HreiE 1 > LIBRARY OF THE UNIVERSITY OF CALIFORNIA. GIFT OF ...GEN....CJiAS,....Jl.....G.J^EJENLEAF..... BIOLOGY LIBRARY ABSORPTION SPECTRA 1. Spectrum of Ar gaud-lamp with Fraunhofefs lines in position. 2. Blood; ie. a strong solution of Oxyhasmoglobm fciemc 3. Blood more dilute. 4. Reduced Hsemoglobin. 5. Carbon Monoxide compound. 6. Acid Hsematin. . 7. Alkaline Hasmatin . 8. Sulphuretted Hydro gen compound. 9. Ox-Me acidulated with Acetic acid and colouring natter dissolved in Chloroform.. ((mn'/t fror/t observations fyrMr.WZepraik>-F'.C.S. 1885, KTEKES1 HlOTD-BOOK OF PHYSIOLOGY HAKD-BOOK OP PHYSIOLOGY BY AV. MOKBANT BAKEE, F'.E.O.S. SURGEON TO ST. BARTHOLOMEW'S HOSPITAL AND CONSULTING SURGEON TO THE EVELINA HOSPITAL FOR SICK CHILDREN; LECTURER ON PHYSIOLOGY AT ST. BARTHOLOMEW'S HOSPITAL, AND LATE MEMBER OF THE BOARD OF EXAMINERS OF THE ROYAL COLLEGE OF SURGEONS OF ENGLAND. AND VINCENT DOEMEE HAEEIS. M.D., LOND. DEMONSTRATOR OF PHYSIOLOGY AT ST. BARTHOLOMEW'S HOSPITAL. ELEVENTH EDITION WITH NEARLY BOO ILLUSTRATIONS VOLUME I ( UNIVERSITY | NEW YORK WILLIAM WOOD & COMPANY 56 & 58 LAFAYETTE PLACE 1885 BIOLOGY LIBRARY G THE PUBLISHERS' BOOK COMPOSITION AND ELECTROTYPING Co., 39 AND 41 PARK PLACE, NEW YORK. PREFACE TO THE ELEVENTH EDITION. IN the preparation of the present edition of Kirkes' Physiology, we have endeavored to maintain its character as a guide for stu- dents, especially at an early period of their career; and, while incorporating new facts and observations which are fairly estab- lished, we have as far as possible omitted the controvertible matters which should only find a place in a complete treatise or in a work of reference. A large number of new illustrations have been added, for many of which we are indebted to the courtesy of Dr. Klein, Professor Michael Foster, Professor Schaefer, Dr. Mahomed, Mr. Gant, and Messrs. McMillan, who have been so good as to allow various figures to be copied. Our thanks are also due to Mr. Wm. Lapraik, F.C.S., who has kindly prepared a table of the absorption spectra of the blood and bile, based upon his own observations; as well as to Mr. S. K. Alcock for several careful drawings of microscopical prepara- tions, and for reading several sheets in their passage through the press. Mr. Danielsson, of the firm of Lebon & Co., has executed all the new figures to our entire satisfaction ; and for the skill and labor he has expended upon them we are much indebted to him. We are desirous also of acknowledging the help we have derived from the following works : Klein's Histology ; M. Foster's Text-Book of Physiology; Pavy's Food and Dietetics; Quain's Anatomy, Yol. II., Ed. ix. ; Wickham Legg's Bile, Jaundice, and Bilious Diseases ; 218839 IV PREFACE. Watney's Minute Anatomy of the Thymus ; Rosenthal's Muscles and Nerves ; Cadiat's Traite" D'Anatomie Ge'ne'rale ; Ranvier's Traite" Technique D'Histologie ; Landois' Lehrbuch der Physiologie des Menschen, and the Journal of Physiology. WIMPOLE STREET, August, 1884. W. MORRANT BAKER. V. D. HARRIS. TO VOLUME I. CHAPTER I. PAGE THE GENERAL AND DISTINCTIVE CHARACTERS OF LIVING BEINGS 1 CHAPTER II. STRUCTURAL BASIS OF THE HUMAN BODY 5 Cells 5 Protoplasm 6 Nucleus ............. 10 Intercellular Substance . ... . . . . . . .17 Fibres 17 Tubules 17 CHAPTER III. STRUCTURE OF THE ELEMENTARY TISSUES 19 Epithelium 19 Connective Tissues ........... 28 Areolar Tissue ........... 31 White Fibrous Tissue 31 Yellow Elastic Tissue 32 Gelatinous 33 Retiform or Adenoid 34 Xeuroglia 34 Adipose . 35 Cartilage 38 Bone ... 42 Teeth 05 CHAPTER IV. THE BLOOD 63 Quantity of Blood 63 Coagulation of the Blood .......... 65 Conditions affecting Coagulation ......... 71 The Blood Corpuscles 74 Vi CONTENTS. THE BLOOD — Continued. PAGE Physical and Chemical Characters of Red Blood-Cells . . - . . 75 The White Corpuscles, or Blood-Leucocytes 79 Chemical Composition of the Blood , 83 The Serum 85 Variations in Healthy Blood under Different Circumstances ... 86 Variations in the Composition of the Blood in Different Parts of the Body 87 Gases contained in the Blood 88 Blood-Crystals 91 Development of the Blood 96 Uses of the Blood 99 Uses of the various Constituents of the Blood 99 CHAPTER V. ClKCTJLATION OF THE BLOOD 101 The Systemic, Pulmonary, and Portal Circulations 102 The Forces concerned in the Circulation of the Blood .... 103 THE HEART 103 Structure of the Valves of the Heart Ill The Action of the Heart . . . . Ill Function of the Valves of the Heart 112 Sounds of the Heart . . . . 117 Impulse of the Heart . . . .119 The Cardiograph 119 Frequency and Force of the Heart's Action ...._.. 122 Influence of the Nervous System on the Action of the Heart . . . 124 Effects of the Heart's Action . . 127 THE ARTERIES. CAPILLARIES, AND VEINS 128 Structure of the Arteries 129 Structure of Capillaries . 133 Structure of Veins . . .... . . . . . 136 Function of the Arteries . .... . . . . . 138 The Pulse 142 Sphygmograph . . 143 Pressure of the Blood in the Arteries, or Arterial Tension . . .148 The Kymograph . . . . ..... . . . 150 Influence of the Nervous System on the Arteries . , . . . 152 Circulation in the Capillaries . . . . . . . . 158 Diapedesis of Blood-Corpuscles . ... . . . . . 159 CIRCULATION IN THE VEINS . , 161 Blood-pressure in the Veins , . . .162 Velocity of the Circulation ... . . . . . .163 Velocity of the Blood in the Arteries . 164 Capillaries 165 Veins . . 165 Velocity of the Circulation as a whole ....... 166 CONTENTS. Vll PAGE PECULIARITIES OP THE CIRCULATION IN DIFFERENT PARTS .... 167 Circulation in the Brain 167 Circulation in the Erectile Structures . 168 Agents concerned in the Circulation 170 • Discovery of the Circulation 170 Proofs of the Circulation of the Blood 171 CHAPTER VI. RESPIRATION . . . . . 172 Position and Structure of the Lungs 173 Structure of the Trachea and Bronchial Tubes 176 Structure of Lobules of the Lungs . . 178 Mechanism of Respiration .......... 183 Respiratory Movements .......... 183 Respiratory Rhythm 188 Respiratory Sounds . . . . . . . . . . . 188 Respiratory Movements of Glottis 188 Quantity of Air Respired 189 Vital or Respiratory Capacity 190 Force exerted in Respiration 191 Circulation of Blood in the Respiratory Organs 191 Changes of the Air in Respiration 192 Changes produced in the Blood by Respiration 198 Mechanism of various Respiratory Actions 198 Influence of the Nervous System in Respiration 201 Effects of Vitiated Air— Ventilation 204 Effect of Respiration on the Circulation . . . . . . . 205 Apnoea — Dyspnoea — Asphyxia 209 CHAPTER VII. FOODS 212 Classification of Foods 213 Foods containing chiefly Nitrogenous Bodies 214 Carbohydrate Bodies 216 Fatty Bodies 217 Substances supplying the Salts 217 Liquid Foods 217 Effects of Cooking 217 Effects of an Insufficient Diet 218 Starvation 219 Effects of Improper Food 221 Effects of too much Food 222 Evict Scale 223 CHAPTER VIII. DIGESTION 224 PASSAGE OF FOOD THROUGH THE ALIMENTARY CANAL 224 Mastication 224 Insalivation .... 22G Vlll CONTENTS. PASSAGE OF FOOD, ETC. — Continued. PAGE The Salivary Glands and the Saliva . 226 Structure of the Salivary Glands ' . 226 The Saliva 229 Influence of the Nervous System on the Secretion of Saliva . • . . 231 The Pharnyx 236 The Tonsils 236 The (Esophagus or Gullet .. . . 236 Swallowing or Deglutition . . . . -, . . . . . . 238 DIGESTION OP FOOD IN THE STOMACH . . . . . . . . 240 Structure of the Stomach . . .241 Gastric Glands ... . . 242 The Gastric Juice . . . . 245 Functions of the Gastric Juice 247 Movements of the Stomach .......... 249 Vomiting ............. 251 Influence of the Nervous System on Gastric Digestion .... 252 Digestion of the Stomach after Death 253 DIGESTION IN THE INTESTINES .......... 254 Structure of the Small Intestine . . .254 Valvulse Conniventes 255 Glands of the Small Intestine 257 TheVilli 259 Structure of the Large Intestine 263 The Pancreas and its Secretion 264 Structure of the Liver ; ... 268 Functions of the Liver 273 The Bile 273 The Liver as a Blood-elaborating Organ 280 Glycogenic Function of the Liver ........ 280 Summary of the Changes which take place in the Food during its Passage through the Small Intestine 284 Succus Entericus 283 Summary of the Process of Digestion in the Large Intestine . . . 286 Defsecation 288 Gases contained in the Stomach and Intestines . 288 Movements of the Intestines ......... 289 Influence of the Nervous System on Intestinal Digestion .... 290 CHAPTEE IX. ABSORPTION 291 The Lacteal and Lymphatic Vessels and Glands 291 Lymphatic Glands 297 Properties of Lymph and Chyle 301 Absorption by the Lacteal Vessels . . 303 Absorption by the Lymphatic Vessels 303 Absorption by Blood-vessels . . . . ..... 305 CONTENTS. IX CHAPTER X. PAGE ANIMAL HEAT 309 Variations in Bodily Temperature 809 ' Sources of Heat 311 ' Loss of Heat 313 Production of Heat 315 Inhibitory Heat-centre 316 CHAPTER XI. SECRETION 317 SECRETING MEMBRANES 319 SEROUS MEMBRANES 319 Mucous MEMBRANES . 321 SECRETING GLANDS 322 PROCESS OP SECRETION 324 CIRCUMSTANCES INFLUENCING SECRETION 326 MAMMARY GLANDS AND THEIR SECRETION ...... 328 CHEMICAL COMPOSITION OF MILK 331 CHAPTER XII. THE SKIN AND ITS FUNCTIONS 333 Structure of the Skin 333 Sudoriparous Glands ........... 337 Sebaceous Glands ............ 339 Structure of Hair 339 Structure of Nails 341 Functions of the Skin 342 CHAPTER XIII. THE KIDNEYS AND URINE 347 Structure of the Kidneys 347 Structure of the Ureter and Urinary Bladder 354 The Urine 355 The Secretion of Urine 365 Micturition . 373 HAND-BOOK OF PHYSIOLOGY. CHAPTER I. THE GENERAL AND DISTINCTIVE CHARACTERS OF LIVING BEINGS. HUMAX PHYSIOLOGY is the science which treats of the \ife of man — • of the way in which he lives, and moves, and has his being. It teaches how man is begotten and born; how he attains maturity; and how he dies. Having, then, man as the object of its study, it is unnecessary to speak here of the laws of life in general, and the means by which they are car^ ried out, further than is requisite for the more clear understanding of those of the life of man in particular. Yet it would be impossible to understand rightly the working of a complex machine without some knowledge of its motive power in the simplest form; and it may be well to see first what are the so-called essentials of life — those, namely, which are manifested by all living beings alike, by the lowest vegetable and the highest animal — before proceeding to the consideration of the structure and endowments of the organs and tissue belonging to man. The essentials of life are these, — Birth, Growth and Development, Decline and Death. The term birth, when employed in this general sense of one of the conditions essential to life, without reference to any particular kind of living being, may be taken to mean, separation from a parent, with a greater or less power of independent life. Taken thus, the term, although not defining any particular stage in development, serves well enough for the expression of the fact, to which no exception has yet been proved to exist, that the capacity for life in all living beings is obtained by inheritance. Growth, or inherent power of increasing in size, although essential to our idea of life, is not confined to living beings. A crystal of common salt, or of any other similar substance, if placed under appropriate condi- VOL. I.— 1. 2 HAND-BOOK OF PHYSIOLOGY. tions for obtaining fresh material, will grow in a fashion as definitely char- acteristic and as easily to be foretold as that of a living creature. It is, therefore, necessary to explain the distinctions which exist in this respect between living and lifeless structures; for the manner of growth in the two cases is widely different. Differences between Living and Lifeless Growth. — (1.) The growth of a crystal, to use the same example as before, takes place merely by additions to its outside; the new matter is laid on particle by particle, and layer by layer, and, when once laid on, it remains unchanged. The growth is here said to be superficial. In a living structure, on the other hand, as, for example, a brain or a muscle, where growth occurs, it is by addition of new matter, not to the surface only, but throughout every part of the mass; the growth is not superficial, but interstitial. (2.) All living structures are subject to constant decay; and life con- sists not, as once supposed, in the power of preventing this never-ceasing decay, but rather in making up for the loss attendant on it by never- ceasing repair. Thus, a man's body is not composed of exactly the same particles dayt after day, although to all intents he remains the same indi- vidual. Almost every part is changed by degrees; but the change is so gradual, and the renewal of that which is lost so exact, that no difference may be noticed, except at long intervals of time. A lifeless structure, as a crystal, is subject to no such laws; neither decay nor repair is a necessary condition, of its existence. That which is true of structures which never had to do with life is true also with respect to those which, though they are formed by living parts, are not themselves alive. Thus, an oyster-shell is formed by the living animal which it encloses, but it is as lifeless as any other mass of inorganic matter; and in accordance with this circumstance its growth takes place, not inter stitially, but layer by layer, and it is not subject to the constant decay and reconstruction which belong to the living. The hair and nails are examples of the same fact. (3.) In connection with the growth of lifeless masses there is no alter- ation in the chemical constitution of the material which is taken up and added to the previously existing mass. For example, when a crystal of common salt grows on being placed in a fluid which contains the same material, the properties of the salt are not changed by being taken out of the liquid by the crystal and added to its surface in a solid form. But the case is essentially different in living beings, both animal and vegeta- ble. A plant, like a crystal, can only grow when fresh material is pre- sented to it; and this is absorbed by its leaves and roots; and animals, for the same purpose of getting new matter for growth and nutrition, take food into their stomachs. But in both these cases the materials are much altered before they are finally assimilated by the structures they are destined to nourish. (4.) The growth of all living things has a definite limit, and the Li\v DISTINCTIVE CHAKACTEKS OF LIVING BEIXGS. ' 3 governs this limitation of increase in size is so invariable that we should be as much astonished to find an individual plant or animal with- out limit as to growth as without limit to life. Development is as constant an accompaniment of life as growth. The term is used to indicate that change to which, before maturity, all living parts are constantly subject, and by which they are made more and more capable of performing their several functions. For example, a full-grown man is not merely a magnified child ; his tissues and organs have not only grown, or increased in size, they have also developed, or become better in quality. ;No very accurate limit can be drawn between the end of development and the beginning of decline; and the two processes may be often seen together in the same individual. But after a time all parts alike share in the tendency to degeneration, and this is at length succeeded by death. Differences between Plants and Animals.— It has been already said that the essential features of life are the same in all living things; in other words, in the members of both the animal and vegetable king- doms. It may be wrell to notice briefly the distinctions which exist be- tween the members of these two kingdoms. It may seem, indeed, a strange notion that it is possible to confound vegetables with animals, but it is true with respect to the lowest of them, in which but little is manifested beyond the essentials of life, which are the same in both. (1.) Perhaps the most essential distinction is the presence or absence of power to live upon inorganic material. By means of their green color- ing matter, chlorophyl — a substance almost exclusively confined to the vegetable kingdom, plants are capable of decomposing the carbonic acid, ammonia, and water, which they absorb by their leaves and roots, and thus utilizing them as food. The result of this chemical action, which occurs only under the influence of light, is, so far as the carbonic acid is concerned, the fixation of carbon in the plant structures and the exhala- tion of oxygen. Animals are incapable of thus using inorganic matter, and never exhale oxygen as a product of decomposition. The power of living upon organic as well as inorganic matter is less decisive of an animal nature; inasmuch as fungi and some other plants derive their nourishment in part from the former source. (2.) There is, commonly, a marked difference in general chemical composition between vegetables and animals, even in their lowest forms; for while the former consist mainly of cellulose, a substance closely allied to starch and containing carbon, hydrogen, and oxygen only, the latter are composed in great part of the three elements just named, together with a fourth, nitrogen; the chief proximate principles formed from these being identical, or nearly so, with albumen. It must not be sup- posed, however, that either of these typical compounds alone, with its allies, is confined to one kingdom of nature. Nitrogenous compounds 4 HAND-BOOK OF PHYSIOLOGY. are freely produced in vegetable structures, although they form a very much smaller proportion of the whole organism than cellulose or starch. And while the presence of the latter in animals is much more rare than is that of the former in vegetables, there are many animals in which traces of it may be discovered, and some, the Ascidians, in which it is found in cpnsiderable quantity. (3. ) Inherent power of movement is a quality which we so commonly consider an essential indication of animal nature, that it is difficult at first to conceive it existing in any other. The capability of simple motion is now known, however, to exist in so many vegetable forms, that it can no longer be held as an essential distinction between them and animals, and ceases to be a mark by which the one can be distinguished from the other. Thus the zoospores of many of the Cryptogamia exhibit ciliary or amoeboid movements (p. 8) of a like kind to those seen in animalcules; and even among the higher orders of plants, many, e. g., Dioncea Mus- cipula (Venus's fly -trap), and Mimosa Sensitiva (Sensitive plant), exhibit such motion, either at regular times, or on the application of external irritation, as might lead one, were this fact taken by itself, to regard them as sentient beings. Inherent power of movement, then, although especially characteristic of animal nature, is, when taken by itself, no proof of it. (4.) The presence of a digestive canal is a very general mark by which an animal can be distinguished from a vegetable. But the lowest animals are surrounded by material that they can take as food, as a plant is surrounded by an atmosphere that it can use in like manner. And every part of their body being adapted to absorb and digest, they have no need of a special receptacle for nutrient matter, and accordingly have no digestive canal. This distinction then is not a cardinal one. It would be tedious as well as unnecessary to enumerate the chief dis- tinctions between the more highly developed animals a*nd vegetables. They are sufficiently apparent. It is necessary to compare, side by side, the lowest members of the two kingdoms, in order to understand rightly how faint are the boundaries between them. CHAPTER II. STRUCTURAL BASIS OF THE HUMAN BODY. BY dissection, the human body can be proved to consist of various dis- similar parts, bones, muscles, brain, heart, lungs, intestines, etc., while, on more minute examination, these are found to be composed of different tissues, such as the connective, epithelial, nervous, muscular, and the like. Cells. — Embryology teaches us that all this complex organization has been developed from a microscopic body about y-J-0- in. in diameter (ovum), which consists of a spherical mass of jelly-like matter enclosing a smaller spherical body (germinal vesicle). Further, each individual tissue can be shown largely to consist of bodies essentially similar to an ovum, though often differing from it very widely in external form. They are termed cells : and it must be at once evident that a correct knowledge of the nature and activities of the cell forms the very foundation of physiology. Cells are, in fact, physiological no less than histological units. The prime importance of the cell as an element of structure was first established by the researches of Schleiden, and his conclusions, drawn from the study of vegetable histology, were at once extended by Schwann to the animal kingdom. The earlier observers defined a cell as a more or less spherical body limited by a membrane, and containing a smaller body termed a nucleus, which in its turn encloses one or more nucleoli. Such a definition applied admirably to most vegetable cells, but the more extended investigation of animal tissues soon showed that in many cases no limiting membrane or cell-wall could be demonstrated. The presence or absence of a cell- wall, therefore, was now regarded as quite a secondary matter, while at the same time the cell-substance came gradually to be recognized as of primary importance. Many of the lower forms of animal life, e.g., the Rhizopoda,were found to consist almost entire- ly of matter very similar in appearance and chemical composition to the cell-substance of higher forms: and this from its chemical resemblance to flesh was termed Sarcode by Dujardin. When recognized in vegetable cells it was called Protoplasm by Mulder, while Remak applied the same name to the substance of animal cells. As the presumed formative mat- ter in animal tissues it was termed Blastema, and in the belief that, wherever found, it alone of all substances has to do with generation and 6 HAND-BOOK OF PHYSIOLOGY. nutrition, Beale has named it Germinal matter or Bioplasm. Of these terms the one most in vogue at the present day is Protoplasm, and inas- much as all life, both in the animal and vegetable kingdoms, is associated with protoplasm, we are justified in describing it, with Huxley, as the "physical basis of life." A cell may now be defined as a nucleated mass of protoplasm,1 of microscopic size, which possesses sufficient individuality to have a life- history of its own. Each cell goes through the same cycle of changes as the whole organism, though doubtless in a much shorter time. Begin- ning with its origin from some pre-existing cell, it grows, produces other cells, and finally dies. It is true that several lower forms of life consist of non-nucleated protoplasm, but the above definition holds good for all the higher plants and animals. Hence a summary of the manifestations of cell-life is really an account of the vital activities of protoplasm. Protoplasm. — Physical characters. — Physically, protoplasm is viscid, varying in consistency from semi-fluid to stronglyc oherent. Chemical characters. — Chemically, living protoplasm is an extremely unstable albu- minoid substance, insoluble in water. It is neutral or weakly alkaline in reaction. It undergoes heat stiffening or coagulation at about 130°F. (54'5°C.), and hence no organism can live when its own temperature is raised beyond this point, though, of course, many can exist for a time in a much hotter atmosphere, since they possess the means of regulating their own temperature. Besides the coagulation produced by heat, pro- toplasm is coagulated by all the reagents which produce this change in albumen. If not-living protoplasm be subjected to chemical analysis it is found to be made up of numerous bodies2 besides albumen, e.g., of gly- cogen, lecithin, salts and water, so that if living protoplasm be, as some believe, an independent chemical body, when it no longer possesses life, it undergoes a disintegration which is accompanied by the appearance of these new chemical substances. When it is examined under the micro- scope two varieties of protoplasm are recognized — the hyaline, and the granular. Both are alike transparent, but the former is perfectly homo- geneous, while the latter (the more common variety) contains small gran- ules or molecules of various sizes and shapes. Globules of watery fluid are also sometimes found in protoplasm; they look like clear spaces in it, and are hence called vacuoles. Vital or Physiological characters. — These may be conveniently treated under the three heads of — I. Motion; II. Nutrition; and III. Repro- duction. 1 In the Luman body the cells range from the red blood-cell (-g^Vo" in.) to the gang- lion-cell (y^-) in. 2 For an account of which, reference should be made to the Appendix. STRUCTURAL BASIS OF THE HUMAN BODY. I. Motion. — It is probable that the protoplasm of all cells is capable at some time of exhibiting movement; at any rate this phenomenon, which not long ago was regarded as quite a curiosity, has been recently observed in cells of • many different kinds. It maybe readily studied in the Amoebae, in the colorless blood -cells of all vertebrata, in the branched cornea-cells of the frog, in the hairs of the stinging-nettle and Trades- cunt ia. arid the cells of Vallisneria and Chara. These motions may be divided into two classes — (a) Fluent and (b) Ciliary. Another variety — the molecular or vibratory — has also been classed by some observers as vital, but it seems exceedingly probable that it is nothing more than the well-known "Brownian" molecular movement, a purely mechanical phenomenon which may be observed in any minute particles, e.g., of gamboge, suspended in a fluid of suitable density, such as water. Such particles are seen to oscillate rapidly to and fro, and not to pro- gress in any definite direction. (a.) Fluent. — This movement of protoplasm is rendered perceptible (1) by the motion of the granules, which are nearly always imbedded in it, and (2) by changes in the outline of its mass. If part of a hair of Tradescantia (Fig. 1) be viewed under a high magni- fying power, streams of protoplasm con- taining crowds of granules hurrying along, like the foot passengers in a busy street, are seen flowing steadily in defi- nite directions, some coursing round the film Which lilies the Ulterior Of the ,, , Cell-wall, and Others liowmo; toward Or FIG. 1.— Cell of Tfcidescantia drawn at successive intervals of two minutes. The cell-contents consist of a central mass con- nected by many irregular processes to a peripheral film: the whole forms a vacuo- . , . - from the irregular maSS in the lated mass of protoplasm, which is continu- „ , , .. ,, ally changing its shape. (Schofield.) centre of the cell-cavity. Many of these streams of protoplasm run together into larger ones, and are lost in the central mass, and thus ceaseless variations of form are produced. In the Amoeba, a minute animal consisting of a shapeless and struc- tureless mass of sarcode, an irregular mass of protoplasm is gradually thrust out from the main body and retracted: a second mass is then pro- truded in another direction, and gradually the whole protoplasmic sub- stance is, as it were, drawn into it. The Amoeba thus comes to occupy a new position, and when this is repeated several times we have locomotion in a definite direction, together with a continual change of form. These movements when observed in other cells, such as the colorless blood- corpuscles of higher animals (Fig. 2) are hence termed amoeboid. Colorless blood-corpuscles were first observed to migrate, i.e., pass HAND-BOOK OF PHYSIOLOGY. through the walls of the blood-vessels (p. 159), by Waller, whose obser- vations were confirmed and extended to connective tissue corpuscles by the researches of Recklirighausen, Cohnheim, and others, and thus the phenomenon of migration has been proved to play an important part in many normal, and pathological processes, especially in that of inflam- mation. This amoeboid movement enables many of the lower animals to capture their prey, which they accomplish by simply flowing round and enclosing it. The remarkable motions of pigment-granules observed in the branched pigment-cells of the frog's skin by Lister are probably due to amoeboid movement. These granules are seen at one time distributed uniformly through the body and branched processes of the cell, while under the action of various stimuli (e.g., light and electricity) they collect in the central mass, leaving the branches quite colorless. (b.) Ciliary action must be regarded as only a special variety of the general motion with which all protoplasm is endowed. The grounds for this view are the following: In the case of the Infu- soria, which move by the vibration of cilia (microscopic hair-like processes projecting from the surface of their bodies) it has been proved that these are simply processes of their protoplasm protruding through pores of the FIG. 2.— Human colorless blood-corpuscle, showing its successive changes of outline within ten minutes when kept moist on a warm stage. (Schofield.) investing membrane, like the oars of a galley, or the head and legs of a tortoise from its shell: certain reagents cause them to be partially re- tracted. Moreover, in some cases cilia have been observed to develop from, and in others to be transformed into, amoeboid processes. The movements of protoplasm can be very largely modified or even suspended by external conditions, of which the following are the most important. 1. Changes of temperature. — Moderate heat acts as a stimulant this is readily observed in the activity of the movements of a human colorless blood-corpuscle when placed under conditions in which its normal tem- perature and moisture are preserved. Extremes of heat and cold stop the motions entirely. 2. Mechanical stimuli. — When gently squeezed between a cover and object glass under proper conditions, a colorless blood-corpuscle is stimu- lated to active amoeboid movement. 3. Nerve influence. — By stimulation of the nerves of the frog's cornea, contraction of certain of its branched cells has been produced. 4. Chemical stimuli. — Water generally stops amoeboid movement, and by imbibition causes great swelling and finally bursting of the cells. STRUCTURAL BASIS OF THE HUMAN BODY. 9 In some cases, however, (myxomycetes) protoplasm can be almost entirely dried up, and is yet capable of renewing its motions when again moistened. Dilute salt-solution and many dilute acids and alkalies, stimulate the movements temporarily. Ciliary movement is suspended in an .atmosphere of hydrogen or car- bonic acid, and resumed on the admission of air or oxygen. 5. Electrical. — Weak currents stimulate the movement, while strong currents cause the corpuscles to assume a spherical form and to become motionless. II. Nutrition. — The nutrition of cells will be more appropriately described in the chapters on Secretion and Nutrition. Before describing the Reproduction of cells it will be necessary to con- sider their structure more at length. Minute Structure of Cells. — (a.) Cell-wall. — We have seen (p. 5) that the presence of a limiting-membrane is no essential part of the defini- tio7i of a cell. In nearly all cells the outer layer of the protoplasm attains a firmer consistency than the deeper portions: the individuality of the cell be- coming more and more clearly marked as this cortical layer becomes more and more differentiated from the deeper portions of cell-substance. Side by side with this physical, there is a gradual chemical differentiation, till at length, as in the case of the fat-cells, we have a definite limiting-mem- brane differing chemically as well as physically from the cell-contents, and remaining as a shriveled-up bladder when they have been removed. Such a membrane is transparent and structureless, flexible, and per- meable to fluids. The cell-substance can, therefore, still be nourished by imbibition through the cell- wall. In many cases (especially in fat) a membrane of some toughness is absolutely necessary to give to the tissue the requisite consistency. When these membranes attain a certain degree of thickness and independence they are termed capsules: as examples, we may cite the capsules of cartilage-cells, and the thick, tough envelope of the ovum termed the "primitive chorion." (b.) Cell contents. — In accordance with their respective ages, positions, and functions, the contents of cells are very varied. The original protoplasmic substance may undergo many transforma- tions; thus, in fat-cells we may have oil, or fatty crystals, occupying nearly the whole cell-cavity: in pigment-cells we find granules of pig- ment; in the various gland-cells the elements of their secretions. Moreover, the original protoplasmic contents of the cell may undergo a gradual chemical change with advancing age; thus the protoplasmic cell- substance of the deeper layers of the epidermis becomes gradually con- verted into keratin as the cell approaches the surface. So, too, the orig- 10 HAND-BOOK OF PHYSIOLOGY. inal protoplasm of the embryonic blood-cells is replaced by the haemo- globin of the mature colored blood-corpuscle. The minute structure of cells has lately been made the subject of care- ful investigation, and what was once regarded as homogeneous proto- plasm with a few scattered granules, has been stated to be an exceedingly complex structure. In colorless blood-corpuscles, epithelial cells, con- nective tissue corpuscles, nerve-cells, and many other varieties of cells, an intracellular network of very fine fibrils, the meshes of which are occupied by a hyaline interstitial substance, has been demonstrated (Heitzmann's network) (Fig. 3). At the nodes, where the fibrils cross, are little swellings, and these are the objects described as granules by the older observers: but in some cells, e.g., colorless blood corpuscles, there are real granules, which appear to be quite free and unconnected with the intra-cellular network. (c. ) Nucleus. — Nuclei (Fig. 3) were first pointed out in the year 1833, by Robert Brown, who observed them in vegetable cells. They are either FIG. 3. — (A). Colorless blood-corpuscle showing intra-cellular network of Heitzmann, and two nuclei with intra-nuclear network. (Klein and Noble Smith.) (B.) Colored blood-corpuscle of newt showing intra-cellular network of fibrils (Heitzmann). Also oval nucleus composeAf limiting-membrane and fine intra-nuclear network of fibrils. X 800. (Klein and Noble Smith.) small transparent vesicular bodies containing one or more smaller particles (nucleoli), or they are semi-solid masses of protoplasm always in the resting condition bounded by a well-defined envelope. In their relation to the life of the cell they are certainly hardly second in importance to the protoplasm itself, and thus Beale is fully justified in comprising both under the term "germinal matter." They exhibit their vitality by ini- tiating the process of division of the cell into two or more cells (fission) by first themselves dividing. Distinct observations have been made show- ing that spontaneous changes of form may occur in nuclei as also in nu- cleoli. Histologists have long recognized nuclei by two important charac- ters:— (1.) Their power of resisting the action of various acids and alkalies, particularly acetic acid, by which their outline is more clearly defined, and they are rendered more easily visible. This indicates some chemical STRUCTURAL BASIS OF THE HUMAN BODY. 11 difference between the protoplasm of the cell and nuclei, as the former is destroyed by these reagents. (2. ) Their quality of staining in solutions of carmine, haematoxylin, etc. Nuclei 'are most commonly oval or round, and do not generally conform to the diverse shapes of the cells; they are altogether less varia- ble elements than cells, even in regard to . size, of which fact one may see a good example in the uniformity of the nuclei in cells so multiform as those of epithelium. But sometimes nuclei appear to occupy the whole of the cell, as is the case in the lymph corpuscles of lymphatic glands and in some small nerve cells. Tlieir position in the cell is very variable. In many cells, especially where active growth is progressing, two or more nuclei are present. The nuclei of many cells have been shown to contain a fine intra- nuclear network in every respect similar to that described above as intra- cellular (Fig. 3), the interstices of which are occupied by semi-fluid pro- toplasm. III. Reproduction.— The life of individual cells is probably very short in comparison with that of the organism they compose: and their constant decay and death necessitate constant reproduction. The mode in which this§takes place has long been the subject of great controversy. In the' case of plants, all of whose tissues are either cellular or com- posed of cells which are modified or have coalesced in various ways, the theory that all new cells are derived from pre-existing ones was early ad- vanced and very generally accepted. But in the case of animal tissues Scliwann and others maintained a theory of spontaneous or free cell for- mation. According to this view a minute corpuscle (the future nucleolus) springs up spontaneously in a structureless substance (blaslbma) very much as a crystal is formed in a solution. This nucleolus attracts the surround- ing molecules of matter to form the nucleus, and by a repetition of the process the substance and wall are produced. This theory, once almost universally current, was first disputed and finally overthrown by Remak and Virchow, whose researches established the truth expressed in the words "Omnis celiula e cellula." It will be seen that this view is in strict accordance with the truth established much earlier in Vegetable Histology that every cell is de- scended from some pre-existing (mother-) cell. This derivation of cells from cells takes place by (1) gemmation, or (2) fission or division. (1.) Gemmation. — This method has not been observed in the human body or the higher animals, and therefore requires but a passing notice. It consists essentially in the budding off and separating of a portion of the parent cell. (2.) Fixxion or Division. — As examples of reproduction by fission, we may select the ovum, the blood coll, and cartilage cells. 12 HAND-BOOK OF PHYSIOLOGY. In the frog's ovum (in which the process can be most readily ob- served) after fertilization has taken place, there is first some amoeboid movement, the oscillation gradually increasing until a permanent dimple appears, which gradually extends into a furrow running completely round the spherical ovum, and deepening until the entire yelk-rnass is divided into two hemispheres of protoplasm each containing a nucleus (Fig. 4, b). This process being repeated by the formation of a second furrow at right angles to the first, we have four cells produced (c): this subdivision is FIG. 4.— Diagram of an ovum (a) undergoing segmentation. In (6) it has divided into two; in (c) into four; in (d) the process has ended in the production of the so-called u mulberry mass." (Frey.) carried on till the ovum has been diyided by segmentation into a mass of cells (mulberry-mass) (d) out of which the embryo is developed. Segmentation is the first step in the development of most animals, and doubtless takes place in man. Multiplication by fission has been observed in the colorless blood-cells of many animals. In some cases (Fig. 5), the process has been seen to commence with the nucleolus which divides within the nucleus. The nucleus then elongates, and soon a well-marked constriction occurs, ren- dering it hour-glass shaped, till finally it is separated into two parts, which gradually recede from each other: the same process is repeated in the cell- substance, and at length we have two cells produced which by /$) t, brighter or darker than the border, according as it is viewed in or mt of focus. Their specific gravity is about 1088. Varieties. — The red corpuscles are not all alike, some being rather larger, paler, and less regular than the majority, and sometimes flat or slightly convex, with a shining particle apparent like a nucleolus. In almost every specimen of blood may be also observed a certain number of corpuscles smaller than the rest. They are termed m.icrocytes, and are probably immature corpuscles. A peculiar property of the red corpuscles, exaggerated in inflammatory blood, may be here again noticed, i.e., their great tendency to adhere to- gether in rolls or columns, like piles of coins. These rolls quickly fasten together by their ends, and cluster; so that, when the blood is spread out thinly on a glass, they form a kind of irregular network, with crowds of corpuscles at the several points corresponding with the knots of the net (Fig. 08). Hence, the clot formed in such a thin layer of blood looks mottled with blotches of pink upon a white ground, and in a larger quan- 76 HAND-BOOK OF PHYSIOLOGY. tity of such blood help, by the consequent rapid subsidence of the cor- puscles, in the formation of the buffy coat already referred to. This tendency on the part of the red corpuscles, to form rouleaux, is probably only a physical phenomenon, comparable to the collection into somewhat similar rouleaux of discs of corks when they are partially im- mersed in water. (Norris.) Mammals. Birds. Reptiles. Amphibia. Fish. FIG. 69.1 1 The above illustration is somewhat altered from a drawing by Gulliver, in the Proceed. Zool. Society, and exhibits the typical characters of the red blood-cells in the main divisions of the Vertebrata. The fractions are those of an inch, and represent the average diameter. .In the case of the oval cells, only the long diameter is here given. It is remarkable, that although the size of the red blood-cells varies so much in the different classes of the vertebrate kingdom, that of the white corpuscles re- mains comparatively uniform, and thus they are, in some animals, much greater, in others much less than the red corpuscles existing side by side with them. THE BLOOD. 77 Action of Reagents. — Considerable light has been thrown on the physical and chemical constitution of red blood- cells by studying the effects produced by mechanical means and by various reagents: the fol- lowing is a brief summary of these reactions: — Pressure. — If the red blood-cells of a frog or man are gently squeezed, they exhibit a wrinkling of the surface, which clearly indicates that there is a superficial pellicle partly differentiated from the softer mass within; airain, if a needle be rapidly drawn across a drop of blood, several cor- puscles will be found cut in two, but this is not accompanied by any es- cape of cell contents; the two halves, on the contrary, assume a rounded form, proving clearly that the corpuscles are not mere membranous sacs with fluid contents like fat-cells. Fluids. — Water. — When water is added gradually to frog's blood, the oval disc-shaped corpuscles become spherical, and gradually discharge their haemoglobin, a pale, transparent stroma being left behind; human red blood-cells change from a discoidal to a spheroidal form, and dis- charge their cell-contents, becoming quite transparent and all but invisible. Saline solution (dilute) produces no appreciable effect on the red FIG. 70. blood-cells of the frog. In the red blood-cells of man the discoid shape is exchanged for a spherical one, with spinous projections, like a horse- chestnut (Fig. 70). Their original forms can be at once restored by the use of carbonic acid. Acetic acid (dilute) causes the nucleus of the red blood cells in the frog to become more clearly defined; if the action is prolonged, the nu- cleus becomes strongly granulated, and all the coloring matter seems to be concentrated in it, the surrounding cell-substance and outline of the cell becoming almost invisible; after a time the cells lose their color alto- gether. The cells in the figure (Fig. 71) represent the successive stages of the change. A similar loss of color occurs in the red cells of human blood, which, however, from the absence of nuclei, seem to disappear entirely. Alkalies cause the red blood-cells to swell and finally disappear. Chloroform added to the red blood-cells of the frog causes them to part with their haemoglobin; the stroma of the cells becomes gradually broken up. A similar effect is produced on the human red blood-cell. Tannin. — When a 2 per cent, solution of tannic acid is applied to frog's blood it causes the appearance of a sharply-defined little knob, pro- jecting from the free surface: the coloring matter- becomes at the same time concentrated in the nucleus, which grows more distinct (Fig. 72). 78 HAND-BOOK OF PHYSIOLOGY. A somewhat similar effect is produced on the human red blood -cell. (Koberts.) Magenta, when applied to the red blood-cells of the [frog, produces a similar little knob or knobs, at the same time staining the nucleus and causing the discharge of the haemoglobin. (Roberts.) The first effect of the magenta is to cause the discharge of the haemoglobin,, then the nucleus becomes suddenly stained, and lastly a finely granular matter issues through the wall of the corpuscle, becoming stained by the magenta, and a macula is formed at the point of escape. A similar macula is produced in the human red blood-cell. Boracic acid. — A 2 per cent, solution applied to nucleated red blood- cells (frog) will cause the concentration of all the coloring matter in the nucleus; the colored body thus formed gradually quits its central position, and comes to be partly, sometimes entirely, protruded from the surface of the now colorless cell (Fig. 73). The result of this experiment led Briicke to distinguish the colored contents of the cell (zooid) from its colorless stroma (oacoid). When applied to the non-nucleated mammalian corpuscle its effect merely resembles that of other dilute acids. Gases — Carbonic acid. — If the red blood-cells of a frog be first exposed Vf* & •» FIG. 73. FIG. 74. FIG. 75. to the action of water-vapor (which renders their outer pellicle more readily permeable to gases), and then acted on by carbonic acid, the nuclei immediately become clearly defined and strongly granulated; when air or oxygen is admitted the original appearance is at once restored. The upper and lower cell in Fig. 74 show the effect of carbonic acid; the middle one the effect of the re-admission of air. These effects can be reproduced five or six times in succession. If, however, the action of the carbonic acid be much prolonged, the granulation of the nucleus becomes permanent; it appears to depend on a coagulation of the paraglobulin. (Strieker.) Ammonia. — Its effects seem to vary according to the degree of con- centration. Sometimes the outline of the corpuscles becomes distinctly crenated; at other times the effect resembles that of boracic acid, while in other cases the edges of the corpuscles begin to break up. (Lankester.) Heat.— The effect of heat up to 120°— 140° F. (50°— 60° C.) is to cause the formation of a number of bud-like processes (Fig. 75). Electricity causes the red blood-corpuscles to become crenated, and at length mulberry-like. Finally they recover their round form and become quite pale. THE BLOOD. 79 The general conclusions to be drawn from these observations have m summed up as follows by Prof. Ray Lankester: — "The red bipod-corpuscle of the vertebrata is a viscid, and at the same :ime elastic disc, oval or round in outline, its surface being differentiated •mewhat from the underlying material, and forming a pellicle or mem- mine of great tenuity, not distinguishable with the highest powers whilst the corpuscle is normal and living), and having no pronounced inner limitation. The viscid mass consists of (or rather yields, since the state >f combination of the components is not known) a variety of albuminoid ind other bodies, the most easily separable of which is haemoglobin; sec- mUy* the matter which segregates to form Roberts'^ macula; and thirdly, residuary stroma, apparently homogeneous in the mammalia (excepting far as the outer surface or pellicle may be of a different chemical lature), but containing in the other vertebrata a sharply definable lucleus, this nucleus being already differentiated, but not sharply deline- bed during life, and consisting of, or separable into, at least two com- ments, one (paraglobulin) precipitable by carbon dioxide, and remov- ible by the action of weak ammonia; the other pellucid, and not gran- dated by acids." The White or Colorless Corpuscles. — In human olood the white >r colorless corpuscles or leucocytes are nearly spherical masses of inular protoplasm without cell wall. The granular appearance, more larked in some than in others (vide infra), is due to the presence of par- :icles probably of a fatty nature. In all cases one or more nuclei exist in )h corpuscle. The size of the corpuscle averages ^--g- of an inch in liameter. In health, the proportion of white to red corpuscles, which, taking average, is about 1 to 500 or 600, varies considerably even in the mrse of the same day. The variations appear to depend chiefly on the imouut and probably also on the kind A B )f food taken; the number of leuco- 3ytes being very considerably increased iy a meal, and diminished again on sting. Also in young persons, dur- ing pregnancy, and after great loss )f blood, there is a larger proportion )f colorless blood-corpuscles, which probably shows that they are more rapidly formed under these circum- stances. In old age, on the other hand, their proportion is diminished. Varieties. — The colorless corpuscles present greater diversities of form than the red ones do. Two chief varieties are to be seen in human blood; one which contains a considerable number of granules, and the other which is paler and less granular. In size the variations are great, for in most specimens of blood it is possible to make out, in addition to FIG. 77.— A. Three colored blood-corpuscles. B. Three colorless blood-corpuscles acted on by acetic acid; the nuclei are very clearly visible. X 900. 80 HAND-BOOK OF PHYSIOLOGY. the full-sized varieties, a number of smaller corpuscles, consisting of a large spherical nucleus surrounded by a variable amount of more or less granular protoplasm. The small corpuscles are, in all probability, the undeveloped forms of the others, and are derived from the cells of the lymph. Besides the above-mentioned varieties, Schmidt describes another form which he looks upon as intermediate between the colored and the colorless forms, viz., certain corpuscles which contain red granules of haemoglobin in their protoplasm. The different varieties of colorless cor- puscles are especially well seen in the blood of frogs, newts, and other cold-blooded animals. Amoeboid movement. — A remarkable property of the colorless cor- puscles consists in their capability of spontaneously changing their shape. This was first demonstrated by Wharton Jones in the blood of the skate. If a drop of blood be examined with a high power of the microscope on a warm stage, or, in other words, under conditions by which loss of mois- ture is prevented, and at the same time the temperature is maintained at about that of the blood in its natural state within the walls of the living vessels, 100° F. (37 "8° C.), the colorless corpuscles will be observed slowly altering their shapes, and sending out processes at various parts of their circumference. This alteration of shape, which can be most conveniently FIG. 78.— Human colorless blood-corpuscle, showing its successive changes of outline within ten minutes when kept moist on a warm stage. (Schofield.) studied in the newt's blood, is called amoeboid, inasmuch as it strongly resembles the movement of the lowly organized amccba. The processes which are sent out are either lengthened or withdrawn. If lengthened, the protoplasm of the whole corpuscle flows as it were into its process, and the corpuscle changes its position; if withdrawn, protrusion of another process at a different point of the circumference speedily follows. The change of position of the corpuscle can also take place by a flowing movement of the whole mass, and in this case the locomotion is compar- atively rapid. The activity both in the processes of change of shape and also of change in position, is much more marked in some corpuscles, viz., in the granular variety, than in others. Klein states that in the newt's blood the changes are especially likely to occur in a variety of the colorless corpuscle, which consists of masses of finely granular protoplasm with jagged outline, containing three or four nuclei, or of large irregular masses of protoplasm containing from five to twenty nuclei. Another phenomenon may be observed in such a specimen of blood, viz., the divi- sion of the corpuscles, which occurs in the following way. A cleft takes place in the protoplasm at one point, which becomes deeper and deeper, THE BLOOD. 81 and then by the lengthening out and attenuation of the connection, and finally by its rupture, two corpuscles result. The nuclei have previously undergone, division. The cells so formed are said to be remarkably active in their movements. Thus we see that the rounded form which the colorless corpuscles present in ordinary microscopic specimens must be looked upon as the shape natural to a dead corpuscle or to one whose vitality is dormant rather than as the shape proper to one living and active. Action of re-agents upon the colorless corpuscles. — Feeding the corpuscles. — If some fine pigment granules, e.g., powdered vermilion, be added to a fluid containing colorless blood-corpuscles, on a glass slide, these will be observed, under the microscope, to take up the pigment. In some cases colorless corpuscles have been seen with fragments of colored ones thus embedded in their substance. This property of the colorless corpuscles is especially interesting as helping still further to connect them with the lowest forms of animal life, and to connect both with the organ- ized cells of which the higher animals are composed. The property which the colorless corpuscles possess of passing through the walls of the blood-vessels will be described later on. Enumeration of the Red and White Corpuscles. — Several methods are employed for counting the blood-corpuscles, most of them depending upon the same principle, i.e., the dilution of a minute volume of blood with a given volume of a colorless solution similar in specific gravity to blood serum, so that the size and shape of the corpuscles is altered as little as possible. A minute quantity of the well-mixed solu- tion is then taken, examined under the microscope, either in a flattened capillary tube (Malassez) or in a cell (Hayem & Nachet, Gowers) of known capacity, and the number of corpuscles in a measured length of the tube, or in a given area of the cell is counted. The length of the tube and the area of the cell are ascertained by means of a micrometer scale in the microscope ocular; or in the case of Gowers' modification, by the division of the cell area into squares of known size. Having ascer- tained the number of corpuscles in the diluted blood, it is easy to find out the number in a given volume of normal blood. Gowers' modifica- tion of Hayem & Cachet's instrument, called by him "Hcvmacytometer," appears to be the most convenient form of instrument for counting the corpuscles, and as such will alone be described (Fig. 79). It consists of a small pipette (A), which, when filled up to a mark on its stem,,, holds 995 cubic millimetres. It is furnished with an india-rubber tube and glass mouth-piece to facilitate filling and emptying; a capillary tube (B) marked to hold 5 cubic millimetres, and also furnished with an india- rubber tube and mouthpiece; a small glass jar (D) in which the dilution of the blood is performed; a glass stirrer (E) for mixing the blood thoroughly, (F) a needle, the length of which can be regulated by a, VOL. I.— 6. 82 HAND-BOOK OF PHYSIOLOGY. . screw; a brass stage plate (c) carrying a glass slide, on which is a cell •one-fifth of a millimetre deep, and the bottom of which is divided into one-tenth millimetre squares. On the top of the cell rests the cover glass, which is kept in its place by the pressure of two springs proceeding from the stage plate. A standard saline solution of sodium sulphate, or similar salt, of specific gravity 1025, is made, and 995 cubic millimetres are measured by means of the pipette into the glass jar, and with this five cubic millimetres of blood, obtained by pricking the finger with a needle, and measured in the capillary pipette (B), are thoroughly mixed by the FIG. 79.— Haemacytometer. glass stirring-rod. A drop of this diluted blood is then placed in the cell and covered with a cover-glass, which is fixed in position by means of the two lateral springs. The preparation is then examined under a micro- scope with a power of about 400 diameters, and focussed until the lines dividing the cell into squares are visible. After a short delay, the red corpuscles which have sunk to the bottom of the cell, and are resting on the squares, are counted in ten squares, and tlje number of white corpuscles noted. By adding together the numbers counted in ten (one-tenth millimetre) squares the number of corpuscles in one-cubic millimetre of blood is obtained. The average number of corpuscles per each cubic millimetre of healthy blood, accord- ing to Vierordt and Welcker, is 5,000,000 in adult men, and rather fewer in women. THE BLOOD. 83 Chemical Composition of the Blood in Bulk. — Water ........ Solids- Corpuscles ..... Proteids ^of serum) Fibrin (of clot) . ... Fatty matters (of serum) Inorganic salts (of serum) Gases, kreatin, urea and other extractive ) matter, glucose and accidental sub- V stances ......) 784 130 70 2-2 1-4 G 216 1,000 Chemical Composition of the Red Corpuscles.— Analysis of a thousand parts of moist blood corpuscles shows the following as the result: — "Water . 688 303.88 8.12—312 1,000 Of the solids the most important is Hcemoglobin, the substance to •liich the blood owes its color. It constitutes, as will be seen from the appended Table, more than 90 per cent, of the organic matter of the corpuscles. Besides haemoglobin there are proteid : and fatty matters, the former chiefly consisting of globulins, and the latter of cholesterin and lecithin. In 1000 parts organic matter are found: — Haemoglobin Proteids ..... Fats 905-4 86-7 7-9 1,000- Of the inorganic salts of the corpuscles, with the iron omitted — In 1000 parts corpuscles (Schmidt) are found : — Potassium Chloride . . . 3-679 Phosphate. . . . 2-343 sulphate . . -132 Sodium "....... . "633 Calcium " . -094 Magnesium " . '060 Soda . . -341 7-282 1 An account of the proteid bodies, etc., will be found in the Appendix, and should "be referred to for explanation of the terms employed in the text. 84 HAND-BOOK OF PHYSIOLOGY. The properties of hsemoglobin will be considered in relation to the Gases of the blood. Chemical Composition of the Colorless Corpuscles. — In conse- quence of the difficulty of obtaining colorless corpuscles in sufficient num- ber to make an analysis, little is accurately known of their chemical com- position; in all probability, however, the stroma of the corpuscles is made up of proteid matter, and the nucleus of nuclein, a nitrogenous phos- phorus-containing body akin to mucin, capable of resisting the action of the gastric juice. The proteid matter (globulin) is soluble in a ten per cent, solution of sodium chloride, and the solution is precipitated on the addition of water, by heat and by the mineral acids. The stroma con- tains fatty granules, and in it also the presence of glycogen has been demonstrated. The salts of the corpuscles are chiefly potassium, and of these the phosphate is in greatest amount. Chemical Composition of the Plasma or Liquor Sanguinis.— The liquid part of the blood, the plasma or liquor sanguinis in which the corpuscles float, may be obtained in the ways mentioned under the head of the Coagulation of the Blood. In it are the fibrin factors, inasmuch as when exposed to the ordinary temperature of the air it undergoes coag- ulation and splits "up into fibrin and serum. It differs from the serum in containing fibrinogen, but in appearance and in reaction it closely resembles that fluid; its alkalinity, however, is less than that of the serum obtained from it. It may be freed from white corpuscles by filtra- tion at a temperature below 41 °F. (5°C.) Fibrin. — The part played by fibrin in the formation of a clot has been already described (p. 66), and it is only necessary to consider here its general properties. It is a stringy elastic substance belonging to the proteid class of bodies. It is insoluble in water and in weak saline solu- tions, it swells up into a transparent jelly when placed in dilute-hydro- chloric acid, but does not dissolve, but in strong acid it dissolves, pro- ducing acid-albumin;1 it is also soluble on boiling in strong saline solu- tions. Blood contains only -2 per cent, of fibrin. It can be converted by the gastric or pancreatic juice into peptone. It possesses the power of liberating the oxygen from solutions of hyclric peroxide HaOa. This may be shown by dipping a few shreds of fibrin in tincture of guaiacum and then immersing them in a solution of hyclric peroxide. The fibrin becomes of a bluish color, from its having liberated from the solution oxygen, which oxidizes the resin of guaiacum contained in the tincture and thus produces the coloration. 1 The use of the two words albumen and albumin may need explanation. The former is the generic, word which may include several albuminous or proteid bodies, e.g., albumen of blood; the latter, which requires to be qualified by another word, is the specific form, and is applied to varieties, e.g., egg-albumin, serum-albumin. THE BLOOD. 85 Salts of the Plasma. — In 1000 parts plasma there are: — Sodium Chloride Soda . Sodium Phosphate Potassium chloride . " sulphate . Calcium phosphate Magnesium phosphate 5-546 1-532 •271 •359 •281 •298 •218 8.505 Serum. — The serum is the liquid part of the blood or of the plasma remaining after the separation of the clot. It is an alkaline, yellowish, transparent fluid, with a specific gravity of from 1025 to 1032. In the usual mode of coagulation, part of the serum remains in the clot, and the rest, squeezed from the clot by its contraction, lies around it. Since the contraction of the clot may continue for thirty-six or more hours, the quantity of serum in the blood cannot be even roughly estimated till this period has elapsed. There is nearly as much, by weight, of serum as there is clot in coagulated blood. Chemical Composition of the Serum. — Water Proteids: a. Serum-albumin ft. Paraglobulin ...... Salts. Fats — including fatty acids, cholesterin, lecithin; and some soaps Grape sugar in small amount ... Extractives — kreatin, kreatinin, urea, etc. Yellow pigment, which is independent of haemo- globin ........ Gases — small amounts of oxygen, nitrogen, and carbonic acid about 900 80 20 1000 Water. — The water of the serum varies in amount according to the amount of food, drink, and exercise, and with many other circumstances. Proteids. — a. Serum-albumin is the chief proteid found in serum. It is precipitated on heating the serum to 140° F. (60° C.), and entirely coagulates at (167° F. 75° C.), and also by the addition of strong acids, such as nitric and hydrochloric; by long contact with alcohol it is precipitated. It is not precipitated on addition of ether, and so differs from the other native albumin, viz., ^(/-albumin. When dried at 104°F. (40° C.) serum-albumin is a brittle, yellowish substance, soluble in water, possessing a Isevo-rotary power of — 56°. It is with great difficulty 86 HAND-BOOK OF PHYSIOLOGY. freed from its salts, and is precipitated by solutions Of metallic salts, e.g. , of mercuric chloride, copper sulphate, lead acetate, sodium tungstate, etc. If dried at a temperature over 167° F. (75° 0.) the residue is insoluble in water, having been changed into coagulated proteid. P. Paraglobulin can be obtained as a white precipitate from cold serum by adding a considerable excess of water and passing through it a current of carbonic acid gas or by the cautious addition of dilute acetic acid. It can also be obtained by saturating serum with crystallized sulphate mag- nesium or chloride sodium. When obtained in the latter way precipita- tion seems to be much more complete than by means of the former method. Paraglobulin belongs to the class of proteids called globulins. The proportion of serum-albumin to paraglobulin in human blood serum is as 1'511 to 1. The salts of sodium predominate in serum as in plasma, and of these the chloride generally forms by far the largest proportion. Fats are present partly as fatty acids and partly emulsified. The fats are triolein, tristearin, and tripalmitin. The amount of fatty matter varies according to the time after, and the ingredients of, a meal. Of cliolesterin and lecithin there are mere traces. Grape sugar is found principally in the blood of the hepatic vein,, about one part in a thousand. The extractives vary from time to time; sometimes uric and hip- puric acids are found in addition to urea, kreatin and kreatinin. Urea- exists in proportion from *02 to *04 per cent. The yellow pigment of the serum and the odorous matter which gives the blood of each particular animal a peculiar smell, have not yet been properly isolated. VARIATIONS IN HEALTHY BLOOD UNDER DIFFERENT CIRCUMSTANCES. The conditions which appear most to influence the composition of the blood in health are these: Sex, Pregnancy, Age, and Temperament. The composition of the blood is also, of course, much influenced by diet. 1. Sex. — The blood of men differs from that of women, chiefly in be- ing of somewhat higher specific gravity, from its containing a relatively larger quantity of red corpuscles. 2. Pregnancy. — The blood of pregnant women has a rather lower specific gravity than the average, from deficiency of red corpuscles. The quantity of white corpuscles, on the other hand, and of fibrin, is in- creased. 3. Age. — It appears that the blood of the foetus is very rich in solid matter, and especially in red corpuscles; and this condition, gradually diminishing, continues for some weeks after birth. The quantity of solid matter then falls during childhood below the average, again rises during adult life, and in old age falls again. THE BLOOD. 87 4. Temperament. — But little more is known concerning the connection of this with the condition of the blood, than that there appears to be a relatively larger quantity of solid matter, and particularly of red corpuscles, in those of a plethoric or sanguineous temperament. 5. Diet. — Such differences in the composition of the blood as are due to the temporary presence of various matters absorbed with the food and drink, as well as the more lasting changes which must result from gener- ous or poor diet respectively, need be here only referred to. Effects of Bleeding. — The result of bleeding is to diminish the specific gravity of the blood; and so quickly, that in a single venesection, the portion of blood last drawn has often a less specific gravity than that of the blood that flowed first. This is, of course, due to absorption of fluid from the tissues of the body. The physiological import of this fact, namely, the instant absorption of liquid from the tissues, is the same as that of the intense thirst wrhich is so common after either loss of blood, or the ab- straction from it of watery fluid, as in cholera, diabetes, and the like. For some little time after bleeding, the want of red corpuscles is well marked; but with this exception, no considerable alteration seems to be produce^ hi the composition of the blood for more than a very short time: the loss of the other constituents, including the pale corpuscles, being very quickly repaired. VARIATIONS IN THE COMPOSITION OF THE BLOOD, IK DIFFERENT PAKTS OF THE BODY. The composition of the blood, as might be expected, is found to vary in different parts of the body. Thus arterial blood differs from venous; and although its composition and general characters are uniform through- out the whole course of the systemic arteries, they are not so throughout the venous system, — the blood contained in some veins differing remarka- bly from that in others. Differences between Arterial and Venous Blood. — The differ- ences between arterial and venous blood are these: — (a.) Arterial blood is bright red, from the fact that almost all its haemoglobin is combined with oxygen (Oxy haemoglobin, or scarlet haemo- globin), while the purple tint of venous blood is due to the deoxida- tion of a certain quantity of its oxyhaemoglobin, and its consequent reduc- tion to the purple variety (Deoxidized, or purple haemoglobin). (#.) Arterial blood coagulates somewhat more quickly. (c. } Arterial blood contains more oxygen than venous, and less carbonic acid. Some of the veins contain blood which differs from the ordinary stand- ard considerably. These are the Portal, the Hepatic, and the Splenic veins. Portal vein. — The blood which the portal vein conveys to the liver is supplied from two chief sources; namely, that in the gastric and mesen- teric veins, which contains the soluble elements of food absorbed from the 88 HAND-BOOK OF PHYSIOLOGY. stomach and intestines during digestion, and that in the splenic vein; it must, therefore, combine the qualities of the blood from each of these sources. The blood in the gastric and mesenteric veins will vary much accord- ing to the stage of digestion and the nature of the food taken, and can therefore be seldom exactly the same. Speaking generally, and without considering the sugar, dextrin, and other soluble matters which may have been absorbed from the alimentary canal, this blood appears to be defi- cient in solid matters, especially in red corpuscles, owing to dilution by the quantity of water absorbed, to contain an excess of albumin, and to yield a less tenacious kind of fibrin than that of blood generally. The blood from the splenic vein is generally deficient in red corpuscles, and contains an unusually large proportion of proteids. The fibrin ob- tainable from the blood seems to vary in 'relative amount, but to be almost always above the average. The proportion of colorless corpuscles is also unusually large. The whole quantity of solid matter is decreased, the diminution appearing to be chiefly in the proportion of red corpuscles. The blood of the portal vein, combining the peculiarities of its two factors, the splenic and mesenteric venous blood, is usually of lower specific gravity than blood generally, is more watery, contains fewer red corpuscles, more proteids, and yields a less firm clot than that yielded by other blood, owing to the deficient tenacity of its fibrin. Guarding (by ligature of the portal vein) against the possibility of an error in the analysis from regurgitation of hepatic blood into the portal vein, recent observers have determined that hepatic venous blood contains less water, albumen, and salts, than the blood of the portal vein; but that it yields a much larger amount of extractive matter, in which is one con- stant element, namely, grape-sugar, which is found, whether saccharine or farinaceous matter have been present in the food or not. THE GASES OF THE BLOOD. The gases contained in the blood are Carbonic acid, Oxygen, and Nitro- gen, 100 volumes of blood containing from 50 to 60 volumes of these gases collectively. Arterial blood contains relatively more oxygen and less carbonic acid than venous. But the absolute quantity of carbonic acid is in both kinds of blood greater than that of the oxygen. Oxygen. Carbonic Acid. Nitrogen. Arterial Blood . . 20 vol. per cent. 39 vol. per cent. 1 to 2 vols. Venous " (from muscles at rest) 8 to 12 " " " 46 " " " 1 to 2 vols. The Extraction of the Gases from the Blood. — As the ordinary air- pumps are not sufficiently powerful for the purpose, the extraction of the gases from the blood is accomplished by means of a mercurial air-pump, of which there are many varieties, those of Ludwig, Alvergnidt, Geissler, and Sprengel being the chief. The principle of action in all is much the THE BLOOD. 89 same. Ludwig's pump, which may be taken as a type, is represented in the figure. It consists of two fixed globes, C and F, the upper one com- municating by means of the stopcock D, and a stout india-rubber tube with another glass globe, L, which can be raised or lowered by means of a pulley; it also communicates by means of a stop-cock, B, and a bent glass tube, A, with a gas receiver (not represented in the figure), A dip- ping into a bowl of mercury, so that the gas may be received over mercury. The lower globe, F, communicates with C by means of the stopcock, E, with / in which the blood is contained by the stopcock G, and with a movable glass globe, M, similar to Z, by means of the stopcock, H, and the stout india-rubber tube, K. In order to work the pump, L and M are filled with mercury, the blood from which the gases are to be extracted is placed in the bulb /, the stopcocks, H, E, D, and B, being open, and G closed. M is raised by means of the pulley until F is full of mercury, and the air is driven out. E is then closed, and L is raised so that C becomes full of mercury, and the air driven off. B is then closed. On lowering L the mercury runs into it from C, and a vacuum is established in 0. On opening E and lower- ing M, a vacuum is similarly established in F; if G be now opened, the blood in / will enter into ebullition, and the gases will pass off into F and (7, and on raising M and then L, the stopcock B being opened, the gas is driven through A, and is received into the receiver over mercury. By repeating the experiment several times the whole of the gases of the speci- men of blood is obtained, and may be estimated. The Oxygen of the Blood.— It has been found that a very small proportion of the oxygen which can be obtained, by the aid of the mer- curial pump, from the blood, exists in a state of simple solution in the plasma. If the gas were in simple solution, the amount of oxygen in any given quantity of blood exposed to any given atmosphere ought to vary with the amount of oxygen contained in the atmosphere. Since, speak- ing generally, the amount of any gas absorbed by a liquid such as plasma would depencl upon the proportion of the gas in the atmosphere to which the liquid was exposed — if the proportion were great, the absorption would be great; if small, the absorption would be similarly small. The absorption would continue until the proportion of the gas in the liquid FIG. 80.— Ludwig's Mercurial Pump. 90 HAND-BOOK OF PHYSIOLOGY, and in the atmosphere became equal. Other things would, of course, in- fluence the absorption, such as the kind of gas employed, nature of the liquid, and the temperature of both, but cceteris paribus, the amount of a gas which a liquid absorbs depends upon the proportion of the gas — the so-called partial pressure — of the gas in the atmosphere to which the liquid is subjected. And conversely, if a liquid containing a gas in solu- tion be exposed to an atmosphere containing none of the gas, the gas will be given up to the atmosphere until its amount in the liquid and in the atmosphere becomes equal. This condition is called a condition of equal tensions. The condition may be understood by a simple illustration. A large amount of carbonic acid gas is dissolved in a bottle of water by ex- posing the liquid to extreme pressure of the gas, and a cork is placed in the bottle and wired down. The gas exists in the water in a condition of extreme tension, and therefore there is a tendency of the gas to escape into the atmosphere, in order that the tension may be relieved; this causes the violent expulsion of the cork when the wire is removed, and if the water be placed in a glass the gas will continue to be evolved until it is almost all got rid of, and the tension of the gas in the water approximates to that of the atmosphere in which, it should be remembered, the carbon dioxide is, naturally, in very small amount, viz., -04 per cent. Now the oxygen of the blood does not obey this law of pressure. For if blood which contains little or no oxygen be exposed to a succession of atmos- pheres containing more and more of that gas, we find that the absorption is at first very great, but soon becomes relatively very small, not being therefore regularly in proportion to the increased amount (or tension) of the oxygen of the atmospheres, and that conversely, if arterial blood be submitted to regularly diminishing pressures of oxygen, at first very little of the contained oxygen is given off to the atmosphere, then suddenly the gas escapes with great rapidity, again disobeying the law of pres- sures. Very little oxygen can be obtained from serum freed from blood cor- puscles, even by the strongest mercurial air-pump, neither can serum be made to absorb a large quantity of that gas; but the small quantity which is so given up or so absorbed follows the laws of absorption according to pressure. . , It must be, therefore, evident that the chief part of the oxygen is con- tained in the corpuscles, and not in a state of simple solution. The chief solid constituent of the colored corpuscles is haemoglobin, which consti- tutes more than 90 per cent, of their bulk. This body has a very re- markable affinity for oxygen, absorbing it to a very definite extent under favorable circumstances, and giving it up when subjected to the action of reducing agents, or to a sufficiently low oxygen pressure. From these facts it is inferred that the oxygen of the blood is combined with haemo- globin, and not simply dissolved; but inasmuch as it is comparatively easy THE BLOOD. 91 to cause the haemoglobin to give up its oxygen, it is believed that the oxygen is but loosely combined with the substance. Haemoglobin.— Haemoglobin is a crystallizable body which constitutes by fur the largest portion of the colored corpuscles. It is intimately dis- tributed throughout their stroma, and must be dissolved out of it before it will undergo crystallization. Its percentage composition is C. 53*85; 11. 7-32; K". 16-17; 0. 21-84; S. -63; Fe. '42; and if the molecule be sup- posed to contain one atom of iron the formula would be C600, H960, N1M, Fe Ss, 0179. The most interesting of the properties of haemoglobin are its powers of crystallizing and its attraction for oxygen and other gases. Crystals. — The haemoglobin of the blood of various animals possesses the power of crystallizing to very different extents (blood-crystals). In some animals the formation of crystals is almost spontaneous, whereas in others crystals are formed either with great difficulty or not at all. Among the animals whose blood coloring-matter crystallizes most readily are the guinea-pig, rat, squirrel, and dog; and in these cases to obtain crystals it is generally sufficient to dilute a drop of recently -drawn blood with water and expose it for a few minutes to the air. Light seems to favor the for- mation of the crystals. In many instances oth ?r means must be adopted, e.f./., the addition of alcohol, ether, or chloroform, rapid freezing, and then thawing, an electric current, a temperature of 140° F. (60° C.), or the addition of sodium sulphate. Human blood crystallizes with difficulty, as does also that of the ox, the pig, the sheep, and the rabbit. FIG. 81.— Crystals of oxy-hsemoglobin— prismatic from human blood. The forms of haemoglobin crystals, as will be seen from the appended figures, differ greatly. Haemogloblin crystals are soluble in water. Both the crystals them- selves and also their solutions have the characteristic color of arterial blood. yz HAND-BOOK OF PHYSIOLOGY. A dilute solution of haemoglobin gives a characteristic appearance with the spectroscope. Two absorption bands are seen between the solar lines D and E (see Plate), one toward the red, with its middle line some little way to the blue side of D, is very intense, but narrower than the other, which lies near to the red side of E. Each band is darkest in the middle and fades away at the sides. As the strength of the solution increases the bands become broader and deeper, and both the red and the blue ends of the spectrum become encroached upon until the bands coalesce to form one very broad band, and only a slight amount of the green remains un- absolved, and part of the red, and on further increase of strength the former disappears. If the crystals of oxy-haemoglobin be subjected to a mercurial air-pump they give off a definite amount of oxygen (1 gramme giving off 1-59 FIG. 82. FIG. 82. — Oxy-hsemoglobin crystals — tetrahedral, from blood of the guinea-pig. FIG. 83.— Hexagonal oxy-heemoglobin crystals, from blood of squirrel. On these hexagonal plates, prismatic crystals, grouped in a stellate manner, not unfrequently occur (after Funke). c.cm. of oxygen), and they become of a purple color; and a solution of oxy- haemoglobin may be made to give up oxygen and to become purple in a similar manner. This change may be also effected by passing through it hydrogen or nitrogen gas, or by the action of reducing agents, of which Stokes's fluid1 is the most convenient. With the spectroscope a solution of deoxidized haemoglobin is found to give an entirely different appearance from that of oxidized haemoglo- bin. Instead of the two bands at D and E we find a single broader but fainter band occupying a position midway between the two, and at the 1 Stokes* 's Fluid consists of a solution of ferrous sulphate, to which ammonia has been added and sufficient tartaric acid to prevent precipitation. Another reducing agent is a solution of stannous chloride, treated in a way similar to the ferrous sulphate, and a third reagent of like nature is an aqueous solution of ammonium sulphide. THE BLOOD. 93 time less of the blue end of the spectrum is absorbed. Even in strong solutions this latter appearance is found, thereby differing from the strong solution of oxidized haemoglobin which lets through only the red and orange rays; accordingly to the naked eye the one (reduced haemoglobin solution) appears purple, the other (oxy-hsemoglobin solu- tion) red. The deoxidized crystals or their solutions quickly absorb oxy- gen on exposure to the air, becoming scarlet. If solutions of blood be taken instead of solutions of haemoglobin, results similar to the whole of the foregoing can be obtained. Venous blood never, except in the last stages of asphyxia, fails to show the oxy-haemoglobin bands, inasmuch as the greater part of the haemoglobin even in venous blood exists in the more highly oxidized condition. Action of Gases on Haemoglobin. — Carbonic oxide, passed through a solution of haemoglobin, causes it to assume a bluish color, and the spec- trum is slightly altered; two bands are still visible, but are somewhat nearer the blue end than those of oxy-haemoglobin (see Plate). The amount of carbonic oxide is equal to the amount of the oxygen displaced. Although the carbonic oxide gas readily displaces oxygen, the reverse is not the case, and upon this property depends the dangerous effect of coal gas poisoning. Coal gas contains much carbonic oxide, and this at once, when breathed, combines with the haemoglobin of the blood, producing a compound which cannot easily be reduced, and since it is by no means an oxygen carrier, death may result from suffocation from want of oxygen notwithstanding the free entry into the lungs of pure air. Crystals of carbonic-oxide haemoglobin closely resemble those of oxyhaemoglobin. Nitric oxide produces a similar compound to the carbonic-oxide haemo- globin, which is even less easily reduced. Nitrous oxide reduces oxyhaemoglobin, and therefore leaves the reduced haemoglobin in a condition to actively take up oxygen. Sulphuretted Hydrogen. — If this gas be passed through a solution of oxyhaemoglobin, the haemoglobin is reduced and an additional band appears in the red. If the solution be then shaken with air, the two bands of oxyhaemoglobin replace that of reduced haemoglobin, but the band in the red persists. PRODUCTS OF THE DECOMPOSITION OF HAEMOGLOBIN. Methaemoglobin. — If an aqueous solution of oxyhaemoglobin be exposed to the air for some time, its spectrum undergoes a change; the two D and E bands become faint, and a new line in the red at c is devel- oped. The solution, too, has become brown and acid in reaction, and is precipitable by basic lead acetate. This change is due to the decomposi- tion of haemoglobin, and to the production of metlicernoglobin. On add- 94 HAND-BOOK OF PHYSIOLOGY. ing ammonium sulphide, reduced haemoglobin is produced, and on shaking this up with air, oxyhsemoglobin. is reproduced. Haematin. — By the action of heat, or of acids or alkalies in the pres- ence of oxygen, haemoglobin can be split up into a substance called H&matin, which contains all the iron of the haemoglobin from which it was derived, and a proteid residue. Of the latter it is impossible to say more than that it is probably made up of one or more bodies of the globu- lin class. If there be no oxygen present, instead of haematin a body called hcemocliromogen is produced, which, however, will speedily undergo oxi- dation into haematin. Haematin is a dark brownish or black non-crystallizable substance of metallic lustre. Its percentage composition is C. 64-30; H. 5 -50; N. 9 -06; Fe, 8-82; 0. 12-32; which gives the formula C68, H70, N8, Fe2, 010 (Hoppe- Seyler). It is insoluble in water, alcohol, and ether; soluble in the caustic alkalies; soluble with difficulty in hot alcohol to which is added sulphuric acid. The iron may be removed from haematin by heating it with fuming hydrochloric acid to 320° F. (160° C.), and a new body, hcematoporpliyrin, is produced. In acid solution. — If to blood an excess of acetic acid be added, the color alters to brown from decomposition of haemoglobin, and' the setting free of haematin; by shaking this solution with ether, solution of the haematin is obtained. The spectrum of the etherial solution shows no less than four absorption bands, viz., one in the red between c and D, one faint and narrow close to D, and then two broader bands, one between D and E, and another nearly midway between I and F. The first band is by far the most distinct, and the acid solution of haematin without ether shows it plainly. In alkaline solution. — The absorption band is still in the red, but nearer to D, and the blue end of the spectrum is partially absorbed to a considerable extent. If a reducing agent be added, two bands resembling those of oxyhaemoglobin, but nearer to the blue, appear; this is the spec- trum of reduced hcematin. On shaking the reduced haematin with air or oxygen the two bands are replaced by the single band of alkaline haematin. Hsematoidin. — This substance is found in the form of yellowish crystals in old blood extravasations, and is derived from the haemoglobin. Their crystalline form and the reaction they give with nitric acid seem to show them to be identical with Bilirubin, the chief coloring matter of the Bile. Hsemin. — One of the most important derivatives of nsematin is Haemin. It is usually called Hydrochlorate of Hcematin (or hydrochlo- ride), but its exact chemical composition is uncertain. Its formula is C0fJ, H70, N8, Fe2, 010, 2 Hcl, and it contains 5*18 per cent, of chlorine, but by some it is looked upon as simply crystallized hamiatin. Although THE BLOOD. 95 difficult to obtain in bulk, a specimen may be easily made for the micro- scope in the following way: — A small drop of dried blood is finely powdered with a few crystals of common salt on a glass slide, and spread out; a cover ), in connection with which is a long and light lever (a). The shock of the heart's impulse being communicated to the ivory knob, and through it to the first tympanum, the effect is, of course, at once transmitted by the column of air in the elastic tube to the interior of the second tympanum, also closed, and through the elastic and movable lid of the latter to the lever, which is placed in connection with a registering appa- 101. ratus, which consists generally of a cylinder or drum covered with smoked paper, revolving according to a definite velocity by clockwork. The point of the lever writes upon the paper, and a tracing of the heart's impulse is thus obtained. By placing three small india-rubber air -bags in the interior respec- FIG. 102.— Marey 's Tambour ( b ), to which the movement of the column of air in the first tym- panum is conducted by the tube,/, and from which it is communicated by the lever, o, to a revolving cylinder, so that the tracing of the movement of the impulse beat is obtained. tively of the right auricle, the right ventricle, and in an intercostal space in front of the heart of living animals (horse), and placing these bags, by means of long narrow tubes, in communication with three levers, arranged FIG. 103.— Tracing of the impulse of the heart of man. (Marey.) one over the other in connection with a registering apparatus (Fig. 104), MM. Chauveau and Marey have been able to measure with much accuracy the variations of the endocardial pressure and the comparative duration CIRCULATION OF THE BLOOD. 121 of the contractions of the auricles and ventricles. By means of the same apparatus, the synchronism of the impulse with the contraction of the ventricles, is also well shown; and the causes of the several vibrations of which it is really composed, have been discovered. In the tracing (Fig 105), the intervals between the vertical lines rep- resent periods of a tenth of a second. The parts on which any given FIG. 104. — Apparatus of MM. Chauveau and Marey for estimating the variations of endocardia! pressure, and production of impulse of the heart. vertical line falls represent, of course, simultaneous events. Thus, — it will be seen that the contraction of the auricle, indicated by the upheaval of the tracing at A in first tracing, causes a slight increase of pressure in the ventricle (A' in second tracing), and produces a tiny impulse (A" in third tracing). So also, the closure of the semilunar valves, while it causes a momen- tarily increased pressure in the ventricle at D', does not fail to affect the pressure in the auri- cle D", and to leave its mark in the tracing of the impulse also, D", The large upheaval of the ventricular and the impulse tracings, between A' and D', and A" and D", are caused by the ventricular con- traction, while the smaller undulatitfns, between B and c, B' and c', B" and c", are caused by the vibrations consequent on the tightening and closure of the auriculo- ventricular valves. Although, no doubt, the method thus de- ., , , • , i - impulse of the heart, to be read Scribed may show a perfectly Correct View of from left to rieht, obtained by , i , , . . , . .,11-iT Chauveau and Marey's apparatus. the endocardiac pressure variations, it should be recollected that the muscular walls may grip the air-bags, even after the complete expulsion of the contents of the chamber, and so the lever might remain for a too long time in the position of extreme tension, and would FIG. 105.— Tracings of (1), In- fra-auricular, and ( 2 ), Intra-ven- tricular pressures, and ( 3 ), of the 122 HAND-BOOK OF PHYSIOLOGY represent on the tracing not only, as it ought to do, the auricular or ventricular pressure on the blood, but, also afterward, the muscular pres- sure exerted upon the bags themselves. (M. Foster.) FREQUENCY AND FORCE OF THE HEART'S ACTION. The heart of a healthy adult iran contracts from seventy to seventy-five times in a minute; but many circumstances cause this rate, which of course corresponds with that of the arterial pulse, to vary even in health. The chief are age, temperament, sex, food and drink, exercise, time of day, posture, atmospheric pressure, temperature. Age. — The frequency of the heart's action gradually diminishes from the commencement to near the end of life, but is said to rise again somewhat in extreme old age, thus: — Before birth the average number of pulses in a minute is 150 Just after birth . . . . . from 140 to 130 During the first year . . . " 130 " 115 During the second year " 115 t( 100 During the third year " 100 " 90 About the seventh year . . . . " 90 " 85 About the fourteenth year, the average number of pulses in a minute is " 85 " 80 In adult age " 80 " 70 In old age " 70 " 60 In decrepitude " 75 " 65 Temperament and Sex. — In persons of sanguine temperament, the heart acts somewhat more frequently than in those of the phlegmatic; and in the female sex more frequently than in the male. Food and Drink. Exercise. — After a meal its action is accelerated, and still more so during bodily exertion or mental excitement; it is slower during sleep. Diurnal Variation. — It appears that, in the state of health, the pulse is most frequent in the morning, and becomes gradually slower as the day advances, and that this diminution of frequency is both more regular and more rapid in the evening than in the morning. Posture. — It is found that, as a general rule, the pulse, especially in the adult male, is more frequent in the standing than in the sitting pos- ture, and in the latter than in the recumbent position; the difference being greatest between the standing and the sitting posture. The effect of change of posture is greater as the frequency of the pulse is greater, and, accordingly, is more marked in the morning than in the evening. By supporting the body in different postures, without the aid of mus- cular effort of the individual, it has been proved that the increased fre- quency of the pulse in the sitting and standing positions is dependent upon the muscular exertion engaged in maintaining them; the usual effect of these postures on the pulse being almost entirely prevented when the usually attendant muscular exertion was rendered unnecessary. (Guy.) CIRCULATION OF THE BLOOD. 123 Atmospheric Pressure. — The frequency of the pulse increases in a corresponding ratio with the elevation above the sea. Temperature. — The rapidity and force of the heart's contractions are largely influenced by variations of temperature. The frog's heart, when excised, ceases to beat if the temperature be reduced to 32° F. (0° C.). When heat is gradually applied to it, both the speed and force of the heart's contractions increase till they reach a maximum. If the tem- perature is still further raised, the beats become irregular and feeble, and the heart at length stands still in a condition of "heat-rigor." Similar effects are produced in warm-blooded animals. In the rabbit, the number of heart -beats is more than doubled when the temperature of the air was maintained at 105° F. (40°.5 C.). At 113°— 114° F. (45° C.), the rabbit's heart ceases to beat. Relative Frequency of the Pulse to that of Respiration. — In health there is observed a nearly uniform relation between the fre- quency of the pulse and of the respirations; the proportion being, on an average, one respiration to three or four beats of the heart. The same relation is generally maintained in the cases in which the pulse is naturally accelerated, as after food or exercise; but in disease this relation usually ceases. In many affections accompanied with increased frequency of the pulse, the respiration is, indeed, also accelerated, yet the degree of its acceleration may bear no definite proportion to the increased number of the heart's actions: and in many other cases, the pulse becomes more fre- quent without any accompanying increase in the number of respirations; or, the respiration alone may be accelerated, the number of pulsations re- maining stationary, or even falling below the ordinary standard. The Force of the Ventricular Systole and Diastole.— The force of the left ventricular systole is more than double that exerted by the contraction of the right: this difference in the amount of force exerted by the contraction of the two ventricles, results from the walls of the left ventricle being about twice or three times as thick as those of the right. And the difference is adapted to the greater degree of resistance which the left ventricle has to overcome, compared with that to be overcome by the right: the former having to propel blood through every part of the body, the latter only through the lungs. The actual amount of the intra- ventricular pressures during systole in the dog has been found to be 2*4 inches (60 mm.) of mercury in the right ventricle, and 6 inches (150 mm.) in the left. During diastole there is in the right ventricle a negative or suction pressure of about | of an inch ( — 17 to —16 mm.), and in the left ventricle from 2 inches to $• of an inch ( — 52 to — 20 mm.). Part of this fall in pressure, and possibly the greater part, is to be referred to the influence of respiration; but with- out this the negative pressure of the left ventricle caused by its active dilatation is about | of an inch (23 mm.) of mercury. The right ventricle is undoubtedly aided by this suction power of the 124 HAND-BOOK OF PHYSIOLOGY. left, so that the whole of the work of conducting the pulmonary circula- tion does not fall upon the right side of the heart, but is assisted by the left side. The Force of the Auricular Systole and Diastole. — The maximum pressure within the right auricle is about \ of an inch (20 mm.) of mercury, and is probably somewhat less in the left. It has been found that during diastole the pressure within both auricles sinks considerably below that of the atmosphere; and as some fall in pressure takes place, even when the thorax of the animal operated upon has been opened, a certain proportion of the fall must be due to active auricular dilatation independent of respiration. In the right auricle, this negative pressure is about —10 mm. Work Done by the Heart. — In estimating the work done by any machine it is usual to express it in terms of the "unit of work." The unit of work is defined to be the energy expended in raising a unit of weight (1 Ib.) through a unit of height (1 ft.). In England, the unit of work is the "foot-pound," in France, the "kilogrammetre." The work done by the heart at each contraction can be readily found by multiplying the weight of blood expelled by the ventricles by the height to which the blood rises in a tube tied into an artery. This height was found to be about 9 ft. in the horse, and the estimate is nearly correct for a large artery in man. Taking the weight of blood expelled from the left ventricle at each systole as 6 oz., i.e., f Ib., we have 9 x f = 3 -375 foot-pounds as the work done by the left ventricle at each systole; and adding to this the work done by the right ventricle (about one-third that of the left) we have 3*375 X 1*125 = 4*5 foot-pounds as the work done by the heart at each eontraction. Other estimates give \ kilogrammetre, or about 3-J- foot-pounds. Haughton estimates the total work of the heart in 24 hours as about 124 foot-tons. Influence of the Nervous System on the Action of the Heart. — The hearts of warm-blooded animals cease to beat almost if not quite immediately after removal from the body, and are, therefore, un- favorable for the study of the nervous mechanism which regulates their action. Observations have hitherto, therefore, been principally directed to the heart of cold-blooded animals, e.g., the frog, tortoise, and snake, which will continue to beat under favorable conditions for many hours after removal from the body. Of these animals, the frog is the one mostly employed, and, indeed, until recently, it was from the study of the frog's heart that the chief part of our information was obtained. If removed from the body entire, the frog's heart will continue to beat for many hours and even days, and the beat has no apparent difference from the beat of the heart before removal from the body; it will take place without the presence of blood or other fluid within its chambers. If the beats have "become infrequent, an additional beat may be induced by stimulating CIRCULATION OF THE BLOOD. 125 the heart by means of a blunt needle; but the time before the stimulus applied produces its result (the latent period) is very prolonged, and as in this way the cardiac beat is like the contraction of unstriped muscle, the method has been likened to a peristaltic contraction. There is much uncertainty about the nervous mechanism of the beat of the frog's heart, but what has just been said shows, at any rate, two things; firstly, that as the heart will beat when removed from the body in a way differing not at all from the normal, it must contain within itself the mechanism of rhythmical contraction; and secondly, that as it can beat without the presence of fluid within its chambers, the movement cannot depend merely on reflex excitation by the entrance of blood. The nervous apparatus existing in the heart itself consists of collections of microscopic ganglia, and of nerve- fibres proceeding from them. These ganglia are -AA AA FIG. 106.— Heart of frog. (Burdon-Sanderson after Fritsche.) Front view to the left, back view to the right. A A. Aortae. V. cs. Venae cavae superiores. At s, left auricle. At d, right auricle. Fen., ventricle. B. ar., Bulbus arteriosus. S. v., Sinus venosus. V. c. i., Vena cava inferior. V. ft ., Venae hepaticae . V . p . , Venae pulmonales . demonstrable as being collected chiefly into three groups; one is in the wall of the sinus venosus (Remakes); a second, near the junction between the auricle and ventricle (Bidder's); and the third in the septum between the auricles. Some very important experiments seem to identify the rhythmical contractions of the frog's heart with these ganglia. If the heart be re- moved entire from the body, the sequence of the contraction of its several beats will take place with rhythmical regularity, viz., of the sinus veno- sus, the auricles, the ventricle, and bulbus arteriosus, in order. If the heart be removed at the junction of the sinus and auricle, the former will continue to beat, but the removed portion will for a short variable time stop beating, and then resume its beats, but with a rhythm different to that of the sinus: and, further, if the ventricle be removed, it will take a still longer time before recommencing its pulsation after its removal than the larger portion consisting of the auricles and ventricle, and its rhythm is different from that of the unremoved portion, and not so regu- lar, nor will it continue to pulsate so long: during the period of stop- page a contraction will occur if the ventricle be mechanically or otherwise stimulated. If the lower two-thirds or apex of the ventricle be removed, the remainder of the heart will go on beating regularly in the body, but 126 HAND-BOOK OF PHYSIOLOGY. this part will remain motionless, and will not beat spontaneously, although it will respond to stimuli. If the heart be divided lengthwise, its parts will continue to pulsate rhythmically, and the auricles may be cut up into pieces, and the pieces will continue their movements of contraction. It will be thus seen that the rhythmical movements appear to be more marked in the parts supplied by the ganglia, and that the apical portion of the ventricle, in which the ganglia are not found, does not possess the power of automatic movement. Although the theory that the pulsations of the rest of the heart are dependent upon that of the sinus, and to stimuli pro- ceeding from it, when connection is maintained, and only to reflex stim- uli when removal has taken place, cannot be absolutely upheld, yet it is evident that the power of spontaneous contraction is strongest in the sinus, less strong in the auricles, and less so still in the ventricle, and that, therefore, the sinus ganglia are probably important in exciting the rhythmical contraction of the whole heart. This is expressed in the fol- lowing way: — "The power of independent rhythmical contraction de- creases regularly as we pass from the sinus to the ventricles," and "The rhythmical power of each segment of the heart varies inversely as its dis- tance from the sinus." (Gaskell.) It has been recently shown that, under appropriate stimuli, even the extreme apex of the ventricle in the tortoise may take on rhythmical contractions, or in other words may be "taught to beat" rhythmically. (Gaskell.) Inhibition of the Heart's Action. — Although, under ordinary conditions, the apparatus of ganglia and nerve-fibres in the substance of the heart forms the medium through which its action is excited and rhythmically maintained, yet they, and, through them, the heart's con- tractions, are regulated by nerves which pass to them from the higher nerve-centres. These nerves are branches from the pneumogastric or vagus and the sympathetic. The influence of the vagi nerves over the heart-beat may be shown by stimulating one (especially the right) or both of the nerves when a record is being taken of the beats of the frog's heart. If a single induction shock be sent into the nerve, the heart, after a short interval, ceases beating, but after the suppression of several beats resumes its action. As already mentioned, the effect of the stimulus is not immediately seen, and one beat may occur before the heart stops after the application of the electric-cur- rent. The stoppage of the heart may occur apparently in one of two ways, either by diminution of the strength of the systole or by increas- ing the length of the diastole. The stoppage of the heart may be brought about by the application of the electrodes to any part of the vagus, but most effectually if they are applied near the position of Remak's ganglia. It is supposed that the fibres of the vagi, therefore, terminate there in CIRCULATION OF THE BLOOD. 127 inhibitory ganglia in the heart-walls, and that the inhibition of the heart's lii'iits bv means of the vagus, is not a simple action, but that it is pro- duced by stimulating centres in the heart itself. These inhibitory centres are paralyzed* by atropin, and then no amount of stimulation of the vagus, or of the heart itself, will produce any effect upon the cardiac beats. "Urari in large doses paralyzes the vagus fibres, but in this case, as the inhibitory action can be produced by direct stimulation of the heart, it is inferred that this drug does not paralyze the ganglia themselves. Mus- carin and pilocarpin appear to produce effects similar to those obtained by stimulating the vagus fibres. If a ligature be tightly tied round the heart over the situation of the ganglia between the sinus and the auricles, the heart stops beating. This experiment (Stannius') would seem to stimulate the inhibitory gan- glia, but for the remarkable fact that atropin does not interfere with its success. If the part (the ventricle) below the ligature be cut off, it will begin and continue to beat rhythmically, this may be explained by sup- posing that the stimulus of section induces pulsation in the part which is removed from the influence of the inhibitory ganglia. ' So far, the effect of the terminal apparatus of the vagi has been con- sidered; there is, however, reason for believing that the vagi nerves are simply the media of an inhibitory or restraining influence over the action of the heart, which is conveyed through them from a centre in the me- dulla oblongata which is always in operation, and, because of its restrain- ing the heart's action, is called the car dio -inhibitory centre. For, on dividing these nerves, the pulsations of the heart are increased in fre- quency, an effect opposite to that produced by stimulation of their divided (peripheral) ends. The restraining influence of the centre in the medulla may be increased reflexly, producing slowing or stoppage of the heart, through influence passing from it down the vagi. As an example of the latter, the well-known effect on the heart of a violent blow on the epigastrium may be referred to. The stoppage of the heart's action is due to the conveyance of the stimulus by fibres of the sympathetic to the medulla oblongata, and its subsequent reflection through the vagi to the inhibitory ganglia of the heart. It is also believed that the power of the medullary inhibitory centre may be reflexly lessened, producing acceler- ated action of the heart. Acceleration of Heart's Action.— Through certain fibres of the sympathetic, the heart receives an accelerating influence from the medulla oblongata. These accelerating nerve-fibres, issuing from the spinal cord in the neck, reach the inferior cervical ganglion, and pass thence to the cardiac plexus, and so to the heart. Their function is shown in the quickened pulsation which follows stimulation of the spinal cord, when the latter has been cut off from all connection with the heart, excepting that which is formed by the accelerating filaments from the inferior cer- 128 HAND-BOOK OF PHYSIOLOGY. vical ganglion. Unlike the inhibitory fibres of the pneumogastric, the accelerating fibres are not continuously in action. The accelerator nerves must not, however, be considered as direct antagonists of the vagus; for if at the moment of their maximum stimu- lation, the vagus be stimulated with minimum currents, inhibition is produced with the same readiness as if these were not acting. The connection of the heart with other organs by means of the nerv- ous system, and the influences to which it is subject through them, are shown in a striking manner by the phenomena of disease. The influence of mental shock in arresting or modifying the action of the heart, the slow pulsation which accompanies compression of the brain, the irregu- larities and palpitations caused by dyspepsia or hysteria, are good evidence of the connection of the heart with other organs through the nervous system. The action of the heart is no doubt also very materially affected by the nutrition of its walls by a sufficient supply of healthy blood sent to them, and it is not unlikely that the apparently contradictory effect of poisons may be explained by supposing that the influence of some of them is either partially or entirely directed to the muscular tissue itself, and not to the nervous apparatus alone. As will be explained presently, the heart exercises a considerable influence upon the condition of the pressure of blood within the arteries, but in its turn the blood-pressure within the arteries reacts upon the heart, and has a distinct effect upon its contrac- tions, increasing by its increase, and vice versd, the force of the cardiac beat, although the frequency is diminished as the blood-pressure rises. The quantity (and quality?) of the blood contained in each chamber, too, has an influence upon its systole, and within normal limits the larger the quantity the stronger the contraction. Kapidity of systole does not of necessity indicate strength, as two weak contractions often do no more work than one strong and prolonged. In order that the heart may do its maximum work, it must be allowed free space to act; for if obstructed, in its action by mechanical outside pressure, as by an excess of fluid within the pericardium, such as is produced by inflammation, or by an over- loaded stomach, or what not, the pulsations become irregular and feeble. THE AKTEKIES. Distribution. — The arterial system begins at the left ventricle in a single large trunk, the aorta, which almost immediately after its origin gives off in its course in the thorax three large branches for the supply of the head, neck, and upper extremities; it then traverses the thorax and abdomen, giving off branches, some large and some small, for the supply of the various organs and tissues it passes on its way. In the abdomen it divides into two chief branches, for the supply of the lower CIRCULATION OF THE BLOOD. 129 extremities. The arterial branches wherever given off divide and sub- divide, until the calibre of each subdivision becomes very minute, and these minute vessels pass into capillaries. Arteries are, as a rule, placed in situations v protected from pressure and other dangers, and are, with few exceptions, straight in their course, and frequently communicate with other arteries (anastomose or inosculate). The branches are usually given off at an acute angle, and the area of the branches of an artery gen- erally exceeds that of the parent trunk; and as the distance from the origin is increased, the area of the combined branches is increased also. After death, arteries are usually found dilated (not collapsed as the veins are) and empty, and it was to this fact that their name was given them, as the ancients believed that they conveyed air to the various parts of the body. As regards the arterial system of the lungs (pulmonary system) it begins at the right ventricle in the pulmonary artery, and is distributed much as the arteries belonging to the general systemic cir- culation. Structure. — The walls of the arteries are composed of three principal coats, termed the external or tunica adventitia, the middle or tunica madia, and the internal coat or tunica intima. The external coat or tunica adventitia (Figs. 107 and 111, t. a.), the strongest and toughest part of the wall of the artery, is formed of areolar FIG. 107. Fio. 108. FIG. 107.— Minute artery viewed in longitudinal section, e. Nucleated endothelial membrane, With faint nuclei in lumen, looked at from above, i. Thin elastic tunica intima. m. Muscular coat or tunica media. «, Tunica adventitia. (Klein and Noble Smith.) X 250. FIG. 108.— Portion of fenestrated membrane from the femoral artery. X 200. a, 6, c. Perfo- rations. t.Henle.) tissue, with which is mingled throughout a network of elastic fibres. At the inner part of this outer coat the elastic network forms in most arteries so distinct a layer as to be sometimes called the external elastic coat (Fig. 123, e.e.). The middle coat (Fig. 107, m) is composed of both muscular and VOL. I.— 9 130 HAND-BOOK OF PHYSIOLOGY. elastic fibres, with a certain proportion of areolar tissue. In the larger arteries (Fig. 110) its thickness is comparatively as well as absolutely much greater than in the small, constituting, as it does, the greater part of the arterial wall. The muscular fibres, which are of the unstriped variety (Fig. 109) are -arranged for the most part transversely to the long axis of the artery •(Fig. 107, m); while the elastic element, taking also a transverse direc- tion, is disposed in the form of closely interwoven and branching fibres, which intersect in all parts the layers of muscular fibre. In arteries of FIG. 109. FIG. 110. FIG. 109.— Muscular fibre-cells from human arteries, magnified 350 diameters. (Kolliker.) a. Nucleus, b. A fibre-cell treated with acetic acid. FIG. 110.— Transverse section of aorta through internal and about half the middle coat. a. Lin- ing eudothelium with the nuclei of the cells only shown. 6. Subepithelial layer of connective tissue. c, d. Elastic tunica intima proper, with fibrils running circularly or longitudinally. e,f. Middle coat. consisting of elastic fibres arranged longitudinally, with muscle-fibres cut obliquely, or longitudinally. (Klein.) various size there is a difference in the proportion of the muscular and elastic element, elastic tissue preponderating in the largest arteries, while this condition is reversed in those of medium and small size. The internal coat is formed by layers of elastic tissue, consisting in part of coarse longitudinal branching fibres, and in part of a very thin and brittle membrane which possesses little elasticity, and is thrown into folds or wrinkles when the artery contracts. This latter membrane, the striated or fenestrated coat of Henle (Fig. 108), is peculiar in its ten- dency to curl up, when peeled off from the artery, and in the perforated CIRCULATION OF THE BLOOD. 131 mid streaked appearance which it presents under the microscope. Its inner surface is lined with a delicate layer of endotfcelium, composed of elongated cells (Fig. 112, a), which make it smooth and polished, and furnish a nearly impermeable surface, along which the blood may flow with the smallest possible amount of resistance from friction. Immediately external to the endothelial lining of the artery is fine connective tissue, sub-endothelial layer, with branched corpuscles. Thus the internal coat consists of three parts, (a) an endothelial lining, (b) the sub-endothelial layer, and (c) elastic layers. Vasa Vasorum. — The walls of the arteries, with the possible excep- tion of the endothelial lining and the layers of the internal coat immedi- ately outside it, are not nourished by the blood which they convey, but are, like other parts of the body, supplied with little arteries, ending in FIG. 111. FIG. 111.— Transverse section of small artery from soft palate, e, endothelial lining, the nuclei of the cells are shown; i, elastic tissue of the intima, which is a good deal folded; c. m. circular mus- . showing the Artery. The endothelial cells are long and narrow ; the trans- vtM-st! markings indicate the muscular cout. t. a. Tunica adventitia. v. Vein, showing the shorter .and wider endothelial cells with which it is lined, c, c. Two capillaries entering the vein. (Schofield.) capillaries and veins, which, branching throughout the external coat, extend for some distance into the middle, but do not reach the internal coat. These nutrient vessels are called vasa vasorum. Lymphatics of Arteries and Veins.— Lymphatic spaces are pres- ent in the coats of both arteries and veins; but in the tunica adventitia or external coat of large vessels they form a distinct plexus of more or less tubular vessels. In smaller vessels they appear as sinous spaces lined by endothelium. Sometimes, as in the arteries of the omentum, mesentery, and membranes of the brain, in the pulmonary, hepatic, and splenic arteries, the spaces are continuous with vessels which distinctly ensheath 132 HAND-BOOK OF PHYSIOLOGY. ihem—perivascular lymphatic sheaths (Fig. 121). Lymph channels are said to be present siso in the tunica media. Nervi Vasorum. — Most of the arteries are surrounded by a plexus of sympathetic nerves, which twine around the vessel very much like ivy round a tree: and ganglia are found at frequent intervals. The smallest f ' Iff FIG. 113.— Blood-vessels from mesocolon of rabbit, a. Artery, with two branches, showing tr. n. nuclei of transverse muscular fibres ; I. n. nuclei of endothelial lining; t. a. tunica advent! tia. v. Vein. Here the transverse nuclei are more oval than those of the artery. The vein receives a small branch at the lower end of the drawing: it is distinguished from the artery among other things by its straighter course and larger calibre, c. Capillary, showing nuclei of endothelial cells. X 300. (Schofield.) arteries and capillaries are also surrounded by a very delicate network of similar nerve-fibres, many of which appear to end in the nuclei of the transverse muscular fibres (Fig. 122). It is through these plexuses that the calibre of the vessels is regulated by the nervous system (p. 152). THE CAPILLARIES. Distribution. — In all vascular textures, except some parts of the corpora cavernosa of the penis, and of the uterine placenta, and of the spleen, the transmission of the blood from the minute branches of the arteries to the minute veins is effected through a network of microscopic vessels, called capillaries. These may be seen in all minutely injected preparations; and during life, in any transparent vascular parts, — such as the web of the frog's foot, the tail or external branchiae of the tadpole, or the wing of the bat. The branches of the minute arteries form repeated anastomoses with ( IliCTLATION OF THE BLOOD. 133 other, and give off the capillaries which, by their anastomoses, com- pose a continuous and uniform network, from which the venous radicles take their rise (Fig. 114). The point at which the arteries terminate and the minute veins commence, cannot be exactly defined, for the transition is gradual; but the capillary network has, neverthe- less, this peculiarity, that the small vessels which compose it maintain the same diameter throughout: they do not diminish in diameter in one direction, like arteries and veins; and the meshes of the net- work that they compose are more uniform in shape and size than those formed by the anastomoses of the minute arteries and veins. Structure. — This is much more simple than that of the arteries or veins. Their walls are com- posed of a single layer of elongated or radiate, flat- tened and nucleated cells, so joined and dovetailed together as to form a continuous transparent mem- brane (Fig. 115). Outside these cells, in the larger capillaries, there is a structureless, or very finely fibrillated membrane, on the inner surface of which they are laid down. In some cases this external membrane is nu- cleated, and may then be regarded as a miniature representative of the tunica adventitia of arteries. Here and there, at the junction of two or more of the delicate endo- thelial cells which compose the capillary wall, pseudo-stomafa may be seen FIG. 114.— Blood-vessels of an intestinal villus, repre- senting the arrangement of capillaries between the ulti- mate venous and arterial branches ; a, a, the arteries ; 6, the vein. FIG. 115.— Capillary blood-vessels from the omentum of rabbit, showing the nucleated endothe- Lal membrane of which they are composed. (Klein and Noble Smith.) resembling those in serous membranes (p. 296). The endothelial cells are often continuous at various points with processes of adjacent connective- tissue corpuscles. 134 1LAKD-BOOK OF PHYSIOLOGY. Capillaries are surrounded by a delicate nerve-plexus resembling, in miniature, that of the larger blood-vessels. The diameter of the capillary vessels varies somewhat in the different textures of the body, the most common size being about -s-oVoth °f an inch. Among the smallest may be mentioned those of the brain, and of the follicles of the mucous membrane of the intestines ; among the largest, those of the skin, and especially those of the medulla of bones. The size of capillaries varies necessarily in different animals in relation to the size of their blood corpuscles: thus, in the Proteus, the capillary circulation can just be discerned with the naked eye. The/orm of the capillary network presents considerable variety in the different textures of the body: the varieties consisting principally of modi- fications of two chief kinds of mesh, the rounded and the elongated. That FIG. 116. FIG. 117. FIG. 116.— Network of capillary vessels of the air-cells of the horse's lung magnified, a, a, cap- illaries proceeding from &, ft, terminal branches of the pulmonary artery. (Frey.) FIG. 117.— Injected capillary vessels of muscle seen with a low magnifying power. (Sharpey.) kind of which the meshes or interspaces have a roundish form is the most common, and prevails in those parts in which the capillary network is most dense, such as the lungs (Fig. 116), most glands, and mucous mem- branes, and the cutis. The meshes of this kind of network are not quite circular but more or less angular, sometimes presenting a nearly regular quadrangular or polygonal form, but being more frequently irregular. The capillary network with elongated meshes (Fig. 117) is observed in parts in which the vessels are arranged among bundles of fine tubes or fibres, as in muscles and nerves. In such parts, the meshes usually have the form of a parallelogram, the short sides of which may be from three to eight or ten times less than the long ones; the long sides always corre- sponding to the axis of the fibre or tube, by which it is placed. The ap- pearance of both the rounded and elongated meshes is much varied CIRCULATION OF THE BLOOD. 135 according as the vessels composing them have a straight or tortuous form. Sometimes the capillaries have a looped arrangement, a single capillary projecting from the common network into some prominent organ, and returning after forming one or more loops, as in the papillae of the tongue and skin. The number of the capillaries and the size of the meshes in different parts determine in general the degree of vascularity of those parts. The parts in which the network of capillaries is closest, that is, in which the meshes or interspaces are the smallest, are the lungs and the choroid membrane of the eye. In the iris and ciliary body, the interspaces are somewhat wider, yet very small. In the human liver the interspaces are of the same size or even smaller than the capillary vessels themselves. In the human lung they are smaller than the vessels; in the human kidney, and in the kidney of the dog, the diameter of the injected capil- laries, compared with that of the interspaces, is in the proportion of one to four, or of one to three. The brain receives a very large quantity of blood; but the capillaries in which the blood is distributed through its substance are very minute, and less numerous than in some otherj^arts. Their diameter, according to E. H. Weber, compared with the long diam- eter of the meshes, being in the proportion of one to eight or ten ; com- pared with the transverse diameter, in the proportion of one to four or six. In the mucous membranes — for example in the conjunctiva and in the cutis vera, the capillary vessels are much larger than in the brain, and the interspaces narrower, — namely, not more than three or four times wider than the vessels. In the periosteum the meshes are much larger. In the external coat of arteries, the width of the meshes is ten times that of the vessels (Henle). It may be held as a general rule, that the more active the functions of an organ are, the more vascular it is. Hence the narrowness of the inter- spaces in all glandular organs, in mucous membranes, and in growing parts; their much greater width in bones, ligaments, and other very tough and comparatively inactive tissues; and the usually complete absence of vessels in cartilage, and such parts as those in which, prob- ably, very little vital change occurs after they are once formed. THE VEINS. Distribution. — The venous system begins in small vessels which are slightly larger than the capillaries from which they spring. These vessels are gathered up into larger and larger trunks until they terminate (as regards the systemic circulation) in the two venae cavae and the coronary veins, which enter the right auricle, and (as regards the pulmonary circu- lation) in four pulmonary veins, which enter the left auricle. The capac- ity of the veins diminishes as they approach the heart; but, as a rule, 136 HAND-BOOK OF PHYSIOLOGY. the capacity of the veins exceeds by several times (twice or three times) that of their corresponding arteries. The pulmonary veins, however, are an exception to this rule, as they do not exceed in capacity the pulmonary arteries. The veins are found after death as a rule to be more or less collapsed, and often to contain blood. The veins are usually dis- tributed in a superficial and a deep set which communicate frequently in their course. Structure. — In structure the coats of veins bear a general resem- blance to those of arteries (Fig. 118). Thus, they possess an outer, TIG. 118.— Transverse section through a small artery and vein of the mucous membrane of a Child's epiglottis: the contrast between the thick- walled artery and the thin- walled vein is well shown. A. Artery, the letter is placed in the lumen of the vessel, e. Endothelial cells with nuclei clearly vis- ible: these cells appear very thick from the contracted state of the vessel. Outside it a double wavy line marks the elastic tunica intima. ra. Tunica media forming the chief part of arterial wall and consisting of unstriped muscular fibres circularly arranged: their nuclei are well seen, a. Part of the tunica adventitia showing bundles of connective-tissue fibres in section, with the circular nuclei of the connective-tissue corpuscles. This coat gradually merges into the surrounding connective- tissue. V. In the lumen of the vein. The other letters indicate the same as in the artery. The mus- cular coat of the vein (m) is seen to be much thinner than that of the artery. X 350. (Klein and Noble Smith.) middle, and internal coat. The outer coat is constructed of areolar tissue like that of the arteries, but is thicker. In some veins it contains mus- cular fibre-cells, which are arranged longitudinally. The middle coat is considerably thinner than that of the arteries; and, although it contains circular unstriped muscular fibres or fibre-cells, these are mingled with a larger proportion of yellow elastic and white fibrous tissue. In the large veins, near the heart, namely the vencs caves and pulmonary veins, the middle coal; is replaced, for some distance from the heart, by circularly arranged striped muscular fibres, continuous with those of the auricles. CIRCULATION OF THE BLOOD. 137 The internal coat of veins is less brittle than the corresponding coat of an artery, but in other respects resembles it closely. Valves.— The chief influence which the veins have in the circulation, is effected with the help of the valves, which are placed in all veins sub- ject to local pressure from the muscles between or near which they run. The general construction of these valves is similar to that of the semi- lunar valves of the aorta and pulmonary artery, already described; but their free margins are turned in the opposite direction, i.e., toward the heart, so as to stop any movement of blood backward in the veins. They are commonly placed in pairs, at various distances in different veins, but almost uniformly in each (Fig. 119). In the smaller veins, single valves are often met with; and three or four are sometimes placed together, or near one another, in the largest veins, such as the subclavian, and at their junction with the jugular veins. The valves are semilunar; the FIG. 119. — 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, snowing the apposition of the edges of the valves in their closed state, c, portion of a distended vein, exhibiting a swelling in the situation of a pair of valves. unattached edge being in some examples concave, in others straight. They are composed of inextensile fibrous tissue, and are covered with endothelium like that lining the veins. During the period of their in- action, when the venous blood is flowing in its proper direction, they lie by the sides of the veins; but when in action, they close together like the valves of the arteries, and offer a complete barrier to any backward movement of the blood (Figs. 119 and 120). Their situation in the superficial veins of the forearm is readily discovered by pressing along its surface, in a direction opposite to the venous current, i.e., from the elbow toward the wrist; when little swellings (Fig. 119, c) appear in the position of each pair of valves. These swellings at once disappear when the pressure is relaxed. Valves are not equally numerous in all veins, and in many they are absent altogether. They are most numerous in the veins of the extremi- ties, and more so in those of the leg than the arm. They are commonly absent in veins of less than a line in diameter, and, as a general rule, 138 HAND-BOOK OF PHYSIOLOGY. there are few or none in those which are not subject to muscular pressure. Among those veins which have no valves may be mentioned the superior and inferior vena cava, the trunk and branches of the portal vein, 'the FIG. 120.— A, vein with valves open. B, vein with valves closed: stream of blood passing off by lateral channel. (Dalton.) hepatic and renal veins, and the pulmonary veins; those in the interior of the cranium and vertebral column, those of the bones, and the trunk and branches of the umbilical vein are also destitute of valves. CIRCULATION IN THE ARTERIES. Functions of the External Coat of Arteries. — The external coat forms a strong and tough investment, which, though capable of exten- sion, appears principally designed to strengthen the arteries and to guard against their excessive distension by the force of the heart's action. It is this coat which alone prevents the complete severance of an artery when a ligature is tightly applied; the internal and middle coats being divided. In it, too, the little vasa vasorum (p. 131) find a suitable tissue in which to subdivide for the supply of the arterial coats. Functions of the Elastic Tissue in Arteries.— The purpose of the elastic tissue, which enters so largely into the formation of all the coats of the arteries, is, (a) to guard the arteries from the suddenly exerted pressure to which they are subjected at each contraction of the ventricles. In every such contraction, the contents of the ventricles are forced into the arteries more quickly than they can be discharged into and through the capillaries. The blood therefore, being, for an instant, resisted in its onward course, a part of the force with which it was im- CIRCULATION OF THE BLOOD. 139 pelled is directed against the sides of the arteries; under this force their elastic walls dilate, stretching enough to receive the blood, and as they stretch, becoming more tense and more resisting. Thus, by yielding, they break the shock of the force impelling the blood. On the subsidence of the pressure, when the ventricles cease contracting, the arte- ries aiv able, by the same elasticity, to resume their former calibre; (b) It equalizes the cur- rent of the blood by maintaining pressure on it in the arteries during the periods at which the ventricles are at rest or dilating. If the arteries had -been rigid tubes, the blood, in- stead of flowing, as it does,, in a constant stream, would have been propelled through the arterial system in a series of jerks corre- sponding to the ventricular contractions, writh intervals of almost complete rest during the inaction of the ventricles. But in the actual condition of the arteries, the force of the suc- cessive contractions of the ventricles is ex- pended partly in the direct propulsion of the blood, and partly in the dilatation of the elastic arteries; and in the intervals between the con- tractions of the ventricles, the force of the re- coil is employed in continuing the same direct propulsion. Of course, the pressure they ex- ercise is equally diffused in every direction, and the blood tends to move backward as well as onward, but all movement backward is pre- vented by the closure of the semilunar arterial valves (p. 114), which takes place at the very commencement of the recoil of the arterial walls. By this exercise of the elasticity of the arteries, all the force of the ventricles is made advantageous to the circulation; for that part of their force which is expended in dilating the arteries, is restored in full when they recoil. There is thus no loss of force; but neither is there any gain, for the elastic walls of the artery cannot originate any force for the propul- sion of the blood — they only restore that which they received from the ventricles. The force with which the arteries are dilated every time the ventricles contract, might be said to be received by them in store, to be all given out again in the next succeeding period of dilatation of the ventricles. It is by this equalizing influence of the successive branches of every artery that, at length, the intermittent accelerations produced in the arterial current by the action of the heart, cease to be observable, and the jetting stream is converted into the continuous and equable movement of the Fi». 121.— Surface view of an artery from the mesentery of a frog, ensheathed in a perivascular lymphatic vessel, a. The artery, with its circular muscular coat (media) indicated by broad trans- verse markings, with an indication of the adventitia outside. I. Lym- phatic vessel ; its wall is a simple endothelial membrane. (Klein and Noble Smith.) 140 HAND-BOOK OF PHYSIOLOGY. blood which we see in the capillaries and veins. In the production of a continuous stream of blood in the smaller arteries and capillaries, the resistance which is offered to the blood-stream in these vessels (p. 158), is a necessary agent. Were there no greater obstacle to the escape of blood from the larger arteries than exists to its entrance into them from the heart, the stream would be intermittent, notwithstanding the elas- ticity of the walls of the arteries. (c.) By means of the elastic tissue in their walls (and of the muscular tissue also), the arteries are enabled to dilate and contract readily in cor- respondence with any temporary increase or diminution of the total quantity of blood in the body; and within a certain range of diminution FIG. 122. FIG. 123. FIG. 122.— Ramification of nerves and termination in the muscular coat of a small artery of the frog. (Arnold.) FIG. 123.— Transverse section through a large branch of the inferior mesenteric artery of a pig. e, enclothelial membrane; i, tunica elastica interna, no subendothelial layer is seen; m, muscular tu- nica media, containing only a few wavy elastic fibres; ee, tunica elastica externa, dividing the media from the connective tissue adventitia, a. (Klein and Noble Smith.) x 350. of the quantity, still to exercise due pressure on their contents; (d.) The elastic tissue assists in restoring the normal state after diminution of its calibre, whether this has been caused by a contraction of the muscular coat, or the temporary application of a compressing force from without. This action is well shown in arteries , to a writing-needle and registering apparatus. FIG. 134. — Diagram of mercu- rial manometer, a. Floatiag rod and pen. b. Tube, which commu- nicates with a bottle containing an alkaline solution, c'. Elastic tube and cannula, the latter being intended for insertion in an artery. FIG. 135.— Normal tracing of arterial pressure in the rabbit obtained with the mercurial kymo- graph. The smaller undulations correspond with the heart beats; the larger curves with the respir- atory movements. (Burdon-Sanderson.) Fig. 137 exhibits an ordinary arterial pulse-tracing, as obtained by the spring-kymograph . From observations which have been made by means of the mercurial manometer, it has been found that the pressure of blood in the carotid of a rabbit is capable of supporting a column of 2 to 3^ inches (50 to 90 CIRCULATION OF THE BLOOD. 151 mm.) of mercury, in the dog 4 to 7 inches (100 to 175 mm.), in the horse 5 to 8 inches (150 to 200 mm.), and in man about the same. To measure the absolute amount of this pressure in any artery, it is necessary merely to multiply the area of its transverse section by the height of the column of mercury which is already known to be supported by the blood- pressure in any part of the arterial system. The weight of a column of mercury thus found will represent the pressure of the blood. Calculated in this way, the blood-pressure in the human aorta is FIG. 136.— A form of Pick's Spring Kymograph, a, tube to be connected with artery: c, hollow spring, the movement of which moves 6, the writing lever; e, screw to regulate height or 6; d, out- side protective spring; gr, screw to fix on the upright of the support. equal to 4 Ib. 4 oz. avoirdupois; that in the aorta of the horse being 11 Ib. 9 oz.; and that in the radial artery at the human wrist only 4 drs. Supposing the muscular power of the right ventricle to be only one- half that of the left, the blood-pressure in the pulmonary artery will be only 2 Ib. 2 oz. avoirdupois. The amounts above stated represent the arterial tension at the time of the ventricular contraction. The blood-pressure is greatest in the left ventricle and at the begin- ning of the aorta, and decreases toward the capillaries. It is greatest in the arteries at the period of the ventricular systole, and is least in the auricles, during diastole, when the pressure there and in the great veins becomes, as we have seen, negative. The mean arterial pressure equals the average of the pressures in all the arteries. The pressure in the veins is never more than one-tenth of the pressure in the corresponding 152 HAND-BOOK OF PHYSIOLOGY. arteries and is greatest at the time of auricular systole. There is no peri- odic variation in venous pressure, as there is in the arterial, except in the great veins. FIG. 137.— Normal arterial tracing obtained with Tick's kymograph in the dog. (Burdon- Sanderson.) Variations of Blood Pressure. — Many circumstances cause con- siderable variations in the amount of the blood-pressure. The following are the chief: — (1) Changes in the beat of the Heart; (2) Changes in the Arteries and Capillaries; (3) 'Changes- due to Nerve Action; (4) Changes in the Blood; (5) Respiratory Changes. 1. Changes in the Beat of the Heart. — The systole and diastole of the muscular chambers. The arterial tension increases during systole and diminishes during diastole. The greater the frequency, moreover, of the heart's contractions, the greater is the blood-pressure, cceteris paribus; although this effect is not constant, as it may be compensated for by the delivery into the arteries at each beat of a comparatively small quantity of blood. The greater the quantity of blood expelled from the heart at each contraction the greater is the blood-pressure. The quantity and quality of the blood nourishing the heart's substance through the coronary arteries must exercise also a very considerable influence upon its action, and therefore upon the blood-pressure. 2. Changes in the Arteries and Capillaries. — Variations in the degree of contraction of the smaller arteries modify the blood -pressure by favor- ing or impeding the accumulation of blood in the arterial system which follows every contraction of the heart; the contraction of the arterial walls increasing the blood-pressure, while their relaxation lowers it. 3. Changes due to Nerve Action. — As with the heart, so with the blood-vessels, the action of the nervous system is very important in rela- tion to the blood-pressure; regulating, as it does, not only the force, fre- quency, and length of the heart's systole, but also the condition of the arteries, both through the central and peripheral vaso- motor centres. As this subject has not yet been fully considered it will be as well to treat of it here. It is upon the muscular coat of the arteries that the nervous system exercises its influence; the elastic element possessing, as must be obvious, rather physical than vital properties. The muscular tissue in the walls of the vessels increases relatively to the other coats as the arteries grow smaller, so that in the smallest arteries it is developed out of all propor- CIRCULATION OF THE BLOOD. 153 tion to the other elements; in fact, in passing from capillary vessels, made up as we have seen of endothelial cells with a ground substance, the first change which occurs as the vessels become larger (on the side of the arteries) is the appearance of muscular fibres. Thus the nervous system is more powerful in regulating the calibre of the smaller than of the larger arteries. It has been shown that if the cervical sympathetic nerve be divided in a rabbit, the blood-vessels of the corresponding side become dilated. The effect is best seen in the ear, which if held up to the light is seen to become redder, and the arteries to become larger. The whole ear is dis- tinctly warmer than the opposite one. This effect is produced by remov- ing the arteries from the influence of the central nervous system, which FIG. 138.— Plethysmograph. By means of this apparatus, the alteration in volume of the arm, E, which is enclosed in a glass tube, A, filled with fluid, the opening through which it passes being firmly closed by a thick gutta percha band, F, is communicated to the lever, D, and registered by a recording apparatus. The fluid in A communicates with that in B, the upper limit of which is above that in A. The chief alterations in volume are due to alteration in the blood contained in the arm. When the volume is increased, fluid passes out of the glass cylinder, and the lever, D, also is raised, and when a decrease takes place the fluid returns again from B to A. It will therefore be evident that the apparatus is capable of recording alterations of blood-pressure in the arm. Apparatus founded upon the same principle have been used for recording alterations in the volume of the spleen and kidney. influence usually passes down the divided nerve; for if the peripheral end of the divided nerve (i.e., that farthest from the brain) be stimulated, the arteries which were before dilated return to their natural size, and the parts regain their primitive condition. And, besides this, if the stimulus which is applied be too strong or too long continued, the point of normal constriction is passed, and the vessels become much more con- tracted than normal. The natural condition, which is somewhere about midway between extreme contraction and extreme dilatation, is called the natural tone of an artery, and if this be not maintained, the vessel is said to have lost tone, or if it be exaggerated, the tone is said to be too great. The influence of the nervous system upon the vessels consists in maintain- ing a natural tone. The effects described as having been produced by section of the cervical sympathetic and by subsequent stimulation are not peculiar to that nerve, as it has been found that for every part of the 154 HAND-BOOK OF PHYSIOLOGY. body there exists a nerve the division of which produces the same effects, viz., dilatation of the arteries; such may be cited as the case with the sciatic, the splanchnic nerves, and the nerves of the brachial plexus: when divided, dilatation of the blood-vessels in the parts supplied by them taking place. It appears, therefore, that nerves exist which have a distinct control over the vascular supply of a part. These nerves are called vaso-motor; or, since they seem to run now in cerebro-spinal nerves, now in the sympathetic, we speak of those nerves as containing vaso-motor fibres, in addition to the fibres which have other functions. Vaso-motor centres. — Experiments by Ludwig and others show that the vaso-motor fibres come primarily from grey matter (vaso-motor centre) in the interior of the medulla oblongata, between the calamus scriptorius and the corpora quadrigemina. Thence the vaso-motor fibres pass down in the interior of the spinal cord, and issuing with the anterior roots of the spinal nerves, traverse the various ganglia on the pras-vertebral cord of the sympathetic, and, accompanied by branches from these ganglia, pass to their destination. Secondary or subordinate centres exist in the spinal cord, and local centres in various regions of the body, and through these, directly under ordinary circumstances, vaso-motor changes are also effected. The influence exerted by the chief vaso-motor centre is called into play in several ways, but chiefly by afferent (sensory) stimuli, and it may be exerted in two ways, either to increase its usual action which main- tains a medium tone of the arteries or to diminish such action. This afferent influence upon the centre may be extremely well shown by the action of a nerve the existence of which was demonstrated by Cyon and Ludwig, and which is called the depressor, because of its characteristic influence on the blood-pressure. Depressor Nerve. — This small nerve arises, in the rabbit, from the superior laryngeal branch, or from this and the trunk of the pneumogas- tric nerve, and after communicating with filaments of the inferior cervical ganglion proceeds to the heart. If during an observation of the blood-pressure of a rabbit this nerve be divided, and the central end (i.e., that nearest the brain) be stimu- lated, a remarkable fall of blood-pressure ensues (Fig. 139). The cause of the fall of blood-pressure is found to proceed from the dilatation of the vascular district supplied by the splanchnic nerves, in consequence of which it holds a much larger quantity of blood than usual, and this very greatly diminishes the blood in the vessels elsewhere, and so materially affects the blood-pressure. This effect of the depressor nerve is presumed to prove that the nerve is a means of conveying to the vaso- motor centre indications of such conditions of the heart as require a diminution of the tension in the blood-vessels; as, for example, when the CIRCULATION OF THE BLOOD. 155 heart cannot, with sufficient ease, propel blood into the already too full or too tense arteries. The action of the depressor nerve illustrates the effect of afferent im- pulses in causing an inhibition of the vaso-motor centre as regards its action upon certain arteries. There exist other nerves, however, the stimulation of the central end of which causes a reverse action of the centre, or, in other words, increases its tonic influence, and by causing FIG. 139.— Tracing showing the effect on blood pressure of stimulating the central end of the De- pressor nerve in the rabbit. To be read from right to left. T, indicates the rate at which the re- cording-surface was traveling, the intervals correspond to seconds; C, the moment of entrance of current; O, moment at which it was shut off. The effect is some time in developing and lasts after the current has been taken off. The larger undulations are the respiratory nerves; the pulse oscilla- tions are very small. (M. Foster.) considerable constriction of certain arterioles, either locally or generally, increases the blood-pressure. Moreover, the effect of stimulating an afferent nerve may be to dilate or constrict the arteries either generally or in the part supplied by the afferent nerve; and it is said that stimula- tion of an afferent nerve may produce a kind of paradoxical effect, causing general vascular constriction and so general increase of blood-pressure but at the same time local dilatation. This must evidently have an immense influence in increasing the flow of blood through a part. Not only may the vaso-motor centre be reflexly affected, but it may also be affected by impulses proceeding to it from the cerebrum, as in the case of blushing from mind disturbance, or of pallor from sudden fear. It will be shown, too, in the chapter on Eespiration that the circulation of deoxygenated blood may directly stimulate the centre itself. Local Tonic Centres. — Although the tone of the arteries is influ- enced by the centres in the cerebro-spinal axis, certain experiments point out that this is not the only way in wrhich it may be affected. Thus the dilatation which occurs after section of the cervical sympathetic in the first experiment cited above, only remains for a short time, and is soon followed — although a portion of the nerve may have been removed entirely — by the vessels regaining their ordinary calibre; and afterward 156 HAND-BOOK OF PHYSIOLOGY. local stimulation, e.g., the application of heat or cold, will cause dilatation or constriction. From this it is probable that there exists a local mechanism distinct for each vascular area, and that the effect produced by the central nervous system acts through it much in the same way as the cardio-inhibitory centre in the medulla acts upon the heart through the ganglia contained within its muscular substance. Central impulses may inhibit or increase the action of these local centres, which may be considered to be sufficient under ordinary circum- stances to maintain the local tone of the vessels. The observations upon the functions of the vaso-motor nerves appear to divide them into four classes: (1) those on division of which dilatation occurs for some time, and which on stimulation of their peripheral end produce constriction; (2) those on division of which momentary dilatation followed by constric- tion occurs, with dilatation on stimulation; (3) those on division of which dilatation is caused, which lasts for a limited time, with constriction if stimulated at once, but dilatation if some time is allowed to elapse before the stimulation is applied; (4) a class, division of which produces no effect but which, on stimulation, cause according to their function either dilatation or constriction. A good example of this fourth class is afforded by the nerves supplying the submaxillary gland, viz., the chorda tympani and the sympathetic. When either of these nerves is simply divided, no change takes place in the vessels of the gland; but on stimulating the chorda tympani the vessels dilate, and, on the other hand, when the sympathetic is stimulated the vessels contract. The nerves acting like the chorda tympani in this case are called vaso-dilators, and those like the sympathetic vaso-constrictors. The third class, which produce at one time dilatation, at another time constriction, are believed to contain both kinds of vaso-motor nerve-fibres, or to act as dilators or contractors according to the condition of the local apparatus. It is probable that these nerves act by inhibiting or augmenting the action of the local nerv- ous mechanism already referred to; and as they are in connection with the central nervous system, it is through this arrangement that that sys- tem is capable of influencing or of maintaining the normal local tone. It may also be supposed that the local nerve-centres themselves may be directly affected by the condition of blood nourishing them. The following table may serve as a summary of the effect of the nerv- ous system upon the arteries and so upon the blood-pressure: — A. An increase of the blood-pressure may be produced:— (1.) By stimulation of the vaso-motor centre in medulla, either a. Directly, as by carbonated or deoxygenated blood. /3. Indirectly, by impressions descending from the cerebrum, e.g., in sudden pallor. y. Reflexly, by stimulation of sensory nerves anywhere. CIRCULATION" OF THE BLOOD. 157 (2.) By stimulation of the centres in spinal cord. Possibly directly or indirectly, certainly reflexly. (3.) By stimulation of the local centres for each vascular area, by the vaso-constrictor nerves, or directly by means of altered blood. B. A decrease of the blood pressure may be produced:— (1.) By stimulation of the vaso-motor centre in medulla, either (a.} Directly, as by oxygenated or aerated blood. (p. ) Indirectly, by impressions descending from the cerebrum — e.g., in blushing. (y.) Reflexly, by stimulation of the depressor nerve, and consequent dilatation of vessels of splanchnic area, and possibly by stimulation of other sensory nerves, the sen- sory impulse being interpreted as an indication for diminished blood-pressure. (2.) By stimulation of the centres in spinal cord. Possibly directly, indirectly, or reflexly. (3.) By stimulation of local centres for each vascular area by the vaso-dilator nerve, or directly by means of altered blood. 4. Changes in the blood. — a. As regards quantity. At first sight it would appear that one of the easiest ways to diminish the blood-pressure would be to remove blood from the vessels by bleeding; it has been found by experiment, however, that although the blood-pressure sinks whilst large abstractions of blood are taking place, as soon as the bleeding ceases it rises rapidly, and speedily becomes normal; that is to say, unless so large an amount of blood has been taken as to be positively dangerous to life, abstraction of blood has little effect upon the blood-pressure. The rapid return to the normal pressure is due not so much to the withdrawal of lymph and other fluids from the body into the blood, as was formerly supposed, as to the regulation of the peripheral resistance by the vaso- motor nerves; in other words, the small arteries contract, and in so doing maintain pressure on the blood and favor its accumulation in the arterial system. This is due to the stimulation of the vaso-motor centre from diminution of the supply of blood, and therefore of oxygen. The failure of the blood-pressure to return to normal in the too great abstraction must be taken to indicate a condition of exhaustion of the centre, and consequently of want of regulation of the peripheral resistance. In the same way it might be thought that injection of blood into the already pretty full vessels would be at once followed by rise in the blood-pressure, and this is indeed the case up to a certain point — the pressure does rise, but there is a limit to the rise. Until the amount of blood injected equals about 2 to 3 per cent, of the body weight the pressure continues to rise gradually; but if the amount exceed this proportion, the rise does not continue. In this case therefore, as in the opposite when blood is ab- 158 HAND-BOOK OF" PHYSIOLOGY. stracted, the vaso motor apparatus must counteract the great increase of pressure by dilating the small vessels, and so diminishing the peripheral resistance, for after each rise there is a partial fall of pressure; and after the limit is reached the whole of the injected blood displaces, as it were, an equal quantity which passes into the small veins, and remains within them. It should be remembered that the veins are capable of holding the whole of the blood of the body. The amount of blood supplied to the heart both to its substance and to its chambers, has a marked effect upon the blood-pressure. 1). As regards quality. The quality of the blood supplied to the heart has a distinct effect upon its contraction, as too watery or too little oxy- genated blood must interfere with its action. Thus it appears that blood containing certain substances affects the peripheral resistance by acting upon the muscular fibres of the arterioles themselves or upon the local centres, and so altering directly, as it were, the calibre of the vessels. 5. Respiratory changes affecting the blood-pressure will be considered in the next Chapter. CIRCULATION IN THE CAPILLARIES. When seen in any transparent part of a living adult animal by means of the microscope (Fig. 140) the blood flows with a constant equable mo- tion; the red blood-corpuscles moving along, mostly in single file, and bending in various ways to accommodate themselves to the tortuous course of the capillary, but instantly recovering their normal outline on reaching a wider vessel. It is in the capillaries that the chief resist- ance is offered to the progress of the blood; for in them the friction of the blood is greatly increased by the enormous multiplication of the surface with which it is brought in con- tact. At the circumference of the stream in the larger capillaries, but chiefly in the small arte- FIG. 140.— capillaries (o in the ries and veins, in contact with the walls of web of the frog s foot connecting a small artery (A) with a small vein v the vessel, and adhering to them, there is (after Allen Thomson). / . °. a layer of liquor sangumis which appears to be motionless. The existence of this still layer, as it is termed, is inferred both from the general fact that such an one exists in all fine tubes traversed by fluid, and from what can be seen in watching the move- ments of the blood-corpuscles. The red corpuscles occupy the middle of the stream and move with comparative rapidity; the colorless lymph-cor- puscles run much more slowly by the walls of the vessel; while next to the wall there is often a transparent space in which the fluid appears to CIRCULATION OF THE BLOOD. 159 be at rest; for if any of tne corpuscles happen to be forced within it, they move more slowly than before, rolling lazily along the side of the vessel, and often adhering to its wall. Part of this slow movement of the pale corpuscles and their occasional stoppage may be due to their having a natural tendency to adhere to the walls of the vessels. Sometimes, in- deed, when the motion of the blood is not strong, many of the white cor- puscles collect in a capillary vessel, and for a time entirely prevent the passage of the red corpuscles. Intermittent flow in the Capillaries. — When the peripheral re- sistance is greatly diminished by the dilatation of the small arteries and capillaries, so much blood passes on from the arteries into the capillaries at each stroke of the heart, that there is not sufficient remaining in the arteries to distend them. 'Thus, the intermittent current of the ventric- ular systole is not converted into a continuous stream by the elasticity of the arteries before the capillaries are reached; and so intermittency of the flow occurs in capillaries and veins and a pulse is produced. The same phenomenon may occur when the arteries become rigid from disease, and when the beat of the heart is so slow or so feeble that the blood at each cardiac systole has time to pass on to the capillaries before the next stroke occurs, the amount of blood sent at each stroke being insufficient to properly distend the elastic arteries. Diapedesis of Blood Corpuscles. — Until with- in the last few years it has been generally supposed that the occurrence of any transudation from the in- terior of the capillaries into the midst of the sur- rounding tissues was confined, in the absence of injury, strictly to the fluid part of the blood; in other words, that the corpuscles could not escape from the circulating stream, unless the wall of the containing blood-vessel were ruptured. It is true that an Eng- lish physiologist, Augustus Waller, affirmed, in 1846, that he had seen blood-corpuscles, both red and white, pass bodily through the wall of the capillary vessel in which they were contained (thus confirming what had been stated a short time previously by Addison) ; and that, as no opening could be seen before their escape, so none could be observed afterward — so rapidly was the part healed. But these observations did not attract much notice until the phenomena of escape of the blood-corpuscles from the capillaries and minute veins, apart from mechanical injury, were re- discovered by Professor Cohnheim in 1867. Cohnheim's experiment demonstrating the passage of the corpuscles through the wall of the blood-vessel, is performed in the following man- Fio. 141.— A large cap- illary from the frog^s mesentery eight hours after irritation had been set up, showing emigra- tion of leucocytes, a, Cells in the act of trav- ersing the capillary 6, some already (Frey.) wall; 160 HAND-BOOK OF PHYSIOLOGY. ner. A frog is urarized, that is to say, paralysis is produced by inject- ing under the skin a minute quantity of the poison called urari; and the abdomen having been opened, a portion of small intestine is drawn out, and its transparent mesentery spread out under a microscope. After a variable time, occupied by dilatation, following contraction of the minute vessels and accompanying quickening of the blood-stream, there ensues a retardation of the current, and blood-corpuscles, both red and white, begin to make their way through the capillaries and small veins. "Simultaneously with the retardation of the blood-stream, the leu- cocytes, instead of loitering here and there at the edge of the axial cur- rent, begin to crowd in numbers against the vascular wall. In this way the vein becomes lined with a continuous pavement of these bodies, which remain almost motionless, notwithstanding that the axial current sweeps by them as continuously as before, though with abated velocity. Now is the moment at which the eye must be fixed on the t outer contour of the vessel, from which, here and there, minute, colorless, button-shaped ele- vations spring, just as if they were produced by budding out of the wall of the vessel itself. The buds increase gradually and slowly in size, until each assumes the form of a hemispherical projection, of width correspond- ing to that of the leucoc}^te. Eventually the hemisphere is converted into a pear-shaped body, the small end of which is still attached to the surface of the vein, while the round part projects freely. Gradually the little mass of protoplasm removes itself further and further away, and, as it does so, begins to shoot out delicate prongs of transparent protoplasm from its surface, in nowise differing in their aspect from the slender thread by which it is still moored to the vessel. Finally the thread is severed and the process is complete." (Burdon Sanderson.) The process of diapedesis of the red corpuscles, which occurs under circumstances of impeded venous circulation, and consequently in- creased blood-pressure, resembles closely the migration of the leuco- cytes, with the exception that they are squeezed through the wall of the vessel, and do not, like them, work their way through by amoeboid movement. Various explanations of these remarkable phenomena have been sug- gested. Some believe that minute openings (stigmata or pseudo stomata) between contiguous endothelial cells (p. 133) provide the means of escape for the blood-corpuscles. But the chief share in the process is to be found in the vital endowments with respect to mobility and contraction of the parts concerned — both of the corpuscles (Bastian) and the capillary wall (Strieker). Burdon-Sanderson remarks, "the capillary is not a dead conduit, but a tube of living protoplasm. There is no difficulty in un- derstanding how the membrane may open to allow the escape of leucocytes, and close again after they have passed out; for it is one of the most strik- ing peculiarities of contractile substance that when two parts of the same CIRCULATION OF THE BLOOD. 161 mass are separated, and again brought into contact, they melt together as if they had not been severed/' Hitherto, the escape of the corpuscles from the interior of the blood- vessels into the surrounding tissues has been studied chiefly in connection with pathology. But it is impossible to say, at present, to what degree the discovery may not influence all present notions regarding the nutrition of the tissues, even in health. Vital Capillary Force. — The circulation through the capillaries must, of necessity, b ^ largely influenced by that which occurs in the vessels on either side of them — in the arteries or the veins; their intermediate posi- tion causing them to feel at once, so to speak, any alteration in the size or rate of the arterhl or venous blood-stream. Thus, the apparent con- traction of the capillaries, on the application of certain irritating sub- stances, and during fear, and their dilatation in blushing, may be referred to the action of the small arteries, rather than to that of the capillaries themselves. But largely as the capillaries are influenced by these, and by the conditions of the parts which surround and support them, their own endowments must not be disregarded. They must be looked upon, not as mere passive channels for the passage of blood, but as possessing endow- ments of their own (vital capillary force), in relation to the circulation. The capillary wall is actively living and contractile; and there is no reason to doubt that, as such, it must have an important influence in connection with the blood-current. Blood-Pressure in the Capillaries.— From observations upon the web of the frog's foot, the tongue and mesentery of the frog, the tails of newts, and small fishes (Roy and Brown), as well as upon the skin of the finger behind the nail (Kries), by careful estimation of the amount of pressure required to empty the vessels of blood under various conditions,, it appears that the blood-pressure is subject to variations in the capillaries, apparently following the variations of that of the arteries; and that up to a certain point, as the extravascular pressure is increased, so does the pulse in the arterioles, capillaries, and venules become more and more evident. The pressure in the first case (web of the frog's foot) has been found to be equal to about 14 to 20 mm. of mercury; in other experiments to be equal to about \ to I- of the ordinary arterial pressure. THE CIKCULATION IN THE VEINS. The blood-current in the veins is maintained by the slight vis a tergo remaining of the contraction of the left ventricle. Very effectual assist- ance, however, to the flow of blood is afforded by the action of the muscles capable of pressing on such veins as have valves. The effect of such muscular pressure may be thus explained. When pressure is applied to any part of a vein, and the current of blood in it is VOL. I.— 11. 162 HAND-BOOK OF PHYSIOLOGY. obstructed, the portion behind the seat of pressure becomes swollen and distended as far back as to the next pair of valves. These, acting like the semiluiiar valves of the heart, and being, like them, inextensible both in themselves and at their margins of attachment, do not follow the vein in its distension, but are drawn out toward the axis of the canal. Then, if the pressure continues on the vein, the compressed blood, tending to move equally in all directions, presses the valves down into contact at their free edges, and they close the vein and prevent regurgitation of the blood. Thus, whatever force is exercised by the pressure of the muscles on the veins, is distributed partly in pressing the blood onward in the proper course of the circulation, and partly in pressing it backward and closing the valves behind (Fig. 128, A and B). The circulation might lose as much as it gains by such compression of the veins, if it were not for the numerous anastomoses by which they communicate, one with another; for through these, the closing up of the venous channel by the backward pressure is prevented from being any serious hindrance to the circulation, since the blood, of which the onward course is arrested by the closed valves, can at once pass through some anastomosing channel, and proceed on its way by another vein. Thus, therefore, the effect of muscular pressure upon veins which have valves, is turned almost entirely to the advantage of the circulation; the pressure of the blood onward is all advantageous, and the pressure of the blood back- ward is prevented from being a hindrance by the closure of the valves and the anastomoses of the veins. The effects of such muscular pressure are well shown by the accelera- tion of the stream of blood when, in venesection, the muscles of the fore- arm are put in action, and by the general acceleration of the circulation during active exercise: and the numerous movements which are continu- ally taking place in the body while awake, though their single effects may be less striking, must be an important auxiliary to the venous circulation. Yet they are not essential; for the venous circulation continues unim- paired in parts at rest, in paralyzed limbs, and in parts in which the veins are not subject to any muscular pressure. Rhythmical Contraction of Veins. — In the web of the bat's wing, the veins are furnished with valves, and possess the remarkable property of rhythmical contraction and dilatation, whereby the current of blood within them is distinctly accelerated. ( Wharton Jones. ) The contraction occurs, on an average, about ten times in a minute; the existence of valves pre- venting regurgitation, the entire effect of the contractions was auxiliary to the onward current of blood. Analogous phenomena have been fre- qu3iitly observed in other animals. Blood-Pressure in the Veins. — The blood-pressure gradually falls as we proceed from the heart to the arteries, from these to the capillaries, .and thence along the veins to the right auricle. The blood-pressure in CIRCULATION OF THE BLOOD. 163 the veins is nowhere very great, but is greatest in the small veins, while in the large veins toward the heart the pressure becomes negative, or, in other words, when a vein is put in connection with a mercurial manometer the mercury* will fall in the area furthest away from the vein and will rise in the area nearest the vein, having a tendency to suck in rather than to push forward. In the veins in the neck this tendency to suck in air is especially marked, and is the cause of death in some operations in that region. The amount of pressure in the brachial vein is said to support 9 mm. of mercury, whereas the pressure in the veins of the neck is about equal to a negative pressure of — 3 to —8 mm. The variations of venous pressure during systole and diastole of the heart are very slight, and a distinct pulse is seldom seen in veins except under very extraordinary circumstances. The formidable obstacle to the upward current of the blood in the Teins of the trunk and extremities in the erect posture supposed to be pre- sented by the gravitation of the blood, has no real existence, since the pressure exercised by the column of blood in the arteries, will be always sufficient to support a column of venous blood of the same height as itself: the two columns mutually balancing each other. Indeed, so long as both arteries and veins contain continuous columns of blood, the force of gravitation, whatever be the position of the body, can have no power to move or resist the motion of any part of the blood in any direction. The lowest blood-vessels have, of course, to bear the greatest amount of pres- sure; the pressure on each part being dire'ctly proportionate to the height of the column of blood above it: hence their liability to distension. But this pressure bears equally on both arteries and veins, and cannot either move, or resist the motion of, the fluid they contain, so long as the col- umns of fluid are of equal height in both, and continuous. » VELOCITY OF THE CIRCULATION. The velocity of the blood-current at any given point in the various divisions of the circulatory system is inversely proportional to their sectional area at that point. If the sectional area of all the branches of a vessel united were always the same as that of the vessel from which they arise, and if the aggregate sectional area of the capillary vessels were equal to that of the aorta, the mean rapidity of the blood's motion in the capillaries would be the same as in the aorta and largest arteries; and if a similar correspondence of capacity existed in the veins and arteries, there would be an equal correspondence in the rapidity of the circulation in them. But the arterial and venous systems may be rep- resented by two truncated cones with their apices directed toward the heart; the area of their united base (the sectional area of the capillaries) being 400 — 800 times as great as that of the truncated apex representing 164 HAND-BOOK OF PHYSIOLOGY. the aorta. Thus the velocity of blood in the capillaries is at least j^-g- of that in the aorta. Velocity in the Arteries. — The velocity of the stream of blood is greater in the arteries than in any other part of the circulatory system, and in them it is greatest in the neighborhood of the heart, and during the ventricular systole; the rate of movement diminishing during the dias- tole of the ventricles, and in the parts of the arterial system most distant from the heart. Chauveau has estimated the rapidity of the blood- stream in the carotid of the horse at over 20 inches per second during the heart's systole, and nearly 6 inches during the diastole (520 — 150 mm.). Estimation of the Velocity. — Various instruments have been devised for measuring the velocity of the blood-stream in the arteries. Ludwig's f "ffiromuhr" (Fig. 142) consists of a U-shaped glass tube dilated at a and #', and whose extremities, Ji and i, are of known calibre. The bulbs can be filled by a common opening at k. The instrument is so contrived that at b and V the glass part is firmly fixed into metal cylinders, which are fixed into a circular horizontal table, c c' , capa- ble of horizontal movement on a similar table d d' about the vertical axis marked in figure by a dotted line. The opening in c c', when the instrument is in position, as in Fig., corresponds exactly with those in d d'\ but if c cr be turned at right angles to its present position, there is no communication between Ji and a, and i and a', but h communicates directly with i\ and if turned through two right angles , c' communicates with d, and c with d' , and there is no direct connection between h and i. The experiment is performed in the following way: — The artery to be experimented upon is divided and connected with two cannulse and tubes which fit it accurately with h and i — Ji the central end, and i the peripheral; the bulb a is filled with olive oil up to a point rather lower than k, and a' and the remainder of a is filled with defibri- nated blood; the tube on k is then carefully clamped; the tubes d and d' are also filled with defibrinated blood. When everything is ready, the blood is allowed to flow into a through Ji, and it pushes before it the oil, and that the defibrinated blood into the artery through i, and replaces it in #'; when the blood reaches the former level of the oil in a, the disc c.c' is turned rapidly through two right angles, and the blood flowing through d into a' again displaces the oil which is driven into a. This is repeated several times, and the duration of the experiment noted. The capacity of a and a' is known; the diameter of the artery is also known by its corresponding with the cannulae of known diameter, and as the number of times a has been filled in a given time is known, the velocity of the current can be calculated. FIG. 142.— Ludwig's Stromuhr. CIRCULATION OF THE BLOOD. 165 Chauveau's instrument (Fig. 143) consists of a thin brass tube, #, in one side of which is a small perforation closed by thin vulcanized india- rubber. Passing through the rubber is a fine lever, one end of which, slightly flattened, extends into the lumen of the tube, while the other moves over the face of a dial. The tube is inserted into the interior of FIQ. 143.— Diagram of Chauveau's Instrument, a. Brass tube for introduction into the lumen of the artery, and containing an index-needle, which passes through the elastic membrane in its side, and moves by the impulse of the blood-current, c. Graduated scale, for measuring the extent of the oscillations of the needle. an artery, and ligatures applied to fix it, so that the movement of the blood may, in flowing through the tube, be indicated by the movement of the outer extremity of the lever on the face of the dial. The Hcematochometer of Vierordt, and the instrument of Lortet, resemble in principle that of Chauveau. Velocity in the Capillaries. — the observations of Hales, E. H. Weber, and Valentin agree very closely as to the rate of the ftood-current in the capillaries of the frog; and the mean of their estimates gives the velocity of the systemic capillary circulation at about one inch (25 mm.) per minute. The velocity in the capillaries of warm-blooded animals is greater. In the dog -^ to T-§-JJ- inch ( '5 to *75 mm. ) a second. This may seem inconsistent with the facts which show that the whole circulation is accomplished in about half a minute. But the whole length of capillary vessels, through which any given portion of blood has to pass, probably does not exceed from -^ th to -^th Of an inch ( '5 mm. ) ; and therefore the time required for each quantity of blood to traverse its own appointed portion of the general capillary system will scarcely amount to a second. Velocity in the Veins. — The velocity of the blood is greater in the veins than in the capillaries, but less than in the arteries: this fact depending upon the relative capacities of the arterial and venous systems. If an accurate estimate of the proportionate areas of arteries and the veins corresponding to them could be made, we might, from the velocity of the arterial current, calculate that of the venous. A usual estimate is, that the capacity of the veins is about twice or three times as great as that of the arteries, and that the velocity of the blood's motion is, therefore, 166 HAND-BOOK OF PHYSIOLOGY. about twice or three times as great in the arteries as in the veins, 8 inches (about 200 mm.) a second. The rate at which the blood moves in the veins gradually increases the nearer it approaches the heart, for the sec- tional area of the venous trunks, compared with that of the branches opening into them, becomes gradually less as the trunks advance toward the heart. Velocity of the Circulation as a whole.— It would appear that a portion of blood can traverse the entire course of the circulation, in the horse, in half a minute. Of course it would require longer to traverse the vessels of the most distant part of the extremities than to go through those of the neck: but taking an average length of vessels to be traversed, and assuming, as we may, that the movement of blood in the human subject is not slower than in the horse, it may be concluded that half a minute represents the average rate. Satisfactory data for these estimates are afforded by the results of experiments to ascertain the rapidity with which poisons introduced into the blood are transmitted from one part of the vascular system to another. The time required for the passage of a solution of potassium ferrocyanide, mixed with the blood, from one jugular vein (through the right side of the heart, the pulmonary vessels, the left cavities of the heart, and the general circulation) to the jugular vein of the opposite side, varies from twenty to thirty seconds. The same substance was transmitted from the jugular vein to the great saphena in twenty seconds; from the jugular vein to the m'asseteric artery, in between fifteen and thirty seconds; to the facial artery, in one experiment, in between ten and fifteen seconds; in another experiment in between twenty and twenty- five seconds; in its transit from the jugular vein to the metatarsal artery, it occupied between twenty and thirty seconds, and in one instance more than forty seconds. The result was nearly the same whatever was the rate of the heart's action. In all these experiments, it is assumed that the substance injected moves with the blood, and at the same rate, and does not move from one part of the organs of circulation to another by diffusing itself through the blood or tissues more quickly than the blood moves. The assumption is sufficiently probable, to be considered nearly certain, that the times above mentioned, as occupied in the passage of the injected substances, are those in which the portion of blood, into which each was injected, was carried from one part to another of the vascular system. Another mode of estimating the general velocity of the circulating blood, is by calculating it from the quantity of blood supposed to be con- tained in the body, and from the quantity which can pass through the heart in each of its actions. But the conclusions arrived at by this method are less satisfactory. For the estimates both of the total quantity of blood, and of the capacity of the cavities of the heart, have as yet only CIRCULATION OF THE BLOOD. 167 approximated to the truth. Still the most careful of the estimates thus made accord very nearly with those already mentioned; and it may be assumed that the blood may all pass through the heart in from twenty- five to fifty seconds. Peculiarities of the Circulation in Different Parts.— The most remarkable peculiarities attending the circulation of blood through differ- ent organs are observed in the cases of the brain, the erectile organs, the lungs, the liver, and the kidney. 1. In the Brain. — For the due performance of its functions, the brain requires a large supply of blood. This object is effected through the number and size of its arteries, the two internal carotids, and the two vertebrals. It is further necessary that the force with which this blood is sent to the brain should be less, or at least should be subject to less vari- ation from external circumstances than it is in other parts, and so the large arteries are very tortuous and anastomose freely in the circle of AVillis, which thus insures that the supply of blood to the brain is uni- form, though it may by an accident be diminished, or in some way changed, through one or more of the principal arteries. The transit of the large arteries through bone, especially the carotid canal of the tem- poral bone, may prevent any undue distension; and uniformity of supply is further insured by the arrangement of the vessels in the pia mater, in which, previous to their distribution to the substance of the brain, the large arteries break up and divide into innumerable minute branches ending in capillaries, which, after frequent communications with one another, enter the brain, and carry into nearly every part of it uniform and equable streams of blood. The arteries are also enveloped in a special lymphatic sheath. The arrangement of the veins within the cranium is also peculiar. The large venous trunks or sinuses are formed so as to be scarcely capable of change of size; and composed, as they are, of the tough tissue of the dura mater, and, in somo instances, bounded on one side by the bony cranium, they are not compressible by any force which the fulness of the arteries might exercise through the substance of the brain; nor do they admit of distension when the flow of venous blood from the brain is obstructed. The general uniformity in the supply of blood to the brain, which'is thus secured, is well adapted, not only to its functions, but also to its con- dition as a mass of nearly incompressible substance placed in a cavity with unyielding walls. These conditions of the brain and skull have appeared, indeed, to some, enough to justify the opinion that the quan- tity of blood in the brain must be at all times the same. It was found that in animals bled to death, without any aperture being- made in the cranium, the brain became pale and anaemic like other parts. And in death from strangling or drowning, congestion of the cerebral vessels; while in death by prussic acid, the quantity of blood in the cavity of the 168 HAND-BOOK OF PHYSIOLOGY. cranium was determined by the position in which the animal was placed after death, the cerebral vessels being congested when the animal was sus- pended with its head downward, and comparatively empty when the animal was kept suspended by the ears. ' That, it was concluded, although the total volume of the contents of the cranium is probably nearly always the same, yet the quantity of blood in it is liable to variation, its increase or diminution being accompanied by a simultaneous diminution or in- crease in the quantity of the cerebro-spinal fluid, which, by readily admitting of being removed from one part of the brain and spinal cord to another, and of being rapidly absorbed, and as readily effused, would serve as a kind of supplemental fluid to the other contents of the cranium, to keep it uniformly filled in case of variations in their quantity (Bur- rows). And there can be no doubt that, although the arrangements of the blood-vessels, to which reference has been made, ensure to the brain an amount of blood which is tolerably uniform, yet, inasmuch as with every beat of the heart and every act of respiration, and under many other circumstances, the quantity of blood in the cavity of the cranium is constantly varying, it is plain that, were there not provision made for the possible displacement of some of the contents of the unyielding bony case in which the brain is contained, there would be often alternations of excessive pressure with insufficient supply of blood. Hence we may con- sider that the cerebro-spinal fluid in the interior of the skull not only subserves the mechanical functions of fat in other parts as & packing material, but by the readiness with which it can be displaced into the spinal canal, provides the means whereby undue pressure and insufficient supply of blood are equally prevented. Chemical Composition of Cerebro-spinal Fluid. — The cerebro-spinal fluid is transparent, colorless, not viscid, with a saline taste and alkaline reaction, and is not affected by heat or acids. It contains 981-984 parts water, sodium chloride, traces of potassium chloride, of sulphates, car- bonates, alkaline and earthy phosphates, minute traces of urea, sugar, sodium lactate, fatty matter, cholesterin, and albumen (Flint). 2. In Erectile Structures. — The instances of greatest variation in the quantity of blood contained, at different times, in the same organs, are found in certain structures which, under ordinary circumstances, are soft and flaccid, but, at certain times, receive an unusually large quantity of blood, become distended and swollen by it, and pass into the state which has been termed erection. Such structures are the corpora caver no sa and corpus spongiosum of the penis in the male, and the clitoris in the female; and, to a less- degree, the nipple of the mammary gland in both sexes. The corpus cavernosum penis, which is the best example of an erectile structure, has an external fibrous membrane or sheath; and from the inner surface of the latter are prolonged numerous fine lamellae which CIRCULATION OF THE BLOOD. 169 divide its cavity into small compartments looking like cells when they are inflated. Within these is situated the plexus of veins upon which the peculiar erectile property of the organ mainly depends. It consists of short veins which very closely interlace and anastomose with each other in all directions, and admit of great variation of size, collapsing in the passive state of the organ, but, for erection, capable of an amount of dila- tation which exceeds beyond comparison that of the arteries and veins which convey the blood to and from them. The strong fibrous tissue lying in the intervals of the venous plexuses, and the external fibrous membrane or sheath with which it is connected, limit the distension of the vessels, and, during the state of erection, give to the penis its con- dition of tension and firmness. The same general condition of vessels exists in the corpus spongiosum urethra?, but around the urethra the fibrous tissue is much weaker than around the body of the penis, and around the glans there is none. The venous blood is returned from the plexuses by comparatively small veins; those from the glans and ^the fore part of the urethra empty themselves into the dorsal veins of the penis; those from the cavernosum pass into deeper veins which issue from the corpora cavernosa at the crura penis; and those from the rest of the urethra and bulb pass more directly into the plexus of the veins about the prostate. For all these veins one condition is the same; namely, that they are liable to the pressure of muscles when they leave the penis. The muscles chiefly concerned in this action are the erector penis and acceler- ator urinae. Erection results from the distension of the venous plexuses with blood. The principal exciting cause in the erection of the penis is nervous irritation, originating in the part itself, or derived from the brain and spinal cord. The nervous influence is communicated to the penis by the pudic nerves, which ramify in its vascular tissue: and after their division in the horse, the penis is no longer capable of erection. This influx of the blood is the first condition necessary for erection, and through it alone much enlargement and turgescence of the penis may ensue. But the erection is probably not complete, nor maintained for any time except when, together with this influx, the muscles already mentioned contract, and by compressing the veins, stop the efflux of blood, or prevent it from being as great as the influx. It appears to be only the most perfect kind of erection that needs the help of muscles to compress the veins; and none such can materially as- sist the erection of the nipples, or that amount of turgescence, just falling short of erection, of which the spleen and many other parts are capable. For such turgescence nothing more seems necessary than a large plexiform arrangement of the veins, and such arteries as may admit, upon occasion, augmented quantities of blood. (3, 4, 5.) The circulation in the Lungs, Liver, and Kidneys will be described under those heads. 170 HAND-BOOK OF PHYSIOLOGY. Agents concerned in the circulation. — Before quitting this sub- ject it will be as well to bring together in a tabular form the various agencies concerned in maintaining the circulation. 1. The Systole and Diastole of the Heart, the former pumping into the aorta and so into the arterial system a certain amount of blood, and the latter to some extent sucking in the blood from the veins. 2. The elastic and muscular coats of the arteries, which serve to keep up an equable and continuous stream. 3. The so-called vital capillary force. 4. The pressure of the muscles on veins ivith valves, and the slight rhythmic contraction of the veins. 5. Aspiration of the Thorax during inspiration, by means of which the blood is drawn from the large veins into the thorax (to be treated of in next Chapter). DlSCOYEKY OF THE CIRCULATION. Up to nearly the close of the sixteenth century it was generally be-* lieved that the blood passed from one ventricle to the other through fora- mina in the "septum ventriculorum." These foramina are of course purely imaginary, but no one ventured to dispute their existence till Ser- vetus boldly stated that he could not succeed in finding them. He fur- ther asserted that the blood passed from the Right to the Left side of the heart by way of the lungs, and also advanced the hypothesis that it is thus "revivified," remarking that the Pulmonary Artery is too large to serve merely for the nutrition of the lungs (a theory then generally accepted). Realdus, Columbo, and Caesalpinus added several important observa- tions. The latter showed that the blood is slightly cooled by passing through the lungs, also that the veins swell up on the distal side of a liga- ture. The existence of valves in the veins had previously been discovered by Fabricius of Aquapendente, the teacher of Harvey. The honor of first demonstrating the general course of the circulation belongs by right to Harvey, who made his grand discovery about 1618. He was the first to establish the muscular structure of the heart, which had been denied by many of his predecessors; and by careful study of its action both in the body and when excised, ascertained the order of con- traction of its cavities. He did not content himself with inferences from the anatomy of the parts, bat employed the experimental method of injection, and made an extensive and accurate series of observations on the circulation in cold-blooded animals. He forced water through the Pulmonary Artery till it trickled out through the Left Ventricle, the tip of which had been cut off. Another of his experiments was to fill the Right side of the heart with water, tie the Pulmonary Artery and the Venae Cavae and then squeeze the Right ventricle: not a drop could be forced through into the Left ventricle, and thus he conclusively disproved the existence of foramina in the septum ventriculorum. "I have suffi- ciently proved," says he, "that by the beating of the heart the blood passes from the veins into the arteries through the ventricles, and is dis- tributed over the whole body." "In the warmer animals, such as man, the blood passes from the Right CIRCULATION OF THE BLOOD. 171 Ventricle of the Heart through the Pulmonary Artery into the Lungs, and thence through the Pulmonary Veins into the Left Auricle, thence into the Left Ventricle." . Proofs of the Circulation of the Blood. — The following are the main arguments by which Harvey established the fact of the circulation: — 1. The heart in half an hour propels more blood than the whole mass of blood in the body. 2. The great force and jetting manner with which the blood spurts from an opened artery, such as the carotid, with every beat of the heart. 3. If true, the normal course of the circulation explains why after death the arteries are commonly found empty and the veins full. 4. If the large veins near the heart were tied in a fish or snake, the heart became pale, flaccid, and bloodless; on removing the ligature, the blood again flowed into the heart. If the artery were tied, the heart be- came distended; the distension lasting until the ligature was removed. 5. The evidence to be derived from a ligature round a limb. If it be drawn very tight, no blood can enter the limb, and it becomes pale and cold. If the ligature be somewhat relaxed, blood can enter but cannot leave the limb; hence it becomes swollen and congested. If the ligature be removed, the limb soon regains its natural appearance. 6. The existence of valves in the veins which only permit the blood to flow toward the heart. 7. The general constitutional disturbance resulting from the introduc- tion of a poison at a single point, e. g., snake poison. To these may now be added many further proofs which have accumu- lated since the time of Harvey, e. g. : — 8. Wounds of arteries and veins. In the former case haemorrhage may be almost stopped by pressure between the heart and the wound, in the latter by pressure beyond the seat of injury. 9. The direct observation of the passage of blood corpuscles from small arteries through capillaries into veins in all transparent vascular parts, as the mesentery, tongue or web of the frog, the tail or gills of a, tadpole, etc. 10. The results of injecting certain substances into the blood. Further, it is obvious that the mere fact of the existence of a hollow muscular organ (the heart) with valves so arranged as to permit the blood to pass only in one direction, of itself suggests the course of the circula- tion. The only part of the circulation which Harvey could not follow is that through the capillaries, for the simple reason that he had no lenses- sufficiently powerful to enable him to see it. Mafpighi (1661) and Leeu- wenhoek (1668) demonstrated it in the tail of the tadpole and lung of the frog. CHAPTEK VI. RESPIRATION. THE maintenance of animal life necessitates the continual absorption of oxygen and excretion of carbonic acid; the blood being, in all animals which possess a well developed blood-vascular system, the medium by which these gases are carried. By the blood, oxygen is absorbed from without and conveyed to all parts of the organism, and, by the blood, carbonic acid, which comes from within, is carried to those parts by which it may escape from the body. The two processes, — absorption of oxygen and excretion of carbonic acid, — are complementary, and their sum is termed the process of Respiration. In all Vertebrata, and in a large number of Invertebrata, certain parts, either lungs or gills, are specially constructed for bringing the blood into proximity with the aerating medium (atmospheric air, or water contain- ing air in solution). In some of the lower Vertebrata (frogs and other naked Amphibia) the skin is important as a respiratory organ, and is capable of supplementing, to some extent, the functions of the proper breathing apparatus; but in all -the higher animals, including man, the respiratory capacity of the skin is so infinitesimal that it may be practi- cally disregarded. Essentially, a lung or gill is constructed of a fine transparent mem- brane, one surface of which is exposed to the air or water, as the case may be, while, on the other, is a network of blood-vessels, — the only separation between the blood and aerating medium being the thin wall of the blood- vessels, and the fine membrane on one side of which vessels are distributed. The diiference between the simplest and the most complicated respiratory membrane is one of degree only. The various complexity of the respiratory membrane, and the kind of aerating medium, are not, however, the only conditions which cause a diiference in the respiratory capacity of different animals. The number and size of the red blood-corpuscles, the mechanism of the breathing ap- paratus, the presence or absence of a pulmonary heart, physiologically distinct from the systemic, are, all of them, conditions scarcely second in importance. In the heart of man and all other Mammalia, the right side from which the blood is propelled into and through the lungs may be termed the RESPIRATION. 173 "pulmonary" heart; while the left side is " : systemic " in function. In many of the lower animals, however, no such distinction can be drawn. Thus, in Fish the heart propels the blood to the respiratory organ (gills); l)ii t there is no contractile sac corresponding to the left side of the heart, to propel the blood directly into the systemic vessels. It may be well to state here that the lungs are only the medium for the exchange, on the part of the blood, of carbonic acid for oxygen. They are not the seat, in any special manner, of those combustion-processes of which the production of carbonic acid is the final result. These occur in all parts of the body — more in one part, less in another: chiefly in the substance of the tissues, but in part in the capillary blood-vessels contained in them. THE RESPIRATORY PASSAGES AND TISSUES. The object of respiration is the interchange of gases in the lungs; for this purpose it is necessary that the atmospheric air shall pass into them and be expelled from them. The lungs are contained in the chest or thorax, which is a closed cavity having no communication with the out- 174 HAND-BOOK OF PHYSIOLOGY. side, except by means of the respiratory passages. The air enters these passages through the nostrils or through the mouth, thence it passes through the larynx into the trachea or windpipe, which about the middle of the chest divides into two tubes, bronchi, one to each (right and left) lung. The Larynx is the upper part of the passage which ieaas exclusively "to the lung; it is formed by the thyroid, cricoid, and arytenoid cartilages (Fig. 145), and contains the vocal cords, by the vibration of which the voice is chiefly produced. These vocal cords are ligamentous bands at- tached to certain cartilages capable of movement by muscles. By their approximation the cords can entirely close the entrance into the larynx; lout under the ordinary conditions, the entrance of the larynx is formed by a more or less triangular chink between them, called the rima glot- tidis. Projecting at an acute angle between the base of the tongue and the larynx to which it is attached, is a leaf-shaped cartilage, with its larger extremity free, called the epiglottis (Fig. 145, e). The whole of the larynx is lined by mucous membrane, which, however, is extremely thin over the cords. At its lower extremity the larynx joins the trachea.1 With the exception of the epiglottis and the so-called cornicula laryngis, the cartilages of the larynx are of the hyaline variety! Structure of Epiglottis. — The supporting cartilage is composed of yellow elastic cartilage, enclosed in a fibrous sheath (perichondrium), and covered on both sides with mucous membrane. The anterior surface, which looks toward the base of the tongue, is covered with mucous mem- iDrane, the basis of which is fibrous tissue, elevated toward both surfaces in the form of rudimentary papillae, and covered with several layers of squamous epithelium. In it ramify capillary blood-vesse.ls, and in its meshes are a large number of lymphatic channels. Under the mucous membrane, in the less dense fibrous tissue of which it is composed, are a number of tubular glands. The posterior or laryngeal surface of the epiglottis is covered by a mucous membrane, similar in structure to that on the other surface, but that the epithelial coat is thinner, the number of strata of cells being less, and the papillse few and less distinct. The fibrous tissue which constitutes the mucous membrane is in great part of the adenoid variety, and this is here and there collected into distinct masses or follicles. The glands of the posterior surface are smaller but more numerous than those on the other surface. In many places the glands which are situated nearest to the perichondrium are directly continuous through apertures in the cartilage with those on the other side, and often the ducts of the glands from one side of the cartilage pass through and open on the mucous surface of the other side. Taste goblets have been 1 A detailed account of the structure and function of the Larynx will be found in Chapter XVI. RESPIRATION. 175 found in the epithelium of the posterior surface of the epiglottis, and in several other situations in the laryngeal mucous membrane. The Trachea and Bronchial Tubes. — The trachea or wind-pipe extends froni the cricoid cartilage, which is on a level with the fifth cervi- FIG. 145. FIG. 146. FIG. 145.— Outline showing the general form of the larynx, trachea, and bronchi, as seen from before, h, the great cornu of the hyoid bone; e, epiglottis; £, superior, and f, inferior cornu of the thyroid cartilage; c, middle of the cricoid cartilage: fr, the trachea, showing sixteen cartilaginous rings: 6, the right, and 6'. the left bronchus. (Allen Thomson. 1 x J^. FIG. 146.— Outline showing the general form of the larynx, trachea, and bronchi, as seen from be- hind, /i, great cornu of the hyoid bone ; t, superior, and t\ the inferior cornu of the thyroid cartilage ; e, the epiglottis; a, points to the back of both the arytenoid cartilages which are surmounted by the cornicula; c, the middle ridge on the back of the cricoid cartilage : tr, the posterior membranous part of the trachea; 6, 6', right and left bronchi. (Allen Thomson.) J& cal vertebra, to a point opposite the third dorsal vertebra, where it divides into the two bronchi, one for each lung (Fig. 146). It measures, on an average, four or four-and-a-half inches in length, and from three-quarters of an inch to an inch in diameter. 176 HAND-BOOK OF PHYSIOLOGY. Structure. — The trachea is essentially a tube of fibro-elastic membrane, within the layers of which are enclosed a series of cartilaginous rings, from sixteen to twenty in number. These rings extend only around the front and sides of the trachea (about two-thirds of its circumference), and are deficient behind; the interval between their posterior extremities being bridged over by a continuation of the fibrous membrane in which they are enclosed (Fig. 145). The cartilages of the trachea and bronchial tubes are of the hyaline variety. FIG. 147.— Section of trachea, a, columnar ciliated epithelium; 6 and c, proper structure of the mucous membrane, containing elastic fibres cut across transversely; d, submucous tissue containing mucous glands, e, separated from the hyaline cartilage, g, by a fine fibrous tissue, /; /i, external in- vestment of fine fibrous tissue. (S. K. Alcock.) Immediately within this tube, at the back, is a layer of unstriped muscular fibres, which extends, transversely., between the ends of the car- tilaginous rings to which they are attached, and opposite the intervals between them, also; their evident function being to diminish, when re- quired, the calibre of the trachea by approximating the ends of the car- tilages. Outside these are a few longitudinal bundles of muscular tissue which, like the preceding, are attached both to the fibrous and cartilagi- nous framework. RESPIRATION. 177 The mucous membrane consists of adenoid tissue, separated from the stratified columnar epithelium which lines it by a homogeneous basement membrane. This is penetrated here and there by channels which connect the adenoid tissue of the mucosa with the intercellular substance of the epithelium. The stratified columnar epithelium is formed of several layers of cells (Fig. 147), of which the most superficial layer is ciliated, and is often branched downward to join connective-tissue corpuscles; while between these branched cells are smaller elongated cells prolonged up toward the surface and down to the basement membrane. Beneath these are one or more layers of more irregularly shaped cells. In the deeper part of the mucosa are many elastic fibres between which lie con- nective-tissue corpuscles and capillary blood-vessels. Numerous mucous glands are situate on the exterior and in the substance of the fibrous framework of the trachea; their ducts perfora- ting the various structures which form the wall of the trachea, and. opening through the mucous membrane into the interior. The two bronchi into which the trachea divides, of which the right is shorter, broader, and more horizontal than the left (Fig. 145), resemble the trachea exactly in structure, and in the arrangement of their carti- laginous rings. On entering the substance of the lungs, however, the; rings, although they still form only larger or smaller segments of a circle,, are no longer confined to the front and sides of the tubes, but are dis- tributed impartially to all parts of their circumference. The bronchi divide and subdivide, in the substance of the lungs, into a number of smaller and smaller branches, which penetrate into every part of the organ, until at length they end in the smaller subdivisions of the lungs, called lobules. All the larger branches still have walls formed of tough membrane, containing portions of cartilaginous rings, by which they are held open, and unstriped muscular fibres, as well as longitudinal bundles of elastic tissue. They are lined by mucous membrane, the surface of which, like that of the larynx and trachea, is covered with ciliated epithelium (Fig. 148). The mucous membrane is abundantly provided with mucous glands. As the bronchi become smaller and smaller, and their walls thinner, the cartilaginous rings become scarcer and more irregular, until, in the smaller bronchial tubes, they are represented only by minute and scattered cartilaginous flakes. And when the bronchi, by successive branches, are reduced to about ^ of an inch in diameter, they lose their cartilaginous element altogether, and their walls are formed only of a tough fibrous elastic membrane, with circular muscular fibres; they are still lined, how- ever, by a thin mucous membrane, with ciliated epithelium, the length of the cells bearing the cilia having become so far diminished, that the cells are now almost cubical. In the smaller bronchi the circular muscular VOL. I.— 12. 178 HAND-BOOK OF PHYSIOLOGY fibres are more abundant than in the trachea and larger bronchi, and form a distinct circular coat. The Lungs and Pleura. — The Lungs occupy the greater portion of the thorax. They are of a spongy elastic texture, and on section appear to the naked eye as if they were in great part solid organs, except here and there, at certain points, where branches of the bronchi or air-tubes may have been cut across, and show, on the surface of the section, their FIG. 148.— Transverse section of a bronchus, about one-fourth of an inch in diameter, e, Epithe- lium (ciliated); immediately beneath it is the mucous membrane or internal fibrous layer, of varying thickness; m, muscular layer; s, m, submucous tissue; /, fibrous tissue; c, cartilage enclosed within the layers of fibrous tissue; gr, mucous gland. (F. E. Schulze.) tubular structure. In fact, however, the lungs are hollow organs, each of which communicates by a separate orifice with a common air-tube, the trachea. The Pleura. — Each lung is enveloped by a serous membrane — the pleura, one layer of which adheres closely to the surface of the lung, FIG. 149.— Transverse section of the chest (after Gray). and provides it with its smooth and slippery covering, while the other adheres to the inner surface of the chest- wall. The continuity of the two layers, which form a closed sac, as in the case of other serous mem- branes, will be best understood by reference to Fig. 149. The appearance KESPIRATION. 179 of a space, however, between the pleura which covers the lung (visceral layer), and that which lines the inner surf ace of the chest (jwrttfoi layer), is inserted in the drawing only for the sake of distinctness. These layers are, in health, everywhere in contact, one with the other; and between them is only just so much fluid as will ensure the lungs gliding easily, in their expansion and contraction, on the inner surface of the parietal layer, which lines the chest-wall. While considering the subject of normal respiration, we may discard altogether the notion of the existence of any space or cavity between the lungs and the wall of the chest. If, however, an opening be made so as to permit air or fluid to enter the pleural sac, the lung, in virtue of its elasticity, recoils, and a consid- erable space is left between the lung and the chest- wall. In other words, the natural elasticity of the lungs would cause them at all times to con- tract away from the ribs, were it not that the contraction is resisted by atmospheric pressure which bears only on the inner surface of the air- tubes and air-cells. On the admission of air into the pleural sac, atmos- pheric pressure bears alike on the inner and outer surfaces of the lung, and their elastic recoil is thus no longer prevented. Structure of the Pleura and Lung. — The pulmonary pleura consists of an outer or denser layer and an inner looser tissue. The former or pleura proper consists of dense fibrous tissue with elastic fibres, covered by endothelium, the cells of which are large, flat, hyaline, and transpar- ent when the lung is expanded, but become smaller, thicker, and gran- ular when the lung collapses. In the pleura is a lymph-canalicular system; and connective tissue corpuscles are found in the fibres and tissue which forms its groundworr. The inner, looser, or subpleural tissue contains lamellae of fibrous connective tissue and connective tissue cor- puscles between them. Numerous lymphatics are to be met with, which form a dense plexus of vessels, many of which contain valves. They are simple endothelial tubes, and take origin in the lymph-canalicular system of the pleura proper. Scattered bundles of unstriped muscular fibre occur in the pulmonary pleura. They are especially strongly developed on those parts (anterior and internal surfaces of lungs) which move most freely in respiration: their function is doubtless to aid in expiration. The structure of the parietal portion of the pleura is very similar to that of the visceral layer. Each lung is partially subdivided into separate portions called lobes; the right lung into three lobes, and the left into two. Each of these lobes, again, is composed of a large number of minute parts, called lobules. Each pulmonary lobule may be considered a lung in miniature, consist- ing, ^as it does, of a branch of the bronchial tube, of air-cells, blood vessels, nerves, and lymphatics, with a sparing amount of areolar tissue. On entering a lobule, the small bronchial tube, the structure of which 180 HAND-BOOK OF PHYSIOLOGY. has been just described (a, Fig. 150), divides and subdivides; its walls at the same time becoming thinner and thinner, until at length they are formed only of a thin membrane of areolar and elastic tissue, lined by a layer of squamous epithelium, not provided with cilia. At the same time, they are altered in shape; each of the minute terminal branches FIG. 150.— Ciliary epithelium of the human trachea, a, Layer of longitudinally arranged elastic fibres; 6, basement membrane; c, deepest cells, circular in form; d, intermediate elongated cells; ey outermost layer of cells fully developed and bearing cilia. X 350. (Kolliker.) i widening out funnel-wise, and its walls being pouched out irregularly into small saccular dilatations, called air-cells (Fig. 151, Z>). Such a funnel-shaped terminal branch of the bronchial tube, with its group of pouches or air-cells, has been called an infundibulum (Figs. 151, 152), FIG. 151. FIG. 152. FIG. 151.— Terminal branch of a bronchial tube, with its infundibula and air-cells, from tte mar- gin of the lung of a monkey, injected with quicksilver, a, terminal bronchial twig; 6 6, infundibula and air-cells, X 10. (F. E. Shulze.) FIG. 152.— Two small infundibula or groups of air-cells, a a, with air-cells, 6 6, and the ultimate bronchial tubes, c c, with which the air-cells communicate. From a new-born child. (Kolliker.) and the irregular oblong space in its centre, with which the air-cells com- municate, an intercellular passage. The air-cells, or air- vesicles, may be placed singly, like recesses from, the intercellular passage, but more often they are arranged in groups or RESPIRATION. 181 even in rows, like minute sacculated tubes; so that a short series of vesicles, all communicating with one another, open by a common orifice into the tube. The vesicles are of various forms, according to the mutual pressure to which they are subject; their walls are nearly in contact, and thcv vary from -^ to ^ of an inch in diameter. Their walls are formed of fine membrane, similar to that of the intercellular passages, and con- tinuous with it, which membrane is folded on itself so as to form a sharp- edged border at each circular orifice of communication between con- tiguous air-vesicles, or between the vesicles and the bronchial passages. Numerous fibres of elastic tissue are spread out between contiguous air- Fio. 153. — From a section of lung of a cat, stained with silver nitrate. A. D. Alveolar duct or in- tercellular passage. S. Alveolar septa. N. Alveoli or air-cells, lined with large flat, nucleated cells, with some smaller polyhedral nucleated cells. Circular muscular fibres are seen surrounding the in- terior of the alveolar duct, and at one part is seen a group of small polyhedral cells continued from the bronchus. (Klein and Noble Smith.) cells, and many of these are attached to the outer surface of the fine membrane of which each cell is composed, imparting to it additional strength, and the power of recoil after distension. The cells are lined by a layer of epithelium (Fig. 153), not provided with cilia. Outside the cells, a network of pulmonary capillaries is spread out so densely (Fig. 154), that the interspaces or meshes are even narrower than the vessels, which are, on an average, -g-gVff °^ an inch in diameter. Between the atmospheric air in the cells and the blood in these vessels, nothing inter- venes but the thin walls of the cells and capillaries; and the exposure of the blood to the air is the more complete, because the folds of membrane between contiguous cells, and often the spaces between the walls of the 182 HAND-BOOK OF PHYSIOLOGY. same, contain only a single layer of capillaries, both sides of which are thus at once exposed to the air. The air-vesicles situated nearest to the centre of the lung are smaller and their networks of capillaries are closer than those nearer to the cir- cumference. The vesicles of adjacent lobules do not communicate; and those of the same lobule or proceeding from the same intercellular passage, do so as a general rule only near angles of bifurcation; so that, when any bronchial tube is closed or obstructed, the supply of air is lost for all the cells opening into it or its branches. Blood-supply. — The lungs receive blood from two sources, (a) the pul- monary artery, (b) the bronchial arteries. The former conveys venous blood to the lungs for its arterialization, and this blood takes no share in the nutrition of the pulmonary tissues through which it passes. (#) The FIG. 154.— Capillary network of the pulmonary blood- vessels in the human lung. x60. (Kolliker.) branches of the bronchial arteries ramify for nutrition's sake in the walls of the bronchi, of the larger pulmonary vessels, in the interlobular con- nective tissue, etc.; the blood of the bronchial vessels being returned chiefly through the bronchial and partly through the pulmonary veins. Lymphatics. — The lymphatics are arranged in three sets: — 1. Irreg- ular lacunae in the walls of the alveoli or air-cells. The lymphatic vessels which lead from these accompany the pulmonary vessels toward the root of the lung. 2. Irregular anastomosing spaces in the walls of the bronchi. 3. Lymph-spaces in the pulmonary pleura. The lymphatic vessels from all these irregular sinuses pass in toward the root of the lung to reach the bronchial glands. Nerves. — The nerves of the lung are to be traced from the anterior and posterior pulmonary plexuses, which are formed by branches of the vagus and sympathetic. The nerves follow the course of the vessels and bronchi, and in the walls of the latter many small ganglia are situated. RESPIRATION. 183 MECHANISM OF RESPIRATION. Respiration consists of the alternate expansion and contraction of the thorax, by means of which air is drawn into or expelled from the lungs. These acts are called Inspiration and Expiration respectively. For the inspiration of air into the lungs it is evident that all that is necessary is such a movement of the side- walls or floor of the chest, or of both, that the capacity of the interior shall be enlarged. By such in- crease of capacity there will be of course a diminution of the pressure of the air in the lungs, and a fresh quantity will enter through the larynx and trachea to equalize the pressure on the inside and outside of the chest. For the expiration of air, on the other hand, it is also evident that, by an opposite movement which shall diminish the capacity of the chest, the pressure in the interior will be increased, and air will be expelled, until the pressures within and without the chest are again equal. In both cases the air passes through the trachea and larynx, whether in entering or leaving the lungs, there being no other communication with the exterior of the body; and the lung, for the same reason, remains under all the circumstances described closely in contact with the walls and floor of the chest. To speak of expansion of the chest, is to speak also of expansion of the lung. AVe have now to consider the means by which the respiratory move- ments are effected. RESPIRATORY MOVEMENTS. A. Inspiration. — The enlargement of the chest in inspiration is a muscular act; the effect of the action of the inspiratory muscles being an increase in the size of the chest-cavity (a) in the vertical, and (b) in the lateral and antero-posterior diameters. The muscles engaged in ordinary inspiration are the diaphragm; the external intercostals; parts of the in- ternal intercostals; the levatores costarum; and serratus posticus superior. (a. ) The vertical diameter of the chest is increased by the contraction and consequent descent of the diaphragm, — the sides of the muscle de- scending most, and the central tendon remaining comparatively unmoved; while the intercostal and other muscles, by acting at the same time, pre- vent the diaphragm, during its contraction, from drawing in the sides of the chest. (b. ) The increase in the lateral and antero-posterior diameters of the chest is effected by the raising of the ribs, the greater number of which are attached very obliquely to the spine and sternum (see Figure of Skele- ton in frontispiece). The elevation of the ribs takes place both in front and at the sides — 184 HAND-BOOK OF PHYSIOLOGY. the hinder ends being prevented from performing any upward movement by their attachment to the spine. The movement of the front extremities of the ribs is of necessity accompanied by an upward and forward move- ment of the sternum to which they are attached, the movement being greater at the lower end than at the upper end of the latter bone. FIG. 155. — Diagram of axes of movement of ribs. The axes of rotation in these movements are two; one corresponding with a line drawn through the two articulations which the rib forms with the spine (a b, Fig. 155); and the other, with a line drawn from one of these (head of rib) to the sternum (A B, Fig. 155, and Fig. 156); the FIG. 156.— Diagram of movement of a rib in inspiration. motion of the rib around the latter axis being somewhat after the fashion of raising the handle of a bucket. The elevation of the ribs is accompanied by a slight opening out of the RESPIRATION. 1*5 angle whicli the bony part forms with its cartilage (Fig. 156, A); and thus an additional means is provided for increasing the antero-posterior diameter of the chest. The muscles by which the ribs are raised, in ordinary quiet inspiration, are the external inter costals, and that portion of the internal intercostal* which is situate between the costal cartilages; and these are assisted by the levatores costarum, and the serratus posticus superior. The action of the levatores and the serratus is very simple. Their fibres, arising from the spine as a fixed point, pass obliquely downward and forward to the ribs, and necessarily raise the latter when they contract. The action of the intercostal muscles is not quite so simple, inasmuch as, passing merely from rib to rib, they seem at first sight to have no fixed point toward which they can pull the bones to which they are attached. A very simple apparatus will explain this apparent anomaly and make their action plain. Such an apparatus is shown in Fig. 157. A B is an upright bar, representing the spine, with which are jointed two parallel bars, C and D, which represent two of the ribs, and are connected in front by movable joints with another upright, representing the sternum. > FIG. 157. FIG. 158. FIG. 157.— Diagram of apparatus showing the action of the external intercostal muscles. FIG. 158.— Diagram of apparatus showing the action of the internal intercostal muscles. If with such an apparatus elastic bands be connected in imitation of the intercostal muscles, it will be found that when stretched 011 the bars after the fashion of the external intercostal fibres (Fig. 157, C D), i.e., passing downward and forward, they raise them (Fig. 157, C' D'); while on the other hand, if placed in imitation of the position of the internal intercostals (Fig. 158, E F), i.e., passing downward and backward, they depress them (Fig. 158, E' F'). , The explanation of the foregoing facts is very simple. The intercostal muscles, in contracting, merely do that which all other contracting fibres 186 HAND-BOOK OF PHYSIOLOGY. do, viz., bring nearer together the points to which they are attached; and in order to do this, the external intercostals must raise the ribs, the points C and D (Fig. 157) being nearer to each other when the parallel bars are in the position of the dotted lines. The limit of the movement in the apparatus is reached when the elastic band extends at right angles to the two bars which it connects — the points oi; attachment C' and D' being then at the smallest possible distance one from the other. The internal intercostals (excepting those fibres which are attached to the cartilages of the ribs), have an opposite action to that of the exter- nal. In contracting they must pull down the ribs, because the points E and F (Fig. 158) can only be brought nearer one to another (Fig. 158, E' F') by such an alteration in their position. On account of the oblique position of the cartilages of the ribs with reference to the sternum, the action of the inter-cartilaginous fibres of the internal intercostals must, of course, on the foregoing principles, re- semble that of the external intercostals. In tranquil breathing, the expansive movements of the lower part of the chest are greater than those of the upper. In forced inspiration, on the other hand, the greatest extent of movement appears to be in the upper antero-posterior diameter. Muscles of Extraordinary Inspiration. — In extraordinary or forced inspiration, as in violent exercise, or in cases in which there is some interference with the due entrance of air into the chest, and in which, therefore, strong efforts are necessary, other muscles than those just enumerated, are pressed into the service. It is very difficult or im- possible to separate by a hard and fast line, the so-called muscles of ordi- nary from those of extraordinary inspiration; but there is no doubt that the following are but little used as respiratory agents, except in cases in which unusual efforts are required — the scaleni muscles, the sternomas- toid, the serratus magnus, the pectorales, and the trapezius. Types of Respiration. — The expansion of the chest in inspiration presents some peculiarities in different persons. In young children, it is effected chiefly by the diaphragm, which being highly arched in expiration, becomes flatter as it contracts, and, descending, presses on the abdominal viscera, and pushes forward the front walls of the abdomen. The move- ment of the abdominal walls being here more manifest than that of any other part, it is usual to call this the abdominal type of respiration. In men, together with the descent of the diaphragm, and the pushing for- ward of the front wall of the abdomen, the chest and the sternum are subject to a wide movement in inspiration (inferior costal type). In women, the movement appears less extensive in the lower, and more so in the upper, part of the chest (superior costal type). (See Figs. 159, 160.) B. Expiration. — From the enlargement produced in inspiration, the chest and lungs return in ordinary tranquil expiration, by their elas- ticity; the force employed by the inspiratory muscles in distending the RESPIRATION. 187 chest and overcoming the elastic resistance of the lungs and chest-walls, being returned as an expiratory effort when the muscles are relaxed. This elastic recoil of the lungs is sufficient, in ordinary quiet breathing, to expel air from the chest in the intervals of inspiration, and no muscular power is required. In all voluntary expiratory efforts, however, as in speak- ing, singing, blowing, and the like, and in many involuntary actions also, as sneezing, coughing, etc., something more than merely passive elastic power is necessary, and the proper expiratory muscles are brought into action. By far the chief of these are the abdominal muscles, which, by FIG. 159. FIG. 160. FIG. 159.— The changes of the thoracic and abdominal walls of the male during respiration. The back is supposed to be fixed, in order to throw forward the respiratory movement as much as possi- ble. The outer black continuous line in front represents the ordinary breathing movement: the ante- rior margin of it being the boundary of inspiration, the posterior margin the limit of expiration. The line is thicker over the abdomen, since the ordinary respiratory movement is chiefly abdominal ; thin over the chest, for there is less movement over that region. The dotted line indicates the movement on deep inspiration, during which the sternum advances while the abdomen recedes. FIG. 160. — The respiratory movement in the female. The lines indicate the same changes as in the last figure. The thickness of the continuous line over the sternum shows the larger extent of the ordinary breathing movement over that region in the female than in the male. (John Hutcninson.) The posterior continuous line represents in both figures the limit of forced expiration. pressing on the viscera of the abdomen, push up the floor of the chest formed by the diaphragm, and by thus making pressure on the lungs, expel air from them through the trachea and larynx. All muscles, how- ever, which depress the ribs, must act also as muscles of expiration, and therefore we must conclude that the abdominal muscles are assisted in their action by the greater part of the internal intercostals, the triangu- laris sterni, the serratus posticus inferior, and quadratus lumborum. When by the efforts of the expiratory muscles, the chest has been squeezed to less than its average diameter, it again, on relaxation of the muscles, returns to the normal dimensions by virtue of its elasticity. The con- 188 HAND-BOOK OF PHYSIOLOGY. struction of the chest-walls, therefore, admirably adapts them for recoiling against and resisting as well undue contraction as undue dilatation. In the natural condition of the parts, the lungs can never contract to the utmost, but are always more or less "on the stretch/' being kept closely in contact with the inner surface of the walls of the chest by atmospheric pressure, and can contract away from these only when, by some means or other, as by making an opening into the pleural cavity, or by the effusion of fluid there, the pressure on the exterior and interior of the lungs becomes equal. Thus, under ordinary circumstances, the degree of contraction or dilatation of the lungs is dependent on that of the boundary walls of the chest, the outer surface of the one being in close contact with the inner surface of the other, and obliged to follow it in all its movements. Respiratory Rhythm. — The acts of expansion and contraction of the chest, take up, under ordinary circumstances, a nearly equal time. The act of inspiring air, however, especially in women and children, is a little shorter than that of expelling it, and there is commonly a very slight pause between the end of expiration and the beginning of the next inspiration. The respiratory rhythm may be thus expressed: — Inspiration 6 Expiration 7 or 8 A very slight pause. Respiratory Sounds. — If the ear be placed in contact with the wall of the chest, or be separated from it only by a good conductor of sound, a faint respiratory murmur is heard during inspiration. This sound varies somewhat in different parts — being loudest or coarsest in the neigh- borhood of the trachea and large bronchi (tracheal and bronchial breath- ing), and fading off into a faint sighing as the ear is placed at a distance from these (vesicular breathing). It is best heard in children, and in them a faint murmur is heard in expiration also. The cause of the vesic- ular murmur has received various explanations. Most observers hold that the sound is produced by the friction of the air against the walls of the alveoli of the lungs when they are undergoing distension (Laennec, Skoda), others that it is due to an oscillation of the current of air as it enters the alveoli (Chauveau), whilst others believe that the sound is pro- duced in the glottis, but that it is modified in its passage to the pulmo- nary alveoli (Beau, Gee). Respiratory Movements of the Nostrils and of the Glottis.— During the action of the muscles which directly draw air into the chest, those which guard the opening through which it enters are not passive. In hurried breathing the instinctive dilatation of the nostrils is well seen, although under ordinary conditions it may not be noticeable. The open- ing at the upper part of the larynx, however, or rima glottidis (Fig. 297), RESPIRATION. 189 is dilated at each inspiration, for the more ready passage of air, and be- comes smaller at each expiration; its condition, therefore, corresponding during respiration with that of the walls of the chest. There is a further likeness between the two acts in that, under ordinary circumstances, the dilatation of the rima glottidis is a muscular act, and itc contraction chiefly an elastic recoil; although, under various conditions, to be here- after mentioned, there may be, in the contraction of the glottis, consider- able muscular power exercised. Terms used to express Quantity of Air breathed. — Breathing or tidal air, is the quantity of air which is habitually and almost uni- formly changed in each act of breathing. In a healthy adult man it is about 30 cubic inches. Complemented air, is the quantity over and above this which can be drawn into the lungs in the deepest inspiration; its amount is various, as will be presently shown. Reserve air. After ordinary expiration, such as that which expels the breathing or tidal air, a certain quantity of air remains in the lungs, which may be expelled by a forcible and deeper expiration. This is termed reserve air. Residual air is the quantity which still remains in the lungs after the most violent expiratory effort. Its amount depends in great measure on the absolute size of the chest, but may be estimated at about 100 cubic inches. The total quantity of air which passes into and out of the lungs of an adult, at rest, in 24 hours, is about 686,000 cubic inches. This quantity, however, is largely increased by exertion; the average amount for a hard- working laborer in the same time, being 1,568,390 cubic inches. Respiratory Capacity. — The greatest respiratory capacity of the chest is indicated by the quantity of air which a person can expel from his lungs by a forcible expiration after the deepest inspiration that he can make; it expresses the power which a person has of breathing in the emergencies of active exercise, violence, and disease. The average capacity of an adult (at 60° F. or 15 '4° C.) is about 225 cubic inches. The respiratory capacity, or as Hutchinson called it, vital capacity, is usually measured by a modified gasometer (spirometer of Hutchinson), into which the experimenter breathes, — making the most prolonged ex- piration possible after the deepest possible inspiration. The quantity of air which is thus expelled from the lungs is indicated by the height to which the air chamber of the spirometer rises; and by means of a scale placed in connection with this, the number of cubic inches is read off. In healthy men, the respiratory capacity varies chiefly with the stature, weight, and age. It was found by Hutchinson, from whom most of our information on 190 HAND-BOOK OF PHYSIOLOGY. this subject is derived, that at a temperature of 60° F., 225 cubic inches is the average vital or respiratory capacity of a healthy person, five feet seven inches in height Circumstances affecting the amount of respiratory capacity. — For every inch of height above this standard the capacity is" increased, on an average, by eight cubic inches; and for every inch below, it is diminished by the same amount. The influence of weight on the capacity of respiration is less manifest and considerable than that of height; and it is difficult to arrive at any definite conclusions on this point, because the natural average weight of a healthy man in relation to stature has not yet been determined. As a general statement, however, it may be said that the capacity of respiration is not affected by weights under 161 pounds, or 11|- stones; but that, above this point, it is diminished at the rate of one cubic inch for every additional pound up to 196 pounds, or 14 stones. By age, the capacity appears to be increased from about the fifteenth to the thirty-fifth year, at the rate of five cubic inches per year; from thirty-five to sixty-five it diminishes at the rate of about one and a half cubic inch per year; so that the capacity of respiration of a man of sixty years old would be about 30 cubic inches less than that of a man forty years old, of the same height and weight. (John Hutchinson.) Number of Respirations, and Relation to the Pulse. — The number of respirations in a healthy adult person usually ranges from fourteen to eighteen per minute. It is greater in infancy and childhood. It varies also much according to different circumstances,. such as exercise or rest, health, or disease, etc. Variations in the number of respirations correspond ordinarily with similar variations in the pulsations of the heart. In health the proportion is about 1 to 4, or 1 to 5, and when the rapidity of the heart's action is increased, that of the chest movement is commonly increased also; but not in every case in equal proportion. It happens occasionally in disease, especially of the lungs or air-passages, Vthat the number of respiratory acts increases in quicker proportion than the beats of the pulse; and, in other affections, much more commonly, that the number of the pulses is greater in proportion than that of the respirations. There can be no doubt that the number of respirations of any given animal is largely affected by its size. Thus, comparing animals of the same kind, in a tiger (lying quietly) the number of respirations was 20 per minute, while in a small leopard (lying quietly) the number was 30. In a small monkey 40 per minute; in a large baboon, 20. The rapid, panting respiration of mice, even when quite still, is familiar, and contrasts strongly with the slow breathing of a large animal such as the elephant (eight or nine times per minute). These facts may be explained as follows: — The heat-producing power of any given animal depends largely on its bulk, while its loss of heat depends to a great extent upon the surface area of its body. If of two animals of similar shape, one be ten times as long as the other, the area of the large animal RESPIRATION. I 9 1 (representing its loss of heat) is 100 times that of the small one, while its bulk (representing production of heat) is about 1000 times as great. Thus in order to balance its much greater relative loss of heat, the smaller animal must vhave all its vital functions, circulation, respiration, etc., carried on much more rapidly. Force of Inspiratory and Expiratory Muscles.— The force with which the inspiratory muscles are capable of acting is greatest in individ- uals of the height of from five feet seven inches to five feet eight inches,, and will elevate a column of three inches of mercury. Above this height, the force decreases as the stature increases; so that the average of men of six feet can elevate only about two and a half inches of mercury. The force manifested in the strongest expiratory acts is, on the average, one- third greater than that exercised in inspiration. But this difference is in u'reat measure due to the power exerted by the elastic reaction of the walls of the chest; and it is also much influenced by the disproportionate strength which the expiratory muscles attain, from their being called into use for other purposes than that of simple expiration. The force of the inspiratory act is, therefore, better adapted than that of the expiratory for testing the muscular strength of the body. (John Hutchinson.) The instrument used by Hutchinson to gauge the inspiratory and ex- piratory power was a mercurial manometer, to which was attached a tube fitting the nostrils, and through which the inspiratory or expiratory effort was made. The following table represents the results of numerous experiments: Power of Power of Inspiratory Muscles. Expiratory Muscles. 1-5 in. Weak 2'0 in. 2-0 3-5 4-5 5-5 6-0 7-0 Ordinary . . 2'5 Strong . . . 3'5 Very strong . .4*5 Kemarkable . . 5'8 Very remarkable . 7*0 Extraordinary . 8 '5 Very extraordinary . 10 '0 . . The greater part of the force exerted in deep inspiration is employed in overcoming the resistance offered by the elasticity of the walls of the •chest and of the lungs. The amount of this elastic resistance was estimated by observing the elevation of a column of mercury raised by the return of air forced, after death, into the lungs, in quantity equal to the known capacity of respira- tion during life; and Hutchinson calculated, according to the well-known hydrostatic law of equality of pressures (as shown in the Bramah press), that the total force to be overcome by the muscles in the act of inspiring ;200 cubic inches of air is more than 450 Ibs. 192 HAND-BOOK OF PHYSIOLOGY. The elastic force overcome in ordinary inspiration is, according to the same authority, equal to about 170 Ibs. Douglas Powell has shown that within the limits of ordinary tranquil respiration, the elastic resilience of the walls of the chest favors inspira- tion; and that it is only in deep inspiration that the ribs and rib-cartilages offer an opposing force to their dilatation. In other words, the elastic resilience of the lungs, at the end of an act of ordinary breathing, has drawn the chest -walls within the limits of their normal degree of expan- sion. Under all circumstances, of course, the elastic tissue of the lungs opposes inspiration, and favors expiration. Functions of Muscular Tissue of Lungs.— It is possible that the contractile power which the bronchial tubes and air-vesicles possess, by means of their muscular fibres may (1) assist in expiration; but it is more likely that its chief purpose is (2) to regulate and adapt, in some measure, the quantity of air admitted to the lungs, and to each part of them, according to the supply of blood; (3) the muscular tissue contracts upon and gradually expels collections of mucus, which may have accumulated within the tubes, and cannot be ejected by forced expiratory efforts, owing to collapse or other morbid conditions of the portion of lung connected with the obstructed tubes (Gairdner). (4) Apart from any of the before- mentioned functions, the presence of muscular fibre in the walls of a hol- low viscus, such as a lung, is only what might be expected from analogy with o.ther organs. Subject as the lungs are to such great variation in size it might be anticipated that the elastic tissue, which enters so largely into their composition, would be supplemented by the presence of much muscular fibre also. EESPIRATOEY CHANGES IK THE Am AKD IK THE BLOOD. A. In the Air. Composition of the Atmosphere. — The atmosphere we breathe has, in every situation in which it has been examined in it* natural state, a nearly uniform composition. It is a mixture of oxygen, nitrogen, carbonic acid, and watery vapor, with, commonly, traces of other gases, as ammonia, sulphuretted hydrogen, etc. Of every 100 volumes of pure atmospheric air, 79 volumes (on an average) consist of nitrogen, the remaining 21 of oxygen. By weight the proportion is N. 75, 0. 25. The proportion of carbonic acid is extremely small; 10,000 volumes of atmospheric air con- tain only about 4 or 5 of carbonic acid. The quantity of watery vapor varies greatly according to the temper- ature and other circumstances, but the atmosphere is never without some. In this country, the average quantity of watery vapor in the atmosphere is 1 '40 per cent. RESPIRATION. 193 Composition of Air which has been breathed. — The changes effected by respiration in the atmospheric air are: 1, an increase of temperature; 2, an increase in the quantity of carbonic acid; 3, a diminution in the quan- tity of oyxgen; 4, a diminution of volume; 5, an increase in the amount of watery vapor; 6, the addition of a minute amount of organic matter and of free ammonia. 1. The expired air, heated by its contact with the interior of the lungs, is (at least in most climates) hotter than the inspired air. Its temperature varies between 97° and 99.5° F. (36° — 37 '5° C.), the lower temperature being observed when the air has remained but a short time in the lungs. Whatever may be the temperature of the air when inhaled, it nearly acquires that of the blood before it is expelled from the chest. 2. The Carbonic Acid in respired air is always increased; but the quantity exhaled in a given time is subject to change from various cir- cumstances. From every volume of air inspired, about 4 '8 per cent, of oxygen is abstracted; while a rather smaller quantity, 4*3, of carbonic acid is added in its place: the air will contain, therefore, 434 vols. of car- bonic acid in 10,000. Under ordinary circumstances, the quantity of carbonic acid exhaled into the air breathed by a healthy adult man amounts to 1346 cubic inches, or about 636 grains per hour. According to this esti- mate, the weight of carbon excreted from the lungs is about 173 grains per hour, or rather more than 8 ounces in twenty-four hours. These quantities must be considered approximate only, inasmuch as various cir- cumstances, even in health, influence the amount of carbonic acid ex- creted, and, correlatively, the amount of oxygen absorbed. Circumstances influencing the amount of carbonic acid excreted. — The following are the chief: — Age and sex. 'Eespiratory movements. Ex- ternal temperature. Season of year. Condition of respired air. Atmos- pheric conditions. Period of the day. Food and drink. Exercise and sleep. a. Age and Sex. — The quantity of carbonic acid exhaled into the air breathed by males, regularly increases from eight to thirty years of age; from thirty to fifty the quantity, after remaining stationary for awhile, gradually diminishes, and from fifty to extreme age it goes on diminish- ing, till it scarcely exceeds the quantity exhaled at ten years old. In females (in whom the quantity exhaled is always less than in males of the same age) the same regular increase in quantity goes on from the eighth year to the age of puberty, when the quantity abruptly ceases to increase, and remains stationary so long as they continue to menstruate. When menstruation has ceased, it soon decreases at the same rate as it does in old men. b. Respiratory Movements. — The more quickly the movements of respiration are performed, the smaller is the proportionate quantity of carbonic acid contained in each volume of the expired air. Although, however, the proportionate quantity of carbonic acid is thus diminished during frequent respiration, yet the absolute amount exhaled into the air within a given time is increased thereby, owing to the larger quantity of VOL. I.— 13. 194 HAND-BOOK OF PHYSIOLOGY. air which is breathed in the time. The last half of a volume of expired air contains more carbonic acid than the half first expired; a circumstance •which is explained by the one portion of air coming from the remote part of the lungs, where it has been in more immediate and prolonged contact with the blood than the other has, which comes chiefly from the larger bronchial tubes. c. External temperature. — The observation made by Vierordt at vari^ ous temperatures between 38° F. and 75° T. (3'4°— 23 '8° C.) show, for warm-blooded animals, that within this range, every rise equal to 10° F. causes a diminution of about two cubic inches in the quantity of carbonic acid exhaled per minute. d. Season of the Year. — The season of the year, independently of temperature, materially influences the respiratory phenomena; spring being the season of the greatest, and autumn of the least activity of the res- piratory and other functions. (Edward Smith.) e. Purity of the Respired Air. — The average quantity of carbonic acid given out by the lungs constitutes about 4*3 per cent, of the expired air; but if the air which is breathed be previously impregnated with car- bonic acid (as is the case when the same air is frequently respired), then the quantity of carbonic acid exhaled becomes much less. /. Hygrometric State of Atmosphere. — The amount of carbonic acid exhaled is considerably influenced by the degree of moisture of the atmos- phere, much more being given off when the air is moist than when it is dry. (Lehmann.) g. Period of the Day. — During the daytime more carbonic acid is ex- haled than corresponds to the oxygen absorbed; while, on the other hand, at night very much more oxygen is absorbed than is exhaled in carbonic acid. There is, thus, a reserve fund of oxygen absorbed by night to meet the requirements of the day. If the total quantity of carbonic acid ex- haled in 24 hours be represented by 100, 52 parts are exhaled during the day, and 48 at night. While, similarly, 33 parts of the oxygen are ab- sorbed during the day, and the remaining 67 by night. (Pettenkofer and Voit.) h. Food and Drink. — By the use of food the quantity is increased, whilst by fasting it is diminished; it is greater when animals are fed on farinaceous food than when fed on meat. The effects produced by spiritu- ous drinks depend much on the kind of drink taken. Pure alcohol tends rather to increase than to lessen respiratory changes, and the amount therefore of carbonic acid expired; rum, ale, and porter, also sherry, have very similar effects. On the other hand, brandy, whisky, and gin, par- ticularly the latter, almost always lessened the respiratory changes, and consequently the amount of carbonic' acid exhaled. (Edward Smith.) i. Exercise — Bodily exercise, in moderation, increases the quantity to about one-third more than it is during rest: and for about an hour after exercise the volume of the air expired in the minute is increased about 118 cubic inches: and the quantity of carbonic acid about 7*8 cubic inches per minute. Violent exercise, such as full labor on the tread wheel, still further increases the amount of the acid exhaled. (Edward Smith.) A larger quantity is exhaled when the barometer is low than when it is high. 3. The oxygen is diminished, and its diminution is generally propor- tionate to the increase of the carbonic acid. RESPIRATION. 195 For every volume of carbonic acid exhaled into the air, 1 -17421 volumes of oxygen are absorbed from it, and 1346 cubic inches, or 636 grains, be- ing exhaled in the hour, the quantity of oxygen absorbed in the same tirrte is 1584 cubic inches, or 542 grains. According to this estimate, there is more oxygen absorbed than is exhaled with carbon to form carbonic acid. 4. The volume of air expired in a given time is less than that of the air inspired (allowance being made for the expansion in being heated), niul that the loss is due to a portion of oxygen absorbed and not returned in the exhaled carbonic acid, all observers agree, though as to the actual quantity of oxygen so absorbed, they differ even widely. The amount of oxygen absorbed is on an average 4 -8 per cent., so that the expired air contains l(j'2 volumes per cent, of that gas. The quantity of oxygen that does not combine with the carbon given off in carbonic acid from the lungs is probably disposed of in forming some of the carbonic acid and water given off from the skin, and in com- bining with sulphur and phosphorus to form part of the acids of the sul- phates and phosphates excreted in the urine, and probably also, with the nitrogen of the decomposing nitrogenous tissues. (Bence Jones.) The quantity of oxygen in the atmosphere surrounding animals, ap- pears to have very little influence on the amount of this gas absorbed by them, for the quantity consumed is not greater even though an excess of oxygen be added to the atmosphere experimented with. It has often been discussed whether Nitrogen is absorbed by or exhaled from the lungs during respiration. At present, all that can be said on the subject is that, under most circumstances, animals appear to expire a very small quantity above that which exhts in the inspired air. During prolonged fasting, on the contrary, a small quantity appears to be ab- sorbed. 5. The watery vapor is increased. The quantity emitted is, as a gen- eral rule, sufficient to saturate the expired air, or very nearly so. Its abso- lute amount is, therefore, influenced by the following circumstances, (1), by the quantity of air respired; for the greater this is, the greater also will be the quantity of moisture exhaled. (2), by the quantity of watery vapor contained in the air previous to its being inspired; because the greater this is, the less will be the amount required to complete the satu- ration of the air; (3), by the temperature of the expired air; for the higher this is, the greater will be the quantity of watery vapor required to saturate the air; (4), by the length of time which each volume of in- spired air is allowed to remain in the lungs; for although, during ordinary respiration, the expired air is always saturated with watery vapor, yet when respiration is performed very rapidly the air has scarcely time to be raised to the highest temperature, or be fully charged with moisture ere it is expelled. 196 HAND-BOOK OF PHYSIOLOGY. . t The quantity of water exhaled from the lungs in twenty-four hours ranges (according to the various modifying circumstances already men- tioned) from about 6 to 27 ounces, the ordinary quantity being about 9 or 10 ounces. Some of this is probably formed by the chemical combina- tion of oxygen with hydrogen in the system; but the far larger propor- tion of it is water which has been absorbed, as such, into the blood from the alimentary canal, and which is exhaled from the surface of the air- passages and cells, as it is from the free surfaces of all moist animal mem- branes, particularly at the high temperature of warm-blooded animals. 6. A small quantity of ammonia is added to the ordinary constituents of expired air. It seems probable, however, both from the fact that this substance cannot be always detected, and from its minute amount when present, that the whole of it may be derived from decomposing particles of food left in the mouth, or from carious teeth or the like; and that it is, therefore, only an accidental constituent of expired air. 7. The quantity of organic matter in the breath is about 3 grains in twenty-four hours. (Ransome.) The following represents the kind of experiment by which the fore- going facts regarding the excretion of carbonic acid, water, and organic matter, have been established. A bird or mouse is placed in a large bottle, through the stopper of which two tubes pass, one to supply fresh air, and the other to carry off that which has been expired. Before entering the bottle, the air is made to bubble through a strong solution of caustic potash, which absorbs the carbonic acid, and then through lime-water, which by remaining limpid, proves the absence of carbonic acid. The air which has been breathed by the animal is made to bubble through lime water, which at once becomes turbid and soon quite milky from the precipitation of cal- cium carbonate; and it finally passes through strong sulphuric acid, which, by turning brown, indicates the presence of organic matter. The watery vapor in the expired air will condense inside the bottle if the sur- face be kept cool. By means of an apparatus sufficiently large and well constructed, exp Briments of the kind have been made extensively on man. METHODS BY WHICH THE KESPIRATORY CHANGES IN THE AIR ARE EFFECTED. The method by which fresh air is inhaled and expelled from the lungs has been considered. It remains to consider how it is that the blood absorbs oxygen from, and gives up carbonic acid to, the air of the alveoli. In the first place, it must be remembered that the tidal air only amounts to about 25. — 30 cubic inches at each inspiration, and that this is of course insufficient to fill the lungs, but it mixes with the stationary air by diffu- sion, and so supplies to it new oxygen. The amount of oxygen in expired air, which may be taken as the average composition of the mixed air in RESPIRATION. 197 the lungs, is about 16 to 17 per cent.; in the pulmonary alveoli it may be rather less than this. From this air the venous blood has to take up oxy- gen in the proportion of 8 to 12 vols. in every hundred volumes of blood, as the difference between the amount of oxygen, in arterial and venous blood is no less than that. It seems therefore somewhat difficult to un- derstand how this can be accomplished at the low oxygen tension of the pulmonary air. But as was pointed out in a previous Chapter (IV.), the oxygen is not simply dissolved in the blood, but is to a great extent chemically combined with the haemoglobin of the red corpuscles; and when a fluid contains a body which enters into loose chemical combination in this way with a gas, the tension of the gas in the fluid is not directly pro- portional to the total quantity of the ga£ taken up by the fluid, but to the excess above the total quantity which the substance dissolved in the fluid is capable of taking up (a known quantity in the case of haemoglobin, viz., 1-59 cm. for one grm. haemoglobin). Ojt the other hand, if the sub- stance be not saturated, i.e., if it be not combined with as much of the gas as it is capable of taking up, further combination leads to no increase of its tension. However, there is a point at which the haemoglobin gives up its oxygen when it is exposed to a low partial pressure of oxygen, and there is also a point at which it neither takes up nor gives out oxygen; in the case of arterial blood of the dog, this is found to be when the oxy- gen tension of the atmosphere is equal to 3*9 per cent, (or 29*6 mm. of mercury), which is equivalent to saying that the oxygen tension of arterial blood is 3 -9 per cent. ; venous blood, in a similar manner, has been found to have an oxygen tension of 2*8 per cent. At a higher temperature, the tension is raised, as there is a greater tendency at a high temperature for the chemical compound to undergo dissociation. It is therefore easy to see that the oxygen tension of the air of the pulmonary alveoli is quite sufficient, even supposing it much less than that of the expired air, to enable the venous blood to take up oxygen, and what is more, it will take it up until the haemoglobin is very nearly saturated with the gas. As regards the elimination of carbonic acid from the blood, there is evidence to show that it is given up by a process of simple diffusion, the only condition necessary for the process being that the tension of the car- tbonic acid of the air in the pulmonary alveoli should be less than the ten- sion of the carbonic acid in venous blood. The carbonic acid tension of the alveolar air probably does not exceed in the dog 3 or 4 per cent., while that of the venous blood is 5 '4 per cent., or equal to 41 mm. of mercury. B. Respiratory Changes in the Blood. * Circulation of Blood in the Respiratory Organs. — To be ex- )( posed to the air thus alternately moved into and out of the air cells and minute bronchial tubes, the blood is propelled from the right ventricle 198 HAND-BOOK OF PHYSIOLOGY. through the pulmonary capillaries in steady streams, and slowly enough to permit every minute portion of it to be for a few seconds exposed to the air, with only the thin walls of the capillary vessels and the air-cells intervening. The pulmonary circulation is of the simplest kind: for the pulmonary artery branches regularly; its successive branches run in straight lines, and do not anastomose: the capillary plexus is uniformly spread over the air-cells and intercellular passages; and the veins derived from it proceed in a course as simple and uniform as that of the arteries, their branches converging but not anastomosing. The veins have no- valves, or only small imperfect ones prolonged from their angles of junc- tion, and incapable of closing the orifice of either of the veins between which they are placed. The pulmonary circulation also is unaffected by changes of atmospheric pressure, and is not exposed to the influence of the pressure of muscles: the force by which it is accomplished, and the course of the blood, are alike simple. Changes produced in the Blood by Respiration. — The most obvious change which the blood of the pulmonary artery undergoes in its passage through the lungs is 1st, that of color, the dark crimson of venous blood being exchanged for the bright scarlet of arterial blood; 2nd, and in connection with the preceding change, it gains oxygen; 3rd, it loses carbonic acid; tth, it becomes slightly cooler (p. 193); 5th, it coagu- lates sooner and more firmly, and, apparently, contains more fibrin (see p. 87). The oxygen absorbed into the blood from the atmospheric air in the lungs is combined chemically with the haemoglobin of the red blood-corpuscles. In this condition it is carried in the arterial blood to- the various parts of the body, and brought into near relation or contact with the tissues. In these tissues, and in the blood which circulates in, them, a certain portion of the oxygen, which the arterial blood contains, disappears, and a proportionate quantity of carbonic acid and water is formed. The venous blood, containing the new-formed carbonic acid, returns to the lungs, where a portion of the carbonic acid is exhaled, and a fresh supply of oxygen is taken in. Mechanism of Various Respiratory Actions. — It will be well here, perhaps, to explain some respiratory acts, which appear at first sight somewhat complicated, but cease to be so when the mechanism by which they are performed is clearly understood. The accompanying dia- gram (Fig. 161) shows that the cavity of the chest is separated from that of the abdomen by the diaphragm, which, when acting, will lessen its curve, and thus descending, will push downward and forward the ab- dominal viscera; while the abdominal muscles have the opposite effect, and in acting will push the viscera upward and backward, and with them the diaphragm, supposing its ascent to be not from any cause inter- fered with. From the same diagram it will be seen that the lungs com- municate with the exterior of the body through the glottis, and further RESPIRATION. 199 on through the mouth and nostrils — through either of them separately, or through both at the same time, according to the position of the soft palate. The stomach communicates with the exterior of the body through the oesophagus, pharynx, and mouth; while below the rectum opens at the anus, and the bladder through the urethra. All these openings, through which the hollow viscera communicate with the exterior of the body, are guarded by muscles, called sphincters, which can act independ- ently of each other. The position of the latter is indicated in the dia- gram. FIG. 161. Sighing. — In sighing there is a rather prolonged inspiration; the air almost noiselessly passing in through the glottis, and by the elastic recoil of the lungs and chest- walls, and probably also of the abdominal walls, being rather suddenly expelled again. Now, in the first, or inspiratory part of this act, the descent of the diaphragm presses the abdominal viscera downward, and of course this pressure tends to evacuate the contents of such as communicate with the exterior of the body. Inasmuch, however, as their various openings are guarded by sphincter muscles, in a state of constant tonic contraction, 200 HAND-BOOK OF PHYSIOLOGY. there is no escape of their contents, and air simply enters the lungs. In the second, or expiratory part of the act of sighing, there is also pressure made on the abdominal viscera in the opposite direction, by the elastic or muscular recoil of the abdominal walls; but the pressure is relieved by the escape of air through the open glottis, and the relaxed diaphragm is pushed up again into its original position. The sphincters cf the stomach, rectum, and bladder, act as before. Hiccough resembles sighing in that it is an inspiratory act; but the inspiration is sudden instead of gradual, from the diaphragm acting sud- denly and spasmodically; and the air, therefore, suddenly rushing through the unprepared rima glottidis, causes vibration of the vocal cords, and the peculiar sound. Coughing. — In the act of coughing, there is most often first an in- spiration, and this is followed by an expiration; but when the lungs have been filled by the preliminary inspiration, instead of the air being easily let out again through the glottis, the latter is momentarily closed by the approximation of the vocal cords, and then the abdominal muscles, strongly acting, push up the viscera against the diaphragm, and thus make pressure on the air in the lungs until its tension is sufficient to burst open noisily the vocal cords which oppose its outward passage. In this way a considerable force is exercised, and mucus or any other matter that may need expulsion from the lungs or trachea is quickly and sharply expelled by the outstreaming current of air. Now it is evident on reference to the diagram (Fig. 161), that pressure exercised by the abdominal muscles in the act of coughing, acts as for- cibly on the abdominal viscera as on the lungs, inasmuch as the viscera form the medium by which the upward pressure on the diaphragm is made, and of necessity there is quite as great a tendency to the expulsion of their contents as of the air in the lungs. The instinctive, and if necessary, voluntarily increased contraction of the sphincters, however, prevents any escape at the openings guarded by them, and the pressure is effective at one part only, namely, the rima glottidis. Sneezing. — The same remarks that apply to coughing, are almost exactly applicable to the act of sneezing; but in this instance the blast of air, on escaping from the lungs, is directed, by an instinctive con- traction of the pillars of the fauces and descent of the soft palate, chiefly through the nose, and any offending matter is thence expelled. Speaking. — In speaking, there is a voluntary expulsion of air through the glottis by means of the expiratory muscles; and the vocal cords are put, by the muscles of the larynx, in a proper position and state of tension for vibrating as the air passes over them, and thus producing sound. The sound is moulded into words by the tongue, teeth, lips, etc. — the vocal cords producing the sound only, and having nothing to do with articu- lation. RESPIRATION. 201 Singing. — Singing resembles speaking in the manner of its produc- tion; the luryngetil muscles, by variously altering the position and degree of tension of the vocal cords, producing the different notes. Words used in the act of singing are of course framed, as in speaking, by the tongue, teeth, lips, etc. Sniffing. — Sniffing is produced by a somewhat quick action of the diaphragm and other inspiratory muscles. The mouth is, however, closed, and by these means the whole stream of air is made to enter by the nostrils. The alge nasi are, commonly, at the same time, instinctively dilated. Sobbing. — Sobbing consists in a series of convulsive inspirations, at the moment of which the glottis is usually more or less closed. Laughing. — Laughing is a series of short and rapid expirations. Yawning. — Yawning is an act of inspiration, but is unlike most of the preceding actions in being always more or less involuntary. It is attended by a stretching of various muscles about the palate and lower jaw, which is probably analogous to the stretching of the muscles of the limbs in which a weary man finds relief, as a voluntary act, when they have been some time out of action. The involuntary and reflex character of yawn- ing depends probably on the fact that the muscles concerned are them- selves at all times more or less involuntary, and require, therefore, something beyond the exercise of the will to set them in action. For the same reason, yawning, like sneezing, cannot be well performed voluntarily. Sucking. — Sucking is not properly a respiratory act, but it may be most conveniently considered in this place. It is caused chiefly by the depressor muscles of the os hyoides. These, by drawing downward and backward the tongue and floor of the mouth, produce a partial vacuum in the latter: and the weight of the atmosphere then acting on all sides tends to produce equilibrium on the inside and outside of the mouth as best it may. The communication between the mouth and pharynx is completely shut off by the contraction of the pillars of the soft palate and descent of the latter so as to touch the back of the tongue; and the equi- librium, therefore, can be restored only by the entrance of something through the mouth. The action, indeed, of the tongue and floor of the mouth in sucking may be compared to that of the piston in a syringe, and the muscles which pull down the os hyoides and tongue, to the power which draws the handle. Influence of the Nervous System in Respiration.— Like all other functions of the body, the discharge of which is necessary to life, respiration must be essentially an involuntary act. Else, life would be in constant danger, and would cease on the loss of consciousness for a few moments, as in sleep. But it is also necessary that respiration should be to some extent under the control of the will. For were it not so, it would 4 202 HAND-BOOK OF PHYSIOLOGY. be impossible to perform those voluntary respiratory acts which have been •just enumerated and explained, as speaking, singing, and the like. The respiratory movements and their rhythm, so far as they are invol- untary and independent of consciousness (as on all ordinary occasions) are under the governance of a nerve-centre in the medulla oblongata correspond- ing with the origin of the pneumogastric nerves; that is to say, the motor nerves, and through them the muscles concerned in the respiratory move- ments, are excited by a stimulus which issues from this part of the nerv- ous system. How far the medulla acts automatically, i.e., how far the stimulus originates in it, or how far it is merely a nerve-centre for reflex action, is not certainly known. Probably, as will be seen, both events happen; and, in both cases, the stimulus is the result of the condition of the blood. The respiratory centre is bilateral or double, since the respiratory movements continue after the medulla at this point is divided in the mid- dle line. As regards its supposed automatic action, it has been shown that if the spinal cord be divided below the medulla, and both vagi be divided so that no afferent impulses can reach it from below, the nasal and laryn- geal respiration continues, and the only possible course of the afferent im- pulses would be through the cranial nerves; and when the cord and me- dulla are intact the division of these produces no effect upon respiration, so that it appears evident that the afferent stimuli are not absolutely necessary for maintaining the respiratory movements. But although au- tomatic in its action the respiratory centre may be reflexly excited, and the chief channel of this reflex influence is the vagus nerve; for when the nerve of one side is divided, respiration is slowed, and if both vagi be cut the respiratory action is still slower. The influence of the vagus trunk upon it is twofold, for if the nerve be divided below the origin of the superior laryngeal branch and the cen- tral end be stimulated, respiratory movements are increased in rapidity, and indeed follow one another so quickly if the stimuli be increased in number, that after a time cessation of respiration in inspiration follows from a tetanus of the respiratory muscles (diaphragm). Whereas if the superior laryngeal branch be divided, although no effect, or scarcely any, follows the mere division, on stimulation of the central end respiration is slowed, and after a time, if the stimulus be increased, stops, but not in inspiration as in the other case, but in expiration. Thus the vagus trunk contains fibres which slow and fibres which accelerate respiration. If we adopt the theory of a doubly acting respiratory centre in the floor of the medulla, one tending to produce inspiration and the other expiration, and acting in antagonism as it were, so that there is a gradual increase in the tendency to produce respiratory action, until it culminates in an in- spiratory effort, which is followed by a similar action of the expiratory RESPIRATION. 203 part of the centre, producing an expiration, we must look upon the main trunk of" the vagus as aiding the inspiratory, and of the superior laryngeal as aiding the expiratory part of the centre, the first nerve possibly in- hibiting the action of the expiratory centre, whilst it aids the inspiratory, and the latter nerve having the very opposite effect. But inasmuch as the respiration is slowed on division of the vagi, and not quickened or affected manifestly on simple division of the superior laryngeal, it must be supposed that the vagi fibres are always in action, whereas the superior laryngeal fibres are not. It appears, however, that there are, in some animals at all events, subordinate centres in the spinal cord which are able, under certain con- ditions, to discharge the function of the chief medullary centre. The centre in the medulla may be influenced not only by afferent im- pulses proceeding along the vagus and laryngeal nerves but also by those proceeding from the cerebrum,, as well as by impressions made upon the nerves of the skin, or upon part of the fifth nerve distributed to the nasal mucous membrane, or upon other sensory nerves, as is exemplified by the deep inspiration which follows the application of cold to the surface of the skin, and by the sneezing which follows the slightest irritation of the nasal mucous membrane. At the time of birth, the separation of the placenta, and the conse- quent non-oxygenation of the foetal blood, are the circumstances which immediately lead to the issue of automatic impulses to action from the respiratory centre in the medulla oblongata. But the quickened action which ensues on the application of cold air or water, or other sudden stimulus, to the skin, shows well the intimate connection which exists between this centre and other parts which are not ordinarily connected with the function of respiration. Methods of Stimulation of the Respiratory Centre.— It is now necessary to consider the method by which the centre or centres are stim- ulated themselves, as well as the manner in which the afferent vagi impulses are produced. The more venous the blood, the more marked are the inspiratory im- pulses, and if the air is prevented from entering the chest, in a short time the respiration becomes very labored. Its cessation is followed by an abnormal rapidity of the inspiratory acts, which make up even in depth for the previous stoppage. The condition caused by obstruction to the entrance of air, or by any circumstance by which the oxygen of the blood is used up in an abnormally quick manner, is known as dyspnaa, and as the aeration of the blood becomes more and more interfered with, not only are the ordinary respiratory muscles employed, but also those extra- ordinary muscles which have been previously enumerated (p. 186), so that as the blood becomes more and more venous the action of the medullary centre becomes more and more active. The question arises as to what 204 HAND-BOOK OF PHYSIOLOGY. condition of the venous bbod causes this increased activity, whether it is due to deficiency of oxygen or excess of carbonic acid in the blood. This has been answered by the experiments, which show on the one hand that dyspnoea occurs when there is no obstruction to the exit of carbonic acid, as when an animal is placed in an atmosphere of nitrogen, and therefore cannot be due to the accumulation of carbonic acid, and sec- ondly, that if plenty of oxygen be supplied, dyspnoea proper does not. occur, although the carbonic acid of the blood is in excess. The respir- atory centre is evidently stimulated to action by the absence of sufficient oxygen in the blood circulating in it. The method by which the vagus is stimulated to conduct afferent im- pulses, influencing the action of the respiratory centre, appears to be by the venous blood circulating in the lungs, or as some say by the condition of the air in the pulmonary alveoli. And if either of these be the stimuli it will be evident that as the condition of venous blood stimulates the peripheral endings of the vagus in the lungs, the vagus action which tends to help oil the discharge of inspiratory impulses from the centre, must tend also to increase the activity of the centre, when the blood in the lungs becomes more and more venous. No doubt the venous condition of the blood will affect all the sensory nerves in a similar manner, but it has been shown that the circulation of too little blood through the centre is quite sufficient by itself for the purpose; as when its blood sup- ply is cut off increased inspiratory actions ensue. Effects of Vitiated Air. — Ventilation.— We have seen that the air expired from the lungs contains a large proportion of carbonic acid and a minute amount of organic putrescible matter. Hence it is obvious that if the same air be breathed again and again, the proportion of carbonic acid and organic matter will constantly increase till fatal results are produced; but long before this point is reached, uneasy sensations occur, such as headache, languor, and a sense of oppres- sion. It is a remarkable fact that the organism after a time adapts itself to such a vitiated atmosphere, and that a person soon comes to breathe, without sensible inconvenience, an atmosphere which, when he first entered it, felt intolerable. Such an adaptation, however, can only take place at the expense of a depression of all the vital functions, which must be injurious if long continued or often repeated. This power of adaptation is well illustrated by the experiments of Claude Bernard. A sparrow is placed under a bell-glass of such a size that it will live for three hours. If now at the end of the second hour (when it could have survived another hour) it be taken out and a fresh healthy sparrow introduced, the latter will perish instantly. The adaptation above spoken of is a gradual and continuous one: thus a bird which will live one hour in a pint of air will live three hours in two pints; and if two birds of the same species, age, and size, be placed RESPIRATION. 205 a quantity of air in which either, separately, would survive three >urs, they will not live 1£ hour, but only 1£ hour. From what has been said it must be evident that provision for a con- it and plentiful supply of fresh air, and the removal of that which is itiaU'd, is of far greater importance than the actual cubic space per head occupants. Not less than 2000 cubic feet per head should be allowed sleeping apartments (barracks, hospitals, etc.), and with this allow- the air can only be maintained at the proper standard of purity by ich a system of ventilation as provides for the supply of 1500 to 2000 ibic feet of fresh air per head per hour. (Parkes.) THE EFFECT OF RESPIRATION ON THE CIRCULATION. Inasmuch as the heart and great vessels are situated in the air-tight lorax, they are exposed to a certain alteration of pressure when the FIG. 162. — Diagram of an apparatus illustrating the effect of inspiration upon the heart and great vessels within the thorax.— I, the thorax at rest; If, during inspiration: p, represents the diaphragm when relaxed; D' when contracted (it must be remembered that this position is a mere diagram), i. e., when the capacity of the thorax is enlarged; H, the heart; v, the veins entering it, and A, the aorta; R/. Ll, the right and left lung; T, the trachea; M, mercurial manometer in connection with the pleura. The increase in the capacity of the box representing the thorax is seen to dilate the heart as well as the lungs, and so to pump in blood through v, whereas the valve prevents reflex through A. The position of the mercury in M shows also the suction which is taking place. (Landois.) capacity of the latter is increased; for although the expansion of the lungs during inspiration tends to counterbalance this increase of area, it never quite does so, since part of the pressure of the air which is drawn 206 HAND-BOOK OF PHYSIOLOGY. into the chest through the trachea is expended in overcoming the elas- ticity of the lungs themselves. The amount thus used up increases as the lungs become more and more expanded, so that the pressure inside the thorax during inspiration as far as the heart and great vessels are con- cerned, never quite equals that outside, and at the conclusion of inspira- tion is considerably less than the atmospheric pressure. It has been ascer- tained that the amount of the pressure used up in the way above described, varies from 5 or 7 mm. of mercury during the pause, and to 30 mm. of mercury when the lungs are expanded at the end of a deep inspiration, so that it will be understood that the pressure to which the heart and great vessels are subjected diminishes as inspiration progresses. It will be understood from the accompanying diagram how, if there wrere no lungs in the chest, but if its capacity were increased, the effect of the increase would be expended in pumping blood into the heart from the veins, but even with the lungs placed as they are, during inspiration the pressure outside the heart and great vessels is diminished, and they have therefore a tendency to expand and to diminish the intra-vascular pres- sure. The diminution of pressure within the veins passing to the right auricle and within the right auricle itself, will draw the blood into the thorax, and so assist the circulation: this suction action aiding, though independently, the suction power of the diastole of the auricle about which we have previously spoken (p. 124). The effect of sucking more blood into the right auricle will, cceteris paribus, increase the amount passing through the right ventricle, which also exerts a similar suction action, and througji the lungs into the left auricle and ventricle and thus into the aorta, and this tends to increase the arterial tension. The effect of the diminished pressure upon the pulmonary vessels will also help toward the same end, i.e., an increased flow through the lungs, so that as far as the heart and its veins are concerned inspiration increases the blood pressure in the arteries. The effect of inspiration upon the aorta and its branches within the thorax would be, however, contrary; for as the pressure outside is diminished the vessels would tend to expand, and thus to diminish the tension of the blood within them, but inasmuch as the large arteries are capable of little expansion beyond their natural calibre, the diminution of the arterial tension caused by this means would be in- sufficient to counteract the increase of arterial tension produced by the effect of inspiration upon the veins of the chest, and the balance of the whole action would be in favor of an increase of arterial tension during the inspiratory period. But if a tracing of the variation be taken at the same time that the respiratory movements are recorded, it will be found that, although speaking generally, the arterial tension is increased during inspiration, the maximum of arterial tension does not correspond with the acme of inspiration (Fig. 163). As regards the effect of expiration, the capacity of the chest is dimin- RESPIRATION. •207 ished, and the intra-thoracic pressure returns to the normal, which is not exactly equal to the atmospheric, pressure. The effect of this on the veins is to increase their intra-vascular pressure, and so to diminish the flow of blood into the left side of the heart, and with it the arterial ten- sion, but this is almost exactly balanced by the necessary increase of arterial tension caused by the increase of the extra-vascular pressure of the aorta and large arteries, so that the arterial tension is not much affected during expiration either way. Thus, ordinary expiration does one limb of a manometer with the pleural cavity. Inspiration begins at i and expiration at e. The intra-thoracic pressure rises very rapidly after the cessation of the inspiratory effort, and then slow- ly falls as the air issues from the chest; at the beginning of the inspiratory effort the fall becomes more rapid. (M. Foster.) » not produce a distinct obstruction to the circulation, as even when the expiration is at an end the intra-thoracic pressure is less than the extra- thoracic. The effect of violent expiratory efforts, however, has a distinct action in preventing the current of blood through the lungs, as seen in the blueness of the face from congestion in straining; this condition being produced by pressure on the small pulmonary vessels. We may summarize this mechanical effect, therefore, and say that in- spiration aids the circulation and so increases the arterial tension, and that although expiration does not materially aid the circulation, yet under ordinary conditions neither does it obstruct. Under extraordinary con- ditions, as in violent expirations, the circulation is decidedly obstructed. But we have seen that there 'IB no exact correspondence between the points of extreme arterial tension and the end of inspiration, and we must look to the nervous system for an explanation of this apparently contra- dictory result. The effect of the nervous system in producing a rhythmical alteration of the blood pressure is twofold. In the first place the cardw-inliibitory centre, is believed to be stimulated during the fall of blood pressure, pro- 208 HAND-BOOK OF PHYSIOLOGY. ducing a slower rate of heart-beats during expiration, which will be noticed in the tracing (Fig. 163), the undulations during the decline of blood-pressure being longer but less frequent. This effect disappears when, by section of the vagi, the effect of the centre is cut off from the heart. In the second place, the vaso-motor centre is also believed to send out rhythmical impulses, by which undulations of blood pressure are pro- duced independently of the mechanical effects of respiration. FIG. 164.— Traube-Hering's curves. (To be read from left to right.) The curves 1, 2, 3, 4, and 5 are portions selected from one continuous tracing forming the record of a prolonged observation, so that the several curves represent successive stages of the same experiment. Each curve is placed in its proper position relative to the base line, which is omitted; the blood-pressure rises in stages from 1, to 2, 3, and 4, but falls again in stage 5. Curve 1 is taken from a period when artificial respiration was being kept up, but the vagi having been divided, the pulsations on the ascent and descent of the undulations do not differ; when artificial respiration ceased these undulations for a while disappeared, and the blood-pressure rose steadily while the heart-beats became slower. Soon, as at 2, new un- dulations appeared ; a little later, the blood-pressure was still rising, the heart-beats still slower, but the undulations still more obvious (3): still later (4), the pressure was still higher, but the heart-beats were quicker, and the undulations flatter, the pressure then began to fall rapidly (5), and continued to fall until some time after artificial respiration was resumed. (M. Foster.) The action of the vaso-motor centre in taking part in producing rhythmical changes of blood-pressure which are called respiratory, is shown in the following way: — In an animal under the influence of urari, record of whose blood-pressure is being taken, and where artificial respi- ration has been stopped, and both vagi cut, the blood-pressure curve rises at first almost in a straight line; but after a time new rhythmical undula- tions occur very like the original respiratory undulatious, only somewhat RESPIRATION. 209 larger. These are called Traubes or Traube- Her ing's curves. They con- tinue whilst the blood-pressure continues to rise, and only cease when the vaso-motor centre and the heart are exhausted, when the pressure speedily falls. These .curves must be dependent upon the vaso-motor centre, as the mechanical effects of respiration have been eliminated by the poison and by the cessation of artificial respiration, and the effect of the cardio- inhibitory centre be the division of the vagi. It may be presumed there- fore that the vaso-motor centre, as well as the cardio-inhibitory, must be considered to take part with the mechanical changes of inspiration and expiration in producing the so-called respiratory undulations of blood- pressure. Cheyne- Stokes' s breathing. — This is a rhythmical irregularity in respi- rations which has been observed in various diseases, and is especially con- nected with fatty degeneration of the heart. Respirations occur in groups, at the beginning of each group the inspirations are very shallow, but each successive breath is deeper than the preceding until a climax is reached, then comes in a prolonged sighing expiration, succeeded by a pause, after which the next group begins. AP^CE A. — D YSP:NXE A. — ASPHYXIA. As blood which contains a normal proportion of oxygen excites the respiratory centre (p. 204), and as the excitement and consequent respir- atory muscular movements are greater (dyspnoea) in proportion to the deficiency of this gas, so an abnormally large proportion of oxygen in the blood leads to diminished breathing movements, and, if the proportion be large enough, to their temporary cessation. This condition of absence of breathing is termed apncea,1 and it can be demonstrated, in one of the lower animals, by performing artificial respiration to the extent of satura- ting the blood with oxygen. When, on the other hand, the respiration is stopped, by, e.g., interference with the passage of air to the lungs, or by supplying air devoid of oxygen, a condition ensues, which passes rapidly from the state of dyspnoea (difficult breathing) to what is termed asphyxia; and the latter quickly ends in death. The ways by which this condition of asphyxia may be produced are very numerous; as, for example, by the prevention of the due entry of oxygen into the blood, either by direct obstruction of the trachea or other part of the respiratory passages, or by introducing instead of ordinary air a gas devoid of oxygen, or, again, by interference with the due inter- change of gases between the air and the blood. Symptoms of Asphyxia. — The most evident symptoms of asphyxia or suffocation are well known. Violent action of the respiratory muscles 1 This term has been, unfortunately, often applied to conditions of dyspncea or asphyxia; but the modern application of the term, as in the text, is the more convenient. VOL. I.— 14. 210 HAND-BOOK OF PHYSIOLOGY. and, more or less, of all the muscles of the body; lividity of the skin and all other vascular parts, while the veins are also distended, and the tissues seem generally gorged with blood; convulsions, quickly followed by in- sensibility, and death. The conditions which accompany these symptoms are — (1) More or less interference with the passage of the blood through the pulmonary blood-vessels. (2) Accumulation of blood in the right side of the heart and in the systemic veins. (3) Circulation of impure (non-aerated) blood in all parts of the body. Cause of Death from Asphyxia.— The causes of these conditions and the manner in which they act, so as to be incompatible with life, may be here briefly considered. (1) The obstruction to the passage of blood through the lungs is not so great as it was once supposed to be; and such as there is occurs chiefly in the later stages of asphyxia, when, by the violent and convulsive action of the expiratory muscles, pressure is indirectly made on the lungs, and the circulation through them is proportionately interfered with. (2) Accumulation of blood, with consequent distension of the right side of the heart and systemic veins, is the direct result, at least in part, of the obstruction to the pulmonary circulation just referred to. Other causes, however, are in operation, (a) The vaso-motor centres stimu- lated by blood deficient in oxygen, causes contraction of all the small arteries with increase of arterial tension, and as an immediate conse- quence the filling of the systemic veins, (b) The increased arterial ten- sion is followed by inhibition of the action of the heart, and, thus, the latter, contracting less frequently, and gradually enfeebled also by defi- cient supply of oxygen, becomes over-distended by blood which it cannot expel. At this stage the left as well as the right cavities are distended with blood. The ill effects of these conditions are to be looked for partly in the heart, the muscular fibres of which, like those of the urinary bladder or any other hollow muscular organ, may be paralyzed by over-stretching; and partly in the venous congestion, and consequent interference with the function of the higher nerve-centres, especially the medulla oblongata. (3) The passage of non-aerated blood through the lungs and its dis- tribution over the body are events incompatible with life, in one of the higher animals, for more than a few minutes; the rapidity with which death ensues in asphyxia being due, more particularly, to the effect of non-oxygenized blood on the medulla oblongata, and, through the coro- nary arteries, on the muscular substance of the heart. The excitability .of both nervous and muscular tissue is dependent on a constant and large supply of oxygen, and, when this is interfered with, is rapidly lost. The diminution of oxygen, it may be here remarked, has a more direct in- RESPIRATION. 211 luence in the production of the usual symptoms of asphyxia than the icreased amount of carbonic acid. Indeed, the fatal effect of a gradual emulation of the latter in the blood, if a due supply of oxygen be luintuined, resembles rather that of a narcotic poison. In some experiments performed by a committee appointed by the [edico-Chirurgical Society to investigate the subject of Suspended Ani- latioti, it was found that, in the dog, during simple asphyxia, i.e., by simple privation of air, as by plugging the trachea, the average duration )f the respiratory movements after the animal had been deprived of air, ras 4 minutes 5 seconds; the extremes being 3 minutes 30 seconds, and minutes 40 seconds. The average duration of the heart's action, on the )therliand, was 7 minutes 11 seconds; the extremes being 6 minutes 40 nets, and 7 minutes 45 seconds. It would seem, therefore, that on an average, the heart's action continues for 3 minutes 15 seconds after the minril has ceased to make respiratory eiforts. A very similar relation was observed in the rabbit. Recovery never took place after the heart's action had ceased. The results obtained by the committee on the subject of drowning were very remarkable, especially in this respect, that whereas an animal may recover, after simple deprivation of air for nearly four minutes, yet, after submersion in water for 1| minute, recovery seems to be impossible. This remarkable difference was found to be due, not to the mere submer- sion, nor directly to the struggles of the animal, nor to depression of tem- perature, but to the two facts, that in drowning, a free passage is allowed to air out of the lungs, and a free entrance of water into them. It is probably to the entrance of water into the lungs that the speedy death in drowning is mainly due. The results of post-mortem examination strongly support this view. On examining the lungs of animals deprived of air by plugging the trachea, they were found simply congested; but in the animals drowned, not only was the congestion much more intense, accom- panied with ecchymosed points on the surface and in the substance of the lung, but the air tubes were completely choked up with a sanious foam, consisting of blood, water, and mucus, churned up with the air in the lungs by the respiratory efforts of the animal. The lung-substance, too, appeared to be saturated and sodden with water, which, stained slightly with blood, poured out at any point where a section was made. The lung thus sodden with water was heavy (though it floated), doughy, pitted on pressure, and was incapable of collapsing. It is not difficult to understand how, by such infraction of the tubes, air is debarred from iva ehing the pulmonary cells; indeed the inability of the lungs to collapse on opening the chest is a proof of the obstruction which the froth occu- pying the air-tubes offers to the transit of air. We must carefully distinguish the asphyxiating effect of an insuffi- cient supply of oxygen from the directly poisonous action of such a gas as carbonic oxide, which is present to a considerable amount in common coal-gas. The fatal effects often produced by this gas (as in accidents from burning charcoal stoves in small, close rooms), are due to its enter- ing into combination with the haemoglobin of the blood -corpuscles (p. 95), and thus expelling the oxygen. CHAPTER VII. FOOD. IK order that life may be maintained it is necessary that th% body should be supplied with food in proper quality and quantity. The food taken in by the animal body is used for the purpose of re- placing the waste of the tissues. And to arrive at a reasonable estimation of the proper diet in twenty-four hours it is necessary to consider the amount of the excreta daily eliminated from the body. The excreta con- tain chiefly carbon, hydrogen, oxygen, and nitrogen, but also to a less extent, sulphur, phosphorus, chlorine, potassium, sodium, and certain other of the elements. Since this is the case it must be evident that, to balance this waste, foods must be supplied containing all these elements to a certain degree, and some of them, viz., those which take the prin- cipal part in forming the excreta, in large amount. We have seen in the last Chapter that carbonic acid and ammonia, i.e., the elements carbon, oxygen, nitrogen, hydrogen, are given off from the lungs. By the excre- tion of the kidneys — the urine — many elements are discharged from the blood, especially nitrogen, hydrogen, and oxygen. In the sweat, the ele- ments chiefly represented are carbon, hydrogen, and oxygen, and also in the faeces. By all the excretions large quantities of water are got rid of daily, but chiefly by the urine. The relations between the amounts of the chief elements contained in these various excreta in twenty-four hours may be represented in the following way (Landois) : Water. C. H. K O. By the lungs . . 330 248-8 — ? 651.15 By the skin . . 660 2.6 7 '2 By the urine . . 1700 9 -8 3*3 15-8 11-1 By the faeces . . 128 20- 3' 3' 12 Grammes • • 2818 281*2 6-3 18 -8 681-41 To this should be added 296- grammes water, which are produced by the union of hydrogen and oxygen in the body during the process of oxi- dation (i.e., 32-89 hydrogen and 263.41 oxygen). There are twenty-six grammes of salts got rid of by the urine and six by the fasces. As the FOOD. 213 water can be supplied as such, the losses of carbon, nitrogen, and oxygen are those to which we should direct our attention in supplying food. For the sake of example, we may now take only two elements, carbon and nitrogen, and, if we discover what amount of these is respectively dis- charged in a given time from the body, we shall be in a position to judge what kind of food will most readily and economically replace their loss. The quantity of carbon daily lost from the body amounts to about 281 '2 grammes or nearly 4,500 grains, "and of nitrogen 18 '8 grammes or nearly 300 grains; and if a man could be fed by these elements, as such, the problem would be a very simple one; a corresponding weight of charcoal, and, allowing for the oxygen in it, of atmospheric air, would be all that is necessary. But an animal can live only upon these elements when they are arranged in a particular manner with others, in the form of an organic compound, as albumen, starch, and the like; and the rela- tive proportion of carbon to nitrogen in either of these compounds alone, is, by no means, the proportion required in the diet of man. Thus, in albumen, the proportion of carbon to nitrogen is only as 3 *5 to 1. If, therefore, a man took into his body, as food, sufficient albumen to supply him with the needful amount of carbon, he would receive more than four times as much nitrogen as he wanted; and if he took only sufficient to supply him with nitrogen, he would be starved for want of carbon. It is plain, therefore, that he should take with the albuminous part of his food, which contains so large a relative amount of nitrogen in proportion to the carbon he needs, substances in which the nitrogen exists in much smaller quantities relatively to the carbon. It is therefore evident that the diet must consist of several substances, not of one alone, and we must therefore turn to the available food-stuffs. For the sake of convenience they may be classified as follows: A. ORGANIC. I. Nitrogenous, consisting of Proteids, e.g. albumen, casein, syn- tonin, gluten, legumin and their allies; and Gelatins, which in- clude gelatin, elastin, and chondrin. All of these contain car- bon, hydrogen, oxygen, and nitrogen, and some in addition, phosphorus and sulphur. II. Non-Nitrogenous, comprising: (1.) Amyloid or saccharine bodies, chemically known as carbo- hydrates, since they contain carbon, hydrogen, and oxygen, with the last two elements in the proportion to form water, i.e., H20. To this class belong starch and sugar. (2.) Oils and fats. — These contain carbon, hydrogen, and oxy- gen; but the oxygen is less in amount than in the amyloids and saccharine bodies. B. IXORGAXIC. I. Mineral and saline matter. II. Water. 214 HAND-BOOK OF PHYSIOLOGY. To supply the loss of nitrogen and carbon, it is found by experience that it is necessary to combine substances which contain a large amount of nitrogen with others in which carbon is in considerable amount; and although, without doubt, if it were possible to relish and digest one or other of the above-mentioned proteids when combined with a due quantity of an amyloid to supply the carbon, such a diet, together with salt and water, ought to support life; yet we find that for the purposes of ordinary life this system does not answer, and instead of confining our nitrogenous foods to one variety of substance we obtain it in a large number of allied substances, for example, in flesh, of bird, beast, or fish; in eggs; in milk; and in vegetables. Arid, again, we are not content with one kind of ma- terial to supply the carbon necessary for maintaining life, but seek more, in bread, in fats, in vegetables, in fruits. Again, the fluid diet is seldom supplied in the form of pure water, but in beer, in wines, in tea and cof- fee, as well as in fruits and succulent vegetables. Man requires that his food should be cooked. Very few organic sub- stances can be properly digested without previous exposure to heat and to other manipulations which constitute the process of cooking. It will be well, therefore, to consider the composition of the various substances employed as food, and then to consider how they are affected by cooking. I A. FOODS CONTAINING PRINCIPALLY NITROGENOUS BODIES. I. — Flesh of Animals, especially of the ox (beef, veal), sheep (mutton, lamb), pig (pork, bacon, ham). Of these, beef is richest in nitrogenous matters, containing about 20 per cent., whereas mutton contains about 18 per cent., veal, 16*5, and pork, 10; the flesh is also firmer, more satisfying, and is supposed to be more strengthening than mutton, whereas the latter is more digestible. The flesh of young animals, such as lamb and veal, is less digestible and less nutritious. Pork is comparatively indigestible, and contains a large amount of fat. Flesh contains: — (1) Nitrogenous bodies: myosin, serum-albumin, gela- tin (from the interstitial fibrous connective tissue); elastin (from the elastic tissue), as well as hcemoglobin. (2) Fatty matters, including lecithin and cholesterin. (3) Extractive matters, some of which are agreeable to the palate, e.g., osmazome, and others which are weakly stimulating, e.g., kreatin. Besides, there are sarcolactic and inositic acids, taurin, xanthin, and others. (4) Salts, chiefly of potassium, calcium, and magnesium. (5) Water, the amount of which varies from 15 per cent, in dried bacon to 39 in pork, 51 to 53 in fat beef and mutton, to 72 per cent, in lean beef and mutton. (6) A certain amount of carbo-hydrate material is found in the flesh of young animals, in the form of inosite, dextrin, grape sugar, and (in young animals) glycogen. FOOD. 215 Table of Per-centage Composition of Beef, Mutton, Pork, and Veal. — (Letheby.) Water. Albumen. Fat. Salts. Beef.— Lean . 72 19-3 3-6 5.1 Fat . Mutton. — Lean Fat Veal . Pork.— Fat 51 14-8 29-8 4-4 72 18.3 4.9 4.8 53 12-4 31-1 3'5 63 16-5 15-8 4-7 39 9.8 48-9 2 '3 Together with the flesh of the above-mentioned animals, that of the deer, hare, rabbit, and birds, constituting venison, game and poultry, should be added as taking part in the supply of nitrogenous substances, and ahofish — salmon, eels, etc., and. shell- fish, e.g., lobster, crab, mussels, oysters, shrimps, scollop, cockles, etc. Table of Per-centage Composition of Poultry and Fish. — (Letheby.) Water. Albumen. Fats. Salts. Poultry 74 21 3 -8 1-2 (Singularly devoid of fat, and so generally eaten with bacon or pork.) White Fish . . . .78 18 -1 2-9 1* Salmon . . . .77 16.1 5 -5 1-4 Eels (very rich in fat) . .75 9-9 13 -8 1-3 Oysters . . ' . .75-74 11 '72 2-42 2.73 Even now the list of fleshy foods is not complete, as nearly all animals have been occasionally eaten, and we may presume that the average com- position of all is nearly the same. II. MM — Is intended as the entire food of young animals, and as such contains, when pure, all the elements of a typical diet. (1) Albu- minous substances in the form of casein and, in small amount, of serum- albumin. (2) Fats in the cream. (3) Carbo-hydrates in the form of lactose or milk sugar. (4) Salts, chiefly calcium phosphate; and (5) "Water. From it we obtain (a) cheese, which is the casein precipitated with more or less fat according as the cheese is made of skim milk (skim cheese), of fresh milk with its cream (Cheddar and Cheshire), or of fresh milk plus cream (Stilton and double Gloucester). The precipitated casein is allowed to ripen, by which process some of the albumen is split up with formation of fat. (/?) Cream, which consists of the fatty globules in- cased in casein, and which being of low specific gravity float to the surface. (y) fitter, or the fatty matter deprived of its casein envelope by the process of churning. (6) Buttermilk, or the fluid obtained from cream after 216 HAND-BOOK OF PHYSIOLOGY. batter has been formed; very rich therefore in nitrogen, (f) Wliey, or the fluid which remains after the precipitation of casein; this contains sugar, salt, and a small quantity of albumen. Table of Composition of Milk, Buttermilk, Cream, and Cheese. — (Lethe- by and Pay en.) Fats' Lactose' Salts' Water' Milk (Cow) Buttermilk Cream Cheese. — Skim . Cheddar 4-1 4-1 2-7 44-8 28-4 26-7 5.2 6-4 2-8 -8 86 -8 88 1-8 66 4-9 44 4.5 36 Non-nitrogenous matter and loss. 6-3 31-1 " Neufchatel (fresh) 8- 40-71 36'58 -51 36.58 III. Eggs. — The yelk and albumen of eggs are in the same relation as food for the embryoes of oviparous animals that milk is to the young of mammalia, and afford another example of the natural admixture of the various alimentary principles. Table of the Per-centage Composition of Fozvls' Eggs. White Yelk Nitrogenous substances. . 20-4 16 Fats. 30-7 Salts. Water. 1-6 1-3 78 52 IV. Leguminous fruits are used by vegetarians, as the chief source of the nitrogen of the food. Those chiefly used are peas, beans, lentils, etc., they contain a nitrogenous substance called legumin, allied to albumen. They contain about 25 '30 per cent, of this nitrogenous body, and twice as much nitrogen as wheat. B. SUBSTANCES SUPPLYING PRINCIPALLY CARBOHYDRATE BODIES. a. Bread, made from the ground grain obtained from various so-called cereals, viz., wheat, rye, maize, barley, rice, oats, etc., is the direct form in which the carbohydrate is supplied in an ordinary diet. Flour, how- ever, besides the starch, contains gluten, a nitrogenous body, and a small amount of fat. Table of Per-centage Composition of Bread and Flour. Bread Flour Nitrogenous Carbo- matters. hydrates. . 8-1 51- 10.8 70-85 Fats. Salts. Water. 2.3 1.7 37 15 FOOD. 217 Various articles of course are made from flour, e.g., macaroni, biscuits, etc., besides bread. /?. Vegetables, especially potatoes. y. Fruits contain sugar, and organic acids, tartaric, malic, citric, and others. C. SUBSTANCES SUPPLYING PRINCIPALLY FATTY BODIES. The chief are butter, lard (pig's fat), suet (beef and mutton fat). D. SUBSTANCES SUPPLYING THE SALTS OF THE FOOD. Nearly all the foregoing substances in A, B, and C, contain a greater or less amount of the salts required in food; but green vegetables and fruit supply certain salts, without which the normal health of the body is not maintained. E. LIQUID FOODS. "Water is consumed alone, or together with certain other substances used to flavor it, e.g., tea, coffee, etc. Tea in moderation is a stimulant, and contains an aromatic oil to which it owes its peculiar aroma, an astrin- gent of the nature of tannin, and an alkaloid, theine. The composition of coffee is very nearly similar to that of tea. Cocoa, in addition to similar substances contained in tea and coffee, contains fat, albuminous matter, and starch, and must be looked upon more as a food. Beer, in various forms, is an infusion of malt (barley which has sprouted, and in which the starch is converted in great part into sugar), boiled with hops and allowed to ferment. Beer contains from 1 '2 to 8 '8 per cent, of alcohol. Cider and Perry, the fermented juice of the apple and pear. Wine, the fermented juice of the grape, contains from 6 or 7 (Ehine wines, and white and red Bordeaux) to 24 — 25 (ports and sherries) per cent, of alcohol. Spirits, obtained from the distillation of fermented liquors. They contain upward of 40 — 70 per cent, of absolute alcohol. Effects c f cooking upon Food. — In general terms this may be said to make food more easily digestible, arid this includes two other alterations, food is made more agreeable to the palate and also more pleas- ing to the eye. Cooking consists in exposing the food to various degrees of heat, either to the direct heat of the fire, as in roasting, or to the in- direct heat of the fire, as in broiling, baking, or frying, or to hot water, as in boiling or stewing. The effect of heat upon flesh is to coagulate the albumen and coloring matter, to solidify fibrin, and to gelatinize tendons 218 HAND-BOOK OF PHYSIOLOGY. and fibrous connective tissue. Previous beating or bruising (as with steaks and chops, or keeping (as in the case of game), renders the meat more tender. Prolonged exposure to heat also develops on the surface certain empyreumatic bodies, which are agreeable both to the taste and smell. By placing meat into hot water, the external coating of albumen is coagulated, and very little, if any, of the constituents of the meat are lost afterward if boiling be prolonged, but if the constituents of the meat are to be extracted, it should be exposed to prolonged simmering at a much lower temperature, and the "broth" will then contain the gelatin and extractive matters of the meat, as well as a certain amount of albu- men. The addition of salt will help to extract the myosin. The effect of boiling upon an egg coagulates the albumen, and helps in rendering the article of food more suitable for adult dietary. Upon milk, the eifect of heat is to produce a scum composed of serum-albumin and a little casein (the greater part of the casein being uncoagulated) with some fat. Upon vegetables, the cooking produces the necessary effect of rendering them softer, so that they can be more readily broken up in the mouth; it also causes the starch to swell up and burst, and so aids the digestive fluids to penetrate into their substance. The albuminous mat- ters are coagulated, and the gummy, saccharine and saline matters are remove'd. The conversion of flour into bread is effected by mixing it with water, a little salt and a certain amount of yeast, which consists of the cells of an organized ferment (Torula cerevisice). By the growth of this plant, which lives upon the sugar produced from the starch of the flour, carbonic acid gas and a small amount of alcohol are formed. It is by means of the former that the dough rises. Another method consists in mixing the flour with water containing a large quantity of the gas in so- lution. By the action of heat during baking the dough continues to expand, and the gluten being coagulated, the bread sets as a permanently vesicu- lated mass. I.— EFFECTS OF AN INSUFFICIENT DIET. Hunger and Thirst. — The sensation of hunger is manifested in consequence of deficiency of food in the system. The mind refers the sensation to the stomach; yet since the sensation is relieved by the intro- duction of food either into the stomach itself, or into the blood through other channels than the stomach, it would appear riot to depend on the state of the stomach alone. This view is confirmed by the fact, that the division of both pneumogastric nerves, which are the principal channels by which the brain is cognizant of the condition of the stomach, does not appear to allay the sensations of hunger. But that the stomach has some share in this sensation is proved by the relief afforded, though only FOOD. 219 temporarily, by the introduction of even non-alimentary substances into this organ. It may, therefore, be said that the sensation of hunger is caused both by a want in the system generally, and also by the condition of the stomach itself, by which condition, of course, its own nerves are more directly affected. The sensation of thirst, indicating the want of fluid, is referred to the fauces, although, as in hunger, this is, in great part, only the local decla- ration of a general condition. For thirst is relieved for only a very short time by moistening the dry fauces; but may be relieved completely by the introduction of liquids into the blood, either through the stomach, or by injections into the blood-vessels, or by absorption from the surface of the skin or the intestines. The sensation of thirst is perceived most naturally whenever there is a disproportionately small quantity of water in the blood: as well, therefore, when water has been abstracted from the blood, as when saline or any solid matters have been abundantly added to' it. And the cases of hunger and thirst are not the only ones in which the mind derives, from certain organs, a peculiar predominant sensation of some condition affecting the whole body. Thus, the sensation of the "necessity of breathing/' is referred especially to the air-passages; but, as Volkmann's experiments show, it depends on the condition of the blood which circulates everywhere, and is felt even after the lungs of animals are removed; for they continue, even then, to gasp and manifest the sensation of want of breath. Starvation. — The effects of total deprivation of food have been made the subject of experiments on the lower animals, and have been but too frequently illustrated in man. (1) One of the most notable effects of starvation, as might be expected, is loss of weight; the loss being greatest at first, as a rule, but afterward not varying very much, day by day, until death ensues. Chossat found that the ultimate proportional loss was, in different animals experimented on, almost exactly the same; death occurring when the body had lost two-fifths (forty per cent.) of its original weight. Different parts of the body lose weight in very different propor- tions. The following results are taken, in round numbers, from the table given by M. Chossat: — Fat Blood . Spleen . Pancreas Liver . Heart . Intestines Muscles of locomotion Stomach Pharynx, ((Esophagus) Skin loses 93 per cent. . 75 " . 71 . 64 . 52 . 44 . 42 . 42 . 39 . 34 33 220 HAND-BOOK OF PHYSIOLOGY. Kidneys Kespiratory apparatus Bones , Eyes . Nervous system loses 31 per cent. . 22 " . 16 ie . 10 2 " (nearly). (2. ) The effect of starvation on the temperature of the various animals experimented on by Chossat was very marked. For some time the vari- ation in the daily temperature was more marked than its absolute and continuous diminution, the daily fluctuation amounting to 5° or 6° F. (3° 0.), instead of 1° or 2° F. (-5° to 1° C.), as in health. But a short time before death, the temperature fell very rapidly, and death ensued when the loss had amounted to about 30° F. (16'5°C.). It has been often said, and with truth, although the statement requires some qualification, that death by starvation is really death by cold; for not only has it been found that differences of time with regard to the period of the fatal result are attended by the same ultimate loss of heat, but the effect of the appli- cation of external warmth to animals cold and dying from starvation, is more effectual in reviving them than the administration of food. In other words, an animal exhausted by deprivation of nourishment is unable so to digest food as to use it as fuel, and therefore is dependent for heat on its supply from without. Similar facts are often observed in the treat- ment of exhaustive diseases in man. (3.) The symptoms produced by starvation in the human subject are hunger, accompanied, or it may be replaced by pain, referred to the region of the stomach; insatiable thirst; sleeplessness; general weakness and emaciation. The exhalations both from the lungs and skin are fetid, indicating the tendency to decomposition which belongs to badly- nourished tissues; and death occurs, sometimes after the additional ex- haustion caused by diarrhoea, often with symptoms of nervous disorder, delirium or convulsions. (4.) In the human subject death commonly occurs within six to ten days after total deprivation of food. But this period may be considerably prolonged by taking a very small quantity of food, or even water only. The cases so frequently related of survival after many days, or even some weeks, of abstinence, have been due either to the last-mentioned circum- stances, or to others no less effectual, which prevented the loss of heat and moisture. Cases in which life has continued after total abstinence from food and drink for many weeks, or months, exist only in the imag- ination of the vulgar. (5. ) The appearances presented after death from starvation are those of general wasting and bloodlessness, the latter condition being least noticeable in the brain. The stomach and intestines are empty and contracted, and the walls of the latter appear remarkably thinned and almost transparent. The various secretions are scanty or absent, with the exception of the FOOD. 221 bile, which, somewhat concentrated, usually fills the gall-bladder. All parts of the body readily decompose. II. — EFFECTS OF IMPROPER DIET. Experiments on Feeding. — Experiments illustrating the ill effects produced by feeding animals upon one or two alimentary substances only have been often performed. Dogs were fed exclusively on sugar and distilled water. During the first seven or eight days they were brisk and active, and took their food and drink as usual; but in the course of the second week, they began to get thin, although their appetite continued good, and they took daily between six and eight ounces of sugar. The emaciation increased during the third week, and they became feeble, and lost their activity and appe- tite. At the same time an ulcer formed on each cornea, followed by an escape of the humors of the eye: this took place in repeated experiments. The animals still continued to eat three or four ounces of sugar daily; but became at length so feeble as to be incapable of motion, and died on a day varying from the thirty-first to the thirty-fourth. On dissection, their bodies presented all the appearances produced by death from starva- tion; indeed, dogs will live almost the same length of time without any food at all. When dogs were fed exclusively on gum, results almost similar to the above ensued. When they were kept on olive-oil and water, all the phe- nomena produced were the same, except that no ulceration of the cornea took place; the effects were also the same with butter. The experiments of Chossat and Letellier prove the same; and in men, the same is shown by the various diseases to which those who consume but little nitrogenous food are liable, and especially by the affection of the cornea which is observed in Hindus feeding almost exclusively on rice. But it is not only the non-nitrogenous substances, which, taken alone, are insufficient for the maintenance of health. The experiments of the Academies of France and Amsterdam were equally conclusive that gelatin alone soon ceases to be nutritive. Savory's observations on food confirm and extend the results obtained by Magendie, Chossat, and others. They show that animals fed exclu- sively on non-nitrogenous diet speedily emaciate and die, as if from starv- ation; that life is much more prolonged in those fed with nitrogenous than by those with non-nitrogenous food; and that animal heat is main- tained as well by the former as by the latter — a fact which proves, if proof were wanting — that nitrogenous elements of food, as well as non- nitrogenous, may be regarded as calorifacient. 222 HAND-BOOK OF PHYSIOLOGY. III. — EFFECT OF TOO MUCH FOOD. Sometimes the excess of food is so great that it passes through the ali- mentary canal, and is at once got rid of by increased peristaltic action of the intestines. In other cases, the unabsorbed portions undergo putre- factive changes in the intestines, which are accompanied by the produc- tion of gases, such as carbonic acid, carburetted and sulphuretted hydro- gen; a distended condition of the bowels, accompanied by symptoms of indigestion, is the result. An excess of the substances required as food may, however, undergo absorption. It is a well-known fact that numbers of people habitually eat too much; especially of nitrogenous food. Dogs can digest an immense amount of meat if fed often, and the amount of meat taken by some men would supply not only tihe nitrogen, but the carbon which is requisite for an ordinary natural diet. A method of get- ting rid of an excess of nitrogen is provided by the digestive processes in the duodenum, to be presently described, whereby the excess of the albu- minous food is capable of being changed before absorption into nitroge- nous crystalline matters, easily converted by the liver into urea, and so easily excreted by the kidneys, affording one variety of what is called luxus consumption; but after a time the organs, especially the liver, will yield to the strain of the over- work, and will not reduce the excess of nitroge- nous material into urea, but into other less oxidized products, such as uric acid; and general plethora and gout may be the result. This state of things, however, is delayed for a long time, if not altogether obviated, when large meat-eaters take a considerable amount of exercise. Excess of carbohydrate food produces an accumulation of fat, which may not only be an inconvenience by causing obesity, but may interfere with the proper nutrition of muscles, causing a feebleness of the action of the heart, and other troubles. The accumulation of fat is due to the excess of carbohydrate being stored up by the protoplasm in the form of fat. Starches when taken in great excess are almost certain to give rise in addition to dyspepsia, with acidity and flatulence. There is a limit to the absorption of starch and of fat, as, if taken beyond a certain amount, they appear unchanged in the faeces. Requisites of a Normal Diet. — It will have been understood that it is necessary that a normal diet should be made up of various articles, that they should be well cooked, and should contain about the same amount of the carbon and nitrogen that are got rid of by the excreta. Without doubt these desiderata may be satisfied in numerous ways, and it would be simply absurd to believe that the diet of every adult should be exactly similar. The age, sex, strength, and circumstances of each individual should ultimately determine his diet. A dinner of bread and hard cheese with an onion contain all the requisites for a meal; but such FOOD. 223 diet would be suitable only for those possessing strong digestive powers. It is a well- known fact that the diet of the continental nations differs from that of our own country, and that of cold from that of hot climates; but the same principle underlies them all, viz., replacement of the loss of the excreta in the most convenient and economical way possible. Without going into detail in the matter, it may be said that any one in active work requires more nitrogenous matter than one at rest, and that children and women require less than adult men. The quantity of food for a healthy adult man of average height and weight may be stated in the following table: — Table of Water and Food required for a Healthy Adult. — (Parkes.) In laborious Af . occupation. Nitrogenous substances, e.g., flesh 6 to 7 oz. av. 2 -5 oz. Fats 3 '5 to 4-5 oz. 1 oz. Carbo-hydrates . . . . 16 to 18 oz. 12 oz. Salts 1.2 to 1.5 oz. .5 oz. 26'7 to 31 oz. 16 oz. The above is the dry food; but as this is nearly always combined with 50 to 60 per cent, of water, these numbers should be doubled, and they would then be 52 to 60 oz., and 32 oz. of so called solid food, and to this should be added 50 to 80 oz. of fluid. Full diet scale for an adult male in hospital (St. Bartholomew's Hospital}. Breakfast. — 1 pint of tea (with milk and sugar), bread and butter. Dinner. — -J-lb. of cooked meat, |lb. potatoes, bread and beer. Tea. — 1 pint of tea, bread and butter. Supper. — Bread and butter, beer. Daily allowance to each patient. — 2 pints of tea, with milk and sugar; 14 oz. bread; \ Ib. of cooked meat: £lb. potatoes: 2 pints of beer, 1 oz. butter. 31 oz" solid, and 4 pints (80 oz.), liquid. CHAPTEK VIII. DIGESTION. THE object of digestion is to prepare the food to supply the waste of the tissues, which we have seen is its proper function in the economy. Few of the articles of diet are taken in the exact condition in which it is possible for them to be absorbed into the system by the blood-vessels and lymphatics, without which absorption they would be useless for the pur- poses they have to fulfil; almost the whole of the food undergoes various changes before it is fit for absorption. Having been received into the mouth, it is subjected to the action of the teeth and tongue, and is mixed with the first of the digestive juices — the saliva. It is then swallowed, and, passing through the pharynx and oesophagus into the stomach, is subjected to the action of the gastric juice. Thence it passes into the intestines, where it meets with the bile, the pancreatic juice and the in- testinal juices, all of which exercise an influence upon that portion of the food not absorbed from the stomach. By this time most of the food is 'capable of absorption, and the residue of undigested matter leaves the body in the form of faeces by the anus. The course of the food through the alimentary canal of man will be readily seen from the accompanying diagram (Fig. 165). The Mouth is the cavity contained between the jaws and inclosed by the cheeks laterally, and by the lips in front; behind it opens into the pharynx by the fauces, and is separated from the nasal cavity by the hard palate in front, and the soft palate behind, which form its roof. The tongue forms the lower part or floor. In the jaws are contained the teeth; and when the mouth is shut these form its anterior and lateral boundaries. The whole of the mouth is lined with mucous membrane, covered by stratified squamous epithelium, which is continuous in front along the lips with the epithelium of the skin, and posteriorly with that of the pharynx. The mucous membrane is provided with numerous glands (small tubular), called mucous glands, and into it open the ducts of the salivary glands, three chief glands on each side. The tongue is not only a prehensile organ, but is also the chief seat of the sense of taste. "We shall now consider, in detail, the process of digestion, as it takes place in each stage of this journey of the food through the alimentary canal. Mastication. — The act of chewing or mastication is performed by DIGESTION. 225 the biting and grinding movement of the lower range of teeth against the upper. The simultaneous movements of the tongue am^heeks assist partly by crushing the softer portions of the food against the hard palate, gums, etc., and thus 'supplementing the action of the teeth, and partly by re- turning the morsels of food to the action of the teeth, again and again, _ FIG. 165.— Diagram of the Alimentary Canal. The small intestine of man is from about 3 to 4 tunes as long as the large intestine. as they are squeezed out from between them, until they have been suffi- ciently chewed. The simple up and down, or biting movements of the lower jaw, are performed by the temporal, masseter, and internal pterygoid muscles, the action of which in closing the jaws alternates with that of the digastric and other muscles passing from the os hyoides to the lower jaw, which open them. The grinding or side to side movements of the lower jaw are performed mainly by the external pterygoid muscles, the muscle of one side acting alternately with the other. When both external ptery- VOL. I.— 15. 226 HAND-BOOK OF PHYSIOLOGY. golds act together, the lower jaw is pulled directly forward, so that the lower incisor teeth ^e brought in front of the level of the upper. Temporo-maxillary Fibro-cartilage.— The function of the inter- articular fibro-cartilage of the temporo-maxillary joint in mastication may be here mentioned. (1) As an elastic pad, it serves well to distrib- ute the pressure caused by the exceedingly powerful action of the masti- catory muscles. (2) It also serves as a joint-surface or socket for the condyle of the lower jaw, when the latter has been partially drawn for- ward out of the glenoid cavity of the temporal bone by the external ptery- goid muscle, some of the fibres of the latter being attached to its front .surface, and consequently drawing it forward with the condyle which moves on it. Nerve-mechanism of Mastication. — As in the case of so many other actions, that of mastication is partly voluntary and partly reflex and involuntary. The consideration of such sensor i-mot or actions will come hereafter (see Chapter 011 the Nervous System). It will suffice here to state that the nerves chiefly concerned are the sensory branches of the fifth and the glosso-pharyngeal, and the motor branches of the fifth and the ninth (hypoglossal) cerebral nerves. The nerve-centre through which the reflex action occurs, and by which the movements of the various muscles are harmonized, is situate in the medulla oblongata. In so far as mastication is voluntary or mentally perceived, it becomes so under the influence, in addition to the medulla oblongata, of the cerebral hemi- spheres. Insalivation. — The act of mastication is much assisted by the saliva which is secreted by the salivary glands in largely increased amount during the process, and the intimate incorporation of which with the food, as it is being chewed, is termed insaUvation. THE SALIVARY GLANDS. The salivary glands are the parotid, the sub-maxillary, and the siib- lingual, and numerous smaller bodies of similar structure, and with sep- arate ducts, which are scattered thickly beneath the mucous membrane of the lips, cheeks, soft palate, and root of the tongue. Structure. — The salivary glands are usually described as compound tubular glands. They are made up of lobules. Each lobule consists of the branchings of a subdivision of the main duct of the gland, which are generally more or less convoluted toward their extremities, and some- times, according to some observers, sacculated or pouched. The convo- luted or pouched portions form the alveoli, or proper secreting parts of the gland. The alveoli are composed of a basement membrane of flattened •cells joined together by processes to produce a fenestrated membrane, the spaces of which are occupied by a homogeneous ground-substance. With- in, upon this membrane, which forms the tube, the nucleated salivary DIGESTION. 227 secreting cells, of cubical or columnar form, are arranged parallel to one another surrounding a middle central canal. The granular appearance which is frequently seen in the salivary cells is due to the very dense net- work of fibrils which they contain. When isolated, the cells not unfre- quently are found to be branched. Connecting the alveoli into lobules is a considerable amount of fibrous connective tissue, which contains both flattened and granular protoplasmic cells, lymph corpuscles, and in some cases fat cells. The lobules are connected to form larger lobules (lobes), in a similar manner. The alveoli pass into the intralobular ducts by a narrowed portion (intercalary), lined with flattened epithelium with elon- gated nuclei. The intercalary ducts pass into the intralobular ducts by a narrowed neck, lined with cubical cells with small nuclei. The intra- lobular duct is larger in size, and is lined with large columnar nucleated - 166.— Section of submaxillary gland of dog. Showing gland-cells, &, and a duct, a, in section. cells, the parts of which, toward the lumen of the tube, presents a fine longitudinal striation, due to the arrangement of the cell network. It is most marked in the submaxillary gland. The intralobular ducts pass into the larger ducts, and these into the main duct of the gland. As these ducts become larger they acquire an outside coating of connective tissue, and later on some unstriped muscular fibres. The lining of the larger ducts consists of one or more layers of columnar epithelium, containing an intracellular network of fibres arranged longitudinally. Varieties. — Certain differences in the structure of salivary glands may be observed according as the glands secrete pure saliva, or saliva mixed with mucus, or pure mucus, and therefore the glands have been classified as: (1) True salivary glands (called most unfortunately by some serous glands), e.g., the parotid of man and other animals, and the sub- maxillary of the rabbit and guinea-pig (Fig. 167). In this kind the alveolar lumen is small, and the cells lining the tubule are short, granular columnar cells, with nuclei presenting the intranuclear network. During rest the cells become larger, highly granular, with obscured nuclei, and the lumen becomes smaller. During activity, and after stimulation of 228 HAND-BOOK OF PHYSIOLOGY. the sympathetic, the cells become smaller and their contents more opaque; the granules first of^all disappearing from the outer part of the cells, and then being found only at the extreme inner part and contiguous border of the cell. The nuclei reappear, as does also the lumen. (2) In the true mucus-secreting glands, as the sublingual of man and other animals, and FIG. 16? FIG. 168. FIG. 167.— From a section through a true salivary gland, a, the gland alveoli, lined with albu- minous " salivary cells;11 b, intralobular duct cut transversely. (Klein and Noble Smith.) FIG. 168. — From a section through a mucous gland in a quiescent state. The alveoli are lined with transparent mucous cells, and outside these are the demilunes of Heidenhain. The cells should have been represented as more or less granular. (Heidenhain.) in the submaxillary of the dog, the tubes are larger, contain a larger lumen, and also have larger cells lining them. The cells are of two kinds, (a) mucous or central cells, which are transparent columnar cells with, nuclei near the basement membrane. The cell substance is made up of a fine network, which in the resting state contains a transparent substance called mucigen, during which the cell does not stain well with logwood (Fig. 168). When the gland is secreting, mucigen is converted into mucin, and the cells swell up, appear more transparent, and stain deeply in logwood (Fig. 109). During rest, the cells become smaller and more granular from having dis- charged their contents, and the nuclei appear more distinct, (b) Semilunes of Heidenhain (Fig. 168), which are cre- scentic masses of granular parietal cells found here and there between the basement membrane and the central cells. These , cells are small, and have a very dense reticulum, the nuclei are spherical, and increase in size during secretion. In the mucous gland there are some large tubes, lined with large transparent central cells, and have besides a few granular parietal cells; other small tubes are lined with small granular parietal FIG. 169.— A part of a section through a mucous gland after prolonged electrical stimulation. The alveoli are lined with small granular cells. (Lavdovski.) DIGESTION. 229 cells alone; and a third variety are lined equally with each kind of cell. (3) In the muco-salivary or mixed glands, as the human submaxillary gland, part of the gland presents the structure of the mucous gland, whilst the remainder has that of the salivary glands proper. Nerves and blood-vessels. — Nerves of large size are found in the sali- vary glands, they are contained in the connective tissue of the alveoli principally, and in certain glands, especially in the dog, are provided with ganglia. Some nerves have special endings in Pacinian corpuscles, some supply the blood-vessels, and others, according to Pfliiger, penetrate the basement membrane of the alveoli and enter the salivary cells. The blood-vessels form a dense capillary network around the ducts of the alveoli, lUing carried in by the fibrous trabeculae between the alveoli, in which also begin the lymphatics by lacunar spaces. Saliva. — Saliva, as it commonly flows from the mouth, is mixed with the secretion of the mucous glands, and often with air bubbles, which, being retained by its viscidity, make it frothy. When obtained from the parotid ducts, and free from mucus, saliva is a transparent watery fluid, the specific gravity of which varies from 1004 to 1008, and in which, when examined with the microscope, are found floating a number of min- ute particles, derived from the secreting ducts and vesicles of the glands. In the impure or mixed saliva are found, besides these particles, numer- ous epithelial scales separated from the surface of the mucous membrane of the mouth and tongue, and the so-called salivary corpuscles, discharged probably from the mucous glands of the mouth and the tonsils, which, when the saliva is collected in a deep vessel, and left at rest, subside in the form of a white opaque matter, leaving the supernatant salivary fluid transparent and colorless, or with a pale bluish-grey tint. In reaction, the saliva, when first secreted, appears to be always alkaline. During fast- ing, the saliva, although secreted alkaline, shortly becomes neutral; and it does so especially when secreted slowly and allowed to mix with the acid mucus of the mouth, by which its alkaline reaction is neutralized. Chemical Composition of Mixed Saliva (Frerichs). Water 994-10 Solids 5-90 Ptyalin .1-41 Fat 0.07 Epithelium and Proteids (including Serum-Al- bumin, Globulin, Mucin, &c.) . . . 2.13 Salts — Potassium Sulpho-Cyanate Sodium Phosphate .... Calcium Phosphate .... Magnesium Phosphate Sodium Chloride .... Potassium Chloride 2-29 5-90 230 HAND-BOOK OF PHYSIOLOGY. The presence of potassium sulphocyanate (or tliiocyanate) {C N K S) in saliva, may be shown by the blood-red coloration which the fluid gives with a solution of ferric chloride (Fe2016), and which is bleached on the addition of a solution of mercuric chloride (HgCla). Rate of Secretion and Quantity. — The rate at which saliva is secreted is subject to considerable variation. When the tongue and muscles concerned in mastication are at rest, and the nerves of the mouth are subject to no unusual stimulus, the quantity secreted is not more than sufficient, with the mucus, to keep the mouth moist. During actual secretion the flow is much accelerated. The quantity secreted in twenty-four hours varies; its average amount is probably from 1 to 3 pints (1 to 2 litres). • Uses of Saliva.— The purposes served by saliva are (1) mechanical and (2) chemical. I. Mechanical.— (1) It keeps the mouth in a due condition of moisture, facilitating the movements of the tongue in speaking, and the mastication of food. (2) It serves also in dissolving sapid substances, and rendering them capable of exciting the nerves of taste. But the principal mechanical purpose of the saliva is, (3) that by mixing with the food during mastication, it makes it a soft pulpy mass, such as may be easily swallowed. To this purpose the saliva is adapted both by quantity and quality. For, speaking generally, the quantity secreted during feed- ing is in direct proportion to the dryness and hardness of the food. The quality of saliva is equally adapted to this end. It is easy to see how much more readily it mixes with most kinds of food than water alone does; and the saliva from the parotid, labial, and other small glands, being more aqueous than the rest, is that which is chiefly braided and mixed with the food in mastication; while the more viscid mucous secre- tion of the submaxillary, palatine, and tonsillitic glands is spread over the surface of the softened mass, to enable it to slide more easily through the fauces and oesophagus. II. Chemical. — Saliva has the power of con- verting starch into glucose or grape-sugar. When saliva, or a portion of a salivary gland, is added to starch paste in a test-tube, and the mixture kept at a temperature of 100° F. (37 -8° C.), the starch is very rapidly transformed into grape-sugar. There is an intermediate stage in which a part or the whole of the starch becomes dextrin. Test for Glucose. — In such an experiment the presence of sugar is at once discovered by the application of Trommer's test, which consists in the addition of a drop or two of a solution of copper sulphate, followed by a larger quantity of caustic potash. When the liquid is boiled, an orange-red precipitate of copper suboxide indicates the presence of sugar; and when common raw starch is masticated and mingled with saliva, and kept with it at a temperature of 90° or 100° F. (30°— 37.8° C.), the starch-grains are cracked or eroded, and their contents are transformed in the same manner as the starch-paste. DIGESTION. 231 Saliva from the parotid is less viscid, less alkaline, clearer, and more watery than that from the submaxillary. It has, moreover, a less power- ful action on starch. Sublingual saliva is the most viscid, and contains more solids kthan either of the other two, but does not appear to be so powerful in its action. The salivary glands of children do not become functionally active till the age of 4 to 6 months, and hence the bad effect of feeding them before this age on starchy food, corn-flour, etc., which they are unable to render soluble and capable of absorption. Action of Saliva on Starch.— This action is due to the presence in the saliva^ of the body called ptyalin. It is a nitrogenous body, and belongs to the order of ferments, which are bodies whose exact chemical composition is unknown, and which are capable of producing by their presence changes in other bodies, without themselves undergoing change. Ptyalin is called a liydrolytic ferment, that is to say, it acts by adding a molecule of water to the body changed. The reaction is supposed to be as follows: 3 C.H1006 + 3 H,0 = C,H,,06 + 2 (C.H,00S) + 2 H50 = 3 O.H,,0, Starch + Water. Glucose Dextrin Glucose But it is not unlikely that the action is by no means so simple. In the first place, recent observers believe that a molecule of starch must be represented by a much more complex formula; next, that the stages in the reaction are more numerous and extensive; and thirdly, that the pro- duct of the reaction is not true glucose, but maltose. Maltose is a sugar more akin to cane than grape sugar, of very little sweetening power, and with less reducing power over copper salts. Its formula is C12H22On. The action of saliva on starch is facilitated by: (a) Moderate heat, about 100° F. (37'8° C.). (b) A slightly alkaline medium, (c) Removal of the changed material from time to time. Its action is retarded by: (a) Cold; a temperature of 32° F. (0° C.) stops it for a time, but does not destroy it, whereas a high temperature above 140° F. (60° C.) destroys it. (b) Acids or strong alkalies either delay or stop the action altogether. (c) Presence of too much of the changed material. Ptyalin, in that it converts starch into sugar, is an amylolytic ferment. Starch appears to be the only principle of food upon which saliva acts chemically: it has no apparent influence on any of the other ternary prin- ciples, such as sugar, gum, cellulose, or on fat, and seems to be equally destitute of power over albuminous and gelatinous substances. Influence of the Nervous System.— The secretion of saliva is under the control of the nervous system. It is a reflex action, and in ordinary conditions is excited by the stimulation of the peripheral branches of two nerves, viz., the gustatory or lingual branch of the in- 232 HAND-BOOK OF PHYSIOLOGY. f erior maxillary division of the fifth nerve, and the glosso-pharyngeal part of the eighth pair of nerves, which are distributed to the mucous mem- brane of the tongue and pharynx. The stimulation occurs on the intro- duction of sapid substances into the mouth, and the secretion is brought about in the following way. From the terminations of these sensory nerves in the mucous membrane an impression is conveyed upward (affer- ent) to the special nerve centre situated in the medulla, which controls the process, and by it is reflected to certain nerves supplied to the salivary glands, which will be presently indicated. In other words, the centre, stimulated to action by the sensory impressions carried to it, sends out impulses along efferent or secretory nerves supplied to the salivary glands, which cause the saliva to be secreted by and discharged from the gland cells. Other stimuli, however, besides that of the food, and other sensory nerves besides those mentioned, may produce reflexly the same effects. Saliva may be caused to flow by irritation of the mucous membrane of the mouth with mechanical, chemical, electrical, or thermal stimuli, also by the irritation of the mucous membrane of the stomach in some way, as in nausea, which precedes vomiting, when some of the peripheral fibres of the vagi are irritated. Stimulation of the olfactory nerves by smell of food, of the optic nerves by the sight of it, and of the auditory nerves by the sounds which are known by experience to accompany the prepa- ration of a meal, may also, in the hungry, stimulate the nerve centre to action. In addition to these, as a secretion of saliva follows the move- ment of the muscles of mastication, it may be assumed that this move- ment stimulates the secreting nerve fibres of the gland, directly or re- flexly. From the fact that the flow of saliva may be increased or dimin- ished by* mental emotions, it is evident that impressions from the cere- brum also are capable of stimulating the centre to action or of inhibiting its action. Secretion may be excited by direct stimulation of the centre in the medulla. A. On the Submaxillary Gland. — The submaxillary gland has been the gland chiefly employed for the purpose of experimentally demonstra- ting the influence of the nervous system upon the secretion of saliva, be- cause of the comparative facility with which, with its blood-vessels and nerves, it may be exposed to view in the dog, rabbit, and other animals. The chief nerves supplied to the gland are: (1) the chorda tympani (a branch given off from the facial portio dura of the seventh pair of nerves), in the canal through which it passes in the temporal bone, in its passage from the interior of the skull to the face; and (2) branches of the sym- pathetic nerve from the plexus around the facial artery and its branches to the gland. The chorda (Fig. 170, ch. t.), after quitting the temporal bone, passes downward and forward, under cover of the external pterygoid muscle, and joins at an acute angle the lingual or gustatory nerve, pro- DIGESTION. 233 ceeds with it for a short distance, and then passes along the submaxillary gland duct (Fig. 170, sm. d.), to which it is distributed, giving branches to the submaxillary ganglion (Fig. 170, sm. gl.), and sending others to terminate in the superficial muscle of the tongue. If this nerve be exposed and divided anywhere in its course from its exit from the skull to the gland, the secretion, if the gland be in action, is arrested, and no stimu- lation either of the lingual or of the glosso-pharyngeal will produce a flow of saliva. But if the peripheral end of the divided nerve be stimulated, an abundant secretion of saliva ensues, and the blood supply is enormously FIG. 170.— Diagrammatic representation of the submaxillary gland of the dog with its nerves and blood-vessels. (This is not intended to illustrate the exact anatomical relations of the several struct- ures.) sm. gld., the submaxillary gland into the duct (sm. d.), of which a cannula has been tied. The sublingual gland and duct are not shown. n.L, n.l'., the lingual or gustatory nerve; ch. t., ch. £'., the chorda tympani proceeding from the facial nerve, becoming conjoined with the lingual at n. I'., and afterward diverging and passing to the gland along the duct; sm. gl.. submaxillary ganglion with its roots; n. /., the lingual nerve proceeding to the tongue; a. car., the carotid artery, two branches of which, a. sm. a. and r. sm. p., pass to the anterior and posterior parts of the gland; v. .S//1.. the anterior and posterior veins from the gland ending in v. j., the jugular vein; v. sym., the con- joined vagus and sympathetic trunks; gl. cer. s., the superior-cervical ganglion, two branches of which forming a plexus, a./., over the facial artery are distributed (n. sym. sm.) along the two glandular arteries to the anterior and posterior portion of the gland. The arrows indicate the direction taken by the nervous impulses; during reflex stimulations of the gland they ascend to the brain by the lin- gual and descend by the chorda tympani. (M. Foster.) increased, the arteries being dilated. The veins even pulsate, and the blood contained within them is more arterial than venous in character. When, on the other hand, the stimulus is applied to the sympathetic filaments (mere division producing no apparent effect), the arteries con- tract, and the blood stream is in consequence much diminished; and from the veins, when opened, there escapes only a sluggish stream of dark blood. The saliva, instead of being abundant and watery, becomes scanty and tenacious. If both chorda tympani and sympathetic branches be di- vided, the gland, released from nervous control, secretes continuously and abundantly (paralytic) secretion. The abundant secretion of saliva, which follows stimulation of the 234 HAND-BOOK OF PHYSIOLOGY. chorda tympani, is not merely the result of a filtration of fluid from the blood-vessels, in consequence of the largely increased circulation through them. This is proved by the fact that, when the main duct is obstructed, the pressure within may considerably exceed the blood-pressure in the arteries, and also that when into the veins of the animal experimented upon some atropin has been previously injected, stimulation of the peripheral end of the divided chorda produces all the vascular effects as before, without any secretion of saliva accompanying them. Again, if an animal's head be cut off, and the chorda be rapidly exposed and stimu- lated with an interrupted current, a secretion of saliva ensues for a short time, although the blood supply is necessarily absent. These experiments serve to prove that the chorda contains two sets of nerve fibres, one set (vaso-dilator) which, when stimulated, act upon a local vaso-motor centre for regulating the blood supply, inhibiting its action, and causing the vessels to dilate, and so producing an increased supply of blood to the gland; while another set, which are paralyzed by injection of atropin, directly stimulate the cells themselves to activity, whereby they secrete and discharge the constituents of the saliva which they produce. These latter fibres very possibly terminate in the salivary cells themselves. If, on the other hand, the sympathetic fibres be divided, stimulation of the tongue by sapid substances, or of the trunk of the lingual, or of the glosso- pharyngeal, continues to produce a flow of saliva. From these experi- ments it is evident that the chorda tympani nerve is the principal nerve through which efferent impulses proceed from the centre to excite the secretion of this gland. The sympathetic fibres appear to act principally as a vaso-constrictor nerve, and to exalt the action of the local vaso-motor centres. The sympathetic is more powerful in this direction than the chorda. There is not sufficient evidence in favor of the belief that the submaxillary gan- glion is ever the nerve centre which controls the secretion of the sub- maxillary gland. B. On the Parotid Gland. — The nerves which influence secretion in the parotid gland are branches of the facial (lesser superficial petrosal) and of the sympathetic. The former nerve, after passing through the otic ganglion, joins the auriculo-temporal branch of the fifth cerebral nerve, and, with it, is distributed to the gland. The nerves by which the stimu- lus ordinarily exciting secretion is conveyed to the medulla oblongata, are, as in the case of the submaxillary gland, the fifth, and the glossopharyn- geal. The pneumogastric nerves convey a further stimulus to the secre- tion of saliva, when food has entered the stomach; the nerve centre is the same as in the case of the submaxillary gland. Changes in the Gland Cells. — The method by which the salivary cells produce the secretion of saliva appears to be divided into two stages, which differ somewhat according to the class to which the gland belongs, DIGESTION. 235 viz., (1) the true salivary, or (2) the mucous type. In the former case, it has been noticed, as has been already described (p. 228), that during the rest which follows an active secretion the lumen of the alveoli be- comes smaller', the gland cells larger, and very granular. During secre- tion the alveoli and their cells become smaller, and the granular appear- ance in the latter to a considerable extent disappears, and at the end of secretion, the granules are confined to the inner part of the cell nearest to the lumen, which is now quite distinct (Fig. 171). It is supposed from these appearances that the first stage in the act of secretion consists in the protoplasm of the salivary cell taking up from the lymph certain materials from which it manufactures the elements of its own secretion, and which are stored up in the form of granules in the cell during rest, the second stage consisting of the actual discharge of c J\. r> \j FIG. 171.— Alveoli of true salivary gland. A, at rest; B, in the first stage of secretion; C, after prolonged secretion. (Langley.) these granules, with or without previous change. The granules are taken to represent the chief substance of the salivary secretion, i.e., the ferment ptyalin. In the case of the submaxillary gland of the dog, at any rate, the sympathetic nerve-fibres appear to have to do with the first stage of the process, and when stimulated the protoplasm is extremely active in manufacturing the granules, whereas the chorda tympani is concerned in the production of the second act, the actual discharge of the materials of secretion, together with a considerable amount of fluid, the latter being an actual secretion by the protoplasm, as it ceases to occur when atropin has been subcutaneously injected. In the mucous-secreting gland, the changes in the cells during secre- tion have been already spoken of (p. 228). They consist in the gradual secretion by the protoplasm of the cell of a substance called mucigen, which is converted into mucin, and discharged on secretion into the canal of the alveoli. The mucigen is, for the most part, collected into the inner part of the cells during rest, pressing the nucleus and the small portion of the protoplasm which remains, against the limiting membrane of the alveoli. The process of secretion in the salivary glands is identical with that of glands in general; the cells which line the ultimate branches of the ducts being the agents by which the special constituents of the saliva are formed. 236 HAND-BOOK OF PHYSIOLOGY. The materials which they have incorporated with themselves are almost at once given up again, in the form of a fluid (secretion), which escapes from the ducts of the gland; and the cells, themselves, undergo disinte- gration,— again to be renewed, in the intervals of the active exercise of their functions. The source whence the cells obtain the materials of their secretion, is the blood, or, to speak more accurately, the plasma, which is filtered off from the circulating blood into the interstices of the glands as of all living textures. THE PHARYNX. That portion of the alimentary canal which intervenes between the mouth and the oesophagus is termed the Pharynx (Fig. 165). It will suffice here to mention that it is constructed of a series of three muscles with striated fibres (constrict- ors), which are covered by a thin fascia externally, and are lined internally by a strong fascia (pharyn- geal aponeurosis), on the inner aspect of which is areolar (submucous) tissue and mucous membrane, continuous with that of the mouth, and, as regards the part concerned in swalloAving, is identical with i^ in general structure. The epithelium of this part of the Pharynx, like that of the mouth, is stratified brane with its papillae; nr\(\ cminrnrmss 6, lymphoid tissue, with an° US' (Key8) lymphoid sacs- The pharynx is well supplied with mucous glands (Fig. 174). The Tonsils. — Between the anterior and posterior arches of the soft palate are situated the Tonsils, one on each side. A tonsil consists of an elevation of the mucous membrane presenting 12 to 15 orifices, which lead into crypts or recesses, in the walls of which are placed nodules of adenoid or lymphoid tissue (Fig. 173). These nodules are enveloped in a less dense adenoid tissue which reaches the mucous surface. The surface is covered with stratified squamous epithelium, and the subepithelial or mucous membrane proper may present rudimentary papillse formed of adenoid tissue. The tonsil is bounded by a fibrous capsule (Fig. 173, e). Into the crypts open a number of ducts of mucous glands. The viscid secretion which exudes from the tonsils serves to lubricate the bolus of food as it passes them in the second part of the act of degluti- tion. THE (ESOPHAGUS OR GULLET. The (Esophagus or Gullet (Fig. 165), the narrowest portion of the alimentary canal, is a muscular and mucous tube, nine or ten inches in length, which extends from the lower end of the pharynx to the cardiac orifice of the stomach. DIGESTION. 237 Structure. — The oesophagus is made up of three coats — viz., the outer, mscular; the middle, submucous; and the inner, mucous. The mus- cular coat (Fig. 175, g and i) is covered externally by a varying amount >f loose fibrous tissue. It is composed of two layers of fibres, the outer ?ing arranged longitudinally, and the inner circularly. At the upper part of the oesophagus this coat is made up principally of striated muscle fibres, as they are continuous with the constrictor muscles of the pharynx; but lower down the unstriated fibres become more and more numerous, and toward the end of the tube form the entire coat. The muscular coat is connected with the mucous coat by a more or less developed layer of FIG. 173.— Vertical section through a crypt of the human tonsil, a, entrance to the crypt, which is divided below by the elevation which does not quite reach the surface ; 6, stratified epithelium ; c, masses of adenoid tissue; d, mucous glands cut across; e, fibrous capsule. (V. D. Harris.) areolar tissue, which forms the submucous coat (Fig 175, /), in which is contained in the lower half or third of the tube many mucous glands, the ducts of which, passing through the mucous membrane (Fig. 175, c) open on its surface. Separating this coat from the mucous membrane proper is a well-developed layer of longitudinal, unstriated muscle (d), called the muscular is mucosce. The mucous membrane is composed of a closely felted meshwork of fine connective tissue, which, toward the surface, is elevated into rudimentary papillae. It is covered with a stratified epithe- lium, of which the most superficial layers are squamous. The epithelium is arranged upon a basement membrane. In newly-born children the mucous membrane exhibits, in many parts, the structure of lymphoid tissue (Klein). Blood and lymph vessels, and nerves, are distributed in the walls of the oesophagus. Between the outer and inner layers of the muscular coat, nerve-ganglia of Auerbach are also found. 238 HAND-BOOK OF PHYSIOLOGY. DEGLUTITION OR SWALLOWING. When properly masticated, the food is transmitted in successive por- tions to the stomach by the act of deglutition or swallowing. This, for the purpose of description,, may be divided into three acts. In the first, particles of food collected to a morsel are made to glide between the sur- face of the tongue and the palatine arch, till they have passed the anterior arch of the fauces; in the second, the morsel is carried through the FIG. 174. FIG. 175. FIG. 174. — Section of a mucous gland from the tongue. A, opening of the duct on the free sur- face; C, basement membrane with nuclei; B, flattened epithelial cells lining duct. The duct divides into several branches, which are convoluted and end blindly, being lined throughout by columnar epithelium. D, lumen of one of the tubuli of the gland, x !X). (Klein and Noble Smith.) FIG. 175. — Longitudinal section of oesophagus of a dog toward the lower end. a, stratified epithe- lium of the mucous membrane; 6, mucous membrane proper; c, duct of mucous gland; d, muscu- laris mucosae ; e, mucous glands;/, submucous coat; g, circular muscular layer; /i, intermuscular layer, in which is contained the ganglion cells of Auerbach; i, longitudinal muscular layer; A-, outside investment of fibrous tissue. X 100. (V. D. Harris.) pharynx; and in the third, it reaches the stomach through the oesophagus. These three acts follow each other rapidly. (1.) Tli3 first act of deglutition may be voluntary, although it is usually performed unconsciously; the morsel of food, when sufficiently masticated, being pressed between the tongue and palate, by the agency of the muscles of the, former, in such a manner as to force it back to the entrance of the pharynx. (2. ) The second act is the most complicated, because the food must pass by the DIGESTION. 239 posterior orifice of the nose and the upper opening of the larynx without mching them. When it has been brought, by the first act, between the anterior arches of the palate, it is moved onward by the movement of the tongue backward, and by the muscles of the anterior arches contract- ing on it and then behind it. The root of the tongue being retracted, and the larynx being raised with the pharynx and carried forward under the base of the tongue, the epiglottis is pressed over the upper opening >f the larynx, and the morsel glides past it; the closure of the glottis being additionally secured by the simultaneous contraction of its own mus- cles: so that, even when the epiglottis is destroyed, there is little danger of food or drink passing into the larynx so long as its muscles can act freely. At the same time, the raising of the soft palate, so that its pos- terior edge touches the back part of the pharynx, and the approximation of the sides of the posterior palatine arch, which move quickly inward like side curtains, close the passage into the upper part of the pharynx and the posterior nares, and form an inclined plane, along the under surface of which the morsel descends; then the pharynx, raised up to receive it, in its turn contracts, and forces it omvard into the oesophagus. (3.) In the third act, in which the food passes through the oesophagus, every part of that tube, as it receives the morsel and is dilated by it, is stimu- lated to contract: hence an undulatory contraction of the oesophagus, which is easily observable in horses while drinking, proceeds rapidly along the tube. It is only when the morsels swallowed are large, or taken too fjiiickly in succession, that the progressive contraction of the oesophagus is slow, and attended with pain. Division of both pnetimogastric nerves paralyzes the contractile power of the oesophagus, and food accordingly accumulates in the tube. The second and third parts of the act of deglu- tition are involuntary. Nerve Mechanism. — The nerves engaged in the reflex act of deglu- tition are: — sensory, branches of the fifth cerebral supplying the soft } Dilate; glosso-pharyngeal, supplying the tongue and pharynx; the supe- rior laryngeal branch of the vagus, supplying the epiglottis and the glot- tis; while the motor fibres concerned are: — branches of the fifth, supply- ing part of the digastric and mylo-hyoid muscles, and the muscles of mastication; the facial, supplying the levator palati; the glosso-pharyn- geal, supplying the muscles of the pharynx; the vagus, supplying the muscles of the larynx through the inferior laryngeal branch, and the hypoglossal, the muscles of the tongue. The nerve-centre by which the muscles are harmonized in their action, is situate in the medulla oblongata. In the movements of the oesophagus, the ganglia contained in its walls, with the pneumogastrics, are the nerve-structures chiefly concerned. It is important to note that the swallowing both of food and drink is a muscular act, and can, therefore, take place in opposition to the force of :) 10 ii ANIM-.OOK OK PHYSIOLOGY. gravity, Tims, borrti 'and many other animals habitually drink uphill, and the same teat can he performed hy jui^lers. TIIK STOMACH. In man and t hose Mammalia which are provided with a : in" lc stomach, il consists of a dilatation of t he alimentary canal placed het ween and con Millions \\ il 1 1 t he (csophaiMis. which enters, its larger or card iac end on t he one hand, and the small intestine, which commences at its, narrowed end or p\ lorus, on I he oilier. It \aries in shape and si/.e accordini',' to its state of distension. The Ifiunhnuils (o\, sheep, deer, etc.) possess \er\ romple\ stomachs; in most of them four distinct cavities are to be distinguished ( l;i" I'iil). I. The run iifh or l\iiin< H, a \ cr\ larrc ca\ il \ \\ In. 'h occupies I he car diac end, and into \\hich lar^e <|uanlities of food are in the lirst instance s\\ allowed \\ilh little or no mast icat i(»n. ?. The /h'/int/tnii, or //onti/- ((»///> stomach, so called from the fact I hat its inn eon.-; memhrane i. posed in a numherol folds enclosing hexagonal cells. ','>. The / •JtfC I'h. I •;•«*, Sl,iin:i,-h..i IH-.-I. ,, .,- -.,.|.l.:ii-.n-.. K,t. ruinrn, /;, •/. ivl i.-iiliiiii; 7V. l»s.'ill.M-itnn, or • ; .l.iilioniMMiin. /),,., luo,r,-miiu; ,/. KI-,.,.V»- froiii .i-s.-pliiiKUN I.. psnll.Tllim. (lluxlvy.) or Mitni/fifft'ti, iii \vhi«-h I he mucous memhrane is MrrMU^ed in very promi- nent longitudinal folds. -I. .l/>tnnnsnni. lu'cd. or lit'/tticf, narrow and elongated, its mucous incmhrane hcin^ much more hi"hl\ vascular than thai of the other divisions. In the process of rumination small portions of the contents of the rumen and rclictilum are siiccessi\ el \ rejMirv.ilalcd illlo the month, and there Miorouj-Jdv ma.licalcd and insalivated (chew iii' ihccud): Miev are then a.",ain s\\ allon cd, heni", this lime directed hy a L^roo\e (\\hich in the li;Mirc is seen runnin.i>, from the lower end of the (esophagus) inlo lht> main plies, and thence into the ahomasuiu. It \\ill thus he seen that the lirst, t \\ o stomachs (paunch and retieulum) have ehicllv the- mechanical functions of storing and moistening t lie fodder: the third (mainplies) prohahlx ads as a st raiucr. only allouin:1; the linely divide*! portions of food to pass on into the fourth stomach, when1 the ":i inc juice is secreted and the process of digestion carried on. The mucous memhrane of the first three stomachs is lowly \ascular, while that of tht' fourth is pulpy, glandular, and highly vascular. In some ot her animals, as the pi." . a similar (list i net ion obtains het w ecu the mucous memhrane in dilTercnl parts of the stomach. Ill the piu" the ;d;ind • in (he cardiac end are few and small, while toward the p\ lorns they arc abundant and lar^e. A similar division of I he stomach into a cardiac (receptive) and a p\ loric (digestive) parl. foreshadowing the complex slomach of riiini naiiK is seen in I he common nil, in which these t \\ • • d i\ i. ion ,; of the .stomach are distinguished, nol only by the characlers of (heir lining membrane, but also Iry a well marked constriction. In birds the function of mastication is performed bv the stomach (^'i/- /ard) which in grauivoroUH orders, c. . I ') nuixrnltu\ (i5) sH/inmrtm*. and (I) mucous Milt \ with blood ve ids, l\ mphatics, and nerves d i ! nbiilc.l m and bet ween them. (1) The fn'i-ilniinil coat. IIM ' rucluiv of serous membrane in veil era! (p. :>l'.l). (I) The iiuisculitr coal consists of Mirce separate la\e|'80r . which, according to their several directions, are named the ilmlinal, eiivnlar. and ohli(|iu). The faiujit utliiHtl set are the most superficial: Miey are cont inuoiis wilh the longitudinal libre.s of t he o-: oph . and spread out in a. dmTviii" manner uverlhe cardiac end and 'omach. They extend as far a:- 1 he p\ lorn;1, heinn especial I \ distinct at the lesser or Upper Clir\alnrc of the slomaeh, alonv \\hieli they PM ';d si roii" bands. The next set are I he rircnhir or tritH*- wrM' fibres, which more or less completely encircle all parts of the stomach; they are most abundant at. 1 he middle MI id in I he p\ lorn- port ion of the •.!•;• MII. and form the chief parl. of t he t hiek projecting ring of the pylorus. These tibi-es are not, simple circles, but, form double or figure of S loops, t be fibre-: i 1 1 1 c i' . •(•( i IIM; very obliquely. The next, and con lently deepest set, of fibres, are the oblique, continuous with the < n cular miisr-nlar fibres of the oesophagus, and having the same double- lo.i|iei| ai Taiiycment . 1 luj.l, prevails in the pi-ecediiiL1: layer: they are eom- p;irati\el\ few in number, and are placed only at the cardiac orifice and portion of 1 he slomach, over both surfaces of which Ihev are spread, ;ome '.hlii|iiel\ from left to rij-ht, others from ri^ht to left, around the '•anliae (.rilice, to which, by llu-ir interlacing, they form a kind of sphincter, continuous with that around the h.wor end of the oosoplu^iiH. The muscular fibres of i he t omach and of t he intestinal canal arc tin sin "/'•'/. l.'ciiij on.iraled, spindle-shaped libre-cell . (;!) and ( I) The mucous membrane of tin st FIG. 190. FIG. 191. FIG. 190.— Section of small intestine showing villi, Lieberkiihn's glands and a Peyer's solitary gland, m, m, muscularis mucosee. (Klein and Noble Smith.) FIG. 191.— Vertical section of a villus of the small intestine of a cat. a, striated basilar border of the epithelium ; b, columnar epithelium ; c, goblet cells ; d, central lymph-vessel ; e, smooth muscular fibres; /, adenoid stroma of the villus in which lymph. corpuscles lie. (Klein.) The epithelium- is of the columnar kind, and continuous with that lining the other parts of the mucous membrane. The cells are arranged with their long axis radiating from the surface of the villus (Fig. 191), and their smaller ends resting on the basement membrane. The free surface of the epithelial cells of the villi, like that of the cells which cover the general surface of the mucous membrane, is covered by a fine border which exhibits very delicate striations, whence it derives its name, "stria- ted basilar border." Beneath the basement or limiting membrane there is a rich supply of blood-vessels. Two or more minute arteries are distributed within each villus; and from their capillaries, which form a dense network, proceed one or two small veins, which pass out at the base of the villus. The layer of the muscularis mucosce in the villus forms a kind of thin hollow cone immediately around the central lacteal, and is, therefore, DIGESTION. 261 situate beneath the blood-vessels. It is without doubt instrumental in the propulsion of chyle along the lacteal. The lacteal vessel enters the base of each villus, and passing up in the middle of it, extends nearly to the tip, where it ends commonly by a closed and somewhat dilated extremity. In the larger villi there may be two small lacteal vessels which end by a loop (Fig. 192), or the lacteals may form a kind of network in the villus. The last method of ending, however, is rarely or never seen in the human subject, although common in some of the lower animals (A, Fig. 192). FIG. 192.— A. Villus of sheep. B. Villi of man. (Slightly altered from Teichmann.) The office of the villi is the absorption of chyle and other liquids from the intestine. The mode in which they affect this will be considered in the Chapter on ABSORPTION. II. The Large Intestine. — The Large Intestine, which in an adult is from about 4 to 6 feet long, is subdivided for descriptive purposes into three portions (Fig. 165), viz.: — the ccecum, a short wide pouch, commu- nicating with the lower end of the small intestine through an opening, guarded by the ileo-ccecal valve; the colon, continuous with the caecum, which forms the principal part of the large intestine, and is divided into an ascending, transverse and descending portion; and the rectum, which, after dilating at its lower part, again contracts, and immediately afterward 262 HAND-BOOK OF PHYSIOLOGY. opens externally through the anus. Attached to the caecum is the small appendix vermiformis. Structure. — Like the small intestine, the large is constructed of four principal coats, viz., the serous, muscular, submucous, and mucous. The serous coat need not be here particularly described. Connected with it are the small processes of peritoneum, containing fat, called appendices epiploiccB. The fibres of the muscular coat, like those of the small in- testine, are arranged in two layers — the outer longitudinal, the inner circu- lar. In the caecum and colon, the longitudinal fibres, besides being, as in the small intestine, thinly disposed in all parts of the wall of the bowel, FIG. 193.— Diagram of lacteal vessels in small intestine. A, lacteals in villi ; p, Peyer's glands; B and D, superficial and deep network of lacteals in submucous tissue; L, Lieberkiihn's glands; E, small branch of lacteal vessel on its way to mesenteric gland; H and o, muscular fibres of intestine; s, peri- toneum. (Teichmann.) are collected, for the most part, into three strong bands, which being shorter, from end to end, than the other coats of the intestine, hold the canal in folds, bounding intermediate sacculi. On the division of these bands, the intestine can be drawn out to its full length, and it then as- sumes, of course, a uniformly cylindrical form. In the rectum, the fas- ciculi of these longitudinal bands spread out and mingle with the other longitudinal fibres, forming with them a thicker layer of fibres than exists on any other part of the intestinal canal. The circular muscular fibres are spread over the whole surface of the bowel, but are somewhat more DIGESTION. 263 marked in the intervals between the sacculi. Toward the lower end of the rectum they become more numerous, and at the anus they form a strong band called the internal sphincter muscle. The mucous membrane of the large, like that of the small intestine, is lined throughout by columnar epithelium, but, unlike it, is quite smooth and destitute of villi, and is not projected in the form of valvulce conni- ventes. Its general microscopic structure resembles that of the small in- testine: and it is bounded below by the muscularis mucosce. The general arrangement of ganglia and nerve-fibres in the large in- testine resembles that in the small (p. 255). Glands of the Large Intestine. — The glands with which the large intestine is provided are of two kinds, (1) the tubular and (2) the lymphoid. FIG. 194.— Horizontal section through a portion of the mucous membrane of the large intestine, showing Lieberktihn's glands in transverse section, a, lumen of gland— lining of columnar cells with c, goblet cells, 6, supporting connective tissue. Highly magnified. (V. D. Harris.) (1.) The tubular glands, or glands of Lieberkiihn, resemble those of the small intestine, but are somewhat larger and more numerous. They are also more uniformly distributed. (2.) Follicles of adenoid or lymphoid tissue are most numerous in the caecum and vermiform appendix. They resemble in shape and structure, almost exactly, the solitary glands of the small intestine. Peyer's patches are not found in the large intestine. Ileo-Caecal Valve.— The ileo-csecal valve is situate at the place of junction of the small with the large intestine, and guards against any re- flex of the contents of the latter into the ileum. It is composed of two semilunar folds of mucous membrane. Each fold is formed by a doubling inward of the mucous membrane, and is strengthened on the outside by 264 HAND-BOOK OF PHYSIOLOGY. some of the circular muscular fibres of the intestine, which are contained between the cuter surfaces of the two layers of which each fold is composed. While the circular muscular fibres, however, of the bowel at the junction of the ileum with the caecum are contained between the outer opposed surfaces of the folds of mucous membrane which form the valve, the longitudinal muscular fibres and the peritoneum of the small and large intestine respectively are continuous with each other, without dipping in to follow the circular fibres and the mucous membrane. In this man- ner, therefore, the folding inward of these two last-named structures is preserved, while, on the other hand, by dividing the longitudinal muscu- lar fibres and the peritoneum, the valve can be made to disappear, just as the constrictions between the sacculi of the large intestine can be made to disappear by performing a similar operation. The inner surface of the folds is smooth; the mucous membrane of the ileum being con- tinuous with that of the caecum. That surface of each fold which looks toward the small intestine is covered with villi, while that which looks to the caecum has none. When the caecum is distended, the margin of the folds are stretched, and thus are brought into firm apposition one with the other. DIGESTION IN THE INTESTINES. After the food has been duly acted upon by the stomach, such as has not been absorbed passes into the duodenum, and is there subjected to the action of the secretions of the pancreas and liver, which enter that portion of the small intestine. Before considering the changes which the food undergoes in consequence, attention should be directed to the structure and secretion of these glands, and to the secretion (succus en- tericus) which is poured out into the intestines from the glands lining them. THE PANCBEAS, AND ITS SECKETION. The Pancreas is situated within the curve formed by the duodenum; and its main duct opens into that part of the small intestine, through a small opening, or through a duct common to it and to the liver, about two and a half inches from the pylorus. Structure. — In structure the pancreas bears some resemblance to the salivary glands. Its capsule and septa, as well as the blood-vessels and lymphatics, are similarly distributed. It is, however, looser and softer, the lobes and lobules being less compactly arranged. The main duct divides into branches (lobar ducts), one for each lobe, and these branches subdivide into intralobular ducts, and these again by their division and branching form the gland tissue proper. The intralobular ducts corre- DIGESTION. 265 spond to a lobule, while between them and the secreting tubes or are longer or shorter intermediary ducts. The larger ducts possess a very distinct lumen and a membrana propria lined with columnar epi- thelium, the cells of which are longitudinally striated, but are shorter than those found in the ducts of the salivary glands. In the intralobular ducts the epithelium is short and the lumen is smaller. The intermediary ducts opening into the alveoli possess a distinct lumen, with a membrana propria lined with a single layer of flattened elongated cells. The alveoli arc branched and convoluted tubes, with a membrana propria lined with a single layer of columnar cells. They have no distinct lumen, its place being taken by fusiform or branched cells. Heidenhain has observed that the alveoli cells in the pancreas of a fasting dog consist of two zones, an inner or central zone, which is finely granular, and which stains feebly, Fro. 195.— Section of the pancreas of a dog during digestion, a, alveoli lined with cells, the outer zone of which is well stained with haematoxylin ; d, intermediary duct lined with squamous epithelium. X 350. (Klein and Noble Smith.) and a smaller parietal zone of finely striated protoplasm, which stains easily. The nucleus is partly in one, partly in the other zone. During digestion, it is found that the outer zone increases in size, and the central zone diminishes; the cell itself becoming smaller from the discharge of the secretion. At the end of digestion the first condition again appears, the inner zone enlarging at the expense of the outer. It appears that the granules are formed by the protoplasm of the cells, from material supplied to it by the blood. The granules are thought to be not the ferment itself, but material from which, under certain conditions, the ferments of the gland are made, and therefore called Zymogen. Pancreatic Secretion. — The secretion of the pancreas has been ob- tained for purposes of experiment from the lower animals, especially the dog, by opening the abdomen and exposing the duct of the gland, which is then made to communicate with the exterior . A pancreatic fistula is thus established. 266 HAND-BOOK OF PHYSIOLOGY. An extract of pancreas made from the gland, which has been removed from an animal killed during digestion, possesses the active properties of pancreatic secretion. It is made by first dehydrating the gland, which has been cut up into small pieces, by keeping it for some days in absolute alcohol, and then, after the entire removal of the alcohol, placing it in strong glycerin.- A glycerin extract is thus obtained. It is a remarkable fact, however, that the amount of the ferment trypsin greatly increases if the gland be exposed to the air for twenty-four hours before placing in alcohol; indeed, a glycerin extract made from the gland immediately upon removal from the body often appears to contain none of that fer- ment. This seems to indicate that the conversion of zymogen in the gland into the ferment only takes place during the act of secretion, and that the gland, although it always contains in its cells the materials (tryp- sinogen) out of which trypsin is formed, yet the conversion of the one into the other only takes place by degrees. Dilute acid appears to assist and accelerate the conversion, and if a recent pancreas be rubbed up with dilute acid before dehydration, a glycerin extract made afterward, even though the gland may have been only recently removed from the body, is very active. Properties. — Pancreatic juice is colorless, transparent, and slightly viscid, alkaline in reaction. It varies in specific gravity from 1010 to 1015, according to whether it is obtained from a permanent fistula — then more watery — or from a newly-opened duct. The solids vary in a tempo- rary^ fistula from 80 to 100 parts per thousand, and in a permanent one from 16 to 50 per thousand. CHEMICAL COMPOSITION OF THE PANCREATIC SECRETION. From a permanent fistula. (Bernstein.) Water . . . 975 Solids — Ferments : Proteids, including Serum — Albumin, Casein, ) -, -, Leucin and Tyrosin, Fats and Soaps . j Inorganic residue, especially Sodium Carbonate . 8 25 1000 Functions. — (1.) It converts proteids into peptones, the intermediate product being not akin to syntonin or acid-albumin, as in gastric diges- tion, but to alkali-albumin. Kiiline believes that the intermediate pro- ducts, both in the peptic and pancreatic digestion of proteids, are two, viz., antialbumose and hemialbumose, and that the peptones formed cor- respond to these, viz., antipeptone and hemipeptone. The hemipeptone is capable of being converted by the action of the pancreatic ferment — DIGESTION. 267 trypsin — into leucin and tyrosin, but is not so changed by pepsin; the antipeptone cannot be further split up. The products of pancreatic digestion are sometimes further complicated by the appearance of certain faecal substances, of which iiidol and naphthilamine are the most impor- tant. (Kiilme.) When the digestion goes on for a long time the indol is formed in con- siderable quantities, and emits a most disagreeable faecal odor, which was attributed to putrefaction till Kiihne showed its true nature. All the al- buminous or proteid substances which have not been converted into pep- tone, and absorbed in the stomach, and the partially changed substances, i.r.. the parapeptones, are converted into peptone by the pancreatic juice, and then in part into leucin and tyrosin. (2.) Nitrogenous bodies other than proteids, are not to any extent altered. Mucin can, however, be dissolved, but not gelatin or horny tis- sues. (3.) Starch is converted into glucose in an exactly similar manner to that which happens with the saliva. As mentioned before, it seems not unlikely that glucose is not formed at once from starch, but that certain dextrines are intermediate products. If the sugar which is at first formed, as is stated by some chemists, be not glucose but maltose, at any rate the pancreatic juice after a time completes the whole change of starch into glucose. There is a distinct amylolytic ferment (Amylopsin) in the pan- creatic juice which cannot be distinguished from ptyalin. (4.) Oils and fats are both emulsified and split up into their fatty acids and glycerin by pancreatic secretion. Even if part of this action is due to the alkalinity of the medium, it is probable that there is a third distinct ferment (Steapsin) which facilitates the change. Several cases have been recorded in which the pancreatic duct being obstructed, so that its secretion could not be discharged, fatty or oily matter was abundantly discharged from the intestines. In nearly all these cases, indeed, the liver was coincidently diseased, and the change or absence of the bile might appear to contribute to the result; yet the frequency of extensive disease of the liver, unaccompanied by fatty dis- charges from the intestines, favors the view that, in these cases, it is to the absence of the pancreatic fluid from the intestines that the excretion or non-absorption of fatty matter should be ascribed. (5.) It possesses the property of curdling milk, containing a special (rennet) ferment for that purpose. The ferment is distinct from trypsin, and will act in the presence of an acid (W. Roberts). Conditions favorable to the Action of the Pancreatic Juice.— These are similar to those which are favorable to the action of the saliva, and the reverse (p. 231). 268 HAND-BOOK OF PHYSIOLOGY. THE LIVEE. The Liver, the largest gland in the body, situated in the abdomen, chiefly on the right side, is an extremely vascular organ, and receives its supply of blood from two distinct vessels, the portal vein and hepatic ar- tery, while the blood is returned from it into the vena cava inferior by the hepatic veins. Its secretion, the bile, is conveyed from it by the hepatic duct, either directly into the intestine, or, when digestion is not going on, into the cystic duct, and thence into the gall-bladder, where it FIG. 196. — The under surface of the liver. G. B., gall-bladder; H. D., common bile-duct; H. A., hepatic artery; v. p., portal vein; L, Q., lobulus quadratus; L. s., lobulus spigelii; L. c., lobulus cau- datus; D.-V., ductus venosus; u. v., umbilical vein. (Noble Smith.) accumulates until required. The portal vein, hepatic artery, and hepatic duct branch together throughout the liver, while the hepatic veins and their tributaries run by themselves. On the outside the liver has an incomplete covering of peritoneum, and beneath this is a very fine coat of areolar tissue, continuous over the whole surface of the organ. It is thickest where the peritoneum is absent, and is continuous on the general surface of the liver with the fine and, in the human subject, almost imperceptible, areolar tissue investing the lobules. At the transverse fissure it is merged in the areolar investment called Glisson's capsule, which, surrounding the portal vein, hepatic ar- tery, and hepatic duct, as they enter at this part, accompanies them in their branchings through the substance of the liver. Structure. — The liver is made up of small roundish or oval portions called lobules, each of which is about -fa of an inch in diameter, and com- posed of the minute branches of the portal vein, hepatic artery, hepatic duct, and hepatic vein; while the interstices of these vessels are filled by the liver cells. The hepatic cells (Fig. 197), which form the glandular or secreting part of the liver, are of a spheroidal form, somewhat polyg- DIGESTION. 269 onul from mutual pressure about -^ to T151jnr inch in diameter, possess- ing one, sometimes two nuclei. The cell-substance contains numerous fatty molecules, and some yellowish-brown granules of bile-pigment. The cells sometimes exhibit slow amoeboid movements. They are held to- gether by a very delicate sustentacular tissue, continuous with the inter- lobular connective tissue. To understand the distribution of the blood-vessels in the liver, it will be well to trace, first, the two blood-vessels and the duct which enter the organ on the under surface at the transverse fissure, viz., the portal vein, hepatic artery, and hepatic duct. As before remarked, all three run in company, and their appearance on longitudinal section is shown in FIG. 197. FIG. 198. FIG. 197.— A. Liver-cells. B, Ditto, containing various sized particles of fat. FIG. 198. — Longitudinal section of a portal canal, containing a portal vein, hepatic artery and hepatic duct, from the pig. P, branch of vena portae, situate in a portal canal formed amongst the lobules of the liver, 1 1, and giving off vaginal branches; there are also seen within the large portal vein numerous orifices of the smallest interlobular veins arising directly from it; a, hepatic artery; d, hepatic duct, x 5. (Kiernan.) Fig. 198. Running together through the substance of the liver, they are contained in small channels called portal canals, their immediate invest- ment being a sheath of areolar tissue (Glisson's capsule). To take the distribution of the portal vein first: — In its course through the liver this vessel gives off small branches which divide and subdivide between the lobules surrounding them and limiting them, and from this circumstance called inter-lobular veins. From these small vessels a dense capillary network is prolonged into the substance of the lobule, and this network, gradually gathering itself up, so to speak, into larger vessels, converges finally to a single small vein, occupying the centre of the lobule, and hence called ^ra-lobular. This arrangement is well seen in Fig. 199, which represents a transverse section of a lobule. 270 HAND-BOOK OF PHYSIOLOGY. The small m^m-lobular veins discharge their contents into veins called (h h h, Fig. 200) ; while these again, by their union, form FIG. 199.— Cross-section of a lobule of the human liver, in which the capillary network between the portal and hepatic veins has been fully injected. 1, section of the mfra-lobular vein; 2, its smaller branches collecting blood from the capillary network; 3, tnfer-k>bular branches of the vena portre with their smaller ramifications passing inward toward the capillary network in the substance of the lobule, x 60. (Sappey.) FIG. 200.— Section of a portion of liver passing longitudinally through a considerable hepatic vein, from the pig. H, hepatic venous trunk, against which the sides of the lobules (I) are applied; /i, 7i, 7i, sublobular hepatic veins, on which the bases of the lobules rest, and through the coats of which they are seen as polygonal figures; t, mouth of the intralobular veins, opening into the sublobular veins; i', intralobular veins shown passing up the centre of some divided lobules; I, I, cut surface of the liver; c, c, walls of the hepatic venous canal, formed by the polygonal bases of the lobules. X 5. (Kiernan.) the main branches of the hepatic veins, which leave the posterior border of the liver to end by two or three principal trunks in the interior vena DIGESTION. 271 cava, just before its passage through the diaphragm. The swi-lobular and hepatic veins, unlike the portal vein and its companions, have little or no areolar tissue around them, and their coats being very thin, they form little more than mere channels in the liver substance which closely surrounds them. The manner in which the lobules are connected with the sub-lobular veins by means of the small intra-lobular veins is well seen in the diagram (Fig. 200 and in Fig. 201), which represent the parts as seen in a longitudinal section. The appearance has been likened to a twig having leaves without footstalks — the lobules representing the leaves, and the sub-lobular vein the small branch from which it springs. On a transverse section, the appearance of the intra-lobular veins is that of 1, Fig. 199, while both a transverse and longitudinal sec- tion are exhibited in Fig. 176. The hepatic artery, the function of which is to distribute blood for nutrition to Glisson's capsule, the walls of the ducts and blood- vessels, and other parts of the liver, is distrib- uted in a very similar manner to the portal vein, its blood being returned by small branches either into the rami- fications of the portal vein, or into the capillary plexus of the lobules which connects the inter and infra lobular veins. FIG. 201. — Diagram showing the manner in which the lobules of the liver rest on the sublobular veins. (After Kiernan.) Fia. 202. — Capillary network of the lobules of the rabbit's liver. The figure is taken from a very •successful injection of the hepatic veins, made by Harting: it shows nearly the whole of two lobules, and parts of three others; p, portal branches running in the interlobular spaces; h, hepatic veins pen- etrating and radiating from the centre of the lobules. X 45. (Kolliker.) The hepatic duct divides and subdivides in a manner very like that of the portal vein and hepatic artery, the larger branches being lined by cylindrical, and the smaller by small polygonal epithelium. 272 HAND-BOOK OF PHYSIOLOGY. The bile-capillaries commence between the hepatic cells, and are bounded by a delicate membranous wall of their own. They appear to be always bounded by hepatic cells on all sides, and are thus separated from the nearest blood-capillary by at least the breadth of one cell (Figs. 203 and 204). The Gall-Bladder.— The Gall-bladder (G, B, Fig. 196) is a pyriform bag, attached to the under surface of the liver, and supported also by the peritoneum, which passes below it. The larger end or fundus, projects beyond the front margin of the liver; while the smaller end contracts into the cystic duct. Structure. — The walls of the gall-bladder are constructed of three principal coats. (1) Externally (excepting that part which is in contact with the liver), is the serous coat, which has the same structure as the peritoneum with which it is continuous. Within this is (2) the fibrous or areolar coat, constructed of tough fibrous and elastic tissue, with which is mingled a considerable number of plain muscu- lar fibres, both longitudinal and circular. (3) Internally the gall-bladder is lined by mucous membrane, and a layer of columnar epithelium. The surface of the mucous membrane presents to the naked eye a minutely honeycombed appearance from a number of tiny polygonal depressions with intervening ridges, by which its surface is mapped out. In the cystic FIG. 203.— Portion of a lobule of liver, a, bile capillaries between liver-cells, the network in which is well seen; 6, blood capillaries. X 350. (Klein and Noble Smith.) FIG. 204.— Hepatic cells and bile capillaries, from the liver of a child three months old. Both fig- ures represent fragments of a section carried through the periphery of a lobule. The red corpuscles of the blood are recognized by their circular contour; vp, corresponds to an interlobular vein in im- mediate proximity with which are the epithelial cells of the biliary ducts, to which, at the lower part of the figures, the much larger hepatic cells suddenly succeed. (E. Bering.) duct the mucous membrane is raised up in the form of crescentic folds, which together appear like a spiral valve, and which minister to the function of the gall-bladder in retaining the bile during the intervals of digestion. DIGESTION. 273 The gall-bladder and all the main biliary ducts are provided with mucous glands, which open on their internal surface. Functions of the Liver. — The functions of the Liver may be classified under the following heads: — 1. The Secretion of Bile. 2. The Elaboration of Blood; under this head may be included the Glycogenic Function. I. THE SECRETION OF BILE. Properties of the Bile. — The bile is a somewhat viscid fluid, of a yellow or reddish-yellow color, a strongly bitter taste, and, when fresh, with a scarcely perceptible odor: it has a neutral or slightly alkaline reac- tion, and its specific gravity is about 1020. Its color and degree of con- sistence vary much, apparently independent of disease; but? as a rule, it becomes gradually more deeply colored and thicker as it advances along its ducts, or when it remains long in the gall-bladder, wherein, at the same time, it becomes more viscid and ropy, of a darker color, and more bitter taste, mainly from its greater degree of concentration, on account of partial absorption of its water, but partly also from being mixed with mucus. Chemical Composition of Human Bile. (Frerichs.) Water Solids Bile salts or Bilin . Fat .... Cholesterin Mucus and coloring matters Salts 859-2 140-8 1000-0 91-5 9-2 2.6 29.8 7-7 140-8 Bile salts, or Bilin, can be obtained as colorless, exceedingly deliques- cent crystals, soluble in water, alcohol, and alkaline solutions, giving to- the watery solution the taste and general characters of bile. They consist of sodium salts of glycocholic and taurocholic acids. The former salt is composed of cholic acid conjugated with glycin (see Appendix), the latter of the same acid conjugated with taurin. The proportion of these two- salts in the bile of different animals varies, e.g., in ox bile the glycocho- late is in great excess, whereas the bile of the dog, cat, bear, and other carnivora contains taurocholate alone; in human bile both are present in about the same amount (glycocholate in excess?). Preparation of Bile Salt. — Bile salts may be prepared in the fol- VOL. I.— 18. 274 HAND-BOOK OF PHYSIOLOGY. lowing manner: mix bile which has been evaporated to a quarter of its bulk with -animal charcoal, and evaporate to perfect dryness in a water bath. Next extract the mass whilst still warm with absolute alcohol. Separate the alcoholic extract by filtration, and to it add perfectly anhy- drous ether as long as a precipitate is thrown down. The solution and precipitate should be set aside in a closely stoppered bottle for some days, when crystals of the bile salts or bilin will have separated out. The gly- cocholate may be separated from the taurocholate by dissolving bilin in water, and adding to it a solution of neutral lead acetate, and then a little .basic lead acetate, when lead glycocholate separates out. Filter and add 'to the filtrate lead acetate and ammonia, a precipitate of lead taurocho- late will be formed, which may be filtered off. In both cases, the lead may be got rid of by suspending or dissolving in hot alcohol, adding hydrogen sulphate, filtering and allowing the acids to separate out by the addition of water. The test for bile salts is known as Pettenkofer's. If to an aqueous solution of the salts strong sulphuric acid be added, the bile acids are first of all precipitated, but on the further addition of the acid are re-dissolved. If to the solution a drop of solution of cane sugar be added, a fine purple color is developed. The re-action will also occur on the addition of grape or fruit sugar instead of cane sugar, slowly with the first, quickly with the last; and a color similar to the above is produced by the action of sulphuric acid and sugar on albumen, the crystalline lens, nerve tissue, oleic acid, pure ether, cholesterin, morphia, codeia and amylic alcohol. The spectrum of Pettenkofer's reaction, when the fluid is moderately diluted, shows four bands — the most marked and largest at E, and a little to the left; another at F; a third between D and E, nearer to D; and the fourth near D. The yellow coloring matter of the bile of man and the Carnivora is termed Bilinibin or Bilifulvin (cJ6HJ8N2o3) crystallizable and insoluble in water, soluble in chloroform or carbon disulphate; a green coloring matter, Biliverdin (c16H20N2o6), which always exists in large amount in the bile of Herbivora, being formed from bilirubin on exposure to the air, or by sub- jecting the bile to any other oxidizing agency, as by adding nitric acid. When the bile has been long in the gall-bladder, a third pigment, Bilipra- sin, may be also found in small amount. In cases of biliary obstruction, the coloring matter of the bile is re- absorbed, and circulates with the blood, giving to the tissues the yellow tint characteristic of jaundice. The coloring matters of human bile do not appear to give characteristic absorption spectra; but the bile of the guinea pig, rabbit, mouse, sheep, ox, and crow do so, the most constant of which appears to be a band at DIGESTION. 275 F. The bile of the sheep and ox give three bands in a thick layer, and four or five bands with a thinner layer, one on each side of D, one near E, and a faint line at F. (McMunn.) . There seems to be a close relationship between the color-matter of the "blood and of the bile, and it may be added, between these and that of the urine (urobilin), and of the fa?ces (stercobilin) also; -it is probable they are, all of them, varieties of the same pigment, or derived from the same source. Indeed it is maintained that Urobilin is identical with Hydro- bilirubin, a substance which is obtained from bilirubin by the action of sodium amalgam, or by the action of sodium amalgam on alkaline haema- tin; both urobilin and hydrobilirubin giving a characteristic absorption band between b and F. They are also identical with stercobilin, which is formed in the alimentary canal from bile pigments. A common test (Gmelin's) for the presence of bile-pigment consists of the addition of a small quantity of nitric acid, yellow with nitrous acid; if bile be present, a play of colors is produced, beginning with green and passing through blue and violet to red, and lastly to yellow. The spec- trum of Gmelin's test gives a black band extending from near b to beyond F. Fatty substances are found in variable proportions in the bile. Besides the ordinary saponifiable fats, there is a small quantity of ChoUsforin, a so-called non-saponifiable fat, which, with the other free fats, is prob- ably held in solution by the bile salts. It is a body belonging to the class of mon- atomic alcohols (c26H44o), and crystallizes in rhombic plates (Fig. 205). It is insoluble in water and cold alcohol, but dissolves easily in boiling alcohol or ether. It gives a red color with strong sulphuric acid, and with nitric acid and ammonia; also a play of colors beginning with blood red and ending with green on the addition of sulphuric acid and chloroform. Lecithin (c44H90^P09), a phosphorus-containing body and Neurin (c6H1BNOa), are also found in bile, the latter probably as a decomposition product of the former. The Mucus in bile is derived from the mucous membrane and glands of the gall-bladder, and of the hepatic ducts. It constitutes the residue after bile is treated with alcohol. The epithelium with which it is mixed may be detected in the bile with the microscope in the form of cylindrical cells, either scattered or still held together in layers. To the presence of the mucus is probably to be ascribed the rapid decomposition undergone by the bilin; for, according to Berzelius, if the mucus be separated, bile will remain unchanged for many days. The Saline or inorganic constituents of the bile are similar to those FIG. 205.— Crystalline scales of cholestefin. 276 HAND-BOOK OF PHYSIOLOGY. found in most other secreted fluids. It is possible that the carbonate and neutral phosphate of sodium and potassium, found in the ashes of bile, are formed in the incineration, and do not exist as such in the fluid. Oxide of iron is said to be a common constituent of the ashes of bile, and copper is generally found in healthy bile, and constantly in biliary calculi. Gas — A certain .small amount of carbonic acid, oxygen, and nitrogen, may be extracted from bile. Mode of Secretion and Discharge. — The process of secreting bile is continually going on, but appears to be retarded during fasting, and accelerated on taking food. This has been shown by tying the common bile-duct of a dog, and establishing a fistulous opening between the skin and gall-bladder, whereby all the bile secreted was discharged at the sur- face. It was noticed that when the animal was fasting, sometimes not a drop of bile was discharged for several hours; but that, in about ten min- utes after the introduction of food into the stomach, the bile began to flow abundantly, and continued to do so during the whole period of diges- tion. (Blondlot, Bidder and Schmidt.) The bile is formed in the hepatic cells; then, being discharged into the minute hepatic ducts, it passes into the larger trunks, and from the main hepatic duct maybe carried at once into the duodenum. But, prob- ably, this happens only while digestion is going on; during fasting, it regurgitates from the common bile-duct through the cystic duct, into the gall-bladder, where it accumulates till, in the next period of digestion, it is discharged into the intestine. The gall-bladder thus fulfils what ap- pears to be its chief or only office, that of a reservoir; for its presence enables bile to be constantly secreted, yet insures its employment in the service of digestion, although digestion is periodic, and the secretion of bile constant. The mechanism by which the bile passes into the gall-bladder is sim- ple. The orifice through which the common bile-duct communicates with the duodenum is narrower than the duct, and appears to be closed, except when there is sufficient pressure behind to force the bile through it. The pressure exercised upon the bile secreted during the intervals of digestion appears insufficient to overcome the force with which the ori- fice of the duct is closed; and the bile in the common duct, finding no exit in the intestine, traverses the cystic duct, and so passes into the gall- bladder, being probably aided- in this retrograde course by the peristaltic action of the ducts. The bile is discharged from the gall-bladder and enters the duodenum on the introduction of food into the small intestine: being pressed on by the contraction of the coats of the gall-bladder, and of the common bile-duct also; for both these organs contain unstriped muscular fibre-cells. Their contraction is excited by the stimulus of the food in the duodenum acting so as to produce a reflex movement, the force of which is sufficient to open the orifice of the common bile-duct. DIGESTION. 277 Bile, as such, is not pre-formed in the blood. As just observed, it is formed by the hepatic cells, although some of the material may be brought to them almost in the condition for immediate secretion. When it is, however, prevented by an obstruction of some kind, from escaping into the intestine (as by the passage of a gall-stone along the hepatic duct) it is absorbed in great excess into the blood, and, circulating with it, gives rise to the well-known phenomena of jaundice. This is explained by the fact that the pressure of secretion in the ducts is normally very low, and if it exceeds f inch of mercury (16 mm.) the secretion ceases to be poured out, and if the opposing force be increased, the bile finds its way into the blood, Quantity. — Various estimates have been made of the quantity of bile discharged into the intestines in twenty-four hours: the quantity doubtless ' varying, like that of the gastric fluid, in proportion to the amount of food taken. A fair average of several computations would give 20 to 40 oz. (600 — 900 cc.) as the quantity daily secreted by man. Uses. — (1) As an excrementitious substance, the bile may serve especially as a medium for the separation of excess of carbon and hydrogen from the blood; and its adaptation to this purpose is well illustrated by the peculiarities attending its secretion and disposal in the foetus. During intra-uterine life, the lungs and the intestinal canal are almost inactive; there is no respiration of open air or digestion of food; these are unneces- sary, on account of the supply of well elaborated nutriment received by the vessels of the foetus at the placenta. The liver, during the same time, is proportionately larger than it is after birth, and the secretion of bile is active, although there is no food in the intestinal canal upon which it can exercise any digestive property. At birth, the intestinal canal is full of thick bile, mixed with intestinal secretion; the meconium, or faeces of the foetus, containing all the essential principles of bile. Composition of Meconium (Frerichs) : Biliary resin Common fat and cholesterin Epithelium, mucus, pigment, and salts 15.6 15.4 69.0 100.0 In the foetus, therefore, the main purpose of the secretion of bile must be the purification of blood by direct excretion, i.e., by separation from the blood, and ejection from the body without further change. Probably all the bile secreted in foetal life is incorporated in the meconium, and with it discharged, and thus the liver may be said to discharge a function in some sense vicarious of that of the lungs. For, in the foetus, nearly all the blood coming from the placenta passes through the liver, previous to its distribution to the several organs of the body; and the abstraction of 278 HAKD-BOOK OF PHYSIOLOGY. carbon, hydrogen, and other elements of bile will purify it, as in extra- uterine life it is purified by the separation of carbonic acid and water at the lungs. The evident disposal of the foetal bile by excretion, makes it highly probable that the bile in extra-uterine life is also, at least in part, destined to be discharged as excrementitious. The analysis of the faeces of both children and adults shows that (except when rapidly discharged in pur- gation) they contain very little of the bile secreted, probably not more than one-sixteenth part of its weight, and that this portion includes chiefly its coloring, and some of its fatty matters, and to only a very slight degree, its salts, almost all of which have been re-absorbed from the intestines into the blood. The elementary composition of bile salts shows, however, such a pre- ponderance of carbon and hydrogen, that probably, after absorption, it combines with oxygen, and is excreted in the form of carbonic acid and water. The change after birth, from the direct to the indirect mode of excretion of the bile, may, with much probability, be connected with a purpose in relation to the development of heat. The temperature of the foetus is maintained by that of the parent, and needs no source of heat within itself; but, in extra-uterine life, there is (as one may say) a waste of material for heat when any excretion is discharged unoxidized; the carbon and hydrogen of the bilin, therefore, instead of being ejected in the faeces, are re-absorbed, in order that they may be combined with oxygen, and that in the combination heat may be generated. A substance, which has been discovered in the faeces, and named ster- corin is closely allied to cholesterin; and it has been suggested that while one great function of the liver is to excrete cholesterin from the blood, as the kidney excretes urea, the stercorin of faeces is the modified form in which cholesterin finally leaves the body. Ten grains and a half of ster- corin are excreted daily (A. Flint). From the peculiar manner in which the liver is supplied with much of the blood that flows through it, it is probable that this organ is excre- tory, not only for such hydro-carbonaceous matters as may need expulsion from any portion of the blood, but that it serves for the direct purification of the stream which, arriving by the portal vein, has just gathered up various substances in its course through the digestive organs — substances which may need to be expelled, almost immediately after their absorption.- For it is easily conceivable that many things may be taken up during digestion, which not only are unfit for purposes of nutrition, but which would be positively injurious if allowed to mingle with the general mass of the blood. The liver, therefore, may be supposed placed in the only road by which such matters can pass unchanged into the general current, jealously to guard against their further progress, and turn them back again into an excretory channel. The frequency with which metallic DIGESTION. 279 poisons are either excreted by the liver, or intercepted and retained, often for a considerable time, in its own substance, may be adduced as evidence for the probable truth of this supposition. (2). As cf digestive fluid. — Though one chief purpose of the secretion of bile may thus appear to be the purification of the blood by ultimate excretion, yet tli3re are many reasons for believing that, while it is in the intestines, it performs an important part in the process of digestion. In nearly all animals, for example, the bile is discharged, not through an excretory duct communicating with the external surface or with a simple reservoir, as most excretions are, but is made to pass into the intestinal canal, so as to be mingled with the chyme directly after it leaves the stomach; an arrangement, the constancy of which clearly indicates that the bile has some important relations to the food with which it is thus mixed. A similar indication is furnished also by the fact that the secre- tion of bile is most active, and the quantity discharged into the intestines much greater, during digestion than at any other time; although, with- out doubt, this activity of secretion during digestion may, however, be in part ascribed to the fact that a greater quantity of blood is sent through the portal vein to the liver at this time, and that this blood contains some of the materials of the food absorbed from the stomach and intestines, which may need to be excreted, either temporarily (to be afterward reab- sorbed) or permanently. Respecting the functions discharged by the bile in digestion there is little doubt that it, (a.) assists in emulsifying the fatty portions of the food, and thus rendering them capable of being absorbed by the lacteals. For it has appeared in some experiments in which the common bile-duct was tied, that, although the process of digestion in the stomach was un- aifected, chyle was no longer well formed; the contents of the lacteals consisting of clear, colorless fluid, instead of being opaque and white, as they ordinarily are, after feeding. (b.) It is probable, also, that the moistening of the mucous membrane of the intestines by bile facilitates absorption of fatty matters through it. (c.) The bile, like the gastric fluid, has a considerable antiseptic power, and may serve to prevent the decomposition of food during the time of its sojourn in the intestines. Experiments show that the con- tents of the intestines are much more foetid after the common bile-duct has been tied than at other times; moreover, it is found that the mixture of bile with a fermenting fluid stops or spoils the process of fermentation. (d.) The bile has also been considered to act as a natural purgative, by promoting an increased secretion of the intestinal glands, and by stimulating the intestines to the propulsion of their contents. This view receives support from the constipation which ordinarily exists in jaundice, from the diarrhoea which accompanies excessive secretion of bile, and from the purgative properties of ox-gall. 280 HAND-BOOK OF PHYSIOLOGY. (e.) The bile appears to have the power of precipitating tlie gastric parapeptones and peptones, together with the pepsin which is mixed up with them, as soon as the contents of the stomach meet it in the duo- denum. The purpose of this operation is probably both to delay any change in the parapeptones until the pancreatic juice can act upon them, and also to prevent the pepsin from exercising its solvent action on the ferments of the pancreatic juice. Nothing is known with certainty respecting the changes which the re- absorbed portions of the bile undergo. That they are much changed appears from the impossibility of detecting them in the blood; and that part of this change is effected in the liver is probable from an experiment of Magendie, who found that when he injected bile into the portal vein, a dog was unharmed, but was killed when he injected the bile into one of the systemic vessels. II. THE LIVER AS A BLOOD-ELABORATING GLAND. The secretion of bile, as already observed, is only one of the purposes fulfilled by the liver. Another very important function appears to be that of so acting upon certain constituents of the blood passing through it, as to render some of them capable of assimilation with the blood gen- erally, and to prepare others for being duly eliminated in the process of respiration. It appears that the peptones, conveyed from the alimentary canal by the blood of the portal vein, require to be submitted to the influ- ence of tne liver before they can be assimilated by the blood; for if such albuminous matter is injected into the jugular vein, it speedily appears in the urine; but if introduced into the portal vein, and thus allowed to traverse the liver, it is no longer ejected as a foreign substance, but is incorporated with the albuminous part of the blood. Albuminous mat- ters are also subject to decomposition by the liver in another way to be immediately noticed (p. 281). The formation of urea by the liver will be again referred to (p. 371). Glycogenic Function. — One of the chief uses of the liver in connec- tion with elaboration of the blood is comprised in what is known as its glycogenic function. The important fact that the liver normally forms glucose or grape sugar, or a substance readily convertible into it, was dis- covered by Claude Bernard in the course of some experiments which he undertook for the purpose of finding out in what part of the circulatory system the saccharine matter disappeared, which was absorbed from the alimentary canal. With this purpose he fed a dog for seven days with food containing a large quantity of sugar and starch; and, as might be expected, found sugar in both the portal and hepatic veins. He then fed a dog with meat only, and, to his surprise, still found sugar in the DIGESTION. 281 hepatic veins. Repeated experiments gave invariably the same result; no sugar being found, under a meat diet, in the portal vein> if care were taken, by applying a ligature on it at the transverse fissure, to prevent reflux of blood from the hepatic venous system. Bernard found sugar also in the substance of the liver. It thus seemed certain that the liver formed sugar, even when, from the absence of saccharine and amyloid matters in the food, none could be brought directly to it from the stomach or intestines. Excepting cases in which large quantities of starch and sugar were taken as food, no sugar was found in the blood after it had passed through the lungs; the sugar formed by the liver, having presumably disappeared by combustion, in the course of the pulmonary circulation. Bernard found, subsequently to the before-mentioned experiments, that a liver, removed from the body, and from which all sugar had been completely washed away by injecting a stream of water through its blood- vessels, will be found, after the lapse of a few hours, to contain sugar in abundance. This post-mortem production of sugar was a fact which could only be explained in the supposition that the liver contained a substance, readily convertible into sugar in the course merely of post-mortem decom- position; and this theory was proved correct by the discovery of a sub- stance in the liver allied to starch, and now generally termed glycogen. We may believe, therefore, that the liver does not form sugar directly from the materials brought to it by the blood, but that glycogen is first formed and stored in its substance; and that the sugar, when present, is the result of the transformation of the latter. Quantity of Glycogen formed. — Although, as before mentioned, glyco- gen is produced by the liver when neither starch nor sugar is present in the food, its amount is much less under such a diet. Average amount of Glycogen in the Liver of Dogs under various Diets. (Pavy.) Diet. Amount of Glycogen in Liver. Animal food ? -19 per cent. Animal food with sugar (about J Ib. of sugar daily) 14*5 " Vegetable diet (potatoes, with bread or barley-meal) 17 '23 " The dependence of the formation of glycogen on the food taken is also well shown by the following results, obtained by the same experimenter: Average quantity of Glycogen found in the Liver of Rabbits after Fasting and after a diet of Starch and Sugar respectively. Average amount of Glycogen in Liver. After fasting for three days .... Practically absent. '* diet of starch and grape-susrar . . . 15*4 per cent. . 16-9 " 282 HAND-BOOK OF PHYSIOLOGY. Regarding these facts there is no dispute. All are agreed that glyco- gen is formed, and laid up in store, temporarily, by the liver-cells; and that it is not formed exclusively from saccharine and amylaceous foods, but from albuminous substances also; the albumen, in the latter case, being probably split up into glycogeii, which is temporarily stored in the liver, and urea, which is excreted by the kidneys. Destination of Glycogen. — There are two chief theories on the sub- ject of the destination of glycogen. (1.) That the conversion of glycogen into sugar takes place rapidly during life by the agency of a ferment also formed in the liver: and the sugar is conveyed away by the blood of the hepatic veins, and soon undergoes combustion. (2.) That the conver- sion into sugar only occurs after death, and that during life no sugar exists in healthy livers; glycogen not undergoing this transformation. The chief arguments advanced in support of this view are, (a) that scarcely a trace of sugar is found in blood drawn during life from the right ventricle, or in blood collected from the right side of the heart im- mediately after an animal has been killed; while if the examination be delayed for a very short time after death, sugar in abundance may be found in such blood; (b), that the liver, like the venous blood in the heart, is, at the moment of death, completely free from sugar, although afterward its tissue speedily becomes saccharine, unless the formation of sugar be prevented by freezing, boiling, or other means calculated to in- terfere with the action of a ferment on the amyloid substance of the organ. Instead of adopting Bernard's view, that normally, during life, glycogen passes as sugar into the hepatic venous blood, and thereby is conveyed to the lungs to be further disposed of, Pavy inclines to the belief that it may represent an intermediate stage in the formation of fat from materials absorbed from the alimentary canal. Liver-sugar and Glycogen. — To demonstrate the presence of sugar in the liver, a portion of this organ, after being cut into small pieces, is bruised in a mortar to a pulp with a small quantity of water, and the pulp is boiled with sodium-sulphate in order to precipitate albuminous and coloring matters. The decoction is then filtered and may be tested for glucose (p. 230). Glycogen (c6H10o&) is an amorphous, starch-like substance, odorless and tasteless, soluble in water, insoluble in alcohol. It is converted into glu- cose by boiling with dilute acids, or by contact with any animal ferment. It may be obtained by taking a portion of liver from a recently killed rabbit, and, after cutting it into small pieces, placing it for a short time in boiling water. It is then bruised in a mortar, until it forms a pulpy mass, and subsequently boiled in distilled water for about a quarter of an hour. The glycogen is precipitated from the filtered decoction by the addition of alcohol. Glycogen has been found in many other structures than the liver. (See Appendix.) DIGESTION. 283 Glycosuria. — The facility with which the glycogen of the liver is transformed into sugar would lead to the expectation that this chemical change, under many circumstances, would occur to such an extent that sugar would' be present not only in the hepatic veins,, but in the blood generally. Such is frequently the case; the sugar when in excess in the blood being secreted by the kidneys, and thus appearing in variable quan- tities in the urine (Glycosuria). Influence of the Nervous System in producing Glycosuria. — Glycosuria may be experimentally produced by puncture of the medulla oblongata in the region of the vaso-motor centre. The better fed the animal the larger is the amount of sugar found in the urine; whereas in the case of a starving animal no sugar appears. It is, therefore, highly probable that the sugar comes from the hepatic glycogeti, since in the one case glycogen is in excess, and in the other it is almost absent. The nature of the influence is uncertain. It may be exercised in dilating the hepatic vessels, or possibly on the liver cells themselves. The whole course of the nervous stimulus cannot be traced to the liver, but at first it passes from the medulla down the spinal cord as far as — in rabbits — the fourth dorsal vertebra, and thence to the first thoracic ganglion. Many other circumstances will cause glycosuria. It has been observed after the administration of various drugs, after the injection of urari, poisoning with carbonic oxide gas, the inhalation of ether, chloroform. etc., the injection of oxygenated blood into the portal venous system. It has been observed in man after injuries to the head, and in the course of various diseases. The well-known disease, didbetus mellitus, in which a large quantity of sugar is persistently secreted daily with the urine, has, doubtless, some close relation to the normal glycogenic function of the liver; but the nature of the relationship is at present quite unknown. The Intestinal Secretion, or Succus Entericus.— On account of the difficulty in isolating the secretion of the glands in the wall of the intestine (Brunner's and Lieberkiihn's) from other secretions poured into the canal (gastric juice, bile, and pancreatic secretion), but little is known regarding the composition of the former fluid (intestinal juice, succus en- tericus). It is said to be a yellowish alkaline fluid with a specific gravity of 1011, and to contain about 2 -5 per cent, of solid matters (Thiry). Functions. — The secretion of Brunner's glands is said to be able to convert proteids into peptones, and that of Lieberkuhn's is believed to convert starch into sugar. To these functions of the succus entericus the powers of converting cane into grape sugar, and of turning cane sugar into lactic, and afterward into butyric acid, are added by some physiologists. It also probably contains a milk-curdling ferment (W. Roberts). 284 HAND-BOOK OF PHYSIOLOGY. The reaction which represents the conversion of cane sugar into grape sugar may be represented thus: — 3C10HMOn + 2H50 = O.^.O,, + O.^O,, Saccharose Water Dextrose Lsevulose The conversion is probably effected by means of a hydrolytic ferment. (Inversive ferment, Bernard.) The length and complexity of the digestive tract seem to be closely connected with the character of the food on which an animal lives. Thus, in all carnivorous animals, such as the cat and dog, and pre-eminently in carnivorous birds, as hawks and herons, it is exceedingly short. The seals, which, though carnivorous, possess a very long intestine, appear to furnish an exception; but this is doubtless to be explained as an adaptation to their aquatic habits: their constant exposure to cold requiring that they should absorb as much as possible from their intestines. Herbivorous animals, on the other hand, and the ruminants especially, have very long intestines (in the sheep 30 times the length of the body) which is no doubt to be connected with their lowly nutritious diet. In others, such as the rabbit, though the intestines are not excessively long, this is compensated by the great length and capacity of the caecum. In man, the length of the intestines is intermediate between the extremes of the carnivora and herbivora, and his diet also is intermediate. Summary of the Digestive Changes in the Small Intestine. In order to understand the changes in the food which occur during its passage through the small intestine, it will be well to refer briefly to the state in which it leaves the stomach through the pylorus. It has been said before, that the chief office of the stomach is not only to mix into a uniform mass all the varieties of food that reach it through the oesophagus, but especially to dissolve the nitrogenous portion by means of the gastric juice. The fatty matters, during their sojourn in the stomach, become more thoroughly mingled with the other constituents of the food taken, but are not yet in a state fit for absorption. The con- version of starch into sugar, which began in the mouth, has been inter- fered with, if not altogether stopped. The soluble matters — both those which were so from the first, as sugar and saline matter, and the gastric peptones — have begun to disappear by absorption into the blood-vessels, and the same thing has befallen such fluids as may have been swallowed, — wine, water, etc. The thin pultaceous chyme, therefore, which during the whole period of gastric digestion, is being constantly squeezed or strained through the pyloric orifice into the duodenum, consists of albuminous matter, broken down, dissolving and half dissolved; fatty matter broken down and melted, but not dissolved at all; starch very slowly in process of conversion into sugar, and afi it becomes sugar, also dissolving in the fluids with which DIGESTION. 285 it is mixed; while,, with these are mingled gastric fluid, and fluid that has been swallowed, together with such portions of the food as are not digest- ible, and will be finally expelled as part of the fseces. On the entrance of the chyme into the duodenum, it is subjected to the influence of the bile and pancreatic juice, which are then poured out, and also to that of the succus entericus. All these secretions have a more or less alkaline reaction, and by their admixture with the gastric chyme its acidity becomes less and less until at length, at about the middle of the small intestine, the reaction becomes alkaline and continues so as far as the ileo-csecal valve. The special digestive functions of the small intestine may be taken in the following order: — (1.) One important duty of the small intestine is the alteration of the fat in such a manner as to make it fit for absorption; and there is no doubt that this change is chiefly effected in the upper part of the small intestine. What is the exact share of the process, however, allotted re- spectively to the bile, to the pancreatic secretion, and to the intestinal juice, is still uncertain, — probably the pancreatic juice is the most impor- tant. The fat is changed in two ways. (a). To a slight extent it is chemically decomposed by the alkaline secretions with which it is mingled, and a soap is the result, (b). It is emulsionized, i.e., its particles are minutely subdivided and diffused, so that the mixture assumes the condi- tion of a milky fluid, or emulsion. As will be seen in the next Chapter, most of the fat is absorbed by the lacteals o2 the intestine, but a small part, which is saponified, is also absorbed by the blood-vessels. (2.) The albuminous substances which have been partly dissolved in the stomach, and have not been absorbed, are subjected to the action of the pancreatic and intestinal secretions. The pepsin is rendered inert by being precipitated together with the gastric peptones and parapeptones, as soon as the chyme meets with bile. By these means the pancreatic fer- ment trypsin is enabled to proceed with the further conversion of the parapeptones into peptones, and of part of the peptones (hemipeptone, Ktilme) into leucin and tyrosin. Albuminous substances, which are chemically altered in the process of digestion (peptones), and gelatinous matters similarly changed, are absorbed by both the blood-vessels and lymphatics of the intestinal mucous membrane. Albuminous matters, in a state of solution, which have not undergone the peptonic change, are probably, from the difficulty with which they diffuse, absorbed, if at all, almost solely by the lymphatics. (3.) The starchy, or amyloid portions of the food, the conversion of which into dextrin and sugar was more or less interrupted during its stay in the stomach, is now acted on briskly by the pancreatic juice and the succus entericus; and the sugar, as it is formed, is dissolved in the intes- tinal fluids, and is absorbed chiefly by the blood-vessels. 286 HAND-BOOK OF PHYSIOLOGY. (4.) Saline and saccharine matters, as common salt, or cane sugar, if not in a state of solution beforehand in the saliva or other fluids which may have been swallowed with them, are at once dissolved in the stomach, and if not here absorbed, are soon taken up in the small intestine; the blood-vessels, as in the last case, being chiefly concerned in the absorp- tion. Cane sugar is in part or wholly converted into grape-sugar before its absorption. This is accomplished partially in the stomach, but also by a ferment in the succus entericus. (5.) The liquids, including in this term the ordinary drinks, as water, wine, ale, tea, etc., which may have escaped absorption in the stomach, are absorbed probably very soon after their entrance into the intestine; the fluidity of the contents of the latter being preserved more by the con- stant secretion of fluid by the intestinal glands, pancreas, and liver, than by any given portion of fluid, whether swallowed or secreted, remaining long unabsorbed. From this fact, therefore, it may be gathered that there is a kind of circulation constantly proceeding from the intestines into the blood, and from the blood into the intestines again; for as all the fluid — a very large amount — secreted by the intestinal glands, must come from the blood, the latter would be too much drained, were it not that the same fluid after secretion is again re-absorbed into the current of blood — going into the blood charged with nutrient products of digestion — com- ing out again by secretion through the glands in a comparatively un- charged condition. At the lower end of the small intestine, the chyme, still thin and pul- taceous, is of a light yellow color, and has a distinctly faecal odor. This odor depends upon the formation of indol. In this state it passes through the ileo-caecal opening into the large intestine. SUMMARY OF THE DIGESTIVE CHANGES IN THE LARGE INTESTINE. The changes which take place in the chyme in the large intestine are probably only the continuation of the same changes that occur in the course ocf the food's passage through the upper part of the intestinal canal. From the absence of villi, however, we may conclude that absorption, especially of fatty matter, is in great part completed in the small intes- tine; while, from the still half-liquid, pultaceous consistence of the chyme when it first enters the cagcum, there can be no doubt that the absorption of liquid is not by any means concluded. The peculiar odor, moreover, which is acquired after a short time by the contents of the large bowel, would seem to indicate a further chemical change in the alimentary mat- ters or in the digestive fluids, or both. The acid reaction, which had dis- appeared in the small bowel, again becomes very manifest in the caecum — probably from acid fermentation-processes in some of the materials of the food. DIGESTION. 287 There seems no reason to conclude that any special "secondary diges- tive" process occurs in the csecurn or in any other part of the large intestine. Probably any constituent of the food which has escaped digestion and absorption in the small bowel may be digested in the large intestine; and the power of this part of the intestinal canal to digest fatty, albuminous, or other matters, may be gathered from the good effects of nutrient ene- mata, so frequently given when from any cause there is difficulty in intro- ducing food into the stomach. In ordinary healthy digestion, however, the changes which ensue in the chyme after its passage into the large in- testine, are mainly the absorption of the more liquid parts, and the com- pletion of the changes which were proceeding in the small intestine, — the process being assisted by the secretion of the numerous tubular glands therein present. Faeces. — By these means the contents of the large intestine, as they proceed toward the rectum, become more and more solid, and losing their more liquid and nutrient parts, gradually acquire the odor and consist- ence characteristic of faces. After a sojourn of uncertain duration in the sigmoid flexure of the colon, or in the rectum, they are finally ex- pelled by the act of defecation. The average quantity of solid faseal matter evacuated by the human adult in twenty-four hours is about six or eight ounces. COMPOSITION OF Water 733-00 Solids 267-00 Special excrementitious constituents: — Excretin, excretoleic acid (Marcet), and stercorin (Aus- tin Flint). Salts: — Chiefly phosphate of magnesium and phos- phate of calcium, with small quantities of iron, soda, lime, and silica. Insoluble residue of the food (chiefly starch grains, woody tissue, particles of cartilage and fibrous \ 267*00 tissue, undigested muscular fibres or fat, and the like, with insoluble substances accidentally introduced with the food). Mucus, epithelium, altered coloring matter of bile, fatty acids, etc. Varying quantities of other constituents o.f bile, and derivatives from them. Length of Intestinal Digestive Period.— The time occupied by the journey of a given portion of food from the stomach to the anus, varies considerably even in health, and on this account, probably, it is that such different opinions have been expressed in regard to the subject. About twelve hours are occupied by the journey of an ordinary meal 288 HAND-BOOK OF PHYSIOLOGY. through the small intestine, and twenty-four to thirty-six hours by the passage through the large bowel. (Brinton.) Defalcation. — Immediately before the act of voluntary expulsion of faeces (defcecation) there is usually, first an inspiration, as in the case of coughing, sneezing, ancl vomiting; the glottis is then closed, and the diaphragm fixed. The abdominal muscles are contracted as in expira- tion; but as the glottis is closed, the whole of their pressure is exercised on the abdominal contents. The sphincter of the rectum being relaxed, the evacuation of its contents takes place accordingly; the effect being, of course, increased by the peristaltic action of the intestine. As in the other actions just referred to, there is as much tendency to the escape of the contents of the lungs or stomach as of the rectum; but the pressure is relieved only at the orifice, the sphincter of which instinctively or in- voluntarily yields (see Fig. 144). Nervous Mechanism of Defaecation. — The anal sphincter muscle is normally in a state of tonic contraction. The nervous centre which governs this contraction is probably situated in the lumbar region of the spinal cord, inasmuch as in cases of division of the cord above this region the sphincter regains, after a time, to some extent the tonicity which is lost immediately after the operation. By an effort of the will, acting through the centre, the contraction may be relaxed or increased. In ordi- nary cases the apparatus is set in action by the gradual accumulation of faeces in the sigmoid flexure and rectum pressing against the sphincter and causing its relaxation; this sensory impulse acting through the brain and reflexly through the spinal centre. Peristaltic action, especially of the sigmoid flexure in pressing onward the faeces against the sphincter, is a very important part of the act. The Gases contained in the Stomach and Intestines. — Under ordinary circumstances, the alimentary canal contains a considerable quantity of gaseous matter. Any one who has had occasion, in a post- mortem examination, either to lay open the intestines, or to let out the gas which they contain, must have been struck by the small space after- ward occupied by the bowels, and by the large degree, therefore, in which the gas, which naturally distends them, contributes to fill the cavity of the abdomen. Indeed, the presence of air in the intestines is so constant, and, within certain limits, the amount in health so uniform, that there can be no doubt that its existence here is not a mere accident, but in- tended to serve a definite and important purpose, although, probably, a mechanical one. Sources. — The sources of the gas contained in the stomach and bowels may be thus enumerated: — 1. Air introduced in the act of swallowing either food or saliva; 2. Gases developed by the decomposition of alimentary matter or of the DIGESTION. 289 secretions and excretions mingled with it in the stomach and intestines; 3. It is probable that a certain mutual interchange occurs between the gases contained in the alimentary canal, and those present in the blood of these gastric and intestinal blood-vessels; but the conditions of the exchange are^not known, and it is very doubtful whether anything like a true and definite secretion of gas from the blflod into the intestines or stomach ever takes place. There can be no doubt, however, that the in- testines may be the proper excretory organs for many odorous and other substances, either absorbed from the air taken into the lungs in inspira- tion, or absorbed in the upper part of the alimentary canal, again to be excreted at a portion of the same tract lower down — in either case as- suming rapidly a gaseous form after their excretion, and in this way, perhaps, obtaining a more ready egress from the body. It is probable- that, under ordinary circumstances, the gases of the stomach and intes- tines are derived chiefly from the second of the sources which have been enumerated (Brinton). COMPOSITION OF GASES CONTAINED IN THE ALIMENTARY CANAL. (TABULATED FROM VARIOUS AUTHORITIES BY BRINTON.) Whence obtained. Composition by Volume. Oxygen. Nitrog. Carbon. Acid. Hydrog. Carburet. Hydrogen. Sulphuret. Hydrogen. Stomach Small Intestines . Caecum 11 71 32 66 35 46 22 14 30 12 57 43 41 4 38 8 6 19 13 8 11 19 1 . y trace i Colon Rectum Expelled per anum . . Movements of the Intestines. — It remains only to consider the manner in which the food and the several secretions mingled with it are moved through the ftitestinal canal, so as to be slowly subjected to the influence of fresh portions of intestinal secretion, and as slowly exposed to the absorbent power of all the villi and blood-vessels of the mucous membrane. The movement of the intestines is peristaltic or vermicular, and is effected by the alternate contractions and dilatations of successive portions of the intestinal coats. The contractions, which may commence at any point of the intestine, extend in a wave-like manner along the tube. In any given portion, the longitudinal muscular fibres contract first, or more than the circular; they draw a portion of the intestine upward, or, as it were, backward, over the substance to be propelled, and then the circular fibres of the same portion contracting in succession from above downward, or, as it were, from behind forward, press on the substance into the portion next below, in which at once the same succession of action next ensues. These movements take place slowly, and, in health, are com- VOL. I.— 19. 290 HAND-BOOK OF PHYSIOLOGY. monly unperceived by the mind; but they are perceptible when they are accelerated under the influence of any irritant. The movements of the intestines are sometimes retrograde; and there is no hindrance to the backward movement of the contents of the small intestine. But almost ^complete security is aiforded against the passage of the contents of the large into the small intestine by the ileo-caecal valve. Besides, — the orifice of communication between the ileum and caecum (at the borders of which orifice are the folds of mucous membrane which form the valve) is encircled with muscular fibres, the contraction of which prevents the undue dilatation of the orifice. Proceeding from above downward, the muscular fibres of the large intestine become, on the whole, stronger in direct proportion to the greater strength required for the onward moving of the faeces, which are gradually becoming firmer. The greatest strength is in the rectum, at the termi- nation of which the circular unstriped muscular fibres form a strong band called the internal sphincter; while an external sphincter muscle with striped fibres is placed rather lower down, and more externally, and as we have seen above, holds the orifice close by a constant slight tonic con- traction. Experimental irritation of the brain or cord produces no evident or con- stant effect on the movements of the intestines during li^e; yet in conse- quence of certain conditions of the mind the movements are accelerated or retarded; and in paraplegia the intestines appear after a time much weak- ened in their power, and costiveness, with a tympanitic condition, ensues. Immediately after death, irritation of both the sympathetic and pneumo- gastric nerves, if not too strong, induces genuine peristaltic movements of the intestines. Violent irritation stops the movements. These stimuli act, no doubt, not directly on the muscular tissue of the intestine, but on the ganglionic plexus before referred to. Influence of the Nervous System on Intestinal Digestion.— As in the case of the oesophagus and stomach, the peVistaltic movements of the intestines are directly due to reflex action through the ganglia and nerve fibres distributed so abundantly in their walls (p. 255); the presence of chyme acting as the stimulus, and few or no movements occurring when the intestines are empty. The intestines are, moreover, connected with the higher nerve-centres by the splanchnic nerves, as well as other branches of the sympathetic which come to them from the coeliac and other abdominal plexuses. The splanchnic nerves are in relation to the intestinal movements, inhibitory — these movements being retarded or stopped when the splanch- nics are irritated. As the vaso-motor nerves of the intestines, the splanch- nics are also much concerned in intestinal digestion. CHAPTER IX. ABSORPTION. THE process of Absorption has, for one of its objects, the introduction into the blood of fresh materials from the food and air, and of whatever comes into contact with the external or internal surfaces of the body; and, for another, the gradual removal of parts of the body itself, when they need to be renewed. In both these offices, i.e., in both absorption from without and absorption from within, the process manifests some variety, and a very wide range of action; and in both two sets of vessels are, or may be, concerned, namely, the Blood-vessels, and the Lymph- vessels or Lymphatics to which the term Absorbents has been also applied. THE LYMPHATIC VESSELS AND GLANDS. Distribution. — The principal vessels of the lymphatic system are, in structure and general appearance, like very small and thin-walled veins, and like them are provided with valves. By one extremity they com- mence by fine microscopic branches, the lymphatic capillaries or lymph- t"/ 'Maries, in the organs and tissues of the body, and by their other ex- tremities they end directly or indirectly in two trunks which open into the large veins near the heart (Fig. 206). Their contents, the lymph and Stifle, unlike the blood, pass only in one direction, namely, from the fine 1 tranches to the trunk and so to the large veins, on entering which they are mingled with the stream of blood, and form part of its constituents. Remembering the course of the fluid in the lymphatic vessels, viz., its passage in the direction only toward the large veins in the neighborhood of the heart, it will readily be seen from Fig. 206 that the greater part of the contents of the lymphatic system of vessels passes through a com- paratively large trunk called the thoracic duct, which finally empties its contents into the blood-stream, at the junction of the internal jugular and subclavian veins of the left side. There is a smaller duct on the right side. The lymphatic vessels of the intestinal canal are called lacteals, because, during digestion, the fluid contained in them resembles milk in appearance; and the lymph in the lacteals during the period of digestion is called chyle. There is no essential distinction, however, between lac- 292 HAND-BOOK OF PHYSIOLOGY. teals and lymphatics. In some parts of their course all lymphatic vessels pass through certain bodies called lymphatic glands. Lymphatic vessels are distributed in nearly all parts of the body. Their existence, however, has not yet been determined in the placenta, the umbilical cord, the membranes of the ovum, or in any of the non-vascular parts, as the nails, cuticle, hair and the like. Lymphatics of head and I^IBWftRnMHiHKHIiBS! Lymphatics of head and neck, right. BHBBgftflifggii KYffSB neck' left Right internal jugular vein. Hflin! Thoracic duct. Right subclavian vein SWiMS E^feifc/ vB XfflSf&BK&n subclavian vein. Lymphatics of right arm. . Thoracic duct. Receptaculum chyli. Lacteals. Lymphatics of lower ex- m**T$& S aSS I Lymphatics of lower ex- tremities. S^5JtS9^9B;i^3H tremities. Q^BMliin&w^lBKKflOTlamiSBB FIG. 206.— Diagram of the principal groups of lymphatic vessels (from Quain). Origin of Lymph Capillaries. — The lymphatic capillaries com- mence most commonly either in closely-meshed networks, or in irregular lacunar spaces between the various structures of which the different organs are composed. Such irregular spaces, forming what is now termed the lymph-canalicular system, have been shown to exist in many tissues. In serous membranes, such as the omentum and mesentery, they occur as a connected system of very irregular branched spaces partly occu- pied by connective-tissue corpuscles, and both in these and in many other tissues are found to communicate freely with regular lymphatic vessels. In many cases, though they are formed mostly by the chinks and crannies between the blood-vessels, secreting ducts, and other parts which may ABSORPTION. happen to form the framework of the organ in which they exist, they are lined by a distinct layer of endothelium. The lacteals offer an illustration of another mode of origin, namely, in blind dilated extremities (Figs. 192 and 193); but there is no essen- tial difference in structure between these and the lymphatic capillaries of other parts. Structure of Lymph Capillaries. — The structure of lymphatic capillaries is very similar to that of blood-capillaries: their walls consist of a single layer of endothelial cells of an elongated form and sinuous outline, which cohere along their edges to form a delicate membrane. Fio. 207.— Lymphatics of central tendon of rabbit's diaphragm, stained with silver nitrate. The ground substance has been shaded diagrammatically to bring out the lymphatics clearly. I. Lym- phatics lined by long narrow endothelial cells, and showing v. valves at frequent intervals (Schofleld). They differ from blood capillaries mainly in their larger and very varia- ble calibre, and in their numerous communications with the spaces of the lymph-canalicular system. Communications of the Lymphatics.— The fluid part of the blood constantly exudes or is strained through the walls of the blood-capillaries, so as to moisten all the surrounding tissues, and occupies the interspaces which exist among their different elements. These same interspaces have been shown, as just stated, to form the beginnings of the lymph-capilla- ries; and the latter, therefore, are the means of collecting the exuded blood-plasma, and returning that part which is not directly absorbed by the tissues into the blood-stream. For many years, the notion of the existence of any such channels between the blood-vessels and lymph-ves- sels as would admit blood-corpuscles, has been given up; observations having proved that, for the passage of such corpuscles, it is not necessary 294 HAND-BOOK OF PHYSIOLOGY. to assume the presence of any special channels at all, inasmuch as blood- corpuscles can pass bodily, without much difficulty, through the walls of the blood-capillaries and small veins (p. 159), and could pass with still less trouble, probably, through the comparatively ill-defined walls of the capillaries which contain lymph. FIG. 208. — Lymphatic vessels of the head and neck and the upper part of the trunk (Mascagni). 1-6.— The chest and pericardium have been opened on the left side, and the left mamma detached and thrown outward over the left arm, so as to expose a great part of its deep surface. The principal lymphatic vessels and glands are shown on the side of the head and face, and in the neck, axilla, and mediastinum. Between the left internal jugular vein and the common carotid artery, the upper as- cending part of the thoracic duct marked 1, and above this, and descending to 2, the arch and last part of the duct. The termination of the upper lymphatics of the diaphragm in the mediastinal glands, as well as the cardiac and the deep mammary lymphatics, is also shown: It is worthy of note that, in many animals, both arteries and veins, especially the latter, are often found to be more or less completely eii- sheathed in large lymphatic channels. In turtles, crocodiles, and many other animals, the abdominal aorta is enclosed in a large lymphatic vessel. Stomata. — In certain parts of the body openings exist by which lymphatic capillaries directly communicate with parts hitherto supposed to be closed cavities. If the peritoneal cavity be injected with milk, an injection is obtained of the plexus of lymphatic vessels of the central tendon of the diaphragm (Fig. 207); and on removing a small portion of the central tendon, with its peritoneal surface uninjured, and examining ABSORPTION. 295 the process of absorption under the microscope, the milk-globules run toward small natural openings or stomata between the epithelial cells, and disappear by parsing vortex-like through them. The stomata, which have a roundish outline, are only wide enough to admit two or three milk- globules abreast, and never exceed the size of an epithelial cell. FIG. 209. FIG. 210. FIG. 209.— Superficial lymphatics of the forearm and palm of the hand, 1-5. 5. Two small glands at the bend of the arm. 6."Radial lymphatic vessels. 7. Ulnar lymphatic vessels. 8, 8. Palmar arch of lymphatics. 9, 9. Outer and inner sets of vessels, b. Cephalic vein. d. Radial vein. e. Median vein. /. Ulnar vein. The lymphatics are represented as lying on the deep fascia. (Mascagni.) FIG. 210.— Superficial lymphatics of right groin and upper part of thigh, 1-6. 1, upper inguinal glands. 2, 2', Lower inguinal or femoral glands. 3, 3'. Plexus of lymphatics in the course of the long saphenous vein. (Mascagni.) Pseudostomata. — When absorption into the lymphatic system takes place in membranes covered by epithelium or endothelium through the interstitial or intercellular cement-substance, it is said to take place through pseudostomata. 296 HAND-BOOK OF PHYSIOLOGY. Demonstration of Lymphatics of Diaphragm. — The stomata on the peritoneal surface of the diaphragm are the openings of short vertical canals which lead up into the lymphatics, and are lined by cells like those of germinating endothelium (p. 23). By introducing a solution of Berlin blue into the peritoneal cavity of an animal shortly after death, and sus- pending it, head downward, an injection of the lymphatic vessels of the diaphragm, through the stomata on its peritoneal surface, may readily be obtained, if artificial respiration be carried on for about half an hour. In this way it has been found that in the rabbit the lymphatics are arranged between the tendon bundles of the centrum tendineum; and they are hence termed interfascicular. The centrum tendineum is coated by endothelium on its pleural and peritoneal surfaces, and its substance con- sists of tendon bundles arranged in concentric rings toward the pleural side and in radiating bundles toward the peritoneal side. FIG. 21 1 .—Peritoneal surface of septum cisternae lymphaticee magnee of frog. The stomata, some of which are open, some collapsed, are surrounded by germinating endothelium. x 160. (Klein.) The lymphatics of the anterior half of the diaphragm open into those of the anterior mediastinum, while those of the posterior half pass into a lymphatic vessel in the posterior mediastinum, which soon enters the tho- racic duct. Both these sets of vessels, and the glands into which they pass, are readily injected by the method above described; and there can be little doubt that during life the flow of lymph along these channels is chiefly caused by the action of the diaphragm during respiration. As it descends in inspiration, the spaces between the radiating tendon bun- dles dilate, and lymph is sucked from the peritoneal cavity, through the widely open stomata, into the interfascicular lymphatics. .During expira- tion, the spaces between the concentric tendon bundles dilate, and the lymph is squeezed into the lymphatics toward the pleural surface. (Klein. ) It thus appears probable that during health there is a continued sucking in of lymph from the .peritoneum into the lymphatics by the "pumping" action of the diaphragm; and there is doubtless an equally continuous exudation of fluid from the general serous surface of the peritoneum. When this balance of transudation and absorption is disturbed, either by increased transudation or some impediment to absorption, an accumula- tion of fluid necessarily takes place (ascites). Stomata have been found in the pleura; and as they may be presumed to exist in other serous membranes, it would seem as if the serous cavities, ABSORPTION. 297 hitherto supposed closed, form but a, large lymph-sinus, or widening out, so to speak, of the lymph-capillary system with which they directly com- municate. Structure of Lymphatic Vessels.— The larger vessels are very like veins, having an external coat of fibro-cellular tissue, with elastic fila- ments; within this, a thin layer of nbro-cellular tissue, with plain mus- cular fibres, which have, principally, a circular direction, and are much more abundant in the small than in the larger vessels; and again, within this, an inner elastic layer of longitudinal fibres, and a lining of epithe- lium; and numerous valves. The valves, constructed like those of veins, and with the free edges turned toward the heart, are usually arranged in pairs, and, in the small vessels, are so closely placed, that when the vessels are full, the valves constricting them where their edges are attached, give them a peculiar beaded or knotted appearance. Current of the Lymph. — With the help of the valvular mechanism (1) all occasional pressure on the exterior of the lymphatic and lacteal vessels propels the lympK toward the heart: thus muscular and other external pressure accelerates the flow of the lymph as it does that of the blood in the veins. The actions of (2) the muscular fibres of the small intestine, and probably the layer of organic muscle present in each intes- tinal villus, seem to assist in propelling the chyle: for, in the small intes- tine of a mouse, the chyle has been seen moving with intermittent pro- pulsions that appeared to correspond with the peristaltic movements of the intestine. But for the general propulsion of the lymph and chyle, it is probable that, together with (3) the vis a tergo resulting from absorp- tion (as in the ascent of sap in a tree), and from external pressure, some of the force may be derived (4) from the contractility of the vessel's own walls. The respiratory movements, also, (5) favor the current of lymph through the thoracic duct as they do the current of blood in the thoracic veins (p. 206). Lymphatic Glands are small round or oval compact bodies varying in size from a hempseed to a bean, interposed in the course of the lym- phatic vessels, and through which the chief part of the lymph passes in its course to be discharged into the blood-vessels. They are found in <*reat numbers in the mesentery, and along the great vessels of the abdo- jnen, thorax, and neck; in the axilla and groin; a few in the popliteal space, but not further down the leg, and in the arm as far as the elbow. Some lymphatics do not, however, pass through glands before entering the thoracic duct. Structure. — A lymphatic gland is covered externally by a capsule of connective tissue, generally containing some unstriped muscle. At the inner side of the gland, which is somewhat concave (hilus) (Fig. 212, a), the capsule sends processes inward in which the blood-vessels are con- tained, and these join with other processes called trabeculce (Fig. 215, t.r.) 298 HAND-BOOK OF PHYSIOLOGY. prolonged from the inner surface of the part of the capsule covering the convex or outer part of the gland; they have a structure similar to that of the capsule, and entering the gland from all sides, and freely commu- nicating, form a fibrous supporting stroma. The interior of the gland is seen on section, even when examined with the naked eye, to be made up of two parts, an outer or cortical (Fig. 212, c, c), which is light- colored, and an inner of redder appearance, the medullary portion (Fig. 212). In the outer or cortical part of the gland (Fig. 215, c) the inter- vals between the trabeculse are comparatively large and more or less trian- FIG. 212. FIG. 213. FIG. 212.— Section of a mesenteric gland f rom the ox, slightly magnified, a, Hilus; b (in the cen- tral part of the figure), medullary substance; c, cortical substance with indistinct alveoli; d, capsule (Kolliker.) FIG. 213.— From a vertical section through the capsule, cortical sinus and peripheral portion of follicle of a human compound lymphatic gland. The section had been shaken, so as to get rid of most of the lymph corpuscles. A. Outer stratum of capsule, consisting of bundles of fibrous tissue cut at various angles. B. Inner stratum, showing fibres of connective tissue with nuclei of flattened con- nective-tissue-corpuscles. Beneath this (between B and C) is the lymph-sinus or lymph-path, contain- ing a reticulum coated by flat nucleated endothelial cells. C. Fine nucleated endothelial membrane, marking boundary of the lymph-follicle. The rest of the section from C to E is the adenoid tissue of the lymph-follicle, which consists of a fine reticulum, E, with numerous lymph-corpuscles, D. They are so closely packed that the adenoid reticulum is invisible till the section has been shaken so as to dislodge a number of the lymph-corpuscles, x 350. (Klein and Isoble Smith.) gular, the intercommunicating spaces being termed alveoli; whilst in the more central or medullary part a finer mesh work is formed by the more free anastomosis of the trabecular processes. In the alveoli of the cortex and in the mesh work formed by the trabeculae in the medulla, is contained the proper gland structure. In the former it is arranged as follows (Fig. 215): occupying the central and chief part of each alveolus, is a more or less wedge-shaped mass (l.h.) of adenoid tissue, densely packed with lymph corpuscles; but at the periphery surrounding the central portion and im- mediately next the capsule and trabeculaa, is a more open meshwork of adenoid tissue constituting the lymph sinus or channel (Is.), and contain- AHSORPTIOX. 209 ing fewer lymph corpuscles. The central mass is enclosed in endothelium, the cells of which join by their processes, the processes of the adenoid framework of the lymph sinus. The trabeculse are also covered with endothelium'. The lining of the central mass does not prevent the passage FIG. 214.— Section of medullary substance of an inguinal gland of an ox: a, a, glandular substance- or pulp forming rounded cords joining in a continuous net (dark in the figure): c, c, trabeculse; the space, b. b. between these and the glandular substance is the lymph-sinus, washed clear of corpuscles- and traversed by filaments of retiform connective-tissue, x 90. (Kolliker.) tr- Fift. 215.— Diagrammatic section of Lymphatic gland, a. I., Afferent; e. L, efferent lymphatics^ C, cortical substance: I. h., reticulating cords of medullary substance: I. »., lymph-sinus; c., fibrous coat sending in trabeculre; t. r., into the substance of the gland. (Sharpey.) of fluids and even of corpuscles into the lymph sinus. The framework of the adenoid tissue of the lymph sinus is nucleated, that of the central mass is non-nucleated. At the inner part of the alveolus, the wedge- 300 HAND-BOOK OF PHYSIOLOGY. .shaped central mass bifurcates (Fig. 215) or divides into two or more .smaller rounded or cord-like masses, and here joining with those from the other alveoli, form a much closer arrangement of the gland tissue (Fig. 214, a) than in the cortex; spaces (Fig. 214, b) are left within those anastomosing cords, in which are found portions of the trabecular mesh- work and the continuation of the lymph sinus (b, c). The essential structure of lymphatic-gland substance resembles that which was described as existing, in a simple form, in the interior of the solitary and agminated intestinal follicles. The lymph enters the gland by several afferent vessels (Fig. 215, a.L) which open beneath the capsule into the lymph -channel or lymph-path; FIG. 216. — A small portion of medullary substance from a mesenteric gland of the ox. d, d, tra- beculae; a, part of a cord of glandular substances from which all but a few of the lymph-corpuscles have been washed out to show its supporting meshwork of retiform tissue and its capillary blood-ves- sels (which have been injected, and are dark in the figure); 6, 6, lymph-sinus, of which the retiform tissue is represented only at c, c. X 300. (.Kolliker.) .at the same time they lay aside all their coats except the endothelial lining, which h continuous with the lining of the lymph-path. The efferent vessels (Fig. 215, e.l. ) begin in the medullary part of the gland, and are continuous with the lymph-path here as the aiferent vessels were with the cortical portion; the endothelium of one is continuous with that of the other. The efferent vessels leave the gland at the hilus, the more or less con- cave inner side of the gland, and generally either at once or very soon after join together to form a single vessel. Blood-vessels which enter and leave the gland at the hilus are freely distributed to the trabecular tissue and to the gland-pulp (Fig. 216). ABSORPTION. 301 The tonsils, in part, and Beyer's glands of -the intestine, are really lymphatic glands, and doubtless discharge similar functions. THE LYMPH AND CHYLE. The lymph, contained in the lymphatic vessels, is, under ordinary cir- cumstances, a clear, transparent, and yellowish fluid. It is devoid of smell, is slightly alkali ae, and has a saline taste. As seen with the microscope in the small transparent vessels of the tail of the tadpole, it usually contains no corpuscles or particles of any kind; and it is only in the larger trunks in which any corpuscles are to be found. These corpus- cles are similar to colorless blood-corpuscles. The fluid in which the cor- puscles float is albuminous, and contains no fatty particles or molecular base; but is liable to variations according to the general state of the blood, and to that of the organ from which the lymph is derived. As it advances- toward the thoracic duct, and after passing through the lymphatic glands, it becomes spontaneously coagulable and the number of corpuscles is much, increased. The fluid contained in the lacteals is clear and transparent during fasting, and differs in no respect from ordinary lymph; but, during digestion, it becomes milky, and is termed chyle. Chyle is an opaque, whitish, milky fluid, neutral or slightly alkaline in reaction. Its whiteness and opacity are due to the presence of innu- merable particles of oily or fatty matter, of exceedingly minute though nearly uniform size, measuring on the average about yg-J-g-g- of an inch. These constitute what is termed the molecular base of chyle. Their number, and consequently the opacity of the chyle, are dependent upon the quantity of fatty matter contained in the food. The fatty nature of the molecules is made manifest by their solubility in ether, and, when the ether evaporates, by their being deposited in various-sized drops of oil. Each molecule probably consists of oil coated over with albumen, in the manner in which oil always becomes covered when set free in minute drops in an albuminous solution. This is proved when water or dilute acetic acid is added to chyle, many of the molecules are lost sight of, and oil-drops appear in their place, as the investments of the molecules have been dissolved, and their oily contents have run together. Except these molecules, the chyle taken from the villi or from lacteals near them, contains no other solid or organized bodies. The fluid in which the molecules float is albuminous, and does not spontaneously coagulate. But as the chyle passes on toward the thoracic duct, and especially, while it traverses one or more of the mesenteric glands, it is elaborated. The quantity of molecules and oily particles gradually dimin- ishes; cells, to which the name of chyle-corpuscles is given, are devel- oped in it; and it acquires the property of coagulating spontaneously. The higher in the thoracic duct the chyle advances, the more is it, in all 302 HAND-BOOK OF PHYSIOLOGY. these respects, developed; the greater is the number of chyle-corpuscles, and the larger and firmer is the clot which forms in it when withdrawn and left at rest. Such a clot is like one of blood without the red cor- puscles, having the chyle corpuscles entangled in it, and the fatty matter forming a white creamy film on the surface of the serum. But the clot of chyle is softer and moister than that of blood. Like blood, also, the chyle often remains for a long time in its vessels without coagulating, but coagulates rapidly on being removed from them. The existence of the materials which, by their union, form fibrin, is, therefore, certain; and their increase appears to be commensurate with that of the corpuscles. The structure of the chyle-corpuscles was described when speaking of the white corpuscles of the blood, with which they are identical. Chemical Composition of Lymph and Chyle. — From what has been said, it will appear that perfect chyle and lymph are, in essential characters, nearly similar, and scarcely diifer, except in the preponder- ance of fatty and proteid matter in the chyle. CHEMICAL COMPOSITION OF LYMPH AND CHYLE. (Owen Eees.) i. ii. in. Lymph Chyle Mixed Lymph & (Donkey). (Donkey). Chyle (Human). Water .... 96*536 90-237 " 90-48 Solids 3-454 9 '763 9-52 Solids— Proteids, including Serum- Albumin, Fibrin, and Globulin Extractives, including in (i and i) Sugar, Urea, Leu- cin and Cholesterin Fatty matter 1-320 3-886 7-08 1.559 1-565 -108 a trace 3 -601 -92 Salts .... -585 -711 -44 From the above analyses of lymph and chyle, it appears that they con- tain essentially the same constituents that are found in the blood. Their composition, indeed, differs from that of the blood in degree rather than in kind. They do not, however, unless by accident, contain colored cor- puscles. Quantity. — The quantity which would pass into a cat's blood in twenty-four hours has been estimated to be equal to about one-sixth of the weight of the whole body. And, since the estimated weight of the blood in cats is to the weight of their bodies as 1 -7, the quantity of lymph daily traversing the thoracic duct would appear to be about equal to the quantity of blood at any time contained in the animals. By another series ABSORPTION. 303 of experiments, the quantity of lymph traversing the thoracic duct of a dog in twenty-four hours was found to be about equal to two-thirds of the blood in the body. (Bidder and Schmidt.) Absorption by the Lacteals. — During the passage of the chyme along the whole tract of the intestinal canal, its completely digested parts are absorbed by the blood-vessels and lacteals distributed in the mucous membrane. The blood-vessels appear to absorb chiefly the dissolved por- tions of the food, and these, including especially the albuminous and sac- charine, they imbibe without choice; whatever can mix with the blood passes into the vessels, as will be presently described. But the lacteals appear to absorb only certain constituents of the food, including par- ticularly the fatty portions. The absorption by both sets of vessels is carried on most actively but not exclusively, in the villi of the small in* tcstine; for in these minute processes, both the capillary blood-vessels and the lacteals are brought almost into contact with the intestinal contents. There seems to be no doubt that absorption of fatty matters during diges- tion, from the contents of the intestines, is effected chiefly between the epithelial cells which line the intestinal tract (Watney), and especially those which clothe the surface of the villi. Thence, the fatty particles are passed on into the interior of the lacteal vessels (Fig. 216, a), but how they pass, and what laws govern their so doing, are not at present exactly known. The process of absorption is assisted by the pressure exercised on the contents of the intestines by their contractile walls; and the absorption of fatty particles is also facilitated by the presence of the bile, and the pan- creatic and intestinal secretions, which moisten the absorbing surface. For it has been found by experiment, that the passage of oil through an animal membrane is made much easier when the latter is impregnated with an alkaline fluid. Absorption by the Lymphatics.— The real source of the lymph, and the mode in which its absorption is effected by the lymphatic vessels, were long matters of discussion. But the problem has been much sim- plified by more accurate knowledge of the anatomical relations of the lymphatic capillaries. The lymph is, without doubt, identical in great part with the liquor sanguinis, which, as before remarked, is always exuding from the blood-capillaries into the interstices of the tissues in which they lie; and as these interstices form in most parts of the body the beginnings of the lymphatics, the source of the lymph is sufficiently obvious. In connection with this may be mentioned the fact that changes in the character of the lymph correspond very closely with changes in the character of either the whole mass of blood, or of that in the vessels of the part from which the lymph is exuded. Thus it appears that the coagulability of the lymph is directly proportionate to that of the blood; and that when fluids are injected into the blood-vessels in sufficient qnan- 304 HAND-BOOK OF PHYSIOLOGY. tity to distend them, the injected substance may be almost directly afterward found in the lymphatics. Some other matters than those originally contained in the exuded liquor sanguinis may, however, find their way with it into the lymphatic vessels. Parts which having entered into the composition of a tissue, and, having fulfilled their purpose, require to be removed, may not be altogether excrementitious, but may admit of being reorganized and adapted again for nutrition; and these may be absorbed by the lym- phatics, and elaborated with the other contents of the lymph in passing through the glands. Lymph-Hearts. — In reptiles and some birds, an important auxiliary to the movement of the lymph and chyle is supplied in certain muscular sacs, named lymph-hearts (Fig. 217), and it has been shown that the caudal heart of the eel is a lymph-heart also. The number and position of these organs vary. In frogs and toads there are usually four, two anterior and two posterior; in the frog, the posterior lymph-heart on each side is situated in the ischiatic region, just beneath the skin; the anterior lies deeper, just over the transverse process of the third vertebra. Into each of these cavities several lymphatics open, the orifices of the vessels being guarded by valves, which prevent the retrograde passage of the FIG. 217.— Lymphatic heart ( 9 lines long, 4 lines broad) of a large species of serpent, the Python, bivittatus. 4. The external cellular coat. 5. The thick muscular coat. Four muscular columns run across its cavity, which communicates with three lymphatics (1— only one is seen here), and with two- veins (2, 2). 6. The smooth lining membrane of the cavity. 7. A small appendage, or auricle, the cav- ity of which is continuous with that of the rest of the organ (after E. Weber). lymph. From each heart a single vein proceeds and conveys the lymph directly into the venous system. In the frog, the inferior lymphatic heart, on each side, pours its lymph into a branch of the ischiatic vein; by the superior, the lymph is forced into a branch of the jugular vein, which issues from its anterior surface, and which becomes turgid each time that the sac contracts. Blood is prevented from passing from the vein into the lymphatic heart by a valve at its orifice. The muscular coat of these hearts is of variable thickness; in some cases it can only be discovered by means of the microscope; but in every case it is composed of striped fibres. The contractions of the heart are rhythmical, occurring about sixty times in a minute, slowly, and, in com- parison with those of the blood-hearts, feebly. The pulsations of the ABSORPTION. 305 cervical pair are not always synchronous with those of the pair in the ischiatic region, and even the corresponding sacs of opposite sides are not always synchronous in their action. Unlike the contractions of the blood-heart, those of the lymph-heart appear to be directly dependent upon a certain limited portion of the spinal cord. For Volkmann found that so long as the portion of spinal cord corresponding to the third vertebra of the frog was uninjured, the cervical pair of lymphatic hearts continued pulsating after all the rest of the spinal cord and the brain were destroyed; while destruction of this portion, even though all other parts of the nervous centres were unin- jured, instantly arrested the heart's movements. The posterior, or ischi- atic, pair of lymph-hearts were found to be governed, in like manner, by the portion of spinal cord corresponding to the eighth vertebra. Division of the posterior spinal roots did not arrest the movements; but division of the anterior roots caused them to cease at once. Absorption by Blood-vessels. — In the absorption by the lym- phatic or lacteal vessels just described, there appears something like the exercise of choice in the materials admitted into them. But the absorp- tion by blood-vessels presents no such appearance of selection of materials; rather, it appears, that every substance, whether gaseous, liquid, or a soluble, or minutely divided solid, may be absorbed by the blood-vessels, provided it is capable of permeating their walls, and of mixing with the blood; and that of all such substances, the mode and measure of absorption are deter- mined solely by their physical or chemical properties and conditions, and by those of the blood and the walls of the blood-vessels. Osmosis. — The phenomena are, indeed, to a great ex- tent, comparable to that passage of fluids through mem- brane, which occurs quite independently of vital conditions, and the earliest and best scientific investigation of which was made by Dutrochet. The instrument which he employed in his experiments was named an endosmometer. It may con- sist of a graduated tube expanded into an open-mouthed bell at one end, over which a portion of membrane is tied (Fig. 218). If now the bell be filled with a solution of a salt — say sodium chloride, and be immersed in water, the water will pass into the solution, and part of the sali will pass out FIG. 218. En- . , ... dosmometer. into the water; the water, however, will pass into the solu- tion much more rapidly than the salt will pass out into the water, and the diluted solution will rise in the tube. To this passage of fluids through membrane the term Osmosis is applied. The nature of the membrane used as a septum, and its affinity for the fluids subjected to experiment, have an important influence, as might be anticipated, on the rapidity and duration of the osmotic current. Thus, VOL. I.— 20. 306 HAND-BOOK OF PHYSIOLOGY. if a piece of ordinary bladder be used as the septum between water and alcohol, the current is almost solely from the water to the alcohol, on account of the much greater affinity of water for this kind of membrane; while, on the other hand, in the case of a membrane of caoutchouc, the •alcohol, from its greater affinity for this substance, would pass freely into the water. Osmosis by Blood-vessels. — Absorption by blood-vessels is the 'consequence of their walls being, like the membranous septum of the •endosmometer, porous and capable of imbibing fluids, and of the blood feeing so composed that most fluids will mingle with it. The process of absorption, in an instructive, though very imperfect degree, may be ob- served in any portion of vascular tissue removed from the body. If 'such a one be placed in a vessel of water, it will shortly swell, and become heavier and moister, through the quantity of water imbibed or soaked into it; and if now, the blood contained in any of its vessels be let out, it will be found diluted with water, which has been absorbed by the blood- vessels and mingled with the blood. The water round the piece of tissue also will become blood-stained; and if all be kept at perfect rest, the stain derived from the solution of the coloring matter of the blood (together with which chemistry would detect some of the albumen and other parts of the liquor sanguinis) will spread more widely every day. The same will happen if the piece of tissue be placed in a saline solution instead of water, or in a solution of coloring or odorous matter, either of which will give their tinge or smell to the blood, and receive, in exchange, the color of the blood. Colloids and Crystalloids. — Various substances have been classified according to the degree in which they possess the property of passing, when in a state of solution in water, through membrane; those which pass freely, inasmuch as they are usually capable of crystallization, being termed crystalloids, and those which pass with difficulty, on account of their, physically, glue-like characters, colloids. (Graham.) This distinction, however, between colloids and crystalloids, which is made the basis of their classification, is by no means the only difference between them. The colloids, besides the absence of power to assume a crystalline form, are characterized by their inertness as acids or bases, and feebleness in all ordinary chemical relations. Examples of them are found in albumin, gelatin, starch, hydrated alumina, hydrated silicic acid, etc. ; while the crystalloids are characterized by qualities the reverse of those just mentioned as belonging to colloids. Alcohol, sugar, and ordinary saline substances are examples of crystalloids. Rapidity of Absorption. — The rapidity with which matters may be absorbed from the stomach, probably by the blood-vessels chiefly, and diffused through the textures of the body, may be gathered from the his- tory of some experiments. From these it appears that even in a quarter ABSORPTION. 307 of an hour after being given on an empty stomach, lithium chloride may be diffused into all the vascular textures of the body, and into some of the non-vascular, as the cartilage of the hip-joint, as well as into the aqueous humor of the eye. Into the outer part of the crystalline lens it ^nay pass after a time, varying from half an hour to an hour and a half. Lithium carbonate, when taken in five or ten-grain doses on an empty stomach, may be detected in the urine in 5 or 10 minutes; or, if the stomach be full at the time of taking the dose, in 20 minutes. It may sometimes be detected in the urine, moreover, for six, seven, or eight days. (Bence Jones.) Some experiments on the absorption of various mineral and vegetable poisons, have brought to light the singular fact, that, in some cases, absorption takes place more rapidly from the rectum than from the stomach. Strychnia, for example, when in solution, produces its poison- ous effects much more speedily when introduced into the rectum than into the stomach. When introduced in the solid form, however, it is absorbed more rapidly from the stomach than from the rectum, doubtless because of the greater solvent property of t}ie secretion of the former than of that of the latter. (Savory.) With regard to the degree of absorption by living blood-vessels, much depends on the facility with which the substance to be absorbed can pene- trate the membrane or tissue which lies between it and the blood-vessels. Thus, absorption will hardly take place through the epidermis, but is quick when the epidermis is removed, and the same vessels are covered with only the surface of the cutis, or with granulations. In general, the absorption through membranes is in an inverse proportion to the thick- ness of their epithelia; so that the urinary bladder of a frog is traversed in less than a second; and the absorption of poisons by the stomach or lungs appears sometimes accomplished in an immeasurably small time. Conditions for Absorption. — 1. The substance to be absorbed must, as a general rule, be in the liquid or gaseous state, or, if a solid, must be soluble in the fluids with which it is brought in contact. Hence the marks of tattooing, and the discoloration produced by silver nitrate taken internally, remain. Mercury may be absorbed even in the metallic state; and in that state may pass into and remain in the blood-vessels, or be deposited from them; and such substances as exceedingly finely-divided charcoal, when taken into the alimentary canal, have been found in the mesenteric veins; the insoluble materials of ointments may also be rubbed into the blood-vessels; but there are no facts to determine how these various substances effect their passage. Oil, minutely divided, as in an emulsion, will pass slowly into blood-vessels, as it will through a filter moistened with water; and, without doubt, fatty matters find their way into the blood-vessels as well as the lymph-vessels of the intestinal canal, although the latter seem to be specially intended for their absorption. 308 HAND-BOOK OF PHYSIOLOGY. 2. The less dense the fluid to be absorbed, the more speedy, as a gen- eral rule, is its absorption by the living blood-vessels. Hence the rapid absorption of water from the stomach; also of weak saline solutions; but with strong solutions, there appears less absorption into, than effusion from, the blood-vessels. 3. The absorption is the less rapid the fuller and tenser the blood-vessels are; and the tension may be so great as to hinder altogether the entrance of more fluid. Thus, if water is injected into a dog's veins to repletion, poison is absorbed very slowly; but when the tension of the vessels is diminished by bleeding, the poison acts quickly. So, when cupping-glasses are placed over a poisoned wound, they retard the absorption of the poison not only by diminishing the velocity of the circulation in the part, but by filling all its vessels too full to admit more. On the same ground, absorption is the quicker the more rapid the cir- culation of the blood; not because the fluid to be absorbed is more quickly imbibed into the tissues, or mingled with the blood, but because as fast as it enters the blood, it is carried away from the part, and the blood being constantly renewed, is constantly as fit as at the first for the reception of the substance to be absorbed. CHAPTER X. ANIMAL HEAT. THE Average Temperature of the human body in those internal parts which are most easily accessible, as the mouth and rectum, is from 98*5° to 99-5° F. (36-9°— 37'4° C.). In different parts of the external surface of the human body the temperature varies only to the extent of two or three degrees (F.), when all are alike protected from cooling influences; and the difference which under these circumstances exists, depends chiefly upon the different degrees of blood-supply. In the arm-pit — the most convenient situation, under ordinary circumstances, for examination by the thermometer — the average temperature is 98 '6° F. (36 '9° C.). In different internal parts, the variation is one or two degrees; those parts and organs being warmest which contain most blood, and in which there occurs the greatest amount of chemical change, e.g., the glands and the muscles; and the temperature is highest, of course, when they are most actively working: while those tissues which, subserving only a mechanical function, are the seat of least active circulation and chemical change, are the coolest. These differences of temperature, however, are actually but slight, on account of the provisions which exist for maintaining uniform- ity of temperature in different parts. Circumstances causing Variations in Temperature.— The chief circumstances by which the temperature of the healthy body is influ- enced are the following: — Age; Sex; Period of the day; Exercise; Cli- mate and Season; Pood and Drink. Age. — The average temperature of the new-born child is only about 1° F. (-54° C.) above that proper to the adult; and the difference becomes still more trifling during infancy and early childhood. The temperature falls to the extent of about -2° — -5° F. from early infancy to puberty, and by about the same amount from puberty to fifty or sixty years of age. In old age the temperature again rises, and approaches that of infancy; but although this is the case, yet the power of resisting cold is less in them — exposure to a low temperature causing a greater reduction of heat than in young persons. The same rapid diminution of temperature has been observed to occur in the new-born young of most carnivorous and rodent animals when they are removed from the parent, the temperature of the atmosphere being 310 HAND-BOOK OF PHYSIOLOGY. between 50° and 53-5° F. (10°-12° C.); whereas while lying close to the body of the mother, their temperature is only 2 or 3 degrees F. lower than hers. The same law applies to the young of birds. Sex. — The average temperature of the female would appear to be very slightly higher than that of the male. Period of the Day. — The temperature undergoes a gradual alteration, to the extent of about 1° to 1*5° F. (*54 — '8° C.) in the course of the day and night; the minimum being at night or in the early morning, the maximum late in the afternoon. Exercise. — Active exercise raises the temperature of the body from 1° to 2° F. (-54°— 1.08° C.). This may be partly ascribed to generally in- creased combustion-processes, and partly to the fact, that every muscular contraction is attended by the development of one or two degrees of heat in the acting muscle; and that the heat is increased according to the number and rapidity of these contractions, and is quickly diffused by the blood circulating from the heated muscles. Possibly, also, some heat may be generated in the various movements, stretchings, and recoilings of the other tissues, as the arteries, whose elastic walls, alternately dilated and contracted, may give out some heat, just as caoutchouc alternately stretched and recoiling becomes hot. But the heat thus developed cannot be great. The great apparent increase of heat during exercise depends, in a great measure, on the increased circulation and quantity of blood, and, therefore, greater heat, in parts of the body (as the skin, and espe- cially the skin of the extremities), which, at the same time that they feel more acutely than others any changes of temperature, are, under ordi- nary conditions, by some degrees colder than organs more centrally situated. Climate and Season. — The temperature of the human body is the same in temperate and tropical climates. (Johnson, Boileau, Furnell.) In summer the temperature of the body is a little higher than in winter; the difference amounting to about a third of a degree F. (Wunderlich.) Food and Drink. The effect of a meal upon the temperature of a body is but small. A very slight rise usually occurs. Cold alcoholic drinks depress the temperature somewhat (-5° to 1° F.). Warm alcoholic drinks, as well as warm tea and coffee, raise the temperature (about -5° F.). In disease the temperature of the body deviates from the normal stand- ard to a greater extent than would be anticipated from the slight effect of external conditions during health. Thus, in some diseases, as pneu- monia and typhus, it occasionally rises as high as 106° or 107° F. (41° — 41 '6° C.); and considerably higher temperatures have been noted. In Asiatic cholera, on the other hand, a thermometer placed in the mouth may sometimes rise only to 77° or 79° F. (25°— 26-2° C.). The temperature maintained by Mammalia in an active state of life, ANIMAL HEAT. 311 according to the tables of Tiedemann and Rudolph i, averages 101° (38.3° C.). The extremes recorded by them were 96° and 106°, the former in the narwhal, the latter in a bat ( Vespertilio pipistrella). In Birds, the average is as high as 107° (41 -2° C.); the highest temperature, 111-25° (40 -2 C.); being in the small species, the linnets, etc. Among Reptiles, while the medium they were in was 75° (23 '9° C.) their average tempera- ture was 82 -5° (31*2° C.). As a general rule, their temperature, though it falls with that of the surrounding medium, is, -in temperate media, two or more degrees higher; and though it rises also with that of the medium, yet at very high degrees it ceases to do so, and remains even lower than that of the medium. Fish and invertebrata present, as a general rule, the same temperature as the medium in which they live, whether that be high or low; only among fish, the tunny tribe, with strong hearts and red meat-like muscles, and more blood than the average of fish have, are generally 7° (3 '8° C.) warmer than the water around them. The difference, therefore, between what are commonly called the warm and the cold-blooded animals, is not one of absolutely higher or lower temperature: for the animals which to us in a temperate climate feel cold (being like the air or water, colder than the surface of our bodies), would in an external temperature of 100° (37 '8° C.) have nearly the same tem- perature and feel hot to us. The real difference is that what we call warm-blooded animals (Birds and Mammalia), have a certain "permanent heat in all atmospheres," while the temperature of the others, which we call cold-blooded, is "variable with every atmosphere." (Hunter.) The power of maintaining a uniform temperature, which Mammalia and Birds possess, is combined with the want of power to endure such changes of body temperature as are harmless to the other classes; and when their power of resisting change of temperature ceases, they suffer serious disturbance or die. Sources and Mode of Production of Heat in the Body.— The heat which is produced in the body arises from combustion, and is due to the fact that the oxygen of the atmosphere taken into the system is combined with the carbon and hydrogen of the tissues. Any changes which occur in the protoplasm of the tissues, resulting in an exhibition of their function, is attended by the evolution of heat and also by the pro- duction of carbonic acid and water; and the more active the changes, the greater the heat produced and the greater the amount of the carbonic acid and water formed. But in order that the protoplasm may perform its function, the waste of its own tissue (destructive metabolism), must be repaired by the supply of food material, and therefore for the produc- tion of heat it is necessary to supply food. In the tissues, therefore, two processes are continually going on: the building up of the protoplasm from the food (constructive metabolism), which is not accompanied by the evolution of heat but possibly by the reverse, and the oxidation of the protoplastic materials, resulting in the production of energy, by which heat is produced and carbonic acid and water are evolved. Some heat will also be generated in the combination of sulphur and phosphorus with oxygen, but the amount, thus produced is but small. 312 HAND-BOOK OF PHYSIOLOGY. It is not necessary to assume that the combustion processes, which ultimately issue in the production of carbonic acid and water, are as sim- ple as the bare statement of the fact might seem to indicate. But com- plicated as the various stages of combustion may be, the ultimate result is as simple as in ordinary combustion outside the body, and the products are the same. The same amount of heat will be evolved in the union of any given quantities of carbon and oxygen, and of hydrogen and oxy- gen, whether the combination be rapid and direct, as in ordinary combus- tion, or slow and almost imperceptible, as in the changes which occur in the living body. And since the heat thus arising will be distributed wherever the blood is carried, every part of the body will be heated equally, or nearly so. This theory, that the maintenance of the temperature of the living body depends on continual chemical change, chiefly by oxidation, of combustible materials existing in the tissues, has long been established by the demonstration that the quantity of carbon and hydrogen which, in a given time, unites in the body with oxygen, is sufficient to account for the amount of heat generated in the animal within the same time: an amount capable of maintaining the temperature of the body at from 98° — 100° F. (36-8° — 37'8° C.), notwithstanding a large loss by radiation and evaporation. It should be remembered that heat may be introduced into the body by means of warm drinks and foods, and, again, that it is possible for the preliminary digestive changes to be accompanied by the evolution of heat. Chief Heat-producing Tissues. — The clfemical changes which produce the body-heat appear to be especially active in certain tissues: — (1), In the Muscles, which form so large a part of the organism. The fact that the manifestation of muscular energy is always attended by the evolution of heat and the production of carbonic acid has been demon- strated by actual experiment; and when not actually in a condition of active contraction, a metabolism, not so active but still actual, goes on, which is accompanied by the manifestation of heat. The total amount set free by the muscles, therefore, must be very great; and it has been calculated that even neglecting the heat produced by the quiet metabolism of muscular tissue, the amount of heat generated by muscular activity supplies the principal part of the total heat produced within the body. (2), In the Secreting glands, and principally in the liver as being the largest and most active. It has been found by experiment that the blood leaving the glands is considerably warmer than that entering them. The metabolism in the glands is very active, and, as we have seen, the more active the metabolism the greater the heat produced. (3), In the Brain; the venous blood having a higher temperature than the arterial. It must be remembered, however, that although the organs above mentioned are the chief heat-producing parts of the body, all living tissues contribute ANIMAL HEAT. 313 their quota, and this in direct proportion to their activity. The blood itself is also the seat of metabolism, and, therefore, of the production of heat; but the share which it takes in this respect, apart from the tissues in which it circulates, is very inconsiderable. Regulation of the Temperature of the Human Body.— The average temperature of the body is maintained under different conditions of external circumstances by mechanisms which permit of (1) variation in the amount of heat got rid of, and (2) variations in the amount of heat produced or introduced into the body. In healthy warm-blooded animals the loss and gain of heat are so nearly balanced one by the other that, under all ordinary circumstances, a uniform temperature, within two or three degrees, is preserved. I. Methods of Variation in the amount of Heat got rid of.— The loss of heat from the human body is principally regulated by the amount lost by radiation and conduction from its surface, and by means of the constant evaporation of water from the same part, and (2) to a much less degree from the air -passages; in each act of respiration, heat is lost to a greater or less extent according to the temperature of the atmosphere; unless indeed the temperature of the surrounding air exceed that of the blood. We must remember too that all food and drink which enter the body at a lower temperature than itself abstract a small measure of heat: while the urine and faeces which leave the body at about its own temperature are also means by which a small amount is lost. (a.) Loss of Heat from the /Surface of the Body : the Skin. — By far the most important loss of heat from the body, — probably 70 or 80 per V / cent, of the whole amount, is that which takes place by radiation, c$n- )( duction, and evaporation from the skin. The means by which the skin is able to act as one of the most important organs for regulating the tem- perature of the blood, are — (1), that it offers a large surface for radiation, conduction, and evaporation; (2), that it contains a large amount of blood; (3), that the quantity of blood contained in it is the greater under those circumstances which demand a loss of heat from the body, and vice /•"w?. For the circumstance which directly determines the quantity of blood in the skin, is that which governs the supply of blood to all the tissues and organs of the body, namely, the power of the vaso-motor nerves to cause a greater or less tension of the muscular element in the walls of the arteries, and, in correspondence with this, a lessening or increase of the calibre of the vessels, accompanied by a less or greater current of blood. A warm or hot atmosphere so acts on the nerve fibres of the skin, as to lead them to cause in turn a relaxation of the muscular fibre of the blood- vessels; and, as a result, the skin becomes full-blooded, hot, and sweating; and much heat is lost. With a low temperature, on the other hand, the blood-vessels shrink, and in accordance with the consequently diminished blood-supply, the skin becomes pale, and cold, and dry; and no doubt a 314 HAND-BOOK OF PHYSIOLOGY. similar effect may be produced through the vaso-motor centre in the medulla and spinal cord. Thus, by means of a self-regulating apparatus, the skin becomes the most important of the means by which the tempera- ture of the body is regulated. In connection with loss of heat by the skin, reference has been made to that which occurs both by radiation and conduction, and by evapora- tion; and the subject of animal heat has been considered almost solely with regard to the ordinary case of man living in a medium colder than his body, and therefore losing heat in all the ways mentioned. The im- portance of the means, however, adopted, so to speak, by the skin for regu- lating the temperature of the body, will depend on the conditions by which it is surrounded; an inverse proportion existing in most cases be- tween the loss by radiation and conduction on the one hand, and by evaporation on the other. Indeed, the small loss of heat by evaporation in cold climates may go far to compensate for the greater loss by radia- tion; as, on the other hand, the great amount of fluid evaporated in hot air may remove nearly as much heat as is commonly lost by both radia- tion and evaporation in ordinary temperatures; and thus, it is possible that the quantities of heat required for the maintenance of a uniform proper temperature in various climates and seasons are not so different as they, at first thought, seem. Many examples may be given of the power which the body possesses of resisting the effects of a high temperature, in virtue of evaporation from the skin. Blagden and others supported a temperature varying between 198°— 211° F. (92°— 100° C.) in dry air for several minutes; and in a subsequent experiment he remained eight minutes in a temperature of 260° F. (126-5* C.). "The workmen of Sir F. Chantrey were accustomed to enter a furnace, in which his moulds were dried, whilst the floor was red-hot and a thermometer in the air stood at 350° F. (177 '8° C.); and Chabert, the fire-king, was in the habit of entering an oven the tempera- ture of which was from 400° to 600° F." (205°— 315° C.) (Carpenter.) But such heats are not tolerable when the air is moist as well as hot, so as to prevent evaporation from the body. 0. James states, that in the vapor baths of Nero he was almost suffocated in a temperature of 112° F. (44-5° C. ), while in the caves of Testaccio, in which the air is dry, he wa,s but little incommoded by a temperature of 176° F. (80° C.). In the former, evaporation from the skin was impossible; in the latter it was abundant, and the layer of vapor which would rise from all the surface of the body would, by its very slowly conducting power, defend it for a time from the full action of the external heat. (The glandular apparatus, by which secretion of fluid from the skin is effected, will be considered in the Section on the Skin.) The ways by which the skin may be rendered more efficient as a cool- ing-apparatus, by exposure, by baths, and by other means which man instinctively adopts for lowering his temperature when necessary, are too well known to need more than to be mentioned. ANIMAL HEAT. 315 Although under any ordinary circumstances, the external application of cold only temporarily depresses the temperature to a slight extent, it is otherwise in cases of high temperature in fever. In these cases a tepid bath may reduce the temperature several degrees, and the effect so pro- duced lasts in some cases for many hours. (b.) Loss of Heat from the Lungs. — As a means for lowering the tem- perature, the lungs and air-passages are very inferior to the skin; although, by giving heat to the air we breathe, they stand next to the skin in im- portance. As a regulating power, the inferiority is still more marked. The air which is expelled from the lungs leaves the body at about the temperature of the blood, and is always saturated with moisture. No inverse proportion, therefore, exists between the loss of heat by radiation and conduction on the one hand, and by evaporation on the other. The colder the air, for example, the greater will be the loss in all ways. Neither is the quantity of blood which is exposed to the cooling influence of the air diminished or increased, so far as is known, in accordance with any need in relation to temperature. It is true that by varying the num- ber and depth of the respirations, the quantity of heat given off by the lungs may be made, to some extent, to vary also. But the respiratory passages, while they must be considered important means by which heat is lost, are altogether subordinate, in the power of regulating the temper- ature, to the skin. (c.) By Clothing. — The influence of external coverings for the body must not be unnoticed. In warm-blooded animals, they are always adapted, among other purposes, to the maintenance of uniform tempera- ture; and man adapts for himself such as are, for the same purpose, fitted to the various climates to which he is exposed. By their means, and by his command over food and fire, he maintains his temperature on all accessible parts of the surface of the earth. II. Methods of Variation in the amount of Heat produced. —It may seem to have been assumed, in the foregoing pages, that the ojily regulating apparatus for temperature required by the human body is one that shall, more or less, produce a cooling effect; and as if the amount of heat produced were always, therefore, in excess of that which is required. Such an assumption would be incorrect. We have the power of regulating the production of heat, as well as its loss. («,) By Regulating the Quantity and Quality of the Food taken.— In food we have a means for elevating our temperature. It is the fuel, indeed, on which animal heat ultimately depends altogether. Thus, when more heat is wanted, we instinctively take more food, and take such kinds of it as are good for combustion; while every-day experience shows the different power of resisting cold possessed, respectively, by the well-fed and by the starved. In northern regions, again, and in the colder seasons of more southern climes, the quantity of food consumed is 316 HAND-BOOK OF PHYSIOLOGY. (speaking very generally) greater than that consumed by the same men or animals in opposite conditions of climate and season. And the food, which appears naturally adapted to the inhabitants of the coldest climates, such as the several fatty and oily substances, abounds in carbon and hydrogen, and is fitted to combine with the large quantities of oxy- gen which, breathing cold dense air, they absorb from their lungs. (b.) By Exercise. — In exercise, we have an important means of raising the temperature of our bodies (p. 310). (c.) By Influence of the Nervous System. — The influence of the nerv- ous system in modifying the production of heat must be very important, as upon nervous influence depends the amount of the metabolism of the tissues. The experiments and observations which best illustrate it are those showing, first, that when the supply of nervous influence to a part is cut oft', the temperature of that part falls below its ordinary degree; and, secondly, that when death is caused by severe injury to, or removal of, the nervous centres, the temperature of the body rapidly falls, even though artificial respiration be performed, the circulation maintained, and to all appearance the ordinary chemical changes of the body be com- pletely effected. It has been repeatedly noticed, that after division of the nerves of a limb its temperature falls; and this diminution of heat has been remarked still more plainly in limbs deprived of nervous influ- ence by paralysis. With equal certainty, though less definitely, the influence of the nervous system on the production of heat, is shown in the rapid and momentary increase, of temperature, sometimes general, at other times qpte local, which is observed in states of nervous excitement; in the general increase*of warmth of the body, sometimes amounting to perspi- ration, which is. excited by passions of the mind; in the sudden rush of heat to* the face, which is not a mere sensation; and in the equally rapid diminution of temperature in the depressing passions. But none of these instances suffice to prove that heat is generated by mere nervous action, independent of any chemical change; all are explicable, on the supposi- tion that the nervous system alters, by its power of controlling the calibre of the blood-vessels, the quantity of blood supplied to a part; while any influence which the nervous system may have in the production of heat, apart from this influence on^ the blood-vessels, is an indirect one, and is derived, from, its power of causing such nutritive change in the tissues as may, by involving the necessity of chemical action, involve the produc- tion of heat. Inhibitory heat-centre. — Whether a centre exists which regulates the production of heat in warm-blooded animals, is still undecided. Experi- ments have shown that exposure to cold at once increases the oxygen taken in, and the carbonic acid given out, indicating an increase in the activity of the metabolism of the tissues, but that in animals poisoned by ANIMAL HEAT. 317 urari, exposure to cold diminishes both the metabolism and the temper- ature, and warm-blooded animals then re-act to variations of the ex-, ternal temperature just in the same way as cold-blooded. These experi- ments seem to suggest that there is a centre, to which, under normal circumstances, the impression of cold is conveyed, and from which by efferent nerves impulses pass to the muscles, whereby an increased metab- olism is induced, and so an increased amount of heat is generated. The centre is probably situated above the medulla. Thus in urarized animals, as the nerves to the muscles, the metabolism of which is so important in the production of heat, are paralyzed, efferent impulses from the centre cannot induce the necessary metabolism for the production of heat, even though afferent impulses from the skin, stimulated by the alteration of temperature, have conveyed to it the necessity of altering the amount of heat to be produced. The same effect is produced when the medulla is cut. Influence of Extreme Heat and Cold. — In connection with the regulation of animal temperature, and its maintenance in health at the normal height, may be noted the result of circumstances too powerful, either in raising or lowering the heat of the body, to be controlled by the proper regulating apparatus. Walther found that rabbits and dogs, when tied to aboard and exposed to a hot sun, reached a temperature of 114-8° F., and then died. Cases of sunstroke furnish us with several examples in the case of man; for it would seem that here death ensues chiefly or solely from elevation of the temperature. In many febrile diseases the immediate cause of death appears to be the elevation of the temperature to a point inconsistent with the continuance of life. The effect of mere loss of bodily temperature in man is less well known than the effect of heat. From experiments by Walther, it appears that rabbits can be cooled down to 48° F. (8.9° C.), before they die, if arti- ficial respiration be kept up. Cooled down to 64° F. (17.8° C.), they cannot recover unless external warmth be applied together with the employment of artificial respiration. Rabbits not cooled below 77° F. (25° C.) recover by external warmth alone. CHAPTER XI. SECRETION. Secretion is the process by which materials are separated from the blood, and from the organs in which they are formed, for the purpose either of serving some ulterior office in the economy, or of being dis- charged from the body as useless or injurious. In the former case, the separated materials are termed secretions; in the latter, they are termed excretions. Most of the secretions consist of substances which, probably, do not pre-exist in the same form in the blood, but require special organs and a process of elaboration for their formation, e.g., the liver for the formation of bile, the mammary gland for the formation of milk. The excretions, on the other hand, commonly or chiefly consist of substances which exist ready-formed in the blood, and are merely abstracted therefrom. If from any cause, such as extensive disease or extirpation of an excretory organ, the separation of an excretion is prevented, and an accumulation of it in the blood ensues, it frequently escapes through other organs, and may be detected in various fluids of the body. But this is never the case with secretions; at least with those that are most elaborated; for after the removal of the special organs by which any of them is elaborated, it is no longer formed. Cases sometimes occur in which the secretion continues to be formed by the natural organ, but not being able to escape toward the exterior, on account of some obstruction, is re-absojbed into the blood, and afterward discharged from it by exudation in other ways; but these are not instances of true vicarious secretion, and must not be thus regarded. These circumstances, and their final destination, are, however, the only particulars in which secretions and excretions can be distinguished; for, in general, the structure of the parts engaged in eliminating excre- tions is as complex as that of the parts concerned in the formation of secretions. And since the differences of the two processes of separation, corresponding with those in the several purposes and destinations of the fluids, are not yet ascertained, it will be sufficient to speak in general terms of the process of separation or secretion. Every secreting apparatus possesses, as essential parts of its structure, a simple and almost textureless membrane, named the primary or base- SECKETION. 319 ment-membrane; certain cells; and blood-vessels. These three structural elements are arranged together in various ways; but all the varieties nw^ be classed under one or other of two principal divisions, namely, mem- branes and glands. ORGANS AND TISSUES OF SECRETION. The principal secreting membranes are (1) the Serous and Synovial membranes; (2) the Mucous membranes; (3) the Mammary gland; (4) the Lachrymal gland; and (5) the Skin. (1) Serous Membranes. — The serous membranes are especially dis- tinguished by the characters of the endothelium covering their free sur- FIG. 219. — Section of synovial membrane, a, endothelial covering of elevations of the membrane ; fo, subserous tissue containing fat and blood-vessels; c, ligament covered by the synovial membrane. face: it always consists of a single layer of polygonal cells. The ground substance of most serous membranes consists of connective-tissue cor- puscles of various forms lying in the branching spaces which constitute the ' 'lymph canalicular system" (p. 292), and interwoven with bundles of white fibrous tissue, and numerous delicate elastic fibrillae, together with blood-vessels, nerves, and lymphatics. In relation to the process of secretion, the layer of connective tissue serves as a groundwork for the ramification of blood-vessels, lymphatics, and nerves. But in its usual form it is absent in some instances, as in the arachnoid covering the dura mater, and in the interior of the ventricles of the brain. The primary membrane and epithelium are always present, and are concerned 320 HAND-BOOK OF PHYSIOLOGY. in the formation of the fluid by which the free surface of tne membrane 48 moistened. Serous membranes are of two principal kinds: 1st. Those which line visceral cavities, — the arachnoid, pericardium, pleura?, peritoneum, and tunicas vaginales. 2nd. The synovial membranes lining the joints, and the sheaths of tendons and ligaments, with which, also, are usually in- cluded the synovial bursce, or bursce mucosce, whether these be subcutane- ous, or situated beneath tendons that glide over bones. The serous membranes form closed sacs, and exist wherever the free surfaces of viscera come into contact with each other or lie in cavities unattached to surrounding parts. The viscera invested by a serous mem- brane are, as it were, pressed into the shut sac which it forms, carrying before them a portion of the membrane, which serves as their investment. To the law that serous membranes form shut sacs, there is, in the human subject, one exception, viz. : the opening of the Fallopian tubes into the abdominal cavity, — an arrangement which exists in man and all Vertebrata, with the exception of a few fishes. Functions. — The principal purpose of the serous and synovial mem- branes is to furnish a smooth, moist surface, to facilitate the movements of the invested organ, and to prevent the injurious effects of friction. This purpose is especially manifested in joints, in' which free and exten- sive movements take place; and in the stomach and intestines, which, from the varying quantity and movements of their contents, are in almost constant motion upon one another and the walls of the abdomen. Serous Fluid. — The fluid secreted from the free surface of the serous membranes is, in health, rarely more than sufficient to ensure the main- tenance of their moisture. The opposed surfaces of each serous sac are at every point in contact with each other. After death, a larger quantity of fluid is usually found in each serous sac; but this, if not the product of manifest disease, is probably such as has transuded after death, or in the last hours of life. An excess of such fluid in any of the serous sacs constitutes dropsy of the sac. The fluid naturally secreted by the serous membranes appears to be identical, in general and chemical characters, with the serum of the blood, or with very dilute liquor saguinis. It is of a pale yellow or straw color, slightly viscid, alkaline, and, on account of the presence of albu- men, coagulable by heat. This similarity of the serous fluid to the liquid part of blood, and to the fluid with which most animal tissues are moist- ened, renders it probable that it is, in great measure, separated by simple transudation, through the walls of the blood-vessels. The probability is increased by the fact that, in jaundice, the fluid in the serous sacs is, equally with the serum of the blood, colored with the bile. But there is reason for supposing that the fluid of the cerebral ventricles and of the arachnoid sac are exceptions to this rule; for they differ from the fluids SECRETION. of the other serous sacs not only in being pellucid, colorless, and of much less specific gravity, but in that they seldom receive the tinge of hil* when present in the blood, and are not colored by madder, or other similar substances introduced abundantly into the blood. Synovial Fluid: Synovia.— It is also probable that the formation of synovial fluid is a process of more genuine and elaborate secretion, by means of the epithelial cells on the surface of the membrane, and espe- cially of those which are accumulated on the edges and processes of the synovial fringes; for, in its peculiar density, viscidity, and abundance of albumin, synovia differs alike from the serum of blood and from the fluid of any of the serous cavities. (2) Mucous Membranes. — The mucous membranes line all those passages by which internal parts communicate with the exterior, and by which either matters are eliminated from the body or foreign substances taken into it. They are soft and velvety, and extremely vascular. The external surfaces of mucous membranes are attached to various other tissues; in the tongue, for example, to muscle; on cartilaginous parts, to perichondrium; in the cells of the ethmoid bone, in the frontal and sphenoidal sinuses, as well as in the tympanum, to periosteum; in the intestinal canal, it is connected with a firm submucous membrane, which on its exterior gives attachment to the fibres of the muscular coat. The mucous membranes line certain principal tracts — Gastro-Pulmonary and Genito-Urinary; the former being subdivided into the Digestive and Respiratory tracts. 1. The Digestive tract commences in the cavity of the mouth, from which prolongations pass into the ducts of the salivary glands. From the mouth it passes through the fauces, pharynx, and oesophagus, to the stomach, and is thence continued along the whole tract of the intestinal canal to the termination of the rectum, being in its course arranged in the various folds and depressions already described, and prolonged into the ducts of the intestinal glands, the pancreas and liver, and 'into the gall-bladder. 2. The Respiratory tract includes the mucous membrane lining the cavity of the nose, and the various sinuses communicating with it, the lachrymal canal and sac, the conjunctiva of the eye and eyelids, and the prolongation which passes along the Eusta- chian tubes and lines the tympanum and the inner surface of the mem- brana tympani. Crossing the pharynx, and lining that part of it which is above the soft palate, the respiratory tract leads into the glottis, whence it is continued, through the larynx and trachea, to the bronchi and their divisions, which it lines as far as the branches of about -^ of an inch in diameter, and continuous with it is a layer of delicate epithelial mem- brane which extends into the pulmonary cells. 3. The Genito-urinary tract, wh:'ch lines the whole of the urinary passages, from their external orifice to the termination of the tubuli uriniferi of the kidneys, extends also into the organs of generation in both sexes, and into the ducts of the VOL. I.— 21. 322 HAND-BOOK OF PHYSIOLOGY. glands connected with them; and in the female becomes continuous with £he serous membrane of the abdomen at the fimbrias of the Fallopian tubes. Structure. — Along each of the above tracts, and in different portions of each of them, the mucous membrane presents certain structural pecu- liarities adapted to the functions which each part has to discharge; }Tet in some essential characters mucous membrane is the same, from whatever part it is obtained. In all the principal and larger parts of the several tracts, it presents, as just remarked, an external layer of epithelium, sit- uated upon basement-membrane, and beneath this, a stratum of vascular tissue of variable thickness, containing lymphatic vessels and nerves which in different cases presents either outgrowths in the form of papillae and villi, or depressions or involutions in the form of glands. But in the prolongations of the tracts, where they pass into gland-ducts, these con- stituents are reduced in the finest branches of the ducts to the epithelium, the primary or basement-membrane, and the capillary blood-vessels spread over the outer surface of the latter in a single layer. The primary or basement-membrane is a thin transparent layer, simple, homogeneous, or composed of endothelial cells. In the minuter divisions of the mucous membranes, and in the ducts of glands, it is the layer continuous and correspondent with this basement-membrane that forms the proper walls of the tubes. The cells also which, lining the larger and coarser mucous membranes, constitute their epithelium, are continuous with, and, often similar to those which, lining the gland- ducts, are called gland-cells. No certain distinction can be drawn be- tween the epithelium-cells of mucous membranes and gland-cells. It thus appears, that the tissues essential to the production of a secretion are, in their simplest form, a membrane, having on one surface blood-vessels, and on the other a layer of cells, which may be called either epithelium-cells or gland-cells. Mucous Fluid : Mucus. — From all mucous membranes there is secreted either from the surface or from certain special glands, or from both, a more or less viscid, greyish, or semi-transparent fluid, of alkaline reaction and high specific gravity, named mucus. It mixes imperfectly with water, but, rapidly absorbing liquid, it swells considerably when water is added. Under the microscope it is found to contain epithelium and leucocytes. It is found to be made up, chemically, of a nitrogenous principle called mucin which forms its chief bulk, of a little albumen, of salts chiefly chlorides and phosphates, and water with traces of fats and extractives. Secreting Glands. — The structure of the elementary portions of a secreting apparatus, namely epithelium, simple membrane, and blood- vessels having been already described in this and previous chapters, we may proceed to consider the manner in which they are arranged to form the varieties of secreting glands. SECRETION. The secreting glands are the organs to which the function of seen It '27 becomes florid when, on the introduction of food, its glands begin to secrete; the mammary gland becomes much more vascular during lacta- tion; and all circumstances which give rise to an increase in the quantity .of material secreted by an organ produce, coincidently, an increased sup- -ply of blood; but we have seen that a discharge of saliva may occur under extraordinary circumstances, without increase of blood-supply (p. 233), and so it may be inferred that this condition of increased blood-supply is not absolutely essential. (2.) When the blood contains more than usual of the materials which the glands are designed to separate or elaborate. Thus, when an excess of nitrogenous waste is in the blood, whether from excessive exercise, or from destruction of one kidney, a healthy kidney will excrete more urea than it did before. (3.) Influence of the Nervous System on Secretion. — The process of secretion is largely influenced by the condition of the nervous system. The exact mode in which the influence is exhibited must still be regarded as somewhat obscure. In part, it exerts its influence by increasing or diminishing the quantity of blood supplied to the secreting gland, in vir- tue of the Jiower which it exercises over the contractility of the smaller blood-vessels; while it also has a more direct influence, as was demon- strated at length in the case of the submaxillary gland, upon the secreting cells themselves; this may be called trophic influence. Its influence over secretion, as well as over other functions of the body, may be excited by causes acting directly upon the nervous centres, upon the nerves going to the secreting organ, or upon the nerves of other parts. In the latter case, a reflex action is produced: thus the impression produced upon the nervous centres by the contact of food in the mouth, is reflected upon the nerves supplying the salivary glands, and produces, through these, a more abundant secretion of saliva (p. 232). Through the nerves, various conditions of the brain also influence the secretions. Thus, the thought of food may be sufficient to excite an abundant flow of saliva. And, probably, it is the mental state which ex- cites the abundant secretion of urine in hysterical paroxysms, as well as the perspirations and, occasionally, diarrhoea, which ensue under the influ- ence of terror, and the tears excited by sorrow or excess of joy. The qual- ity of a secretion may also be affected by the mind; as in the cases in which, through grief or passion, the secretion of milk is altered, and is sometimes so changed as to produce irritation in the alimentary canal of the child, or even death (Carpenter). Relations between the Secretions.— The secretions of some of the glands seem to bear a certain relation or antagonism to each other, by which an increased activity of one is usually followed by diminished activity of one oT more of the others; and a deranged condition of one is apt to entail a disordered state in the others. Such relations appear to 328 HAND-BOOK OF PHYSIOLOGY. exist among the various mucous membranes; and. the close relation be- tween the secretion of the kidney and that of the skin is a subject of con- stant observation. THE MAMMARY GLANDS AND THEIR SECRETION: — MILK. Structure. — The mammary glands are composed of large divisions or lobes, and these are again divisible into lobules, — the lobules being com- posed of the convoluted subdivision of ducts (alveoli). The lobes and lobules are bound together by areolar tissue; penetrating between the lobes, and covering the general surface of the gland, with the exception of the nipple, is a considerable quantity of yellow fat, itself lobulated by FIG. 221.— Dissection of the lower half of the female mamma during the period of lactation. %.— In the left-hand side of the dissected part the glandular lobes are exposed and partially unrav- eled; and on the right-hand side, the glandular substance has been removed to show the reticular loculi of the connective-tissue in which the glandular lobules are placed: 1, upper part of the mainilla or nipple; 2, areola; 3, subcutaneous masses of fat; 4, reticular loculi of the connective-tissue which support the glandular substance and contain the fatty masses ; 5. one of three lactiferous ducts shown passing toward the mamilla where they open; 6, one of the sinus lactei or reservoirs; 7, some of the glandular lobules which have been unraveled; 7', others massed together. (Luschka.) sheaths and processes of tough areolar tissue (Fig. 221) connected both with the skin in front and the gland behind; the same bond of connection extending also from the under surface of the gland to the sheathing connective tissue of the great pectoral muscle on which it lies. The main ducts of the gland, fifteen to twenty in number, called the lactiferous or galactophorous ducts, are formed by the union of the smaller (lobular) ducts, and open by small separate orifices through the nipple. At the points of junction of lobular ducts to form lactiferous difcts, and just be- fore these enter the base of the nipple, the ducts are dilated (6, Fig. 221); SECRETION. 329 and, during lactation, the period of active secretion by the gland, the dilatations form reservoirs for the milk, which collects in them and dis- tends them. The walls of the gland-ducts are formed of areolar and elas- tic with some muscular tissue, and are lined internally by short columnar •and near the nipple by squamous epithelium. The alveoli consist of a membrana propria of flattened endothelial cells lined by low columnar epithelium, and are filled with fat globules. The nipple, which contains the terminations of the lactiferous ducts, is composed also of areolar tissue, and contains unstriped muscular fibres. Blood-vessels are also freely supplied to it, so as to give it a species of erectile structure. On its surface are very sensitive papillae; and around it is a small area or areola of pink or dark-tinted skin, on which are to be seen small projections formed by minute secreting glands. Blood-vessels, nerves, and lymphatics are plentifully supplied to the mammary glands; the calibre of the blood-vessels, as well as the size of the glands, varying very greatly under certain conditions, especially those of pregnancy and lactation. Changes in the Glands at certain Periods.-— The minute changes which occur in the mammary gland during its periods of evolu- FIG. 222.— Section of mammary gland of rabbit near the end of pregnancy, showing six acini, e, epithelial cells of a polyhedral or short columnar form, with which the acini are packed. ' X 200. tion (pregnancy), and involution (when lactation has ceased), are the fol- lowing:— The most favorable period for observing the epithelium of the mam- mary gland fully developed is shortly before the end of pregnancy. At this period the acini which form the lobules of the gland, are found to be lined with a mosaic of polyhedral epithelial cells (Fig. 222), and sup- ported by a connective tissue stroma. The rapid formation of milk during lactation results from a fatty metamorphosis of the epithelial cells: "The secretion may be said to be produced by a transformation of the substance of successive generations 330 HAND-BOOK OF PHYSIOLOGY. of epithelial cells, and in the state of full activity this transformation is so complete that it may be called a deliquescence" (Creighton). In the earlier days of lactation, epithelial cells partially transformed are discharged in the secretion: these are termed "colostrum corpuscles," but later on the cells are completely transformed before the secretion is discharged. After the end of lactation, the mamma gradually returns to its original size (involution). The acini, in the early stages of involution, are lined with cells in all degrees of vacuolation (Fig. 223). As involution proceeds the acini diminish considerably in size, and at length, instead of a mosaic of lining epithelial cells (twenty to thirty in each acinus), we have five or six nuclei ( some with no surrounding protoplasm) lying in an irregular heap FIG. 223. — Section of mammary gland of ewe shortly after the end of lactation, showing parts of four acini, which contain numerous epithelial cells undergoing vacuolation in situ; they very closely resemble young fat-cells, and are in fact just like " Colostrum corpuscles.11 X 300. (Creighton.) within the acinus. During the later stages of involution, large yellow granular cells are to be seen. As the acini diminish in size, the con- nective tissue and fatty matter between them increase, and in some ani- mals, when the gland is completely inactive, it is found to consist of a thin film of glandular tissue overlying a thick cushion of fat. Many of the products of waste are carried off by the lymphatics. During pregnancy the mammary glands undergo changes (evolution) which are readily observable. They enlarge, become harder and more distinctly tabulated: the veins on the surface become more prominent. The areola becomes enlarged and dusky, with projecting papillae; the nipple too becomes more prominent, and milk can be squeezed from the orifices of the ducts. This is a very gradual process, which commences about the time of conception, and progresses steadily during the whole period of gestation. The acini enlarge, and a series of changes occur, exactly the reverse of those just described under the head of Involu- tion. SECRETION. 331 THE MAMMARY SECRETION: — MILK. Under tKe microscope, milk is found to contain a number of globules of various sizes (Fig. 224), the majority about TTj¥FO- of an inch in diam- eter. They are composed of oily matter, probably coated by a fine layer of albuminous material, and are called milk-globules; while, accompany- ing these, are numerous minute particles, both oily and albuminous, which exhibit ordinary molecular movements. The milk which is secreted in the first few days after parturition, and which is called the rnlnsfrum, differs from ordinary milk in containing a larger quantity of solid matter; and under the microscope are to be seen certain granular FIG. 224.— Globules and molecules of Cow's milk. X 400. masses called colostrum-corpuscles. These, which appear to be small masses of albuminous and oily matter, are probably secreting cells of the gland, either in a state of fatty degeneration, or old cells which in their attempt at secretion under the new circumstances of active need of milk, are filled with oily matter; which, however, being unable to discharge, they are themselves shed bodily to make room for their successors. Colos- trum-corpuscles have been seen to exhibit contractile movements and to squeeze out drops of oil from their interior (Strieker). Chemical Composition. — Milk is in reality an emulsion consisting of numberless little globules of fat, coated with a thin layer of albumi- nous matter, floating in a large quantity of water which contains in solu- tion casein, serum-albumin, milk-sugar (lactose), and several salts. Its percentage composition has been already mentioned, but may be here repeated. Its reaction is alkaline: its specific gravity about 1030. 332 HAND-BOOK OF PHYSIOLOGY. TABLE OF THE CHEMICAL COMPOSITION OF MILK. Human. Cows. Water 890 ... 858 Solids 110 142 1000 1000 Proteids, including Casein and Serum-Albumin . . 35 . .68 Fats or Butter . . . .25 . . .38 Sugar (with extractives) . 48 . .30 Salts 2 6 110 142 When milk is allowed to stand, the fat globules, being the lightest portion, rise to the top, forming cream. If a little acetic acid be added to a drop of milk under the microscope, the albuminous film coating the oil drops is dissolved, and they run together into larger drops. The same result is produced by the process of churning, the effect of which is to break up the albuminous coating of the oil drops: they then coalesce to form butter. Curdling of Milk. — If milk be allowed to stand for some time, its reaction becomes acid: in popular language it "turns sour/' This change appears to be due to the conversion of the milk-sugar into lactic acid, which causes the precipitation of the casein (curdling): the curd con- tains the fat globules: the remaining fluid (whey) consists of water hold- ing in solution albumin, milk-sugar and certain salts. The same effect is produced in the manufacture of cheese, which is really casein coagu- lated by the agency of rennet (p. 248). When milk is boiled, a scum of serum-albumin forms on the surface. Curdling Ferments. — The effect of the ferments of the gastric, pan- creatic, and intestinal juices in curdling milk (curdling ferments) has already been mentioned in the Chapter on Digestion. The salts of milk are chlorides, sulphates, phosphates, and carbonates of potassium, sodium, calcium. CHAPTEK XII. THE SKIN AND ITS FUNCTIONS. THE skin serves — (1), as an external integument for the protection of the deeper tissues, and (2), as a sensitive organ in the exercise of touch; it is also (3), an important excretory, and (4), an absorbing organ; while it plays an important part in (5) the regulation of the temperature of the body. Structure of the Skin. — The skin consists, principally, of a vascu- lar tissue, named the corium, derma, or cut is vera, and an external cover- ing of epithelium termed the cuticle or epidermis. Within and beneath the corium are imbedded several organs with special function, namely sudoriferous glands, sebaceous glands, and hair follicles; and on its surface are sensitive papilla. The so-called appendages of the skin — the hair and nails — are modifications of the epidermis. Epidermis. — The epidermis is composed of several strata of cells of various shapes, and closely resembles in its structure that which lines the mouth. The following four layers may be distinguished. 1. Stratum conieum (Fig. 225, «), consisting of many superposed layers of horny scales. The different thickness of the epidermis in different regions of the body is chiefly due to variations in the thickness of this layer; e.g., on the horny parts of the palms of the hands and soles of the feet it is of great thickness. The stratum corneum of the buccal epithelium chiefly differs from that of the epidermis in the fact that nuclei are to be dis- tinguished in some of the cells even of its most superficial layers. 2. Stratum lucidum, a bright homogeneous membrane consisting of squamous cells closely arranged, in some of which a nucleus can be seen. 3. Stratum granulosum, consisting of one layer of flattened cells which appear fusiform in vertical section: they are distinctly nucleated, and a number of granules extend from the nucleus to the margins of the cell. 4. Stratum Malpighii or Rete mucosum, which consists of many strata, The deepest cells, placed immediately above the ctitis vera, are columnar with oval nuclei: this layer of columnar cells is succeeded by a number of layers of more or less polyhedral cells with spherical nuclei; the cells of the more superficial layers are considerably flattened. The deeper sur- face of the rete mucosum is accurately adapted to the papillae of the true skill, being, as it were, moulded on them. It is very constant in thickness in all parts of the skin. The cells of the middle layers of the 334 HAND-BOOK OF PHYSIOLOGY. stratum Malpighii are almost all connected by processes, and thus form "prickle cells" (p. 21). The pigment of the skin, the varying quantity of which causes the various tints observed in different individuals and different races, is contained in the deeper cells of the rete mucosum; the pigmented cells as they approach the free surface gradually losing their color. Epidermis maintains its thickness in spite of the constant wear and tear to which it is subjected. The columnar cells of the deepest layer of the "rete mucosum" elongate, and their nuclei divide into two FIG. 225.— Vertical section of the epidermis of the prepuce, a, stratum corneum, of very few layers, the stratum lucidum and stratum granulosum not being distinctly represented: 6, c, d, and e, the layers of the stratum Malpighii, a certain number of the cells in layers d and e showing signs of segmentation; layer c consists chiefly of prickle or ridge and furrow cells; /, basement membrane; <7, cells in cutis vera. (Cadiat.) FIG. 226.— Vertical section of skin of the negro, a, a. Cutaneous papillae, b. Undermost and dark-colored layer of oblong vertical epidermis-cells, c. Stratum Malpighii. d. Superficial layers, including stratum corneum, stratum lucidum, and stratum granulosum, the last two not differen- tiated in figure. X 250. (Sharpey.) (Fig. 225, e). Lastly the upper part of the cell divides from the lower; thus from a long columnar cell are produced a polyhedral and a short columnar cell: the latter elongates and the process is repeated. The polyhedral cells thus formed are pushed up toward the free surface by the production of fresh ones beneath them, and become flattened from pres- sure: they also become gradually horny by evaporation and transforma- tion of their protoplasm into keratin, till at last by rubbing they are detached as dry horny scales at the free surface. There is thus a con- stant production of fresh cells in the deeper layers, and a constant throw- ing off of old ones from the free surface. When these two processes are accurately balanced, the epidermis maintains its thickness. When, by THE SKIN AND ITS FUNCTIONS. 335 intermittent pressure, a more active cell-growth is stimulated, the produc- tioii of cells exceeds their waste and the epidermis increases in thickness, as we see in the horny hands of the laborer. The thickness of the epidermis on different portions of the skin is directly proportioned to the friction, pressure, and other sources of injury to which it is exposed; for it serves as well to protect the sensitive and vascular cutis from injury from without, as to limit the evaporation of fluid from the blood-vessels. The adaptation of the epidermis to the latter purposes may be well shown by exposing to the air two dead hands or feet, t>f which one has its epidermis perfect, and the other is deprived of it; in a day, the skin of the latter will become brown, dry, and horn- like, while that of the former will almost retain its natural moisture. Cutis vera. — The cor mm or cutis, which rests upon a layer of adi- pose and cellular tissue of varying thickness, is a dense and tough, but yielding and highly elastic structure, composed of fasciculi of fibro- cellular tissue, interwoven in all directions, and forming, by their inter- lacements, numerous spaces or areolae. These areolae are large in the deeper layers of the cutis, and are there usually filled with little masses of fat (Fig. 228): but, in the superficial parts, they are small or entirely obliterated. Plain muscular fibre is also abundantly present. Papillae. — The papillae are conical elevations of the cutis vera, with a single or divided free extremity, more prominent and more densely set at some parts than at others (Figs. 227 and 230). The parts on which they are most abundant and most prominent, are the palmar surface of the FIG. 227.— Compound papillae from the palm of the hand; a, basis of a papilla: 6, 6, divisions or branches of the same; c, c, branches belonging to papillae, of which the bases are hidden from view. XGO. (Kolliker.) hands and fingers, and the soles of the feet — parts, therefore, in which the sense of touch is most acute. On these parts they are disposed in double rows, in parallel curved lines, separated from each other by depressions. Thus they may be seen easily on the palm, whereon each raised line is composed of a double row of papillae, and is intersected by short transverse lines or furrows corresponding with the interspaces between the successive pairs of papillae. Over other parts of the skin they are more or less thinly scattered, and are scarcely elevated above the surface. Their average length is about y^- of an inch, and at their base 336 HAND-BOOK OF PHYSIOLOGY. they measure about ^J-g- of an inch in diameter. Each papilla is abun- dantly supplied with blood, receiving from the vascular plexus in the cutis one or more minute arterial twigs, which divide into capillary loops in its substance, and then reunite into a minute vein, which passes out at its base. The abundant supply of blood which the papillae thus receive explains the turgescence or kind of erection which they undergo when the circulation through the skin is active. The majority, but not all, of FIG. 228.— Vertical section of skin. A. Sebaceous gland opening into hair-follicle. B. Muscular fibres. C. Sudoriferous or sweat-gland. D. Subcutaneous fat. E. Fundus of hair-follicle, with hair- papillae. (Klein and Noble Smith.) the papillae contain also one or more terminal nerve-fibres, from the ultimate ramifications of the cutaneous plexus, on which their exquisite sensibility depends. Nerve-terminations. — In some parts, especially those in which the sense of touch is highly developed, as, for example, the palm of the hand and the lips, the nerve-fibres appear to terminate, in many of the papillae, by one or more free ends in the substance of an oval-shaped body, occupy- ing the principal part of the interior of the papillae, and termed a touch- THE SKIN AND ITS FUNCTIONS. 337 corpuscle (Fig. 229). The nature of this body is obscure. Some regard it as little else than a mass of fibrous or connective tissue, surrounded by elastic fibres, and formed, according to Huxley, by an increased develop- ment of th6 primitive sheaths of the nerve-fibres, entering the papillae. Others, however, believe that, instead of thus consisting of a homogeneous mass of connective tissue, they are special and peculiar bodies of lami- nated structure, directly concerned in the sense of touch. They do not occur in all the papilla? of the parts where they are found, and, as a rule, in the papillae in which they are present there are no blood- vessels. Since FIG. 229.— Papillae from the skin of the hand, freed from the cuticle and exhibiting tactile cor- puscles. A. Simple papilla with four nerve-fibres: a, tactile corpuscles: 6, nerves. B. Papilla treated with acetic acid; a, cortical layer with cells and fine elastic filaments; ft, tactile corpuscle with trans- verse nuclei; c, entering nerve with neurilemma or perineurium ; d, nerve-fibres winding round the corpuscle, c. Papilla viewed from above so as to appear as a cross-section: a, cortical layer; 6, nerve- fibre; c, sheath of the tactile corpuscle containing nuclei; d, core. X 350. (Kolliker.) these peculiar bodies in which the nerve-fibres end are only met with in the papillae of highly sensitive parts, it may be inferred that they are specially concerned in the sense of touch, yet their absence from the papillae of other tactile parts shows that they are not essential to this sense. Closely allied in structure to the touch-corpuscles, are some little bodies called end-lulls, about -g-J-g- inch in diameter (Krause). They are gener- ally oval or spheroidal, and composed externally of a coat of connective tissue enclosing a softer matter, in which the extremity of a nerve termi- nates. These bodies have been found chiefly in the lips, tongue, palate, and the skin of the glans penis (Fig. 230). Glands of the Skin. — The skin possesses glands of two kinds: (a) Sudoriferous, or Sweat Glands; (b) Sebaceous Glands. (a) Sudoriferous, or Sweat Glands. — Each of these glands consists of a small lobular mass, formed of a coil of tubular gland-duct, surrounded by blood-vessels and embedded in the subcutaneous adipose tissue (Fig. 228, c.). From this mass, the duct ascends, for a short distance, in a spiral manner through the deeper part of the cutis, then passing straight, VOL. I.— 22. 338 HAND-BOOK OF PHYSIOLOGY. and then sometimes again becoming spiral, it passes through the -cuticle and opens by an oblique valve-like aperture. In the parts where the epi- dermis is thin the ducts themselves are thinner and more nearly straight in their course (Fig. 228). The duct, which maintains nearly the same diameter throughout, is lined with a layer of columnar epithelium (Fig. FIG. 230.— End-bulbs in papillae (magnified) treated with acetic acid. A, from the lips: the white loops in one of them are capillaries. B, from the tongue. Two end-bulbs seen in the midst of the simple papillae: a, a, nerves. (Kolliker.) 231) continuous with the epidermis; while the part which passes through the epidermis is composed of the latter structure only; the cells which immediately form the boundary of the canal in this part being somewhat differently arranged from those of the adjacent cuticle. FIG. 231.— Glomeruli of sudoriferous gland, divided in various directions, a, sheath of the gland ; &, columnar epithelial lining of gland tube; c, lumen of tube; d, divided blood-vessel- * loose-con- nective-tissue, forming a capsule to the gland. (Biesiadecki.) The sudoriferous glands are abundantly distributed over the whole sur- face of the body; but are especially numerous, as well as very large, in the skin of the palm of the hand, and of the sole of the foot. The glands THE SKIN AND ITS FUNCTIONS. 339 by which the peculiar odorous matter of the axillae is secreted form a nearly complete layer under the cutis, and are like the ordinary sudorifer- ous glands, except in being larger and having very short ducts. The peculiar bitter yellow substance secreted by the skin of the exter- nal auditory passage is named cerumen, and the glands themselves ceru- min ous glands; but they do not much diifer in structure from the ordi- nary sudoriferous glands. (b) Sebaceous Glands. — The sebaceous glands (Fig. 232), like the sudo- riferous glands, are abundantly distributed over most parts of the body. They are most numerous in parts largely supplied with hair, as the scalp FIG. 232.— Sebaceous gland from human skin. (Klein and Noble Smith.) and face, and are thickly distributed about the entrances of the various passages into the body, as the anus, nose, lips, and external ear. They are entirely absent from the palmar surface of the hand and the plantar surfaces of the feet. They are minutely lobulated glands composed of an aggregate of small tubes or sacculi filled with opaque white substances, like soft ointment. Minute capillary vessels overspread them; and their ducts open either on the surface of the skin, close to a hair, or, which is more usual, directly into the follicle of the hair. In the latter case, there are generally two or more glands to each hair (Fig. 228). Hair. — A hair is produced by a peculiar growth and modification of the epidermis. Externally it is covered by a layer of fine scales closely imbricated, or overlapping like the tiles of a house, but with the free 340 HAND-BOOK OF PHYSIOLOGY. edges turned upward (Fig. 233, A). It is called the cuticle of the hair. Beneath this is a much thicker layer of elongated horny cells, closely packed together so as to resemble a fibrous structure. This, very com- FIG. 233. — Surface of a white hair, magnified 160 diameters. The wave lines mark the upper or free edges of the cortical scales. J5, separated scales, magnified 350 diameters. (Kolliker.) monly, in the human subject, occupies the whole of the inside of the hair; but in some cases there is left a small central space filled by a substance called the medulla or pitli, composed of small collections of irregularly shaped cells, contain- ing sometimes pigment granules or fat, but mostly air. The follicle, in which the root of each hair is contained (Fig. 235), forms a tubular de- pression from the surface of the skin, — descend- ing into the subcutaneous fat, generally to a greater depth than the sudoriferous glands, and at its deepest part enlarging in a bulbous form, and often curving from its previous rectilinear course. It is lined throughout by cells of epi- thelium, continuous with those of the epider- mis, and its walls are formed of pellucid mem- brane, which commonly, in the follicles of the largest hairs, has the structure of vascular fibrous tissue. At the bottom of the follicle is a small papilla, or projection of true skin, and it is by the production and out-growth of epi- dermal cells from the surface of this papilla that the hair is formed. The inner wall of the follicle is lined by epidermal cells continuous with those covering the general surface of the skin; as if indeed the follicle had been formed by a simple thrusting in of the surface of the integument (Fig. 234). This epidermal lining of the hair follicle, or root-sheath of the hair, (Kolliker.) See ^ composed of two layers, the inner one of c, knob; d, hair cuticle; e, internal, and /, external root-sheath; gi, /i, dermic coat of follicle; i, papilla; k, k, ducts of sebaceous glands; I, corium; m, mucous layer of epi- dermis; o, upper limit of internal X THE SKIN AND ITS FUNCTIONS. 341 which is so moulded on the imbricated scaly cuticle of the hair, that its inner surface becomes imbricated also, but of course in the opposite direction. When a hair is pulled out, the inner layer of the root-sheath and part of vthe outer layer also are commonly pulled out with it. Nails. — A nail, like a hair, is a peculiar arrangement of epidermal cells, the undermost of which, like those of the general surface of the integument, are rounded or elongated, while the superficial are flattened, FIG. 235. FIG. FIG. 235.— Magnified view of the root of a hair, a, stem or shaft of hair cut across; 6, inner, and c, outer layer of the epidermal lining of the hair-follicle, called also the inner and outer root-sheath; d, dermal or external coat of the hair-follicle, shown in part; e, imbricated scales about to form a cor- tical layer on the surface of the hair. The adjacent cuticle of the root-sheath is not represented, and the papilla is hidden in the lower part of the knob where that is represented lighter. (Kohlraush.) FIG. 236. — Trans'verse section of a hair and hair-follicle made below the opening of the sebaceous gland, a, medulla or pith of the hair; 6, fibrous layer or cortex; c, cuticle; d, Huxley's layer, e, Henle's layer of internal root-sheath; /and #, layers of external root-sheath, outside of g is a light layer, or " glassy membrane." which is equivalent to the basement membrane; h. fibrous coat of hair sac; i, vessels. (Cadiat.) and of more horny consistence. That specially modified portion of the corium, or true skin, by which the nail is secreted, is called the matrix. The back edge of the nail, or the root as it is termed, is received into a shallow crescentic groove in the matrix, white the front part is free and projects beyond the extremity of the digit. T^e intermediate portion of the nail rests by its broad under-surface on the front part of the matrix, which is here called the led of the nail. This part of the matrix is not uniformly smooth on the surface, but is raised in the form of longitudi- nal and nearly parallel ridges or laminae, on which are moulded the epi- dermal cells of which the nail is made up (Fig. 237). The growth of the nail, like that of the hair, or of the epidermis 342 HAND-BOOK OF PHYSIOLOGY. generally, is effected by a constant production of cells from beneath and behind, to take the place of those which are worn or cut away. Inas- much, however, as the posterior edge of the nail, from its being lodged in a groove of the skin, cannot grow backward, on additions being made to it, so easily as it can pass in the opposite direction, any growth at its hinder part pushes the whole forward. At the same time fresh cells are added to its under surface, and thus each portion of the nail becomes gradually thicker as it moves to the front, until, projecting beyond the FIG. 237.— Vertical transverse section through a small portion of the nail and matrix largely magnified. A, corium of the nail-bed, raised into ridges or laminae a, fitting in between correspond- ing laminae 6. of the nail. B, Malpighian, and C, horny layer of nail; d, deepest and vertical cells; e, upper flattened cells of Malpighian layer. (Kolliker.) surface of the matrix, it can receive no fresh addition from bene/ith, and is simply moved forward by the growth at its root, to be at last worn away or cut off. FUNCTIONS OF THE SKIN. (1.) By means of its toughness, flexibility and elasticity, the skin is eminently qualified to serve as the general integument of the body, for defending the internal parts from external violence, and readily yielding and adapting itself to their various movements and changes of position. (2.) The skin is the chief organ of the sense of touch. Its whole sur- face is extremely sensitive; but its tactile properties are due more espe- cially to the abundant papillae with which it is studded. (See Chapter on Special Senses.) Although destined especially for the sense of touch, the papillae are not so placed as to come into direct contact with external objects; but THE SKIN AND ITS FUNCTIONS. 343 like the rest of the surface of the skin, are covered by one or more layers of epithelium, forming the cuticle or epidermis. The papilla? adhere very intimately to the cuticle, which is thickest in the spaces between them, but tolerably level on its outer surface: hence, when stripped off from the cutis, as after maceration, its internal surface presents a series of pits and elevations corresponding to the papillae and their interspaces, of which it thus forms a kind of mould. Besides affording by its imper- meability a check to undue evaporation from the skin, and providing the sensitive cutis with a protecting investment, the cuticle is of service in relation to the sense of touch. For by being thickest in the spaces, be- tween the papillae, and only thinly spread over the summits of these pro- cesses, it may serve to subdivide the sentient surface of the skin into a number of isolated points, each of which is capable of receiving a distinct impression from an external body. By covering the papillae it renders the sensation produced by external bodies more obtuse, and in this manner also is subservient to touch : for unless the very sensitive papillae were thus defended, the contact of substances would give rise to pain, instead of the ordinary impressions of touch. This is shown in the extreme sensi- tiveness and loss of tactile power in a part of the skin when deprived of its epidermis. If the cuticle is very thick, however, as on the heel, touch becomes imperfect, or is lost. (3.) The Secretion of Sebaceous Glands, and Hair-follicles.— The secretion of the sebaceous glands and hair-follicles (for their products cannot be separated) consists of cast-off epithelium-cells, with nuclei and granules, together with an oily matter, extractive matter, and stearin; in certain parts, also, it is mixed with a peculiar odorous principle, which contains caproic, butyric, and rutic acids. It is, perhaps, nearly similar in composition to the unctuous coating, orvernix caseosa, which is formed on the body of the foetus while in the uterus, and which contains large quantities of ordinary fat. Its purpose seems to be that of keeping the skin moist and supple, and, by its oily nature, of both hindering the evapora- tion from the surface, and guarding the skin from the effects of the long- continued action of moisture. But while it thus serves local purposes, its removal from the body entitles it to be reckoned among the excretions of the skin; though the share it has in the purifying of the blood cannot be discerned. (4.) The Excretion of the Skin: the Sweat— The fluid secreted by the sudoriferous glands is usually formed s% gradually, that the watery portion of it escapes by evaporation as fast as it reaches the surface. But, during strong exercise, exposure to great external warmth, in some dis- eases, and when evaporation is prevented, the secretion becomes more sensible, and collects on the skin in the form of drops of fluid. The perspimfion of the skin, as the term is sometimes employed in physiology, includes all that portion of the secretions and exudations from 344 HAND-BOOK OF PHYSIOLOGY. the skin which passes off by evaporation; the sweat includes that which may be collected only in drops of fluid on the surface of the skin. The two terms are, however, most often used synonymously; and for distinc- tion, the former is called insensible perspiration; the latter sensible per- spiration. The fluids are the same, except that the sweat is commonly mingled with various substances lying on the surface of the skin. The contents of the sweat are, in part, matters capable of assuming the form of vapor, such as carbonic acid and water, and in part, other matters which are deposited on the skin, and mixed with the sebaceous secretion. Table of the Chemical Composition of Sweat. Water 995 Solids:— Organic Acids (formic, acetic, butyric, pro- ) .^ pionic, caproic, caprylic) j Salts, chiefly sodium chloride . . . 1 *8 Neutral fats and cholesterin . . . •? Extractives (including urea), with epithelium 1-6 5 1000 Of these several substances, however, only the carbonic acid and water need particular consideration. Watery Vapor. — The quantity of watery vapor excreted from the skin is on an average between 1^- and 2 Ib. daily. This subject has been estimated very carefully by Lavoisier and Sequin. The latter chemist enclosed his body in an air-tight bag, with a mouth-piece. The bag being closed by a strong band above, and the mouth-piece adjusted and gummed to the skin around the mouth, he was weighed, and then re- mained quiet for several hours, after which time he was again weighed. The difference in the two weights indicated the amount of loss by pul- monary exhalation. Having taken off the air-tight dress, he was imme- diately weighed again, and a fourth" time after a certain interval. The difference between the Wo weights last ascertained gave the amount of the cutaneous and pulmonary exhalation together; by subtracting from this the loss by pulmonary exhalation alone, while he was in the air-tight dress, he ascertained the amount of cutaneous transpiration. During a state of rest, the average ftss by cutaneous and pulmonary exhalation in a minute, is eighteen grains, — the minimum eleven grains, the maximum thirty-two grains; and of the eighteen grains, eleven pass off by the skin, and seven by the lungs. The quantity of watery vapor lost by transpiration is of course influ- enced by all external circumstances which affect the exhalation from other evaporating surfaces, such as the temperature, the hygrometric THE SKIN AND ITS FUNCTIONS. 345 state, and the stillness of the atmosphere. But, of the variations to which it is subject under the influence of these conditions, no calculation has been exactly made. Carbonic Acid. — The quantity of carbonic acid exhaled by the skin on an average is about y^- to -%fa of that furnished by the pulmonary respiration. The cutaneous exhalation is most abundant in the lower classes of animals, more particularly the naked Amphibia, as frogs and toads, whose skin is thin and moist, and readily permits an interchange of gases be- tween the blood circulating in it and the surrounding atmosphere. Bischoff found that, after the lungs of frogs had been tied and cut out, about a quarter of a cubic inch of carbonic acid gas was exhaled by the skin in eight hours. And this quantity is very large, when it is remem- bered that a full-sized frog will generate only about half a cubic inch of carbonic acid by his lungs and skin together in six hours. (Milne- Edwards and M tiller.) The importance of the respiratory function of the skin, which was once thought to be proved by the speedy death of animals whose skins, after removal of the hair, were covered with an impermeable varnish, has been shown by further observations to have no foundation in fact; the immediate cause of death in such cases being the loss of temperature. A varnished animal is said to have suffered no harm when surrounded by cotton wadding, and to have died when the wadding was removed. Influence of the Nervous System on Excretion. — Any increase in the amount of sweat secreted is usually accompanied by dilatation of the cutaneous vessels. It is, however, probable that the secretion is like the other secretions, e.g., the saliva, under the direct action of a special nervous apparatus, in that various nerves contain fibres which act directly upon the cells of the sweat glands in the same way that the chorda tym- pani contains fibres which act directly upon the salivary cells. The nerve fibres which induce sweating may act independently of the vaso-motor fibres, whether vaso-dilator or vaso-constrictor. The local apparatus is under control of the central nervous system — sweat centres probably ex- isting both in the medulla and spinal cord — and may be reflexly as well as directly excited. This will explain the fact that sweat occurs not only when the skfti is red, but also when it is pale, and the cutaneous circula- tion languid, as in the sweat which accompanies syncope or fainting, or which immediately precedes death. (5.) Absorption by the Skin.— Absorption by the skin has been already mentioned, as an instance in which that process is most actively accomplished. Metallic preparations rubbed into the skin have the same action as when given internally, only in a less degree. Mercury applied in this manner exerts its specific influence upon syphilis, and excites sali- vation; potassio-tartrate of antimony may excite vomiting, or an eruption extending over the whole body; and arsenic may produce poisonous 346 HAND-BOOK OF PHYSIOLOGY. effects. Vegetable matters, also, if soluble, or already in solution, give rise to their peculiar effects, as cathartics, narcotics, and the like, when rubbed into the skin. The effect of rubbing is probably to convey the particles of the matter into the orifices of the glands, whence they are more readily absorbed than they would be through the epidermis. When simply left in contact with the skin, substances, unless in a fluid state, are seldom absorbed. It has long been a contested question whether the skin covered with the epidermis has the power of absorbing water; and it is a point the more difficult to determine because the skin loses water by evaporation. But, from the result of many experiments, it may now be regarded as a wrell-ascertained fact that such absorption really occurs. The absorption of water by the surface of the body may take place in the lower animals very raj)idly. Not only frogs, which have a thin skin, but lizards, in which the cuticle is thicker than in man, after having lost weight by being kept for some time in a dry atmosphere, were found to recover both their weight and plumpness very rapidly when immersed in water. When merely the tail, posterior extremities, and posterior part of the body of the lizard were immersed, the water absorbed was distributed throughout the system. And a like absorption through the skin, though to a less extent, may take place also in man. In severe cases of dysphagia, when not even fluids can be taken into the stomach, immersion in a bath of warm water or of milk and water may assuage the thirst; and it has been found in such cases that the weight of the body is increased by the immersion. Sailors also, when destitute of fresh water, find their urgent thirst allayed by soaking their clothes in salt water and wearing them in that state; but these effects are in part due to the hindrance to the evaporation of water from the skin. (6.) Regulation of Temperature. — For an account of this impor- tant function of the skin, see Chapter on Animal Heat. CHAPTER XIII. THE KIDNEYS AND THE EXCRETION OF URINE. THE Kidneys are two in number, and are situated deeply in the lum- bar region of the abdomen, on either side of the spinal column, behind the peritoneum. They correspond in position to the last two dorsal and two upper lumbar vertebrae; the right being slightly lower than the left in consequence of the position of the liver on the right side of the abdo- men. They are characteristic in shape, about 4 inches long, 2% inches broad, and 1-J- inch thick. The weight of each kidney is about 4| oz. FIG. 238.— Plan of a longitudinal section through the pelvis and substance of the right kidney. U; a, the cortical substance: 6, 6, broad part of the pyramids of Malpighii: c, c, the divisions of the pel- vis named calyces, laid open; c'. one of those unopened; d, summit of the pyramids of papillae pro- jecting into calyces: e, e, section of the narrow part of two pyramids near the calyces: p, pelvis or enlarged divisions of the ureter within the kidney; it, the ureter; s, the sinus; h, the hilus. Structure of the Kidneys.— The kidney is covered by a rather tougk fibrous capsule, which is slightly attached by it's inner surface to the proper substance of the organ by means of very fine fibres of areolar tissue and minute blood-vessels. From the healthy kidney, therefore, it may be easily torn off without injury to the subjacent cortical portion of the organ. At the hilus or notch of the kidney, it becomes continuous with the external coat of the upper and dilated part of the ureter (Fig. 238). 348 HAND-BOOK OF PHYSIOLOGY. On making a section lengthwise through the kidney (Fig. 238) the main part of its substance is seen to be composed of two chief portions, called respectively the cortical and the medullary portion, the latter being also sometimes called the pyramidal portion, from the fact of its being composed of about a dozen conical bundles of urine-tube, each bundle being called a pyramid. The upper part of the duct of the organ, or the ureter, is dilated into what is called the pelvis of the kidney; and this, again, after separating into two or three principal divisions, is finally sub- divided into still smaller portions, varying in number from about 8 to 12, or even more, and called calyces. Each of these little calyces or cups, which are often arranged in a double row, receives the pointed extremity or papilla of a pyramid. Sometimes, however, more than one papilla is received by a calyx. The kidney is a compound tubular gland, and both its cortical and medullary portions are composed essentially of secreting tubes, the tuliili uriniferi, which, by one extremity, in the cortical portion, end commonly in little saccules containing blood-vessels, called Malpigliian bodies, and, by the other, open through the papillae into the pelvis of the kidney, and thus discharge the urine which flows through them. FIG. 239.— A. Portion of a secreting tubule from the cortical substance of the kidnej'. B. The epi- thelial or gland-cells. X 700 times. In the pyramids the tubes are chiefly straight— dividing and diverg- ing as they ascend through these into the cortical portion; while in the latter region they spread out more irregularly, and become much branched and convoluted. Tubuli Uriniferi. — The tubuli uriniferi (Fig. 239) are composed of a nearly homogeneous membrane, and are lined internally by epithelium. They vary considerably in size in different parts of their course, but are, on an average, about -g-}-^ of an inch in diameter, and are found to be THE KIDNEYS AND URINE. 349 made up of several distinct sections which differ from one another MTV markedly, both in situation and structure. According to Klein, the fol- lowing segments maybe made out: (1) The Malpighian corpuscle (Figs. FIG. 240.— A Diagram of the sections of uriniferous tubes. A, Cortex limited externally by the capsule : without Mali tubule of Schachowa* 5. descending lirnb of Henle's loop: 6, the loop proper; 7, thick part of the as- cending limb; 8. spiral part of ascending limb; 9, narrow ascending limb in the medullary ray; 10, the irregular tubule; 11. the intercalated .section of Schweigger-Seidei, or the distal convoluted tubule; 12, the curved collecting tubule: 13, the straight collecting tubule of the medullary ray: 14. the col- lecting tube of the boundary layer; 15. the large collecting tube of the papillary part which, joining with similar tubes, forms the duct. (Klein and Noble Smith.) 240, 241), composed of a hyaline membrana propria, thickened by a vary- ing amount of fibrous tissue, and lined by flattened nucleated epithelial 350 HAND-BOOK OF PHYSIOLOGY. plates. This capsule is the dilated extremity of the uriniferous tubule, and contains within it a glomerulus of convoluted capillary blood-vessels supported by connective tissue, and covered by flattened epithelial plates. The glomerulus is connected with an efferent and an afferent vessel. (2) The constricted neck of the capsule (Fig. 240, 2), lined in a similar man- ner, connects it with (3) The Proximal convoluted tubule, which forms several distinct curves and is lined with short columnar cells, which vary somewhat in size. The tube next passes almost vertically downward, forming (4) The Spiral tubule, which is of much the same diameter, and FIG. 241.— From a vertical section through the kidney of a dog— the capsule of which is supposed to be on the right, a. The capillaries of the Malpighian corpuscle — viz., the glomerulus, are arranged in lobules; n, neck of capsule; c, convoluted tubes cut in various directions: 6, irregular tubule; d, e, and /, are straight tubes running toward capsules forming a so-called medullary ray; d, collecting tube; e, spiral tube; /, narrow section of ascending limb. X 380. (Klein and Noble Smith.) is lined in the same way as the convoluted portion. So far the tube has been contained in the cortex of the kidney, it now passes vertically down- ward through the most external part (boundary layer) of the Malpighian pyramid into the more internal part (papillary layer), where it curves up sharply, forming altogether the ( 5 and 6) Loop of Henle, which is a very narrow tube lined with flattened nucleated cells. Passing vertically up- ward just as the tube reaches the boundary layer (7) it suddenly enlarges and becomes lined with polyhedral cells. (8) About midway in the boun- dary layer the tube again narrows, forming the ascending spiral of Henle's loop, but is still lined with polyhedral cells. At the point where the tube enters the cortex (9) the ascending limb narrows, but the diame- THE KIDNEYS AND URINE. 351 ter varies considerably; here and there the cells are more flattened, but both in this as in (8) the cells are in many places very angular, branched, and imbricated. It then joins (10) the "irregular tubule" which has a very irregular and angular outline, and is lined with angular and imbri- cated cells. The tube next becomes convoluted, (11) forming the dixfal convoluted tube or intercalated section of Schiveigger-Seidel, which is identical in all respects with the proximal convoluted tube (12 and 13). The curved and straight collecting tubes, the former entering the latter at right angles, and the latter passing vertically downward, are lined with polyhedral, or spindle-shaped, or flattened, or angular cells. The straight collecting tube now enters the boundary layer (14), and passes on to the OTfc FIG. 242. FIG. 243. FIG. 242.— Transverse section of a renal papilla; a, larger tubes or papillary ducts: 6, smaller tubes of Henle: c, blood-vessels, distinguished by their flatter epithelium; d, nuclei of the stroma. (Kolliker.) x 300. FIG. 243.— Diagram showing the relation of the Malpighian body to the uriniferous ducts and blood-vessels, a, one of the interlobular arteries; a', afferent artery passing into the glomerulus; c, capsule of the Malpighian body, forming the termination of and continuous with t, the uriniferous tube; e', e', efferent vessels which subdivide in the plexus jp, surrounding the tube, and finally ter- minate in the branch of the renal vein e (after Bowman). papillary layer, and, joining with other collecting tuoes, form larger tubes, which finally open at the apex of the papilla. These collecting tubes are lined with transparent nucleated columnar or cubical cells (14, 15, 16). The cells of the tubules with the exception of Henle's loop and all parts of the collecting tubules, are, as a rule, possessed of the mtra-nuclear as well as of the intra-cellular network of fibres, of which the vertical rods are most conspicuous parts. Heidenhain observed that indigo-sulphate of sodium, and other pig- ments injected into the jugular vein of an animal, were apparently ex- creted by the cells which possessed these rods, and therefore concluded that the pigment passes through the cells, rods, and nucleus themselves. 352 HAND-BOOK OF PHYSIOLOGY. Klein, however, believes that the pigment passes through the intercellular substances, and not through the cells. In some places, it is stated that a distinct membrane of flattened cells can be made out lining the lumen of the tubes (centrotubular membrane). Blood-vessels of Kidneys. — In connection with the general distri- bution of blood-vessels to the kidney, the Malpighian Corpuscles may be further considered. They (Fig. 243) are found only in the cortical part of the kidney, and are confined to the central part, which, however, makes up about seven-eighths of the whole cortex. On a section of the organ, some of them are just visible to the naked eye as minute red points; others are too small to be thus seen. Their average diameter is about T|~o of an inch. Each of them is composed, as we have seen above, of the dilated extremity of a urinary tube, or Malpighian capsule, enclosing a tuft of blood-vessels. The renal artery divides into several branches, which, passing in at the hilus of the kidney, and covered by a fine sheath of areolar tissue derived from the capsule, enter the substance of the organ in the inter- vals between the papillae, chiefly at ths junction between the cortex and the boundary layer. The chief branches then pass almost horizontally, giving off smaller branches upward to the cortex and downward to the medulla. The former are for the most part straight, they pass almost vertically to the surface of the kidney, giving off laterally in all directions longer or shorter branches, which supply the afferent arteries to the Mal- pighiaii bodies. The small afferent artery (Figs. 243 and 245) which enters the Mal- pighian corpuscle, breaks up as before mentioned in the interior into a dense and convoluted and looped capillary plexus, which is ultimately gathered up again into a single small efferent vessel, comparable to a min- ute vein, which leaves the Malpighian capsule just by the point at which the afferent artery enters it. On leaving, it does not immediately join other small veins as might have been expected, but again breaking up into a network of capillary vessels, is distributed on the exterior of the tubule, from whose dilated end it had just emerged. After this second breaking up it is finally collected into a small vein, which, by union with others like it, helps to form the radicles of the renal vein. Thus, in the kidney, the blood entering by the renal artery traverses two sets of capillaries be- fore emerging by the renal vein, an arrangement which may be compared to the portal system in miniature. The tuft of vessels in the course of development is, as . were, thrust into the dilated extremity of the urinary tubule, which finally completely invests it just as the pleura invests the lungs or the tunica vaginalis the testicle. Thus the Malpighian capsule is lined by a parietal layer of squamous cells and a visceral or reflected layer immediately covering the vascular tuft (Fig. 241), and sometimes dipping down into its interstices. THE KIDNEYS AND VRINE. 353 This reflected layer of epithelium is readily seen in young subjects, but cannot always be demonstrated in the adult. (See Figs. 244 and 245.) The vessels \viiich enter the medullary layer break up into smaller arterioles, which pass through the boundary layer and proceed in a straight course between the tubules of the papillary layer, giving off on their way branches, which form a fine arterial meshwork around the tubes, and end in a similar plexus, from which the venous radicles arise. Besides the small afferent arteries of the Malpighian bodies, there are, of course, others which are distributed in the ordinary manner, for nutri- tion's sake, to the different parts of the organ; and in the pyramids, be- FIG. 244. FIG. 245. lie and tuft, with the commencement of a FIG. 244.— Transverse section of a developing Malpighian capsule and tuft (human) x 300. From a foetus at about the fourth month; a, flattened cells growing to form the capsule; 6, more rounded cells, continuous with the above, reflected round c, and finally enveloping it; c, mass of embryonic cells which will later become developed into blood-vessels. (W. Pye.) FIG. 245. — Epithelial elements or a Malpighian ca; urinary tubule showing the afferent and efferent capsule ; b, similar, but rather lar the vessels of the capillary tuft of it. (W. Pye.) tween the tubes, there are numerous straight vessels, the vasta recta, sup- posed by some observers to be branches of vasa efferentia from Malpighian bodies, and therefore comparable to the venous plexus around the tubules in the cortical portion, while others think that they arise directly from small branches of the renal arteries. Between the tubes, vessels, etc., which make up the substance of the kidney, there exists, in small quantity, a fine matrix of areolar tissue. Nerves. — The nerves of the kidney are derived from the renal plexus. Structure of the Ureters. — The duct of the kidney, or ureter, is a tube about the size of a goose-quill, and from a foot to sixteen inches in length, which, continuous above with the pelvis of the kidney, ends below by perforating obliquely the walls of the bladder, and opening on VOL. I.— 23. 354 HAND-BOOK OF PHYSIOLOGY. its internal surface. It is constructed of three principal coats (a) an outer, tough, fibrous and elastic coat; (b) a middle, muscular coat, of which the fibres are unstriped, and arranged in three layers — the fibres of the central layer being circular, and those of the other two longitudinal in direction; and (c) an internal mucous lining continuous with that of the pelvis of the kidney above, and of the urinary bladder below. The epithelium of all these parts (Fig. 246) is alike stratified and of a some- what peculiar form; the cells on the free surface of the mucous mem- brane being usually spheroidal or polyhedral with one or more spherical or oval nuclei; while beneath these are pear-shaped cells, of which the broad ends are directed toward the free surface, fitting in beneath the cells of the first row, and the apices are prolonged into processes of various lengths, among which, again, the deepest cells of the epithelium are found spheroidal, irregularly oval, spindle-shaped or conical. Structure of Urinary Bladder. — The urinary bladder, which forms a receptacle for the temporary lodgment of the urine in the intervals of its expulsion from the body, is more or less pyriform, its widest part, which is situate above and behind, being termed the fundus: and the narrow constricted portion in front and below, by which it becomes con- tinuous with the urethra, being called its cervix or neck. It is constructed of four principal coats, — serous, muscular, areolar or submucous, and mucous, (a) The serous coat, which covers only the posterior and upper half of the bladder, has the same structure as that of the peritoneum. FIG. 246.— Epithelium of the bladder; a, one of the cells of the first row; 6, a cell of the second row; c, cells in situ, of first, second, and deepest layers. (Obersteiner.) with which it is continuous, (b) The fibres of the muscular coat, which are unstriped, are arranged in three principal layers, of which the external and internal (Ellis) have a general longitudinal, and the middle layer a circular direction. The latter are especially developed around the cervix of the organ, and are described as forming a sphincter vesicce. The mus- cular fibres of the bladder, like those of the stomach, are arranged not in simple circles, but in figure-of-8 loops, (c) The areolar or submucous coat is constructed of connective tissue with a large proportion of elastic fibres, (d) The mucous membrane, which is rugose in the contracted state of the organ, does not differ in essential structure from mucous THE KIDNEYS AND URINE. 355 membranes in general. Its epithelium is stratified and closely resembles that of the pelvis of the kidney and the ureter (Fig. 240). The mucous membrane is provided with mucous glands, which are more numerous near the neck of the bladder. The bladder is well provided with blood and lymph vessels, and with nerves. The latter are branches from the sacral plexus (spinal) and hypo- gastric plexus (sympathetic). A few ganglion-cells are found, here and there, in the course of the nerve-fibres. THE EXCRETION OF THE KIDNEY : — THE URINE. Physical Properties. — Healthy urine is a perfectly transparent, amber-colored liquid, with a peculiar, but not disagreeable odor, a bitter- ish taste, and slight acid reaction. Its specific gravity varies from 1015 to 1025. On standing for a short time, a little mucous appears in it as a flocculent cloud. Chemical Composition. — The urine consists of water, holding in solution certain organic and saline matters as its ordinary constituents, and occasionally various matters taken into the stomach as food — salts, coloring matter, and the like. * Table of the Chemical Composition of the Urine (modified from Becquer el). Water . 967 Urea 14.230 Other nitrogenous crystalline bodies — Uric acid, principally in the form of alkaline urates, a trace only free. Kreatinin, xanthin, hypoxanthin. Hippuric acid, leucin, tyrosin, taurin, cys- tin, etc., all in small amounts and not constant. Mucus and pigment. Salts :— Inorganic — Principally sulphates, phosphates, and chlo- rides of sodium, and potassium, with phos- phates of magnesium and calcium, traces 10-635 8-135 of silicates and of chlorides. Organic — Lactates, hippurates, acetates and formates, which only appear occasionally. Sugar . a trace sometimes. Gases (nitrogen and carbonic acid principally). 1000 Reaction of the Urine — The normal reaction of the urine is slightly acid. This acidity is due to acid phosphate of sodium, and is 356 HAND-BOOK OF PHYSIOLOGY. less marked after meals. The urine contains no appreciable amount uof free acid, as it gives no precipitate with sodium hyposulphite. After standing for some time the acidity increases from a kind of fermentation, due in all probability to the presence of mucus, and acid urates or free uric acid is deposited. After a time, varying in length according to the temperature, the reaction becomes strongly alkaline from the change of urea into ammonium carbonate — while at the same time a strong ammoni- acal and foetid odor appears, with deposits of triple phosphates and alka- line urates. As this does not occur unless the urine is exposed to the air, or, at least, until air has had access to it, it is probable that the de- composition is due to atmospheric germs. Reaction of Urine in different classes of Animals. — In most herbivo- rous animals the urine is alkaline and turbid. The difference depends, not on any peculiarity in the mode of secretion, but on the differences in the food on which the two classes subsist: for when carnivorous animals, such as dogs, are restricted to a vegetable diet, their urine becomes pale, turbid, and alkaline, like that of an herbivorous animal, but resumes its former acidity on the return to an animal diet; while the urine voided by herbivorous animals, e.g., rabbits, fed for some time exclusively upon animal substances, presents the acid reaction and other qualities of the urine of Carnivora, its ordinary alkalinity being restored only on the substitution of a vegetable for the animal diet. Human urine is not usually rendered alkaline by vegetable diet, but it becomes so after the free use of alkaline medicines, or of the alkaline salts with carbonic or vegetable acids; for these latter are changed into alkaline carbonates pre- vious to elimination by the kidneys. AVERAGE QUANTITY OF THE CHIEF CONSTITUENTS OF THE URINE EXCRETED IN 24 HOURS BY HEALTHY MALE ADULTS (PARKES). • Water 52- fluid ounces. Urea 512 '4 grains. Uric acid .... 8-5 Hippuric acid, uncertain probably 10 to 15* " Sulphuric acid 31-11 " Phosphoric acid 45* " Potassium, Sodium, Ammonium Chlorides ) 323-25 " and free Chlorine . . . . j Lime 3'5 Magnesia 3* Mucus 7* " {Kreatinin Sffin }• . . 154- Hypoxanthin Eesinous matter, etc. Variations in Quantity of Constituents.— From these proportions, however, most of the constituents are, even in health, liable to variations. THE KIDNEYS AND URINE. 357 The variations of the water in different seasons, and according to the quantity of drink and exercise, have already been mentioned. The water of the urine is also liable to be influenced by the condition of the nervous system, being sometimes greatly increased in hysteria, and some other nervous affections; and at other times diminished. In some diseases it is enormously increased; and its increase may be either attended with an aug- mented quantity of solid matter, as in ordinary diabetes, or may be nearly the sole change, as in the affection termed diabetes insipidus. In other diseases, e.g. . the various forms of albuminuria, the quantity may be con- siderably diminished. A febrile condition almost always diminishes the quantity of water; and a like diminution is caused by any affection which draws off a large quantity of fluid from the body through any other chan- nel than that of the kidneys, e.g., the bowels or the skin. Method of estimating the Solids. — A useful rule for approximately 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 sp. gr. 1025, 2 '33x25 =58 '25 grains of solids, are con- tained in 1000 grains of the urine. In using this method it must be remembered that the limits of error are much wider in diseased than in healthy urine. Variations in the Specific Gravity. — The specific gravity of the human urine is about 1020. Probably no other animal fluid presents so many varieties in density within twenty-four hours as the urine does; for the relative quantity of water and of solid constituents of which it is composed is materially influenced by the condition and occupation of the body during the time at which it is secreted, by the length of time which has elapsed since the last meal, and by several other accidental circum- stances. The existence of these causes of difference in the composition of the urine has led to the secretion being described under the three heads of urina sanguinis, urina potus, and urina cibi. The first of these names signifies the urine, or that part of it which is secreted from the blood at times in which neither food nor drink has been recently taken, and is applied especially to the urine which is evacuated in the morning before breakfast. The term urina potus indicates the urine secreted shortly after the introduction of any considerable quantity of fluid into the body: and the urina cibi, the portions secreted during the period immediately succeeding a meal of solid food. The last kind con- tains a larger quantity of solid matter than either of the others; the first or second, being largely diluted with water, possesses a comparatively low specific gravity. Of these three kinds, the morning urine is the best calculated for analysis in health, since it represents the simple secretion unmixed with the elements of food or drink; if it be not used, the whole of the urine passed during a period of twenty-four hours should be taken. 358 HAND-BOOK OF PHYSIOLOGY. In accordance with the various circumstances above-mentioned, the specific gravity of the urine may, consistently with health, range widely on both sides of the usual average. The average healthy range may be stated at from 1015 in the winter to 1025 in the summer; but variations of diet and exercise, and many other circumstances, may make even greater differences than these. In disease, the variation may be greater; some- times descending, in albuminuria, to 1004, and frequently ascending in diabetes, when the urine is loaded with sugar, to 1050, or even to 1060. Quantity. — The total quantity of urine passed in twenty-four hours is affected by numerous circumstances. On taking the mean of many observations by several experimenters, the average quantity voided in twenty-four hours by healthy male adults from 20 to 40 years of age has been found to amount to about 52 -J- fluid ounces (1-J- to 2 litres). Abnormal Constituents. — In disease, or after the ingestion of special foods, various abnormal substances occur in urine, of which the following may be mentioned — serum-albumin, globulin, ferments (ap- parently present in health also), blood, sugar, bile acids, and pigments, fats, oxalates, various salts taken as medicine, and other matters, as bac- teria and renal casts. THE SOLIDS OF THE UKINE. Urea (CH4N20). — Urea is the principal solid constituent of the urine, forming nearly one-half of the whole quantity of solid matter. It is also the most important ingredient, since it is the chief substance by which the nitrogen of decomposed tissue and superfluous food is excreted from the body. For its removal, the secre- tion of urine seems especially provided; and by its retention in the blood the most per- nicious effects are produced. Properties. — Urea, like the other solid constituents of the urine, exists in a state of solution. But it may be procured in the solid state, and then appears in the form of delicate silvery acicular crystals, which, under the microscope, appear as four-sided prisms (Fig. 247). It is obtained in this FIG. 247.-Crystaisof urea. state bJ evaporating urine carefully to the consistence of honey, acting on the inspis- sated mass with four parts of alcohol, then evaporating the alcoholic solution, and purifying the residue by repeated solution in water or alco- hol, and finally allowing it to crystallize. It readily combines with some acids, like a weak base; and may thus be conveniently procured in the form of crystals of nitrate or oxalate of urea. THE KIDNEYS AND URIXE. 359 U.ea is colorless when pure; when impure, yellow or brown: without smell, and of a cooling nitre-like taste; has neither an acid nor an alka- line reaction, and deliquesces in a moist and warm atmosphere. At 59° F. (15° C.) it requires for its solution less than its weight of water; it is dissolved in all proportions by boiling water; but it requires five times its weight of cold alcohol for its solution. It is insoluble in ether. At 248° F. (120° C.) it melts without undergoing decomposition; at a still higher temperature ebullition takes place, and carbonate of ammonium sublimes; the melting mass gradually acquires a pulpy consistence; and if the heat is carefully regulated, leaves a grey-white powder, cyanic acid. Chemical Nature of Urea. — The chemical nature of urea is ex- plained elsewhere,1 but it will be as well to mention here that urea is isomeric with ammonium cyanate, and that it was first artificially pro- duced from this substance. Thus: — Ammonium cyanate (NH4.CNO) = urea (CH4~N"20). The action of heat upon urea in evolving ammonium carbonate and leaving cyanic acid, is thus explained. A similar de- composition of the urea with development of ammonium carbonate ensues spontaneously when urine is kept for some days after being voided, and explains the ammoniacal odor then evolved (p. 356). The urea is some- times decomposed before it leaves the bladder, when the mucous mem- brane is diseased, and the mucus secreted by it is both more abundant, and, probably, more prone to act as a ferment; although the decomposi- tion does not often occur unless atmospheric germs have had access to the urine. Variations in the Quantity of Urea. — The quantity of urea ex- creted is, like that of the urine itself, subject to considerable variation. For a healthy adult 500 grains (about 32 -5 grms.) per diem maybe taken as rather a high average. Its percentage in healthy urine is 1 *5 to 2 '5. It is materially influenced by diet, being greater when animal food is ex- clusively used, less when the diet is mixed, and least of all with a vegeta- ble diet. As a rule, men excrete a larger quantity than women, and per- sons in the middle periods of life a larger quantity than infants or old people. The quantity of urea excreted by children, relatively to their body-weight, is much greater than in adults. Thus the quantity of urea excreted per kilogram of weight was, in a child, 0'8 grm. : in an adult only 0*4 grm. Regarded in this way, the excretion of carbonic acid gives similar result, the proportion in the child and adult being as 82 : 34. The quantity of urea does not necessarily increase and decrease with that of the urine, though on the whole it would seem that whenever the amount of urine is much augmented, the quantity of urea also is usually increased; and it appears that the quantity of urea, as of urine, may be especially increased by drinking large quantities of water. In various 1 Appendix. 360 HAND-BOOK OF PHYSIOLOGY. diseases the quantity is reduced considerably below the healthy standard, while in other affections it is above it. Estimation of Urea. — A convenient apparatus for estimating the quantity of urea in a given sample of urine is that devised by Russell and West. Urea contains nearly half its weight of nitrogen; hence this gas may be taken as a measure of the urea. A small quantity of urine is mixed with a large excess of solution of sodium hypobromite, which completely decomposes the urea, liberating all the nitrogen in a gaseous form: a gentle heat promotes the reaction. The percentage of urea can of course be readily calculated from the volume of nitrogen evolved from a measured quantity of the urine, but this calculation is avoided by graduating the tube in which the nitrogen is collected with numbers which indicate the corresponding percentage of urea. CON2H4 -j- 3NaBrO -f- 2NaHO = 3NaBr + 3H20 + Na2C03 + N9. Uric Acid (C5H4N403). — This substance, which was formerly termed lithic acid, on account of its existence in many forms of urinary calculi, is rarely absent from the urine of man or animals, though in the feline tribe it seems to be sometimes entirely replaced by urea. The pro- portionate quantity of uric acid varies considerably in different animals. In man, and Mammalia generally, especially the Herbivora, it is com- paratively small. . In the whole tribe of birds, and of serpents, on the other hand, the quantity is very large, greatly exceeding that of the urea. In the urine of granivorous birds, indeed, urea is rarely if ever found, its place being entirely supplied by uric acid. Variations in Quantity.— The quantity of uric acid, like that of urea, in human urine, is increased by the use of animal food, and de- creased by the use of food free from nitrogen, or by an exclusively vege- table diet. In most febrile diseases, and in plethora, it is formed in un- naturally large quantities; and in gout it is deposited in, and around, joints, in the form of urate of soda, of which the so-called chalk-stones of this disease are principally composed. The average amount secreted in twenty -four hours is 8*5 grains (rather more than half a gramme). Condition of Uric Acid in the Urine. — The condition in which uric acid exists in solution in the urine has formed ths subject of some discussion, because of its difficult solubility in water. It is found chiefly in the form of urate of sodium, produced by the uric acid as soon as it is formed, combining with part of the base of the alkaline sodium phosphate of the blood. Hippuric acid, which exists in human urine also, acts upon the alkaline phosphate in the same way, and increases still more the quan- tity of acid phosphate, on the presence of which it is probable that a part of the natural acidity of the urine depends. It is scarcely possible to say whether the union of uric acid with the base sodium and probably ammo- nium, takes place in the blood, or in the act of secretion in the kidney: THE KIDNEYS AND URINE. 361 the latter is the more likely opinion; but the quantity of either uric acid or urates in the blood is probably too small to allow of this question being solved. Owing to its existence in combination in healthy urine, uric acid for examination must generally be precipitated from its bases by a stronger acid. Frequently, however, when excreted in excess, it is deposited in a crystalline form (Fig. 248), mixed with large quantities of ammonium or sodium urate. In such cases it may be procured for microscopic exami- nation by gently warming the portion of urine containing the sediment; this dissolves urate of ammonium and sodium, while the comparatively insoluble crystals of uric acid subside to the bottom. The most common form in which uric acid is deposited in urine, is that of a brownish or yellowish powdery substance, consisting of granules of FIG. 248.— Various forms of uric acid crystals. FIG. 349.— Crystals of hippuric acid. ammonium — or sodium urate. "When deposited in crystals, it is most frequently in rhombic or diamond-shaped laminae, but other forms are not uncommon (Fig. 248). When deposited from the urine, the crystals are generally more or less deeply colored, from being combined with the coloring principles of the urine. There are two chief tests for uric acid besides the microscopic evidence of its crystalline structure: (1) The Murexide test, which consists of evaporating to dryness a mixture of strong nitric acid and uric acid in a water bath. This leaves a yellowish-red residue of Alloxan (C4H2N204) and urea, and -this, on addition of ammonium hydrate, gives a beautiful purple (ammonium purpurate, C8H4 (NH4) Nfi06), deepened on addition of caustic potash. (2) Schiff's test. Dissolve the uric acid in sodium carbonate solution, and drop some of it on a filter paper moistened with silver nitrate, a black spot appears, which corresponds to the reduction of silver by the uric acid. Hippuric Acid (C9H9N03) has long been known to exist in the urine of herbivorous animals in combination with soda. It also exists naturally 362 HAND-BOOK OF PHYSIOLOGY. in the urine of man, in quantity equal or rather exceeding that of the uric acid. Pigments. — The coloring matters of the urine are: (1) Uro-MUn, a substance connected with the coloring matters of the blood and bile (p. 275); it is especially seen in febrile urine and exists normally, but to less amount; it is of a yellowish-red color; (2) Uro-clirome, which on exposure undergoes oxidation, and becomes Uro-erythrin, the former being yellowish and the latter sandy red; and (3) Indican is occasionally present. Indican is not itself pigmentary, though by its decomposition indigo blue and indigo red are produced. Its presence can usually be detected by adding to a small quantity of urine an equal bulk of strong hydrochloric acid, and gently heating the solution; on the addition of two or three drops of strong nitric acid a delicate purplish tint is developed, and indigo blue and red crystals separate out. Mucus. — Mucus in the urine consists principally of the epithelial debris of the mucous surface of the urinary passages. Particles of epithe- lium, in greater or less abundance, may be detected in most samples of urine, especially if it has remained at rest for some time and the lower strata are then examined (Fig. 250). As urine cools, the mucous is some- FIG. 250.— Mucus deposited from urine. times seen suspended in it as a delicate opaque cloud, but generally it falls. In inflammatory affections of the urinary passages, especially of the bladder, mucus in large quantities is poured .forth, and speedily un- dergoes decomposition. The presence of the decomposing mucus excites (as already stated, p. 356) chemical changes in the urea, whereby ammo- nia, or carbonate of ammonium, is formed, which, combining with the excess of acid in the super-phosphates in the urine, produces insoluble neutral or alkaline phosphates of calcium and magnesium, and phosphate of ammonium and magnesium. These mixing with the mucus, constitute the peculiar white, viscid, mortar-like substance which collects upon the mucous surface of the bladder, and is often passed with the urine, form- ing a thick tenacious sediment. THE KIDNEYS AND URINE. 363 Extractives. — Besides mucus and coloring matter, urine contains a considerable quantity of nitrogenous compounds, usually described under the generic name of extractives. Of these, the chief are: (1) Kreatinin. (C4H7N3O) a substance derived, probably, from the metamorphosis of mus- cular tissue, crystallizing in colorless oblique rhombic prisms; a fairly definite amount of this substance, about 15 grains (1 grm.), appears in the urine daily, so that it must be looked upon as a normal constituent; it is increased on an increase of the nitrogenous constituents of the food; (2) Xanthin (C6N4H402), an amorphous powder soluble in hot water; (3) Hypo-zanthin, or sarkin (CBN4H40); (4) Oxaluric acid (C3H4N204), in combination with ammonium; (5) Allantoin (C4H6N203), in the urine of the new-born child. All these extractives are chiefly interesting as being closely connected with urea, and mostly yielding that substance on oxidation. Leucin and tyrosin can scarcely be looked upon as normal constituents of urine. Saline Matter. — The sulphuric acid in the urine is combined chiefly or entirely with sodium or potassium; forming salts which are taken in very small quantity with the food, and are scarcely found in other fluids or tissues of the body; for the sulphates commonly enumerated among the constituents of the ashes of the tissues and fluids are for the most part, or entirely, produced by the changes that take place in the burn- ing. Only about one-third of the sulphuric acid found in the urine is derived directly from the food (Parkes). Hence the greater part of the sulphuric acid which the sulphates in the urine contain, must be formed in the blood, or in the act of secretion of urine; the sulphur of which the acid is formed being probably derived from the decomposing nitrogenous tissues, the other elements of which are resolved into urea and uric acid. It may be in part derived also from the sulphur-holding taurin and cystin, which can be found in the liver, lungs, and other parts of the body, but not generally in the excretions; and which, therefore, must be broken up. The oxygen is supplied through the lungs, and the heat gen- erated during combination with the sulphur, is one of the subordinate means by which the animal temperature is maintained. Besides the sulphur in these salts, some also appears to be in the urine, uncombined with oxygen; for after all the sulphates have been re- moved from urine, sulphuric acid may be formed by drying and burning it with nitre. From three to five grains of sulphur are thus daily ex- creted. The combination in which it exists is uncertain: possibly it is in some compound analogous to cystin or cystic oxide (p. 365). Sulphuric acid also exists normally in the urine in combination with phenol (C6H6O) as phenol sulphuric acid or its corresponding salts, with sodium, etc. The phosphoric acid in the urine is combined partly with the alkalies, partly with the alkaline earths — about four or five times as much with 364 HAND-BOOK OF PHYSIOLOGY. the former as with the latter. In blood, saliva, and other alkaline fluids of the body, phosphates exist in the form of alkaline, neutral, or acid salts. In the urine they are acid salts, viz., the sodium, ammonium, calcium, and magnesium phosphates, the excess of acid being (Liebig) due to the appropriation of the alkali with which the phosphoric acid in the blood is combined, by the several new acids which are formed or dis- charged at the kidneys, namely, the uric, hippuric, and sulphuric acids, all of which are neutralized with soda. The phosphates are taken largely in both vegetable and animal food; some thus taken are excreted at once; others, after being transformed and incorporated with the tissues. Calcium phosphate forms the prin- cipal earthy constituent of bone, and from the decomposition of the osse- ous tissue the urine derives a large quantity of this salt. The decompo- sition of other tissues also, but especially of the brain and nerve-sub- stance, furnishes large supplies of phosphorus to the urine, which FIG. 251. — Urinary sediment of triple phosphates (large prismatic crystals) and urate of am- monium, from urine which had undergone alkaline fermentation. phosphorus is supposed, like the sulphur, to be united with oxygen, and then combined with bases. This quantity is, however, liable to consid- erable variation. Any undue exercise of the brain, and all circumstances producing nervous exhaustion, increase it. The earthy phosphates are more abundant after meals, whether on animal or vegetable food, and are diminished after long fasting. The alkaline phosphates are increased after animal food, diminished after vegetable food. Exercise increases the alkaline, but not the earthy phosphates (Bence Jones). Phosphorus uncombined with oxygen appears, like sulphur, to be excreted in the urine (Ronalds). When the urine undergoes alkaline fermentation, phosphates are deposited in the form of a urinary sediment, consisting chiefly of ammonio-magnesium phosphate (triple phosphate) (Fig. 251). This compound does not, as such, exist in healthy urine. The ammonia is chiefly or wholly derived from the decomposition of urea (p. 359). The chlorine of the urine occurs chiefly in combination with sodium, but slightly also with ammonium, and perhaps potassium. As the chlo- THE KIDNEYS AND URINE. 365 rides exist largely in food and in most of the animal fluids, their occur- rence in the urine is easily understood. Cystin (C3H,NSOa) (Fig. 252) is an occasional constituent of urine. It resembles tauriu in containing a large quantity of sulphur — more than 25 per cent. It does not exist in healthy urine. Another common morbid constituent of the urine is oxalic acid, whicli is frequently deposited in combination with calcium (Fig. 253) as a FIG. 252.— Crystals of cystin. FIG. 253.— Crystals of calcium oxalate. urinary sediment. Like cystin, but much more commonly, it is the chief constituent of certain calculi. Of the other abnormal constituents of the urine mentioned it will be unnecessary to speak at length in this work. Gases. — A small quantity of gas is naturally present in the urine in a state of solution. It consists of carbonic acid (chiefly) and nitrogen and a small quantity of oxygen. THE METHOD OF THE EXCKETION OF UKINE. The excretion of the urine by the kidney is believed to consist of two more or less distinct processes — viz., (1.) of filtration, by which the water and the ready-formed salts are eliminated; and (2.) of true secretion, by which certain substances forming the chief and more important part of the urinary solids are removed from the blood. This division of function corresponds more or less to the division in the functions of other glands of which we have already treated. It will be as well to consider them separately. (1.) Of Filtration. — This part of the renal function is performed within the Malpighian corpuscles by the renal glomeruli. By it not only the water is strained off, but also certain other constituents of the urine, e.g., sodium chloride, are separated. The amount of the fluid filtered off depends almost entirely upon the blood -pressure in the glomeruli. 366 HAND-BOOK OF PHYSIOLOGY. The greater the blood-pressure in the arterial system generally, and consequently in the renal arteries, the greater, cceteris paribus, will be the blood-pressure in the glomeruli, and the greater the quantity of urine separated; but even without increase of the general blood-pressure, if the renal arteries be locally dilated, the pressure in the glomeruli will be increased and with it the secretion of urine. On the other hand, if the local blood-pressure be diminished, the amount of fluid will be lessened. All the numerous causes, therefore, which increase the blood-pressure (p. 152) will, as a rule, secondarily increase the secretion of urine. Of these the heart's action is amongst the most important. When its contractions are increased in force, increased diuresis is the result. Similarly, causes which lower the blood-pressure, e.g., enfeebled action of the heart, great loss of blood, etc., will diminish the activity of the secretion of urine. The close connection between the blood-pressure generally and the nervous system has been before considered, and it will be clear, therefore, that the amount of urine secreted depends greatly upon the influence of the nervous system. Thus, division of the spinal cord, by producing general vascular dilatation, causes a great diminution of blood-pressure, and so diminishes the amount of water passed; since the local dilatation in the renal arteries is not sufficient to counteract the general diminution of pressure. Stimulation of the cut cord produces, strangely enough, the same results — i.e., a diminution in the amount of the urine passed, but in a different way, viz., by constricting the arteries generally, and, among others, the renal arteries; the diminution of blood-pressure result- ing from the local resistance in the renal arteries being more potent to diminish blood-pressure in the glomeruli than the general increase of blood-pressure is to increase it. Section of the renal nerves or of any others which produce local dilatation without greatly diminishing the general blood-pressure will cause an increase in the quantity of fluid The fact that in summer or in hot weather the urine is diminished may be attributed partly to the copious elimination of water by the skin in the form of sweat which occurs in summer, as contrasted with the greatly diminished functional activity of the skin in winter, but also to the dilated condition of the vessels of the skin causing a decrease in the general blood-pressure. Thus we see that in regard to the elimination of water from the system, the skin and kidneys perform similar functions, and are capable to some extent of acting vicariously, one for the other. Their relative activities are inversely proportional to each other. The intimate connection between the condition of the kidney and the blood-pressure has been exceedingly well shown by the introduction of an instrument called the Oncometer, recently introduced by Roy, which is a modification of the plethysmograph (Fig. 138). By means of this appa- ratus any alteration in the volume of the kidney is communicated to an THE KIDNEYS AND URINE. 367 apparatus (oncograph) capable of recording graphically, with a writing ICYCT, such variations. It lias been found that the kidney is extremely sensitive to any alteration in the general blood-pressure, every fall in the general blood-pressure being accompanied by a decrease in the volume of the kidney, and every rise, unless produced by considerable constriction of the peripheral vessels, including those of the kidney, being accompanied by a corresponding increase of volume. Increase of volume is followed by an increase in the amount of urine secreted, and decrease of volume by a decrease in the secretion. In addition, however, to the response of the kidney to alterations in the general blood-pressure, it has been fur- ther observed that certain substances, when injected into the blood, will also produce an increase in volume of. the kidney, and consequent increased now of urine, without affecting the general blood-pressure — such bodies as sodium acetate and other diuretics. These observations appear to prove that local dilatation of the renal vessel^ may be produced by alterations in the blood upon a local nervous mechanism, as the effect is produced when all of the renal nerves have been divided. The alterations are not only produced by the addition of drugs, but also by the introduction of comparatively small quantities of water or saline solution. To this altera- tion of the blood acting upon the renal vessels (either directly or) through a local vaso- motor mechanism, and not to any great alteration in the general blood-pressure, must we attribute the effect of meals, etc., ob- served by Roberts. "The renal excretion is increased after meals and diminished during fasting and sleep. The increase began within the first hour after breakfast, and continued during the succeeding two or three hours; then a diminution set in, and continued until an hour or two after dinner. The effect of dinner did not appear until two or three hours after the meal; and it reached its maximum about the fourth hour. From this period the excretion steadily decreased until bedtime. During sleep it sank still lower, and reached its minimum — being not more than one- third of the quantity excreted during the hours of digestion." The in- creased amount of urine passed after drinking large quantities of fluid probably depends upon the diluted condition of the blood thereby in- duced. The following table1 will help to explain the dependence of the filtra- tion function upon the blood-pressure and the nervous system: — Table of the Relation of the Secretion of Urine to Arterial Pressure. A. Secretion of Urine may be increased— a. By increasing the general blood-pressure, by 1. Increase of force or frequency of heart-beat. 2. Constriction of small arteries of areas other than the kidney. 1 Modified from M. Foster. 368 HAND-BOOK OF PHYSIOLOGY. b. By relaxation of the renal artery without compensating relaxa- tion elsewhere, by 1. Division of the renal nerves (causing polyuria). 2. " and afterward stimulating cord below medulla (causing greater polyuria). 3. Division of the splanchnic nerves; but polyuria is less than in 1 or 2, as these nerves are distributed to a wider area, the dilatation of the renal artery is accompanied by dila- tation of other vessels, and therefore with a somewhat diminished general blood supply. 4. Puncture of the floor of fourth ventricle or mechanical irri- tation of the superior cervical ganglion of the sympathetic, possibly from dilatation of the renal arteries. B. Secretion of urine may be diminished — a. By diminishing the general blood-pressure, by 1. Diminishing the force or frequency of the heart-beats. 2. Dilatation of capillary areas other than the kidney. 3. Division of spinal cord below medulla, which causes dilata- tion of general abdominal area, and urine generally ceases being secreted. b. By increasing the blood-presstire, by stimulation of spinal cord below medulla, the constriction of the renal artery not being compensated for by the increase of .general blood-pressure. c. By constriction of the renal artery, by stimulating the renal or splanchnic nerves, or by stimulating the spinal cord. Although it is convenient to call the processes which go on in the renal glomeruli, filtration, there is reason to believe that they are not absolutely mechanical, as the term might seem to imply, since, when the epithelium of the Malpighian capsule has been, as it were, put out of order by liga- ture of the renal artery, on removal of the ligature, the urine has been found temporarily to contain albumen, indicating that a selective power resides in the healthy epithelium, which allows a certain constituent part of the blood to be filtered off and not others. (2.) Of True Secretion. — That there is a second part in the process of the excretion of urine, which is true secretion, is suggested by the structure of the tubuli uriniferi, and the idea is supported by various experiments. It will be remembered that the convoluted portions of the tubules are lined with epithelium, which bears a close resemblance to the secretory epithelium of other glands, whereas the Malpighian capsules and portions of the loops of Henle are lined simply by endothelium. The two functions are, then, suggested by the differences of epithelium, and also by the fact that the blood supply is different, since the convoluted tubes are surrounded by capillary vessels derived from the breaking up of the efferent vessels of the Malpighian tufts. The theory first suggested by Bowman (1842), and still generally accepted, of the function of the THE KIDNEYS AND URINE. 369 two parts of the tubules,, is that the cells of the convoluted tubes, by a process of true secretion, separate from the blood substances such as urea, whereas from the glomeruli are separated the water and the inor- ganic salts.. Another theory suggested by Ludwig (1844) is that in the glomeruli is filtered off from the blood all the constituents of the urine in a very diluted condition. When this passes along the tortuous uriniferous tube, part of the water is re-absorbed into the vessels surrounding them, leaving the urine in a more concentrated condition — retaining all its proper constituents. This osmosis is promoted by the high specific gravity of the blood in the capillaries surrounding the convoluted tubes, but the return of the urea and similar substances is prevented by the secretory epithelium of the tubules. Ludwig's theory, however plausible, must, we think, give way to the first theory, which is more strongly supported by direct experiment. By using the kidney of the newt, which has two distinct vascular sup- plies, one from the renal artery to the glomeruli, and the other from the renal portal vein to the convoluted tubes, Nussbaum has shown that cer- tain substances, e.g., peptones, sugar, when injected into the blood, are eliminated by the glomeruli, and so are not got rid of when the renal arteries are tied; whereas certain other substances, e.g., urea, when injected into the blood, are eliminated by the convoluted tubes, even when the renal arteries have been tied. This evidence is very direct that urea is excreted by the convoluted tubes. Heidenhain also has shown by experiment that if a substance (sodium sulphindigotate), which ordinarily produces blue urine, be injected into the blood after section of the medulla which causes lowering of the blood- pressure in the renal glomeruli, that when the kidney is examined, the cells of the convoluted tubules (and of these alone) are stained with the substance, which is also found in the lumen of the tubules. This appears to show that under ordinary circumstances the pigment at any rate is eliminated by the cells of the convoluted tubules, and that when by diminishing the blood-pressure, the filtration of urine ceases, the pigment remains in the convoluted tubes, and is not, as it is under ordinary cir- cumstances, swept away from them by the flushing of them which ordi- narily takes place with the watery part of urine derived from the glom- eruli. It therefore is probable that the cells, if they excrete the pigment, excrete urea and other substances also. But urea acts somewhat differ- ently to the pigment, as when it is injected into the blood of an animal in which the medulla has been divided and the secretion of urine stopped, a copious secretion of urine results, which is not the case when the pigment is used instead under similar conditions. The flow of urine, independent of the general blood-pressure, might be supposed to be due to the action of the altered blood upon some local vaso-motor mechanism; and, indeed, the local blood-pressure is directly affected in this way, but there is reason VOL. I.— 24. 370 HAND-BOOK OF PHYSIOLOGY. for believing that part of the increase of the secretion is due to the direct stimulation of the cells by the urea contained in the blood. To sum up, then, the relation of the two functions: (1.) The process of nitration, by which the chief part if not the whole of t\\Q fluid is elim- inated, together with certain inorganic salts, and possibly other solids, is directly dependent upon blood-pressure, is accomplished by the renal glomeruli, and is accompanied by a free discharge of solids from the tubules. (2.) The process of secretion proper, by which urea and the principal urinary solids are eliminated, is only indirectly, if at all, de- pendent upon blood-pressure, and is accomplished by the cells of the con- voluted tubes. It is sometimes accompanied by the elimination of copious fluid, produced by the chemical stimulation of the epithelium of the same tubules. SOURCES OF THE NITROGENOUS URINARY SOLIDS. Urea. — In speaking of the method of the secretion of urine, it was assumed that the part played by the cells of the uriniferous tubules was that of mere separation of the constituents of the urine which existed ready-formed in the blood: there is considerable evidence to favor this assumption. What may be called the specially characteristic solid of the urine, i.e., urea (as well as most of the other solids), may be detected in the blood, and in other parts of the body, e.g., the humors of the eye (Mil- Ion), even while the functions of the kidneys are unimpaired; but when from any cause, especially extensive disease or extirpation of the kidneys, the separation of urine is imperfect, the urea is found largely in the blood and in most other fluids of the body. It must, therefore, be clear that the urea is for the most part made somewhere else than in the kidneys, and simply brought to them by the blood for elimination. It is not absolutely proved, however, that all the urea is formed away from these organs, and it is possible that a small quantity is actually secreted by the cells of the tubules. The sources of the urea, which is brought to the kidneys for excretion, are stated to be two. (1.) From the splitting up of the Elements ef the Nitrogenous Food. — The origin of urea from this source is shown by the increase which ensues on substituting an animal or highly nitrogenous for a vegetable diet; in the much larger amount — nearly double — excreted by Carnivora than Herbivora, independent of exercise; and in its diminution to about one- half during starvation, or during the exclusion of non-nitrogenous prin- ciples of food. Part, at any rate, of the increased amount of urea which appears in the urine soon after a full meal of proteid material may be attributed to the production of a considerable amount of leucin and ty- rosin as by-products of pancreatic digestion. These substances are car- THE KIDNEYS AND URINE. 371 ried by the portal vein to the liver, and it is there that the change in all probability takes place; as when the functions of the organ are irrnvolv interfered with, as in the case of acute yellow atrophy, the amount of uiva is distinctly diminished, and its place appears to be taken by leucin and tyrosin. It has been found by experiment, too, that if these substances be introduced into the alimentary canal, the introduction is followed by a corresponding increase in the amount of urea, but not by the presence of the bodies themselves in the urine. (2.) From the Nitrogenous metabolism of the Tissues. — This second ori- gin of urea is shown by the fact that it continues to be excreted, though in smaller quantity than usual, when all nitrogenous substances are strictly excluded from the food, as when the diet consists for several days of sugar, starch, gum, oil, and similar non-nitrogenous substances (Lehmann). It is excreted also, even though no food at all be taken for a considerable time; thus it is found in the urine of reptiles which have fasted for months; and in the urine of a madman who had fasted eighteen days, Lassaigne found both urea and all the components of healthy urine. Turning to the muscles, however, as the most actively metabolic tissue, we find as a result of their activity not urea, but kreatin; and although it may be supposed that some of this latter body appears natur- ally as kreatinin, yet it is not in sufficient quantity to represent the large amount of it formed by the muscles, and, indeed, by others of the tissues. It is assumed that kreatin therefore is the nitrogenous antecedent of urea; where its conversion into urea takes place is doubtful, but very likely the liver, and possibly the spleen, may be the seats of the change. It may be, however, that part — but if so, a small part — reaches the kidneys without previous change, leaving it to the cells of the renal tubules to complete the action. In speaking of kreatin as the antecedent of urea, it should be recollected that other nitrogenous products, such as xanthin (C6H4N402), appear in conjunction with it, and that these may also be converted into urea. It was formerly taken for granted that the quantity of urea in the urine is greatly increased by active exercise; but numerous observers have failed to detect more than a slight increase under such circumstances; and our notions concerning the relation of this excretory product to the de- struction of muscular fibre, consequent on the exercise of the latter, have undergone considerable modification. There is no doubt, of course, that like all parts of the body, the muscles have but a limited term of exist- ence, and are being constantly although very slowly renewed, at the same time that a part of the products of their disintegration appears in the urine in the form of urea. But the waste is not so fast as it was formerly supposed to be; and the theory that the amount of work done by the muscle is expressed by the quantity of urea excreted in the urine must without doubt be given up. 372 HAND-BOOK OF PHYSIOLOGY. Uric Acid. — Uric acid probably arises much in the same way as urea, either from the disintegration of albuminous tissues, or from the food. The relation which uric acid and urea bear to each other is, however, still obscure: but uric acid is said to be a less advanced stage of the oxidation of the products of proteid metabolism. The fact that they often exist together in the same urine, makes it seem probable that they have differ- ent origins; but the entire replacement of either by the other, as of urea by uric acid in the urine of birds, serpents, and many insects, and of uric acid by urea, in the urine of the feline tribe of Mammalia, shows that either alone may take the place of the two. At any rate, although it is true that one molecule of uric acid is capable of splitting up into two molecules of urea and one of mes-oxalic acid, there is no evidence for believing that uric acid is an antecedent of urea in the nitrogenous metabolism of the body. Some experiments seem to show that uric acid is formed in the kidney. Hippuric Acid (C9H9N03). — Hippuric acid is closely allied to benzoic acid; and this substance when introduced into the system, is excreted by the kidneys as hippuric acid (lire). Its source is not satisfactorily deter- mined: in part it is probably derived from some constituents of vegetable diet, though man has no hippuric acid in his food, nor, 'commonly, any benzoic acid that might be converted into it; in part from the natural disintegration of tissues, independent of vegetable food, for Weismann constantly found an appreciable quantity, even when li< ng on an exclu- sively animal diet. Hippuric acid arises from the union of benzoic acid with glycin (C2H5N02 + C7H6O2 = C9H9N03 + H20), which union may take place in the kidneys themselves, as well as in the liver. Extractives. — The source of the extractives of the urine is probably in chief part the disintegration of the nitrogenous tissues, but we are unable to say whether these nitrogenous bodies are merely accidental, having resisted further decomposition into urea, or whether they are the representatives of the decomposition of special tissues, or of special forms of metabolism of the tissues. There is* however, one exception, and this is in the case of kreatinin; there is great reason for believing that the amount of this body which appears in the urine is derived from the metab- olism of the nitrogenous food, as when this is diminished, it diminishes, and when stopped, it no longer appears in the urine. THE PASSAGE OF URINE INTO THE BLADDER. As each portion of urine is secreted it propels that which is already in the tubes onward into the pelvis of the kidney. Thence through the ureter the urine passes into the bladder, into which its rate and mode of entrance has been watched in cases of ectopia vesicce, i.e., of such fissures in the anterior or lower part gf the walls of the abdomen, and of the front THE KIDNEYS AND URINE. 373 wall of the bladder, as expose to view its hinder wall together with the orifices of the ureters. The urine does not enter the bladder at any reg- ular rate, nor is there a synchronism in its movement through the two ureters. During fasting, two or three drops enter the bladder every minute, each drop as it enters first raising up the little papilla on which, in these cases, the ureter opens, and then passing slowly through its orifice, which at once again closes like a sphincter. In the recumbent posture, the urine collects for a little time in the ureters, then flows gently, and, if the body be raised, runs from them in a stream till they are empty. Its flow is increased in deep inspiration, or straining, and in active exer- cise, and in fifteen or twenty minutes after a meal (Erichsen). The urine collecting is prevented from regurgitation into the ureters by the mode in which these pass through the walls of the bladder, namely, by their lying for between half and three-quarters of an inch between the muscular and mucous coats before they turn rather abruptly forward, and open through the latter into the interior of the bladder. Micturition. — The contraction of the muscular walls of the bladder may by itself expel the urine with little or no help from other muscles, when the sphincter of the organ is relaxed. In so far, however, as it is a voluntary act, micturition is performed by means of the abdominal and other expiratory muscles which, in their contraction, press on the abdom- inal viscera, the diaphragm being fixed, and cause the expulsion, of the contents of the bladder. The muscular coat of the bladder co-operates, in micturition, by reflex involuntary action, with the abdominal muscles; and the act is completed by the accelerator urince, which, as its name implies, quickens the stream, and expels the last drops of urine from the urethra. The act, so far as it is not directed by volition, is under the control of a nervous centre in the lumbar spinal cord, through which, as in the case of the .similar centre for defaecation (p. 288), the various muscles concerned are harmonized in their action. It is well known that the act may be reflexly induced, e.g., in children who suffer from intes- tinal worms, or other such irritation. Generally the afferent impulse which calls into action the desire to micturate is excited by over disten- tion of the bladder, or even by a few drops of urine passing into the urethra. END OF VOL. I. THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW AN INITIAL FINE OF 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO SO CENTS ON THE FOURTH DAY AND TO $1.OO ON THE SEVENTH DAY OVERDUE.., « «• JAN 3 1961 > y *M*»»W** **** c? ' £f\£LA D*M9« APR 2 6 1967 - LD 21-95m-7,'37 THE UNIVERSITY OF CALIFORNIA LIBRARY