
 fissures, which separate one part from another. These fis- 
 sures are always present, and upon them depends the deter- 
 mination of the division of the cerebrum into lobes. Fissures 
 which are of use in locating the lobes of cerebral matter are 
 the fissure of Rolando, the fissure of Sylvius, and the parieto- 
 occipital fissure (Fig. 95). 
 
 Convolutions : The surface of the brain is further cut up by 
 a number of other clefts, known as sulci ; and these separate 
 the surface into a number of distinct masses or convolutions. 
 The depth of the sulci and their number determine the 
 quality of the brain in respect to its degree of development ; 
 thus, the convolutions in man are much deeper and more 
 numerous than in the lower animals. The sulci are not in- 
 variable in position or number in different brains. 
 
 Regions of the cerebrum: (1) Frontal lobe: This lobe is 
 bounded by the fissure of Rolando, and contains several con- 
 volutions which include the forward portion of the brain. 
 
 (2) The parietal lobe lies behind the fissure of Rolando, 
 and extends posteriorly to the occipito-parietal fissure. The 
 convolutions are well marked, and are separated by a well- 
 marked sulcus (sometimes known as the intra-parietal fissure) ; 
 and the posterior branch of the fissure of Sylvi us is enfolded 
 by an inferior parietal convolution, known as the " supramar- 
 ginal convolution." 
 
 (3) The tempo ro-sphenoidal, or temporal lobe, is below the 
 Sylvian fissure and in front of the occipital lobe. Its convo- 
 lutions are well marked. 
 
 13 Phys. 
 
1 ( J4 
 
 NERVOUS SYSTEM. 
 
 (4) The occipital lobe is found at the posterior end of the 
 cerebral hemisphere, and its convolutions are continuous with 
 those of the parietal and temporo-sphenoidal lobes, except 
 within the longitudinal fissure, where it is cut off from the 
 parietal by the parieto-occipital fissure. 
 
 Plan of the human brain in profile, showing its fissures and convolutions. S, fissure 
 of Sylvius ; S', anterior branch ; S", posterior branch ; R, fissure of Rolando ; P, 
 intraparietal fissure. 
 
 (5) The central lobe, or island of Rctt, is within the fissure 
 of Sylvius, and is covered by convolutions of the frontal and 
 parietal and temporal lobes (see 5 in Fig. 96). 
 
 Besides these well-defined lobes, the portion of the cerebral 
 surface which is trithin fin- longitudinal fixture is marked l>v 
 sulci and convolutions. Convolutions of the frontal, parietal, 
 and occipital lobes are found here: the marginal convolu- 
 tion, the gyms fornicatus lying above the corpus eallosum, 
 the paracentral lobule, the quadrate lobule, and the cuneato 
 lobule are among the principal landmarks. 
 
ARRANGEMENT OF THE GRAY MATTER. 195 
 
 Arrangement of the gray matter : The increase in the area 
 
 Horizontal section of the hemispheres at the level of the cerebral ganglia. 1, 
 great longitudinal fissure between frontal lobes ; 2, great longitudinal fissure 
 between occipital lobes : 3, anterior part of corpus callosum ; 4, fissure of 
 Sylvius ; 5, convolutions of the insula ; 6, caudate nucleus of corpus striatum ; 
 7, lenticular nucleus of corpus striatum ; 8, optic thalamus ; 9, internal capsule ; 
 10, external capsule ; 11, claustrum. 
 
 of the surface of the hemispheres by the infolding of the 
 sulci adds very greatly to the amount of gray substance in 
 
196 
 
 NERVOUS SYSTEM. 
 
 FIG. 97. Gray matter of the cerebral 
 cortex (Muyiicrt). 
 
 the brain ; for the entire sur- 
 face i.s composed of gray sub- 
 stance, and this follows the 
 sulci and fissures (Fig. 96) 
 in all their folds, and is not 
 cut into by them. 
 
 Besides the gray matter in 
 the convolutions, there are 
 certain other grav masses in 
 the substance of the white 
 matter; the optic thalami, 
 the corpora striata, and the 
 claustrum (Fig. 96) are the 
 chief of these gray masses. 
 Minute structure of the gray 
 matter : The gray matter of 
 the cortex is made up of gan- 
 glion-cells of various shapes 
 and sizes lying in a loose 
 neuroglia-stroma, more abun- 
 dant at the surface. The 
 cells are the source of numer- 
 ous nerve-fibres, which par-s 
 out into the white matter 
 (Fig. 97). There are counted 
 five layers of these ganglion ie 
 tissues; and while these zones 
 merge into one another, they 
 are tolerably distinct. In 
 the middle (and widest) Inver 
 large multi polar cells are very 
 numerous, and the fibres may 
 be seen to pass through the 
 deeper layers in bundles into 
 the white matter. 
 
 Chemistry of brain-tissue : 
 Brain-tissue consists of some 
 peculiar bodies allied to the 
 rats, but containing nitrogen ; 
 
COURSE OF THE FIBRES IN THE HEMISPHERES. 197 
 
 of these, cerebrin and lecithin are the more prominent. Aside 
 from these, the constituents are proteid and fatty substances, 
 with salts, chiefly potassium and magnesium phosphates, and 
 water. 
 
 Weight of brain : About three pounds. In size it exceeds 
 the brains of all the lower animals except those of the ele- 
 phant and whale. Its weight is about one-fortieth of the 
 total body-weight, and this ratio is greater than in the lower 
 animals, with a few exceptions among the smaller birds and 
 monkeys. In women the weight is about one-tenth less than 
 in men. 
 
 Relation of size of brain to the intellect: In some degree 
 the size of the brain bears a direct relation to the intellect of 
 the individual, but this is not absolute. The depth of the 
 sulci and the consequent size and complexity of the convolu- 
 tions are a more efficient measure of the brain-power. In the 
 largest of the apes the brain of an adult animal is about the 
 same in weight as that of a human infant at birth. Idiots, 
 as a rule, have brains much smaller than the normal, and in 
 them the convolutions are apt to be ill-marked and uncom- 
 plicated, as is the case in the lower animals. 
 
 Course of the fibres in the hemispheres : The course of these 
 fibres may be classified in three groups : 1, commissural fibres; 
 2, fibres of association ; and 3, medullary fibres. 
 
 (1) The eommissural fibres are those which connect one 
 hemisphere with the other, and it may be said that these 
 fibres connect each set of convolutions with the corresponding 
 set of the opposite side. The convolutions of the portion of 
 the brain lying above the fissure of Sylvius communicate by 
 the corpus callosum. 
 
 (2) Fibres of association are those fibres which connect the 
 convolutions of one hemisphere. These fibres pass in bundles 
 just beneath the cortical gray matter of the convolutions, and 
 it is thought that most of the important convolutions of each 
 hemisphere intercommunicate in this way. 
 
 (3) The medullary fibres are those which connect the cere- 
 brum and medulla, and are regarded as indirect and direct, 
 according as they do or do not pass to the gray ganglia at the 
 base of the cerebrum. In considering the course of the fibres 
 
198 NERVOUS SYSTEM. 
 
 from the medulla through the crura cerebri it was noted that 
 the motor and sensory fibres were to some extent separated. 
 The fibres pass from the crusta to the internal capsule, and 
 hence the "direct fibres" pass to the cerebral convolutions 
 through the corona radiata ; while the " indirect fibres " from 
 the legmen turn pass to the corpora striata and optic thalami, 
 and communicate with ganglion-cells in them. 
 
 Function of the corpora striata and optic thalami: These 
 "basal ganglia," with the other collections of gray substance, 
 seem to have a controlling influence upon the spinal system. 
 It is through these ganglia that all voluntary impulses, ex- 
 cept those by the direct medullary fibres, must pass. These 
 basal ganglia communicate through the corona radiata with 
 the convolutions of the cortex, and it is probable that we 
 may regard this part as acting as a middleman to elaborate 
 and coordinate the voluntary impulses of the cortex and to 
 act in matters not requiring the intervention of the higher 
 endowments of the mind. This status of these ganglia is 
 quite theoretical, but the function may be considered as a 
 sort having the properties of both the automatism of the gray 
 matter of the medulla and cord and the voluntary function 
 of convolutions. In this consideration, however, we must 
 not undervalue the communication with the cortex which 
 these basic ganglia possess. 
 
 Lesions of the basic ganglia : So far as has been observed, 
 the corpora striata may be involved by considerable lesions 
 without causing persistent motor or sensory disturbances, 
 and the same may be said of the optic thalami ; but if the 
 lesion encroaches upon the white matter of the internal 
 capsule, or crura cerebri, the effect is to cause more or less 
 paralysis, depending upon the severity of the lesion and its 
 position. 
 
 Functions of the cerebrum: The motor and sensory func- 
 tions which have been seen to belong to other nuclei or gray 
 matter are centred here, but infinitely broadened, for the cells 
 in the convolutions of the cerebrum can originate the eilcivnt 
 and perceive the afferent nerve-impulses. In fact, it is iu 
 this portion of the brain that the intelligence is centred : it 
 is the organ of the mind. Memory, reason, emotions, and all 
 
SENSORY AREAS. 199 
 
 the other attributes of the mind are dependent upon its func- 
 tional power. 
 
 Unilateral action of the brain : There are instances in which 
 injury or disease of one-half of the cerebrum has left the 
 intellectual faculties not gravely impaired. From a consider- 
 ation of such cases it has been held that the action of one of 
 the hemispheres is sufficient for the purposes of the mind. 
 There is, however, an absolute dependence for motor and 
 sensory functions upon the integrity of both sides, for the one 
 side cannot act for the other in these functions. As a rule, 
 it is safe to assume that the hemispheres act in unison. 
 
 Localization of brain-function : While the brain is regarded 
 as an organ of the mind, it is probable that the various func- 
 tions may be regarded as belonging to definite portions of the 
 convolutions which are appropriated for that purpose. The 
 functions of the convolutions have not been assigned, except 
 for a small portion of the brain-surface and for some of the 
 simpler actions. For the most part, our knowledge of the 
 exact localization of brain-functions is confined to "motor 
 areas," in which it has been determined that stimulation of a 
 certain group of cells will cause a definite action. Besides 
 this, certain other centres are located, as of sight and speech. 
 
 Determination of motor areas: When the surface of the 
 brain is exposed in animals or in man, the stimulation of 
 certain areas of the cortex by a mild electrical current will 
 give rise to motion in the peripheral muscles ; and it is found 
 that the stimulation of the same region in the same or other 
 animals will cause the same results. These centres of motor 
 impulses are situated almost entirely upon the convolutions 
 about the fissure of Rolando (Fig. 98). 
 
 Sensory areas: These have not been, by any means, so 
 definitely fixed as the motor centres ; but the centres for sen- 
 sation may be said to exist, and probably in the convolutions 
 of the posterior portion of the cerebrum. The centre for 
 vision in the convolutions about the posterior branch of the 
 fissure of Sylvius is generally accepted ; or in the cuneate 
 lobule (14, 15, in Fig. 98). The centre for hearing is toler- 
 ably defined in the temporo-sphenoidal lobe along the pos- 
 terior branch of this fissure (16, Fig. 98). The speecA-centre 
 
200 
 
 NERVOUS SYSTEM. 
 
 is also located with seeming accuracy along the anterior 
 branch of the fissure of Sylvius and in the third frontal convo- 
 lution. This centre seems to be much more developed upon 
 the left side of the brain. In Fig. 98 this centre may be 
 indicated roughly by reference to the tongue-centres (8 and (h. 
 
 FIG. 98. 
 
 10 
 
 Brain of monkey, showing the position of the motor and sensory centres as ascer- 
 tained by Ferrier. The actions all occur on the side of the body opposite to the 
 part of the brain irritated. 1, the eyes open widely, the pupils dilate, and head 
 and eyes turn toward opposite side ; 2, extension "forward of the opposite arm 
 and hand, as if to reach something in front; 3, movements of tail (and trunk) : 
 4, retraction with adduction of opposite arm; 5, supination and llexioii of the 
 forearm, by which the arm is raised toward the mouth ; 0, action of zygomatics, 
 by which the angle of mouth is retracted and elevated; 7, elevation of ala of 
 nose and upper lip; 8, opening of mouth with protrusion of tongue: 9. retrac- 
 tion of tongue ; 10, retraction of opposite angle of mouth ; a, f>, <\ <l, prehensile 
 movements; 11, retraction and adduction of opposite arm; VJ. advance of tin- 
 opposite hind limb; 13, complex movements of thigh, leg, and foot; 14, 16, vision 
 (sensory) ; 16, hearing (sensory). 
 
 Pathological support of localization : Injuries and diseases 
 involving the motor areas are followed by paralysis so well 
 defined that it Is frequently possible to locate the seat of the 
 lesion from its result upon the muscular system. Tumors. 
 abscesses, and depressed bone, for example, are capable of 
 accurate localization in this way. The more indefinite sen- 
 sory paralyses do not so accurately point out their origin. On 
 ;he evidence of pathology bears out in full the 
 experimental irttemlts. The crossed action of all the nervous 
 
 LI BRARY 
 
ARRANGEMENT OF THE GRAY MATTER. 201 
 
 structures is especially to be noted. In the case of a right 
 paralysis in which the speech is affected, as compared with a 
 left hemiplegia and speech unaffected, this crossed action is 
 impressed when we remember the localization of the centre 
 for speech in the left hemisphere near the motor area. 
 
 Terms used in defining paralysis : Anaesthesia = loss of sen- 
 sation. 
 
 Hemiansesthesia = loss of sensation in one lateral half of 
 the body. 
 
 Hemiplegia = loss of muscular power in one lateral half of 
 the body. 
 
 Paraplegia = symmetrical loss of muscular power in the 
 lower portion of the body and extremities. 
 
 Aphasia = loss of power to talk : amnesic when words are 
 forgotten ; ataxic when the power to articulate is lost, though 
 the words are known. 
 
 The Cerebellum. 
 
 The cerebellum is a mass of nerve-substance situated pos- 
 teriorly at the base of the skull. It consists of a median 
 lobe and two lateral hemispheres, and is connected with the 
 rest of the cerebro-spinal system by numerous white fibres 
 collected in bundles known as peduncles. Of these, the larger 
 peduncles pass to and largely make up the pons Varolii 
 (middle peduncles), thus connecting the lateral hemispheres 
 of the cerebellum. The superior peduncles pass beneath the 
 corpora quadrigemina, and the fibres pass into the cerebrum, 
 decussating as they meet beneath the corpora quadrigemina. 
 The inferior peduncles pass to the medulla, where they form 
 the restiform bodies. Thus it is seen that the entire cerebro- 
 spinal system communicates very freely with the cerebellum. 
 
 Arrangement of the gray matter : The arrangement in con- 
 volutions is not the same as in the cerebrum, but there are 
 numerous transverse sulci which divide and subdivide, the 
 gray matter being disposed about them in a thin layer. This 
 causes a section of the organ to have a peculiar tree-like 
 appearance, which originates the name, " arbor vitse," given 
 to these sections of the cerebellum. Besides this, there is a 
 
 ntral collection of gray substance the corpus dentatum. 
 
 central coll( 
 
202 
 
 NERVOUS SYSTEM. 
 FIG. 99. 
 
 External gray or 
 cellular layer. 
 
 Corpuscles of Pnrkinje. 
 
 Internal or rust- 
 colored layer. 
 
 White substance. 
 
 Vertical section through the gray matter of the human cerebellum im 
 
 about 100 diameters : Klein and Noble Smith). Two branched capillaries are 
 seen at the upper part passing into the gray matter from the pia mater. 
 
 Microscopic examination of gray matter : Under the micro- 
 scope it is found to consist of throe layers (Fig. 99). The 
 
MOTOR TRACT. 203 
 
 outer is a layer of delicate " connective tissue " which supports 
 fine nerve-fibres and small spindle-shaped, branching nerve- 
 cells. The middle layer is characterized by irregularly dis- 
 posed large ganglion-cells,, and the branching processes from 
 these ramify in the superficial layer. These cells are known as 
 Purkinjrfs cells. The inner layer is made up of a mass of small 
 spheroidal cells, and gradually merges into the white substance. 
 Function of the cerebellum : The cerebellum seems to exert 
 no influence upon the sensory nerves, for sensibility is not 
 affected by its injury or disease. The motor system is, how- 
 ever, entirely disorganized by lesions of the organ. Coor- 
 dination of the voluntary muscles is accomplished by this 
 portion of the brain, and it is originated in the gray matter 
 of the part. It has no effect upon the senses nor upon the 
 intellect, so far as is known. 
 
 Tracts in Brain and Cord. 
 
 The motor tract consists of bundles of medullated nerve- 
 fibres originating in cells of the motor area of the brain. 
 These fibres pass downward, between the optic thai am us and 
 caudate nucleus on the inner side and the lenticular nucleus 
 on the outer side. During this part of their course the fibres 
 form the internal capsule. 
 
 Passing down in the crustce, the fibres reach the pons. 
 Here the fibres change position, so that the facial fibres cross 
 over from the inner side of one-half the motor tract so as to lie 
 in the inner half of the opposite motor tract. The leg- and 
 arm-fibres continue down in their respective positions without 
 decussating among the ventral longitudinal fibres of the pons. 
 
 On leaving the pons the face-fibres pass out through the 
 respective cranial nerves to the muscles of the face. 
 
 The leg- and arm-fibres enter the medulla and decussate to 
 the opposite side as the crossed pyramidal tract, and run down 
 as the "crossed" column of the cord (the lateral). A few 
 fibres continue without decussating, in the anterior column 
 (column of Tiirck), and are known as the direct pyramidal tract. 
 Thence the motor fibres pass to various levels of the cord. 
 
 Lesions of the motor tract : From the definite anatomical 
 course of the motor tract we may conclude that definite lesions 
 
204 NERVOUS SYSTEM. 
 
 at any point of its course will give definite results. Such is the 
 case. Naturally a lesion of the motor tract gives paralysis as a 
 marked symptom. The particular nerves and the n tun her in- 
 volved assist us in locating the exact area of the tract affected. 
 
 1. Lesions on the cortex or in the internal capsule result in 
 a variable amount of paralysis ; but the paralysis is on the 
 opposite side from the lesion. 
 
 2. Lesions at the upper border of the pons result in paralysis 
 of the face on the same side of the body, but of the arm and 
 leg on the opposite side from the lesion. 
 
 3. Lesions below the decussation of the faee-fibrea and above 
 that of the arm and leg leave the face unaffected, but paraly/e 
 the arm and leg of the opposite side of the body. 
 
 Sensory tract : Starting with the posterior columns of the 
 cord (columns of Goll and Burdach), the sensory fibres pass 
 into the medulla as the funiculi graciles and cuneati. Here 
 they decussate (decussation of the fillet) posterior to the 
 median raphe. In the pons they form the straight fillet, 
 ascending in the crura cerebri dorsal ly to the motor fibres 
 (tegmentum). As part of the corona radiata, sensory fibres 
 ,are then distributed to that portion of the cerebral cortex 
 situated well behind the fissure of Rolando /. <-., posterior 
 parts of the parietal and occipital lobes. Their terminations 
 are end-arborizations with sensory cells. 
 
 Mutilations. 
 
 Mutilation of brain : Numerous experiments have been con- 
 ducted upon animals showing the effect produced on the 
 animal of the removal of different parts of the brain. Thus 
 we have learned by deduction the functions of ninny parts 
 of the cerebro-spinal system. One of the simplest experi- 
 ments, and one also frequently observed in surgery, is a 
 division of the spinal cord. 
 
 Division of the spinal cord: The result is a complete loss 
 of conductivity between the two segments of the cord, above 
 and below the point of division. The manifestation is a loss 
 of sensation, and paralysis of the parts supplied by nerves 
 emerging from the cord at a point below the section. Only 
 such reflexes are present in the affected parts as have their 
 
REMOVAL OF THE CEREBELLUM. 205 
 
 seats in that portion of the cord (below the section) still in 
 connection with the affected areas. The parts still in con- 
 nection with the brain (above the section) retain their normal 
 function. If the section be made between the medulla and the 
 point of origin of the phrenic nerves, death from asphyxia 
 results. 
 
 In a frog, whose spinal cord has been cut close to the 
 medulla, and whose medulla has been destroyed, the follow- 
 ing results are noticed : although the frog does not respire 
 through his lungs, he still lives, as he absorbs oxygen through 
 the skin, provided it be kept moist. The animal lies prone 
 on its belly. If dropped into a basin of water, it sinks, mak- 
 ing no attempt to swim ; nor does it swallow food, even if 
 placed on the tongue. 
 
 If the section be made anterior (above) to the medulla, the 
 frog breathes, sits in a normal position, swims in a basin of water 
 until it strikes a suitable landing, then crawls out and sits 
 still. It makes no motion unless irritated, then hops away ; 
 and swallows food placed on the tongue. 
 
 Removal of the cerebellum: When small portions are re- 
 moved the animals become feeble and uncertain in "their 
 movements, but are able to move for ordinary purposes. As 
 the amount removed increases the want of coordination of 
 the voluntary muscles increases. With the entire cerebellum 
 gone the condition is absolute animals cannot stand nor walk, 
 nor bring any of the muscles into orderly action. If the 
 animal is laid upon the back, it cannot recover itself, but 
 struggles vaguely in the attempt. The senses are apparently 
 normal and the will-power is present : if a blow is threatened, 
 an attempt is made to avoid it. When the lesion is confined 
 to one hemisphere, the lack of coordination is noticed in the 
 opposite half of the body. Under these circumstances the 
 animals are apt to fall to the opposite side and roll over and 
 over rapidly. Such movements are known as forced move- 
 ments. This condition may persist for several days. Pigeons 
 from which the cerebellum is removed may live for a con- 
 siderable time, sometimes for several months, after the opera- 
 tion. In some cases there is a return of power to coordinate, 
 after partial removal, at the end of some days. 
 
206 NERVOUS SYSTEM. 
 
 Removal of the cerebral hemispheres : In some of the lower 
 animals the cerebrum may be entirely removed without kill- 
 ing them. When this is done, for example, in the case of a 
 pigeon, the bird remains quiet in one position, and is not dis- 
 turbed by noises ; or if thrown from its perch, it Hies and 
 alights in a nearly normal manner. If a foot be pinched, it 
 withdraws it and perhaps changes its position. The bird is 
 capable of reflex actions of various complicated kinds, but 
 there is no spontaneous exercise of volition : all its move- 
 ments are excited by the nerve-stimuli of the moment. There 
 is no perception of stimuli ; the intelligence is gone. 
 
 Cranial Nerves. 
 
 The cranial nerves are a set of twelve pairs of nerves which 
 arise from the brain. They are varied in their functions, but 
 all arise from ganglia of the gray matter in the brain and 
 medulla. The floor of the fourth ventricle is particularly 
 rich in nuclei in which these cranial nerves originate. 
 
 Classification of the cranial nerves: In the order of their 
 emergence, by numbers : (I) olfactory ; (II) optic ; (III) 
 motor oculi ; (IV) patheticus ; (V) trigeminus ; (Y I) alxlu- 
 cens; (VII) facial; (VIII) auditory ; (IX) glosso-pharyn- 
 geal ; (X) pueumogastric ; (XI) spinal accessory ; ( X 1 1 ) hy- 
 poglossal. In the relation of their functions they may be 
 arranged as nerves of special sense, nerves of common sen>a- 
 tion, motor nerves, and mixed nerves (/. e., sensorv and motor). 
 
 C (I) olfactory, (II) optic, (VIII) 
 
 XT f . , auditorv and parts of the (Y) 
 
 Nerves of special sense, < * i / T v\ 
 
 ] trigeminus and (IX) glasso- 
 
 ^ pharyngeal. 
 
 Nerves of common sen- f The greater portion of the (V) 
 sation, \ trigeminus. 
 
 " (III) motor oculi,(IV) pathcticus, 
 (V) lesser division of the tri- 
 
 Motor nerves, 
 
 geminus, ( V [)abducens, ( V 1 1 ) 
 
 facial, and (XII) hypoglossal, 
 (XI) spinal accessory (?). 
 
 ( (IX) crlosso-pharyngeal and (X) 
 Mixed nerves, 
 
 | pneumogastrio. 
 
777 NERVE. 
 
 207 
 
 FIG. 100. 
 
 Of the nerves of special sense, (I) olfactory, (II) optic, 
 and (VIII) auditory will be 
 explained later, and may be 
 omitted from further consider- 
 ation for the present. 
 
 Ill nerve : It arises from a 
 nucleus of gray matter just in 
 front of the pons beneath the 
 iter e tertio ad quartum ven- 
 triculum (aqueduct of Sylvius), 
 passing out through the cms 
 cerebri, and emerging from the 
 skull in the orbit (Fig. 100). 
 It gives off some fibres to the 
 lenticular ganglion. It is dis- 
 tributed to all the muscles of 
 the eyeball, with the exception 
 of the superior oblique and 
 the external rectus muscles. 
 It also supplies the levator 
 palpebrse superioris muscle, 
 and by its connection with 
 the lenticular ganglion con- 
 trols the ciliary and pupillary 
 muscles. 
 
 It is purely a motor nerve, 
 function is best described 
 by showing the paralyses which 
 "low its division : by paraly- 
 
 of the elevator of the up- 
 lid we have ptosis; by 
 paralysis of the muscles of the 
 eyeball we have inability to 
 move the organ up or down 
 or inward ; by the unopposed 
 action of the external rectus 
 the eyeball becomes turned 
 
 outward (external strabismus) ; by paralysis of the muscle of 
 the iris the pupil remains dilated and does not respond to 
 
 A partly diagrammatic view of the 
 floor of the aqueduct, looking upward 
 (dorsally), nuclei of the third and 
 fourth nerves, and the decussating 
 fibres of the latter all shown; the 
 third nerve nuclei are subdivided 
 into an anterior nucleus, the Edinger- 
 Westphal nucleus (a and 6), and a 
 posterior nucleus ; the posterior nu- 
 cleus has a dorsal, a ventral, and a 
 mesal portion; the decussation of 
 the fibres from the dorsal portion of 
 the posterior nucleus of the third 
 nerve is shown (Edingerj. 
 
208 NERVOUS SYSTEM. 
 
 light ; and by paralysis of the ciliary muscle the accommo- 
 dation of the lens for near vision is prevented. 
 
 The control of the pupil is not a voluntary one; but the 
 effect of a strong voluntary effort, exerted through the third 
 nerve, shows itself in contraction of the pupil, as when the 
 eyeball is turned strongly inward and upward. 
 
 IV nerve : It arises close by the third nerve beneath the 
 aqueduct of Sylvius, and emerges, after decussation, from the 
 valve of Yieussens. Thence, passing around the crus cere- 
 bri, it runs parallel with the motor oculi (third) nerve to the 
 orbit, where it is supplied to the superior oblique muscle. 
 Its paralysis prevents the muscle from maintaining the hori- 
 zontal plane of the eyeball. If this paralysis occurs, there 
 is double vision, and the image seen by the affected eye ap- 
 pears oblique and inferior to the image of the other eye. This 
 may be corrected by inclining the head to the opposite side. 
 This nerve is also known as the trochlearis or trochlear nerve. 
 
 V nerve : This nerve resembles the spinal nerves in having 
 a motor and a sensory root, the latter possessing a ganglion 
 (Gasserian). The origin of the nerve seems to be in centres, 
 separate for motor and sensory, in the floor of the fourth ven- 
 tricle (Fig. 101). There are fibres which join the trunk of 
 the nerve which are derived from the spinal cord. It emerges 
 from the pons Varolii as two distinct nerve-roots. The 
 larger of the two, the sensory, soon enters the Gasserian 
 ganglion, the motor root passing beneath without communica- 
 tion. The nerve then breaks up into three branches: of 
 these the first and second are formed entirely from the sen- 
 sory root, while the third carries all the motor fibres, and with 
 them some of the sensory, so that the third branch of the 
 nerve is partly sensory and partly motor. There is a partial 
 decussation- of the fibres in the medulla, but many pass direct 
 to the same side. 
 
 Muscles supplied by the motor root, V nerve : The muscles 
 supplied are those of mastication. The temporal, ma>-< !< T, 
 and both pterygoid muscles, as well as the anterior belly of 
 the digastric muscle and the mylo-hyoid, receive their inuer- 
 vatiou from the motor root of the fifth nerve. Besides this, 
 the tensor palati and tensor tympnni muscles are supplied 
 
SENSORY FIBRES. 
 
 209 
 
 by this nerve through its communication with the otic gan- 
 glion of the sympathetic system. A branch to the buccinator 
 
 View of the posterior surface of the medulla, the roof of the fourth ventricle being 
 removed to show the rhomboid sinus clearly. The left half of the figure repre- 
 sents : On, funiculus cuneatus and, (j, funiculus gracilis ; 0, obex; sp, nucleus 
 of the spinal accessory ; p, nucleus of the pneumogastric ; p + up, ala cinera ; R, 
 restiform body; XII', nucleus of the hypoglossal; t, funiculus teres ; a, nucleus 
 of the acusticus; m, strife medullares'; 1, 2, and 3, middle, superior, and infe- 
 rior cerebellar peduncles respectively ; /, fovea anterior; 4, eminentiateres (genu 
 nervi facialis) ; 5, locus eceruleus. The right half of the figure represents the 
 nerve-nuclei diagrammatically : V, motor trigeminal nucleus; V, median and, 
 V", inferior sensory trigeminal nuclei; VI. nucleus of abducens; VII, facial 
 nucleus; VIII, posterior median acoustic nucleus; VIIF, anterior median; 
 VIII", posterior lateral: VIII'", anterior lateral acoustic nuclei; IX, glosso- 
 pharyngeal nucleus ; A', XI. and XII, nuclei of vagus, spinal accessory, and 
 hypoglossal nerves respectively. The Roman numerals at the side of the figure, 
 from 'T to XII, represent the corresponding nerve-roots (Erb). 
 
 muscle is probably not motor, but sensory. Lesions of the 
 nerves paralyze these muscles. 
 
 The sensory fibres of the fifth nerve are distributed in all 
 three branches, and supply sensation to the skin of the face 
 
210 
 
 NERVOUS SYSTEM. 
 
 and anterior portion of the head, emerging from the bony 
 canals upon the face at the supraorbital, infraorbital, and 
 mental foramina. Sensory fibres are also supplied to the 
 mucous membrane of the mouth and tongue (by the lingual 
 branch) and to the muscles of the part (Fig. 102). 
 
 FIG. 102. 
 
 Diagram of the fifth nerve and its distribution. 1, sensitive root; 2, motor root; 3, 
 Gasserian ganglion: I, ophthalmic division; II, superior maxillary division; 
 III, inferior maxillary division ; 4, supraorbilal nerve, distributed to the skin 
 of the forehead, inner angle of the eye, and root of the nose; 5, infra-orbital 
 nerve, to the skin of the lower eyelid, side of the nose, and skin and mucous 
 membrane of the upper lip; 6, mental nerve, to the integument of the chin and 
 edge of the lower jaw, and skin and mucous membrane of the lower lip ; , //, 
 
 external terminations of the nasal branch of the ophthalmic division, to the 
 mucous membrane of the inner part of the eye and the nasal passages, and to 
 the base, tip, and wing of the nose ; t, temporal branch of the superior maxillary 
 
 division, to the skin of the temporal region ; m, malar branch of the superior 
 maxillary division, to the skin of the cheek and neighboring parts: !>, bucral 
 branch of the inferior maxillary division, passing along the surface of the buc- 
 cinator muscle, and distributee! to the mucous membrane of the cheek and to 
 the mucous membrane and skin of the lips; /.lingual nerve, to the mucous 
 membraneof the anterior two-thirds of the tongue; of, auriculo-temporal branch 
 of the inferior maxillary division, to the skin of the anterior part of the exter- 
 nal ear and adjacent temporal region; x, x, x, muscular branches, to the tcin 
 poral, masseter, and internal and external ptervgoid muscles: //, muscular 
 branch, to the mylo-hyoid and anterior belly of the diagastric ; /, sensitive 
 branch of communication to the facial nerve. 
 
 Destruction of the sensory root results in complete anaesthe- 
 sia of the skin of the face and mucous membrane of the 
 mouth. 
 
VI NERVE, 211 
 
 The trophic influence of the sensory root is of very great value. 
 If it be divided, the complete anaesthesia of the conjunctiva, 
 of the nostrils, and of the lips prevents the reflex self-protec- 
 tion which belongs to the parts, and they become injured very 
 easily. Aside from that, the direct influence upon all the 
 parts is great, so that when it is cut off there is a rapid degen- 
 eration resulting, which is specially apparent in the mucous 
 membrane of the nose and in the cornea. 
 
 Influence of the sensory branch on the special senses : (1) Its 
 division causes total anesthesia to the skin and mucous mem- 
 brane ; the loss of the sense of touch in the part is of great 
 importance, for the tongue and lips are used much for this 
 purpose. (2) Upon the sense of sight it has a very control- 
 ling influence, for, as we have seen, the trophic influence is 
 essential to the maintenance of the integrity of the eye. (3) 
 Upon the sense of smell. Here the influence is the same as 
 with the eyes, trophic. The smell is soon lost on account of 
 degeneration of the mucous membrane after division of the 
 fifth nerve. (4) Taste, probably, is not a direct function of 
 the nerve ; but if the tactile sensibility is gone and the tro- 
 phic changes are begun, the sense of taste soon disappears in 
 the anterior portion of the tongue. (5) Upon the hearing 
 the effect is more gradual and less distinct. The secretions 
 of the cavity of the tympanum and of the external auditory 
 canal are of great importance in maintaining normal condi- 
 tions. They are under the trophic influence of the fifth nerve, 
 both through its auriculo-temporal branch and through its 
 communication with the otic ganglion. The tensor tympani 
 muscle is also supplied by the motor root. Thus, the auditory 
 apparatus is considerably under the control of the nerve. 
 
 Symptoms due to pathological changes in the sensory root : 
 Headaches of the scalp and deeper tissues, and more especially 
 the frontal sinuses, are common. Toothache and facial neu- 
 ilgia are due to irritation or disease of parts of the nerves. 
 douloureux is a persistent neuralgia of some or all of the 
 
 inches of the nerve. 
 
 VI nerve : It arises from a nucleus of gray matter in the 
 floor of the fourth ventricle, and its nucleus is more or less 
 directly connected with those of the third, fourth, and seventh 
 
212 
 
 NERVOUS SYSTEM. 
 
 nerves. It emerges without decussation at the posterior border 
 of the pons Varolii, and passes forward to the orbit with the 
 third and fourth nerves. In its course it has many commu- 
 nications with the sympathetic nerves, but their significance 
 is unknown. It is supplied to the external rectus muscle of 
 the eye, and its stimulation causes external squint, and paraly- 
 sis causes internal. 
 
 VII nerve : It arises in the floor of the fourth ventricle, 
 and its fibres emerge from the upper part of the groove be- 
 
 Fio. 103. 
 
 Diagram of the facial nerve and its distribution. 1, facial nerve at its entrance into 
 the internal auditory meatus : 2, its exit at the stylo-mastoid foramen; 3,4, 
 temporal and posterior auricular branches, distributed to the muscles of the 
 external ear and to the occipilalis; 5, branches to the frontalis muscle; r>, 
 branches to thestylo-hyoid and digastric muscles ; 7, branches to the upper part 
 of the platysma myoides: 8, branch of communication with the superficial cer- 
 vical nerve of the cervical plexus. 
 
 tween the olivary and restiform bodies in company with the 
 (eighth) auditory nerve (sometimes known as the portin mol- 
 lis ; the facial being then called the portio dura of the "sev- 
 enth" pair, when the classification of the cranial nerves is 
 made into nine pairs). It passes into the internal auditory 
 
CHORDA TYMPANI BRANCH. 213 
 
 canal, and escapes from the skull by way of the aqueduct of 
 Fallopius and the stylo-mastoid foramen. 
 
 It is almost wholly a motor nerve, and is distributed to all 
 of the muscles of the face (Fig. 103) except those mentioned 
 as controlled by the motor branch of the trigeminus nerve. 
 The muscles of the eyelids and some of the muscles of the 
 palate in part are innervated by it, as well as the parotid and 
 submaxillary glands through the chorda tympani. In the neck 
 it supplies the posterior belly of the digastric and the platysma 
 myoides muscles. It also sends branches to the stapedius 
 muscle of the internal ear and to all of the muscles of the 
 external ear. The branches passing to the salivary glands 
 are secretory in their function ; and this is the only exception 
 to the motor influence of the nerve. 
 
 Function of the VII nerve : It is the motor nerve which 
 parallels in its distribution the sensory root of the fifth ; it 
 supplies the superficial muscles, as the latter does the skin. 
 It is the nerve of "expression," by which the features are 
 made to reflect the emotions. 
 
 Paralysis of the VII nerve : If the nerve be divided or dis- 
 eased, the face of that side is devoid of motion (Fig. 104), 
 and becomes smooth and expressionless, while the sound side 
 is held in its customary pose. The eyelids cannot close them- 
 selves, and the lips do not oppose properly, on account of the 
 defective action of the orbicular muscle. There is difficulty 
 in drinking and in articulation for the same reason. 
 
 The eyelids remain open in facial paralysis, and the con- 
 junctiva is subject to injury by drying and by foreign bodies ; 
 but the injury is not so great as in paralysis of the fifth 
 nerve, because the seventh has no trophic influence. 
 
 Chorda tympani branch : The chorda tympani is a small 
 filament given off from the facial in the aqueduct of Fallo- 
 pius, some of whose fibres are distributed to the submaxillary 
 gland. If this nerve be divided, the secretion of saliva from 
 the gland is greatly diminished, while stimulation of the 
 nerve will excite a copious flow. This is an active secretion, 
 and is not a simple filtration due to vaso-motor changes. A 
 similar influence is noted in the corresponding half of the 
 tongue. 
 
214 
 
 NERVOUS SYSTEM. 
 
 There is a similar distribution of fibres from the facial to 
 the parotid gland, which also receives secretory fibres from 
 the glosso-pharyngeal through the lesser superficial petrosal 
 
 Fio 104. 
 
 Facial paralysis of the right side. 
 
 nerve, but their action has not been so thoroughly analyzed 
 as in the case of the submaxillary and chorda tympani. 
 
 The chorda tympani has still further an effect upon the 
 sense of taste in the anterior portion of the tongue. If it be 
 divided, the taste is much blunted on the affected side. It is 
 
FUNCTION OF THE IX NERVE. 215 
 
 now known that this is due to the communication with the 
 glosso-pharyngeal nerve, thus : the chorda tympani has fibres 
 from the otic ganglion, which, in its turn, receives the lesser 
 superficial petrosal nerve from the glosso-pharyngeal. 
 
 IX nerve : It arises in the medulla from centres near those 
 for the vagus and spinal accessory nerves. Its fibres pass 
 through the substance of the medulla and emerge in com- 
 pany with those of the vagus and spinal accessory, to pass 
 with them from the skull through the jugular foramen. It 
 gives off a small branch, which passes to the tympanum and 
 Eustachian tube (Jacobson's nerve) while in the jugular fora- 
 men, and presents a small ganglion, the petrosal ; and it has 
 communicating branches to the seventh and tenth nerves and 
 to the otic ganglion. 
 
 The nerve divides as it passes down, one branch passing 
 forward to the tongue, and one going to the pharynx (whence 
 its name). 
 
 The portion which passes to the tongue is distributed to the 
 posterior portion of the organ, to the circumvallate papillae, 
 and the mucous membrane behind them, some fibres going to 
 the lining of the soft palate, pillars of the fauces, and tonsils. 
 The other branch is distributed to the mucous membrane of 
 the pharynx, and by direct branches and communication with 
 other nerves to all the muscles involved in swallowing. 
 
 Function of the IX nerve : (1) It is the nerve of taste; and 
 (2) it is essentially a nerve of deglutition. 
 
 (1) It is only in the latter part of the stay of food in the 
 mouth that it reaches the region directly supplied by this 
 nerve. When the food is to be swallowed, it is pressed 
 by the base of the tongue against the palate arch and pushed 
 into the pharnyx. It is then that the sense of taste is here 
 exercised. The reflex stimuli then excited start up the 
 motor chain, which pushes the bolus on to the stomach. At 
 one time there was considerable question as to whether the 
 trigeminal or glosso-pharyngeal was really the conductor of 
 this sense, but it is quite likely that both are essential to 
 its proper appreciation. 
 
 (2) Whether by reason of its communications with other 
 nerves or not, in its distribution the nerve is a motor nerve as 
 
NERVOUS SYSTEM. 
 
 well as sensory. Its distribution is to all the muscles of 
 deglutition, and stimulation causes contraction of the muscles, 
 while division paralyzes them. The very numerous connec- 
 tions of the nerve complicate its anatomical origin very 
 greatly, and interfere with a clear comprehension of the un- 
 aided function of* the nerve. 
 
 The reflex for swallowing originates in the medulla ob- 
 longata, where the origin of the nerve is situated. 
 
 X nerve : The Xth nerve is also known by two other 
 names : " pneumogastric," from its distribution and function ; 
 " vagus " or " par vagum," from its scattered distribution 
 (vagus, Latin, wanderer). 
 
 It arises from the gray matter in the floor of the fourth 
 ventricle, its nucleus being very close to those of the glnsso- 
 pharyngeal and spinal accessory. Its fibres pass through the 
 substance of the medulla oblongata, and emerge from its lat- 
 eral surface with the roots of its associate nerves, the glosso- 
 pharyngeal, and spinal accessory. It passes from the skull 
 with them by the jugular foramen. It has at this point a 
 ganglionic enlargement. From here it passes down the 
 neck, and is distributed more diffusely than any other cranial 
 nerve. 
 
 It is supplied to the organs by which air and food enter 
 the body, and besides this has several important connections 
 with the sympathetic system. (1) To the larnyx it supplies 
 sensation and motion through the superior and inferior lari/n- 
 geal branches. (2) In the chest it forms the pulmonary 
 plexuses, which innervate the bronchi and lungs. (3) Branches 
 to the cardiac plexus supply important stimuli to the heart 
 and great vessels. (4) There are branches to the pharyngeal 
 and cesophageal plexuses which are both sensory and motor, 
 supplying both the mucous membrane and the muscular 
 structures of the parts. (5) Its terminal branches supply 
 the sensory and motor nerves to the stomach, the left nerve 
 being distributed on its anterior wall, and the right poste- 
 riorly. (6) Branches also pass to the liver and spleen and 
 communicate with the solar plexus. 
 
 Communication between X nerve and other nerves : Soon 
 after leaving its origin in the medulla the vagus enters into 
 

 EFFECT OF SECTION OF X NERVE ON RESPIRATION. 217 
 
 so many communications with other nerves, both sensory and 
 motor, that it is difficult to know the real fibres of the original 
 root and to determine what are original and what derived 
 functions. The sympathetic system sends fibres in all the 
 branches of the pneumogastric, and the pneumogastric sends 
 branches to many of the important sympathetic plexuses and 
 ganglia ; the pharyngeal, laryngeal, resophageal, pulmonary, 
 cardiac, and solar plexuses are so made up by branches from 
 both. The spinal accessory nerve is an important contributor, 
 in that it sends a large branch which is incorporated in the 
 vagus. The fibres from the spinal accessory nerve are motor, 
 and are, most of them, carried in the recurrent laryngeal 
 nerve. There are also communications to the glosso-pharyn- 
 geal and hypoglossal nerves, and it also receives motor fibres 
 from the facial and upper two cervical nerves. 
 
 The original nerve is probably entirely sensory, and its 
 motor function is derived from these connections with motor 
 nerves. 
 
 Function of X nerve in respiration : The nerve supplies, as 
 has been said, the motor and sensory functions of the larynx, 
 and in this is of value to the respiratory function both in the 
 prevention of foreign substances entering the rima glottidis, 
 and in the opening of that orifice for the entrance of air. 
 Besides this, it supplies sensory fibres to the pulmonary 
 plexus which transmit the reflex stimulus to the medulla, by 
 which the motor apparatuses excited to action. 
 
 The muscles of the larynx involved in the production 
 of sound are supplied by this nerve, and, as the approxi- 
 mation of the chordae vocales is necessary for this, it fol- 
 lows that the voice is dependent upon the fibres of the 
 pneumogastric supplied by the inferior or recurrent laryn- 
 geal nerve. 
 
 Effect of section of X nerve on respiration : Respiration is 
 slowed immediately to about half its usual rate, and soon 
 drops to five or six to the minute, and even slower. The 
 respiration is easy inspiration slow and full, expiration 
 harsh and sudden. Death follows this operation in a short 
 time (one to six days), and the animal during the time is 
 sluggish and apparently suffers from slow carbonic-oxide 
 
218 NERVOUS SYSTEM. 
 
 narcosis. It is inferred from this that the vagus is the nerve 
 which carries to the automatic centre the stimuli which are 
 needed to keep up the automatism, and that the medulla is 
 incapable of originating the motor impulses unless controlled 
 by afferent stimuli. 
 
 Function of X nerve in deglutition: Deglutition both in the 
 pharynx and the oesophagus is under the influence of the 
 vagus, which gives innervation directly to the thoracic part 
 of the latter and through the inferior laryngeal branch to the 
 cervical part. The sensory fibres act as conductors of the 
 stimulus which results in the reflex peristalsis by which the 
 food is carried on through the oesophagus. The sensory dis- 
 tribution to the larynx must not be forgotten in this connec- 
 tion, for by it food is kept from the respiratory organs. Sec- 
 tion of the vagi causes paralysis of swallowing, and food is 
 apt to pass the glottis on an attempt to swallow, not even a 
 cough being excited by such an accident. The closure of the 
 glottis in swallowing is caused by a reflex action known as 
 the "action of arrest," and is derived from the sensory fibres 
 of the vagus. 
 
 Relation of X nerve to stomach : The stomach receives both 
 motor and sensory function through the vagus. The stomach 
 receives its warning of the presence of food through the sen- 
 sory fibres, and the muscular fibres excite the organ to con- 
 tract upon it and " churn " it about during digestion. There 
 is also a vaso-motor influence derived from the vagus. AVhen 
 the nerve is cut but little food can reach the stomach, because 
 of the paralysis of the oesophagus, and what food does enter 
 is digested very slowly, so that the function of the pncu mo- 
 gastric may be considered essential to stomach digestion. 
 The connection with the solar plexus also involves the intes- 
 tines in the action of the vagus. 
 
 Influence of X nerve on the heart: There are numerous 
 branches to the cardiac plexus from the trunk of the vagus 
 and from its inferior laryngenl branch. Stimulation of the 
 pheumogastric nerve diminishes the frequency, or, if strong, 
 entirclv stops the heart in diastole. The nerve is therefore 
 regarded as having an inhibitory (trfion. 'Phis is an nnnsual 
 effect, for in other cases the stimulation of nerves going to 
 
FUNCTION OF XI NERVE. 219 
 
 muscles causes contraction : the heart, however, becomes 
 flaccid under the influence of the stimulated vagus. 
 
 Other functions of X nerve : The vagus nerve is the channel 
 for excito-motor reflexes in coughing and vomiting, as well 
 as for many other less essential reflexes, such as sighing, 
 hiccoughing, and the like. 
 
 XI nerve : The origin of the Xlth nerve is twofold. One 
 root arises in the gray matter of the medulla near the nucleus 
 for the vagus, while the other arises from the lateral tract of 
 the cord as low as the fifth or sixth cervical vertebra, and 
 passes up between the anterior and posterior spinal nerve-roots 
 to join the medullary (or accessory) portion at its emergence 
 from the medulla. The united nerve soon divides and passes 
 out through the jugular foramen with the glosso-pharyngeal 
 and pneumogastric nerves, the medullary portion joining the 
 trunk of the pneumogastric, w r hile the spinal root supplies the 
 sterno-mastoid and trapezius muscles. 
 
 Function of XI nerve : The nerve is a motor to all intents, 
 though it has some sensory fibres, as is shown by the pain 
 caused by pinching it. 
 
 (1) The anastomatic branch, which joins the pneumogastric, 
 is apparently largely given off in the recurrent laryngeal 
 nerve ; but its section does not produce the same effect upon 
 the larynx as section of the trunk of the vagus or of its in- 
 ferior laryngeal branch. There is paralysis of the voice, but 
 not of the movements of the glottis for respiration. There 
 are probably some fibres of this nerve also given off to the 
 cardiac plexus. 
 
 (2) The muscular branch supplies the sterno-mastoid and 
 trapezius muscles; but these muscles are also supplied by the 
 cervical spinal nerves, and their action is not paralyzed by 
 the section of this branch of the spinal accessory. It is 
 found, however, that the relation of these muscles to respira- 
 tion is impaired by isolation from this nerve that is, when 
 the breath is held in any violent exertion, as straining or 
 pushing, or when a loud cry is uttered, the sterno-mastoid 
 and trapezius muscles contract to fix the head and hold the 
 spine steady. This action seems to be prevented by the 
 section of this muscular branch of the spinal accessory. 
 
220 THE SENSES. 
 
 XII nerve : It arises in the gray matter at the inferior 
 extremity of the floor of the fourth ventricle, mesial to the 
 origin of the spinal accessory and pneumogastric nerves. 
 The fibres pass through the substance of the medulla ob- 
 longata, between the pyramid and the olivary body, and, 
 emerging in a number of small bundles, connect into a nerve- 
 trunk which emerges from the skull by the anterior condyloid 
 foramen. It passes down the neck to about the level of the 
 hyoid bone, where it curves forward and into the tongue, 
 giving off branches to the muscles which move that organ. 
 
 Function of XII nerve : It is a motor nerve, but po>- 
 some sensory fibres derived from the cervical spinal nerves 
 and from the trigeminus, with whose lingual branch it inos- 
 culates on the side of the tongue. Filaments from it arc 
 distributed to all the muscles which move the tongue, and to 
 the depressors of the hyoid bone through its descendiixj 
 branch. 
 
 The latter branch, although in the anatomical sheath with 
 the hypoglossal nerve, is not an integral part of the nerve, 
 but is derived from the upper cervical nerves. 
 
 Influence of XII nerve on digestion : It is important in mas- 
 tication, for its muscles move the food about for the better 
 action of the teeth. In animals, after division, drinking is 
 impossible, because they are unable to lap up fluids, and the 
 food is swallowed with difficulty because it is not carried back 
 into the pharynx by the tongue after mastication. 
 
 Connection of XII nerve with speech : Articulation of most 
 sounds involves movements of the tongue. Impaired articu- 
 lation is an early symptom in bulbar or glosso-labio-laryn- 
 geal paralysis. 
 
 THE SENSES. 
 
 A peripheral organ for the reception of an impression, a 
 nerve for its conduction, and a centre in the brain for the 
 perception, are the organs necessary for sensation. It i> by 
 means of impressions so received and conducted to it that the 
 mind is able to control the body and to take cognizance of the 
 external world. 
 
COMMON AND SPECIAL SENSATIONS. 221 
 
 Classification of sensations : Common sensations and special 
 sensations. These last are commonly called " the senses." 
 
 Common sensations : Such perceptions as cannot be dis- 
 tinctly located in any organ or set of organs, such as fatigue, 
 hunger, thirst, satiety. Besides these, there are some sensa- 
 tions which involve certain organs which must be classed 
 under this head ; thus inclinations to cough or to sneeze or 
 to vomit are common sensations, and, similarly, to urinate or 
 defecate. Many of these sensations occupy a border-line be- 
 tween common sensibility and the special sense of touch, such 
 as itching and tickling. 
 
 Pain is a common sensation, but is very closely allied to 
 the sense of touch. The two may be differentiated, however. 
 If one touch a sharp instrument, he may perceive its shape 
 and condition ; but if the pressure be increased, the ability 
 to perceive its form is lost, and instead the sensation of pain 
 is established. The relation of the two is curiously shown 
 in partial anaesthesia by drugs, as when one takes nitrous- 
 oxide gas for the extraction of a tooth, and is able to feel the 
 operation and to know what has been done, without in the 
 least feeling pain. 
 
 The seat of the senses is the brain, or sensorium. The organ 
 of the mind, which perceives the thing which the organ of 
 sense has taken an impression from, is the fundamental struct- 
 ure in the necessary chain. 
 
 Hallucination is the perception of an object as a real presence 
 without the presence of the object to justify the perception ; 
 that is, it is an act of the brain which refers its action to an 
 organ of the senses. Thus, in delirium tremens a person may 
 perceive many curious and uncanny things, which his mind 
 hears and sees and feels, but which his senses could not 
 take cognizance of, because they are only " creatures of the 
 mind." 
 
 Difference between common and special sensations : The 
 most important distinction between common and special sen- 
 sations, is that the former are strictly limited to the condition 
 of our bodies, while by the latter we gain, in addition, infor- 
 mation respecting affairs outside of our bodies. This differ- 
 ence may be explained if we compare the sensations of pain 
 
222 THE SENSES. 
 
 and touch, the one a common, the other a special sensation. 
 For example, if the point of a needle be gently pi 
 against the tip of the finger, we only feel this point by our 
 sense of touch and refer the sensation to the object causing 
 it. But if the needle be pressed harder, so as to enter the 
 skin, we feel at once a sensation of pain, which is no longer 
 referred to the needle, but to the finger itself. The sensation 
 of pain is not able to cause us to recognize the object which 
 caused it, nor its nature. 
 
 Sensations and perceptions : Our habit of referring sensa- 
 tions to outside causes leads us to consider as properties of 
 external bodies the sensations which they excite in us. "When 
 we speak of anything as having a bad taste, we forget that 
 it only tastes bad to us. This habit pertains especially to 
 sensations of touch and sight. From constant exercise of it 
 we finally come to believe implicitly in the " evidence of our 
 senses." 
 
 Judgments : There is a distinction between a sensation and 
 a judgment (which is often unconsciously based on sensations). 
 When we estimate the distance of an object from ourselves 
 we form a judgment based on past experience of many sensa- 
 tions, such as the number of steps we must take before we 
 touch it, etc. 
 
 Nerves of special sense: The special nerves have no other 
 function than the special one for which they are set apart ; 
 and when they are separated from their special orpins for 
 receiving impressions, they no longer respond to the custom- 
 ary stimuli. The special senses are touch, taste, smell, hearin</, 
 and sight 
 
 Touch. 
 
 The organ of touch consists of the skin and mucous mem- 
 branes adjoining it. The nails and teeth too exercise a peculiar 
 function in this regard, and the hair in some regions c. //., 
 eyelashes. Touch is really only a specialized development of 
 common sensation or sensibility. The sensations of touch, 
 therefore, are conveyed to the central nervous system by 
 those nerves which confer ordinary sensation on the differ- 
 
MEASURE OF ACUTENESS OF TOUCH. 223 
 
 ent parts of the body that is, the sensory cerebral nerves 
 and those arising from the posterior roots of the spinal 
 nerves. By means of the sense of touch we acquire knowl- 
 edge of the size, shape, and other external peculiarities of 
 bodies. 
 
 Varieties of touch : (1) Tactile sensibility, or touch proper ; 
 (2) the sense of pressure or weight ; (3) the sense of temper- 
 ature. All of these, when carried beyond moderate limits, 
 are merged into the sensation of pain. 
 
 Acuteness of touch : The distribution of the end-organs of 
 the sensory nerves varies in different parts of the body, and 
 the more numerous the touch-corpuscles, the more acute the 
 sensibility of the part. Again, the thickness of the epidermis 
 has marked influence in determining the tactile ability, por- 
 tions of the hands and feet, when callous, having very blunted 
 sensibility. The hardness and elasticity of bodies, the quality 
 of the surface as to smoothness, the size and form and the 
 temperature, and wet or dry condition, are all easily deter- 
 mined by touch. 
 
 The hand is of great value as an organ of touch because 
 of the acuteness of its sensibility. Further than this, the 
 hand is so constructed as to be capable of forming impres- 
 sions of bodies by reason of its power to grasp them and to 
 test them as to weight. 
 
 Measure of acuteness of touch is by means of a pair of com- 
 passes whose points are blunted. The legs of the instrument 
 are separated, and the distance between the points which can 
 just be distinguished as two separate contacts, measures the 
 sensibility. From the accompanying table it will be seen 
 that the touch is most acute in the tip of the tongue and in 
 the fingers and tips, while in other portions the sense of touch 
 is so vague that two points of contact are not distinguished 
 until they are two and a half inches apart. It is found that 
 the points of the compasses must be more widely separated 
 
 Iwhen the test is made in the long axis of a limb than when 
 across it (the table is from Kirke's Handbook) : 
 
224 THE SENSES. 
 
 Table of Variations in the Tactile Sensibility of the Different 
 Partff. (The measurement indicates the least distance 
 at which the two blunted points of a pair of compa < - 
 could be separately distinguished. E. H. Weber.) 
 
 Tip of tongue ( inch. 
 
 Palmar surface of third phalanx of forefinger . . . T ^ 
 
 Palmar surface of second phalanges of fingers . . . 
 
 Red surface of under lip 
 
 Tip of the nose 
 
 Middle of dorsum of tongue 
 
 Palm of hand fy 
 
 Centre of hard palate 
 
 Dorsal surface of first phalanges of fingers ^ 2 
 
 Back of hand l| 
 
 Dorsum of foot near toes 1 " 
 
 Gluteal region l| " 
 
 Sacral region l| " 
 
 Upper and lower parts of forearm 1 " 
 
 Back of neck near occiput 2 " 
 
 Upper dorsal and mid-lumbar regions 2 " 
 
 Middle part of forearm 2j " 
 
 Middle of thigh 2| " 
 
 Mid-cervical region 2^ " 
 
 Mid-dorsal region 2J " 
 
 The sense of touch may be greatly educated and special- 
 ized. This is seen in many of the arts where great dex- 
 terity obtains by reason of an educated touch. The read- 
 ing raised letters by the blind is a familiar example of edu- 
 cated touch. 
 
 Pressure-sensation: When weight is added to an ordinary 
 touch the sensation of the pressure of the weight is felt, and 
 by it one can judge with considerable accuracy the amount of 
 the pressure, and determine the comparative pressure of two 
 weights with approximate correctness within limits of press- 
 ure. This is known as the sense of pressure. 
 
 Muscular sense: By taking a body in the hand and raising 
 it we feel a sense of resistance in the muscles, by whose in- 
 tensity we can much more accurately determine the weight. 
 This is the muscular sense. It is developed to an exceedingly 
 fine degree in some occupations; for example, postal clerks 
 detect overweight letters with wonderful accuracy and quick- 
 ness. 
 
TASTE. 225 
 
 It has been urged that the muscular sense is of central 
 origin, and depends upon the strength of the impetus which 
 must be sent to the muscles to cause them to do certain work. 
 It may, however, be due to a training of the sensibility of 
 the muscle, whereby the relative strength of a contraction is 
 perceived as a sensation. The centre for muscular sense is in 
 the upper part of the quadrate lobule on the mesial surface 
 of the hemisphere. Its involvement by pressure brings about 
 inability to locate the position, say, of hand or foot without 
 the aid of sight. Thus, the individual can move his upper 
 extremity ; but if the hand is placed out of range of vision, 
 he does not know where it is. 
 
 Temperature-sense : The surface of the body is very sen- 
 sible of temperature-changes ; and that this is distinct from 
 ordinary tactile sensation has been inferred from the fact that 
 when the ordinary touch is blunted the temperature-sense 
 may remain unimpaired. Temperature-sensations are not 
 accurate ; they are only relative that is, we infer from the 
 temperature of the skin or of our habitual surroundings the 
 warmth or coldness of the thing tested. It is related that 
 Arctic explorers have found the water feel warm when swim- 
 ming in pools on icebergs, and a drop of the mercury to 80 
 F. is said to feel cold in torrid climates. A more simple 
 illustration is that of immersing one hand in water at 40 F. 
 and the other in water at 120 F., and then both in water at 
 80 F., when one hand will feel hot and the other cold, 
 though both are subjected to the same temperature. Again, 
 during a chill the temperature of the body is often very con- 
 siderably elevated, and yet the sensation is entirely of cold. 
 
 Taste. 
 
 Taste necessary conditions: Aside from the conditions 
 which are always necessary for sense-perception viz., proper 
 organs for receiving, communicating, and perceiving the sen- 
 sory impulse there must be present a sapid substance which 
 must be in solution. The solution in the case of dry sub- 
 stances is effected by the saliva. It is also necessary that the 
 surface of the organs of taste shall be moist. The substances 
 
 15 Phys. 
 
226 THE SENSES. 
 
 which excite the special sensation of "taste" act by produc- 
 ing a change in the condition of the terminal filaments of the 
 gustatory nerve, and this change furnishes to it the required 
 stimulus. 
 
 Origin of taste : Chiefly from the tongue, though there is 
 some power to taste resident in the soft palate, fauces, tonsils, 
 and pharynx. In the tongue the taste is more acutely devel- 
 oped in the posterior portion, though in most the tip and 
 sides are sensitive to taste. The central portion of the dor- 
 sum is not an actively sensitive taste-organ. The under sur- 
 face of the tongue is little if at all sensitive to taste. 
 
 The nerve-supply for sense of taste is probably the glosso- 
 pharyngeal. The lingual branch of the fifth (or " gustatory ") 
 is also a conductor of taste-impressions for the front of the 
 tongue, but by means of the fibres from the chorda tympani 
 and otic ganglion (see page 172). 
 
 The tongue is a flattened muscular organ covered by epithe- 
 lium. It is controlled by intrinsic and extrinsic muscles, 
 which give it a remarkable flexibility of movement ; the 
 latter for its larger, and the former for its more delicate 
 actions. 
 
 There are three varieties of papilla found, which are 
 known as filiform, fungiform, and circumvallate papilla?. 
 These are set chiefly upon the dorsum of the tongue; 
 and over its whole surface are numerous mucous follicles, 
 whose secretions keep the tongue moist (Figs. 105, 106, 
 and 107). 
 
 The filiform papillce are set upon the middle of the dorsum, 
 and are scattered over the entire surface, and are far more 
 numerous than any other kind. They are conical in shape, 
 and are covered with epithelium, which projects in a brush- 
 like tuft from the apex. Their function is mostly tactile, 
 and in animals, especially of the cat tribe, are very promi- 
 nent. 
 
 The fa/nffiform papUlcc are chiefly distributed over the sides 
 and tip of the organ, and sparsely upon the dorsum. They 
 are larger at tin- surface than at the base, club-shaped, and 
 arc supplied with bloodvessels and nerves. Their function is 
 probably sciiH.ry (Fig. 106). 
 
OTHER SENSATIONS IN THE TONGUE. 227 
 
 The circumvallate papillae are somewhat similar in shape to 
 the fungi form, but considerably larger. They are situated at 
 the posterior portion of the dorsum in a V-shaped arrange- 
 ment, and number only eight or ten. Around the circum- 
 
 FIG. 105. 
 
 Upper surface of the tongue. 
 
 valla te papillse are the taste-goblets, or gustatory buds, which 
 are the form of nerve-ending characterizing the parts where 
 this sense is developed (Fig. 107). 
 
 Other sensations in the tongue : The sense of touch is very 
 highly developed here, and with it the sense of temperature, 
 pressure, pain, etc.: upon these tactile and muscular senses to 
 
228 
 
 THE SENSES. 
 
 a great extent depend the accuracy of the tongue in many of 
 its important uses speech, mastication, deglutition, sucking. 
 
 FIG. 106. 
 
 B 
 
 Surface and sectional view of a fungiform papilla. A, the surface of a fungiform 
 papilla partiallv denuded of the epithelium (3o diameters) : p, secondary papillae; 
 a, epithileum. "B, section of a " 
 
 a, artery ; t>, vein ; c, capillar 
 ered by epithelium (from K6 
 
 a fungiform papilla with the bloodvessels injected: 
 y loops of simple papillae in the neighborhood, cov- 
 lliker, after Todd and Bowman). 
 
 The tactile sense is very important, too, in the sense of taste, 
 for with many substances the taste is largely due to their me- 
 
 Vertical section of a circnmvallate papilla, from the calf (35 diameters). A, the 
 papilla; B, the adjacent surface. The figure shows the nerves of the papilla 
 spreading toward the surface and toward the taste-buds which are imbedded 
 in the epithelium at the sides; in the sulcus on the left the duct of a gland 
 is seen to open (Engelmann). 
 
 chanical condition : this is the case with mucilaginous, oily, 
 and chalky tastes. 
 
 Association of smell and taste : It is important, for with 
 many substances particularly aromatic substances of food 
 
SMELL. 229 
 
 and drink the association of smell and taste is very essential 
 to a thorough appreciation of a flavor. Most cooked foods 
 lose their savor if the nose is obstructed ; thus with a " cold " 
 in the nose " everything tastes alike." 
 
 The principal tastes are sweet, bitter, acid, alkaline, and 
 saline. Besides these, the general sensibility of the tongue 
 detects pungent or caustic and styptic tastes, as well as the 
 oily and mucilaginous tastes. 
 
 Sensibility of tongue : It is quite acute. A solution of acid 
 or bitter substances is tasted when very dilute : strychnine is 
 said to be tasted in a 1 : 600,000 solution ; sulphuric acid, 
 1 : 1000. 
 
 After-taste : After an aromatic substance has been tasted 
 there remains in the mouth an impression of that flavor ; and 
 if such substances be taken in rapid succession, the apprecia- 
 tion of their flavor is lost. This impression, which is left by 
 a strong flavor, is called the after-taste, and is utilized some- 
 times to cover the taste of a disagreeable medicine, a strongly 
 flavored aromatic preceding it. 
 
 Smell. 
 
 Smell conditions : The first essentials are a special nerve 
 and nerve-centre, the changes in whose condition are per- 
 ceived as sensations of odor. No other nerve-structure is 
 capable of such sensations, even when acted on by the same 
 cause. The special organs for this sense for the reception, 
 conduction, and perception of the stimulus, as in the case of 
 any of the senses, must be in their normal condition, and a 
 stimulus (an odor) must be present to excite them. 
 
 Odors are caused either by minute particles of solid matter 
 or by gases which are in the atmosphere, and they must be 
 capable of solution in the mucus of the Schneiderian mem- 
 brane. The substance must pass in a current of air through 
 the nostrils or it is not perceived as an odor. This is accom- 
 plished by " sniffing" the air, and thus creating an intermit- 
 ting current which is tested by the olfactory sense. In this 
 way a trace of a gas or impalpable powder may be de- 
 tected which cannot be traced by chemical or other means. 
 
230 
 
 THE SENSES. 
 
 If the substance be applied as a solution, it is not detected ; 
 thus, rose-water in a nasal douche is not noticed while the 
 nostrils are full of fluid, and yet as soon as the nostrils are 
 free the odor appears. 
 
 The olfactory nerves are the functional nerves of the sense, 
 and are spread out in a fine network (Fig. 109) over the sur- 
 
 FIG. 108. 
 
 Cells and terminal nerve-fibres of the olfactory region, highly magnified. 1, from 
 the frog; 2, from man: a, epithelial cell,' extending deeply into a ramified 
 
 peripheral rods ; e, their extremities, seen 
 their central filaments ; 3, olfactory ni-rvr- 
 fibrilUe (Frey, after Schultze). 
 
 tne irog; z, irom man: a, epitneiiai ceil,' exi 
 process ; b, olfactory cells : c, their peripheral 
 in 1 to be prolonged into fine hairs ; d, their cent 
 fibres from the do} ; n, the division into fine fi 
 
 face of the superior turbinated bone and on the upper third 
 of the septum. The nerves end in special end-organs, known 
 as olfactory celts (Fig. 108), which lie under the ciliated epithe- 
 lium of the part. 
 
 Origin of olfactory nerves: The nerves arise from a mass >!' 
 gray matter lying beneath the anterior lobe of the brain upon 
 
ORIGIN OF OLFACTORY NERVES. 
 
 231 
 
 the cribriform plate of the ethmoid bone. This is the olfac- 
 tory bulb, and it is connected by the olfactory tract with the 
 cerebrum. Each olfactory tract arises from the cerebrum by 
 three roots, two of which are composed of white matter, the 
 other largely of gray matter. By these it is connected with 
 the olfactory centres. 
 
 The lining membrane of the nasal cavity is very sensitive 
 to irritation, the nasal branch of the fifth nerve and branches 
 from the spheno-palatine ganglion furnishing the ordinary 
 
 FIG. 109. 
 
 Distribution of nerves in the nasal passages; 1, olfactory bulb, with its nerves; 
 2. nasal branch of the fifth pair ; 3, spheno-palatine ganglion. 
 
 and tactile sense. Therefore we can perceive, by the nose, 
 the sensations of cold, heat, itching, tickling, pain, and ten- 
 sion or pressure. 
 
 The perceptions of the olfactory and of the nerves of touch 
 often resemble each other, and some stimuli affect both nerves. 
 The common sensibility is evoked by such substances as are 
 irritating and acrid : ammonia gas has no odor, but it stimu- 
 lates the mucous membrane by its irritating properties. The 
 tactile or common sensibilities remain when the olfactory are 
 gone. The relation between the two kinds of perception is 
 
232 THE SENSES. 
 
 lost to us, and we speak of the smell of ammonia or of alco- 
 hol when it is probably not an olfactory, but a sensory, per- 
 ception. 
 
 Acuteness of smell : The sense of smell is very acute, but 
 not so sharp in man as in many of the lower animals. The 
 distribution of the olfactory nerves is much wider in some of 
 the animals, and the cerebral development is correspondingly 
 increased. In man the range of susceptibility is, however, 
 probably greater. The variety of odors and the very minute 
 quantity of stimulant substance required to produce a sensa- 
 tion of smell are quite wonderful. The most delicate analy- 
 sis may fail to show traces of the substances which can be 
 appreciated by the sense of smell. For instance 0.000000005 
 gramme of oil of peppermint in 1 litre of air can be appreci- 
 ated. 
 
 There are some odors pleasant to some which others find 
 almost intolerable. Musk, for example, is a pleasant per- 
 fume to some, while to others it is quite unendurable. In 
 the same way, the acuteness of this sense in some is more 
 marked than in others, and yet this may apply only to certain 
 kinds of odors. Like the sense of touch and the other special 
 senses, that of smell can be very much developed by practice. 
 Large salaries are paid to experts in discrimination of the 
 quality of wines, etc. Often in cases of mental disease there 
 are hallucinations of smell, which also may occur in cases of 
 disease of the olfactory centres, when there may be frequent 
 complaint of a bad smell. With normal organs there may 
 be a sensation of an odor which cannot be detected by others 
 present. 
 
 Sneezing : The act of sneezing is a violent and sudden ex- 
 pulsion of air through the nasal passages. The act is a reflex 
 one and the exciting cause is a stimulation of the nasal ii la- 
 ments of the fifth or trifacial nerve. 
 
 Hearing. 
 
 The auditory apparatus consists, in brief, of (1) the external 
 ear; (2) the middle car; (3) the internal ear; and (4) the 
 auditory nerve. 
 
MIDDLE EAR, 
 
 233 
 
 External ear : The external ear consists of the auricle and 
 external auditory canal. The former serves to receive the 
 sound-waves and to indicate the direction from which they 
 come in animals which possess the power of moving the organ. 
 Through the external auditory canal the sound-waves are 
 conducted to the middle ear. 
 
 The middle ear, or tympanum, is a cavity in the temporal 
 bone which is shut off from the external auditory canal by 
 the membrana tympani. The Eustachian tube connects this 
 cavity with the pharynx. The lining of the middle ear is 
 
 FIG. 110. 
 
 Right temporal bone of the new-born infant, seen from its inner side, showing the 
 membrana tympani and chain of bones in their natural position (Riidinger). 
 
 partly ciliated epithelium, continued from the mucous mem- 
 brane of the pharynx through the Eustachian tube. There 
 are two openings of importance the fenestra rotunda and the 
 fenestra ovalis in the bony wall, but they are covered, the 
 former by a membrane, the latter by the stapes. The middle 
 ear also communicates posteriorly with the mastoid-cells, 
 which are air-cavities in the mastoid process of the temporal 
 bone. Its only communication with the external air, how- 
 ever, is through the Eustachian tube. There is a chain of 
 small bones (ossicles) which connect the membrana tympani 
 and the fenestra ovalis. 
 
 
234 
 
 THE SENSES. 
 
 Membrana tympani : It is a tough, tense, fibrous membrane 
 set in the bony opening of the external auditory canal. The 
 degree of tension of the membrane is regulated by the tensor 
 tympani muscle. 
 
 Ossicles: They are three in number (Fig. Ill), and are so 
 
 Fco. ill. 
 
 Bones of the tympanum of the left side. A, malleus : 1, long or slender process ; 2, 
 near neck ; 3, the handle; 4, short process ; 5, head. B, incus: 1, body ; 2, short 
 or posterior process ; 3, the long process with the orbicular process. C, stapes : 
 1 and 2, head ; 3, neck ; 4, 5, crura; 6, base. D, the three bones in their natural 
 connection ; TO, malleus ; sc, incus ; , stapes. 
 
 articulated as to communicate the vibration of the membrana 
 tympani to the internal ear (Fig. 110). The handle of the 
 malleus is attached to the membrane, so that this bone moves 
 with each vibration. This motion is communicated to the 
 incus, which passes it on to the stapes. The stapes rocks in 
 the fenestra ovalis, and is therefore capable of transmitting to 
 
SEMICIRCULAR CANALS. 
 
 235 
 
 FIG. 112. 
 
 the fluid in the cavity of the labyrinth the impulses which it 
 receives. 
 
 Eustachian tube : The Eustachian tube or canal leads from 
 the cavity of the pharynx to that of the middle ear. It is 
 completely pervious and allows a free passage of air from the 
 pharynx to the middle ear. 
 
 Its chief purpose is to provide for the maintenance of an 
 equal pressure on both sides of the membrana tympani, by 
 keeping the air in the middle ear in communication with the 
 outside air. It also serves to render sounds clearer (as the 
 apertures in violins do), and as an outlet for mucus. 
 
 Internal ear : The proper organ of hearing is formed by the 
 distribution of the auditory nerve within the internal ear or 
 bony and membranous labyrinths. The bony labyrinth is situ- 
 ated in the dense petrous portion of the temporal bone, and 
 consists of three essential parts : 
 the vestibule (Fig. 112), and open- 
 ing from it the semicircular canals 
 and the cochlea. There is another 
 opening, the aqueductus vestibuli, 
 whose use is doubtful, and still 
 others for the entrance of the audi- 
 tory nerve-filaments. Within the 
 bony labyrinth is the membranous 
 labyrinth, a series of tubes and sacs 
 composed of fibrous tissue, lined 
 with epithelium, which contains a 
 colorless fluid, the endolymph, while 
 a fluid surrounds this membranous 
 labyrinth, the perilymph. 
 
 Semicircular canals : These canals 
 are arched cylindrical spaces in the 
 solid bone which open at each end 
 of the arch into the vestibule. 
 They are three in number, and two are nearly vertical and 
 one is horizontal. These canals are arranged in such a man- 
 ner that the planes of the two vertical canals are at right 
 angles, one being antero-posterior, and the other transverse 
 (Fig. 112). These canals have within them complete mem- 
 
 External view of a cast of the left 
 labyrinth (Henle). /, fenestra 
 rotunda, or round window ; a, 
 fenestra ovalis, or oval window ; 
 b, ampulla of superior semi- 
 circular canal; c, ampulla of 
 horizontal semicircular canal; 
 (1, common shaft of union of 
 these two canals ; e, ampulla 
 of posterior semicircular canal ; 
 g, promontory (the line should 
 extend more to the right). 
 
236 
 
 THE SENSES. 
 
 branous tubes, considerably smaller than themselves ; so that 
 the perilymph occupies the space between the bony wall and 
 the membranous wall, while the endolymph occupies the cavity 
 of the membranous semicircular canals (Fig. 113). 
 
 Within the cavity of the membranous semicircular canals 
 are found the terminations of some filaments of the auditory 
 nerve. These filaments end in collections of cells called 
 " cristae acustica?." A similar collection of nerve-cells, called 
 " macula acustica," is found in the membranous chamber 
 
 FIG. 113. 
 
 Membranous labyrinth. Cs, semicircular canals; U, utriculus ; S, sacculus; 
 A, aqueduct of vestibule; Cr, ductus reunions ; Co, cochlea. 
 
 (utricle), situated in the vestibule, into which the membranous 
 semicircular canals open. 
 
 The me of the semicircular canals does not seem to be 
 directly connected with the auditory function of the part, but 
 to be connected more with the sense of equilibrium. The 
 movement of the fluids in the canals, arranged in the direc- 
 tions of the three dimensions, may serve to produce sensations 
 upon the cristse acusticaB which lead to the formation of ac- 
 curate judgment of changes in the position of the body. 
 
 Cochlea : It is a part of the bony labyrinth which derives 
 its name from its resemblance to a snail-shell. It is divided 
 into two parts by a bony and membranous septum which 
 runs parallel from base to apex of the spiral (Fig. 114). The 
 " upper " passage opens out of the vestibule, and is known 
 as the scala vestibuli ; the "lower," the scala tympani, is shut 
 off by a membrane, which covers the fenestra rotunda, from 
 the cavity of the 'tympanum. The scala vestibuli is sub- 
 divided by a membrane, which passes from the bom lamina 
 spiralis to the wall of the scala vestibuli, shutting off a tri- 
 
CANALIS COCHLEARTS. 237 
 
 angular space (canalis cochlearis). The floor of this space is 
 the membranous partition (membrana basilaris) which sepa- 
 
 FIG. 114. 
 
 Bony cochlea of the human ear, right side, opened from its anterior face 
 (Cruveilhier). 
 
 rates the scala tympani from it, and upon this membrane is 
 the organ of Corti. 
 
 The roof of the triangular space is the membrane of Reissner. 
 
 Canalis cochlearis : The canalis cochlearis, or scala media, 
 is the representative of the membranous labyrinth occupying 
 the bony cochlea. It is a single continuous tube, spiral in 
 shape so as to conform to the shape of the bony cochlea. On 
 cross-section it is seen to be triangular, or, more correctly 
 speaking, the segment of a circle. Its apex lies just over the 
 edge of the lamina spiralis, and its base against the circum- 
 ference of the bony cochlea. Its upper side is the membrane 
 of Reissner, and its lower side the basilar membrane. 
 
 At the apex of the spiral cochlea the canalis cochlearis 
 terminates as a blind end. At the base of the cochlea the 
 canalis cochlearis connects by means of a tiny duct (canalis 
 reuniens) with a round membranous chamber (the saccule). 
 The saccule and utricle are those portions of the membranous 
 labyrinth occupying the bony vestibule. The saccule and 
 utricle communicate with each other by means of the "ductus 
 endolymphaticus," a minute tube lying in the aqueductus 
 
238 THE SENSES. 
 
 vestibuli. Thus it is seen that the canalis cochlearis is filled 
 with endolymph, freely communicating with the interior of the 
 rest of the membranous labyrinth ; but nowhere does the 
 endolymph communicate with perilymph. 
 
 Organ of Corti : Upon the basilar membrane is arranged 
 a series of rafter-like bodies which roof in a small canal 
 (Fig. 115) ; upon this are spread the functional nerve-endings 
 of the auditory nerve. These rafter-like bodies are large 
 nucleated cells, the rods of Corti, having resting upon them 
 other epithelial cells with hair-like processes which project 
 into the canalis cochlearis or scala media. When looked at 
 from above the cells have an appearance similar to the key- 
 
 FIG. 115. 
 
 Diagrammatic section of the organ of Corti. 1, membrana basilaris; 2, 3, internal 
 and external rods of Corti ; 4, epithelial cells near inner and outer borders ; 5, 
 hair-cells lying in contact with the rods (magnified 500 diameters). 
 
 board of a piano. Fibres of the auditory nerve spread to 
 these cells from the bony lamina spiralis. 
 
 It is probable that each of the functional cells in the organ 
 of Corti responds to a particular shade of sound. 
 
 Auditory nerve : The Ylllth cranial or auditory nerve is 
 purely centripetal in its functions. Anatomically we say 
 that its fibres arise from a nucleus of gray matter in the floor 
 of the fourth ventricle, and from this source pass out through 
 the substance of the medulla in a number of small bundles 
 which unite with another root which has connections with 
 the cerebellum to form a trunk. This passes with the facial 
 nerve into the internal auditory canal, and terminates in 
 special end-organs in the internal ear. 
 
 Its fibres contain numerous ganglion-cells. In the cochlea 
 there are many of these cells, and they form plexuses of 
 nerve-fibres to supply the hair-cells. The absence of neuri- 
 
COURSE OF SOUND-WAVES. 239 
 
 lemma in the auditory nerve gives it a soft feel which has 
 caused the name " portio mollis" to be given to it when it 
 and the facial were considered as a single nerve. 
 
 Course of sound-waves : Sound-waves of the air are gath- 
 ered by the concha, carried into the external auditory canal 
 and vibrate against the membrana tympani. The mem- 
 brane taking up the vibrations transmits them through the 
 chain of ossicles to the stapes in the fenestra ovalis. The 
 stapes imparts its motion to the perilymph of the vestibule 
 
 FIG. 116. 
 
 IDTMil 
 
 membranous cochlea; LS, lamina 'ossea; EM, eustachian tube ;~ AN, auditory 
 nerve ; N, canalis reuniens. 
 
 (Fig. 116). There is now set up in the perilymph a fluid- 
 wave that travels in all directions. Some of this fluid-wave 
 travels along the scala vcstibtili to the apex of the cochlea, 
 then through the aperture of communication with the scala 
 tympani, then down the latter until it expends itself against 
 the membrane in the fenestra rotunda. In its passage along 
 the scala vestibuli and scala tympani, the fluid-wave vibrates 
 against the membrane of Reissner and basilar membrane ; 
 and this sets up similar vibrations in the endolymph of 
 
240 
 
 Till-: SENSES. 
 
 the canalis cochlearis. The fluid- wave in the canalis coch- 
 learis irritates the hair-cells of the organ of Corti. These 
 cells seem to be able to respond to particular tones by their 
 sensitiveness in selecting each one its particular fluid-wave 
 with its particular rate of vibration. 
 
 The remainder of the fluid-wave is expended in a similar 
 manner through the vestibule and semicircular canals, with 
 similar effects on the saccule, utricle, and membranous 
 canals. 
 
 Localization of hearing : The branch of the eighth nerve, 
 " arising" in the organ of Corti, having received its impulses 
 from the organ of Corti cells, transmits its impulse to the 
 
 FIG. 117. 
 
 Position of the auditory centre in the first temporal convolution (Gowers). 
 
 centre under the acoustic tubercle in the floor of the fourth 
 ventricle; thence fibres pass by means of the trapezium (in 
 the pons) to the opposite side, and thence through the lower 
 fillet of that side to the posterior quadrigeminal body, whence, 
 by means of its brachium, internal geniculate body, optic 
 thalamus, and internal capsule, they proceed to the cortex 
 of the first and second temporal convolutions (Fig. 117). 
 
 Distance: We can only judge of the distance of the source 
 of a sound by its intensity. The sound itself is in the ear. 
 Ventriloquists take advantage of this fact, and, by modify- 
 ing the intensity of the voice in imitation of the effect of 
 distance, cause us to think that it really originates at a 
 distance. 
 
 Subjective hearing : By this heading is meant those sounds 
 
PRODUCTION OF VOICE. 241 
 
 that are distinctly heard and yet are not produced by phys- 
 ical sound-waves, nor are they hallucinations. They may be 
 due to disturbances of the auditory apparatus or to abnormal 
 conditions of surrounding organs. Thus, buzzing or ringing 
 in the ears may result from the hypersemia of the parts and 
 exaggerated rush of blood, or from a defect in the circulating 
 apparatus (as by an aneurism), or from disease in the auditory 
 nerve or some other portion of the apparatus. Hallucina- 
 tions of hearing are very common among the insane, and are 
 purely creations of the disordered brain. 
 
 Musical range of hearing : The range of musical notes that 
 can be appreciated by the human ear is about seven octaves. 
 There are about three thousand hair-cells in the organ of 
 Corti, and it will be easily seen that this would allow an 
 enormous capability to differentiate sounds and musical tones. 
 This corresponds to a range of from 40 to about 4000 vibra- 
 tions per second. The range of audibility, on the other hand, 
 is about eleven octaves, or from 16 to 38,000 vibrations per 
 second. With less than 16 vibrations per second we are 
 conscious only of separate shocks, while with more than the 
 larger number we are unconscious of sound altogether. 
 
 Voice or Speech. 
 
 Although the voice or speech cannot be called part of the 
 senses, nevertheless it seems appropriate to describe its mechan- 
 ism under the general subject of " The Senses." 
 
 The larynx : The larynx is the organ of voice. It is a 
 cavity closed laterally, but communicating with the trachea 
 below and the pharynx above. The walls are made up of 
 the thyroid, cricoid, and arytenoid cartilages, together with 
 various muscles and membranes (Fig. 118). For a detailed 
 description see Quain's or Gray's Anatomy. 
 
 Across the cavity of the chamber are stretched in an 
 antero-posterior direction the two vocal cords or " mem- 
 branes." The free passage between the vocal cords is the 
 glottis, the cords forming part of the rima glottidis. 
 
 Production of voice : Voice is a result of the vibrations 
 of the vocal cords. The vibration of the vocal cords is 
 
 16 Phys. 
 
242 
 
 THE SENSES. 
 
 produced by the passage of the air in expiration, never 
 
 naturally in inspiration. The 
 I' I<; - 118 - quality of the voice as regards 
 
 pitch depends upon the length 
 of the vocal cords, the crico- 
 thyroid muscles acting to in- 
 crease the tension, while the 
 thyro-arytenoids relax the 
 cords and the crico-arytenoids 
 dilate and contract the rim a 
 glottidis. Falsetto and high- 
 pitched notes in a naturally 
 low-pitched voice are due to 
 vibration at the edges of the 
 cords. The hollow spaces 
 about the oral and nasal cav- 
 ities are of use as resonators 
 or sounding-boards. 
 
 Articulate speech : The voice 
 comes from the larynx ; but 
 articulate speech is the result 
 of the modification of the 
 voice by the tongue, etc. 
 (Fig. 119). 
 
 The organs used in articu- 
 late speech are : The tongue 
 and teeth in the formation of 
 the linguals and dentals ; the 
 nasal sounds by the cavity 
 of the nose ; the other sounds 
 are formed largely by modi- 
 fications in the shape of the 
 mouth in one or another part. 
 
 Musical range of the voice : 
 The musical range of a hu- 
 man voice is from one to 
 three octaves. In this, culti- 
 vation and natural aptitude 
 are factors which permit great variability. The total range 
 
 Longitudinal section of the human 
 larynx, showing the vocal mem- 
 branes. 1, ventricle of the larynx ; 2, 
 superior vocal membrane ; 3, inferior 
 vocal membrane ; 4, arytenoid car- 
 tilage ; 5, section of the arytenoid 
 muscle; 6, 6, inferior portion of the 
 cavity of the larynx ; 7, section of 
 the posterior portion of the cricoid 
 cartilage ; 8. section of the anterior 
 portion of the cricoid cartilage : 9, 
 superior border of the cricoid cartil- 
 age ; 10, section of the thyroid car- 
 tila-c : 11, 11, superior portion of the 
 cavity of the larynx ; 12, 13, aryten- 
 oid gland; 14, 16, epiglottis; 15, 17, 
 adipose tissue; 18, section of the 
 hyoid bone ; 19, 19, 20, trachea. 
 
EYELIDS. 
 
 243 
 
 of the human voice from the highest soprano to the lowest 
 bass is about four octaves. Thus it will be seen that the 
 
 Section of the parts concerned in the formation of vowels. Z, tongue ; p, soft pal- 
 ate ; e, epiglottis ; g, glottis ; h, hyoid bone ; 1, thyroid : 2, 3, cricoid ; 4, arytenoid 
 cartilage (Landois). 
 
 range of sounds which can be appreciated by the ear is far 
 beyond the capacity of the voice. 
 
 Sight. 
 
 The visual apparatus is the eye with its accessory organs 
 and the optic nerve. 
 
 The function of the eye is the reception of stimuli of light, 
 whereby we are able to perceive the impressions of form, 
 color, and conditions of our surroundings in infinite variety. 
 It is far the most complex in structure of any of the organs 
 of special sense, and the most rapid and delicate in its actions. 
 The stimulus received by the eye is transmitted along the 
 optic nerve to the brain. 
 
 Accessory organs of the eye : Under this heading we class the 
 (1) eyelids, (2) lachrymal gland, (3) extrinsic muscles of the 
 eyeball. 
 
 Eyelids : Each eye has two lids, an upper and a lower. Each 
 consists of a thin plate of elastic tissue with a covering of 
 loose skin and a smooth lining of mucous membrane the 
 conjunctiva which is reflected upon the eyeball. Along the 
 
244 THE SENSES. 
 
 edges of the lids are a number of short curved hairs which 
 screen the eye from foreign bodies. The extreme sensitive- 
 ness of the conjunctiva helps in this by giving immediate 
 warning when any foreign substance gets in the eye. 
 
 The muscles of the eyelids are the levator palpebrse supe- 
 riores and the orbicularis palpebrarum. 
 
 Lachrymal gland : It is a small racemose gland lodged in 
 the upper and outer part of the orbit. It has several ducts, 
 which lead to the surface of the conjunctiva of the upper lid. 
 The secretion of the gland is usually just sufficient to keep the 
 eye moist, but under the stimulus of pain or intense emotion the 
 secretion is increased, and appears in drops which flow from 
 the eyes tears. Under ordinary circumstances a slight ex- 
 cess of this moisture is drained into the nasal cavity by the 
 lachrymal duct. This secretion is slightly alkaline, and con- 
 tains about 1 per cent, of solids, chiefly sodium chloride. 
 
 Meibomian glands : They consist of a number of small 
 racemose glands, lying beneath the conjunctiva, which secrete 
 an oily protective substance. The ducts of these glands open 
 along the edge of the lid. 
 
 Extrinsic muscles of the eye : There are six muscles to each 
 eye superior rectus, external rectus, inferior rectus, internal 
 rectus situated respectively above, below, and to the inner, and 
 outer sides of the eyeball ; also the superior oblique at the 
 upper and inner angle of the orbit, and the inferior oblique 
 at the lower and inner angle. 
 
 The recti serve to turn the eye up, down, in, or out, accord- 
 ing to which muscles or combination of muscles are acting. 
 The oblique muscles tend to rotate the eyeball on an antero- 
 posterior axis. 
 
 The superior and inferior recti of both eyes work synchro- 
 nously, but the action of the external rectus of one eye is 
 synchronous with the internal rectus of the other; and the 
 
 same is true as between the superior oblique of one eye ;m<l 
 
 ique of the other. The objec 
 of all these muscles is to turn the eyeballs toward the object 
 
 the inferior oblique of the other. The object of the action 
 
 to be seen, thus causing it to receive the majority of the rays 
 from the object at right angles to the surface of the eye. The 
 superior oblique muscles are supplied by the fourth cranial 
 
COATS OF THE EYEBALL. 
 
 245 
 
 nerves ; external recti by the sixth ; the other muscles by the 
 third cranial nerves. 
 
 The eyeball consists of a tough, opaque globe (Fig. 120), 
 having a somewhat more sharply-curved translucent portion, 
 the cornea, at the front. It has in the anterior portion a lens, 
 and in front and behind this are chambers which contain 
 
 FIG. 120. 
 
 Horizontal section of the right eyeball. 1, optic nerve; 2, sclerotic coat: 3, cornea; 
 4, canal of Schlemm ; 5, choroid coat ; 6, ciliary muscle ; 7, iris ; 8, crystalline 
 lens ; 9, retina ; 10, hyaloid membrane ; 11, canal of Petit ; 12, vitreous body. 
 
 fluids : the one in front is the anterior chamber, and contains 
 the aqueous fluid, while in the posterior is the vitreous humor. 
 These structures fill the eyeball and give it a tense feel to 
 the touch. 
 
 Coats of the eyeball: The anterior portion of the eye, 
 which has already been described as being more sharply 
 curved than the rest, is the cornea. If we examine the rest 
 of the eyeball (Fig. 121), it will be found to consist of three 
 
246 THE SENSES. 
 
 coats : (1) The sclera, or sclerotic coat, is external, and covers 
 about five-sixths of the globe. The cornea is continuous with 
 it in front. It is composed of tough white fibres arranged in 
 intercommunicating layers. (2) The choroid coat is very 
 vascular, being composed of a mesh of capillaries. There is 
 outside of this a layer of connective tissue containing pigmeut- 
 
 FIG. 121. 
 
 Choroid membrane and iris exposed by the removal of the sclerotic and cornea. 
 Twice the natural size, rf, one of the segments of the sclerotic thrown back; 
 I and k, iris ; c, ciliary nerves ; e, one of the vasa vorticosa or choroidal veins 
 (Quain). The ciliary muscle is crossed by the line from k, and should be repre- 
 sented as radiating. 
 
 granules, so that the choroid is black. (3) The retina, which 
 is the seat of the end-organs of the optic nerve. 
 
 The purpose of the sclera is solely to act as a capsule for 
 .the contents of the eye. The choroid being black prevents 
 any reflection of light. The retina is the nervous organ for 
 receiving the sensations. 
 
 The cornea is continuous with the sclera in the front of the 
 eye, and occupies about one-sixth of the surface (3, Fig. 120). 
 Its shape is that of a small dome set upon the globe of the 
 eye. It has in front several layers of epithelial cells, and at 
 
CILIARY MUSCLE. 247 
 
 the posterior surface a thin epithelial lining (membrane of 
 Descemet) ; but the main body of the structure consists of 
 interlacing connective-tissue fibres, which have spaces in 
 which are found branching cells peculiar to the structure. 
 The cornea is perfectly transparent ; it has no bloodvessels. 
 
 The aqueous humor is a watery fluid contained in the ante- 
 rior chamber. It acts with the cornea as a refracting medium 
 to concentrate rays of light upon the lens, to maintain the 
 globular form of the cornea, and to float the iris and allow it 
 freedom of motion. 
 
 The indices of refraction for cornea and aqueous humor are 
 about the same ; so, as far as being media of refraction, we 
 consider the cornea and aqueous humor as one, with an index 
 of refraction of 1.33. 
 
 The crystalline lens is a double convex lens (8, Fig. 120) 
 of high refractive power which is suspended in the anterior 
 portion of the eye immediately behind the anterior chamber. 
 Its function is to bring the rays of light to a focus upon the 
 retina. In structure the lens is composed of concentric layers 
 of long, slender fibres enclosed in a thin capsule. The index 
 of refraction for the crystalline lens is about 1.45. The crys- 
 talline lens is suspended in its capsule by the suspensory lig- 
 ament, and this is controlled by the ciliary muscle. At rest 
 the eye is focussed for seeing at a distance, and the lens is held 
 somewhat flattened by the tension of the suspensory ligament. 
 When focussing upon a near object the ciliary muscle contracts, 
 and the lens is permitted to project more as the tension of the 
 ligament relaxes. 
 
 The ciliary muscle extends as a narrow zone of muscle- 
 fibres near the anterior part of the choroid. The muscle- 
 fibres originate at about the junction of the cornea and sclera 
 and pass backward meridianally to be inserted in the choroid 
 coat. On contraction the ciliary muscles draw the choroid 
 coat forward ; this relaxes the suspensory ligament of the lens 
 and the lens becomes more convex. 
 
 When the ciliary muscle relaxes the reverse takes place, 
 the choroid being replaced by the natural tension of the con- 
 tents of the eye. The nerves to the ciliary muscle are from 
 the ciliary ganglion. 
 
248 THE SPJNSES. 
 
 The iris is a curtain of muscular tissue placed vertically in 
 front of the lens. The fibres of the muscular tissue are both 
 circular and radiating, so that they serve to decrease and in- 
 crease the size of the pupil as one or the other set of fibres 
 acts. It has a pigment-layer upon the inner surface, which 
 is continued from the choroid, and upon the amount of the 
 coloring-matter depends the " color of the eyes." 
 
 In the centre of the iris is a circular opening, through 
 which light enters the "dark-chamber" of the eye. This 
 opening is the pupil. 
 
 Nervous control of the iris : Contraction or dilatation of the 
 pupil is a reflex act, and the afferent stimulus is carried 
 through the optic nerve and the motor through the third 
 cranial nerve, acting from a centre just beneath the aqueduct 
 of Sylvius and the corpora quadrigemina. The increase in 
 the amount of light which reaches the retina causes a con- 
 traction of the pupil, and a decrease is followed by dilatation. 
 Aside from this, the needs of the eye regulate the amount of 
 light ; thus, for near work the pupil contracts, and dilates 
 when the eye is focussed upon a distant objec.t. 
 
 The pupil is controlled also through the sympathetic and 
 the fifth nerve, through the connection of the third and fifth 
 nerves with the ciliary ganglion of the sympathetic system. 
 Drugs are active also, both locally and internally, in control- 
 ling the action of the iris without reference to the reflex 
 fibres : atropine both locally and internally dilates the pupil ; 
 opium internally, and eserine locally contract it. 
 
 Vitreous humor : The vitreous body (or humor) is a semifluid 
 gelatinous substance which fills the posterior chamber and 
 constitutes about four-fifths of the bulk of the eye. It is 
 quite transparent, and acts to maintain the tension of the eye- 
 ball, and as a refracting medium through which light reaches 
 the retina. 
 
 Refraction : In order clearly to understand the nature of the 
 image received by the eye, it will be wise to review the im- 
 ages cast by a convex lens. If we take, for example, a double 
 convex lens and note the image formed by a luminous object, 
 we see that it is an inverted image at the point of focus of 
 the lens if the luminous object is placed at a distance (Fig. 
 
REFRACTION IN THE EYE. 249 
 
 122). Referring to this figure, it will be seen that the rays 
 originating at A will be twice refracted, once by the lens and 
 again in leaving it, so that all rays from A reaching the lens 
 are joined at a. The same is true for B and 6. Therefore a 
 
 FIG. 122. 
 
 Formation of image by convex lens. 
 
 screen placed at the focus, F, will receive an inverted image, 
 a 6, of the luminous object, A B. 
 
 If the lens were more convex, the image would be formed 
 nearer the lens ; if the lens were flatter, the image would be 
 further from the lens. 
 
 Again, on the other hand, if we decide to have the image 
 formed at a definite spot, the further the object is from the 
 lens the flatter the lens must be, and vice versa, the nearer 
 the object the more curved the lens must be. 
 
 Thus, with a double convex lens we see that the image 
 formed is a real, inverted image on the opposite side of the 
 lens from the object. 
 
 Refraction in the eye : The crystalline lens is a double 
 convex lens and so obeys the laws referred to in the previous 
 paragraph. 
 
 In addition to the crystalline lens the other refracting 
 media (Fig. 123) of the eye are the cornea, aqueous and 
 vitreous humors. The tendency of all these refracting media 
 is to bring together to one focus all divergent rays of light ; 
 thus they may be considered as a group of double convex 
 lenses. The crystalline lens, however, is the most important, 
 as it possesses the power, by virtue of the ciliary muscles, 
 of increasing or diminishing its curvature. 
 
250 
 
 THE SENSES. 
 
 B, a candle placed at the side of 
 the eye that is. as much to the 
 side of the centre of the cornea 
 as possible. B', interior luminous 
 source, formed by the rays of 
 light concentrated by the crys- 
 talline lens upon the extreme 
 lateral portion of the eye. CD, 
 two vessels of the retina (the size 
 of the retina is here greatly ex- 
 aggerated). The shadow of these 
 two vessels is seen as if projected 
 at D' and C '. Experiment by 
 Purkinje. 
 
 Accommodation: By accommodation we mean the power 
 
 of the crystalline lens to change 
 its amount of curvature so as to 
 throw the image of an object in 
 exact focus on a fixed screen (the 
 retina) whether the object be 
 near or far from the lens. At 
 the same time the pupil is ex- 
 panded or contracted to admit 
 the necessary amount of light. 
 Thus, if an object be near the 
 eye, in order to produce a sharp 
 image the lens is more curved, 
 owing to contraction of the cil- 
 iary muscle, and the pupil is con- 
 tracted. If, on the other hand, 
 the object be on the horizon, the 
 ciliary muscle relaxes, the lens is 
 flatter, and the pupil is dilated. 
 Comparison of eye to photographic camera : The eye may be 
 compared to the photographic camera. It contains various 
 media for the refraction of light, and a screen at the back for 
 receiving the image. The refracting media are the cornea, 
 aqueous humor, crystalline lens, and the vitreous humor : 
 the screen is the retina. The pigment of the retina and 
 choroid makes the interior dark, a necessary feature in such 
 an apparatus. The mechanism of the lens enables the eye to 
 be focussed for distance, while the iris regulates the proper 
 admission of light. 
 
 In a camera the ground-glass screen, or the sensitive plate, 
 is moved nearer or further from the back of the lens in order 
 to bring it in focus i. e., make the image clear. In the eye 
 the sensitive plate (the retina) is at a fixed distance from the 
 lens, and so the focussing is done by a change in the curvature 
 of the lens (accommodation). 
 
 The retina is comparable to the photographic sensitive 
 plate. It receives the images formed upon it by the lens and 
 transmits the impressions to the optic nerve, whence they are 
 carried to the brain. 
 
RODS AND CONES. 
 
 251 
 
 FIG. 124. 
 
 It will be remembered that the retina forms the most cen- 
 tral of the layers of the eyeball, but does not extend as far 
 forward as do the choroid and sclera, but terminates at about 
 half way. 
 
 The fibres of the optic nerve, after piercing the sclera and 
 choroid at the back of the eye, spread out divested of neuri- 
 lemma and medullary sheath into the innermost layer of the 
 retina. The fibres then pass, with more or less direct com- 
 munications, peripherally through the other layers until they 
 may be said to terminate in the 
 layers of rods and cones, exter- 
 nal to which is a pigment-layer. 
 
 Rods and cones : They are 
 closely packed on the outer sur- 
 face of the retina, the rods be- 
 ing the more numerous in most 
 situations. The cones seem to 
 be modifications of the rods, and 
 their office is essentially sim- 
 ilar. The rods (Fig. 124) are 
 straight cylindrical bodies of a 
 transparent substance, and are 
 placed parallel to one another and 
 perpendicular to the surface of 
 the eyeball. In length they are 
 about five to seven times the di- 
 ameter of a red blood-corpuscle, 
 and in diameter about one-twen- 
 tieth of their length. The cones 
 are very similar, except that their 
 conical shape makes them appear 
 to be of different character. The 
 cones do not always reach to the 
 same level as the rods. When 
 
 viewed from the peripheral SUr- 
 f .1 j /> ,1 j j 
 
 tace the ends Ol the rods and 
 
 cones give the appearance of a 
 fine mosaic. These organs are 
 connected with the subjacent layers, and, ultimately, more or 
 
 Diagrammatic section from the 
 posterior portion of the human 
 retina. 1, layer of rods and 
 
 layer f nuclei 
 
252 THE SENSES. 
 
 less directly, with the axis-cylinders of the fibres of the optic 
 nerve. 
 
 The optic nerve pierces the eyeball not exactly at its most 
 posterior point, but a little to the inner side. At the exact 
 centre of the retina that is, the most posterior point of the 
 eye there is a small yellow area (macula luted) with a cen- 
 tral depression (fovea central-is). Here are found none of the 
 fibres of the optic nerve, but a great increase in the numbers 
 of the cones , as well as an increase in their size. 
 
 Area of most acute vision : If the object looked at is focussed 
 directly upon the macula lutea, the image is then seen with 
 the greatest clearness. This is to be expected, for in the 
 macula lutea we find the end-organs of the optic nerve most 
 highly developed. In every-day life we look directly at an 
 object so as to receive the image on the macula lutea and 
 thus render the perception more acute. Rays of light enter- 
 ing the eye on an angle are focussed on some other part of 
 the retina and are not so clearly defined. 
 
 Blind spot : If the left eye is covered and the right directed 
 steadily upon the cross in Fig. 125, the circular spot will be 
 
 FIG. 125. 
 
 visible at the same time, though less distinctly. As the book 
 is moved slowly backward and forward, a point will be found 
 at which the round spot disappears, reappearing as the book 
 is held nearer or farther or as it is inclined in cither direction 
 and the image is carried away from the "blind spot." 
 
 The blind spot is the point where the optic nerve enters 
 the eye. If the image be focussed on this point no perception 
 follows, as that part of the retina is deficient in rods and 
 cones (Fig. 126). 
 
FIBRES OF NERVES AND TRACTS. 253 
 
 FIG. 126. 
 
 The posterior half of the retina of the left eye viewed from before. Twice its 
 natural size, s, cut edge of the sclerotic ; ch, chproid ; r, retina : in the interior 
 at the middle the macula lutea with the depression of the fovea centralis is rep- 
 resented by a slight oval shade : toward the left side the light spot indicates the 
 colliculus or eminence at the entrance of the optic nerve, from the centre of 
 which the arteria centralis is seen sending its branches into the retina, leaving 
 the part occupied by the macula entirely free (Henle). 
 
 Optic nerve : If one examines the optic nerves in a super- 
 ficial manner, they will be seen to leave the back of each eye, 
 passing backward through the optic foramina until they 
 reach the body of the sphenoids. Here the optic nerves 
 cross one another in the form of an X (the optic chiasm), the 
 fibres intermingling, and the right nerve apparently passing 
 over to the left side and the left nerve to the right side. 
 The posterior limbs of the X pass backward and are called 
 the optic tracts. The optic tracts in their backward course 
 curve around the crura cerebri to terminate in the ganglion- 
 cells of the pulvinar, anterior quadrigemina, and external 
 geniculate bodies. From the ganglion-cells of the pulvinar, 
 anterior quadrigemina and external geniculate bodies, fibres, 
 called the optic radiations, pass backward to terminate in the 
 ganglion-cells of the cortex of the posterior part of the occip- 
 ital lobes. 
 
 Fibres of nerves and tracts : A more minute examination 
 of the optic nerves will show that each optic nerve consists 
 of two distinct bundles of fibres laterally placed. The inner 
 
254 
 
 THE SENSES. 
 
 set of fibres being the fibres from the inner half of the retina ; 
 the outer bundle of fibres coming from the outer half of the 
 retina. If we trace these bundles backward to the optic 
 
 FIG. 127. 
 
 Left Eye 
 
 Right Eye 
 
 Optic 
 
 ic nerve 
 
 Optic radiation 
 
 Optic radiation 
 
 rlc'x of occipital 
 lobe with cortical cells 
 
 1, external geniculate body; 2, pulvinar; 3, anterior quadrigeminate body; 4, in- 
 ternal genioulate body ; 5, commissure of (Judden. 
 
 chiasm, it is noted that only the inner bundles decussate 
 and pass to the opposite side of the brain. The external 
 bundles do not decussate, but pass directly backward as part 
 
BINOCULAR VISION. 255 
 
 of the optic tracts to terminate in the ganglia on their respec- 
 tive sides of the brain. 
 
 Thus the left pulvinar, left anterior quadrigeminate and 
 external geniculate bodies receive the fibres from the inner 
 half of the right eye and the outer half of the left eye. The 
 right ganglia receive fibres from the inner half of the left eye 
 and outer half of the right eye. 
 
 Commissure of Gudden : There is also in the optic tracts a 
 bundle of fibres arising from the internal geniculate body of 
 one side, passing forward, as a third and innermost bundle 
 of the optic tracts, to the back part of the optic chiasm ; here 
 the fibres bend on themselves and pass backward along the 
 inner margin of the opposite optic tract to terminate in the 
 other internal geniculate body. These commissure! fibres 
 form the commissure of Gudden, and serve to connect the two 
 internal geniculate bodies. They play no part in vision. 
 
 Nervous mechanism of vision : The image, properly re- 
 ceived on the retina, stirs the rods and cones into functional 
 activity. The u vibrations " are then passed along the optic 
 nerves and optic tracts to terminate in the pulvinares, exter- 
 nal geniculate and anterior quadrigeminate bodies. These 
 structures may be called the primary vision centres. Here 
 the impressions of sight are received in a physical sense, but 
 the mind does not as yet appreciate the sight impression. 
 
 The impression received by the ganglia are now trans- 
 mitted along the optic radiations to the cortical cells of the 
 occipital lobes. When the cortical cells are stimulated the 
 mind is capable of appreciating that " we see" So we may 
 call the ganglia the seat of physical sight, but the cortical 
 cells are the seat of physiological sight. 
 
 Binocular vision : In normal vision both eyes are used, so 
 that a separate image is received on each retina. Through 
 the intimate association of the two halves of the brain we are 
 conscious of but one image. 
 
 A further advantage of binocular vision is that each eye 
 looking at an object from a slightly different standpoint sees 
 a little more on one side or other of the object than does the 
 other eye. Thus the combined image formed contains a little 
 more of the object than would the image from one eye alone. 
 
256 
 
 Till': SENSES. 
 
 Thus the perceptive faculties can judge more correctly of the 
 form and diddnce of an object. 
 
 The stereoscope illustrates this point. In this instrument 
 two photographs are taken by cameras so placed as to repre- 
 sent the position of the eyes in vision, and the two views of 
 one object are then superimposed by the use of prisms (Fig. 
 128). 
 
 Photographic views seen through a stereoscope possess a 
 rounded-out, lifelike appearance not seen in ordinary photo- 
 graphs. 
 
 Inversion of the image : From the laws of optics we know 
 that the image formed on the retina is an inverted image of 
 
 FIG. 128. 
 
 Illustrating the principle of the stereoscope and binocular vision. 
 
 the object. Yet we perceive the object in its upright posi- 
 tion. This is the result of lifelong habit. A baby sees an 
 object; the next step is to touch it; by practice the child 
 finds out which is the top of the object through the touch- 
 perception. He then corrects his mental impression. Very 
 speedily the brain learns to make the correction, and the les- 
 son once learned lasts through life. 
 
 The correction is made by the brain in its perception of the 
 image. It is an act of mental and not of physical origin. 
 Tims, objects which are projected upon the left of the retinal 
 surface look to be, as they are, on the right of the body ; and 
 so with all the directions : the inversion of the retinal image 
 is corrected by the mind. 
 
 Duration of visual sensations: The duration of a visual sen- 
 sation is always greater than that of the stimulus which has 
 caused it. However brief the luminous impression, the effect 
 on the retina lasts about one-eighth of a second. The spokes 
 
RETINAL RED. 257 
 
 of a rapidly revolving wheel for this reason do no not appear 
 as spokes, but as a solid mass, each following one another so 
 rapidly that one impression cannot fade away before another 
 lias replaced it. 
 
 Mental processes acting on visual perceptions : We are able to 
 estimate by the aid of the brain the size, direction, distance, 
 form, and speed of motion of a thing which we have seen. 
 All of these are judgments based largely upon previous ex- 
 perience. All of these deductions are liable to error by rea- 
 son of faulty judgment or faulty vision, but this is the usual 
 method of forming such estimates. As an example of visual 
 illusion, the two centre squares shown 
 in Fig. 129 are exactly the same size, 
 yet the white square on the black 
 ground appears larger than the black 
 square on the white ground. Also 
 in Fig. 130, the heavy black lines 
 appear to converge, though in reality 
 
 they are parallel. Illustration of irradiation 
 
 , , , (McKendnck). 
 
 Clearness of vision depends on the 
 
 space between the cones in the point of clearest vision, the 
 macula hi tea. It has been calculated that an object must 
 subtend an arc of at least 60 to 70 seconds in the field of 
 vision to be clearly seen. Such an object makes an image of 
 about i2ihroth of an inch in the retina ; and this is about the 
 distance between the cones at the macula lutea. Similarly, 
 two points to be clearly distinguished must be separated suf- 
 ficiently to allow this amount of separation in the retinal 
 image. 
 
 Retinal red : When the retina of a recently-killed animal 
 is examined it is colorless ; but during life or if extracted 
 without exposure to light, it is of a purple-red hue, and the 
 color is found in the rods of the retina. It is derived from 
 the pigment of the outer layer of the retina. It is the " ret- 
 inal red " or " visual purple/ 7 as it is variously named, which 
 one sees in the reflex of the retina. 
 
 Exposure to light destroys it, and for this reason it was long 
 unknown. It disappears after a brief exposure to sunlight, 
 about half a minute. 
 
 17 Phys. 
 
258 
 
 THE 
 
 By throwing a beam of light into the eye by a mirror, as 
 by the ophthalmoscope, a red glow is observed in the pupil. 
 
 FIG. 130. 
 
 Nl 
 
 s 
 s 
 
 N 
 N 
 S 
 
 S 
 
 S 
 
 N 
 S 
 N 
 
 S 
 
 s 
 
 N 
 S 
 N 
 
 S 
 
 L. 
 
 M 
 
 S / 
 
 s / 
 
 V 
 
 1 
 
 \ X 
 
 s / 
 s / 
 s x 
 s x 
 
 V 
 
 II 
 
 I 
 
 11 
 
 s x 
 
 V 
 V 
 
 k. JM 
 
 II 
 
 S w 
 
 1 
 
 % 
 
 II 
 
 s 
 
 s 
 s 
 s 
 s 
 s 
 s 
 s 
 s 
 s 
 s 
 s 
 
 K K 
 s 
 
 s 
 
 s 
 
 Zollner's figure showing an illusion of direction (McKendrick). 
 
 This is called the retinal reflex. The red glow is produced 
 by the retinal red. 
 
 Optograms are pictures which appear upon the retina after 
 exposure to light. They are due to the fact that an exposure 
 to light bleaches the retinal red, leaving it dark in the shaded 
 portions. 
 
 An optogram may be obtained by the following experi- 
 ment: The eye is removed from an animal in a dark room 
 and kept in a covered box until exposed to a brightly illumi- 
 nated skylight or window for some minutes. The eye is then 
 replaced in the dark room and the retina examined. It will 
 he found that the panes of the window are shown in light 
 color, while the sash is in dark outline. This soon fades on 
 exposure to daylight; but if the retina is dried in the dark, 
 the optogram is much more durable. 
 
AFTER-IMAGES. 259 
 
 Pigment of choroid and retina : The student must not con- 
 found the " visual purple " with the pigment granules of the 
 choroid and retina. The latter are dark brown or black, and 
 serve to keep the chamber of the eye as a dark box. The 
 black cloth of the photographer serves the same purpose. 
 All optical instruments are painted black on the inside to 
 prevent un desired reflection of light. So with the eye. 
 
 Color-perception : It is probable that particular rods and 
 cones are capable of responding to rays of light of a certain 
 wave-length, and to those rays alone. It is well known that 
 the rays of red light are of a certain length of vibration. 
 The same is true of yellow and of green rays. We can con- 
 ceive that each primary color has its own set of cones and 
 rods capable of responding to its stimulus, and that by com- 
 binations of these stimuli the complementary colors and varia- 
 tions of shade may be perceived by the resulting stimuli act- 
 ing upon the brain-centres. Such teaching is, of course, 
 speculative, but this is one theory which has acceptance. 
 
 Achromatism : If in obtaining an image of an object 
 through a double convex lens the lens be too large, there will 
 be seen around the image formed a halo of prismatic colors. 
 This is called a chromatic ring, and is produced by an un- 
 equal refraction of light-rays by the peripheral portions of the 
 lens. The unequal refraction results in a dispersion of the 
 light, so that it is broken up into the seven primary colors. 
 To remedy this defect, we put a "photographic shutter" in 
 front of the lens, thus limiting the entrance of light to the 
 central portions of the lens, where the index of refraction is 
 " constant " or " true." In the eye the iris acts as the pho- 
 tographic shutter, thus rendering the image achromatic. It 
 may, however, be said that there may be a visible band of 
 color seen by some defective eyes where there is considerable 
 fault in the focus of the image on the retina. 
 
 After-images : It has already been noted that vision lasts 
 longer than the stimulus which excites it. Under some con- 
 ditions it may last a perceptibly long time : it is then known 
 as an after-image. If one looks at an intense light, the sun, 
 the sense of light remains for some time in the eye. Similarly, 
 if one looks intently at a white spot on a black background, 
 
260 THE SENSES. 
 
 and then turns to a white surface, one has the image of a 
 gray spot. The first of these conditions cited is known as a 
 positive after-image, and the latter as a negative. In the 
 first case the phenomenon results as a continuation of the 
 same sensation, and in the latter a new perception results. 
 
 These images appear to have the complementary color of 
 the original object ; thus, green excites a reddish after-image ; 
 orange, blue ; and so on. They may be explained as a result 
 of exhaustion. The part of the retina on which the image 
 has fallen becomes tired, and when the eye is turned upon a 
 white ground, the white light coming to the retina docs not 
 produce as much sensation in the tired portion. The colored 
 negative after-images may be similarly explained. 
 
 Near-point : The " near-point " is the nearest point to the 
 eye at which vision is distinct, the shortest focus of the crys- 
 talline lens. It is usually about five or six inches. 
 
 Defective eyes : Although hardly within the scope of physi- 
 ology, it may be perfectly appropriate to discuss here some of 
 the more common defects of the eyes depending on abnormal 
 conditions in the optical apparatus. 
 
 Emmetropic eye : It is the normal eye that is, an eye 
 in which parallel rays or rays from objects at a distance are 
 focussed upon the retina without an effort at accommodation. 
 Such a distance, for practical purposes, is considered to be any 
 point beyond twenty feet. Absolutely emmetropic eyes are 
 not common. 
 
 Myopia or " near sight " is the term applied to an eye in 
 which the rays from a distance are focussed in front of the 
 retina, and the image is blurred. Such an eye is permanently 
 focussed for near objects (Fig. 132). 
 
 Myopia is produced in two ways by the antoro-posterior 
 diameter of the eye being too great, or by the convexity of 
 the lens being exaggerated. In either case the focus of the 
 lens will fall in front of the retina. 
 
 The first condition is essentially a congenital defect, 
 whereas too great convexity of the lens may be either con- 
 genital or the result of disease. 
 
 Myopia is corrected by the use of a concave Ions which 
 diverges the rays, and in this way prevents their coming to a 
 
PRESBYOPIA. 
 
 261 
 
 focus too soon. Such glasses are seldom needed except for 
 distant vision. 
 
 Hypermetropia, or "far sight/ 7 is the reverse of myopia 
 (Fig. 131). In hypermetropia the antero-posterior axis of 
 
 FIG. 131. 
 
 the eye is too short, or else there is an abnormal flattening of 
 the lens, which does not allow accommodation for near vision. 
 The result is that the image of an object near by is focussed 
 behind the retina ; but objects at a distance are clearly seen. 
 
 FIG. 132. 
 
 Hypermetropic eye and myopic eye (far-sighted and near-sighted eye). 1, hyper- 
 metropic eye. The luminous rays arriving from an infinite distance (parallels) 
 produce an ocular cone, the summit of which falls beyond the retina (at A), 
 either because the cone is too long (lack of converging power in the media of 
 the eye), or because the retina is too far forward (the eye being too short) ; 2, 
 myopic eye ; the luminous rays from an infinite distance (parallels) produce an 
 ocular cone, the summit of which falls in front of the retina (at B), either be- 
 cause this cone is too short (excess of converging power in the media), or be- 
 cause the retina is placed too far back (the eye being too long). Bonder's re- 
 searches seem to show that short-sightedness is owing to this latter cause, as is 
 well shown in the figure (the ocular globe being greatly elongated from back to 
 front) (Kuss). 
 
 Hypermetropia is corrected by the use of convex lenses, 
 which add to the refractive power of the eye. 
 
 Presbyopia is defective vision due to the loss of power in 
 advanced years. The elasticity of the lens becomes less, and 
 the convexity cannot be increased for near vision. The 
 
262 THE SENSES. 
 
 ciliary muscle may also be weaker and aid in the production 
 of the error. A weak convex glass commonly corrects the 
 lack of refraction-power. 
 
 Thus we see that presbyopia is identical with hypermetropia 
 due to flattening of the lens. 
 
 Astigmatism is a defect in the vision due to the irregularity 
 in the globe of the eye, whereby the diameter in one plane is 
 greater than in another. Thus, the retina may be an uneven 
 surface, and the image focus accurately in one part and falsely 
 in another. In this condition vertical and horizontal lines are 
 not seen with equal distinctness. 
 
 Astigmatism is corrected by the use of cylindrical or pris- 
 matic glasses, which have to be accurately adapted to the 
 needs of each case. This error, if serious, is usually com- 
 bined with other defects of vision, frequently myopia. 
 
 Diplopia is the condition which results from a want of har- 
 mony in the eyes, so that the image of each eye is perceived 
 separately ; that is, one sees double. 
 
 Diplopia is commonly caused by paralysis or spasm in one 
 of the lateral straight muscles, which does not allow the eye 
 to be turned in harmony with the other. If the eyes are turned 
 so that the axes of vision are separated, the condition is 
 known as external strabismus or squint ; if the axes are crossed, 
 it is called internal strabismus or cross-eye. 
 
 Color-blindness is an inability to perceive some colors. The 
 colors which are usually mistaken are green and red. Fre- 
 quently it is found that a distinction cannot be made between 
 these colors. This is sometimes known as Daltonism. 
 
 Theories of normal color-perception : Ordinary white light 
 if decomposed is resolved into the seven primary colors 
 violet, indigo, blue, green, yellow, orange, and red. Each 
 of these primary colors has a different wave-length. Other 
 colors than the seven primary colors are the result of the 
 mixture of two or more of the primary colors in various 
 proportions. We are ignorant of the manner in which the 
 rods and cones are made to vibrate by ordinary images, 
 and we are equally ignorant as to the nature of the process 
 that allows the diiVcrcnt color-effects to be conveyed to the 
 optic nerve. 
 
THEORIES OF NORMAL COLOR-PERCEPTION. 263 
 
 As it is impossible to go fully into the matter in this book, 
 it is hoped that the following will suffice : 
 
 The different color theories assume that there are different 
 substances in the retina capable of responding to different 
 wave-lengths of light (comparable to a photo-chemical pro- 
 cess). 
 
 Red, green, and violet (Fig. 133) are the fundamental 
 
 FIG. 133. 
 
 Diagram of three primary color-sensations. 1 is the so-called " red," 2 "green," and 
 3 "violet" primary color sensation; R, 0, Y, etc., represents the red, orange, 
 yellow, etc., color of the spectrum, and the diagram shows, by the height of the 
 curve in each case, to what extent the several primary color-sensations are re- 
 spectively excited by vibrations of different wave-lengths (Foster). 
 
 colors, and all others may be made from combinations of these 
 three. 
 
 Working on this basis, Young and Helmholtz assumed 
 three chemical substances in the retina capable of replying 
 to the three fundamental colors. 
 
 Hering assumed three substances responding respectively 
 to white or " black " (absence of light), red or green, and 
 yellow or blue light. In this theory the white, red, and yel- 
 low rays are katabolic in their effect on their individual re- 
 cipient substances; the "black/ 7 green, and blue being ana- 
 bolic e. g.j the substance responding to white is "broken 
 down " by white light, but is regenerated ("built up") by 
 "black light" i. e., absence of light. Mrs. Franklin assumes 
 in her theory that in early life the eye possesses no color-per- 
 ception, but merely perception of luminosity i. e., white or 
 
264 THE SENSES. 
 
 black. The substance responding to luminosity she calls 
 " gray-perceiving." As the development progresses, some of 
 the " gray " is differentiated into a blue- and a yellow-per- 
 ceiving substance. The yellow-perceiving substance is still 
 further differentiated in the course of development into a red- 
 and a green-perceiving substance ; thus : 
 
 Gray. 
 
 I 
 
 Blue. Yellow. 
 
 I 
 
 Green. Red. 
 
 Many objections have been raised against each of these 
 three color-theories, and it is true that each leaves some points 
 unexplained ; but Mrs. Franklin's is, so far, the best, and 
 more readily explains the peculiarities of color-blindness. 
 
 Causes of color-blindness : The followers of Helmholtz and 
 Hering say that color-blindness is due to an absence of one 
 or more of the fundamental color-perceiving substances. 
 
 Mrs. Franklin's theory assumes a lack of full development 
 or complete absence of development of the " gray "-perceiv- 
 ing substance. 
 
 Thus, in a case of absolute color-blindness the " gray " 
 substance has undergone no development, and the individual 
 sees everything as without color, but in different shadings of 
 light or darkness. To such a person a highly colored paint- 
 ing would look like a black-and-white etching. 
 
 Again, working on the development theory, we may assume 
 that the gray differentiated into "blue"- and " yellow "-per- 
 ceiving substances and there stopped. Clinically we find in- 
 dividuals capable of distinguishing blues and yellows, but 
 reds and greens are unknown to them. 
 
 Color-blindness in different sexes: Males are far more liable 
 to be color-blind than female (16 to 1). Only about one 
 woman in four hundred is color-blind. The reason for the 
 preponderance of color-blind men may be accounted for on 
 the theory that although the differentiation of the "gray"- 
 perceiving substance into red, green, and blue is a natural 
 
TEST FOR COLOR-BLINDNESS. 265 
 
 process, nevertheless it can be perfected by practice and color- 
 education. Such an education is given early in life to little 
 girls in matching colors for doll's clothing, etc., whereas, it is 
 neglected in boys. 
 
 Importance of the defect : In marine and land locomotion, 
 red and green signals are used to indicate opposite conditions, 
 and the failure to distinguish them has frequently been the 
 cause of serious accidents. 
 
 Test for color-blindness : By laying a number of skeins of 
 yarn of various colors in a heap, and requiring the person to 
 be tested to select all resembling a certain skein from the 
 heap. 
 
EMBRYOLOGY. 
 
 Embryology deals with the reproduction and development of 
 individuals, whether of animal or plant life. AVe shall first 
 study how the parent gives origin to the offspring, and later 
 on the development of that offspring until it becomes a fully 
 developed member of its species. 
 
 REPRODUCTION. 
 
 By species we mean a class of organized beings in which 
 the individuals composing it die off, but which nevertheless 
 repeats itself and maintains its complement by the continued 
 accession of similar forms. 
 
 Heredity is the inherent property of the individual by 
 virtue of which the individual is of the same species as the 
 parent, and furthermore has certain individual characteristic's 
 of the parent. We are human beings because our parents 
 were human beings, and we inherit the form and character- 
 istics of the species. Still further, we may have certain 
 tricks of speech, a peculiar gait or method of thinking, in- 
 herited from our individual parents. 
 
 Reproduction is the process by which a species is perpetu- 
 ated, notwithstanding the limited existence of the individual 
 members. 
 
 The law governing reproduction is that the young are of 
 the same kind as their parents. By this law, which i- s<> 
 commonly observed as to seem a truism, is maintained the 
 anatomical identity of individuals of a species, as well as the 
 physiological fact of an unbroken continuance of the species 
 by reproduction. 
 
 Methods of reproduction : Reproduction takes place by one 
 
 266 
 
THEORY OF REPRODUCTION. 267 
 
 of two entirely distinct methods asexual reproduction and 
 sexual reproduction. 
 
 Asexual reproduction is the usual method among plants 
 and animals whose organism consists of but one cell. It is 
 also the method in some of the lower multicellular animals 
 and many higher forms of plants. 
 
 When considering the amoeba it was stated that it sub- 
 divided, with the result that from the single cell we had 
 two distinct units, each being members of the same species. 
 No sexual relations have taken place, and the offspring is the 
 child of but one parent. 
 
 Sexual reproduction : Sexual reproduction consists of the 
 union of elements produced separately by the female and the 
 male. In some of the lower organisms there is no direct 
 output from the male and female, but the two parents fuse 
 together, and the resultant mass develops into the offspring ; 
 such a method is called " conjugation." 
 
 As we rise in the animal scale we find that the female 
 produces the ovum, or egg, which is capable of being devel- 
 oped into a living offspring only when it is fecundated or im- 
 pregnated by the seminal or spermatic element from the male. 
 
 In some animals (worms) both the male and female ele- 
 ments exist in the same individual ; but still the offspring is 
 the result of " sexual reproduction," although there is but 
 one parent. 
 
 Theory of reproduction: Just why a cell should subdivide 
 into two secondary cells, or why there should be the necessity 
 for sexual reproduction, is a difficult problem to answer. 
 
 Asexual generation may be explained according to certain 
 principles laid down by Herbert Spencer. Spencer pointed 
 out conclusively that the mass of a cell grows as the cube, 
 whereas the surface grows only as the square ; from this it 
 follows that the mass to be nourished soon outgrows the ab- 
 sorbing or nourishing surface, hence fission results to insure 
 a relative increase of surface to the mass. Such division of 
 cells goes on for a variable number of times, until finally the 
 cell-protoplasm becomes enfeebled and worn out. In certain 
 infusoria the number of divisions may be from 150 to 450; 
 after that conjugation is necessary for a continuance of the 
 
268 REPRODUCTION. 
 
 method. From such observations one may reason that sexual 
 reproduction insures a fresh conjugation of protoplasm for 
 each individual, thus keeping the standard up to the maxi- 
 mum. 
 
 Also sexual reproduction tends to preserve the type of the 
 species ; for if the individual were the offspring of but one 
 parent, certain characteristics of that parent would be exag- 
 gerated in the course of several generations; but as the 
 individual springs from two parents, it becomes the menu 
 between those parents, with the result that the individual 
 tends to become the composite of the entire species. 
 
 Fecundation : The junction of the male and female delimit* 
 in sexual generation is called fecundation. At the time when 
 the male and female discharge their respective elements it is 
 not necessary that the parents should be in juxtaposition. In 
 deep-sea fishes the female discharges her spawn ; the male, 
 which is destined to fecundate these ova, may be miles away 
 and discharge his spermatozoa into the ocean ; the male and 
 female elements may float about until finally they meet, with 
 the result that the ova become fecundated. 
 
 In fishes like trout, salmon, etc., the female lays her eggs 
 on the spawning-bed, and later on the male deposits his ele- 
 ments directly on the spawn. 
 
 Still further along in the scale we find juxtaposition essen- 
 tial, the male grasping the female and both discharging their 
 elements at the same time, and the ova are fecundated as soon 
 as they leave the female. 
 
 Of course, in " viviparce " not only is juxtaposition essential, 
 but there is an actual discharge of the male elements into the 
 cavity of the female generative organs (such an act is called 
 " copulation "). 
 
 Human Female Organs of Generation. 
 
 The female organs consist of two or (trie*, in which the 
 ova are formed, and their oviducts or F<illi>i<tn ////*, which 
 carry the ova to the uterus, in which they may develop if 
 fecundated by the male ; and the ntf/hia for the reception of 
 the male organ in copulation and for the subsequent discharge 
 of the foetus. 
 
GRAAFIAN FOLLICLES. 
 
 269 
 
 The ovaries are two organs lying one on each side of the 
 uterus, attached to the broad ligament. In size they are 
 about 1J inches long, 1 inch wide, and l inch in thickness. 
 Besides their attachment to the broad ligament, they are 
 stayed in their position by folds or ligaments running to the 
 
 FIG. 134. 
 
 Generative organs of the human female, a, a, ovaries ; &, b, Fallopian tubes ; c, body 
 of the uterus ; d, cervix ; e, vagina (upper part). 
 
 fund us of the uterus and to the fimbriated extremity of the 
 Fallopian tube. 
 
 If an ovary be minutely examined, it is seen to be a duct- 
 less gland in which the composing elements are : (1) A stroma 
 of connective tissue and unstriped muscle-cells, and with 
 them a great number of peculiar spindle-shaped branching 
 cells ; and (2) the glandular portion, characterized by the 
 Graafian follicles. 
 
 The Graafian follicles are best observed during the child- 
 bearing age. They lie in the periphery, and present various 
 appearances as they are more or less matured. Some are 
 large enough to be seen by the unaided eye, while others are 
 very minute. In the matured follicle the interstitial tissue 
 will be found to have collected in a wall, quite well defined, 
 which is lined by an epithelial layer ; and upon one of this 
 
270 
 
 REPRODUCTION. 
 
 FIG. 135. 
 
 Human ovum, ruptured by 
 pressure, showing the vitel- 
 lus partially expelled, the 
 germinative vesicle, with its 
 germi native spot, at o, and 
 the smooth fracture of the 
 vitelline membrane. 
 
 layer epithelium is heaped up into a mass, the germ-hill 
 (cumulus or discus proligerus), which contains the ovum. The 
 remainder of the follicle is filled with a colorless fluid. 
 
 As the Graafian follicles mature they approach, and often 
 project above, the surface of the ovary. The fluid contents 
 of the follicle increase and the wall 
 becomes thinner over it, until finally 
 it bursts, and the ovum with some 
 of its surrounding epithelium escapes. 
 The ovary is covered on one sur- 
 face with a thin layer of epithelium 
 (the germinal epithelium), and not by 
 the peritoneum. This is of great 
 importance in the life of the ovum, 
 for it renders it possible for it to en- 
 ter the orifice of the Fallopian tube 
 without interfering with the peri- 
 toneum and without having to pass so 
 dense a structure. 
 
 From puberty to the menopause 
 
 the formation of new Graafian follicles is continuous, and a 
 very great number are produced ; but many do not develop 
 ova, and so waste away without going through the changes 
 described. 
 
 The ovum is a very highly developed cell, which is derived 
 from the germinal epithelium covering the ovary. In the 
 development of the ovary this epithelium dips into the sur- 
 face of the organ, and a certain portion is finally walled oil' 
 by growth of the surface-cells. Thus a ball of epithelial cells 
 is introduced into the body of the organ, and one cell devel- 
 ops the ovum, the rest going on to make up the (Jraafiau fol- 
 licle and the germ-hill (see 5, 6, 7, 8, 9, Fig. 136). 
 
 If the ovum in its perfected state, as it leaves the Graafian 
 follicle, be examined, it will be found to be a minute globular 
 cell containing a nucleus and nucleolus as well as a cell- 
 membrane. 
 
 In diameter the ovum is a little less than yj-^th inch. The 
 component parts of the ovum have received special names and 
 are worthy of separate description. 
 
THE OVUM. 
 
 271 
 
 The cell-wall is called the " zona pellucida" or " radiata" or 
 
 FIG. 136. 
 
 Section of the ovary (after Schron). 1, outer covering; 1', attached b9rder : 2, cen- 
 tral stroma ; 3, peripheral stroma ; 4, bloodvessels ; 5, Graafian follicles in their 
 earliest stage ; 6, 7, 8, more advanced follicles ; 9, an almost mature follicle; 9', 
 follicle from which the ovum has escaped; 10, corpus luteum. 
 
 (IV 
 
 Semi-diagrammatic representation of a mammalian ovum .highly magnified, zp, 
 zona pellucida ; vi, vitellus ; gv, germinal vesicle ; gs, germinal spot. 
 
 " vitelline membrane," and is a thick hyaline membrane enclos- 
 ing the cell-body. 
 
272 REPRODUCTION. 
 
 The cell-body is a mass of granular protoplasm, called the 
 " vitellus." 
 
 The cell-nucleus, or "germinal vesicle" is a somewhat large 
 transparent and well-defined body set somewhat eccentrically 
 in the vitellus or egg-yolk. 
 
 The nucleolus of the cell is called the "germinal spot." 
 The latter is a small, dark, almost opaque spot, situated in the 
 nearly transparent fluid nucleus (Fig. 135). 
 
 Fallopian tubes : The tubes are about 3^ inches in length, 
 and extend from the fundus of the uterus laterally on each 
 side. The calibre of the tubes gradually narrows from with 
 out inward, until at the uterus the opening is very minute. 
 The external covering is peritoneum, but the lining is mucous 
 membrane having ciliated epithelium. The outer end of the 
 Fallopian tube is free and fringed the fimbriated extremity. 
 
 The function of the fimbriated extremity is to grasp the 
 ovary, and thus act as a funnel into which the ovum is dis- 
 charged by the rupture of the Graafian follicle. It frequently 
 happens that ova are expelled from the ovary and miss the 
 mouth of the fimbriated end of the Fallopian tube, either be- 
 cause the fimbrium failed to grasp the ovary at the proper 
 point or else had failed altogether to make any attempt to 
 grasp the ovary. Under such circumstances the ovum lodges 
 in the peritoneal cavity and usually dies, but occasionally be- 
 comes impregnated. 
 
 Between the peritoneal covering of the Fallopian tube and 
 its mucous membrane lining is a coat of circular and longi- 
 tudinal muscle-fibres. These muscle-fibres serve to force the 
 ovum received by its fimbriated end along the tube, and so 
 into the uterus. This action is also aided by the ciliated 
 epithelium. 
 
 The uterus is a somewhat pear-shaped organ, and is about 
 3 inches in length, its wider part being about 2 inches wide 
 and the cervix 1 inch. It is described as consisting of a 
 fundus, body, and cervix. This body unites the fundus with 
 the cervix, which extends into the vagina. 
 
 It is covered over nearly all of its external surface with 
 peritoneum. Its bulk is made a p of un striped muscle, which 
 occurs in longitudinal and circular bundles and layers. This 
 

 PUBERTY. 273 
 
 muscular tissue increases enormously during pregnancy, and 
 by its strength helps to extrude the foetus. The lining is of 
 mucous membrane, which is formed in its superficial layer of 
 ciliated columnar epithelium. In the mucous membrane of 
 the cervix are a number of follicles which secrete a viscid, 
 tenacious mucus, by which the os uteri is frequently found 
 to be plugged. 
 
 The vagina is a musculo-membranous canal about 5 inches 
 long, extending from the uterus to the external genitals. It 
 is lined with mucous membrane, which in the ordinary con- 
 tracted state is thrown into folds, its anterior and posterior 
 walls being in contact. There is considerable erectile tissue 
 in the mucous membrane. At the orifice of the vagina ex- 
 ternally is a sphincter which only partially contracts it, and 
 besides this there are longitudinal and transverse unstriped 
 muscle-fibres in the submucous tissue. The outlet of the 
 vagina is sometimes also partially closed in the virgin by the 
 hymen, a fold of mucous membrane. 
 
 The external organs of generation are not immediately con- 
 nected with the function of reproduction, and may be enu- 
 merated as the labia majora, labia minora, and clitoris. 
 
 Functional activity of female generative organs : Under this 
 heading we have two manifestations to study viz., ovulation 
 and menstruation. Both of these events are closely associated 
 with the childbearing period of a woman's life, and are also 
 closely associated together. Much dispute has arisen over 
 the association of menstruation and ovulation, and without 
 attempting to weigh the comparative merits of the different 
 theories we shall accept and describe only those most gen- 
 erally accepted. 
 
 Menstruation is a phenomenon inherent in all women be- 
 tween puberty and the menopause. It consists of a flow of 
 blood from the uterus, together with an exfoliation of part or 
 of the whole of the mucous membrane of the uterus. At the 
 menstrual period there are, in addition, certain physical and 
 psychical manifestations involving to a more or less degree 
 the entire individual. 
 
 By puberty is meant that age at which a woman begins her 
 functional (childbearing) existence. In temperate climates 
 
 IS Phys. 
 
274 REPRODUCTION. 
 
 we may say the average age is fourteen years. In southern 
 countries it is somewhat earlier, and in the arctic regions a 
 year or two later. However, no fixed rule can be given, as 
 i he time of arrival at puberty varies with every individual, 
 depending on race, temperament, hygiene, and general sur- 
 roundings. 
 
 At puberty is the time when the girl changes into the 
 woman. The event is not accomplished at once, but extends 
 over considerable time. The girl undergoes a gradual change 
 in figure, the hips broaden, the breasts develop, pubic hair 
 grows abundantly, etc. She now begins to realize the differ- 
 ence in sex between herself and her boy companions. She 
 becomes more bashful and retiring. Also for the first time a 
 menstrual flow is noticed. At first the menstrual periods are 
 scanty and irregular, but after a few months they settle down 
 to the characteristic rate and duration. The girl is now a 
 woman. 
 
 By menopause, or climacteric, is meant the physiological 
 cessation of the menstrual flow. The woman's functional 
 activity is over. The ovaries become smaller ; no more 
 Graafian follicles are developed ; the Fallopian tubes atrophy ; 
 the pubic hair becomes thin and straight. The age of meno- 
 pause varies as does the age of puberty ; in general we may 
 say the earlier the puberty the earlier the menopause, and 
 vice versa. In temperate climates the average period for 
 the arrival of the menopause is at the age of forty-five years. 
 Thus we see a woman's functional activity lasts thirty years. 
 
 Frequency of menstruation : When once established men- 
 struation occurs on the average every twenty-eight days al- 
 though it is not without the bounds of normal health for 
 some women to have a menstrual flow every twenty-one days, 
 and others do not menstruate oftener than once in six weeks. 
 Menstruation is in abeyance during y>m//m>/r// and lactation. 
 
 Duration of menstruation: The menstrual flow lasts on an 
 average five days, the amount of blood lost gradually in- 
 creasing until the third day, and then gradually diminishing. 
 
 Nature of menstruation: At the beginning of menstruation 
 there is a general congestion of the generative organs, in- 
 cluding the breasts. A few days before menstruation there 
 
LIFE-HISTORY OF THE UNIMPREGNATED OVUM 275 
 
 has developed a hypertrophy of the mucous membrane (su- 
 perficial layers) of the uterus. At the beginning of the 
 menstrual period this hypertrophied mucous membrane is 
 gradually shed, leaving its underlying vessels exposed, and 
 they bleed. At the end of menstruation a new mucous mem- 
 brane is developed. The shed mucous membrane is called 
 the "decidua menstrualis." During menstruation, especially 
 t the beginning of the period, the woman is apt to be 
 peevish, irritable, complains of headache, loss of appetite, 
 and a sense of pelvic oppression that may even amount to 
 severe pain. 
 
 Character of menstrual discharge : It is a thin, bloody fluid 
 of a dark color and having a peculiar odor. It consists of 
 blood, epithelium, and mucus from the uterus and vagina, to- 
 gether with the decidua menstrualis. The blood does not clot. 
 
 Ovulation : The commonly accepted theory is that about or 
 shortly before the age of puberty the Graafian follicles begin 
 to discharge their ova, and that this process continues until 
 the menopause. Doubtless many Graafian follicles only par- 
 tially develop and atrophy without discharging mature ova. 
 The frequency with which well-developed ova are discharged 
 is the subject of much dispute. The most conservative view 
 is that there is one mature ovum discharged for each men- 
 strual epoch. On the other hand, other embryologists claim 
 that there is an almost daily discharge of ova, but only a few 
 enter the Fallopian tubes, while the rest are lost in the peri- 
 toneal cavity. Whichever view the student cares to follow is 
 immaterial, but nevertheless we must agree that only about 
 as many mature ova reach the uterine cavity as there are 
 menstrual epochs. 
 
 Life-history of the unimpregnated ovum : On leaving the ovary 
 and entering the Fallopian tube the ovum is surrounded by 
 a few cells derived from the discus proligerus of the Graafian 
 follicle. These cells may serve as a source of nourishment, 
 but soon disappear. There are now certain changes to be 
 observed in the ovum itself; first, the vitelline substance 
 seems to contract slightly, so as to leave a narrow rim or 
 space between the vitellus and zona pellucida the peri vitel- 
 line space. 
 
276 REPRODUCTION. 
 
 At this time the nucleus or germinal vesicle undergoes a 
 karyokinetic division into two parts, one part then being ex- 
 pelled from the ovum proper into the peri vitel line space as a 
 "polar body" the remaining portion of the original nucleus, 
 again subdividing into two parts by karyokinesis, with the 
 protrusion of one part as a second " polar body." What is 
 now left of the original nucleus is the "female pronudeus " ; 
 the polar bodies are apparently useless. Up to this point all 
 ova develop alike, and now are fit for impregnation. If im- 
 pregnation does not take place, the ovum dies and is caM nil'. 
 If impregnation does occur, there is further development of 
 the ovum, as we shall see in a later paragraph. 
 
 Corpus luteum : After the escape of an ovum there is an 
 effusion of blood into the cavity of the Graafian follicle. 
 The clot which follows is disposed of by the same retrogressive 
 processes which extravasated blood may undergo in any part 
 of the body. The serum is absorbed, the cells disintegrate. 
 and the coloring-matter is in part taken up by the tissues and 
 in part crystallizes or takes up other constituents, and pre- 
 sents variations of coloring. Hand in hand with these 
 changes in the blood go important changes in the surround- 
 ing tissues. The epithelial cells which are left behind pro- 
 liferate and form a sort of yellowish, very vascular tissue, 
 which presently undergoes fatty degeneration. This yellow 
 mass surrounding and enclosing the remains of the extrava- 
 sated blood constitutes the corpus ufeum,and as it disappears 
 its place is occupied by a dense, firm connective-tissue cica- 
 trix, which may be pigmented. 
 
 The changes described above are those that take place if 
 the ovum fails to become impregnated. If, on the other hand, 
 fecundation ocvurs, the corpus luteum undergoes certain 
 characteristic changes, widely differing from the degenera- 
 tion of the corpus luteum of non-pregnancy. If the ovum he 
 impregnated, the corpus luteum then does not degenerate and 
 disappear rapidly as after menstruation, but continues fully 
 as large as at the beginning for several months, and at the 
 end of pregnancy still remains as a clearly marked body. 
 This is shown in the following table from Dalton : 
 
 
MALE GENERATIVE ORGANS. 
 
 277 
 
 At the end of 
 three weeks. 
 One month. 
 
 Two months. 
 Four months. 
 
 Six months. 
 Nine months. 
 
 Corpus Luteum of Menstrua- 
 tion. 
 
 f inch in diameter ; central 
 
 pale. 
 Smaller ; convoluted wall 
 
 bright yellow ; clot still 
 
 reddish. 
 Reduced to the condition of 
 
 an insignificant cicatrix. 
 
 Absent or unnoticeable. 
 
 , 
 
 \ 
 
 Corpus Luteum of Pregnancy 
 (Dal ton). 
 
 lot reddish ; convoluted wall 
 
 Larger ; convoluted wall 
 bright yellow ; clot still 
 reddish. 
 
 | inch in diameter ; convo- 
 luted wall bright yellow ; 
 clot perfectly decolorized. 
 
 Size about as at two months; 
 clot pale and fibrinous; 
 convoluted wall dull yel- 
 low. 
 
 Absent. Still as large as at the end 
 
 of the second month. Clot 
 fibrinous. Convoluted wall 
 paler. 
 
 Absent. inch in diameter ; central 
 
 clot converted into a radi- 
 ating cicatrix ; external 
 wall tolerably thick and 
 convoluted, but without 
 any bright yellow color. 
 
 Connection between ovulation and menstruation : Whether 
 ovulation depends upon menstruation or menstruation upon 
 ovulation, or whether either has any connection with the 
 other, is a matter of lengthy controversy. 
 
 However, the general view is that both ovulation and 
 menstruation are the result of a common cause (cause un- 
 known), but either may exceptionally occur without the 
 other. 
 
 It is generally accepted that ovulation, or discharge of 
 yum from a Graafian follicle, takes place a few days before 
 
 e onset of the menstrual period. 
 
 Human male generative organs. 
 
 The generative organs of the male consist of the two tes- 
 icks, which produce the seminal fluid ; and the vas deferens, 
 r duct leading from each to join with the duct of the corre- 
 ponding seminal vesicle, in which the secretion is stored (?) 
 
 until it is discharged through the penis and the prostate 
 
 gland. 
 
 
278 
 
 REPRODUCTION. 
 
 FIG. 138. 
 
 Testicles : Each testicle is made up of a dense connective- 
 tissue framework and a secreting portion. The connective- 
 tissue stroma, tunica albuginea, surrounds the outside of the 
 organ, and sends incomplete partitions into the central por- 
 tion of the organ, dividing it into a number of communicating 
 cavities. In these cavities are winding tubules which con- 
 stitute the secreting portion of the organ. These tubules in- 
 osculate in a sort of mesh (rete testis), and finally all unite in 
 the epididymis. The secreting tubules are called the semi- 
 niferous tub lit ex. 
 
 Each tubule has, in the active organ, a limiting membrane, 
 upon which are a number of layers of flattened cells. In- 
 ternal to these are seminal cells in two or more layers. The 
 seminal cells contain nuclei which are capable of division, so 
 that each nucleus may develop several new nuclei. The 
 nuclei are the spermatoblasts, or cells from which the sper- 
 matozoa originate. The cells before the di- 
 vision of the nuclei resemble the ordinary 
 cuboid epithelium, and it is in the superficial 
 layers (i. e., toward the lumen of the tubuli) 
 that this function of the cells takes place. 
 
 The seminiferous tubules all converge to- 
 ward the epididymis, a tortuous tubule which 
 is lined with mucous membrane, and lies 
 beside the testis in a long, convoluted mass 
 which may be unravelled, and is found to be 
 about 20 feet long. This empties contents, 
 or rather continues on, into the va# dejer- 
 ens, which conveys the semen to the junction 
 with the seminal vesicle. During this passage 
 the mucous membrane adds a viscid mucous 
 secretion in which the spermatozoa are liber- 
 ated and, so to speak, diluted. 
 
 Spermatozoa : In the seminiferous tubules 
 the developing spermatozoa may be seen with 
 niMciii- i.irre; d, the heads all united in the cells from which 
 
 tails; e, end-piece ,1 ,1 , i , 
 
 of the tail. they arise, the tails projecting 
 
 the cavity of the tube. Bu; 
 separated. They then consist of a head and a 
 
THE URETHRA. 279 
 
 In length they are about ^th to -A^th of an inch. The 
 head is somewhat elliptical and the tail gradually tapers. In 
 other animals than man the size and form vary from those 
 of man, though in a general way they conform. 
 
 There is a very active vibratory motion of the tail of the 
 spermatozoon, which allows it quite free motion in a fluid 
 medium. It is by this swimming motion, in which it may be 
 compared to a tadpole, that the seminal cell is able to reach 
 the ovum against the action of the cilia in the uterus and Fal- 
 lopian tube. 
 
 Seminal vesicles : They are tubules which join the vasa 
 deferentia, and lie upon the base of the bladder, emptying 
 into the urethra by the ejaculatory ducts through the prostate 
 gland. In structure the vesiculse seminales are convoluted and 
 dendritic. They are lined by a mucous membrane and are con- 
 voluted and folded so as to present a sacculated appearance. 
 
 Prostate gland : It is a gland lying at the base of the 
 bladder and surrounding the urethra at its beginning. It has 
 the general structure of the glandular organs, and in addi- 
 tion a considerable amount of muscular tissue. Its acini 
 empty into ducts which empty into the urethra. Its function 
 is not exactly known. 
 
 The penis consists of three more or less cylindrical bodies 
 of erectile tissue enclosed in fibrous sheaths. The two cor- 
 pora cavernosa lie above, and receive between them, below, 
 the corpus spongiosum, in which the urethra is contained. 
 The glows penis is continuous with the corpus spongiosum. 
 The covering of the penis is of loose skin, but over the glans 
 penis and lining the prepuce it resembles mucous membrane. 
 In this region there is an abundant subcutaneous nerve- 
 plexus, and the Pacinian bodies are quite numerous, so that 
 it is possessed of acute sensibility. 
 
 The urethra extends from the bladder through the corpus 
 
 spongiosum to the end of the penis. It is lined with mucous 
 
 membrane, and is furnished in its deeper layers with numer- 
 
 ous muscular fibres. There are a number of ducts of glands 
 
 it whose function is not fully understood, though 
 
 m is supposed to be added to that of the seminal 
 
 nake up the semen. 
 
280 REPROD UCTION. 
 
 Erectile tissue of the penis : The erectile tissue consists of a 
 system of distensible vacuoles containing venous blood, lying 
 in the interstices of a fibrous connective tissue. The erector 
 penis muscle by its contraction compresses the veins of the 
 organ, and the veins become turgid with blood. The arteries 
 enter the structure of the erectile tissue along the pubic 
 bone, and are not pressed upon by the contraction of the 
 muscle. 
 
 Impregnation in the Human Species. 
 
 Impregnation, or fecundation, are the terms applied to the 
 junction of the male and female elements (spermatozoon and 
 ovum), by virtue of which the joined elements become one, 
 and by developmental growth eventually become an indi- 
 vidual of the species. If no junction of sperm atazoon and 
 ovum takes place, each dies and is cast off. If, however, the 
 ovum is fertilized by the spermatazoon, a new life is begun. 
 
 Methods of fertilization : The methods by which the male 
 spermatazoon and ovum are brought in contact vary for dif- 
 ferent classes of animals. As has already been mentioned, 
 in some classes of fishes the female ejects her spawn and the 
 male his elements, at different places, and owing to the ocean 
 currents the male elements are brought into contact with the 
 female elements. In frogs the male fertilizes the ova just as 
 the latter leave the female. In mammalia the male intro- 
 duces the spermatozoa into the genital passages of the female, 
 and this act is called coitus. 
 
 Coitus : The act of coitus is preceded by a preliminary 
 period of sexual excitement, more marked in the male, during 
 which the penis becomes swollen, turgid, and erect. The 
 penis is then introduced into the female vagina. As a result of 
 muscular movements there is friction upon the delicate sen- 
 sory nerve end-organs of the glans penis and clitoris, pro- 
 ducing intense nervous sensations, leading finally to a climax 
 of excitement on the part of both male and female that 
 gradually fades away. During the climax (or orgasm) there 
 is an ejaculation <>i' seminal fluid on the part of the male 
 into the upper end of the vagina of the female. There 
 
DETAILS OF IMPREGNATION. 281 
 
 is also a flow of secretion from the glands of Bartolini of the 
 female, and also, presumably, a rhythmical opening and clos- 
 ing of the cervical canal. 
 
 Site of impregnation : Although the seminal fluid of the male 
 is lodged, at the close of coitus, in the vagina of the female, the 
 spermatozoa are not yet in contact with the ovum. By virtue 
 of their inherent mobility the spermatozoa travel along the 
 cervical canal into the cavity of the uterus, there to meet the 
 ovum. The spermatozoa may even travel along the Fallo- 
 pian tubes, impregnating the ovum in the lumen of the tube ; 
 or may even leave the tubes by their fimbriated ends and 
 impregnate the ovum on the surface of the ovary. 
 
 Time of impregnation : Probably immediately before the 
 menstrual period ; but owing to the fact that both the female and 
 the male elements may remain in the genital passages of the 
 female for some days in a healthy condition, it is difficult to 
 fix the time of actual impregnation of the ovum. 
 
 Impregnation is generally supposed to occur a short time 
 before menstruation, on the following grounds : 
 
 (1) It is probable that in most instances the rupture of the 
 Graafian follicle occurs just before the menstrual period. (2) 
 The uterus is in the most favorable condition to sustain the 
 fecund ovum at that time, because of the presence of the 
 decidua menstrual is. (3) Among the Jews, a remarkably 
 prolific race, coitus is prohibited by the religious law for a 
 week after menstruation. 
 
 Details of impregnation : The spermatozoon travels along 
 the uterus or Fallopian tubes until it comes in contact with 
 the ovum. The spermatozoon, by lashing its tail, wriggles 
 through the zona radiata (pellucida) of the ovum and enters 
 the perivitelline space. Several spermatozoa may succeed in 
 effecting an entrance as far as the perivitelline space ; but be- 
 yond this, for some unknown reason, but one spermatozoon 
 goes further and enters the vitellus proper ; the others die. 
 The spermatozoon destined to fertilize the ovum now loses its 
 tail, and the head and centre-piece are called the male pro- 
 nucleus. The male pronucleus and female pronucleus now 
 fuse together in the centre of the egg and form the first seg- 
 mentation-nucleus. 
 
DEVELOPMENT. 
 
 On the formation of the first segmentation-nucleus the act 
 of imi>r<-<iiniti<ni is complete, and the subsequent changes in 
 the growth of the ovum come under the head of " Develop- 
 ment," 
 
 DEVELOPMENT. 
 
 Methods of study of development : The early development 
 of the human ovum has not been studied with accuracy, but 
 we have reasoned by analogy, from observations upon the 
 lower animals. One method is to watch the changes in the 
 development of the egg of the common fowl. This is on 
 account of the accuracy with which the time of development 
 inav be watched, and the convenience to the observer of such 
 simple growth by incubation compared with uterine growth. 
 The processes of development are not materially different. 
 
 Segmentation : The most frequent site of impregnation is 
 probably the Fallopian tubes, and while there the ovum re- 
 ceives a layer of clear albuminous material, which adds con- 
 siderably to its bulk. This corresponds to the white of a 
 hen's egg. 
 
 The next change which occurs in the impregnated eg<r is 
 the splitting up of the vitellus or yelk, first in halves, then 
 in quarters, and so on until the vitellus becomes a mass of 
 minute granular-looking nucleated cells (Fig. 139). The 
 segmentation of the nucleus precedes and continues with the 
 corresponding change in the yelk. 
 
 Germinal membrane: After the yelk has subdivided into a 
 large number of cells these cells undergo a centrifugal action, 
 with the result that they form a complete inner lining for 
 the /ona pellucida of closely packed polygonal cells, leaving 
 a central clear cavity containing the vitelline liquid. This 
 lining is the germinal or blastodermic membrane. 
 
 Site of segmentation : So far the ovum has probably re- 
 mained in the Fallopian tube, but now descends into the 
 uterus. The descent into the uterus is estimated to take 
 place about ten days after impregnation. 
 
 Before studying the subsequent development of the blasto- 
 tli-nn. let ii- see what changes have taken place in the lining 
 of the uterus to prepare it for the reception of the ovum. 
 
CHANGES IN THE BLASTODERM. 
 
 283 
 
 Changes in the uterine lining : The decidua menstrualis has 
 been mentioned as specially suitable for the reception of the 
 ovum. But if impregnation occur, it is not called by this 
 name, as menstruation does not occur. It is then known as 
 the decidua vera. It consists of a thick, succulent mucous 
 membrane caused by the proliferation of the subepithelial 
 cells. Into this decidua the ovum falls, and its shaggy 
 chorion implants its villi in the crypts of the mucous mem- 
 
 FIG. 139. 
 
 Segmentation of the vitellus in the impregnated egg of the rabbit (Coste). 
 
 brane. The decidua soon envelops it, and the portion which 
 is reflected over the ovum is known as the decidua reflexa. 
 
 Changes in the blastoderm : There appears at one point an 
 opaque streak (Fig. 140), which is found to be due to the 
 proliferation of the cells of the blastoderm. This is the 
 primitive trace, and it grows in length and breadth. 
 
 The surrounding area of increased cell-proliferation is 
 called the " area germinativa." The blastoderm ?. e., that 
 portion or area of the blastodermic membrane in which the 
 embryo is actually developing increases in area from the 
 rapid proliferation of cells, and folds up at each end trans- 
 
284 DEVELOPMENT. 
 
 versely and at the sides longitudinally. These folds are 
 of great importance, for it is in this way that the contour 
 of the body is outlined, and if it were not for them the 
 blastoderm would continue to develop as a flat surface. 
 The transverse folds are at each end, and are known as 
 the head and tail folds. The longitudinal folds define the 
 outlines of the body (see Amnion). There also occurs a con- 
 striction of the entire ovum ; above the constriction is the 
 developing embryo, and below the constriction is the yelk-sac 
 (see page 287). Together with these changes the cells of the 
 
 FIG. 140. 
 
 Diagram of the area germinativa, showing the primitive trace and area pellucida. 
 
 blastoderm and blastodermic membrane split up into three con- 
 centric layers the epiblast, mesoblast, and hypoblast (Fig. 141); 
 and along the axis of the primitive trace a groove is formed 
 which is destined to become the cerebro-spinal axis. This is 
 the primitive groove, or medullary groove. 
 
 Development of the medullary groove : Certain ridges or folds 
 appear in the epiblast on either side (mesial to and smaller 
 than the ones mentioned above). They continue to thicken, 
 and finally coalesce dorsally, leaving a lining of cells within 
 a tube. These cells develop the cerebro-spinal axis (cord and 
 brain) and follow the curves of the blastoderm longitudinally. 
 It is to be noticed that the enclosure of the spinal canal in 
 
STRUCTURES DERIVED FROM THE MESOBLAST. 285 
 
 this way is by a folding process, and all through the process 
 of development this peculiarity is very marked. 
 
 Meanwhile the mesoblast has developed a number of proc- 
 esses, which become a primitive spinal column. 
 
 
 Section of a blastoderm at right angles to the long axis of the embryo, near its 
 middle, after eight hours' incubation (from Foster and Balfour). A, epiblast 
 formed of two layers of cells ; B, mesoblast, thickened below the primitive 
 groove; C, hypoblast, formed of one layer of flattened cells; pr, primitive 
 groove ; me, mesoblast cell ; bd, formative cells in the so-called segmentation or 
 subgerminal cavity (the line of separation between the epiblast and mesoblast 
 below the primitive groove is too strongly marked in the figure). 
 
 Changes in the mesoblast : The mesoblast throughout a por- 
 tion of its distance subdivides into two layers, one part of the 
 split mesoblast adhering to the epiblast, while the remainder 
 joins the hypoblast. The former is known as the somato- 
 pleure, and the latter as the splanchnoplture, and the included 
 space becomes the pleuro-peritoneal cavity, which subse- 
 quently divides and diiferentiates to form the pleural, pericar- 
 diac, and peritoneal cavities. 
 
 Structures derived from the epiblast : The epiblast develops 
 into the epidermis and appendages of the skin, the great 
 nervous centres, the nerves, and the principal portions of the 
 organs of special sense eye, ear, nose. 
 
 Structures from the mesoblast : The bones, muscles, fasciae, 
 and connective tissues of the body. It also develops the 
 vascular stem. It must be remembered that very early in 
 embryonal life this tissue divides to join with the epiblast and 
 hypoblast, and we can therefore understand how it may de- 
 velop the muscular structures of the intestinal canal. 
 
286 DEVELOPMENT. 
 
 Structures from the hypoblast : The epithelial elements of the 
 glands and the mucous membranes lining the alimentary and 
 pulmonary tracts. 
 
 Destiny of the splanchnopleure : The splanchnopleure (6', Fig. 
 142) folds in over the remainder of the ovum, and so walls 
 in, so to speak, the yelk-sac, which communicates freely with 
 the interior of the embryo. Later on, after the formation 
 of the amnion, the yelk-sac forms a blind pouch which is 
 lined with hypoblast and has an external covering of meso- 
 blast, as is shown at 6 in the accompanying cut. The upper 6 
 
 Transverse sections through the embryo chick, before and some time after the 
 closure of the medullary canal, to show the upward and downward inflections 
 of the blastoderm (after Remak) on the third day in the lumbar region. 1, noto- 
 chord in its sheath ; 2, medullary canal, now closed in ; 3, section of the medul- 
 lary substance of the spinal cord ; 4, epiblast ; 5, somatopleure of the 
 mesoblast; 5', splanchnopleure (the figure is placed in the pleuro-peritnneal 
 cavity); 6, layers of hypoblast in the intestines, spreading also over the yelk; 
 4x5, part of the fold of the amnion formed by the epiblast and somatopleure. 
 
 is in the primitive gut, which derives its epithelial elements 
 from the hypoblast and its muscular and serous coverings 
 from the mesoblast. 
 
 Umbilical vesicle : After the constriction of the vitellus or 
 ovum (page 285), separating the main portion of the vitellus 
 from the cavity of the future alimentary tract, the con- 
 stricted portion, or tube, is known as the "vitelline duct," 
 and the rest of the vitellus is called the " umbilical vesicle," 
 both at an earlier period of development being known as the 
 ydk-tnc. 
 
 From the latter the embryo derives its sustenance in the 
 
PURPOSE OF THE AMNION. 
 
 287 
 
 earlier stages. Early in the development bloodvessels begin 
 to form, and they ramify over the surface of the umbilical 
 vesicle and help to absorb its contents. 
 
 Amnion : While one portion of the split mesoblast (splanch- 
 nopleure) unites with the hypoblast to form the splanchnoblast 
 and alimentary organs, the outer layer (somatopleure) and 
 epiblast are united to form the skin and walls of the body as 
 the somatoblast. The somatoblast now folds up and around 
 the embyro, above and lateral to the folds of the medullary 
 groove already mentioned. It must be remembered, however, 
 that the entire globe of the ovum is invested by the somato- 
 blast, and that in folding up in this way its cells are in a 
 
 Diagram of the fecundated egg, farther 
 advanced, a, umbilical vessel ; b, 
 amniotic cavity, not yet complete ; 
 c, allantois. 
 
 Diagram of the fecundated egg, with 
 allantois nearly complete, a, inner 
 lamina of amniotic fold ; 6, outer 
 lamina of amniotic fold; c, point 
 where the amniotic folds come in 
 contact. The allantois is seen pene- 
 trating between the inner and outer 
 laminae of the amniotic folds. 
 
 measure raised away from the splanchnoblast. This " rais- 
 ing away " is further aided by the sinking of the embryo. The 
 layers of the somatoblast fold up until they meet and unite 
 behind the embryo, and in this way form a layer of membrane 
 which lines the ovum and another layer which encloses the 
 embryo (Fig. 143). This latter layer forms the true amnion. 
 (This is better understood by reference to the cuts.) 
 
 Purpose of amnion : It covers the embryo in the early stages 
 very closely ; but soon becomes distended with a pale watery 
 fluid, which serves to float the foetus and give it equal me- 
 
288 DEVELOPMENT. 
 
 chanical support on all sides. The outer layer of the amnion 
 
 becomes very thin and adheres to the chorion. 
 
 The amniotic fluid consists of water containing a small 
 
 amount of albumin, urea and salt. 
 
 Allantois : During the development of the amnion from 
 
 the somatoblast a change has occurred in the splanchnoblast. 
 From near the caudal extremity of 
 the primitive gut there has budded 
 a small mass which develops rap- 
 idly, following the outline of the 
 amnion (see Figs. 143, 144, 14")), 
 and grows fast to its chorion layer. 
 This structure, the allantois, soon 
 becomes very vascular and carries 
 its bloodvessels to the chorion. 
 
 Purpose of the allantois : It nourishes 
 the growing embryo. The chorion 
 
 Diagram of the fecundated / ii\il IJT_ i> i 
 
 iw. with the allantois luiiy (see below) has already become tutted 
 
 Sm^'SjSi with capillary loops, and has estab- 
 
 lished a connection with the decidua 
 
 of maternal growth. As the vessels of the allantois communi- 
 cate more and more with the chorion, the embryo derives 
 more of its sustenance from the mother, and the remains of 
 the yelk-sac (umbilical vesicle) dwindle as the need is less 
 and the substance is consumed (see Figs. 143, 144, 145). 
 Subsequent history of the allantois : After the development 
 of the placenta the allantois dwindles away, all except the por- 
 tion nearest the foetus ; this becomes the urinary bladder and 
 the urachus (the latter, in the adult, is an impervious cord 
 extending from the bladder to the umbilicus). 
 
 Chorion : the chorion is the outer zone of the ovum, and 
 from its surface there project centrifugally a large number of 
 villi. 
 
 The chorion consists of several layers which fuse into one 
 vascular membrane: the allantois, the outer layer of the 
 amnion, and the vitelline membrane are united in the chorion. 
 As the embryo develops the vessels of the chorion become 
 thinner on the side toward the uterine cavity, and more dis- 
 tinct on the opposite side. This change continues as the 
 
ASSOCIATION OF FCETAL AND MATERNAL BLOOD. 289 
 
 embryo increases, until the placenta is formed by the branch- 
 ing of the embryonic vessels and the increase of the decidua 
 at the corresponding point. 
 
 Association of decidua and chorion : In the deeper part of 
 the mucous membrane of the uterus, at the implantation of the 
 chorion, there are hollowed-out spaces or sinuses in the tissues, 
 which communicate both with a maternal vein and an artery 
 that is, special arrangements are made for the rapid circula- 
 tion of a large amount of blood in the uterine mucous mem- 
 brane at the placental site. At the same time the glandular 
 structures of the uterine mucous membrane are increased, and 
 the follicles run deeply into the thick and succulent tissues. 
 
 The villi dip down and develop new tufts of capillaries in 
 the deepened crypts of mucous membrane, so that the tufts 
 of capillaries of the chorion may be said to resemble in a 
 way a glove filled with foetal blood dipping into a vessel filled 
 with maternal blood. 
 
 The placenta : So far the villi throughout the entire surface 
 of the ovum become associated with the decidua. Now, as 
 development advances, that portion of the chorionic villi that 
 is lined by the central portion of allantois grows still further 
 in size, while the rest of the chorionic villi atrophy and disap- 
 pear. The loops of bloodvessels of the allantois project into 
 the villi of the chorion (like a finger into a glove), and thus 
 are brought into closer contact with the blood of the decidua 
 (maternal blood). The portion of villi of chorion containing 
 the vessels of the allantois is the placenta. 
 
 Thus we see that the placenta consists really of two parts 
 a foetal portion, consisting of fcetal bloodvessels contained 
 in the chorionic villi ; and a maternal portion, consisting of 
 follicles or depressions in the uterine wall, surrounded by 
 bloodvessels so enlarged as to form blood-chambers (uterine 
 sinuses). The chorionic villi are lodged in the uterine follicles, 
 or between the follicles, according to some observers. 
 
 Association of foetal and maternal blood : The foetal blood 
 never comes directly in contact with the maternal blood. 
 The two blood-currents are nearest each other while circulat- 
 ing through the placenta. 
 
 While in the placenta there are four layers of cells between 
 
 19 Phys. 
 
290 DEVELOPMENT. 
 
 the maternal and the foetal blood : 1, wall of chorion capil- 
 lary ; 2, cells of chorion; 3, cells of uterine follicle; and 4, 
 wall of the uterine sinus. 
 
 Interchange between foetal and maternal blood : Although 
 there is no direct communication between the blood of the foetus 
 and that of the mother, nevertheless while passing through 
 the placenta there is an exchange by osmosis between the 
 mother's blood and the foetal blood. 
 
 The mother's blood furnishes to the foetal blood food and 
 oxygen, and in turn removes the carbonic acid and excre- 
 mentitious material which the foetus must lose that is, the 
 placental circulation supplies the place taken in after-life by 
 the alimentary and the respiratory tracts. 
 
 Umbilical cord : The umbilical cord or funis is the stalk 
 connecting the placental with the foetus, and its purpose is to 
 
 l>e a framework or support for the 
 Fro. 146. umbilical arteries and veins. The 
 
 tissues of the umbilical cord are 
 formed from the vascular allantois, 
 which carries the arteries and veins. 
 It also has an external coating 
 of the amnion and the shrivelled 
 umbilical vesicle and its duct (Fig. 
 146). How this occurs will readily 
 be seen by reference to the accom- 
 panying cut. 
 
 Human embryo and its envel- \, n 
 
 opes at the end of the third At Iirst two arteries COI1VCV 
 
 SenfoV'Smnio 1 ;' 6nlarge " the blood from the foetus to the 
 placenta, and two veins carry 
 
 the purified blood from the placenta to the foetus. Later on 
 in foetal life one of the veins is lost. At term the umbilical 
 cord is a rope-like structure between 18 inches and 36 indies 
 long, and consists of one vein and two arteries spirally twisted ; 
 the vessels are enclosed in a layer of jelly-like substance 
 (Wharton's jelly), and the whole is surrounded by a con- 
 nective-tissue sheath. The cord is about one-half inch in 
 diameter. 
 
 Destiny of placenta : The foetal part is almost all, excepting 
 some of the capillary tufts which are torn off, discharged in 
 

 PLACENTAL CIRCULATION. 291 
 
 the after-birth ; but the decidua is not entirely disposed of in 
 this way, the portions remaining being in part absorbed and 
 in part found in the lochia which occur for a fe\v days after 
 the birth. 
 
 When the placenta is expelled a part of the maternal 
 tissue is left behind, and there is, of course, a loss of the 
 blood contained in the uterine sinuses, but the general bal- 
 ance of the circulation is not disturbed at childbirth. The 
 reason for this is the oblique entrance of the placental vessels. 
 They enter the sinuses at an angle, and are therefore com- 
 pressed by the muscular tissue of the uterus in its contracted 
 state. 
 
 Appearance of placenta : The placenta at term appears as a 
 thick, cake-like disk of vascular tissue. Its maternal and 
 foetal portions are so intermingled that they cannot be sepa- 
 rated. In size it covers about one-third of the uterine 
 wall. 
 
 Period of placental formation : The placenta is formed at 
 about the third month of pregnancy. Before that time the 
 chorion is covered by the decidua reflexa and nourishes the 
 embryo, but as the placenta becomes more developed other 
 parts of the chorion atrophy. 
 
 Foetal Circulation. 
 
 Types of foetal circulation : One meets with two distinct 
 types of circulation in foetal life : the vitelline circulation and 
 the placental circulation. In both types the blood is the circu- 
 lating medium driven on by the heart, the essential difference 
 being the site where the foetal blood is enriched. The vitel- 
 line circulation precedes that of the placenta, and as soon as 
 the latter is formed the former disappears. 
 
 Vitelline circulation : In the vitelline circulation the vessels 
 from the foetus (omphalo-mesentric vessels) pass over the 
 yelk-sac and carry nutrition to it from the growing organism. 
 The vitelline circulation in the human ovum is not very long- 
 lived, for the chorion is early formed and the stock of nutri- 
 ent protoplasm in the yelk-sac is very small. 
 
 Placental circulation : In the placental circulation the foetal 
 
292 
 
 DEVELOPMENT. 
 
 blood is purified and enriched by osmosis with the maternal 
 blood in the placenta. 
 
 Development of circulatory apparatus : Among the earliest 
 changes in the blastoderm, occurring in the second week of 
 impregnation, is the formation of bloodvessels and blood- 
 corpuscles. This occurs by the proliferation of certain 
 branched cells of the mesoblast, and 
 FIG. 147. these cells form a closed system of 
 
 branching capillaries, their nuclei 
 acquiring a red color and becoming 
 the blood-corpuscles. This area is 
 external to but connected with the 
 embryo, and is known as the " area 
 vasculosa." 
 
 The area vasculosa extends all 
 about the blastoderm upon the sur- 
 face of the vitellus, and as the folds 
 of the embryo occur the vessels are 
 brought to enter the body through 
 the space at which the vitellus is shut 
 in to form the primitive gut. There 
 are then two arteries and two veins 
 which are known as the omphalo- 
 mesenteric vessels. This form of 
 circulation soon gives way to the placental, and the vessels 
 passing to the umbilical vesicle waste, those belonging to that 
 portion of the original vitelline cavity which forms the intes- 
 tine, becoming the mesenteric vessels. 
 
 Formation of heart : About the time of the formation of 
 the area vaseulosa certain cells of the visceral layer of the 
 incsoblast (splanchnopleure) develop a tube upon each side of 
 the body, and these two tubes soon coalesce to form a single 
 tube (Fig. 148), which receives two veins at its lower end and 
 gives off two arteries at its upper. This is the primitive 
 heart, and pulsations begin in it very feebly almost as soon 
 as there is a trace of the originating cells. This structure 
 soon develops a muscular tissue and a circulating fluid which 
 shortly presents the character of blood. 
 
 The heart then bends on itself so as to assume a U-shape, 
 
 Diagram of embryo and its 
 vessels, showing the circu- 
 lation of the umbilical ves- 
 icle, and also that of the 
 allantois, beginning to be 
 formed. 
 
COURSE OF THE FCETAL CIRCULATION. 
 
 293 
 
 which shortly is twisted in such manner that the arterial end 
 of the heart crosses in front of the venous (Fig. 149), and 
 the loop suggests the outline of the ventricles. 
 
 In the next stage of development the septum between the 
 ventricles grows, and separates the heart into two divisions ; 
 and at about the same time the auricles are developed and 
 the valves become well marked. These changes occur in the 
 fourth to the eighth week of embryonic life. 
 
 FIG. 148. 
 
 FIG. 149. 
 
 FIG. 150. 
 
 FIG. 148. Earliest form of the foetal heart. 1, venous extremity; 2, arterial ex- 
 tremity. 
 
 FIG. 149. Foetal heart bent upon itself. 1, venous extremity ; 2, arterial extremity. 
 
 FIG. 150. Foetal heart still further developed. 1, aorta; 2, pulmonary artery; 3,3, 
 pulmonary branches ; 4, ductus arteriosus. 
 
 Characteristics of placental circulation : After the cessation 
 of vitelline circulation the needs of the fetus are supplied by 
 the placental circulation until birth. The placental circula- 
 tion presents two prominent features in which it diifers from 
 adult circulation : 
 
 (1) In the arterial circulation some conditions of the heart 
 and great vessels are necessary to modify the pulmonary cir- 
 culation before the air enters the lungs at birth. (2) In the 
 circulation of the liver the veins present modifications to 
 allow for the return placental circulation. 
 
 Course of foetal circulation : Ductus venosus : The foetal 
 blood, purified and enriched in the placenta, passes, by the 
 umbilical vein in the umbilical cord, to the umbilicus. The 
 umbilical vein then courses from the umbilicus to the under 
 surface of the liver ; here the vein divides into two parts. 
 One portion of the blood enters into the liver-substance, 
 and after traversing its capillaries is poured out by the hepatic 
 
294 DEVELOPMENT. 
 
 veins into the inferior vena cava. The other portion of 
 blood passes directly from the umbilical vein into the inferior 
 vena cava by means of a blood-channel, the ductus venom n*. 
 
 Foramen ovale : The blood in the vena cava inferior empties 
 into the right auricle of the foetal heart. Instead of passing 
 from the right auricle into the right ventricle, as is the case in 
 the adult circulation, the blood from the inferior vena cava 
 passes from the right auricle into the left auricle by means 
 of an opening in the interauricular septum. The opening is 
 called the "foramen ovale" The flow of blood from the 
 inferior vena cava through the foramen ovale and into the 
 left auricle is facilitated by the fact that the inferior vena 
 cava points almost directly into the foramen ovale. 
 
 The Eustachian valve also favors this peculiar course of the 
 blood. The Eustachian valve consists of a crescentic fold of 
 fibrous tissue covered with endocardium. The fold extends 
 from a point between the opening of the superior and inferior 
 venae cavse over to the lower and anterior margin of the fora- 
 men ovale. The base of the fold lies on the right auriculo- 
 ventricular ring, and the concavity of the fold is directed 
 upward. From its position the Eustachian valve acts as a 
 guiding-groove or gutter for passing the blood from the in- 
 ferior vena cava to the foramen ovale. 
 
 Ductus arteriosus : On entering the left auricle, the blood 
 is passed into the left ventricle and thence into the aorta, to 
 be distributed all over the body ; but principally to the head 
 and upper extremities. 
 
 The blood from the head and upper extremities returns to 
 the heart by the superior vena cava. On entering the right 
 auricle the blood from the superior vena cava passes in front 
 of the stream that flows from the inferior vena cava to the 
 foramen ovale, and enters the right ventricle. 
 
 The direction in which the superior vena cava points (to- 
 ward the auriculo-ventricular ring), and also the Eustachian 
 valve, arc the factors that determine the separation of these 
 two streams. On entering the right ventricle the blood from 
 the superior vena cava is forced into the pulmonary artery 
 toward the lungs. Before reaching the lungs this blood meets 
 with a channel of communication between the pulmonary 
 
EFFECTS OF FCETAL CIRCULATION. 295 
 
 artery and the aorta. Into this channel (ductus arteriosus) 
 the larger portion of the blood in the pulmonary artery enters 
 and mingles with the blood of the aorta ; the remainder 
 passes along the pulmonary artery to the structure of the 
 lungs, which it nourishes, and thence back to the left auricle 
 by means of the pulmonary veins. 
 
 Hypogastric, arteries : The blood in the aorta that comes 
 from the left ventricle passes, as has been already stated, 
 largely to the head and upper extremities. The blood in the 
 aorta that enters from the ductus arteriosus largely passes into 
 the descending aorta. 
 
 On passing down the descending aorta, some of the blood 
 enters the mesenteric arteries, and thence back to the venous 
 circulation by means of the portal vein and the liver. Some 
 of the blood enters the iliac arteries and nourishes the lower 
 extremities ; but the major part of the blood leaves the foetal 
 body by the hypogastric arteries. The hypogastric arteries 
 are branches of the internal iliacs and course along the abdo- 
 men to leave the foetal body at the umbilicus. On emerging 
 from the umbilicus, the hypogastric arteries change their 
 name, and are now known as the umbilical arteries, and form 
 part of the structure of the umbilical cord on their way to 
 the placenta. 
 
 Effects of arrangement of ftetal circulation : The liver, re- 
 ceiving the freshest blood (from the umbilical vein), is the 
 best nourished of all the organs of the foetus. The result is 
 that the foetal liver is vastly larger in proportion than the 
 adult liver. Also the circulation of the blood is made more 
 perfect, for the branches of the aorta given off to the head 
 and upper extremities distribute blood from the inferior vena 
 cava ; while the ductus arteriosus, carrying the blood from 
 the superior cava and right ventricle, enters the aorta in such 
 a way that most of its blood is sent to the lower extremities 
 and abdominal organs and umbilical arteries. In this way the 
 deoxidized blood is sent back to the placenta for the renewal 
 of its oxygen. The lower extremities are less well developed 
 than the upper. There are probably two reasons for this : (1) 
 the blood is less well aerated and less nutritious ; (2) the in- 
 ternal iliac arteries, giving off the umbilical arteries, probably 
 
296 DEVELOPMENT. 
 
 divert a considerable portion of the blood-supply of the ex- 
 ternal iliacs which go to the lower extremities. 
 
 In addition, we note that, owing to the ductus arteriosus, 
 only a little blood goes to the lung-tissues. The amount is 
 quite sufficient to keep up the nutrition of the lungs, and as 
 they have no function before birth they do not need a la rue 
 blood-supply. 
 
 Change from foetal to adult circulation : The respiratory cen- 
 tre in the medulla, which has been quiescent because it has 
 been sufficiently well supplied with oxygen, is awakened as 
 soon as the connection with the uterine sinuses is interrupted. 
 As soon as the supply of oxygen sinks to a certain point, an 
 impulse of inspiration is generated, and the infant breathes 
 and the lungs assume a condition of partial expansion. With 
 the diminished resistance in the expanded lungs the amount 
 of blood in the pulmonary circulation increases, and, the 
 amount passing through the ductus arteriosus diminishing, 
 this is soon obliterated. At the same time, the blood return- 
 ing to the left auricle increases in quantity, and the intra- 
 auricular pressure is greater; then, too, the inferior venacavu 
 sends less blood, for the ductus venosus no longer carries the 
 blood from the placental circulation, and, therefore, the fora- 
 men ovale is not used, and is soon closed by the adhesion of 
 its valve-like curtain. Thus, we have the adult circulation 
 established in the place of the foetal in consequence of the 
 respiratory movements. 
 
 Also, owing to the division and occlusion of the umbilical 
 cord, blood no longer passes through the umbilical vessels, 
 with the result that the umbilical vein degenerates into a 
 fibrous cord (round ligament of the liver). The hypogastric 
 arteries remain pervious for the first part of their 'course, as 
 the superior vesicle arteries ; but the rest of their course is 
 obliterated ; they degenerate into fibrous cords. 
 
 Development of vertebral column: Early in the development 
 of an embryo there is formed, beneath the medullary groove, 
 in the mesoblast a thin thread of soft cartilage known as 
 the chorda dorsalis, or iwtorhorrf. This soon becomes in- 
 cluded in a sort of fibrous sheath, and is the primary axis 
 
DEVELOPMENT OF THE FACE. 297 
 
 around which the bodies of the vertebrae are developed. On 
 either side of the notochord are developed small centres 
 which subsequently split (mesoblastic somites). These are the 
 protovertebrce. From these are developed the vertebrae and 
 the heads of the ribs by the inner part; and by the outer 
 (or posterior) part the muscles and skin of the back, the 
 epidermis being derived from the epiblast. 
 
 The vertebrae are not formed by direct ossification of the 
 protovertebrse, but they separate in such a way that adjacent 
 protovertebrae each contributes half to the vertebra formed. 
 That is, two protovertebrae form parts of two vertebrae, one 
 above and the other below, and also form a whole vertebrae by 
 their adjacent portions. 
 
 Development of cranium : The cranium is developed from 
 the prolongation of the tissues over the protovertebrae to the 
 cephalic end of the embryo. Here it develops three seg- 
 ments, corresponding to the three primary vesicles which are 
 the forerunners of the brain. These centres of ossification 
 are at the base of the skull, the bones of the vertex being de- 
 veloped from membrane. 
 
 Development of the face : At the head fold of the embryo 
 the mesoblast does not split into two parts, as below, but 
 folds in from the side, covered without and within by the epi- 
 blast and hypoblast. These folds develop certain clefts from 
 which the face is derived, the mesoblast furnishing the bone 
 and muscle structures, and the epiblast the epidermis, while the 
 hypoblast gives the mucous membrane which lines its cavities. 
 
 Immediately below the anterior cranial vesicle there occurs 
 on either side a cleft in the lateral fold of the embryo extend- 
 ing to the vesicle for the eye. In the space of this cleft there 
 is developed a sort of secondary cleavage of the parts, which 
 by the rapid growth of the parts included between the clefts 
 resembles a budding (Fig. 151). It is by the growth of these 
 buds or processes that the outline of the face is formed. From 
 each side sprouts the superior maxillary process, and the proc- 
 esses unite in the median line, and with the nasal or inter- 
 maxillary process from the upper border of the cleft. The 
 portion below is cut off by a branchial cleft, below which is 
 the mandibular process which forms the lower jaw. 
 
298 DEVELOPMENT. 
 
 When the processes do not unite as they should, various 
 defects occur ; most common are those about the mouth viz., 
 cleft palate and hare-lip, by failure of the superior maxillary 
 j n-ix v-.-es to unite or by failure of the intermaxillary process 
 to unite with the maxillary. 
 
 The other branchial clefts do not persist in later life. They 
 become closed as they accomplish their use in developing cer- 
 tain organs: as pathological factors, however, we are often 
 convinced of their non-union or of flaws in their develop- 
 
 FIG. 151. 
 
 Development during first month. 
 
 ment, cysts and tumors of various kinds and certain fistula 
 being attributable to this cause. 
 
 Development of the extremities : They develop as buds from 
 the somatoblast early in foetal life, and the formation of the 
 joints by cleavage, and lesser details of structure are gradu- 
 ally worked out. At about the third month the separation 
 of the fingers and division of the extremity into joints is 
 about completed. The arm develops somewhat in advance 
 of the leg, and grows rather more rapidly in the earlier 
 period of intra-uterine life. 
 
 Formation of the spinal cord: It will be remembered that 
 the medullary canal encloses in its cavity cells from the epi- 
 blast which line it. These cells by proliferation and differ- 
 entiation develop nerve-cells and nerve-fibres, the latter at 
 first not medullated. The cells also gradually close in upon 
 the medullary canal, and form a central lined with epithe- 
 lium, a layer of nerve-cells (gray matter) and a layer of 
 nerve-fibres (white matter). 
 
DEVELOPMENT OF THE BRAIN. 299 
 
 When the spinal cord first appears it fills the entire spinal 
 canal, but at the time of birth the cord has apparently not 
 grown so rapidly as the vertebral column, for it then ends at 
 the third lumbar vertebra, and in the adult it ends at the 
 first. Thus we are able to explain the apparent origin of 
 the spinal nerves above their point of exit from the canal, 
 and the increasing obliquity of the nerves from above 
 down, until finally, in the tuft of vertical nerves below the 
 extremity of the cord, we see the extreme degree of this 
 peculiarity. 
 
 Development of the spinal nerves : The axis-cylinders arise 
 from cells of the epiblast lining the medullary groove. 
 Before the closure of this groove to form the medullary canal 
 an offshoot from the epiblast may be observed, which is the 
 source of the posterior nerve-roots ; and they become attached 
 to the cord as it develops. The anterior roots spring from 
 the cord after it has developed fibres. The two roots then 
 join and the nerve grows out into the mesoblast. 
 
 Development of the cranial nerves : In much the same way 
 the cranial nerves arise primarily, except the nerves of spe- 
 cial sense. In function the motor nerves seem to form a 
 sort of anterior root for the sensory, so that they may be 
 arranged in pairs corresponding to the anterior and pos- 
 terior roots of the spinal nerves ; and it does not seem 
 entirely fanciful to regard their development as somewhat 
 similar, thus : 
 
 Third, fourth, sixth and seventh, motor; fifth, sensory. 
 Twelfth, motor ; ninth, sensory. Eleventh, motor ; tenth, 
 sensory. 
 
 Development of the Brain. 
 
 It has already been shown how from the growth and fusion 
 of the two sides of the primitive medullary groove a tube 
 is formed ; this tube representing the cerebro-spinal axis. 
 Starting with this hollow cylindrical tube, closed at both 
 ends, the spinal cord and brain are formed as a result of 
 changes in the size of the lumen of the tube, alternate thick- 
 enings and thinnings of the walls of the tube, and various 
 foldings and reduplications of the tube on itself. 
 
300 
 
 DEVELOPMENT. 
 
 Earliest rudimentary brain: The first demarcation between 
 brain and spinal cord consists of a widening of the medullary 
 canal at its anterior end. At the same time 
 FIG. 152. this primitive brain is subdivided into three 
 
 portions by two transverse constrictions. 
 The three chambers are known as the an- 
 terior primary vesicle, middle primary vesicle, 
 and posterior primary vesicle (Fig. 152). 
 
 Secondary vesicles : As the result of further 
 development the posterior primary vesicle 
 is subdived into two parts by a transverse 
 constriction. The anterior primary vesicle 
 is also further developed by a forward 
 growth of two projections, one on either 
 side of the median line (hemisphere vesicles, 
 Fig. 153). 
 
 Ventricles of the brain : The various ven- 
 tricles of the brain are the successors of the 
 original lumen of the cerebral axis. Thus 
 we see that the lumen of the prosencephalon 
 is known in the developed brain as the 
 lateral ventricles. The lumen of the thala- 
 mencephalon is the third ventricle, and the 
 communication between the two lateral ventricles and the 
 third ventricle is called the foramen of Monro. The lumen 
 of the mesencephalon (mid-brain) becomes the aqueduct of 
 Sylvius. The cavity of the epencephalon (pons and cere- 
 bellum) and of the metencephalon (medulla) is the fourth 
 ventricle. 
 
 Development of the walls of the cerebral tube : Commensu- 
 rate with the division of the primary brain into its vesicles, 
 there are changes going on in the walls of the tube. These 
 changes consist of thickenings at some parts and thinnings at 
 others. Thus the prosencephalon shows a more or less uni- 
 form increase in thickness, destined to become the substance 
 of the cerebral hemispheres, corpora striata, etc. 
 
 The pons Varolii is a great increase ventrally of the wall 
 halon, while the cerebellum is a corresponding 
 the same vesicle. 
 
 Formation of the ce- 
 rebro-spinal axis. 
 1, anterior primary 
 vesicle ; 2, middle 
 primary vesicle ; 3, 
 posterior primary 
 vesicle. 
 
 3 R A R V 
 
DEVELOPMENT OF WALLS OF CEREBRAL TUBE. 301 
 FIG. 153. 
 
 Anterior primary vesicle. 
 
 Middle primary vesicle. 
 
 Posterior primary vesicle. 
 
 Formation of secondary vesicle, 
 (diencephalon) 
 
 1, 1, prosencephalon ; 
 mesencephalon ; 4, epencephalon ; 5, metencephalon. 
 
 2, thalamencephalon 
 
 I. Anterior 
 primary 
 vesicle. 
 
 II. Middle 
 primary 
 vesicle. 
 
 III. Posterior 
 primary 
 vesicle. 
 
 (Cerebral hemispheres, 
 corpora striata, cor- 
 pus callosum, fornix, 
 lateral ventricles, ol- 
 (^ factory bulb. 
 2. Thalamenceph- f Thalami optici, third 
 
 1. Prosencepha- 
 lon. 
 
 alon. 
 
 \ 
 
 3. Mesencephalon. < ina 
 
 4. Epencephalon. 
 
 5. Metencephalon. 
 
 ventricle,optic nerve. 
 
 Corpora quadrigem- 
 crura cerebri, 
 aqueduct of Sylvius. 
 
 Cerebellum, pons Va- 
 rolii, anterior part of 
 fourth ventricle. 
 
 Medulla oblongata, 
 posterior part of 
 fourth ventricle, au- 
 ditory nerve. 
 
302 DE VELOPMEXT. 
 
 The preceding table enumerates the changes described 
 above. 
 
 The roof of the fourth ventricle, in its lower half, is de- 
 scribed as consisting of but a single layer of epithelial cells. 
 This is a result of a thinning of the dorsal wall of the meten- 
 cephalon. 
 
 Folding of the brain-axis: So far we have described the 
 brain as consisting of a straight tube with various constric- 
 tions and changes in the thickness of its walls. But the de- 
 velopment is not so simple as that. The brain is enclosed in 
 an unyielding box (the skull), which develops and grows at 
 the same time that the brain grows, but not commensurately. 
 The brain tends to grow in the direction of its long axis, but 
 the skull grows as a sphere; hence to accommodate itself to 
 the containing cavity, the brain must fold on itself i. e., coil 
 up. So changes take place, with the result that the cercf>r<tt 
 hemispheres, instead of projecting anteriorly, grow upward 
 and backward so as to overlie the third ventricle. There is 
 also a partial turn at the junction of the mesencephalon and 
 epencephalon. 
 
 Convolutions of cerebrum: The same explanation (different 
 rates of growth of brain and skull) serves to account for the 
 presence of the cerebral convolutions. The surface of the 
 cerebrum is " puckered/' as it were, in order to be squeezed 
 into the skull. 
 
 Development of the eye: About as soon as the cerebral 
 vesicles are distinctly formed a budding of two projections- 
 one from either side of the anterior vesicle occurs. These 
 are the primary optic vesicles. They are formed before the 
 vesicles which make the hemispheres (prosencephalon). The 
 projections approach the external epiblast, and at that period 
 consist of a finger-like process having a globular dilatation 
 at the end. This subsequently forms the optic nerve and the 
 retina. 
 
 Opposite the optic vesicle the superficial epiblast is de- 
 pressed and forms a sort of pit, forcing the optic ve>icle to 
 fold in upon itself. The follicle of epiblast is shut off at the 
 surface, and a ball of its substance left in the cup of the in- 
 
DEVELOPMENT OF THE ALIMENTARY CANAL. 303 
 
 folded optic vesicle. This ball forms the rudimentary lens, 
 and the anterior layer of the vesicle is the retina. 
 
 The muscular and vascular structures, as well as the con- 
 nective tissue and humors, are derived from the mesoblast, 
 which in part enfolds the ocular vesicle and in part enters it 
 between the lens and the edge of the cup-like depression. 
 The cornea is of later formation, and is derived from the 
 epiblast of the skin. 
 
 Development of the auditory apparatus : Very early in the 
 life of an embryo there is a depression on either side of the 
 head which passes through the same process as that men- 
 tioned for the crystalline lens and for the germinal epithelium 
 in the formation of ova. The mass of epiblast thus separated 
 forms the epithelium of the labyrinth and vestibule, the sur- 
 rounding mesoblast furnishing the bony and muscular struct- 
 ures. The auditory nerve is developed with other cranial 
 nerves, and grows in to its end-organs from its central 
 origin. 
 
 Development of the olfactory apparatus : In a similar way 
 to the internal ear and the lens. The nasal fossa is primarily 
 a depression in the superficial epiblast, which widens and 
 deepens and receives the nerve-filaments from the olfactory 
 lobe. This lobe is originally a bud from the prosencephalon. 
 The primary olfactory depression continues to widen until it 
 opens into the mouth, and is again shut oif by the growth of 
 the " branchial arch/' which forms the superior maxilla. 
 The nose is similarly derived from the mesial and lateral 
 nasal processes. 
 
 Development of the alimentary canal : As has already been 
 explained, the primitive alimentary canal is formed from the 
 involution of the splanchnopleure, and is really a portion of 
 the yelk-sac partially shut oif from the rest. It is at each 
 end a blind pouch which follows the head and tail folds. 
 The portions have received the names fore-gut and hind-gut 
 as they occupy one or other of these folds. 
 
 The fore-gut joins with the mouth-cavity by the folding 
 back of the epiblast in the formation of the stomadoeum, and 
 from it are formed the pharynx, oesophagus, and stomach. 
 
 By a similar involution of the epiblast the anus and lower 
 
304 DEVELOPMENT. 
 
 part of the rectum are formed, into which the hind-gut opens 
 to complete the alimentary tract. 
 
 The oesophagus is sometimes impervious at birth, and the 
 rectum or anus may also be imperibrate. This is caused by 
 the non-union of the segments developed from the epiblast 
 with those developed from the hypoblast. 
 
 Glands of the alimentary tract : (1) The salivary glands are 
 developed from the epiblast lining the oral cavity. They a it- 
 pear primarily as a simple tube which develops branches, 
 about which the alveoli are formed. 
 
 (2) The pancreas is similarly developed from the hypoblast 
 of the fore-gut. 
 
 (3) The liver is primarily a protrusion, into a mass of meso- 
 blastic tissue, of the hypoblast of the fore-gut, which appears 
 as soon as the bloodvessels begin to show themselves. The 
 omphalo-mesenteric vein, from the umbilical vesicle, breaks 
 up into a capillary plexus in this same tissue, and the hepatic 
 cells develop about it. 
 
 Derivation of the lungs : The lungs first appear as a bud at 
 the junction of pharynx and oesophagus which soon forms a 
 separate tube (the trachea). The cells from the hypoblast ex- 
 tend into the surrounding mesoblast, and it is from this 
 structure that all of the tissues of the lungs, except its epithe- 
 lium, are formed. 
 
 The Wolffian body is first seen as early as the third week as 
 a series of transverse tubes which develop in the cells of the 
 mesoblast, just inside of its division into parietal and visceral 
 layers, on each side of the vertebral column. It is not a 
 permanent organ. Internal to it develop the internal organs 
 of generation, while behind the Wolffian body the rudimen- 
 tary kidney develops. 
 
 The Wolffian body is a sort of temporary kidney. At first 
 it is a large vascular body, resembling the kidney in structure, 
 and opens by its tubes (outer ends, the inner ends being blind) 
 into the Wolffian duct, which leads to and opens into the 
 cloaca. At about the sixth week of foetal life the kidney 
 begins to grow and the temporary organ to atrophy. As this 
 occurs a duct for the kidney (the ureter) is developed from 
 the Wolffian duct. The use of the organ seems to be that of 
 
PARTURITION. 305 
 
 a temporary kidney ; but by the end of the third month it 
 has been replaced by the permanent organ, and has almost 
 entirely disappeared. 
 
 Formation of the internal genitals : The body (germinal 
 epithelium) which appears on the inner side of the Wolman 
 body is the nucleus of the future testicle or ovary, while along 
 the outer side are formed two ducts (Miiller's and the Wolf- 
 fian), which pass down to the cloaca or lower end of the 
 hind-gut. At first it is impossible to determine the sex of the 
 foetus. 
 
 If the foetus is to become a female, the ducts of Muller 
 join to form the uterus and vagina, while the ununited por- 
 tions remain as the Fallopian tubes. The Wolffian ducts are 
 rudimentary in the female and appear as the ducts of Gart- 
 ner. 
 
 On the other hand, if the male type is to be formed, the 
 Wolffian ducts become convoluted tubules, and each is at- 
 tached to the testis as the epididymis and vas deferens. 
 Miiller's duct is rudimentary in the male, and is only found 
 as the sinus pocularis and the hydatids of Morgagni. 
 
 Formation of external genitals : In both sexes in early foetal 
 life the external genitals are alike, consisting of a body re- 
 sembling a penis with a fold of skin at either side. In the 
 female this body becomes proportionally smaller, and appears 
 as the clitoris, the two lateral masses becoming the labia ma- 
 jora. In the male a groove on the under surface unites at its 
 borders to form the urethra, while the scrotum is formed from 
 the folds of skin at the side. This differentiated condition 
 may persist in adult life, and has been mistaken for hermaph- 
 rodism. 
 
 PARTURITION. 
 
 By parturition is meant the expulsion of the foetus at a 
 viable age from the mother. The average time for the full 
 development of the foetus is given at two hundred and sev- 
 enty-eight days. During this time (period of gestation) the 
 foetus depends absolutely for its existence upon the mother. 
 After parturition the child aerates its blood, ingests food, and 
 purifies its body of wastes for itself,^ 
 
 20-Ph.ys. 
 
306 PARTURITION. 
 
 Method of expulsion of foetus : The foetus is expelled in 
 part by the contraction of the uterine muscles, and in part by 
 the pressure exerted by the abdominal walls. The uteri IK? 
 contractions are the first to appear, and it is not until the 
 foetus enters the vagina that the abdominal muscles are brought 
 into play. 
 
 Causes of uterine contractions : As to this no satisfactory 
 answer has been given. Why the uterus should contain the 
 growing embryo for months, and then be suddenly thrown into 
 action to expel it, cannot be explained. 
 
 Nature of parturition : It is a reflex action depending upon 
 a centre in the lumbar spinal cord. Whence the stimuli are 
 derived which excite the reflex is unknown, but probably 
 from the organ itself. 
 
 Character of uterine contractions : They are rhythmical in 
 character, and may be compared to the contractions of the 
 heart-muscle. Each "pain" begins feebly, gradually in- 
 tensifies until it reaches a maximum, and then gradually de- 
 clines until it entirely dies away, to be succeeded by another 
 similar contraction and pause. This rhythmical action con- 
 tinues until the uterine contents are expelled, and then the 
 organ enters into a condition of tonic contraction. 
 
 After parturition, by a process of involution lasting for a 
 few weeks, the uterus returns to its normal unimpregnated 
 state. 
 
APPENDIX. 
 
 
 TABLE OF THE DEVELOPMENT OF AN EMBRYO. 
 
 (Modified from Gray's Anatomy.) 
 
 1st Week. Ovum in Fallopian tube. Segmentation of vitellus. 
 
 2d Week. Ovum in uterine decidua. Chorion. Formation of 
 blastoderm and division of mesoderm. Heart and medullary groove. 
 Amnion and umbilical vesicle formed. Allantois. 
 
 3d Week. Head and tail flexures. Closure of medullary canal, and 
 formation of primary cerebral vesicles and ocular and auditory vesi- 
 cles. Branchial arches. Wolffian bodies. Limbs. 
 
 4th Week. Limbs increased. Anal opening. Interventricular sep- 
 tum begins. Ant. spinal nerve-roots. Olfactory fossae. Lungs. Pleurae. 
 
 5th Week. Allantois vascular. Trace of feet and hands. Miiller's 
 duct and genital gland. 
 
 6th Week. Umbilical vesicle disused. Branchial clefts close. Post- 
 spinal nerve-roots. Membranes of the nervous centres. Bladder. 
 Kidneys. Tongue. Larynx. 
 
 7th Week. Muscles perceptible. Many centres of ossification appear. 
 
 8th Week. Joints appear in extremities; fingers and toes separate. 
 Crystalline lens. Salivary glands. Spleen. Interventricular septum 
 complete. Sympathetic nerves. 
 
 9th Week. Distinction between ovary and testicle. Genital furrow. 
 Pericardium. 
 
 3d Month. Formation of placenta. External genitals separate from 
 anus. Eyelids, hairs, and nails. Duct of Wolffian body joins testicle. 
 
 Jf,th Month. Middle- ear bones. Tympanum and labyrinth. Scrotum 
 and prepuce. 
 
 5th Month. Germs of teeth. Hair- and sweat-glands. Brunner's 
 glands. Uterus and vagina distinctly separate. 
 
 6th Month. Papillae of skin. Sebaceous glands. Peyer's patches. 
 Free border of nails. 
 
 7th Month. Cerebral convolutions. Pupillary membrane disappears. 
 
 8th Month. Descent of testis. 
 
 9th Month. Opening of eyelids. Ossification of cochlea. 
 
 CHEMICAL TESTS USED COMMONLY IN PHYSIOLOGI- 
 CAL ANALYSIS. 
 
 FOR PROTEIDS : 
 
 Nitric Acid coagulates all except peptones. 
 
 Heat. All are coagulated by boiling, except peptones. 
 
 307 
 
308 APPENDIX. 
 
 XanthojH'Oteic Reaction. A solution boiled with strong nitric acid 
 becomes yellow : the color is deepened by the addition of ammonia. 
 
 Biuret RatHinn. With a trace of copper sulphate and an excess of 
 potassium or sodium hydrate they give a purple reaction. 
 
 Millon's Reaction. With a solution of metallic mercury in strong 
 nitric acid (Millon's reagent) they give a white or pinkish rear lion, 
 and the color becomes more pink on boiling. 
 
 FOR STARCH: 
 
 Iodine Reaction. Add to a solution of starch a small quantity of 
 tincture of iodine, and a blue reaction results. The color disappears 
 on heating and returns on cooling. 
 
 Glycoyen. Same test gives reddish reaction, port-wine color, which 
 disappears on heating and returns on cooling. 
 
 FOR SUGAR (GLUCOSE) : 
 
 Moore's Test. Boil solution of sugar with an excess of potassium 
 hydrate, brown color-reaction. 
 
 Trommer's Test. Add to solution a sufficient amount of potassium 
 hydrate to render it quite strongly alkaline. Then add a solution of 
 copper sulphate, drop by drop, until a distinct blue tinge is visible. 
 Heat, and the presence of sugar is shown by the appearance of red, 
 yellow, or orange color-reaction. 
 
 Fehling's Test Solution. An alkaline copper solution by which a 
 quantitative test may be made. The solution is somewhat unstable, 
 and is for this reason to be tested by boiling before using. The strength 
 of the solution is such that 1 cubic cm. (15 minims) will be exactly 
 decolorized by ^yth of a gramme (.075 grain) of glucose. This test 
 is very delicate, and is quite commonly used for urinary examinations 
 to detect glycosuria. 
 
 The Fermentation Text. If a small quantity of yeast be added to a 
 sugar solution, the fungus of the yeast (saccharomyces) will cause the 
 sugar to be decomposed into carbonic acid and alcohol. If the process 
 be continued until the sugar is entirely broken up, the amount of car- 
 bonic acid evolved indicates the proportion of sugar present. 
 
 FOR BILE-SALTS : 
 
 Pettenkofer's Test. Upon the addition of sulphuric acid to a solution 
 of bile-salts in water there is a precipitation of the salts, which are 
 redissolved by a further addition of the acid. If a drop of a solution 
 of cane-sugar be added, a deep cherry color is developed. 
 
 FOR BILE-PIGMENTS : 
 
 Gmeliii's Test. Add a small quantity of nitroso-nitric acid to a solu- 
 tion of the bile-piirments, and a play of colors result, l>eirmnin<: with 
 green and changing to blue, violet, red, and yellow. This is seen best 
 on a white background ; therefore a plate is often used for this test. 
 
APPENDIX. 309 
 
 METRIC SYSTEM. 
 
 1 Inch 12 ' 3 
 
 1 1 1 1 1 1 1 1 2 i 3 ,4 15 |6 |7 18 |910 
 
 Millimetres. Centimetres. 
 
 Square i 
 
 Centi- ; 
 
 The area of the figure within the heavy lines is 
 that of a square decimetre. A cube one of whose 
 sides is this area is a cubic decimetre or litre. A 
 litre of water at the temperature of 4 C. weighs a 
 kilogramme. 
 
 A litre is 1.76 pint; a pint is 0.568 of a litre. 
 
 The smaller figures in dotted lines represent the 
 areas of a square centimetre and of a squre inch. 
 
 A cubic centimetre of water at 4 C. weighs a 
 gramme. 
 
 Square Inch. 
 
 Metre = 39f inches. 
 Centimetre = f inch. 
 Millimetre = ^ inch. 
 Micromillimetre = ^tjnu inch. 
 
 Gramme = 15^ grains. 
 Centigramme = ^ grain. 
 Milligramme = ^ifo grain. 
 Kilogramme = 2.2 pounds. 
 
INDEX. 
 
 A. 
 
 Absorption, 111-115 
 
 carbohydrates, 113 
 
 destination of food, 113 
 
 fats, 113 
 
 favoring factors, 111 
 
 from stomach, 101 
 
 intestinal, 102 
 
 peptones, 113 
 
 salts, 113 
 
 sites, 111 
 
 sugars, 113 
 
 water, 113 
 
 Accommodation, 250 
 Achromatism, 259 
 Acid, hippuric, 135 
 
 hydrochloric, 97, 98 
 
 uric, 135 
 After-images, 259 
 
 negative, 260 
 
 positive, 260 
 Air, 82-84 
 
 complementary, 83 
 
 expired, 83 
 composition, 33 
 weight, 83 
 
 inspired, 83 
 composition, 83 
 
 reserve, 82 
 
 residual, 83 
 
 tidal, 82 
 
 vitiated, 88 
 Albumin, serum, 114 
 Allantois, 289 
 
 history, 289 
 
 purpose of, 289 
 Am n ion, 288 
 
 fluid, 289 
 
 purpose of, 288 
 Amoeba, 22 
 
 functions, 22, 23 
 Amylopsin, 105 
 Anabolism, 18 
 
 Anaesthesia, 201 
 Animal heat, 140-142 
 loss of, 141 
 regulation of, 141 
 
 centres, 142 
 sources of, 140 
 
 chemical action, 140 
 friction, 141 
 
 oxidation of tissues, 140 
 warm media, 141 
 Aphasia, 201 
 Apncea, 87 
 Apparatus, 23 
 Aqtieductus vestibuli, 237 
 Aqueous humor, 247 
 Area germinativa, 284 
 
 vasculosa, 293 
 Arterial contraction and dilatation 
 
 (see also Arteries), 66 
 tension (see also Arteries), 59 
 Arteries, 54 
 action, 67 
 contraction, 66 
 dilatation, 66 
 elasticity, 58 
 nerve-supply, 67 
 vaso-constricior, 67 
 vaso-dilator, 67 
 resiliency, 56 
 size, 55 
 structure, 54 
 tension, 59 
 
 conditions modifying, 59 
 tone, 67 
 
 vasa vasorum, 54 
 vaso-motor nerves, 54 
 Asphyxia, 87 
 Assimilation, 140 
 Astigmatism, 262 
 
 Atmosphere, vitiated 'see also Air), 88 
 Auditory apparatus, 232 
 canal," 233, 238 
 external, 233 
 internal, 238 
 
 311 
 
312 
 
 INDEX. 
 
 Auditory nerve, 238 
 Auricle, 233 
 
 Auricles of heart, 51 
 
 action, ">1 
 
 regurcitation hindered, 52 
 Axis-cylinder, 159, 160, 161 
 Axons^ 163 
 
 B. 
 
 Bacterium lactis, 121 
 Bile, 106 
 amount, 107 
 character, 107 
 composition, 107 
 pigments, 108 
 
 (imelin's test, 108 
 tests for, 310 
 salts, 107 
 
 Pettenkofer's test, 108 
 test for, 310 
 use of, in digestion, 109 
 Bilirubin, 108 
 Biliverdin, 108 
 Bladder, 129 
 Blastoderm, 284 
 Blastoderm ic membrane, 283 
 Blind-spot, 252 
 Blood, 30-46 
 arterial, 31 
 circulation (see also Circulation of 
 
 blood), 48-70 
 frog's foot, 59 
 coagulation (see also Coagulation of 
 
 blood), 42 
 coagulum, 44 
 buffy-coat, 44 
 corpuscles (see also Corpuscles of 
 
 blood), 32-40 
 plates, 32-40 
 red, 32-38 
 white, 32-38 
 foatal, 290, 291 
 function of, 46 
 uases, 42 
 
 -i IKS appearance, 30 
 lack of oxygen, 87 
 liquor sanguinis, 32 
 maternal. 290, 291 
 opacity, 31 
 
 physical characteristics, 31 
 -plasma, :;_', 40 
 clotting, 41, 42 
 properties, 41 
 
 -plates, 40 
 
 -pivs<mv (>ee also Circulation of 
 \ 57 
 
 Blood, quantity, 32 
 
 reaction, 31 
 
 -serum, 41 
 
 specific gravity, 31 
 
 taste, 31 
 
 venous, 31 
 Body, analysis, 24 
 
 energy of, 138 
 
 expenditures, 138 
 
 results of, 138 
 
 temperature of, 140 
 
 limits, 142 
 Brain (see also Cerebrum), 192 .'<)! 
 
 development, 300-303 
 
 fibres, 197 
 association, 197 
 commissural, 197 
 medullary, 197 
 
 relation of size to intellect, 197 
 
 ventricles of, 301 
 
 weight, 197 
 
 Branchial cleft, 298, 299 
 Bronchi, 77 
 
 c. 
 
 Canal is cochlearis, 237 
 
 reunions, 237 
 Capillaries, 54 
 Carbohydrates, 29, 30, 113 
 Cells, 18-24 
 
 blood (see also Blood), 23 
 
 connective tissue, 24 
 
 decay, 21 
 
 development, 21 
 
 endothelium, 24 
 
 epithelium, 23 
 varieties, 23, 24 
 
 gemmation, 20 
 
 karyokinesis, 20 
 
 nerve, (see also Nervous system', 23 
 
 nucleolus, 19 
 
 nucleus, 19 
 
 protoplasm, 19-22 
 difference between plants and 
 animals, 23 
 
 specialization, 23 
 
 structure, 18 
 Centimetre, 311 
 Centres (see ^/limil cord, Mlull<i ub- 
 
 lo-ngata, and Cerebrum). 
 Cerebellum, 201-203 
 
 function. 203 
 
 gray matter, 201, 202 
 
 peduncles, 201 
 
 removal of, 205 
 Cerebro-spinal system, 169, 174-220 
 
INDEX. 
 
 313 
 
 Cerebrum, 192-201 
 
 chemistry of brain-tissue, 196 
 convolutions, 193 
 cortex, 196 
 functions, 198 
 
 localization of, 199, 200 
 centres of special senses, 199 
 motor areas, 199 
 sensory areas, 199 
 gray matter, 195 
 lesions, 204 
 lobes, 193, 194 
 mutilations, 204, 206 
 regions, 193 
 surface, 193 
 unilateral action, 199 
 Chlorophyl, 27 
 Cholesterine, 109 
 Chorda tympani (see also Cranial 
 
 nerves), 213 
 Chorion, 289 
 
 association with decidua, 290 
 villi, 289 
 Choroid, 246, 259 
 pigment of, 259 
 Chyle, 47 
 Chyme, 100, 111 
 Ciliary muscle, 247 
 Circulation of the blood, 48-70 
 apparatus, 48 
 
 arteries (see also Arteries), 48 
 capillaries (see also Capillaries), 49 
 heart (see also Heart), 48 
 veins (see also Veins), 49 
 blood-pressure, 57 
 in arteries, 58 
 continuous, 58 
 intermittent, 58 
 small, 58 
 in capillaries, 58 
 manometers, 57 
 in veins, 58 
 course, 49 
 aorta. 49 
 arteries, 49 
 capillaries, 49 
 left auricle, 49 
 left ventricle, 49 
 pulmonary arteries, 50 
 
 veins, 49 
 right auricle, 49 
 veins, 49 
 foetal, 252 
 
 change from, to adult, 295 
 course, 294 
 effects of, 294 
 
 I Circulation, forces, 56 
 
 arterial resiliency, 56 
 contraction of muscles, 56 
 
 of veins, 57 
 heart, 56 
 suction, cardiac, 56 
 
 thoracic, 56, 69 
 placenta, 292 
 
 characteristics, 294 
 portal, 50 
 pulmonary, 50 
 speed, 57 
 
 in arteries, 57 
 in capillaries, 57 
 in veins, 57 
 
 ratio between, and pressure, 57 
 systemic, 50 
 vitelline, 292 
 Climacteric, 275 
 Coagulation of blood, 42-45 
 conditions affecting, 43 
 hastening, 43 
 air, 43 
 
 foreign bodies, 43 
 rest, 43 
 warmth, 43 
 water, 43 
 retarding, 43 
 acids, 43 
 agitation, 43 
 alkalies, 43 
 cold, 43 
 ferments, 43 
 heat, 43 
 
 living tissues, 43 
 no air, 43 
 salts, 43 
 
 viscid substances, 43 
 water, 43 
 corpuscles, 43 
 explanation, 44 
 fibrin, 43 
 plasma, 43 
 serum, 43 
 
 Cochlea, 235, 236-238 
 Coitus, 281 
 Collaterals, 175 
 Color-blindness, 262 
 causes, 264 
 
 in different sexes, 264 
 importance of, 265 
 test for, 265 
 
 Color-perception, 259, 262 
 normal, 262 
 
 theories of, 262, 263 
 Colostrum, 120 
 
314 
 
 INDEX. 
 
 Colostrum corpuscles, 120 
 Commissure of Gudden, 255 
 Cones, 251 
 
 Connective tissue, 24 
 Contractions, uterine (see also Uterus, 
 
 ('infractions of), 307 
 Coordination, 184 
 Copulation, 269 
 Cornea, 245, 246 
 Corpora quadrigemina, 191, 192 
 
 striata, 196, 198 
 Corpus callosum, 192 
 lut i-ii in. 277 
 of menstruation, 277 
 of pregnancy, 277 
 Corpuscles of blood, 32-40, 59 
 Pacinian, 164 
 plates, 32, 40 
 red, 32-38 
 color, 33 
 diapedesis, 37 
 function, 35 
 globulin, 35, 36 
 hsematin, 35, 36 
 hsemin, 35, 36 
 haemoglobin, 35, 37 
 oxy-, 37 
 reduced, 37 
 spectra, 37, 38 
 number, 32 
 origin, 34 
 
 physical characteristics, 32, 33 
 specific gravity, 33 
 of vertebrates, 33 
 touch, 164 
 
 white (see also Leukocytes), 38-40 
 Corti, organ of, 238 
 
 rods of, 238 
 Cranial nerves, 206-220 
 
 I. nerve (see also Nerve, olfactory), 
 
 230 
 
 II. nerve (see also Nerve, optic), 253 
 
 III. nerve, 207 
 function, 207 
 origin, 207 
 
 IV. nerve, 208 
 function, 208 
 origin, 208 
 
 portio dura, 2] 2 
 portio moll is, 212 
 trochlear, 208 
 
 V. nerve, 208 
 origin, 208 
 route, 208 
 
 motor, 208 
 sensory, 208, 209 
 
 Cranial nerves, V. nerve, sensory route, 
 
 trophic influence, 211 
 influence on special senses, 211 
 
 VI. nerve, 211 
 
 VII. nerve, 212 
 chorda tyrupani, 213 
 
 eflect on taste, 214 
 
 secretion, 213 
 distribution, 213 
 function, 213 
 origin, 212 
 paralysis of, 213 
 
 VIII. nerve (see also Nerve, audi- 
 tory), 238 
 
 IX. nerve, 215 
 function, 215 
 
 deglutition, 215 
 taste, 215 
 origin, 215 
 
 X. nerve, 216 
 communication with other nerves, 
 
 216 
 
 in deglutition, 218 
 distribution, 216 
 function, 217, 218, 219 
 influence on heart, 218 
 origin, 216 
 
 relation to stomach, 218 
 in respiration, 86, 87, 217 
 
 XI. nerve, 219 
 functions, 219 
 
 holding breath, 219 
 voice, 219 
 origin, 219 
 
 XII. nerve, 220 
 functions, 220 
 
 indigestion, 220 
 
 speech, 220 
 origin, 220 
 Cream, 120 
 Cristse acusticse, 236 
 Crura cerebri, 191, 192 
 Crystalline lens, 247 
 Cumulus proligerus, 271 
 
 D. 
 
 Decidua nienstrualis, 276, 284 
 
 reflexa, 284 
 
 vera, 284 
 Decimetre, cubic, 311 
 
 square, 311 
 Defecation, 110 
 
 centre, 183 
 Defective eyes, 260 
 Definition of physiology, 17 
 
INDEX. 
 
 315 
 
 Deglutition, 94 
 actions of, 94 
 nerves in, 94 
 Deiidrites, 162 
 Development, 283-307 
 alimentary canal, 304 
 auditory apparatus, 304 
 of brain, 300-303 
 of circulatory apparatus, 293 
 of cranial nerves, 300 
 of cranium, 298 
 of extremities, 299 
 of eye, 303 
 of face, 298 
 of genitals, 306 
 
 internal, 306 
 
 external, 306 
 of heart, 293 
 of kidney, 305 
 of liver, 305 
 of lungs, 305 
 
 of olfactory apparatus, 304 
 of ovary, 306 
 of pancreas, 305 
 of salivary glands, 305 
 of spinal cord, 299 
 of spinal nerves, 300 
 of testicle, 306 
 of ureter, 305 
 of uterus, 306 
 vagina, 306 
 
 of vertebral column, 297 
 Dextrose, 114 
 Dialysis, 111 
 
 Diastole (see also Heart), 61 
 blood-supply, 63 
 force, 63 
 inner vation, 65 
 
 accelerator, 66 
 
 depressor, 66 
 
 ganglia, 65 
 
 inhibitory, 65 
 
 sympathetic, 66 
 
 vagus, 65 
 sounds, 62 
 
 first, 63 
 
 second, 63 
 systole 
 
 auricular, 61 
 
 ventricular, 61 
 Diet, 138, 139 
 "exclusive," 138 
 normal, 139 
 over-feeding, 139 
 Digestion, 90-108, 111 
 gastric (see also Gastric digestion), 100 
 
 Digestion, intestinal, 101 
 
 large intestine, 110 
 
 pancreatic, 106 
 
 products of, 113 
 Diplopia, 262 
 Discus proligerus, 271 
 Distance, 240 
 Drink, 137 
 Duct, 
 
 Gartner's, 305 
 
 Miiller's, 305 
 
 Wolflian, 306 
 Due bus arteriosus, 295 
 
 endolyniphaticus, 237 
 
 venosus, 294 
 Dyspnoea, 87 
 
 E. 
 
 Ear, 232 
 
 external, 232, 233 
 
 internal, 232, 235 
 
 middle, 232, 233 
 Elimination, channels of, 18 
 Embryo, development of, 309 
 Embryology, 267-307 
 Emulsification, 105 
 Encephalon, 301, 302 
 
 ep-, 302 
 
 nies, 302 
 
 met-, 302 
 
 pros-, 302 
 
 thalam-, 302 
 Eudolymph, 235, 239 
 Endothelium, 24 
 End-plates, 163. 
 Epiblast, 285 
 
 structures derived from, 286 
 Epididymis, 279 
 Epithelium, 23, 24 
 
 germinal, 271 
 
 varieties, 23, 24 
 Equilibrium, 236 
 Eustachian tube, 233, 235 
 
 valve, 295 
 Excretion, 115, 137 
 
 process of, 115 
 
 Expiration (see also Respiration), 81 
 Eye, 243, 245 
 
 accessory regions, 243 
 Eyeball, 245 
 
 coats of, 245 
 choroid, 246 
 cornea, 245, 246 
 retina, 246 
 sclerotic, 246 
 
 development, 303 
 
316 
 
 INDEX. 
 
 Eyeball, eminetropic, 260 
 function, 243 
 lids, 244 
 muscles of, 244 
 
 F. 
 
 Facial neuralgia, 211 
 
 paralysis, 213 
 Fallopian tubes, 273 
 
 function, 273 
 Fats, 29, 30, 113 
 Fecundation, 2<>9, 281 
 Fenestra oval is, 233 
 
 rotunda, 233 
 
 Ferments, pancreatic, 105 
 Fertilization, methods, 281 
 Fibrin, 44 
 
 ferment, 44 
 Fibrinogen, 40, 41, 44 
 Foatal circulation (see also Circulation, 
 
 festal), 292 
 
 Foetus, expulsion, 307 
 Folds, 285, 298 
 Food, 137 
 Food-stuffs, 30 
 
 carbohydrates, 29, 30 
 
 fats, 29, 30 
 
 proteids, 28, 30 
 Foramen ovale, 295 
 Fovea centralis, 252 
 Funiculus cuneatus, 187 
 
 gracilis, 187 
 
 G. 
 
 Gall (see also Bile), 106 
 -bladder, 106 
 -ducts, 106 
 
 Ganglia of sympathetic (see also Sym- 
 pathetic system}, 171, 172 
 Ganglion, 171 
 cervical, 172 
 cceliac, 172 
 impar, 172 
 ophthalmic, 171 
 otic, 171 
 semi lunar, 172 
 spheno-palatine, 171 
 submaxillary, 171 
 thoracic, 172 
 (iasrs in blood, 42 
 
 carbon dioxide, 42 
 nitrogen, 42 
 oxygen, 42 
 Gastric digestion, 100 
 
 conditions favoring, 100 
 
 Gastric digestion, nervous mechanism, 
 
 100 
 
 time required, 100 
 juice, 97 
 
 composition, 97 
 functions, 98 
 secretions, 98 
 Gelatins, 28 
 Gemmation, 20 
 Generation, asexual, 268 
 organs of, 269, 278 
 female, 269-278 
 male, 278-280 
 Geniculate bodies, 255 
 Germ-hill. 271 
 
 Germinal epithelium, 271, 300 
 membrane, 283 
 spot, 273 
 vesicle, 273 
 Gestation, 306 
 Glands, ductless. 135 
 
 purpose of, 136 
 of intestine (see also Intestine), 102- 
 
 104 
 
 lachrymal, 244 
 mammary (see also Mammary glands), 
 
 119 
 
 Meibomian, 244 
 prostate, 280 
 sebaceous, 122 
 sweat, 122 
 vascular, 135 
 Glandular activity, 117 
 
 conditions affecting, 117 
 amount of blood, 117 
 
 of material, 117 
 nervous system, 117 
 Glosso-labio-laryngeal paralysis, 191 
 Glottis, 241 
 Glycogen. 110, 114 
 
 in muscle, 145 
 Graafian follicle, 270 
 
 maturation of, 271 
 Gramme, 311 
 Gustatory-buds, 227 
 Gut, fore', 304 
 hind, 304 
 
 H. 
 
 Hair, 124 
 
 -follicle, 124 
 Hallucinations, 221 
 11. a ring, 232-241 
 
 c.-ntre, 199 
 
 localization, 199, 240 
 
 musical range of, ~ 1 1 
 
INDEX. 
 
 317 
 
 Hearing, subjective, 240 
 Heart, 51-54, 61 
 
 action, 61 
 
 apparent elongation, 61 
 
 auricles, 51 
 
 beat, 61 
 diastole, 61 
 systole, 61 
 
 cardiac cycle, 62 
 
 development of, 293 
 
 rate, 61 
 
 situation, 51 
 
 size, 51 
 
 ventricles, 51 
 
 weight, 51 
 Heat, animal (see also Animal 
 
 140-142 
 Hemiansesthesia, 201 
 Hemiplegia, 201 
 Hemispheres of cerebellum, 201 
 
 of cerebrum, 192 
 Heredity, 267 
 Hippuric acid, 135 
 Hymen, 274 
 Hypermetropia, 261 
 Hyperpnoea, 87 
 Hypoblast, 285 
 
 structures derived from, 287 
 
 I. 
 
 Impregnation, 281 
 details, 282 
 site of, 282, 283 
 time of, 282 
 Incus, 234 
 Inhibition, 185-189 
 Insalivation, 92 
 Inspiration (see also Respiration), 
 
 81 
 
 Intestine, juice, 104 
 large, 110 
 
 absorption, 110 
 digestion, 110 
 structure, 110 
 peristaltic action, 102-111 
 small, 101-104 
 glands, 102-104 
 agminate, 104 
 Bru nner's, 103 
 Lieberkiihn's, 103 
 Peyer's, 103 
 solitary, 103 
 Iris, 248, 259 
 
 78- 
 
 Judgments, 222 
 
 J. 
 
 K. 
 
 Caryokinesis, 20 
 Catabolism, 18 
 Kidneys, 126-135 
 blood-supply, 128 
 arteries, 129 
 afferent, 129 
 arterise rectse, 129 
 iuterlobular, 129 
 veins, 129 
 efferent, 129 
 interlobular, 129 
 venae rectse, 129 
 cortical portion, 127 
 medullary portion, 127 
 size, 126 
 weight, 127 
 
 L. 
 
 Labyrinth, bony, 235 
 
 membranous, 235 
 Lacteals, 70-113 
 ^actose, 121 
 Lamina spiral is, 236 
 Larynx, 76, 241 
 
 lesions in brain and cord, 203, 204 
 Leukocytes, 38-40 ; 46, 59 
 characteristics, 38 
 chemical composition, 39 
 death, 40 
 function, 40 
 emigration, 38, 60 
 phagocytosis, 40 
 number, 32 
 occurrence, 38 
 origin, 39 
 varieties, 39 
 lymphocytes, 39 
 mononuclear, 39 
 polynuclear, 39 
 Life, 17 
 
 living body compared to machine, 17 
 Litre, 311 
 Liver, 106-110 
 functions, 106 
 
 elaboration of urea, 106, 110 
 excretion, 106, 109 
 glycogenic, 106, 109 
 secretion, 106 
 Lochia, 292 
 Lungs, 77 
 
 capacity of, 82 
 minute anatomy, 77 
 Lymph, 46-48 
 
318 
 
 INDEX. 
 
 Lymph coagulation, 47 
 chyle, 47 
 circulation, 70 
 composition, 46 
 flow, 70 
 
 factors in, 73 
 ganglia, 73 
 pressure, 72 
 
 Lymph spaces, 46, 70, 113 
 sources, 47, 72 
 
 intercellular spaces, 47 
 lacteals, 47 
 uses, 47 
 Lymphatic nodes, 73 
 
 purpose, 74 
 Lymphatics, 70 
 structure, 72 
 Lymphocytes, 39 
 
 M. 
 
 Macula acustica, 236 
 
 lutea, 252 
 Malleus, 234 
 Malpighian bodies, 127 
 Mammary glands, 119 
 secretion, 119 
 structure, 119 
 alveoli, 119 
 lobes, 119 
 lobules, 119 
 Mastication, 90 
 
 muscles, 92 
 Mastoid cells, 233 
 Medulla oblongata, 185-191 
 automatic action, 189 
 centres, 189 
 conduction, 188 
 function, 188-190 
 gray matter, 187 
 gross anatomy, 185 
 inhibition, 189 
 reflex action, 188 
 Medullary canal, 299 
 groove, 285 
 sheath, 159, 160 
 Membrana basilaris, 237 
 
 tympani, 234 
 
 Membrane, blastodermic, 283 
 germinal, 283 
 of Reissner, 237 
 vitelline, 272 
 Menopause, 275 
 Menstruation, 274 
 connection with ovulation, 278 
 corpus luteum of, 278 
 
 Menstruation, definition, 274 
 discharge, 276 
 duration, 275 
 frequency of, 275 
 nature, 275 
 Mesoblast, 285 
 changes in, 286 
 structures derived from, 286 
 Metabolism, 18 
 Metric system, 311 
 Microcytes, 40 
 Micturition, 133 
 Milk, 119 
 
 composition, 119 
 secretion, 120 
 Mouth, 90 
 Mucin, 118 
 Mucus, 118 
 Muller's duct, 306 
 Muscle, 142-159 
 chemistry of, 144 
 conductivity, 155 
 contractility, 148, 149 
 contraction, 148 
 artificial stimuli, 150 
 chemical, 150 
 
 electrical, 150, 151, 152, 153 
 mechanical, 150 
 response to, 151 
 thermal, 150 
 path of stimulus, 148 
 Pfliiger's law. !."> 
 results of, 157 
 currents, ascending, 156 
 descending, 156 
 of rest, 1 "> 1 
 electrical state, 154 
 excitability, 155 
 fatigue, 147 
 general properties, 144 
 latent period, 147, 152 
 apparent, 147 
 true, 147 
 as levers, 146 
 nerve-muscle preparation. 157 
 
 conditions influencing results, 
 
 157 
 
 order of fatigue, 157 
 oxygen-supply, 1 1<> 
 physiology of, 145 
 activity, 145 
 rest, 145 
 rigor, 145 
 plasma, 144 
 varieties, 142 
 non-striated, 142 
 
INDEX. 
 
 319 
 
 Muscle, varieties, striated, 142 
 involuntary, 142, 144 
 voluntary, 142, 143 
 Mutilations, 204, 205 
 
 brain, 204 
 
 cerebellum, 204 
 
 cord, 204 
 Myopia, 260 
 Myosin, 144 
 Myosinogen, 144 
 
 N. 
 
 Nails, 124 
 matrix, 124 
 root, 124 
 Nasal cavity, 231 
 Near-point, 260 
 Nerve-cells, 159, 162, 175 
 ganglia, 159, 162 
 salivary secretion, 93 
 -degeneration, 167, 177 
 
 histologies! changes, 168 
 -endings, 163 
 
 efferent nerves, 163 
 sensory nerves, 163 
 -fibres, 159 
 
 centrifugal, 162 
 centripetal, 162 
 function, 161 
 of hemispheres, 197 
 rnedullated, 159 
 motor, 179, 203 
 non-medullated, 159, 161 
 of Eemak, 161 
 sensory, 179, 204 
 of sympathetic, 169 
 -impulse, 165 
 direction of, 166 
 
 experiments, 166 
 nature of, 165 
 olfactory, 230 
 origin, 230 
 speed of, 167 
 -regeneration, 168 
 -roots, 174, 176 
 anterior, 174, 176 
 
 course, 176 
 
 degeneration, 167, 177 
 posterior, 174, 176 
 
 course, 176 
 trophic centres, 177 
 -trunks, 161 
 
 vaso-motor, 66, 173 
 Nerves, auditory, 238 
 centres, 199 
 
 Nerves, cranial (see also Cranial nerves), 
 
 206 
 
 nuclei of, 188 
 nucleus, 238 
 optic, 253 
 
 fibres of, 251, 253 
 pneumogastric, in respiration, 86,217 
 
 section of, 87 
 spinal, 174 
 roots, 174 
 
 Nervous system, 159-220 
 Neurilemma, 159, 160 
 Neuroglia, 175 
 Neuron, 164 
 
 Nitrogen in atmosphere, 84 
 Nitrogenous equilibrium, Io9 
 Nodes of Eanvier. 160 
 Nose, 231 
 Nutrition, 136-138 
 
 o. 
 
 Odors, 229 
 Olfactory bulb, 231 
 
 cells, 230 
 
 nerves, 230 
 
 tract, 231 
 
 Olivary bodies, 187 
 Optagrams, 258 
 Optic chiasm, 253 
 
 nerve (see also Nerves, optic), 253 
 radiations, 253 
 
 thalamus, 196, 198 
 
 tracts, 253 
 Organ of Corti, 238 
 Organs, 23 
 Osmosis, 111 
 Ossicles, 234 
 Ovaries, 270 
 
 Graafian follicles, 270 
 
 strom a, 270 
 Ovulation, 276 
 
 connection with menstruation, 278 
 
 frequency of, 276 
 Ovum, 271, 282 
 
 constriction, 285 
 
 unimpregnated, 276 
 
 history of, 276 
 Oxidation, 18 
 Oxygen, 137 
 
 P. 
 
 Pacinian corpuscle, 164 
 Pain, 181, 221 
 Pancreas, 104 
 
320 
 
 INDEX. 
 
 Pancreas, juice, 104 
 composition, 105 
 function, 106 
 Paraglobulin, 41, 44 
 Paraplegia, 201 
 Parturition. :soi> 
 
 nature, 307 
 
 time, 306 
 Penis, 280 
 
 erectile tissue, 281 
 
 glans, 280 
 Pepsin, 97, 98, 105 
 Pepsinogen, 98 
 Peptones, 91). li:; 
 Perceptions, 222 
 
 visual, 257 
 
 mental processes of, 257 
 Perilymph, 235, 239 
 Perspiration, 122, 124 
 
 amount. 1 -.'."> 
 
 insensible, 125 
 
 necessity, 126 
 
 nervous mechanism, 125 
 
 odor, 125 
 
 purpose, 125 
 Placenta, 290 
 
 appearance of, 292 
 
 destiny of, 291 
 
 foetal, 290 
 
 layers of cells, 290 
 
 maternal, 290 
 
 period of formation, 292 
 Place ntal circulation (sec also Circula- 
 tion, plnceutal), 292, 294 
 Plasma, 40 
 
 of muscle, 144 
 Pleura, 77 
 Plexus, pelvic, 172 
 
 solar, 172 
 Polar body, 277 
 Pons Varolii, 191 
 Presbyopia, 261 
 Primitive groove, 285 
 
 trace, 2S4 
 Processes, intermaxillary, 299 
 
 maxillary, _'!>!> 
 Pronucleus, female, 277 
 
 malr, 282 
 
 Prostate gland, 280 
 Proteids, 28, 30 
 
 albumins, 28 
 
 fibrin, 28 
 
 globulins, 28 
 
 peptones, 28 
 
 t<-sts for, 309 
 Proteolytic action, 99 
 
 Protoplasm, 19, 22 
 Protovertebne, 298 
 Proximate principles, 25-29 
 inorganic, 25, 26 
 distribution, 26 
 uses, 26 
 organic, 25 
 list of, 28, 29 
 nitrogenous, 27, 28 
 non-nitrogenous, 27, 28 
 source, 27 
 uses, 27 
 Puberty, 274 
 Pulse, 68-70 
 extinction, 69 
 sphygmograph, 68 
 
 tracings, (>9 
 varieties, 68 
 venous, 54, 69 
 
 Pyramidal tracts, 177, 186, 203 
 crossed, 1S6, 203 
 direct, 186, 203 
 Pyramids of medulla, 186 
 
 B. 
 
 Reflex action of cord, 181, 182 
 
 of medulla, 188 
 Refraction (eye), 248, 249 
 Rennin, 121 
 Reproduction, 267-283 
 methods of, 267 
 
 asexual, 2(>S 
 
 sexual, 268, 269 
 theory of, 268 
 Respiration. 75-90 
 abdominal, 80 
 act of, 75 
 
 associated movements, 82 
 automatic impulses, 86 
 centres, 86 
 
 synchronism of, 87 
 effects of, on circulation, 88 
 expiration, 81 
 
 muscles, 81 
 external, 84 
 force of, 83 
 forced, 81 
 frequency, 82 
 inspiration, 78-81 
 
 muscles, 78 
 internal. >.", 
 movements. 75 
 nerves, 86 
 
 nervous mechanism, 85 
 reflex influences, 85 
 
INDEX. 
 
 321 
 
 Respiration sounds, 82 
 special acts, 89 
 sighing, 89 
 sneezing, 89 
 laughing, etc., 90 
 thoracic, 80 
 tract, 75 
 
 Kestiform body, 187 
 Retina, 246, 250, 259 
 inversion of image, 25(5 
 pigment of, 259 
 Retinal red, 257 
 
 reflex, 258 
 Rigor mortis, 158 
 causes of, 159 
 disappearance of, 159 
 Rima glottidis, 241 
 Rods, 251 
 
 8. 
 
 Saccule, 237 
 Saliva, 92 
 mixed, 92 
 secretion, 93 
 
 chorda tympani, 93 
 nerve-control, 93 
 Saponification, 105 
 Scala media, 237 
 tympani, 236 
 vestibuli, 236 
 Sclera, 246 
 Sebaceous glands, 122 
 
 secretion, 125 
 Secreting glands, 116 
 racemose, 116 
 tubular, 116 
 Secretion, 115-136 
 correlation, 118 
 discharge of, 117 
 milk, 120 
 mucous, 118 
 mucus, 118 
 processes of, 115, 116 
 chemical, 117 
 physical, 116 
 serous, 118 
 
 peritoneum, 118 
 pleura. 118 
 table of, 136 
 Segmentation, 283 
 
 nucleus, 283 
 Semicircular canals, 235 
 Seminal cells, 279 
 
 vesicles, 280 
 Seminiferous tubules, 279 
 
 21 Phys. 
 
 Sensations, centres, 199 
 classification, 221 
 common, 221 
 organs necessary for, 220 
 pressure, 224 
 special, 221 
 visual, 256 
 
 duration of, 256 
 Senses, the, 220-265 
 nerves of, 222 
 seat of, 221 
 special, 222 
 muscle, 224 
 
 centre, 225 
 temperature, 225 
 Sense-organs, 163 
 
 Pacinian corpuscles, 164 
 touch-corpuscles, 164 
 Sensibility, tactile, 224 
 
 variations, 224 
 Serum, 41, 118 
 -albumin, 41 
 Sight, 243-265 
 Skin, 121-124 
 absorption by, 126 
 corium, 121, 122 
 cuticle, 121 
 cutis vera, 121, 122 
 derma, 121, 122 
 epidermis, 121 
 papillae, 122 
 Smell, 229-232 
 acuteness, 232 
 conditions for, 229 
 Sneezing, 232 
 Sodium glycocholate, 107 
 
 taurocholate, 107 
 Somatopleure, 286, 288 
 Somites, mesoblastic, 298 
 Sound-waves, 239 
 
 course of, 239 
 Species, 267 
 Speech, 241 
 articulate, 242 
 
 organs used in, 242 
 centre, 199 
 Spermatozoa, 279 
 Spermatozoon, 281, 282 
 Sphygmograph, 68 
 Spinal cord, 174-185 
 augmentation, 184 
 automatic acts, 184 
 columns, 175, 186 
 anterior, 186 
 lateral, 187 
 posterior, 187 
 
322 
 
 INDEX. 
 
 Spinal cord, coordination, 184 
 enlargements, 177 
 functions, 178 
 
 conduction, 178 
 gray matter, 175 
 gross anatomy, 174 
 lesions, 203 
 
 microscopic examination, 175 
 mutilations, 204 
 recurrent-sensibility fibres, 177 
 reflex action, 181, 182 
 
 special reflexes, 182 
 transference, 181 
 white substance, 175 
 Splanchnopleure, 286, 287, 288 
 Spleen, 136 
 Stapes, 234 
 Starch, tests for, 310 
 Starvation, 138 
 Steapsin, 105 
 Stercobilin, 109 
 Stercorin, 109 
 Stereoscope, 256 
 Stomach, 94-99 
 
 absorption from, 101 
 
 capacity, 100 
 
 digestion, gastric (see also Gastric 
 
 digestion), 100 
 after death, 101 
 glands, 96 
 peptic, 96 
 pyloric, 96, 97 
 muscular action, 99 
 structure, 94 
 Stomata, 71 
 Strabismus, 262 
 external, 262 
 internal, 262 
 Succus entericus, 104 
 Sugar, test for, 310 
 Sweat, 122, 124 
 
 -glands, 122 
 
 Sympathetic system, 169-173 
 function, 173 
 ganglia, 169, 171-172 
 abdominal, 172 
 cephalic, 171 
 cervical, 172 
 thoracic, 172 
 
 relation to secreting glands, 173 
 sensory and motor influence, 173 
 vaso-motor fibres, 173 
 Systole (see also Heart), 61 
 
 Taste, ir>-J 
 
 T. 
 
 Taste, after-, 229 
 
 a.-v-MH-iatioi! with smell, 228 
 
 -goblets, 227 
 
 necessary conditions for, 225 
 
 origin of, 226 
 Teeth, 91 
 
 permanent, 91 
 
 temporary, 91 
 Temperature of body, 140 
 
 srii>ations, 181 
 Testicles, 279 
 
 tubules, 279 
 
 tunica albuginea, 279 
 Thoracic duct, 70, 114 
 Thymus, 136 
 Thyroid, 136 
 Tic douloureux, 211 
 Tissue, 23 
 Tongue, 90, 226 
 
 papillae, 226 
 
 sensibility, 229 
 
 taste-goblets, 227 
 
 touch, 227 
 
 varieties, 226 
 Tonsils, 136 
 Tooth, 91 
 
 cavity, 92 
 
 cement, 92 
 
 crown, 91 
 
 crusta petrosa, 92 
 
 dentine, 92 
 
 enamel, 92 
 
 fang, 91 
 
 neck, 91 
 
 pulp, 92 
 Touch, 181, 222-225 
 
 acuteness of, 223 
 measure of, 223 
 
 corpuscles, 164 
 
 organ of, 222 
 
 varieties of, 223 
 Trachea, 76 
 Tracts, 203, 204 
 
 motor, 203 
 lesions, 203, 204 
 
 sensory, 204 
 Trypsin, 105 
 Tympanum, 233 
 
 membrane, 233, 234 
 
 u. 
 
 Umbilical arteries, 291, 296, 297 
 cord, 291 
 veins, 291 
 vesicle, 287 
 
INDEX. 
 
 323 
 
 Urea, 134 
 amount, 135 
 as a waste, 135 
 Ureters, 129 
 pelvic, 129 
 Urethra, 280 
 Uric acid, 135 
 Urine, 129 
 acidity, 131 
 
 acid sodium phosphate, 131 
 amount, 131 
 coloring-matter, 130 
 composition, 130 
 course in tubules, 133 
 estimation of solids, 135 
 properties, 129 
 secretion, 130 
 
 conditions affecting, 132 
 epithelial action, 130 
 nitration, 130 
 
 relation to arterial pressure, 132 
 Uriniferous tubules, 127 
 
 course, 127 
 Uterine sinuses, 290 
 Uterus, 273 
 
 contractions of, 307 
 causes, 307 
 characters of, 307 
 Utricle, 237 
 
 V. 
 
 Valves of heart, 53 
 
 of veins, 55 
 
 Valvulse conniventes, 102, 111 
 Vas defereus, 279 
 Veins, 55 
 
 contraction, 57 
 
 pulsation of jngular, 54 
 
 size, 56 
 
 structure, 55 
 
 Veins, valves, 55 
 
 Ventricle, fourth, floor of, 188 
 
 of heart, 51, 52 
 action, 52 
 
 lateral, 193 
 Vesicles, primary, 301, 302 
 
 secondary, 301, 302 
 Vestibule, 235, 237 
 Villi, 111, 112 
 
 structure, 112 
 Vision, area of most acute, 252 
 
 binocular, 255 
 
 centre for, 199 
 
 clearness, 257 
 
 nervous mechanism of, 255 
 Vitelline duct, 287 
 
 membrane, 272 
 Vitellus, 273, 287 
 Vitreous humor, 248 
 Vocal cords, 241 
 Voice, 241 
 
 musical range of, 242 
 
 production, 241 
 Vomiting, 101 
 
 w. 
 
 Waste-products, 18 
 Whartou's jelly, 291 
 Wolffian body, 305 
 duct, 305 
 
 Y. 
 
 Yolk-sac, 287, 292 
 
 Z. 
 
 Zona pellucida, 272 
 Zymogen, 104 
 
CATALOGUE OF PUBLICATIONS OF 
 
 LEA BROTHERS & COMPANY, 
 
 706, 708 & 710 Saiisom St., Philadelphia. 
 Ill Fifth Ave. (Cor. 18th St.), New York. 
 
 The books in the annexed list will be sent by mail, post-paid, to any Post-Office in the 
 United States, on receipt of the printed prices. 
 
 INDEX. 
 
 ANATOMY. Gray, p. 11 ; Treves, 30 ; Gerrish, 11; Brockway, 4. 
 
 DICTIONARIES. Dunglison, p. 8 ; Duane, 8 ; National, 4. 
 
 PHYSICS. Draper, p. 8 ; Robertson, 24 ; Martin & Rockwell, 20. 
 
 PHYSIOLOGY. Foster, p. 10; Chapman, 5; Schofield, 25; Collins 
 & Rockwell, 6. [Luff, 19 ; Remsen, 24. 
 
 CHEMISTRY. Simon, p. 26 ; Attfield, 3 ; Martin & Rockwell, 20; 
 
 PHARMACY. Caspari, p. 5. [Bruce, 4 : Schleif, 25. 
 
 MATERIA MEDICA. Culbretb, p. 6 ; Maisch, 19 ; Farquharson, 9 ; 
 
 DISPENSATORY. National, p. 21. 
 
 THERAPEUTICS. Hare, p. 13 ; Fothergill, 10 ; Whitla, 31 ; Hayem 
 & Hare, 14 ; Bruce, 4 ; Schleif, 25 ; Cushny, 6. 
 
 PRACTICE. Flint, p. 9 ; Loomia & Thompson, 19 ; Malsbary, 20. 
 
 DIAGNOSIS. Musser, p. 21 ; Hare, 12; Simon, 25; Herrick, 15; Hutchi- 
 son & Rainey, 16 ; Collins, 6. 
 
 CLIMATOLOGY. Solly, p. 26 ; Hayem & Hare, 14. 
 
 NERVOUS DISEASES. Dercum, p. 7 ; Gray, 11 ; Potts, 23. 
 
 MENTAL DISEASES. Clouston, p. 5 ; Savage, 24 ; Folsom, 10. 
 
 BACTERIOLOGY. Abbott, p. 2 ; Vaughan & Novy, 30 ; Senn's 
 (Surgical), 25. Park, 22 ; Coates, 6. [Vale, 21. 
 
 HISTOLOGY. Klein, p. 17 ; Schafer's, 25 ; Dunham, 8 ; Nichols & 
 
 PATHOLOGY. Green, p. 12; Gibbes, 10; Coats, 6; Nichols & Vale, 21. 
 
 SURGERY. Park, p. 22; Dennis, 7; Roberts, 24; Ashhurst, 3; Treves, 29; 
 Cheyne & Burghard, 5 ; Gallaudet, 10. 
 
 SURGERY OPERATIVE. Stimson, p. 27 ; Smith, 26 ; Treves, 29. 
 
 SURGERY ORTHOPEDIC. Young, p. 31 ; Gibney, 10. 
 
 SURGERY MINOR. Wharton, p. 30. [Ballenger & 
 
 FRACTURES and DISLOCATIONS. Stimson, p. 27. [Wippern, 3. 
 
 OPHTHALMOLOGY. Norris & Oliver, p. 21 ; Nettleship, 21; Juler, 17; 
 
 OTOLOGY. Politzer, p. 23; Burnett, 5; Field, 9; Bacon, 4. 
 
 LARYNGOLOGY and RHINOLOGY. Coakley, p. 6 ; 
 
 DENTISTRY. Essig (Prosthetic), p. 9 ; Kirk (Operative), 17 ; Ameri- 
 can System, 2 ; Coleman, 6; Burchard 4. 
 
 URINARY DISEASES. Roberts, p. 24 ; Black, 4 ; Morris, 20. 
 
 VENEREAL DISEASES. Taylor, p. 28 ; Hayden, 14 ; Cornil, 6 ; 
 Likes, 19. 
 
 SEXUAL DISORDERS. Fuller, p. 10 ; Taylor, 29. 
 
 DERMATOLOGY. Hyde, p. 16 ; Jackson, 16 ; Pye-Smith, 24 ; Mor- 
 ris, 20 ; Jamieson, 16 ; Hardaway, 12 ; Grindon, 12. 
 
 GYNECOLOGY. American System, p. 3 ; Thomas & Munde", 29 
 Emmet, 9 ; Davenport, 7 ; May, 20 ; Dudley, 8 ; Crockett, 6. 
 
 OBSTETRICS. American System, p. 3 ; Davis, 7 ; Parvin, 22 ; Play- 
 fair, 23 ; King, 17 ; Jewett, 17 ; Evans, 9. 
 
 PEDIATRICS. Smith, p. 26 ; Thomson, 29 ; Williams, 31 ; Tattle, 30. 
 
 HYGIENE. Egbert, p. 9 ; Richardson, 24 ; Coates, 6. 
 
 MEDICAL JURISPRUDENCE. Taylor, p. 28. 
 
 QUIZ SERIES, POCKET TEXT-BOOKS and MANUALS. 
 
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2 LEA BROTHERS & Co., PHILADELPHIA AND NEW YORK. 
 
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 DAVENPORT (F. EL). DISEASES OF WOMEN. A Manual of 
 
 Gynecology. For the use of Students and Practitioners. New 
 (3d) edition. In one handsome 12mo. volume of 387 pages, with 150 
 illustrations. Cloth, $1.75, net. Just ready. 
 
 DAVIS (EDWARD P.). A TREATISE ON OBSTETRICS. FOR 
 STUDENTS AND PRACTITIONERS. In one very handsome 
 octavo volume of 546 pages, with 217 engravings and 30 full-page 
 plates in colors and monochrome. Cloth, $5 ; leather, $6. 
 
 This work must become the prac- 
 titioner's text-book as well as the 
 student's. It is up to date in every 
 respect. Va. Med. Semi- Monthly. 
 
 A work unequalled in excellence. 
 The Chicago Clinical Review. 
 
 Decidedly one of the best text- treatise on obstetrics. Med. News. 
 
 DAVIS (F. H.). LECTURES ON CLINICAL MEDICINE. Second 
 edition. In one 12mo. volume of 287 pages. Cloth, $1.75. 
 
 DE LA HECHE'S GEOLOGICAL OBSERVER. In one large octavo 
 volume of 700 pages, with 300 engravings. Cloth, $4. 
 
 DENNIS (FREDERIC S.) AND BILLINGS (JOHN S.). A SYS- 
 TEM OF SURGERY. In contributions by American Authors. 
 Complete work in four very handsome octavo volumes, containing 
 3652 pages, with 1585 engravings and 45 full-page plates in colors 
 and monochrome. Per volume, cloth, $6.00; leather, $7.00; half 
 Morocco, gilt back and top, $8.50. For sale by subscription only. 
 Full prospectus free on application to the publishers. 
 
 books on the subject. It is exception- 
 ally useful from every standpoint. 
 Nashville Jour, of Med. and Surgery. 
 From a practical standpoint the 
 work is all that could be desired. A 
 thoroughly scientific and brilliant 
 
 It is worthy of the position which 
 surgery has attained in the great 
 Republic whence it comes. The 
 London Lancet. 
 
 It may be fairly said to represent 
 
 American surgery and is thoroughly 
 practical. Annals of Surgery. 
 
 No work in English can be con- 
 sidered as the rival of this. The 
 American Journal of the Medical 
 
 the most advanced condition of j Sciences. 
 
 DERCUM (FRANCIS X M EDITOR). A TEXT-BOOK ON 
 NERVOUS DISEASES. By American Authors. In one handsome 
 octavo volume of 1054 pages, with 341 engravings and 7 colored 
 plates. Cloth, $6.00 ; leather, $7.00. Net. 
 
 Representing the actual status of 
 our knowledge of its subjects, and 
 the latest and most fully up-to-date 
 of any of its class. Jour, of Amer- 
 ican Med. Association. 
 
 The most thoroughly up-to-date 
 treatise that we have on this subject. 
 American Journal of Insanity. 
 
 The work is representative of the 
 best methods of teaching, as devel- 
 oped in the leading medical colleges 
 of this country. Alienist and Neu- 
 rologist. 
 
 The best text-book in any lan- 
 guage. The Medical Fortnightly. 
 
 DE SCHWE1NITZ (GEORGE E.). THE TOXIC AMBLYOPIAS. 
 Their Classification, History, Symptoms, Pathology and Treatment. 
 Very handsome octavo, 240 pages, 46 engravings, and 9 full-page 
 plates in colors. Limited edition, de luxe binding, $4. Net. 
 
8 LEA BROTHERS & Co., PHILADELPHIA AND NEW YORK. 
 
 DRAPER (JOHN O.). MEDICAL PHYSICS. A Text-book for Stu- 
 dents and Practitioners of Medicine. In one handsome octavo volume 
 of 734 pages, with 376 engravings. Cloth, $4. 
 
 DRUITT (ROBERT). THE PRINCIPLES AND PRACTICE OF 
 MODERN SURGERY. A new American, from the twelfth London 
 edition, edited by STANLEY BOYD, F. R. C. S. In one large octavo 
 volume of 965 pages, with 373 engravings. Cloth, $4 ; leather, $5. 
 
 DUANE (ALEXANDER). THE STUDENT'S DICTIONARY OF 
 MEDICINE AND THE ALLIED SCIENCES. New edition. Com- 
 prising the Pronunciation, Derivation and Full Explanation of Medi- 
 cal Terms, with much Collateral Descriptive Matter. Numerous Tables, 
 etc. Square octavo of 658 pages. Cloth, $3.00; half leather, $3.25; 
 full sheep, $3.75. Thumb-letter Index, 50 cents extra. 
 Far superior to any dictionary for 1 convenience and thoroughness. 
 
 the medical student that we know of. Medical Record. 
 
 Western Med. and Surg. Reporter. 
 The book is brought accurately to 
 
 The best student's dictionary. 
 Canada Lancet. 
 
 date. It is a model of conciseness, 
 
 DUDLEY (E. C.). THE PRINCIPLES AND PRACTICE OF 
 GYNECOLOGY. Handsome octavo of 652 pages, with 422 illustra- 
 tions in black and colors. Cloth, $5.00, net ; leather, $6.00, net. Just 
 rtady. 
 
 The book can be safely recom- 
 mended as a complete and reliable 
 
 tice of modern gynecology. Inter- 
 national Medical Magazine. 
 
 exposition of the principles and prac- 
 DUNCAN (J. MATTHEWS). CLINICAL LECTURES ON THE 
 DISEASES OF WOMEN. Delivered in St. Bartholomew's Hospital. 
 In one octavo volume of 175 pages. Cloth, $1.50. 
 
 DUNGLJSON (ROBLEY). A DICTIONARY OF MEDICAL SCI- 
 ENCE. Containing a full explanation of the various subjects and 
 terms of Anatomy, Physiology ; Medical Chemistry, Pharmacy, Phar- 
 macology, Therapeutics, Medicine, Hygiene, Dietetics, Pathology, Sur- 
 gery, Ophthalmology, Otology, Laryngology, Dermatology, Gynecol- 
 ogy, Obstetrics, Pediatrics, Medical Jurisprudence, Dentistry, etc., etc. 
 By ROBLEY DUNGLISON, M. D., LL. D., late Professor of Institutes 
 or Medicine in the Jefferson Medical College of Philadelphia. Edited 
 by RICHARD J. DUNGLISON, A. M., M. D. Twenty-first edition, thor- 
 oughly revised and greatly enlarged and improved, with the Pronuncia- 
 tion, Accentuation and Derivation of the Terms. With Appendix. 
 In one magnificent imperial octavo volume of 1225 pages. Cloth, $7 ; 
 leather, $8. Thumb-letter Index for quick use, 75 cents extra. 
 The most satisfactory and authori- 1 scarcely be measured. Med. Record. 
 tative guide to the derivation, defini- j Pronunciation is indicated by the 
 tion and pronunciation of medical \ phonetic system. The definitions are 
 terms. The Charlotte Med. Journal. unusu& u y c i ear and concise. The 
 
 Covering the entire field of medi- 
 cine, surgery and the collateral 
 
 book is wholly satisfactory. Uni- 
 versity Medical Magazine. 
 
 sciences, its range of usefulness can 
 
 DUNHAM (EDWARD K.). MORBID AND NORMAL HIS- 
 TOLOGY. Octavo, 450 pages,with 363 illustrations. Cloth, $3.25, m-t. 
 Just ready. 
 The best one- volume text or refer- I of published in America. Virginia 
 
 ence book on histology that we know I Medical Semi-Monthly. 
 
 EDES (ROBERT T.). TEXT-BOOK OF THERAPEUTICS AND 
 MATERIA MEDICA. In one 8vo. volume of 544 pages. Cloth, $3.50 ; 
 leather, $4.50. 
 
 EDIS (ARTHUR W.). DISEASES OF WOMEN. A Manual for 
 Students and Practitioners. In one handsome 8vo. volume of 576 pages, 
 with 148 engravings. Cloth, $3 ; leather, $4. 
 
LEA BROTHERS & Co., PHILADELPHIA AND NEW YORK. 9 
 
 EGBERT (SENECA). A MANUAL OF HYGIENE AND SANI- 
 TATION. In one 12mo. volume of 359 pages, with 63 illustrations. 
 Just ready. Cloth, Net, $2.25. 
 It is written in plain language, 1 ligence. The writer has adapted it 
 
 and, while primarily designed for to American conditions, and his 
 
 physicians, it can be studied with j suggestions are, above all, practical. 
 
 profit by any one of ordinary Intel- | The New York Medical Journal. 
 
 ELL.IS (GEORGE VINER). DEMONSTRATIONS IN ANATOMY. 
 Eighth edition. Octavo, 716 pages, with 249 engravings. Cloth, 
 $4.25 ; leather, $5.25. 
 
 EMMET (THOMAS ADDIS). THE PRINCIPLES AND PRAC- 
 TICE OF GYNAECOLOGY. Third edition. Octavo, 880 pages, with 
 150 original engravings. Cloth, $5 ; leather, $6. 
 
 ERICHSEN (JOHN E.). THE SCIENCE AND ART OF SUR- 
 GERY. Eighth edition. In two large octavo volumes containing 
 2316 pages, with 984 engravings. Cloth, $9 ; leather, $11. 
 
 ESSIG (CHARLES J.). PROSTHETIC DENTISTRY. See American 
 Text-Books of Dentistry, page 2. 
 
 EVANS (DAVID J.). A POCKET TEXT-BOOK OF OBSTETRICS. 
 In one handsome 12mo. volume of about 300 pages, with many illustra- 
 tions. Cloth, $1.50, net. Shortly. Lea's Series of Pocket Text-books, 
 edited by BERN B. GALLAUDET, M. D. See page 18. 
 
 FARQUHARSON (ROBERT). A GUIDE TO THERAPEUTICS. 
 Fourth American from fourth English edition, revised by FRANK 
 WOODBURY, M. D. In one 12mo. volume of 581 pages. Cloth, $2.50. 
 
 FIELD (GEORGE P.). A MANUAL OF DISEASES OF THE 
 EAR. Fourth edition. In one octavo volume of 391 pages, with 73 
 engravings and 21 colored plates. Cloth, $3.75. 
 
 To those who desire a concise j It is just such a work as is needed 
 work on diseases of the ear, clear by every general practitioner. 
 and practical, this manual com- American Practitioner and News. 
 mends itself in the highest degree. ' 
 
 FLINT (AUSTIN). A TREATISE ON THE PRINCIPLES AND 
 PRACTICE OF MEDICINE. Seventh edition, thoroughly revised 
 by FREDERICK P. HENRY, M. D. In one large 8vo. volume of 1143 
 pages, with engravings. Cloth, $5.00 ; leather, $6.00. 
 The work has well earned its lead- { medicine in the medical schools. 
 ing place in medical literature. j Northwestern Lancet. 
 
 Medical Record. 
 The leading text-book on general 
 
 The best of American text-books 
 on Practice. Amer. Medico-Surgical 
 Bulletin. 
 
 A MANUAL OF AUSCULTATION AND PERCUSSION ; of 
 the Physical Diagnosis of Diseases of the Lungs and Heart, and of 
 Thoracic Aneurism. Fifth edition, revised by JAMES C. WILSON, M. D. 
 In one handsome 12mo. volume of 274 pages, with 12 engravings. 
 
 A PRACTICAL TREATISE ON THE DIAGNOSIS AND 
 TREATMENT OF DISEASES OF THE HEART. Second edition 
 enlarged. In one octavo volume of 550 pages. Cloth, $4. 
 
 A PRACTICAL TREATISE ON THE PHYSICAL EXPLO- 
 RATION OF THE CHEST, AND THE DIAGNOSIS OF DIS- 
 EASES AFFECTING THE RESPIRATORY ORGANS. Second 
 and revised edition. In one octavo volume of 591 pages. Cloth, $4.50. 
 
 MEDICAL ESSAYS. In one 12mo. vol. of 210 pages. Cloth, $1.38. 
 
 ON PHTHISIS : ITS MORBID ANATOMY. ETIOLOGY, ETC. 
 A Series of Clinical Lectures. In one 8vo. volume of 442 pages. 
 Cloth, $3.50. 
 
10 LEA BROTHERS & Co., PHILADELPHIA AND NEW YORK. 
 
 FOLSOM (C. P.). AN ABSTRACT OF STATUTES OF U. S. 
 
 ON CUSTODY 9F THE INSANE. In one 8vo. vol. of 108 pages. 
 
 Cloth, $1.50. With Clouston on Mental Diseases (new edition, see 
 
 page 6) $5.00, net, for the two works. 
 FORMULARY, POCKET, see page 32. 
 
 FOSTER (MICHAEL.). A TEXT-BOOK OF PHYSIOLOGY. New 
 (6th) and revised American from the sixth English edition. In one 
 large octavo volume of 923 pages, with 257 illustrations. Cloth, $4.50 ; 
 leather, $5.50. 
 
 Unquestionably the best book that i This single volume contains all 
 can be placed in the student's hands, j that will be necessary in a college 
 and as a work of reference for the course, and all that the physician 
 busy physician it can scarcely be will need as well. Dominion Med. 
 excelled. ThePhila. Poly clinic. \ Monthly. 
 
 FOTHERGILL (J. MILNER). THE PRACTITIONER'S HAND- 
 BOOK OF TREATMENT. Third edition. In one handsome octavo 
 volume of 664 pages. Cloth, $3.75 ; leather, $4.75. 
 
 clearly stated, cannot fail to prove 
 a great convenience to many thought- 
 ful but busy physicians. The prac- 
 
 busy p 
 due of 
 
 tical value of the volume is greatly 
 increased by the introduction of many 
 prescriptions New York Med. Jour. 
 
 To have a description of the 
 normal physiological processes of an 
 organ and of the methods of treat- 
 ment of its morbid conditions 
 brought together in a single chapter, 
 and the relations between the two 
 
 FOWNES (GEORGE). A MANUAL OF ELEMENTARY CHEM- 
 ISTRY (INORGANIC AND ORGANIC). Twelfth edition. Em- 
 bodying WATTS' Physical and Inorganic Chemistry. In one royal 
 12mo. volume of 1061 pages, with 168 engravings, and 1 colored 
 plate. Cloth, $2.75 ; leather, $3.25. 
 
 FRANKLAND (E.) AND JAPP (F.R.). INORGANIC CHEMISTRY. 
 In one handsome octavo volume of 677 pages, with 51 engravings and 
 2 plates. Cloth, $3.75 ; leather, $4.75. 
 
 FULLER (EUGENE). DISORDERS OF THE SEXUAL OR- 
 GANS IN THE MALE. In one very handsome octavo volume of 
 238 pages, with 25 engravings and 8 full-page plates. Cloth, $2. 
 
 It is an interesting work, and one 
 which, in view of the large and 
 profitable amount of work done in 
 this field of late years, is timely and 
 well needed. Medical Fortnightly. 
 
 The book is valuable and instruc- 
 
 tive and brings views of sound 
 pathology and rational treatment to 
 many cases of sexual disturbance 
 whose treatment has been too often 
 fruitless for good. Annals of 
 Surgery. 
 
 FULLER (HENRY). ON DISEASES OF THE LUNGS AND AIR 
 PASSAGES. Their Pathology, Physical Diagnosis, Symptoms and 
 Treatment. From second English edition. In one 8vo. volume of 475 
 pages. Cloth, $3.50. 
 
 GALLAUDET (BERN B.). A POCKET TEXT-BOOK ON SUR- 
 GERY. In one handsome 12mo. volume of about 400 pages, with many 
 illustrations. Cloth, $1.50, net. Shortly. Lea's Series of Pocket Text- 
 honks, edited by BERN B. < JAKLAUDKTJ M. D. See page 18. 
 
 GANT (FREDERICK JAMES). THE STUDENT'S SURGERY. A 
 M ii 1 1 ii in in Parvo. In one square octavo volume of 845 pages, with 
 159 engravings. Cloth, $3.75. 
 
 GIBBES (HENEAGE). PRACTICAL PATHOLOGY AND MORBID 
 HISTOLOGY. Octavo, 314 pages, with 60 illustrations. Cloth, $2.75. 
 
 GD3NEY (V. P.). ORTHOPEDIC SURGERY. For the use of Practi- 
 tioners and Students. In one 8vo. vol. profusely illus. Preparing. 
 
LEA BROTHERS & Co., PHILADELPHIA AND NEW YORK. 11 
 
 GERRISH (FREDERIC H.). A TEXT-BOOK OF ANATOMY. 
 By American Authors. Edited by Frederic H. Gerrish, M. D. In one 
 imp. octavo volume of 915 pages, with 950 illustrations in black and 
 colors. Just ready. Clth,$6.50; flexible waterproof, $7; leath.,$7.50,we. 
 
 In this, the first representative treatise on Anatomy produced in America, 
 no effort or expense has been spared to unite an authoritative text with the 
 most successful anatomical pictures which have yet appeared in the world. 
 
 The editor has secured the co-operation of the professors of anatomy in 
 leading medical colleges, and with them has prepared a text conspicuous 
 for its simplicity, unity and judicious selection of such anatomical facts as 
 bear on physiology, surgery and internal medicine in the most compre- 
 hensive sense of those terms. The authors have endeavored to make a 
 book which shall stand in the place of a living teacher to the student, and 
 which shall be of actual service to the practitioner in his clinical work, 
 emphasizing the most important subjects, clarifying obscurities, helping 
 most in the parts most difficult to learn, and illustrating everything by all 
 available methods. 
 
 GOULD (A. PEARCE). SURGICAL DIAGNOSIS. In one 12mo. 
 
 vol. of 589 pages. Cloth, $2. See Student's Series of Manuals, p. 27. 
 
 GRAY (HENRY). ANATOMY, DESCRIPTIVE AND SURGICAL. 
 
 New and thoroughly revised American edition, much enlarged in text, 
 and in engravings in black and colors. In one imperial octavo volume 
 of 1239 pages, with 772 large and elaborate engravings on wood. Price 
 of edition with illustrations in colors : cloth, $7 ; leather, $8. Price 
 of edition with illustrations in black : cloth, $6 ; leather, $7. 
 
 This is the best single volume 
 upon Anatomy in the English 
 language. University Medical Mag- 
 azine. 
 
 Gray's Anatomy affords the student 
 more satisfaction than any other 
 treatise with which we are familiar. 
 Buffalo Med. Journal. 
 
 The most largely used anatomical 
 text-book published in the English 
 language. Annals of Surgery. 
 
 Particular stress is laid upon the 
 practical side of anatomical teach- 
 
 ing, and especially the Surgical 
 Anatomy. Chicago Med. Recorder. 
 
 Holds first place in the esteem of 
 both teachers and students. The 
 Brooklyn Medical Journal. 
 
 The foremost of all medical text- 
 books. Medical Fortnightly. 
 
 Gray's Anatomy should be the 
 first work which a medical student 
 should purchase, nor should he be 
 without a copy throughout his pro- 
 fessional career. Pittsburg Medical 
 Review. 
 
 GRAY (L.ANDON CARTER). A TREATISE ON NERVOUS AND 
 MENTAL DISEASES. For Students and Practitioners of Medicine. 
 New (2d) edition. In one handsome octavo volume of 728 pages, with 
 172 engravings and 3 colored plates. Cloth, $4.75 ; leather, $5.76. 
 An up-to-date text-book upon measures which are often the physi- 
 
 nervous and mental diseases com- 
 bined. A well-written, terse, ex- 
 plicit, and authoritative volume 
 treating of both subjects is a step in 
 the direction of popular demand. 
 The, Chicago Clinical Review. 
 
 "The word treatment," says the 
 author, " has been construed in the 
 broadest sense to include not only 
 medicinal and non-medicinal agents, 
 but also those hygienic and dietetic 
 
 ciau's best reliance." The Journal 
 of the American Medical Association. 
 The descriptions of the various 
 diseases are accurate and the symp- 
 toms and differential diagnosis are 
 set before the student in such a way 
 as to be readily comprehended. The 
 author's long experience renders his 
 views on therapeutics of great value. 
 The Journal of Nervous and Men- 
 tal Disease. 
 
12 LEA BROTHERS & Co., PHILADELPHIA AND NEW YORK. 
 
 GREEN (T. HENRY). AN INTRODUCTION TO PATHOLOGY 
 AND MORBID ANATOMY. New (8th) American from the eighth 
 London edition. In one handsome octavo volume of 582 pages, with 
 216 engravings and a colored plate. Cloth, $2.50, net. Just ready. 
 
 A work that is the text-book of 
 probably four-fifths of all the stu- 
 dents of pathology in the United 
 States and Great Britain stands in 
 no need of commendation. The work 
 precisely meets the needs and wishes 
 of the general practitioner. The 
 American Practitioner and News. 
 
 Green's Pathology is the text-book 
 
 of the day as much so almost as 
 Gray's Anatomy. It is fully up-to- 
 date in the record of fact, and so pro- 
 fusely illustrated as to give to each 
 detail of text sufficient explanation. 
 The work is an essential to the prac- 
 titioner whether as surgeon or phys- 
 ician. It is the best of up-to date 
 text-books. Virginia Med. Monthly. 
 
 GREENE (WILLIAM H.). A MANUAL OF MEDICAL CHEM- 
 ISTRY. For the Use of Students. Based upon BOWMAN'S Medical 
 Chemistry. In one 12mo. vol. of 310 pages, with 74 illus. Cloth, $1.75. 
 
 GROSS (SAMUEL D.). A PRACTICAL TREATISE ON THE DIS- 
 EASES, INJURIES AND MALFORMATIONS OF THE URINARY 
 BLADDER, THE PROSTATE GLAND AND THE URETHRA. 
 Third edition. Octavo, 574 pages, with 170 illustrations Cloth, $4.50. 
 
 GRINDON (JOSEPH). A POCKET TEXT-BOOK OF SKIN 
 DISEASES. In one handsome 12mo. volume of 350 pages, with 
 many illustrations. Shortly. Cloth, $1.50, net. Lea's Seri<* <>f P,,,-l-,t 
 Text-books, edited by BERN B. GALLATJDET, M. D. See page 18. 
 
 HABERSHON (S. O.). ON THE DISEASES OF THE ABDOMEN 
 Second American from the third English edition. In one octavo vol- 
 ume of 554 pages, with 11 engravings. Cloth, $3.50. 
 
 HALL (WINFIELD S.) TEXT-BOOK OF PHYSIOLOGY. Octavo 
 about 500 pages, richly illustrated. In press. 
 
 HAMILTON (ALLAN MCLANE). NERVOUS DISEASES, THEIR 
 DESCRIPTION AND TREATMENT. Second and revised edition. 
 In one octavo volume of 598 pages, with 72 engravings. Cloth, $4. 
 
 HARDAWAY (W. A.). MANUAL OF SKIN DISEASES. New (2d) 
 edition. In one 12mo. volume of 560 pages, with 40 illustrations and 
 2 plates. Cloth, $2.25, net. Just ready. 
 
 The best of all the small books to 
 recommend to students and practi- 
 tioners. Probably no one of our 
 dermatologists has had a wider every- 
 
 day clinical experience. His great 
 strength is in diagnosis, descriptions 
 of lesions and especially in treat- 
 ment. Indiana Medical Journal. 
 
 HARE (HOB ART AMORY). PRACTICAL DIAGNOSIS. THE 
 USE OF SYMPTOMS IN THE DIAGNOSIS OF DISEASE. New 
 (4th) edition. In one octavo volume of 623 pages, with 205 engravings 
 and 14 full-page colored plates. Cloth, $5.00, net. Jtmt r, <>,/>/. 
 
 It is unique in many respects, and he will become a better diaguosti- 
 the author has introduced radical cian. This is a companion to /Vac- 
 changes which will be welcomed by | tical Therapeutics, by the same 
 alJ. Anyone who reads this book i author, and it is difficult to conceive 
 will become a more acute observer, of any two works of greater practical 
 will pay more attention to the simple utility. Medical Review. 
 yet indicative signs of disease, and 
 
LEA BROTHERS & Co., PHILADELPHIA AND NEW YORK. 13 
 
 HARE (HOBART AMORY). A TEXT-BOOK OF PRACTICAL 
 
 THERAPEUTICS, with Special Reference to the Application of Reme- 
 dial Measures to Disease and their Employment upon a Rational 
 Basis. With articles on various subjects by well-known specialists. 
 New (7th) and revised edition. In one octavo volume of 776 pages. 
 Cloth, $3.75, net; leather, $4.50, net. 
 
 Its classifications are inimitable, 
 and the readiness with which any- 
 thing can be found is the most won- 
 derful achievement of the art of in- 
 dexing. This edition takes in all 
 the latest discovered remedies. 
 The St. Louis Clinique. 
 
 The great value of the work lies 
 in the fact that precise indications 
 for administration are given. A 
 complete index of diseases and 
 remedies makes it an easy reference 
 work. It has been arranged so that 
 
 it can be readily used in connection 
 with Hare's Practical Diagnosis. 
 For the needs of the student and 
 general practitioner it has no equal. 
 Medical Sentinel. 
 
 The best planned therapeutic work 
 of the century. American Prac- 
 titioner and News. 
 
 It is a book precisely adapted to 
 the needs of the busy practitioner, 
 who can rely upon finding exactly 
 what he needs. The National Med- 
 ical Review. 
 
 HARE (HOBART AMORY) ON THE MEDICAL COMPLICA 
 TIONS AND SEQUELAE OF TYPHOID FEVER. Octavo, 276 
 pages, 21 engravings and two full-page plates. Just ready. Cloth, 
 $2.40, net. 
 
 A very valuable production. One 
 of the very best products of Dr. 
 Hare and one that every man can 
 
 read with great profit. Cleveland 
 Journal of Medicine. 
 
 HARE (HOBART AMORY, EDITOR). A SYSTEM OF PRAC- 
 TICAL THERAPEUTICS. In a series of contributions by eminent 
 practitioners. In four large octavo volumes comprising about 4500 
 pages, with about 550 engravings. Vol. IV., just ready. For sale by sub- 
 scription only. Full prospectus free on application to the Publishers. 
 Regular price, Vol. IV., cloth, $6 ; leather, $7 ; half Russia, $8. 
 Price Vol. IV. to former or new subscribers to complete work, cloth, 
 $5 ; leather, $6 ; half Russia, $7. Complete work, cloth, $20 ; leather, 
 $24 ; half Russia, $28. 
 
 The great value of Hare's System of Practical Therapeutics has led to a 
 widespread demand for a new volume to represent advances in treatment 
 made since the publication of the first three. More than fulfilling this 
 request the Editor has secured contributions from practically a new corps 
 of equally eminent authors, so that entirely fresh and original matter is 
 ensured. The plan of the work, which proved so successful, has been fol- 
 lowed in this new volume, which will be found to present the latest devel- 
 opments and applications of this most practical branch of the medical art. 
 The entire System is an unrivalled encyclopaedia on the practical parts of 
 medicine, and merits the great success it has won for that reason. 
 
14 LEA BROTHERS & Co., PHILADELPHIA AND NEW YORK. 
 
 HARTSHORNE (HENRY). ESSENTIALS OF THE PRINCIPLES 
 AND PRACTICE OF MEDICINE. Fifth edition. In one 12mo. 
 volume, 669 pages, with 144 engravings. Cloth, $2.75 . 
 
 A HANDBOOK OF ANATOMY AND PHYSIOLOGY. In one 
 
 12mo. volume of 310 pages, with 220 engravings. Cloth, $1.75. 
 
 A CONSPECTUS OF THE MEDICAL SCIENCES. Comprising 
 
 Manuals of Anatomy, Physiology, Chemistry, Materia Medica, Prac- 
 tice of Medicine, Surgery and Obstetrics. Second edition. In one royal 
 12mo. vol. of 1028 pages, with 477 iUus. Cloth, $4.25 ; leather, $5. 
 
 HAYDEN (JAMES B.). A MANUAL OF VENEREAL DISEASES. 
 New (2d) edition. In one 12mo. volume of 304 pages, with 54 en- 
 gravings. Cloth, $1.50, net. Just ready. 
 
 It is practical, concise, definite 
 and of sufficient fulness to be satis- 
 factory. Chicago Clinical Review. 
 
 This work gives all of the prac- 
 tically essential information about 
 the three venereal diseases, gon- 
 orrhoea, the chancroid and syphilis. 
 In diagnosis and treatment it is par- 
 
 ticularly thorough, and may be 
 relied upon as a guide in the man- 
 agement of this class of diseases. 
 Northwestern Lancet. 
 
 It is well written, up to date, and 
 will be found very useful. Inter- 
 national Medical Magazine. 
 
 HAYEM (GEORGES) AND HARE (H. A.). PHYSICAL AND 
 NATURAL THERAPEUTICS. The Remedial Use of Heat, Elec- 
 tricity, Modifications of Atmospheric Pressure, Climates and Mineral 
 Waters. Edited by Prof. H. A. HARE, M. D. In one octavo volume 
 of 414 pages,with 113 engravings. Cloth, $3. 
 
 This well-timed up-to-date volume 
 is particularly adapted to the re- 
 quirements of the general practi- 
 tioner. The section on mineral 
 waters is most scientific and prac- 
 tical. Some 200 pages are given up 
 to electricity and evidently embody 
 the latest scientific information on 
 the subject. Altogether this work 
 is the clearest and most practical aid 
 to the study of nature's therapeutics 
 that has yet come under our obser- 
 vation. The Medical Fortnightly. 
 
 For many diseases the most potent 
 remedies lie outside of the materia 
 medica, a fact yearly receiving wider 
 
 recognition. Within this large 
 range of applicability, physical 
 agencies when compared with drugs 
 are more direct and simple in their 
 results. Medical literature has long 
 been rich in treatises upon medical 
 agents, but an authoritative work 
 upon the other great branch of 
 therapeutics has until now been a 
 desideratum. The section on climate, 
 rewritten by Prof. Hare, will, for 
 the first time, place the abundant 
 resources of our country at the in- 
 telligent command of American 
 practitioners. The Kansas City 
 I Medical Index. 
 
 HERMAN (G. ERNEST). FIRST LINES IN MIDWIFERY. In 
 one 12mo. vol. of 198 pages, with 80 engravings. Cloth, $1.25. See 
 Student's Series of Manuals, page 27. 
 
 HERMANN (Li.). EXPERIMENTAL PHARMACOLOGY. A Hand- 
 book of the Methods for Determining the Physiological Actions of 
 Drugs. Translated by ROBERT MEADE SMITH, M. D. In one 12mo, 
 volume of 199 pages, with 32 engravings. Cloth, $1.50. 
 
LEA BROTHEBS & Co., PHILADELPHIA AND NEW YORK. 15 
 
 HERRICK (JAMES B.). A HANDBOOK OF DIAGNOSIS. In 
 
 one handsome 12mo. volume of 429 pages, with 80 engravings and 2 
 colored plates. Cloth, $2.50. 
 
 Excellently arranged, practical, 
 concise, up-to-date, and eminently 
 well fitted for the use of the prac- 
 titioner as well as of the student. 
 Chicago Med. Recorder. 
 
 This volume accomplishes its ob- 
 jects more thoroughly and com- 
 pletely than any similar work yet 
 published. Each section devoted to 
 diseases of special systems is pre- 
 ceded with an exposition of the 
 methods of physical, chemical and 
 
 microscopical examination to be em- 
 ployed in each class. The technique 
 of blood examination,including color 
 analysis, is very clearly stated. 
 Uranalysis receives adequate space 
 and care. New York Med. Journal. 
 We commend the book not only to 
 the undergraduate, but also to the 
 physician who desires a ready means 
 of refreshing his knowledge of diag- 
 nosis in the exigencies of professional 
 life. Memphis Medioal Mo 
 
 HILL (BERKELEY). SYPHILIS AND LOCAL CONTAGIOUS 
 
 DISORDERS. In one 8vo. volume of 479 pages. Cloth, $3.25. 
 
 HILLDER (THOMAS). A HANDBOOK OF SKIN DISEASES. 
 Second edition. In one royal 12mo. volume of 353 pages, Avith two 
 plates. Cloth, $2.25. 
 
 HIRST (BARTON C.) AND PIERSOL (GEORGE A.). HUMAN 
 
 MONSTROSITIES. Magnificent folio, containing 220 pages of text 
 and illustrated with 123 engravings and 39 large photographic plates 
 from nature. In four parts, price each, $5. Limited edition. For sale 
 by subscription only. 
 
 HOBLYN (RICHARD D.). A DICTIONARY OF THE TERMS 
 USED IN MEDICINE AND THE COLLATERAL SCIENCES. 
 In one 12mo. volume of 520 double-columned pages. Cloth, $1.50 ; 
 leather, $2. 
 
 HODGE (HUGH L.). ON DISEASES PECULIAR TO WOMEN, 
 INCLUDING DISPLACEMENTS OF THE UTERUS. Second and 
 revised edition. In one 8vo. vol. of 519 pp., with illus. Cloth, $4.50. 
 
 HOFFMANN (FREDERICK) AND POWER (FREDERICK B.). 
 
 A MANUAL OF CHEMICAL ANALYSIS, as Applied to the 
 Examination of Medicinal Chemicals and their Preparations. Third 
 edition, entirely rewritten and much enlarged. In one handsome octavo 
 volume of 621 pages, with 179 engravings. Cloth, $4.25. 
 
 HOLMES (TIMOTHY). A TREATISE ON SURGERY. Its Prin- 
 ciples and Practice. A new American from the fifth English edition. 
 Edited by T. PICKERING PICK, F.R.C.S. In one handsome octavo vol- 
 ume of lOOS.pages, with 428 engravings. Cloth, $6 ; leather, $7. 
 
 A SYSTEM OF SURGERY. With notes and additions by various 
 American authors. Edited by JOHN H. PACKARD, M. D. In three 
 very handsome 8vo. volumes containing 3137 double-columned pages, 
 with 979 engravings and 13 lithographic plates. Per volume, cloth, $6 ; 
 leather, $7 ; half Russia, $7.50. For tale by tubscription only. 
 
16 LEA BROTHERS & Co., PHILADELPHIA AND NEW YORK. 
 
 HORNER (WILLIAM E.). SPECIAL ANATOMY AND HIS- 
 TOLOGY. Eighth edition, revised and modified. In two large 8vo. 
 volumes of 1007 pages, containing 320 engravings. Cloth, $6. 
 
 HUDSON (A.). LECTURES ON THE STUDY OF FEVER. In one 
 octavo volume of 308 pages. Cloth, $2.50. 
 
 HUTCHISON (ROBERT) AND RAINY (HARRY). CLINICAL 
 METHODS. A GUIDE TO THE PRACTICAL STUDY OF 
 MEDICINE. In one 12mo. volume of 562 pages, with 137 engrav- 
 ings and 8 colored plates. Cloth, $3.00. 
 
 A comprehensive, clear and re- 
 markably up-to-date guide to clinical 
 diagnosis. The illustrations are 
 plentiful and excellent. As exam- 
 ples of the more recent additions to 
 
 medical knowledge which receive 
 recognition, we mention Widal's 
 test for typhoid and the Neuron 
 theory of the nervous system. 
 Montreal Medical Journal. 
 
 HUTCHINSON (JONATHAN). SYPHILIS. In one pocket-size 12mo. 
 volume of 542 pages, with 8 chromo-lithographic plates. Cloth, $2.25. 
 See Series of Clinical Manuals, p. 25. 
 
 HYDE (JAMES NEVINS). A PRACTICAL TREATISE ON DIS- 
 EASES OF THE SKIN. New (4th) edition, thoroughly revised. 
 In one octavo volume of 815 pages, with 110 engravings and 12 full- 
 page plates, 4 of which are colored. Cloth, $5.25 ; leather, $6.25. 
 
 This edition has been carefully re- 
 vised, and every real advance has 
 been recognized. The work answers 
 the needs of the general practitioner, 
 the specialist, and the student. The 
 Ohio Med. Jour. 
 
 A treatise of exceptional merit 
 characterized by conscientious care 
 and scientific accuracy. Buffalo 
 Med. Journal. 
 
 A complete exposition of our 
 knowledge of cutaneous medicine as 
 it exists to-day. The teaching in- 
 culcated throughout is sound as well 
 
 as practical. The American Jour- 
 nal of the Medical Sciences. 
 
 It is the best one-volume work 
 that we know. The student who 
 gets this book will find it a useful 
 investment, as it will well serve him 
 when he goes into practice. Vir- 
 ginia Medical Semi-Monthly. 
 
 A full and thoroughly modern 
 text-book on dermatology. The 
 Pittsburg Medical Review. 
 
 It is the most practical hand- 
 book on dermatology with which we 
 are acquainted. The Chicago Med- 
 ical Recorder. 
 
 JACKSON (GEORGE THOMAS). THE READY-REFERENCE 
 HANDBOOK OF DISEASES OF THE SKIN. New (3d) edition. 
 In one 12mo. volume of 637 pages, with 75 illustrations and a colored 
 plate. Just ready. Cloth, $2.50, nff. 
 
 Asa student's manual, it may be 
 considered beyond criticism. The 
 book is singularly full. St. Louis 
 (td Surgical Journal. 
 
 Without doubt forms one of the 
 best guides for the beginner in der- 
 matology that is to be found in the 
 English language. Medic inc. 
 
 JAMIESON (W. AJLL.AN). DISEASES OF THE SKIN. Third 
 edition. In one octavo volume of 656 pages, with 1 engraving afld 9 
 double-page chromo-lithographic plates, Cloth, $6, 
 
LEA BROTHERS & Co., PHILADELPHIA AND NEW YORK. 17 
 
 JEWETT (CHARLES). ESSENTIALS OF OBSTETRICS. In one 
 
 12mo. volume of 356 pages, with 80 engravings and 3 colored plates. 
 
 Cloth , $2 . 25. Just ready. 
 
 An exceedingly useful manual for ing it in attractive and easily tangi- 
 student and practitioner. The au- ble form. The book is well illus- 
 thor has succeeded unusually well trated throughout. Nashville Jour. 
 in condensing the text and in arrang- of Medicine and Surgery. 
 
 American Authors. 
 
 One large octavo volume of 763 pages, with 441 engravings in black 
 and colors, and 22 full-page colored plates. Just ready. Cloth, 
 
 THE PRACTICE OF OBSTETRICS. By 
 
 ith 441 
 
 $5.00, net; leather, $6.00, net. 
 A clear and practical treatise upon 
 obstetrics by well-known teachers of 
 the subject. A special feature of 
 this work would seem to be the 
 excellent illustrations with which 
 
 the book abounds. The work is 
 sure to be popular with medical 
 students, as well as being of extreme 
 value to the practitioner. The 
 Medical Age. 
 
 JONES (C. HANDF1EL.D). CLINICAL OBSERVATIONS ON 
 FUNCTIONAL NERVOUS DISORDERS. Second American edi- 
 tion. In one octavo volume of 340 pages. Cloth, $3.25. 
 
 JULER (HEXRY). A HANDBOOK OF OPHTHALMIC SCIENCE 
 AND PRACTICE. Second edition. In one octavo volume of 549 
 pages, with 201 engravings, 17 chromo-lithographic plates, test-types of 
 Jaeger and Siiellen, and Holmgren's Color-Blindness Test. Cloth, 
 $5.50 ; leather, $6.50. 
 
 The volume is particularly rich in | color blindness, etc. The sections 
 matter of practical value, such as | devoted to treatment are singularly 
 directions for diagnosing, use of full and concise. Medical Age. 
 instruments, testing for glasses, for | 
 
 KING (A. F. A.). A MANUAL OF OBSTETRICS. Seventh edition. 
 In one 12mo. volume of 573 pages, with 223 illustrations. Cloth, 
 $2.50. 
 
 From first to finish it is thoroughly j cyclopedias. The well-arranged 
 ractical, concise in expression, well index renders the book useful to 
 
 illustrated, and includes a statement 
 of nearly every fact of importance 
 
 the practitioner who is in haste to 
 refresh his memory. Virginia 
 
 discussed in obstetric treatises or ! Medical Semi-Monthly. 
 
 KIRK (EDWARD C.). OPERATIVE DENTISTRY. Handsome 
 octavo of 700 pages, with 751 illustrations. Just ready. See American 
 Text-Books of Dentistry, page 2. 
 
 We have only the highest praise 
 for this valuable work. It is replete 
 in every particular, and surpasses 
 anything of the kind heretofore at- 
 
 tempted. We can heartily recom- 
 mend it to the profession. The 
 Ohio Dental Journal. 
 
 KLEIN (E.). ELEMENTS OF HISTOLOGY. New (5th) edition. In 
 one 12mo. volume of 506 pages, with 296 engravings. Just ready. 
 Cloth, $2.00, net. See Student's Series of Manuals, page 27. 
 
 This work deservedly occupies a 
 
 It is the most complete and con- 
 cise work of the kind that has yet 
 emanated from the press. The Med- 
 ical Age. 
 
 first place as a text-book on his- 
 tology. Canadian Practitioner. 
 
18 LEA BROTHERS & Co., PHILADELPHIA AND NEW YORK. 
 
 L.ANDIS (HENRY G.). THE MANAGEMENT OF LABOR. In one 
 handsome 12mo. volume of 329 pages, with 28 illus. Cloth, $1.75. 
 
 LiA ROCHE (R.). YELLOW FEVER. In two 8vo. volumes of 1468 
 pages. Cloth, $7. 
 
 LAURENCE (J. Z.) AND MOON (ROBERT C.). A HANDY- 
 BOOK OF OPHTHALMIC SURGERY. Second edition. In one 
 octavo volume of 227 pages, with 66 engravings. Cloth, $2.75. 
 
 LEA'S SERIES OP POCKET TEXT-BOOKS, edited by BKRN 
 B. GALLAUDET, M. D. Covering the entire field of Medicine in a 
 series of 16 very handsome cloth-bound 12mo. volumes of 350-450 
 pages each, profusely illustrated. Compendious, clear, trustworthy and 
 modern, and issued at the very moderate price of $1.50, net, per 
 volume. The following volumes constitute the series. 
 
 Co ATES' Bacteriology and Hygiene. BROCKWAY'S Anatomy. COM .INS 
 and ROCKWELL'S Physiology. MARTIN and ROCKWELL'S < 'hemistry 
 and Physics. NICHOLS and VALE'S Histology and Pathology. 
 SCHLEIF'S Materia Medica, Therapeutics, Medical Latin, etc. MALS- 
 BARY'S Practice of Medicine. COLLINS' Diagnosis. POTTS' Nervous 
 and Mental Diseases. GALLAUDET'S Surgery. LIKES' Genito- 
 Urinary and Venereal Diseases. GRINDON'S Dermatology. BALLKN- 
 GER and WIPPERN'S Diseases of the Eve, Ear, Throat and Nose. 
 EVANS' Obstetrics. CROCKETT'S Gynecology. TUTTLK'S Diseases of 
 Children. 
 
 For separate notices see under various authors' names. 
 
 LEA (HENRY C.). A HISTORY OF AURICULAR CONFESSION 
 AND INDULGENCES IN THE LATIN CHURCH. In three 
 octavo volumes of about 500 pages each. Per volume, cloth, $3.00. 
 
 CHAPTERS FROM THE RELIGIOUS HISTORY OF SPAIN; 
 
 CENSORSHIP OF THE PRESS; MYSTICS AND ILLUMINATI- 
 THE ENDEMONIADAS; EL SANTO NlftO DE LA GUARDIA; 
 BRIANDA DE BARDAXI. 12mo., 522 pages. Cloth, $2.50. 
 
 FORMULARY OF THE PAPAL PENITENTIARY. In one 
 
 octavo volume of 221 pages, with frontispiece. Cloth, $2.50. 
 
 SUPERSTITION AND FORCE; ESSAYS ON THE WAGER 
 
 OF LAW, THE WAGER OF BATTLE, THE ORDEAL AND 
 TORTURE. Fourth edition, thoroughly revised. In one hand- 
 some royal 12mo. volume of 629 pages. Cloth, $2.75. 
 
 STUDIES IN CHURCH HISTORY. The Rise of the Temporal 
 
 Power Benefit of Clergy Excommunication. New edition. In one 
 handsome 12mo. volume of 605 pages. Cloth, $2.50. 
 
 AN HISTORICAL SKETCH OF SACERDOTAL CELIBACY 
 
 IN THE CHRISTIAN CHURCH. Second edition. In one hand- 
 some octavo volume of 685 pages. Cloth, $4.50. 
 
 LEHMANN (C. G.). A MANUAL OF CHEMICAL PHYSIOLOGY. 
 In one 8vo. volume of 327 pages, with 41 engravings. Cloth, $2.25, 
 
LEA BROTHERS & Co., PHILADELPHIA AND NEW "XORK. 19 
 
 LIKES (SYLVAN H.). A POCKET TEXT-BOOK OF GENITO- 
 URINARY AND VENEREAL DISEASES. In one handsome 
 12rao. volume of about 350 pages, with many illustrations. Shortly. 
 Cloth, $1.50, net. Lea's Series of Pocket Text-books, edited by BEEN 
 B. GALLAUDET, M. D. See page 18. 
 
 LOOMIS (ALFRED L.) AND THOMPSON (W. OILMAN, 
 
 EDITORS). A SYSTEM OF PRACTICAL MEDICINE. In 
 Contributions by Various American Authors. In four very hand- 
 some octavo volumes of about 900 pages each, fully illustrated in 
 in black and colors. Complete work now ready. Per volume, cloth, 
 $5 ; leather, $6 ; half Morocco, $7. For sale by subscription only. 
 Full prospectus free on application to the Publishers. See American 
 System of Practical Medicine, page 2. 
 
 LUFF (ARTHUR P.). 
 
 Students of Medicine, 
 engravings. Cloth, $2. 
 
 MANUAL OF CHEMISTRY, for the use of 
 In one 12mo. volume of 522 pages, with 36 
 See Student's Series of Manuals, page 27. 
 
 LYMAN (HENRY M.). THE PRACTICE OF MEDICINE. In one 
 
 very handsome octavo volume of 925 pages, with 170 engravings. 
 Cloth, $4.75 ; leather, $5.75. 
 
 Complete, concise, fully abreast of i Practical, systematic, complete and 
 the times and needed by all students well balanced. Chicago Med. Re- 
 and practitioners. Univ. Med. Mag. corder. 
 
 An exceedingly valuable text-book. ' 
 
 LYONS (ROBERT D.). A TREATISE ON FEVER. In one octavo 
 volume of 362 pages. Cloth, $2.25. 
 
 MACKENZIE (JOHN NOLAND). ON THE NOSE AND THROAT. 
 
 Handsome octavo, about 600 pages, richly illustrated. Preparing. 
 
 MAISCH (JOHN M.). A MANUAL OF ORGANIC MATERIA 
 MEDICA. New (7th) edition, thoroughly revised by H. C. C. MAISCH, 
 Ph. G., Ph. D. In one very handsome 12mo. volume of 512 pages, with 
 285 engravings. Just ready. Cloth, $2.50, net. 
 
 Used as text-book in every college 
 of pharmacy in the United States 
 and recommended in medical col- 
 leges. American Therapist. 
 
 Noted on both sides of the Atlantic 
 and esteemed as much in Germany as 
 
 in America. The work has no equal. 
 Dominion Med. Monthly. 
 
 The best handbook upon phar- 
 macognosy of any published in this 
 country. Boston Med. & Sur. Jonr. 
 
LEA BROTHERS & Co., PHILADELPHIA AND NEW YORK. 
 
 MALSBARY (GEORGE E.). A POCKET TEXT-BOOK OF 
 THEORY AND PRACTICE OF MEDICINE. In one handsome 
 12mo. volume of about 350 pages. Cloth, $1.50, net. Shortly. Lea's 
 r/Vx of Pocket Text-books, edited by BERN B. GALLAUDET, M. D. 
 See page 18. 
 
 MANUALS. See Students Quiz Series, page 27, Student's Series of 
 Manuals, page 27, and Series of Clinical Manuals, page 25. 
 
 MARSH (HOWARD). DISEASES OF THE JOINTS. In one 12mo. 
 volume of 468 pages, with 64 engravings and a colored plate. Cloth, $2. 
 See Series of Clinical Manuals, page 25. 
 
 MARTIN (EDWARD). A MANUAL OF SURGICAL DIAGNOSIS. 
 In one 12mo. volume of about 400 pp., fully illustrated. Preparing. 
 
 MARTIN (WALTON) AND ROCKWELL, (WM. H.). A POCKET 
 TEXT-BOOK OF CHEMISTRY AND PHYSICS. In one hand- 
 some 12mo. volume of about 350 pages, with many illustrations. Cloth, 
 $1.50, net. Shortly. Lea's Series of Pnr/.-rf Text-books, edited by 
 I'.KKN B. GALLAUDET, M. D. See page 18. 
 
 MAY (C. H.). MANUAL OF THE DISEASES OF WOMEN. For 
 
 the use of Students and Practitioners. Second edition, revised by L. 
 S. RAU, M. D. In one 12mo. volume of 360 pages, with 31 engrav- 
 ings. Cloth, $1.75. 
 
 MEDICAL NEWS POCKET FORMULARY, see page 32. 
 
 MITCHELL (S. WEIR). CLINICAL LESSONS ON NERVOUS 
 DISEASES. In one 12mo. volume of 299 pages, with 19 engravings 
 and 2 colored plates. Cloth, $2.50. Of the hundred numbered copies 
 with the Author's signed title page a few remain ; these are offered 
 in green cloth, gilt top, at $3.50, net. 
 
 The book treats of hysteria, recur- 
 rent melancholia, disorders of sleep, 
 choreic movements, false sensations 
 of cold, ataxia, hemiplegic pain, 
 treatment of sciatica, erytnromelal- 
 gia, reflex ocularneurosis, hysteric 
 
 contractions, rotary movements in 
 the feeble minded, etc. Few can 
 speak with more authority than the 
 author. The Journal of the Ameri- 
 can Medical Association. 
 
 MITCHELL (JOHN K.). REMOTE CONSEQUENCES OF IN- 
 JURIES OF NERVES AND THEIR TREATMENT. In one 
 handsome 12mo. volume of 239 pages, with 12 illustrations. Cloth, $1.75. 
 
 Injuries of the nerves are of fre- 
 quent occurrence in private practice, 
 and often the cause of intractable 
 and painful conditions, conse- 
 quently this volume is of especial 
 interest. Doctor Mitchell has had 
 
 access to hospital records for the last 
 thirty years, as well as to the 
 government documents, and has 
 skilfully utilized his opportunities. 
 The Med. Age. 
 
 MORRIS (MALCOLM). DISEASES OF THE SKIN. New (2d) 
 edition. In one 12mo. volume of 601 pages, with 10 chromo-litho- 
 graphic plates and 26 engravings. Cloth, $3.25, net. Just ready. 
 
 MULLER (J.). PRINCIPLES OF PHYSICS AND METEOROL- 
 OGY. In one large 8yo. vol. of 623 pages, with 638 cuts. Cloth, $4.50. 
 
LEA BROTHERS & Co., PHILADELPHIA AND NEW YORK. 21 
 
 MUSSER (JOHN H.). A PEACTICAL TEEATISE ON MEDICAL 
 DIAGNOSIS, for Students and Physicians. New (3d) edition, thor- 
 oughly revised. In one octavo volume of about 1000 pages, with about 
 220 engravings and 48 full-page colored plates. In press. 
 Notices of previous edition are appended. 
 
 We have no work of equal value 
 in English. University Medical 
 Magazine. 
 
 His descriptions of the diagnostic 
 manifestations of diseases are accu- 
 rate. This work will meet all the 
 requirements of student and physi- 
 cian. The Medical News. 
 
 From its pages may be made the 
 diagnosis of every malady that 
 afflicts the human body, including 
 those which in general are dealt 
 with only by the specialist. North- 
 western Lancet. 
 
 It so thoroughly meets the precise 
 demands incident to modern research 
 that it has been adopted as a leading 
 text-book by the medical colleges 
 of this country. North American 
 Practitioner. 
 
 Occupies the foremost place as a 
 thorough, systematic treatise. Ohio 
 Medical Journal. 
 
 The best of its kind, invaluable to 
 the student, general practitioner and 
 teacher. Montreal Medical Journal. 
 
 NATIONAL DISPENSATORY. See Stille, Maisch & Caspari, p. 27. 
 
 NATIONAL FORMULARY. See Stille, Maisch & Caspari' 8 National 
 Dispensatory, page 27. 
 
 NATIONAL MEDICAL DICTIONARY. See Billings, page 4. 
 
 NETTLESHIP (E.). DISEASES OF THE EYE. New (5th) American 
 from sixth English edition, thoroughly revised. In one 12mo. volume 
 of 521 pages, with 161 engravings, and 2 colored plates, test-types, 
 formulae and color-blindness test. Cloth, $2.25. Just ready. 
 
 By far the best student's text-book 
 on the subject of ophthalmology and 
 is conveniently and concisely ar- 
 ranged. The Clinical Review. 
 
 It has been conceded by ophthal- 
 mologists generally that this work 
 for compactness, practicality and 
 clearness has no superior in the 
 
 English language. Journal of 
 Medicine and Science. 
 
 The present edition is the result 
 of revision both in England and 
 America, and therefore contains the 
 latest and best ophthalmological 
 ideas of both continents. The Phy- 
 sician and Surgeon. 
 
 NICHOLS (JOHN B.) AND VALE (F. P.). A POCKET TEXT- 
 BOOK OF HISTOLOGY AND PATHOLOGY. In one handsome 
 12mo. volume of about 350 pages, with many illustrations. In press. 
 Cloth, $1.50, net. Lea's Series of Pocket Text-books, edited by BERN 
 B. GALLATJDET, M. D. See page 18. 
 
 NORRIS (WM. F.) AND OLIVER (CHAS. A.). TEXT-BOOK OF 
 OPHTHALMOLOGY. In one octavo volume of 641 pages, with 357 
 engravings and 5 colored plates. Cloth, $5 ; leather, $6. 
 
 A safe and admirable guide, well best, the safest and the most conif re- 
 qualified to furnish a working he nsive volume upon the subject that 
 knowledge of ophthalmology. has ever been offered to the Ainer- 
 Johns Hopkins Hospital Bulletin. ican medical public. Annals of 
 
 It is practical in its teachings. Ophthalmology and Otology. 
 We unreservedly endorse it as the 
 
22 LEA BROTHKBS & Co., PHILADELPHIA AND NEW YOBK. 
 
 OWEN (EDMUND). SURGICAL DISEASES OF CHILDREN. 
 In one 12mo. volume of 525 pages, with 85 engravings and 4 colored 
 plates. Cloth, $2. See Series of Clinical Manuals, page 25. 
 
 PARK (ROSWEL.L.). A TREATISE ON SURGERY BY AMERI- 
 CAN AUTHORS. New and condensed edition. JH /y/vxx. In one 
 royal octavo volume of about 1250 pages, witli about 1000 engravings 
 and many full-page plates. JS7' This work is also published in a 
 larger edition, comprising two volumes. Volume I., General Suryery, 
 799 pages, with 356 engravings and 21 full-page plates, in colors and 
 monochrome. Volume II., Special Surycry, 800 pages, with 430 engra- 
 vings and 17 full-page plates, in colors and monochrome. Per volume, 
 cloth, $4.50 ; leather, $5.50. Net. 
 
 The work is fresh, clear and practi- way that they add great force to the 
 cal, covering the ground thoroughly j text. The Chicago Medical Re- 
 yet briefly, and well arranged for ! corder. 
 
 rapid reference, so that it will be of The various writers have em- 
 special value to the student and busy bodied the teachings accepted at 
 practitioner. The pathology is the present hour. The North Amer- 
 oroad, clear and scientific, while the ican Practitioner. 
 suggestions upon treatment are Both for the student and practi- 
 clear-cut, thoroughly modern and tioner it is most valuable. It is 
 admirably resourceful. Johns Hop- I thoroughly practical and yet thor- 
 kins Hospital Bulletin. oughly scientific. Medical News. 
 
 The latest and best work written A truly modern surgery, not only 
 
 upon the science and art of surgery. 
 Columbus Medical Journal. 
 
 The illustrations are almost en- 
 tirely new and executed in such a 
 
 in pathology, but also in sound 
 surgical therapeutics. New Or- 
 leans Med. and Surgical Journal. 
 
 PARK (WILLIAM H.). BACTERIOLOGY IN MEDICINE AND 
 SURGERY. 12mo., about 550 pages, fully illustrated. In press. 
 
 PARRY (JOHN S.). EXTRA-UTERINE PREGNANCY, ITS 
 CLINICAL HISTORY, DIAGNOSIS, PROGNOSIS AND TREAT- 
 MENT. In one octavo volume of 272 pages. Cloth, $2.50. 
 
 PARVIN (THEOPHIL.US). THE SCIENCE AND ART OF OB- 
 STETRICS. Third edition. In one handsome octavo volume of 
 677 pages, with 267 engravings and 2 colored plates. Cloth, $4.25 ; 
 leather, $5.25. 
 
 In the foremost rank among the 
 most practical and scientific medical 
 works of the day. Medical News. 
 
 It ranks second to none in the 
 English language. Annals of Gyne- 
 cology and Pediatry. 
 
 The book is complete in every de- 
 partment, and contains all the neces- 
 sary detail required by the modern 
 
 practising obstetrician. Interna- 
 tional Medical Magazine. 
 
 Parvin's work is practical, con- 
 cise and comprehensive. We com- 
 mend it as first of its class in the 
 English language. Medical Fort- 
 nightly. 
 
 It is an admirable text-book in 
 every sense of the \vord.-Nashville 
 Journal of Medicine and Surgery. 
 
LEA BKOTHEKS & Co., PHILADELPHIA AND NEW YOKK. 23 
 
 PEPPER'S SYSTEM OF MEDICINE. See page 3. 
 
 PEPPER (A. J.). FORENSIC MEDICINE. In press. See Student's 
 
 Series of Manuals, page 27. 
 
 SURGICAL PATHOLOGY. In one 12mo. volume of 511 pages, 
 with 81 engravings. Cloth, $2. See Student's Series of Manuals, p. 27. 
 
 PICK (T. PICKERING). FRACTURES AND DISLOCATIONS. 
 
 In one 12mo. volume of 530 pages, with 93 engravings. Cloth, $2. 
 See Series of Clinical Manuals, page 25. 
 
 PLAYFAIR (W. S.). A TREATISE ON THE SCIENCE AND 
 PRACTICE OF MIDWIFERY. Seventh American from the ninth 
 English edition. In one octavo volume of 700 pages, with 207 
 engravings and 7 plates. Cloth, $3.75 net; leather, $4.75, net. Just 
 ready. 
 
 In the numerous editions which obstetrician. It holds a place among 
 
 the ablest English-speaking authori- 
 
 have appeared it has been kept con- 
 stantly in the foremost rank. It is 
 a work which can be conscientiously 
 recommended to the profession. 
 The Albany Medical Annals. 
 
 This work must occupy a fore- 
 most place in obstetric medicine as 
 a safe guide to both student and 
 
 ties on the obstetric &rt. Buffalo 
 Medical and Surgical Journal. 
 
 An epitome of the science and 
 practice of midwifery, which em- 
 bodies all recent advances. The 
 Medical Fortnightly. 
 
 THE SYSTEMATIC TREATMENT OF NERVE PROSTRA- 
 TION AND HYSTERIA. In one 12mo. volume of 97 pages. 
 Cloth, $1. 
 
 POCKET FORMULARY, see page 32. 
 POCKET TEXT-BOOKS, see page 18. 
 
 POL.ITZER (ADAM). A TEXT-BOOK OF THE DISEASES OF THE 
 EAR AND ADJACENT ORGANS. Second American from the 
 third German edition. Translated by OSCAR DODD, M. D., and 
 edited by SIR WILLIAM DALEY, F. R. C. S. In one octavo volume of 
 748 pages, with 330 original engravings. Cloth, $5.50. 
 
 The anatomy and physiology of ment are clear and reliable. We 
 
 each part of the organ of hearing 
 are carefully considered, and then 
 follows an enumeration of the dis- 
 eases to which that special part of 
 the auditory apparatus is especially 
 liable. The indications for treat- 
 
 can confidently recommend it, for it 
 contains all that is known upon the 
 subject. London Lancet. 
 
 A safe and elaborate guide into 
 every part of otology. American 
 Journal of the Medical Sciences. 
 
 POTTS (CHARLES S.). A POCKET TEXT-BOOK. OF NERVOUS 
 AND MENTAL DISEASES. In one handsome 12ino. volume of 
 about 450 pages. Cloth, $1.50, net. Shortly. Lea's Series of Pocket 
 Text-books, edited by BERN B. GALLAUDET, M. D. See page 18. 
 
 PROGRESSIVE MEDICINE, see page 32. 
 
 PURDY (CHARLES WA BRIGHT'S DISEASE AND ALLIED 
 AFFECTIONS OF THE KIDNEY. In one octavo volume of 288 
 pages, with 18 engravings. Cloth, $2. 
 
24 LEA BROTHERS & Co., PHILADELPHIA AND NEW YORK. 
 
 PYE-SMITH (PHILIP H.). DISEASES OF THE SKIN. In one 
 
 12mo. vol. of 407 pp., with 28 illus., 18 of which are colored. Cloth, $2. 
 
 QUIZ SERIES. See Student's Quiz Series, page 27. 
 
 KALFE (CHARLES H.). CLINICAL CHEMISTRY. In one 
 12mo. volume of 314 pages, with 16 engravings. Cloth, $1.50. See 
 Student's Series of Manuals, page 27. 
 
 RAMSBOTHAM (FRANCIS H.). THE PRINCIPLES AND PRAC- 
 TICE OF OBSTETRIC MEDICINE AND SURGERY. In one 
 imperial octavo volume of 640 pages, with 64 plates and numerous 
 engravings in the text. Strongly bound in leather, $7. 
 
 REICHERT (EDWARD T.). A TEXT-BOOK ON PHYSIOLOGY. 
 In one handsome octavo volume of about 800 pages, richly illustrated. 
 Preparing. 
 
 REMSEN (IRA). THE PRINCIPLES OF THEORETICAL CHEM- 
 ISTRY. New (5th) edition, thoroughly revised. In one 12mo. vol- 
 ume of 326 pages. Cloth, $2. 
 
 A clear and concise explanation that the work has met with general 
 of a difficult subject. We cordially favor. This is further established 
 recommend it. The London Lancet. \ by the fact that it has been trans- 
 
 The book is equally adapted to the lated into German and Italian. The 
 
 student of chemistry or the practi- 
 tioner who desires to broaden his 
 theoretical knowledge of chemistry. 
 New Orleans Med. and Surg. Jour. 
 The appearance of a fifth edition 
 of this treatise is in itself a guarantee 
 
 treatise is especially adapted to the 
 laboratory student. It ranks unusu- 
 ally high among the works of this 
 class. This edition has been brought 
 fully up to the times. American 
 Medico-Surgical Bulletin. 
 
 RICHARDSON (BENJAMIN WARD). PREVENTIVE MEDI- 
 CINE. In one octavo volume of 729 pages. Cloth, $4 ; leather, $5. 
 
 ROBERTS (JOHN B.). THE PRINCIPLES AND PRACTICE OF 
 MODERN SURGERY. New (2d) edition. In one octavo volume of 
 about 800 pages, with about 500 engravings. Shortly. 
 
 THE COMPEND OF ANATOMY. For use in the Dissecting 
 
 Room and in preparing for Examinations. In one 16mo. volume of 
 196 pages. Limp cloth, 75 cents. 
 
 ROBERTS (SIR WILLIAM). A PRACTICAL TREATISE ON 
 URINARY AND RENAL DISEASES, INCLUDING URINARY 
 DEPOSITS. Fourth American from the fourth London edition. In 
 one very handsome 8vo. vol. of 609 pp., with 81 illus. Cloth, $3.50. 
 
 ROBERTSON (J. MCGREGOR). PHYSIOLOGICAL PHYSICS. 
 In one 12mo. volume of 537 pages, with 219 engravings. Cloth, $2. 
 See Student's Series of Manuals, page 27. 
 
 ROSS (JAMES). A HANDBOOK OF THE DISEASES OF THE 
 NERVOUS SYSTEM. In one handsome octavo volume of 726 pagee, 
 with 184 engravings. Cloth, $4.50 ; leather, $5.50. 
 
 SAVAGE (GEORGE H.). INSANITY AND ALLIED NEUROSES, 
 PRACTICAL AND CLINICAL. In one 12mo. volume of 551 pages, 
 with 18. typical engravings. Cloth, $2. See Series of Clinical Man- 
 ualt, page 25. 
 
LEA BROTHERS & Co., PHILADELPHIA AND NEW YORK. 25 
 
 SCHAFER (EDWARD A.). THE ESSENTIALS OF HISTOL- 
 OGY, DESCRIPTIVE AND PRACTICAL. For the use of Students. 
 New (5th) edition. In one handsome octavo volume of 359 pages, 
 with 392 illustrations. Cloth, $3.00, net. Just ready. 
 
 Nowhere else will the same very 
 moderate outlay secure as thoroughly 
 useful and interesting an atlas of 
 structural anatomy. The American 
 Journal of the Medical Sciences. 
 
 The most satisfactory elementary 
 text-book of histology in the Eng- 
 lish language. The Boston Med. and 
 Sur. Jour. 
 
 A COURSE OF PRACTICAL HISTOLOGY. New(2d) edition. 
 In one 12mo. volume of 307 pages, with 59 engravings. Cloth, $2.25. 
 
 The book very nearly approaches 
 perfection. Methods are given with 
 an accuracy of detail and prevision 
 of difficulties which can hardly be 
 
 overpraised. It bears eloquent tes- 
 timony to the wide knowledge and 
 untiring industry of its author. 
 The Scottish Med. and Surg. Jour. 
 
 SCHLEIF (WILLIAM). MATERIA MEDICA, THERAPEUTICS, 
 PRESCRIPTION WRITING, MEDICAL LATIN, ETC. 12mo., 
 
 352 pages. Cloth, $1.50, net. Just ready. Lea's Series of Pocket 
 Text-books. Edited by BERN B. GALLATJDET, M. D. See page 18. 
 
 SOHMITZ AND ZUMPT'S CLASSICAL SERIES. Advanced 
 Latin Exercises. Cloth, 60 cts. Schmidt's Elementary Latin Exer- 
 cises. Cloth, 50 cents. Sallust. Cloth, 60 cents. Nepos. Cloth, 60 
 cents. Virgil. Cloth, 85 cents. Curtius. Cloth, 80 cents. 
 
 SCHOFIELD (ALFRED T.). ELEMENTARY PHYSIOLOGY 
 FOR STUDENTS. In one 12mo. volume of 380 pages, with 227 
 engravings and 2 colored plates. Cloth, $2. 
 
 SCHREIBER (JOSEPH). A MANUAL OF TREATMENT BY 
 MASSAGE AND METHODICAL MUSCLE EXERCISE. Octavo 
 volume of 274 pages, with 117 engravings. 
 
 SENN (NICHOLAS). SURGICAL BACTERIOLOGY. Second edi- 
 tion. In one octavo volume of 268 pages, with 13 plates, 10 of which 
 are colored, and 9 engravings. Cloth, $2. 
 
 SERIES OF CLINICAL MANUALS. A Series of Authoritative 
 Monographs on Important Clinical Subjects, in 12mo. volumes of about 
 550 pages, well illustrated. The following volumes are now ready : 
 YEO on Food in Health and Disease, new (2d) edition, $2.50; CARTER 
 and FROST'S Ophthalmic Surgery, $2.25 ; HUTCHINSON on Syphilis, 
 $2.25; MARSH on Diseases of the Joints, $2; OWEN on Surgical Dis- 
 eases of Children, $2; PICK on Fractures and Dislocations, $2; SAVAGE 
 on Insanity and Allied Neuroses, $2. 
 For separate" notices, see under various authors' names. 
 
 SERIES OF STUDENT'S MANUALS. See page 27. 
 
 SIMON (CHARLES B.). CLINICAL DIAGNOSIS, BY MICRO- 
 SCOPICAL AND CHEMICAL METHODS. New (2d) edition. In 
 one very handsome octavo volume of 530 pages, with 135 engravings 
 and 14 full-page colored plates. Cloth, $3.50. Just ready. 
 
 This book thoroughly deserves its 
 success. It is a very complete, authen- 
 tic and useful manual of the micro- 
 scopical and chemical methods 
 which are employed in diagnosis. 
 Very excellent colored plates illus- 
 trate this work. New York Medical 
 Journal. 
 
 In all respects entirely up to date. 
 
 spects entirely up 
 Record. 
 
 Medical 
 
 The chapter on examination of 
 the urine is the most complete and 
 advanced that we know of in the 
 English language. Canadian Prac- 
 titioner, 
 
26 LEA BROTHERS & Co., PHILADELPHIA AND NEW YORK. 
 
 SIMON (W.). MANUAL OF CHEMISTRY. A Guide to Lectures 
 and Laboratory Work for Beginners in Chemistry. A Text-book 
 specially adapted for Students of Pharmacy and Medicine. New (6th) 
 edition. In one 8vo. volume of 536 pages, with 46 engravings and 8 
 plates showing colors of 64 tests. Cloth, $3.00, ><> t. Jnut ready. 
 
 It is difficult to see how a better the covers of this book. The North- 
 
 book could be constructed. No man western Lancet. 
 
 who devotes himself to the practice Its statements are all clear and its 
 
 of medicine need know more about teachings are practical. Virginia 
 
 chemistry than is contained between Med. Monthly. 
 
 SLADE (D. D.). DIPHTHERIA; ITS NATURE AND TREAT- 
 MENT. Second edition. In one royal 12mo. vol., 158 pp. Cloth, $1.25. 
 
 SMITH (EDWARD). CONSUMPTION; ITS EARLY AND REME- 
 DIABLE STAGES. In one 8vo. volume of 253 pp. Cloth, $2.25. 
 
 SMITH (J. LEWIS). A TREATISE ON THE DISEASES OF IN- 
 FANCY AND CHILDHOOD. Eighth edition, thoroughly revised 
 and rewritten and much enlarged. In one large 8vo. volume of 983 
 pages, with 273 engravings and 4 full-page plates. Cloth, $4.50; 
 leather, $5.50. 
 
 The most complete and satisfac- j can more than hold its own against 
 tory text-book with which we are [ any other work treating of the same 
 acquainted . American Gynecologi- 
 cal and Obstetrical Journal. 
 
 It truly is the most evenly bal- 
 anced, clear in description and 
 
 thorough in detail of any of the I For years the leading text-book on 
 books published in this country on children's diseases in America. 
 this subject. Medical Fortnightly. Chicago Medical Recorder. 
 A treatise which in every respect 
 
 SMITH (STEPHEN). OPERATIVE SURGERY. Second and thor- 
 oughly revised edition. In one octavo volume of 892 pages, with 
 1005 engravings. Cloth, $4 ; leather, $5. 
 
 dium for the modern surgeon. Bos- 
 ton Medical and Surgical Journal. 
 
 subject. American Medico- Surgica I 
 Bulletin. 
 
 A safe guide for students and phy- 
 sicians. The Am. Jour, of Obstetrics. 
 
 One of the most satisfactory works 
 on modern operative surgery yet 
 published. Tne book is a compen- 
 
 SOLL.Y (S. EDWIN). A HANDBOOK OF MEDICAL CLIMA- 
 TOLOGY. In one handsome octavo volume of 462 pages, with en- 
 gravings and 11 full-page plates, 5 of which are in colors. Cloth, $4.00. 
 Just ready. 
 
 A clear and lucid summary of 
 what is known of climate in relation 
 to its influence upon human beings. 
 The Therapeutic Gazette. 
 
 The book is admirably planned, 
 clearly written, and the author speaks 
 from an experience of thirty years as 
 
 an accurate observer and practical 
 therapeutist. Maryland Med. Jour. 
 Every practitioner of medicine 
 should possess himself of a copy and 
 study it, and we are sure he will 
 never regret it. St. Louis Medical 
 and Surgical Journal. 
 
 ST1LLE (ALFRED). CHOLERA; ITS ORIGIN, HISTORY, CAUS- 
 ATION, SYMPTOMS, LESIONS, PREVENTION AND TREAT- 
 MENT. In one 12mo. volume of 163 pages, with a chart showing 
 routes of previous epidemics. Cloth, $1.25. 
 
 THERAPEUTICS AND MATERIA MEDICA. Fourth and 
 
 revised edition. In two octavo volumes, containing 1936 pages. 
 Cloth, $10; leather, $12. 
 
LEA BROTHERS & Co., PHILADELPHIA AND NEW YORK. 27 
 
 STLLLiB (ALFRED), MAISCH (JOHN M.) AND CASPABI 
 (CHAS. JR.). THE NATIONAL DISPENSATORY: Containing 
 the Natural History, Chemistry, Pharmacy, Actions and Uses of 
 Medicines, including those recognized in the latest Pharmacopeias of 
 the United States, Great Britain and Germany, with numerous refer- 
 ences to the French Codex. Fifth edition, revised and enlarged, 
 including the new U. S. Pharmacopoeia, Seventh Decennial Revision. 
 With Supplement containing the new edition of the National Formu- 
 lary. In one magnificent imperial octavo volume of about 2025 pages, 
 with 320 engravings. Cloth, $7.25; leather, $8. With ready reference 
 Thumb-letter Index. Cloth, $7.75 ; leather, $8.50. 
 Recommended most highly for the amount of information contained in 
 
 physician 
 druererist.- 
 
 and invaluable to the 
 ruggist. Therapeutic Gazette. 
 It is the oflicial guide for the Med- 
 ical and Pharmaceutical professions. 
 Buffalo Med. and Sur. Jour. 
 The readiness with which the vast 
 
 this work is made available is indi- 
 cated by the twenty-five thousand 
 references in the two indexes. Bos- 
 ton Medical and Surgical Journal. 
 Should be recognized as a national 
 standard. North Am. Practitioner. 
 
 STIMSON (LJEWIS A.). A MANUAL OF OPERATIVE SURGERY. 
 
 New (3d) edition. In one royal 12mo. volume of 614 pages, with 306 
 engravings. Cloth, $3.75. 
 
 A useful and practical guide for 
 all students and practitioners. Am. 
 Journal of the Medical Sciences. 
 
 The book is worth the price for the 
 illustrations alone. Ohio Medical 
 Journal. 
 
 STIMSON (LEWIS A.). A TREATISE ON FRACTURES AND 
 
 DISLOCATIONS. In one handsome octavo volume of 831 pages, 
 
 with 326 engravings and 20 plates. Just ready. Cloth, $5.00, net ; 
 
 leather, $6.00, net. 
 
 Preeminently the authoritative Taken as a whole, the work is the 
 
 text-book upon the subject. The best one in English to-day. *. 
 
 vast experience of the author gives j Louis Medical and Surgical Journal. 
 
 to his conclusions an unimpeachable i Pointed, practical, comprehensive, 
 
 value. The work is profusely il- ! exhaustive, authoritative, well writ- 
 
 lustrated. It will be found indis- ten and well arranged. Denver 
 
 pensable to the student and the prac- Medical Times. 
 
 titioner alike. The Medical Age. \ 
 
 STUDENT'S QUIZ SERIES. Thirteen volumes, convenient, author- 
 itative, well illustrated, handsomely bound in cloth. 1. Anatomy 
 (double number); 2. Physiology; 3. Chemistry and Physics; 4. Histol- 
 ogy, Pathology, and Bacteriology; 5. Materia Medica and Thera- 
 peutics ; 6. Practice of Medicine ; 7. Surgery (double number); 8. Genito- 
 
 Anatomy and Surgery, which being double numbers are priced at 
 $1.75 each. Full specimen circular on application to publishers. 
 
 STUDENT'S SERIES OF MANUALS. 12mos. of from 300-540 
 pages, profusely illustrated, and bound in red limp cloth. HERMAN'S 
 First Lines in Midwifery, $1.25; LUFF'S Manual of Chemistry, $2; 
 BRUCE'S Materia Medica and Therapeutics (sixth edition), $1.50. net. 
 
 "RlTT T >e C*i\m-r\avo+\\TO A naisvmir or\(\ "PVnroirilrKTTT- <fcO! ROBERT- 
 
 BELL'S Comparative Anatomy and Physiology, 
 SON'S Physiological Physics, $2; GOULD'S Surgical Diagnosis, $2; 
 KLEIN'S Elements of Histology (5th edition), $2.00, net ; PEPPER'S 
 Surgical Pathology, $2; TREVES' Surgical Applied Anatomy, $2; 
 RALFE'S Clinical Chemistry, $1.50; and CLARKE and LOCKWOOD'S 
 Dissector's Manual, $1.50. The following is in press: PEPPER'S 
 Forensic Medicine. 
 For separate notices, see under various author's names. 
 
LEA BROTHERS A Co., PHILADELPHIA AND NEW YORK. 
 
 STURGES (OCTAVIUS). AN INTRODUCTION TO THE STUDY 
 OF CLINICAL MEDICINE. In one 12mo. volume. Cloth, $1.25. 
 
 SUTTON (JOHN BLAND). SURGICAL DISEASES OF THE 
 OVARIES AND FALLOPIAN TUBES. Including Abdominal 
 Pregnancy. In one 12mo. volume of 513 pages, with 119 engravings 
 and 5 colored plates. Cloth, $3. 
 
 TAIT (LAWSON). DISEASES OF WOMEN AND ABDOMINAL 
 SURGERY. In two handsome octavo volumes. Vol. I. contains 546 
 pages and 3 plates. Cloth, $3. 
 
 TANNER (THOMAS HAWKES) ON THE SIGNS AND DIS- 
 EASES OF PREGNANCY. From the second English edition. In 
 one octavo volume of 490 pages, with 4 colored plates and 16 engrav- 
 ings. Cloth, $4.25. 
 
 TAYLOR (ALFRED S.). MEDICAL JURISPRUDENCE. New 
 American from the twelfth English edition, specially revised by CLARK 
 BELL, ESQ., of the N. Y. Bar. In one 8vo. vol. of 831 pages, with 54 
 engrs. and 8 full-page plates. Cloth, $4.50; leather, $5.50 Just ready. 
 
 To the student, as to the physician, 
 we would say, get Taylor first, and 
 then add as means and inclination 
 enable you. American Practitioner 
 and News. 
 
 It is the authority accepted as 
 final by the courts of all English- 
 speaking countries. This is the im- 
 portant consideration for medical 
 men, since in the event of their 
 being summoned as experts or wit- 
 
 nesses, it strongly behooves them to 
 be prepared according to the princi- 
 ples and practice everywhere ac- 
 cepted. The work will be found to 
 be thorough, authoritative and 
 modern. Albany Law Journal. 
 
 Probably the best work on the 
 subject written in the English lan- 
 guage. The work has been thor- 
 oughly revised and is up to date. 
 Pacific Medical Journal. 
 
 ON POISONS IN RELATION TO MEDICINE AND MEDI- 
 CAL JURISPRUDENCE. Third American from the third London 
 edition. In one octavo volume of 788 pages, with 104 illustrations 
 Cloth, $5.50 ; leather, $6.50. 
 
 TAYLOR (ROBERT W.). THE PATHOLOGY AND TREAT- 
 MENT OF VENEREAL DISEASES. New (2d) edition. In one 
 very handsome octavo volume of about 700 pages, with about 200 en- 
 gravings and 6 colored plates. In press. 
 Notices of previous edition are appended. 
 
 By long odds the best work on 
 venereal diseases. Louisville Medi- 
 cal Monthly. 
 
 In the observation and treatment 
 of venereal diseases his experience 
 has been greater probably than that 
 of any other practitioner of this con- 
 tinent. New York Medical Journal. 
 
 The clearest, most unbiased and 
 ably presented treatise as yet pub- 
 lished on this vast subject. The 
 Medical News. 
 
 Decidedly the most important and 
 authoritative treatise on venereal 
 
 diseases that has in recent years ap- 
 peared in English. American Jour- 
 nal of the Medical Sciences. 
 
 It is a veritable storehouse of our 
 knowledge of the venereal diseases. 
 It is commended as a conservative, 
 practical, full exposition pf the 
 greatest value. Chicago Clinicnl 
 Review. 
 
 The best work on venereal dis- 
 eases in the English language. It 
 is certainly above everything of the 
 kind. The St. Louis Medical and 
 Surgical Journal. 
 
LEA BROTHERS & Co., PHILADELPHIA AND NEW YOBK. 29 
 
 TAYLOR (ROBERT W.). A PRACTICAL TREATISE ON SEX- 
 UAL DISORDERS IN THE MALE AND FEMALE. In one 
 8vo. vol. of 448 pp., with 73 engravings and 8 colored plates. Cloth. 
 
 $3. Net. 
 
 It is a timely boon to the medical 
 profession that an observer of Dr. 
 Taylor's skill and experience has 
 written a work on this hitherto 
 neglected and little understood class 
 of diseases which places them on a 
 scientific basis and renders them so 
 clear that the physician who reads 
 its pages can treat this class of 
 patients intelligently. Sterility in 
 
 the female is presented in an exhaus- 
 tive manner, all of the causes pro- 
 ducing it being described. The 
 author has presented to the profes- 
 sion the ablest and most scientific 
 work as yet published on sexual 
 disorders, and one which, if carefully 
 followed, will be of unlimited value 
 to both physician and patient. 
 Medical News. 
 
 A CLINICAL ATLAS OF VENEREAL AND SKIN DISEASES. 
 
 Including Diagnosis, Prognosis and Treatment. In eight large folio 
 parts, measuring 14 x 18 inches, and comprising 213 beautiful figures 
 on 58 full-page chromo-lithographic plates, 85 fine engravings and 425 
 pages of text. Complete work now ready. Price per part, sewed in 
 heavy embossed paper, $2.50. Bound in one volume, half Russia, 
 $27 ; half Turkey Morocco, $28. For sale by subscription only. Address 
 the publishers. Specimen plates by mail on receipt of ten cents. 
 
 TAYLOR (SEYMOUR). INDEX OF MEDICINE. A Manual for 
 the use of Senior Students and others. In one large 12mo. volume of 
 802 pages. Cloth, $3.75. 
 
 THOMAS (T. GAILLARD) AND MUNDE (PAUL. P.). A PRAC 
 TICAL TREATISE ON THE DISEASES OF WOMEN. Sixth 
 edition, thoroughly revised by PAUL F. MTTNDE, M. D. In one 
 large and handsome octavo volume of 824 pages, with 347 engravings. 
 Cloth, $5 ; leather, $6. 
 
 The best practical treatise on the 
 subject in the English language. 
 It will be of especial value to the 
 general practitioner as well as to the 
 specialist. The illustrations are very 
 satisfactory. Many of them are new 
 and are particularly clear and attrac- 
 tive. Boston Med. and Sur. Jour. 
 
 This work, which has already gone 
 through five large editions, and has 
 been translated into French, Ger- 
 man, Spanish and Italian, is the 
 most practical and at the same time 
 the most complete treatise upon the 
 subject. The Archives of Gynecol- 
 ogy, Obstetrics and Pediatrics. 
 
 THOMPSON (SIR HENRY). CLINICAL LECTURES ON DIS- 
 EASES OF THE URINARY ORGANS. Second and revised edi- 
 tion. In one octavo vol. of 203 pp., with 25 engravings. Cloth, $2.25. 
 
 THE PATHOLOGY AND TREATMENT OF STRICTURE 
 
 OF THE URETHRA AND URINARY FISTULA. From the 
 third English edition. In one octavo volume of 359 pages, with 47 
 engravings and 3 lithographic plates. Cloth, $3.50. 
 
 THOMSON (JOHN). DISEASES OF CHILDREN. In one crown 
 octavo volume of 350 pages, with 52 illus. Cloth, $1.75, net. Just ready. 
 
 TODD (ROBERT BENTLEY). CLINICAL LECTURES ON CER- 
 TAIN ACUTE DISEASES. In one 8vo. vol. of 320 pp., cloth, $2.50. 
 
 TREVES (FREDERICK). OPERATIVE SURGERY. In two 
 8vo. vols. containing 1550 pp., with 422 illus. Cloth, $9 ; leath., $11. 
 
 A SYSTEM OF SURGERY. In Contributions by Twenty-five 
 
 English Surgeons. In two large octavo volumes. Vol. I., 1178 pages, 
 with 463 engravings and 2 colored plates. Vol. II., 1120 pages, with 
 487 engravings and 2 colored plates. Complete work, cloth, $16.00. 
 
30 LEA BROTHERS & Co., PHILADELPHIA AND NEW YORK. 
 
 TBEVES (FREDERICK). SURGICAL APPLIED ANATOMY. In 
 one 12mo. volume of 540 pages, with 61 engravings. Cloth, $2. See 
 Student's Series of Manuals, page 27. 
 
 TDTTLE (GEORGE M.). A POCKET TEXT-BOOK OF DISEASES 
 OF CHILDREN. In one handsome 12mo. volume of about :iOO pages, 
 with many illustrations. Cloth, $1.50, net. Shortly. Lea'* .SV/vY.s \ of 
 Pocket Text-books, edited by BERN B. GALLAUDET, M. D. See p 18. 
 
 VAUGHAN (VICTOR C.) AND NOVY (FREDERICK G.). 
 
 PTOMAINS, LEUCOMAINS, TOXINS AND ANTITOXINS, 
 or the Chemical Factors in the Causation of Disease. New (3d) edition. 
 In one 12mo. volume of 603 pages. Cloth, $3. 
 
 The work has been brought down j The present edition has been not 
 to date, and will be found entirely only thoroughly revised throughout 
 satisfactory. Journal of the Ameri- \ but also greatly enlarged, ample 
 can Medical Association. j consideration being given to the new 
 
 The most exhaustive and most re- subjects of toxins and antitoxins. 
 
 cent presentation of the subject. 
 American Jour, of the Med. Sciences. 
 
 Tri-State Medical Journal. 
 
 VISITING LIST. THE MEDICAL NEWS VISITING LIST for 1899. 
 Four styles : Weekly (dated for 30 patients); Monthly (undated for 
 120 patients per month) ; Perpetual (undated for 30 patients each 
 week); and Perpetual (undated for 60 patients each week). The 60- 
 patient book consists of 256 pages of assorted blanks. The first three 
 styles contain 32 pages of important data, thoroughly revised, and 
 160 pages of assorted blanks. Each in one volume, price, $1.25. 
 With thumb-letter index for quick use, 25 cents extra. Special rates 
 to advance-paying subscribers to THE MEDICAL NEWS or THE 
 AMERICAN JOURNAL OF THE MEDICAL SCIENCES, or both. See p. 32. 
 
 WATSON (THOMAS). LECTURES ON THE PRINCIPLES AND 
 PRACTICE OF PHYSIC. A new American from the fifth and 
 enlarged English edition, with additions by H. HARTSHORNE, M. D. 
 In two large 8vo. vols. of 1840 pp., with 190 cute. Cloth, $9 ; leather, $11. 
 
 WEST (CHARLES). LECTURES ON THE DISEASES PECULIAR 
 TO WOMEN. Third American from the third English edition. In 
 one octavo volume of 543 pages. Cloth, $3.75 ; leather, $4.75. 
 
 ON SOME DISORDERS OF THE NERVOUS SYSTEM IN 
 
 CHILDHOOD. In one small 12mo. volume of 127 pages. Cloth, $1. 
 
 WHARTON (HENRY B.). MINOR SURGERY AND BANDAG- 
 ING. New (4th) edition. In one 12mo. vol. of about 600 pages, with 
 about 500 engravings, many of which are photographic. Shortly. 
 Notices of previous edition are appended. 
 
 We know of no book which more 
 thoroughly or more satisfactorily 
 covers the ground of Minor Surgery 
 and Bandaging. Brooklyn Medical 
 Journal. 
 
 Well written, conveniently ar- 
 ranged and amply illustrated. It 
 covers the field so fully as to render 
 it a valuable text-book, as well as a 
 
 work of ready reference for sur- 
 geons. North Amer. Practitioner. 
 The part devoted to bandaging is 
 perhaps the best exposition of the 
 subject in the English language. It 
 can be highly commended to the 
 student, the practitioner and the 
 specialist. The Chicago Medical 
 Recorder. 
 
LEA BEOTHEES & Co., PHILADELPHIA AND NEW YOBK. 31 
 
 WHITLA (WILLIAM). DICTIONARY OF TREATMENT, OR 
 THERAPEUTIC INDEX. Including Medical and Surgical Thera- 
 peutics. In one square octavo volume of 917 pages. Cloth, $4. 
 
 WILLIAMS (DAWSON). THE MEDICAL DISEASES OF CHIL- 
 DREN. In one 12mo. volume of 629 pages, with 18 illustrations. 
 Just ready. Cloth, $2.50, net. 
 
 The descriptions of symptoms are 
 full, and the treatment recommended 
 will meet general approval. Under 
 each disease are given the symptoms, 
 
 diagnoses, prognosis, complications, 
 and treatment. The work is up to 
 date in every sense. The Charlotte 
 Medical Journal. 
 
 WILSON (ERASMUS). A SYSTEM OF HUMAN ANATOMY. 
 
 A new and revised American from the last English edition. Illustrated 
 with 397 engravings. In one octavo volume of 616 pages. Cloth, $4 ; 
 leather, $5. 
 
 THE STUDENT'S BOOK OF CUTANEOUS MEDICINE, 
 one 12mo. volume. Cloth, $3.50. 
 
 In 
 
 WINCKEL ON PATHOLOGY AND TREATMENT OF CHILDBED. 
 Translated by JAMES R. CHADWICK, A. M., M. D. With additions 
 by the Author. In one octavo volume of 484 pages. Cloth, $4. 
 
 WOHLER'S OUTLINES OF ORGANIC CHEMISTRY. Translated 
 from the eighth German edition, by IRA REMSEN, M. D. In one 
 12mo. volume of 550 pages. Cloth, $3. 
 
 YEAR-BOOK OF TREATMENT FOR 1892, 1893, 1896, 1897 and 1898. 
 Critical Reviews for Practitioners of Medicine and Surgery. In con- 
 tributions by 25 well-known medical writers. 12mos., aoout500 pages 
 each. Cloth, $1.50. In combination with THE MEDICAL NEWS and 
 THE AMERICAN JOURNAL OP THE MEDICAL SCIENCES, 75 cents. 
 
 YEO (I. BURNEY). FOOD IN HEALTH AND DISEASE. New 
 (2d) edition. In one 12mo. volume of 592 pages, with 4 engravings. 
 Cloth, $2.50. See Series of Clinical Manuals, page 26. 
 
 We doubt whether any book on 
 dietetics has been of greater or more 
 widespread usefulness than has this 
 much-quoted and much-consulted 
 
 work of Dr. Yeo's. The value of 
 the work is not to be overestimated. 
 New York Medical Journal. 
 
 - A MANUAL OF MEDICAL TREATMENT, OR CLINICAL 
 THERAPEUTICS. Two volumes containing 1275 pages. Cloth, $5.50. 
 
 YOUNG (JAMES K.). ORTHOPEDIC SURGERY. In one 8vo. 
 volume of 475 pages, with 286 illustrations. Cloth, $4; leather, $5. 
 
 In studying the different chapters, j surgical specialty and every page 
 one is impressed with the thorough- j abounds with evidences of prac- 
 ness of the work. The illustrations ticality. It is the clearest and most 
 are numerous the book thoroughly modern work upon this growing de- 
 practical Medical News. | partment of surgery. The Chicago 
 
 It is a thorough, a very cpmpre- ! Clinical Review, 
 hensive work upon this legitimate ! 
 
PERIODICALS. 
 
 PROGRESSIVE MEDICINE. 
 
 A Quarterly Digest of New Methods, Discoveries, and Improvements 
 in the Medical and Surgical Sciences by Eminent Authorities. Edited by 
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